An Improved Zero-Forcing Detection Algorithm of Spread OFDM for Underwater Acoustic Communications

The so-called spread OFDM(S-OFDM) system is designed to resist frequency-dependent attenuation by using Walsh-Hadamard (WH) code for spreading the frequency-domain OFDM symbols in the transmitter, and linear detectors, like ZF or MMSE, are usually used to recover the signals in the receiver. In this paper, an improved ZF detection algorithm is proposed for reducing the problem of amplifying noise compared with common ZF algorithm for spread OFDM in underwater acoustic channels. In contrast to the MMSE, the proposed algorithm dose not require estimating the variance of noise. Simulation results show that the proposed ZF algorithm has much better performance than that of common ZF method in all SNR range. Even if compared with MMSE, the proposed algorithm also gets much performance gain in high SNR range. Keywords-OFDM; underwater acoustic communication; Walsh-Hadamard (WH); zero force; minimum mean square error