"Carpooling in the atmosphere"

When Guglielmo Marconi invented wireless communications over a hundred years ago, he had the entire radio frequency (RF) spectrum to himself. Now, organizations, governments, and industries are competing for every available frequency as countless technologies—from cell phones to global positioning satellites—require pieces of the finite spectrum.

We've come a long way in spectrum use since Marconi invented wireless communications in the late 19th century. For decades, spectrum use was wide open and there was no need to worry about access. Today, however, the radio frequency spectrum (also called the electromagnetic spectrum) is becoming increasingly scarce as supply can no longer meet current needs. To meet future needs, users today—from the military to commercial companies to air traffic control and public safety agencies—must not only use their current spectrum allocation efficiently, they must competitively identify and justify their future spectrum requirements in order to maintain current allocations and/or obtain new allocations. And, with the continuing revolution in modern electronics and mobile computing, the need for a piece of the spectrum will greatly increase in the decades to come.

MITRE is assisting two of its sponsors—the Department of Defense (DOD) and Federal Aviation Administration (FAA)—with spectrum resource management. To facilitate work projects and knowledge-sharing among our customers, as well as among MITRE teams, Jim Chadwick, MITRE's director of spectrum management, formed a spectrum coordination group. "Without new and efficient ways to allocate, use, and share the RF spectrum, key upgrades now in development for MITRE's military and FAA customers will be impossible to field. There's simply not enough bandwidth to accommodate all the needs of all potential users," says Chadwick. "Everyone wants mobile computing today, and the government has to compete for mobile-range spectrum with an increasing number of commercial companies. The most common ways to accommodate new users or new capabilities are through sharing, displacement, or by another's obsolescence. At the same time, just keeping current spectrum can be a challenge, too."

The federal government is focused on finding ways for both government and commercial organizations to get what they need from the limited spectrum. For example, Congress recently passed a bill that would accelerate the process of selling portions of the government radio waves to the private sector. This means that some groups, primarily the DOD, would change the frequencies they use, giving up some to commercial companies that can use them for wireless technology. The cost of relocating government systems is paid by the new commercial user from auction proceeds.

Sharing the Road

"Because the spectrum is limited, the long-term answer to the problem is to find technologically advanced ways to share the spectrum," explains Chadwick. "One way to do this involves temporal and spatial displacement techniques. Like the Washington, D.C., beltway, where different drivers use different lanes and leave at different times, spectrum users can use different frequencies in different time-periods and take advantage of distance effects," he explains. "Next, various modulation and coding techniques can be applied to minimize spectrum use and/or interference effects. There are many novel ways for multiple users to use the same spectrum; it's rather like carpooling in the atmosphere." And MITRE has some world-class talent in the area of spread-spectrum techniques and is using it to find new solutions and advise customers on GPS projects and other satellite system efforts.

"The key is technical innovation and intelligent spectrum management on the part of spectrum users," explains Chadwick. The idea is to prevent conflict between competing users for resources, which spectrum regulators in the United States have to sort out. (The National Telecommunications and Information Administration (NTIA), which oversees federal usage of the spectrum, and the Federal Communications Commission (FCC), which oversees non-federal use, have this responsibility.) Recently, MITRE's technical know-how came into play when it helped the DOD and FAA convince the FCC to adopt power limits on ultra-wideband systems to protect GPS from interference. "This was critical to both of our sponsor communities as GPS is used for numerous military and air safety management systems," explains Chadwick.

	Obsolete? How does a user become obsolete? Here's an example: AT&T was allocated two bands of the spectrum about 1950 for its microwave network, but stopped using it around 1985 as fiber optic cables took over.

As systems engineers on a variety of communications projects for the DOD and FAA, "we tell our customers that it is essential when building modern communications and other advanced technology projects to consider spectrum at all stages of a project's development," he continues. "It makes no sense to develop a system that can't be fielded due to spectrum conflicts. In this regard, MITRE performs numerous technical studies and does analytical modeling, laboratory and field testing, and requirements development for customers. Consider the range of 960 MHz to 1200 MHz—very familiar to us because a lot of important DOD and FAA systems are in that range. We've found that sharing spectrum-related information and analysis techniques among MITRE teams has translated into better and more cost-effective solutions. And, when it comes to helping our customers sort out cross-sponsor issues, the key to our success is our ability to be objective. That is one of MITRE's key characteristics."

The DOD's Crucial Needs

Six years ago, the DOD decided it needed to better manage and allocate spectrum resources. "It began taking a strategic look that recognized both the national and international implications," explains David Roth, manager of MITRE's Joint Wireless and SATCOM Systems Engineering Department. "It needed a big picture view on how the whole DOD uses spectrum, how it needs to manage spectrum for effective use, and the steps it needs to take to ensure the military has the spectrum it needs when it needs it."

The Defense Information Systems Agency, which led DOD's efforts in the strategic aspect of spectrum management, asked MITRE to support this new and important effort. Subsequently, MITRE wrote Joint Spectrum Vision 2010 (JSV 2010) and the strategic plan that defines the roadmap to the vision. These documents provide a big picture view of the DOD's spectrum needs and challenges, as well as suggestions on how to respond to these challenges from both technology and legislative perspectives.

"Battlespace mobility requires real-time 'untethered' communications," explains Roth. "The DOD wants to give our troops in the field high-throughput wireless access, and that's going to require access to spectrum." And, with increased emphasis on homeland security, better communications and related infrastructure are even more critical. The DOD is working with entities, such as the NTIA and the International Telecommunications Union, on an ongoing basis to ensure the military has the spectrum it needs when it needs it. Without adequate access to spectrum, the majority of our advanced warfighting system would be unusable and ineffective.

"On the basis of our research, we proposed new ways to use technology to make spectrum use more efficient," adds Roth. This work included analyzing and investigating the many dimensions of the problem from frequency, spatial, and temporal perspectives. The corporation then recommended implementing advanced modulation techniques, advanced error correction coding compression and efficient protocols, and the use of automated management tools to better manage spectrum. In addition to the technical recommendations, MITRE also offered "business" related recommendations, such as how the acquisition process could be improved to better manage spectrum, and how the DOD could better train its workforce to understand and value the importance of spectrum.

As part of this work, a MITRE research team developed a prototype radio system, the next-generation radio, which uses the concept of "adaptive spectrum use." Adopting this approach, the radio senses the spectrum environment and adapts its propagated signal to use any available spectrum. "In some ways, it's similar to our highway system. If one lane is backed up, cars look for the open lanes and 'adapt' their lane usage. It's the same with an adaptive spectrum concept. We know spectrum users rarely use the spectrum they've been licensed for 24 hours a day, seven days a week," adds Roth. "Adaptive spectrum understands and works with those ebbs and flows."

—by Nadine G. Monaco

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