The authors suggest a parallel processing structure using the proposed international standard for visual telephony (CCITT P*64 kbs standard) as processing elements, to compress digital high definition television (HDTV) pictures. The basic idea is to partition an HDTV picture, in space or in frequency, into smaller sub-pictures and then compress each sub-picture using a CCITT P*64 kbs coder. This seems to be a cost-effective solution to the HDTV hardware. Since each sub-picture is processed by an independent coder, without coordination these coded sub-pictures may have unequal picture quality. To maintain a uniform quality HDTV picture, the following two issues are studied: sub-channel control strategy (bits allocated to each sub-picture); and quantization and buffer control strategy for individual sub-picture coders. Algorithms to resolve these problems and their computer simulations are presented.>

High Definition Television (HDTV) promises to offer wide-screen, much better quality pictures as compared to the today’s television. However, without compression a digital HDTV channel may cost up to one Gbits/sec transmission bandwidth. We suggest a parallel processing structure using the proposed international standard for visual telephony (CCITT Px64 kbs standard) as processing elements, to compress the digital HDTV pictures. The basic idea is to partition an HDTV picture into smaller sub-pictures and then compress each sub-picture using a CCITT Px64kbs coder, which is cost-effective, by today’s technology, only on small size pictures. Since each sub-picture is processed by an independent coder, without coordination these coded sub-pictures may have unequal picture quality. To maintain a uniform quality HDTV picture, the following two issues are studied: (l) sub-channel control strategy (bits allocated to each sub-picture), and (2) quantization and buffer control strategy for individual sub-picture coder. Algorithms to resolve the above problems and their computer simulations are presented.

We describe an experimental system for demonstrating time-compression multiplexing (TCM) of two NTSC color television signals in a satellite channel of 36 MHz. The system employs digital processing to derive line or field differentials from each picture. The television signals are then converted into interleaved lines (or fields) of unimpaired baseband video and companded line (or field) differentials. These signal components are finally time compressed and multiplexed into a combined signal for single-carrier FM transmission. With 4.5-m earth stations, the field-differential technique offers extremely good transmission quality suitable for TV distribution to cable head-ends (weighted signal-to-noise ratio, WSNR ≈ 51.5 dB), while the line-differential method provides a slightly lower WSNR ( ≈ 49 dB). We recommend the field-differential approach because of its superior overall picture quality. For larger receive stations (7m), higher picture quality (WSNR ≈ 56 dB) could be obtained. If 10-m earth stations are employed, the received video performance is practically indistinguishable from the corresponding one in the one-television-per-transponder case, and we infer that three pictures can indeed be sent with a graceful degradation as previously suggested. By choosing the parameters properly, the current TCM system can be optimized for a wide variety of applications with higher channel capacity.

We describe a time-frequency multiplexing (TFM) method for transmitting two television signals over one satellite transponder, which gives significant improvement over existing methods. The complexity of the hardware implementation is similar to existing time-division multiplexing (TDM) systems, but the picture quality, when received on a 10 m earth station, approaches that which is currently being requested by the major television networks. Unlike existing frequency-division multiplexing (FDM) systems, TFM needs no backoff of the satellite transponder. The general philosophy of TFM is described, including the benefits of using a difference signal to reduce the overall required bandwidth. Also discussed is companding of the difference signal as a means of improving the overall signal-to-noise ratio. Several alternative methods of implementation are considered, along with those which have been explored in some detail. We then describe an experimental TFM system which was implemented using digital field memories and tested with a 10 m earth station operating through the COMSTAR D2 satellite. Received picture quality was excellent in all cases. Weighted SNR was 53-56 dB, and in practically all instances subjects could not tell any difference between single-picture FM transmission and TFM dual-picture transmission.

Interframe coder simulation results are described for standard-broadcast-rate monochrome television in applications where the television camera is largely stationary, such as TV-conferencing or video telephone. An algorithm for coding at 1.5 Mbits/s, whose parameters were optimized via trial and error, produces pictures with little resolution loss for low-to-moderate movement, but somewhat visible moving-area resolution loss for higher movements.