Pulse or digital communications – Receivers – Automatic frequency control
Patent
1997-02-28
1999-08-17
Pham, Chi H.
Pulse or digital communications
Receivers
Automatic frequency control
375326, 375329, 375331, H04L 2706
Patent
active
059404507
ABSTRACT:
Improved carrier recovery methods and apparatus suitable for use with QAM, QPSK and a wide variety of other modulation formats is described. In accordance with the invention, the phase error between received symbols, representing a frequency error, is determined using one of a plurality of techniques. The estimated frequency error is used to adjust the phase and/or frequency of a received carrier signal to achieve a frequency lock. The methods and apparatus of the present invention can be easily integrated into existing carrier recovery designs to supplement known frequency In accordance with a first embodiment of the present invention, the receipt of pairs of consecutive outer symbols is detected, a frequency error associated with each pair of consecutive symbols is generated, and the frequency error is compared to a selected threshold value to determine if it is a non-ambiguous estimate of the frequency error. If the frequency error is non-ambiguous and from a pair of consecutive outer symbols, it is used to adjust the frequency and/or phase of a received carrier signal. In the second embodiment, the receipt of pairs of consecutive outer symbols are detected. An estimate of the frequency error, determined as the phase error between received symbols, is made in the second embodiment by doing a symbol to symbol, as opposed to a symbol to target comparison.
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Koslov Joshua L.
Lane Frank A.
Emmanuel Bayard
Hitachi America Ltd.
Michaelson Peter L.
Pham Chi H.
Straub Michael P.
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