An adaptive, soft-decision multiuser receiver for underwater acoustical channels

A technique for resolving the collision of inband and asynchronous packets, with the goal of demodulating both strong and weak signals within a fixed amount of time, is presented. The particular case of coherent, binary phase shift keying (BPSK) for each data packet is discussed. The transmitting waveforms are assumed to be known by the central receiver for all modems, but the amplitude, Doppler, fine synchronization, and phase are a priori unknown and slowly time-varying. It is shown that the proposed technique wastes far less signal energy for a given user to combat interference than algorithms of similar (linear) complexity and decoding delay and approaches the performance of dynamic programming detectors with unbounded demodulation delay and exponential complexity. The effectiveness of this scheme is demonstrated using an example in which a collision is resolved between two independent acoustic telemetry systems operating simultaneously in the same frequency band