AT+CESQ signal strength 255 (unknown) yet connection works great

[GJSea]

Hi,

In order to determine signal strength we parse the AT+CESQ response and regularly get +CESQ: 99,99,255,255,255,255 (the final number being the strength), but the connection and connectivity is perfectly fine. Is there a reason 255 is returned for the strength even though all connectivity is good?

Thanks! 

[Carl Richard]

Hi, GJSea!

Are you using Power Saving Mode(PSM) in your project? While the device is in PSM the radio is off and the device is disconnected. 

I have not seen a similar behavior in any other cases, so I must reach out to the modem team if the above is not the case.

Best regards,
Carl Richard

[GJSea]

Hi Carl, 

Ahh you're right, the device was in a PSM state, and I'd say 2 out of 10 times we get 'unknown'. Our intent is to send the signal strength over MQTT, but if PSM isn't exited until the modem is awoken when sending the MQTT payload then there is a good chance of receiving unknown. Is the only workaround to send a dummy HTTP request at the beginning of our wake cycle, then poll the signal strength, then upload our main payload?

Thanks!

[Carl Richard]

Hi again!

Glad we figured that out! It's unfortunately a sort of "chicken and egg" scenario as you must be out of PSM before RSRP can be fetched. A dummy HTTP request should be an ok workaround, but any transmission from the modem will trigger a wakeup so from a power consumption perspective a dummy UDP message could be cheaper.

Best regards,
Carl Richard