Risk-Informed Interference Assessment: A Quantitative Basis for Spectrum Allocation Decisions

Abstract

The trade-off between the benefits of a new radio service allocation and its risk to incumbents has to date been based on “worst case” analyses that focus on the single scenario with the most severe negative consequence, regardless of its likelihood. This is no longer a tenable approach since it leads to over-conservative allocations that limit the social benefits of new services while giving incumbents more protection than they need.This paper describes an alternative to worst case reasoning: the use of quantitative risk assessment (QRA) to analyze the harm that may be caused by changes in radio service rules. QRA considers both the likelihood and the consequences for multiple hazard scenarios, not just the most severe consequence, regardless of likelihood, as in worst case. While quantitative risk assessment has been used for decades in many regulated industries it has not yet been applied to spectrum management. This paper identifies four key elements of a systematic, quantitative analysis of radio interference hazards, and illustrates them with examples: (1) make an inventory of all significant harmful interference hazard modes; (2) define a consequence metric to characterize the severity of hazards; (3) assess the likelihood and consequence of each hazard mode; and (4) aggregate them into a basis for decision making. The four elements are illustrated by examples from spectrum policy questions past and present; the focal case study is the determination of geographic exclusion zones to protect weather satellite earth stations from co-channel cellular mobile transmitters.In order to reap the benefits of risk-informed interference analysis, the paper rec-ommends that regulators (1) develop know-how through a variety of educational initiatives; (2) use quantitative risk assessment in their analysis of harmful interference, and publish the results; and (3) pilot this approach in proceedings with limited scope, like selected site-specific license waiver proceedings. There is also a role for legislators and the executive branch: (1) they can require risk-informed assessments as part of their spectrum oversight activities; (2) when presented with politically charged claims of harmful interference, they can avoid the temptation of nightmare scenarios and instead make assessments that consider both the likelihood and consequences of interference harms; and (3) they can support regulators that use risk-informed interference assessments rather than basing decisions on worst case analysis.