Space-time receiver for multi-rate CDMA systems: multi-code and variable spreading length access methods comparison

Linear space-time multiuser detectors are proposed for CDMA systems which support users transmitting at different bit rates. The performance of the LMMSE space-time dual-rate receiver is studied in the context of two multi-rate access methods: multi-code (MC) access where high data rate users multiplex information streams onto multiple codes, and variable spreading length (VSL) access where signature sequences of different lengths are assigned to users with different data rates. Simulation results show that the proposed LMMSE space-time dual-rate receiver can significantly enhance the multimedia services that can be provided by multi-rate CDMA systems, and the VSL access system offers a distinct advantage over the MC system.