Invited passengers aboard select busses rolling the streets of Las Vegas next week will witness a public demonstration of Advanced-VSB technology in action as Sinclair Broadcast Group-owned KVMY transmits the Samsung Electronics-designed DTV enhancement to receivers onboard.
The demonstration during the CES 2007 trade show will be the first major public showing of the technology since initial tests in Baltimore and Buffalo, NY, by Samsung and Sinclair proved that the system worked.
At its facilities in South Korea, Samsung began work on A-VSB as a way to facilitate reception of DTV signals by mobile receivers — such as those in moving cars and trains, or in laptop computers or cell phones. Eventually, the company proposed A-VSB as an open standard, and ATSC began work on its standardization in December 2005.
A-VSB promises broadcasters a way to expand their traditional business model and reach mobile viewers directly rather than through third-party cellular phone service providers. A-VSB will require broadcasters to buy relatively inexpensive remultiplexing equipment, not new towers, antennas and transmitters to reach mobile viewers, said John Godfrey, vice president of government and public affairs for Samsung Information Systems America.
"Because the cost of entry is relatively low," he said, "we think and hope broadcasters can justify this on the basis of free, ad-supported TV."
According to Godfrey, A-VSB is completely backwards compatible with 8-VSB, so legacy over-the-air DTV receivers will continue to work without interruption when A-VSB is transmitted.
A-VSB is significant for broadcasters because the existing ATSC digital transmission standard was never designed for dynamic interference, especially the multipath problems that arise with a moving receiver where every echo is a moving echo.
A-VSB attacks these multipath interference problems by inserting a supplementary tracking signal (SRS) into a portion of the ATSC MPEG transport stream known as the adaptation field, Godfrey said. While legacy receivers ignore the SRS data, A-VSB receivers use it to lock onto the transmitted signal by "continually training the receiver equalizer," he said.
With the SRS, the receiver has a constant against which it can compare the signal that's being received and "use the difference to correct for errors in the environment…There's a big problem with DTV reception when a car goes by or a person walks by. With SRS, you can lock on and retain reception even in the presence of dynamic multipath reception," he said.
Contributing to A-VSB's reliable performance in mobile applications is the use of a mathematical technique known as turbo coding for the multicast stream devoted to A-VSB transmission. Through turbo coding, A-VSB reception in low signal-to-noise environments is possible.
While A-VSB reception in vehicles, such as trains moving at up to 170mph in an urban environment, has been proven to work with a standard single transmitter broadcast setup, a side benefit of A-VSB may be in easy implementation of distributed TV transmitting systems, Godfrey said.
Insertion of the SRS into the ATSC transmission includes a way "of fixing where frames start," something that's beyond the conventional ATSC transmission standard, he said. As a result, A-VSB provides an easy way to synchronize multiple transmitters.
In Las Vegas, select conventioneers will be invited to ride the A-VSB-equipped busses to experience mobile DTV firsthand. Broader implementation, however, is only likely to happen after ATSC approves the A-VSB standard, something Godfrey says he and Samsung are hoping will happen in the first half of this year.
According to Godfrey, the first products incorporating A-VSB receivers will be aimed at the laptop computer and portable television markets, with the possibility of A-VSB-equipped cell phones to come later.
