Emergency Cell Tower On A Budget

Cell phone towers are something we miss when we’re out of range, but imagine how we’d miss them if they had been destroyed by disastrous weather. In such emergencies it is more important than ever to call loved ones, and tell them we’re safe. [Matthew May] and [Brendan Harlow] aimed to make their own secure and open-source cellular network antenna for those occasions. It currently supports calling between connected phones, text messaging, and if the base station has a hard-wired internet connection, users can get online.

This was a senior project for a security class, and it seems that the bulk of their work was in following the best practices set by the Center for Internet Security. They adopted a model intended for the Debian 8 operating system which wasn’t a perfect fit. According to Motherboard their work scored an A+, and we agree with the professors on this one.

Last year, the same SDR board, the bladeRF, was featured in a GSM tower hack with a more sinister edge, and of course Hackaday is rife with SDR projects.

Thank you [Alfredo Garza] for the tip.

22 thoughts on “Emergency Cell Tower On A Budget

  1. Interesting…. might have to look into what I can abuse this for in conjunction with java app capable camera phones set up as security cameras… (Phones like the old razr v3 don’t have wifi.)

    1. Arguably, phones like the old razr v3 also have terrible cameras by today’s standards. 0.3mp just doesn’t really cut it anymore…
      Plus you can literally score 720p Chinese 2.4Ghz wifi enabled IP cameras for under $10.

  2. I bet you could easily hook this up to an AMPRNet and expand the range of the network with a few nodes. You could have temporary phone usage for an area the size of Orlando in about a day or two.

  3. It’s not that difficult to create your own cell phone network these days but unfortunately non of the main players will let your network talk to their own networks, so you’re stuck with talking to a couple of your mates and that’s it.

    1. It’s not as easy to setup but if one wanted to interoperate with other phone networks then one could use more comprehensive cellular base station software like OpenBTS. OpenBTS can use an Asterisk PBX to provide dialout, and with some extra effort dialin, service to cell phones so you can call any phone number from your base station. If you have a SIP trunk provider and DIDs then you should be able to have a pretty seamless carrier experience, in theory. (Ignoring the likely configuration nightmare, lack of documentation, and the fact you only have one base station.)

    2. Not really, you could probably set up a gateway to talk sip or even POTS to the world, so long as you are picking up the cost of the tariff outbound, your callers could break out over whatever was available that your personal cell tower could “see”, be that commercial internet, or even a ham radio link to a further gateway.

    3. Not to mention that with the suggested use during an emergency when no other near by cell towers are operational, I wouldn’t expect a lack of “communicate with near by cell towers” feature to be very much of an issue.

        1. That’s easy, you can see it in the headline picture of this article: Have the phones register on your network, then send them a text message telling them their own number and maybe the number of an emergency operator.

          Getting the phones on your network is easy, in the absence of any other network, they will try to register to any network they can see (as long as it is not a forbidden network listed on their SIM cards). As long as only GSM is used, no encryption or authentication is required, so no dedicated SIM cards for your network are required. This will not work for 3G or LTE though.

  4. Right, but unless you have previously handed out these preprogrammed custom SIMs (and unless you have a dual SIM phone, you gotta remember where you put it), you can’t just set this thing up and instantly have a roamable local network, since it doesn’t know the keys for the wild SIMs trying to connect to it.

    1. That’s just about how I understand it too. What would be needed would be an entirely new kind of protocol for a new phones to be able to operate on one emergency frequency that is already programmed into every sent card. Or something like that anyway.

    2. That’s not entirely correct. GSM alloẃs unciphered and unauthenticated operation and devices will try to roam on any network available in the absence of their respective home network. So no dedicated SIM is needed for an emergency network to operate.

    3. If it’s going to be a public service, do you need to exclude people from it? Anyone in-range is your potential customer. If people start abusing the service, you can keep a blacklist, or just set up a time limit on each call, or whatever.

      If it’s just meant to be for you and your friends, you’re even less likely to get away with polluting the mobile phone bands than you are by providing a public service. And even then you’ve basically no chance. Legitimate providers will claim you’re hindering their attempts to return service, and interfering (or potentially, which is just as bad legally) with emergency services.

      Apart from Burning Man and other places where you’re well out of range of ordinary mobile, and thus undetected or cared about be the big providers, you’ve almost no chance of getting away with this. That said I’m not sure the police are gonna helicopter out just to arrest you.

        1. Wait…I’m wrong. While there’s overlap in the bands, none of the uplink/downlink pairs fit, so you’d have to reprogram the baseband in order to have a working phone.

  5. If you’re interested how “Disaster Recovery” works for one of Europes biggest Telco, there is a corporate blog post about it. Pictures cover mostly fixed line equipment, but be sure there is simolar containers for mobile networlük coversge as well.

    During the time there are no disasters (doesnt happen too often luckily) They use their mobile spare equipment to serve huge events.


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