Patent ID: 7792216

Claim:
A timing estimator of an OQPSK demodulator comprising: an A/D converter for converting an analog reception signal into a digital reception signal: a differential circuit section for delaying the digital reception signal from the A/D converter by a preset time and obtaining a phase difference between a conjugate complex number signal of the delayed digital reception signal and the digital reception signal from the A/D converter to offset a frequency error contained in the digital reception signal; a correlation operation section for performing a correlation operation between a reference symbol differentiated in the same way as a differentiation of the differential circuit section and the reception signal from the differential circuit section to obtain each correlation value; and a coherent detector for detecting a coherent point on the basis of the correlation value from the correlation operation section; wherein the differential circuit section comprises: a delay for delaying the digital reception signal from the A/D converter by a preset time; a conjugate complex number section for extracting a conjugate complex number signal from a signal from the delay; and a multiplier for multiplying the digital reception signal from the A/D converter with the conjugate complex number signal from the conjugate complex number section; and wherein the correlation operation section comprises: a first matched filter for performing a correlation operation between a real number part of the reference symbol differentiated in the same way as the differentiation of the digital reception signal and a real number part of the digital reception signal from the differential circuit section; a second matched filter for performing a correlation operation between an imaginary number part of the reference symbol differentiated in the same way as the differentiation of the digital reception signal and an imaginary number part of the digital reception signal from the differential circuit section; a third matched filter for performing a correlation operation between the real number part of the reference symbol differentiated in the same way as the differentiation of the digital reception signal and the imaginary number part of the digital reception signal from the differential circuit section; a fourth matched filter for performing a correlation operation between the imaginary number part of the reference symbol differentiated in the same way as the differentiation of the digital reception signal and the real number part of the digital reception signal from the differential circuit section; a first adder for adding correlation values of the first and second matched filters; a second adder for adding correlation values of the third and fourth matched filters; a first squaring section for obtaining the square of an output value from the first adder; a second squaring section for obtaining the square of an output value from the second adder; and an adder for outputting values of the first and second squaring sections.