Energy Efficiency Tradeoff Mechanism Towards Wireless Green Communication: A Survey
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paper_title: Spatial Modulation for Generalized MIMO: Challenges, Opportunities, and Implementation

paper_content:

A key challenge of future mobile communication research is to strike an attractive compromise between wire- less network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, espe- cially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless commu- nications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communica- tions, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Further- more, it has received sufficient research attention to be im- plemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field.
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paper_title: Green spectrum management for mobile operators

paper_content:

This paper proposes intra-operator dynamic spectrum access, i.e., dynamic spectrum access by an operator's networks of its available spectrum bands, as a means to improve power efficiency. It is based around four areas of interest: (i) dynamically moving users into particularly active bands from other bands to allow radio network equipment in those other bands to be switched off when possible, (ii) the dynamic sharing of spectrum in order to take advantage of better propagation bands and reduce necessary transmission power, (iii) the sharing of spectrum to allow channel bandwidths to be increased thus allowing transmission power to be significantly decreased, and (iv) the better hierarchical management of spectrum in cases where different types of cells coexist. Numerical results show a significant potential for such spectrum management solutions to reduce power consumption for the operator by some 50% or more, with further potential saving if there is a lower correlation in traffic loads among the operator's networks/frequencies. It is noted that although the main objective of this paper is power saving, the concepts presented can also be used for other purposes, such as to increase achievable capacity.
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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: 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: Quality-Oriented Multiple-Source Multimedia Delivery Over Heterogeneous Wireless Networks

paper_content:

This paper proposes a novel quality-oriented algorithm for multiple-source delivery of multimedia over heterogeneous wireless networks, which enables maintaining high levels of user-perceived quality. Unlike existing solutions, which perform delivery adaptation by adjusting the original multimedia quality to varying network conditions, this solution is based on dynamically balancing the multimedia content among multiple streams in order to achieve its goal. The proposed scheme and three other known approaches are compared in terms of estimated user-perceived quality. Simulation results show how this scheme outperforms the other solutions, including cases where the number of simultaneous receivers increases significantly. In addition, real environment tests show how the proposed scheme provides higher quality in terms of both objective and subjective metrics than competing approaches.
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paper_title: A survey of energy-efficient caching in information-centric networking

paper_content:

To better cope with the Internet usage shift from host-centric end-to-end communication to receiver-driven content retrieval, innovative information-centric networking (ICN) architectures have been proposed. A notable advantage of these novel networking architectures is to provide transparent and ubiquitous in-network caching to speed up content distribution and improve network resource utilization. With the explosive increase of global network traffic, the energy efficiency issue in ICN is a growing concern. In this article, we provide a brief survey of energy-efficient caching techniques in ICN from the placement, content placement, and requestto- cache routing perspectives. We also outline some challenges and future research directions about caching policies for green ICN.
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paper_title: A survey of energy efficient network protocols for wireless networks

paper_content:

Wireless networking has witnessed an explosion of interest from consumers in recent years for its applications in mobile and personal communications. As wireless networks become an integral component of the modern communication infrastructure, energy efficiency will be an important design consideration due to the limited battery life of mobile terminals. Power conservation techniques are commonly used in the hardware design of such systems. Since the network interface is a significant consumer of power, considerable research has been devoted to low-power design of the entire network protocol stack of wireless networks in an effort to enhance energy efficiency. This paper presents a comprehensive summary of recent work addressing energy efficient and low-power design within all layers of the wireless network protocol stack.
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paper_title: Towards green wireless access networks

paper_content:

As wireless communications experience exponential growth, energy consumption has became a crucial problem in the wireless industry. Energy efficiency of wireless systems has to be significantly improved in order to guarantee the sustainable growth of the wireless industry. Plenty of efforts have been carried on to achieve so called green wireless world. In this paper, focusing on energy saving in wireless access networks, we provide an overview on energy saving studies currently conducted in 3GPP LTE standard body. The aim of the paper is to gain a better understanding on energy consumption problems in wireless access networks and identify key research problems in this field. Currently most of research focus on base station energy saving with efforts to reduce energy consumed by power amplifiers. Less attention are spent on the network level. We believe a holistic network level solution based on novel architecture and methods, such as relay, user cooperation, as well as cognitive approaches, will be prosing enablers towards green wireless access networks.
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paper_title: Survey of Green Radio Communications Networks: Techniques and Recent Advances

paper_content:

Energy efficiency in cellular networks has received significant attention from both academia and industry because of the importance of reducing the operational expenditures and maintaining the profitability of cellular networks, in addition to making these networks “greener.” Because the base station is the primary energy consumer in the network, efforts have been made to study base station energy consumption and to find ways to improve energy efficiency. In this paper, we present a brief review of the techniques that have been used recently to improve energy efficiency, such as energy-efficient power amplifier techniques, time-domain techniques, cell switching, management of the physical layer through multiple-input multiple-output (MIMO) management, heterogeneous network architectures based on Micro-Pico-Femtocells, cell zooming, and relay techniques. In addition, this paper discusses the advantages and disadvantages of each technique to contribute to a better understanding of each of the techniques and thereby offer clear insights to researchers about how to choose the best ways to reduce energy consumption in future green radio networks.
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paper_title: GREENET - An Early Stage Training Network in Enabling Technologies for Green Radio

paper_content:

In this paper, we describe GREENET (an early stage training network in enabling technologies for green radio), which is a new project recently funded by the European Commission under the auspices of the 2010 Marie Curie People Programme. Through the recruitment and personalized training of 17 Early Stage Researchers (ESRs), in GREENET we are committed to the development of new disruptive technologies to address all aspects of energy efficiency in wireless networks, from the user devices to the core network infrastructure, along with the ways the devices and equipment interact with one another. Novel techniques at the physical, link, and network layers to reduce the energy consumption and carbon footprint of 4G devices will be investigated, such as Spatial Modulation (SM) for Multiple-Input-Multiple-Output (MIMO) systems, Cooperative Automatic Repeat reQuest (C-ARQ) protocols, and Network Coding (NC) for lossy networks. Furthermore, cooperation and cognition paradigms will be exploited as additional assets to improve the energy efficiency of wireless networks with the challenging but indispensable constraint of optimizing the system capacity without degrading the user's Quality-of-Service (QoS).
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paper_title: A Survey of Energy-Efficient Scheduling Mechanisms in Sensor Networks

paper_content:

Sensor networks have a wide range of potential, practical and useful applications. However, there are issues that need to be addressed for efficient operation of sensor network systems in real applications. Energy saving is one critical issue for sensor networks since most sensors are equipped with nonrechargeable batteries that have limited lifetime. To extend the lifetime of a sensor network, one common approach is to dynamically schedule sensors' work/ sleep cycles (or duty cycles). Moreover, in cluster-based networks, cluster heads are usually selected in a way that minimizes the total energy consumption and they may rotate among the sensors to balance energy consumption. In general, these energy-efficient scheduling mechanisms (also called topology configuration mechanisms) need to satisfy certain application requirements while saving energy. In this paper, we provide a survey on energy-efficient scheduling mechanisms in sensor networks that have different design requirements than those in traditional wireless networks. We classify these mechanisms based on their design assumptions and design objectives. Different mechanisms may make different assumptions about their sensors including detection model, sensing area, transmission range, failure model, time synchronization, and the ability to obtain location and distance information. They may also have different assumptions about network structure and sensor deployment strategy. Furthermore, while all the mechanisms have a common design objective to maximize network lifetime, they may also have different objectives determined by their target applications.
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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: On exploiting cognitive radio to mitigate interference in macro/femto heterogeneous networks

paper_content:

To successfully deploy femtocells underlaying the macrocell as a heterogeneous network, which has been proven to greatly improve indoor coverage and system capacity, the cross-tier interference among the macrocell and femtocells as well as the intratier interference among femtocells must be mitigated. However, some unique features present a challenge in interference mitigation in a two-tier heterogeneous network such as random deployment for femtocells, nonexistence of macro-femto backhaul coordination, and mandates allowing no modifications of existing macrocells. Carefully examining the existing distributed information acquisition mechanisms, cognitive radio is the most promising solution for two-tier heterogeneous networks. We therefore study possible interference mitigation approaches, including orthogonal radio resource assignment in the time-frequency and antenna spatial domains, as well as interference cancellation via novel decoding techniques. According to the information acquired by cognitive radio technology, recent innovations such as game theory and the Gibbs sampler have been explored to mitigate both cross-tier and intratier interferences. Performance evaluations show that considerable performance improvement can be generally achieved, and thus demonstrate the potential of applying cognitive radio in mitigating interference.
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paper_title: Energy Efficiency of Heterogeneous Cellular Network

paper_content:

The growing energy consumption driven by dramatic increases in the number of users and data usage becomes the key issue for operators in meeting demands on cost reduction and environmental impact targets. Deployment of low power base stations or relay stations in traditional macro cells is expected to reduce the total energy consumption of cellular radio networks. This paper investigates the cell's energy efficiency and area energy efficiency measured by "bit per Joule" and "energy efficiency per unit area". The simulation results suggest that introducing pico stations into macro cells to form heterogeneous network can achieve improved energy efficiency and increased throughput as well.
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paper_title: Quality-Oriented Multiple-Source Multimedia Delivery Over Heterogeneous Wireless Networks

paper_content:

This paper proposes a novel quality-oriented algorithm for multiple-source delivery of multimedia over heterogeneous wireless networks, which enables maintaining high levels of user-perceived quality. Unlike existing solutions, which perform delivery adaptation by adjusting the original multimedia quality to varying network conditions, this solution is based on dynamically balancing the multimedia content among multiple streams in order to achieve its goal. The proposed scheme and three other known approaches are compared in terms of estimated user-perceived quality. Simulation results show how this scheme outperforms the other solutions, including cases where the number of simultaneous receivers increases significantly. In addition, real environment tests show how the proposed scheme provides higher quality in terms of both objective and subjective metrics than competing approaches.
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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: 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: Enhanced Inter-Cell Interference Coordination Challenges in Heterogeneous Networks

paper_content:

3GPP LTE-Advanced has recently been investigating heterogeneous network (HetNet) deployments as a cost effective way to deal with the unrelenting traffic demand. HetNets consist of a mix of macrocells, remote radio heads, and low-power nodes such as picocells, femtocells, and relays. Leveraging network topology, increasing the proximity between the access network and the end users, has the potential to provide the next significant performance leap in wireless networks, improving spatial spectrum reuse and enhancing indoor coverage. Nevertheless, deployment of a large number of small cells overlaying the macrocells is not without new technical challenges. In this article, we present the concept of heterogeneous networks and also describe the major technical challenges associated with such network architecture. We focus in particular on the standardization activities within the 3GPP related to enhanced intercell interference coordination.
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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 scope of handoff strategies in macro-femtocell environments

paper_content:

Energy consumption in downlink mode is becoming an important topic as cellular communications grow into a large scale enterprise. The search for high rates keeping energy constraints low has put forward the idea that cells with smaller size may improve not only the capacity of the network, but also reduce the amount of energy that is needed to achieve such capacities. When using heterogeneous networks, users can be encouraged to handoff to a femtocell, that offers better capacity per unit energy spent, by means of different handoff strategies. These strategies may also improve the energy use of the network if the handoff priority is given to both, capacity, and energy use.
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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 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: Monitoring and Assessing Energy Consumption and CO2 Emissions in Cloud-Based Systems

paper_content:

The development and maintenance of cloud sites are often characterized by energy waste and high CO2 emissions. Energy efficiency and the decrease of the CO2 emissions in cloud-based systems can be only obtained by adopting suitable actions and techniques (e.g., utilization of green energy sources, reduction of the number of physical and virtual machines, usage of the greener machines). In order to evaluate the suitability of these different actions, it is necessary to define a measure for greenness of the whole system. For this reason, this paper defines a set of metrics to assess the greenness of a cloud infrastructure. In order to provide a detailed view of the behaviour of the system and to facilitate the identification of the causes of the energy waste, metrics have been defined at different layers of the system (i.e., application, virtualization, infrastructure layers). The monitoring infrastructure that is necessary to retrieve all the data required for the assessment of the identified set of metrics is also described.
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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: Cross-Layer Energy and Delay Optimization in Small-Scale Sensor Networks

paper_content:

The general joint design of the physical, MAC, and routing layers to minimize network energy consumption is complex and hard to solve. Heuristics to compute approximate solutions and high-complexity algorithms to compute exact solutions have been previously proposed. In this paper, we focus on synchronous small-scale networks with interference-free link scheduling and practical MQAM link transmission schemes. We show that the cross-layer optimization problems can be closely approximated by convex optimization problems that can be efficiently solved. There are two main contributions of this paper. First of all, we minimize the total network energy that includes both transmission and circuit energy consumptions, where we explore the tradeoff between the two energy elements. Specifically, we use interference-free TDMA as the medium access control scheme. We optimize the routing flow, TDMA slot assignment, and MQAM modulation rate and power on each link. The results demonstrate that the minimum energy transmission scheme is a combination of multihop and single-hop transmissions for general networks; including circuit energy favors transmission schemes with fewer hops. Secondly, based on the solved optimal transmission scheme, we quantify the best trade-off curve between delay and energy consumption, where we derive a scheduling algorithm to minimize the worst-case packet delay.
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paper_title: Power-Based Routing for Two-Hop OFDMA Cellular Networks with Fixed Relay Stations

paper_content:

This paper addresses aspects of routing strategy of a cellular network enhanced with two-hop fixed relay nodes. The routing strategy for each user is important design parameter because the terminal is energy-limited. To enhance the radio resource utility, a utility maximization framework via pricing is adopted for multi-cell distributed power allocation. Under the optimization physical layer transmission strategy, an efficient power-based routing algorithm is proposed in reverse link which selects the best route in the tradeoff between power consumption and data rate. It is demonstrated through intensive system-level simulation that the performance of our proposed routing algorithm is superior to several known routing algorithms.
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paper_title: Characterizing Energy Efficiency and Deployment Efficiency Relations for Green Architecture Design

paper_content:

Global warming and climate changing is among the major challenges in the 21st century. In wireless communications, green architecture design is an urgent demand for operators, not only because of the social responsibilities but also their willingness to reduce the network construction and operating cost. Previous literatures tried to tackle deployment cost and energy efficiency in a separated manner. However, these two aspects are interacting with each other and the design of green architecture needs a holistic consideration of both. In this paper, we try to shed some light on the green architecture design by analytically characterizing the open relations between energy efficiency and deployment efficiency, which is found somehow different from our intuition and there might not be a simple tradeoff between the two. This study has positive impact on the future network planning and optimization.
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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: Characterizing and improving energy-delay tradeoffs in heterogeneous communication systems

paper_content:

Communication systems with multiple computing resources are gaining popularity. These devices consume a considerable amount of energy, and require that the system resources be fully utilized at all times. In this paper, we aim to reduce the energy consumption and also improve the system utilization by incorporating performance-enhancement and power-optimization techniques into a multi-resource heterogeneous communication system. We study the performance and energy improvements contributed by our techniques, using a traditional evaluation framework. However, this framework fails to clearly model the performance-energy tradeoffs in the system. Hence, we propose a more relevant framework with a new metric named Energy-resource efficiency (ERE) to study these systems. ERE defines a link between the performance and energy variations in a system to clearly highlight the various performance-energy tradeoffs. Our experimental results shown that, when ERE is used to calibrate the performance-energy tradeoffs, one can achieve up to 80% performance and energy gains in a power-aware heterogeneous communication system.
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paper_title: Cross-Layer Energy and Delay Optimization in Small-Scale Sensor Networks

paper_content:

The general joint design of the physical, MAC, and routing layers to minimize network energy consumption is complex and hard to solve. Heuristics to compute approximate solutions and high-complexity algorithms to compute exact solutions have been previously proposed. In this paper, we focus on synchronous small-scale networks with interference-free link scheduling and practical MQAM link transmission schemes. We show that the cross-layer optimization problems can be closely approximated by convex optimization problems that can be efficiently solved. There are two main contributions of this paper. First of all, we minimize the total network energy that includes both transmission and circuit energy consumptions, where we explore the tradeoff between the two energy elements. Specifically, we use interference-free TDMA as the medium access control scheme. We optimize the routing flow, TDMA slot assignment, and MQAM modulation rate and power on each link. The results demonstrate that the minimum energy transmission scheme is a combination of multihop and single-hop transmissions for general networks; including circuit energy favors transmission schemes with fewer hops. Secondly, based on the solved optimal transmission scheme, we quantify the best trade-off curve between delay and energy consumption, where we derive a scheduling algorithm to minimize the worst-case packet delay.
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paper_title: Lower Bound of Energy-Delay Tradeoff of Cooperative MIMO Communications

paper_content:

Cooperative MIMO (CMIMO) communications have transformed channel fading from a negative factor that should be mitigated into a positive factor that can be exploited in wireless networks to improve capacity. Meanwhile, CMIMO scheme has been proved to be an effective solution to improve the energy efficiency of a network. However, an inherent feature of wireless channels, unreliability caused by channel fading is neglected in related studies. In this paper, on the basis of an unreliable link model, the trade-off between the energy consumption and the transmission delay of CMIMO scheme is investigated from the viewpoint of cross-layer, and a lower bound of energy-delay tradeoff is provided which offers a deep insight into the benefits of CMIMO compared with classical multi-hop communications. Moreover, a cross-layer framework is introduced to optimize the parameters at the physical and protocol layers.
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paper_title: Energy-efficient cooperative relay selection scheme in MIMO relay cellular networks

paper_content:

Power saving is an important issue in wireless networks. This paper proposed an energy-efficient cooperative relay selection scheme that utilized the transmission power more efficiently in cooperative relaying systems. The nodes in the network were deployed with multiple antennas and the decode-and-forward relaying protocol was used. The optimization problem of energy efficiency in cooperative relaying was defined. Based on a suboptimal solution, the energy-efficient relay selection scheme was given, which selected the relay stations with the best energy efficiency and decided the optimal number of cooperative relay stations. Compared with the fixed relay cooperation, the simulation results showed that the proposed scheme could improve the energy efficiency as well as the system capacity, irrespective of the channel state conditions. It could be concluded that the proposed cooperative relay selection scheme improved the radio resource efficiency effectively.
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paper_title: Optimal Transmission Range for Minimum Energy Consumption in Wireless Sensor Networks

paper_content:

Energy efficiency is a hot topic in Wireless Sensor Networks (WSNs) because of the limited power supply. Routing strategies have a major impact on total energy consumption of network. Long-hop routing strategies demand substantial transmission power but are capable of reducing energy consumed by relay nodes. Short-hop routing strategies are just the reverse. This paper explores how multi-hop routing strategies are more energy efficient for periodic monitoring applications. We propose an energy efficiency metric for periodic monitoring applications, referred to as the Energy Distance Ratio per bit (EDRb). The concept of unreliable links is integrated into the proposed energy model to take transmission errors into account. By minimizing EDRb, an optimal hop distance is obtained for which related parameters such as optimal transmission power, optimal signal noise ratio (SNR) and optimal bit error rate (BER) are found in Rayleigh fading environment. On the basis of the obtained optimal hop distance, the low bound of mean EDRb for multi- hop path is computed. Finally, theoretical results are compared to simulations. It is shown that the network's lifetime can be extended significantly by optimizing the hop length in a classical routing scheme.
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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: New scheduling scheme for green communications in long term evolution networks

paper_content:

Green communications has been paid much attention recently, to provide energy efficient networks with a high level of quality of service (QoS). In this study, the authors propose a cross-layer scheduling scheme for the downlink of long-term evolution networks, considering the buffer state which may be empty in some times. Their target is to minimise energy consumption under the constraints of limited average transmitting power in the base station, and maximum tolerable delay as QoS of heterogeneous users. In the proposed scheme, the authors use an effective capacity link layer model to consider the data link layer characteristics, such as probability of non-empty buffer and probability of maximum delay, along with the physical layer parameters. Simulation results show more than 48% reduction of energy consumption in peak traffic loads.
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paper_title: The impact of QoS constraints on the energy efficiency of fixed-rate wireless transmissions

paper_content:

Transmission over wireless fading channels under quality of service (QoS) constraints is studied when only the receiver has channel side information. Being unaware of the channel conditions, transmitter is assumed to send the information at a fixed rate. Under these assumptions, a two-state (ON-OFF) transmission model is adopted, where information is transmitted reliably at a fixed rate in the ON state while no reliable transmission occurs in the OFF state. QoS limitations are imposed as constraints on buffer violation probabilities, and effective capacity formulation is used to identify the maximum throughput that a wireless channel can sustain while satisfying statistical QoS constraints. Energy efficiency is investigated by obtaining the bit energy required at zero spectral efficiency and the wideband slope in both wideband and low-power regimes assuming that the receiver has perfect channel side information (CSI). In both wideband and low-power regimes, the increased energy requirements due to the presence of QoS constraints are quantified. Comparisons with variable-rate/fixed-power and variable-rate/variable-power cases are given. Energy efficiency is further analyzed in the presence of channel uncertainties. The optimal fraction of power allocated to training is identified under QoS constraints. It is proven that the minimum bit energy in the low-power regime is attained at a certain nonzero power level below which bit energy increases without bound with vanishing power.
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paper_title: Energy Efficiency in the Low-SNR Regime under Queueing Constraints and Channel Uncertainty

paper_content:

Energy efficiency of fixed-rate transmissions is studied in the presence of queueing constraints and channel uncertainty. It is assumed that neither the transmitter nor the receiver has channel side information prior to transmission. The channel coefficients are estimated at the receiver via minimum mean-square-error (MMSE) estimation with the aid of training symbols. It is further assumed that the system operates under statistical queueing constraints in the form of limitations on buffer violation probabilities. The optimal fraction of power allocated to training is identified. Spectral efficiency-bit energy tradeoff is analyzed in the low-power and wideband regimes by employing the effective capacity formulation. In particular, it is shown that the bit energy increases without bound in the low-power regime as the average power vanishes. A similar conclusion is reached in the wideband regime if the number of noninteracting subchannels grow without bound with increasing bandwidth. On the other hand, it is proven that if the number of resolvable independent paths and hence the number of noninteracting subchannels remain bounded as the available bandwidth increases, the bit energy diminishes to its minimum value in the wideband regime. For this case, expressions for the minimum bit energy and wideband slope are derived. Overall, energy costs of channel uncertainty and queueing constraints are identified, and the impact of multipath richness and sparsity is determined.
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paper_title: Throughput-delay trade-off in energy constrained wireless networks

paper_content:

The random network model assumed in this paper is a generalization of the model that incorporates transmission energy consumption. The throughput, delay and energy-per-bit for a communication scheme are related through the scheme's average transmission range, i.e., average hop distance is considered. For mobile networks, the same model with additional feature that each node moves with velocity according to an independent Brownian motion is considered.
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paper_title: Transmission Strategies in Multiple-Access Fading Channels With Statistical QoS Constraints

paper_content:

Effective capacity, which provides the maximum constant arrival rate that a given service process can support while satisfying statistical queueing constraints, is analyzed in a multiuser scenario. In particular, the effective capacity region of fading multiple-access channels in the presence of quality of service (QoS) constraints is studied. Perfect channel side information is assumed to be available at both the transmitters and the receiver. It is initially assumed that the transmitters send the information at a fixed power level and, hence, do not employ power control policies. Under this assumption, the performance achieved by superposition coding with successive decoding techniques is investigated. It is shown that varying the decoding order with respect to the channel states can significantly increase the achievable throughput region. In the two-user case, the optimal decoding strategy is determined for the scenario in which the users have the same QoS constraints. The performance of orthogonal transmission strategies is also analyzed. It is shown that for certain QoS constraints, time-division multiple access can achieve better performance than superposition coding if fixed successive decoding order is used at the receiver side. In the subsequent analysis, power control policies are incorporated into the transmission strategies. The optimal power allocation policies for any fixed decoding order over all channel states are identified. For a given variable decoding-order strategy, the conditions that the optimal power control policies must satisfy are determined, and an algorithm that can be used to compute these optimal policies is provided.
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paper_title: Using cognitive radio to deliver ‘Green’ communications

paper_content:

This paper discusses different ways of delivering ‘green’ cognitive radio based systems. Fundamental is the need to exploit the free spectrum available and power efficient modulation where possible. The paper describes a variable power/bandwidth efficient modulation strategy where the modulation level is adjusted by cognitively determining the assignment and use of the available spectrum, taking into account the channel occupancy probability. Battery life for different techniques is also considered. Secondly, the paper discusses ways to reduce the complexity overall of cognitive radio systems, particularly in the need for spectrum sensing by exploiting distributed artificial intelligence. Techniques presented show how it is possible to largely eliminate the need for spectrum sensing, along with the associated energy consumption, by using reinforcement learning to develop a preferred channel set in each device. Finally, the paper discusses the potential benefits of the use of antenna directionality to improve energy efficiency, and the associated problems that still must be solved before this technique can deliver ‘green’ radio.
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paper_title: Energy and throughput tradeoff in wireless networks with processing energy considerations

paper_content:

Many wireless network studies pertain to the derivation of throughput bounds and cross-layer optimization for energy conservation. From a practical perspective, often a network must meet the competing objective of attaining high throughput while conserving energy for prolonged operation. The tradeoff between these two important network metrics has not been adequately addressed in the literature. A further deficiency in existing research lies in the suppression of non-distance-dependent processing energy in energy models, which can lead erroneously to routing on paths with large number of hops. We model processing energy explicitly, and show that for a particular implementation of wireless network, the average path power is a monotonically increasing, piecewise linear function of throughput. Furthermore, we quantify a network region size threshold such that in a small region relative to the threshold, direct transmission routing is both energy conserving and throughput achieving. For larger regions, path power optimal routing may not achieve the maximum throughput. Higher throughput may be achieved with suboptimal routing schemes that lead to higher marginal power increase as the throughput increases
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paper_title: Throughput, energy and path length tradeoffs in Bluetooth scatternets

paper_content:

In this work, we determine an analytical relationship between the average path length of traffic connections of a Bluetooth scatternet and the overall throughput and power consumption of the network. Results obtained implementing this analytical relationship to different scatternet topologies are presented and discussed. By reducing the hop count in a scatternet we can achieve better performance in terms of throughput and power consumption. Therefore, the issue of minimizing the hop count in the presence of mobility, changing traffic flows and varying interference receives an important role. In our analysis we also show the impact of the link quality on the overall throughput. The obtained results motivate the importance of heuristics aimed at reducing the communication path length in a scatternet.
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paper_title: The capacity of wireless networks

paper_content:

When n identical randomly located nodes, each capable of transmitting at W bits per second and using a fixed range, form a wireless network, the throughput /spl lambda/(n) obtainable by each node for a randomly chosen destination is /spl Theta/(W//spl radic/(nlogn)) bits per second under a noninterference protocol. If the nodes are optimally placed in a disk of unit area, traffic patterns are optimally assigned, and each transmission's range is optimally chosen, the bit-distance product that can be transported by the network per second is /spl Theta/(W/spl radic/An) bit-meters per second. Thus even under optimal circumstances, the throughput is only /spl Theta/(W//spl radic/n) bits per second for each node for a destination nonvanishingly far away. Similar results also hold under an alternate physical model where a required signal-to-interference ratio is specified for successful receptions. Fundamentally, it is the need for every node all over the domain to share whatever portion of the channel it is utilizing with nodes in its local neighborhood that is the reason for the constriction in capacity. Splitting the channel into several subchannels does not change any of the results. Some implications may be worth considering by designers. Since the throughput furnished to each user diminishes to zero as the number of users is increased, perhaps networks connecting smaller numbers of users, or featuring connections mostly with nearby neighbors, may be more likely to be find acceptance.
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paper_title: Power Limited Channels: Coding, Multiaccess, and Spread Spectrum

paper_content:

This is a slightly edited version of a paper written, but not published, in the mid-eighties. Its age is symbolic of my much older friendship and respect for Dave Forney, and it is dedicated to that friendship. It’s age should not be taken as any claim for precedence of the results, but merely to excuse the lack of up-to-date references.
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paper_title: Power-Based Routing for Two-Hop OFDMA Cellular Networks with Fixed Relay Stations

paper_content:

This paper addresses aspects of routing strategy of a cellular network enhanced with two-hop fixed relay nodes. The routing strategy for each user is important design parameter because the terminal is energy-limited. To enhance the radio resource utility, a utility maximization framework via pricing is adopted for multi-cell distributed power allocation. Under the optimization physical layer transmission strategy, an efficient power-based routing algorithm is proposed in reverse link which selects the best route in the tradeoff between power consumption and data rate. It is demonstrated through intensive system-level simulation that the performance of our proposed routing algorithm is superior to several known routing algorithms.
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paper_title: Energy-efficient cooperative relay selection scheme in MIMO relay cellular networks

paper_content:

Power saving is an important issue in wireless networks. This paper proposed an energy-efficient cooperative relay selection scheme that utilized the transmission power more efficiently in cooperative relaying systems. The nodes in the network were deployed with multiple antennas and the decode-and-forward relaying protocol was used. The optimization problem of energy efficiency in cooperative relaying was defined. Based on a suboptimal solution, the energy-efficient relay selection scheme was given, which selected the relay stations with the best energy efficiency and decided the optimal number of cooperative relay stations. Compared with the fixed relay cooperation, the simulation results showed that the proposed scheme could improve the energy efficiency as well as the system capacity, irrespective of the channel state conditions. It could be concluded that the proposed cooperative relay selection scheme improved the radio resource efficiency effectively.
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paper_title: Power-Bandwidth Tradeoff in Dense Multi-Antenna Relay Networks

paper_content:

We consider a dense fading multi-user network with multiple active multi-antenna source-destination pair terminals communicating simultaneously through a large common set of K multi-antenna relay terminals in the full spatial multiplexing mode. We use Shannon-theoretic tools to analyze the tradeoff between energy efficiency and spectral efficiency (known as the power-bandwidth tradeoff) in meaningful asymptotic regimes of signal-to-noise ratio (SNR) and network size. We design linear distributed multi-antenna relay beamforming (LDMRB) schemes that exploit the spatial signature of multi-user interference and characterize their power-bandwidth tradeoff under a system-wide power constraint on source and relay transmissions. The impact of multiple users, multiple relays and multiple antennas on the key performance measures of the high and low SNR regimes is investigated in order to shed new light on the possible reduction in power and bandwidth requirements through the usage of such practical relay cooperation techniques. Our results indicate that point-to-point coded multi-user networks supported by distributed relay beamforming techniques yield enhanced energy efficiency and spectral efficiency, and with appropriate signaling and sufficient antenna degrees of freedom, can achieve asymptotically optimal power-bandwidth tradeoff with the best possible (i.e., as in the cutset bound) energy scaling of K-1 and the best possible spectral efficiency slope at any SNR for large number of relay terminals. Furthermore, our results help to identify the role of interference cancellation capability at the relay terminals on realizing the optimal power- bandwidth tradeoff; and show how relaying schemes that do not attempt to mitigate multi-user interference, despite their optimal capacity scaling performance, could yield a poor power- bandwidth tradeoff.
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paper_title: Energy-bandwidth tradeoff with spatial reuse in wireless multi-hop networks

paper_content:

In this paper, we investigate the energy-bandwidth tradeoff of wireless multi-hop networks with spatial reuse. For the end-to-end bandwidth utilization, we consider the number of information bits transmitted (end-to-end) per coded symbol transmitted by any node in the network that is forwarding the data. The total energy consumption per information bit by the network includes the energy transmitted and the receiver processing energy. Spatial reuse is considered to enhance the bandwidth efficiency by allowing simultaneous transmission. Bounds on the energy-bandwidth tradeoff are derived from convex optimization problem. With receiver processing energy, it is shown that spatial reuse degrades the energy efficiency but improves the bandwidth utilization. We demonstrate that this degraded total energy consumption can be improved by varying the minimum separation of simultaneous transmitters.
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paper_title: End-to-End Energy–Bandwidth Tradeoff in Multihop Wireless Networks

paper_content:

In this paper, energy-constrained wireless multihop networks with a single source-destination pair are considered. A network model that incorporates both the energy radiated by the transmitter and the energy consumed by the circuits that process the received signals is proposed. The rate of communication is the number of information bits transmitted (end-to-end) per coded symbol transmitted by any node in the network that is forwarding the data. The tradeoff between the total energy consumption and the end-to-end rate of communication is analyzed. The performance (either energy or rate) depends on the transmission strategy of each node, the location of the relay nodes, and the data rate used by each node. Communication strategies include the rate of transmission on each link, the scheduling of links, and the power used for each link. Strategies that minimize the total energy consumption for a given rate are found. Two communication strategies that capture the inherent constraints of some practical networks are also considered and compared with the optimum strategies. In the case of equispaced relays, analytical results for the tradeoff between the energy and the end-to-end data rate are provided. The minimum energy over all possible data rates is also obtained. Low rates incur a significant penalty because the receiver is on for a long time period while high rates require high transmission energy. At high rates routes with fewer hops minimize the energy consumption while at lower rates more hops minimize the energy consumption.
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paper_title: A Tradeoff between Energy and Bandwidth Efficiency in Wireless Networks

paper_content:

In this paper, we study the bandwidth efficiency and energy efficiency of wireless ad hoc networks in which the energy supply of nodes and bandwidth are the primary resource constraints. For bandwidth efficiency, we consider the total number of channel uses between source and destination node. Also, energy consumption of the receiver in order to process each coded bit is considered as well as the wasted energy of a nonideal amplifier in the transmitter. With the location of relaying nodes, we investigate the impact on bandwidth efficiency and energy efficiency for both common rate and common power Schemes. All nodes in a network operate in half-duplex mode, hence more channel uses are required in a multihop transmission. This leads to a loss in bandwidth efficiency but a potential gain in energy efficiency because each node can save its transmitting power. We investigate this tradeoff between energy efficiency and bandwidth efficiency of the network similar in nature to that found by Shannon for a single link. We also develop performance characterizations in terms of transport efficiency, which combines bandwidth efficiency and energy efficiency into a single metric. It is shown that equidistant relaying cases perform better than non-equidistant relaying cases for either common rate or common power schemes. For non-equidistant relaying cases, it is also shown that common power schemes achieve a higher bandwidth efficiency than do common rate schemes, whereas energy efficiency depends on the received signal-to-noise ratio at the destination node.
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paper_title: Optimal Transmission Range for Minimum Energy Consumption in Wireless Sensor Networks

paper_content:

Energy efficiency is a hot topic in Wireless Sensor Networks (WSNs) because of the limited power supply. Routing strategies have a major impact on total energy consumption of network. Long-hop routing strategies demand substantial transmission power but are capable of reducing energy consumed by relay nodes. Short-hop routing strategies are just the reverse. This paper explores how multi-hop routing strategies are more energy efficient for periodic monitoring applications. We propose an energy efficiency metric for periodic monitoring applications, referred to as the Energy Distance Ratio per bit (EDRb). The concept of unreliable links is integrated into the proposed energy model to take transmission errors into account. By minimizing EDRb, an optimal hop distance is obtained for which related parameters such as optimal transmission power, optimal signal noise ratio (SNR) and optimal bit error rate (BER) are found in Rayleigh fading environment. On the basis of the obtained optimal hop distance, the low bound of mean EDRb for multi- hop path is computed. Finally, theoretical results are compared to simulations. It is shown that the network's lifetime can be extended significantly by optimizing the hop length in a classical routing scheme.
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paper_title: Energy-bandwidth tradeoff with spatial reuse in wireless multi-hop networks

paper_content:

In this paper, we investigate the energy-bandwidth tradeoff of wireless multi-hop networks with spatial reuse. For the end-to-end bandwidth utilization, we consider the number of information bits transmitted (end-to-end) per coded symbol transmitted by any node in the network that is forwarding the data. The total energy consumption per information bit by the network includes the energy transmitted and the receiver processing energy. Spatial reuse is considered to enhance the bandwidth efficiency by allowing simultaneous transmission. Bounds on the energy-bandwidth tradeoff are derived from convex optimization problem. With receiver processing energy, it is shown that spatial reuse degrades the energy efficiency but improves the bandwidth utilization. We demonstrate that this degraded total energy consumption can be improved by varying the minimum separation of simultaneous transmitters.
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paper_title: Joint bandwidth-power allocation for energy efficient transmission in multi-user systems

paper_content:

The pressure of the energy bill from operators and the request of the environmental protection from the governments and public results in more urgent requirement on the energy consumption and CO 2 emission. Traditionally, the bandwidth and the transmit power are jointly considered to maximize the throughput of the wireless networks, while the energy efficiency of the wireless transmission is ignored. In this paper, we shall introduce a circuit-level power modeling to analyze the above effects and propose the joint bandwidth-power scheduling algorithms for energy efficiency in the wireless communication systems. We show that bandwidth and power shall be considered jointly for different channel statistic to maximize the energy efficiency. In addition, we characterize the bandwidth-power-energy efficiency relationship to obtain the design insights for future energy efficient communication networks.
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paper_title: Lower Bound of Energy-Delay Tradeoff of Cooperative MIMO Communications

paper_content:

Cooperative MIMO (CMIMO) communications have transformed channel fading from a negative factor that should be mitigated into a positive factor that can be exploited in wireless networks to improve capacity. Meanwhile, CMIMO scheme has been proved to be an effective solution to improve the energy efficiency of a network. However, an inherent feature of wireless channels, unreliability caused by channel fading is neglected in related studies. In this paper, on the basis of an unreliable link model, the trade-off between the energy consumption and the transmission delay of CMIMO scheme is investigated from the viewpoint of cross-layer, and a lower bound of energy-delay tradeoff is provided which offers a deep insight into the benefits of CMIMO compared with classical multi-hop communications. Moreover, a cross-layer framework is introduced to optimize the parameters at the physical and protocol layers.
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paper_title: Distributed Multi-Cell Power Allocation Algorithm for Energy Efficiency in OFDMA Relay Systems

paper_content:

The power allocation problem with co-channel interference is studied in multi-cell OFDMA cellular relay systems. Based on non-cooperative game theory and using a two-hop data rate balance, a distributed multi-cell power allocation (DMPA) algorithm is proposed, which reduces the transmission power cost and improves the system throughput. The non-cooperative power allocation game model is given in the first time subslot for base stations (BSs) and in the second time subslot for relay stations (RSs) respectively. Furthermore, the power is reduced by matching the data rate of the two-hop links for each RS. The simulation results of system throughput and transmission power of BS and RS are given with different numbers of users. Compared with equal power allocation on each subchannel, the system energy consumption is reduced and the throughput is improved.
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paper_title: Energy efficient OFDMA: Trade-off between computation and transmission energy

paper_content:

We study minimization of overall energy consumption of OFDMA systems, which are widely adopted in future wireless communications. Based on the existing resource allocation to minimize transmission energy, the computation energy increases due to the complexity of allocating algorithms. Since high performance algorithms usually have high complexity, there exist trade-offs between transmission energy and computation energy. To systematically minimize overall energy consumption comprised of transmission and computation, we propose to minimize transmission energy by resource allocation while keeping the computation energy low via reduced-complexity algorithm. We further extend this idea to relay since it is well known to reduce transmission energy but only a few of works to minimize total energy consumption. In our numerical results, we demonstrate that in the scenario without relay, our algorithm can achieve near-minimum transmission energy (80% savings) under quite computation energy. In the scenario with relay, our algorithm can do even better by saving more transmission energy (88% savings) under a minor increase of computation energy. Both scenarios suggest that the global energy minimum can be achieved by proper trade-off between communication and computation energy consumption.
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paper_title: On the transmission-computation-energy tradeoff in wireless and fixed networks

paper_content:

In this paper, a framework for the analysis of the transmission-computation-energy tradeoff in wireless and fixed networks is introduced. The analysis of this tradeoff considers both the transmission energy as well as the energy consumed at the receiver to process the received signal. While previous work considers linear decoder complexity, which is only achieved by uncoded transmission, this paper claims that the average processing (or computation) energy per symbol depends exponentially on the information rate of the source message. The introduced framework is parametrized in a way that it reflects properties of fixed and wireless networks alike. ::: The analysis of this paper shows that exponential complexity and therefore stronger codes are preferable at low data rates while linear complexity and therefore uncoded transmission becomes preferable at high data rates. The more the computation energy is emphasized (such as in fixed networks), the less hops are optimal and the lower is the benefit of multi-hopping. On the other hand, the higher the information rate of the single-hop network, the higher the benefits of multi-hopping. Both conclusions are underlined by analytical results.
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paper_title: Improving Energy Efficiency through Bandwidth, Power, and Adaptive Modulation

paper_content:

The pressure of the energy bill from operators and the request of the environmental protection from the governments and publics results in more urgent requirement on the energy consumption and CO$_2$ emission. Traditionally, adaptive modulation has been proven to be an efficient solution to improve the system performance over the radio fading channels. To obtain the design insights for energy efficient adaptive modulation scheme, we shall introduce a circuit-level power modeling to analyze the effects and characterize the bandwidth-power-energy efficiency tradeoff relations for wireless communication systems. We show that different bandwidth, power and modulation schemes shall be used under different channel conditions to maximize the energy efficiency and the adaptive modulation scheme can greatly help to improve the tradeoff curves.
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paper_title: Coding tradeoffs for reduced energy consumption in sensor networks

paper_content:

We consider the design of error control schemes in wireless sensor networks. Unlike in traditional communications systems, in which coding is almost always beneficial, in sensor networks, the relatively short communications range and the lack of energy resources may lead to different conclusions. In particular, the energy spent for decoding may actually exceed that saved due to the coding gain. In this environment, interesting tradeoffs can be identified and non-traditional ways to perform error control may be proposed.
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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: Energy-Efficient Multi-Carrier Link Adaptation with Sum Rate-Dependent Circuit Power

paper_content:

Energy-efficient link adaptation is studied for transmission on a frequency-selective parallel AWGN channel. The total power dissipation model includes a circuit power that varies with the sum rate and a power amplifier efficiency that varies with the bandwidth used. The mathematical analysis provides insight into how the subcarrier rates should be chosen for optimal energy efficiency and suggests a simple fixed-point algorithm that finds the solution in few iterations. Moreover, ways of improving the energy efficiency are discussed based on the dependence on bandwidth and distance between transmitter and receiver.
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paper_title: Energy and throughput tradeoff in wireless networks with processing energy considerations

paper_content:

Many wireless network studies pertain to the derivation of throughput bounds and cross-layer optimization for energy conservation. From a practical perspective, often a network must meet the competing objective of attaining high throughput while conserving energy for prolonged operation. The tradeoff between these two important network metrics has not been adequately addressed in the literature. A further deficiency in existing research lies in the suppression of non-distance-dependent processing energy in energy models, which can lead erroneously to routing on paths with large number of hops. We model processing energy explicitly, and show that for a particular implementation of wireless network, the average path power is a monotonically increasing, piecewise linear function of throughput. Furthermore, we quantify a network region size threshold such that in a small region relative to the threshold, direct transmission routing is both energy conserving and throughput achieving. For larger regions, path power optimal routing may not achieve the maximum throughput. Higher throughput may be achieved with suboptimal routing schemes that lead to higher marginal power increase as the throughput increases
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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: Distributed Multi-Cell Power Allocation Algorithm for Energy Efficiency in OFDMA Relay Systems

paper_content:

The power allocation problem with co-channel interference is studied in multi-cell OFDMA cellular relay systems. Based on non-cooperative game theory and using a two-hop data rate balance, a distributed multi-cell power allocation (DMPA) algorithm is proposed, which reduces the transmission power cost and improves the system throughput. The non-cooperative power allocation game model is given in the first time subslot for base stations (BSs) and in the second time subslot for relay stations (RSs) respectively. Furthermore, the power is reduced by matching the data rate of the two-hop links for each RS. The simulation results of system throughput and transmission power of BS and RS are given with different numbers of users. Compared with equal power allocation on each subchannel, the system energy consumption is reduced and the throughput is improved.
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paper_title: Coverage and energy tradeoff in density control on sensor networks

paper_content:

In dense wireless sensor networks, density control is an important technique for prolonging network's lifetime while providing sufficient sensing coverage. In this paper, we develop three new density control protocols by considering the tradeoff between energy usage and coverage. The first one, non-overlapping density control, aims at maximizing coverage while avoiding the overlap of sensing areas of active sensors. Under the ideal case, a set of optimality conditions are derived to select sensors such that the sensing space is covered systematically to maximize the usage of each sensors and the coverage gap is minimized. Based on the optimality conditions, we develop a distributed protocol that can be efficiently implemented in large sensor networks. Next, we present a protocol called non-overlapping density control based on distances that does not require location information of the nodes. This protocol is more flexible and easier to implement than existing location-based methods. Finally, we present a new range-adjustable protocol called non-overlapping density control for adjustable sensing ranges. It allows heterogenous sensing ranges for different sensors to save energy consumption. Extensive simulation shows promising results of the new protocols.
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paper_title: Maintaining Sensing Coverage and Connectivity in Large Sensor Networks

paper_content:

In this paper, we address the issues of maintaining sensing coverage and connectivity by keeping a minimum number of sensor nodes in the active mode in wireless sensor networks. We investigate the relationship between coverage and connectivity by solving the following two sub-problems. First, we prove that if the radio range is at least twice the sensing range, complete coverage of a convex area implies connectivity among the working set of nodes. Second, we derive, under the ideal case in which node density is sufficiently high, a set of optimality conditions under which a subset of working sensor nodes can be chosen for complete coverage. Based on the optimality conditions, we then devise a decentralized density control algorithm, Optimal Geographical Density Control (OGDC), for density control in large scale sensor networks. The OGDC algorithm is fully localized and can maintain coverage as well as connectivity, regardless of the relationship between the radio range and the sensing range. Ns-2 simulations show that OGDC outperforms existing density control algorithms [25, 26, 29] with respect to the number of working nodes needed and network lifetime (with up to 50% improvement), and achieves almost the same coverage as the algorithm with the best result.
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paper_title: Energy-efficient routing using timer-based MAC protocol in power-controlled multihop cellular networks

paper_content:

Ahstract- In this paper, we propose a novel cross-layer design method for implementing the metric, minimizing consumed energy per packet, by using a conventional on-demand routing protocol in power-controlled multihop cellular networks. If CSMAICA is used as the MAC layer algorithm of each mobile node, the routing algorith m using flooding selects a shortest hop path regardless of its metric. Thus, the established path has no power­ saving effect compared with the shortest hop path. To solve this problem, we consider not only an energy-effici ent routing algorithm, but also a MAC layer algorithm that is adequate to optimize its performance. Computer simulati ons show that the proposed scheme outperforms the conventional schemes with respect to the average total consumed power, while maintaining a similar average success rate. Moreover, the proposed scheme approximates the optimal solution calculated by CPLEX, and is scalable since each mobile node operates in a distributed manner.
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paper_title: Green resource allocation for OFDMA wireless cellular networks

paper_content:

Packet scheduling algorithms are viewed as one of the key mechanisms for increasing the diversity order, robustness and effectiveness of a wireless multi-user communication system. Traditional packet scheduling are mainly designed to increase the system capacity. In this paper we present a novel scheduling algorithm that improves the scheduling energy efficiency in OFDMA based wireless cellular networks. Our goal is to reduce the overall downlink energy consumption while adapting the target of spectral efficiency to the actual load of the system and meeting the Quality of Service (QoS). Our analysis reveals how the proposed approach permits to achieve notable energy gain over traditional scheduling algorithm especially in not saturated scenarios.
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paper_title: Energy, latency and capacity trade-offs in wireless multi-hop networks

paper_content:

This paper concentrates on characterizing energy, latency and capacity trade-offs in multi-hop wireless ad-hoc networks. Therefore, a multiobjective framework is proposed to derive the Pareto-optimal set of solutions with respect to these three criteria. The work presented in this paper assumes a linear network where transmission powers and relay positions are optimization variables. We study the asymptotic state where the distance between source and destination is very high such that the number of hops tends to infinite. Two types of traffic are considered in the following. First, low rate traffic is analyzed by characterizing the multiobjective performance of a single packet transmission using an interference free multi-hop relaying strategy. Second, a continuous flow of packets from a unique source is considered. In the first case, we show an important theorem which states that all Pareto optimal solutions with respect to delay and energy metrics provide the same target SNR at the receiver side. In the second case, our analytical results highlight how the energy/delay Pareto front moves when considering a capacity constraint and the optimal re-use factor is derived.
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paper_title: Energy-delay tradeoffs for data collection in TDMA-based sensor networks

paper_content:

We consider a wireless sensor network where the nodes have limited energy. We first analyze the delay performance of a transmission scheme based on time division multiple access (TDMA). We propose a simple link scheduling algorithm to find the minimum-delay schedule given the slot lengths for all the links. We then combine these results with our previous work on energy-optimal cross-layer design to minimize the delay in transferring a fixed number of bits from the source nodes to the sink, in an energy-constrained manner. We also study the tradeoff between the total energy consumption and delay. Pareto optimal energy-delay curves are computed by solving a series of convex optimization problems where each objective function is a weighted sum of the delay and the total energy consumption. The computation is done for networks with and without link adaptation capabilities.
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paper_title: Energy-latency tradeoffs for data gathering in wireless sensor networks

paper_content:

We study the problem of scheduling packet transmissions for data gathering in wireless sensor networks. The focus is to explore the energy-latency tradeoffs in wireless communication using techniques such as modulation scaling. The data aggregation tree - a multiple-source single-sink communication paradigm - is employed for abstracting the packet flow. We consider a real-time scenario where the data gathering must be performed within a specified latency constraint. We present algorithms to minimize the overall energy dissipation of the sensor nodes in the aggregation tree subject to the latency constraint. For the off-line problem, we propose (a) a numerical algorithm for the optimal solution, and (h) a pseudo-polynomial time approximation algorithm based on dynamic programming. We also discuss techniques for handling interference among the sensor nodes. Simulations have been conducted for both long-range communication and short-range communication. The simulation results show that compared with the classic shutdown technique, between 20% to 90% energy savings can be achieved by our techniques, under different settings of several key system parameters. We also develop an on-line distributed protocol that relies only on the local information available at each sensor node within the aggregation tree. Simulation results show that between 15% to 90% energy conservation can be achieved by the on-line protocol. The adaptability of the protocol with respect to variations in the packet size and latency constraint is also demonstrated through several run-time scenarios.
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paper_title: Stability-Energy Consumption Tradeoff among Mobile Ad Hoc Network Routing Protocols

paper_content:

We present an ns-2 simulation based analysis on the energy consumption of the stability-oriented on- demand mobile ad hoc network (MANET) routing protocols. The stability-oriented routing protocols studied include Associativity Based Routing (ABR) [16], Flow-oriented Routing Protocol (FORP) [15] and Route-lifetime Assessment Based Routing (RABR) [1] protocol. Our simulation results show that FORP routes are more stable than RABR routes, which are more stable than ABR routes. On the other hand, based on the energy consumed per packet and the average energy used per node, ABR is better than RABR, which is better than FORP. Thus, we see a stability-energy consumption tradeoff within the class of stability- oriented routing protocols. Regarding the fairness of node usage, we observe that there is an appreciable variation in the energy consumption per node as only the chain of nodes that form stable routes are exhausted to a greater extent.
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paper_title: Cross-Layer Energy and Delay Optimization in Small-Scale Sensor Networks

paper_content:

The general joint design of the physical, MAC, and routing layers to minimize network energy consumption is complex and hard to solve. Heuristics to compute approximate solutions and high-complexity algorithms to compute exact solutions have been previously proposed. In this paper, we focus on synchronous small-scale networks with interference-free link scheduling and practical MQAM link transmission schemes. We show that the cross-layer optimization problems can be closely approximated by convex optimization problems that can be efficiently solved. There are two main contributions of this paper. First of all, we minimize the total network energy that includes both transmission and circuit energy consumptions, where we explore the tradeoff between the two energy elements. Specifically, we use interference-free TDMA as the medium access control scheme. We optimize the routing flow, TDMA slot assignment, and MQAM modulation rate and power on each link. The results demonstrate that the minimum energy transmission scheme is a combination of multihop and single-hop transmissions for general networks; including circuit energy favors transmission schemes with fewer hops. Secondly, based on the solved optimal transmission scheme, we quantify the best trade-off curve between delay and energy consumption, where we derive a scheduling algorithm to minimize the worst-case packet delay.
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paper_title: Green cooperative communication using threshold-based relay selection protocols

paper_content:

This paper proposes new approach to relay selection using a threshold-based transmission protocol for a system with multiple amplify-and-forward relays and users. The novelty of this protocol includes (1) economical feedback that reduces signal processing complexity, as well as (2) adaptively interrupted transmission that can save significant RF power when the selection requirement is not met. Applied to the downlink, this protocol uses a threshold on the first-hop (base-station-to-relay) SNR for relay selection. One-bit feedback is sent from each relay to the base station, reporting the comparison result between the base station-relay link SNR and threshold. Transmission takes place for a relay satisfying the selection condition of having its received SNR greater than a threshold or is otherwise switched off. Numerical results show that for low average SNR scenarios (where relaying is required), the selection threshold can be appropriately chosen relative to the number of relays to dramatically reduce transmit power without sacrificing outage performance.
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paper_title: Power-Based Routing for Two-Hop OFDMA Cellular Networks with Fixed Relay Stations

paper_content:

This paper addresses aspects of routing strategy of a cellular network enhanced with two-hop fixed relay nodes. The routing strategy for each user is important design parameter because the terminal is energy-limited. To enhance the radio resource utility, a utility maximization framework via pricing is adopted for multi-cell distributed power allocation. Under the optimization physical layer transmission strategy, an efficient power-based routing algorithm is proposed in reverse link which selects the best route in the tradeoff between power consumption and data rate. It is demonstrated through intensive system-level simulation that the performance of our proposed routing algorithm is superior to several known routing algorithms.
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paper_title: Energy conservation and routing efficiency tradeoff in multi-hop wireless ad hoc networks

paper_content:

This paper analyzes the problem of energy conservation and routing efficiency tradeoff in multi-hop wireless ad hoc networks, which problem is important to understand because it affects routing protocol design issues. This paper presents this tradeoff in more than just qualitative terms. Specific mathematical measure functions of energy conservation and routing efficiency are derived and analyzed for a given propagation environment. The analytical results show that they depend upon each other. Finally, we present the hints given by the analysis results for routing protocol design issues in multi-hop wireless ad hoc networks.
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paper_title: On the User Performance of LTE UE Power Savings Schemes with Discontinuous Reception in LTE

paper_content:

The UTRAN long-term evolution (LTE) specifications provide flexible means to achieve micro-sleep operation for user equipment (UE) even though it is in active mode and running a service. By means of a discontinuous reception (DRX) framework, pauses in the transmission due to natural traffic characteristics or network prioritization can be utilized. The specifications give a number of options to optimize the performance. In this paper two of those possibilities are compared. Long DRX with the use of an inactivity timer is compared to the usage of short DRX on top of long DRX. The performance is evaluated in terms of user throughput, power consumption, and network performance, while using a realistic RF modem power consumption model for the UE. For bursty traffic, short DRX shows a gain of up to 100% over DRX with just an inactivity timer, when measuring throughput per power unit consumed in case of one or multiple users being present in the cell.
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paper_title: Cloud-Based Augmentation for Mobile Devices: Motivation, Taxonomies, and Open Challenges

paper_content:

Recently, Cloud-based Mobile Augmentation (CMA) approaches have gained remarkable ground from academia and industry. CMA is the state-of-the-art mobile augmentation model that employs resource-rich clouds to increase, enhance, and optimize computing capabilities of mobile devices aiming at execution of resource-intensive mobile applications. Augmented mobile devices envision to perform extensive computations and to store big data beyond their intrinsic capabilities with least footprint and vulnerability. Researchers utilize varied cloud-based computing resources (e.g., distant clouds and nearby mobile nodes) to meet various computing requirements of mobile users. However, employing cloud-based computing resources is not a straightforward panacea. Comprehending critical factors (e.g., current state of mobile client and remote resources) that impact on augmentation process and optimum selection of cloud-based resource types are some challenges that hinder CMA adaptability. This paper comprehensively surveys the mobile augmentation domain and presents taxonomy of CMA approaches. The objectives of this study is to highlight the effects of remote resources on the quality and reliability of augmentation processes and discuss the challenges and opportunities of employing varied cloud-based resources in augmenting mobile devices. We present augmentation definition, motivation, and taxonomy of augmentation types, including traditional and cloud-based. We critically analyze the state-of-the-art CMA approaches and classify them into four groups of distant fixed, proximate fixed, proximate mobile, and hybrid to present a taxonomy. Vital decision making and performance limitation factors that influence on the adoption of CMA approaches are introduced and an exemplary decision making flowchart for future CMA approaches are presented. Impacts of CMA approaches on mobile computing is discussed and open challenges are presented as the future research directions.
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paper_title: Energy Aware Routing Based on Energy Characterization of Devices: Solutions and Analysis

paper_content:

The paper copes with the reduction of network power consumption by the definition of new routing algorithms, able to take into account the energy consumed by the network devices. In particular, based on the power consumption characterization of the network devices obtained using the Energy Profile (EP) concept, the paper presents the analysis of the exact solution of the Energy Aware Routing (EAR) problem solved with a Mixed Integer Programming solver. The analysis is aimed at evaluating the impact on the performance of three relevant aspects of the problem: the approximation of the actual EP, the traffic load and the topology of the network. Furthermore, the paper proposes a heuristic solution of the EAR, denoted as Dijkstra-based Power Aware Routing Algorithm (DPRA), defined in order to cope with the complexity of the exact solution.
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paper_title: Green Software: Greening What and How Much?

paper_content:

In applications in which embedded devices cooperate with ICT (information and communication technology) systems to make industrial processes more efficient, reduce waste or raw materials, and save the environment, the concept of green software becomes increasingly complex. To deal with this issue, the green-software community has introduced the concepts of greening ICT or greening through ICT.
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paper_title: Energy-aware routing: A reality check

paper_content:

In this work, we analyze the design of green routing algorithms and evaluate the achievable energy savings that such mechanisms could allow in several realistic network scenarios. We formulate the problem as a minimum energy routing optimization, which we numerically solve considering a core-network scenario, which can be seen as a worst-case for energy saving performance (as nodes cannot be switched off). To gather full-relief results, we analyze the energy savings in various conditions (i.e., network topology and traffic matrix) and under different technology assumptions (i.e., the energy profile of the network devices). These results give us insight into the potential benefits of different “green” technologies and their interactions. In particular, we show that depending on the topology and traffic matrices, the optimal energy savings can be modest, partly limiting the interest for green routing approaches for some scenarios. At the same time, we also show that the common belief that there is a trade off between green network optimization and performance does not necessarily hold: in the considered environment, green routing has no effect on the main network performances such as maximum link utilization.
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paper_title: Energy Profile Aware Routing

paper_content:

Energy efficient communication devices are essential to minimize the operational cost of future networks and to reduce the negative effects of global warming. In this paper we propose a novel energy reduction approach on network level that takes load-dependent energy consumption information of communication equipment into account. Case study calculation results show that energy savings of more than 35% and with it operational cost can be saved by applying energy profile aware routing.
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paper_title: New scheduling scheme for green communications in long term evolution networks

paper_content:

Green communications has been paid much attention recently, to provide energy efficient networks with a high level of quality of service (QoS). In this study, the authors propose a cross-layer scheduling scheme for the downlink of long-term evolution networks, considering the buffer state which may be empty in some times. Their target is to minimise energy consumption under the constraints of limited average transmitting power in the base station, and maximum tolerable delay as QoS of heterogeneous users. In the proposed scheme, the authors use an effective capacity link layer model to consider the data link layer characteristics, such as probability of non-empty buffer and probability of maximum delay, along with the physical layer parameters. Simulation results show more than 48% reduction of energy consumption in peak traffic loads.
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paper_title: Optimal Utility-Energy tradeoff in Delay Constrained Random Access Networks

paper_content:

Rate, energy and delay are three main parameters of interest in ad-hoc networks. In this paper, we discuss the problem of maximizing network utility and minimizing energy consumption while satisfying a given transmission delay constraint for each packet. We formulate this problem in the standard convex optimization form and subsequently discuss the tradeoff between utility, energy and delay in such framework. Also, in order to adapt for the distributed nature of the network, a distributed algorithm where nodes decide on choosing transmission rates and probabilities based on their local information is introduced.
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paper_title: Cross-Layer Design with Adaptive Modulation: Delay, Rate, and Energy Tradeoffs

paper_content:

We present a cross-layer framework for optimizing the performance of wireless networks as measured by applications or upper layer protocols. The approach combines adaptive modulation with network utility maximization. We extend the approach to find optimal source rates and transmitter power and rate policies without explicit knowledge of the distribution of channel states. These optimal power and rate policies balance delay (backlog), transmission rate and energy to maximize network performance under constraints on average transmitter power and link buffer arrival and departure rates. Explicit policies are found for single links, and algorithmic methods presented to find optimal policies for complex interfering networks.
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paper_title: Dynamic association for load balancing and interference avoidance in multi-cell networks

paper_content:

In promising OFDMA systems, downlink signals originating from the same base station (BS) are orthogonal, while those from different BSs interfere with each other. As a consequence, inter-cell interference (ICI) becomes major performance degradation factor. Particularly, boundary users suffer from severe ICI in addition to the inherent near-far problem. To improve cell edge performances and support a more balanced data rate among all users, partial frequency reuse (PFR) and load-balancing schemes are investigated in this paper. We have formulated a utility maximization problem with network-wide proportional fairness (PF) as an objective in a multi-cell network with PFR. To solve this problem, we propose an offline optimal algorithm and also efficient online algorithms. Our online algorithms are based on simple inter/intra-handover and cell-site selection in which a metric is changed from the signal strength to the average throughput. Through extensive simulations, we demonstrate that our online algorithms can achieve network-wide PF very closely. Compared to the conventional system with a universal frequency reuse where a user is bound to the best signal strength base station, the proposed algorithms bring two types of performance gain: interference avoidance (IA) and load balancing (LB) gain. These gains improve the system performance, especially for users at the cell boundary.
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paper_title: Dynamic transmission capacity control schemes for power saving using a mixture of the history and the latest information

paper_content:

Power saving technology for the Internet has become a vital issue because of the growing energy consumption, caused by the increasing traffic demand. Thus, we have proposed a scheme to dynamically control the transmission capacity between switches in order to reduce the power consumption on the basis of the change in traffic volume. In this paper, the transmission capacity is better estimated by taking into account the history information of the amount of arriving traffic. We propose two types of schemes, which slightly differ in their use of a mixture of the history information and the latest information. Using simulation studies including an evaluation with real traffic, we show that the proposed schemes can achieve high power saving capability as well as sufficient communication quality.
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paper_title: Energy consumption of TCP Reno, Newreno, and SACK in multi-hop wireless networks

paper_content:

In this paper we compare the energy consumption behavior of three versions of TCP --- Reno, Newreno, and SACK. The experiments were performed on a wireless testbed where we measured the energy consumed at the sender node. Our results indicate that, in most cases, using total energy consumed as the metric, SACK outperforms Newreno and Reno while Newreno performs better than Reno. The experiments emulated a large set of network conditions including variable round trip times, random loss, bursty loss, and packet reordering. We also estimated the idealized energy for each of the three implementations (i.e., we subtract out the energy consumed when the sender is idle) and here, surprisingly, we find that in many instances SACK performs poorly compared to the other two implementations. We conclude that if the mobile device has a very low idle power consumption then SACK is not the best implementation to use for bursty or random loss. On the other hand, if the idle power consumption is significant, then SACK is the best choice since it has the lowest overall energy consumption.
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paper_title: ERTP: Energy-efficient and Reliable Transport Protocol for data streaming in Wireless Sensor Networks

paper_content:

Emerging data streaming applications in Wireless Sensor Networks require reliable and energy-efficient Transport Protocols. Our recent Wireless Sensor Network deployment in the Burdekin delta, Australia, for water monitoring [T. Le Dinh, W. Hu, P. Sikka, P. Corke, L. Overs, S. Brosnan, Design and deployment of a remote robust sensor network: experiences from an outdoor water quality monitoring network, in: Second IEEE Workshop on Practical Issues in Building Sensor Network Applications (SenseApp 2007), Dublin, Ireland, 2007] is one such example. This application involves streaming sensed data such as pressure, water flow rate, and salinity periodically from many scattered sensors to the sink node which in turn relays them via an IP network to a remote site for archiving, processing, and presentation. While latency is not a primary concern in this class of application (the sampling rate is usually in terms of minutes or hours), energy-efficiency is. Continuous long-term operation and reliable delivery of the sensed data to the sink are also desirable. This paper proposes ERTP, an Energy-efficient and Reliable Transport Protocol for Wireless Sensor Networks. ERTP is designed for data streaming applications, in which sensor readings are transmitted from one or more sensor sources to a base station (or sink). ERTP uses a statistical reliability metric which ensures the number of data packets delivered to the sink exceeds the defined threshold. Our extensive discrete event simulations and experimental evaluations show that ERTP is significantly more energy-efficient than current approaches and can reduce energy consumption by more than 45% when compared to current approaches. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended WSN is increased.
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paper_title: Energy efficient Reactive Store-and-Forward protocol for intermittently connected networks

paper_content:

Hop-by-hop transport and in-network storage have been widely used in intermittently connected networks. As a way to provide hop-by-hop congestion control, backpressure has been used in hop-by-hop transport and in-network storage protocols to provide quick congestion alleviation. However, relying on backpressure to direct traffic can introduce large packet delays, especially when traffic load is light, which in turn can degrade the energy efficiency of the system. In this paper, we propose a cross-layer protocol, Reactive Store-and-Forward (ReSaF). This protocol adopts a conditional-forwarding routing algorithm to route packets on a per-block basis. The conditional-forwarding algorithm takes advantage of estimated delivery probability, available buffer space and energy level of nodes to provide an energy efficient way to delivery packets with a high rate of success.
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paper_title: Energy-Efficient and Reliable Transport Protocols for Wireless Sensor Networks: State-of-Art

paper_content:

New wireless sensor network applications (e.g., military surveillance) require higher reliability than a simple best effort service could provide. Classical reliable transport protocols like Transmission Control Protocol (TCP) are not well suited for wireless sensor networks due to both the characteristics of the network nodes (low computing power, strong energy constraints) and those of the main applications running on those nodes (low data rates). Recent researches present new transport protocols for wireless sensor networks providing various type of reliability and using new mechanisms for loss detection and recovery, and congestion control. This paper presents a survey on reliable transport protocol for WSNs.
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paper_title: Energy/throughput tradeoffs of TCP error control strategies

paper_content:

Today's universal communications increasing involve mobile and battery-powered devices (e.g. hand-held, laptop, IP-phone) connected over wired and wireless networks. Energy efficiency, as well as throughput are becoming service characteristics of dominant importance in communication protocols. The wide applicability of IP-networks/devices, and the wide range of TCP-based applications, have rendered TCP the de facto reliable transport protocol standard not only for wired, but also for wireless and mixed (wired/wireless) communications. TCP's congestion control algorithms have been refined to achieve higher throughput. Even with these modifications, however, TCP versions do not incorporate a flexible error recovery strategy that is responsive to distinct environmental characteristics and device constraints. We have compared the energy- and throughput-efficiency of TCP error control strategies based on results gathered from our implementation of TCP Tahoe, Reno, and New Reno. We show that, depending on the frequency and duration of the error, each demonstrates appropriate behavior under specific circumstances, with Tahoe more-or-less the most energy conserving of the three. None of them, however, possesses a clear-cut overall advantage that would render it the version of choice for wired/wireless heterogeneous networks.
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paper_title: Transport Protocol Behavior and Energy-Saving Potential

paper_content:

We investigate the energy-saving potential of transport protocols. We seek an answer to strategic issues of maximizing energy and bandwidth exploitation, without damaging the dynamics of multiple-flow equilibrium. We claim that (i) an energy-saving strategy of the transport level needs to be associated with some energy potential index which, unlike energy expenditure, is not device-specific and (ii) system-wise an energy-efficient system of flows is not always a better choice: we show that a less energy-efficient system may be more reliable in terms of packet multiplexing and, in turn, may reduce the probability that some flows may expend their energy with zero gain. We present results using a real testbed.
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paper_title: On the transmission-computation-energy tradeoff in wireless and fixed networks

paper_content:

In this paper, a framework for the analysis of the transmission-computation-energy tradeoff in wireless and fixed networks is introduced. The analysis of this tradeoff considers both the transmission energy as well as the energy consumed at the receiver to process the received signal. While previous work considers linear decoder complexity, which is only achieved by uncoded transmission, this paper claims that the average processing (or computation) energy per symbol depends exponentially on the information rate of the source message. The introduced framework is parametrized in a way that it reflects properties of fixed and wireless networks alike. ::: The analysis of this paper shows that exponential complexity and therefore stronger codes are preferable at low data rates while linear complexity and therefore uncoded transmission becomes preferable at high data rates. The more the computation energy is emphasized (such as in fixed networks), the less hops are optimal and the lower is the benefit of multi-hopping. On the other hand, the higher the information rate of the single-hop network, the higher the benefits of multi-hopping. Both conclusions are underlined by analytical results.
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paper_title: Tradeoffs among Delay, Energy and Accuracy of Partial Data Aggregation in Wireless Sensor Networks

paper_content:

Due to the Recent development in wireless technology, wireless sensor networks attract researchers’ attention because of their applicability in many fields for effective collection of sensing data with low cost. Wireless sensor networks have many applications; some of the applications are military application, environmental application and flood detection. For example, in an environmental application for forest fire detection, the sensor nodes sense the fire information, then transmit or relay the information to base station in a multi-hop way. In wireless sensor networks, energy saving is critical issue as sensor nodes are battery-powered. Here we propose, partial data aggregation as one of the energy saving technique. In this paper, we analyze the tradeoffs among communication delay, energy consumption, and data accuracy of the partial data aggregation technique and discuss the results. First, we analyze the partial data aggregation with Markovian chain; analytical result shows that, non-aggregation method suffers large energy consumption while full aggregation suffers long transmission delay. From the analysis results, we find that the proposed partial aggregation method WRP (Waterfalls Random partial aggregation) can trade off energy consumption and transmission delay. Thus, we discuss the tradeoffs among data accuracy, transmission delay and energy consumption with different criteria and parameters. The results show that we could control the significance of transmission delay, energy consumption and data accuracy by tradeoffs index (TOI). We also analyze the several applications of wireless sensor networks with different significance based on the TOI. From the observed results, we found that we could set the significance of transmission delay, energy consumption and data accuracy for different applications based on different criteria TOI. Thus, by evaluating and comparing the criteria with different data generation rate as well as aggregation factor, we get the least TOI value, which denotes the desired tradeoffs among them.
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paper_title: Trade-off between reliability and energy-efficiency in Transport Protocol for Wireless Sensor Networks

paper_content:

Efficient design and implementation of wireless sensor networks has become a hot area of research in recent years. In comparison with other existing networks, wireless sensor networks (WSN) have some limitations. Typically, nodes in WSN have limited power, computational capacity, and memory. These problems require the need of having particular protocols designed for WSN. Currently, many research focused on developing transport protocols. This paper proposes a probability model that can be applied in transport protocols using hop-by-hop and end-to-end mechanism. From this model, we evaluate the number of hops that a packet has to pass when it is being sent from source to destination. We also solve the optimal number of transmissions in transport layer. The result from this model shows that there is a trade-off between reliability and energy-efficiency.
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paper_title: Energy-precision tradeoffs in mobile Graphics Processing Units

paper_content:

In mobile devices, limiting the Graphics Processing Unitpsilas (GPUpsilas) energy usage is of great importance to extending battery life. This paper focuses on the first stage of the graphics processor pipeline - the vertex transformation stage - and introduces an approach to lowering its switching activity by reducing the precision of arithmetic operations. As a result, the approach enables a tradeoff between energy efficiency and the quality of the rendered image. This paper makes the following specific contributions: 1) a transition-based energy model for quantifying energy consumed as a function of arithmetic precision, and 2) detailed simulation results on several real-world graphics applications to evaluate the tradeoff between energy and precision. In most examples, over 23% of the energy can be saved by lowering arithmetic precision while still maintaining a faithful reproduction of the full-precision image. Pushing the idea further, over 36% energy can be saved by further lowering the precision while preserving acceptable result accuracy. We assert that this represents a significant energy savings that warrants further investigation and extension of our approach to the remaining stages of the graphics processor pipeline.
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paper_title: Energy-Efficient Cooperative Techniques for Multimedia Services over Future Wireless Networks

paper_content:

In this paper we develop and analyze energy- efficient cooperative techniques for multimedia streaming applications in wireless networks. The concept of combined cellular- SR network architecture is coupled here with different video coding schemes for the goal of achieving robust transmission over wireless channels and energy saving. The strategies are analyzed in different technology settings, showing promising power saving potentials in comparison to the state-of-the-art non-cooperative operation.
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paper_title: A new approach for energy management in user-centric applications

paper_content:

Energy reduction has become an important design problem. Although most of consumer electronic systems are user centric, existing energy management methods are device centric. These methods either assume unchangeable operational environment or rely on very simplified policies, which eventually lead to large energy losses. In this paper, we present a new energy management approach that allows systems to monitor their users for energy saving. We discuss applications of this approach in personal computers, TV sets and home automation system and show the experimental results.
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paper_title: Cloud-Based Augmentation for Mobile Devices: Motivation, Taxonomies, and Open Challenges

paper_content:

Recently, Cloud-based Mobile Augmentation (CMA) approaches have gained remarkable ground from academia and industry. CMA is the state-of-the-art mobile augmentation model that employs resource-rich clouds to increase, enhance, and optimize computing capabilities of mobile devices aiming at execution of resource-intensive mobile applications. Augmented mobile devices envision to perform extensive computations and to store big data beyond their intrinsic capabilities with least footprint and vulnerability. Researchers utilize varied cloud-based computing resources (e.g., distant clouds and nearby mobile nodes) to meet various computing requirements of mobile users. However, employing cloud-based computing resources is not a straightforward panacea. Comprehending critical factors (e.g., current state of mobile client and remote resources) that impact on augmentation process and optimum selection of cloud-based resource types are some challenges that hinder CMA adaptability. This paper comprehensively surveys the mobile augmentation domain and presents taxonomy of CMA approaches. The objectives of this study is to highlight the effects of remote resources on the quality and reliability of augmentation processes and discuss the challenges and opportunities of employing varied cloud-based resources in augmenting mobile devices. We present augmentation definition, motivation, and taxonomy of augmentation types, including traditional and cloud-based. We critically analyze the state-of-the-art CMA approaches and classify them into four groups of distant fixed, proximate fixed, proximate mobile, and hybrid to present a taxonomy. Vital decision making and performance limitation factors that influence on the adoption of CMA approaches are introduced and an exemplary decision making flowchart for future CMA approaches are presented. Impacts of CMA approaches on mobile computing is discussed and open challenges are presented as the future research directions.
---
paper_title: Energy Aware Routing Based on Energy Characterization of Devices: Solutions and Analysis

paper_content:

The paper copes with the reduction of network power consumption by the definition of new routing algorithms, able to take into account the energy consumed by the network devices. In particular, based on the power consumption characterization of the network devices obtained using the Energy Profile (EP) concept, the paper presents the analysis of the exact solution of the Energy Aware Routing (EAR) problem solved with a Mixed Integer Programming solver. The analysis is aimed at evaluating the impact on the performance of three relevant aspects of the problem: the approximation of the actual EP, the traffic load and the topology of the network. Furthermore, the paper proposes a heuristic solution of the EAR, denoted as Dijkstra-based Power Aware Routing Algorithm (DPRA), defined in order to cope with the complexity of the exact solution.
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paper_title: Time for a "Greener" Internet

paper_content:

It is anticipated that the Internet traffic will continue to grow exponentially for the foreseeable future, which will require ever-growing energy (electricity). Since a lot of the Internet traffic growth comes from predictable services (such as video) there is a huge potential for decreasing future Internet energy requirements by synchronizing the operation of routers and scheduling traffic in advance, thus reducing complexity (e.g., header processing, buffer size, switching fabric speedup and memory access bandwidth speedup). Today, scheduling and synchronizing large-scale data transfer operations can be easily achieved by utilizing a choice of tens of global time sources, freely available on earth and in space. In a way, this manuscript shows how to "trade" global time for electricity utilized by the global Internet.
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paper_title: An analytical model for designing and controlling new-generation green devices

paper_content:

In this paper, we focus on energy-aware devices able to reduce their energy requirements by adapting their performance. We consider the device to be able to save energy through two main energy-aware primitives, namely, low power idle and power scaling. In such an environment, we propose a novel and original model for accurately representing how the joint usage of the previously cited primitives can impact on both energy consumption and network performance. As shown by the results achieved, the proposed model can be effectively applied in order to design and control energy-aware hardware of next-generation network devices.
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paper_title: Performance Constrained Power Consumption Optimization in Distributed Network Equipment

paper_content:

The concept of "green" and energy-efficient networking has begun to spread over the past few years, gaining an increasing popularity and interest from service and network providers, as well as equipment manufacturers. In this contribution, we propose an analytical framework that can effectively be adopted to optimize power consumption of a network device with respect to its expected forwarding performance. In detail, the proposed analytical framework is specifically designed in order to well suit a heterogeneous set of distributed architectures, generally used for developing today's network equipment, and ranging from crossbar and line-cards based devices to multi-core SW routers.
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paper_title: Intelligent energy managed service for green base stations

paper_content:

Energy consumption and CO 2 emissions have recently become topics of particular interest across the cellular telecommunication industry. This situation is moving this industry towards the introduction of renewable sources of energy, such as solar energy, wind energy, etc. for the energy supply to their networks. These solutions are environmentally friendly and technically proven, but when it comes to real implementation there are several drawbacks that limit their applicability (e.g. instable sources of energy, number and size of energy system infrastructure elements, as solar panels). To cope with these constraints, in this paper, a method / system, jointly with some results of early implementations, is described for adapting the service (i.e. coverage and/or capacity) provided by a base station, as a function of the weather forecast (regarding the renewable energy source), the stored energy in the back-up battery supply, and historical base station power consumption data, over a time period.
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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: 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: On the User Performance of LTE UE Power Savings Schemes with Discontinuous Reception in LTE

paper_content:

The UTRAN long-term evolution (LTE) specifications provide flexible means to achieve micro-sleep operation for user equipment (UE) even though it is in active mode and running a service. By means of a discontinuous reception (DRX) framework, pauses in the transmission due to natural traffic characteristics or network prioritization can be utilized. The specifications give a number of options to optimize the performance. In this paper two of those possibilities are compared. Long DRX with the use of an inactivity timer is compared to the usage of short DRX on top of long DRX. The performance is evaluated in terms of user throughput, power consumption, and network performance, while using a realistic RF modem power consumption model for the UE. For bursty traffic, short DRX shows a gain of up to 100% over DRX with just an inactivity timer, when measuring throughput per power unit consumed in case of one or multiple users being present in the cell.
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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: Delay versus energy consumption of the IEEE 802.16e sleep-mode mechanism

paper_content:

We propose a discrete-time queueing model for the evaluation of the IEEE 802.16e sleep-mode mechanism of power saving class (PSC) I in wireless access networks. Contrary to previous studies, we model the downlink traffic by means of a discrete batch Markov arrival process (D-BMAP) with N phases, which allows to take traffic correlation into account. The tradeoff between energy saving and increased packet delay is discussed. In many situations, the sleep-mode performance improves for heavily correlated traffic. Also, when compared to other strategies, the exponential sleep-period update strategy of PSC I may not always be the best.
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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: A cell breathing approach in green heterogeneous networks

paper_content:

Femto base stations constitute a promising solution to cope with the dramatic increase in mobile data traffic, but they also contribute to increase the network power consumption. Traditionally, full power transmissions are used to satisfy the users' data rate demands, causing interference to neighboring cells. Cell breathing can reduce the total transmit power by adjusting the cell size to the traffic load, hence limiting interference. However, it requires full knowledge of the channel conditions and power allocation strategies of neighboring cells. Its implementation becomes more challenging in broadband heterogeneous networks due to the channel frequency selectivity, the power difference between base station types, and the required network coordination. Therefore, we propose a cell breathing approach for green heterogeneous networks, referred to as path loss-based cell breathing (PL-CB), which uses only path loss information to limit the interference caused to neighboring cells. It achieves a higher energy efficiency and a larger achievable rate region than other state-of-the-art techniques with negligible degradation with respect to the approach with full knowledge of the channel and transmit powers of neighboring cells.
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paper_title: Cell breathing, sectorization and densification in cellular networks

paper_content:

In this paper, we establish a closed form formula of the other-cell interference factor f for omni-directional and sectored cellular networks. That formula is based on a fluid model that approximates the discrete base stations (BS) entities by a continuum of transmitters which are spatially distributed in the network. Simulations show that the obtained closed-form formula is a very good approximation, even for the traditional hexagonal network. From f, we are able to derive the outage probability on the downlink as a function of the mobile density and the coverage range. From a maximum acceptable outage probability, we can deduce the link between cell coverage and mobile density and thus highlight with a new, easy and fast method the notion of cell breathing. At last, we show how an operator can use this approach in order to evaluate the impact of sectorization or BS densification on the cell coverage.
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paper_title: Dynamic energy-aware network re-configuration for cellular urban infrastructures

paper_content:

Energy saving management aims to match the capacity offered by operators to the actual traffic demand at off-peak times when the network load under-utilizes the maximum capacity dimension. Such a process is relatively complex in cellular infrastructures since mobility and user activity patterns may create load fluctuations. This paper introduces energy-aware network re-configuration methods to flexibly re-act to load variations encouraging none or minimal extra energy consumption. A simulation-based study evaluates the performance of the proposed schemes considering the network service quality and energy cost.
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paper_title: Receiver-oriented load-balancing and reliable routing in wireless sensor networks

paper_content:

Routing protocols in wireless sensor networks (WSNs) typically employ a transmitter-oriented approach in which the next hop node is selected based on neighbor or network information. This approach incurs a large overhead when the accurate neighbor information is needed for efficient and reliable routing. In this paper, a novel receiver-oriented load-balancing and reliable routing (RLRR) protocol is proposed. In RLRR, an intermediate node solicits next hop candidates, each of which is to respond with its own backoff time dubbed a temporal gradient (TG). In this way, the next hop is selected without any central coordination on a packet-by-packet basis. Thus, each node needs not maintain any neighbor information. The remaining energy level used to determine the TG is always accurate and up-to-date. Furthermore, neighbor nodes whose hop count is less than the soliciting node participate in the next-hop selection process with loop-free operation guarantee. Comprehensive simulations are carried out to show that RLRR achieves relatively longer network lifetime and higher reliability than other existing schemes. Copyright © 2007 John Wiley & Sons, Ltd.
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paper_title: Resource allocation for energy efficient cellular systems

paper_content:

The need for more throughput in wireless cellular networks has been increasing in recent years. It has led to an increase in operational costs due to higher energy use as operators deploy more cell sites or increase transmission power at existing ones to satisfy demand. Energy costs are a major expense, and reducing them is a priority. This article presents a scheduler which aims to solve the problem of energy efficient resource allocation in orthogonal frequency division multiple access (OFDMA) cellular systems. The suggested approach is to make the resource scheduling process also consider energy costs as well as allow it to manipulate these by exploiting time/frequency vs energy efficiency trade-offs that are present in the system. The energy efficient score-based scheduler (EESBS) is a novel scheduler which takes energy costs into account when allocating resource blocks (RBs) to users. This allows it to promote energy efficiency in the system alongside throughput and fairness maximization. One of the means it has to manipulate users' expended energy is the bandwidth expanded mode (BEM). BEM is a technique that allows the scheduler to decrease a user's energy consumption by allocating it more RBs and maintaining a constant data rate. This is possible when the energy consumption is dominated by the energy used for data communication as opposed to control channel overhead transmission. Time compression mode (TCoM) is a technique that is complementary to BEM. It allows for energy savings through a reduction of the number of allocated RBs to a user when the energy consumption is dominated by the transmission of signaling traffic. Both BEM and TCoM need to be employed by an energy-aware scheduler like EESBS in order to extract the maximum performance gains. A realistic framework modeling future cellular systems is established to test the performance of the proposed techniques. Within this framework, EESBS generates an average energy saving of 29% over a frequency selective proportional fair (FsPF) benchmark. EESBS coupled with BEM or TCoM achieves a saving of 38% over the same benchmark. These savings are achieved with no detriment to user satisfaction in terms of achieved data rate.
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paper_title: Micro base stations in load constrained cellular mobile radio networks

paper_content:

Future cellular mobile radio networks will exhibit a much more dense base station deployment than 2nd or 3rd generation communications systems, particularly with regard to traffic coverage. Hence, a significant increase in power consumption of cellular networks can be expected. In order to counter this trend, energy efficiency of such networks should be increased considerably. Concerning energy efficiency, utilizing micro base stations with their smaller power consumption capabilities appear promising. In this paper we study various homogeneous and heterogeneous deployment strategies incorporating micro base stations with focus on energy efficiency represented by power consumption and throughput. Further, we deal with the impact of different load scenarios on energy efficiency of the various network topologies in more detail.
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paper_title: Intra-operator spectrum sharing concepts for energy efficiency and throughput enhancement

paper_content:

Cognitive radio and other dynamic spectrum sharing paradigms have enjoyed the limelight recently for their potential to realize a number of benefits for communications systems. The majority of investigated solutions thus far have looked at primary/secondary access and sharing of spectrum among different spectrum owners. In contrast, this paper investigates solutions for spectrum sharing among different bands owned by the same entity, such as a mobile operator, and demonstrates considerable potential for such solutions to improve power efficiency for the network and to increase throughput. The paper utilizes four means to achieve this potential: spectrum sharing through the opportunistic movement of users between bands allowing radio network equipment in other bands to be switched off when possible, spectrum sharing to opportunistically improve links' propagation characteristics therefore reducing necessary transmission power, better interference management in spectrum sharing to reduce necessary transmission power, and the opportunistic aggregation of spectrum bands to increase achievable throughput. Power consumption reductions of over 50%, both in terms of mains power draw and in terms of necessary transmission power, are demonstrated. Moreover, throughput enhancements of up to 20% are achieved.
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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: Green spectrum management for mobile operators

paper_content:

This paper proposes intra-operator dynamic spectrum access, i.e., dynamic spectrum access by an operator's networks of its available spectrum bands, as a means to improve power efficiency. It is based around four areas of interest: (i) dynamically moving users into particularly active bands from other bands to allow radio network equipment in those other bands to be switched off when possible, (ii) the dynamic sharing of spectrum in order to take advantage of better propagation bands and reduce necessary transmission power, (iii) the sharing of spectrum to allow channel bandwidths to be increased thus allowing transmission power to be significantly decreased, and (iv) the better hierarchical management of spectrum in cases where different types of cells coexist. Numerical results show a significant potential for such spectrum management solutions to reduce power consumption for the operator by some 50% or more, with further potential saving if there is a lower correlation in traffic loads among the operator's networks/frequencies. It is noted that although the main objective of this paper is power saving, the concepts presented can also be used for other purposes, such as to increase achievable capacity.
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paper_title: Optimized green operation of LTE networks in the presence of multiple electricity providers

paper_content:

Energy efficiency aspects in cellular networks can significantly contribute to the reduction of greenhouse gas emissions and help to save the environment. The base station (BS) sleeping strategy has become a well-known technique to achieve energy savings by switching off redundant BSs mainly for lightly loaded networks. Besides, introducing renewable energies as alternative power sources becomes a real challenge to network operators. In this paper, we propose a method that reduces the energy consumption of BSs by not only shutting down underutilized BSs but also by optimizing the amounts of energy procured from different retailers (Renewable energy and electricity retailers). We formulate an optimization problem that leads to the maximization of the profit of a Long-Term Evolution (LTE) cellular operator, and at the same time to the minimization of CO 2 emissions in green wireless cellular networks without affecting the desired Quality of Service.
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paper_title: Repetitive message effect in green marketing communication

paper_content:

This study paid attention to the effects of repetition message on Planned Behavior Theory. An experiment was conducted in which communication effect were examined for a message repetition at three levels of message exposure. The obtained data demonstrated the results of this conceptual perspective in examining repetitive communicating of message effectiveness in recycling issue of green marketing.
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paper_title: Taxation for green communication

paper_content:

Nowadays energy saving and reduction of electromagnetic pollution become important issues. One approach to these problems is the introduction of taxes on the energy dissipation. In this paper we investigate a taxation game between a user or a provider or a group of users and the taxation authority. This is a Stackelberg game where the taxation authority acts as a leader and users or service providers act as followers. Clearly too big taxes will strongly discourage the user of wireless technology and hinder the progress and too small taxes will lead to a wasteful use of the energy resources and may also lead to reckless use of the radio resources. We study several important particular cases with complete and partial information. We focus on the problem of finding taxation strategy in closed form and investigating how incomplete information of authorities about users impacts the equilibrium strategy.
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paper_title: Energy-efficient infrastructure sharing in multi-operator mobile networks

paper_content:

Network infrastructure sharing and base station switching off mechanisms have been recently introduced as promising solutions toward energy and cost reduction in cellular networks. Although these techniques are usually studied independently, their combination offers new alternatives to MNOs for serving their users and could potentially provide them with additional benefits. In this article we introduce the concept of intra-cell roaming-based infrastructure sharing, where the MNOs may switch off their BSs and roam their traffic to active BSs operated by other MNOs in the same cell. Motivated by the coexistence of multiple operators in the same area, we present possible network deployments and architectures in current and future cellular scenarios, discussing their particular characteristics. In addition, we propose an innovative distributed game theoretic BS switching off scheme, employing an integrated cost function that takes into account all the different cases for a given operator to serve its own traffic (i.e. through active BSs of neighboring cells or exploiting intra-cell roaming-based infrastructure sharing). Finally, we demonstrate some indicative simulation results in realistic scenarios to quantify the potential energy and financial benefits that our proposed scheme offers to the MNOs in multioperator environments, providing them with the necessary incentives to participate in the infrastructure sharing.
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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: Five Disruptive Technology Directions for 5G

paper_content:

New research directions will lead to fundamental changes in the design of future 5th generation (5G) cellular networks. This paper describes five technologies that could lead to both architectural and component disruptive design changes: device-centric architectures, millimeter Wave, Massive-MIMO, smarter devices, and native support to machine-2-machine. The key ideas for each technology are described, along with their potential impact on 5G and the research challenges that remain.
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paper_title: Accelerating 5G QoE via public-private spectrum sharing

paper_content:

Fifth generation wireless systems (5G) must achieve high user Quality of Experience (QoE) in order to compete for market share. Each candidate 5G wireless radio frequency (RF) band offers advantages such as longer range or higher data rate than 2G, 3G, and 4G, but no single band or air interface standard by itself fully achieves ubiquitous levels of QoE for the complete range of wireless access devices. Spectrum clearing cannot keep pace with user demand, so public-private spectrum sharing is emerging as an affordable, near-term method of increasing radio access network (RAN) capacities for content delivery. This paper presents a fresh look at QoE; spectrum scarcity; public uses that underutilize candidate 5G radio frequency (RF) spectrum; and emerging public-private radio interference management frameworks that enable near-term spectrum sharing, with positive consequences for 5G price, performance, and total user QoE.
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paper_title: Optimized data sharing in multicell MIMO with finite backhaul capacity

paper_content:

This paper addresses cooperation in a multicell environment where base stations (BSs) wish to jointly serve multiple users, under a constrained-capacity backhaul. We point out that for finite backhaul capacity a tradeoff between sharing user data, which allows for full MIMO cooperation, and not doing so, which reduces the setup to an interference channel but also requires less overhead, emerges. We optimize this tradeoff by formulating a rate splitting approach in which non-shared data (private to each transmitter) and shared data are superimposed. We derive the corresponding achievable rate region and obtain the optimal beamforming design for both shared and private symbols. We illustrate how the capacity of the backhaul determines how much of the user data is worth sharing across multiple BSs.
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paper_title: Cloud technologies for flexible 5G radio access networks

paper_content:

The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. Two key enablers will allow the realization of the vision of 5G: very dense deployments and centralized processing. This article discusses the challenges and requirements in the design of 5G mobile networks based on these two key enablers. It discusses how cloud technologies and flexible functionality assignment in radio access networks enable network densification and centralized operation of the radio access network over heterogeneous backhaul networks. The article describes the fundamental concepts, shows how to evolve the 3GPP LTE architecture, and outlines the expected benefits.
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paper_title: Dynamic Spectrum Management for Intercell Interference Coordination in LTE Networks Based on Traffic Patterns

paper_content:

Next-generation cellular networks will provide users with better experience employing smaller cells, which results in high dynamics and strong interference. Conventional intercell interference coordination (ICIC) approaches are based on fixed or dynamic frequency reuse, which more or less underutilize frequency resources or reduce network-wide performance. As a result, the benefit brought by ICIC is questionable in practical networks. In this paper, we tackle this problem from the self-organizing network (SON) viewpoint by optimizing fractional frequency reuse (FFR) and adapting to dynamic traffic maps. The approach proposed by this paper formulates this problem as an optimization problem with multiple key performance indicators (Multi-KPIs), and a traffic-based dynamic spectrum management (DSM) algorithm is proposed to reduce the call drop and block ratio (CDBR) and to also improve the network throughput. To reduce further the cost of spectrum partition and assignment, we conduct data mining for the traffic maps from realistic networks and then obtain traffic stable states for a longer specific period of time. DSM based on the stable states (DSM-SS) approach brings further benefits for Long Term Evolution networks in terms of operational costs. Simulation results show that the proposed schemes significantly outperform the traditional schemes.
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paper_title: Cloud-Based Augmentation for Mobile Devices: Motivation, Taxonomies, and Open Challenges

paper_content:

Recently, Cloud-based Mobile Augmentation (CMA) approaches have gained remarkable ground from academia and industry. CMA is the state-of-the-art mobile augmentation model that employs resource-rich clouds to increase, enhance, and optimize computing capabilities of mobile devices aiming at execution of resource-intensive mobile applications. Augmented mobile devices envision to perform extensive computations and to store big data beyond their intrinsic capabilities with least footprint and vulnerability. Researchers utilize varied cloud-based computing resources (e.g., distant clouds and nearby mobile nodes) to meet various computing requirements of mobile users. However, employing cloud-based computing resources is not a straightforward panacea. Comprehending critical factors (e.g., current state of mobile client and remote resources) that impact on augmentation process and optimum selection of cloud-based resource types are some challenges that hinder CMA adaptability. This paper comprehensively surveys the mobile augmentation domain and presents taxonomy of CMA approaches. The objectives of this study is to highlight the effects of remote resources on the quality and reliability of augmentation processes and discuss the challenges and opportunities of employing varied cloud-based resources in augmenting mobile devices. We present augmentation definition, motivation, and taxonomy of augmentation types, including traditional and cloud-based. We critically analyze the state-of-the-art CMA approaches and classify them into four groups of distant fixed, proximate fixed, proximate mobile, and hybrid to present a taxonomy. Vital decision making and performance limitation factors that influence on the adoption of CMA approaches are introduced and an exemplary decision making flowchart for future CMA approaches are presented. Impacts of CMA approaches on mobile computing is discussed and open challenges are presented as the future research directions.
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paper_title: When the Smart Grid Meets Energy-Efficient Communications: Green Wireless Cellular Networks Powered by the Smart Grid

paper_content:

Recently, there is great interest in considering the energy efficiency aspect of cellular networks. On the other hand, the power grid infrastructure, which provides electricity to cellular networks, is experiencing a significant shift from the traditional electricity grid to the smart grid. When a cellular network is powered by the smart grid, only considering energy efficiency in the cellular network may not be enough. In this paper, we consider not only energy-efficient communications but also the dynamics of the smart grid in designing green wireless cellular networks. Specifically, the dynamic operation of cellular base stations depends on the traffic, real-time electricity price, and the pollutant level associated with electricity generation. Coordinated multipoint (CoMP) is used to ensure acceptable service quality in the cells whose base stations have been shut down. The active base stations decide on which retailers to procure electricity from and how much electricity to procure. We formulate the system as a Stackelberg game, which has two levels: a cellular network level and a smart grid level. Simulation results show that the smart grid has significant impacts on green wireless cellular networks, and our proposed scheme can significantly reduce operational expenditure and CO_2 emissions in green wireless cellular networks.
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paper_title: Green Software: Greening What and How Much?

paper_content:

In applications in which embedded devices cooperate with ICT (information and communication technology) systems to make industrial processes more efficient, reduce waste or raw materials, and save the environment, the concept of green software becomes increasingly complex. To deal with this issue, the green-software community has introduced the concepts of greening ICT or greening through ICT.
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paper_title: Energy-efficient infrastructure sharing in multi-operator mobile networks

paper_content:

Network infrastructure sharing and base station switching off mechanisms have been recently introduced as promising solutions toward energy and cost reduction in cellular networks. Although these techniques are usually studied independently, their combination offers new alternatives to MNOs for serving their users and could potentially provide them with additional benefits. In this article we introduce the concept of intra-cell roaming-based infrastructure sharing, where the MNOs may switch off their BSs and roam their traffic to active BSs operated by other MNOs in the same cell. Motivated by the coexistence of multiple operators in the same area, we present possible network deployments and architectures in current and future cellular scenarios, discussing their particular characteristics. In addition, we propose an innovative distributed game theoretic BS switching off scheme, employing an integrated cost function that takes into account all the different cases for a given operator to serve its own traffic (i.e. through active BSs of neighboring cells or exploiting intra-cell roaming-based infrastructure sharing). Finally, we demonstrate some indicative simulation results in realistic scenarios to quantify the potential energy and financial benefits that our proposed scheme offers to the MNOs in multioperator environments, providing them with the necessary incentives to participate in the infrastructure sharing.
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paper_title: Energy efficiency is a subtle concept: fundamental trade-offs for cognitive radio networks

paper_content:

This article discusses the implications of facilitating higher energy efficiency in cognitive radio networks from the perspective of fundamental trade-offs (i.e, what needs to be sacrificed to be energy-efficient). These trade-offs are identified as QoS, fairness, PU interference, network architecture, and security, which are also essential network design dimensions. We analyze these dimensions and their interactions focusing on energy efficiency. Furthermore, future research directions related to the integration of CRN with other networking paradigms and energy efficiency are introduced and discussed.
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paper_title: Analytical Evaluation of Fractional Frequency Reuse for Heterogeneous Cellular Networks

paper_content:

Interference management techniques are critical to the performance of heterogeneous cellular networks, which will have dense and overlapping coverage areas, and experience high levels of interference. Fractional frequency reuse (FFR) is an attractive interference management technique due to its low complexity and overhead, and significant coverage improvement for low-percentile (cell-edge) users. Instead of relying on system simulations based on deterministic access point locations, this paper instead proposes an analytical model for evaluating Strict FFR and Soft Frequency Reuse (SFR) deployments based on the spatial Poisson point process. Our results both capture the non-uniformity of heterogeneous deployments and produce tractable expressions which can be used for system design with Strict FFR and SFR. We observe that the use of Strict FFR bands reserved for the users of each tier with the lowest average \sinr provides the highest gains in terms of coverage and rate, while the use of SFR allows for more efficient use of shared spectrum between the tiers, while still mitigating much of the interference. Additionally, in the context of multi-tier networks with closed access in some tiers, the proposed framework shows the impact of cross-tier interference on closed access FFR, and informs the selection of key FFR parameters in open access.
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paper_title: Energy-aware routing algorithms in Software-Defined Networks

paper_content:

The feature of centralized network control logic in Software-Defined Networks (SDNs) paves a way for green energy saving. Router power consumption attracts a wide spread attention in terms of energy saving. Most research on it is at component level or link level, i.e. each router is independent of energy saving. In this paper, we study global power management at network level by rerouting traffic through different paths to adjust the workload of links when the network is relatively idle. We construct the expand network topology according to routers' connection. A 0-1 integer linear programming model is formulated to minimize the power of integrated chassis and linecards that are used while putting idle ones to sleep under constraints of link utilization and packet delay. We proposed two algorithms to solve this problem: alternative greedy algorithm and global greedy algorithm. For comparison, we also use Cplex method just as GreenTe does since GreenTe is state of the art global traffic engineering mechanism. Simulation results on synthetic topologies and real topology of CERNET show the effectiveness of our algorithms.
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paper_title: How do we design CoMP to achieve its promised potential?

paper_content:

Coordinated multipoint, or CoMP, transmission has been recognized as a spectrally efficient technique for full frequency reuse cellular systems, in which base stations cooperate to reduce or eliminate intercell interference. However, there are still many obstacles before it can be put into practical use. In this article, we first discuss the features of CoMP systems and channels that are distinct from single-cell multi-antenna systems. We then give an overview of state-of-the-art approaches for coping with the factors that limit the potential of CoMP. A major issue is the acquisition of channel state information, which creates different challenges for TDD and FDD systems. Another set of challenges arises from the limited capacity available on the backhaul connections between the cooperating base stations. Both the fundamentals of possible solutions and their relations to cellular standards are discussed.
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paper_title: A novel architecture for LTE-B :C-plane/U-plane split and Phantom Cell concept

paper_content:

This paper introduces a novel approach in increasing the capacity of LTE cellular networks. The solution is based on massive deployment of small cells by leveraging high frequency reuse at high frequency bands in conjunction with a Macrocell. The presence, discovery and usage of the small cells are controlled dynamically by a Macrocell in a master-slave configuration hence they are called Phantom Cells. To realize this concept, a new method of managing the connections between mobile terminals and small cell nodes is introduced. It is achieved by splitting the Control and User (C/U) planes of the radio link. The combination of C/U-plane split and Phantom Cells can achieve high capacity enhancement using small cells at the same time taking into consideration mobility, scalability and flexibility requirements for massive deployment. The advantages of this approach as well as the implementation aspects are described in the paper. Simulations were also conducted to verify the concept and the results show some promising capacity enhancements. The rest of the paper describes the Phantom Cell concept as well as the challenges of deploying small cells in LTE networks.
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paper_title: Green Cognitive Mobile Networks With Small Cells for Multimedia Communications in the Smart Grid Environment

paper_content:

High-data-rate mobile multimedia applications can greatly increase energy consumption, leading to an emerging trend of addressing the “energy efficiency” aspect of mobile networks. Cognitive mobile networks with small cells are important techniques for meeting the high-data-rate requirements and improving the energy efficiency of mobile multimedia communications. However, most existing works do not consider the power grid, which provides electricity to mobile networks. Currently, the power grid is experiencing a significant shift from the traditional grid to the smart grid. In the smart grid environment, only considering energy efficiency may not be sufficient since the dynamics of the smart grid will have significant impacts on mobile networks. In this paper, we study green cognitive mobile networks with small cells in the smart grid environment. Unlike most existing studies on cognitive networks, where only the radio spectrum is sensed, our cognitive networks sense not only the radio spectrum environment but also the smart grid environment, based on which power allocation and interference management for multimedia communications are performed. We formulate the problems of electricity price decision, energy-efficient power allocation, and interference management as a three-stage Stackelberg game. A homogeneous Bertrand game with asymmetric costs is used to model price decisions made by the electricity retailers. A backward induction method is used to analyze the proposed Stackelberg game. Simulation results show that our proposed scheme can significantly reduce operational expenditure and $\hbox{CO}_{2}$ emissions in cognitive mobile networks with small cells for multimedia communications.
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paper_title: A Survey on Software-Defined Network and OpenFlow: From Concept to Implementation

paper_content:

Software-defined network (SDN) has become one of the most important architectures for the management of largescale complex networks, which may require repolicing or reconfigurations from time to time. SDN achieves easy repolicing by decoupling the control plane from data plane. Thus, the network routers/switches just simply forward packets by following the flow table rules set by the control plane. Currently, OpenFlow is the most popular SDN protocol/standard and has a set of design specifications. Although SDN/OpenFlow is a relatively new area, it has attracted much attention from both academia and industry. In this paper, we will conduct a comprehensive survey of the important topics in SDN/OpenFlow implementation, including the basic concept, applications, language abstraction, controller, virtualization, quality of service, security, and its integration with wireless and optical networks. We will compare the pros and cons of different schemes and discuss the future research trends in this exciting area. This survey can help both industry and academia R&D people to understand the latest progress of SDN/OpenFlow designs.
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paper_title: Spectral and Energy Spectral Efficiency Optimization of Joint Transmit and Receive Beamforming Based Multi-Relay MIMO-OFDMA Cellular Networks

paper_content:

We first conceive a novel transmission protocol for a multi-relay multiple-input--multiple-output orthogonal frequency-division multiple-access (MIMO-OFDMA) cellular network based on joint transmit and receive beamforming. We then address the associated network-wide spectral efficiency (SE) and energy spectral efficiency (ESE) optimization problems. More specifically, the network's MIMO channels are mathematically decomposed into several effective multiple-input--single-output (MISO) channels, which are essentially spatially multiplexed for transmission. Hence, these effective MISO channels are referred to as spatial multiplexing components (SMCs). For the sake of improving the SE/ESE performance attained, the SMCs are grouped using a pair of proposed grouping algorithms. The first is optimal in the sense that it exhaustively evaluates all the possible combinations of SMCs satisfying both the semi-orthogonality criterion and other relevant system constraints, whereas the second is a lower-complexity alternative. Corresponding to each of the two grouping algorithms, the pair of SE and ESE maximization problems are formulated, thus the optimal SMC groups and optimal power control variables can be obtained for each subcarrier block. These optimization problems are proven to be concave, and the dual decomposition approach is employed for obtaining their solutions. Relying on these optimization solutions, the impact of various system parameters on both the attainable SE and ESE is characterized. In particular, we demonstrate that under certain conditions the lower-complexity SMC grouping algorithm achieves 90% of the SE/ESE attained by the exhaustive-search based optimal grouping algorithm, while imposing as little as 3.5% of the latter scheme's computational complexity.
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paper_title: Large-Scale MIMO Versus Network MIMO for Multicell Interference Mitigation

paper_content:

This paper compares two distinct downlink multicell interference mitigation techniques for wireless cellular networks: large-scale (LS) multiple-input multiple-output (MIMO) and network MIMO. The considered cellular network operates in a time-division duplex (TDD) fashion and includes non-overlapping cooperating clusters, where each cluster comprises B base-stations (BSs), each equipped with multiple antennas, and schedules multiple single-antenna users. In the LS-MIMO system, each BS is equipped with BM antennas, serving its K scheduled users using zero-forcing (ZF) beamforming, while sacrificing its excess number of spatial degrees of freedom (DoF) using interference coordination to prevent causing interference to the other K (B - 1) users within the cooperating cluster. In the network MIMO system, although each BS is equipped with M antennas, the intra-cluster interference cancellation is enabled by data and channel state information sharing across the cooperating BSs and joint downlink transmission to BK users via ZF beamforming. Accounting for uplink-downlink channel reciprocity provided by TDD and invoking the orthogonality principle of ZF beamforming, respectively, the channel acquisition overhead in each cluster and the number of spatial DoF per user are identical in both systems. Therefore, it is not obvious whether one system is superior to the other from the performance point of view. Building upon the channel distribution functions in the two systems and adopting tools from stochastic orders, this paper shows that in fact an LS-MIMO system provides considerably better performance than a network MIMO system. Thus, given the likely lower cost of adding excess number of antennas, LS-MIMO could be a preferred multicell coordination approach for interference mitigation.
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paper_title: Cloud gaming: a green solution to massive multiplayer online games

paper_content:

Advanced video gaming is a computationally intensive application. Sophisticated graphics renderings are employed in computer games to produce realistic scenes and smooth actions. As a result, video gaming often requires powerful hardware that is beyond the capability of many mobile devices or even personal computers. Meanwhile, playing a high-quality game while on the move is highly desirable with the growing popularity of high-speed mobile and broadband Internet, and mobile devices such as smartphones and tablets. Instead of equipping mobile devices with powerful but battery-hungry computation engines, cloud gaming, which utilizes cloud computing for gaming, offers an emerging green solution to bring the high-quality immersive gaming experience to thin or mobile clients. Cloud gaming leverages communication infrastructures to shift heavy computation to cloud servers. In this article, we provide an overview of cloud gaming from a green media perspective (in addition to the conventional energy perspective). We argue that cloud gaming can lead to less software maintenance, more economical scaling, and longer service life spans of hardware equipment. We also briefly present a novel scheme, layered coding, which leverages the increasing graphics processing capability of a mobile client to reduce the bit rate of game streaming. We then discuss green designs of major cloud gaming subsystems: a cloud data center, graphics rendering, video compression, and network delivery. We review existing services and a testbed for cloud gaming. We also identify potential research challenges of cloud gaming in achieving green media for the future.
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Title: Energy Efficiency Tradeoff Mechanism Towards Wireless Green Communication: A Survey
Section 1: Introduction
Description 1: Introduce the need for energy-efficient wireless communication and the growth of wireless networks, along with the challenges of power consumption and CO2 emissions.

Section 2: Wireless Networks
Description 2: Discuss the heterogeneous wireless environment, including different types of networks and technologies, their coexistence, and energy-efficient operating points.

Section 3: Power Consumption Model
Description 3: Detail the power consumption models for different Base Stations (macrocells, microcells, picocells, femtocells) and factors affecting their power consumption.

Section 4: Green Metrics
Description 4: Define green metrics for energy-efficient communications, including component-level, equipment-level, and system/network-level metrics.

Section 5: Tradeoff Mechanisms Overview
Description 5: Provide an overview of various tradeoff mechanisms used to enhance energy efficiency in wireless networks.

Section 6: EE Tradeoffs in Physical Layer
Description 6: Explore tradeoffs in the physical layer such as SE-Bit Energy, SE-EE, Throughput-Energy, Energy-Bandwidth, Energy-Distance, Energy-Delay, Transmission-Computation-Energy, and their impacts.

Section 7: EE Tradeoffs in MAC Layer
Description 7: Discuss tradeoffs in the MAC layer including Energy-Latency, scheduling efficiencies, and stability-energy tradeoffs.

Section 8: EE Tradeoffs in Network Layer
Description 8: Present tradeoffs in the network layer, such as EE-hopping, EE-routing, and their importance in efficient network management.

Section 9: EE Tradeoffs in Transport Layer
Description 9: Analyze the tradeoffs in the transport layer involving congestion control, reliability, and energy management.

Section 10: EE Tradeoffs in Application Layer
Description 10: Discuss tradeoffs in the application layer for tasks such as video streaming, computation, and graphics processing to enhance energy efficiency.

Section 11: Tradeoffs in Infrastructure Domain
Description 11: Examine the impact of deployment strategies on power consumption, including the use of sleep mode, cell breathing, and cell zooming techniques.

Section 12: Discussion
Description 12: Summarize the impact of different tradeoffs on various types of wireless networks, including cellular, sensor, WiFi, adhoc, and cognitive radio networks.

Section 13: Conclusion and Future Research Issues
Description 13: Conclude the survey with a summary of findings and suggest future research directions for achieving energy-efficient wireless communications.