Casper the Friendly Ghost Canceller

Linx Electronics has developed an 8VSB receiver technology that the company claims dramatically reduces the effects of multipath interference.
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Linx Electronics has developed an 8VSB receiver technology that the company claims dramatically reduces the effects of multipath interference.

The technology, called "Casper" after the famed animated ghost, is one of an expected series of technical developments intended to make DTV reception friendlier to consumers. Officials at the ATSC said that Casper was a promising technology.

"I have seen it and it is very impressive," said Mark Richer, president of the ATSC. "I think it confirms the choice of VSB as the optimal [DTV] system."

Officials at Linx Technology, which is located in Palatine, Ill., are tight-lipped about how the technology works, but an independent laboratory in Canada tested a prototype receiver in March 2002. The tests, at the Communications Research Centre (CRC) in Ottawa, confirmed that Casper was able to receive DTV in a wide range of multipath conditions, including some instances when two signals of equal strength were received.

(click thumbnail)The Casper system was awarded a Mario Award at NAB2002.
"I'm quite impressed with the results that were measured by the CRC, which is a well-respected lab," said Richer.

Ed Williams, a senior engineer with the DTV strategic services group at PBS, was also impressed with a demonstration of the Casper technology that he saw at NAB2002.

"It's apparent that they have a new method of demodulation," Williams said. "It promises to dramatically improve reception of DTV signals."

As measured by the CRC, Casper can correct for a -10 dB single echo within a delay range of -29.5 to +38.5 ìs. With an echo of -3 dB - half the power of the primary signal - the correction range is -9.0 to +38.5 ìs.

With an echo of 0 dB - the same power as the primary signal - the CRC measured a 12 ìs correction window.

Wayne Li, Jingsong Xia and Shawn Yang founded Linx Electronics in 1999, and Li is the company's president and CEO. The three founders worked on various DTV technologies at consumer electronics companies.

According to Li, Casper uses multipath energy to enhance - rather than cause nulls in - the main signal. He said that Casper includes improvements in equalizer design, carrier recovery synchronization and has built-in antenna diversity capability, although much of Casper's potential is available when using a single antenna.

Li said that receiver/decoder chips with the Casper technology will be available in quantity in the second quarter of 2003. He also said that the company is developing a "smart antenna" that works with a receiver to automatically adjust to the optimum reception conditions.

Critics of the 8VSB standard are adopting a wait-and-see attitude with regard to Casper.

"It is refreshing to see new approaches being developed to deal with the problems of receiving 8VSB," said Nat Ostroff, vice president for new technology at Sinclair Broadcasting, a longtime 8VSB critic.

For a technical review of Casper, look for Charlie Rhodes' Digital TV column in the next issue of TV Technology.