That said, I'm not sure a commercial handset would connect to anything in that range. You could probably get an SDR-based UE (UE is telecom-speak for "thing that connects to a cell network") to work.

There are unlicensed variants of LTE/5G, but worth noting that these often are designed to use the unlicensed spectrum as supplemental downlink (i.e. License Assisted Access (LAA) in LTE), rather than actually allowing for uplink and downlink in the unlicensed spectrum.

The reason for that is simple politics - mobile operators are powerful lobbyists, and part of a powerful standards group (GSMA), and don't really fancy the idea you should be able to run what a customer will perceive as a mobile network without significant investment in spectrum (a finite resource).

LTE-U and LAA won't let you run a network by yourself just on unlicensed spectrum. Multefire should, but is quite rare for the obvious political reasons outlined above.

Sorry I cant find the part that mention political reasons in OP. I thought Multefire never took off was simply licensing issues.

The idea of being able to deliver a full mobile service to mobile phones is "sellable" - operators like to think of themselves as being the only ones able to provide the service people expect to a mobile handset. Then they can bundle handsets with service provision.

If you are interested in this topic, it's worth looking at the fraught relationship between mobile operators and WiFi. Operators historically rejected WiFi from handsets early on - WiFi was a rival to their high-price, high-margin mobile data services. Until perhaps the mid-3G days, when the idea of using WiFi for offload, due to the limited spectrum for mobile data started to become a tempting idea for operators.

Even that's controversial - the "enterprise" market around WiFi wasn't hugely keen on that either, since they felt the mobile operators were just trying to snap up and freeload on the license-exempt spectrum for extra capacity, and use up (finite) WiFi spectrum capacity while providing an operator-badged service.

In my view, Multefire hasn't taken off due to the general high complexity of the tech stack people would need to understand to use it (fine for me with a telecoms engineering background, less fine if you are from the pure IT world and just want something quick - it's a lot more effort and complexity than setting up a couple of WiFi APs), and the lack of pressure from mobile operators to support it. Handset support for features comes from operator demand/desire. Multefire isn't something handset makers will add, unless operators demand it. Absent that, it risks alienating or upsetting them, by opening up the handsets to competition, and since operators are the main route to market for your handsets, market dictates the rules...

While LTE-U does have some advantages over WiFi for WISP use (e.g. better handling of a large number of clients per AP), the higher cost (around ~$9k for an LTE-U eNodeB compared to as low as $500 for a WISP-grade 5GHz WiFi AP) and scarcity of vendors means that it's not very commonly used. We'll see if that changes over time, but WiFi has a huge amount of inertia in that space so it seems difficult for LTE-U to catch up considering that the power levels are limited to such an extent that it doesn't have a huge range advantage over WiFi with good antennas.

In fact, just looking at Baicells it seems that they offer fewer models for LTE-U than they used to, so they may be finding that sales aren't enough to keep up the product line.

Apparently, there are overlaps between common LTE bands and both ham radio bands and unlicensed (... low-power) ones... the above page states that any device with the right bands will work (... and they even got them working presumably?)

I believe OpenAirInterface can handle TDD, although it was firmly "research grade" code last time I looked at it.

The positive from CBRS is that it should (or at least is intended to) spawn a new generation of lower cost small cell base stations, using this band, and speaking the CBRS "protocol" for spectrum access coordination. And that has potential to help reduce prices of radio equipment.

Handset compatibility is coming on this band quicker because some existing mobile operators have purchased PALs (priority access licenses) for CBRS spectrum, and intend to use this for some extra capacity.

P.S. just as a very minor technical correction, CBRS is defined for band 48, rather than 42, although with some overlap. B48 is 3550 to 3700 MHz, while B42 is 3.4 to 3.6 GHz as you said. Therefore when looking for devices, it's best to look for B48 (although at a push, if you're doing your own R&D, B42 will be fine for use in the lower 50 MHz section of the band).

The problem is exactly what you described: there are currently no commercial UE or base stations. So yeah, I suppose one is supposed to use SDR for the 5Ghz band.

https://www.nokia.com/networks/solutions/community-hosted-ne...

is this the same?

there is zero information about nokia kuha! interesting if this can hold more 24/7 broadband clients than wifimax et al.

It seems that this is aimed exclusively at operators that already have the infrastructure to issue SIM cards et al, and communities that are barred from deploying their own infrastructure but willing to pay for it. A weird use case but clearly aimed at US and AU markets I'd guess.

You need a community that will want to front the cost of laying fiber, and then instead of distributing or starting a small ISP/coop will give that new termination to a telecom giant who will plug this device into their existing billing network to provision their new subscribers with access under the existing plans costs.

From memory, a 1-year local spectrum license should cost about £50.

Most of the learning curve comes from the lingo. Especially now that 5G introduces softwarization of many of the network functions, the terms used by the cellular and software industries clash and may be confusing at times. But you can definitely learn the high-level idea of how the cellular networks function in this way.

For physical level things, I imagine that a degree in signal processing is required. And for more advanced software interfaces, I am afraid that you can only read about them, as most devices on which the software is implemented is proprietary. The open-source software you can find is in no-way as fully implemented as the actual software which runs commercial networks.

lol, I've found a lot of terminology around digital communications seem to be confusing. Terms meaning two or three different things depending on context, etc.

Noob question, sorry, but: Why not Wifi?

Network and smartphone monitor nearby cells. If you're just about to switch the cell because the quality becomes too bad, everything is already being prepared in the next cell.

802.11ax was basically moving some of the LTE tools over to WiFi ( OFDMA ) and completely failed. And pushing back some intended features to 802.11be.

Spectrum licensing is more about ensuring exclusive use of spectrum - in a busy built up area (less common during current times hopefully), you'll still suffer from "spectrum suffocation" like with WiFi - if you ever experienced data stalling where your phone indicated a signal, but weren't getting any actual traffic through, you were on a cell that was hitting the limits of the air interface capacity.

The nice part of cellular networks is that you can add more base stations using other licensed spectrum the operator has, in order to get more capacity. So with 3.5 GHz 5G bands, and wider cell widths supported, these can take some of the load in busy places. Otherwise the alternative is to deploy more base stations with lower power on each, to better and more effectively reuse the spectrum.

Since the same operator runs all the equipment on their own spectrum, they can coordinate this much more effectively than ad-hoc multi operator WiFi in a congested area. The downside is the vastly increased complexity of a cellular solution (the sheer number of pages of standards), and the "entrenched player lock-in" available to legacy telecoms operators who already hold spectrum.