Almanac (GNSS)

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In satellite navigation (e.g. GPS ), an almanac is a list with less precise, but longer valid orbital data of the satellites compared to the ephemeris (supplemented by information about the integrity of the transmitted signals).

The almanac data is not necessary, but useful because it speeds up the search for satellite signals when the receiver is switched on by narrowing down the area to search. This is not about a search for the satellites in the sky, but in the two-dimensional space of the frequency deviation due to the Doppler effect on the one hand and the time shift between transmitted and pseudo-random code sequences generated in the receiver on the other. Furthermore, the stand also available on the internet Almanac for planning sessions GNSS (GNSS: Global Navigation Satellite System , English global navigation satellite system) used, e.g. B. to determine whether and when particularly good results can be achieved on one point.

In addition to the highly precise orbital data required to use its signals, the ephemeris, each satellite also sends the almanac data of all satellites in the system, albeit in a longer cycle. Modern GNSS receivers store this data and thus reduce the time until the first position fix is ​​available. The advantage depends on the length of time in which the device had no reception. The current data is also available on the Internet and can be loaded into the device with appropriately programmed devices via USB cable or via a chargeable service via cellular network ( A-GPS ).

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