Soft Decision Parallel Interference Cancellationfor Scrambled/Unscrambled DS-CDMA System

A soft decision linear parallel interferencecancellation for the direct sequence spread spectrum CDMAsystems 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 anymutual interference and a number of additional users at theexpense of a small signal-to-noise ratio. Two sets of orthogonalGold codes are used, one for the first N users and the other forthe additional users. Both the N users and additional users areoverlaid by a set-specific pseudonoise scrambling sequence. Theperformance of scrambled and unscrambled system formatched filter and linear parallel interference cancellation isanalyzed and the scrambled system is found better thanunscrambled system. The allowable load of this scheme isinvestigated, so that the uncoded performance with linearparallel interference cancellation detector using soft (SDIC)decision functions remains close to the single user bound for N=64 at 33% overloading.