Adaptive algorithms for asynchronous DS-CDMA receivers

Issues relating to the choice of adaptive algorithms for use in single user minimum mean square error (MMSE) direct sequence (DS) code division multiple access (CDMA) receivers are discussed. Such receivers have the potential to dramatically increase capacity of CDMA systems compared to systems with conventional correlator receivers, without the high complexity associated with many proposed multi-user receivers. To be practical for many applications, the convergence rate of the adaptive algorithms must be improved, while maintaining low residual mean-squared error (MSE), robustness to noise and realisable complexity. The slow convergence of the least mean squares (LMS) algorithm is highlighted for this application. Recursive least squares (RLS) algorithms are shown to give much quicker convergence, but have much higher sensitivity to thermal noise. Algorithms normally termed "Fast-RLS", are shown to more complex than the conventional RLS algorithm when used in a CDMA receiver.