Can Cellphones be used for Ad Hoc Communication?

Question

Can Cell Phones be (legally) used Adhoc, (ie, Point-to-Point) Communication? For example, let's say I'm in a remote area of the woods, or a valley. Can I configure cell phones to be used as true walkie-talkies even though neither one of them use has a cell phone tower?

(Besides, it might be handy to use this on, oh, say, a drone, for photography purposes. I intend to comply with all regulations regarding use of my drone.)

This goes for those modules too, I can hook them up to a raspberry pi, for example.

In the latter case I could just buy a nice antenna, I guess....

What kind of range would either of these things have if they are feasible?

I wanted to get my ham radio license, but I have my second year of engineering school to finish up.

Also: Might you suggest any alternatives (I hope this doesn't make my askance too open- but, it may be worth noting this question, or moreover, it's very upvotable answer! Alas, I doubt they have too much bandwidth...)

Answer 1

No, they cannot. Cell phones contain cell modems, like the green module pictured in the question. They are controlled using "AT" commands, patterned after (but greatly extending) the AT commands developed in the original Hayes modems thirty years ago.

There is a core set of AT commands that are common across all cell modems; these generally have a prefix of "AT+". Then there are a number of proprietary AT commands developed by each cell modem manufacturer, they have prefixes like "AT$" or "AT%" etc where the third character is unique to the manufacturer.

I have worked with cell modems from four different manufacturers. The documentation for these commands typically runs over 500 pages long.

These are all designed to work with a cell tower. There is a command to get the signal strength (AT+CSQ), which is used to update the bars on the screen. There are commands to check whether the cell modem has registered on the network (connected to a cell tower). Another command to get the list of carriers supported by the cell tower.

A command to dial a call (ADT, just like the dial up modems from the past). When a call answers, the response is CONNECT. When an incoming call comes in, the modem says RING ... RING etc (sound familiar?). More commands to send SMS messages, send and receive data (used for accessing the Internet), commands to access the phone book, etc.

If these were to work for point-to-point communication with another cell phone, that other cell phone would have to have all of the capability of a cell tower. But there is no provision for that. There are no commands in any cell modem AT set which allow a cell phone to behave that way.

Answer 2

There are apps that let you connect to WiFi and form ad hoc.

There is a device called a Beartooth that will serve as the cell tower It comes with the phone then uses 900mhz

Open source software called lifenet allows for zero infrastructure ad hoc networks etc.

Answer 3

It is possible, and has been commercialized by GoTenna. The review aren't stellar. It does not contain voice or pictures, but text messaging and GPS are functional.

I dont believe it actually uses the phones antenna though, but rather it's own under MURS frequencies. It just uses the phones screen as a GUI and has it's own system.

Answer 4

Actually there have been phones that could probably be convinced to play this way, the Motorola C123 springs to mind, but you need some smt skills to hardware hack the TX output filters.

The usual use case is using the thing as a BTS in its own right, often with openBTS or the like as a protocol analysis and debug tool, but you could probably come up with a way to have it work (horribly inefficiently) in a mesh.

The nice thing about this particular phone is that the RF interface has been comprehensively reversed, so unlike most the real low level RF stuff is available (PLL settings, modulation, the whole lot).