Performance analysis of a wireless multirate DS-CDMA in multipath fading channels

A new multirate technique for DS-CDMA mobile radio system is proposed tested and analyzed. In this technique, a variable processing gain multirate concept is used, but with another spreading strategy, serial time-orthogonal spreading. Every user in the cell is assigned a unique spreading code with the highest spreading factor regardless of its data rate. If the user is to send voice, the whole code is used in spreading bit by bit. For higher data rates, the user specific code is partitioned to several subcodes, according to the data rate. Each subcode is used to spread the corresponding data bit. A complete performance analysis of the proposed system is presented on a multipath fading channel. In addition, the validity of the analysis results is demonstrated by computer simulations. A coded multirate CDMA system (using turbo-codes) is also simulated using different data rates. Performance results using decorrelating multi-user detection are also introduced and discussed. Both analysis and simulations show a performance improvement and a capacity enhancement.