nrf91 gps Hot Start

[SebastianF]

Hi,

I'd like to test how long it takes to get a gps signal and send the nmea string via udp. Therefore I took the example 'udp_gps'.

As far as I know the program starts gps and searches satellites. Once enough satellits have been found, I get the first fix. The program waits 3 fixes and than the position (nmea string) is printed and the pgs stoppes. After gps stopped it is possible to send some data via udp.

> My question is now, if it is possible to restart the gps with a hot start. For now it seems to me as the gps restarts with a cold start because the time that passes from the 'gps operation started' till the first fix is often more than 1 min and not as described as in the product specification (1.3 sec). Is there a sample how to do a hot start, that would help a lot.

> Am I right that it is not possible to send something via udp while continuous gps tracking is active?

KR, Sebastian

[Sigurd]

Hi,

SebastianF said:

> My question is now, if it is possible to restart the gps with a hot start. For now it seems to me as the gps restarts with a cold start because the time that passes from the 'gps operation started' till the first fix is often more than 1 min and not as described as in the product specification (1.3 sec). Is there a sample how to do a hot start, that would help a lot.

How fast you get a GPS fix will depend on the GPS coverage and the weather conditions you have in your area at a given time. To get a fix faster, I recommend using an external GPS antenna, as the on-board GPS frontend on the v0.8.5 DK is not ideal (will be improved in the next revision of the DK).

Testing the udp_gps sample here now with external antenna, in cloudy weather and tracking 5 satellites, I get a fix in about ~6 seconds after GPS mode is enabled. This is a hot start. To reduce this even further, open sky is required. Note that if are using the default udp_gps sample, then CONFIG_GPS_CONTROL_FIRST_FIX_CHECK_DELAY is set to 120 seconds, so you might want to lower this value, or else it will always take 2min+.

SebastianF said:

> Am I right that it is not possible to send something via udp while continuous gps tracking is active?

As of today this is correct. For concurrent GPS+LTE mode with modem fw 1.0.0, the GPS can only be active in LTE PSM(Power Saving Mode) mode, but we will improve this in a future release.