Broadband digital modem
Abstract
The objective of this program was to develop a practical modem technique providing the means to trunk a large volume of digitized voice 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 b/N 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 b/N sub o of 20 db was bettered by approximately 0.5 db in laboratory tests.
- Publication:
-
Final Report
- Pub Date:
- May 1976
- Bibcode:
- 1976harc.rept.....L
- Keywords:
-
- Broadband;
- Digital Systems;
- Microwave Equipment;
- Modems;
- Bits;
- Frequency Shift Keying;
- Multichannel Communication;
- Performance Prediction;
- Communications and Radar