Investigation of Real Interference Effects on Conventional GNSS Receivers

One of the main characteristics of the Global Navigation Satellite System (GNSS) signals is the low level of the received signal strength. For the signals of both the Global Positioning System (GPS) and Galileo the power spectral density of the received signal is approximately 20 dB/Hz below the thermal noise floor and using conventional receiving antennas and hardware, the signal at the front end output is masked by noise. Given this scenario, the presence of interfering sources in the operating scenario bounds the achievable accuracy performance, limiting also the development of effective applications. For these reasons the interest towards interference monitoring techniques is growing, also for mass-market applications in urban environments. Several different electromagneticsources, that populate the crowded radio frequency spectrum might be potential interferers on the GNSS bandwidths. Due to their different characteristics (i.e.: transmitting power, bandwidth, carrier frequency), these interference signals can affect the regular signal processing within the navigation receiver in different ways. This paper describes the impact ofa real interference on a conventional GPS receivers. Several data sets have been collected in a harsh environment sited approximately 1.5 km away from two transmitting antenna used to broadcast analog and digital TV. The paper aims at describing the experimental setup and the data collection campaign analysing how strong out-of-band signals placed in Very High Frequency (VHF) and Ultra High Frequency (UHF) bands, since they can produce secondary harmonics which fall into the GPS bands, lead to a degradation of the receiver performance.