Discrete-Rate Adaptive Modulation for MIMO-OFDM Systems with Space-Frequency Block Code in Rayleigh Fading Channels

The performance analysis of discrete-rate adaptive modulation (AM) for MIMO-OFDM systems with space-frequency block code (SFBC) in Rayleigh fading channels is presented. The fading gain value in each subchannel is partitioned into a number of regions by which the modulation is adapted in terms of the region the fading gain falls in. The fading gain region boundaries are attained for attaining maximum spectral efficiency (SE) under a target bit error rate (BER) constraint. Based on accurate BER expression, the improved switching thresholds for the AM are proposed. By the switching thresholds, we obtain accurate closed-form expressions of the SE and average BER. With these expressions, the system performance can be effectively evaluated. Simulation results show that the SE based on the improved switching thresholds is higher than that based on the conventional ones, and the derived theoretical SE and BER are in good agreement with the corresponding simulation results.