| PhD Viva

Name of the Speaker: Mr. Sreeraj S J (EE17D033)
Guide: Dr. Deepa Venkitesh
Venue: Online
Online meeting link: https://meet.google.com/cvg-jupr-mzg
Date/Time: 3rd July (Wednesday) 2024, at 10AM
Title: Analog Optical Technologies for Generation, Transport and Sensing of mmWave Signals

Abstract :

In this work, we delve into the realm of microwave photonics, showcasing some of its applications across both civilian and military domains. This work demonstrates the potential of microwave photonics to supersede traditional radio frequency (RF) systems, with enhanced ultra-broadband capabilities, low loss, and minimal electromagnetic interference, among other advantages. This thesis covers analytical and time-domain models of radio frequency over fiber (RFoF) links, which are described in detail and validated with available literature and experiments. An intuitive MATLAB-based application designed for the seamless design of RFoF links has been implemented. A work that proved to be of significant contribution to the experimental demonstrations in this thesis includes the development of a dither-free any-point bias controller. The algorithms that enabled precise control are discussed in sufficient detail. This is further enhanced by multichannel implementation, allowing for the simultaneous control of multiple modulators with reduced hardware requirements. Specifically, this thesis demonstrates a multi-channel IF upconversion system comprising five modulators, tailored for 5G signal transport. Further, this thesis explores the application of analog radio over fiber for mmWave fronthaul in 5G networks. Fronthaul data rates in case of millimeter wave (mmWave) wireless systems scale up to several Gbps in the currently deployed digitized radio over fiber solutions, resulting in large complexity remote radio heads (RRHs). The thesis propose a promising solution involving optical frequency doubling and quadrupling, where all complex digital processing are moved to the centralized base band unit (BBU), thereby allowing placement of large number of low-complex RRHs at long distances. Further experimental demonstrations are discussed with optical frequency doubling and quadrupling for the generation and transport of millimeter wave mmWave signals with OFDM containing QPSK, 16/64/256-QAM modulation formats over a distance of 2 km. These schemes enable the use of low-frequency RF signals at the BBU for the generation of mmWaves at the RRH. The performance of the systems were conducted in terms of error vector magnitude (EVM) and out-of-band emissions of the upconverted data. The results show that the proposed schemes achieve EVM values within the 3GPP 5G standard requirements. We also investigate the tunability and scalability of the proposed schemes across the n258 band (24.25 - 27.5 GHz) and discuss the feasibility of implementing dense wavelength division multiplexing (DWDM) for servicing multi-channel operation required for multisector antennas. The proposed schemes can support high data rate transmission for future wireless networks including 6G. For most of the experiments, in house built multichannel bias controller was used. Lastly, this work investigates photonic technologies in cognitive radio and defense applications, particularly focusing on instantaneous frequency measurement (IFM) systems. This thesis lays the theoretical groundwork for a novel sub-Nyquist sampled IFM system and proposes future work aimed at its experimental implementation.