The Research Of Blind Equalization Algorithm In Satellite Channel

Satellite communication is one of the most promising communication technologies. Satellite communication has a long communication distance and is less susceptible to a variety of radio interference on the ground. However, group delay characteristics of the satellite channel largely influences data transmission quality and make the Inter-symbol interference very serious. Equalization technology can effectively improve the distortion of symbols caused by variety of channel noise and interference. If the channel parameters are known, the training sequence can be used to adjust the tap coefficients of the equalizer to make the equalizer transit to the ideal state by comparing the difference between the known transmitted sequence and the received sequence. But sending a large number of training sequences will take up more bandwidth that cause the reduction of the transmission efficiency of effective information. In this case, the Equalization technology which don’t know the channel parameters or training sequence and just use some priori information of the signal to achieve channel equalization becomes the focus of the researcher. For group delay characteristic of satellite channel, this paper focus on the blind equalization technology in the satellite channel model and does the following work:Firstly, this paper analyses the transmission characteristics of the satellite channel and show that the satellite transmission has a very urgent requirement for equalization technology. Then the paper selects the channel parameters which have the satellite channel characteristics as the simulation channel.Secondly, this paper introduces the basic knowledge of the equalizer, including the concepts of traditional adaptive equalization techniques and blind equalization techniques, the corresponding structure of the equalizers and their mutual differences.Thirdly, for different types of blind equalization algorithms, this paper provides an overview of blind equalization algorithm based on second-order cyclostationary statistics, Introduces the basics of knowledge of cyclostationary signal, Describes the relevant characteristics of the single-order cyclostationary signal and second-order cyclostationary signal. A single-channel blind identification algorithm based on using cyclostationary signal during the modulation process is analyzed according to the characteristics of the cyclostationary signal. This blind identification method does not need to know the signal parameters, it can use the mathematical methods based on characteristics of the cyclostationary signal to analyze and calculate the channel parameters. Cyclic Wiener equalizer is designed on the basis of single-channel blind identification algorithm. FROST algorithm is used to solve the limited adaptive optimization problem during the design process of the equalizer.Fourthly, another kind of widely used blind equalization algorithm-Bussgang class blind equalization algorithm is introduced. This paper simply explains the definition of Bussgang process, describes several classic Bussgang class blind equalization algorithms, focus on the constant modulus algorithm(CMA). Then modified constant modulus algorithm(MCMA) is proposed to solve the shortcoming of inadequate adjustment to the phase rotation of constant modulus algorithm. For the drawbacks of fix step size of MCMA, a kind of new error function is proposed and a nonlinear function between the step-size factor and the error function to optimize the performance of the MCMA is built in the paper, the variable step-size modified constant modulus algorithm(VS-MCMA) not only improves the convergence speed but also reduces the steady-state error compared with the traditional MCMA.Finally, multi-mode algorithm is introduced based on the existing single-mode equalization algorithm. The principle of constitution and the advantages and disadvantages of multi-mode algorithms are elaborated. A new dual-mode blind equalization algorithm is proposed on the basis of the most widely used multi-mode algorithm. In the new algorithm, both the switching dual-mode and the weighted dual-mode are applied to combine VS-MCMA and the decision directed least mean square (DDLMS) algorithm to form the VS-MCMA+DDLMS algorithm to improve the performance of the system, the rate of convergence of the proposed new dual-mode equalization algorithm is improved and the residual errors have a great degree of reduction.