Chapter 24 Constant Modulus Blind Equalization Algorithm for Multi-Carrier Combining of Digital Phase-Locked Loop and Pilot Sequence

摘要

Due to the characteristics of frequency division multiplexing (OFDM) system providing a higher rate of transmission, a new blind equalization algorithm based on an OFDM system for underwater acoustic channel is proposed. In this proposed algorithm, the frequency domain response of channel is simply estimated by a pilot sequence firstly, then the multi-carrier system is equivalent to multiple parallel independent single-carrier system, and the received signal of each subcarrier is equalized by single-tap constant modulus algorithm (ST-CMA). As the constant modulus algorithm is not sensitive to phase information, a digital phase-locked loop (DPLL) technology is used to overcome a constellation offset caused by the equivalent channel on each subcarrier. The computer simulation in underwater acoustic channel shows that the performance of the proposed ST-CMA + DPLL outperforms the constant modulus algorithm within the direct modulation of the single-carrier system.