ATSC standard faces chicken-and-egg dilemma
HAMILTON, N.J.
Approved by the ATSC in July 2004, Enhanced VSB (or "E-VSB") is in a state of suspended animation because there is no market demand for it. And since there is no market demand, manufacturers are not motivated to develop DTV receivers that can support it.
Transmitter vendors told TV Technology that until someone comes forward with a business plan that sparks investment capital, E-VSB is not likely to be marketed.
Among the potential applications for E-VSB are fall-back audio; programming targeted to DTV receivers with simple indoor antennas; non-real-time transmissions of file-based information to handheld and pedestrian receivers; and robust data broadcasting to devices like laptop computers.
And, while conventional ATSC streams are limited to MPEG-2 encoding; with E-VSB, DTV broadcasters have the flexibility to use MPEG-4 and Windows Media 9 (VC-1) advanced compression. But again, the transmitter vendors told us that, to their knowledge, there are no E-VSB-enabled receivers capable of supporting E-VSB, let alone a stream encoded with MPEG-4 or VC-1.
And they felt it was highly doubtful that E-VSB enabled receivers would be built into cell phones or other handheld devices to facilitate the killer app--mobile TV. They noted that DVB-H and FLO, two technologies already competing in the mobile TV space--are better positioned for mobile TV because they don't put an undue burden on handheld receivers.
ROBUST SIGNAL
"There is not a significant market demand for E-VSB at this time," said Rich Schwartz, director of marketing and product management for Axcera in Lawrence, Pa. "Most broadcasters have been focused on the initial step of simply getting their DTV signals on the air. Since the primary purpose of E-VSB is to improve coverage of a signal, E-VSB has been a lower priority for broadcasters at this time.
"It is certainly possible to make [E-VSB] work from a technology perspective, but production equipment will not become available until market demand increases. That said, Axcera customers are ready for this if it happens. All Axcera digital ATSC modulators are capable of operating in an E-VSB environment with only software updates," Schwartz said.
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.
GEARING UP
To transmit an E-VSB signal, a broadcaster would have to make a slight modification to the transmitter, add an E-VSB adapter, and provide multiple program streams.
However, Schwartz said, "These modifications are much less of an issue than the fact that there are no available consumer E-VSB receivers. So even if the broadcaster provided E-VSB content, consumers would not be able to view the robust portion of the stream."
It would be possible to use the robust portion of the signal to deliver content other than SD video. One could theorize putting multiple channels of digital audio into the robust portion of the E-VSB stream, creating a sort of terrestrial version of satellite radio.
"A solid business plan would be required before a consumer equipment manufacturer would consider developing the required receivers for such a concept, making such a scenario unlikely at this time," Schwartz said.
"There is currently a proposal in front of the ATSC to consider an A-VSB mode," Schwartz said, referring to Advanced-VSB. "The proponents of A-VSB believe that it will provide flexibility to the ATSC standard allowing robust modes, single frequency networks, and more. However, it is in its infancy. The ATSC is awaiting, and has been for quite some time, a full proposal from the proponents of this system."
"What drove the development of E-VSB was that broadcasters saw the need for greater flexibility to deliver a better on-air product," said Dave Glidden, director of TV strategy and business development for Harris Broadcast, in Mason, Ohio.
During its development, Glidden said, "Early laboratory and field data tests using prototype receivers appeared to support the notion that when the E-VSB signal was also 'online,' it had the characteristics that it could help the receiver equalizer maintain and track the main E-VSB signal. With the improved reception capability of next-generation DTV receivers, perhaps this need is no longer as pressing."
Glidden's colleague, Product Manager Joe Seccia, agrees that greater flexibility and a more robust OTA signal in signal-challenged conditions made development of E-VSB a worthwhile undertaking.
"One of the initial applications envisioned for E-VSB was fall-back audio, which has a parallel to NTSC. When an NTSC OTA signal is weak, and the TV picture fades in and out, usually the viewer will still get the program audio," Seccia said. "With DTV, it's all or nothing. But with E-VSB carrying a separate, robust audio stream, broadcasters would have confidence that their program was still being heard if not seen until the reception problem could be resolved."
With respect to using E-VSB for mobile TV applications, Glidden said DVB-H and FLO--two competing mobile transmission technologies--had an advantage over E-VSB because they were designed to not place a burden on the receiving device, typically a handheld unit like a cell phone.
On datacasting to PCs, Glidden said, "Where there's available bandwidth, there are potential applications that could take advantage of E-VSB. But we would need to have specialized E-VSB-enabled receivers developed for laptops and other computers. For example, E-VSB could be used to transmit video or data to first responders in the event of a public emergency."
At Thales Broadcast & Multimedia, (a division of Thomson/Grass Valley), in Southwick, Mass., Brett Jenkins, vice president of engineering, agrees with the assessment that there is no broad-based market demand for E-VSB and no receivers capable of supporting it.
"From what I see in the industry, there seem to be a lot of hurdles to getting E-VSB off the ground. Maybe the timing's just not right and down the road, the market will find a new application that E-VSB would be well-suited to and receivers would become available," Jenkins said. "The industry has changed considerably since E-VSB was first put on the table. The original problem E-VSB was designed to solve--ensuring reliable indoor reception using a simple antenna--has already been resolved by next-generation DTV receivers."
Jenkins added that fall-back audio is a potential application for E-VSB.
"But broadcasters need to be aware that they must be prepared to sacrifice bits to accommodate that second audio stream. For example, if they decided to devote 1 Mbps to that second stream of audio, encoded using the E-VSB process, from their 19.39 Mbps total allotment, they might lose as much as 4 to 5 Mbps to the overhead associated with E-VSB processing."
Jenkins feels that the application is key, and that broadcasters are more interested in looking for a solution to mobile media delivery, which is likely to come from technologies still under development like A-VSB.
Because of this overhead issue, Jenkins said that broadcasters are waiting for advanced compression schemes, like MPEG-4 and VC-1 (which was recently approved as a SMPTE standard), that will help them use their bandwidth more efficiently to accommodate an E-VSB stream before taking E-VSB seriously. The use of MPEG-4 and VC-1 are currently making their way through an ATSC committee; along with the implementation guidelines for E-VSB.
Jenkins said they got their first inquiry about when E-VSB equipment would be ready to test last month, "but the customer did not reveal his intended application. It's important that broadcasters have a viable application, even if it's simply to support their core mission, before buying E-VSB equipment."
When customers are ready, Thales offers the ADAPT-IV exciter, which has been designed with hooks for E-VSB so that it could be added through a software and firmware upgrade. Thales will support the development of A-VSB and also look to embed this technology on the ADAPT-IV exciter platform.
MOOT POINT
At Baltimore-based Acrodyne Industries--the Rohde & Schwarz U.S. representative that uses Rohde & Schwarz exciters--Senior Staff Consultant Mark Aitken said, "E-VSB does allow an improvement in the signal level tolerance or noise threshold tolerance. You need 5 to 6dB less signal with E-VSB to be able to recover a useful transport stream. E-VSB's sole objective is to offer noise margin improvement.
"What this means for viewers is that they may be able to receive the OTA DTV signal using a simple non-directional antenna, like simple rabbit ears, instead of a more powerful set-top directional antenna--the difference between the two is about 6 dB."
But the discussion is moot at this point because, Aitken noted, there are no DTV receivers on the market that are capable of supporting E-VSB. Aitken also serves as the director of advanced technology for Sinclair Broadcast Group, in Baltimore, Md., which supported the development of the E-VSB standard. Aitken also is a co-author with Zenith Electronics' Wayne Bretl and MSTV's Victor Tawil of "Indoor Reception Tests with E-VSB," a paper presented at the NAB2006 Broadcast Engineering Conference.
Rohde & Schwarz America, in Columbia, Md. has decided not to develop products for E-VSB, according to Eddy Vanderkerken, director of sales for broadcast products.
"The biggest challenge with getting E-VSB off the ground is that there is no end-to-end solution, and no market demand for it. The problem we're facing here is that manufacturers need to develop receiver chips, multiplexers, and transmission components. And since no one company has all of these products in its portfolio, no one has control over how this can be developed."
