Adaptive Equalisation for Downlink UMTS Terrestrial Radio Access

The third generation mobile system Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) has been mainly specified to provide various multimedia capabilities and good service quality. However, since UMTS is based on direct sequence CDMA (DS-CDMA) techniques the performance and the capacity of such systems is significantly limited by multiuser access interference (MAI) and inter-symbol interference (ISI). Therefore, robust and reliable detectors are required to mitigate these effects. Specifically, the multi-user detector exhibits a significant improvement in capacity and spectrum efficiency compared with the conventional matched filter receiver and single-user detector. Nevertheless, its complexity and prior knowledge requirement render it unsuitable for application in the downlink due to handset constraints. In this thesis, we propose a new robust and simple blind multiuser equaliser for downlink DS-CDMA systems, the so-called filtered-R multiple error CM algorithm (FIRMER-CMA) equaliser. The latter has a relatively low computational complexity, shows good convergence behaviour and a BER performance close to the MMSE solution. The FIRMER-CMA is further modified to be ready reconfigured to different modes such as partial loading schemes, multi-rate transmission, and semi-blind adaptation employing the aid of pilots. A considerable complexity reduction is achieved by adopting a novel adaptation strategy based on considering a new small virtual population of active users. The robustness of the FIRMER-CMA to carrier frequency offset is addressed whereby a combined scheme based on FIRMER-CMA equaliser and a blind carrier frequency offset estimator is introduced. Furthermore, convergence speed of the proposed algorithm is increased by introducing an affine projection scheme, and steady state MSE is lowered by adopting a concurrent FIRMER-CMA and decision directed (DD) mode. A system relying on both latter principles is derived whereby substantial performance improvements can be gained over either technique on its own. Finally, a significant gain in data rate and spectrum efficiency is achieved by adopting a new homogeneous burst type and a semi-blind approach based on the proposed algorithm for the UMTS TDD component.