JPH11275130A - Cable network system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability by preventing a transmission line switchgear from malfunctioning by pseudo transmission display signals. SOLUTION: When respective subscriber modems transmit transmission display signals, their own ID codes are included, spectrum spreading is performed and transmission is performed. In a gate switch unit 30, at the time of receiving the transmission display signals, by collating the ID code included in the signals with the ID code of the subscriber modem registered beforehand in a transmission origin judgement circuit 39, whether or not it is transmission from a normal subscriber modem is judged. Then, only in the case of the transmission from the normal subscriber modem, a gate switch 37 is turned conductive and incoming signals sent out from the subscriber modem are passed through to an upstream.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bidirectional C
ATV (Cable Television) system and HFC (Hybrid
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable network system configured as a tree or a star, such as a fiber and coaxial system.

[0002]

2. Description of the Related Art In recent years, video broadcasting services
An ATV system is bi-directional, an online service for personal computers, a real-time communication service such as a telephone or a video phone, and a VOD (video-on-demand system) that immediately provides a desired movie video or the like in response to a user request. There is a growing movement to provide more diverse two-way transmission services such as Video On Demand) services.

[0003] However, as in the case of a CATV system, a cable whose transmission path branches in a tree or star shape is used.
In order to realize an interactive service in a network system, it is necessary to take measures against ingress noise.

That is, in each subscriber's house, for example, there is a connector open end to which no home device is connected, or a coaxial cable having insufficient electromagnetic shielding characteristics is used even when a home device is connected. Then, interference radio waves such as short-wave broadcasting and electromagnetic noise from an electric motor of a vacuum cleaner or a motorcycle flow from these open ends of the connectors and the coaxial cable. As described above, when noise flows into each subscriber's house, the noise from each subscriber's house joins on the upstream transmission line and becomes a higher level and is transmitted to the head end. Such noise is generally called ingress noise (Ingress Nois
Although this is referred to as e), this ingress noise not only causes deterioration of transmission quality, but also in some cases, may render the system untransmittable.

Accordingly, the present inventors have disclosed in Japanese Patent Application No. 8-1979.
In No. 49, a transmission line switching device is installed in an upstream transmission line of a bidirectional transmission line, and the transmission line switching device is used by the transmission line switching device during the passing period of the upstream signal according to a transmission display signal transmitted from a subscriber unit. A technique has been proposed in which an upstream transmission line of a transmission line is set to a conductive state, while the upstream transmission line is set to a blocking state during other periods.

[0006] By doing so, while the subscriber unit is not transmitting an uplink signal, the uplink transmission line is held in a cut-off state by the transmission line switching device. For this reason, even if noise is introduced into the upstream transmission line, for example, because the connector end in the subscriber's house is open or a coaxial cable having insufficient electromagnetic shielding characteristics is used, this inflow noise is The transmission path is not blocked by the transmission path switching device and does not flow out to the upstream side of the bidirectional transmission path. For this reason, the ingress noise level on the bidirectional transmission path is suppressed to a low level, whereby bidirectional transmission can be performed under a high quality transmission environment.

[0007]

However, in the above system, a signal modulated by a carrier, for example, a random signal is used as a transmission display signal. For this reason, for example, when noise is intentionally injected into the upstream transmission path together with the pseudo transmission display signal on the open end of the connector in the subscriber's home or on the upstream transmission path from the subscriber's home to the transmission path switching device, the pseudo transmission display The signal causes the transmission line opening / closing device to malfunction and become conductive. As a result, the inflow noise is directly transmitted to the upstream upstream transmission line, and there is a concern that the transmission quality may be significantly deteriorated or the system may be down.

The present invention has been made in view of the above circumstances, and has as its object to improve the reliability of a cable network system by preventing a transmission line switching device from malfunctioning due to a pseudo transmission display signal. It is to provide.

Another object of the present invention is to enable the center device to easily grasp the operation management information of the system such as the usage status of the system by each subscriber device without newly using a special control signal or the like. The purpose of the present invention is to provide an improved cable network system.

Another object of the present invention is to provide a cable network system capable of efficiently and reliably specifying a noise source by remote control from a center device.

[0011]

In order to achieve the above object, the present invention provides a method for transmitting a signal between a center device and a plurality of subscriber devices via a bidirectional transmission line configured in a tree or star configuration. In a cable network system in which a bidirectional transmission is performed and a transmission line switching device for intercepting ingress noise in the bidirectional transmission line is installed, each of the above-mentioned subscriber units is connected to a center device. When transmitting a signal, a transmission display signal representing the transmission period of the uplink signal and including the identification information of the own device is generated, and the transmission display signal is spectrum-spread by a predetermined spreading code sequence and transmitted, and In the transmission path switching device, the transmission display signal transmitted from each of the subscriber units is subjected to spectrum despreading and reproduction by the predetermined spreading code sequence, and is included in the reproduced transmission display signal. It is determined whether or not the source subscriber device is a legitimate subscriber based on the identification information, and if it is determined that the source subscriber device is a legitimate subscriber as a result of this determination, An uplink transmission path of the bidirectional transmission path is set to a conductive state during a period represented by the reproduced transmission display signal, and an uplink signal transmitted from the subscriber device is passed. .

According to the present invention, when identification information is not included in the transmission display signal, or when the identification information included is not for a regular subscriber, the transmission path switching device performs uplink transmission. Do not make the road conductive. For this reason, even if the noise accompanying the pseudo transmission indication signal is intentionally injected into the upstream transmission line on the open end of the connector in the subscriber's home or on the upstream transmission line from the subscriber's home to the transmission line switching device, this pseudo There is no need to worry that the transmission path switching device will malfunction and become conductive due to the transmission display signal. Therefore, a problem that the transmission quality is significantly deteriorated or the system is down due to intentional noise inflow is prevented.

According to another aspect of the present invention, there is provided a center apparatus for reproducing a transmission display signal having passed through the transmission path switching device by despreading the spectrum, and identifying an identification signal included in the transmission display signal. The transmitting apparatus is recognized based on the information, and the use state of the system by the subscriber apparatus is managed based on the recognition result.

That is, the center device uses the transmission display signal sent from the subscriber device to control the opening / closing of the transmission line switching device, and ascertains the system use status of each subscriber. It is. By doing this,
Each subscriber device can be managed in the center device without separately transmitting management data from each subscriber device.

According to another aspect of the present invention, a polling signal including a transmission control signal transmission control request is selectively transmitted from a center device to each subscriber device. When a polling signal addressed to the own device is received from the center device, the transmission start signal is transmitted or stopped in accordance with the content of the transmission control request included in the polling signal.

By doing so, it becomes possible to cause each of the subscriber units to transmit the transmission display signal or stop the transmission in response to a request from the center unit. By utilizing this, for example, when a large ingress noise is received by the center device, each subscriber device is individually connected to the upstream transmission line and the noise reception level is detected, thereby enabling the noise source to be generated. It can be specified accurately.

Further, according to the present invention, a polling signal in which a desired data collection request is selectively inserted is transmitted from the center device to each subscriber device, and the subscriber device receives a polling signal addressed to itself from the center device. If you do
It is also characterized in that the data held by the own device is included in the transmission display signal and transmitted according to the content of the data collection request included in the polling signal.

By doing so, the center device can individually collect subscriber holding data such as meter reading data, monitor data indicating the operating state of the subscriber device, maintenance management data, etc. from each subscriber device. It becomes possible. In addition, since the transmission of the subscriber holding data from each subscriber device to the center device is performed using the transmission display signal, it is not necessary to separately provide a new signal.

[0019]

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

The system of this embodiment is an HFC system, and tens of thousands of subscribers connected to the head end can be combined with an optical fiber and a coaxial cable to a maximum of 500 home paths per subsystem. It is subdivided into: Note that the home path is the number of homes where a cable is routed near the house or under the eaves, and the service can be provided immediately if requested by the subscriber.

In FIG. 1, a head end (H / E) (not shown) is provided for receiving television broadcasting signals transmitted via a communication satellite or the like, and for providing various interactive services. Information transmission facilities such as servers, routers, and exchanges are installed.

The H / E has a plurality of distribution hubs (D / H:
The Distribution Hubs 2, 2,... Are connected in a star shape by dedicated optical fibers 3, 3,. D / H2,2
.., The television broadcast signal sent from the H / E and the downstream signal for various interactive services are modulated and mixed, and then converted into an optical signal. F / N) 5, 5,...

The F / Ns 5, 5,... Convert the optical signal sent from the D / H2 into an electric signal and transmit it to a subsystem having a unit of 500 home paths. The subsystem connects a trunk coaxial cable 6 (hereinafter abbreviated as a trunk cable) that forms a bidirectional transmission path centered on the F / N 5 in a tree or star shape. A branch (tap-off) 8 is provided on these trunk cables 6, 6,... To drop a drop coaxial cable 9 (hereinafter abbreviated as a drop cable), and these drop cables 9, 9,. Is drawn into the subscriber's house 10.

An in-home distributor 11 is provided in the subscriber's home 10. The in-home distributor 11 includes, for example, a personal computer 15, a television device 16, and a telephone device 16 as in-home terminal devices. Modem (PC modem) 12 for personal computer, set top box (STB) 13 and telephone modem 14
Connected through. The trunk cable 6,6
Are provided with a plurality of bidirectional main line amplifiers 7 for compensating signal attenuation.

Using the personal computer 15, the television device 16, and the telephone device 16, the VOD
When receiving the service or the PC online service, the upstream signal transmitted from the STB or the modem is transmitted to the F / N 5 via the drop cable 9, the tap-off 8, and the trunk cable 6, and the F / N 5 transmits the optical signal. After being converted into a signal, it is sent to the D / H 2 via the optical fiber 4. The signal is converted into an electric signal by the D / H2, demodulated, and sent to an H / E server for processing.

The trunk cable 6 and the drop cable
On the cable 9, the upstream signal and the downstream signal are transmitted in different frequency bands. For example, in Japan,
70 MHz or more is allocated to the upstream signal band, and 48 MHz or less is allocated to the downstream signal band.

By the way, the subscriber modems such as the PC modem 12, the STB 13 and the telephone modem 14 provided in the subscriber homes 10, 10,... Are constituted as follows. FIG. 2 is a circuit block diagram showing the configuration.

The subscriber modem includes a frequency band separation circuit 21
And a demodulation circuit (DEM) 23 for demodulating a downlink signal and outputting received data, and a modulation circuit (MOD) 24 for modulating and transmitting transmission data transmitted from a home terminal device such as a personal computer 15. In addition, a transmission data detection circuit 25 and a transmission display signal generation circuit 26 are provided.

The frequency band separation circuit 21 is composed of a filter 22a for passing the frequency band H in the downward direction and a filter 22b for passing the frequency band L in the upward direction. Connected to the in-home distributor 11.

The transmission data detection circuit 25 is a personal data
It monitors the presence or absence of transmission data output from the in-home terminal device such as the computer 15 and outputs a detection signal during a period in which the transmission data is being output. Transmission display signal generation circuit 26
Generates a transmission indication signal including the identification information (ID code) assigned to the modem during the period when the detection signal is output from the transmission data detection circuit 25, and spreads the transmission indication signal by spectrum spreading. I do.

FIG. 3 is a circuit block diagram showing a specific example of the configuration of the transmission display signal generation circuit 26. The transmission display signal generation circuit 26 includes a random data generation circuit 41,
An identification information generating circuit 43; The random data generation circuit 41 generates random data during a period when the detection signal is output from the transmission data detection circuit 25. The identification information generation circuit 43 generates an ID code assigned to its own modem in advance.

The random data generated by the random data generation circuit 41 and the ID code generated by the identification information generation circuit 43 are mutually multiplexed by a multiplexer 42, and then multiplexed by a serial / parallel converter (S / P) 4
4 converts the signal into a parallel signal. The parallel signal is encoded by, for example, a DQPSK method by a four-phase differential encoder 45, and then input to a mixer 46.
In step 6, the PN code generated by the PN code generating circuit 48 is multiplied, and thereby the spectrum is spread. The parallel signal subjected to the spread spectrum is supplied to a multiplexer 47.
After that, the signal is converted into a single-system signal, and then band-limited by a band-pass filter (BPF) 49 so as to be a signal within the upstream signal band. Then, the signal is mixed with the carrier signal generated from the carrier signal generation circuit 51 by the mixer 50, converted into a carrier frequency, and then amplified by the transmission power amplifier 52 and transmitted.

The system of this embodiment is close to the tap-offs 8, 8,... In the drop cables 9, 9,... Between the tap-offs 8, 8,. In position, gate switch unit (GSU) 3
0, 30, ... are provided. This GSU 30, 30, ...
Sets the up transmission path to the conductive state only during the period when the transmission indication signal transmitted from the subscriber modems 12, 13, 14 is received, whereby the subscriber modems 12, 13, 14
14 through the upstream signal transmitted.

FIG. 4 is a circuit block diagram showing the structure of the GSUs 30, 30,. GSU30, 30, ...
Includes first and second frequency separation circuits 31, 33, a delay circuit 35, and an amplifier 36, and further includes a gate switch 37, a transmission display signal detection circuit 38, and a transmission source determination circuit 39. ing.

First and second frequency separation circuits 31, 33
Are respectively composed of filters 32a and 34a that pass the frequency band H in the down direction and filters 32b and 34b that pass the frequency band L in the up direction.

The transmission indication signal detection circuit 38 is for detecting the transmission indication signal transmitted from the subscriber modems 12, 13, and 14, and is configured as shown in FIG. 5, for example. That is, the transmission display signal is first mixed by the mixer 61 with the carrier signal generated from the carrier signal generation circuit 62 and converted into an intermediate frequency signal. It is mixed with two local oscillation signals different by π / 2 and further converted to a baseband frequency. The local oscillation signal is generated by a local oscillator 65 and a π / 2 phase shifter 66.

The signal output from the mixer 64 is converted into a digital signal by an analog / digital converter (A / D) 67, and the frequency error is corrected by a complex multiplier 68. And the spectrum is despread by the matched filter 70. The despread signal is decoded by a four-phase differential decoder 71, and the decoded signal is converted to a serial signal by a parallel / serial conversion circuit 72, and then input to a transmission source determination circuit 39.

The transmission source judging circuit 39 controls the I / O of each of the subscriber modems 12, 13, and 14 connected to the downstream side of its own GSU.
It has a table that stores D codes. Then, an ID code is extracted from the reproduction signal output from the transmission display signal detection circuit 38. If the ID code is extracted, the table is searched to determine whether the ID code is stored. . And if memorized,
Judging that the signal is a transmission indication signal transmitted from a legitimate subscriber modem, a gate control signal is supplied to the gate switch 37, thereby turning on the gate switch 37.

The delay circuit 35 detects the transmission display signal by the transmission display signal detection circuit 38 and then determines by the transmission source determination circuit 39 the time required for determining that the signal is from a legitimate subscriber modem. , For delaying the upstream signal.

The system of this embodiment is provided with a modem polling / ID detecting device 2a and a real-time spectrum analyzer 2b for measuring ingress noise at distribution hubs (D / H) 2, 2,. I have.

The modem polling / ID detecting device 2a
The subscriber modems 12, 13, at each subscriber home 10, 10,.
A polling signal into which information for requesting the transmission or stoppage of the transmission display signal is inserted is transmitted to the transmission signal via the downlink transmission path. Further, at the time of steady state, and after the transmission of the polling signal, the subscriber modems 12, 1 are transmitted.
The transmission source of the transmission indication signal coming from 3, 14 is detected by identifying the ID code of the subscriber modem included in the transmission indication signal.

The real-time spectrum analyzer 2b analyzes the level and the nature of the ingress noise included in the upstream signal arriving via the upstream transmission line, and analyzes the analysis result to the transmission display signal currently being received. Along with the transmission source ID code detected from, the data is transmitted to a head end (H / E) (not shown) or a monitoring center connected to the head end.

Next, the operation of the system configured as described above will be described. At a certain subscriber's house, a user uses a television device 16 to operate a head end (H).
/ E) is requested to transmit a program. Then, the TV device 16 sends the STB
13, the transmission request data is output. In the STB 13, the transmission request data is modulated by the modulation circuit 24, and then transmitted to the upstream transmission path via the filter 22b.
At the same time, the transmission request data is detected by the transmission data detection circuit 25, and the transmission display signal generation circuit 26 generates a transmission display signal in response to the detection signal. At this time, the transmission display signal includes the ID code assigned to its own STB 13. This transmission display signal is spread on the spectrum and then transmitted on the upstream transmission line via the filter 22b.

FIG. 6 shows a comparison between the spectrum characteristics of the uplink transmission signal transmitted to the uplink transmission line and the spectrum-spread transmission display signal. As is apparent from the figure, the signal intensity of the transmission display signal becomes extremely small due to the spread spectrum, and as a result, even if the band of the transmission display signal overlaps with the band of the uplink transmission signal, the uplink transmission signal remains It can transmit with little interference. In other words, it is not necessary to separately prepare a band for transmitting the transmission display signal, and the bandwidth of the uplink transmission path can be expanded accordingly, and the capacity of the subscriber can be increased.

When the uplink transmission signal and the transmission display signal arrive from the STB 13, the transmission display signal is first detected by the transmission display signal detection circuit 38 in the GSU 30. The detection of the transmission display signal is performed by frequency-converting the received signal, despreading the spectrum, and then decoding the signal by a four-phase differential decoding method.

When the transmission display signal is detected, the transmission source determination circuit 39 detects ID data from the transmission display signal. When the ID data is detected,
By searching the table, it is determined whether the detected ID data matches the ID code of the subscriber modem registered in advance. If there is a matching ID data, it is determined that the transmission is from a legitimate subscriber modem, and a gate control signal is supplied to the gate switch 37. As a result, the gate switch 37 is turned on.
Accordingly, the upstream transmission signal passes through the gate switch 37, and is transmitted from the filter 32b to the upstream transmission path.

The upstream transmission signal that has passed through the GSU 30 is transferred to the upstream transmission line of the trunk cable 6 via the tap-off 8, and further converted into an optical signal by the fiber node (F / N) 5, and then transmitted. The data is transferred to the head end via the fiber transmission line 4 and the distribution hub (D / H) 2. Upon receiving the uplink transmission signal, the head end identifies the content of the request and performs processing according to the content of the request. For example, in this case, since it is a program transmission request, the requested program is selected from the program database and its broadcast signal is transmitted to the requesting subscriber via the downlink transmission path.

At this time, the distribution hubs (D / H) 2,
In 2,..., The monitoring operation of the transmission source subscriber is performed using the transmission indication signal. That is, the transmission indication signal transferred together with the uplink transmission signal from the STB 13 is received by the modem polling / ID detection device 2a, and the ID code is detected. In addition, reception of this transmission display signal and ID
The detection of the code is performed in the same manner as in the transmission display signal detection operation and the transmission source determination operation in the GSU 30 described above.
The detected ID code is transmitted to the headend (H) together with information necessary for subscriber management such as the length of transmission time.
/ E) or to the management center connected to it. The headend or the management center manages, for example, the system usage status for each subscriber based on the transmitted information. This management process is performed by the distribution hubs (D / H) 2, 2,
... may be performed.

The distribution hubs (D / H) 2, 2,.
.. For each subscriber home 10, 10,...
Polling is performed every 2, 13 and 14 to control the transmission or stop of the transmission display signal, thereby controlling, for example, a noise source.

That is, for example, when ingress noise exceeding a predetermined level is detected, distribution hubs (D / H) 2, 2,.
Transmits, to each of the subscriber modems 12, 13, and 14, individually, information for requesting transmission or stoppage of the transmission indication signal and a polling signal including the ID code of the destination subscriber modem. The transmission of the polling signal is also performed by spectrum spreading similarly to the transmission of the transmission display signal described above. By doing so, it is not necessary to provide a band for the polling signal on the downlink transmission path, and it is possible to ensure a sufficiently wide transmission band for the downlink signal.

Each of the subscriber modems 12, 13, and 14 is configured as shown in FIG.
Although not shown, the transmission display signal detection circuit 3 described above is used.
8 is provided with a polling signal detection circuit having the same configuration as that of FIG. 8, and when a polling signal arrives, the polling signal is received and demodulated to determine whether or not the polling signal is addressed to itself. If the polling signal is the self-addressed polling signal, the transmission display signal is transmitted or stopped by controlling the transmission display signal generation circuit 26 in response to a request included in this signal. By transmitting or stopping the transmission indication signal, the GSU 30 located upstream of the subscriber modem is turned on or off.

After transmitting the polling signal, the distribution hubs (D / H) 2, 2,... Confirm the response of the subscriber modem from the transmission indication signal arriving from the subscriber modem of the transmission partner, and at this time, the GSU 30 The level and nature of the ingress noise coming through
The analysis is performed by the analyzer 2b. Then, the noise source is specified based on the result of the analysis.

As described above, in this embodiment, when each of the subscriber modems 12, 13, and 14 transmits a transmission indication signal, it transmits its own signal by including its own ID code and performing spectrum spreading. When the transmission indication signal is received, the ID code included in the signal is compared with the ID code of the subscriber modem registered in advance to determine whether or not the transmission is from a legitimate subscriber modem. The gate switch 37 is made conductive only when the transmission is from a legitimate subscriber modem, so that the upstream signal transmitted from the subscriber modem is passed upstream.

Therefore, if the ID code is not included in the transmission indication signal, or if the included ID code is not for a proper subscriber modem, the GSU 30
Does not set the uplink transmission path to a conductive state. For this reason, even if the noise accompanying the pseudo transmission indication signal is intentionally injected into the upstream transmission path from the connector open end in the subscriber home or the upstream transmission path from the subscriber home 10 to the GSU 30, the pseudo transmission display The signal does not cause the GSU 30 to malfunction and become conductive. Therefore, a problem that the transmission quality is significantly deteriorated or the system is down due to intentional noise inflow is prevented.

In this embodiment, the transmission indication signal transmitted to the upstream side through the GSU 30 is transmitted to the distribution hub (D / D).
H) Receiving in step 2, the ID code is detected, and this ID code is added to communication management information such as transmission time and transferred to the headend or management center. By doing so, it is possible to manage the use status of the system by each subscriber by using the transmission display signal which is originally used only for controlling the opening and closing of the GSU 30.

Further, the distribution hub (D / H) 2 sends a polling signal for requesting transmission of a transmission indication signal or stop of the transmission indication signal to each of the subscriber modems 12, 13, and 14 individually. , 14 receive or send their own polling signal, and transmit or stop the transmission display signal according to the contents of the request. Therefore, the transmission of the transmission indication signal by each subscriber modem and its stop can be controlled by remote control from the distribution hub (D / H) 2, whereby the gate switch 37 of the GSU 30 can be controlled to open and close. This makes it possible to efficiently and reliably specify the noise source in the distribution hub (D / H) 2.

The present invention is not limited to the above embodiment. For example, meter reading data may be collected using a transmission display signal. That is, as shown in FIG. 1, each subscriber's home 10, 10,... Is provided with a meter reader 18 and this meter reader 18 is connected to the drop cable 9 via the data modem 17. Then, a polling signal requesting transmission of meter reading data is transmitted from the head end or the meter reading center connected to the head end to each of the subscriber homes 10, 10,.... Spread spectrum is also used when transmitting this polling signal. When the data modem 17 receives the polling signal addressed to itself,
The meter reading data stored in the meter reading unit 17 is read, the meter reading data is inserted into the transmission display signal, and the spectrum is spread and transmitted.

In this way, GSU3
Meter reading data can be collected using the transmission display signal used for opening / closing control of 0, 30,..., And as a result, an upstream transmission channel (band) is not allocated for transmission of meter reading data. Meter reading data can be transmitted using existing signals.

Further, in the above-described embodiment, the case where the transmission display signal detection circuit 38 is configured using the matched filter 70 has been described. However, as in the transmission display signal detection circuit 380 shown in FIG. Alternatively, a configuration using a surface acoustic wave (SAW) convolver 76 is also possible.

Further, when the ID code and the meter reading data are included in the transmission display signal and transmitted, the ID code and the meter reading data may be encrypted. As the encryption method, a public key method, a DES method, or the like can be used. In this way, the security of the system can be kept high.

In addition, the type of data transmitted using the transmission display signal, the signal format of the transmission display signal, the configuration of the transmission display signal generation circuit and the transmission display signal detection circuit,
The configuration of the transmission source determination circuit, the use of the transmission display signal, and the like can be variously modified without departing from the scope of the present invention.

[0062]

As described in detail above, according to the present invention, when each subscriber unit transmits an uplink signal to the center unit, the transmission unit indicates the transmission period of the uplink signal and includes the identification information of the own unit. A display signal is generated, the transmission display signal is spectrum-spread by a predetermined spreading code sequence and transmitted, and the transmission path switching device performs spectrum despreading on the transmission display signal transmitted from each of the subscriber units. Playback is performed, and it is determined whether or not the transmission source subscriber apparatus is a valid subscriber based on the identification information included in the reproduction transmission display signal. If it is determined to be a subscriber, the uplink transmission path of the bidirectional transmission path is set to a conductive state during a period represented by the reproduced transmission indication signal, and an uplink signal transmitted from the subscriber unit. Go through It is as to cause.

Therefore, according to the present invention, if the transmission display signal does not include the identification information, or if the identification information included is not for the authorized subscriber, the transmission path switching device will Do not make the transmission path conductive. For this reason, even if the noise accompanying the pseudo transmission indication signal is intentionally injected into the upstream transmission line on the open end of the connector in the subscriber's home or on the upstream transmission line from the subscriber's home to the transmission line switching device, this pseudo There is no need to worry that the transmission path switching device will malfunction and become conductive due to the transmission display signal. Therefore, a problem that the transmission quality is significantly deteriorated or the system is down due to intentional noise inflow is prevented.

That is, it is possible to provide a cable network system in which the transmission path switching device is prevented from malfunctioning due to the pseudo transmission display signal and reliability is improved.

According to the present invention, in the center device, the transmission display signal passed through the transmission path switching device is despread in spectrum and reproduced, and the transmission signal is transmitted based on the identification information included in the transmission display signal. Recognizing the subscriber device,
By managing the usage status of the system by the subscriber device based on the recognition result, the system operation management information such as the usage status of the system by each subscriber device is newly used by a special control signal. It is possible to provide a cable network system that can be easily grasped by the center device without performing.

Further, according to the present invention, a polling signal including a transmission control signal transmission control request is selectively transmitted from the center device to each subscriber device, and each subscriber device transmits the polling signal from the center device to its own device. When the polling signal is received, the transmission display signal is started or stopped according to the content of the transmission control request included in the polling signal, so that the noise generation source can be remotely controlled from the center device side. It is possible to provide a cable network system capable of efficiently and surely specifying the cable network system.

[Brief description of the drawings]

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

FIG. 2 is a circuit block diagram showing a configuration of a subscriber modem of the system shown in FIG.

FIG. 3 is a circuit block diagram showing a specific configuration of a transmission indication signal generation circuit of the subscriber modem shown in FIG.

FIG. 4 is a circuit block diagram showing a configuration of a GSU of the system shown in FIG. 1;

FIG. 5 is a circuit block diagram showing a specific configuration of a GSU transmission display signal detection circuit shown in FIG. 4;

FIG. 6 is a diagram showing the relationship between the signal intensity of a transmission display signal and the uplink signal after spectrum spreading.

FIG. 7 is a circuit block diagram showing another embodiment of the transmission display signal detection circuit according to the present invention.

[Explanation of symbols]

 2, 2, distribution hub (D / H) 3, 4, optical fiber 5, 5, wy fiber node (F / N) 6, 6, trunk cable 7, 7, bidirectional trunk amplifier 8, 8 ,... Branch unit (tap-off) 9, 9,... Drop cable 10, 10,... Subscriber home 11. Computer 16 Television device 17 Telephone device 18 Meter reader 19 Data meter 21 for meter reading Frequency band separation circuit 22a, 22b Filter 23 Demodulation circuit 24 Modulation circuit 25 Transmission data detection circuit 26 Transmission display Signal generation circuit 30 Gate switch unit (GSU) 31, 33 Frequency band separation circuit 32a, 32b, 34a, 34b Filter 35 Extension circuit 36 ... amplifier 37 ... gate switches 38,380 ... transmission indication signal detecting circuit 39 ... transmission source determining circuit

Claims (4)

[Claims] 1. A bidirectional transmission of a signal between a center device and a plurality of subscriber units via a bidirectional transmission line configured in a tree or star shape, and a signal flowing through the bidirectional transmission line. A cable network system including a transmission line switching device for intercepting a combined noise, wherein each of the subscriber units represents a transmission period of the uplink signal when transmitting the uplink signal to a center device. And a display signal generating means for generating a transmission display signal including identification information of the apparatus itself; and a display signal transmitting means for performing spectrum transmission on a transmission display signal generated by the display signal generation means using a predetermined spreading code sequence and transmitting the signal. The transmission path switching device comprises: a display signal detecting means for reproducing the transmission display signal transmitted from each of the subscriber units by spectrum despreading with the predetermined spread code sequence. Based on the identification information included in the transmission display signal reproduced by the display signal detecting means, determining means for determining whether the transmission source subscriber device is a legitimate subscriber, When it is determined that the transmission source subscriber device is a legitimate subscriber, the up transmission path of the bidirectional transmission path is set to a conductive state during a period represented by the reproduced transmission indication signal, A cable means for passing an upstream signal transmitted from the subscriber unit. 2. A display signal reproducing means for receiving said transmission display signal passing through said transmission path switching device, and for despreading and reproducing said received transmission display signal with a predetermined spreading code sequence. Recognizing means for recognizing the transmitting subscriber device based on the identification information included in the transmission display signal reproduced by the display signal reproducing device; and a system for the subscriber device based on the recognition result by the recognizing device. 2. The cable network system according to claim 1, further comprising management means for managing usage status. 3. The center device includes means for selectively transmitting a polling signal including a transmission control signal transmission control request to each of the subscriber devices, wherein each of the subscriber devices is addressed from the center device to its own device. 2. A cable network according to claim 1, further comprising means for starting or stopping transmission of a transmission indication signal in response to the content of the transmission control request included in the polling signal when the polling signal is received. system. 4. The center device comprises means for selectively transmitting a polling signal in which a desired data collection request is inserted to each subscriber device, wherein the subscriber device sends a polling signal from the center device to its own device. 2. A device according to claim 1, further comprising means for transmitting, when a polling signal is received, data included in the own device in a transmission display signal in accordance with the content of a data collection request included in the polling signal. Cable network system.