Open Spectrum

Open Spectrum Reform

The spectrum available for broadcasting, cellular telephony, wireless broadband, etc.. is not scarce, but kept scarce by legislation based on outdated technological realities. The Open Spectrum reform movement intends to change this.

This entry mostly applies to the situation in the U.S.A.

Discussion

The rationale for Open Spectrum reform

"The notion that the airwaves need to be meted out carefully is based on the fact that, in the early 1900s, radio equipment was easily thrown off when signals of the same frequency from more than one source overlapped. We call this phenomenon “interference." In fact, the waves sent out by different transmitters don’t interfere with each other at all. They pass right through each other unchanged. Interference occurs in the receiver, when its antenna picks up multiple signals of the same frequency and has trouble telling them apart. In other words, interference is a function of the intelligence designed into the receiver, not a function of what happens in the airwaves—and receivers can be a lot more intelligent than they were 90 years ago. Recent advances are enabling radio signals to be coded digitally so they can easily be separated from each other. No longer is there a need to chop the airwaves into distinct regions of frequency and geography." (http://www.reed.com/dprframeweb/dprframe.asp?section=openspec )

Summary of technical ‘Open Spectrum’ advances

by David Reed

“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. 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 summary is by David Reed for the IEEE Spectrum magazine, but the article is no longer available at the original URL, http://www.spectrum.ieee.org/WEBONLY/publicfeature/mar04/0304scar.html)

More Information

A very useful briefing on open spectrum issues: Open Spectrum, New America Foundation, at http://www.newamerica.net/index.cfm?pg=article&pubID=1002