Interference Protection for EGNOS RIMS

C. Neville, K. Ashton

Abstract:	The GPS signal-in-space vulnerability to interference is an issue that is well understood. For EGNOS, protection of the network of Ranging and Integrity Monitoring Stations (RIMS) from unintentional interference sources is vital in order to meet the stringent performance requirements of the system. The RF environment within which the RIMS are located must therefore conform to a minimum standard that is contained within the EGNOS System Requirement Document (SRD) [ref 1]. This standard is provided in the form of a mask that defines an acceptable level of interference within the GLONASS and GPS L1&L2 frequency bands. As well as the RF environment there are many other constraints that potential RIMS sites must satisfy, regarding security and infrastructure availability. Often these requirements are only met in areas where the potential for interference is high. It is not surprising therefore that during the site survey process several candidate sites were identified as unacceptable using the strictly defined RF criteria. It was felt however that the real impact of the observed interference did not justify the rejection of all of these sites. Since many of the detected interference sources could be fully characterised it was felt that by simulating and determining their effect on the RIMS, a relaxation to the mask could be achieved, the current requirements making no allowance for interference characteristics other than for signal bandwidth in the case of in-band interference at GPS L1. This paper presents the results of a study to determine the effect of the observed interference on a representative RIMS receiver (Novatel Millennium OEM3). The potential interference sources identified during the site surveys fall into the following generic categories DME, Radar, Scanning Radars, Pulse Compression Radars as well as generic FM and CW sources. The effects of the modeled interference on the Carrier to Noise Ratio, Pseudo-Range, Time to Acquire and Number of Tracked Satellites were recorded across each of the defined frequency bands. The results were used to derive new masks specific to the type, power and center frequency of each interference source, to define the maximum acceptable interference power levels at which there is no degradation to the receiver performance.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1440 - 1448
Cite this article:	Neville, C., Ashton, K., "Interference Protection for EGNOS RIMS," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1440-1448.
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