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Telecom / Wireless

The End of Spectrum Scarcity

New technologies and regulatory reform will bring a bandwidth bonanza

By Gregory Staple, Kevin Werbach  /  March 2004

 

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Illustrations: Bryan Christie

SPECTRAL CORNUCOPIA: Current uses of the radio spectrum are concentrated in frequencies below 10GHz [green]. So, too, are opportunities to apply spectrum to a wide ariety of new uses, propelled by new technologies and changes to government regulations. [Note: Spectrum allocations are not drawn to scale.]

Radio spectrum may be one of the most tightly regulated resources of all time. From cellphones to police scanners, from TV sets to garage-door openers, virtually every wireless device depends on access to the radio frequency wireless spectrum. But access to spectrum has been chronically limited ever since RF transmissions were first regulated in the early 20th century. Now that's all about to change. New technologies that use spectrum more efficiently and more cooperatively, unleashed by regulatory reforms, may soon overcome the spectrum shortage.

Since the 1920s, regulators have assumed that new transmitters will interfere with other uses of the radio spectrum, leading to the "doctrine of spectrum scarcity." As a result, every wireless system has required an exclusive license from the government. With virtually all usable radio frequencies already licensed to commercial operators and government entities, the upshot has been, in the words of former U.S. Federal Communications Commission (FCC) chair William Kennard, a "spectrum drought." We've become accustomed to seeing every new commercial service, from satellite broadcasting to wireless local-area networks, compete for licenses with numerous existing users, including the government--all of which guard their spectrum jealously. Cellular phone service, for example, was demonstrated in the lab in 1949 but not deployed until the 1980s, largely because of licensing delays.

That world is coming to an end. At least in the United States, new technologies and regulatory reforms may soon free up enough RF capacity to transform wireless-industry economics, especially for popular mobile telephony and wireless Internet services. In fact, there's every reason to think we're on the cusp of a spectrum explosion--one that will trigger major shifts in investment, business models, and services.

In the spectrum-rich future, wireless connections for new voice, music, and video services should abound, benefiting consumers and businesses alike. In our homes, devices such as TVs, stereos, DVD players, and PCs will come with built-in high-capacity wireless links to swap information. Outside, new networks will let movies and other huge multimedia files zip across town or across the country. Billions, or perhaps trillions, of wireless sensors will be embedded virtually everywhere. Wireless data, voice, and video connections will be increasingly available when we are on the move, in cars, trains, and perhaps planes, too. New services--everything from personal music channels to video-on-demand to mobile computing utilities and, yes, to the latest in ever-profitable adult entertainment--will flourish. So, too, will the markets for the hand-held devices needed to deliver these services.

These scenarios do not require infinite bandwidth. Relatively modest capacity increases--from either new spectrum allocations or new technologies--can have dramatic consequences. Today, satellite radio is delivering scores of new music choices to millions of listeners nationwide using just 25 megahertz of spectrum, about the same bandwidth as four analog television channels. Personal communications services have sparked a sea change in data services delivered to cellphones, using about 90 MHz. The Wi-Fi (the popular name of the IEEE 802.11 standard) revolution in wireless local-area networking was started with only 84 MHz. Now imagine more new spectrum made available simultaneously in the next few years than is now used by the satellite TV, PCS, and Wi-Fi industries combined [see table, " "].

The era of future abundance will be as foreign to us as our world today would have been to Marconi and Tesla, whose early spark-gap radios occupied the entire usable spectrum for each individual Morse code message. The U.S. government's first tables of spectrum allocation, in the 1920s, extended only to 60 MHz, with frequencies above 23 MHz labeled "experimental." The bands of spectrum covered by international treaties were similarly limited. In contrast, our current allocation tables regulate spectrum up to 300 000 MHz (300 gigahertz), with the vast majority of services operating above the 60 MHz that was once the top of the chart, beginning with the FM radio band (88­108 MHz).

Before we look further at what it means to live in an age of spectrum abundance, let's look more closely at the two main reasons for the past era of scarcity: the state of available radio technologies and government policies. What's extraordinary about the present period is that both these historical constraints are simultaneously going through radical change. Let's start with technology.

To understand the impact new radio technologies are having on spectrum availability, it is helpful first to address a common misconception: that spectrum is a concrete and finite resource. Not so. Radio waves do not pass through some ethereal medium called "spectrum"; they are the medium. What's licensed by governments is not a piece of a finite pie but simply the right to deploy transmitters and receivers that operate in particular ways.

Moreover, interference is not some inherent property of spectrum. It's a property of devices. A better receiver will pick up a transmission where an earlier one heard only static. Whether a new radio system "interferes" with existing ones is entirely dependent on the equipment involved. Consequently, the extent to which there appears to be a spectrum shortage largely depends not on how many frequencies are available but on the technologies that can be deployed. Many regulations intended to promote harmony of the airwaves have instead, by putting artificial limits on technology, created massive inefficiency in spectrum utilization.

Last year, a Spectrum Policy Task Force, organized by the FCC, recognized that much of the spectrum already licensed is not really in short supply. If you scan portions of the radio spectrum, even premium frequencies below 3 GHz in dense, revenue-rich urban areas, you will find that most bands are quiet most of the time. One study found that only four of 18 UHF television channels were used in Washington, D.C. Sometimes that's by design, as with "guard bands"--spectral equivalents of highway shoulders, in which no radio signals are permitted. Fifty years ago, when TV sets still used vacuum tubes, guard bands were the only way those sets could distinguish signals on adjacent channels. In some other cases, an apparent lack of spectrum use reflects system design, as with cellular-phone towers, which transmit actively only when communicating with a nearby handset.

That's why what's happening now is so exciting. New radio transmission and networking technologies can squeeze more and more capacity out of the same spectrum. Some of the improvement comes from the shift from analog to digital transmission. For example, at least five digital TV shows can be broadcast on the same frequencies that a single analog channel now occupies. Similarly, digital cellular systems now carry three times as many phone calls as their analog predecessors.

Even greater improvements in spectrum usage will come from a family of technologies that use the computational intelligence of today's wireless devices to allow multiple systems to "share" the same spectrum. The first of these, spread spectrum, replaces ancient high-power, undifferentiated narrowband transmissions with modern low-power, coded wideband signals [see figure, " What's the Frequency?"]. First described during World War II, spread-spectrum technology is already used in many cellular phone networks and in Wi-Fi, but newer systems promise even greater capacity improvements.

A newly permitted method of using spectrum, ultrawideband, takes spread spectrum to its logical conclusion, operating at such low power that, subject to appropriate safeguards, it can underlie existing licensed services. That is, preexisting users of the same spectrum bands won't even know the ultrawideband transmissions are there. It will be as if we figured out a way for freight trains to travel on highways, with cars being none the wiser. Standards work is already under way to make ultrawideband the core technology for home entertainment networks, transferring video, audio, and photos among home PCs, stereos, high-definition televisions, and DVD players.

And this is only the beginning. Another recent innovation, smart antennas, can focus adaptively to "lock into" a directional signal. Instead of radiating a signal in all directions equally, they figure out where a user is located and direct the radiation accordingly, reducing effective interference with other transmitters. Now, too, novel coding algorithms can take factors that traditionally hampered transmission, such as physical obstacles and motion, and use them to generate information that increases capacity.

Perhaps the greatest technological gain in wireless capacity, however, will come from systems that work cooperatively. In a network architecture called a mesh , each RF receiver also acts as a transponder, retransmitting data sent by other devices in the network. In other words, every new device uses some of the network's capacity but also adds capacity back. Because a device in a mesh no longer needs to send information all the way to its ultimate destination (such as a cell tower), it can use less power. That allows the network to add more devices without any noticeable increase in interference. The approach resembles the distributed architecture of the Internet, in which every router can move traffic along an efficient path.

Software radios are a key enabler for all these advances. A software radio can receive and transmit across a broad range of frequencies; because it processes signals in software, it is far more adaptable than a traditional radio. In principle, a software radio originally used for cellular telephony could, for example, download new software and begin to receive broadcast television signals, or, more likely, access a network that uses a new cellular transmission protocol. Even more sophisticated "cognitive radios" would work cooperatively, analyzing other nearby radios and adapting on the fly to avoid other transmissions.

The spectrum "dividends" possible from these new technologies have not been lost on regulators. Traditional spectrum licenses were technology- and service-specific, precluding most of the capacity-enhancing mechanisms described above. Led by FCC chair Michael Powell, the U.S. government has embarked on a historic effort to update the way spectrum is managed. It has three main strands:

Spectrum reallocation: the reallocation of bandwidth from government and other long-standing users to new services, such as mobile communications, broadband Internet access, and video distribution.

Spectrum leases: the relaxation of the technical and commercial limitations on existing spectrum licenses by, for example, permitting existing licensees to use their spectrum for new or hybrid (for example, satellite and terrestrial) services and granting most mobile radio licensees the right to lease their spectrum to third parties.

Spectrum sharing: the allocation of an unprecedented amount of spectrum that could be used for unlicensed or shared services.

Spectrum reallocation The FCC's reallocation of 120 MHz of spectrum for third-generation (3-G) mobile services has probably received the greatest media attention. It stemmed, in part, from a landmark 2002 agreement with the U.S. military to free at least 45 MHz of government spectrum. What's more, as part of the digital television transition, the FCC is reclaiming and auctioning approximately 85 MHz of UHF broadcast spectrum, which might be used for mobile communications services in the future.

Once TV stations commence all-digital broadcasting on their newly assigned channels--perhaps as early as 2007--t

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