Broadcast TV Spectrum Efficiency Gains Not Seen in Advanced Compression or DTS
Advances in audio-visual compression technology and the advent of distributed transmission systems will not help the FCC reclaim spectrum from the TV band without significant hurdles, such as a second major DTV transition, executives from Fox and CBS said at an FCC engineering forum on the TV band Friday. HDTV sets and DTV converter boxes receive MPEG-2 encoded signals, and no further gains in MPEG-2 efficiency are anticipated, said Andrew Setos, president of engineering at the Fox Entertainment Group.
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That makes a proposal in the FCC’s broadband plan to have two TV stations share the spectrum of one channel unfeasible economically, because in order to deliver both signals, one would have to be degraded, Setos said. He was speaking on behalf of a group of industry engineers who met earlier Friday to discuss the issue. “There was no disagreement among the group that this is really not viable for two different licensees,” he said. Sports leagues and other content owners would then become reluctant to license their content to broadcasters, who would no longer be able to guarantee high-quality delivery to the consumer, he said. And advertisers would flee to platforms where quality could be assured, he said.
Not even statistical multiplexing, a boon to spectrum efficiency of pay-TV operators, would help much, he said, because with only two channels to share, very little gains can be made. Pay-TV operators have a much larger pool of programming streams to work with on statistical multiplexing, in which bits are allocated where and when they're needed across a range of channels, he said.
To adopt more efficient codecs such as MPEG-4 Part 10 would take 13 years or more and require another transition like the DTV switchover, he said. “Current TV receivers and converter boxes will not be able to display newer coding technology, so a second digital transition plan would be required,” he said. Soon, all TV programming will be broadcast in HD, just as the color TV fully displaced black and white broadcast, so there won’t be any utility in sharing spectrum between SD-only stations, he said.
Cellularizing the broadcast band also won’t achieve any worthwhile spectrum efficiency gains, especially in population centers, said Bob Seidel, executive vice president of engineering and advanced technology at CBS. He was speaking for a separate group of industry engineers that discussed that topic earlier Friday. “Very little improvement in overall spectrum efficiency might be expected in major urban corridors,” he said.
Single frequency networks would fail in this effort because there would be too much interference in areas where reception overlapped, Seidel said. “No spectrum is likely to be recovered in major urban corridors with the current 8-VSB modulation,” he said. OFDM-based systems might be more suited to DTS, he said. Though multiple frequency networks could improve reception, in some cases, building them would require using even more spectrum that is already allocated to the TV band, Seidel said.
After our deadline Friday, presentations on improvements in VHF technology and methodologies for repacking the TV band were scheduled at the forum.