The National Association of Broadcasters took the gloves off in a recent meeting with FCC engineering staffers over TV white spaces (TVWS) -- the use of broadcast spectrum for unlicensed uses like wireless broadband -- calling it a failing experiment.

Microsoft has been pushing the FCC to allow unlicensed devices operating in the TV band to do so closer to existing TV channels, but NAB told the engineering staffers in a meeting last week that the computer company's proposal on how to determine if a channel is available for unlicensed use is disingenuous and in service of white spaces deployments whose success has been "grossly exaggerated."

The FCC voted last year on a Notice of Proposed Rulemaking freeing up more "white spaces" spectrum between TV channels for wireless broadband by allowing for taller towers and higher powers for mobile and fixed wireless so signals can reach farther and over more difficult terrain. But it sought further comment on changing the interference calculation as Microsoft had wanted.

Also Read: NAB, Microsoft Spar Over TVWS

While NAB and Microsoft struck a compromise on some updates to TVWS pushed by the latter, NAB has balked at changing how the FCC calculates sufficient interference protections, particularly if it means allowing use on the first channel adjacent to broadcasters, saying that Microsoft's proposal is too close for comfort and a recipe for interference just as broadcasters are trying to roll out the new ATSC 3.0 transmission standard that could make them a broadband player as well as delivering ultra high-definition pictures and interactive content.

Microsoft has been telling the FCC that it can use a "terrain-based" approach to determining if unlicensed use is going to interfere with a TV channel rather than the "current overly-conservative distance-based protection" approach. 

But in the May 5 meeting, NAB execs said that Microsoft has failed to demonstrate that its proposal will not create potentially harmful interference, referencing a limited test with a professional grade receiver, limited testing NAB calls Microsoft's reliance on "disingenuous."

Microsoft's reference to the success of TV white spaces devices to date -- the computer company has billed TVWS as a route to closing the rural broadband divide  -- as "grossly exaggerated," with backers of TVWS (it does not call out Microsoft by name in the FCC document describing the meeting)--referencing expanded deployments "that do not appear to exist."

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"There are just over 300 TVWS devices operating nationwide, more than a dozen years after the Commission authorized unlicensed operations in the television bands and despite multiple attempts to boost deployment of this technology. It is unclear how ongoing rulemakings dedicated to a failing experiment that has never achieved measurable success represent a sound use of Commission resources," NAB execs told the commission.

Pointing out its compromise with Microsoft on other TVWS issues, NAB signaled it was about done.

"It it is long past time for the Commission to stop tinkering with its rules to boost a technology that has no demonstrated track record of success," says NAB deputy general counsel Patrick McFadden in the ex parte document describing the meeting. "At some point, white spaces proponents should be asked to actually accomplish something before asking for further handouts." 

Broadcasters are telling the FCC that using a popular method of determining signal reach could undo the good work the commission has done to help them better serve the public.

It is the latest volley in the battle between broadcasters and computer companies--specifically Microsoft--over opening up the TV band for more unlicensed (so-called TV white spaces, or TVWS) broadband use. 

That volley came in comments by the National Association of Broadcasters to the FCC this week on a Further Notice of Proposed Rulemaking (FNPRM) approved last October.

The FCC voted in October to open TV white spaces to higher powered wireless devices, saying it could do so while protecting those TV signals from potential interference. That item, which was approved unanimously, was based on a petition by Microsoft for more spectrum and an agreement between the computer company and NAB on how to do that while protecting incumbent broadcasters.

But the FCC also approved the FNPRM, which sought input on how to determine where Microsoft and others could use the spectrum without interfering with broadcasters. Microsoft suggests using the familiar Longley-Rice terrain-based model. NAB said definitely not. 

That is the model the FCC used to determine coverage areas in repacking TV stations after the broadcast incentive auction. Broadcasters weren't so happy with its use in updated form there, either.

The FCC currently defines white spaces in reference to a station’s protected contour. Microsoft said Longley-Rice will provide a more accurate picture of where available channels are. NAB said it definitely won't. It argues the model has an unacceptably high error rate.

In comments filed this week, the association said using that terrain-based propagation model, with its high error rate, would lead to "harmful interference to television service in pursuit of marginal, and likely illusory, gains in spectrum efficiency.

It suggests the Longley-Rice predictive model is not nimble enough to account for differences in seasonal foliage or atmospheric conditions, or individual antennal performance characteristics, and so will wind up allowing TVWS operations that cause interference. Plus, it said, getting that more precise information on which to predict channel availability is a nonstarter because "there is no remotely accurate way of determining the precise location of individual television receivers that might allow for more granular determinations of coverage."

NAB also argues that the commission doesn't want to reverse the gains it has made toward a more robust broadcast service, including allowing for greater flexibility in the use of distributed transmission systems and authorizing deployment of ATSC 3.0, so-called Next Gen TV. Combined with the changes the FCC has already made, per that Microsoft/NAB agreement, to authorize higher power TV white spaces devices, greater antenna heights and more, NAB said this is exactly the wrong time to change the way the FCC determines channel availability, "risk[ing] more interference in the very areas where television coverage is already challenging at the very moment when broadcasters are trying to improve it."

Marking the halfway point in its Airband rural broadband initiative, Microsoft said it is now in 25 states and one territory and is on track to meet its goal of three million more rural Americans with broadband access. 

Airband is Microsoft's promotion of unlicensed wireless in the TV white spaces to extend broadband access. 

Related: Microsoft Brands Rural Divide National Crisis 

In a blog post from Shelley McKinley, VP of Microsoft Technology and Corporate Responsibility Group, talked about a team of Amish-owned horses dragging a load up a ridge in rural New York state, pointing out that the only thing that distinguished the scene from a Norman Rockwell painting was that it was a load of telecom equipment. 

She gave the FCC credit for its effort to improve broadband data and mapping, saying that it remains problematic when the FCC data show access where none exists. 

But saying the country can't wait on perfect data, McKinley reeled of some numbers to indicate Microsoft's progress. That included reaching 633,000 previously unserved people.  

She also said the price of TV white spaces devices continues to drop, including by 50% in the last year. 

She also applauded the FCC's vote last week to increase tower heights and boost power levels--things Microsoft had proposed--to expand the use of TV white spaces for unlicensed broadband, as well as its $20 billion-plus rural broadband subsidy fund.