A GPS and GLONASS L1 Vector Tracking Software-Defined Receiver

Abstract

Originally designed for military navigation, GPS has exploded into a modern tool used by government, industrial, and commercial sectors. The increasing demand for navigation has led to the operation of GPS receivers in challenging signal environments that include suburbs, forested areas, and metropolitan cities. In recent years, GPS receivers have also come under attack from commercial jamming and spoofing devices. To assure the integrity of GPS, the ability for receivers to overcome challenging signal environments must be solved. GPS vectorized signal tracking (vector tracking) has been shown to enhance receiver performance by 2 to 6 dB in poor signal environments over traditional tracking methods that rely on loop filters (scalar tracking). GLONASS, the Russian Federation’s equivalent to GPS, is another system that can be used for navigation. Today, many receivers use both GPS and GLONASS with scalar processing. Implementing the constellations into a centralized vector tracking filter gives the opportunity of enhanced navigation capability in challenging areas. In this thesis, the development and analysis of a software receiver that uses GPS and GLONASS vector tracking is performed. Specifically, the software receiver uses a centralized Vector Delay/Frequency Lock Loop (VDFLL) Kalman filter implementation to track the code and carrier dynamics of the satellite signals. Cascaded Phase Lock Loop (PLL) aiding is applied to the satellite channels to maintain carrier phase lock. Simulation results showed the software receiver’s ability to maintain accurate navigation in GPS or GLONASS jamming environments. In GPS jamming environments, GLONASS was able to maintain accurate tracking replicas of the GPS channels through the VDFLL. Experimental results from forested areas and urban canyons showed that the software receiver performed better with vector tracking than scalar tracking. Depending on the experiment, GPS and GLONASS vector tracking outperformed GPS-only vector tracking. In some environments, GLONASS became degraded, which caused noise sharing issues in the software receiver’s vector processing algorithm. ii