Open Spectrum, Anyone?

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We can glimpse the possibilities of open spectrum when we view the success of existing unlicensed bands, such as the ISM (a set of radio frequencies centered around 2.4 GHz) and the U-NII bands (three 100 MHz unlicensed spectral bands between 5.15 GHz and 5.8 GHz), which are open for anyone to transmit within certain technical parameters such as power limits.

As the reader should now understand, technologies developed in recent years make it relatively easy to allow more than one user to occupy the same range of frequencies at the same time. Those innovative techniques serve to obviate the need for exclusive licensing. Instead, they could support a true open spectrum environment, which hopefully would allow the same degree of openness, flexibility and scalability for communication that the Internet promotes for applications and content. Thus, like the Internet, open spectrum is an idea with tremendous commercial potential. Open spectrum would also help to ensure that Wi-Fi technologies continue to thrive.

There are two ways to implement an open spectrum environment. The first is to designate specific bands for unlicensed devices, with general rules to foster co-existence among users. This is the method that allows Wi-Fi to flourish in the 2.4 GHz and 5 GHz bands. The second mechanism is to "overlay" unlicensed technologies in existing bands, with the proviso that the "sitting tenant's" services will not be disturbed. This approach effectively manufactures new capacity by increasing spectrum efficiency. Overlays can be achieved either by using an extremely weak signal or by employing agile radios that are able to identify and move around competing transmissions.

Both unlicensed spectrum and overlays have their place. Eventually overlay approaches will be more significant because they can work across the entire spectrum rather than requiring the creation of designated "commons" or "parks." But for this to come about requires the removal of limitations in existing rules, creation of additional unlicensed bands, establishment of rules to facilitate additional forms of overlay, and funding for research into next-generation technologies to support this paradigm.

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A spectrum "commons" or "park" refers to an area of spectrum where users multilaterally coordinate their communications using communication protocols embedded in end-user equipment, without the need for a licensing process.

However, the notion of using smart technology (and smart devices) instead of intelligent networks runs counter to the received wisdom within the communications industry. Moreover, companies that spent huge amounts of money acquiring spectrum licenses and then built out expensive networks based on that spectrum will naturally oppose any change to the status quo.

Another roadblock to open spectrum is that current spectrum rules don't provide enough unlicensed spectrum or the right equipment parameters for a true spectrum commons. For instance, current regulations prevent spread spectrum devices from overlaying on licensed bands at low power.

Note 

The FCC proposed the use of overlays during the 1980s and voiced its support for the idea that spread spectrum radios could transmit effectively at such low power that they would be unnoticeable to high-power licensed services. Unfortunately, that proposal drew so much opposition and concern about interference from major industry players that the agency decided not to go forward with it. A more recent FCC proceeding on ultrawideband technology (a variant of spread spectrum that operates on very wide channels with extremely low power) generated similarly intense responses. It's not only carriers who are concerned about changes to the status quo. Public-safety organizations, the military, the airline industry and global positioning system (GPS) vendors are also opponents.

The limited amount of available open spectrum is keeping the Wi-Fi industry from realizing its full potential-from growing as explosively as, say, the computer industry, which saw tremendous growth once open source software became the norm. Of course, the other technological revolution that continues to grow in an open environment is the Internet-the open access communications scheme of the Internet has spurred innovation that few (if any) developments in history can match.

It is hoped that regulatory agencies will see the light and provision more open spectrum so that Wi-Fi and other innovative wireless technologies may follow a similar path. Admittedly, this will not happen overnight. So far, few regulatory bodies have shown a willingness to take such a monumental step and most, for the near future, will continue to issue limited, exclusive licenses affordable only by large corporations.

On a more positive note, in late 2002, the FCC's Spectrum Policy Task Force recommended modernization of the spectrum management rules. This would allow the system to evolve from the traditional government "command-and-control" model to a more flexible, consumer-oriented approach, according to the FCC's November 7, 2002 statement that accompanied the task force's report. (For more information on the task force and to obtain copies of the reports, go to www.fcc.gov/sptf.)

And, in Europe, the CEPT states that it endorses the principle of adopting a harmonized European Table of Frequency Allocations and Utilizations. The European Common Frequency Allocation Table, which covers major usage of the frequency bands, including Wi-Fi-enabled services, is slated to be adopted by CEPT administrations by 2008. (The Table can be found at the ERO website-www.ero.dk.)

Regulatory agencies worldwide have begun to reevaluate the current scheme of spectrum allocation. Yet any changes must be made with a clear understanding of the implications that new technology brings to the table. By grasping the benefits that these new technologies provide, it will be easier for these regulatory bodies to take affirmative steps to free up more spectrum by way of the commons and overlay models.

At the moment, however, it appears that rendering the allocation system obsolete is unlikely to occur in the near to medium term (e.g. CEPT's 2008 timeline). Interference concerns and existing treaty obligations will continue to require specifying ranges of radio frequencies for the foreseeable future.

But, in the long term, an enlightened model of spectrum management could serve to reduce spectrum scarcity-due to the efficiency-enhancing technologies available today. This is similar to how Digital Subscriber Line (DSL) technologies have served to reduce copper exhaust (i.e. scarcity of copper lines) in many urban areas.

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