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Amateur LTE - Overview

The power, flexibility, and intensely complicated debugging of your LTE networking, but by hams, for hams, on ham spectrum under 47 CFR Part 97 (Amateur Radio).

What

By pure luck, LTE band 40 has overlap with out privileges in a way that we can use it. China and some other asian countries are the only users of LTE band 40.

We can purchase decommissioned 4G LTE equipment meant for the Chinese market, and deploy real networks with real hardware.

We can also experiment with SDRs, and eventually explore making our own equipment.

UE (User Equipment - phones!) largely already supports Band 40 thanks to globalization and the streamlining of modems. iPhones since at least iPhone 7, Google Pixels since at least Pixel 4, and many more modern phones already support Band 40. The phone you have in your pocket almost certainly does.

All you need to get started? A callsign and a sim card.

Who

  • W2FBI - Mike McGinty, USA.

  • BA7JKX - Licheng Mao, China. Hardware procurement, testing.

  • KC8QBA - Stephen Saletta, USA. EPC testing.

  • And a whole pile of existing open source projects, companies, and individuals that we depend on but haven’t talked to specifically yet - Osmocom, Sysmocom, Open5GS, srsRAN, github.com/herlesupreeth in particular, and many more.

How

We learned enough about LTE to follow existing tutorials, but set up and experiment on our frequencies.

Then we had to figure out how to comply with FCC regulations. See the LEGALITY sheet for that.

LTE has a lot of moving parts. IT folks with Linux, networking, and/or programming experience will pick it up.

Without that experience, you will have a very steep climb ahead of you, but it can still be fun. One benefit is that much of 4G and later is built on tools the tech industry is already familiar with.

Why

What do you mean why? Because we’re hams and it’s cool.

Amateur radio has stagnated so badly that a competitor to D-STAR, M17, is the coolest thing we’ve seen in two fucking decades despite having fewer features, almost no radio support, and still being in its infancy.

And it is cool, but maybe we can skip ahead a bit.

NEARFest

What you see here is:

  • Battery and solar powered
  • an eNodeB (Base station, basically) transmitting a 10MHz LTE signal (50 resource blocks).
  • Several UE (phones, etc) connected to it, demonstrating some of the current capabilities as well as some of the complications across platforms.
  • A small computer, running the EPC (Evolved Packet Core, the network backend) and a hand-built live view into that same EPC.
  • SIM programming hardware and software.
  • A starlink uplink. Not necessary for local calls, txts, or data, just cool and provides internet!
  • Me, W2FBI, talking your ear off.

Where are we now? What’s next?

Currently:

  • Data works on nearly everything. This means you can browse internet, stream video, use Discord and other apps like ATAK, whatever.
  • VoLTE Phone calls work, including experimental dial-by-callsign (!).
  • Text messages sometimes work, depending on UE. IMS does, SGs does not, and routing is quirky because of UE SIP URI mangling.
  • eNBs are femtocells or SDRs. (Low power, short range)
  • I issue sims (sysmocom) and esims (simlessly)
  • Android Carrier Config - @herlesupreeths CoIMS app with Carrier privileges, via ARA-M.
  • Documentation and small community of friendly experimenters
  • As compliant with 47 CFR 97 as all your other favorite non-RTTY data modes, including built-in UE and eNB identification.
  • EEA0 (null cipher) by default. Optional specification for deriving keys from callsigns.

Coming soon (ordered by likelihood/effort required):

  • Built-in local conferencing and other ham-centric tools
  • Better UE support through carrier config.
  • VoWiFi - basically a VPN back to the EPC to support calls and texts. (So you can be on the network without having to be in range of an eNB).
  • (once conferencing is working) Cross-mode-capable repeater and network links.
  • Custom PLMN (999-73)
  • EPC federation

Long term dreams:

  • Real-PTT compatible backend server?
  • MMS messaging
  • MCPTT
  • Tactical cell towers with pre-programmed sims for
  • PLMN assigned by 3GPP, somehow, so we can get into Android and IOS carrier configurations.
  • Proper cell towers

What’s special about Ham LTE?

  • Operation under Amateur Radio rules. Of course. Don’t take this for granted, we are uniquely unfettered and are just given spectrum to play with. We should be using it to the fullest extent we can, and the fact that we don’t is why we keep losing valuable spectrum, like 2310-2390 MHz.
  • Experimentation, research and development, without almost any limitations.
  • Testing with real networks with real users, including security testing.
  • Not driven by financial requirements. Can be focused on disaster services, working without relying on an internet uplink or indeed any central authority. Local services can include takserver, openwebrx, chat servers, voice servers, offline wikipedia and reference material (https://internet-in-a-box.org/)