Saturday, February 11, 2012

Incremental management of reception: When protection limits are not sufficient

As the growing demand for wireless services squeezes radio operations ever closer together, we can no longer afford to ignore the costs that poor receivers and ambiguous interference standards impose on society. There’s a growing consensus that radio regulation needs to attend to reception issues as much as to transmission, which has led to a clamor for receiver standards.  As I’ve argued in the June 2011 post Receiver protection limits: a better way to manage interference than receiver standards, however, the best way to manage receivers is to specify the radio environment in which they have to operate (i.e. receiver protection limits) rather than government getting into the minutiae of setting performance requirements (i.e. receiver standards).

However, while protection limits are necessary, there may be cases where they’re not sufficient. In this post I outline a progression of increasingly interventionist steps in managing reception, starting with protection limits and adding more and more requirements until one reaches full-strength government-imposed receiver standards.

One scenario where protection limits may not be sufficient envisages that the radio environment around a certain band is currently quieter than the protection limits specify. A multitude of manufacturers might sell tens of millions of devices to consumers that would not work if the environment were as noisy as allowed, but that do work today, because its quiet. When a neighbor then attempts to operate, the tens of millions of devices constitute “facts on the ground” that preclude this new operation politically, if not legally. The two commonly cited examples of this scenario are the “garage door problem” and GPS.

Some therefore argue that one needs more than just protection limits; there needs to be some upfront check that receivers can operate successfully when the environment is as noisy as the protection limits allow.

Still: every step beyond simple protection limits is fraught with regulatory risk, for all the usual reasons: additional up-front regulation may try to solve problems that never happen; the additional measures will lock in a set of technology and business assumptions, precluding innovative alternatives; and the upfront requirements may be more complicated than necessary, imposing unnecessary costs.

Fortunately there is a graded set of steps of increasing specificity available to the regulator. Each builds on the previous one. The first step, protection limits, step one, is necessary in all cases. If/when that’s not sufficient, the regulator could add progressively more requirements:

  • Protection Limits: Establish a limit that states interference <= a limit profile over frequency
Neighboring assignments will be made such that their interference <= limit, providing a protection guarantee for reception. Receiver operator may only claim harmful interference if interference > limit
  • Fit for Purpose Warranty: Manufacturer warrants on retail packaging that device suffers no harmful interference as part of a service as long as 2nd party interference <= limit
Harmful Interference is defined in accordance with language of 47 C.F.R. § 2.1: The manufacturer warrants that as long as interference <= limit, its functioning will not be endangered if it is a radionavigation service or of other safety service, or that it will not suffer serious degradation, obstruction, or repeated interruptions if it is a radiocommunication service
  • Self-certification: Manufacturer self-certifies that device suffers no harmful interference if interference <= limit
Submits to FCC a testing protocol and associated success criteria that allows testing of its claim of no harmful interference. The appropriate equipment authorization method is applied.
  • Simple Selectivity: FCC requires that receivers implement a front-end filter with specified OOB attenuation
Equipment authorization using Part 15-like procedure
  • Receiver Standards: FCC determines what harmful interference means (e.g. QoS criteria) and defines device performance parameters (e.g. ACIR, minimum desired signal levels etc.) that have to be met in order to ensure device doesn’t suffer harmful interference when interference <= limit
Equipment authorization using Part 15-like procedure

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