Automatic frequency control circuit

Details Automatic frequency control circuit Automatic frequency control circuit

1997-11-24

2000-11-21

Ghebretinsae, Temesghen

Pulse or digital communications

Receivers

Automatic frequency control

4551922, H04L 2706

Patent

active

061513717

ABSTRACT:
Disclosed is an automatic frequency control circuit for correcting the influence of frequency offset in a radio data communication terminal of a scheme in which transmission path characteristics are obtained during the preamble period by narrow-band modulation to equalize the received signal. The automatic frequency control circuit includes, on the transmitter side, a unit for repeatedly transmitting the pattern of a predetermined pseudo noise (PN) signal serving as a preamble signal, on the receiver side, a unit for calculating the phase difference per PN cycle on the basis of the component (real and imaginary part amplitude values) of a PN signal one cycle before that is quadrature-modulated during a predetermined period of the preamble, and the component of a current PN signal, a unit for dividing the phase difference by the number of symbols of one PN cycle to obtain the phase difference (.DELTA..theta.) of the unit symbol, a unit for holding .DELTA..theta. during the burst period, a unit for integrating .DELTA..theta. in units of symbols during data demodulation, a unit for converting the integrated value into real and imaginary part amplitude values, and a unit for correcting the phase of the demodulated received signal on the basis of the obtained real and imaginary part amplitude values.

REFERENCES:
patent: 5400366 (1995-03-01), Iwamatsu
patent: 5579346 (1996-11-01), Kanzaki
patent: 5696797 (1997-12-01), Bucher et al.

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