Exclusive: We Found T-Mobile's Secret Weapon Against C-Band

pcmag.com:

T-Mobile isn't sitting still now that AT&T and Verizon have launched their new C-band 5G networks. The carrier is turning on a new technology that's focused not on speed, but on range—hoping to leapfrog its competitors' C-band buildout by taking "ultra-capacity" 5G to more places, faster.

5G carrier aggregation (5G CA, or NR CA for New Radio carrier aggregation) lets T-Mobile combine two 5G channels for better speed, or better range. T-Mobile has said the capability is out there, but has been frustratingly coy as to exactly where. In three days of wandering around three boroughs of New York City with a compatible phone, I found it on seven blocks of Brooklyn.

The capability requires a Samsung Galaxy S21, S21+, S21 Ultra, or iPhone 13 series, with relatively recent (but not the absolute latest) firmware update. T-Mobile says it'll be available on more phones "in the coming months."

While testing Verizon's C-band in Brooklyn, my T-Mobile Samsung Galaxy S21+ picked up the first evidence I've seen of 5G CA in the wild. Along a stretch of Throop Avenue in Bedford-Stuyvesant, my phone started reporting that it was no longer using 80MHz of band 41 5G; it was now combining it with 10MHz of band 71, or even with another 80MHz of band 41.

That widened the bandwidth I was using to a total of 200MHz: 40MHz of 4G LTE and 160MHz of 5G. That's far more than AT&T and Verizon have available to them outside of their very limited millimeter-wave 5G coverage, even with C-band.

I'm getting these details because I'm running Ookla's new Wind software, which gives highly detailed data on cellular connections. (Note: Ookla is owned by Ziff Davis, PCMag.com's parent company.)

The average speeds I saw with 5G CA—340Mbps down and 82Mbps up—weren't