Comparative study of adaptive-rate CDMA transmission employing joint-detection and interference cancellation

Abstract

Spread adaptive quadrature amplitude modulation (AQAM) is proposed as a powerful means of exploiting the time variant channel capacity fluctuations of wireless channels and studied in comparison to the variable spreading factor (VSF) method. These two adaptive rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive code division multiple access (ACDMA) systems. More explicitly, these exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen AQAM mode or spreading factor is communicated to the remote receiver either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes with the conclusion that JD outperformed the SIC receiver in the ACDMA schemes, at the cost of increased complexity.