Spectrum friction

Wireless use of vacant TV white space is on the horizon. The principal remaining issues include whether portable devices will be authorized in white space and exactly when the roll-out will begin.


The idea of white-space use (of the vacant spectrum that shows up as white areas on a map of channel usage) first emerged in the mid-1980s, when the FCC allocated the remaining spectrum under 1000MHz. In those purely analog TV days, the need to separate stations on the same and adjacent channels, and the complex spacing requirements for UHF stations, resulted in every market having dozens of empty channels. Signals in the TV band propagate well, so wireless companies eyed the white-space channels with increasing fervor as frequency congestion worsened through the 1990s.

In late 2002, the FCC issued a notice of inquiry on the feasibility of letting unlicensed devices similar to Wi-Fi operate in the white-space spectrum. A notice of proposed rulemaking followed in May 2004. Even then, the concept was still just a rough outline, but it focused on allowing both fixed systems, for delivering broadband to homes and businesses, and portable devices, such as laptops and PDAs.

Broadcasters opposed the inquiry because they were concerned that wireless devices would interfere with TV reception. In response, the rulemaking offered three alternate means to keep wireless devices away from the channels being used for TV in a given area. First, the device could determine its location and consult a database to find out what frequencies are safe to use there. Second, a central transmitter could send out a control signal that notifies devices of the locally safe frequencies. Third, each unlicensed device could monitor for TV signals and automatically avoid the channels on which it found any.

Broadcasters were not happy with any of these proposals. Analog television is highly sensitive to interference — even from weak signals — and none of the proposed methods kept wireless devices far enough away from TV sets on the same channel.

IEEE weighs in

The IEEE proposed that base stations, operated by service providers, be professionally installed, taking into account locally used TV channels. Subscribers could buy and install their own equipment, but a subscriber station could not operate until it first picked up a base station signal, which carries a list of locally suitable channels. Moreover, all of the devices on the system would continuously monitor for TV activity on all channels, share this information and mutually lock out frequencies that were detected and confirmed as TV activity.

Responding to Congress

In response to pressure from Congress, in 2006, the FCC adopted rules that authorize wireless operations in TV white spaces effective Feb. 18, 2009, after the DTV transition. Today, the FCC only permits fixed use, in accordance with the IEEE recommendation.

The commission also prohibited low-power devices from operating on TV Channel 37 (to protect the radio astronomy services) and Channels 52-69 (to protect the wireless and public safety services authorized to operate on these channels).

Many details remain open. To further complicate matters, there are four bills pending in Congress that would require the FCC to authorize both fixed and portable devices.

Harry C. Martin is a past president of the Federal Communications Bar Association and a member of Fletcher, Heald and Hildreth PLC.


June 1 is the deadline for TV stations in Michigan and Ohio to file their 2007 biennial ownership reports.

TV, Class A and LPTV stations that produce their own programming in the following states must place their annual EEO reports in their public files by June 1: Arizona, the District of Columbia, Idaho, Maryland, Michigan, Nevada, New Mexico, Ohio, Utah, Virginia, West Virginia and Wyoming.

Send questions and comments to:harry.martin@penton.com