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

Abstract

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 WalshHadamard 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.

Error Free Despreading Of Orthogonal Codes In Quasi-Synchronous Cellular CDMA Communication

“…The reason is that the capacity of an S-CDMA system is limited by the maximum number of different codewords, whereas that of an A-CDMA is limited by the interference noise. To overcome the limitation of maximum number of orthogonal codes in an synchronous CDMA system, cell overloading schemes have been proposed in [4], [5]. However synchronous CDMA system requires accurate synchronization between all transmitters.…”

BER Analysis of Hard Decision Interference Cancellation Receiver for Overloaded DS-CDMA System

“…QOS are balance O/O sets, so that the correlation between any set 1 and set 2 user is equalized, i.e., they are equicorrelated. Performance of a similar type of equicorrelated overloading scheme (O/s-O), has been evaluated by present authors in [6]. A hybrid overloading scheme has been proposed by the present authors [7] where set 1 users are assigned synchronous orthogonal sequence but the set2 users are assigned asynchronous PN sequence to get better BER performance.…”