JP2005269041A - Digital transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital transmission system for transmitting digital signals through a CATV network capable of easily deciding a cause to fault occurrence when any signal fault takes place. <P>SOLUTION: A digital modulator 15 is provided with a particular information detection section 18 for detecting a synchronizing signal and SI information in an MPEG-TS signal, selects the MPEG-TS signal while detecting the synchronizing signal and the SI information, selects a pseudo signal generated by a pseudo signal generating section 16 when the particular information detection section 18 cannot detect the synchronizing signal and the SI information, digitally modulates the pseudo signal and transmits the resulting signal to a digital receiver 21 via the CATV network 20. The digital receiver 21 demodulates the received signal, a signal decision processing section 26 decides whether or not demodulation is normally carried out and whether or not the synchronizing signal and the SI information can normally be detected, a signal processing section 27 processes the received signal when the decision indicates all normal and a display apparatus 23 displays the received signal, and the signal decision processing section 26 outputs a message corresponding to the abnormality to the signal processing section 27 and the display apparatus 23 displays the message when any abnormality exists. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital transmission system that receives a digital broadcast by a satellite or a terrestrial digital broadcast and retransmits the digital broadcast by a CATV network.

  BS digital broadcasting has already started in December 2000, and Terrestrial Integrated Services Digital Broadcasting (ISTB-T) has been in service since December 2003 in the Kanto, Kinki and Chukyo regions. Broadcasting has begun. Further, terrestrial digital (television) broadcasting is scheduled to start broadcasting in other regions by 2006.

In a CATV digital transmission system in which the digital broadcast wave is received by a CATV headend device and retransmitted by a CATV network, the received digital broadcast is demodulated, multiplexed, divided, etc. In this case, each channel is mixed and retransmitted via the CATV network. The standard of the CATV digital transmission system is defined by the Japan CATV Technology Association (see, for example, Non-Patent Document 1).
Japan CATV Technology Association Standard “Digital Cable Television Broadcasting”, Japan CATV Technology Association, May 27, 2000, p. 24-146

  The headend device in the CATV digital transmission system receives a digital broadcast, performs predetermined signal processing, and then retransmits it via the CATV network. However, for some reason, the reception state of the broadcast signal has deteriorated. Even in this case, the re-transmission process is continued as it is, and the detection process of the cause of failure is performed in that state.

  As described above, even if the reception state of the broadcast signal is deteriorated, the conventional headend device performs the digital modulation or the like as it is and outputs the TV signal to the CATV network, and therefore receives the TV signal. In the receiver side, if a problem occurs in the signal reception state, whether the reception state of the satellite broadcast or the terrestrial digital broadcast in the head end device side is bad, the digital modulation device is defective, or the CATV network The cause of the failure, such as whether a failure occurred, could not be determined, resulting in trouble with maintenance.

  The present invention has been made to solve the above-described problems, and causes a failure when a failure occurs in the signal reception state on the receiver side that receives a signal transmitted via the CATV network. It is an object of the present invention to provide a digital transmission system that can reliably determine the above.

The present invention relates to a digital transmission system that receives a digital television broadcast, modulates an MPEG-TS signal by a digital modulation device, and retransmits the signal to a digital reception device by a CATV network.
The digital modulation device detects specific information from an input MPEG-TS signal to determine whether the MPEG-TS signal is normal, and if normal, digitally modulates the MPEG-TS signal to perform CATV network. If it is abnormal, the pseudo signal is digitally modulated instead of the MPEG-TS signal and output to the CATV network.
The digital reception device receives and demodulates a signal transmitted from the digital modulation device via a CATV network, determines whether the demodulated signal is normal or abnormal, and if it is normal, the demodulated signal is sent to a display device. Output and display, and when it is determined to be abnormal, message data corresponding to the content of the abnormality is output and displayed on the display device.

  According to the present invention, in the digital modulation device, it is determined whether the MPEG-TS signal is normal or abnormal, and if normal, the MPEG-TS signal is digitally modulated and transmitted to the CATV network. Since the pseudo signal is digitally modulated instead of the signal and sent to the CATV network, when an abnormality occurs in the transmission signal, the digital receiver side determines at which stage the abnormality has occurred from the state of the received signal. It is possible to contribute to an immediate response at the time of maintenance.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a digital transmission system in which a digital broadcast is received and processed and then retransmitted to the receiver side via a CATV network.
In FIG. 1, reference numeral 10 denotes a head-end device, which includes a signal processing device 14 for processing a reception signal of the satellite reception antenna 11 and the terrestrial antenna 12, an output signal of the independent broadcast station 13, and a digital modulation device 15 and the like. ing. The satellite receiving antenna 11 receives digital broadcasts from satellites such as BS and CS, and the terrestrial antenna 12 receives digital terrestrial broadcasts. The independent broadcasting station 13 is a broadcasting station that performs digital broadcasting.

  The signal processing device 14 tunes the input digital broadcast, demodulates and separates it into TS (Transport Stream), and performs TS multiplex processing on the tuning information separated into the TS. At the same time, NIT / PCR (Network Information Table / Program Clock Reference) conversion is performed for CATV, and MPEG-TS (Moving Picture Experts Group-Transport Stream) is output as a digital signal stream.

  The NIT (Network Information Table) is a table that provides a combination of TS (Transport Stream) and tuning information related to it, and information on physical conditions such as frequency and modulation method used in the network. Used for transmission. The above-mentioned PCR (Program Clock Reference) is an MPEG (Moving Picture Experts Group) decoder including a video and audio decoder, and an STC (reference synchronization information) value intended as a time reference is a value intended on the encoder side. This is information for setting and proofreading.

  In addition, in the MPEG-TS signal, in addition to programs such as program broadcasts provided by broadcasting stations, the structure and properties of streams and other necessary information are inserted as SI (Service Information) information.

  The MPEG-TS signal output from the signal processing device 14 is sent to the digital modulation device 15 using, for example, the QAM modulation method. The digital modulation device 15 includes a pseudo signal generator 16, a switch circuit 17 that selects an MPEG-TS sent from the signal processor 14 and a pseudo signal output from the pseudo signal generator 16, and the signal processor 14, a specific information detection unit 18 that detects the presence or absence of SI information in MPEG-TS sent from 14 and switches the switch circuit 17, and a digital that digitally modulates a signal selected by the switch circuit 17 by, for example, a QAM modulation method The modulation processing unit 19 is used.

  The pseudo signal generator 16 generates a pseudo signal composed of a synchronization signal and random data. This pseudo signal does not include SI information. The switch circuit 17 always selects the MPEG-TS signal processed by the signal processing device 14, but switches to the pseudo signal generation unit 16 side when an abnormality is detected by the specific information detection unit 18.

  Further, the specific information detection unit 18 is assigned a synchronization signal and a specific PID (Packet Identifier) such as a PAT (Program Association Table) and NIT (Network Information Table) among SI information included in the MPEG-TS signal. The switch circuit 17 is switched by detecting the presence or absence of SI information. When the SI information is detected, the switch circuit 17 is switched to the MPEG-TS signal side, and when the SI information cannot be detected, the switch circuit 17 is switched. Is switched to the pseudo signal generation unit 16 side, and the selected signal is input to the digital modulation processing unit 19.

  The digital modulation processing unit 19 modulates the MPEG-TS signal or pseudo signal selected by the switch circuit 17 and outputs the modulated signal to the CATV network 20.

  The digital modulation device 15 is provided for each channel, and digitally modulates and outputs the video and audio data converted for CATV by the signal processing device 14. The signals digitally modulated by the digital modulation device 15 for each channel are mixed and output to the CATV network 20.

  The CATV network 20 is connected to a digital receiving device 21 installed in a subscriber's house of a CATV system, for example. The digital reception device 21 includes a digital demodulation device 22 and a display device 23. The digital demodulator 22 includes a digital demodulator 25, a signal determination processor 26, and a signal processor 27.

  The digital demodulator 25 demodulates the television signal sent from the head end device 10 and outputs the demodulated signal to the signal determination processor 26. The signal determination processing unit 26 detects the reception state from the signal demodulated by the digital demodulation unit 25, and determines whether the MPEG-TS signal is normally received, whether the pseudo signal is received, or the like. If the reception state is normal, the television signal demodulated by the digital demodulator 25 is output to the signal processor 27. If the signal determination processing unit 26 determines that the MPEG-TS signal has not been normally received, the signal determination processing unit 26 reads a corresponding message from the memory and outputs the message to the signal processing unit 27. The signal determination processing unit 26 stores a message corresponding to a reception abnormality assumed in advance in a memory.

  The signal processing unit 27 processes the television signal demodulated by the digital demodulation unit 25 or a message output from the signal determination processing unit 26 when reception is abnormal, and displays it on the display device 23.

Next, the overall operation of the digital transmission system according to the above embodiment will be described.
The signal processing device 14 receives a digital broadcast by the satellite receiving antenna 11 and the terrestrial antenna 12, etc., selects and demodulates it, and separates it into TSs. FIG. 2 shows the packet structure of the MPEG-TS signal, and shows a 4-byte (32-bit) packet header. It consists of a part 31 and an adaptation field of 184 bytes (1472 bits) and / or a payload part 32.

  The packet header portion 31 is composed of an 8-bit synchronization byte 33, a 13-bit PID packet identifier 34, and the like.

  The MPEG-TS signal is a signal having a total period of 204 bytes by adding a 16-byte RS (Reed-Solomon) code after the 188-byte TS packet shown in FIG.

  Further, in the adaptation field and / or the payload section 32, a specific PID (Packet Identifier) such as PAT (Program Association Table), NIT (Network Information Table) is inserted as SI (Service Information) information. Which PID is inserted is indicated by the PID packet identifier 34 of the packet header 31.

  As described above, the MPEG-TS signal constitutes a fixed-length stream, and a synchronization signal (synchronization byte 33) is added for each specific period. Further, in addition to signals composed of programs such as various media program broadcasts, the MPEG-TS signal is inserted as SI information with the configuration and properties of the stream to be transmitted and other necessary additional information.

  The MPEG-TS signal output from the signal processing device 14 is sent to the digital modulation device 15. In the digital modulation device 15, normally, that is, in a state where signal reception is normally performed, the MPEG-TS signal is selected by the switch circuit 17 and is input to the specific information detection unit 18 and the digital modulation processing unit 19. Is done.

  The specific information detection unit 18 includes a synchronization signal indicated by the synchronization byte 33 of the packet header unit 31 in the MPEG-TS signal, and PAT and NIT inserted as SI information in the adaptation field and / or the payload unit 32. Detect a specific PID. Which of PAT and NIT is inserted is indicated by the PID packet identifier 34 of the packet header 31 as described above.

The synchronization byte 33 is assigned a specific synchronization code such as [0100,0111] ([47H]), a specific code such as [0000H] for PAT and [0010H] for NIT. The detection unit 18 can detect a specific PID such as a synchronization signal and SI information such as PAT and NIT.
As a method for detecting SI information by the specific information detection unit 18, for example, means for storing in advance in a memory (not shown) in the digital modulation device 15 can be considered.

  The specific information detection unit 18 determines that the MPEG-TS signal is normally output from the signal processing device 14 when the synchronization signal or the specific PID in the MPEG-TS signal can be detected. The switch circuit 17 is kept switched to the signal processing device 14 side. Therefore, in this state, the MPEG-TS signal output from the signal processing device 14 is input to the digital modulation processing unit 19, is digitally modulated, and is transmitted to the digital receiving device 21 side via the CATV network 20.

  In addition, when the specific information detection unit 18 cannot detect the synchronization signal or SI information in the MPEG-TS signal, the signal processing unit 14 causes a satellite digital broadcast or terrestrial signal for some reason such as a decrease in signal level. It is determined that the digital broadcast could not be received normally, and the switch circuit 17 is switched to the pseudo signal generator 16.

  Therefore, in this state, the pseudo signal generated by the pseudo signal generation unit 16 is input to the digital modulation processing unit 19, is digitally modulated, and is transmitted to the digital reception device 21 side via the CATV network 20.

  As described above, the head-end device 10 outputs the MPEG-TS signal to the CATV network 20 in a state in which satellite digital broadcast or terrestrial digital broadcast is normally received, and the reception state deteriorates for some reason, and the satellite digital broadcast When the broadcast or the terrestrial digital broadcast cannot be normally received, the pseudo signal generated by the pseudo signal generator 16 is output to the CATV network 20 instead of the MPEG-TS signal.

  On the other hand, the digital receiver 21 receives a digital broadcast signal transmitted from the headend device 10 via the CATV network 20, demodulates the received signal by the digital demodulator 25, and inputs it to the signal determination processor 26. . The signal determination processing unit 26 determines whether the demodulation is normally performed from the demodulated signal, and detects the synchronization signal and the SI information in the same manner as the specific information detection unit 18 of the digital modulation device 15.

When the signal determination processing unit 26 (1) the demodulation is normal from the demodulated signal and the synchronization signal and SI information can be detected normally,
(2) When the demodulation is normal and the synchronization signal can be detected normally, but the SI information cannot be detected normally,
(3) If the demodulation is abnormal and the synchronization signal and SI information cannot be detected normally,
The following three types can be recognized.

  When the MPEG-TS signal is normally sent from the head end device 10, the demodulation is normal and the synchronization signal and SI information can be detected normally as in (1) above.

  When a pseudo signal is sent from the headend device 10, the demodulation is normal and the synchronization signal can be detected as in (2), but the SI information cannot be detected normally.

  When a failure such as a disconnection occurs in the CATV network 20, neither the MPEG-TS signal nor the pseudo signal can be detected. Therefore, as shown in the above (3), the demodulation is abnormal, and the synchronization signal and SI information are also normal. It cannot be detected.

  When the demodulation is normal and the synchronization signal and SI information can be normally detected as in (1) above, the signal determination processing unit 26 outputs the MPEG-TS signal demodulated by the digital demodulation unit 25 as it is. The data is output to the processing unit 27. The signal processing unit 27 processes the demodulated MPEG-TS signal and outputs the image signal to the display device 23 for display. At this time, an audio signal is also sent to a speaker (not shown) and output.

  Further, as described in (2) above, the signal determination processing unit 26 is able to detect the synchronization signal with normal demodulation, but cannot detect the SI information normally, that is, the pseudo signal is received from the headend device 10. If it is sent, the CATV network 20 is normal, but message data indicating that an abnormality has occurred in front of the digital modulation device 15, for example, “a correct transmission signal has not been sent. "Is read from the memory and displayed on the display device 23 via the signal processing unit 27.

  The signal determination processing unit 26 determines that an abnormality has occurred in the CATV network 20 when demodulation is abnormal as shown in (3) above and the synchronization signal and SI information cannot be detected normally. For example, message data “Transmission system is abnormal” is read from the memory and displayed on the display device 23 via the signal processing unit 27.

  When an abnormality occurs in the headend device 10 or the CATV network 20 as described above, a message corresponding to the abnormality is displayed on the display device 23 of the digital reception device 21. Therefore, the occurrence state of the abnormality is identified from the message content. An immediate response is possible.

  In the above-described embodiment, when an abnormality occurs, the message data indicating the occurrence of the abnormality is displayed on the general digital reception device 21 subscribed to the CATV system. Message data indicating the occurrence of an abnormality may be displayed on the monitor device that is monitoring.

  Further, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.

1 is a diagram illustrating an overall system configuration of a digital transmission system according to an embodiment of the present invention. It is a figure which shows the data structure of the MPEG-TS signal in the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Head end apparatus, 11 ... Satellite reception antenna, 12 ... Terrestrial antenna, 13 ... Independent broadcasting station, 14 ... Signal processing apparatus, 15 ... Digital modulation apparatus, 16 ... Pseudo signal generation part, 17 ... Switch circuit, DESCRIPTION OF SYMBOLS 18 ... Specific information detection part, 19 ... Digital modulation process part, 20 ... CATV network, 21 ... Digital receiver, 22 ... Digital demodulator, 23 ... Display apparatus, 25 ... Digital demodulator, 26 ... Signal determination process part, 27 ... Signal processing part, 31 ... Packet header part, 32 ... Payload part, 33 ... Synchronization byte, 34 ... PID packet identifier.

Claims (1)

In a digital transmission system that receives a digital television broadcast, modulates an MPEG-TS signal by a digital modulator, and retransmits the signal to the digital receiver via a CATV network.
The digital modulation device detects specific information from an input MPEG-TS signal to determine whether the MPEG-TS signal is normal, and if normal, digitally modulates the MPEG-TS signal to perform CATV network. If it is abnormal, the pseudo signal is digitally modulated instead of the MPEG-TS signal and output to the CATV network.
The digital reception device receives and demodulates a signal transmitted from the digital modulation device via a CATV network, determines whether the demodulated signal is normal or abnormal, and if it is normal, the demodulated signal is sent to a display device. A digital transmission system that outputs and displays, and when it is determined that there is an abnormality, message data corresponding to the abnormality content is output and displayed on a display device.

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