Abstract
A soft decision linear parallel interference cancellation for the direct sequence spread spectrum CDMA systems which can accommodate more users (K = N+M >N) than the processing gain of the system is analyzed in this paper. The proposed technique accommodates N users without any mutual interference and a number of additional users at the expense of a small signal-to-noise ratio. Two sets of orthogonal Gold codes are used, one for the first N users and the other for the additional users. Both the N users and additional users are overlaid by a set-specific pseudonoise scrambling sequence. The performance of scrambled and unscrambled system for matched filter and linear parallel interference cancellation is analyzed and the scrambled system is found better than unscrambled system. The allowable load of this scheme is investigated, so that the uncoded performance with linear parallel interference cancellation detector using soft (SDIC) decision functions remains close to the single user bound for N= 64 at 33% overloading.
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