Frequency shift offset quadrature modulation and demodulation
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United States of America Patent
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Jul 6, 1982
Grant Date -
N/A
app pub date -
Jul 30, 1980
filing date -
Jul 30, 1980
priority date (Note) -
Expired
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Abstract
A Frequency Shift Offset Quadrature (FSOQ) signal which is a constant envelope frequency-shift keyed version of an offset quaternary phase shift keyed (O-QPSK) transmission is provided. A technique for generating an FSOQ signal in a manner similar to O-QPSK by modulating offset quadrature channels with selectable pulse shapes which yields the desired 3-tone continuous phase FSK approximation of O-QPSK is disclosed. Receiver synchronization circuits are also provided which enable FSOQ to be detected as a special case of O-QPSK, whereby the detection performance of synchronous coherent QPSK, rather than the relatively inferior performance of FSK detection, is obtained. FSOQ provides a constant envelope and requires less bandwidth than minimum shift keying (MSK).
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