The concept is that wireless frequencies could be shared among many users rather than assigned in exclusive licenses to individual companies. Smart devices subject to rules ensuring that no one player could hog the airwaves would replace networks defined by governments and service providers. Spectrum would be used more efficiently. Bandwidth would be cheaper and more ubiquitous.
It's a deeply subversive idea, just as the Internet was for networking and open source is for software development. But it's an idea whose time has come.
"We could have the greatest wave of innovation since the Internet...if we could unlock the spectrum to explore the new possibilities," said David Reed, formerly chief scientist at Lotus and a researcher involved in the original development of the Internet.
All it would take to open the floodgates for innovation are a few government decisions to make more wireless spectrum available for "unlicensed" services. Unfortunately, the companies that have paid for exclusive spectrum licenses oppose alternatives that would make the airwaves shared and virtually free. They argue that unlicensed services would cause ruinous interference--a "tragedy of the commons." The real tragedy is that today's spectrum owners are preventing a commons that could benefit all.
No government has yet taken the open spectrum idea seriously. There's new hope today, though, thanks to the runaway success of 802.11b (WiFi) technology. It uses a small, congested sliver of spectrum set aside for unlicensed use. WiFi was designed for the mundane purpose of replacing Ethernet cables for connecting office PCs. Despite these limitations, WiFi is taking off as an alternative mechanism for Internet access. There will be 10 million WiFi devices installed by the end of this year, and 4,000 public wireless access points in locations such as airports and cafes.
Communications as computing
Ever since Congress passed the Radio Act of 1927, the electromagnetic spectrum has been seen as a fixed resource that must be divided up to prevent interference. That may have been true with the technology of the 1920s, but it isn't true today. New York University law professor Yochai Benkler's 1998 law review article showed how opening up the spectrum to shared usage would promote both economic efficiency and democratic values.
Benkler summarizes open spectrum's most startling claim: "Bandwidth is just a parameter in an equation; it's not a naturally bounded resource." Electromagnetic signals don't really travel between specific points; they radiate outward indefinitely, until they become undetectable. The magic happens at the endpoint devices.
When your mobile phone or wireless e-mail device receives a message, what it's doing is picking out one signal from all the radio waves washing over it, and disentangling that signal from background noise. The radio waves themselves pass through each other; what we call "interference" is a function of each receiver's ability to distinguish among them. Communication is inherently an exercise in computation.
If I want to send you a wireless message, my first instinct is to use a strong signal, so that you can easily distinguish it from background noise. But my high-power signal will drown out other people's transmissions, giving them an incentive to use even more power. The result is congestion. Imagine trying to understand someone across a crowded room in which everyone is shouting at the top of their lungs. Historically, the solution to this problem was to split up the spectrum into narrow bands and assign them exclusively to providers in a defined region. A monopoly within each band led to some degree of diversity overall.
However, if the receivers are smart enough, many transmitters can send signals with low power over a wider range of bands and not interfere. The signals are split up into coded chunks that are reassembled on the other end, much as routers manage traffic on the Internet. Everyone in the room can talk at once, as long as they do so quietly. And if you listen carefully, you'll recognize the unique pitch of a friend's voice across the room despite the distance and the large number of simultaneous conversations.
This approach is called spread spectrum. It's widely employed in mobile telephony, radar, satellite and military networks. For example, Qualcomm's code division multiple access (CDMA) technology, the basis for many of the world's cellular networks, uses spread spectrum techniques. But this approach is more than a mechanism to use licensed spectrum efficiently; it challenges the need for licensing to begin with. Spread spectrum systems can share frequencies with each other. One variant, called ultra-wideband, uses such low power that it can share frequencies with licensed services, because to them it is indistinguishable from background noise.
WiFi is a spread spectrum technology. It takes advantage of the same frequencies as cordless phones and other devices to deliver 11mbps of connectivity. All it requires are sub-$100 networking cards and a $150 access point tied to an Internet connection to put everyone in an office, a coffee shop or a conference hall online.
A Microsoft-sponsored survey of 180 companies with at least 500 PCs found that 40 percent were already using wireless networks, and another 31 percent intended to within 18 months. Companies such as Wayport and MobileStar are putting WiFi systems into hotels, airports and other highly trafficked areas. Community groups in many cities are establishing public access points in neighborhoods and parks.
We the transmitters
The rise of WiFi shows the power of open spectrum. However, it only gives a taste of what is possible. WiFi is for short-range connections. Access points still must hook into traditional wired networks, rather than supplanting them. And these systems don't take advantage of the full range of techniques for sharing spectrum efficiently.
Using smart "software-defined" radios, nodes in unlicensed wireless networks could cooperate actively. Devices can act as repeaters for traffic between nodes. They could dynamically select power levels and coding schemes based on the behavior of other nodes. And they could cooperatively sample and adapt to background noise. Through these mechanisms, which could be encouraged through equipment certification rules, the spectrum would go from a fixed resource to one that expands with additional computing power and technical innovation. New users could actually increase the bandwidth available by contributing to the cooperative intelligence of the network.
Unfortunately, current spectrum rules preclude most of these techniques. Ultra-wideband services aren't allowed to "overlay" on licensed bands because of overheated fears about interference. Very little unlicensed spectrum is available, and it comes with limitations that prevent companies from taking full advantage of it.
What's needed is an intelligent radio "bill of rights." This idea was suggested by Bran Ferren, a consultant who was formerly head of research and development for Disney Imagineering. The bill of rights would define the privileges and responsibilities of smart devices communicating over the airwaves, ensuring that they cooperated effectively. If the Federal Communications Commission were to promulgate such a document and make sufficient unlicensed spectrum available, it would give investors the confidence to fund further development of cooperative wireless technologies.
Open spectrum wouldn't break the bandwidth bottleneck overnight. The necessary technology is still immature. In practice, there are still limits on how many users can communicate effectively, depending on available frequencies, power, competing uses and the design of transmitters and receivers. The benefit of open spectrum is that it's more efficient than the traditional licensing model, and that gap will widen over time.
The airwaves are a public resource. Thanks to technology, licensing them for exclusive use is no longer the best way to reap their benefits. By opening up the spectrum, we could build the foundations for a communications industry that works more like the computer industry, with rapid innovation and active competition. Instead of a tragedy of the commons, the result would be a triumph.