Energy Efficiency of Multiple-Input, Multiple-Output Architectures: Future 60-GHz Applications

Large antenna systems at millimeter-wave (mmwave) can concentrate the transmit power and the receive region over narrow beams, as well as enable spatial multiplexing. Thanks to these benefits, large antenna systems at mm-wave are the core technologies for future wireless local area network (WLAN) and 5G/ beyond 5G (B5G) cellular standards. Energy efficiency is a crucial design objective for new technologies to reduce operating costs, minimize the environmental impact, and enable battery-powered applications. Power consumption and system performance depend on the design of the beamforming architecture. The objective of this article is to compare the energy efficiency of three different architectures using power consumption measurements of a 60-GHz CMOS transceiver. We compare a full digital architecture, in which each digital chain is connected to a single antenna, against hybrid partially connected (HPC) and hybrid fully connected (HFC) architectures, using fewer digital chains than antennas. The system throughput performance is evaluated considering the hardware nonidealities, including power amplifier saturation, quantization, and phase noise (PN). We show that the number of users spatially multiplexed impacts the hybrid beamforming tradeoff. When few users are multiplexed, the main drain of energy is the digital front end, as it needs to execute operations such as filtering and fast Fourier transform (FFT) on a wide modulation bandwidth of 1.76 GHz. In this case, reducing digital redundancy using a hybrid architecture is beneficial, and a HPC architecture is the most attractive. Scaling the system to a massive multiple-input, multiple-output (mMIMO) scenario instead allows full digital architectures to achieve the highest energy efficiency.