Opportunistic Collaborative Beamforming with One-Bit Feedback

An energy-efficient opportunistic collaborative beamformer with one-bit feedback is proposed for ad hoc sensor networks over Rayleigh fading channels. In contrast to conventional collaborative beamforming schemes in which each source node uses channel state information to correct its local carrier offset and channel phase, the proposed beamforming scheme opportunistically selects a subset of source nodes whose received signals combine in a quasi-coherent manner at the intended receiver. No local phase-precompensation is performed by the nodes in the opportunistic collaborative beamformer. As a result, each node requires only one-bit of feedback from the destination in order to determine if it should or shouldn't participate in the collaborative beamformer. Theoretical analysis shows that the received signal power obtained with the proposed beamforming scheme scales linearly with the number of available source nodes. Since the the optimal node selection rule requires an exhaustive search over all possible subsets of source nodes, two low-complexity selection algorithms are developed. Simulation results confirm the effectiveness of opportunistic collaborative beamforming with the low-complexity selection algorithms.Comment: Proceedings of the Ninth IEEE Workshop on Signal Processing Advances in Wireless Communications, Recife, Brazil, July 6-9, 200

Energy-Efficient and Overhead-Aware Cooperative Communications

Due to the rapid growth of energy-hungry wireless multimedia services, telecom energy consumption is increasing at an extraordinary rate. Besides negative environmental impacts and higher energy bills for operators, it also affects user experience as improvements in battery technologies have not kept up with increasing mobile energy demands. Therefore, how to increase the energy efficiency (EE) of wireless communications has gained a lot of attention recently. Cooperative communication, where relays cooperatively retransmit the received data from the source to the destination, is seen as a promising technique to increases EE. Nevertheless, it requires more overhead than direct communication that needs to be taken into account for practical wireless cooperative networks. In order to achieve potential energy savings promised by cooperative communications in practical systems, overhead-aware cooperative relaying schemes with low overhead are imperative. For the case that not all relays can hear each other, i.e., hidden relays exist, an energy-efficient and a low-overhead cooperative relaying scheme is proposed. This scheme selects a subset of relays before data transmission, through the proactive participation of available relays using their local timers. Theoretical analysis of average EE under maximum transmission power constraint, using practical data packet length, and taking account of the overhead for obtaining channel state information (CSI), relay selection, and cooperative beamforming, is performed and a closed-form approximate expression for the optimal position of relays is derived. Furthermore, the overhead of the proposed scheme and the impact of data packet lengths on EE, are analysed. The analytical and simulation results reveal that the proposed scheme is significantly more energy-efficient than direct transmission, best relay selection, all relay selection, and a state-of-the-art existing cooperative relaying scheme. Moreover, the proposed scheme reduces the overhead and achieves higher energy savings for larger data packets. The conventional cooperative beamforming schemes rely on the feedback of CSIs of the best relays from the destination, which cause extra energy consumption and are prone to quantization errors in practical systems. In the case of clustered relays with location awareness and timer-based relay selection, where relays can overhear the transmission and know the location of each other, an energy-efficient overhead-aware cooperative relaying scheme is proposed, making CSI feedback from the destination dispensable. In order to avoid possible collisions between relay transmissions during best relays selection, a distributed mechanism for the selected relays to appropriately insert guard intervals before their transmissions is proposed. Average EE of the proposed scheme considering the related overhead is analysed. Moreover, the impact of the number of available relays, the number of selected relays and the location of relay cluster on EE is studied. The simulation results indicate that the proposed cooperative relaying scheme achieves higher EE than direct communication, best relay selection, and all relay selection for relay clusters located close to the source. Independent of the relay cluster location, the proposed scheme exhibits significantly higher EE than an existing cooperative relaying scheme. Device-to-device (D2D) communication in cellular networks that enable direct transmissions between user equipments (UEs) is seen as a promising way to improve both EE and spectral efficiency (SE). If the source UE (SUE) and the destination UE (DUE) are far away from each other or if the channel between them is too weak for direct transmission, then two-hop D2D communications, where relay UEs (RUEs) forward the SUE's data packets to the DUE, can be used. An energy- and spectral-efficient optimal adaptive forwarding strategy (OAFS) for two-hop D2D communications is proposed. In a distributed manner, the OAFS adaptively chooses between the best relay forwarding (BRF) and the cooperative relay beamforming (CRB) with the optimal number of selected RUEs, depending on which of them provides the higher instantaneous EE. In order to reduce the computational complexity of relay selection, a low-complexity sub-optimal adaptive forwarding strategy (SAFS) is proposed that selects between the BRF and the CRB with two RUEs by comparing their instantaneous EE. Theoretical analysis of the average EE and SE for the proposed adaptive forwarding strategies is performed considering maximum transmission power constraints, circuit power consumption and the overhead for the acquisition of CSI, forwarding mode selection and cooperative beamforming. The theoretical and simulation results show that the proposed OAFS and SAFS exhibit significantly higher EE and SE than the BRF, CRB, direct D2D communications and conventional cellular communications. For short to moderate SUE-to-DUE distances, SAFS is almost as energy- and spectral-efficient as OAFS

Energy-Efficient and Low Signaling Overhead Cooperative Relaying With Proactive Relay Subset Selection

Energy efficient wireless communications have recently received much attention, due to the ever-increasing energy consumption of wireless communication systems. In this paper, we propose a new energy-efficient cooperative relaying scheme that selects a subset of relays before data transmission, through proactive participation of available relays using their local timers. We perform theoretical analysis of energy efficiency under maximum transmission power constraint, using practical data packet length, and taking account of the overhead for obtaining channel state information, relay selection, and cooperative beamforming. We provide the expression of average energy efficiency for the proposed scheme, and identify the optimal number and location of relays that maximise energy efficiency of the system. A closedform approximate expression for the optimal position of relays is derived. We also perform overhead analysis for the proposed scheme and study the impact of data packet lengths on energy efficiency. The analytical and simulation results reveal that the proposed scheme exhibits significantly higher energy efficiency as compared to direct transmission, best relay selection, all relay selection, and a state-of-the-art existing cooperative relaying scheme. Moreover, the proposed scheme reduces the signalling overhead and achieves higher energy savings for larger data packets

Adaptive Relay-Selection In Decode-And-Forward Cooperative Systems

In the past few years adaptive decode-and-forward cooperative diversity systems have been studied intensively in literature. Many schemes and protocols have been proposed to enhance the performance of the cooperative systems while trying to alleviate its drawbacks. One of the recent schemes that had been shown to give high improvements in performance is the best-relay selection scheme. In the best-relay selection scheme only one relaying nodes among the relays available in the system is selected to forward the source\u27s message to the destination. The best relay is selected as the relay node that can achieve the highest end-to-end signal-to-noise ratio (snr) at the destination node. Performance improvements have been reported as compared to regular fixed decode-and-forward relaying in which all relays are required to forward the source\u27s message to the destination in terms of spectral efficiency and diversity order. In this thesis, we use simulations to show the improvement in the outage performance of the best-relay selection scheme

A Study Of Cooperative Spectrum Sharing Schemes For Internet Of Things Systems

The Internet of Things (IoT) has gained much attention in recent years with the massive increase in the number of connected devices. Cognitive Machine-to-Machine (CM2M) communications is a hot research topic in which a cognitive dimension allows M2M networks to overcome the challenges of spectrum scarcity, interference, and green requirements. In this paper, we propose a Generalized Cooperative Spectrum Sharing (GCSS) scheme for M2M communication. Cooperation extends the coverage of wireless networks as well as increasing their throughput while reducing the energy consumption of the connected low power devices. We study the outage performance of the proposed GCSS scheme for M2M system and derive exact expressions for the outage probability. We also analyze the effect of varying transmission powers on the performance of the system

Proposed different relay selection schemes for improving the performance of cooperative wireless networks

Relay selection is a new method currently used to develop and improve cooperative wireless networks. One of the main advantages of this new technology is that it can achieve cooperative diversity gain without installing multiple antennas in the transmitter or receiver. Relay selection algorithms can be used to select one node to become a relay node from a set of N candidate relays with optimization criteria as the outage probability or frame error rate. The selection process is preferable to operate in a distributed fashion and offers only reasonable costs in terms of manufacturing complexity and flexible handling over wireless cooperative networks. In this work, different relay selection schemes are proposed to enhance the cooperative wireless networks in terms of different approaches including: 1) Relay selection-based destination feedback scheme, 2) Relay selection based a ready-to-send/clear-to-send (RTS/CTS) messages scheme, 3) Relay selection-based identification messages (IDM) table scheme, and 4) Relay selection-based relay power consuming scheme. The experimental results via suggested case study show that the performance of overall cooperative network is enhanced in terms of increasing throughput, energy saving (efficiency maximization), blocking reduction and outage reduction (PER minimization)

Splitting Algorithms for Fast Relay Selection: Generalizations, Analysis, and a Unified View

Relay selection for cooperative communications promises significant performance improvements, and is, therefore, attracting considerable attention. While several criteria have been proposed for selecting one or more relays, distributed mechanisms that perform the selection have received relatively less attention. In this paper, we develop a novel, yet simple, asymptotic analysis of a splitting-based multiple access selection algorithm to find the single best relay. The analysis leads to simpler and alternate expressions for the average number of slots required to find the best user. By introducing a new `contention load' parameter, the analysis shows that the parameter settings used in the existing literature can be improved upon. New and simple bounds are also derived. Furthermore, we propose a new algorithm that addresses the general problem of selecting the best $Q \ge 1$ relays, and analyze and optimize it. Even for a large number of relays, the algorithm selects the best two relays within 4.406 slots and the best three within 6.491 slots, on average. We also propose a new and simple scheme for the practically relevant case of discrete metrics. Altogether, our results develop a unifying perspective about the general problem of distributed selection in cooperative systems and several other multi-node systems.Comment: 20 pages, 7 figures, 1 table, Accepted for publication in IEEE Transactions on Wireless Communication

Security-reliability tradeoff analysis of artificial noise aided two-way opportunistic relay selection

In this paper, we investigate the physical-layer security of cooperative communications relying on multiple twoway relays using the decode-and-forward (DF) protocol in the presence of an eavesdropper, where the eavesdropper appears to tap the transmissions of both the source and of the relay. The design-tradeoff to be resolved is that the throughput is improved by invoking two-way relaying, but the secrecy of wireless transmissions may be degraded, since the eavesdropper may overhear the signals transmitted by both the source and relay nodes. We conceive an artificial noise aided two-way opportunistic relay selection (ANaTWORS) scheme for enhancing the security of the pair of source nodes communicating with the assistance of multiple two-way relays. Furthermore, we analyze both the outage probability and intercept probability of the proposed ANaTWORS scheme, where the security and reliability are characterized in terms of the intercept probability and the security outage probability. For comparison, we also provide the security-reliability tradeoff (SRT) analysis of both the traditional direct transmission and of the one-way relaying schemes. It is shown that the proposed ANaTWORS scheme outperforms both the conventional direct transmission and the one-way relay methods in terms of its SRTs. More specifically, in the low main-userto- eavesdropper ratio (MUER) region, the proposed ANaTWORS scheme is capable of guaranteeing secure transmissions, whereas no SRT gain is achieved by the conventional one-way relaying. In fact, the one-way relaying scheme may even be inferior to the traditional direct transmission scheme in terms of its SRT