Author

Pranav Patel

Date of Award

9-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Electrical and Computer Engineering

First Advisor

Richard K. Martin, PhD

Abstract

In legacy Global Positioning System (GPS) Satellite Navigation (SatNav) payloads, the architecture does not provide the flexibility to adapt to changing circumstances and environments. GPS SatNav payloads have largely remained unchanged since the system became fully operational in April 1995. Since then, the use of GPS has become ubiquitous in our day-to-day lives. GPS availability is now a basic assumption for distributed infrastructure; it has become inextricably tied to our national power grids, cellular networks, and global financial systems. Emerging advancements of easy to use radio technologies, such as software-defined radios (SDRs), have greatly lowered the difficulty of discovery and exploitation of vulnerabilities to these systems. The promise of a Direct Digital Synthesis (DDS) architecture provides the flexibility of incorporating countermeasures to emerging threats while maintaining backward capability with existing GPS signals. The objective of the proposed research is to determine if DDS architecture is a viable replacement for legacy GPS SatNav payloads. The overall performance of several architectures is analyzed and evaluated. The architecture with the best performance is chosen and implemented onto a programmable logic device, and GPS signals are generated. The advantages and disadvantages of using the DDS model are discussed and an end-to-end numerical and mathematical models are developed. The end-to-end mathematical model analyzes the quantization effects of the DDS architecture, and it predicts the location and power levels of the desired signal and spurious content present in the spectrum. The spurious content may potentially cause intermodulation distortion to the desired signal. The appropriate DDS architecture and resources are selected by the information gained from the mathematical model.

AFIT Designator

AFIT-ENG-DS-20-S-014

DTIC Accession Number

AD1109193

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