Constant envelope offset QPSK modulator

Details Constant envelope offset QPSK modulator Constant envelope offset QPSK modulator

1984-05-02

1986-09-23

Griffin, Robert L.

Pulse or digital communications

Repeaters

Testing

332 16R, 332 23R, H04L 2718

Patent

active

046139761

ABSTRACT:
The modulator comprises a serial to parallel converter which separates alternate bits of a serial-binary data stream into I and Q bit streams that are stored in associated shift registers, a pair of ROMs that drive associated D/A converters, and a quadrature-phase modulator. Each bit of the I and Q bit streams has a duration of 2T, where T is the bit interval or period of a data bit. Each of the ROMs comprises blocks of memory that contain a plurality of digital words. The present and immediate past I and Q bits in the shift registers, and a baud clock signal of one-half the data signal rate, are applied to address inputs of the ROMs for selecting associated memory blocks in the 2 ROMs. A counter then clocks the ROMs for sequentially outputting the contents of the addressed memory blocks to the converters which produce analog voltages that phase modulate a carrier signal for moving a resultant signal vector with a constant envelope during each bit interval. The contents of the ROMs are selected to provide a substantially constant amplitude vector whose rate of change w of phase satisfies the criteria:

REFERENCES:
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patent: 4229821 (1980-10-01), De Jager et al.
patent: 4417219 (1983-11-01), Brossard et al.
patent: 4504802 (1985-03-01), Heatherington
Kato et al, "Cross-Correlated Phase Shift Keying System with Improved Envelope Fluctuation", 1982, IEEE Proceeding on Comm., pp. 2E.11-2E.15.
Feher et al, "New Modulation Techniques for Low Cost Power and Bandwidth Efficient Satellite Earth Stations", IEEE Transaction on Communication, vol. COM-30, No. 1, Jan. 82, pp. 275-283.
De Jager et al, "Tamed Frequency Modulation, A Novel Method to Achieve Spectrum Economy in Digital Transmission", IEEE Transaction on Communication, vol. COM-26, No. 5, May 1978, pp. 534-542.
D. Muilwijk, "Correlative Phase Shift Keying a Class of Constant Envelope Modulation Techniques", IEEE Transaction on Communication, vol. COM 29, Mar. 1981, pp. 226-236.
C. Dekker, "The Application of Tamed Frequency Modulation to Digital Transmission Via Radio", 1979 IEEE NTC, 1979, pp. 55.3.1-55.3.7.
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