first step, download and install the Fastboot and ADB tool first. It will enable you to flash files into your device. I use this:
Minimal ADB and Fastboot:
http://minimal-adb-and-fastboot.software.i...r.com/download/second step, download the M11 modem file here:
http://forum.xda-developers.com/oneplus-on...ection-t2858734select and download the ColorOS modem file.
third step, boot your device into fastboot mode. Follow this site:
http://www.androidexplained.com/boot-onepl...-fastboot-mode/Plug your device into your laptop or workstation after it is in Fastboot mode.
fourth step, copy the M11 modem file into the Minimal ADB and Fastboot program file folder. By default its this path: C:\Program Files (x86)\Minimal ADB and Fastboot
finally, open command prompt and go to C:\Program Files (x86)\Minimal ADB and Fastboot. follow this command:
1) fastboot devices (this is to check whether your device is connected to your workstation or not. If it is connected, you will see some random codes of characters and numbers followed by fastboot.)
2) fastboot flash modem <name of modem file>.bin (It will show OK and finished with total time once its done)
3) fastboot reboot. (Your device will now normal reboot.)
That's about it. QC your device to determine if the signal strength issue resolved.

Nice job ! Anyone already test the fix, let us know. So that the fix can be add into the first page.