Ofcom's DECT guard band award as a club good auction

Toby Youell (@tobyyouell, linkedin) pointed out to me that Ofcom’s 2006 sale of DECT guard band licenses was an auction of spectrum club goods (cf. my blog post). It’s a great insight, and a helpful comparison.

Obviating mandatory receiver standards

Two remarks I heard at a meeting of a DC spectrum advisory committee helped me understand that endless debates about radio receiver standards are the result of old fashioned wireless rights definitions. The new generation of rights definitions could render the entire receiver standards topic moot.

First, a mobile phone executive explained to me that his company was forced to develop and install filters in the receiver cabinets used by broadcasters for electronic newsgathering because it had a “statutory obligation to protect” these services, even though they operated in different frequency ranges.

Second, during the meeting the hoary topic of receiver standards was raised again; it’s long-rehearsed problem that shows no sign of being solved. It’s a perennial topic because wireless interference depends as much on the quality of the receiver as the characteristics of the transmitted signal. A transmission that would be ignored by a well-designed receiver could cause severe degradation in a poor (read: cheap) receiver. Transmitters are thus at the mercy of the worst receiver they need to protect.

A statutory obligation to protect effectively gives the protectee a blank check; for example, the protectee can change to a lousy receiver, and force the transmitting licensee to pay for changes (in either their transmitters or the protectee’s receivers) to prevent interference. This is an open-ended transfer of costs from the protectee to the protector.

The protectors thus dream of limiting their downside by having the regulator impose receiver standards on the protectee. If the receiver’s performance can be no worse than some lower limit, there is a limit on the degree of protection the transmitter has to provide.

The problem with mandatory receiver standards is that it gets the regulator into the game of specifying equipment. This is a bad idea, since any choice of parameters (let alone parameter values) enshrines a set of assumptions about receiver design, locks in specific solutions, and obviates innovation that might solve the problem in new ways. Manufacturers have always successfully blocked the introduction of mandatory standards on the basis that they constrain innovation and commercial choice.

An open-ended statutory obligation to protect therefore necessarily leads to futile calls for receiver standards.

One could moot receiver standards by changing how wireless rights are defined. Rather than bearing an open-ended obligation to protect, the transmitter should have an obligation to operate within specific limits on energy delivered into frequencies other than their own. These transmission limits could be chosen to ensure that adjacent receivers are no worse off than they were under an “open-ended obligation to protect” regime. (The “victim” licensee will, though, lose the option value of being able to change their system specification at will.)

The main benefit is certainty: the recipient of a license will know at the time of issue what kind of protection they’ll have to provide. The cellular company mentioned above didn’t find out until after the auction how much work they would have to do to protect broadcasters since nobody (including the FCC) understood how lousy the broadcasters’ receivers were.

The regulatory mechanisms for doing this are well known, and have been implemented; they include the “space-centric” licensing approach used in Australia (PDF), and Spectrum Usage Rights (SURs) in the UK.

Moving to new rights regimes is a challenging; Ofcom’s progress has been slow. One of the main difficulties is that licensees for new allocations prefer to do things the old, known, way. One of the supposed drawbacks of SURs is that the benefits of certainty seem to accrue a licensee’s neighbor, rather than the new licensee themselves. However, removing the unlimited downside in an open-ended obligation to protect adjacent operations should prove attractive. The whining will now come from the neighbors who will lose their blank check; careful definition of the licensee’s cross-channel interference limits to maintain the status quo should take the sting out of the transition.

Spectrum Databases (Not)

The idea of using a database to regulate radio operation – or, to “control access to spectrum”, to use the S-word nomenclature – has been gaining ground.

For example, both Michael Calabrese (The End of Spectrum ‘Scarcity’, New America Foundation Wireless Future Program Working Paper No. 25, June 2009) and Kevin Werbach (Castle in the Air: A Domain Name System for Spectrum, TPRC September 2009) have argued that the database(s) contemplated to manage device operation in the TV white spaces could be the foundation for a method to increase the amount of radio operation.

Thinking through how such a database might be used shows the advantage of approaching radio regulation as coordinating operations, rather than using conventional approach of “dividing up spectrum”.

The regulatory challenge is therefore not "spectrum databases" but "radio operation databases".

In a first approximation – and perhaps even as the ultimate solution, if one uses the “spectrum” approach – a database would be a listing of “vacant” channels; a device would query the database for “available” channels, and operate in one. When one starts from the basis that spectrum is an asset like land to be divided up and distributed, vacancy is a self-evident concept; it derives from the attributes of the underlying asset, and not by reference to the intended use.

However, context is everything in radio operation. Whether harmful interference will result from the operation of an added radio system depends not only on its transmissions, but also the transmit and receive characteristics of the incumbent system.

Consider, for example, three channels: A, B, and C. Let’s say incumbent system #1 operates using channel A. Channels B and C are nominally vacant. Can an incoming system #2 operate in those channels? If both system #1 and #2 use traditional cellular technology (i.e. FDM, e.g. 3G), the answer is yes. But if #1 uses 3G and #2 uses TDM technology like WiMAX, then the answer is No: there needs to be a guard band between them, and system #2 can only use Channel C. Channel B needs to be left “vacant”. (This is a live issue: see e.g. Ars Technica on the argument between T-Mobile and M2Z over the rules for the AWS-3 band band.)

A mental model informed by spectrum-as-land is therefore not an ideal guide to understanding what needs to be in the database. (More generally, one needs to refine the metaphor to better guide regulation, as Weiser and Hatfield did last year by introducing the concept of "zoning the spectrum" in Spectrum Policy Reform and the Next Frontier of Property Rights, 15 Geo. Mason L. Rev. 549.)

An approach grounded in coordinating operations, on the other hand, leads to the understanding that what needs to be in the database is not just a frequency range and geographic region, but all the relevant parameters of an incumbent operation. The short list would add receiver performance (ability to reject interference) and duty cycle (near-constant transmission like cellular systems, vs. very intermittent but intense uses like firefighting) to the usual suspects of transmitter location, emitted power, and transmit mask.

The task is not to find a “vacant channel”, but to determine if an incoming operator will cause harmful interference. This requires, in addition to the operating parameters of the incumbent and incoming systems, information about the spatial distribution of incumbent and incoming radios, and a propagation model to connect the two.

Ofcom is the regulator that has thought most deeply about ways to better characterize the interference characteristics of radio systems; see e.g. Ofcom’s Guide to Spectrum Usage Rights (SURs) and William Webb’s recent paper Licensing Spectrum: A discussion of the different approaches to setting spectrum licensing terms.

A well-founded framework for generalizing the white space database – where interference management between incumbents and new entrants hard-coded into the FCC rules for white space device operation – could benefit from new radio operating metaphors (grind axe: see my De-situating spectrum: Rethinking radio policy using non-spatial metaphors, DySPAN 2008) and the application of a SUR-like approach.

One will also have to think carefully about the minimal set of parameters needed to facilitate interference avoidance, since it's easy but economically inefficient to come up with a very long list of attributes that describe radio operations. The Silicon Flatirons Center recently examined this issue in a summit on defining out-of-band operating rules.