JPH11150716A - Signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain digital broadcast data in a 2nd network that are correctly received at a reception terminal even when an NIT detected from digital broadcast data in a 1st network is failed. SOLUTION: An ECC decoder 43 obtains broadcast data S3 in digital satellite broadcast, a detection circuit 44 detects a table NITa from the broadcast data S3, and a control section 31 revises it to obtain a table NITb in matching with a CATV. A replacement circuit 48 detects the NIT from the broadcast data S3 and replaces the NIT with the table NITb to obtain broadcast data S4 in the CATV. When the table NITa is failed, a standby table NITc stored in a memory 31M is changed based on a fault avoidance operation or the like by the user to obtain a table NITd in matching with the CATV. Then the table NITd is used in place of the table NITb above to replace the NIT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing apparatus suitable for use in delivering a digital broadcast program broadcast on an arbitrary network over another network. Specifically, an NIT (Network Information Table) of digital broadcast data in the first network is detected, and the NIT is detected in the second network.
To obtain digital broadcast data in the second network by replacing the NIT of the digital broadcast data in the first network with the above-mentioned changed NIT.
T is stored, and when the NIT detected from the digital broadcast data in the first network is abnormal, the NIT is replaced by using the spare NIT, so that the receiving terminal can correctly receive the NIT. 2 relates to a signal processing device for obtaining digital broadcast data in a network.

[0002]

2. Description of the Related Art For example, a digital television broadcasted on an arbitrary network, such as a digital television broadcasting service provided by a cable television company or the like using a network within its own facility to provide a distribution service using a modulation conversion transmission device or the like. It is conceivable that the program is distributed on another network.

[0003]

In this case, the digital broadcast data is an NIT having physical information on a transmission path.
Therefore, a digital broadcast program broadcasted on the first network cannot be distributed on the second network simply by converting the modulation method using a modulation conversion transmitting device or the like.

Therefore, the NIT of digital broadcast data in the first network is detected, and the NIT is detected in the second network.
It is conceivable that the digital broadcast data in the second network is obtained by replacing the NIT of the digital broadcast data in the first network with the above-mentioned changed NIT. However, in this case, when the NIT detected from the digital broadcast data in the first network is abnormal, the NIT used for replacement also becomes abnormal, and the digital broadcast in the second network that can be correctly received by the receiving terminal. You will not be able to get data.

According to the present invention, even if the NIT detected from digital broadcast data in the first network is abnormal, the signal processing apparatus can obtain digital broadcast data in the second network which can be correctly received by the receiving terminal. The purpose is to provide.

[0006]

According to the present invention, there is provided a signal processing apparatus comprising:
A digital broadcasting signal of a predetermined transmission frequency on a second network, the first digital broadcasting signal being frequency-converted to obtain a first digitally modulated signal. A first frequency converter, a demodulator for demodulating the first digital modulation signal to obtain digital broadcast data, and a NIT (network) having physical information on a transmission path from the digital broadcast data output from the demodulator. Table detecting means for detecting the information table, table changing means for changing the NIT detected by the table detecting means so as to be compatible with the second network, and NIT of the digital broadcast data output from the demodulating means. Replacement with NIT obtained by changing table by means of table change Means for modulating the digital broadcast data whose NIT has been replaced by the table replacing means to obtain a second digitally modulated signal, and frequency converting the second digitally modulated signal to obtain a second digitally broadcast signal. And a table storage unit for storing a spare NIT. When the NIT detected by the table detection unit is abnormal, the table replacement unit stores the NIT in the table storage unit. A spare NIT is used to replace the NIT.

[0007] A first digital broadcast signal on the first network has a predetermined transmission frequency.
Is converted into a digital modulation signal by frequency conversion and further demodulated to obtain digital broadcast data in the first network. Digital broadcast data in the first network has NIT suitable for the first network.

An NIT is detected from digital broadcast data in the first network, and the NIT is
Will be changed to fit the network. For example,
In the case where a cable television company or the like provides a distribution service of a satellite digital multi-channel broadcast by a modulation conversion transmission device using a network in its own facility, the frequency information of the NIT is changed. When the number of digital broadcast signals on the second network is smaller than the number of digital broadcast signals on the first network, the digital broadcast signals on the second network among the digital broadcast signals on the first network are Information related to the digital broadcast signal not corresponding to the signal is deleted.

Then, the digital broadcast data in the second network is formed by replacing the NIT of the digital broadcast data in the first network with an NIT obtained by changing the data to be suitable for the second network. The digital broadcast data in the second network is modulated into a digitally modulated signal, which is further frequency-converted to obtain a second digital broadcast signal to be transmitted on the second network. Thereby, the first
The digital broadcast program being broadcast on the second network can be distributed on the second network.

Here, the NIT detected from the digital broadcast data in the first network may become abnormal. The cause may be that the table detecting means is abnormal, or that the NIT itself included in the digital broadcast data in the first network is abnormal. If the NIT is abnormal, the N
By displaying the contents of the IT, the user can easily know.

As described above, when the NIT detected from the digital broadcast data in the first network is abnormal, the NIT obtained by changing the NIT by the table changing means is obtained.
IT also becomes abnormal. Therefore, at this time, the table replacement means replaces the NIT using the spare NIT stored in the table storage means. This makes it possible to obtain digital broadcast data in the second network that can be correctly received by the receiving terminal.

In this case, the spare NIT stored in the table storage means may be, for example, an NIT (compatible with the first network) detected by the table detection means before the NIT detected by the table detection means becomes abnormal. Or the NI obtained by changing the NIT by the table changing means.
T (compatible with the second network). If the spare NIT is suitable for the first network, and if the NIT detected by the table detecting means is abnormal, the spare NIT is changed by the table changing means to the second NIT.
It is modified to fit the network and used for replacement. On the other hand, if the spare NIT is suitable for the second network and the NIT detected by the table detecting means is abnormal, the spare NIT is used for replacement as it is.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a digital CATV (cable television) system 10 using satellite digital multi-channel broadcasting as an embodiment. This system 10 includes an antenna 11 for receiving digital broadcast signals from a plurality of transponders (satellite repeaters) of a communication satellite 20, and a CA that changes the transmission frequency and modulation method of the received digital broadcast signals.
And a modulation conversion transmitting device 12 for generating a digital broadcasting signal for TV and transmitting it to the transmission line 13. Incidentally, the transmission line 13, the receiving terminal is a set top box (home receiving device) 14 _-1 to 14 _-m are connected, these set-top boxes 14 _-1 to 14 _-m
The image of the channel number selected in step 15 is displayed on the monitor 15 _-1 to 15
Displayed for _-m .

Here, a digital broadcast signal transmitted from the communication satellite 20 will be described. In the present embodiment, this digital broadcast signal is a digital broadcast signal (DVB).
deoBroadcasting) system. FIG. 2B shows a frame configuration of digital broadcast data in the DVB system. One frame is composed of eight MPEG2 transport packets (see FIG. 2A). In this case, the synchronization byte in the packet (= 4
7 _H ), the synchronization byte is inverted once for every 8 packets (=
B8 _H ) to obtain frame synchronization.
Each MPEG2 transport packet (MPEG
Reed-Solomon (204, 18)
The error correction code according to 8) is added. The digital broadcast data shown in FIG. 2B is QPSK (Quadrature Phase Shi
ft Keying) modulation, and then frequency conversion to the SHF band to become a digital broadcast signal transmitted from the communication satellite 20.

FIG. 3 shows a packet structure of an MPEG2 transport packet. The first four bytes of 188 bytes constitute a packet header. A PID (Packet Identification: Packet Identifier) indicating an attribute of an individual stream (data string) of the packet is arranged in the packet header. As is well known, the payload (data portion) of the MPEG2 transport packet has a PES (Packetized Ele
mentary Stream) packet is subdivided and distributed, and P
PAT (Program Association Tabl) as SI (Program Specific Information)
e), PMT (Program Map Table), NIT (Network
Information Table) is also provided.

Here, the PSI is information necessary for realizing simple channel selection operation and program selection. PA
T is, for each program number (16 bits), the PI of the PMT that transmits information on the packets that constitute the program.
FIG. 5 shows a table structure of the PAT. The PID of the PAT itself is fixed PI
D = "0" is assigned.

The main contents will be described. Table ID
Indicates the type of the table, and is "0x00" (hexadecimal notation) in the PAT. The TS (transport stream) ID identifies a stream (multiplexed coded data), and corresponds to a transponder in the case of a satellite. The version number is incremented each time the contents of the table are updated. The current next indicator is used for identification when the new and old versions are transmitted simultaneously. The program number identifies each channel. The network PID is the PID of NIT when the program number is “0 × 0000”.
It shows. Program map PID is PM
This shows the PID of T.

The PMT is provided for each program number.
It indicates the PID of a packet that transmits a stream of video, audio, additional data, and the like that constitute the program. The PID of the PMT itself is specified by the PAT as described above. FIG. 6 shows a table structure of the PMT. Main contents not overlapping with the PAT will be described. The table ID indicates the type of the table.
In MT, it is “0 × 02”. The PCR PID indicates a PID of a packet including a clock (PCR) serving as a reference for decoding. The stream type indicates the type of signal transmitted in a stream, such as video, audio, and additional data.

The NIT indicates physical information about the transmission path, that is, for a satellite, the orbit of the satellite, the polarization, the frequency of each transponder, and the like. The PID of the NIT itself is specified by the PAT as described above. FIG.
Indicates the table structure of the NIT. PAT, PM
Main contents that do not overlap with T will be described. Table I
D indicates the type of the table. The network is “0 × 40”, and the other networks are “0 × 41”. The network ID identifies a network. Satellites correspond to individual satellites.

Further, two descriptors that play an important role as a part of the NIT will be described. First,
The satellite delivery system descriptor will be described. This descriptor is used as the first of the descriptors repeated according to the TS (transport stream) descriptor length, and is paired with the TS (transport stream) ID.

FIG. 8 shows the structure of the satellite delivery system descriptor. The descriptor tag is defined by DVB and indicates the type of the descriptor. In this descriptor,
It becomes “0 × 43”. The frequency indicates a transmission frequency for each stream (here, a transponder). The orbit / west longitude / east longitude flag / polarization indicates the orbit and polarization of the satellite. The modulation / symbol rate / inner error correction coding rate indicates the specifications regarding the transmission system.

Next, the service list descriptor will be described. This descriptor is used as the second and subsequent descriptors repeated according to the TS (transport stream) descriptor length, and indicates the ID of a service (channel) multiplexed on the stream (here, transponder). is there. That is, a plurality of service list descriptors are attached to one TS (transport stream) ID.

FIG. 9 shows the structure of the service list descriptor. The descriptor tag is DV
B, and indicates the type of the descriptor. In this descriptor, it is “0 × 41”.
The service ID identifies a service. Usually, the service matches the channel that the viewer tunes to.
The service type indicates the content of the service, such as video, audio, and data.

Here, an example of the operation of a receiver for receiving the above-mentioned digital broadcast signal transmitted from the communication satellite 20 will be briefly described. In PAT and PMT, the program number is used.
D corresponds to the channel number selected by each viewer. Furthermore, while the NIT contains information of the whole network, ie all transponders, and the same table is transmitted in parallel by all transponders,
T and PMT each consist of only information of a program in the transponder to be transmitted, and have different contents for each transponder.

Assume that the viewer tunes to the "M" channel at the receiver. At the receiver, N
After receiving the IT, "M" is searched for the service ID in the service list descriptor of the NIT. Then, it receives the satellite delivery system descriptor combined before the service list descriptor including the service ID “M”, recognizes the frequency of the transponder transmitting the “M” channel, and Control the frequency. And "M"
A PAT is detected from a digital broadcast signal from a transponder transmitting a channel, and "M" is searched for a program number in the PAT.

The program number "M" in the PAT
, The PMT is received by the program map PID associated with the program number "M" in the PAT. After recognizing an elementary PID for each stream type (video, audio, etc.) corresponding to the program number "M" in the PMT, a transport stream packet having a PID matching the elementary PID is separated. . Then, the separated packets are decoded by the respective decoders, and video and audio signals of the “M” channel selected by the viewer are output.

FIG. 10 shows a configuration of the modulation conversion transmission device 12 in the digital CATV system 10 of FIG. The transmitting device 12 is provided with first to N-th communication satellites 20.
Change the transmission frequency and modulation method of the digital broadcast signal sent from the transponder (satellite repeater)
A digital broadcast signal for ATV is generated and transmitted to the transmission line 13. Note that programs of a plurality of channels are multiplexed on each digital broadcast signal.

The transmission device 12 includes a microcomputer, and controls a whole operation of the device,
A digital broadcast signal in the SHF (Super High Frequency) band transmitted from the first to Nth transponders of the communication satellite 20 is processed and VHF (Very High Frequency) is processed.
Band or UHF (Ultra High Frequency) band CATV
First through to produce a digital broadcast signal BS ₁ to BS _N of use
Has a signal processing unit 32 _-1 to 32 _-N of the N, and an adder 33 to be transmitted to the transmission path 13 by adding these digital broadcast signals BS ₁ to BS _N. Note that the control unit 31 displays an operation unit 34 for performing setting of a reception frequency in the tuner of the signal processing units 32 _-1 to 32 _-N, the state of the delivery device 12, a liquid crystal display or the like Display 35 composed of
Is connected.

The signal processing unit 32 _-1, a plurality of digital broadcast signals SHF band received by the antenna 11, selects the first digital broadcast signal is the incoming transmitted from the transponder of the communication satellite 20, the digital broadcast A tuner 41 that performs a frequency conversion process on a signal to obtain a QPSK modulated signal S1, and a demodulator 42 that demodulates the QPSK modulated signal S1 to obtain a signal S2 having a DVB frame configuration.
And error correction is performed on the DVB frame-structured signal S2 output from the demodulator 42, and the MPEG-2 transport packet S as digital broadcast data is corrected.
And an ECC (Error Correction Code) decoder 43 that sequentially obtains 3.

The signal processing unit _32-1 includes an NIT detection circuit 44 for detecting a NIT (network information table) from the MPEG2 transport packet S3 sequentially output from the ECC decoder 43, and a NIT detection circuit 44. It has a memory 45 for storing the detected table NITa, and a memory 46 for storing the table NITa obtained by changing the table NITa stored in the memory 45 so as to be compatible with CATV by the control unit 31. I have. The NIT detection circuit 44 detects NIT based on the fixed PID.

As described above, the table structure of the NIT in the digital broadcast data relating to the communication satellite 20 is as shown in FIG. 7, and the table structure of the table NITa detected by the NIT detection circuit 44 is the same.
In obtaining the table NITb, the control unit 31
A satellite delivery system descriptor having transmission frequency information and the like in the table NITa (FIG. 8)
) Is changed to a CATV delivery system descriptor whose structure is shown in FIG.

The main contents will be described. The descriptor tag is defined by DVB and indicates the type of the descriptor. In this descriptor, “0x4
4 ". The frequency indicates a transmission frequency for each stream (multiplexed coded data) in CATV. The FEC (outer code) indicates an error correction code as an outer code. In this descriptor,
It becomes “0010”. The modulation / symbol rate / FEC (inner code) indicates the specification regarding the transmission system.

In some cases, the number of digital broadcasting signals in CATV is smaller than the number of digital broadcasting signals in satellite digital broadcasting. That is, the communication satellite 2
0 has L transponders and the number of digital broadcast signals in the satellite digital broadcast is L, C
In the ATV, N (N <L) digital broadcast signals of the L digital broadcast signals may be selectively used. In that case, the control unit 31 sets the table NI
To obtain Tb, CA in table NITa
TS corresponding to digital broadcast signals not used in TV
(Transport stream) Information on ID (FIG. 7)
, The information from the transport stream ID to the descriptor) is deleted.

The writing and reading of the memories 45 and 46 are controlled by the control unit 31 via the interface 47. The reception frequency of the tuner 41 described above is also controlled by the control unit 31 via the interface 47.

As described above, the NIT detection circuit 44
And the table NITa stored in the memory 45
Is based on, for example, the operation of the operation unit 34 by the user.
Displayed on the display unit 35 under the control of the control unit 31. For example, based on the satellite delivery system descriptor and the service list descriptor in the table NITa, the relationship between the frequency and the service ID of each transponder is displayed. By referring to this display, the user can determine whether or not the table NITa detected by the NIT detection circuit 44 is abnormal. Possible causes of the table NITa to be abnormal include a case where the NIT detection circuit 44 is abnormal or a case where the NIT itself included in the digital broadcast data is abnormal.

Although not described above, the memory 31M in the control unit 31
Stores a table NITc as a spare NIT. This table NITc is stored in the NIT detection circuit 4
Before the table NITa detected in step 4 becomes abnormal,
The table NITa detected by the NIT detection circuit 44
It is. For example, NIT detection in the NIT detection circuit 44 is performed only once a day under the control of the control unit 31, but a normal table NITa detected one day ago is stored in the memory 31M as a table NITc.

As described above, in principle, the table NITa detected by the NIT detection circuit 44 is changed by the control unit 31 so as to conform to CATV, and the table NTa obtained is obtained.
ITb is stored in the memory 46. However, when the table NITa detected by the NIT detection circuit 44 is abnormal, the table NITb obtained by changing the table NITa also becomes abnormal.

Therefore, in this embodiment, when the user recognizes that the table NITa is abnormal based on the contents of the table NITa displayed on the display unit 35, the user operates the operation unit 34 to avoid the NIT abnormality. Operation can be performed. When the operation for avoiding the abnormality is performed, the control unit 31 obtains a table NITd by changing the table NITc stored in the memory 31M so as to conform to CATV, and replaces the table NITd with the above-described table NITb. It is stored in the memory 46. When the operation for avoiding the abnormality is performed, the memory 3
In 1M, the table NITc used for obtaining the table NITd is held as a spare NIT.

Further, the signal processing unit 32 _-1 detects NIT from the MPEG2 transport packet S3, sequentially output from the ECC decoder 43, the memory 4 the NIT
NITb or NITd stored in table 6
And a NIT replacement circuit 48 for replacing This N
The IT replacement circuit 48 also performs NIT based on the fixed PID.
Is detected. Also, the control unit 31 controls the table NIT.
In order to obtain b or NITd, as described above, when information relating to a TS (Transport Stream) ID corresponding to a digital broadcast signal not used in CATV in the table NITa or NITc is deleted, the NIT replacement circuit 48 Dummy bits are inserted into portions related to the deleted information.

Further, the signal processing unit 32 _-1, to the MPEG2 transport packet S4 for NIT is replaced with NIT substitution circuit 48, Reed-Solomon (204,
188), an ECC encoder 49 that obtains a DVB frame-structured signal S5 (see FIG. 2B) by adding an error correction code, and the like.
4QAM and (Quadrature Amplitude Modulation) modulator 50 which performs modulation, frequency to obtain a digital broadcast signal BS ₁ for CATV in the VHF band or UHF band by converting the output of the 64QAM-modulated signal outputted from the modulator 50 And a converter 51.

[0041] The signal processing unit 32 _-2 to 32 _-N includes a tuner 41 in the signal processing unit 32 _-1, respectively above,
Demodulator 42, ECC decoder 43, interface 4
7, an NIT replacement circuit 48, an ECC encoder 49, a modulator 50, and a frequency converter 51. The signal processing unit 32 in the NIT substitution circuit 48 of _-2 to 32 _-N, each signal processing unit 32 _-1 memory 46
The NIT is replaced using the table NITb or NITd stored in the NIT. In the tuners of the signal processing units 32 _{-2 to} 32 _-N , digital broadcast signals transmitted from the second to Nth transponders of the communication satellite 20 are selected from a plurality of digital broadcast signals received by the antenna 11 respectively. Then, a frequency conversion process is performed on the digital broadcast signal to obtain a QPSK modulated signal S1. The reception frequencies of the tuners of the signal processing units 32 _{-2 to} 32- _N are controlled by the control unit 31 through the interface 4.
7 is controlled. Further, the signal processor 32 _{-2 to} 3
In the 2- _N frequency converter 51, the digital broadcast signal BS
Transmission frequency of ₁ to BS _N is frequency-converted differently respectively.

Next, the modulation conversion transmitting device 12 shown in FIG.
Will be described. A plurality of digital broadcast signals received SHF band in the antenna 11 is supplied to a tuner 41 of the signal processor 32 _-1. In the tuner 41, the communication satellite 2
0, a digital broadcast signal sent from the first transponder is selected, and the digital broadcast signal is subjected to a frequency conversion process to generate a QPSK modulated signal S1.
Is obtained. This QPSK modulated signal S1 is supplied to a demodulator 42, which demodulates the QPSK modulated signal S1 to obtain a DVB frame-structured signal S2 (see FIG. 2B). The signal S2 having the DVB frame structure is supplied to the ECC decoder 43. The ECC decoder 43 performs an error correction process on the signal S2 having the DVB frame structure, and outputs the MPEG2 transport packet S3 as digital broadcast data. Are sequentially obtained (see FIG. 2A).

The MPEG2 transport packet S3 sequentially output from the ECC decoder 43 is supplied to the NIT detection circuit 44, where the NIT detection circuit 44
NIT is detected from the PEG2 transport packet S3. Then, the detected table NITa is supplied to the memory 45 and stored.

The control unit 31 stores the table N in the memory 45
The ITa is read, and the satellite delivery system descriptor in the table NITa is read (FIG. 8).
) To the CATV delivery system descriptor (see FIG. 11), and furthermore, the table NITa
Table N adapted to CATV by deleting information related to TS (Transport Stream) ID corresponding to digital broadcast signals not used in CATV
ITb is obtained, and this table NITb is stored in the memory 46.

The display unit 3 is controlled by the control unit 31.
5 shows the table NITb detected by the NIT detection circuit 44
Is displayed. The control unit 31 allows the user to operate the operation unit 3.
When performing the operation for avoiding the abnormality in step 4, the table NITc as a spare NIT is read from the memory 31M, and the table NITc is changed to obtain a table NITd conforming to CATV. Instead of the table NITb described above,
This table NITd is stored in the memory 46.

The MPEG2 transport packet S3 sequentially output from the ECC decoder 43 is supplied to a NIT replacement circuit 48, where the NIT replacement circuit 48
The IT is detected, and the NIT portion is replaced with a table NITb or NITd stored in the memory 46. In this case, when the control unit 31 obtains the table NITb or NITd, if the information related to the TS (transport stream) ID corresponding to the digital broadcast signal not used in CATV in the table NITa or NITc is deleted, the NIT replacement circuit At 48, a dummy bit is inserted into a portion related to the deleted information.

The MPEG2 transport packet S4 whose NIT has been replaced by the NIT replacement circuit 48 is an ECC
The ECC encoder 49
In this case, a signal S5 having a DVB frame structure is added by adding an error correction code of Reed-Solomon (204, 188).
Is formed. The signal S5 having the DVB frame configuration is supplied to the modulator 50. The modulator 50 performs 64QAM modulation processing on the signal S5 having the DVB frame configuration to obtain a 64QAM modulated signal S6. And this 6
The 4QAM modulation signal S6 is supplied to the frequency converter 51,
The frequency converter frequency conversion processing to 64QAM modulated signal at 51 is performed digital broadcast signal BS ₁ for CATV of a predetermined transmission frequency of the VHF band or UHF band is obtained.

The plurality of SHF band digital broadcast signals received by the antenna 11 are sent to the signal processing units 32 _{-2 to} 32 _-2.
-N , and each tuner selects a digital broadcast signal transmitted from the second to Nth transponders of the communication satellite 20, performs a frequency conversion process on the digital broadcast signal, and performs a QPSK modulation signal. S1 is obtained. Then, the memory 4 of the signal processing unit 32 _-2 to 32 in _-N, signal processing unit 32 _-1 in each NIT substitution circuit 48
NITb or NITd stored in table 6
Are used to replace the NIT, etc., and the same processing as that of the signal processing unit _32-1 is performed.
Digital broadcast signal BS ₂ to BS _N for CATV of predetermined transmission frequency F band is obtained.

Further, as described above, the signal processing units 32 _-1 to 32 _-1 .
The digital broadcast signals BS _{1 to} BS _N obtained by the 32- _N are supplied to an adder 33 and added thereto.
V is transmitted to the transmission line 13. Thus, the digital broadcast signal BS ₁ to BS _N for CATV, of PSI (Program Specification Information) in digital satellite broadcasting, N
Only the IT is changed. Therefore, the set as a receiving terminal connected to the CATV transmission path 13
In the top boxes 14 _{-1 to} 14 _-m , the channel selection operation is performed in the same manner as the above-described channel selection operation in the satellite digital broadcast receiver.

As described above, in the present embodiment, the modulation conversion transmitting device 12 converts the MPEG2 transport packet S3 as digital broadcast data in satellite digital broadcast (first network) into NIT data.
NIT is detected by the detection circuit 44, and the detected table N
By changing ITa, a table NITb conforming to CATV (second network) is obtained, and the NIT of the MPEG2 transport packet S3 as digital broadcast data in satellite digital broadcasting is replaced with NITb.
MPEG as digital broadcast data in ATV
2 transport packets S4 are obtained. Accordingly, it becomes possible to distribute a digital broadcast program broadcasted by satellite digital broadcast on CATV.

When the detected table NITa is abnormal and the user performs an operation for avoiding the abnormality using the operation unit 34, the table NITC as the spare NIT stored in the memory 31M of the control unit 31 is stored in the CATV. Is obtained to obtain a table NITd, and the NIT is replaced using this table NITd instead of the abnormal table NITb. Therefore, even if the detected table NITa is abnormal, digital broadcasting data in CATV that can be correctly received by the receiving terminal can be obtained.

In the above embodiment, the normal table NITc detected by the NIT detection circuit 44 is stored in the memory 31M of the control unit 31 as a spare NIT. Part 31
Table NIT conforming to CATV obtained by changing
d may be stored. In this case, when the user performs an operation for avoiding an abnormality using the operation unit 34, the control unit 31
Reads the table NITd from the memory 31M and stores it in the memory 46.

Further, in the above-described embodiment, when the user performs an operation for avoiding an abnormality on the operation unit 34, the control unit 3
A table NITc as a spare NIT stored in the memory 31M of the first NIT is used.
The control unit 31 determines the abnormality of the table NITa based on whether or not predetermined information is obtained from the table NITa detected by the detection circuit 44, and based on the determination result, the spare NIT automatically stored in the memory 31M is determined. May be determined whether or not to use the table NITc.

In the above embodiment, the NIT
The contents of the table NITa detected by the detection circuit 44 are displayed on the display unit 35. The user can refer to this display to determine whether or not the table NITa is abnormal. part 32 _-1 to 32 to select a predetermined channel from the digital broadcast signal BS ₁ to BS _N outputted from _-N depending on whether an image can be displayed for example on the monitor can also be determined the abnormality of the table NITa.

[0055]

According to the present invention, the NIT of the digital broadcast data in the first network is detected by the table detecting means, and the NIT is changed so as to be compatible with the second network. This is a method for obtaining digital broadcast data in the second network by replacing the NIT of broadcast data with the above-mentioned changed NIT. A spare NIT is stored, and the NIT detected from the digital broadcast data in the first network is stored. When abnormal, the NIT is replaced by using the spare NIT.

Therefore, when the table detecting means is abnormal, or when the NIT included in the digital broadcast data in the first network is abnormal, the NIT detected by the table detecting means is abnormal. Even so, it is possible to obtain digital broadcast data in the second network that can be correctly received by the receiving terminal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital CATV system as an embodiment.

FIG. 2 is a diagram showing an MPEG2 transport packet and a frame configuration of a DVB system.

FIG. 3 is a diagram showing a packet structure of an MPEG2 transport packet.

FIG. 4 is a diagram showing a packet structure of a PES packet.

FIG. 5 shows a program association table (P
FIG. 4 is a diagram showing a table structure of AT).

FIG. 6 is a diagram showing a table structure of a program map table (PMT).

FIG. 7 is a diagram showing a table structure of a network information table (NIT).

FIG. 8 is a diagram showing a structure of a satellite delivery system descriptor in NIT.

FIG. 9 is a diagram showing a structure of a service list descriptor in NIT.

FIG. 10 is a block diagram illustrating a configuration of a modulation conversion transmission device that configures a digital CATV system.

FIG. 11 is a diagram showing a structure of a CATV delivery system descriptor.

[Explanation of symbols]

10 ... CATV system, 11 ... antenna, 1
2 ... Modulation conversion transmission device, 13 ... CATV transmission line, 14 _{-1 to} 14 _-m ... Set top box,
15 _-1 to 15 _-m: monitor, 20: communication satellite, 3
1 ... control unit, 31M ... memory, 32 _{-1 to} 32- _N
... Signal processing unit, 33 ... Adder, 34 ... Operation unit, 35 ... Display unit, 41 ... Tuner, 42 ...
Demodulator, 43 ECC decoder, 44 NI
T detection circuit, 45, 46 ... memory, 47 ... interface, 48 ... NIT replacement circuit, 49 ... E
CC encoder, 50: modulator, 51: frequency converter

Claims (5)

[Claims] 1. A signal processing device for converting a first digital broadcast signal of a predetermined transmission frequency on a first network into a second digital broadcast signal of a predetermined transmission frequency on a second network, First frequency conversion means for frequency-converting one digital broadcast signal to obtain a first digital modulation signal; demodulation means for demodulating the first digital modulation signal to obtain digital broadcast data; Table detecting means for detecting a network information table having physical information on a transmission path from the output digital broadcast data; and a network information table detected by the table detecting means.
Table changing means for changing an information table so as to be compatible with the second network; and a network obtained by changing the network information table of digital broadcast data outputted from the demodulating means by the table changing means. Table replacing means for replacing the information table with the information table; modulating means for modulating the digital broadcast data whose network information table has been replaced by the table replacing means to obtain a second digital modulation signal; A second frequency conversion means for converting the frequency of the signal to obtain the second digital broadcast signal; and a table storage means for storing a spare network information table; It said network detected by the detecting means,
When the information table is abnormal, the table replacement means replaces the network information table using the spare network information table stored in the table storage means. Processing equipment. 2. A network information table suitable for the first network is stored in the table storage means, and when the network information table detected by the table detection means is abnormal, the table information is stored in the network information table. The spare network information stored in the table storage means
2. The signal processing apparatus according to claim 1, wherein a table is changed by said table changing means and used by said table replacing means. 3. A network information table suitable for the second network is stored in the table storage means, and when the network information table detected by the table detection means is abnormal, the network information table is stored. The spare network information stored in the table storage means
2. The signal processing apparatus according to claim 1, wherein the table is used as it is by the table replacement means. 4. The signal processing apparatus according to claim 1, further comprising table content display means for displaying the contents of the network information table detected by said table detection means. 5. The spare network information table stored in the table storage means is a network information table detected by the table detection means.
The network information table detected by the table detecting means before the information table becomes abnormal or the network information table obtained by changing the network information table by the table changing means. The signal processing device according to claim 1, wherein: