W-OFDM công nghệ hiện đang được sử dụng trong các hệ thống Wi-LAN truy cập băng thông rộng không dây và cho phép thực hiện đa điện năng thấp RF mạng giảm thiểu can thiệp với các mạng lân cận. Các kết quả trong can thiệp giảm, do đó cho phép các kênh độc lập | 18 DIGITAL TELEVISION TRANSMISSION STANDARDS ANTENNA HEIGHT AND POWER In the United States the antenna height above average terrain HAAT and AERP for DTV stations operated by existing licensees is designed to provide equivalent noise-limited coverage to a distance equal to the present NTSC grade B service contour. The maximum permissible power for new DTV stations in the UHF band is 316 kW. The maximum antenna height is 2000 ft above average terrain. For HAATs below this value higher AERP is permitted to achieve equivalent coverage. The maximum AERP is 1000 kW regardless of HAAT. The minimum AERP for UHF is 50 kW. Power allocations for VHF range from 200 W to slightly more than 20 kW. MPEG-2 Although the source encoding and transport layer are distinct from the transmission system they are closely associated. It is therefore important that the transmission system engineer have an understanding of MPEG-2. The following discussion is a cursory overview for more details the interested reader is referred to ATSC A 53 or the Implementation Guidelines for DVB-T which point to additional documents. In accordance with the International Telecommunications Union Radio Sector ITU-R digital terrestrial broadcast model the transport layer supplies the data stream to the RF transmission system. This is illustrated in Figure 1-13. Since there is no error protection in the transport stream compatible forward error correction codes are supplied in the transmission layer as already described. Figure 1-13. Digital television broadcast model. From ATSC DTV Standard A 53 Annex D used with permission. MPEG-2 19 MPEG-2 refers to a set of four standards adopted by the International Standards Organization ISO . Together these standards define the syntax for the source coding of video and audio and the packetization and multiplexing of video audio and data signals for the DTV DVB-T and ISDB-T systems. MPEG-2 defines the protocols for digital compression of the video and audio data. These .
