Performance Analysis of LDPC Codes over Shallow Water Acoustic Channels

The major obstacle to shallow water acoustic communication is the interference of multipath signal results from surface and bottom reflections. Channel coding is indispensable in practical system to accommodate these adverse channel transmission characteristics due to the coding gain. In this paper, a channel model including time-varying fading, multipath and additive noise for the shallow water acoustic channels is built. Based on the channel model, the Probability Density Function (PDF) of initial decoding messages with Belief Propagation (BP) algorithm of LowDensity Parity-Check (LDPC) codes is deduced. The performance of the LDPC codes with BP algorithm is simulated, and the effects of multipath, fading velocity and channel interleaver on the decoding performance are studied. As the result, the following conclusions can be given: The performance of LDPC codes is excellent (Bit Error Rate (BER) is less than 10^-4) over three-multipath shallow water acoustic channels, with 3~5 iterative decoding times and about 1000 bits code lengths; The BER of LDPC codes degrades with the increasing of the number of multipath; The BER of LDPC codes degrades slowly with the decreasing of the fading velocity, which shows the proposed channel code is not sensitive to the fading velocity of the channel.