SIGNAL STRENGTH TRUMPS MODULATION AND RECEIVER IN DTV QUALITY

“I sometimes tell people that ‘it’s the power, stupid,'” said ATSC Exec. Dir. Mark Richer, mirroring President Clinton’s reelection mantra. “People have been trying to blame the [8-VSB] standard, but most things come down to power and signal.” Task force did consider studying alternative modulation standard, COFDM, but dropped idea rather quickly after determining it provided no significant reception advantage, Richer said.

“Indoor reception of DTV with set-top antennas may be… available only to a minority of viewers in some television markets,” task force said, blaming problem mainly on weak signal. It said advances in DTV receivers could improve that, but “expectations of widespread indoor reception are inconsistent with the DTV planning factors and link budget variables.” Report said indoor reception could be improved, for example, by cutting DTV’s maximum data rate.

Key factor is amount of signal that arrives at receiver from transmitter, called link margin, report said, following year-long study. Consumers have “enormous influence” on margin, it said, through factors such as antenna selection, location, height, orientation. Antenna makers already have begun cooperating on “Smart Antenna” interface that would help antenna and DTV set work together, as well as electronically-steered antennas and other technologies that would improve signal arriving at DTV set.

Both set makers and transmitter makers are doing generally adequate job with their portions of transmission links, report said. It concluded that transmitters “contribute minimally” to link budget degradation, and “no significant DTV receiver innovations are needed” to avoid undue interference. It said some receivers didn’t comply fully with FCC planning factors, but said they generally were improving rapidly.

“Unrealistic expectations” about DTV reception anywhere NTSC could be received are big problem, task force said. NTSC reception can be considered “acceptable” at signal levels below where DTV can function, it said, even though consumers wouldn’t be willing watch such TV pictures, causing “perceived failure” of DTV to replicate NTSC coverage. Richer said he was convinced that DTV already could be received anywhere there was truly acceptable NTSC reception.

FCC’s DTV planning factors don’t do adequate job of predicting who would be able to receive DTV signal, task force said. Richer said industry needed to develop new “metrics” for predicting reception.

Despite direct relation of power to DTV reception, Richer said he wasn’t aware of any broadcasters’ planning to seek DTV power increase, although some might become interested in on- channel repeaters (OCRs). OCRs (CD April 12/00 p8, Sept 4/98 p3) are low-power cellular-like transmitters that repeat TV station’s signal on same channel that station broadcasts on, making signal receivable in areas where main signal is blocked. Richer said several transmitter manufacturers were working on OCRs, but it wasn’t clear when announcement would be made. OCRs may require some FCC approval, but Richer said it probably would not be major proceeding. Key question, he said, is whether broadcast business model would justify cost of installing additional transmitters.

Broadcasters also should look to transmission improvements, rather than receiver upgrades, if they're interested in mobile DTV reception, task force said. It said fully mobile reception would be “major challenge” because of multipath and signal strength problems, and even reception at walking speeds would be difficult for several reasons, including antenna design and height. It said portable reception would be possible over only “limited portion” of DTV service area.

Other findings in report included: (1) Signal strength might have to be increased by as much as 47 dB to make indoor reception as robust as current outdoor reception. Richer called that “worst case” scenario. (2) Signal strength at ground level is 12-16 dB lower than on 30’ antenna, height used in original DTV service area planning. Study included results showing that DTV reception capability fell from 75% of all sites with 30’ antenna, to 32% of all indoor sites. (3) ATSC should study including more robust audio mode in DTV standard. (4) Lack of advertising standardization is confusing consumers in selection of antenna.

ATSC, meanwhile, said it received 10 responses to its request for proposals for ATSC transmission standard enhancements. Responses are to be evaluated on accelerated schedule, Richer said, with new specifications to be drafted by end of year. Responses came from ADC Telecom, Broadcom, Conexant, Merrill Weiss Group, Patel-Limberg-McDonald, NxtWave, Oren Semiconductor, Philips, Sarnoff, Zenith.