[Discuss-gnuradio] Ranging (measure distance) between two radios

[Mario Ruz]

Hello,

This is my first post in the community. I have been thinking about doing this question, but after having reviewed some of the theory with digital signal processing, usrp architecture and some approaches for positioning/raning, I think I need to ask to the expert community, mainly to find a line of work and to know the restrictions for the application we want to carry out.

I would like to measure the distance between two radios at short distances (we have two UN-210 and two XCVR2450 or 1 WBX and 1 DBSRX2, let's say to 1 m, 2m....up to for example 20 meters), starting from off-line experiments and finishing with real time measures in line of sight. My questions are:

- What would be, from your experience, the best approach to do this (transmitted signal and digital processing in the receiver part), what accuracy should I expect in line of sight?

I am looking mainly for a starting point, the signal structure to transmit and the receiver structure. For example, one of the thoughts I have is a correlation in the receiver of a pseudorandom (spread spectrum) transmited signal, this approach could serve to measure time of arrival by measuring the delay of the pseudo-noise code signal, when comparing it with an exact copy at the receiver. Another approach I have seen is the estimation of the Channel impulse response (CIR), that maybe (as far as i know) could serve also for estimating distances. I have seen that there is some code to do a correlation inside the FPGA of the USRP1. 

So far my references are (which maybe can be helpul for those who are working in the same field):

- "Advancing Wireless Link Signatures for Location Distinction". Here, they do not carry out ranging/positioning, but a change in the transmitter position is detected. In my case (in the case ranging is not possible), to detect if a distance is crossed would be my objective  (e.g. the transmitter go closer than 1 meter to the receiver).

- "RF Ranging for Location Awareness". In this dissertation they use an arquitecture similar to the USRP hardware.

As you can see what I am looking for is for some sort of radar/ranging application and some starting point. Also, my questions are very generic for now and I apologize for it, mainly because I am still looking how to focus the problem.

Then, any help (references, similar work done) will be very useful.

Kind regards,

Mario