Carrier recovery apparatus for digital QAM receivers
First Claim
1. A carrier recovery apparatus for use at a demodulating end of a communication system, comprising:
- a phase detector detecting a first and a second components of a signal to be demodulated, and outputting a phase error parameter according to a correlation between said first and second components;
a frequency locker electrically connected to said phase detector, generating a frequency adjusting value and an estimated frequency error value in response to said phase error parameter; and
a lock controller electrically connected to said frequency locker, outputting a first flag status signal to said frequency locker according to a comparing result of said frequency adjusting value with a first threshold value, and controlling a changing status of said estimated frequency error value in response to said first flag status signal, said estimated frequency error value being processed according to said changing status and provided for a carrier frequency generator at said demodulating end of said communication system to generate a recovered carrier.
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Accused Products
Abstract
A carrier recovery apparatus for digital Quadrature Amplitude Modulation (QAM) receivers is disclosed. The carrier recovery apparatus includes a phase detector, a lock controller, a frequency locker and a phase loop filter, and provide phase/frequency error information for a numerically controlled oscillator (NCO) to generate recovered carrier frequency. The phase detector detects the symbol energy information and the phase error information of the extracted symbols from the I/Q extractor. The lock controller monitors the symbol energy from the phase detector, separates the extracted symbols into two groups: valid and non-valid, and outputs the control flag of valid symbols into both the frequency locker and the phase loop filter. To achieve a wide range acquisition and a good tracking performance, the lock controller controls the operation of the frequency locker and the phase loop filter in three operations. The detected frequency offset from the frequency locker and the phase offset detected from the phase loop filter are both fed into the NCO to recover the carrier offset.
11 Citations
21 Claims
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1. A carrier recovery apparatus for use at a demodulating end of a communication system, comprising:
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a phase detector detecting a first and a second components of a signal to be demodulated, and outputting a phase error parameter according to a correlation between said first and second components; a frequency locker electrically connected to said phase detector, generating a frequency adjusting value and an estimated frequency error value in response to said phase error parameter; and a lock controller electrically connected to said frequency locker, outputting a first flag status signal to said frequency locker according to a comparing result of said frequency adjusting value with a first threshold value, and controlling a changing status of said estimated frequency error value in response to said first flag status signal, said estimated frequency error value being processed according to said changing status and provided for a carrier frequency generator at said demodulating end of said communication system to generate a recovered carrier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A carrier recovery apparatus for use in a Quadrature Amplitude Modulation (QAM) receiver, comprising:
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a phase detector outputting a phase error parameter in response to an in-phase and a quadrature components of a QAM signal; a frequency locker electrically connected to said phase detector, generating a frequency adjusting value and an estimated frequency error value in response to said phase error parameter; a phase loop filter electrically connected to said phase detector, outputting an estimated phase error value in response to said phase error parameter; and a lock controller electrically connected to said frequency locker and said phase loop filter, outputting a first flag status signal to said frequency locker according to a comparing result of said frequency adjusting value with a first threshold value, and outputting a second flag status signal to said phase loop filter according to a comparing result of said frequency adjusting value with a second threshold value in order to control a first changing status of said estimated frequency error value in response to said first flag status signal, and control a second changing status of said estimated phase error value in response to said second flag status, wherein said estimated frequency error value and estimated phase error value are processed according to said first and second changing status, respectively, and provided for a carrier frequency generator at said QAM receiver to generate a recovered carrier. - View Dependent Claims (21)
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Specification