Doppler frequency calculating apparatus and method and OFDM demodulating apparatus

1. A Doppler frequency calculating apparatus that calculates a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of a transmission path through which an orthogonal frequency-division multiplexing (OFDM) signal is transmitted, the apparatus comprising:

received signal point memory means for storing a received signal point of a sub-carrier having a reference carrier signal of the OFDM signal;

modulated component eliminating means for eliminating a modulated component from the received signal point stored in the received signal point memory means;

fast Fourier transform calculating means for receiving the signal point from the modulated component eliminating means from which the modulated component has been eliminated and for performing a fast Fourier transform thereon for each sub-carrier; and

Doppler frequency calculating means for receiving an output from the fast Fourier transform calculating means and for calculating therefrom a maximum Doppler frequency above a predefined amplitude threshold.

2. The Doppler frequency calculating apparatus according to claim 1 , wherein the reference carrier signal is one of transmission control information, an AC (Auxiliary Channel) signal and a CP (Continual Pilot) signal.

3. A Doppler frequency calculating apparatus that calculates a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of a transmission path through which an orthogonal frequency-division multiplexing (OFDM) signal is transmitted, the apparatus comprising:

received signal point memory means for storing a received signal point of a sub-carrier having a reference carrier signal of the OFDM signal;

modulated component eliminating means for eliminating a modulated component from the received signal point stored in the received signal point memory means; and

Doppler frequency calculating means for calculating a Doppler frequency by performing frequency analysis on the received signal point of each sub-carrier from which the modulated component has been eliminated by the modulated component eliminating means,

wherein the Doppler frequency calculating means performs a Fourier transform for each sub-carrier, the received signal point from which the modulated component has been eliminated by the modulated component eliminating means and calculates a maximum frequency above a threshold amplitude as the Doppler frequency,

and further comprising

error correction decoding means for performing error correction decoding on transmission control information,

wherein the Doppler frequency calculating means defines the threshold amplitude when the error correction decoding fails as larger than the threshold amplitude when the error correction decoding succeeds.

4. A Doppler frequency calculating method that calculates a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of a transmission path through which an orthogonal frequency-division multiplexing (OFDM) signal is transmitted, the method comprising:

storing a received signal point of a sub-carrier having a reference carrier signal of the OFDM signal;

eliminating a modulated component from the received and stored signal point;

performing a fast Fourier transform on the signal point from which the modulated component has been eliminated for each sub-carrier by using a fast Fourier transform circuit; and

receiving an output from the fast Fourier transform circuit and calculating therefrom a maximum Doppler frequency above a predefined amplitude threshold.

5. An OFDM demodulating apparatus that demodulates an orthogonal frequency-division multiplexing (OFDM) signal having a pilot signal discretely in a predetermined sub-carrier within a transmission symbol where the transmission symbol results from the division and orthogonal modulation of information for multiple sub-carriers within a predetermined band and is handled as a transmission unit, and the pilot signal has a specific amount of power and a specific phase, the apparatus comprising:

Fourier converting means for performing a Fourier conversion on the OFDM signal in transmission symbols;

pilot signal extracting means for extracting the pilot signal for each transmission symbol from a signal converted by the Fourier-converting means;

wave-equalizing means for estimating a characteristic of a transmission path of all sub-carriers within a transmission symbol by interpolating the pilot signal extracted by the pilot signal extracting means using a time direction interpolation filter and a frequency direction interpolation filter and wave-equalizing a signal having undergone Fourier-conversion by the Fourier converting means based on the estimated characteristic of the transmission path of the sub-carriers; and

Doppler frequency calculating means for storing, in a received signal point memory, the received signal point of the sub-carrier having the pilot signal of the OFDM signal, for eliminating a modulated component from the received signal point stored in the received signal point memory, and for calculating a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of the transmission path, by performing frequency analysis on the received signal point of each sub-carrier from which the modulated component has been eliminated,

wherein the wave-equalizing means calculates the characteristics of the transmission paths of all of the sub-carriers within the transmission symbol by performing interpolation using the frequency direction interpolation filter only when the Doppler frequency calculated by the Doppler frequency calculating means is larger than a threshold frequency.

6. A Doppler frequency calculating apparatus that calculates a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of a transmission path through which an orthogonal frequency-division multiplexing (OFDM) signal is transmitted, the apparatus comprising:

a received signal point memory operable to store a received signal point of a sub-carrier having a reference carrier signal of the OFDM signal;

a modulated component eliminating section operable to eliminate a modulated component from the received signal point stored in the received signal point memory;

a fast Fourier transform calculating circuit to receive the signal point from the modulated component eliminating section from which the modulated component has been eliminated and to perform a fast Fourier transform thereon for each sub-carrier; and

a Doppler frequency calculating section operable to receive an output from the fast Fourier transform calculating circuit and calculate therefrom a maximum Doppler frequency above a predefined amplitude threshold.

7. An OFDM demodulating apparatus that demodulates an orthogonal frequency-division multiplexing (OFDM) signal having a pilot signal discretely in a predetermined sub-carrier within a transmission symbol where the transmission symbol results from the division and orthogonal modulation of information for multiple sub-carriers within a predetermined band and is handled as a transmission unit, and the pilot signal has a specific amount of power and specific phase, the apparatus comprising:

a Fourier converting section operable to perform a Fourier conversion on the OFDM signal in transmission symbols;

a pilot signal extracting section operable to extract the pilot signal for each transmission symbol from a signal converted by the Fourier-converting section;

an wave-equalizing section operable to estimate a characteristic of a transmission path of all sub-carriers within a transmission symbol by interpolating the pilot signal extracted by the pilot signal extracting section using a time direction interpolation filter and a frequency direction interpolation filter and wave-equalizing a signal having undergone Fourier-conversion by the Fourier converting section based on the estimated characteristic of the transmission path of the sub-carriers; and

a Doppler frequency calculating section operable to store, in a received signal point memory section, the received signal point of the sub-carrier having the pilot signal of the OFDM signal, to eliminate a modulated component from the received signal point stored in the received signal point memory section, and to calculate a Doppler frequency, which is a magnitude of a time-dependent fluctuation of a characteristic of the transmission path, by performing frequency analysis on the received signal point of each sub-carrier from which the modulated component has been eliminated,

wherein the wave-equalizing section calculates the characteristics of the transmission paths of all of the sub-carriers within the transmission symbol by performing interpolation using the frequency direction interpolation filter only when the Doppler frequency calculated by the Doppler frequency calculating section is larger than a threshold frequency.