| 摘要 |
A carrier lock detector for a QPSK or 4-QAM system implements, a lock detection algorithm that maps detected signals onto one of first and second areas associated with nominal states defined by (I<SUB>2</SUB>⊕I<SUB>3</SUB>).(Q<SUB>2</SUB>⊕Q<SUB>3</SUB>) and {overscore (Q<SUB>1</SUB>⊕Q<SUB>2</SUB>)}.(I<SUB>1</SUB>{overscore (I<SUB>2</SUB>I<SUB>3</SUB>)}+{overscore (I<SUB>1</SUB>)}I<SUB>2</SUB>I<SUB>3</SUB>)+({overscore (I<SUB>1</SUB>⊕I<SUB>2</SUB>)}).(Q<SUB>1</SUB>{overscore (Q<SUB>2</SUB>Q<SUB>3</SUB>)}+{overscore (Q<SUB>1</SUB>)}Q<SUB>2</SUB>Q<SUB>3</SUB>), or alternatively, by ({overscore (I<SUB>1</SUB>⊕I<SUB>2</SUB>)}.{overscore (Q<SUB>2</SUB>⊕Q<SUB>3</SUB>)})+({overscore (Q<SUB>1</SUB>⊕Q<SUB>2</SUB>)}.{overscore (I<SUB>2</SUB>⊕I<SUB>3</SUB>)}), respectively. When detected signals map onto one of the first areas, a first signal is generated. When detected signals map onto one of the second areas, a second signal is generated. When a difference between the first and second signals exceeds a threshold, a carrier lock detection signal is generated to enable a decoder. The carrier lock detector is able to detect carrier lock at a raw BER of 1e-2 or greater at a very low signal-to-noise ratio.
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