Are mmWave Low-Complexity Beamforming Structures Energy-Efficient? Analysis of the Downlink MU-MIMO

摘要

Future cellular systems based on the use of above-6 GHz frequencies, theso-called millimeter wave (mmWave) bandwidths, will heavily rely on the use ofantenna arrays both at the transmitter and at the receiver, possibly with alarge number of elements. For complexity reasons, fully digital precoding andpostcoding structures may turn out to be unfeasible, and thus suboptimalstructures, making use of simplified hardware and a limited number of RFchains, have been investigated. This paper considers and makes a comparativeassessment, both from a spectral efficiency and energy efficiency point ofview, of several suboptimal precoding and postcoding beamforming structures forthe downlink of a cellular multiuser MIMO (MU-MIMO) system. Based on the mostrecently available data for the energy consumption of phase shifters andswitches, we show that there are cases where fully-digital beamformers mayachieve a larger energy efficiency than lower-complexity solutions, as well asthat structures based on the exclusive use of switches achieve quiteunsatisfactory performance in realistic scenarios.