JPH11346177A - Method, device and system for noise mixing part detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To variably set a reference voltage for noise detection of a noise detection device, in accordance with a mixing level of the noise. SOLUTION: A control device 18 enables a status monitor 25 to detect noise on a transmission line by changing and adjusting a reference voltage of a voltage comparison circuit 14 for detecting the noise of a guard band, in accordance with signal characteristics of a transmission band detected by a detection circuit 17 and a predetermined noise mixing level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a system for detecting a noise-mixed portion for detecting a mixed portion of an ingress noise mixed in a transmission line, for example, an upstream ingress noise of a CATV system.

[0002]

2. Description of the Related Art Conventionally, for example, in a CATV system of this type, a gate switch provided in a relay amplifier is turned on / off to detect whether or not upstream ingress noise is mixed, thereby forming a tree-like structure. Although the upstream transmission line was partially closed, the portion was separated from the CATV system to detect the mixing point of the ingress noise. In this system, however, the upstream transmission line was partially closed. The subscriber station connected to the transmission line has a trouble such as interruption of the communication service, and it is not possible to quickly detect a noise-mixed portion.

In order to improve such a situation, for example, a reference voltage for detecting noise is set to a fixed value in advance at the time of installation of the apparatus, as shown in a noise mixing point detecting apparatus of Japanese Patent Application No. 8-339506. In some cases, for example, noise in a frequency band of a guard band, which is not used for normal transmission, is detected based on the reference voltage and a noise mixing section is specified.

[0004]

However, in the above detection device, since the reference voltage for detecting noise is set to a fixed value, the reference voltage is changed in accordance with the level of noise contamination due to environmental changes or the like. Even if it was necessary to change the reference voltage, the reference voltage could not be changed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method of detecting a noise-containing portion, in which the reference voltage of the noise detecting device can be variably set in accordance with a noise-mixing level, and a device and a system thereof. With the goal.

Another object of the present invention is to provide a method and a system for detecting a noise-containing portion in which a noise detection device can change a reference voltage according to a noise-mixing level from a remote place such as a center station or the like. To provide.

[0007]

In order to achieve the above object, according to the present invention, among noise signals mixed in a transmission line, a noise signal having a frequency other than the frequency band of a main signal is compared with a voltage of a noise detector. The noise detection means, which is a circuit, detects the noise by comparing it with the voltage level of the reference voltage (reference level), and detects a noise-incorporated portion based on the detection result, and performs control based on a predetermined control signal. A method of detecting a noise-containing portion, wherein the reference level control means, which is an apparatus, operates a reference level changing means to control the reference level;
An apparatus and a system are provided.

That is, when the voltage comparison circuit of the noise detection device cannot detect the noise even though the signal level difference between the noise signal and the main signal is a level at which it is determined that noise is mixed, the noise can be detected. The control signal is transmitted so that the reference level is changed until the reference level is changed, thereby enabling the noise detection device to change the reference level.

Further, the noise detecting device includes a signal characteristic detecting means which is a detecting circuit for detecting a signal characteristic of a main signal on a transmission line in a transmission band, and a signal characteristic detecting means based on a detection result of the signal characteristic. It is preferable that the apparatus further comprises reference level control means for controlling the reference level by operating the reference level changing means.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a noise mixed place detecting apparatus for a CATV system according to the present invention will be described with reference to FIGS.

FIG. 1 is a configuration diagram showing the configuration of a CATV system according to the present invention. In the figure, bidirectional CATV
In the system, for example, a center station 1 and a plurality of subscriber stations 2 are connected by a transmission line configured in a tree shape, and the center station 1
The communication between the subscriber stations is performed via the.

In such a bidirectional CATV system, a broadcast wave received from an antenna 3 is distributed to each subscriber station 2 via a downlink and a signal transmitted from each subscriber station 2 via an uplink is converted. , A center station 1 for transmitting data to a downlink, and a relay for compensating for attenuation of a signal transmitted via a transmission line (for example, a coaxial cable or an optical fiber) 4 connecting each of the subscriber stations 2 and the center station 1. Amplifier 5 and each subscriber station 2
And a protector 7 for electrically protecting each subscriber station 2. In addition, 8
It is a two-way home terminal of the subscriber station 2.

For example, the transmission frequency band used for the uplink of the 750 MHz CATV system is 10 to 50 MHz.
z, transmission frequency band used for downlink is 70-75
0 MHz. The signal transmitted from the subscriber station 2 using the uplink is converted by the center station 1 into a frequency used for the downlink and retransmitted.

Since the wiring form of the transmission path is a tree,
Noise that has entered the end of the transmission line 4 or in the middle of the transmission line 4 joins at the branch point of the transmission line 4 (branch point of the amplifier 5 and the tap-off 6), and further approaches the center station 1 at each branch point. While repeating the addition of the noise in the transmission band used in the above, all the noises that have entered the uplink and the thermal noise of the amplifier 5 are collected in the center station 1. This noise is generally called ingress noise. As described above, there are various frequencies of noise mixed into the transmission line from the outside.If noise of a certain frequency enters from a crack in a cable or a loose connector, noise radio waves existing at other frequencies also enter It will be.

Therefore, in the present invention, the use of another frequency band, which is not the transmission frequency actually used for communication, is used to detect the presence or absence of noise intrusion and to notify a predetermined point such as a center station of each other. A noise detection device 9 for detecting such noise is connected to the relay amplifier 5.

As shown in the first embodiment of FIG. 2, the noise detection device 9 of the present invention includes a branch circuit 10 connected to the transmission line 4 on the downstream side of the branching filter 20, a band-pass filter circuit 11, , An amplification circuit 12, a detection circuit 13, and a voltage comparison circuit 14 which constitutes a noise detection means of the present invention and compares a voltage level of a reference voltage which is a reference level of the present invention and a voltage level of an input voltage. A voltage holding circuit 15 connected to a status monitor 25 to be described later, a branch circuit 16 connected to the upstream transmission line 4, and a detection circuit connected to the branch circuit 16 which constitutes the signal characteristic detecting means of the present invention. A circuit 17 and a control device 18 which constitutes the reference level control means and the reference level changing means of the present invention and variably adjusts the reference voltage of the voltage comparison circuit 14. It is output to. The relay amplifier 5 includes demultiplexing filters 20 and 21 including a high-pass filter and a low-pass filter, and these demultiplexing filters 20 and 2.
The amplifiers 22 and 23 connected between them, the branch circuit 24 connected to the transmission line for upstream transmission, and the state of temperature and current consumption, which have been monitored conventionally, and the state of noise according to the present invention are monitored. And a status monitor 25 for transmitting the information to the center station.

Normally, in this CATV system, a guard band (50 to 50) which is a frequency between upstream transmission and downstream transmission is used.
The signal within 70 MHz is removed by the operation of the demultiplexing filters 20 and 21 and is not transmitted. Therefore, in this embodiment, a signal (noise) of a guard band of 50 to 70 MHz is used.
Is detected by the band-pass filter circuit 11 of the noise detection device 9, thereby enabling the center station 1 to specify the noise mixing section.

The center station 1 has a head-end device 30 connected to the transmission line 4 and a section detecting device 31 for monitoring and controlling noise.
Reference numeral 5 denotes a host computer, a polling machine, and a transceiver (not shown), and the center station 1 operates the relay amplifiers 5 at time intervals set by the polling method as in the related art.
The status monitor 25 is called to fetch information on various states including the noise. The center station 1 can determine the location where noise is mixed based on this information.

That is, the signal of the guard band jumped onto the transmission line 4 is branched by the branch circuit 10,
After passing through the band-pass filter circuit 11, the amplification circuit 12
To enter. The signal is amplified by the amplifier circuit 12 and further detected by the detection circuit 13 to be applied as a DC voltage to the voltage comparison circuit 14.

The detection circuit 17 detects the signal level of the main signal from the transmission line for performing the upstream transmission, and outputs the signal level to the control device 18. The control device 18 applies the value (V1−V2) obtained by subtracting the specified value V2 from the signal level V1 of the main signal input from the detection circuit 17 to the voltage comparison circuit 14 as a reference voltage.

The reference voltage (V1-V2) is compared with the DC voltage (guard band signal level) V by the voltage comparison circuit 14.
Compared to 3.

At this time, when the DC voltage is higher than the set reference voltage, that is, when the detected noise level is strong V1-V2 ≦ V3, the output voltage level of the voltage comparison circuit 14 is changed from the low level to the low level. Become a high level,
Output to the voltage holding circuit 15. Since the noise is not always present, the voltage holding circuit 15 holds the output voltage level from the voltage comparison circuit 14 for a certain time. The status monitor 25 detects the presence or absence of noise contamination by monitoring the output state from the connected voltage holding circuit 15.
The noise mixing section is detected from the information of No. 5 (output state, for example, alarm and identification information of each relay amplifier).

In this embodiment, for example, the specified value V2 is set to 10 dB, and the level of the main signal is reduced by -10.
If noise of a level higher than dB is mixed in the guard band, it is regarded as a transmission path failure and the status monitor 25
Raises an alarm. Here, the specified value V
2 may be set as appropriate, for example, by setting a value suitable for the environment in which the system is installed, such as an electric field concentration area such as a city center or an electric field dispersion area such as a rural area.

At this time, since the transmission loss varies depending on the length of the transmission path to the noise detection device and the number of transmission line devices such as tap-off units inserted in the middle, the transmission reaching the noise detection device depends on the transmission path. The main signal level of the band is different. Therefore, it is necessary to change the threshold of the reference level at which the alarm at which the guard band level becomes -10 dB should be raised according to the input level of the main signal to the noise detection device determined by the transmission loss. Therefore, the main signal level and the guard band level are measured, and the threshold level is set to be −10 dB from the main signal level.

In this example, -10 dB is used as one guide, but this value may be changed according to the potential electric field strength existing around each of the relay amplifiers. For example, if the potential electric field strength is high, even a small defect will cause a large level of noise contamination,
Increase the set value (for example, -5 dB). Further, when the potential electric field strength is low, there is a possibility that only a small level of noise is mixed even in the case of a large malfunction, so the set value is reduced (for example, -15 dB).

The strength of the potential electric field can be determined by referring to a result of a previous electric field strength measurement performed before constructing a CATV transmission line, or by measuring an ambient electric field with an antenna or the like installed in a relay amplifier. It can also be used as a criterion.

Here, for example, in FIG.
There is a crack in the cable at point g between
If it is assumed that a noise signal over a wide band including near Hz is mixed, the noise can be detected by the noise detection device 9 on the upstream side (left side of point g in the figure) of the noise mixing point. That is, this noise is blocked by the demultiplexing filters 20 and 21 in the relay amplifier 5 to which the noise detection device 9 is connected, and does not exist in the next-stage relay amplifier. Only 9 is detected,
The output state is held in the voltage holding circuit 15.

The output state is stored in the voltage holding circuit 15.
Monitoring and collecting by the status monitor 25 connected to
The data is transmitted to the center station 1. The control device 34 of the center station 1 can detect, based on the transmitted information, that the noise mixing section is between a and b among the sections in the CATV system.

As described above, in the present embodiment, the reference voltage of the voltage comparison circuit for the noise detection device itself to detect the noise contamination is variably changed according to the noise contamination level due to environmental changes such as a surrounding electric field. Since the noise contamination is detected by setting, if the signal level difference between the noise and the main signal is a level determined to be noise contamination, the status monitor can accurately detect the noise contamination.

In this embodiment, the guard band (50
７０70 MHz) is used as the frequency of noise detection. In this frequency band, there are few signals to be noise, and it is considered that versatility in practical use is considered to be poor. Proposed, in which case the FM present in the guard band is
Radio broadcasts can be targeted for noise monitoring.

Further, in this embodiment, frequencies not used for normal transmission, that is, neither for uplink transmission nor for downlink transmission, include frequency bands other than the guard band. For example, a frequency band of 750 MHz or more in a 750 MHz CATV system and a frequency band of 450 MHz or more in a 450 MHz CATV system correspond to the frequency. In the former, a signal of UHF television broadcasting can be set as a target, and in the latter, a signal of mobile communication can be set as a target of the noise monitoring. . Furthermore, the frequency bands of 10 MHz or less in these systems are also included in frequencies not used for normal transmission, and short-wave broadcasting, amateur radio, medium-wave broadcasting, and the like can be targets for noise monitoring.

In this embodiment, the case where noise is mixed in the main line has been described. However, the present invention is not limited to this, and a device comprising a noise detection device, a demultiplexing filter and a status monitor is replaced with a branch line relay amplifier. It can also be built-in or externally attached to a tap-off of a service line, a security device, or the like. In this case, it is possible to detect a further subdivided noise mixing section.

FIG. 3 shows a second embodiment in which the reference voltage can be controlled from the section detecting device. In the following drawings, the same components as those in FIG. 2 are denoted by the same reference numerals for convenience of explanation.

Referring to FIG. 3, the section detecting device 31 of the present invention
Is a modem 3 provided in the center station 1 and connected to the branching filter 32 and the high-pass filter of the branching filter 32.
3, a status monitor 34 connected to the low-pass filter of the demultiplexing filter 32, and a control device 35 constituting reference level control means of the present invention and connected to these devices 33 and 34.

In the noise detection device 9 of the present embodiment, the downstream transmission line 4 is replaced with the control device 18 of the first embodiment.
A modem 27 connected to a branch circuit 26 provided in the
A D / A converter 28 for converting a signal fetched by the modem 27 into an analog signal. The D / A converter 28 outputs a reference voltage to the voltage comparison circuit 14. The modem 27 includes a filter 27a for passing a high-frequency signal output from the modem 33, a demodulator 27b for demodulating the signal, and a power supply 27c. Further, the signal level of the guard band detected by the detection circuit 13 and the signal level of the main signal detected by the detection circuit 17 are applied to the status monitor 25. The state information of both signal levels is sent to the section detection device 31 together with the identification information.

That is, the status monitor 34 of the section detecting device 31 fetches status information including an alarm from the status monitor 25 on the downstream side, and outputs this status information to the control device 35. The control device 35 determines the location of the noise-containing location based on the state information.
Further, as shown in FIG. 4, the control device 35 holds, for example, different reference voltages V1 to V4 and two-bit bit strings 00 to 11 in association with each other, so that even when the status monitor 25 cannot detect noise contamination, When the signal level difference between the noise from the status monitor 34 and the main signal is at a level at which it is determined that noise is mixed, an arbitrary bit string is appropriately selected from the bit strings and output to the modem 33.

The bit string is converted into a high-frequency signal by the modem 33, output to the noise detection device 9 via the demultiplexing filter 32, branched by the branch circuit 26, and received by the modem 27 which takes in the high-frequency component. . D
The / A converter 28 outputs the 2-bit bit string 00 to
11 is converted to analog voltages V1 to V4, and a voltage corresponding to a bit string signal demodulated by the modem 27 is sequentially output as a reference voltage of the voltage comparison circuit 14.

Accordingly, in this embodiment, the reference voltage of the voltage comparison circuit is changed from the center station so that the status monitor can detect noise contamination. It can be set variably according to the mixing level.

As described above, in the present embodiment, the reference voltage in the voltage comparison circuit of each noise detection device is controlled by the centralized management in the center station, so that, for example, the transmission line arrangement and the used frequency band are changed. This also makes it possible to easily identify the location where noise is mixed.

It should be noted that the present invention is not limited to the above embodiment, and it is also possible to provide a section detection device in a distant device other than the center station and control the change of the reference voltage from the distant device.

The noise detector shown in FIG. 2 has a modem 27 connected to a branch circuit 26 provided on the downstream transmission line 4 as in the second embodiment. It is also possible to adopt a configuration in which the input signal is input to the control circuit 18. In this case, the control device 18 and the control device 35 of the section detection device hold, for example, the voltages V1 to V4 illustrated in FIG.

Also in this case, the center station can send the signal of the bit string to each noise detection device when the reference level of each noise detection device is changed in accordance with a change in the design of the transmission line or the like. For example, since the control device 18 of the noise detection device 9 can set the voltage corresponding to the bit string as the reference voltage of the voltage comparison circuit, the reference level of the noise detection device can be changed collectively.

Thus, in the present embodiment, the control for changing the reference voltage in the noise detecting device and the collective changing control from the center station can be appropriately selected, so that the detection accuracy of the noise-containing portion detecting device can be further improved. It becomes possible.

In the present embodiment, the control device of the noise detection device and the section detection device performs the variable adjustment of the reference voltage by the voltage corresponding to the signal of the two-bit string shown in FIG. However, the present invention is not limited to this. For example, it is also possible to finely set a voltage corresponding to a signal of a 3-bit string or a 4-bit string, and variably adjust a reference voltage by the voltage. Further, in addition to the pattern shown in FIG. 4, a plurality of patterns having different inclinations in the relationship between the voltage and the bit string are held, and the selection of the pattern and the signal transmission of the bit string are performed between the control devices, thereby obtaining the reference voltage. Can be variably adjusted. As a result, in the present invention, the reference voltage can be further finely variably adjusted.

The simplest way to perform variable adjustment of the reference voltage is, for example, as shown in FIG.
Is connected to the reference voltage terminal 14b, and the reference voltage is adjusted by changing the resistance value of the variable resistor 14c. In the case of this embodiment, the reference voltage can be adjusted according to the noise mixing level by a simple means of connecting a variable resistor.

As described above, in these embodiments, by variably adjusting the reference voltage of the noise detection device, the noise detection range width of the noise detection device can be selected in accordance with the location where noise is mixed.

In this embodiment, the tree-like CATV
Although the ingress noise in the transmission path has been described, since the ingress noise also exists in a bus-like or star-like transmission path,
The present invention can be applied to a system using the bus-like or star-like transmission line, for example, a LAN system.

[0048]

As described above, according to the present invention, the noise signal having a frequency other than the frequency band of the main signal among the noise signals mixed into the transmission path is compared with the reference level by the noise detection means. In the method for detecting a noise-containing portion based on the detection result, the reference-level control means operates the reference-level changing means to change the reference level based on the control signal. The reference level of the voltage can be variably set in accordance with the noise mixing level, and the section can be variably adjusted from a distant place by providing the section detection device at the center station or the like.

Since the reference level is changed based on the signal characteristics of the main signal on the transmission line in the transmission band,
The reference voltage can be variably set according to the noise mixing level, and the noise detection device itself can perform variable adjustment, so that a change instruction from a distant place such as a center station is not required.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a CATV system according to the present invention.

FIG. 2 is a block diagram showing a configuration of a first embodiment of a main part of the CATV system shown in FIG. 1;

FIG. 3 is a block diagram showing a configuration of a second embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a voltage held in a control circuit according to the present invention and a bit string.

FIG. 5 is a circuit diagram showing an example of the configuration of a voltage comparison circuit according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 center station 2 joining station 3 antenna 4 transmission line 5 relay amplifier 6 tap-off 7 protector 8 bidirectional home terminal 9 noise detector 10, 16, 24, 26, branch circuit 11 band-pass filter circuit 12 amplifying circuit 13, 17 detection Circuit 14 Voltage comparison circuit 14c Variable resistor 15 Voltage holding circuit 18, 35 Control device 20, 21, 32 Demultiplexing filter 22, 23 Amplifier 25, 34 Status monitor 27, 33 Modem 28 D / A converter 31 Section detection device

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masayuki Mizusako 4-7-1 Hatchobori, Chuo-ku, Tokyo Inside Japan Telecom Co., Ltd.

Claims (9)

[Claims] 1. A noise signal having a frequency other than the frequency band of a main signal among noise signals mixed in a transmission path is detected by comparing the noise signal with a reference level by a noise detection means, and based on the detection result. A method for detecting a noise-containing portion, wherein the reference level is changed as necessary. 2. The method according to claim 1, wherein the reference level is changed based on a control signal. 3. The method according to claim 1, wherein the reference level is determined based on a signal level in a transmission band of a main signal on the transmission line. 4. The method according to claim 1, wherein the reference level is determined based on a surrounding electric field strength. 5. A noise-mixed portion detecting apparatus comprising: a noise detection unit that detects a noise signal having a frequency other than the frequency band of a main signal by comparing the noise signal with a reference level among noise signals mixed in a transmission path. And a reference level changing means for changing a reference level of the noise detecting means. 6. The noise-mixed portion detecting apparatus according to claim 5, further comprising a reference level control unit that controls the reference level by operating the reference level changing unit based on a predetermined control signal. 7. A signal characteristic detecting means for detecting a signal characteristic in a transmission band of a main signal on the transmission line, and operating the reference level changing means based on a detection result of the signal characteristic by the signal characteristic detecting means. 6. A reference level control means for controlling the reference level.
2. A device for detecting a noise-containing part according to item 1. 8. The apparatus according to claim 5, wherein the reference level changing unit has a variable resistor that changes the reference level. 9. A noise detection means for detecting a noise signal having a frequency other than the frequency band of the main signal by comparing the noise signal with a reference level among noise signals mixed in the transmission path;
A noise mixing point detecting device having reference level changing means for changing a reference level of the noise detecting means is installed for each predetermined section, and the reference level of the noise mixing point detecting device can be collectively controlled. Noise detection system.