Differential decoding for SFBC OFDM systems in underwater MIMO channels

We investigate the use of differential space fre- quency block codes (SFBCs) with orthogonal frequency division multiplexing (OFDM) over underwater acoustic channels. While SFBC efficiently exploits spatial transmit diversity, differentially coherent detection eliminates the need for extensive signal pro- cessing required for channel tracking. System performance is demonstrated using real data transmitted in the 12 !26 kHz acoustic band from a vehicle moving at 0.5 !2 m/s and received over a 100 m shallow water channel, using 4-QAM and a varying number of carriers ranging from 128 to 2048. Performance results demonstrate the advantage of the differentially coherent SFBC detection over the conventional, coherent SFBC detection which suffers from imperfect channel estimation.