Unsymmetrical QPSK demodulator

Details Unsymmetrical QPSK demodulator Unsymmetrical QPSK demodulator

1987-12-14

1989-03-21

Grimm, Siegfried H.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

331 4, 331 12, 331DIG2, 375 81, 375 83, 375120, H04L 2722

Patent

active

048147192

ABSTRACT:
The present invention is a demodulator for demodulating an unsymmetrical QPSK signal (1), i.e., one in which the amplitudes of the I and Q channels are different, and the I and Q channels have been modulated by signals having differnt bit rates. Analog versions of the I and Q modulating baseband signals are first extracted from the carrier. Each baseband signal is then subjected to a bit-rate-matched low pass filter (23, 13). The channel having the higher bit rate is subjected to a delay (32) to time-align the two baseband signals. The time-aligned filtered signals are then amplified by amplifiers (22, 12) having unequal gains that are preselected to substantially equalize the amplifier (22, 12) outputs. The amplified time-aligned filtered signals are then subjected to a phase error (E) generating means (15, 25, 16, 26, 34). The phase error (E) is passed through a loop integrator (38) and a VCO (30) and back to the baseband signal extracting means to complete a phase lock loop. Frequency searching means (40), frequency lock detect means (42, 44), and AGC control ( 46, 8) are optionally present.

REFERENCES:
patent: 4027265 (1977-05-01), Kobayashi et al.
patent: 4079329 (1978-03-01), England et al.
patent: 4085378 (1978-04-01), Ryan et al.
patent: 4092606 (1978-05-01), Ryan
patent: 4344178 (1982-08-01), Waters
patent: 4559499 (1985-12-01), Bursztejn et al.
patent: 4581586 (1986-04-01), Rubin
patent: 4713630 (1987-12-01), Matthews

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