Distributed Space-Time Cooperative Schemes for Underwater Acoustic Communications

In resource limited, large scale underwater sensor networks, cooperative communication over multiple hops offers opportunities to save power. Intermediate nodes between source and destination act as cooperative relays. Herein, protocols coupled with space-time block code (STBC) strategies are proposed and analyzed for distributed cooperative communication. Amplify-and-forward type protocols are considered, in which intermediate relays do not attempt to decode the information. The Alamouti-based cooperative scheme for flat-fading channels is modified in order work in the presence of multipath, which is a main characteristic of underwater acoustic channels. A time-reversal distributed space-time block code (TR-DSTBC) is employed, which extends the classical TR-STBC approach to a cooperative communication scenario. We show that, just like in the multi-antenna STBC case, TR along with the orthogonality of the DSTBC essentially allows for decoupling of the vector ISI detection problem into separate scalar problems, and therefore significant complexity reduction.