Dell, Intel, Microsoft and Google, among other companies, have cast their eyes longingly at delivering high-speed Internet services over "unused" TV airwaves.

U.S. TV broadcasters and cable operators are leery of allowing such transmissions over "white spaces" by a device until it can be conclusively proven that they won’t interfere with their transmissions. The proponents want to provide Internet access by beaming through the white spaces into customers’ computers and mobile devices.

The National Cable & Telecommunications Association filed its official comments regarding cable’s concerns in February and then filed additional comments that responded to policy group New American Foundation‘s comments, and others, on March 2. Now that the FCC has completed its records on the proceedings, the interested parties will start lobbying the Office of Engineering and Technology. FCC Chairman Kevin Martin has been questioned about the use of the white spaces in recent oversight committee hearings in both the Senate and House. Martin has said he hopes to have the proceeding completed by this summer, and there have recently been several bills introduced by lawmakers who want to ensure that the FCC will be finished with its rulemaking by this coming fall.

"NCTA supports the concept of introducing advanced wireless communications devices in the TV broadcast bands; however, we want to ensure that appropriate technical rules are adopted to ensure that the new devices don’t cause interference with cable service in customer homes," Bill Check, NCTA’s SVP for Science and Technology, said via email. "We urge the Commission to proceed with caution and to conduct comprehensive testing to assure that only those devices that can coexist with cable services without causing harmful interference are approved. The failure to take adequate interference-avoidance steps could hamper cable and other broadband providers in their ability to serve their customers with new and innovative services."

As part of its filings, the NCTA commissioned consultant Dave Large, co-author of Modern Cable Television Technology and a 33-year veteran of the cable industry, to author a technical appendix to its comments on whether the device could interfere with cable, and the short answer is, "Yes, it could."

In 2004, the FCC first proposed allowing the use of unlicensed transmitting devices within nominally unused TV channels, subject to rules that would prevent interference with reception of licensed TV broadcast signals. The devices would be allowed to operate on TV channels 5-13, 21-36 and 38-5, and possibly channels 2-4 and 14-20, and would have to suppress out-of-band spurious transmissions.

First off, "white space" is something of misnomer for cable since it uses every channel to provision cable-programming services in the home, unlike the broadcasters who are concerned about the use of their vacant or adjacent channels. The NCTA asked that channels 2 through 4 be exempted since those have been historically used for outputting video, and other program services, from set-top boxes to receivers. Possible interference on two fronts The NCTA’s concerns fall into two main areas: the issue of direct pickup and interference with cable’s over-the-air signaling at headends. The device "sniffs out" airwaves that it thinks aren’t being used to beam through. A simplified example of direct pickup is when a cable consumer is watching a show on channel 23, but the broadcaster in the city doesn’t transmit on channel 23. Since the broadcaster isn’t using channel 23, the proposed device could decide it’s free and start transmitting it while the cable consumer is trying to watch that same channel.

According to Large, direct pickup interference is in regards to the shielding effectiveness of the television receiver. Tests run by C.T. Jones for CableLabs a few years ago showed that most receivers did not meet the FCC shielding requirements, especially at VHF channels. The result is that a unlicensed device in one apartment can interfere with reception in an adjoining apartment (as well as with reception in the same apartment). Furthermore, since cable operators typically use every channel to feed “cable-ready” receivers (where no converter is required), there is no way for the unlicensed device to avoid channels in use.

In the scenario regarding interference with a cable operator’s over-the-air signals at headends, the device sniffs out a channel, sees that it’s not being used in that city and starts transmitting through it. The interference comes when cable operator is using that channel the headend in to pull in distant signals.

A third scenario could also occur if the there is a wireless microphone being used at, for example, a sporting event. The wireless microphone also uses unused TV channels, but the device could chose to use the same channel.

The device, which was developed by Intel, hasn’t surfaced yet for external testing, so the NCTA has asked that the FCC do a through job of testing it on the interference issues that cable is concerned about.

The device comes in two flavors. One is similar to a Wi-Fi device that sends out signals wirelessly and sits on a shelf with other networking gear or in a PDA device. The other version is a more powerful, pole-mounted fixed device. Since the devices are unlicensed, they don’t have to give out their locations, but at least the pole-mounted devices are in fixed locations, which is helpful if there is a problem with interference. The PDA devices, on the other hand, could be anywhere and could be problematic in multi-dwelling units where a neighbor’s device could interfere with a cable customer next door.

The FCC comments and reply comments are, not surprisingly, rather long. But for those who wish for a deeper dive into the topic, here are some links provided by NCTA:


Appendix I

Appendix II 
Reply comments
Mike Robuck

The Daily


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