1 post tagged “preparedness”

A few years ago I was taking part in a meeting to brainstorm ideas on how we (our global society) should plan to survive a flu pandemic or other widespread disaster. One of the things that became very clear to me was the critical importance of information and communication: people need accurate information in a timely manner in order to help them decide what to do. Absent that, they either make bad decisions or panic.

During the meeting it also became clear that our communications infrastructure was basically fragile. Power outages or equipment failures can quickly cause radio, TV, and cell phone networks to fail. Natural disasters can either destroy communications systems directly, or overwhelm them as people try to call their loved ones.

Throughout these discussions, one thing kept nagging at me: we all have cell phones in our pockets. There are at least two billion cell phones throughout the world. Each one of these phones is a two-way radio: it broadcasts and receives, at a range of several miles at least. But each of these phones is completely useless if cell towers within its range fail. To me that seemed somehow basically wrong, and eminently frustrating in the case of a disaster where urgent broadcast communication could save lives or prevent panic, but where towers were blown down or not available.

So I had a pretty obvious idea, I thought: find a way to turn cell phones into an ad-hoc peer to peer communication network. There must be people working on this, and it would only be a matter of time before somebody figured it out. In fact, somebody did, and developed a product suite around mobile mesh networks. Seems interesting, but too complicated to implement on top of billions of cell phones.

So here's my proposal: a simple peer-to-peer emergency text messaging forwarding system. Here's how it would work. Cell phone handsets would be programmed to listen for a special, authenticated text message on whatever frequency they normally listen on. Receiving such a message, it would display it to the user, and then broadcast it over the same frequency for a short period of time. That's basically it. A simple solution in concept at least.

I've thought a little bit more about how you could implement this and safeguard it from abuse, and how you could possibly expand it. Here a some more detailed points:

• The primary objective of this system would be to allow authorities or officials to broadcast a text message to the public, even in the absence of electricity, radio transmitters, or cell phone towers. It's not designed for a member of the public to send a message to call for help, although I have some ideas about how you could implement that in a future phase.

• Authentication: you would probably want to use some form of public key cryptography, so that handsets could verify that the text message package was officially authenticated, and that eavesdroppers couldn't learn enough to spoof an official message. My limited understanding of PKC says that this is possible.
  

• Here's how a message would be sent. In an emergency, an official would use a specially-programmed handset (or one into which an authentication code could be entered) and would author and send a special emergency message. The message would be broadcast on the special "listen" frequency that cell phones use to receive messages from a cell network tower. The broadcast would be repeated something like every minute for 10 minutes (network engineers can figure out what a good rate would be).

• Ordinary handsets would be listening in to the tower frequency even if they aren't in range of a working tower. (I'm not sure how exactly handsets operate when towers are down or out of range, but presumably they are least hunting at regular intervals. Perhaps they would have to be programmed to be listening constantly for a special message, which might cause more battery drain; I'm not sure.) When the handset receives and authenticates the special text message, it displays it and then rebroadcasts it every minute for 10 minutes.

• You would probably use message IDs and a rate limiter to avoid overwhelming transmission or unnecessarily repeating a message.

• The net result is that if your handset is within a few miles of another handset, it should receive the emergency message within minutes, even if there is no power, no cell phone towers, etc.

I'm not a network engineer and I'm more of a software person than hardware, so I'm sure there are some technical issues with the above that I'm not seeing. On the surface, it seems like it's basically a software problem, telling phones to listen for a special message on existing frequencies. Here are some possible problems:

• Reduced battery life. It's critical in a power-loss disaster to preserve the existing battery charge of every cell phone, so you would want to make sure they weren't transmitting unnecessarily. I don't know if "listening" for emergency text messages would require pulling more battery power: perhaps an engineer could answer that question?
• Multiple frequency networks. GSM phones don't talk to CDMA phones, etc., and phones only listen to frequencies that are related to their carrier, obviously. Therefore, in order to reach the entire phone population, emergency messages would have to be sent on each network from separate handsets. Interoperability seems like it might be more trouble than it's worth. Just have the official key in the same message into three or four different handsets or however many to cover all the networks in the region.
• Interference caused by large numbers of handsets re-broadcasting the same message. Message IDs would prevent the same handset from displaying or rebroadcasting the same message, but there's probably some interference effect of having hundreds of handsets in a small region trying to send the same message on the same frequency. Again, I'm hopeful a network/radio engineer would know how to solve this problem. You could also use software tricks like rate limits and random broadcast intervals I suppose.
  

I've talked to several people about this idea over the past few years; more so recently. There haven't been any immediately-obvious stumbling blocks. It seems like a capability you could add to the next version of your handset's firmware. If you're in the cell phone network business or understand these technologies, I encourage you to critique this idea. If it seems sensible, I encourage you to implement it!

Recent disasters have shown again and again that official communication has a hard time reaching people in a time of urgent need. This system seems like it would offer a consistent and reliable way to reach people, without relying on expensive network infrastructure.