Energy-efficient mobile data collection adopting node cooperation in an underwater acoustic sensor network

This paper considers an underwater acoustic sensor network with one mobile surface node to collect data from multiple underwater nodes, where the mobile destination requests retransmission from each underwater node individually employing traditional automatic-repeat-request (ARQ) protocol. We propose a practical node cooperation (NC) protocol to enhance the collection efficiency, utilizing the fact that underwater nodes can overhear the transmission of others. To reduce the source level of underwater nodes, the underwater data collection area is divided into several sub-zones, and in each sub-zone, the mobile surface node adopting the NC protocol could switch adaptively between selective relay cooperation (SRC) and dynamic network coded cooperation (DNC). The difference of SRC and DNC lies in whether or not the selected relay node combines the local data and the data overheard from undecoded node(s) to form network coded packets in the retransmission phase. The NC protocol could also be applied across the sub-zones due to the wiretap property. In addition, we investigate the effects of different mobile collection paths, collection area division and cooperative zone design for energy saving. The numerical results show that the proposed NC protocol can effectively save energy compared with the traditional ARQ scheme.