# How do IR rangefinders accomplish centimeter precision without high speed / high cost parts?

I'm currently working on a system that requires an RF rangefinder with ~15 cm precision, over a range of about 50 meters. My research into the field has shown that I'll need complex and expensive electronics, clocked at nearly 2GHz, to get anywhere near my desired accuracy. 1 / (time for light to travel 15 CM). My question, then, is what method do IR rangefinders (the simple little ones for hobby robotics use) use to accomplish the centimeter precision that they display in such a small, inexpensive package? Is the method that they use something that could translate to RF to power my project?

Background info:
I'm trying to localize an aircraft within a defined box for autolanding purposes (think home-grown ILS localizer). So, I'm currently thinking about the system described here, where the aircraft has a small repeater to throw back any received signals, for a time-of-flight range calculation. 3 ground beacons arranged in a triangle, and you have X,Y,Z coordinates. Obviously IR as a medium is out, because the systems needs to operate in broad daylight, over 50 to 100 meters. I considered using an RF signal strength based rangefinder (beacon on the aircraft with a tightly controlled transmitting power), however between the RF noise from the motors and control systems and the trees and buildings surrounding my testing area, I don't think that is going to work within my required accuracy.