Test results for the WAAS Signal Quality Monitor

Abstract

The signal quality monitor (SQM) is an integrity monitor for the wide area augmentation system (WAAS). The monitor detects L1 signal waveform deformation of a GPS or a geosynchronous (GEO) satellite monitored by WAAS should that event occur. When a signal deformation occurs, the L1 correlation function measured by the receiver becomes distorted. The distortion will result in an error in the L1 pseudorange. The size of the error depends on the design characteristics of the user receiver. This paper describes test results for the WAAS SQM conducted using prototype software. There are two groups of test cases: the nominal testing and the negative path testing. For nominal test cases, recorded data are collected from a test facility in four 5-day periods. These four data sets include SQM correlation values for SV-receiver pairs, and satellite error bounds for satellites. They are used as input to the prototype. The prototype processes these data sets, executes the algorithm, and records test results. Parameters such as the "maximum median-adjusted detection metric over threshold" (i.e., the maximum detection test), "UDRE forwarded from upstream integrity monitors," and "UDRE supported by SQM" are shown and described. The magnitude of the maximum detection test for all GPS and GEO satellites are also shown. For negative path testing, this paper describes two example simulated signal deformation test cases. A 2-day data set is collected from the prototype. A few example ICAO signal deformations are simulated based on this data set and are inserted in different time slots in the 2-day period. The correlator measurements for selected satellites are pre- processed to simulate the signal deformation. The results demonstrate the sensitivity of the Signal Quality Monitor to the simulated deformation, and shows when the event is detected and subsequently cleared. It also shows that the SQM will not adversely affect WAAS performance.