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Abstract

This research investigates approaches to Millimeter-Wave (mmWave) beamforming practices to improve upon existing methods, in particular for wireless communication standards, such as 5G/New Radio (NR) and 802.11ad/ay. The current methods rely on an inefficient linear search over all possible steering directions for initial alignment, and require highly manual configurations to maintain alignment over time. We leverage state-of-theart algorithms from areas such as reinforcement learning to improve upon these existing practices, in particular Multi-Armed Bandit (MAB) algorithms. Our work shows that our algorithms are competitive with scenarios in which full Channel-State Information (CSI) is exploited for Bayesian decision making on the steered beam directions. Our algorithms also provide a low computational overhead alternative to algorithms considered optimal in sample complexity as a trade-off. First we review the current state-of-the-art algorithms for initial alignment and tracking in Chapter 1. In Chapter 2, we describe our system model that precisely defines the problem space in which we make contributions. We also show a hierarchical codebook induces structure in our system model that allows opportunities for efficient exploitation. Then, we present Successive Subtree Elimination (SSE) in Chapter 3, an algorithm for the initial beam alignment problem that exploits the structure induced by a hierarchical beamforming codebook. SSE uses a MAB algorithm in the fixedconfidence setting with a hierarchical graph level-by-level approach in which we eliminate several beamforming vectors for narrow beams at once by eliminating ones corresponding to broader beams. In Chapter 4, we provide an algorithm, Hierarchical Optimal Sampling for Unimodal Bandits (HOSUB), that uses depth-first search through the hierarchical graph to more quickly align than the level-by-level approach used in other algorithms using a hierarchical codebook. Unfortunately, the analysis proves to be too difficult to make theoretical guarantees for this particular framework and remains an open problem. In Chapter 5, we extend SSE initial alignment algorithm to compensate for motion. Our extended algorithm,Dynamic Beam Zooming (DBZ), adjusts the beamforming vector selection to widen and narrow the beamwidth to mitigate the severe outages associated with mmWave channels. Our simulations and metrics consider that the alignment and tracking sensing problems must co-exist with the ultimate goal of communicating between entities, which comprises an Integrated Sensing and Communication (ISAC) approach. In Chapter 6, we demonstrate the trade-off between using optimal algorithms adapted for tracking versus other algorithms that require significantly less computational overhead. We do this by adapting the Trackand-Stop (TAS) framework for best arm identification to dictate beamforming selection and compensate for motion. Lastly, in Chapter 7 we provide perspectives and conclusions on our major contributions.

Details

1010268
Title
Mmwave Beamforming Facilitated by Hierarchical Codebooks and Structural Bandit Algorithms
Number of pages
152
Publication year
2025
Degree date
2025
School code
0078
Source
DAI-A 87/5(E), Dissertation Abstracts International
ISBN
9798263326463
Committee member
Sundaresan, Karthikeyan; Romberg, Justin; Durgin, Gregory; Lan, Guanghui
University/institution
Georgia Institute of Technology
University location
United States -- Georgia
Degree
Ph.D.
Source type
Dissertation or Thesis
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
32308092
ProQuest document ID
3275477872
Document URL
https://www.proquest.com/dissertations-theses/mmwave-beamforming-facilitated-hierarchical/docview/3275477872/se-2?accountid=208611
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works; open.access
Database
2 databases
  • ProQuest One Academic
  • ProQuest One Academic