As digital TV reception controversy dims, E-VSB gets another look

May 8th, 2006

Reports of over-the-air reception problems once threatened to derail the digital TV standard chosen for the U.S. Today, as America prepares to say goodbye to analog television broadcasts in 2009, the reception controversy has been set aside.

The most recent evidence: Mark Aitken of Sinclair Broadcast Group told Broadcasting & Cable last month that converter boxes with fifth-generation digital TV chip technology will allow viewers to receive broadcasts reliably, if the box delivers a clean signal. Why is that remarkable? Because as recently as last summer, another Sinclair official charged that ATSC (the U.S. standard) “simply is not capable of meeting the needs of the average non–cable-connected viewer.”

The loudest complaints about ATSC reception shortcomings concern its modulation standard, called 8-VSB, used to decode the signal. In 2004, the Advanced Television Systems Committee approved a standard known as Enhanced VSB, or E-VSB, a technology designed to allow broadcasters’ digital TV signals to reach more households. Claudia Kienzle of TV Technology:

The primary purpose of E-VSB is to provide a robust signal that can be received in areas where a standard ATSC signal cannot. E-VSB could be used to simulcast a robust SD version of a primary HD program, allowing viewers located in fringe coverage areas to still view a program, albeit in standard definition, when they would otherwise receive no signal.

But despite the early buzz, E-VSB has gone nowhere, and Kienzle offers a look at why neither the manufacturers of TV sets or transmitters have adopted it.

In August, I asked Frank Eory of Freescale (the chipmaker, formerly part of Motorola) about Enhanced VSB’s prospects. Eory was principal author and editor of a report prepared for the ATSC in 2001 by an ad-hoc group that identified causes of failed digital TV reception.

“The simple truth,” Eory told me, “is that 8-VSB is a poor choice for a digital modulation standard, not only for DTV, but for any other digital wireless communication system. It is inferior to COFDM, which is used for broadcast DTV in most other countries, and also inferior to most digital cellular phone standards and wireless LAN standards that are in use around the world today.” Nonetheless, 8-VSB should not get all the blame for digital TV reception problems in the U.S., Eory said in an email exchange. Part of the problem is that “the FCC was given a nearly impossible task—to allocate an additional 6 MHz TV channel to every licensed TV broadcaster in the U.S., to be used for a ‘reliable’ DTV broadcast system, while simultaneously limiting interference to and co-existing with the existing analog TV broadcast channels.”

To design the nation’s digital TV system, then, compromises were made. The system that we now must live with allows little margin for error, and is designed to deliver digital television only to those viewers who currently get “good” analog TV reception. “Those who put up with snowy or ghosty analog TV pictures may or may not be able to receive DTV at all,” Eory explained.

Which brings us to E-VSB. Frank Eory:

“In the aftermath of the 8-VSB ad-hoc group’s report, the ATSC embarked on modifications to the 8-VSB standard, which led to something known as ‘Enhanced VSB.’ Unfortunately, the approved enhancements do little to improve urban reception, which is often interference-limited by multipath echoes. The enhancements can, however, extend the reach of DTV signals to viewers in outlying areas far from the TV transmitter. Some manufacturers are supporting E-VSB, but it does not seem to be gaining traction, since most people in the industry understand that it doesn’t address any of the fundamental reception problems. Quite simply, it adds cost to the receiver, with only a modest benefit for a small number of viewers. To make matters worse, E-VSB takes data away from the HDTV signal, potentially degrading HDTV picture quality.”

Broadcasters, having collectively spent billions on HD equipment, have recently opposed proposals that would allow cable companies to downconvert their high-definition signals for delivery to subscribers. By rejecting E-VSB (thus far), they have also shown reluctance to downgrade the images and sound on their own. The irony, of course, is that without Enhanced VSB, local stations will become even more dependent upon cable and satellite systems to deliver their programming to some viewers.

Digital TV converter boxes due later this year
Senate bill would allow cable to downconvert digital TV broadcasts
Antenna aimed at digital-TV multipath reception problems
Will new chips improve digital TV reception?
LG set-top prototype uses 5th-generation chip

• Link: TV Technology

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