Performance of Orthogonal Wireless Relay Networks with Multiple SNR-Thresholds and Multiple Hard-Decision Detections

This paper investigates the diversity performance of wireless relay networks with multiple parallel relays communicating with the destination over orthogonal channels. The networks under consideration employ two signal-to-noise ratio (SNR) thresholds and multiple hard-decision detections (HDD) at the destination. One SNR threshold is used to select transmitting relays in the second phase: a relay retransmits to the destination if its received SNR is larger than the threshold, otherwise, it remains silent. The other threshold is used at the destination for detection: the destination makes a hard decision on the received signal from a relay if its SNR is higher than the threshold, otherwise, the destination makes an erasure decision. Then the destination simply combines all the hard-decision results and makes the final binary decision based on majority voting. Focusing on the decode-and-forward (DF) relaying protocol, the paper derives the end-to-end bit error and outage probabilities, and presents the diversity analysis of the proposed method. It is shown that the full diversity order can be achieved by setting appropriate thresholds even when the destination does not know the exact or average SNRs of the source-relay links. The diversity analysis is further extended to multi-hop cooperation and/or with the presence of a direct link where multiple thresholds are needed.