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03.09

Public Safety Benefits from DTV Transition

By George McClure

The growth of high-density commercial wireless systems has increased harmful interference to 700-800 MHz public safety communication systems (such as police, fire, and emergency rescue). To cope with this, the Federal Communications Commission in July 2004 adopted a comprehensive plan to reconfigure the band, using digital television (DTV) to increase both capacity and quality. The move from traditional analog signals was mandated in the Digital Television Transition and Public Safety Act of 2005.

More spectrum during transition

The FCC allocated another 6 MHz of spectrum to each TV broadcaster, so they could vacate the initial spectrum for public safety use and begin digital broadcasting. Digital signals are more efficient users of spectrum than analog signals. The new digital channels can accommodate High Definition TV (HDTV), Enhanced Definition TV (EDTV) and Standard Definition TV (SDTV) plus other services as well. A 6 MHz channel can accommodate a data rate of 19.4 Mb/s which, with audio data compression and Vestigial Sideband (VSB) modulation for the video signal, can provide the viewer with multiple ghost-free program channels, as many as eight in one designated radio frequency (RF) channel in some cable systems. HDTV requires more bandwidth, so fewer added SDTV programs can be provided on an RF channel transmitting a HDTV signal.

Public safety services benefit

During the transition period, public safety services began to use TV channels 63-64 (764-776 MHz) and 68-69 (794-806 MHz) for two-way radio communications. After the end of the transition period, TV channels 60-62 (746-764 MHz) and 65-67 (776-794 MHz) were opened to use by new commercial wireless services, with licenses awarded by government auction. After full DTV conversion, TV broadcasters will be required to give up one of the two channels (they have used both during the transition period).

The initial transition envisioned ending analog broadcasting generally in 2006, but there were delays. Sprint-Nextel was occupying some of the spectrum required for public safety services, and had to vacate first. The transition period was rescheduled to end on 17 February 2009, but there have been problems [www.fcc.gov/mb/policy/dtv/].

DTV is a new type of broadcasting technology that transforms television as we now know it. DTV technology will allow broadcasters to offer television with movie-quality picture and CD-quality sound, along with a variety of other enhancements. DTV technology can also be used to transmit large amounts of other data into the home, which may be accessible by using your computer or television set.

Digital tuners or converter boxes

To prepare for DTV, the FCC required that all television receivers imported into the U.S. or shipped in interstate commerce as of March 1, 2007, must have a digital tuner. While cable and satellite subscribers will have the channel conversions done by their services, and can therefore continue to use analog tuner TVs, those receiving signals over the air must have a digital-to-analog converter box to receive DTV. The National Telecommunications and Information Administration (NTIA) is administering a program to provide requesting citizens up to two coupons, worth $40 each, for the purchase of converter boxes. The coupons expire 90 days after mailing [www.fcc.gov/cgb/consumerfacts/digitaltv.html].

The $1.34 billion budget for coupons has run out, and new requests are put on a wait-list, pending expiration of unused coupons issued earlier. There have been several initiatives to delay the complete transition to DTV, but public safety organizations that have invested in new 700 MHz interoperable radio communication systems for first responders — law enforcement, fire, emergency medical and other public-safety applications — opposed any delay that will affect their use of the new systems. Mobile phone wireless carriers paid nearly $20 billion on 700 MHz licenses at a government auction last year and they also oppose any delay.

Wireless broadband to benefit, too

The FCC is working on a plan to re-auction 10 MHz of spectrum in the 700 MHz band as part of an effort to create a national network or a group of regional systems that would provide public-safety and commercial wireless broadband services [www.rcrwireless.com/article/20090112/WIRELESS/901129982/-1/rss01]

About 14 percent of households receive off-air TV signals (the rest are served by cable or satellite systems) [www.tvtechnology.com/article/18732]. These are the users who will require the DTV converter boxes. Some users have already noted that DTV signals are weaker than analog TV signals and may need booster VHF-UHF preamplifiers for satisfactory off-air reception. Industry has responded with an array of DTV accessories including high-gain antennas and antenna rotators.

In early February, out of concern that some of the public were not yet ready for a switch to DTV, Congress passed a bill making the switch from analog to digital TV signals on 17 February voluntary. The hard date under that bill would be 12 June to stop analog broadcasting. President Obama indicated that he would sign the bill.

To dig deeper

1. The status of television stations regarding DTV is found at http://www.fcc.gov/mb/video/dtvstatus.html
    

2. An overview of coding and modulation for DTV transmission is found at http://eeweb.poly.edu/~yao/EE4414/digitalTV_transmission.pdf
    

3. The work of the Advanced Television Systems Committee (ATSC) in developing DTV standards is described at www.atsc.org, where the candidate standard for mobile and handheld digital TV, dated 1 Dec. 2008, is also found.

George McClure is Technology Policy editor for IEEE-USA Today’s Engineer and a member of IEEE-USA's Committee on Transportation and Aerospace policy. Comments on this article may be submitted to todaysengineer@ieee.org.