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Federal Register / Vol. 86, No. 36 / Thursday, February 25, 2021 / Proposed Rules
different white space device operational modes and use cases?
6. What modepoint-to-point or areais appropriate for each situation?
For fixed white space devices, it would seem intuitive to use the point-to-point mode to examine a specific radio path to the television station contour.
However, the Commission seeks comment on what specific path should be examinedthe shortest path to the contour or possibly a different path where the white space device and television contour are further apart, but due to terrain shielding effects, may have less attenuation. How would each path be determined and how many specific paths would need to be evaluated before a determination can be made as to whether a channel is available for white space device use? Or would it be better to run the propagation model in area mode to determine the points along the television contour with the highest coand adjacent channel D/
U ratios and then run the model again in point-to-point mode for those specific transmission paths? Should a D/U
threshold be set to determine which paths need further examination? If so, how close to the 23 dB co-channel and 33 dB adjacent channel thresholds do they need to be? And if an initial area mode calculation must be performed, what grid size is appropriate and what point within each grid cell should be used for analysis purposes? Using similar logic, how could the model be applied to determine less congested areas and operating locations for personal/portable, mobile or narrowband white space devices?
Should it be run only in area mode or must additional point-to-point calculations also be performed?
Commenters should provide detail regarding how the model can be applied to each of the situations likely to be encountered for various white space device types.
7. The Commission also seeks comment on whether the Longley-Rice model would always determine the same or shorter separation distances from a TV contour than the current model, or whether there are cases where it could require greater separation distances, and therefore reduce white space device channel availability. How justified are the concerns expressed by the NAB regarding the use of the Longley-Rice model to protect television reception? NAB argues that the LongleyRice model requires transmitter and receiver locations to be known with precision, while television receiver locations are not reflected in any database and cannot be passively detected, and that current television
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receiver protection requirements for white space devices are not overly conservative or based on worst-case assumptions. The Commission seeks comment on NABs assertions.
Commenters that favor use of the Longley-Rice model should provide specific reasons regarding how NABs concerns can be addressed.
8. The Commission further seeks comment on whether the Longley-Rice model should be the exclusive means of determining white space channel availability, or whether it should be an optional alternative to the current protection model. As an alternative model, would it be more appropriate to use the Longley-Rice model in combination with other propagation models in some circumstances such as the Commission requires for 6 GHz unlicensed devices, where different propagation models are specified at different distances? Finally, the Commission seeks comment on whether the Longley-Rice model can or should be used for modeling the TV coverage itself, and therefore possibly allowing white space device operation within a TV protected contour as calculated using the F50,90 curves so long as the minimum D/U ratios are met.
9. The Commission also seeks comment on the technical requirements that need to be specified if the Commission permits the use of the Longley-Rice model. What inputs are necessary for using the model in either point-to-point mode or area mode for each white space device type, potential use situation as well as for determining less congested areas and protection distances for each type of protected entity? Which of these inputs should be specified by rule and which can be determined either by the white space device operator or the database?
Commenters should be as specific as possible regarding their preference for input parameters and provide engineering justification for those preferences. What grid size and which location within each grid cell should be used for determining white space channel availability?
10. The Commission further seeks comment on the terrain database that should be used with the Longley-Rice model or any alternative terrain-based model that the Commission specifies.
Should the Commission require the use of a particular terrain database, such as one based on 3-arc second data or 1-arc second data? Should the Commission instead simply specify some minimum criteria for a terrain database, e.g., granularity, and allow the use of any terrain database that meets or exceeds that criteria?

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11. Model Implementation. The Commission seeks comment on the various implementation factors that must be considered if the Commission adopts rules to allow the use of the Longley-Rice model or another terrainbased propagation model. As an initial matter, the white space database administrator would need time to implement this change to its system.
How long should the Commission provide for the database administrator to implement these necessary changes?
What type of testing should be performed to ensure that a white space database using a terrain-based model provides accurate results? Should the Commission perform its own testing or should it require public testing as it did when initially designating white space database administrators? The Commission also seeks comment on any effect that these changes might have on database and network performance. If the amount of overhead data necessary to use the Longley-Rice model significantly increases over what is necessary under the existing rules, would the result be slower response times as Sennheiser suggests? If so, would this detrimentally affect the utility of white space devices? Would such changes affect the capacity of the database to handle large numbers of white space devices simultaneously?
12. Are changes needed to white space devices if the database is modified to base channel availability on the Longley-Rice model? Does the information sent from white space devices to the database need to change from the data set currently sent? If so, could all existing devices be updated? If not, how should the database deal with devices that can send the necessary data and those that cannot? Should the Commission require that devices be updated within a specific time period?
What should that time period be?
Would any of the needed changes to a white space device affect its emissions and necessitate a change to its equipment authorization records?
13. How would the database using the Longley-Rice model account for any device location uncertainty? What actions should be taken if the propagation model determines that an existing operational white space device on a specific channel based on current protection distances no longer meets the D/U ratios after performing the required calculations? Should that device no longer be permitted to operate on that channel at its current power level or could the existing separation distances specified in the rules be considered a safe harbor for operations?

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