Affine projection adaptive algorithm for multiuser MMSE receivers in frequency-selective fading channels for asynchronous W-CDMA systems

In this paper we propose the use of affine projection adaptive (APA) filtering algorithm for multiuser adaptive minimum mean square error (MMSE) receivers for asynchronous wideband code division multiple access systems (W-CDMA) in multipath fading channels. Performance of APA algorithm is compared with least mean square (LMS), normalized least mean square (NLMS), and recursive least square (RLS) algorithms. It is found that APA algorithm outperforms LMS and NLMS. Though RLS, algorithm offers better convergence characteristics but at much higher computational complexity. Three adaptive multiuser receiver architectures are considered, all employ chip-matched filter (CMF) at their front end. In the first two architectures perfect estimation of time delay of individual user is assumed and one CMF is employed per user. The difference between two architectures is that, in the first the samples collected from CMFs are cross-coupled and in the second architecture samples collected for individual users are not combined. In the third architecture, there is no need to estimate the time delay, but fractional sampling is used. It is shown that first architecture outperforms the other two architectures.