Specifics of the LAAS Context Model (G(x))

Bruce DeCleene, Tim Murphy, Trent A. Skidmore

Abstract:	Efforts to develop standards to support a public use precision approach system based on Differential GNSS are ongoing. The Federal Aviation Administration (FAA) has been leading the development of the Local Area Augmentation System (LAAS) in conjunction with the RTCA Special Committee 159. To SUppOlt interoperability of equipment made by different manufacturers, the LAAS design must clearly allocate all aspects of the required system performance between the ground, space and airborne subsystems. An explicit definition of the format and performance of the signal-in-space must be developed. Recent work by RTCA Special Committee 159 (Working Group 4) has addressed these issues by allocating requirements and defining how the signal-in-space elements are interrelated (the G(x) concept, also known as the LAAS context model). The interrelationships of the signal-in-space elements are defined in terms of mathematical formulas or generalized algorithms. The intent is to specify the necessary relationships without dictating an implementation design. All the subsystems must adhere to the context model when creating or using elements of the LAAS signal-in-space. The context model will eventually be embodied in the LAAS Interface Control Document (ICD), LAAS Minimum Aviation Systems Performance Specification (MASPS), LAAS airborne equipment Minimum Operational Performance Specification (MOPS) and LAAS Ground System Specification, which are all under development at the RTCA. This paper describes these .allocations and interrelationships for LAAS. Specific relationships between elements of the LAAS signal-in-space are defined. Particular attention is given to the aspects of the system which pertain to the signal-in-space integrity monitoring and allocation of system accuracy to the subsystems.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1583 - 1592
Cite this article:	DeCleene, Bruce, Murphy, Tim, Skidmore, Trent A., "Specifics of the LAAS Context Model (G(x))," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1583-1592.
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