AT+CSQ reports received signal strength and bit error rate in the format:

+CSQ: <RSSI>,<BER>

RSSI is the Received Signal Strength Indication, valid RSSI values are 0–31, where higher values indicate stronger signals. A value of 99 means no signal. Aim for an RSSI of at least 15. BER is the Bit Error Rate and can generally be ignored in this context.

Physical location of the modem can significantly impact signal. If signal strength remains under 10, try moving the test set up near a window. If that fails to improve signal try moving the test setup close to a cell tower.

Band locking can further improve connection stability by forcing the modem to remain on a preferred band instead of hopping between weaker ones. To check which band the device is on currently, perform the command AT+QNWINFO which indicates network information such as the access technology selected, the operator, and the band selected. Commands for locking the band are:

• Lock to a band: AT+QCFG=BAND,0,<mask>,0
  • To undo the lock and restore all bands: AT+QCFG=BAND,0,0,0
• Reset modem after making changes: AT+CFUN=1,1

If this fails, another method is to factory reset RAT/bands and put the modem in full auto:

• Auto mode (LTE-M + NB-IoT + GSM fallback): AT+QCFG=nwscanmode,0,1
• Try the RATs in this order -> Cat-M/LTE-M first, then GSM, then NB-IoT: AT+QCFG=nwscanseq,020301,1
• Auto select between CAT-M & NB-IoT: AT+QCFG=iotopmode,2,1
• Enable all bands: AT+QCFG=BAND,0,0,0

Always make sure that antennas are connected. If RSSI remains low, experiment with antenna placement and orientation.