Improving GPS Coverage and Continuity: Indoors and Downtown

Per Enge, Rod Fan, Anil Tiwari, Andrew Chou, Wallace Mann, Anant Sahai, Jesse Stone and Ben Van Roy

Abstract:	These days, GPS use is being extended into areas where hitherto it simply was not available. For years, it has served society remarkably well for survey, aviation use, maritime use and a host of other applications where the receiver is in the open and the satellites are clearly visible. Now however, society wants more utility from GPS. We want to get position fixes in urban environments and even inside. This requires the GPS receiver to operate at very low signal to noise ratios, integrate every imaginable source of aiding information, and combat multipath. @Road and Enuvis are responding to this new GPS challenge. @Road has deployed a GPS assistance reference network (GARNET) that provides GPS assistance data. In the fullness of time, this network will provide a data stream that replaces the satellite ephemeris and clock coefficients contained in the GPS navigation message. An alternate source of this data will be most welcome, because signal blockages wreak havoc with the relatively fragile navigation message. GARNET will also replace the Z count in the navigation message, so the receiver can determine the most significant bits in the measured pseudoranges. Finally, it will develop information that will increase receiver sensitivity by reducing the search area and enabling the use of longer averaging times. Enuvis has designed algorithms that significantly enhance the sensitivity of the GPS receiver, while being robust to uncertainties in the actual signal environment including multipath. In addition, the Enuvis algorithms readily incorporate many sources of aiding data where the quality of this side information may be uncertain. These algorithms can be realized either on the mobile station (thick client) or a network server (thin client). This paper has two goals. First, it begins the development of formal assessment metrics for these complicated systems. In time, these metrics will be used to measure the performance of GPS based algorithms indoors and in urban environments. Second, we use some of these preliminary metrics to describe the performance of our prototype system. Our system is still evolving and so the performance will change relative to what is shown here. In addition, we only show a subset of the current results, because our page count is limited. By the way, @Road and Enuvis have no formal business relationship, and their collaboration is currently limited to the authorship of this paper.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	3067 - 3076
Cite this article:	Enge, Per, Fan, Rod, Tiwari, Anil, Chou, Andrew, Mann, Wallace, Sahai, Anant, Stone, Jesse, Van Roy, Ben, "Improving GPS Coverage and Continuity: Indoors and Downtown," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 3067-3076.
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