LG Electronics and Samsung, the two competing consumer electronics companies most intimately involved with the development of the ATSC A/153 Mobile DTV standard, are proposing similar but slightly different amendments to the standard to provide better bandwidth efficiency, flexibility, scalability and performance for broadcasters and other program providers looking to send video to portable devices via an over-the-air signal.
The standard as it stands today does not allow the full use of a 19.5Mb/s channel for mobile, handheld signal delivery. The new proposals — the LG proposal supported by Harris and the Samsung version supported by Rohde & Schwarz — are part of an initiative to change the standard to include a “scalable, full-channel mobile mode.” They are both fully compatible with the ATSC A/153 Mobile DTV Standard adopted last October.
“We’re talking about taking the basic building blocks that are already there in the A/153 standard and extending them to give users more data rate possibility and fill in some of the other gaps that exist which limit what users can do with it,” said Mike Simon, advanced technologies manager of the broadcast division at Rohde & Schwarz.
The limitation to the A/153 standard today is that if a licensed broadcaster wanted to use broadcast-only mobile services, it can only utilize 75 percent of the entire 6MHz channel capacity, because the government mandates that a broadcaster has to broadcast at least one SD channel that replicates coverage (and quality) of its previous NTSC channel.
The proposed amendments are in response to a desire on the part of nonbroadcasters like satellite TV provider DISH Network that operate in the 700MHz frequency (outside the Channel 2-51 spectrum allocated to broadcasters) as well as some traditional broadcasters that want to perhaps do more than the current standard allows. The proposals are now being discussed within the S4-5 ATSC group assigned to look at the issue.
Organizations like DISH Network are not bound by this mandate but may want to be compatible with local broadcasters and perhaps offer some of the stations’ signals as part of a multichannel mobile service. DISH now owns Channel 56 in most of the country (which it won at auction last year), which would allow it to provide about 15 channels of video, but, in order to compete with existing mobile services, they could use some of broadcasters’ local spectrum and integrate it as part of a larger service offering that would be seamless to the consumer via an overarching electronic user guide (which is written into the ATSC A/153 spec). So, the A/153 standard has to be amended to allow them to do this.
If the amendments are passed, users will get a much better user experience, and broadcasters could easily partner in potential business ventures with organizations like DISH, so there are benefits for everyone involved.
“We realize there are applications for digital broadcasting that go far beyond the services transmitted by TV stations,” said Dr. Jong Kim, president of LG Electronics’ U.S. R&D lab. “Companies that own 700MHz spectrum are beginning to ask how they might put the power of ATSC mobile digital broadcasting to use, and we’re responding by creating a new method of utilizing digital transmission to transmit even more programs. With our Scalable Full-Channel Mobile Mode system, we can offer multiple programs for mobile devices and a ‘barker program’ that can be seen by in-home viewers.”
Traditional broadcasters have also expressed an interest in making subtle changes to the Mobile DTV standard so that they can get better spectral efficiency out of their channel and be allowed to use more of it than the 75 percent (about 4.5Mb/s) currently available to them.
Also part of the proposed amendments, broadcasters could take advantage of an additional mobile data system turbo coding option, which would improve reception by allowing the signal to stay locked to the receiver while the device is moving around a coverage area. Right now, as described by the A/153 standard, broadcasters can choose between a half-rate code and a one-quarter rate-coding scheme. The one-quarter coding rate is better for mobile reception, but uses more data to get the job done. The new proposals both suggest using a one-third rate to give broadcasters better spectral efficiency. They also propose significant changes in the block formats that are used to generate the various segments of the mobile signal.
“Even if broadcasters choose to use only up to 75 percent of their bandwidth for mobile, these new amendments could provide them with better spectral efficiency by using a code rate that falls between one-half and one-quarter and get better performance,” Simon said. “At the end of the day, it’s up to each broadcaster to figure out what works best for them and ensuring a good end-user experience.”
And, with all of the advancements in compression technology, it’s not inconceivable that a broadcaster could distribute a single SD channel with less than 5Mb/, and open up more capacity for mobile service, according to Simon.
“Broadcasters I talk to are saying ‘why should the ATSC Mobile DTV standard dictate how much bandwidth I can use for mobile,’ and I agree with them,” he said. “If these mobile services begin to take off with consumers, business models need to be flexible and can't be constrained by technical specifications.”
The LG and Samsung proposals are now being discussed within the TSG S4-5 Group of the ATSC and should be approved, on one form or another, by the end of this year. At least that’s the goal.
While the demonstration seen at NAB were only prototype, “the finished product will require nothing more than a software upgrade” for current mobile DTV equipment owners, according to Jay Adrick, vice president of broadcast technology for Harris.
