ADAPTIVE RECEIVER STRUCTURES FOR ASYNCHRONOUS CDMA SYSTEMS

Adaptive linear and decision feedback receiver structures for coherent demodulation in asynchronous code division multiple access (CDMA) sys tems are considered. It is assumed that the adaptive receiver has no k nowledge of the signature waveforms and timing of other users. The rec eiver is trained by a known training sequence prior to data transmissi on and continuously adjusted by an adaptive algorithm during data tran smission. The proposed linear receiver is as simple as a standard sing le-user detector receiver consisting of a matched filter with constant coefficients, but achieves essential advantages with respect to timin g recovery, multiple access interference elimination, near/far effect, narrowband and frequency-selective fading interference suppression, a nd user privacy. An adaptive centralized decision feedback receiver ha s the same advantages of the linear receiver but, in addition, achieve s a further improvement in multiple access interference cancellation a t the expense of higher complexity. The proposed receiver structures a re tested by simulation over a channel with multipath propagation, mul tiple access interference, narrowband interference, and additive white Gaussian noise.