It operates under ham radio rules, on ham radio frequencies, for ham radio purposes, by ham radio operators. What else would it be?
Once the spectrum’s handled, the usual regulatory concerns are encryption and identification.
Spectrum
We use amateur allocations, obviously. But first we need to talk about LTE bands. In short, these are standardized frequency ranges and ‘modes’. If your cell phone lists band N, and your carrier lists band N, your phone is very likely to work.
Our workhorse is Band 40, 2300-2400 MHz, giving us two 10 MHz channels in the 13 cm band (2300–2310 and 2390–2400). There’s also the lower end of B42 (~3.4 GHz), and, for 4G specifically, a Band 8 cell squeezed into the 33 cm band (902–928) with a non-standard duplex. Power at this demo is modest. Think hotspot, not repeater.
Band 40 is our workhorse because it is widely supported on off the shelf phones, like the one in your pocket.
For a better view of all band and spectrum concerns, take a look at https://rf.band and you can trivially see the overlap.
The overall idea of this project, of course, is to scale up, but to do that we need you excited about the possibilities.
(Want to play without a license? CBRS/B48 is the separate, Part 96 bench for that.)
Encryption
Part 97 bars encoding messages for the purpose of obscuring their meaning. We don’t.
Encryption isn’t the same as obscuring, and the reflex that encryption is against the rules is misguided. Whether encryption is outright legal in the service is a longer argument. N2IRZ makes it clearly (see “Data Encryption Is Legal”) and I agree with him.
If the FCC ever disagrees with N2IRZ and me, Amateur cellular is not doomed. We have several knobs to pull to stay in compliance: publish or escrow the keys, publish packet captures, run the null cipher (EEA0), and more. Any one of them keeps us perfectly clean and legal.
Open inspectable signals are half the point and for us, culturally required. Otherwise, you can’t learn.
Identification
97.119 says we must identify by callsign.
For data, 97.119(b)(3) wants a “specified digital code.” 97.309(a) lists them: Baudot, AMTOR, ASCII. Then (4): any technique “documented publicly, such as CLOVER, G-TOR, or PacTOR.”
(4) is a member of that list of specified digital codes. Therefore, whatever (4) authorizes is a specified digital code, and (4) authorizes anything publicly documented.
Read plainly, a documented digital code is a specified digital code. LTE is publicly documented, and with my additions an xcl.is compliant installation meets part 97 requirements, so xcl.is cellular networks qualify as specified digital codes. QED.
For more details, you’ll want the advanced reference sheet handout.
TODO: post advanced reference sheet handout