Digital signal demodulation of an OFDM signal with error correction

• US 20050175113A1
• Filed: 12/15/2004
• Published: 08/11/2005
• Est. Priority Date: 12/16/2003
• Status: Abandoned Application

• Current Assignee: Hideo Okuyama
• Original Assignee: Hideo Okuyama
• Inventors: Okuyama, Hideo
• Application Number:
  US11/014,533
• Publication Number:
  US 20050175113A1
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

A digital signal demodulator digitizes an OFDM signal at a sampling frequency from a sampling oscillator to produce a digital OFDM signal. The digital OFDM signal is converted into I and Q components using a carrier frequency from a carrier oscillator. The IQ components are transformed into digital complex symbols, and pilot signals are extracted from the complex symbols. A processor calculates an inter-symbol difference of phase differences between pilot signals to control the sampling oscillator to correct the sampling frequency; calculates an inter-symbol difference for one of the pilot signals to control the carrier oscillator to correct the carrier frequency; and calculates a phase angle for one of the subcarriers at a frequency in the middle of the plurality of subcarriers for the OFDM signal to control the carrier oscillator to correct the carrier frequency phase.

Claims

1. A digital signal demodulator for an OFDM signal comprising:

means for digitizing the OFDM signal at a given sampling frequency to produce a digital OFDM signal having complex components;

means for transforming the complex components to complex symbols;

means for extracting pilot signals from the complex symbols;

means for calculating an inter-symbol difference of phase differences between the pilot signals; and

means for correcting the given sampling frequency according to the inter-symbol difference.

2. The digital signal demodulator as recited in claim 1 wherein the calculating means comprises:

means for determining a plurality of inter-symbol differences; and

means for smoothing the plurality of inter-symbol differences to obtain the inter-symbol difference.

3. A digital signal demodulator for an OFDM signal comprising:

means for digitizing the OFDM signal at a given sampling frequency to produce a digital OFDM signal;

means for converting the digital OFDM signal to complex components using a carrier frequency;

means for transforming the complex components into complex symbols;

means for extracting pilot signals from the complex symbols in the frequency domain;

means for calculating an inter-symbol difference of phase angles for one of the pilot signals; and

means for correcting the carrier frequency according to the inter-symbol difference.

4. A digital signal demodulator for an OFDM signal comprising:

means for digitizing the OFDM signal at a given sampling frequency to produce a digital OFDM signal;

means for converting the digital OFDM signal to complex components using a carrier frequency;

means for transforming the complex components to complex symbols;

means for extracting pilot signals from the complex symbols;

means for calculating a phase angle of one of a plurality of subcarriers used by the OFDM signal using phase angles of the pilot signals; and

means for correcting a phase of the carrier frequency according to the phase angle.

5. The digital signal demodulator as recited in claim 4 wherein the one subcarrier comprises a frequency selected from approximately a center of the plurality of subcarriers.