u03b8 0 is equal to the phase u03b8 3 of the 3rd frame 2003 step s 209 the symbol detector 141 receives a phase u03b8 4 of 4th frame 2004 outputted from the fft 130 difference between the reference phase u03b8 0 and the phase u03b8 4 of the 4th frame 2004 is 90 u00b0 as stated above the ttr indication signal ttr_i leads 45 u00b0 ahead of an original signal origin at the fext interference period but lags 45 u00b0 behind the original signal origin at the next interference period therefore when a prior frame is a fext signal and a present frame is a next signal a phase difference therebetween is 90 u00b0 also when the prior frame is a next signal and the present frame is a fext signal a phase difference therebetween is u2212 90 u00b0 accordingly the symbol detector 141 defines a symbol of each of the 0th to 3rd frames 2000 2003 as fext interference steps s 210 s 220 and s 221 defined symbols of the 0th to 3rd frames 2000 2003 are stored in a file 144 of fig7 according to the foregoing method symbols of the 345 frames are stored in the file 144 the correlator 145 correlates a pre defined hyperframe 146 to frames stored in the file 144 to discern which frame of the hyperframe 146 is the first frame stored in the file 144 the hyperframe 146 is illustrated in fig5 the first frame stored in the file 144 may be one of 0 th frame to 344 th frame of the hyperframe 146 fig1 exemplarily illustrates that the first frame stored in the file 144 is the 21 st frame of the hyperframe 146 even if the first frame stored in.