Novel millimeter wave beamforming architectures and procedures for initial access
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Ghunney, Edith
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Abstract
The objective of the dissertation is to explore a combination of novel architectural and procedural changes in mmWave systems, to shorten initial access delay, reduce angle estimation error in the acquisition phase, and increase the capacity or spectral efficiency in the data communication phase. To improve initial access delay, we show that the wrong second beam can be selected in the auxiliary beam pair (ABP) technique when the target or user is near the center of one of the beams and the coincident nulls of the other beams. We propose to eliminate the coincident nulls problem by using non-orthogonal beam sets for the beam scanning process. We explore three different approaches to generate the non-orthogonal beam sets. First, we introduce the narrowed beam gap approach, which utilizes reduced spacing between the beams formed using conventional phased array beamforming. For the other two approaches, we maintain the orthogonal beam spacing as used in ABP but adopt different array patterns with larger mainlobes, created using the Dolph-Chebyshev and Gaussian array pattern synthesis methods. We compare the performance of the three beam sets in terms of root mean-squared angle estimation error, the number of beams required to cover the sector (which influences initial access delay), and the effective received signal-to-noise ratio, taking into account the tapering loss inherent in non-uniform beamforming weights. Because good mmWave channels have line-of-sight, we propose to increase the capacity by applying methods that improve free-space MIMO performance, specifically, by increasing the sub-array spacing for mmWave MIMO channels and by using a novel array architecture called the array-of-slanted subarrays, which allows a non-zero relative angle between subarrays on a terminal. Considering 2-D (azimuth-only) beamforming, two sub-arrays per terminal, and a range of base station and user equipment relative rotations, we identify the optimal slanting of subarrays under four different channel models of propagation, in terms of the average spectral efficiency of the link.
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2024-12-08
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Dissertation (PhD)