this is my first question on electronics, so I hope I will get it right. :) GSM and GPS are topics which are quite new to me, but I will try to be as clear as I can. Is it possible to collect data about all the present GSM devices in the room or on a floor, with my device, and then calculate via GPS the distance between my GSM device and all the others? Can it be done via GPS or should it be done via GSM module? Can that kind of collecting be done, at all? Thanks in advance!
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
3
You can use GPS to calculate the position of your own device if you happen to have a good enough sky view to receive the GPS signal. Otherwise, GPS is not useful. GPS is the Global Positioning System. A GPS receiver uses signals transmitted by GPS satellites to determine it's location. However, the GPS signals are very weak and cannot penetrate effectively through buildings so GPS is of little use indoors. Also, a GPS receiver can only determine the location of it's antenna. It cannot be used to determine the location of another device.
As for tracking GSM devices, the best you will be able to do is radio direction finding, and then only when the units are transmitting. It may be possible to extract some information about the GSM devices, but it will require a highly specialized receiver. A software defined radio unit would probably be the most economical route. Also, you would likely have to break GSM's encryption if you want to gather any information about these devices. This is likely illegal. Another possibility is to build your own base station and set it up so that the phones connect to you. However, this is far more complicated and even more illegal because you would have to transmit on licensed frequencies.
answered Nov 10, 2013 at 17:57
-
\$\begingroup\$ I wonder if GSM triangulation through picocell / femtocell type repeaters would be an option: Those devices exist and are legal in many jurisdictions. \$\endgroup\$ Commented Nov 10, 2013 at 18:54
-
\$\begingroup\$ Thanks @alex. I didn9t want to collect any information about the devices, but only to see how many cell phones are around me and their distance from my cell phone. I was guessing that they have to transmit constantly, since the base station has to locate them somehow. Or not? That is what I wanted to catch, just their signal. \$\endgroup\$– NebbsCommented Nov 10, 2013 at 19:09
-
\$\begingroup\$ I'm actually not sure about what the GSM base station handshake consists of. You will definitely be able to easily detect them if someone decides to make a call or browse the web, but I am not sure about when they're just sitting idle. I do not think the base station keeps a continuous lock on a phone unless the phone is actually communicating data with the tower, so it may be difficult to detect an idle phone. \$\endgroup\$ Commented Nov 11, 2013 at 0:49
\$\begingroup\$
\$\endgroup\$
1
They transmit very intermittently on high power (you can occasionally hear "bipping" on cheap computer speakers when SMSing, see Why does GSM cause speakers to buzz?). If you fill a building with 900MHz recievers you could probably do time-of-flight direction finding, but it would be neither cheap nor easy.
GPS is recieve-only. So you'd need the cooperation of the phones via an app or similar.
-
\$\begingroup\$ Thanks. I know I need the phones cooperation, but I thought there was an easier way to do it. (The easier being cheaper :) ). I wanted to do it solely by making an app that would scan the room, and find their "signatures" or something.... \$\endgroup\$– NebbsCommented Nov 12, 2013 at 0:10