JP2019009564A - Receiver, reception method and control program - Google Patents

Abstract

To provide a receiver capable of receiving a signal transmitted in amplitude modulation, and properly eliminating noise.SOLUTION: A receiver 10 for receiving a signal transmitted in amplitude modulation includes: a frequency converter 12 for generating a complex baseband signal by converting an amplitude modulation signal received by an antenna 11; a frequency phase correction unit 13 for correcting a frequency offset and a phase offset on a complex baseband signal generated by the frequency converter 12; a noise elimination unit 14 for eliminating a noise component, contained in a real part of a complex baseband signal after correction by the frequency phase correction unit 13, by processing of referencing an imaginary part of the complex baseband signal; and a demodulator 15 for performing amplitude demodulation of the real-part signal of the complex baseband signal whose noise component is eliminated by the noise elimination unit 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a receiving apparatus for signals transmitted using amplitude modulation, and a receiving method and a control program used in the receiving apparatus.

  As for the sound reproduced by the receiving device that receives a signal (for example, AM radio broadcast signal) transmitted using amplitude modulation (AM), the noise level increases as the received electric field strength decreases. In addition, for example, stationary sound due to radiation from the power transmission line is mixed in the vicinity of the power transmission line in the audio reproduced by the receiving apparatus that receives a practical AM radio broadcast. Beat noise such as a sine wave or pulse noise having an instantaneous amplitude peak due to unnecessary radiation of an electric component such as a wiper. In the in-vehicle AM radio receiver, the received electric field strength or the state of disturbing waves such as radiation from the power transmission line varies with time as the vehicle moves.

  Conventionally, a noise removal method using spectral subtraction described in Patent Document 1 is known as a method for removing noise. In this noise removal method, a noise spectrum is estimated from a silent section, and stationary noise is removed from an AM demodulated signal by spectrum subtraction. As a circuit for removing pulse noise, a noise removal circuit described in Patent Document 2 is known.

Japanese Patent No. 3451146 Japanese Patent No. 3213495

  In the noise removal method of Patent Document 1, since the noise spectrum is estimated from a silent section outside the speech section in order to remove noise in the speech section, the estimation accuracy is low and the received electric field strength etc. fluctuates, that is, with time. In situations where the noise fluctuates, it is not very effective.

  Therefore, the present invention provides a receiving apparatus that receives a signal transmitted by amplitude modulation and can remove noise more appropriately than a conventional noise removing method. The present invention also provides a receiving method and a control program used in the receiving apparatus.

  In order to solve the above-described problem, a receiving apparatus according to one embodiment of the present invention is a receiving apparatus that receives a signal transmitted by amplitude modulation, and converts a complex modulated baseband by converting an amplitude modulated signal received by an antenna. A frequency conversion unit that generates a signal, a frequency phase correction unit that corrects a frequency offset and a phase offset in the complex baseband signal generated by the frequency conversion unit, and the complex baseband signal that has been corrected by the frequency phase correction unit The noise component included in the real part signal is removed by processing referring to the imaginary part signal of the complex baseband signal, and the real part signal from which the noise component is removed by the noise removing unit And a demodulator that demodulates the signal.

  In order to solve the above-described problem, a reception method according to an aspect of the present invention is a reception method in a reception apparatus that includes an antenna and receives a signal transmitted by amplitude modulation, the amplitude modulation received by the antenna. A frequency conversion step of generating a complex baseband signal by converting the signal, a frequency phase correction step of correcting a frequency offset and a phase offset in the complex baseband signal generated in the frequency conversion step, and the frequency phase correction step The noise removal step of removing the noise component contained in the real part signal of the complex baseband signal after correction in step 1 by the process referring to the imaginary part signal of the complex baseband signal, and the noise removal step And a demodulating step for amplitude demodulating the real part signal from which the noise component has been removed. That.

  In order to solve the above problem, a control program according to one embodiment of the present invention is a control program for causing a reception device including an antenna and a microprocessor to execute a reception process of receiving a signal transmitted by amplitude modulation. The reception processing includes a frequency conversion step of generating a complex baseband signal by converting an amplitude modulation signal received by the antenna, a frequency offset in the complex baseband signal generated in the frequency conversion step, and Refer to the imaginary part signal of the complex baseband signal for the noise component included in the real part signal of the complex baseband signal after the frequency phase correction step for correcting the phase offset and the frequency phase correction step. The noise removal step to be removed and the noise removal step The real part signal components have been removed is a control program that includes a demodulation step for amplitude demodulation.

  According to the present invention, noise can be appropriately removed even under a situation where the received electric field strength varies.

3 is a block diagram showing a configuration of a receiving apparatus according to Embodiment 1. FIG. It is a block diagram which shows the structure of the frequency phase correction | amendment part of a receiver. It is a figure for demonstrating the effect | action of the frequency phase correction | amendment part of a receiver. It is a block diagram which shows the structure of the noise removal part of a receiver. It is a block diagram which shows the modification 1 of a structure of the noise removal part of a receiver. It is a block diagram which shows the modification 2 of the structure of the noise removal part of a receiver. It is a block diagram which shows the modification 3 of a structure of the noise removal part of a receiver. It is a block diagram which shows the modification 4 of the structure of the noise removal part of a receiver. It is a flowchart which shows an example of the reception process in a receiver.

  A receiving apparatus according to an aspect of the present invention is a receiving apparatus that receives a signal transmitted by amplitude modulation, and generates a complex baseband signal by converting the amplitude modulated signal received by an antenna. A frequency phase correction unit that corrects a frequency offset and a phase offset in the complex baseband signal generated by the frequency conversion unit, and a real part signal of the complex baseband signal that has been corrected by the frequency phase correction unit. A noise removing unit that removes the noise component being processed by referring to the imaginary part signal of the complex baseband signal, and a demodulating unit that amplitude-demodulates the real part signal from which the noise component has been removed by the noise removing unit, It is a receiver provided with. As a result, the frequency and phase correction unit eliminates the deviation of the frequency offset and the phase offset of the amount deviated from the frequency and phase of the complex baseband signal when the signal transmitted from the transmission source is received by an ideal receiving device. It is corrected to. For this reason, the audio signal component is removed from the imaginary part signal of the complex baseband signal after correction, and the noise component can be constantly observed from the imaginary part signal. Can be performed appropriately. Therefore, according to this receiving apparatus, it is possible to restore a sound from which noise has been appropriately removed from the received signal.

  The frequency phase correction unit receives the complex baseband signal generated by the frequency conversion unit, and outputs a low-pass component of the complex baseband signal; and the low-pass filter A sine wave generating unit that detects the frequency offset from the output of the unit and generates a sine wave having the detected frequency offset as a frequency, and the sine wave generated by the sine wave generating unit, the low pass filter unit A phase correction unit that performs correction to remove the effect of phase rotation that has occurred between the input and output, and the complex baseband signal generated by the frequency conversion unit to the sine wave corrected by the phase correction unit A multiplier that removes the frequency offset and the phase offset in the complex baseband signal by multiplying by a complex conjugate. Good. Thereby, the frequency phase correction | amendment part can remove appropriately the frequency offset and phase offset in the complex baseband signal which a frequency conversion part outputs.

  The noise removing unit converts the real part signal of the complex baseband signal corrected by the frequency phase correcting unit from a time signal to a frequency signal having components of a plurality of frequencies and outputs the converted signal. A first time frequency conversion unit, and the imaginary part signal of the complex baseband signal corrected by the frequency phase correction unit is converted from a time signal to a frequency signal having components of each of the plurality of frequencies and output. A two-time frequency converter, a first power spectrum calculator that converts the output of the first time-frequency converter into a power spectrum having components of each of the plurality of frequencies, and the second time-frequency converter A second power spectrum calculation unit that converts the output of the power into a power spectrum having components of each of the plurality of frequencies and outputs the power spectrum, and the second power By referring to the output of the spectrum calculation unit, the noise component included in the output of the first power spectrum calculation unit is estimated, and the gain for each of the plurality of frequencies for removing the estimated noise component is calculated. A noise reduction gain calculation unit, a gain multiplication unit that outputs a complex signal by multiplying the output of the first time frequency conversion unit by the gain calculated by the noise reduction gain calculation unit, and the gain multiplication unit that outputs It is good also as having a frequency time conversion part which converts a complex signal from a frequency signal into a time signal. Thereby, stationary noise is appropriately removed by spectral subtraction.

  The noise removal unit further includes a peak detection unit that detects a peak frequency that is one or a plurality of frequencies that are peaks of the power spectrum output from the second power spectrum calculation unit among the plurality of frequencies. The noise removal gain calculation unit calculates a gain for each of the plurality of frequencies for removing the estimated noise component and removing the peak frequency component detected by the peak detection unit. It is good to do. Thereby, beat noise is removed.

  Further, the noise removing unit further detects a peak frequency that is one or a plurality of frequencies that become a peak of a power spectrum output from the second power spectrum calculation unit among the plurality of frequencies, and A notch filter coefficient calculation unit for calculating a filter coefficient used for removing the peak frequency component detected by the peak detection unit by a notch filter; and the notch filter coefficient for the output of the frequency time conversion unit A notch filter unit that applies the notch filter using the filter coefficient calculated by the calculation unit may be included. Thereby, beat noise is appropriately removed by the notch filter.

  The noise removing unit converts the imaginary part signal of the complex baseband signal after correction by the frequency phase correction unit from a time signal to a frequency signal having components of the plurality of frequencies, and outputs the frequency signal. A time frequency conversion unit; a power spectrum calculation unit that converts the output of the time frequency conversion unit into a power spectrum having components of each of the plurality of frequencies; and the power spectrum calculation unit among the plurality of frequencies. A peak detector for detecting a peak frequency that is one or a plurality of frequencies that become a peak of a power spectrum output from the power source, and a peak frequency component detected by the peak detector is used to remove by a notch filter A notch filter coefficient calculation unit for calculating a filter coefficient, and the frequency phase correction unit after the correction With respect to the real part signal containing baseband signal, it is also possible to have a notch filter unit for applying the notch filter using the filter coefficient calculated in the notch filter coefficient calculator. Also by this, beat noise is appropriately removed by the notch filter.

  The noise removing unit detects a period in which pulse noise is included in the imaginary part signal of the complex baseband signal after correction by the frequency phase correcting unit, and is detected by the pulse noise detecting unit. And a pulse noise removing unit that removes pulse noise from the real part signal of the complex baseband signal after the correction by the frequency phase correcting unit based on the set period. Thereby, the removal of pulse noise is performed with high accuracy.

  The signal received by the receiving device may be a radio broadcast signal. Thereby, noise is appropriately removed from the sound of the radio broadcast.

  A reception method according to one embodiment of the present invention is a reception method in a reception apparatus that includes an antenna and receives a signal transmitted by amplitude modulation, and that performs complex processing by converting the amplitude modulation signal received by the antenna. A frequency conversion step for generating a baseband signal, a frequency phase correction step for correcting a frequency offset and a phase offset in the complex baseband signal generated in the frequency conversion step, and the complex after the correction in the frequency phase correction step. The noise component included in the real part signal of the baseband signal is removed by processing referring to the imaginary part signal of the complex baseband signal, and the noise component is removed in the noise removing step. And a demodulating step for amplitude-demodulating the real part signal. Thereby, noise is appropriately removed from the received signal.

  A control program according to an aspect of the present invention is a control program for causing a reception device including an antenna and a microprocessor to execute a reception process of receiving a signal transmitted by amplitude modulation, and the reception process includes: A frequency conversion step for generating a complex baseband signal by converting an amplitude modulation signal received by the antenna, and a frequency phase for correcting a frequency offset and a phase offset in the complex baseband signal generated in the frequency conversion step Noise that removes the noise component included in the real part signal of the complex baseband signal after the correction step and the frequency phase correction step by referring to the imaginary part signal of the complex baseband signal Removing the noise component in the noise removing step Signal which is a control program that includes a demodulation step for amplitude demodulation. By causing the processor of the receiving apparatus to execute this control program, it is possible to appropriately remove noise from the received signal.

  These general or specific aspects may be realized by a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM. The system, method, integrated circuit, computer You may implement | achieve with arbitrary combinations of a program or a recording medium.

  Hereinafter, a receiving apparatus using the receiving method according to the embodiment will be described with reference to the drawings. Each of the embodiments shown here shows a specific example of the present invention. Therefore, numerical values, components, arrangement and connection forms of components, and steps and order of steps as processing elements shown in the following embodiments are merely examples and do not limit the present invention. . Among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims can be arbitrarily added. Each figure is a mimetic diagram and is not necessarily illustrated strictly.

(Embodiment 1)
Hereinafter, receiving apparatus 10 according to the present embodiment will be described. The receiving device 10 is a device that receives a signal (for example, an AM radio broadcast signal) in which acoustic information such as an audio signal is transmitted by amplitude modulation (AM). The receiving device 10 is, for example, an in-vehicle AM radio receiving device or the like, and is realized by an integrated circuit including a memory, a processor (microprocessor), an antenna, an analog circuit, or the like.

[1. Overall configuration of receiving apparatus 10]
FIG. 1 shows a configuration of the receiving device 10. As illustrated in FIG. 1, the receiving device 10 includes an antenna 11, a frequency conversion unit 12, a frequency phase correction unit 13, a noise removal unit 14, a demodulation unit 15, and an output unit 16.

  The antenna 11 receives a radio wave such as a carrier wave transmitted by amplitude modulation from an AM radio broadcasting station or the like. The frequency of the carrier wave is 1 MHz, for example.

  The frequency converter 12 receives an amplitude modulation signal, which is an analog signal received by the antenna 11, and generates a complex baseband signal as a digital signal by performing A / D conversion or the like on the amplitude modulation signal. Output. The digital signal is a time-series signal composed of samples (that is, signal data) for each sample point sampled at a specific sampling (sampling) frequency (for example, 16 kHz). The complex baseband signal is a time-series signal in which an audio signal mixed with noise is represented by a complex number. Here, the real part signal corresponding to the real number of the complex time series signal is referred to as the I (In-phase) component of the time series signal, and the imaginary part signal corresponding to the imaginary number of the complex time series signal is This is referred to as a Q (Quadrature-phase) component of the sequence signal. In the receiving apparatus 10, for example, a buffer that stores a certain amount of signal data is used, and each signal data of the complex baseband signal output from the frequency converter 12 is sequentially stored in the buffer, and the signal in the buffer is stored. Each unit can execute processing with reference to the data.

  The frequency phase correction unit 13 receives the complex baseband signal generated and output by the frequency conversion unit 12 and corrects the frequency offset and the phase offset in the complex baseband signal. The frequency offset (or phase offset) indicates an amount deviated from the frequency (or phase) of the complex baseband signal when a signal transmitted by a transmission source such as an AM radio broadcasting station is received by an ideal receiving device. The frequency phase correction unit 13 corrects and outputs the complex baseband signal so as to eliminate the deviation, that is, to approach a correct state in which the frequency offset and the phase offset are zero. The frequency offset and the phase offset are caused by, for example, an accuracy error (for example, an error of 40 ppm to 50 ppm) of a crystal oscillator used for conversion by the frequency conversion unit 12 of the receiving device 10. By correcting the frequency offset and the phase offset by the frequency phase correction unit 13, the Q component of the output complex baseband signal does not include the audio signal component, and only the noise component is included. The output I component includes a noise component and an audio signal component. The frequency phase correction unit 13 will be described in detail later with reference to FIGS. 2 and 3.

  The noise removing unit 14 receives the corrected complex baseband signal output from the frequency phase correcting unit 13 as an input, and converts the noise component contained in the real part signal, that is, the I component of the corrected complex baseband signal, It is removed by referring to the imaginary part signal of the complex baseband signal, that is, the Q component. Since the Q component does not include a voice signal component and always includes a noise component, the noise removing unit 14 can estimate noise with high accuracy and appropriately remove noise from the I component. In other words, since the situation where the noise removal timing in the I component and the noise estimation timing in the Q component are not significantly different does not occur, noise removal is performed appropriately. The noise removing unit 14 outputs a signal obtained by removing the noise component from the I component. The noise removal unit 14 will be described in detail later with reference to FIGS.

  The demodulator 15 receives the I component signal of the complex baseband signal from which the noise component has been removed by the noise remover 14 as input, and amplitude-demodulates the input signal. This amplitude demodulation is in response to amplitude modulation performed by a transmission source such as an AM radio broadcasting station. The demodulator 15 transmits an audio signal as a result of amplitude demodulation to the output unit 16.

  The output unit 16 outputs the audio signal transmitted from the demodulation unit 15. The output unit 16 amplifies the audio signal and reproduces acoustic information such as audio by a speaker or the like, for example.

[2. Configuration of Frequency Phase Correction Unit 13]
FIG. 2 shows the configuration of the frequency phase correction unit 13. As shown in the figure, the frequency phase correction unit 13 includes a low-pass filter unit 131, a sine wave generation unit 132, a phase correction unit 133, and a multiplication unit 134.

  The low-pass filter unit 131 acts as a low-pass filter, receives the complex baseband signal generated and output by the frequency converter 12 and outputs a low-frequency component of the complex baseband signal. The low-pass filter passes a component having a frequency lower than the cut-off frequency with almost no attenuation, and gradually reduces a component having a frequency higher than the cut-off frequency. Specifically, the cutoff frequency is, for example, 100 Hz. This low-pass filter is used, for example, to pass a signal of 40 to 50 Hz that appears due to an accuracy error of 40 ppm to 50 ppm of a crystal oscillator with respect to a 1 MHz carrier wave and to remove an audio signal having a frequency higher than 100 Hz. It is done. Note that the low-pass filter causes phase rotation according to the frequency, but the phase correction unit 133 removes the influence of this phase rotation.

  The sine wave generator 132 detects the frequency offset as the frequency of the input signal using the low-frequency component of the complex baseband signal output from the low-pass filter 131 as an input signal, and uses the detected frequency offset as the frequency. Generate a sine wave. The sine wave generator 132 outputs a complex sine wave that is a complex signal of the generated sine wave.

  The phase correction unit 133 corrects the complex sine wave output from the sine wave generation unit 132 to remove the effect of phase rotation generated between the input and output of the low-pass filter unit 131, and the corrected sine wave The complex signal is output.

  The multiplication unit 134 multiplies the complex baseband signal generated and output by the frequency conversion unit 12 by the complex conjugate of the sine wave complex signal corrected by the phase correction unit 133, thereby generating a frequency offset and a complex baseband signal. Outputs a complex signal with the phase offset removed.

  Hereinafter, the operation of the frequency phase correction unit 13 will be described with reference to FIG.

  The complex baseband signal output from the frequency converter 12 is input to the frequency phase corrector 13. The I component 21a of the input IQ signal in FIG. 3 is a real part signal of the complex baseband signal, and the Q component 21b is an imaginary part signal of the complex baseband signal. In the IQ two-dimensional plane 20a, an amplitude modulation signal, which is a time-series signal such as an audio signal related to the input IQ signal, can be represented by line segments 24a to 24d that rotate with time. On the IQ two-dimensional plane 20a, a noise component is expressed by a dot pattern.

  The I component 22a and the Q component 22b after removing the frequency offset and the phase offset from the input IQ signal in FIG. 3 are a line segment 24e related to an amplitude modulation signal that is a time-series signal such as an audio signal on the IQ two-dimensional plane 20b. I can express. In the IQ two-dimensional plane 20b, a noise component is expressed by a dot pattern.

  The I component 23a and the Q component 23b after the phase correction unit 133 performs phase correction on the I component 22a and the Q component 22b in FIG. 3 are time series signals such as audio signals on the IQ two-dimensional plane 20c. It can be represented by a line segment 24f related to the amplitude modulation signal. On the IQ two-dimensional plane 20c, a noise component is expressed by a dot pattern. The line segment 24f is on the I axis, and the audio signal does not appear on the Q axis. Further, only the noise component appears on the Q axis in the IQ two-dimensional plane 20c.

  As described above, the frequency phase correction unit 13 includes the audio signal component that is amplitude-modulated in the I component and the audio signal component in the Q component by removing the frequency offset and the phase offset and performing the phase correction. A corrected complex baseband signal including a noise component is output.

[3. Configuration of noise removing unit 14]
FIG. 4 shows the configuration of the noise removal unit 14. As shown in the figure, the noise removal unit 14 includes a first time frequency conversion unit 141a, a second time frequency conversion unit 141b, a first power spectrum calculation unit 142a, a second power spectrum calculation unit 142b, A removal gain calculation unit 143, a gain multiplication unit 144, and a frequency time conversion unit 145 are included.

  The first time frequency conversion unit 141a receives an I component that is a real part signal of the complex baseband signal after correction by the frequency phase correction unit 13, and converts the real part signal from the time signal to components of a plurality of frequencies. It converts into the frequency signal which it has, and outputs. In FIG. 4, this frequency signal is represented as a complex signal composed of a real part signal Re and an imaginary part signal Im. The second time frequency conversion unit 141b receives, as an input, a Q component that is an imaginary part signal of the complex baseband signal after correction by the frequency phase correction unit 13, and converts the imaginary part signal from the time signal to components of a plurality of frequencies. Is converted into a frequency signal having The first time frequency conversion unit 141a and the second time frequency conversion unit 141b use, for example, an FFT (Fast Fourier Transform) algorithm of 512, 1024, or 2048 sample points to generate a frequency signal of the time signal (for the sample points). To a signal having a frequency component).

  The first power spectrum calculation unit 142a converts the output of the first time frequency conversion unit 141a into a power spectrum having components of the frequencies of the above-described sample points, and outputs the power spectrum. This power spectrum has a value corresponding to the square of the amplitude in the output signal of the first time-frequency converter 141a. The second power spectrum calculation unit 142b converts the output of the second time frequency conversion unit 141b into a power spectrum having components of the frequencies of the above-described sample points, and outputs the power spectrum. This power spectrum has a value corresponding to the square of the amplitude in the output signal of the second time frequency converter 141b. Since the output of the second power spectrum calculation unit 142b is a signal based on the Q component that is the imaginary part signal of the complex baseband signal corrected by the frequency phase correction unit 13, a noise spectrum that does not include an audio signal is obtained. Show.

  The noise removal gain calculation unit 143 estimates the noise component included in the output of the first power spectrum calculation unit 142a by referring to the output of the second power spectrum calculation unit 142b indicating the noise spectrum, and calculates the estimated noise component. A gain G is calculated for each frequency of the above-described sample points for removal.

  The gain multiplication unit 144 outputs a complex signal as a multiplication result by multiplying the output of the first time frequency conversion unit 141a by the gain G calculated by the noise removal gain calculation unit 143. In FIG. 4, a complex signal including a real part signal Re ′ and an imaginary part signal Im ′ is shown as a multiplication result.

  The frequency time conversion unit 145 converts the complex signal output from the gain multiplication unit 144 from a frequency signal to a time signal by inverse conversion corresponding to the conversion in the first time frequency conversion unit 141a, and outputs the converted signal. This output is a signal obtained by removing the noise component due to the effect of the gain multiplier 144 from the I component, which is the real part signal of the corrected complex baseband signal, which is input to the first time-frequency converter 141a. Become.

  As described above, since the Q component of the corrected complex baseband signal that is input does not include the audio signal component but includes the noise component, the noise removing unit 14 uses the spectral subtraction based on the reference of the Q component to perform the correction. The stationary noise component of the I component of the complex baseband signal is removed. Thereby, it becomes possible to suppress noise, for example, about 3 dB to 6 dB. The configuration of the noise removing unit 14 shown here estimates the noise component by referring to the Q component of the corrected complex baseband signal, and uses the estimation result to correct the I of the complex baseband signal after correction. This is merely an example of a configuration for removing noise from components, and a Wiener filter or the like may be used, or another modified configuration may be used.

  Hereinafter, various modifications of the noise removing unit 14 will be described.

[4. Modification 1 of the noise removal unit 14]
FIG. 5 shows a configuration of a noise removal unit 14 a obtained by modifying a part of the noise removal unit 14.

  In the noise removing unit 14a, a configuration for removing beat noise is added in addition to the configuration of the noise removing unit 14. As shown in FIG. 5, the noise removal unit 14a includes a first time frequency conversion unit 141a, a second time frequency conversion unit 141b, a first power spectrum calculation unit 142a, a second power spectrum calculation unit 142b, A removal gain calculation unit 143a, a gain multiplication unit 144, a frequency time conversion unit 145, and a peak detection unit 146 are included. Among the components of the noise removal unit 14a, the same components as those of the noise removal unit 14 (see FIG. 4) described above are denoted by the same reference numerals in FIG. 5 as those in FIG. .

  The peak detection unit 146 receives as input a power spectrum having components of each of a plurality of frequencies (that is, the above-described number of sample points) output from the second power spectrum calculation unit 142b, and one or a plurality of frequencies that become the peak of the power spectrum The peak frequency which is is detected. Note that beat noise appears as a peak. The peak detection unit 146 detects a peak frequency by specifying, as a peak, a peak having a kurtosis obtained by a calculation for obtaining a kurtosis for each frequency using a power spectrum as a peak.

  The noise removal gain calculation unit 143a is obtained by modifying a part of the noise removal gain calculation unit 143 described above. The noise removal gain calculation unit 143a refers to the output of the second power spectrum calculation unit 142b, estimates the noise component included in the output of the first power spectrum calculation unit 142a, removes the estimated noise component, and The gain G is calculated for each frequency of the above-described sample points for removing the peak frequency component detected by the peak detection unit 146.

  The gain multiplication unit 144 outputs a complex signal as a multiplication result by multiplying the output of the first time frequency conversion unit 141a by the gain G calculated by the noise removal gain calculation unit 143a.

  With such a configuration, the noise removing unit 14a removes the stationary noise component and the beat noise component of the I component of the corrected complex baseband signal by referring to the Q component of the input complex baseband signal after correction.

[5. Modification 2 of the noise removal unit 14]
FIG. 6 shows a configuration of a noise removing unit 14b in which a part of the noise removing unit 14 is modified.

  In addition to the configuration of the noise removing unit 14, the noise removing unit 14b has a configuration for removing beat noise using a notch filter. As shown in FIG. 6, the noise removal unit 14b includes a first time frequency conversion unit 141a, a second time frequency conversion unit 141b, a first power spectrum calculation unit 142a, a second power spectrum calculation unit 142b, A removal gain calculation unit 143, a gain multiplication unit 144, a frequency time conversion unit 145, a peak detection unit 146, a notch filter coefficient calculation unit 147, and a notch filter unit 148 are included. Among the components of the noise removing unit 14b, the same components as those of the noise removing unit 14 (see FIG. 4) or the noise removing unit 14a (see FIG. 5) described above are denoted by the same reference numerals in FIG. The description is appropriately omitted here.

  The notch filter coefficient calculation unit 147 calculates a filter coefficient used for removing the peak frequency component detected by the peak detection unit 146 by the notch filter.

  The notch filter unit 148 applies a notch filter using the filter coefficient calculated by the notch filter coefficient calculation unit 147 to the output of the frequency time conversion unit 145. Beat noise is removed by this notch filter. In the notch filter, beat noise can be greatly suppressed to, for example, 10 dB or more.

  With such a configuration, the noise removing unit 14b removes the stationary noise component and the beat noise component of the I component of the corrected complex baseband signal by referring to the Q component of the input complex baseband signal after correction.

[6. Modification Example 3 of Noise Removing Unit 14]
FIG. 7 shows a configuration of a noise removing unit 14 c obtained by modifying the noise removing unit 14.

  The noise removing unit 14c has a configuration for removing beat noise using a notch filter. As shown in FIG. 7, the noise removal unit 14 c includes a time-frequency conversion unit 141, a power spectrum calculation unit 142, a peak detection unit 146, a notch filter coefficient calculation unit 147, and a notch filter unit 148. The time frequency conversion unit 141 is the same as the second time frequency conversion unit 141b in the noise removal unit 14 (see FIG. 4), and the power spectrum calculation unit 142 is the same as the second power spectrum calculation unit 142b in the noise removal unit 14. It is. Among the components of the noise removing unit 14c, the same components as those of the noise removing unit 14b (see FIG. 6) described above are denoted by the same reference numerals as those in FIG. .

  The peak detection unit 146 receives a power spectrum having each component of a plurality of frequencies (that is, the above-described number of sample points) output from the power spectrum calculation unit 142, and is one or a plurality of frequencies that are peaks of the power spectrum. Detect peak frequency.

  The notch filter unit 148 applies a notch filter using the filter coefficient calculated by the notch filter coefficient calculation unit 147 to the I component that is the real part signal of the complex baseband signal after correction by the frequency phase correction unit 13. .

  With such a configuration, the noise removing unit 14c removes the beat noise component of the I component of the corrected complex baseband signal by referring to the Q component of the input complex baseband signal after correction. In the receiving apparatus 10 (see FIG. 1), for example, a noise removing unit 14c may be provided at the subsequent stage of the noise removing unit 14. In this case, the noise removing unit 14c uses a notch filter that uses the filter coefficient calculated by the notch filter coefficient calculating unit 147 based on the Q component of the corrected complex baseband signal output from the frequency phase correcting unit 13, This is applied to the signal after the noise removal of the I component of the corrected complex baseband signal output by the noise removal unit 14.

[7. Modified example 4 of the noise removing unit 14]
FIG. 8 shows a configuration of a noise removing unit 14d obtained by modifying the noise removing unit 14.

  The noise removing unit 14d includes a pulse noise detecting unit 1401 and a pulse noise removing unit 1402, as shown in FIG.

  The pulse noise detection unit 1401 receives a Q component that is an imaginary part signal of the complex baseband signal corrected by the frequency phase correction unit 13 and detects a period in which the pulse noise in the Q component is included. For example, the pulse noise detection unit 1401 detects a period in which the amplitude of the Q component signal exceeds a predetermined threshold as a period in which the pulse noise is included. Note that since the audio signal is not included in the Q component that is input to the pulse noise detection unit 1401, the pulse noise detection unit 1401 accurately detects the period in which the pulse noise is included.

  The pulse noise removal unit 1402 performs a pulse from an I component that is a real part signal of the complex baseband signal corrected by the frequency phase correction unit 13 based on the period including the pulse noise detected by the pulse noise detection unit 1401. Remove noise. The pulse noise removing unit 1402 outputs a signal from which the pulse noise has been removed. For example, the pulse noise removing unit 1402 removes the pulse noise by interpolating the signal waveform of the I component so as to connect the signal values before and after the period including the pulse noise.

  With such a configuration, the noise removing unit 14a removes the pulse noise component of the I component of the corrected complex baseband signal by referring to the Q component of the input complex baseband signal after correction.

(Other embodiments)
As described above, the first embodiment has been described as an example of the technique according to the present invention. However, the technology according to the present invention is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present invention.

  (1) In the above embodiment, an AM radio broadcast signal is shown as an example of a signal received by the receiving device 10, but the receiving device 10 may receive a transmission signal transmitted in a form other than broadcasting. Good. Further, the frequency of the carrier wave of the signal received by the receiving apparatus 10 is not limited to 1 MHz, and may be higher or lower than 1 MHz.

  (2) The receiving device 10 shown in the above embodiment is realized by an integrated circuit including a memory, a processor, and the like. However, the program stored in the memory is executed by the processor and is received by software. The functions of the components of the apparatus 10 (for example, the frequency conversion unit 12, the frequency phase correction unit 13, the noise removal unit 14, and the demodulation unit 15) may be realized, or by dedicated hardware (digital circuit or the like). The function may be realized without using a program. Further, a combination of a plurality of components may be configured as a single circuit. Moreover, you may change the function allocation of each component of the receiver 10. FIG.

  (3) A part or all of the constituent elements constituting the receiving apparatus 10 in the above embodiment may be configured by one system LSI (Large Scale Integration). The system LSI is an ultra-multifunctional LSI manufactured by integrating a plurality of components on a single chip. Specifically, the system LSI is a computer system including a microprocessor, a ROM, a RAM, and the like. . A computer program is recorded in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program. In addition, each part of the constituent elements constituting each of the above devices may be individually made into one chip, or may be made into one chip so as to include a part or all of them. Although the system LSI is used here, it may be called IC, LSI, super LSI, or ultra LSI depending on the degree of integration. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used. Furthermore, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied as a possibility.

  (4) As one aspect of the present invention, a reception method including steps as a processing procedure for realizing the function of the reception device 10 described above may be used. In addition, as one aspect of the present invention, a control program (computer program) for causing a processor in an apparatus having a processor to execute a reception process according to the reception method may be used. FIG. 9 is a flowchart illustrating an example of a reception process executed by the reception device 10 using a control program. A receiving apparatus 10 that includes an antenna 11 and that executes a control program related to reception processing for receiving a signal transmitted by amplitude modulation by a processor, converts the amplitude modulated signal received by the antenna to generate a complex baseband signal The conversion step S1, the frequency phase correction step S2 for correcting the frequency offset and the phase offset in the complex baseband signal generated in the frequency conversion step S1, and the real part signal of the complex baseband signal after the correction in the frequency phase correction step S2 A noise removal step S3 for removing the noise component contained in the signal by referring to the imaginary part signal of the complex baseband signal, and amplitude demodulation of the real part signal from which the noise component has been removed in the noise removal step S3 Demodulation step S4 and the sound obtained by amplitude demodulation in demodulation step S4 It executes an output step S5 to perform an output corresponding to distribution or the like. The order of execution of the processing procedures shown in FIG. 9 is not necessarily limited to the order described above, and the order of execution is changed or parallel processing is performed or a part thereof is omitted without departing from the gist of the invention. Can be. Further, as one aspect of the present invention, a digital signal including the above-described computer program may be used. In one embodiment of the present invention, the computer program or the digital signal can be read by a computer, such as a flexible disk, a hard disk, a CD-ROM, an MO, a DVD, a DVD-ROM, a DVD-RAM, and a BD. (Blu-ray (registered trademark) Disc), recorded on a semiconductor memory, or the like. The digital signal may be recorded on these recording media. Further, as one aspect of the present invention, the computer program or the digital signal may be transmitted via an electric communication line, a wireless or wired communication line, a network typified by the Internet, data broadcasting, or the like. Further, an aspect of the present invention may be a computer system including a microprocessor and a memory, the memory recording the computer program, and the microprocessor operating according to the computer program. . Also, by recording and transferring the program or the digital signal on the recording medium, or by transferring the program or the digital signal via the network or the like, by another independent computer system It may be carried out.

  (5) Embodiments realized by arbitrarily combining the constituent elements and functions shown in the embodiment and the modified examples are also included in the scope of the present invention.

  The present invention is applicable to, for example, an in-vehicle AM radio receiver.

DESCRIPTION OF SYMBOLS 10 Reception apparatus 11 Antenna 12 Frequency conversion part 13 Frequency phase correction part 14, 14a-14d Noise removal part 15 Demodulation part 16 Output part 131 Low-pass filter part 132 Sine wave generation part 133 Phase correction part 134 Multiplication part 141 Time frequency conversion Unit 141a first time frequency conversion unit 141b second time frequency conversion unit 142 power spectrum calculation unit 142a first power spectrum calculation unit 142b second power spectrum calculation unit 143, 143a noise removal gain calculation unit 144 gain multiplication unit 145 frequency time conversion Unit 146 peak detection unit 147 notch filter coefficient calculation unit 148 notch filter unit 1401 pulse noise detection unit 1402 pulse noise removal unit

Claims (10)

A receiving device for receiving a signal transmitted by amplitude modulation,
A frequency converter that generates a complex baseband signal by converting an amplitude modulation signal received by an antenna;
A frequency phase correction unit that corrects a frequency offset and a phase offset in the complex baseband signal generated by the frequency conversion unit;
A noise removing unit that removes a noise component included in the real part signal of the complex baseband signal after the correction by the frequency phase correcting unit by referring to the imaginary part signal of the complex baseband signal;
A receiving device comprising: a demodulator that amplitude-demodulates the real part signal from which a noise component has been removed by the noise removing unit. The frequency phase correction unit is
A low-pass filter unit that inputs the complex baseband signal generated by the frequency converter and outputs a low-frequency component of the complex baseband signal;
Detecting the frequency offset from the output of the low-pass filter unit, and generating a sine wave having the detected frequency offset as a frequency; and
About the sine wave generated by the sine wave generation unit, a phase correction unit that performs correction to remove the influence of phase rotation generated between the input and output of the low-pass filter unit;
Multiplication for removing the frequency offset and the phase offset in the complex baseband signal by multiplying the complex baseband signal generated by the frequency converter by the complex conjugate of the sine wave corrected by the phase correction unit. The receiving device according to claim 1. The noise removing unit
A first time-frequency conversion unit that converts the real part signal of the complex baseband signal after correction by the frequency phase correction unit from a time signal to a frequency signal having components of a plurality of frequencies, and outputs the frequency signal;
A second time-frequency conversion unit that converts the imaginary part signal of the complex baseband signal after correction by the frequency phase correction unit from a time signal to a frequency signal having a component of each of the plurality of frequencies, and outputs the frequency signal;
A first power spectrum calculation unit that converts the output of the first time frequency conversion unit into a power spectrum having components of each of the plurality of frequencies and outputs the power spectrum;
A second power spectrum calculation unit for converting the output of the second time frequency conversion unit into a power spectrum having components of each of the plurality of frequencies and outputting the power spectrum;
By referring to the output of the second power spectrum calculation unit, the noise component included in the output of the first power spectrum calculation unit is estimated, and the estimated noise component is removed for each of the plurality of frequencies. A denoising gain calculator for calculating gain;
A gain multiplier that outputs a complex signal by multiplying the output of the first time frequency converter by the gain calculated by the noise removal gain calculator;
The receiving apparatus according to claim 1, further comprising: a frequency time conversion unit that converts the complex signal output from the gain multiplication unit from a frequency signal to a time signal. The noise removal unit further includes a peak detection unit that detects a peak frequency that is one or a plurality of frequencies that become a peak of a power spectrum output from the second power spectrum calculation unit among the plurality of frequencies,
The noise removal gain calculation unit calculates a gain for each of the plurality of frequencies for removing the estimated noise component and removing the peak frequency component detected by the peak detection unit. Item 4. The receiving device according to Item 3. The noise removing unit further includes
Among the plurality of frequencies, a peak detection unit that detects a peak frequency that is one or a plurality of frequencies that become a peak of a power spectrum output from the second power spectrum calculation unit;
A notch filter coefficient calculation unit for calculating a filter coefficient used for removing the peak frequency component detected by the peak detection unit by a notch filter;
The receiving apparatus according to claim 3, further comprising: a notch filter unit that applies the notch filter using the filter coefficient calculated by the notch filter coefficient calculation unit to the output of the frequency time conversion unit. The noise removing unit
A time frequency conversion unit that converts the imaginary part signal of the complex baseband signal after correction by the frequency phase correction unit from a time signal to a frequency signal having a component of each of the plurality of frequencies, and outputs the frequency signal;
A power spectrum calculator that converts the output of the time-frequency converter into a power spectrum having components of each of the plurality of frequencies,
Among the plurality of frequencies, a peak detection unit that detects a peak frequency that is one or a plurality of frequencies that become a peak of a power spectrum output by the power spectrum calculation unit;
A notch filter coefficient calculation unit for calculating a filter coefficient used for removing the peak frequency component detected by the peak detection unit by a notch filter;
A notch filter unit that applies the notch filter using the filter coefficient calculated by the notch filter coefficient calculation unit to the real part signal of the complex baseband signal corrected by the frequency phase correction unit. The receiving device according to claim 1 or 2. The noise removing unit
A pulse noise detection unit for detecting a period in which pulse noise is included in the imaginary part signal of the complex baseband signal after correction by the frequency phase correction unit;
2. A pulse noise removal unit that removes pulse noise from the real part signal of the complex baseband signal after correction by the frequency phase correction unit based on the period detected by the pulse noise detection unit. Or the receiving apparatus of 2. The receiving device according to any one of claims 1 to 7, wherein the signal received by the receiving device is a radio broadcast signal. A reception method in a receiving apparatus that includes an antenna and receives a signal transmitted by amplitude modulation,
A frequency conversion step of generating a complex baseband signal by converting an amplitude modulation signal received by the antenna;
A frequency phase correction step for correcting a frequency offset and a phase offset in the complex baseband signal generated in the frequency conversion step;
A noise removal step of removing a noise component included in the real part signal of the complex baseband signal after the correction in the frequency phase correction step by a process referring to the imaginary part signal of the complex baseband signal;
And a demodulation step for amplitude-demodulating the real part signal from which noise components have been removed in the noise removal step. A control program for causing a receiving device including an antenna and a microprocessor to execute a reception process for receiving a signal transmitted by amplitude modulation,
The reception process includes
A frequency conversion step of generating a complex baseband signal by converting an amplitude modulation signal received by the antenna;
A frequency phase correction step for correcting a frequency offset and a phase offset in the complex baseband signal generated in the frequency conversion step;
A noise removal step of removing a noise component included in the real part signal of the complex baseband signal after the correction in the frequency phase correction step by a process referring to the imaginary part signal of the complex baseband signal;
A control program comprising: a demodulation step for amplitude-demodulating the real part signal from which a noise component has been removed in the noise removal step.

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