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A codec f o r digital transmission of HDTV i s described. The bit-rate compression algorithm i s b a s e d o n a d v a n c e d t e c h n i q u e s s u c h as: spatial Discrete Cosine Transform (DCT), tem-poral Differential PCM (DPCM), variable length coding. The codec is designed to operate with b o t h t h e i n t e r l a c e d s t u d i o s y s t e m s 1125/60 a n d 1250/50 a n d , t h a n k s t o t h e i n h e r e n t flexibility of t h e p a c k e t s t r u c t u r e , a wide range of line bit-rates can be used as a compromise between video q u a l i t y a n d b i t -r a t e c o n s t r a i n t s of t h e digital transmission link. The flexibility of t h e HDTV codec is highlightened t h r o u g h examples of applications over satellite digital links in practical situations. 508.6.1

The perspectives for digital HDTV on satellite channels are examined at the light of the recent progress on bit‐rate reduction algorithms and on modulation and channel coding techniques. The experimental HDTV transmissions at 70 Mbit/s carried out by the RAI during the «1990 Football Worldcup» are shortly described. A preliminary configuration of the future HDTV network architecture has been identified, including terrestrial and satellite links. Two advanced modulation and coding systems, suitable for operating in the 30/20 GHz frequency range, have been studied by computer simulations: a) QPSK modulation and concatenated convolutional and Reed‐Solomon coding, and b) Trellis‐coded 8‐PSK modulation and concatenated Reed‐Solomon coding. The satellite channel has been optimized as regards the transmitting and receiving filters partitioning and the TWTA operating point. An example of design of a complete satellite chain at 30/20 GHz shows the feasibility of a 140 Mbit/s HDTV transmission system based on the described techniques.

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