Asynchronous direct-sequence code-division multiple access systems : low complexity data detection and robust detectors
T. Ostman · 1997
The subject of this thesis is data detection in an asynchronous DS-CDMA system. The problem of estimating the transmitted symbols in a near-far scenario is considered. Both systems using short codes and long codes are discussed. It is shown that there exist low complexity detection methods using linear transformations. Transformations based on least squares and minimum mean squared error criteria are derived and the performance is analyzed analytically and by simulations. The issue of chip asynchronous sampling and data reduction is considered. Furthermore, the impact of using a band limited channel is considered. The implications of using a band limited pulse and chip asynchronous samples are studied. Algorithms which are able to deal with uncertainties in the estimates of the channel are also presented. Simulations indicate that the performance of a linear detector can be greatly improved by minor modifications of the algorithms.