JP2017220752A - Noise cancelling device, receiving device, and noise cancelling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise cancelling device, a receiving device, and a noise cancelling method that can keep down a processing load of phase synchronization.SOLUTION: A noise cancelling device according to an embodiment includes a signal generation unit, a separation unit, and a noise removing unit. The signal generation unit generates an output signal of which the phase is synchronized with a carrier wave of a modulation signal by applying PLL processing to the received modulation signal. The separation unit separates an I component and a Q component from the modulation signal on the basis of the output signal generated by the signal generation unit. The noise removing unit removes noise included in the I component on the basis of the Q component separated by the separation unit.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a noise canceling device, a receiving device, and a noise canceling method.

  2. Description of the Related Art Conventionally, for example, a noise canceling device that removes noise by orthogonally detecting an AM (Amplitude Modulation) modulated radio broadcast wave and separating an I component and a Q component is known.

  Such an apparatus separates the I component and the Q component by synchronizing the phases of the carrier wave and the sine wave used for quadrature detection based on the separated I component and Q component (see, for example, Patent Document 1).

JP 2004-96645 A

  However, the conventional apparatus has a large processing load for phase synchronization. Specifically, the conventional apparatus calculates the angle corresponding to the phase difference using the I component and the Q component. However, since the calculation for calculating the angle is complicated, the processing load for phase synchronization is large.

  The present invention has been made in view of the above, and an object of the present invention is to provide a noise canceling device, a receiving device, and a noise canceling method that can suppress the processing load of phase synchronization.

  In order to solve the above-described problems and achieve the object, a noise cancellation device according to the present invention includes a signal generation unit, a separation unit, and a noise removal unit. The signal generator generates an output signal whose phase is synchronized with the carrier wave of the modulated signal by performing PLL processing on the received modulated signal. The separation unit separates the I component and the Q component from the modulated signal based on the output signal generated by the signal generation unit. The noise removing unit removes noise included in the I component based on the Q component separated by the separating unit.

  According to the present invention, the processing load of phase synchronization can be suppressed.

FIG. 1 is a diagram illustrating an outline of a noise cancellation method according to the embodiment. FIG. 2 is a block diagram illustrating a configuration of the receiving apparatus according to the embodiment. FIG. 3 is a block diagram illustrating a configuration of the noise cancellation device according to the embodiment. FIG. 4 is a diagram illustrating processing contents of the frequency correction unit. FIG. 5 is a diagram illustrating processing contents of the conversion unit. FIG. 6 is a diagram showing the processing content of the BPF. FIG. 7 is a flowchart illustrating a processing procedure of noise removal processing executed by the noise cancellation device according to the embodiment. FIG. 8 is a block diagram illustrating a configuration of a noise cancellation device according to a modification of the embodiment.

  Hereinafter, embodiments of a noise cancellation device, a reception device, and a noise cancellation method disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

  In the following embodiment, a case where a noise canceling device is mounted on a radio serving as a receiving device will be described. It is assumed that such a receiving apparatus receives an AM (Amplitude Modulation) modulated radio broadcast wave (hereinafter referred to as a modulated signal).

  The receiving device is not limited to a radio, and may be any communication device that can receive an AM-modulated signal. The modulation signal is not limited to a radio sound signal, and may be a video signal, for example.

  First, the outline of the noise cancellation method according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an outline of a noise cancellation method according to the embodiment. FIG. 1 shows a modulated signal 100 of a predetermined frequency selected from among various modulated signals received by a radio station.

  As shown in FIG. 1, in the noise cancellation method according to the embodiment, the phase is synchronized with the carrier wave included in the modulation signal 100 by performing a PLL (Phase Locked Loop) process as the phase synchronization process for the modulation signal 100. Generate an output signal. Then, the I component and the Q component are separated from the modulation signal 100 based on the generated output signal.

  The I component is a component in phase with the carrier wave of the modulation signal 100 and is a component mainly including an audio signal, noise, and the like. The Q component is a component having a quadrature phase with respect to the carrier wave of the modulation signal 100, and is a component mainly including noise.

  Here, an example of general phase synchronization processing will be described. In such phase synchronization processing, the I component and the Q component are separated by performing quadrature detection. The I component and the Q component cause a phase shift with the receiving side due to the influence of the phase shift between the transmitting side and the receiving side (hereinafter referred to as I component and Q component including the shift). That is, the phase shift is calculated and the calculated phase shift is corrected to synchronize with the carrier wave.

  Specifically, in a general phase synchronization process, an I component and a Q component including a deviation are plotted on a complex plane, and an angle corresponding to a phase difference is calculated (so-called arc tangent process). Then, the calculated angle is corrected to synchronize with the carrier wave. However, since the calculation for calculating the angle by the arc tangent process is complicated, the processing load of the phase synchronization process is large.

  Therefore, in the noise cancellation method according to the embodiment, the phase is synchronized by using the above-described PLL process instead of the arc tangent process. Specifically, first, the received modulated signal 100 is subjected to PLL processing to generate an output signal 101 whose phase is synchronized with the carrier wave of the modulated signal 100 (step S1).

  Subsequently, the I component and the Q component are separated based on the generated output signal 101 (step S2). Then, noise included in the I component is removed based on the separated Q component (step S3).

  As described above, the noise canceling method according to the embodiment does not need to calculate an angle like the arctangent process by performing the phase synchronization process using the PLL process. That is, according to the noise cancellation method according to the embodiment, the processing load can be suppressed.

  Next, the configuration of the receiving device 1 on which the noise cancellation device 10 is mounted will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration of the receiving device 1 according to the embodiment. As illustrated in FIG. 2, the reception device 1 includes an A / D conversion unit 2, a detection unit 3, and an output unit 4 in addition to the noise cancellation device 10. An antenna 20 is connected to the receiving device 1.

  The antenna 20 receives a plurality of modulated signals transmitted from various radio broadcast stations. Such a modulated signal includes a carrier wave of a predetermined frequency (for example, an RF (Radio Frequency) band), an audio signal, noise, and the like. The A / D converter 2 converts the modulated signal 100 received by the antenna 20 from an analog signal to a digital signal.

  The detection unit 3 separates an I component and a Q component including a shift from the modulation signal 100 by performing quadrature detection of the selected modulation signal 100 among the plurality of modulation signals input from the A / D conversion unit 2. To do. Specifically, the detection unit 3 first converts the modulation signal 100 from the time domain to the frequency domain by performing a Fourier transform. Subsequently, the detector 3 generates a sine wave having the same frequency as the carrier wave of the modulation signal 100 based on the modulation signal 100 shown in the frequency domain. The detector 3 does not necessarily need to perform Fourier transform if the selected frequency is known.

  Subsequently, the detection unit 3 frequency-converts the frequency of the carrier wave to 0 Hz by mixing the generated sine wave and the modulation signal 100 with a mixer. Thereby, since the carrier wave component of the modulation signal 100 can be ignored, the detection unit 3 can separate the I component including the deviation from the modulation signal 100.

  Further, the detector 3 generates an orthogonal sine wave orthogonal to the sine wave by shifting the phase of the generated sine wave by 90 degrees. And the detection part 3 converts the frequency of a carrier wave into 0 Hz by mixing the produced | generated orthogonal sine wave and the modulation signal 100 with a mixer.

  Thereby, the detection part 3 can isolate | separate the Q component containing the deviation orthogonal to the I component containing the deviation. Further, the detector 3 outputs an I component and a Q component including the separated deviation to the noise canceling device 10.

  The detection unit 3 generates a sine wave having the same frequency as that of the carrier wave, thereby separating the I component and the Q component including the shift from the modulation signal 100, but is not limited thereto.

  For example, the detection unit 3 may output the modulation signal 100 obtained by frequency-converting the frequency of the carrier wave from the RF band to the IF (Intermediate Frequency) band to the noise cancellation device 10. That is, the detection unit 3 does not have to separate the I component and the Q component including a shift from the modulation signal 100. This point will be described later with reference to FIG.

  The noise cancellation apparatus 10 generates an I component and a Q component whose phases are synchronized by performing a PLL process based on the I component and the Q component including the deviation.

  Further, the noise canceling apparatus 10 removes noise included in the I component based on the generated Q component, and outputs the I component to the output unit 4. The configuration of the noise cancellation device 10 will be described later with reference to FIG.

  The output unit 4 performs a process of outputting the I component acquired from the noise cancellation device 10 to an external device such as a speaker. Specifically, the output unit 4 converts an I component that is a digital signal into an analog signal.

  Further, the output unit 4 performs, for example, audio mute processing or high cut processing for removing high frequency components on the I component of the analog signal, and then outputs the I component as audio, for example, via a speaker. Therefore, according to the receiving device 1 according to the embodiment, a signal from which noise has been removed by the noise canceling device 10 can be output. Note that the output unit 4 may perform high cut processing on the digital signal before being converted into the analog signal.

  Next, the structure of the noise cancellation apparatus 10 is demonstrated using FIG. FIG. 3 is a block diagram illustrating a configuration of the noise cancellation device 10 according to the embodiment. As shown in FIG. 3, the noise cancellation apparatus 10 includes a frequency correction unit 10a, a conversion unit 10b, a BPF (Band-pass filter) 10c, a signal generation unit 10d, a delay unit 10e, and a separation unit 10f. A phase conversion unit 10g and a noise removal unit 10h are provided.

  The frequency correction unit 10a performs so-called automatic frequency control. The frequency correction unit 10a corrects the frequency deviation from the predetermined frequency for the carrier wave converted to the predetermined frequency by the detection unit 3.

  For example, when the carrier wave that should have been converted to 0 Hz deviates from 0 Hz for some reason, the frequency correction unit 10a corrects the frequency deviation and sets the frequency of the carrier wave to 0 Hz. The processing content of the frequency correction unit 10a will be described later with reference to FIG.

  The conversion unit 10b performs a process of converting again the I component including the deviation acquired from the frequency correction unit 10a into a second modulation signal (hereinafter referred to as “second modulation signal” in order to distinguish it from the modulation signal 100). Specifically, the conversion unit 10b generates a sine wave having a predetermined frequency and mixes it with the I component, thereby frequency-converting the carrier wave from 0 Hz to the predetermined frequency. As a result, the I component returns to the second modulated signal including a carrier wave having a predetermined frequency, which will be described later with reference to FIG.

  The BPF 10c is a bandpass filter that selectively passes a carrier wave in the second modulated signal generated by the conversion unit 10b. That is, the BPF 10c removes the audio signal and noise by performing bandpass processing around the carrier wave in the second modulated signal. Note that the BPF 10c passes a frequency region having a predetermined width including the frequency of the carrier wave.

  The BPF 10c outputs the passed carrier wave to the signal generation unit 10d. The processing content of the BPF 10c will be described later with reference to FIG.

  The signal generation unit 10d generates an output signal whose phase is synchronized with the carrier wave by performing PLL processing on the carrier wave that has passed through the BPF 10c. Specifically, the signal generation unit 10d includes, for example, a phase comparator, a loop filter, and a digitally controlled oscillator (DCO).

  The phase comparator multiplies the second modulated signal that is only the carrier wave by the sine wave that is the output signal 101 generated by the DCO, and outputs the result to the loop filter.

  The loop filter integrates the input from the phase comparator. When the phase of the carrier wave of the second modulation signal and the sine wave of the output signal 101 are synchronized, that is, when the time difference is zero, the integral value of the loop filter is zero.

  The DCO corrects the phase of the output signal 101 so as to synchronize with the phase of the carrier wave in accordance with the integration value input from the loop filter. The oscillator outputs the output signal 101 whose phase is corrected to the separation unit 10f.

  Further, the oscillator feeds back the output signal 101 to the phase comparator and compares the phase with the carrier wave again. That is, the oscillator synchronizes the output signal 101 so as to follow the phase of the carrier wave by feedback control. Thus, the signal generation unit 10d can synchronize the output signal 101 with the phase of the carrier wave without calculating the angle.

  The delay unit 10e delays the second modulation signal acquired from the conversion unit 10b by a predetermined time and supplies the second modulation signal to the separation unit 10f. The delay time is set according to the processing time of the BPF 10c and the signal generator 10d. That is, the delay unit 10e delays the input timing of the second modulation signal so that the second modulation signal and the output signal 101 are input to the separation unit 10f substantially simultaneously.

  The separation unit 10f separates the I component and the Q component from the second modulated signal based on the output signal 101 generated by the signal generation unit 10d. Specifically, the separation unit 10f includes a first mixer 10fa and a second mixer 10fb.

  The first mixer 10fa mixes the output signal 101 and the second modulation signal input from the delay unit 10e, and frequency-converts the carrier wave included in the second modulation signal to 0 Hz. Thereby, the first mixer 10fa separates the I component from the second modulated signal.

  The second mixer 10fb mixes the quadrature output signal input from the phase converter 10g and the second modulation signal, and frequency-converts the carrier wave included in the second modulation signal to 0 Hz. Accordingly, the second mixer 10fb separates the Q component from the second modulated signal. Here, the phase converter 10g performs a process of generating an orthogonal output signal in which the phase of the output signal 101 input from the signal generation unit 10d is shifted by 90 degrees.

  The noise removing unit 10h removes noise included in the I component based on the Q component separated by the separating unit 10f. The noise removing unit 10h can use an adaptive filter that determines a filter coefficient in accordance with, for example, an LMS (Least Mean Square) algorithm.

  Specifically, the noise removal unit 10h detects the noise N from the Q component acquired from the separation unit 10f according to the LMS algorithm, and determines the filter coefficient so as to remove the detected noise N. The noise removing unit 10h removes noise included in the I component using a filter having the determined filter coefficient. The noise removing unit 10 h outputs the I component from which noise has been removed to the output unit 4.

  Next, processing contents of the frequency correction unit 10a shown in FIG. 3 will be described with reference to FIG. FIG. 4 is a diagram illustrating the processing contents of the frequency correction unit 10a. FIG. 4 shows the frequency characteristics of the input signal to the frequency correction unit 10a as a graph. Such a graph shows amplitude on the vertical axis and frequency domain on the horizontal axis. As shown in the graph, the I component includes a carrier wave C, an audio signal D, and noise N. In FIG. 4, the audio signal D is shown as a signal having a predetermined frequency in order to simplify the description.

  Here, the detection unit 3 separates the I component including the deviation from the modulation signal 100 by frequency-converting the carrier wave to 0 Hz. However, as shown in FIG. 4, the frequency of the I component carrier wave C including the deviation may actually slightly deviate from 0 Hz (0.001 kHz in FIG. 4). This is because the detection unit 3 is affected by, for example, the ambient temperature and generates a sine wave having a changed frequency.

  For this reason, the carrier wave C becomes a 0.001 kHz sine wave in the time domain when inverse Fourier transform is performed. Therefore, the frequency correction unit 10a generates a 0.001 kHz sine wave based on the sine wave.

  Subsequently, the frequency correction unit 10a corrects the frequency of the carrier C to 0 Hz by mixing the carrier C and the generated 0.001 kHz sine wave. As described above, the frequency correction unit 10a can improve the separation accuracy of the I component and the Q component by the separation unit 10f by correcting the frequency shift of the carrier wave C.

  The frequency correction unit 10a may feed back the detected frequency deviation to the detection unit 3. By correcting the sine wave used for the quadrature detection so that the frequency shift unit 3 does not cause such a frequency shift, the frequency correction unit 10a does not need to correct the frequency shift, so that the processing load can be suppressed.

  In addition, although the frequency correction | amendment part 10a detected and correct | amended the frequency shift only about I component containing a shift | offset | difference, it is not limited to this. The frequency correction unit 10a may determine a correction value comprehensively from the frequency shift of each of the I component and the Q component by detecting the frequency shift of the Q component including the shift.

  Next, the processing content of the conversion part 10b shown in FIG. 3 is demonstrated using FIG. FIG. 5 is a diagram illustrating processing contents of the conversion unit 10b. FIG. 5 shows a graph of signals that are input to the conversion unit 10b and output from the conversion unit 10b. The inputs shown in the graph on the left side of FIG. 5 are the I component and the Q component acquired from the frequency correction unit 10a, and include a 0 Hz carrier wave C, audio signals D1 and D2, and noise N.

  And the conversion part 10b outputs the signal which frequency-converted the frequency of the carrier wave C to 20 kHz, for example, as shown in the graph on the right side of FIG. The frequency conversion of the carrier wave C is performed by, for example, generating a 20 kHz sine wave and mixing it with the 0 Hz carrier wave C.

  The output from the converter 10b includes a 20 kHz carrier wave C, audio signals D1 and D2, and noise N. Note that the audio signals D1 and D2 are located symmetrically about the carrier wave C. Further, the noise N is located in the frequency region on the audio signal D1 side with respect to the carrier wave C. That is, the conversion unit 10b converts the input I component and Q component as outputs into the second modulated signal.

  With respect to the second modulated signal thus converted, the signal generation unit 10d can perform the PLL process to synchronize the phase with the carrier wave C of 20 kHz. The frequency of the carrier C is preferably a frequency lower than that of the RF band, for example, a frequency lower than the intermediate frequency (IF) band or IF band, so-called Low-IF band (for example, 20 kHz).

  By doing in this way, the processing amount in a back | latter stage can be reduced. However, the frequency of the carrier C may be any frequency that can convert the I component into the second modulated signal, and may be a frequency higher than the RF band.

  Next, processing contents of the BPF 10c shown in FIG. 3 will be described with reference to FIG. FIG. 6 is a diagram showing the processing contents of the BPF 10c. As shown in FIG. 6, the BPF 10c passes only the 20 kHz carrier wave C in the second modulated signal acquired from the converter 10b.

  Here, if components such as the audio signal D and noise N are also passed, in the PLL processing by the signal generation unit 10d, it is synchronized with the phase of the audio signals D1, D2 and noise N instead of the carrier wave C. The synchronization accuracy of the output signal 101 may not be stable.

  For this reason, by using BPF 10c as a band-pass filter in a band that does not include audio signals D1 and D2 and noise N, components other than the carrier wave can be removed, and the synchronization accuracy of PLL processing in signal generation unit 10d can be stabilized. Can do.

  Next, with reference to FIG. 7, a processing procedure of noise removal processing executed by the noise cancellation device 10 according to the embodiment will be described. FIG. 7 is a flowchart illustrating a processing procedure of noise removal processing executed by the noise cancellation device 10 according to the embodiment.

  As shown in FIG. 7, the frequency correction unit 10a corrects the frequency shift from the predetermined frequency for the carrier C converted to the predetermined frequency by the detection unit 3 (step S101). In addition, when the frequency correction | amendment part 10a feedback-controls the frequency shift concerning the detection part 3, and this frequency deviation disappears, you may skip this process (step S101) after the first time.

  Subsequently, the conversion unit 10b converts the I component carrier wave acquired from the frequency correction unit 10a into a predetermined frequency to generate a second modulated signal (step S102). The BPF 10c selectively passes the carrier wave in the second modulated signal acquired from the conversion unit 10b (step S103).

  The BPF 10c may omit this process (step S103) as long as the output signal 101 whose phase is synchronized with the carrier wave C can be stably generated by the subsequent signal generation unit 10d.

  The signal generation unit 10d performs PLL processing on the component of the second modulated signal that has passed through the BPF 10c, that is, the carrier wave, thereby generating the output signal 101 whose phase is synchronized with the carrier wave (step S104).

  Subsequently, the separation unit 10f separates the I component and the Q component from the second modulated signal based on the output signal 101 generated by the signal generation unit 10d (step S105). Then, the noise removal unit 10h removes noise included in the I component based on the Q component separated by the separation unit 10f (step S106), and ends the process.

  As described above, the noise cancellation device 10 according to the embodiment includes the signal generation unit 10d, the separation unit 10f, and the noise removal unit 10h. The signal generation unit 10d performs PLL processing on the received modulated signal 100, thereby generating an output signal 101 whose phase is synchronized with the carrier wave C of the modulated signal 100 (or the second modulated signal). The separation unit 10f separates the I component and the Q component from the modulation signal 100 based on the output signal 101 generated by the signal generation unit 10d. The noise removing unit 10h removes noise included in the I component based on the Q component separated by the separating unit 10f. Thereby, the noise cancellation apparatus 10 can suppress the processing load of phase synchronization.

  In the above-described embodiment, the case where the detection unit 3 separates the I component and the Q component including the deviation from the modulation signal 100 has been described. However, the present invention is not limited to this. The Q component may not be separated.

  Specifically, the detection unit 3 may convert the frequency of the RF band modulation signal 100 into, for example, an IF band modulation signal 100 and output the IF band modulation signal 100 to the noise cancellation apparatus 10. Here, the case where the IF band modulation signal 100 is used will be described with reference to FIG.

  FIG. 8 is a block diagram illustrating a configuration of the noise cancellation device 10 according to a modification of the embodiment. Note that the modification shown in FIG. 8 will be described focusing on differences from the above-described noise canceling apparatus 10.

  As illustrated in FIG. 8, the signal generation unit 10 d acquires the IF band modulation signal 100 that is frequency-converted by the detection unit 3. Subsequently, the signal generation unit 10 d generates an IF band output signal 101 based on the acquired modulation signal 100.

  Thus, in the noise cancellation apparatus 10 which concerns on a modification, it is not necessary to produce | generate a 2nd modulation | alteration signal from I component and Q component which include deviation by the conversion part 10b. For this reason, by omitting the processing of the conversion unit 10b, the configuration of the noise cancellation device 10 can be simplified.

  In the block diagram shown in FIG. 8, a BPF 10c that selectively allows the IF band carrier wave C to pass therethrough may be provided before the signal generation unit 10d. That is, the signal generation unit 10d can perform PLL processing on the IF band carrier wave C that has passed through the BPF 10c, so that the phase synchronization accuracy can be improved.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Reception apparatus 2 A / D conversion part 3 Detection part 4 Output part 10 Noise cancellation apparatus 10a Frequency correction part 10b Conversion part 10c BPF
10d Signal generation unit 10e Delay unit 10f Separation unit 10g Phase converter 10h Noise removal unit 20 Antenna 100 Modulation signal 101 Output signal C Carrier waves D, D1, D2 Audio signal N Noise

Claims (5)

A signal generation unit that generates an output signal whose phase is synchronized with the carrier wave of the modulation signal by performing PLL processing on the received modulation signal;
A separation unit that separates an I component and a Q component from the modulation signal based on the output signal generated by the signal generation unit;
A noise canceling device comprising: a noise removing unit that removes noise contained in the I component based on the Q component separated by the separating unit. A band pass filter that selectively passes the carrier in the modulated signal;
The signal generator is
The noise cancellation apparatus according to claim 1, wherein the PLL processing is performed on a signal that has passed through the band-pass filter. The noise cancellation apparatus according to claim 1, further comprising a frequency correction unit that corrects a frequency shift from the predetermined frequency for the carrier wave converted to a predetermined frequency. The noise cancellation device according to any one of claims 1 to 3,
An antenna,
A detection unit that outputs the modulation signal to the noise cancellation device by detecting a signal received by the antenna;
An output unit that outputs a signal acquired from the noise cancellation device to an external device. A signal generation step of generating an output signal whose phase is synchronized with the carrier wave of the modulation signal by performing PLL processing on the received modulation signal;
A separation step of separating an I component and a Q component from the modulation signal based on the output signal generated by the signal generation step;
And a noise removing step of removing noise contained in the I component based on the Q component separated by the separating step.

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