JP4531446B2 - Digital broadcast receiver - Google Patents

Description

  The present invention relates to a channel search technique in a terrestrial digital broadcast receiver.

  In Japan, terrestrial digital television broadcasting of ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) standard has been started. The ISDB-T standard is a broadcasting system that employs OFDM as a modulation system. In terrestrial digital television broadcasting, similarly to analog broadcasting, channel search is performed in the initial state, and processing for setting a reception frequency in advance is performed. For example, in the case of a stationary digital television used at home, opportunities for channel search are limited when the television is purchased or when it is moved. On the other hand, in a digital television mounted on a car together with a car navigation system, the frequency of a broadcasting station changes with the movement of the car, so it is necessary to frequently perform a channel search.

  As described above, a channel search is also performed on a digital television. Conventionally, a channel search on a digital television takes about 2 seconds for a 1ch search. For this reason, for example, a time of 2 to 3 minutes is required to perform a search for 60 channels.

  FIG. 2 is a diagram illustrating the time from when a tuner receives a broadcast signal until video synchronization ends in a digital television broadcast receiver. As described above, conventionally, since channel detection is performed when video synchronization is completed, a long time is required for a 1ch search.

  In view of the above problems, an object of the present invention is to provide a digital television receiver capable of performing a channel search in a short time.

To solve the above problems, an invention according to claim 1, an apparatus for receiving terrestrial digital television broadcasting, the received signal or, et al., The tuner selects and outputs a signal of the specified frequency band, A guard ratio detection circuit that detects a guard interval ratio in a symbol signal from a signal output from the tuner, and specifies the frequency band for the tuner, and whether a broadcast signal exists in the specified frequency band. and a control unit for performing channel detection process of detecting, the control unit performs the channel sensing process in accordance with the presence or absence of the detection of the guard interval ratio definitive the guard ratio detection circuit, after the channel sensing processes, Specify a new frequency band .

According to a second aspect of the invention, terrestrial digital television An apparatus for receiving a broadcast, the received signal or, et al., The tuner selects and outputs a signal of the specified frequency band, the signal output from the tuner After performing the FFT conversion, a frequency shift detection circuit for detecting a reception frequency shift, and the frequency band for the tuner are specified, and whether or not a broadcast signal exists in the specified frequency band. and a control unit for performing channel detection process of detecting, the control unit performs the channel sensing process in accordance with the presence or absence of the detection of the reception frequency shift definitive to the frequency shift detecting circuit, after the channel sensing process Specify a new frequency band .

According to a third aspect of the invention, terrestrial digital television An apparatus for receiving a broadcast, the received signal or, et al., The tuner selects and outputs a signal of the specified frequency band, the signal output from the tuner After performing the FFT conversion, a timing detection circuit for detecting a clock error between the transmitting and receiving devices, and specifying the frequency band for the tuner and whether or not a broadcast signal exists in the specified frequency band. and a control unit for performing channel detection process of detecting, the control unit performs the channel sensing process in accordance with the presence or absence of the detection of the clock error between the definitive transmitting and receiving apparatus to the timing detection circuit, after the channel sensing process Specify a new frequency band .

According to the present invention, with respect to the signal of the previous time domain to the FFT operation of the digital broadcasting signal, since the channel sensing by gas chromatography De interval ratio is detected, it is possible to shorten the channel search time is there.

  In addition, according to the present invention, channel detection is performed by performing frequency shift or timing detection on the signal in the frequency domain after the FFT operation. Enable search.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a digital television broadcast receiving apparatus 1 according to an embodiment of the present invention that receives terrestrial digital television broadcasts. The digital television broadcast receiving apparatus 1 includes an antenna 5, a front end processing unit 10, a back end processing unit 20, a control unit 30, and a memory 31. A broadcast signal transmitted from a digital television broadcast transmitter (not shown) is received by the antenna 5.

  The front end processing unit 10 includes a tuner 11, a mode / guard ratio search circuit 12, a carrier / timing search circuit 13, a frame synchronization circuit 14, and a time deinterleave circuit 15. In addition, the back end processing unit 20 includes a video synchronization circuit 21. The control unit 30 is configured by a CPU or the like, and controls each circuit of the front-end processing unit 10 and the back-end processing unit 20 and executes various software processes. The memory 31 stores channel information searched by the control unit 30.

  Next, a channel search procedure will be described. First, the control unit 30 transmits to the tuner 11 a signal designating a minimum frequency in a band for performing a channel search. Here, a case where the search is performed in order from the low frequency will be described as an example. However, the search order is not particularly limited, and the search may be performed from the high frequency side. The tuner 11 receives a received signal from the antenna 5 and outputs a signal in a frequency band designated by the control unit 30.

  The signal output from the tuner 11 is input to the mode / guard ratio search circuit 12. The ISDB-T digital broadcast signal has three modes (Mode1, Mode2, Mode3) with different OFDM carrier intervals (different symbol lengths) in consideration of resistance to Doppler shift in mobile reception. . The mode / guard ratio search circuit 12 has a function of detecting in which mode the received signal is transmitted. Here, the effective symbol lengths in the case of Mode 1, Mode 2 and Mode 3 are defined as 252 μs, 504 μs and 1.008 ms, respectively.

  The guard ratio indicates the guard interval ratio. As described above, the ISDB-T digital broadcast signal adopts the OFDM modulation method, and the transmission signal in the OFDM modulation method has a guard interval embedded in a signal of one symbol. In the ISDB-T standard, four types of ratios of 1/4, 1/8, 1/16, and 1/32 of the guard interval with respect to the effective symbol length are defined. The mode / guard ratio search circuit 12 has a function of detecting which guard interval ratio the received signal is.

  After the mode / guard ratio is searched, the received signal is converted from a time domain signal to a frequency domain signal by FFT conversion. Then, the signal after the FFT conversion is input to the carrier / timing search circuit 13. The carrier search is a process for detecting a reception frequency shift, that is, a reception frequency shift. The timing search is a process for detecting a clock error between a transmission apparatus (not shown) that transmits a digital broadcast and the digital television broadcast reception apparatus 1. The digital television broadcast receiving apparatus 1 can receive a normal broadcast signal by performing frequency deviation correction processing based on the detected reception frequency shift amount and performing clock correction based on the detected clock error amount. Become.

  The signal output from the carrier / timing search circuit 13 is input to the frame synchronization circuit 14. Here, the head position of one frame of the ISDB-T digital broadcast signal is detected. The signal output from the frame synchronization circuit 14 is input to the time deinterleave circuit 15, and the signal interleaved in the time direction is restored. The signal output from the time deinterleave circuit 15 is input to the video synchronization circuit 21 as a TS (Transport Stream) signal, and the video synchronization circuit 21 reproduces the video stream.

  Conventionally, the TS signal input to the video synchronization circuit 21 is monitored, and channel detection is performed based on whether or not the video synchronization is normally performed from the TS signal. Channel detection is performed during the mode type or guard interval ratio detection process, or during the above-described frequency shift or clock error detection process.

  First, an embodiment in which channel detection is performed at the time of mode type or guard interval ratio detection processing will be described. When the mode / guard ratio search circuit 12 detects the mode type or the guard interval ratio, the mode / guard ratio search circuit 12 notifies the control unit 30 of information indicating that the detection was possible. Thereby, the control unit 30 determines that the broadcast signal exists in the frequency band currently designated for the tuner 11. Then, the control unit 30 writes information indicating that a broadcast program exists in the current frequency band in the memory 31.

  Although it has been described that the control unit 30 performs channel detection when the mode type is detected or when the guard interval ratio is detected, the channel detection is performed after confirming that both the mode type and the guard interval ratio are detected. May be performed.

  Conversely, when the mode type cannot be detected or when the guard interval ratio cannot be detected, information indicating that no broadcast program exists in the current frequency band is written in the memory 31.

  In this way, when the channel search for the lowest frequency is completed, the control unit 30 notifies the tuner 11 of information specifying the frequency for performing the next channel search. Then, by repeating the process described above for the newly designated frequency band, the channel detection process is performed for the sequentially designated frequency band. When channel detection is performed in each frequency band, the information is written in the memory 31, and channel map information is generated in the memory 31.

  As described above, in the present embodiment, channel detection is performed on the received signal in the time domain before the FFT conversion process, so that the channel search time can be shortened.

  Next, an embodiment in which channel detection is performed during frequency shift or clock error detection processing will be described. When detecting a frequency shift or detecting a clock error, the carrier / timing search circuit 13 notifies the control unit 30 of information indicating that detection was possible. Thereby, the control unit 30 determines that the broadcast signal exists in the frequency band currently designated for the tuner 11. Then, the control unit 30 writes information indicating that a broadcast program exists in the current frequency band in the memory 31.

  Although it has been described that the control unit 30 performs channel detection when a frequency shift is detected or when a clock error is detected, the channel detection is performed after confirming that both the frequency shift and the clock error are detected. May be performed.

  On the contrary, when the frequency shift cannot be detected or when the clock error cannot be detected, information indicating that there is no broadcast program in the current frequency band is written in the memory 31.

  In this way, when the channel search for the lowest frequency is completed, the control unit 30 notifies the tuner 11 of information specifying the frequency for performing the next channel search. Then, by repeating the process described above for the newly designated frequency band, the channel detection process is performed for the sequentially designated frequency band. When channel detection is performed in each frequency band, the information is written in the memory 31, and channel map information is generated in the memory 31.

  As described above, in this embodiment, channel detection is performed when a frequency shift or clock error is detected for a received signal in the frequency domain after the FFT conversion process, so that the channel search time is shortened. Is possible.

  In the above embodiments, the method for performing channel detection when the mode type or guard interval ratio is detected, or the method for performing channel detection when frequency deviation or clock error is detected has been described. Either of these methods may be adopted, or channel detection may be performed by performing both detections.

  FIG. 2 is a diagram showing the time required from the frequency tuning to the end of video synchronization. In the example shown here, the time required under the conditions of mode3, GI (guard interval ratio) = 1/8 and IL (time interleaving) = 2 is shown. Specifically, the frequency tuning process by the tuner 11 is 100 ms, the mode / guard ratio search process by the mode / guard ratio search circuit 12 is 60 ms, the carrier / timing search process by the carrier / timing search circuit 13 is 50 ms, and the frame synchronization circuit 14 Frame synchronization processing (time for detecting the frame start position of ISDB-T, including TMCC acquisition time) is 500 ms, time deinterleaving processing by the time deinterleaving circuit 15 is 250 ms, and video by the video synchronization circuit 21 The synchronization process requires 1000 ms.

  Therefore, in the case of the conventional digital television broadcast receiving apparatus, it took about 2 seconds to detect a channel of one frequency, but in the case of the digital television broadcast receiving apparatus 1 of the present embodiment, When channel detection is performed in the mode / guard ratio search process, a channel of one frequency can be detected in about 160 ms. Alternatively, when channel detection is performed in the carrier / timing search process, it is possible to detect a channel of one frequency in about 210 ms. Thus, for example, a channel search of 60 channels can be performed in a time of about 12 seconds. Therefore, even in the case where it is necessary to frequently perform a channel search in a digital television mounted on the car navigation system in a short time. All channels can be searched.

It is a functional block diagram of the digital television broadcast receiving apparatus concerning this Embodiment. It is the figure which showed the time required from receiving a received signal to ending video synchronization for each process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital television broadcast receiver 5 Antenna 11 Tuner 12 Mode / guard ratio search circuit 13 Carrier / timing search circuit

Claims (3)

A device for receiving terrestrial digital television broadcasting,
Received signal or, et al., The tuner selects and outputs a signal of the specified frequency band,
A guard ratio detection circuit for detecting a guard interval ratio in the symbol signal from the signal output from the tuner;
A control unit that performs channel detection processing for specifying whether or not a broadcast signal exists in the specified frequency band while specifying the frequency band for the tuner ;
With
Wherein the control unit performs the channel sensing process in accordance with the presence or absence of the detection of the guard interval ratio definitive the guard ratio detection circuit, after the channel sensing process, the digital broadcast receiving apparatus that specifies the new frequency bands. A device for receiving terrestrial digital television broadcasting,
Received signal or, et al., The tuner selects and outputs a signal of the specified frequency band,
A frequency shift detection circuit that detects a received frequency shift after performing FFT conversion on the signal output from the tuner;
With specifying the frequency band to the tuner, and a control unit for performing channel detection process of detecting whether or not the broadcasting signal on the frequency band specified exists,
With
Wherein the control unit, the performs the channel sensing process in accordance with the presence or absence of the detection of the reception frequency shift definitive to frequency shift detecting circuit, after the channel sensing process, the digital broadcast receiving apparatus that specifies the new frequency bands. A device for receiving terrestrial digital television broadcasting,
Received signal or, et al., The tuner selects and outputs a signal of the specified frequency band,
A timing detection circuit that detects a clock error between the transmission and reception devices after performing FFT conversion on the signal output from the tuner;
A control unit that performs channel detection processing for specifying whether or not a broadcast signal exists in the specified frequency band while specifying the frequency band for the tuner ;
With
Wherein the control unit performs the channel sensing process in accordance with the presence or absence of the detection of the clock error between the definitive transmitting and receiving apparatus to the timing detection circuit, after the channel sensing process, the digital broadcast receiving apparatus that specifies the new frequency bands.

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