Carrier recovery circuit for offset QPSK demodulators

Details Carrier recovery circuit for offset QPSK demodulators Carrier recovery circuit for offset QPSK demodulators

1994-08-05

1996-01-16

Chin, Stephen

Pulse or digital communications

Receivers

Automatic frequency control

375327, 329307, H04L 2706, H03D 318

Patent

active

054854890

ABSTRACT:
The present invention relates to a carrier recovery (CR) circuit for recovering carriers from offset quadrature phase shift keying (O-QPSK) modulated carriers, in which each of two orthogonal sequences of burst signals, to be modulated by the O-QPSK system, has a preamble field set in a prescribed bit pattern. In a Costas loop for recovering carriers by the QPSK system, a 1/2 symbol delay circuit makes the phases of burst signals inputted to two orthogonal channels identical to each other. A phase comparator for the bit timing recovery field adds with an adder 193 a detected carrier value detected by an arc tangent calculating circuit and a value resulting from the delaying of the detected carrier value with a one-symbol delay circuit, and supplies the added detected carrier value. A switching circuit switches and supplies the outputs of phase comparators, and enters the output into a loop filter.

REFERENCES:
patent: 4871975 (1989-10-01), Nawata et al.
patent: 5150384 (1992-09-01), Cahill

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