Opportunistic Feedback in Clustered OFDM Systems

This paper proposes a random access based feedback protocol for the clustered orthogonal frequency division multiplexing (OFDM) downlink, which allows users to feed back their channel information to the base station (BS) in a distributed fashion. The proposed protocol employs a contention channel that consists of fixed amount of system resource to carry the feedback for each cluster. Active users send a feedback message with some probability if their average channel quality on one cluster is above a threshold. The threshold and feedback probability are jointly adjusted to maximize a tight upper bound to the average sum rate of all users. The main advantage of this protocol is that it achieves multiuser diversity with only a small amount of feedback overhead.