OFDM amplitude or frequency correction using pilots

Field of the Invention

0001The The present invention relates generally to a method to transfer and a method for receiving modulated carrier data and a transfer device and a receiving device thereof.

Description of the Prior technology

0002In recent years, the communication comprising an orthogonal frequency-division multiplexed (Hereinafter referred to as OFDM) signal is used, attention paid in mobile digital sound transmission, earthbound digital television broadcasting or similar. The reason for this is that the OFDM signal a high spectrum efficiency has, and allows a large to transmit amount of data at high speed, so that its characteristics are hardly deteriorated by a reflected wave even if there is no waveform equalizer. In addition, its signal waveform in a form which is close to random noise, whereby another Service is not easily subjected to radio interference. A transmission system, which uses an OFDM signal having such properties, disclosed in the <patcit><text>Japanese Patent Publication No.. 167 633</text></patcit>/ 1993 (hereinafter referred to as first prior art), "conjures generation home service Exceeds television " described on pages 101 to 124 in Nikkei Electronics (no. 574), released on February 15, 1993 (hereinafter referred to as second prior art), and "OFDM system and its development " written by Masanori Saito at NHK Science and Technical Research Laboratories, Tokyo, on pages 1 to 15 in materials of EIAJ Technical Seminar on 14 September 1994 (hereinafter referred to as third State of the art).

0003<figref idrefs="S47">11</figref> is a diagram showing the structure of a conventional OFDM signal, where <figref>11 (a)</figref> respective symbols of an OFDM signal along shows the time axis, and <figref>11 (b)</figref> a in <figref>11 (a)</figref> shown part α in a enlarged manner shows. As in<figref>11 (a)</figref> shown, a OFDM signal S constructed by arranging symbols Sm (m = 1, 2, ...) along the time axis. Each of the symbols Sm is constructed by subjecting each of a plurality of (tens to thousands thereof, eg, 512) carriers, which are orthogonal in symbol time ts, where each of the carriers modulated is by using a digital modulation (eg QPS (Quadrature Phase Shift Keying) modulation or 16QAM (Quadrature Amplitude Modulation)), which to be transmitted by Data is modulated and OFDM symbols are generated by multiplexing the modulated carrier on the frequency axis by using an inverse FFT (Fast Fourier Transform) operation. Therefore, each of the symbols Sm a random Amplitude distribution, as in <figref>11 (b)</figref> shown. The OFDM signal S takes the form of a complex signal, in which a real part and an imaginary part are superposed with respect each of the symbols Sm on a general conference line.

0004Such an OFDM signal is transmitted from the End to the receiving end through wired or wireless transmission line Posted. In the cable transmission line is limited by its transmission characteristics you occupied frequency band. On the other hand, in the radio transmission line, is limited by law and regulation her occupied frequency band. Therefore, on the transmitted End of the OFDM signal converted into an OFDM signal in the occupied Frequency band of the transmission line of an OFDM signal in an intermediate frequency band. on the other hand the received OFDM signal converted to the receiving end in an OFDM signal in an intermediate frequency band for demodulating operation of an OFDM signal in the occupied frequency band of the transmission line in Demodulierungsdaten.

0005Of the mentioned above first prior art discloses a receiver having a bandpass filter, Frequency converter and a low pass filter for converting a OFDM signal transmitted from the End is transmitted, into an OFDM signal in a base band, an analog-to-digital (A / D) converter for Sampling the OFDM signal in the base band and converting the sampled OFDM signal into a digital signal, an FFT demodulator to time axis data to be subjected to Fourier transform to obtain data on the frequency axis to receive each carrier, a Signal point coordinate Berurteilungsschaltung to assess the Amplitude and the phase on a complex plane for each Carrier, to obtain complex data, a coupling circuit for received Data for converting the complex data into digital data and Coupling the data dependent on the number of transmitted bits by each carrier, a bit stream to produce, and a Deinterleave matrix and error-correcting code circuit for obtaining received Data by subjecting the bit stream a Deinterleave and Error correction.

0006Of the mentioned above third prior art discloses a receiver having a bandpass filter, a quadrature detector and a low pass filter for converting an OFDM signal which is transmitted from the transmitting end, into an OFDM signal in a base band, an A / D converter for sampling of the OFDM signal in the base band and converting the abgetasended OFDM signal into a digital signal, an FFT demodulator for subjecting time axis data to a Fourier transform to Obtaining data on the frequency axis for each carrier, and a parallel-serial conversion circuit for converting parallel data on the frequency axis into serial Data to obtain received data.

0007<figref idrefs="S48">12</figref> is is a block diagram showing the construction of a receiver of an OFDM signal, which simply the first prior art and the third prior art can be analogized. In<figref idrefs="S48">12</figref> has recipient an input terminal <figref>1</figref> on to which a received OFDM signal is inputted, a frequency converter <figref>100</figref>, A quadrature detector <figref>300</figref>. a Fourier transformer <figref>400</figref> and a detector <figref>500</figref> demodulated Data. The quadrature detector<figref>300</figref> has a branching filter <figref>301</figref>. detectors <figref>302</figref> and <figref>303</figref> and a carrier recovery device <figref>304</figref> on.

0008the OFDM signal in an occupied frequency band (its center frequency fr) of a transmission line, shown in <figref idrefs="S47">11</figref>Which received by the receiver is input to the frequency converter <figref>100</figref> by the input terminal <figref>1</figref>, The frequency converter<figref>100</figref> shifts only a predetermined fixed frequency, to the OFDM signal in the occupied frequency band of the transmission line to convert into an OFDM signal in an intermediate frequency band (Its center frequency fc).

0009the branching filter <figref>301</figref> in the quadrature detector <figref>300</figref> Splits the OFDM signal, which from the frequency converter <figref>100</figref> is issued in two signals, and outputs each of the by dividing the OFDM signal signals obtained from the detectors <figref>302</figref> and <figref>303</figref>, The carrier recovery apparatus <figref>304</figref> gives an in-phase carrier, which has a center frequency fc has, from the detector and gives an Quadrature carrier, which has a center frequency fc to the detector <figref>303</figref> out. The detector <figref>302</figref> then multiplies the OFDM signal, which from the branching filter <figref>301</figref> is issued with the In-phase carrier, outputting a real part of the OFDM signal. The detector<figref>303</figref> multiplied the OFDM signal outputted from the branching filter <figref>301</figref> output is mixed with the quadrature carrier, an imaginary outputting the OFDM signal. That is, the quadrature detector<figref>300</figref> converted the OFDM signal in the intermediate frequency band into an OFDM signal in a baseband.

0010Of the Fourier transformer <figref>400</figref> subjecting the Collective Real part of the OFDM signal from the detector <figref>302</figref> output is, and the Imaginärrteil of the OFDM signal, which from the detector <figref>303</figref> output is, egg ner Fourier transformation operation to each of a real part and an imaginary modulated part of each of the multiplexed on the frequency axis to separate shafts. The detector<figref>500</figref> forms demodulated data on a complex plane the real part and the imaginary part of each of the digital modulated waves, and demodulates data, which are obtained by modulating each of the carriers of its mapped position in accordance with a within which set threshold value to demodulated data from an output terminal O output.

0011Although the above-mentioned transmitted OFDM signal is from a sender to a receiver via a wired or radio transmission line, is the OFDM signal steamed in two lineages. Of the Amount of attenuation of the OFDM signal varies depending of the change in the distance of the radio transmission line, while it varies, depending for example the number of bifurcations of the cable transmission line. If the Amount of attenuation of the OFDM signal varies, then varies the receiving level of the OFDM signal in the receiver. However results the in <figref idrefs="S48">12</figref> Recipient data demodulation shown from, even when the receiving level of the OFDM signal varies, without any correction the variation. In the detector,<figref>500</figref> be demodulated data therefore the demodulated data frequently erroneously judged.

0012In an FM (Frequency Modulation) receiver or the like is an amplifier with automatic gain control provided in such a manner adapted to the variation in the receiving level to correct, on the basis of the variation in an envelope of a received signal. It was considered that such a Correction process on the in <figref idrefs="S48">12</figref> shown receiver is applied. In the OFDM signal, however, a number of modulated carriers multiplexed on the frequency axis, whereby the patterns of the amplitude and the phase of the OFDM signal randomly changing in each of symbol sections, in contrast to that in an FM signal which a single carrier includes. Therefore, the envelope waveform of the OFDM signal changes frequently on the time axis. When the amplifier with automatic gain control is controlled on the basis of such an envelope waveform, the reinforcement the amplifier unstable with automatic gain control, whereby stable control can not be performed. Further in the OFDM signal to data distinguish which by modulating each of the carriers are obtained from each other, whereby the variation in the envelope waveform and the variation are not always correlated in the reception level. Even if the level correction method in the FM receiver is applied to the receiver of the OFDM signal, therefore, the variation in the receiving level not with high precision Getting corrected.

0013Furthermore is in the in <figref idrefs="S48">12</figref> shown the receiver Amount of frequency shift in the frequency converter <figref>100</figref> fixed. Even when the frequency band is shifted, that is, the frequency band varies, the variation can not be corrected in the frequency band will. Therefore, the demodulated data is frequently erroneously judged.

0014In an AM (Amplitude Modulation) receiver or the like, a frequency converter provided in such a manner adapted to the variation in the frequency band to correct, on the basis of the variation in frequency discrimination a received signal. It was also considered that such a Correction process on the in <figref idrefs="S48">12</figref> shown receiver is applied. In the OFDM signal, however, a number of modulated carriers multiplexed on the frequency axis, whereby the patterns of the amplitude and the phase of the OFDM signal randomly changing in each of symbol sections, in contrast to that in an AM signal, a single carrier includes. Therefore, a waveform change in frequency discrimination of OFDM signal frequently on the frequency axis. When the frequency converter on the basis of such a waveform is controlled in frequency discrimination, is the amount of frequency shift of the frequency converter unstable, whereby stable control can not be performed. Furthermore, in the OFDM signal to data distinguish which by modulating each of the carriers are obtained from each other, whereby the variation in the waveform in frequency discrimination and the variation in the amount of frequency shift are not always correlated. Even if the method of correction applied the amount of the frequency shift in the AM receiver is applied to the receiver of the OFDM signal, therefore, the variation in the frequency band not with high precision Getting corrected.

0015On Another document of the prior art is the publication "Multi Carrier CDMA system with cochannel interference cancellation ", Kondo S; Milstein LB, Vehicular Technology Conference, 1994 IEEE 44th, Stockholm, Sweden, for example, to 10 June 1994 New York, NY, USA, IEEE, pages 1640 until 1644. In this document, the pilot and data simultaneously spread with different code sequences themselves length on different carriers.

0016On Another document of the prior art is the patent <patcit><text>SE500986</text></patcit>Which an OFDM system disclosed wherein a sync frame with data frame mixed is. The carrier, forming the synchronization frame, have random phases.

SUMMARY OF THE INVENTION

0017The Invention is carried out by a signal transmission method, a signal receiving method, a signal transmission device and a Signalempfanpgsvorrichtung as in the appended claims 1 to 8th.

BRIEF DESCRIPTION OF THE DRAWINGS

0018<figref idrefs="S37">1</figref> is a diagram showing an example of the structure of an OFDM signal, which from the transmitting transmit end of the present invention is shows;

0019<figref idrefs="S38">2</figref> is a block diagrams, which in accordance with the configuration of a receiver of a first embodiment of the present invention;

0020<figref idrefs="S39">3</figref> is a waveform diagram showing signals in each of the sections of in <figref idrefs="S38">2</figref> shown recipient shows;

0021<figref idrefs="S40">4</figref> is a diagram, another example of the structure of an OFDM signal which from the transmitting transfer end is shows;

0022<figref idrefs="S41">5</figref> is is a block diagram showing the construction of a receiver according to a second embodiment, of the present invention;

0023<figref idrefs="S42">6</figref> is a waveform diagram showing signals in each of the in <figref idrefs="S41">5</figref> shown Portions of the receiver shows;

0024<figref idrefs="S43">7</figref> is is a block diagram showing the construction of a receiver according to a third embodiment of the present invention;

0025<figref idrefs="S44">8th</figref> is a waveform diagram for explaining one in <figref idrefs="S43">7</figref> shown frequency range energy detector <figref>71</figref>;

0026<figref idrefs="S45">9</figref> is is a block diagram showing the construction of a receiver according to a fourth embodiment of the present invention;

0027<figref idrefs="S46">10</figref> is a waveform diagram showing signals in each section of a in <figref idrefs="S45">9</figref> shown control signal output device <figref>80</figref> shows;

0028<figref idrefs="S47">11</figref> is a diagram showing the structure of a conventional OFDM signal of the transmitting transfer end is shows; and

0029<figref idrefs="S48">12</figref> is is a block diagram showing the construction of a receiver of an OFDM signal, which of the first prior art to the third prior Technology is analogized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0030It are now embodiments of the present invention will be described based on drawings. <figref idrefs="S37">1</figref> is a diagram showing an example of the structure of an OFDM signal which from the transmitting End is transmitted to the receiving end in the present invention, shows. In particular shows<figref>1 (a)</figref> respective symbols an OFDM signal along the time axis, and <figref>1 (b)</figref> shows a portion α, which in <figref>1 (a)</figref> is shown in a enlarged manner.

0031As in <figref>1 (a)</figref> shown is an OFDM signal S constructed by arranging a particular symbol S0 for automatic Gain control, indicated by hatching and symbols Sm (m = 1, 2, ...) for demodulation, said without hatching along the Time axis. The symbol S0 is inserted for each predetermined symbol interval (Eg each interval of 15 symbols). The OFDM signal S takes the form of a superimposed analog complex signal in which a real part and an imaginary part are relative to each of the symbols S0 and Sm on a transmission line.

0032Each the symbols Sm is constructed by multiplexing (performing a inverse fast Fourier operation of) a plurality of (ten to Thousands of, eg, 512) carriers, which differ in frequency (which are orthogonal in symbol time ts) on the frequency axis. Each of the carriers is digital modulation (Eg QPSK modulation or 16QAM) subjected by data are to be demodulated at the receiving end. Therefore, each the symbols Sm a random Amplitude distribution before, as in <figref>1 (b)</figref> shown.

0033Each of the symbols S0 is constructed by performing an inverse fast Fourier operation of, for example a signal in which one of the plurality of carriers (eg fc its frequency) is left as a non-modulated single Audio signal and the other carriers repressed are. Therefore, each of the symbols S0 an amplitude distribution of a particular pattern, such as in <figref>1 (b)</figref> shown. In such a symbol S0 are a time axis component and a Frequency axis component known. The OFDM signal S is transmitted from the transmitting End to the receiving end through a wired or wireless transmission line (Not shown). Therefore, the OFDM signal S on the transmission line steamed. To the damping on the transmission line to compensate for the demodulation of data at the receiving End, therefore, the level of the received OFDM signal S must be corrected will. Such an operation of correcting the receiving level of the OFDM signal S is performed with use of the symbol S0. Of the the reason for this is that the symbol S0 always includes a signal of the same pattern, whereby the change accurately measured in the receiving level of the waveform of the symbol S0 can be.

0034<figref idrefs="S38">2</figref> is is a block diagram showing the construction of a receiver according to a first embodiment of the present invention. In<figref idrefs="S38">2</figref> has recipient an input terminal <figref>1</figref> on to which a received input OFDM signal is a band pass filter <figref>1</figref>, An amplifier <figref>2</figref> With automatic gain control, a quadrature detector <figref>3</figref>, A / D converter <figref>7</figref> and <figref>8th</figref>. a Fourier transformer <figref>4</figref>, A detector <figref>5</figref> demodulated Data, a control signal output device <figref>6</figref> and one Output terminal O. The quadrature detector <figref>3</figref> has a branching filter <figref>31</figref>. detectors <figref>32</figref> and <figref>33</figref> and a carrier recovery device <figref>34</figref> on. The control signal output device <figref>6</figref> includes an envelope detector <figref>61</figref>. one reference timing generator <figref>62</figref>, A symbol timing synchronization circuit <figref>64</figref>. a symbol energy detector <figref>64</figref>, A control signal switching device <figref>65</figref>. a sample and hold device <figref>66</figref> and a low pass filter <figref>67</figref> on.

0035<figref idrefs="S39">3</figref> is a waveform diagram showing signals in the respective sections of in <figref idrefs="S38">2</figref> shown recipient shows. Referring now on <figref idrefs="S39">3</figref> the operations of the in <figref idrefs="S38">2</figref> shown receiver described.

0036the from receiver received OFDM signal (see <figref idrefs="S37">1</figref>) becomes converted from an OFDM signal in an occupied frequency band the transmission line in an OFDM signal in an intermediate frequency band (its center frequency fc) by a frequency converter (not shown), after which the OFDM signal in the Intermediate frequency band is inputted to the band-pass filter <figref>1</figref> by the input terminal <figref>1</figref>, The band-pass filter<figref>1</figref> away a signal component in an unnecessary band from the OFDM signal in the intermediate frequency band, and takes only an OFDM signal in a necessary ribbon. From said band-pass filter<figref>1</figref> output OFDM signal is supplied to the quadrature detector <figref>3</figref> through the amplifier <figref>2</figref> With automatic gain control.

0037the branching filter <figref>31</figref> in the quadrature detector <figref>3</figref> Splits from said amplifier <figref>2</figref> With automatic gain control outputted OFDM signal into two signals, and outputs each of the signals, which by dividing the OFDM signal is obtained at the detectors <figref>32</figref> and <figref>33</figref> out. The carrier recovery apparatus <figref>34</figref> gives an in-phase carrier, which has a center frequency fc to the detector <figref>32</figref> out and outputs a quadrature carrier, which one a center frequency fc has, to the detector <figref>33</figref> out. Of the detector <figref>32</figref> multiplied by said branching filter <figref>31</figref> output OFDM signal with the in-phase carrier to output a real part of the OFDM signal. The detector<figref>33</figref> multiplied the from the branching filter <figref>31</figref> outputted OFDM signal with the quadrature carrier, an imaginary outputting the OFDM signal. That is, the quadrature detector<figref>3</figref> converted the OFDM signal in the intermediate frequency band into an OFDM signal in a baseband. The A / D converter<figref>7</figref> converts the real part of the of the detector <figref>32</figref> outputted OFDM signal from a analog signal to a digital signal. The A / D converter<figref>8th</figref> converted imaginary of the of the detector <figref>33</figref> outputted OFDM signal from a Analog signal into a digital signal.

0038Of the Fourier transformer <figref>4</figref> subjecting the Collective Of the real part of the A / D converter <figref>7</figref> outputted OFDM signal and the imaginary part of from the A / D converter <figref>8th</figref> outputted OFDM signal to Fourier transformation to thereby form a real part and an imaginary part of each of digital modulated waves to be separated on the frequency axis. The Fourier transformer<figref>4</figref> has a clock terminal <figref>4c</figref> and starts setting the timeline a time window for which Fourier transform is used, on the basis of a symbol synchronizing signal which of the symbol timing synchronization circuit <figref>63</figref> output is, and starts Fourier transform of each of the symbols. The detector<figref>5</figref> forms demodulated data the real part and the imaginary part of each of the digital modulated waves on a complex plane from and demodulates data obtained by modulating each of the carriers is, from their position shown according to a threshold, which is set within the same.

0039Of the Operation mode of the control signal output device <figref>6</figref> includes a first mode in which a control signal of the amplifier <figref>2</figref> With automatic gain control is generated on the basis of an envelope waveform of an output signal of the quadrature detector <figref>3</figref> and a second mode in which a control signal of the amplifier <figref>2</figref> With generating automatic gain control is on the basis of the symbol energy of an output signal of the Fourier transformer <figref>4</figref>, The control signal output device <figref>6</figref> is operated in the first mode when the receiving of the OFDM signal is started, while it is operated in the second mode after the operation of the Fourier transformer <figref>4</figref> stabilized (that is, after it is synchronized with a received signal). The operation of the control signal output device <figref>6</figref> becomes in more detail described.

0040Of the envelope detector <figref>61</figref> enveloping-detect each of the detectors of <figref>32</figref> and <figref>33</figref> issued OFDM signals to an envelope signal output, which envelope a represents the signal. The ner of the Einhüllendenerken<figref>61</figref> output Envelope signal is out to the reference timing generator <figref>62</figref>, And is fed to a Control signal input terminal <figref>65a</figref> the control-signal switching device <figref>65</figref> by the low pass filter <figref>67</figref> for smoothing the variation.

0041Of the Reference Timing Generator <figref>62</figref> previously stores single tone, which with a particular pattern of the symbol S0 inside thereof correspond. The reference timing generator<figref>62</figref> finds Correlation between the envelope signal, which of the envelope detector <figref>61</figref> output is, and the stored single tone along the time axis for each Icon to a reference timing signal output, indicating if the symbol S0 is detected or not. Specifically are the reference timing generator<figref>62</figref> on Reference timing signal to a high level (at a voltage Vhigh) from when the symbol S0 is detected, while outputting a reference timing signal outputs to a low level (at a voltage Vlow) when the symbol Sm, which contains no specific pattern is recognized, , as shown in <figref>3 (a)</figref> and <figref>3 (b)</figref>, The reference timing generator<figref>62</figref> gives the timing reference signal to a low level (at a voltage V low) from, even if the symbol is received S0 until his identification operation is stabilized (synchronized) with respect to a received Signal (that is, while an asynchronous period). The timing of the reference generator<figref>62</figref> output reference timing signal is respectively inputted to the symbol timing synchronization circuit <figref>63</figref> and one clock terminal <figref>66c</figref> the sample and hold device <figref>66</figref>,

0042The Symbol timing synchronization circuit <figref>63</figref> is a symbol synchronization signal (please refer <figref>3 (c)</figref>) From which synchronizes is connected to each of the symbol on the basis of the reference timing signal, which of the reference timing generator <figref>62</figref> is supplied. Specifically, the symbol timing synchronization circuit <figref>63</figref> a Clock circuit within the same, and outputs a clock pulse (a Clock pulse, which the symbol time ts used as one period) out, is that synchronizes with the head end of each of the symbols, ie a symbol synchronizing signal from the clock circuit every time when the leading Edge of the reference timing signal is detected. The symbol synchronizing signal is respectively input to the clock terminal <figref>4c</figref> of the Fourier transformer <figref>4</figref> and a clock terminal <figref>64c</figref> the symbol energy detector <figref>64</figref>,

0043Furthermore are the symbol timing Synchronisierungsschaltung <figref>63</figref> on engaged / not-engaged signal (see <figref>3 (d)</figref>) on the basis of the reference timing signal, which of the reference timing generator <figref>62</figref> is supplied, out. The engaged / not-engaged signal takes its unlatched State to a low level, whereas it its latched State to a high level assumes. At the beginning of the start of receiving is the engaged / not-locked signal in the unlatched State. The symbol timing synchronizing circuit<figref>63</figref> includes a counter for counting the clock pulses, within the same and resets the counter every time when leading the recognizes edge of the reference timing signal. The symbol timing synchronizing circuit<figref>63</figref> rated, that the adjustment of the time window in the Fourier transformer <figref>4</figref> completed is a state where the internal counter is reset at the time, where he counted a predetermined Value (a symbol interval at which the symbol S0 is inserted, 15 is achieved in this case) is repeated a predetermined Number of times (that is, when the symbol S0 a predetermined Number entered stable of times) to the Detent / non-latched Signal from the non-locked state to the locked switch state. The Detent / non-locked signal in a clock terminal<figref>65c</figref> the Control signal switching device <figref>65</figref> entered.

0044Of the Symbol energy detector <figref>64</figref> includes within it a Digital-to-analog (D / A) converter (Not shown). The symbol energy detector<figref>64</figref> squares and integrated (integrated the square of) a signal component of each of the carrier on the axis in sequence each of the symbols, which from the Fourier transformer <figref>4</figref> output is in the symbol period ts by a digital operation in synchronization with the symbol synchronizing signal outputted from the symbol timing synchronizing circuit <figref>63</figref> is supplied, in order to find the energy of the symbol once it as a digital value present. The found digital energy value by the D / A converter converted into an analog value to output an analog symbol energy signal, which represents the energy of the symbol. This energy is directly proportional to the average level of each of the symbols. The Signal component of each carrier is squared, as the amplitude of the carrier on the positive and negative Sides along the time axis varies, the absolute value thereof to find. In addition, the signal component of each of the supports integrated to the mean value the same finding. The symbol of the power detector<figref>64</figref> output symbol energy signal is at a control signal input terminal <figref>65b</figref> the control-signal switching device entered.

0045The Control signal switching device <figref>65</figref> selects from the envelope detector <figref>61</figref> output Envelope signal, when the Detent / non-locked-signal to the clock terminal <figref>65c</figref> entered is, is in the locked state, while the symbol of the power detector <figref>64</figref> output Symbol energy signal selects, if it is in the non-locked state, and outputs the selected signal as a control signal of the control amplifier with automatic gain <figref>2</figref> out.

0046The Sample and hold device <figref>66</figref> samples and holds the of the control-signal switching device <figref>65</figref> selected control signal, when the reference timing signal to a voltage V high of the reference timing generator <figref>62</figref> to the clock terminal <figref>66c</figref> is inputted, that is, when the special Symbol S0 from the control amplifier automatic gain <figref>2</figref> output is. Launched by the sample and hold device<figref>66</figref> held control signal is a control terminal of <figref>2c</figref> the control amplifier automatic gain <figref>2</figref> supplied. The reinforcement A of the control amplifier automatic gain <figref>2</figref> varies depending on the voltage level of the control signal generated by the sample and hold device <figref>66</figref> is supplied.

0047If the receiving level of the OFDM signal is increased, the level of is Envelope signal or the symbol energy signal of the symbol S0 in proportion to the increased Receiving level increases, whereby the voltage level of the control signal to the control amplifier automatic gain <figref>2</figref> is supplied, elevated is. At this time, lowers the control amplifier with automatic gain<figref>2</figref> the reinforcement A, so as to reduce the level of the received OFDM signal. On the other hand, when the receiving level of the OFDM signal is lowered, the level of the envelope signal or the symbol energy signal is the symbol S0 in proportion to the lowered reception level lowered, whereby the voltage level of the control signal, which corresponds to the control amplifier <figref>2</figref> With automatic gain supplied lowered will: increase at this time The control amplifier automatic gain <figref>2</figref> the A gain, so as to increase the level of the received OFDM signal. As a result, the control amplifier with automatic gain <figref>2</figref> the Variation in the receiving level of the OFDM signal to a suitable correct level.

0048the Symbol energy signal is the energy of each of the symbols S0 and is by a digital operation found, where the symbol energy signal few Error contains. On the other hand, the envelope signal is an envelope, which compounds according to the peak values ​​of the waveform of each of the symbols S0det, wherein the envelope signal the difference between the waveform and the envelope the symbol S0 includes as an error. In addition, the required Envelope signal Filter processing (performed by the low pass filter <figref>67</figref>), As it as a control signal the control amplifier automatic gain <figref>2</figref> used is where an error occurs in the filtering processing. Therefore, the control precision the control amplifier automatic gain <figref>2</figref> in a case where the symbol energy signal is used, better be improved than in a case where the envelope signal is used.

0049Of the Fourier transformer <figref>4</figref> starts the adjustment of the time axis with those for the Fourier transform time window used when the symbol synchronizing signal of the symbol timing synchronization circuit <figref>63</figref> is output. However, it takes a long time to adjust the time axis of the time window. When the receiving of the OFDM signal is started, therefore, a State where the time window and the received symbol is not are synchronized (that is, a state in which d as a time window is plurality of symbols which adjoin each set) occur. the normal operation of the Fourier transformer are in such a state and the symbol energy detector <figref>64</figref> not ensured.

0050Therefore , the control signal output device <figref>6</figref> the gain of the control amplifier automatic gain <figref>2</figref> in the first operation mode, that is, the based on the envelope signal Symbol S0 for some time after the start of the reception of the OFDM signal (until the adjustment of the time axis of the time window of the Fourier transformer <figref>4</figref> completely is completed). Thereafter, the control signal output device controls<figref>6</figref> the reinforcement the control amplifier automatic gain in the second operating mode, that is, the on the basis of the symbol energy signal Symbol S0.

0051As described above, according to the in <figref idrefs="S38">2</figref> shown embodiment, is the particular symbol S0 periodically by the reference timing generator <figref>62</figref> recognized and the envelope signal or the symbol energy signal of the symbol S0 is represented by the sample and retaining means <figref>66</figref> sampled and held, and is to the control terminal of <figref>2c</figref> the control amplifier automatic gain <figref>2</figref> recycled, whereby the precision the gain control the amplifier automatic gain control <figref>2</figref> improved can be. additionally is the damping the transmission line compensated for by the gain control, that is, the receiving level is corrected, whereby demodulated data can be prevented from, to be mispriced.

0052Although in the above embodiment the symbol S0 is inserted at intervals of 15 symbols, the symbol can be added to other S0 symbol intervals. Furthermore, although in the above-mentioned embodiment the symbol S0 is constructed by using only one carrier as a a non-modulated single tone signal and suppression of other carriers, the symbol can be constructed by other methods, provided that it is a signal whose time axis component and frequency axis component are known and whose amplitude and phase along the time axis be changed in predetermined particular pattern. For example, the amplitude of a carrier be modulated by a variety of known data (for example, data of "1" and data of "2"). In this case, contact small irregularities in the envelope of the of the envelope detector <figref>61</figref> output envelope signal. Since the irregularities However, through the low pass filter <figref>67</figref> are smoothed, the envelope signal be used as a control signal.

0053Furthermore, although mentioned in the above embodiment the bebene out from the quadrature detector OFDM signal in the base band to the envelope detector <figref>61</figref> entered is, an output of each of the amplifiers with automatic gain control <figref>2</figref> and the subsequent sections, that is, the amplifier with automatic gain control <figref>2</figref>. the A / D converter <figref>7</figref> and <figref>8th</figref> and the Fourier transformer <figref>4</figref>. the envelope detector <figref>61</figref> entered will.

0054Although in the above embodiment the output of the Fourier transformer <figref>4</figref> the Symbol energy detector <figref>64</figref> is input, an output each of the amplifiers automatic gain <figref>2</figref> and the following sections, ie the amplifier with automatic gain control <figref>2</figref>. of the quadrature detector <figref>3</figref> and the A / D converter <figref>7</figref> and <figref>8th</figref>. the symbol energy detector <figref>64</figref> be entered.

0055Although in the above embodiment the A / D converter <figref>7</figref> and <figref>8th</figref> are provided, these can be removed in order to perform Fourier transform and symbol energy detection when the OFDM signal is analog.

0056Furthermore, although in the embodiment above the control signal output device <figref>6</figref> so is adapted to be operated in two modes of operation, can they be designed even so, only in the first mode of operation to will. In this case, comprises the control signal output device only the envelope detector <figref>61</figref>. the reference timing generator <figref>62</figref> and the sample and hold device <figref>66</figref>,

0057In addition, the control signal output device <figref>6</figref> be such to be operated in the second operation mode. In this Case includes the control signal output device only the envelope detector <figref>61</figref>. the reference timing generator <figref>62</figref>, The symbol timing synchronization circuit <figref>63</figref>. the symbol energy detector <figref>64</figref> and the sample and hold device <figref>66</figref>,

0058<figref idrefs="S40">4</figref> is a diagram showing another example of the structure of the the transmitting end transmitted to the receiving end of the OFDM signal of the present invention. In particular shows<figref>4 (a)</figref> respective symbols of the OFDM signal along the time axis, and <figref>4 (b)</figref> shows one in <figref>4 (a)</figref> shown part α in a enlarged manner.

0059As in <figref>4 (a)</figref> shown is an OFDM signal S formed by arranging a particular symbol S0 for controlling the frequency conversion, indicated by hatching, and symbols Sm (M = 1, 2, ...) for demodulation in without hatching along the time axis. The symbol S0 is for each predetermined symbol interval Embed (Eg at intervals of 15 symbols). The OFDM signal S takes the Form a complex signal at, in wel chem a real part and an superimposed imaginary are relative to each of the symbols S0 and Sm on the transmission line.

0060Each the symbols Sm is created by multiplexing (performing a inverse fast Fourier operation of) a plurality of (ten to Thousands of, eg, 512) carriers, which differ in frequency (which in symbol time are orthogonal ts) on the frequency axis. Each of the carriers is digital modulation (eg, QPSK modulation or 16QAM) by data subject which are to be demodulated at the receiving end. Therefore, each of the symbols Sm a random amplitude distribution on, as shown in <figref>4 (b)</figref> shown.

0061Each of the symbols S0 is created by performing an inverse fast Fourier operation a signal, in which one of the plurality of carriers (its fc frequency, for example) is left as a pseudo random signal by Amplitude modulation are suppressed using a binary (for example, "1" and "2") pseudo random code and the other carriers. Therefore, each of the symbols S0, an amplitude distribution of a special pattern on, as shown in <figref>4 (b)</figref> shown. In such a symbol S0 both a time axis component are as also known a frequency axis component.

0062The Data speed of the pseudo random code is preferably used as selected integral multiples of the OFDM symbol rate. As a result of this is a integer number of pseudo random code information in a symbol S0 contain, whereby synchronization at the receiving end just is achieved. Further, the repetition period of the pattern is the pseudo-random codes are preferably identical to the symbol period selected. In this case, the number of times of occurrence of a code (Eg "1") and the number of times of occurrence of the other code (eg "2") are identical, whereby the correlation is easily accomplished at the receiving end.

0063the OFDM-signal S, in which <figref idrefs="S40">4</figref> is shown, over days ends of the End to the receiving end through a wired or wireless transmission line (Not shown) is sent. Therefore, (not shown) at the transmitting end the OFDM signal S into an OFDM signal in an occupied frequency band (With center frequency fr) of the transmission line of an OFDM signal in an intermediate frequency band (its center frequency fc) converted. On the other hand, at the receiving end, the received S-OFDM signal of an OFDM signal in the occupied frequency band the transmission line converted into an OFDM signal in an intermediate frequency band to Demodulierungsarbeit (with Center frequency fc) in demodulated data. In a below Described embodiment is an operation of frequency-converting the OFDM signal S from the occupied Frequency band in the intermediate frequency band carried out under Use of the symbol S0. The reason for this is that the symbol S0 always a signal of the same pattern includes, whereby the conversion accurately measured in the frequency band of the waveform of the symbol S0 can be.

0064<figref idrefs="S41">5</figref> is is a block diagram showing the construction of a receiver according to a second embodiment, of the present invention. In<figref idrefs="S41">5</figref> includes recipient an input terminal I to which a receiving OFDM signal inputted is a frequency converter <figref>10</figref>, A quadrature detector <figref>3</figref>. a Fourier transformer <figref>4</figref>, A detector for demodulated data <figref>5</figref>, A control signal output device <figref>60</figref> and an output terminal O. The quadrature detector <figref>3</figref> includes a branching filter <figref>31</figref>, detectors <figref>32</figref> and <figref>33</figref> and a Carrier recovery device <figref>34</figref>, The control signal output device <figref>60</figref> includes an envelope detector <figref>61</figref>. one reference timing generator <figref>62</figref>, A symbol timing synchronization circuit <figref>63</figref>. a sample and hold device <figref>66</figref> and a frequency discriminator <figref>68</figref>, To illustrate the correspondences are the same sections such as those in the embodiment in the <figref idrefs="S38">2</figref> is shown, the same reference numerals in the embodiment, what a <figref idrefs="S41">5</figref> is shown associated.

0065<figref idrefs="S42">6</figref> is a waveform diagram showing signals in the respective sections of in <figref idrefs="S41">5</figref>shown recipient shows. Referring now on <figref idrefs="S42">6</figref> the operations of the in <figref idrefs="S41">5</figref> shown receiver to be discribed.

0066On OFDM signal (see <figref>6 (a)</figref>) Occupied in a Frequency band (its center frequency fr) of a transmission line, which of received the receiver is input to the input terminal I, and is in a OFDM signal in an intermediate frequency band (its center frequency fc) by the frequency converter <figref>10</figref> converted, after which the OFDM signal in the intermediate frequency band to the quadrature detector <figref>3</figref> entered is.

0067the branching filter <figref>31</figref> in the quadrature detector <figref>3</figref> Splits that of the frequency converter <figref>10</figref> outputted OFDM signal in two signals, and outputs each of the signals, which are obtained by dividing the OFDM signal to the detectors <figref>32</figref> and <figref>33</figref>, The Carrier recovery device <figref>34</figref> gives an in-phase carrier from, which has a center frequency fc to the detector <figref>32</figref>. and outputs a quadrature carrier, which has a center frequency fc to the detector <figref>33</figref> out. The detector <figref>32</figref> multiplied by said branching filter <figref>31</figref> output OFDM signal with the in-phase carrier, outputting a real part of the OFDM signal. The detector<figref>33</figref> multiplied the from the branching filter <figref>31</figref> outputted OFDM signal with the quadrature carrier, an imaginary outputting the OFDM signal. That is, the quadrature detector<figref>3</figref> converted the OFDM signal in the intermediate frequency band into an OFDM signal in a baseband.

0068Of the Fourier transformer <figref>4</figref> subjecting the by the detector <figref>32</figref> issued Real part of the OFDM signal and that of the detector <figref>33</figref> issued imaginary of the OFDM signal in common to a Fourier transform operation, to thereby form a real part and an imaginary part of each of digital modulated Waves to be separated on the frequency axis. The detector demodulated data <figref>5</figref> forms the real part and the imaginary part of each the digital modulated waves on a complex plane from and demodulated data, which are obtained by modulating each the carrier from its position shown according to one within the same set threshold.

0069The Operation of the control signal output device <figref>60</figref> is in more detail to be discribed. The envelope detector<figref>61</figref> enveloping-detect each of the symbols of the OFDM signal from the frequency converter <figref>10</figref> is output, an envelope signal output, which envelope a the symbol represents. the Envelope signal, which of the envelope detector <figref>61</figref> output is, is the reference generator Timing <figref>62</figref> supplied.

0070Of the Reference Timing Generator <figref>62</figref> previously stores binary pseudo random data, which correspond to a particular pattern of a symbol S0, within thereof. The reference timing generator<figref>62</figref> takes for each the symbols, the correlation between the envelope signal outputted from the envelope detector <figref>61</figref> output is, and the stored binary Pseudo-random data along the time axis to be a reference timing signal output which indicates whether the symbol is detected or not S0. Specifically are the reference timing generator <figref>62</figref> a reference timing signal to a high level (at a voltage V1) when the symbol S0, containing a particular pattern is detected, while a reference timing signal to a low level (at a voltage V2) when a symbol Sm which no particular pattern contains, is detected, as in <figref>6 (a)</figref> and <figref>6 (b)</figref> shown. The timing of the reference generator<figref>62</figref> output Reference timing signal to a clock terminal <figref>66c</figref> the Sample and hold device <figref>66</figref> and the symbol timing synchronization circuit <figref>63</figref> entered.

0071The Symbol timing synchronization circuit <figref>63</figref> is a symbol synchronization signal of which is synchronized with each of the symbols on the basis of of the reference timing signal from the reference timing generator <figref>62</figref> is supplied. Specifically includes the symbol timing synchronization circuit <figref>63</figref> a Clock circuit within the same and outputs a clock pulse (a clock pulse, which the symbol time ts used as a period) from which is synchronized with the head of each of the characters, ie, a Symbol synchronizing signal from the clock circuit every time the leading edge the reference timing signal is recognized. The symbol synchronizing signal is in a clock terminal<figref>4c</figref> of Fourier transformer <figref>4</figref> entered.

0072Of the Fourier transformer <figref>4</figref> subjecting the by the detector <figref>32</figref> issued Real part of the digital OFDM signal from the detector and <figref>33</figref> issued imaginary of the digital OFDM signal in common to a Fourier transform operation to characterized the real part and the imaginary part of each of digital modulated Waves to be separated on the frequency axis. The Fourier transformer<figref>4</figref> Has the clock terminal <figref>4c</figref> and starts to adapt to the Time axis of a time window, which for the Fourier transform is used, based on the symbol synchronization signal, which of the symbol timing synchronization circuit <figref>63</figref> output is, and starts the Fourier transform each of the symbols. The detector demodulated data<figref>5</figref> forms the real part and the imaginary part of each the digital modulated waves on a complex plane from and demodulated data which is obtained by modulating each the carrier from its mapped position in accordance with one within the same stored threshold.

0073Of the frequency discriminator <figref>68</figref> frequency-discriminates each of Symbols to generate a voltage which is the frequency of the symbol equivalent. The sample and holding device <figref>66</figref> samples and holds a frequency discriminating signal, which from the frequency discriminator <figref>68</figref> is output, when the reference timing signal to a voltage V1 from the reference timing generator <figref>62</figref> to the clock terminal <figref>66c</figref> is inputted, that is, when the special Symbol S0 from the frequency converter <figref>10</figref> is output. the in the sample and hold device <figref>66</figref> held frequency discrimination signal is used as a control signal to a control terminal of <figref>10c</figref> of frequency converter <figref>10</figref> entered. The amount of frequency shift of the frequency converter <figref>10</figref> varies depending on the voltage level the control signal generated by the sample and hold device <figref>66</figref> is supplied.

0074If the frequency band of from the frequency converter <figref>10</figref> issued OFDM signal is increased, is also level of the frequency discrimination of the signal from the frequency discriminator <figref>68</figref> output symbol S0 increases in proportion to the increased Frequency band, whereby the voltage level of the frequency converter to the <figref>10</figref> control signal applied elevated is. At this time increased of the frequency converter <figref>10</figref> the amount of frequency shift, so as to decrease the frequency band of the outputted OFDM signal. On the other hand, when the frequency of the OFDM signal is decreased, is also the level of the frequency discrimination signal of the symbol S0 decreased in proportion to the decreased frequency, whereby the Voltage level of the frequency converter <figref>10</figref> control signal applied is lowered. At this time, lowers the frequency converter<figref>10</figref> the Amount of frequency shift so as the frequency band of the output OFDM signal to increase. As a result, the frequency converter <figref>10</figref> the variation in the frequency band of the OFDM signal to a suitable intermediate frequency band correct (with center frequency fc).

0075As described above, according to the in <figref idrefs="S41">5</figref> shown second embodiment, the particular symbol S0 is periodically detected by the reference timing generator <figref>62</figref>. and the frequency discrimination signal of the symbol S0 is sampled and held as a control signal, and the control signal is the control terminal <figref>10c</figref> of the frequency converter <figref>10</figref> recycled, whereby the precision the control of the amount of the frequency shift of the frequency converter <figref>10</figref> improved can be. additionally the variation in the frequency band is corrected by the control of the Amount of the frequency shift. Accordingly, there is no Shift from the intermediate frequency band, whereby demodulated protected data before are to be mispriced.

0076<figref idrefs="S43">7</figref> is is a block diagram showing the construction of a receiver according to a third embodiment of the present invention. Sections, which sections the where in <figref idrefs="S41">5</figref> receiver shown correspond, are assigned the same reference numerals and therefore the description is thereof is not repeated. It should in the third embodiment be noted that a frequency range power detector <figref>71</figref> instead of in <figref idrefs="S41">5</figref> shown frequency discriminator <figref>68</figref> used is to a control signal output device <figref>70</figref> to form.

0077<figref idrefs="S44">8th</figref> is a waveform diagram for explaining the operation of the frequency range power detector <figref>71</figref>, which one in <figref idrefs="S43">7</figref> is shown. In particular shows<figref>8 (a)</figref> the Power spectrum of a symbol S0 along the frequency axis, <figref>8 (b)</figref> shows an integrated value of the in <figref>8 (a)</figref> shown power spectrum and <figref>8 (c)</figref> a frequency domain signal energy. Regarding <figref idrefs="S44">8th</figref> the operations of in <figref idrefs="S43">7</figref> shown receiver are described.

0078Of the Frequency range power detector <figref>71</figref> performs a sequence of operations, as described below, for each symbol in synchronization with a symbol synchronizing signal by that of a symbol timing synchronization circuit <figref>63</figref> to a clock terminal <figref>71c</figref> is supplied. First, notify the Frequency range power detector <figref>71</figref> Carrier (which with a binary pseudo-random signal are amplitude modulated), which in a frequency range of 0 to fs in an output of a Fourier transformer <figref>4</figref> distributed are, in two areas α1 and α2, wherein (1/2) fs is used as its border, as in <figref>8 (a)</figref> shown, where fs is the frequency of a in the Fourier transformer <figref>4</figref> sampling used is. Further, the spectrum of each of the symbols is folded, wherein (1/2) fs is used as a boundary, whereby a high frequency component and low-frequency component in each case in the region α1 whose Frequency is α2 than (1/2) fs and the region of low whose Frequency is higher as (1/2) fs, appear.

0079Of the Frequency range power detector <figref>71</figref> squared and integrated then each have a power spectrum component in the region α1 and a power spectrum component in the region α2 to Energy E1 in the region α1 and energy E2 in the region α2 to find, as in <figref>8 (b)</figref> shown. The Energy E1 and the energy E2 are proportional to the average Level of each of the symbols. The power spectrum component is squared, since the amplitude of each of the carrier on the posititive and negative sides along the time axis is varied, the absolute value to find the same. In addition, the power spectrum component is integrated to the average value thereof in each of the symbols to find.

0080Of the Frequency range power detector <figref>71</figref> then compares the Energy E1 in the region α1 and the energy E2 in the region α2, to generate a frequency region energy signal which is a has voltage value corresponding to the difference of energy - corresponding to (E1 E2) as in <figref>8 (c)</figref> shown. The frequency range signal power takes a positive voltage value VHIGH to when the energy E1 in the region α1 is greater while it takes a negative value V LOW when the power is greater in the region α2. are In the symbol S0, when there is no shift in the frequency band, Power distribution in the areas .alpha..sub.a and α2 identical to each other, thereby the voltage value of the frequency domain signal energy is zero. Consequently, the shift direction and amount of displacement are from the center frequency fc on the basis of the polarity and Voltage value of the frequency range energy signal of the symbol S0 found.

0081A Sample and hold device <figref>66</figref> samples and holds the frequency range energy signal, which of the frequency range power detector <figref>71</figref> output , when a reference timing signal at a voltage V1 of a Reference Timing Generator <figref>62</figref> a clock terminal <figref>66c</figref> is inputted, ie, when the special symbol <figref>50</figref> by a frequency converter <figref>10</figref> output is. The in the sample and hold device<figref>66</figref> held Frequency range power signal as a control signal to a control terminal <figref>10c</figref> of the frequency converter <figref>10</figref> supplied. Of the Amount of frequency shift of the frequency converter <figref>10</figref> varies dependent of the voltage level of the sample and hold device <figref>66</figref> supplied control signal.

0082If the frequency band of from the frequency converter <figref>10</figref> issued OFDM signal is increased, the voltage value V HIGH of from the frequency domain energy detector <figref>71</figref> issued Frequency energy signal of the symbol S0 in the positive direction elevated, whereby the voltage of the frequency converter <figref>10</figref> control signal applied is also increased in the positive direction. At this time increases the frequency converter<figref>10</figref> the Amount of frequency shift so as the frequency band of the output OFDM signal to degrade. On the other hand, when the frequency band of the OFDM signal is lowered, the voltage value V LOW the frequency range energy signal of the symbol S0 is increased in the negative direction, whereby the voltage of the the frequency converter <figref>10</figref> control signal applied also in increases the negative direction is. At this time, lowers the frequency converter<figref>10</figref> the Amount of frequency shift to the frequency of the outputted OFDM signal to increase. As a result, the frequency converter <figref>10</figref> the variation in the frequency band of the OFDM signal in a suitable intermediate frequency band correct (with center frequency fc). Launched by the sample and hold device<figref>66</figref> sampled and held control signal may have a Plurality of periods of the symbol S0 are averaged.

0083As described in the foregoing, according to the in <figref idrefs="S43">7</figref> shown third embodiment, the particular symbol S0 is periodically detected by the reference timing generator <figref>62</figref>. and the frequency range energy signal of the symbol S0 is sampled and held as a control signal and is supplied to the control terminal of <figref>10c</figref> of frequency converter <figref>10</figref> recycled, whereby the precision the control of the amount of the frequency shift of the frequency converter <figref>10</figref> improved ver can be. additionally the variation in the frequency band is corrected by the controller the amount of the frequency shift. Accordingly, there is no Shift from the intermediate frequency band, whereby demodulated Data can be prevented from, erroneously judged to be.

0084<figref idrefs="S45">9</figref> is is a block diagram showing the construction of a receiver according to a fourth embodiment of the present invention. Sections, which sections the where in <figref idrefs="S41">5</figref> receiver shown correspond, are assigned the same reference numerals and therefore the description is thereof is not repeated. It should in the present embodiment, be noted that a correlation detector <figref>81</figref> and a peak frequency detector <figref>82</figref> instead of in <figref idrefs="S41">5</figref> shown frequency discriminator <figref>68</figref> are used to a control signal output device <figref>80</figref> to form.

0085<figref idrefs="S46">10</figref> is a waveform diagram showing signals in each section of the in <figref idrefs="S45">9</figref> shown control signal output device <figref>80</figref> shows. Especially shows <figref>10 (a)</figref> a correlation signal along the frequency axis, <figref>10 (b)</figref> on Peak frequency signal. Referring now to<figref idrefs="S46">10</figref> will the operations in <figref idrefs="S45">9</figref> described shown recipient will.

0086Of the correlation detector <figref>81</figref> prestores information of a ideal frequency component with respect to a particular symbol S0 as reference information. The correlation detector<figref>81</figref> finds Correlation between the reference information and data on the frequency axis, which from a Fourier transformer <figref>4</figref> are issued, a Correlation signal output, as in <figref>10 (a)</figref> shown. Although a correlation detection operation in the correlation detector <figref>81</figref> for each Symbol in synchronization with a symbol synchronizing signal, that of a symbol timing synchronization circuit <figref>63</figref> to a clock terminal <figref>81c</figref> is fed, is carried out, it has significance especially when the particular symbol S0 of the Fourier transformer <figref>4</figref> is output. Therefore, a Case will be described in which the particular symbol S0 of the Fourier transformer <figref>4</figref> is output. In this case stores the correlation detector <figref>81</figref> Information with respect to the symbol S0 as to be recognized information in an internal Memory (not shown). Both the reference information previously in the correlation detector <figref>81</figref> has been stored, and stored in the internal memory to be detected information are digital pseudo-random signals distributed in a Manner on the frequency axis exist. The correlation detector<figref>81</figref> overlapped the information to be detected and the reference information on the Frequency axis, multiplying in the information contained Code information and finds the sum of the information. To this Time finds the correlation detector <figref>81</figref> the sum of the results of Multiplication between the information to be recognized and the reference information, while he position of the information to be detected on the frequency axis for each shifts Code. The amount of the sums is a correlation signal. The correlation signal has a peak when respective correspondences between code information stored in the information to be recognized are included, and code information stored in the reference information is included, match with each other on the frequency axis.

0087In a case where the symbol S0 from the Fourier transformer <figref>4</figref> output , when the shift in frequency .DELTA.f for example, "0", is the correlation detector <figref>81</figref> a correlation signal from which a peak in the position of the center frequency fc has, as indicated by β1, as in <figref>10 (a)</figref> shown. Next, in a Case where the symbol S0 is outputted, when the shift in frequency .DELTA.f for example, on the side of higher Frequency occurs, the correlation detector <figref>81</figref> a correlation signal from, shifted its peak and on the side of higher frequency is generated on the frequency axis, as indicated by β2 shown in <figref>10 (a)</figref> shown. Consequently, the Shift direction and the magnitude of the displacement direction of the Frequency are detected from the correlation signal.

0088Of the Peak frequency detector <figref>82</figref> compares the place where the peak value of the correlation of detector <figref>81</figref> generated Correlation signal exists, and the center frequency fc, to a outputting peak frequency signal (see <figref>10 (b)</figref>) which a voltage value .DELTA.V has, with the difference .DELTA.f corresponds.

0089A Sample and hold device <figref>66</figref> samples and holds the peak value frequency signal, which from the peak value frequency detector <figref>82</figref> output , when a reference timing signal to a voltage V1 of a Reference Timing Generator <figref>62</figref> a clock terminal <figref>66c</figref> entered is, that is, when the particular symbol S0 by a frequency converter <figref>10</figref> output is. The peak frequency signal and in the sample holding device <figref>66</figref> is held as a control signal is to a control terminal of <figref>10c</figref> of the frequency converter <figref>10</figref> supplied. Of the Amount of frequency shift of the frequency converter <figref>10</figref> varies dependent from the voltage level of the control signal generated by the sample and hold device <figref>66</figref> is supplied.

0090If the frequency band of from the frequency converter <figref>10</figref> issued OFDM signal is increased, is also the level .DELTA.V the peak-frequency signal of the symbol S0, which of the Peak-frequency detector <figref>82</figref> is output in the positive Direction increases, whereby the voltage level of the control signal, which frequency converter the <figref>10</figref> is supplied, elevated is. At this time increased of the frequency converter <figref>10</figref> the amount of frequency shift, so as to decrease the frequency band of the outputted OFDM signal. On the other hand, when the frequency of the OFDM signal is decreased, the level .DELTA.V the peak-frequency signal of the symbol S0 in negative direction elevated, whereby the voltage level of the frequency converter <figref>10</figref> supplied control signal is increased in negative direction. At this time, lowers the frequency converter<figref>10</figref> the Amount of frequency shift so as the frequency band of the output OFDM signal to increase. As a result, the frequency converter <figref>10</figref> the variation in the frequency band of the OFDM signal in a suitable center frequency band correct (with center frequency fc).

0091As described in the foregoing, according to the in <figref idrefs="S45">9</figref> shown fourth embodiment, is the particular symbol S0 periodically by the reference timing generator <figref>62</figref> recognized and the peak-frequency signal of the symbol S0 is sampled and held as a control signal and is supplied to the control terminal of <figref>10c</figref> of frequency converter <figref>10</figref> recycled, whereby the precision the control of the amount of the frequency shift of the frequency converter <figref>10</figref> improved can be. additionally is the variation in the frequency band by controlling the amount the frequency shift corrected. Accordingly, there is no Shift from a Zwischenfrequency band, whereby demodulated Data will be preserved from being mispriced.

0092Although in the above-mentioned second to fourth embodiments the symbol S0 is inserted at intervals of 15 symbols, it can be pasted to other intervals of symbols. Continue , although mentioned in the above second to fourth embodiments each of the symbols S0 is formed by amplitude modulation only a carrier by a binary Pseudorandom code and suppressing the other carrier, the symbol S0 formed by another method, provided that it is a signal known whose time axis component and frequency axis component and whose amplitude and phase along the time axis in predetermined special pattern changed will. For example, the symbol S0 may be formed by a Signal in which only one carrier is used as a non-modulated single tone signal and the other carriers repressed (see <figref idrefs="S37">1</figref>).

0093Although in the above-mentioned second to fourth embodiments the OFDM signal in the intermediate frequency band by the frequency converter <figref>10</figref> output is the envelope detector <figref>61</figref> (continue the frequency discriminator <figref>68</figref> in the second embodiment) is input, the output of each of the frequency converter <figref>10</figref> and the subsequent sections, that is, the frequency converter <figref>10</figref>. The quadrature detector <figref>3</figref> and the Fourier transformer <figref>4</figref>. the envelope detector <figref>61</figref> (and the frequency discriminator <figref>68</figref>) Are entered.

0094Furthermore, although in the third and fourth embodiments, the output of the Fourier transformer <figref>4</figref> respectively the frequency range power detector <figref>71</figref> and the correlation detector <figref>81</figref> is input, an Issue either of the frequency converter <figref>10</figref> or the following Section, ie, the frequency converter <figref>10</figref> and the quadrature detector <figref>3</figref>. in the frequency range power detector <figref>71</figref> and correlation detector <figref>81</figref> entered will.

0095In addition, Although the first embodiment is formed so that it corrects the variation in the reception level, and the second to fourth embodiments are formed so that they correct the variation in the frequency band, such a receiving circuit which, both the variation in the receiving level and the variation in the frequency band is corrected, are formed by combining one of the second to fourth embodiments with the first embodiment.

0096Although the present invention described and illustrated in detail was, it is clearly understood that this is the only way the Illustration and exemplification and is not construed as a limitation may be because of the scope of the present invention solely by the Provisions of the appended claims limited is.