Patent ID: 7701841

Claim:
An orthogonal frequency division multiplexing (OFDM) demodulating apparatus that handles a transmission symbol containing a valid symbol resulting from modulation of multiple sub-carriers by multiple pieces of data resulting from division of information and a guard interval resulting from a copy of a partial signal waveform of the valid symbol as a transmission unit and demodulates an OFDM signal with the transmission symbol having a predetermined sub-carrier discretely containing pilot signals with a specific amount of power and a specific phase, the apparatus comprising: delay profile creating means for creating a delay profile from the OFDM signal by a predetermined method of a time domain; Fourier converting means for defining a calculation range for a valid symbol period from each transmission symbol of the OFDM signal and for performing a Fourier conversion on the defined calculation range; pilot signal extracting means for extracting, for each transmission symbol, the pilot signals from the signal converted by the Fourier converting means; transmission path characteristic estimating means for estimating a transmission path characteristic of all of the transmission symbols by interpolating the pilot signals extracted by the pilot signal extracting means using a time-direction interpolation filter; inverse Fourier converting means for creating a delay profile by performing an inverse Fourier conversion, for each transmission symbol, on the transmission path characteristic estimated by the transmission path characteristic estimating means; and window control means for creating a delay profile for defining a calculation range based on the delay profile created by the delay profile creating means and the delay profile created by the inverse Fourier converting means and for controlling the calculation range based on the delay profile for defining a calculation range, wherein the window control means creates the delay profile for defining a calculation range by leaving a path which exists at a same position in both the delay profile created by the delay profile creating means and the delay profile created by the inverse Fourier converting means and the number of times of detection of which path is equal to or higher than a threshold value and defines a higher threshold value for the path at a predetermined position from the position of the main path within the delay profile created by the inverse Fourier converting means than for the paths at the other positions, wherein the delay profile creating means creates the delay profile by extracting a signal waveform of the guard interval part of the main path from each of the transmission symbols of the OFDM signals and obtaining the coherence between the guard interval part and the other part of the transmission symbol.