I am developing a project where I want to detect mobile devices based on GSM and/or LTE signals.
I do not want to decrypt the signal nor do I want to build an IMSI-catcher or fake base station.
The goal is to use my project to locate lost individuals in areas with no reception. Therefore I need to find a signal, identify the unit that broadcasts it, and measure the signal strength.
My question is what sort of hardware can I use to detect GSM and LTE signals? In my country GSM and LTE signals are broadcast in 700MHz, 800MHz, 900MHz, 2.1GHz, 2.6GHz
All my researching efforts lead into jamming, decryption, repeating, etc.
Do you mean, "lost in the woods" kind of lost? So you have no idea where in an area half the size of the upper Amazon the subject is?
You would need a helicopter, equipped with massive antenna arrays, and state of the art communications receivers. I say helicopter because the signals are line of sight, and the original reason why they can't just pick up the phone and make a call, is usually that there are no towers near enough to reach over the RF horizon.
Nearby, you can use a communications receiver preferably with a spectrum analyzer with a waterfall display and learn to use it. One problem, a lot of phone signals now are spread spectrum, they aren't easy to detect by simple reception unless you have the spreading code and temporal synchronization.
GSM is easy to detect, but most 3G phones don't even use it any more. They use EGSM.
You should try to get your hands on a good spectrum analyzer, to get started.
