| The underwater acoustic channel is time-varying and frequency-varying, it also haslimited bandwith and strong multipath interference. Orthogonal frequency divisionmultiplexing (OFDM) takes advantage of the orthogonality between subcarriers, thus it hasmuch higher frequeney spectrum efficiency than traditional frequency division multiplexing.OFDM can also decrease the influence of multipath interference, so numerous researchesfocuses on it in the field of high rate underwater acoustic communication for the past fewyears. However, the characteristic of time-varying causes doppler spread and introducesinter-carrier interference (ICI), destroys the orthogonality between subcarriers, whichdegrades the performance of the underwater acoustic OFDM system seriously. Therefore it isimportant to study on channel equalization technologies in order to cancel ICI.This paper researches on the channel equalization technologies of OFDM intime-varying UWA channel. The author’s works are listed as follows:1. Introduce the common model of the underwater acoustic OFDM system. Research onthe encoding and decoding theory of trellis-coded modulation (TCM), and then apply TCM tothe underwater acoustic OFDM system. Simulate and experiment the performance of OFDMwith TCM. The result of simulation and experiment demonstrates the effectiveness of thealgorithm.2. Analysis the influence of time-varying channel on underwater acoustic OFDMsystem, mainly focus on the offset of sampling frequency, the offset frequency of carriers andthe effect of doppler spread. Then study on modeling and simulation of time-varyingunderwater acoustic channel.3. Research on the channel equalization technologies of OFDM in time-varying UWAchannel. First disscuss zero forcing (ZF) equalizer, minimum mean square error (MMSE)equalizer and successive interference cancellation (SIC) equalizer. Then study on decreasingthe computational complexity of algorithms above. Compare the performance between thesemethods and the traditional one-tap equalization on simulation and experiment. The result ofsimulation and experiment manifests the validness of the proposed methods. |
