GNSS receivers start in 3 possible modes:
- Cold start: This is seldom used. It happens when the receiver has been off for extended periods of time (weeks) or powers up far away from its last known position (hundreds of km). In this case, it needs to rebuild its almanac (satellite constellation database).
- Warm start: This is the most likely condition. The receiver powers up in proximity of its last known position, after more than about two hours from the last fix. This requires to rebuild ephemeris data but not the almanac. Fix time is about 30 seconds.
- Hot start: The receiver powers up less than about two hours from the last known fix, and not far away from it. It takes some seconds to get a fix.
If the XA2 GNSS receiver takes 15 minutes or more to get a fix (it took 1 hour some days ago), then there is a problem. It might lie in the software, where someone destroys the almanac, which maybe did not turn up until now thanks to A-GPS assistance; or maybe someone destroys the almanac on purpose, thinking that A-GPS will step in anyway (which it does no more). It might also lie in the hardware, where no backup power is supplied to hold the data, but it’s a big design flaw and not likely to happen in a product such as a mobile phone from an established manufacturer.
Now I am trying to leave GPSInfo on (which will leave the GNSS receiver powered) until this afternoon. If I get a fix in a reasonable time, this means that something bad happens when the receiver is powered on.