Abstract
Direct sequence code-division multiple-access (DS-CDMA) has been widely investigated over the past decade and has been chosen as the air interface technique for the third generation mobile communication systems.It is well known that the capacity of the conventional receiver in the CDMA systems is limited by the multiple access interference and the near-far effect. There are two solutions to these two problems: power control and multiuser detection. In this thesis, power control and various interference suppression algorithms are studied. Ulukus and Yates proposed an algorithm which combines the minimum mean square error (MMSE) interference suppression and power control. This algorithm exhibits impressive performance; however, it involves high complexity in computing the filter coefficients. In this thesis, we use adaptive algorithms to replace the instantaneous MMSE algorithm in interference suppression for complexity reduction. We then propose a power control scheme with adaptive interference suppression for turbo coded DS-CDMA systems. Moreover, we propose a modified power control with MMSE interference suppression scheme, which performs pre-cancellation of the interference by using the soft information from the turbo decoders’ outputs, to further reduce the interference. Computer simulation results show that the modified scheme can achieve efficient power control in a DS-CDMA system.