Although the basic standards that define DTV were completed several years ago, work continues to refine the system and expand the suite of functions and features enabled by the digital television system. The Advanced Television Systems Committee has a number of major initiatives underway now intended to increase the competitive edge of DTV. The ATSC, an international non-profit organization developing voluntary standards for digital television, has over 200 member organizations representing the broadcast, broadcast equipment, motion picture, consumer electronics, computer, cable, satellite, and semiconductor industries.
The work of the ATSC is carried out by scores of top engineers from companies around the world who dedicate their time to develope and refine standards for the DTV environment. More than a dozen committees are active within the ATSC, addressing a wide array of subjects. At present, the three most visible efforts include:
- The DTV Application Software Environment
- Interactive services
- VSB enhancements
These efforts, like all other ATSC standards work, are being carried out in an open environment in which all viewpoints are considered. The specialist groups of the ATSC operate on the basis of consensus wherein all practical technical solutions to a given objective are evaluated by experts. It is within this process that the standards documents are developed. The approval process of a draft document is structured and ultimately is determined by a vote of the full ATSC membership.
The DTV Application Software Environment (DASE) is a classic example of the flexibility of the ATSC DTV system. The DASE standard will define a software layer (middleware) that allows programming content and applications to run on a “common receiver.” Interactive and enhanced applications need access to common receiver features in a platform-independent manner. This standard will provide enhanced and interactive content creators the specifications necessary to ensure that their applications and data will run uniformly on all brands and models of receivers. Manufacturers will be able to choose hardware platforms and operating systems for receivers, but provide the commonality necessary to support applications made by many content creators.
The DASE undertaking is enormous; the effort — which began three years ago — is nearing completion. The DASE standard is composed of a suite of standards documents. Five of the eight documents have been developed and are now in their first ballot/comment period. It is expected that the entire DASE suite will be finalized and approved by the full ATSC membership later this year.
The work on interactive services is intended to define session-level protocols carried over interaction channels associated with interactive services. The interaction channel may be one- or two-way and connects a user (operating through a DTV receiver) with a service provider. The ATSC Interactive Services Protocols are intended to operate on a variety of physical networks, by focusing on higher layer protocols but not addressing specific applications. Work on this project is ongoing, with completion slated for later this year.
Recent studies have proven that the 8VSB modulation system is clearly the best choice for broadcasters. Still, the need for better receivers and — possibly — enhancements to the transmitted signal itself have been identified as an important area for further study. Responding to the evolving needs of broadcasters, the ATSC has initiated standards activity aimed at enhancing the VSB modulation specifications that are a part of the ATSC Digital Television standard (document A/53 and others). The new effort, being carried out by specialist group T3/S9, is intended to improve reception by fixed and indoor receivers, and to give broadcasters additional flexibility — including the ability to transmit programming and data to portable and mobile receivers. The effort by T3/S9 is moving forward in parallel with the DTV implementation process already well underway.
The first step in this effort was the issuance of a request for proposals (RFP) that seeks to identify possible approaches. A number of DTV receiver and chipset manufacturers, among others, have indicated they will respond with formal submissions.
While the RFP applies to compatible through non-compatible VSB enhancements, the highest priority is placed on compatible 8VSB enhancements. The RFP invites proposals covering a wide range of technologies involving modulation and/or payload enhancements; for example, adding training signals or other data intended to improve performance of the overall system. The compatible improvement of fixed and indoor 8VSB terrestrial DTV service is the top priority of this work.
In addition to fixed and indoor service, other service modes have been identified as desirable, including:
Portable service: a transmission/reception system that will allow the receiving device to be moved from place-to-place, using a self-contained receiving antenna, but which remains essentially stationary during operation.
Pedestrian service: a transmission/reception system that will allow a receiver with a self-contained antenna to operate successfully while the receiver is moving at speeds up to 5 kilometers per hour.
Mobile service: a transmission/reception system that will allow successful operation of a receiving device at speeds greater than 5 kilometers per hour.
On-channel signal boosters and repeaters: systems that permit the reception of DTV signals in areas where signal shading from terrain or man-made objects make reception difficult.
The T3/S9 VSB enhancement project is on an aggressive schedule. Critical landmarks include the following:
Invitation to present proposals sent to proponents: May 2, 2001
Selection of technology for field tests: Sept. 14, 2001
Field tests begin: Nov. 14, 2001
Review of field tests: Jan. 15, 2002
Adoption of Standard or Revision to A/53 by T3/S9: Jan. 31, 2002
It should be noted that this schedule will be reviewed on a regular basis by T3/S9 and may be amended, if necessary.
Unlike the NTSC color television standard, the ATSC DTV system is intended to expand and grow as market requirements and business opportunities permit. The flexible nature of the fundamental digital architecture makes possible this unprecedented degree of flexibility.
Mark Richer is the executive director, ATSC, Washington, D.C.