nrf9160, AGPS works longer than GPS

[Stas Jis]

We use nRF9160 on our own board.
The firmware "Serial lte modem" is installed on the chip with a connection to an external MCU (#define MQTT_MESSAGE_BUFFER_LEN 8192)
We tested the environment with periodic switching from AGPS to GPS.
And in tests, we constantly see that the operating time with AGPS is twice as long as with just using GPS.

Average waiting time when using AGPS: 1 minute + 10-15 seconds;
Average waiting time when using GPS: 30-40 seconds.

What could be the reason for such behavior? It was expected that the operating time with AGPS would be significantly faster than with GPS.

The command sequence for AGPS:
AT+CEREG=5
AT+CFUN=1
AT#XNRFCLOUD=1
AT#XAGPS=1,1

The command sequence for GPS:
AT+CEREG=5
AT+CFUN=31
AT#XGPS=1,1

The tests were carried out statically, without movement.

[Roman1982]

Our application is operates like a tracker and have a two operation modes: 

1. send location every 15 min 

2. stream continues location one at 1 min

the application is LOW poser and this is why the lock duration is importend .

the sequence that this case begins is a sequence we are currently using.

please advice 

[Håkon Alseth]

You only need to load the AGPS data once, to ensure that you do not start the GPS in a cold start (which takes min. 40 seconds to obtain fix).

Subsequent fixes does not need to use AT#XAGPS.

 

There are some scenarios where you usually want to always fetch AGPS, but this is normally when obtaining a location fix in a higher interval (>4 hours).

Roman1982 said:

2. stream continues location one at 1 min

This can potentially be problematic in some networks, where you're not able to enter PSM (or other idle modes) this quickly. All networks has a required paging period, and that can potentially block the GPS from running.

 

Kind regards,

Håkon