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Real-Time Interprocessor Serial Communications Software for Skynet EHF Trails.

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The EHF Extremely High Frequency Skynet Trials consisted of several week-long accesses over Skynet 4A during 1993. The whole link from transmitting ground terminal to Skynet to receiving ground terminal was used to simulate an EHF down-link from a payload to a ground terminal. Use of the Skynet satellite allowed the experimentation at EHF with the ground terminal and payload simulators over a link that had real satellite effects such as link degradations caused by satellite motion and weather. To conduct the trials, it was recognized that many tasks needed to be active at once pointing of antennas, monitoring power levels, synchronization, data communications and result logging. To shorten development time and simplify integration requirements, a distributed processing system multiple computers was chosen. This paper describes the communications software which provided the services necessary for the distributed processing used in the trials. The challenge was to develop a system that was easy to integrate with the user software as well as to ensure that the communications hardware and software did not conflict with special purpose boards in the various computers. For simplicity, stop-and-wait ARQ Automatic Repeat Request protocol was used for high-level message passing. Low-level communications services that do not require handshaking, were also provided for equipment control. The communications among all the processors of the distributed system.

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  • Radio Communications
  • Unmanned Spacecraft

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