Energy and Latency of Beamforming Architectures for Initial Access in mmWave Wireless Networks

Abstract

Future millimeter-wave systems, 5G cellular or WiFi, must
rely on highly directional links to overcome severe pathloss in these frequency bands. Establishing such links requires the mutual discovery of
the transmitter and the receiver, potentially leading to a large latency and
high energy consumption. In this work, we show that both the discovery
latency and energy consumption can be significantly reduced using fully
digital front-ends. In fact, we establish that by reducing the resolution
of the fully digital front-ends we can achieve lower energy consumption
compared to both analog and high-resolution digital beamforming.
Since beamforming through analog front-ends allows sampling in only
one direction at a time, the mobile device is “on” for a longer time compared to a digital beamformer, which can get spatial samples from all
directions in one shot. We show that the energy consumed by the analog
front-end can be four to six times more than that of the digital front-ends,
depending on the size of the employed antenna arrays. We recognize,
however, that using fully digital beamforming post beam discovery, i.e.,
for data transmission, is not viable from a power consumption standpoint.
To address this issue, we propose the use of digital beamformers
with low-resolution analog to digital converters (4 bits). This reduction
in resolution brings the power consumption to the same level as analog
beamforming for data transmissions while benefiting from the spatial
multiplexing capabilities of fully digital beamforming, thus reducing initial
discovery latency and improving energy efficiency