Performance Analysis of IRA Codes for Underwater Acoustic OFDM Communication System

Recently, multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been actively investigated in underwater acoustic communications for its effective algorithms to handle the channel time-variability. In order to improve the performance of the underwater acoustic OFDM communication system, the irregular repeat accumulate (IRA) code as a channel coding scheme is proposed in this paper. We analyzed the effect of parameters of the IRA code on the performance of the system. Computer simulation has been implemented and the sea trial has been carried out in shallow water acoustic channels near Xiamen port. The simulation results show that the IRA coding scheme has improved the SNR (signal noise ratio) performance of the system at range of 14 dB to 16 dB compared with the system without coding and the BER performance of the IRA code will get improvement with the increase of the code length and the iteration of decoding to a certain degree, and then tends to stable. Field test experiment results obtained with the IRA code are provided, demonstrating the feasibility of the proposed channel coding for underwater acoustic OFDM communication system.