Efficient High Performance Decorrelator Designs for Multiuser Detection in CDMA Based Asynchronous Wireless Communication Systems

Abstract

The linear decorrelator provides a good solution for multiuser detection in code division multiple access (CDMA) systems. However, the computations needed to invert the correlation matrix have rendered its implementation difficult in practice. Considerable interest has been shown on realization of multiuser asynchronous CDMA reception by a finite length decorrelator of small window size. One-shot and extended window based decorrelators reported in literature are near-far resistant, however, they have considerable enhancement of noise power with increase in the number of users that limits their user capacity. Truncated window based algorithms, on the other hand, suffer from edge effects that introduce multiple access interference (MAI) which degrades the performance with increased number of users and also results in near–far dependence. Thus the existing finite length decorrelator algorithms show variable tradeoffs between the performance, complexity and user capacity. In this thesis some aspects of design improvements for improved tradeoff between the performance and the user capacity of finite length decorrelators in asynchronous system, while keeping the computational overheads low, is considered.