FCC white paper shows that “spectrum efficiency” is meaningless

The FCC Technical Advisory Council’s (TAC) draft white paper on spectrum efficiency metrics (25 September 2011) is an excellent piece of work. It is authoritative, instructive, and demonstrates decisively that spectrum [1] efficiency metrics are a meaningless concept.

While they don’t say this in so many words, members of the Sharing Working Group perhaps intended this conclusion to be drawn; “spectrum efficiency” is a DC catchphrase that is hard to avoid, and it would probably be unwise to refute it overtly…

The following elements of the paper imply that the “spectrum efficiency” concept is useless:

1. There is no metric that can be applied across the myriad of different wireless services.
2. The metrics are incomplete, even within a service.
3. While the paper suggests metrics for specific services, the taxonomy of services is arbitrary.

Consequently

• There is no way to compare the “efficiency” of one radio service (aka one “spectrum use”) to another, denying politicians the pseudo-scientific rationale they dream of for converting a frequency band allocation from one use to another.

• Even within a given service type, there is no defensible way to rate one deployment’s performance over another; even if one scored much lower using the relevant efficiency metric, its defenders could invoke any of the long list of “additional efficiency considerations” to deny that the comparison was valid.

The paper also misses an opportunity: It hints at the importance of cost effectiveness rather than mere efficiency, but doesn’t address this broader context.

Follow-up posts:

• From spectrum efficiency metrics to parameter spaces (December 2011)
•  Three meanings of “spectrum efficiency” (October 2012)

The extent of FCC/NTIA frequency sharing

Take a guess: What percentage of US frequencies are controlled by the Federal government (represented by the NTIA), and what percentage is shared with non-Federal [1] users, who are under FCC jurisdiction? And what’s the remainder, devoted solely to non-Federal users?

My intuition, for what it's worth, was completely wrong. I thought the Fed/non-Fed split was roughly 50/50, with a bit (say 10%) being shared. As I pointed out in my recent post about partitioning Fed and non-Fed allocations, the amount of sharing should be easy enough to establish. It turns out that Peter Tenhula of Shared Spectrum Company has done a lot of work on this [2], and he pointed me to the FCC’s spectrum dashboard where one can download an XML snapshot of the allocation database (currently the API only covers the range 225-3700 MHz).

The answer? It depends on the frequency range and how one counts [3], but very roughly 10% is Federal, 40% shared, and 50% non-Federal (i.e. FCC) only.

Here's a picture (click it to enlarge); an Excel file with my analysis is here.

Update, 21 October 2011: Perhaps the flaw didn't lie with my intuition, but with my interpretation of the data. A senior FCC person has pointed out to me that many supposedly "shared" allocations are, to all intents and purposes, controlled by Federal agencies, and non-Federal (i.e. FCC-managed) services are present only on sufferance, if at all (e.g. 220-2290 MHz); or "sharing" only occurs both Federal and non-Federal entities used the same service (e.g. air traffic or maritime radar). So the question still stands, pending further digging: how much sharing (for various values of "sharing") is really going on?

Partition, not sharing: An alternative approach to the Fed/non-Fed spectrum divide

South Sudan. Serbia/Kosovo. India/Pakistan. Britney Spears and Kevin Federline. Sometimes a clean break is best for everyone, particularly when there are fundamental differences in mindset. Enforced coexistence is not, for many couples, the best way to live.

Sharing between Federal and non-Federal wireless users (aka Fed and non-Fed) is a favored way to realize the FCC’s dream of finding 500 MHz for commercial mobile broadband services; as reported in TheHill.com, “It is unclear where the 500 megahertz of spectrum will come from, but a large portion will likely come from government agencies that do not use the frequencies efficiently.”

Fed/non-Fed sharing can be made to work, and worthy efforts are being made. However, I doubt it’s worth the effort, given the insane difficulty of negotiating band re-allocations, let alone sharing agreements; questions over whether 500 MHz is, in fact, either needed or would make a dent on cellular companies’ problems; and fundamental concerns about jurisdiction (see my August 2011 post No Common Authority: Why spectrum sharing across the Fed/non-Fed boundary is a bad idea).

It would be a better use of time and effort to go in the opposite direction: make the partition between Federal and non-Federal as clean as possible, and let each group of figure out sharing among its own constituents.

Licensed Unlicensed: Having your Coase, and your Commons too

I lighted on the notion of issuing a handful of receiver licenses in allocations where transmitter licensees don’t control receivers (e.g. TV, GPS) to facilitate negotiations between operators in neighboring bands; details blogged here.

The same idea could be applied to unlicensed allocations, where the unbounded number of operators makes it essentially impossible for Coasian adjustments to be made: a neighbor that would like quieter unlicensed devices has nobody to make a deal with, nor do unlicensed users have an effective way to band together to make a deal if they’d like to increase their own transmit power. This approach also has the benefit, as in the receiver license case, of giving the regulator a tool for changing operating expectations over time, e.g. ratcheting down receiver protections or increasing receiver standards.

The catch-phrase “licensed unlicensed” is obviously a contradiction in terms; it’s shorthand for a regime where non-exclusive operating permissions are issued to a limited number of entities, while retaining the key characteristic that has made unlicensed successful: the ability of end users to choose for themselves what equipment to buy and deploy. These entities can use or sub-license these authorizations to build and/or sell devices to end-users.

Follow-up post

• Stamps and stampholders: a third way to regulate radio operation

TV white space databases: A bad idea for developing countries

Now that TV white space rulemakings are in the can in the US and UK, proponents will be pitching the technology to any government that’ll listen, e.g. at the Internet Governance Forum meeting to be held in Nairobi on 27-30 September.

It’s understandable: the more widespread white space database rules, the larger device volumes will be, and thus the lower the equipment cost, leading to wider adoption – a positive feedback loop. However, white space database technology is unnecessary in many countries, particularly developing ones.

Yet it verges on dodgy ethics for companies to hype this technology to countries that don’t need it, particularly since there’s a better solution: dedicating part of the TV frequencies that are freed as a result of the transition to digital TV (the “Digital Dividend”) to unlicensed operation, without the white space bells and whistles.

Spectrum “sharing”: the convenient ambiguity of an English verb

I realized while writing Spectrum Sharing: Not really sharing, and not just spectrum that my confusion over the meaning of spectrum sharing derives from two meanings of the English verb "to share":

(1) to divide and distribute in shares, to apportion;

(2) to use, experience or occupy with others, to have in common.

For example, the first is sharing a bag of peanuts, and the second is sharing a kitchen or an MP3 file. Cellular operators and economists tend to use the word with the first meaning, and Open Spectrum advocates with the second.

But that raises the question: is the double meaning inherent in the concept, or is it just an accident of English vocabulary?

I asked some friends about the regulatory terminology in other languages; so far I have information about Arabic, Chinese and German. If you could shed light on regulatory terminology in other languages, for example French, Japanese or Spanish, please get in touch.

Time limiting unlicensed authorizations

I’m coming around to Tom Hazlett’s view that unlicensed devices in the TV whitespaces are a bad idea because they preclude alternative future uses for the channels now being used for TV. (For his main objections, see “Shooting Blanks on Wireless Policy,” FT.com October 5, 2010 PDF) It’s a figure-ground problem; defining whitespace operating rules on the basis of TV operations reciprocally defines viable operations in the TV “blackspace”.

One could get around the problem and still have unlicensed use, though, by time limiting the unlicensed authorization. [1] Just like build-out conditions on licenses, there would be a fixed time window within which widespread deployment should occur. If it doesn’t, the authorization is revoked.

This approach seems particularly relevant when an authorization holds great promise, but that promise is very uncertain, e.g. when the technology or the market is changing rapidly. “Sunsets” on rules are important since the passage of time invariably invalidates the premises of regulation, even as it entrenches the interests that coalesce around those regulations. [2]

Licensing radio receivers as a way to facilitate negotiation about interference

It’s a curious fact that, while receivers are just as much responsible for breakdowns in radio operations as transmitters [a], regulation is aimed pretty much exclusively at transmitters [b].

Since one can’t ignore the receivers in practice, arguments over interference almost invariably turn to receiver standards. Even if receiver standards were a good idea (and I don’t think they are - see my post Receiver protection limits: a better way to manage interference than receiver standards), the ability to adjust receiver performance by fiat or negotiation is limited when receivers are operated independently of transmitters.

I suspect that receiver licenses may be necessary to reach the optimum outcome in at least some cases. This post is going to take that idea out for a first test drive.

Regulators evidently have managed without receiver licenses (beyond their use as a way to fund traditional broadcasting) so far. Why introduce them now? I’ll give my usual answer: the dramatically increased demand for wireless is squeezing radio operators of widely varying kinds together to an unprecedented extent, and we no longer have the luxury of the wide gaps that allowed regulators to ignore receiver performance, and ways of managing it.

Follow-up post

• Stamps and stampholders: a third way to regulate radio operation

The dark side of whitespace databases

Back in May 2009 I drafted a blog about the unintended side-effects of regulating unlicensed radios using databases. I was in the thick of TV whitespace proceeding (on the side of the proponents), and decided not to post it since it might have muddied the waters for my client.

Databases have become the Great White Hope of “dynamic spectrum access” over the last two-plus years. They are seen not only as a way to compensate for the weaknesses of “spectrum sensing” solutions, but as a way for regulators to change the rules quickly, and for unlicensed devices to work together more efficiently. For a quick background, see: FCC names nine white-space database providers, FierceWireless, Jan 2011; Michael Calabrese, “Ending Spectrum Scarcity: Building on the TV Bands Database to Access Unused Public Airwaves,” New America Foundation, Wireless Future Working Paper #25 (June 2009).

Looking back at my note, I think it's still valid. Rather than rewrite it, I’ve decided simply to repost it here as originally drafted (omitting a couple of introductory paragraphs).

No Common Authority: Why spectrum sharing across the Fed/non-Fed boundary is a bad idea

The ISART conference this year was about sharing in the radar bands, in line with the Administration’s efforts to encourage frequency sharing between Federal and non-Federal (e.g. commercial and civilian) users (NTIA Fast Track Evaluation PDF, FCC proceeding ET docket 10-123).

While it’s true that the NTIA has studied the feasibility of reallocating Federal Government spectrum, or relocating Federal Government systems, the current political focus is on “spectrum sharing” (cf. my post Spectrum Sharing: Not really sharing, and not just spectrum) – and Federal/non-Federal sharing is the hardest possible problem.

Federal/non-Federal sharing is hard for many reasons, notably the chasm between the goals and incentives between the two groups, and thus a profound lack of trust. I’m going to focus here, though, on a seemingly technical but profound problem: the lack of a common authority that can resolve conflicts.

Follow-up post

• Partition, not sharing: An alternative approach to the Fed/non-Fed spectrum divide

Spectrum Sharing: Not really sharing, and not just spectrum

There was endless talk about spectrum sharing at ISART in Boulder last week. I’ve become increasingly confused about what those words mean, since wireless has been about more than one radio system is operating at the same time and place pretty much since the beginning.
For example, whitespace devices are said to share the UHF band with television, but the operating rules have been drawn up to ensure that whitespace devices never interfere with TV, i.e. never operate in the same place, channel and time. What’s “sharing” about that? The purpose of radio allocation from the start has been to avoid harmful interference between different radio operations, which has always been done by ensuring that two systems don’t operate in the same place, channel and time – such as two TV stations not interfering with each other.

It seems that the “new sharing” has three characteristics: (1) more boundaries (in geography, frequency and particularly time) than ever before; (2) the juxtaposition of different kinds of services that differ more from each other than they used to; and (3) sharing without central control. It’s a difference in degree, not in kind.

It’s not about sharing, since the goal is to avoid interference, i.e. to avoid sharing. It’s not about spectrum, i.e. radio frequencies, since non-interference is achieved not only by partitioning frequencies but also by dividing space, time, transmit power and the right to operate.

The LightSquared Mess Shouldn’t Count Against Coase

It seems there’s a new meme floating around DC: I’ve been asked from both sides of the spectrum rights polemic whether the Lightsquared/GPS situation proves that Coasian make-spectrum-property advocates are crazy because the rights seem to be pretty well defined in this case, and yet the argument drags on at the FCC rather than being resolved through market deals. I suspect the source is Harold Feld’s blog My Insanely Long Field Guide to Lightsquared v. The GPS Guys where he says:

For a spectrum wonk such as myself, it simply does not get better than this. I also get one more real world example where I say to all the “property is the answer to everything” guys: “Ha! You think property is so hot? The rights are clearly defined here. Where’s your precious Coasian solution now, smart guys?”

The “Coasian” position does have its problems (see below), but this isn’t an example of one of them. I think Harold’s premise is incorrect: the rights are NOT well-defined. While LightSquared’s transmission rights are clear, GPS’s right to protection – or equivalently, LightSquared’s obligation to protect GPS receivers from its transmissions – is entirely unclear. There’s no objective, predictable definition of the protection that’s required, just a vague generalities, built into statute (see e.g. Mike Marcus’s Harmful Interference: The Definitional Challenge).

LightSquared’s transmission permissions are in some sense meaningless, since “avoiding harmful interference” will always trump whatever transmit right they have, and there’s no way to know in advance what will constitute harmful interference. I believe that’s a fundamental problem with almost all radio rights definitions to date, and why I’ve proposed the Three Ps.

The “Coasian” position’s real important problems are on view elsewhere:

(1) While negotiation between cellular operators to shift cell boundaries show that transactions can succeed in special cases, there is no evidence yet that transaction costs for disputes between different kinds of service will be low, and thus that negotiations will succeed in the general case. Even if one can ensure that rights are well defined, it may prove politically impossible to reduce the number of negotiating parties to manageable levels since radio licenses are a cheap way for the government to distribute largesse to interest groups. This is most obvious in the case of unlicensed operation, but many licensed services such as public safety and rural communications also result in a myriad of licensees.

(2) The FCC’s ability and proclivity to jump in and change operating rules (i.e. licensees rights) in the middle of the game makes regulatory lobbying more efficient than market negotiation. This may be unavoidable given law and precedent. There is no way for today’s Commission to bind tomorrow’s Commission to a path of action; legislation is the only way to do that, and even statute is subject to change.

(3) A significant chunk of radio services aren’t amenable to market forces since they’re operated by government agencies that can’t put a monetary value on their operations, and/or can’t take money in exchange for adjusted rights. Nobody is willing to quantify the cost of a slightly increased risk that an emergency responder won’t be able complete a call, or that a radar system won’t see a missile, even if those systems have a non-zero failure rate to begin with. And even if the Defense Department were willing to do a deal with a cellular company to enable cellular service somewhere, it can’t take the Cellco’s money; the dollars would flow to the Treasury, so there’s absolutely no incentive for the DoD (let alone the people who work for it) to come to some arrangement.

Protection Limits are not "Interference Temperature Redux"

My post Receiver Protection Limits may have left the impression that reception protection limits are similar to the dreaded and ill-fated interference temperature notion introduced in 2002 by the FCC’s Spectrum Policy Task Force.

Receiver protections are part of the "Three Ps" approach (Probabilistic reception Protections and transmission Permissions - see e.g. the earlier post How I Learned to Stop Worrying and Love Interference, or the full paper on SSRN). While both the Three P and Interference Temperatur approaches share a desire to “shift the current method for assessing interference which is based on transmitter operations, to an approach that is based on the actual radiofrequency (RF) environment,” to quote from the first paragraph of the Interference Temperature NOI and NPRM (ET Docket No. 03-237), the Three Ps approach differs from Interference Temperature in four important ways:

1. The Three Ps focus on solving out-of-band, cross-channel interference, whereas Interference Temperature is concerned with in-band, co-channel operation

2. The Three Ps are used to define new operating rights, whereas Interference Temperature tried to open up opportunities for additional operations in frequencies allocated to existing licensees

3. The Three Ps do not grant second party rights, whereas Interference Temperature permits second party operation.

4. Three Ps rights are probabilistic, whereas Interference Temperature definitions are deterministic.

Receiver protection limits: Two Analogies

I argued in Receiver protection limits that there are better ways to manage poor receivers causing cross-channel interference problems than specifying receiver standards. Here are two analogies to sharpen one’s intuition for the most appropriate way to handle such situations.

Cities increase the salinity of rivers running through them, affecting downstream agriculture. However, the choices that farmers make determine the degree of harm; some crops are much more salt-tolerant than others. In order to ensure that farms bear their part of the burden, regulators have a choice: they can either regulate which crops may be grown downstream, or they can specify a ceiling on the salinity of the water leaving the city limits, leaving it up to farmers to decide whether to plant salt-tolerant crops, perform desalination, or move their business elsewhere. Limits on salinity protection are a less interventionist solution, and don’t require regulators to have a deep understanding of the interaction between salinity, crops and local geography.

Sound pollution is another analogy to radio operation. Let’s imagine that the state has an interest in the noise levels inside houses near a freeway. It can either provide detailed regulations prescribing building set-backs and comprehensive specifications on how houses should be sound-proofed, or it could ensure that the noise level at the freeway-residential boundary won’t exceed a certain limit, leaving it up to home-owners to decide where and how to build. Again, noise ceilings are a simple and generic regulatory approach that does not limit the freedom of citizens to live as they choose, and that does not require the regulator to keep pace with ever-evolving technologies to sound-proof buildings.

Receiver protection limits: a better way to manage interference than receiver standards

Radio interference cannot simply be blamed on a transmitter; a service can also break down because a receiver should be able to, but does not, reject a signal transmitted on an adjacent channel.

More on this topic in subsequent posts:

Receiver protection limits: Two Analogies (June 2011)
Protection Limits are not "Interference Temperature Redux" (June 2011)
The LightSquared Mess Shouldn’t Count Against Coase (June 2011)
Licensing radio receivers as a way to facilitate negotiation about interference (August 2011)
Incremental management of reception: When protection limits are not sufficient (February 2012)
Four Concerns about Interference Limits (May 2012)
Transmitter versus receiver specifications: measuring loudness versus understanding (July 2012)
Testimony: Harm Claim Thresholds (November 2012)
Receiver Interference Tolerance: The Tent Analogy (November 2012)

I have also written a two-page summary document, see http://sdrv.ms/ReceiverLimits.

The LightSquared vs. GPS bun fight is a good example of this “two to tango” situation. GPS receivers – some more so than others – are designed to receive energy way outside the allocated GPS bands which means that operation in the adjacent band due to a new service like LightSquared can cause satellite location services to fail. Without the LightSquared transmissions, there wouldn’t be a problem; but likewise, if GPS receivers were designed with the appropriate filters, they could reject the adjacent LightSquared transmissions while continuing to receive the satellite location signal and function normally. [1]

While the responsibility for interference is, in theory, shared between transmitters and receivers, radio regulation has traditionally placed the onus on a new transmitter to fix any problems that may arise. [2] As I will argue, receiver standards are an impractical response; limits on reception protection, formulated in terms of the RF environment rather than equipment performance, are preferable.