Spectrum Management
In the United States, the function of spectrum management is shared by the FCC and the National Telecommunication and Information Administration NTIA .Other countries have their own national regulatory bodies charged with similar responsibilities, such as the U.K. Office of Telecommunications (Oftel, www.oftel.org or the Japanese Association of Radio Industries and Businesses ,.
The FCC is responsible for managing use of the RF spectrum by the public, including state and local governments. The NTIA, an agency of the U.S. Department of Commerce, is responsible for managing federal government use of spectrum. The functions in the FCC are divided between the FCC Mass Media Bureau , which regulates activities of TV and radio broadcasters and archives the major decisions concerning digital TV standards; and the Wireless Transport Bureau , which oversees most other aspects of spectrum management, including allocation, licensing, auctions, cellular telephony, paging, public safety, and other private uses. The joint responsibilities of the FCC and NTIA responsibilities are listed here:
Spectrum allocation— Defining the type of use allowed involves determining such categories as fixed, or mobile, exclusive or shared use, governmental, broadcast, and so on. If spectrum is allocated for shared use, then primary users and secondary users must be designated. Both primary and secondary users can transmit in the assigned band, but secondary users must accept interference from primary users, whereas primary users cannot be adversely affected by secondary users.
Assignment rules— Having defined spectrum allocation rules, assignment rules define who gets to use the spectrum and for what period of time. Frequencies are assigned by auctions and automated licensing procedures.
Service rules— Having defined who gets to use the assigned spectrum, rules are defined for its use. For example, rules might govern the maximum transmit power, point-to-multipoint use, two-way or one-way use, and whether the user is compelled to accept interference from others in the band.
Enforcement— Finally, the appropriate bodies must see to it that license holders abide by the service rules.
Assignment rules, services rules, and enforcement are the more administrative functions of spectrum management. Assignment rules govern the conduct of auctions and other methods to convey allocated spectrum to users. Service rules are largely an engineering function to ensure proper use of the assigned spectrum. Enforcement is a policing function to ensure the assigned entities observe service rules. The most controversial function of spectrum management is spectrum allocation.
Contrary to some conventional wisdom, RF spectrum is not infinite. While it is true that technological advances—primarily digital modulation and compression—make more efficient use of spectrum, those same technical advances induce new service providers and consumers to demand more spectrum. New demand makes spectrum allocation a continuing problem.
New requests for bandwidth occur all the time from new entrants that desire to provide new broadband wireless services. For example, in July 1997, Skybridge and Northpoint Technology petitioned the FCC to authorize use of spectrum in the range of 10.7 GHz to 12.7 GHz for new services. The problem was that the frequencies 12.2 GHz to 12.7 GHz were already in use by geostationary satellites, namely direct broadcast satellite. Of course, the direct satellite vendors objected to Skybridge's request.
As a result of the request, a Notice of Proposed Rulemaking (NPRM) was issued in November 1998. In this document, the FCC asked for comments on technical approaches to ensure that the DBS vendors were not impaired and that international agreements would not be violated. Such headaches are the daily fare at the FCC as the organization tries to accommodate new demand from entrepreneurs and established businesses alike.
Spectrum sharing is one technique to accommodate new demand. Spectrum sharing allows two or more license holders to occupy the same frequencies. This is possible if users are geographically dispersed. Therefore, maritime and some land-based transmitters share common spectrum. Otherwise, spectrum use can be coordinated through technical means such as sectorization or antenna discrimination.
Another technique to accommodate new demand is bandclearing, which involves the relocation of users from one spectrum location to another. Usually, the vacated spectrum is lightly used or is used by government administrations. The FCC's Emerging Technology Policy 1992 required that the new user pay the incumbent for the costs of relocation (typically new transmitters and receivers) or somehow protect the incumbent from interference. Parties negotiate these costs themselves. Relocation costs were an important consideration when fixed microwave was relocated to make wave for PCS voice. Bandclearing was also used to create spectrum for cellular by reallocating TV channels 70 through 83 in the 1970s. Similarly, new frequency allocation was provided in the 1980s for DTV in 12.2 GHz to 12.7 GHz.
One upcoming example of bandclearing is the clearing of TV channels 60 to 69 (746 MHz to 806 MHz); very few broadcasters use these channels over the air (they are frequently used for cable TV channels). The first step toward this reallocation of analog TV spectrum was undertaken in July 1997 (FCC 97-245, "Reallocation of Television Channels 60–69, the 746–806 MHz Band"). In that NPRM, the FCC proposed that this spectrum be reallocated before the end of the DTV transition period, now scheduled to end in the year 2006. Under the terms of the NPRM, 36 MHz is to be allocated for public safety use, and the remaining 24 MHz is to be allocated for auction.
The big bonanza of bandclearing will come when all analog TV channels can be cleared when over-the-air TV goes digital. However, for now, all nooks and crannies of RF spectrum are heavily used. This means more sharing and less bandclearing.