Study On Underwater Acoustic Communication Technique Between Mobile Platforms

This paper aims to develop mobile underwater acoustic communication (UWA)techniques under large Doppler conditions. So the paper is composed of the following fourareas of research. When designing the receiver the impacts of mobile UWA channelcharacteristics have to be considered. The design of corresponding waveform andprocessing structure must accord to the characteristics of mobile UWA channel in order toobtain better communication performance.First the paper analyzed the structure of the mobile UWA channel as well as theimpacts on the communication signal which lay the foundation for subsequent study. Thenthe energy and waveform conversion which UWA channel brings to the signal have beenstudied. The multi-path coherent channel model has been introduced and mobile UWAchannel’s time-varying characteristics are analyzed. Doppler effects are introduced intoUWA channel.Second the estimate of the Doppler effects in mobile UWA has been studied. Thepaper uses the fractional Fourier transform to estimate chirp rate change of LFM signal toget the Doppler coefficient. And the estimate performance is compared with other methods.Then the pattern time delay shift coding (PDS) UWA communication technique hasbeen studied. A differential pattern time delay shift coding (DPDS) UWA communicationtechnique with a non-fixed code width based on the PDS has been proposed. Theinformation is carried by the time delay between adjacent code elements. The DPDSsystem has the ability to anti inter-symbol interference (ISI) and Doppler effects. Thecomputer simulation and lake tests proved that the DPDS system can improve thecommunication rate, inhibit the ISI caused by the multi-path channel and anti the Dopplereffects. It is proved that the system has an effectiveness and robustness.At last the direct-sequence spread spectrum UWA communication technique has beenstudied. And the direct-sequence differential phase-shift keying underwater acousticcommunication technique based on differential coherent demodulation is proposed.Differential coherent demodulation is adopted at the receiver to overcome the difficulty ofestimating the carrier in UWA communication and overcome the frequency and phase errorresulting from carrier frequency drift. Anti-multipath, anti-Doppler, low-error-rate,effective and robust features of the system for a complex underwater acoustic channel wereverified in a lake experiment.