Opportunistic ARQ with bidirectional overhearing for reliable multihop underwater networking

As reliable data delivery over a long-range single-hop underwater acoustic link is considerably challenging due to severe channel impairments, multihop data transmission schemes over one or more relay nodes have been proposed. In this paper, we propose a data delivery scheme using a fully-opportunistic ARQ that employs bidirectional overhearing, whereby nodes leverage on the broadcast nature of acoustic channels and their spatial and temporal variance to overhear (i) data packets from all upstream (nearer to source) nodes to speed up data delivery and (ii) data & acknowledgement packets from all downstream (nearer to sink) nodes as implicit acknowledgements. The cross-layer scheme uses implicit acknowledgements to purge duplicates at both data-link and network layer. We demonstrate using simulations that, when implemented on an Interweaved TDMA MAC scheme, the proposed delivery scheme achieves better reliability, energy-efficiency and latency as compared to non-opportunistic or semi-opportunistic schemes in multihop underwater acoustic networks with linear topology. Over a 10-hop network, the proposed scheme outperforms its non-opportunistic counterpart, delivers 88% more packets, consumes 43% less energy and achieves an 8% improvement in latency (per packet delivered).