JPH08251135A - Transmission method for orthogonal frequency division multiplex signal and its reception device - Google Patents

Abstract

PURPOSE: To provide the transmission method and the reception device of an orthogonal frequency multiplex signal, which can precisely correct the fluctuation in a reception level and/or a frequency band and by which the erroneous judgement of demodulation data does not occur as a result. CONSTITUTION: Specified symbols S0 having specified patterns which are previously decided are intermittently included in an orthogonal frequency division multiplex signal transmitted from a transmission side to a reception side in addition to symbols Sm including data to be transmitted. On the reception side, the fluctuation in the reception level and/or the fluctuation in the frequency band of a reception signal is detected and corrected based on the received specified symbols S0. The specified symbols S0 have the specified patterns and therefore the level change and/or the fluctuation in the frequency is strongly correlated with the fluctuation in the reception level and/or the frequency band of the reception signal. Thus, the fluctuation in the reception level and/or the frequency band of the reception signal can precisely be detected from the specified symbol S0 and highly precise correction can be realized as a result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of transmitting an orthogonal frequency multiplex signal and a receiving apparatus thereof, and more specifically, to a receiving side from a transmitting side via a predetermined transmission line.
The present invention relates to a method of transmitting an orthogonal frequency division multiplex signal for each symbol of a predetermined length and a receiving apparatus thereof.

[0002]

2. Description of the Related Art In recent years, orthogonal frequency multiplexing (Orthogonal Frequency D) has been used in mobile digital audio broadcasting, terrestrial digital television broadcasting and the like.
ivision Multiplexing; O
Communication using signals (called FDM) is drawing attention. Because the OFDM signal has good frequency utilization efficiency,
This is because a large amount of data can be transmitted at high speed and the characteristic deterioration due to reflected waves is small even without a waveform equalizer. Also, since the signal waveform has a shape close to random noise, interference with other services is less likely to occur. A transmission method using an OFDM signal having such characteristics is disclosed in Japanese Patent Laid-Open No. Hei 5
No. 167633 (hereinafter referred to as "first prior art"), Nikkei Electronics (no. 574), issued Feb. 15, 1993, pp. 101-124, "The next-generation home service is TV. "Beyond" (hereinafter referred to as "second prior art") and September 1, 1994.
It is disclosed in "OFDM system and its development trend" (hereinafter referred to as the third prior art) written by Masanori Saito of NHK Broadcasting Technology Research Laboratories on pages 1 to 15 of the EIAJ technical seminar materials dated 4th. There is.

FIG. 11 is a diagram showing the structure of a conventional OFDM signal. In particular, FIG. 11 (a) shows each symbol of the OFDM signal along the time axis, and FIG. 11 (b) shows FIG.
The part α of (a) is shown enlarged. As shown in FIG. 11A, the OFDM signal S has a symbol Sm (m =
1, 2, ...) are arranged along the time axis. Each symbol Sm is composed of a plurality of carriers (several tens to thousands, for example 512) having different frequencies (symbol time t).
which are orthogonal to each other in s) are digitally modulated (for example, QPSK modulation, 16
QAM) and modulated carriers are multiplexed on the frequency axis by inverse FFT (Fast Inverse Fourier Transform) calculation. Therefore, each symbol Sm
All show random amplitude distributions, as shown in FIG. On the transmission path, such an OFDM signal S takes the form of a complex signal in which a real part and an imaginary part are superimposed on each symbol Sm.

By the way, such an OFDM signal is sent from the transmitting side to the receiving side via a wired or wireless transmission path. In a wired transmission line, the occupied frequency band is regulated by the transmission characteristics of the transmission line. Further, in the wireless transmission path, the occupied frequency band is regulated by legal regulations.
Therefore, the transmission side converts the OFDM signal from the intermediate frequency band to the occupied frequency band of the transmission path. On the other hand, on the receiving side, the received O
The FDM signal is converted from the occupied frequency band of the transmission line to the intermediate frequency band for the demodulation work.

In the above-mentioned first conventional technique, a band pass filter, a frequency converter and a low pass filter for converting an OFDM signal transmitted from the transmitting side into a base band OFDM signal, and a base band OFDM signal A / D converter for sampling and converting to digital signal, FFT demodulator for Fourier transforming time axis data to obtain data on frequency axis for each carrier, and amplitude and phase on complex plane for each carrier A signal point coordinate determination circuit for determining the complex data to obtain complex data and a reception data combination circuit for converting the complex data into digital data and combining the data according to the number of bits transmitted on each carrier to generate a bit stream. And a deinterleave matrix that obtains received data by performing deinterleave and error correction on the bitstream. Receiver including a fine error correction code circuit is disclosed.

In the above-mentioned third conventional technique, a bandpass filter, a quadrature detector and a lowpass filter for converting an OFDM signal transmitted from the transmitting side into a baseband OFDM signal, and a baseband OFDM signal A / D converter for sampling and converting to a digital signal, FFT demodulator for Fourier transforming time axis data to obtain frequency axis data for each carrier, and parallel data axis frequency parallel data conversion Is disclosed with a parallel-serial conversion circuit that obtains received data.

FIG. 12 is a block diagram showing the structure of an OFDM signal receiving apparatus which can be easily inferred from the first and third conventional techniques. In FIG. 12, this receiving device has an input terminal I to which the received OFDM signal is input,
The frequency converter 100, the quadrature detector 300, the Fourier transformer 400, and the demodulation data detector 500 are provided.
The quadrature detector 300 includes a demultiplexer 301, a detector 302,
Includes 303 and carrier regenerator 304.

The OFDM signal in the occupied frequency band (center frequency fr) of the transmission line shown in FIG. 11 received by the receiving apparatus is input to the frequency converter 100 via the input terminal I. The frequency converter 100 shifts by a predetermined fixed frequency so that the OFD of the occupied frequency band of the transmission path is obtained.
OFDM of the intermediate frequency band (center frequency fc)
Convert to signal.

The demultiplexer 301 of the quadrature detector 300 demultiplexes the OFDM signal output from the frequency converter 100 into two signals, and outputs the demultiplexed OFDM signals to the detectors 302 and 303, respectively. Carrier regenerator 304
Outputs the in-phase carrier having the center frequency fc to the detector 302 and outputs the quadrature carrier having the center frequency fc to the detector 303. The detector 302 outputs the real part of the OFDM signal by multiplying the OFDM signal output from the demultiplexer 301 by the in-phase carrier. Detector 30
3 outputs the imaginary part of the OFDM signal by multiplying the OFDM signal output from the demultiplexer 301 by the orthogonal carrier. That is, the quadrature detector 300 converts the OFDM signal in the intermediate frequency band into the OFDM signal in the baseband.

The Fourier transformer 400 includes a detector 303 and a real part of the OFDM signal output from the detector 302.
The Fourier transform operation is collectively performed on the imaginary part of the OFDM signal output from the above to separate the real part and the imaginary part of each digital modulated wave multiplexed on the frequency axis. The demodulated data detector 500 maps the real number part and the imaginary number part of each digital modulated wave on a complex plane, demodulates the data obtained by modulating each carrier from the mapping position according to the threshold value set therein, and outputs the demodulated data. The demodulated data is output from the terminal O.

[0011]

[Problems to be Solved by the Invention]
The signal is transmitted from the transmitting device to the receiving device via a wireless or wired transmission line, and the OFDM signal is attenuated in any transmission line. The attenuation amount of the OFDM signal changes according to the change in the distance in the wireless transmission line, and changes in the wired transmission line according to the number of branches of the transmission line and the like. OF
When the attenuation amount of the DM signal changes, the OFD
The reception level of the M signal varies. However, the receiving apparatus of FIG. 12 performs data demodulation processing without any correction even if the reception level of the OFDM signal fluctuates. Therefore, there is a problem that the demodulated data detector 500 frequently causes erroneous determination of demodulated data.

By the way, an FM receiver or the like is provided with an automatic gain control amplifier for correcting the fluctuation of the reception level based on the fluctuation of the envelope of the received signal.
It is possible to apply such a correction method to the receiving apparatus of FIG. 12, but unlike the FM signal of a single carrier,
Since many modulation carriers are multiplexed on the frequency axis in the OFDM signal, the amplitude and phase patterns in each symbol section change randomly. Therefore, OFD
The envelope waveform of the M signal also changes frequently on the time axis,
If the automatic gain control amplifier is controlled based on such an envelope waveform, the gain of the automatic gain control amplifier becomes unstable, and stable control cannot be performed. Further, in the OFDM signal, since the modulation data of each carrier are different from each other, the fluctuation of the envelope waveform and the fluctuation of the reception level are not always correlated. Therefore, even if the level correction method in the FM receiver is applied to the OFDM signal receiving apparatus, it is not possible to accurately correct the fluctuation of the reception level.

Further, in the receiving apparatus of FIG. 12, since the frequency shift amount in the frequency converter 100 is fixedly set, even if the frequency band shifts, that is, the frequency band changes, this frequency band change also occurs. Cannot be corrected. Therefore, there is a problem that erroneous determination of demodulated data frequently occurs.

By the way, the AM receiver and the like are provided with a frequency converter for correcting the fluctuation of the frequency band based on the fluctuation of the frequency discrimination of the received signal. It is possible to apply such a correction method to the receiving apparatus of FIG. 12, but unlike the AM signal of a single carrier, since a large number of modulated carriers are multiplexed on the frequency axis in the OFDM signal, The amplitude and phase patterns in the symbol section change randomly. Therefore, the frequency discrimination waveform of the OFDM signal also frequently changes on the frequency axis, and if the frequency converter is controlled based on such a frequency discrimination waveform, the frequency shift amount of the frequency converter becomes unstable and stable. Cannot control. Further, in the OFDM signal, since the modulation data of each carrier is different from each other, the fluctuation of the frequency discrimination waveform and the fluctuation of the frequency shift amount do not always correlate. Therefore, even if the method of correcting the frequency shift amount in the AM receiver is applied to the OFDM signal receiving apparatus, it is not possible to accurately correct the fluctuation of the frequency band.

Therefore, it is an object of the present invention to provide a method for transmitting an orthogonal frequency multiplexed signal and a receiving apparatus therefor, which can accurately correct fluctuations in the reception level and, as a result, will not cause erroneous determination of demodulated data. is there. Another object of the present invention is to provide a method for transmitting an orthogonal frequency multiplex signal and a receiving apparatus for the same, which can correct fluctuations in the frequency band with high accuracy and as a result do not cause erroneous determination of demodulated data.

[0016]

According to a first aspect of the present invention, orthogonal frequency division multiplexing is performed for each symbol of a predetermined length from a transmission side to a reception side via a wired or wireless transmission path. The present invention is directed to a method for transmitting a signal, in which a transmitting side continuously transmits a first symbol including data to be transmitted, the multiplex signal of which has a random change, and has a predetermined specific pattern. The second symbol is transmitted intermittently every time a predetermined number of the first symbols are transmitted,
The receiving side is characterized in that it demodulates the data based on the received first symbol and corrects the fluctuation of the receiving level based on the received second symbol.

As described above, in the first aspect, the second symbol having a predetermined specific pattern is intermittently inserted and transmitted in the first symbol including the data to be transmitted. There is. Then, the receiving side detects and corrects the fluctuation of the reception level based on the received second symbol. Since the second symbol has a specific pattern, its level change is strongly correlated with the received level fluctuation. Therefore, the fluctuation of the reception level can be accurately detected from the second symbol, and highly accurate correction can be performed.

A second aspect of the present invention is to receive an orthogonal frequency division multiplex signal transmitted from a transmitting side for each symbol of a predetermined length via a wired or wireless transmission path, and receive the received orthogonal frequency division multiplex. It is directed to a device that demodulates data from a signal, and a specific symbol having a predetermined specific pattern is intermittently inserted in an orthogonal frequency multiplex signal, and a control terminal is provided and the control terminal is provided. The automatic gain control amplification unit that changes the level of the received orthogonal frequency division multiplex signal by changing the gain according to the control signal input to, and the orthogonal frequency after the level is changed by the automatic gain control amplification unit. A control signal output unit is provided which detects a specific symbol from the division multiplexed signal and generates a signal corresponding to the level change of the specific symbol.
By feeding back the signal generated by the control signal output unit to the automatic gain control amplification unit as a control signal,
It is characterized in that the fluctuation of the reception level of the orthogonal frequency division multiplexed signal is corrected.

As described above, in the second aspect, the control signal output section detects a specific symbol from the orthogonal frequency division multiplexed signal and generates a signal corresponding to the level change. The generated signal is fed back to the automatic gain control amplification unit as a control signal. As a result, variations in the reception level of the orthogonal frequency division multiplexed signal are automatically corrected.
In the past, data was demodulated without any correction even if the reception level of the OFDM signal changed.
Since the present invention corrects the fluctuation of the reception level, it is possible to prevent erroneous determination of demodulated data.

In the second aspect, in a preferred embodiment, the envelope signal of the specific symbol is given to the automatic gain control amplification section as a control signal. Therefore, even if the symbols are not synchronized with each other in the receiving apparatus, it is possible to correct the fluctuation of the reception level.

In the above second aspect, in another preferred embodiment, the symbol energy signal of a specific symbol is
The control signal is given to the automatic gain control amplification section. Therefore, the fluctuation of the reception level can be detected more accurately. In this case, the energy of the specific symbol is preferably obtained by digital calculation. This makes it possible to detect variations in the reception level more accurately.

In the second aspect described above, in still another preferred embodiment, the envelope signal of the specific symbol at the start of reception and the symbol energy signal of the specific symbol after the operation of the Fourier transform unit are stabilized are automatically gain-controlled and amplified. The control signal is given to the department. Therefore, the fluctuation of the reception level can be corrected over the entire period from the start of reception.

A third aspect of the present invention is directed to a method of transmitting an orthogonal frequency division multiplex signal for each symbol of a predetermined length from a transmitting side to a receiving side via a wired or wireless transmission path. , The transmitting side continuously transmits the first symbol including the data to be transmitted, the multiplex signal of which changes randomly, and the second symbol having the predetermined specific pattern is changed to the first symbol. Are transmitted intermittently every predetermined number of times, the receiving side demodulates the data based on the received first symbol, and corrects the fluctuation of the frequency band based on the received second symbol. It is characterized by

As described above, in the third aspect, the second symbol having a predetermined specific pattern is intermittently inserted and transmitted in the first symbol containing the data to be transmitted. ing. Then, on the receiving side, the fluctuation of the frequency band is detected and corrected based on the received second symbol. Since the second symbol has a specific pattern, the change in the frequency thereof is strongly correlated with the change in the change in the frequency band. Therefore, from the second symbol,
Changes in the frequency band can be accurately detected, and highly accurate correction can be performed.

A fourth aspect of the present invention is to receive an orthogonal frequency division multiplex signal transmitted from a transmitting side for each symbol of a predetermined length via a wired or wireless transmission path, and receive the received orthogonal frequency division multiplex signal. It is directed to a device that demodulates data from a signal, and a specific symbol having a predetermined specific pattern is intermittently inserted in an orthogonal frequency division multiplex signal, which has a control terminal, A frequency converter that changes the frequency band of the orthogonal frequency division multiplexed signal by changing the frequency shift amount according to the control signal input to the terminal, and the orthogonal frequency division after the frequency band is changed by the frequency converter. The control signal output unit includes a control signal output unit that detects a specific symbol from the multiplex signal and generates a signal corresponding to a change in the frequency band of the specific symbol. By feeding back a more generated signal as a control signal, and corrects the variation in the frequency band of the orthogonal frequency division multiplex signal.

As described above, in the fourth aspect, the control signal output section detects a specific symbol from the orthogonal frequency division multiplexed signal and generates a signal corresponding to the change in the frequency band. The generated signal is fed back to the frequency conversion unit as a control signal. As a result, fluctuations in the frequency band of the orthogonal frequency division multiplexed signal are automatically corrected. Conventionally, data demodulation processing was performed without any correction even if the frequency band of the OFDM signal fluctuates, but since the present invention corrects the frequency band fluctuation, erroneous determination of demodulated data is prevented. it can.

In the fourth aspect, in a preferred embodiment, the frequency discrimination signal of a specific symbol, the frequency domain energy signal or the peak value frequency signal is given to the frequency conversion section as a control signal. For this reason,
Changes in the frequency band can be accurately detected, and highly accurate correction can be performed.

In each of the aspects of the present invention described above, various configurations of the specific symbol are possible.
For example, only one carrier may be left as an unmodulated single tone signal, and a signal in which other carriers are suppressed may be included. Alternatively, a signal in which only one carrier is modulated with predetermined data and other carriers are suppressed may be included. In this case, it is preferable to use a pseudo random code as the data used for modulation. This is because the use of the pseudo-random code facilitates correlation on the receiving side. The data rate of the pseudo random code is preferably selected to be an integral multiple of the symbol rate of the orthogonal frequency division multiplexing signal. This facilitates synchronization on the receiving side.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of a configuration of an OFDM signal transmitted from a transmission side to a reception side in the present invention. In particular, FIG. 1A shows each symbol of the OFDM signal along the time axis, and FIG. 1B shows an enlarged part α of FIG. 1A.

As shown in FIG. 1A, the OFDM signal S
By arranging a specific symbol S0 for automatic gain control shown with hatching and a demodulation symbol Sm (m = 1, 2, ...) Shown without hatching along the time axis. It is configured. The symbols S0 are inserted at predetermined symbol intervals (for example, 15 symbol intervals). It should be noted that such an OFDM signal S takes the form of an analog complex signal in which the real part and the imaginary part are superimposed on each symbol S0, Sm on the transmission path.

For each symbol Sm, a plurality of carriers (several tens to thousands, for example 512) having different frequencies (which are orthogonal to each other at the symbol time ts) are multiplexed (fast inverse Fourier calculation) on the frequency axis. It is composed by. Each carrier is digitally modulated (for example, QPSK modulation, 16QAM, etc.) with data to be demodulated on the receiving side. Therefore, each symbol Sm exhibits a random amplitude distribution as shown in FIG.

For each symbol S0, one of the above-mentioned carriers (for example, the frequency fc) is left as an unmodulated single tone signal, and the other carriers are suppressed by fast inverse Fourier calculation. It is configured. Therefore, each symbol S0 shows an amplitude distribution of a specific pattern, as shown in FIG. Such a symbol S0 has a known time axis component and also a known frequency axis component.

By the way, the OFDM signal S is transmitted from the transmitting side to the receiving side via a wired or wireless transmission path (not shown). Therefore, the OFDM signal S is attenuated on the transmission path. Therefore, on the receiving side, when demodulating the data, in order to supplement the attenuation that occurred on the transmission line,
It is necessary to correct the level of the received OFDM signal S. Such an operation of correcting the reception level of the OFDM signal S is performed using the symbol S0. because,
The symbol S0 always contains the same pattern of signals, so
This is because the change in the reception level can be accurately measured from the waveform of the symbol S0.

FIG. 2 is a block diagram showing the configuration of the receiving apparatus according to the first embodiment of the present invention. In FIG.
This receiving device includes an input terminal I to which a received OFDM signal is input, a bandpass filter 1, an automatic gain control amplifier 2, a quadrature detector 3, and A / D converters 7 and 8.
It includes a Fourier transformer 4, a demodulated data detector 5, a control signal output device 6, and an output terminal O. Quadrature detector 3
Includes a demultiplexer 31, detectors 32 and 33, and a carrier regenerator 34. The control signal output device 6 includes an envelope detector 61, a reference timing generator 62, a symbol timing synchronization circuit 63, a symbol energy detector 64, a control signal switching device 65, and a sample hold device 6.
6 and a low pass filter 67.

FIG. 3 is a waveform diagram showing signals at various parts of the receiving apparatus shown in FIG. Hereinafter, referring to FIG. 3, FIG.
The operation of the receiving device will be described. OF received by the receiving device
The DM signal (see FIG. 1) is converted from the occupied frequency band of the transmission line to the intermediate frequency band (center frequency fc) by a frequency converter (not shown), and then input to the band pass filter 1 via the input terminal I. . The band pass filter 1 removes a signal component in an unnecessary band from the OFDM signal in the intermediate frequency band and extracts only an OFDM signal in the necessary band. The OFDM signal output from the band pass filter 1 is given to the quadrature detector 3 via the automatic gain control amplifier 2.

The demultiplexer 31 of the quadrature detector 3 demultiplexes the OFDM signal output from the automatic gain control amplifier 2 into two, and outputs the demultiplexed OFDM signals to the detectors 32 and 33, respectively. The carrier regenerator 34 outputs an in-phase carrier having a center frequency fc to the detector 32,
An orthogonal carrier having a center frequency fc is output with respect to 3. The detector 32 outputs the real part of the OFDM signal by multiplying the OFDM signal output from the demultiplexer 31 by the in-phase carrier. The detector 33 outputs the imaginary part of the OFDM signal by multiplying the OFDM signal output from the demultiplexer 31 by the orthogonal carrier. That is, the quadrature detector 3 converts the OFDM signal in the intermediate frequency band into the OFDM signal in the baseband. The A / D converter 7 converts the real part of the OFDM signal output from the detector 32 from an analog signal into a digital signal. The A / D converter 8 is
The imaginary part of the OFDM signal output from the detector 33 is converted from an analog signal to a digital signal.

The Fourier transformer 4 has a real part and A / D of the digital OFDM signal output from the A / D converter 7.
The Fourier transform operation is collectively performed on the imaginary part of the digital OFDM signal output from the D converter 8 to separate the real part and the imaginary part of each digital modulated wave on the frequency axis. The Fourier transformer 4 is
Based on the symbol synchronization signal output from the symbol timing synchronization circuit 63, which has the clock terminal 4c, the adjustment of the time axis of the time window used for the Fourier transform is started, and the Fourier transform of each symbol is started. The demodulated data detector 5 maps the real number part and the imaginary number part of each digitally modulated wave on a complex plane, and demodulates the data obtained by modulating each carrier from the mapping position according to the threshold value set therein.

The operation mode of the control signal output device 6 is the first mode in which the control signal of the automatic gain control amplifier 2 is generated based on the envelope waveform of the output signal of the quadrature detector 3,
A second mode for generating a control signal for the automatic gain control amplifier 2 based on the symbol energy of the output signal of the Fourier transformer 4. The control signal output device 6 operates in the first mode at the start of reception of the OFDM signal, and the Fourier transformer 4
After the operation is stabilized (that is, after synchronizing with the received signal), the operation is performed in the second mode. Hereinafter, the operation of the control signal output device 6 will be described in more detail.

The envelope detector 61 envelope-detects each symbol of the OFDM signals output from the detectors 32 and 33 to output an envelope signal representing the envelope of each symbol. The envelope signal output from the envelope detector 61 is given to the reference timing generator 62, and the control signal switch 65 is passed through the low-pass filter 67 that smoothes the fluctuation.
Control signal input terminal 65a.

The reference timing generator 62 uses the symbol S
Single tone data corresponding to a specific pattern of 0 is previously stored therein. Then, the reference timing generator 62 uses the envelope detector 61 for each symbol.
By obtaining the correlation between the envelope signal output from the device and the stored single tone data along the time axis, the reference timing signal indicating whether or not the symbol S0 is detected is output. That is, as shown in FIGS. 3A and 3B, the reference timing generator 62 outputs a high-level (voltage Vhigh) reference timing signal when the symbol S0 is detected, and the reference timing generator 62 does not include the specific pattern. Low level (voltage Vlow) when Sm is detected
The reference timing signal of is output. It should be noted that the reference timing generator 62 maintains the detection operation until it stabilizes (synchronizes) with the received signal (that is, during the asynchronous period).
Even when the symbol S0 is received, the low-level (voltage Vlow) reference timing signal is output. The reference timing signal output from the reference timing generator 62 is input to the symbol timing synchronization circuit 63 and the clock terminal 66c of the sample hold unit 66, respectively.

The symbol timing synchronization circuit 63 outputs a symbol synchronization signal (see FIG. 3C) synchronized with each symbol based on the reference timing signal provided from the reference timing generator 62. That is, the symbol timing synchronization circuit 63 has a clock circuit inside thereof, and every time the rising edge of the reference timing signal is detected, a clock pulse (symbol time ts is one cycle is synchronized with the head of each symbol from the clock circuit). Clock pulse), that is, a symbol synchronization signal is output. The symbol synchronization signal is input to the clock terminal 4c of the Fourier transformer 4 and the clock terminal 64c of the symbol energy detector 64, respectively.

Further, the symbol timing synchronization circuit 63
Is a lock / unlock signal (see FIG. 3) based on the reference timing signal provided from the reference timing generator 62.
(See (d)) is output. The lock / unlock signal indicates an unlocked state at a low level and a locked state at a high level. At the beginning of reception, the lock / unlock signal is in the unlocked state. The symbol timing synchronization circuit 63 has a counter for counting the clock pulses therein, and resets the counter each time the rising edge of the reference timing signal is detected. If the internal timing of the symbol timing synchronization circuit 63 reaches a predetermined count value (the symbol interval at which the symbol S0 is inserted, which is 15 in this case) and is reset for a predetermined number of times (that is, the symbol S0 is When the Fourier transform circuit 4 completes the adjustment of the time window, the lock / unlock signal is switched from the unlocked state to the locked state. This lock / unlock signal is sent to the control signal switch 6
5 is input to the clock terminal 65c.

The symbol energy detector 64 has a D / A converter (not shown) therein. The symbol energy detector 64 includes a symbol timing synchronization circuit 63.
In synchronism with the symbol synchronization signal given by the above, the signal component of each carrier on the frequency axis of each symbol output from the Fourier transformer 4 is digitally calculated and the square integral (squared product) is obtained within the symbol period ts. The energy of each symbol is once obtained as a digital value by performing integration. Then, the obtained digital energy value is converted into an analog value by the D / A converter to output an analog symbol energy signal representing the energy of each symbol. Note that this energy is directly proportional to the average level of each symbol. The reason for squaring is that the amplitude of each carrier fluctuates positively and negatively along the time axis, and therefore its absolute value is taken. Also, the reason for integrating is to find the average. The symbol energy signal output from the symbol energy detector 64 is the control signal switch 6
5 is input to the control signal input terminal 65b.

The control signal switch 65 has a clock terminal 65.
When the lock / unlock signal input to c is in the locked state, the envelope signal output from the envelope detector 61 is selected, and when in the unlocked state, the symbol energy signal output from the symbol energy detector 64 is selected. Then, each is output as a control signal of the automatic gain control amplifier 2.

The sample and hold device 66 receives the voltage Vhi from the reference timing generator 62 with respect to the clock terminal 66c.
When the gh reference timing signal is input, that is, when the specific symbol S0 is output from the automatic gain control amplifier 2, the control signal selected by the control signal switch 65 is sampled and held. The control signal held by the sample hold unit 66 is given to the control terminal 2c of the automatic gain control amplifier 2. The gain A of the automatic gain control amplifier 2 changes according to the voltage level of the control signal supplied from the sample hold unit 66.

When the reception level of the OFDM signal increases, the level of the envelope signal of the symbol S0 or the symbol energy signal also increases in direct proportion thereto, so that the voltage level of the control signal applied to the automatic gain control amplifier 2 increases. . At this time, the automatic gain control amplifier 2
Reduces its gain A so as to reduce the level of the received OFDM signal. On the other hand, when the reception level of the OFDM signal decreases, the level of the envelope signal or the symbol energy signal of the symbol S0 also decreases in direct proportion to this, so that the voltage level of the control signal applied to the automatic gain control amplifier 2 decreases. At this time,
The automatic gain control amplifier 2 increases its gain A so as to increase the level of the received OFDM signal. As a result, the automatic gain control amplifier 2 can correct the fluctuation of the reception level of the OFDM signal to an appropriate level.

Since the symbol energy signal is the energy of each symbol S0 and is obtained by digital operation, it contains almost no error. On the other hand, since the envelope signal is an envelope connecting the vertices of the waveform of each symbol S0, it contains the difference between the waveform of each symbol S0 and the envelope as an error. Moreover, since the envelope signal is used as a control signal of the automatic gain control amplifier 2, a filtering process (low-pass filter 6
7) is required, and an error occurs in this filtering process. Therefore, using the symbol energy signal rather than the envelope signal can improve the gain control accuracy of the automatic gain control amplifier 2.

However, when the symbol synchronization signal is output from the symbol timing synchronization circuit 63, the Fourier transformer 4 starts adjusting the time axis of the time window used for the Fourier transform. Since adjustment takes time, at the start of reception of an OFDM signal, a state in which the time window and the received symbol are not synchronized (that is, a state in which the time window is set across a plurality of adjacent symbols) occurs. There is a risk. In such a state, the Fourier transformer 4 and the symbol energy detector 6
Normal operation of 4 is not guaranteed.

Therefore, the control signal output device 6 keeps the first signal for a while after the reception of the OFDM signal is started (until the adjustment of the time axis of the time window of the Fourier transformer 4 is completely completed).
In the operation mode (1), that is, based on the envelope signal of the symbol S0, the gain of the automatic gain control amplifier 2 is controlled. Thereafter, the control signal output device 6 controls the gain of the automatic gain control amplifier 2 in the second operation mode, that is, based on the symbol energy signal of the symbol S0.

As mentioned above, according to the embodiment of FIG.
A specific symbol S0 is generated by the reference timing generator 62
Is periodically detected, the envelope signal or the symbol energy signal for this symbol S0 is sampled and held by the sample and hold device 66, and the automatic gain control amplifier 2
Since it is fed back to the control terminal 2c of, the accuracy of the gain control of the automatic gain control amplifier 2 can be improved. Moreover, since the attenuation in the transmission path is complemented by the gain control, that is, the reception level is corrected, erroneous determination of demodulated data can be prevented.

In the above embodiment, the symbol S0
Are inserted at intervals of 15 symbols, but may be inserted at intervals of other symbols. In the above embodiment, the symbol S0 is configured by using only one carrier as a non-modulated single tone signal and suppressing the other carriers. However, the symbol S0 has a time axis component and a frequency axis component. Other known methods may be used as long as they are known signals whose amplitude and phase changes along the time axis show a predetermined specific pattern. For example, the amplitude of one carrier may be amplitude-modulated by a plurality of known data (for example, "1" data and "2" data). In this case, although the envelope of the envelope signal output from the envelope detector 61 has some irregularities, it is smoothed by the low-pass filter 67 and can be used as a control signal.

In the above embodiment, the baseband OFDM signal output from the quadrature detector 3 is input to the envelope detector 61. However, if it is the automatic gain control amplifier 2 or later, the automatic gain control amplifier is used. 2, the output of any one of the A / D converters 7 and 8 and the Fourier converter 4 may be input to the envelope detector 61.

In the above embodiment, the output of the Fourier transformer 4 is input to the symbol energy detector 64. However, if it is the automatic gain control amplifier 2 or later, the automatic gain control amplifier 2 and the quadrature detector 3 are provided. , A / D converter 7 or 8 may be input to the symbol energy detector 64.

Further, although the A / D converters 7 and 8 are provided in the above embodiment, they may be deleted and the Fourier transform and the symbol energy detection may be performed as they are in analog form.

Further, although the control signal output device 6 is configured to operate in two operation modes in the above embodiment, it may be configured to operate only in the first operation mode. In this case, the control signal output device includes only the envelope detector 61, the reference timing generator 62 and the sample and hold device 66.

Further, the control signal output device 6 may be configured to operate only in the second operation mode. In this case, the control signal output device is the envelope detector 61, the reference timing generator 62, the symbol timing synchronization circuit 6
3, only the symbol energy detector 64 and the sample and hold device 66 will be provided.

FIG. 4 is a diagram showing another example of the structure of the OFDM signal transmitted from the transmitting side to the receiving side in the present invention. In particular, FIG. 4A shows each symbol of the OFDM signal along the time axis, and FIG. 4B shows the part α of FIG. 4A.
Are enlarged and shown.

As shown in FIG. 4A, the OFDM signal S
By arranging the specific symbol S0 for frequency conversion control shown with hatching and the demodulation symbol Sm (m = 1, 2, ...) Shown without hatching along the time axis. It is configured. The symbols S0 are inserted at predetermined symbol intervals (for example, 15 symbol intervals). Note that such an OFDM signal S takes the form of a complex signal in which a real part and an imaginary part are superimposed on each symbol S0 and Sm on the transmission path.

For each symbol Sm, a plurality of carriers (several tens to thousands, for example 512) having different frequencies (which are orthogonal to each other at the symbol time ts) are multiplexed (fast inverse Fourier calculation) on the frequency axis. It is composed by. Each carrier is digitally modulated (for example, QPSK modulation, 16QAM, etc.) with data to be demodulated on the receiving side. Therefore, each symbol Sm exhibits a random amplitude distribution as shown in FIG.

Each symbol S 0 is pseudo-modulated by, for example, amplitude-modulating one of the plurality of carriers (for example, the frequency fc) with a binary pseudo random code (for example, “1” and “2”). It is configured by performing a fast inverse Fourier operation on what is left as a random signal and suppressed from other carriers. Therefore, each symbol S0
Shows the amplitude distribution of a specific pattern, as shown in FIG. Such a symbol S0 has a known time axis component and also a known frequency axis component.

The data speed of the pseudo random code is preferably selected to be an integral multiple of the OFDM symbol rate. By doing so, the integer number of pseudo-random code information is contained in one symbol S0, and it becomes easy to establish synchronization on the receiving side. Further, it is preferable that the repetition period (repetition period) of the pattern of the pseudo random code used is the same as the symbol period. In this case, the number of appearances of one code (for example, “1”) and the number of appearances of the other code (for example, “2”) become equal, and it becomes easy to take correlation on the receiving side.

By the way, the OFDM signal S shown in FIG.
It is sent from the transmitting side to the receiving side via a wired or wireless transmission path (not shown). Therefore, the transmitting side (not shown)
The FDM signal S is converted from the intermediate frequency band (center frequency fc) to the occupied frequency band (center frequency fr) of the transmission line. On the other hand, on the receiving side, when demodulating data, the received OFDM signal S is converted from the occupied frequency band of the transmission path to the intermediate frequency band (center frequency fc) for the demodulation work. In the embodiment described below, the operation of frequency-converting the OFDM signal S from the occupied frequency band to the intermediate frequency band is performed using the symbol S0. This is because the symbol S0 always contains signals of the same pattern, and therefore the change of the frequency band can be accurately measured from the waveform of the symbol S0.

FIG. 5 is a block diagram showing the configuration of a receiving apparatus according to the second embodiment of the present invention. In FIG.
The receiving device has an input terminal I to which the received OFDM signal is input, a frequency converter 10, a quadrature detector 3, a Fourier transformer 4, a demodulated data detector 5, a control signal output device 60, and an output. And a terminal O. The quadrature detector 3
It includes a branching device 31, detectors 32 and 33, and a carrier regenerator 34. The control signal output device 60 includes an envelope detector 61, a reference timing generator 62, a symbol timing synchronization circuit 63, and a sample hold device 66.
And a frequency discriminator 68. For the purpose of clarifying the correspondence, in the embodiment of FIG. 5, the same components as those of the embodiment of FIG. 2 are designated by the same reference numerals.

FIG. 6 is a waveform diagram showing signals of respective parts of the receiving apparatus shown in FIG. The operation of the receiving apparatus shown in FIG. 5 will be described below with reference to FIG. The OFDM signal (see FIG. 6 (a)) in the occupied frequency band (center frequency fr) of the transmission path received by the receiver is input to the input terminal I, and the frequency converter 10 converts the intermediate frequency band (center frequency fc) After being converted into an OFDM signal, it is input to the quadrature detector 3.

The demultiplexer 31 of the quadrature detector 3 demultiplexes the OFDM signal output from the frequency converter 10 into two, and outputs the demultiplexed OFDM signals to the detectors 32 and 33, respectively. The carrier generator 34 outputs an in-phase carrier having a center frequency fc to the detector 32 and outputs a quadrature carrier having a center frequency fc to the detector 33. Detector 3
2 outputs the real part of the OFDM signal by multiplying the OFDM signal output from the demultiplexer 31 by the in-phase carrier. The detector 33 outputs the O output from the demultiplexer 31.
By multiplying the FDM signal by the orthogonal carrier, the OF
Output the imaginary part of the DM signal. That is, the quadrature detector 3
Is an OFDM signal in the intermediate frequency band and an OF in the baseband.
Convert to DM signal.

The Fourier transformer 4 collectively performs a Fourier transform operation on the real part of the OFDM signal output from the detector 32 and the imaginary part of the OFDM signal output from the detector 33 to obtain the frequency On the axis, the real and imaginary parts of each digital modulated wave are separated. The demodulated data detector 5 maps the real number part and the imaginary number part of each digital modulated wave on the complex plane, and demodulates the data obtained by modulating each carrier from the mapping position according to the threshold value set therein.

Next, the operation of the control signal output device 60 will be described in more detail. The envelope detector 61 envelope-detects each symbol of the OFDM signal output from the frequency converter 10 to output an envelope signal representing the envelope of each symbol. The envelope signal output from the envelope detector 61 is given to the reference timing generator 62.

The reference timing generator 62 uses the symbol S
Binary pseudo random data corresponding to a specific pattern of 0,
It is stored inside in advance. Then, the reference timing generator 62 obtains, for each symbol, the correlation between the envelope signal output from the envelope detector 61 and the stored binary pseudo-random data along the time axis, thereby obtaining the symbol S0. The reference timing signal indicating whether or not is output. That is, as shown in FIGS. 6A and 6B, the reference timing generator 62 outputs a high-level (voltage V1) reference timing signal when the symbol S0 including the specific pattern is detected, and the specific pattern is generated. When the symbol Sm not including is detected, a low-level (voltage V2) reference timing signal is output. The reference timing signal output from the reference timing generator 62 is input to the clock terminal 66c of the sample hold device 66 and the symbol timing synchronization circuit 63.

The symbol timing synchronization circuit 63 outputs a symbol synchronization signal synchronized with each symbol based on the reference timing signal supplied from the reference timing generator 62. That is, the symbol timing synchronization circuit 6
3 has a clock circuit therein, and every time the rising edge of the reference timing signal is detected, a clock pulse synchronized with the beginning of each symbol from the clock circuit (clock pulse having a symbol time ts as one cycle),
That is, the symbol synchronization signal is output. This symbol synchronization signal is input to the clock terminal 64c of the clock terminal 4c of the Fourier transformer 4.

The Fourier transformer 4 detects the real part of the digital OFDM signal output from the detector 32 and the detector 3
The Fourier transform operation is collectively performed on the imaginary part of the digital OFDM signal output from 3 to separate the real part and the imaginary part of each digital modulated wave on the frequency axis. The Fourier transformer 4 has a clock terminal 4c, starts adjustment of the time axis of the time window used for Fourier transform based on the symbol synchronization signal output from the symbol timing synchronization circuit 63, and
Start the Fourier transform of each symbol. The demodulated data detector 5 maps the real number part and the imaginary number part of each digitally modulated wave on a complex plane, and demodulates the data obtained by modulating each carrier from the mapping position according to the threshold value set therein.

The frequency discriminator 68 discriminates the frequency of each symbol to generate a voltage corresponding to the frequency of each symbol. The sample hold unit 66 receives the voltage V1 from the reference timing generator 62 with respect to the clock terminal 66c.
When the reference timing signal (1) is input, that is, when the specific symbol S0 is output from the frequency converter 10, the frequency discrimination signal output from the frequency discriminator 68 is sampled and held. The frequency discrimination signal held in the sample hold device 66 is given to the control terminal 10c of the frequency converter 10 as a control signal.
The frequency shift amount of the frequency converter 10 changes according to the voltage level of the control signal supplied from the sample hold unit 66.

OFDM output from the frequency converter 10
When the frequency band of the signal becomes higher, the level of the frequency discriminant signal of the symbol S0 output from the frequency discriminator 68 also increases in direct proportion to this, so that the voltage level of the control signal supplied to the frequency converter 10 increases. . At this time, the frequency converter 10 increases the frequency shift amount so as to lower the frequency band of the output OFDM signal. On the other hand, when the frequency of the OFDM signal becomes low, the level of the frequency discrimination signal of the symbol S0 also decreases in direct proportion thereto, so that the voltage level of the control signal supplied to the frequency converter 10 decreases. At this time, the frequency converter 10 reduces the frequency shift amount so as to raise the frequency band of the output OFDM signal. As a result, the frequency converter 10 can correct the fluctuation of the frequency band of the OFDM signal to an appropriate intermediate frequency band (center frequency fc).

As described above, according to the second embodiment of FIG. 5, the reference timing generator 62 periodically detects a specific symbol S0, and the frequency discrimination signal at this symbol S0 is sample-held as a control signal. Since the control signal is fed back to the control terminal 10c of the frequency converter 10, the accuracy of frequency shift amount control of the frequency converter 10 can be improved. Also, since the frequency band fluctuation is corrected by the frequency shift amount control,
The deviation from the intermediate frequency band is eliminated, and erroneous determination of demodulated data can be prevented.

FIG. 7 is a block diagram showing the configuration of the receiving apparatus according to the third embodiment of the present invention. In addition, the same reference numerals are given to the portions corresponding to those of the receiving apparatus in FIG. 5, and the description thereof will be omitted. It should be noted that the frequency domain energy detector 71 is used instead of the frequency discriminator 68 of FIG. 5 in the third embodiment.
That is, the control signal output device 70 is configured by using.

FIG. 8 is a waveform diagram for explaining the operation of the frequency domain energy detector 71 of FIG. In particular, FIG.
8A shows the power spectrum of the symbol S0 along the frequency axis, FIG. 8B shows the integrated value of the power spectrum of FIG. 8A, and FIG. 8C shows the frequency domain energy signal. There is. The operation of the receiving apparatus shown in FIG. 7 will be described below with reference to FIG.

The frequency domain energy detector 71 performs a series of operations as described below for each symbol in synchronization with the symbol terminal synchronizing signal supplied from the symbol timing synchronizing circuit 63 with respect to its clock terminal 71c. First, as shown in FIG. 8A, the frequency domain energy detector 71 has a carrier (amplitude modulated by a binary pseudo random signal) distributed in the frequency range of 0 to fs in the output of the Fourier transformer 4. Are divided into two regions α1 and α2 with (1/2) fs as a boundary. Where fs is
It is the frequency of the sampling clock used in the Fourier transformer 4. The spectrum of each symbol is
Since it is folded back at (1/2) fs, the high-frequency component is in the region α1 where the frequency is lower than (1/2) fs, and the low-frequency component is in the region where the frequency is higher than (1/2) fs. It appears in α2.

Next, the frequency domain energy detector 71
As shown in FIG. 8B, the energy E1 of the region α1 and the energy E1 of the region α1 are obtained by square-integrating the power spectrum component of the region α1 and the power spectrum component of the region α2, respectively.
The energy E2 of the area α2 is obtained. These energies E1 and E2 are proportional to the average level of each symbol. The reason for squaring is that the amplitude of each carrier fluctuates positively and negatively along the time axis, and therefore its absolute value is taken. Further, the integration is performed to obtain the average of each symbol.

Next, the frequency domain energy detector 71
The energy E1 of the area α1 and the energy E2 of the area α2 are compared, and as shown in FIG. 8C, the energy difference (E1
Generate a frequency domain energy signal having a voltage value corresponding to -E2). This frequency domain energy signal has a positive voltage value VHI when the energy E1 of the domain α1 is larger.
GH shows a negative voltage value VLOW when the energy E2 of the region α2 is larger. By the way, in the symbol S0, when there is no shift in the frequency band, the power distributions in the areas α1 and α2 are equal, and the voltage value of the frequency domain energy signal is zero. Therefore, the deviation direction and deviation amount from the center frequency fc can be known based on the polarity and voltage value of the frequency domain energy signal of the symbol S0.

The sample and hold device 66 supplies the voltage V1 from the reference timing generator 62 to the clock terminal 66c.
When the reference timing signal (1) is input, that is, when the specific symbol S0 is output from the frequency converter 10, the frequency domain energy signal output from the frequency domain energy detector 71 is sampled and held. The frequency domain energy signal held by the sample and hold device 66 is given to the control terminal 10c of the frequency converter 10 as a control signal. The frequency shift amount of the frequency converter 10 changes according to the voltage level of the control signal supplied from the sample hold unit 66.

OFDM output from the frequency converter 10
When the frequency band of the signal becomes higher, the voltage value VHIGH of the frequency domain energy signal of the symbol S0 output from the frequency domain energy detector 71 increases in the positive direction, so that the voltage of the control signal supplied to the frequency converter 10 also becomes positive. Grows in the direction. At this time, the frequency converter 10 outputs O
The frequency shift amount is increased so that the frequency band of the FDM signal is lowered. On the other hand, when the frequency band of the OFDM signal decreases, the voltage VLOW of the frequency domain energy signal of the symbol S0 increases in the negative direction.
The voltage of the control signal applied to 0 also increases in the negative direction.
At this time, the frequency converter 10 reduces the frequency shift amount so as to increase the frequency of the output OFDM signal. As a result, the frequency converter 10 changes the fluctuation of the frequency band of the OFDM signal into an appropriate intermediate frequency band (center frequency f
c) can be corrected. The control signal sampled and held by the sample and hold device 66 may be averaged over a plurality of cycles of the symbol S0.

As described above, according to the third embodiment of FIG. 7, the reference timing generator 62 periodically detects a specific symbol S0 and samples the frequency domain energy signal at this symbol S0 as a control signal. Since it is held and fed back to the control terminal 10c of the frequency converter 10, the accuracy of the frequency shift amount control of the frequency converter 10 can be improved. Further, since the frequency band variation is corrected by the frequency shift amount control, there is no deviation from the intermediate frequency band, and erroneous determination of demodulated data can be prevented.

FIG. 9 is a block diagram showing the configuration of the receiving apparatus according to the fourth embodiment of the present invention. In addition, the same reference numerals are given to the portions corresponding to those of the receiving apparatus in FIG. 5, and the description thereof will be omitted. What should be noted in this embodiment is that the control signal output device 80 is configured by using the correlation detector 81 and the peak value frequency detector 82 instead of the frequency discriminator 68 of FIG.

FIG. 10 is a waveform diagram showing signals of respective parts of the control signal output device 80 of FIG. Particularly, FIG. 10A shows the correlation signal along the frequency axis, and FIG. 10B shows the peak value frequency detection signal. The operation of the receiving apparatus shown in FIG. 9 will be described below with reference to FIG.

The correlation detector 81 stores in advance information on the ideal frequency component for a specific symbol S0 as reference information. The correlation detector 81 outputs the correlation signal as shown in FIG. 10A by obtaining the correlation between the reference information and the data on the frequency axis output from the Fourier transformer 4. The correlation detection operation in the correlation detector 81 is synchronized with the symbol synchronization signal supplied from the symbol timing synchronization circuit 63 to the clock terminal 81c,
This is performed for each symbol, but it becomes significant especially when a specific symbol S0 is output from the Fourier transformer 4. Therefore, the case where a specific symbol S0 is output from the Fourier transformer 4 will be described. The correlation detector 81 once stores the information of the symbol S0 in an internal memory (not shown) as detection target information. Here, the reference information stored in advance in the correlation detector 81 and the detection target information stored in the internal memory thereof are both digital pseudo-random signals discretely existing on the frequency axis. The correlation detector 81 superimposes the detection target information and the reference information on the frequency axis, multiplies the code information included in each of them, and further obtains the sum thereof. At this time, the correlation detector 81 shifts the position of the detection target information on the frequency axis for each code unit, and calculates the sum of the multiplication results with the reference information. Then, the set of this total becomes a correlation signal. The correlation signal exhibits a peak on the frequency axis when the correspondence between the code information included in the detection target information and the code information included in the reference information matches.

When the symbol S 0 is output from the Fourier transformer 4, for example, the frequency deviation Δf is “0”.
Then, the correlation detector 81 outputs a correlation signal having a peak value at the position of the center frequency fc, as shown by β1 in FIG. 10 (a). When the symbol S0 is output, for example, when there is a frequency shift Δf in the higher side, the correlation detector 81 shifts the appearance of the peak value as shown by β2 in FIG. The correlation signal generated on the high side in the frequency axis is output. Therefore, it is possible to detect the frequency shift direction and the shift amount from such a correlation signal.

The peak value frequency detector 82 compares the location of the peak value of the correlation signal output from the correlation detector 81 with the center frequency fc, and has a peak value frequency having a voltage value ΔV corresponding to the difference Δf. Signal (see Fig. 10 (b))
Is output.

The sample and hold device 66 supplies the voltage V1 from the reference timing generator 62 to the clock terminal 66c.
When the reference timing signal (1) is input, that is, when the specific symbol S0 is output from the frequency converter 10, the peak value frequency signal output from the peak value frequency detector 82 is sampled and held. The peak value frequency signal held in the sample hold device 66 is used as a control signal in the control terminal 10 of the frequency converter 10.
given to c. The frequency shift amount of the frequency converter 10 changes according to the voltage level of the control signal supplied from the sample hold unit 66.

OFDM output from the frequency converter 10
When the frequency band of the signal becomes high, the peak value frequency detector 8
Since the level .DELTA.V of the peak value frequency signal of the symbol S0 output from 2 also increases in the positive direction, the frequency converter 1
The voltage level of the control signal applied to 0 increases. At this time, the frequency converter 10 increases the frequency shift amount so as to lower the frequency band of the output OFDM signal. On the other hand, when the frequency of the OFDM signal decreases, the level ΔV of the peak value frequency signal of the symbol S0 also increases in the negative direction, so the voltage level of the control signal supplied to the frequency converter 10 increases in the negative direction. At this time, the frequency converter 10 reduces the frequency shift amount so as to raise the frequency band of the output OFDM signal. As a result, the frequency converter 10 can correct the fluctuation of the frequency band of the OFDM signal to an appropriate intermediate frequency band (center frequency fc).

As described above, according to the fourth embodiment of FIG. 9, the reference timing generator 62 periodically detects a specific symbol S0 and samples the peak value frequency signal at this symbol S0 as a control signal. Hold,
Since the feedback is provided to the control terminal 10c of the frequency converter 10, the accuracy of the frequency shift amount control of the frequency converter 10 can be improved. Further, since the frequency band variation is corrected by the frequency shift amount control, there is no deviation from the intermediate frequency band, and erroneous determination of demodulated data can be prevented.

In the second to fourth embodiments, the symbols S0 are inserted at 15 symbol intervals, but they may be inserted at other symbol intervals. In the second to fourth embodiments, each symbol S0 is configured by amplitude-modulating only one carrier with a binary pseudo-random code and suppressing the other carriers. However, the symbol S0 is Other methods may be used as long as the signals have known time axis components and frequency axis components, and changes in amplitude and phase along the time axis exhibit a predetermined specific pattern. For example, only one carrier may be used as an unmodulated single tone signal, and a signal in which other carriers are suppressed (see FIG. 1) may be used.

In the second to fourth embodiments, the OFDM of the intermediate frequency band output from the frequency converter 10 is used.
The signal is sent to the envelope detector 61 (in the second embodiment,
Further, the signal is input to the frequency discriminator 68). However, if it is the frequency converter 10 or later, the output of either the quadrature detector 3 or the Fourier transformer 4 is supplied to the envelope detector 61.
(And the frequency discriminator 68) may be input.

Furthermore, in the third and fourth embodiments, the output of the Fourier transformer 4 is input to the frequency domain energy detector 71 and the correlation detector 81, respectively. In this case, either the output of the frequency converter 10 or the quadrature detector 3 may be input to the frequency domain energy detector 71 and the correlation detector 81.

Further, the first embodiment is configured to correct the fluctuation of the reception level, and the second to fourth embodiments are configured to correct the fluctuation of the frequency band. By combining any one of the four embodiments with the first embodiment, a receiving circuit capable of correcting both the fluctuation of the reception level and the fluctuation of the frequency band may be configured.

[Brief description of drawings]

FIG. 1 is an OFD transmitted from a transmission side in the present invention.
It is a figure which shows an example of a structure of M signal.

FIG. 2 is a block diagram showing a configuration of a receiving device according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram showing signals of respective parts of the receiving apparatus shown in FIG.

FIG. 4 is an OFD transmitted from a transmission side in the present invention.
It is a figure which shows the other example of a structure of M signal.

FIG. 5 is a block diagram showing a configuration of a receiving device according to a second embodiment of the present invention.

6 is a waveform diagram showing signals of respective parts of the receiving apparatus shown in FIG.

FIG. 7 is a block diagram showing a configuration of a receiving device according to a third embodiment of the present invention.

8 is a waveform diagram for explaining the operation of the frequency domain energy detector 71 shown in FIG.

FIG. 9 is a block diagram showing a configuration of a receiving device according to a fourth embodiment of the present invention.

10 is a waveform diagram showing signals of respective parts of the control signal output device 80 shown in FIG.

FIG. 11 is a diagram showing a configuration of a conventional OFDM signal transmitted from a transmission side.

FIG. 12: O inferred from the first and third prior arts
It is a block diagram which shows the structure of the receiver of an FDM signal.

[Explanation of symbols]

 1 ... Band pass filter 2 ... Automatic gain control amplifier 3 ... Quadrature detector 31 ... Demultiplexer 32, 33 ... Detector 34 ... Carrier regenerator 4 ... Fourier transformer 5 ... Demodulated data detector 6 ... Control signal output device 61 ... Envelope detector 62 ... Reference timing generator 63 ... Symbol timing synchronization circuit 64 ... Symbol energy detector 65 ... Control signal switcher 66 ... Sample hold device 67 ... Low pass filter 7,8 ... A / D converter 10 ... Frequency conversion Device 60 ... Control signal output device 68 ... Frequency discriminator 70 ... Control signal output device 71 ... Frequency domain energy detector 80 ... Control signal output device 81 ... Correlation detector 82 ... Peak value frequency detector S ... OFDM signal S0, Sm … Symbol ts… Symbol time

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location // H04L 27/34 (72) Inventor Yuji Oue 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In-house (72) Inventor Uno Yashiro Hiroshi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yasuo Nagaishi 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (19)

[Claims] 1. A method of transmitting an orthogonal frequency division multiplex signal for each symbol of a predetermined length from a transmission side to a reception side via a wired or wireless transmission path, wherein the transmission side should transmit. A first symbol including data, the multiplex signal of which changes randomly, is continuously transmitted, and a second symbol having a predetermined specific pattern is transmitted every time a predetermined number of the first symbols are transmitted. Intermittently transmitting to the receiving side, the receiving side demodulates data based on the received first symbol, and corrects fluctuations in the receiving level based on the received second symbol. Yes, the transmission method. 2. A reception for receiving an orthogonal frequency division multiplex signal transmitted from a transmitting side for each symbol of a predetermined length via a wired or wireless transmission path and demodulating data from the received orthogonal frequency division multiplex signal. A device, in the orthogonal frequency multiplexed signal, a specific symbol having a predetermined specific pattern is intermittently inserted, has a control terminal, to the control signal input to the control terminal An automatic gain control amplifying means for changing the level of the received orthogonal frequency division multiplex signal by changing the gain according to the gain, and an orthogonal frequency division multiplex signal after the level is changed by the automatic gain control amplifying means. The control signal output means for detecting the specific symbol from the control circuit and generating a signal corresponding to the level change of the specific symbol. A receiving apparatus, characterized in that the fluctuation of the reception level of the orthogonal frequency division multiplexed signal is corrected by feeding back the signal generated by the stage as the control signal to the automatic gain control amplification means. 3. The envelope detecting means for outputting an envelope signal representing an envelope of each symbol by performing envelope detection on each of the symbols, the pattern of the envelope signal and a specific pattern stored in advance. And a reference timing generating means for generating a reference timing signal indicating whether or not the specific symbol is detected by comparing each symbol, and the reference timing signal indicates a detection state of the specific symbol. The receiving apparatus according to claim 2, further comprising: a sample-hold unit that samples and holds the envelope signal output from the envelope detecting unit as the control signal. 4. The delimiter detection means for detecting a delimiter between the symbols and outputting a symbol synchronization signal indicating the demarcation; and the control signal output means for synchronizing each symbol with the symbol synchronization signal. By square-integrating the signal components in 1 symbol period,
Symbol energy detecting means for outputting a symbol energy signal representing energy of each symbol; specific symbol detecting means for detecting whether or not the specific symbol is included in the received orthogonal frequency division multiplexed signal; The receiving device according to claim 2, further comprising: a sample and hold unit that samples and holds the symbol energy signal output from the symbol energy detection unit as the control signal when the symbol detection unit detects the specific symbol. 5. An orthogonal frequency division multiplexed signal whose level has been changed by the automatic gain control amplification means,
By performing a Fourier transform operation for each symbol using the time window, further comprises a Fourier transform means for separating a plurality of carriers on the frequency axis, the control signal output means, by envelope detection of each of the symbols, Envelope detection means for outputting an envelope signal representing the envelope of each symbol, by comparing the pattern of the envelope signal and a specific pattern stored in advance for each symbol, to determine whether or not the specific symbol is detected. A reference timing generating means for generating a reference timing signal representing the signal, and a symbol synchronization signal representing a delimiter between the respective symbols based on the reference timing signal, and further, an unlocked state at the start of reception, the Fourier transforming means. After the operation of is stabilized, a lock / unlock signal indicating the locked state is generated. And a symbol timing synchronization means to be formed, and by performing a square integration within one symbol period, the signal component of each carrier on the frequency axis of each symbol output from the Fourier transform means in synchronization with the symbol synchronization signal, Symbol energy detection means for outputting a symbol energy signal representing the energy of each symbol, and the envelope signal is selected when the lock / unlock signal is in the unlocked state, and the symbol energy signal is selected when the locked / unlocked signal is in the locked state. Control signal switching means, and a sample for holding the envelope signal or the symbol energy signal selected by the control signal switching means as the control signal when the reference timing signal represents the detection state of the specific symbol. The holding device according to claim 2, further comprising holding means. The receiving device. 6. The receiver according to claim 5, wherein the symbol energy detecting means obtains the energy of each symbol by digital calculation. 7. A signal in which only one carrier is left as an unmodulated single-tone signal and the other carriers are suppressed in the specific symbol intermittently inserted in the orthogonal frequency division multiplexing signal. The receiving device according to claim 2, characterized in that 8. The specific symbol intermittently inserted in the orthogonal frequency division multiplexed signal includes a signal in which only one carrier is modulated with predetermined data and other carriers are suppressed. 3. The method according to claim 2, wherein
The receiving device according to 1. 9. The specific symbol intermittently inserted into the orthogonal frequency division multiplexed signal includes a signal in which only one carrier is modulated with a pseudo-random code and the other carriers are suppressed. The receiving device according to claim 8, wherein: 10. The receiving apparatus according to claim 9, wherein the data rate of the pseudo-random code is selected to be an integral multiple of the symbol rate of the orthogonal frequency division multiplexed signal. 11. A method of transmitting an orthogonal frequency division multiplexed signal for each symbol of a predetermined length from a transmission side to a reception side via a wired or wireless transmission path, wherein the transmission side should transmit. A first symbol including data, the multiplex signal of which changes randomly, is continuously transmitted, and a second symbol having a predetermined specific pattern is transmitted every time a predetermined number of the first symbols are transmitted. Intermittently transmitting to the receiving side, the receiving side demodulates data based on the received first symbol, and corrects the fluctuation of the frequency band based on the received second symbol. Yes, the transmission method. 12. A receiver for receiving an orthogonal frequency division multiplex signal transmitted from a transmitting side for each symbol of a predetermined length via a wired or wireless transmission path and demodulating data from the received orthogonal frequency division multiplex signal. In the device, a specific symbol having a predetermined specific pattern is intermittently inserted in the orthogonal frequency division multiplex signal, has a control terminal, and has a control signal input to the control terminal. A frequency shift means for changing the frequency band of the orthogonal frequency division multiplex signal by changing the frequency shift amount according to the above, and from among the orthogonal frequency division multiplex signals after the frequency band is changed by the frequency conversion means. A control signal output means for detecting the specific symbol and generating a signal corresponding to a change in the frequency band of the specific symbol; The receiving device is characterized in that the fluctuation of the frequency band of the orthogonal frequency division multiplex signal is corrected by feeding back the signal generated by the input means as the control signal. 13. The control signal output means outputs an envelope signal representing an envelope of each symbol by performing envelope detection on each of the symbols, and a pattern of the envelope signal and a specific pattern stored in advance. And a reference timing generating means for generating a reference timing signal indicating whether or not the specific symbol is detected, and a frequency discrimination corresponding to the frequency of each symbol by discriminating the frequency of each symbol. Frequency discriminating means for generating a signal, and sample and hold means for sampling and holding the frequency discriminating signal output from the frequency discriminating means as the control signal when the reference timing signal represents the detection state of the specific symbol. The receiving device according to claim 12, comprising: 14. The envelope detecting means for outputting an envelope signal representing an envelope of each symbol by performing envelope detection on each of the symbols, the control signal output means, a pattern of the envelope signal and a specific pattern stored in advance. And a reference timing generating means for generating a reference timing signal indicating whether or not the specific symbol is detected, and a signal component on the frequency axis of each symbol having a predetermined center frequency. Is divided into two regions with the center frequency as a boundary, and the energy in the low frequency region with respect to the center frequency is compared with the energy in the high frequency region with respect to the center frequency to determine the difference between the two regions. Frequency domain energy detecting means for generating a corresponding frequency domain energy signal, and the reference timing The sample holding means for sampling and holding the frequency domain energy signal output from the frequency domain energy detecting means as the control signal when the signal represents the detection state of the specific symbol. Receiver. 15. The control signal output means detects an envelope of each of the symbols to output an envelope signal representing an envelope of each symbol, a pattern of the envelope signal and a specific pattern stored in advance. And a reference timing generating means for generating a reference timing signal indicating whether or not the specific symbol is detected by comparing with each symbol, and the frequency component of each of the symbols and the specific symbol stored in advance. Correlation strength with frequency components, and a correlation detection means for outputting a correlation signal representing a deviation from a predetermined center frequency, and a frequency at which a peak value of the correlation strength exists from the correlation signal output from the correlation detection means The peak corresponding to the difference between the detected frequency and the predetermined center frequency. Peak value frequency detecting means for outputting a frequency signal, when the reference timing signal represents the detection state of the specific symbol, the peak value frequency signal output from the peak value frequency detecting means as the control signal And a sample holding means for holding the sample,
The receiving device according to claim 12. 16. A signal in which only one carrier is left as a non-modulated single-tone signal and the other carriers are suppressed in the specific symbol intermittently inserted in the orthogonal frequency division multiplex signal. 13. The receiver according to claim 12, characterized in that is included. 17. The specific symbol intermittently inserted in the orthogonal frequency division multiplexed signal includes a signal in which only one carrier is modulated with predetermined data and other carriers are suppressed. The receiving device according to claim 12, wherein: 18. The specific symbol intermittently inserted into the orthogonal frequency division multiplexed signal includes a signal in which only one carrier is modulated with a pseudo-random code and the other carriers are suppressed. The receiving device according to claim 17, wherein: 19. The receiving apparatus according to claim 18, wherein the data rate of the pseudo-random code is selected to be an integral multiple of the symbol rate of the orthogonal frequency division multiplexed signal.