GPS相关知识定义及说明.pdf

GPS January 5, 2006 Version 1.0 1.0 GPS 1 2 2 2 2.1 U-BLOX 2 2.2 GE1100 5 2.3 UNAV 6 3 NMEA-0183 VERSION3.0 4 RTCM 8 5 9 Page 1 of 19 1.0 GPS 1 GPS 2 2.1 u-blox Depending on the receiver’s knowledge of last position, current time and ephemeris Data, the receiver will apply different strategies to start-up, namely: Coldstart In Coldstart, the receiver has no knowledge of its last position or time. This is the case when the RTC has not been running, no valid ephemeris data or almanac data is available (This is the case if the receiver has never been navigating or the battery backup memory is lost). Warmstart Warmstart is performed whenever the receiver has only access to valid almanac data, and has not significantly moved since the last valid position calculation. This is typically the case, if the receiver has been shut off for more than 2 hours, but still has knowledge of last position, time and almanac. This allows it to predict the current visible SVs. However, since ephemeris data is not available or outdated, the receiver needs to wait for the ephemeris broadcast to complete. Hotstart Hotstart is performed whenever the receiver still has access to valid ephemeris data and precise time. Th