Design and Assessment of a Dual Frequency GPS Intelligent Signal Tracking Loop for Interference Mitigation

A.M. Kamel

Abstract:	Unmanned Ariel Vehicles (UAVs) are playing a major role in nowadays battle scenarios. Using UAVs in the autonomous mode means that the vehicle is totally dependent on its sensors to complete the required mission. The main navigation sensor in most of the UAVs is the Global Positioning System (GPS) receiver. The main disadvantage of using GPS as a primary mean of navigation is the dependence on the received very weak GPS satellite signals. This disadvantage lead to main and easy way to threat the UAV by intentionally transmits a jamming signal to its GPS antenna. A new GPS signal phase and frequency lock loops (PLLs and FLLs) that depend on intelligent control and particularly fuzzy logic systems have been firstly introduced in (Kamel 2010). This design has been modified to cope with interference and proved a robust performance in the presence of dynamics and low and moderate levels of signal jamming as presented in (Kamel, Borio et al. 2011) and (Kamel, Borio et al. 2011). The used Fuzzy Frequency Phase Lock Loop (FFPLL) uses both frequency and phase discriminators outputs to generate the required frequency change to tune the Numerically Controlled Oscillator (NCO) that generates the local signal to follow the incoming signal frequency and phase. The main core of any fuzzy system is its Membership Functions (MF) that map the inputs/outputs to defined linguistic variables describe the input/output state. The system discriminators input signals are mainly contaminated by thermal noise which is considered the main source of signal noise. The distribution of signal noise is affected by signal dynamics and signal power level or in other words; the carrier-to-noise density ratio (C/No) and hence the interference level. The Fuzzy system MFs are designed such that they cover the signal normal distribution. The MF mean is affected by the signal dynamics and MF standard deviation is affected by the signal power. At certain level of interference the system is not able to continuously track the incoming signal and lock is lost (Kamel, Borio et al. 2011). This motivated the use of another GPS signal to aid the main L1 C/A signal. In this paper the possibility of expanding the design of the fuzzy tracking system to include a second GPS frequency particularly L2C signal is explored. System design of possible integrated configurations, test and analysis are introduced. Test results show that using L2C Doppler aiding to the L1 fuzzy tracking loop enables the system to maintain signal lock at high levels of L1 signal interference which was not possible using the classical techniques of the original fuzzy system design.
Published in:	Proceedings of the 2014 International Technical Meeting of The Institute of Navigation January 27 - 29, 2014 Catamaran Resort Hotel San Diego, California
Pages:	327 - 339
Cite this article:	Kamel, A.M., "Design and Assessment of a Dual Frequency GPS Intelligent Signal Tracking Loop for Interference Mitigation," Proceedings of the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2014, pp. 327-339.
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