In one of the several manifestations, the future cellular networks are required to accommodate a massive number of devices, several orders of magnitude compared to today's networks. At the same time, the future cellular networks will have to fulfill stringent latency constraints. To that end, one problem that is posed as a potential showstopper is extreme congestion for requesting uplink scheduling over the physical random access channel (PRACH). Indeed, such congestion drags along scheduling delay problems. In this paper, the use of self-organized device-to-device (D2D) clustering is advocated for mitigating PRACH congestion. To this end, this paper proposes two D2D clustering schemes, namely, random-based clustering and channel-gain-based clustering. Accordingly, this paper sheds light on random access within the proposed D2D clustering schemes and presents a case study based on a stochastic geometry framework. For the sake of objective evaluation, the D2D clustering is benchmarked by the conventional scheduling request procedure. Accordingly, this paper offers insights into useful scenarios that minimize the scheduling delay for each clustering scheme. Finally, this paper discusses the implementation algorithm and some potential implementation issues and remedies.

In one of the several manifestations, 5G networks are required to accommodate a massive number of devices; an order of magnitude compared to today's networks. At the same time, 5G networks will have to observe stringent latency constraints. To that end, one problem that is posed as a potential showstopper is extreme congestion over random access resources in the cellular uplink. Indeed, congestion drags along delay problems. In this paper, the use of network-orchestrated device-to-device (D2D) relaying is advocated for the mitigation of random access congestion. In particular, it is shown that D2D relaying reduces access delay only at high device densities but is rather an overkill for lower densities. For the sake of an objective evaluation, the overhead of device clustering protocols must be accounted for. As such, this paper provides protocol designers with benchmarks on how much protocol overhead can be tolerated. The feasibility of D2D relaying is demonstrated via extensive system-level simulations run on a super computer and based on a foundation of real-life networks parameters.

Unprecedented bandwidth-intensive, ultra-low latency multi-media services and applications are expected to be delivered through the fifth generation (5G) network. Thus, efficient radio resource management will continue to play an important role as the network service providers strive to provide rich media contents to their users. Therefore, in this work, we consider a cross-layer based framework for efficient allocation of network resources for the transmission of HE VC encoded video streams over 5G-aligned V2X application in mmWave environments. We adopt application and physical layer models, and formulate a multi-vehicle resource allocation problem taking into account the abstracted information of the two corresponding layers. Such a framework is compared with three other standard resource allocation schemes using computed Mean Opinion Score (MOS). Numerical results show that our proposed radio resource management scheme offers a significant improvement of viewer-perceived quality of service compared to the reference approaches.

Various standardization activities leading to 4G and beyond networks have considered the synergy of OFDMA and multihop relaying thus giving way for the fixed relay station (FRS)-based radio access network. As such, the next-generation networks will comprise a plethora of performance enhancing devices among which is the plug-and-play nomadic relay station (NRS). It is essential for such dense and inevitably frequency reuse-aggressive networks to employ efficient mechanisms to mitigate the co-channel interference and to provide prudent energy utilization; this brings about the timely environmental concerns and the so-called green wireless initiative in designing future wireless networks. We present a novel joint power and subchannel allocation algorithm for the emerging OFDMA-based nomadic-augmented fixed relay networks. This NRS-directed algorithm performs adaptive power control (APC) within the autonomous opportunistic NRS medium access and channel reuse, using two different approaches. The APC mechanism is realized in an open-loop manner requiring no feedback from the WT. We demonstrate the power savings and user throughput improvement obtained through the joint scheme. We also identify a throughput-power saving trade-off in terms of the number of deployed FRSs. Through this work, the authors further establish their pioneering techniques for realizing the concept of NRS-augmented networks.

The provision of very high data rates in a ubiquitous manner throughout the service area is a great challenge for 4G and beyond-4G wireless networks. Towards that end, the deployment of fixed relays by the operators has become an accepted radio access network concept in various standardization activities including LTE-A and 802.16j. It is envisaged that next-generation networks will comprise a plethora of wireless relay stations. Worthy of mention is the plug-and-play type of relay known as nomadic relay. We devise novel radio resource management (RRM) schemes to facilitate the operation of fixed relay stations (FRSs) and nomadic relay stations (NRSs) in OFDMA-based multicellular networks. Two schemes of different decentralization levels are devised and classified as distributed and semi-centralized. A novel user-based dynamic routing or link selection that significantly reduces the feedback overhead is employed. We develop methods by which the NRSs act autonomously to acquire radio resources without relying on a central entity. NRS operation is the same in the two schemes and can be extended to any other OFDMA-based RRM scheme. Through the asynchronous opportunistic medium access of the NRSs, smart and opportunistic intra-cell channel reuse is attained. This is different from the static intra-cell reuse patterns often adopted in literature. Furthermore, we introduce a method to enable the cooperation between an NRS and a serving FRS to assist a troubled wireless terminal (WT). We thus establish the concept of nomadic relay-augmented fixed relay networks. To the extent of our knowledge of the literature, no other work has undertaken this task so far.

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. Although distributed schemes are more attractive, it is essential to seek outstanding performance benchmarks to which various decentralized schemes can be compared. Therefore, this paper provides a comprehensive centralized RRM algorithm for downlink OFDMA cellular fixed relay networks in a way to ensure user fairness with minimal impact on network throughput. In contrast, it has been observed that pure opportunistic schemes and fairness-aware schemes relying solely on achievable and allocated capacities may not attain the desired fairness, e.g., proportional fair scheduling. The proposed scheme is queue-aware and performs three functions jointly; dynamic routing, fair scheduling, and load balancing among cell nodes. We show that the proposed centralized scheme is different from the traditional centralized schemes in terms of the substantial savings in complexity and feedback overhead.

The provision of very high data rates in a ubiquitous and fair manner throughout the service area is a great challenge for 4G and beyond-4G wireless networks. Towards that end, the deployment of fixed relays by the operators has become an accepted radio access network concept in various standardization activities including LTE-A and 802.16m. In this paper, we present a fair resource allocation scheme that can significantly reduce the co-channel interference and improve spectrum utilization in OFDMA-based multi-cellular networks enhanced by fixed relays. The major goal is to obtain an effective throughput-fairness trade-off through the combination of dynamic resource allocation, in-cell routing, traffic diversity, and history of users' past service. The proposed scheme achieves substantial fairness, throughput, and latency improvements in comparison to the reference schemes as well as to another scheme proposed, earlier by the authors. Numerical results indicate that the proposed scheme provides an almost ubiquitous high-data-rate service to users, irrespective of their locations (including cell-edge users), with a minimal sacrifice in the overall network throughput.

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.

In this letter the performance of multiple relay channels is analyzed for the situation in which multiple antennas are deployed only at the relays. The simple repetition-coded decode and-forward protocol with two different antenna processing techniques at the relays is investigated. The antenna combining techniques are maximum ratio combining (MRC) for reception and transmit beamforming (TB) for transmission. It is shown that these distributed antenna combining techniques can exploit the full spatial diversity of the relay channels regardless of the number of relays and antennas at each relay, and offer significant power gain over distributed space-time coding techniques.

In this paper, a two-hop cooperative multi-relay communication network is considered. Selection relaying schemes are attracting considerable attention due to their prudent bandwidth utilization and ability to provide full diversity. The recent developments in selection relaying (SR) have largely focused on information theoretic analyses such as outage performance. Some of these analyses are accurate only in high SNR regimes. This paper provides exact outage and capacity performance expressions for selection relaying and tight approximation over a sufficiently wide range of SNR regimes for selection cooperative relaying. The outage capacity for SR is also provided. The motivation for this work is that practical systems operate at far lower SNR values than those supported by the high SNR analysis. Therefore, designers should be able to evaluate system performance to a reasonable degree of accuracy over practical SNR values. Simulations are used to corroborate the analytical results and close agreement is observed.

Interest in selection relaying is growing. The recent developments in this area have largely focused on information theoretic analyses such as outage performance. Some of these analyses are accurate only at high SNR regimes. In this paper error rate analyses that are sufficiently accurate over a wide range of SNR regimes are provided. The motivations for this work are that practical systems operate at far lower SNR values than those supported by the high SNR analysis. To enable designers to make informed decisions regarding network design and deployment, it is imperative that system performance is evaluated with a reasonable degree of accuracy over practical SNR regimes. Simulations have been used to corroborate the analytical results, as close agreement between the two is observed.

This paper studies selective relaying schemes based on signal-to-noise-ratio (SNR) to minimize the end-to-end (e2e) bit error rate (BER) in cooperative digital relaying systems using BPSK modulation. In the SNR-based selective relaying, the relay either retransmits or remains silent depending on the SNRs of the source-relay, relay-destination, and source-destination links. Different models assuming the availability of different sets of instantaneous and average SNR information at the relay are studied. For each model, the optimal strategy to minimize the e2e BER is a different threshold rule on the source-relay SNR, if the link SNRs are uncorrelated in time and space. Approximations for the optimal threshold values that minimize the e2e BER and the resulting performance are derived analytically for BPSK modulation. Using the derived threshold the e2e BER can be reduced significantly compared to simple digital relaying. By studying the performance under different models, it is shown that knowledge of the instantaneous source-destination SNR at the relay can be exploited. The gain from this knowledge is higher when the average source-destination SNR is large. However, knowledge of the instantaneous relay-destination SNR at the relay does not change performance significantly.

In this paper we analyze the performance of multiple relay channels when multiple antennas are deployed only at relays. Specifically, we investigate the simple repetition-coded decode-and-forward protocol and apply two antenna combining techniques at relays, namely maximum ratio combining (MRC) on receive and transmit beamforming (TB). We assume that the total number of antennas at all relays is fixed to N. With a reasonable power constraint at the relays, we show that the antenna combining techniques can exploit the full spatial diversity of the relay channels and can achieve the same diversity multiplexing tradeoff as achieved by more complex space-time distributed coding techniques, such as those proposed by Laneman and Womell (2003).

We study selective digital relaying schemes where the relay may choose to retransmit or to remain silent based on the qualities of the links between the source, relay and the destination. We first analyze a baseline scheme, called static relaying, where the relaying decisions are based only on the average signal-to-noise ratio (SNR) values of all the links. The second scheme, dynamic relaying, allows the relay to make decisions based on the instantaneous SNR of the source-relay link and average SNRs of the relay-destination and source-destination links. We show that, in dynamic relaying the optimal strategy to minimize the average end-to-end bit error rate is a threshold rule on the instantaneous SNR of the source-relay channel. In this case, the optimal threshold value is a function of average SNR of relay-destination and source-destination channels. We derive closed-form expressions for the optimal threshold and the bit error performance achieved by this threshold. We show that dynamic relaying can provide significant performance advantage over static relaying.

Space, cost, and signal processing constraints, among others, often preclude the use of multiple antennas at wireless terminals. This paper investigates distributed decode-and-forward fixed relays (infrastructure-based relaying) which are engaged in cooperation in a two-hop wireless network as a means of removing the burden of multiple antennas on wireless terminals. In contrast to mobile terminals, the deployment of a small number of antennas on infrastructure-based fixed relays is feasible, thus, the paper examines the impact of multiple antennas on the performance of the distributed cooperative fixed relays. Threshold-based maximal ratio combining (MRC) and threshold-based selection combining (SC) of these multiple antenna signals are studied and analyzed. It is found that the end-to-end (E2E) error performance of a network which has few relays with many antennas is not significantly worse than that which has many relays each with a fewer antennas. Obviously, the former network has a tremendous deployment cost advantage over the latter. It is also observed that the E2E error performance of a network in which the multiple antennas at relays are configured in SC fashion is not significantly worse than that in which MRC is used. For implementation, SC presents a significantly lower complexity and cost than a full-blown MRC. The analysis in this paper uses the versatile Nakagami fading channels in contrast to the Rayleigh model used in most previous works

In many scenarios the commonly assumed symmetry in multiple relay channels is unrealistic. Therefore, this paper, through analytical and simulation efforts, investigates asymmetric relay deployment where the links of cooperating nodes to destination experience unequal signal strength. An analysis of the cooperative error rate at the destination node in such networks is presented. Using the derived expressions for the cooperative error, in conjunction with the approaches used in earlier works, the end-to-end (E2E) performance of a two- hop network can be obtained. Moreover, the derived expression represents, in certain scenarios, a tight bound for the E2E error rate of the two-hop network such as when relay adopts threshold decode-and-forward strategy and/or multi-antenna processing to improve the reliability of its detection.

Cooperative diversity through mobile terminals is faced with a number of deployment challenges such as security (as terminals have to detect partner's signals), incentive and coercion packages (as users have to be motivated to use their terminals to assist others), and huge capital investment (as terminals have to be modified to make them ready for cooperation). This paper discusses fixed relay-enabled user cooperation that are being considered in the WINNER project for deploying beyond 3G wireless communication networks. The schemes operate by engaging two users in cooperation without their knowledge. The schemes which can be viewed as an add-on to network facility have significant impact on the costs, security and end-to-end (E2E) performance of two-hop wireless networks. In addition, the proposed schemes can be used in a number of networks since current terminals do not require any modifications.

Multiple antenna schemes can provide performance enhancement but the small size and cost constraints of wireless terminals preclude their use at these terminals. This paper investigates distributed fixed relays (infrastructure-based relaying) which are engaged in cooperation in a two-hop wireless network as a means of removing the burden of multiple antennas on wireless terminals. In contrast to mobile terminals, a small number of antennas can be deployed on infrastructure-based fixed relays. Hence, the paper investigates performance of the distributed cooperative multi-antenna fixed relays. Threshold maximal ratio combining and threshold selection combining of these multiple antenna signals are studied and analyzed. The following results are derived. For a given performance requirement, the multiple antennas at relays can significantly reduce the number of relays required in a network area, ultimately, reducing system deployment cost. In addition, threshold selection combining at the relays represents an excellent compromise between performance and system cost. Finally, the analysis performed in this paper uses the versatile Nakagami fading channel model

We investigate microdiversity-augmented macrodiversity techniques in wireless communication networks. The setup consists of K widely separated access ports each carrying N antennas. The conventional selection macrodiversity (Scheme I) and two proposed methods (Scheme II and Scheme III) for port selection are investigated and their performance are compared. Scheme II utilizes the advancement in distributed antennas and radio-on-fiber technologies whereas Scheme III utilizes these technologies in a way similar to the soft handover of CDMA systems. After the port selection, the microdiversity uses n strongest signals (n les N) of the selected port for diversity combining if practical constraints preclude the use of all N signals. Analytical performance expressions for the probability of error and outage probability for Scheme I are developed. Simulations are used to investigate Scheme II and Scheme III and it is observed that these latter schemes exhibit performance superiority over the conventional macrodiversity selection method. The power savings obtained using the proposed architecture and new selection schemes could be used either for coverage extension or to increase capacity in wireless networks

We investigate hybrid macro/microdiversity employed in the reverse-link of microcellular wireless networks where low power, small and cost-effective radio access ports are linked to a central unit. We propose a new macro-selection strategy to improve the conventional macrodiversity selection technique. Furthermore, the issue of macrodiversity maximal ratio combining in non-CDMA microcellular networks is investigated as a natural extension of the soft handover of the already established CDMA cellular systems. The proposed schemes have performance advantage over the conventional macrodiversity method at a modest extra processing. Although the presented analysis is for a non-CDMA system, it can be extended to a CDMA system.

The performance of hybrid microdiversity, in the form of generalized selection combining (GSC), and macrodiversity is presented for lognormal shadowed Rayleigh fading channels. The GSC-augmented macrodiversity consists of K ports in a cell, each port carrying N microscopic diversity antennas. The macroscopic diversity involves selecting the port with the highest long-term local mean SNR among the K ports, and the GSC uses n strongest signals of the N branch received signals from that port for processing. We derive analytical expressions for error probability and outage for systems employing this hybrid scheme. The expressions are valid for any configurations of K,N, n. In microcell systems substantial correlation could exist among the ports in contrast to macrocell; results are also shown for correlated lognormal shadowed Rayleigh channels. Extensive simulations are carried out to validate the analytical expressions derived.

A performance criterion for any coded modulation schemes is the cutoff rate. This is examined for schemes employing generalized selection combining (GSC). The cutoff rate expression is derived and presented for the GSC. A simplified performance analysis of coherent M-ary phase shift keying (nPSK) for GSC is also given for independently and identically distributed Rayleigh fading. These expressions are valid for any arbitrary number of diversity branches, M and combining order, m.

The demand for high speed wireless systems dictates the use of bandwidth efficient modulation schemes. Trellis coded I-Q 16-QAM is shown here to be suitable for such applications. The performance of this scheme with decision feedback equalization is evaluated over a two-ray Rayleigh channel. Comparisons between the I-Q scheme with a conventional TCM scheme based on 8-PSK show coding gains of about 4 dB at a BER of 10/sup -3/.