Impact of Number of RF Chains on Spectral and Energy Efficiency of Massive MIMO Systems

Beamforming techniques have a significant impact on the capacity of downlink transmission in cellular systems. Beamforming can offer significant performance enhancements for wireless systems by allowing directional signal transmission which can improve the Signal to Noise Ratio (SNR), co-channel interference, and network capacity. These benefits can be substantial in Massive MIMO systems but there are costs associated with the large number of antenna elements. In this paper, the trade-off between spectral efficiency and energy efficiency of digital and hybrid beamforming of Massive MIMO are analyzed for different numbers of RF chains. Based on simulation results, suitable ratios for the number of RF chains to the number of antennas are determined for the base station in order to achieve a good trade-off between spectral and energy efficiency.