Space-time block coding for undersea acoustic links

Abstract

Current research in undersea communication scenario focuses on the applications of undersea acoustic networks in environmental data collection, pollution monitoring, offshore surveillance, coastal surveillance, etc. The various constraints encountered in undersea acoustic communications are mainly low bandwidth, high latency, high failure rates of acoustic links, and multipath propagation effects. Multipath effects in undersea environments are due to the reflection of sound by the sea surface and sea bottom as well as refraction of sound in water. As a result, the receiver gets a bewildering mix of signals. The receiving subsystems of the undersea networks perform special signal processing techniques for regenerating the data streams from the multipath composite signals in a MIMO configurable network. The performance of Space-Time Block Coding (STBC) diversity technique has been adopted in this paper for improving the reliability of the undersea network. In the simplest form of MIMO configuration, two transmitting transducers send out the data stream and its modified versions in two time slots on independently fading environments, leading to substantial improvements in the error rate performance. For a shallow water medium range channel, which exhibits the Rayleigh fading characteristics, the error rate performance has been found to be 7 x 10-6 for 16-QAM based STBC.