Exploiting multiuser diversity using multiple feedback thresholds

This paper describes a novel scheduling algorithm that takes advantage of multiuser diversity to obtain the maximum system spectral efficiency and uses multiple feedback thresholds to reduce the feedback load to a minimum. In this scenario the relevant users are probed with a set of carrier-to-noise ratio (CNR) thresholds. The users are first probed with the highest threshold. If none of the users are above this threshold the threshold value is sequentially lowered until one or more users are found. A closed-form expression for the average, normalized feedback load (NFL) is found. It can be argued that it is wise to minimize this average NFL to minimize the guard time needed for the feedback process. Consequently, the optimal CNR thresholds which minimize the average NFL are found. We also develop closed-form expressions for the overall capacity using quantized feedback. Plots show that the number of transmitted symbols between feedback queries has great impact on the overall capacity and that one bit feedback is optimal in all cases. The scheduling outage probability has also been analyzed, and the results show that the scheduling outage probability increases dramatically when a scheduling deadline is exceeded.