I am researching a method to speed up the GPS acquisition in cold start. Rather than an exhaustive search on all satellites, I observed that the satellite distribution can give some information to reduce the number of searches.
For example, if I can find the first satellite with Doppler value. I think there exists some way to calculate the probability of detection of other satellites.
Could you recommend some references to start looking at?
Thank you.
I don'y have any references in my mind, but I had a very old android mobile phone which was not able to store almanac files, so any single time I turned on its GPS, a cold start was needed. I installed the app GPS STATUS which was able, if I'm not mistaken, to download low-volume almanac files from the internet and assist the GPS receiver to avoid the time-consuming cold start process. I would recommend you to look into this method.
Yusof Ghiasi Thanks for your info. It is interesting. I had an assisted GPS already, so I want to extend its capability in challenging situations like cold start without any help from cellular networks.
Nice job! Fantastic.
I had done a similar task before. That was about predicting satellite locations based on orbital data and time. Orbital data, for each satellite, can be found in almanac files, which can be valid for a couple of weeks but with a reduced accuracy, which should be fine for your case. You just need to use orbital equations and values to determine satellites' location at any given time.
Did i get the point?
As soon as the receiver identifies the satellites using Doppler values, then that will no longer be the cold start but rather the warm start. At this stage, the receiver uses the recent almanac in memory to map the satellites and their Doppler offsets. Thus, what is necessary is only to check the anticipated pseudorandom noise (PRN) codes at the expected Doppler offsets. Henceforth, searching the sky becomes worthless.
How can we determine the satellite during cold start?
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Other than using the Doppler values, the positions of the other satellites may be detected using the orbital data from the almanac. In any given constellation, each satellite transmits orbital parameters for all satellites alongside auxiliary health and status information. Since the ephemeris data is transmitted only for each individual satellite, then you may simply compute the satellite positions using the orbital equations at any given point in time.
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Apart from that, you may get the ephemeris and clock information from the cellphone link rather than through the satellite link, a concept which may be termed as assisted satellite positioning. The strength of this approach is that the amount of time required to get all the critical information shortened.
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While the orbit design has something to do with the overall satellite configuration, the receiver architecture has a vital role in the task of identifying the satellites in order to calculate its own 3D position and clock offset, on the other hand. Therefore, the overall cold start searching time may improve with multi-corellator and high-sensitivity Global Navigation Satellite System (GNSS) receivers.
I had done a similar task before. That was about predicting satellite locations based on orbital data and time.
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