Radio freq. round trip signal time.

There have been many similar questions posted on EngTips for short range RF location, with no solid answers available.

However, new devices based around Zigbee or 802.15.4 can be used to co-locate over short distances. In a mesh-type setup, the approximate location of a single unit can be estimated based on the signal strength at several locations providing a location within a few meters provided the environment is not heavily obstructed. I have seen demos from companies like and . There are other companies doing this with UWB type radios and proprietary designs. No doubt there are other companies out there doing similar things.

Finding a location without line of sight will be difficult. I agree with Comcokid that you can probably work around a few obstructions.

If you have many obstructions the only way I can think of, assuming your obstructions are static, is to 'calibrate' your system by taking measurements at fixed locations around the area. For 10 meter accuracy you'd need to take readings every 1-2.5 meters (10:1, or the minimum 4:1 as seen in other posts). Thats about 300-800 calibration points if I have my math correct. If you are dealing with dynamic obstructions you'll need to be smarter than I am because I don't see how you would do it. Unless maybe some UWB (ultra-wide-band) technique (ding!) that I'm not familiar with?

Thanks, guys. I am curently having a little chat with the some guys from a company that said they have done this before. We'll see how they do, if not i will try to think of a GPS solution because allthow everything is possible it looks like access to schematics and PCB's are limited also to chips and information regarding them, but what i know for sure is that this already exists. The GSM is one example of how this is done. Other than that you can use a radar system to detect metals. If you guys know different metals have a different signature (radio freq.) almost every object has, you just have to tune into it and use a powerfull antenna to detect it
Anyway the need is not that much of a problem a GPS company for sure they will jump with a solution to my problem as soon as i ask.

Thanks again for your reply, guys.