Is DTV Reception Problem Solved?
September 8, 2004
Zenith's receiver draws kudos
The scramble to switch television broadcasting to digital sometimes overlooked what occurred at the final link in the over-the-air broadcast chain: the viewer.
Although megabucks have been spent to upgrade stations and simultaneously transmit analog and digital signals, stable and reliable over-the-air DTV reception has been a crapshoot. However, the latest generation of DTV receiver technology from LG/Zenith seems to have solved the worst of the problems and is receiving praise from both broadcasters and other interested parties.
Dubbed the "fifth-generation" receiver, the new technology has converted some early DTV skeptics into believers.
"The performance that we got out of the fifth-generation receiver was as good as what we had seen with COFDM," said Nat Ostroff, president and CEO of Ai and vice president of new technology for Sinclair Broadcasting in Hunt Valley, Md.
Ostroff recently observed tests of the LG/Zenith fifth-generation receiver at several particularly difficult reception locations in Baltimore, where Sinclair conducted tests of earlier receivers and comparison tests using COFDM modulation. He had been outspoken in his criticism of the early adoption of the 8-VSB modulation scheme by the ATSC, pointing out that field tests up until now showed that reception in many places was simply impossible.
THE CLIFF EFFECT
The 8-VSB transmission system adopted by the ATSC for DTV transmission in the U.S. has had many critics among broadcasters and television insiders, primarily because--until now--consistent reception in a typical viewing environment was tricky at best. The term "cliff effect" described what too often happened when watching DTV off the air using earlier equipment: Either the signal looked perfect on the TV or it completely dropped out, as if falling off a cliff.
The fifth-generation receiver was far more immune to the cliff effect during Sinclair Broadcasting's tests of the receiver.
"We had always said that all we are interested in was a viable over-the-air receiving system and we didn't have it," Ostroff said. "When 8-VSB can be received as well as a COFDM signal, we'll be the first to declare that to be the case and congratulate the winner, and that's exactly what we've done."
Ostroff was enthusiastic about the potential of the fifth-generation receiver.
"It's the only receiver so far that enables reception indoors with simple antennas," he said.
The tests Ostroff witnessed in Baltimore used a simple bow-tie antenna and he said reception was unperturbed by the movement of people in the vicinity and even active vehicle traffic just a few feet away.
Sinclair Broadcasting's tests were informally duplicated and confirmed by Mark Schubin, a well-known consulting engineer on television issues and the creator of "Mark's Monday Memo" that discusses issues in broadcasting.
Schubin has tried various 8-VSB DTV receivers in his New York apartment with virtually no reception success, until he was able to test an LG LST-3100A receiver--a fourth-generation model--that had been upgraded with the fifth-generation DTV receiving and processing technology.
Like Ostroff, Schubin reported that reception was stable while using a simple set-top UHF antenna and people moved around the room.
"It was possible to find a location and orientation that caused problems, but I had to really try, " Schubin said in a recent issue of the memo.
Richard Lewis, vice president of research and technology for Zenith, said that the inner workings of this latest DTV receiver are a blend of well-known techniques as well as some proprietary designs.
"The fifth-generation is a much more radical approach," Lewis said. "It uses a 50 microsecond equalizer window to handle pre-ghost or post-ghost [multipath] and was really focused on indoor reception and ease-of-reception with simple antennas."
Earlier generations of receivers could also do pre- and post-ghost correction but did not have the long pre-ghost window that the latest generation has.
"The main change was a departure in architecture away from what had been used [previously]," Lewis said. "It is proprietary so I can't really get into the details, but it was a chance to throw out the old design book and take a fresh start at it."
Other interested parties have all responded favorably to the tests done with LG/Zenith's fifth-generation receiver.
Mark Richer, president of the ATSC, has been a leading proponent of 8-VSB modulation used in the U.S. for digital broadcasting.
"It has always been my view that 8-VSB receiver technology would advance quickly," Richer said. "In this highly competitive marketplace, you are going to see rapid advancement of DTV receiver technology from a number of manufacturers."
Manufacturers feel that after years of vilification by broadcasters, finally they've been vindicated.
"We've said over the years that ATSC reception would improve and I'm glad that we were proven right," said Mike Petricone, vice president of technology policy for the Consumer Electronics Association.
Sinclair Broadcasting's Ostroff said that his company is so excited about the new possibilities of DTV that it produced public service announcements to promote DTV for consumers. The spots are not specific to Sinclair and the company is offering them free of charge to any broadcaster as a way to generate viewer interest in DTV.
Others pursuing LG/Zenith's technology include USDTV, the Salt Lake City broadcaster that has launched a pay over the air DTV service using spectrum pooled from participating broadcasters. The company recently announced it will use fifth-generation DTV receiver chips in its latest set-top box and expects to ship the product by the end of this year.
Lewis said that Zenith expects to ship the product this fall.