Underwater Acoustic Channel Simulation And Application Based On Propagation Model

Due to the presence of surface and floor, the shallow water acoustic channel is a strongmultipath channel. When many signal processing techniques of radio communication wereintroduced to underwater acoustics, the results were less than ideal. In order to improve thesonar system performance in the multipath channel, further studies on underwater acousticchannel properties are necessary.The underwater acoustic channel simulation technique is a method to simulate the actualchannel characteristics in the laboratory. Because the environmental parameters are easy tocontrol, channel simulation is important to study on the signal processing performance inmultipath channel. In this paper, based on the physical model of sound propagation, theunderwater acoustic channel simulation techniques are studied. And the channel simulationresults are applied to source localization and signal detection.The sound propagation model is the mathematical basis of underwater acoustic channelsimulation. The classical channel simulation techniques always focus on the macroscopicproperties such as transmission loss, in order to forecast the sonar detecting range. In this paper,based on ray model and wave model, the microscopic characteristics such as channel impulseresponse simulation techniques are studied. The simulation results are used to forecastperformance of signal processing methods. According to the time‐varying characteristics ofthe underwater acoustic channel, three channel models are defined, namely time invariantchannel, deterministic time variant channel and stochastic time variant channel. For thetime‐invariant channel, the image method and ray model are used to simulate the channelimpulse response. In addition, the fast algorithm based on normal mode model and Fouriersynthesis is discussed to simulate channel impulse response. When the hydrophone is inuniform motion, using the movement velocity component along the multipath arrival angle andtime scale transformation, the received signals can be simulated rapidly. Furthermore, usingChirpZ transform algorithm, the computation cost of time scale transformation can besignificantly reduced. For the stochastic time variant channel, the stochastic characteristic canbe simulated by using the time‐dependent ray interpolation algorithm. Based on Kirchhoffapproximation of time variant sea surface, the surface scatter can be replaced by the pointsources. Then the simulation speed of stochastic time variant channel can be greatly improved.The channel estimation is an effective method to obtain channel characteristics from thereceived signal. The ideal channel impulse response can be obtained by using projections onto convex sets algorithm to estimate time invariant channel. Its resolution is better than thetraditional maximum likelihood estimator‐matched filter. The phase shift caused byboundary reflection can be estimated by expanding POCS algorithm to the complex domain.The phase shift estimation results can be used to distinguish between the surface and bottomreflection. Using the different Doppler shifted emitted signal as the reference signal of POCS toestimation array, the channel impulse response can be estimated in the delay‐frequency shiftplane. This estimation method can be used to estimate the impulse response of deterministicand stochastic time variant channel.The simulated channel analysis results show that, time invariant channel impulse responsedoes not change over time. And there is no frequency shift or spectrum spread. Thedeterministic time variant channel impulse response changes over time in certainty. And thefrequency shift changes with the multipath time delay. The stochastic time variant channelimpulse response changes randomly. And the frequency shift and spectrum spread also changerandomly. The simulated channel estimated results show that, the Doppler shift is inverselyproportional to the multipath reflection number. The lower numbered paths frequency shift isclosed to hydrophone velocity, while the higher numbered paths frequency shift is smaller thanhydrophone velocity. The frequency shift and spectrum spread of the stochastic time variantchannel are proportional to the multipath reflection number. The lower numbered pathsfrequency shift and spectrum spread can be ignored, while the higher numbered pathsfrequency shift and spectrum spread are obvious.In shallow water acoustic channel, the single hydrophone source localization method canbe obtained by using boundary reflection estimated results. Using the POCS algorithmestimated results of direct arrival, surface reflected arrival and bottom reflected arrival, basedon image method localization equation analysis results show that, a hyperbola that opens downis defined by the time delay between direct arrival and surface reflected arrival, while ahyperbola that opens up is defined by the time delay between direct arrival and bottom reflectedarrival. The intersection point of these two hyperbolas is the source location. Based on the Rakereceiver matching characteristics of the underwater acoustic channel, the single hydrophonematched field localization method can be obtained. The ambiguity plane of matched fieldlocalization has the same hyperbolic curves. The Rake receiver output peak changed rapidlynear the hyperbola. The intersection point of hyperbolas is the source location.The source localization results in simulated channel show that based on channel estimationlocalization method can be used to locate single frequency impulsive source at a certain SNR.This method will not be affected by channel time‐varying characteristics. Based on Rake receiver, the matched field localization method can be used to locate wide band impulsivesource at a lower SNR. But the performance will be affected by channel time‐varyingcharacteristics. The experimental data processing results show that these two methods arefeasible in a real channel. And they have the advantages of simple structure and low cost.The simulation results of the underwater acoustic channel can be widely used in sonarsystems. It can be used to evaluate and test signal processing method and sonar systems. Thelocalization method based on channel model can be used in underwater acousticcommunication and acoustic position systems, in order to improve their performance inmultipath channel.