Adaptive subcarrier and bit allocation for multiuser MIMO-OFDM transmission

Subcarrier and bit allocation schemes for SISO-OFDM systems in the multiuser downlink scenario are well-documented. We extend it to MIMO-OFDM systems and design a transmit scheme as a concatenation of dynamic subcarrier assignment, adaptive modulation and beamforming. With the goal of minimizing the overall transmit power required to meet the target BER, we propose an adaptive OFDM subcarrier allocation approach based on the maximum eigenvalue (referred to as λ_max) of the matrix, H^HH, for each user´s channel frequency response matrix, H; that is, each OFDM subcarrier is assigned to a specific user who has the largest λ_max among all users. Simulation results show that our proposed algorithm considerably outperforms multiuser MIMO-OFDM with the static FDMA technique. We have also evaluated the performance of the presented system under various numbers of transmit and receive antennas.