On the Multiuser Diversity of Relay-Aided Downlink Systems Using Reduced Feedback

We introduce an efficient multiuser scheduling method using amplify-and-forward relaying in relay-aideddownlink systems, consisting of one base station (BS), one relay station, and multiple mobilestations (MSs). In our scheme, the BS opportunistically selects both the transmission mode, that is, eitherone- or two-hop transmission, and the desired user (i.e., the desired MS). Closed-form expressions forthe average achievable rates are derived for the two transmission modes with multiuser scheduling, andits asymptotic solutions are also analyzed in the limit of large number of MSs. Based on the analysis, wepropose a feedback-efficient two-step multiuser scheduling algorithm: the transmission mode selectionfollowed by the user selection that only needs a partial feedback for instantaneous signal-to-noise ratios(SNRs) to the BS. We also analyze the average SNR condition such that the multiuser diversity gainis fully exploited for two-hop transmission. The proposed two-step scheduling algorithm exhibits thequite comparable achievable rates to those of the optimal one using full feedback information, while itsrequired feedback information is reduced by half of the optimal one.