Adaptive multilevel code selection and MUI cancellation for DS/CDMA over fading channel

For transmission of speech or multimedia information in a time-varying mobile channel, fixed rate codes are normally used designed for average or worst channel conditions. However, fixed rate codes fail to explore the time-varying nature of the mobile channel. In their previous work the authors have shown that a multilevel code, when used in conjunction with multiuser interference (MUI) cancellation in cascade, yields better performance than a conventional coded modulation scheme applied to CDMA. They show that, when multilevel codes are changed with varying channel conditions (i.e. are chosen adaptively according to the channel state information (CSI)), the throughput (average number of information bits per symbol duration) can be increased without too much performance degradation. Code selection criteria as well as some codes with appropriate thresholds are also presented