Combined coherent frequency and phase shift keying modulation system
AssigneeNorthrop Corporation
InventorRobert Malm
Life of this patent
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Abstract
A system of modulation and demodulation for the transmission of binary data in the presence of multipath. The binary data modulates the phase of the carrier and the same binary data, after a delay of ".delta." bits, also modulates the frequency of the carrier. Following reception, the binary data is obtained either by frequency demodulation or by a method of coherent phase shift demodulation wherein the mark or the space frequency is selected for detection of each bit in accord with the bit received "n" bits previously. The system selects between the demodulation methods to obtain one which operates satisfactorily in the instant electromagnetic environment.
Claims6
A system for use in the modulation of binary digital data on an electromagnetic carrier and the demodulation of said data from said carrier, comprising:
- modulator means for effecting both coherent frequency and phase shift keying of said carrier in accordance with said data,
- first demodulator means for quasi-CPSK demodulating the phase shifted carrier components representing the data from said carrier,
- second demodulator means for NCFSK demodulating the frequency shifted carrier components representing the data from said carrier,
- error predictor means for determining when said first or second demodulator means has an unacceptable error rate, and
- means responsive to said error predictor means for selecting the output of the other one of said demodulating means as the demodulated output of said system whenever the current demodulating means has an unacceptable error rate.
Dependencies are inferred from the claim text.