Digital television broadcast standards

This chapter summarizes the standards for digital television broadcasting. All digital broadcast systems that have been standardized are based upon Moving Picture Experts Group (MPEG-2) compression, described in MPEG-2 video compression. High Definition Television (HDTV) transmission systems were conceived to deliver the images in twice vertical and twice horizontal resolution of Standard-definition television (SDTV), that is, about 2 megapixels in a 6 MHz analog channel. MPEG-2 can compress 2 megapixel images at 30 frames per second to about 20 Mb/s. The chapter also explains that the basic parameters of the 525-1ine, 60-field-persecond interlaced transmission scheme have been frozen since the introduction of black-and-white television in 1941. The modulation scheme requires that potential channels at many locations remain unused, owing to potential interference into other channels. Some consumer HDTV displays use 1080i scanning, but on a 4:3 display surface (“4:3 glass”). To use such a display for standard 16:9 aspect ratio HDTV requires vertical downsampling by a ratio of 4:3. This yields 810 picture lines, rather than 1080; the display format is denoted 810i.