Investigations into GPS Receiver Performance with an Increased Noise Floor Due to New Signals Broadcast from New and Amended GNSS Constellations

A. Grant, J. Safár and M. Bransby

Abstract:	GPS receivers are used on the bridge of ships and within Aids-to-Navigation (AtoN), wherever positioning, navigation or timing (PNT) information is required. It is common for vessels to have multiple GPS receivers and for data from these units to be used throughout the bridge in many of the different systems [1]. While GPS is the predominant Global Navigation Satellite System (GNSS) in operation, other systems are available and continue to be developed. It is expected that by around 2020 there may be four or more GNSS fully operational (GPS, GLONASS, Galileo & BeiDou), along with a number of regional systems, such as IRNSS and QZSS, and satellite based augmentation systems (SBAS), such as WAAS and EGNOS. In order to encourage system interoperability, many of these services will broadcast on the L1 frequency. The use of this common frequency allows receiver hardware to be simplified so that a receiver can use signals from multiple GNSS; however, all signals that are not used can be considered noise and contribute to the background noise level from which the wanted signal must be extracted. Several papers have reported that there is a limit at which increased numbers of satellites no longer improve the PNT performance from the receiver [2, 3]. The key issue is that older receivers, for example those developed against the original IMO performance specification developed in the late 1990’s [4], may still be used on some vessels. Such receivers were designed to track one constellation but could now be exposed to four, with 40+ satellites in view at any time (by 2020-2025). As such, it is unclear whether these receivers would be able to recover the wanted signal from the increased background noise level and whether the subsequent performance of that receiver would be degraded. This paper reports on a series of trials undertaken with the use of GNSS signal simulators and a selection of maritime receivers. The simulators were used to model the expected radio frequency environment expected today and in 2020 from which it was possible to investigate and measure the effect of the receiver being exposed to an increased number of satellite signals. Receivers were selected to represent legacy and current maritime user experiences.
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:	782 - 786
Cite this article:	Grant, A., Safár, J., Bransby, M., "Investigations into GPS Receiver Performance with an Increased Noise Floor Due to New Signals Broadcast from New and Amended GNSS Constellations," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 782-786.
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