H - Electricity – 03 – C
Patent
H - Electricity
03
C
332/60
H03C 3/00 (2006.01) H04L 27/20 (2006.01)
Patent
CA 1207039
CONSTANT ENVELOPE OFFSET QPSK MODULATOR BY AKE SEWERINSON AND ANDREW VICTOR HELLQUIST ABSTRACT OF DISCLOSURE 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: Image where W and 2W are constant phase velocities that rotate the signal vector a total of 45° and 90°, respectively, in a bit or symbol interval.
466153
Hellquist Andrew V.
Sewerinson Ake
British Columbia Telephone Company
R. William Wray & Associates
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