An HDTV bit-rate reduction codec at the STM-1 rate of SDH

摘要

An HDTV bit-rate reduction codec was developed, aimed at the transmission of an HDTV signal for distribution use. This codec can perform the coding of an 1125 lines/60 Hz HDTV video signal accompanied with 4-channel sound signals at about 133 Mbit/s, and transmit it at the STM-1 rate of 155.52 Mbit/s in the xynchronous digital hierarchy (SDH). The sampling frequencies are selected considering the simple relation with the studio standard as well as the required bandwidth for HDTV distribution. A hybrid DPCM/DCT coding scheme is employed as a bit-rate reduction algorithm, where intrafield 8 × 8 DCT is first performed and then interframe DPCM is carried out in the DCT coefficient domain. An adaptive intrafield/interframe mode selection is performed only for low-frequency DCT coefficients and the intrafield mode is always used for high frequency coefficients because the interframe correlation of the high frequency coefficients is fairly weak. Computer simulation experiments were carried out to examine the performance of this coding scheme. The codec hardware was implemented and transmission experiments, as well as laboratory experiments, were carried out using actual SDH transmission systems. From these experiments, it was confirmed that this codec can transmit HDTV at the STM-1 rate with a picture quality satisfactory for distribution use. The technical and operational feasibilty of HDTV digital transmission through SDH transmission systems was also demonstrated.