A Linea Adaptive Fractionally Spaced Single User Receiver for Asynchronous Cdma Systems

Abstract
A fully asynchronous single user receiver in a code-division multiple-access (CDMA ) system is considered. It is assumed that the receiver has no knowledge of the signature waveforms or timing information of other users. The receiver is trained by a known training sequence prior to data transmission, and continuously adjusted by an adaptive algorithm during data transmission. An adaptive, fractionally spaced least mean square (LMS) filter is employed for each user separately, instead of matched filters with constant coefficients. The proposed receiver is as simple as a standard single user detector receiver but it achieves essential advantages with respect to timing recovery, multiple-access interference elimination, narrowband interference suppression and user privacy. In comparison to the centralized linear multi-user detectior it has the same bit error performance while the computation complexity is substantially lower and independent of the number of users. The receiver structure is investigated and tested by simulation using a set of Gold sequences of length 31. Experimental results show that a considerable improvement in bit error rate is achieved with respect to the convention single-user receiver.

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