08.07.2009 10:50 AM
Compressing Space and Money
WASHINGTON
The satellite newsgathering business has greatly evolved since it took off in the 1980s with the development of the first truck-based Ku uplink system, CONUS1, built by (satellite newsgathering) pioneer Hubbard Communications. No longer was a huge C-Band dish needed for uplinks—instead smaller Ku-band dishes were fitted to maneuverable trucks suited for the emerging business of satellite-based mobile newsgathering.

The first Ku SNG trucks were capable of uplinking a single analog signal to an available satellite transponder or channel. The need for multiple signals from a single truck led to the assembly of trucks that were capable of dual-path uplinks, or two signals rather than one. The issue then became the amount of equipment needed for each signal path. The large tube-based amplifiers occupy a great amount of rack space and require a large generator or shore power.

There is also an efficiency bottleneck at the satellite. Each satellite has only a finite number of transponders, which means that during big news events, scheduling segments becomes difficult, and highly desired time slots, such as the top of the hour, are often not available. To tackle this bottleneck, transponders are carefully divided into two segments. Advancements in uplink systems and receivers allow two signals to be oppositely polarized into a single transponder space, creating "half-transponder" channels.

Harmonic introduced its new line of Ellipse MPEG-4 encoders for DSNG at NAB.
Once SNG became a commodity rather than just a competitive resource, broadcasters demanded a lower cost to doing business as well as more availability. The development of digital satellite newsgathering (DSNG) was the beginning of technologies that have both shrunk the amount and size of necessary equipment and trucks, as well as reduced the cost of doing business.

ENCODING & DECODING SIGNALS

The MPEG-2 video compression scheme was the first to be used widely by many broadcasters. By using MPEG compression, DSNG trucks are able to fit as many as eight standard definition signals on a sole transponder. With the advent of high definition, this drastically reduced the signal count due to the bandwidth needed. For many broadcasters like HD news pioneer HDNET, this has worked well.

"All our live transmissions are MPEG-2," said Philip Garvin, COO of Dallas-based HDNet. Because they are usually uplinking a single news event solely for their use, the benefits of MPEG-4 (also called H.264 or AVC) would not make a difference in their current business model.

"There is nothing antiquated about MPEG-2," said Matthew Goldman, vice president of technology for Tandberg Television. He feels that for many broadcasters, using it for both SD and HD makes perfect sense. Broadcasters who have a large deployment of existing MPEG-2 equipment can continue to use it in order to recoup their investment, while those considering new deployments can weigh the benefits of both.

What has held MPEG-4 back for many years in SNG work is its licensing structure, according to Goldman. "AVC has a license fee for usage, where MPEG-2 is hardware-based," he said. Through his work at Tandberg, Goldman helped the compression industry obtain a clarification letter from the MPEG-4 patent holders two years ago that has made SNG's role more defined and subject to a lower cost licensing structure.

"The choice to upgrade from MPEG-2 to MPEG-4 for SNG work should be based on whether there is a need for a lower bitrate for the same image, accessing more services or if a combination of the two is desired," said Goldman. He added that MPEG-2 has a proven track record and low latency that has served broadcasters well for many years.

"Latency is the holy grail in live TV," said Keith Dunford, vice president for Fujitsu's Video Systems Group. "In the compression industry, we achieved very low latency with MPEG-2, but the heavy processing requirements for MPEG-4 brought the latency back up."

Manufacturers like Fujitsu have worked on overcoming this issue with new hardware solutions like single chip encoding and software that maximizes ROI (region of interest) processing. "Now its all about the optimization," Dunford said.

In order to develop a satellite IRD (integrated receiver/decoder) for a broadcast network customer, Dunford's group approached South Dakota-based satellite receiver manufacturer Sencore with a collaborative plan. "Fujitsu came to us with a unique GOP [group of pictures] structure that they wanted us to write our software to, in order to minimize signal latency," said Jack Vickers, product manager for receivers and decoders at Sencore in Sioux Falls, S.D. "We were able to achieve a minimal delay of 300 to 350 milliseconds from the encode to the decode while still maintaining a true Dolby decode."

According to Ken Christensen, Sencore's marketing manager, "the combination of the Fujitsu IP-9500 encoder and software written for the MPEG-4 decoder in our Atlas line of modular receivers now gives minimal latency, making the combination ideal for SNG work." Both the Fujitsu encoder and Sencore IRD can be used in conjunction with other manufacturers' encoders and decoders, but only together do they maximize hardware and software efficiencies to reduce latency through their collaborative efforts.

WHY GO MPEG-4?

According to Goldman, "bandwidth, picture quality and latency are all interrelated and have to be considered along with deployment costs. For SNG work, low bitrate and low latency are most important, but, say for a venue like live sports, the picture quality moves up in the equation." He adds that for costs," the advantage of MPEG-4 is that you can get almost twice as many services on the same transponder, but you may need all new equipment at both the encode and receive end."

This can result in a major cost difference, specifically in the number of decoders that would need to be replaced.

"The cost of professional MPEG-4 receivers is a challenge in the adoption of MPEG-4 because the cost is relatively high, making an end-to-end solution less attractive due to the economics," said Tom Lattie, director of New Media Solutions for Sunnyvale California-based Harmonic. "An MPEG-2 IRD is cheaper than its MPEG-4 counterpart."

Commenting on early MPEG-4 receivers, "initially most manufacturers could not get latency under 500 ms, and the quality was not as good," Lattie said. "Today relatively few manufacturers make professional MPEG-4 decoders. Due to our purchase of Scopus in January, Harmonic will be shipping our new Harmonic branded unit later this summer." Prior to purchasing Scopus Video Networks, Harmonic was the reseller of Fujistu encoders in the United States.

"There is clearly a value in the MPEG-4 solution for SNG, but for HD event coverage such as sports, it may be a more dubious use," said Lattie. He believes that the newsgathering segment is the best near-term migration path from MPEG-2 to MPEG-4.

Goldman concedes, "slowly over time and by attrition, MPEG-2 will be replaced by MPEG-4." He believes that as the processing power for the encoding of MPEG-4 improves, the bandwidth and cost efficiencies of using it in most end-to-end solutions will win out.



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