Spectrum Management | Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

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Wi-Fi operates under a spectrum management system that is 90 years old, albeit with the help of some late 20th century contributions by the regulators. There have been, historically, four core assumptions underlying all governmental spectrum management policies, none of which hold relevance in today's society:

Unregulated radio interference will lead to chaos.
Spectrum is a scarce resource.
Government command and control of the scarce spectrum resource is the only way chaos can be avoided.
The public interest centers on government choosing the "highest and best use" for the spectrum.

These archaic assumptions have guided regulatory decision-making for far too long. Let's look at some of the erroneous decisions, as they pertain to these four assumptions. We'll use the FCC Commissioner, Michael Powell's October 12, 2002 speech entitled, "Broadband Migration III: New Directions in Wireless Policy," given at the Silicon Flatirons Telecommunications Program at the University of Colorado at Boulder, as our guide as we investigate the details of these four assumptions. In that speech, Commissioner Powell gave voice to his belief that today's environment has strained the previously outlined assumptions to the breaking point. Powell also said, "Modern technology has fundamentally changed the nature and extent of spectrum use. So the real question is, how do we fundamentally alter our spectrum policy to adapt to this reality? The good news is that while the proliferation of technology strains the old paradigm, it is also technology that will ultimately free spectrum from its former shackles."

Interference. There are many different ways to deal with radio interference outside of the strict spectrum allocation model. Technologies such as Dynamic Frequency Selection (DFS), Transmitter Power Control (TPC), and spread spectrum can permit far more intensive use of a frequency band since they can keep the level of interference down. Imposing limits on certain technical parameters such as output power can also minimize interference.

Powell states, "Due to the complexity of interference issues and the RF environment, interference protection solutions may be largely technology driven." He further said, "Interference is not solely 'caused' by transmitters, which many seem to assume-and on which our regulations are almost exclusively based. Instead, interference is often more a product of receivers; that is receivers are too dumb or too sensitive or too cheap to filter out unwanted signals. Yet, our decades old rules have generally ignored receivers."

He recommends, "The time has come to consider an entirely new paradigm for interference protection. A more forward looking approach requires that there be a clear quantitative application of what is acceptable interference for both license holders and the devices that can cause interference. Transmitters would be required to ensure that the interference level-or 'interference temperature'-is not exceeded. Receivers would be required to tolerate an interference level."

Scarcity. Spectrum appears scarce only because current regulations put draconian limitations on its use. As a former FCC chief economist once quipped, "The only way you can waste spectrum is not to use it. And the FCC has wasted enormous amounts of spectrum. It is a classic vicious cycle: spectrum is scarce, so FCC regulation is necessary, and FCC regulation ensures that spectrum stays scarce."

According to Powell, "Much of the Commission's spectrum policy was driven by the assumption of acute spectral scarcity-the assumption that there is never enough for those who want it. Under this view, spectrum is so scarce that government rather than market forces must determine who gets to use the spectrum and for what. The spectrum scarcity argument shaped the Supreme Court's Red Lion decision [Red Lion v. FCC, 395 U.S. 367 (1969)], which gave the Commission broad discretion to regulate broadcast media on the premise that spectrum is a unique and scarce resource."

He went on to say that "the presumptions of Red Lion and similar broadcasting regulation based on scarcity have been called into doubt by the proliferation of media sources," and that "we question the continued utility of the pervasive scarcity assumption for spectrum based services." He added that recent studies by the FCC's Enforcement Bureau have shown that "most of spectrum is not in use most of the time."

The Commissioner even acknowledges that "innovative technologies like software defined radio and adaptive transmitters can bring additional spectrum into the pool of spectrum available for use." Although he does say that "scarcity will not be replaced by abundance; there will still be places and times when services are spectrum constrained. However, scarcity need no longer be the lodestar by which we guide the spectrum ship of state."

Powell's recommendation: There is a substantial amount of "white space" that's out there, which is not being used by anybody. In particular, certain timeslots can lay dormant for as much as second at a time, and sometimes much more in the case of point-to-point communications, such as a large trucking company's mobile communication network. "One way the Commission can take advantage of this white space is by facilitating access in the time dimension."

Methods such as overlay techniques (where more than one service shares a licensed band) and interference minimizing technology can serve to move spectrum management from "command and control" to a more democratic policy, including open spectrum, i.e. establishing a spectrum "commons" or "park" to accommodate unlicensed services. Even a policy of re-allocation of occupied bands (where sharing isn't possible) could be put in place. Such relocation has occurred in the past. A perfect example is that of the FCC enabling the Personal Communications Service (PCS) to be built on spectrum formerly occupied by "fixed microwave" licensees, who used their spectrum for statewide industrial functions. PCS auction winners paid those licensees to move to alternative bands that were, fortunately, available. Is it any wonder this almost century old system is no longer adequate to serve the world we live in today?

Government Command and Control. The "highest and best use" approach has always been problematic. Creating broad service classifications and applying block allocations can serve to ease administrative duties. Block allocation also simplifies control. Spectrum can be dedicated to desirable ends, such as fostering a centralized vision of new technology (e.g., interactive television initially flopped in a massive display of the limits of central planning). Also, consider the nationwide block allocation of UHF television channels 14 through 69-even in the largest metropolitan areas, less than a handful of UHF stations actually broadcast, resulting in a vast amount of prime spectrum nationwide lying idle. The same situation can be found elsewhere in various service classifications. But block allocation can also create overcrowding: administrative miscalculation of enormous and intensive demand for spectrum in an allocated band can result not only in overcrowding, but also interference and delays. A good example is the vast range of frequencies from 500 kHz to 30 GHz, which are most desirable because of the physical characteristics of the waveforms that invite innovative modulation techniques to enable them to be used in a number of unique ways. But perhaps the reason the block system is still in place, despite all of its inequities, is because it protects incumbents and is a barrier to entry for competitors.

Commissioner Powell suggests that "government spectrum policy continues to be constrained by allocation and licensing systems from a bygone era." He also says, however, that "In the last twenty years, two alternative models to command and control have developed, and both have flexibility at their core. First, the 'exclusive use' or quasi property rights model, which provides exclusive, licensed rights to flexible use frequencies, subject only to limitations on harmful interference. These rights are freely transferable. Second, the 'commons' or 'open access' model, which allows users to share frequencies on an unlicensed basis, with usage rights that are governed by technical standards but with no right to protection from interference." Powell feels that "the Commission has employed both models with significant success" and concludes that "we will undoubtedly use both models as we move forward."

He even recommends that going forward, "license holders should be granted the maximum flexibility to use-or allow others to use-the spectrum, within technical constraints, to provide any services demanded by the public. With this flexibility, service providers can be expected to move spectrum quickly to its highest and best use." Powell however, does add the caveat, "Such flexibility should not come at the cost of clearly defined rules."

Public Interest Standard. Powell also addresses the meaning of the phrase "public interest, convenience or necessity." He states, "The public interest must reflect the realities of the marketplace and current spectrum use. Today, I would suggest that full and complete consumer choice of wireless devices and services is the very meaning of the public interest. Certainly government telling consumers what types of services and devices they should have or own is not my view of the public's interest." He also says that public interest goals include "national defense, public safety, and critical infrastructure."

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