Interference Localisation within the GNSS Environmental Monitoring System (GEMS) - Initial Field Test Results

This paper presents field test results from a prototype GPS interference localisation system that uses spatially separated sensor nodes containing antenna arrays to localise interference using both Direction of Arrival (DOA) at each array and Time Difference of Arrival (TDOA) measurements between arrays. The synergy between antenna arrays and TDOA systems are explored and it is found that antenna arrays bring many important benefits to TDOA systems. They can be used to improve time synchronisation between nodes by steering a null at the interference and beams at GPS satellites. They can also be used to steer a beam at the interference to improve its Signal-to-Noise Ratio (SNR) when estimating the TDOA between nodes. Finally the DOA measurements themselves can be used to localise the interference even for very narrowband signals for which TDOA becomes unusable. In this paper the use of the GPS signals themselves for array calibration is also explored, and the GPS signals are used to estimate the orientation of each antenna array, calibrate the phase errors in each antenna array and improve the synchronisation between spatially separated nodes. The experimental antenna array nodes developed are intended for integration into the GNSS Environment Monitoring System (GEMS) developed by GPSat Systems which consists of a number of low-cost sensor nodes that comprehensively monitor GNSS system performance in a given area.