JP2003110524A - Ofdm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OFDM (orthogonal frequency division multiplex) receiver by which an influence of signal distortion caused by a clock error can be relaxed without performing clock control using a PLL. SOLUTION: In the OFDM receiver for reproducing a data stream by receiving an OFDM signal generated by performing processing including inverse FFT on the data stream according to a transmitting side clock signal transmitted from an OFDM transmitter, this device has a receiving part 11 for performing receiving processing including processing for sampling an OFDM signal transmitted from the OFDM transmitter according to a receiving side clock signal, an FFT processing part 14 for performing the FFT processing on the received OFDM signal concerning an FFT processing block, a reproducing part 21 for reproducing the data stream from the signal which is subjected to the FFT processing, a clock error detecting part 20 for detecting the frequency error of the receiving side clock signal in respect to the transmitting side clock signal, and a window control part 15 for controlling a position of the FFT processing block corresponding to the detected frequency error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to O in a wireless communication system for transmitting OFDM (Orthogonal Frequency Multiplex) signals.
The present invention relates to an FDM receiver.

[0002]

2. Description of the Related Art In recent years, demand for high-speed wireless communication systems indoors or outdoors has increased. OFDM (Orthogonal Frequency Division Multiplexing) is drawing attention as a transmission method in such a wireless communication system. In the OFDM transmitter, the inverse F
OFD by processing including FT (Inverse Fast Fourier Transform)
Generate and transmit M signal. The OFDM receiver reproduces the original data signal from the received OFDM signal by a process including FFT (Fast Fourier Transform).

Generally, in a wireless communication system for realizing high-speed data communication, a high-speed sampling clock is used in a transmitting device and a receiving device (hereinafter, sampling used in the transmitting device is called a transmitting side clock and sampling used in the receiving device is called a receiving side clock). Need. The OFDM transmitter performs processing including an inverse FFT according to the clock on the transmission side, and the OFDM receiver performs processing including FFT using the clock on the reception side.

In order for the receiving device of the wireless communication system to correctly reproduce the data, the frequency error (also referred to as clock error) of the receiving side clock with respect to the transmitting side clock must be suppressed as small as possible. For example, OF
The DM receiver performs a synchronization process using a preamble sequence that is added to the beginning of the OFDM signal and transmitted from the OFDM transmitter, and determines the position of the FFT processing section (FFT window) for the OFDM signal. If there is a clock error here, the position of the FFT window with respect to the data series separated from the preamble series is displaced, so that the signal after the FFT processing is distorted.

[0005]

In order to reduce the above clock error, the clock error is detected on the receiving side,
VCXO (voltage controlled crystal oscillator)
The so-called PLL (Phase Locked L
It is conceivable that the frequency of the receiving clock is made to follow the frequency of the transmitting clock by using oop). In that case, since a clock error is detected from the received signal after the analog / digital conversion to control the VCXO, a digital / analog converter for converting the clock error detection signal obtained as a digital signal into an analog signal. Is required.

As described above, in the wireless communication system using OFDM, when the clock control by the PLL is performed on the receiving side in order to reduce the clock error, the PL is set in the receiving device.
L circuit and a digital / digital converter for converting a clock error detection signal obtained as a digital signal into an analog signal.
There is a problem that the circuit scale increases because an analog converter is required. Since the OFDM receiver is mounted on, for example, a mobile terminal that requires portability, it is not desirable that the circuit scale be large.

An object of the present invention is to provide an OFDM receiver which can mitigate the influence of signal distortion due to a clock error without performing the clock control by the PLL, which causes a complicated circuit configuration.

[0008]

In order to solve the above problems, according to one aspect of the present invention, a process including an inverse FFT is performed on a data sequence according to a clock signal on the transmission side, which is transmitted from an OFDM transmitter. Generated OFD
An OFDM receiving apparatus for receiving an M signal and reproducing a data sequence, the OFDM transmitting apparatus transmitting the OFDM signal
Receiving means for performing a receiving process including a process of sampling a signal according to a clock signal on the receiving side;
F for FFT processing the FDM signal for the FFT processing section F
OFDM having a basic configuration including FT processing means and reproducing means for reproducing a data sequence from an FFT processed signal
The apparatus has a detection unit that detects a frequency error of the reception-side clock signal with respect to the transmission-side clock signal, and a control unit that controls the position of the FFT processing section according to the detected frequency error. Another aspect of the present invention is, in an OFDM receiver having the same basic configuration, a detection unit that detects a frequency error of a reception side clock signal with respect to a transmission side clock signal, and distortion due to the frequency error based on the detected frequency error. Distortion inverse characteristic imparting means for imparting the inverse characteristic of the signal to the FFT-processed signal.

Another aspect of the present invention is, in an OFDM receiver having the same basic configuration, a detecting means for detecting a frequency error of the receiving side clock signal with respect to the transmitting side clock signal, and the detected frequency error is equal to or more than a predetermined value. At this time, the control means for controlling the position of the FFT processing section according to the frequency error, and when the detected frequency error is less than a predetermined value, the inverse characteristic of the distortion due to the frequency error is FFT processed based on the frequency error. Distortion inverse characteristic imparting means for imparting to the generated signal.

With such a configuration, the OF according to the present invention
The DM receiver can reduce the influence of signal distortion due to a clock error without performing clock control by the PLL.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows the configuration of an OFDM receiving apparatus according to the first embodiment of the present invention. OFD not shown
In the M transmitter, the inverse FF is applied to the digital data series.
After generating an OFDM signal by performing processing including T (Inverse Fast Fourier Transform) processing, digital / analog conversion, quadrature modulation and frequency conversion (up conversion)
The OFDM signal is transmitted by performing processing necessary for transmission including the above. The OFDM signal transmitted from the OFDM transmitter is received by the antenna 10. These processes are performed according to the clock signal (transmission side clock signal) generated by the clock generator 12. The clock generator 12
It may be a simple VCXO in which the PLL is not formed.

The OFDM signal received by the antenna 10 is subjected to processing necessary for reception such as frequency conversion (down conversion), quadrature demodulation and analog / digital conversion by the receiving unit 11 and converted into a digital baseband signal. . Receive O during analog / digital conversion
The FDM signal is, for example, a clock generator 1 composed of a VCXO.
2 is sampled according to the clock signal (receiver side clock signal) generated by 2; The reception side clock signal is also supplied to each unit other than the reception unit 11.

The OFDM signal converted into the digital baseband signal output from the receiving unit 11 is first input to the synchronization processing unit 13 and subjected to time synchronization and frequency synchronization processing. By the time synchronization process, the packet start position,
Also, the window position in the FFT (Fast Fourier Transform) processing performed in units of symbols is determined. The frequency synchronization processing absorbs distortion due to the frequency error of the local oscillator used in each OFDM transmitter / receiver. OF
The local oscillator used in the DM receiver is included in the receiver 12.

The OFDM signal that has been subjected to the synchronization processing by the synchronization processing unit 13 is input to the FFT processing unit 14, and the FFT processing is performed in a predetermined FFT processing section (hereinafter, referred to as FFT window). The position of the FFT processing section, that is, the FFT window position is basically determined by the synchronization unit 13. However, when the clock error between the OFDM transmitter / receivers is detected, the FFT window position determined by the synchronization processing unit 13 is According to the clock error, the window control unit 15 controls to shift a predetermined amount back and forth.

Generally, in a wireless communication system, a known signal for calculating a channel response is added before a data sequence. In the present embodiment, the known signal for calculating the channel response that is added before the data sequence of the received OFDM signal is output from the FFT processing unit 14 and input to the channel response inverse characteristic estimation unit 16. , The inverse characteristics of the channel response are estimated by calculation. Here, the transmission path response is the response characteristic of the transmission path of the OFDM signal from the OFDM transmission apparatus to the OFDM reception apparatus, and the inverse characteristic of this transmission path response is the transmission path response inverse characteristic.

On the other hand, the data signal sequence in the received OFDM signal is FFT-processed by the FFT processing section 14 to obtain a received subcarrier signal. The received subcarrier signal is input to the transmission line response correction unit 17, and the transmission line response inverse characteristic estimated by the transmission line response inverse characteristic estimation unit 16 is multiplied here to compensate for the distortion due to the transmission line response. . The transmission line response correction unit 17 may compensate for both the amplitude distortion and the phase distortion of the received carrier signal, or may compensate only the phase distortion. The reception subcarrier signal whose distortion due to the transmission line response is compensated by the transmission line response correction unit 17 is a phase correction unit 18 and a phase correction signal generation unit 19
And the clock error detector 20.

OFDM transmitted from the OFDM transmitter
A transmission subcarrier signal of a signal is usually composed of a data subcarrier shown by a solid line and a known pilot subcarrier shown by a chain line, as shown in FIG.
FIG. 2 is an example of a frequency spectrum of a transmission subcarrier signal including four pilot subcarriers.

When the OFDM receiving apparatus of FIG. 1 receives an OFDM signal having such a transmission subcarrier signal, the reception subcarrier signal output from the FFT processing unit 14 is the transmission line response correction unit as described above. Although the distortion due to the transmission line response is compensated by 17, the phase distortion due to the phase noise remains. The phase noise is noise generated by the phase fluctuation of the above-mentioned local oscillator for frequency conversion in the OFDM transmitter and the OFDM receiver. The phase rotation amount of the phase distortion due to this phase noise is O
It is the same for all subcarrier signals in the FDM symbol.

The output of the transmission line response correction unit 17 further includes a distortion component due to a frequency error (clock error) of the reception side clock signal with respect to the transmission side clock signal. The distortion due to the clock error has the property that the amount of phase rotation is proportional to the frequency. For example, as shown in FIG. 2, the subcarrier signal interval (hereinafter referred to as the subcarrier interval) is Δf, and the frequencies of the four pilot subcarrier signals indicated by the alternate long and short dash line are −mΔf and −nΔ, respectively.
Assuming f, nΔf, and mΔf, the phase rotation amount of the distortion due to the clock error of the received pilot subcarrier signal after correction by the transmission line response correction unit 17 is θ−mφ, respectively.
θ−nφ, θ + nφ, θ + mφ. Here, θ is the phase rotation amount of phase distortion due to the same amount of phase noise in all pilot subcarrier signals, and φ is the phase rotation amount of distortion due to clock error per subcarrier interval Δf.

In the phase correction signal generator 19, the phase rotation amounts θ-mφ and θ-n of the received pilot subcarrier signal are obtained.
A phase rotation amount θ of phase distortion due to phase noise is estimated from φ, θ + nφ, and θ + mφ, and a phase correction signal corresponding to the phase rotation amount θ is generated. The phase corrector 18 corrects the distortion due to the phase noise by rotating the phase of the received subcarrier signal by −θ according to the phase correction signal.

On the other hand, the clock error detector 20 detects the above-mentioned clock error. More specifically, in this embodiment, the phase rotation amount φ of the received pilot carrier signal generated by the clock error is detected by the clock error detection unit 20. If there is a clock error, OFDM
Since the sampling intervals are different between the transmitter and receiver, the sampling position in the receiver gradually shifts from the sampling position in the transmitter.

This state is shown in FIG. 3 (a) is O
FFT window position in inverse FFT processing unit in FDM transmitting apparatus and FFT processing unit 1 in OFDM receiving apparatus
4 shows the FFT window position, and FIG. 3 (b) shows the sampling position and sampling interval at the beginning of each FFT window. Further, FIG. 3C shows changes in subcarrier intervals in the transmission device and the reception device corresponding to the shift of the FFT window position between the OFDM transmission / reception devices in FIG. 3B.

Assuming that the FFT size is N and the sampling interval in the OFDM transmitter is T / N, the sampling interval in the OFDM receiver is different from T / N due to a clock error as shown in FIG. 3 (b). By Δt _sm . As the sampling progresses, the sampling interval difference Δt _sm between the OFDM transmitting and receiving devices is integrated, and the OF
The sampling position of the OFDM receiver gradually shifts from the sampling position of the DM transmitter. Due to the deviation of the sampling positions between the OFDM transmitter / receivers, the FFT window position in the OFDM receiver shifts by NΔt _{sm from} the FFT window position on the transmitter side as shown in FIG.

As a result, as shown in FIG.
For subcarrier spacing Δf in the FDM transmitter, O
The subcarrier spacing in the FDM receiver is shifted by the time corresponding to NΔt _sm . Therefore, the clock error detection unit 20 can detect the clock error as the phase rotation amount φ due to the clock error from the subcarrier interval Δf ′ of the received pilot subcarrier signal corrected by the transmission path response correction unit 17.

Here, when the phase rotation amount φ of the received pilot carrier signal due to the clock error becomes φ ≧ 2π / N, it means that the sampling positions are deviated by one sample or more between the OFDM transmitter / receivers. The window position control unit 15 monitors the phase rotation amount φ, and φ ≧ 2π /
When it becomes N, the FFT window position in the FFT processing unit 14 is controlled so as to shift the FFT window position by a time period of one sample (one cycle of the receiving clock) or more. By doing so, it becomes possible to compensate the distortion of the signal after the FFT processing due to the clock error.

In this way, in the FFT processing section 14, the window position control section 15 controls the window position to compensate for the distortion due to the clock error, and the transmission path response correcting section 17 compensates for the distortion due to the transmission path response. The received subcarrier signal after the distortion due to the phase noise is compensated by the correction unit 18 is reproduced by the reproduction unit 21.
To the digital data sequence, and the digital data sequence is reproduced by performing processes such as demapping, determination, and decoding.

As described above, the OFDM of this embodiment
The receiving device detects a clock error which is a frequency error of the receiving side clock signal with respect to the transmitting side clock signal from the received pilot subcarrier, and the clock error is a predetermined value (2π / N in the phase rotation amount φ of the pilot carrier signal).
FFT window position (FFT processing section)
By performing the control of shifting by 1 sample or more, the distortion of the OFDM signal after the FFT processing due to the clock error can be compensated.

Therefore, according to this embodiment, it is not necessary to use the PLL circuit to match the frequency of the receiving side clock signal with the transmitting side clock signal, and the VCX included in the PLL circuit is not required.
Since the digital / analog converter for generating the clock error detection signal used for the O frequency control as an analog signal is not required, the circuit scale of the OFDM receiver can be greatly reduced.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
2 shows a configuration of an OFDM receiving apparatus according to the embodiment of FIG. The present embodiment is configured to compensate the distortion due to the clock error by multiplying the signal after the FFT processing by the inverse characteristic of the distortion caused by the clock error. In order to perform this processing, a subcarrier phase correction unit 22 is provided, and the subcarrier phase correction unit 22 uses an FF to obtain the inverse characteristics of the distortion due to the phase noise and the distortion due to the clock error.
These two distortions are simultaneously compensated by multiplying the subcarrier signal which is the signal after the T processing.

The OFDM receiving apparatus of FIG. 4 will be described below with the same components as those of FIG. 1 assigned the same reference numerals. The OFDM signal received by the antenna 10 is input to the FFT processing unit 14 via the receiving unit 11 and the synchronization processing unit 13, and the FF
The point that the T process is performed is the same as in the first embodiment.
However, in the present embodiment, the window control unit 15 provided in FIG. 1 does not exist, and the window position in the FFT processing unit 14 is fixed to the position determined by the synchronization processing unit 13.

Among the outputs of the FFT processing unit 14, the known signal for calculating the channel response is input to the channel response inverse characteristic estimating unit 16 for estimating the channel response inverse characteristic. Also, FF
Of the output of the T processing unit 14, the received subcarrier signal obtained by performing FFT processing on the data signal sequence is input to the transmission path response correction unit 17, where it is calculated by the transmission path response inverse characteristic estimation unit 16. By multiplying the inverse characteristics of the transmission line response, both amplitude and phase distortions or only phase distortions are compensated.

The received subcarrier signal whose distortion due to the transmission line response is compensated by the transmission line response correction unit 7 is input to the phase correction signal generation unit 19, the clock error detection unit 20, and the subcarrier phase correction unit 22. As described with reference to FIG. 2, the phase correction signal generation unit 19 estimates the phase rotation amount θ due to phase noise from the phase rotation amount of the received pilot subcarrier and generates the phase correction signal corresponding to the phase rotation amount θ. Then, the clock error detector 10 detects the phase rotation amount φ per subcarrier interval caused by the clock error.

In the subcarrier phase correction unit 22, based on the phase rotation amount θ due to the phase noise and the phase rotation amount φ per subcarrier interval caused by the clock error,
Phase correction is performed on each received subcarrier signal so as to simultaneously compensate for phase rotation distortion due to both phase noise and clock error. Specifically, the subcarrier phase correction unit 22 gives a phase rotation of −θ−kφ to the received subcarrier signal of the kth frequency. In this way, different phase rotations may be given to each frequency of the received subcarrier signal, but since the circuit scale necessary for calculating the amount of phase rotation becomes large, the received subcarrier signal is divided for each frequency. You may divide into several groups and give the same phase rotation to each group.

The received subcarrier signal after the phase noise and the distortion due to the clock error have been compensated by the subcarrier phase correction unit 22 is input to the reproduction unit 21 where processing such as demapping, determination and decoding is performed. The digital data sequence is reproduced by.

As described above, in the OFDM receiver of this embodiment, the clock error is detected from the received pilot subcarrier, and the inverse characteristic of the distortion caused by the clock error is F
Multiply the signal after TT processing. More specifically, reverse rotation of phase rotation distortion due to a clock error is applied to the received subcarrier signal according to its frequency. As a result, the distortion of the signal after the FFT processing due to the clock error can be compensated, so that it is not necessary to match the frequency itself of the receiving side clock with the transmitting side clock as in the first embodiment, and the circuit scale of the OFDM receiving apparatus is Can be greatly reduced.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention.
It is a figure which shows the structure of the OFDM receiver which concerns on embodiment of FIG. In the second embodiment, the distortion due to the transmission path response is corrected for the received subcarrier signal, and then the distortion due to the phase noise and the distortion due to the clock error are corrected. On the other hand, in the present embodiment, these three types of distortion correction for the received subcarrier signals are collectively performed.

The OFDM receiving apparatus of FIG. 5 will be described by assigning the same reference numerals to the same components as those of FIG.
OFDM received by the antenna 10 as in the embodiment of
The signal is input to the FFT processing unit 14 via the receiving unit 11 and the synchronization processing unit 13, and the FFT processing is performed at the fixed window position determined by the synchronization processing unit 13.

Among the outputs of the FFT processing section 14, the known signal for calculating the channel response is input to the channel response inverse characteristic estimating section 16, and the channel response inverse characteristic output from the channel response inverse characteristic estimating section 16 is It is input to the distortion inverse characteristic estimation unit 23. On the other hand, among the outputs of the FFT processing unit 14, the received subcarrier signal obtained by performing the FFT process on the data signal sequence is input to the distortion correction unit 24, and the distortion inverse characteristic estimation unit 23 outputs the inverse distortion. By multiplying the characteristics, all the transmission line response, the phase noise, and the distortion due to the clock error are collectively corrected.

In general, the distortion inverse characteristic estimating unit 23 calculates and estimates the distortion inverse characteristic by using the received subcarrier signal one symbol or more before. Therefore, in the received subcarrier signal whose distortion is corrected by the distortion correction unit 24, the fluctuation component of the phase noise from the time when the distortion characteristic estimation unit 23 calculates the inverse distortion characteristic and the fluctuation of the phase rotation distortion due to the clock error. Contains ingredients.

The received subcarrier signal after distortion correction output from the distortion correction unit 24 is input to the phase correction signal generation unit 19 and the clock error detection unit 20. The phase correction signal generation unit 19 estimates the amount of phase rotation fluctuation Δθ due to phase noise from the distortion inverse characteristic used in the distortion correction unit 24, and generates information on Δθ as a phase correction signal. The clock error detector 20 estimates the phase rotation distortion variation amount Δφ caused by the clock error and outputs the information of Δφ.

Δ output from the phase correction signal generator 19
Information on θ and Δφ output from the clock error detection unit 20 is input to the distortion inverse characteristic estimation unit 23. The distortion inverse characteristic estimation unit 23 gives rotation of −Δθ−kΔφ to the distortion inverse characteristic with respect to the frequency of the k-th received subcarrier signal. As a result, the distortion inverse characteristic by which the distortion correction unit 24 multiplies the received subcarrier signal is updated.

The received subcarrier signal whose distortion due to the transmission line response, phase noise and clock error is compensated by the distortion correction unit 24 is input to the reproduction unit 21 where processing such as demapping, determination and decoding is performed. The digital data sequence is reproduced by.

In the OFDM receiver of this embodiment, a clock error is detected by the received pilot subcarrier, and the inverse characteristic of the distortion caused by this clock error is F
By multiplying the signal after TT processing and compensating for the distortion of the signal after FFT processing due to the clock error, the same effect as in the second embodiment can be obtained, and the distortion inverse characteristic is always updated, so it should be detected. The range of the phase rotation amount due to the phase distortion and the clock error becomes narrow, and the phase correction signal generation unit 19
Also, there is an advantage that the circuit scale of the clock error detection unit 20 can be reduced.

In the present embodiment, the distortion correction unit 24 collectively corrects the distortion due to the transmission line response of the received subcarrier signal, the distortion due to the phase noise, and the distortion due to the clock error. It is also possible to apply to one configuration. In that case, regarding the distortion due to the clock error, the window control unit 15 shown in FIG.
The distortion correction unit may collectively correct the distortion due to the remaining transmission line response and the distortion due to the phase noise by controlling the window position with.

(Fourth Embodiment) FIG. 6 shows a fourth embodiment of the present invention.
2 shows a configuration of an OFDM receiving apparatus according to the embodiment of FIG. In this embodiment, when the clock error becomes large, the FFT window position is controlled, and when the clock error is small, reverse rotation of the phase rotation distortion according to the clock error is given to the received subcarrier signal. This embodiment has a configuration in which the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 4 are combined.

The OFDM signal received by the antenna 10 is input through the receiving section 11 and the synchronization processing section 13 to the FFT.
It is input to the processing unit 14 and the FFT processing is performed at a predetermined window position (window processing section). In this case, when the clock error detected by the clock error detection unit 20 becomes larger than a predetermined value, the window control unit 15 controls the window position determined by the synchronization processing unit 13 to shift back and forth.

Of the outputs of the FFT processing unit 14, the reception subcarriers that are input to the transmission channel response inverse characteristic estimation unit 16 for estimating the transmission channel response inverse characteristic and obtained by FFT processing of the data signal sequence. The signal is input to the transmission line response correction unit 17, where the transmission line response inverse characteristic estimation unit 16
By multiplying the inverse characteristics of the transmission line response calculated by, the distortion of both the amplitude and the phase or only the phase distortion is compensated.

The received subcarrier signal in which the distortion due to the transmission line response is compensated by the transmission line response correction unit 17 is input to the phase correction signal generation unit 19, the clock error detection unit 20, and the subcarrier phase correction unit 22. In the subcarrier phase correction unit 22, the phase rotation amount θ due to the phase noise detected from the phase rotation amount of the received pilot subcarrier in the phase correction signal generation unit 19 and the subcarrier caused by the clock error detected in the clock error detection unit 20. Based on the phase rotation amount φ per interval, correction is performed on each received subcarrier signal so as to compensate for phase rotation distortion due to phase noise and clock error.

The information on the phase rotation amount φ per subcarrier interval detected by the clock error detection unit 10 is F
It is input to the FT window control unit 15. The FFT window control unit 15 has φ ≧ 2π / as in the first embodiment.
When it becomes N, the FFT window position is controlled by the FFT processing unit 14 so that the FFT window position is shifted by one sample time, thereby compensating for the distortion due to the clock error.

On the other hand, in the range of φ <2π / N, the subcarrier phase correction unit 22 compensates the distortion due to the clock error by giving the phase rotation of −θ−kφ to the received subcarrier signal of the kth frequency. To do.

As described above, in this embodiment, when the clock error becomes large, the FFT window position is controlled, and when the clock error is small, the reverse rotation of the phase rotation distortion corresponding to the clock error is applied to the received subcarrier signal. As a result, the distortion due to the clock error can be compensated.

(Fifth Embodiment) FIG. 7 shows a fifth embodiment of the present invention.
It is a figure which shows the structure of the OFDM receiver which concerns on embodiment of FIG. Similar to the fourth embodiment, this embodiment controls the FFT window position when the clock error becomes large, and when the clock error is small, reverse rotation of the phase rotation distortion corresponding to the clock error is performed on the received subcarrier signal. Although it is a giving method, it has a configuration in which the first embodiment shown in FIG. 1 and the third embodiment shown in FIG. 5 are combined.

The OFDM signal received by the antenna 10 passes through the receiving section 11 and the synchronization processing section 13 and then the FFT processing section 14
To the FFT processing at the fixed window position determined by the synchronization processing unit 13. Among the outputs of the FFT processing unit 14, the known signal for calculating the channel response is input to the channel response inverse characteristic estimation unit 16, and the channel response inverse characteristic output from the channel response inverse characteristic estimation unit 16 is the distortion inverse characteristic. Estimator 2
Input to 3.

Of the outputs of the FFT processing unit 14, the received subcarrier signal obtained by FFT processing the data signal sequence is input to the distortion correction unit 24 and output from the distortion inverse characteristic estimation unit 23. By multiplying by, all of the transmission line response, the phase noise, and the distortion due to the clock error are collectively corrected.

The received subcarrier signal after distortion correction output from the distortion correction unit 24 is input to the phase correction signal generation unit 19 and the clock error detection unit 20, and is used by the distortion correction unit 24 in the phase correction signal generation unit 19. The phase rotation fluctuation amount Δθ due to the phase noise is estimated from the obtained inverse distortion characteristic,
Information on Δθ is generated as a phase correction signal. The clock error detector 20 estimates the phase rotation distortion variation amount Δφ caused by the clock error and outputs the information of Δφ.

Δ output from the phase correction signal generator 19
Information on θ and Δφ output from the clock error detection unit 20 is input to the distortion inverse characteristic estimation unit 23. The distortion inverse characteristic estimation unit 23 gives rotation of −Δθ−kΔφ to the distortion inverse characteristic with respect to the frequency of the k-th received subcarrier signal. As a result, the distortion inverse characteristic by which the distortion correction unit 24 multiplies the received subcarrier signal is updated.

Phase rotation distortion variation amount Δφ caused by the clock error detected by the clock error detection unit 10.
Is also input to the clock error integration unit 25. The clock error integrating unit 25 integrates the phase rotation amount Δφ to obtain the phase rotation amount φ, which is the clock error from the beginning of the packet to the current time, and the information of this phase rotation amount φ is input to the FFT window control unit 15. To be done.

As in the first and fourth embodiments, the FFT window control section 15 sets F when φ ≧ 2π / N.
By controlling the FFT window position in the FFT processing unit 14 so that the FT window position is shifted by one sample time, the distortion due to the clock shift is compensated.
On the other hand, in the range of φ <2π / N, the distortion inverse characteristic estimating unit 23
Is rotated by −kΔφ with respect to the distortion inverse characteristic with respect to the frequency of the k-th received subcarrier signal,
Compensate for distortion due to clock error.

When φ ≧ 2π / N and the FFT window control unit 15 shifts the FFT window position by one sample, the inverse distortion characteristic rotates by −2π / N. So FFT
When the FFT window position is shifted, the window control unit 15 sets the distortion inverse characteristic to the distortion inverse characteristic estimating unit 23 by 2
A control signal for rotating π / N is output. This makes it possible to correctly estimate the inverse distortion characteristic even when the FFT window position shifts.

As described above, also in the present embodiment, the FFT window position is controlled when the clock error becomes large as in the fourth embodiment, and when the clock error is small, the received subcarrier signal is responded to the clock error. By giving the reverse rotation of the phase rotation distortion, the distortion due to the clock error can be compensated.

[0061]

As described above, the OF according to the present invention
According to the DM receiver, it is possible to mitigate the influence of distortion due to the clock error.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an OFDM receiving apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of a transmission subcarrier signal used for OFDM signal transmission.

FIG. 3 is an FFT due to a clock error in the embodiment.
Figure for explaining the control operation of the window position

FIG. 4 is a block diagram showing a configuration of an OFDM receiving apparatus according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of an OFDM receiving apparatus according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an OFDM receiving apparatus according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of an OFDM receiving apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Antenna 11 ... Reception part 12 ... Clock generation part 13 ... Synchronization processing part 14 ... FFT processing part 15 ... Window control part (control means) 16 ... Transmission path response inverse characteristic estimation part 17 ... Transmission path response correction part (transmission path) Response distortion inverse characteristic imparting means) 18 ... Phase correcting section (phase noise distortion inverse characteristic imparting means) 19 ... Phase correction signal generating section 20 ... Clock error detecting section 21 ... Reproducing section 22 ... Subcarrier phase correcting section (distortion inverse characteristic imparting section) Means) 23 ... Distortion inverse characteristic estimation section 24 ... Distortion correction section (distortion inverse characteristic imparting means) 25 ... Clock error integration section

Claims (8)

[Claims] 1. An OFDM receiver for receiving an OFDM signal generated by performing a process including an inverse FFT on a data sequence according to a clock signal on the transmitting side, which is transmitted from the OFDM transmitter, and reproducing the data sequence. In, reception means for performing reception processing including processing for sampling an OFDM signal transmitted from the OFDM transmission device according to a reception side clock signal, FFT processing means for performing FFT processing on the reception-processed OFDM signal for FFT processing intervals, Reproducing means for reproducing the data sequence from the FFT processed signal, detecting means for detecting a frequency error of the receiving side clock signal with respect to the transmitting side clock signal, and the FFT processing section according to the detected frequency error An OFDM receiver comprising: a control unit that controls the position of the. 2. The OFDM subjected to the FFT processed signal
2. The OF according to claim 1, further comprising transmission path response distortion inverse characteristic imparting means for imparting an inverse characteristic of distortion due to a transmission channel response of an OFDM signal from the transmitter to the OFDM receiver.
DM receiver. 3. The OFDM receiver according to claim 1, further comprising a phase noise distortion inverse characteristic imparting means for imparting an inverse characteristic of phase distortion due to phase noise to the FFT-processed signal. 4. An OFDM receiving apparatus for receiving an OFDM signal generated by performing a process including an inverse FFT on a data sequence according to a clock signal on the transmitting side, which is transmitted from the OFDM transmitting apparatus, and reproducing the data sequence. In, reception means for performing reception processing including processing for sampling an OFDM signal transmitted from the OFDM transmission device according to a reception side clock signal, FFT processing means for performing FFT processing on the reception-processed OFDM signal for FFT processing intervals, Reproducing means for reproducing the data sequence from the FFT processed signal, detecting means for detecting a frequency error of the receiving side clock signal with respect to the transmitting side clock signal, and distortion due to the frequency error based on the detected frequency error Inverse distortion which gives the inverse characteristic of the signal to the FFT processed signal OFDM receiving apparatus comprising a sexual imparting means. 5. An OFDM receiving apparatus for receiving an OFDM signal generated by performing a process including an inverse FFT on a data sequence according to a clock signal on the transmission side, which is transmitted from the OFDM transmitting apparatus, and reproducing the data sequence. In, reception means for performing reception processing including processing for sampling an OFDM signal transmitted from the OFDM transmission device according to a reception side clock signal, FFT processing means for performing FFT processing on the reception-processed OFDM signal for FFT processing intervals, Reproducing means for reproducing the data sequence from the FFT-processed signal, detecting means for detecting a frequency error of the receiving side clock signal with respect to the transmitting side clock signal, and the detected frequency error being equal to or more than a predetermined value, A controller for controlling the position of the FFT processing section according to the frequency error And, when the detected frequency error is less than the predetermined value, distortion inverse characteristic imparting means for imparting an inverse characteristic of distortion due to the frequency error to the FFT processed signal based on the frequency error. Receiver. 6. The OFDM reception according to claim 1, wherein the control means shifts the position of the FFT processing section by a time period of one cycle or more of the reception side clock signal when the frequency error exceeds a predetermined value. apparatus. 7. The distortion inverse characteristic imparting means adds an inverse characteristic of distortion due to the frequency error to the FFT-processed signal, and a transmission path of an OFDM signal from the OFDM transmitter to the OFDM receiver. The OFDM according to claim 4 or 5, wherein the inverse characteristics of at least one of distortion due to response and phase distortion due to phase noise are simultaneously given.
Receiver. 8. The OFDM signal includes a known subcarrier signal, and the detecting means detects the clock error using the known subcarrier signal. OFDM receiver.