Friday, February 15, 2008

De-situating Spectrum: Non-spatial metaphors for wireless communication

Today’s spectrum policy debate is conducted in terms of a pervasive metaphor: that spectrum is spatial, signals are phenomena in space, and radios are agents (see my DYSPAN 2007 paper “Imagining Radio: Mental Models of Wireless Communication”, PDF).

Metaphors are not right or wrong, but a dominant metaphor can forestall new insights. Any metaphor highlights some aspects of the situation it is explaining, and suppresses others. We are so used to thinking about spectrum in spatial terms that the metaphor’s disadvantages have become invisible, and alternatives to it are barely thinkable. Spectrum allocation is imagined in terms of property rights in real estate, and cognitive radios are conceived of as smart agents acting within delimited, space-like frequency domains. Alternative metaphors can stimulate new approaches for policy making and research by de-familiarizing wireless communications.

It is useful for a new metaphor to have some overlaps with existing ways of thinking. An entirely different conceptual structure that shares no referents or mappings with the dominant view – like the “wireless communications are like the Internet” metaphor proposed by Open Spectrum advocates – will be so alien that it has trouble getting traction. This paper therefore explores conceptual models for wireless communication that have similar concept-to-concept mappings as the spectrum-as-space analogy, but that do not rely on a spatial metaphor.

One possible alternative metaphor is to imagine spectrum to be like all the crafts practiced in a medieval city. A spectrum license is like the letters patent that give a particular guild a monopoly in their respective crafts. The spectrum licensee is the guild. License-exempt spectrum is that set of trade activities that do not require letters patent. A spectrum part corresponds to a specific craft. Signals are like the practice of the craft. Radios are like craftspeople and their customers. The regulator corresponds to the King or city burgesses who issue charters.

One can model different types of allocation as different terms on the business practice monopoly that is issued to a craft guild. Command-and-control spectrum allocation would be analogous to the state not only issuing a charter to (say) the weavers’ guild to make textiles, but also specifying the kinds of fabric they may make, and the prices they can charge. They need the Crown’s permission to change any of the parameters, and weavers have to stay weavers. The analogy of transferable, flexible-use allocation would be that weavers still need letters patent to practice their craft, but can make any kind of fabric they like, charge any price, and can sell on their practice to anyone they wish.

In short, this is a “spectrum-as-business-practices” model. Other non-spatial metaphors include spectrum-as-intellectual-property-rights, and spectrum-as-markets (as distinct from markets in spectrum).

A new metaphor highlights hidden assumptions in the dominant conceptual model by emphasizing and downplaying issues differently. For example, the spectrum-as-business-practices analogy blurs the distinction between the craft of a weaver and the act of making and selling textiles; that is, the distinction between spectrum and signal is played down. By comparison, the dominant spectrum-as-space metaphor emphasizes that spectrum exists independently from signals, which are “added” to the space. It implies that one can clearly separate the underlying asset (spectrum) from what you do with it (the signals), just as land is distinct from the buildings on it. The business practices metaphor therefore calls into question the meaning of the term “spectrum resource”, and the entire project of maximizing the utility of a nation’s spectrum resources, since spectrum is not an asset independent of use.

The spectrum-as-business-practices metaphor also stresses that the primary regulatory consideration is permission to perform a set of behaviors within certain constraints; the use of a resource, which is primary in the spectrum-as-land conception, is downplayed. A business license is a set of rules of permitted behavior, rather than use-neutral title to an asset conceived as a space-like frequency interval. It therefore invites a formulation of wireless communication policy purely in terms of signals and radios, with no privileging of frequency above other operational parameters.

Through these and other comparisons, non-spatial metaphors for wireless communications mark out an alternative conceptual model for spectrum policy and cognitive radio research that can lead to new solutions.

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