Work Begins on Mobile-Handheld DTV Standard
The ATSC has begun work to develop a standard for mobile and handheld services using compatible enhancements to the ATSC DTV system. Designated ATSC-M/H, the standard will be backward-compatible, allowing existing DTV services to operate in the same RF channel, without adverse impact on existing receiving equipment. A key element of the work is ensuring that broadcasters will be able to allocate a portion of their 19.39 Mbps 8-VSB signal to mobile and handheld while continuing to transmit services such as HDTV. This work is being conducted in the ATSC Specialist Group on ATSC-M/H (TSG/S4), led by Mark Aitken of Sinclair Broadcast Group.ATSC M/H SERVICES
Discussion of ATSC-M/H has been underway for some time. It was designated a major priority in the ATSC strategic plan and approved by the board of directors last December. The strategic plan recognizes a growing consensus that mobile and handheld capability is essential to the future of local broadcasting. The mobile and handheld TV market is seeing rapid growth and it is expected to continue to expand. Mobile and handheld services using ATSC-compatible transmissions from broadcasters could be one of the technologies in this future landscape. Broadcasters have the advantage of a nationwide infrastructure of local terrestrial DTV transmission facilities and wide coverage bandwidth available through local terrestrial TV. Such capabilities within the ATSC suite of standards will leverage the existing capital infrastructure and provide value-added services to consumers that are not available through other means of delivery of the broadcasters’ signals.
It is expected that ATSC-M/H technology will be utilized for a variety of services to mobile and handheld devices, which may include but are not limited to:
- Free (advertiser-supported) television content and other services delivered in real-time;
- Mobile and handheld subscription-based TV, video-on-demand, pay-per-view, and electronic sell-through services;
- Non real-time content download, to playback later;
- Interactive television;
- Real-time navigation data for in-vehicle use.
These new services may transmit various types and quantities of content that may be versions of regular TV programming optimized for handheld and/or mobile reception (simulcasting) or specific audio-visual content and/or data produced for mobile reception.
Broadcasters have indicated they would like the opportunity to announce new ATSC-based mobile and handheld broadcast services before the close of analog services in February 2009. The planned work schedule for a mobile/handheld solution, therefore, is based on this premise. The target dates for completion of the standards documentation are intended to take into account the time needed for professional and consumer manufacturers to develop equipment for implementation before such services can be introduced. This emphasizes the need for the standards work to be completed as soon as possible.
In May, the ATSC issued a request for proposal for mobile and handheld services. The general categories included in the RFP were:
- Scope of the planned work;
- Overall architecture, emphasizing that ATSC is looking to standardize on a complete systems solution;
- Target project schedule;
- Details regarding the materials required for submission;
- The consideration process by which the Technology and Standards Group will review the submissions;
- Administrative and process issues.
Last month, the ATSC announced that it had received a total of 10 proposals, (see related story, p. 6). Detailed descriptions for all submitted proposals were due at ATSC, July 6.
As with all ATSC work, protecting legacy receivers and the existing valuable services is a top priority. In addition, ATSC references the standards of other organizations where appropriate, as reinventing the wheel is seldom a useful exercise. And, wherever possible, harmonization with other industries and services is an important goal.
The Specialist Group on ATSC-Mobile/Handheld, TSG/S4, has been charged with developing standards and, where applicable, associated informational documents for mobile and handheld services using DTV broadcast signals. This activity will include communicating with other specialists and planning groups inside the ATSC, as well as other standards development organizations and technology committees working on standards that include mobile and handheld technologies.
TSG/S4 will focus first on evaluating the proposals submitted in response to the RFP. Selection criteria were being developed at presstime. The following general categories are likely to emerge as key elements:
- Backward compatibility—are there any legacy DTV receiver impairments?
- Video and audio quality;
- Service area and reliability;
- Scope of services and system flexibility;
- Interoperability with other mobile systems and/or platforms;
- Extensibility—can the system grow or expand as needs demand or as technology progresses?
- ATSC plans to create a comprehensive and complete solution to enable compelling mobile and handheld services and products. The ATSC-M/H standard must specify, at minimum, the following:
- Physical layer—including modulation and forward error correction coding;
- Transport, signaling, and announcement—including an electronic program guide optimized for mobile and handheld services;
- Other parameters, as necessary, for the carriage of video, audio, and data essence and metadata.
Wherever practical, ATSC will try to maximize interoperability by incorporating existing solutions, which may be accomplished by reference to existing standards.ATSC-M/H REQUIREMENTS
In the design of any new broadcast service, it is important to clearly identify the minimum target system requirements and capabilities. In the case of ATSC-M/H, these services will be carried in DTV broadcast channels. The presence of these services will not preclude or prevent operation of current ATSC services in the same RF channel, or have any adverse impact on legacy receiving equipment.
Current ATSC receivers are not expected to be able to decode or display ATSC-M/H services. Any ATSC-M/H solution should have sufficient flexibility to offer a viable service with bit-rates that do not devalue existing DTV services, including HDTV. No specific bit-rate allocation restriction exists, except that U.S. broadcasters are to provide a service that continues to conform to FCC requirements.
The service areas for mobile and handheld services will, at a minimum, correspond as closely as possible to the service area for DTV using 8-VSB. Larger service areas are desirable.
The reliability of service for devices operating within the ATSC-M/H service area should be comparable to or exceed that of cell phone and other handheld devices enabling similar services.
Service area, reliability of service, and other technical considerations will take account of practical antennas for mobile and handheld devices, which differ significantly from traditional 30-foot antenna assumptions.
The ATSC-M/H system will enable modes of operation that allow mobile reception by devices permanently mounted in cars, buses, and trains, at speeds up to at least 75 mph. Furthermore, the system will support modes of operation that allow reception by handheld devices that are stationary or moving at walking speeds of about 3 mph (5 km/h).
Specific technical targets for ATSC-M/H have been developed, including:
- Real-time broadcasting and a nonreal-time mode (by reference to other work currently underway within ATSC);
- Video resolutions up to 480p at variable frame rates for screens installed in vehicles;
- Video resolutions up to 352x288 (CIF) at variable frame rates for screens in handheld devices (and perhaps up to 480p in a nonreal-time mode);
- Stereo audio for systems installed in vehicles, ideally with support for up to 5.1 channels;
- Mono or stereo audio for handheld devices, possibly with support for up to 5.1 channels;
- Use of bandwidth efficient advanced codecs for video and audio to provide for scalable quality and quantity of mobile and handheld services;
- Messaging capabilities;
- Use of digital on-channel repeaters and translators, and distributed transmission for fill-in service coverage as necessary.
Work within ATSC is open to all organizations with a direct and material interest. If you are interested in contributing to ongoing efforts to develop ATSC-M/H, please contact the author. Additional information on the ATSC can be found at www.atsc.org.