/diy/ - Do It Yourself

I have a question regarding TOF range measurements.
Nowerdays optical TOF range measurement is cheap enogh for consumer devices and achieves at least cm level accuracy.
Could the same be done with RF and an active target to be used as local positioning system for robots?
>Device 1 sends out a signal
>Device 2 recieves the signal and sends a response
>Device 1 recieves the response and can calculate the distance to device 2
Clock drift between the devices shouldnt matter to much since all device 2 does is sending out a response once it gets the signal.

There must be a problem with my thinking since any existing system I can find gets down to meters at best. Why can't it achieve the same resolution as optical TOF?