A rake receiver which adapts to fast fading

Abstract

An ideal rake-receiver has as many correlators as there are propagation paths in the channel. All practical implementations, however, have much fewer correlators. On a channel that fades very quickly, these few correlators collect the signal from the paths that are strongest on average. In this situation the classical analysis of the ideal rake receiver found in the textbooks can be applied to receivers with fewer correlators than propagation paths. Often, however, the fast fading is slow enough for the receiver to collect the signal of the paths with the largest momentary power. This leads to a combination of selection and maximum ratio combining. The error performance of such receivers is analysed under the assumption of a simplified channel model. The presence of the rapid adaptation causes a significant improvement in error performance when many propagation paths are present. The increased effective diversity also improves the coding gain, in particular, when interleaving does not lead to independently fading code chips.<>