FCC Testing Complicated by Failure of Microsoft Devices
The Office of Engineering and Technology faces major challenges as it completes bench tests of various white spaces devices at its Columbia, Md., lab, due in large part to the failure of the Microsoft device, which had the most capabilities of any device submitted to the lab for testing (CD March 31 p1). The biggest problem, sources familiar with the testing process said, is that the lab was committed to testing interference caused by the devices, but only the Microsoft device had a transmitter with high enough power to test. OET will start field tests when it wraps up lab tests.
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Only two devices submitted to the lab had a transmitter, the Microsoft device and one built by Silicon Valley startup Adaptrum. While the Microsoft device transmitted at about 100 milliwatts (mw) the Adaptrum device transmits at only 10 mw. “I think they're still struggling with what to do,” said a broadcast industry source.
Ed Thomas, former OET chief, who represents Microsoft on the issue, said Wednesday the FCC can complete testing by working around the problem. “Fortunately, the FCC can use conventional testing equipment to generate a signal that would be representative of the types of signals used by white space devices, just as it did when it conducted direct pickup interference tests of DTV receivers,” he said. “As long as the tested signals fall within the transmission mask proposed by the White Spaces Coalition, we are confident that the FCC can obtain all of the information it needs regarding the effects of white space transmissions.”
“The loss of the Microsoft device shouldn’t be such a big blow,” agreed a Motorola official. “Even though the other devices don’t have transmitters, the FCC could always just use a separate transmitter if they want to test interference from a transmitter,” he said. “In fact, this might be preferable since it would be tightly controlled.
Another potential problem with the failure of the Microsoft device was that it was one of only two, with a device submitted by Philips, that senses wireless microphones. Wireless microphone maker Shure and users of the microphones have been active in asking the FCC not to allow use of unlicensed, portable devices in the broadcast spectrum by devices that would use the spectrum to access the Internet. Sources who favor opening the white spaces to unlicensed, portable devices noted that the FCC also has data from the Microsoft device before it failed to draw on in writing a report on the tests.
The Association for Maximum Service TV, which is observing the tests at the FCC lab, determined that the sensing devices often detect broadcast signals when they aren’t present, and sometimes fail to report that other channels are occupied, according to a filing the group made at the FCC. The Adaptrum device, for example, “reported signals on some channels such as 28 and 37 that do not have signals,” MSTV said. The device “failed to detect on others such as DTV channel 35 or NTSC channel 20 that were clearly observable on the spectrum analyzer being used to monitor the test,” it said. MSTV reported similar problems with devices submitted by Motorola and Philips. The Philips device “reports all channels… occupied” when using an antenna and almost all channels occupied in tests in the FCC’s sealed anechoic chamber when tested without an antenna. MSTV said as a result data in wireless microphone tests are nearly meaningless.
The Motorola official said the device his company submitted had very few false positives. “I don’t have specifics on how many false senses each of the devices gave, but I know that it… shouldn’t be a significant factor that would prevent them from going forward with testing,” he said.