Sunday, August 31, 2014

5G on Twitter: NodeXL social network analysis

A NodeXL SNApshot is a great way to catch up with who's saying what about a topic on Twitter. This post discusses the SNApshot http://bit.ly/snapshot-26748 that graphs the 1,963 tweets containing the hashtag #5G posted over the period 17 Jul - 29 Aug 2014.

Here's the Gallery Glimpse video:




Wednesday, June 04, 2014

Adjudication versus Enforcement

Mike Marcus (web site) has suggested that enforcement problems can be divided into two categories:
#1. Cases where behavior explicitly violates existing rules, e.g. use of the wrong frequency, or equipment that doesn't comply with rules.
#2. Unanticipated interactions between systems that either lead to service degradation but do not self-evidently violate any rules, or raise complex legal issues of whether there is a violation.
Mike suggests that the second category includes "cellular booster" interference to cellular systems, police radar detector "fuzzbuster" interference to VSATs, the Nextel/public safety intermod problem in 800 MHz, and impairment of 700 MHz cellular due to FM transmitter harmonics (discussed on Mike’s blog).
The fact that the spectrum community informally refers to both categories as enforcement problems while the second is actually a question of adjudication highlights a problem caused by the FCC’s rudimentary judicial function: while it has more than 250 people in the Enforcement Bureau (2014 Budget), it only has one (!) administrative law judge.

It seems to me that (1) being clear about the enforcement/adjudication distinction and (2) actually having an adjudication function separate from both rule making (the legislative function) and enforcement (the executive function) would not only help us think more clearly about spectrum problems but would also lead to quicker resolution, to everyone's benefit.

Discussion

As an administrative agency (caveat: IANAL) the FCC combines the three branches of government under one roof: legislative, judicial and executive. It makes rules (legislative), decides whether they have been broken (judicial), and takes action to detect alleged violations, and punish them if violations are found (executive).

Mike’s Category #1 (explicit violations of existing rules) is enforcement, defined by the OED as “the act of compelling observance of or compliance with a law, rule, or obligation”: it presupposes that adjudication has already taken place. The examples in Category #2 (unanticipated interactions) are actually questions of adjudication, i.e. “A formal judgment on a disputed matter” per the OED: they're difficult precisely because it's not clear whether there's been a violation, or by whom.

The FCC is very loosey-goosey on this distinction, as has been pointed out over the years; see e.g. Ellen Goodman’s 2004 Telecosm paper, Phil Weiser’s 2009 FCC Reform paper and our recent Hamilton Project paper.

Distinguishing clearly between these two categories could also address a blind spot about the need for enforcement in the Dynamic Spectrum Access (DSA) community. If enforcement is addressed at all by advocates of Spectrum Access Systems (SAS), it’s usually waved away with assurances that the rules in the database will solve all problems. (Jerry Park’s presentation at the January 2014 FCC 3.5 GHz SAS workshop is an exception, but even he focuses on attacks on the database, rather on how to decide disputes.)

Mike's distinction made me realize that the DSA/SAS community probably equates enforcement with Category #1. It's then plausible to believe that a system that prevents explicit rules violations solves, or more accurately obviates, "enforcement problems." However, the arcane interactions between radio systems in the wild and the difficulty in assigning responsibility for them make it important to highlight the Category #2 problems: these unintended issues are not only more likely to cause problems – and cause them unexpectedly – that failures in rule sets, but by their nature they will require judgment (in both a legal sense, and in the sense of requiring assessment of hard-to-compute complexities) to resolve.

Sunday, March 02, 2014

RF Mirror Worlds: Supercomputing meets propagation models, 3D terrain data and ubiquitous sensors

Petri Mähönen has observed that wireless researchers haven’t exploited supercomputing as much as one might expect, especially in comparison with other scientific disciplines such as aerospace, meteorology, oceanography, biology, sociology... If they had, we could be exploring thousands or millions of “Test Cities” rather than just the one contemplated in the PCAST Report (pdf, Chapter 6 and Appendix G). The PCAST budget for the first three years of a Test City (Table G.1) runs to $21 million in operating expenses and $15 million in capital expenses – that would buy a lot of computation!

I suspect (hope!) we’re on the verge of a step change in using software simulation, aka “mirror worlds”, to understand and manage radio systems. The underlying technology has been on the exponential growth curve we’ve all heard about, but hasn’t broken through to high profile visibility. It may soon.

Saturday, February 22, 2014

DoD treats Spectrum as Territory

The U.S. Department of Defense released a spectrum strategy document on Thursday (press release, pdf). I’ll leave discerning what (if anything) is actually new in it to the Pentagon watchers.

I was struck by the implications of the language used: the DoD conceives of spectrum as a place. Given that military success often seems to be framed as controlling or denying territory, this is not an auspicious starting point for spectrum sharing – which is about wireless system coexistence in many intangible dimensions, rather than all-or-nothing control of territory.

Wednesday, October 16, 2013

Unlicensed’s success: physics, not regulation?

Unlicensed allocations have generated a massive, and to many surprising, amount of innovation and value (see the References below). The question is: Why?

Almost all of the value so far has come in the 2.4 GHz ISM band, mostly due to Wi-Fi but also to a lesser extent Bluetooth applications. There is never a single, simple answer to a Why question about a complicated nexus of technology, politics and user behavior, but my impression is that unlicensed partisans believe that it's due pretty much exclusively to the techno-economic characteristics enabled by the rights assignment regime: “openness” (Benkler), “managed commons” (Milgrom, Levin & Eilat), or “rule-based access” (Thanki).

I think it's at least plausible that Wi-Fi's undoubted success has been due to a fortuitous coincidence of band choice, physics and timing as much as to regulation: It turned out that the interference range was small enough that users didn’t really degrade each other’s performance; and the networking needs of their applications could be met by the bandwidth available around them. In other words: the capacity of the channel was larger than the number of people who interfered with each other, multiplied by the data they wanted to move.

Wednesday, October 09, 2013

The Emperor has Objections: Replies to feedback on our “Is Wi-Fi Congested?” paper

Our TPRC 2013 paper “The Emperor has no Problem: Is Wi-Fi Spectrum Really Congested?” (http://ssrn.com/abstract=2241609) has generated quite a bit of interest. Here are responses to some pointed questions and comments we've received.

Monday, March 18, 2013

Counting Spectrum in an Age of Sharing

Mike Marcus’s recent blog post Dueling Spectrum Charts - Part 2 is a nice reminder (not that anyone who reads his blog needs it) that spectrum isn’t just MHz. The current focus on “spectrum sharing” underlines the fact that one has to think of space and time as well as frequency. A more accurate (but also much more geeky) metric would divide MHz by percentage of population covered, and percentage of time allocated.

Thursday, March 14, 2013

Using an auction to decide the number of 3.5 GHz spectrum access administrators


The FCC faces a choice of whether to authorize one database administrator or many to run the spectrum access system (SAS) that will manage small cell operation in the 3.5 GHz band. This resembles the choice between an exclusive-use licensing or unlicensed regime. The FCC could use an auction to let the market decide by using a simplified version of the 2008 Bykowsky, Olson and Sharkey proposal.

Monday, December 31, 2012

Harm claim thresholds for satellite earth stations

I'm reasonably confident at this point about deriving harm claim thresholds for cellular neighbors and TV receivers (see e.g. the TPRC 2012 paper http://ssrn.com/abstract=2018080). Here's a first cut (a few months old, but I'm behind on blogging...) at thresholds for satellite earth stations.

Tuesday, December 11, 2012

TV/cellular guard bands - second thoughts

In a recent post ("The FCC's TV/cellular guard bands don't compute") I wondered whether the guard bands between TV and cellular service that the FCC proposed in its Incentive Auction NPRM (pdf) had been designed to make room for more unlicensed in the TV bands. Having spoken to some experts, I’ve concluded that I was probably wrong about that: my new best guess is that they’re a benefit for the cellular industry.

Wednesday, December 05, 2012

800 MHz receiver criteria as harm claim thresholds

Bob Pavlak at the FCC prompted me to read the 800 MHz “unacceptable interference” rules in the context of an interference limits approach (root post).

The 2004 Report & Order (pdf) introduced the concept of unacceptable interference, “a term of art adopted for the limited purposes of this proceeding … that defines a bright-line test for interference protection that takes into account, among other factors, the strength of the desired signal and the characteristics of the receiver being employed” (Report & Order, footnote 8). While this sounds like a receiver performance requirement, I think it actually amounts to an interference limit or harm claim threshold. In fact, if it is reformulated as a harm claim threshold, it becomes more powerful because it does not enshrine a particular set of receiver performance parameters in the rules, leaving manufacturers and system operator with more flexibility.

Friday, November 30, 2012

Receiver Interference Tolerance: The Tent Analogy

A postcript to my testimony (see previous post) at the House sub-committee on Communications and Technology hearing on receivers: It sounded like Rep. Walden, who chairs the sub-committee, hoped my oral presentation would've mentioned the tent analogy I included in the written testimony. So since at least one person liked it, here it is:

Testimony: Harm Claim Thresholds

I was privileged to testify yesterday at the House Committee on Energy and Commerce’s sub-committee on Communications and Technology hearing on the topic “The Role of Receivers in a Spectrum Scarce World.”

My testimony (pdf; my oral testimony at time code 0:17:23 in the YouTube video on the hearing web page; the members' questions start at 0:27:00; some press here and here) tried to make four points:
  1. We need to improve the ability of radio systems in one frequency band to tolerate reasonable signals in adjacent bands. 
  2. Receiving system operators must bear some of the responsibility, but need to know what those responsibilities are.
  3. Regulators can bring receiving systems into the mix by setting harm claim thresholds (aka interference limits or receiver protection limits), i.e. the interference levels that a service needs to tolerate without being able to bring a harmful interference claim.
  4. Congress can play a role by keeping up the pressure, allowing the FCC to move ahead, and funding FCC technical investigations.

Saturday, November 03, 2012

The FCC's TV/cellular guard bands don't compute

The FCC incentive auction NPRM [1] proposes 6 MHz guard bands between cellular and TV services (actually 6-11 MHz, depending on how the auction works out). The number is arbitrary, and could well have been chosen on political grounds to make room for more unlicensed in the TV bands.

The impact on interference from cellular systems into TV receivers is much the same whether the guard band is 1 or 20 MHz: most receivers will be unaffected, and for the small but significant number that suffer harm (0.5-5%?), only receiver filters will really help. The real question is: who's responsible for buying and installing those filters - the consumer or the cellular companies?