Optimal Search Strategy in a Multi-constellation Environment

E. Anyaegbu, B.R. Townsend and R. Zuo

Abstract:	Traditional methods for satellite search and acquisition have been dominated by methods best suited for GPS. For example, search strategies used for GLONASS acquisition were often adapted from GPS search techniques and did not exploit the properties of the GLONASS signal structure such as its short PRN code sequence and the fact that two GLONASS satellites are transmitted on the same frequency channel if they are located in antipodal slots of a single orbital plane. Also, GLONASS is more robust to interference compared to GPS. For instance, an interference source that may disrupt one GLONASS FDMA signal would disrupt all GPS CDMA signals simultaneously. Existing and projected open service (OS) signals up until 2020 create a challenge for Global Navigation Satellite System (GNSS) manufacturers as to which signals to exploit for the best performance and user experience. This paper will focus on signals at or near the L1 GPS (1575.42MHz) frequency band. We would also focus on methods that are suitable for use in a mobile platform which has tight constraints on power consumption and silicon area. The diversity of constellations and signals includes GPS L1 C/A, GLONASS L1 C/A, Galileo E1 OS, BeiDou B1 as the main candidates. Other signals such as the Japanese Quasi-Zenith Satellite System (QZSS), which has a similar signal structure to the GPS L1 C/A signal and the Space-based Augmentation System (SBAS) are also considered in this analysis. The signal performance analyses using all these different constellations are combined to give an optimal search strategy which exploits the advantages of the signal structures of the different GNSS signals. The growth in the GNSS applications market has resulted in a wide range of user-defined test scenarios. These users require search strategies that operate well for different start conditions and in urban environments. These environments are far from ideal for satellite navigation systems due to signal obscuration, attenuation and increased number of multipath contaminated signals. The test criteria defined by manufacturers are mainly simulator-based and are often used as product differentiators to increase the market demand for their products. These test cases include the 3rd Generation Partnership Project (3GPP) Margin tests which measures the acquisition sensitivity of the GNSS receiver. On the other hand, the test requirements developed by the users are based on their experiences which are in real-life environments. In this paper, the best search strategy that achieves a consistent performance across different test scenarios will be discussed. These scenarios are defined by the amount of assistance information available at the start of the test. Multi-constellation search strategies for these test scenarios will also be analyzed.
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:	321 - 329
Cite this article:	Anyaegbu, E., Townsend, B.R., Zuo, R., "Optimal Search Strategy in a Multi-constellation Environment," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 321-329.
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