How the Networks Are Taming the HD Bandwidth Hog

[Gregg Lengling]

By Peter J. Brown
Broadcasting & Cable
11/18/2002
 
   Broadcasters have always loved satellites, but they love leaner satellite budgets even more. And that's why the rollout of HDTV programming, in all its bandwidth-hog glory, is providing a challenge.

Edward Caleca, senior vice president of PBS technology and operations, says that PBS has sliced and diced its satellite transponders more aggressively to manage HDTV.

"We are probably the most aggressive in the industry when it comes to HDTV distribution by putting a pair of HDTV channels on a transponder," he says. That aggressiveness takes some clever thinking, Caleca says. PBS uses the 19.4 Mbps stream as native 19.4, not as 45 Mbps, allowing it to get two HDTV signals on a 36-MHz transponder.

For CBS sports
At CBS, the pressure is on to expand the weekly HDTV sports-programming lineup, while keeping HDTV production costs as low as possible.

"When it comes to college football, there is not a lot of fiber available, especially in the Southeast Conference," says Brent Stranathan, vice president of broadcast distribution at CBS (CBS broadcasts an SEC football game in HD each week). "So we are saving money by multiplexing our HDTV and SDTV signals together on a single 36 MHz transponder, rather than bringing back two separate satellite feeds off two separate transponders."

CBS maintains 10 C-Band and two Ku-Band transponders. The C-Band capacity is located on Loral Skynet's Telstar 6, with one backup C-Band transponder on Telstar 4. Uplinking for CBS on the East Coast is performed by Ascent Media, Stamford, Conn.

On the West Coast, CBS operates its own satellite facility in Los Angeles. Motorola's DigiCipher II Plus is used for digital compression of SDTV network feeds and a combination of Motorola and Aastra/Harris for HDTV.

"Wherever possible, we are taking advantage of the synergies flowing out of the Viacom merger and using CBS satellite capacity on Loral Skynet's Telstar 6 to distribute syndicated content from King World and Paramount, for example," he says. "We hope to be able to move a majority of this syndicated traffic, which goes out on the equivalent of 21/2 C-Band transponders today, to a single C-Band transponder in the near future by deploying a store-and-forward IP multicast system."

"With advanced modulation techniques, we may see this throughput improve to two feeds per transponder, and where we are now sending our SDTV feeds at 15 Mbps per channel on a 36- MHz transponder today, we think we can reduce that to 9 or 10 Mbps per channel, allowing four channels rather than three on the same transponder," says Stranathan.

ABC scripted shows
At ABC, the transition of SDTV from analog to digital is expected to be finished in 2005, according to Richard P. Wolf, vice president of telecommunications at ABC Broadcast Operations and Engineering. Currently, ABC distributes all its scripted dramas, comedies and theatrical movies in 720p HD.

"One of the advantages of the progressive [720 p] format is its ability to endure aggressive compression schemes enabling efficient transponder loading," says Wolf. "We are also actively pursuing more aggressive modulation such as 8-PSK with the goal of achieving transponder throughput in excess of 60 Mbps on a 36 MHz transponder."

Wolf notes that a leap from QPSK modulation to 8-PSK requires careful analysis, planning and evaluation. "If we have a satellite downlink which is a good distance away from the station in question, for example, getting this larger block of bandwidth to a station where co-location does not exist can be a big problem," Wolf says.
To the Rescue
To handle HDTV's larger bandwidths, cable and broadcast networks are looking for the next generation of video compression to squeeze more HD channels through their satellite transponders. They may not have to wait long.

The industry is hard at work on the Advanced Video Compression (AVC) standard, or H.264. If all goes well, the standard should be set next year, and gear should be available in 2004. Making AVC backwards-compatible with MPEG-2 should help speed its adoption. Distributors can implement it with the satellite network infrastructure now in place.

Don Shulsinger, executive vice president at Sand Video, which has been engaged in developing the technology for a broad range of video applications, says there has been a lot of buzz around the standard, with good reason. "How often do you encounter a new standard that triples the performance of the old standard with their existing network infrastructure."

Bob Zitter, senior vice president for technology operations at HBO Time Warner Entertainment, says AVC is a key to handling HDTV more affordably. "MPEG-4 has many bells and whistles, but MPEG-4's multimedia attributes are simply not applicable to our video-distribution requirements."—