GPS / A-GPS

Technology Overview

GPS, a satellite-based positioning system, is operated by the United States Department of Defense and was officially put into operation in 1995. Using the difference in the radio signal propagation times of at least three or more of the 32 GPS satellites, a GPS receiver can accurately determine its position worldwide to within a few meters using trilateration. The planned European Galileo system will be largely compatible with GPS.

Assisted GPS (A-GPS) is mainly used in mobile terminals to enhance performance by means of faster localization (time to first fix, TTFF) and higher accuracy. A-GPS uses the coordinates of the base station serving the radio cell in which the mobile terminal is located and transmits this information to the mobile terminal via an assisted channel. An initial approximation of the position of the mobile terminal is possible, thus considerably shortening the time until exact GPS position data is available. The assisted data is transmitted via an IP channel (secure user plane location, SUPL) as defined by the Open Mobile Alliance (OMA).

Applications

GPS has become a widely used aid for navigation worldwide, and a valuable tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a precise time reference used in many applications including the scientific study of earthquakes and the synchronization of telecommunications networks.

A-GPS is becoming more and more popular and is already implemented in a wide range of mobile terminals and in cellular networks. For operation, A-GPS needs to be supported by both the cellular network provider and the used mobile terminal. A-GPS also delivers higher localization accuracy in case of an emergency call.

Rohde & Schwarz Test Solutions

Rohde & Schwarz signal generators provide real-world GPS signals with real navigation data and real almanac data for up to eight satellites. The GPS/A-GPS options enable the simulation not only of fixed positions but also of moving receivers. Any navigation data or satellite track parameter can be modified, providing maximum flexibility to custom-build all kinds of GPS scenarios.

For A-GPS in GSM and WCDMA networks and for SUPL, Rohde & Schwarz offers complete solutions that cover all A-GPS test requirements from a single source using the R&S®SMU200A signal generator as the satellite simulator and the R&S®CRTU protocol tester as the system simulator. This configuration provides validated test cases for protocol and conformance tests as defined by the Global Certification Forum (GCF). For SUPL tests, the R&S®CMU200 wireless communications tester can also be used instead of the R&S®CRTU. Rohde & Schwarz offers also GPS signal generation within the R&S®CMW500 wireless communications tester for the production test of mobile terminals.

Key Parameters

Standardization

Developed by the United States Department of Defense, GPS is officially named NAVSTAR. The satellite constellation is managed by the United States Air Force 50th Space Wing.