Studying the Effects of Interference on GNSS Signals

Global Navigation Satellite System (GNSS) signals, such as those from United States Global Positioning System (GPS), Europe’s Galileo, and Russia’s Global Navigation Satellite System (GLONASS), typically have extremely low received signal strengths at the Earth’s surface and are therefore susceptible to a range of interference signals. Such interference examples include, but not limited to, intentional sources such as Personal Privacy Devices (PPD) and unintentional sources such as Digital Enhanced Cordless Telecommunications (DECT) and Long Term Evolution (LTE) signal. Recent studies into such interference sources have identified GNSS jamming as having a major impact on geo-location positioning and communications technologies. One such study is the U.K. government funded Sentinel trial which investigated the density of jamming technologies at various road-side locations across the U.K. Another is the THV Galatea trial conducted by the Ministry of Defence in 2009 which documented the impact of interference signals on maritime navigation and communication systems [6]. Assessing the vulnerability of GNSS signals to such interference sources in real world scenarios is a challenging and time-consuming task which is subject to numerous environmental uncertainties. This paper describes a synthetic test environment which can model the effects of interference sources on GNSS signals and thus provide accurate, repeatable control of the signal characteristics in the laboratory. The system provides real-time control of both the GNSS and interference signal characteristics including definition of the receiving vehicle dynamics, signal modulation type, on/off periods, power level and center frequency. Of particular interest is the ability to introduce custom or user-defined modulation types which enables easy utilization of application critical waveforms during testing. This paper demonstrates the effect of several common broadband noise signals, as might be seen with a PPD, on a GNSS receiver. The results and conclusions of the investigation are supported by examining the receiver’s carrier-to-noise density (C/N0) and performance impact as a result of the interference sources throughout the test cases.