TOKYO Nippon Television Network Corp. (NTV) has developed a prototype of a studio system that can multicast two channels of 720 progressive and 480 progressive signals in a 6-MHz bandwidth.NTV, one of Japan's major commercial broadcasters, will demonstrate the system at the National Association of Broadcasters convention next week (April 19-22) in Las Vegas.
Broadcasters want a second channel, with HDTV as the main channel, said Yoshio Sugimori, executive managing director of NTV, who is in charge of engineering and R&D. He said NTV had succeeded in putting two channels, one of them HDTV, in a 6-MHz bandwidth "with picture quality almost the same as the original."
Using an encoder codeveloped with partner manufacturers, NTV compressed the 720p signal to 12 Mbits/second and 480p signal to 6 Mbits/s to make them fit in the 19.4-Mbit/s transfer rate used for the U.S. terrestrial broadcasting.
The 1080 interlaced, or1080I, has been the format of choice for HDTV broadcasting. But, Sugimori said, a progressive signal "can be compressed more efficiently than an interlaced signal. 1080I's compression efficiency is about 50 percent lower than that of progressive, so multicast of 1080I and one SD channel in a 6-MHz bandwidth is impossible," he said.
NTV has been the most aggressive of Japan's commercial broadcasters in developing digital-TV technology. "We've been pursuing compression technology. The 720p and 480p multicasting employs our encoding algorithm," said Sugimori.
NTV intends to apply the HDTV multicasting to coming DTV broadcasting in Japan. Digital broadcast-satellite broadcasting, which is scheduled to start next year, will use a 22-Mbit/s rate for broadcasters. While that is slightly faster than 19.4 Mbits/s, it's not enough to send multiple channels, including HDTV. "So our technology will work," said Sugimori. Japan's terrestrial TV broadcasting, which is scheduled to start test broadcasting in 2000 and regular broadcasting by 2003, will also use a 6-MHz band.