JP2007124303A - Frequency control device, frequency control method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency control device etc. which is used for easily correcting the frequency of a subcarrier even if a large shift occurs in the frequency of the subcarrier of signals subjected to frequency-division multiplexing. <P>SOLUTION: When OFDM (Orthogonal Frequency Division Multiplexing) signals where preamble signals containing pilot signals formed of unmodulated subcarrier are contained are supplied to a frequency converting unit 6, the frequency converting unit 6 mixes them with frequency correction signals, furthermore a Fourier transformation unit 7 subjects the mixed signals to Fast Fourier Transform and generates two or more FFT (Fast Fourier Transform) output data. A frequency control volume output unit 10 specifies the FFT output data that represent the pilot signals on the basis of the power of a component represented by each FFT output data and decides a coarse adjustment volume so as to enable the pilot signals to be represented by the FFT data located at a right position. On the basis of a phase change volume in the pilot signals, a fine adjustment volume is decided so as to change a component corresponding to the pilot signals to an original frequency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a frequency control device, a frequency control method, and a program, and more particularly, to a frequency control device, a frequency control method, and a program for generating a signal that follows a carrier frequency of a modulated wave.

  In recent years, a technology of frequency division multiplexing that superimposes and transmits a large number of modulated waves with different subcarrier frequencies has been widely used. In particular, OFDM (Orthogonal Frequency Division Multiplexing), which is a type of this technology, is used for each subcarrier. This technology multiplexes each modulated wave with orthogonality between them, and has the advantage that the interval between modulated waves in the transmission band can be narrowed while suppressing the interference between modulated waves, so it is widely spread is doing.

In order to receive an OFDM signal generated by the OFDM technique and accurately demodulate each modulated wave in the OFDM signal, it is necessary to accurately specify the subcarrier frequency of each modulated wave. However, the subcarrier frequency of each frequency in the OFDM signal transmitted through space or the like usually varies due to the Doppler effect or the like. For this reason, an apparatus that demodulates an OFDM signal needs to be able to generate a signal that follows fluctuations in subcarrier frequency in order to perform frequency conversion and the like. Therefore, a technique for generating a signal that follows a fluctuating subcarrier frequency has been considered (see, for example, Patent Document 1).
JP 2001-308821 A

  However, the frequency of the subcarrier has a large shift exceeding a half of the frequency interval between the subcarriers due to, for example, the secular change of the characteristics of the crystal oscillator of the crystal oscillator that generates the subcarrier. There may be. On the other hand, in the technique of Patent Document 1, when the deviation of the subcarrier frequency becomes such large, it is necessary to obtain an average of a very large number of symbols in order to correct the deviation accurately. There is. Therefore, the technique of Patent Document 1 cannot easily correct a large shift in subcarrier frequency.

  The present invention has been made in view of such a conventional problem, and a frequency for easily correcting even if there is a significant shift in the frequency of subcarriers of a frequency division multiplexed signal. It is an object to provide a control device, a frequency control method, and a program.

In order to achieve this object, a frequency control device according to the first aspect of the present invention provides:
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. Frequency correction means for generating a corrected modulated wave composed of components, and
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the coarse adjustment amount from the previous frequency when the coarse adjustment amount is determined;
It is characterized by that.

  According to such a frequency control device, even if there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

Moreover, the frequency control device according to the second aspect of the present invention provides:
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. Frequency correction means for generating a corrected modulated wave composed of components, and
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. Fine adjustment amount determining means for determining the fine adjustment amount in a range less than one half of the subcarrier interval;
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount,
It is characterized by that.

  Even with such a frequency control device, when there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

  The modulated wave may include a preamble portion consisting only of the pilot signal. In this case, the coarse adjustment amount determination means may identify a frequency component including a component corresponding to the pilot signal from the predetermined frequency components included in the preamble portion of the corrected modulated wave. That's fine.

The modulated wave may include a plurality of the pilot signals,
In this case, the rough adjustment amount determining means
Means for identifying the sum of the intensities of the components belonging to the combination of a plurality of components whose relative positional relationship on the frequency axis is the same as that of the plurality of pilot signals among the corrected modulated waves; ,
Means for specifying a combination in which the specified total reaches a predetermined first threshold, and specifying a component belonging to the specified combination as a frequency component including a component corresponding to the pilot signal; It may be a thing.
With such a configuration, the frequency is corrected more accurately.

  The coarse adjustment amount determining means obtains an average intensity of a predetermined frequency component of the corrected modulated wave for a period of a plurality of symbols of the corrected modulated wave, and determines each predetermined frequency based on the calculated average. Means may be provided for identifying a frequency component including a component corresponding to the pilot signal from among the components. Even in such a configuration, the frequency is corrected more accurately.

  The coarse adjustment amount determining means, for example, out of the predetermined frequency component of the corrected modulated wave, the intensity has reached a predetermined second threshold, and the intensity of a component adjacent on the frequency axis is A component that does not reach the second threshold is specified as a frequency component including a component corresponding to the pilot signal, and the difference between the frequency of the specified component and the frequency that the pilot signal should originally take is roughly adjusted. What is necessary is just to determine with quantity.

  In addition, the coarse adjustment amount determination unit, for example, is adjacent on the frequency axis among the predetermined frequency components of the corrected modulated wave, and the intensity reaches a predetermined second threshold value. 2 components are identified as frequency components including components corresponding to the pilot signal, and the difference between the intermediate value of the frequencies of the two identified components and the frequency that the pilot signal should take is roughly adjusted. By determining the quantity, the modulated wave may be corrected by a unit of half of the interval between the subcarriers.

The frequency control method according to the third aspect of the present invention is
A frequency correction signal generating step for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A frequency correction step for generating a corrected modulated wave composed of components, and
In the frequency correction signal generation step,
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. Thus, the coarse adjustment amount is determined by a unit of 1/2 of the subcarrier interval of the modulated wave,
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated.
It is characterized by that.

  According to such a frequency control method, even if there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

The frequency control method according to the fourth aspect of the present invention is:
A frequency correction signal generating step for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A frequency correction step for generating a corrected modulated wave composed of components, and
In the frequency correction signal generation step,
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. Thus, the coarse adjustment amount is determined by a unit of 1/2 of the subcarrier interval of the modulated wave,
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. A fine adjustment amount is determined in a range less than one half of the subcarrier interval of
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount;
It is characterized by that.

  Even with such a frequency control method, when there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

A program according to the fifth aspect of the present invention is
Computer
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A program for causing a frequency control unit configured to generate a corrected modulated wave composed of components and a frequency control device configured to include:
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the coarse adjustment amount from the previous frequency when the coarse adjustment amount is determined;
It is characterized by that.

  According to the computer that executes such a program, even if there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

A program according to the sixth aspect of the present invention is
Computer
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A program for causing a frequency control unit configured to generate a corrected modulated wave composed of components and a frequency control device configured to include:
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. Fine adjustment amount determining means for determining the fine adjustment amount in a range less than one half of the subcarrier interval;
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount,
It is characterized by that.

  Even with a computer that executes such a program, if there is a significant shift in the frequency of the modulated wave, this shift is accurately detected and the frequency is corrected.

  According to the present invention, a frequency control device, a frequency control method, and a program for realizing easy correction even when there is a significant shift in the frequency of subcarriers of a frequency division multiplexed signal are realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking as an example a demodulator that demodulates a plurality of QPSK (Quadrature Phase Shift Keying) modulated waves multiplexed by an OFDM (Orthogonal Frequency Division Multiplexing) technique. To do.

FIG. 1 is a diagram showing a configuration of a demodulation device according to an embodiment of the present invention.
As shown in the figure, this demodulator includes an antenna 1, a local oscillator 2, a phase shifter 3, mixers 4I and 4Q, A / D (Analog-to-Digital) converters 5I and 5Q, Frequency conversion unit 6, Fourier transform unit 7, power calculation unit 8, phase difference calculation unit 9, frequency control amount output unit 10, NCO (Numerically Controlled Oscillator) 11, demodulation unit 12 It is made up of.

  The antenna 1 receives the OFDM signal and supplies the OFDM signal to the mixing units 4I and 4Q. An OFDM signal received by the antenna 1 is composed of a plurality of QPSK modulated waves in which subcarriers are arranged at a predetermined frequency interval. Each of these subcarriers has a predetermined frequency, and these subcarriers are orthogonal to each other.

  The head portion of this OFDM signal constitutes a preamble signal. The preamble signal is a signal included in the OFDM signal for the purpose of being used for AFC (automatic frequency control), channel estimation, and the like.

  It is assumed that the preamble signal has a spectrum as schematically shown in FIG. That is, the preamble signal is composed of only one or more pilot signals corresponding to unmodulated subcarriers of a predetermined one or more QPSK modulated waves in the OFDM signal including the preamble signal. It is assumed that the position where the pilot signal occupies on the frequency axis is known, and when the preamble signal includes a plurality of pilot signals, the frequency of these pilot signals is at least twice the interval of the subcarriers. Suppose that

  FIG. 2 shows a case where the OFDM signal is composed of 30 QPSK modulated waves, and among them, the relative positions on the frequency axis are (−12), (−4), (+4) and (+12). This is a schematic illustration of the spectrum of the preamble signal in the case where the preamble signal is composed of a total of four pilot signals corresponding to subcarriers when the wave is not modulated.

  In FIG. 2, the relative positions occupied by the first, second,..., 15th, 16th,. (−15), (−14),..., (−1), (+1),... (+14) and (+15) (in other words, the frequency at the relative position (0) is sub Shall not be occupied by the carrier). Then, when the power of each pilot signal in the preamble signal is “1.0”, the relative positions (−15), (−14),... (−1), (+1),. The power of the signals (+14) and (+15) is represented by the symbol “*”.

The local oscillating unit 2 is configured by a known oscillation circuit or the like, generates a local oscillation signal having a predetermined frequency, and supplies it to the phase shift unit 3 and the mixing unit 4I.
The phase shift unit 3 is composed of a known phase shift circuit or the like, and generates a signal corresponding to the phase of the local oscillation signal supplied from the local oscillation unit 2 delayed by (π / 2) [radians]. To the mixing unit 4Q.

The mixing units 4I and 4Q have substantially the same configuration, and each is configured by, for example, a known multiplication circuit.
The mixing unit 4I mixes the OFDM signal including the preamble signal supplied from the antenna 1 and the local oscillation signal supplied from the local oscillation unit 2, thereby generating a component having a frequency corresponding to the difference between the two frequencies. Then, it is supplied to the A / D converter 5I as a signal corresponding to the I signal in QPSK.
The mixing unit 4Q receives the OFDM signal including the preamble signal supplied from the antenna 1 and the signal supplied from the phase shift unit 3 (that is, a local oscillation signal whose phase is delayed by (π / 2) [radians]). By mixing, a component having a frequency corresponding to the difference between the two frequencies is generated and supplied to the A / D conversion unit 5Q as a signal corresponding to the Q signal in QPSK.

The A / D converters 5I and 5Q have substantially the same configuration, and each is configured by, for example, a known A / D converter.
The A / D conversion unit 5I converts the signal supplied from the mixing unit 4I into a digital signal and supplies it to the frequency conversion unit 6. The A / D conversion unit 5Q converts the signal supplied from the mixing unit 4Q into a digital signal and supplies it to the frequency conversion unit 6.

The frequency converter 6, Fourier transformer 7, power calculator 8, phase difference calculator 9, frequency control amount output unit 10, NCO 11, and demodulator 12 all have a DSP (Digital Signal Processor) or CPU (Central Processing Unit). ) And a memory for storing a program to be executed by the processor.
It should be noted that a single processor performs some or all of the functions of the frequency conversion unit 6, Fourier transform unit 7, power calculation unit 8, phase difference calculation unit 9, frequency control amount output unit 10, NCO 11, and demodulation unit 12. It may be.

  The frequency converter 6 is supplied with a digital I signal from the A / D converter 5I, is supplied with a digital Q signal from the A / D converter 5Q, and is supplied with a frequency correction signal described later from the NCO 11. Then, a signal having a frequency corresponding to the difference (or sum) between the frequency of the supplied I signal and the frequency of the frequency correction signal (that is, the frequency of the I signal is shifted by the frequency of the frequency correction signal). Is supplied to the Fourier transform unit 7. In addition, a signal having a frequency corresponding to the difference (or sum) between the frequency of the supplied Q signal and the frequency of the frequency correction signal (that is, a signal obtained by shifting the frequency of the Q signal by the frequency of the frequency correction signal). Generated and supplied to the Fourier transform unit 7.

  The Fourier transform unit 7 is a 1 representing the phase of a predetermined frequency component constituting the spectrum of the OFDM signal (including the preamble signal) represented by the set of two signals supplied from the frequency transform unit 6. A total of n FFT output data from the nth to the nth is generated by a fast Fourier transform (FFT) technique. Then, the generated n FFT output data are supplied to the phase difference calculation unit 9 and the demodulation unit 12. Note that n is an integer greater than or equal to the number of subcarriers in the OFDM signal, and the (j + 1) th FFT output data has a frequency corresponding to one subcarrier interval from the frequency component in which the jth FFT output data represents the phase. Represents a phase of a high frequency component (where j is an integer of 1 to less than n). If these n FFT output data correctly capture the component corresponding to the frequency of the subcarrier included in the OFDM signal received by the demodulator, the baseband signal of each modulated wave included in the OFDM signal Is a signal corresponding to.

  The NCO 11 performs frequency correction of a frequency corresponding to the sum of a predetermined initial value (for example, 0 Hz) or the frequency of the frequency correction signal currently supplied by itself and the correction amount instructed by the frequency control amount output unit 10. A signal is generated and continuously supplied to the frequency converter 6.

  The phase difference calculation unit 9 specifies the change amount of the phase between the current symbol interval and the previous symbol interval for the predetermined FFT output data supplied from the Fourier transform unit 7, and specifies the specified change amount Based on the above, data (phase difference data) representing the amount of change of the phase of the component corresponding to the pilot signal per cycle is sequentially generated. Then, the generated phase difference data is sequentially supplied to the frequency control amount output unit 10.

  Note that the FFT output data used for generating the phase difference data may be a component corresponding to a subcarrier at a predetermined relative position in an OFDM signal including a preamble signal on which a pilot signal for phase comparison is superimposed, for example. . If the FFT output data captures the phase of this component, the phase difference data generated based on the FFT output data has a substantially constant value. That is, for example, assuming that the period for specifying the phase of the FFT output data is synchronized with the period of the pilot signal for phase comparison, and if the component corresponding to the FFT output data exactly matches the pilot signal for phase comparison, Since the amount of phase change is 0, the value of the phase difference data is 0, and even if they do not exactly match, the amount of phase delay or advance per cycle is a substantially constant value.

  For the FFT output data supplied from the Fourier transform unit 7 that represents the phase of the preamble signal, the power calculation unit 8 uses, for example, the predetermined frequency component of the preamble signal based on the amplitude of the corresponding FFT output data. N data (power data) representing power is sequentially generated and supplied to the frequency control amount output unit 10 in sequence. Hereinafter, power data generated based on the kth FFT output data is referred to as kth power data.

  When the frequency control amount output unit 10 is supplied with n pieces of power data from the power calculation unit 8 and is supplied with phase difference data from the phase difference calculation unit 9, the frequency control amount output unit 10 described above is based on the power data and the phase difference data. A correction amount is determined, and the NCO 11 is instructed.

Specifically, the frequency control amount output unit 10 determines the correction amount according to, for example, the procedure shown in FIG.
That is, the Fourier transform unit 7 performs FFT to generate FFT output data (FIG. 3, step S1), and the power calculation unit 8 generates power of a predetermined frequency component of the preamble signal based on the FFT output data. When n power data items are generated and supplied to the frequency control amount output unit 10 (step S2), the frequency control amount output unit 10 first causes a peak representing the pilot signal to appear correctly in the FFT output data at a predetermined position. Is determined based on the power data (step S3). If it is determined that it is not correctly represented, the process proceeds to step S4. If it is determined that it is represented, the process proceeds to step S5.

  The determination in step S3 is, for example, “generated from other FFT output data in which the value of the power data generated from the corresponding FFT output data has reached a predetermined threshold and the FFT output data is adjacent in order. This is done by determining whether or not the value of the power data has not reached the threshold value.

A specific example of the determination method in step S3 will be described with reference to FIGS. Assume that the spectrum of the actually transmitted preamble signal is as shown in FIG. 2, and the FFT output data generated by the Fourier transform unit 7 is (−15) th to (+15) th in order from the one representing the low frequency component. It is assumed that there are 31 items in total. Further, it is assumed that the pilot signal power is 1.0 and the above-described threshold is 0.3.
In this case, the (-15) th FFT output data indicates the phase of the component at the relative position (-15), the (-14) th FFT output data indicates the phase of the component at the relative position (-14), and so on. When the x-th (x is an integer) FFT output data correctly represents the phase of the component of the relative position x of the preamble signal, the power value indicated by each power data generated from each FFT output data is For example, as shown in FIG. 4 (a), only a value obtained from the (-12) th, (-4) th, (+4) th and (+12) th FFT output data exceeds a threshold value. Thus, the value obtained from other FFT output data is almost zero. In this case, in step S3, the frequency control amount output unit 10 determines that the FFT output data that should represent the phase of the pilot signal correctly represents the phase of the pilot signal.

  On the other hand, the correspondence between the FFT output data and the component in the preamble signal is shifted by about twice the subcarrier interval, and the phase of the component at the relative position x of the preamble signal is represented by the (x + 2) th FFT output data. Assuming that it is in the state, the power value indicated by each power data generated from each FFT output data is, for example, (−10) th, (−2), as shown in FIG. Only the values obtained from the () th, (+6) th and (+14) th FFT output data are large values exceeding the threshold value, and the values obtained from the other FFT output data are almost zero. That is, the value of the power data obtained from the (−12) th, (−4) th, (+4) th, and (+12) th FFT output data that should originally represent the phase of the pilot signal is approximately 0. Therefore, in this case, in step S3, the frequency control amount output unit 10 determines that the peak of the pilot signal does not appear correctly in the FFT output data at a predetermined position.

  The correspondence between the FFT output data and the components in the preamble signal is shifted by about 2.5 times the subcarrier interval, and the components at the relative position x of the preamble signal are (x + 2) th and (x + 3) th. 4C, for example, the power value indicated by each power data generated from each FFT output data is shown in FIG. 4C. Thus, (-10) th, (-9) th, (-2) th, (-1) th, (+6) th, (+7) th, (+14) th and (+15) th FFT outputs The value obtained from the data is a large value exceeding the threshold value, and the other minute values are values that do not reach the threshold value. Accordingly, in this case as well, in step S3, the frequency control amount output unit 10 determines that the peak of the pilot signal does not appear correctly in the FFT output data at the predetermined position.

  The determination in step S3 is whether or not the value of the power data generated from the FFT output data (and the FFT output data adjacent thereto) that should represent the phase of the pilot signal individually reaches the above threshold value. Instead, it is determined whether or not the total power indicated by the power data generated from the FFT output data (and the FFT output data adjacent thereto) that should represent the phase of each pilot signal has reached a predetermined threshold value. It may be done by doing.

When performing the determination in step S3 using the sum of the power data, the frequency control amount output unit 10 has the same relative positional relationship on the frequency axis as the pilot signal, for example, from the set of FFT output data. Various combinations of those representing multiple components are identified.
For example, when the spectrum of each pilot signal in the preamble signal has an interval of 8 relative positions as shown in FIG. 2, the FFT output data generated by the Fourier transform unit 7 has a low frequency. If there are a total of 31 items from the (-15) th to the (+15) th in order from the component,
(A): (-15) th, (-7) th, (+1) th and (+9) th combination of FFT output data (B): (-14) th, (-6) th, (+2) (C): (−13) th, (−5) th, (+3) th and (+11) th FFT output data combination (D): (−12) ) Th, (-4) th, (+4) th and (+12) th FFT output data combinations (E): (-11) th, (-3) th, (+5) th and (+13) th Combination of FFT output data (F): (−10) th, (−2) th, (+6) th and (+14) th FFT output data combination (G): (−9) th, (−1) , (+7) th and (+15) th FFT outputs There are seven possible combinations of force data. Among these combinations, (D) is a combination of FFT output data that should originally represent the phase of the pilot signal.
In this case, for example, for the combination (D), the frequency control amount output unit 10 first obtains the sum of the values of the power data generated from the FFT output data belonging to the combination, and the obtained sum is a predetermined total value threshold value. It may be determined whether or not (for example, 2.0) has been reached. Then, when the sum obtained from the combination of (D) does not reach the total value threshold, it may be determined that the peak of the pilot signal does not appear correctly in the FFT output data at a predetermined position. On the other hand, when the total obtained from the combination of (D) has reached the threshold for total value, it is a combination of FFT output data adjacent to the FFT output data included in the combination of (D) (C) or (E ) Is further calculated, and if none of the calculated totals has reached the total value threshold, it is determined that the peak of the pilot signal appears correctly in the FFT output data at the predetermined position, and otherwise What is necessary is just to determine that it does not appear correctly.
When it is determined that the peak of the pilot signal does not appear correctly in the FFT output data at the predetermined position, the frequency control amount output unit 10 determines whether or not the sum of the power data values has reached the total value threshold value. The processing to be discriminated is shifted from the combination of (D) (for example, in the order of (E), (C), (F), (B), (G), (A), or (C), (E) , (B), (F), (A), (G)), and so on, until the corresponding combination is found. When a combination whose sum reaches the threshold for total value is found, the sum may be further calculated for the combination of FFT output data adjacent to the FFT output data included in the combination.
For example, assuming that the found combination is shifted to the high frequency side by about N times the subcarrier interval when viewed from the combination (D), all the sums obtained for the combinations adjacent to the found combination have reached the total value threshold. If not, it may be determined that the peak of the pilot signal appears at a position shifted from the original position to the high frequency side by about N times the interval between the subcarriers. On the other hand, if the total obtained for the combination that is adjacent to the found combination on the high frequency side (or on the low frequency side) has also reached the total value threshold, the peak of the pilot signal is the interval between the subcarriers from the original position. What is necessary is just to discriminate | determine that it has appeared in the position which shifted about (N + 0.5) times (or N-0.5 times) high frequency side.

  The determination in step S3 is obtained by averaging the power data values generated from the FFT output data (and the FFT output data adjacent thereto) that should represent the phase of the pilot signal over a plurality of symbol intervals. The average value obtained may be used instead of the value of the power data.

  When the process proceeds from step S3 to step S4, the frequency control amount output unit 10 should originally have an amount in which the correspondence relationship between the FFT output data and the component in the preamble signal is shifted, that is, the frequency correction signal generated by the NCO 11. The amount deviating from the frequency is specified in units of 0.5 times the subcarrier interval based on the power data. Then, a correction amount that cancels the specified deviation is determined, and the NCO 11 is instructed.

  Specifically, for example, the spectrum of the preamble signal is as shown in FIG. 2, and the FFT output data generated by the Fourier transform unit 7 starts from (−15) th to (+15) in order from the one representing the low frequency component. Assume that there are a total of 31 items up to the first, and that the power values indicated by the power data generated from the FFT output data are as shown in FIG. In this case, in step S4, the frequency control amount output unit 10 determines that the “(-12) th, (−4) th, (+4) th, and (+12) th” FFT output data should represent the phase of the pilot signal. However, since the correspondence relationship between the FFT output data and the component in the preamble signal is shifted by about twice the subcarrier interval, the (−10) th, (−2) th, (+6) th and It is determined that the (+14) th FFT output data represents the phase of the pilot signal. Then, the amount of deviation is specified as twice the subcarrier interval, and the correction amount is determined to be a value that is -2 times the subcarrier interval, and the NCO 11 is instructed.

Further, for example, the spectrum of the preamble signal is as shown in FIG. 2, and the FFT output data generated by the Fourier transform unit 7 is from (−15) th to (+15) th in order from the one representing the low frequency component. Assuming that there are a total of 31, the power values indicated by the power data generated from the FFT output data are as shown in FIG. In the case of FIG. 4 (c), the number of FFT output data indicating power exceeding the threshold is twice the number of pilot signals, and these FFT output data are paired adjacent to each other to form a pilot signal. And the same number of pairs.
In this case, in step S4, the frequency control amount output unit 10 reads “correspondence between the FFT output data and the components in the preamble signal where the (−12) th FFT output data should represent one phase of the pilot signal. Since the relationship is shifted by about 2.5 times the frequency subcarrier interval, the power indicated by the (−10) -th and (−9) -th FFT output data is erroneously caused by the pilot signal. It is determined that the condition is exceeded. Similarly, “the power peak that should originally appear at the (−4) th position is erroneously (−2) and (−1) th”, and “the power that should appear at the (+4) th position”. , And the peak of the power that should originally appear at the (+12) th position is erroneously displayed at the (+14) th and (+15) th positions, respectively. It is determined that Then, the amount of deviation is specified to be about 2.5 times the subcarrier interval, and the correction amount is determined to be a value of -2.5 times the subcarrier interval, and instructed to the NCO 11.

  When the process of step S4 ends, the frequency control amount output unit 10 waits for the Fourier transform unit 7 to perform the process of step S1 and the power calculation unit 8 to perform the process of step S2.

  On the other hand, when moving from step S3 to step S5, the frequency control amount output unit 10 obtains the phase difference data from the phase difference calculation unit 9, and the amount by which the frequency correction signal generated by the NCO 11 deviates from the frequency that should originally exist. Is specified in a range of less than 0.5 times the subcarrier interval based on the phase difference data and the power data supplied in step S2. Then, a correction amount that cancels the specified error is determined, and the NCO 11 is instructed. The frequency control amount output unit 10 then repeats the process of step S5 as needed.

In step S5, the frequency control amount output unit 10 specifically cancels the change in the phase difference indicated by the phase difference data supplied from the phase difference calculation unit 9, and sets the value of the phase difference data supplied thereafter. An amount that converges to a certain value may be specified as the correction amount.
For example, it is assumed that it is found from the phase difference data that the phase delay for each cycle of the FFT output data corresponding to the pilot signal is θ [degrees]. This indicates that the frequency of the pilot signal equivalent component represented by the phase difference data is lower by {(θ · Δf) / 360} [Hz] than the original frequency Δf [Hz] of the pilot signal. (Because the pilot signal consists of unmodulated subcarriers, the phase change rate is constant). Therefore, in this case, the frequency control amount output unit 10 may determine {− (θ · Δf) / 360} [Hz] as the correction amount.

  When the frequency control amount output unit 10 completes the processing up to step S4 in FIG. 3, the frequency of the frequency correction signal supplied to the frequency conversion unit 6 by the NCO 11 was supplied before the processing in FIG. 3 was started. A value obtained by adding the correction amount determined in step S4 to the frequency of the frequency correction signal. Thereafter, in step S5, a small correction within one half of the subcarrier interval is further added as needed.

5A to 5E are shifted when the frequency correction signal generated by the NCO 11 has the correct frequency that should be inherent and within the range of one subcarrier interval. It is a figure which shows distribution of the value of electric power data in various cases.
Specifically, the spectrum of the preamble signal is as shown in FIG. 2, and the FFT output data generated by the Fourier transform unit 7 is (−15) th to (+15) th in order from the one representing the low frequency component. FIG. 5A shows the distribution of power data values when the frequency of the frequency correction signal is correct, and specifically, the frequency of the frequency correction signal is the subcarrier interval. 5 (b) shows a case where it is shifted by 0.25 times, FIG. 5 (c) shows a case where it is shifted by 0.4 times, and FIG. 5 (d) shows a case where it is shifted by 0.5 times. However, FIG. 5E shows a case where the deviation is 0.75 times.

As shown in FIG. 5A, when there is no deviation in the frequency of the frequency correction signal, large peaks in the power data are the (-12) th, (−4) th, (+4) th and the original positions. It appears only at the four points corresponding to the (+12) th FFT output data.
On the other hand, when the frequency of the frequency correction signal has a deviation of less than 0.5 times the subcarrier interval, a large peak of power data also appears at these four points, which are the original positions, but FIG. ) And (c), there are significant peaks at positions corresponding to the (-11) th, (−3) th, (+5) th and (+13) th FFT output data adjacent to these four points. appear.
Further, when the frequency shift of the frequency correction signal is 0.5 times the interval between the subcarriers, the peak height of the power data is 4 points that are the original positions as shown in FIG. Each peak that appears is substantially equal to the peak at the above-described four points adjacent to the four points that are their original positions.
Further, when the frequency shift of the frequency correction signal exceeds 0.5 times the subcarrier interval, as shown in FIG. 5 (e), these peaks appear from the four peaks appearing at the original positions. The peaks at the above-mentioned four points adjacent to the original four points are higher.

  The demodulator 12 uses the FFT output data supplied from the Fourier transform unit 7 to represent the phase of the QPSK modulated wave (that is, the baseband signal of the QPSK modulated wave). Is extracted, data representing the extracted symbol is generated and output to the outside.

  As a result of the operation described above, this demodulator can quickly detect this frequency deviation and correct the frequency even if the frequency of the OFDM signal exceeds a half of the subcarrier interval. In addition, even when the phase of the pilot signal cannot be correctly captured due to the frequency shift of the OFDM signal, the phase of the pilot signal can be quickly captured, so that the frequency variation of the OFDM signal can be accurately followed. Extract symbols accurately.

Note that the configuration of this demodulator is not limited to that described above.
For example, the modulated wave included in the OFDM signal does not need to be a QPSK modulated wave, and may be a modulated wave generated in, for example, 16QAM or any other modulation format. The demodulator 12 only needs to demodulate the modulated wave and output the obtained demodulated signal.

  Further, this demodulator does not necessarily need to include the antenna 1, and the mixing units 4I and 4Q may acquire the OFDM signal to be demodulated from a wired line or the like.

  Further, the frequency converter 6 may generate components corresponding to the I signal and the Q signal. In this case, the demodulating device does not need to include the local oscillating unit 2, the mixing unit 4I, the mixing unit 4Q, the A / D conversion unit 5I, or the A / D conversion unit 5Q, but instead converts the OFDM signal received by the antenna 1 to A What is necessary is just to provide the A / D converter which / D converts and supplies to the frequency conversion part 6. Then, the frequency conversion unit 6 generates a signal corresponding to, for example, a phase of the frequency correction signal delayed by (π / 2) [radians], and the original OFDM signal supplied from the A / D converter and the original Generate a signal representing a component corresponding to the frequency difference between the frequency correction signal and a signal representing a component corresponding to the frequency difference between the OFDM signal and the phase-corrected frequency correction signal, and perform a Fourier transform on the two signals. What is necessary is just to make it supply to the part 7. FIG.

Although the embodiments of the present invention have been described above, the frequency control device according to the present invention can be realized using a normal computer system, not a dedicated system.
For example, a computer including an oscillation circuit, a phase shift circuit, and an A / D converter is added to the above-described frequency conversion unit 6, Fourier transform unit 7, power calculation unit 8, phase difference calculation unit 9, frequency control amount output unit 10, NCO 11, and By installing the program from a recording medium (CD-ROM, MO, flexible disk, etc.) storing a program for executing the operation of the demodulator 12, the above-described demodulator can be configured.

Further, for example, this program may be uploaded to a bulletin board (BBS) of a communication line and distributed via the communication line. Also, a carrier wave is modulated by a signal representing this program, and the obtained modulated wave is A device that transmits and receives the modulated wave may demodulate the modulated wave to restore these programs.
The above-described processing can be executed by starting this program and executing it under the control of the OS in the same manner as other application programs.

  When the OS shares a part of the processing, or when the OS constitutes a part of one component of the present invention, a program excluding the part is stored in the recording medium. May be. Also in this case, in the present invention, it is assumed that the recording medium stores a program for executing each function or step executed by the computer.

It is a block diagram which shows the structure of the demodulation apparatus which concerns on embodiment of this invention. It is a figure which shows typically the spectrum of the preamble signal of the object which the demodulation apparatus of FIG. 1 receives. It is a flowchart which shows the process which a frequency converter, an electric power calculation part, a phase difference calculation part, and a frequency control amount output part perform. (A) is a graph showing the distribution of power data values when the phase of the pilot signal appears in the FFT output data at the correct position, and (b) and (c) are the phases of the pilot signal being incorrect It is a graph which shows distribution of the value of the electric power data when it appears in the FFT output data of a position. (A) is a graph showing the distribution of power data values when the phase of the pilot signal appears in the FFT output data at the correct position, and (b) to (e) are the phases of the pilot signal being incorrect. It is a graph which shows distribution of the value of the electric power data when it appears in the FFT output data of a position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Local oscillation part 3 Phase shift part 4I, 4Q mixing part 5I, 5Q A / D conversion part 6 Frequency conversion part 7 Fourier transformation part 8 Power calculation part 9 Phase difference calculation part 10 Frequency control amount output part 11 NCO
12 Demodulator

Claims (11)

A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. Frequency correction means for generating a corrected modulated wave composed of components, and
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the coarse adjustment amount from the previous frequency when the coarse adjustment amount is determined;
The frequency control apparatus characterized by the above-mentioned. A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. Frequency correction means for generating a corrected modulated wave composed of components, and
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. Fine adjustment amount determining means for determining the fine adjustment amount in a range less than one half of the subcarrier interval;
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount,
The frequency control apparatus characterized by the above-mentioned. The modulated wave includes a preamble portion consisting only of the pilot signal, and the coarse adjustment amount determining means includes the pilot signal out of the predetermined frequency components included in the preamble portion of the corrected modulated wave. A frequency component including a component corresponding to
The frequency control apparatus according to claim 1 or 2, wherein The modulated wave includes a plurality of the pilot signals,
The coarse adjustment amount determining means includes
Means for identifying the sum of the intensities of the components belonging to the combination of a plurality of components whose relative positional relationship on the frequency axis is the same as that of the plurality of pilot signals among the corrected modulated waves; ,
Means for specifying a combination in which the specified total reaches a predetermined first threshold, and specifying a component belonging to the specified combination as a frequency component including a component corresponding to the pilot signal; ,
The frequency control device according to claim 1, 2, or 3. The coarse adjustment amount determining means obtains an average intensity of a predetermined frequency component of the corrected modulated wave for a period of a plurality of symbols of the corrected modulated wave, and determines each predetermined frequency based on the calculated average. Means for identifying a frequency component including a component corresponding to the pilot signal from among the components;
The frequency control apparatus according to any one of claims 1 to 4, wherein The coarse adjustment amount determination means has an intensity that reaches a predetermined second threshold value among the predetermined frequency components of the corrected modulated wave, and the intensity of a component adjacent on the frequency axis is the second frequency component. Is determined as a frequency component including a component corresponding to the pilot signal, and the difference between the frequency of the specified component and the frequency that the pilot signal should be taken as a rough adjustment amount decide,
The frequency control apparatus according to any one of claims 1 to 5, wherein the frequency control apparatus includes: The coarse adjustment amount determining means includes two predetermined frequency components of the corrected modulated wave that are adjacent to each other on the frequency axis, and whose intensity has reached a predetermined second threshold value. A component is specified as a frequency component including a component corresponding to the pilot signal, and a difference between an intermediate value of the frequencies of the two specified components and a frequency that the pilot signal should originally take is determined as a coarse adjustment amount. ,
The frequency control apparatus according to claim 1, wherein the frequency control apparatus is configured as described above. A frequency correction signal generating step for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A frequency correction step for generating a corrected modulated wave composed of components, and
In the frequency correction signal generation step,
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. Thus, the coarse adjustment amount is determined by a unit of 1/2 of the subcarrier interval of the modulated wave,
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated.
A frequency control method characterized by the above. A frequency correction signal generating step for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A frequency correction step for generating a corrected modulated wave composed of components, and
In the frequency correction signal generation step,
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. Thus, the coarse adjustment amount is determined by a unit of 1/2 of the subcarrier interval of the modulated wave,
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. A fine adjustment amount is determined in a range less than one half of the subcarrier interval of
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount;
A frequency control method characterized by the above. Computer
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A program for causing a frequency control unit configured to generate a corrected modulated wave composed of components and a frequency control device configured to include:
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the coarse adjustment amount from the previous frequency when the coarse adjustment amount is determined;
A program characterized by that. Computer
A frequency correction signal generating means for generating a frequency correction signal;
Acquires a frequency-division-multiplexed modulated wave including a pilot signal composed of unmodulated subcarriers and the frequency correction signal, and corresponds to the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal. A program for causing a frequency control unit configured to generate a corrected modulated wave composed of components and a frequency control device configured to include:
The frequency correction signal generating means is
Of the corrected modulated wave, a component corresponding to the pilot signal out of each predetermined frequency component based on the intensity of a plurality of predetermined frequency components having an interval equal to the interval between subcarriers of the modulated wave And the frequency of the frequency correction signal is changed from the previous frequency by an amount corresponding to an amount that cancels the difference between the frequency of the specified component and the frequency that the pilot signal should originally take. As described above, coarse adjustment amount determining means for determining the coarse adjustment amount in a unit of half of the subcarrier interval of the modulated wave;
Based on the phase change amount of a predetermined frequency component of the corrected modulated wave, the modulated wave so that the frequency of the component corresponding to the pilot signal of the corrected modulated wave converges to the predetermined frequency. Fine adjustment amount determining means for determining the fine adjustment amount in a range less than one half of the subcarrier interval;
When the coarse adjustment amount is determined, the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the coarse adjustment amount is generated. When the fine adjustment amount is determined, the fine adjustment amount is determined from the previous frequency. Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the adjustment amount,
A program characterized by that.

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