Study on the Improvement Scheme of RAKE Receiver for CDMA Downlink

Rake receiver should be employed in 3G mobile system based on CDMA technology, which is an effective method to overcome the multipath effect. In the process of coherent demodulation of Rake receiver, the carrier phase synchronization of multipath radio frequency (RF) components with local recovery carrier is inherently needed. However, in general RAKE receiver, it is only realized between main path component and local recovery carrier. For other secondary multipath components, there are random phase differences caused by time delay. So the demodulation of secondary path RF components is non-coherent demodulation and a RF loss factors will be introduced into the demodulation signals, which have a seriously effect on the performance of traditional RAKE receiver and may even cause its failure. Based on the analysis, a RF loss factor elimination method is proposed, which can estimate the phase difference of each multipath component from main path component as well as the instantaneous track of the changes of phase and make the perfectly multipath coherent demodulation possible. With using the method, two feasible Rake receiver implement schemes are presented lastly, which are multipath coherent demodulation RF implement scheme and multipath non-coherent demodulation baseband implement scheme respective. The performance analyses show that the proposed schemes are feasible.