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First AGPS - now BGPS: instantaneous precise positioning anywhere / I. Petrovski in GPS world, vol 19 n° 11 (November 2008)

Public [article]  inGPS world > vol 19 n° 11 (November 2008) . - pp 42 - 48 Titre : First AGPS - now BGPS: instantaneous precise positioning anywhere Type de document : Article/Communication Auteurs : I. Petrovski, Auteur ; H. Hojo, Auteur ; Toshiaki Tsujii, Auteur Année de publication : 2008 Article en page(s) : pp 42 - 48 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] GPS assisté pour la navigation (technologies) [Termes IGN] lever mobile [Termes IGN] positionnement cinématique en temps réel [Termes IGN] réseau géodésique [Termes IGN] signal GPS Résumé : (Editeur) Instant GPS positioning appears to be at hand. For better or worse, we live in fast communications, and fast cars, and have come to expect instant responses when we want something. [...] After switching on our receiver, we typically have to wait for some time before we can start navigating. This time to first fix (TTFF) depends on the quality of the received signals and the age of the receiver's stored almanac and ephemerides used to determine the positions of the satellites. It's also affected by how well the receiver knows the exact time. So there are several kinds of TTFF. If a receiver has no knowledge of its last position, doesn't know the approximate time, and has no almanac, it starts searching for signals blindly. This called a cold start. Depending on signal quality and design to the receiver, it can take anywhere from 60 seconds to 12 minutes or more before the receiver acquires signals, obtains ephemeris data, measures pseudoranges and gets its first position fix. If the receiver knows the approximate time as well as its approximate position and has a recent almanac but not a current ephemeris, it can produce a position fix within about 30 seconds or so after it is switched on - the time required to receive orbit and clock data from the tracked satellites. This is called a warm start. A hot start occurs when a receiver is powered on with a current ephemeris (received within the past four hours). It can take up to 6 seconds or more before the first fix as the receiver must typically acquire times marks from the satellite navigation messages to resolve the pseudorange ambiguities. Assisted GPS, or AGPS, can reduce TTFF by suplying current ephemeris data and accurate time over a mobile phone network. In some situations, TTFF can be reduced to just a second or two. However, the receiver does need to be connected to an AGPS network and so cannot operate autonomously. Enter BGPS. In this month's column we learn about an innovative approach that can produce accurate fist fixes within one second and without a network connection ? Copyright Questex Media Group Inc Numéro de notice : A2008-449 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29518 [article]

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