Simulation And Experimental Research On Underwater Acoustic Channel For Long Range Shallow Water Communication

The important strategy of East China Sea(ECS) contributes to essential long range(>200km)communication across the seas. Characteristics of channel include time-varing, space-variationand frequency dispersion effect become more intensive when communication through long rangeshallow-water. Thus it is important to premastery the relevant parameters of the communicationchannel in order to design reliable telecommunication system. Modeling and experimentmeasures are studied in this thesis. Different credible channel models of the ECS correspondingto different combinations of various conditions, such as distribution of ocean tempreture andsalinity, sea windscales, and so on, were built in this paper. Reliable characteristics of theacoustic propagation were gained through calculating the above models. One method onestimating parameters of channel based on Fractional Fourier Transform is studied, whichexhibites low computional complexity, high precision and favorable stability. The main contentsof this dissertation are as follows:Firstly, the impact of signal frequency, depth of emitter and receiver on the acousticpropagation as well as the time expansion and frequency selectivity are investigated. Theoutcomes indicate that the variation of the acoustic field is inapparent if the sound speed isuniform, and the transmmsion loss decreases if the emitter and receiver are placed at a lowerdepth when the sound speed increase as the depth of water growing, while when the sound speeddiminished as the depth of water growing., the emitter and receiver depth gives contrast impacton the transimission loss.Secondly, the influence of some factors such as water temperature and salinity, sourcefrequency, depth of emmiter and receiver, ocean windscale and wave on ECS acousticpropagation was studied. Characteristics of ECS channels corresponding to differentcombinations of these factors were also analyzed both in time and frequency domain.Transmission loss of the above chnnels is about120dB，and the maxmal delay time is above100ms. The results would surpass150dB and150ms if it came to a terrible weather condition.Thirdly, the choosing principle of waveform, impulse width and period, and bandwidth ofchannel sounding signal are introduced according to the autocorrelation analysis of different signals and the specific request of measuring channel parameters. An estimation method basedon Fractional Fourier Transform of underwater acoustic channel involving Doppler shift ispresented. The influence of sample rate and signal-noise-ratio on this approach is also studied.The simulation results show that the proprosed method is efficient as its well stability, lowcomputional complexity and high accuracy.Lastly, the practicability of acquiring transmission loss and multipath delay-time bymodeling is verified via lake experiment at Moganshan. The average error of transmission lossbetween modeling results and measuring results is about1.65dB if the source frequency is800Hz and2.0dB while the source frequency is4kHz bellow1km. The estimation error ofmaximal delay time of500m acoustic channel is3.16%, while1010m is5.82%. The result showsthat it is possible and credible to obtain underwaeter acoustic communication channel parametersby building and then resolving a mathmatics model of the channel.