An Overview of Radio Resource Management in Relay-Enhanced OFDMA-Based Networks
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paper_title: Opportunities and Challenges in OFDMA-Based Cellular Relay Networks: A Radio Resource Management Perspective

paper_content:

The opportunities and flexibility in relay networks and orthogonal frequency-division multiple access (OFDMA) make the combination a suitable candidate network and air-interface technology for providing reliable and ubiquitous high-data-rate coverage in next-generation cellular networks. Advanced and intelligent radio resource management (RRM) schemes are known to be crucial toward harnessing these opportunities in future OFDMA-based relay-enhanced cellular networks. However, it is not very clear how to address the new RRM challenges (such as enabling distributed algorithms, intra-cell/inter-cell routing, intense and dynamic co-channel interference (CCI), and feedback overhead) in such complex environments comprising a plethora of relay stations (RSs) of different functionalities and characteristics. Employment of conventional RRM schemes in such networks will highly be inefficient if not infeasible. The next-generation networks are required to meet the expectations of all wireless users, irrespective of their locations. High-data-rate connectivity, mobility, and reliability, among other features, are examples of these expectations. Therefore, fairness is a critical performance aspect that has to be taken into account in the design of prospective RRM schemes. This paper reviews some of the prominent challenges involved in migrating from the conventional cellular architecture to the relay-based type and discusses how intelligent RRM schemes can exploit the opportunities in relay-enhanced OFDMA-based cellular networks. We identify the role of multiantenna systems and explore the current approaches in literature to extend the conventional schedulers to next-generation relay networks. This paper also highlights the fairness aspect in such networks in the light of the recent literature, provides some example fairness metrics, and compares the performances of some representative algorithms.
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paper_title: Adaptive Fair Subcarrier/Rate Allocation in Multirate OFDMA Networks: Radio Link Level Queuing Performance Analysis

paper_content:

This paper presents a semi-analytical methodology for radio link level performance analysis in a multirate "orthogonal frequency-division multiple-access" (OFDMA) network with adaptive fair rate allocation. Multirate transmission is assumed to be achieved through adaptive modulation, and fair rate allocation is based on the principle of generalized processor sharing to allocate the subcarriers adaptively among the users. The fair rate allocation problem is formulated as an optimization problem with the objective of maximizing system throughput while maintaining fairness (in terms of transmission rate) among the users. The "optimal" fair rate allocation is obtained by using the "Hungarian method." A heuristic-based approach, namely the "iterative approach," that is more implementation friendly is also presented. The throughput performance of the iterative fair rate allocation is observed to be as good as that of optimal fair rate allocation and is better than that of the static subcarrier allocation scheme. Also, the iterative fair allocation provides better fairness compared to that for each of the optimal and the static subcarrier allocation schemes. To this end, a queuing model is formulated to analyze radio link level performance measures such as packet dropping probability and packet transmission delay under the above rate allocation schemes. In this formulation, packet arrivals are modeled by the discrete Markov modulated Poisson process, which is flexible to model different types of traffic arrival patterns. The proposed framework for radio link level performance analysis of multirate OFDMA networks is validated by extensive simulations. Also, examples on the application of the proposed model for connection admission control and quality-of-service provisioning are illustrated
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paper_title: Radio Resource Allocation Algorithms for the Downlink of Multiuser OFDM Communication Systems

paper_content:

This article surveys different resource allocation algorithms developed for the downlink of multiuser OFDM wireless communication systems. Dynamic resource allocation algorithms are categorized into two major classes: margin adaptive (MA) and rate adaptive (RA). The objective of the first class is to minimize the total transmit power with the constraint on users' data rates whereas in the second class, the objective is to maximize the total throughput with the constraints on the total transmit power as well as users' data rates. The overall performance of the algorithms are evaluated in terms of spectral efficiency and fairness. Considering the trade-off between these two features of the system, some algorithms attempt to reach the highest possible spectral efficiency while maintaining acceptable fairness in the system. Furthermore, a large number of RA algorithms considers rate proportionality among the users and hence, are categorized as RA with constrained-fairness. Following the problem formulation in each category, the discussed algorithms are described along with their simplifying assumptions that attempt to keep the performance close to optimum but significantly reduce the complexity of the problem. It is noted that no matter which optimization method is used, in both classes, the overall performance is improved with the increase in the number of users, due to multiuser diversity. Some on-going research areas are briefly discussed throughout the article.
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paper_title: Capacity and power investigation of opportunity driven multiple access (ODMA) networks in TDD-CDMA based systems

paper_content:

ODMA is a multi-hop relaying routing protocol, the use of which has been investigated in conventional cellular scenarios. This paper compares the performance of ODMA with direct transmission for cases where links may be required directly to other nodes, as well as to a controlling (backbone) node. For an interference-limited system, it is shown that whereas the topology is not supportable by a conventional (single-hop) system, a relayed system is able to provide service. A new admission control and routing algorithm based on receiver interference is presented which is shown to further enhance performance.
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paper_title: Towards Systems Beyond 3G Based on Adaptive OFDMA Transmission

paper_content:

High data rates, high spectral efficiency, flexibil- ity, and low delays over the air interface will be important features in next-generation wireless systems. The overall challenge will be packet scheduling and adaptive radio transmission for multiple users, via multiple antennas and over frequency-selective wideband channels. This problem needs to be structured to obtain feasible solutions. The basic simplifying assumptions used here are clustering of antennas into cells, orthogonal transmission by use of cyclic-prefix orthogonal frequency-division multiplexing (OFDM) and a time-scale separation view of the total link adaptation, scheduling and intercell coordination problem. Based on these assumptions, we survey techniques that adapt the transmission to the temporal, frequency, and spatial channel properties. We provide a systematic overview of the design problems, such as the dimensioning of the allocated time-frequency resources, the influence of duplexing schemes, adaptation control issues for downlinks and uplinks, timing issues, and their relation to the required performance of channel predictors. Specific design choices are illustrated by recent research within the Swedish Wireless IP program and the EU IST-WINNER project. The presented results indicate that high-performance adaptive OFDM transmission systems are indeed feasible, also for challenging scenarios that involve vehicular velocities, high carrier frequencies, and high bandwidths.
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paper_title: On Improving the Performance of IEEE 802.11 with Relay-Enabled PCF

paper_content:

Integrating wireless LAN (WLAN) techniques with the third generation cellular networks has become a promising way to improve the performance of wireless systems. As WLANs play an important role in such heterogeneous systems, the performance of WLANs becomes important to the whole system. It is well known that WLANs provide a physical layer multi-rate capability, and hence MAC layer mechanisms are needed to exploit this capability. In this paper, we propose a novel MAC layer relay-enabled point coordination function (PCF) protocol, called r PCF, to exploit the physical layer multi-rate capability. Since WLAN supports multiple data rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. To enable MAC layer relay, the access point needs to collect information about the channel conditions, and notify the mobile nodes which data rate to use and whether to transmit the data through a relay station. We design protocols to achieve this goal and refine these protocols to minimize the control overhead. Simulation results show that r PCF can significantly improve the system performance in terms of system throughput and transmission delay by adding only a negligible control overhead.
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paper_title: Principles of IEEE 802.11s

paper_content:

In 2003, interests in the Institute of Electronics and Electrical Engineering (IEEE) 802.11 Working Group (WG) led to the formation of Task Group (TG) "S". 802.11s develops a Wireless Mesh Network (WMN) amendment. Unlike existing Mesh products, 802.11s forms a transparent 802 broadcast domain that supports any higher layer protocols. Therefore, 802.11s provides frame forwarding and path selection at layer-2. 802.11i describes a security concept for stations that associate with an Access Point (AP). However, in a Mesh Basic Service Set (BSS) devices need to mutually authenticate to provide integrity of the network. Thus, 802.11s adds additional elements to the concepts of 802.11L While traditional Wireless Local Area Networks (WLANs) are AP centred an 802.11 Mesh is fully distributed. Hence, 802.11s considers extensions to the Medium Access Control (MAC) too. The authors have contributed to the standardization of 802.11s since 2003. As constant participants we give insight to draft 1.02 of TG "s" and provide an outlook to future evolution of 802.11's first Mesh standard.
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paper_title: rDCF: a relay-enabled medium access control protocol for wireless ad hoc networks

paper_content:

It is well known that IEEE 802.11 provides a physical layer multi-rate capability, and hence MAC layer mechanisms are needed to exploit this capability. Several solutions have been proposed to achieve this goal. However, these solutions only consider how to exploit good channel quality for the direct link between the sender and the receiver. Since IEEE 802.11 supports multiple transmission rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. In this paper, we propose a novel MAC layer relay-enabled distributed coordination function (DCF) protocol, called rDCF, to further exploit the physical layer multi-rate capability. We design a protocol to assist the sender, the relay node and the receiver to reach an agreement on which data rate to use and whether to transmit the data through a relay node. Considering various issues such as bandwidth utilization and channel errors, we propose techniques to further improve the performance of rDCF. Simulation results show that rDCF can significantly improve the system performance when the channel quality of the direct link is poor.
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paper_title: Overview of PCS unlicensed wireless standards in the US

paper_content:

The demand for wireless services is growing rapidly. The extension of services into the in-building environments and in public pedestrian areas further enhance this trend. This trend is no exception in the United States. With the availability of spectrum in the PCS unlicense band it becomes apparent that standardization is required to provide cost-effective solutions for in-building business applications. This paper discuss the three user premise equipment wireless standards developed in the TIA (Telecommunications Industry Association). The main purpose of this organization was to develop the standards for inter-vendor operability for operation in the US PCS unlicense band. The three user premise equipment wireless standards are PWT (Personal Wireless Terminal), PCI (Personal Communication Interface) and PACS (Personal Access Communication System). Operation in the unlicense band is first discussed. Both voice or isochronous type services and data or asynchronous services are accommodated in the PCS unlicense band. Different rules of access governs each service type. A process of channel monitoring with a listen-before-transmit protocol is provided to allow for sharing of channels in the band. This process, also better known as the "etiquette rule" or "spectrum etiquette", together with standardization of the three over-the-air protocols in the TIA provides a significant new opportunity for the extension of personal communications for the in-building business applications.
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paper_title: Transmit Optimization for Relay-Based Cellular OFDMA Systems

paper_content:

This paper considers a broadband cellular orthogonal frequency-division multiple-access (OFDMA) system with relay nodes operating in decode-and-forward and half-duplex mode. Two transmit resource allocation problems for sum-rate maximization are formulated for such a system. The first one is the optimization of subcarrier allocation with predetermined power assignment for each subcarrier, and the other is the joint optimization of power and subcarrier allocation. Since these problems can't be solved easily in direct forms, we make continuous relaxation and solve the dual problems using a subgradient method. Numerical results show that a remarkable increment in sum-rate is achieved, with the aid of relay nodes and sophisticated resource allocation, compared to a system without relay nodes.
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paper_title: Hybrid RRM Architecture for Future Wireless Networks

paper_content:

The concept of ubiquitous and scalable system is applied in the IST WINNER II project to deliver optimum performance for different deployment scenarios from local area to wide area wireless networks. The integration of cellular and local area networks in a unique radio system will provide a great advantage to final users and operators, compared with the nowadays situation with many disconnected systems and users equipped with different subscriptions, radio interfaces and terminals. To this issue, the IST project WINNER II has defined three system modes suited to local, metropolitan and wide area respectively. The aim of this paper is twofold: first, it presents an architectural solution for scalable and hybrid radio resource management to efficiently integrate the different WINNER modes; second, it proposes a hybrid handover mechanism to exploit the availability of the different modes in the WINNER system.
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paper_title: Resource Allocation for OFDMA Relay Networks With Fairness Constraints

paper_content:

This paper studies the resource allocation for orthogonal frequency-division multiple-access relay network with multiple source nodes, multiple relay nodes, and a single destination node. The optimal source/relay/subcarrier allocation problem with fairness constraint on relay nodes is formulated as a binary integer programming problem. The problem is then tackled using a graph theoretical approach by transforming it into a linear optimal distribution problem in a directed graph. Upper bound of the solution is discussed and simulation results are studied to evaluate the algorithm performance
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paper_title: Adaptive resource allocation in multiuser OFDM systems with proportional rate constraints

paper_content:

Multiuser orthogonal frequency division multiplexing (MU-OFDM) is a promising technique for achieving high downlink capacities in future cellular and wireless local area network (LAN) systems. The sum capacity of MU-OFDM is maximized when each subchannel is assigned to the user with the best channel-to-noise ratio for that subchannel, with power subsequently distributed by water-filling. However, fairness among the users cannot generally be achieved with such a scheme. In this paper, a set of proportional fairness constraints is imposed to assure that each user can achieve a required data rate, as in a system with quality of service guarantees. Since the optimal solution to the constrained fairness problem is extremely computationally complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. In the proposed algorithm, subchannel allocation is first performed by assuming an equal power distribution. An optimal power allocation algorithm then maximizes the sum capacity while maintaining proportional fairness. The proposed algorithm is shown to achieve about 95% of the optimal capacity in a two-user system, while reducing the complexity from exponential to linear in the number of subchannels. It is also shown that with the proposed resource allocation algorithm, the sum capacity is distributed more fairly and flexibly among users than the sum capacity maximization method.
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paper_title: Proportional Fair Scheduling for Downlink OFDMA

paper_content:

In this paper, the author studies the sum throughput maximization with proportional fair scheduling (PFS) for downlink orthogonal frequency division multiple access (OFDMA) channels. The author proposes selective multiuser diversity (SMuD) schemes with normalized channel signal-to-noise ratio (n-SNR)-based ranking for user selection at each carrier, and assigns the transmit power to the assigned carriers using either equal power allocation (EPA) or water-filling (WF). The author also proposes a modified absolute channel SNR (a-SNR)-ranking based SMuD scheme, which provides an improved performance than the original a-SNR SMuD scheme. Closed-form throughput and average access probability (AAP) expressions for both n-SNR and a-SNR SMuD schemes with EPA over independent but not necessarily identically distributed (i.n.d.) Rayleigh channels (for different users and carriers) are derived. These results put new insight into the achievable downlink OFDMA performance with proportional fairness and the effects of various system and channel parameters.
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paper_title: Efficient Cooperative Diversity Schemes and Radio Resource Allocation for IEEE 802.16j

paper_content:

This paper studies various cooperative diversity schemes for orthogonal frequency division multiple access (OFDMA)- time division duplex (TDD) based two-hop cellular networks in low mobility scenarios, where the instantaneous channel state information is available at the base station. A user scheduling and radio resource allocation technique is developed in order to efficiently integrate various cooperative diversity schemes for the emerging IEEE 802.16j based systems. The analysis of the system with this scheduler shows that a simple cooperative diversity scheme which dynamically selects the best scheme between conventional relaying and direct transmission is promising in terms of throughput and implementation complexity. The conventional relaying refers to the scheme where the destination relies solely on the signals received through the relay.
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paper_title: Resource-Aware Routing Algorithms for Multi-hop Cellular Networks

paper_content:

The cellular network systems are expected to evolve into Multi-hop Cellular Network (MCN). While a mobile terminal and the base station have a direct connection in a conventional cellular network, in MCN a mobile terminal may reach the base station via relays by using multi-hopping. The relay can be either mobile terminal referred to client relay or dedicated relay referred to infra relay that has capabilities like those of the base station. In this paper, we focus on routing mechanism in multi-hop cellular networks. In particular, we study routing performance metrics for multi-hop cellular networks which consider energy efficiency and the relay capabilities.
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paper_title: On the performance of adaptive modulation in cellular systems

paper_content:

Adaptive modulation techniques have the potential to substantially increase the spectrum efficiency and to provide different levels of service to users, both of which are considered important for third-generation cellular systems. In this work, we propose a general framework to quantify the potential gains of such techniques. Specifically, we study the throughput performance gain that may be achieved by combining adaptive modulation and power control. Our results show that: (1) using adaptive modulation even without any power control provides a significant throughput advantage over using signal-to-interference-plus-noise ratio (SINR) balancing power control and (2) combining adaptive modulation and a suitable power control scheme leads to a significantly higher throughput as compared to no power control or using SINR-balancing power control. The first observation is especially important from an implementation point of view. Adjusting the modulation level without changing the transmission power requires far fewer measurements and feedback as compared to the SINR-balancing power control or the optimal power control. Hence, it is significantly easier to implement. Although presented in the context of adaptive modulation, the results also apply to other variable rate transmission techniques, e.g., rate adaptive coding schemes, coded modulation schemes, etc. This work provides valuable insight into the performance of variable rate transmission techniques in multi-user environments.
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paper_title: Resource Allocation in Multi-Hop OFDMA Wireless Backhaul Networks With Cooperative Relaying

paper_content:

An optimal resource allocation strategy for OFDMA multi-hop wireless backhaul networks is considered. A cross-layer optimization problem is formulated that maximizes the balanced end-to-end throughput under the routing and the PHY/MAC constraints. A dual method is employed to solve the problem efficiently and optimally by decoupling it into different layers as well as into different OFDM tones. A cooperative relaying technique is incorporated into the framework to improve the performance. Mutual interference between the links is explicitly modeled to allow maximal spatial reuse of the spectral resources, and half-duplex operation of the radios is assumed. The numerical results exhibit how the bottleneck phenomenon typical in multi-hop backhaul networks can be alleviated by the proposed techniques to yield significant improvement in the throughput.
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paper_title: Joint Optimization of Relay Strategies and Resource Allocations in Cooperative Cellular Networks

paper_content:

This paper considers a wireless cooperative cellular data network with a base station and many subscribers in which the subscribers have the ability to relay information for each other to improve the overall network performance. For a wireless network operating in a frequency-selective fading environment, the choices of relay node, relay strategy, and the allocation of power and bandwidth for each user are important design parameters. The design challenge is compounded further by the need to take user traffic demands into consideration. This paper proposes a utility maximization framework for such a network. We show that for a cellular system employing orthogonal frequency-division multiple-access (OFDMA), the optimization of physical layer transmission strategies can be done efficiently by introducing a set of pricing variables. The proposed solution incorporates both user traffic demand and the physical channel realization in a cross-layer design that not only allocates power and bandwidth optimally for each user, but also selects the best relay node and best relay strategy (i.e, decode-and-forward vs. amplify-and-forward) for each source-destination pair.
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paper_title: Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review

paper_content:

Orthogonal frequency division multiple access (OFDMA) has recently attracted vast research attention from both academia and industry and has become part of new emerging standards for broadband wireless access. Even though the OFDMA concept is simple in its basic principle, the design of a practical OFDMA system is far from being a trivial task. Synchronization represents one of the most challenging issues and plays a major role in the physical layer design. The goal of this paper is to provide a comprehensive survey of the latest results in the field of synchronization for OFDMA systems, with tutorial objectives foremost. After quantifying the effects of synchronization errors on the system performance, we review some common methods to achieve timing and frequency alignment in a downlink transmission. We then consider the uplink case, where synchronization is made particularly difficult by the fact that each user's signal is characterized by different timing and frequency errors, and the base station has thus to estimate a relatively large number of unknown parameters. A second difficulty is related to how the estimated parameters must be employed to correct the uplink timing and frequency errors. The paper concludes with a comparison of the reviewed synchronization schemes in an OFDMA scenario inspired by the IEEE 802.16 standard for wireless metropolitan area networks.
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paper_title: Resource Allocation for Wireless Networks: Basics, Techniques, and Applications

paper_content:

Merging the fundamental principles of resource allocation with the state-of-the-art in research and application examples, Han and Liu present a novel and comprehensive perspective for improving wireless systems performance. Cross-layer multiuser optimization in wireless networks is described systematically. Starting from the basic principles, such as power control and multiple access, coverage moves to the optimization techniques for resource allocation, including formulation and analysis, and game theory. Advanced topics such as dynamic resource allocation and resource allocation in antenna array processing, and in cooperative, sensor, personal area, and ultrawideband networks, are then discussed. Unique in its scope, timeliness, and innovative author insights, this invaluable work will help graduate students and researchers to understand the basics of wireless resource allocation whilst highlighting modern research topics, and will help industrial engineers to improve system optimization.
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paper_title: Performance of cellular networks with relays and centralized scheduling

paper_content:

Future cellular wireless networks could include multihop transmission through relays. We propose a centralized downlink scheduling scheme in a cellular network with a small number of relays. The scheduling scheme has the property that it guarantees stability of the user queues for the largest set of arrival rates. We obtain throughput results by simulation for various scenarios and study the effect of number of relays, relay transmit power relative to the base station (BS) power, and the effect of distributing a given total power between the BS and different numbers of relays. We also present results for the case without channel fading to determine what fraction of the throughput gain is achieved from diversity reception. We find that, with four relays deployed in each sector, it is possible to achieve significant throughput gain including the signaling overhead.
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paper_title: Relayer selection strategies in cellular networks with peer-to-peer relaying

paper_content:

We consider a TDMA cellular multihop network where relaying - via wireless terminals that have a good communication link to the base station - is used as a coverage enhancement technique. Provided that the subscriber density is not very low, relaying via wireless terminals can have a significant impact on coverage, capacity, and throughput. This is mainly due to the fact that the signals only have to travel through shorter distances and/or improved paths. In this work, we investigated the effects of relaying node selection strategies (essentially a routing issue) and maximum relayer transmit power level on coverage. Our simulation results show that with a very modest level of relaying node transmit power and with some moderate intelligence incorporated in the relaying node selection scheme, the (high data rate) coverage can be improved significantly through two-hop relaying without consuming any additional bandwidth.
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paper_title: Range extension without capacity penalty in cellular networks with digital fixed relays

paper_content:

The concept of relaying is a promising solution for the challenging throughput and high data rate coverage requirements of future wireless cellular networks. In this paper, we demonstrate that the area that a single BS (base station) can provide high data rate coverage can significantly be increased by the employment of digital fixed relays without any penalty in capacity. This network architecture, which allows two-hop links, is expected to facilitate cost-efficient high data rate coverage in beyond-3G cellular wireless networks. In particular, we considered the downlink of a non-CDMA network where 6 digital fixed relays are placed around each BS in a hexagonal layout. The improved two-hop links can be exploited to yield higher throughput through the use of adaptive modulation and coding.
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paper_title: WLC15-5: QoS Provisioning in the Absence of ARQ in Cellular Fixed Relay Networks through Inter-Cell Coordination

paper_content:

We propose an interference management scheme for providing quality of service (QoS) in the absence of automatic repeat request (ARQ) in cellular networks augmented with fixed relays. The high packet error rate in a system with ARQ not only incurs additional packet delay, which is undesirable for real-time services, but also reduces link throughput because of the increased over-the-air signaling overhead and retransmissions. The proposed scheme strives for improvements in packet error rate and net throughput while maintaining acceptable delay through the use of inter-cell coordination. The inter-cell coordination uses backbone network for information exchange and thereby transfers over-the-air signaling overhead to the high-speed backbone network. In our scheme, a group of base stations, each of which is either a recipient of or a contributor to dominant interference, form an interferer group and exchange channel state information with each other. Based on this instantaneous channel quality information, the proposed scheme makes intelligent scheduling and routing decisions taking the interference into account. The performance of the scheme is compared with that of an uncoordinated scheme through extensive simulations. It has been observed that the proposed scheme achieves significant performance benefits in terms of packet error rate and net throughput.
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paper_title: On the radio resource allocation in enhanced uplink UTRA-FDD with fixed relay stations

paper_content:

In this paper, an integrated radio resource allocation (IRRA) algorithm is proposed for enhanced uplink UTRA-FDD with fixed relay stations (RSs). It comprises three entities: load based route manager (LBRM), base station resource scheduler (BSRS), and relay station load balancer (RSLB). LBRM is responsible for the selection of user transmission routes, BSRS is for the scheduling of user transmission time and rates based on the available base station (BS) capacity, and RSLB is for the fine-tuning of user resource assignments (e.g. assigned rates) so as to prevent the overloading of RSs. The three entities operate periodically, synchronously, and with coordinated interactions. By system level simulations, the proposed algorithm is evaluated and compared with two other cases: 1) non-relaying, 2) relaying with a benchmark approach. The results show that IRRA can ensure significant gains in terms of cell throughput
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paper_title: Relayer selection strategies in cellular networks with peer-to-peer relaying

paper_content:

We consider a TDMA cellular multihop network where relaying - via wireless terminals that have a good communication link to the base station - is used as a coverage enhancement technique. Provided that the subscriber density is not very low, relaying via wireless terminals can have a significant impact on coverage, capacity, and throughput. This is mainly due to the fact that the signals only have to travel through shorter distances and/or improved paths. In this work, we investigated the effects of relaying node selection strategies (essentially a routing issue) and maximum relayer transmit power level on coverage. Our simulation results show that with a very modest level of relaying node transmit power and with some moderate intelligence incorporated in the relaying node selection scheme, the (high data rate) coverage can be improved significantly through two-hop relaying without consuming any additional bandwidth.
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paper_title: Interference modeling and analysis in two-hop cellular network with fixed relays in FDD mode

paper_content:

Relaying network is expected to play an important role in the future wireless network. This paper presents a scheme of two-hop cellular network with fixed relay nodes (FRN). Based on this scheme, co-channel interference and SIR received by BS and FRN are analyzed. Both the theoretical analysis and simulation results show that the SIR can be improved significantly when relays are employed in the network. We also show that the antenna height of FRN and the cell radius of BS and FRN influence SIR received by BS and FRN greatly.
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paper_title: Range extension without capacity penalty in cellular networks with digital fixed relays

paper_content:

The concept of relaying is a promising solution for the challenging throughput and high data rate coverage requirements of future wireless cellular networks. In this paper, we demonstrate that the area that a single BS (base station) can provide high data rate coverage can significantly be increased by the employment of digital fixed relays without any penalty in capacity. This network architecture, which allows two-hop links, is expected to facilitate cost-efficient high data rate coverage in beyond-3G cellular wireless networks. In particular, we considered the downlink of a non-CDMA network where 6 digital fixed relays are placed around each BS in a hexagonal layout. The improved two-hop links can be exploited to yield higher throughput through the use of adaptive modulation and coding.
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paper_title: Adaptive Resource Allocation Based on Channel Information in Multihop OFDM Systems

paper_content:

In this paper, we investigate the adaptive resource allocation problem in multiuser multihop OFDM systems. Assuming that base station(BS) knows all channel information, we formulate capacity maximization problem(CMP) and fairness constrained capacity maximization problem(FCMP) for adaptive resource allocation. The CMP considers joint subchannel, power and path allocation problem for maximizing the system capacity, while the FCMP considers the same problem with guaranteeing a minimum number of subchannels for each user. The proposed optimization problems are productive, because BS can allocate the subchannel, power and routing path to MSs by solving one optimization problem. Since these optimizations should be performed in real time, we propose two efficient heuristic algorithms, one of which considers CMP and the other considers FCMP. In the heuristic algorithms, we separate the optimization problem into three steps, namely subchannel allocation, load balancing, and power distribution to reduce computational complexity. The proposed heuristic algorithms are simple in that the iterative computations are removed, and accurate in that two heuristic algorithms achieve a similar performance compared with optimum solution.
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paper_title: Transmit Optimization for Relay-Based Cellular OFDMA Systems

paper_content:

This paper considers a broadband cellular orthogonal frequency-division multiple-access (OFDMA) system with relay nodes operating in decode-and-forward and half-duplex mode. Two transmit resource allocation problems for sum-rate maximization are formulated for such a system. The first one is the optimization of subcarrier allocation with predetermined power assignment for each subcarrier, and the other is the joint optimization of power and subcarrier allocation. Since these problems can't be solved easily in direct forms, we make continuous relaxation and solve the dual problems using a subgradient method. Numerical results show that a remarkable increment in sum-rate is achieved, with the aid of relay nodes and sophisticated resource allocation, compared to a system without relay nodes.
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paper_title: Radio Resource Allocation Algorithm for Relay-Aided Cellular OFDMA System

paper_content:

We address the problem of radio resource allocation in the Downlink (DL) of relay-aided cellular system, based on OFDMA transmission technology. There has been little work on specific resource allocation algorithms for this system in the literature, although these are the key elements for realizing the potential capacity and coverage increase offered by the relay. Therefore, we propose two resource allocation algorithms which improve the overall throughput and coverage compared to a system without relay. The advantage of our algorithms is that they perform well while minimizing the complexity and the required amount of Channel State Information (CSI), making them suitable for practical use.
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paper_title: Fairness-Aware Adaptive Resource Allocation Scheme in Multihop OFDMA Systems

paper_content:

We investigate a fairness-aware adaptive resource allocation scheme for the downlink of multihop OFDMA systems. Assuming that the base station has all the channel information, we formulate an optimization problem for an adaptive subchannel-, path- and power-allocation scheme that maximizes system capacity while guaranteeing minimum resources for each user. Since the optimization should be performed in real time, we propose an efficient heuristic algorithm composed of subchannel-allocation, load-balancing and power-distribution steps. The proposed algorithm is simple in that the iterative computations are removed, and accurate in that it performs similarly to the optimum solution
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paper_title: Relayer selection strategies in cellular networks with peer-to-peer relaying

paper_content:

We consider a TDMA cellular multihop network where relaying - via wireless terminals that have a good communication link to the base station - is used as a coverage enhancement technique. Provided that the subscriber density is not very low, relaying via wireless terminals can have a significant impact on coverage, capacity, and throughput. This is mainly due to the fact that the signals only have to travel through shorter distances and/or improved paths. In this work, we investigated the effects of relaying node selection strategies (essentially a routing issue) and maximum relayer transmit power level on coverage. Our simulation results show that with a very modest level of relaying node transmit power and with some moderate intelligence incorporated in the relaying node selection scheme, the (high data rate) coverage can be improved significantly through two-hop relaying without consuming any additional bandwidth.
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paper_title: Resource-Allocation for OFDMA Multi-Hop Relaying Downlink Systems

paper_content:

This paper proposes resource-allocation algorithms to maximize the sum-rate in orthogonal frequency-division multiple-access multi-hop relaying downlink systems. With advance subchannel allocation to users and relay stations, Lagrange dual-decomposition solves the power-allocation problem. This paper shows the optimal solution to be a modified water-filling algorithm, where an inner-outer bisection method determines the optimal water-levels. Further, proposed heuristic resource- allocation algorithms rely on the Karush-Kuhn-Tucker conditions. Simulation results show that the multi-hop OFDMA relaying systems outperform the conventional OFDMA systems by more than 30% with use of the proposed resource-allocation algorithms.
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paper_title: Resource Allocation for OFDMA Relay Networks With Fairness Constraints

paper_content:

This paper studies the resource allocation for orthogonal frequency-division multiple-access relay network with multiple source nodes, multiple relay nodes, and a single destination node. The optimal source/relay/subcarrier allocation problem with fairness constraint on relay nodes is formulated as a binary integer programming problem. The problem is then tackled using a graph theoretical approach by transforming it into a linear optimal distribution problem in a directed graph. Upper bound of the solution is discussed and simulation results are studied to evaluate the algorithm performance
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paper_title: Opportunistic Scheduling and Spectrum Reuse in Relay-Based Cellular OFDMA Networks

paper_content:

We investigate the spectral efficiency performance of channel-aware (i.e., opportunistic) multiuser scheduling algorithms over relay-assisted broadband cellular networks; with special focus on orthogonal frequency-division multiple-access (OFDMA) resource allocation. Capacity analysis and system-level simulation results for various spectrum reuse policies are presented including (i) fully orthogonal resource sharing across the base station (BS) and relay stations (RSs) in each cell, and (ii) simultaneous transmissions (i.e., at the same time and frequency) by the BS and multiple RSs in each cell, using realistic broadband channel models. Our study provides insights on the potential performance enhancements from multihop routing and spectrum reuse policies in the presence of multiuser diversity gains from opportunistic scheduling and helps to identify the key design tradeoffs associated with interference management in relay-assisted multiuser communication.
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paper_title: Adaptation, Coordination, and Distributed Resource Allocation in Interference-Limited Wireless Networks

paper_content:

A sensible design of wireless networks involves striking a good balance between an aggressive reuse of the spectral resource throughout the network and managing the resulting co-channel interference. Traditionally, this problem has been tackled using a Bdivide and conquer( approach. The latter consists in deploying the network with a static or semidynamic pattern of resource reutilization. The chosen reuse factor, while sacrificing a substantial amount of efficien- cy, brings the interference to a tolerable level. The resource can then be managed in each cell so as to optimize the per cell capacity using an advanced air interface design. In this paper, we focus our attention on the overall network capacity as a measure of system performance. We consider the problem of resource allocation and adaptive transmission in multicell scenarios. As a key instance, the problem of joint scheduling and power control simultaneously in multiple transmit-receive links, which employ capacity-achieving adap- tive codes, is studied. In principle, the solution of such an optimization hinges on tough issues such as the computational complexity and the requirement for heavy receiver-to- transmitter feedback and, for cellular networks, cell-to-cell channel state information (CSI) signaling. We give asymptotic properties pertaining to rate-maximizing power control and scheduling in multicell networks. We then present some promising leads for substantial complexity and signaling reduction via the use of newly developed distributed and game theoretic techniques.
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paper_title: Radio Resource Management for a Two-hop OFDMA Relay System in Downlink

paper_content:

In this paper, we propose two radio resource control (RRC) schemes where both base station (BS) and relay station (RS) perform dynamic resource allocation. The target system is a two-hop mobile communication system employing OFDMA technique. These schemes operate in such a distributed manner that both BS and RS control the mobile stations directly connected to each of them. However, the mobile station (MS) connected to RS is influenced by BS-RS and RS-RS links as well in addition to RS-MS link. To solve this problem, a BS-RS link control mechanism based on the information from RS should be supplemented into the system. The proposed mechanism, a semi-distributed method, is that BS allocates resources to the directly connected mobile stations and relay stations, first. Then RS allocates resources to the connected mobile stations in two ways; RS uses the assigned subcarriers from BS or all system subcategories independently. The former method is called the 'separate and sequential allocation (SSA)' and the latter the 'separate and reuse allocation (SRA)'. The SSA method yields a superior quality without regard to the location of RS, but the SRA method reveals performance results depending on the location of RS. Computer simulations show that the two proposed methods have almost the same performance as the existing centralized method but lower complexity and higher flexibility compared to the centralized method.
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paper_title: Adaptive Resource Allocation Based on Channel Information in Multihop OFDM Systems

paper_content:

In this paper, we investigate the adaptive resource allocation problem in multiuser multihop OFDM systems. Assuming that base station(BS) knows all channel information, we formulate capacity maximization problem(CMP) and fairness constrained capacity maximization problem(FCMP) for adaptive resource allocation. The CMP considers joint subchannel, power and path allocation problem for maximizing the system capacity, while the FCMP considers the same problem with guaranteeing a minimum number of subchannels for each user. The proposed optimization problems are productive, because BS can allocate the subchannel, power and routing path to MSs by solving one optimization problem. Since these optimizations should be performed in real time, we propose two efficient heuristic algorithms, one of which considers CMP and the other considers FCMP. In the heuristic algorithms, we separate the optimization problem into three steps, namely subchannel allocation, load balancing, and power distribution to reduce computational complexity. The proposed heuristic algorithms are simple in that the iterative computations are removed, and accurate in that two heuristic algorithms achieve a similar performance compared with optimum solution.
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paper_title: Transmit Optimization for Relay-Based Cellular OFDMA Systems

paper_content:

This paper considers a broadband cellular orthogonal frequency-division multiple-access (OFDMA) system with relay nodes operating in decode-and-forward and half-duplex mode. Two transmit resource allocation problems for sum-rate maximization are formulated for such a system. The first one is the optimization of subcarrier allocation with predetermined power assignment for each subcarrier, and the other is the joint optimization of power and subcarrier allocation. Since these problems can't be solved easily in direct forms, we make continuous relaxation and solve the dual problems using a subgradient method. Numerical results show that a remarkable increment in sum-rate is achieved, with the aid of relay nodes and sophisticated resource allocation, compared to a system without relay nodes.
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paper_title: Fairness-Aware Adaptive Resource Allocation Scheme in Multihop OFDMA Systems

paper_content:

We investigate a fairness-aware adaptive resource allocation scheme for the downlink of multihop OFDMA systems. Assuming that the base station has all the channel information, we formulate an optimization problem for an adaptive subchannel-, path- and power-allocation scheme that maximizes system capacity while guaranteeing minimum resources for each user. Since the optimization should be performed in real time, we propose an efficient heuristic algorithm composed of subchannel-allocation, load-balancing and power-distribution steps. The proposed algorithm is simple in that the iterative computations are removed, and accurate in that it performs similarly to the optimum solution
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paper_title: Resource Allocation in Multi-Hop OFDMA Wireless Backhaul Networks With Cooperative Relaying

paper_content:

An optimal resource allocation strategy for OFDMA multi-hop wireless backhaul networks is considered. A cross-layer optimization problem is formulated that maximizes the balanced end-to-end throughput under the routing and the PHY/MAC constraints. A dual method is employed to solve the problem efficiently and optimally by decoupling it into different layers as well as into different OFDM tones. A cooperative relaying technique is incorporated into the framework to improve the performance. Mutual interference between the links is explicitly modeled to allow maximal spatial reuse of the spectral resources, and half-duplex operation of the radios is assumed. The numerical results exhibit how the bottleneck phenomenon typical in multi-hop backhaul networks can be alleviated by the proposed techniques to yield significant improvement in the throughput.
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paper_title: Joint Optimization of Relay Strategies and Resource Allocations in Cooperative Cellular Networks

paper_content:

This paper considers a wireless cooperative cellular data network with a base station and many subscribers in which the subscribers have the ability to relay information for each other to improve the overall network performance. For a wireless network operating in a frequency-selective fading environment, the choices of relay node, relay strategy, and the allocation of power and bandwidth for each user are important design parameters. The design challenge is compounded further by the need to take user traffic demands into consideration. This paper proposes a utility maximization framework for such a network. We show that for a cellular system employing orthogonal frequency-division multiple-access (OFDMA), the optimization of physical layer transmission strategies can be done efficiently by introducing a set of pricing variables. The proposed solution incorporates both user traffic demand and the physical channel realization in a cross-layer design that not only allocates power and bandwidth optimally for each user, but also selects the best relay node and best relay strategy (i.e, decode-and-forward vs. amplify-and-forward) for each source-destination pair.
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paper_title: Resource-Allocation for OFDMA Multi-Hop Relaying Downlink Systems

paper_content:

This paper proposes resource-allocation algorithms to maximize the sum-rate in orthogonal frequency-division multiple-access multi-hop relaying downlink systems. With advance subchannel allocation to users and relay stations, Lagrange dual-decomposition solves the power-allocation problem. This paper shows the optimal solution to be a modified water-filling algorithm, where an inner-outer bisection method determines the optimal water-levels. Further, proposed heuristic resource- allocation algorithms rely on the Karush-Kuhn-Tucker conditions. Simulation results show that the multi-hop OFDMA relaying systems outperform the conventional OFDMA systems by more than 30% with use of the proposed resource-allocation algorithms.
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paper_title: Resource Allocation for OFDMA Relay Networks With Fairness Constraints

paper_content:

This paper studies the resource allocation for orthogonal frequency-division multiple-access relay network with multiple source nodes, multiple relay nodes, and a single destination node. The optimal source/relay/subcarrier allocation problem with fairness constraint on relay nodes is formulated as a binary integer programming problem. The problem is then tackled using a graph theoretical approach by transforming it into a linear optimal distribution problem in a directed graph. Upper bound of the solution is discussed and simulation results are studied to evaluate the algorithm performance
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paper_title: Resource Allocation for Wireless Networks: Basics, Techniques, and Applications

paper_content:

Merging the fundamental principles of resource allocation with the state-of-the-art in research and application examples, Han and Liu present a novel and comprehensive perspective for improving wireless systems performance. Cross-layer multiuser optimization in wireless networks is described systematically. Starting from the basic principles, such as power control and multiple access, coverage moves to the optimization techniques for resource allocation, including formulation and analysis, and game theory. Advanced topics such as dynamic resource allocation and resource allocation in antenna array processing, and in cooperative, sensor, personal area, and ultrawideband networks, are then discussed. Unique in its scope, timeliness, and innovative author insights, this invaluable work will help graduate students and researchers to understand the basics of wireless resource allocation whilst highlighting modern research topics, and will help industrial engineers to improve system optimization.
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paper_title: Transmit Optimization for Relay-Based Cellular OFDMA Systems

paper_content:

This paper considers a broadband cellular orthogonal frequency-division multiple-access (OFDMA) system with relay nodes operating in decode-and-forward and half-duplex mode. Two transmit resource allocation problems for sum-rate maximization are formulated for such a system. The first one is the optimization of subcarrier allocation with predetermined power assignment for each subcarrier, and the other is the joint optimization of power and subcarrier allocation. Since these problems can't be solved easily in direct forms, we make continuous relaxation and solve the dual problems using a subgradient method. Numerical results show that a remarkable increment in sum-rate is achieved, with the aid of relay nodes and sophisticated resource allocation, compared to a system without relay nodes.
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paper_title: Radio Resource Allocation Algorithm for Relay-Aided Cellular OFDMA System

paper_content:

We address the problem of radio resource allocation in the Downlink (DL) of relay-aided cellular system, based on OFDMA transmission technology. There has been little work on specific resource allocation algorithms for this system in the literature, although these are the key elements for realizing the potential capacity and coverage increase offered by the relay. Therefore, we propose two resource allocation algorithms which improve the overall throughput and coverage compared to a system without relay. The advantage of our algorithms is that they perform well while minimizing the complexity and the required amount of Channel State Information (CSI), making them suitable for practical use.
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paper_title: Radio Resource Management for a Two-hop OFDMA Relay System in Downlink

paper_content:

In this paper, we propose two radio resource control (RRC) schemes where both base station (BS) and relay station (RS) perform dynamic resource allocation. The target system is a two-hop mobile communication system employing OFDMA technique. These schemes operate in such a distributed manner that both BS and RS control the mobile stations directly connected to each of them. However, the mobile station (MS) connected to RS is influenced by BS-RS and RS-RS links as well in addition to RS-MS link. To solve this problem, a BS-RS link control mechanism based on the information from RS should be supplemented into the system. The proposed mechanism, a semi-distributed method, is that BS allocates resources to the directly connected mobile stations and relay stations, first. Then RS allocates resources to the connected mobile stations in two ways; RS uses the assigned subcarriers from BS or all system subcategories independently. The former method is called the 'separate and sequential allocation (SSA)' and the latter the 'separate and reuse allocation (SRA)'. The SSA method yields a superior quality without regard to the location of RS, but the SRA method reveals performance results depending on the location of RS. Computer simulations show that the two proposed methods have almost the same performance as the existing centralized method but lower complexity and higher flexibility compared to the centralized method.
---
paper_title: Resource-Allocation for OFDMA Multi-Hop Relaying Downlink Systems

paper_content:

This paper proposes resource-allocation algorithms to maximize the sum-rate in orthogonal frequency-division multiple-access multi-hop relaying downlink systems. With advance subchannel allocation to users and relay stations, Lagrange dual-decomposition solves the power-allocation problem. This paper shows the optimal solution to be a modified water-filling algorithm, where an inner-outer bisection method determines the optimal water-levels. Further, proposed heuristic resource- allocation algorithms rely on the Karush-Kuhn-Tucker conditions. Simulation results show that the multi-hop OFDMA relaying systems outperform the conventional OFDMA systems by more than 30% with use of the proposed resource-allocation algorithms.
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paper_title: Fairness-Aware Joint Routing and Scheduling in OFDMA-Based Cellular Fixed Relay Networks

paper_content:

Relaying and orthogonal frequency division multiple access (OFDMA) are the accepted technologies for emerging wireless communications standards. The activities in many wireless standardization bodies and forums, for example IEEE 802.16 j/m and LTE-Advanced, attest to this fact. The availability or lack thereof of efficient radio resource management (RRM) could make or mar the opportunities in these networks. This paper therefore provides a comprehensive RRM algorithm for OFDMA-based multi-cellular fixed relay networks in a way to ensure fairness among users with minimal impact on the network throughput (in contrast, pure opportunistic RRM techniques always favor users with good channel conditions). Unlike the majority of works in the literature, our proposed scheme is queue-aware and jointly performs routing, fair scheduling, and load balancing among cell nodes. The routing strategy has inherent learning ability and it dynamically converges to better routes.
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Title: An Overview of Radio Resource Management in Relay-Enhanced OFDMA-Based Networks

Section 1: Introduction
Description 1: Introduce the basic concepts of OFDMA and relay-enhanced networks, and highlight the importance of intelligent RRM algorithms for improving network performance.

Section 2: Activities on Relay-Based Architecture Among Standardization Bodies, Forums, and Consortiums
Description 2: Discuss the ongoing research and standardization efforts by various organizations focused on relay-based architectures in wireless networks.

Section 3: The RRM Problem Statement
Description 3: Define the RRM problem in relay-enhanced OFDMA-based networks and explain the typical resource allocation challenges and objectives.

Section 4: Scheduling
Description 4: Provide an overview of different scheduling policies used in RRM, including round-robin, max-SINR, and proportional-fair schedulers.

Section 5: Routing
Description 5: Describe the importance of routing in relay-enhanced networks and discuss various routing strategies and their impact on network performance.

Section 6: Link Adaptation: Adaptive Modulation and Coding
Description 6: Explain adaptive modulation and coding (AMC) techniques and their role in optimizing the use of radio resources in varying channel conditions.

Section 7: Cooperative Relaying in OFDMA Networks
Description 7: Explore cooperative communication strategies and cross-layer optimization techniques for improving system performance in OFDMA-based relay networks.

Section 8: Earlier RRM Research in Relay Networks
Description 8: Review previous RRM schemes for non-OFDMA relay networks and discuss their relevance as building blocks for current research.

Section 9: RRM in OFDMA Fixed-Relay Networks
Description 9: Examine RRM algorithms specifically designed for OFDMA relay networks, categorized into centralized and distributed schemes.

Section 10: Optimization Techniques and Complexity Issues
Description 10: Discuss optimization techniques used to manage the complexity of RRM algorithms and highlight methods to simplify these problems.

Section 11: Fairness Metric Examples
Description 11: Introduce common fairness metrics used in RRM and provide interpretations for these metrics with specific examples.

Section 12: Channel Models and Numerical Examples
Description 12: Present the channel models used in RRM research and provide numerical examples to demonstrate their impact on network performance.

Section 13: Conclusion
Description 13: Summarize the key points discussed in the paper and suggest future research directions in RRM for OFDMA-based relay networks.