The FCC Office of Engineering and Technology has completed some of its outdoor testing of white space devices, and Motorola claims its geolocation concept for interference protection in the DTV white spaces is moving forward.
Steve Sharkey, Motorola senior director for regulatory and spectrum policy, said tests by the OET created “general agreement that geolocation provides an extremely high-level of protection and is a very reliable approach.”
The Motorola device pulled information from a database about what television stations were in the area, and could figure out what channels were available and what power level it can use, he said.
The Association for Maximum Service Television acknowledged that geolocation technology may be part of what’s needed for operation of white space devices without causing interference to DTV. MSTV said the first round of OET tests showed that no devices can rely on sensing technology to avoid interference to DTV and wireless mics.
“Under appropriate circumstances and conditions, geolocation technologies may offer the potential for viable interference protection,” MSTV wrote the commission. “But even with geolocation technologies, the FCC must also focus on protection against adjacent channel interference, requirements to assure an accurate database to support geolocation methodologies, robust certification procedures, and powerful and effective policing mechanisms.”
Motorola’s vision for future uses of white space would involve two tiers of unlicensed devices—higher-power devices, up to 4 W, would use geolocation technology and detection of beacons (signaling the presence of incumbent users). Lower-power devices (less than 10 mW), for home networks, for example, would involve beacon sensing but not the geolocation data.
Spectrum sensing technology would also be used in the higher-power devices to avoid interference with incumbent users such as newsgathering operations, which spontaneously operate in unplanned locations. Frequencies used during major events such as NFL games should be included in the geolocation database as the data is developed, Sharkey said.
Microsoft withdrew its device from the tests in July but remains interested in the technology and can learn from the tests of others’ devices. Google is also interested in the technology but conducted its own tests. Philips has a device undergoing testing, as do less-known Adaptrum and Infocomm.
Cable operators also have concerns about white space interference, both in the consumer’s home (through set-top boxes or the cables themselves), and at headends that receive over-the-air channels, especially outside those channels’ Grade B contours. The National Cable and Telecommunications Association says FCC test results showed that operations as low as 4.26 mW can cause interference to cable reception at a distance of 2 meters.
Motorola, which itself makes cable set-top boxes, says it is addressing the home-interference issue. While most boxes will resist interference well, some cables, especially those not professionally installed, could be vulnerable. “And that’s one of the reasons why our low-power device [would be] limited to 10 mW,” said Sharkey. “We’re confident that at that level, the direct-pickup interference would not be problem.”
TV Technology columnist Doug Lung has more on the white space testing in this week’s RF Report.
