Reliable method for LTE-M signal verification

RE: Reliable method for LTE-M signal verification

Hakon — Thu, 28 May 2020 09:19:50 GMT

So the device will not connect to the MQTT broker even when you are registered? Could it be that it loses coverage while you are trying to connect?

RE: Reliable method for LTE-M signal verification

Gmaciek — Tue, 26 May 2020 12:30:33 GMT

Hi Hakon, thank you for answer.

[quote userid="73166" url="~/f/nordic-q-a/60935/reliable-method-for-lte-m-signal-verification/248985"] If CEREG returns 5 or 1 it means that the device is connected and should be able to send and receive. Otherwise, if the signal is too weak it should return 4.[/quote]

So that means that the CEREG output 5 or 1 should be the sufficient indicator, that the device is able to connect to MQTT client and send data?

I did some outdoor tests and my device recovered from no coverage state and succesfully reconnected few times, but sometimes it doesn't do that. The only thing I verify related to network status is checking the registration status with AT+CEREG output - if it's registered I proceed to connecting to MQTT client and sending data, if not - I wait and check again each few seconds. I'm trying to disqualify the network registration, signal strength or any other networking related problems as a possible reason of failure.

RE: Reliable method for LTE-M signal verification

Hakon — Fri, 08 May 2020 13:41:18 GMT

Hey,

[quote user=""]- is it correct to say that the network can be registered (CEREG will return 5 or 1), but the signal will be to weak and the client connection or data publish procedure will fail?[/quote]

If CEREG returns 5 or 1 it means that the device is connected and should be able to send and receive. Otherwise, if the signal is too weak it should return 4.

[quote user=""]- if so, what is the required signal strength to perform this procedure?[/quote]

You can find the receiver sensitivity in the product specification under section 7.6. Then if the RSRP drops below that, the device could be disconnected from the network. The RSRP can be read with the AT+CESQ command.

[quote user=""]- is it true that if modem gets the AT+CFUN=21 command once, it will automatically try to reconnect to the network after losing the signal (no need for sending AT+CFUN=21 again)[/quote]

Yes, it's true.

[quote user=""]- since in the last modem firmware version (1.1.1) there were introduced AT+CFUN= 21, 31 and other parameters related to activating/deactivating LTE and GPS (or at least I wasn't aware of them in the 1.1.0 and previous versions of MFW), is it correct to say that the AT+CFUN=21 "activates LTE" in a sense that previously was done by AT+CFUN=1 together with AT+CEREG=5?[/quote]

AT+CFUN=21 just activates the LTE without changing whether the GNSS services are turned on or off. I'm not sure if that answers your question.