JP2013070299A - Digital radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain more natural sound quality in receiving audio through digital communication by wireless.SOLUTION: A digital radio receiver (1) comprises: a demodulation circuit (10) which receives and demodulates a high-frequency signal (101), and converts the signal into a digital signal (102); a decoding circuit (20) which decodes the digital signal (102) to obtain encode data and decodes the encode data to convert the data into an audio signal (103); a noise-extraction circuit (30) which obtains a noise signal (104) from the digital signal (102); and an adder (40) which synthesizes the noise signal (104) and the audio signal (103).

Description

  The present invention relates to a digital wireless receiver, and more particularly to an apparatus for wirelessly receiving audio by digital communication.

  Noise is superimposed on the sound in an environment where the sound is wirelessly received by analog communication, particularly in an environment where FM (Frequency Modulation) broadcasting is received. Noise appears more prominently as the electric field strength is weaker. This is a weak point of analog communication and a factor that narrows the wireless transmission range.

  On the other hand, in digital communication, voice is treated as digital data encoded by data compression processing by a vocoder or the like, and error correction is performed on the digital data. For this reason, in digital communication, even in an area where noise is superimposed in analog communication, good wireless communication can be performed without deterioration in voice quality.

  However, in a general digital wireless receiver, if the electric field strength becomes so weak that error correction is impossible, the sound is interrupted and silenced due to the error detection function, or erroneous data is decoded as it is. May be output as annoying noise.

  This phenomenon suddenly occurs at the boundary of the communication area. For this reason, the user is dissatisfied with the voice quality rapidly deteriorating even though the wireless transmission range of the digital wireless receiver is wider than that for analog communication. In contrast, in analog communication, noise gradually increases according to the electric field strength. For this reason, the user can recognize that he / she is located in an area where the electric field strength is weak, and often does not feel such dissatisfaction.

  Techniques for dealing with this problem are described in, for example, Patent Documents 1 and 2. The digital wireless telephone described in Patent Literature 1 sounds an alarm sound when the electric field strength decreases. The mobile phone described in Patent Document 2 sounds an alarm sound according to the electric field strength.

  However, Patent Documents 1 and 2 have a problem that an alarm sound hinders a call for a user. This is because the alarm sound is completely unrelated to the original received voice.

  Techniques for dealing with this problem are described in Patent Documents 3 and 4. Each of the digital wireless receivers described in Patent Documents 3 and 4 stores a pseudo noise signal in advance, and adjusts the output levels of the pseudo noise signal and the audio signal according to the electric field strength.

JP-A-7-274248 JP-A-9-238102 JP-A-9-148950 JP 2009-10857 A

  However, the inventor of the present application has found that the above-mentioned Patent Documents 3 and 4 have a problem that sound quality is unnatural compared to analog communication. This is because the level adjustment of the pseudo noise signal according to the electric field strength cannot follow the rapid fluctuation of the electric field strength in the real environment due to fading or the like, or the instantaneous electric wave interruption such as shadowing, etc. This is because unnatural noise is output.

  Therefore, an object of the present invention is to obtain a more natural sound quality when wirelessly receiving sound by digital communication.

In order to achieve the above object, a digital radio receiver according to an aspect of the present invention receives a high-frequency signal, demodulates the high-frequency signal, converts the high-frequency signal into a digital signal, and decodes the digital signal A decoding processing circuit that obtains encoded data, decodes the encoded data and converts it into an audio signal, a noise extraction circuit that obtains a noise signal from the digital signal, the noise signal, and the audio signal And an adder.
Preferably, the noise extraction circuit includes a band-pass filter that extracts a noise signal component of a predetermined band from the digital signal, and a frequency conversion that converts the frequency of the noise signal component into an audible frequency band to obtain the noise signal. It is good to include a vessel.
Alternatively, the noise extraction circuit encodes the encoded data, reproduces a modulation waveform at a transmission source of the high-frequency signal, and subtracts the modulation waveform from a waveform exhibited by the digital signal, and outputs the noise signal. And a subtractor for obtaining
Preferably, the noise extraction circuit further includes an amplifier that amplifies the noise signal and outputs the amplified noise signal to the adder.
Preferably, the digital radio receiver may further include a controller for controlling a gain so that an output signal from the adder is constant.

  According to the present invention, it is possible to obtain a more natural sound quality when wirelessly receiving sound by digital communication.

It is the block diagram which showed the structural example of the digital radio receiver which concerns on Embodiment 1 of this invention. It is the block diagram which showed the structural example of the demodulation processing circuit used for the digital radio receiver which concerns on Embodiment 1 of this invention. It is the block diagram which showed the structural example of the decoding process circuit used for the digital radio receiver which concerns on Embodiment 1 of this invention. It is the block diagram which showed the structural example of the noise extraction circuit used for the digital radio receiver which concerns on Embodiment 1 of this invention. It is the graph which showed the frequency characteristic example of the detection waveform in the digital radio receiver which concerns on Embodiment 1 of this invention. It is the graph which showed the operation example of the digital radio receiver which concerns on Embodiment 1 of this invention. It is the block diagram which showed the structural example of the digital radio receiver which concerns on Embodiment 2 of this invention. It is the block diagram which showed the structural example of the digital encoding part used for the digital radio receiver which concerns on Embodiment 2 of this invention. It is the time chart figure which showed an example of the detection waveform in the digital radio receiver which concerns on Embodiment 2 of this invention. It is the time chart figure which showed the other example of the detection waveform in the digital radio receiver which concerns on Embodiment 2 of this invention. It is the block diagram which showed the structural example of the digital radio receiver which concerns on Embodiment 3 of this invention.

  Embodiments 1 to 3 of the digital radio receiver according to the present invention will be described below with reference to FIGS. In the drawings, the same components are denoted by the same reference numerals, and redundant description is omitted as necessary for the sake of clarity.

[Embodiment 1]
As shown in FIG. 1, the digital radio receiver 1 according to the present embodiment includes a demodulation processing circuit 10 and a decode processing circuit 20, similarly to a general digital radio receiver. In addition, the digital radio receiver 1 includes a noise extraction circuit 30 and an adder 40, unlike a general digital radio receiver.

  Among these, the demodulation processing circuit 10 receives the high-frequency signal 101 via the antenna, and demodulates the high-frequency signal 101 to convert it into a digital signal 102. Specifically, as shown in FIG. 2, the demodulation processing circuit 10 includes an RF (Radio Frequency) unit 11 and a detection unit 12. The RF unit 11 includes an RF amplifier 13, a local oscillator 14, a mixer 15, and an IF (Intermediate Frequency) amplifier 16. The RF amplifier 13 amplifies the high frequency signal 101 received via the antenna. The mixer 15 mixes the high-frequency signal amplified by the RF amplifier 13 and the local signal output from the local oscillator 14 to obtain an IF signal. The IF amplifier 16 amplifies the IF signal output from the mixer 15 and outputs the amplified IF signal to the detection unit 12. On the other hand, the detector 12 includes an A / D (Analog to Digital) converter 17 and a detector (demodulator) 18. The IF signal input from the RF unit 11 is demodulated via the A / D converter 17 and the detector 18 to become a digital signal 102. Here, the IF signal may be digitally converted by the A / D converter 17 after detection by the detector 18. The digital signal 102 is output to both the decode processing circuit 20 and the noise extraction circuit 30.

  The decode processing circuit 20 decodes the digital signal 102 to obtain encoded data, and also decodes the encoded data and converts it into the audio signal 103. Specifically, as shown in FIG. 3, the decoding processing circuit 20 includes a reception baseband filter 21, a digital decoding unit 22, and a data decoding unit 23. Among these, the reception baseband filter 21 performs band limitation on the digital signal 102 so that a desired reception bandwidth is obtained. The digital decoding unit 22 includes a clock reproduction unit 24, a synchronization detection unit 25, a data acquisition unit 26, and an error correction decoding unit 27. The data acquisition unit 26 decodes the output signal from the reception baseband filter 21 according to the symbol clock timing obtained by the clock recovery unit 24 and the frame synchronization timing obtained by the synchronization detection unit 25, and acquires the digital data 106. The error correction decoding unit 27 performs error correction using the error correction data, and obtains encoded data 107. Here, the encoded data 107 includes audio data encoded by a predetermined data compression process and upper layer data. Further, the data decoding unit 23 includes an audio decoder 28 and a data analysis unit 29. The audio decoder 28 decodes the audio data to obtain an audio signal 103. The audio signal 103 is input to one terminal of the adder 40. The data analysis unit 29 analyzes upper layer data for processing in the upper layer and the like.

  On the other hand, as shown in FIG. 4, the noise extraction circuit 30 includes a BPF (Band Pass Filter) 31, an amplifier 32, and a frequency converter 33. The noise signal component included in the digital signal 102 is extracted from the digital signal 102. Specifically, the BPF 31 extracts a signal in a predetermined band higher than the band necessary for demodulation (the band of the reception baseband filter 21 shown in FIG. 6) from the digital signal 102. The extracted noise signal component is amplified by the amplifier 32 and then input to the frequency converter 33. The frequency converter 33 converts the frequency of the input noise signal component into an audible frequency band, thereby obtaining the noise signal 104. The noise signal 104 is input to the other terminal of the adder 40.

  Further, the adder 40 synthesizes the audio signal 103 output from the decoding processing circuit 20 and the noise signal 104 output from the noise extraction circuit 30. The synthesized signal 105 thus obtained is sounded by a subsequent speaker (not shown) or the like.

  Next, an operation example of the present embodiment will be described with reference to FIGS.

  FIG. 5 shows the frequency characteristics of the digital signal 102 output from the detector 12. Normally, the modulated wave on the transmission side of the high-frequency signal 101 has a half band of the symbol rate according to the Nyquist theorem. Therefore, in a strong electric field, the detection waveform on the reception side (the waveform of the digital signal 102) appears in the band of the modulated wave itself. As the electric field strength decreases, noise is superimposed on the detected waveform. This noise is noise itself generated in a weak electric field in the case of analog communication.

  Therefore, in the present embodiment, the reception baseband filter 21 in the decoding processing circuit 20 extracts the band of the modulated wave as shown by the one-dot chain line in FIG. 6, and thus the S / N ratio (Signal to Noise ratio). Improve.

  On the other hand, in the noise extraction circuit 30, the digital signal 102 is subjected to band extraction by the BPF 31 before being input to the reception baseband filter 21, and as shown by a dotted line in FIG. The signal component of is extracted. The signal component extracted by the BPF 31 is noise that increases as the electric field strength decreases. This noise is adjusted to a level that is easy for the user to hear with the amplifier 32, and then converted into a noise signal 104 in the audible frequency band with the frequency converter 33.

  Then, the adder 40 adds the noise signal 104 to the audio signal 103, thereby generating the same noise as in the case of analog communication.

  Thus, in this embodiment, the detected waveform is used as the source of the noise signal. For this reason, the level of the noise signal varies depending on the actual electric field strength. Further, the noise signal is not a pseudo signal but is obtained from an actual received signal. Therefore, according to the present embodiment, it is possible to obtain far more natural sound quality as compared with Patent Documents 3 and 4 described above when wirelessly receiving sound by digital communication.

[Embodiment 2]
As shown in FIG. 7, the digital radio receiver 1a according to the present embodiment differs from the first embodiment in that a noise extraction circuit 30a is provided instead of the noise extraction circuit 30 shown in FIG. .

  Specifically, the noise extraction circuit 30 a includes a digital encoding unit 34, a subtracter 35, and an amplifier 36. The digital encoding unit 34 encodes the encoded data 107 output from the decoding processing circuit 20 in the same procedure as that of the transmitting side that transmits the signal received by the digital wireless receiver 1 according to the present embodiment. Thus, the modulation waveform 108 on the transmission side is reproduced (reproduced). Specifically, the digital encoding unit 34 includes an error correction encoding unit 37 and a transmission baseband processing unit 38 as shown in FIG. The error correction encoding unit 37 performs the same operation as the error correction encoding performed on the transmission side. The transmission baseband processing unit 38 performs transmission baseband processing such as a filter having characteristics equivalent to the filter processing performed on the transmission side, sample rate conversion for conversion from digital data to a modulated waveform, aperture correction, and the like. As described above, the digital encoding unit 34 reproduces the modulation waveform 108 by executing the transmission baseband processing by the transmission baseband processing unit 38 via the error correction coding unit 37. On the other hand, the subtracter 35 subtracts the modulation waveform 108 from the waveform (detection waveform) exhibited by the digital signal 102. The amplifier 36 amplifies the output signal from the subtractor 35 and outputs the amplified signal to the adder 40 as a noise signal 104.

  Next, an operation example of the present embodiment will be described with reference to FIGS.

  FIG. 9 shows an example of a detection waveform in a strong electric field. As a premise, the modulation waveform on the transmission side is a smooth waveform that exhibits a symbol data value at symbol clock timing. Since there is no noise (or very small) in a strong electric field, the detection waveform on the reception side is substantially the same as the modulation waveform.

  For this reason, the modulation waveform 108 reproduced by the digital encoding unit 34 is substantially the same as the detection waveform. Therefore, the level of the output signal from the subtractor 35 (that is, the noise signal 104) becomes substantially zero, and the synthesized signal 105 output from the adder 40 is equivalent to the audio signal 103.

  On the other hand, as shown in FIG. 10, the detection waveform in the weak electric field is a waveform in which noise is superimposed on the modulation wave. However, the modulation waveform 108 reproduced by the digital encoding unit 34 is a waveform similar to that in FIG. 9 without noise. For this reason, the output signal from the subtractor 35 is a signal expressed only by noise. Therefore, by adding the noise signal 104 and the audio signal 103 by the adder 40, it is possible to generate the same noise as in the case of analog communication.

  As described above, according to the present embodiment, as in the first embodiment, it is possible to obtain far more natural sound quality compared to the above-described Patent Documents 3 and 4 when wirelessly receiving voice by digital communication. it can. Further, as in the first embodiment, the noise can be adjusted to a level that is easy for the user to listen to.

  Alternatively, the modulation waveform 108 may be reproduced by performing transmission baseband processing on the output of the data acquisition unit 26 (see FIG. 3) without performing processing such as error correction decoding and encoding.

[Embodiment 3]
As shown in FIG. 11, the digital radio receiver 1b according to the present embodiment is provided with a controller 50 that performs AGC (Automatic Gain Control) in addition to the configuration of the digital radio receiver 1 shown in FIG. This is different from the first embodiment described above. In the digital wireless receiver 1b, the noise extraction circuit 30a shown in FIG. 7 may be provided instead of the noise extraction circuit 30. Also in this case, the following description applies similarly.

  In operation, the controller 50 performs AGC so that the average value or the peak value of the amplitude of the synthesized signal 105 output from the adder 40 is constant, so that both levels of the audio signal and the noise signal are set to the user. Adjust to a level comfortable for you.

  Here, also in analog communication, the reception band is limited, and the maximum level of the synthesized signal of noise and voice is limited. Therefore, according to the present embodiment, it is possible to impose a limit on the maximum level of the synthesized signal by AGC, and thereby bring the sound quality closer to analog communication.

  Note that the present invention is not limited to the above-described embodiments, and it is apparent that various modifications can be made by those skilled in the art based on the description of the scope of the claims.

DESCRIPTION OF SYMBOLS 1, 1a, 1b Digital wireless receiver 10 Demodulation processing circuit 11 RF part 12 Detection part 13 RF amplifier 14 Local oscillator 15 Mixer 16 IF amplifier 17 A / D converter 18 Detector (demodulator)
DESCRIPTION OF SYMBOLS 20 Decoding processing circuit 21 Reception baseband filter 22 Digital decoding part 23 Data decoding part 24 Clock reproduction part 25 Synchronization detection part 26 Data acquisition part 27 Error correction decoding part 28 Speech decoder 29 Data analysis part 30, 30a Noise extraction circuit 31 BPF
32, 36 Amplifier 33 Frequency converter 34 Digital encoding unit 35 Subtractor 37 Error correction encoding unit 38 Transmission baseband processing unit 40 Adder 50 Controller 101 High frequency signal 102 Digital signal 103 Audio signal 104 Noise signal 105 Synthetic signal 106 Digital Data 107 Encoded data 108 Modulation waveform

Claims (5)

A demodulation processing circuit that receives a high-frequency signal and demodulates the high-frequency signal into a digital signal;
A decoding processing circuit that decodes the digital signal to obtain encoded data, decodes the encoded data and converts it into an audio signal;
A noise extraction circuit for obtaining a noise signal from the digital signal;
An adder for synthesizing the noise signal and the audio signal;
Digital wireless receiver equipped with. In claim 1,
The noise extraction circuit is
A bandpass filter for extracting a noise signal component of a predetermined band from the digital signal;
A frequency converter for converting the frequency of the noise signal component into an audible frequency band to obtain the noise signal;
A digital radio receiver characterized by including. In claim 1,
The noise extraction circuit is
An encoder that encodes the encoded data and reproduces a modulation waveform at a transmission source of the high-frequency signal;
Subtracting the modulation waveform from the waveform exhibited by the digital signal to obtain the noise signal;
A digital radio receiver characterized by including. In claim 2 or 3,
The noise extraction circuit is
An amplifier that amplifies the noise signal and outputs the amplified signal to the adder;
A digital radio receiver further comprising: In any one of Claims 1-4,
A controller for controlling the gain so that the output signal from the adder is constant;
A digital radio receiver characterized by further comprising:

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