The Global Positioning System (GPS) signal simulator plays a critical role in developing and testing GPS receivers. Unfortunately, very few commercial GPS signal simulators are user-friendly for security researchers because they fail to generate abnormal GPS signals, which are fundamentally important. In this thesis, we develop a cost efficient software defined GPS signal simulator. To reduce the design complexity, we make some reasonable assumptions about the GPS system. This simulator is able to generate clean GPS signals, as well as polluted GPS signals by jamming, multi-path, and spoofing interferences. In addition to simulating GPS signals for a single stand alone antenna, our simulator is also able to simulate GPS signals for multiple antennas, simultaneously. These features of the simulator will immensely help the security researchers in the GPS community. / Master of Science

Global Positioning System (GPS) is a satellite-based navigation system that has been used widely both in civilian and military for positioning, navigation, timing and other position related applications. The hardware-based GPS receivers provide the least user flexibility. Thus, it is necessary to have Software-based GPS receivers for easy and quick implementation, simulation and analysis of algorithms. Software-based GPS receiver processes the GPS signal at the radio frequency or intermediate frequency depending on the hardware configuration of the receiver. In this development of the acquisition and tracking processes of the software receiver, the front-end device that converts the radio frequency signal from the antenna to an intermediate frequency is the Mitel 2021 GPS receiver board. An analog-to-digital (A/D) converter then digitizes the output signal from the RF front-end. The data is then processed using MATLAB programs to achieve acquisition and tracking of the GPS signals. The software GPS receiver can perform acquisition and tracking using different parameters and threshold values. This flexibility of operation allows weaker signals to be tracked and processed. In this software receiver design, the focus is on the acquisition and tracking of L1 band C/A code GPS signals used by most civilian applications. The purpose of this thesis is to develop the acquisition and tracking algorithms to extract the navigation data bits from the raw GPS signals. The navigation data bits provide all the necessary information to compute the pseudorange between the receiver and the visible satellites and determine the receiver location. Both MATLAB simulated GPS data and realistic GPS signals from a GSS 6560 simulator are used to verify the performance of the acquisition and tracking programs. The acquisition program is capable of locating the beginning of the C/A code and the carrier frequency to within the desired accuracy. From the output of the acquisition program, the tracking program can decode the navigation data bits. The tracking algorithm implemented is based on the block adjustment of synchronizing signal (BASS) method. / Master of Science

The Global Positioning System (GPS) satellite signals provide not only traditional radionavigation service but inexpensive and convenient radio beacons for signal propagation studies on ionosphere and atmosphere. This thesis describes the development and testing of a specialized GPS sensor which measures, plots and records real-time high-resolution L1 (1575.42MHz) GPS signal strength at a data rate of up to 10Hz. The instrument is based on an open architecture GPS receiver development kit that can be modified and rebuilt. The signal strength is defined as mean-square signal strength in the thesis. The coarse/acquisition code (C/A-code) correlation is applied and the raw correlation data from a GPS correlator chip is obtained to calculate the signal strength. The gain variation of the automatic gain control (AGC) in the GPS signal link is considered, and a model is designed and implemented in data post-processing to reduce the AGC distortion to GPS signal strength measurements. Speed limitation of 1,000 knots and height limitation of 60,000 feet are removed so that it can track spacecraft such as low earth orbit (LEO) satellite. Four testing plans are developed and conducted to test the GPS signal strength sensor. A GPS simulator is used and the testing results prove that the space-borne sensor is fully operational and the signal strength resolution can be smaller than 0.05dB. Additionally, a COM-port-to-TCP/IP GPS simulation remote control gateway is designed and implemented for the senor and the GPS simulator to conduct formation flying. A graphic user interface (GUI) program is also built to retrieve data from a commercial high-performance space-borne GPS receiver for comparison. A Red Hat Linux signal strength sensor based on the National Aeronautics and Space Administration (NASA) PiVoT GPS receiver is achieved by modifications. The NASA PiVoT sensor, working together with the former signal strength sensor and the commercial space-borne GPS receiver, will strengthen our academic research strength in the studies on the ionospheric and atmospheric effects and irregularities which cause GPS signal degradation and scintillations. / Master of Science