Patent ID: 6028900
Filing Date: 2000-02-22
Classification: H04L

Abstract:
A method of tuning a digital broadcast receiver having a local oscillator and a discrete-Fourier-transform processor, in order to receive a PSK-OFDM signal having a frame-synchronization symbol, a phase-reference symbol, and data symbols, the receiver down-shifting the PSK-OFDM signal by mixing the PSK-OFDM signal with an unmodulated signal output by the local oscillator, thereby obtaining a baseband signal in which a plurality of subcarriers occur with a certain subcarrier frequency spacing, the discrete-Fourier-transform processor obtaining therefrom an array of frequency-domain data, and the phase-reference symbol encoding known data as phase angles of subcarriers of said PSK-OFDM signal, comprising the steps of:(a) detecting said frame-synchronization symbol;(b) synchronizing said discrete-Fourier-transform processor to said frame-synchronization symbol;(c) detecting a first frequency error of said local oscillator by processing the frequency-domain data obtained by said discrete-Fourier-transform processor from said phase-reference symbol, said first frequency error being equal to an integer multiple of said subcarrier frequency spacing;(d) detecting a second frequency error of said local oscillator by processing the frequency-domain data obtained by said discrete-Fourier-transform processor from said phase-reference symbol, said second frequency error not exceeding said subcarrier frequency spacing;(e) detecting a third frequency error of said local oscillator by processing phase information in the frequency-domain data obtained by said discrete-Fourier-transform processor from said data symbols;(f) adjusting said local oscillator responsive to said first frequency error and said third frequency error until said first frequency error is reduced to zero and said third frequency error does not exceed a first threshold;(g) adjusting said local oscillator responsive to said second frequency error after said step (f), if said second frequency error exceeds a second threshold; and(h) repeating said steps (f) and (g) until said first frequency error is zero and said second frequency error does not exceed said second threshold, and continuing thereafter to adjust said local oscillator responsive to said third frequency error.