Lernkarten

Roland Schenkel
Karten 101 Karten
Lernende 12 Lernende
Sprache English
Stufe Universität
Erstellt / Aktualisiert 17.01.2012 / 23.01.2021
Lizenzierung Kein Urheberrechtsschutz (CC0)
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0 Exakte Antworten 89 Text Antworten 12 Multiple Choice Antworten
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Formular 2.21, discuss, what speed is v? For GPS?

U = newtonian gravitationl potential at the location of the clock // va = velocity of the atomic clock // c = speed of light // delta_tau_geo = purely geometrical (or newtonian) delay difference between the arrival times of a wavefront at both telescopes. v ist die Geschwindigkeit der Atomuhr verglichen mit dem Massenzentrum des Systems. ca. 4km/s (Speed of a GPS-Satellite with respect to the Earth) ca. 29km/s (Speed of Earth with respect to the sun)

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Charactericits of the GPS satellite constellation?

a: 26'600km, Periode: 11h58, I: 55°, 6 Ebenen mit 60° spacing, 24 Satelliten, CDMA (PRN-Codes)

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Structure of the GPS signals?

L1: f1 = 1575 MHz, _ = 19cm, C/A-Code, P-Code // L2: f2 = 1227 MHz, _ = 24cm, P-Code

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C/A-Code?

(clear access / coarse acquisition), 1023bits (chips), repeats after 1ms,

chip length (1 bit) = 293m, only modulated on L1, each GPS-Satellite sends own code-sequence.

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P-Code?

(protected / precise), repeats after 266.4 days (=2.35*10^14 chips), chip length = 29.3m, transmitted on L1 and L2

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Nav-Message of GPS Signal?

on L1 and L2, contains broadcast ephemerides (pseud-keplerian elements), satellite clock corrections (polynomial of 2nd degree), almanach data (approximate orbit info for long-term predictions), information about ionosphere, health status of the satellites

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Which mechanisms exist for the artificial degradation of the GPS signals?

Selective Availability (SA): The accuracy of the positioning is degraded. This works with the so called dithering. There the satellite clock is manipulated in the range of 2 s, witch correspond to 60m. With relative positioning the SA wasn’t a problem. The SA was switched off at May 2, 2000. Anti-Spoofing (AS): The P-Code is encrypted by superposing a additional W-code. => Y-code. The AS was implemented to avoid that position quality can be degraded by a “wrong” artificial GPS-signal. Because of the AS there is an increased noise level in the code measurements ans especially in the carrier phase measurements.

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Which mechanisms exist for the artificial degradation of the GLNASS signals?

no signal degradation mechanisms