Cooperative ARQ using distributed relay selection and inter-relay opportunistic listening

This paper presents a new cooperative ARQ with a distributed relay selection that exploits overhearing of inter-relay channels to achieve higher diversity during retransmission. The relays employ decode and forward (DF) to establish the link between the source and the destination. Upon reception from the source, the number of relays available to contend for transmission depends on the conditions of source-relay channels. Such relay availability dependency over source-relay channels can be reduced if erroneous relays exploit inter-relay channels to opportunistically listen (OL) to the transmission of a relay that has no errors. By combining the erroneous signals received from the source with the same signal overheard from the error-free relay and decoding again, the relays originally with errors may be able to decode the signals successfully. This results in an increase in relay availability to contend for transmission in subsequent retransmissions. A new selection protocol that can make full use of the increased relay availability is also considered. It is shown that the selection protocol based on end to end channel quality approach is not optimal for the proposed cooperative ARQ. Our protocol considers only relay-destination channels. The performance of the proposed relay system is verified by both theoretical analysis and simulations. The numerical results show that the proposed cooperative ARQ is very effective in improving successful packet arrival rate.