Utility maximization for chunk-based OFDMA systems with multiple ber requirements

In wireless orthogonal frequency division multipleaccess (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 propose the optimal resource allocation scheme that maximizes a utility function of average user rates. With proper formulation, the relevant optimization problem is cast as an mixed-integer program, 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 on-line algorithm is developed to approach the optimal strategy without knowledge of intended wireless channels a priori. Numerical results show that the proposed optimal chunk allocation schemes with different α-fair utility functions can nicely trade off total network throughput for fairness among users.