Research On Blind Equalization Algorithm Based On Signal Constellation

In the underwater acoustic communication system, blind equalization technique can overcome the inter-symbol interference caused by multi-path fading without training sequence, so it becomes hot topic in the underwater acoustic communication. Quadrature Amplitude Modulation (QAM) has been widely used because of the higher channel band efficiency. And the structure of the QAM constellation directly affect band efficiency and sensitivity which caused by channel distortion. So, this paper deeply studies blind equalization algorithm based on signal constellation on the base of introducing blind equalization theory and constellation characteristic. The main work is as follows:(1)By studying the principle of Adaptive varying Modulus Algorithm, improved a class Adaptive varying Modulus Algorithm with neighbour. Adaptive Varying Modulus Algorithm can equalise every signal point and reduce the inter-symbol interference,but too detailed constellation division method makes algorithm has higher misjudgments,slows down the rate of convergence. Adaptive Varying Modulus Algorithm with Neighbour takes adjoining signal point into account, then uses the error function of DD algorithm to control error dynamically. Finally, by means of different order QAM signals’ simulation experiments in different underwater acoustic channels to prove new algorithm’s feasibility and effectiveness all sidedly.(2)Taking Adaptive Varying Modulus Algorithm with Neighbour as a start algorithm and combine it with DD algorithm, use Run-and-Go algorithm and region based on point decision as two switch methods, get two dual-mode algorithms. These two dual-mode algorithms can reduce the inter-symbol interference effectively on the basis of guaranteeing the convergence rate. At the same time, two switch methods’ effect to the performance of the algorithm is analyzed.(3)Taking the cross QAM signals as the research object, on the basis of the cross QAM multi-mode algorithm, a new underwater acoustic channel multi-mode algorithm based on constellation division is putted forward. According to the distribution of cross QAM constellation, its constellation points can be divided into square QAM constellation points and nonsquare QAM constellation points, equalise every nonsquare constellation point. On the basis of guaranteeing convergence rate of the algorithm, it reduces the inter-symbol interference effectively. At the same time, phase rotation of32QAM is studied and modified algorithm is put forward.