High Tech Group, Broadcasters Clash OET White Spaces Test Data Interpretation
Low-power devices can operate in broadcast white spaces without causing harmful interference, a high tech coalition said. According to the White Spaces Coalition, data from FCC Office of Engineering & Technology (OET) tests support that conclusion. NCTA, NAB and MSTV called the FCC study a good first step, but urged more research. In March, OET sought comments on results from out-of-channel interference tests on 8 DTV receivers with 5th-generation tuners. OET said it took 2,055 measurements; commenters disputed their meaning.
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“OET’s extensive analysis demonstrates that other over- the-air broadcast DTV signals present a greater risk of harmful interference to DTV receivers than would low-power white space devices using appropriate operating parameters,” the coalition said: “In the vast majority of cases, if a DTV receiver is capable of rejecting interference from other DTV broadcasts, it will not suffer interference from personal/portable white space devices.” The coalition includes Dell, EarthLink, Google, Hewlett-Packard, Intel, Microsoft, Philips and Samsung. The filing was submitted by former OET Chief Ed Thomas, now of Harris, Wiltshire & Grannis.
Devices will work even better than in early tests when ready for market, the coalition said. “The performance of DTV receivers will be even better by the time that white space devices would first be allowed to operate,” the group said: “Receivers tested by OET already are one to two generations behind the current state of the art, which can be expected to improve even further in the two years leading up to the DTV transition deadline. Among other things, manufacturers presumably will increasingly rely on modern semiconductor tuners, which have the potential for greater interference rejection than the decades-old tuner designs they will replace.”
The test data show that fixed and mobile devices will be able to operate safely in the white spaces, Motorola said. But the company urged caution in setting rules for initial rollouts so that “future opportunities are not diminished by haphazard early deployments.”
The FCC data are a good first step but more work is needed, said NCTA, NAB and the Assn. for Maximum Service TV (MSTV). “The Commission’s laboratory measurements were limited to the out-of-channel interference rejection of a representative sample of 8 DTV receivers,” NCTA’s filing said Mon.: “As the [FCC’s] public notice points out, however, ’this information is only one element of many that must be examined.'” Reply comments to the FCC data are due May 15.
In a March 30 report, the agency said it tested 30 DTV receivers, limiting most of the work to 8 devices marketed 2005-2006. No receiver met ATSC guidelines for interference rejection -- cause for concern, a joint NAB/MSTV filing said: “Even the best performing of the 8 receivers appears to have failed the guidelines at one channel offset. The data shows that TV band devices would cause significant interference… [and] substantiates MSTV and NAB’s previously filed interference concerns and analyses.” The test results stoke their fear that unlicenced operation of any personal or portable device in the broadcast spectrum will “significantly diminish consumers’ access to digital TV programming and services just as they are poised to benefit from the multibillion dollar DTV investment of the broadcast and consumer electronics industries,” the groups said.
The Commission finding that DTV reception degrades more quickly than analog when experiencing interference also drew NAB/MSTV comments. The FCC confirmed a “cliff effect” where total loss of TV picture occurs quickly, the agency said. A receiver 1-2 db below median performance levels “ceases to display any picture or sound, making use of media performance standards inappropriate,” said NAB and MSTV.
NCTA asked the FCC to evaluate receivers’ direct pickup (DPU) interference or rely on private data it commissioned. “The tests document that TV receivers are highly susceptible to interference from devices operating in close proximity” to other devices, NCTA said: “We continue to urge DPU testing… The high probability of both near-field interference to TV receivers and fringe-area headend reception interference calls for adoption of appropriate technical and operational rules.” The FCC has more work, NAB/MSTV said: “In addition to testing a greater number of receivers, the Commission must also test other varieties of receivers, including mobile and handheld devices, which were not within the scope of the FCC report.”