8-VSB8-VSB (8-level vestigial sideband ) is a standard radio frequency ( RF ) modulation format chosen by the Advanced Television Systems Committee ( ATSC ) for the transmission of digital television ( DTV ) to consumers in the United States and other adopting countries. In the US, the standard is specified by the Federal Communications Commission (FCC) for all digital television broadcasting. Countries in Europe and elsewhere have adopted an alternative format called Coded Orthogonal Frequency Division Multiplexing ( COFDM ). The main ATSC standards for DTV are 8-VSB, which is used in the transmission of video data, MPEG-2 for video signal compression, and Dolby Digital for audio coding. The 8-VSB mode includes eight amplitude levels that support up to 19.28 Mbps of data in a single 6 Mhz channel . There is also a 16-VSB mode that has 16 amplitude levels and supports up to 38.57 Mbps of data on a 6 Mhz channel. 8-VSB is considered effective for the simultaneous transmission of more than one DTV program (multicasting) and the transmission of data along with a television program (datacasting) because it supports large data payloads. The ATSC adopted the VSB transmission system because of its large bandwidth , which is needed to transmit HDTV (high definition television) programming. Detractors claim that this larger bandwidth is irrelevant if customers cannot view the transmitted program because of multipath effects. When a signal is transmitted, it is met with obstructions such as canyons, buildings, and even people, which scatter the signal, causing it to take two or more paths to reach its final destination, the television set. The late arrival of the scattered portions of the signal causes ghost images. For this reason, some consumers in metropolitan areas or areas with rugged terrain opt for cable television instead of fighting their antennas for better reception. Because a VSB signal is transmitted on one carrier, it scatters like water blasted on a wall when met with obstacles, which is not a problem with COFDM, the European standard modulation technique, because it transmits a signal on multiple carriers. VSB advocates state that simply buying an outdoor antenna that rotates solves the multipath interference problem, but critics worry that customers do not want to buy an expensive rotating outdoor antenna to view free television programs. They also worry that the poor reception and the added expense of an outdoor antenna are slowing the transition to DTV in ATSC-compliant countries. The VSB scheme also does not support mobile television viewing. VSB equipment manufacturers are working on solutions to these two problems.
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| Last updated on:
Sep 21, 2005 |
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