The performance of multi-hop underwater acoustic network is known to be limited by the long propagation delays and by the limited bandwidth of the underwater acoustic (UW-A) channel. Recent work on analog network coding (ANC) has shown that significant throughput gains can be achieved in multi-hop wireless networks. However, implementing ANC for UW-A communications is very challenging as the UW-A channel is severely affected by multipath. In this paper, we propose CE-CDMA, a collision-enabling

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... irect-sequence code-division multiple-access scheme for multi-hop underwater acoustic sensor networks (UW-ASNs). In CE-CDMA two nodes, separated by two hops, are assigned the same code-division channel (i.e., spreading code) to communicate concurrently. The transmission of packets by the two nodes will therefore collide at the intermediate (relay) node. However, we show that by exploiting a priori information, i.e., the interfered packet previously received from one of the nodes, and an adaptive RAKE receiver that jointly estimates the two multipath-affected channels, the relay node can cancel the interference before decoding the packet of interest. Experiments demonstrate that for a 1 − 2 dB tradeoff in signal-to-noise ratio (SNR) the proposed scheme can potentially improve the channel utilization of a unidirectional multi-hop linear network by up to 50 %. We also outline the basic functionalities of a MAC protocol (CE-MAC) designed to support the proposed scheme.