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Re: [Discuss-gnuradio] Picking up RF cellular signals

From: Meny Sidar
Subject: Re: [Discuss-gnuradio] Picking up RF cellular signals
Date: Tue, 15 Mar 2016 18:14:52 +0200

Thanks again. Very helpful as always.
Of course those are 2 completely different approaches, but this one can also be useful to me.
I'll start looking in to it right now.


2016-03-15 18:02 GMT+02:00 Marcus Müller <address@hidden>:
That is direction finding, not distance estimation based on signal power. Two totally different approaches. You'll need at least two antennas for direction estimation.

Meny, you're an engineer, read up on the theory; it's actually fun to see these signal and geometric equations fall into place.

In this case, Walter Kaminsky (who made that device from the video) holds a granted patent [1] on this specific device, and as a skimming of the abstract of that patent shows, direction finding is done by phase comparison. You'll find more details in the patent and if you look up direction finding in the literature/the internet.
Direction finding through phase difference isn't such a complex concept mathematically, but non-trivial to implement in hardware (which is why Walter was granted a patent on a device that implements a rather well-known application); but if you have phase-coherent receivers, also not impossibly hard to build such a system with GNU Radio. It all boils down to writing a direction estimator. There's a *lot* of approaches and algorithms out there, but I'd recommend you start with something intuitive – maybe finding the relative phase of a received signal by estimating the phases of signals, and based on these phase relationship estimate the angle of the wavefront relative to your antenna array.

Best regards,

[1] http://www.google.de/patents/US6239747

On 03/15/2016 03:17 PM, Meny Sidar wrote:
Thank you for your comments.
Marcus, sorry for bugging you with this issue.
I am well aware of the previous discussions with you, and have learned from them as well as from other people.
however, when i come across something like this for example:
i keep thinking that there is some kind of heat signature in the spectrum that the cellular produces (please correct me if im wrong)
how else can you explain this works?

I know my approch is not ideal, and i'm not ruling out opening a bts base station,
but i cant find a way to make phones register to my station automatically..

thanks again for your comments guys,
really appreciate it.


2016-03-15 4:11 GMT+02:00 Nikos Balkanas <address@hidden>:
Indeed, there is phone locator protocol, and a service offered as by some companies. They work through provider contracts. The problem is that you have to know the phone number beforehand and the carrier. Not very useful in a disaster case :(


On Mon, Mar 14, 2016 at 5:50 PM, Marcus Müller <address@hidden> wrote:
    True, at least unless you send them something they have to react to. Which the phone will only do if you're the infrastructure, and usually implies you authenticate as such[2]. Which will hence most likely only work if the cellular providers cooperate with you.


On 03/14/2016 03:54 PM, Meny Sidar wrote:
Hi guys,

I am currently working on a project for my university, where i'm trying to locate cellular phones using SDR (USRP B210).
The idea of the project is to be able to find survivors/victims in disaster areas, such as earthquakes, by assuming they have their cellular on them.

What i did so far, is a program that calculates and outputs in a loop the power transmitted from a cellular phone from it's uplink channel. that can tell me my distance to it.
problem is, that cellular phones are usually in idle mode and not transmitting at all. 
So it works, but only if the phone is currently transmitting to the network (phone call, internet, etc..)

I'm trying to find a solution for this,
There has to be a way of knowing that some kind of RF transmitter/receiver is near me...
If anyone can shed some light on this subject, what can i do or if i need to go in another way, i'll be very grateful! 
right now i'm stuck.

Thanks a lot,

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