Iterative Equalizer for OFDM-CDMA Multiple Access Communication Systems

摘要

In this paper, the receivers with adaptiveequalizer and turbo decoder are investigated for orthogonalfrequency division multiplexing-code division multipleaccess (OFDM-CDMA) systems in multipath channels. Thede-spreading equalizer which combines de-spreading andequalization is used to mitigate the MAI and ISI. Thestochastic gradient based LMS algorithm is used as theadaptive algorithm for the equalizer. Three receiverarchitectures are investigated: The first one is thetraditional receiver called de-spreading equalizer disjointedwith turbo decoder. In this scheme, the equalizer and turbodecoder operate independently and the equalizer relies onslicer output to adapt its filter coefficients. However, theextrinsic information from turbo decoder can provide morereliable information of the transmitted data. Hence thesecond receiver architecture is called as de-spreadingequalizer jointed with turbo decoder, where turbo decodergives the extrinsic information as feedback to the adaptiveequalizer as the desired information. Finally, the equalizerjointed with turbo decoder is extended to differential codedsignaling in OFDM-CDMA system and its performance ispresented and discussed.