JP2002335225A - Device and method for ofdm receiving - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set an FFT time window at an optimal position corresponding to receiving conditions. SOLUTION: An OFDM receiving device 1 is provided with a frequency converting part 12, orthogonal demodulating part 13 for generating the OFDM signal of a baseband, FFT arithmetic part 14 for outputting the OFDM signal of a frequency area by applying Fourier transformation to the OFDM signal of the baseband, equalizer 15, group delay calculating part 16 and time window position setting part 17. The group delay calculating part 16 calculates the group delay from the phase difference of respective carrier waves in the OFDM signal of the frequency area, to which FFT arithmetic is applied. Corresponding to the calculated group delay, the time window position setting part 17 sets the time window of Fourier transformation at the optimal position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an orthogonal frequency division multiplex (OFDM).
exing) O applied to digital broadcasting etc. by the transmission method
The present invention relates to an FDM receiving apparatus and method.

[0002]

2. Description of the Related Art In recent years, as a method for transmitting digital signals, orthogonal frequency division multiplexing (OFDM) has been proposed.
A modulation scheme called quency division multiplexing has been proposed. In this OFDM system, a number of orthogonal carriers (subcarriers) are provided in a transmission band, data is allocated to the amplitude and phase of each subcarrier, and P
SK (Phase Shift Keying) and QAM (Quadrature Amp)
This is a method of performing digital modulation by litude modulation.

In this OFDM system, since the transmission band is divided by a number of subcarriers, the band per subcarrier wave is narrowed and the modulation speed is reduced, but the total transmission speed is not different from the conventional modulation system. It has the feature of.

[0004] Further, the OFDM system has a feature that the symbol rate is reduced because a large number of subcarriers are transmitted in parallel. Therefore, in the OFDM system, the time length of the multipath relative to the time length of the symbol can be shortened, and multipath interference is reduced. Further, in the OFDM method, data is allocated to a plurality of subcarriers, so that IFFT (Inverse Fast Fou ou) that performs inverse Fourier transform during modulation is performed.
A transmitter / receiver circuit can be configured by using a FT (Fast Fourier Transform) arithmetic circuit that performs a Fourier transform at the time of demodulation.

[0005] From the above characteristics, the OFDM system has been widely studied for application to terrestrial digital broadcasting which is strongly affected by multipath interference. Such OF
In Japan, terrestrial digital broadcasting adopting the DM system is ISDB-T (Integrated Services Di
gital Broadcasting-Terrestrial) has been proposed.

[0006] A transmission signal according to the OFDM scheme is transmitted in a symbol unit called an OFDM symbol as shown in FIG. The OFDM symbol in this time domain is composed of an effective symbol and a guard interval. The guard interval is provided to reduce the influence of the multipath signal, and is a copy of the waveform at the end of the effective symbol as it is. The guard interval is 1/4, 1/8, 1/16, 1/3 of the effective symbol.
The signal has a time length of 2.

An OFD that receives such an OFDM signal
The M receiver demodulates the received OFDM signal into a frequency domain by performing an FFT operation. The FFT operation uses OFD composed of an effective symbol and a guard interval.
For M symbols, the effective symbol length calculation range (FFT
Time window) and set the data in the set range to OFDM
Cut out from the symbol and perform FFT operation.

A case where an FFT time window is set for an OFDM symbol will be described with reference to FIG. This FIG.
In OFDM symbol j, the effective symbol length t _u ,
And it is configured from the guard interval t _g. Since the guard interval is a copy of the end portion of the effective symbol, the orthogonality of FFT can be maintained even when the FFT time window is set to include the guard interval like Win1 or Win2. In addition, orthogonality can be maintained even in the case of setting according to the effective symbol length as in Win3.

However, adjacent OFDs such as Win4
When the FFT time window is set so as to include M symbols k, OFDM symbol j and OFDM symbol k interfere with each other, and the orthogonality of FFT cannot be maintained.

Therefore, the OFDM receiving apparatus
When demodulating an FDM signal, an FFT time window is always set to a single OFD to prevent interference between adjacent symbols.
It is necessary to set to include only M symbols.

Next, a method of setting the FFT time window will be described. In this setting method, the correlation between the waveform of the guard interval portion and the waveform of the latter half of the OFDM symbol is obtained, and the boundary position of the OFDM symbol is obtained. And
An FFT time window is set based on the obtained OFDM symbol boundary position.

[0012] Specifically, as shown in FIG.
The received signal and s (t), an OFDM delayed signal delayed by the effective symbol length _{t u} of the OFDM received signal s
When (t−t _u ), a complex correlation function ρ (t) as shown in the following equation is obtained.

[0013]

(Equation 1)

An end portion of the effective symbol of the main signal s (t) and an OFDM delay signal s obtained by copying this end portion.
The waveforms of the guard interval (t− _tu ) match.
Therefore, as shown in FIG. 9, is delayed by the effective symbol length t _u a delay signal, the absolute value of the complex correlation function [rho (t) is maximized. By detecting the maximum absolute value of the complex correlation function ρ (t), the boundary position of the OFDM symbol can be obtained. For example, the number of clocks is counted from the boundary position of the obtained OFDM symbol, and
The timing at which the FT time window is turned ON (FFT start timing) can be determined.

Next, a specific configuration example of the OFDM receiver 5 will be described with reference to FIG.

The OFDM receiving apparatus 5 includes a receiving antenna unit 5
1, a frequency converter 52, a quadrature demodulator 53, an FFT
A computing unit 54, a time window position setting unit 55, and an equalizer 5
6 and a data output terminal 57.

The receiving antenna unit 51 outputs OF waves as broadcast waves.
It receives the DM signal and outputs it to the frequency converter 52.

The frequency converter 52 converts the frequency of the input OFDM signal in the radio frequency band to the intermediate frequency band. The frequency conversion section 52 outputs the frequency-converted OFDM signal to the quadrature demodulation section 53.

The quadrature demodulation unit 53 has a frequency-converted OF
A DM signal is orthogonally demodulated to generate a baseband OFDM signal. The quadrature demodulation unit 53 outputs the generated baseband OFDM signal to the FFT calculation unit 54 and the time window position setting unit 55.

The FFT operation unit 54 performs an FFT operation on the baseband OFDM signal in the time domain with respect to the FFT operation range of the effective symbol length to generate a frequency domain OFDM signal. The calculation range (FFT time window) is controlled by the time window position setting unit 55. A specific configuration example of the time window position setting unit 55 will be described later in detail.

The generated frequency domain OFDM signal is
It is output to the equalizer 56. This equalizer 56
For example, using a pilot signal, OFDM in the frequency domain
By performing phase equalization, amplitude equalization, and the like of a signal, a distortion component in a transmission path is removed. The equalizer 56 outputs the OFDM signal subjected to these processes to a reception data output terminal 57.
Output to

Next, a specific configuration example of the time window position setting section 55 will be described with reference to FIG.

The time window position setting unit 55 includes an effective symbol delay circuit 101, a complex conjugate multiplication circuit 102, a cumulative addition circuit 103, an absolute value circuit 104, and a comparison circuit 105
, A selection circuit 106, a first register 107, a counter 108, a second register 109, a third register 110, an AND circuit 111, and an offset amount setting circuit 112.

The effective symbol delay circuit 101, a baseband OFDM signal inputted from the orthogonal demodulation section 53 only the effective symbol length _{t u} is delayed, outputs to the complex conjugate circuit 102.

The complex conjugate circuit 102 receives signals from the quadrature demodulation unit 53 and the effective symbol delay circuit 101. Further, the complex conjugate circuit 102 and the cumulative addition circuit 103 calculate a correlation value ρ from the input signal.

The absolute value circuit 104 includes a cumulative addition circuit 103
Is input. The absolute value circuit 104 compares the absolute value of the input correlation value ρ with the comparison circuit 10.
5 and the selection circuit 106.

The comparison circuit 105 receives the absolute value of the correlation value ρ from the absolute value circuit 104,
7, the correlation value ρ ′ is input. This comparison circuit 105
Is the correlation value ρ input from the absolute value circuit 104 and the first
Of the correlation value ρ ′ input from the register 107 of
When the correlation value ρ is larger, the selection circuit 106 is controlled to select the correlation value ρ input from the absolute value circuit 104, and the value of the counter 108 is stored in the second register 109. Control.

The selection circuit 106 receives the absolute value of the correlation value ρ from the absolute value circuit 104,
7, the correlation value ρ ′ is input. In the selection circuit 106, the correlation value ρ input from the absolute value circuit 104 and the first
And selects one of the correlation values ρ ′ input from the register 107, and outputs the selected correlation value to the first register 107. The selection of the correlation value is performed by the comparison circuit 1
05.

The first register 107 temporarily stores the input correlation value and compares the temporarily stored correlation value ρ ′ with the comparison circuit 1.
05 and the selection circuit 106. By repeating the above processing, finally, the maximum value ρ _MAX of the correlation value is temporarily stored in the register 107.

The counter 108 is a counter for counting clocks in an OFDM symbol.

The second register 109 includes a comparator 105
, The value of the counter 108 is stored. The stored value is output to the third register 110. Eventually, the time position when the correlation value ρ is the maximum is stored in the second register 109.

The third register 110 stores the time position when the correlation value ρ is maximum for each OFDM symbol.
The stored time position becomes a boundary position of the OFDM symbol.

The AND circuit 111 includes a third register 11
By ANDing 0 with the counter 108, the boundary position of the OFDM symbol is output.

The offset amount setting circuit 112 sets the start timing of the FFT based on the boundary position of the OFDM symbol input from the AND circuit 111. The offset amount setting circuit 112 outputs to the FFT calculation unit 54 the start timing of the FFT in which a fixed time delay has been applied to the boundary position of the OFDM symbol.

By receiving the OFDM signal by the conventional OFDM receiver 5, the boundary position of the OFDM symbol can be obtained, so that the FFT start timing can be set based on the obtained boundary position.

[0036]

However, in the case of terrestrial broadcasting, OFDM is strongly affected by the multipath signal due to the terrain around the receiving position and the surrounding environment such as buildings.
The signal received by the receiving device becomes a combined wave obtained by combining a plurality of multipath signals (hereinafter, a signal having the highest power among the combined waves is referred to as a main signal). Since the time position where the correlation value becomes maximum is dominated by the main signal having a large power, the FFT time which is not affected by the multipath signal can be obtained by using the time position where the correlation value of the main signal becomes the maximum as a reference. Windows can be set.

In general, a multipath signal is generated by a signal broadcast from a broadcasting station being reflected by a building, a mountain, or the like, and is therefore delayed compared to the main signal. In such a case, for example, as shown in FIG.
Is set in accordance with the end of the OFDM symbol j of the main signal. With this setting, for the main signal, the effective symbol position and the position of the FFT time window match, so that orthogonality can be maintained. For a multipath signal, data in the guard interval of the OFDM symbol j is cut out. Since the guard interval is a copy of the end portion of the effective symbol, the orthogonality of FFT can be maintained. Thereby, stable reception without inter-symbol interference can be realized.

However, in some cases, reception must be realized in a situation where the multipath signal is ahead of the main signal.

As such a case, for example, reception in a gap filler environment as shown in FIG. 13 can be considered.
In FIG. 13, point A is a point where the main transmitting station 121 is installed. Point B is a point where the gap filler station 122 is installed. The gap filler station 122 normally transmits the transmission signal a from the main transmission station 121.
The wave is received, the wave a is relay-amplified, and retransmitted as the wave b. Therefore, the b-wave is transmitted later than the a-wave, and the receiver 123 at the point C receives the b-wave later than the a-wave. Here, since the b-wave is amplified in the gap filler station 122, the level is often higher than that of the a-wave. That is, a high-level b wave can be considered as a main signal, and a low-level a wave can be considered as a multipath signal. In particular, mobile receivers use omni-directional antennas as receiving antennas due to their mobility, and receive all signals.Therefore, there are cases where a multipath signal that is earlier in phase than the main signal is received. Many.

In the case where such a multipath signal having a phase preceding the main signal exists, if the FFT time window is set in accordance with the end of the symbol j of the main signal as shown in FIG. Will occur. Therefore, even in such a case, it is necessary to set the FFT time window at an appropriate position according to the reception situation.

However, the conventional OFDM device 5
Since the FFT time window is uniformly set based on the FFT start timing, it is not possible to flexibly cope with the reception situation, and intersymbol interference may occur.

Therefore, the present invention has been proposed in view of the above-mentioned situation, and even if the multipath signal is ahead of the main signal, the FFT is located at an optimum position according to the reception situation. An object of the present invention is to provide an OFDM receiving apparatus and method capable of setting a time window.

[0043]

In order to achieve the above object, an OFDM receiving apparatus according to the present invention comprises:
Frequency conversion means for converting the frequency of the M signal to an intermediate frequency, and OFD frequency-converted by the frequency conversion means
A quadrature demodulation unit for quadrature demodulating the M signal to output a baseband OFDM signal; an OFDM modulation unit for performing a Fourier transform on the baseband OFDM signal to output a frequency domain OFDM signal; Group delay calculating means for calculating a group delay from a phase characteristic of each carrier of the signal, and the OF according to the calculated group delay
A time window position setting means for setting a time window of the Fourier transform in the DM modulation means.

This OFDM receiver calculates a group delay from the phase difference of each carrier in the Fourier-transformed frequency-domain OFDM signal, and sets a Fourier transform time window at an optimum position according to the calculated group delay. To achieve the above object, an OFDM receiving method according to the present invention is an OFDM receiving method for receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising: converting a frequency of a received OFDM signal to an intermediate frequency; Orthogonally demodulates the generated OFDM signal to generate a baseband OFDM signal, Fourier transforms the generated baseband OFDM signal to generate a frequency domain OFDM signal, and generates each carrier of the generated frequency domain OFDM signal. , A group delay is calculated from the phase characteristics in the above, and the OFD is calculated according to the calculated group delay.
It is characterized in that a time window of the Fourier transform in the M modulation means is set.

In this OFDM receiving method, the group delay is calculated from the phase difference between the respective carriers in the Fourier-transformed frequency-domain OFDM signal, and the time window of the Fourier transform is set at an optimum position according to the calculated group delay.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS OFDM to which the present invention is applied
An embodiment of a receiving device and a method will be described in detail with reference to the drawings.

FIG. 1 shows an OF according to the first embodiment of the present invention.
FIG. 1 shows a configuration diagram of a DM receiver 1.

The OFDM receiver 1 includes a receiving antenna unit 1
1, the frequency converter 12, the quadrature demodulator 13, the FFT
Operation unit 14, equalizer 15, group delay calculation unit 16
, A time window position setting unit 17, and a data output terminal 20.

The receiving antenna section 11 outputs
It receives the DM signal and outputs it to the frequency converter 12.

The frequency converter 12 converts the frequency of the input OFDM signal in the radio frequency band to an intermediate frequency band. The frequency converter 12 outputs the frequency-converted OFDM signal to the quadrature demodulator 13.

The quadrature demodulation unit 13 converts the frequency-converted OF
A DM signal is orthogonally demodulated to generate a baseband OFDM signal. The quadrature demodulation unit 13 outputs the generated baseband OFDM signal to the FFT calculation unit 14 and the time window position setting unit 17.

The FFT operation unit 14 performs an FFT operation on the baseband OFDM signal in the time domain with respect to the FFT operation range of the effective symbol length to generate a frequency domain OFDM signal. The calculation range (FFT time window) is controlled by the time window position setting unit 17. A specific configuration example of the time window position setting unit 17 will be described later in detail.

The generated frequency domain OFDM signal is
Output to the equalizer 15. This equalizer 15
For example, using a pilot signal, OFDM in the frequency domain
By performing phase equalization, amplitude equalization, and the like of a signal, a distortion component in a transmission path is removed. The equalizer 15 outputs the processed OFDM signal to the group delay calculator 16 and the data output terminal 20.

The group delay calculator 16 calculates the group delay of the input OFDM signal in the frequency domain. The calculation method will be described later in detail. The group delay calculation unit 16 outputs the calculation result of the group delay to the time window setting unit 17.

The time window position setting section 17 obtains the boundary position of the OFDM symbol, and sets the FFT start timing from the obtained boundary position. The time window position setting unit 17 controls the FFT start timing when performing the FFT calculation according to the input group delay.

Next, the procedure for setting the FFT time window of the OFDM receiver 1 to which the present invention is applied will be described with reference to FIG.

First, in the initial setting step ST1, the OFDM receiver 1 initializes an FFT time window.
The initial setting of the FFT time window is performed by controlling the FFT start timing in the time window position setting unit.
The FFT start timing is set with reference to the boundary position of the OFDM symbol of the main signal.

In FIG. 3, the boundary position of the OFDM symbol of the main signal is represented by h in FIG.
(T) and then, OFDM delayed signal h only delayed the effective symbol length _{t u} on the OFDM symbol j of the main signal
(T−t _u ), the complex correlation function ρ shown in the following equation
It can be obtained by calculating (t).

[0059]

(Equation 2)

The end portion of the effective symbol of the main signal h (t) and the OFDM delay signal h obtained by copying this end portion
Since the guard interval of the waveform of (t-t _u) coincides, as shown in FIG. 3, when delaying the delayed signal by the effective symbol length t _u of the main signal, the absolute value of the complex correlation function [rho (t), the maximum Becomes By detecting the maximum absolute value of the complex correlation function ρ (t), the boundary position of the OFDM symbol can be obtained.

Accordingly, the FFT start timing can be determined by counting, for example, the number of clocks from the boundary of the obtained OFDM symbol.

The FFT start timing is initially set by the time window position setting unit 17.

The time window position setting section 17 is provided, for example, in FIG.
As shown in FIG. 1, an effective symbol delay circuit 101, a complex conjugate multiplication circuit 102, a cumulative addition circuit 103, an absolute value circuit 104, a comparison circuit 105, a selection circuit 106,
It comprises a first register 107, a counter 108, a second register 109, a third register 110, an AND circuit 111, and an offset amount setting circuit 112.

[0064] effective symbol delay circuit 101, a baseband OFDM signal inputted from the orthogonal demodulation section 13 only the effective symbol length _{t u} is delayed, outputs to the complex conjugate circuit 102.

The complex conjugate circuit 102 receives signals from the quadrature demodulator 13 and the effective symbol delay circuit 101. Further, the complex conjugate circuit 102 and the cumulative addition circuit 103 calculate a correlation value ρ from the input signal.

The absolute value circuit 104 is
Is input. The absolute value circuit 104 compares the absolute value of the input correlation value ρ with the comparison circuit 10.
5 and the selection circuit 106.

The comparison circuit 105 receives the absolute value of the correlation value ρ from the absolute value circuit 104,
7, the correlation value ρ ′ is input. This comparison circuit 105
Is the correlation value ρ input from the absolute value circuit 104 and the first
Of the correlation value ρ ′ input from the register 107 of
When the correlation value ρ is larger, the selection circuit 106 is controlled to select the correlation value ρ input from the absolute value circuit 104, and the value of the counter 108 is stored in the second register 109. Control.

The selection circuit 106 receives the absolute value of the correlation value ρ from the absolute value circuit 104,
7, the correlation value ρ ′ is input. In the selection circuit 106, the correlation value ρ input from the absolute value circuit 104 and the first
And selects one of the correlation values ρ ′ input from the register 107, and outputs the selected correlation value to the first register 107. The selection of the correlation value is performed by the comparison circuit 1
05.

The first register 107 temporarily stores the input correlation value, and compares the temporarily stored correlation value ρ ′ with the comparison circuit 1
05 and the selection circuit 106. By repeating the above processing, finally, the maximum value ρ _MAX of the correlation value is temporarily stored in the register 107.

The counter 108 is a counter for counting clocks in an OFDM symbol.

The second register 109 includes a comparator 105
, The value of the counter 108 is stored. The stored value is output to the third register 110. Eventually, the time position when the correlation value ρ is the maximum is stored in the second register 109.

The third register 110 stores the time position when the correlation value ρ is maximum for each OFDM symbol.
The stored time position becomes a boundary position of the OFDM symbol.

The AND circuit 111 is connected to the third register 11
By ANDing 0 with the counter 108, the boundary position of the OFDM symbol is output.

The offset amount setting circuit 112 sets the start timing of the FFT based on the boundary position of the OFDM symbol input from the AND circuit 111. The offset amount setting circuit 112 outputs the start timing of the FFT in which a fixed time delay is applied to the boundary position of the OFDM symbol to the FFT calculation unit 14 as the initial setting timing.

When the FFT time window is initialized, the FFT
The process proceeds to operation step ST2, where the above-mentioned initialized FF is set.
Performs FFT operation in the range of T time window,
Generate a DM signal. After the end of the FFT operation, the process proceeds to the equalization processing step ST3.

In the equalization processing step ST3, the equalizer 15 obtains the phase characteristics of the carrier of the input OFDM reception signal in the frequency domain, and performs equalization processing and the like. The equalizer 15 outputs the obtained phase characteristics to the group delay calculator 16, and proceeds to a group delay calculation step ST4.

In the group delay calculating step ST4, a group delay is calculated from the phase characteristics of each carrier allocated for each frequency. The formula for calculating the group delay can be described as follows.

[0078]

(Equation 3)

[0079] from the expression of the group delay, each carrier for each advance to the next carrier phase is gradually rotated by -2πf ₀ τ _g. That is, if the phase difference Δθ between adjacent carriers is obtained, the group delay τ _g can be calculated.

For example, when the phase of the FFT start timing of the FFT time window j for performing the FFT operation on the OFDM symbol j is set as the origin, the group delay is determined as follows.
Phase θ _K of DM symbol j and OF of K + 1th carrier
The phase difference Δθ of the phase θ _{K + 1} of the DM symbol j (= θ _K −
θ _{K + 1} ). That is, by substituting the obtained phase difference into the above-described group delay equation, the FFT
The group delay τ ₁ of the OFDM symbol j with respect to the FFT start timing of the time window j can be quantitatively obtained. Note that this group delay τ ₁ is not only obtained from the difference between two carrier waves as described above, but also obtained by averaging the obtained group delays by calculating the phase difference between three or more carriers. Good.

The group delay calculating section 16 obtains a group delay τ ₁ from the phase difference of each carrier of the multipath signal. This gives F
The relative time difference between the FT start timing and the boundary position of the OFDM symbol of the multipath signal can be obtained.

When the multipath signal is ahead of the FFT time window, for example, as shown in FIG.
Control is performed to advance the FT time window. How much to advance the FFT time window is determined based on the calculated group delay amount.

On the other hand, the group delay calculating section 16
As shown in (b), when the multipath signal is delayed compared to the FFT time window, orthogonality between symbols can be maintained and normal reception can be realized. No special control is performed on the position control unit 17.

After controlling the time window position control section 17 according to the reception status, the group delay calculation section 16 proceeds to the time window resetting step ST5.

In the time window resetting step ST 5, the time window position controller 17 resets the FFT time window based on the control of the group delay calculator 16. After the resetting, the process returns to the FFT calculation step ST2, and performs the FFT calculation again on the OFDM reception signal. This makes it possible to sequentially confirm the relative time difference between the FFT start timing and the boundary position of the OFDM symbol of the multipath signal for each symbol. Also, based on this time difference, the FFT time window can be reset to an optimal position for each symbol.

The OFDM receiver 1 to which the present invention is applied
By calculating the group delay from the phase difference for each carrier,
OFD of multipath signal with respect to FFT start timing
A relative time difference at the boundary position of M symbols can be obtained. This makes it possible to identify whether the time reference of the multipath signal is ahead of or delayed from the FFT start timing. Furthermore,
Since the time window of the FFT can be automatically and accurately reset according to the calculated group delay amount, normal reception can be realized while preventing interference between symbols.

Next, FIG. 5 shows a configuration diagram of an OFDM receiver 2 according to a second embodiment of the present invention.

The OFDM transmitting apparatus 2 includes a receiving antenna unit 1
1, the frequency converter 12, the quadrature demodulator 13, the FFT
Arithmetic unit 14, equalizer 15, time window position setting unit 1
7, a pilot signal gate unit 18, and a group delay calculation unit 1
9 and a data output terminal 20. The OFDM receiving apparatus 2 in FIG.
The same components as those of the receiving device 1 are denoted by the same reference numerals, and description thereof will be omitted.

The pilot signal gate section 18 receives the OFDM signal demodulated in the FFT operation section 14 as an input. The pilot signal is a reference signal for measuring the amount of phase and amplitude distortion during waveform equalization. Pilot signal gate section 18 extracts a pilot signal and obtains its phase. Pilot signal gate section 18 outputs each phase of the obtained pilot signal to group delay calculation section 19.

The group delay calculator 19 calculates a group delay from each phase of the inputted pilot signal in the same manner as in the first embodiment. A plurality of information carriers exist between adjacent pilot signals, for example, as shown in FIG. The group delay calculator 19 includes a pilot signal a and a pilot signal b
Is obtained. The group delay calculation unit 19 calculates a group delay from the obtained phase difference based on the above-described group delay equation. In the above formula of the group delay, the carrier interval frequency f
₀ includes the frequency band of the information carrier provided between the pilot signal a and the pilot signal b. By calculating the group delay, the relative position of the boundary of the OFDM symbol with respect to the start timing of the FFT time window can be determined. That is, from the group delay amount calculated from the phase of the pilot signal, it is possible to determine whether the start position of the OFDM symbol is ahead of or delayed from the FFT start timing. In addition,
This group delay can be calculated not only from the phase difference between the two pilot signals as described above, but also by calculating the phase difference between three or more pilot signals and averaging the obtained group delays. Good.

The group delay can be determined by comparison with a predetermined reference value. For example, when the group delay τ ₁ is smaller than the reference value, it is determined that the multipath signal is ahead of the FFT time window, and the FFT time window position controller 17 is determined similarly to the first embodiment. To advance the FFT time window.

The time window position controller 17 advances the FFT start timing according to the control from the group delay calculator. Thereby, even when the multipath signal precedes the main signal, the time window of the FFT can be automatically controlled, and the same OF signal is used for both the main signal and the multipath signal.
A DM symbol can be received.

An OFDM receiver 2 to which the present invention is applied
By calculating the group delay from the pilot signal, the relative position of the multipath signal from the FFT time window can be specified. Thereby, whether the time reference of the multipath signal is ahead of the FFT start timing,
Alternatively, it can be identified whether or not it is late. Further, the time window of the FFT can be automatically and accurately reset according to the calculated group delay amount.

The OFDM receiver 2 is not limited to the above embodiment. By using a scattered pilot carrier as the pilot signal, the present invention can be applied to a case where a group delay is calculated. The present invention is also applicable to a case where the FFT window phase is controlled by calculating a group delay by using a scattered pilot signal having an amplitude equal to or larger than a predetermined value. Further, the OFDM receiver 2 uses only those transmitted in the same OFDM symbol as scattered pilot carriers, thereby providing a single OFD
The present invention is also applicable to a case where the FFT window phase is controlled only for M symbols. Further, by sequentially updating and using scattered pilot signals transmitted in a plurality of OFDM symbols, OFDM symbols can be obtained.
The present invention can also be applied to a case where the FFT window phase is sequentially controlled for each symbol.

The OFDM receiving apparatus to which the present invention is applied can perform normal reception not only when the multipath signal is delayed than the main signal but also in a gap filler environment where the multipath signal is ahead of the main signal. Can be realized. Also, depending on the reception situation,
Since a time window of T can be set, reception can be performed with high accuracy while always maintaining orthogonality between symbols. Further, since the OFDM receiver can determine the FFT start timing only by calculating the group delay, the above effects can be obtained with a simple circuit configuration.

[0096]

As described in detail above, the OFDM receiver according to the present invention calculates the group delay from the phase characteristic of the Fourier-transformed frequency-domain OFDM signal, and performs the Fourier transform according to the calculated group delay. A time window can be set. As a result, the time window of the FFT can be set to an optimum position according to the reception situation, so that even when the multipath signal is ahead of the main signal, the orthogonality between the symbols is maintained. , High-accuracy reception can be realized.

The OFDM receiving method according to the present invention
A group delay is calculated from the phase characteristics of the Fourier-transformed OFDM signal in the frequency domain, and a time window of the Fourier transform can be set according to the calculated group delay. As a result, the time window of the FFT can be set to an optimum position according to the reception situation, so that even when the multipath signal is ahead of the main signal, the orthogonality between the symbols is maintained. , High-accuracy reception can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment of an OFDM receiving apparatus to which the present invention has been applied.

FIG. 2 is a flowchart showing a procedure for setting an FFT time window.

FIG. 3 is a diagram illustrating setting of a time reference of a main signal.

FIG. 4 shows an FFT at an optimum position based on a calculated group delay.
It is a figure for explaining the case where a time window is set.

FIG. 5 is a diagram illustrating an OFDM receiver according to a second embodiment of the present invention;

FIG. 6 is a diagram for describing a case where a group delay is calculated based on the phase of a pilot signal.

FIG. 7 is a diagram for describing an OFDM symbol.

FIG. 8 is a diagram for describing setting of an FFT time window.

FIG. 9 is a diagram for explaining setting of a time reference.

FIG. 10 is a diagram illustrating a configuration example of a conventional OFDM receiver.

FIG. 11 is a diagram illustrating an example of a circuit configuration of a time window position setting unit.

FIG. 12 shows an FF in the presence of a multipath signal
It is a figure for explaining setting of a T time window.

FIG. 13 is a diagram illustrating a reception situation in a gap filler environment.

FIG. 14 is a diagram illustrating intersymbol interference when a multipath signal is ahead of a main signal.

[Explanation of symbols]

1 OFDM receiving apparatus, 11 receiving antenna section, 12
Frequency conversion unit, 13 orthogonal demodulation unit, 14 FFT operation unit,
15 Equalizer, 16, 19 Group delay calculator, 17
Time window position setting section, 18 pilot signal gate section, 2
0 Data output terminal

Claims (4)

[Claims] 1. An OFDM receiving apparatus for receiving an orthogonal frequency division multiplexing (OFDM) signal, comprising: a frequency conversion means for converting the frequency of the received OFDM signal into an intermediate frequency; and an OFDM signal frequency-converted by the frequency conversion means. Quadrature demodulation means for performing quadrature demodulation and outputting a baseband OFDM signal; and Fourier transforming the baseband OFDM signal,
OFDM modulation means for outputting a frequency domain OFDM signal; group delay calculation means for calculating a group delay from phase characteristics of each carrier of the frequency domain OFDM signal; and the OFDM modulation means according to the calculated group delay And a time window position setting means for setting a time window of the Fourier transform in the OFDM receiver. 2. A pilot signal extracting means for extracting a pilot signal of the frequency domain OFDM signal input from the OFDM modulating means and outputting the pilot signal to the group delay calculating means, wherein the group delay calculating means comprises a pilot signal 2. The OFDM according to claim 1, wherein the group delay is calculated from the phase of
Receiver. 3. An OFDM receiving method for receiving an orthogonal frequency division multiplexing (OFDM) signal, comprising: converting a frequency of a received OFDM signal to an intermediate frequency; orthogonally demodulating the frequency-converted OFDM signal; Generating a signal, performing a Fourier transform on the generated baseband OFDM signal, generating a frequency domain OFDM signal, calculating a group delay from a phase characteristic of each generated carrier of the generated frequency domain OFDM signal, and calculating An OFDM receiving method comprising: setting a time window of a Fourier transform in the OFDM modulating means according to the group delay. 4. The OFDM receiving method according to claim 3, wherein a group delay is calculated from a phase of the pilot signal of the generated OFDM signal in the frequency domain.