JPH10200875A - Bidirectional catv system and head end, bidirectional relay amplifier, subscriber terminal and transmission line monitoring method used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a transmission line by transmitting corresponding address signals and outgoing control signals to a bidirectional relay amplifier by a head end, receiving the signals by the bidirectional relay amplifier, providing an output switch for turning ON/OFF the output of an amplifier for incoming signals and turning ON/OFF the output switch by the outgoing control signals. SOLUTION: Outgoing subscriber data signals from this head end 11 are inputted from a subscriber terminal pull-in line connection terminal 60, sent through a branching filter 61 to a demodulator 70, demodulated to digital data and decoded in a transmission line encoder-decoder 71. An outgoing signal format is composed of bit synchronization and an error correction code and commands are provided with transmission permission, output switch conducting and an incoming quality value request, etc. The bidirectional relay amplifier 13 obtains the bit synchronization by bit synchronizing signals and obtains the synchronization of a frame unit by frame synchronizing signals. When an address specified by the head end 11 matches, a succeeding command is fetched and interpreted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CATV system, a bidirectional repeater amplifier, a headend, an electronic circuit technology of a subscriber terminal, a control system technology, and a technology of monitoring the transmission quality of a bidirectional CATV transmission line. .

[0002]

2. Description of the Related Art A general connection diagram of a CATV transmission line is shown in FIG.
Shown in As shown in the figure, the configuration of the CATV transmission line is as follows.
From head end 11 to trunk lines 12a-f, relay amplifier 13
a to g or a plurality of distribution lines 1 via the branching devices 14a to 14c
It branches into 5a-d and is connected to the subscriber terminals 17a-d via tap-offs 16a-i, and has a configuration called a tree system (also called a tree and branch system). Similarly, even in the case of a bidirectional CATV, the configuration of the transmission path is generally a tree method.

In the uplink of such a bidirectional CATV network, noise called ingress noise which is transmitted to the head end 11 while being mixed together at various points such as the end of a transmission path and a branch point. Accordingly, there is an essential problem that a bit error is likely to occur in digital transmission on the upstream transmission path, and a communication error occurs. Regarding this problem, Japanese Patent Publication No. 53-41487, which is a known example of a conventional bidirectional CATV transmission path monitoring system, describes a quality detection system for an upstream transmission path.

[0004] According to this, the headend 11 and the subscriber terminal 17 of a general subscriber are linked via a plurality of bidirectional relay amplifiers 13 composed of a downstream signal amplifier and a upstream signal amplifier connected in parallel to each other. In the configuration described above, the transmission path monitoring signal is transmitted from the subscriber terminal 17 to the head end 11, and the head end 11 calculates the transmission quality from the received transmission path monitoring signal, thereby obtaining the head end 1 signal.
1, the quality of the uplink transmission path was detected.

An example of detecting the quality of a transmission path at the head end 11 by detecting a failure of a plurality of relay amplifiers 13 installed in a CATV network is disclosed in Japanese Patent Publication No. 52-3.
No. 691.

The relay amplifier 13 has means for transmitting the carrier for monitoring the transmission path to the head end 11 and means for stopping transmission of the carrier for monitoring the transmission path when a failure is detected, and the head end 11 always monitors the transmission path. This is a system for detecting a failure of the relay amplifier 13 by monitoring the carrier wave for use.

As another conventional system, an introduction to cable television technology, Chapter 4 Transmission Line Monitoring and Subscriber Management P172
(Supervised by Izumi Takehiro, published by Corona Co., Ltd. on April 20, 1994) is a status monitor system.

The head end 11 has means for transmitting an address signal and a downlink control signal corresponding to each relay amplifier 13 to the relay amplifier 13, and the relay amplifier 13 transmits the downlink control signal from the head end 11. In response to the,
This is a system having means for returning failure information detected by itself to the head end 11.

[0009]

In such a transmission line monitoring system of the prior art, it is possible to judge that the quality of the uplink transmission line is degraded at the head end, but noise rises from anywhere in the tree-shaped CATV network. It is not possible to determine the mixing point as to whether it is mixed in the transmission path. For this reason, it is difficult to improve the quality of the transmission path because it is not possible to take measures to prevent mixing at the mixing point. In order to identify the mixing point, the trunk line, the bidirectional relay amplifier, the distribution wiring, and the tap-off, which are manually connected to the headend, must be sent to each installation location to perform a failure inspection and a noise mixing test.

This operation is equivalent to checking the entire CATV network, and is almost impossible with a large-scale CATV transmission line. In addition, there is a fatal problem that the CATV service must be stopped to perform inspections and tests, and the service cannot be performed while providing the service.

[0011]

SUMMARY OF THE INVENTION To solve the above problems, the present invention provides a head coupled via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel with each other. In a bidirectional CATV system including an end and a subscriber terminal, the headend has headend transmitting means for transmitting an address signal and a downlink control signal corresponding to the bidirectional relay amplifier toward the bidirectional relay amplifier, The bidirectional relay amplifier includes: a receiving unit that receives an address signal and a downlink control signal corresponding to the bidirectional relay amplifier from the head end; an output switch that turns on and off an output of the uplink signal amplifier; Control means for turning on / off the switch, a detector for detecting the uplink transmission quality, a detection result detected by the detector and its own address And having a transmission quality transmission means for transmitting the signal toward the headend, and a line monitoring signal generator for generating a transmission path monitoring signals to be transmitted to the headend, a two-way CATV system.

Further, the present invention relates to a bidirectional CATV system including a head end and a subscriber terminal, which is linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other. A head end transmitting means for transmitting an address signal corresponding to the bidirectional relay amplifier and a first downlink control signal for turning on and off an output switch of the bidirectional relay amplifier;
Bidirectional relay amplifier monitoring signal requesting means for transmitting a second downstream control signal for causing the bidirectional relay amplifier to transmit an address signal corresponding to the bidirectional relay amplifier and a transmission path monitoring signal from the bidirectional relay amplifier to the head end; A detector for detecting transmission quality from the transmission path monitoring signal, wherein the bidirectional relay amplifier includes an address signal corresponding to the bidirectional relay amplifier from the head end, a first downlink control signal from the head end, and a second Receiving means for receiving the downlink control signal, an output switch for turning on and off the output of the amplifier for the uplink signal,
A bidirectional CATV system characterized by comprising control means for turning on / off an output switch by a first downlink control signal and a transmission path monitoring signal generator for generating a transmission path monitoring signal by a second downlink control signal.

Further, the present invention relates to a bidirectional CATV system having a head end and a subscriber terminal, which is linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other. A head end transmitting means for transmitting a repeater address signal and a repeater control signal corresponding to the bidirectional repeater amplifier toward the bidirectional repeater amplifier; a terminal address signal corresponding to the subscriber terminal; A subscriber terminal monitoring signal requesting unit for transmitting a terminal control signal to the subscriber terminal; and a detector for detecting transmission quality from the transmission path monitoring signal. Receiving means for receiving the signal and the repeater control signal, an output switch for turning on and off the output of the amplifier for the upstream signal, and output by the repeater control signal. And control means for turning on and off the switch, the subscriber terminal includes receiving means for receiving the terminal address signals and the subscriber terminal control signals from the head end,
A bidirectional communication system comprising: a transmission path monitoring signal generator for generating a transmission path monitoring signal according to a subscriber terminal control signal; and transmitting means for transmitting the transmission path monitoring signal and its own terminal address signal to a head end. It is a CATV system.

The present invention provides a head end, a two-way repeater amplifier, a subscriber terminal,
And a transmission path monitoring method for these systems.

Thus, the bidirectional relay amplifier is provided with an output switch for cutting the output signal of the amplifier and terminating the transmission line to reduce noise, and the output signal of the amplifier for the upstream signal is controlled by the control signal from the head end. It can be cut off, divides the entire CATV network into parts, detects the quality of the transmission path, and attempts to identify the location where noise is mixed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the invention according to claims 1 to 3 and 10 will be described. The headend according to the second aspect, the bidirectional relay amplifier according to the third aspect, and the transmission line monitoring method according to the tenth aspect are used for the bidirectional CATV system according to the first aspect. Therefore, the inventions according to claims 1 to 3 and 10 will be collectively described below.

FIG. 2 shows an example of the entire configuration of the bidirectional CATV system according to the first aspect of the present invention. The bidirectional CATV system includes a headend 11, trunk lines 12a to e, bidirectional relay amplifiers 13a to d, branching devices 14a and b, distribution lines 15a and b, tap-offs 16a to c, and a subscriber terminal 17a. To 1 and drop-in lines 18a to 18l.

A trunk line 12a from the head end 11 is connected to a branching unit 14a, and is branched into three trunk lines 12b to 12d by the branching unit 14a. The trunk lines 12b and d are connected to bidirectional relay amplifiers 13b and 13c, respectively. Is done. Bidirectional relay amplifier 1
3b, a plurality of tap-offs 16 are provided by a distribution line 15a.
a, b. From tap-offs 16a, b, 4
It is branched and connected to four subscriber terminals 17a-d and 17e-h via drop lines 18a-d and 18e-h, respectively. Bidirectional repeater amplifier 13c to splitter 14b
Is connected to the bidirectional relay amplifier 13d by the trunk line 12e. It is connected to the tap-off 16c from the bidirectional relay amplifier 13d by the distribution line 15b. Tap-off 16
From c, it is branched into four and connected to four subscriber terminals 17i to 17 via drop lines 18i to l.

An example of the detailed configuration of the head end 11 shown in FIG. 2 used in the bidirectional CATV system according to the first and second aspects of the present invention will be described with reference to FIG.
The head end 11 includes a video input terminal 21a, b, a television modulator 22a, b, a high frequency amplifier 23a, b, a second high frequency amplifier 35a, b, a combiner 24, and a duplexer 2
5, a trunk connection terminal 26, demodulators 27a and 27b, transmission line encoders and decoders 28a and 28b, and modulators 34a and 34b.
Control unit 36, subscriber terminal control unit 29, output interface units 30a and 30b, output interface terminal 31
a, b, input interface units 33a, b, and input interface terminals 32a, b.

The head end used in the bidirectional CATV system according to the first aspect of the present invention is a conventional bidirectional CATV.
The difference from the head end used in the V system is that it has a head end transmitting means for transmitting an address signal and a downlink control signal corresponding to the bidirectional relay amplifier toward the bidirectional relay amplifier.

A video input signal is input from a video input terminal 21a and is synthesized with an audio signal in a television modulator 22a.
The frequency is converted to a predetermined channel frequency in a downlink frequency band. The video signal is amplified by the high frequency amplifier 23a, and is synthesized by the synthesizer 24 with the video signal of another channel and the downlink data signal. As shown, there are a plurality of video channels, and the operation from the video input terminal 21b to the high-frequency amplifier 23b, which is another channel in the figure, is the same. The combined downstream signal is subjected to frequency band limitation by the demultiplexer 25 and output from the trunk connection terminal 26.

The upstream subscriber terminal signal input from the trunk connection terminal 26 is separated from the signal on the combiner 24 side by the demultiplexer 25, sent to the demodulator 27a, and demodulated into digital data by the demodulator 27a. The signal is decoded by the transmission line encoder / decoder 28a and transmitted to the subscriber terminal controller 29.

The subscriber terminal control unit 29 sends a CR to the output interface unit 30a, if necessary, according to the received information.
It outputs data to a display device such as a T display. A display device such as a CRT display is connected to the output interface terminal 31a, and a signal to the display device is output from the output interface terminal 31a to a CRT display or the like.

For transmission to the subscriber terminal 17, a signal from an input device such as a keyboard connected to the input interface terminal 32a is input to the subscriber terminal control unit 29 via the input interface unit 33a, and a control command is transmitted. Are generated, the control command and the like are transmission path encoded by the transmission path encoding / decoding unit 28a. The transmission path coded signal is modulated by the modulator 34a and frequency-converted to a downlink subscriber data channel frequency in a downlink frequency band. The subscriber channel frequency signal is amplified by the second high-frequency amplifier 35a and combined by the combiner 24 with another signal.

The upstream signal from the bidirectional relay amplifier 13 is:
The signal is input from the main line connection terminal 26,
The signal is separated from the signal on the fourth side and sent to the demodulator 27b, demodulated to digital data by the demodulator 27b, decoded by the transmission path encoder / decoder 28b, and transmitted to the control unit 36.

The control section 36 outputs data to a display device such as a CRT display to the output interface section 30b if necessary according to the received information. A signal to the display device is output from the interface terminal 31b to a CRT display or the like.

As described above, the head end 11 receives the upstream signal from the bidirectional relay amplifier 13 by the demultiplexer 25, the demodulator 27b, the transmission line coder / decoder 28b, and the like.

Transmission to the bidirectional relay amplifier 13 is performed by inputting a signal from an input device such as a keyboard connected to the input interface terminal 32b to the control unit 36 via the input interface unit 33b. When a control command or the like is generated, the control command or the like is channel-encoded by the channel encoder / decoder 28b. The channel-encoded signal is modulated by the modulator 34b and frequency-converted to a downlink data channel frequency in a downlink frequency band. The channel frequency signal is amplified by the second high-frequency amplifier 35b and is combined with another signal by the combiner 24.

The head-end transmitting means for transmitting the address signal and the downlink control signal corresponding to the bidirectional relay amplifier to the bidirectional relay amplifier includes a transmission line encoder / decoder 28.
b, the modulator 34b, and the like.

An example of the detailed configuration of the bidirectional relay amplifiers 13a to 13d used in the bidirectional CATV system according to the first and third aspects of the present invention will be described with reference to FIG. . The bidirectional relay amplifier 13 includes an input / output terminal 41
a, b, the duplexers 42a, b, and the high-frequency couplers 43a to 43b.
c, a downstream amplifier 44, a demodulator 45, a transmission line encoding / decoding unit 46, a control unit 47, a modulator 48, an upstream amplifier 49, an output switch 50, a transmission line monitoring signal generator 51 , Demodulation path switch 52, transmission quality detector 5
And 3.

The bidirectional relay amplifier used in the bidirectional CATV system according to the first aspect of the present invention is a conventional bidirectional CATV system.
As compared with the bidirectional relay amplifier used in the ATV system, a receiving means for receiving an address signal and a downlink control signal corresponding to the bidirectional relay amplifier from the head end, and an output switch for turning on and off the output of the amplifier for the uplink signal Control means for turning on and off an output switch by a downlink control signal, a detector for detecting uplink transmission quality, and transmission quality transmitting means for transmitting a detection result detected by the detector and its own address signal to a head end. In that it has

The bidirectional repeater amplifier 13 connected to the head end 11 via the trunk line 12 is connected to the trunk line at the input / output terminal 41a, and receives a down signal (“outgoing signal”) at the duplexer 42a.
Also say. ) And an upstream signal (also referred to as a “return signal”).
And distributed to. The downstream signal is branched by the high-frequency coupler 43a, and one is input to the downstream amplifier 44 and the other is input to the demodulator 45 via the demodulation path switch 52.

On the other hand, the downstream signal is amplified by the downstream amplifier 44 to a level required for the downstream transmission line, and then band-limited to the downstream frequency band by the demultiplexer 42b, and output to the main line. At the same time, the signal passes through the demodulation path switch 52, is demodulated into digital data by the demodulator 45, and is signal-processed by the transmission line encoder / decoder 46.

FIG. 5 shows an embodiment of the frequency assignment of the uplink and downlink signals. The details will be described later. The demodulator 45 is based on a digital modulation method determined by the system, and examples other than FSK include a BPSK demodulator, a QPSK demodulator, and an MSK demodulator.

The transmission line encoder / decoder 46 is generally called a channel codec, and performs signal processing such as decomposing information from a formatted data sequence, and conversely, assembling and formatting information. FIG. 6 shows an embodiment of the uplink signal format, and FIG. 7 shows an embodiment of the downlink signal format. The details will be described later.

The control unit 47 controls the transmission line coder / decoder 46 to transmit the upstream signal to the head end.
The encoded data is output to the modulator 48.

The modulator 48 FSK modulates the control channel frequency with the input data. The modulated wave is mixed with the upstream signal by the coupler 43c, and then amplified by the upstream amplifier 49 to a level required for the upstream transmission line. .

The output signal of the upstream amplifier 49 is output from the duplexer 42a to the main line through the output switch 50 in a conductive state.

When the demodulation path switch 52 is switched to the upstream signal side, the transmission quality detector 53 detects the transmission quality using the transmission path monitoring signal of the upstream signal.

The output switch 50 passes the output signal of the upstream amplifier 49 when in the conductive state, and is in a state of matching with the load impedance when in the disconnected state.
Since the upstream amplifier 49 is terminated, this switch has an effect of not transmitting noise to a load. As the output switch 50, for example, an antenna switch, a high-frequency transmission switch,
Examples include a coaxial attenuator and a step attenuator.

The receiving means for receiving the address signal and the downlink control signal corresponding to the bidirectional relay amplifier from the head end include a demultiplexer 42b, a demodulation path switch 52, a demodulator 45, a transmission line encoding / decoding device. The control unit 47 corresponds to the control means for turning on / off the output switch by the downlink control signal, and transmits the detection result detected by the detector and its own address signal to the head end. The means corresponds to the transmission line encoder / decoder 46, the modulator 48 and the like.

The subscriber terminals 17a to 17l shown in FIG. 2 used in the bidirectional CATV system according to the first aspect of the present invention.
An example of the detailed configuration will be described with reference to FIG. Claim 1
Is the same as the conventional one.
The subscriber terminal 17 includes a drop-in connection terminal 60, a duplexer 61, a tuner unit 62, a tuning unit 63, a video detection unit 64, an audio detection unit 65, an RF modulation unit 66, and a video output terminal. 67, an audio output terminal 68, and a television output terminal 6
9, a demodulator 70, a transmission line encoder / decoder 71, a modulator 72, a high-frequency amplifier 73, a control unit 74, an operation unit 75, and a display unit 76.

To explain the operation of the subscriber terminal, the video signal from the head end input from the drop-in connection terminal 60 is input to the tuner 62 through the duplexer 61. The tuner 62 mixes the signal with the signal from the tuner 63 to obtain an IF band signal. The video signal is detected by a video detector 64 into a video signal, and is simultaneously detected by an audio detector 65 into an audio signal, and output from a video output terminal 67 and an audio output terminal 68 to a video input terminal and an audio input terminal of the television, respectively. For a television without a video input terminal and an audio input terminal, the frequency is converted to a television frequency band by the RF modulation section 66 and output from the television output terminal 69 to the antenna input terminal of the television. The operation of the operation unit 7 such as a push button
The control unit 74 controls the tuning unit 63 based on the signal from the control unit 5 and performs the control.

The downstream subscriber data signal from the head end 11 is input from the drop-in connection terminal 60, is sent to the demodulator 70 through the duplexer 61, is demodulated into digital data by the demodulator 70, and is transmitted to the transmission line code. The data is decoded by the decoding / decoding unit 71 and transmitted to the control unit 74. The control unit 74 displays the received information on the display unit 76 if necessary according to the received information. When transmission to the head end 11 is necessary, the control unit 74 generates a control command or the like, and the control command or the like is transmission path coded by the transmission path coder / decoder 71. The transmission path coded signal is modulated by a modulator 72 and frequency-converted to an uplink subscriber data channel frequency in an uplink frequency band. The channel frequency signal is amplified by the high-frequency amplifier 73 and output from the duplexer 61 to the service line.

The bidirectional CAT according to the first aspect of the present invention will now be described.
Monitoring of the transmission quality of the transmission path of the V system will be described.

FIG. 5 shows an embodiment of frequency allocation to be used.
This will be described with reference to FIG. In this embodiment, the downlink frequency band 70
75 to 450 MHz as a repeater control downlink signal.
MHz is selected as the downlink signal of the subscriber terminal, 74 MHz is selected, and 45 MHz is selected as the uplink signal for the repeater control and 44 MHz is selected as the uplink signal of the subscriber terminal in the uplink frequency band of 10 to 50 MHz. In the downlink frequency band, subscriber uplink data and repeater uplink data are transmitted, and in the downlink frequency band, subscriber downlink data, repeater downlink data, and a plurality of video data CH1 to CHn are transmitted. The modulation method is FSK (frequency shift keying).
Besides, BPSK, QPSK, MSK and the like are also possible.
A system capable of this bidirectional data transmission is also referred to as a 2-way addressable system.

An example of a downlink signal format to be used is:
This will be described with reference to FIG. The downlink signal format includes bit synchronization, frame synchronization, address, command, and error correction code.
101010 (B), frame synchronization is 87A4B (H)
The commands include inquiry (ENQ), transmission permission, output switch conduction, output switch disconnection, bit error rate measurement code transmission, bit error rate measurement code stop, uplink quality measurement start, and uplink quality value request. Each is placed. The bidirectional relay amplifier 13 performs bit synchronization with a bit synchronization signal (also referred to as a “preamble signal”),
Synchronize on a frame basis with a frame synchronization signal unique to the system. If the address specified by the head end 11 matches its own address, the subsequent command is fetched and interpreted. If it doesn't match your address,
Subsequent commands are ignored.

Next, an example of an upstream signal format transmitted from the bidirectional relay amplifier 13 to the head end 11 will be described with reference to FIG. The uplink signal format includes bit synchronization, frame synchronization, address, data length, response, and error correction code.
010101010 (B), but the frame synchronization is 31BA
F (H) is the data length, the number of bytes of the response, the response is acknowledgment (ACK), non-acknowledgement (NACK),
The bit error correction code and the bit error rate are respectively listed. The bidirectional relay amplifier 13 (FIG. 2) sends an uplink frame synchronization signal following the bit synchronization signal, and subsequently sends its own address and the data length of the response section in byte units.
Then, a response and an error correction code from the address to the response are sent.

The method in which the head end side is mainly used and the interrogation is sequentially performed with each relay amplifier as a slave is generally called a polling method.

A tenth aspect of the present invention is a transmission line monitoring method for a CATV system according to the first aspect of the present invention. One embodiment of the method will be described with reference to the connection diagram of FIG. 1 and the flowchart of FIG.

In FIG. 1, the head end 11, the trunk line 1
2a-f, bidirectional relay amplifiers 13a-g, branching device 14a
-C, distribution lines 15a-d, tap-offs 16a-i, and subscriber terminals 17a-d.

During normal operation, the output switch 50 (FIG. 4)
To the conductive state, the bidirectional relay amplifiers 13a to 13g
Is designed to allow an upstream signal to pass through.

(1) It is assumed that the total number of bidirectional relay amplifiers in the system is Max (Max = 7 in FIG. 1).

(2) One of the two-way repeater amplifiers having no two-way repeater amplifier at the subsequent stage (on the side opposite to the head end 11), for example, 13f Is selected as the transmission path monitoring signal transmission point.

(3) The head end 11 starts monitoring the transmission line, and first, in accordance with step 302 in FIG. 9, m (m indicates the number of the bidirectional relay amplifier, and from a, 1, 2, 3,...
It is. ) Is substituted with 0.

(4) According to step 303 in FIG.
Substitute 1.0 for Rm. (As the bit error rate BERm, a large value that cannot be obtained is substituted.)

(5) According to step 304 in FIG. 9, 1 is substituted for m.

(6) In accordance with step 305 in FIG. 9, the head end 11 sends a command to the output path 50 (FIG. 4) to the bidirectional relay amplifier 13a on the downstream transmission line in accordance with the signal format of the downstream command in FIG. Send.

(7) In accordance with step 306 in FIG. 9, a command "output switch disconnection of bidirectional relay amplifiers 13b-e, g" is sent.

(8) In accordance with step 307 in FIG. 9, the command “transmit bidirectional relay amplifier 13f transmission path monitoring signal” is transmitted to bidirectional relay amplifier 13f. The bidirectional relay amplifier 13f generates a bit error rate measurement code, which is a transmission path monitoring signal, in the transmission path monitoring signal generator 51 (FIG. 4), and transmits it as an uplink signal. Here, the transmission line monitoring signal generator 51 (FIG. 4) only needs to have at least one bidirectional relay amplifier among the plurality of bidirectional relay amplifiers 13 in the bidirectional CATV system. In the example, the bidirectional relay amplifier 13f corresponds to the transmission path monitoring signal generator 51a.
(FIG. 4) may not be provided. The code for measuring the bit error rate may be determined to be a code common to the bidirectional relay amplifiers in the system. Generally, a pseudo random noise code such as a PN9-stage code, a PN15-stage code, a PN23-stage code, or the like is used. Can be

(9) In accordance with step 308 in FIG. 9, a command "start bidirectional repeater amplifier 13a uplink quality measurement" is sent to bidirectional repeater amplifier 13a. The bidirectional relay amplifier 13a switches the demodulation path switch 52 (FIG. 4) to the upstream signal side, and the transmission quality detector 53 (FIG. 4) uses the bit error rate measurement code from the bidirectional relay amplifier 13f to change the bit error rate. Is measured to obtain a bit error rate measurement value BER1.

(10) In accordance with the step 309 in FIG. 9, the command “Stop bidirectional relay amplifier 13f transmission path monitoring signal”
Send. The bidirectional relay amplifier 13f stops transmitting the bit error rate measurement code, and the bidirectional relay amplifier 13a sets the demodulation path switch 5
2 (FIG. 4) is returned to the downstream signal side.

(11) In accordance with step 310 of FIG. 9, the head end 11 issues the command “bidirectional relay amplifier 13a
Sending an upstream quality value request. ”The bidirectional relay amplifier 13a
The measured value BER1 is sent to the head end 11 on the upstream transmission line according to the upstream signal format of FIG. At this time, the upstream quality BER1 received by the head end 11 is the same as the branch line 12b, all the trunk lines 12e including the tap-offs 16e and 16f,
This is the quality of the transmission path limited to the head end 11 side from 13b of c, and to the head end 11 side to 13c of 12d.
That is, the transmission path on the subscriber terminal side is evaluated from the measurement point. If the head end 11 is considered to be the root, it is a part of the transmission line on the branch side from the relay amplifier 13a.

(12) According to step 311 in FIG. 9, the head end 11 stores the quality BER 1 at this time.

(13) In step 312 of FIG.
Compare 1 with BER0. Here, dBER is a difference amount of the bit error rate for determining that the transmission quality has deteriorated,
For example, when dBER = 1.0 × 10E−3,
The bit error rate of 0 × 10E-4 becomes 1.4 × 10
If it changes to E-3, it is determined that noise is mixed.
In each CATV system, the optimal value of dBER may be determined from the characteristics of the actual transmission path and the allowable bit error rate of the system. BER0 = 1.
0, so that BER1−BER0 <dBER, and
Branch to N side and proceed to the next step.

(14) According to step 314 in FIG.
Is substituted for m + 1, that is, 2 is substituted for m.

(15) At step 315 in FIG. 9, it is determined whether m is the maximum value Max, and the flow branches to N.

(16) In accordance with step 305 in FIG. 9, the head end 11 sets the bidirectional relay amplifiers 13a and 13b on the downlink transmission line according to the signal format of the downlink command in FIG.
Command to make the output switch 50 (FIG. 4) conductive.

(17) In accordance with step 306 in FIG. 9, a command "output switch disconnection of bidirectional relay amplifiers 13c-e, g" is sent.

(18) In accordance with step 307 in FIG. 9, a command “13f transmission line monitoring signal transmission” is transmitted to the bidirectional relay amplifier 13f. Bidirectional relay amplifier 13f
Is a bit error rate measurement code, which is a transmission path monitoring signal,
It is generated by the transmission path monitoring signal generator 51 (FIG. 4) and transmitted as an uplink signal.

(19) In accordance with step 308 in FIG. 9, the command "13a start uplink quality measurement" is sent to the bidirectional relay amplifier 13a. The bidirectional relay amplifier 13a switches the demodulation path switch 52 (FIG. 4) to the upstream signal side, and the transmission quality detector 53 (FIG. 4) uses the bit error rate measurement code from the bidirectional relay amplifier 13f to change the bit error rate. Is measured to obtain a bit error rate measurement value BER2.

(20) In accordance with the step 309 in FIG. 9, the command “Stop bidirectional relay amplifier 13f transmission path monitoring signal”
Send. The bidirectional relay amplifier 13f stops transmitting the bit error rate measurement code, and the bidirectional relay amplifier 13a sets the demodulation path switch 5
2 (FIG. 4) is returned to the downstream signal side.

(21) According to step 310 in FIG. 9, the head end 11 issues the command “bidirectional relay amplifier 13a
Sending an upstream quality value request. ”The bidirectional relay amplifier 13a
The measured value BER2 is sent to the head end 11 on the upstream transmission line according to the upstream signal format of FIG.

(22) In accordance with step 311 in FIG. 9, the head end 11 stores the quality BER 2 at this time. The uplink quality BER received by the head end 11 at this time
2 is a branch side of the bidirectional relay amplifier 13a of the trunk line 12a,
All trunk lines 12c, all trunk lines 12e including tap-offs 16e, f, trunk lines 12 including tap-offs 16a, b
b indicates the quality of the transmission path limited to the headend 11 side from the bidirectional relay amplifier 13c of the trunk 12d.

(23) In step 312 of FIG.
2 and BER1. Here, the difference between BER2 and BER1 is that the tap-offs 16a and 16b of the trunk line 12b are included in the measurement range.
BER2 becomes worse than BER1 when noise is mixed in from the service line branching from the subscriber terminal 17 to the subscriber terminal 17. In other words, if BER2 is worse than BER1 by dBER, it is possible to specify that noise corresponding to the degraded amount dBER has entered the upstream transmission line on the tap-off side from relay amplifier 13b.

(24) The head end 11 is BER2-
If BER1> dBER, the fact that noise is mixed in from the bidirectional relay amplifier 13b is stored, and the process proceeds to the next measurement step.

(25) According to step 314 in FIG.
Is substituted for m + 1.

(26) The process branches at step 315 of FIG.

(27) Steps 305 to 315 in FIG. 9 are repeated.

(28) By sequentially receiving the uplink quality BER, the head end 11 can finally identify the noise-mixed portion of the entire CATV network.

In the above description, the transmission path monitoring signal is transmitted from the bidirectional relay amplifier 13f, but the bidirectional relay amplifier for transmitting the transmission path monitoring signal is switched following the switching of the output switch ( Bidirectional relay amplifier 13
It is to be added that a system configured to transmit from m.) is also an embodiment of the present invention.

As described above, according to the first to third and tenth aspects of the present invention, the location of the ingress noise in the bidirectional CATV transmission line can be automatically specified without manual inspection, and the ingress noise can be specified. There is an effect that the problem of can be solved.

The frequency allocation can be shared without allocating another band for the repeater and that for the subscriber terminal. For this purpose, an address corresponding to each subscriber terminal and a corresponding relay amplifier are used. Address should not overlap. In this case, the polling method of the relay amplifier is the same as the polling method of the subscriber terminal. In this embodiment shown in FIG. 10, the frequency allocation in this case is 75 MHz as downlink data in the downlink frequency band of 70 to 450 MHz and 80 as video CHs 1, 2, 3,.
Up to 450 MHz, and the upstream frequency band is 10 to 5
Of the 0 MHz, 45 MHz is selected as the uplink data. The modulation method is FSK (frequency shift keying), but other modulation methods such as BPSK, QPSK, and MSK are also possible.

Next, an embodiment of the invention according to claims 4 to 6 and 11 will be described. The headend of the invention according to claim 5, the bidirectional relay amplifier of the invention according to claim 6, and the transmission line monitoring method of the invention according to claim 11 are each described in claim 4.
Since the present invention is used in the bidirectional CATV system of the invention according to the invention, the inventions according to claims 4 to 6 and 11 will be described together.

One example of the entire configuration of the bidirectional CATV system according to the fourth aspect of the invention is the bidirectional CTV system according to the first aspect of the invention.
As in the ATV system, it is shown in FIG. 2 and detailed description thereof is omitted.

An example of the detailed configuration of the head end 11 shown in FIG. 2 used in the bidirectional CATV system according to the fourth and fifth aspects of the present invention will be described with reference to FIG. The head end 11 includes video input terminals 21a and 21b,
TV modulators 22a, b and high-frequency amplifiers 23a, b
, Second high-frequency amplifiers 35a and 35b, combiner 24, duplexer 25, trunk connection terminal 26, and demodulators 27a and 27b.
, Transmission line encoder / decoder 28a, b, and modulator 34
a, b, a control unit 36, a subscriber terminal control unit 29, output interface units 30a, b, output interface terminals 31a, b, and input interface units 33a, b
, Input interface terminals 32 a and 32 b, and a transmission quality detector 37.

The head end used in the bidirectional CATV system according to the fourth aspect of the present invention is compatible with a bidirectional relay amplifier as compared with the head end used in the bidirectional CATV system according to the first aspect of the present invention. Bidirectional relay amplifier monitoring signal requesting means for transmitting a second downlink control signal for causing the bidirectional relay amplifier to transmit the address signal and the transmission path monitoring signal from the bidirectional relay amplifier to the head end,
The difference is that a detector for detecting the transmission quality from the transmission path monitoring signal is provided.

The video input signal is input from the video input terminal 21a and is synthesized with the audio signal in the television modulator 22a.
The frequency is converted to a predetermined channel frequency in a downlink frequency band. The video signal is amplified by the high frequency amplifier 23a, and is synthesized by the synthesizer 24 with the video signal of another channel and the downlink data signal. As shown, there are a plurality of video channels, and the operation from the video input terminal 21b to the high-frequency amplifier 23b, which is another channel in the figure, is the same. The combined downstream signal is subjected to frequency band limitation by the demultiplexer 25 and output from the trunk connection terminal 26.

The upstream subscriber terminal signal input from the trunk connection terminal 26 is separated from the signal on the combiner 24 side by the demultiplexer 25, sent to the demodulator 27a, and demodulated into digital data by the demodulator 27a. The signal is decoded by the transmission line encoder / decoder 28a and transmitted to the subscriber terminal controller 29.

The subscriber terminal control unit 68 sends the CR to the output interface unit 30a, if necessary, according to the received information.
It outputs data to a display device such as a T display. A display device such as a CRT display is connected to the output interface terminal 31a, and a signal to the display device is output from the output interface terminal 31a to a CRT display or the like.

For transmission to the subscriber terminal 17, a signal from an input device such as a keyboard connected to the input interface terminal 32a is input to the subscriber terminal control unit 29 via the input interface unit 33a, and a control command is transmitted. Are generated, the control command and the like are transmission path encoded by the transmission path encoding / decoding unit 28a. The transmission path coded signal is modulated by the modulator 34a and frequency-converted to a downlink subscriber data channel frequency in a downlink frequency band. The subscriber channel frequency signal is amplified by the second high-frequency amplifier 35a and combined by the combiner 24 with another signal.

The upstream signal from the bidirectional relay amplifier 13 is:
The signal is input from the main line connection terminal 26,
The signal is separated from the signal on the fourth side and sent to the demodulator 27b, demodulated to digital data by the demodulator 27b, decoded by the transmission path encoder / decoder 28b, and transmitted to the control unit 36.

The bit error rate measurement code, which is a transmission path monitoring signal from the bidirectional relay amplifier, is demodulated into digital data by the demodulator 27b, and the transmission quality is detected by the transmission quality detector 37.

The control unit 36 outputs data to a display device such as a CRT display to the output interface unit 30b if necessary according to the received information. A signal to the display device is output from the interface terminal 31b to a CRT display or the like.

As described above, the head end 11 is connected to the duplexer 2
5. The demodulator 27b, the transmission line encoder / decoder 28b, the quality detector 37, etc. receive the upstream signal and the transmission line monitoring signal from the bidirectional relay amplifier, and detect the upstream transmission quality.

For transmission to the bidirectional relay amplifier 13, a signal from an input device such as a keyboard connected to the input interface terminal 32b is input to the control unit 36 via the input interface unit 33b. When a control command or the like is generated, the control command or the like is channel-encoded by the channel encoder / decoder 28b. The channel-encoded signal is modulated by the modulator 34b and frequency-converted to a downlink data channel frequency in a downlink frequency band. The channel frequency signal is amplified by the second high-frequency amplifier 35b and is combined with another signal by the combiner 24.

Head-end transmitting means for transmitting an address signal corresponding to the bidirectional relay amplifier and a first downlink control signal for turning on / off the output switch of the bidirectional relay amplifier; an address signal corresponding to the bidirectional relay amplifier; A bidirectional relay amplifier monitoring signal requesting unit for transmitting a second downlink control signal for transmitting a transmission line monitoring signal from the relay amplifier to the headend to the bidirectional relay amplifier includes a modulator 34b, a transmission line encoding and decoding The container 28b corresponds to this.

An example of the detailed configuration of the bidirectional relay amplifiers 13a to 13d shown in FIG. 2 used in the bidirectional CATV system according to the fourth and sixth aspects of the present invention will be described with reference to FIG. The bidirectional relay amplifier 13 includes input / output terminals 41 a and 41 b, duplexers 42 a and 42 b, and a high-frequency coupler 43.
a, c, a down amplifier 44, a demodulator 45, a transmission line encoding / decoding device 46, a control unit 47, a modulator 48, an up amplifier 49, an output switch 50, a transmission line monitoring signal generation And a vessel 51.

The bidirectional relay amplifier used in the bidirectional CATV system according to the fourth aspect of the present invention is different from the bidirectional relay amplifier used in the bidirectional CATV system according to the first aspect of the present invention in that it has a second downstream. It has a transmission line monitoring signal generator that generates a transmission line monitoring signal in response to a control signal, but differs in that it does not have a detector that detects uplink transmission quality.

The bidirectional repeater amplifier 13 connected to the head end via the trunk line is connected to the trunk line at the input / output terminal 41a, and receives a down signal (also referred to as "outgoing signal") and an up signal at the duplexer 42a. (Also referred to as “return signal”). The downstream signal is branched by the high-frequency coupler 43a,
One is input to the downstream amplifier 44 and the other is input to the demodulator 45.

On the other hand, the downstream signal is amplified by the downstream amplifier 44 to a level required for the downstream transmission line, and then band-limited to the downstream frequency band by the demultiplexer 42b, and output to the main line. At the same time, the data is demodulated into digital data by the demodulator 45 and signal-processed by the transmission line coding / decoding unit 46.

The frequency allocation of the uplink and downlink signals is performed according to the bidirectional CA of the invention according to claim 1 shown in FIG.
This is similar to the case of the TV system. This demodulator 45
It is based on the digital modulation method determined by the system,
Examples other than FSK are BPSK demodulator, QPSK demodulator, M
An SK demodulator or the like is possible.

The transmission line encoder / decoder 46 is generally called a channel codec, and performs signal processing such as decomposing information from a formatted data sequence, and conversely, assembling and formatting information. One embodiment of the uplink and downlink signal formats is shown in FIGS.

The control unit 47 controls the transmission line coder / decoder 46 to transmit the uplink signal to the head end 11 and outputs the coded data to the modulator 48.

The modulator 48 FSK modulates the control channel frequency with the input data. The modulated wave is mixed with the upstream signal by the coupler 43c, and then amplified by the upstream amplifier 49 to a level required for the upstream transmission line. .

The output signal of the upstream amplifier 49 is output from the duplexer 42a to the main line via the output switch 50 in a conductive state. Here, the output switch 50 passes the output signal of the upstream amplifier 49 when in the conductive state, and is in a state of matching with the load impedance when in the disconnected state, and at the same time, terminates the upstream amplifier 49 to transmit noise to the load. There is no effect switch. As this output switch, for example, an antenna switch, a high-frequency transmission switch,
Examples include a coaxial attenuator and a step attenuator.

The receiving means for receiving the address signal corresponding to the bidirectional relay amplifier from the head end and the first down control signal and the second down control signal from the head end includes a demultiplexer 42b, a demodulator 45, The control unit 47 corresponds to the control means for turning on / off the output switch by the first downlink control signal, and transmits the transmission path monitoring signal and its own address signal to the head end. The transmission line encoding / decoding device 46, the modulator 48, and the like correspond to the bidirectional relay amplifier transmission line monitoring signal transmission means.

The subscriber terminal used in the two-way CATV system according to the fourth aspect of the present invention is the same as the subscriber terminal used in the CATV system according to the first aspect of the present invention, and is an embodiment thereof. The subscriber terminal 17a shown in FIG.
The description of ~ l is omitted.

Hereinafter, the bidirectional CAT according to the invention of claim 4 will be described.
Monitoring of the transmission quality of the transmission path of the V system will be described.

An example of the frequency allocation to be used is described in claim 1
5 is the same as that of the bidirectional CATV system according to the invention according to the present invention, and is shown in FIG.

The downstream signal format of this embodiment is the same as that of the bidirectional CATV system according to the first aspect of the present invention, and is shown in FIG. 6 and its description is omitted.

Next, the format of the upstream signal transmitted by the bidirectional relay amplifier 13 (FIG. 12) to the head end is the same as that of the bidirectional CATV system according to the first aspect of the present invention.
The description is omitted in FIG.

An eleventh aspect of the present invention is a transmission path monitoring method for a bidirectional CATV system according to the fourth aspect of the present invention. One embodiment will be described with reference to the connection diagram of FIG. 1 and the flowchart of FIG. .

In FIG. 1, the head end 11, the trunk line 1
2a-f, bidirectional relay amplifiers 13a-f, branching device 14a
-C, distribution lines 15a-d, tap-offs 16a-i, and subscriber terminals 17a-d.

During normal operation, the output switch 50 (FIG. 1)
By setting 2) to the conductive state, the bidirectional relay amplifier 13a
Ｇg allow the upstream signal to pass through.

(1) It is assumed that the total number of bidirectional relay amplifiers in the system is Max (Max = 7 in FIG. 8).

(2) Of the bidirectional relay amplifiers on the transmission line of the bidirectional CATV network, the bidirectional relay amplifier 13 having no bidirectional relay amplifier at the subsequent stage (on the side opposite to the head end 11)
n is selected as the transmission path monitoring signal transmission point. (In FIG. 1, n
= F)

(3) The head end 11 starts monitoring the transmission path, and first, according to step 402 in FIG. 13, m (m is
Indicates the number of the bidirectional relay amplifier, and from a, 1, 2, 3, ...
・ ・) Is substituted with 0.

(4) According to step 403 in FIG.
Substitute 1.0 for ERm. (Substitute a large value that cannot be taken as the bit error rate)

(5) According to step 404 in FIG.
Is substituted for 1.

(6) In accordance with step 405 in FIG. 13, the head end 11 transmits a command “transmit bidirectional relay amplifier 13f transmission path monitoring signal” to the bidirectional relay amplifier 13f. The bidirectional relay amplifier 13f generates a bit error rate measurement code, which is a transmission path monitoring signal, by the transmission path monitoring signal generator 44 (FIG. 12) and transmits it as an uplink signal.

(7) In accordance with step 406 in FIG. 13, the head end 11 sends a command to make the output switch 50 (FIG. 12) conductive to the bidirectional relay amplifier 13a on the downstream transmission line according to the signal format of the downstream command in FIG. Send.

(8) In accordance with step 407 of FIG. 13, the command "output switch disconnection of bidirectional relay amplifiers 13b to 13g" is sent.

(9) In accordance with the bit error rate measurement code received from the bidirectional repeater amplifier 13f, the transmission quality detector 37 of the head end 11 follows step 408 in FIG.
(FIG. 11) measures the bit error rate to obtain a bit error rate measurement value BER1. At this time, the upstream quality BER1 measured by the head end 11 is all of the trunk lines 12a, all of the trunk lines 12c, all of the trunk lines 12e including tap-offs 16e, 16f, the head end 11 side of 13b of 12b, and the head end 11 of 13c of 12d. This is the quality of the transmission path limited to the side.

(10) According to step 409 in FIG.
The head end 11 stores the quality BER1 at this time.

(11) In step 410 of FIG.
Compare R1 and BER0. Here, dBER is a difference amount of the bit error rate for determining that the transmission quality has deteriorated. For example, when dBER = 1.0 × 10E−3,
If the bit error rate, which was 3.0 × 10E-4, changed to 1.4 × 10E-3 at the next measurement, it is determined that noise was mixed. In each CATV system, the optimal value of dBER may be determined from the characteristics of the actual transmission path and the allowable bit error rate of the system. Since BER0 = 1.0, BER1-BER0
<DBER, branch to N side, proceed to next step.

(12) According to step 412 in FIG.
Substitute m + 1 for m, that is, 2 for m.

(13) At step 413 in FIG. 13, it is determined whether m is the maximum value Max, and the flow branches to N.

(14) According to step 406 in FIG.
The head end 11 transmits the bidirectional relay amplifier 13a to the downstream transmission line according to the signal format of the downstream command in FIG.
A command to make the output switch 50 (FIG. 12) conductive is sent to b.

(15) According to step 407 of FIG.
A command "output switch disconnection of bidirectional relay amplifiers 13c-e, f" is sent.

(16) According to step 408 of FIG.
The transmission quality detector 37 (FIG. 11) measures the bit error rate using the bit error rate measurement code received from the bidirectional relay amplifier 13f, and obtains a bit error rate measurement value BER2.
At this time, the upstream quality BER2 measured by the headend 11
Are all trunk lines 12a, all 12c, tap-off 16
e, all of the trunk 12e including f, tap-off 16a,
b indicates the quality of the transmission line limited to the headend 11 side from the bidirectional relay amplifier 13c of the trunk line 12d for all the trunk lines 12b.

(17) According to step 409 in FIG.
The head end 11 stores the quality BER2 at this time.

(18) In step 410 of FIG.
Compare R2 and BER1. Here BER2 BER1
The difference from the above is that the tap-offs 16a and 16b of the trunk line 122 are included in the measurement range. It gets worse. In other words, if BER2 is worse than BER1 by dBER, it is possible to specify that noise corresponding to the degraded amount dBER has entered the upstream transmission line on the tap-off side from relay amplifier 13b.

(19) The head end 11 has a BER2-
If BER1> dBER, the fact that noise is mixed in from the bidirectional relay amplifier 13b is stored, and the process proceeds to the next measurement step.

(20) According to step 412 in FIG.
Substitute m + 1 for m.

(21) The process branches in step 413 of FIG.

(22) Steps 406 to 413 in FIG.
repeat.

(23) By sequentially receiving the bit error rate measurement signals, the head end 11
Finally, it is possible to specify a noise-mixed portion of the entire CATV network.

In the above description, the transmission path monitoring signal is transmitted from the bidirectional relay amplifier 13f. However, the bidirectional relay amplifier for transmitting the transmission path monitoring signal is switched following the switching of the output switch ( Bidirectional relay amplifier 13
It is to be added that a system configured to transmit from m.) is also an embodiment of the present invention.

As described above, according to the fourth to sixth and eleventh aspects of the present invention, the location of the ingress noise in the bidirectional CATV transmission line can be automatically specified without manual inspection, and the ingress noise can be specified. There is an effect that the problem of can be solved.

Next, one embodiment of the invention according to claims 7 to 9 and 12 will be described. The headend of the invention according to claim 8, the subscriber terminal of the invention according to claim 9, and claim 1
Since the transmission line monitoring method according to the second aspect of the present invention is used for the bidirectional CATV system according to the seventh aspect of the present invention, the inventions according to the seventh to ninth and twelfth aspects will be described below.

The entire structure of the bidirectional CATV system according to the seventh aspect of the present invention is the same as that of the bidirectional CATV system according to the first and fourth aspects of the present invention, and is shown in FIG. 2 and detailed description thereof is omitted.

An example of a detailed configuration of the head end 11 shown in FIG. 2 used in the bidirectional CATV system according to the seventh and eighth aspects of the present invention will be described with reference to FIG. The head end 11 includes video input terminals 21a and 21b,
TV modulators 22a, b and high-frequency amplifiers 23a, b
, Second high-frequency amplifiers 35a and 35b, combiner 24, duplexer 25, trunk connection terminal 26, and demodulators 27a and 27b.
, Transmission line encoder / decoder 28a, b, and modulator 34
a, b, a control unit 36, a subscriber terminal control unit 29, output interface units 30a, b, output interface terminals 31a, b, and input interface units 33a, b
, Input interface terminals 32 a and 32 b, and a transmission quality detector 37.

The head end used in the bidirectional CATV system according to the seventh aspect of the present invention is compared with the head end used in the bidirectional CATV system according to the first and fourth aspects of the present invention. Inventive bidirectional CAT
The head end used in the V system includes a head end transmitting means for transmitting a repeater address signal and a repeater control signal corresponding to the bidirectional repeater amplifier toward the bidirectional repeater amplifier, and a terminal corresponding to the subscriber terminal. Claims 1 and 2 comprise subscriber terminal monitoring signal requesting means for transmitting an address signal and a subscriber terminal control signal to a subscriber terminal, and a detector for detecting transmission quality from a transmission path monitoring signal. The head end used in the bidirectional CATV system of the present invention is different from the head end in that it has a head end transmitting means for transmitting an address signal and a downlink control signal corresponding to the bidirectional relay amplifier to the bidirectional relay amplifier. The head end used in the bidirectional CATV system according to the fourth aspect of the present invention includes an address signal corresponding to a bidirectional repeater amplifier and a bidirectional relay amplifier. A head-end transmitting means for transmitting a first downlink control signal for turning on and off an output switch of the relay amplifier, and a bi-directional relay of an address signal corresponding to the bi-directional relay amplifier and a transmission path monitoring signal from the bi-directional relay amplifier to the head end The difference is that a bidirectional relay amplifier monitoring signal requesting means for transmitting a second downlink control signal to be transmitted by the amplifier and a detector for detecting transmission quality from the transmission path monitoring signal are provided.

The video input signal is input from the video input terminal 21a and is synthesized with the audio signal in the television modulator 22a.
The frequency is converted to a predetermined channel frequency in a downlink frequency band. The video signal is amplified by the high frequency amplifier 23a, and is synthesized by the synthesizer 24 with the video signal of another channel and the downlink data signal. As shown, there are a plurality of video channels, and the operation from the video input terminal 21b to the high-frequency amplifier 23b, which is another channel in the figure, is the same. The combined downstream signal is subjected to frequency band limitation by the demultiplexer 25 and output from the trunk connection terminal 26.

The upstream subscriber terminal signal input from the trunk connection terminal 26 is separated from the signal on the combiner 24 side by the demultiplexer 25, sent to the demodulator 27a, and demodulated into digital data by the demodulator 27a. The signal is decoded by the transmission line encoder / decoder 28a and transmitted to the subscriber terminal controller 29.

The bit error rate measuring code, which is a transmission path monitoring signal from the subscriber terminal 17, is demodulated into digital data by the demodulator 27a, and the transmission quality is detected by the transmission quality detector 37.

According to the received information, the subscriber terminal control unit 29 sends the CR to the output interface unit 30a if necessary.
It outputs data to a display device such as a T display. A display device such as a CRT display is connected to the output interface terminal 31a, and a signal to the display device is output from the output interface terminal 31a to a CRT display or the like.

For transmission to the subscriber terminal 17, a signal from an input device such as a keyboard connected to the input interface terminal 32a is input to the subscriber terminal control unit 29 via the input interface unit 33a, and a control command is transmitted. Are generated, the control command and the like are transmission path encoded by the transmission path encoding / decoding unit 28a. The transmission path coded signal is modulated by the modulator 34a and frequency-converted to a downlink subscriber data channel frequency in a downlink frequency band. The subscriber channel frequency signal is amplified by the second high-frequency amplifier 35a and combined by the combiner 24 with another signal.

The uplink signal from the bidirectional relay amplifier 13 is
The signal is input from the main line connection terminal 26,
The signal is separated from the signal on the fourth side, sent to the demodulator 34a, demodulated into digital data by the demodulator 27b, decoded by the transmission line encoder / decoder 28b, and transmitted to the control unit 36.

The control unit 36 outputs data to a display device such as a CRT display to the output interface unit 30b if necessary according to the received information. A signal to the display device is output from the interface terminal 31b to a CRT display or the like.

As described above, the head end 11 is connected to the demodulator 27
a, transmission path encoder / decoder 28a, transmission quality detector 37
Therefore, the upstream transmission quality can be detected from the transmission path monitoring signal from the subscriber terminal 17.

Transmission to the bidirectional relay amplifier 13 is performed by inputting a signal from an input device such as a keyboard connected to the input interface terminal 32b to the control unit 36 via the input interface unit 33b. When a control command or the like is generated, the control command or the like is channel-encoded by the channel encoder / decoder 28b. The channel-encoded signal is modulated by the modulator 34b and frequency-converted to a downlink data channel frequency in a downlink frequency band. The channel frequency signal is amplified by the second high-frequency amplifier 35b and is combined with another signal by the combiner 24.

Head-end transmitting means for transmitting a repeater address signal and a repeater control signal corresponding to the bidirectional repeater amplifier toward the bidirectional repeater amplifier, a terminal address signal corresponding to the subscriber terminal, and a subscriber terminal control signal A modulator 34b, a transmission line coder / decoder 28b, and the like correspond to the subscriber terminal monitoring signal request means for transmitting a signal to the subscriber terminal.

The bidirectional relay amplifier 13 shown in FIG. 2 used in the bidirectional CATV system according to the seventh aspect of the present invention.
An example of a detailed configuration of a to d will be described with reference to FIG.
The bidirectional relay amplifier 13 includes input / output terminals 41a and 41b, demultiplexers 42a and 42b, high-frequency couplers 43a and 43c, a down-amplifier 44, a demodulator 45, and a transmission line encoder / decoder 46.
, A control unit 47, a modulator 48, an upstream amplifier 49,
And an output switch 50.

The bidirectional relay amplifier used in the bidirectional CATV system according to the invention of claim 7 is the same as that of claims 1 and 4.
Compared with the bidirectional relay amplifier used in the bidirectional CATV system according to the invention according to the present invention, the bidirectional relay amplifier used in the bidirectional CATV system according to the invention according to claim 7 is:
A receiving means for receiving a repeater address signal and a repeater control signal from the head end, an output switch for turning on and off the output of the amplifier for the upstream signal, and a control means for turning on and off the output switch by the repeater control signal But
A bidirectional relay amplifier used in the bidirectional CATV system according to the first aspect of the present invention includes: a receiving unit that receives an address signal and a downlink control signal corresponding to the bidirectional relay amplifier from a head end; Output switch for turning on / off the output of the switch, control means for turning on / off the output switch by a downlink control signal, a detector for detecting uplink transmission quality, and a detection result detected by the detector and its own address signal directed to the head end. Transmission quality sending means, and a transmission path monitoring signal generator for generating a transmission path monitoring signal to be transmitted to the head end.
The bidirectional relay amplifier used in the bidirectional CATV system according to the fourth aspect of the present invention includes: an address signal corresponding to the bidirectional relay amplifier from the head end; a first downlink control signal from the head end; Receiving means for receiving a downlink control signal, an output switch for turning on and off the output of an amplifier for an uplink signal, control means for turning on and off an output switch by a first downlink control signal, and generating a transmission path monitoring signal by a second downlink control signal And a transmission line monitoring signal generator.

The bidirectional repeater amplifier 13 connected to the head end 11 via the trunk line 12 is connected to the trunk line at the input / output terminal 41a, and receives a downstream signal (“outgoing signal”) at the duplexer 42a.
Also say. ) And an upstream signal (also referred to as a “return signal”).
And distributed to. The downstream signal is branched by the high-frequency coupler 43a, and one is input to the downstream amplifier 44 and the other is input to the demodulator 45.

On the other hand, the downstream signal is amplified by the downstream amplifier 44 to a level required for the downstream transmission line, and then band-limited to the downstream frequency band by the demultiplexer 42b, and output to the main line. At the same time, the data is demodulated by the demodulator 45 into digital data, and the signal is processed by the transmission line encoder / decoder 46.

The frequency allocation of the uplink and downlink signals is performed by the bidirectional CA of the invention according to claim 1 shown in FIG.
Similar to a TV system. The demodulator 45 is based on a digital modulation method determined by the system, and
Other examples include a BPSK demodulator, a QPSK demodulator, and an MSK demodulator.

The transmission line encoder / decoder 46 is generally called a channel codec, and performs signal processing such as decomposing information from a formatted data sequence, and conversely, assembling and formatting information. The uplink and downlink signal formats are shown in FIGS.

The control unit 47 controls the transmission line coder / decoder 46 to output the coded data to the modulator 48 in order to transmit the upstream signal to the head end 11.

The modulator 48 FSK modulates the control channel frequency with the input data, and the modulated wave is mixed with the upstream signal by the coupler 43c, and then amplified by the upstream amplifier 49 to a level necessary for the upstream transmission path. .

The output signal of the upstream amplifier 49 is output from the duplexer 42a to the main line via the output switch 50 in a conductive state. Here, the output switch 50 passes the output signal of the upstream amplifier 49 when in the conductive state, and is in a state of matching with the load impedance when in the disconnected state, and at the same time, terminates the upstream amplifier 49 to transmit noise to the load. There is no effect switch. As this output switch, for example, an antenna switch, a high-frequency transmission switch,
Examples include a coaxial attenuator and a step attenuator.

An example of the detailed configuration of the subscriber terminals 18a to 18 shown in FIG. 2 used in the bidirectional CATV system according to the seventh and ninth aspects of the present invention will be described with reference to FIG. The subscriber terminal 17 has a drop-in connection terminal 60.
, A duplexer 61, a tuner section 62, a tuning section 63,
Video detector 64, audio detector 65, RF modulator 66
, A video output terminal 67, an audio output terminal 68, a television output terminal 69, a demodulator 70, a transmission line coder / decoder 71, a modulator 72, a high frequency amplifier 73, and a control unit 7.
4, an operation unit 75, a display unit 76, and a transmission path monitoring signal generator 77.

The subscriber terminal used in the two-way CATV system according to the seventh aspect of the present invention is different from the subscriber terminal used in the two-way CATV system according to the first and fourth aspects of the present invention from the head end. Receiving means for receiving the terminal address signal and the subscriber terminal control signal, a transmission path monitoring signal generator for generating a transmission path monitoring signal based on the subscriber terminal control signal, and a head for transmitting the transmission path monitoring signal and its own terminal address signal. It is different in that it has transmission means for transmitting to the end.

The operation of the subscriber terminal 17 will be described. The video signal from the head end 11 input from the drop-in connection terminal 60 is input to the tuner 62 through the duplexer 61. The tuner 62 mixes the signal with the signal from the tuner 63 to obtain an IF band signal. The video detector 64 detects the video signal, and the audio detector 65 detects the audio signal at the same time.
Each is output to the video input terminal and audio input terminal of the television. To TV without video input terminal and audio input terminal,
The frequency is converted to a television frequency band by the RF modulation section 66 and output from the television output terminal 69 to the antenna input terminal of the television. The control unit 74 controls the channel selection unit 63 based on a signal from the operation unit 75 such as a push button to select a reception channel.

The downstream subscriber data signal, the terminal address signal and the subscriber terminal control signal from the head end 11 are input from the drop-in connection terminal 60 and
To the demodulator 70, demodulated into digital data by the demodulator 70, decoded by the transmission line coding / decoding unit 71,
It is transmitted to the control unit 74. The control unit 74 displays the received information on the display unit 76 if necessary according to the received information. If it is necessary to transmit to the head end 11, the control unit 7
Reference numeral 4 generates a control command and the like, and the control command and the like are subjected to transmission line encoding by a transmission line encoding / decoding device 71. A transmission path monitoring signal to be transmitted to the head end is generated by a transmission path monitoring signal generator 77 and similarly transmitted path encoded by a transmission path encoding / decoding unit 71. The transmission path coded signal is modulated by a modulator 72 and frequency-converted to an uplink subscriber data channel frequency in an uplink frequency band. The channel frequency signal is amplified by the high-frequency amplifier 73 and output from the duplexer 61 to the service line.

The receiving means for receiving the terminal address signal and the subscriber terminal control signal from the head end includes a demodulator 7
0, a transmission line coder / decoder 71, a control unit 74, and the like. Transmission means for transmitting a transmission line monitoring signal and its own terminal address signal to the head end include a transmission line coder / decoder 71, a high frequency The amplifier 73 corresponds to this.

The bidirectional CAT according to the seventh aspect of the present invention will now be described.
Monitoring of the transmission quality of the transmission path of the V system will be described.

An example of frequency allocation to be used is described in claim 1
And FIG. 4 are the same as those of the bidirectional CATV system according to the inventions of FIGS.

An example of a downlink signal format to be used is also the same as that of the bidirectional CATV system according to the first and fourth aspects of the present invention, and is shown in FIG. 6 and the description thereof is omitted.

An example of an uplink signal format to be used is the same as that of the bidirectional CATV system according to the first and fourth aspects of the present invention, and is shown in FIG. 7 and the description thereof is omitted.

A twelfth aspect of the present invention is a transmission line monitoring method for a bidirectional CATV system according to the seventh aspect of the present invention. One embodiment of the method will be described with reference to the connection diagram of FIG. 1 and the flowchart of FIG. .

In FIG. 1, the head end 11, the trunk line 1
2a-e, bidirectional relay amplifiers 13a-f, splitter 14a
-C, distribution lines 15a-d, tap-offs 16a-i, and subscriber terminals 17a-d.

During normal operation, the output switch 50 (FIG. 1)
By setting 5) to a conductive state, the bidirectional relay amplifier 13a
Ｇg allow the upstream signal to pass through.

(1) It is assumed that the total number of bidirectional relay amplifiers in the system is Max (Max = 7 in FIG. 1).

(2) Of the bidirectional relay amplifiers on the transmission line of the bidirectional CATV network, the bidirectional relay amplifier 13 having no bidirectional relay amplifier at the subsequent stage (on the side opposite to the head end 11)
n is selected as a transmission path monitoring signal relay point. (In FIG. 1, n
= F)

(3) The subscriber terminal 17x relayed by the two-way relay amplifier 13n is selected as a transmission line monitoring signal transmission point. (In FIG. 1, the subscriber terminal 17a)

(4) The head end 11 starts monitoring the transmission path, and first, according to step 502 in FIG. 17, m (m is
Indicates the number of the bidirectional repeater amplifier.
・ It is. ) Is substituted with 0.

(5) According to step 503 in FIG.
Substitute 1.0 for ERm. (Substitute a large value that cannot be taken as the bit error rate)

(6) According to step 504 in FIG.
Is substituted for 1.

(7) In accordance with step 505 in FIG. 17, the head end 11 sends a command to the output path 50 to the bidirectional relay amplifier 13f in the downlink transmission path in accordance with the signal format of the downlink command in FIG. Send.

(8) In accordance with step 506 in FIG. 17, the head end 11 sends a command “transmit subscriber line 17a transmission line monitoring signal” to the subscriber terminal 17a.

(9) In accordance with step 507 in FIG. 17, the head end 11 sends a command “output switch conduction of the bidirectional relay amplifier 13a” to the bidirectional relay amplifier.

(10) According to step 508 in FIG.
A command "output switch disconnection of bidirectional relay amplifiers 13b-e and g" is sent.

(11) According to step 509 in FIG.
Based on the bit error rate measurement code received from the subscriber terminal 17a, the transmission quality detector 37 at the head end (FIG. 14)
Measures the bit error rate, and measures the bit error rate BER1
Get. The upstream quality B measured by the head end 11 at this time
ER1 is all of the trunk lines 12a, all of the trunk lines 12c, all of the trunk lines 12e including the tap-offs 16e, f, and 13 of the trunk lines 12b.
This is the quality of the transmission path limited to the headend 11 side from b and to the headend 11 side from 13c 12d.

(12) According to step 510 in FIG.
The head end 11 stores the quality BER1 at this time.

(13) In step 511 of FIG.
Compare R1 and BER0. Here, dBER is a difference amount of the bit error rate for determining that the transmission quality has deteriorated. For example, when dBER = 1.0 × 10E−3,
If the bit error rate, which was 3.0 × 10E-4, changed to 1.4 × 10E-3 at the next measurement, it is determined that noise was mixed. In each CATV system, the optimal value of dBER may be determined from the characteristics of the actual transmission path and the allowable bit error rate of the system. Since BER0 = 1.0, BER1-BER0
<DBER, branch to N side, proceed to next step.

(14) According to step 513 of FIG.
Substitute m + 1 for m, that is, 2 for m.

(15) At step 514 in FIG. 17, it is determined whether m is the maximum value Max, and the flow branches to the N side.

(16) According to step 507 of FIG.
The head end 11 sends a command “output switch conduction of the bidirectional relay amplifiers 13a and 13b” to the bidirectional relay amplifier.

(17) According to step 508 in FIG.
A command "output switch disconnection of bidirectional relay amplifiers 13c to 13e and g" is sent.

(18) According to step 509 in FIG.
Based on the bit error rate measurement code received from the subscriber terminal 17a, the transmission quality detector 37 at the head end (FIG. 14)
Measures the bit error rate and obtains a measured bit error rate BER2
Get. The upstream quality B measured by the head end 11 at this time
ER2 is all of the trunk lines 12a, all of the trunk lines 12c, all of the trunk lines 12e including the tap-offs 16e, f, and the tap-off 1
This is the quality of the transmission line limited to the headend 11 side from 13c of 12d for all trunk lines 12b including 6a and 6b.

(19) According to step 510 in FIG.
The head end 11 stores the quality BER2 at this time.

(20) In step 511 of FIG.
Compare R1 and BER0. Here BER2 BER1
Is that the tap-offs 16a and 16b of the trunk line 12b are included in the measurement range.
BER2 is worse than BER1 when noise is mixed in from the service line branching from a to the subscriber terminal.
In other words, if BER2 is dBER worse than BER1,
The noise corresponding to the degradation dBER is generated by the relay amplifier 13.
From b, it can be specified that it has been mixed into the upstream transmission path on the tap-off side.

(21) The head end 11 has a BER2-
If BER1> dBER, the fact that noise is mixed in from the bidirectional relay amplifier 13b is stored, and the process proceeds to the next measurement step.

(22) According to step 513 of FIG.
Substitute m + 1 for m.

(23) The process branches at step 514 in FIG.

(24) Steps 507 to 514 in FIG.
repeat.

(25) By sequentially receiving the bit error rate measurement signals, the head end 11 can finally specify the noise-mixed portion of the entire CATV network.

In the above description, the transmission path monitoring signal is transmitted from the subscriber terminal 17a, but the subscriber terminal transmitting the transmission path monitoring signal is switched following the switching of the output switch (bidirectional). It is to be added that a system in which the signal is transmitted from the subscriber terminal 17x relayed by the relay amplifier 13m) is also an embodiment of the present invention.

As described above, according to the seventh to ninth and twelfth aspects of the present invention, it is possible to automatically specify the location of the ingress noise in the bidirectional CATV transmission line without manual inspection, and There is an effect that the problem of can be solved.

[0203]

According to the present invention described above, bidirectional CATV
A bidirectional CATV system can be realized which can identify a noise mixing point in an upstream transmission line in a network and can solve the ingress noise problem in the upstream transmission line.

[Brief description of the drawings]

FIG. 1 is a connection diagram of a general bidirectional CATV system.

FIG. 2 shows a bidirectional CATV according to the first, fourth and seventh aspects of the present invention.
FIG. 1 is an explanatory diagram of an overall system configuration.

FIG. 3 is an explanatory view of a head end according to the invention according to claim 2;

FIG. 4 is an explanatory diagram of a bidirectional relay amplifier according to the invention according to claim 3;

FIG. 5 is an explanatory diagram of a subscriber terminal used in the two-way CATV system according to the first and fourth aspects of the invention.

FIG. 6 is a bidirectional CATV according to the first, fourth, and seventh aspects of the present invention;
FIG. 2 is an explanatory diagram of frequency allocation used in the system.

FIG. 7 is a bidirectional CATV according to the first, fourth, and seventh aspects of the present invention;
FIG. 2 is an explanatory diagram of a downlink signal format of the present invention used in the system.

FIG. 8 is a bidirectional CATV according to the present invention.
FIG. 2 is an explanatory diagram of an uplink signal format of the present invention used in the system.

FIG. 9 is an explanatory diagram of a flowchart used in the bidirectional CATV system of the invention according to claim 1;

FIG. 10 is an explanatory diagram of a second frequency allocation used in the bidirectional CATV system according to the first embodiment;

FIG. 11 is an explanatory view of a head end according to the invention according to claim 5;

FIG. 12 is an explanatory diagram of a bidirectional relay amplifier according to the invention according to claim 6;

FIG. 13 is an explanatory diagram of a flowchart used in the bidirectional CATV system of the invention according to claim 4;

FIG. 14 is an explanatory diagram of a head end according to the invention according to claim 8;

FIG. 15 is an explanatory diagram of a bidirectional relay amplifier used in the bidirectional CATV system according to the invention according to claim 7;

FIG. 16 is an explanatory diagram of a subscriber terminal of the invention according to claim 9;

FIG. 17 is an explanatory view of a flowchart used in the bidirectional CATV system according to the invention according to claim 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Head end 12a-f Trunk line 13a-g Bidirectional relay amplifier 14a-c Splitter 15a-d Distribution line 16a-i Tap-off 17a-l Subscriber terminal 18a-l Drop-in line 21a, b Head-end video input terminal 22a, b Head-end television modulator 23a, b Head-end high-frequency amplifier 24 Head-end synthesizer 25 Head-end splitter 26 Head-end trunk line connection terminal 27a, b Head-end demodulator 28a, b Head-end transmission line encoder / decoder 29 Head End subscriber terminal control units 30a, b Head end output interface units 31a, b Head end output interface terminals 32a, b Head end input interface terminals 33a, b Head end input interface units 34a, b Head end modulators 35a, b D-end second high-frequency amplifier 36 Head-end control unit 37 Head-end transmission quality detector 41a, b Bi-directional relay amplifier input / output terminal 42a, b Bi-directional relay amplifier duplexer 43a-c Bi-directional relay amplifier high-frequency coupler 44 bi-directional Relay amplifier downlink amplifier 45 bidirectional relay amplifier demodulator, 46 bidirectional relay amplifier transmission line coding / decoding device 47 bidirectional relay amplifier control unit 48 bidirectional relay amplifier modulator 49 bidirectional relay amplifier upstream amplifier 50 bidirectional relay amplifier Output switch 51 Bidirectional relay amplifier transmission path monitoring signal generator 52 Bidirectional relay amplifier demodulation path switch 53 Bidirectional relay amplifier transmission quality detector 60 Subscriber terminal drop-in connection terminal 61 Subscriber terminal duplexer 62 Subscriber terminal tuner Unit 63 Subscriber terminal tuning unit 64 Subscriber terminal video detector 65 Subscriber end Audio detector 66 Subscriber terminal RF modulator 67 Subscriber terminal video output terminal 68 Subscriber terminal audio output terminal 69 Subscriber terminal TV output terminal 70 Subscriber terminal demodulator 71 Subscriber terminal transmission line encoder / decoder 72 Subscription Subscriber terminal modulator 73 Subscriber terminal high-frequency amplifier 74 Subscriber terminal control unit 75 Subscriber terminal operation unit 76 Subscriber terminal display unit 77 Subscriber terminal transmission line monitoring signal generator 301-316 Flowchart steps 401-415 Flowchart steps 501-516 Flowchart steps

Continued on the front page (72) Inventor Tsutomu Noda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Multimedia Systems Development Division of Hitachi, Ltd. (72) Inventor Takatoshi Josugi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Multimedia System Development Division

Claims (12)

[Claims] 1. A bidirectional CATV system comprising a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other, wherein the headend comprises: And a head-end transmitting means for transmitting an address signal and a downlink control signal corresponding to the bidirectional relay amplifier toward the bidirectional relay amplifier. The bidirectional relay amplifier is adapted to correspond to the bidirectional relay amplifier from the headend. Receiving means for receiving an address signal and a downlink control signal, an output switch for turning on and off an output of an amplifier for an uplink signal, control means for turning on and off an output switch by a downlink control signal, a detector for detecting uplink transmission quality; Transmission quality transmitting means for transmitting the detection result detected by the transmitter and its own address signal to the head end; Bidirectional CATV systems; and a transmission path monitoring signal generator for generating a transmission path monitoring signals to be transmitted to end. 2. A head for use in a bidirectional CATV system having a headend and a subscriber terminal, which is linked via a bidirectional relay amplifier having an amplifier for a downstream signal and an amplifier for an upstream signal connected in parallel to each other. A head end, comprising: a head end transmitting means for transmitting, to the bidirectional relay amplifier, an address signal corresponding to the bidirectional relay amplifier and a downlink control signal for turning on / off an output switch of the bidirectional relay amplifier. 3. Both used in a bidirectional CATV system with a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other. Receiving means for receiving an address signal and a downlink control signal corresponding to the bidirectional relay amplifier from the head end, an output switch for turning on and off the output of the amplifier for the uplink signal,
Control means for turning on / off an output switch by a downlink control signal; a detector for detecting uplink transmission quality; transmission quality transmitting means for transmitting a detection result detected by the detector and its own address signal to a head end; A transmission path monitoring signal generator for generating a transmission path monitoring signal to be transmitted to an end. 4. A bidirectional CATV system comprising a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other, wherein the headend comprises: Head-end transmitting means for transmitting an address signal corresponding to a bidirectional relay amplifier and a first downlink control signal for turning on and off an output switch of the bidirectional relay amplifier; address signal and bidirectional relay corresponding to the bidirectional relay amplifier A bidirectional relay amplifier monitoring signal requesting means for transmitting a second downlink control signal for causing the bidirectional relay amplifier to transmit a transmission path monitoring signal from the amplifier to the headend; and a detector for detecting transmission quality from the transmission path monitoring signal. A bidirectional relay amplifier having an address signal and a head corresponding to the bidirectional relay amplifier from the head end. Receiving means for receiving a first downlink control signal and a second downlink control signal from a switch, an output switch for turning on and off an output of an amplifier for an uplink signal, control means for turning on and off an output switch by the first downlink control signal, 2. A bidirectional CATV system comprising: a transmission path monitoring signal generator for generating a transmission path monitoring signal in response to a downstream control signal. 5. A head for use in a bidirectional CATV system having a headend and a subscriber terminal, which is linked via a bidirectional relay amplifier comprising a downstream signal amplifier and a upstream signal amplifier connected in parallel to each other. At the end, a head-end transmitting means for transmitting an address signal corresponding to the bidirectional relay amplifier and a first downlink control signal for turning on / off an output switch of the bidirectional relay amplifier; and an address signal corresponding to the bidirectional relay amplifier and both. Bidirectional relay amplifier monitoring signal requesting means for transmitting a second downlink control signal for causing a bidirectional relay amplifier to transmit a transmission path monitoring signal from the relay amplifier to the headend, and a detector for detecting transmission quality from the transmission path monitoring signal And a head end comprising: 6. Both used in a bidirectional CATV system with a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other. Receiving means for receiving an address signal and a first downlink control signal and a second downlink control signal corresponding to a bidirectional relay amplifier from a head end; and an output switch for turning on and off an output of an amplifier for an uplink signal. A bidirectional relay amplifier comprising: control means for turning on and off an output switch according to a first downlink control signal; and a transmission path monitoring signal generator for generating a transmission path monitoring signal according to a second downlink control signal. 7. A bidirectional CATV system comprising a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other, wherein the headend comprises: A head-end transmitting means for transmitting a repeater address signal and a repeater control signal corresponding to the bidirectional repeater amplifier toward the bidirectional repeater amplifier, and a terminal address signal and a subscriber terminal control signal corresponding to the subscriber terminal. A subscriber terminal monitoring signal requesting means for sending to the subscriber terminal; and a detector for detecting transmission quality from the transmission path monitoring signal. The bidirectional repeater amplifier includes a repeater address signal from the head end and a repeater. Receiving means for receiving the control signal; an output switch for turning on and off the output of the amplifier for the upstream signal; and an output switch for turning on and off the output switch by the repeater control signal. Control means for turning off, a subscriber terminal receiving means for receiving a terminal address signal and a subscriber terminal control signal from a head end, and a transmission path monitoring signal for generating a transmission path monitoring signal based on the subscriber terminal control signal. A bidirectional CATV system comprising: a signal generator; and transmission means for transmitting a transmission path monitoring signal and its own terminal address signal to a head end. 8. A head for use in a bidirectional CATV system having a headend and a subscriber terminal, linked via a bidirectional relay amplifier having a downstream signal amplifier and an upstream signal amplifier connected in parallel to each other. At the end, a head-end transmitting means for transmitting a repeater address signal and a repeater control signal corresponding to the bidirectional repeater amplifier toward the bidirectional repeater amplifier, and a terminal address signal and subscriber terminal control corresponding to the subscriber terminal A head end comprising: a subscriber terminal monitoring signal requesting unit that sends a signal to a subscriber terminal; and a detector that detects transmission quality from a transmission path monitoring signal. 9. A subscription for use in a bidirectional CATV system comprising a headend and a subscriber terminal, linked via a bidirectional relay amplifier having an amplifier for downstream signals and an amplifier for upstream signals connected in parallel to each other. Receiving means for receiving a terminal address signal and a subscriber terminal control signal corresponding to a subscriber terminal from a head end, and a transmission path monitoring signal generator for generating a transmission path monitoring signal based on the subscriber terminal control signal And a transmitting means for transmitting a transmission path monitoring signal and its own terminal address signal to the head end. 10. A head end and a subscriber linked via a bidirectional relay amplifier having a downstream signal amplifier, a upstream signal amplifier, and an output switch for turning on and off an output of the upstream signal amplifier, which are connected in parallel with each other. A method of monitoring a transmission path of a bidirectional CATV system including a terminal, comprising: controlling an output switch of a bidirectional relay amplifier by controlling a headend, and causing the bidirectional relay amplifier to detect uplink transmission quality. Transmission line monitoring method. 11. A head end and a subscriber linked via a bidirectional relay amplifier having a downstream signal amplifier, a upstream signal amplifier, and an output switch for turning on and off an output of the upstream signal amplifier connected in parallel with each other. A transmission line monitoring method for a bidirectional CATV system including a terminal, controlling a headend to control an output switch of the bidirectional relay amplifier, causing the bidirectional relay amplifier to output a transmission line monitoring signal, and And a head end detecting a transmission quality. 12. A head end and a subscriber linked via a bidirectional relay amplifier having a downstream signal amplifier, a upstream signal amplifier, and an output switch for turning on and off an output of the upstream signal amplifier connected in parallel with each other. A transmission line monitoring method for a bidirectional CATV system having a terminal, controlling a head end, controlling an output switch of a bidirectional relay amplifier, causing a subscriber terminal to output a transmission line monitoring signal, and A transmission path monitoring method, wherein a head end detects transmission quality.