A multi-carrier spread-spectrum approach to broadband underwater acoustic communications

摘要

The paper presents a detailed Monte-Carlo simulation study of a nvel MC-CDMA system operating in the medium-range shallow underwater acoustic channel. The new system uses random phase signals to multiplex the data onto orthonal sub-carriers. The frame structure of the signal allows the random phase signal to be used for channel sounding and synchronisation. Carrier and frame synchronisation is achieved by exploiting the excellent auto-correlation property of the random phase signal and synchronisation is achieved in levels of noise down to-3dB SNR under conditions of limited Doppler. By adjusting the phases of the carriers, the `crest factor' of the transmitted signal can be optimsed. Spectrum spreading is used in conjunction with COFDM modulation to provide a flexible system that is able to maintain an acceptable BER in low SNR conditions by trading data rate for spread-spectrum process gain.