Iterative Demodulation and Channel Estimation of Orthogonal Signaling Formats in Asynchronous DS-CDMA Systems

Erik G. STROM  Scott L. MILLER  

IEICE TRANSACTIONS on Electronics   Vol.E85-C   No.3   pp.442-451
Publication Date: 2002/03/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Signals, Systems and Electronics Technology)
Category: Digital Transmission
code division multiple access (CDMA),  channel estimation,  interference cancellation,  multiuser detection,  iterative detection,  

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Iterative schemes for demodulating M-ary orthogonal signaling formats in direct-sequence code-division multiple access (DS-CDMA) systems are proposed and compared with the standard noncoherent matched filter receiver. Interference cancellation, i.e., (approximative) removal of the multiple access interference (MAI) by means of subtraction is studied. The considered system is similar to the uplink (reverse link) of an IS-95 system. Hence, the received signals from the concurrent users are asynchronous, and no pilot signals are available for channel estimation. A decision-directed algorithm is proposed for estimating the time-varying complex channel gains of a multipath channel. The receivers are evaluated on Rayleigh-fading channels and are shown to provide large capacity gains compared with the conventional receiver.