JPH11340853A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reflect sense of audible noise on a reference value for evaluating the received state of a reproduced output by extracting protection level information from a reception signal, for certifying the reference value corresponding to the extracted protection level information, and deciding the reception state of the reception signal based on the reference value and the reception signal. SOLUTION: A MUSICAM(mask patterned adapted universal sub-band integrated coding and multiplexing) decoder 16 of a digital audio broadcasting(DAB) receiving parts outputs the frame error information A of received data, and an RDS decoder 23 of an FM receiving part outputs the block error information B of the RDS data received. A system control part 1 calculates the error ratio of the DAB and FM receiving parts based on the error information A and B and compares the error ratio of the DAB receiving part with a reference value selected from among the reference values corresponding to the protection level of a storage part 5, and evaluates the reception state of a DAB station. As a result, the sense of audible noise and the decision result can always be made to match.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast receiver, and more particularly to a digital audio broadcast receiver which is already in practical use in Europe.
ng; hereinafter referred to as DAB).

[0002]

2. Description of the Related Art As a system for transmitting and receiving a broadcast wave having a data signal of a predetermined format including a digital audio signal, a European standard (Eureka 14) is used.
There is a DAB system conforming to 7). In DAB, 1
An ensemble consists of several services, each of which consists of several components, such as English and German.

FIG. 7 shows an example of a service configuration of the DAB system. The services (three in this case) constituting the ensemble 1, each component (six in this case) and the D
FIG. 3 is a diagram illustrating a link with an OFDM signal transmitted from an AB station.

The OFDM signal transmitted from the DAB station is
It is divided into FIC (Fast Information Channel) and MSC (Main Service Channel).

Each sub-channel (Su) constituting the MSC
bCh0 to 63) have a correspondence with the above components, and the FIC includes information on services available in the ensemble and information indicating links between services, components, and subchannels.

[0006] Therefore, in DAB, when a certain ensemble is received, information on a plurality of services and components included in the ensemble can be obtained.
It is possible to switch instantly to different services and components without changing the reception frequency.

One of the uses of the DAB receiver for receiving the broadcast is a service follow-up function for FM stations that provide the same program. This function will be described below. In the DAB, various information data included in the FIC can include information about an FM station that broadcasts the same program as the program being received. For example, identification information and frequency information of an FM station that broadcasts the same program correspond to this.

Therefore, such information is obtained from the FIC obtained from the DAB station during reception, and based on this information, R
FM that broadcasts the same program by controlling the DS receiver
It is possible to easily tune to the station.

Therefore, the reception state of the currently tuned DAB station is compared with the reception state of the tuned FM station. If the reception state of the DAB station deteriorates, the reproduction output is switched to the audio output of the FM station broadcasting the same program ( Service follow) can maintain good reproduction sound.

On the other hand, in DAB, the bit rate of audio information can be defined for each sub-channel, and further, the protection level (1 to 5) of transmission can be defined.

The protection level indicates the strength against a transmission error (the larger the number, the higher the coding rate, the lower the redundancy and the weaker the error), and convolutional coding and coding according to the protection level. An encoding rate is defined by extracting (puncturing) a part of the subsequent signal. DAB specifies that the average code rate obtained from the bit rate and the protection level of audio information takes a value of 0.34 to 0.75. This information is also transmitted by FIC.

[0012]

However, without considering the protection level of audio information, for example,
Only parameters such as error rate (error rate)
When trying to determine the reception state of the AB station, there is a problem that the noise perception differs depending on the protection level even at the same error rate. In other words, between a program with a high protection level and a program with a low protection level, a program with a high protection level has a greater noise perception even at the same error rate, and the detection accuracy of the reception state varies greatly. Therefore, for example, a problem arises in that the sense of noise at the time of switching the service follow differs depending on the protection level of the selected service.

In view of the above, it is an object of the present invention to reflect a sense of noise in the audibility to a reference value for evaluating a reception state of a reproduction output.

[0014]

According to the present invention, a plurality of protection levels are provided, and a coding rate of a signal to be transmitted can be changed corresponding to each protection level. A digital broadcast receiver for receiving a digital audio broadcast capable of transmitting the protection level information, wherein the digital broadcast receiver extracts the protection level information from a received signal, and determines a reference value corresponding to the extracted protection level information. A reception state of the reception signal is determined based on a value and the reception signal.

According to a second aspect of the present invention, in the digital broadcast receiver according to the first aspect, the digital broadcast receiver has a table for associating a plurality of reference values with a plurality of the protection levels. And determining a reference value of 1 from the table based on the extracted protection level information.

According to a third aspect of the present invention, in the digital broadcast receiver according to the first aspect, the digital audio broadcast can further transmit audio bit rate information of the digital audio information. The audio bit rate information is extracted from the received signal, and the reference value is determined using the extracted bit rate information.

According to a fourth aspect of the present invention, in the digital broadcast receiver according to the third aspect, the digital broadcast receiver comprises a plurality of reference values, a plurality of the protection levels, and a plurality of the audio bit rates. A table for associating the information with the information, and based on the extracted protection level information and audio bit rate information,
Is determined from the table.

According to the fifth aspect of the present invention, the FM receiving section including the RDS decoder, the DAB receiving section, the receiving state of the FM receiving signal received by the FM receiving section, and the DA receiving section.
And a control unit that controls the output of the receiving unit that indicates a good reception state to be the output of the receiver based on the reception state of the DAB reception signal received by the B reception unit. In addition, the control unit has an extracting unit that extracts at least protection level information from the DAB reception signal, and determines a reception state of the DAB reception signal based on the extracted protection level information and the DAB reception signal. It is characterized by doing.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a digital broadcast receiver provided with an RDS receiver according to a first embodiment of the present invention. The receiver includes a DAB receiving section for receiving digital broadcasting, an FM receiving section for receiving RDS broadcasting, a system control section 1, a switching section 2, an amplifier 3, a speaker 4, a storage section 5, It is composed of

The DAB receiving section includes a DAB-FE (DAB front end) 11 for performing tuning control for the DAB station, an A / D converter 12 for converting a received analog signal into a digital signal, and demodulates an OFDM wave. (Fast Fourier transform) unit 13 for decoding, a differential demodulation unit 14 for demodulating differential modulation, a Viterbi decoding unit 15 for error correction, and converting compressed audio data (Musicam Data) into original audio data. Musiccam decoder for restoration (Musicam
Decoder) 16 and the like, but the specific configuration of each section is known in various documents and will not be described in detail here. Also, the music cam decoder 16 outputs frame error information relating to an error in the audio frame of the received data to the system control unit 1.

The FM receiving section includes an FM-FE (Front End for FM) 21 for performing tuning control to the FM station, an FM signal for amplifying the intermediate frequency (IF) signal, and detecting a composite signal from the signal. The detector 22 extracts an RDS signal from the composite signal and demodulates the RDS signal.
Although a decoder 23 and the like are included, such a configuration is also known in various documents and will not be described in detail here. In addition, the RDS that the FM receiver receives as well as the DAB receiver
The block error information relating to the data block error is output to the system control unit 1.

The system control unit 1 includes a DAB receiving unit, an FM
While controlling the receiving unit, the DAB receiving unit
The IC information is read, and various information data included in the data is stored in the storage unit 5. The stored information includes:
Information on services available in the ensemble, information indicating links between services, components, and sub-channels, information on FM stations (PI code, FI (Freque
ncy Information) list information). Further, the system control unit 1 outputs the read PI code and FI list information to the FM-FE unit 21 and the RDS decoder 23 so that the FM receiving unit can quickly detect a candidate station for service follow. I do.

The system control unit 1 further controls the switching unit 2. Specifically, if it is determined that the service received by the DAB receiving unit has a better reception status (or the reception status is approximately the same) than the service received by the FM reception unit, the DAB The reproduction sound of the reception unit is selectively output, and when it is determined that the reception state of the FM reception unit is better than the reception state of the DAB reception unit, the reproduction sound of the FM reception unit is selectively output. The output reproduced sound is amplified by the amplifier 3 and output from the speaker 4. The above is the outline of the digital broadcast receiver.

Next, the operation of the system control unit 1 according to the present invention will be described in detail. FIG. 2 is a flowchart showing the operation of the system control unit 1 in the service follow mode. Note that this flowchart is executed in response to an instruction to perform a service follow being input by a user. When an instruction to perform service follow is input by the user, the system control unit 1
It is determined whether or not the DAB receiving unit is currently tuned to one of the ensembles (step S1).

In the case of tuning to any of the ensembles, the transmitted FIC data can be obtained. Therefore, the FIC data is decoded, and the information on the protection level and the bit rate, which is available in the ensemble, is obtained from the decoded FIC data. The information of the service, the information indicating the service, the component, the link between the sub-channels, the PI code, the FI list information, and the like are extracted and stored in the storage unit 5 (step S2).

Thereafter, a service desired by the user is selected based on the acquired information, and the selected service is output from the speaker 4 (step S3).

After outputting the sound, the system control unit 1
The error rate BER of each of the receiving units is calculated based on the error information supplied from the receiving unit and the FM receiving unit (step S4). A specific method of calculating the error rate will be described later.

Next, the DAB calculated in step S4
The error rate BER of the signal is compared with a reference value (Step S)
5). At this time, first, based on the information on the protection level acquired and held in step S2, a reference value for evaluating the reception state of the currently selected subchannel is selected from a corresponding table in the storage unit 5.

FIG. 3 shows an example of a table configured in the storage unit 5. The table is created so as to correspond to the protection level PL, and is configured so that reference values corresponding to selectable protection levels 1 to 5 defined by DAB can be obtained.

For example, if the protection level of the currently received DAB reception signal is 1, a reference value 1 is determined as a corresponding reference, and this is selected as a reference value for comparison.

Next, the selected reference value and the D
The error rate BER of the AB signal is compared with the error rate BER. As a result of the comparison,
If it is determined that the error rate BER of the DAB signal calculated this time is smaller than the reference value (step S5: small), DAB
Since the reception state of the station has not deteriorated, the flow returns to step S4, and the error rate BER is calculated again based on the frame error information supplied at that time (step S4), and is compared with a reference value (step S5). . Therefore, when the reception state is good, the loop of steps S4 and S5 is circulated.

On the other hand, if the result of comparison between the selected reference value and the error rate BER calculated this time indicates that the error rate calculated this time is larger than the reference value (step S5: large),
Since this means that the reception state of the DAB station has deteriorated, the process shifts to step S6 to determine whether service follow-up to the RDS station broadcasting the same program is possible. In particular,
First, it is determined whether or not the same program is being broadcast in the FM band (step S6), and then it is determined whether or not there is the same program FM-RDS station with a better reception status from the DAB station (step S7).

If it is determined in step S7 that the service follow is possible, the system control unit 1 controls the switching unit 2 in step S8 to reproduce the sound of the RDS station.

On the other hand, if it is determined in steps S6 and S7 that an RDS station suitable for service follow cannot be found, the process returns to step S4 to continue monitoring the reception status of both receivers. For example, if the reception state of the FM receiving unit improves during this monitoring, it is determined that service follow is possible in step S7, and the system control unit 1 controls the switching unit 2 to reproduce the sound of the RDS station ( Step S
8).

The above is the operation of the service follow. In the present invention, when the reception state of the DAB station is evaluated in step S5, the optimum operation is performed based on the information on the protection level of the currently received DAB reception signal. By determining the evaluation reference value and determining the reception status based on the reference value and the DAB reception signal, always,
This makes it possible to match the sense of noise in the auditory sense with the determination result.

Next, the error rate calculation processing in step S4 will be described in detail. In the present invention, the DAB signal and the FM
Error information detected by each receiving unit is used as a parameter for evaluating a signal reception state. Specifically, FM
The reception state of the FM reception signal received by the reception unit is configured to be evaluated based on the block error rate of the received RDS data, and the DAB reception by the DAB reception unit is performed.
The reception state of the reception signal is configured to be evaluated based on the frame error rate of audio data (Musicam Data) constituting the sub-channel. This is based on the following findings.

FIG. 4 is a diagram comparing RDS data with audio data transmitted by DAB. In FIG. 4A,
FIG. 4B shows a configuration of DAB audio data.
3 shows a configuration of DS data.

As is well known, the RDS data has an offset A
~ D constitutes one group with four data blocks,
This is a transmission method capable of detecting the presence or absence of an error in a block unit, and one block is composed of 22 ms.

On the other hand, the audio data of DAB is MPEG1
According to Layer 2, one frame is composed of 24 ms. Not only the data of each subband but also a DAB header, bit allocation information, Sc
Information such as FSI is arranged. In addition, DAB
A CRC provided for error detection of a header, bit allocation information and ScFSI, and a CRC provided for error detection of a scale factor are included in one frame. Therefore, the presence / absence of an error can be detected in units of frames (hereinafter, referred to as blocks in the same manner as RDS data for convenience of description) by such CRC.

The applicant of the present application has noticed that the length of one block in both systems is substantially the same, and uses the block error rate BER of the audio data to determine the reception state of the DAB reception signal. The block error rate of the RDS data was used for the determination of the reception state.

The reason for this is as follows. If the number of blocks serving as the denominator of the block error rate is set to be substantially the same, the time error of the data group used for the judgment is reduced by 10% between the two methods.
This is because it is possible to determine the reception state under extremely close conditions.

Further, there is a proportional relationship between the block error rate of the RDS data and the sense of noise of the analog voice.
Can be accurately correlated with the FM error reception state.

Therefore, the use of the block error rate makes it possible to evaluate both receiving units having different transmission systems under extremely close conditions.

(Second Embodiment) In the first embodiment, an example in which the block error rates are compared in order to perform service follow satisfactorily has been presented. However, in the second embodiment,
An example in which an estimated error rate for estimating an error based on input / output data of a Viterbi decoder is employed as a detection method of a reception state of a DAB station will be described.

FIG. 5 is a block diagram of a digital broadcast receiver adopting such a method. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description will be omitted.

The difference from the digital broadcast receiver shown in FIG. 1 is a re-encoding unit 17 provided for detecting the reception status of the DAB station. The output of the Viterbi decoder 15 as an error correcting means is subjected to convolutional coding and puncturing processing again by the re-encoding unit 17, and the system control unit 31
Is output to

The system control unit 31 delays the input signal of the Viterbi decoder 15 by a predetermined time in order to match the position of the data to be compared, and compares the delayed input data of the Viterbi decoder 15 with the re-encoded data. , A bit error of the DAB reception signal is detected.

Next, the error rate of the DAB reception signal is estimated by dividing the number of detected errors by the total number of compared samples. Next, an optimum reference value is determined based on the protection level information of the DAB reception signal, and the reception state of the DAB reception signal is determined based on the reference value and the calculated error rate.

The system control unit 31 controls the attenuator 32 based on the evaluated reception state. Specifically, the output of the speaker 4 is variably controlled by increasing the amount of attenuation in accordance with the deterioration of the reception state.

In the second embodiment, DAB
The evaluation of the reception state can be performed based on the evaluation criterion corresponding to the protection level of the reception signal.

(Other Embodiments) In the above embodiment, attention is paid to protection level information transmitted together with audio information. However, the present invention is not limited to this, and the same applies to audio bit rate information of audio data constituting a sub-channel. May be configured to determine the optimum reference value based on the audio bit rate information of the currently selected sub-channel. In other words, DAB uses MUSICA as an audio compression method.
M, audio bit rate is 32k
Since it can be changed from bit / s to 384 kbit / s,
This audio bit rate information is extracted from the DAB reception signal, and the optimum reference value is determined using the extracted information. Furthermore, the two can be combined to determine an optimum reference value based on protection level information and audio bit rate information.

FIG. 6 shows an example of creating a table in this case. In the figure, PL and BR are protection levels, respectively.
Indicates the audio bit rate. If the protection level information and the audio bit rate information are extracted from the received signal, one reference value can be determined using this table. For example, if the protection level is 1 and the audio bit rate is 32 kbit / s, the reference value 1.1 is determined.

Further, the D used in the first embodiment is used.
Instead of the block error rate of the AB data, the estimated error rate used in the second embodiment is used for determining the reception status of the DAB data, or the RD used in the first embodiment is used.
Instead of the block error rate of the S data, the received electric field strength can be used to determine the reception status of the RDS station.

[0054]

As described above, according to the present invention,
Since the protection level information is extracted from the received signal, and the reference value corresponding to the extracted protection level information is determined, the reception state of the received signal is determined based on the reference value and the received signal. The evaluation of the reception state can be performed based on the evaluation criterion corresponding to the protection level of the reception signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital broadcast receiver including an RDS receiving unit according to a first embodiment of the present invention.

FIG. 2 is a flowchart executed by the system control unit 1.

FIG. 3 is a table configured inside a storage unit 5;

FIG. 4 is a diagram comparing DAB data and RDS data.

FIG. 5 is a block diagram of a digital broadcast receiver according to a second embodiment of the present invention.

FIG. 6 is a table configured inside a storage unit 5;

FIG. 7 is a service configuration example of a DAB system.

[Explanation of symbols]

 1 System control unit 2 Switching unit 3 Amplifier 4 Speaker 5 Storage unit 11 Front end 12 A / D conversion Unit 13 FFT 14 Differential demodulation unit 15 Viterbi decoder 16 Music cam decoder 17 Re-encoding unit 21 Front end 22 Detector 23 RDS decoder 31 System control unit 32 Attenuator

Claims (5)

[Claims] 1. A digital audio broadcast having a plurality of protection levels, wherein a coding rate of a signal to be transmitted can be changed corresponding to each protection level, and a digital audio broadcast capable of transmitting at least the protection level information together with digital audio information. A digital broadcast receiver, wherein the protection level information is extracted from a received signal,
A digital broadcast receiver, comprising: after determining a reference value corresponding to the extracted protection level information, determining a reception state of the received signal based on the reference value and the received signal. 2. The digital broadcast receiver according to claim 1, further comprising a table for associating a plurality of reference values with the plurality of protection levels, and determining one reference value from the table based on the extracted protection level information. The digital broadcast receiver according to claim 1, wherein: 3. The digital audio broadcast can further transmit audio bit rate information of the digital audio information, extract the audio bit rate information from a received signal, and use the extracted bit rate information. The digital broadcast receiver according to claim 1, wherein the reference value is determined. 4. The digital broadcast receiver has a table associating a plurality of reference values, a plurality of the protection levels, and a plurality of the audio bit rate information, wherein the extracted protection level information, the audio bit rate information, 4. The digital broadcast receiver according to claim 3, wherein one reference value is determined from the table based on the following. 5. An FM receiving unit including an RDS decoder,
An AB receiving unit, a receiving state of an FM receiving signal received by the FM receiving unit, and a DA receiving by the DAB receiving unit.
A control unit that controls the output of the receiving unit that indicates a good reception state based on the reception state of the B reception signal and the output of the receiver, and the control unit includes: A digital broadcast comprising extracting means for extracting at least protection level information from the DAB reception signal, and determining a reception state of the DAB reception signal based on the extracted protection level information and the DAB reception signal. Receiving machine.