FCC Announces White-Space Device Testing Plans
January 18, 2008
The FCC Office of Engineering and Technology (OET) announced it will begin a second phase of laboratory bench testing of prototype type TV white space devices (WSDs) on Jan. 24. To make the process as open and transparent as possible, OET released a copy of the Plan for Tests of Prototype Personal/Portable TV White Space Devices (Phase II) and said the testing will be open to observation by any interested parties. See the Public Notice has information on who to contact to observe the testing.
The laboratory bench testing is expected to take four to six weeks and will be followed immediately by the field testing, which is also expected to take four to six weeks. OET will make any update or changes to the testing schedule available on its Web site at http://www.fcc.gov/oet/projects/tvbanddevice/.
For the laboratory tests, WSD scanners, which are used to determine if a channel is in use, will be tested with RF capture signals identified in the draft IEEE 802.22 standard, as well as clean RF signals. Plots of the RF capture signals are available in the online IEEE 802.22 SigPlots directory. The WSD scanners will be tested on three channels across the TV band. If performance is the same on all channels, then further testing will be done on only one channel. Testing will also evaluate the ability of the WSD scanners to detect a weak clean RF signal in the presence of a strong (–28 dBm) signal on a designated adjacent or second adjacent channel.
In the field, an existing rooftop or temporary telescoping mast-mounted antenna will be used to determine which DTV signals are receivable at a given location. The scanner function of the WSD will be tested inside and outside the test site to see what signals can be detected. All WSD scanners will use a common laboratory-grade calibrated receive antenna. This is important, as it will allow calculation of the device's actual detection threshold based on the gain (or, more likely, loss) of the antennas proposed for production WSD scanners. The DTV levels at the WSD scanner location will also be measured with a spectrum analyzer.
For WSD devices that are able to transmit, testing will involve interference to off-air TV reception, both on main and—if filters are available—adjacent channels. If cable service is available at the test site, interference into cable boxes will also be tested.
An outdoor test, probably done on FCC laboratory property, will be used to determine how close a WSD transmitter can be to an antenna receiving an off-air DTV signal at the lowest possible level—as close as possible to the threshold of visibility. The tests may also include a demonstration of the interference potential from WSD transmissions on adjacent and second adjacent channels.
The test plan says WFPT-DT, Channel 28 in Washington, is the signal most likely to be used for this test. The test plan also says external bandpass filters will be needed to enable testing on the adjacent channels. It isn't clear if these filters would be used on the WSD transmitter or the receiver, but in my opinion the receiver should not have additional filters added, as they won't be present in the receivers that consumers have.
Charlie Rhodes has identified intermodulation interference from signals combining in the receiver's tuner. If filters are used on the receiver, this type of interference may not be detected.
The FCC received several prototype devices for Phase II testing and listed four, from Adaptrum, Microsoft, Motorola and Philips.
Earlier in the week, NAB responded to a letter from the Wireless Innovation Alliance (WIA) sent to NAB President and CEO David K. Rehr reiterating the WIA's desire to introduce unlicensed devices in the broadcast spectrum. WIA claimed NAB engaged in a "misinformation campaign" and that the testing process "should be left to the FCC's expert engineers."
NAB Executive Vice President Dennis Wharton responded. "A successful consumer transition from analog to digital television is now imperiled by a cadre of companies that have been hoisted on their own flawed technology petard," he said. "Try as they might, portable unlicensed device advocates like Google and Microsoft cannot run and hide from the fact that their own technology utterly failed FCC testing. That is not 'misinformation,' but rather an inconvenient truth."
NAB also listed 70 lawmakers who have expressed concern over the use of unlicensed personal-portable devices in the broadcast spectrum.