Correlation value calculation method and correlator using the same
Object: Even in the case where a receiving signal including a long delayed path having an equivalent power are received, deterioration of the receiving characteristics caused by inter symbol interference is reduced by reducing the variation of the maximum correlation time location and stabilizing the FFT time synchronization. Solution: By correlation calculation method of the correaltor 20, the receiving signal S 19 is inputted, three correlation values having different time locations from each other are calculated by the delay circuits 21 - 2 - 21 - 5, the multiplying circuits 22 - 1 - 22 - 3, and the integration circuit 23 - 1 - 23 - 3, the three correlation values thereof are added by the adding circuit 24, and the above adding result is outputted as one correlation value. Consequently, since a strong correlation appears in the midpoint between the main arriving path and the long-delayed path when the long-delayed path having the equivalent power to the main arriving path exists, jitter of the time synchronization thereof can be restrained.
1 . A correlation value calculation method being characterized by comprising;
a step for calculating a plural of correlation values located different time locations by delaying receiving OFDM modulated signals having effective symbols added by guard intervals; and
a step for generating a correlation output signal for FFT time synchronization by adding said plural of correlation values each other.
2 . The correlation value calculation method according to claim 1 , wherein said plural of correlation values are added after being weighted.
3 . The correlation value calculation method according to any of claim 1 , wherein the number of said plural of correlation values is three.
4 . A correlator being characterized by comprising;
a correlation value calculation means for calculating a plural of correlation values located different time locations by delaying receiving OFDM modulated signals having effective symbols added by guard intervals; and
an adding means for adding said plural of correlation values each other and outputting a correlation output signal for FFT time synchronization.
5 . The correlator according to claim 4 , being characterized by further comprising;
a weighting means for weighting said plural of correlation values calculated by said correaltion value calculation means and making said adding means add said plural of weighted correlation values.
6 . The correlator according to any of claim 4 , wherein said correlation value calculation means comprises
a multiplying means for multiplying a not-delayed receiving signal and a delayed signal in said delaying means,
a integration means for integrating the multiplying results of said multiplying means and getting said plural of correlation values having a constant delay time interval between each other.
7 . The correlator according to claim 6 , wherein said delay means comprises a plural of delay circuits.
8 . The correlator according to claim 6 , wherein said delay means includes a memory for storing said receiving signal, and outputting said receiving signal by delaying said receiving signal by a required delay time.
9 . The correlator according to claim 6 , wherein said delay means comprises
a memory for storing said receiving signal and delaying said receiving signal by a required delay time, and
an address decoder for making the delay time interval between outputs from said memory changeable by changing generated address values.
10 . The correlator according to any of claims 5 , wherein said weighting means comprises a gain circuit for multiplying a constant.
11 . The correlator according to any of claims 5 , wherein the number of said plural of correlation values is three.
12 . The correlator according to claim 11 , wherein said weighting means comprises two gain circuits for multiplying two correlation values except one correlation value located in the time center out of said three correlation values by a constant.