Multiuser detection for CDMA antenna array receivers

Under consideration are ways to increase the capacity on the reverse (mobile to base) link of a cellular direct sequence CDMA system whilst avoiding system complexity. It has been demonstrated for asynchronous transmission that the capacity of a conventional receiver based on a bank of matched filters can be significantly increased by employing sectorized antenna arrays or by employing multiuser detection techniques. We investigate base station receivers employing beamforming followed by multiuser detection, which provides better bit error rates than either technique employed alone but may be complex to implement. The performances of five detectors are evaluated. Our investigation assumed that all users transmit at the same constant power and that each user transmits over a single path. It is demonstrated that it is possible to achieve close to single-user performance by using subtractive interference cancellation, applied after beamforming. This is one of the least computationally complex methods of multiuser detection.