This paper presents a new cooperative ARQ protocol for a hybrid mobile wireless sensor network. The mobile relay nodes decode the signal from the source sensor using cyclic redundancy check (CRC) and forward it to the destination sink. A distributed relay selection that exploits overhearing of inter-relay node transmission is employed to achieve higher selection diversity gain during retransmissions. Upon reception from the source sensor, the number of relay nodes available to contend for transmission depends on the conditions of source-relay channels. When source-relay channels are instantaneously poor, achievable selection diversity gain decreases. 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 the error-free selected relay. By combining the initially received erroneous signals with the signal overheard from the selected relay and decoding again, erroneous relays may be able to decode the signals successfully thanks to the spatial diversity. This results in an increase in relay availability for distributed selection in subsequent retransmissions. It is also shown that the selection protocol based on end to end channel quality approach cannot make full use of the increased relay availability. The proposed cooperative ARQ protocol ensures to make full use of the increased relay availability. The numerical results show that the proposed cooperative ARQ significantly improves the successful packet arrival rate.
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