Digital Television Broadcasting: Nondisruptive Improvement over Time

Abstract

The Federal Communications Commission (FCC) decided, at an early date, that it was important for the digital broadcasting system to be upgradeable over time. Therefore, it established, as an important desideratum for the system to be chosen, that it could be improved in a nondisruptive manner i.e., without making the original equipment obsolete. An effective way to do this is to formulate a single baseline system that produces standard-definition imagery, and to carry out any later upgrading exclusively by adding one or more enhancement signals. Enhanced receivers would extract all data streams to create improved imagery. This approach to upgrading permits the manufacture of digital receivers (and set-top converters for NTSC receivers) of the lowest possible cost since high-definition decoding and signal-processing capability is unnecessary If the enhancement signals are transmitted by means of nonuniform constellation, then they will appear to be random noise to baseline receivers, guaranteeing that such receivers will continue to be usable regardless of the exact nature of the enhancement signal(s). While it would be preferable for the baseline system to be progressively scanned, it would be possible to permit both interlaced (I) and progressive (P) baseline formats to be used and yet to design enhanced receivers in such a way that they would operate properly with both. The source coding required in such a system is already well known by such names as pyramid coding, layered coding, or multiresolution coding. Channel-coding methods are also described that permit receivers to extract data from the transmitted signal in accordance with the local SNR and their signal-processing capabilities.