JP4535780B2 - Frequency control device, frequency control method and program - Google Patents

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 technique of frequency division multiplexing that superimposes and transmits a large number of modulated waves having different subcarrier frequencies has been widely used. 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;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. And a frequency correction means for generating a corrected modulated wave composed of components corresponding to
The frequency correction signal generating means is
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining means for determining a first correction amount;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. Second correction amount determining means for determining the second correction amount as described above,
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the sum of the first and second correction amounts from a previous frequency ,
The first correction amount determining means determines the frequency of the frequency correction signal when the component substantially including the component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency. The first correction amount is determined so as to change quantitatively.
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.

In addition, with such a configuration, even if the pilot signal cannot be correctly captured due to a shift in the frequency of the modulation wave, the pilot signal is accurately captured, and the shift in the frequency of the modulation wave is reduced. Correct accurately.

The first correction amount determination means includes means for specifying and accumulating a change amount of a phase change amount of each of the plurality of predetermined frequency components of the corrected modulated wave a plurality of times, and the accumulated result On the basis of the component of the predetermined frequency, the component substantially including the component corresponding to the pilot signal may be specified,
The second correction amount determining means includes means for specifying and accumulating a phase change amount of the component of the predetermined frequency in the corrected modulated wave a plurality of times, and based on the accumulated result, The amount of correction may be determined.
With such a configuration, the first and second correction amounts can be determined more accurately.

A third correction is made so that the frequency of the component converges to the frequency that the pilot signal should be based on the amount of change in the phase of the component of the frequency that the pilot signal should be originally taken out of the corrected modulated wave. A third correction amount determining means for determining the amount may further be provided,
In this case, the frequency correction signal generation unit may generate the frequency correction signal having a frequency changed from the previous frequency by an amount corresponding to the sum of the first, second, and third correction amounts. .
With such a configuration, in a state in which the pilot signal is corrected so as to substantially take its original frequency, the first and second correction amounts emphasize the accuracy based on the cumulative number of variables. Whereas the third correction amount is determined quickly, the pilot signal is captured accurately and quickly.

The frequency control method according to the second aspect of the present invention is:
A frequency correction signal generating step for generating a frequency correction signal;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. And a frequency correction step for generating a corrected modulated wave consisting of components corresponding to
The frequency correction signal generation step includes
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining step for determining a first correction amount ;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. A second correction amount determining step for determining the second correction amount as described above ,
Generating the frequency correction signal having a frequency changed from a previous frequency by an amount corresponding to the sum of the first and second correction amounts,
In the first correction amount determining step, when a component substantially including a component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency, the frequency of the frequency correction signal is determined. The first correction amount is determined so as to change quantitatively.
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.

A program according to the third aspect of the present invention is:
Computer
A frequency correction signal generating means for generating a frequency correction signal;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. A program for functioning as a frequency correction means for generating a corrected modulated wave consisting of components corresponding to
The frequency correction signal generating means is
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining means for determining a first correction amount;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. Second correction amount determining means for determining the second correction amount as described above,
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the sum of the first and second correction amounts from a previous frequency ,
The first correction amount determining means determines the frequency of the frequency correction signal when the component substantially including the component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency. The first correction amount is determined so as to change quantitatively.
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.

  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 a demodulator that demodulates at least one of a plurality of QPSK (Quatrature Phase Shift Keying) modulated waves multiplexed by an OFDM (Orthogonal Frequency Division Multiplexing) technique, as shown in the drawings. Will be described with reference to FIG.

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 high frequency amplifier 2, a local oscillator 3, a phase shifter 4, mixing units 5I and 5Q, and A / D (Analog-to-Digital) conversion. Units 6I and 6Q, a correction calculation unit 7, a Fourier transform unit 8, a correction amount determination unit 9, and a demodulation unit 10 are included.

  The high frequency amplification unit 2 is configured by a known high frequency amplification circuit or the like, receives an OFDM signal via the antenna 1, amplifies the OFDM signal, and supplies the amplified signal to the mixing units 5I and 5Q.

It is assumed that the OFDM signal received by the high frequency amplifier 2 has a spectrum as schematically shown in FIG. That is, this OFDM signal is configured by arranging a plurality of QPSK modulated waves M and one or more pilot signals P corresponding to subcarriers at the time of non-modulation at a frequency Δf interval. The time length of one symbol of the OFDM signal is Δt including the guide interval, and the value of Δt corresponds to an integral multiple of the period of each pilot signal P.
However, it is assumed that the subcarriers of the QPSK modulated wave M and the pilot signal P are orthogonal to each other. Further, the order in which the pilot signals P are arranged on the frequency axis and the frequency of the pilot signal P are determined in advance (FIG. 2 shows the third from the lowest frequency and the third from the highest frequency. The case where the pilot signal P occupies is illustrated).

The local oscillation unit 3 includes a known oscillation circuit and the like, generates a local oscillation signal having a predetermined frequency, and supplies it to the phase shift unit 4 and the mixing unit 5I.
The phase shift unit 4 is configured by 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 3 delayed by (π / 2) [radians]. To supply to the mixing section 5Q.

The mixing units 5I and 5Q have substantially the same configuration, and each is configured by, for example, a known multiplication circuit.
The mixing unit 5I mixes the OFDM signal supplied from the high-frequency amplification unit 2 and the local oscillation signal supplied from the local oscillation unit 3, thereby generating a component having a frequency corresponding to the difference between the two frequencies in QPSK. A signal corresponding to the I signal is supplied to the A / D converter 6I.
The mixing unit 5Q mixes the OFDM signal supplied from the high frequency amplification unit 2 and the signal supplied from the phase shift unit 4 (that is, a local oscillation signal whose phase is delayed by (π / 2) [radians]). Then, a component having a frequency corresponding to the difference between the two frequencies is generated and supplied to the A / D converter 6Q as a signal corresponding to the Q signal in QPSK.

The A / D converters 6I and 6Q have substantially the same configuration, and each is configured by, for example, a known A / D converter.
The A / D conversion unit 6I converts the signal supplied from the mixing unit 5I into a digital signal and supplies it to the correction calculation unit 7. The A / D conversion unit 6Q converts the signal supplied from the mixing unit 5Q into a digital signal and supplies it to the correction calculation unit 7.

The correction calculation unit 7, the Fourier transform unit 8, the correction amount determination unit 9, and the demodulation unit 10 are all processors such as DSP (Digital Signal Processor) and CPU (Central Processing Unit), and programs to be executed by the processor. It is comprised from the memory etc. which memorize | store.
A single processor may perform some or all of the functions of the correction calculation unit 7, the Fourier transform unit 8, the correction amount determination unit 9, and the demodulation unit 10.

  The correction calculation unit 7 is supplied with an I signal in digital form from the A / D conversion unit 6I, is supplied with a Q signal in digital format from the A / D conversion unit 6Q, and is further subjected to frequency correction described later from the correction amount determination unit 9. When the signal is supplied, 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 is generated and supplied to the Fourier transform unit 8. A signal having a frequency corresponding to the difference (or sum) between the frequency of the Q signal and the frequency of the frequency correction signal is generated and supplied to the Fourier transform unit 8.

  The two signals supplied from the correction calculation unit 7 to the Fourier transform unit 8 are obtained by shifting the frequency of the I signal and the Q signal of the OFDM signal received by the demodulation device by the frequency of the frequency correction signal. The corresponding signal.

The Fourier transform unit 8 measures the first to nth phases representing the phases of predetermined frequency components constituting the spectrum of the OFDM signal among the OFDM signals represented by the set of two signals supplied from the correction calculation unit 7. n pieces of phase data are generated by a fast Fourier transform technique. Then, the generated n pieces of phase data are supplied to the correction amount determination unit 9 and the demodulation unit 10. Note that n is an integer greater than or equal to the number of subcarriers in the OFDM signal, and the (j + 1) th phase data represents the phase of a frequency component whose frequency is higher by Δf than the frequency component in which the jth phase data represents the phase. (Where j is an integer greater than or equal to 1 and less than n).
If these n phase 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 included in the n phase data. The corresponding signal.

  As described above, since the pilot signal P is composed of unmodulated subcarriers, the value of the phase data supplied by the Fourier transform unit 8 that represents the phase of the pilot signal P is, for example, FIG. As shown in FIG. On the other hand, the value of the phase data representing the phase of the modulated subcarrier or the like, which is different from the pilot signal P, changes irregularly as shown in FIG. 4A, for example.

  As shown in FIG. 1, the correction amount determination unit 9 functionally includes a frequency correction signal generation unit 91, a phase difference detection unit 92, a phase difference change amount detection unit 93, an absolute value calculation unit 94, The cumulative addition units 95 and 97, a pilot determination unit 96, a frequency correction amount calculation unit 98, and a pilot extraction unit 99 are configured.

  The frequency correction signal generation unit 91 performs a function of a numerically controlled oscillator (NCO), (a) a predetermined initial value (for example, 0 hertz), and (b) instructed by the pilot determination unit 96. First correction amount described later, (c) second correction amount described later from frequency correction amount calculation unit 98, and (d) third correction amount specified by pilot extraction unit 99. A frequency correction signal having a frequency corresponding to the sum of the two is generated and continuously supplied to the correction calculation unit 7.

  The phase difference detection unit 92 specifies the value of the phase data for each of the n pieces of phase data supplied from the Fourier transform unit 8 in a period substantially equal to the above-described value Δt, and based on the specified phase, Data (one-time difference data) representing the amount of change in each phase of the phase indicated by the phase data is sequentially generated. Then, the generated n-time difference data in total is used as the k-th difference data generated based on the k-th phase data (k is an integer between 1 and n), and the phase difference This is sequentially supplied to the change amount detector 93, the cumulative adder 97, and the pilot extractor 99.

Since the pilot signal P is a signal corresponding to an unmodulated subcarrier, if the phase data captures the phase of the pilot signal P, the one-time difference data generated based on the phase data is, for example, FIG. As shown in (b), the value is almost constant. That is, when the component whose phase is represented by the phase data exactly matches the pilot signal P, the amount of phase change specified for each period is substantially 0, and does not exactly match. Even in this case, the amount of phase delay or advance for each period is a substantially constant value.
On the other hand, when the phase data represents the phase of a component other than the pilot signal P, the value of the one-time difference data generated based on the phase data is irregular as shown in FIG. 4B, for example. To change.

  The phase difference change amount detection unit 93 specifies the phase change amount represented by each one-time difference data supplied from the phase difference detection unit 92 with a period substantially equal to the value Δt, and is based on the specified change amount. Then, data (two-time difference data) representing the amount of change of the phase change amount represented by the one-time difference data is sequentially generated, and the generated n number of two-time difference data is converted into the kth 1 The twice-difference data generated based on the first-time difference data is supplied to the absolute value calculation unit 94 as the k-th two-time difference data. In other words, the twice-difference data is data representing the amount of change in the amount of change in each phase of the phase represented by the phase data supplied by the Fourier transform unit 8.

  The value of the one-time difference data representing the amount of change in the phase of the pilot signal P is a substantially constant value as described above. Accordingly, the value of the twice-difference data generated based on such once-difference data is almost 0 as shown in FIG. 3C, for example. On the other hand, the value of the twice-difference data representing the amount of change in the phase change amount of the component other than the pilot signal P changes irregularly as shown in FIG. 4C, for example.

  The absolute value calculation unit 94 sequentially generates absolute value data representing the absolute values of the values represented by the two-time difference data supplied from the phase difference change amount detection unit 93, and a total of n absolute values obtained are obtained. The absolute value data generated based on the k-th twice-difference data is supplied to the accumulative addition unit 95 as the k-th absolute value data.

  When n absolute value data are supplied from the absolute value calculation unit 94, the cumulative addition unit 95 stores values represented by the respective absolute value data. Then, each time a new value is stored, for each absolute value data, accumulated result data representing a result obtained by adding the values of the latest predetermined number of times (for example, the latest 10 times) among the values stored by itself to each other. The total n pieces of generated result data generated and the generated result data generated based on the k-th absolute value data are supplied to the pilot determination unit 96 as the k-th accumulated result data.

  Whenever the n cumulative result data are newly supplied from the cumulative adder 95, the pilot determination unit 96 determines whether any of these cumulative result data is within a predetermined upper limit value. Determine whether or not.

When the twice-difference data represents the amount of change in the phase change amount of the pilot signal P, the value of the twice-difference data is almost 0 as described above. Therefore, the result of adding the absolute value of the difference data twice at a plurality of different time points also becomes a low value close to zero. On the other hand, when the change amount of the phase change amount of the component other than the pilot signal P is expressed, the value of the twice difference data irregularly changes, so that the absolute value of the twice difference data at a plurality of different time points The result of adding the values is a larger value than that representing the change amount of the phase change amount of the pilot signal P.
Therefore, if the above-described upper limit value is appropriately set, the above-described determination processing performed by the pilot determination unit 96 determines whether there is any phase data that captures the phase of the pilot signal P. This corresponds to the processing to be performed.

  When it is determined that there is no accumulated result data whose value falls below the upper limit value (that is, there is no phase data capturing the phase of the pilot signal P), the pilot determination unit 96 causes the frequency correction signal generation unit 91 to As the above-described first correction amount, a new value that is changed (increased or decreased) by a predetermined amount (for example, (Δf / 2)) from the previously instructed value is instructed (the pilot determination unit 96 The value 0 may be instructed to the frequency correction signal generation unit 91 immediately after the start of the operation, for example, as the initial value of the first correction amount). On the other hand, each time the pilot determination unit 96 determines that there is no phase data that captures the phase of the pilot signal P, each of the cumulative addition units 95 and 97 is stored in response to the determination. Clear the existing value (set it to 0).

  If there is no phase data that captures the phase of the pilot signal P, this may be the case where each phase data captures the phase of a component having a frequency approximately in the middle of the subcarrier of the OFDM signal. Conceivable. Therefore, it is considered that each phase data correctly captures the phase of the subcarrier including the pilot signal P by changing the first correction amount by (Δf / 2).

  On the other hand, if it is determined that there is accumulated result data whose value is less than or equal to the upper limit value (that is, there is phase data capturing the phase of the pilot signal P), the pilot determination unit 96 determines the order of the corresponding phase data. Specify based on accumulated result data. Then, based on the specified order and the original frequency of the pilot signal P, the amount of deviation of the frequency of the OFDM signal is specified in increments of Δf, and the first correction amount is less than the value instructed previously. The frequency correction signal generation unit 91 is instructed with a new value that is changed in the direction to cancel the shift by the same amount as the amount.

  Specifically, for example, when the frequency of the pilot signal P is a predetermined original frequency, the phase of the pilot signal P is the initial state of the frequency correction signal generation unit 91 (that is, first to third). In the case where the correction amount of each is 0), the order of the phase data identified as capturing the phase of the pilot signal P is (m + d). ) Th (m is an integer of 1 to n and d is an integer of 0 or more). In this case, pilot determination unit 96 specifies that the amount of deviation in the upward direction of the frequency of the OFDM signal received by the demodulator from the original frequency is (d · Δf), and correction calculation unit 7 outputs The first correction amount is changed so as to decrease the frequency of the OFDM signal represented by the signal to be reduced by (d · Δf). For example, if the correction calculation unit 7 generates a signal having a frequency corresponding to the difference between the frequency of the I signal or the Q signal and the frequency of the frequency correction signal, the pilot determination unit 96 determines the first correction amount. It is only necessary to raise it by (d · Δf).

  On the other hand, when n pieces of difference data are supplied from the phase difference detection unit 92, the cumulative addition unit 97 stores values represented by the supplied one-time difference data. Then, each time a new value is stored, for each one-time difference data, a difference accumulated data indicating a result of adding the latest predetermined number of values among the values stored therein is generated and generated. The total n difference accumulation data is supplied to the frequency correction amount calculation unit 98 as the difference accumulation data generated based on the kth difference data as the kth difference accumulation data. If the predetermined number of times that the cumulative addition unit 97 performs the addition of the difference data is set to be approximately the same as the number of times that the cumulative addition unit 95 performs the addition of the absolute value data, for example, the cumulative addition units 95 and 97 are almost identical to each other. Since the processes can be performed at the same timing, it is easy to speed up the frequency correction process by updating the first and second correction amounts almost simultaneously.

  The frequency correction amount calculation unit 98 determines the above-described second correction amount based on these difference accumulation data every time n difference accumulation data is newly supplied from the accumulation addition unit 97, and the frequency correction signal The generation unit 91 is instructed.

  Specifically, the frequency correction amount calculation unit 98 selects, for example, the difference accumulated data representing the addition result of the phase change amount of the pilot signal P, and based on the selected difference accumulated data, the pilot signal Specify an average value of the phase change amount for each period of P, cancel the phase change corresponding to the specified average value, and converge the value of the selected difference accumulated data to 0 What is necessary is just to specify as 2nd correction amount.

  Since the time length Δt for one symbol of the OFDM signal received by this demodulator corresponds to y times (y is a natural number) of the period (1 / Δf) of the pilot signal P, the phase for each period represented by the phase data. When the delay of x is [degree], this means that the frequency of the component whose phase is represented by the phase data is {(x · Δf) / (360 -Y)} indicates that it is low. Therefore, in this case, the frequency correction amount calculation unit 98 may specify {− (x · Δf) / (360 · y)} as the second correction amount.

  More specifically, for example, it is assumed that the cumulative addition unit 97 supplies data indicating the addition result of the latest 10 values of the one-time difference data to the frequency correction amount calculation unit 98 as difference cumulative data. Assuming that the accumulated data indicates a phase advance of 360 [degrees], in this case, the frequency correction amount calculation unit 98 considers that the average of the phase advance for each period of the pilot signal P is 36 [degrees]. In order to delay the phase of the pilot signal P by 36 [degrees] per cycle, the second correction amount may be determined as {Δf / (10 · y)}.

In order to enable the frequency correction amount calculation unit 98 to select the difference accumulation data representing the addition result of the phase change amount of the pilot signal P, for example, the pilot determination unit 96 includes the phase data representing the phase of the pilot signal P. The frequency correction amount calculation unit 98 is notified of the order, and the frequency correction amount calculation unit 98 selects the difference accumulation data in the notified order as representing the addition result of the phase change amount of the pilot signal P. That's fine.
In addition, since there are a plurality of pilot signals P in the OFDM signal, the frequency correction amount calculation unit 98 is selected when a plurality of accumulated difference data representing the addition result of the phase change amount of the pilot signal P is selected. What is necessary is just to use the average value of the correction amount calculated from each difference accumulation data as a 2nd correction amount.

  The pilot extraction unit 99 is supplied with n pieces of difference data from the phase difference detection unit 92 at a timing after the time when the first and second correction amounts are instructed to the frequency correction signal generation unit 91. The one-time difference data supplied is selected to represent the amount of change in the phase of the pilot signal P, the above-described third correction amount is determined based on the selected one-time difference data, and the frequency correction signal The generation unit 91 is instructed. Specifically, the pilot extraction unit 99 cancels the phase change represented by the selected one-time difference data, and sets the third correction amount to an amount that converges the value of the one-time difference data to 0. It may be specified as

Since the first and second correction amounts are instructed to the frequency correction signal generation unit 91, as a result of correction by the correction calculation unit 7, the corrected OFDM signal (represented by the signal output by the correction calculation unit 7). The frequency of the (OFDM signal) substantially matches the original frequency. Therefore, when the frequency of the OFDM signal is the original frequency, the pilot extraction unit 99 performs the one-time difference generated from the phase data that should represent the phase of the pilot signal P without correction by the correction calculation unit 7. The data may be selected as representing the amount of change in the phase of the pilot signal P. For example, if the phase of the pilot signal P in the initial state of the frequency correction signal generation unit 91 having the original frequency is represented as the mth phase data as in the above-described example, pilot extraction is performed. The unit 99 may select the m-th one-time difference data as representing the amount of change in the phase of the pilot signal P.
In addition, when a plurality of one-time difference data representing the amount of change in the phase of pilot signal P is selected because there are a plurality of pilot signals P in the OFDM signal, pilot extraction section 99 selects each of the selected one times. An average value of correction amounts calculated from the difference data may be used as the third correction amount.

  Based on the phase data supplied from the Fourier transform unit 8 and indicating the phase of the QPSK modulated wave (that is, the baseband signal of the QPSK modulated wave), the demodulator 10 represents the symbol represented by the QPSK modulated wave. Extract, generate data representing the extracted symbols and output to the outside.

  As a result of performing the operation described above, this demodulator can quickly detect and correct the frequency even if the OFDM signal has a frequency that exceeds (Δf / 2). Even if the phase of the pilot signal P cannot be correctly captured due to the frequency shift of the OFDM signal, the phase of the pilot signal P can be quickly captured. Is extracted 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 10 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 high frequency amplifier 2 may acquire an OFDM signal from a wired line. In addition, if the intensity of the OFDM signal to be demodulated is sufficiently high, the demodulator does not necessarily need to include the high-frequency amplifying unit 2. In this case, the mixing units 5I and 5Q directly output the OFDM signal to be demodulated. Get it.

  Further, the correction calculation unit 7 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 3, the mixing unit 5I, the mixing unit 5Q, the A / D conversion unit 6I, or the A / D conversion unit 6Q. Instead, the OFDM signal amplified by the high frequency amplification unit 2 is used. An A / D converter may be provided that performs A / D conversion and supplies the correction to the correction calculation unit 7. Then, for example, the correction calculation unit 7 generates a signal corresponding to the 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 8. 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 having a high-frequency amplifier circuit, an oscillation circuit, a phase shift circuit, and an A / D converter is caused to execute the operations of the correction calculation unit 7, the Fourier transform unit 8, the correction amount determination unit 9, and the demodulation unit 10. The demodulator described above can be configured by installing the program from a recording medium (CD-ROM, MO, flexible disk, etc.) storing the program.

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 OFDM signal of the object which the demodulation apparatus of FIG. 1 receives. (A) is a graph which shows the change of the value of the phase data which correctly represents the phase of the pilot signal, and (b) shows the change of the value of the one-time difference data generated based on this phase data. It is a graph and (c) is a graph which shows the change of the value of 2 times difference data produced | generated based on this 1 time difference data. (A) is a graph which shows the change of the value of the phase data which does not represent the phase of a pilot signal correctly, (b) shows the change of the value of the once difference data produced | generated based on this phase data. It is a graph and (c) is a graph which shows the change of the value of 2 times difference data produced | generated based on this 1 time difference data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 High frequency amplification part 3 Local oscillation part 4 Phase shift part 5I, 5Q mixing part 6I, 6Q A / D conversion part 7 Correction calculation part 8 Fourier transformation part 9 Correction amount determination part 91 Frequency correction signal generation part 92 Phase difference detection Unit 93 Phase difference change amount detection unit 94 Absolute value calculation unit 95, 97 Cumulative addition unit 96 Pilot determination unit 98 Frequency correction amount calculation unit 99 Pilot extraction unit 10 Demodulation unit

Claims (5)

A frequency correction signal generating means for generating a frequency correction signal;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. And a frequency correction means for generating a corrected modulated wave composed of components corresponding to
The frequency correction signal generating means is
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining means for determining a first correction amount;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. Second correction amount determining means for determining the second correction amount as described above,
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the sum of the first and second correction amounts from a previous frequency ,
The first correction amount determining means determines the frequency of the frequency correction signal when the component substantially including the component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency. The first correction amount is determined so as to change quantitatively.
The frequency control apparatus characterized by the above-mentioned. The first correction amount determination means includes means for specifying and accumulating a change amount of a phase change amount of each of the plurality of predetermined frequency components of the corrected modulated wave a plurality of times, and the accumulated result Based on the above, a component substantially including a component corresponding to the pilot signal is specified from the components of the predetermined frequency,
The second correction amount determining means includes means for specifying and accumulating a phase change amount of the component of the predetermined frequency in the corrected modulated wave a plurality of times, and based on the accumulated result, Is to determine the correction amount of
The frequency control apparatus according to claim 1 . A third correction is made so that the frequency of the component converges to the frequency that the pilot signal should be based on the amount of change in the phase of the component of the frequency that the pilot signal should be originally taken out of the corrected modulated wave. A third correction amount determining means for determining the amount;
The frequency correction signal generating means generates the frequency correction signal having a frequency changed by an amount corresponding to the sum of the first, second, and third correction amounts from a previous frequency.
The frequency control apparatus according to claim 2 . A frequency correction signal generating step for generating a frequency correction signal;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. And a frequency correction step for generating a corrected modulated wave consisting of components corresponding to
The frequency correction signal generation step includes
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining step for determining a first correction amount ;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. A second correction amount determining step for determining the second correction amount as described above ,
Generating the frequency correction signal having a frequency changed from a previous frequency by an amount corresponding to the sum of the first and second correction amounts,
In the first correction amount determining step, when a component substantially including a component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency, the frequency of the frequency correction signal is determined. The first correction amount is determined so as to change quantitatively.
A frequency control method characterized by the above. Computer
A frequency correction signal generating means for generating a frequency correction signal;
A frequency division multiplexed modulated wave including a pilot signal consisting of substantially unmodulated subcarriers and the frequency correction signal are obtained, and the sum or difference between the frequency of the modulated wave and the frequency of the frequency correction signal is acquired. A program for functioning as a frequency correction means for generating a corrected modulated wave consisting of components corresponding to
The frequency correction signal generating means is
Based on the amount of change in the amount of change of the phase of a plurality of predetermined frequency components in the corrected modulated wave at a predetermined time, a component corresponding to the pilot signal is substantially out of the components of the predetermined frequency. The component 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. A first correction amount determining means for determining a first correction amount;
Based on the amount of change of the phase of the component of the predetermined frequency in the corrected modulated wave at a predetermined time, the frequency of the component corresponding to the pilot signal in the corrected modulated wave converges to the predetermined frequency. Second correction amount determining means for determining the second correction amount as described above,
Means for generating the frequency correction signal having a frequency changed by an amount corresponding to the sum of the first and second correction amounts from a previous frequency ,
The first correction amount determining means determines the frequency of the frequency correction signal when the component substantially including the component caused by the pilot signal cannot be specified from the plurality of components of the predetermined frequency. The first correction amount is determined so as to change quantitatively.
A program characterized by that.

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