Use is made of a digitally assisted DATV to effect a bandwidth reduction encoding and bandwidth reduction decoding, in addition to MAC-coding and MAC-decoding, of at least three picture signal channels (PC) each having a different picture signal refresh period equal to, for example, 80, 40 and 20 ms...http://www.google.com/patents/US5027206?utm_source=gb-gplus-sharePatent US5027206 - High-definition television systems
