FCC Releases DTV Interference Test Results

April 6, 2007
FCC engineers are seeking feedback on the results of a DTV interference-rejection capability report. The report is part of the white space docket--the proceeding to allow unlicensed devices into taboo TV broadcast channels.

The 221-page report covers how well eight DTV receivers are able to cope with interference from signals in the white space. The white space--bands of spectrum between broadcast channels--is typically left fallow to prevent TV signals from interfering with one another. However, pressure has increased in recent years to open that spectrum up on an unlicensed basis for small consumer devices. The interference report is part of the FCC's proceeding to open the spectrum by Feb. 17, 2009, when analog TV broadcasting ends.

The commission's test sample included eight, 2005 and 2006 model receivers, all with fifth-generation tuners. A total of 2,055 measurements were taken from tests in which an interfering signal was injected in the channels surrounding one that carried the desired signal.

A memo on the peer review of the tests revealed some concern that eight receivers was too few, as were the characteristics of the signal types used for the testing.

"Two reviewers thought that 'the use of more varied signal types would have given a better indication of what to expect if the interfering signals were pulsed frequency hopping or centered between two channels.'" Another noted "the suppression of splatter from undesired sources into the desired channel 'might not be appropriate since in real-world situations, the splatter would be important.'"

The reviewer who questioned the receiver sample size pointed out that later model sets could have greater interference-rejection capacity.

Comments on the study are due April 30, with reply comments due May 15. All filings should reference docket No. 04-186.

The FCC, in releasing the report, emphasized "this information is only one element of many that must be examined in evaluating the possibilities for operation of new low-power devices in unused portions of the TV broadcast bands."

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