QAM and QPRS digital broadband cable systems


  • K. Sreenath,

    1. University of Ottawa, Ottawa, Ontario, Canada KIY 4H7
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  • Kamilo Feher,

    1. Electrical Engineering, Keio University, Tokyo, Japan
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    • Kamilo Feher, Professor of Electrical Engineering, University of California, Davis, and Director, Consulting Group, DIGCOM, Inc., has 24 years of industrial and academic R&D, teaching, management and consulting experience. He has been Consultant to U.S., Canadian, and to many overseas corporations and to governments and has been presenting numerous short courses. He is known as a very productive world–class research engineer, consultant and a dynamic enthusiastic instructor. He has six U.S. and international patents. He has coauthored over 230 original research papers and is the author of five books:Advanced Digital Communications: Systems and Signal Processing Techniques (Prentice-Hall, Englewood Cliffs, NJ, 1987); K. Feher and Engineers of Hewlett Packard: Telecommunications Measurements, Analysis and Instrumentation (Prentice-Hall, Englewood Cliffs, NJ, 1987); Digital Communications: Satellite Earth Station Engineering (Prentice-Hall, Englewood Cliffs, NJ, 1983); Digital Communications: Microwave Applications (Prentice-Hall, Englewood Cliffs, NJ, 1981) and Digital Modulations Techniques in an Interference Environment, (Don White Consultants, Gainesville, VA, 1977). He has been supervising large digital communications (university and industry based) research teams. His inventions are used by internationally acclaimed major corporations throughout the world.

      His more recent major discoveries of emerging digital cellular radio (modulation-demodulation) communications and digital satellite mobile systems are expected to have most significant contributions to the ultimate objective of communications—to enable anyone to communicate instantly with anyone else from anywhere.

      For his contribution to Digital Communications R&D (as a professor at the University of Ottawa, Canada), Dr. Feher has been awarded the Steacie Memorial Fellowship, the most prestigious award of the Natural Sciences and Engineering Research Council of Canada (NSERC), the ‘Engineering Medal, Ontario, Canada’ and elected Fellow of the IEEE. He is very active in advanced technology transfer from university to industry.

  • Iwao Sasase

    1. Consulting Group, DIGCOM, Inc. and Department of Electrical Engineering, University of California, Davis, Davis, CA 95616, U.S.A.
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The performance of high-level modulation schemes in non-linear broadband digital communication systems is investigated. The tolerance of 16-, 64-, 256-QAM and 49-, 225-QPRS schemes to these non-linearities is given in terms of their phase margins. Our research results show that high level QAM schemes are less sensitive to non-linearities when operated in offset mode. Comparison of non-linearly amplified broadband QAM and QPRS schemes reveals that QPRS schemes need less carrier-to-noise ratio (CNR) than corresponding QAM schemes for identical operating conditions. Also, when the non-linearities are not severe, the degradation in performance is controlled by AM/PM characteristic of the broadband amplifier.