Space-time block coding MIMO system for underwater acoustic communications

To improve the channel capacity, a new Alamouti space-time block coding (STBC) multiple-input multiple-output (MIMO) system was employed for underwater communications. To cope with frequency selective fading caused by intersymbol interference (ISI), a MIMO decision feedback equalizer (DFE) was used to change the channel into a frequency non-selective one, which was jointly optimized with a second order phase-locked loop (PLL) to compensate the carrier phase shift. Then maximum likelihood decoding can be implemented to decouple the signal transmitted from different antennas. Simulation results show that the proposed system is effective. Comparing with single-input single-output (SISO) system and space-time trellis codes (STTC) MIMO system show that both MIMO systems have twice fold spectral efficiency and lower bit error rate than SISO. The bit error rate performance of STBC is worse than STTC but the computational complexity of STBC is much lower than STTC.