Time-Compression Multiplexing (TCM) of Three Broadcast-Quality TV Signals in a Satellite Transponder

The problem of transmitting two or more high-quality TV signals through a satellite transponder of 36 MHz continues to be a challenge in optimizing the use of available transponders in current as well as near-future satellites. It was recently proposed1 that by combining the concepts of Time-Compression Multiplexing (TCM)2'3 and differential signals,4 two or more National Television System Committee (NTSC) TV signals can be time multiplexed with bandwidth reduction for transmission with a single FM carrier in a satellite channel. This avoids crosstalk between the pictures. In fact, straightforward TCM alone would permit the transmission of two TVs in a transponder with performance close to broadcast quality [i.e., peak-to-peak video signal to weighted root-mean-square (rms) noise ratio, s/n ^ 56 dB] if 12meter receive earth stations were used in a satellite system such as COMSTAR. The additional application of time-companded (timecompressed or expanded) differential signals reduces the TCM signal bandwidth and thus can enhance the transmitted picture quality or enable the inclusion of a third TV signal. However, the implementation of such a system as described in Ref. 1 involves converting the input TV scan pattern from interlacing to sequential. This would mean considerable memory needed, particularly in the case of three TVs per transponder. Here, we describe an implementation that offers significant saving in memory, considerable relaxation in timing requirements, and easy adaptation to existing hardware.