JPH08274711A - Optical transmission equipment, reception device, and cable television system - Google Patents

Abstract

PURPOSE: To obtain an optical transmission equipment which can set a difference in light power between an optical transmitter and an optical receiver large and use low-cost optical components by converting an analog modulated signal into a digital modulated signal and optically transmitting it. CONSTITUTION: Analog modulated signals 4-1 to 4-m inputted to the optical transmission equipment are converted by the encoder 6 of an analog modulated signal processor 23 into binary digital signals. Then they are converted by a QAM modulator 7 into digital modulated signals, which are multiplexed by frequency division through a multiplexer 8. Then the optical transmitter 11 converts the signal into a light-intensity modulated signal, which is sent out to an optical fiber 12. This constitution relaxes the demand for a carrier-to-noise ratio and eliminates the need to use optical components with low distortion characteristics, so the difference in light power between the optical transmitter 11 and optical nodes 2(1)-2(p) can be set large. Further, the optical transmission equipment, a reception device, and a CAT system consisting of them in combination can be actualized by using low-cost optical components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device using optical fiber transmission, and more particularly to an optical transmission device, a receiving device and a cable television system suitable for a cable television system.

[0002]

2. Description of the Related Art Conventional cable television (hereinafter referred to as CATV)
As a configuration example of a network that provides a system, a CATV center (hereinafter, may be referred to as a headend) as described in pages 94 and 95 of the Nikkei Communication August 1, 1994 issue. A network is known in which an optical fiber cable is used for a trunk system between optical nodes and a coaxial cable is used for a distribution system from an optical node to each home. This consists of laying three optical fibers in the trunk system, two of which are used for downlink signals that transmit signals from the headend to the optical node, and the remaining one transmits signals from the optical node to the headend. It is used for upstream signals to provide a video distribution service from CATV centers to homes (users). One of two downstream signal optical fibers is used for analog modulation signal transmission.
The remaining one is allocated and used for transmitting the digital modulation signal. In the above-mentioned system, the analog modulation signal is a signal obtained mainly by receiving television broadcasting represented by terrestrial waves at the head end, and its modulation method is mainly amplitude modulation (AM). Then, normally, all channels of television broadcasting are distributed to each home, and the channel selection is performed by the home tuner.
That is, in the conventional CATV system, the analog modulated signal is mainly converted into the light intensity modulated signal as the AM signal and is optically transmitted. On the other hand, the digital modulation signal is a digital signal provided from a video server or the like which is a signal source arranged at the head end, and is usually a signal stored in the video server as a binary digital signal subjected to digital compression signal processing. Is read from a video server in response to a request from each home, information of a plurality of channels is digitally multiplexed, and then these are collectively converted into a digital modulation signal and transmitted. The digital modulation method for transmission is quadrature amplitude modulation (QAM).
ulation) is used.

[0003]

As described above, in the optical transmission device of the conventional system, the analog modulation signal obtained by receiving the television broadcast is converted into the light intensity modulation signal to convert between the head end and the optical node. Is transmitted. However, since the AM signal has a very strict requirement for the carrier-to-noise ratio (CNR) of about 50 dB or more, the difference in optical power (loss of transmission line) between the optical transmitter and the receiver is about 10 d.
It must be suppressed to B or less, and the transmission distance in the optical fiber is limited by using the analog modulation signal. In addition, for optical transmission of analog modulated signals, complex distortion
An optical component with a low distortion of 60 dBc or less is essential, which has been a cause of increasing the cost of the transmission device.

Therefore, an object of the present invention is to provide an optical transmission device and a receiving device at home for improving the performance and price, which eliminate the above-mentioned restrictions, and further improve the performance and price by combining them. Another object is to provide a transmission system (CATV system). More specifically, compared to the conventional system, the optical power difference between the optical transmitter and receiver can be set to be large, and an optical transmission device or a receiving device that can use low-cost optical components, and those It is to provide a combined transmission system (CATV system).

[0005]

In order to solve the above-mentioned problems, according to the present invention, after the analog modulation signal is converted into a binary digital signal by an encoder and the digital signal is further digitally modulated on the transmission side of the system. The signal is converted into a light intensity modulated signal for optical fiber transmission, and on the receiving side, the reverse conversion is performed, that is, the light intensity modulated signal is converted into a digital modulated signal, and the signal is demodulated into a binary digital signal. Is further decoded to obtain an analog modulated signal. This is because, in general, the CNR required for a digital modulation signal is smaller than the required value for an analog modulation signal, and the requirement for low distortion characteristics is lenient. For example, the digital modulation method is 64QAM
, The required CNR is about 30 dB (the code error rate is 10 −6), and the required distortion is also about −40 dBc or more in the composite distortion value. In addition to QAM, phase shift keying (PSK: Ph
ase Shift Keying, including polyphase PSK), Frequency Shift Keying (FSK), Residual Sideband Pulse Amplitude Modulation (PAM-VSB: Pulse Amplitud)
e Modulation-Vestigial SideBand, Orthogonal Frequency Division Multiple (OFDM)
plexing) etc. are also available.

[0006]

According to the present invention, since an analog modulated signal is converted into a digital modulated signal for optical transmission, the requirement for CNR can be relaxed and an optical component having a low distortion characteristic can be provided as compared with a conventional system. Since there is no need to use it, the difference in optical power between optical transmitters and receivers can be set larger than that in the conventional CATV system, and an optical transmission device and a receiving device using low-cost optical components, and a CATV that combines these devices are used. The effect is that the system can be realized.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical transmission device, receiving device, and
With regard to the embodiments of the cable television system, detailed description will be given with reference to the drawings by taking an example of transmission of a downlink signal from a head end of a transmission system using AM modulation for analog modulation and QAM for digital modulation to optical nodes and homes. Explained. In the description of this embodiment, the transmission of the upstream signal is
Since it can be realized by using the same device and method as the conventional one, the description of the device related to the upstream signal transmission is omitted from each drawing. Further, in the drawings after FIG. 2 excluding FIG. 1, which first describes the configuration and operation of the entire system, a device for receiving an analog modulated signal such as a television broadcast and a device for receiving 2
For devices such as video servers that supply value digital signals, devices similar to conventional systems are used.
Although not described except for FIG. 1, the system of each drawing will be described assuming that it operates by receiving an analog modulated signal and a digital signal from a device such as a video server as in FIG.

<First Embodiment> FIG. 1 is a system configuration diagram showing an embodiment of a cable television system (including an optical transmission device and a receiving device) according to the present invention. In FIG. 1, a cable television system is an optical transmitter 1 in a head end, and a radio wave (broadcast wave) 3 broadcast as a terrestrial television broadcast is used.
From the m-channel (m ≧ 1) AM modulated signal 4 (4-1 to 4-m) obtained by the broadcast wave receiver 31 receiving 0 and the demultiplexer 32 separating for each channel, and from the video server 34. The obtained n-channel (n ≧ 1) digital signal 5 (5-1 to 5-1) is a binary digital signal that has been digitally compressed by the MPEG (Motion Picture Expert Group) method.
5-n) is received, and p (p ≧ 1) optical nodes 2 are received.
This is a system for transmitting video information to a home 3 that receives distribution of signals connected to each of the optical nodes 2 via (2 (1) to 2 (p)). The subscripts (1) and (p) in parentheses after the reference numerals assigned to the blocks (details will be described later) shown in the figure indicate that the output signals of the blocks of the optical transmitter 1 are the optical nodes 2 respectively. (1) and 2 (p) are addressed.

The configuration and operation of the cable television system of FIG. 1 according to the present invention will be described in detail below. The AM signal 4 input to the optical transmitter 1 is converted into a binary digital signal by the encoder 6 of the analog modulation signal processing unit 23, and then further converted into a QAM signal by the QAM modulator 7. When there are a plurality of AM signals (m ≧ 2), which A
The M signal is also frequency-division-multiplexed by the multiplexer 8 after the same processing. For example, each AM signal band is 4M
If the bit rate of the output digital signal of the encoder 6 is about 20 Mb / s or less at about Hz, the QAM modulator 7 is used to convert the digital signal to 64 QAM with a bandwidth of about 6 MHz or less.
It can be converted into a signal. The multiplexed signal is branched by the divider 9 into the p direction. On the other hand, as for the digital signal 5, a plurality of channels (n) are input to the digital multiplexer 10 to be time-division multiplexed, and the multiplexed signal is QAM.
It is converted into a QAM signal by the modulator 7. As an example, if the digital signal 5 has a bit rate of about 6 Mb / s that is digitally compressed by the MPEG system, about 4 channels can be input to the digital multiplexer 10, and the output signal of the digital multiplexer is QAM. Bandwidth of about 6M by modulator 7
It can be converted into a 64 QAM signal of Hz. This Q
The signal converted into the AM signal is frequency division multiplexed by the multiplexers 8 (1) to 8 (p) for each optical node to be transmitted.
Further, the frequency division multiplexed signals are frequency division multiplexed with the output signals from the dividers 9 by the multiplexers 19 (1) to 19 (p), respectively, and then converted into optical intensity modulation signals by the optical transmitter 11. It is sent to the optical fiber 12.

Each optical node 2 (2 (1) to 2 (p)) is
The optical receiver 1 receives the optical signal transmitted from the optical fiber 12.
3 receives and converts the received signal into an electric signal, and the received signal is branched by the divider 9 corresponding to the coaxial cable 14 for transmitting the signal to each home 3 and distributed to each home 3. The number of branches by the divider 9 is determined according to the number of homes covered by each optical node. An amplifier (not shown) is appropriately installed on the coaxial cable 14 as needed, and a signal is branched from the coaxial cable 14 by the tap 20 and the signal is drawn into the home 3.

A receiver 24 is installed in each home 3, and a plurality of types of receivers 24 can be used with the system configuration of the present invention. Hereinafter, in this embodiment,
Configuration examples 24 (a) and 24 (b) of the two types of receiving devices will be described in detail. The first receiving device 24 (a) is a multiplexer that processes the received signal by the demultiplexer 15 and the frequency division multiplexed signal and the digital signal output from the analog modulation signal processing unit 23 of the optical transmitting device 1. 8 (8 (1) ~
8 (p)), and the frequency division multiplexed signal outputted from 8 (p)) is separated. From the former signal, the tuner 16 selects a one-channel QAM signal, and the selected signal is
The QAM demodulator 17 demodulates into a binary digital signal. Further, the demodulated signal is converted into an AM signal by the decoder 18. The decoder 18 of this embodiment may output either a baseband AM signal or an AM signal having a predetermined carrier frequency.
Further, the carrier frequency may be different from the frequency when it is input to the optical transmitter 1, or may be fixed regardless of the channel of the AM signal. Similarly, in the latter case of the frequency division multiplexed signal, the tuner 16 selects a one-channel QAM signal, and the selected signal is demodulated by the QAM demodulator 17 into a binary digital signal. Further, the demodulated signal is separated into a plurality of binary digital signals by the digital separator 21, and then selected by the signal selector 22 into one channel and output. Since the selected signal 5 is encoded by MPEG or the like, the image is restored by being decoded by a decoding processing device (a signal processing device opposite to the transmission side) not shown. With the above configuration and operation, the receiving device 24
In (a), one-channel AM signal and one-channel binary digital signal can be selectively received. The switching of the selected channel can be realized by controlling the tuner 16.

The second receiving device 24 (b) has a tuner 1
6 and the QAM demodulator 17 are commonly used to simplify the configuration of the receiving device 24. The signal branched from the coaxial cable 14 by the tap 20 is first input to the tuner 16. When an arbitrary QAM signal 1 channel is selected from the frequency division multiplexed signal by the tuner 16, this selected signal is converted into a binary digital signal by the QAM demodulator 17. The receiving device 24 (b) switches the output destination of the digital signal with the switch 28. That is, if the signal is a signal obtained by encoding the AM signal 4 on the transmitting side, it is sent to the decoder 18, and if it is a signal obtained by multiplexing the digital signal 5 on the transmitting side, then it is a digital separator 21. Is output to. The signal processing performed by the decoder 18 and the digital separator 21 is the same as that of the first receiving device 24 (a).

As described above, according to the cable television system (including the optical transmission device and the reception device) of the present invention, an AM signal can be converted into a QAM signal for optical transmission, so that a conventional AM signal is transmitted. Compared to the system,
The demand for CNR is about 20 dB from about 50 dB to about 30 dB.
Since it is possible to alleviate dB and the distortion characteristics are alleviated from about −60 dBc to about −40 dBc to about 20 dB, it is not necessary to use an optical component with low distortion characteristics, and the light between the optical transmitter and the receiver is less than that of the conventional CATV system. CAT can be set by using a relatively low-cost optical component that can set a large power difference.
An effect that a V system can be realized is obtained.

<Embodiment 2> FIG. 2 is a system configuration diagram showing another embodiment of the cable television system according to the present invention. The present embodiment is an example of a system using a high-efficiency digital compression encoder such as MPEG as the encoder 6 of the analog modulation signal processing unit 23 in the optical transmitter 1, and is different from the previous embodiment. The configurations of the analog modulation signal processing unit 23 in the optical transmission device 1 and the home receiving device 24 are different, and the other parts are the same. Hereinafter, the configuration and operation of another cable television system according to the present invention will be described, focusing on different parts. First, the configuration and operation of the analog modulation signal processing unit 23 in the optical transmitter 1 will be described. When the encoder 6 is the MPEG encoder (in this embodiment, the MPEG2 encoder is used) as in the present invention, the bit rate of the encoded signal can be around 6 MHz, The coded signals of 4 channels can be input to one digital multiplexer 10 to obtain a time division multiplexed signal of around 24 Mb / s. This signal can be converted by the QAM modulator 7 into a QAM signal having a band of about 6 HMHz. A plurality of QAM signals are frequency division multiplexed by the multiplexer 8. The subsequent signal processing is the same as in the case of the previous embodiment. According to the system of the present invention, one-channel QAM
Since it can transmit 4-channel AM signals,
The number of AM modulators 7 is 1 / compared with the system of the first embodiment.
It can be reduced to 4. Furthermore, since the bands of electric and optical signals are reduced, it is possible to use low-priced components, and it is possible to reduce the cost of the optical transmission device and the system.

Next, the configuration and operation of the receiving device 24 will be described. Even in the system configuration of the present invention, a plurality of types of receiving devices 24 can be used as in the previous embodiment.
Hereinafter, in the present embodiment, a configuration example 24 of two types of receiving devices
(C) and 24 (d) will be described in detail. The third receiving device 24 (c) selects the first digital signal shown in FIG. 1 in order to select an arbitrary digital signal from the multiplexed digital signals.
QAM demodulator 17 and decoder 1 of the receiving device 24 (a) of
A digital separator 21 and a selector 22 are added between 8 and 8. Here, when the encoding system of the encoder 6 of the analog modulation signal processing unit 23 and the encoding system applied to the digital signal 5 are the same, the modulation system and the encoding system are common. As in the fourth receiving device 24 (d), the receiving device is configured so that the tuner 16, the QAM demodulator 17, the digital separator 21, the selector 22, and the decoder 18 are all shared, and the output signal The signal 4 or the decoded signal 5 can be obtained as 29. When it is desired to output a plurality of channels at the same time, the signal from the coaxial cable 14 may first be branched at the tap 20, and the fourth receiving device 24 (d) may be installed for each branched signal. According to the system of the present invention, since the parts of the receiving device 24 can be shared, it is possible to reduce the cost of the receiving device as well as the cost of the system.

<Third Embodiment> FIG. 3 is a system configuration diagram showing another embodiment of the cable television system according to the present invention. In this embodiment, in order to expand the amount of information that can be distributed to each home, a coaxial cable 14 connecting the optical node 2 used in the system shown in Embodiments 1 and 2 and each home 3 is used as the optical fiber 12. The optical transmitter 1 and the receiver 24 are the same as those used in the first and second embodiments, the configuration of the optical node 2 is changed, and the optical receiver 13 is installed in each home 3, The output signal is input to the receiving device 24. The branching of the optical signal to each home is realized by the optical coupler 25 provided in the optical fiber 12. Further, the optical coupler 25 may be an optical star coupler that performs multiple branching of 3 or more.

As the optical node 2 used in the cable television system according to the present invention, the receiving device 2 provided in the home 3 is used.
As in the case of 4, the optical node 2 having a plurality of types of configurations can be used.
In the present embodiment, a configuration example of three types of optical nodes 2 will be described with reference to FIG. The first optical node 2 (1) is connected to the optical receiver 13
The signal received in 1. is branched by the divider 9, each branched signal is converted into an optical signal again by the optical transmitter 11, and the optical signal is transmitted to the optical fiber. This is an effective configuration when the optical transmitter is inexpensive. . In addition, the second optical node 2 (2) converts the signal received by the optical receiver 13 into an optical signal by the optical transmitter 11, and then splits the optical signal by using the optical star coupler 26 and the optical amplifier 27. The configuration is effective when the optical amplifier is inexpensive. The third optical node 2 (3) branches the optical signal transmitted from the optical transmitter 1 as an optical signal without directly converting it into an electrical signal. The optical signal is amplified by the optical amplifier 27 in order to prevent the deterioration of the ratio, which is an effective configuration when the optical amplifier is more inexpensive. As described above, according to the present embodiment, while utilizing the equipment of the system using the optical fiber and the coaxial cable, if the change of the optical node 2, the introduction of the optical fiber to the home, and the optical receiver 13 at the home 3 are sequentially performed, It is possible to expand the amount of information that can be distributed to each household by using optical fibers, and it is easy to develop and shift from the system shown in the previous example, considering the cost of optical parts, and based on the needs of users. The effect is that it can be carried out while determining the order.

The effects of the optical transmission device, the receiving device, and the cable television system according to the present invention shown in the first to third embodiments are not limited to the above-mentioned embodiments. The analog modulation method may be phase modulation or frequency modulation in addition to AM modulation, and the encoder 6 and the decoder 18 may be phase modulation signals corresponding to the modulation method adopted in the system. Or a device for frequency modulated signals. Further, the digital modulation system may be PSK, FSK, PAM-VSB, OFDM, etc. other than QAM, and the modulator 7 and the demodulator 17 are PSK, FSK,
It may be for PAM-VSB or OFDM. Further, an optical amplifier or a coaxial amplifier may be appropriately arranged at appropriate positions of the optical and coaxial cables. Further, the demultiplexer 15 can be replaced with a power divider.

<Fourth Embodiment> Further, in the future, television broadcasting will be digitized, and QA will be used as a broadcast wave instead of the AM signal.
When digitally modulated signals such as M, PSK, FSK, PAM-VSB, and OFDM are directly transmitted,
A receiving device corresponding to these signals may be installed in the head end (optical transmitting device 1), and the received signal may be directly converted into a light intensity modulated signal for optical transmission. FIG. 4 is a block diagram showing an embodiment of an apparatus for receiving a broadcast wave of digital broadcasting provided in the system according to the present invention (the optical transmitter 1 or the like as in the previous embodiment). In this device, various kinds of digital broadcast waves 30 as described above are received by a broadcast wave receiving device 31, and an output signal thereof is branched by a divider 9. At this time, the demodulator 1 of the receiving device 24 provided in the home 3
It is also necessary to change 7 to a system compatible with digital broadcasting, but the configuration of the other devices is the same as the configuration of the previous embodiment. Of course, if there are multiple types of broadcast waves,
A plurality of receiving devices are required (for example, terrestrial waves and satellite waves), and a plurality of received signals may be frequency-multiplexed.

FIG. 5 is a block diagram showing another embodiment of an apparatus for receiving a broadcast wave of digital broadcasting provided in the system according to the present invention (the optical transmitter 1 etc. as in the previous embodiment). , Digital modulation signals received at the headend (QAM, PSK, FSK, PAM-VSB, OFD
M or the like) is once demodulated into a binary digital signal, and the obtained signal is converted into a QAM signal directly or after time-division multiplexing of a plurality of channels. Like the device of FIG. 4, this device receives the broadcast wave 30 by the broadcast wave receiving device 31, separates the received signal for each carrier wave by the demultiplexer 32, and then the digital modulation signal by the decoder 33. Is demodulated and converted into a binary digital signal, and the decoder 33 becomes an OFDM decoder if the output signal of 32 is an OFDM signal, for example. At this time, the configurations of the other devices are the same as those in the previous embodiment. Of course, when there are multiple types of broadcast waves, multiple receivers are required (for example, terrestrial waves and satellite waves), and multiple received signals may be frequency-multiplexed.

Another example of the configuration of the receiving device 24 provided in the home 3 of the system according to the present invention will be described below with reference to FIGS. 6 and 7. FIG. 6 shows a fifth receiving device 24 (e).
2 is a block configuration diagram showing in detail the configuration of, particularly the configuration of a decoder 18. FIG. The signal demodulated into a binary digital signal by the demodulator 17 through the tuner 16 is first input to the decoder 35 that outputs an analog video signal and outputs an analog video signal. If the television receiver has a video terminal, the output of the decoder 35 can be viewed directly on the television. However, for a television receiver that does not have a video terminal, it is necessary to put a video signal on a predetermined carrier frequency and convert it into an analog modulation signal. In this embodiment, the oscillator 37 supplies the carrier frequency, and the modulator 36 converts the video signal into an analog modulated signal. As the frequency of the oscillator 37, in this embodiment, the frequency of 2 channels generally used for video input is used among the 1 to 12 VHF band television channels in Japan. FIG. 7 is a block diagram showing the configuration of the sixth receiving device 24 (f), and shows an example of the configuration of the receiving device 24 that simultaneously outputs all broadcast waves at different carrier frequencies. A digital modulated signal including a broadcast wave that is a signal input to the demultiplexer 15 is demultiplexed for each signal by the demultiplexer 15, and the broadcast wave is input to the analog modulation signal inverse processing unit 38 here. A digitally modulated signal including a signal from a video server or the like is output from the demultiplexer 15 and input to the tuner 16 while being frequency-multiplexed. In the inverse processing section 38 of each analog modulation signal, demodulation into a binary digital signal is performed by the demodulator 17, and the analog signal is converted into an analog video signal by the decoder 35. Finally, the modulator 36 and the oscillator 37 are used to output the analog modulated signal on the carrier. Since the frequency of the oscillator 37 differs for each inverse processing unit 38, the output signal 4-1
~ 4-m are different carrier frequencies. Each oscillator 37-
By adjusting the frequency from 1 to 37-m, the same carrier frequency as the broadcast wave can be realized and the output signal can be viewed on a normal television receiver. The receiving device having such a configuration is effective, for example, in a difficult-to-view area.

FIG. 8 is a block diagram showing a configuration example of the encoder 6 used in the apparatus of each system shown in the above embodiment. In the encoder of the system of the present invention, an envelope detector is used as a circuit for converting the input analog modulation signal 4 into a baseband analog video signal, and the baseband analog video signal is converted into a binary digital signal. An MPEG encoder was used as the encoder.

FIG. 9 is a spectrum distribution diagram of each signal for explaining the operation of the above various embodiments. FIG. 1A is an example of the broadcast wave 30, and generally, an analog modulation signal is frequency-multiplexed on the frequency axis.
f4-1 to f4-m are analog modulation signals 4-1 to 4-1
-M carrier frequency. In the figure, (b-1), (b-
2) to (b-m) are spectrum examples of the analog modulation signals frequency-separated by the demultiplexer 32. This signal is converted into a binary digital signal by the decoder 6 shown in FIG. 8, for example, and each has a spectrum as shown in FIG. 9C. Each binary digital signal is converted into a digital modulation signal by the modulator 7, and is converted into a digital modulation signal shown in FIG.
1) and (d-2) to (dm) are examples of spectra of each digital modulation signal. Here, each carrier frequency fd-1
Fd-m are different frequencies, and the carrier frequency can be set by a frequency converter built in each modulator 7, and can be changed by adjusting the frequency converter. Further, FIG. 6E is an example of the spectrum of the output signal of the multiplexer 19, and FIGS. 1D-1 and 1D-2 to FIG.
m) is a signal obtained by frequency-multiplexing the signal resulting from the signal 5 with the signal obtained by frequency-multiplexing the signal by the multiplexer 8, and this signal is collectively converted into an optical signal. FIG. 6F is an example of the spectrum of the digital modulation signal selected by the tuner 16, and shows the case where a signal having the carrier frequency fd-2 is selected. This signal is caused by the signal 4-2 on the transmission side, and after the digital modulation signal is converted into a binary digital signal (the spectrum is the same as in FIG. 7C) by the demodulator 17, for example, It is converted into an analog modulation signal by a decoder 18 as shown in FIG.

The embodiments of the optical transmission device, the receiving circuit, and the cable television system according to the present invention have been described above. However, in the above-mentioned embodiments, the devices arranged in each home or the devices arranged at the head end are described. Even if some or all of them are arranged in the optical node, the same effect is obtained. The analog modulated signal may be obtained by satellite broadcast wave reception or direct reception from a television studio in addition to ground wave reception. Similarly, the binary digital signal may be supplied from a device other than the video server.

In the above embodiment, the downlink signal transmission of the system has been described as an example, but the digital modulation method may be applied to the uplink signal as well as the downlink signal.
For example, it is possible to apply QAM to all downlink signals and uplink signals. In addition, the upstream signal is converted to 4-phase PSK
A modulation method such as

[0026]

According to the present invention, since an AM signal can be converted into a digital modulation signal for optical transmission, the requirement for CNR can be relaxed as compared with the prior art, and an optical component with low distortion characteristics can be obtained. Since it is not necessary to use the optical transmission device and the CATV system, it is possible to set a large difference in optical power between optical transmitters and receivers as compared with the conventional CATV system and to use relatively low-cost optical components. Get the effect that you can. Further, the large set optical power difference can be assigned to the expansion of the optical branch loss as well as the expansion of the optical fiber transmission loss. Further, according to the present invention, when the band required for optical transmission is narrower than that of the conventional system, it is possible to transmit signals of more channels by using the surplus transmission band.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of a cable television system according to the present invention.

FIG. 2 is a system configuration diagram showing another embodiment of the cable television system.

FIG. 3 is a system configuration diagram similarly showing another embodiment of the cable television system.

FIG. 4 is a block diagram showing an embodiment of an apparatus for receiving broadcast waves according to the present invention.

FIG. 5 is a block diagram showing another embodiment of the device for receiving broadcast waves.

FIG. 6 is a block diagram showing an embodiment of a receiving device according to the present invention.

FIG. 7 is a block configuration diagram showing another embodiment of the receiving device.

FIG. 8 is a block diagram showing an embodiment of an encoder according to the present invention.

FIG. 9 is a spectrum distribution diagram of each signal in the cable television system according to the present invention.

[Explanation of Codes] 1 ... Optical transmitter, 2 ... Optical node,
3 ... home, 4 ... analog modulation signal, 5 ... binary digital signal, 6 ... encoder, 7 ... QAM modulator,
8 ... Multiplexer, 9 ... Divider, 10 ... Digital multiplexer, 11 ... Optical transmitter, 12 ... Optical fiber cable, 13 ... Optical receiver, 14 ... Coaxial cable,
15 ... demultiplexer, 16 ... tuner,
17 ... QAM demodulator, 18 ... Decoder, 19
... multiplexer, 20 ... tap, 21 ... digital separator, 22 ... selector, 23 ... analog modulation signal processing unit, 24 ... receiver, 25 ... optical coupler, 26 ... optical star coupler, 27 ... optical amplifier, 28 ... Switch, 29 ... Output signal,
30 ... Broadcast wave, 31 ... Broadcast wave receiving device, 3
2 ... Demultiplexer, 33 ... Decoder, 34 ... Video server, 35 ... Decoder for outputting analog video signal, 36 ... Analog modulator, 37 ... Oscillator, 3
8 ... Analog modulation signal inverse processing unit.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H04N 7/16 H04N 7/16 Z 7/22 7/22

Claims (42)

[Claims] 1. A broadcast wave receiver for receiving a broadcast wave to obtain an analog modulated signal, an encoder for converting the analog modulated signal into a binary digital signal, and a converter for converting the binary digital signal into a digital modulated signal. And an optical transmitter for converting the modulated signal into an optical signal. 2. A broadcast wave receiver for receiving a broadcast wave to obtain a frequency-multiplexed analog modulated signal, and a demultiplexer for frequency-separating the multiplexed analog modulated signal to obtain a plurality of analog modulated signals. A plurality of encoders for converting each of the plurality of analog modulated signals into a binary digital signal, a plurality of modulators for converting each of the binary digital signals into a digital modulated signal, and the digital An optical transmission device comprising a multiplexer for frequency-multiplexing a modulated signal and an optical transmitter for converting the frequency-multiplexed signal into an optical signal. 3. A broadcast wave receiving device for receiving a broadcast wave to obtain a frequency-multiplexed analog modulated signal, and a demultiplexer for frequency-dividing the multiplexed analog modulated signal to obtain a plurality of analog modulated signals. A plurality of encoders for converting each of the plurality of analog modulated signals into a binary digital signal, a multiplexer for time-division multiplexing the binary digital signal, and the time-division multiplexed signal An optical transmission device comprising a modulator for converting the modulated signal into a digital modulated signal, and an optical transmitter for converting the modulated signal into an optical signal. 4. A broadcast wave receiving apparatus for receiving a broadcast wave to obtain a frequency-multiplexed analog modulated signal, and frequency division of the multiplexed analog modulated signal for N channels (N is a natural number of 2 or more). A duplexer that obtains the analog modulated signal of
N encoders for converting each of the N-channel analog modulated signals into binary digital signals, and a plurality of multiplexers for time-division multiplexing the binary digital signals for every n channels (N> n) A plurality of modulators for converting each of the plurality of time division multiplexed signals into digital modulated signals, a multiplexer for frequency multiplexing the plurality of digital modulated signals, and the frequency multiplexed signal An optical transmission device composed of an optical transmitter for converting an optical signal into an optical signal. 5. A broadcast wave receiving apparatus for receiving a broadcast wave to obtain a first digital modulated signal, a demodulator for converting the first digital modulated signal into a binary digital signal, and the binary digital signal. An optical transmission device comprising a modulator for converting into a second digital modulation signal and an optical transmitter for converting the second digital modulation signal into an optical signal. 6. A first frequency-multiplexed system for receiving broadcast waves
A broadcast wave receiving apparatus for obtaining a digitally modulated signal of
A demultiplexer for frequency-dividing the digitally modulated signal of 1 to obtain a plurality of second digitally modulated signals, and a plurality of encoders for converting each of the second digitally modulated signals into a binary digital signal, Each of the binary digital signals has a third
Optical modulator comprising a plurality of modulators for converting the frequency-multiplexed signals into optical signals, a multiplexer for frequency-multiplexing the third digital modulated signals, and an optical transmitter for converting the frequency-multiplexed signals into optical signals. Transmission equipment. 7. A first frequency-multiplexed system for receiving broadcast waves
A broadcast wave receiving apparatus for obtaining a digitally modulated signal of
A demultiplexer for frequency-dividing the digitally modulated signal of 1 to obtain a plurality of second digitally modulated signals, and a plurality of encoders for converting each of the second digitally modulated signals into a binary digital signal, A multiplexer that time-division-multiplexes the binary digital signal, a modulator that converts the time-division-multiplexed signal into a third digital modulation signal, and a light that converts the third digital modulation signal into an optical signal. An optical transmission device composed of a transmitter. 8. A first frequency-multiplexed receiving broadcast wave
A broadcast wave receiving apparatus for obtaining a digitally modulated signal of
Of the N channel (N is a natural number of 2 or more) second demultiplexer for frequency-separating the digital modulated signal of No. 2 and a binary digital signal of each of the second digital modulated signals of the N channels. N encoders for converting to
A plurality of multiplexers for time-division multiplexing the binary digital signal for every n channels (N> n), and a plurality of modulations for converting the plurality of time-division multiplexed signals into third digital modulation signals, respectively. And an optical transmitter that converts the frequency-multiplexed signals into optical signals, and a multiplexer that frequency-multiplexes the plurality of third digitally modulated signals. 9. A broadcast wave receiving device for receiving a broadcast wave to obtain a frequency-multiplexed digital modulated signal, and an optical transmitter for converting the multiplexed digital modulated signal into an optical signal. Optical transmission equipment. 10. A divider for branching a signal input to the optical transmitter into a plurality of dividers, and a plurality of optical transmitters for converting each of the branched signals into an optical signal. Optical transmission equipment. 11. A plurality of video servers which output binary digital signals, a multiplexer which time-division multiplexes the plurality of binary digital signals, and a converter which converts the time-division multiplexed signals into digital modulation signals. And a at least one multiplexer for frequency-multiplexing the modulator output signal and the signal to be input to the optical transmitter, and the output signal from the multiplexer is provided to the optical transmitter. The optical transmission device according to any one of claims 1 to 10, wherein 12. Q number of video servers (Q is a natural number of 2 or more) outputting binary digital signals and the Q binary digital signals are time-division multiplexed every q channels (Q> q). A plurality of multiplexers, a plurality of modulators that convert each of the plurality of time division multiplexed signals into digital modulation signals, and a first multiplexer that frequency multiplexes the plurality of digital modulation signals, The second multiplexer is provided with at least one second multiplexer that frequency-multiplexes the multiplexer output signal and the signal to be input to the optical transmitter according to any one of claims 1 to 9. The optical transmission device according to any one of claims 1 to 10, wherein the output signal of (1) is input to the optical transmitter. 13. The optical transmission device is provided with at least one optical fiber for transmitting an optical signal, an optical receiver is provided at an output end of each optical fiber, and each optical receiver is provided with each optical receiver. 13. The optical transmission device according to claim 1, wherein at least one coaxial cable for transmitting the output signal of 1 is provided, and a tap for branching the output signal is connected to each coaxial cable. 14. The optical transmission device is provided with at least one divider for branching an output signal of an optical receiver, a coaxial cable for transmitting each branch signal is provided, and a tap for branching a signal is provided on each coaxial cable. The optical transmission device according to claim 13, wherein the optical transmission device is connected. 15. The optical transmission device is provided with at least one first optical fiber for transmitting an optical signal, and a first optical receiver is provided at an output end of each of the first optical fibers. A divider for branching an output signal is provided in each of the optical receivers, an optical transmitter for converting each of the branched signals from the divider into an optical signal is provided, and each of the optical signals from the optical transmitter is transmitted. Two optical fibers are provided, an optical coupler that branches an optical signal is provided in each of the second optical fibers, and a second optical receiver that receives each branched optical signal from the optical coupler is provided. 13. The optical transmission device according to any one of 1 to 12. 16. The optical transmission device is provided with at least one first optical fiber for transmitting an optical signal, and a first optical receiver is provided at an output end of each of the first optical fibers. An optical transmitter that converts each received signal of the optical receiver into an optical signal again is provided, and a first optical coupler that branches the optical signal output by the optical transmitter is provided, and the first optical coupler is provided.
Second optical fibers for transmitting the optical signals respectively branched by the optical couplers, and a second optical coupler for branching the respective optical signals is connected to the second optical fiber. The optical transmission device according to any one of claims 1 to 12, further comprising a second optical receiver for receiving the optical signals branched by the above. 17. The optical transmission device according to claim 16, wherein an optical amplifier is provided at an input end, an output end, or both an input end and an output end of the first optical coupler. 18. An optical coupler is provided at an input end, an output end or both an input end and an output end of the optical amplifier.
The optical transmission device according to. 19. A frequency-multiplexed signal obtained by frequency-multiplexing a digital modulation signal of a channel (a is a natural number of 2 or more) and frequency-multiplexing a digital modulation signal of b channel (b is a natural number, a> b). The first signal and the c channel (c
Is a natural number, a> c, a = b + c) and a duplexer for obtaining a second signal in which a digitally modulated signal is frequency-multiplexed, and an arbitrary one-channel digitally modulated signal is selected from the first signal. A video signal receiving apparatus comprising a tuner, a demodulator for converting the selected digital modulation signal into a binary digital signal, and a decoder for converting the binary digital signal into an analog video signal. 20. An a-channel (a is a natural number of 2 or more) digitally-modulated signal is frequency-multiplexed to frequency-separate a signal, and a b-channel (b is a natural number, a> b) digitally-modulated signal is frequency-multiplexed. The first signal and the c channel (c
Is a natural number, a demultiplexer for obtaining a second signal in which a digital modulated signal of a> c, a = b + c) is frequency-multiplexed, and a first digital modulated signal of any one channel from the first signal. The first tuner for selecting the
A first demodulator for converting the digitally modulated signal of the first binary digital signal into a first binary digital signal, and a first demodulator for the first binary digital signal.
Decoder for converting into an analog video signal of, a second tuner for selecting a second digital modulation signal of any one channel from the second signal, and the selected second digital modulation A second demodulator for converting the signal into a second binary digital signal; a separator for time-divisionally separating the second binary digital signal into a plurality of second binary digital signals; A selector for selecting an arbitrary one-channel third value digital signal from a plurality of second binary digital signals, and a second for converting the selected third binary digital signal into a second analog video signal. Video signal receiving device comprising the above decoder. 21. The reception according to claim 19, further comprising an analog modulator for converting at least one of the analog video signals into an analog modulation signal having a predetermined carrier frequency. apparatus. 22. A tuner for selecting an arbitrary digital modulation signal of one channel from a signal obtained by frequency-multiplexing digital modulation signals of a plurality of channels, and two selected signals.
Value digital signal, a demodulator, a divider for branching the binary digital signal into at least two to obtain a first digital signal and a second digital signal signal, and an analog video signal from the first digital signal And a video signal receiving device comprising a decoder for obtaining the video signal. 23. A tuner for selecting an arbitrary digital modulation signal of one channel from a signal in which digital modulation signals of a plurality of channels are frequency-multiplexed, and two selected signals.
Value digital signal, a demodulator for dividing the binary digital signal into at least two to obtain a first digital signal and a second digital signal, and an analog video signal from the first digital signal. A first decoder for obtaining, a separator for time-divisionally separating the second digital signal into a plurality of third binary digital signals, and a plurality of the third two
A video signal receiving apparatus comprising a selector for selecting an arbitrary one-channel signal from a value digital signal and a second decoder for converting the selected third binary digital signal into an analog video signal. 24. The method according to claim 23, wherein the divider is replaced by a switch for selectively outputting either the first digital signal or the second digital signal.
4. The receiving device according to any one of 4. 25. The receiving apparatus according to claim 22, further comprising an analog modulator for converting at least one of the analog video signals into an analog modulation signal having a predetermined carrier frequency. 26. An a-channel (a is a natural number of 2 or more) digitally-modulated signal is frequency-multiplexed to separate the frequency-divided signal, and a b-channel (b is a natural number, a> b) digitally-modulated signal is frequency-multiplexed. The first signal and the c channel (c
Is a natural number, a> c, a = b + c) and a duplexer for obtaining a second signal in which a digitally modulated signal is frequency-multiplexed, and an arbitrary one-channel digitally modulated signal is selected from the first signal. Tuner, demodulator for converting the selected digital modulation signal into a first binary digital signal, and separator for time-divisionally separating the first binary digital signal into a plurality of second binary digital signals And a plurality of the separated second
And a decoder for converting the selected second binary digital signal into an analog video signal. Video signal receiving device. 27. A frequency-divided signal obtained by frequency-multiplexing a digital modulation signal of a channel (a is a natural number of 2 or more) and frequency-multiplexing a digital modulation signal of b channel (b is a natural number, a> b). The first signal and the c channel (c
Is a natural number, a demultiplexer for obtaining a second signal in which a digital modulated signal of a> c, a = b + c) is frequency-multiplexed, and a first digital modulated signal of any one channel from the first signal. The first tuner for selecting the
Demodulator for converting the digitally modulated signal of the above into a first binary digital signal, and a first separator for time-divisionally separating the first binary digital signal into a plurality of second binary digital signals A first selector for selecting an arbitrary one-channel second binary digital signal from the plurality of separated second binary digital signals; and a second selector for selecting the selected second binary digital signal. A first decoder for converting into one analog video signal, and a second of any one channel from said second signal
A second tuner for selecting the digital modulated signal, a second demodulator for converting the selected second digital modulated signal into a third binary digital signal, and the third binary digital signal. A second separator for time-division-separating into a plurality of fourth binary digital signals and an arbitrary one-channel fourth binary digital signal is selected from the plurality of separated fourth binary digital signals. A video signal receiving device comprising a second selector and a second decoder for converting the selected fourth binary digital signal into a second analog video signal. 28. An analog modulator for converting at least one of the analog video signals into an analog modulation signal having a predetermined carrier frequency.
The receiving device according to any one of claims. 29. A tuner for selecting an arbitrary one-channel digital modulation signal from a signal obtained by frequency-multiplexing multiple-channel digital modulation signals, and demodulation for converting the selected signals into a first binary digital signal. And a separator that time-division-separates the binary digital signal into a plurality of second binary digital signals, and a second 2 of any one channel from the plurality of separated second binary digital signals. A video signal receiving apparatus comprising a selector for selecting a value digital signal and a decoder for converting the selected second binary digital signal into an analog video signal. 30. The receiving apparatus according to claim 29, further comprising an analog modulator for converting the analog video signal into an analog modulation signal having a predetermined carrier frequency. 31. A demultiplexer for demultiplexing a signal in which digital modulation signals of a plurality of channels are frequency-multiplexed into a plurality of digital modulation signals, and a plurality of demultiplexers for converting each of the plurality of digital modulation signals into a binary digital signal. Demodulator, a plurality of decoders for converting the plurality of binary digital signals into a plurality of analog video signals, and a plurality of modulations for converting each of the plurality of analog video signals into analog modulation signals of different carrier frequencies A receiver comprising a receiver and an oscillator. 32. The receiving device according to claim 31, wherein said receiving device comprises a plurality of separators for time-divisionally separating each of said plurality of binary digital signals into a plurality of binary digital signals. 33. A cable television system, wherein the output signal of the tap or the output signal of the second optical receiver according to any one of claims 13 to 18 is used in the above-mentioned claim 1.
A cable television system serving as an input signal of the receiving device according to any one of 9 to 32. 34. A cable television system, comprising a television terrestrial wave, a satellite broadcast wave, or both as the broadcast wave input to the optical transmission device according to any one of claims 1 to 18. system. 35. The optical transmission apparatus according to claim 1, wherein the digital modulation of the modulator selectively uses quadrature amplitude modulation, vestigial sideband pulse amplitude modulation, or quadrature frequency division multiplexing. . 36. A quadrature amplitude modulation, a vestigial sideband pulse amplitude modulation, or a quadrature frequency division multiplexing is selectively used for digital modulation of the modulator.
33. The receiving device according to any one of 32 to 32. 37. The digital modulation of the modulator is selected from quadrature amplitude modulation, vestigial sideband pulse amplitude modulation, and quadrature frequency division multiplexing.
Alternatively, the cable television system according to any one of 34. 38. The digital modulation of the modulator uses quadrature amplitude modulation and a modulation method selected from either vestigial sideband pulse amplitude modulation or quadrature frequency division multiplexing. The optical transmission device as described in 1. 39. The digital modulation of the modulator uses quadrature amplitude modulation and a modulation method selected from either vestigial sideband pulse amplitude modulation or quadrature frequency division multiplexing. The receiving device according to claim 1. 40. The digital modulation of the modulator is performed by using quadrature amplitude modulation and a modulation method selected from either vestigial sideband pulse amplitude modulation or quadrature frequency division multiplexing. The cable TV system described in Crab. 41. The digital modulation of the modulator comprises a selective combination of quadrature amplitude modulation, vestigial sideband pulse amplitude modulation, quadrature frequency division multiplexing, phase shift keying and frequency shift keying. Alternatively, the cable television system according to any one of 34. 42. An MP easy encoder / decoder is used as at least a part of the encoder / decoder. Cable TV system.