Research On Technologies Of Turbo Equalization

With the rapid development of communication technology and constantly improvements of the users’ requirements, wireless communication systems need to provide abundant multimedia business in the future, so that spectrum efficiency and data transfer rate of the communication systems is put for higher requirements. However, the phenomenon of the signal multipath transmission resulted from suffer of wireless channel’s frequency selective fading bring about signal distortion and inter-symbol interference at the receiving end during transmission. Channel equalization is a kind of signal processing technology used to suppress and combat inter-symbol interference. With the in depth study of the decoding technology of the turbo code, iterative processing art was extended to many other research fields. Douillard and his partners applied the turbo principle to the filed of channel equalization and proposed Turbo equalization in 1995.This thesis mainly studied the Turbo equalization technology, its’ main work includes the following contents:At the first, the characteristics of wireless channel are analyzed and the cause of the channel equalization and discrete time model of the ISI channel are analyzed, the basic principles of channel equalization and the traditional methods of channel equalization are sumed up.Then the Turbo equalization system model and the iterative process of Turbo equalization havd analyzed and the basic MAP algorithm is deduced.Next, Turbo equalization based on the MAP algorithm is studied, the formula of MAP equalization and decoding algorithm are deduced. The import of the two kinds of external information calculation formulas which affecting the system BER performance are discussed and the performance are analyzed and verifed via simulation.Third, linear turbo equalization and decision feedback turbo equalization based on MMSE algorithm are studied. On the basis of analysis of the two kinds of simplified algorithms of the former, a class of decision feedback turbo equalization algorithms with low complexity are proposed, two improved algorithm of DFE-Turbo equalization are presented, the scaled factor are calculate via high order moment method and empirical method respectively. Finally, another external information calculation of DFE-Turbo equalization method and its’ simplified algorithm are derived in detail and verifed via simulation.