All-digital Systems Research Articles

The HDTV Grand Alliance System

Broadcast television in the United States has remained essentially unchanged in the last 50 years except for the addition of color and stereo sound. Today, personal computers are meeting the need for random access of high-resolution images and CD-quality audio. Furthermore, advances in digital video compression and digital communication technology have cleared the way toward offering high-resolution video and audio services to consumers using traditional analog communications channels. In 1987, the US Federal Communications Commission (FCC) chartered an advisory committee to recommend an advanced television system for the United States. From 1990 to 1992, the Advanced Television Test Center (ATTC) tested four all-digital systems, one analog high-definition television (HDTV) system, and one enhancement NTSC system using broadcast and cable television environment simulators. The formation of the HDTV Grand Alliance in May 1993 resulted from the withdrawal of the only analog HDN system from the competition and a stalemate between the other four all-digital systems. The HDTV Grand Alliance system is composed of the best components from previously competing digital systems demonstrated to the FCC. The Moving Pictures Experts Group (MPEG-2) syntax is used with novel encoding techniques to deliver a set of video scanning formats for a variety of applications. This article describes the important features and concepts embodied in the HDTV Grand Alliance system.

Advanced television systems for terrestrial broadcasting: Some problems and some proposed solutions

The first part of this paper discusses the requirements that must be met by a new television broadcasting system to maximize its acceptability to the various stakeholders, including broadcasters, equipment manufacturers, program producers, regulatory authorities, and viewers. The most important performance factors are efficient use of over-the-air spectrum, coverage versus quality, cost, interoperability, and the existence of a practical transition scenario. It is concluded that all receivers need not have the same peformance, and that low-cost receivers must be available for noncritical locations in the home. If this variation in price and performance is made possible by appropriate system design, then interoperability is facilitated and nondisruptive improvement over time is made possible, as desired by the Federal Communications Commission. In the second part of the paper, techniques that may permit meeting these requirements are discussed. These include joint multiresolution source and channel coding, multicarrier modulation, and hybrid analog/digital coding and transmission. The analog transform coefficients are subjected to spread-spectrum processing, and coded orthogonal frequency-division multiplex (COFDM) is applied to the complex hybrid symbols to be transmitted through the channel. Various methods of equalization and of improving noise, interference, and multipath rejection are compared. Finally, an example is given of a system that meets the various requirements by making use of a number of the techniques discussed. The system provides extended coverage, albeit at lower quality than currently proposed all-digital systems, and equal or higher quality than such systems in much of their service area. It also features self-optimization at each receiver depending on signal quality and receiver characteristics, and facilitates the design of receivers of lower cost and performance for less-critical applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Avionics: All digital jets on the horizon: The Boeing 767 is the most talked about new airliner in years because of its ambitious use of digital avionics

Discusses the advantages of the all-digital avionics system which unlike analogue systems, can reduce fuel consumption through a flight management computer. The computer minimizes fuel costs by integrating navigation and guidance with engine-thrust management. All-digital systems, moreover, may have at least a 40 percent longer mean time between failures than comparable analogue systems, and they are expected to be easier to maintain.