JPH1198103A - Orthogonal frequency division multiplex signal generator, frequency controller and its method, receiver and communication equipment and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the frequency controller that produces an automatic frequency control AFC signal used to trace a frequency deviation of an orthogonal frequency division multiplex OFDM signal. SOLUTION: Cross point of two high and low envelopes of an energy distribution of metrics obtained by applying discrete Fourier transform to an OFDM signal by a discrete Fourier transform section 1200 is estimated through calculation by an arithmetic processing section 1322, and a difference from a theoretical frequency center and a control signal generating section 1350 generates an automatic frequency control AFC signal in response to the frequency difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal frequency division multiplex signal generating apparatus for generating an orthogonal frequency division multiplex signal including information for frequency synchronization, and an apparatus for frequency synchronizing with the orthogonal frequency division multiplex signal. The present invention relates to a frequency control device and method, a receiving device, a communication device and a method, and in particular, an orthogonal frequency division multiplex signal generating device suitable for frequency synchronization with respect to a shift of half or more of a subcarrier frequency interval, The present invention relates to a control device and method, a receiving device, a communication device and a method.

[0002]

2. Description of the Related Art Orthogonal Frequency Division Multiplexing is a modulation method for digital communication.
iplexing; OFDM. Hereinafter, it is called OFDM. ) The system is being put to practical use.

[0003] As a method to which OFDM is applied, for example, there is EUREKA-147 SYSTEM. This is generally DAB (Digital Audio Broadcas
ting), Eureka 147 DAB system and the like. Hereinafter, it is referred to as an Eureka 147 DAB system. The Eureka 147 DAB system was launched in November 1994
It has been recognized as System-A by the TU-R and has become an international standard. This standard is issued as "ETS 300401".

[0004] In the OFDM system, data is transmitted after being divided and multiplexed into a plurality of subcarriers orthogonal to each other. The frequency of each subcarrier is selected to be an integral multiple of a certain fundamental frequency in the baseband. Assuming that one cycle of the fundamental frequency is an effective symbol period, the product of different subcarriers has zero integration in the effective symbol period. This is called that the subcarriers are orthogonal to each other.

In the OFDM system, when a frequency difference occurs between the transmitting side and the receiving side, orthogonality between subcarriers is destroyed during demodulation. This causes interference between the subcarriers and causes errors in the demodulated data. Causes of the frequency difference include, for example, errors and fluctuations in the oscillation frequency of the reference oscillator on each of the transmitting side and the receiving side, and Doppler shift due to relative motion between the transmitting side and the receiving side. More specifically, for example, a frequency error due to lack of manufacturing accuracy of the oscillator, accuracy of assembly adjustment, etc., a frequency change caused by a temperature change of a use environment and a temperature characteristic, when mounted on an automobile or the like Frequency shift may occur due to the Doppler effect or the like.

[0006] In order to obtain demodulated data with few errors even when a frequency difference occurs, a frequency synchronization method is being studied. For example, there is a frequency synchronization method described in “Study of a new frequency synchronization method using a guard period in OFDM” (Technical Report of the Institute of Television Engineers of Japan, Vol. 19, No. 38, pp. 13-18). In this frequency synchronization method, the signal waveform in the effective symbol period is cyclically repeated,
(Guard Interval) is used.

That is, a received signal is converted into a base band by a quadrature detection circuit, and each carrier component is demodulated by an FFT circuit. (1) of FIG. 12 shows an in-phase axis output of the quadrature detector. Here, the n-th OFDM symbol includes a guard portion Gn (the number of samples Ng) and an effective symbol portion Sn (the number of samples Ns), and the signal Gn in the guard period includes Gn which is a part of the effective symbol. 'Has been copied. (2) of FIG. 12 is obtained by delaying the signal of (1) of FIG. 12 by an effective symbol period. FIG.
(3) is a result obtained by multiplying the signals of (1) and (2) and calculating a moving average of the guard period width (Ng samples) to obtain a correlation between the two signals. Gn and G
Since n ′ is the same signal waveform, the correlation output shows a peak at the symbol boundary as shown in (3) of FIG.

The peak value of the correlation between the in-phase axis data and the in-phase axis data delayed by the effective symbol period is represented by Sii.
If the peak value of the correlation between the in-phase axis data and the quadrature axis data delayed by the effective symbol period is Siq, the frequency error δ becomes

[0009]

(Equation 1)

[0010]

[0011]

However, in the above-described method of obtaining the frequency error using the arctangent function, the frequency offset normalized by the subcarrier interval and
The relationship with the error signal δ obtained as described above has a periodicity in which the subcarrier interval is one cycle as shown in FIG. For this reason, it is not distinguished in which cycle the frequency offset corresponding to the error signal δ is.
For example, in FIG. 13, when an error signal of δ ₁ is obtained, in addition to the point A, the points B and C correspond. Therefore,
Even if the true normalized frequency offset is O _A , it cannot be distinguished from offsets O _B , O _C, etc. Therefore, when a deviation of 1/2 or more of the subcarrier interval can occur, it is difficult to specify the frequency offset, and the direction of the offset may be erroneously reversed.

[0012] However, in OFDM, the interval between subcarriers is generally set narrow, and it is difficult to suppress the frequency difference to less than 1/2 of this interval.

For example, in mode I of the Eureka 147 DAB system, the center frequency is set to 230 MHz, and the subcarrier interval is set to 1 kHz. That is,
The frequency corresponding to 1/2 of the subcarrier interval is 50
0 Hz, which results in a frequency accuracy of about 2.2 PPM. However, it is not easy to suppress the frequency difference between the transmission frequency and the reception frequency within 2.2 PPM. Achieving this accuracy is not practical, for example, with the cost of the oscillator.

When the relative distance between the transmitting side and the receiving side changes, for example, in the case of receiving a broadcast in a receiving device installed in a mobile body, a frequency shift (Doppler shift) due to the Doppler effect is generated. Occurs. Therefore, there is a problem that the relative speed between the transmitting side and the receiving side is limited when the Doppler shift is within 1/2 of the subcarrier interval.

Further, the above-mentioned method has a problem that the application is limited to an OFDM signal including a guard period, and if no guard period is provided, it is difficult to detect a frequency shift.

According to the present invention, an OFD suitable for easily and accurately detecting a frequency shift over several times the frequency interval of a subcarrier of an OFDM signal on a receiving side is provided.
It is an object of the present invention to provide an orthogonal frequency division multiplexing signal generation device, a transmission device and a method, a communication device and a method capable of transmitting an M signal.

It is another object of the present invention to provide a frequency control apparatus, a frequency control apparatus, a frequency control apparatus, a frequency control apparatus, and a reception apparatus capable of easily detecting a frequency shift of several times the frequency interval of a subcarrier of an OFDM signal and performing frequency synchronization. And

[0018]

According to a first aspect of the present invention, there is provided an orthogonal frequency division multiplexing apparatus for generating an orthogonal frequency division multiplexed signal on a plurality of subcarriers. The multiplexed signal generator is provided with power conversion means for changing the power distribution of the multiplexed signal so that the envelope of the power spectrum of the multiplexed signal to be generated has a specified frequency dependency. An orthogonal frequency division multiplex signal generator is provided.

According to a second aspect of the present invention, in an orthogonal frequency division multiplexing signal generator for generating a multiplexed signal which is orthogonal frequency division multiplexed on a plurality of subcarriers, the data to be transmitted is A data string conversion means for serial / parallel conversion into a plurality of data strings corresponding to each of the plurality of subcarriers; and converting the serial / parallel converted data strings into powers indicated by the data strings for each column. As changing at a predetermined ratio, power conversion means for conversion, including each of the converted plurality of data strings as sub-carriers in orthogonal relationship in the frequency domain, real axis signals orthogonal to each other and Discrete Fourier transform means for generating a time axis waveform of an imaginary axis signal, a real axis signal and an imaginary number generated by the discrete Fourier transform means Orthogonal frequency division multiplexed signal generating apparatus characterized by having a quadrature modulating means for combining signals quadrature modulation on is provided.

Here, in the first and second aspects, the power conversion means may include, for example, a shape in which the power increases as the envelope of the envelope of the power spectrum approaches the distribution center (a mountain shape). Alternatively, the power of each subcarrier is changed so that the power becomes a shape (a valley shape) in which the power decreases as approaching the distribution center.

According to a third aspect of the present invention, in a frequency control apparatus for frequency-synchronizing a multiplexed signal orthogonally frequency-division multiplexed to a plurality of subcarriers, the multiplexed signal is quadrature-detected. Orthogonal detection means for obtaining a first detection axis signal and a second detection axis signal orthogonal to each other, and sampling the time axis waveforms of the two detection axis signals at a predetermined sampling frequency, And,
Discrete Fourier transform of these sampled data,
Discrete Fourier transform means for obtaining a plurality of metrics distributed in the frequency domain, frequency dependency detecting means for detecting the frequency dependency of the envelope of the metric distribution obtained by the discrete Fourier transform means, and the envelope Based on the frequency dependence, a central frequency of the multiplexed signal, a frequency difference with respect to a predetermined reference frequency, a calculation control means for generating an instruction for a frequency change according to the frequency difference,
There is provided a frequency control device comprising frequency changing means for changing the frequency of a signal input to the discrete Fourier transform means in accordance with an instruction generated by the arithmetic control means.

Here, in the third embodiment, for example, the calculating means changes the frequency so that the frequency difference between the frequency corresponding to the center of gravity of the metric power distribution and a predetermined reference frequency becomes small. An instruction to cause the frequency conversion unit is given. More specifically, the difference between the sum of the powers for the metrics at frequencies higher than the predetermined reference frequency and the sum of the powers for the metrics at frequencies lower than the reference frequency is calculated, and the difference obtained is reduced. To change the frequency so that
This is given to the frequency changing means.

As another mode of the processing in the arithmetic control means, a power spectrum is obtained based on a metric distribution obtained by the discrete Fourier transform means, and a power spectrum distribution predetermined by the power conversion means is obtained. From, a power change rate for a metric of a frequency higher than a predetermined reference frequency and a power change rate for a metric of a frequency lower than the reference frequency are obtained, and according to the obtained change rate, a predetermined reference frequency is obtained. From a first approximation line approximating the power envelope for the higher frequency metrics and a second approximation line approximating the power envelope for the lower frequency metrics, the estimated center frequency And the estimated center frequency obtained above and Instructing, can be given to the frequency change means the difference between the reference frequency which is that to change the frequency so as to reduce.

According to the fourth aspect of the present invention, a receiving apparatus for receiving a multiplexed signal subjected to orthogonal frequency division multiplexing receives a high-frequency signal including the multiplexed signal and determines a predetermined high-frequency signal from the received high-frequency signal. A band-pass filter unit for selecting a frequency band obtained, orthogonally detecting the frequency-converted signal using a reproduction carrier, performing discrete Fourier transform, and operating the frequency of the reproduction carrier to perform frequency synchronization. A frequency control unit, a demodulation unit for demodulating the data subjected to the discrete Fourier transform, and an output unit for outputting the demodulated signal; There is provided a receiving device characterized by being configured using a frequency control device.

According to the fifth aspect of the present invention, in a communication apparatus for communicating using a multiplexed signal subjected to orthogonal frequency division multiplexing, a carrier indicated by input signal is orthogonal frequency division multiplexed. A transmitter for modulating and transmitting a multiplexed signal, and a receiver for detecting modulated data by orthogonal frequency division multiplex demodulation of the received signal and outputting a signal indicated by the modulated data, The transmission unit
It is configured using the orthogonal frequency division multiplexed signal generation device according to any one of the first aspect and the second aspect, and the reception unit is configured using the reception device according to the fourth aspect. A communication device is provided.

According to a sixth aspect of the present invention, in a communication method using a multiplexed signal which has been subjected to orthogonal frequency division multiplexing on a plurality of subcarriers, when transmitting the multiplexed signal, the frequency of the multiplexed signal is The frequency index information indicating the position on the axis is transmitted using the frequency dependency in the envelope of the power spectrum of the multiplexed signal, and upon receiving the multiplexed signal, the frequency index information is obtained from the envelope in the power spectrum of the multiplexed signal. A communication method is provided, wherein information is acquired, and frequency synchronization is performed using the acquired frequency index information.

According to a seventh aspect of the present invention, in a transmission method for transmitting information using a multiplexed signal that has been orthogonally frequency-division multiplexed to a plurality of subcarriers, the multiplexed signal is transmitted. And transmitting frequency index information indicating a position on the frequency axis of the multiplexed signal using frequency dependence of an envelope of a power spectrum of the multiplexed signal.

According to an eighth aspect of the present invention, in a frequency control method for frequency synchronization with a multiplexed signal orthogonally frequency-division multiplexed on a plurality of subcarriers, a time axis waveform of the received multiplexed signal is Converted to the frequency domain, from the frequency dependence of the spectrum distribution obtained by converting to the frequency domain, determine the center frequency of the spectrum distribution, the center frequency of the spectrum distribution, and a predetermined reference frequency The frequency control method is characterized in that the frequency of the multiplexed signal before being converted to the frequency domain is changed so that the difference between the multiplexed signals is reduced.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.

Referring to FIG. 1, orthogonal frequency division multiplexing signal generating apparatus 10000 according to the present embodiment includes data sequence converting section 10100, power converting section 10200, inverse discrete Fourier transform section 10300, and orthogonal modulating section 10400.
And is configured.

The data string converter 10100 converts the data string given in serial (serial state) into an OFD
This is for converting the data into a data string having the number of columns corresponding to the number of subcarriers of the M signal. For example, Eureka 14
In the case of 7DAB mode I, since the OFDM signal has 1536 subcarriers, the serial data string is converted into 1536 data strings. The data string converter 10100 can be configured using, for example, a serial / parallel converter.

Each subcarrier in the OFDM signal includes two data of in-phase axis data and quadrature axis data. For this reason, 2-bit data is allocated to each subcarrier. Therefore, 3072 bits of data can be transmitted for each symbol.

The power converter 10200 converts the power of each complex data converted into a parallel data string by the data string converter 10100 at a predetermined ratio. For example, in the case of the mode I of Eureka 147 DAB described above, the power of the 1536 sets of complex data including the in-phase axis data and the orthogonal axis data is converted at a predetermined ratio. More specifically, for example, as shown in FIG. 3, the power of the complex data is converted such that the power of the subcarrier increases as the frequency approaches the center frequency. For example, the power of the subcarriers at both ends farthest from the center is set to 1 (1
00%), the power of each subcarrier is increased by 1%. At this time, the power increase in the subcarrier adjacent to the center frequency is 768%.

The inverse discrete Fourier transform unit 10300 is
This is for synthesizing a plurality of subcarriers into a time axis waveform. An inverse discrete Fourier transform unit 10300 performs a DFT (Discrete) for performing an inverse discrete Fourier transform on complex data.
te Fourier Transform (discrete Fourier transform) circuit 103
And D / A (Digital to Analog) for converting the in-phase axis data and the quadrature axis data of the complex data subjected to the inverse discrete Fourier transform into analog waveforms and generating mutually orthogonal real axis signals and imaginary axis signals. )
It is configured to include conversion units 10320 and 10330.

The quadrature modulator 10400 is for quadrature modulating a carrier using the real axis signal and the imaginary axis signal. The quadrature modulator 10400 generates the oscillator 104 for generating two signals having a phase difference of 90 degrees.
10 and two multipliers 10320 and 10330 for multiplying one of the two signals and the real axis signal, and the other signal and the imaginary axis signal, respectively.
And an adder 10440 for adding two signals obtained by the multiplication to each other.

The oscillating unit 10410 includes, for example, a local oscillator 104 for oscillating a signal having a frequency serving as a carrier wave.
12, a splitter 10414 for splitting the oscillated signal into two, and a phase shifter 10416 for giving a phase delay of 90 degrees to one of the split signals. Note that the oscillation unit 10410 may be configured to include two oscillators that oscillate with a phase difference of 90 degrees.

As described above, the OFDM signal in which the power distribution of the subcarrier is changed is received by the receiving apparatus shown in FIG.

In the above description, the power converter 10
200 is provided between the data sequence converter 10100 and the inverse discrete Fourier transformer 10300, and converts the power of each complex data input to the inverse discrete Fourier transformer 10300 to change the power distribution of the subcarrier. Although the configuration has been described, the mode of operating the shape of the envelope of the power spectrum in the present invention is not limited to this. For example, a power conversion unit may be provided at the subsequent stage of the quadrature modulation unit 10400 to change the frequency dependency of the quadrature-modulated signal waveform to control the shape of the envelope of the power spectrum. Such a power conversion unit is configured using, for example, a filter circuit in which the frequency dependence of the attenuation characteristic has a predetermined shape, an amplification circuit in which the frequency dependence of the amplification factor has a predetermined shape, and the like. be able to. This makes it possible to simplify the power conversion unit and easily increase the processing speed for power conversion. In this case, by normalizing the power of the complex data input to the inverse discrete Fourier transform unit 10300 to a predetermined value, the power transform unit can be formed into the shape of the envelope of the power spectrum. Having a frequency dependency corresponding to This allows
The frequency dependence of the shape of the envelope can be easily verified, and the prospect of adjustment of the power conversion unit can be improved.

Referring to FIG. 2, a frequency controller 1000
Are a quadrature detector 1100 and a discrete Fourier transformer 120
0 and a frequency deviation detection unit 1300.

The quadrature detection section 1100 receives the OFDM signal and obtains two detection axis signals orthogonal to each other by using a reproduction carrier. The two detection axes can be selected, for example, as an in-phase axis (I-phase axis) in phase with the received signal and a quadrature axis (Q-phase axis) orthogonal to the received signal. Note that the two detection axes are not limited to these phases as long as they are orthogonal to each other. For example, with respect to a received signal, a detection axis having a phase of +45 degrees,
Alternatively, a detection axis having a phase of -45 degrees may be selected.

The quadrature detection unit 1100 includes, for example, a splitter 1150 for splitting the received signal into two signals,
A reproduction carrier generator 1119 for oscillating two reproduction carriers X and Y having a phase difference of two degrees, and two multipliers for multiplying the two distributed signals by the reproduction carriers X and Y, respectively. 1107A, 110
7B.

The reproduction carrier generator 1119 includes, for example, a variable frequency oscillator 116 capable of changing the oscillation frequency.
0, a branch circuit 1180 for distributing the oscillated signal into two, and a phase shifter 1170 for imparting a phase delay of 90 degrees to one of the divided signals. The reproduction carrier can be generated using the reproduction carrier generator 1119 configured as described above. Further, the variable frequency oscillator 1160 can change its oscillation frequency in accordance with the AFC signal provided from the frequency shift detector 1300.

The discrete Fourier transform unit 1200 calculates the OF
At the sampling points larger than the number of subcarriers included in the DM signal, the I-phase axis signal and the Q-phase axis signal are respectively sampled, and these are subjected to discrete Fourier transform. The discrete Fourier transform unit 120
0 includes, for example, two A / D (Analog to Digital) converters 1208A and 1208B, and a DFT circuit 1209 for executing a discrete Fourier transform process. In the DFT circuit 1209, as a calculation algorithm for performing the discrete Fourier transform, for example, the calculation may be performed according to a definition formula of DFT,
Fast Fourier Transform (FFT)
Or the like may be used. By performing the calculation using the FFT, the DFT can be calculated at a high speed. The DFT circuit 1209 is configured by, for example, a dedicated hardware logic. It should be noted that a general-purpose arithmetic device equipped with a program for executing the DFT processing may be used.

The frequency deviation detecting section 1300 receives the metrics obtained by the discrete Fourier transform section 1200 and calculates a frequency difference from the received OFDM signal.
This is for performing arithmetic control for performing frequency synchronization so as to reduce the obtained frequency difference. The frequency deviation detecting unit 1300 includes, for example, an arithmetic processing unit 1322 for performing arithmetic processing for obtaining a frequency difference, and an arithmetic processing unit 132
AFC (Automatic Freque
and a control signal generator 1350 for generating an ncy control (automatic frequency control) signal.

The control signal generation unit 1350 includes, for example,
D / A for generating a signal having a voltage corresponding to the operation result
(Digital to Analog) converters can be used.
When a numerically controlled oscillator is used as the reproduced carrier generator 1119 in the quadrature detector 1100, the control signal generator 1350 may be omitted and the signal indicated by the operation result may be directly provided. In this way, it is possible to generate an AFC signal indicating a frequency change amount according to the calculation result.

It should be noted that the magnitude of the amount of change indicated by the AFC signal may be set to a constant value, and the presence or absence of the change and its direction may be changed according to the result of the above calculation. By setting the magnitude of the change amount to a constant value, the control signal generation unit 1350 and
Regenerated carrier generator 11 in quadrature detector 1100
19 can be easily configured.

In the present embodiment, the quadrature detector 11
The mode in which the frequency of the signal input to the DFT circuit 1209 is changed by changing the frequency of the reproduction carrier at 00 is described.
The mode in which the frequency of the signal input to the 209 is changed is not limited to this. For example, as shown in FIG. 11, when a frequency conversion unit 3000 for converting a received OFDM signal to an intermediate frequency is provided in a stage preceding the quadrature detection unit 1100, an AFC signal is given to the frequency conversion unit 3000, The amount of frequency conversion by the frequency conversion unit 3000 can be changed.

Next, referring to FIGS. 2, 3 and 4,
The operation of the frequency control device configured as described above will be described.

First, an OFDM signal provided to the frequency control device will be described with reference to FIG.

As shown in FIG. 4, the baseband of the OFDM signal has a time axis waveform in which a plurality of subcarriers having different frequencies are superimposed. FIG. 4 shows an OFDM signal demultiplexed and multiplexed on 24 subcarriers, but the number of subcarriers is not limited to this. It is also assumed that each subcarrier has been power-converted by power conversion section 9140 of transmitting apparatus 9170 at a predetermined ratio such that the power increases as the frequency approaches the center frequency, as described above.

The baseband of the OFDM signal has a spectrum shown in FIG. 3 in the frequency domain. This corresponds to the Fourier transform of the time axis waveform shown in FIG.
In FIG. 3, a plurality of subcarriers are arranged on the frequency axis, and each subcarrier includes a sideband component due to modulation.

Next, the operation of the frequency control device according to the present embodiment will be described with reference to FIG.

First, in the orthogonal detection unit 1100, the OF
The DM signal is received, and an I-phase axis signal and a Q-phase axis signal that are orthogonal to each other are obtained.

Then, in the discrete Fourier transform unit 1200, the signals on the two detection axes (I-phase axis signal and Q-phase axis signal) are respectively sampled (sampled) on the time axis waveform.
Is done. Discrete Fourier transform unit 12 in the present embodiment
At 00 (see FIG. 2), sampling is performed at sampling points larger than the number of subcarriers, and a discrete Fourier transform is calculated for the sampled data.

That is, the sampled I-phase axis data and Q-phase axis data are expressed as complex quantities (for example,
The sampled value of the I-phase axis signal is a real part, and the sampled value of the Q-phase axis signal is an imaginary part. By the discrete Fourier transform, a metric (complex metric) Z is obtained for each of the number of frequency slots corresponding to the number N _S of sampling points (sampling points). The N A of the _S metrics Z, in addition to the active metrics corresponding to the number N _C of sub-carrier, the number sampling points exceeds the number of sub-carrier N _OS (= N _S -
N _C ). The invalid metric is a component due to noise and leakage from each subcarrier. As a metric distribution obtained as a result of the discrete Fourier transform, for example, N _C
Effective metrics are arranged in a row, and on both sides,
In some cases, (N _OS / 2) invalid metrics are arranged.

Here, assuming that the imaginary unit is j and the suffix indicating the frequency slot from which the metric is obtained is i, each metric Z _i is represented by (a _i + jb _i ). Results of calculation of the discrete Fourier transform, metrics sampling points _{N S {Z i} (i} = 1,2,
3,..., N _s ), two series of data {a _i }, {b
_i ｝ is obtained.

For example, the mode I OFDM signal in the Eureka 147 DAB system has 1536 subcarriers. With respect to such a signal, the frequency control device 1000 according to the present embodiment uses
Sampling is performed at 2048 (2 10) sampling points, which is more than 36. In this case, FIG.
As shown in FIG.
Two invalid metrics are obtained.

Note that by performing sampling at the number of sampling points equal to the power of 2, the DFT operation becomes
The effect of speeding up by FT can be improved.

Next, the frequency deviation detecting section 1300 performs an arithmetic operation for calculating a difference between the metric distribution {a _i + jb _i } obtained by the discrete Fourier transform section 1200 and a predetermined distribution. An AFC signal is generated according to the result of the arithmetic processing.

In the present embodiment, frequency synchronization is performed by changing the frequency of the reproduction carrier such that the center of gravity of the metric power distribution obtained from the received OFDM signal approaches a predetermined reference frequency. That is, the frequency deviation detection unit 1300 obtains the center of gravity of the power distribution of the metrics, and compares the frequency of the center of gravity with a predetermined reference frequency. Then, a frequency difference between the frequency of the center of gravity and the reference frequency is obtained, and an instruction to change the frequency of the reproduction carrier so as to reduce the difference is given to the orthogonal detector 1100 (see FIG. 2).

As an operation for obtaining the frequency difference between the frequency of the center of gravity and the reference frequency, for example, a frequency corresponding to the center of gravity of the power distribution {P _i } is calculated from a metric distribution {z _i }. The frequency difference from the frequency can be obtained.

[0063] The power P is, for example, the complex conjugate of Z as ^{Z *, P = Z 2 =} Z · Z * = Z * · Z ... (101) and can be defined. That is, metrics Z
When Z = (a + jb), the power of this metric is given by P = (a + jb) (a−jb) = (a · a + b · b) (102)

The details of the arithmetic processing performed by the arithmetic processing unit 1322 (see FIG. 2) will be described below.

First, the discrete Fourier transform unit 1200 (FIG. 2)
) Distribution of N _S metrics obtained in） A _i +
For jB _i ｝ (i | 1, 2, 3,..., N _S ), the sum W of the powers of the metrics belonging to the frequency slots (1 to C) having a lower frequency than the frequency slot C corresponding to the predetermined reference frequency _L and frequency slots (C to C) having a frequency higher than the frequency slot corresponding to the reference frequency.
N _S ) and the sum W _H of the powers of the metrics belonging to N _s ). As the reference frequency, for example, when a signal having a frequency equal to the sampling frequency is received,
The center frequency of the power distribution of the effective metrics that is theoretically expected can be selected. At this time, the frequency slot C corresponding to the reference frequency is C = N _S / 2.

Then, the total sum W _L and the total sum W _H obtained above are compared with each other, and a frequency difference is obtained from a difference δW between these total sums.
The sum difference δW can be calculated, for example, according to the following equation.

[0067]

(Equation 2)

In this equation, the center of gravity of the power distribution is obtained using all of the acquired metrics. However, the calculation may be performed for a range of effective metrics that is theoretically expected. Further, the same calculation is repeatedly performed for the reference frequency C, so that this can be omitted. That is, for the reference frequency C theoretically expected,

[0069]

(Equation 3)

Thus, the difference between the sums can be obtained. By calculating according to this equation, it is possible to calculate which of the C-th and C + 1-th slots is bounded, which distribution of the spectral power is biased. The reference frequency C can be selected according to a theoretical frequency setting. For example, when the sampling point is 2048, the reference frequency C can be selected as C = 2048/2 = 1024.

Further, the influence of the transmission path can be avoided by using a signal whose power distribution is known. That is, from the metrics {An _i + jBn _i } for the OFDM signal acquired in the null symbol period and the metrics {As _i + jBs _i } for the signal symbol period,

[0072]

(Equation 4)

Is obtained, and this metric is used for calculation.

Further, the sum Wt of the power of the metrics for all the frequency slots is obtained, whereby the difference δW of the sum can be standardized. That is, the total power Wt of the power for all the frequency slots is

[0075]

(Equation 5)

The standardized sum difference δW / Wt can be obtained by using this. This is given to the control signal generator 1350 (see FIG. 2) as a frequency shift amount. Thereby, even when the power of the incoming OFDM signal fluctuates, this effect can be reduced.

Next, an example of a calculation procedure when using standardized metrics will be described with reference to FIGS.

First, in step S121 of FIG.
For each symbol period, the received signal is subjected to discrete Fourier transform using FFT.

Then, in step S122, the metric in the symbol period is normalized with the metric obtained from the null symbol.

Next, in step S123, the metrics standardized in step S122 are divided into two regions with the reference frequency as a boundary, and the sum of power in each region is calculated. Then, the difference between the power sums in the two regions is obtained.

At this time, if there is no frequency difference, the two divided areas are symmetrical, and as shown in FIG. 5A, the total sum W _L in the area lower than the reference frequency is obtained.
And the sum W _H in the high-frequency region becomes equal. When there is a frequency difference, the two regions are asymmetric. For example, when a signal shifted to the low frequency side is received, as shown in FIG. 5B, the sum W _L in the area lower than the reference frequency becomes the sum W W in the area higher than the reference frequency. _It becomes larger than _H.

If the received signal is affected by fading or the like, the frequency shift is corrected in step S124.

The frequency synchronization can be performed by changing the frequency of the reproduction carrier so as to reduce the frequency difference obtained as described above.

Next, a second embodiment of the present invention will be described.

In this embodiment, the transmitting apparatus is configured in the same manner as in the first embodiment, but differs in the method of estimating the center frequency in the frequency control apparatus. The following description focuses on the differences.

In the present embodiment, the power distribution of the metrics obtained from the received OFDM signal is determined by setting the power of the subcarriers at both ends farthest from the center to 1, as determined in advance by the transmitter. Since the carrier power has been increased by 1%, the rate of change of power for metrics at frequencies higher than a predetermined reference frequency and the rate of change of power for the number of metrics at frequencies lower than the reference frequency are: A frequency shift is detected by utilizing a monotonic linear distribution.

That is, a first approximation line for approximating a power envelope for a metric having a frequency higher than a predetermined reference frequency, and a second approximation line for approximating a power envelope for a metric having a frequency lower than the reference frequency. From the approximate line, the intersection point is set as the estimated center frequency.

The instruction to change the frequency of the reproduction carrier so as to reduce the difference between the estimated center frequency obtained as described above and the reference frequency is issued to the quadrature detector 1.
100 (see FIG. 2).

The details of the arithmetic processing performed by the arithmetic processing unit 1322 (see FIG. 2) will be described below.

First, a discrete Fourier transform unit 1200 (FIG. 2)
) Distribution of N _S metrics obtained in） A _i +
For jB _i ｝ (i | 1, 2, 3,..., N _S ), the powers of the metrics belonging to all the frequency slots (1 to N _S ) are obtained. As the reference frequency, for example, when a signal having a frequency equal to the sampling frequency is received, the center frequency of the power distribution of effective metrics that is theoretically expected can be selected. At this time, the reference frequency is C = N _S / 2. For example, when the sampling point is 2048, C = 2048/2 = 1024 can be selected.

The first approximation line is obtained, for example, from a subcarrier having a frequency higher than a predetermined reference frequency by at least 8 kHz and a frequency having a frequency of at least 8 kHz higher than a subcarrier having the highest frequency, in consideration of a possible frequency error range. The power of each metric up to the subcarrier having the lower frequency can be approximated by a linear approximation of a linear line by the least square method (see FIG. 5).

Similarly, the above-mentioned second approximation line also takes into account, for example, a frequency error range that is at least 8 kHz lower than a predetermined reference frequency, taking into account a possible frequency error range. The power of each metric up to a subcarrier having a frequency higher than that of the carrier by at least 8 kHz can be approximated by a linear approximation of a linear line by the least square method (FIG. 5).
reference).

The estimated center frequency E may be a value of a frequency at a point where the first approximate line and the second approximate line intersect when each is extended. Therefore, if the first approximate line is P = α ₁ · i + β ₁ (201) and the second approximate line is P = α ₂ · i + β ₂ (202), α ₁ · i + β ₁ = α ₂ · i + β ₂ (203) By using i, E can be easily obtained. That is, E is

[0094]

(Equation 6)

Is obtained.

Then, the estimated center frequency obtained above is compared with the reference frequency, and a frequency difference is obtained from the difference δf. The frequency difference δf can be obtained, for example, according to the following equation (see FIG. 5).

Δf = E−C (205) Further, the influence of the transmission path can be avoided by using a signal whose power distribution is known. That is, the metric ΔA for the OFDM signal acquired in the null symbol period
n _i + jBn _i } and the metrics of the signal symbol period {As _i + jBs _i },

[0098]

(Equation 7)

Then, the metric {A _i + jB _i }
Is used for the calculation.

Next, an example of a calculation procedure when using standardized metrics will be described with reference to FIGS.

First, in step S221, discrete Fourier transform is performed on the received signal for each symbol period using FFT.

The metrics obtained from the null symbols are used to normalize the metrics for the symbol period (S22).
2).

In step S223, the power is calculated for the metrics in all the frequency slots standardized in step S222. At this time, when there is no frequency difference, the frequency is symmetric with respect to the reference frequency C as shown in FIG. When there is a frequency difference, for example, when a signal shifted to the low frequency side is received, the signal becomes asymmetric as shown in FIG. 5B.

Next, in step S224, the power envelope for the effective metric on the high frequency side is linearly approximated. In the linear approximation, for example, as in the present embodiment, the power value of each metric is calculated as 1 by the least square method.
There is a method of approximating the following straight line. The calculated first approximation line is represented by the following equation.

[0105]

(Equation 8)

The first approximation line is obtained, for example, from the subcarrier (i = 1032) having a frequency higher than the predetermined reference frequency C by at least 8 kHz in consideration of a possible frequency error range. A linear approximation of a first-order straight line by the least squares method is performed on the power of each metric up to a subcarrier (i = 1784) whose frequency is at least 8 kHz lower than that of the subcarrier.

In step S225, the power envelope for the effective metric on the low frequency side is linearly approximated in the same manner as in step S224. The calculated first approximation line is represented by the following equation.

[0108]

(Equation 9)

The second approximation line is obtained, for example, from the subcarrier (i = 1016) having a frequency lower than the predetermined reference frequency C by at least 8 kHz, taking into account a possible frequency error range. A linear approximation of a first-order straight line by the least squares method is performed on the power of each metric up to a subcarrier (i = 264) having a frequency higher than that of the subcarrier by at least 8 kHz.

In step S226, step S2
An intersection where the two approximate lines obtained in step S25 and step S226 intersect is obtained, and a frequency slot corresponding to this intersection is set as an estimated center frequency E. Therefore, the estimated center frequency E
Is obtained by the following equation.

[0111]

(Equation 10)

At step S227, at step S2
The difference between the estimated center frequency E obtained in step 26 and a predetermined reference frequency C is obtained and is referred to as a frequency shift difference δf. That is, δf = E−C (209) As the frequency difference thus obtained decreases,
Frequency synchronization can be achieved by changing the frequency of the reproduction carrier.

In the first and second embodiments described above, the envelope of the power spectrum of the orthogonal frequency division multiplexed signal approaches the distribution center as shown in FIG. Although the case where the power is increased, that is, a mountain-shaped envelope shape has been described, the shape of the envelope is not limited to this. For example, the envelope of the power spectrum may have a shape in which the power decreases as approaching the distribution center, that is, a valley-shaped envelope shape. However, in order to perform the frequency control in the first embodiment, the sensitivity for detecting the frequency difference can be further improved in the case of a mountain-shaped envelope shape.

Further, a predetermined sub-carrier,
The power of each sub-carrier may be changed so that the power ratio between the sub-carrier adjacent to the sub-carrier and the sub-carrier becomes larger than a predetermined value. For example, it is also possible to increase the power of the subcarrier near the center frequency, detect a subcarrier having a power exceeding a predetermined threshold value, and compare the detected frequency with a predetermined frequency.

Further, the envelope shape of the power spectrum of the orthogonal frequency division multiplexed signal to be transmitted from the transmitting side during communication is determined to be a predetermined shape, and the received orthogonal frequency division multiplexed signal is converted by the discrete Fourier transform at the receiving side. By comparing the shape obtained by the conversion with the predetermined shape, frequency synchronization can be achieved.

For example, the discrete Fourier transformer 1200 is designed so that the flatness of the power spectrum of the orthogonal frequency division multiplexed signal obtained through a filter having an attenuation characteristic opposite to that of the envelope to be transmitted is maximized.
The frequency of the signal input to (see FIG. 2) can be converted to perform frequency synchronization. Also, the discrete Fourier transform unit 12 is designed to maximize the correlation coefficient between the envelope shape to be transmitted and the envelope shape of the received signal.
00 (see FIG. 2) may be frequency-synchronized by converting the frequency of the signal input thereto. When frequency synchronization is performed in this way, the envelope shape of the power spectrum of the orthogonal frequency division multiplexed signal may be specified in common for the transmitting side and the receiving side, and the shape may be freely determined. it can. In addition, the envelope shape may be fixedly designated in advance for the transmitting side and the receiving side, or may be designated by an external instruction.

Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment is an OFDM receiver that performs frequency synchronization using the arithmetic processing described in any of the first and second embodiments.

In FIG. 9, a receiving apparatus 200 includes an input terminal 1, a band-pass filter 2, an amplifier 3, a multiplier 4, a SAW (Surface Acoustic Wave; surface acoustic wave) filter 5, and an intermediate frequency amplifier 6. And the multiplier 7
A, 7B, A / D converters 8A, 8B, and FFT circuit 9
, AGC circuit 10, synchronization detection circuit 11, differential demodulation circuit 12, first local oscillator 18, and second local oscillator 1
9, a first reference oscillator 20A, and a second reference oscillator 20B
, Timing circuit 21 and frequency error calculation circuit 22
, A time axis detection circuit 23 and a phase error detection circuit 24. The multipliers 7A and 7B and the second local oscillator 19 constitute a quadrature detection circuit.

In the receiving device 200, the input terminal 1
The RF signal added to the RF signal is filtered by a band-pass filter 2 to remove noise outside a predetermined band, then amplified by an amplifier 3, multiplied by a multiplier 4 by a local oscillation signal from a first local oscillator 18, and It is converted to a frequency signal. The converted intermediate frequency signal is band-limited by the SAW filter 5, then amplified to a predetermined level by the intermediate frequency amplifier 6, and then guided to two systems of multipliers 7A and 7B.

Multipliers 7A and 7B are connected to second local oscillator 19
, A two-phase local signal having a phase difference of 90 degrees is input and multiplied by an intermediate frequency signal, which is the other input, to form a quadrature detection circuit. Multiplier 7
After the outputs of A and 7B are converted into digital data by the A / D converters 8A and 8B, the valid data period is taken into the FFT circuit 9 except for the guard period and subjected to FFT processing.

After the FFT processing, the signal is differentially demodulated and finally converted into an audio signal. The description of the details of this process is omitted.

On the other hand, the output of the FFT circuit 9 inputs the metric to the frequency error calculation circuit 22, where it performs the above-described calculation and supplies the frequency difference component to the first reference oscillator 20A as an AFC signal. If necessary, the output signal of the differential demodulation circuit 12 also includes an AFC signal for controlling the phase error detected by the phase error detection circuit 24 within ± 1/2 of the subcarrier interval from the first reference. It is supplied to the oscillator 20A.

According to the present embodiment, frequency synchronization can be performed even if a frequency difference of 1/2 or more of the subcarrier interval occurs. This receiving apparatus 200 can be used, for example, for receiving digital audio broadcasting in the Eureka 147 DAB system.

Next, a sixth embodiment of the present invention will be described with reference to FIG. In this embodiment, the OFD
It is an example of a communication device for performing communication using an M signal.

In FIG. 10, a communication apparatus 9001 receives an incoming OFDM signal, and receives a transmission section 9002 for outputting information indicated by the OFDM signal, and a transmission section for receiving information to be transmitted and transmitting the information as an OFDM signal. And a part 4.

The receiving section 9002 includes a filter section 2000 for selecting a signal of a predetermined band from an incoming electromagnetic wave, a frequency converting section 3000 for converting a signal having a selected band to an intermediate frequency, and a detection section. And a frequency control unit 1000 for performing frequency synchronization, a demodulation unit 4000 for demodulating the detected signal, and an output unit 5000 for outputting information indicated by the demodulated signal. .

The frequency control unit 3000 can be configured, for example, in the same manner as the frequency control devices according to the first to fourth embodiments. For example, a quadrature detection unit 1100 for acquiring an in-phase detection axis signal (I-phase axis signal) and a quadrature detection axis signal (Q-phase axis signal), and a discrete Fourier for performing a discrete Fourier transform on the I-phase signal and the Q-phase signal A conversion unit 1200 and a frequency deviation detection unit 1300 for detecting a frequency deviation using a signal subjected to discrete Fourier transform
And a configuration having:

The output section 5000 includes, for example, a voice output device for outputting voice information, an image output device for displaying an image, a data output device for outputting data, and the like.

The audio output device can be configured using, for example, an amplifier, a speaker, and the like.

The image output device can be constituted by using, for example, an image display circuit and a display device.

The data output device can be configured using, for example, an interface circuit, a buffer circuit, a signal conversion circuit, and the like.

In the receiving section 9002, the filter section 2000, the frequency conversion section 3000, the frequency control section 1000, and the demodulation section 4000 may be formed in one case, and this may be used as a tuner section 9003. Accordingly, it is possible to change the combination of the output devices, respond to the preference of the quality of displaying information, and the like in accordance with the mode in which information is output.

The transmitting section 9004 receives the information,
An input unit 6000 for converting the signal into a signal, and a modulator 700 for modulating a carrier with the converted signal.
0, RF transmitter 8 for transmitting the modulated carrier
000. Modulation section 7000 is configured using the orthogonal frequency division multiplexed signal generation device according to the above-described first or second embodiment.

The communication device 9001 communicates with other devices connected to the interface unit 9005 for transmitting and receiving OFDM signals. Interface unit 9005
For example, an antenna, an optical / electrical converter, an electric signal connector, or the like can be used depending on the form in which the communication device 9001 is connected. Note that the interface unit 9005 may be externally attached as in the illustrated example, or may be embedded in the communication device 9001.

According to the present embodiment, even in a state where a frequency difference occurs between the transmitting side and the receiving side, communication can be performed in frequency synchronization.

[0136]

According to the present invention, information for frequency synchronization can be transmitted using the envelope shape of the spectrum distribution of the OFDM signal to be transmitted. For this reason, when receiving an OFDM signal, by detecting the envelope shape of the spectrum distribution, it is possible to acquire information for frequency synchronization with the signal.

For example, for an OFDM signal having a plurality of columns of complex data composed of in-phase axis data and quadrature axis data, the power for changing the power at a predetermined ratio so that the power of the complex data increases as the center frequency is approached. A transmission device including a conversion unit is provided. In a receiving apparatus that receives an OFDM signal transmitted from such a transmitting apparatus, a frequency shift of a synchronous detection frequency for demodulating the received OFDM signal is calculated by using a precision of an operation for detecting a frequency corresponding to a center of gravity of a spectrum distribution. Can be improved. Therefore, even if a frequency shift of several times the frequency interval of the multiplex carrier obtained by performing the FFT processing on the received signal occurs, it is possible to generate a highly accurate frequency control signal and control the frequency of the reference oscillator. Therefore, frequency control suitable for practical use can be performed, and the OFDM signal can be received in a stable state.

Further, the frequency deviation of the synchronous detection frequency for demodulating the received OFDM signal can be obtained from the intersection of two high-frequency and low-frequency approximation lines that approximate the spectrum envelope. Also in this case, even if a frequency shift occurs several times as large as the frequency interval of the multiplex carrier, it is possible to generate a highly accurate frequency control signal and control the frequency of the reference oscillator.

Also, according to the present invention, the received OFD
A frequency control device capable of performing frequency synchronization even if a synchronous detection frequency for demodulating an M signal has a frequency difference of several times the frequency interval of a multiplexed carrier obtained by performing a discrete Fourier process on a received signal. Provided.

As a result, even if a deviation occurs between the reference frequency on the transmission side and the reference frequency on the reception side,
Information can be transmitted. Further, there is provided a frequency control device capable of performing frequency synchronization even when a Doppler shift occurs due to relative movement between a transmission side and a reception side.

Further, it is possible to constitute a receiving device equipped with the above-mentioned frequency control device, and to provide a receiving device capable of stably receiving a broadcast by an OFDM signal. Such a broadcast includes, for example, a broadcast of the Eureka 145 system DAB.

Further, a communication device equipped with the above-mentioned frequency control device can be constituted. As a result, frequency synchronization in a digital telephone or the like can be stabilized. The application of the OFDM method is facilitated, and therefore, it is possible to cope with communication with a large amount of transmission information, such as a videophone for communicating a signal including an image signal. In addition, since the frequency difference that can be frequency synchronized can be made large, the management of the reference frequency in each device becomes easy. Furthermore, in communication by a mobile unit, even when a frequency difference occurs due to Doppler shift, communication can be performed in a frequency-synchronized state.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an orthogonal frequency division multiplexed signal generation device according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a receiving device of the present invention.

FIG. 3 is an explanatory diagram showing a power distribution in the frequency domain of the metric of an OFDM signal to which the present invention is applied.

FIG. 4 is a waveform diagram illustrating a frequency domain structure of OFDM signal metrics.

FIGS. 5A and 5B are explanatory diagrams schematically showing a power distribution of metrics divided into two regions, wherein FIG. 5A is a distribution when there is no frequency difference, and FIG. 5B is a distribution when there is a frequency difference.

FIG. 6 is a flowchart showing a calculation procedure according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing an envelope and an approximation line in a power distribution of metrics; FIG. 7A is an explanatory diagram of a power distribution when there is no frequency difference; FIG. FIG.

FIG. 8 is a flowchart showing a calculation procedure according to the second embodiment of the present invention.

FIG. 9 is a block diagram showing a receiving device to which the present invention is applied.

FIG. 10 is a block diagram showing a communication device to which the present invention is applied.

FIG. 11 is a block diagram showing another aspect of the communication device to which the present invention is applied.

FIG. 12 is an explanatory diagram showing correlation of signals used for frequency difference detection in a conventional frequency control method.

FIG. 13 is a graph showing a relationship between a correlation signal and a frequency offset in a conventional frequency control method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Band pass filter, 3 ... Amplifier, 4 ... Multiplier, 5 ... SAW filter, 6 ... Intermediate frequency amplifier, 7A, 7B ... Multiplier, 8A, 8B ... A / D converter, 9 ... FFT circuit, 10 AGC circuit, 11 synchronization detection circuit, 12 differential demodulation circuit, 18 first local oscillator, 19 second local oscillator, 20A first reference oscillator
20B: second reference oscillator, 21: timing circuit, 22
... Frequency error calculation circuit, 23 ... Time axis detection circuit, 24 ...
Phase error detection circuit, 200: receiving device, 1000: frequency control device, 1100: quadrature detector, 1107A, 11
07B Multiplier, 1150 Distributor, 1119 Regenerated carrier generator, 1160 Variable frequency oscillator, 117
0: phase shifter, 1180: branch circuit, 1200: discrete Fourier transform unit, 1208A, 1208B: A / D converter,
1209: DFT circuit, 1300: frequency deviation detector,
1322 arithmetic processing unit, 1350 control signal generation unit, 2
000: filter section, 3000: frequency conversion section, 30
10 Multiplier, 3020 Frequency variable oscillator, 4000
... demodulation section, 5000 ... output section, 6000 ... input section, 70
00: modulator, 8000: RF transmitter, 9001: communication device, 9002: receiver, 9003: tuner, 9
004: transmission unit, 9005: interface unit, 100
00: orthogonal frequency division multiplex signal generator, 10100 ...
Data string converter, 10200 ... power converter, 103
00: inverse discrete Fourier transform unit, 10310: DFT circuit, 10320, 10330: D / A converter, 1040
0: Quadrature modulator, 10410: Oscillator, 10412: Local oscillator, 10414: Divider, 10416: Phase shifter,
10420, 10430 ... multiplier, 10440 ... adder.

Claims (17)

[Claims] 1. An orthogonal frequency division multiplexing signal generator for generating a multiplexed signal which is orthogonal frequency division multiplexed on a plurality of subcarriers, wherein an envelope of a power spectrum of a multiplexed signal to be generated is specified. An orthogonal frequency division multiplexing signal generating apparatus, comprising: a power conversion means for changing a power distribution of a multiplexed signal so as to have a dependency. 2. An orthogonal frequency division multiplexing signal generator for generating a multiplexed signal which is orthogonal frequency division multiplexed on a plurality of subcarriers, wherein data to be transmitted corresponds to each of the plurality of subcarriers. A data string converting means for performing serial / parallel conversion into a plurality of data strings; and converting each of the serial / parallel converted data strings to a power indicated by the data string at a ratio determined for each column. Power converting means for converting, and generating mutually orthogonal real axis signals and imaginary axis signals, each of which shows a time axis waveform including each of the plurality of converted data strings as subcarriers having an orthogonal relationship to each other. Means for orthogonally modulating and synthesizing a real axis signal and an imaginary axis signal generated by the discrete Fourier transform means. Quadrature modulating means and the orthogonal frequency division multiplexed signal generating apparatus characterized by having for. 3. The orthogonal frequency division multiplex signal generator according to claim 1, wherein the power converting means increases or decreases the power as the envelope of the power spectrum approaches the distribution center. An orthogonal frequency division multiplex signal generator, wherein the power of each subcarrier is changed so as to have a shape. 4. The orthogonal frequency division multiplexing signal generating apparatus according to claim 1, wherein said power conversion means comprises a power ratio between a specific subcarrier and a subcarrier adjacent to said specific subcarrier. Wherein the power of each subcarrier is changed such that the power is larger than a predetermined value. 5. A frequency control apparatus for frequency-synchronizing a multiplexed signal that has been orthogonally frequency-division multiplexed to a plurality of subcarriers, wherein the multiplexed signal is orthogonally detected and a first detection axis signal orthogonal to each other is provided. And quadrature detection means for obtaining a second detection axis signal; and sampling the time axis waveforms of the two detection axis signals at a predetermined sampling frequency, respectively, and analyzing these sampled data. Discrete Fourier transform means for performing a discrete Fourier transform to obtain a plurality of metrics distributed in a frequency domain; and frequency dependency for detecting a frequency dependency in an envelope of a distribution of the metrics obtained by the discrete Fourier transform means. A predetermined frequency of the center frequency of the multiplexed signal is determined based on the frequency dependence of the detection means and the envelope. An arithmetic control unit for obtaining a frequency difference with respect to the obtained reference frequency and generating an instruction for a frequency change according to the frequency difference; and a frequency of a signal input to the discrete Fourier transform unit is generated by the arithmetic control unit. Frequency changing means for changing the frequency in accordance with a given instruction. 6. The frequency control device according to claim 5, wherein the arithmetic and control means comprises: a sum of powers for metrics at frequencies higher than a predetermined reference frequency; and a power at metrics for frequencies at frequencies lower than the reference frequency. A frequency control unit that obtains a difference from the sum of the above and gives an instruction to change the frequency so as to reduce the obtained difference to the frequency changing unit. 7. The frequency control device according to claim 5, wherein the arithmetic control unit obtains a power spectrum based on a metric distribution obtained by the discrete Fourier transform unit, and the power control unit determines the power spectrum in advance. From the distribution of the power spectrum, a power change rate for a metric at a frequency higher than a predetermined reference frequency and a power change rate for a metric at a frequency lower than the reference frequency are determined. From a first approximation line approximating the power envelope for the metric at a higher frequency than the reference frequency and a second approximation line approximating the power envelope for the metric at a lower frequency than the reference frequency. Is obtained as the estimated center frequency, and the above estimated center frequency is obtained. , It instructs the difference between the reference frequency that is determined in advance to change the frequency so as to reduce the frequency control device, characterized in that applied to said frequency changing means. 8. The frequency control apparatus according to claim 5, wherein the frequency changing means changes the frequency of a reproduction carrier used for quadrature detection in the quadrature detection means, and performs the discrete Fourier modulation. A frequency control device for changing the frequency of a signal input to a conversion means. 9. The frequency control device according to claim 5, wherein a frequency for converting a frequency of a multiplexed signal input to the quadrature detection means is provided before the frequency control device. Conversion means, wherein the frequency changing means changes the amount of conversion of the frequency to be converted by the frequency conversion means to change the frequency of a signal input to the discrete Fourier transform means. Control device. 10. The frequency control device according to claim 5, wherein said discrete Fourier transform means sets each of said two detection axis signals to be larger than the number of said multiplexed subcarriers. A frequency control device for sampling at a number of sampling points. 11. The frequency control device according to claim 5, wherein said discrete Fourier transform means performs sampling on a carrier frequency of a lowest-order subcarrier among said plurality of subcarriers. A frequency control device, wherein the frequency control is performed for a period including a period corresponding to one cycle. 12. The frequency control device according to claim 5, wherein said arithmetic control means obtains a power spectrum based on a distribution of metrics obtained by said discrete Fourier transform means, A frequency control device, wherein an instruction to change a frequency so that a distribution center of a spectrum approaches a predetermined reference frequency is given to the frequency changing means. 13. A receiving apparatus for receiving an orthogonal frequency division multiplexed multiplexed signal, a band for receiving a high frequency signal including the multiplexed signal and selecting a predetermined frequency band from the received high frequency signal. A pass filter unit, a quadrature detection of the frequency-converted signal using a reproduction carrier, a discrete Fourier transform, and a frequency control unit for operating the frequency of the reproduction carrier to perform frequency synchronization, and the discrete Fourier transform And a demodulation unit for demodulating the demodulated data; and an output unit for outputting the demodulated signal, wherein the frequency control unit is a frequency control device according to any one of claims 5 to 12. A receiving device comprising: 14. A communication apparatus for communicating using a multiplexed signal subjected to orthogonal frequency division multiplexing, wherein the multiplexed signal is transmitted by orthogonal frequency division multiplex modulation of a carrier with data indicated by an input signal. And a receiving unit for detecting the modulated data by orthogonal frequency division multiplex demodulation of the received signal and outputting a signal indicated by the modulated data. 14. A communication device comprising: the orthogonal frequency division multiplexed signal generation device according to any one of claims 13 to 14, wherein the reception unit is configured to use the reception device according to claim 13. 15. A communication method using a multiplexed signal that has been subjected to orthogonal frequency division multiplexing to a plurality of subcarriers, wherein, when transmitting the multiplexed signal, frequency index information indicating a position on the frequency axis of the multiplexed signal. Is transmitted using the frequency dependence of the envelope of the power spectrum of the multiplexed signal. Upon receiving the multiplexed signal, frequency index information is obtained from the envelope of the power spectrum of the multiplexed signal, and the obtained frequency A communication method characterized in that frequency synchronization is performed using index information. 16. A transmission method for transmitting information using a multiplexed signal that has been subjected to orthogonal frequency division multiplexing to a plurality of subcarriers, wherein the multiplexed signal is transmitted on a frequency axis of the multiplexed signal. Transmitting the frequency index information indicating the position of the multiplexed signal using the frequency dependence of the envelope of the power spectrum of the multiplexed signal. 17. A frequency control method for frequency-synchronizing a multiplexed signal orthogonally frequency-division multiplexed to a plurality of subcarriers, comprising: converting a time axis waveform of the received multiplexed signal into a frequency domain; From the frequency dependence of the spectrum distribution obtained by converting to, the center frequency of the spectrum distribution is obtained, and the difference between the center frequency of the spectrum distribution and a predetermined reference frequency is reduced. A frequency control method characterized by changing a frequency of a multiplexed signal before being converted to a frequency domain.