GNSS Nominal Signal Distortions - Estimation, Validation and Impact on Receiver Performance

S. Thoelert, C. Enneking, M. Vergara, M. Sgammini, F. Antreich, M. Meurer, D. Brocard, C. Rodriguez

Abstract:	Safety critical applications within the fields of aviation and ground transportation using Global Navigation Satellite Systems (GNSS) signals are present or in the stage of certification in these days. In this context the effect of nominal signal distortions on user error has to be assessed. Actually the GNSS signals radiated by satellites do not match perfect waveforms. This is due to several non-idealities of the satellite payloads; Some of them are observed under payload nominal conditions which are called ”nominal distortions”, and others encountered under failure conditions are called ”anomalous signal deformations” (or evil waveforms). It is of importance for several GNSS applications (e.g. civil aviation) to carefully assess the undesired effects of nominal distortions for each satellite of a given GNSS constellation, as different satellites introduce different distortions [1]. In this work we use a method for jointly estimating analog and digital (nominal) distortions presented in [4,5]. In addition to previous work we analyse the nominal distortions over time. Measurements of DLR’s 30m high gain antenna are used to derive estimates of nominal distortions for different GNSS satellites over the duration of the snapshot (short term) and the full path. This will provide first insight into the stability of nominal signal deformations. In this work we do not restrict ourselves to modelling linear analog distortions by a specific characteristic, e.g. a second order system. The reason for that is that the second order system model is not always accurate for legacy L1 signals as other previous studies have shown [2]. Moreover, as will be shown in the final paper, especially for signals with lower time-bandwidth product as e.g. the new GPS L5 or Galileo E5a signals the second order system model turns out not to provide a satisfactory modelling accuracy. We will show validation methods of the signal modelling versus real signal measurements to ensure the usability of the presented results and proposed options for future modelling strategies to improve the accuracy of future signal distortion analyses. Furthermore, these estimates of analog distortions as well as the related models are input to a GNSS receiver performance model following the ones given in [3] and [4] with which the tracking error bias and variance are derived with respect to discriminator types, receiver bandwidth, correlator spacing, etc. This will provide means to assess nominal user error behavior and also derive assumptions for nominal receiver errors for different GNSS satellites. We also will provide means to select receiver parameters in order to achieve small differential user error bias. In addition to previous work, we will also consider the derivation of user error bias for an example of satellite constellations in order to study the effect of the derived user error biases in positioning domain. The above described work supports European standardization activities and was partially performed within the activity Single European Sky ATM Research Programme (SESAR) funded by the European Commission and EUROCONTROL with respect to Multi-GNSS CAT II/III GBAS (Ground Based Augmentation Systems). This work is also targeting to contribute to the definition of the future SBAS (Space Based Augmentation Systems) L1/L5 multi-constellation user avionics standard, which is an evolution of the current SBAS GPS L1 SBAS standard. [1] R. Eric Phelts and Dennis M. Akos, “Effects of signal deformations on modernized GNSS signals,” Journal of Global Positioning Systems, vol. 5, no. 1, pp. 2–10, 2006. [2] R. E. Phelts, Todd Walter, and Per Enge,“Characterizing Nominal Analog Signal Deformation on GNSS Signals,” in Proceedings of the 22nd International Technical Meeting of The Satellite Division of the Institute of Navigation (ITM 2009), Savannah, GA, September, 2009. [3] M. Vergara, F. Antreich, and M. Meurer, “Effect of Multipath on Code-Tracking Error Jitter of a Delay Locked Loop,” in Fourth European Workshop on GNSS signals and signal processing, GNSS Signal 2009, Wessling, Germany, December, 2009. [4] M. Vergara, M. Sgammini, Y. Zhu, S. Thoelert, and F. Antreich, “Tracking Error Modeling in Presence of Satellite Imperfections”, Proceedings of the ION International Technical Meeting (ITM) 2014, January, San Diego, CA, U.S.A., 2014 [5] S. Thoelert, M. Vergara, C. Enneking, F. Antreich, M. Meurer, D. Brocard, C. Rodriguez, “Characterization of Nominal Signal Distortions and Impact on Receiver Performance for GPS (IIF) L5 and Galileo (IOV) E1 /E5a Signals”, ION GNSS+, 10.-12. Sep. 2014, Tampa, Florida, USA
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	1902 - 1923
Cite this article:	Thoelert, S., Enneking, C., Vergara, M., Sgammini, M., Antreich, F., Meurer, M., Brocard, D., Rodriguez, C., "GNSS Nominal Signal Distortions - Estimation, Validation and Impact on Receiver Performance," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 1902-1923.
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