Two TV Signals on a 45 Mbit/sec Channel

Abstract

An algorithm and its implementation to transmit two TV signals over a 45 Mbit/sec channel are described. Although the reproduced picture does not show any visible coding degradations for many of the test scenes, a waveform monitor shows that it does not meet current network requirements established for analog signals. Scene adaptive differential pulse-code modulation (DPCM) coding and predictor selection are used with variable word-length coding of the quantized samples. The variable data rate generated by the coder requires buffering to interface to a constant rate channel. Buffer overflow is prevented by controlling coarseness of quantization and by subsampling. An adaptive interpolation scheme is used to reconstruct samples omitted from transmission. Several operating modes are used for best picture reproduction. The occurrence and duration of high spatial and temporal activity of the two scenes is generally uncorrelated; thus dynamic sharing of the channel is generally advantageous compared to allocating half the channel rate to each TV signal.