A2GC update: equipment acquisition and bring-up

As promised, I strive to keep this community updated on the work of American 2G Cooperative, the non-profit company that seeks to build a new GSM/2G network in USA. Today's post will be about cell site equipment.

Many of you here already run personal single-cell GSM networks in your homes, using low-cost SDR hardware and Osmocom software stack. However, the same equipment (cheap SDR) would not be sufficient for running a real cell site, the kind that can operate above ground (meaning the opposite of the figurative, non-literal meaning of "underground") under a license from FCC. Equipment that powers a real cell site needs to exhibit the following capabilities, none of which are present in typical home SDR setups used by hobbyists:

• For several reasons, real cell sites need to be sectored. Divide the circle around the cell site into 3 sectors of 120 degrees each and beam a different signal in each of the 3 sector directions from a separate sectorial antenna, as opposed to a single omnidirectional antenna that beams the same signal out full circle. Thus BTS (base transceiver station) equipment has to be triplicated (expensive), or the BTS equipment has to be designed with 3 separate radio chains (one for each sector) driven by the same digital unit.
• For capacity reasons, BTS equipment needs to be able to put out multiple GSM carriers per sector. A single-carrier cell, consisting of just the BCCH carrier, can support up to 7 simultaneous calls, or more realistically just 6 if we dedicate one time slot for SDCCH. (Numbers for full-rate channels; one can double the capacity by running half-rate channels, but that approach cannot support truly old phones and is thus unattractive to us.) However, in almost all scenarios we are currently considering, we will have enough spectrum to allocate at least 2 (or maybe even 3 or 4) ARFCNs to each sector - therefore, we need BTS equipment that can put out as many carriers (or TRXes as they are called in the specs and in OsmoBSC config) as needed for capacity.
• A real cell needs to put out Tx power in the range of 10 to 20 watts per carrier, in order to provide good distance range. In GSM850 band FCC rules will require us to cover at least 50 contiguous square miles; in PCS1900 band there is no coverage area requirement, but at least 25% of the area population need to be within coverage - hence we still need to aim for maximum range from each cell site. Because Rx sensitivity of the BTS is approximately 10 dB better than that of mobiles, optimal Tx power output from the BTS needs to be about 10 dB higher than that of phones - which is how we arrive at the figure of 10 to 20 W per carrier.

Where do we get BTS equipment that satisfies these requirements? The answer should be obvious: the surplus market, professional BTS equipment that was previously owned by AT&T or T-Mobile or some other carrier, but then ended up on the aftermarket. Some equipment ends up on the surplus market because it was decommissioned (pulled from towers) during "upgrades" to whatever-G, other times a planned site build ends up not happening for some reason and NOS (new old stock) equipment still in its original factory packaging ends up on the market.

There is also the issue of compatibility: at A2GC we are still committed to running Osmocom stack from the BSC up, which means that we need to have OsmoBSC driving whatever professional-grade BTS we get from the surplus market. Thankfully Osmocom community figured out how to drive both Ericsson and Nokia BTS from OsmoBSC, thus we can use both BTS types. (The brands of BTS which Osmocom does not know how to drive, namely Huawei and ZTE, are the same ones that are blacklisted from use in USA, hence those are out of consideration anyway.) In the case of both Ericsson and Nokia, the generation of BTS which we can drive from OsmoBSC is around mid-2010s - not too old.

Then there is the complex nature of the surplus market. Very rarely a single piece of this or that big BTS component shows up on ebay where people like me can just grab it - but such occasions are rare. In any case, the very intermittent supply of components on ebay is not sufficient for acquiring a proper fleet of BTS. Each of these mid-2010s base stations is not a single piece: in order to put together a functional BTS, either Ericsson or Nokia, multiple components are needed, which are always sold separately on the equipment market. Thus if an operator such as A2GC needs to acquire enough BTS equipment to operate, say, 3 or 4 separate sites, all of the same or sufficiently close model for consistency, ebay is not sufficient. Instead we have to turn to professional telecom equipment surplus dealers - it's an entire industry - and navigate their ways of doing business, which are much more complicated than an ebay-style open market.

Finally, there is the issue of frequency bands. A lot of PCS1900 equipment on the surplus market is former property of T-Mobile, as evidenced by their very distinctive asset inventory stickers. Ex-TMO PCS equipment is so plentiful on the surplus market that even on ebay I was able to buy both Ericsson and Nokia radio units for this band. But with FCC rules being as they are, we will need to make our first deployment (or several such deployments) in GSM850 band instead - and here we need equipment beyond ebay. Both Ericsson and Nokia radio units for GSM850 band are rare enough that they don't show up on ebay - hence we have to work with professional telecom equipment dealers instead, which are slower, more difficult to work with and often more expensive.

As I just wrote in a comment under my previous update post, we recently recovered $5000 out of the $7500 that was swindled from us in 2025. We are now using this money to procure the big BTS equipment that we need. We already grabbed everything we could from ebay, and we are now engaging with one of the professional dealers to get the remaining components which we need, particularly GSM850 radios. I have to be vague on the details until this equipment is secured in our hands, but we expect to spend several thousand USD on this gear, as we are buying enough to support at least 3 sites.

We are also probably a week or two away from having our first test setup in our lab, using faster-arriving equipment sourced from ebay. I will post here when this lab setup is up and running, serving as a prototype toward our planned real build-out.