JP2003110439A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital broadcast receiver capable of receiving signals even if the received signals contain much noise comparatively. SOLUTION: The receiver is provided with an output mode setting means 25 for setting an output mode according to a code error rate of a received signal, a decoding means 27, a D/A converter 29, and a noise reducing means 33 for reducing noises in an output signal from the means 29. If the code error rate of a received code signal is smaller than a first limit code error rate, an analog audio signal is outputted without substantially involving the means 33. The code error rate of a received signal is not less than the first limit code error rate and not greater than a second limit error rate, and an analog audio signal is outputted through the means 33. The code error rate of a received signal is larger than the second limit code error rate, and an output from the means 27 or from the means 29 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiving apparatus, and more particularly to an output mode when a received signal contains a large amount of noise.

[0002]

2. Description of the Related Art In digital broadcasting, audio information signals, image information signals, character information signals, etc. are compressed in a predetermined format, and information signals of a plurality of services are multiplexed and transmitted as data signals so as to support a plurality of services. To be done. As a system for transmitting and receiving data signals of the predetermined format including digital voice, for example, DAB (Digital Audi) compliant with the European standard (Eureka 147).
o Broadcasting: hereinafter also abbreviated as DAB) The system has been put to practical use. In the DAB system, one ensemble is composed of a plurality of services, and each service is also composed of a plurality of components. Since the details are described in the DAB standard, the description is omitted.

FIG. 6 is a diagram showing the structure of a transmission frame in the DAB system. The transmitted DAB signal is an orthogonal frequency division multiplex modulation system, that is, OFDM (Orthogonal).
OFD modulated by Frequency Division Multiplex)
The transmission frame (Tran) shown in FIG.
smission frame) is obtained from a demodulated OFDM signal obtained by demodulating the OFDM signal. As shown in FIG. 6, the transmission frame in the demodulated OFDM signal has a synchronization channel (Synchronization Channel) and an FIC (Fast Informa).
tion Channel: High-speed information channel), MSC (Main Ser
vice Channel: Main service channel). The FIC transmits information necessary for the receiver to select a program, auxiliary information for the program, and the MSC is a subchannel for voice and data.
l) is transmitted.

The FIC for one frame has three FIBs.
It consists of a data block called (Fast Information Block), and the MSC is 1 to 4 depending on the transmission mode.
CIF (Common Interleaved Frame), and is time-interleaved in CIF units. A plurality of sub-channels are multiplexed in the CIF, and one sub-channel corresponds to one program. Therefore, when the user wants to receive one program, he or she selects a specific sub-channel from the CIF and selects it. When a certain ensemble is received, the DAB system can obtain information about a plurality of services and components included in the ensemble, and can instantaneously switch to different services and components without changing the reception frequency. ing.

A synchronization channel block is provided at the beginning of the transmission frame. This synchronization channel block is composed of a null signal portion for coarse synchronization and a reference phase symbol that carries a reference phase for differential QPSK demodulation in OFDM demodulation. Channel selection in the DAB receiver is performed in units of ensembles, and when other ensembles are received, frequency change, that is, ensemble up / down is performed.

FIG. 4 is a block diagram showing an example of a conventional digital broadcast receiving apparatus. Hereinafter, a conventional digital broadcast receiver will be described with reference to FIG. 4 by taking a DAB receiver as an example. In this DAB, the modulation method is OFDM
(Orthogonal Frequency Divi
sion Multiplex) is adopted as the explanation. In the digital broadcast receiver 50 shown in FIG. 4,
The front end 13 receives the DAB carrier wave via the antenna 11 and processes the RF signal. In the signal processing, the RF signal is converted into an intermediate frequency signal (IF signal) capable of digital signal processing, and output to the analog / digital converter (A / D converter) 15. A /
The D converter 15 converts the analog signal into a digital information signal and supplies the digital information signal to the I / Q detector 16. OFDM demodulator 2 with I / Q detector 16, FFT 17, and DSP 18
1 is configured.

The I / Q detector 16 is divided into an I signal and a Q signal so that the OFDM signal can be processed in a subsequent stage.
It is supplied to FT17. In the FFT 17, a fast Fourier transform is performed using a DSP (digital arithmetic unit) 18 and supplied to the channel decoder 23. In the channel decoder 23, de-interleaving (de-interleaving) for returning the order of signals to the original order, de-pancturing (de-pancturing) for inserting untransmitted code bits to return to the original data, and error Code detection and correction are performed. Microprocessor (MPU) 3
1, the code error rate is calculated together with the correction of the error code in cooperation with the channel decoder 23, and the code error rate is set to a predetermined value (this code error rate is also referred to as a limit code error rate in the following description). MP) when it becomes larger than
The mute control signal for stopping the decoding operation in the EG decoder 27 and the transmission of the decoded signal obtained by the decoding is 0.
To 1 (or L to H) and is given to the D / A converter 29. The channel decoder 23 will be described in detail later.

The compressed audio information is supplied from the channel decoder 23 to the MPEG decoder 27, and MP
The EG decoder 27 decodes the compressed audio information and decompresses it, and the digital / analog converter (D / A converter) 29 converts it into analog information and outputs it as an analog audio signal.

FIG. 5 is a flowchart showing a procedure for generating a mute control signal in the conventional example. The flowchart shown in FIG. 5 shows the processing performed by the channel decoder 23. In FIG. 5, first, in step S11, de-interleaving for canceling the frequency interleave for randomizing the error on the frequency axis and returning it to the original is performed, and the transmission frame shown in FIG. 6 is obtained.

Next, the FIC and MSC perform step S.
Separated at 13. Vidabi decoding is performed on the FIC data in step S15, and MP in step S17.
The code error rate is calculated by the error rate calculation means composed of U31 and the like. Steps S15 and S17
Is actually performed almost simultaneously by the MPU 31 or the like, and the code error rate ERN is a predetermined value (the limit code error rate E
RL), the mute control signal for stopping the decoding of the MPEG audio signal and the sending of the decoded signal changes from 0 to 1 (or L to H) and D
/ A converter 29. The calculation of the code error rate ERN in step S17 is performed by comparing the data error-corrected by the Viterbi decoding in step S15 with the data before error correction.
Next, in step S19, the scramble is descrambled (descramble), and in step S21, a CRC check is performed and a microprocessor (MPU) 31 for controlling the entire digital broadcast receiving apparatus 50 as a mute control signal.
Is supplied to.

On the other hand, in step S25, the subchannel data corresponding to the program selected by the user is separated from the plurality of subchannels. Next, step S2
In 7, time de-interleaving for canceling time interleaving for randomizing errors on the time axis is performed. By the way, for FIC,
No interleaving is done. Then, in step S29
Then, Viterbi decoding is performed, descrambling is performed in step S31, and DAB audio frame (DAB
Audio frame) is the MPEG decoder 2 of FIG.
It is output to 7. In step S29, the FI
Similar to the case of C, the code error detection and correction for the convolutionally encoded data is performed by Viterbi decoding.

OFDM, which is a DAB modulation system, is a type of multi-carrier modulation system and is said to be capable of stable reception in mobile communications, which is unlikely to suffer from multipath and fading. However, actually, the received data will have some degree of code error due to various causes. Therefore, as described above, the FIC or MSC data is error-corrected by Viterbi decoding, the error-corrected data is re-encoded, and the code error rate is calculated by comparing with the data before the error correction. . When the bit error rate exceeds a predetermined value, MP
The operation of the EG decoder 27 is stopped, and the D / A converter 29
The output from is stopped.

[0013]

However, the code error rate using Viterbi decoding does not always match the magnitude of noise and distortion on the actual hearing, which is why
Although the code error rate is smaller than a predetermined limit code error rate (threshold value), noise or distortion may be noticeable in the acoustic signal output from the speaker.

On the other hand, depending on the user who receives the data and the type of the source (signal source) of the received broadcast, it may be desired to keep the output uninterrupted even if there is some noise or distortion. For example, when the received program is news or traffic information, the user wants to continue the reception if he / she can grasp the broadcast content even if there is some noise or the sound quality is poor. Think In such a case, in the conventional digital broadcast receiving apparatus, the limit code error rate, which is a threshold value for starting the mute operation, is fixed for each digital broadcast receiving apparatus, and exceeds a preset limit code error rate. Unconditionally MPEG
There is a problem in that the output of the decoder 27 or the D / A 29 is stopped, and it is not possible to meet various requests generated for each user or each case.

The present invention has been made in view of the above problems, and an object thereof is to make it possible to change the mode of the mute operation as necessary, and to receive even when the received signal contains a relatively large amount of noise. It is an object of the present invention to provide a digital broadcast receiving device capable of performing the above.

[0016]

The present invention has the following structure to achieve the above object. First
According to another aspect of the present invention, an error rate calculating means for calculating a code error rate of a received signal during reception of a digital broadcast, and a magnitude of a code error rate of the received signal, a first limit code error rate and a second code error rate. , An output mode setting means for setting the output mode, a decoding means for decoding the received data of the digital broadcast, a D / A converter for converting the output of the decoding means into an analog signal, and the D / A conversion. A digital broadcast receiving apparatus comprising: a noise reducing unit for reducing noise of an analog audio signal output from a receiver, wherein the code error rate of the received signal is substantially smaller than the first limit code error rate. The analog audio signal is output without passing through the noise reducing means, and the code error rate of the received signal is equal to or higher than the first limit code error rate.
When the code error rate is less than or equal to the limit code error rate of, the analog audio signal is output through the noise reduction means, and when the code error rate of the received signal is larger than the second limit code error rate, the decoding means or the It is a digital broadcast receiving device in which the output of a D / A converter is stopped.

According to a second aspect of the present invention, the digital broadcast receiving apparatus of the first aspect further comprises error rate setting means for setting the first limit code error rate or the second limit code error rate. It is a digital broadcast receiving device.

A third aspect of the present invention is the digital broadcast receiving apparatus according to the first or second aspect of the invention, wherein the noise reduction means is a bandpass filter that passes only signals in a predetermined frequency range. It is a device.

A fourth aspect of the invention is a digital broadcast receiving apparatus according to the second aspect of the invention, wherein the operator can set the first limit code error rate or the second limit code error rate from outside. It is a device.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A digital broadcast receiving apparatus of the present invention comprises an output mode setting means for setting an output mode according to a code error rate of a received signal, and a decoding means for decoding compressed received data of a digital broadcast. A D / A converter for converting the output of the decoding means into an analog signal, and the D / A
Noise reducing means for reducing noise of the analog audio signal output from the converter, and when the code error rate of the received signal is smaller than the first limit code error rate, the noise reducing means is not substantially used. The analog audio signal is output to the first and the code error rate of the received signal is
Is equal to or more than the second limit code error rate and is equal to or less than the second limit code error rate, an analog audio signal is output through the noise reducing means, and the code error rate of the reception signal is the second
The output of the decoding means or the D / A converter is stopped when the bit error rate is larger than the limit code error rate.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a digital broadcast receiving apparatus of the present invention. In FIG.
Elements having the same functions as those of the above are denoted by the same reference numerals, and the description thereof may be omitted in the following description. In the digital broadcast receiving apparatus 10 shown in FIG. 1, the digital broadcast wave coming from the antenna 11 is the same as that of the conventional example described in FIG. 4, and an audio information signal and an image information signal,
Character information and the like are transmitted after being compressed in a predetermined format. In the digital broadcast receiver of the embodiment of the present invention described below, DAB (Digital Audio Broadcas
ting) A receiver will be described as an example. Further, in this DAB, it is assumed that OFDM (Orthogonal Frequency Division Multiplexing Method) is adopted as a modulation method.

In FIG. 1, the main points different from FIG. 4 are output mode setting means 25, error rate setting means 35, and filter 3.
3 is provided and the frequency characteristic of the filter 33 is controlled by the MPU 32 according to the output of the output mode setting means 25. The filter 33 is, for example, a bandpass filter (bandpass filter) that passes only signals in a predetermined frequency range, and reduces noise included in the analog audio signal output from the D / A 29,
It is a filter for giving to the audio amplifier of the next stage. The frequency characteristic of the filter can be switched by the MPU 32, and the filter can be substantially turned through. Further, the filter 33 may be a low pass filter.

In the following description, a state in which the filter 33 has a flat frequency characteristic is referred to as a filter OFF state or a through state, and a state in which the filter 33 is a bandpass filter is referred to as a filter ON state. Filter OFF
In this condition, the output of the D / A 29 is substantially the same as that of the filter 33.
Is supplied to the audio amplifier of the next stage without passing through the filter. In the state of the filter ON, the output of the D / A 29 is substantially supplied to the audio amplifier of the next stage via the filter 33.
The output mode setting means 25 and the error rate setting means 35 may be configured not by independent hardware, but by the microprocessor (MPU) 32 to which the input means is connected to achieve their functions.

In the channel decoder 23, the code error of the code string in the demodulated OFDM signal output from the OFDM demodulator is detected by using Viterbi decoding, and the error using the MPU 32 or the like is detected, as described in the conventional example. The bit error rate of the received signal is calculated by the rate calculation means. In the error rate setting means 35, the first and second marginal code error rates are set or selected by the user and stored in the memory of the microprocessor (MPU) 32.

In the output mode setting means 25, the code error rate (ERN) output from the channel decoder 23,
From the output mode setting means 25, the magnitudes of the first limit code error rate (ERL) and the second limit code error rate (ERH) set or selected by the user are compared, and the output mode according to the result is compared. It is given to the MPU 32. MP
U32 controls the mute mode according to the output mode given from the output mode setting means 25. That is, ON / OFF of the filter 33 according to the output mode,
It controls execution / stop of decoding in the MPEG decoder 27.

Specifically, when the code error rate (ERN) of the received signal is smaller than the first limit code error rate (ERL), substantially without passing through the filter 33,
That is, the filter 33 is turned through and the analog audio signal is output from the filter 33 to the audio amplifier.
When the code error rate (ERN) of the received signal is equal to or higher than the first limit code error rate (ERL) and equal to or lower than the second limit code error rate (ERH), the filter 33 is turned on to output an analog audio signal. When the code error rate of the received signal is output and is larger than the second limit code error rate (ERH), the decoding operation of the MPEG decoder 27 is stopped and the output of the D / A 29 is stopped. In addition, D / A29
To prevent the decoded signal from being output from MP,
By not supplying power to the EG decoder 27, power can be saved.

FIG. 2 is a flow chart showing the procedure for generating the output mode signal in the present invention. In FIG. 2, FIG.
The same reference numerals are given to the steps of the same processing as, and the description thereof may be omitted. 2 is different from FIG. 5 in that an output mode setting step S40 including steps S35 and S37 is provided in FIG. 2, and an output mode signal indicating the output mode is obtained in step S17. Code error rate (ERN) and the first limit error rate (limit code error rate) (E) set or selected in step S35.
RL) and the second marginal error rate (marginal bit error rate) (E
It is generated according to the magnitude comparison result with RH). The code error rate ERN obtained in step S17 is the code error rate calculated using the data of the FIC being received, as described in the conventional example, and is actually the FIC data separated in step S13. On the other hand, Vidabi decoding is done,
Data that has been error-corrected by the Viterbi decoding is re-encoded,
Error detection is performed by comparing with the data before error correction, and the code error rate is calculated. The error rate calculating means for calculating the code error rate is actually composed of the MPU 32 or the like.

In step S35, the user sets or selects the first limit code error rate ERL and the second limit code error rate ERH by the error rate setting means 35. When the user sets the limit code error rate, the filter 33 is turned off to receive the digital broadcast, and when the reception condition deteriorates until the user feels that the reception limit is reached, the user sets the error rate setting means 35. By pressing the setting button of, the code error rate ERN at that time is stored in the memory of the MPU 32 as the first limit code error rate ERL.
Further, when the filter 33 is turned ON for reception and the reception state deteriorates before the user feels that the reception limit is reached, the user presses the setting button of the error rate setting means 35, and the code at that point is displayed. The error rate ERN is stored in the memory of the MPU 32 as the second limit code error rate ERH.

When the user selects the limit code error rate, a plurality of options of the limit code error rate are preset in the digital broadcast receiving apparatus for each of the first limit code error rate and the second limit code error rate. Then, the prepared plurality of options are displayed on the display means 37, the user selects one of them, and the selected code error rate is used as the first or second limit code error rate. It may be stored in the memory of the error rate setting means 35.

In step S37, the code error rate ERN of the received signal is compared with the first limit code error rate ERL and the second limit code error rate ERH to determine the code error rate ERN of the received signal. When it is smaller than the first limit code error rate ERL, the output mode signal is 0.
When 0 is given to the MPU 32 and the code error rate ERN of the received signal is not less than the first limit code error rate ERL and not more than the second limit code error rate ERH, 01 is given as the output mode signal to the MPU 32. , The code error rate ERN of the received signal is the second limit code error rate ERH
When it is larger, 11 is MP as the output mode signal.
Given to U32.

When the output mode signal is 00, based on the control signal given from the MPU 32,
The filter 33 is controlled to be OFF, and the MPEG decoder 2
The output of 7 is not affected by the filter 33, and the output of D / A 29
Is output via. When the output mode signal is 01, the filter 33 is controlled to be ON based on the control signal given from the MPU 32, and the output of the MPEG decoder 27 is band-limited by the filter 33 to reduce noise, Is output. Furthermore, when the output mode signal is 11, the decoding operation of the MPEG decoder 27 is stopped or the D / A 29 of the D / A 29 is stopped based on the control signal supplied from the MPU 32. The output is stopped and the mute operation is performed.

On the other hand, from the MSC data separated in step S13, a specific subchannel is separated in step S25 in order to receive a desired program, and time de-interleave and Vidabi are added to the separated data. Decryption and descrambling are performed, and D is performed in step S31.
AB audio frame (DAB Audio Fra
me) is output. As the code error rate of the received signal used in step S37, the code error rate of the received signal obtained in step S17 is replaced with step S29.
The code error rate of the received signal obtained in step 1 may be adopted. Alternatively, the output mode may be set using both the code error rate of the received signal obtained in step S17 and the code error rate of the received signal obtained in step S29.

FIG. 3 is a flow chart showing the output mode setting procedure in the present invention. In FIG. 3, in step S51, the current code error rate ERN is calculated, and the process proceeds to step S53. In step S53, it is determined whether or not the current code error rate ERN is equal to or higher than the first limit code error rate ERL, and if affirmative, the process proceeds to step S55, and if negative, an output mode signal [00] is output. Step S57
Go to. In step S57, the decoding by the MPEG decoder 27 is started or continued, and the analog audio signal is output from the filter 33 to the next-stage audio amplifier while the filter 33 is OFF (through). Then, the process proceeds to step S63.

At step S55, the current code error rate ER
It is determined whether N is larger than the second limit code error rate ERH, and if affirmative, the output mode signal [11] is output and the process proceeds to step S59.
[01] is output and the process proceeds to step S61. Step S5
At 9, the decoding by the MPEG decoder 27 is stopped, or the output of the D / A 29 is stopped and muted, and the process proceeds to step S63. In step S59, if the power supply to the MPEG decoder 27 is stopped, the power consumption can be reduced. In step S61, MPE
The decoding by the G decoder 27 is started or continued, and the filter 3
Filter 3 for analog audio signals when 3 is ON
3 to the audio amplifier of the next stage, and step S6
Go to 3. In step S63, it is determined whether or not the reception stop button has been pressed, and if there is a stop instruction, step S6
5, the process proceeds to step S51 if there is no cancel instruction. In step S65, the power of the tuner is turned off to stop this flow.

As described in detail above, according to the embodiment to which the present invention is applied, the limit code error rate is not set to one fixed value at the time of manufacturing the digital broadcast receiving apparatus as in the conventional case. , A first limit code error rate and a second code error rate are set. When the code error rate of the received signal is equal to or higher than the first limit code error rate and equal to or lower than the second code error rate, the audio signal converted into the analog signal by the MPEG decoding is noisy using the band limiting filter. The noise is suppressed by the reducing means and output to the audio amplifier in the next stage.

Therefore, when there is a lot of noise in a weak electric field area or the like, it becomes possible to view a broadcast that could not be viewed due to the operation of the mute circuit, so that important information such as news and traffic information can be continued. It becomes possible to watch. Further, by making it possible to set the first limit code error rate and the second limit code error rate according to the user's request, it becomes possible to meet the individual request. That is, it is possible to change the mode of the mute operation to the optimum mode by resetting the limit code error rate according to the individual feeling of the user and the broadcast content. For example, in the case of music broadcasting, the critical code error rate is set small, and in the narration of news, traffic information, weather forecast, etc., the critical code error rate is set large, so that important news, traffic information, weather forecast, etc. The risk of being missed is reduced.

When a program type signal indicating whether the broadcast being transmitted is a video-centric broadcast, an audio-centric broadcast, an emergency broadcast, or the like, when the broadcast content is transmitted, The limit code error rate may be automatically set based on the program type signal. Further, in the above-described embodiment, when the code error rate of the received signal is smaller than the first limit code error rate, the analog audio signal is output substantially without going through the noise reduction means. In case,
When the analog audio signal is output through the first filter having a wide pass band, and the code error rate of the received signal is equal to or higher than the first limit code error rate and equal to or lower than the second limit code error rate, Even if the analog audio signal is output via the second filter having a narrower pass band than that of the first filter, it does not depart from the gist of the present invention and the same effect can be obtained. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a digital broadcast receiving apparatus of the present invention.

FIG. 2 is a flowchart showing a procedure for generating an output mode signal in the present invention.

FIG. 3 is a flowchart showing an output mode setting procedure in the present invention.

FIG. 4 is a block diagram showing an example of a conventional digital broadcast receiving apparatus.

FIG. 5 is a flowchart showing a procedure for generating an output mode signal in a conventional example.

FIG. 6 is a diagram showing a structure of a transmission frame in the DAB system.

[Explanation of symbols]

21 OFDM demodulator 23 channel decoder 25 Output mode setting means 27 MPEG decoder 29 D / A converter 32 microprocessors (MPU) 33 Noise reduction means (filter) 35 Error rate setting means 37 display means

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5C026 DA06 DA09                 5C063 AA20 AB03 AC05                 5K052 AA01 BB04 DD02 EE12 EE17                       EE40 FF07 FF12 GG03                 5K061 AA10 BB06 CC25 CC42 CC45                       CD08 FF12 JJ06

Claims (4)

[Claims] 1. An error rate calculating means for calculating a code error rate of a received signal during reception of a digital broadcast, and a code error rate of the received signal, a first limit code error rate and a second code error rate. An output mode setting means for comparing the magnitudes to set an output mode, a decoding means for decoding received data of digital broadcasting, a D / A converter for converting an output of the decoding means into an analog signal, and the D / A. A digital broadcast receiving apparatus comprising: a noise reducing unit for reducing noise of an analog audio signal output from a converter, wherein a code error rate of the received signal is smaller than the first limit code error rate, The analog audio signal is output without substantially passing through the noise reduction means, and the second limit code error is equal to or higher than the first limit code error rate of the received signal. When the ratio is less than or equal to the ratio, an analog audio signal is output via the noise reduction means, and when the code error rate of the received signal is larger than the second limit code error rate, the decoding means or the D /
A digital broadcast receiving apparatus characterized by stopping the output of an A converter. 2. The digital broadcast receiving apparatus according to claim 1, further comprising error rate setting means for setting the first limit code error rate or the second limit code error rate. Digital broadcasting receiver. 3. The digital broadcast receiving apparatus according to claim 1 or 2, wherein the noise reduction means is a bandpass filter that passes only signals in a predetermined frequency range. 4. The digital broadcast receiving apparatus according to claim 2, wherein the first limit code error rate or the second limit code error rate can be set from the outside.