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Coding and Processing for Reliable Data Transmission,
ARMY COMMUNICATIONS RESEARCH AND DEVELOPMENT COMMAND FORT MONMOUTH NJ
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The coding and processing techniques discussed in this paper are designed to improve the reliability of digital message reception in the presence of noise. High noise conditions occur quite frequently during radio reception especially when these signals originate at forward area military positions. The usual cause for this poor radio reception is related to the constraints imposed by low transmitter power, limits on air time, and unfavorable terrain conditions. The importance of improving the reliability of forward area message reception is stressed because the information so obtained provides essential descriptors that are pertinent to command and control functions. In an effort to determine the cause of message delivery failure in the presence of increasing noise, laboratory tests were performed under controlled noise conditions. The results of these tests indicated that as the signal-to-noise power ratio decreased errors first appeared in the data character framing information. It should be noted that the message synchronizing procedure used to decode received digital data is hierarchical in nature involving bit synchronization, data character framing, and message block identification. If any one of these functions is not correctly implemented the transmitted message cannot be successfully decoded. Ideally, as increased noise degrades the data communications channel the synchronizing system should not fail before the message information becomes unintelligible a condition that is presently not satisfied because data character framing requires error-free code reception. Author
APPROVED FOR PUBLIC RELEASE