JPH11150717A - Signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain distribution service of a digital broadcast program through a 2nd network that has been broadcast through a 1st network. SOLUTION: A tuner 41 selects a digital broadcast signal with transmission frequency to obtain an MPEG2TS packet S3 as digital data in a digital satellite broadcast. An NIT detection circuit 44 detects an NIT with the MPEG2TS packet S3 and a control section 31 revises it to obtain a table NITb in matching with a CATV. An NIT replacement circuit 48 detects the NIT from the MPEG 2TS packet S3, replaces it with the table NITb to obtain an MPEG2TS packet S4 as digital broadcast data in the CATV. Then addition processing of an error correction code, modulation processing and frequency conversion processing are applied to the MPEG2TS packet S4 to obtain a digital broadcast signal BS1 with a prescribed transmission frequency for the CATV.

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.
Is changed to be compatible with the first network, and 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, thereby being broadcast on the first network. The present invention relates to a signal processing device that enables a digital broadcast program to be distributed over a second 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.

Accordingly, in the present invention, the digital broadcast program broadcasted on the first network is replaced with the NIT of the digital broadcast data in the first network by the NIT adapted to the second network. An object of the present invention is to provide a signal processing device capable of providing a distribution service. In the present invention,
It is an object of the present invention to provide a signal processing device that can determine whether or not the above-mentioned NIT replacement is performed correctly.

[0005]

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 network having physical information on a transmission path from the digital broadcast data output from the demodulator. First table detecting means for detecting the information table, table changing means for changing the network information table detected by the first table detecting means so as to be compatible with the second network, and demodulating means. Network information of digital broadcast data to be output A table replacing means replaces the network information table obtained by changing the table at table change means, network Information in this table replacement means
Modulating means for modulating the digital broadcast data whose table has been replaced to obtain a second digital modulated signal, and second frequency converting means for converting the frequency of the second digital modulated signal to obtain a second digital broadcast signal Is provided.

The 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. The digital broadcast data in the first network has an NIT (Network Information Table) 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.

The digital broadcast data in the second network is formed by replacing the NIT of the digital broadcast data in the first network with the 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.

In the signal processing apparatus according to the present invention, the second table detecting means for detecting the NIT from the digital broadcast data whose NIT has been replaced by the table replacing means, and the second table detecting means detects the NIT. NI
The apparatus may further include a replacement determining unit that compares T with the NIT changed by the table changing unit and determines whether the NIT is correctly replaced by the table replacing unit. If the replacement has been performed correctly, the NIT detected by the second table detecting means matches the NIT changed by the table changing means.

By displaying such a determination result of replacement on, for example, a display device, the user can know whether or not replacement has been performed correctly. And, for example,
When it is determined that the replacement has not been performed correctly, the first table detecting means makes the first table detecting means detect the NIT again from the digital broadcast data output from the demodulating means, and the table replacing means detects the NIT detected again by the table changing means. Control means for controlling the use of the NIT obtained by changing in step (1).

[0011]

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 the packet structure of an MPEG2 transport packet. The first 4 bytes of the 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 on 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 the receiver for receiving the above-described 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.

Then, 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 the 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 sending 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 detecting 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 detecting 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.

There are cases where 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.

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
NI to replace with table NITb stored in No. 6
It has a T replacement circuit 48. This NIT replacement circuit 48
However, the NIT is detected based on the fixed PID. When the control unit 31 obtains the table NITb, as described above, the CAT in the table NITa is used.
TS corresponding to digital broadcast signals not used in V
When the information related to the (transport stream) ID is deleted, the NIT replacement circuit 48 inserts a dummy bit into a portion 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 frequency of the 64QAM-modulated signal outputted from the modulator 50 And a converter 51.

[0035] 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. Then, the signal processing unit 32 _-2 to 32 _-N NIT substitution circuit 48 of the table NITb that are respectively stored in the memory 46 of the signal processor 32 _-1 is used to replace the NIT is carried out. The signal processing units 32 _{-2 to} 32 _-N
Of the communication satellite 20 from the plurality of digital broadcast signals received by the antenna 11 respectively.
, A digital broadcast signal transmitted from the transponder is selected, and the digital broadcast signal is subjected to frequency conversion processing 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 via the interface 47. Further, the signal processing unit 32 _-2 to 32 _-N in the frequency converter 51, the transmission frequency of the digital broadcast signal BS 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. Even without the above, this NIT
The operation of detecting the NIT in the detection circuit 44 is performed only once a day, for example. The control unit 31 reads the table NITa from the memory 45, changes the satellite delivery system descriptor (see FIG. 8) in the table NITa to the CATV delivery system descriptor (see FIG. 11), and further changes the table NITa in the table NITa. TS (Transport Stream) corresponding to digital broadcast signals not used in CATV
A table NITb conforming to CATV is obtained by deleting information related to the ID, and this table NITb is stored in the memory 4.
6 is stored.

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

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.

A 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
6 using the table NITb stored in
Like T replacement is made, the signal processing unit 32 _-1 same processing is performed with a digital broadcast signal for CATV of a predetermined transmission frequency of the VHF band or UHF band BS ₂ to BS _N
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 transmission device 12 converts the MPEG2 transport packet S3 as digital broadcast data in satellite digital broadcast (first network) into NIT data.
Is detected and the detected table NITa is changed to CA
Table NIT suitable for TV (second network)
b of the MPEG2 transport packet as digital broadcast data in satellite digital broadcasting.
By replacing T with NITb, an MPEG2 transport packet S4 as digital broadcast data in CATV is obtained. Accordingly, it becomes possible to distribute a digital broadcast program broadcasted by satellite digital broadcast on CATV.

FIG. 12 shows another configuration of the modulation conversion transmission device 12. 12, parts corresponding to those in FIG. 10 are denoted by the same reference numerals, and detailed description thereof will be omitted. The signal processing unit 32 _-1, NI in NIT substitution circuit 48
It has an NIT detection circuit 61 for detecting an NIT from the MPEG2 transport packet S4 in which T has been replaced, and a memory 62 for storing a table NITc detected by the NIT detection circuit 61. NIT detection circuit 61
In, the NIT is detected based on the fixed PID. The writing and reading of the memory 62 are controlled by the control unit 31 via the interface 47.

The control section 31 detects a table NITc detected by the NIT detection circuit 61 and stored in the memory 62 and a table NIT for replacement stored in the memory 46.
By comparing the ITb, it determines whether replacing the NIT in NIT substitution circuit 48 of the signal processing unit 32 _-1 are correct. In this case, table NITc and table N
When the ITb are coincident, NIT of the signal processor 32 _-1
The replacement circuit 48 determines that the replacement has been performed correctly.

Further, the signal processing unit 32 _-2 to 32 _-N is also not shown, NIT detection circuit in the signal processing unit 32 _- 16
1 and a memory 62. Then, the control unit 31 similarly stores the table NITc stored in the memory 62 of the signal processing units 32 _{-2 to} 32 _-N and the signal processing unit 32
By comparing the NIT with the table NITb stored in the memory 46 of ₋₁ , it is determined whether or not NIT replacement is correctly performed by the NIT replacement circuit 48 of the signal processing units 32 _{-2 to} 32 _-N .

The above-described signal processing unit 32 _-1 to 32 _-N in NI
The result of the determination as to whether or not the NIT has been properly replaced by the T replacement circuit 48 is displayed on the display unit 35 under the control of the control unit 31. The control unit 31, when determining the replacement of the NIT in NIT substitution circuit 48 of the signal processing unit 32 _-1 to 32 _-N is not performed correctly, for example, NI
T detecting circuit 44 NIT is detected again, NIT at the detected give table NITa new table NITb to modify the signal processing unit 32 _-1 in to 32 _-N NIT substitution circuit 48 of the new table NITb To be replaced.

As shown in FIG.
Is determined by the NIT replacement circuit 48 of the signal processing units 32 _{-1 to} 32- _N to determine whether or not NIT replacement is correctly performed, and the determination result is displayed on the display unit 35. the user NIT by the signal processing unit 32 _-1 to 32 _-N
Can be easily known whether or not NIT has been correctly replaced, and it is possible to immediately cope with a case where NIT is not correctly replaced. In addition, by incorporating the check circuit in the modulation conversion transmitting device 12 in this manner, the system configuration can be simplified as compared with the case where an external check circuit is provided. Can be built.

The modulation conversion transmitting device 12 shown in FIG.
Now, the table NIT detected by the NIT detection circuit 44
The memory 45 for storing a and the memory 62 for storing a table NITc detected by the NIT detection circuit 61 are separately provided. However, since the NIT detection in the NIT detection circuit 44 is performed only once a day, for example, the memory 45 may be used without using the memory 62. As a result, the required memory capacity can be reduced, and the cost of the system can be reduced.

[0049]

According to the present invention, an NIT (Network Information Table) of digital broadcast data in the first network is detected and the NIT is detected.
Change T to be compatible with the second network,
NIT of Digital Broadcasting Data in Japanese Network
Is replaced with the changed NIT to obtain digital broadcast data in the second network.
A digital broadcast program broadcast on the second network can be distributed on the second network.

Further, the NIT is detected from the digital broadcast data in which the NIT has been replaced by the table replacing means, and the detected NIT is compared with the NIT changed by the table changing means.
By judging whether the replacement of T has been performed correctly and displaying the result of the determination on a display, for example, the user can easily know whether or not the replacement has been performed correctly, and the replacement has been performed correctly. If not, it will be possible to take immediate action. By incorporating the check circuit in the apparatus as described above, the system configuration can be simplified as compared with the case where an external check circuit is provided, and a highly reliable system can be constructed while saving space and cost.

[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.

FIG. 12 is a block diagram showing another configuration of the modulation conversion transmission device that constitutes the digital CATV system.

[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, 32 _{-1 to} 32- _N ... signal processing unit, 3
3 ... Adder, 34 ... Operation unit, 35 ... Display unit, 41 ... Tuner, 42 ... Demodulator, 43 ...
・ ECC decoder, 44, 61... NIT detection circuit,
45, 46, 62 memory, 47 interface, 48 NIT replacement circuit, 49 ECC encoder, 50 modulator, 51 frequency converter

Claims (6)

[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; First table detecting means for detecting a network information table having physical information on a transmission path from the output digital broadcast data; and detecting the network information table detected by the first table detecting means. Table changing means for changing the table so as to be compatible with the second network; Table replacement means for replacing the network information table of digital broadcast data output from the means with the network information table obtained by changing the information by the table changing means; and replacing the network information table with the table replacement means Modulation means for modulating the obtained digital broadcast data to obtain a second digital modulation signal; and second frequency conversion means for converting the frequency of the second digital modulation signal to obtain the second digital broadcast signal. A signal processing device comprising: 2. The signal processing apparatus according to claim 1, wherein said table changing means changes at least transmission frequency information of a network information table detected by said first table detecting means. . 3. 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 table changing means includes a step for changing the number of digital broadcast signals on the first network. 2. The signal processing apparatus according to claim 1, wherein information related to a digital broadcast signal that does not correspond to the digital information signal on the second network is deleted from the broadcast signal. 4. The apparatus according to claim 1, wherein said table replacement means inserts a dummy bit into a portion related to the information deleted by said table change means in a network information table of digital broadcast data output from said demodulation means. The signal processing device according to claim 3. 5. A second table detecting means for detecting a network information table from digital broadcast data whose network information table has been replaced by said table replacing means, and said network information table is detected by said second table detecting means. The network information table and the network information table changed by the table changing means.
2. The signal according to claim 1, further comprising replacement determination means for comparing the table with a table to determine whether replacement of the network information table by the table replacement means has been performed correctly. Processing equipment. 6. When the replacement determining means determines that the replacement is not performed correctly, the first table detecting means converts the network information table from the digital broadcast data output from the demodulating means. The apparatus further comprises control means for detecting the network information table again by the table replacing means and using the network information table changed by the table changing means by the table changing means. The signal processing device according to claim 5.