Patent ID: 6904098
Filing Date: 2005-06-07
Classification: H03D,H03J,H04L

Abstract:
1. 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.