This is the big barrier here, and unfortunately, it is legally impossible to open source.
In most countries, the spectrum that cell phone carriers use is licensed to the carrier, under the condition they only connect devices that are guaranteed to comply with the requirements of using that spectrum. The end user (i.e. the person with the phone) has no license to use the spectrum. So in order to get regulatory certification, basically every modem has to be locked down so that the end user cannot operate it in a way that would violate any rules or regulations for using that spectrum.
So basically, it's illegal to have open source modem firmware. At least, as long as cell phones are operating on spectrum that isn't open for public use.
Ultimately, if you want to open source a modem, you first need to build your own cell phone network.
this is the same thing with wifi. There are different channels and transmission power rules depending on country. Something you cannot change even if you are root or build your own kernel, as it's built in to the wifi hardware (eg. raspberry pi)
Don't cbrs devices need to be part 96 certified? The spectrum might not be licensed but you still may need a certified device to legally use the spectrum. Which you could do, but that is a tall hill to climb for a FOSS enthusiast. And when you're done -- what network are you going to connect it to? A cheap SIM from the corner store is probably out of the question :)
looks like they need.
but it still gives you more possibilities compared to usual spectrum. if there is enough coverage from SAS you (or FSF) can build your own cbrs network that will have open source modem/firmware (yet, still will have to comply with part96).
there are also all kind of open source lte/cbrs projects iirc
It's a fun thought exercise, but putting "part 96 certification" at the end of my build pipeline sounds pretty expensive. And building a physical cell phone network is stupidly capital intensive. Maybe there are some interesting small scale niches that this would be useful for. But as a daily driver cell phone, I don't think we're ever gonna have an open source modem, at least not until there are significant changes to the spectrum that's in use.
Haven't there been projects trying to do this since 802.11b? I think the last time I looked one of these mash networks up, there wasn't even decent coverage in the dense city I lived in.
In most countries, the spectrum that cell phone carriers use is licensed to the carrier, under the condition they only connect devices that are guaranteed to comply with the requirements of using that spectrum. The end user (i.e. the person with the phone) has no license to use the spectrum. So in order to get regulatory certification, basically every modem has to be locked down so that the end user cannot operate it in a way that would violate any rules or regulations for using that spectrum.
So basically, it's illegal to have open source modem firmware. At least, as long as cell phones are operating on spectrum that isn't open for public use.
Ultimately, if you want to open source a modem, you first need to build your own cell phone network.