ORTHOGONAL FREQUENCY DIVISION MULTIPLEX (OFDM) SIGNAL EQUALIZIER
An equalizer equalizes a received orthogonal frequency division multiplex (OFDM) signal which includes periodic pilot symbols. The equalizer includes a channel estimation unit which estimates a frequency response the received OFDM signal, and an equalization circuit which equalizes the received OFDM signal in accordance with the frequency response estimated by the channel estimation circuit so as to output a resultant equalized OFDM signal. The channel estimation circuit determines complex gain amounts of respective propagation channels of the OFDM signal based on the pilot symbols, applies the complex gain amounts to a window function circuit which passes given complex gain amounts among the complex gain amounts which are contained within a predetermined time region window, and computes the frequency response based on the given complex gain amounts which are contained within the predetermined time region window.
1 . An equalizer which equalizes a received orthogonal frequency division multiplex (OFDM) signal which includes periodic pilot symbols, said equalizer comprising:
a channel estimation unit which estimates a frequency response the received OFDM signal; and
an equalization circuit which equalizes the received OFDM signal in accordance with the frequency response estimated by the channel estimation circuit, and which outputs a resultant equalized OFDM signal;
wherein the channel estimation circuit determines complex gain amounts of respective propagation channels of the OFDM signal based on the pilot symbols, applies the complex gain amounts to a window function circuit which passes given complex gain amounts among the complex gain amounts which are contained within a predetermined time region window, and computes the frequency response based on the given complex gain amounts which are contained within the predetermined time region window.
2 . The equalizer of claim 1 , wherein the channel estimation unit comprises:
an extraction circuit which extracts the pilot symbols from the received OFDM signal;
an inverse Fourier transform circuit which subjects the extracted pilot symbols to inverse Fourier transformation to calculate a complex gain amount for each of the propagation channels;
a delay circuit which delays the complex gain amounts calculated by the inverse Fourier transform circuit, and which applies the delayed complex gain amounts to the window function circuit;
a comparison circuit which compares an electric power of the given complex gain amounts passed by the window function circuit with reference value, and the filtered complex gain amounts among the given complex gain amounts which exceed the reference value; and
a Fourier transform circuit which subjects the filter complex gains to Fourier transformation to obtain the frequency response of the transmission channel.
3 . The equalizer of claim 2 , further comprising an addition circuit operatively interposed between the comparison circuit and the Fourier transform circuit, wherein the addition circuit adds a predetermined value to the filtered complex gain amounts, and supplies an addition result to the Fourier transform circuit.
4 . The equalizer according to claim 1 , wherein the time region window has a time width a-b, where “a” is one symbol period, and “b” is less than “a”.
5 . The equalizer according to claim 1 , further comprising a delay circuit which delays the received OFDM signal, and applies the OFDM signal to the equalization circuit.
6 . The equalizer according to claim 1 , further comprising a second delay circuit which delays the received OFDM signal, and applies the OFDM signal to the equalization circuit.
7 . The equalizer according to claim 6 , wherein respective delay times of the second delay circuit and the delay circuit of the channel estimation circuit each correspond to one symbol period.
8 . The equalizer according to claim 1 , wherein the OFDM signal is Fourier transformed digital complex baseband signal derived from a received OFDM broadcast signal.