A Risk-Informed Interference Assessment of MetSat/LTE Coexistence

Quantitative risk assessment has recently been proposed to assess the impact of a new radio service allocation on incumbents. This paper demonstrates its viability by performing a risk-informed interference assessment in a recent U.S. case: the protection of meteorological satellite earth stations from interference by cellular mobile transmitters. We find that the hazard selected by policy makers (co-channel interference with the receiving antenna at 5 elevation) was not the most severe, and that their worst case approach overlooked more significant risks, notably adjacent band interference. We begin with an inventory of the performance hazards. We survey consequence metrics that quantify the severity of interference, and select the interference protection criteria defined in Recommendation ITU-R SA.1026-4. We then use Monte Carlo modeling to calculate probability distributions of resulting interference due to co-channel and adjacent band transmissions. We identify a co-channel exclusion distance that keeps interference risk below the SA.1026-4 criteria. We show that the binding constraint is not the ITU-R "long-term" interference mode (5 antenna elevation), but rather the "short-term" interference when the elevation is 13 degrees. We give an extensive sensitivity analysis showing that the propagation modeling, and particularly the choice of clutter model, can have a significant effect on the results. We conclude that quantitative risk assessment yields useful insights for analyzing coexistence. Protection criteria that combine an interfering power level with statistical exceedance limits were essential to our analysis, and we recommend that policy makers adopt statistical service rules more widely to support future risk analysis. Our analysis was limited by the unavailability of baseline values for service metrics, and the lack of transparency in previous studies, notably ITU-R recommendations. We recommend that regulators encourage parties to provide baseline values and the methods underlying interference criteria and coexistence assessments.