Threshold Based Relay Selection in Cooperative Wireless Networks

Abstract

Abstract-This paper considers two-hop cooperative relaying using multiple relays and proposes a threshold based relay selection protocol. In this protocol the relays are selected among those having received SNR higher than a threshold value. The relay selection is performed by the destination based on the received SNRs at the destination during the last hop. The exact bit error rate of this protocol is derived and it is shown that it achieves full diversity order. Unlike some other full diversity achieving protocols in the literature, the requirement that the exact/average SNRs of the source-relay links be known at the destination is eliminated using an appropriate SNR threshold. I. INTRODUCTIONCooperative relaying can induce spatial diversity in wireless networks without any reliance on multiple antennas. Various decode-and-forward protocols have been proposed based on selective relaying, distributed space-time coding and relay selection, and have been shown to achieve full diversity [1]- [3]. Recently, detection aspects of cooperative relaying have been analyzed [4]-[8]. These works study digital (or demodulate-and-forward) cooperative relaying protocols, in which the relaying does not rely on any error correction or detection codes. Such protocols are particularly attractive for wireless sensor networks, for which coded transmission can be costly due to severe energy limitations.Unlike ideal decode-and-forward relaying, in digital relaying the relays can forward erroneous information, and with a conventional combining scheme such as Maximal Ratio Combining (MRC), these errors propagate to the destination, causing end-to-end (e2e) detection errors. Existing techniques for mitigating error propagation can be classified into two groups. The first of these comprises selective and adaptive relaying techniques, which include link adaptive relaying (LAR) [4], [5] and threshold digital relaying (TDR) [9]-[11]. Both techniques use link SNRs to evaluate the reliability of the data received by the relay. In TDR a relay forwards the received data only when its received SNR is above a threshold value. In LAR the relay transmits with a fraction α of its maximum transmit power, where α depends on the source-relay and relay-destination SNRs. In [4], a function for calculating α

One-Bit CSI Feedback Selection Schemes for Energy-Efficient Multiuser and Multirelay Systems

“…We consider centralized and distributed selection schemes under limited feedback. Compared to previous works [19], [21]- [23], [25]- [27], the schemes are not based on best SNR selection, and only one bit of CSI feedback is required for performing the selection. In addition, selection schemes for which outage performance is traded off against extra energy savings and/or reduced complexity and feedback are investigated.…”

“…Relay selection is then performed by exploiting the CSI from the second hop. In [25]- [27], only the relay having the highest signal-to-noise ratio (SNR) among reliable relays 1536-1276/12$31.00 © 2012 IEEE is selected for transmission to achieve cooperative diversity while limiting bandwidth expansion. In [29], selection methods employing limited feedback are proposed along with a diversity-multiplexing trade-off analysis.…”

“…Numerous relay selection schemes have been proposed that utilize AF and DF protocols [19]- [27]. The system models considered can be classified into: 1) point-to-point with multiple relays applicable to static mesh networks of access points [25], and 2) point-to-multipoint with multipleuser access which models cellular systems and other startopology networks such as sensor networks in IEEE 802.…”

“…15.4 in a nonbeaconing mode [28]. Most selection schemes have been designed for point-to-point systems including [24]- [27], [29] that employ DF relaying. These schemes select one among a set of reliable relays, that are grouped according to likelihood of success in cooperative transmission, e.g.…”

Cooperative Beamforming for Two-Hop Multi-Relay Decode-and-Forward Networks

“…Selection relaying is an alternative for optimal or near-optimal detectors (cooperative maximal ratio combiner for example) [20]. However, proper selection of the threshold plays a key role in the performance of cooperative systems based on selection relaying [21], [22]. A novel decoding algorithm for a cooperative decode-and-forward beamforming system that takes the potential errors in forwarded signals into account in the computation of the likelihood ratio of coded bits is proposed in [23].…”