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What is spectrum?

May 9, 2012

IEEE DySPAN papers are due next week. They were originally due six months ago. I nearly had a paper written for that deadline and of course the minute the deadline was delayed I stopped writing and now six months later I find myself back under pressure with an unfinished paper. I am pathetic! I should be writing the paper now of course – let’s say I am thinking out loud about some of the issues.

So what is spectrum really?

Possibly a bit late to be asking that question in my line of work.

I would not say that my thoughts are super original but I am hoping at least to bring some kind of structure to them. Basic microeconomic theory ranks all publicly and commercially available resources in a given society along two criteria: (i) excludability (or exclusiveness), which defines property rights and access; and (ii) rivalry, which examines simultaneous use and depletion. A good or service is said to be excludable when it is possible to prevent people who have not paid for it from having access to it, and non-excludable when it is not possible to do so. A rival good is a good whose consumption by one consumer prevents simultaneous consumption by other consumers. On the other hand a non-rival good can be consumed simultaneously by many without the experience of anyone user being detrimentally affected. Some examples are  shown in the table below.

Broadcast TV is an interesting resource. Satellite TV is a good that is considered to be non-rival and excludable. It is possible to broadcast the signals in a way that can only be received by those people who pay and therefore acquire the systems and codes to unlock the signal. Free-to-air TV is however available to all and therefore in principle considered non-rival and non-excludable. Hence TV broadcasting, depending on the specifics of the technology used and the details of the implementation, can fall under more than one heading. The is even more so the case for spectrum.

Spectrum actually falls along the continuum of excludable/nonexcludable and rival/non-rival. The figure below is my current attempt at capturing this as the above table is too simplistic to capture the concepts.

Spectrum is a rival/excludable good from a static ownership and usage perspective. The large red dot marks this point on the graph. The emergence of certain technologies that allow chunks of spectrum to be dynamically accessed in a coordinated and managed way can turn spectrum from a private good into a club good – in other words can push spectrum from being a rival/excludable good to a nonrival/excludable good. It could also be argued of course that the kinds of practices that we see make it ‘less’ excludable. This is akin to arguing that the ‘club’ becomes a very large ‘club’. From a technical perspective advanced management techniques will allow more into the club for example. Hence in  the diagram above DSA techniques, spectrum pooling, managed access etc are indicated as moving mainly along the y-axis from the starting point of static ownership but do also move the spectrum resource along the x-axis.

The kinds of practices associated with WiFi usage (i.e. Part 15 rules and the right to transmit) or the practices around unlicensed TV white space access also have an effect. The ‘Tragedy of the Commons’ implies that there is a point at which one user’s consumption of the good does in fact affect the others so the good is rival in that sense. However it can be argued that the point at which this happens, depending on the rules and technologies in play, can mean the good appears to be effectively non-rival. Therefore in the above diagram, the effect of practices as we currently understand in the WiFi world and other such TV whitespace practices move spectrum mainly along the x-axis into the non-excludable space but also move the good up the y-axis. There may be no such thing as an absolutely non-rivalrous and non-excludable good but the graph does allow for the possibility of this emerging or in fact for the limits of existing techniques to be pushed so far that the difference is not worth noting.

The answer to my question is therefore spectrum is any kind of good you want it to be.

I believe that this fact needs to be taken into account more when regulating.  I think it might be a very good idea to regulate for rival/excludable, non-rival/excludable, rival/non-excludable, non-rival/non-excludable spectrum rather than thinking in terms of licensed an un-licensed, exclusive, share etc.

I am trying to build a set of guidelines for how to do this. This way of considering the resource allows for every possible option from exclusive use, to sharing, to using underlays and overlays etc.  If we can view technology as something that can push spectrum around the rival/non-rival – excludable/non-excludable continuum but not care exactly how perhaps it can free up some of the regulatory approaches. Perhaps we can separate the technical mechanisms for doing this from the core regulatory principles. And also perhaps we can let things come to their own equilibrium within the continuum of goods classification rather than select in advance the mix? Many more questions?

One Comment
  1. Linda, there is a table on page 27 of our report to the European Commission on the “value of shared spectrum access” which attempts to create a similarly general framework for thinking about spectrum. After discussing rivalry/sharing and cooperation/competition, we opt for a 2×2 matrix which uses the categories of

    coexistent vs cooperative


    sharing-among-equals vs sharing-among-unequals.

    This was inspired by Jon Peha’s analysis in “Sharing Spectrum through Spectrum Policy Reform and Cognitive Radio” –

    Unfortunately, it gets more complicated when simultaneous users of a frequency band have different economic aims, legal status or understandings of the resource. Radio is flexible enough for that to happen, as you note.

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