註釋 Space-based positioning, navigation and timing (PNT) systems, such as Global Positioning System (GPS), are vulnerable to radio frequency interference (RFI) and spoofing. We can defend against these types of attacks by having alternate sources of positioning, navigation and timing information, however, delays in detection can result in cascading, negative consequences to users. This is especially true with GPS-dependent critical infrastructure and key resource (CIKR) sectors such as the electric power grid, telecommunications, transportation and emergency services. While detection of RFI is becoming a trivial problem, spoofing remains a tough problem to comprehensively solve. Spoofing can involve maliciously altering the modulated direct sequence spread spectrum codes, the broadcast navigation message, or the carrier wave. Current spoofing detection methods are focused on the monitoring and processing of direct line-of-sight global navigation satellite system (GNSS) signals and navigation message authentication. With resources, a dedicated, technologically advanced attacker can overcome all currently proposed defenses of the unencrypted civil signals [1]. GNSS spoofing attacks, like jamming and interference, are on the rise. Many CIKR rely on fixed GNSS receivers. These prolific fixed GNSS receivers can be leveraged as spoofing detection sensors without any modifications. The existing observables from both direct line-of-sight and reflected GNSS signals can be exploited to defend fixed receivers within CIKR sectors from data and measurement spoofing. This thesis includes a new theory, methodology and applied implementation of GNSS interferometric reflectometry signature-based defense of fixed receivers. I first demonstrate the theory behind GNSS interferometric reflectometry signature based defense. Applying signal propagation concepts to empirical and rigorous signal models reveals that a spoofer will be unable to perfectly mimic the true GNSS signatures without contributing its own signature. Next, this methodology is evaluated by determining the variability of field observations from actual and representative CIKR sector fixed sites. For this evaluation, we created a prototype GNSS-IR signature-based detector that implements our new model for generating truth calibration signatures and then performs input validation on new observations. We developed and implemented two detection algorithms. We used two types of simulated spoofers to evaluate the performance using receiver operating characteristic (ROC) curves demonstrating its ability to yield a probability of detection of over 90 percent while maintaining a false alarm rate of less than 0.00001. In all cases, we were able to detect spoofing in 3 seconds or less. Finally, I have developed a cross-layered framework for CIKR sector fixed receiver networks to host the GNSS-IR signature-based defense. I detail the baseline requirements and implementation strategies for CIKR. I leveraged the field environment of candidate CIKR sectors to evaluate the usefulness of the derived baseline requirements and implementation strategies for the most effective employment of GNSS-IR signature-based defenses. We have also included an evaluation of GNSS-IR signature-based defense in built versus natural environments, dynamic versus static reflection zones and antenna installation strategies. We have determined both the communications, energy sectors and v portions of the transportation sector to be good candidates for GNSS-IR signature-based defenses. The ideal location being on a building or structure that has good water mitigation, or drainage, and controlled access around the antenna such as a roof. Our real-time experiment of a prototype cross-layered integrity processing and alerting service framework demonstrates the usefulness, speed and security of my invention. 