DTV Debut for Games

China’s plans for the 2008 Summer Olympics include more than 50,000 buses equipped with two to four HDTVs displaying live game transmissions. And Beijing hopes that consumers riding on a high-speed train or subway will be watching the same free-to-air content on their cell phones that they can access on their home TVs.
A fleet of 2000 cars will be equipped with in-dash mobile HDTVs to transport dignitaries and game committee officials. Journalists covering the Summer Olympics will receive USB receivers to plug into their laptops so they can view the games in HD from any location while on assignment in Beijing.
At the centre of these plans is a Fremont, Calif.-based company called Legend Silicon, which co-developed China’s new high-definition digital television broadcast standard — GB20600. According to a recent company press release, Legend Silicon is the sole supplier of demodulator chipsets for Chinese HDTVs, transmitters, set-top boxes, handheld devices, USB receivers and mobile TV car systems.
The company also reported that Samsung, Sharp and several Chinese firms are shipping systems and boards that use Legend’s chips. Partnerships with Texas Instruments, STMicroelectronics, Analog Devices and Renesas are designing low-cost portable products for the Chinese market.

The Grand Plan
In 2000, China asked for a digital terrestrial TV standard that would meet four key goals.

(click thumbnail)An in-car system similar to what will be used in Beijing.The first goal was to significantly improve the reception in fixed, portable, and mobile receivers. The second was to accommodate HDTV, SDTV, data broadcasting, instant messaging, Internet access, and future IP-based applications. Number three was to support mobile digital terrestrial television broadcasting (DTTB) on the same platform as fixed transmissions without deploying new equipment at the head ends or receivers. And lastly, China asked that the standard would not require broadcasters to upgrade their encoder equipment.

Two alumni from Beijing’s Tsinghua University, Dr. Lin Yang and Dr. Hong Dong, took up the challenge, formed Legend Silicon, co-founded the Digital TV Technology Research Center with Tsinghua University, and developed a multiple-carrier modulation technology called Time Domain Synchronous-Orthogonal Frequency Division Multiplexing (TDS-OFDM). TDS-OFDM differentiates itself from the OFDM modulation standards favored by Europe and Japan by inserting a pseudo-noise sequence to better synchronize mobile and burst data broadcasts and improve channel estimation.

Dr. Lin explained that the PN sequence—essentially a set of bits generated to be statistically random—eliminated the need for the data-consuming pilot tones and cyclic prefixes utilized by Europe’s COFDM. Lowering the technology “overhead,” he concluded, enabled faster channel estimation and synchronization and significantly increased data capacity.

“COFDM requires a certain minimum number of symbols to fully complete the channel estimation,” he said. “In TDS-OFDM, only one symbol is required to achieve the same result.”

While Tsinghua developed TDS-OFDM, Shanghai’s Jiaotong University developed a vestigial sideband (VSB) modulation called Advanced Digital Television Broadcast-Terrestrial (ADTB-T). Like the ASTC 8-VSB standard used in the United States, ADTB-T is based on single-carrier frequency, though it also includes modulation schemes of 4QAM-NR and 32 QAM. More importantly, it too can support mobile TV service, thanks to its own pseudo-random noise sequence: PN595.

China’s new GB20600-2006 standard offers both the multiple and single-carrier options developed by these respective universities. It also incorporates the low density parity check [LDPC] forward error correction [FEC] specification that was co-developed by China’s Academy of Broadcast Science and China’s State Administration of Radio, Film and Television in the 1950s.

“LDPC is the world’s best FEC technology,” said Dr. Lin. What’s more, he noted, the vintage technology also resolves backward compatibility concerns and carries no patent royalty burdens.

“GB20600-2006 takes the best of both the U.S. and European standards and improves on them further with technologies like TDS-OFDM, LDPC error correction, Single Frequency Network support (more efficient use of UHF/VHF spectrum), higher payload rate (25 Mbps), and very fast synchronization time,” said Dr. Lin. “TV programs will be encoded in MPEG-2 so there should be minimal signal conversion.”

Legend Silicon’s Product Timeline

Using TDS-OFDM, Legend Silicon and Tsinghua University patented and brought to market a new terrestrial DTV broadcasting protocol—Digital Media/TV Broadcasting-Terrestrial/Handheld (DMB-TH). The first draft of the DMB-TH protocol emerged in the second quarter of 2000.

(click thumbnail)USB receiver devices will be available for media covering the Games.The first generation of DMBT-T ASIC (Application Specific Integrated Circuits) emerged in the first quarter of 2001, and was deemed a “unique intellectual property” by the government by the third quarter of 2002. A fourth generation DMB-T demodulator was unveiled in the first quarter of 2004. By the third quarter of that year, a first DMB-T network was deployed in Henan Province. DMB-TH products emerged during the next two years, followed by full-blown GB20600 products in 2007. A fourth generation of GB20600 products appeared during the second quarter of 2008.

“You can receive an HDTV broadcast at 200 km/h,” said Dr. Lin of the latest technology. “You will get a solid picture with no interruptions.”

At press time, Dr. Lin estimated that approximately 30 mainland cities, including Beijing, were covered by the network; 40 other cities were planning their inclusion in time for the Olympics. Hong Kong officially came on board on Dec 31, 2007, and anticipated reaching 75 percent of its population by the end of 2008 and 100 percent by 2011, he said.

According to Dr. Lin, this standard protocol could be deployed by other countries. But, to date, he said, there are no other deployments outside of China.

In answer to criticism that the technology was relatively expensive, he noted that GB20600 is a new technology, and as demand grows and production improves, the cost of these chips should decrease.