Turbo array receiver for underwater telemetry

We describe a novel, turbo-based array receiver architecture for underwater channels with large delay-Doppler spreading. We demonstrate performance on data from an underwater BPSK telemetry experiment with rapid fading, and on simulated data extended to MPSK. Compared to a classical decision-directed LS-MMSE receiver of comparable observation and filter sizes, our proposed algorithm shows dramatically improved performance. The architecture is built around a block-based multi-channel linear model that considers deterministic time-invariant (TIV) multipath and random fading. Symbol estimates are decomposed by approximated conditional mean and variance components to reflect varying degrees of uncertainty. By approximating TIV coefficients with previous estimates, observation components due to symbol uncertainty conform to a linear model. The turbo cycle refines estimates for both predicted symbols and multipath parameters, effectively mitigating decision delay in rapidly time-varying channels with large delay spread. Our presentation includes a practical and robust computation approach, essential for problems of this size.