Comparison of Maximum Likelihood - basedDetection for Two Multi - rate Access Schemes forCDMA

| Future wireless systems will need to accommodate information sources with diierent data rates. Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a multiple access technique that is well suited to provide multi-rate access. Thus, in this paper, multi-rate communication systems are considered for the transmission of DS/CDMA wireless signals. Performance for maximum likelihood-based detection is studied in the context of two multi-rate access methodologies: multi-code access where high data rate users multiplex their information streams onto multiple codes; and variable spreading length access where signature sequences of diierent lengths are assigned to users with diierent data rates. Various maximum likelihood-based detection schemes for the variable spreading length system are considered as they can achieve near-optimal performance and thus provide reference points for comparison with sub-optimal schemes. In addition, asymp-totic multiuser performance measures are calculated and bounded to compare performance of the two systems.