CyanogenMod 13 fall down to 2G when data connection is OFF
I am using cyanogenmod in my Xiaomi Redmi 1s, I used to do this steps :


Open dialer, and type *#*#4636#*#*.(I think this setting code may vary with each device manufacturer, search appropriate code for your device)
It will enter into Testing mode.
Inside that, tap on Phone Information, look for Set preferred network type, and set it as WCDMA only.


This Setting will be lost after every reboot.