Spectrum Search: How High Will They Go?

Looking for spectrum? There's a nice chunk at 220GHz that you might want to consider.

No, this is not like those infamous deals for swampland in Florida. Spectrum in the upper reaches is being eyed for wireless services requiring large amounts of bandwidth by the Task Force on 60+GHz, recently formed by the Wireless Communications Association (WCA).

Andrew Kreig, WCA president & CEO, said the European telecom community has been interested in the 40GHz band for the past five years or so.

What's new is a more intense effort in the United States to use not just 40GHz, but even higher bands.

Doug Lockie, Endwave executive vice president & task force chairman, explained that there's an oxygen absorption window around 60GHz where the oxygen converts a lot of the microwave energy into heat and attenuates it as it goes through the atmosphere.

“That's why the FCC several years ago set aside 5GHz of spectrum at 59GHz to 64GHz for very short-range applications,” Lockie said.

The signal could not go far, so the spectrum could be reused many times. In fact, in about 85% of this country — the areas where rain attenuation is not so much of a problem — a link could travel about a kilometer with up to four 9s of reliability, he said.

Harmonix is one company currently offering a radio that operates at 60GHz. It markets the radio as a wireless extension of fiber, with applications such as campus area networks, metropolitan area networks, backhaul and temporary or emergency services.

Although the oxygen line falls off after 60GHz, Lockie said there is another “nice window at 94GHz.” Last summer the FCC held a session about possible uses of that band. Lockie attended, and said that 94GHz would be good for gigabit and 10Gb data links, what the Ethernet community needs for linking computers.

“Computers have very, very wide bandwidth data rates in their LANs at gigabit Ethernet and 10Gb Ethernet,” Lockie explained. “But the instance that you have to go across the street, you slam back down to maybe a megabit that you get with DSL unless you happen to be in one of those 5% of buildings on fiber.”

The initial mission of the WCA committee was to develop a set of rules for the 94GHz band that could be presented to the FCC, something Lockie expects by early summer. However, it could be several years before the band actually is allocated.

The task force has expanded now to look at spectrum from 40GHz through 300GHz, which is where the FCC regulates. Both the 140GHz and 220GHz bands have potential, according to Lockie, who pointed out that there's currently not much competition for spectrum up in the “nosebleed” region.

“I believe, and others agree, that there's maybe 100GHz of additional spectrum that could be allocated to terrestrial communications,” Lockie said.

The computer industry will drive the search for more bandwidth.

“Computers would like to talk to each other,” Lockie said. “The most efficient communication is when they are at some major fraction of the operation speed of the computer.”

As far as the telecom industry is concerned, Lockie noted that the primary application for millimeter-wave radios today is cell-site backhaul.

“In the old AMPS and CDMA and GSM days, 4 to 5 to 10Mb is enough to go back to the central office,” Lockie said. “With 3G we see that going to 100, 200 or 500Mb. We probably won't see the mobile community driving this to more than maybe a gigabit over the next few years.”

Lockie believes the potential computer-to-computer market is five times bigger than the telecom market. And he agrees with those who say that eventually computing and communicating will become virtually indistinguishable.