Practical multiuser diversity with fair channel assignment

Inspired by the information theoretic results concerning multiuser diversity, we address practical issues in implementing multiuser diversity in a realistic multiple access wireless setting. The users are allowed to have different average channel powers and the important issue of fairness is investigated. Using a fair channel assignment strategy that assigns the channel to only the user with the greatest instantaneous SNR-to-average-SNR ratio, our emphasis is on the effect of channel feedback delay in downlink transmissions. A novel optimization criterion based on an outage probability constraint is proposed. Applying the outdated channel feedback model, we illustrate the impact of channel feedback delay on the achievable multiuser diversity gain with the number of users. A robust, constant power, variable rate M-QAM scheme that is less sensitive to feedback delay is proposed using the optimal set of switching thresholds, which is derived to maximize the average throughput, subject to an outage probability constraint.