A throughput enhancement scheme for DS-CDMA systems using linearmultiuser detectors

摘要

It is well-known that the performance of linear multiuserndetectors such as decorrelators and MMSE deteriorates as number of usersnexceeds the available code dimension. This paper shows that thesendetectors are much less sensitive to this problem in asynchronous CDMAnsystems than in synchronous case. We further show that with optimalnspreading factors, single-cell asynchronous CDMA systems with linearnmultiuser detectors are able to maintain a good error performance evennif number of users grows exceedingly beyond the spreading factor. Wenproceed to suggest a scheme to enhance the throughput of a single-cellnDS-CDMA system by employing multiuser detection and controlled randomnuser transmission delays. This method has the potential of exceeding thensingle-cell capacity of orthogonal CDMA by a factor of 4 or more.nFurther, we extend this mechanism to a multicell environment