JP2003283349A - Signal processing apparatus, signal receiving apparatus, and signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of difficulty of removing a multi-pass noise in FM receiving. <P>SOLUTION: A multi-pass noise reducing processing unit 14 implements a treatment for reducing a multi-pass noise from a composite signal 13 of an FM detecting unit 12 to generate an output signal 21. In this process, the multi- pass noise is detected on the basis of a difference in amplitude between a current composite signal 13 and a past output signal 21 to attenuate the composite signal 13. A multi-pass detecting unit 18 detects a multi-pass section based on an S meter 17 and feeds a switching unit 20 with a switching signal 19 for permitting the operation of a multi-pass noise reduction processing unit 14. In the switching unit 20, switching control is so carried out that an output signal 21 from the multi-pass noise reduction processing unit 14 is entered into a stereo modulation unit 22 in the multi-pass section and a composite signal 13 generated from the FM detecting unit 12 is entered into the stereo modulation unit 22 in the other section. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing technique, and more particularly to a signal processing device, a signal receiving device and a signal processing method for detecting and reducing noise.

[0002]

2. Description of the Related Art In an FM receiver mounted on a moving body such as an automobile, when receiving an audio signal, multipath noise is caused by reflection of electromagnetic waves from surrounding obstacles such as mountains and high-rise buildings. Occurs. In this multipath noise, the indirect wave reflected by the reflector is combined with the direct wave received directly from the receiving antenna, and part of the direct wave depends on the phase relationship between the direct wave and the indirect wave. Caused by being canceled by. When multipath noise occurs, the quality of the audio signal output from the FM receiver is significantly reduced.

As a method of removing the multipath noise of the demodulated signal after the FM detection, the multipath interval is detected by detecting the generation interval of the multipath noise and holding the signal strength before the generation of the multipath noise. A pre-interpolation method for doing this is disclosed in Japanese Patent Laid-Open No. 2001-36422. There is also a method of muting the FM demodulated signal after FM detection when the electric field strength is drastically reduced.

In addition, a stereo noise control (S
NC) and the high-cut control (HCC) that removes high-frequency components, S of the FM demodulated signal in a weak electric field
A method for improving the / N ratio is also well known in the art. In the case of multipath noise, multipath distortion, that is, noise appears in the detection output due to the interference of direct waves and indirect waves. This noise is a high-frequency component of the L-R sub-signal band,
Since it appears remarkably in the L + R main signal band, SNC and H
The processing by CC has the effect of reducing multipath noise.

[0005]

However, depending on the degree of multipath noise, annoying noise may remain even if SNC and HCC are fully utilized. On the other hand, the method of pre-interpolating the FM demodulated signal in the multipath section or the method of muting is effective for the pulse-like waveform generated by the multipath, but a certain section generated when PLL detection is used. There is a problem in that the filtering process also works on waveforms that are out of phase, and the original signal itself is erroneously removed. Furthermore, if the setting of the parameter for detecting the multipath section is inappropriate, noise may remain due to the deviation of the multipath detection section.

The present invention has been made in view of such a situation, and an object thereof is to provide a signal processing technique capable of detecting and reducing noise. Another purpose is FM
It is to provide a signal reception technique for reducing multipath noise in reception.

[0007]

One aspect of the present invention relates to a signal processing device. This apparatus includes a noise reduction processing unit that attenuates an input signal to generate an output signal. The noise reduction processing unit is a difference determination unit that detects noise by determining whether or not the difference between the intensity of the input signal at the current sampling time and the intensity of the output signal at the past sampling time exceeds a predetermined threshold value. And an attenuation processing unit that, when the noise is detected, attenuates the input signal at the time of current sampling to generate the output signal at the time of current sampling.

The output signal is a signal after the input signal is subjected to an attenuation process for reducing noise. However, when no noise is detected, the output signal is the same as the input signal because the input signal is not attenuated. The strength of the input and output signals may be a measure of the amplitude of those signals, or the absolute value or square of the amplitude. The threshold value used to evaluate the magnitude of the difference between the strength of the current input signal and the strength of the past output signal is set to a value that is sufficiently larger than the normal range of significant signal strength. May be.

The difference determining section calculates a difference between the intensity of the input signal at the current sampling and each of the intensities of the output signals at a plurality of past samplings, and determines whether each difference exceeds a predetermined threshold value. Noise may be detected by determining whether or not. For example, at the current sampling time n
Of the input signal intensity x (n) and the intensity y (n−1) of the output signal one sampling before exceed the first threshold A, and The intensity x (n) and the intensity y (n-
Determination of whether the difference from 2) exceeds the second threshold value B,
Evaluation is performed in combination with the determination as to whether or not the difference between the intensity x (n) of the input signal at the time of the current sampling n and the intensity y (n−3) of the output signal before three samplings exceeds the third threshold value C. The presence or absence of noise may be detected. The first threshold value A, the second threshold value B, and the third threshold value C may be set to values that increase in this order.

The noise reduction processing unit further includes a smoothing processing unit that smoothes the input signal for a predetermined sampling period, and the difference determination unit and the attenuation processing unit apply the smoothed input signal to the input signal. Processing may be performed. The smoothing processing unit may smooth the input signal by calculating a moving average of the input signal for a certain period. The smoothing processing unit may smooth the input signal by removing a high frequency component of the input signal using a low pass filter or the like.

The signal processing section may further include an attenuation rate setting section for adaptively setting the attenuation rate of the intensity of the input signal in the noise reduction processing section based on the intensity of the input signal. The attenuation rate of the strength of the input signal at the current sampling may be set based on the strength of the input signal at the past sampling.

Another aspect of the present invention relates to a signal receiving device. This device is based on the received FM transmission radio waves
An FM detection unit that outputs a demodulated signal, a signal processing unit that reduces and outputs noise of the FM demodulated signal, and a period in which multipath noise may occur in the received FM transmission radio wave is detected. A multipath detecting unit that operates the signal processing unit and an output thereof while the signal processing unit is operating, and outputs the FM demodulated signal by stereo demodulating while the signal processing unit is not operating. And a stereo demodulation unit. The signal processing unit includes a noise reduction processing unit that attenuates the FM demodulated signal as an input signal to generate an output signal, and the noise reduction processing unit includes the intensity of the input signal at the current sampling and the past sampling. Difference determination unit that determines whether or not the difference in the intensity of the output signal at a time exceeds a predetermined threshold value, and detects the noise, and attenuates the input signal at the current sampling when the noise is detected. And an attenuation processing unit that generates the output signal at the time of current sampling. The threshold value used for the difference determination may be set to a value corresponding to the intensity of very large and jarring noise recognized as so-called multipath noise.

Yet another aspect of the present invention relates to a signal processing method. This method detects a period during which the intensity of the input signal greatly changes, and only during that period, the input signal is filtered to reduce noise to generate an output signal. The filtering process sequentially calculates a difference between the intensity of the input signal at the current sampling and the intensity of the output signal at the past sampling for each sampling, and when the difference exceeds a predetermined threshold, the current sampling is performed. Attenuating the input signal at time to produce the output signal at the current sampling time.

The method may further include a pre-processing step of detecting a period in which the noise may occur, and the filtering process may be applied to the input signal in the period detected in the pre-processing step. As a result, even if there is some deviation in the noise generation period detected in the pre-processing step, the original signal is erroneously removed because the subsequent filtering processing performs the attenuation processing based on the threshold determination. It is possible to reduce noise.

It is to be noted that any combination of the above constituent elements and the expression of the present invention converted between methods, devices, systems, etc. are also effective as an aspect of the present invention.

[0016]

1 shows the configuration of an FM receiver according to an embodiment. The received FM transmission radio wave is converted into an intermediate frequency (IF) signal 10 in a front end section (not shown). The FM detector 12 receives the IF signal 10
FM demodulates the stereo composite signal 13 (hereinafter,
It is called a composite signal).

The signal processing section 24 performs processing for removing multipath noise on the composite signal 13 received from the FM detection section 12 as necessary, and supplies it to the stereo demodulation section 22. The signal processing unit 24 includes a multipath noise reduction processing unit 14, an attenuation rate setting unit 16, and a switching unit 20.

The multipath noise reduction processing unit 14 appropriately performs a later-described attenuation process for reducing multipath noise on the composite signal 13 to generate an output signal 21. The attenuation rate setting unit 16 obtains the attenuation rate 15 used in the attenuation processing in the multipath noise reduction processing unit 14 based on the amplitude of the composite signal 13, and sets the attenuation rate 15 in the multipath noise reduction processing unit 14. .

The multipath detector 18 detects a section where multipath noise may occur (hereinafter referred to as a multipath section) based on the AC component of the signal meter 17 (hereinafter referred to as an S meter), and multipath is detected in the section. A switching signal 19 for permitting the operation of the path noise reduction processing unit 14 is supplied to the switching unit 20. The signal used for multipath detection is not limited to the S meter 17, and may be another signal as long as multipath can be detected.

Based on the switching signal 19 provided from the multipath detecting unit 18, the switching unit 20 outputs the output signal 21 output as a signal after the attenuation processing from the multipath noise reduction processing unit 14 in the multipath section. In other sections, switching control of the input signal 23 of the stereo demodulation unit 22 is performed so that the composite signal 13 output from the FM detection unit 12 is input to the stereo demodulation unit 22. The stereo demodulation unit 22 stereo demodulates the input signal 23 and outputs an audio signal.

FIG. 2 shows the multipath noise reduction processing unit 14.
3 is a functional configuration diagram of FIG. The smoothing processing unit 30 samples the composite signal 13 and calculates a moving average of the amplitude of the composite signal 13 for a certain sampling period to smooth and output the composite signal 13. A method other than the moving average may be used as the smoothing process.

The difference calculator 31 calculates the difference between the amplitude of the smoothed composite signal 13 at the current sampling time and the amplitude of the output signal 21 at the past sampling time for each sampling. The difference determination unit 32 detects the presence or absence of multipath noise by comparing the difference calculated by the difference calculation unit 31 with a predetermined threshold value, and when the multipath noise is generated, the attenuation processing unit 34. The switching signal 37 for permitting the operation of is supplied to the switching unit 36. The attenuation processing unit 34 attenuates and outputs the smoothed composite signal 13 at the current sampling based on the attenuation rate 15 set by the attenuation rate setting unit 16.

Based on the switching signal 37 provided from the difference determining unit 32, the switching unit 36 outputs the composite signal 13 when the multipath noise is not generated and when the multipath noise is generated, the multipath signal is generated. , Attenuation processing unit 34
The switching control of the output signal 21 is performed so as to output the signal 35 that is attenuated by. In this way, the result of the appropriate attenuation processing according to the detection result of the multipath noise is output to the switching unit 20 via the switching unit 36. This output signal 21 is further sent to the stereo demodulation unit 2 via the switching unit 20.
2 is supplied. The value of the amplitude of this output signal 21 is
The difference calculation unit 31 is temporarily stored in a memory (not shown).
When calculating the difference in, the value is used as the amplitude value of the output signal 21 at the time of past sampling.

3A and 3B show the attenuation rate setting unit 16
3 is a functional configuration diagram of FIG. In the functional configuration of FIG. 3A, the input composite signal 13 is converted into an absolute value by the absolute value calculation unit 40, the low-pass component passes through the loop filter 42, and the rough amplitude is estimated. Further, after being normalized by the normalizing unit 44 so that it falls within a certain value range, the difference between the constant and the constant is calculated by the adding unit 46, and finally the attenuation rate is determined based on the upper limit set by the limiter 48. 15 is output.

FIG. 3B shows another functional configuration of the attenuation rate setting unit 16. The processing of the absolute value calculation unit 40 and the loop filter 42 for the input composite signal 13 is the same as that of FIG. 3A, and the output value thereof is limited to the value range by the limiter 48, and then the table reference unit 50. Is entered. The table reference unit 50 refers to a table in which the amplitude value and the attenuation rate are associated with each other, so that the attenuation rate 1
5 is directly determined and output. In this configuration, the loop filter 42 may be another low pass filter.

A multipath noise reduction procedure performed by the FM receiving apparatus having the above configuration will be described with reference to the flowcharts of FIGS. 4 and 5 and the graphs of FIGS. 6 to 9.

FIG. 4 is a flow chart for explaining the overall flow of multipath detection and multipath noise reduction processing. The multipath detector 18 detects a section in which multipath noise occurs based on the S meter 17 (S100).
FIG. 6 is an explanatory diagram of a section where multipath noise is generated.
The graph shows the time course of the amplitude of the composite signal 13. Multipath noise occurs in the sections 60, 61, and 62. When viewed macroscopically, the multipath noise has a relatively long time width represented by such an envelope, and a section having this time width is detected as a multipath section.

Returning to FIG. 4, when the multipath section is detected (Y in S100), the multipath detecting section 18 gives the switching signal 19 to the switching section 20 to operate the multipath noise reduction processing section 14. to approve. The multipath noise reduction processing unit 14 performs processing for reducing multipath noise on the composite signal 13 in the multipath section (S110). When the multi-pass section ends,
Returning to step S100 again, step S is performed until the next multipath section is detected by the multipath detector 18.
The multipath noise reduction process of 110 is interrupted. By repeating the multipath detection and the multipath noise reduction processing as described above, the multipath noise reduction processing is applied to the composite signal 13 only in the multipath section.

FIG. 5 is a flow chart for explaining the detailed procedure of the multipath noise reduction processing in step S110 of FIG. The difference determination unit 32 of the multipath noise reduction processing unit 14 samples the composite signal 13 to obtain the input signal X (n) at the sampling time n (S10). Input signal X (n) at sampling time n
Assuming that the output signal Y (n) is a signal that has been subjected to an attenuation process as necessary, the difference determination unit 32 determines that the input signal X (n) is equal to 1 sampling before, 2 sampling before, 3 sampling.
Output signals Y (n-1), Y (n-) before sampling
2) and the difference with Y (n-3) is calculated (S1).
2). Further, the difference determination unit 32 detects multipath noise by determining whether the absolute value of these differences is larger than a predetermined threshold value (S14).

This determination is made by evaluating whether the following inequality holds. | X (n) -Y (n-1) |> threshold value A ... (1) | X (n) -Y (n-2) |> threshold value B (2) | X (n)- Y (n-3) |> threshold value C (3)

The mechanism by which multipath noise is detected by this determination will be described with reference to FIGS. 7 and 8. Figure 7
It is the figure which expanded a part of multi-pass area of FIG. Microscopically, the multipath section is a section 80 in which noise is generated due to the occurrence of a certain section with a phase shift,
81, 82 and significant signal sections 70, 71, 72, 73 in which noise is not generated. In order to remove the multipath noise, it is necessary to detect a steep peak of the signal waveform in the multipath section.

FIG. 8 is a diagram for explaining the difference determination for detecting a steep peak. The difference determination unit 32 determines whether or not the amplitude of the input signal X (n) at the sampling time n changes to an abnormally large value as compared with the amplitude of the significant signal by comparing with the output signal at the past sampling. It is judged by evaluating. The output signal at the time of past sampling is a signal that has already been attenuated as necessary, and if compared with it, if it exceeds the significant signal amplitude range sufficiently, the current sampling time n It can be determined that the input signal X (n) has a steep peak.

At the time of past sampling, in the above inequalities (1) to (3), the output signals Y (n-1), Y (n-2), and Y (n-3) up to three samplings before are used. However, using the output signal at the previous sampling time,
The same difference determination may be performed, or conversely, the difference determination may be performed using only the output signal Y (n-1) one sampling before.

Returning to FIG. 5, the difference determining section 32 uses the above 3
If any one of the two inequalities (1) to (3) is satisfied, it is determined to be multipath noise (S1).
4), the attenuation processing unit 34 performs the attenuation processing represented by the following equation on the input signal X (n) at the sampling time n and outputs the output signal Y (n) (S16).

Y (n) = α × X (n) However, α is the attenuation rate 15 set by the attenuation rate setting unit 16, and takes a value of 0 or more and less than 1.

The difference determination unit 32 has three inequalities (1) to
If none of (3) is satisfied, it is determined that the noise is not multipath noise (N in S14), and the attenuation processing unit 34 does not perform attenuation processing on the input signal X (n) as in the following equation. The output signal Y (n) is output as it is (S1).
8). That is, in this case, Y (n) = X (n).

In determining whether it is multipath noise, the first, second, and third inequalities (1) to (3) are determined.
The third thresholds A, B and C are set to empirically optimum values. In the above, the attenuation process is performed if any one of the three inequalities (1) to (3) is satisfied, but whether the attenuation process is performed by any combination of the established states of the three inequalities (1) to (3). You may decide. In the experiment, the first, second, and third thresholds A, B, and C of the three inequalities (1) to (3) are set to values that satisfy A ≦ B ≦ C, and the inequalities (1) to (3) are set. The preferable result was obtained when the attenuation treatment was performed when any one of the above conditions was satisfied.

Returning to FIG. 5, after the attenuation processing of the input signal X (n) at the sampling time n is performed as necessary, the sampling time n is incremented by 1 (S2
0), the stop condition of the multipath noise reduction processing is confirmed (S22). To check the stop condition, check the multipath detector 1
It is carried out by judging whether or not it is still within the multipath section based on the switching signal 19 from 8. If stopped (Y of S22), the multipath noise reduction processing is ended, and if not stopped (N of S22), the procedure returns to step S10, and a series of multipath noise reduction processing is repeated.

FIG. 9 shows the waveform of the output signal after the multipath reduction process is applied to the composite signal of FIG. It can be seen that the steep peak in FIG. 7 has been removed.

As described above, according to the embodiment,
Noise countermeasures such as monaural conversion and high frequency component removal can reduce residual multipath noise. Especially when a multipath section is detected, the presence / absence of multipath noise is further determined in that section, and the attenuation processing for reducing the multipath noise is performed.
Even if the detection sensitivity of multipath is raised too much, it is possible to properly remove multipath noise without being affected by it, and it is possible to prevent residual noise and prevent accidental removal of the original signal. .

The present invention has been described above based on the embodiments. It is understood by those skilled in the art that these embodiments are mere examples, and that various modifications can be made to the combinations of the respective constituent elements and the respective processing processes, and that such modifications are also within the scope of the present invention. By the way. Each component is illustrated as a functional block, and those skilled in the art will understand that these functional blocks can be realized in various forms by only hardware, only software, or a combination thereof.

As a modification, in the embodiment, the smoothing processing unit 30 is provided in the multipath noise reduction processing unit 14 as shown in FIG.
The composite signal 13 output from the FM detector 12 is first smoothed by being provided immediately after the M detector 12.
The composite signal 13 may be smoothed even outside the multipath section and input to the stereo demodulation unit 22 via the switching unit 20.

In the embodiment, the case where the received signal is a stereo signal has been described, but the multipath noise reduction processing of the present invention can be applied to a monaural signal.

According to the present invention, noise can be detected and appropriately reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an FM receiving apparatus according to an embodiment.

FIG. 2 is a functional configuration diagram of a multipath noise reduction processing unit in FIG.

3 (a) and 3 (b) are functional configuration diagrams of an attenuation rate setting unit in FIG.

FIG. 4 is a flowchart illustrating the overall flow of multipath detection and multipath noise reduction processing.

FIG. 5 is a flowchart illustrating a detailed procedure of multipath noise reduction processing of FIG.

FIG. 6 is an explanatory diagram of a section where multipath noise occurs.

7 is an enlarged view of a part of the multipath section of FIG.

FIG. 8 is a diagram illustrating difference determination for detecting a steep peak.

FIG. 9 is a diagram illustrating a waveform of an output signal after a multipath reduction process is performed.

[Explanation of symbols]

10 IF signal, 12 FM detection section, 13 composite signal, 14 multipath noise reduction processing section, 1
5 attenuation rate, 16 attenuation rate setting section, 17S meter, 18 multipath detection section, 19 switching signal,
20 switching unit, 21 output signal, 22 stereo demodulation unit, 24 signal processing unit, 30 smoothing processing unit, 3
2 difference determination unit, 34 attenuation processing unit, 40 absolute value calculation unit, 42 loop filter, 44 normalization unit,
46 adder, 48 limiter, 50 table reference.

Claims (9)

[Claims] 1. A noise reduction processing unit for attenuating an input signal to generate an output signal, wherein the noise reduction processing unit includes a strength of the input signal at a current sampling time and a value of the output signal at a past sampling time. A difference determination unit that determines whether or not the difference in intensity exceeds a predetermined threshold value to detect noise, and, when the noise is detected, attenuates the input signal at the current sampling to attenuate the input signal at the current sampling. A signal processing device, comprising: an attenuation processing unit that generates an output signal. 2. The difference determination unit calculates a difference between the intensity of the input signal at the current sampling time and the intensity of the output signal at a plurality of past sampling times,
The signal processing device according to claim 1, wherein noise is detected by determining whether each difference exceeds a predetermined threshold value. 3. The noise reduction processing unit further includes a smoothing processing unit that smoothes the input signal for a predetermined sampling period, and the difference determining unit and the attenuation processing unit apply the smoothed input signal to the input signal. The signal processing device according to claim 1, wherein the signal processing device performs processing on the signal processing device. 4. The method according to claim 1, further comprising an attenuation rate setting section that adaptively sets the attenuation rate of the intensity of the input signal in the noise reduction processing section based on the intensity of the input signal. The signal processing device according to any one of 3 above. 5. An FM detection unit that outputs an FM demodulated signal based on the received FM transmitted radio wave, a signal processing unit that reduces and outputs noise of the FM demodulated signal, and the received FM transmitted radio wave. At a period in which multipath noise may occur, and a multipath detection unit that operates the signal processing unit during the period, and an output of the signal processing unit while the signal processing unit is operating, the signal processing unit operates. And a stereo demodulation unit that stereo-demodulates and outputs the FM demodulation signal while the noise reduction processing unit generates an output signal by performing an attenuation process using the FM demodulation signal as an input signal. The noise reduction processing unit determines whether the difference between the intensity of the input signal at the current sampling time and the intensity of the output signal at the past sampling time exceeds a predetermined threshold value. And a difference determining unit that detects noise, and an attenuation processing unit that, when the noise is detected, attenuates the input signal at the time of current sampling to generate the output signal at the time of current sampling. Signal receiving device. 6. The signal processing unit further includes an attenuation rate setting unit that adaptively sets the attenuation rate of the intensity of the input signal in the noise reduction processing unit based on the intensity of the input signal. The signal receiving device according to claim 5. 7. An output signal is generated by detecting a period during which the intensity of the input signal greatly changes, and performing filtering processing for reducing noise on the input signal only during the period. Signal processing method. 8. The filtering process sequentially calculates a difference between the intensity of the input signal at the current sampling time and the intensity of the output signal at the past sampling time for each sampling time, and the difference exceeds a predetermined threshold value. In case,
8. The signal processing method according to claim 7, further comprising: attenuating the input signal at the current sampling time to generate the output signal at the current sampling time. 9. A preprocessing step of detecting a period in which the noise may occur, wherein the filtering processing is performed on the input signal in the period detected in the preprocessing step. Item 7 or 8
The signal processing method described in.