Digital television terrestrial transmission has to deal with various reception conditions: a plug-free TV set receives a much lower a signal thanone with a roof-top antenna. It is hence interesting to provide a signal that conveys two types of information: a "basic" picture for portable receivers, this information must be transmitted most reliably; and additional information to be added to the basic picture in order to get a higher definition picture, this lesser protected information can be decoded by fixed receivers only. This implies multi-protection-or hierarchical-channel coding, including very efficient codes to protect the basic picture. This article describes a hierarchical channel coding and modulation scheme that, together with a new family of binary codes, is believed to allow the design of good hierarchical transmission systems.
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