Date of Award

Fall 2023

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

Alphan Sahin

Abstract

This dissertation presents circularly-shifted chirps (CSCs), synthesized within orthogonal frequency domain multiplexing (OFDM) framework, as a novel solution for integrating radar, communication, and computation functionalities to a wireless network. Firstly, {index modulation (IM)} with circularly-shifted chirps (CSCs) (CSC-IM) for dual-function radar and communication (DFRC) system is discussed. The proposed scheme encodes the information bits with the CSC indices and the phase-shift keying (PSK) symbols. It allows the receiver to exploit the frequency selectivity naturally in fading channels by combining IM and wideband CSCs. It also leverages the fact that a CSC is a constant-envelope signal to achieve a controllable peak-to-mean envelope power ratio (PMEPR). For radar functionality, CSC-IM maintains the good autocorrelation (AC) properties of a chirp by ensuring that the transmitted CSCs are separated apart sufficiently in the time domain through index separation (IS). We investigate the impact of IS on spectral efficiency (SE) and obtain the corresponding mapping functions. For theoretical results, we derive the union bound (UB) of the block error rate (BLER) for arbitrary chirps. We also prove that complementary sequences (CSs) can be constructed through CSCs by linearly combining the Fourier series of CSCs. Finally, through comprehensive comparisons, we demonstrate the efficacy of the proposed scheme for DFRC scenarios. We also demonstrate CSCs for an over-the-air computation (OAC) scheme to detect the majority votes (MVs) in a wireless network for federated edge learning (FEEL) and distributed localization. With the proposed approach, a group of votes is mapped to an index of a linear chirp at each edge device (ED). From superposed chirp signals, the corresponding MVs at the edge server (ES) are then detected non-coherently with a set of energy comparators by exploiting the bit representation of the indices. The proposed scheme is power-efficient and has low out-of-band emission while it does not use the channel state information (CSI) at the EDs and ES. Hence, it paves the way for long-distance FEEL and distributed localization based on MVs in a wireless sensor network with low-complexity devices. For FEEL, we comprehensively demonstrate the efficacy of the proposed approach under heterogeneous data distribution. For localization, we propose iterative refinements and multiple repetitions to improve the localization performance. We show that the proposed strategies minimize the distance between the root-mean-square error (RMSE) error and quantization bound.

Rights

© 2024, Safi Shams Muhtasimul Hoque

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