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Federal Register / Vol. 86, No. 36 / Thursday, February 25, 2021 / Proposed Rules This is a summary of the Commissions further notice of proposed rulemaking FNPRM, in ET Docket No. 2036, FCC
20156, adopted on October 27, 2020, and released on October 28, 2020. The full text of this document is available for public inspection and can be downloaded at: https www.fcc.gov/
document/fcc-increases-unlicensedwireless-operations-tv-white-spaces-0 or by using the search function for ET
Docket No. 2036 on the Commissions ECFS web page at www.fcc.gov/ecfs.

SUPPLEMENTARY INFORMATION:

Synopsis 1. Discussion. The Commission addresses Dynamic Spectrum Alliance, Wireless Internet Service Providers Association WISPA, and Public Interest Spectrum Coalition arguments that the Commission should determine white space channel availability using a terrain-based model, such as the Longley-Rice Irregular Terrain Model Longley-Rice model, which they assert will determine channel availability more accurately than the current contour-based model used by the Commission. For example, a terrainbased model could permit a white space device to deploy at a location where the television signal is shielded by a large hill or mountain, whereas the existing methodology does not account for such shielding. National Association of Broadcasters NAB and Sennheiser, however, oppose using the Longley-Rice model due to concerns about its accuracy in protecting TV receivers and because it may slow operation of the white space database.
2. Current protection model. Under current rules, white space devices must generally operate outside the defined co-channel and adjacent channel television station protected contours.
The rules provide a table of separation distances beyond the protected contour that white space devices must meet that is based on the white space devices equivalent isotropic radiated power EIRP and height above average terrain HAAT. These distances are based on a desired-to-undesired D/U signal ratio of 23 dB at the edge of the protected contour for co-channel operation, and 33 dB at the edge of the protected contour for adjacent channel operation, with a 14 dB allowance for TV receive antenna front-to-back ratio. The distances were calculated using the F50,10 curves for separation distances of greater than 15 kilometers, the F50,50 curves for separation distances of 1.5 to 15 kilometers, and the TM91
1 model for separation distances of less than 1.5 kilometers.

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3. Longley-Rice model. The LongleyRice model is used to make predictions of radio signal field strength using the median attenuation calculated as a function of distance and the signal variability in time and space. The model can be run in point-to-point mode where it examines a specific radio signal path between a transmitter and a receiver, or in area mode in which it predicts field strength at many geographic points within a specified area. Each operational mode uses a terrain elevation profile in making predictions; in the point-to-point mode path-specific parameters can be determined from the terrain profile between the transmitter and receiver, and in area mode the elevation profile between the transmitter and each specific reception point is examined.
The model may require a large number of reception points to be individually examined. It also requires a large set of input parameters encompassing system parameters e.g., frequency, polarization, antenna heights, environmental parameters e.g., terrain irregularity, electrical ground constants, surface refractivity, climate information, deployment parameters, and statistical parameters e.g., reliability and confidence level. Based on the predicted radio signal attenuation and using additional factors such as transmitter power and antenna directivity, the D/U signal ratio can be estimated and compared against the 23
dB co-channel and 33 dB adjacent channel standards used as the basis when developing the white space device rules to predict whether harmful interference is likely to occur to television reception.
4. The Longley-Rice model can be implemented using a variety of methodologies. For example, the area subject to calculation can be divided into rectangular cells, e.g., a 1-by-1
kilometer grid, and the field strength predictions are calculated at a point in each cell, such as the geographic center or the population centroid. The Commission notes that as computing power has increased over the years, it is most common to execute the model in point-to-point mode and use a batch process to evaluate each grid cell within a specified area. Nevertheless, the Commission seeks comment on various implementations for white space device evaluation which include both area and point to point mode as it is concerned about the available processing power, capabilities and time requirements to run many simultaneous batch processes to evaluate a large number of white space devices that may query the
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database for available channel information at the same time. The Commission seeks comment on whether it should specify a specific operational mode and how the model should be implemented under a specific mode or both operational modes.
5. As a threshold matter, the Commission seeks comment on whether using a terrain-based model, and in particular the Longley-Rice model, would better serve the white space device community as well as television broadcasters and other protected entities in the television bands. Commenters should specify the pros and cons of their preferred approach as it relates either to the Commissions existing contour method or other terrain-based propagation models. The Commission seeks comment on how the LongleyRice model could be used to determine available white space channels. Would it be used only to determine if a white space device at a specific geographic location and power level meets the coand adjacent channel D/U ratios? Or should the propagation model be used for wider applicability such as for determining separation distances necessary to ensure other protected entities such as licensed wireless microphones, television translator receive sites, cable headends, and land mobile stations do not experience harmful interference? In such cases, what criteria should be used to determine the protection distances?
Should D/U ratios be used here too, or some other metric such as an interference-to-noise ratio? Commenters should provide detailed technical reasoning regarding how the metric they support achieves the necessary protection levels. In addition, the Commission seeks comment on whether the propagation model can be used to determine which areas are less congested and thus subject to more flexible rules. In this case, what criteria should be used as the basis for determining a less congested area as it relates to use of the propagation model? Could using the Longley-Rice propagation model for this purpose permit additional areas to be designated as less congested to provide more flexibility for white space devices?
Similarly, the Commission seeks comment on whether the propagation model can be applied not only to fixed white space devices, but also to personal/portable, mobile and narrowband IoT white space devices. In each context, are there specific provisions required for how the model is implemented to account for the
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