Energy-Efficient Base-Stations Sleep-Mode Techniques in Green Cellular Networks: A Survey
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paper_title: A Survey on Green Mobile Networking: From The Perspectives of Network Operators and Mobile Users

paper_content:

Efficient usage of energy in wireless networks represents a major concern in academia and industry, mainly because of environmental, financial, and quality-of-experience considerations. Various solutions have been proposed to enable efficient energy usage in wireless networks, and these approaches are referred to as green wireless communications and networking. In this survey, we mainly focus on energy-efficient techniques in base stations and mobile terminals as they constitute the major sources of energy consumption in wireless access networks, from the operator and user perspectives, respectively. Unlike the existing articles and surveys, we aim to present a unified treatment of green solutions and analytical models for both network operators and mobile users. Such a unified treatment will help in the future to develop green solutions that enable an improved and balanced efficient usage of energy by operators and end users.
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paper_title: Energy efficiency analysis of small cell networks

paper_content:

Small cell networks have recently been proposed as an important evolution path for the next-generation cellular networks. While such approach has the potential of meeting the growing network throughput requirement, the energy efficiency of small cell networks is of great concern as the base station (BS) density will be significantly increased. The objective of this paper is to analyze the energy efficiency in small cell networks. To do so, we adopt a random spatial network model, where BSs and users are modeled as two independent spatial Poisson point processes (PPPs). We shall derive analytical results for the network energy efficiency, which show that the BS power consumption model plays a critical role. In particular, it will be shown that increasing the BS density can actually improve the energy efficiency if the BS power consumption that is not related to signal transmission is less than a certain threshold. By comparing the cases between single-antenna and multi-antenna BSs, we find that single-antenna BSs provide a higher energy efficiency if the circuit power is larger than a threshold. Simulation results will demonstrate that our conclusions which are based on the random network model also hold in a regular grid-based model.
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paper_title: Breathe to stay cool: adjusting cell sizes to reduce energy consumption

paper_content:

Reducing the energy consumption of a wireless cellular network is an important and urgent problem. This paper studies the effect of cell sizes on the energy consumed by the network, assuming base station technologies of today and the future. Making cell sizes too small or too large can significantly increase energy consumption. We show that the optimal cell size from an energy perspective depends on a number of factors, including base station technology, data rates, and traffic demands. Given that traffic varies significantly during a day, dynamically adjusting cell sizes can help reduce energy consumption. We propose a practical, 2-level scheme that adjusts cell sizes between two fixed values, and show an energy saving of up to 40%. The paper also proposes some self-organizing techniques to allow this dynamic cell size adjustment.
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paper_title: Energy Consumption Optimization for Multihop Cognitive Cellular Networks

paper_content:

Cellular networks are faced with serious congestions nowadays due to the recent booming growth and popularity of wireless devices and applications. Opportunistically accessing the unused licensed spectrum, cognitive radio can potentially harvest more spectrum resources and enhance the capacity of cellular networks. In this paper, we propose a new multihop cognitive cellular network (MC $^2$ N) architecture to facilitate the ever exploding data transmissions in cellular networks. Under the proposed architecture, we then investigate the minimum energy consumption problem by exploring joint frequency allocation, link scheduling, routing, and transmission power control. Specifically, we first formulate a maximum independent set (MIS) based energy consumption optimization problem, which is a non-linear programming problem. Different from most previous work assuming all the MISs are known, finding which is in fact NP-complete, we employ a column generation based approach to circumvent this problem. We develop an $\epsilon$ -bounded algorithm, which can obtain a feasible solution that are less than $(1+\epsilon)$ and larger than $(1-\epsilon)$ of the optimal result of MP, and analyzed its computational complexity. We also revisit the minimum energy consumption problem by taking uncertain channel bandwidth into consideration. Simulation results show that we can efficiently find $\epsilon$ -bounded approximate results and the optimal result as well.
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paper_title: A Survey of Green Networking Research

paper_content:

Reduction of unnecessary energy consumption is becoming a major concern in wired networking, because of the potential economical benefits and of its expected environmental impact. These issues, usually referred to as "green networking", relate to embedding energy-awareness in the design, in the devices and in the protocols of networks. In this work, we first formulate a more precise definition of the "green" attribute. We furthermore identify a few paradigms that are the key enablers of energy-aware networking research. We then overview the current state of the art and provide a taxonomy of the relevant work, with a special focus on wired networking. At a high level, we identify four branches of green networking research that stem from different observations on the root causes of energy waste, namely (i) Adaptive Link Rate, (ii) Interface proxying, (iii) Energy-aware infrastructures and (iv) Energy-aware applications. In this work, we do not only explore specific proposals pertaining to each of the above branches, but also offer a perspective for research.
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paper_title: A Survey of Green Mobile Networks: Opportunities and Challenges

paper_content:

The explosive development of Information and Communication Technology (ICT) has significantly enlarged both the energy demands and the CO 2 emissions, and consequently contributes to make the energy crisis and global warming problems worse. However, as the main force of the ICT field, the mobile networks, are currently focusing on the capacity, variety and stability of the communication services, without paying too much severe concerns on the energy efficiency. The escalating energy costs and environmental concerns have already created an urgent need for more energy-efficient "green" wireless communications. In this paper, we survey and discuss various remarkable techniques toward green mobile networks to date, mainly targeting mobile cellular networks. We also summarize the current research projects related to green mobile networks, along with the taxonomy of energy-efficiency metrics. We finally discuss and elaborate future research opportunities and design challenges for green mobile networks.
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paper_title: High Efficiency WCDMA Envelope Tracking Base-Station Amplifier Implemented with GaAs HVHBTs

paper_content:

A record high-performance GaAs high-voltage HBT (HVHBT)-based WCDMA base-station power amplifier is presented, which uses an envelope tracking bias system to achieve high efficiency and linearity. A wideband envelope amplifier provides dynamic collector supply biasing to the RF stage. A digital pre-distortion technique is employed to satisfy the linearity specifications of WCDMA. The measured overall power-added efficiency reached 58% with a normalized root-mean-square (RMS) error of 2.9% and an adjacent channel leakage ratio (ACLR) of -49ndBc at 5-MHz offset at an average output power of 42 W and a gain of 10.3 dB for a single carrier WCDMA signal with 6.6-dB peak-to-average power ratio. A memory mitigation algorithm further improves the linearity, resulting in an ACLR of -70 dBc and a normalized RMS error of 0.3%. Measurements were made to quantify separately the efficiency contributions of the HVHBT-based RF stage, and of the envelope amplifier. The measurements show that the RF stage operates at collector efficiency above 85% over most of the instantaneous power range of the WCDMA signal. This remarkably high efficiency is the result of low ldquoon-resistancerdquo and low (and nearly voltage independent) output capacitance of the HVHBT.
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paper_title: Cell size breathing and possibilities to introduce cell sleep mode

paper_content:

Global warming has put the energy consumption of all industries into focus. In 2005 mobile communications contributed to about 0.2% of global CO 2 emissions. Mobile operators have been reporting annual increases from 300% to 700% in 3G data traffic volumes. Such a steady growth in traffic requires regular upgrades in the infrastructure. While network equipment is in itself becoming more efficient, these upgrades still increase the overall energy consumption of the networks. This paper investigates the energy saving potential of exploiting cell size breathing by putting low loaded cells into sleep mode. The energy consumption and network performance of the resulting network are used to quantify the potential of this feature. The investigation is carried out on a tilt optimized network. Since putting cells into sleep mode results in a non- optimum antenna tilt configuration, this paper also investigates the possible gains of re-optimizing antenna tilting. The results show that by allowing sleep mode, over a restricted period of 12 hours, an energy saving of 33% is possible. While this energy saving comes at no expense of the overall network performance, the gain in average user data rate is noted to decrease by 21%.
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paper_title: Energy- and Spectral-Efficiency Tradeoff in Downlink OFDMA Networks

paper_content:

Conventional design of wireless networks mainly focuses on system capacity and spectral efficiency (SE). As green radio (GR) becomes an inevitable trend, energy-efficient design is becoming more and more important. In this paper, the fundamental tradeoff between energy efficiency (EE) and SE in downlink orthogonal frequency division multiple access (OFDMA) networks is addressed. We first set up a general EE-SE tradeoff framework, where the overall EE, SE and per-user quality-of-service (QoS) are all considered, and prove that under this framework, EE is strictly quasiconcave in SE. We then discuss some basic properties, such as the impact of channel power gain and circuit power on the EE-SE relation. We also find a tight upper bound and a tight lower bound on the EE-SE curve for general scenarios, which reflect the actual EE-SE relation. We then focus on a special case that priority and fairness are considered and suggest an alternative upper bound, which is proved to be achievable for flat fading channels. We also develop a low-complexity but near-optimal resource allocation algorithm for practical application of the EE-SE tradeoff. Numerical results confirm the theoretical findings and demonstrate the effectiveness of the proposed resource allocation scheme for achieving a flexible and desirable tradeoff between EE and SE.
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paper_title: Energy cooperation in cellular networks with renewable powered base stations

paper_content:

In this paper, we propose a model for energy cooperation between cellular base stations (BSs) with individual renewable energy sources, limited energy storages and connected by resistive power lines for energy sharing. When the renewable energy profile and energy demand profile at all BSs are deterministic or known ahead of time, we show that the optimal energy cooperation policy for the BSs can be found by solving a linear program. We show the benefits of energy cooperation in this regime. When the renewable energy and demand profiles are stochastic and only causally known at the BSs, we propose an online energy cooperation algorithm and show the optimality properties of this algorithm under certain conditions. Furthermore, the energy-saving performances of the developed offline and online algorithms are compared by simulations, and the effect of the availability of energy state information (ESI) on the performance gains of the BSs' energy cooperation is investigated.
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paper_title: Energy savings in mobile networks based on adaptation to traffic statistics

paper_content:

The traffic load in mobile networks is very unevenly distributed both over time and over cells. Excessive waste of energy occurs in low traffic situations since the radio system is optimized for maximum load. Drastic improvements can be achieved by adapting to the actual traffic demand. The solutions we introduce below rely on automatically switching off unnecessary cells, modifying the radio topology, and reducing the radiated power with methods such as bandwidth shrinking and cell micro-sleep. The challenge is to maintain reliable service coverage and quality of service (QoS) in the related area, while simultaneously consuming the lowest energy. The self-organizing network (SON) supports proper selection of the appropriate energy saving mechanism and automatic collaborative reconfiguration of cell parameters with the neighbor cells.
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paper_title: Energy-Efficient Resource Allocation in OFDMA Networks

paper_content:

The widespread application of multimedia wireless services and requirement of ubiquitous access have triggered rapidly booming energy consumption at both the base station side. Hence, energy-efficient design in wireless networks is very important and is becoming an inevitable trend. In this paper, we study energy-efficient resource allocation in downlink cellular OFDMA networks. For the downlink transmission, the weighted energy efficiency (EE) is maximized under certain prescribed per-user quality- of-service (QoS) requirements. We first obtain the optimal solution then propose a suboptimal approach by exploring the inherent structure and property of the energy-efficient design to reduce complexity. Simulation results show that the energy-efficient design greatly improves EE compared with that of the conventional spectral-efficient design and our low- complexity suboptimal approaches can achieve promising tradeoff between performance and complexity.
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paper_title: Energy Efficiency in Telecom Optical Networks

paper_content:

Since the energy crisis and environmental protection are gaining increasing concerns in recent years, new research topics to devise technological solutions for energy conservation are being investigated in many scientific disciplines. Specifically, due to the rapid growth of energy consumption in ICT (Information and Communication Technologies), lot of attention is being devoted towards "green" ICT solutions. In this paper, we provide a comprehensive survey of the most relevant research activities for minimizing energy consumption in telecom networks, with a specific emphasis on those employing optical technologies. We investigate the energy-minimization opportunities enabled by optical technologies and classify the existing approaches over different network domains, namely core, metro, and access networks. A section is also devoted to describe energy-efficient solutions for some of today's important applications using optical network technology, e.g., grid computing and data centers. We provide an overview of the ongoing standardization efforts in this area. This work presents a comprehensive and timely survey on a growing field of research, as it covers most aspects of energy consumption in optical telecom networks. We aim at providing a comprehensive reference for the growing base of researchers who will work on energy efficiency of telecom networks in the upcoming years.
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paper_title: Dynamic idle mode procedures for femtocells

paper_content:

The concept of a user-deployed femtocell that operates in licensed spectrum and provides cellular coverage in the home has attracted much interest in the wireless industry and an extensive deployment of femtocells is expected in the future. However, several issues arise when femtocells become more widely deployed. One concern is the additional energy consumption caused by femtocells due to their continuous receiver processing and signal transmissions, which can be significant with a large number of femtocells. Secondly, the increase in the number of active cells can result in a high increase in core networks signaling for mobility procedures. Finally, the continuous pilot transmissions can cause interference, particularly in dense urban areas. In this paper all these issues are addressed by a novel idle mode procedure which allows the femtocell transmissions and associated processing to be switched off completely at all times when the femtocell does not need to support an active call.
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paper_title: Downlink power consumption of HetNets based on the probabilistic traffic model of mobile users

paper_content:

Heterogeneous networks (HetNets) are considered as a standard part of the future generation of wireless networks where masses of low power, low cost smallcells (e.g., femtocells) are anticipated to support the existing macrocell networks. While HetNets are increasing the spectral efficiency and decreasing the over-the-air signaling and uplink power consumption compared to macro networks, the large scale deployment of many lightly loaded smallcells is expected to increase the downlink power consumption of the HetNets. This paper studies the impact of smallcell population on the downlink power consumption of the HetNets. In this context, we propose that the population of smallcells is strictly depending on the traffic load due to active mobile users, which is a random variable and time-varying. We derive the mathematical framework to calculate the required population of smallcells based on the probabilistic traffic models where the number of total mobile users and number of active mobile users have different probabilistic distributions such as different combinations of Binomial and Poisson distributions. The proposed method guarantees the reduction in downlink power consumption of HetNets by forcing the smallcells to turn on the sleeping mode under low and medium traffic load conditions. Several simulation results are included to illustrate the impact of traffic load dependent population of smallcells on the downlink power consumption of HetNets. Moreover, it is shown that the mathematical and simulation results are in perfect agreement.
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paper_title: Fundamental tradeoffs and evaluation methodology for future green wireless networks

paper_content:

To meet the global challenge of reducing greenhouse gas emissions and the exponentially growing data traffic, green design of cellular network is becoming a urgent issue for wireless network operators. In this paper, we first discuss the performance evaluation methodology for future wireless networks from the viewpoint of five basic metrics, i.e., throughput, power consumption, deployment cost, bandwidth, and latency. We then study the fundamental tradeoffs from Shannon's perspective based on the five metrics. Furthermore, we extend the tradeoff relation from point-to-point link to a heterogeneous network scenario taking into account realistic base station power model. Our study provides useful insights for the evaluation, modeling and deployment of future green wireless networks.
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paper_title: Femtocell Networks: A Survey

paper_content:

The surest way to increase the system capacity of a wireless link is by getting the transmitter and receiver closer to each other, which creates the dual benefits of higher-quality links and more spatial reuse. In a network with nomadic users, this inevitably involves deploying more infrastructure, typically in the form of microcells, hot spots, distributed antennas, or relays. A less expensive alternative is the recent concept of femtocells - also called home base stations - which are data access points installed by home users to get better indoor voice and data coverage. In this article we overview the technical and business arguments for femtocells and describe the state of the art on each front. We also describe the technical challenges facing femtocell networks and give some preliminary ideas for how to overcome them.
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paper_title: Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks

paper_content:

We consider radio applications in sensor networks, where the nodes operate on batteries so that energy consumption must be minimized, while satisfying given throughput and delay requirements. In this context, we analyze the best modulation and transmission strategy to minimize the total energy consumption required to send a given number of bits. The total energy consumption includes both the transmission energy and the circuit energy consumption. We first consider multi-input-multi-output (MIMO) systems based on Alamouti diversity schemes, which have good spectral efficiency but also more circuitry that consumes energy. We then extend our energy-efficiency analysis of MIMO systems to individual single-antenna nodes that cooperate to form multiple-antenna transmitters or receivers. By transmitting and/or receiving information jointly, we show that tremendous energy saving is possible for transmission distances larger than a given threshold, even when we take into account the local energy cost necessary for joint information transmission and reception. We also show that over some distance ranges, cooperative MIMO transmission and reception can simultaneously achieve both energy savings and delay reduction.
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paper_title: Effects of joint macrocell and residential picocell deployment on the network energy efficiency

paper_content:

Rising energy costs and the recent international focus on climate change issues has resulted in a high interest in improving the energy efficiency in the telecommunications industry. In this paper the effects of a joint deployment of macrocells for area coverage and publicly accessible residential picocells on the total energy consumption of the network is investigated. The decreasing energy efficiency of todaypsilas macrocellular technologies with increasing user demand for high data rates is discussed. It is shown that a joint deployment of macro- and publicly accessible residential picocells can reduce the total energy consumption by up to 60% in an urban area with todaypsilas technology. Furthermore the impact of future technologies for both macro- and femtocells on the energy efficiency is investigated. It is shown that the benefits of a joint macro- and picocell deployment will increase further as both technologies mature, and will result in a significant reduction of the network energy consumption as the user demand for high data rates increases.
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paper_title: Energy efficiency of modern cellular base stations

paper_content:

By improving the energy efficiency of base stations in cellular networks, a great savings can be obtained in both environmental and cost point of view. Methods dealing with improved transmitter efficiency, system features, fresh air cooling, alternative energy sources and energy saving during low traffic are given in this paper.
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paper_title: Clustering based power saving algorithm for self-organized sleep mode in femtocell networks

paper_content:

A large-scale deployment of femtocell BSs (FBSs) causes the substantial energy consumption. One fairly intuitive way to minimize the energy consumption is to switch off the wireless air interface, or to keep FBSs in the energy saving mode for the most time while preserving the quality of service (QoS) experienced by users. Utilizing this concept, this paper proposes a clustering based power saving algorithm (CPSA) for self-organized sleep mode in femtocell networks. Firstly, CPSA builds a leader-member cluster framework, in which each FBS is either a FBS leader (FL) or a FBS member (FM). Then, the FL acts as an autonomous entity and is responsible for detecting active calls in the cluster coverage, while the FMs without the active user can entirely shut down pilot transmissions and the related processing all the time. So it is suited for self-organizing networks (SONs). With the practical LTE system parameters, simulation results show that the proposed algorithm outperforms three prominent related schemes in terms of average energy consumption and accumulative interference time. Furthermore, the results provide some guidelines for deploying energy efficient femtocell networks.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
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paper_title: Power consumption modeling of different base station types in heterogeneous cellular networks

paper_content:

In wireless communications micro cells are potentially more energy efficient than conventional macro cells due to the high path loss exponent. Also, heterogeneous deployments of both cell types can be used to optimize the energy efficiency. Energy efficiency of any deployment is impacted by the power consumption of each individual network element and the dependency of transmit power and load. In this paper we developed such power models for macro and micro base stations relying on data sheets of several GSM and UMTS base stations with focus on component level, e.g., power amplifier and cooling equipment. In a first application of the model a traditional macro cell deployment and a heterogeneous deployment are compared.
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paper_title: Energy Efficiency Aspects of Base Station Deployment Strategies for Cellular Networks

paper_content:

In the strive for lessening of the environmental impact of the information and communication industry, energy consumption of communication networks has recently received increased attention. Although cellular networks account for a rather small share of energy use, lowering their energy con- sumption appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular radio networks. This paper investigates on the impact of deployment strategies on the power consumption of mobile radio networks. We consider layouts featuring varying numbers of micro base stations per cell in addition to conventional macro sites. We introduce the concept of area power consumption as a system performance metric and employ simulations to evaluate potential improvements of this metric through the use of micro base stations. The results suggest, that for scenarios with full traffic load, the use of micro base stations has a rather moderate effect on the area power consumption of a cellular network.
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paper_title: Traffic-Aware Base Station Sleeping Control and Power Matching for Energy-Delay Tradeoffs in Green Cellular Networks

paper_content:

In this paper, traffic-aware sleeping control (SC) and power matching (PM) of a single base station (BS) in cellular networks are studied. The objective is to find the sleeping control and power matching configurations that achieve the Pareto optimal tradeoff between total power consumption and average delay. Two types of sleeping control schemes are considered: The BS goes to sleep whenever there is no active user, and wakes up when N users are assembled or after a period of multiple or single vacation time. We first discuss when to incorporate sleeping control into power matching energy efficiently. The explicit relationship between total power consumption and average delay with varying service rate is analyzed theoretically, indicating that sacrificing delay cannot always be traded for energy saving, and we also provide conditions under which the energy-optimal rate exists. Moreover, the optimal pair of sleeping parameter and service rate to achieve the optimal energy-delay tradeoff, and the energy consumption lower bound are also derived. Both the analytical and simulation results show that tolerable sacrifice of delay performance can be traded for substantial amount of energy saving given that careful designs were made according to our analysis.
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paper_title: Reducing Energy Consumption in LTE with Cell DTX

paper_content:

This paper discusses how energy consumption can be significantly reduced in mobile networks by introducing discontinuous transmission (DTX) on the base station side. By introducing DTX on the downlink, or cell DTX, we show that it is possible to achieve significant energy reductions in an LTE network. Cell DTX is most efficient when the traffic load is low in a cell but even when realistic traffic statistics are considered the gains are impressive. The technology potential for a metropolitan area is shown to be 90% reduced energy consumption compared to no use of cell DTX. The paper also discusses different drives for the increased focus on energy efficient network operation and also provides insights on the impact of cell DTX from a life cycle assessment perspective.
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paper_title: Green last mile: how fiber-connected massively distributed antenna systems can save energy

paper_content:

We introduce a novel last-mile architecture that integrates the advantages of a distributed antenna system with centralized processing capability, connected through an optical fiber medium. The proposed broadband wireless access with fiber-connected massively distributed antenna system (BWA-FMDA) is capable of enhancing spectral efficiency of the network through coordinated multipoint transmissions at the femtocell scale. Furthermore, by shortening the lastmile communication link and lowering the power consumption, BWA-FMDA represents a viable green wireless access solution. Through our detailed and extensive simulation results, we demonstrate the potentially superior performance of BWA-FMDA in comparison with micro base station and femtocell deployments.
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paper_title: Exploiting Network Cooperation in Green Wireless Communication

paper_content:

There is a growing interest in energy efficient or so-called "green" wireless communication to reduce the energy consumption in cellular networks. Since today's wireless terminals are typically equipped with multiple network access interfaces such as Bluetooth, Wi-Fi, and cellular networks, this paper investigates user terminals cooperating with each other in transmitting their data packets to the base station (BS), by exploiting the multiple network access interfaces, called inter-network cooperation. We also examine the conventional schemes without user cooperation and with intra-network cooperation for comparison. Given target outage probability and data rate requirements, we analyze the energy consumption of conventional schemes as compared to the proposed inter-network cooperation by taking into account both physical-layer channel impairments and upper-layer protocol overheads. It is shown that distances between different network entities (i.e., user terminals and BS) have a significant influence on the energy efficiency of proposed inter-network cooperation scheme. Specifically, when the cooperating users are close to BS or the users are far away from each other, the inter-network cooperation may consume more energy than conventional schemes without user cooperation or with intra-network cooperation. However, as the cooperating users move away from BS and the inter-user distance is not too large, the inter-network cooperation significantly reduces the energy consumption over conventional schemes.
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paper_title: High efficiency linear GaAs MMIC amplifier for wireless base station and Femto cell applications

paper_content:

We have demonstrated a 1W 1.8∼2.2GHz high efficiency and high linearity power amplifier that was fabricated in a InGaP hetero-junction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) technology. The 2-stage power amplifier was biased at Class AB with 60mA quiescent current and showed 28dB gain. In conjunction with the linearization active bias circuit, harmonic trap circuits were incorporated with the matching networks to simultaneously achieve good bandwidth response, low distortion and low harmonic spurious output. The power amplifier exhibited a 45dBm output third-order intercept point (OIP3) at 5V power supply. This is one of the highest third-order intercept points reported given such a low quiescent current. The power amplifier can be used as a linear driver amplifier in wireless base station applications as well as an output stage in Femto cell or repeater applications.
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paper_title: Consumer perceptions of “green power”

paper_content:

This study examines the relationship between consumers’ perceptions of the environmental impact of different energy resources and consumers’ stated willingness‐to‐pay a premium for “green power” (electricity generated by more environmentally‐friendly means). Those developing green power products can choose to include any number of energy resources in their offerings. Given this, information about potential purchasers’ preferences is extremely valuable. To investigate this further, a total of 480 residents of Waterloo Region, a community in southern Ontario (Canada), were surveyed. The aforementioned relationship was investigated using chi‐square tests and analysis of variance procedures. Significant differences between those who stated a willingness to pay a large premium for green power and those who stated a willingness to pay only a small (or no) premium for green power were found for three of 11 energy resources investigated – namely, nuclear power, large‐scale hydropower and natural gas. Therefore, these energy resources are not as popular among the most environmentally‐mobilized section of the consumer market as general surveys would suggest. A variety of managerial implications are drawn from the results. Future directions for research are also offered.
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paper_title: TACT: A Transfer Actor-Critic Learning Framework for Energy Saving in Cellular Radio Access Networks

paper_content:

Recent works have validated the possibility of improving energy efficiency in radio access networks (RANs), achieved by dynamically turning on/off some base stations (BSs). In this paper, we extend the research over BS switching operations, which should match up with traffic load variations. Instead of depending on the dynamic traffic loads which are still quite challenging to precisely forecast, we firstly formulate the traffic variations as a Markov decision process. Afterwards, in order to foresightedly minimize the energy consumption of RANs, we design a reinforcement learning framework based BS switching operation scheme. Furthermore, to avoid the underlying curse of dimensionality in reinforcement learning, a transfer actor-critic algorithm (TACT), which utilizes the transferred learning expertise in historical periods or neighboring regions, is proposed and provably converges. In the end, we evaluate our proposed scheme by extensive simulations under various practical configurations and show that the proposed TACT algorithm contributes to a performance jumpstart and demonstrates the feasibility of significant energy efficiency improvement at the expense of tolerable delay performance.
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paper_title: Opportunistic Distributed Space-Time Coding for Decode-and-Forward Cooperation Systems

paper_content:

In this paper, we consider a decode-and-forward (DF) cooperation system consisting of two cooperative users in sending their information to a common destination, for which the distributed space-time coding (DSTC) is applied in an opportunistic manner, called opportunistic DSTC (O-DSTC), depending on whether the two users succeed in decoding each other's information or not. We propose two O-DSTC schemes for the full-duplex and half-duplex relaying scenarios, which are, respectively, referred to as the full-duplex and half-duplex-based O-DSTC. We evaluate the outage performance of the proposed O-DSTC as well as the conventional selective DF (S-DF) cooperation and fixed DSTC (F-DSTC) schemes. Numerical results show that the O-DSTC outperforms the conventional S-DF and F-DSTC schemes considering both full-duplex and half-duplex. In addition, we develop the diversity-multiplexing tradeoff (DMT) of the proposed O-DSTC, conventional S-DF and F-DSTC schemes by considering the two cooperative users with different data rates (also known as different multiplexing gains). We show that, for both the full-duplex and half-duplex modes, the proposed O-DSTC strictly outperforms the conventional S-DF and F-DSTC in terms of DMT. It is also shown that, in the full-duplex-based O-DSTC scheme, the diversity gain obtained by any of the two cooperative users not only depends on its own multiplexing gain, but also relates to its partner's multiplexing gain. By jointly considering the two users' DMT, the full-duplex-based O-DSTC scheme can achieve the optimal diversity gain when the two users are with the same multiplexing gain. For the half-duplex-based O-DSTC scheme, the DMT performance of the two users are independent of each other, which differs from the full-duplex-based O-DSTC scheme where mutual dependence exists between the cooperative users in terms of DMT.
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paper_title: Femtocell based green power consumption methods for mobile network

paper_content:

This paper presents the analytical models of power consumption in macrocell, microcell, picocell and femtocell based networks. Five case studies are presented in this paper where macrocells, microcells, picocells and femtocells are deployed based on the number of mobile subscribers present in a region, mobile user traffic in that region and the area of the region where cellular coverage has to be provided. A comparative study is performed between the power consumption by the base stations in each of these five cases and that of the only macrocell based network. The simulation results demonstrate that using each of these five strategies the power consumption by the base stations can be minimized than that of only macrocell based network. Based on the power consumption by the base stations in these five schemes, we have categorized the networks into five classes, A, B, C, D and E, each of which contains cells of different types to reduce power consumption to achieve green cellular network.
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paper_title: Stochastic Geometry for Modeling, Analysis, and Design of Multi-Tier and Cognitive Cellular Wireless Networks: A Survey

paper_content:

For more than three decades, stochastic geometry has been used to model large-scale ad hoc wireless networks, and it has succeeded to develop tractable models to characterize and better understand the performance of these networks. Recently, stochastic geometry models have been shown to provide tractable yet accurate performance bounds for multi-tier and cognitive cellular wireless networks. Given the need for interference characterization in multi-tier cellular networks, stochastic geometry models provide high potential to simplify their modeling and provide insights into their design. Hence, a new research area dealing with the modeling and analysis of multi-tier and cognitive cellular wireless networks is increasingly attracting the attention of the research community. In this article, we present a comprehensive survey on the literature related to stochastic geometry models for single-tier as well as multi-tier and cognitive cellular wireless networks. A taxonomy based on the target network model, the point process used, and the performance evaluation technique is also presented. To conclude, we discuss the open research challenges and future research directions.
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paper_title: Fundamental trade-offs on green wireless networks

paper_content:

Traditional mobile wireless network mainly design focuses on ubiquitous access and large capacity. However, as energy saving and environmental protection become global demands and inevitable trends, wireless researchers and engineers need to shift their focus to energy-efficiency-oriented design, that is, green radio. In this article, we propose a framework for green radio research and integrate the fundamental issues that are currently scattered. The skeleton of the framework consists of four fundamental tradeoffs: deployment efficiency-energy efficiency, spectrum efficiency-energy efficiency, bandwidth-power, and delay-power. With the help of the four fundamental trade-offs, we demonstrate that key network performance/cost indicators are all strung together.
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paper_title: Green cellular network: Deployment solutions, sensitivity and tradeoffs

paper_content:

A prominent challenge faced by the communication industry and society is the reduction of energy consumption. How the cellular network can maintain a quality of service (QoS), whilst decreasing its operational energy is investigated from both a deployment and scheduling perspective. This paper presents results showing the dominant factors which reduce the radio access network (RAN) energy consumption and point the way for future research. A large proportion of energy consumption is due to the static overhead power of base-stations and the paper considers sleep mode operation as a solution for a variety of network conditions. Furthermore, a significant contributor to transmission inefficiency is due to the performance of cell edge users. The paper proposes a vertical sector antenna deployment scheme and demonstrate that our proposals can yield significant operational energy and transmission efficiency savings, as well as insight into the tradeoff relationship between energy consumption and network performance. Furthermore, the paper also gives a comprehensive performance sensitivity analysis, which yields insight into both the validity of results and the parameters which can significantly influence future development.
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paper_title: Green Cellular Networks: A Survey, Some Research Issues and Challenges

paper_content:

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technology
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paper_title: A Survey of Green Networking Research

paper_content:

Reduction of unnecessary energy consumption is becoming a major concern in wired networking, because of the potential economical benefits and of its expected environmental impact. These issues, usually referred to as "green networking", relate to embedding energy-awareness in the design, in the devices and in the protocols of networks. In this work, we first formulate a more precise definition of the "green" attribute. We furthermore identify a few paradigms that are the key enablers of energy-aware networking research. We then overview the current state of the art and provide a taxonomy of the relevant work, with a special focus on wired networking. At a high level, we identify four branches of green networking research that stem from different observations on the root causes of energy waste, namely (i) Adaptive Link Rate, (ii) Interface proxying, (iii) Energy-aware infrastructures and (iv) Energy-aware applications. In this work, we do not only explore specific proposals pertaining to each of the above branches, but also offer a perspective for research.
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paper_title: Energy Efficiency in Telecom Optical Networks

paper_content:

Since the energy crisis and environmental protection are gaining increasing concerns in recent years, new research topics to devise technological solutions for energy conservation are being investigated in many scientific disciplines. Specifically, due to the rapid growth of energy consumption in ICT (Information and Communication Technologies), lot of attention is being devoted towards "green" ICT solutions. In this paper, we provide a comprehensive survey of the most relevant research activities for minimizing energy consumption in telecom networks, with a specific emphasis on those employing optical technologies. We investigate the energy-minimization opportunities enabled by optical technologies and classify the existing approaches over different network domains, namely core, metro, and access networks. A section is also devoted to describe energy-efficient solutions for some of today's important applications using optical network technology, e.g., grid computing and data centers. We provide an overview of the ongoing standardization efforts in this area. This work presents a comprehensive and timely survey on a growing field of research, as it covers most aspects of energy consumption in optical telecom networks. We aim at providing a comprehensive reference for the growing base of researchers who will work on energy efficiency of telecom networks in the upcoming years.
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paper_title: Traffic engineering of the radio interface for cellular mobile networks

paper_content:

The paper reviews traffic-related issues in the operation of the radio interface in cellular mobile networks operating with FDMA, TDMA, or CDMA technology. The emphasis is on issues which affect the traffic performance of the network, rather than on transmission technology, or transmission quality measures such as bit error rate. The author reviews the important traffic performance measures for cellular systems and the issues of channel assignment, handoff, access control, traffic modeling, and traffic management. Traffic modeling for all types of networks is considered in some depth, both by drawing analogies with fixed-wire networks, and by considering cellular-specific modeling. From the modeling results, he concludes that reuse-based networks such as FDMA and TDMA possess quite different traffic characteristics from CDMA networks. >
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paper_title: NeXt generation/dynamic spectrum access/cognitive Radio Wireless Networks: A Survey

paper_content:

Today's wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 15% to 85% with a high variance in time. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm is referred to as NeXt Generation (xG) Networks as well as Dynamic Spectrum Access (DSA) and cognitive radio networks. The term xG networks is used throughout the paper. The novel functionalities and current research challenges of the xG networks are explained in detail. More specifically, a brief overview of the cognitive radio technology is provided and the xG network architecture is introduced. Moreover, the xG network functions such as spectrum management, spectrum mobility and spectrum sharing are explained in detail. The influence of these functions on the performance of the upper layer protocols such as routing and transport are investigated and open research issues in these areas are also outlined. Finally, the cross-layer design challenges in xG networks are discussed.
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paper_title: Challenges and enabling technologies for energy aware mobile radio networks

paper_content:

Mobile communications are increasingly contributing to global energy consumption. In this article, a holistic approach for energy efficient mobile radio networks is presented. The matter of having appropriate metrics and evaluation methods that allow assessing the energy efficiency of the entire system is discussed. The mutual supplementary saving concepts comprise component, link and network levels. At the component level the power amplifier complemented by a transceiver and a digital platform supporting advanced power management are key to efficient radio implementations. Discontinuous transmission by base stations, where hardware components are switched off, facilitate energy efficient operation at the link level. At the network level, the potential for reducing energy consumption is in the layout of networks and their management, that take into account slowly changing daily load patterns, as well as highly dynamic traffic fluctuations. Moreover, research has to analyze new disruptive architectural approaches, including multi-hop transmission, ad-hoc meshed networks, terminal-to-terminal communications, and cooperative multipoint architectures.
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paper_title: Mobile Networks Unplugged

paper_content:

Mobile network access has seemingly become ubiquitous in industrialized countries. With data services becoming sufficiently fast, usable, and affordable, demand is growing rapidly, both in the number of users and in capacity -- since most Internet/web resources continue being tailored for fast fixed line access. A lot of engineering has gone into making mobile devices appealing and sufficiently power-conserving to last for at least a day in spite of the many emerging network-driven applications. However, this device-centric view fails to recognize the "other side": the mobile access infrastructure. There, too, power consumption raises technical issues (not just) when moving towards faster mobile access and is de-facto an inhibiting factor for cellular expansion: for practical and for cost reasons. In this paper, we seek to raise awareness of the power consumption issues of mobile networks. We argue that mobile access will become, in addition to data centers and PCs, another contributing factor from the ICT sector to greenhouse gas emissions and that current mobile access technologies limit further network expansion in rural areas. Thus, we need to start working on making mobile networks much more energy-efficient than they are today, maybe even fully self-sustainable using renewable energy sources.
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paper_title: Downlink power consumption of HetNets based on the probabilistic traffic model of mobile users

paper_content:

Heterogeneous networks (HetNets) are considered as a standard part of the future generation of wireless networks where masses of low power, low cost smallcells (e.g., femtocells) are anticipated to support the existing macrocell networks. While HetNets are increasing the spectral efficiency and decreasing the over-the-air signaling and uplink power consumption compared to macro networks, the large scale deployment of many lightly loaded smallcells is expected to increase the downlink power consumption of the HetNets. This paper studies the impact of smallcell population on the downlink power consumption of the HetNets. In this context, we propose that the population of smallcells is strictly depending on the traffic load due to active mobile users, which is a random variable and time-varying. We derive the mathematical framework to calculate the required population of smallcells based on the probabilistic traffic models where the number of total mobile users and number of active mobile users have different probabilistic distributions such as different combinations of Binomial and Poisson distributions. The proposed method guarantees the reduction in downlink power consumption of HetNets by forcing the smallcells to turn on the sleeping mode under low and medium traffic load conditions. Several simulation results are included to illustrate the impact of traffic load dependent population of smallcells on the downlink power consumption of HetNets. Moreover, it is shown that the mathematical and simulation results are in perfect agreement.
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paper_title: Green heterogeneous small-cell networks: toward reducing the CO2 emissions of mobile communications industry using uplink power adaptation

paper_content:

Heterogeneous small cell networks, or Het- SNets, are considered as a standard part of future mobile networks in which multiple lowpower low-cost user deployed base stations complement the existing macrocell infrastructure. This article proposes an energy-efficient deployment of the cells where the small cell base stations are arranged around the edge of the reference macrocell, and the deployment is referred to as cell-on-edge (COE) deployment. The proposed deployment ensures an increase in the network spectral and energy efficiency by facilitating cell edge mobile users with small cells. Moreover, COE deployment guarantees reduction of the carbon footprint of mobile operations by employing adaptive uplink power control. In order to calibrate the reduction in CO2 emissions, this article quantifies the ecological and associated economical impacts of energy savings in the proposed deployment. Simulation results quantify the improvements in CO2 emissions and spectral and energy gains of the proposed COE deployment compared to macro-only networks and typical small cell deployment strategies where small cells are randomly deployed within a given macrocell.
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paper_title: Green Cellular Networks: A Survey, Some Research Issues and Challenges

paper_content:

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technology
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paper_title: A Survey on Green Mobile Networking: From The Perspectives of Network Operators and Mobile Users

paper_content:

Efficient usage of energy in wireless networks represents a major concern in academia and industry, mainly because of environmental, financial, and quality-of-experience considerations. Various solutions have been proposed to enable efficient energy usage in wireless networks, and these approaches are referred to as green wireless communications and networking. In this survey, we mainly focus on energy-efficient techniques in base stations and mobile terminals as they constitute the major sources of energy consumption in wireless access networks, from the operator and user perspectives, respectively. Unlike the existing articles and surveys, we aim to present a unified treatment of green solutions and analytical models for both network operators and mobile users. Such a unified treatment will help in the future to develop green solutions that enable an improved and balanced efficient usage of energy by operators and end users.
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paper_title: Device Power Saving and Latency Optimization in LTE-A Networks Through DRX Configuration

paper_content:

Discontinuous reception (DRX) saves battery power of user equipment (UE) usually at the expense of potential increase in latency in the Long Term Evolution (LTE) networks. Therefore, an optimization is needed to find the best tradeoff between latency and power saving. In this paper, we first develop an analytical model to estimate power saving achieved and latency incurred by DRX mechanism for active and background mobile traffic. A tradeoff scheme is then formulated to maintain a balance between these two performance parameters based on operator's preference for power saving and latency requirement of traffic. The analytical model is validated using system level simulation results obtained from OPNET Modeler. The results show that the proposed tradeoff scheme is efficient in keeping a balance between power saving and latency. The results also indicate that DRX short cycles are very effective in reducing latency for active traffic, while shorter inactivity timer is desirable for background traffic to enhance power saving. We also proposed a mechanism to switch DRX configuration based on traffic running at UE, using UE assistance procedure recently adopted by 3GPP in Release 11. DRX configuration switching increases the power saving significantly without any noticeable increase in latency of active traffic.
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paper_title: Energy Consumption Issues on Mobile Network Systems

paper_content:

This paper describes energy consumption demographic data in operating real mobile networks. We examine published data from NTT DoCoMo, which is the largest mobile telecommunication operator in Japan and operating nationwide 3G networks, and identify the most power consuming part is of radio access networks including base tranciever stations. We also investigate power consumption of terminals, and find that the consumption ratio of terminal v.s. networks is about 1:150. Our daily energy consumption per a customer is 0.83 Wh/day for a terminal and 120 Wh/day for the mobile network. The terminal side energy consumption is negligible in view of total CO2 emission though, limitation of its battery performance raises another issue called "energy starvation of mobile devices." The demographic data leads our discussion to (1) radio-on-fiber access network architecture as green networks and (2) thin client models as the key to sustain the evolution toward the future.
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paper_title: Enablers for Energy Efficient Wireless Networks

paper_content:

Mobile communications are increasingly contributing to global energy consumption. The EARTH (Energy Aware Radio and neTworking tecHnologies) project tackles the important issue of reducing CO2 emissions by enhancing the energy efficiency of cellular mobile networks. EARTH is a holistic approach to develop a new generation of energy efficient products, components, deployment strategies and energy-aware network management solutions. In this paper the holistic EARTH approach to energy efficient mobile communication systems is introduced. Performance metrics are studied so to assess the theoretical bounds of energy efficiency and the practical achievable limits. Moreover, various deployment strategies focusing on their potential to reduce energy consumption are studied, whilst providing uncompromised coverage and user experience. This includes heterogeneous networks with a sophisticated mix of different cell sizes, which may be further enhanced by energy efficient relaying and base station cooperation technologies. Finally, scenarios leveraging the capability of advanced terminals to operate on multiple radio access technologies (RAT) are discussed with respect to their energy savings potential.
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paper_title: Energy efficiency metrics for green wireless communications

paper_content:

Recently the concern on energy efficiency in wireless communications has been growing rapidly as energy consumption increasingly becomes a global environment problem. Lots of research and development efforts have been spent in wireless industry, aiming for energy efficient solutions which lead to green wireless communications. In this paper we provide a brief overview on those efforts, with an emphasis on introducing energy efficiency metrics. Since energy efficiency metrics are indicators of efficiency, understanding those metrics provides us a better view on how energy efficiency can be achieved in wireless systems/networks. Observing energy is a concern at every corner of a wireless system/network, we describe those metrics from at component, equipment and system/networks level, respectively. From our observation, energy efficiency metrics for components and equipments have been well established. However, studied for system/network level solutions and metrics deserve more attention. We believe new energy efficient architecture and associated metrics will be the key for the energy consumption problem in wireless industry.
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paper_title: To Slow or Not to Slow: The Economics of The Greenhouse Effect

paper_content:

Over the last decade, scientists have studied extensively the greenhouse effect, which holds that the accumulation of carbon dioxide (CO2) and other greenhouse gases (GHGs) is expected to produce global warming and other significant climatic changes over the next century. Along with the scientific research have come growing alarm and calls for drastic curbs on the emissions of greenhouse gases, as for example the reports of the Intergovernmental Panel on Climate Change (IPCC [I990]) and the Second World Climate Conference (October I990). To date, these call to arms for forceful measures to slow greenhouse warming have been made without any serious attempt to weigh the costs and benefits of climatic change or alternative control strategies. The present study presents a simple approach for analyzing policies to slow climate change. We begin by summarizing the elements of an economic analysis of different approaches to controlling greenhouse warming. We then sketch a mathematical model of economic growth that links the economy, emissions, and climate changes and summarize the empirical evidence on the costs of reducing emissions and concentrations of greenhouse gases and on the damages from greenhouse warming, relying primarily on data for the United States. The different sections are then integrated to provide estimates of the efficient reduction of greenhouse gases, after which the final section summarizes the major results.
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paper_title: Cognitive radio and cooperative strategies for power saving in multi-standard wireless devices

paper_content:

Energy is a critical resource in the design of wireless networks since wireless devices are usually powered by batteries. Without any new approaches for energy saving, 4G mobile users will relentlessly be searching for power outlets rather than network access, and becoming once again bound to a single location. To avoid the so called 4G “energy trap” and to help wireless devices become more environment friendly, there is a clear need for disruptive strategies to address all aspects of power efficiency from the user devices through to the core infrastructure of the network and how these devices and equipment interact with each other. The ICT-C2POWER project is the vehicle that will address these issues through cognitive techniques and cooperation. The C2POWER case study is to research, develop and demonstrate energy saving technologies for multi-standard wireless mobile devices, exploiting the combination of cognitive radio and cooperative strategies, while still enabling the required performance in terms of data rate and QoS to support active applications.
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paper_title: Rethinking energy efficiency models of cellular networks with embodied energy

paper_content:

The continuous increase in energy consumption by cellular networks requires rethinking their energy efficiency. Current research indicates that one third of operating energy could be saved by reducing the transmission power of base stations. However, this approach requires the introduction of a range of additional equipment containing more embodied energy - consumed by all processes associated with the production of equipment. This problem is addressed first in this article. Furthermore, a new cellular network energy efficiency model with embodied energy is proposed, and optimization between the number of cells and their coverage is investigated. Contrary to previous works, we have found that embodied energy accounts for a significant proportion of total energy consumption and cannot be neglected. The simulation results confirm an important trade-off between operating and embodied energies, which can provide some practical guidelines for designing energy-efficient cellular access networks. The new model considering embodied energy is not limited to just cellular networks, but to other telecommunications, such as wireless local area networks and wired networks.
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paper_title: Enablers for Energy Efficient Wireless Networks

paper_content:

Mobile communications are increasingly contributing to global energy consumption. The EARTH (Energy Aware Radio and neTworking tecHnologies) project tackles the important issue of reducing CO2 emissions by enhancing the energy efficiency of cellular mobile networks. EARTH is a holistic approach to develop a new generation of energy efficient products, components, deployment strategies and energy-aware network management solutions. In this paper the holistic EARTH approach to energy efficient mobile communication systems is introduced. Performance metrics are studied so to assess the theoretical bounds of energy efficiency and the practical achievable limits. Moreover, various deployment strategies focusing on their potential to reduce energy consumption are studied, whilst providing uncompromised coverage and user experience. This includes heterogeneous networks with a sophisticated mix of different cell sizes, which may be further enhanced by energy efficient relaying and base station cooperation technologies. Finally, scenarios leveraging the capability of advanced terminals to operate on multiple radio access technologies (RAT) are discussed with respect to their energy savings potential.
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paper_title: The global footprint of mobile communications: The ecological and economic perspective

paper_content:

This article quantifies the global carbon footprint of mobile communication systems, and discusses its ecological and economic implications. Using up-to-date data and life cycle assessment models, we predict an increase of CO2 equivalent emissions by a factor of three until 2020 compared to 2007, rising from about 86 to 235 Mto CO2e, suggesting a steeper increase than predicted in the well-known SMART2020 report. We provide a breakdown of the global carbon footprint, which reveals that production of mobile devices and global radio access network operation will remain the major contributors, accompanied by an increasing share of emissions due to data transfer in the backbone resulting from rising mobile traffic volumes. The energy bill due to network operation will gain increasing importance in cellular business models. Furthermore, technologies to reduce energy consumption are considered a key enabler for the spread of mobile communications in developing countries. Taking into account several scenarios of technological advancement and rollout, we analyze the overall energy consumption of global radio access networks and illustrate the saving potential of green communication technologies. We conclude that, conditioned on quick implementation and alongside other "classical" improvements of spectral efficiency, these technologies offer the potential to serve three orders of magnitude more traffic with the same overall energy consumption as today.
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paper_title: Energy efficiency metrics for green wireless communications

paper_content:

Recently the concern on energy efficiency in wireless communications has been growing rapidly as energy consumption increasingly becomes a global environment problem. Lots of research and development efforts have been spent in wireless industry, aiming for energy efficient solutions which lead to green wireless communications. In this paper we provide a brief overview on those efforts, with an emphasis on introducing energy efficiency metrics. Since energy efficiency metrics are indicators of efficiency, understanding those metrics provides us a better view on how energy efficiency can be achieved in wireless systems/networks. Observing energy is a concern at every corner of a wireless system/network, we describe those metrics from at component, equipment and system/networks level, respectively. From our observation, energy efficiency metrics for components and equipments have been well established. However, studied for system/network level solutions and metrics deserve more attention. We believe new energy efficient architecture and associated metrics will be the key for the energy consumption problem in wireless industry.
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paper_title: Energy Efficiency and Spectral Efficiency Tradeoff in Downlink Distributed Antenna Systems

paper_content:

This letter investigates the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in downlink multiuser distributed antenna systems (DAS). Given the SE requirement and maximum power limit, a constrained optimization problem is formulated to maximize EE. Because of the multi-dimensional and non-convex nature of the problem, we first transform the multicriteria optimization problem with high complexity into a simpler single objective optimization problem. Then a novel power allocation algorithm is proposed to achieve maximum EE. Simulation results demonstrate the effectiveness of the proposed scheme as well as illustrate the fundamental tradeoff between energy efficient and spectral efficient transmission in downlink multiuser DAS.
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paper_title: Bit per Joule efficiency of cooperating base stations in cellular networks

paper_content:

Energy consumption is lately receiving increased interest, and research efforts to assess the energy efficiency of cellular communication networks are made. This paper addresses the tradeoffs between gains in cell throughput that can be expected from coordinated multi point transmission and reception technologies and the increased energy consumption that they induce in cellular base stations. We explicitly consider effective transmission rates, taking into account the additional pilot, control and feedback overhead required for CoMP schemes, and determine the bit per Joule efficiency of network models for common propagation parameters under varying network densities and cooperation cluster sizes.
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paper_title: Bits-per-Joule Capacity of Energy-Limited Wireless Networks

paper_content:

For a wireless network in which every node is bounded in its energy supply, we define a new concept of network capacity called "bits-per-Joule capacity", which is the maximum total number of bits that the network can deliver per Joule of energy deployed into the network. For a fixed network size, a finite number of information bits is delivered for each source-destination pair, under a fixed end-to-end probability of error constraint. We prove that under the one-to-one traffic model in which every node wants to send traffic to a randomly chosen destination node, the bits-per-Joule capacity of a stationary wireless network grows asymptotically as Omega((N/logN)(q-1)/2 ), where N is the number of nodes randomly deployed onto the surface of a sphere and q is the path loss exponent. Further, the length of the block codes used grows only logarithmically in N, which indicates manageable decoder complexity as the network scales. The fact that the bits-per-Joule capacity grows with the number of nodes contrasts sharply with the scaling laws that have been derived for throughput capacity and implies that large-scale deployments for energy-limited sensor and ad hoc networks may be suitable for delay-tolerant data applications
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paper_title: Optimal wake-up mechanism for single base station with sleep mode

paper_content:

Base station (BS) sleeping is an effecting way to improve the energy-efficiency of cellular networks. Considering BS sleep mode operation under different scenarios, we focus on three wake-up policies: single vacation (SV) policy, multiple vacation (MV) policy and N policy. A hysteresis time is also considered to avoid frequent BS mode-changing operation. By modeling the systems as M/G/1 vacation queues, we derive two performance measures of interest, expected system response time and energy consumption per bit. The impacts of sleep mode operation parameters and setup time are also studied. In order to determine the optimal parameter settings, which allows for a flexible tradeoff between energy-efficiency and mean delay, a two-step optimization method is proposed. We numerically analyze and investigate the energy-delay tradeoff for different policies, and find that both the MV policy and the N policy have better performance than the SV policy if the sniffing cost is not considered. However, these advantages diminish when the sniffing cost increases.
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paper_title: Enablers for Energy Efficient Wireless Networks

paper_content:

Mobile communications are increasingly contributing to global energy consumption. The EARTH (Energy Aware Radio and neTworking tecHnologies) project tackles the important issue of reducing CO2 emissions by enhancing the energy efficiency of cellular mobile networks. EARTH is a holistic approach to develop a new generation of energy efficient products, components, deployment strategies and energy-aware network management solutions. In this paper the holistic EARTH approach to energy efficient mobile communication systems is introduced. Performance metrics are studied so to assess the theoretical bounds of energy efficiency and the practical achievable limits. Moreover, various deployment strategies focusing on their potential to reduce energy consumption are studied, whilst providing uncompromised coverage and user experience. This includes heterogeneous networks with a sophisticated mix of different cell sizes, which may be further enhanced by energy efficient relaying and base station cooperation technologies. Finally, scenarios leveraging the capability of advanced terminals to operate on multiple radio access technologies (RAT) are discussed with respect to their energy savings potential.
---
paper_title: Channel capacity in bits per joule

paper_content:

Underwater acoustic telemetry has a total input energy constraint, since the energy is stored in the transmitter's batteries. This work is primarily rephrasing the work in channel capacity in terms of C_{J} bit/J as compared to C bit/s, to emphasize the energy efficiency and to deemphasize the speed of the telemetry. The energy channel capacity C_{J} , for any waveform channel with well-defined capacity C bit/s at signal power S watts, is defined as C/S bit/J. It is shown that for coherent binary frequency shift keying (BFSK) and waveform channels, the supremum of C_{J} over S is approached as S approaches zero. For the Gaussian channel the best coding uses narrow bands with the highest S/N.
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paper_title: Energy efficiency metrics for green wireless communications

paper_content:

Recently the concern on energy efficiency in wireless communications has been growing rapidly as energy consumption increasingly becomes a global environment problem. Lots of research and development efforts have been spent in wireless industry, aiming for energy efficient solutions which lead to green wireless communications. In this paper we provide a brief overview on those efforts, with an emphasis on introducing energy efficiency metrics. Since energy efficiency metrics are indicators of efficiency, understanding those metrics provides us a better view on how energy efficiency can be achieved in wireless systems/networks. Observing energy is a concern at every corner of a wireless system/network, we describe those metrics from at component, equipment and system/networks level, respectively. From our observation, energy efficiency metrics for components and equipments have been well established. However, studied for system/network level solutions and metrics deserve more attention. We believe new energy efficient architecture and associated metrics will be the key for the energy consumption problem in wireless industry.
---
paper_title: Green Cellular Networks: A Survey, Some Research Issues and Challenges

paper_content:

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technology
---
paper_title: Energy Efficient Radio Access Architectures for Green Radio: Large versus Small Cell Size Deployment

paper_content:

In this paper new architectural approaches that improve the energy efficiency of a cellular radio access network (RAN) are investigated. The aim of the paper is to characterize both the energy consumption ratio (ECR) and the energy consumption gain (ECG) of a cellular RAN when the cell size is reduced for a given user density and service area. The paper affirms that reducing the cell size reduces the cell ECR as desired while increasing the capacity density but the overall RAN energy consumption remains unchanged. In order to trade the increase in capacity density with RAN energy consumption, without degrading the cell capacity provision, a sleep mode is introduced. In sleep mode, cells without active users are powered-off, thereby saving energy. By combining a sleep mode with a small-cell deployment architecture, the paper shows that the ECG can be increased by the factor n = (R/R) while the cell ECR continues to decrease with decreasing cell size.
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paper_title: JouleSort: a balanced energy-efficiency benchmark

paper_content:

The energy efficiency of computer systems is an important concern in a variety of contexts. In data centers, reducing energy use improves operating cost, scalability, reliability, and other factors. For mobile devices, energy consumption directly affects functionality and usability. We propose and motivate JouleSort, an external sort benchmark, for evaluating the energy efficiency of a wide range of computer systems from clusters to handhelds. We list the criteria, challenges, and pitfalls from our experience in creating a fair energy-efficiency benchmark. Using a commercial sort, we demonstrate a JouleSort system that is over 3.5x as energy-efficient as last year's estimated winner. This system is quite different from those currently used in data centers. It consists of a commodity mobile CPU and 13 laptop drives connected by server-style I/O interfaces.
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paper_title: Area green efficiency (AGE) of two tier heterogeneous cellular networks

paper_content:

Small cell networks are becoming standard part of the future heterogeneous networks. In this paper, we consider a two tier heterogeneous network which promises energy savings by integrating the femto and macro cellular networks and thereby reducing CO 2 emissions, operational and capital expenditures (OPEX and CAPEX) whilst enhancing the area spectral efficiency (ASE) of the network. In this context, we define a performance metric which characterize the aggregate energy savings per unit macrocell area and is referred to as area green efficiency (AGE) of the two tier heterogeneous network where the femto base stations are arranged around the edge of the reference macrocell such that the configuration is referred to as femto-on-edge (FOE). The mobile users in macro and femto cellular networks are transmitting with the adaptive power while maintaining the desired link quality such that the energy aware FOE configuration mandates to (i) save energy, and (ii) reduce the co-channel interference. We present a mathematical analysis to incorporate the uplink power control mechanism adopted by the mobile users and calibrate the uplink ASE and AGE of the energy aware FOE configuration. Next, we derive analytical expressions to compute the bounds on the uplink ASE of energy aware FOE configuration and demonstrate that the derived bounds are useful in evaluating the ASE under worst and best case interference scenarios. Simulation results are produced to demonstrate the ASE and AGE improvements in comparison to macro-only and macro-femto configuration with uniformly distributed femtocells.
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paper_title: Dynamic idle mode procedures for femtocells

paper_content:

The concept of a user-deployed femtocell that operates in licensed spectrum and provides cellular coverage in the home has attracted much interest in the wireless industry and an extensive deployment of femtocells is expected in the future. However, several issues arise when femtocells become more widely deployed. One concern is the additional energy consumption caused by femtocells due to their continuous receiver processing and signal transmissions, which can be significant with a large number of femtocells. Secondly, the increase in the number of active cells can result in a high increase in core networks signaling for mobility procedures. Finally, the continuous pilot transmissions can cause interference, particularly in dense urban areas. In this paper all these issues are addressed by a novel idle mode procedure which allows the femtocell transmissions and associated processing to be switched off completely at all times when the femtocell does not need to support an active call.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
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paper_title: Energy Efficiency Aspects of Base Station Deployment Strategies for Cellular Networks

paper_content:

In the strive for lessening of the environmental impact of the information and communication industry, energy consumption of communication networks has recently received increased attention. Although cellular networks account for a rather small share of energy use, lowering their energy con- sumption appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular radio networks. This paper investigates on the impact of deployment strategies on the power consumption of mobile radio networks. We consider layouts featuring varying numbers of micro base stations per cell in addition to conventional macro sites. We introduce the concept of area power consumption as a system performance metric and employ simulations to evaluate potential improvements of this metric through the use of micro base stations. The results suggest, that for scenarios with full traffic load, the use of micro base stations has a rather moderate effect on the area power consumption of a cellular network.
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paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
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paper_title: Generalized area spectral efficiency: An effective performance metric for green wireless communications

paper_content:

Area spectral efficiency (ASE) was introduced as a metric to quantify the spectral utilization efficiency of cellular systems. Unlike other performance metrics, ASE takes into account the spatial property of cellular systems. In this paper, we generalize the concept of ASE to study arbitrary wireless transmissions. Specifically, we introduce the notion of affected area to characterize the spatial property of arbitrary wireless transmissions. Based on the definition of affected area, we define the performance metric, generalized area spectral efficiency (GASE), to quantify the spatial spectral utilization efficiency as well as the greenness of wireless transmissions. After illustrating its evaluation for point-to-point transmission, we analyze the GASE performance of several different transmission scenarios, including dual-hop relay transmission, three-node cooperative relay transmission and underlay cognitive radio transmission. We derive closed-form expressions for the GASE metric of each transmission scenario under Rayleigh fading environment whenever possible. Through mathematical analysis and numerical examples, we show that the GASE metric provides a new perspective on the design and optimization of wireless transmissions, especially on the transmitting power selection. We also show that introducing relay nodes can greatly improve the spatial utilization efficiency of wireless systems. We illustrate that the GASE metric can help optimize the deployment of underlay cognitive radio systems.
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paper_title: Multiple daily base station switch-offs in cellular networks

paper_content:

In this paper we study base station sleep modes, which are today considered a viable approach to improve the energy efficiency of cellular access networks, by reducing power consumption in periods of low traffic. When some base stations are switched off, radio coverage and service provisioning are taken care of by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This is a realistic assumption in the case of the dense base station layouts of urban areas, which consume most of the network energy. We develop simple analytical models that allow optimal base station switch-off times to be identified as a function of the daily traffic pattern, in the cases in which either just one switch-off per day is possible (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several switch-offs per day are permitted (progressively reducing the number of active base stations and the network power). We first assume that any fraction of base stations can be switched off, then we consider a realistic case. We quantify the percentage of energy which can be saved with base station sleep modes, proving that it can be close to 50% of the total network energy consumption.
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paper_title: Optimal Energy Savings in Cellular Access Networks

paper_content:

In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.
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paper_title: Absolute energy efficiency metric for carbon footprint resource management and network optimisation

paper_content:

We describe the first attempt to define an absolute energy efficiency figure that can be applied to any data network or ICT device to provide an understanding of its absolute energy efficiency. The resulting equation can be used as an objective comparative tool to assist in comparing the energy-efficiency performances of equivalently functional systems. More importantly, it also gives a guide as to how much more energy efficiency should theoretically be able to be squeezed out of a system. We describe how our absolute energy efficiency figure can be applied within a networking context to achieve optimised carbon footprint resource allocation. Based on Dijkstra's algorithm for open shortest path first (OSPF) traffic engineering, we show how additional “green” control bits can be added to the latest internet protocol (IP) standard to achieve scalable and enhanced-functionality solutions in the problem of carbonfootprint minimization. Our techniques find generic application.
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paper_title: Energy Efficient Radio Access Architectures for Green Radio: Large versus Small Cell Size Deployment

paper_content:

In this paper new architectural approaches that improve the energy efficiency of a cellular radio access network (RAN) are investigated. The aim of the paper is to characterize both the energy consumption ratio (ECR) and the energy consumption gain (ECG) of a cellular RAN when the cell size is reduced for a given user density and service area. The paper affirms that reducing the cell size reduces the cell ECR as desired while increasing the capacity density but the overall RAN energy consumption remains unchanged. In order to trade the increase in capacity density with RAN energy consumption, without degrading the cell capacity provision, a sleep mode is introduced. In sleep mode, cells without active users are powered-off, thereby saving energy. By combining a sleep mode with a small-cell deployment architecture, the paper shows that the ECG can be increased by the factor n = (R/R) while the cell ECR continues to decrease with decreasing cell size.
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paper_title: Self-organized energy efficient cellular networks

paper_content:

Base stations (BSs) are the main energy expenditure elements of cellular networks, considering the high coverage requirements and the fact that the total provisioned capacity is intended to match peak hour traffic demand. In this paper, we introduce energy saving algorithms based on coordination between network elements. We introduce the notion of energy partitions - associations of powered-on and powered-off BSs - to deliver energy saving with the objective of matching offered capacity with the traffic demand in a flexible manner. Our energy saving algorithms are based on shared knowledge of load and coverage information and enable an appropriate cell reconfiguration for achieving a network-level energy saving. Through a simulation-based evaluation, we analyze the performance of centralized and distributed algorithms under different network topologies and traffic conditions, highlight the benefits and drawbacks, and provide recommendations for deployment scenarios.
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paper_title: Base Station Operation and User Association Mechanisms for Energy-Delay Tradeoffs in Green Cellular Networks

paper_content:

Energy-efficiency, one of the major design goals in wireless cellular networks, has received much attention lately, due to increased awareness of environmental and economic issues for network operators. In this paper, we develop a theoretical framework for BS energy saving that encompasses dynamic BS operation and the related problem of user association together. Specifically, we formulate a total cost minimization that allows for a flexible tradeoff between flow-level performance and energy consumption. For the user association problem, we propose an optimal energy-efficient user association policy and further present a distributed implementation with provable convergence. For the BS operation problem (i.e., BS switching on/off), which is a challenging combinatorial problem, we propose simple greedy-on and greedy-off algorithms that are inspired by the mathematical background of submodularity maximization problem. Moreover, we propose other heuristic algorithms based on the distances between BSs or the utilizations of BSs that do not impose any additional signaling overhead and thus are easy to implement in practice. Extensive simulations under various practical configurations demonstrate that the proposed user association and BS operation algorithms can significantly reduce energy consumption.
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paper_title: Optimal control for base station sleep mode in energy efficient radio access networks

paper_content:

In this paper1, we investigate network sleep mode for reducing energy consumption of radio access networks. We propose an offline-optimized controller that associates to each traffic an activation/deactivation policy that maximizes a multiple objective function of the Quality of Service (QoS) and the energy consumption. We focus on practical implementation issues that may affect the QoS and the stability of the system. We namely consider the activation time issue that results in the degradation of the throughput and the ping-pong effect that results in unnecessary ON/OFF oscillations. We illustrate our results numerically in beyond 3G networks.
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paper_title: Energy savings for cellular network with evaluation of impact on data traffic performance

paper_content:

We present a concrete methodology for saving energy in future and contemporary cellular networks. It is based on re-arranging the user-cell association so as to allow shutting down under-utilized parts of the network. We consider a hypothetical static case where we have complete knowledge of stationary user locations and thus the results represent an upper bound of potential energy savings. We formulate the problem as a binary integer programming problem, thus it is NP-hard, and we present a heuristic approximation method. We simulate the methodology on an example real cellular network topology with traffic-and user distribution generated according to recently measured patterns. Further, we evaluate the energy savings, using realistic energy profiles, and the impact on the user-perceived network performance, represented by delay and throughput, at various times of day. The general findings conclude that up to 50% energy may be saved in less busy periods, while the performance effects remain limited. We conclude that practical, real-time user-cell re-allocation methodology, taking into account user mobility predictions, may thus be feasible and bring significant energy savings at acceptable performance impact.
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paper_title: Sleep mode implementation issues in green base stations

paper_content:

In this paper, we focus on practical issues when implementing sleep mode in base stations. Our aim being to reduce energy consumption without affecting the Quality of Service (QoS) perceived by users, we expose some problems that my occur when applying sleep mode and propose practical solutions to cope with the resulting QoS degradation. We namely consider activation time issue that may result in blocking new or handover calls, and the ping-pong effect resulting in unnecessary ON/OFF oscillations. We show, using a realistic large-scale simulator, how to choose sleep mode implementation that achieves the best tradeoff between QoS preservation and energy consumption reduction.
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paper_title: On energy-delay tradeoff in base station sleep mode operation

paper_content:

Base station (BS) sleep mode operation is one of the effective ways to save energy, but it may lead to longer delay to the customers. In order to evaluate the tradeoffs between energy consumption and customer delay, we model the BS sleep mode operation as an N-policy M/G/1 vacation queue with setup and close-down times, where the BS enters sleep mode if no customers arrive during the close-down time after the queue becomes empty and it starts to setup when it sees N customer arrivals during its sleep period. Several closed-form formulas are derived to demonstrate the tradeoffs between energy consumption and mean delay by changing the close-down time and N. It is shown that the relationship between the energy consumption and the mean delay is linear by changing the close-down time. Besides, larger N reduces the energy consumption, but there may exist N > 1 that minimizes the mean delay. We also investigate the bound on given percentile of overall delay. We observe that the delay bound is nearly linear in mean delay in the cases tested. Therefore, similar tradeoffs exist between energy consumption and the delay bound.
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paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
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paper_title: Energy Consumption Issues on Mobile Network Systems

paper_content:

This paper describes energy consumption demographic data in operating real mobile networks. We examine published data from NTT DoCoMo, which is the largest mobile telecommunication operator in Japan and operating nationwide 3G networks, and identify the most power consuming part is of radio access networks including base tranciever stations. We also investigate power consumption of terminals, and find that the consumption ratio of terminal v.s. networks is about 1:150. Our daily energy consumption per a customer is 0.83 Wh/day for a terminal and 120 Wh/day for the mobile network. The terminal side energy consumption is negligible in view of total CO2 emission though, limitation of its battery performance raises another issue called "energy starvation of mobile devices." The demographic data leads our discussion to (1) radio-on-fiber access network architecture as green networks and (2) thin client models as the key to sustain the evolution toward the future.
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paper_title: CAPS: A peer data sharing system for load mitigation in cellular data networks

paper_content:

The exponential growth of mobile data users and services places a heavy burden on the limited wireless bandwidth of cellular data networks. The situation will be exacerbated with the advent of high bandwidth multimedia applications for mobile devices. We propose an architecture called the cellular-based ad hoc peer data sharing system (CAPS) to reduce the load on the cellular network while improving request response times. In CAPS, mobile hosts in a cellular network form an overlay multihop wireless network. This ad hoc network acts as a 'virtual cache' that enables data sharing among mobile hosts. Participating mobiles share the contents of their local caches with other mobiles. A subset of mobile hosts keep track of the location of objects with minimal overhead. Using CAPS, popular objects can be obtained over the ad hoc network without accessing the cellular infrastructure, thereby reducing the load on the cellular network and improving data access latency. We have extensively evaluated the performance of this architecture through simulations in ns-2 across a wide range of scenarios, and find that CAPS reduces the timeouts of the user requests by 70-90% and reduces the load at the base station by up to 60%.
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paper_title: Device Power Saving and Latency Optimization in LTE-A Networks Through DRX Configuration

paper_content:

Discontinuous reception (DRX) saves battery power of user equipment (UE) usually at the expense of potential increase in latency in the Long Term Evolution (LTE) networks. Therefore, an optimization is needed to find the best tradeoff between latency and power saving. In this paper, we first develop an analytical model to estimate power saving achieved and latency incurred by DRX mechanism for active and background mobile traffic. A tradeoff scheme is then formulated to maintain a balance between these two performance parameters based on operator's preference for power saving and latency requirement of traffic. The analytical model is validated using system level simulation results obtained from OPNET Modeler. The results show that the proposed tradeoff scheme is efficient in keeping a balance between power saving and latency. The results also indicate that DRX short cycles are very effective in reducing latency for active traffic, while shorter inactivity timer is desirable for background traffic to enhance power saving. We also proposed a mechanism to switch DRX configuration based on traffic running at UE, using UE assistance procedure recently adopted by 3GPP in Release 11. DRX configuration switching increases the power saving significantly without any noticeable increase in latency of active traffic.
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paper_title: Energy Saving Performance Comparison of Coordinated Multi-Point Transmission and Wireless Relaying

paper_content:

Currently, two cooperative transmission strategies, Coordinated Multi-Point (CoMP) Transmission and wireless relaying, are expected to be deployed in future cellular systems to improve the performance of cell-edge users. Due to the cooperation diversity, these technologies can potentially lead to more energy saving. Therefore in this paper, we analyze their energy saving performance with an average outage constraint. The impact of the traffic intensity and BS density are also investigated. Based on the typical parameters setting, our calculation results show that traffic intensity can be divided into three classes: ``coverage-limited'' region, ``energy-efficient'' region, and ``capacity-limited'' region. The coverage-limited region prefers offline fixed algorithms, while dynamic online algorithms are more suitable for the energy-efficient region. As BS density goes higher, the energy-efficient region becomes larger. However, the traffic load region where the cooperation schemes bring benefits becomes smaller. To overcome CoMP, relay stations need to consume energy as small as possible. Even through relay cost energy low enough, the traffic intensity region where wireless relaying overcomes CoMP will become smaller as network goes denser. Our analytical results are of great help for future ``green'' network planning.
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paper_title: A traffic prediction based sleeping mechanism with low complexity in femtocell networks

paper_content:

Dynamic sleeping of base stations under off-peak time is an efficient way to reduce the energy consumption of cellular networks. However, traffic in femtocell networks is always under fluctuation, which leads to the high complexity of the existing sleeping approaches. To overcome this problem, in this paper a traffic prediction based sleeping (TPBS) mechanism with low complexity is proposed in femtocell networks. Artificial neural network (ANN) model is used to predict future traffic in each base station. Then based on prediction results, we propose a dynamic base station switching algorithm with low complexity, where base station can be switched off/on dynamically according to the traffic in real time. We show that this approach can minimize the number of active base stations while providing a satisfying service with low blocking probability to all users and, at the same time, the algorithm complexity is low compared with the Markov Decision Process (MDP) based sleeping method. Simulation results are used to evaluate the performance of our schemes considering energy saving and algorithm complexity.
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paper_title: Understanding the characteristics of cellular data traffic

paper_content:

Because of rapidly growing subscriber populations, advances in cellular communication technology, increasingly capable user terminals, and the expanding range of mobile applications, cellular networks have experienced a significant increase in data traffic, the dominant part of which is carried by the http protocol. Understanding the characteristics of this traffic is important for network design, traffic modeling, resource planning and network control. In this study we present a comprehensive characterization study of mobile http-based traffic using packet level traces collected in a large cellular network. We analyze the traffic using metrics at packet level, flow level and session level. For each metric, we conduct a comparison between traffic from different applications, as well as comparison to traffic in a wired network. Finally, we discuss the implications of our findings for better resource utilization in cellular infrastructures.
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paper_title: Traffic-driven power saving in operational 3G cellular networks

paper_content:

Base stations (BSes) in the 3G cellular network are not energy proportional with respect to their carried traffic load. Our mea- surements show that 3G traffic exhibits high fluctuations both in time and over space, thus incurring energy waste. In this paper, we propose a profile-based approach to green cellular infrastruc- ture. We profile BS traffic and approximate network-wide energy proportionality using non-load-adaptive BSes. The instrument is to leverage temporal-spatial traffic diversity and node deployment heterogeneity, and power off under-utilized BSes under light traf- fic. Our evaluation on four regional 3G networks shows that this simple scheme yields up to 53% energy savings in a dense large city and 23% in a sparse, mid-sized city.
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paper_title: TACT: A Transfer Actor-Critic Learning Framework for Energy Saving in Cellular Radio Access Networks

paper_content:

Recent works have validated the possibility of improving energy efficiency in radio access networks (RANs), achieved by dynamically turning on/off some base stations (BSs). In this paper, we extend the research over BS switching operations, which should match up with traffic load variations. Instead of depending on the dynamic traffic loads which are still quite challenging to precisely forecast, we firstly formulate the traffic variations as a Markov decision process. Afterwards, in order to foresightedly minimize the energy consumption of RANs, we design a reinforcement learning framework based BS switching operation scheme. Furthermore, to avoid the underlying curse of dimensionality in reinforcement learning, a transfer actor-critic algorithm (TACT), which utilizes the transferred learning expertise in historical periods or neighboring regions, is proposed and provably converges. In the end, we evaluate our proposed scheme by extensive simulations under various practical configurations and show that the proposed TACT algorithm contributes to a performance jumpstart and demonstrates the feasibility of significant energy efficiency improvement at the expense of tolerable delay performance.
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paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
---
paper_title: Toward self-organizing sectorization of LTE eNBs for energy efficient network operation under QoS constraints

paper_content:

Energy efficiency is one of the central concerns for future cellular networks, which could be accomplished by adaptively reconfiguring the networks with the changing traffic environment. In this paper, we propose and analyze a dynamic sectorization scheme of evolved node Bs (eNBs) in long term evolution (LTE) systems for saving energy at radio access network (RAN) level. Under the proposal, based on the instantaneous traffic, each eNB dynamically reconfigures itself in real-time utilizing minimum number of sectors, while maintaining the quality of service (QoS). The proposed technique is implemented in each eNB requiring no correspondence with other eNBs, while no human intervention is required as well. Thus, the proposed technique is of distributed and self-organizing in nature. We thoroughly investigate the performance of the proposed system under a wide range of traffic scenarios, eNB power profiles, user distributions and QoS requirements. Simulation results indicate a significant reduction in network energy consumption. Furthermore, the proposed technique is simple, but effective and easy to implement. Comparison with other research is also presented, which proves the superiority of our proposal.
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paper_title: Self-organizing Load Balancing for Relay Based Cellular Networks

paper_content:

A self-organizing load balancing framework is proposed in this paper. It provides self-optimizing load balancing policies to improve adaptation and robustness of Fixed Relay Station (FRS) based cellular networks. The framework proposes a Self-organizing Cooperative Partner Cluster (SCPC) concept to dynamically select optimal partners of each BS and RS. A novel Comprehensive Load Balancing Policy Stack (CLBPS) is also proposed to utilize merits of various load balancing policies. Load balancing performance, signaling costs and user experience are taken into account in both SCPC and CLBPS. Simulation results show that the call blocking rate is reduced and the network throughput of FRS networks is improved.
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paper_title: Cell Zooming for Power Efficient Base Station Operation

paper_content:

With enormous growth in the telecommunication industry, energy efficiency has become a critical issue. Base stations and the core network account for a large amount of energy consumption today. Traditional energy saving techniques switch some base stations off completely during light loads to save energy. This creates problems for the backhaul network and also for quickly returning to full capacity when demand increases. In this paper, we propose novel cell zooming techniques to reduce energy consumption at base stations. With cell zooming, base stations dynamically adjust their coverage radius and hence their transmit powers based on user locations. The transmit power is set to the minimum required level depending on user locations, signal to interference and noise ratio (SINR) and quality of service (QoS) requirements of the users. Base stations are never completely switched off. Our simulations show that the proposed cell zooming algorithm reduces the energy consumption of base stations by up to 40% compared to traditional static-coverage-area base stations without compromising on the QoS requirements of any user in the cell.
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paper_title: Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

paper_content:

Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile charging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is applied to derive the tradeoffs between the network parameters including p, q, and the BS/PB densities under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product the BS density decreases with increasing p following a power law where the exponent is proportional to the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product between q, the PB density, and the BS density raised to a power proportional to the path-loss exponent has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, a similar result is obtained with the aforementioned product increased by the array gain. Last, similar results are derived for the case of mobiles having small energy storage.
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paper_title: Base Station Operation and User Association Mechanisms for Energy-Delay Tradeoffs in Green Cellular Networks

paper_content:

Energy-efficiency, one of the major design goals in wireless cellular networks, has received much attention lately, due to increased awareness of environmental and economic issues for network operators. In this paper, we develop a theoretical framework for BS energy saving that encompasses dynamic BS operation and the related problem of user association together. Specifically, we formulate a total cost minimization that allows for a flexible tradeoff between flow-level performance and energy consumption. For the user association problem, we propose an optimal energy-efficient user association policy and further present a distributed implementation with provable convergence. For the BS operation problem (i.e., BS switching on/off), which is a challenging combinatorial problem, we propose simple greedy-on and greedy-off algorithms that are inspired by the mathematical background of submodularity maximization problem. Moreover, we propose other heuristic algorithms based on the distances between BSs or the utilizations of BSs that do not impose any additional signaling overhead and thus are easy to implement in practice. Extensive simulations under various practical configurations demonstrate that the proposed user association and BS operation algorithms can significantly reduce energy consumption.
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paper_title: Breathe to stay cool: adjusting cell sizes to reduce energy consumption

paper_content:

Reducing the energy consumption of a wireless cellular network is an important and urgent problem. This paper studies the effect of cell sizes on the energy consumed by the network, assuming base station technologies of today and the future. Making cell sizes too small or too large can significantly increase energy consumption. We show that the optimal cell size from an energy perspective depends on a number of factors, including base station technology, data rates, and traffic demands. Given that traffic varies significantly during a day, dynamically adjusting cell sizes can help reduce energy consumption. We propose a practical, 2-level scheme that adjusts cell sizes between two fixed values, and show an energy saving of up to 40%. The paper also proposes some self-organizing techniques to allow this dynamic cell size adjustment.
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paper_title: Cell size breathing and possibilities to introduce cell sleep mode

paper_content:

Global warming has put the energy consumption of all industries into focus. In 2005 mobile communications contributed to about 0.2% of global CO 2 emissions. Mobile operators have been reporting annual increases from 300% to 700% in 3G data traffic volumes. Such a steady growth in traffic requires regular upgrades in the infrastructure. While network equipment is in itself becoming more efficient, these upgrades still increase the overall energy consumption of the networks. This paper investigates the energy saving potential of exploiting cell size breathing by putting low loaded cells into sleep mode. The energy consumption and network performance of the resulting network are used to quantify the potential of this feature. The investigation is carried out on a tilt optimized network. Since putting cells into sleep mode results in a non- optimum antenna tilt configuration, this paper also investigates the possible gains of re-optimizing antenna tilting. The results show that by allowing sleep mode, over a restricted period of 12 hours, an energy saving of 33% is possible. While this energy saving comes at no expense of the overall network performance, the gain in average user data rate is noted to decrease by 21%.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
---
paper_title: Energy savings for cellular network with evaluation of impact on data traffic performance

paper_content:

We present a concrete methodology for saving energy in future and contemporary cellular networks. It is based on re-arranging the user-cell association so as to allow shutting down under-utilized parts of the network. We consider a hypothetical static case where we have complete knowledge of stationary user locations and thus the results represent an upper bound of potential energy savings. We formulate the problem as a binary integer programming problem, thus it is NP-hard, and we present a heuristic approximation method. We simulate the methodology on an example real cellular network topology with traffic-and user distribution generated according to recently measured patterns. Further, we evaluate the energy savings, using realistic energy profiles, and the impact on the user-perceived network performance, represented by delay and throughput, at various times of day. The general findings conclude that up to 50% energy may be saved in less busy periods, while the performance effects remain limited. We conclude that practical, real-time user-cell re-allocation methodology, taking into account user mobility predictions, may thus be feasible and bring significant energy savings at acceptable performance impact.
---
paper_title: Energy-efficient cellular network operation via base station cooperation

paper_content:

The rising cost of energy and increased environmental awareness have sparked a keen interest in the development and deployment of energy-efficient communication technologies. The energy efficiency of cellular networks can be increased significantly by selectively switching off some of the base stations (BSs) during periods of low traffic load. In this paper, we propose a scalable BS switching strategy and use cooperative communications and power control to extend network coverage to the service areas of the switched-off BSs. The outage probability and the achievable power savings of the proposed scheme are analyzed, both analytically and numerically, and a potential of up to 50% power saving is observed in the numerical results.
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paper_title: Greening cellular radio access networks: A numerical method for the selection of detachable base stations in low traffic scenarios

paper_content:

In the last years there had been several contributions about decreasing the energy consumption of communication networks. In mobile communication networks, the major part of the energy consumption incurs in the radio access network. In this paper we present a numerical method which finds the maximum subset of detachable ceils for a given base station topology. Additionally our algorithm calculates the antenna downtilt settings for the remaining cells to guarantee full network coverage. We evaluate our new method and the energy saving potentials by means of two German urban/suburban 3G mobile network scenarios and different mobile data services.
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paper_title: Self-organized energy efficient cellular networks

paper_content:

Base stations (BSs) are the main energy expenditure elements of cellular networks, considering the high coverage requirements and the fact that the total provisioned capacity is intended to match peak hour traffic demand. In this paper, we introduce energy saving algorithms based on coordination between network elements. We introduce the notion of energy partitions - associations of powered-on and powered-off BSs - to deliver energy saving with the objective of matching offered capacity with the traffic demand in a flexible manner. Our energy saving algorithms are based on shared knowledge of load and coverage information and enable an appropriate cell reconfiguration for achieving a network-level energy saving. Through a simulation-based evaluation, we analyze the performance of centralized and distributed algorithms under different network topologies and traffic conditions, highlight the benefits and drawbacks, and provide recommendations for deployment scenarios.
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paper_title: Understanding traffic dynamics in cellular data networks

paper_content:

We conduct the first detailed measurement analysis of network resource usage and subscriber behavior using a large-scale data set collected inside a nationwide 3G cellular data network. The data set tracks close to a million subscribers over thousands of base stations. We analyze individual subscriber behaviors and observe a significant variation in network usage among subscribers. We characterize subscriber mobility and temporal activity patterns and identify their relation to traffic volume. We then investigate how efficiently radio resources are used by different subscribers as well as by different applications. We also analyze the network traffic from the point of view of the base stations and find significant temporal and spatial variations in different parts of the network, while the aggregated behavior appears predictable. Broadly, our observations deliver important insights into network-wide resource usage. We describe implications in pricing, protocol design and resource and spectrum management.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
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paper_title: Stochastic analysis of energy savings with sleep mode in OFDMA wireless networks

paper_content:

The issue of energy efficiency (EE) in Orthogonal Frequency-Division Multiple Access (OFDMA) wireless networks is discussed in this paper. Our interest is focused on the promising concept of base station (BS) sleep mode, introduced recently as a key feature in order to dramatically reduce network energy consumption. The proposed technical approach fully exploits the properties of stochastic geometry, where the number of active cells is reduced in a way that the outage probability, or equivalently the signal to interference plus noise (SINR) distribution, remains the same. The optimal EE gains are then specified with the help of a simplified but yet realistic BS power consumption model. Furthermore, the authors extend their initial work by studying a non-singular path loss model in order to verify the validity of the analysis and finally, the impact on the achieved user capacity is investigated. In this context, the significant contribution of this paper is the evaluation of the theoretically optimal energy savings of sleep mode, with respect to the decisive role that the BS power profile plays.
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paper_title: Energy-Efficient Repulsive Cell Activation for Heterogeneous Cellular Networks

paper_content:

In this paper, we consider a two-tier heterogeneous cellular network (HCN) where macrocells and distributed low power cells, namely daughtercells, are operated in a common spectrum. Due to the ad-hoc nature of daughtercell BS deployments such as pico and femto cells, the mutual interference varies and obviously the coverage probability behaves differently in terms of transmit powers and densities of macrocells and daughtercells. In this paper, we employ repulsive cell activation in the interfering daughtercell network and see the impact of a minimum separation distance between the daughtercell BSs in terms of coverage under open access and power efficiency. The control of the minimum separation distance plays a role in balancing cell load effectively according to changing user density and is justified for the coexistence of low power daughtercells. The optimal minimum separation distance in terms of user density and target per-tier user throughput requirements is found by a numerical search based on a simple bisection method. Numerical results show the benefit of cell repulsion in terms of increased user density support and less area power consumption.
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paper_title: Greening cellular radio access networks: A numerical method for the selection of detachable base stations in low traffic scenarios

paper_content:

In the last years there had been several contributions about decreasing the energy consumption of communication networks. In mobile communication networks, the major part of the energy consumption incurs in the radio access network. In this paper we present a numerical method which finds the maximum subset of detachable ceils for a given base station topology. Additionally our algorithm calculates the antenna downtilt settings for the remaining cells to guarantee full network coverage. We evaluate our new method and the energy saving potentials by means of two German urban/suburban 3G mobile network scenarios and different mobile data services.
---
paper_title: Challenges and enabling technologies for energy aware mobile radio networks

paper_content:

Mobile communications are increasingly contributing to global energy consumption. In this article, a holistic approach for energy efficient mobile radio networks is presented. The matter of having appropriate metrics and evaluation methods that allow assessing the energy efficiency of the entire system is discussed. The mutual supplementary saving concepts comprise component, link and network levels. At the component level the power amplifier complemented by a transceiver and a digital platform supporting advanced power management are key to efficient radio implementations. Discontinuous transmission by base stations, where hardware components are switched off, facilitate energy efficient operation at the link level. At the network level, the potential for reducing energy consumption is in the layout of networks and their management, that take into account slowly changing daily load patterns, as well as highly dynamic traffic fluctuations. Moreover, research has to analyze new disruptive architectural approaches, including multi-hop transmission, ad-hoc meshed networks, terminal-to-terminal communications, and cooperative multipoint architectures.
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paper_title: Device Power Saving and Latency Optimization in LTE-A Networks Through DRX Configuration

paper_content:

Discontinuous reception (DRX) saves battery power of user equipment (UE) usually at the expense of potential increase in latency in the Long Term Evolution (LTE) networks. Therefore, an optimization is needed to find the best tradeoff between latency and power saving. In this paper, we first develop an analytical model to estimate power saving achieved and latency incurred by DRX mechanism for active and background mobile traffic. A tradeoff scheme is then formulated to maintain a balance between these two performance parameters based on operator's preference for power saving and latency requirement of traffic. The analytical model is validated using system level simulation results obtained from OPNET Modeler. The results show that the proposed tradeoff scheme is efficient in keeping a balance between power saving and latency. The results also indicate that DRX short cycles are very effective in reducing latency for active traffic, while shorter inactivity timer is desirable for background traffic to enhance power saving. We also proposed a mechanism to switch DRX configuration based on traffic running at UE, using UE assistance procedure recently adopted by 3GPP in Release 11. DRX configuration switching increases the power saving significantly without any noticeable increase in latency of active traffic.
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paper_title: Adaptive Power Saving Strategies for IEEE 802.16e Mobile Broadband Wireless Access

paper_content:

IEEE 802.16e is an emerging standard for mobile wireless broadband access systems. In any mobile networks, power saving is one of the most important features for the extension of devices' lifetime. In this paper, we introduce the sleep-mode operation of IEEE 802.16e and parameters related to this operation. Then, we adapt these parameters according to different traffic types for efficient power saving. For CBR traffic, by setting a proper initial-sleep window size, the maximum delay can be guaranteed while saving the average power consumption. For FTP traffic, by sleeping during queue-empty periods, the throughput performance is barely sacrificed while efficient power saving is accomplished.
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paper_title: Cell switch off technique combined with coordinated multi-point (CoMP) transmission for energy efficiency in beyond-LTE cellular networks

paper_content:

With the ever increasing usage of wireless devices, the power consumption and energy efficiency of cellular networks have become important performance indicators. In recent years, various types of energy saving schemes have been proposed for cellular networks. However, most of these schemes do not take advantage of the advanced features offered by the recent cellular standards, such as the 3GPP release 10 (also known as LTE-Advanced) and beyond. One of the recently proposed energy saving schemes in cellular networks is the cell switch off technique in which a lightly loaded cell is completely switched off and the traffic in that region is absorbed by the nearby cells whose transmit powers are increased to enable larger coverage areas. In this paper, we propose to use the cell switch off scheme without increasing the transmit powers of the active cells; instead, we propose to use the coordinated multipoint (CoMP) transmission radio technology, which is being standardized for the beyond-LTE cellular networks, to enable a sufficient received power level from a number of nearby cells whenever possible. Through simulations with realistic parameters, we demonstrate that the above described cell switch off + CoMP combination used with proper CoMP active set degree yields a more energy efficient solution with better received user experience in comparison to the traditional cell switch off schemes. In the proposed scheme, channel estimations are needed in order to determine the CoMP active set accurately. We analyze the performance by modeling the channel estimation error as a Gaussian random variable with 4, 8, and 12 dB standard deviation and observe that perfect channel estimation can provide up to 46% capacity and 24% energy efficiency increase in comparison to the scenarios with the channel estimation errors.
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paper_title: Energy saving in OFDMA cellular systems using base-station sleep mode: 3GPP-LTE a case study

paper_content:

Green Radio has emerged as one of the most important considerations in the present scenario of global warming. It is known that the power consumption of a Base Station is not only due to the radio power transmitted and the power consumed by the digital signal processing transceiver units but also due to the huge amount of power consumed by the cooling system and power backup units. It has been seen that although traffic load varies over a large range during a 24 hour cycle the power consumption does not vary proportionally. Traffic load dependent power saving is one of the foci of this work. An important aspect included in this work is the huge penetration loss that is added to the system Signal to Interference plus Noise Ratio (SINR) during night time when most of the users are considered to be indoor. This work focuses on the performance evaluation cell sleep mode to save power (reduce carbon foot print). Results relating to three sector urban micro-cell scenario as per International Telecommunication Union (ITU) specification are presented. Traffic load threshold for activating the sleep mode is also identified.
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paper_title: Clustering based power saving algorithm for self-organized sleep mode in femtocell networks

paper_content:

A large-scale deployment of femtocell BSs (FBSs) causes the substantial energy consumption. One fairly intuitive way to minimize the energy consumption is to switch off the wireless air interface, or to keep FBSs in the energy saving mode for the most time while preserving the quality of service (QoS) experienced by users. Utilizing this concept, this paper proposes a clustering based power saving algorithm (CPSA) for self-organized sleep mode in femtocell networks. Firstly, CPSA builds a leader-member cluster framework, in which each FBS is either a FBS leader (FL) or a FBS member (FM). Then, the FL acts as an autonomous entity and is responsible for detecting active calls in the cluster coverage, while the FMs without the active user can entirely shut down pilot transmissions and the related processing all the time. So it is suited for self-organizing networks (SONs). With the practical LTE system parameters, simulation results show that the proposed algorithm outperforms three prominent related schemes in terms of average energy consumption and accumulative interference time. Furthermore, the results provide some guidelines for deploying energy efficient femtocell networks.
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paper_title: "Green" distance-aware base station sleeping algorithm in LTE-Advanced

paper_content:

In this paper, we propose a switch on/off algorithm for Base Stations (BSs), which exploits the knowledge of the distance between the User Equipments (UEs) and their associated BS. Our novel approach hopes to provide an improvement to the problem of energy consumption. The major concern lies on reducing the energy consumption of the telecommunication networks by optimizing the power utilization without sacrificing the offered Quality of Service (QoS). Our proposed scheme achieves a significant power saving, based on switching off the Base Stations that are underutilized during low traffic periods (especially during night) in the LTE-Advanced.
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paper_title: Stochastic analysis of energy savings with sleep mode in OFDMA wireless networks

paper_content:

The issue of energy efficiency (EE) in Orthogonal Frequency-Division Multiple Access (OFDMA) wireless networks is discussed in this paper. Our interest is focused on the promising concept of base station (BS) sleep mode, introduced recently as a key feature in order to dramatically reduce network energy consumption. The proposed technical approach fully exploits the properties of stochastic geometry, where the number of active cells is reduced in a way that the outage probability, or equivalently the signal to interference plus noise (SINR) distribution, remains the same. The optimal EE gains are then specified with the help of a simplified but yet realistic BS power consumption model. Furthermore, the authors extend their initial work by studying a non-singular path loss model in order to verify the validity of the analysis and finally, the impact on the achieved user capacity is investigated. In this context, the significant contribution of this paper is the evaluation of the theoretically optimal energy savings of sleep mode, with respect to the decisive role that the BS power profile plays.
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paper_title: Reducing Energy Consumption in LTE with Cell DTX

paper_content:

This paper discusses how energy consumption can be significantly reduced in mobile networks by introducing discontinuous transmission (DTX) on the base station side. By introducing DTX on the downlink, or cell DTX, we show that it is possible to achieve significant energy reductions in an LTE network. Cell DTX is most efficient when the traffic load is low in a cell but even when realistic traffic statistics are considered the gains are impressive. The technology potential for a metropolitan area is shown to be 90% reduced energy consumption compared to no use of cell DTX. The paper also discusses different drives for the increased focus on energy efficient network operation and also provides insights on the impact of cell DTX from a life cycle assessment perspective.
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paper_title: Dual connectivity in LTE HetNets with split control- and user-plane

paper_content:

Recently, a new network architecture with split control-plane and user-plane has been proposed and gained a lot of momentum in the standardisation of Long Term Evolution (LTE) Release 12. In this new network architecture, the control-plane, which transmits system information and handles user connectivity, and the user-plane, which manages user data, are split and no longer transmitted necessarily by the same network node. This dual connectivity confers a large flexibility to the system, and allows for a more energy efficient operation and enhanced mobility management. In this paper, we present a detailed description of our dual connectivity framework based on the latest LTE-Advanced enhancements, in which macrocell-assisted (MA) small cells use different channel state information-reference signals (CSI-RS) to differentiate among each other and allow User Equipment (UE) to take adequate measurements for cell (re)selection. Taking into account the limited number of available CSI-RSs, we study the assignment problem of CSI-RSs to MA small cells, analyse CSI-RS collision and confusion issues and present simulation results to demonstrate the flexibility of the proposed network architecture.
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paper_title: How green the LTE technology can be?

paper_content:

Reducing Carbon emissions in general in ICT from the present 3 percent and in particular in Mobile communications has been of a serious concern. In the next generation cellular technologies like LTE, base stations are very energy hungry, as they need to provide high spectral efficiency and wide coverage. Given that there is no cooling required for modern systems, the transmit power in a typical link is the most important constituent in a base station. This is mainly due to its power amplifiers and also due to energy loss in the power supply. LTE uses OFDM in downlink, which requires huge complex computations, and the power consumption of the transceiver hardware. With the latest CMOS technology, a two-fold reduction in the operating voltage from 130 nm technology to 22 nm technology, results in a four-fold reductions in the transceiver power consumption. With the LTE technology poised to take off, it is interesting to see the energy consumption assessment of LTE considering the projection of technology and exploiting the different mode of operation and the methods of reducing energy consumption. This paper discusses about the various possibilities and makes a practical assessment of a possible green form of LTE.
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paper_title: A novel time-domain sleep mode design for energy-efficient LTE

paper_content:

This paper describes a time-domain approach for base station transmission sleep modes, taking the Long Term Evolution (LTE) system as a specific example. The idea of this design is to enable the base station to reduce RF energy consumption in low traffic conditions, while still properly supporting active user connections. By switching off traffic during a certain time period and delivering all user information with fewer transmissions under the same rate targets, the energy consumption can be reduced since the control signalling during non-active time is gated off. Taking the example of single user system for simplification, the optimum on-off time with associated power allocation are derived, which enables the energy consumption of the base station to scale with traffic loading. Compared with the corresponding non-sleep mode, this can achieve an up to 90% energy reduction in low traffic conditions.
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paper_title: Self-organized energy efficient cellular networks

paper_content:

Base stations (BSs) are the main energy expenditure elements of cellular networks, considering the high coverage requirements and the fact that the total provisioned capacity is intended to match peak hour traffic demand. In this paper, we introduce energy saving algorithms based on coordination between network elements. We introduce the notion of energy partitions - associations of powered-on and powered-off BSs - to deliver energy saving with the objective of matching offered capacity with the traffic demand in a flexible manner. Our energy saving algorithms are based on shared knowledge of load and coverage information and enable an appropriate cell reconfiguration for achieving a network-level energy saving. Through a simulation-based evaluation, we analyze the performance of centralized and distributed algorithms under different network topologies and traffic conditions, highlight the benefits and drawbacks, and provide recommendations for deployment scenarios.
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paper_title: Toward dynamic energy-efficient operation of cellular network infrastructure

paper_content:

The operation of cellular network infrastructure incurs significant electrical energy consumption. From the perspective of cellular network operators, reducing this consumption is not only a matter of showing environmental responsibility, but also of substantially reducing their operational expenditure. We discuss how dynamic operation of cellular base stations, in which redundant base stations are switched off during periods of low traffic such as at night, can provide significant energy savings. We quantitatively estimate these potential savings through a first-order analysis based on real cellular traffic traces and information regarding base station locations in a part of Manchester, United Kingdom. We also discuss a number of open issues pertinent to implementing such energy-efficient dynamic base station operation schemes, such as various approaches to ensure coverage, and interoperator coordination.
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paper_title: System Selection and Sleep Mode for Energy Saving in Cooperative 2G/3G Networks

paper_content:

I n this paper 1 , we focus on developing energy- efficient radio resource management (RRM) algorithms for heterogeneous networks. Our aim is to optimize energy con- sumption at the network scale, while preserving the Quality of Service (QoS) perceived by users. We develop a system selection algorithm that finds the optimal traffic allocation for the different systems that minimizes power consumption while insuring the target QoS. We apply our algorithm to a cooperative 2G/3G network and show that only a little gain can be obtained, as base stations still have a large energy consumption even if they have no traffic. We then propose a network scale "sleep mode" where an entire system (2G or 3G) can be desactivated for some traffic scenarios. We show that this mode, together with the energy- aware system selection, achieves large energy reductions. consumption of the base stations. We then propose in Section III an energy-aware system selection scheme that splits the traffic between the two systems in an optimal way so that the energy consumption is minimized subject to a Quality of Service (QoS) constraint. We show that some energy savings up to 10% can be achieved using this proposed scheme. In order to further reduce energy consumption of the access network, we study in Section IV the impact of implementing a sleep mode on the systems. We show that large energy savings can be achieved provided that a small degradation of the QoS. Section V eventually concludes the paper.
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paper_title: Base Station Operation and User Association Mechanisms for Energy-Delay Tradeoffs in Green Cellular Networks

paper_content:

Energy-efficiency, one of the major design goals in wireless cellular networks, has received much attention lately, due to increased awareness of environmental and economic issues for network operators. In this paper, we develop a theoretical framework for BS energy saving that encompasses dynamic BS operation and the related problem of user association together. Specifically, we formulate a total cost minimization that allows for a flexible tradeoff between flow-level performance and energy consumption. For the user association problem, we propose an optimal energy-efficient user association policy and further present a distributed implementation with provable convergence. For the BS operation problem (i.e., BS switching on/off), which is a challenging combinatorial problem, we propose simple greedy-on and greedy-off algorithms that are inspired by the mathematical background of submodularity maximization problem. Moreover, we propose other heuristic algorithms based on the distances between BSs or the utilizations of BSs that do not impose any additional signaling overhead and thus are easy to implement in practice. Extensive simulations under various practical configurations demonstrate that the proposed user association and BS operation algorithms can significantly reduce energy consumption.
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paper_title: Optimal control for base station sleep mode in energy efficient radio access networks

paper_content:

In this paper1, we investigate network sleep mode for reducing energy consumption of radio access networks. We propose an offline-optimized controller that associates to each traffic an activation/deactivation policy that maximizes a multiple objective function of the Quality of Service (QoS) and the energy consumption. We focus on practical implementation issues that may affect the QoS and the stability of the system. We namely consider the activation time issue that results in the degradation of the throughput and the ping-pong effect that results in unnecessary ON/OFF oscillations. We illustrate our results numerically in beyond 3G networks.
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paper_title: Minimizing Energy Consumption via Sleep Mode in Green Base Station

paper_content:

In this paper, we develop new energy-efficient, radio resource management schemes for green wireless networks. Our goal is to optimize energy consumption at the network scale while preserving the Quality of Service (QoS) perceived by users. We specifically propose two new sleep mechanisms for base station where a number of resources in system can be shut down for some traffic scenarios in one of two ways: a dynamic way where resources are activated/deactivated in real-time as a function of the instantaneous load of the system, and a semi-static one where resources are kept unchanged during longer time intervals, in the order of one hour. We apply the proposed schemes to 2G and HSPA (High Speed Packet Access) systems and show that the dynamic one achieves larger energy reductions while the semi-static one has an acceptable performance with low complexity
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paper_title: Energy efficient coverage planning in cellular networks with sleep mode

paper_content:

In this paper, we consider energy efficient coverage planning in cellular networks. To save energy, each base station (BS) can work in sleep mode when there is no user in its coverage or the users can be served by neighbor base stations. With increasing coverage overlap, there is a tradeoff between the number of BSs per unit area and the proportion of active base stations. Analytical and numerical methods are presented to evaluate coverage planning schemes with different inter-BS distance. Evaluation results show that compared with the minimum coverage overlap scheme, the optimal planning scheme can reduce the network energy consumption by more than 20%, and the performance improvement depends on the user density, network topology, and the power consumption of sleep mode.
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paper_title: Sleep mode implementation issues in green base stations

paper_content:

In this paper, we focus on practical issues when implementing sleep mode in base stations. Our aim being to reduce energy consumption without affecting the Quality of Service (QoS) perceived by users, we expose some problems that my occur when applying sleep mode and propose practical solutions to cope with the resulting QoS degradation. We namely consider activation time issue that may result in blocking new or handover calls, and the ping-pong effect resulting in unnecessary ON/OFF oscillations. We show, using a realistic large-scale simulator, how to choose sleep mode implementation that achieves the best tradeoff between QoS preservation and energy consumption reduction.
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paper_title: Optimal wake-up mechanism for single base station with sleep mode

paper_content:

Base station (BS) sleeping is an effecting way to improve the energy-efficiency of cellular networks. Considering BS sleep mode operation under different scenarios, we focus on three wake-up policies: single vacation (SV) policy, multiple vacation (MV) policy and N policy. A hysteresis time is also considered to avoid frequent BS mode-changing operation. By modeling the systems as M/G/1 vacation queues, we derive two performance measures of interest, expected system response time and energy consumption per bit. The impacts of sleep mode operation parameters and setup time are also studied. In order to determine the optimal parameter settings, which allows for a flexible tradeoff between energy-efficiency and mean delay, a two-step optimization method is proposed. We numerically analyze and investigate the energy-delay tradeoff for different policies, and find that both the MV policy and the N policy have better performance than the SV policy if the sniffing cost is not considered. However, these advantages diminish when the sniffing cost increases.
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paper_title: Energy efficient management of two cellular access networks

paper_content:

In this paper we evaluate the energy saving that can be achieved with the energy-aware cooperative management of the cellular access networks of two operators offering service over the same area. We evaluate the amount of energy that can be saved by using both networks in high traffic conditions, but switching off one of the two during the periods when traffic is so low that the desired quality of service can be obtained with just one network. When one of the two networks is off, its customers are allowed to roam over the one that is on. Several alternatives are studied, as regards the switch-off pattern: the one that balances the switch-off frequencies, the one that balances roaming costs, the one that balances energy savings, and the one that maximizes the amount of saved energy. Our results indicate that a huge amount of energy can be saved, and suggest that, to reduce energy consumption, new cooperative attitudes of the operators should be encouraged with appropriate incentives, or even enforced by regulation authorities.
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paper_title: Multiple daily base station switch-offs in cellular networks

paper_content:

In this paper we study base station sleep modes, which are today considered a viable approach to improve the energy efficiency of cellular access networks, by reducing power consumption in periods of low traffic. When some base stations are switched off, radio coverage and service provisioning are taken care of by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This is a realistic assumption in the case of the dense base station layouts of urban areas, which consume most of the network energy. We develop simple analytical models that allow optimal base station switch-off times to be identified as a function of the daily traffic pattern, in the cases in which either just one switch-off per day is possible (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several switch-offs per day are permitted (progressively reducing the number of active base stations and the network power). We first assume that any fraction of base stations can be switched off, then we consider a realistic case. We quantify the percentage of energy which can be saved with base station sleep modes, proving that it can be close to 50% of the total network energy consumption.
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paper_title: Optimal Energy Savings in Cellular Access Networks

paper_content:

In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.
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paper_title: Energy Efficient Radio Access Architectures for Green Radio: Large versus Small Cell Size Deployment

paper_content:

In this paper new architectural approaches that improve the energy efficiency of a cellular radio access network (RAN) are investigated. The aim of the paper is to characterize both the energy consumption ratio (ECR) and the energy consumption gain (ECG) of a cellular RAN when the cell size is reduced for a given user density and service area. The paper affirms that reducing the cell size reduces the cell ECR as desired while increasing the capacity density but the overall RAN energy consumption remains unchanged. In order to trade the increase in capacity density with RAN energy consumption, without degrading the cell capacity provision, a sleep mode is introduced. In sleep mode, cells without active users are powered-off, thereby saving energy. By combining a sleep mode with a small-cell deployment architecture, the paper shows that the ECG can be increased by the factor n = (R/R) while the cell ECR continues to decrease with decreasing cell size.
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paper_title: Optimal Control of Wake Up Mechanisms of Femtocells in Heterogeneous Networks

paper_content:

We study, in this work, optimal sleep/wake up schemes for the base stations of network-operated femto cells deployed within macro cells for the purpose of offloading part of its traffic. Our aim is to minimize the energy consumption of the overall heterogeneous network while preserving the Quality of Service (QoS) experienced by users. We model such a system at the flow level, considering a dynamic user configuration, and derive, using Markov Decision Processes (MDPs), optimal sleep/wake up schemes based on the information on traffic load and user localization in the cell, in the cases where this information is complete, partial or delayed. Our results quantify the energy consumption and QoS perceived by the users in each of these cases and identify the tradeoffs between those two quantities. We also illustrate numerically the optimal policies in different traffic scenarios.
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paper_title: A Model to Analyze the Energy Savings of Base Station Sleep Mode in LTE HetNets

paper_content:

In this paper we study the base station (BS) sleep mode as an approach to decrease the energy consumption of LTE HetNets. We present an energy model which takes into account that (i) macro, micro and pico BSs have different power consumption profiles, (ii) macro BS power consumption is varying with the load, and (iii) communication through a macro, micro or pico cell has different radio resource utilization. Furthermore, we introduce two sleep algorithms, namely single sleep and multiple sleep, to determine the time instant to enable micro or pico BSs sleep mode. Finally, we analyze the two proposed algorithms in different HetNet topologies and with different traffic requirements to evaluate the network energy consumption and the savings that the sleep mode can achieve.
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paper_title: A cross-layer optimization of the joint macro- and picocell deployment with sleep mode for green communications

paper_content:

Picocells are viewed as a promising option to provide high-data-rate services and improve coverage in wireless communication systems. As traffic load increases, picocells are deployed rapidly, which may cause an energy consumption explosion. Nowadays, base station (BS) sleeping technique becomes a hot topic to save energy in cellular systems. In this paper, we aim to analyze the energy efficiency when sleeping mode is introduced into a heterogeneous system with macro- and picocells. A cross-layer optimization problem is formulated to find the optimal operation mode of this system (the active set of cells, and the access BS selection for each user). We proved that this problem is an NP-hard problem and an operation mode decision algorithm is developed to get the sub-optimal solution. Simulation results show significant energy reduction by introducing the proposed algorithm into heterogeneous system.
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paper_title: Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

paper_content:

Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile charging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is applied to derive the tradeoffs between the network parameters including p, q, and the BS/PB densities under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product the BS density decreases with increasing p following a power law where the exponent is proportional to the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product between q, the PB density, and the BS density raised to a power proportional to the path-loss exponent has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, a similar result is obtained with the aforementioned product increased by the array gain. Last, similar results are derived for the case of mobiles having small energy storage.
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paper_title: Clustering based power saving algorithm for self-organized sleep mode in femtocell networks

paper_content:

A large-scale deployment of femtocell BSs (FBSs) causes the substantial energy consumption. One fairly intuitive way to minimize the energy consumption is to switch off the wireless air interface, or to keep FBSs in the energy saving mode for the most time while preserving the quality of service (QoS) experienced by users. Utilizing this concept, this paper proposes a clustering based power saving algorithm (CPSA) for self-organized sleep mode in femtocell networks. Firstly, CPSA builds a leader-member cluster framework, in which each FBS is either a FBS leader (FL) or a FBS member (FM). Then, the FL acts as an autonomous entity and is responsible for detecting active calls in the cluster coverage, while the FMs without the active user can entirely shut down pilot transmissions and the related processing all the time. So it is suited for self-organizing networks (SONs). With the practical LTE system parameters, simulation results show that the proposed algorithm outperforms three prominent related schemes in terms of average energy consumption and accumulative interference time. Furthermore, the results provide some guidelines for deploying energy efficient femtocell networks.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
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paper_title: Stochastic analysis of energy savings with sleep mode in OFDMA wireless networks

paper_content:

The issue of energy efficiency (EE) in Orthogonal Frequency-Division Multiple Access (OFDMA) wireless networks is discussed in this paper. Our interest is focused on the promising concept of base station (BS) sleep mode, introduced recently as a key feature in order to dramatically reduce network energy consumption. The proposed technical approach fully exploits the properties of stochastic geometry, where the number of active cells is reduced in a way that the outage probability, or equivalently the signal to interference plus noise (SINR) distribution, remains the same. The optimal EE gains are then specified with the help of a simplified but yet realistic BS power consumption model. Furthermore, the authors extend their initial work by studying a non-singular path loss model in order to verify the validity of the analysis and finally, the impact on the achieved user capacity is investigated. In this context, the significant contribution of this paper is the evaluation of the theoretically optimal energy savings of sleep mode, with respect to the decisive role that the BS power profile plays.
---
paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
---
paper_title: Cognitive Small Cell Networks: Energy Efficiency and Trade-Offs

paper_content:

Heterogeneous networks using a mix of macrocells and small cells are foreseen as one of the solutions to meet the ever increasing mobile traffic demand. Nevertheless, a massive deployment of small cell access points (SAPs) leads also to a considerable increase in energy consumption. Spurred by growing environmental awareness and the high price of energy, it is crucial to design energy efficient wireless systems for both macrocells and small cells. In this work, we evaluate a distributed sleep-mode strategy for cognitive SAPs and we analyze the trade-off between traffic offloading from the macrocell and the energy consumption of the small cells. Using tools from stochastic geometry, we define the user discovery performance of the SAP and derive the uplink capacity of the small cells located in the Voronoi cell of a macrocell base station, accounting for the uncertainties associated with random position, density, user activity, propagation channel, network interference generated by uncoordinated activity, and the sensing scheme. In addition, we define a fundamental limit on the interference density that allows robust detection and we elucidate the relation between energy efficiency and sensing time using large deviations theory. Through the formulation of several optimization problems, we propose a framework that yields design guidelines for energy efficient small cell networks.
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paper_title: Optimal Combination of Base Station Densities for Energy-Efficient Two-Tier Heterogeneous Cellular Networks

paper_content:

In this paper, the optimal BS (Base Station) density for both homogeneous and heterogeneous cellular networks to minimize network energy cost is analyzed with stochastic geometry theory. For homogeneous cellular networks, both upper and lower bounds of the optimal BS density are derived. For heterogeneous cellular networks, our analysis reveals the best type of BSs to be deployed for capacity extension, or to be switched off for energy saving. Specifically, if the ratio between the micro BS cost and the macro BS cost is lower than a threshold, which is a function of path loss and their transmit power, then the optimal strategy is to deploy micro BSs for capacity extension or to switch off macro BSs (if possible) for energy saving with higher priority. Otherwise, the optimal strategy is the opposite. The optimal combination of macro and micro BS densities can be calculated numerically through our analysis, or alternatively be conservatively approximated with a closed-form solution. Based on the parameters from EARTH, numerical results show that in the dense urban scenario, compared to the traditional macro-only homogeneous cellular network with no BS sleeping, deploying micro BSs can reduce about 40% of the total energy cost, and further reduce up to 35% with BS sleeping capability.
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paper_title: Energy Saving Performance Comparison of Coordinated Multi-Point Transmission and Wireless Relaying

paper_content:

Currently, two cooperative transmission strategies, Coordinated Multi-Point (CoMP) Transmission and wireless relaying, are expected to be deployed in future cellular systems to improve the performance of cell-edge users. Due to the cooperation diversity, these technologies can potentially lead to more energy saving. Therefore in this paper, we analyze their energy saving performance with an average outage constraint. The impact of the traffic intensity and BS density are also investigated. Based on the typical parameters setting, our calculation results show that traffic intensity can be divided into three classes: ``coverage-limited'' region, ``energy-efficient'' region, and ``capacity-limited'' region. The coverage-limited region prefers offline fixed algorithms, while dynamic online algorithms are more suitable for the energy-efficient region. As BS density goes higher, the energy-efficient region becomes larger. However, the traffic load region where the cooperation schemes bring benefits becomes smaller. To overcome CoMP, relay stations need to consume energy as small as possible. Even through relay cost energy low enough, the traffic intensity region where wireless relaying overcomes CoMP will become smaller as network goes denser. Our analytical results are of great help for future ``green'' network planning.
---
paper_title: Switching off low utilization base stations via store carry and forward relaying

paper_content:

Recent research studies on green cellular networking indicate that most of the traffic is serviced by a few cell sites while the rest of the cells remain under-utilized, contributing to significant energy consumption levels. Previous proposals suggest turning off Base Stations (BSs) during low utilization periods to save energy by allowing neighboring cells to increase their coverage to provide the necessary connectivity. In this paper, an alternative (and also complimentary) method is proposed, based on the store-carry and forward (SCF) relaying paradigm that allows BSs with low utilization levels to be switched-off. The proposed SCF relaying scheme exploits the mobility of relay nodes to migrate traffic from BSs of very low utilization to neighbour BSs, allowing in that respect these sites to be switched off. To this end, a joint routing and scheduling problem is formulated to maximize the number of cell sites that can be switched off by also taking into account the communication cost of operating the network. Numerical investigations reveal that significant energy gains can be attained using the proposed SCF relaying scheme for switching off BSs.
---
paper_title: Sleep control for base stations powered by heterogeneous energy sources

paper_content:

This paper considers a cellular network with base stations (BSs) powered by heterogeneous energy sources, i.e., besides conventional BSs connected to the power grid, some BSs are purely powered by the renewable energy. BS sleep is introduced not only to save grid power, but also to store renewable energy for future use when the temporal traffic variation does not match with the energy arrivals. The challenge of the BS sleep control lies in the possible energy outage of those BS powered by the renewable energy, and this will lead to network coverage hole and thus severely affect the service quality. The optimal sleep policy is obtained through dynamic programming, and due to its high complexity, we further propose a simple heuristic algorithm. By simulations, we evaluate and compare the proposed algorithms with a greedy scheme that utilizes renewable energy whenever possible, and show that the greedy scheme can lead to severe energy outage, while our algorithms wisely store harvested energy through BS sleep.
---
paper_title: Optimal Control of Wake Up Mechanisms of Femtocells in Heterogeneous Networks

paper_content:

We study, in this work, optimal sleep/wake up schemes for the base stations of network-operated femto cells deployed within macro cells for the purpose of offloading part of its traffic. Our aim is to minimize the energy consumption of the overall heterogeneous network while preserving the Quality of Service (QoS) experienced by users. We model such a system at the flow level, considering a dynamic user configuration, and derive, using Markov Decision Processes (MDPs), optimal sleep/wake up schemes based on the information on traffic load and user localization in the cell, in the cases where this information is complete, partial or delayed. Our results quantify the energy consumption and QoS perceived by the users in each of these cases and identify the tradeoffs between those two quantities. We also illustrate numerically the optimal policies in different traffic scenarios.
---
paper_title: Minimizing Energy Consumption via Sleep Mode in Green Base Station

paper_content:

In this paper, we develop new energy-efficient, radio resource management schemes for green wireless networks. Our goal is to optimize energy consumption at the network scale while preserving the Quality of Service (QoS) perceived by users. We specifically propose two new sleep mechanisms for base station where a number of resources in system can be shut down for some traffic scenarios in one of two ways: a dynamic way where resources are activated/deactivated in real-time as a function of the instantaneous load of the system, and a semi-static one where resources are kept unchanged during longer time intervals, in the order of one hour. We apply the proposed schemes to 2G and HSPA (High Speed Packet Access) systems and show that the dynamic one achieves larger energy reductions while the semi-static one has an acceptable performance with low complexity
---
paper_title: Energy Saving Performance Comparison of Coordinated Multi-Point Transmission and Wireless Relaying

paper_content:

Currently, two cooperative transmission strategies, Coordinated Multi-Point (CoMP) Transmission and wireless relaying, are expected to be deployed in future cellular systems to improve the performance of cell-edge users. Due to the cooperation diversity, these technologies can potentially lead to more energy saving. Therefore in this paper, we analyze their energy saving performance with an average outage constraint. The impact of the traffic intensity and BS density are also investigated. Based on the typical parameters setting, our calculation results show that traffic intensity can be divided into three classes: ``coverage-limited'' region, ``energy-efficient'' region, and ``capacity-limited'' region. The coverage-limited region prefers offline fixed algorithms, while dynamic online algorithms are more suitable for the energy-efficient region. As BS density goes higher, the energy-efficient region becomes larger. However, the traffic load region where the cooperation schemes bring benefits becomes smaller. To overcome CoMP, relay stations need to consume energy as small as possible. Even through relay cost energy low enough, the traffic intensity region where wireless relaying overcomes CoMP will become smaller as network goes denser. Our analytical results are of great help for future ``green'' network planning.
---
paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
---
paper_title: Multiple daily base station switch-offs in cellular networks

paper_content:

In this paper we study base station sleep modes, which are today considered a viable approach to improve the energy efficiency of cellular access networks, by reducing power consumption in periods of low traffic. When some base stations are switched off, radio coverage and service provisioning are taken care of by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This is a realistic assumption in the case of the dense base station layouts of urban areas, which consume most of the network energy. We develop simple analytical models that allow optimal base station switch-off times to be identified as a function of the daily traffic pattern, in the cases in which either just one switch-off per day is possible (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several switch-offs per day are permitted (progressively reducing the number of active base stations and the network power). We first assume that any fraction of base stations can be switched off, then we consider a realistic case. We quantify the percentage of energy which can be saved with base station sleep modes, proving that it can be close to 50% of the total network energy consumption.
---
paper_title: Optimal Control of Wake Up Mechanisms of Femtocells in Heterogeneous Networks

paper_content:

We study, in this work, optimal sleep/wake up schemes for the base stations of network-operated femto cells deployed within macro cells for the purpose of offloading part of its traffic. Our aim is to minimize the energy consumption of the overall heterogeneous network while preserving the Quality of Service (QoS) experienced by users. We model such a system at the flow level, considering a dynamic user configuration, and derive, using Markov Decision Processes (MDPs), optimal sleep/wake up schemes based on the information on traffic load and user localization in the cell, in the cases where this information is complete, partial or delayed. Our results quantify the energy consumption and QoS perceived by the users in each of these cases and identify the tradeoffs between those two quantities. We also illustrate numerically the optimal policies in different traffic scenarios.
---
paper_title: A Model to Analyze the Energy Savings of Base Station Sleep Mode in LTE HetNets

paper_content:

In this paper we study the base station (BS) sleep mode as an approach to decrease the energy consumption of LTE HetNets. We present an energy model which takes into account that (i) macro, micro and pico BSs have different power consumption profiles, (ii) macro BS power consumption is varying with the load, and (iii) communication through a macro, micro or pico cell has different radio resource utilization. Furthermore, we introduce two sleep algorithms, namely single sleep and multiple sleep, to determine the time instant to enable micro or pico BSs sleep mode. Finally, we analyze the two proposed algorithms in different HetNet topologies and with different traffic requirements to evaluate the network energy consumption and the savings that the sleep mode can achieve.
---
paper_title: Clustering based power saving algorithm for self-organized sleep mode in femtocell networks

paper_content:

A large-scale deployment of femtocell BSs (FBSs) causes the substantial energy consumption. One fairly intuitive way to minimize the energy consumption is to switch off the wireless air interface, or to keep FBSs in the energy saving mode for the most time while preserving the quality of service (QoS) experienced by users. Utilizing this concept, this paper proposes a clustering based power saving algorithm (CPSA) for self-organized sleep mode in femtocell networks. Firstly, CPSA builds a leader-member cluster framework, in which each FBS is either a FBS leader (FL) or a FBS member (FM). Then, the FL acts as an autonomous entity and is responsible for detecting active calls in the cluster coverage, while the FMs without the active user can entirely shut down pilot transmissions and the related processing all the time. So it is suited for self-organizing networks (SONs). With the practical LTE system parameters, simulation results show that the proposed algorithm outperforms three prominent related schemes in terms of average energy consumption and accumulative interference time. Furthermore, the results provide some guidelines for deploying energy efficient femtocell networks.
---
paper_title: Energy savings for cellular network with evaluation of impact on data traffic performance

paper_content:

We present a concrete methodology for saving energy in future and contemporary cellular networks. It is based on re-arranging the user-cell association so as to allow shutting down under-utilized parts of the network. We consider a hypothetical static case where we have complete knowledge of stationary user locations and thus the results represent an upper bound of potential energy savings. We formulate the problem as a binary integer programming problem, thus it is NP-hard, and we present a heuristic approximation method. We simulate the methodology on an example real cellular network topology with traffic-and user distribution generated according to recently measured patterns. Further, we evaluate the energy savings, using realistic energy profiles, and the impact on the user-perceived network performance, represented by delay and throughput, at various times of day. The general findings conclude that up to 50% energy may be saved in less busy periods, while the performance effects remain limited. We conclude that practical, real-time user-cell re-allocation methodology, taking into account user mobility predictions, may thus be feasible and bring significant energy savings at acceptable performance impact.
---
paper_title: Green Mobile Access Network with Dynamic Base Station Energy Saving

paper_content:

The explosive development of ICT (information and communication technology) industry has emerged as one of the major sources of world energy consumption. Therefore, this paper concerns about the BS (base station) energy saving issue, for most energy consumption of the communication network comes from the BSs and the core network. Particularly, we consider dynamically turning off certain BSs when the network traffic is low. Centralized and decentralized implementations are investigated. Simulations demonstrate the energy efficiency of the proposed algorithms and the tradeoff between energy saving and coverage guarantee.
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paper_title: Self-organized energy efficient cellular networks

paper_content:

Base stations (BSs) are the main energy expenditure elements of cellular networks, considering the high coverage requirements and the fact that the total provisioned capacity is intended to match peak hour traffic demand. In this paper, we introduce energy saving algorithms based on coordination between network elements. We introduce the notion of energy partitions - associations of powered-on and powered-off BSs - to deliver energy saving with the objective of matching offered capacity with the traffic demand in a flexible manner. Our energy saving algorithms are based on shared knowledge of load and coverage information and enable an appropriate cell reconfiguration for achieving a network-level energy saving. Through a simulation-based evaluation, we analyze the performance of centralized and distributed algorithms under different network topologies and traffic conditions, highlight the benefits and drawbacks, and provide recommendations for deployment scenarios.
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paper_title: Energy efficient coverage planning in cellular networks with sleep mode

paper_content:

In this paper, we consider energy efficient coverage planning in cellular networks. To save energy, each base station (BS) can work in sleep mode when there is no user in its coverage or the users can be served by neighbor base stations. With increasing coverage overlap, there is a tradeoff between the number of BSs per unit area and the proportion of active base stations. Analytical and numerical methods are presented to evaluate coverage planning schemes with different inter-BS distance. Evaluation results show that compared with the minimum coverage overlap scheme, the optimal planning scheme can reduce the network energy consumption by more than 20%, and the performance improvement depends on the user density, network topology, and the power consumption of sleep mode.
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paper_title: Traffic engineering of the radio interface for cellular mobile networks

paper_content:

The paper reviews traffic-related issues in the operation of the radio interface in cellular mobile networks operating with FDMA, TDMA, or CDMA technology. The emphasis is on issues which affect the traffic performance of the network, rather than on transmission technology, or transmission quality measures such as bit error rate. The author reviews the important traffic performance measures for cellular systems and the issues of channel assignment, handoff, access control, traffic modeling, and traffic management. Traffic modeling for all types of networks is considered in some depth, both by drawing analogies with fixed-wire networks, and by considering cellular-specific modeling. From the modeling results, he concludes that reuse-based networks such as FDMA and TDMA possess quite different traffic characteristics from CDMA networks. >
---
paper_title: Multiple daily base station switch-offs in cellular networks

paper_content:

In this paper we study base station sleep modes, which are today considered a viable approach to improve the energy efficiency of cellular access networks, by reducing power consumption in periods of low traffic. When some base stations are switched off, radio coverage and service provisioning are taken care of by the base stations that remain active, so as to guarantee that service is available over the whole area at all times. This is a realistic assumption in the case of the dense base station layouts of urban areas, which consume most of the network energy. We develop simple analytical models that allow optimal base station switch-off times to be identified as a function of the daily traffic pattern, in the cases in which either just one switch-off per day is possible (bringing the network from a high-power, fully-operational configuration, to a low-power reduced configuration), or several switch-offs per day are permitted (progressively reducing the number of active base stations and the network power). We first assume that any fraction of base stations can be switched off, then we consider a realistic case. We quantify the percentage of energy which can be saved with base station sleep modes, proving that it can be close to 50% of the total network energy consumption.
---
paper_title: Rethinking energy efficiency models of cellular networks with embodied energy

paper_content:

The continuous increase in energy consumption by cellular networks requires rethinking their energy efficiency. Current research indicates that one third of operating energy could be saved by reducing the transmission power of base stations. However, this approach requires the introduction of a range of additional equipment containing more embodied energy - consumed by all processes associated with the production of equipment. This problem is addressed first in this article. Furthermore, a new cellular network energy efficiency model with embodied energy is proposed, and optimization between the number of cells and their coverage is investigated. Contrary to previous works, we have found that embodied energy accounts for a significant proportion of total energy consumption and cannot be neglected. The simulation results confirm an important trade-off between operating and embodied energies, which can provide some practical guidelines for designing energy-efficient cellular access networks. The new model considering embodied energy is not limited to just cellular networks, but to other telecommunications, such as wireless local area networks and wired networks.
---
paper_title: A Model to Analyze the Energy Savings of Base Station Sleep Mode in LTE HetNets

paper_content:

In this paper we study the base station (BS) sleep mode as an approach to decrease the energy consumption of LTE HetNets. We present an energy model which takes into account that (i) macro, micro and pico BSs have different power consumption profiles, (ii) macro BS power consumption is varying with the load, and (iii) communication through a macro, micro or pico cell has different radio resource utilization. Furthermore, we introduce two sleep algorithms, namely single sleep and multiple sleep, to determine the time instant to enable micro or pico BSs sleep mode. Finally, we analyze the two proposed algorithms in different HetNet topologies and with different traffic requirements to evaluate the network energy consumption and the savings that the sleep mode can achieve.
---
paper_title: Energy-efficient planning and management of cellular networks

paper_content:

We study base stations energy-efficient management algorithms in a cellular access network taking into account different planning strategies. To provide energy savings, sleep modes are adopted at the Base Stations (BSs). We propose two switch-off strategies that are based either on the cell load or the BS coverage overlap. Our results show that energy savings between 10% and 30% can be achieved also for the deployment already planned to be energy-efficient, while even higher savings are achievable with the other deployments. Moreover, we find that both the proposed switch-off strategies obtain similar results, suggesting that the order at which the BSs are switched-off, and the set of BSs selected to be switched off, do not change significantly the average estimation of potential energy savings. Furthermore, on a realistic case study, comparisons are made between the results obtained by using deterministic channel estimation models and empirical formulations.
---
paper_title: Minimizing Energy Consumption via Sleep Mode in Green Base Station

paper_content:

In this paper, we develop new energy-efficient, radio resource management schemes for green wireless networks. Our goal is to optimize energy consumption at the network scale while preserving the Quality of Service (QoS) perceived by users. We specifically propose two new sleep mechanisms for base station where a number of resources in system can be shut down for some traffic scenarios in one of two ways: a dynamic way where resources are activated/deactivated in real-time as a function of the instantaneous load of the system, and a semi-static one where resources are kept unchanged during longer time intervals, in the order of one hour. We apply the proposed schemes to 2G and HSPA (High Speed Packet Access) systems and show that the dynamic one achieves larger energy reductions while the semi-static one has an acceptable performance with low complexity
---
paper_title: Dynamic idle mode procedures for femtocells

paper_content:

The concept of a user-deployed femtocell that operates in licensed spectrum and provides cellular coverage in the home has attracted much interest in the wireless industry and an extensive deployment of femtocells is expected in the future. However, several issues arise when femtocells become more widely deployed. One concern is the additional energy consumption caused by femtocells due to their continuous receiver processing and signal transmissions, which can be significant with a large number of femtocells. Secondly, the increase in the number of active cells can result in a high increase in core networks signaling for mobility procedures. Finally, the continuous pilot transmissions can cause interference, particularly in dense urban areas. In this paper all these issues are addressed by a novel idle mode procedure which allows the femtocell transmissions and associated processing to be switched off completely at all times when the femtocell does not need to support an active call.
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paper_title: Fundamental tradeoffs and evaluation methodology for future green wireless networks

paper_content:

To meet the global challenge of reducing greenhouse gas emissions and the exponentially growing data traffic, green design of cellular network is becoming a urgent issue for wireless network operators. In this paper, we first discuss the performance evaluation methodology for future wireless networks from the viewpoint of five basic metrics, i.e., throughput, power consumption, deployment cost, bandwidth, and latency. We then study the fundamental tradeoffs from Shannon's perspective based on the five metrics. Furthermore, we extend the tradeoff relation from point-to-point link to a heterogeneous network scenario taking into account realistic base station power model. Our study provides useful insights for the evaluation, modeling and deployment of future green wireless networks.
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paper_title: Cellular Energy Efficiency Evaluation Framework

paper_content:

In order to quantify the energy savings in wireless networks, the power consumption of the entire system needs to be captured and an appropriate energy efficiency evaluation framework must be defined. In this paper, the necessary enhancements over existing performance evaluation frameworks are discussed, such that the energy efficiency of the entire network comprising component, node and network level contributions can be quantified. The most important addendums over existing frameworks include a sophisticated power model for various base station (BS) types, which maps the RF output power radiated at the antenna elements to the total supply power of a BS site. We also consider an approach to quantify the energy efficiency of large geographical areas by using the existing small scale deployment models along with long term traffic models. Finally, the proposed evaluation framework is applied to quantify the energy efficiency of the downlink of a 3GPP LTE radio access network.
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paper_title: Energy saving in OFDMA cellular systems using base-station sleep mode: 3GPP-LTE a case study

paper_content:

Green Radio has emerged as one of the most important considerations in the present scenario of global warming. It is known that the power consumption of a Base Station is not only due to the radio power transmitted and the power consumed by the digital signal processing transceiver units but also due to the huge amount of power consumed by the cooling system and power backup units. It has been seen that although traffic load varies over a large range during a 24 hour cycle the power consumption does not vary proportionally. Traffic load dependent power saving is one of the foci of this work. An important aspect included in this work is the huge penetration loss that is added to the system Signal to Interference plus Noise Ratio (SINR) during night time when most of the users are considered to be indoor. This work focuses on the performance evaluation cell sleep mode to save power (reduce carbon foot print). Results relating to three sector urban micro-cell scenario as per International Telecommunication Union (ITU) specification are presented. Traffic load threshold for activating the sleep mode is also identified.
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paper_title: "Green" distance-aware base station sleeping algorithm in LTE-Advanced

paper_content:

In this paper, we propose a switch on/off algorithm for Base Stations (BSs), which exploits the knowledge of the distance between the User Equipments (UEs) and their associated BS. Our novel approach hopes to provide an improvement to the problem of energy consumption. The major concern lies on reducing the energy consumption of the telecommunication networks by optimizing the power utilization without sacrificing the offered Quality of Service (QoS). Our proposed scheme achieves a significant power saving, based on switching off the Base Stations that are underutilized during low traffic periods (especially during night) in the LTE-Advanced.
---
paper_title: Energy savings for cellular network with evaluation of impact on data traffic performance

paper_content:

We present a concrete methodology for saving energy in future and contemporary cellular networks. It is based on re-arranging the user-cell association so as to allow shutting down under-utilized parts of the network. We consider a hypothetical static case where we have complete knowledge of stationary user locations and thus the results represent an upper bound of potential energy savings. We formulate the problem as a binary integer programming problem, thus it is NP-hard, and we present a heuristic approximation method. We simulate the methodology on an example real cellular network topology with traffic-and user distribution generated according to recently measured patterns. Further, we evaluate the energy savings, using realistic energy profiles, and the impact on the user-perceived network performance, represented by delay and throughput, at various times of day. The general findings conclude that up to 50% energy may be saved in less busy periods, while the performance effects remain limited. We conclude that practical, real-time user-cell re-allocation methodology, taking into account user mobility predictions, may thus be feasible and bring significant energy savings at acceptable performance impact.
---
paper_title: Power consumption modeling of different base station types in heterogeneous cellular networks

paper_content:

In wireless communications micro cells are potentially more energy efficient than conventional macro cells due to the high path loss exponent. Also, heterogeneous deployments of both cell types can be used to optimize the energy efficiency. Energy efficiency of any deployment is impacted by the power consumption of each individual network element and the dependency of transmit power and load. In this paper we developed such power models for macro and micro base stations relying on data sheets of several GSM and UMTS base stations with focus on component level, e.g., power amplifier and cooling equipment. In a first application of the model a traditional macro cell deployment and a heterogeneous deployment are compared.
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paper_title: Optimal wake-up mechanism for single base station with sleep mode

paper_content:

Base station (BS) sleeping is an effecting way to improve the energy-efficiency of cellular networks. Considering BS sleep mode operation under different scenarios, we focus on three wake-up policies: single vacation (SV) policy, multiple vacation (MV) policy and N policy. A hysteresis time is also considered to avoid frequent BS mode-changing operation. By modeling the systems as M/G/1 vacation queues, we derive two performance measures of interest, expected system response time and energy consumption per bit. The impacts of sleep mode operation parameters and setup time are also studied. In order to determine the optimal parameter settings, which allows for a flexible tradeoff between energy-efficiency and mean delay, a two-step optimization method is proposed. We numerically analyze and investigate the energy-delay tradeoff for different policies, and find that both the MV policy and the N policy have better performance than the SV policy if the sniffing cost is not considered. However, these advantages diminish when the sniffing cost increases.
---
paper_title: Reducing Energy Consumption in LTE with Cell DTX

paper_content:

This paper discusses how energy consumption can be significantly reduced in mobile networks by introducing discontinuous transmission (DTX) on the base station side. By introducing DTX on the downlink, or cell DTX, we show that it is possible to achieve significant energy reductions in an LTE network. Cell DTX is most efficient when the traffic load is low in a cell but even when realistic traffic statistics are considered the gains are impressive. The technology potential for a metropolitan area is shown to be 90% reduced energy consumption compared to no use of cell DTX. The paper also discusses different drives for the increased focus on energy efficient network operation and also provides insights on the impact of cell DTX from a life cycle assessment perspective.
---
paper_title: TACT: A Transfer Actor-Critic Learning Framework for Energy Saving in Cellular Radio Access Networks

paper_content:

Recent works have validated the possibility of improving energy efficiency in radio access networks (RANs), achieved by dynamically turning on/off some base stations (BSs). In this paper, we extend the research over BS switching operations, which should match up with traffic load variations. Instead of depending on the dynamic traffic loads which are still quite challenging to precisely forecast, we firstly formulate the traffic variations as a Markov decision process. Afterwards, in order to foresightedly minimize the energy consumption of RANs, we design a reinforcement learning framework based BS switching operation scheme. Furthermore, to avoid the underlying curse of dimensionality in reinforcement learning, a transfer actor-critic algorithm (TACT), which utilizes the transferred learning expertise in historical periods or neighboring regions, is proposed and provably converges. In the end, we evaluate our proposed scheme by extensive simulations under various practical configurations and show that the proposed TACT algorithm contributes to a performance jumpstart and demonstrates the feasibility of significant energy efficiency improvement at the expense of tolerable delay performance.
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paper_title: Rethinking energy efficiency models of cellular networks with embodied energy

paper_content:

The continuous increase in energy consumption by cellular networks requires rethinking their energy efficiency. Current research indicates that one third of operating energy could be saved by reducing the transmission power of base stations. However, this approach requires the introduction of a range of additional equipment containing more embodied energy - consumed by all processes associated with the production of equipment. This problem is addressed first in this article. Furthermore, a new cellular network energy efficiency model with embodied energy is proposed, and optimization between the number of cells and their coverage is investigated. Contrary to previous works, we have found that embodied energy accounts for a significant proportion of total energy consumption and cannot be neglected. The simulation results confirm an important trade-off between operating and embodied energies, which can provide some practical guidelines for designing energy-efficient cellular access networks. The new model considering embodied energy is not limited to just cellular networks, but to other telecommunications, such as wireless local area networks and wired networks.
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paper_title: Energy Efficiency Improvements through Micro Sites in Cellular Mobile Radio Networks

paper_content:

Efforts to increase the energy efficiency of infor- mation and communication systems in general and cellular mobile radio networks in particular has recently gained mo- mentum. Besides positive environmental effects, lowering the energy consumption of mobile radio systems appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular mobile radio networks. In this paper we investigate that matter in more detail from a deployment perspective. We evaluate potential improvements of the area power consumption achievable with network layouts featuring varying numbers of micro sites in addition to conventional macro sites for given system performance targets under full load conditions.
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paper_title: Optimal Energy Savings in Cellular Access Networks

paper_content:

In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.
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paper_title: Fundamental trade-offs on green wireless networks

paper_content:

Traditional mobile wireless network mainly design focuses on ubiquitous access and large capacity. However, as energy saving and environmental protection become global demands and inevitable trends, wireless researchers and engineers need to shift their focus to energy-efficiency-oriented design, that is, green radio. In this article, we propose a framework for green radio research and integrate the fundamental issues that are currently scattered. The skeleton of the framework consists of four fundamental tradeoffs: deployment efficiency-energy efficiency, spectrum efficiency-energy efficiency, bandwidth-power, and delay-power. With the help of the four fundamental trade-offs, we demonstrate that key network performance/cost indicators are all strung together.
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paper_title: Introduction to Queueing Theory and Stochastic Teletraffic Models

paper_content:

The aim of this textbook is to provide students with basic knowledge of stochastic models that may apply to telecommunications research areas, such as traffic modelling, resource provisioning and traffic management. These study areas are often collectively called teletraffic. This book assumes prior knowledge of a programming language, mathematics, probability and stochastic processes normally taught in an electrical engineering course. For students who have some but not sufficiently strong background in probability and stochastic processes, we provide, in the first few chapters, background on the relevant concepts in these areas.
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paper_title: Green cellular network: Deployment solutions, sensitivity and tradeoffs

paper_content:

A prominent challenge faced by the communication industry and society is the reduction of energy consumption. How the cellular network can maintain a quality of service (QoS), whilst decreasing its operational energy is investigated from both a deployment and scheduling perspective. This paper presents results showing the dominant factors which reduce the radio access network (RAN) energy consumption and point the way for future research. A large proportion of energy consumption is due to the static overhead power of base-stations and the paper considers sleep mode operation as a solution for a variety of network conditions. Furthermore, a significant contributor to transmission inefficiency is due to the performance of cell edge users. The paper proposes a vertical sector antenna deployment scheme and demonstrate that our proposals can yield significant operational energy and transmission efficiency savings, as well as insight into the tradeoff relationship between energy consumption and network performance. Furthermore, the paper also gives a comprehensive performance sensitivity analysis, which yields insight into both the validity of results and the parameters which can significantly influence future development.
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paper_title: "Green" distance-aware base station sleeping algorithm in LTE-Advanced

paper_content:

In this paper, we propose a switch on/off algorithm for Base Stations (BSs), which exploits the knowledge of the distance between the User Equipments (UEs) and their associated BS. Our novel approach hopes to provide an improvement to the problem of energy consumption. The major concern lies on reducing the energy consumption of the telecommunication networks by optimizing the power utilization without sacrificing the offered Quality of Service (QoS). Our proposed scheme achieves a significant power saving, based on switching off the Base Stations that are underutilized during low traffic periods (especially during night) in the LTE-Advanced.
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paper_title: Energy Efficient Heterogeneous Cellular Networks

paper_content:

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.
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paper_title: Energy savings for cellular network with evaluation of impact on data traffic performance

paper_content:

We present a concrete methodology for saving energy in future and contemporary cellular networks. It is based on re-arranging the user-cell association so as to allow shutting down under-utilized parts of the network. We consider a hypothetical static case where we have complete knowledge of stationary user locations and thus the results represent an upper bound of potential energy savings. We formulate the problem as a binary integer programming problem, thus it is NP-hard, and we present a heuristic approximation method. We simulate the methodology on an example real cellular network topology with traffic-and user distribution generated according to recently measured patterns. Further, we evaluate the energy savings, using realistic energy profiles, and the impact on the user-perceived network performance, represented by delay and throughput, at various times of day. The general findings conclude that up to 50% energy may be saved in less busy periods, while the performance effects remain limited. We conclude that practical, real-time user-cell re-allocation methodology, taking into account user mobility predictions, may thus be feasible and bring significant energy savings at acceptable performance impact.
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paper_title: Energy-efficient cellular network operation via base station cooperation

paper_content:

The rising cost of energy and increased environmental awareness have sparked a keen interest in the development and deployment of energy-efficient communication technologies. The energy efficiency of cellular networks can be increased significantly by selectively switching off some of the base stations (BSs) during periods of low traffic load. In this paper, we propose a scalable BS switching strategy and use cooperative communications and power control to extend network coverage to the service areas of the switched-off BSs. The outage probability and the achievable power savings of the proposed scheme are analyzed, both analytically and numerically, and a potential of up to 50% power saving is observed in the numerical results.
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paper_title: Improving cellular network energy efficiency by joint management of sleep mode and transmission power

paper_content:

Energy efficiency is one of the main challenges to be faced by mobile communications in the near future. The growth of the mobile communications market which is boosted by the increasing penetration of smartphones and laptops requires an increase of the network capacity and, consequently, a great leap forward also for the infrastructures. In this scenario, in order to reduce the operative expenditures, the network operators pay attention to energy saving strategies that may also contribute to the reduction of greenhouse emissions. In this paper the exponential smoothing technique is applied to forecast traffic in a given area considering daily and weekly variations. The availability of a reliable prediction of the future traffic values allows the adaptation of macro base station transmission power and the introduction of a sleep mode for micro base stations and permits to guarantee the requested network capacity while saving energy consumption. Results show the effectiveness of traffic forecast technique for capacity prediction and the usefulness of the proposed algorithms for energy efficiency maximization, affording very good performance, very close to the optimum one.
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paper_title: Optimal Energy Savings in Cellular Access Networks

paper_content:

In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.
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paper_title: Green Mobile Access Network with Dynamic Base Station Energy Saving

paper_content:

The explosive development of ICT (information and communication technology) industry has emerged as one of the major sources of world energy consumption. Therefore, this paper concerns about the BS (base station) energy saving issue, for most energy consumption of the communication network comes from the BSs and the core network. Particularly, we consider dynamically turning off certain BSs when the network traffic is low. Centralized and decentralized implementations are investigated. Simulations demonstrate the energy efficiency of the proposed algorithms and the tradeoff between energy saving and coverage guarantee.
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paper_title: Traffic-aware base station sleeping in dense cellular networks

paper_content:

The energy consumption of information and communication technology (ICT) industry has become a serious problem, which mostly comes from the network infrastructure, rather than the mobile terminals. In this paper, we consider densely deployed cellular networks where the coverage of base stations (BSs) overlaps and the traffic intensity varies over time and space. An energy saving algorithm is proposed by dynamically adjusting the working modes (active or sleeping) of BSs according to the traffic variation with respect to certain blocking probability requirement. In addition, to prevent frequent mode switching, BSs are set to hold their current working modes for at least a given interval. Simulations demonstrate that the proposed strategy can greatly reduce energy consumption with blocking probability guarantee, and the performance is insensitive to the mode holding time within certain range.
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paper_title: An energy efficient and spectrum efficient wireless heterogeneous network framework for 5G systems

paper_content:

In this article we explore a system framework of cooperative green heterogeneous networks for 5G wireless communication systems. We first survey the state-of-the-art on spectrum efficiency (SE), energy efficiency (EE), and quality of service (QoS) based mobile association, multi-layer interference management and power control, network wide cooperation and dynamic resource allocation for heterogeneous wireless networks. We also present the system framework of cooperative green heterogeneous networks, which aims at balancing and optimizing SE, EE, and QoS in heterogeneous wireless networks. We discuss the design principles and show some preliminary performance results on the tradeoffs among SE, EE, and QoS. Finally, we identify the technical challenges that remain in the cooperative green heterogeneous network design. The presented wireless system framework is expected to advance the understandings of the critical technical issues toward energy and spectrum efficient 5G wireless communication systems.
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paper_title: Energy-efficient planning and management of cellular networks

paper_content:

We study base stations energy-efficient management algorithms in a cellular access network taking into account different planning strategies. To provide energy savings, sleep modes are adopted at the Base Stations (BSs). We propose two switch-off strategies that are based either on the cell load or the BS coverage overlap. Our results show that energy savings between 10% and 30% can be achieved also for the deployment already planned to be energy-efficient, while even higher savings are achievable with the other deployments. Moreover, we find that both the proposed switch-off strategies obtain similar results, suggesting that the order at which the BSs are switched-off, and the set of BSs selected to be switched off, do not change significantly the average estimation of potential energy savings. Furthermore, on a realistic case study, comparisons are made between the results obtained by using deterministic channel estimation models and empirical formulations.
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paper_title: A survey on green 5G cellular networks

paper_content:

In this article, we present a brief survey on green 5G cellular networks, and explore some research issues and challenges of the enabling techniques for green broadband wireless networks. The trend of achieving green power in cellular networks is driving network operators and standardization authorities to work together to reduce carbon footprint of their products in order to bring eco friendly 5G green radio cellular base stations. We will first provide an overview on 5G wireless system architecture and the corresponding new protocol stacks. Next, hybrid multiple access schemes, such as combining orthogonal (OFDMA) and non-orthogonal (CDMA) approaches, aiming at improving the both capacity and coverage performances simultaneously are discussed. Since base stations consume the maximum portion of the total energy in current cellular systems, we explore important renewable energy techniques for green base stations, We will provide a comprehensive survey on how to generate renewable energy, such as solar, wind and fuel cells, for green base stations in 5G green cellular networks.
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paper_title: Energy saving in OFDMA cellular systems using base-station sleep mode: 3GPP-LTE a case study

paper_content:

Green Radio has emerged as one of the most important considerations in the present scenario of global warming. It is known that the power consumption of a Base Station is not only due to the radio power transmitted and the power consumed by the digital signal processing transceiver units but also due to the huge amount of power consumed by the cooling system and power backup units. It has been seen that although traffic load varies over a large range during a 24 hour cycle the power consumption does not vary proportionally. Traffic load dependent power saving is one of the foci of this work. An important aspect included in this work is the huge penetration loss that is added to the system Signal to Interference plus Noise Ratio (SINR) during night time when most of the users are considered to be indoor. This work focuses on the performance evaluation cell sleep mode to save power (reduce carbon foot print). Results relating to three sector urban micro-cell scenario as per International Telecommunication Union (ITU) specification are presented. Traffic load threshold for activating the sleep mode is also identified.
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paper_title: Radio Interface Evolution Towards 5G and Enhanced Local Area Communications

paper_content:

The exponential growth of mobile data in macronetworks has driven the evolution of communications systems toward spectrally efficient, energy efficient, and fast local area communications. It is a well-known fact that the best way to increase capacity in a unit area is to introduce smaller cells. Local area communications are currently mainly driven by the IEEE 802.11 WLAN family being cheap and energy efficient with a low number of users per access point. For the future high user density scenarios, following the 802.11 HEW study group, the 802.11ax project has been initiated to improve the WLAN system performance. The 3GPP LTE-advanced (LTE-A) also includes new methods for pico and femto cell's interference management functionalities for small cell communications. The main problem with LTE-A is, however, that the physical layer numerology is still optimized for macrocells and not for local area communications. Furthermore, the overall complexity and the overheads of the control plane and reference symbols are too large for spectrally and energy efficient local area communications. In this paper, we provide first an overview of WLAN 802.11ac and LTE/LTE-A, discuss the pros and cons of both technology areas, and then derive a new flexible TDD-based radio interface parametrization for 5G local area communications combining the best practices of both WiFi and LTE-A technologies. We justify the system design based on local area propagation characteristics and expected traffic distributions and derive targets for future local area concepts. We concentrate on initial physical layer design and discuss how it maps to higher layer improvements. This paper shows that the new design can significantly reduce the latency of the system, and offer increased sleeping opportunities on both base station and user equipment sides leading to enhanced power savings. In addition, through careful design of the control overhead, we are able to improve the channel utilization when compared with LTE-A.
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paper_title: Greening of the internet

paper_content:

In this paper we examine the somewhat controversial subject of energy consumption of networking devices in the Internet, motivated by data collected by the U.S. Department of Commerce. We discuss the impact on network protocols of saving energy by putting network interfaces and other router & switch components to sleep. Using sample packet traces, we first show that it is indeed reasonable to do this and then we discuss the changes that may need to be made to current Internet protocols to support a more aggressive strategy for sleeping. Since this is a position paper, we do not present results but rather suggest interesting directions for core networking research. The impact of saving energy is huge, particularly in the developing world where energy is a precious resource whose scarcity hinders widespread Internet deployment.
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Title: Energy-Efficient Base-Stations Sleep-Mode Techniques in Green Cellular Networks: A Survey

Section 1: Introduction
Description 1: This section provides a comprehensive background and motivation for energy conservation in cellular networks, highlighting the increasing energy costs and ecological impacts.

Section 2: Objectives of Traditional Mobile Networks Design
Description 2: This section discusses the traditional design objectives of mobile networks, which include optimizing coverage, capacity, and other metrics, but not specifically energy efficiency.

Section 3: Energy Consumption of Mobile Networks Today
Description 3: This section presents recent data and trends related to energy consumption in cellular networks, emphasizing the impact of modern user devices such as smartphones and tablets.

Section 4: Improvement on Energy Efficiency in User Equipment
Description 4: This section outlines historical and current improvements in energy efficiency for user equipment like mobile phones and explores the motivation behind these advancements.

Section 5: Problems Faced by Mobile Network Operators
Description 5: This section analyzes the economic and operational challenges faced by mobile network operators due to rising energy costs and explores their motives for improving energy efficiency.

Section 6: Summary
Description 6: This section summarizes the background, achievements, and concerns associated with green cellular networks, setting the stage for the survey's focus on base station sleep-mode techniques.

Section 7: Relevant Energy Efficiency Metrics
Description 7: This section reviews metrics proposed by academia and industry to measure energy efficiency at various levels, including component, node, and system metrics relevant to base station sleep modes.

Section 8: Energy Saving Potential and Technical Feasibility of BS Sleeping
Description 8: This section discusses the potential energy savings and technical feasibility of sleep-mode techniques in base stations, addressing key challenges such as traffic variation and hardware requirements.

Section 9: BS Sleep Mode Applications
Description 9: This section explores the practical applications of sleep-mode techniques across different cellular network standards and environments, including 4G and legacy networks, as well as integration with other energy-saving strategies.

Section 10: Performance Comparison
Description 10: This section compares various sleep-mode techniques and their effectiveness, such as fixed vs. dynamic switching schemes and centralized vs. distributed algorithms.

Section 11: Practical Issues and Areas for Potential Improvement
Description 11: This section critiques the over-simplifications in existing research models and assumptions, presenting a case study to demonstrate the impact of traffic load on power consumption.

Section 12: The Way Forward
Description 12: This section discusses future challenges and opportunities in the development of sleep-mode techniques, including the implications of upcoming 5G networks and the integration with other green technologies.

Section 13: Concluding Remarks
Description 13: This section concludes the survey by summarizing key findings and emphasizing the importance of further research in sleep-mode techniques for green cellular networks.