Receiver Directed Adaptation of Multicode CDMA Transmission for Frequency-Selective Rayleigh Fading Channels

Future wireless communication systems require highly efficient use of radio parameters. Adaptability to changing environment conditions and to service application requirements is of great importance for the design of link adaptation. In this paper, we consider the joint optimization of CDMA radio parameters to maximize the instantaneous throughput for a bit error rate (BER) target. In order to increase the granularity of the adaptation in CDMA systems, combined adaptive multicode and multilevel modulation is employed. We show that this combined adaptation additionally enhances throughput in frequency-selective environments. Optimized link adaptation requires the knowledge of the channel impulse response as well as the used receiver model. Therefore, we assume that the receiver user equipment reports to the transmitter the optimum transport format maximizing the instantaneous bit rate so that a BER target is met. Joint optimization of radio parameters is based on analytical receiver performance evaluation. We assume single user multicode CDMA transmission during each time-slot. The available throughput is evaluated over frequency-selective channels for RAKE receivers and for more advanced equalizers such as joint multi-code block linear equalizers.