JP2009267780A - Multipath noise reduction device, fm receiver, and multipath noise reduction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent quality deterioration of a sound signal in FM reception. <P>SOLUTION: An intensity determination part 111 determines whether or not a level of an intensity signal S14 is smaller than a first threshold. A DU ratio determination part 112 determines whether or not ratio of field intensity of reflected wave to field intensity of direct wave is larger than a second threshold based on the intensity signal S14. A multipath noise determination part 113 determines that multipath noise is generated in an IF signal S12 when it is determined that the level of the intensity signal S14 is smaller than the first threshold by the intensity determination part 111, and when it is determined that the ratio is larger than the second threshold by the DU ratio determination part 112. A multipath noise reduction part 114 sets an IQ signal S20 after noise reduction to a value of an IQ signal S13 immediately before generation of the multipath noise to output the IQ signal S13 when it is determined that the multipath noise is generated in the IF signal S12 by the multipath noise determination part 113. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for reducing multipath noise of a received signal in FM communication.

  When an FM receiver mounted on a moving body such as an automobile receives audio radio waves, multipath occurs due to reflection of electromagnetic waves by obstacles such as surrounding mountains and high-rise buildings. Specifically, since the reflected wave reflected by the obstacle that is a reflector reaches the receiving antenna through a different path from the direct wave directly received by the receiving antenna, a phase shift occurs between the direct wave and the reflected wave, Part of the direct wave is canceled by the reflected wave. As a result, multipath noise is generated in the received audio wave, and the quality of the audio signal output to the speaker or the like by the FM receiver is significantly reduced.

In Patent Document 1, the AM component of the IF signal is detected, the level of the AM component is compared with a predetermined threshold value, and the audio signal output by the demodulator when the AM component level is equal to or lower than the predetermined threshold value. A multipath noise reduction method (hereinafter, referred to as “first method”) for holding the previous value with respect to is disclosed. Further, a method of comparing the DU ratio with a predetermined threshold instead of comparing the AM component level with a predetermined threshold (hereinafter referred to as “second method”) is also disclosed.
JP 60-39929 A

  However, when the previous value hold is performed when the AM component is equal to or lower than the predetermined level as in the first method of Patent Document 1, the FM signal is transmitted from the broadcast station with a large modulation degree. In some cases, the previous value hold is performed even though the AM component falls and no multipath noise is generated. If the previous value hold is performed when multipath noise is not generated, the quality of the audio signal is degraded.

  Further, as in the second method of Patent Document 1, it is determined whether or not to hold the previous value based on the DU ratio. Value hold is performed, and the quality of the audio signal may deteriorate.

  In view of the above-described points, an object of the present invention is to avoid unnecessary multipath noise reduction processing in FM reception and prevent deterioration in quality of an audio signal.

  In order to solve the above problems, the present invention provides an intensity determination process for determining whether or not the level of an intensity signal indicating the electric field intensity of an IF signal is smaller than a first threshold, and a direct wave based on the intensity signal. DU ratio determination processing for determining whether or not the ratio of the electric field strength of the reflected wave to the electric field strength of the current is greater than a second threshold, and in the strength determination processing, the level of the strength signal is determined to be smaller than the first threshold. And a multipath noise determination process for determining that multipath noise is generated in the IF signal when the ratio is determined to be larger than a second threshold in the DU ratio determination process, and the multipath noise. When it is determined that multipath noise is generated in the IF signal in the determination process, the value of the IQ signal based on the IF signal or the value of the audio signal obtained by demodulating the IQ signal And having a multipath noise reducing process for replacing a predetermined value.

  Thereby, when the level of the intensity signal is smaller than the first threshold and the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is larger than the second threshold, the value of the IQ signal based on the IF signal or The value of the audio signal obtained by demodulating the IQ signal is replaced with a predetermined value. On the other hand, the level of the intensity signal is smaller than the first threshold, but the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is less than or equal to the second threshold, and the electric field intensity of the reflected wave with respect to the electric field intensity of the direct wave Is greater than the second threshold, but the level of the intensity signal is greater than or equal to the first threshold, the replacement is not performed. Therefore, the value of the IQ signal or the value of the audio signal demodulated from the IQ signal is prevented from being replaced unnecessarily, and unnecessary multipath noise reduction processing is avoided, so that the quality of the audio signal is reduced. Is prevented.

  According to the present invention, unnecessary multipath noise reduction processing is avoided, so that deterioration of the quality of the audio signal is prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, components having functions similar to those of the other embodiments are denoted by the same reference numerals and description thereof is omitted.

Embodiment 1
As shown in FIG. 1, the FM receiver according to Embodiment 1 of the present invention includes an antenna 101, a frequency conversion unit 102, an IF signal processing unit 103, an intensity signal generation unit 106, a multipath noise reduction device 110, and a demodulation unit 104. And a speaker 105. The multipath noise reduction device 110 includes an intensity determination unit 111, a DU ratio determination unit 112, a multipath noise determination unit 113, a multipath noise reduction unit 114, and an external setting unit 115.

  The antenna 101 receives the high frequency signal S11.

  The frequency converter 102 converts the high-frequency signal S11 received by the antenna 101 into an IF (Intermediate Frequency) signal S12 and outputs it.

  The IF signal processing unit 103 converts the IF signal S12 output from the frequency conversion unit 102 into an IQ (In-Phase / Quadrature-Phase) signal S13 and outputs the signal.

  The intensity signal generation unit 106 generates an intensity signal S14 indicating the electric field intensity of the IF signal S12 from the IQ signal S13 output by the IF signal processing unit 103.

  The intensity determination unit 111 determines whether the level of the intensity signal S14 is smaller than the first threshold indicated by the threshold signal S15 (whether the intensity signal S14 has a large degree of depression) and determines the level of the intensity signal S14. Is lower than the first threshold value, an H (High) level signal is output as the intensity determination signal S17. On the other hand, when the intensity signal S14 level is equal to or higher than the first threshold value, L (Low) is output as the intensity determination signal S17. ) Output a level signal.

Based on the intensity signal S14, the DU ratio determination unit 112 determines whether the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is larger than the second threshold indicated by the threshold signal S16. When the ratio is greater than the second threshold, an H level signal is output as the DU ratio determination signal S18, whereas when the ratio is equal to or less than the second threshold, the DU ratio determination signal S18 is at the L level. The signal is output. Specifically, when the electric field intensity of the direct wave is Ed and the electric field intensity of the reflected wave is Eu, the DU ratio determination unit 112 determines that 20 log ₁₀ (Eu / Ed) based on the upper and lower peak values of the intensity signal S14. Is calculated, and it is determined whether or not the calculated value is larger than a threshold Th corresponding to the threshold signal S16 (second threshold). When the upper and lower peak widths of the intensity signal S14 are large, the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave increases.

  The multipath noise determination unit 113 determines that the level of the intensity signal S14 is smaller than the first threshold by the intensity determination unit 111, and the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is determined by the DU ratio determination unit 112. When it is determined that the value is larger than the second threshold value, it is determined that multipath noise is generated in the IF signal S12. Specifically, the logical product of the intensity determination signal S17 output by the intensity determination unit 111 and the DU ratio determination signal S18 output by the DU ratio determination unit 112 is output as the multipath noise determination signal S19.

  When the multipath noise determination unit 113 determines that no multipath noise is generated in the IF signal S12, that is, when the multipath noise determination signal S19 is at the L level, the multipath noise reduction unit 114 is an IF signal processing unit. The IQ signal S13 output at 103 is output as it is as an IQ signal S20 after noise reduction. On the other hand, when it is determined by the multipath noise determination unit 113 that multipath noise is occurring in the IF signal S12, that is, when the multipath noise determination signal S19 is at the H level, the noise-reduced IQ signal S20 is used as the multipath noise. The value of the IQ signal S13 immediately before the noise is generated is output. That is, during the period when multipath noise is occurring in IF signal S12, multipath noise reduction section 114 continues to hold and output the value of post-noise reduction IQ signal S20 (IQ signal S13) immediately before the occurrence of multipath noise. (Hold previous value).

  The external setting unit 115 sets the first threshold value and the second threshold value used by the intensity determination unit 111 according to the user input, and the threshold signal S15 indicating the first threshold value and the threshold signal indicating the second threshold value. S16 is output.

  The demodulator 104 demodulates the noise-reduced IQ signal S20 to obtain an audio signal (audio data) S21.

  The speaker 105 radiates sound waves based on the audio signal S21.

In the FM receiver configured as described above, the intensity signal S14 is as shown in FIG. 2A, and 20log ₁₀ (Eu / Ed) calculated by the DU ratio determination unit 112 is as shown in FIG. In such a case, a multipath noise determination signal S19 as shown in FIG. 2 (e) is obtained. When the multipath noise determination signal S19 is at the H level, the noise-reduced IQ signal S20 is set to the value of the IQ signal S13 immediately before the occurrence of the multipath noise. On the other hand, when the multipath noise determination signal S19 is at the H level, the IQ signal S13 output by the IF signal processing unit 103 is output as it is as a noise-reduced IQ signal S20.

According to the present embodiment, as shown in FIGS. 2A to 2E, when the electric field strength of the IF signal S12 is smaller than the first threshold but no multipath noise is generated, the multipath noise is generated. Is erroneously determined to have occurred (FIG. 2C). Further, when 20log ₁₀ (Eu / Ed) is larger than the threshold value Th corresponding to the second threshold value, but multipath noise is not generated, it is erroneously determined that multipath noise is generated ( FIG. 2 (d)) is prevented. Therefore, the FM receiver according to the present embodiment can correctly determine whether or not multipath noise has occurred. Therefore, when no multipath noise has occurred, the noise-reduced IQ signal S20 is held at the previous value. Therefore, a high quality audio signal can be obtained. For example, when the FM signal is transmitted from a broadcasting station with a large modulation degree, the electric field strength of the IF signal S12 tends to drop, but in addition to the electric field strength of the IF signal S12, the electric field of the reflected wave with respect to the electric field strength of the direct wave Since it is determined whether or not multipath noise has occurred based on the intensity ratio, erroneous determination is less likely than in the past.

<< Embodiment 2 >>
As shown in FIG. 3, the FM receiver according to Embodiment 2 of the present invention includes a multipath noise reduction device 210 on the output side of the demodulation unit 104, not on the input side of the demodulation unit 104. In the present embodiment, the demodulator 104 demodulates the IQ signal S13 before noise reduction instead of the noise-reduced IQ signal S20 to obtain the audio signal S22. Then, the multipath noise reduction device 210 performs processing on the audio signal S22 acquired by the demodulation unit 104 instead of the IQ signal S13.

  The multipath noise reduction device 210 includes a multipath noise reduction unit 214 instead of the multipath noise reduction unit 114 of the multipath noise reduction device 110. When the multipath noise determination unit 113 determines that no multipath noise has occurred in the IF signal S12, the multipath noise reduction unit 214 directly reduces the noise of the audio signal S22 acquired by the demodulation unit 104. It is output as a rear audio signal S23. On the other hand, when the multipath noise determining unit 113 determines that multipath noise is occurring in the IF signal S12, the noise signal after noise reduction S23 is set to the value of the sound signal S22 immediately before the occurrence of the multipath noise. Output. That is, during the period when multipath noise is generated in IF signal S12, multipath noise reduction unit 214 holds and outputs the value of post-noise reduction audio signal S23 (audio signal S22) immediately before the occurrence of multipath noise. (Hold previous value).

<< Other Embodiments >>
In the first and second embodiments, the external setting unit 115 sets the first threshold value and the second threshold value in accordance with the user input. You may make it set according to a signal.

  Further, the external setting unit 115 may not be provided, and fixed values may be used as the first threshold value and the second threshold value.

The DU ratio determination unit 112 does not necessarily calculate 20 log ₁₀ (Eu / Ed), and the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is second based on the intensity signal S14. Any device may be used as long as it outputs a determination result as to whether or not it is larger than the threshold value.

  In the first and second embodiments, when the multipath noise reduction units 114 and 214 determine that the multipath noise is generated in the IF signal S12 by the multipath noise determination unit 113, the IQ signal S13, the sound The signal S22 is replaced with a value immediately before the occurrence of multipath noise and output as a noise-reduced IQ signal S20 and a noise-reduced audio signal S23. However, other predetermined values may be substituted to reduce multipath noise. For example, the IQ signal S13 and the audio signal S22 may be replaced with values immediately after the elimination of multipath noise, or values obtained by linear interpolation based on values immediately before the occurrence of multipath noise and values immediately after the elimination of multipath noise. You may make it replace with. In the first embodiment, the IQ signal S13 may be replaced with 0.

  In the present invention, unnecessary multipath noise reduction processing is avoided, and deterioration of the quality of the audio signal is prevented, which is useful for improving the sound quality of the FM receiver.

It is a block diagram which shows the structure of the FM receiver which concerns on Embodiment 1 of this invention. (A) is a timing chart which shows the electric field strength of IF signal S12. (B) is a timing chart showing a value of 20 log ₁₀ (Eu / Ed). (C) is a timing chart showing a signal for determining whether the electric field strength of the IF signal S12 is smaller than the first threshold value. (D) is a timing chart showing a signal for determining whether or not 20log ₁₀ (Eu / Ed) is larger than a threshold value Th. (E) is a timing chart showing the multipath noise determination signal S19. It is a block diagram which shows the structure of the FM receiver which concerns on Embodiment 2 of this invention.

Explanation of symbols

101 Antenna 102 Frequency converter 103 IF signal processor 104 Demodulator 105 Speaker 106 Intensity signal generator 110 Multipath noise reduction device 111 Intensity determination unit 112 DU ratio determination unit 113 Multipath noise determination unit 114 Multipath noise reduction unit 115 External Setting unit 210 Multipath noise reduction device 214 Multipath noise reduction unit

Claims (9)

An intensity determination unit that determines whether or not the level of the intensity signal indicating the electric field intensity of the IF signal is smaller than a first threshold;
A DU ratio determination unit that determines whether a ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is greater than a second threshold based on the intensity signal;
When the intensity determination unit determines that the level of the intensity signal is lower than a first threshold and the DU ratio determination unit determines that the ratio is higher than a second threshold, the IF signal is multipathed. A multipath noise determination unit that determines that noise is generated;
When the multipath noise determination unit determines that multipath noise is generated in the IF signal, the value of the IQ signal based on the IF signal or the value of the audio signal obtained by demodulating the IQ signal is set to a predetermined value. A multipath noise reduction device comprising a multipath noise reduction unit for replacement. The multipath noise reduction apparatus according to claim 1,
A multipath noise reduction apparatus comprising: an external setting unit that sets the first threshold value and the second threshold value. The multipath noise reduction apparatus according to claim 1,
The multipath noise reduction apparatus characterized in that the predetermined value is a value of the signal to be replaced immediately before the occurrence of multipath noise or immediately after cancellation of multipath noise. The multipath noise reduction apparatus according to claim 1,
The predetermined value is a value obtained by linear interpolation based on a value of the signal to be replaced immediately before the occurrence of multipath noise and a value of the signal to be replaced immediately after cancellation of multipath noise. apparatus. The multipath noise reduction device of claim 1;
An antenna for receiving high-frequency signals;
A frequency converter that converts the high-frequency signal received by the antenna into an IF signal and outputs the IF signal;
An IF signal processing unit that converts the IF signal output by the frequency conversion unit into the IQ signal and outputs the IQ signal;
An intensity signal generation unit that generates the intensity signal from the IQ signal output by the IF signal processing unit;
A demodulator that demodulates the IQ signal output by the IF signal processor to obtain the audio signal;
An FM receiver comprising: a speaker that emits a sound wave based on the audio signal acquired by the demodulator. An intensity determination step for determining whether or not the level of the intensity signal indicating the electric field intensity of the IF signal is smaller than a first threshold;
A DU ratio determination step for determining whether the ratio of the electric field intensity of the reflected wave to the electric field intensity of the direct wave is greater than a second threshold based on the intensity signal;
If it is determined in the intensity determination step that the level of the intensity signal is lower than a first threshold value and the ratio is determined to be higher than a second threshold value in the DU ratio determination step, the IF signal is multipathed. A multipath noise determination step for determining that noise is generated,
When it is determined in the multipath noise determination step that multipath noise is generated in the IF signal, the value of the IQ signal based on the IF signal or the value of the audio signal obtained by demodulating the IQ signal is set to a predetermined value. A multipath noise reduction method comprising performing a multipath noise reduction step of replacing. The multipath noise reduction method according to claim 6,
The multipath noise reduction method, wherein the first threshold value and the second threshold value are set by an external setting unit. The multipath noise reduction method according to claim 6,
The method for reducing multipath noise, wherein the predetermined value is a value of the signal to be replaced immediately before occurrence of multipath noise or immediately after cancellation of multipath noise. The multipath noise reduction method according to claim 6,
The predetermined value is a value obtained by linear interpolation based on a value of the signal to be replaced immediately before the occurrence of multipath noise and a value of the signal to be replaced immediately after cancellation of multipath noise. Method.

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