UW communication system design for severely dispersed channels

The shallow underwater acoustic environment provides a particularly hostile communications channel exhibiting severe time, frequency and angular selectivity. Latest developments indicate the feasibility of fully coherent, bandwidth efficient modulation schemes using single carrier modulation (SCM) techniques in conjunction with powerful time domain equalisation to provide reliable communications over such channels. Whilst proven statically, there are few reported results demonstrating the capability of this technology for high Doppler platforms in such environments. This paper considers the suitability of time domain adaptive equalisers for a shallow water, high Doppler environment. It is concluded that the time adaptive approach is constrained by the severe time spreads (hundreds of symbols) and differential Doppler temporal scaling experienced in the shallow water channel at high platform speeds. Under such circumstances spatially coherent processing is favoured as a means of containing the ray differential Doppler problem