Broadband Digital Modem
Final rept. 13 May 74-13 Nov 75
HARRIS CORP MELBOURNE FL GOVERNMENT ELECTRONIC SYSTEMS DIV
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The objective of this program was to develop a practical modem technique providing the means to trunk a large volume of digitized vocie channels within the present FDM-FM bandwidth allocations. Specifically, a bandwidth efficiency of 2 bits per hertz of RF bandwidth and a bit error of 10 to the 7th power or less at an E sub bN sub o of 20 dB were desired. These characteristics, provided in conjunction with hard-limiting radio sets, allow efficient conversion of analog FDM-FM line-of-sight microwave systems to digital operation by replacement of the modulation elements. It was determined that 4- ary FSK was the best signal design, given the performance objectives and the constant-envelope constraint. A continuous-phase, coherent detection, multisymbol observation modem was constructed and successfully tested. The performance objective of a 10 to the 7th power bit error rate at an E sub bN sub o of 20dB was bettered by approximately 0.5 db in laboratory tests.
- Radio Communications