JP3842585B2 - Digital broadcast receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital broadcast receiver.
[0002]
[Prior art]
In the conventional digital broadcast receiver, as shown in the flowchart of FIG. 8, when the digital broadcast receiver is used for the first time or when the digital broadcast receiver is reset (step S31), a broadcast station that can currently receive is selected. All the stations are searched and it is checked whether or not the frequency table of the broadcasting station is stored in the preset memory or the like (step S32). If it is determined that it is not stored, all the broadcasting stations that can be currently received are searched. Then, the frequency of the broadcasting station that can be received by the search is stored in the preset memory or the like in the form of a frequency table (step S33), and the preset key is pressed to select and receive (step S33). S34).
[0003]
In step S32, when it is determined that the frequency table of the broadcasting station that can be currently received is stored in the preset memory or the like, the current reception area checked from the instruction manual or the like by operating the menu screen A number is designated (step S36), and a preset key is pressed to select a channel for reception (step S34).
[0004]
In step S31, when it is not at the time of initial use or when it is not reset, channel selection is performed by directly pressing a preset key to perform reception.
[0005]
Further, in the in-vehicle digital broadcast receiver or the like, as shown in FIG. 9, the digital broadcast reception tuner 31 and the digital broadcast reception tuner 32 are used for the purpose of improving the deterioration of the reception situation caused by the movement of the reception position. When the diversity digital broadcast receiver is used, for example, as shown in the flowchart of FIG. 10, while the tuner 31 receives a digital broadcast, the tuner 32 searches for other broadcast stations (step S41). A frequency table of receivable broadcasting stations is created by the search (step S42), and it is checked whether or not the frequency table created in step S42 has changed from the already created frequency table (step S43).
[0006]
When it is determined in step S43 that the frequency table has changed, it is checked whether or not the reception state by the tuner 31 has changed (step S44). When it is determined that the reception state has changed, it is stored in a new frequency table. It is also possible to receive a broadcast station having a frequency at the tuner 32 (step S45).
[0007]
[Problems to be solved by the invention]
However, according to the above-described conventional method, for example, in the case of digital broadcasting performed in Europe, since there are various combinations of broadcasting systems unlike current analog broadcasting, it takes time to identify the broadcasting station. There is a problem that a considerable amount of time is required for searching.
[0008]
In addition, since it is a digital broadcast, there is a problem that it is difficult to search for a broadcast station at a speed similar to that of a radio for an analog broadcast, which takes time.
[0009]
Furthermore, in order for the user to select an area at the time of initial use, it is necessary to check the area number from the instruction manual or the like and enter its input mode. There was a problem that it took time to turn on the region after turning on the power.
[0010]
Furthermore, there is a problem that it is inefficient to use a plurality of tuners.
[0011]
An object of the present invention is to provide a digital broadcast receiver that can obtain information such as whether or not a broadcast station of another frequency can be received without substantially interrupting the received sound with one tuner.
[0012]
[Means for Solving the Problems]
The digital broadcast receiver according to the present invention automatically searches for other receivable broadcast stations in a reception null symbol period during broadcast reception of an arbitrary broadcast station after power-on or reset, and the frequency of the received broadcast station A means for creating and storing a table is provided.
[0013]
According to the digital broadcast receiver of the present invention, other receivable broadcast stations are automatically searched for in a reception null symbol period during broadcast reception of an arbitrary broadcast station after power-on or reset. Since the frequency table is created and stored, it is possible to obtain information such as whether or not to receive broadcast stations of other frequencies without substantially interrupting the received sound with one tuner.
[0014]
In addition, unlike analog broadcasting, digital broadcasting is interrupted for more than the time used for switching if switching at a certain timing, but in the digital broadcasting receiver of the present invention, search is performed during the null symbol period. This is not the case and the output sound is not interrupted.
[0017]
In the digital broadcasting receiver of the present invention, while receiving a broadcast station search period of the received null symbol period, characterized by comprising a means for stopping the synchronization flag detection processing of the detected broadcasting station.
[0018]
According to the digital broadcast receiver of the present invention , since the detection of the synchronization flag of the detected broadcast station is stopped during the reception broadcast station search period of the reception null symbol period, it is originally received during the search for other broadcast stations. The decoding of other information outside the null symbol period of the broadcasting station that is being performed is not stopped.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a digital broadcast receiver according to the present invention will be described according to an embodiment.
[0020]
FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiver according to an embodiment of the present invention, and illustrates a case of a DAB broadcast receiver.
[0021]
Before describing the configuration of the digital broadcast receiver 1 according to the embodiment of the present invention, a transmission frame in DAB will be described.
[0022]
In DAB, OFDM modulation is used. As shown in FIGS. 5 and 6, a DAB transmission frame (in the case of mode 1) has a transmission frame (period of one transmission frame = 96 ms) as a null symbol (null symbol period). (Tnull = 1.297 ms)), PRS (Phase Reference Symbol), which is a fixed symbol for timing calculation, and 12 FIB (Fast Information Block), and FIC (Fast Information Channel) used for high-speed information access , 63 CIF (Common Interleaved Frame), and is composed of an MSC (Main Service Channel) used for audio and data component transmission.
[0023]
The PRS, FIB, and CIF have a time length of 1.296 ms, and include a guard interval of 0.246 ms and an effective symbol length Tu of 1 ms.
[0024]
Returning to FIG. 1, in the digital broadcast receiver 1, the received signal is supplied to the AGC circuit 4 including the variable gain amplifier 2 and the control circuit 3 that controls the gain of the variable gain amplifier 2, and is amplified. Is detected by the detector 5. Based on the detection output of the detector 5, the gain of the variable gain amplifier 2 is controlled via the control circuit 3 by the output obtained by converting the output from the microcomputer 18 for control by the D / A converter 20.
[0025]
The detection output from the detector 5 is frequency-mixed with the output of the PLL circuit 7 in the mixer 6 and converted into an intermediate frequency signal, and the intermediate frequency signal is supplied to the band pass filter 8 to be band-limited.
[0026]
The output from the band pass fill 8 is supplied to an AGC circuit 12 comprising a variable gain amplifier 9 and a power detector 11 for controlling the gain of the variable gain amplifier 9, amplified, and converted into digital data by an A / D converter 10. Then, it is supplied to the FFT circuit 12 via the power detector 11 and subjected to FFT conversion, and demodulated by the demodulator 14 and output as an audio signal.
[0027]
More specifically, the PLL circuit 7 receives the frequency division ratio information output from the microcomputer 18 and is set to a frequency that is frequency-mixed by the mixer 6, and the mixer 6 converts the received RF signal into an intermediate frequency signal. The intermediate frequency signal is A / D converted and then supplied to the power detector 11 and AGCed by the variable gain amplifier 9 so as to maintain an appropriate level.
[0028]
The output from the variable gain amplifier 9 is supplied to the detector 15 for detection, and the detection output from the detector 15 is A / D converted by the A / D converter 16 and supplied to the microcomputer 18 for detection by the detector 5. The detection output from the A / D converter 17 is also A / D converted by the A / D converter 17 and supplied to the microcomputer 18, and the received radio wave level of the broadcast received by the microcomputer 18 is recognized.
[0029]
On the other hand, a constant output from the output and the microcomputer 18 from the FF T circuitry 12 is multiplied by the multiplier 19 is supplied to the microcomputer 18, the microcomputer 18 based on the maximum multiplication output of the multiplier 19 A synchronization flag is detected.
[0030]
More specifically, the input PRS signal is subjected to FFT conversion by an FFT circuit 13, and the constant that is a conjugate complex number of the FFT-converted PRS signal and the FFT-converted PRS signal are converted by a multiplier 19. The cross correlation is obtained by multiplication, and an impulse response is obtained by performing inverse Fourier transform on the cross correlation power spectrum of the cross correlation, and this impulse response is output as a synchronization flag. Based on the detection timing of the synchronization flag, it is possible to distinguish between FIB in FIC and CIF in MSC.
[0031]
In the digital broadcast receiver 1 configured as described above, the operation within the null symbol time will be described with reference to FIGS.
[0032]
In the digital broadcast receiver 1, information on the reception frequency table of each region and a frequency table z of only representative frequencies (frequency of NHK broadcasting stations in Japan) are stored in the memory.
[0033]
When the digital broadcast receiver 1 is reset, the broadcast reception of the default broadcast station is accessed by accessing the broadcast reception of the default channel broadcast station (step S1). Following step S1, it is checked whether or not synchronization has been established. If it is determined that synchronization has not been established, a broadcast of the next frequency is searched according to the frequency table z (step S3).
[0034]
When it is determined in step S3 that synchronization has been achieved, demodulation is performed and an audio signal is output (step S4). Subsequent to step S4, a frequency table storing the received broadcast station frequency is called from the memory (step S5). Subsequent to step S5, only the broadcast of the corresponding frequency is sequentially searched during the null symbol period, and the broadcast of the frequency is received and detected (step S6).
[0035]
It is checked whether or not the level of the detection output in step S6 is greater than or equal to a threshold value (step S7). If it is determined in step S7 that it is not equal to or greater than the threshold value, the process is repeated from step S6. When it is determined in step S7 that the frequency is equal to or higher than the threshold value, the frequency of the broadcasting station is stored (step S8), the broadcast reception of the next frequency is performed (step S9), and the search operation from step S6 is repeated. When the frequencies of n broadcasting stations are stored (step S10), the frequency table x obtained by step S10 is compared with the frequency table in the memory, and the corresponding frequency table x is selected (step S11).
[0036]
Subsequent to step S11, the frequency table x is updated to the frequency table obtained in step S10 (step S12).
[0037]
By executing steps S1 to S12, the frequency table x is changed at the time of resetting.
[0038]
In addition, after the frequency table x is selected, all broadcast stations are searched and detected during the null symbol period (step S14), and it is checked whether or not the detection output is based on the reception of a broadcast at a frequency other than the existing frequency table. (Step S15). If it is determined in step S15 that the detection output is not based on broadcast reception of a frequency other than the existing frequency table, the process is repeated from step S14.
[0039]
If it is determined in step S15 that the output is a detection output based on broadcast reception at a frequency other than the existing frequency table, it is checked whether or not it is applicable to the frequency of the broadcast station in another frequency table y of the current frequency table x ( Step S16).
[0040]
If it is determined in step S16 that this is not the case, the frequency of the new broadcasting station is added to the frequency table x to form a new frequency table x (step S17), and the process is repeated from step S14.
[0041]
If it is determined in the check in step S16, following step S16, only the broadcast stations of frequency table x and frequency table y are sequentially received and detected (step S18), and at the time of broadcast reception of the frequency of frequency table y. It is checked whether the detection output exceeds the threshold and the detection output at the time of broadcast reception of the frequency in the frequency table x is less than the threshold (step S19).
[0042]
In the check in step S9, when the detection output at the time of broadcast reception of the frequency in the frequency table y does not exceed the threshold value and the detection output at the time of broadcast reception of the frequency in the frequency table x is greater than or equal to the threshold value, the processing is repeated from step S18. When the detection output at the time of broadcast reception of the frequency in the frequency table y exceeds the threshold value and the detection output at the time of broadcast reception of the frequency in the frequency table x is less than the threshold value, the frequency table y is changed (step S20). ).
[0043]
By repeating the above, a frequency table with a signal level equal to or higher than the threshold value is generated, and by comparing this generated frequency table with the recorded reception frequency table of each district in advance, it is possible to specify the region. Become.
[0044]
Next, in step S6 and step S14, the search during the null symbol period will be described with reference to FIG.
[0045]
While the broadcast of the broadcasting station A is being received, step S6 or step S14 is executed (step S101).
[0046]
Following step S101, it is checked whether (T1) ms has elapsed since the synchronization flag was detected (step S102). Here, (T1) ms is selected as 94.704 ms (= Tf−Tnull) <T1 <T2 <96 ms (= Tf).
[0047]
Here, in DAB, a signal is sent in a configuration as shown in FIG. Although the null symbol contains TII (broadcast station identification) information, there is basically nothing. Accordingly, although the null symbol period differs depending on the mode, information during the null symbol period is not necessary, and thus the tuner can search for signals from other stations during this period.
[0048]
The time for searching for another station is 96 ms after 94.704 ms after the next null symbol comes in the mode 1 from the synchronization flag obtained in the previous transmission frame, and the current reception immediately before 96 ms. If the control of the digital broadcast receiver 1 is matched with the broadcasting station, synchronization is not lost and all information except TII information is secured.
[0049]
When it is determined in step S102 that (T1) ms has elapsed, the AGC is fixed, that is, the gain of the variable gain amplifier is fixed, and the synchronization process is stopped (step S103).
[0050]
In step S103, the gains of the variable gain amplifiers 2 and 9 by the AGC circuits 4 and 12 are fixed because the variable gain by the AGC circuits 4 and 12 depends on the reception level of the broadcast station when searching for a broadcast station of another frequency. This is because the gains of the amplifiers 2 and 9 are changed so that the reception is not possible even when the reception signal level of the other broadcasting station is low.
[0051]
In addition, the synchronization process is stopped in step S103 because a new broadcast station is searched and received. Therefore, detection of the PRS signal in the received signal of the new broadcast station and detection of the synchronization flag are stopped. This is because the FIB in the FIC and the CIF in the MSC are not decoded.
[0052]
Subsequent to step S103, the broadcasting station A is set to N (step S104), and then it is checked whether N is a broadcasting station with the highest reception frequency (step S105). When it is determined in step S5 that N is a broadcasting station having the highest reception frequency, step S105 is executed with N being the broadcasting station having the highest reception frequency (step S106).
[0053]
When it is determined in step S105 that N is not the broadcasting station having the highest reception frequency, the broadcasting station is adjusted to the frequency of the next broadcasting station (N + 1) and detection is performed (step S107), and the detection output is equal to or greater than a predetermined threshold value. Is checked (step S108). When it is determined in step S108 that the threshold value is exceeded, the frequency of the broadcast station (N + 1) is stored (step S109), and it is checked whether (T2) ms has elapsed since the synchronization flag was generated (step S110).
[0054]
In step S110, when it is determined that (T2) ms have passed, the process returns to broadcasting station A (step S111).
[0055]
If it is determined in step S108 that the value is less than the threshold and it is determined that (T2) ms has elapsed since the generation of the synchronization flag (step S112), step S111 is executed. If it is determined in step S108 that the value is less than the threshold value and it is determined that (T2) ms has not elapsed since the generation of the synchronization flag, broadcasting station N = N + 1 is executed (step S114), and then the process is repeated from step S105. Executed.
[0056]
Following step S111, the AGC fixing process is released, that is, the gain of the variable gain amplifier is released, the synchronization process is stopped (step S115), and the synchronization flag is detected following step S115. After waiting (step S116), the broadcast station A returns to broadcast reception.
[0057]
As described above, when the user first turns on or resets the digital broadcast receiver 1, the frequency of the default broadcast station is first accessed. If this broadcast station does not exist, a representative of each region is accessed. The search is performed according to the frequency table of only the correct channel.
[0058]
The broadcast of the first broadcasting station that can be received in this operation is received, demodulated, and output as audio. Thereafter, another broadcast station is searched. At this time, in order to increase efficiency, only one or more frequency table channels to which the first received channel is registered are sought. While doing this work, the audio is virtually uninterrupted.
[0059]
It is not possible within this null symbol period to go to this other station search and accurately determine whether there is a DAB signal. This is because the null symbol period is 1.297 ms in the mode 1 and the PRS is 1.246 ms. For example, even if the station B is selected during the null symbol period of the station A, the station B of synchronization flag detection is for not be null symbol period is to detecting a signal of the frequency. If a signal level equal to or higher than a certain threshold exists, it is assumed that a broadcasting station exists for the time being.
[0060]
Further, synchronization is taken at the head of the PRS, and as a reference in terms of time, as shown in FIG. 6, the search for other broadcast stations is performed on the basis of information being sent after ts time. Further, as shown in FIG. 7 instead of FIG. 6, another broadcast station may be searched in the null symbol period indicated by the oblique line of the second transmission frame, with two transmission frames as one unit.
[0061]
Further, if the OFDM signal and other recognition are surely performed, as shown in FIG. 4, for example, three filters may be used for identification.
[0062]
That is, as shown in FIG. 4A and FIG. 4B, a bandpass filter 22 having a bandwidth of 100 kHz with the center frequency of the intermediate frequency that is the output of the bandpass filter 8 as the center frequency, A bandpass filter 21 having a bandwidth of 100 kHz having a center frequency of −500) kHz and a bandpass filter 23 having a bandwidth of 100 kHz having a center frequency of (the center frequency + 500) kHz are provided; This is because the output of 23 is detected by the detectors 24, 25, and 26, so that when the outputs from the detectors 24, 25, and 26 are generated, it can be determined that the signal is an OFDM signal.
[0063]
This is because the OFDM-modulated waves are transmitted at substantially the same level over a band having a bandwidth of 1.536 MHz with the center frequency as the center.
[0064]
In addition, when the position is moved by an in-vehicle digital broadcast receiver or the like, different situations may occur, such as inability to receive broadcast stations having the frequencies stored in the registered frequency table. Since such a situation may occur, the detection operation is performed for all broadcast stations after the frequency table is once determined. In this way, it is possible to recognize that the detection output level of a broadcasting station that could not be received has increased, and the detection output level of a broadcasting station that has been able to be received has decreased. It becomes possible to change automatically.
[0065]
【The invention's effect】
As described above, the digital broadcast receiver according to the present invention automatically searches for another receivable broadcast station in the reception null symbol period during broadcast reception of any broadcast station after power-on or reset. Since the broadcast frequency table is created and stored, the frequency table for other broadcast stations can be obtained without substantially interrupting the output sound.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiver according to an embodiment of the present invention.
FIG. 2 is a flowchart for explaining the operation of the digital broadcast receiver according to the embodiment of the present invention.
FIG. 3 is a flowchart for explaining the operation of the digital broadcast receiver according to the embodiment of the present invention.
FIG. 4 is a block diagram showing a schematic configuration of a DFDM signal identification circuit in the digital broadcast receiver according to the embodiment of the present invention.
FIG. 5 is an explanatory diagram for explaining a DAB transmission frame;
FIG. 6 is a flowchart for explaining a null symbol period for searching for another broadcast station in the digital broadcast receiver according to the embodiment of the present invention.
FIG. 7 is a flowchart for explaining a null symbol period for searching for another broadcast station in the digital broadcast receiver according to the embodiment of the present invention.
FIG. 8 is a flowchart for explaining a search operation of another broadcast station in a conventional digital broadcast receiver.
FIG. 9 is a block diagram showing a schematic configuration showing a configuration of a conventional two-tuner digital broadcast receiver.
FIG. 10 is a flowchart for explaining a search operation of another broadcast station in a conventional two-tuner digital broadcast receiver.
[Explanation of symbols]
2 and 9 Variable gain amplifiers 4 and 12 AGC circuits 5 and 15 Detector 6 Mixer 13 FFT circuit 18 Microcomputer 19 Multiplier

Claims (2)

Provided with means for automatically searching for other receivable broadcast stations in the received null symbol period during broadcast reception of any broadcast station after power-on or reset, and creating and storing a frequency table of the received broadcast station A digital broadcast receiver characterized by that. 2. The digital broadcast receiver according to claim 1, further comprising means for stopping the synchronization flag detection processing of the detected broadcast station during the reception broadcast station search period of the reception null symbol period. .

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