Adaptive MIMO detection of OFDM signals in an underwater acoustic channel

Frequency and time correlation of the underwater channel are exploited to obtain an adaptive channel estimation algorithm for MIMO spatial multiplexing with low complexity and low overhead. Non-uniform Doppler compensation is performed by extending the adaptive synchronization method to multiple transmitters. Algorithm performance is demonstrated on experimental data recorded in several shallow water channels over distances on the order of 1 km. Nearly error-free performance is observed for two and four transmitters with BCH(64,10) encoded QPSK signals. We report in detail on an experiment where an information rate of 23 kbps (4 transmitters times 0.75 sps/Hz/transmitter times 2 bits/symbol times 10/64 times 24 kHz) is achieved using 2048 carriers in a 24 kHz bandwidth.