The Research And Design On Adaptive Equalizer In Stratum Channel Based On Elastic Wave

In the low-frequency elastic wave through-the-earth communication system, severe Inter-Symbol Interference (ISI) is generated and the bit error rate (BER) is increased after transmission because of the multipath transmission caused by the characteristics of the layered earth. However, adaptive equalization technique can decrease ISI, the effect of noise, and BER. As a result, the problem about serious distortion of Elastic wave signal can be solved. On the basis of the study of stratum channel based on elastic wave, the cause of ISI is discussed and a multipath channel model is introduced in this paper. The main purpose of this dissertation is to design the adaptive equalizer suitable for stratum channel based on elastic wave.This paper is mainly composed of the following three sections:the selection of equalizer structure and adaptive equalization algorithm, the design of equalization scheme for stratum channel based on elastic wave.In this paper, the equalizer architecture is studied firstly. In addition, simulations and analysis are given. Simulations are done by the linear equalizer and decision feedback equalizer, through the simulation results it can be that the decision feedback equalizer is effective for stratum channel equalization based on elastic wave.Then the advantages and disadvantages of common adaptive algorithm are compared and analyzed, and a modified LMS algorithm of variable step size is proposed based on the improvement for traditional LMS. On the base of principle and simulation analysis, the improved LMS algorithm is analyzed and the performances are compared between the improved LMS algorithm and traditional LMS algorithm. In the improved algorithm, the contradiction between convergence speed and the steady-state error is considered at the same time. Therefore, the improved algorithm has good convergence properties and the channel-tracking performance.Finally, according to the characteristics of stratum channel based on elastic wave, the requirement of equalizer design for the stratum channel is provided. Meanwhile, the stratum channel equalization scheme which combines channel estimation and adaptive equalization techniques is given. This scheme can offset deficiencies using adaptive equalizer separately, and realize fast equalization and good equalization performance. The feasibility of the solution is verified by mean of many simulations.