The debate over whether the ‘white spaces’ in US television spectrum can be opened up for license-exempt wireless use rages on. Although Microsoft, which has been leading a group of vendors in submitting prototype devices to the FCC for testing, has so far failed to strike gold, Motorola and Philips are both claiming success for their own prototypes, and the methods they use to avoid interference with TV broadcasts.
Motorola made some bullish statements last week, though the FCC has not released any verdict on its devices yet. But licensed wireless operators and broadcasters clearly feel threatened by the prospect of new entrants into the unused spaces, and are denying the device vendors’ claims. Verizon leads the opposition of the cellcos, and executive VP Tom Tauke put a very different interpretation on the (publicly available) FCC test results to that of Motorola and Philips. He said no company’s prototype had yet passed the regulator’s test requirements for non-interference, countering the statements by Motorola’s senior director of regulatory policy, Steve Sharkey, that his company’s geolocation technology had enabled Moto devices to perform well.
Meanwhile, the National Association of Broadcasters continues to argue that white space devices may interfere with existing broadcasts, as well as users of wireless microphones, a point of view supported by the microphone sector, notably Shure, which said last week that the FCC’s tests of prototypes at FedEx F before an NFL game between the Redskins and the Buffalo Bills ‘conclusively showed’ that spectrum sensing white space products “will cause harmful interference to wireless microphones during live events’. He said the devices were unable consistently to identify operating wireless microphones, to notice when a microphone was switched on, or to distinguish occupied from unoccupied TV channels.
When the FCC concludes its outdoor testing, it will prepare a report and make overall recommendations. While it is favorable to increasing broadband availability and competition by opening up the white spaces – which it argues are now unnecessary given advances in TV technology since spectrum policy was originally set in the bands ‘ it will have to err on the side of caution on the interference issue given the scale of opposition.
Motorola is determined that its approach of using a geolocation database to counter interference will address the issues. The system tracks mobile devices through their specific IP address, MAC address, RFID or other location-based information. Then the database looks at what licensed channels are being used within a given area, and ranks those left available by their strength and their closeness to spectrum already in use. The database can then select the best channel for the device and will switch this as the device moves around.
“The key for successfully testing our device has been having access to the database and then knowing what channels are open and then using sensing capabilities to rank the channels,” Sharkey said in an interview.
Motorola is hoping to steal a march on other members of the White Spaces Coalition, which is lobbying for the opening of the spectrum, and has centered many of its prototyping efforts on Microsoft. But most devices tested so far have not used geolocation, but ‘smart wireless’ techniques that rely on lowering or shutting off power when in the presence of licensed spectrum products. However, they cannot intelligently interact with other devices in the area and so interference risk is increased.