The Research For Underwater Communication Algorithm Based On Chaos Techniques

Along with the application field of underwater acoustic (UWA), communication has expanded. How to realize the data transmission with high speed and to overcome intersymbol interference introduced by channel multipath propagation is very important. In recent years, the efficiency and the quality of UWA is improved by introducing blind equalization and spread spectrum techniques. So it is necessary to design a useful algorithm to realize blind equalization, and to produce simple effective spread spectrum sequences to improve the anti-interference ability of UWA. Constant modulus algorithm (CMA) is widely applied for its simple structure and small amount of calculation. However, there are also some defects such as slow convergent speed, large mean square error (MSE) and fall into local minimum points easily. There are limited of address and poor mutual correlation for traditional spread spectrum. In order to overcome the ISI, and realize the high reliability of UWA, Chaos optimization algorithm and chaotic spread spectrum technology has been introduced into UWA communication system. The validity of proposed algorithm and chaotic spread technology has been proved by simulation results in underwater acoustic channel. The main contributions are as follows:1. Proposing blind algorithm of orthogonal wavelet transform (WT) based on chaos optimization. According to the disadvantages of CMA, orthogonal wavelet transform and chaos optimization algorithm are introduced. On the one hand, it improves the convergence rate of equalizer by using WT to normalize the input signal. On the other hand, it adopts chaos algorithm to optimize weight vectors to avoid convergence to local minimum. The performances of proposed algorithm are proved by computer simulation in UWA channel。2. Proposing constant modulus of wavelet transform based on chaos and support vector machines optimization (CSVM-WTCMA). To avoid local minima, the algorithm employs support vector machines (S VM) to initialize the weight vectors of equalizer. In order to improve the fitting ability of SVM, take the parameters selection as combinatorial optimization and establish optimization objective function, then the hybrid optimization algorithm is used to search for the optimal objective function values. Because of the way high order QAM modulation has been adapted, the weighted multiple modulus algorithm (WMMA) is introduced into CSVM-WTCMA to improve the utilization of frequency. In this way wavelet transform weighted multi-modulus blind equalization algorithm based on chaos and support vector machines is proposed. The simulation results in the underwater acoustic channel show that the proposed algorithm has higher convergence speed and smaller residual mean square error than WMMA and WT-WMMA.3. Proposing underwater acoustic communication algorithm based on differential chaotic spread spectrum. Due to the sending signal of UWA, communication system has numerous defects such as a narrow-band characteristic, poor self-correlation, weak anti-interference ability and so on. Some of the purposes of the algorithm include:enhancing anti-interference ability, reducing ISI and multipath fading. The algorithm processes the sending signal with chaotic spread spectrum, and de-spreads the signal at the receiver. The performance of the proposed technique is best proved by computer simulation in underwater acoustic channel.4. Proposing underwater acoustic communication algorithm based on orthogonal chaotic spread spectrum. This method uses logistic mapping and Hilbert transform to get a pair of chaotic sequences which are mutual orthogonal. The QAM modulation signals are spread spectrum by the pair of orthogonal chaotic sequences on the sender side, and de-spread on the receive side. Improve communication efficiency and enhance the ability of anti-noise are the main purposes of the method. The performance of orthogonal spread spectrum is proved by computer simulation results in UWA.