How does satellite radio work?

If this is in the wrong section, I apologize.

I was gleefully listening to my XM while driving my taco earlier, and it occurred to me that I didn't know how exactly my radio knew it was allowed to play. I mean I know how satellites work in general, and I have a very good knowledge of how GPS devices work, and I assume, like GPS, that our radios don't actually send any signals back to the satellite.

My initial theory is that XM has a list of radio ID's that have valid subscriptions and that list is uploaded to the satellites. The list would be modified anytime someone starts or stops their subscription, the list is updated. Every 10 minutes or so (just a wild guess on the time), the list is included in the data stream that is sent out from the satellites. If the radio finds its key in the list, then it knows it is allowed to play. I have three problems with my theory:

1. With 18 million subscribers, it seems like the list would be too big to be transmitted in the data stream without robbing bandwidth from the audio.

2. Wouldn't people just figure out how to clone the radio ID like you can do with MAC addresses?

3. It seems like people also would figure out how to bypass the list or add their ID to the list once it has been received with some sort of mod.

I am working on another theory that involves encryption keys, but it is still a work in progress. Any fellow nerds out there wish to enlighten me? I don't know where this curiosity came from, but it will bug me until I know how this works

 

I believe that when you activate a receiver, SiriusXM's satellite sends an activation signal to the receiver which unlocks it so it can receive only the channels you paid for. Later they can send another signal to deactivate your receiver or remove some channels.

Bandwidth is not an issue, if Sirius can add a seemingly unlimited number of channels which are all broadcasting CD quality audio and Program-Assisted Data for each channel, then they should have no problem dedicating one channel for activations/deactivations (Sirius 184).

 

Sounds like a question for the Juggalos out there.

 

Hmm, interesting. Makes sense.

Stupid clowns!

I can google too but that doesn't address my question in the slightest.

 

my raido was cancelled but i still get signal and listen to it all the time

so it couild be a list of subscription id's. i think anyways.