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Nichols, Mitchell

University of British Columbia

Wireless communication in the millimetre wave bands has attracted significant research interest for fifth generation (5G) networks due to the large amount of unused bandwidth at these frequencies. However, there are significant challenges associated with millimetre wave communications due to the high path loss of the propagation environment and the high power consumption of millimetre wave transceivers. Hybrid beamforming with massive multiple-input multiple-output (MIMO) has emerged as a solution to these problems by combining the performance and flexibility of digital beamforming with the energy efficiency of analog beamforming. Optical beamforming has recently been considered as a potential pathway to implement the analog component of a hybrid beamformer, which may offer improvements in size, weight and power consumption in comparison to conventional millimetre wave electronics. This thesis proposes a new approach to implement an optical beamforming system based on microring weight banks, which is a type of photonic tensor core using microring resonators as weight elements with wavelength-divison-multiplexing for input signal encoding. We analyze the performance of the photonic tensor core for millimeter wave signal processing and identify several limitations related to the signal delays through the optical circuit that may inhibit the scalability of an optical beamformer in a massive MIMO system. We propose a modified microring weight bank with tunable delay elements to equalize the path-dependent delay through the system. We also describe a procedure to calibrate a pair of microring weight banks as a phase shifter for beamforming applications. A numerical simulation was implemented to evaluate the performance of the system and a link budget analysis is provided to highlight the feasibility of the proposed optical beamformer, accounting for the signal-to-noiser power ratio and linearity requirements of a 5G base station. Finally, we perform an experimental demonstration of a small scale optical beamformer with phase shifters implemented by an on-chip microring resonator weight bank with integrated photodetectors and off-chip modulators. Our numerical and experimental results show that microring weight banks can be calibrated accurately for phase shifting in analog beamforming system with less than 2 degrees root-mean-square (RMS) phase error and 0.3 dB RMS amplitude error.

Text

2024-04-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84577

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/