A comparative evaluation of joint versus sequential demodulation of spatially modulated underwater acoustic telemetry signals

Spatial modulation over multiple-input/multiple-output (MIMO) communication channels has been a rich area of research for terrestrial wireless communication and, more recently, underwater acoustic communication. By appropriately including spatial as well as temporal degrees of freedom in the signal design, it has been shown that one can potentially achieve significant capacity gains, reduce power requirements, and increase spectral efficiency. The benefits are analogous to having additional bandwidth and, as such, are well suited for bandwidth-limited conditions, as opposed to power-limited conditions. Spatial modulation uses separate, resolvable propagation paths between a transmitter and receiver array as parallel communication channels and, as such, requires both availability of arrays at both ends of the link and a propagation channel with some level of multipath. The combination of rich, complex reverberation and the inherent bandwidth limitations of the underwater acoustic telemetry channel make it well suited for application of spatial modulation techniques.