Study On Equalization Technology In Wireless Communication System

The multipath effect of the wireless communication signal in transmission as well as the wireless channel's band width finiteness and the non-ideal, can create the intersymbol interference (ISI). The ISI will cause the increase of receiver error and reducing transmission efficiency of the communication system even makes communication system doesn't work. In order to overcome the ISI, the equalizer is used usually at the receiving end to correct or compensate system characteristics, to reduce the influence of the ISI. The adaptive equalization technology using the training sequences is simple in structure, reliable in performance, and used widely in existing communication systems. In addition, the blind adaptive equalization technique that needs no training sequence in recent years has also been extensively researched and applied.Based on the study of the wireless communication channel characteristic, this thesis has studied many kinds of equalizer structures as well as the equalization algorithms, proposed an improved program of the blind adaptive equalization, and has realized one kind of T/2 fractional interval decision feedback equalizer according to the actual need design. This thesis research content includes:1) The characteristics of the wireless communication channel and the selective fading, flat fading, Doppler spread and delay spread in the wireless channel are studied and simulation analyzed in terms of the feature of electromagnetic wave propagation. The forming principle of the intersymbol interference is studied through the mathematical model.2) The principle of the equalizer structures is fully described and their merits and shortcomings are analyzed. And the basic adaptive equalization algorithm has been studied and analyzed. The principle of the blind adaptive equalization is centrally studied. And the usual blind equalization algorithm is studied and analyzed the algorithm's merits and shortcomings.3) With respect to the problem of the slow convergence speed of MCMA and the sensitivity to the sampling time of the decision feedback equalizer, an improved equalization scheme--the variable step size MCMA, which is based on the FS-DFE structure--is proposed. The scheme exploit the merit of the MCMA in correcting the carrier's frequency and phase deviation while restoring the constellation diagram, the character of the variable step control of using the longer step size in equalization capturing period in order to converge quickly and using the smaller step size in tracking period in order to gain lower deviation, the low sensitivity to the sampling time of the fractional interval structure in FS-DFE, and the good nature of countering multipath in decision feedback structure, to realize the quick convergence of algorithm and decrease steady state error. By simulating the result, the scheme, under the circumstance of 16QAM modulation method, with the signal passing through the multipath channel having Gaussian White noise and Doppler shifting, serves good in raising convergence speed and decreasing steady state error in contrast with the fixed-step MCMA.4) According to the actual need, a T/2 fractional interval decision feedback equalizer is designed. Through theoretical analysis and experimental simulating deduction, the validity of the scheme is proved. The design of all parts of the equalizer is fully presented. And the scheme is implemented in FPGA. By stimulating actual communication circumstances, the timing stimulation has been carried out, and it can operate normally in FPGA.