The introduction of Machine Learning (ML) and Deep Learning (DL) techniques into modern radio communications system, a field known as Radio Frequency Machine Learning (RFML), has the potential to provide increased performance and flexibility when compared to traditional signal processing techniques and has broad utility in both the commercial and defense sectors. Existing RFML systems predominately utilize supervised learning solutions in which the training process is performed offline, before deployment, and the learned model remains fixed once deployed. The inflexibility of these systems means that, while they are appropriate for the conditions assumed during offline training, they show limited adaptability to changes in the propagation environment and transmitter/receiver hardware, leading to significant performance degradation. Given the fluidity of modern communication environments, this rigidness has limited the widespread adoption of RFML solutions to date.
Transfer Learning (TL) is a means to mitigate such performance degradations by re-using prior knowledge learned from a source domain and task to improve performance on a "similar" target domain and task. However, the benefits of TL have yet to be fully demonstrated and integrated into RFML systems. This dissertation begins by clearly defining the problem space of RF TL through a domain-specific TL taxonomy for RFML that provides common language and terminology with concrete and Radio Frequency (RF)-specific example use- cases. Then, the impacts of the RF domain, characterized by the hardware and channel environment(s), and task, characterized by the application(s) being addressed, on performance are studied, and methods and metrics for predicting and quantifying RF TL performance are examined. In total, this work provides the foundational knowledge to more reliably use TL approaches in RF contexts and opens directions for future work that will improve the robustness and increase the deployability of RFML. / Doctor of Philosophy / The field of Radio Frequency Machine Learning (RFML) introduces Machine Learning (ML) and Deep Learning (DL) techniques into modern radio communications systems, and is expected to be a core component of 6G technologies and beyond. While RFML provides a myriad of benefits over traditional radio communications systems, existing approaches are generally incapable of adapting to changes that will inevitably occur over time, which causes severe performance degradation. Transfer Learning (TL) offers a solution to the inflexibility of current RFML systems, through techniques for re-using and adapting existing models for new, but similar, problems. TL is an approach often used in image and language-based ML/DL systems, but has yet to be commonly used by RFML researchers. This dissertation aims to provide the foundational knowledge necessary to reliably use TL in RFML systems, from the definition and categorization of RF TL techniques to practical guidelines for when to use RF TL in real-world systems. The unique elements of RF TL not present in other modalities are exhaustively studied, and methods and metrics for measuring and predicting RF TL performance are examined.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/117881 |
| Date | 06 February 2024 |
| Creators | Wong, Lauren Joy |
| Contributors | Electrical Engineering, Michaels, Alan J., Freeman, Laura June, Huang, Jia-Bin, Williams, Ryan K., Dhillon, Harpreet Singh |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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