JP2018196027A - Reception signal processing apparatus, reception signal processing method, and program - Google Patents

Abstract

To provide a reception signal processing apparatus, a reception signal processing method, and a program that can suppress degradation of reception quality.SOLUTION: The reception signal processing apparatus includes: a determination unit (for example, a silence determination unit of the embodiment) that determines whether a sound signal included in a received signal is voiced or silent; and a removing unit (for example, a noise identifying unit, a delay unit, and an adder of the embodiment) for removing from the received signal a noise component extracted on the basis of a signal obtained by reducing a predetermined sinusoidal component from the received signal when the determination unit determines that the sound signal is silent.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a received signal processing device, a received signal processing method, and a program.

  In recent years, systems that perform various processes by electronic control are increasing, and a technique for performing high-speed control for further performance improvement is employed. In such high-speed control, it is necessary to increase the speed of arithmetic processing using a CPU (Central Processing Unit) using a high frequency.

  By the way, during the CPU operation, the clock signal and the internal signal emit electromagnetic waves. When a CPU operating at a high frequency is used as a processing device for wireless communication, a noise source may interfere with a signal used for wireless communication. In particular, analog wireless communication is a real-time communication that does not have a function for error correction, and therefore is easily affected by unnecessary electromagnetic waves. As countermeasures against this, it is conceivable to reduce the level of a noise source, block a path through which unnecessary electromagnetic waves are transmitted, or change the frequency of unnecessary electromagnetic waves by changing the clock frequency. For example, Patent Document 1 discloses a technique for accurately detecting the level of a noise component included in a frequency band of a signal component.

JP 2012-178804 A

  However, in the conventional technique, when a noise source having a frequency near the center frequency in the reception band is mixed, the reception quality may not be sufficiently maintained.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a received signal processing device, a received signal processing method, and a program capable of suppressing deterioration in received quality. .

  (1): a determination unit (for example, the silence determination unit 238 of the embodiment) that determines whether the broadcast sound signal included in the received signal is sounded or silent, and the sound signal is silenced by the determination unit A removal unit that removes a noise component extracted from the received signal based on a signal obtained by reducing the broadcast control signal from the received signal (for example, the noise specifying unit 237 and the delay unit of the embodiment) 235 and an adder 236).

  (2): a determination unit (for example, the silence determination unit 238 of the embodiment) that determines whether the sound signal included in the received signal is sounded or silent, and the sound signal is silent by the determination unit A removal unit that removes a noise component extracted from the received signal based on a signal obtained by reducing a predetermined sine wave component from the received signal (for example, the noise specifying unit 237, the delay unit 235 of the embodiment, And an adder 236).

  (3): In (2), the predetermined sine wave component is a sine wave component corresponding to at least the carrier signal of the received signal.

  (4): In any one of (1) to (3), a storage unit (for example, the noise signal storage unit 239 of the embodiment) that stores information regarding the noise component specified by the specifying unit; The removing unit further includes the noise component from the received signal based on information on the noise component stored in the storage unit when the sound signal is determined to be sound by the determining unit. What to remove.

  (5): In any one of (1) to (4), the received signal is a received signal modulated by an FM modulation method.

  (6): When the computer determines whether the sound signal included in the received signal is sounded or silent, and determines that the sound signal is silent, a predetermined sine wave component from the received signal A received signal processing method for removing a noise component to be extracted based on a signal with reduced noise from the received signal.

  (7): Lets the computer determine whether the sound signal included in the received signal is sounded or silenced, and if it is determined that the sound signal is silent, a predetermined sine wave from the received signal The program which removes the noise component extracted based on the signal which reduced the component from the said received signal.

  According to (1) to (7), by specifying a noise component included in the broadcast signal using a period in which the sound signal included in the broadcast signal is silent, deterioration in reception quality can be suppressed. .

It is a block diagram which shows the structure of the transmission signal processing apparatus 10 which concerns on embodiment. It is a block diagram which shows the structure of the received signal processing apparatus 20 which concerns on embodiment. It is FIG. 1 which shows the frequency characteristic of the signal received in the received signal processing apparatus 20 which concerns on embodiment. It is FIG. 1 which shows the frequency characteristic of the signal which demodulated the signal received in the received signal processing apparatus 20 which concerns on embodiment. It is FIG. 2 which shows the frequency characteristic of the signal which demodulated the signal received in the received signal processing apparatus 20 which concerns on embodiment. It is a 1st block diagram which shows the structure of the noise reduction part 23 which concerns on embodiment. It is FIG. 2 which shows the frequency characteristic of the signal received in the received signal processing apparatus 20 which concerns on embodiment. It is a 2nd block diagram which shows the structure of the noise reduction part 23 which concerns on embodiment. It is a flowchart which shows the flow of the process which the noise reduction part 23 which concerns on embodiment performs. It is FIG. 3 which shows the frequency characteristic of the signal which demodulated the signal received in the received signal processing apparatus 20 which concerns on embodiment.

  Hereinafter, embodiments of a received signal processing device, a received signal processing method, and a program according to the present invention will be described with reference to the drawings.

  In the present embodiment, an FM stereo broadcast signal will be described as an example of a signal used for transmission / reception. However, the present invention is not limited to this, and a signal used for transmission / reception may be any signal that can detect the presence or absence of sound included in the signal. For example, the signal used for transmission / reception may be an FM monaural signal, an AM stereo signal, or an AM monaural signal.

  FIG. 1 is a configuration diagram illustrating a configuration of a transmission signal processing device 10 according to the embodiment. As illustrated in FIG. 1, the transmission signal processing device 10 includes a baseband transmission processing unit 11, an FM modulation unit 12, and an orthogonal modulation unit 13. The transmission signal processing apparatus 10 performs digital signal processing based on a digital signal obtained by AD (Analog-to-Digital) conversion of an analog signal such as a sound signal. The transmission signal processing device 10 generates an FM stereo broadcast signal that is processed by the reception signal processing device 20 according to the embodiment. The transmission signal processing device 10 is a signal processing device that is installed in, for example, an FM radio broadcasting station and converts sound of broadcast content into an electrical signal. The electrical signal converted by the transmission signal processing device 10 is superimposed on the radio wave in the carrier band by an RF front end unit (not shown) and transmitted by an antenna (not shown).

  The baseband transmission processing unit 11 includes, for example, pre-emphasis units 110 and 112, adders 111 and 117, a subtractor 113, a subcarrier modulation unit 114, a multiplication unit 115, and a bandpass filter 116. .

  The baseband transmission processing unit 11 receives signals corresponding to L-channel stereo sound, R-channel stereo sound, and a stereo pilot signal (for example, a sine wave having a frequency of 19 [kHz]). The In FM stereo broadcasting, a main signal (sum signal) (L + R) and a sub signal (difference signal) (LR) are transmitted by dividing the frequency band. Here, “L” is an L channel sound signal, and “R” is an R channel sound signal. For example, the main signal is transmitted in a frequency band (for example, 20 [Hz] to 15 [kHz]) corresponding to the voice band. The sub signal is transmitted in a frequency band corresponding to multiplication of the stereo pilot signal (for example, a band centered on 38 [kHz]). In FM stereo broadcast, a stereo pilot signal indicating that the signal is a stereo signal is transmitted instead of a monaural broadcast.

  The pre-emphasis unit 110 amplifies a portion on the high frequency side of the frequency of the input signal with respect to the input signal. In order to correct the deterioration of the signal-to-noise ratio (SNR) on the high frequency side of the frequency of the modulation signal due to triangular noise generated when performing frequency modulation, the frequency of the input signal is increased in advance. This is to amplify the modulation degree on the band side. L channel stereo sound is input to the pre-emphasis unit 110. The function of the pre-emphasis unit 112 is the same as that of the pre-emphasis unit 110, and a description thereof will be omitted. The pre-emphasis unit 112 receives an input signal and R channel stereo sound.

  The adder 111 outputs a signal obtained by adding two input signals. The adder 111 receives signals from the pre-emphasis unit 110 and the pre-emphasis unit 112, respectively. The adder 111 outputs a signal obtained by adding these two input signals, that is, a main signal (L + R).

  The subtractor 113 outputs a signal obtained by subtracting two input signals. The subtractor 113 receives signals from the pre-emphasis unit 110 and the pre-emphasis unit 112, respectively. The adder 111 outputs a signal obtained by subtracting these two input signals, that is, a sub-signal (LR).

  The subcarrier modulation unit 114 modulates the amplitude of the input signal using a reference frequency signal having a specific frequency. A sub signal (LR) is input to the sub carrier modulation unit 114 as an input signal. In addition, a signal from a bandpass filter 116 described later is input to the subcarrier modulation unit 114 as a reference signal having a reference frequency. The reference signal from the band pass filter 116 is a sine wave having a reference frequency (for example, 38 [kHz]). That is, the subcarrier modulation unit 114 outputs a signal obtained by amplitude-modulating the sub signal with the reference signal.

  The multiplier 115 multiplies the frequency band of the input signal with respect to the input signal. For example, the multiplication unit 115 performs sampling (upsampling) at a frequency twice the sampling frequency of the input signal. As a result, the multiplier 115 outputs a signal including the frequency of the input signal and the frequency twice the input signal.

  The band-pass filter 116 passes a signal having a frequency in a predetermined frequency band with respect to the input signal and blocks a signal having a frequency outside the predetermined frequency band. For example, the band-pass filter 116 allows the signal from the multiplier 115 to pass a signal having a frequency twice that of the signal input to the multiplier 115, and the signal input to the multiplier 115 has the original signal. Block signals with frequency. That is, the band pass filter 116 outputs a signal (for example, a sine wave of 38 [kHz]) having a frequency twice that of the stereo pilot signal input to the multiplier 115.

  The adder 117 outputs a signal obtained by adding three input signals. The adder 117 receives the signals from the adder 111 and the subcarrier modulation unit 114 and the stereo pilot signal. The adder 117 is a signal (composite signal) obtained by superimposing a signal obtained by adding these three input signals, that is, a signal obtained by amplitude-modulating the main signal (L + R), the sub signal (LR), and the stereo pilot signal. Signal).

  The FM modulation section 12 is a signal obtained by frequency-shifting a value corresponding to the difference in amplitude from the composite signal sampled immediately before the composite signal output from the baseband transmission processing section 11 (hereinafter referred to as frequency). Output a deviation signal). The FM modulator 12 outputs a reference frequency shift signal and a signal obtained by rotating the frequency shift signal by, for example, 90 °.

  The quadrature modulation unit 13 includes an oscillator 130, a phase 90 ° shift unit 131, multipliers 132 and 133, and an adder 134. The quadrature modulation unit 13 performs quadrature modulation on the signal from the FM modulation unit 12. Further, the quadrature modulation unit 13 outputs a frequency modulation signal (FM transmission signal) obtained by adding the I signal and the Q signal after the quadrature modulation.

  The oscillator 130 outputs a sine wave having a predetermined frequency (hereinafter also referred to as an intermediate frequency or a carrier frequency). The phase 90 ° shift unit 131 outputs a signal obtained by rotating the phase by 90 ° with respect to the input signal.

  The multiplier 132 outputs a signal obtained by multiplying two input signals. Signals from the FM modulation unit 12 and the phase 90 ° shift unit 131 are input to the multiplier 132, respectively. Multiplier 132 outputs a signal obtained by multiplying two input signals, that is, a signal obtained by multiplying a signal obtained by rotating a phase shift signal and a sine wave having an intermediate frequency by 90 °.

  The multiplier 133 outputs a signal obtained by multiplying two input signals. Signals from the FM modulator 12 and the oscillator 130 are input to the multiplier 133, respectively. The multiplier 133 outputs a signal obtained by multiplying two input signals, that is, a signal obtained by multiplying a frequency shift signal and a sine wave having an intermediate frequency.

  The adder 134 outputs a signal obtained by adding two input signals. Signals from the multiplier 132 and the multiplier 133 are input to the adder 134, respectively. The adder 134 is a signal obtained by adding these two input signals, that is, a signal obtained by multiplying a frequency shift signal and a signal obtained by rotating a sine wave having an intermediate frequency by 90 °, a frequency shift signal, and an intermediate signal. A signal obtained by adding a signal obtained by multiplying a sine wave having a frequency is output. Thus, based on the addition theorem, the adder 134 outputs a frequency modulation signal whose frequency shifts based on the frequency shift signal with the intermediate frequency as the center.

  FIG. 2 is a configuration diagram illustrating a configuration of the reception signal processing device 20 according to the embodiment. As illustrated in FIG. 2, the reception signal processing device 20 includes a bandpass filter 21, an orthogonal demodulation unit 22, a noise reduction unit 23, an FM bitone unit 24, and a baseband reception processing unit 25.

  The reception signal processing device 20 demodulates an FM stereo broadcast signal received by an antenna (not shown), for example, a frequency modulation signal converted from a carrier wave frequency to an intermediate frequency by an RF front end unit (not shown). The reception signal processing device 20 performs digital signal processing based on a digital signal obtained by AD (Analog-to-Digital) conversion of an analog signal from the RF front end unit or the like.

  The band-pass filter 21 passes a signal having a frequency in a predetermined frequency band with respect to the input signal and blocks a signal having a frequency outside the predetermined frequency band. An FM reception signal is input to the band pass filter 21. The FM reception signal corresponds to a signal in which noise such as thermal noise (dark noise) generated in the signal processing or clock noise due to the clock signal is mixed into the FM transmission signal output from the transmission signal processing device 10. . The band-pass filter 21 passes, for example, a signal having a predetermined bandwidth centered on the center frequency of the carrier band to the FM reception signal, and blocks signals having other frequencies. By doing so, the bandpass filter 21 outputs only a signal having a frequency band necessary for frequency demodulation.

  The quadrature demodulation unit 22 includes an oscillator 220, a phase 90 ° shift unit 221, multipliers 222 and 223, and low-pass filters 224 and 225. The orthogonal demodulator 22 performs orthogonal demodulation on the signal from the bandpass filter 21. The orthogonal demodulation is a process corresponding to the process performed by the orthogonal modulation unit 13 on the transmission side. The quadrature demodulator 22 cuts off and outputs a high-frequency component (for example, a signal corresponding to multiplication of the intermediate frequency) generated by the quadrature demodulation. Thereby, the orthogonal demodulator 22 outputs a signal corresponding to the signal output from the FM modulator 12 on the transmission side.

  Each of the oscillator 220, the phase 90 ° shift unit 221, and the multipliers 222 and 223 is equivalent to the oscillator 130, the phase 90 ° shift unit 131, and the multipliers 132 and 123 included in the quadrature modulation unit 13. Therefore, the description thereof is omitted.

  The low-pass filter 224 passes a signal having a frequency lower than a predetermined frequency, and blocks a signal having a frequency higher than the predetermined frequency. The I signal from the multiplier 223 is input to the low pass filter 224. The low-pass filter 224 blocks and outputs a high frequency component (for example, a signal corresponding to multiplication of an intermediate frequency) included in the I signal after quadrature demodulation.

  Since the low-pass filter 225 has the same function as the low-pass filter 224, the description thereof is omitted. The Q signal from the multiplier 222 is input to the low pass filter 224.

  The noise reduction unit 23 reduces a noise component included in the signal from the signal from the quadrature demodulation unit 22. The noise component included in the signal will be described later with reference to FIGS. The configuration of the noise reduction unit 23 will be described later with reference to FIG.

  The FM double-tone unit 24 performs frequency demodulation on the input signal. In frequency demodulation, a value corresponding to the frequency shift amount of the frequency of the input signal is output as a signal amplitude. The FM double tone unit 24 receives the I signal and the Q signal from the noise reduction unit 23. The FM double-tone unit 24 calculates a phase from the I signal and the Q signal. Further, the FM double tone unit 24 calculates the difference between the calculated phase and the phase calculated from the signal sampled immediately before and the Q signal. This phase difference is the amount of frequency deviation. The FM double tone unit 24 adjusts the amplitude of the frequency shift obtained by the calculation as necessary, and outputs it as a baseband signal.

  The baseband reception processing unit 25 includes a low-pass filter 250, a delay unit 251, an adder 252, band-pass filters 253, 257, and 259, a subcarrier demodulation unit 254, a subtracter 256, and a multiplication unit 258. Is provided. The baseband reception processing unit 25 performs a demodulation process corresponding to the modulation process performed by the baseband transmission processing unit 11 on the transmission side. A baseband signal from the FM double tone unit 24 is input to the baseband reception processing unit 25. The baseband reception processing unit 25 outputs sound signals corresponding to the L channel stereo sound and the R channel stereo sound.

  The baseband signal from the FM double tone unit 24 is input to the low pass filter 250. The low-pass filter 250 passes a signal having a frequency lower than the upper limit frequency (for example, 15 [kHz]) of the band included in the main signal (L + R) included in the baseband signal, and is higher than the band including the main signal. Block signals with. Thereby, the low-pass filter 250 outputs a main signal.

  The delay unit 251 outputs a signal obtained by delaying the input signal by a predetermined number of samples. The delay unit 251 uses a predetermined signal to adjust a signal timing when an adder 252 described later adds a main signal and a sub signal (LR) from a subcarrier demodulation unit 254 described later. The signal is delayed by the number of samples. The number of samples (delay amount) by which the delay unit 251 delays the signal is based on, for example, the filter order of the low-pass filter 250 and a band-pass filter 253 described later, the processing delay amount generated by the processing performed by the subcarrier demodulation unit 254, and the like. Determined.

  The adder 252 receives the main signal (L + R) from the delay unit 251 and the sub signal (LR) from the subcarrier demodulation unit 254, respectively. The adder 252 outputs a signal obtained by adding these two input signals, that is, an L channel stereo signal.

  The baseband signal from the FM double tone unit 24 is input to the bandpass filter 253. The band-pass filter 253 has a band (for example, a band of ± 15 [kHz] centered on 38 [kHz], that is, 23 [kHz] to 53 [kHz] included in the sub-signal (LR) included in the baseband signal. ]) And a signal having a frequency outside the band including the sub-signal are blocked. Thereby, the band pass filter 253 outputs a sub signal.

  The subcarrier demodulation unit 254 performs a demodulation process corresponding to the modulation process performed by the transmission-side subcarrier modulation unit 114. Specifically, subcarrier demodulation section 254 outputs a signal obtained by amplitude demodulating the amplitude-modulated subsignal. Here, in the above description, it has been described that the signal output from the subcarrier demodulation unit 254 is the subsignal (LR). However, since the subcarrier modulation unit 114 modulates the amplitude of the subsignal, it is more accurate. The signal output from the subcarrier demodulator 254 is an amplitude-modulated subsignal. The subcarrier demodulator 254 receives the amplitude-modulated subsignal from the bandpass filter 253 and a reference signal (for example, a 38 [kHz] sine wave) from the bandpass filter 259 described later. The subcarrier demodulator 254 outputs a subsignal (LR) obtained by amplitude-demodulating the amplitude-modulated subsignal with the reference signal.

  Subtracter 256 receives main signal (L + R) from delay unit 251 and sub signal (LR) from subcarrier demodulation unit 254, respectively. The adder 252 outputs a signal obtained by subtracting these two input signals, that is, an R channel stereo signal.

  The baseband signal from the FM double tone unit 24 is input to the bandpass filter 257. The bandpass filter 257 passes a signal having a frequency of a stereo pilot signal (for example, a sine wave having a frequency of 19 [kHz]) included in the baseband signal, and blocks a signal having a frequency outside the band. Thereby, the band pass filter 253 outputs a stereo pilot signal.

  Since the multiplier 258 and the band pass filter 259 have the same functions as the multiplier 115 and the band pass filter 116 on the transmission side, the description thereof is omitted.

Here, noise components included in the received signal will be described with reference to FIGS. FIG. 3 is a first diagram illustrating frequency characteristics of a signal received by the received signal processing device 20 according to the embodiment. FIG. 3 shows an example of frequency characteristics of the received FM broadcast signal. In FIG. 3, the horizontal axis represents frequency [Hz] and the vertical axis represents signal amplitude [dB].
As shown in FIG. 3, the frequency of the FM broadcast signal is distributed between the center frequencies ± 100,000 [Hz] to ± 150,000 [Hz]. Among these, the signals whose FM broadcast signal amplitude is about −20 [dB] to −60 [dB] are distributed in the range of the center frequency ± 100,000 [Hz]. Further, clock noise is mixed at a location of +4000 [Hz] from the center frequency. The signal amplitude of the clock noise is about −10 [dB].
As shown in FIG. 3, the received signal may be mixed with clock noise caused by the clock frequency that operates when digital signal processing is performed. Such clock noise may have a clock frequency or a frequency multiplied by the clock frequency.

FIG. 4 is a first diagram illustrating frequency characteristics of a signal obtained by demodulating a signal received by the reception signal processing device 20 according to the embodiment. In the example of FIG. 4, the noise reduction unit 23 does not perform processing for reducing noise.
FIG. 4 shows a demodulated signal (sound signal) when the received signal processing device 20 demodulates the signal when a signal obtained by frequency-modulating a 400 [Hz] sine wave tone signal (sound signal) is received. The frequency characteristics of are shown. 4A shows a case where the received signal does not include the clock noise shown in FIG. 3, and FIG. 4B shows a case where the received signal contains the clock noise. . 4A and 4B, the horizontal axis represents frequency [Hz] and the vertical axis represents signal amplitude [dB].

As shown in FIG. 4A, the peak of the demodulated signal is confirmed at 400 [Hz], which is the same frequency as the frequency modulated on the transmission side. The signal amplitude of the demodulated signal is about −15 [dB]. On the other hand, the signal amplitude of the floor noise is about −100 [dB]. That is, the SINAD (Signal-to-noise and distortion ratio) of the demodulated signal is about 85 [dB]. Generally, when SINAD is 65 [dB] or more, noise included in a signal can hardly be recognized by human perception. That is, the sinusoidal tone signal modulated on the transmission side is demodulated on the reception side without quality degradation.
As shown in FIG. 4B, the peak of the demodulated signal is confirmed at 400 [Hz] having the same frequency as that of the transmission side, but the peak of the demodulated signal is also confirmed at other frequencies. The signal amplitude of the demodulated signal having 400 [Hz] is about −15 [dB]. There are at least a plurality of demodulated signals having a frequency other than 400 [Hz] and a signal amplitude of about −40 [dB]. In this case, the SINAD of the demodulated signal is about 25 [dB], and noise that is clearly recognized by human perception is mixed in the demodulated signal. In this case, the 400 [Hz] sinusoidal tone signal generated on the transmission side is not reproduced on the reception side.

FIG. 5 is a second diagram illustrating frequency characteristics of a signal obtained by demodulating a signal received by the reception signal processing device 20 according to the embodiment. In the example of FIG. 5, the noise reduction unit 23 does not perform processing for reducing noise.
FIG. 5 shows a demodulated signal (sound signal) when a signal obtained by frequency-modulating a 1000 [Hz] sine wave tone signal (sound signal) is demodulated by the received signal processing device 20. The frequency characteristics of are shown. 5A shows a case where the received signal does not include the clock noise shown in FIG. 3, and FIG. 5B shows a case where the received signal contains the clock noise. FIG. 5C shows a case where clock noise is included in the received signal, but the clock noise is removed in the demodulation process performed by the received signal processing device 20. 5A to 5C, the horizontal axis represents frequency [Hz] and the vertical axis represents signal amplitude [dB].

  As shown in FIG. 5A, the peak of the demodulated signal is confirmed at 1000 [Hz], which is the same frequency as the frequency modulated on the transmission side. In FIG. 5A, the SINAD of the demodulated signal is sufficiently secured, and the sinusoidal tone signal modulated on the transmission side is demodulated on the reception side without deterioration in quality.

  As shown in FIG. 5B, the peak of the demodulated signal is confirmed at 1000 [Hz] of the same frequency as the transmission side, but the peak (distortion) of the demodulated signal is also confirmed at other frequencies. In FIG. 5B, distortion occurs in the frequency multiplied by 1000 [Hz], and noise that is clearly recognized by human perception is mixed in the demodulated signal.

In the example of FIG. 5C, the clock noise shown in FIG. 3 is reduced by a notch filter before the frequency demodulation process. As for the frequency characteristics of the notch filter, for example, the band where the signal level is attenuated by −3 [dB] or more is in the range of +4000 [Hz] ± 1000 [Hz].
As shown in FIG. 5 (c), the peak of the demodulated signal is confirmed at 1000 [Hz], which is the same frequency as that of the transmission side, but distortion is confirmed at other frequencies multiplied by 1000 [Hz]. Thus, even when the signal component having a frequency corresponding to the clock noise is reduced by the notch filter, the noise is mixed into the demodulated signal. This is because the notch filter removes not only clock noise but also a modulation signal having the same frequency as the clock noise. That is, as a result of the sound signal information necessary for demodulation being removed by the notch filter, the demodulated demodulated signal is distorted.

Here, the structure of the noise reduction part 23 is demonstrated using FIG.
FIG. 6 is a first configuration diagram illustrating a configuration of the noise reduction unit 23 according to the embodiment.

As shown in FIG. 6, the noise reduction unit 23 includes delay units 235-I and 235-Q, adders 236-I and 236-Q, a noise specifying unit 237, a silence determination unit 238, and a noise signal storage. Part 239.
Among the components of the noise reduction unit 23, those with “−I” attached to the reference sign process the I signal, and those with “−Q” attached to the reference sign process the Q signal. Is an element. Since components having the same numerical value and suffixed with “-I” or “-Q” have equivalent functions, components having “-I” at the end will be described below. Only the function will be described, and the description of the function will be omitted for the components having “-Q” at the end. In addition, in the case where components having the same numerical value and suffixed with “−I” or “−Q” are not distinguished from each other, only the numerical value of the symbol is described. For example, when the delay units 235-I and 235-Q are not distinguished from each other, they are simply described as the delay unit 235.

  The delay unit 235-I outputs a signal delayed by M samples, which is a predetermined number of samples, with respect to the input signal. The I signal after quadrature demodulation is input to the delay unit 235-I. The delay unit 235-I adjusts the timing of the signal when the adder 236-I described below subtracts the noise component specified in the noise specifying unit 237 described later by the number of M samples. Performs processing to delay the signal. The delay amount is determined based on the delay amount of the noise specifying unit 237, for example.

  The adder 236-I receives a signal from the delay unit 235-I and a signal obtained by inverting a noise component specified by a noise specifying unit 237 described later. The adder 236-I outputs a signal obtained by adding these two signals, that is, a signal obtained by subtracting a noise component from the I signal after quadrature demodulation.

The Q signal after quadrature demodulation is input to the delay unit 235-Q.
The adder 236-Q receives a signal from the delay unit 235-Q and a signal obtained by inverting a noise component specified by a noise specifying unit 237 described later. The adder 236-Q outputs a signal obtained by adding these two signals, that is, a signal obtained by subtracting a noise component from the Q signal after quadrature demodulation.

  The noise specifying unit 237 specifies a noise component included in the input signal. The noise identifying unit 237 performs processing for identifying a noise component included in the input signal based on a determination result determined by a silence determination unit 238 described later.

  When the determination result from the silence determination unit 238 indicates that the sound signal is silent, the noise specifying unit 237 specifies a noise component included in the input signal. Moreover, the noise specific | specification part 237 outputs the specified noise component to the noise signal storage part 239 mentioned later, when the determination result from the silence determination part 238 shows that a sound signal is silence.

  The noise specifying unit 237 receives the I signal after quadrature demodulation and the Q signal after quadrature demodulation. The noise specifying unit 237 outputs a noise component I signal and a noise component Q signal, respectively. The processing performed by the noise specifying unit 237 will be described in detail later.

  The silence determination unit 238 determines whether the sound signal included in the input signal is silence or sound. Silence determination section 238 receives I signal after quadrature demodulation and Q signal after quadrature demodulation. The I signal after quadrature demodulation and the Q signal after quadrature demodulation are frequency modulated signals.

For example, when the center frequency of the input signal shifts, the silence determination unit 238 determines that the sound signal included in the input signal is in a sound state. Further, the silence determination unit 238 determines that the sound signal included in the input signal is silent when the center frequency of the input signal does not shift. The silence determination unit 238 calculates the phase of these signals from, for example, the I signal after quadrature demodulation and the Q signal after quadrature demodulation. Then, the silence determination unit 238 calculates the difference between the calculated phase and the phase calculated from the previously sampled I signal after quadrature demodulation and the Q signal after quadrature demodulation. If the difference is not 0 (zero) or is greater than or equal to a predetermined range, the silence determination unit 238 determines that the sound signal is in a sound state because the center frequency is shifted. On the other hand, if the difference is 0 (zero) or less than the predetermined range, the silence determination unit 238 determines that the sound signal is silent because the center frequency is not shifted.
The silence determination unit 238 determines that the sound signal is silent when the above-described silence state continues for a predetermined time interval (for example, 1 [sec]). The silence determination unit 238 outputs the determined determination result to the noise specifying unit 237.

  The noise signal storage unit stores noise components specified by the adaptive filters 232 -I and 232 -Q, respectively. The noise signal storage unit is realized by, for example, an HDD (Hard Disc Drive), a flash memory, an EEPROM (Electrically Erasable Programmable Read Only Memory), or a RAM (Random Access Memory).

  The noise specifying unit 237 includes high-pass filters 230-I and 230-Q, a delay unit 231, adaptive filters 232-I and 232-Q, adders 233-I and 233-Q, and a band-pass filter 234-I. 234-Q.

  The high-pass filter 230-I passes a signal having a frequency higher than a predetermined frequency with respect to the input signal, and blocks a signal having a frequency lower than the predetermined frequency. The I signal after quadrature demodulation is input to the high pass filter 230-I. The high-pass filter 230-I passes a signal having a frequency higher than the center frequency with respect to the I signal after quadrature demodulation, and blocks a signal having a frequency lower than the center frequency. The center frequency is, for example, 0 [Hz]. As a result, the high-pass filter 230-I outputs a signal in which the signal component having the center frequency included in the I signal after quadrature demodulation is reduced.

  The delay unit 231 outputs a signal delayed by D samples, which is a predetermined number of samples, with respect to the input signal. The delay unit 231 receives a signal from the high-pass filter 230-I. For example, the delay unit 231 outputs the signals from the high-pass filter 230-I together for each D sample.

  The adaptive filter 232 -I specifies a noise component included in the input signal group with respect to the input signal group. The adaptive filter 232 -I is a filter that self-adapts its transfer function according to, for example, an optimization algorithm. For example, an adaptive filter ALE (Adaptive Line Enhancer) algorithm is used as the adaptive filter 232 -I. For example, the signals from the delay unit 231 are input to the adaptive filter 232 -I together as a signal group for each D sample. The adaptive filter 232 -I specifies a noise component included in the signal group from the signal group from the delay unit 231 using a transfer function generated according to the algorithm. The adaptive filter 232 -I outputs the identified noise component to the adder 233 -I and the band pass filter 234 -I, respectively.

  The adder 233-I receives a signal obtained by inverting the noise component from the adaptive filter 232-I and a signal from the high-pass filter 230-I. The adder 233-I outputs a signal obtained by adding these two signals, that is, a signal obtained by subtracting the noise component from the signal from the high-pass filter 230-I.

  Further, the signal from the adder 233 -I is input to the adaptive filter 232 -I, as indicated by the dotted line in FIG. The adder 233-I outputs a signal obtained by subtracting the noise component from the signal from the high-pass filter 230-I. For example, when there is a residual noise component in the signal obtained by subtracting the noise component based on the signal from the high-pass filter 230-I, the adaptive filter 232-I considers the residual noise component again. A noise component included in the signal group is specified using the generated transfer function.

  The noise component from the adaptive filter 232 -I is input to the band pass filter 234 -I. The band pass filter 234-I reduces a predetermined sine wave component with respect to the noise component. The predetermined sine wave component is, for example, a frequency component that the stereo pilot signal has. The predetermined sine wave component to be reduced by the band pass filter 234-I will be described later. The band pass filter 234-I outputs a signal obtained by reducing a predetermined sine wave component included in the noise component to the adder 236-I as a noise component I signal.

  The high-pass filter 230-Q receives the Q signal after quadrature demodulation. The high pass filter 230-Q outputs a signal having a frequency higher than the center frequency from the quadrature demodulated Q signal to an adder 233-Q to be described later.

  A signal obtained by inverting the noise component from the adaptive filter 232 -Q and a signal from the high pass filter 230 -Q are input to the adder 233 -Q, respectively. The adder 233-Q outputs a signal obtained by adding these two signals, that is, a signal obtained by subtracting the noise component from the signal from the high-pass filter 230-Q.

  As shown by the dotted line in FIG. 6, the signal from the adder 233-Q is input to the adaptive filter 232-Q. The adaptive filter 232 -Q considers the residual noise component again when there is a residual noise component in the signal obtained by subtracting the noise component based on the signal from the high-pass filter 230 -Q, for example. A noise component included in the signal group is specified using the generated transfer function.

Here, the predetermined sine wave component to be reduced by the band pass filter 234-I will be described with reference to FIG.
FIG. 7 is a second diagram illustrating frequency characteristics of a signal received by the reception signal processing device 20 according to the embodiment. FIG. 7 shows an example of frequency characteristics of an FM broadcast signal when a sound signal included in the received FM broadcast signal is silent. In FIG. 7, the horizontal axis represents frequency [Hz] and the vertical axis represents signal amplitude [dB].
As shown in FIG. 7, the FM broadcast signal when the sound signal is silent includes a sine wave having a center frequency indicating the carrier signal (described as “Carrier” in FIG. 7), and a center frequency ± of the stereo pilot signal. A sine wave having 19 [kHz] and a sine wave having a center frequency ± (19 × 2) [kHz] included in the reference signal used for modulating the subcarrier are confirmed. When the sound signal is silent, such frequency characteristics are constantly confirmed.
As shown in FIG. 7, even when the sound signal is silent, clock noise caused by the same clock frequency as in FIG. 3 is confirmed at a location of +4000 [Hz] from the center frequency. As a result, when the sound signal is silent, the signal after the frequency components of the broadcast control signals such as the carrier signal, stereo pilot signal, and reference signal are removed from the FM broadcast signal is clock noise. Can do.

  In the received signal processing device 20 of this embodiment, in order to specify clock noise, when the sound signal is silent, for example, the frequency (for example, 19) of the stereo pilot signal is determined from the noise component specified by the adaptive filter 232. [KHz]) is reduced by the band pass filter 234. Thereby, the noise component which has clock noise as a main component can be extracted.

Here, processing when the determination result from the silence determination unit 238 indicates that the sound signal is sound will be described with reference to FIG.
FIG. 8 is a second configuration diagram illustrating the configuration of the noise reduction unit 23 according to the embodiment.
As shown in FIG. 8, when the sound signal is sound, the noise reduction unit 23 inputs the noise component of the I signal stored in the noise signal storage unit 239 to the band pass filter 234 -I. When the sound signal is sound, the noise component of the Q signal stored in the noise signal storage unit 239 is input to the band pass filter 234-Q. The noise signal storage unit 239 stores the noise component of the I signal specified by the adaptive filter 232 -I and the noise component of the Q signal specified by the adaptive filter 232 -Q when the sound signal is silent. Yes.

  When the sound signal is sound, the noise component is specified using the noise component specified when the sound signal is silent, thereby suppressing an erroneous process of specifying the sound signal as a noise component. be able to.

Here, the flow of processing for reducing noise performed by the noise reduction unit 23 will be described with reference to FIG.
FIG. 9 is a flowchart illustrating a flow of processing performed by the noise reduction unit 23 according to the embodiment.

First, the noise reduction unit 23 determines whether or not a predetermined frequency-modulated broadcast signal has been received (step S1). The noise reduction unit 23 broadcasts, for example, when the average value of the amplitude at a predetermined time interval is equal to or greater than a predetermined value in one or both of the I signal after quadrature demodulation and the Q signal after quadrature demodulation. It is determined that a signal has been received.
When it is determined that the broadcast signal has been received (step S1, Yes), the noise reduction unit 23 determines whether the sound signal included in the broadcast signal is silent (step S2).
When the noise reduction unit 23 determines that the sound signal is silent (step S2, Yes), the noise reduction unit 23 reduces a predetermined frequency component included in the broadcast signal (step S3).
And the noise reduction part 23 specifies the noise component contained in the broadcast signal which reduced the predetermined frequency component (step S4).
The noise reduction unit 23 stores the identified noise component (step S5).
The noise reduction part 23 reduces the noise component contained in a broadcast signal based on the specified noise component (step S6).

  On the other hand, when it is determined in step S2 that the sound signal is sound (No in step S2), the noise reduction unit 23 determines whether or not the noise component specified during silence is stored (step S7). . And the noise reduction part 23 reduces the noise component contained in a broadcast signal based on the noise component memorize | stored at the time of silence (step S8).

  On the other hand, if the noise reduction unit 23 does not determine in step 1 that a broadcast signal has been received (No in step S1), the noise reduction unit 23 returns to step S1 again and performs a process of determining whether or not a broadcast signal has been received.

  In the above-described flowchart, the noise reduction unit 23 performs a process of reducing a predetermined sine wave component included in the broadcast signal in step S3 prior to step S4 for specifying the noise component, but from step S4. A subsequent step may be performed to reduce a predetermined sine wave component. Further, the noise reduction unit 23 may perform a process of reducing a predetermined sine wave component in both the step before step S4 and the step after step S4.

  As described above, the reception signal processing device 20 of the present embodiment includes the silence determination unit 238 that determines whether the sound signal of the broadcast included in the reception signal is sound or silence, and the silence determination unit 238. A noise specifying unit 237, a delay unit 235, and an addition for removing a noise component extracted from the received signal based on a signal obtained by reducing the broadcast control signal from the received signal when it is determined that the sound signal is silent. Instrument 236.

  Thereby, the received signal processing apparatus 20 of this embodiment can suppress deterioration of the reception quality when the broadcast is received. By using the period when the broadcast sound included in the received signal is silent, the noise component such as clock noise included in the signal that has been reduced in the broadcast control signal such as the reference signal is specified, so that the noise from the received signal This is because the components can be subtracted (removed).

  In addition, the received signal processing apparatus 20 of the present embodiment includes a silence determination unit 238 that determines whether a sound signal included in the received signal is sounded or silenced, and the sound signal is silenced by the silence determination unit 238. A noise specifying unit 237, a delay unit 235, and an adder 236 for removing a noise component extracted from the received signal based on a signal obtained by reducing a predetermined sine wave component from the received signal.

  Thereby, the received signal processing apparatus 20 of this embodiment can suppress degradation of reception quality. By using the period during which the audio included in the received signal is silent, the noise component such as clock noise included in the signal with the specified sine wave component reduced, such as the reference signal, is identified. This is because the value can be subtracted (removed).

  Also, the received signal processing apparatus 20 of the present embodiment includes a noise signal storage unit 239 that stores information on the noise component specified by the noise specifying unit 237, and the delay unit 235 and the adder 236 include the noise specifying unit. If the sound signal is determined to be sound by the unit 237, the noise component is removed from the received signal based on the information regarding the noise component stored in the noise signal storage unit 239. Thereby, in the received signal processing apparatus 20 of this embodiment, when the sound contained in the received signal is sound, the noise component specified when the sound is silent is used to remove the noise component from the received signal. Can be subtracted (removed). For this reason, it is possible to suppress degradation of reception quality without erroneously removing signal components necessary for demodulation even when the sound is sound.

  In the reception signal processing device 20 of the present embodiment, the predetermined sine wave component is a sine wave component corresponding to at least the carrier signal of the reception signal. As a result, the received signal processing apparatus 20 of the present embodiment can identify a noise component from which at least a sine wave component corresponding to a carrier signal used for modulation is removed, and erroneously detects a signal component necessary for demodulation. Deterioration of reception quality can be suppressed without removal.

  In the reception signal processing device 20 of the present embodiment, the reception signal is a reception signal modulated by the FM modulation method. As a result, the received signal processing apparatus 20 of the present embodiment can identify a noise component from which a predetermined sine wave component such as a stereo pilot signal unique to the FM modulation method is removed, and erroneously detects a signal component necessary for demodulation. Therefore, it is possible to suppress the degradation of the reception quality without removing it.

Here, the effect of the noise reduction processing performed by the received signal processing apparatus 20 of the present embodiment will be described with reference to FIG.
FIG. 10 is a third diagram illustrating frequency characteristics of a signal obtained by demodulating a signal received by the received signal processing device 20 according to the embodiment.
FIG. 10 shows the frequency characteristics of the demodulated signal when the received signal processing apparatus 20 demodulates the signal when a frequency-modulated signal of a sound signal output from classical music is received. 10A shows a case where the received signal does not include the clock noise shown in FIG. 3, and FIG. 10B shows a case where the received signal contains the clock noise. c) shows a case where the received signal contains clock noise, and the noise reduction unit 23 reduces the noise component including the clock noise. 10A to 10C, the horizontal axis represents time [sec], and the vertical axis represents frequency [Hz].
As shown in FIG. 10A, when the received signal does not include clock noise, a signal component having a frequency component higher than the frequency 4 k [Hz] (for example, a signal corresponding to the tone color of a musical instrument). The strength of the component is clear.
On the other hand, as shown in FIG. 10B, when the received signal includes clock noise, the strength of the signal component having a frequency component higher than the frequency 4 k [Hz] is not clear, and the frequency 4 k A signal having a higher frequency than [Hz] is a signal having the same intensity as a whole. In the example of FIG. 10B, it is considered that more distortion components are included in the frequency component higher than the frequency 4 k [Hz] compared to the case where the clock noise is not included.
As shown in FIG. 10C, when the noise reduction unit 23 does not perform noise reduction processing, even if the signal may cause a large number of distortions as shown in FIG. As a result, the strength of the signal component having a frequency component higher than the frequency 4 k [Hz] is clarified, and it is confirmed that the generation of the distortion component is suppressed. In the noise reduction processing of the embodiment, a predetermined time (for example, about 0.15 [sec]) is required from when the processing is started until the noise component is actually reduced. For this reason, noise based on unnecessary noise components may be output for a predetermined time from the start of processing. As a countermeasure, for example, when the sound signal on the transmission side is frequency-modulated, the sound output portion may be forcibly silenced for a predetermined time. In general, even when a sound output portion is forcibly silenced for about 0.15 [sec], it is considered that the silence portion is not recognized as uncomfortable by human hearing.

  As mentioned above, although the form for implementing this invention was demonstrated using embodiment, this invention is not limited to such embodiment at all, In the range which does not deviate from the summary of this invention, various deformation | transformation and substitution Can be added.

DESCRIPTION OF SYMBOLS 10 ... Transmission signal processing apparatus, 20 ... Reception signal processing apparatus, 23 ... Noise reduction part, 235 ... Delay part (removal part), 236 ... Addition part (removal part), 237 ... Noise specification part (removal part), 238 ... Silence determination unit (determination unit), 239... Noise signal storage unit (storage unit).

Claims (7)

A determination unit that determines whether the sound signal of the broadcast included in the received signal is sounded or silent;
A removing unit for removing, from the received signal, a noise component extracted based on a signal obtained by reducing the broadcast control signal from the received signal when the determining unit determines that the sound signal is silent;
A received signal processing apparatus. A determination unit that determines whether the sound signal included in the received signal is sounded or silent;
A removing unit for removing, from the received signal, a noise component extracted based on a signal obtained by reducing a predetermined sine wave component from the received signal when the determining unit determines that the sound signal is silent;
A received signal processing apparatus. The predetermined sine wave component is a sine wave component corresponding to at least the carrier signal of the received signal,
The received signal processing apparatus according to claim 2. A storage unit for storing information on the noise component;
Further comprising
The removing unit removes the noise component from the received signal based on information on the noise component stored in the storage unit when the sound signal is determined to be sound by the determining unit;
The received signal processing apparatus according to any one of claims 1 to 3. The received signal is a received signal modulated by an FM modulation scheme.
The received signal processing device according to any one of claims 1 to 4. Computer
Determine whether the sound signal included in the received signal is voiced or silent,
When it is determined that the sound signal is silent, a noise component extracted based on a signal obtained by reducing a predetermined sine wave component from the reception signal is removed from the reception signal;
Received signal processing method. On the computer,
Determine whether the sound signal included in the received signal is voiced or silent,
When it is determined that the sound signal is silent, a noise component extracted based on a signal obtained by reducing a predetermined sine wave component from the reception signal is removed from the reception signal;
program.