5G mobile networks have started arriving but only in very limited areas and amidst misleading claims by wireless carriers.

While all four major nationwide carriers in the United States have overhyped 5G to varying degrees, T-Mobile today made a notable admission about 5G's key limitation. T-Mobile Chief Technology Officer Neville Ray wrote in a blog post that millimeter-wave spectrum used for 5G "will never materially scale beyond small pockets of 5G hotspots in dense urban environments." That would seem to rule out the possibility of 5G's fastest speeds reaching rural areas or perhaps even suburbs.

Ray made his point with this GIF, apparently showing that millimeter-wave frequencies are immediately blocked by a door closing halfway while the lower 600MHz signal is unaffected:

High frequency, small coverage area

With 4G, carriers prioritized so-called "beachfront spectrum" below 1GHz in order to cover the entire US, both rural areas and cities.

5G networks will use both low and high frequencies, but they're supposed to offer their highest speeds on millimeter waves. Millimeter-wave spectrum is usually defined to include frequencies between 30GHz and 300GHz. But in the context of 5G, carriers and regulators have generally targeted frequencies between 24GHz and 90GHz. T-Mobile's high-frequency spectrum includes licenses in the 28GHz and 39GHz bands.

Millimeter waves generally haven't been used in cellular networks because they don't travel far and are easily blocked by walls and other obstacles. This has led us to wonder how extensive higher-speed 5G deployments will be outside major cities, and now T-Mobile's top technology official is saying explicitly that millimeter-wave 5G deployments will just be for "small pockets" of highly populated areas.

Ray wrote his blog post primarily to complain about AT&T and Verizon claiming to be the first carriers to offer 5G, so his statement about high-frequency limitations was made partly to explain why T-Mobile hasn't yet launched 5G. (There's also the small matter of there not being any 5G phones in the market aside from a Motorola phone sold by Verizon that requires a hardware attachment to access 5G.)

"Verizon's mmWave-only 5G plan is only for the few. And it will never reach rural America," Ray wrote. Ray pointed out that early reviewers of Verizon's small 5G launch had trouble finding a signal.

"Some of this is physics—millimeter wave (mmWave) spectrum has great potential in terms of speed and capacity, but it doesn't travel far from the cell site and doesn't penetrate materials at all," Ray continued. "It will never materially scale beyond small pockets of 5G hotspots in dense urban environments."

The 5G industry standard was designed to make higher frequencies viable in cellular networks with improved beamforming and massive MIMO technology. The 5G industry standard works on everything from sub-1GHz to millimeter-wave frequencies, but spectrum "[a]bove 6GHz is needed to meet the ultra-high broadband speeds envisioned for 5G. Currently, the 26GHz and/or 28GHz bands have the most international support in this range," the GSMA mobile industry group said in a white paper in November 2018.

GSMA called the use of spectrum above 24GHz "vital" for high-speed 5G. This is largely because of the sheer amount of unused spectrum in higher bands—it's much harder to find large unused blocks of spectrum below 1GHz.

“A very small footprint”

T-Mobile intends to use millimeter-wave spectrum to provide "massive capacity over a very small footprint," Ray wrote today. "It holds big promise for speed and capacity in dense urban areas and venues where large numbers of people gather." But low- and mid-band spectrum will still be needed to cover wider areas with 5G, he wrote.

Ray criticized Verizon for "roll[ing] out technology that is nowhere near ready for primetime." He also criticized AT&T for relabeling 4G as "5G E" and for rolling out 5G in some cities without selling any actual 5G phones.

"I have the exact same 5G mmWave network equipment and software that AT&T and Verizon do, and there's no way we would launch this for customers right now," he wrote.

The 5G standard calls for download speeds of 20Gbps and 1ms latency. One Verizon 5G speed test in Chicago found download speeds of 762Mbps and latency of 19ms. But Verizon's 5G coverage in Chicago and Minneapolis, its two launch cities, is hard to find.

T-Mobile over-hypes 5G, too

Despite Ray's realism about the limitations of millimeter-wave signals, T-Mobile hasn't shied away from exaggerating the benefits of 5G. CEO John Legere began a recent blog post by complaining that "there is so damn much noise and misinformation about 5G in the marketplace that it's virtually impossible to separate truth from BS."

But in the very next paragraph, Legere claimed that 5G "is the most transformative technology of our lifetime" while providing no evidence to support that grand statement.

T-Mobile has also claimed that it can only build a robust nationwide 5G network if the government lets it buy Sprint, even though the companies' own previous statements about their 5G plans contradicted those claims.

Ray's blog post once again made this merger-related claim, even as recent reports suggest that US regulators are not convinced. Ray argued that T-Mobile and Sprint together will make "a broad and deep truly nationwide 5G network" using a mix of low-band, mid-band, and high-band spectrum.

While Verizon is charging an extra $10 a month for 5G, Ray promised that T-Mobile "won't charge our customers more for 5G, while Verizon and AT&T continue to jack up prices."