Performance Evaluation of Orthogonal/Scrambled-Orthogonal Overloaded DS-CDMA System

Overloading is a bandwidth efficient scheme to accommodate more number of users than the spreading factor, N in a DS-CDMA system. In this paper, the performance of an overloading scheme in which the first N users are assigned Walsh-Hadamard orthogonal codes and extra users are assigned the same WH codes but overlaid by a common scrambling sequence is evaluated. The allowable load of this scheme is investigated, so that the uncoded performance with iterative multistage interference cancellation detector using hard (HDIC) and soft (SDIC) decision functions remains close to the single user bound. It is shown that this scheme provides 19% and 11% overloading with SDIC technique for N= 16 and 64 respectively.