GNSS Interference: Effects and Solutions

In this paper we firstly analyze the effects of RF interference among GNSS systems for realistic current (January 2015) and next generation (2017, 2020) scenarios. Intersystem interference is computed for signals where GPS, Galileo, Compass, GLONASS systems share the same band. In essence, the GNSS signals operating in overlapping bands are identified, and, for each of them, the Spectral Separation Coefficient (SSC) is computed. Moreover, the Effective Carrier Power to Noise Density, versus the number of visible satellites and power levels of each interfering constellation is evaluated with main focus is addressed to Galileo E1BC and GPS L1 C/A signals. For each investigated scenario, the analysis results show that interference effects on GNSS user receiver increase almost linearly with the number of visible interfering satellites. Finally, the paper describes a possible solution to the RF interference: an innovative design of a Controlled Radiation Pattern Antenna (CRPA) operating in Radio Frequency interference conditions as a means to mitigate the navigation performance degradation caused by the interference. Specifically, FRPA (Fixed Radiation Pattern Antenna), and CRPA phased array design of L-band RHCP micro-strip antennas is studied by means of electro-magnetic commercial tools and optimization algorithms. Phased array single radiator is designed in conventional and meta-material technology. Different CRPA configurations are traded-off in terms of “beam-forming” capability (e.g. radiation pattern nulls depth and width), antenna gain and RF pattern shape, antenna physical envelope. Advantages and drawbacks for GNSS applications are highlighted. In order to evaluate the CRPA benefits in terms of interference resilience, a realistic interference scenario is studied, considering the geometry-dependent and time-varying terms such as GNSS space constellation, RF interfering sources, signal modulation, emission RF power levels, satellite antenna gain and GNSS receiver characteristics. GNSS service performances (i.e., user location accuracy, and service time availability) are computed taking into account the adaptive array radiation pattern in two different modes (i.e., FRPA or CRPA) and under band-limited white noise interference. More specifically, to assess the performance of the proposed mitigation scheme, “ad – hoc” simulation making use of a GNSS simulator has been employed. The simulator consists of a) a Satellite Orbit Generator providing precision ephemeris to support evaluation of accurate propagation delays and Doppler effects, b) a propagation module evaluating the transformations affecting the satellite signals received at a specific location, including incremental ionosphere and troposphere incremental delays, c) a GNSS receiver motion generator computing the Kinematic data of a receiver on board of a mobile unit; d) a jammer signal generator; e) a GNSS receiver; f) the GNSS Localization module.