Asynchronous cooperative transmission for three-dimensional underwater acoustic networks

Although the techniques of cooperative transmission have been developed for terrestrial sensor networks in recent years to improve the bit-error-rate (BER) performance, the unique characteristics of the underwater acoustic communication channel, such as large and variable propagation delay and the three-dimensional network topology, make it necessary to reconsider the implementation and analysis of cooperative transmission in underwater acoustic networks. In this study, two asynchronous forwarding schemes, namely underwater amplify-and-forward (UAF) and underwater decode-and-forward (UDF), are proposed. Although the fading model for underwater channel is complex and there is still no consensus in the research community on a model which is applicable for all underwater channels, the authors simulation results show that both UDF and UAF have better performance than direct transmission under different underwater channel configurations, and there is a breathing effect for BER performance improvement caused by underwater multi-path fading. Finally, some insights on choosing the proper parameters to improve performance of underwater cooperative transmission are provided.