Compass Signal Structure and First Measurements

On April 13 China launched the first middle earth orbiting (MEO) satellite in its Compass GNSS system, 21,550 kilometers above the Earth. China’s radionavigation satellite system which is currently under development is planned to begin operation in 2012. It will consist in a constellation of 27 MEO, 3 Inclined Geosynchronous (IGSO) and 5 geostationary satellites. The current frequency filings for radio bands made by China to the International Telecommunications Union (ITU) indicate that Compass satellites will broadcast signals in four frequency bands in which the carrier frequencies are 1561 MHz (E2’), 1589 MHz (E1’), 1268 MHz (E6) and 1207 MHz (E5b). Compass signals will then overlap some of GPS, Galileo and Glonass signals. On the one hand this suggests potential benefit for users as interoperability of Compass with GPS, Galileo and Glonass would mean increased user performance. On the other hand it arouses concerns as radionavigation L-bands are already congested. It is then necessary that development of Compass is done in cooperation with existing systems to ensure compatibility and interoperability. Compass first MEO satellite began transmitting signal on three frequencies shortly after launch. The satellite was then tracked at both CNES (Toulouse, France) and Monitoring Earth Station of Leeheim (Germany) using high gain parabolic antennas. Compass signals could be observed at frequencies 1207 MHz, 1268 MHz and 1561 MHz. Processing of recorded signals enabled determination of Compass code structure. Results are presented here.