Variable power and rate allocation using simple CQI for multiuser OFDMA-CDM systems

This paper presents variable power and rate allocation (PRA) for a multiuser orthogonal frequency division multiple access code division multiplexing (OFDMA-CDM) system which exploits both orthogonality among users and symbol-level diversity. To predict the link performance, we analyze the postprocessing SNR as the transmit power (TP) varies when the minimum mean square error combiner (MMSEC) is employed. It is shown from analysis that the MMSEC SNR is nonlinear in TP, but is bounded by the harmonic and the arithmetic means of the subcarrier SNRs. From the observation, we propose two variable PRA methods using a simple channel quality indication and a required TP estimation method. Simulation results show that the proposed methods not only guarantee the target performance but also increase the throughput at the same or slightly increased feedback overhead compared with the fixed TP allocation case.