To investigate the signal quality of your device, you can use AT commands to check the modem configuration and connection status directly through your modem's serial interface.
Checking Basic Signal Strength
You can query the basic signal strength (RSSI) and bit error rate using the AT+CSQ command. The command returns an RSSI index where higher values indicate a better connection:
-
0-9: Poor (below -95 dBm) -
10-14: Fair (-95 to -85 dBm) -
15-19: Good (-85 to -75 dBm) -
20-31: Excellent (above -75 dBm) -
99: Unknown or not detectable
Checking Extended Signal Quality
For more detailed metrics on 3G and 4G networks, use the AT+CESQ command. This command returns six values, including Reference Signal Received Quality (RSRQ) and Reference Signal Received Power (RSRP) for 4G networks.
AT+CESQ is supported by most modern modems, but some older modems may not support it. If the command returns an error, use AT+CSQ instead or check your modem's manual for a vendor-specific alternative.
Some modem manufacturers also offer proprietary commands that return detailed serving cell information, such as frequency bands, channel numbers, and additional signal quality measurements.
Device Limitations
While every modem has a serial interface, not all devices provide a way to access it. If you are using a third-party device that does not allow direct access to the serial interface, refer to the device's instruction manual or contact the manufacturer for alternative troubleshooting steps.
For more information on diagnosing connection issues, refer to the Advanced Troubleshooting documentation.