On Nov. 14, 2008, the FCC released its controversial “White Spaces” Order, which allows unlicensed TV band radio transmitting devices (TVBDs) to operate in unused broadcast television spectrum (the unused spectrum is referred to as “white spaces” or “white space”).
In an effort to encourage the development of new broadband data and other services, the FCC's White Spaces Order allows for unlicensed fixed and portable TVBDs to be deployed in TV white spaces on an unlicensed basis, subject to numerous technical restrictions designed to protect broadcaster transmissions from RF interference. This advisory provides a high-level explanation of what this means and how unlicensed TV white space usage will work.
Background
The FCC first proposed allowing unlicensed devices to operate in TV white spaces in 2004. During the subsequent debate, television broadcasters and potential new users of the white spaces have sharply divided over whether any interference standards for unlicensed use would adequately protect the transmissions of broadcasters and other existing licensed and unlicensed white space users, such as wireless radio operations in 13 metropolitan areas and unlicensed wireless microphone use.
There was also significant disagreement over whether fixed and/or mobile device use should be allowed within white space spectrum. Incumbent television broadcasters generally opposed mobile services, as mobile can be more likely to cause interference, and that interference can be more difficult to remedy once it occurs.
The FCC's White Spaces Order comes three months in advance of the nation's broadcast digital television transition, set to occur on Feb. 17, 2009. Although white spaces have existed and will continue to exist in both the analog and digital broadcast spectrum band allocations, the locations of the TV white spaces—both geographically and along the radio spectrum—will change following the transition.
Currently, TV stations broadcast in analog over designated channels 2 to 69 in four bands of frequencies: 54-72 MHz, 76-88 MHz, 174-216 MHz and 470-806 MHz. Due to the increased spectrum efficiency of digital broadcasting, following the digital transition all television stations will operate only on newly designated digital channels 2-51 in five spectrum bands: 54-60 MHz, 76-88 MHz, 174-216 MHz, 470-608 MHz, and 614-698 MHz.
Spectrum in the 698-806 MHz band was set aside for public safety or auctioned by the FCC for licensed wireless services, most recently in Auction 73. Accordingly, the new rules allowing white space use will go into effect along with the new vacant geographic areas and channel spaces that will exist in the reorganized digital TV broadcast frequency bands starting in 2009. Indeed, the marketing of white space wireless devices is prohibited until Feb 18, 2009.
New rules for white space use
Unlicensed use only. The FCC approved the operation of both fixed and portable devices in the white space spectrum on an unlicensed basis. Despite the advocacy of television broadcasters, the cable industry and certain wireless industry groups, the FCC refused to provide for licensed use of any white space spectrum.
Several wireless companies had pressed for some licensed use of the bands, arguing that the propagation characteristics of TV frequencies are well suited for wireless backhaul options, which at present are either in short supply or too expensive. While the FCC plans to issue a Notice of Inquiry on the issue of increased power over white spaces in rural areas, licensed use of the spectrum is not expected to be included in that proceeding.
Fixed use. The new rules allow fixed devices to operate on any channel between 2 to 51, except for channels 3, 4 and 37. In addition, fixed devices will be excluded from operating on channels 14 through 20 in certain geographic areas where private and commercial wireless facilities are licensed to operate. The FCC is prohibiting operation of fixed devices on channels 3 and 4 in order to prevent direct pick-up interference when poorly shielded TVs are connected to VCRs, DVRs and cable set-top boxes that output on channels 3 or 4.
Fixed devices may operate at power levels of up to 4 watts EIRP. The most likely fixed device use of the white space spectrum in the near term is expected to be by wireless Internet Service Providers (WISPs) to extend the service range of their operations. Fixed use is considered particularly likely in rural areas where the greatest quantity of white space spectrum is available.
Portable use. Portable wireless devices will be allowed to operate on an unlicensed basis in the higher portion of this band only, from channels 21 to 51, with the exception of channel 37. Due to their greater risk of interference to licensed services, the power level of portable devices will be limited to up to 100 milliwatts EIRP, although the maximum power limit will be lowered if the antenna gain of the portable device exceeds 0 dBi.
The FCC refused the cable industry's request for lower power limits on portable devices due to concerns about direct pick-up interference to cable-ready receivers. The commission did note that it would closely monitor the situation for any reports of interference, and that it expects new device equipment suppliers to assist consumers in correcting any direct pick-up interference. Possible portable device uses of white space spectrum include wireless laptop computer Internet connections in homes or business locations, similar to the current use of unlicensed Wi-Fi spectrum in the 2.4 GHz band.
Technical rules. In addition to the power level and emission limits adopted, the FCC imposed certain unique technical rules designed to ensure that these new fixed and portable wireless devices operating in the white spaces do not cause harmful interference.
First, in most cases, devices will have to include geolocation technology, which uses technologies such as global positioning system (GPS) to match a white space device's location against a preexisting database of spectrum users. All unlicensed devices must first access the database to determine permitted channels before operating.
In addition, most fixed and portable devices must register certain information concerning the location of their operations in the database. Used in tandem, the geolocation and database access features should allow fixed and portable white space devices to detect whether they are in danger of causing interference to incumbent users and redirect their transmissions accordingly, possibly ceasing transmissions when necessary.
Finally, the FCC will also require new unlicensed white space transmitters to include spectrum-sensing technology allowing them to detect the presence of protected signals operating in their vicinity.
Exception to geolocation requirement. During the white spaces rulemaking proceeding, many software and device manufacturers argued that spectrum-sensing technology alone was sufficient to ensure white space transmitting devices would not cause interference to incumbent TV band users. They argued that the proposed geolocation and database system approaches were unnecessarily burdensome and would make deployment of unlicensed white space wireless facilities more expensive and less desirable.
While the FCC generally rejected these arguments, it did adopt an exception to the device geolocation capability requirement. Specifically, the FCC will permit the use of devices that rely solely on spectrum-sensing technology to avoid causing interference, as long as the manufacturer undergoes a more rigorous equipment certification process than will be required for devices that incorporate the geolocation capability. The enhanced certification process will require direct testing by FCC laboratories, notice and comment on those test results by interested parties, and equipment approval that can only be issued by majority vote of the FCC commissioners.
Notice of Inquiry
In the White Spaces Order, the FCC stated that it will issue a Notice of Inquiry to examine whether to permit higher power transmissions in white space spectrum in rural areas than the new rules allow. In separate statements, Commissioners Robert McDowell and Jonathan Adelstein both supported this concept and expressed belief that even unlicensed high power white spaces operations in rural areas could still lead to the development of effective wireless backhaul services.
Commissioner Deborah Tate went further in her support for wireless backhaul and dissented from the decision to allow unlicensed spectrum available in all TV bands. Commissioner Tate pointed out that some estimates of white space availability show that even a smaller unlicensed allocation of channels 31-51 would have made available 24 noncontiguous MHz in urban areas and up to 100 MHz in rural areas for unlicensed broadband—more than enough with room to spare for designated backhaul uses.