Abstract

A direct spread spectrum (DSS) communication system is presented, which uses optimized spread spectrum sequence (SSS) and adaptive soft-iteration (Turbo) equalization (ASIE). The scheme using multiple receiver is similar to MIMO systems. The average cross-correlation of SSS is regarded as a critical factor to search optimized sequences used in under water acoustic (UWA) multi-access burst communication. The comparison of performance between optimized sequence and Gold sequence is presented. More importantly, a low-complexity Turbo equalization is used to eliminate severe inter-symbol interference (ISI) and multi-access interference (MAI). By combing with DSS system, the enhanced system is able to realize communications with higher transmitting speed in highly dispersive channels. The presented equalization utilizes least mean square (LMS) algorithm to decrease the computational complexity and isolates embedded phase-locked loop (PLL) to track the changing phase caused by Doppler. The performance of enhanced Turbo equalization has been verified through both simulation and experimental data.

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