Research On Pre-equalization Technology In Uplink MC-CDMA Systems

With the improvement of people's living quality,the requirement of mobile communication is becoming higher and higher,especially in data transmit service aspect,today the data transmit speed of mobile communication system is gradually can not content consumer's demand, The fourth generation mobile communication system in the future needs to provide high data transmission.Thus,MC-CDMA,which combines virtues of Orthogonal Frequency Division Multiplexing(OFDM) and Code Division Multiple Access(CDMA) is regarded as one of the candidates technology of the fourth generation mobile communication system and is prosperous.Over the past several years,MC-CDMA emerged as the most promising candidate for the downlink in next generation for wireless mobile communication systems has been proved to be a suitable technique for the downlink transmission.On the other hand,considering MC-CDMA for uplink transmission introduces some additional problems due to the more complex propagation conditions.Especially,difficulty in channel estimation and the compensation problem comes from MAI which result in require more complex algorithms.So how to eliminate the interfere effectively becomes the key to improve the performance of system.traditional MC-CDMA system recover signal by collecting energy scattered in all subchannels at receiver.so a diversity combining method is crucial for the performance of the receiver. In this thesis,the performance of an uplink TDD/MC-CDMA system over Rayleigh fading channel is investigated,the TDD mode enables pre-equalization of the channel influence on the uplink signal already at the mobile station based on the channel estimation from the downlink signal,we exploits the strong correlation between up and downlink channel conditions of the slowly time-varying channels,obtain the channel estimation from the downlink signal and move the diversity combining operation from base station to mobile station,namely pre-qualize the signal before transmit,thus can avoid pilot insertion on the uplink which decrease the efficiency of system and decrease the influence of MAI to performance of BER of the system.The aim of this thesis is to carry out a performance comparison of different TDD/MC-CDMA channel pre-equalization techniques in the uplink,we discussed various diversity combining methods of MC-CDMA and their simulations and performance comparison of different channel pre-equalization techniques are presented with various user numbers and SNRs in the uplink of mobile communication.compared with original equalization in the base station,the conclusion that the CE pre-equalization and quasi-MMSE pre-equalization outperform other pre-equalization techniques is obtained and we discussed different power constraint of different pre-equalization techniques,at last the conclusions that the MC-CDMA frame lengths namely the coherence time of the channel is the crucial parameter that determines the limits of TDD applicability to uplink MC-CDMA are given.