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In this study, Global Positioning System (GPS) simulation is used to evaluate the effect of varying GPS signal power levels on the accuracy of two handheld GPS receivers; Garmin GPSmap 60CSx (evaluated GPS receiver) and Garmin GPSmap 60CS (reference GPS receiver). Both receivers employ the GPS L1 coarse acquisition (C/A) signal. With decreasing GPS signal power level, probable error values increase due to decreasing carrier-to-noise density (C/N0 levels for GPS satellites tracked by the receiver. Varying probable error patterns are observed for readings taken at different locations and times. This is due to the GPS satellite constellation being dynamic, causing varying GPS satellite geometry over location and time, resulting in GPS accuracy being location / time dependent. For all the readings taken, the evaluated GPS receiver recorded lower probable error values as compared to the reference GPS receiver. This occurred as the evaluated GPS receiver has higher receiver sensitivity, and hence, is able to obtain lower position dilution of precision (PDOP) values. In addition, it has lower receiver noise, reducing the value of its user equivalent ranging error (UERE). [ABSTRACT FROM AUTHOR]

In order to study the effect of radio frequency interference (RFI) on the global positioning system (GPS) L1 coarse acquisition (C/A) signal, the Instrumentation & Electronics Technology Division (BTIE), Science & Technology Research Institute for Defence (STRIDE), conducted a series of tests specifically aimed at evaluating the minimum interference signal power levels required to jam various GPS receivers. However, interference signals with power levels below the minimum jamming threshold could still severely distort GPS accuracy, rendering it useless for applications requiring high precision. BTIE conducted a test on 8th April 2010 to evaluate the effect of RFI on the accuracy of a Garmin GPS map 60CSx handheld receiver, which employs the GPS L1 C/A signal. As expected, the probable error values of the location fixes increased as the transmuted interference signal power level was increased, until the GPS receiver was completely jammed. The amount of increase of probable error values and the minimum jamming power levels varied significantly based on GPS coverage and various error parameters, including ionospheric and tropospheric delays, and satellite clock, ephemeris and multipath errors. On the whole, this test has demonstrated the disadvantages of field global navigation satellite system (GNSS) evaluations; without the ability to control the various GNSS error parameters, it is difficult to effectively study the effect of any particular error parameter, in the case of this test, interference, on GNSS accuracy. This highlights the importance of using a GNSS simulator for such tests, whereby the tests could be done under repeatable user-controlled conditions. [ABSTRACT FROM AUTHOR]