US 6,904,098 B1Granted

Linear phase robust carrier recovery for QAM modems

AssigneeWideband Semiconductors, Inc.

InventorsDavid Bruce Isaksen, Byron Esten Danzer

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Abstract

In a QAM demodulator including an adaptive equalizer, a method of carrier tracking comprising the following steps is disclosed: (A) sampling a QAM signal received from a transmission channel; (B) recovering a symbol clock function from the sampled QAM signal; (C) applying the sampled QAM signal to the adaptive equalizer in order to obtain a QAM equalized signal in a Blind Equalization (BE) mode; (D) using a slicer to locate a nearest plant point for the QAM Blind equalized signal for each recovered symbol clock; (E) using a complex conjugate multiplier to obtain an instantaneous inphase component and an instantaneous quadrature component of a phase angle error signal; (F) using a linear phase detector to obtain an instantaneous phase angle error for each symbol clock; (G) averaging the instantaneous phase angle error signal by using a carrier loop filter; (H) using a complex multiplier to insert an inverse of the averaged phase angle error signal into the QAM Blind equalized signal to compensate for the carrier phase angle error; and (I) repeating the steps (D-H) to close a carrier frequency loop.

Claims35

Dependent claims

In a QAM demodulator including an adaptive equalizer, a method of carrier tracking comprising the steps of:

(A) sampling a QAM signal received from a transmission channel;
(B) recovering a symbol clock function from said sampled QAM signal;
(C) applying said sampled QAM signal to said adaptive equalizer in order to obtain a QAM equalized signal in a Blind Equalization (BE) mode;
(D) using a slicer to locate a nearest plant point for said QAM Blind equalized signal for each said recovered symbol clock;
(E) using a complex conjugate multiplier to obtain an instantaneous inphase component and an instantaneous quadrature component of a phase angle error signal by comparing an inphase component and a quadrature component of said QAM Blind equalized signal and an inphase and a quadrature component of said nearest plant point for each said symbol clock;
(F) using a phase detector to translate said inphase component and said quadrature component of said phase angle error signal into an instantaneous phase angle error for each said symbol clock;
(G) averaging said instantaneous phase angle error signal by using a carrier loop filter;
(H) using a complex multiplier to insert an inverse of said averaged phase angle error signal into said QAM Blind equalized signal to compensate for said carrier phase angle error;
and
(I) repeating said steps (D-H) to close a carrier frequency loop, wherein said carrier frequency loop includes said complex multiplier, said slicer, said phase detector including said complex conjugate multiplier, and said carrier loop filter, and wherein said QAM input signal includes said input carrier frequency within an acquisition bandwidth of said carrier frequency loop.

7 more elements

An apparatus for robust carrier recovery in a QAM demodulator, said apparatus comprising:

a sampling block configured to sample a QAM signal received from a transmission channel;
a symbol clock recovery block coupled to said sampling block;
said symbol clock recovery block configured to recover a symbol clock function from said sampled QAM signal;
an adaptive equalizer coupled to said symbol clock recovery block;
said adaptive equalizer configured to transform said sampled QAM signal into a QAM equalized signal in a Blind Equalization (BE) mode;
a slicer configured to locate a nearest plant point for said QAM Blind equalized signal for each said recovered symbol clock;
a complex conjugate multiplier coupled to said slicer, said complex conjugate multiplier configured to obtain an instantaneous inphase component and an instantaneous quadrature component of a phase angle error signal by comparing an inphase component and a quadrature component of said QAM Blind equalized signal and an inphase and a quadrature component of said nearest plant point for each said symbol clock;
a linear phase detector configured to translate said inphase component and said quadrature component of said phase angle error signal into an instantaneous phase angle error for each said symbol clock;
a carrier loop filter configured to average said instantaneous phase angle error signal;
and
a complex multiplier configured to insert an inverse of said averaged phase angle error signal into said QAM Blind equalized signal to compensate for said carrier phase angle error;
wherein said QAM input signal includes an input carrier frequency within an acquisition bandwidth of said carrier frequency loop.

9 more elements

Dependencies are inferred from the claim text.