Characterization of GNSS Integrity Threats in Terrestrial Applications Using Real Signal Captures

E. Domínguez, G. Seco-Granados, J. Salcedo, D. Egea, E. Aguado, D. Lowe, D. Naberezhnykh, F. Dovis, J.P. Boyero, I. Fernandez

Abstract: The Integrity GNSS Receiver (IGNSSRX) is a European Commission funded project with three main objectives: a) The development of two platforms to capture and store GNSS radio frequency signal samples and a reference trajectory from representative low-, medium- and high-end sensors in terrestrial applications. b) An extensive data collection campaign aiming to characterize error sources, magnitudes and probabilities for two important GNSS terrestrial application areas: automotive and pedestrian users. c) The research and development of techniques and algorithms to mitigate the integrity threats in the two terrestrial environments studied using the collected data, thus allowing reliable terrestrial applications within these domains. This paper presents the results for the first two objectives of the IGNSSRX project, providing the GNSS measurement error characterization results obtained from the analysis of the real data collected using the developed platforms during the acquisition campaign, together with a preliminary report on the developed techniques and algorithms. Data Collection Platforms Two Data Acquisition and Storage Units (DASU) have been developed within the IGNSSRX project for the data collection campaign in the vehicular and pedestrian domains: ? Vehicular DASU: - RF Front-Ends: a high resolution FE and a three-antenna FE system working both in the GPS L1 and Galileo E1 bands and the GLONASS L1 band. The high-resolution FE allows the application of DSP techniques to detect the integrity threat and the three antenna array allows the use of the direction of arrival (DOA) information to identify non line-of-sight (NLOS) signals. - Record raw data from medium and low cost COTS sensors, such as IMUs and odometer, for PVT hybridisation with GNSS as well as to provide a reference of the performance or representative medium and low cost solutions used in these applications - Truth reference equipment using a high accuracy/high availability reference system based on high geodetic-grade GPS&GLONASS dual-frequency receiver, tactical-grade IMU and digital wheel probe, processed using a dedicated COTS post-processing software. - Common atomic clock (CSAC Caesium clock) synchronizing the platform with the truth reference equipment. ? Pedestrian DASU: - RF Front-Ends: a high resolution FE in the GPS L1 and GLONASS L1 bands. - Records GSM and Wi-Fi measurements to augment/hybridise with GNSS and mobile phone platform as a COTS reference - Truth reference equipment based on a GPS&GLONASS L1/L2 geodetic receiver plus route trace. - Common atomic clock (CSAC Caesium clock) synchronizing the platform with the truth reference equipment. Data Collection Campaigns Using the two DASU an extensive data collection campaign has been carried out covering representative road and pedestrian user environments: ? Vehicular campaign: fourteen days of road data collection covering a motorway route with open sky (best case), and an urban route through typical city environments with canyons and tunnels. ? Pedestrian campaign: a number of different routes around city areas in three cities. Of these routes there are two "city centre" routes, where there is a mixture of closely spaced buildings, covered arcades and wider roads; two in "out of town" shopping centres with large car parks for initialisation and limited visibility in the remaining of the route; and a rural/suburban route around a park area. ? Interference campaign: the collected data is complemented by tests performed with a signal simulator to test the impact of interferences and spoofing. Offline Analysis Unit (OAU) Based on the SRX software receiver [1] for processing the collected RF samples and by taking advantage of the accurate reference system and a common reference atomic clock integrated in the DASU platforms, the measurement errors (code, carrier phase and Doppler) can be accurately determined, and by using precise orbit, clock and ionosphere data from reliable sources (such as the IGS) it is possible to distinguish between local and non-local error contributions. DSP techniques applied to the collected RF samples allow identifying the nature of the local sources of error or interferences (e.g. by means of spectral and temporal analysis of the signals, multi-antenna analysis, etc.). Characterization Results Data analysis, aimed at identifying and characterising the integrity threats in terrestrial environments, has been performed. This analysis allows the construction of real-data scenarios which encapsulate the failure events encountered. Considerable research has been already done in other projects analysing urban threats to GNSS positioning, but little emphasis has been put on measurement error characterisation, especially with regard to the integrity implications. This is quite possibly due to the complexity and variety of error sources in urban environments, and the great difficulty associated with the discrimination of the actual error sources in the individual measurements. The sophisticated vehicular and pedestrian Data Acquisition and Storage Unit (DASU) platforms and the Offline Analysis Unit (OAU) enable the detailed study and characterisation of threats at both signal and measurement levels. Special attention is paid to those threats known to be major causes of positioning error in harsh environments, such as NLOS tracking, multipath, spoofing and interference. Summarizing, this paper presents the platforms developed to collect real measurements along with the tools used for their analysis and provides the characterization of the integrity threats affecting GNSS terrestrial applications.
Published in: Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014)
September 8 - 12, 2014
Tampa Convention Center
Tampa, Florida
Pages: 954 - 966
Cite this article: Domínguez, E., Seco-Granados, G., Salcedo, J., Egea, D., Aguado, E., Lowe, D., Naberezhnykh, D., Dovis, F., Boyero, J.P., Fernandez, I., "Characterization of GNSS Integrity Threats in Terrestrial Applications Using Real Signal Captures," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 954-966.
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