High-band 5G, which Verizon has labeled "true 5G," promises gigabit-plus speeds but at the expense of coverage and signal penetration. Now, we're starting to get some idea of how carriers will have to densify networks to support propagation in 5G millimeter wave networks.

Notably, Qualcomm Inc. (Nasdaq: QCOM) has been comparing the coverage of prospective 28GHz 5G small cells and unlicensed 4G Licensed Assisted Access (LAA) 5GHz small cells, which don't offer as much transmit power as traditional 4G macro cell deployments. The chipmaker finds that mmWave networks will offer 96% of the coverage of the 4G networks if the 5G small cells are deployed at a range of around 100 meters to 200 meters apart, said Peter Carson, senior director of product marketing at Qualcomm.

Recall that Verizon Communications Inc. (NYSE: VZ) has previously said that its 5G fixed wireless tests have shown downloads of more than 1.4 Gigabits per second to nearly 600 Megabits per second at a distance of up to 1,000 feet. At distances of between 1,000 feet to 2,000 feet, the download speeds drop to just below 1.4 Gbit/s down to just above 400Mbit/s. Beyond connection ranges of 2,000 feet, the top download speeds are listed at just over 1 Gbit/s. One thousand feet to 2,000 feet correlates to 300 to 600 meters, although Verizon was testing with fixed connections, while Qualcomm was looking at mobile usage. (See Verizon Says 'Up to 5' Fixed 5G Markets Will Go Live in 2H18.)

As I've reported before, mmWave can suffer propagation issues with energy-efficient glass and certain types of building materials. This led T-Mobile US Inc. 's CTO Neville Ray to recently say that the operator will use the high-band spectrum in urban, outdoor areas, rather than try and deal with "outside-in" propagation issues. (See Could 5G Have Found Its Glass Ceiling? and T-Mobile Walks a Fine Line on 5G Spectrum.)

As Nokia Corp. (NYSE: NOK) Vice President Tod Sizer said back in November: "We can't change the laws of physics." (See Nokia Bell Labs & Verizon Stretch Fixed 5G to the Home.)

So what does this mean for mmWave small cell networks in the future? Qualcomm's Carson thinks operators will need to double the density over 4G LTE to get the same coverage. (See 5G in the USA: Where We At?)

— Dan Jones, Mobile Editor, Light Reading