DIGITAL TV TRI-STATE DELTA MODULATION SYSTEM FOR SPACE SHUTTLE KU-BAND DOWNLINK
NASA/Johnson Space Center
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AbstractThe anticipated requirements for Shuttle Orbiter Ku-band downlink communication include the transmission of a digital video signal which, in addition to accommodating the black-and-white TV pictures, must also be able to relay to the ground the color TV information encoded in either field-sequential or NTSC color formats. Furthermore, at the expense of additional onboard hardware and increased bandwidth due to the digitization process, the picture privacy feature can be provided for the downlink. Thus, an objective for the future Space Shuttle TV equipment is the development of a digitization technique which is not only compatible with data rates in the range of 20 -30 Mbps, but also provides good quality pictures. This paper desribes a tri-state delta modulation/demodulation (TSDM) technique which is a good compromise between implementation complexity and performance. The salient feature of TSDM is that it provides for efficient run-length encoding of constant-intensity segments of a TV picture. Axiomatix has developed a hardware implementation of a highspeed TSDM transmitter and receiver for black-and-white TV or field-sequential color or NTSC format color. The hardware aspects of this TSDM are discussed in the paper also.
SponsorsInternational Foundation for Telemetering