#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.
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.