POSSIBLE USE OF BROADCAST SPECTRUM FOR WI-FI DRAWS MIXED REVIEWS

The FCC in Dec. opened an inquiry on making additional spectrum available for unlicensed devices, citing Wi-Fi as an example of the type of technology that used cognitive, frequency-agile radios to share spectrum with incumbents. The inquiry, which stemmed from recommendations in last fall’s Spectrum Policy Task Force report, sought feedback on whether unlicensed devices should be able to operate in bands beyond those allowed under Part 15 of the FCC’s Rules, including TV broadcast spectrum, and at spectrum locations and times when a band wasn’t in use. It also sought comments on the feasibility of allowing unlicensed devices in bands such as 3650-3700 MHz at power levels higher than other unlicensed transmitters, with minimal technical requirements to prevent interference to licensed users. The inquiry focused on the possibility of additional spectrum below 900 MHz and at 3 GHz.

The Wi-Fi Alliance called those bands “ideal” for unlicensed point-to-point systems “because the spectrum could be used to provide data communications over great distances, tying together and providing backhaul for islands of local coverage.” Along with higher frequency wireless LANs, “a remote community could be interconnected with Internet services on a cost-effective, unlicensed basis,” the alliance said. The group told the FCC the ability of unlicensed systems to share spectrum with incumbents had improved. Devices in the unlicensed 5 GHz band, for which the FCC plans allocation to wireless LANs such as Wi-Fi, will use dynamic frequency selection (DFS) and channel monitoring to protect incumbent radars, it said. “While further investigation would be required to determine if DFS is a workable scheme for protecting incumbents in the TV broadcast band, other avoidance schemes are also available that allow devices to determine the environment in which they operate and to adapt to ensure noninterference with existing users,” the group said.

The Bluetooth Special Interest Group also endorsed making spectrum available for unlicensed devices in the spectrum. The group, which has backing from IBM, Intel, Microsoft, Motorola, Ericsson, Nokia and others, acknowledged that due to varying uses of adjacent radio channels, “successful coexistence of low-power unlicensed radios may require some rule differences for the bands below 900 MHz.” Such differences shouldn’t stop the FCC from making that spectrum available, it said: “There is nothing wrong with having more than one flavor of unlicensed wireless services.” Similarly, the Information Technology Industry Council (ITI) said allowing unlicensed devices to operate in those bands was feasible, “subject to reasonable conditions of compatibility and keeping in mind the distinct circumstances that exist within the proposed frequency bands.” ITI stressed the importance of finding additional spectrum now to prepare for the anticipated continued growth of unlicensed devices. “This spectrum is also very suitable for potential last-mile broadband solutions given the attributes inherent in its placement in the lower end of the spectrum,” ITI said. “The spectral characteristics of the band below 1 GHz offer some unique and rare opportunities to solve some of the distance and coverage issues.”

But broadcasters raised concerns. A joint filing by the NAB, the Assn. of Public TV Stations and MSTV said now wasn’t the time to introduce “untested and largely uncontrollable devices” into the broadcast spectrum, particularly at this “fragile and fluid stage” of the DTV transition: “Allowing unlicensed devices into the broadcast band at this time would pose serious risks to the integrity of over-the-air broadcasting… while offering few benefits to the proponents of unlicensed devices.”

Unlicensed devices probably won’t be advanced enough technologically to avoid interfering with TV broadcasts, the broadcasters said, and they, unlike other communications networks, don’t control the receivers so they can’t assure that they are upgraded to screen out interference. “Also to be weighed on the scales is the strong risk that permitting unlicensed uses in the broadcast spectrum now would preclude far more productive uses of the spectrum after the digital transition has been completed,” they said.

Adopting a “listen before talk” spectrum etiquette for unlicensed devices will be “fraught with significant technical challenges,” the broadcasters said, citing a study they submitted with their filing. They also said it would triple the cost of such unlicensed devices, once devices reached consumer hands it would be nearly impossible to stop their use if they did interfere, and DTVs could be particularly subject to interference, especially in areas where the DTV signal was weak.

Separately, Cox Bcstg., which owns 14 commercial TV stations, said in its comments it supported the concept of allowing noninterfering unlicensed devices to operate in the broadcast spectrum and believed it was reasonable to begin considering the best means for testing and implementation. But Cox also said the FCC should refrain from the “actual introduction” of any unlicensed devices until after the DTV transition because doing so would “prevent unnecessary interference and avoid needless uncertainty.” It said it believed that introducing “yet another unknown and uncertain element to the DTV mix during the transition only will complicate and extend it.”

Allowing unlicensed operation in the extended C-band “has the potential to cause harmful interference” for satellite signals used to deliver TV programming to cable headends, the Coalition of Program Networks & Distributors said. The group offered to do analysis and testing on the potential impacts.

Manufacturers See ‘Possibilities’

Consumer electronics manufactures are “excited about the possibilities” of new unlicensed spectrum, CEA Vp Michael Petricone said, but the new devices can’t be allowed to interfere with TV reception. He said broadcasters, set makers and others should be “integrally involved in testing” unlicensed devices. CEA’s filing said there was “significant unused spectrum capacity within the broadcast TV band,” but the new devices should be allowed to use that spectrum “only with approved interference technology.”

Intel said the “fixed and well-understood nature of the TV transmitters” made unlicensed operation of the TV bands feasible. Intel hired the Communications Research Centre Canada to study the issues, and said that research showed such services were “technically viable” even in major metropolitan areas.

The Land Mobile Communications Council (LMCC) backed banning or limiting operation of unlicensed devices in the TV spectrum to protect land mobile facilities from interference. LMCC members operate facilities in TV spectrum shared by land mobile services in 11 of the largest markets or plan to operate facilities in the 700 MHz public safety and guard bands occupied by broadcasters in advance of the DTV transition. LMCC said the thrust of the FCC’s inquiry was that it would be possible to design equipment to monitor shared TV spectrum to detect and avoid in-use frequencies. It said the inquiry anticipated devices using GPS to ascertain where they were and which channels were licensed in an area. “The Commission’s vision may become reality at some future date,” LMCC said. “However, the comments filed in response to the SPTF [Spectrum Policy Task Force] reports indicate that technology has not yet reached the FCC’s expectations.”

Unlike TV stations that transmit continuously at constant power, land mobile stations authorized to share certain TV channels must limit transmissions to the minimum necessary, LMCC said. Land mobile stations, including those operated by critical infrastructure entities, aren’t on or off “on a predictable basis,” the Council said. The inquiry said some areas of TV spectrum, including Ch. 37 where radio astronomy services operate, could face certain issues if unlicensed devices operated. “If the FCC had reservations about the interference potential to wireless medical telemetry and even radio astronomy operations in these bands, those concerns will be magnified many times when contemplating the risk to public safety and other critical communications transmitted routinely by land mobile licensees,” LMCC said.

Some local govts. weighed in strongly against allowing increased unlicensed use of TV broadcast bands. The city and county of San Francisco objected to the unlicensed use of 470-512 MHz. They said the FCC noted that due to minimum separation requirements, there were some vacant channels throughout the country and that conversion from analog to DTV would free additional channels. “Those statements do not reflect the fact that television stations are not the only licensed entities that use the TV band spectrum,” the filing said. The city and county said nearly a dozen major metro areas used part of the TV spectrum for municipal services. San Francisco’s citywide municipal transit system uses it for operational and safety communications, including emergencies. “Allowing additional, unlicensed use of the TV band spectrum will increase the problematic interference that municipalities and cities already suffer from,” the filing said. While the FCC indicates there “may” be technologies to ward off interference, San Francisco said it “offers no assurance” they are available or that unlicensed users would have to use them.

L.A. County warned that while the FCC’s Part 15 rules for unlicensed devices had been successful, “the very real risk to the public today is too great to justify the current proposal.” Allowing unlicensed devices to operate at 470-512 MHz in L.A. County would hamper emergency responders, the county said. Limits related to power or field strengths wouldn’t effectively reduce the risk of interference raised by unlicensed devices, in part because many of the devices used by public safety officers already are low-powered and mobile, it said.

The Electronic Frontier Foundation (EFF) linked allocating additional spectrum for unlicensed wireless services with the First Amendment. Historically, FCC rules balanced “restriction of access to spectrum -- which is a proxy for speech… with the need to preserve orderliness in the airwaves so that harmful interference is minimized,” EFF said. The point was that if “anyone were allowed to speak in any way,” the resulting degree of interference would lead to a world “where no one was heard,” EFF said. But unlicensed spectrum rules at 2.4 GHz have shown technology has overcome such concerns, it said. “The Commission has regulated speech because spectrum is considered to be a scarce resource, but the hothouse flowering of the 2.4 GHz band has demonstrated that some of that scarcity was an artifact of regulation, not physics,” EFF said.

Wireless LAN developers Intersil and Symbol said the success of the unlicensed wireless industry justified dedicated spectrum. “Information theory restricts how much interference any device can tolerate, and this in turn limits the number of devices that can operate simultaneously in a given area. Without its own spectrum, continued growth may ultimately threaten the industry’s success,” the companies said. The 3650-3700 MHz band is “well-suited” to unlicensed operation, they said, suggesting the FCC protect incumbent radar systems and earth stations with protection criteria defined by power flux density. The idea of unlicensed operation in unused TV spectrum is “worth exploring,” Intersil and Symbol said. “We urge that any implementation be capable of fully protecting TV reception, even in the case of TV stations being moved and modified. If feasible, however, the approach would make valuable use of otherwise wasted spectrum,” the filing said.

The Satellite Industry Assn. (SIA) said the Commission couldn’t authorize unlicensed devices in the 3650-3700 MHz band because there was potentially significant interference to incumbent fixed satellite service (FSS) operations in that band. Determining instances of potential interference is difficult with unlicensed devices because technical parameters haven’t been set, SIA said. The association’s own technical analysis revealed that “interference from all but extremely low-power unlicensed devices would cause unacceptable degradation in the C-band downlink receivers.” If the FCC does allow unlicensed devices in the band, they would need to be operated outside exclusion zones that would be determined based on power levels, SIA said, but there’s no way to enforce operations outside certain areas. “The FCC might consider requiring each emitter to have both an on- board GPS unit to determine its precise location and distance from licensed users and an automatic shut-down circuit,” SIA said, although it was unclear whether such a devise was feasible. There’s also a risk of out-of-band (OOB) emissions from unlicensed devices because FSS earth stations in the 3700-4200 MHz band are very sensitive, SIA said: “Because the conventional C-band is the primary source of video downlinks in the [U.S.], interference in the band would be devastating, impairing the distribution of news, weather, sports” and other programming “on which life and safety can depend.”