Symbol Duration and Adaptive Guard Length for Underwater Acoustic OFDM Systems

Abstract

This paper focuses on determining the appropriate symbol duration and adaptive guard length for the orthogonal frequency-division multiplexing (OFDM) system using the channel modeling which is derived from the measurement data of the real underwater acoustic (UWA) channel. Especially, the guard length is not fixed as conventional UWA-OFDM systems but adapted to the SNR of the UWA-OFDM system which helps reduce losses in signal energy and spectral efficiency caused by adding guard length. The system has been investigated for different lengths of not only the symbol duration but also the guard length time. For the given system bandwidth of 8 kHz of the considered UWA-OFDM system, the optimal number of subcarriers is specified as 1024 that means the symbol duration of 128 ms. The results of guard length determination are G of 50, 150, 250, and 268 for the SNRs of 20 dB, 25 dB, 30 dB, and 35 dB, respectively. It can be seen that the lower level of SNR is, the shorter length of CP is.These optimal results of symbol duration and guard length are useful for improvements in UWA-OFDM system capacity and performance.