Digital broadcast receiver

A digital broadcast receiver for receiving a QPSK-OFDM signal with subcarrier frequencies .omega..sub.k, where k ranges over a set of consecutive integers in subcarrier frequency order, having a local oscillator with a controllable oscillation frequency, a mixer for down-converting said QPSK-OFDM signal to an intermediate-frequency signal by mixing said QPSK-OFDM signal with a signal generated by said local oscillator, and demodulating circuits for obtaining an array of complex-valued frequency-domain data X'(.omega..sub.k) from said intermediate-frequency signal, said data X'(.omega..sub.k) representing subcarrier phase information of said QPSK-OFDM signal, said QPSK-OFDM signal including a phase-reference symbol with known data z.sub.k, where z.sub.k and X'(.omega..sub.k) are encoded in subcarrier .omega..sub.k, comprising:

• a multiplier for multiplying the data X'(.omega..sub.k) demodulated from said phase-reference symbol by a complex conjugate of X'(.omega..sub.k-N), where N is a fixed integer such that z.sub.k is equal to z.sub.k-N, thereby obtaining an array of values Y'.sub.k ;
• at least one first data selector coupled to said multiplier, for selecting Y'.sub.k values from a first set of positions k, at which z.sub.k and z.sub.k-1 differ by zero radians;
• at least one second data selector coupled to said multiplier, for selecting Y'.sub.k values from a second set of positions k, at which z.sub.k and z.sub.k-1 differ by .pi. radians;
• at least one third data selector coupled to said multiplier, for selecting Y'.sub.k values from a first set of positions k, at which z.sub.k+1 and z.sub.k differ by zero radians;
• at least one fourth data selector coupled to said multiplier, for selecting Y'.sub.k values from a fourth set of positions k, at which z.sub.k+1 and z.sub.k differ by .pi. radians;
• at least one first averaging means, coupled to said first data selector, for calculating an additive mean value of the Y.sub.k values selected by said first data selector;
• at least one second averaging means, coupled to said second data selector, for calculating an additive mean value of the Y.sub.k values selected by said second data selector;
• at least one third averaging means, coupled to said third data selector, for calculating an additive mean value of the Y.sub.k values selected by said third data selector;
• at least one fourth averaging means, coupled to said fourth data selector, for calculating an additive mean value of the Y.sub.k values selected by said fourth data selector;
• a first subtractor, coupled to said first averaging means and said second averaging means, for calculating a first difference between the additive mean value calculated by said first averaging means and the additive mean value calculated by said second averaging means;
• a second subtractor, coupled to said third averaging means and said fourth averaging means, for calculating a second difference between the additive mean value calculated by said third averaging means and the additive mean value calculated by said fourth averaging means;
• and
• a frequency offset detector coupled to said first subtractor and said second subtractor, for calculating a frequency offset from said first difference and said second difference, and adjusting the oscillation frequency of said local oscillator according to said frequency offset.