Differential spatial modulated OFDM in underwater acoustic communications

Underwater acoustic (UWA) communication channel features relatively fast time variation. Spatial modulation (SM) combined with orthogonal frequency division multiplexing (OFDM) transmission can be applied to UWA communications. Channel estimation may induce a performance penalty for SM since only one transmit antenna is activated to carry pilots. Recently, a differential solution has been proposed for SM, which dispenses with channel estimation and restricts the signal-to-noise (SNR) loss to a relatively low level under quasi-static channel conditions. Hence, the application of differential SM (DSM) to OFDM UWA communications is of particular interest. Simulation results show that when applied to UWA communications, DSM has an obvious performance enhancement in bit error rate (BER) over SM.