Linear adaptive transmitter-receiver structures for asynchronous CDMA systems

Adaptive linear receiver and transmitter structures for coherent demodulation in asynchronous code-division multiple-access (CDMA) systems are considered. It is assumed that the adaptive receiver and transmitter have no knowledge of the signature waveforms and timing of other users. The receiver and transmitter are trained by a known training sequence prior to data transmission and continuously adjusted by an adaptive algorithm during data transmission. The proposed linear structure is as simple as a standard single-user-detector receiver consisting of a matched filter with constant coefficients except that it requires separate channel for the transmitter adaptation. The concept of an adaptive transmitter maintains advantages with respect to timing recovery, near far effect, narrow-band and frequency selective fading interference suppression and user privacy compared to the systems with conventional matched filter receiver and further improves multiple-access interference elimination compared with the systems employing an adaptive receiver only. The proposed concept of adaptive transmitter and receiver are tested by simulation over a channel with multiple access interference and additive white Gaussian noise