Adaptive M-QAM modulation for MIMO systems

Adaptive modulation substantially increases the throughput of a wireless network by adjusting the modulation index to the channel conditions. In this paper, we propose algorithms for implementing adaptive M-QAM modulation for both OL- and CL-MIMO systems. The goal is to maximize the throughput subject to a target BER constraint. For OL-MIMO, the algorithm proposed finds the number of transmit antennas and the modulation index to be used for all streams. For CL-MIMO, the authors propose a new rate maximization scheme that, on the average, has 23% throughput improvement over OL-MIMO. The authors modify the water-filling and MMSE solutions to accommodate adaptive modulation and BER constraints. Flat Rayleigh-fading channel model is used in the simulations and assumes a perfect channel estimation.