JPH11150719A - Digital catv system and its receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the burden of a CATV station at the time of retransmitting digital ground broadcasting to a CATV transmission line by providing the CATV station with a sending means sending a broadcasting signal through two kinds of digital modulation systems. SOLUTION: This CATV station transmits a signals obtained by modulating a signal from the sending source 8 of a program produce by the CATV station as CATV broadcasting by a 64QAM modulator 12, a signal obtained by modulating a signal obtained by receiving digital satellite broadcasting through a receiving antenna 5 and demodulating it by a receiver for the digital satellite broadcasting 7 through a 64QAM modulator 11 and a signal obtained by receiving the digital broadcasting through an antenna 6, frequency-converting it to an optical channel through a frequency converter 10 and by frequency-multiplexing it through a synthesizer 14. in this case, digital ground broadcasting of the same transmission band width as a digital CATV signal is demodulated not to make it 64QAM-modulated but the digital ground broadcasting received by the CATV station is sent out to a channel in which the CATV station desires to transmit it only by frequency-converting it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable television system and a receiving technique thereof, and more particularly to a CATV system in which different types of digitally modulated signals are frequency-multiplexed on the same cable, and a receiving apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, both terrestrial broadcasting and cable television using a CATV transmission line are NTSC (National Television System).
Committee) method, the composite video signal of the vestigial sideband was transmitted with amplitude modulation, so it can be received by the same demodulation means,
Even when re-transmitting terrestrial broadcasting on CATV, it was able to be received by the CATV-dedicated receiving terminal. On the other hand, even television receivers that mainly receive terrestrial broadcasts have commercialized a CATV-compatible television receiver equipped with a tuner that can tune to the use frequency range of CATV, and have been able to receive CATV programs without viewing restrictions.

[0003] Television broadcasting called cable television and related terrestrial broadcasting and satellite broadcasting are described in "Introduction to Cable Television Technology", edited by the Cable Machinery Technical Committee of the Electronic Machinery Manufacturers Association issued by Corona. I have.

On the other hand, with the recent development of digital transmission technology and the like, the transmission channel of NTSC video which is an analog signal
A plurality of digitized images are about to be transmitted on one channel. Regarding digital transmission of cable television, see the Telecommunications Society of Japan Technical Report (vol.19.No.42) published on September 21, 1995, vol. Broadcast transmission experiment ".

According to this report, MPEG2 (MPEG2)
It is converted into a data stream in a format called a transport stream in which digital data such as images compressed by digital image compression technology called multiplexed, and subjected to signal processing such as Reed-Solomon error correction, and 64QAM (Quadra
It is modulated by a digital modulation technique called “ture Amplitude Modulation (64-level quadrature amplitude modulation)” and transmitted over a CATV transmission line.

For digital transmission by satellite, 19
Technical Report of the Institute of Television Engineers of Japan published on September 21, 1995 (vo
l.19.No.42) `` Overview of CS Digital Broadcasting System '' on pages 25-30 and Nikkei Electronics September 2, 1996, p. 149, `` Japan's first digital Satellite broadcasting ".

[0007] In these reports and papers, each transmission method is common until it is composed of a data stream in a format called a transport stream such as image compression technology. The modulation method is CATV, 64QAM is used, and the satellite uses QPSK (Quadrature). Phase
Shift Keying (four-phase modulation) is adopted, and the error correction method is also different.

[0008] Behind this is the Telecommunications Technology Council of the Ministry of Posts and Telecommunications of Japan and the DVB (Digital Video Broadcasting:
In standardization organizations such as digital video broadcasting),
The parts that can be shared as much as possible, such as information source coding and multiplexing methods such as digital image compression technology, have the concept of cross-media that is the same for CATV, terrestrial broadcasting, and satellite broadcasting.

In CATV, terrestrial broadcasting, and satellite broadcasting, transmission path coding such as a modulation method, which is a unique part due to different transmission paths, is different.

[0010] Based on this idea, digitalization of terrestrial broadcasting has been studied, and OFDM (OFD) has been used as one of the terrestrial modulation methods.
M: orthogonal frequency multiplexing). Regarding the application of the OFDM system to terrestrial broadcasting, for example, see the SMPTE Journal, May 1995, pages 258 to 265 (SMPTE Jour
nal, May 1995 pp.258-265), `` Performance Simulat
ion of COFDM for TV Broadcast Application ". This terrestrial broadcast and cable TV have different transmission paths between terrestrial and CATV, but both have a transmission bandwidth of 6M.
Same as Hz.

[0011]

In the above technique,
Digital CATV broadcasting uses the 64QAM modulation method,
For example, when retransmitting digital satellite broadcasts with different transmission bandwidths using CATV, the digital satellite broadcast QP
The SK-modulated signal is demodulated, and 64QAM modulation, which is the modulation method of the CATV transmission path, is performed again and transmitted.

At this time, 64 QAMs are required for the number of channels to be retransmitted.
A modulator is required. Similarly, when digital terrestrial broadcasting is retransmitted by CATV, if the CATV station demodulates the OFDM modulated signal and transmits again by 64QAM modulation, 64QAM modulators for the number of channels to be retransmitted are required. CATV
The increase in station equipment and the economic burden are conceivable.

An object of the present invention is to provide digital terrestrial broadcasting with CA.
An object of the present invention is to provide a CATV system and a receiving apparatus for reducing the burden on a CATV station when retransmitting to a TV transmission path.

[0014]

According to the present invention, there is provided a digital CATV system comprising: a digital CA;
CATV digital terrestrial broadcasting with transmission bandwidth equal to TV signal
When retransmitting from a station, the digital terrestrial broadcast received by the CATV station is transmitted only by converting the frequency to the channel desired by the CATV station, without demodulating the digital terrestrial broadcast and performing 64QAM modulation. CATV station configuration.

Further, as the receiving apparatus, a demultiplexing means for separating desired video signal data, audio signal data, and the like from the digital data in the transport stream format, and a desired video signal data output from the demultiplexing means. Video signal format conversion means for converting a signal into a signal format for displaying video, and audio signal format conversion means for converting desired audio signal data output from the demultiplexing means into an analog signal format for outputting audio. In a digital broadcast receiving apparatus, a demodulation unit corresponding to two types of demodulation systems is provided to select and demodulate a desired digital modulation signal and output digital data in a transport stream format. Selects the demodulation method that matches the modulation method of the channel signal, and the appropriate reception configuration And control means for performing control to switch to.

According to these means, in the CATV system, the burden on the CATV station can be reduced and the digital terrestrial broadcasting can be retransmitted, and the digital modulation system of the channel desired by the subscriber is controlled by the control means in the receiving device. Can be switched to a demodulation method corresponding to the demodulation method and a reception configuration suitable for the demodulation method, so that the same receiving apparatus can receive digital broadcasts of different modulation methods.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the present invention. In the figure, 1 is a CATV transmission line, 2 is a subscriber terminal, 3 is a device for broadcast reception and data communication, 4 is a display device such as a television receiver (TV), 5 is a reception antenna for satellite broadcasting, 6 is A terrestrial broadcasting receiving antenna, 7 is a digital satellite broadcasting receiver, 8 is a program independently produced by a CATV station (for example, a program from a studio in a CATV station, a program supplied on a tape or disk of a movie, etc.). 9 is a viewing management controller, 10 is a frequency converter, 11, 1
2 is a 64QAM modulator, 13 is a data modulator / demodulator, and 14 is a combiner.

In the CATV station, a signal obtained by modulating a signal from a transmission source 8 of a program independently produced by the CATV station with a 64QAM modulator 12 and a digital satellite broadcast are received by a receiving antenna 5 as a CATV broadcast. The signal demodulated by the receiver 7 is modulated by the 64QAM modulator 11, the signal is received by the antenna 6 for receiving digital terrestrial broadcasting, and the frequency converted to an arbitrary channel by the frequency converter 10 is frequency-multiplexed through the synthesizer 14. And transmit. In this case, the transmission bandwidth of one channel of digital terrestrial broadcasting is equal to the transmission bandwidth of one channel of digital CATV broadcasting. It is easy to replace with

A signal obtained by modulating data from the viewing management controller 9 by the data modulator / demodulator 13 is also used by the synthesizer 1.
4 and frequency-multiplexed with the above CATV broadcast and transmitted. CA
The TV transmission path 1 multiplexes the CATV broadcast signal and the data signal (hereinafter, referred to as a downlink data signal) in a downlink direction (here, a direction from a cable TV station to a subscriber's house) and transmits the multiplexed signal. The CATV transmission line 1 and the subscriber's home are connected by a subscriber terminal 2, and the subscriber terminal is connected to the broadcast receiving and data communication terminal 3 through the home wiring of the subscriber's home.

The broadcast receiving and data communication terminal 3 receives the downlink data signal, inputs the data to the CPU that performs demodulation, decoding, and control, compares the data with the channel selection information of the subscriber, and receives the CATV broadcast signal. In this case, it has functions such as channel selection, demodulation, and signal processing for outputting to a display device 4 such as a television receiver.

Particularly in channel selection and demodulation, 64QA
Two demodulators corresponding to the M system and the OFDM system are provided, and control is performed such that the demodulation unit is switched according to the modulation system of the selected channel to receive. Between the terminal 3 and the display device 4,
Connect with an AV cord or coaxial cable. In the bidirectional CATV system, the terminal 3 transmits a data signal (hereinafter, referred to as an uplink data signal) such as viewing information and contract information to the CATV station side.
Enter

With this configuration, in the CATV system,
When retransmitting a digital terrestrial broadcast having the same transmission bandwidth as a digital CATV signal from a CATV station, the CATV station does not demodulate the digital terrestrial broadcast and performs 64QAM modulation. CATV to transmit only by frequency conversion to the desired channel for retransmission
It is possible to retransmit digital terrestrial broadcasting by reducing the burden on the station, and switch to a demodulation method according to the digital modulation method of the channel desired by the subscriber and a reception structure suitable for it by the control means in the receiving device. Therefore, digital broadcasts of different modulation schemes can be received by the same receiving device.

Next, an embodiment of the broadcast receiving and data communication terminal 3 will be described with reference to FIG. In the figure, the same parts as those in FIG. 20 is an input / output terminal, 21 is a filter for passing a downlink data signal band,
22 is a demodulation unit for a downlink data signal, 23 is a filter for passing an uplink data signal band, 24 is a modulation unit for an uplink data signal, 25 is a tuner, 26 is a filter for passing an output signal of a tuner 25, 27 is a down converter, 28
Is a 64QAM demodulator, 29 is an OFDM demodulator, 30 is a descrambler, 31 is a demultiplexer, 32 is a video decoder,
33 is an audio decoder, 34 is an NTSC encoder, 35 is an audio output circuit, 36 is a switching circuit, 37 is an AGC voltage setting circuit, 40 is a control microcomputer, 41 is a video output terminal, and 42 is an audio output terminal.

[0024] Terminal 3 from the subscriber terminal 2 through the home wiring
A 64QAM signal, an OFDM signal, and a downlink data signal are frequency-multiplexed and input to the input / output terminal 20. The downstream data signal is selected by the filter 21, demodulated by the demodulation unit 22, and input to the control microcomputer 40. The downlink data signal includes information such as a channel table (correspondence table between the number assigned to the channel broadcasted by the CATV station and the channel number actually received by the terminal 3) and viewing permission based on the subscriber's contract status. In the embodiment, the information further includes discrimination information of 64QAM modulation or OFDM modulation for each broadcasting channel. Based on this information, control is performed from the control microcomputer 40 so that a reception configuration according to the channel selection state of the subscriber is obtained.

The tuning information from the subscriber is input to the control microcomputer 40, and the tuner 25
Is provided with information on the receiving channel. The tuner 25 converts the desired reception channel into an intermediate frequency signal and outputs it.

Unnecessary out-of-band signal components are suppressed by a filter 26 that allows only the intermediate frequency signal to pass, thereby suppressing the occurrence of interference thereafter. The output of the filter 26 is converted by a down converter 27 into a low frequency suitable for demodulation of 64QAM or OFDM. By converting the frequency to a lower frequency, the operation speed required for the analog-to-digital converter in the demodulation unit at the subsequent stage can be reduced, so that the degree of freedom in selecting the circuit configuration and elements is increased.

The control microcomputer 40 selects either the 64QAM demodulation unit 28 or the OFDM demodulation unit 29 according to the modulation scheme of the channel desired to be received, and simultaneously switches the switching circuit 36. AGC (Automatic Gain Control)
l) Control so that a signal can be applied.

The 64QAM demodulation section 28 and OFDM demodulation section 29 each convert an analog signal input by an analog / digital conversion circuit into a digital signal, perform demodulation according to each modulation method including waveform equalization, and perform digital demodulation. According to the data signal processing method of the modulated wave, error correction according to the error correction code and decoding processing of the data signal processing performed on the transmission side such as interleaving processing and energy spreading processing are performed.

By switching the AGC signal in accordance with the selected demodulation section, it is possible to perform optimal signal level control for each modulated signal. The signal output from the demodulation unit is digital data in the form of a transport stream, and is used as a control microcomputer 4 based on subscriber selection information.
Under control from 0, the demultiplexing circuit 31 separates the desired compressed video data and compressed audio data from each other,
To the audio decoder 33.

The compressed video data is converted into video data by a video decoder 32,
Convert to SC video signal. The compressed audio data is converted into an analog audio signal by an audio decoder 33, and signal processing such as surround is performed by an audio output circuit 35, for example.

An NTSC video signal is output from an output terminal 41, and an analog audio signal is output from an output terminal 42. The TV signal shown in FIG.
And the like, and can display the video and audio of the broadcast service selected by the subscriber.

In the present embodiment, the demodulation method according to the digital modulation method of the channel desired by the subscriber and the reception structure suitable for the demodulation method can be switched by the control means in the receiving apparatus. Broadcast can be received by the same receiving device.

Further, by using the receiving apparatus described in the present embodiment, in a CATV system, when a digital terrestrial broadcast having the same transmission bandwidth as a digital CATV signal is retransmitted from a CATV station, the digital terrestrial broadcast is demodulated. Then 64
The digital terrestrial broadcasting received by the CATV station can be transmitted only by frequency conversion to the channel that the CATV station wants to retransmit without QAM modulation. Transmission becomes possible.

In this embodiment, the analog / digital conversion circuit is included in each demodulation unit.
It is also possible to provide a digital conversion circuit independently and to make it common to both digital modulation signals. In that case, since the number of analog-to-digital conversion circuits is one, the circuit scale can be reduced. Further, in the present embodiment, the digital modulation method of the reception channel is given to the control microcomputer 40 as information in advance, but demodulation is started by one demodulation unit, and if demodulation is possible, the demodulation is continued. If it is impossible, an automatic discrimination such as switching to the other demodulation unit is also possible. In this case, since it is not necessary to supply digital modulation information for each channel in advance, the amount of downlink data can be reduced.

Next, an embodiment from the tuner 25 to the down converter 27 in the broadcast receiving and data communication terminal 3 will be described with reference to FIGS. FIG. 3 shows a case where a so-called single super system is used for the tuner 25. In the figure, 50 is an input terminal, 51 is an input tuning filter, 52 and 58 are variable gain amplifiers, 37 is an AGC voltage setting circuit, 53 is an interstage tuning filter, 54 and 59 are frequency converters, 55 and 60 are local Oscillators, 56 and 62 are amplifiers,
26 is a band-pass filter, 61 is a low-pass filter, 6
3 is an output terminal, and 64 is a PLL (Phase Locke).
d Loop) circuit.

From the signal input to the input terminal 50, the desired channel to be received is selectively passed through the input tuning filter 51, the signal level is adjusted to the signal level suitable for the subsequent signal processing by the variable gain amplifier 52, and the signal is again adjusted by the interstage tuning filter 53. The band is limited and input to the frequency converter 54. In the frequency converter 54, the signal is mixed with the signal from the local oscillator 55 and converted into an intermediate frequency. The intermediate frequency commonly used in Japan is 57
MHz. This intermediate frequency signal (hereinafter, referred to as a first intermediate frequency signal) is amplified by the amplifier 56. When a digital signal is received, the intermediate frequency is converted to a lower second intermediate frequency signal because the intermediate frequency increases the processing speed of the analog-to-digital converter and increases the difficulty in circuit configuration. Thus, the band for one channel is passed by the band-pass filter 26, the signal level is adjusted by the variable gain amplifier 58, the signal is mixed with the signal from the local oscillator 60 by the frequency converter 59, and the second intermediate frequency having a lower frequency is further added. The signal is converted into a signal, the second intermediate frequency signal is passed through a low-pass filter 61, the signal from the local oscillator 60 is suppressed, and an amplifier 62
Amplifies and outputs the second intermediate frequency signal. The bandpass filter 26 requires a steep out-of-band suppression degree characteristic, and a surface acoustic wave filter is used. The variable gain amplifiers 52 and 58 perform gain control according to the AGC signal from the demodulation unit.
In order to reduce the deterioration of the ratio, when decreasing the gain, the gain is reduced from the variable gain amplifier 58 at the subsequent stage, and then the gain of the variable gain amplifier 52 is reduced. To increase the gain, the gain of the variable gain amplifier 52 is increased, and then the gain of the variable gain amplifier 58 is increased. The AGC voltage setting circuit 37 sets the gain distribution between the two. For example, when both the variable gain amplifiers have a high gain when the applied AGC voltage is high, and when the gain is low when the AGC voltage is low. Sets the threshold of the AGC voltage to the variable gain amplifier 52 so that the gain is reduced from a certain AGC voltage, and the variable gain amplifier 52 is delayed to decrease the gain from the lower AGC voltage. When the setting of the gain distribution is different between the OFDM modulation signal and the 64QAM modulation signal, the threshold can be changed by changing the setting with data from the control microcomputer 40 shown in FIG. Become.
The frequency control of the local oscillator 55 is performed by providing tuning data (information such as a frequency dividing ratio) from the control microcomputer 40 shown in FIG. 2 to the PLL circuit 64, and the PLL circuit 64 performs local control in accordance with the data. A tuning voltage is output so that the oscillation frequency of the oscillator 55 becomes a desired frequency. With this tuning voltage, the pass bands of the input tuning filter 51 and the interstage tuning filter 53 are simultaneously tuned to the desired channel, and the desired channel is input to the frequency converter 54. If the transmission bandwidths of the OFDM modulation signal of digital terrestrial broadcasting and the 64QAM modulation signal of digital CATV are equal, filters 51, 53, 2
6 also have a common pass bandwidth, so that the tuner and the downconverter of the present embodiment can be used for both modulated signals.

As described above, in the present embodiment, the tuner and the down-converter section in the broadcast receiving and data communication terminal 3 have the second frequency lower than the intermediate frequency signal normally used for analog broadcast reception. Since the signal is converted into the intermediate frequency signal, the signal processing of the digital signal demodulation unit, particularly the processing speed of the analog-to-digital conversion unit, is reduced, and there is an effect that the circuit configuration is easy and the conversion accuracy is increased. Also,
Since it can be commonly used for receiving OFDM modulated signals and 64QAM modulated signals having the same transmission bandwidth, the configuration of the broadcast receiving and data communication terminal 3 is simplified, and the circuit scale can be reduced.

FIG. 4 shows a case where a so-called double super system is used for the tuner 25. In the figure, the same parts as those in FIG. 71 is an input filter, 72 is a variable gain amplifier, 73 and 77 are frequency converters, 74 and 78 are local oscillators, 76 and 80 are amplifiers,
75 and 79 are band pass filters, and 81 and 82 are PLL circuits.

A signal band including a channel desired to be received is selectively passed through an input filter 71 from a signal input to an input terminal 50, a signal level suitable for subsequent signal processing is obtained by a variable gain amplifier 72, and the signal is sent to a frequency converter 73. input. The frequency converter 73 mixes with the signal from the local oscillator 74,
The desired channel is converted into an intermediate frequency signal having a higher frequency than the signal band input to the input terminal 50.

As a result, it is possible to reduce interference caused by interference between input signals and eliminate image interference with the frequency converter 73. In addition, since the local oscillation signal also has a higher frequency than the signal band input to the input terminal 50, even if the local oscillation signal leaks from the input terminal 50 and is input to another receiving device, it is disturbed by another receiving device. Never be.

From the intermediate frequency signal, a band pass filter 75
Then, the signal is selectively passed through a desired signal band, amplified by an amplifier 76, input to a frequency converter 77, mixed with a signal from a local oscillator 78, and converted into a first intermediate frequency shown in FIG. This first intermediate frequency signal is passed through a bandpass filter 79.
, And selectively amplified by the amplifier 80.

The frequency control of the local oscillators 74 and 78 is shown in FIG.
The tuning data (information such as the frequency division ratio) from the control microcomputer 40 shown in FIG.
2, and the PLL circuits 81 and 82 output a tuning voltage according to the data so that the oscillation frequencies of the local oscillators 74 and 78 become a desired frequency. Unlike the case of FIG. 3, the pass band of the tuning filter is not changed by using the tuning voltage, and any receiving channel has a uniform frequency characteristic determined by the band pass filter 75, and the demodulation characteristic between the receiving channels is reduced. Good digital demodulation with no difference is possible.

The blocks after the band-pass filter 26 convert to a second intermediate frequency signal of a lower frequency, as in the description of FIG. The variable gain amplifiers 72 and 58 perform gain control in accordance with the AGC signal from the demodulation unit, and the AGC voltage setting circuit 37 sets the gain distribution of both variable gain amplifiers as in the description of FIG.

When the transmission bandwidths of the OFDM modulation signal of digital terrestrial broadcasting and the 64QAM modulation signal of digital CATV are equal, the pass bandwidths of the filters 75, 79, and 26 are also common. The down converter can be used for both modulated signals.

As described above, in the present embodiment, in the tuner and the down-converter unit in the broadcast receiving and data communication terminal 3, the double super system is used for the tuner, so that the interference caused by the interference between the input signals is prevented. It is possible to reduce the noise and eliminate image interference with the frequency converter 73, and to have a good frequency characteristic in which each receiving channel has a uniform frequency characteristic determined by the band-pass filter 75 and has no difference in demodulation characteristics between the receiving channels. Digital demodulation becomes possible. In addition, since the local oscillation signal also has a higher frequency than the signal band input to the input terminal 50,
Even if the local oscillation signal leaks from the input terminal 50 and is input to another receiving device, it does not interfere with the other receiving device.

As in the case of FIG. 3, the signal processing of the digital signal demodulator for converting the signal into a second intermediate frequency signal having a lower frequency than the intermediate frequency signal generally used for receiving analog broadcasting, -The processing speed of the digital conversion unit is reduced, and there is an effect that the circuit configuration is easy and the conversion accuracy is increased. Furthermore, since it can be shared for receiving OFDM modulated signals and 64QAM modulated signals having the same transmission bandwidth, the configuration of the broadcast receiving and data communication terminal 3 can be simplified, and the circuit scale can be reduced.

[0047]

According to the present invention, in a CATV system, when digital terrestrial broadcasting having the same transmission bandwidth as a digital CATV signal is retransmitted from a CATV station, demodulation of the digital terrestrial broadcasting and 64QAM modulation are performed. Without, CATV
A CATV station is configured to transmit digital terrestrial broadcasts received by the station only by frequency-converting the digital terrestrial broadcast received by the station to a channel desired to be retransmitted.

Further, as the receiving device, a demultiplexing means for separating desired video signal data and audio signal data from the digital data in the transport stream format, and the desired video signal data output from the demultiplexing means. Video signal format conversion means for converting a signal into a signal format for displaying video, and audio signal format conversion means for converting desired audio signal data output from the demultiplexing means into an analog signal format for outputting audio. In a digital broadcast receiving apparatus, a demodulation unit corresponding to two types of demodulation systems is provided to select and demodulate a desired digital modulation signal and output digital data in a transport stream format. Selects the demodulation method that matches the modulation method of the channel signal, and the appropriate reception configuration And control means for performing control to switch to.

According to these means, in the CATV system, the burden on the CATV station can be reduced, retransmission of digital terrestrial broadcasting can be performed, and the digital modulation system of the channel desired by the subscriber is controlled by the control means in the receiving device. Can be switched to a demodulation method corresponding to the demodulation method and a reception configuration suitable for the demodulation method, so that the same receiving apparatus can receive digital broadcasts of different modulation methods.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of the present invention.

FIG. 2 is a block diagram of a terminal showing an embodiment of the present invention.

FIG. 3 is a block diagram supplementing an embodiment of the present invention.

FIG. 4 is a block diagram supplementing an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CATV transmission line, 2 ... Subscriber terminal, 3 ... Broadcast reception and data communication apparatus, 4 ... Display equipment, such as a television receiver, 5 ... Satellite broadcast receiving antenna, 6 ... Terrestrial broadcast receiving antenna, 7: Digital satellite broadcast receiver, 8: Program transmission source, 9: Viewing management controller, 10: Frequency converter, 11, 12: 64QAM modulator, 13: Data modem, 14: Combiner, 21 , 23 ... Filter, 22 ...
Downlink data signal demodulation unit, 24 ... Uplink data signal modulation unit, 25 ... Tuner, 26 ... Filter, 27 ... Down converter, 28 ... 64QAM demodulation unit, 29 ... OFDM demodulation unit, 3
0: descrambling unit, 31: demultiplexing circuit, 32:
Video decoder, 33 ... Audio decoder, 34 ... NTSC encoder, 35 ... Audio output circuit, 36 ... Switching circuit, 37 ... AG
C voltage setting circuit, 40 ... control microcomputer,
51: input tuning filter, 52, 58: variable gain amplifier, 37: AGC voltage setting circuit, 53: interstage tuning filter, 54, 59: frequency converter, 55, 60: local oscillator, 56, 62: amplifier, 61 ... Filter, 63 ... Output terminal, 64 ... PLL circuit, 71 ... Input filter, 72 ...
Variable gain amplifiers, 73, 77 ... frequency converters, 74, 7
8. Local oscillator, 76, 80 ... Amplifier, 75, 79 ... Bandpass filter, 81, 82 ... PLL circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsutomu Noda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Multimedia Systems Development Headquarters, Hitachi, Ltd. (292) Inventor Ikuo Murata 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Hitachi Information Systems, Ltd.

Claims (7)

[Claims] (1) A CATV station and a CATV station transmitted from the CATV station or the CA
In a CATV system configured by a transmission path of a signal input to a TV station and a subscriber receiving device connected to the transmission path,
A CATV system, characterized in that the CATV station is provided with transmitting means for transmitting a broadcast signal according to two types of digital modulation methods. 2. A CATV station and a signal transmitted from the CATV station or the CA
In a CATV system configured by a transmission path of a signal input to a TV station and a subscriber receiving device connected to the transmission path,
The subscriber receiving apparatus has a demodulation unit corresponding to two types of digital modulation schemes, and a method of modulating a signal of the channel of the two types of digital modulation schemes when receiving a channel desired by the subscriber. A receiver for selecting a demodulation unit corresponding to the demodulation unit. 3. A CATV station and a CATV station transmitted from the CATV station or the CA
In a CATV system configured by a transmission path of a signal input to a TV station and a subscriber receiving device connected to the transmission path,
In the case where the CATV station transmits broadcast signals in two types of digital modulation schemes, and receives, in the subscriber receiving apparatus, a demodulation unit corresponding to the two types of digital modulation schemes and a channel desired by the subscriber for viewing. CA means for selecting a demodulation unit according to a modulation method of a signal of the channel from the two types of digital modulation methods.
TV system. 4. A CATV station and a signal transmitted from the CATV station or the CA
In a CATV system configured by a transmission path of a signal input to a TV station and a subscriber receiving device connected to the transmission path,
The subscriber receiving device, at least one tuner, two types of demodulation units corresponding to two types of digital modulation schemes, a multiplex separation circuit that separates only the data of the channel desired to be viewed from the output of the demodulation unit, A video decoder for decoding video information from the separated data, an audio decoder for decoding audio information from the separated data, and a tuning control unit, wherein the tuning control unit performs the demodulation according to a reception channel. A receiving device, wherein the receiving is performed by switching a unit. 5. A CATV station and a signal transmitted from the CATV station or the CA
In a CATV system configured by a transmission path of a signal input to a TV station and a subscriber receiving device connected to the transmission path,
In the subscriber receiver, a demodulation unit corresponding to two types of digital modulation schemes, a tuner unit shared for receiving signals of the two types of digital modulation schemes, and when receiving a channel desired by the subscriber to view And a selecting unit for selecting a demodulation unit according to a modulation method of a signal of the channel from the two types of digital modulation methods. 6. The CATV system according to claim 1, wherein said two kinds of digital modulation schemes are 64QAM modulation and OFDM.
CATV system characterized by DM modulation. 7. The receiving apparatus according to claim 2, wherein said two kinds of digital modulation schemes are 64QAM modulation and OF modulation.
A receiving device characterized by DM modulation.