Hybrid Precoding and Combining Based on Rate Balancing for Wideband mmWave Multiuser MIMO Systems

Considering wideband millimeter wave (mmWave) multiuser multiple-input multiple-output (MIMO) systems, we propose a new hybrid precoding and combining method for rate balancing among users. The orthogonal frequency division multiple access (OFDMA) scheme is employed for multiuser transmission, and a greedy-based algorithm is developed for subband allocation under the max-min user rate criterion. A new algorithm is derived that optimizes the radio frequency (RF) precoder and combiners under the constant-modulus constraints as well as the baseband precoders and combiners under the rate balancing power allocation criterion. The proposed algorithm iteratively updates the RF precoder and combiners using the conjugate gradient method, and baseband precoders and combiners through the singular value decomposition and numerical gradient-based power allocation among users and subcarriers. The complexity of the proposed method is compared to existing wideband hybrid processing schemes through analysis and numerical runtime measurement. The convergence of the proposed algorithm is verified via numerical simulations in mmWave MIMO-OFDMA systems. It is also shown through numerical simulations that the proposed wideband hybrid processing method outperforms the existing wideband hybrid techniques in terms of the minimum user rate, regardless of the signal-to-noise ratio, the number of antennas, and the number of users. Moreover, simulation results present that the proposed scheme is more advantageous than the conventional hybrid processing methods under channel uncertainty.