Hello, We are using GPS on HE910 in standalone mode.
1) The problem that if module standing in a sleep mode long time (4-5 hours and more) then to get GPS fix can take up to 30 minutes, but if module was standing just 10 minutes , GPS fix is quite fast.
How to get fast fix ? maybe update gps every 20 minutes ? is it some recommended interval for update ?
1) it is possible that after 4-5 hours, the module has to perform a cold start since the validity of ephemeris
is dictated by the particular satellite and may be valid up to 4 to 6 hours. In any case 30 minutes is a lot of time but it could depends on the fact that not so many stellites are in use or the signal received is low.
What is the average time at module power on e.g. very first power on, to get a fix? Normally how many satellites are used and which is the SNR value ? At least 3 SV as to be used to get a fix.
2) After a full power reset, i.e. power disconnection the module looses all the GPS information contained in RAM, therefore both almanac and ephemeris have to be downloaded again.
Can I ask why the HE910 loses this information when VBATT is removed, where the DE910 appears to hold this information in nonvolatile storage? The DE910 can get a fix in < 5 seconds after a full power off – even in my case, 12+ hours of being without power. This seems like a pretty huge oversight for the GPS solution in the HE910 knowing it is for embedded applications.
In the HE910 the ephemeris and almanac info are stored in RAM therefore they are maintained as long as VBATT is connected.
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