Carrier lock detector for a QAM system

Details Carrier lock detector for a QAM system Carrier lock detector for a QAM system

1990-02-15

1991-01-22

Grimm, Siegfried H.

Demodulators

Phase shift keying or quadrature amplitude demodulator

Input signal combined with local oscillator or carrier...

329310, 331DIG2, 375 81, 375120, H04L 2738

Patent

active

049873750

ABSTRACT:
A carrier lock detector for a quadrature amplitude modulation system includes Exclusive-OR gating circuits for determining when detected signal points occur within first areas centered on signal point positions in a phase plane diagram or second areas between the signal point positions, and for producing corresponding output signals. An integrated difference between these output signals is produced by an integrator and compared with a threshold level to provide a carrier lock detection signal. The arrangement is such that the integrated difference is substantially zero when the carrier is unlocked, so that the threshold level can be set to a low value to enable reliable operation of the detector at low signal-to-noise ratios.

REFERENCES:
patent: 4736386 (1988-04-01), Nichols
patent: 4855692 (1989-08-01), Kennard et al.
Article entitled, "Digital Amplitude-Phase Keying with M-ary Alphabets", by C. Melvil Thomas et al., IEEE Transactions on Communications, Feb. 1974, pp. 168-179.

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