JP4601696B2 - Noise source detection apparatus, information providing system, and noise source detection method - Google Patents

Description

  The present invention relates to a noise source detection apparatus, an information providing system, and a noise source detection method.

A plurality of techniques related to inflow noise countermeasures in a transmission network (for example, CATV (Common Antenna TeleVision) network) configured in a tree shape have been proposed. For example, in Patent Document 1, when the communication failure is caused by noise, the gate switch of the trunk branch amplifier is sequentially cut off, and the noise occurrence location is identified by detecting the decrease in the amount of noise measured at this time. Technology is disclosed. Further, for example, in Patent Document 2, in a joint noise detection / cutoff device inserted into a line in a bidirectional CATV system, a controller detects a joint noise level in a predetermined band of an uplink signal and detects the detected stream. A technique is disclosed in which, when the noise level exceeds a predetermined threshold value, control is performed to block the uplink signal band of the above-described line and transmit a data signal including an error notification having a device address. . Furthermore, for example, in Patent Document 3, a monitoring device is provided on a trunk line of a cable line, a plurality of detection devices are provided on branch lines branched and distributed from the trunk line, and the “voltage level fluctuation time” detected by the monitoring device. And a “voltage level fluctuation time” detected by each detection device, a technique for specifying a noise transmission route to be searched is disclosed.
JP 2001-326916 A JP 2005-123870 A JP 2004-40737 A JP 11-355755 A JP-A-11-252526 JP 2004-72477 A JP 2003-111043 A Japanese Patent Laid-Open No. 10-200875 Japanese Patent Application Laid-Open No. 10-144771

  A plurality of techniques relating to ingress noise countermeasures in a transmission network configured in a tree shape have been proposed. However, for example, in the case of the technique described in Patent Document 1, it takes time and effort to change the gate switch, and there are concerns that the service may be stopped and the service quality may be lowered due to the gate operation. In addition, this technology cannot be applied to equipment such as a gate switch that cannot operate a network. For example, in the case of the technique described in Patent Document 2, a device capable of transmitting a data signal including an error notification having a device address is required. That is, in a system that does not have such a function, it is necessary to newly install a device having such a function on the transmission side. Furthermore, in the case of the technique described in Patent Document 3, it is necessary to provide a detection means separately in the existing system.

  It is also conceivable to acquire terminal-related information of the bidirectional terminal and narrow down defective portions of the transmission network from the terminal service quality deterioration status. However, simply analyzing the noise included in the so-called uplink signal transmitted from the terminal to the center reports the added noise to the center as inflow noise, so it is difficult to identify a defective part.

  In the present invention, in view of the above-described problems, the present invention relates to a technique related to inflow noise suppression in a transmission network configured in a tree shape. Let it be an issue.

  In the present invention, in order to solve the above-described problem, the management apparatus uses the management device as information related to the terminal to receive a signal-to-noise ratio represented by a noise ratio with respect to a reception signal received by the terminal, and for each terminal to perform the management. The transmission signal-to-noise ratio expressed by the noise ratio of the transmission signal transmitted to the device to the signal arriving at the management device is acquired, and the transmission signal-to-noise ratio and the reception signal-to-noise ratio for each acquired terminal are acquired. We decided to narrow down the location of noise generation based on the correlation with

  Specifically, the present invention provides a management apparatus that provides predetermined content to a plurality of terminals, a tree-shaped transmission line that extends toward the plurality of terminals with the management apparatus as a base, and the tree-shaped transmission path. A noise generation source detection device for detecting a generation source of noise generated in an information providing system having the plurality of terminals provided on a front end side of a transmission path, and transmitted from the plurality of terminals to the management device Terminal-related information acquisition means for acquiring terminal-related information related to each terminal from the uplink signal, and a generation source for detecting a noise source by analyzing the terminal-related information acquired by the terminal-related information acquisition means Detecting means, and the terminal-related information acquiring means includes, as the terminal-related information, a received signal-to-noise ratio represented by a noise ratio with respect to a received signal received by each terminal, and each of the terminals includes the management device. A transmission signal-to-noise ratio represented by a noise ratio of a transmission signal to be transmitted to a signal arriving at a management device, and the source detection means includes a reception signal-to-noise ratio of each terminal The noise source is detected by narrowing down the noise source based on the correlation with the transmission signal-to-noise ratio.

  In the noise source detection apparatus according to the present invention, the source detection means for providing predetermined content, for example, video and audio content, has a terminal-related information of each terminal, that is, a noise ratio with respect to a received signal received by each terminal. And a received signal-to-noise ratio represented by: and a transmission signal-to-noise ratio represented by a noise ratio with respect to a signal arriving at the management device of a transmission signal transmitted by each terminal toward the management device, and The noise source can be detected by narrowing down the noise source based on the correlation. The terminal-related information can be obtained from the uplink signal as the received signal-to-noise ratio and the transmitted signal-to-noise ratio. In more detail, the received signal-to-noise ratio can be obtained from the uplink signal from the terminal as the noise ratio with respect to the received signal received by each terminal, and the transmitted signal-to-noise ratio is transmitted from the terminal in the management apparatus. It can be obtained by receiving a signal. And in this invention, the existing terminal which has the function to transmit an uplink signal can be utilized as it is. Therefore, it is possible to detect a source of noise generated in the information providing system without newly providing equipment. Note that the management device may provide services such as an Internet connection service and a telephone connection service in place of or together with predetermined content.

  The information providing system includes a management device, a tree-shaped transmission path, and a plurality of terminals. As described above, the management device provides, for example, video and audio content, an Internet connection service, and a telephone connection service to a plurality of terminals. Further, the management device can receive information from a plurality of terminals and manage the state of the terminal, the state of the transmission path, and the like. Video and audio content includes various information such as character information, music information, and video information. Since the transmission line has a tree shape, the transmission line has a plurality of branch points. The branch points can be provided with amplification means for performing branching and signal amplification. The tree-shaped transmission path is exemplified by a cable television network, for example, and the noise source detection apparatus according to the present invention generates noise that constitutes confluence noise that can occur in such a cable television network. It can be suitably used as a source detection device. The terminal only needs to have a transmission function of transmitting a signal to at least the management apparatus side, and the configuration is not particularly limited.

The terminal related information acquisition unit acquires terminal related information from uplink signals transmitted from a plurality of terminals to the management apparatus. The terminal-related information includes a received signal-to-noise ratio (hereinafter also referred to as a received signal to noise ratio (SNR)) represented by a noise ratio with respect to a received signal received by each terminal, and each terminal transmits to the management apparatus. A transmission signal-to-noise ratio (hereinafter also referred to as a transmission SNR (Signal to Noise Ratio)) represented by a noise ratio of a transmission signal to be transmitted to a signal received by the management apparatus.

  The source detection means analyzes the terminal related information of the terminal and the terminal management information of the management device, that is, noise based on the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio of each terminal. The source of noise is detected by narrowing down the source of noise. Correlation means that when one variable increases, the other variable increases or decreases. In the present invention, for example, when the received signal-to-noise ratio increases, the transmitted signal-to-noise ratio increases or decreases. Means that. The present invention is characterized in that the noise source is detected by narrowing down the noise source based on such correlation. More specifically, the present invention uses a characteristic found by the applicant that noise in a wide frequency range has a tendency that the positive correlation tends to be strong in a terminal that is close to the noise source. It is characterized by narrowing down.

  Note that this correlation tends to be stronger at a terminal closer to the noise source than at a terminal far from the noise source in noise over a wide frequency range. Therefore, in the noise source detection apparatus according to the present invention described above, the source detection means compares the correlation of the terminals, determines the terminal having the strongest correlation as the terminal closest to the noise source, You may make it narrow down the generation source of noise.

  Further, in the noise source detection apparatus according to the present invention, the source detection means, when the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio exceeds a predetermined threshold, has a correlation exceeding that of the predetermined terminal. It may be determined that there is a noise source near the terminal. The predetermined threshold value can be obtained by experiments or the like. Note that such a threshold value is adjusted so that after the noise source is detected by the noise detection apparatus according to the present invention, the noise source is actually confirmed, and the actually confirmed result is reflected. It may be. Thereby, the detection accuracy of the detection of the noise generation source can be further increased. When detecting the source of noise, the correlation of each terminal may be compared, and if the correlation is similar, it may be determined that the noise sent to each terminal is from the same noise source. This makes it possible to specify the noise source more accurately. Whether or not the correlations are similar can be determined, for example, by comparing linear data indicating the correlation and comparing the start time when the correlation starts to appear. If the start times when the correlation appears are the same, it can be determined that the influence is caused by the same noise source. Also, a plurality of noise sources can be detected by the correlation between a plurality of terminals.

The present invention includes a management device provided with the above-described noise generation source detection device, a tree-shaped transmission line extending toward the plurality of terminals from the management device, and a tree-shaped transmission line. It is good also as an information provision system provided with these terminals provided in the tip side. Specifically, an information providing system according to the present invention includes a management device that provides predetermined content to a plurality of terminals, and a tree-shaped transmission path that extends toward the plurality of terminals with the management device as a base. And a plurality of terminals provided on the front end side of the tree-shaped transmission path, wherein the management device detects noise generation sources that generate noise in the information providing system A terminal detection information acquisition unit configured to acquire terminal related information related to each terminal from uplink signals transmitted from the plurality of terminals to the management device. And a source detection unit that detects a source of noise by analyzing the terminal related information acquired by the terminal related information acquisition unit, and the terminal related information acquisition unit includes the terminal related information and The reception signal-to-noise ratio represented by the noise ratio to the reception signal received by each terminal, and the noise ratio to the signal reaching the management device of the transmission signal transmitted by each terminal toward the management device The transmission source-to-noise ratio is obtained, and the source detection means narrows down the noise source based on the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio of each terminal. Detect the source of

  Further, the present invention may be a method for realizing the processing executed by the above-described noise source detection apparatus. Specifically, the present invention provides a management apparatus that provides predetermined content to a plurality of terminals, a tree-shaped transmission line that extends toward the plurality of terminals with the management apparatus as a base, and the tree-shaped transmission path. A noise generation source detection method for detecting a generation source of noise generated in an information providing system having the plurality of terminals provided on a front end side of the transmission path, from the plurality of terminals toward the management device A terminal-related information acquisition step for acquiring terminal-related information related to each terminal from the transmitted uplink signal, and a generation for detecting a noise source by analyzing the terminal-related information acquired in the terminal-related information acquisition step A source detection step, wherein in the terminal-related information acquisition step, a reception signal-to-noise ratio expressed by a noise ratio with respect to a reception signal received by each terminal, and each terminal to the management device A transmission signal-to-noise ratio represented by a noise ratio of a transmission signal to be transmitted to a signal reaching the management device, and in the source detection step, a reception signal-to-noise ratio from each terminal The noise source is detected by narrowing down the noise source based on the correlation with the transmission signal-to-noise ratio.

  Further, the present invention may be a program that realizes processing executed by the above-described noise source detection apparatus. Furthermore, the present invention may be a computer-readable recording medium that records such a program. In this case, the function can be provided by causing a computer or the like to read and execute the program of the recording medium. Note that a computer-readable recording medium is a recording medium that accumulates information such as data and programs by electrical, magnetic, optical, mechanical, or chemical action and can be read from a computer or the like. Say.

  ADVANTAGE OF THE INVENTION According to this invention, regarding the technique regarding the inflow noise countermeasure in the transmission type | system | group network comprised in the tree form, while being able to utilize the existing equipment, the technique which can pinpoint the noise generation source can be provided. In addition, by acquiring terminal-related information of each terminal and detecting a noise generation source, a plurality of noise generation sources can be specified.

  An embodiment of a noise source detection apparatus according to the present invention will be described. In the following description, the noise source detection device (inflow noise monitoring and control device) according to the present invention is a cable television network (hereinafter also referred to as CATV network and corresponds to the information providing system of the present invention). An example will be described in which the present invention is applied as a detection device for a noise generation source that constitutes confluence noise that can occur in FIG.

<Overall configuration>
FIG. 1 shows a schematic configuration of a CATV network according to the embodiment. As shown in the figure, a center device 1, a CATV coaxial cable network 2, and a home coaxial network 3 are provided in the CATV network. In this document, hereinafter, a signal from the center device 1 toward the home coaxial network 3 is referred to as a downstream signal, and a signal from the home coaxial network 3 to the center device 1 is referred to as an upstream signal.

[Center equipment]
The center device 1 corresponds to the management device of the present invention. In this aspect, the terminal data collection device 11, the cable modem center device 12, the head end device 13, the CATV coaxial cable monitoring control device 14, the upstream signal measurement device 15, the IP The telephone system device 16, the Internet system device 17, and the video system device 18 are configured. The center device 1 is provided with an inflow noise monitoring control device 19 corresponding to the noise source detection device of the present invention.

  The terminal data collection device 11 is connected to each terminal such as an amplifying device 21 and a tap-off device 22 provided in the CATV coaxial cable network 2 and a television receiver 31 and a cable modem 33 provided in the home coaxial network 3. Connection is possible, and terminal-related information for each terminal is collected from the uplink signal to manage each terminal.

  The inflow noise monitoring control device 19 extracts information necessary for specifying the noise source from the terminal related information collected for each terminal by the terminal data collection device 11, and detects the noise source. Details of the ingress noise monitoring controller 19 will be described later.

  The cable modem center device 12 is a modem provided on the center device 1 side, and includes an upstream signal measuring device 15, an IP telephone system device 16, an Internet system device 17, and a video system device 18 described later, and the terminal data collection device described above. 11 is modulated and demodulated to communicate signals from the respective devices via the set top box 32, the cable modem 33 and the head end device 13. In FIG. 1, one cable modem center device 12 is shown for convenience of explanation, but a plurality of cable modem center devices 12 may be provided.

  The head end device 13 has an optical transceiver (not shown), and one end of an optical fiber cable is connected to the optical transceiver. An optical transceiver is also connected to the other end of the optical fiber cable, and a coaxial cable constituting the trunk line system 23 is connected to the optical transceiver on the other end side. In other words, the optical fiber is converted from an optical fiber to a coaxial cable in the optical transceiver on the other end side, and a signal from the head end device 13 is distributed to the home coaxial network 3 via the CATV coaxial cable network 2. The head end device 13 may be directly connected to the coaxial cable constituting the trunk line system 23 without using the optical transceiver and the optical fiber cable.

  The uplink signal measuring device 15 measures the noise level of the uplink signal. The uplink signal measuring device 15 can be configured by an existing spectrum analyzer. The uplink signal measuring device 15 is used as a device for detecting noise in an existing CATV network, in other words, as a device for quality control of the CATV network. In the conventional uplink CATV network, the source of noise is specified by switching the gate switch in the amplification device, the tap-off device, or the switch in the switch device based on such information from the uplink signal measurement device 15. However, such a method is time-consuming and troublesome for the switching operation of the gate switch, and in some cases, there is a concern that the service may be stopped due to the gate operation or the service quality may be deteriorated. On the other hand, in the CATV network according to the present embodiment, the ingress noise monitoring control device 19 is provided, and the ingress noise monitoring control device 19 is collected for each terminal (cable modem) collected in the terminal data collection device 11. 33) and the like, the noise generation source is specified. Therefore, the uplink signal measuring device 15 is unnecessary in the sense of specifying the noise generation source, but can continue to be used as a device for detecting the inflow noise itself. Note that the ingress noise monitoring control device 19 may be triggered by the detection of noise by the upstream signal measurement device 15 as a trigger.

The IP telephone system 16, the Internet system 17, and the video system 18 are also provided in the conventional CATV network in the same manner as the upstream signal measuring device 15, but the upstream signal measuring device 15 performs quality control of the CATV network. On the other hand, the IP telephone device 16, the Internet device 17, and the video device 18 are devices for realizing services provided to customers. Specifically, the IP telephone system device 16 is connected to an Internet network (not shown) and is connected to the telephone 34 in the home coaxial network 3 with an IP (Internet).
Protocol) Necessary functions for providing a telephone service are provided. The Internet system device 17 is also connected to an Internet network (not shown) and has necessary functions for enabling Internet connection through the personal computer 35 in the home coaxial network 3. The video system device 18 is connected to a video transmission device that transmits video (not shown), the Internet network, a database storing video information, and the like, and provides video information to the television receiver 31 and the like in the home coaxial network 3. It has the function to do. Although details of the home coaxial network 3 will be described later, the television receiver 31, the set top box 32, the cable modem 33, the telephone 34, and the personal computer 35 provided in the home coaxial network 3 are the same as those in the present invention. It corresponds to a terminal. The terminal only needs to have a function of transmitting an uplink signal to the center apparatus 1, that is, a bidirectional communication function. Further, the tap-off device 22 in the CATV coaxial cable network 2 and the distribution device 37 in the home coaxial network 3 can be included in the terminal.

  The CATV coaxial cable monitoring control device 14 is connected to the head end device 13 and can communicate with the amplification device 21 in the CATV coaxial cable network 2. Then, the CATV coaxial cable monitoring control device 14 performs control such as switching of a gate switch provided in the CATV coaxial cable network 2 based on information from the upstream signal measurement device (for example, information on inflow noise). . The gate switch is provided in the amplifying device 21 and the tap-off device 22 and is omitted in the drawing.

[CATV coaxial cable network]
The CATV coaxial cable network 2 includes an amplification device 21, a tap-off device 22, and a trunk line system 23 and a distribution system 24 that electrically connect these devices. The trunk line system 23 and the distribution system 24 correspond to the transmission path of the present invention, and both are constituted by coaxial cables. In this document, an upstream transmission line connected to an optical fiber cable extending from the head end device 13 in the center device 1 is referred to as a trunk line system 23. Further, a transmission line that is branched by the main line amplifying device 21 and that is provided with only the tap-off device 22 is referred to as a distribution system 24. The main line amplification device 21 has a function of amplifying a signal flowing through the main line system 23 and branching a signal flowing through the main line system 23. The distribution system 24 is finally connected to a home amplifying device 36 in the home coaxial network 3 via the tap-off device 22. In this aspect, a tap-off device that divides signals into four is used as the tap-off device 22, but the tap-off device 22 is not limited to such an aspect.

[In-house coaxial network]
The home coaxial network 3 includes a home amplifying device 36, a distribution device 37, a television receiver 31, a set top box 32, a cable modem 33, a personal computer 35, and a coaxial cable for electrically connecting these devices. And an in-home wiring system 38 composed of a television receiver terminal. The home amplifying device 36 amplifies the signal drawn into the home coaxial network 3 via the tap-off device 22. The distribution device 37 distributes the signal drawn into the home coaxial network 3 to the television receiver 31, the set top box 32, the cable modem 33, and the personal computer 35. In the figure, for convenience of explanation, only one in-home coaxial network 3 is shown, but each in-home coaxial network 3 is provided on the downstream side of the tap-off device 22. The residential coaxial network 3 is exemplified by one provided in a detached house or one provided in an apartment house. The in-house amplifier 36, the distribution device 37, the television receiver 31, the set top box 32, the cable modem 33, the personal computer 35, and the like are existing devices and devices, and thus description thereof is omitted.

<Infusion noise monitoring and control device>
Next, the infusion noise monitoring control device 19 corresponding to the noise source detection device of the present invention will be described. Here, FIG. 2 shows a functional block diagram of the ingress noise monitoring controller 19 according to the embodiment. As shown in the figure, the ingress noise monitoring control device 19 according to the embodiment includes a terminal data collection device interface unit 191, an upstream signal measurement device interface unit 192, a CATV coaxial cable monitoring control device interface unit 193, and a correlation. The evaluation unit 194, the storage unit 195, the noise source output unit 196, the setting input unit 197, the operation device 198, and the monitor device 199 are configured. The terminal data collection device interface unit 191, the uplink signal measurement device interface unit 192, the CATV coaxial cable monitoring control device interface unit 193, the correlation evaluation unit 194, the noise source output unit 196, and the setting input unit 197 are executed on the CPU 190. It can be configured as a computer program. Each of these functional units may be configured as a dedicated processor. The CPU 190 is connected to each hardware as each functional unit via a bus. The CPU 190 controls each hardware and executes predetermined processing according to a control program stored in a ROM serving as the storage unit 195, for example.

  The terminal data collection device interface unit 191 corresponds to the terminal related information acquisition unit of the present invention, is connected to the terminal data collection device 11, and acquires terminal related information related to each terminal collected by the terminal data collection device 11. . More specifically, the terminal data collection device interface unit 191 accesses the terminal data collection device 11, accesses the received SNR of the terminal as terminal related information of the terminal, and accesses the cable modem center device 12 via the terminal data collection device. Then, the transmission SNR collected by the cable modem center device 12 is acquired.

  The uplink signal measurement device interface unit 192 is connected to the uplink signal measurement device 15 and acquires information related to infusion noise acquired by the uplink signal measurement device 15. The CATV coaxial cable monitoring control device interface unit 193 is connected to the CATV coaxial cable monitoring control device 14 and is related to the switching state of the gate switches in the amplification device 21 and the tap-off device 22 that are monitored and controlled by the CATV coaxial cable monitoring control device. Etc.

  The correlation evaluation unit 194 corresponds to the generation source detection unit of the present invention, and analyzes the terminal-related information (received SNR and transmission SNR) of the terminal acquired from the terminal data collection device interface unit 191 to detect a noise source. . More specifically, the correlation evaluation unit 194 compares the correlation between the transmission SNR and the reception SNR for each terminal (hereinafter also simply referred to as correlation), and determines the terminal having the strongest correlation as the terminal near the noise source. In particular, the noise source is detected. The detection of the noise source by the correlation evaluation unit 194 is based on the following principle.

  That is, a terminal closer to the noise source and a terminal far from the noise source tend to have different correlation strengths between the source noise and the reaching noise. Specifically, the correlation is weak for a terminal far from the noise source, and the correlation is strong for a terminal near the noise source. Here, FIG. 3A is a diagram showing a correlation of a certain terminal far from the noise generation source, and FIG. 3B is a diagram showing a correlation of a certain terminal near the noise generation source. 3A and 3B, the transmission SNR is a noise ratio with respect to a signal transmitted from a target terminal, and the transmission SNR is a noise ratio with respect to a signal received by the center apparatus 1 when viewed from the center apparatus 1 side. This corresponds to a certain center side reception SNR. In addition, the reception SNR in FIGS. 3A and 3B is a noise ratio with respect to a signal received by a target terminal. As shown in FIGS. 3A and 3B, the correlation of the terminal far from the noise source shown in FIG. 3A is weaker than the correlation of the terminal near the noise source shown in FIG. 3B. Therefore, it is possible to determine whether the target terminal is near or far from the noise source by determining the strength of the correlation.

The strength of the correlation occurs for the following reason. That is, most of the noise has a high-band frequency characteristic, has a characteristic of wrapping around to a downstream signal via a distribution device, a branching device, etc., and has a received SNR (noise ratio with respect to a signal received by a terminal). affect. For example, when noise occurs in the immediate vicinity of a certain terminal A1, the terminal A2 is also affected by the noise generated in the immediate vicinity of the terminal A1. That is, the relationship of the following formula (1) is established for the reception SNR of the terminal A1, and the relationship of the following formula (2) is established for the reception SNR of the terminal A2. Nr1 and Nr2 are inherent reception noises of the terminal A1 and the terminal A2 at the normal time, and f1 (Nz1) is a downstream noise value due to the joint noise Nz1 generated in the immediate vicinity of the terminal A1, and f2 (Nz
1) is a downstream noise value affected by Nz1 via a distribution device, a branching unit, etc., and both the terminal A1 reception SNR and the terminal A2 reception SNR are affected by Nz1 and have a correlation with each other. The condition indicated by f2 causes a difference in the correlation with Nz1. Here, Sr1 and Sr2 are received signal levels of the terminals A1 and A2.

  Then, such an influence on the received SNR, that is, a change in the received SNR, has a strong correlation with a change in the transmitted SNR accompanying the generation of noise. On the other hand, such a change in received SNR becomes more noticeable as the distance from the noise source becomes shorter. This is because the amount of attenuation increases as the distance increases because noise also attenuates. Note that such noise attenuation becomes more prominent when passing through the tap-off device 22, for example. This is because the connection through the tap-off device 22 is affected by the coupling loss of the tap-off device 22. Here, FIG. 4 shows an example of the coupling loss of the tap-off device. The tap-off device 22 shown in FIG. 4 is a 4-distribution tap-off device, and is provided in the distribution system 24 in this embodiment. In FIG. 4, an arrow (←) pointing left on the page indicates an up signal, and an arrow (→) pointing on the right of the page indicates a down signal. In the tap-off device shown in FIG. 4, the passage loss when simply passing through the tap-off device (passing through the trunk line system) is 0.9 dB on the upstream and 1.6 dB on the downstream. The coupling loss when the distribution system 24 passes through the tap-off device 22 from the home coaxial network 3 via the tap-off device 22 is 20 dB, and the coupling loss when the tap-off device 24 passes from the home coaxial network 3 to the distribution system 24 is 30 dB. is there. Further, the coupling loss when passing through the tap-off device 22 from one home coaxial network 3 to another home coaxial network 3 is 25 dB. Thus, when passing through the tap-off device 22, the signal is attenuated, and at this time, the noise is also affected by the attenuation. Therefore, when the terminal receives noise via the tap-off device 22, the change in the received SNR is small. When the terminal receives noise without passing through the tap-off device 22, the change in the received SNR is large. Become.

That is, regarding the transmission SNR, since the synthesized noise of all the noises that arrive at the center apparatus from the entire tree-shaped transmission path becomes a uniform noise component, there is no difference between the terminals, but the reception SNR , The received SNR varies uniquely depending on the position from the noise source. Therefore, if there is a correlation between changes by comparing the received SNR for each terminal, it is possible to determine whether or not the influence is due to the same noise source. Then, comparing the transmission SNR and the reception SNR of a certain terminal, it can be confirmed that the closer to the noise source, the stronger the correlation. That is, the transmission SNR and the reception SNR of the terminal A1 are correlated with the noise source Nz1 via the relational expressions fo (Nz1) and fr1 (Nz1) from the relation of the following expression (3) and the above expression (1). Holds. Further, the transmission SNR and the reception SNR of the terminal A2 are correlated with the noise source Nz1 via the relational expressions fo (Nz1) and fr2 (Nz1) from the relation of the following expression (4) and the above expression (2). Holds.

  That is, the temporal behaviors of fo (Nz1) (noise value of the noise Nz1 reaching the center device) and fr1 (Nz1) (downstream noise value due to the inflow noise generated in the immediate vicinity of the terminal A1) are equal and the amount of change is also closer. For example, the correlation coefficient of reception SNR / transmission approaches 1. In the present invention, the position of the noise generation source is specified by examining the degree of influence from the noise generation source using the correlation of the SNR.

  A threshold value or the like is input to the setting input unit 197 via the operation device 198. The operation device 198 includes a computer input device such as a keyboard and a pointing device. The keyboard transmits an electrical signal corresponding to the input key to a keyboard controller (not shown) of the keyboard in response to a user input operation. The keyboard controller transmits a code corresponding to the electrical signal to the CPU.

  The noise source output unit 196 outputs the noise source specified by the correlation evaluation unit 194. The output noise source is displayed on the screen of the monitor device 199. The monitor device 199 is, for example, a liquid crystal display device, a plasma display panel, a CRT (Cathode Ray Tube), an electroluminescence panel, or the like.

  The storage unit 195 includes a volatile RAM (Random Access Memory) and a nonvolatile ROM (Read Only Memory). The ROM includes a rewritable semiconductor memory such as a flash memory, an EPROM (Erasable Programmable Read-Only Memory), and an EEPROM (Electrically Erasable Programmable Read-Only Memory).

<Processing flow>
Next, processing (hereinafter also referred to as noise monitoring processing) executed by the ingress noise monitoring control device 19 will be described. The processing described below is realized by a computer executing a program. In the following description, it is assumed that noise has occurred in the vicinity of the terminal 22d among the terminals 22a to 22d of the tap-off 22 that divides the downstream signal into four (see FIG. 5). That is, the description will be made assuming that the coaxial cable downstream of the terminal 22d connected to the terminal 22d is damaged.

  Here, FIG. 6 shows a noise monitoring processing flow executed by the ingress noise monitoring controller 19. In the figure, processing executed by another device related to the noise monitoring processing executed by the ingress noise monitoring control device 19 is also shown. First, the data collection processing executed by the terminal data collection device 11 and the uplink signal measurement processing executed by the uplink signal measurement device 15 which are the premise of the processing executed by the ingress noise monitoring control device 19 will be described.

[Data collection processing]
In step S01, the terminal data collection device 11 collects terminal data possessed by each terminal from the upstream signal and collects terminal data possessed by the cable modem center device 12. The terminal data includes reception SNR and transmission SNR for each terminal as terminal related information for each terminal. The collected terminal data is sent to the ingress noise monitoring control device 19, and the noise monitoring processing (steps S21 to S25) by the infusion noise monitoring control device 19 is executed.

  Here, when sending terminal data to the ingress noise monitoring control device 19, a threshold value may be set, and only data outside the set threshold value may be sent to the infusion noise monitoring control device 19. Steps S02 and S03 show processing in such a case. Specifically, in step S02, a predetermined threshold value is read. This threshold value is a threshold value for determining whether the transmission SNR or the reception SNR is deteriorated, and can be set as a quality standard for maintaining the system. The threshold value may be set in advance via an operation unit (for example, a keyboard) connected to the terminal data collection device. When the reading of the threshold is completed, the process proceeds to step S03.

  In step S03, it is determined whether or not the terminal data satisfies a set condition (threshold), and data that does not satisfy the condition, in other words, terminal data that deviates from the threshold is transmitted to the ingress noise monitoring and control apparatus as degraded data. The Thereafter, the noise monitoring process by the inflow noise monitoring controller 19 is started.

[Uplink signal measurement processing]
Next, the uplink signal measurement process executed by the uplink signal measurement device 15 will be described. First, in step S11, the infusion noise level (dBμV) is measured. Subsequently, in step 12, the inflow noise abnormality threshold is read. The infusion noise abnormality threshold value can be set as a reference value for determining whether the infusion noise is normal or abnormal. The inconsistency noise abnormality threshold value can be set in advance via an operation unit (for example, a keyboard or the like) connected to the upstream signal measurement device. When the reading of the mixed noise abnormality threshold is completed, the process proceeds to step S13.

  In step S13, it is determined whether the inflow noise level is normal. Specifically, it is determined whether or not the infusion noise level is within a preset infusion noise abnormality threshold. If the infusion noise level is within the infusion noise abnormality threshold, it is determined to be normal. On the other hand, if the infusion noise level is outside the infusion noise abnormality threshold, it is determined that the infusion noise is abnormal, and that fact is reported to the infusion noise monitoring controller 19. Even when it is determined to be normal, the fact may be reported to the ingress noise monitoring control device 19. The ingress noise monitoring control device 19 starts executing the noise monitoring process when receiving the report of the abnormality. That is, in this case, the report of abnormality from the upstream signal control device 15 serves as a trigger when executing the noise monitoring process.

[Noise monitoring processing]
Next, noise monitoring processing executed in the inflow noise monitoring apparatus will be described. First, in step S21, terminal related information related to each terminal is extracted as data necessary for narrowing down noise sources. More specifically, the transmission SNR and reception SNR for each terminal are extracted as terminal data for each terminal. Here, the terminal data indicates a terminal transmission level, a terminal reception level, a transmission SNR, a reception SNR, and the like, and data at regular intervals in a time zone to be evaluated is processed as a target for correlation evaluation. FIG. 7 shows the signals, noises, and SNRs of the four terminals (22a to 22d) of the tap-off device 22 for each center-arrival SNR in a certain time zone in which noise in the present aspect occurs, and the terminals 22a and 22d. The result of estimation of the synthesis is shown. The center arrival SNR is an SNR that reaches the center apparatus 1 and corresponds to a noise ratio to a signal transmitted from each terminal (22a to 22d), that is, a transmission SNR. In this aspect, the terminal 22d is a noise generation source. The synthesized noise is a synthesized value of noise that circulates through the tap-off 22 and affects each terminal. In this aspect, it is assumed that the signal has no fluctuation, high level fluctuation noise is generated only at the terminal 22d, and other noise is low level and constant. . If extraction of terminal related information is completed, it will progress to step S22.

The calculation of the composite noise will be briefly described as follows. That is, when the inter-terminal coupling loss of the tap-off device 22 is 25 dB as in this aspect, the noise N4 of a terminal (for example, the terminal 22d) of the tap-off device 22 is reduced to the noise N1 of the other terminal (for example, the terminal 22a) by 17. It becomes 1/8 and is added. That is, −25 = 20 Log (1 / 17.8) (minus means attenuation). Therefore, the noise N1t appearing at the terminal 22a is the noise N1t synthesized at the terminal 22a with the reduction of the coupling loss between the terminals from the noise N1 of the own terminal and the noises N2, N3, and N4 mixed from the other terminals 22b, 22c, and 22d. If the noise is in phase with the voltage notation (μV),
N1t = N1 + N2 / 17.8 + N3 / 17.8 + N4 / 17.8
Can be expressed as When the noise waveform of N2 to N4 is random with respect to N1, the synthesized noise is smaller than this voltage addition value, the influence of noise wraparound from other terminals is further reduced, and the noise of the own terminal is more dominant. become.

In step S22, a correlation coefficient is extracted. In other words, in step S22, a correlation value between the transmission SNR and the reception SNR for each terminal is calculated. Here, based on the estimated values in FIG.
FIG. 8 is a graph showing the correlation between the terminal 22a and the terminal 22d. The horizontal axis is the transmission SNR, and the vertical axis is the reception SNR. As shown in the figure, the correlation value (correlation coefficient) of the terminal 22a is 1.4458, and the correlation value of the terminal 22d is 3.936. When the calculation of the correlation value is completed, the process proceeds to step S23.

  In step S23, the terminals are ranked based on the correlation value. It is possible to identify the noise source by performing the ranking. In this aspect, since the correlation value (correlation coefficient) of the terminal 22a is 1.4458 and the correlation value of the terminal 22d is 3.936, the correlation value of the terminal 22d is larger than that of the terminal 22a. Therefore, it is possible to specify that the terminal 22d is close to the noise generation source. In FIG. 8, only the terminals 22a and 22d are displayed as an example. Similarly, the other terminals are also ranked based on correlation values with all terminals by calculating correlation values. It is possible to specify that the terminal having the largest correlation value is closest to the noise generation source (however, in this aspect, the conditions of the terminals 22b and 22c are the same as the conditions of the terminal 22a. The correlation values of 22b and 22c are the same as the correlation value of the terminal 22a.) When the ranking of the terminals based on the correlation value is completed, the process proceeds to step S24.

  In step S24, a predetermined threshold value is read. This threshold value is for specifying the noise source, and can be calculated by experiments or the like. For example, if the threshold value is set to 3 or more, only the terminals 4 that are noise generation sources are narrowed down. When the reading of the threshold is completed, the process proceeds to step S25.

  In step S25, the noise source is identified and output. Specifically, the source of noise is displayed on the monitor device 199. As a result, for example, an administrator (one who manages the CATV network) can recognize the noise generation source. In the present embodiment, information regarding the identified noise source is sent to the CATV coaxial cable monitoring control device 14.

[Gate control processing]
In step S41, gate switch control is executed in the CATV coaxial cable monitoring control device 14. Specifically, control such as switching of the gate switch in the amplifying device 21 and the tap-off device 22 in the CATV coaxial cable network 2, for example, blocking of the route of the noise source is performed. Since the generation of noise is generally caused by a cause such as breakage of the coaxial cable, there is a concern that if the signal is kept flowing as it is, the entire CATV network is hindered. Therefore, in the present embodiment, the information regarding the noise generation source is not only displayed on the monitor device 199 and warned to the administrator, but also when an emergency is required, a CATV coaxial cable monitoring control is performed by setting an emergency level threshold. It is automatically sent to the device 14, and the CATV coaxial cable monitoring control device 14 can automatically switch the gate switch in the CATV coaxial cable network 2. The CATV coaxial cable monitoring control device 14 can also monitor a gate switch or the like as a process independent of the gate control process.

  In the CATV network according to the present embodiment described above, the inflow noise monitoring control device 19 causes the noise generation source based on the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio for each terminal of the tap-off device 22. The source of noise can be detected by narrowing down. That is, the vicinity of the terminal 22d of the tap-off device 22 can be specified as the noise generation source. The terminal related information is included in the uplink signal, and an existing terminal (here, the tap-off device 22) having a function of transmitting the uplink signal can be used as it is. Therefore, it is possible to detect the source of noise generated in the CATV network without newly providing equipment or the like.

<Modification>
In the above-described aspect, the noise generation source is specified at each terminal level of the tap-off device 22. However, the inflow noise monitoring control device 19 (corresponding to the noise source detection device according to the present invention) can detect noise at the level of the distribution device 37 in the home coaxial network 3 instead of the tap-off device 22. Here, FIG. 9 shows a correlation state between the transmission SNR and the reception SNR when noise occurs in the home coaxial network 3. As shown in the figure, in this aspect, a noise generation source exists on the downstream side of the distribution device 37 in the home coaxial network 3. In the figure, a region surrounded by a dotted-line rectangle indicates a residential coaxial network 3 provided in a detached house and a housing complex. The numbers assigned to the terminals (301 to 316) are ranked correlation values at this time. It should be noted that processing for identifying the noise source, that is, processing such as extraction of terminal-related information, extraction of correlation coefficients, and ranking is performed based on the processing flow described above. In this aspect, as shown in FIG. 9, the correlation value of the terminal 301 closest to the noise source is the highest at 0.196. With respect to the terminal 301, no other terminal or distribution device is interposed between the noise source and the terminal 301. That is, the generated noise is directly sent to the terminal 301. On the other hand, for example, in the terminal 302 having the second largest correlation value, noise is sent through two distribution devices such as the distribution device 37a and the distribution device 37b, and each distribution device includes noise. The signal is attenuated. As a result, the correlation value of the terminal 302 is smaller than the correlation value of the terminal 301. Thus, according to the inflow noise monitoring control device 19, not only the noise source below the tap-off device 22 but also the noise source in the home coaxial network 3 can be specified. Therefore, it is possible to specify a more accurate noise source.

1 shows a schematic configuration of a CATV network. The functional block diagram of an inflow noise monitoring control apparatus is shown. The correlation of a certain terminal far from the noise source is shown. The correlation of a certain terminal close to the noise source is shown. The example of the coupling loss of a tap-off apparatus is shown. The image figure of a tap-off apparatus in case a noise generation source exists in the terminal vicinity is shown. The noise monitoring process flow performed by the inflow noise monitoring control apparatus is shown. An example of terminal related information is shown. A graph showing the correlation of each terminal is shown. A correlation state between the transmission SNR and the reception SNR when noise occurs in the home coaxial network is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Center apparatus 2 ... CATV coaxial cable network 3 ... In-home coaxial network 11 ... Terminal data collection apparatus 12 ... Cable modem center apparatus 13 ... Head end apparatus 14 ... CATV coaxial cable Supervisory control device 15 ... Uplink signal measuring device 16 ... IP telephone system device 17 ... Internet system device 18 ... Video system device 21 ... Amplifying device 22 ... Tap-off device 23 ... Trunk line System 24 ... Distribution system 31 ... Television receiver 32 ... Set top box 33 ... Cable modem 35 ... Personal computer 36 ... Home amplification device 37 ... Distribution device 191 ... Terminal data collection device interface unit 192... Upstream signal measurement device interface unit 193... CATV coaxial cable monitoring and control device Centers face portion 194 ... correlation evaluation section 195 ... storage unit 196 ... noise source output portion 197 ... setting input unit 198 ... operating device 199 ... monitor device 301-316 ... terminal

Claims (5)

A management apparatus that provides predetermined content to a plurality of terminals, a tree-shaped transmission path that extends toward the plurality of terminals with the management apparatus as a base, and a tip end of the tree-shaped transmission path A noise generation source detection apparatus for detecting a generation source of noise generated in an information providing system having the plurality of terminals,
Terminal-related information acquisition means for acquiring terminal-related information related to each terminal from uplink signals transmitted from the plurality of terminals to the management device;
A source detection unit that detects a source of noise by analyzing the terminal related information acquired by the terminal related information acquisition unit,
The terminal-related information acquisition means includes, as the terminal-related information, a reception signal-to-noise ratio represented by a noise ratio with respect to a reception signal received by each terminal, and a transmission signal transmitted by each terminal toward the management device Obtaining a transmission signal-to-noise ratio represented by a noise ratio to a signal arriving at the management device;
The noise source detection device detects the noise source by narrowing down the noise source based on the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio of each terminal. .   2. The noise generation according to claim 1, wherein the source detection unit compares the correlation of the terminals, determines the terminal having the strongest correlation as the terminal closest to the noise generation source, and narrows down the noise generation source. Source detection device.   When the correlation between the reception signal-to-noise ratio and the transmission signal-to-noise ratio exceeds a predetermined threshold, the generation source detection unit has the noise generation source in the vicinity of a terminal having a correlation exceeding the predetermined threshold. The noise generation source detection apparatus according to claim 1, wherein the noise generation source detection apparatus is determined. A management device that provides predetermined content to a plurality of terminals;
A tree-shaped transmission line extending toward the plurality of terminals with the management device as a base;
A plurality of terminals provided on a front end side of the tree-shaped transmission path, and an information providing system comprising:
The management device has a noise source detection device that detects a source of noise generated in the information providing system,
The noise source detection apparatus is
Terminal-related information acquisition means for acquiring terminal-related information related to each terminal from uplink signals transmitted from the plurality of terminals toward the management device;
A source detection unit that detects a source of noise by analyzing the terminal related information acquired by the terminal related information acquisition unit,
The terminal-related information acquisition means includes, as the terminal-related information, a reception signal-to-noise ratio represented by a noise ratio with respect to a reception signal received by each terminal, and a transmission signal transmitted by each terminal toward the management device A transmission signal-to-noise ratio represented by a noise ratio to a signal reaching the management device, and
The information providing system, wherein the source detection unit detects a noise source by narrowing down the source of noise based on a correlation between a reception signal-to-noise ratio and a transmission signal-to-noise ratio of each terminal. A management apparatus that provides predetermined content to a plurality of terminals, a tree-shaped transmission path that extends toward the plurality of terminals with the management apparatus as a base, and a tip end of the tree-shaped transmission path A noise generation source detection method for detecting a generation source of noise generated in an information providing system having the plurality of terminals,
A terminal-related information acquisition step of acquiring terminal-related information related to each terminal from uplink signals transmitted from the plurality of terminals toward the management device;
A source detection step of detecting a source of noise by analyzing the terminal related information acquired in the terminal related information acquisition step,
In the terminal-related information acquisition step, a received signal-to-noise ratio represented by a noise ratio with respect to a received signal received by each terminal, and a signal that reaches the management apparatus of a transmission signal that each terminal transmits to the management apparatus A transmission signal-to-noise ratio expressed as a noise ratio with respect to
In the generation source detection step, a noise generation source detection that detects a noise generation source by narrowing down a noise generation source based on a correlation between a reception signal-to-noise ratio and a transmission signal-to-noise ratio from each terminal. Method.

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