DS/CDMA throughput of a multi-hop sensor network in a Rayleigh fading underwater acoustic channel

Asynchronous half-duplex Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a suitable candidate for the MAC protocol design of underwater acoustic (UWA) sensor networks owing to its many attractive features. Our ad-hoc multi-hop network is infrastructureless in that it is without centralized base stations or power control. Hence, we develop an asynchronous distributed half-duplex control protocol to regulate between the transmitting and receiving phases of transmissions. Furthermore, multi-hop communications are very sensitive to the time variability of the received signal strength in the fading channel and the ambient noise dominated by snapping shrimp in harsh underwater environments, because a broken link in the multi-hop path is enough to disrupt communications and initiate new route searches. In our configuration, we use the Ad hoc On-demand Distance Vector (AODV) routing protocol optimized for UWA networks. Empirical studies show that we can model the channel as a slow-varying frequency non-selective Rayleigh fading channel. We theoretically analyze the throughput of our configuration by considering three salient features: the ability of the receiver to demodulate the data, the effect of our control protocol and the effect of disconnections on the generation of routing packets. The throughput under various operating conditions is then examined. It is observed that at optimal node separation, the throughput is improved by a factor of 10. Copyright (C) 2007 John Wiley & Sons, Ltd.