Abstract:

For orthogonal frequency division multiplexing (OFDM) signal transmission over underwater acoustic channel, the subcarrier orthogonality is quite easily destroyed by the time varying characteristic of underwater environment, which will cause great inter carrier interference, and increase the bit error ratio of the underwater acoustic communication system. An adaptive underwater acoustic OFDM equalization algorithm is proposed, which adopts adaptive joint time frequency combination of the two dimension spectrum of the received signal obtained by a sliding window based subblock short time Fourier transform (STFT). The adaptive equalization algorithm is implemented by adaptively tracking the time varying channel characteristic by least mean square (LMS) method, then adaptively combine the time frequency sequences with the coefficients updated by adaptive decision feedback equalization. Simulation results show that the proposed OFDM equalization method over time varying channel can decrease the bit error ratio of the underwater acoustic communication effectively.