LTE increases power consumption by 10 Watts

[stephan2024]

Being still at the beginning of my OPNsense (v23.7.10) journey, I have managed to reduce the power consumption of my purpose-built appliance from 14 watts to 7 watts by enabling the C3 processor power state. However, after setting up an LTE interface as backup Internet access (via the well-known Sierra Wireless EM7455 running the latest firmware), the power drawn increased to 17 watts without user traffic. I could not observe an increased CPU load. Just deleting the PPP interface brings the system back to 7 watts.

Ten watts for an idle LTE connection looks too much, especially considering the EM7455 connects to the mobile network without OS or application support (checked via AT command interface). I wonder if something is missing in the USB power-saving settings or if FreeBSD driver issues could exist. Some Internet research did not reveal something helpful.

What are your experiences? Do you have any tips or pointers to reduce the idle LTE connection's power consumption or help further troubleshoot?

Thanks for your thoughts.

Update: The CPU temperature decreased from 31 °C to 22 °C after deleting the PPP interface, suggesting the issue is on the OS/driver/application side and not on the EM7455.