C-Cube's encoder chip competition for HDTV. LU/IBM, Mitsubishi.............
tvbroadcast.com
Gearing Up For HDTV
By Joseph Maar
NEW YORK--Just in time for the rollout of digital television in November, new high-definition technology that will compress the digital signal for transmission between remote locations, networks, and their affiliates should be arriving at major broadcast studios in the next few weeks. According to industry insiders, each of the four commercial networks and PBS are at very different stages in this process. By early August, some had yet to choose a vendor for their signal compression needs. Meanwhile, at the local level questions remain about what exactly this new equipment is, and how it will affect day-to-day operations.
Although home viewers will receive a standard ATSC signal (running at 19.4 Mbps), most networks will be sending higher data-rates to their affiliates. "That increased bandwidth will increase the amount of resolution maintained," said Tim Phillips, president of Dallas/Fort Worth based Global Broadcasting Corporation (GBC); whose company provides transmission services for "occasional-use" stations and production facilities.
Experts often refer to this higher rate transmission as a "contribution level" signal, delivering more than twice the data-rate of ATSC. Each of the four major commercial networks says an initial data-rate of 45 Mbps is likely.
"The (ATSC) system was not designed to be decompressed and recompressed, especially with new information," commented Tom Hankinson, director of advanced TV technology for ABC-Owned Stations. "It's doable, but the results are not tremendous. The higher data rate--meaning less compression--gives local stations a higher quality signal to work with in adding their own content; whether it's superimposing a bug or being able to insert commercials, which can't be done well in the compressed domain."
Phillips added that the method used to move programming "must allow the signal to be encoded and decoded three or four times without picture loss and must be fully editable and keyableÉ via normal production systems. Contribution levels will be used for both the link from network-to-affiliate as well as from a remote truck to master control."
Charting their own course, PBS confirmed they plan to originate their ATSC signal from the network's master control. Insiders speculate that since PBS neither runs regional, inter-program commercials nor has the same production demands, originating an ATSC signal from the network is a viable option for their system.
The desire to send a compressed signal to affiliates stems from the high cost of transmitting uncompressed HDTV (1.5 Gbps). "A 1.5 gigabit stream [uses] a lot of bandwidth," said Phillips. "One uncompressed, high definition signal is equivalent to 22,500 simultaneous telephone calls, while a digital NTSC signal is around 2,100 phone calls."
He compared this to the networks' planned 45 Mbps contribution level HDTV signal, "It's equivalent to only 672 phone calls, about a third of uncompressed NTSC."
In order to move 1.5 gigabits of information through a 45 Mb link and then back to 1.5 Gb at the other end, networks will use a "codec." "Codec is really a shorthand term for encoder and decoder," said John Mailhot, director of engineering for Lucent Digital Video. "The idea is you have an encoder that takes a video signal and compresses it down to the digital signal you're going to carryÉ and then at the other end you decode it back into a video signal." (Lucent's HDTV encoder is being marketed by Harris Broadcast under the brand name FlexiCoder).
Stations who carry HDTV must have at least one decoder that matches the type used by their network. In general, the networks have been reluctant to say which vendor's codecs they plan to purchase. However, a consortium of Tektronix-Grass Valley-Mitsubishi recently announced they will be delivering their second generation codec MH1100 to CBS for this fall HDTV kickoff. ABC, for its part, has placed a substantial order for Tiernan signal processing equipment (see August 1998 TVB "News"). And in another recent announcement, Fox plans to provide a DS3 fiber line--as opposed to satellite--to their five or six affiliates using NDS' E5810 high definition codecs.
Industry and network insiders say that even though vendors are adhering to an MPEG standard, there is no initial guarantee different manufacturers' units will talk to each other. Unlike ATSC, there is no mandated standard for contribution level signals and the equipment is so new that vendors haven't had time for compatibility testing.
Manufacturers known or rumored to be working on contribution level HDTV codecs include Lucent Digital Video, the Tektronix/Mitsubishi collaboration, Scientific Atlanta, Snell & Wilcox, Global Presence, General Instrument, Tiernan Communications, NDS Americas, GTE, NORTEL, and Alcatel.
Depending on the level of equipment processing capability, vendors say the price range for an encoder is $200,000-$300,000. On the decoder side, local stations will be using units that range from $10,000 to $100,000--depending on resolution capabilities. In addition, networks will likely purchase a pair of these units for live mobile broadcasts.
Most of the contribution codecs available today are first-generation units. According to Mitsubishi Vice President Frank Benna and Tektronix Applications Engineering Manager Bruce Lane, an exception to this is their newly available encoder model MH1100E.
"Mitsubishi is the only company that is selling a second-generation device, everyone else is on their first generation," said Lane. "We've seen, between our first and second generation encoder, a 20-25 percent efficiency (increase) in encoding. What we've been able to do is run the second-generation encoder at a 20 percent less data-rate and have the same picture quality; or run the same data-rate with better picture quality."
Some of the contribution codecs available today are ATSC-compliant units that vendors are modifying to accommodate a 45 Mbps transfer rate. In the case of the Mitsubishi/Tektronix unit, engineers have designed their device for even higher data rates from the beginning. "It is capable of up to 100 Mbps," commented Lane, "so you can choose to use the (codec) at 66 Mbps over a satellite link and at 44 Mbps over a DS3 link."
A future resting point for contribution level transmissions is likely to be greater than 45 Mbps. "Our overall goal is to get up to 68 Mbps at some point," said ABC's Hankinson, "because that provides a higher level of quality and more efficient use of the transponder spectrum."
"If you use QPSK modems (capable of running up to 45 Mbps) you can do 45 Mbps easily and they're pretty widely available," added Lucent's Mailhot. "However, if you use 8-PSK modems (capable of running above 45 Mbps) they're a little bit newer to the market andÉ you need better downlinks."
Mailhot also said that the existing infrastructure at the station plays a role in how easily they can adopt a higher rate. "ABC has more uniform downlinks at all their affiliates," he commented. "Every affiliate has roughly the same dish size, the same LNB and it's all engineered about the sameÉ so they can actually engineer a transition to get 68 or 70 Mbps out of their link. CBS has a lot more variety at their affiliates [as to] what the downlinks are like and so they can't as easily [reconfigure their infrastructure] so that all affiliates are going to be able to receive a 68 Mbps signal."
CBS thinks there are many other advantages to using a 45 Mbps system. "CBS cites about eight reasons why they want to use 45 Mbps," Mailhot continued, "which have to do with things like: when the earth station is not located at the studio, then you need to downlink from the satellite and transmit the signal back to the studio. [The] microwave modems you can buy also do 45 Mbps; so you can have a digital downlink, stay digital, and just send that through a 45 Mbps signal back to the studio."
This is not to say that higher rates are not possible today, just more difficult to attain. "The hardware that lets you do higher than 45 Mbps is not as available," he added. "There are people making the devices, but they're not nearly as field tried as the 45 Mbps units."
In addition, GBC's Phillips commented, "The building block for high-speed telephone company circuits is 45 Mbps. There are 45 Mbps channels throughout the United States (including fiber, coax, digital microwave and satellite)."
However, for internal production the networks will likely stay uncompressed or use relatively loss-less, "mezzanine level" compression. ABC's Hankinson describes "mezzanine" as a light level of compression that will preserve a facility's present routing structure.
"It would allow stations at either 360 Mbps or 270 Mbps to send data around their plants though their existing routing infrastructure," he said. However he adds that there are such small "islands of HDTV" among the owned stations that they are not considering mezzanine compression at this time.
At the network level, NBC vice-president of technology Peter Smith commented, "Within production facilities, a high bit rate (gentle compression) mezzanine level has been proposed to fit signals into existing digital paths while maintaining the highest quality to ensure that the signal remains virtually transparent through the process."
One possible example of mezzanine compression would be to interconnect different production facilities in the same city over a fiber line.
For many local or regional broadcasters wanting to do a live, high definition production of their own, the price of purchasing contribution level encoders and additional decoders is likely prohibitive--particularly for only one or two productions. Global Broadcasting offers a boon to those wanting to do a live, HDTV program or demonstration.
Instead of having to purchase compression equipment, GBC's service includes contribution level codecs, satellite modems and the expertise needed for sending a 45 Mbps signal from the production location to master control, the transmitter and/or any viewing sites. "We're an occasional-use service provider," said GBC's Phillips.
"To help local affiliates launch HDTV," he commented, "we have recently provided backhaul for baseball telecasts, concerts, local affiliates, and STLs." This month alone [August], they're working on two HDTV football telecasts.
One key advantage to a production service is not getting saddled with technology that's out-of-date before you open the box or that doesn't work well in with other gear. One insider who preferred not to be identified commented, "The contribution level infrastructure is going to have compatibility issues in the early yearsÉ and there's going to be a lot of gray hair before the year is out."
For more information, contact Global Broadcasting Corporation (GBC) at (972) 618-4524, Lucent Digital Video (Harris FlexiCoder) at (800) 288-1618, and Tektronix-Grass Valley-Mitsubishi at (800) 547-8949 (On menu press 1 and then press 2).
|
