Optimization of multilevel coding scheme associated with multiuser interference cancellation for CDMA

Direct sequence code division multiple access (DS-CDMA) has attracted great attention in commercial mobile and personal communication systems and proved to be a probable candidate for greatly increasing the traffic capacity. For the transmission of speech or multimedia information in a time varying mobile channel fixed rate codes are normally used which are designed for average or worst channel conditions. However, fixed rate codes fail to explore the time varying nature of the mobile (fading) channel. In our previous work we have shown that a multilevel code when used in conjunction with multiuser interference (MUI) cancellation in cascade yields a better performance than a conventional coded modulation scheme applied to CDMA. However, we did not consider the channel state information (CSI). We take into consideration the CSI and propose an adaptive multilevel coding scheme associated with MUI cancellation for CDMA which yields significant performance improvement. A suitable code selection criterion is also discussed