A very easy solution is to have all phones sold in US preconfigured to be subscribed a specific cell broadcast topic. If you don't want the alerts just unsubscribe with the phone's standard interface.
Yep, that's essentially what this does. There are thirty topics reserved just for CMAS alerts. Phones will come pre-subscribed to some of those. The main difference here is that the "standard" CBS application isn't used to handle messages received on these topics. The reason is because there are some specific actions the phone must take when receiving these messages - playing a tone, vibra, etc.
But there's no real reason why an old phone which supports generic CBS couldn't receive the alerts, if it was subscribed to them. Part of the problem is that some phone makers limited the range of topic ids you can subscribe to using the UI, and the CMAS topics are outside of that range.
No need for a special chip (oooh, I forgot that someone has to pay for the personal planes of large companies and decision makers).
As I said in another post, this "special chip" stuff is completely bogus. I have no idea where the article got that from. On the phone-side of things, you only need CBS support in the cell modem (which should already be there) and a CMAS application (just software).
First: Is there any sort of method in-place wherein a message can be repeatedly broadcast, but only alert subscribers on the first successfully received message?
Yes, that's part of the CBS specification and and the emergency system uses this as well. The messages are broadcast for a set amount of time at a set repetition rate. They also contain serial numbers so that the handsets can distinguish between old and new messages. There is also a provision for sending updates to messages which have already been transmitted.
With what geographic granularity will the broadcasts be sent (or perhaps more properly, received)?
I'm not sure how granular it will be in practice, but it could technically get down to the individual cell level. Most likely, the carriers know which cells approximately serve which zip codes and would group based on that. The specs don't say exactly how this should be done, except that the "Cell Broadcast Center" should determine the affected cell sites for the geolocation (geo-code, polygon, circle) of the emergency message.
Third: Is there any pertinent documentation available that I can ogle?
There really isn't much documentation which is publicly available. Here are a few things, although they're short on real details:
Announcements: FEMA FCC CTIA
Standards (paywalled): ATIS 0700006 Joint ATIS/TIA J-STD-100
Sorry I don't have links to the actual specifications content. For some reason, you have to be a member company or pay for them.
I should have referred to the system by its proper name -- in the U.S., it's called the Commercial Mobile Alert System (CMAS). There are similar systems being set up in other countries which closely follow the U.S. specifications, and those systems should be compatible with CMAS (at least that's the plan).
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