JP2002374467A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital broadcast receiver which can obtain information showing whether broadcasting stations of other frequencies can be received by one tuner substantially without break in video or sound. SOLUTION: In a reception guard-band period in the reception of a broadcast from an arbitrary broadcasting station after power-on or resetting, other receivable broadcasting stations are automatically searched for to generated and store a frequency table of the receivable broadcasting stations. During the period of the receivable broadcasting station search, the gains of variable gain amplifies 2 and 9 are fixed to the gains right before starting the search for the receivable broadcasting stations and synchronous detection processing by a microcomputer 20 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital broadcast receiver.

[0002]

2. Description of the Related Art In a conventional digital broadcast receiver, as shown in the flowchart of FIG. 8, when the digital broadcast receiver is initially used or when the digital broadcast receiver is reset (step S31), the current reception is performed. It is checked whether or not the frequency table of the broadcasting station is stored in the preset memory or the like (step S32), and if it is determined that the frequency table is not stored, it can be currently received. All the broadcasting stations are searched, and the frequencies of the broadcasting stations that can be received by the search are stored one by one in a preset memory or the like in the form of a frequency table (step S33), and a preset key is pressed to select a station. (Step S3
4).

If it is determined in step S32 that the frequency table of a broadcast station that can be received at present is already stored in the preset memory or the like, the menu screen is operated to check the current table determined from the instruction manual or the like. Is designated (step S36), and a preset key is pressed to select a station and perform reception (step S36).
34).

In step S31, when it is not the time of initial use or when it is not reset,
Tuning is performed by directly pressing the preset key, and reception is performed.

As shown in FIG. 9, a digital broadcast receiving tuner 31 and a digital broadcast receiving tuner 32 are used in an on-board digital broadcast receiver or the like, as shown in FIG.
In the case of using a diversity digital broadcast receiver using the following, for example, as shown in the flowchart of FIG. 10, while the digital broadcast is being received by the tuner 31, another broadcast station is searched by the tuner 32 (step S41). A frequency table of receivable broadcast stations is created by this search (step S42), and it is checked whether the frequency table created in step S42 has changed from the already created frequency table (step S42). S43).

If it is determined in step S43 that the frequency table has changed, it is checked whether or not the reception state of the tuner 31 has changed (step S4).
4) When it is determined that the reception state has changed, the tuner 32 may receive the broadcast station of the frequency stored in the new frequency table (step S45).

[0007]

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 the current analog broadcasting, there are various combinations. There is a problem that it takes a long time for identification and a considerable time is required for searching for a broadcasting station.

In addition, since digital broadcasting is used, a search for a broadcasting station cannot be performed at a speed as in the case of analog broadcasting.

Further, in order for the user to select a region at the time of initial use, it is necessary to check a region number from an instruction manual or the like and to enter an input transmission mode. This operation is one of the menu selection operations. For this reason, there is a problem that it takes time from turning on the power to ending the area selection.

[0010] Furthermore, there is a problem that the use of a plurality of tuners is inefficient.

An object of the present invention is to provide a digital broadcast receiver capable of obtaining information such as whether or not a broadcast station can receive another frequency without substantially interrupting the image and the received sound with one tuner. I do.

[0012]

SUMMARY OF THE INVENTION A digital broadcast receiver according to the present invention automatically controls other receiving broadcasting stations during a receiving guard band period during reception of broadcasting of any broadcasting station after power-on or reset. Means for generating a frequency table of the receiving broadcast station and storing the frequency table.

[0013] The digital broadcast receiver according to the present invention provides a terminal guard band period portion during a reception effective guard band period during power reception or after a broadcast of an arbitrary broadcast station after a reset, and a subsequent OFDM symbol period. In the guard band period, a means for automatically searching for another receiving broadcast station, creating a frequency table of the receiving broadcast station, and storing the frequency table is provided.

[0014] According to the digital broadcast receiver of the present invention, after the power is turned on or after the reset, an arbitrary guard station receives a broadcast during a reception guard band period or a terminal guard band period during a reception effective symbol period. In the part and the subsequent guard band period in the next OFDM symbol period, another receiving station is automatically searched and a frequency table of the receiving station is created and stored. Can be obtained without substantially interrupting the transmission of information.

Also, unlike the analog broadcasting, the digital broadcasting, if not switched at a certain timing, causes the sound to be interrupted more than the time used for the switching. However, the digital broadcasting receiver of the present invention searches during the guard band period. Therefore, such a situation does not occur, and the output sound is not interrupted.

The digital broadcast receiver according to the present invention is characterized in that a means for fixing the gain of the variable gain amplifier constituting the AGC circuit to the gain immediately before the start of the reception broadcast station search is provided during the period during the search for the reception broadcast station. .

According to the digital broadcast receiver of the present invention, since the gain of the variable gain amplifier constituting the AGC circuit is fixed to the gain immediately before the start of the search for the receiving broadcast station, the search is performed during the search for the receiving broadcast station. The gain of the AGC circuit is varied according to the received level of the broadcast station, and when the received level of the searched broadcast station is low, it is not determined that the signal can be received by the AGC circuit.

[0018] The digital broadcast receiver according to the present invention is characterized in that the digital broadcast receiver is provided with means for stopping the synchronization detection process during the reception broadcast station search period.

According to the digital broadcast receiver of the present invention, since the synchronization detection process is stopped, during the search for another broadcast station, the terminal guard band period portion during the reception effective symbol period and the subsequent OFDM symbol period Decoding of other information outside the guard band period is not stopped.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A digital broadcast receiver according to the present invention will be described below with reference to an embodiment.

FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiver according to an embodiment of the present invention, which is a terrestrial DVB (Digital Video) in the current Europe.
Broadcasting) receiver.

Before describing the configuration of the digital broadcast receiver 1 according to an embodiment of the present invention, a transmission frame in DVB will be described.

In DVB, OFDM modulation is used. As shown in FIG. 5, the DVB transmission system employs two transmission modes of 2k and 8k as a transmission mode, and １ ／ and ８ of an effective symbol length as a guard interval. , 1/1
6, 1/32, coding rate 1/2, 2 /
5, 3/4, 5/6, and 7/8, three types of modulation methods, QPSK, 16-QAM, and 64-QAM, none for multiplexing, and four types of (1, 2, 4), There are three types of bandwidths: 8, 7, and 6 MHz.

As shown in FIG. 6 (a), one OFDM symbol is composed of a guard band period and an effective symbol period, and the guard band is located after the effective symbol period (1/4, 1/8, 1/8, 1/8, 1/8 of the effective symbol period). 1/16 or 1
/ 32 is copied before the effective symbol as a guard band.

Therefore, the digital broadcast receiver 1 performs a search process for another channel during the guard band period. However, depending on the possible combinations shown in FIG. 5, the guard band period is short, and if the processing is slow, the search processing may not be possible. For example, if the transmission mode is 8k, the guard interval is 1/8, 112 μs, the transmission mode 2
For k, guard interval 1/32, there is only 7 μs. When the search period is short as described above, two guard interval periods of two OFDM symbol periods are used.

That is, if two consecutive OFDMs are taken, as shown in FIG. 6 (b), a part copied before the valid symbol as a guard band after the valid symbol and a guard band following the valid symbol are two guard band period lengths in the two OFDM symbol periods. In this period (the portion indicated by the thick arrow in FIG. 6B), another channel search process is performed, and the remaining effective symbol period before and after the period and the data in the guard band period before and after are searched for demodulated data. And

As shown in FIG. 7A, when the transmission frame has a transmission mode of 8k, a guard interval of 1/8, a coding rate of 3/4, 16QAM, and a bandwidth of 8 MHz,
Frame period length Tf = 68.544 ms, OFDM symbol length Ts (= Tu + Δ) = 1.008 ms, effective symbol length Tu = 0.896 ms, guard interval length Δ
= 0.112 ms, 1 frame = 680 symbols, FIG.
As shown in (b), superframe = 4 frames.

Further, a CP (continuous pilot) of a reference signal is included in one OFDM frame.
There are two signals called SP (scattered pilot) (see FIG. 7C). Some of the SPs and CPs overlap, and the SP or CP is located at the end, and the SPs are arranged at equal intervals except for the carrier at the end. Note that these are not modulated and only the real part is sent. The input level of these two signals is 16/9 of the data level, and the transmission output is higher than the signal containing other data, so that it is possible to identify them.

Here, the CP is fixed according to a certain calculation formula. Therefore, the timing of the input signal is determined by comparing the signal position with the signal position stored in the memory (frame synchronization). Since the SPs are also arranged in a distributed manner according to the calculation formula, the timing of this and the input signal is taken (frequency synchronization).

In addition, one OFDM frame has a TPS
There is a signal called (transmission parameter signaling). This is arranged at a fixed position like the CP, and unlike the data signal, the DBPSK (differential
Although transmitted by bi-phase shift keying, the transmission power level is the same as the data signal. This information is composed of a total of 68 bits, and there is one bit information per one OFDM symbol, and one information can be finally obtained by 68 OFDM symbols corresponding to two frames. FIG. 7D shows a configuration diagram of the TPS. Also, if the transmission mode is 8k in one OFDM symbol, 68 transmission modes and the transmission mode 2k
There are 17 of them, and they send exactly the same information in parallel.

As shown in FIG. 7D, the TPS has a parity check of the BCH code. After the parity check, the synchronization signal is obtained, the modulation method of the input signal is read, and the data signal is demodulated.

The terrestrial DVB is included in the MPEG-TS except for the information obtained by this TPS, and other information cannot be obtained without MPEG decoding.

Returning to FIG. 1, the digital broadcast receiver 1
The received signal is supplied to an AGC circuit 4 comprising a variable gain amplifier 2 and a control circuit 3 for controlling the gain of the variable gain amplifier 2 and amplified. The output of the AGC circuit 4 is detected by a detector 5. Based on the detection output of the detector 5, the output of the microcomputer 20 for control is converted by the D / A converter 18 to control the gain of the variable gain amplifier 2 via the control circuit 3.

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. The intermediate frequency signal is supplied to the band-pass filter 8 and band-limited.

The output from the band-pass filter 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 to be amplified. The data is converted into data, supplied to the demapper 13 via the power detector 11, and demapped.

The demapped output is supplied to an FFT circuit 14, where it is subjected to FFT conversion and demodulation. The FFT-converted and demodulated signal is deinterleaved in a deinterleave circuit 21, and the deinterleaved output is output in an error correction circuit 22. The error-corrected and error-corrected output is decoded by the MPEG decoder 23, and the PAL /
The video output is decoded by the NTSC decoder,
The audio signal being decoded and output from the MPEG decoder 23 is D
The signal is converted into an audio signal by the / A converter 25.

More specifically, the PLL circuit 7 receives the frequency division ratio information output from the microcomputer 20 and sets the frequency to be mixed in the mixer 6.
The mixer 6 converts the received RF signal into an intermediate frequency signal. The intermediate frequency signal is subjected to A / D conversion and a power detector 1
1 and is subjected to AGC by the variable gain amplifier 9 so as to maintain an appropriate level.

The output from the variable gain amplifier 9 is supplied to a detector 15
And the detection is performed, and the detection output from the detector 15 is A
A / D converted by the / D converter 16 and supplied to the microcomputer 20, and the detection output from the detector 5 is also A / D
The signal is A / D-converted by the converter 17 and supplied to the microcomputer 20, and the microcomputer 20 recognizes the received radio wave level of the broadcast being received.

On the other hand, the output from the FFT circuit 14 is supplied to the microcomputer 20, and the microcomputer 20 performs a synchronization process for detecting CP and SP. The reading of the TPS is performed by the synchronization processing, and during the guard band period, or in the case of substantially 2 shown in FIG.
In the guard band period, the division ratio of the PLL circuit 7 is sequentially changed, and another broadcast station is searched.

During the search, the gains of the variable gain amplifiers 2 and 9 constituting the AGC circuits 4 and 12 are controlled by the output of the microcomputer 20 via the power detector 11 and the D / A converter 18. It is fixed to the gain immediately before the search. In the guard band period,
Alternatively, in the substantially two guard band periods shown in FIG. 6B, the synchronization process is stopped over a period in which another broadcast station is being searched.

In the digital broadcast receiver 1 configured as described above, within the guard band period or in FIG.
2 will be described with reference to FIGS. 2 and 3.

The digital broadcast receiver 1 previously stores in the memory information of a reception frequency table of each region and a frequency table z of only a representative frequency of each region (a frequency of an NHK broadcasting station in Japan). ing.

When the digital broadcast receiver 1 is reset, the broadcast receiver of the default channel is accessed to start the broadcast reception of the default broadcast station (step S1). After step S1, it is checked whether or not synchronization has been achieved by the synchronization processing. If it is determined that synchronization has not been achieved, a broadcast of the next frequency is searched for in accordance with the frequency table z (step S3).

The synchronization process will be described with reference to FIG.

When it is determined in step S3 that synchronization has been achieved, demodulation is performed and a video signal and an audio signal are output (step S4). Subsequent to step S4, a frequency table storing the frequency of the received broadcast station is called from the memory (step S5). Subsequent to step S5, during the guard band period or substantially two guard band periods, only the broadcast of the corresponding frequency is sequentially searched to receive and detect the broadcast of the frequency (step S6).

It is checked whether or not the level of the detection output in step S6 is equal to or higher than a threshold (step S7). If it is determined in step S7 that the difference is not equal to or larger than the threshold, the process is repeated from step S6. If it is determined in step S7 that the frequency is equal to or higher than the threshold value, the frequency of the broadcast station is stored (step S8), the broadcast is shifted to the next frequency (step S9), and the search operation from step S6 is repeated. When the frequencies of the n broadcast stations are stored (step S10), the frequency table obtained in step S10 is compared with the frequency table in the memory, and the corresponding frequency table x is selected (step S1).
1).

After step S11, the frequency table x
Is updated to the frequency table obtained in step S10 (step S12).

By executing steps S1 to S12, the frequency table x at the time of resetting is changed.

Further, after the frequency table x is selected, all the broadcasting stations are searched and detected during the guard band period (step S14), and whether or not the detection output is based on the broadcast reception of a frequency other than the existing frequency table is performed. Is checked (step S15). In step S15, when it is determined that the detection output is not the detection output based on the broadcast reception of the frequency other than the already-existing frequency table, the processing is repeated from step S14.

If it is determined in step S15 that the output is a detection output based on the broadcast reception of a frequency other than the already-existing frequency table, it is checked whether or not the output corresponds to the frequency of the broadcasting station in the other frequency table y of the current frequency table x. Is performed (step S16).

If it is determined in the check in step S16 that the frequency does not apply, the frequency of the new broadcasting station is added to the frequency table x, and the frequency table x is newly added.
(Step S17), and the process is repeated from Step S14.

If it is determined in the check of step S16 that the above condition is satisfied, following step S16, only the broadcasting stations of the frequency table x and the frequency table y are sequentially received and detected (step S18), and the frequency table y is detected.
The detection output at the time of broadcast reception of the frequency exceeds the threshold,
Also, it is checked whether the detection output at the time of receiving the broadcast of the frequency of the frequency table x is less than the threshold (step S1).
9).

In the check in step S9,
When the detection output at the time of receiving the broadcast of the frequency of the frequency table y does not exceed the threshold and the detection output at the time of receiving the broadcast of the frequency of the frequency table x is equal to or more than the threshold, the processing is repeatedly executed from step S18, and the frequency table y If the detection output at the time of receiving the broadcast of the frequency of the frequency exceeds the threshold and the detection output at the time of receiving the broadcast of the frequency of the frequency table x is less than the threshold, the frequency is changed to the frequency table y (step S20).

By repeating the above, a frequency table having a signal level equal to or higher than the threshold is generated, and the generated frequency table is compared with a pre-recorded reception frequency table of each area to specify the area. Becomes possible.

Next, with respect to steps S6 and S14, the search during the null symbol period will be described with reference to FIG.

While the broadcast of broadcast station A is being received, execution of step S6 or step S14 is started (step S101).

After step S101, it is checked whether (T1) ms has elapsed since the detection of the synchronization flag (step S102). Here, 0.896 ms <T1
<T2 <1.008 ms is selected.

If 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).

In step S103, the gains of the variable gain amplifiers 2 and 9 by the AGC circuits 4 and 12 are fixed because the AGC circuits 4 and 12 depend on the reception level of the broadcasting station when searching for a broadcasting station of another frequency. , The gains of the variable gain amplifiers 2 and 9 are varied,
This is so as not to determine that reception is possible even when the reception signal level of the other broadcast station is low.

The reason why the synchronization process is stopped in step S103 is that the synchronization process in the received signal of the new broadcast station is stopped and the OFDM symbol is demodulated in order to search for and receive a new broadcast station. This is because they do not.

After step S103, broadcast station A is set to N
(Step S104), and it is checked whether N is the broadcast station having the highest reception frequency (step S10).
5). If it is determined in step S5 that N is the broadcast station having the highest reception frequency, step S105 is executed with N being the broadcast station having the highest reception frequency (step S105).
106).

If it is determined in step S105 that N is not the broadcast station having the highest reception frequency, the broadcast station is tuned to the frequency of the next broadcast station (N + 1) to perform detection (step S107), and the detection output is determined in advance. It is checked whether it is equal to or greater than the threshold value (step S108). Step S
If it is determined at 108 that the value is above the threshold, the broadcast station (N +
The frequency of 1) is stored (step S109), and it is checked whether (T2) ms has elapsed since the synchronization was detected (step S110).

In step S110, (T2) ms
When it is determined that the time has elapsed, the process returns to the broadcasting station A (step S111).

If it is determined in step S108 that the value is less than the threshold value and (T2) ms has elapsed since the synchronization was detected (step S112), step S11 is performed.
1 is executed. In step S108, when it is determined that the value is less than the threshold value and that (T2) ms has not elapsed since the generation of the synchronization flag, the broadcast station N = N + 1 is executed (step S114), and subsequently, step S105
It is executed repeatedly from.

Subsequent to step S111, the AGC fixing process is released, that is, the gain of the variable gain amplifier is released, and the suspension of the synchronization process is released (step S11).
5) After the step S115, the process waits for the detection of the synchronization flag (step S116), and returns to the broadcast reception of the broadcast station A.

As described above, after the user first turns on or resets the digital broadcast receiver 1, the user first accesses the default broadcast station frequency,
If this broadcast station does not exist, a search is performed according to a frequency table of only representative channels in each region.

The broadcast of the first broadcast station that can be received in this operation is received, demodulated, and video output and audio output are performed. Thereafter, a search for another broadcast station is performed. At this time, in order to improve the efficiency, only one or more frequency table channels in which the initially received channel is registered are sought. While doing this work,
The audio is virtually unbroken.

Next, the synchronization processing will be described with reference to FIG.

Upon entering the synchronization process, the bandwidth, transmission mode, and guard interval are set to default values. First, the bandwidth is set to the default value of 8 MHz (step S201), the transmission mode is set to the 2k transmission mode (step S202), the guard interval is set to 1/32 (step S203), and the CP and SP are detected. It is checked whether or not it has been performed (step S
204).

In step S204, CP and SP
Is detected, TPS is read (step S205), and demodulation processing is performed (step S206).

In step S204, CP and S
If it is not determined that P has been detected, step S204
Subsequently, it is checked whether or not the guard interval is 1/4 (step S207). When it is determined that the guard interval is not 1/4, the guard interval period length is set to twice (step S208), and step S204 is performed. Will be executed again. Therefore, when the CP and SP are detected due to the setting change, step S205 is executed and it is determined that synchronization has been achieved.

If it is determined in step S207 that the guard interval is 1/4, the process proceeds to step S2
After step 07, it is checked whether the transmission mode is the 8k mode (step S209). If it is determined that the transmission mode is not 8k, the transmission mode is set to the 8k mode (step S210) and the processing is executed again from step S203. You. When the CP and SP are detected by this execution, step S205 is executed and it is determined that synchronization has been achieved.

In step S209, the transmission mode is 8k
If it is determined that the mode is the mode, it is checked whether or not the bandwidth is 6 MHz following step S209 (step S211). If it is determined that the bandwidth is not 6 MHz, the bandwidth is reduced by 1 MHz (step S212). ), And are executed again from step S202. By this execution C
When P and SP are detected, step S205 is executed and it is determined that synchronization has been achieved.

At step S211, the bandwidth is 6 MHz.
If it is determined to be z, the process is executed again from step S201 following step S211. When the CP and SP are detected by this execution, step S205 is executed and it is determined that synchronization has been achieved.

As described above, each combination is sequentially changed and C
The synchronization is determined until P and SP are detected, and the routine for searching for another broadcast station is continued.

Further, when the position is moved by an in-vehicle digital broadcast receiver or the like, a different situation may occur such that a broadcast station of a frequency stored in a registered frequency table cannot be received. Since such a situation may occur, once the frequency table is determined,
The detection operation is performed for all broadcasting stations. By doing so, it is possible to recognize that the detection output level of a broadcasting station that could not be received until now has risen, and conversely, that the detection output level of a broadcasting station that has been able to receive has dropped, and that the changed frequency table Can be changed automatically.

[0077]

As described above, according to the digital broadcast receiver according to the present invention, after the power is turned on or after resetting, any other broadcast station can receive another broadcast station during the reception guard band period during broadcast reception. Was automatically searched to create a broadcast frequency table and store it.
A frequency table for another broadcasting station can be obtained without substantially interrupting the video signal and the output audio.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiver according to one 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 illustrating an operation of the digital broadcast receiver according to the embodiment of the present invention.

FIG. 4 is a flowchart for explaining an operation of the digital broadcast receiver according to the embodiment of the present invention;

FIG. 5 is an explanatory diagram for explaining a DVB transmission signal;

FIG. 6 is an explanatory diagram for explaining a DVB transmission signal;

FIG. 7 is an explanatory diagram for explaining a DVB transmission signal;

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 illustrating a schematic 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 amplifier 4 and 12 AGC circuit 5 and 15 Detector 6 Mixer 14 FFT circuit 20 Microcomputer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 7/08 H04N 7/08 Z 7/081

Claims (4)

[Claims] An automatic search for another receiving broadcast station during a reception guard band period during reception of a broadcast of an arbitrary broadcast station after power-on or after resetting to create a frequency table of the received broadcast station, A digital broadcast receiver comprising means for storing. 2. A reception band in a terminal guard band period portion during a reception effective guard band period during a broadcast reception of an arbitrary broadcasting station after power-on or reset, and a subsequent reception in a guard band period in a subsequent OFDM symbol period. A digital broadcast receiver comprising means for automatically searching for a broadcasting station, creating a frequency table of a receiving broadcasting station, and storing the frequency table. 3. The digital broadcast receiver according to claim 1, further comprising means for fixing a gain of the variable gain amplifier constituting the AGC circuit to a gain immediately before the start of the search for the receiving broadcast station. A digital broadcast receiver, comprising: 4. The digital broadcast receiver according to claim 1, further comprising means for stopping synchronization detection processing during a reception broadcast station search period.