Proposed GNSS Navigation Messages for Improved Performance
TTFF depends crucially on the availability and timeliness of the satellite ephemerides and clock information when a receiver starts up and, accordingly, there are three types of start-up with correspondingly different TTFF. A cold start (sometimes also called a factory start) occurs when the receiver has no knowledge of its current position, time or the positions of the satellites and their clock offsets. The receiver must do a blind search of the sky trying different possible Doppler frequency shifts and pseudorange delays for all the satellites in the constellation. Once satellites are found and tracked, the ephemerides and clock information must be collected. This is repeated in each satellite's navigation message every 30 seconds. In addition, the information on the offset between GNSS system time and UTC must be collected along with the ionospheric delay correction parameters and the almanac (an approximate ephemeris for all active satellites in the constellation) to be used for faster subsequent signal acquisition. This data is only transmitted once in the 12.5-minute-long navigation message. Therefore, the TTFF for a cold start can take up to 12.5 minutes and even longer especially if the GNSS signals are hard to acquire such as in obstructed environments.
немного – это сколько?
Тогда и летать можно по пачке Беломора.
Ещё лучше наблюдать на второй, третьей и т. д. частотах. Тем более, навигационные модули наблюдения на двух частотах для смартфонов давно существуют.
А коэффициенты ионосферной модели где?
GPS World 2015-8, p 42
Proposed GNSS Navigation Messages for Improved Performance
Скажите пожалуйста, сколько времени занимает приём эфемерид GPS?
А ГЛОНАСС?
Геоидом или квазигеоидом? Какую модель поля предпочитаете? С высокими порядками разложения проблем нет? Алгоритм свой или какой-нибудудь известный?
Скажите пожалуйста, что вы сейчас обсчитываете? Выводите «свои» параметры?