As cellular phone companies, radio stations and civilian and military agencies battle for increasingly thinner portions of airwave space, it would appear there just isn’t enough spectrum to go around. The demands of modern technology might eventually exhaust the seemingly limited airwave supply.
But not necessarily, according to Jon Peha.
Earlier this year, Peha, an associate director for the Carnegie Mellon Center for Wireless and Broadband Networks in Pittsburgh, conducted an experiment to get an idea of just how much of the airwaves are actually being used. The surprising results could point the way to entirely new ways of using the radio spectrum.
Peha and Marvin Sirbu, a professor, dispatched a few students to set up two lookout posts: one on top of a campus building at Carnegie Mellon, and the other on a bluff overlooking Pittsburgh. From these, they measured how much bandwidth was being used by radio stations, cellular phones and other users of the airwaves.
They found that while some bands were used, others weren’t used as much as expected. Some others weren’t used at all.
“Spectrum use was highly sporadic,” Peha said. Although the findings were based on a limited sample, they suggest that plenty of spectrum is available if it is used more efficiently, he said. This requires looking at spectrum use differently. Rather than viewing it as a property to be cut up and parceled out to users, it should be treated like highways and roads: Everyone has access to the roads, but people drive at different times.
“Measuring samples of spectrum may be more like observing activity on a highway. You see bursts of cars, you see gaps. There is real value to the fact we share that highway,” Peha said. New technologies are being developed that use the airwaves more efficiently, paving the way for complex integration work for government integrators.
Most notable in the government space is the Joint Tactical Radio System, a next-generation military communications system commissioned by the Army’s Communications-Electronics Command. In June, the Boeing Co. won the lead integrator role for the first of four phases of this militarywide system, valued at approximately $2 billion.
JTRS is based on a new concept called software-based radio. A software-based radio decodes and encodes signals using software, rather than relying solely on hardware designed to work only in particular frequencies and waveforms.
Such flexibility will allow military units to talk to one another with their own radios, freely choosing those frequencies and waveforms that are most secure.
Software radio also sets the stage for another concept, called cognitive radio, according to pioneering software radio engineer Joseph Mitola, a consulting scientist for Mitre Corp., McLean, Va., and a member of the Defense Science Board task force on wideband radio spectrum.
While software radio lets users pick the frequency and waveform, cognitive radio draws on artificial intelligence to allow radios to automatically negotiate the best transmission path based on factors it evaluates internally. These factors range from output power to how heavily its preferred frequency is being used.
“Cognitive radio is a goal-driven framework in which the radio autonomously observes the radio environment, infers context, assesses alternatives, generates plans, supervises multimedia services and learns from its mistakes,” Mitola said in a white paper on the subject. “This approach could expand the bandwidth available for conventional uses.”
Another development in this field comes from ArrayComm Inc., San Jose, Calif., which has developed a “smart antenna” that pinpoints users and sends signals directly to them rather than broadcasting in all directions, reducing the number of base stations needed. The company claims that telecommunications companies in Japan have found they can allow 10 times as many users to share a single channel.
In June, DynCorp, Reston, Va., signed a partnership agreement with ArrayComm to explore using the company’s antenna technology for government markets, particularly public safety.
Despite these advances, shuffling users among different sets of airwaves is anything but assured.
“The problem I see is that we have this huge, embedded infrastructure in the United States that is built on restricted frequencies,” said Robert Manchise, chief scientist for Anteon International Corp. in Fairfax, Va. “A lot of military communications, the Federal Aviation Administration, emergency response channels all have their own frequencies. To change these set frequencies would be very expensive and would meet a lot of resistance.”
Another problem is the physical constraints of wireless transmission itself, Manchise said. Some frequencies are simply more popular than others because they are more suited as communications conduits.
“There is a relationship between how high in the frequency range the signal is and how far it goes and how much data it can carry. The higher the frequency, the longer the range,” he said.
Regardless of the eventual outcome, these technologies should push agencies to look at smarter ways to use the spectrum.
“Hopefully, regulators will ask if they are using the spectrum as efficiently as they can, or if there are new technologies that can better use the existing spectrum,” said Bradley Holmes, a senior vice president for ArrayComm.
