Interaction between fast scheduling diversity and RAKE receivers

Recent results indicate that multiuser diversity can provide significant improvements in total system capacity in fading multiuser channels. This paper investigates the simultaneous presence of link diversity and multiuser diversity and analyzes their mutual interaction. The results show that two types of diversity affect each other considerably. In particular, the use of link diversity reduces the capacity gains possible from multiuser diversity. We illustrate this by using selective RAKE receivers (with limited number of fingers) as an example of link diversity. We then present the performance trade-offs by showing the statistics of achieved SNR at the receiver as a function of the number of fingers, number of users, and number of available multipaths in the channel.