January 5, 1999

A PUBLIC FORUM THAT’S ON OUR WAVELENGTH

by Andy Oram
American Reporter Correspondent

CAMBRIDGE, MASS.—Wouldn’t you like to end the local telephone monopoly for once and for all? How about offering digital networks to school systems while sparing them the expense of tearing up their walls to install wiring? And consider even grander wireless visions, such as devices that can find hikers lost in a snowstorm or the land mines that beset old battlegrounds.

All these hopes converged, along with even more startling possibilities, in the many responses posted last month to an FCC notice that suggested opening up a wide range of the radio spectrum to digital transmissions. This notice, released by the FCC on September 1, referred to a class of devices called “ultra-wideband transmission systems.”

Companies interested in ultra-wideband technology propose a number of interesting applications in radar and other particular areas. But of most interest to the public is the possibility of using the spectrum for general-purpose Internet access, transmitting packets at blazing speeds without the need for costly phone lines.

The Internet is ideal for digital radio transmissions. The characteristics that make it robust over wires are even better suited to radio. Because the Internet Protocol breaks data into small packets that can be sent in any order or at any speed, and because higher-level protocols handle lost packets elegantly, the protocol offers a built-in response to the natural noise and unreliability of radio.

Democratic activists often speak of the importance of “public spaces” like town meetings and city squares, where communities can share ideas outside the control of commercial or government rulekeepers. Just as the malling of America has reduced the time that people spend in public spaces, the commercial division of the radio spectrum threatens to fence in the media that most of us use for information and entertainment.

Over the past decades, a proliferation of new technologies—particularly cellular phones and digital television broadcasting—has driven the FCC to sell or give away huge ranges of spectrum. These ranges are strictly controlled by the companies who win them and exploited for the highest-paying application, whether it be telephones for the affluent or sports programming with high advertising potential.

Thus, the aforementioned democratic activists, in pursuits such as community networking and federal policy regarding digital television, have applauded the idea of saving some of the spectrum as a “public space.” Internet radio is the perfect medium to use in that space.

In a seemingly magical defiance of everyday assumptions about spectrum, everybody and anybody can transmit simultaneously in a digital packet radio system. The system operates like Ethernet on a campus network, where each device listens to just the transmissions it wants to receive. But given the right frequency range, digital radio can stretch much farther geographically than a campus network, and send a large quantity of data faster.

Traditional radio broadcasting exploits, fairly uniformly, a range of spectrum assigned by the FCC (or whatever body is responsible in each country). For instance, suppose you tune your radio to station 90.1 FM. This means the radio will receive all radio waves coming through the air from 90025 to 90175 kilohertz (thousands of vibrations per second).

The frequency of the radio waves in FM radio map directly to the frequency of pitches in the sounds being transmitted. Thus, the lowest note that can be sent over the radio will be transmitted at 90025 kilohertz, and the highest overtone at 90175 kilohertz.

Note that the lower and upper limits represent a band slightly less than 200 kilohertz in width. This number is a typical, moderate amount of bandwidth. The whole band is centered on 90100 kilohertz or 90.1 megahertz, which gives the station its call number.

Spread spectrum technology like ultra-wideband, which sends digitized information and uses a wide range of frequencies, operates in a completely different manner. Spread spectrum uses the range of frequencies available to the device as a set of numbers to play with. Then it encodes data using algorithms that squeeze as much information into the bandwidth as possible (along with compression, error-checking, and probably encryption for privacy’s sake).

Typically, the code is sent as a sequence of extremely short pulses—perhaps shorter than a nanosecond, which is one billionth of a second. While copper phone lines struggle to deliver 56 kilobits a second (or 1.5 megabits over the new ADSL technologies) comments to the FCC on ultra-wideband transmission promised transmission speeds in the gigabit range, given a sufficiently broad frequency range.

There are two questions to answer before permitting ultra-wideband transmission. The first is whether the spectrum should be used for these applications rather than to expand older offerings like cellular phones. The conflict over limited spectrum makes enemies of the cellular phone companies, represented by the Wireless Information Networks Forum, or WINForum.

The second question is whether ultra-wideband transmissions could interfere with current applications. A blip on your fancy thousand-dollar digital TV screen would certainly be annoying; a jammed transmission from an air traffic control tower to a pilot could have somewhat worse consequences.

Thus, it is no surprise that the main question that commenters to the FCC wrangled over was whether ultra-wideband would cause significant interference. On the cautionary side lay the WINForum and other users of existing applications; the more sanguine responders included companies that create digital devices for various purposes. While both sides submitted models filled with mind-numbing equations, they tended to talk past each other.

WINForum devotes many pages to finding the rate of interference (as a function of the speed with which the digital devices transmit pulses, the bandwidth of the device that is being interfered with, or both). But interestingly, they do not try to predict the amount of interference that would hurt operation.

Their submission says that “the current rules permit high relative levels of interference…for some emission types” and “the rules are excessively strict for some emission types.” While advising limits on the power of ultra-wideband devices, the submission does not go so far as to say categorically that the levels of interference are expected to be harmful.

The most concrete—and alarming—evidence in the WINForum comments comes in a table comparing normal noise to potential interference from digital devices. The worst case shows an enormous amount of interference (ten thousand times as much as normal noise), a scary scenario.

But the conditions under which this amount of interference would occur are a high rate of transmissions in a narrow frequency range—not the actual conditions called for in the ultra-wideband proposal. The conditions used by real devices in this proposal are closer to those shown in the opposite corner of the table, where interference is shown to be only a few times greater than normal noise.

A more forgiving comment comes from Multispectral Solutions, claiming that ultra-wideband devices should be prohibited from frequencies used by current applications. It softens this requirement by saying that common forms of control over signals “can result in systems which can avoid operation in restricted bands.” In other words, the comment believes ultra-wideband devices are still feasible even with restrictions on the frequencies used.

More than one comment measured the output of an ultra-wideband digital device against that of a personal computer and found them very similar. The personal computer is just one example of the hundreds of types of everyday equipment that emit noise in the frequencies occupied by current applications but obviously do not interfere with these applications. The commenters thus claim that the digital devices are safe.

For instance, the Time Domain Corporation says that “literally billions” of devices already emit noise in the frequencies that the FCC has to protect. And the XtremeSpectrum telecom company, claiming to use its own “worst case assumptions,” finds that the cumulative effects of many devices would be no worse than the interference of a single device. Their model was confirmed by the Interval Research Corporation, who concluded that “substantial noise build-up does not and will not occur.”

Ultra-wideband proponents go so far as to suggest that these devices can make good use of an overcrowded spectrum precisely because they use the same frequencies as traditional applications like television. The TV station and the Internet digital device can share the frequencies, each using it in a way appropriate to its medium without knowing each other exists.

The current FCC inquiry is not the first time a public space for digital radio has been proposed. In 1995, the FCC received a petition for bandwidth that could be used by schools and other public institutions for low-cost digital transmissions. The source of the petition, interestingly, was neither a phone company nor a public interest group, but Apple Computer.

In 1997, the FCC did allocate some of the requested spectrum in what it called Unlicensed National Information Infrastructure (UNII) bands. The name reflected the rhetoric of the time, but the allocation was severely limited and found almost no takers.

Community networking expert Dave Hughes, in his typically frank comment to the current inquiry, calls the UNII allocation a failure. It was supposed to permit low-cost devices, extend over wide areas so as to facilitate rural communications, and offer high bandwidth, but fell hopelessly short in all three promises.

Hughes reports that a typical device for UNII costs nine thousand dollars, operates at a range of only three miles, and delivers measly bandwidth. He enthusiastically supports the current ultra-wideband proposal and has done more than everyone else put together to publicize the issue.

Yesterday was the original deadline for comments to the FCC on the ultra-wideband proceeding, 98-153, but at the request of some commenters the deadline has been extended to February 3. Given the clashing views of experts from different sides and the low visibility that the issue has in the public eye, the FCC will probably take quite a while to decide whether the technology becomes an everyday reality.


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