On November 30, NAB along with MSTV filed Comments on an FCC proposal to allow unlicensed devices to operate on a noninterference basis using vacant TV channels (TV white spaces.) The Commission's proposals is intended to foster the development of new and innovative types of unlicensed broadband devices and services for businesses and consumers by using broadcast television spectrum at locations where the spectrum is not in use by television stations. The FCC also stated in their proposal that unlicensed operations in the TV bands could benefit wireless Internet service customers by extending the service range of current wireless Internet service providers' (WISPs) existing operations, particularly in rural and underserved areas.

In our comments, NAB and MSTV urged the Commission to, at a minimum, defer the introduction of any new shared uses in broadcast television spectrum until after the conclusion of the digital transition. The interference caused by unlicensed devices could result in the DTV service being branded as unreliable. Consumers would then be less inclined to adopt DTV technology thus slowing the transition. Also, during the DTV channel election and repacking process, there will likely be very few white spaces available. The environment in which unlicensed devices would operate would be crowded, shifting and uncertain, especially in metropolitan areas. Finally we told the Commission that, if after completion of the transition the Commission still sees a need for overlay operation in the television broadcast spectrum, it should design, articulate, test and solicit public comment on a new proposal with well-defined and predictable parameters for the protection of the public's free, over-the-air television service.

As part of the comments, we filed data from two studies commissioned by MSTV that were designed to assess the impact of the FCC's proposal on NTSC and DTV service.

The first study was conducted by the Communications Research Center in Ottawa Canada. It was a laboratory evaluation of interference to both analog and digital broadcast television caused by a portable unlicensed device operating in close proximity of television receivers. The test used an NTSC signal transmitted on a low UHF channel, a DTV signal transmitted on a high UHF channel and a simulated "unlicensed device" with a "noise-like" emission of another broadcast television channel. The power of the unlicensed device emission was conservatively adjusted so that the power into the broadcast channels were at least 3 dB below the FCC limit of 200 µV/m (46 dBµV/m) within a 120 kHz bandwidth measured at a distance of 3 meters. Measurements were taken using bandwidths of 0.43, 1.3, and 5.6 MHz for the unlicensed-device and the unlicensed device antenna was separated from the television receivers' antenna by distances varying from 3 to 24 meters-either line-of-sight or with an intervening wall constructed of drywall plaster board with steel studs (typical of apartment or office walls). Three NTSC receivers and five DTV receivers were used for the tests.

It was found that the emission from the unlicensed device "desensitized both the NTSC and DTV receivers i.e. the interference caused the AGC circuit in the receivers to reduce its tuner gain thus, impairing its reception of weak TV signals on all channels. For example, Figure 1 shows the desensitization of DTV receivers by out-of-band interference from a single unlicensed device with a wideband (5.6 MHz) emission into the TV channel.

Figure 1

TechWare Inc. of Chantilly, Virginia performed the second study, which focused on the availability of vacant spectrum within the TV bands for use by unlicensed fixed installations base stations. The study used the FCC broadcast propagation curves (as proposed by the FCC) to compute the field strengths for both the desired and the undesired signals in order to identify the areas where these unlicensed transmitters could be placed. The study modeled a grid of fixed unlicensed transmitters representing a network of unlicensed devices that was superimposed at different geographic regions within the U.S. to determine the number of vacant channels available at these locations. The study used four watts ERP for the unlicensed transmitter with an omni-directional antenna placed at every intersection of a 30-second grid (latitude and longitude) across major populated regions of the U.S. The unlicensed transmitter height was set at a modest 30 meters (HAAT) and the number of available channels was determined for each 30-second grid (i.e. approximately one square mile area). Color-coded maps were generated showing the number of available vacant channels in various regions of the country. The TechWare analysis generally concluded that, using the FCC proposed parameters for protecting TV reception, little if any TV channels are available for unlicensed device operation within the broadcast TV band in the major metropolitan areas of the U.S. Television channels are only available in the less populated and rural areas of the country. For example, Figure 2 depicts the availability of unlicensed devices channels in the northeast region of the U.S.

For more details on these two studies see the comments filed by NAB and MSTV in ET Docket 04-186, available on the FCC ECFS system at http://gullfoss2.fcc.gov/prod/ecfs/comsrch_v2.cgi. Type 04-186 in the "Proceeding" box and 11/30/2004 in the "Date Submitted" box and click the "Retrieve Document List" button at the bottom of the screen. Reply comments in this docket are due on December 30, 2004.

Figure 2

Reminder: January 1, 2005 Effective Date for Implementation
of Updated ATSC Standard

In 2002, a change to ATSC standard A/53 was adopted which prohibits the use of MPEG-2 Packet Identifiers (PID) in the range below 0x0030 effective January 1, 2005. As of that date using these values will be prohibited by the FCC rules (since compliance with A/53C is now required by the Rules) and broadcasters must not use PID values below 0x0030. Be advised that field experience with some receivers indicates that changes in PID values and/or program numbers can "confuse" some DTV sets, resulting in consumer calls. Don't forget to insure that all equipment (e.g., video encoders, multiplexers and PSIP generator) is using the same values for each component when you make the change. Broadcasters can make this change any time before January 1, 2005.