Joint Bit Allocation and Hybrid Beamforming Optimization for Energy Efficient Millimeter Wave MIMO Systems

In this paper, we aim to design highly energy efficient end-to-end communication for millimeter
wave multiple-input multiple-output systems. This is done by jointly optimizing the digital-to-analog
converter (DAC)/analog-to-digital converter (ADC) bit resolutions and hybrid beamforming matrices.
The novel decomposition of the hybrid precoder and the hybrid combiner to three parts is introduced
at the transmitter (TX) and the receiver (RX), respectively, representing the analog precoder/combiner
matrix, the DAC/ADC bit resolution matrix and the baseband precoder/combiner matrix. The unknown
matrices are computed as a solution to the matrix factorization problem where the optimal fully digital
precoder or combiner is approximated by the product of these matrices. A novel and efficient solution
based on the alternating direction method of multipliers is proposed to solve these problems at both
the TX and the RX. The simulation results show that the proposed solution, where the DAC/ADC bit
allocation is dynamic during operation, achieves higher energy efficiency when compared with existing
benchmark techniques that use fixed DAC/ADC bit resolutions.