Japan's digital TV standard will use MPEG-2 audio encoding.........
techweb.cmp.com
Posted: 3:00 p.m. EST, 2/12/98
Japan sets broadcast-satellite digital-TV
standards
By Yoshiko Hara
TOKYO -- Japan has nailed down standards for the delivery of digital TV
via broadcast satellite,specifying six video formats with MPEG-2
Advanced Audio Coding (AAC). Service is expected to start in Japan
around the year 2000.
The Telecommunication Technology Council (TTC), an advisory body for
the Ministry of Posts and Telecommunications (MPT) submitted the final
recommendation for broadcast-satellite (BS) digital-TV broadcasting
earlier this week.
The video formats to be used are: 1,080 vertical lines x 1,920 pixels (16:9)
at both 60i and 60p picture rate; 720 lines x 1,280 pixels (16:9) at 60p;
and 480 lines x 720 pixels at 60i (both 16:9 and 4:3) and 60p (16:9).
Unlike the Advanced Television System Committee (ATSC) specifications
in the United States, 30p and 24p picture rates are not included, thus
reducing the number of formats.
Of these six formats, 720p and 1,080p were included with reservations,
because they haven't yet been put through a field experiment. The 1,080p
format must also be tested to see whether a single transponder can send
two 1,080p channels.
An MPT official, Masato Iwasaki, said that "720p has not been verified in
field experiments. If it is proved to be no problem through field
experiments, it will be officially added."
In satellite broadcasting, one transponder sends two HDTV channels.
Iwasaki, deputy director of the Digital Broadcasting System Development
Division at MPT's Broadcasting Bureau, said, "To send two 1,080p
channels with one transponder is difficult unless compression technology
makes further progress. It is expected to take several years. But these
formats are Japan's BS digital-TV specifications that broadcasters can
choose."
MPEG-2 Audio (AAC) became an ISO/IEC standard last April. "We
believe that Japan is the first to adopt MPEG-2 Audio (AAC)," said
Iwasaki. It has no compatibility with current MPEG-2 Audio (backward
compatible), but has twofold compression efficiency. With MPEG-2 Audio
(AAC), CD-quality stereo sound can be transmitted at 128 kbits/second.
Based on the previously agreed presumption that BS digital broadcasting
will be devoted mainly to HDTV programs, the council defined the
specifications so that two HDTV channels can be transmitted by one
satellite transponder for the first time ever.
To provide services such as data broadcasting in addition to HDTV
programs, a wider bandwidth is desirable. The recommendation listed three
possible bandwidths--27 MHz, the same as current satellite broadcasting;
33 MHz and 34.5 MHz. Even with the 27-MHz width, the rate will be 39
Mbits/s, allowing two channels of 18-Mbit/s HDTV programs. "For better
picture quality, 34.5-MHz width is desirable," said Iwasaki of MPT. If
34.5 MHz width can be used, the maximum bit rate reaches 51 Mbits/s
with TC8PSK (Trellis-coding eight-phase shift keying), a high density
transmission coding. Japan will negotiate at the International
Telecommunication Union to expand the assigned bandwidth.
Two broadcasters in Japan--DirecTV and PerfecTV--already deliver
digital-satellite TV-broadcasting service. But these services use
communication satellites and send 480i standard-definition programs. |
