Bidirectional blind equalization based on the constant modulus and subspace-based algorithms

A bidirectional blind equalization based on the constant modulus algorithm (CMA) and subspace-based algorithm (SBA) is proposed in this paper. Without any training sequence or channel estimation, blind equalization improves the transmission efficiency significantly in underwater acoustic communications. The combining scheme in which two outputs run in opposite directions exploits the diversity and suppresses the error propagation. Moreover, a single-input multiple-output (SIMO) system is adopted in the algorithm to obtain the multiple receivers diversity gain and achieves a much better performance. The simulation results demonstrate that the proposed bidirectional CMA shows much better performance in a high SNR than that in a low SNR, and the bidirectional SBA outperforms the conventional method by approximately 2dB in BPSK system and 2.5dB in QPSK system.