WCDMA was proposed as the candidate air interface for the global 3G standard, however it will exist in three main modes of operation; the MC-CDMA to be employed in America based on the commercial IS-95 standard, with TDD, and FDD mode in Asia, and Europe. ETSI was the main European standardisation player for the evolution of the UMTS system, but activities were then passed on to the 3rd Generation Partnership Project group, which have released several versions of the standard, the latest being "Release6". Now, we are entering the early deployment phase, where recent field trials suggest that up to 384 kb/s throughput can be reasonable expected from UMTS in vehicular environments. The first round of downlink receivers will be based on the RAKE architecture, that requires advanced estimation techniques to overcome the adverse effects of the channel. In this thesis, we investigate several channel estimation techniques based on classical, and Bayesian estimation theory. We conclude that not one filter can operate satisfactorily under all channel conditions, thus providing impetus for investigating hybrid estimation schemes based on the joint application of linear interpolation with Kalman filtering. Normalised LMS algorithm, and raised cosine interpolation. In the domain of delay estimation, the MUSIC estimator performance was investigated and compared with the traditional sliding correlator filter. It was concluded that the MUSIC can provide an additional dimension in performance by overcoming the near-far effect. The main target was to address signal subspace tracking techniques to track the time-varying statistics of the channel. We concluded that the MUSIC algorithm in unison with the Minimum Description Length function, and the PASTd algorithm can provide robust performance over the required operating range. We refer to this solution as the "Adaptive MUSIC estimator". In the last chapter, we address the joint application of the raised cosine interpolation filter with the Adaptive MUSIC estimator on RAKE receiver performance. It was concluded that these two schemes could be a practical solution to the estimation problem for the first batch of UMTS receivers. In unison they provide a comprehensive solution in terms of robust estimation in low SNR environments and over the required mobile velocity range, blind detection, low complexity, and adaptivity to a time-varying channel environment.