Publication: Initial access and beam-steering mechanisms for mmWave wireless systems
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2020-07
Defense date
2020-10-23
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Abstract
Future millimeter-wave networks will support very high densities of devices and access
points. This vastly increases the overhead required for access point selection and beam
training. Due to unfavorable radio propagation, mmWave systems will exploit largescale
MIMO and adaptive antenna arrays at both the transmitter and receiver to realize
sufficient link margin. Beamforming is vital to overcome the high attenuation in wireless
millimeter-wave networks. It enables nodes to steer their antennas in the direction of
communication. Fortunately, the quasi-optical properties of millimeter-wave channels
make location-based network optimization a highly promising technique to reduce control
overhead in such millimeter-wave WLANs.
In this thesis we present tools to improve mmWave systems. We start by designing
an effective lightweight sector beam-pattern design for using as a baseline for hybrid
analog-digital structures. We deal with practical constraints of mmWave transceivers
and propose a novel, geometric approach to synthesize multi-beamwidth beam patterns
that can be leveraged for simultaneous multi-direction scanning. Then we make use of this
multi-direction scanning to create a beam training protocol which effectively accelerates
the link establishment by exploiting the ability of mobile users to simultaneously receive
from multiple directions. We propose smart beam training and tracking strategies for
fast mm-wave link establishment and maintenance under node mobility. We leverage the
ability of hybrid analog-digital transceivers to collect channel information from multiple
spatial directions simultaneously and formulate a probabilistic optimization problem to
model the temporal evolution of the mm-wave channel under mobility. We propose a
mechanism to extract full channel state information (CSI) regarding phase and magnitude
from coarse signal strength readings on off-the-shelf IEEE 802.11ad devices. Using this
CSI, transmitters dynamically compute a transmit beam pattern that maximizes the
signal strength at the receiver. Channel properties and antenna design at 60GHz are
ideal for path angular information extraction, following an almost ideal geometric channel
model. Due to this, we present some localization method specifically designed for the
60GHz band. We merge the ideas presented in this thesis and by extracting channel
state information from off-the-shelf routers we estimate the user location to manage a
location aware beam-training and device handling method. The resulting scheme can predict blockage, optimize access point association, and select the most suitable antenna
beam patterns while significantly reducing the beam training overhead.
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Keywords
Beam pattern synthesis, Sector beam, Uniform linear arrays (ULAs), MIMO communications