JPH11136208A - Frequency controller, receiver and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure synchronization of frequency by sampling respectively detection axis signals which are orthogonal to each other, providing a predetermined frequency dependence on a metric distribution obtained by discrete Fourier transform and decreasing a difference between total sum of power of the metrics with frequencies higher than a reference frequency and total sum of power of the metrics with frequencies lower than the reference frequency. SOLUTION: A recovery carry generating section 119 oscillates two recovery carriers X, Y with a phase difference of 90 degrees, and a frequency variable oscillator 1160 changes the oscillating frequency according to an AFC signal received from a frequency shift detection section 1300. A discrete Fourier transform section 1200 samples I and Q phase signals respectively, at sampling points whose number is more than number of subcarriers included in an OFDM signal and applies discrete Fourier transform to them. The frequency deviation detection section 1300 receives a metrics obtained by the discrete Fourier transform section 1200 and obtains a frequency difference from the OFDM signal and conducts processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency control device, a receiving device, and a communication device for frequency synchronization with a multiplexed signal subjected to orthogonal frequency division multiplexing. The present invention relates to a frequency control device, a reception device, and a communication device suitable for frequency synchronization with a multiplexed signal having a shift.

[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.

[0005] In the OFDM system, when a frequency difference occurs between the transmitting side and the receiving side, orthogonality with other subcarriers is destroyed during demodulation. This causes an error in data demodulated due to interference. 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.

[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. FIG. 8A shows the 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. 8 is obtained by delaying the signal of (1) of FIG. 8 by an effective symbol period. (3) in FIG.
Is a result obtained by multiplying the signals of (1) and (2) to obtain a moving average of the guard period width (Ng samples) to obtain the correlation between the two signals. Since Gn and Gn 'have 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 cycle with one subcarrier interval 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. 9, when an error signal of δ1 is obtained, in addition to the point A, the points B and C correspond. Therefore, even if the true normalized frequency offset is OA, it cannot be distinguished from offsets OB, OC, 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.

However, in OFDM, since the interval between subcarriers is generally set to be small, it is difficult to suppress the frequency difference to less than 1/2.

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, the relative speed between the transmitting side and the receiving side, the above Doppler shift,
There is a problem that it is limited to a case where the distance is less than 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, the frequency deviation of the OFDM signal is
It is a first object of the present invention to provide a frequency control device capable of specifying this shift amount and synchronizing the frequency even when the distance is equal to or longer than 1/2 of the subcarrier interval.

It is a second object of the present invention to provide a frequency control device capable of detecting a frequency shift of an OFDM signal that does not include a guard period and performing frequency synchronization.

It is a third object of the present invention to provide a receiving apparatus and a communication apparatus suitable for a case where the relative distance between the transmitting side and the receiving side changes and a Doppler shift of 1/2 or more of the subcarrier interval occurs. .

[0019]

According to a first aspect of the present invention, there is provided a multiplexed signal obtained by orthogonal frequency division multiplexing on a plurality of subcarriers, in order to achieve the first and second objects. A frequency control device for frequency-synchronizing the multiplexed signal with orthogonal detection means for orthogonally detecting the multiplexed signal to obtain a first detection axis signal and a second detection axis signal orthogonal to each other; Discrete Fourier for sampling each time axis waveform of the axis signal at a predetermined sampling frequency, and performing discrete Fourier transform of the sampled data to obtain a plurality of metrics distributed in the frequency domain. A power distribution of the multiplexed signal so that the distribution of the metrics obtained by the discrete Fourier transform has a predetermined frequency dependency. Power conversion means for changing, and a difference between a sum of powers for metrics at frequencies higher than a predetermined reference frequency and a sum of powers for metrics at frequencies lower than the reference frequency is calculated. And an arithmetic control unit for giving an instruction to change the frequency so that the frequency is reduced to the frequency changing unit, and changing the frequency of the signal input to the discrete Fourier transform unit in accordance with the instruction generated by the arithmetic control unit. A frequency control device comprising:

According to a second aspect of the present invention, there is provided a receiving apparatus for receiving a multiplexed signal subjected to orthogonal frequency division multiplexing, the high frequency signal including the multiplexed signal. And a band-pass filter unit for selecting a predetermined frequency band from the received high-frequency signal, quadrature detection of the frequency-converted signal using a reproduction carrier, discrete Fourier transform, and the reproduction carrier A frequency control unit for operating and synchronizing the frequency of the frequency, a demodulation unit for demodulating the data subjected to the discrete Fourier transform, and an output unit for outputting the demodulated signal, A frequency control unit is provided using the frequency control device according to the first aspect, and a receiving device is provided.

According to a third aspect of the present invention, in a communication apparatus for communicating using a multiplexed signal subjected to orthogonal frequency division multiplexing, a carrier wave is orthogonalized by data indicated by an input signal. 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 receiver is
A communication device characterized by being configured using the receiving device according to the second aspect is provided.

[0022]

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 FIG.

In FIG. 1, a frequency control device 1000
Are a quadrature detector 1100 and a discrete Fourier transformer 120
0 and a frequency deviation detection unit 1300.

The quadrature detector 1100 receives the OFDM signal and obtains two orthogonal detection axis signals 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 detector 1100 includes, for example, a divider 1150 for dividing the received signal into two signals,
A reproduction carrier generator 1119 for oscillating the two reproduction carriers X and Y having a phase difference of two degrees, and the reproduction carrier X and the signal Y are added to the two distributed signals.
Multipliers 1107A, 1107 for respectively multiplying
107B.

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 above-described discrete Fourier transform unit 1200 performs the OF
At the sampling points larger than the number of subcarriers included in the DM signal, the I-phase signal and the Q-phase signal are respectively sampled, and these are subjected to discrete Fourier transform. The discrete Fourier transform unit 1200
Is, for example, two A / D (Analog to Digital) converters 1208A and 1208B, and a DFT (Discrete Fourier Transform;
(Discrete Fourier transform) circuit 1209. In the DFT circuit 1209, as a calculation algorithm for executing the discrete Fourier transform, for example,
The calculation may be performed in accordance with the definition formula of DFT, or a fast Fourier transform (FFT) may be used. By calculating using FFT,
DFT calculation can be performed at high speed. DFT circuit 1
209 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 generating unit 1350 for generating an ncy control (automatic frequency control) signal.

The control signal generator 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 given. In this way, it is possible to generate an AFC signal indicating a frequency change amount according to the calculation result.

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 the direction thereof may be changed according to the result of the calculation. By setting the magnitude of the change amount to a constant value, the reproduction carrier generator 1119 in the signal generator 1350 and the quadrature detector 1100
Can be simply configured.

In the present embodiment, the quadrature detector 11
Although the mode of changing the frequency of the reproduction carrier at 00 has been described, the mode of changing the frequency is not limited to this. For example, when a frequency converter 3000 for converting the received OFDM signal into an intermediate frequency is provided at a stage preceding the quadrature detector 1100, the AFC signal is supplied to the frequency converter, and the frequency is converted by the frequency converter. Can be changed.

Next, the operation of the frequency control device configured as described above will be described with reference to FIGS.

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

As shown in FIG. 2A, the baseband of the OFDM signal has a time axis waveform on which a plurality of subcarriers having different frequencies are superimposed. FIG. 2 (a)
OFD demultiplexed into 24 subcarriers
Although the M signal is illustrated, it is needless to say that the number of subcarriers is not limited to this.

The baseband of the OFDM signal has a spectrum shown in FIG. 2B in the frequency domain. This corresponds to the Fourier transform of the time axis waveform shown in FIG. In FIG. 2B, 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 of 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. 1), 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 corresponding to each of the number of frequency slots corresponding to the number NS of the sampling points (sampling points). Among the NS metrics Z, in addition to the effective metrics corresponding to the number of subcarriers NC, the number of sampling points exceeding the number of subcarriers NOS (= NS−
NC). 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, NC
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 Zi is represented by (ai + jbi).
As a result of the operation of the discrete Fourier transform, the metric {Zi} (i = 1, 2, 3, 3) of the number of sampling points NS
.., NS), two series of data {ai}, {bi}
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, 15
Thirty-six valid metrics and 512 invalid metrics are obtained.

By performing sampling with a power of two, the effect of speeding up the DFT operation by FFT can be improved.

Next, in the frequency deviation detecting section 1300, an arithmetic processing for obtaining a difference between the metric distribution {ai + jbi} obtained by the discrete Fourier transform section 1200 and a predetermined distribution is performed. An AFC signal is generated according to the result of the above.

As an arithmetic process for obtaining the difference, for example, a power distribution {Pi} is obtained from a metric distribution {Zi}, and a frequency corresponding to the distribution center of the power distribution {Pi} is determined based on a predetermined reference. The difference from the frequency can be determined. Power P, 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)

Next, the details of the arithmetic processing performed by the frequency deviation detecting section 1300 will be described.

In this embodiment, a power conversion for changing the power distribution of the multiplexed signal is performed so that the envelope of the power spectrum of the metric obtained from the received OFDM signal has a predetermined frequency dependency. Is performed by power conversion means. In this power conversion, the power of each subcarrier is changed such that the envelope of the power spectrum has an M-shaped shape in which the power decreases as the distribution approaches the distribution center.

In the present embodiment, each subcarrier of the power spectrum is numbered (i) in order so that the envelope of the power spectrum has an M-shaped shape in which the power decreases as it approaches the distribution center. The absolute value (| ci |) of the difference between the reference number (c) and the number (i) assigned to each subcarrier to the power of each subcarrier, with the subcarrier at the center of the envelope distribution as the reference number (c).
To change the power of each subcarrier.

The center of gravity of the power distribution thus obtained is obtained, and the frequency of this center of gravity is compared 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. 1).

Since the power conversion means changes the power distribution of the multiplexed signal so that the power decreases as it approaches the center of the distribution, it is possible to improve the accuracy of the frequency of the center of gravity when the center of gravity of the power distribution is obtained. it can. Therefore, the accuracy of the frequency difference from the reference frequency is increased, and a more accurate AFC signal can be obtained.

The details of the arithmetic processing performed by the arithmetic processing unit 1322 (see FIG. 1) will be described below.

First, a discrete Fourier transform unit 1200 (FIG. 1)
) Distribution of NS metrics obtained in） Ai +
For jBi｝ (i | 1, 2, 3,..., NS), the total sum WL 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; The sum WH of the powers of the metrics belonging to the frequency slots (C to NS) having a higher frequency than the frequency slot is 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 the effective metrics that is theoretically expected can be selected. At this time, the reference frequency is C = NS / 2.

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

[0054]

(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,

[0056]

(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, C = 2048/2 = 1024 can be selected.

Further, the influence of the transmission path can be avoided by using a signal whose power distribution is known. That is, from the metric {Ani + jBni} for the OFDM signal acquired in the null symbol period and the metric {Asi + jBsi} for the signal symbol period,

[0059]

(Equation 4)

And this metric is used in the calculation.

Further, the sum Wt of the powers 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

[0062]

(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. 1) 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 S21, discrete Fourier transform is performed on the received signal for each symbol period using FFT.

The metrics obtained during the symbol period are standardized by the metrics obtained from the null symbols (S2).
2).

In step S23, the metrics standardized in step S22 are divided into two regions with the reference frequency as a boundary, and the sum of the power in each region is calculated. At this time, if there is no frequency difference, the divided 2
The two regions are symmetric as shown in FIG. Further, when there is a frequency difference, for example, when a signal shifted to the low frequency side is received, the two regions are asymmetric as shown in FIG. Then, the difference between the power sums in the two regions is obtained.

If the received signal is affected by fading or the like, the frequency shift is corrected in step S24.

Next, a second 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 the first embodiment.

In FIG. 5, a receiving apparatus 200 includes an input terminal 1, a band-pass filter 2, an amplifier 3, a multiplier 4, a SAW filter 5, an intermediate frequency amplifier 6,
Multipliers 7A and 7B, A / D converters 8A and 8B, FF
A T circuit 9, an AGC circuit 10, a synchronization detection circuit 11,
Differential demodulation circuit 12, first local oscillator 18, second local oscillator 19, first reference oscillator 20A, second reference oscillator 20B, timing circuit 21, frequency error calculation circuit 22, time axis detection Circuit 23 and phase error detection circuit 2
4. The multipliers 7A and 7B and the second local oscillator 19 constitute a quadrature detection circuit.

In the receiving apparatus 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.

The multipliers 7A and 7B are connected to the second local oscillation circuit 1
From 9, a two-phase local signal having a phase difference of 90 degrees is input and multiplied by the 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, as for the output of the FFT circuit 9, the metric is input to the frequency error calculating circuit 22, where the above-described calculation is performed and the frequency difference component is converted to the first signal as the AFC signal.
It is supplied to the reference oscillator 20A. Further, the differential demodulation circuit 12
, An AFC signal for controlling the phase error detected by the phase error detection circuit 24 within ± 1/2 of the subcarrier interval is also supplied to the first reference 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 third embodiment of the present invention will be described with reference to FIG. In this embodiment, OFDM
It is an example of a communication device for performing communication using a signal.

Referring to FIG. 6, 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 the incoming electromagnetic waves, a frequency converting section 3000 for converting the signal having the selected band to an intermediate frequency, and a detecting 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 device according to the first embodiment. 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 Conversion unit 12
00 and a frequency deviation detection unit 1300 for detecting a frequency deviation using a signal subjected to discrete Fourier transform.

The output section 5000 includes, for example, an audio output device for outputting audio 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 configured 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 housing, 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.

The communication device 9001 communicates with another device 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 when a frequency difference occurs between the transmitting side and the receiving side, communication can be performed in frequency synchronization.

[0088]

According to the present invention, the synchronous detection frequency for demodulating the received OFDM signal is several times the frequency interval of the multiplexed carrier obtained by performing the discrete Fourier processing on the received signal, and a frequency difference occurs. However, a frequency control device capable of accurately detecting a frequency difference and performing frequency synchronization is provided.

Thus, information can be transmitted even when a difference occurs between the reference frequencies on the transmitting side and the receiving side. Further, a frequency control device capable of accurately detecting a Doppler shift and performing frequency synchronization even when a Doppler shift occurs due to a relative movement between a transmitting side and a receiving side is provided.

Further, it is possible to constitute a receiving device on which the above-mentioned frequency control device is mounted, and to provide a receiving device capable of stably receiving a broadcast by OFD. As such a broadcast, for example, Eureka 1
45 system DAB broadcasting.

Further, it is possible to constitute a communication device equipped with the above frequency control device. Thereby, frequency synchronization in a digital telephone or the like can be made more stable. 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, even in the case where a frequency difference occurs due to Doppler shift in communication by a mobile body, communication can be performed in a frequency-synchronized state.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a frequency control device to which the present invention is applied.

FIG. 2 is an explanatory diagram showing an OFDM signal, wherein (a)
It is a waveform diagram showing a structure in a time domain, and (b) is a spectrum diagram showing a structure in a frequency domain.

FIGS. 3A and 3B are explanatory diagrams schematically showing a power distribution of metrics divided into two regions, wherein FIG. 3A shows a distribution when there is no frequency difference, and FIG. 3B shows a distribution when there is a frequency difference.

FIG. 4 is a flowchart showing a calculation procedure according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a receiving apparatus to which the present invention is applied.

FIG. 6 is a block diagram showing a communication device to which the present invention is applied.

FIG. 7 is a block diagram showing another aspect of the communication device to which the present invention is applied.

FIG. 8 is an explanatory diagram showing correlation of signals used for frequency difference detection in a conventional frequency control method.

FIG. 9 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.

Claims (5)

[Claims] 1. A frequency control apparatus for frequency-synchronizing a multiplexed signal orthogonally frequency-division-multiplexed to a plurality of subcarriers, comprising: a quadrature detector for detecting the multiplexed signal; Quadrature detection means for obtaining a second detection axis signal; sampling the time axis waveform of each of the two detection axis signals at a predetermined sampling frequency; and discretizing the sampled data. A discrete Fourier transform unit for performing a Fourier transform to obtain a plurality of metrics distributed in a frequency domain; and the multiplexing so that the distribution of the metrics obtained by the discrete Fourier transform unit has a frequency dependency specified in advance. Power conversion means for changing the power distribution of the digitized signal, and a metric having a frequency higher than a predetermined reference frequency. And calculating a difference between the sum of the powers of the power sources and the sum of the powers of the metrics having a frequency lower than the reference frequency, and giving an instruction to the frequency changing means to change the frequency so that the obtained difference becomes smaller. Means for changing a frequency of a signal input to the discrete Fourier transform means in accordance with an instruction generated by the arithmetic control means. 2. The frequency control device according to claim 1, wherein the power conversion means changes the power of each subcarrier such that the power decreases as the envelope of the power spectrum approaches the distribution center. Characteristic frequency control device. 3. The frequency control device according to claim 2, wherein the power conversion means assigns a number to each sub-carrier of the power spectrum in order, and uses the number of the sub-carrier at the center of the envelope distribution as a reference number. A frequency controller characterized by multiplying the power of a subcarrier by the absolute value of the difference between the number assigned to each subcarrier and a reference number. 4. A band for receiving a high-frequency signal including a multiplexed signal and selecting a predetermined frequency band from the received high-frequency signal in a receiving apparatus for receiving a multiplexed signal subjected to orthogonal frequency division multiplexing. 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 4. A frequency control device according to claim 1, further comprising: a demodulation unit for demodulating the demodulated data; and an output unit for outputting the demodulated signal. A receiving device comprising: 5. A communication apparatus for communicating using a multiplexed signal subjected to orthogonal frequency division multiplexing, wherein a carrier wave is orthogonal frequency division multiplex modulated by data indicated by an input signal and a multiplexed signal is transmitted. 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, wherein the receiving unit is configured as described in claim 4. A communication device comprising a receiving device.