Integrated use of GPS and GLONASS in civil aviation navigation I: coverage and data models
Pursuant to a bilateral agreement signed in 1988, both US and USSR are currently in the process of examining integrated use of GPS and GLONASS for sole-means civil aviation navigation. This paper presents results from the initial phase of a program underway at MIT Lincoln Laboratory to support this effort. Specifically, we present results on satellite coverage and quality of the range measurements from GPS and GLONASS. The coverage results highlight the extent to which each system alone falls short of providing a self-contained system integrity check. In integrated use, however, there are enough redundant measurements to make receiver autonomous integrity monitoring (RAIM) practical. The data quality results are based on statistical analysis of the range measurements from GPS, at various levels of selective availability (SA), collected over extended periods. We present empirical cumulative distribution function of the range error, and RMS value of its component, defined as the 'effective' range error, relevant to position estimation. These results are used to project the position estimation. These results are used to project the position estimation accuracy achievable globally with GPS, when operational. Comparable results for GLONASS are being developed. The coverage and data quality results together provide a basis for development of the navigation and RAIM algorithms for the integrated use. This will be addressed in the next phase of the program. The important considerations in the design of these algorithms, including the differences in the reference systems for space and time employed by the two systems, are briefly reviewed.