Automatic frequency control method and apparatus therefor

Details Automatic frequency control method and apparatus therefor Automatic frequency control method and apparatus therefor

1995-03-27

1996-10-15

Chin, Stephen

Pulse or digital communications

Receivers

Angle modulation

375344, 329304, 4551641, 4551922, H04L 2722

Patent

active

055662110

ABSTRACT:
An automatic frequency control apparatus used in an MPSK communication system detects a frequency offset between a carrier and a local oscillation signal for adjustment of a local oscillation frequency. A phase difference detector generates a first phase difference detection signal having, as a phase value, a difference between the phases of various samples of the sampled signal. A phase altering unit generates a second phase difference detection signal having a phase value different from that of the first phase difference detection signal. A frequency offset signal generator estimates transmission phase information by using the phase value of the second phase difference detection signal and reference phase signals used for MPSK modulation, thereby generating a frequency offset signal which is determined by the transmission phase signal and the second phase difference detection signal. The result is that the number of the reference phases which are used for determination of the transmission phase information by altering the phase of the phase difference signal, is reduced. Accordingly, the hardware cost for implementing the apparatus can be lowered. The invention can be used for automatic frequency control in a modem which is used for all the types of MPSK modulation.

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AFT Tracking Algorithms, Francis D. Natali, IEEE Transactions on Communication, COM-32, No. 8, Aug. 1984, pp. 935-947.
WAM 11.8, A new QPSK Demondulator for Digital DBS Receivers, Ishikawa et al., Video & Electronics Media Engineering Lab. Toshiba Corporation, IEEE 1992, pp. 192-193.

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