Theoretical and Practical Sensitivity Limits for Assisted GNSS Receivers Using Legacy and Future GNSS Signals

L.R. Weill

Abstract:	The last decade has seen increasing interest in the development of very high sensitivity GNSS receivers for use in poor signal environments. A major application is incorporation of such receivers in cell phones, thus enabling a user to automatically transmit his location to rescue authorities in emergencies such as a 911 call. Such a receiver must be able to reliably operate deep within buildings or heavy vegetation which severely attenuates the GNSS signals. In order to achieve the requisite reliable and rapid positioning for such applications, a GNSS receiver must be assisted by data from a base station receiver at a location having good signal reception. The assisting data can include base station location, satellite ephemeris data, the demodulated navigation data bit stream, frequency calibration data, and timing information. This data can be transmitted via a cell phone or other radio link. In some cases the assisting information can be transmitted over the internet and relayed to a cell phone via a local area wireless link. During the past three years the author has been involved in the development of such an assisted high-sensitivity GPS positioning system, described in [1]. High-sensitivity assisted GNSS (AGNSS) receivers are currently being produced by a number of major manufacturers who are claiming sensitivities in the range of –155 to –165 dBm. In designing such receivers it is important to have quantitative knowledge about the many factors which place theoretical and practical limits on receiver sensitivity. Without this knowledge it is difficult to establish how closely receiver performance approaches what is theoretically and practically possible with current technology. Compounding this problem is the difficulty of obtaining dependable sensitivity measurements under controlled conditions at the extremely low signal levels characteristic of poor signal areas. This paper is a comprehensive investigation of both the theoretical and practical limitations inherent in the design of high-sensitivity GNSS receivers. A major goal is to provide quantitative results which can set realistic performance goals and guide the receiver design process.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	2930 - 2943
Cite this article:	Weill, L.R., "Theoretical and Practical Sensitivity Limits for Assisted GNSS Receivers Using Legacy and Future GNSS Signals," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 2930-2943.
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