Demodulation apparatus and method for reducing time delay of on-channel repeater in terrestrial digital TV broadcasting system

Abstract

Provided is a demodulation apparatus capable of reducing time delay of an on-channel repeater in a terrestrial digital television (TV) broadcasting system and a demodulation method thereof. The demodulation method includes the steps of a) converting an analogue intermediate frequency (IF) signal into a digital IF signal; b) generating an in-phase (I) signal and a quadrature (Q) signal by converting the frequency of the digital IF signals and down-converting the frequencies of the pilot components of the I and Q signals so that the center frequencies of the I and Q signals could be shifted to 0; c) filtering the down-converted I and Q signals and maximizing signal-to-noise ratio; d) up-converting the filtered I and Q signals into baseband signals in which the center frequencies of the filtered I and Q signals are placed in baseband and shifting the frequency of the pilot components of the filtered I and Q signals to 0; and e) adding up the up-converted I and Q signals to restore the signals into baseband signals for broadcasting.

1 . A demodulation apparatus that can reduce time delay of an on-channel repeater in a terrestrial digital television broadcasting system, comprising: 
 an analogue-to-digital conversion means for converting an analogue intermediate frequency (IF) signal into a digital IF signal;    a down-converting means for generating an in-phase (I) signal and a quadrature (Q) signal by converting the frequency of the digital IF signal and for down-converting the frequencies of the pilot components of the I and Q signals so that the center frequencies of the I and Q signals could be shifted to 0;    a filtering means for filtering the down-converted I and Q signals and maximizing signal-to-noise ratio;    an up-converting means for up-converting the filtered I and Q signals into baseband signals in which the center frequencies of the filtered I and Q signals are placed in baseband and the pilot components of the filtered I and Q signals are shifted to 0; and    an adding means for adding up the up-converted I and Q signals to restore the signals into baseband signals for broadcasting.    
   
   
       2 . The demodulation apparatus as recited in  claim 1 , wherein the down-converting means includes: 
 a first down-converter for generating an in-phase (I) component by multiplying cos(2π·f C ·nT) by the digital IF signal, f C  denoting a frequency that down-converts the pilot frequency of IF bandwidth to −2.69 MHz; and    a second down-converter for generating a quadrature (Q) component by multiplying sin(2π·f C ·nT) by the digital IF signal.    
   
   
       3 . The demodulation apparatus as recited in  claim 1 , wherein the up-converting means includes: 
 a first up-converter for shifting the center frequency to 2.69 MHz by multiplying cos(2π·f D ·nT) by the filtered I signal, f D  being a frequency that shifts the center frequency of the filtered I signal to 2.69 MHz, that is, f D  shifts the pilot component of a signal to 0; and    a second up-converter for shifting the center frequency to a frequency of 2.69 MHz, thus placing the pilot component of a signal at a frequency of 0 by multiplying sin(2π·f D ·nT) by the filtered Q signal.    
   
   
       4 . The demodulation apparatus as recited in  claim 1 , wherein the filtering means includes a first matched filter for the I signal and a second matched filter for the Q signal, performs the function of a low pass filter, and determines time delay according to the number of filter taps used in each filter, and the summation of the time delays caused by the first and second matched filters is the same as the time delay caused by one matched filter.  
   
   
       5 . A demodulation method that can reduce time delay of an on-channel repeater in a terrestrial digital television (TV) broadcasting service, comprising the steps of: 
 a) converting an analogue intermediate frequency (IF) signal into a digital IF signal;    b) generating an in-phase (I) signal and a quadrature (Q) signal by converting the frequency of the digital IF signal and down-converting the frequencies of the pilot components of the I and Q signals so that the center frequencies of the I and Q signals could be shifted to 0;    c) filtering the down-converted I and Q signals and maximizing signal-to-noise ratio;    d) up-converting the filtered I and Q signals into baseband signals in which the center frequencies of the filtered I and Q signals are placed in baseband and shifting the pilot components of the filtered I and Q signals at 0; and    e) adding up the up-converted I and Q signals to restore the signals into baseband signals for broadcasting.    
   
   
       6 . The demodulation method as recited in  claim 5 , wherein, at the step b), an in-phase (I) component is generated by multiplying cos(2π·f C ·nT) by the digital IF signal, f C  being a frequency that down-converts the pilot frequency of IF bandwidth to −2.69 MHz; and a quadrature (Q) component is generated by multiplying sin(2π·f C ·nT) by the digital IF signal.  
   
   
       7 . The demodulation method as recited in  claim 5 , wherein, at the step d), the center frequency of the filtered I signal is shifted to a frequency of 2.69 MHz by multiplying cos(2π·f D ·nT) by the filtered I signal, f D  being a frequency that shifts the center frequency to 2.69 MHz, that is, shifts the frequency of the pilot component of a signal to 0; and the center frequency is shifted to a frequency of 2.69 MHz, thus placing the pilot component of a signal at a frequency of 0 by multiplying sin(2π·f D ·nT) by the filtered Q signal.