radio

Abstract

To provide a radio capable of performing squelch control with little erroneous determination regardless of the voice quality of a speaker. [Solution] The radio 20 in this example comprises an SSB demodulation unit 21 that performs SSB demodulation processing on the received signal, a noise cancellation unit 22 that performs noise cancellation processing on the audio signal resulting from demodulation by the SSB demodulation unit 21, a pitch period calculation unit 23 that calculates the pitch period of the audio from the audio signal after noise cancellation processing, and a squelch control unit 24 that controls the opening and closing of the squelch of a squelch circuit 25 based on the pitch period calculated by the pitch period calculation unit 23.

Description

[Technical Field]

[0001] The present invention relates to a radio device equipped with a squelch function for blocking noise when there is no signal. [Background technology]

[0002] Conventionally, radios equipped with a squelch function for blocking noise when there is no signal have been in practical use. For example, a technique called audio squelch is used to control the squelch for demodulated audio obtained by SSB (Single Side Band) demodulation. An overview of audio squelch will be explained with reference to FIGS. 1A and 1B. As shown in FIG. 1A, when the squelch function of radio 10 is turned OFF (disabled), a buzzing noise is output from the speaker when noise is received without voice communication. On the other hand, when the squelch function of radio 10 is turned ON (enabled), when noise is received without voice communication, the squelch is closed, blocking audio output to the speaker and silencing the speaker.

[0003] Figure 2 shows an example of a processing block related to a conventional audio squelch. In the radio 10 shown in the figure, noise components of the demodulated audio are extracted by noise extraction filter 11 and averaged by power averaging unit 13, and audio components of the demodulated audio are extracted by audio extraction filter 12 and averaged by power averaging unit 14, and these are input to comparison unit 15. Comparison unit 15 compares the power of the noise and audio components, and if the noise components are larger than the audio components, controls squelch circuit 16 to close the squelch and silence the speaker output. On the other hand, if the noise components are smaller than the audio components, controls squelch circuit 16 to open the squelch and output the demodulated audio from the speaker.

[0004] Prior art in the technical field of the present invention includes the following. For example, Patent Document 1 discloses an invention that improves reception quality by removing an interference signal from a received signal that includes an interference signal and a spread signal that has been spread-modulated by a CDMA (Code Division Multiple Access) system. Furthermore, Patent Document 2 discloses an invention that prevents the desired signal from being removed when an interference signal is removed from an input signal that includes a wideband desired signal and a narrowband interference signal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-312167 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-135143 Summary of the Invention [Problem to be solved by the invention]

[0006] Radios used in aircraft such as rotorcraft and propeller planes have a problem in that the movement of the rotors or propellers generates low-frequency, steady-state noise that gets carried over into the received signal. Squelch control in such radios is generally achieved by pitch extraction, but there is a risk that the steady-state noise will be mistakenly detected as voice due to pitch extraction, resulting in incorrect squelch control.

[0007] Furthermore, one of the characteristics of voice quality is a feature called "formant," which is a frequency distribution in the voice frequency spectrum that appears stronger than the surrounding area. It is known that the frequency distribution in which formants appear varies depending on the speaker or the sound produced. The audio extraction filter in conventional audio squelch systems is set to pass the frequency band in which the average formant appears, without taking into account individual differences in formants. Therefore, depending on the formant of the transmitting speaker, noise may pass through the noise extraction filter, and the peak power of the voice may not necessarily pass through the audio extraction filter, which can lead to erroneous squelch control decisions. Thus, conventional audio squelch systems have the drawback of frequently making erroneous decisions depending on the voice quality of the transmitting speaker.

[0008] The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to provide a radio device capable of performing squelch control with fewer erroneous determinations regardless of the voice quality of the speaker. [Means for solving the problem]

[0009] In order to achieve the above object, a radio according to one aspect of the present invention is configured as follows: That is, a radio equipped with a squelch function for blocking noise when there is no signal includes a noise cancellation unit that performs noise cancellation processing on an audio signal obtained by demodulating a received signal, a pitch period calculation unit that calculates the pitch period of the audio from the audio signal after the noise cancellation processing, and a squelch control unit that controls opening and closing of the squelch based on the pitch period calculated by the pitch period calculation unit.

[0010] Here, in the above radio device, the squelch control unit may be configured to control the squelch to open if the current pitch period is time-correlated with the past pitch period, and to control the squelch to close if not.

[0011] Furthermore, in the above radio device, the squelch control unit may control opening and closing of the squelch based on a determination result as to whether or not the following conditions are satisfied: a difference between the pitch period of the current block and the pitch period of the immediately preceding block is equal to or less than a first reference value, the pitch period of the current block is equal to or greater than a second reference value, and a normalized correlation peak value obtained by normalizing the autocorrelation value related to the pitch period of the current block is greater than a threshold value.

[0012] The radio device may further include an operation unit for receiving an adjustment of the threshold value from a user of the radio device. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a radio device that can perform squelch control with fewer erroneous determinations regardless of the voice quality of the speaker. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 10 is a diagram illustrating an example in which squelch control is OFF. [Figure 1B] FIG. 10 is a diagram illustrating an example in which squelch control is ON. [Figure 2] FIG. 1 is a diagram illustrating an example of a processing block related to a conventional audio squelch. [Figure 3] 1 is a diagram illustrating an example of the configuration of a radio device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described with reference to the drawings. Here, a radio that performs SSB demodulation and is used in aircraft such as rotorcraft and propeller planes will be described as an example, but it goes without saying that the present invention is not limited to this.

[0016] 3 shows an example of the configuration of a radio according to one embodiment of the present invention. The radio 20 in the figure includes an SSB demodulator 21, a noise canceller 22, a pitch period calculator 23, a squelch controller 24, and a squelch circuit 25. The radio 20 also includes an operation unit (not shown) for receiving a user's input to adjust a threshold value, which will be described later.

[0017] The SSB demodulation unit 21 performs SSB demodulation processing on the received signal input from the receiving antenna, and outputs the demodulated audio signal to the noise cancellation unit 22.

[0018] The noise cancellation unit 22 performs noise cancellation processing on the audio signal obtained by the SSB demodulation unit 21. The noise cancellation processing extracts signal components (current audio) that are time-correlated with past audio from the audio signal to be noise-cancelled, and removes signal components (noise) that are not time-correlated. The noise cancellation method may be the method disclosed in Patent Document 1 or Patent Document 2, or another method. By clarifying the audio during a call using noise cancellation processing, it is possible to prevent erroneous determination and make it easier for the user (listener) of the radio device 20 to hear the audio.

[0019] The pitch period calculation unit 23 calculates the pitch period of the voice from the voice signal after noise cancellation processing by the noise cancellation unit 22. In addition to formants, human voice has a characteristic called "pitch," which is the pitch of the sound, and this can be detected using a pitch extraction method. The pitch period is the time from one peak to the next peak of a sound wave, and the shorter this time, the higher the pitch. Below, we will explain how to calculate the pitch period from a voice signal using an autocorrelation function.

[0020] If the audio sample at time n is S(n) and the update period is X, then the block signal for the X period is S(n-X+1) to S(n). When this is combined with the signals S(n-LX+1) to S(nX) of the past L blocks (where L is an integer equal to or greater than N, where LX is equivalent to 20 msec), the result is a block signal S(n-LX+1) to S(n) equivalent to 20 msec. By using N of these samples for autocorrelation calculation, the same processing as conventional methods is achieved.

[0021] The autocorrelation value ρ(D) is obtained by the following equation (1).

number

[0022] Generally, the pitch period of a vowel changes gradually. However, detection errors frequently occur in a noisy environment. To solve this problem, the squelch control unit 24 statistically determines the change in the pitch period and then controls the opening and closing of the squelch. Here, the pitch period calculated by the pitch period calculation unit 23 for block section m is designated as D1(m). A pitch determination counter and a squelch determination counter are also provided, and their initial values ​​are set to 0.

[0023] First, the squelch control unit 24 calculates the received power P with respect to the autocorrelation value ρ(D1(m)) in the pitch period D1(m) as shown in the following equations (2) and (3). r Normalization is performed by the normalized correlation peak value ρ N Get.

number

number

[0024] Next, the squelch control unit 24 determines whether or not the following (Condition 1a) to (Condition 1c) are satisfied. (Condition 1a) Abs[D1(m)-D1(m-1)]≦5 (Condition 1b) D1(m)≧20 (Condition 1c)ρ N >Threshold Here, Abs[·] is a function that calculates an absolute value. The threshold is a value in the range of 0 to 1, and can be freely set / adjusted by the user of the radio device 20. The closer the threshold is to 0, the easier it is for the squelch to open.

[0025] If all of the above (Condition 1a) to (Condition 1c) are satisfied, i.e., if the difference between the pitch period of the current block and the pitch period of the immediately preceding block is equal to or less than the first reference value (=5), the pitch period of the current block is equal to or greater than the second reference value (=20), and the normalized correlation peak value obtained by normalizing the autocorrelation value related to the pitch period of the current block is greater than the threshold, then 1 is added to the pitch decision counter (pitch decision counter = pitch decision counter + 1). Otherwise, 1 is subtracted from the pitch decision counter (pitch decision counter = pitch decision counter - 1). Here, the maximum value of the pitch decision counter is set to 3, and the minimum value is set to 0.

[0026] Next, the squelch control unit 24 determines whether the following (Condition 2) is satisfied. (Condition 2) Pitch determination counter = 3 If the above (Condition 2) is met, the squelch determination counter is set to 100. If not, 1 is subtracted from the squelch determination counter (squelch determination counter = squelch determination counter - 1). Here, the maximum value of the squelch determination counter is set to 100, and the minimum value is set to 0.

[0027] Next, the squelch control unit 24 determines whether or not the following (Condition 3) is satisfied. (Condition 3) Squelch determination counter > 0 If the above (Condition 3) is satisfied, the squelch circuit 25 is controlled to open the squelch, otherwise the squelch circuit 25 is controlled to close the squelch.

[0028] As described above, the radio 20 of this example includes an SSB demodulation unit 21 that performs SSB demodulation processing on the received signal, a noise cancellation unit 22 that performs noise cancellation processing on the audio signal demodulated by the SSB demodulation unit 21, a pitch period calculation unit 23 that calculates the pitch period of the audio from the audio signal after noise cancellation processing, and a squelch control unit 24 that controls the opening and closing of the squelch of the squelch circuit 25 based on the pitch period calculated by the pitch period calculation unit 23. In this way, by performing noise cancellation as preprocessing for squelch control by pitch extraction, erroneous pitch detection can be suppressed. As a result, squelch control with fewer erroneous detections can be performed regardless of the speaker's voice quality.

[0029] It should be noted that the numerical values ​​given in the above explanation are merely examples, and any value can be used depending on the system requirements, operation mode, etc. Also, a method other than the method using the above conditional equation may be used to determine whether or not there is a time correlation between the current pitch period and past pitch periods, and if there is a time correlation, control to open the squelch is performed, and if there is not, control to close the squelch is performed.

[0030] Although the embodiments of the present invention have been described above, these embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take on various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the present invention. These embodiments and modifications thereof are included in the scope and spirit of the invention described in this specification, etc., and are included in the invention described in the claims and their equivalents.

[0031] Furthermore, the present invention can be provided not only as devices such as those described above or as systems composed of these devices, but also as methods executed by these devices, programs for realizing the functions of these devices using a processor, and storage media for storing such programs in a computer-readable manner. [Industrial Applicability]

[0032] The present invention can be used in a radio equipped with a squelch function for blocking noise when there is no signal. [Explanation of symbols]

[0033] 10: Radio, 11: Noise extraction filter, 12: Audio extraction filter, 13, 14: Power averaging section, 15: Comparison section, 16: Squelch circuit, 20: Radio, 21: SSB demodulation section, 22: Noise cancellation section, 23: Pitch period calculation section, 24: Squelch control section, 25: Squelch circuit

Claims

1. In radios equipped with a squelch function to block noise when there is no signal, a noise cancellation unit that performs noise cancellation processing on an audio signal obtained by demodulating a received signal; a pitch period calculation unit that calculates a pitch period of the speech from the speech signal after the noise cancellation processing; a squelch control unit that controls opening and closing of a squelch based on the pitch period calculated by the pitch period calculation unit; A radio device comprising:

2. 2. The radio device according to claim 1, The squelch control unit controls to open the squelch when the current pitch period has a time correlation with the past pitch period, and controls to close the squelch when there is no time correlation.

3. 2. The radio device according to claim 1, the squelch control unit controls opening and closing of the squelch based on a determination result of whether or not the following conditions are satisfied: a difference between the pitch period of a current block and the pitch period of an immediately preceding block is equal to or less than a first reference value, the pitch period of the current block is equal to or greater than a second reference value, and a normalized correlation peak value obtained by normalizing an autocorrelation value related to the pitch period of the current block is greater than a threshold value.

4. 4. The radio device according to claim 3, A radio comprising an operation unit for receiving an adjustment of the threshold value from a user of the radio.

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