Threshold-Based Relay Selection for Detect-and-Forward Relaying in Cooperative Wireless Networks

EURASIP Journal on Wireless Communications and Networking, May 2010

This paper studies two-hop cooperative demodulate-and-forward relaying using multiple relays in wireless networks. A threshold based relay selection scheme is considered, in which the reliable relays are determined by comparing source-relay SNR to a threshold, and one of the reliable relays is selected by the destination based on relay-destination SNR. The exact bit error rate of this scheme is derived, and a simple threshold function is proposed. It is shown that the network achieves full diversity order ( ) under the proposed threshold, where is the number of relays in the network. Unlike some other full diversity achieving protocols in the literature, the requirement that the instantaneous/average SNRs of the source-relay links be known at the destination is eliminated using the appropriate SNR threshold.

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Threshold-Based Relay Selection for Detect-and-Forward Relaying in Cooperative Wireless Networks

EURASIP Journal on Wireless Communications and Networking Hindawi Publishing Corporation Threshold-Based Relay Selection for Detect-and-Forward Relaying in Cooperative Wireless Networks Furuzan Atay Onat 1 2 Yijia Fan 0 Halim Yanikomeroglu 2 H. Vincent Poor 0 George Karagiannidis 0 Department of Electrical Engineering, Princeton University , Princeton, NJ 08544 , USA 1 ASELSAN Inc. , 06172 Ankara , Turkey 2 Department of Systems and Computer Engineering, Carleton University , Ottawa, ON , Canada K1S 5B6 This paper studies two-hop cooperative demodulate-and-forward relaying using multiple relays in wireless networks. A threshold based relay selection scheme is considered, in which the reliable relays are determined by comparing source-relay SNR to a threshold, and one of the reliable relays is selected by the destination based on relay-destination SNR. The exact bit error rate of this scheme is derived, and a simple threshold function is proposed. It is shown that the network achieves full diversity order (N + 1) under the proposed threshold, where N is the number of relays in the network. Unlike some other full diversity achieving protocols in the literature, the requirement that the instantaneous/average SNRs of the source-relay links be known at the destination is eliminated using the appropriate SNR threshold. - 1. Introduction 1.1. Background. Cooperative relaying can induce spatial diversity in wireless networks without the need for multiple antennas on a single terminal. Various decode-andforward protocols have been proposed based on selective relaying, distributed space-time coding, and relay selection and have been shown to achieve full diversity [ 1–5 ]. Recently, detection aspects of cooperative relaying have been analyzed [ 5–10 ]. These works study the detect-and-forward (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 systems that do not use error detection/correction codes due to tight energy constraints. One possible application is sensor networks, which typically function under extremely limited battery-supplied energy. Most coding schemes can consume significant energy, and thus their use reduces sensor and network lifetime if each relay decodes the data. Moreover, the messages transmitted in sensor networks are usually very short while coding is usually efficient only for long messages. Another relaying scheme that does not rely on any error correction or detection is the amplify-and-forward protocol, in which the relay amplifies and forwards the received waveforms to the destination. The main disadvantage of this scheme is noise amplification, which cannot be avoided due to the physical presence of the thermal noise at the relay receiver. The focus of this paper is on detect-and-forward relaying. 1.2. Related Work. The detect-and-forward protocol has the well-known disadvantage of error propagation. Unlike in ideal decode-and-forward relaying, in detect-and-forward 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) [ 6 ] and threshold digital relaying (TDR) [ 11– 13 ]. 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 [ 6 ], a function for calculating α is provided, and the resulting scheme is shown to achieve full diversity if the relays are capable of adjusting their transmit powers continuously. However, the proposed function cannot provide diversity if reduced to two power levels, that is, on/off power adaptation. TDR can also be viewed as on/off power adaptation, and it is shown in [ 13 ] that it can achieve full diversity in the single relay case. In [ 5 ], a relay selection scheme similar to ours is studied. In this paper an approximate expression for bit error probability is derived as a function of relay threshold assuming that MRC is performed at the destination. It is observed that the performance of threshold based relay selection is sensitive to the value of threshold. The second approach to mitigate error propagation is to develop better combining schemes for the destination. These schemes take the possibility of error propagation into account and require the relays to send their sourcerelay link SNRs (average or instantaneous) to the destination. In [ 8 ], Wang et al. ass (...truncated)


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Furuzan Atay Onat, Yijia Fan. Threshold-Based Relay Selection for Detect-and-Forward Relaying in Cooperative Wireless Networks, EURASIP Journal on Wireless Communications and Networking, 2010, pp. 721492, Volume 2010, Issue 1, DOI: 10.1155/2010/721492