Coverage Improvement for Dual Frequency SBAS

Todd Walter, Juan Blanch, and Per Enge

Abstract:	In the next few years GPS will start broadcasting civil signals suitable for aviation use on both the L1 and L5 frequencies. In addition, Galileo and other constellations will offer an even greater number of dual frequency ranging measurements. The Wide Area Augmentation System (WAAS) and the other Satellite Based Augmentation Systems (SBASs) can also be updated to exploit these new signals. Such updates offer a variety of improvements over existing single frequency systems. These dual frequency systems will be fully robust against ionospheric gradients that currently limit vertical guidance during severe ionospheric disturbances. Further, they offer improved resistance against interference as operations can proceed when aircraft lose access to one frequency or the other. However, the largest benefit to a user taking advantage of both frequencies is that their availability can extend much farther away from the reference station network. The uncertainty in the ionospheric behavior at the user is essentially eliminated, allowing this increase in coverage. Importantly, this availability can be extended into equatorial areas where the current single-frequency, twodimensional grid can be a very poor fit to actual behavior. Thus, availability to these regions can be reliably provided for the first time. This paper examines the coverage that will be offered by SBAS systems when they upgrade to dual-frequency operation. It will examine the coverage offered to the user through the combined coverage of existing and planned systems. Further, we will examine how, with small extensions in their reference station networks, nearly global coverage of LPV-200 service may be achieved. Finally, we will present the improvement to coverage that can be provided by also integrating additional constellations into the SBAS coverage. Additional ranging signals dramatically improve the users geometry, even further extending coverage from reference station networks.
Published in:	Proceedings of the 2010 International Technical Meeting of The Institute of Navigation January 25 - 27, 2010 Catamaran Resort Hotel San Diego, CA
Pages:	344 - 353
Cite this article:	Walter, Todd, Blanch, Juan, Enge, Per, "Coverage Improvement for Dual Frequency SBAS," Proceedings of the 2010 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2010, pp. 344-353.
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