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]

what the period for tables refresh ?

what the AT command that assistant tables update is complete?

(in order not to wait a lot of time)

does ordinary GPS operated always with assistant table (AT+CFUN=31 .AT#XGPS=1,1)

or we need to configure it that it starts with hot start

[Håkon Alseth]

Hi,

 

Ephemerides are valid in 4 hours (+/- 2 hours), and the almanac is valid for up to 90 days. 

The GPS will start from a warm/hot start if the interval is <4 hours since last successful fix.

 

If the above is in order, it will provide a fix within a shorter time period, provided that you are able to track satellites successfully.

Roman1982 said:

or we need to configure it that it starts with hot start

No configuration needed, other than just starting the GPS.

Roman1982 said:

what the period for tables refresh ?

what the AT command that assistant tables update is complete?

When the GPS is running, it will continuously fetch the latest updates from the satellites. This happens automatically.

 

Kind regards,

Håkon