A throughput enhancement scheme for DS-CDMA systems using linear multiuser detectors

It is well-known that the performance of linear multiuser detectors such as decorrelators and MMSE deteriorates as number of users exceeds the available code dimension. This paper shows that these detectors are much less sensitive to this problem in asynchronous CDMA systems than in synchronous case. We further show that with optimal spreading factors, single-cell asynchronous CDMA systems with linear multiuser detectors are able to maintain a good error performance even if number of users grows exceedingly beyond the spreading factor. We proceed to suggest a scheme to enhance the throughput of a single-cell DS-CDMA system by employing multiuser detection and controlled random user transmission delays. This method has the potential of exceeding the single-cell capacity of orthogonal CDMA by a factor of 4 or more. Further, we extend this mechanism to a multicell environment.