Dependence of the mean SNR on the interaction between multiuser diversity, multipath diversity, and feedback delay

We examine wireless systems employing Rake receivers and fast scheduling over multiple users. The interactions between multipath diversity, multiuser diversity, and the feedback delay are investigated in terms of the mean signal-to-noise ratio (SNR). It is assumed that all users experience the same propagation characteristics, i.e., the same number of taps and power-delay profile (PDP). The results are exact as well as asymptotic (in the number of users) expressions that quantify this interaction. It is found that as the number of taps in the channel increases, the multiuser diversity gain decreases but better robustness against feedback delay is achieved. Furthermore, the asymptotic results derived show good agreement with the exact results for an exponential PDP, even for few users. Thus, we obtain expressions for the mean SNR that are compact and easy to evaluate.