A receiver autonomous integrity monitoring @AIM) algorithm is proposed, and used to analyze the integrity monitoring capabilities of potential sole-means (or stand-alone) systems based on integrated use of GPS and GLONASS, GPS supplemented with a geostationary overlay, and enhanced GPS constellations. As in the other RAIM algorithms, the idea is to take advantage of the redundant measurements. Our focus, however, is on the quality of the position estimate, rather than on diagnosing whether the system is working as intended.The proposed approach uses the redundant measurements to generate a position estimate and a measure of its quality. The latter, called integrity level, is defined as an upper bound on the position error. The estimation of the integrity level is the main innovation in the proposed scheme. The RAIM algorithm is tailored to an abundant redundancy of the measurements, and addresses the following issue: Given a snapshot of the pseudorange measurements, one of which may be in error, can we compute a position estimate that can be shown with high confidence to meet the user's accuracy requirement?
A satellite navigation data collection and analysis facility, comprising GPS and GLONASS receivers and the supporting computer systems, has been established at Lincoln Laboratory under the sponsorship of the Federal Aviation Administration. In this paper, we present results based on an analysis of the measurements from GLONASS collected at this facility over a 6 month period (FebruaryJuly 1991). While our main interest is in the positioning results obtained from GLO-NASS, we also examine some important issues related to the system operations. The findings are generally consistent with the technical data provided by the Soviets. The GLONASS positioning results are comparable to those provided by the GPS Standard Positioning Service (SPS) when the Selective Availability (SA) feature of the latter is off. When the GPS signal is degraded via SA, the GLONASS position estimates will clearly be better. Of course, the positioning accuracy reflects directly on the quality of the system upkeep and control. We have analyzed the navigation messages in order to understand the nominal patterns of data uploads, changes in parameter values at uploads, and the handling of system anomalies. We discuss these findings and identify some issues requiring further clarification.
This paper describes the design and flight test results of an experimental Global Positioning System receiver installed in a general aviation aircraft. These tests were part of a GPS test and evaluation project conducted for the Federal Aviation Administration by M.I.T. Lincoln Laboratory. The purpose of the project was to design a GPS C/A-code receiver that: 1) meets the current FAA requirements for two-dimensional area navigation (RNAV) systems, 2) employs techniques which could potentially lead to low-cost commercial avionics, and 3) is operationally compatible with existing ATC procedures and aircrew practices.Novel features of the design are: 1) the use of a dual-channel CA-code receiver, and 2) the tracking of all visible satellites in view rather than a minimum set of four satellites. The system employs two DEC LSI-11123 computers, one to perform position fixing and receiver control, and the other to perform navigation and data recording tasks. Pilot displays include a conventional course deviation indicator (CDI), omni-bearing selector COBS), and intelligent control and display unit (CDU).The GPS receiver was flight tested at a large urban airport, at several small general aviation airports, and over mountainous terrain. The horizontal system accuracy during typical aircraft flight profiles was measured to be 333 feet (95% confidence). This level of accuracy meets the FAA's current accuracy requirements for two-dimensional area navigation systems and is consistent with future navigational accuracy requirements.
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