FM broadcast wave correction device, FM broadcast wave transmission system, FM broadcast wave processing device, FM broadcast wave correction method, and FM broadcast wave transmission method

Abstract

To suppress image waves in FM broadcast waves by simple processing.SOLUTION: An FM broadcast wave correction device comprises: a reception unit that receives demodulated data based on a demodulated signal having been orthogonally demodulated from a radio frequency (RF) signal including a frequency modulation (FM) broadcast wave; a conversion unit that Fourier transforms the modulated data so as to generate frequency-axis data that indicates a frequency spectrum of the demodulated signal; a correction unit that carries out a correction process of attenuating intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data; and an inverse conversion unit that inverse Fourier transforms the frequency spectrum indicated by the frequency-axis data after the correction process so as to generate time-axis data.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an FM broadcast wave correction device, an FM broadcast wave transmission system, an FM broadcast wave processing device, an FM broadcast wave correction method, and an FM broadcast wave transmission method.

Background Art

[0002] Conventionally, a technique for suppressing an image wave in a quadrature-modulated signal has been known.

[0003] For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2021-145260) discloses a demodulator as follows. That is, the demodulator includes a first quadrature demodulation unit that quadrature-demodulates an input analog high-frequency signal, which is a quadrature modulation signal, to generate a first intermediate demodulation signal and a second intermediate demodulation signal each having an intermediate frequency, an AD conversion unit that performs AD conversion processing on each of the first intermediate demodulation signal and the second intermediate demodulation signal to generate a first digital intermediate demodulation signal and a second digital intermediate demodulation signal, a signal extraction unit that extracts a first image component and a second image component from each of the first digital intermediate demodulation signal and the second digital intermediate demodulation signal, a correction coefficient calculation unit that calculates a correction coefficient so that the first image component and the second image component cancel each other out, a correction unit that causes the correction coefficient to act on the first digital intermediate demodulation signal and the second digital intermediate demodulation signal to generate a first intermediate correction signal and a second intermediate correction signal, and a second quadrature demodulation unit that generates a first digital demodulation signal and a second digital demodulation signal using components orthogonal to each other generated by digitally quadrature-demodulating the first intermediate correction signal and the second intermediate correction signal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Beyond the technology described in Patent Document 1, a technology capable of suppressing image waves in FM (Frequency Modulation) broadcast waves with simple processing is desired.

[0006] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide an FM broadcast wave correction device, an FM broadcast wave transmission system, an FM broadcast wave processing device, an FM broadcast wave correction method, and an FM broadcast wave transmission method capable of suppressing image waves in FM broadcast waves with simple processing.

Means for Solving the Problems

[0007] The FM broadcast wave correction device of the present disclosure includes a receiving unit that receives demodulation data based on a demodulated signal obtained by quadrature demodulating an RF (Radio Frequency) signal including an FM broadcast wave, a conversion unit that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data received by the receiving unit, a correction unit that performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion unit, and an inverse conversion unit that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction unit.

[0008] One aspect of the present disclosure can be realized not only as an FM broadcast wave correction device including such a characteristic processing unit, but also as a semiconductor integrated circuit that realizes part or all of the FM broadcast wave correction device, or as a system including the FM broadcast wave correction device.

Effects of the Invention

[0009] According to the present disclosure, image waves in FM broadcast waves can be suppressed with simple processing.

Brief Description of the Drawings

[0010]

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[0011] First, the contents of the embodiments of the present disclosure will be listed and described.

[0012] (1) The FM broadcast wave correction device according to an embodiment of the present disclosure includes a receiving unit that receives demodulation data based on a demodulated signal obtained by quadrature demodulating an RF signal including an FM broadcast wave, a conversion unit that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data received by the receiving unit, a correction unit that performs a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion unit, and an inverse conversion unit that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction unit.

[0013] In this way, by performing a Fourier transform on the demodulation data to generate frequency-axis data, performing a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data, and performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process to generate time-axis data, the component of the image wave can be suppressed by performing arithmetic processing on a partial frequency region of the frequency-axis data. Therefore, the component of the image wave can be suppressed by less arithmetic processing. Accordingly, the image wave in the FM broadcast wave can be suppressed by a simple process.

[0014] (2) In the above (1), the receiving unit may receive the demodulation data based on the demodulated signal obtained by quadrature demodulating the RF signal using a local signal. The local frequency, which is the frequency of the local signal, may be set to a value such that the frequency obtained by folding back the frequency of the first FM broadcast wave included in the RF signal at the local frequency does not overlap with the frequency of the first FM broadcast wave. When the RF signal further includes a second FM broadcast wave, the local frequency may be further set to a value such that the frequency obtained by folding back the frequency of the first FM broadcast wave at the local frequency does not overlap with the frequency of the second FM broadcast wave.

[0015] With such a configuration, when the demodulated signal includes an image wave, the FM broadcast wave and the image wave can be separated on the frequency axis. Therefore, the image wave can be suppressed without attenuating the FM broadcast wave in the correction process.

[0016] (3) In the above (1) or (2), the conversion unit may perform a Fourier transform on the demodulated data for each number of samples that is a power of 2.

[0017] With such a configuration, since butterfly operations can be used in the Fourier transform and the inverse Fourier transform, the time required for the Fourier transform and the inverse Fourier transform can be made shorter.

[0018] (4) In any of the above (1) to (3), the correction unit may attenuate the intensity in the frequency domain by multiplying the frequency axis data by an attenuation coefficient representing a cosine wave for one period in the correction process.

[0019] With such a configuration, the occurrence of ripples in the time axis data generated by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency axis data after the correction process can be suppressed.

[0020] (5) The broadcast wave transmission system according to the embodiment of the present disclosure includes an RF receiving device that receives an RF signal including an FM broadcast wave and generates a demodulated signal obtained by quadrature demodulating the received RF signal, and a conversion device that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulated data based on the demodulated signal generated by the RF receiving device, a correction device that performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion device, an inverse conversion device that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction device, and an RF transmitting device that generates modulated data obtained by quadrature modulating the time-axis data generated by the inverse conversion device and transmits an RF signal based on the generated modulated data.

[0021] In this way, by performing a Fourier transform on the demodulated data to generate frequency-axis data, performing a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data, and performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process to generate time-axis data, the component of the image wave can be suppressed by arithmetic processing on a part of the frequency region of the frequency-axis data. Therefore, the component of the image wave can be suppressed by less arithmetic processing. Accordingly, the image wave in the FM broadcast wave can be suppressed by a simple process.

[0022] (6) The FM broadcast wave processing apparatus according to an embodiment of the present disclosure includes a receiving unit that receives an RF signal including an FM broadcast wave, a demodulating unit that generates a demodulated signal by quadrature demodulating the RF signal received by the receiving unit using a first local signal, a converting unit that generates frequency axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on demodulated data based on the demodulated signal generated by the demodulating unit, a correcting unit that performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency axis data generated by the converting unit, an inverse converting unit that generates time axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency axis data after the correction process by the correcting unit, and a modulating unit that generates modulated data by quadrature modulating the time axis data generated by the inverse converting unit using a second local signal having a frequency different from that of the first local signal.

[0023] In this way, by performing a Fourier transform on demodulated data to generate frequency axis data, performing a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency axis data, and performing an inverse Fourier transform on the frequency spectrum indicated by the frequency axis data after the correction process to generate time axis data, the component of the image wave can be suppressed by performing arithmetic processing on a part of the frequency region of the frequency axis data. Therefore, the component of the image wave can be suppressed with less arithmetic processing. Accordingly, the image wave in the FM broadcast wave can be suppressed with a simple process. Further, by generating modulated data by quadrature modulating using a second local signal having a frequency different from that of the first local signal, the frequency of the FM broadcast wave can be changed and output.

[0024] (7) The FM broadcast wave correction method according to an embodiment of the present disclosure is an FM broadcast wave correction method in an FM broadcast wave correction apparatus, including: receiving demodulation data based on a demodulated signal obtained by quadrature demodulating an RF signal including an FM broadcast wave; generating frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the received demodulation data; performing a correction process of attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the generated frequency-axis data; and generating time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process.

[0025] In this way, by performing a Fourier transform on the demodulation data to generate frequency-axis data, performing a correction process of attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data, and performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process to generate time-axis data, the component of the image wave can be suppressed by performing arithmetic processing on a part of the frequency region of the frequency-axis data. Therefore, the component of the image wave can be suppressed by less arithmetic processing. Accordingly, the image wave in the FM broadcast wave can be suppressed by a simple process.

[0026] (8) The broadcast wave transmission method according to an embodiment of the present disclosure includes: receiving an RF signal including an FM broadcast wave, and generating a demodulated signal obtained by quadrature demodulating the received RF signal; generating frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data based on the demodulated signal; performing a correction process of attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data; generating time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process; generating modulated data obtained by quadrature modulating the time-axis data, and transmitting an RF signal based on the generated modulated data.

[0027] In this way, the demodulated data is Fourier-transformed to generate frequency-axis data, correction processing is performed to attenuate the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data, and the frequency spectrum indicated by the frequency-axis data after the correction processing is inverse Fourier-transformed to generate time-axis data. With this configuration, the component of the image wave can be suppressed by performing arithmetic processing on a part of the frequency region of the frequency-axis data, so that the component of the image wave can be suppressed with less arithmetic processing. Therefore, the image wave in the FM broadcast wave can be suppressed with simple processing.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions are not repeated. Also, at least a part of the embodiments described below may be arbitrarily combined.

[0029] <First Embodiment> [Configuration and Basic Operation] FIG. 1 is a diagram showing the configuration of a transmission system according to the first embodiment of the present disclosure. Referring to FIG. 1, the transmission system 401 includes an FM receiver 101 and an FM transmitter 201. The transmission system 401 may be configured to include a plurality of FM receivers 101, or may be configured to include a plurality of FM transmitters 201. The transmission system 401 is an example of an FM broadcast wave transmission system. The FM receiver 101 is an example of an RF receiver. The FM transmitter 201 is an example of an RF transmitter. The transmission system 401 transmits an FM broadcast wave in a predetermined transmission band TB having a bandwidth of 6 MHz, for example.

[0030] For example, the FM receiver 101 is provided in the building of a radio broadcasting station. Also, for example, the FM transmitter 201 is provided outside the building of the radio broadcasting station and near the user's home.

[0031] (FM Receiver) FIG. 2 is a diagram showing the configuration of an FM receiver according to a first embodiment of the present disclosure. Referring to FIG. 2, the FM receiver 101 includes a receiving unit 11, an orthogonal demodulator 12, an LFO (Local Frequency Oscillator) 13, LPFs (Low Pass Filters) 14I and 14Q, ADCs (Analog-to-Digital Converters) 15I and 15Q, a balance correction unit 16, and an IP (Internet Protocol) transmitter 17. The balance correction unit 16 is an example of an FM broadcast wave correction device.

[0032] The receiving unit 11 receives an RF signal including FM broadcast waves of a plurality of channels in the transmission band TB. As an example, the receiving unit 11 receives, via an antenna (not shown), an RF signal including an FM broadcast wave Wa having a center frequency Fa with a predetermined bandwidth, an FM broadcast wave Wb having a center frequency Fb with a predetermined bandwidth, an FM broadcast wave Wc having a center frequency Fc with a predetermined bandwidth, and an FM broadcast wave Wd having a center frequency Fd with a predetermined bandwidth. Here, the center frequencies Fd, Fc, Fb, and Fa are in descending order. Hereinafter, each of the FM broadcast waves Wa, Wb, Wc, and Wd is also referred to as an FM broadcast wave Wfm. Note that the receiving unit 11 may be configured to receive an RF signal including FM broadcast waves of two, three, or five or more channels. The receiving unit 11 amplifies the received RF signal and outputs it to the orthogonal demodulator 12.

[0033] The LFO 13 is, for example, a crystal oscillator, generates a reference signal having a frequency Fx, and outputs the generated reference signal to the orthogonal demodulator 12. The frequency Fx is an example of a local frequency.

[0034] The frequency Fx is set to a value such that the frequency obtained by folding back the frequency Ffm of the FM broadcast wave Wfm at the frequency Fx does not overlap with the frequency of the FM broadcast wave Wfm. Here, the "frequency Ffm of the FM broadcast wave Wfm" means any frequency included in the frequency band of the FM broadcast wave Wfm, and the "frequency obtained by folding back the frequency Ffm at the frequency Fx" means the frequency obtained by inverting the frequency Ffm with respect to the frequency axis with the frequency Fx as a reference, that is, the frequency on the opposite side of the frequency Fx from the frequency Ffm. That is, the frequency Fx is set to a value different from the frequencies of the FM broadcast waves Wa, Wb, Wc, and Wd.

[0035] Also, the frequency Fx is set to a value such that the frequency obtained by folding back the frequency of the first FM broadcast wave at the frequency Fx does not overlap with the frequency of the second FM broadcast wave. Here, the first FM broadcast wave and the second FM broadcast wave are any two of the FM broadcast waves Wa, Wb, Wc, and Wd. That is, when the bandwidth of the first FM broadcast wave is W1 and the bandwidth of the second FM broadcast wave is W2, the frequency Fx is set to a value deviated by at least 1 / 4 of the sum of W1 and W2 from the frequency at the midpoint between the center frequency of the first FM broadcast wave and the center frequency of the second FM broadcast wave on the frequency axis. Note that the frequency Fx may be set to a value such that, for some combinations of the first FM broadcast wave and the second FM broadcast wave, that is, for some of the six combinations of two of the FM broadcast waves Wa, Wb, Wc, and Wd, the frequency obtained by folding back the frequency of the first FM broadcast wave at the frequency Fx overlaps with the frequency of the second FM broadcast wave, provided that, for example, the quality of the FM broadcast required by the system is satisfied.

[0036] FIG. 3 is a diagram showing the configuration of a quadrature demodulator in an FM receiver according to the first embodiment of the present disclosure. Referring to FIG. 3, the quadrature demodulator 12 includes a PLL (Phase Locked Loop) section 41 and mixers 42I and 42Q. The quadrature demodulator 12 receives an RF signal from the receiving section 11 and generates a demodulated signal in the baseband band by performing direct conversion and quadrature demodulation on the received RF signal.

[0037] More specifically, the PLL unit 41 generates a local signal LI, which is a local oscillation signal synchronized with the reference signal received from the LFO 13, and also generates a local signal LQ whose phase is shifted by π / 2 with respect to the local signal LI. The PLL unit 41 outputs the generated local signals LI and LQ to the mixers 42I and 42Q, respectively.

[0038] The mixer 42I generates a baseband signal BI by down-converting the RF signal received from the receiving unit 11 using the local signal LI received from the PLL unit 41, and outputs the generated baseband signal BI to the LPF 14I.

[0039] The mixer 42Q generates a baseband signal BQ by down-converting the RF signal received from the receiving unit 11 using the local signal LQ received from the PLL unit 41, and outputs the generated baseband signal BQ to the LPF 14Q. The baseband signals BI and BQ are an example of demodulated signals.

[0040] Referring to FIG. 2 again, the LPF 14I attenuates components outside the predetermined passband PB among the frequency components of the baseband signal BI received from the quadrature demodulator 12. The passband PB is, for example, -3 MHz or higher and 3 MHz or lower.

[0041] The LPF 14Q attenuates components outside the passband PB among the frequency components of the baseband signal BQ received from the quadrature demodulator 12.

[0042] The ADC 15I converts the baseband signal BI that has passed through the LPF 14I into digital demodulation data DI at a predetermined sampling frequency fs, and outputs the converted demodulation data DI to the balance correction unit 16. The sampling frequency fs is set according to the transmission band TB and is, for example, 8.25 MHz.

[0043] The ADC 15Q converts the baseband signal BQ that has passed through the LPF 14Q into digital demodulation data DQ at the sampling frequency fs, and outputs the converted demodulation data DQ to the balance correction unit 16.

[0044] FIG. 4 is a diagram showing the configuration of a balance correction unit in an FM receiver according to the first embodiment of the present disclosure. Referring to FIG. 4, the balance correction unit 16 includes a receiving unit 31, a conversion unit 32, a correction unit 33, and an inverse conversion unit 34. Part or all of the receiving unit 31, the conversion unit 32, the correction unit 33, and the inverse conversion unit 34 are realized by, for example, a processing circuit (Circuitry) including one or more processors. The conversion unit 32 is an example of a conversion device. The correction unit 33 is an example of a correction device. The inverse conversion unit 34 is an example of an inverse conversion device.

[0045] The receiving unit 31 receives demodulation data DI and DQ based on baseband signals BI and BQ obtained by quadrature demodulating RF signals including FM broadcast waves Wa, Wb, Wc, and Wd from ADCs 15I and 15Q, respectively.

[0046] FIG. 5 is a diagram showing an example of frequency components included in a baseband signal indicated by demodulation data received by the receiving unit in the balance correction unit according to the first embodiment of the present disclosure. In FIG. 5, the horizontal axis represents frequency.

[0047] Referring to FIG. 5, the baseband signals BI and BQ indicated by the demodulation data DI and DQ received by the receiving unit 31 include a frequency component Ca of a frequency Fax which is a difference between the center frequency Fa of the FM broadcast wave Wa and the frequency Fx of the reference signal output by the LFO 13, a frequency component Cb of a frequency Fbx which is a difference between the center frequency Fb of the FM broadcast wave Wb and the frequency Fx, a frequency component Cc of a frequency Fcx which is a difference between the center frequency Fc of the FM broadcast wave Wc and the frequency Fx, and a frequency component Cd of a frequency Fdx which is a difference between the center frequency Fd of the FM broadcast wave Wd and the frequency Fx.

[0048] The baseband signals BI and BQ indicated by the demodulated data DI and DQ may further include frequency components CIa of frequency Faxn with the sign of frequency Fax reversed, frequency components CIb of frequency Fbxn with the sign of frequency Fbx reversed, frequency components CIc of frequency Fcxn with the sign of frequency Fcx reversed, and frequency components CId of frequency Fdxn with the sign of frequency Fdx reversed, as image waves of the FM broadcast waves Wa, Wb, Wc, and Wd, according to the amplitude or phase deviation between the baseband signals BI and BQ. For example, the frequency Fx is preset according to the known center frequencies Fa, Fb, Fc, and Fd so that the frequency components Ca, Cb, Cc, Cd and the frequency components CIa, CIb, CIc, CId do not overlap.

[0049] Referring again to FIG. 4, the receiving unit 31 packs the demodulated data DI and DQ every power-of-two number of samples and outputs them to the conversion unit 32. As an example, the receiving unit 31 packs the demodulated data DI received from ADC15I every N samples and outputs it to the conversion unit 32, and packs the demodulated data DQ received from ADC15Q every N samples and outputs it to the conversion unit 32. Here, N is a power of two, for example, 512.

[0050] The conversion unit 32 generates frequency-axis data FDI and FDQ indicating the frequency spectra of the baseband signals BI and BQ indicated by the demodulated data DI and DQ by performing a Fourier transform on the demodulated data DI and DQ. For example, the conversion unit 32 performs a Fourier transform on the demodulated data DI and DQ every power-of-two number of samples.

[0051] More specifically, the conversion unit 32 receives the N-sample demodulated data DI packed from the receiving unit 31, and performs FFT (Fast Fourier Transform) using butterfly operations on the received demodulated data DI to generate N-sample frequency-axis data FDI that divides the frequency range from -fn to fn into N parts. Here, fn is the Nyquist frequency and is 1 / 2 of the sampling frequency fs.

[0052] FIG. 6 is a diagram showing an example of a frequency spectrum indicated by frequency-axis data generated by a conversion unit in a balance correction unit according to the first embodiment of the present disclosure. FIG. 6 shows a part of the frequency spectrum indicated by the frequency-axis data FDI, and shows the frequency spectrum of a frequency region including frequencies Fax and Faxn. In FIG. 6, the horizontal axis represents frequency, and the vertical axis represents spectrum intensity.

[0053] In the same manner as the frequency-axis data FDI, the conversion unit 32 receives the demodulated data DQ of 512 samples packed from the reception unit 31, and performs an FFT using a butterfly operation on the received demodulated data DQ to generate N-sample frequency-axis data FDQ obtained by dividing the frequency region from -fn to fn into N parts. The conversion unit 32 outputs the generated frequency-axis data FDI and FDQ to the correction unit 33.

[0054] The correction unit 33 performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data FDI and FDQ generated by the conversion unit 32. For example, in the correction process, the correction unit 33 multiplies the frequency-axis data FDI and FDQ by an attenuation coefficient Ac representing a cosine wave for one period to attenuate the intensity of the frequency region.

[0055] FIG. 7 is a diagram showing an example of a frequency spectrum indicated by frequency-axis data after the correction process by the correction unit in the balance correction unit according to the first embodiment of the present disclosure. FIG. 7 shows a part of the frequency spectrum indicated by the frequency-axis data FDIP which is the frequency-axis data FDI after the correction process, and shows the frequency spectrum of a frequency region including frequencies Fax and Faxn. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents spectrum intensity.

[0056] Referring to FIG. 7, the correction unit 33 multiplies the attenuation coefficient Ac to a frequency region FWa with a predetermined width including the frequency Faxn, a frequency region FWb with a predetermined width including the frequency Fbxn, a frequency region FWc with a predetermined width including the frequency Fcxn, and a frequency region FWd with a predetermined width including the frequency Fdxn in the frequency axis data FDI, thereby generating frequency axis data FDIP indicating a frequency spectrum in which the frequency components CIa, CIb, CIc, and CId that are image waves are attenuated.

[0057] In the same manner as the frequency axis data FDIP, the correction unit 33 multiplies the attenuation coefficient Ac to the frequency regions FWa, FWb, FWc, and FWd in the frequency axis data FDQ, thereby generating frequency axis data FDQP indicating a frequency spectrum in which the frequency components CIa, CIb, CIc, and CId that are image waves are attenuated. The correction unit 33 outputs the generated frequency axis data FDIP and FDQP to the inverse transform unit 34.

[0058] The inverse transform unit 34 generates time axis data TDIP and TDQP by performing an inverse Fourier transform on the frequency spectra indicated by the frequency axis data FDIP and FDQP after the correction process by the correction unit 33.

[0059] More specifically, the inverse transform unit 34 receives N samples of frequency axis data FDIP and FDQP from the correction unit 33, and performs IFFT (Inverse FFT) using butterfly operations on the received frequency axis data FDIP and FDQP, thereby generating N samples of time axis data TDIP and TDQP. The inverse transform unit 34 outputs the generated time axis data TDIP and TDQP to the IP transmission unit 17.

[0060] The IP transmission unit 17 includes the time-axis data TDIP and TDQP received from the inverse conversion unit 34 in an IP packet and transmits the data to the FM transmission device 201 via the IP network 311. More specifically, the IP transmission unit 17 generates an IP packet PI including the time-axis data TDIP and transmits the generated IP packet PI to the FM transmission device 201 via the IP network 311. Further, the IP transmission unit 17 generates an IP packet PQ including the time-axis data TDQP and transmits the generated IP packet PQ to the FM transmission device 201 via the IP network 311.

[0061] (FM transmission device) FIG. 8 is a diagram showing the configuration of the FM transmission device according to the first embodiment of the present disclosure. Referring to FIG. 8, the FM transmission device 201 includes an IP reception unit 51, a digital quadrature modulator 52, an LFO 53, a DAC (Digital-to-Analog Converter) 54, and an RF amplifier unit 55.

[0062] The IP reception unit 51 receives the IP packets PI and PQ from the FM reception device 101 via the IP network 311. The IP reception unit 51 acquires the time-axis data TDIP and TDQP from the received IP packets PI and PQ and outputs the data to the digital quadrature modulator 52.

[0063] The LFO 53 is, for example, a crystal oscillator, generates a local signal Ly having a frequency Fy, and outputs the generated local signal Ly to the digital quadrature modulator 52. The frequency Fy may be the same as or different from the frequency Fx.

[0064] The digital quadrature modulator 52 generates modulated data obtained by quadrature modulating the time-axis data TDIP and TDQP received from the IP reception unit 51. More specifically, the digital quadrature modulator 52 generates modulated data by quadrature modulating the time-axis data TDIP and TDQP using the local signal Ly received from the LFO 53, and outputs the generated modulated data to the DAC 54.

[0065] The DAC54 generates an RF signal by analog-converting the modulation data received from the digital quadrature modulator 52, and outputs the generated RF signal to the RF amplifier section 55.

[0066] The RF amplifier section 55 amplifies the RF signal received from the DAC54 and transmits it to the CATV network 321.

[0067] [Operation flow] FIG. 9 is a flowchart defining an example of an operation procedure when the balance correction section according to the first embodiment of the present disclosure performs correction processing.

[0068] Referring to FIG. 9, first, the balance correction section 16 waits for the number of samples of the demodulation data DI and DQ received from the ADCs 15I and 15Q to reach N (NO in step S11). When the number of samples of the demodulation data DI and DQ reaches N (YES in step S11), frequency-axis data FDI and FDQ are generated by performing an FFT using a butterfly operation on the N-sample demodulation data DI and the N-sample demodulation data DQ (step S12).

[0069] Next, the balance correction section 16 performs correction processing. More specifically, in the correction processing, the balance correction section 16 multiplies the frequency-axis data FDI and FDQ by an attenuation coefficient Ac to generate frequency-axis data FDIP and FDQP indicating a frequency spectrum in which frequency components CIa, CIb, CIc, and CId that are image waves are attenuated (step S13).

[0070] Next, the balance correction section 16 generates time-axis data TDIP and TDQP by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data FDIP and FDQP (step S14).

[0071] Next, the balance correction section 16 outputs the generated time-axis data TDIP and TDQP to the IP transmission section 17 (step S15).

[0072] Next, the balance correction unit 16 waits for the number of samples of the demodulated data DI and DQ to reach N again (NO in step S11).

[0073] FIG. 10 is a diagram showing an example of a sequence of transmission of an FM broadcast wave in a transmission system according to the first embodiment of the present disclosure.

[0074] Referring to FIG. 10, first, the FM receiver 101 starts receiving an RF signal including FM broadcast waves Wa, Wb, Wc, and Wd (step S21).

[0075] Next, the FM receiver 101 generates baseband signals BI and BQ by down-converting the RF signal using local signals LI and LQ (step S22).

[0076] Next, the FM receiver 101 converts the baseband signal BI that has passed through the LPF 14I and the baseband signal BQ that has passed through the LPF 14Q into digital demodulated data DI and DQ (step S23).

[0077] Next, the FM receiver 101 generates frequency-axis data FDI and FDQ by performing an FFT using a butterfly operation on N samples of the demodulated data DI and N samples of the demodulated data DQ (step S24).

[0078] Next, the FM receiver 101 performs a correction process. More specifically, in the correction process, the FM receiver 101 multiplies the frequency-axis data FDI and FDQ by an attenuation coefficient Ac to generate frequency-axis data FDIP and FDQP indicating a frequency spectrum in which frequency components CIa, CIb, CIc, and CId that are image waves are attenuated (step S25).

[0079] Next, the FM receiver 101 generates time-axis data TDIP and TDQP by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data FDIP and FDQP (step S26).

[0080] Next, the FM receiver 101 includes the generated time-axis data TDIP and TDQP in IP packets PI and PQ, and transmits them to the FM transmitter 201 via the IP network 311 (step S27).

[0081] Next, the FM transmitter 201 acquires the time-axis data TDIP and TDQP from the IP packets PI and PQ received from the FM receiver 101 via the IP network 311, and generates modulated data obtained by quadrature-modulating the time-axis data TDIP and TDQP (step S28).

[0082] Next, the FM transmitter 201 generates an RF signal by analog-converting the generated modulated data (step S29).

[0083] Next, the FM transmitter 201 amplifies the generated RF signal and transmits it to the CATV network 321 (step S30).

[0084] Note that in the FM receiver 101 according to the first embodiment of the present disclosure, the receiving unit 11 is configured to receive an RF signal including FM broadcast waves of a plurality of channels, but the present disclosure is not limited thereto. The receiving unit 11 may be configured to receive an RF signal including an FM broadcast wave of one channel.

[0085] Also, in the FM receiver 101 according to the first embodiment of the present disclosure, the conversion unit 32 in the balance correction unit 16 is configured to perform Fourier transform on the demodulated data DI and DQ for each number of samples that is a power of 2, but the present disclosure is not limited thereto. The conversion unit 32 may be configured to perform Fourier transform on the demodulated data DI and DQ for each number of samples that is not a power of 2.

[0086] Also, in the FM receiver 101 according to the first embodiment of the present disclosure, although the correction unit 33 in the balance correction unit 16 is configured to multiply the frequency-axis data FDI and FDQ by the attenuation coefficient Ac in the correction process, the present disclosure is not limited thereto. The correction unit 33 may be configured to multiply the frequency-axis data FDI and FDQ by a predetermined attenuation coefficient different from the attenuation coefficient Ac in the correction process, or may be configured to remove data in a part of the frequency region in the frequency spectrum indicated by the frequency-axis data FDI and FDQ.

[0087] (Modification Example 1) FIG. 11 is a diagram showing the configuration of an FM transmitter according to Modification Example 1 of the first embodiment of the present disclosure. Referring to FIG. 11, the FM transmitter 202 includes an orthogonal modulator 62 instead of the digital orthogonal modulator 52, an LFO 63 instead of the LFO 53, and DACs 64I and 64Q instead of the DAC 54, as compared with the FM transmitter 201. The transmission system 401 may be configured to include the FM transmitter 202 instead of the FM transmitter 201.

[0088] The LFO 63 is, for example, a crystal oscillator, generates a reference signal with a frequency Fv, and outputs the generated reference signal to the orthogonal modulator 62. The frequency Fv may be the same as or different from the frequency Fx.

[0089] The IP receiver 51 outputs the time-axis data TDIP acquired from the IP packet PI to the DAC 64I, and outputs the time-axis data TDQP acquired from the IP packet PQ to the DAC 64Q.

[0090] The DAC 64I generates a time-axis signal TIP by analog-converting the time-axis data TDIP received from the IP receiver 51, and outputs the generated time-axis signal TIP to the orthogonal modulator 62.

[0091] The DAC64Q generates a time-axis signal TQP by analog-converting the time-axis data TDQP received from the IP receiver 51, and outputs the generated time-axis signal TQP to the quadrature modulator 62.

[0092] The quadrature modulator 62 generates an RF signal obtained by quadrature-modulating the time-axis signals TIP and TQP received from the DAC64I and 64Q. More specifically, the quadrature modulator 62 generates a local signal LIv, which is a local oscillation signal synchronized with the reference signal received from the LFO 63, and a local signal LQv whose phase is shifted by π / 2 with respect to the local signal LIv. The quadrature modulator 62 generates an RF signal by quadrature-modulating the time-axis signals TIP and TQP using the local signals LIv and LQv, and outputs the generated RF signal to the RF amplifier section 55.

[0093] (Modification Example 2) In the transmission system 401 according to the first embodiment of the present disclosure, it was assumed that the FM receiver 101 includes the balance correction unit 16 and the time-axis data TDIP and TDQP are transmitted from the FM receiver 101 to the FM transmitter 201, but the present disclosure is not limited thereto.

[0094] FIG. 12 is a diagram showing the configuration of a transmission system according to Modification Example 2 of the first embodiment of the present disclosure. Referring to FIG. 12, the transmission system 402 according to Modification Example 2 of the first embodiment includes an FM receiver 102 instead of the FM receiver 101 and an FM transmitter 203 instead of the FM transmitter 201 as compared with the transmission system 401. In the transmission system 402, the demodulated data DI and DQ are transmitted from the FM receiver 102 to the FM transmitter 203. This will be specifically described below.

[0095] (FM Receiver) FIG. 13 is a diagram showing the configuration of an FM receiver according to Modification Example 2 of the first embodiment of the present disclosure. Referring to FIG. 13, the FM receiver 102 does not include the balance correction unit 16 as compared with the FM receiver 101.

[0096] ADC15I converts the baseband signal BI that has passed through LPF14I into digital demodulated data DI for each sampling frequency fs, and outputs the converted demodulated data DI to the IP transmission unit 17. Also, ADC15Q converts the baseband signal BQ that has passed through LPF14Q into digital demodulated data DQ for each sampling frequency fs, and outputs the converted demodulated data DQ to the IP transmission unit 17.

[0097] The IP transmission unit 17 includes the demodulated data DI and DQ received from ADC15I and 15Q in IP packets and transmits them to the FM transmission device 203 via the IP network 311. More specifically, the IP transmission unit 17 generates an IP packet PI including the demodulated data DI, and transmits the generated IP packet PI to the FM transmission device 203 via the IP network 311. Also, the IP transmission unit 17 generates an IP packet PQ including the demodulated data DQ, and transmits the generated IP packet PQ to the FM transmission device 203 via the IP network 311.

[0098] (FM Transmission Device) FIG. 14 is a diagram showing the configuration of an FM transmission device according to Modification 2 of the first embodiment of the present disclosure. Referring to FIG. 14, the FM transmission device 203 further includes a balance correction unit 16 as compared with the FM transmission device 201.

[0099] The IP reception unit 51 receives the IP packets PI and PQ from the FM reception device 102 via the IP network 311. The IP reception unit 51 acquires the demodulated data DI and DQ from the received IP packets PI and PQ and outputs them to the balance correction unit 16.

[0100] In the balance correction unit 16, the receiving unit 31 receives the demodulated data DI and DQ from the IP receiving unit 51. The conversion unit 32 generates frequency-axis data FDI and FDQ by performing a Fourier transform on the demodulated data DI and DQ. The correction unit 33 generates frequency-axis data FDIP and FDQP by performing a correction process that attenuates the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data FDI and FDQ. The inverse conversion unit 34 generates time-axis data TDIP and TDQP by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data FDIP and FDQP. The inverse conversion unit 34 outputs the generated time-axis data TDIP and TDQP to the digital quadrature modulator 52.

[0101] The digital quadrature modulator 52 generates modulated data obtained by performing quadrature modulation on the time-axis data TDIP and TDQP received from the balance correction unit 16, and outputs the generated modulated data to the DAC 54.

[0102] (Modification Example 3) FIG. 15 is a diagram showing the configuration of a transmission system according to Modification Example 3 of the first embodiment of the present disclosure. Referring to FIG. 15, a transmission system 403 according to Modification Example 3 of the first embodiment includes an FM receiving device 103 instead of the FM receiving device 101 and an FM transmitting device 204 instead of the FM transmitting device 201 as compared with the transmission system 401. In the transmission system 403, a part of the processing in the balance correction unit 16 is performed in the FM receiving device 103, and another part of the processing in the balance correction unit 16 is performed in the FM transmitting device 204. For example, in the transmission system 403, the frequency-axis data FDIP and FDQP are transmitted from the FM receiving device 103 to the FM transmitting device 204. Specific description will be given below.

[0103] (FM Receiving Device) FIG. 16 is a diagram showing the configuration of an FM receiving device according to Modification Example 3 of the first embodiment of the present disclosure. Referring to FIG. 16, the FM receiving device 103 includes a data processing unit 16A1 instead of the balance correction unit 16 as compared with the FM receiving device 101.

[0104] FIG. 17 is a diagram showing the configuration of a data processing unit in an FM receiver according to Modification 3 of the first embodiment of the present disclosure. Referring to FIG. 17, the data processing unit 16A1 does not include an inverse conversion unit 34 as compared with the balance correction unit 16.

[0105] In the data processing unit 16A1, the receiving unit 31 receives demodulated data DI and DQ from the ADCs 15I and 15Q, respectively. The conversion unit 32 generates frequency-axis data FDI and FDQ by performing a Fourier transform on the demodulated data DI and DQ. The correction unit 33 performs a correction process of attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data FDI and FDQ, thereby generating frequency-axis data FDIP and FDQP. The correction unit 33 outputs the generated frequency-axis data FDIP and FDQP to the IP transmission unit 17.

[0106] The IP transmission unit 17 includes the frequency-axis data FDIP and FDQP received from the correction unit 33 in an IP packet and transmits the IP packet to the FM transmitter 204 via the IP network 311. More specifically, the IP transmission unit 17 generates an IP packet PI including the frequency-axis data FDIP, and transmits the generated IP packet PI to the FM transmitter 204 via the IP network 311. Further, the IP transmission unit 17 generates an IP packet PQ including the frequency-axis data FDQP, and transmits the generated IP packet PQ to the FM transmitter 204 via the IP network 311.

[0107] (FM Transmitter) FIG. 18 is a diagram showing the configuration of an FM transmitter according to Modification 3 of the first embodiment of the present disclosure. Referring to FIG. 18, the FM transmitter 204 includes a data processing unit 16A2 instead of the balance correction unit 16 as compared with the FM transmitter 203 according to Modification 2.

[0108] The IP reception unit 51 receives the IP packets PI and PQ from the FM receiver 102 via the IP network 311. The IP reception unit 51 acquires the frequency-axis data FDIP and FDQP from the received IP packets PI and PQ and outputs the frequency-axis data FDIP and FDQP to the data processing unit 16A2.

[0109] FIG. 19 is a diagram showing the configuration of a data processing unit in an FM transmission apparatus according to Modification 3 of the first embodiment of the present disclosure. Referring to FIG. 19, the data processing unit 16A2 does not include the conversion unit 32 and the correction unit 33 as compared with the balance correction unit 16.

[0110] In the data processing unit 16A2, the receiving unit 31 receives the frequency-axis data FDIP and FDQP from the IP receiving unit 51. The inverse conversion unit 34 generates time-axis data TDIP and TDQP by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data FDIP and FDQP. The inverse conversion unit 34 outputs the generated time-axis data TDIP and TDQP to the digital quadrature modulator 52.

[0111] Note that, in the transmission system 403 according to Modification 3 of the first embodiment of the present disclosure, instead of the data processing unit 16A1 in the FM receiver 103 not including the correction unit 33, the data processing unit 16A2 in the FM transmitter 204 may include the correction unit 33. That is, the digital data transmitted from the FM receiver 103 to the FM transmitter 204 may be the frequency-axis data FDI and FDQ.

[0112] FIG. 20 is a diagram showing another example of the configuration of a data processing unit in an FM transmission apparatus according to Modification 3 of the first embodiment of the present disclosure. Referring to FIG. 20, the data processing unit 16B2 further includes a removal unit 36 as compared with the data processing unit 16A2. The FM transmitter 204 may be configured to include the data processing unit 16B2 instead of the data processing unit 16A2.

[0113] In the data processing unit 16B2, the receiving unit 31 receives the frequency-axis data FDIP and FDQP from the IP receiving unit 51. The receiving unit 31 outputs the received frequency-axis data FDIP and FDQP to the removal unit 36.

[0114] The removal unit 36 performs a removal process of removing frequency components derived from a predetermined FM broadcast wave preselected by an administrator of the transmission system 403. For example, the removal unit 36 removes the frequency component Ca derived from the FM broadcast wave Wc in the removal process.

[0115] More specifically, the removal unit 36 generates frequency-axis data FDIPd in which the frequency component Ca is attenuated by multiplying a frequency region FWcd having a predetermined width including the frequency Fcx in the frequency-axis data FDIP received from the reception unit 31 by an attenuation coefficient Acd representing a cosine wave for one period. For example, the frequency region FWcd is larger than the frequency region FWc in which the attenuation coefficient Ac is multiplied in the correction process by the correction unit 33.

[0116] In the same manner as the frequency-axis data FDIPd, the removal unit 36 generates frequency-axis data FDQPd in which the frequency component Ca is attenuated by multiplying the attenuation coefficient Acd by the frequency region FWcd in the frequency-axis data FDQP. The removal unit 36 outputs the generated frequency-axis data FDIPd and FDQPd to the inverse conversion unit 34.

[0117] The inverse conversion unit 34 generates time-axis data TDIPd and TDQPd by performing an inverse Fourier transform on the frequency spectra indicated by the frequency-axis data FDIPd and FDQPd received from the removal unit 36. The inverse conversion unit 34 outputs the generated time-axis data TDIPd and TDQPd to the digital orthogonal modulator 52.

[0118] In this way, with the configuration in which the data processing unit 16B2 in the FM transmitter 204 includes the removal unit 36, in the FM transmitter 204, the FM broadcast wave output to the CATV network 321 can be selectively transmitted or discarded.

[0119] Note that, in the FM receiver 101 according to the first embodiment of the present disclosure, the balance correction unit 16 may have a configuration including the removal unit 36.

[0120] By the way, a technique capable of suppressing an image wave in an FM broadcast wave with a simple process is desired.

[0121] More specifically, in a conventional transmission system that transmits FM broadcast waves for audio broadcasting using a CATV network, it is common to amplify an RF signal received via an antenna using an analog amplifier, perform frequency conversion using a heterodyne method, and output it to the CATV network. However, in such a transmission method, there is a problem that maintenance management of the analog amplifier in the transmission network between the FM receiver that receives the RF signal and the FM transmitter that outputs the RF signal to the CATV network is required, and the maintenance cost is high. Also, when it is necessary to replace the frequency of the FM broadcast wave, complex processing may be required in the heterodyne method.

[0122] Therefore, in recent years, a technique has been proposed that quadrature demodulates the received RF signal and digitally transmits the FM broadcast wave between the FM receiver and the FM transmitter, eliminating the need for maintenance management in the transmission network.

[0123] However, in each process of quadrature demodulation of the RF signal, filtering of the baseband signals BI and BQ obtained by quadrature demodulation, AD conversion of the filtered baseband signals BI and BQ, and quadrature modulation of the demodulated data DI and DQ obtained by AD conversion, if there is a deviation in amplitude or phase between the I signal and the Q signal, an image wave may appear at the mirror frequency of the FM broadcast wave.

[0124] When an image wave occurs in video broadcasting, only the quality of the video reproduced on the television receiver deteriorates. On the other hand, when an image wave occurs in audio broadcasting, if a radio receiver that has received the RF signal tunes to the frequency of the image wave, the audio based on the image wave will be reproduced. Therefore, in a radio receiver, malfunction such as automatic tuning to the frequency of the image wave may occur.

[0125] In the technique described in Patent Document 1, the component of the image wave can be removed using a correction coefficient in the demodulated signal which is a time-axis signal. However, in the technique described in Patent Document 1, in order to remove the component of the image wave, it is necessary to filter the demodulated signal using an FIR filter with a large number of taps. Therefore, in the technique described in Patent Document 1, for example, when the number of samples of the demodulated signal is N, in order to remove the component of the image wave in the demodulated signal in the time-axis domain, it is necessary to perform N×N complex multiplications.

[0126] On the other hand, in the balance correction unit 16 according to the first embodiment of the present disclosure, the receiving unit 31 receives demodulation data DI, DQ based on the baseband signals BI, BQ obtained by quadrature demodulating an RF signal including FM broadcast waves Wa, Wb, Wc, Wd. The conversion unit 32 generates frequency-axis data FDI, FDQ indicating the frequency spectra of the baseband signals BI, BQ by performing a Fourier transform on the demodulation data DI, DQ received by the receiving unit 31. The correction unit 33 performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data FDI, FDQ generated by the conversion unit 32. The inverse conversion unit 34 generates time-axis data TDIP, TDQP by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data FDIP, FDQP after the correction process by the correction unit 33.

[0127] In this way, the demodulated data DI and DQ are Fourier-transformed to generate frequency-axis data FDI and FDQ, and a correction process is performed to attenuate the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data FDI and FDQ. The frequency spectrum indicated by the corrected frequency-axis data FDIP and FDQP is inverse Fourier-transformed to generate time-axis data TDIP and TDQP. With this configuration, the component of the image wave can be suppressed by performing arithmetic processing on a partial frequency region of the frequency-axis data FDI and FDQ. Therefore, the component of the image wave can be suppressed with less arithmetic processing. Specifically, when the number of samples of the baseband signals BI and BQ is N, the component of the image wave can be suppressed by N×log2(N) operations. Therefore, the image wave in the FM broadcast wave can be suppressed with a simple process.

[0128] Next, another embodiment of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0129] <Second Embodiment> This embodiment relates to a signal processor 501 that generates an RF signal based on the frequency-axis data FDIP and FDQP after correction processing, as compared with the FM receiver 101 according to the first embodiment. Except for the content described below, it is the same as the FM receiver 101, the FM transmitter 201, and the transmission system 401 according to the first embodiment.

[0130] FIG. 21 is a diagram showing the configuration of a signal processor according to the second embodiment of the present disclosure. Referring to FIG. 21, the signal processor 501 includes a digital quadrature modulator 52, an LFO 56, a DAC 54, and an RF amplifier section 55 instead of the IP transmission section 17, as compared with the FM receiver 101 according to the first embodiment. The signal processor 501 is an example of an FM broadcast wave processing device. The quadrature demodulator 12 is an example of a demodulation section. The digital quadrature modulator 52 is an example of a modulation section.

[0131] As described above, LFO13 is, for example, a crystal oscillator, generates a reference signal of frequency Fx, and outputs the generated reference signal to the quadrature demodulator 12.

[0132] LFO56 is, for example, a crystal oscillator, generates a local signal Lz of frequency Fz, and outputs the generated local signal Lz to the digital quadrature modulator 52. The frequency Fz is different from the frequency Fx.

[0133] The quadrature demodulator 12 generates baseband signals BI, BQ by down-converting the RF signal received from the receiving unit 11 using local signals LI, LQ of frequency Fx based on the reference signal received from LFO13, and outputs the generated baseband signals BI, BQ to LPF14I, 14Q respectively. The baseband signals BI, BQ are an example of demodulated signals. The local signals LI, LQ are an example of the first local signals.

[0134] The inverse conversion unit 34 in the balance correction unit 16 generates time-axis data TDIP, TDQP of N samples, and outputs the generated time-axis data TDIP, TDQP to the digital quadrature modulator 52.

[0135] The digital quadrature modulator 52 generates modulation data by quadrature-modulating the time-axis data TDIP, TDQP generated by the inverse conversion unit 34 in the balance correction unit 16 using the local signal Lz of frequency Fz received from LFO56, and outputs the generated modulation data to the DAC54.

[0136] The DAC54 generates an RF signal including FM broadcast waves Wa, Wb, Wc, Wd of center frequencies Fap, Fbp, Fcp, Fdp different from the center frequencies Fa, Fb, Fc, Fd by analog-converting the modulation data received from the digital quadrature modulator 52, and outputs the generated RF signal to the RF amplifier unit 55.

[0137] The RF amplifier unit 55 amplifies the RF signal received from the DAC 54 and transmits it to the CATV network 321. Note that the RF amplifier unit 55 may be configured to output the amplified RF signal to a device other than the signal processor 501 instead of transmitting it to the CATV network 321.

[0138] FIG. 22 is a diagram showing the configuration of a signal processor according to a modification of the second embodiment of the present disclosure. Referring to FIG. 22, the signal processor 502 includes a balance correction unit 66 instead of the balance correction unit 16 as compared with the signal processor 501.

[0139] FIG. 23 is a diagram showing the configuration of the balance correction unit in the signal processor according to a modification of the second embodiment of the present disclosure. Referring to FIG. 23, the balance correction unit 66 includes a correction removal unit 35 instead of the correction unit 33 as compared with the balance correction unit 16.

[0140] In addition to the correction process, the correction removal unit 35 performs a removal process of removing frequency components derived from a predetermined FM broadcast wave preselected by the user of the signal processor 502. For example, the correction removal unit 35 removes the frequency component Ca derived from the FM broadcast wave Wc in the removal process.

[0141] More specifically, the correction removal unit 35 multiplies a decay coefficient Acd representing a cosine wave for one period by a predetermined width frequency region FWcd including the frequency Fcx in the frequency axis data FDI, thereby generating frequency axis data FDIPd in which the frequency component Ca is attenuated. For example, the frequency region FWcd is larger than the frequency region FWc where the attenuation coefficient Ac is multiplied in the correction process.

[0142] The correction removal unit 35 generates frequency axis data FDQPd in which the frequency component Ca is attenuated by multiplying the decay coefficient Acd by the frequency region FWcd in the frequency axis data FDQ in the same manner as the frequency axis data FDIPd. The correction removal unit 35 outputs the generated frequency axis data FDIPd and FDQPd to the inverse conversion unit 34.

[0143] The inverse conversion unit 34 generates time-axis data TDIPd and TDQPd by performing an inverse Fourier transform on the frequency spectra indicated by the frequency-axis data FDIPd and FDQPd received from the correction removal unit 35, and outputs the generated time-axis data TDIPd and TDQPd to the digital quadrature modulator 52.

[0144] The digital quadrature modulator 52 generates modulation data by performing quadrature modulation on the time-axis data TDIPd and TDQPd generated by the inverse conversion unit 34 in the balance correction unit 66 using the local signal Lz of the frequency Fz received from the LFO 56, and outputs the generated modulation data to the DAC 54.

[0145] The DAC 54 generates an RF signal that includes FM broadcast waves Wa, Wb, and Wd but does not include the FM broadcast wave Wc by analog-converting the modulation data received from the digital quadrature modulator 52, and outputs the generated RF signal to the RF amplifier unit 55.

[0146] The above embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

[0147] Each process (each function) of the above-described embodiment is realized by a processing circuit including one or more processors. The processing circuit may be configured by, in addition to the one or more processors, an integrated circuit in which one or more memories, various analog circuits, and various digital circuits are combined. The one or more memories store a program (instruction) for causing the one or more processors to execute each of the above processes. The one or more processors may execute each of the above processes according to the program read from the one or more memories, or may execute each of the above processes according to a logic circuit designed in advance to execute each of the above processes. The processor may be various processors suitable for computer control, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit). Note that the plurality of physically separated processors may cooperate with each other to execute each of the above processes. For example, the processors mounted on each of a plurality of physically separated computers may cooperate with each other via a network such as a LAN (Local Area Network), a WAN (Wide Area Network), and the Internet to execute each of the above processes. The program may be installed in the memory via the network from an external server device or the like, or may be distributed in a state stored in a recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), and a semiconductor memory, and may be installed in the memory from the recording medium.

[0148] The above description includes the features appended below. [Appendix 1] A receiving unit that receives demodulation data based on a demodulated signal obtained by quadrature demodulating an RF signal including an FM broadcast wave; A conversion unit that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data received by the receiving unit; A correction unit that performs a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion unit; An inverse conversion unit that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction unit, and an FM broadcast wave correction device. The conversion unit Fourier-transforms the demodulation data using a butterfly operation for every number of samples that is a power of 2. The inverse conversion unit generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data using a butterfly operation.

[0149] [Appendix 2] Comprising a processing circuit, The processing circuit, Receives demodulation data based on a demodulated signal obtained by quadrature demodulating an RF signal including an FM broadcast wave, Generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the received demodulation data, Performs a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the generated frequency-axis data, Generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process, and an FM broadcast wave correction device.

Explanation of Reference Numerals

[0150] 11 Receiving unit 12 Quadrature demodulator 13,53,56,63 LFO 14I,14Q LPF 15I,15Q ADC 16,66 Balance correction unit 16A1, 16A2, 16B2 data processing unit 17 IP transmission unit 31 receiving unit 32 conversion unit 33 correction unit 34 inverse conversion unit 35 correction removal unit 36 removal unit 41 PLL unit 42I, 42Q mixers 51 IP receiving unit 52, 62 digital quadrature modulators 54, 64I, 64Q DACs 55 RF amplification unit 101, 102, 103 FM receivers 201, 202, 203, 204 FM transmitters 311 IP network 321 CATV network 401, 402, 403 transmission systems 501, 502 signal processors

Claims

1. A receiving unit that receives demodulated data based on a demodulated signal obtained by quadrature demodulating an RF (Radio Frequency) signal including an FM (Frequency Modulation) broadcast wave; A conversion unit that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulated data received by the receiving unit; A correction unit that performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion unit; An FM broadcast wave correction apparatus comprising: an inverse conversion unit that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction unit.

2. The receiving unit receives the demodulated data based on the demodulated signal obtained by quadrature demodulating the RF signal using a local signal, The local frequency, which is the frequency of the local signal, is set to a value such that the frequency obtained by folding back the frequency of the first FM broadcast wave included in the RF signal at the local frequency does not overlap with the frequency of the first FM broadcast wave, The FM broadcast wave correction apparatus according to claim 1, wherein when the RF signal further includes a second FM broadcast wave, the local frequency is further set to a value such that the frequency obtained by folding back the frequency of the first FM broadcast wave at the local frequency does not overlap with the frequency of the second FM broadcast wave.

3. The conversion unit according to claim 1 or claim 2, wherein the conversion unit performs a Fourier transform on the demodulated data for each number of samples that is a power of 2.

4. The correction unit according to claim 1 or claim 2, wherein in the correction process, the correction unit attenuates the intensity of the frequency region by multiplying the frequency-axis data by an attenuation coefficient representing a cosine wave for one period.

5. An RF receiving apparatus that receives an RF signal including an FM broadcast wave and generates a demodulated signal obtained by quadrature demodulating the received RF signal; A conversion apparatus that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulated data based on the demodulated signal generated by the RF receiving apparatus; A correction apparatus that performs a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion apparatus; An inverse conversion device that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction device; An FM broadcast wave transmission system comprising: an RF transmission device that generates modulation data obtained by quadrature-modulating the time-axis data generated by the inverse conversion device, and transmits an RF signal based on the generated modulation data. **Claim 6** A receiving unit that receives an RF signal including an FM broadcast wave; A demodulation unit that generates a demodulated signal by quadrature-demodulating the RF signal received by the receiving unit using a first local signal; A conversion unit that generates frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data based on the demodulated signal generated by the demodulation unit; A correction unit that performs a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the frequency-axis data generated by the conversion unit; An inverse conversion unit that generates time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process by the correction unit; An FM broadcast wave processing device comprising: a modulation unit that generates modulation data by quadrature-modulating the time-axis data generated by the inverse conversion unit using a second local signal having a frequency different from that of the first local signal. **Claim 7** An FM broadcast wave correction method in an FM broadcast wave correction device, the method comprising: receiving demodulation data based on a demodulated signal obtained by quadrature-demodulating an RF signal including an FM broadcast wave; generating frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the received demodulation data; performing a correction process for attenuating the intensity of a partial frequency region in the frequency spectrum indicated by the generated frequency-axis data; and generating time-axis data by performing an inverse Fourier transform on the frequency spectrum indicated by the frequency-axis data after the correction process. **Claim 8** An FM broadcast wave transmission method in an FM broadcast wave transmission system, the method comprising: receiving an RF signal including an FM broadcast wave and generating a demodulated signal obtained by quadrature-demodulating the received RF signal; generating frequency-axis data indicating the frequency spectrum of the demodulated signal by performing a Fourier transform on the demodulation data based on the demodulated signal; Performing a correction process for attenuating the intensity of a part of the frequency region in the frequency spectrum indicated by the frequency axis data; Generating time axis data by performing inverse Fourier transform on the frequency spectrum indicated by the frequency axis data after the correction process; A method for transmitting an FM broadcast wave, including generating modulated data obtained by quadrature modulating the time axis data and transmitting an RF signal based on the generated modulated data.

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