Optimal Chunk-Based Resource Allocation for OFDMA Systems With Multiple BER Requirements

Abstract

In wireless orthogonal frequency-division multiple-access (OFDMA) standards, subcarriers are grouped into chunks, and a chunk of subcarriers is made as the minimum unit for subcarrier allocation. We investigate the chunk-based resource allocation for OFDMA downlink, where data streams contain packets with diverse bit-error-rate (BER) requirements. Supposing that adaptive transmissions are based on a number of discrete modulation and coding modes, we derive the optimal resource-allocation scheme that maximizes the weighted sum of average user rates under the multiple BER requirements and total power constraints. With proper formulation, the relevant optimization problem is cast as an integer linear program (ILP), and it is shown that the optimal strategy for this problem can be obtained through Lagrange dual-based gradient iterations with fast convergence and low computational complexity per iteration. Furthermore, a novel online algorithm is developed to approach the optimal strategy without knowing the statistics of the intended wireless channels a priori. The proposed approach is also generalized to utility maximization of average user rates to leverage the total throughput and fairness among users. Numerical results are provided to gauge the performance of the proposed schemes.