Performance Comparison Between Variable and Fixed Signature Codes in DS-CDMA Systems

Abstract

In a CDMA or SCMA system, users can use a fixed signature for the whole transmission interval. But there is the possibility for two users to have highly correlated signatures. Hence, high interference exists in the system, and it will degrade the performance. On the other hand, if the users use variable signatures for spreading each modulation symbol, then the interference between the users will not be fixed for all the transmissions.In this way, we are avoiding clustering error symbols resulted from the high interference. As we show in this thesis, this prediction about better performance of variable spreading is not always true. We have discussed several scenarios and shown the performance for both the fixed and variable signature codes