Research On Key Techniques Of Blind Equalization Algorithm And Its Application In Anti Multipath Interference

In telemetering system,the signal transmission between plane and groud is affected by many undesirable characteristics,such as noise in the information channel, frequency selective fading,band limited transmission etc.These characteristics will create multipath fading which bring about serious Inter-symbol interference.In order to enable the receiver to receive the signal accurately, we need to take some corresponding measures to promote the amplitude frequency characteristic and phase frequency characteristic of channel, which helps to counteract the impact of the Inter-symbol interference. Among these measures, effectual channel equalization techniques are an effective way to eliminate the Inter-symbol interference in communication systems.The filter that can compensate the channel’s characteristic of distortion often called equalizer. Equalizer is divided into the adaptive equalizer and the blind equalizer by whether need training sequence.But blind equalizer still can eliminate Inter-symbol interference without training sequence that to compensate the impact caused by the channel distortion.Blind equalization technology is the focus of this thesis.The following work has been finished.First of all, the factors causing multipath interference in wireless channel are introduced. The multipath channel transmission mode is described focusing on the principles of the intersymbol interference. The classification of equalizer is summarized.Then, the principles of adaptive equalization and blind adaptive equalization are described in detail.Some adaptive algorithms are researched such as LMS and RLS. The simulation experiments and performance comparison have been done. The principle of Bussgang algorithm is described and several kinds of algorithm based on Bussgang properties are introduced focusing on the constant modulus(CMA) principle and the performance of it. A variable step size algorithm based on MSE has been proposed in order to solve the CMA algorithm with fixed step size making the contradictory problem between convergence speed and steady residual error.Finally the structure and principle of the linear equalizer and decision equalizer are introduced.Serveral computer simulation experiments are given to show the BER performance and the decision feedback equalizer is more suitable telemetry system regarding the results of simulation.The principle of decision-feedback blind equalization algorithm is introduced in detail on based that and two kinds of improved methods are proposed. The first improved method is by using the weighted algorithm to reduce the error propagation in decision feedback equalizer. The second improved method is by using a variable step size CMA algorithm to replace the traditional CMA algorithm. The results of the analysis of the computer simulation are shown that he improved method was improved in convergence speed, error rate, residual error etc.Some equalization algorithms are researched in this thesis and a series of computer simulation are given to show their performance. At last an equalization algorithm which is suited for telemetry receiving equipment and resistantd to multipath interference is proposed.