| In the recent years, there has been a growing interest in the underwater acoustic (UWA) communication in various application areas such as telemetry, remote control, speech or image transmission. Because a large class of UWA channels can be characterized as rapidly varying time, frequency, space dispersive channels. The rate of transmission is low, and the efficiency of bandwidth is limited, and intersymbol interference is high.Recently Land Mobile Communication System has made great technical progress, A great deal of new communication techniques, such as digital modulation and demodulation techniques, spread spectrum, is used successfully to resolve and combat the ISI. And the successful application of these techniques in UMA communication depends on characteristics of UWA channelAt present, large amount of sonar with great array on our warship is multichannel structure, in the paper we will take advantage of the structure to realize multichannel diversity and equalization and reduce ISI in the UWA communication. It has already been applied in engineering practice and good results obtained.A theoretically optimal multichannel receiver for intersymbol interference communication channels is derived, and its suboptimal versions with linear and decision feedback equalizer are presented. A practical receiver based on any of these structures encounters difficulties in the underwater acoustic channels in which the extended time varying multipath is accompanied by phase instabilities. A receiver which overcomes these problems by jointly performing adaptive mean squared error diversity combining, multichannel carrier phase synchronization and decision feedback equalization is proposed. Its performance is demonstrated on the experimental telemetry data from deep and shallow water long range acoustic channels. Presented results indicate superior quality of coherent PSK and QAM reception obtained through joint equalization of very few channels.
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