Rake receivers for direct sequence spread spectrum systems

This paper investigates the structure of a continuous and a discrete time Rake receivers. The former receiver is the most used and consists on combining the output of correlators locked on the most significant paths. Since the conventional synchronisation module of this receiver is nor able to distinguish closer paths, we propose a maximum likelihood acquisition algorithm and an enhanced tracking loop. The tatter receiver was recently suggested and works without the knowledge of path delays and their number. It is based on a global estimation of the impulse response of the multipath channel convolutionned with the shaping filter. Performance comparison of the two receivers is established for the FDD mode of the UMTS interface.