Performance of an OFDM based downlink multiple access system for indoor wireless communications

We have analyzed the downlink performance of a multiuser Orthogonal Frequency Division Multiplexing based multiple access system for indoor wireless communications. The optimization problem for minimizing the total transmit power from a base station while satisfying the bit-rate and bit-error rate criterion of the various portable users in the system has been outlined. The analytical solution obtained cannot be realized in a simple manner and we present a realizable method for the combined allocation of subcarriers, modulation mode, and power to the signals transmitted to the different users. Simulation results are used to compare the performance of the analytical solution with that using the new method under various channel conditions. Performance comparisons between the new method and an OFDM-TDMA system clearly indicate the advantages of the new algorithm under most conditions. The correlation of the frequency-domain channel strengths among the various users is shown to have an influence on the performance of the new algorithm.