Solving the spectrum squeeze (Unabridged version)

Future of IT: We need new approaches and new technology to make the most of a finite resource

This is the unabridged version of an article that appeared in GCN's Dec. 10, 2007 issue.

Few technological advances have transformed the way we live and work in the world more than wireless communications. However, the exponential growth in demands for wireless applications has us headed on a collision course with the reality that electromagnetic spectrum is a finite resource.

We've all seen and been part of the explosion of mobile and wireless services in the commercial market. Statistics from CTIA, the international wireless association, show that the number of wireless subscribers within the U.S. has grown nearly ten fold in 12 years, to 208 million in June of 2007. In just the past two years, the number of subscribers swelled by 50 million. More telling, the proportion of wireless-only households in the U.S. has reached nearly 13 percent. That's a huge shift.

Globally, wireless adoption in countries such as India and China has grown even faster than in the U.S. A staggering 2.5 billion subscribers were using mobile phones based on the GSM standard (the most commonly deployed digital cellular standard) as of June 2007; that number will reach 3 billion by 2009. Bandwidth demand is not just for voice, but for significant increases in data and multi-media applications. The commercial appetite for spectrum has grown so dramatically that when the U.S. government auctioned off spectrum for advanced wireless services last year, some 107 licensees paid approximately $14 billion to secure more than 1000 licenses.

Government Spectrum Demands

Communication, however, is just one aspect of the demands on spectrum. From the military's perspectives, there are serious concerns about spectrum requirements for radar, sensors, navigation, and a whole slew of capabilities that war fighters depend on. Spectrum conflicts on the battle field, especially when coordinating with coalition forces, can have lethal consequences. The military and the government are also using wireless for security systems, intrusion detections, video surveillance, sensors that detect biohazards for instance and report them back to control centers.

Estimates discussed at the recent World Radiocommunications Conference suggest that next generation wireless, or International mobile telecommunications (IMT) advance, will require as much as 1gigahertz (GHz) in additional spectrum. That's a tall order given the desire to operate below the 5GHz band, which is best suited for this type of communication, but which is also the most congested spectrum across the world.

The bottom line is, the projected requirements for using electromagnetic spectrum are much greater than what is really feasible in today's environment.

Complicating matters is the fact that each country has sovereign rights over how spectrum is used within its borders and tends to use their spectrum in different ways. The desire is to identify globally-harmonized bands of spectrum which can be used wherever anybody is in the world. But the political reality makes that very difficult to achieve. And it will be well into the next decade before some of the technologies tailored for newly-allocated bands of spectrum become more widely available.

All this is putting tremendous stress on our use of the spectrum--especially in lower frequency bands, which are better for mobile types of services. And because electromagnetic spectrum is a precious natural resource, and we can't produce more, we have no choice but to identify better ways to utilize the spectrum, creating better efficiencies, technologies and techniques that promote coexistence and sharing among multiple services or users.

Future Technologies

Emerging technologies are often seen as the means for extending these limits. There are several types of technologies, developed by industry and other government entities that we at the Defense Information Systems Agency and the Defense Spectrum Organization continue to monitor and explore. Among them:
  • Advanced (Smart) Radio Systems ' Radio systems, including software-defined and cognitive radios that can automatically adapt to different spectrum environments by changing frequencies, power levels and other operational characteristics.
  • Channel Capacity Improvement Technologies ' These use advanced modulation and coding techniques to increase channel utilization, squeezing more data over existing amounts of spectrum.
  • Modeling and Simulation ' Efforts to optimize methods to model and test the next generation of spectrum-dependent systems with improved capabilities.
  • Multi-Dimensional Spectrum-Sharing Technologies ' Looking at ways to optimize reuse of spectrum by looking at factors such as time, frequency, signal coding and geographic space.
  • Networking Technologies ' Seeking greater spectrum efficiency by improvements across Open Systems Interconnection (OSI) layers, from the network layer through the link layer and down to the physical layer (the radios themselves).
  • Microwave and Free-Space Optical Technologies -- Exploring the use of higher-frequency bands (e.g., from 30-300 GHz) and free-space (un-wired) optics to relieve congestion in the lower radio-frequency bands (below 6 GHz).
  • Wireless/Mobile Systems ' Exploring commercial wireless (terrestrial and satellite) technologies (e.g., WiMAX or broadband mobile) for military applications.

Perhaps the most promising of these are the smart radio systems that will use dynamic spectrum access solutions such as software-defined and cognitive radios. These solutions would lead to devices that would recognize where in the world they were. They could also automatically apply policies appropriate at that location--by consulting a national allocation table that defines what frequencies can and cannot be used within a region or a nation. And they could sense--and adapt to--the radio frequency environment, switching to frequencies that are not being used. Another technology is adaptive antennas that allow devices to better interact with that environment and mitigate interference.

Many of the required pieces are being worked on today. DARPA, for instance is doing a lot of work in that area with a program called XG, for next generation, pulling together a variety of technologies as they mature with the aim of integrated them.

At the same time, we need to our due diligence and understand how we are going to use any emerging wireless technology to avoid unintended consequences. For example, WiMax is a great technology we all want. It would enhance our capabilities from the military stand point. But it relies on multiple bands to operate and one of those bands impacts our military radar system. So we have to make sure when we deploy a new technology, we use it in a way that does not degrade our operations.

What really keeps me up at night? Too often, when we are dealing with spectrum use and management, we've viewed it collectively in terms of a zero-sum proposition: If somebody needs more spectrum, then somebody has to give some up.

Rather, we need to look at these problems through a different lens: to create a win-win proposition by going back and looking at technologies and techniques that improve efficiencies or might allow coexistence of services that perhaps could not coexist before. We need to share spectrum rather then somebody getting it and somebody loosing it.

My greatest cause of hope? It is that when ever you have something that everyone agrees is needed, that creates energy. We all want greater spectrum access to satisfy requirements across the board'to include economic prosperity and growth as well as national security. When you create an environment in which everyone has a common goal, you can harness the resources across the globe, across industry, government and academia. That is a powerful thing.

Spectrum is the ultimate team sport. It really takes everyone pulling together and trusting one another to be successful.

Paige Atkins is the Director of the Defense Spectrum Organization, Defense Information Systems Agency (DISA). She provides executive leadership to the Department of Defense's center of excellence for electromagnetic spectrum engineering and management, including planning, policy development and implementation, electromagnetic environmental effects(E3), information systems, modeling and simulation, acquisition and operations support.

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