Tests Show Promise for Using Millimeter Waves for Cellular Networks

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Millimeter waves traveled more than 10 kilometers in rural Virginia this summer in a 5G experiment. The tests by New York University students have key ramifications for 5G, according to IEEE Spectrum.

The students erected a transmitter on the front porch of the mountain home of their professor, Ted Rappaport, and parked in a van with a test receiver in 36 locations. They searched for millimeter waves emanating from the transmitter broadcasting at 73 GHz at less than 1 watt of power.

“The team detected millimeter waves at distances up to 10.8 kilometers at 14 spots that were within line of sight of the transmitter, and recorded them up to 10.6 kilometers away at 17 places where their receiver was shielded behind vegetation, according to the account. “I expected we’d be able to go a few kilometers in non-line-of-sight but we were able to go beyond ten,” Rappaport says.  

The results show millimeter waves could potentially be used us rural macrocells, or for large cellular base stations. Currently, millimeter waves deliver broadband internet through fixed wireless, where data travels between two stationary points, but not for cellular, according to the account.

Many previously thought it wasn’t possible to use millimeter waves for cellular networks in cities or in rural regions because the waves were too easily absorbed by molecules in the air and couldn’t penetrate windows or buildings, reports IEEE Spectrum. But Rappaport’s previous work showed the tendency of these signals to reflect off of urban surfaces, including streets and building facades was reliable enough to provide consistent network coverage at street level — outside.

The 73 GHz frequency band is higher than the sub-6 GHz frequencies traditionally used for cell signals. In June, the FCC opened 11 GHz of spectrum in the millimeter range (30 to 300 GHz) to carriers developing 5G technologies.

Wireless expert at the University of Texas at Austin Robert Heath, says the latest tests are valuable “in the sense that a lot of people in 5G are not thinking about the extended ranges in rural areas, they’re thinking that range is, incorrectly, limited at high carrier frequencies,” Rappaport tells IEEE Spectrum.

The NYU team is one of the first to explore this potential for rural cellular, and he feels it could soon be incorporated into commercial systems for a variety of purposes including wide-band backhaul and as a replacement for fiber.

However Gabriel Rebeiz, a professor of electrical and computer engineering who leads wireless research at the University of California, San Diego, points out the NYU group ran their tests on two clear days. Rain can degrade 73-GHz signals. “The second it starts raining — if it just mists — you lose your signal.”   

November 9, 2016

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