Doug Lung / RF Report
03.03.2014 11:14 AM
FCC Extends Wireless Broadband/TV Interference Prediction Comment Window
Only one comment filed by original deadline
The original deadline for filing comments on the FCC Public Notice describing a proposed method for determining if and how UHF spectrum could be shared between DTV stations and wireless broadband base stations operating on the same or adjacent frequencies has been delayed to March 17, 2014.
 
 The request for extension was filed jointly by National Association of Broadcaster, ABC Television Affiliates Association, CBS Television Network Affiliates Association, FBC Television Affiliates Association, NBC Television Affiliates, The Walt Disney Company, 21st Century Fox, Inc., NBCUniversal Media, CBS Corp., Univision Television Group, the Association of Public Television Stations and Public Broadcasting Service.
 
The only comment filed before the extension was granted was from Linley Gumm and Charles Rhodes. In their comments, Gumm and Rhodes stated that the FCC is using an “overly optimistic receiver model” when calculating interference, leading to “overly optimistic assumptions about how little interference will be inflicted on DTV viewers.”
 
They noted that: “Projections of downlink and uplink interference based on actual DTV receiver performance should be made. If, as it appears that there will be appreciable interference, then policy and plans should be made as to the rights and responsibilities of all the individuals that will be affected. To go forward without doing so is to court harm to many interested parties.”
 
See COMMENTS of Linley Gumm and Charles Rhodes to the Public Notice for details. Many of the interference they outline will be familiar to readers of Charles Rhodes' TV Technology columns.
 
The FCC's Feb. 21, 2014 workshop provided some additional details on the Public Notice and its technical appendix. See the FCC LEARN Workshop on Interservice Interference Prediction webpage to view the entire workshop and download the presentation slides. From the presentation, it appears one goal of this methodology would be to place some TV stations in the guard band between the uplink and downlink wireless spectrum in markets where the FCC was unable to clear the desired amount of spectrum for wireless broadband. This would support a band plan where the downlink spectrum was fixed across the country but the amount of uplink spectrum varied depending on how much spectrum was available in a given area.
 
While it was agreed this approach would add complexity, Matthew Hussey, the FCC’s associate chief for policy, said the benefits of a more precise methodology outweigh the increase in complexity. He noted the FCC is already using TVStudy for interference between TV stations and said improving accuracy is a consistent theme in the proceeding.
 
Martin Doczkat, an FCC electronics engineer, explained that the FCC used the NTIA MSAM Suite for Spectrum Management to determine the amount of interference between DTV signals and wireless signals of different bandwidths with different frequency overlaps. The methodology is explained in NTIA's Frequency Dependent Rejection (FDR) Overview, part of NTIA's Microcomputer Spectrum Analysis Models (MSAM).
 
Another FCC engineer, Barbara Pavon, pointed out that clutter loss was applied to interference paths to and from the wireless sites but not from the TV transmitter site to TV receive antennas. In response to a question, she explained that clutter was not applied the path from the TV transmitter antenna to the TV receive antenna because they wanted to follow OET-69 as close as possible and that path was more direct than the path from wireless base stations at the assumed 30 meter height.
 
There was a question as to why a 50 percent time probability (F50,50) was used for interference into LTE base stations rather than the 10 percent time probability (F50,10) used for interference to broadcast reception.
 
Robert Weller, chief of the FCC’s technical analysis branch, explained that LTE includes features like MIMO that don't exist for TV. This, and LTE's ability to fall back to more robust modes justify the use of the F50,50 probabilities. Barbara Pavon invited comments on the use of F50,50 for interference to LTE base stations.
 
One person asked if the overlap interference model considered non-linearity and other factors. Martin Doczkat responded that they used a simple power ratio, but based the study on a wider filter to make it more conservative.
 
Follow the comments on the Public Notice on Interference Prediction Methodology by visiting the FCC's Electronic Comment Filing System Search page and entering “14-14” in the Proceeding Number box. I expect to see more criticism of the assumptions used in the interference prediction analysis.
 
The results of the proposal interference methodology may be more precise, but that doesn't guarantee that they are any more accurate.
 


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