Comparison of maximum-likelihood-based detection for two multirate access schemes for CDMA signals

Future wireless systems will need to accommodate information sources with d ifferent data rates. Direct-sequence code-division multiple-access (DS/CDMA ) is a multiple access technique that is well suited to provide multirate a ccess. Thus, in this paper, multirate communication systems are considered for the transmission of DS/CDMA wireless signals, Performance for maximum-l ikelihood-based detection is studied in the contest of two multirate access methodologies: multicode access, where high data rate users multiples thei r information streams onto multiple codes; and variable spreading length ac cess where signature sequences of different lengths are assigned to users w ith different data rates. Various maximum-likelihood-based detection scheme s for the variable spreading length system are considered as they can achie ve near-optimal performance and thus provide reference points for compariso n with suboptimal schemes. In addition, asymptotic multiuser performance me asures are calculated and bounded to compare performance of the two systems .