Method and digital receiver for receiving orthogonal frequency-division multiplexed signals

A digital receiver for receiving an OFDM signal in which a plurality of subcarriers, mutually separated by a certain subcarrier frequency spacing, are modulated by differential phase-shift keying, and in which valid symbol intervals having a duration t.sub.S are separated by guard intervals having a duration t.sub.G, the digital receiver being of the type that has a local oscillator and mixer for down-converting the OFDM signal, a processor for obtaining a first array containing phase information of each subcarrier in the OFDM signal, a buffer memory for obtaining a second array by storing and thereby delaying the first array, and a differential demodulator for obtaining a differentially demodulated array representing phase differences between the first array and the second array, comprising:

• a carrier offset detector for detecting, from said first array, an integer m representing a carrier offset of said first array as a multiple of said subcarrier frequency spacing;
• a frequency controller coupled to said carrier offset detector, for tuning said local oscillator, thereby making said integer m a multiple of an integer .alpha., .alpha. being an integer closest to t.sub.S /t.sub.G ;
• and
• a carrier shifter coupled to said differential demodulator, for shifting said differentially demodulated array according to said carrier offset and selecting data of said subcarriers from the shifted differentially demodulated array.

A method of receiving an OFDM signal in which a plurality of subcarriers, mutually separated by a certain subcarrier frequency spacing, are modulated by differential phase-shift keying, the method being of the type that down-converts the OFDM signal by mixing the OFDM signal with a signal output by a local oscillator, obtains a first array containing phase information of each subcarrier in the OFDM signal, obtains a second array by delaying the first array, and obtains a differentially demodulated array representing phase differences between the first array and the second array, comprising the steps of:

• detecting, from said first array, an integer m representing a carrier offset of said first array as a multiple of said subcarrier frequency spacing;
• calculating a phase correction from said carrier offset;
• applying said phase correction to one array among said first array, said second array, and said differentially demodulated array;
• shifting said differentially demodulated array according to said carrier offset;
• and
• selecting data of said subcarriers from the shifted differentially demodulated array.

A method of receiving an OFDM signal in which a plurality of subcarriers, mutually separated by a certain subcarrier frequency spacing, are modulated by differential phase-shift keying, and in which valid symbol intervals having a duration t.sub.S are separated by guard intervals having a duration t.sub.G, the method being of the type that down-converts the OFDM signal by mixing the OFDM signal with a signal output by a local oscillator, obtains a first array containing phase information of each subcarrier in the OFDM signal, obtains a second array by delaying the first array, and obtains a differentially demodulated array representing phase differences between the first array and the second array, comprising the steps of:

• detecting, from said first array, an integer m representing a carrier offset of said first array as a multiple of said subcarrier frequency spacing;
• tuning said local oscillator, thereby making said integer m a multiple of an integer .alpha., .alpha. being an integer closest to t.sub.S /t.sub.G ;
• shifting said differentially demodulated array according to said carrier offset;
• and
• selecting data of said subcarriers from the shifted differentially demodulated array.