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JP2017216510

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DESCRIPTION JP2017216510
Abstract: To provide a noise reduction device and a noise reduction method capable of reducing a
plurality of noise signals included in a received signal. A noise reduction apparatus according to
an aspect of an embodiment includes a detection unit, a calculation unit, and a reduction unit.
The detection unit detects frequency components of a plurality of noise signals included in the
received signal based on the frequency spectrum of the received signal. The calculation unit
calculates the coefficient based on the frequency component detected by the detection unit. The
reduction unit reduces n (n is a positive number of 2 or more) noise signals that are at least a
part of the plurality of noise signals from the reception signal according to the coefficient
calculated by the calculation unit. [Selected figure] Figure 1A
Noise reduction device and noise reduction method
[0001]
The present invention relates to a noise reduction device and a noise reduction method.
[0002]
Conventionally, when a system for receiving radio broadcast waves is mounted on a vehicle, for
example, such a system may receive a noise signal due to switching processing performed at the
time of power conversion of a battery of the vehicle.
Therefore, in the conventional system, the noise signal is reduced by reducing the output
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intensity of the peak frequency having the highest intensity among the frequency components
included in the reception signal (see, for example, Patent Document 1).
[0003]
JP, 2013-9066, A
[0004]
However, the prior art only reduces the noise signal of the highest intensity peak frequency.
Therefore, for example, when a plurality of noise signals are included in the reception signal,
such noise signals can not be reduced, and there is a possibility that the noise signal will remain
in the reception signal.
[0005]
The present invention has been made in view of the above, and an object of the present invention
is to provide a noise reduction device and a noise reduction method capable of reducing a
plurality of noise signals included in a received signal.
[0006]
In order to solve the above-mentioned subject and achieve an object, a noise reduction device of
the present invention is provided with a detection part, a calculation part, and a reduction part.
The detection unit detects frequency components of a plurality of noise signals included in the
received signal based on the frequency spectrum of the received signal. The calculation unit
calculates a coefficient based on the frequency component detected by the detection unit. The
reduction unit reduces n (n is a positive number of 2 or more) noise signals that are at least a
part of the plurality of noise signals from the reception signal according to the coefficient
calculated by the calculation unit.
[0007]
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According to the present invention, it is possible to provide a noise reduction device and a noise
reduction method capable of reducing a plurality of noise signals included in a received signal.
[0008]
FIG. 1A is a block diagram showing the configuration of a receiving apparatus according to the
first embodiment.
FIG. 1B is a diagram showing a received signal received by the receiving device according to the
first embodiment. FIG. 1C is a diagram showing a received signal from which a noise signal has
been removed by the receiving device according to the first embodiment. FIG. 2 is a block
diagram showing the configuration of a receiving apparatus according to the second
embodiment. FIG. 3 is a diagram showing the frequency distribution of the noise signal according
to the second embodiment. FIG. 4 is a flowchart showing noise reduction processing according to
the second embodiment. FIG. 5 is a block diagram showing the configuration of a receiving
apparatus according to the third embodiment. FIG. 6 is a flowchart showing noise reduction
processing according to the third embodiment. FIG. 7 is a block diagram showing the
configuration of a receiving apparatus according to a modification. FIG. 8 is a flowchart showing
noise reduction processing according to a modification.
[0009]
Hereinafter, embodiments of the noise reduction device and the noise reduction method
disclosed in the present application will be described in detail with reference to the
accompanying drawings. Note that the present invention is not limited by the embodiments
described below.
[0010]
First Embodiment A receiving device 1 according to a first embodiment of the present invention
will be described with reference to FIGS. 1A to 1C. FIG. 1A is a block diagram showing the
configuration of the receiving device 1 according to the present embodiment. Moreover, FIG. 1B
is a figure which shows the received signal which the receiver 1 which concerns on this
embodiment receives. FIG. 1C is a diagram showing a received signal from which a noise signal
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has been removed by the receiving device 1 according to the present embodiment.
[0011]
The receiving device 1 is mounted on a vehicle such as an automobile, for example. Further, the
receiving device 1 receives an amplitude-modulated radio broadcast wave (hereinafter also
referred to as an AM radio broadcast wave) transmitted using, for example, a medium wave band
of 526.5 kHz to 1606.5 kHz. It is assumed that the AM radio broadcast wave contains
information on voice (hereinafter also referred to as voice data).
[0012]
In addition, although this embodiment demonstrates the case where this receiving device 1 is
mounted in a vehicle, it is not limited to this. The receiving device 1 may be mounted, for
example, on a mobile object such as a train or an airplane, or an electric appliance such as a
radio receiver or a personal computer. Also, the receiving device 1 only needs to receive the
amplitude-modulated reception signal, and does not necessarily have to receive the radio
broadcast wave.
[0013]
<Receiver 1> As shown in FIG. 1A, the receiver 1 includes a noise reduction apparatus 10, an
antenna 20, and an RF (Radio Frequency) unit 30. The antenna 20 receives, for example, an AM
radio broadcast wave as a reception signal.
[0014]
The RF unit 30 performs signal processing such as amplification processing, A / D conversion
processing, down conversion, etc. on the reception signal received via the antenna 20.
[0015]
The noise reduction device 10 reduces a plurality of noise signals from the received signal.
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The noise reduction device 10 includes a detection unit 110, a calculation unit 120, and a
reduction unit 130.
[0016]
The detection unit 110 detects frequency components of a plurality of noise signals included in
the received signal based on the frequency spectrum of the received signal. As shown in FIG. 1B,
the reception signal includes the carrier wave Sc of the carrier frequency fc and the modulation
waves Sm1 and Sm2 of the upper side band Wm1 and the lower side band Wm2. Also, the
reception signal includes a plurality of noise signals such as periodic noise signals Sn11 to Sn13
generated from an inverter, and a noise signal Sn2 generated from a DCDC converter, for
example. Hereinafter, the noise signals Sn11 to Sn13 and Sn2 are collectively referred to as a
noise signal Sn. The noise signal Sn is a so-called peak noise having a peak at a specific
frequency.
[0017]
The detection unit 110 detects frequency components and signal levels of the plurality of noise
signals Sn, for example, by comparing the threshold value with the frequency spectrum of the
reception signal. Note that FIG. 1B illustrates the case where there are four noise signals Sn.
[0018]
The calculation unit 120 calculates a coefficient based on the frequency component and the
signal level detected by the detection unit 110. Such a coefficient is, for example, a filter
coefficient of the filtering process performed by the reduction unit 130. The calculation unit 120
calculates a coefficient so as to reduce the signal level of the received signal in the frequency
component detected by the detection unit 110 according to the signal level detected by the
detection unit 110. The coefficient may be calculated each time the detection unit 110 calculates
the noise signal Sn, but it is more preferable to perform the coefficient at a timing at which the
frequency as noise may change. The timing may be, for example, a timing of every predetermined
time or the like in consideration of the possibility of time fluctuation (a factor such as a
temperature change) when the operating condition of the converter (voltage conversion) changes
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when the vehicle is started.
[0019]
The reduction unit 130 reduces n (n is a positive number of 2 or more) noise signals Sn that are
at least a part of the plurality of noise signals Sn from the reception signal according to the
coefficient calculated by the calculation unit 120. The reducing unit 130 has, for example, a
filter, and reduces the noise signal Sn from the received signal by using the coefficient calculated
by the calculating unit 120 as a filter coefficient. As shown in FIG. 1C, the reception signal
obtained by reducing the plurality of noise signals Sn is reduced in the plurality of noise signals
Sn11 to Sn13 and Sn2, and becomes a signal including the carrier signal Sc and the modulation
signals Sm1 and Sm2. In FIG. 1C, the reduction unit 130 removes n = 4, that is, all the detected
noise signals Sn, but is not limited to this. The reduction unit 130 may reduce at least a part of
the detected noise signal Sn, such as reducing two noise signals Sn.
[0020]
Thus, the noise reduction device 10 of the reception device 1 according to the embodiment
detects the frequency components of the plurality of noise signals Sn. Further, the noise
reduction device 10 reduces the plurality of noise signals Sn from the received signal according
to the coefficient based on the detected frequency component. Thereby, the noise reduction
device 10 can reduce the plurality of noise signals Sn from the received signal.
[0021]
Second Embodiment A receiving apparatus 1A according to a second embodiment will be
described with reference to FIGS. FIG. 2 is a block diagram showing the configuration of the
receiving device 1A according to the second embodiment. The same components as those of the
receiving device 1 shown in FIG.
[0022]
<Receiver 1A> The receiver 1A shown in FIG. 2 includes a noise reduction device 10A. The noise
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reduction device 10A includes a detection unit 110A, a calculation unit 120A, a reduction unit
130A, and a storage unit 140.
[0023]
The detection unit 110A includes an analysis unit 111, a difference calculation unit 112, and a
noise detection unit 113. Further, the reduction unit 130A includes n first to n-th filters 131 to
13 n. Note that FIG. 2 shows the case of n = 4.
[0024]
The analysis unit 111 analyzes the frequency spectrum of the received signal. The analysis unit
111 performs FFT (Fast Fourier Transform: Fast Fourier Transform) processing on the received
signal to calculate the spectral intensity in each frequency component.
[0025]
The difference calculation unit 112 calculates the difference between the upper side band Wm1
and the lower side band Wm2 of the frequency spectrum of the received signal. Here, the
reception device 1A receives an AM radio broadcast wave as a reception signal. As shown in FIG.
1B, in AM radio broadcasting, signals are transmitted with predetermined bandwidths Wm1 and
Wm2 centering on the carrier frequency fc. Here, it is assumed that the predetermined
bandwidth is 15 kHz (fc ± 7.5 kHz).
[0026]
Further, the signals transmitted by AM radio broadcast have the same frequency distribution in
the bandwidth Wm1 (upper side band) on the high frequency side and the bandwidth Wm2
(lower side band) on the low frequency side from the carrier frequency fc.
[0027]
In the present embodiment, paying attention to this point, the modulation component of the
reception signal is reduced by calculating the difference between the spectral intensities of the
upper and lower sidebands Wm1 and Wm2 of the reception signal, and the detection accuracy of
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the noise component is improved.
[0028]
Specifically, the difference calculation unit 112 calculates the difference between the spectral
intensities of the upper and lower sidebands Wm1 and Wm2 located equidistant from the carrier
frequency fc among the spectral intensities of the upper and lower sidebands Wm1 and Wm2 of
the received signal. .
The difference calculation unit 112 calculates, for example, the result of subtracting the lower
sideband Wm2 from the upper sideband Wm1 located equidistant from the carrier frequency fc
as a difference.
[0029]
As described above, the signals transmitted by AM radio broadcast have upper and lower
sidebands Wm1 and Wm2 and a frequency distribution of line symmetry centered on the carrier
frequency fc.
Therefore, for example, when the difference between the upper and lower sidebands Wm1 and
Wm2 of the received signal is calculated, the frequency distribution of the difference is, as shown
in FIG. 3, the spectral intensity of the modulated signal Sm1 and Sm2 transmitted by AM radio
broadcast approximately zero And a distribution in which a plurality of noise signals Sn remain.
FIG. 3 is a diagram showing the frequency distribution of the noise signal Sn. Further, the
spectral intensity of the carrier frequency fc is removed by, for example, a notch filter or the like,
and is not used for correction of the spectral intensity or detection of noise.
[0030]
The noise detection unit 113 compares the absolute value of the difference calculated by the
difference calculation unit 112 with the threshold value Th1. When the difference before
calculating the absolute value is negative, it is the frequency component of the lower sideband,
and when it is positive, it is the frequency component of the upper sideband. The noise detection
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unit 113 sets the frequency component of the spectral intensity equal to or higher than the
threshold Th1 as the frequency component of the noise signal Sn. Further, the spectral intensity
L of the detected frequency component, that is, the signal level difference L between the upper
and lower sidebands in the detected frequency component is taken as the signal level of the noise
signal.
[0031]
In this manner, the difference calculation unit 112 calculates the difference between the upper
and lower sidebands Wm1 and Wm2 of the received signal, and the noise detection unit 113
detects a plurality of noise signals Sn based on the difference, thereby achieving higher accuracy.
Noise can be detected.
[0032]
The calculation unit 120A calculates a coefficient for each frequency component based on the
frequency component and the signal level detected by the noise detection unit 113.
Here, the coefficients are filter coefficients of the first to nth filters 131 to 13 n of the reduction
unit 130A. The calculation unit 120A calculates the coefficient by, for example, selecting a
coefficient according to the coefficient database (DB) 141 stored in the storage unit 140.
[0033]
The coefficient DB 141 stores coefficients for each frequency component and signal level. The
calculation unit 120A selects a coefficient with reference to the coefficient DB 141 based on the
frequency component and the signal level detected by the noise detection unit 113. The
calculation unit 120A selects a coefficient with reference to the coefficient DB 141 for each of
the plurality of noise signals Sn detected by the noise detection unit 113.
[0034]
Here, the case where the number M of noise signals Sn detected by the noise detection unit 113
is larger than the number n of noise signals that can be reduced by the noise reduction device
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10A (M> n) will be described. At this time, the noise reduction device 10A reduces, for example,
the n noise signals Sn in descending order of signal level. That is, the calculation unit 120A
selects n coefficients according to the frequency component of the noise signal Sn and the signal
level in descending order of the signal level.
[0035]
Thereby, the noise reduction device 10A can reduce the noise signal Sn in accordance with the
magnitude of the signal level.
[0036]
Alternatively, the noise reduction device 10A may select the n noise signals Sn to be reduced in
the priority order according to the audibility characteristics.
As described above, AM radio broadcast waves include audio data. Therefore, the noise reduction
device 10A can reduce the noise signal Sn of the frequency component more easily heard by the
user by reducing the noise signal Sn in accordance with the audibility characteristic of the voice.
[0037]
Specifically, for example, the calculation unit 120A selects a coefficient for each frequency
component of the n noise signals Sn in the priority order according to the high cut processing
performed by the demodulation unit (not shown) in the rear stage of the reception device 1A. .
[0038]
Here, although the number M of noise signals Sn detected by the detection unit 110A is larger
than the number of first to nth filters 131 to 13n, the present invention is not limited to this.
The number M of the noise signals Sn may be smaller than the number n of the first to nth filters
131 to 13 n. In this case, the calculation unit 120A selects, for example, the coefficients of the
first to Mth filters 131 to 13M. Further, the noise reduction device 10A does not operate the
remaining (M + 1) th to nth filters 13 (M + 1) to 13n. Alternatively, the calculating unit 120A may
select the coefficients such that the (M + 1) th to n-th filters 13 (M + 1) to 13n output the same
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signal as the received signal as the input signal.
[0039]
The first to nth filters 131 to 13n of the reduction unit 130A are, for example, FIR (Finite
Impulse Response) notch filters, and reduce peak noise from the received signal. The first to nth
filters 131 to 13 n are connected in series. The first to nth filters 131 to 13 n sequentially filter n
noise signals Sn in accordance with the coefficients selected by the calculation unit 120A.
[0040]
The storage unit 140 stores information necessary for processing performed by each unit of the
noise reduction device 10A, such as the coefficient DB 141 and the threshold Th1. The storage
unit 140 also stores the processing result performed by each unit of the noise reduction device
10A. The storage unit 140 is, for example, a semiconductor memory device such as a random
access memory (RAM), a flash memory, or a storage device such as a hard disk or an optical disk.
[0041]
Here, although the noise reduction device 10A includes the storage unit 140, the present
invention is not limited to this. For example, the receiving device 1A may include the storage unit
140.
[0042]
<Noise reduction processing> The noise reduction processing performed by the noise reduction
device 10A will be described with reference to FIG. FIG. 4 is a flowchart showing noise reduction
processing according to the present embodiment. The noise reduction process executes the noise
reduction process, for example, when the antenna 20 receives a received signal. The noise
reduction process is repeatedly performed in a predetermined cycle while the reception device
1A receives the reception signal.
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[0043]
First, the noise reduction device 10A analyzes the frequency of the received signal (step S101).
The noise reduction device 10A calculates the difference between the upper and lower sidebands
Wm1 and Wm2 of the received signal based on the analysis result (step S102). The noise
reduction device 10A compares the calculated absolute value of the difference with the threshold
value Th1 (step S103). If the absolute value of the difference is smaller than the threshold Th1
(step S103; No), the noise reduction device 10A ends the process.
[0044]
On the other hand, if the absolute value of the difference is greater than or equal to the threshold
Th1 (step S103; Yes), the noise reduction device 10A detects a plurality of frequency
components and signal levels of the difference whose absolute value exceeds the threshold Th1
(step S104). The noise reduction device 10A selects a coefficient for each of the plurality of
detected frequency components (step S105). The noise reduction device 10A reduces at least n
noise signals Sn among the plurality of noise signals Sn from the reception signal for each
frequency component of the noise signal Sn according to the selected coefficient (step S106), and
ends the processing. .
[0045]
Although the noise reduction device 10A ends the process when the absolute value of the
difference is smaller than the threshold Th1 in step S103, the present invention is not limited to
this. If the absolute value of the difference is smaller than the threshold Th1, the noise reduction
device 10A determines that the received signal does not include the noise signal Sn. Therefore,
the noise reduction device 10A may output the reception signal generated by the RF unit 30 as it
is to the processing unit (not shown) in the subsequent stage.
[0046]
As described above, in the noise reduction device 10A according to the second embodiment, the
noise signal Sn is reduced using the n first to n-th filters 131 to 13 n to reduce the plurality of
noise signals Sn from the reception signal. It can be reduced.
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[0047]
In the above embodiment, the difference L between the upper and lower sidebands Wm1 and
Wm2 of the received signal is the signal level of the noise signal Sn.
As a result, the noise reduction device 10A can reduce the noise signal Sn with high accuracy as
compared to, for example, reducing the reception signal in the frequency component of the noise
signal Sn by a predetermined level. In addition, for example, the continuity of the frequency
spectrum of the received signal can be maintained, and the reception accuracy of the received
signal can be improved, as compared with the case where the signal level of the received signal
in the frequency component of the noise signal Sn is "0". it can. The signal level of the reception
signal reduced by the reduction unit 130A may be reduced by a predetermined level, or the
signal level of the reception signal is “0”, depending on the required reduction accuracy of the
noise signal Sn or the reception accuracy of the reception signal. It may be reduced to
[0048]
Third Embodiment A receiver 1B according to a third embodiment will be described with
reference to FIGS. 5 and 6. FIG. 5 is a block diagram showing the configuration of a receiving
device 1B according to the third embodiment. The same components as those of the receiving
device 1A shown in FIG.
[0049]
<Receiver 1B> The receiver 1B shown in FIG. 5 includes a noise reduction device 10B. The noise
reduction device 10B includes a calculation unit 120B, a reduction unit 130B, and a storage unit
140B. The calculating unit 120 </ b> B includes a coefficient calculating unit 121 and a
converting unit 122. The reduction unit 130B includes a filter 131B.
[0050]
The coefficient calculation unit 121 calculates coefficients in the frequency domain based on the
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frequency components and signal levels of the plurality of noise signals Sn detected by the noise
detection unit 113. The coefficient calculation unit 121 reduces signal levels of at least n (n is a
positive number of 2 or more) frequency components of the plurality of noise signals Sn detected
by the noise detection unit 113 by the signal levels detected by the noise detection unit 113
Calculate the factor to be The coefficient calculated here is one. Further, here, the signal levels of
all noise signals Sn detected by the noise detection unit 113 are reduced.
[0051]
For example, the coefficient calculation unit 121 calculates a coefficient α obtained by adding
together the coefficients in the frequency domain of the first to nth filters 131 to 13n calculated
by the calculation unit 120A illustrated in FIG. 2 as the coefficient α of the reduction unit 130B.
[0052]
The conversion unit 122 converts the coefficients in the frequency domain calculated by the
coefficient calculation unit 121 into coefficients in the time domain.
The transform unit 122 performs, for example, an IFFT (Inverse Fast Fourier Transform) process.
[0053]
For example, the transform unit 122 performs inverse Fourier transform on the coefficient α in
the frequency domain to calculate the coefficient β in the time domain.
[0054]
The reduction unit 130B includes one filter 131B as described above.
The filter 131B is, for example, an FIR notch filter. The filter 131B reduces at least n noise
signals Sn among the plurality of noise signals Sn from the reception signal according to the time
domain coefficient β converted by the conversion unit 122.
[0055]
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The storage unit 140B is the same as the storage unit 140 illustrated in FIG. 2 except that the
coefficient DB 141 is not included.
[0056]
<Noise reduction processing> The noise reduction processing performed by the noise reduction
device 10B will be described using FIG.
FIG. 6 is a flowchart showing noise reduction processing according to the present embodiment.
The same processing as the noise reduction processing shown in FIG. 4 is denoted by the same
reference numeral, and redundant description will be omitted.
[0057]
The noise reduction device 10B calculates the coefficient α in the frequency domain for
reducing the signal level L of the detected noise signal Sn in the frequency components of the
noise signal Sn detected in step S104 (step S201). The noise reduction device 10B converts the
coefficient α in the frequency domain into the coefficient β in the time domain (step S202). The
noise reduction device 10B reduces the n noise signals Sn from the reception signal according to
the coefficient β in the time domain (step S203), and ends the processing.
[0058]
As described above, the noise reduction device 10B according to the present embodiment
reduces, for example, n noise signals Sn with one filter 131B by converting the coefficient α
calculated in the frequency domain into the coefficient β in the time domain. be able to. As a
result, the processing amount and circuit size of the reduction unit 130B can be reduced
compared to the noise reduction device 10A of the second embodiment.
[0059]
Further, in the noise reduction device 10A, for example, the coefficient is selected with reference
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to the coefficient DB 141, but the noise reduction device 10B according to the present
embodiment calculates the coefficient α by adding the coefficients for each frequency
component of the noise signal Sn. . Thereby, for example, even a noise signal Sn of a frequency
component not stored in the coefficient DB 141 can be reliably reduced from the reception
signal.
[0060]
In the noise reduction device 10A, the number of noise signals Sn that can be reduced is equal to
the number of first to nth filters 131 to 13n included in the reduction unit 130A. On the other
hand, in the noise reduction device 10B according to the present embodiment, the coefficient α
can be calculated regardless of the number of noise signals Sn. Therefore, even if there is only
one filter 131B, all the plurality of noise signals Sn detected by the detection unit 110A can be
reduced.
[0061]
In the noise reduction device 10B according to the present embodiment, the filter 131B of the
reduction unit 130B is one, but is not limited to this. The coefficients for reducing the plurality of
noise signals Sn may be collectively converted into coefficients in the time domain, and, for
example, the number of filters of the reduction unit 130B may be two or more.
[0062]
Modified Example Next, a modified example of the third embodiment will be described using
FIGS. 7 and 8. FIG. 7 is a block diagram showing a configuration of a receiver 1C according to the
present modification. The receiver 1C of this modification is different from the receiver 1B that
reduces the noise signal Sn in the time domain in that the noise signal Sn is reduced in the
frequency domain.
[0063]
The receiver 1C has a noise reduction device 10C. The noise reduction device 10C includes a
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calculation unit 120C, a reduction unit 130C, an area conversion unit 150, and an inverse
conversion unit 160.
[0064]
The calculation unit 120C is the same as the calculation unit 120B except that the conversion
unit 122 is not provided. The calculator 120C calculates the coefficient α in the frequency
domain.
[0065]
Region conversion unit 150 converts the received signal from a signal in the time domain to a
signal in the frequency domain. Region transformation section 150 generates a reception signal
in the frequency domain by performing FFT processing on the reception signal.
[0066]
The reduction unit 130C includes an attenuator that reduces n noise signals Sn from the
reception signal in the frequency domain according to the coefficient α in the frequency domain.
The reduction unit 130C reduces n noise signals Sn from the reception signal in the frequency
domain according to the coefficient α.
[0067]
The inverse transform unit 160 converts the reception signal in the frequency domain in which
the n noise signals Sn are reduced into a reception signal in the time domain. The inverse
transform unit 160 generates a reception signal in the time domain in which the n noise signals
Sn are reduced by performing an IFFT process on the reception signals in which the n noise
signals Sn are reduced.
[0068]
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<Noise reduction processing> The noise reduction processing performed by the noise reduction
apparatus 10C will be described with reference to FIG. FIG. 8 is a flowchart showing noise
reduction processing according to the present modification. The same processing as the noise
reduction processing shown in FIG. 6 will be assigned the same reference numerals and
overlapping descriptions will be omitted.
[0069]
After calculating the coefficient α in the frequency domain in step S201, the noise reduction
device 10C converts the received signal into a signal in the frequency domain next (step S301).
The noise reduction device 10C reduces the noise signal Sn from the reception signal in the
frequency domain according to the coefficient α (step S302). The noise reduction device 10C
converts the reception signal obtained by reducing the noise signal Sn into a reception signal in
the time domain (step S303), and ends the process.
[0070]
Here, after the coefficient α is calculated in step S201, the received signal is converted into a
signal in the frequency domain in step S301. However, the present invention is not limited to
this. Before the noise signal Sn is reduced from the reception signal in step S302, it may be
converted into a reception signal in the frequency domain, and may be performed between step
S101 and step S104. Alternatively, processing may be performed in parallel with these
processing.
[0071]
As described above, the noise reduction device 10C according to the present modification
achieves the same effects as the noise reduction device 10B according to the third embodiment,
and reduces a plurality of noise signals Sn from the reception signal also in the frequency
domain. be able to.
[0072]
In the above-mentioned modification, although processing which returns to a time domain is
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performed to a received signal which reduced noise signal Sn, such processing can also be
omitted.
For example, when the signal processing is performed on the reception signal in the frequency
domain in the subsequent processing, the noise reduction device 10C may output the reception
signal in the frequency domain to the processing unit (not illustrated) in the subsequent stage.
Good. In this case, the inverse conversion unit 160 can be omitted.
[0073]
Moreover, in the said modification, although each of the analysis part 111 and the area | region
transformation part 150 performed FFT processing, it is not limited to this. For example, the
difference calculating unit 112 calculates the difference between the upper and lower sidebands
Wm1 and Wm2 of the received signal using the received signal in the frequency domain
converted by the region converting unit 150, and so on. It can also be integrated.
[0074]
As described above, the noise reduction devices 10 and 10A to 10C according to the
embodiments and the modifications include the detection units 110 and 110A, the calculation
units 120 and 120A to 120C, and the reduction units 130 and 130A to 130C. The detection
units 110 and 110A detect frequency components of the plurality of noise signals Sn included in
the reception signal based on the frequency spectrum of the reception signal. The calculation
units 120 and 120A to 120C calculate coefficients based on the frequency components detected
by the detection units 110 and 110A. The reduction units 130 and 130A to 130C calculate n (n
is a positive number of 1 or more) noise signals Sn among the plurality of noise signals Sn from
the reception signal according to the coefficients calculated by the calculation units 120 and
120A to 120C. Reduce.
[0075]
Accordingly, the noise reduction devices 10, 10A to 10C according to the embodiments and the
modifications can reduce the plurality of noise signals Sn from the reception signal.
[0076]
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In addition, the reduction unit 130A of the noise reduction device 10A according to the second
embodiment includes n first to nth filters 131 to 13n that respectively filter n noise signals Sn.
Further, the calculation unit 120A calculates coefficients for each of the n first to n-th filters 131
to 13 n for each of the n frequency components detected by the detection unit 110A.
[0077]
Thus, the noise reduction device 10A can reduce the plurality of noise signals Sn from the
reception signal by reducing the noise signal Sn using the n first to n-th filters 131 to 13n.
[0078]
The detection unit 110A of the noise reduction device 10B according to the third embodiment
detects the signal levels of the n noise signals Sn.
In addition, the calculation unit 120B includes a coefficient calculation unit 121 and a conversion
unit 122. The coefficient calculation unit 121 calculates the coefficient α in the frequency
domain based on the frequency component and the signal level detected by the detection unit
110A. The conversion unit 122 converts the coefficient α in the frequency domain calculated by
the coefficient calculation unit 121 into a coefficient β in the time domain. In addition, the
reduction unit 130B reduces n noise signals Sn from the reception signal in the time domain
according to the time domain coefficient β converted by the conversion unit 122.
[0079]
As described above, the noise reduction device 10B can reduce n noise signals Sn with, for
example, one filter 131B by converting the coefficient α calculated in the frequency domain into
the coefficient β in the time domain. Thereby, the processing amount and circuit scale of the
noise reduction device 10B of the third embodiment can be reduced.
[0080]
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The detection unit 110A of the noise reduction device 10C according to the modification detects
the signal levels of the n noise signals Sn. Further, the calculation unit 120C calculates the
coefficient α in the frequency domain based on the frequency component and the signal level
detected by the detection unit 110A. The reduction unit 130C reduces n noise signals Sn from
the reception signal in the frequency domain according to the coefficient β in the frequency
domain calculated by the calculation unit 120C.
[0081]
As described above, the noise reduction device 10C according to the modification can obtain the
same effect as the noise reduction device 10B according to the third embodiment, and reduce the
plurality of noise signals Sn from the reception signal also in the frequency domain. it can.
[0082]
In addition, the detection units 110A of the noise reduction devices 10A to 10C according to
each embodiment and modification include a difference calculation unit 112 and a noise
detection unit 113.
The difference calculation unit 112 calculates the difference between the upper and lower
sidebands Wm1 and Wm2 of the frequency spectrum of the received signal. The noise detection
unit 113 detects the frequency component and the signal level based on the difference calculated
by the difference calculation unit 112.
[0083]
In this manner, the difference calculation unit 112 calculates the difference between the upper
and lower sidebands Wm1 and Wm2 of the received signal, and the noise detection unit 113
detects a plurality of noise signals Sn based on the difference, thereby achieving higher accuracy.
Noise can be detected.
[0084]
Further, the noise detection units 113 of the noise reduction devices 10A to 10C according to
each embodiment and modification reduce the signal level difference L between the upper and
lower sidebands Wm1 and Wm2 in the frequency components of the noise signal Sn by the
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21
reduction units 130A to 130C. Signal level.
[0085]
As a result, the noise reduction devices 10A to 10C can reduce the noise signal Sn with high
accuracy as compared to, for example, reducing the reception signal in the frequency component
of the noise signal Sn by a predetermined level.
[0086]
Further effects and modifications can be easily derived by those skilled in the art.
Thus, the broader aspects of the invention are not limited to the specific details and
representative embodiments represented and described above.
Accordingly, various modifications may be made without departing from the spirit or scope of
the general inventive concept as defined by the appended claims and their equivalents.
[0087]
Reference Signs List 1 receiver 10 noise reduction device 110 detection unit 111 analysis unit
112 difference calculation unit 113 noise detection unit 120 calculation unit 121 coefficient
calculation unit 122 conversion unit 130 reduction unit
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