Across the world, free-to-air (FTA) broadcast television is rapidly shifting from analog to digital format. Digital television (DTV) deployment—combined with rapid growth in the personal media market—is creating opportunities for many broadcasters to deliver television content not only to large screen displays, but also to mobile and portable devices.
This article will provide an overview of major DTV standards that are being deployed worldwide, with a specific focus on those in use in Europe, North America, and China The article will also provide a more comprehensive examination of the China Digital Television Terrestrial Broadcasting (DTTB) System Standard, also known as GB20600-2006, which is unique among all the digital broadcast television standards for its capability to deliver high-definition television (HDTV) to mobile devices moving at speeds of greater than 200 km/hour.
Digital Television Architecture
A top-level view of DTV architecture, with the main building blocks connected from end-to-end, is shown in Figure 1. The UHF/VHF antenna grabs the digital television broadcast signal from the air. The front-end is comprised of a tuner and demodulator, which includes complex error correction. In any given DTV, the number and the type of tuners and demodulators is dependent on how many and what types of signals are being received by the TV; for instance, whether it is receiving and demodulating HDTV or analog TV. The front-end separates the digital audio/video signal from the radio frequency (RF) and converts it into an intermediate frequency so it can be digitally processed. The demodulator also performs complex error correction on the RF signal. This demodulation produces a transport stream (TS) containing the compressed and encoded audio, video, and program data, which is then transferred to the back-end section of the television circuit.
The back-end is comprised of two major blocks: audio and video decode and scaler-de-interlacing-post processing. It performs any necessary conditional access function and decodes the TS, which then is passed on to the post-processing circuitry before being displayed on the DTV screen.
There are separate standards that govern the technology for both the front-end and back-end building blocks. The front-end block specification is usually referred to as an “air-interface standard,” signifying the specification of the method by which the digital information of the programming is packed, modulated, and sent over the air-waves using the RF carrier.
The DTV standards examined in this article refer to the front-end air-interface standards.
DTV Standards Comparison
The transition from analog to digital television is taking place at different rates around the world. Table 1 outlines the timeframes and identifies which DTV standards are being used, as well as other unique characteristics of those standards.
Regardless of the geographical region and the specific type of the standard itself, the motivation behind the specification of a digital TV standard is the same: to enhance the consumer’s television viewing experience and to create new business models for the next-generation digital era. However, as is apparent in Table 1, the United States, Europe, Japan, South Korea, and China each have adopted a different terrestrial DTV standard.
A common feature to all the standards is the MPEG-2 compression scheme, which is used to encode the audio-video content into a TS. Then, depending on the region and the standard, this TS stream is packed into frame, modulated, and transmitted over airwaves using the scheme described in the terrestrial DTV standard specification.
In the U.S., the Advanced Television Systems Committee (ATSC) standard uses 8-vestigial side-band (VSB) signaling. A modulation scheme called coded orthogonal frequency division multiplexing (COFDM) is employed in Europe’s digital video broadcast (DVB) standard. Japan utilizes the concept of integrated services digital broadcasting (ISDB), in which the structure of segmented OFDM is used for terrestrial broadcasting (ISDB-T). In South Korea, the terrestrial digital multimedia broadcasting (T-DMB) standard also employs a variation of the OFDM. China’s GB20600-2006 employs a unique and innovative variation on the OFDM, called time-domain synchronous OFDM (TDS-OFDM).
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