Browsing by Author "Roy, Arijit"

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    Chirp Waveform Design for Wireless Communication, Radar, and Energy-harvesting Systems
    (2022) Roy, Arijit
    A chirp waveform is a frequency modulated signal in which the signal duration and bandwidth can be adjusted independently. In this thesis, an exhaustive study on the design of chirp waveforms and the analysis of associated systems employing the waveforms are performed for wireless communication, radar, Internet of Things (IoT), and wireless energy transfer (WET) applications. The design and analysis studies are broadly divided into three parts. In the first part, designs of new waveforms using chirp, e.g., phase-coded chirp waveform, set of orthogonal chirp waveforms, symmetry chirp waveform with multiple chirp rates (SC-MCR) have been explored for multiuser communication systems and IoT applications, and the performances of the associated systems, evaluated under different channel fading scenarios, indicate improved performance over the reported designs. In the second part, novel designs of a set of discrete frequency-coding waveforms (DFCWs) using linear chirp (LC) and nonlinear chirp (NLC), e.g., DFCWs-PNLC, DFCWs-NLC, are developed for multiuser and MIMO radar applications. Analytical expressions of ambiguity functions are derived to analyze the waveform performances, and optimization process based on genetic algorithm is performed for the appropriate selection of waveform parameters value. It is observed that the proposed DFCWs-PNLC and DFCWs-NLC provides major improvement in peak sidelobe level performance over the reported DFCW designs while attaining an increase in the number of available waveforms as well. WET is an emerging technology intended to be used for energy-constrained wireless sensor networks (WSN). In the third part, the potential of chirp waveforms is investigated for downlink (DL) WET from a multi-antenna access point (AP) to a group of sensors over orthogonal subbands based on their channel estimates while maintaining the peak transmit power constraint. Accordingly, the design of a novel superposed chirp waveform is presented. New analytical expressions using order statistics are derived for the average harvested energy based on DL-WET via superposed chirp waveforms, and max-min optimal power control coefficients in closed form are evaluated. Through analysis and simulations, it is proved and elucidated that DL-WET via superposed chirp waveforms improves the max-min harvested energy, extends the operating range of WET, and widens the energy-information transfer region in comparison with DL-WET via conventional fixed-frequency waveform.