An adaptive resource allocation for multiaccess MIMO/OFDM systems was developed to enhance power efficiency by exploiting multiuser diversity, and channel variations in the time, frequency, and space domains [1]. However, by increasing the number of antennas, the scheme has a limitation in the affordable maximum data rate due to constraints on the maximum modulation order even without transmit power constraint. More antennas should allow more users to share the same subcarriers such that total affordable maximum data rates should increase accordingly. The paper presents an enhanced version of the scheme to remedy this problem. After the subcarrier assignment, the proposed scheme relaxes the maximum modulation order constraint in the bit loading process and presents an iterative bit swapping procedure, which are the two points deviated from the scheme in [1] and solve the related above-mentioned problem. A model of the multi-user channel on uplink with subcarrier reuse is considered. The proposed scheme aims to minimize the total user transmit power while satisfying the required data rates, the maximum transmit power constraint, and the bit error rate of each user. The proposed algorithm offers better performance than the high complexity greedy multi-user algorithm as illustrated in the simulation results. 0-35% improvement in terms of percentage in meeting the required data rates is observed from the simulation results and 0 similar to 5 dB transmit power gain is achieved.
