Detection and localisation of radio frequency interference to GNSS reference stations

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Copyright: Thompson, Ryan
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Abstract
Global Navigation Satellite Systems (GNSS) are increasingly being relied upon in many applications. Reference stations provide corrections to errors inherent in GNSS processing, allowing GNSS to be used in more applications. The GNSS satellite signals are relatively weak and receivers are susceptible to Radio-Frequency Interference (RFI). To maintain the integrity of these reference stations any RFI must be detected and localised quickly. The research presented in this thesis investigates the detection and localisation of RFI using a sensor network. The first part of this thesis investigates RFI detection. For stationary receivers located in a stable environment, variations in the Carrier-to-Noise Density Ratio (C/No) can be used for detection. Weaker RFI can be detected if variations due to multipath are removed as they repeat with each satellite groundtrack. Issues associated with using the Automatic-Gain-Control (AGC) for RFI detection are also investigated. The drift in the AGC due to temperature is characterised and it could be reduced using a gain/temperature model, allowing the AGC to be used for detecting weaker RFI. The second part of this thesis investigates RFI localisation. An analysis using Dilution-of-Precision (DOP) showed that the Received-Signal-Strength (RSS) technique has potential. RSS performance was evaluated using simulations and real measurements and was found to suffer degradation due to the presence of ground reflections, resulting in the concluding that RSS is not appropriate. Time-Difference-Of-Arrival (TDOA) is another potential localisation method. Different aspects that affect TDOA were investigated, including time synchronization and effect of GNSS satellite cross-correlations. It was found that a number of time-delay measurements could be made before the timing from jammed GPS timing receivers degraded significantly, and that the GNSS satellite cross-correlation peaks make detecting and localising weaker RFI difficult. The explored C/No and AGC techniques are suitable for implementation into a sensor network and could detect weaker RFI using methods proposed in this thesis. For RFI localisation, TDOA was found superior to the RSS but some issues were found concerning weak RFI. The effectiveness of TDOA was demonstrated in a prototype system with real RFI and performance could be improved through an offline time synchronisation technique.
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Author(s)
Thompson, Ryan
Supervisor(s)
Dempster, Andrew
Cetin, Ediz
Balaei, Asghar
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Publication Year
2013
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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