JP5661425B2 - Inflow noise detection apparatus and CATV system - Google Patents

Description

  The present invention is an apparatus that detects inflow noise generated in upstream communication of a CATV system and identifies the generation source, and a CATV system including the apparatus.

  In recent years, telephone services are frequently provided in addition to Internet connection services in CATV systems, and the importance of upstream communication quality is increasing. As a factor that deteriorates uplink communication quality, there is a problem of inflow noise caused by the CATV system having a tree-type network structure.

  In the current CATV system, the gate control system (GCS) built in the nodes and trunk amplifiers in the system is controlled from the side closer to the center in order to identify the location where the inflow noise is generated, and the system is divided in stages. By performing the work, the source of the inflow noise is roughly specified.

  Patent Document 1 discloses that each subscriber is provided with a joint noise detection / blocking device that detects and blocks the occurrence of joint noise. In the ingress noise detection / cutoff device disclosed in Patent Document 1, the carrier level and the noise level are measured to calculate the CNR (carrier-to-noise ratio), and the CNR is compared with the CNR threshold value. It is shown that when the threshold value is exceeded, ingress noise is judged to be generated and the upstream signal is blocked.

JP 2005-123870 A

  However, in the method of identifying the source of the infusion noise in stages by separating the network by GCS, it is easy to isolate the infusion noise source that is continuously mixed, but the terminal that suddenly generates noise is isolated. It is difficult. Therefore, there is a need for a CATV system that can constantly monitor inflow noise as close as possible to a terminal, search for the terminal that causes the inflow noise in a short time, and identify the generation source.

  Further, in Patent Document 1, since there is a difference in transmission distance from each ingress noise detection / cutoff device to the center device, even when the ingress noise level at a certain ingress noise detection / cutoff device is equal, May have different ingress noise levels. Therefore, the ingress noise level in the ingress noise detection / cutoff device that impedes the uplink communication is different for each ingress noise detection / cutoff device, and it is necessary to set a predetermined CNR threshold value individually. Patent Document 1 does not show any method for setting the CNR threshold at that time. For this reason, it is difficult to easily detect the ingress noise in the ingress noise detection cutoff device of Patent Document 1. Further, in Patent Document 1, since the carrier level is measured for calculating the CNR, it is not possible to cope with uplink communication channel bonding, channel band change or expansion, and the versatility is low. Further, in Patent Document 1, since the CNR is calculated by measuring the carrier level and the noise level, inflow noise cannot be detected except when uplink communication is performed.

  Accordingly, an object of the present invention is to realize an infusion noise detection apparatus that can easily detect infusion noise and a CATV system including the infusion noise detection apparatus.

According to a first aspect of the present invention, the occurrence of ingress noise is detected in upstream communication of a CATV system that performs bidirectional communication between a center device and each terminal device via a tree-type network having at least a branch line as a coaxial cable. In the infusion noise detecting device for giving an alarm to the center device, the infusion noise detecting device is inserted into a coaxial cable of a branch line of the network and generates a test carrier signal, and a test carrier signal level. and allowed to set the attenuation damping advance so that the prescribed level when the center apparatus reaches, upstream communication a first attenuator you output a test carrier signal to the center apparatus via a network, from a radio wave to transmit coaxial cable extracting noise bandwidth, attenuation of the test carrier signal at a first attenuator (units d A), and the second attenuator sum of the attenuation of noise level (in dB) attenuates the noise level to be constant, the noise from the second attenuator is input, the noise level detecting means for detecting the noise level And a comparison means for comparing the noise level detected by the noise level detection means with the noise level threshold, and the test carrier signal generation means is controlled so as to always generate a test carrier signal, or the comparison by the comparison means As a result, when the noise level is equal to or greater than the noise level threshold, the test carrier signal generation means is controlled to generate a test carrier signal, and the noise level is equal to or greater than the noise level threshold. If, by modulating the test carrier signal with a signal to alert the occurrence of ingress noise, which is the modulated Tesutoki And alarm signal generation means for outputting a rear signal to the first attenuator, the center device, when receiving a signal to alert the occurrence of ingress noise, the control signal transmitted from the center apparatus is received via the network, And a control unit that blocks uplink communication transmitted through the coaxial cable based on the control signal, or attenuates the signal of the uplink communication.

  A digital attenuator may be used as the first and second attenuators. If the digital control signal that controls the attenuation amount of the digital attenuator has an inverted relationship between the digital control signal input to the first attenuator and the control signal input to the second attenuator, the test at the first attenuator It is possible to easily control the sum of the attenuation amount (unit dB) of the carrier signal and the attenuation amount (unit dB) of the noise level to be constant.

The digital control signal to be input to the first attenuator may be inputted to the second attenuator is inverted by the inverter, even if a digital control signal to be input to the second attenuator is input to the first attenuator inverted by inverter Good.

  The test carrier signal may be a signal such as a status monitor signal that is constantly output. The use of the status monitor signal is advantageous in that it is not necessary to separately reserve a band for the test carrier signal.

  The CATV system of the present invention may be a CATV system in which the transmission line is configured only by a coaxial cable, or may be a CATV system of an HFC network in which a trunk line is an optical fiber cable and a branch line is a coaxial cable.

The second invention is Oite to the first invention, the alarm signal generating means is always controlled to the test carrier signal generating means for generating a test carrier signal, or from the noise level is above the noise level threshold In the case of large intensities, the infusion noise detector is characterized in that the test carrier signal is modulated with a signal for alarming the occurrence of inflow noise.

A third invention is a CATV system that performs bidirectional communication between a center device and each terminal device via a tree-type network having at least a branch line as a coaxial cable, and is inserted into the coaxial cable at the branch line of the network. has ingress noise detecting device for detecting the occurrence of ingress noise, ingress noise detection device, defines a test carrier signal generating means for generating a test carrier signal, the level of the test carrier signal, when the center apparatus reaches level so as to then set the attenuation damping advance, to extract a first attenuator you output a test carrier signal to the center apparatus via a network, the noise of the uplink communication band from the radio waves to transmit coaxial cable, Attenuation amount of test carrier signal (unit dB) at first attenuator and attenuation amount of noise level (single unit) The second attenuator for attenuating the noise level so that the sum of the signal and the unit dB) is constant, noise from the second attenuator, noise level detecting means for detecting the noise level, and noise level detecting means The comparison means for comparing the noise level and the noise level threshold value, and the test carrier signal generation means are controlled so that the test carrier signal is always generated, or as a result of the comparison by the comparison means, the noise level becomes a noise level. Controls the test carrier signal generation means to generate a test carrier signal when the threshold value is greater than or greater than the threshold, and also alerts the occurrence of ingress noise when the noise level is greater than or equal to the noise level threshold signal modulates the test carrier signals to, and outputs the modulated test carrier signal to the first attenuator A broadcast signal generating means, the center device, when receiving a signal to alert the occurrence of ingress noise, the control signal transmitted from the center apparatus is received via the network, based on the control signal, a coaxial cable A control unit that blocks uplink communication to be transmitted or attenuates an uplink communication signal, and the center device has a signal level of uplink communication when the center device reaches the level of the test carrier signal when the center device reaches the center device. The CATV system is characterized in that the signal level of the uplink communication output from each terminal device is controlled so as to match.

A fourth invention is Oite to the third aspect of the present invention, the test carrier signal generating means is means for generating a status monitor signal, it is ingress noise detection apparatus according to claim.

  According to the infusion noise detection apparatus of the present invention, the CNR threshold value (noise level threshold value) can be automatically set regardless of the transmission distance to the center apparatus, and the infusion noise can be easily detected. can do. Moreover, the infusion noise detection apparatus of the present invention can be used regardless of the bandwidth of the upstream signal, and is highly versatile. In addition, since the infusion noise detection apparatus of the present invention detects the infusion noise from the test carrier signal, it can detect the infusion noise not only during uplink communication.

Further , if the status monitor signal is used as the test carrier signal, it is not necessary to secure a band for the test carrier signal, and convenience is improved.

The figure which showed the structure of the CATV system. The figure which showed the structure of the inflow noise detection apparatus.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram showing a configuration of a CATV system. The CATV system includes a center device 10, a tree-type network 12 configured by coaxial cables connected to the center device 10, a plurality of inflow noise detection devices 11 connected to the network 12, and each subscriber's home. The CM (cable modem) 13 and the STB (set top box) 14 are arranged and connected to the inflow noise detector 11 via the distributor 18. The center apparatus 10 includes an STM (status monitor system) 10a, a CMTS (cable modem termination system) 10b, and a TV signal transmission unit 10c. The network 12 is a coaxial cable network in which a trunk line from the center apparatus 10 is branched by a trunk branch amplifier 20 and a branch line is further branched by using a branching device 21 to branch in a tree shape. The CM 13 is connected to the PC 15 or the telephone 16 and the STB 14 is connected to the TV receiver 17 or the like. CM 13 corresponds to the terminal device of the present invention.

  The inflow noise detection device 11 is disposed, for example, at a coaxial cable entrance in each subscriber's house. In the case of an apartment house or the like, a plurality of subscribers may be combined into one unit, and the inflow noise detector 11 may be arranged for each unit, or may be arranged for each apartment house. However, in order to know the generation source of the infusion noise in a short time in detail, it is desirable to provide the infusion noise detector 11 for each subscriber.

In this CATV system, an interactive communication service such as an Internet connection service or a telephone service between the CMTS 10b of the center apparatus 10 and each CM 13 and the TV signal transmission unit 10c of the center apparatus 10 to the TV receiver 17 via the STB 14 are provided. Provide TV broadcast service. The CMTS 10b controls the level of the uplink communication signal output from each CM 13 so that the level of the uplink communication signal from each CM 13 when reaching the center device 10 is aligned with a specified level. Since the transmission loss from each CM 13 to the CMTS 10b varies depending on the difference in transmission path length, the level of the uplink communication signal output from each CM 13 also varies.

  In the downlink communication band, 70 to 770 MHz is used for Internet connection, IP telephone, and TV signal transmission. The uplink communication band is 10 to 50 MHz for both Internet connection and IP telephone.

  FIG. 2 is a diagram illustrating a configuration of the inflow noise detection device 11. Hereinafter, while showing the structure of the inflow noise detection apparatus 11, operation | movement of the CATV system of Example 1 is demonstrated.

  The inflow noise detector 11 includes a duplexer 100 connected to the CM 13 and the STB 14 via a coaxial cable and distributor 18, and a duplexer 101 connected to the center device 10 side via the network 12. ing.

  The low-pass filter side of the duplexer 100 (the side that blocks the downstream communication band and passes the upstream communication band) is connected to the low-pass filter side of the duplexer 101. In the meantime, a gate switch 105 and branching devices 106 and 107 are inserted in series in this order from the duplexer 100 side.

  The high-pass filter side of the duplexer 101 (the side that transmits the downstream communication band and blocks the upstream communication band) is connected to the high-pass filter side of the duplexer 100, and the branching device 102 is inserted between them. Has been.

  The branch side of the branching device 102 is connected to the reception control unit 103 via a BPF (band pass filter) 104. The BPF 104 passes only the band of the control signal among the downlink communication signals. The reception control unit 103 controls the gate switch 105 and the test carrier control circuit 110, respectively. The reception control unit 103 and the gate switch 105 correspond to the control unit of the present invention.

  Downlink communication signals input from the center device 10 to the duplexer 101 are output from the high-pass filter side of the duplexer 101, and most are input to the high-pass filter side of the duplexer 100 to the CM13 and STB14 side. And a part is branched by the branching unit 102.

  Further, the upstream communication signal input to the duplexer 100 from the CM 13 and STB 14 side is output from the low-pass filter side of the duplexer 100, passes through the gate switch 105, the branching units 106 and 107, and the low-pass of the duplexer 101. Input to the filter side and output to the center device 10 side. In the gate switch 105, the upstream communication signal is blocked / conducted or attenuated under the control of the reception control unit 103.

  The test carrier control circuit 110 controls on / off of the oscillation of the oscillator 111 that oscillates the test carrier signal, and also controls the modulation unit 112 that modulates the test carrier signal. The oscillator 111 is connected to the first attenuator 114 via the BPF 113.

  The branch side of the branching device 106 is connected to the second attenuator 115 via the BPF 108 and the amplifier 109. The BPF 108 passes only the frequency of the band not including the upstream communication signal in the vicinity of the upstream communication signal, and extracts noise by this.

  The first attenuator 114 and the second attenuator 115 are digital attenuators whose attenuation is variable in 32 steps in 1 dB increments in the range of 0 to 31 dB. The amount of attenuation is controlled by a control signal from the DIP switch 116. Here, the control signal is input to the first attenuator 114 as it is, but is input to the second attenuator 115 after being inverted by the inverter 117. Therefore, if the attenuation amount of the first attenuator 114 is A (dB) and the attenuation amount of the second attenuator 115 is B (dB), A + B is constant at 31. Further, the attenuation amount of the first attenuator 114 is set so that the level of the test carrier signal at the time when the test carrier signal reaches the center apparatus 10 becomes a specified level. As a result, all the levels of the test carrier signals from the respective inflow noise detecting devices are aligned in the center device 10.

  In contrast to the above, the control signal may be input to the second attenuator 115 as it is, and the control signal may be inverted and input to the first attenuator 114 by an inverter.

  The test carrier signal attenuated by the first attenuator 114 is input to the branch side of the branching unit 107 and output to the low-pass filter side of the duplexer 101. The test carrier signal input from the low-pass filter side of the duplexer 101 is output to the center device 10 side.

In the center apparatus 10, the upstream communication signal is input to the CMTS 10b and the test carrier signal is input to the STM 10a by the duplexer. The CMTS 10b of the center device 10 refers to the level of the test carrier signal when reaching the center device 10, and the level of the uplink communication signal from each CM 13 when reaching the center device 10 is the level of the test carrier signal when reaching the center device 10. The level of the uplink communication signal output from each CM 13 is controlled so as to be equal to the level. Thereby, the CNR (carrier-to-noise ratio ) of the uplink communication signal and the CNR of the test carrier signal can be regarded as the same.

  The noise attenuated by the second attenuator 115 is input to the noise detector 118, the noise level is detected, and the comparator 119 compares the noise level with a predetermined noise level threshold value.

Here, (1) the test carrier level is attenuated by the first attenuator 114 in the STM 10a of the center apparatus 10 so that it becomes a specified value, and (2) the noise level input to the comparator 119 is reduced by the second attenuator 115. The noise level threshold is reduced for two reasons: the sum of the attenuation by the first attenuator 114 at the test carrier level and the attenuation by the second attenuator 115 at the noise level is constant. The value can be a constant value regardless of the difference in transmission loss due to the difference in distance from the inflow noise detector 11 to the center device 10.

Further, in addition to (1) and (2), (3) the control of the level of the uplink communication signal of the CM 13 makes it possible to identify the CNR of the uplink communication signal and the CNR of the test carrier signal as noise. Comparing the level with the noise level threshold is equivalent to comparing the CNR (carrier-to-noise ratio ) of the upstream communication signal with the CNR threshold of a predetermined value. That is, the ingress noise detection apparatus 11 can automatically set the CNR threshold value assuming the CNR in the center apparatus 10 by operating as in (1) to (3). Therefore, even if there is a difference in transmission loss due to a difference in the distance from the inflow noise detection device 11 to the center device 10, even if there is a difference in the level of the upstream communication signal output from each CM 13, the inflow noise detection device 11. There is no need to set different CNR thresholds for each.

  When the noise level is smaller than the noise level threshold, it is in a state where no inflow noise is generated, and the comparator 119 outputs a low level signal to the test carrier control circuit 110. The test carrier control circuit 110 turns off the oscillator 111 except when the reception control unit 103 receives a command to turn on the oscillator 111. If the oscillator 111 is already off, the oscillator 111 is continuously turned off. Then, uplink communication is performed as usual.

On the other hand, when the noise level is above the noise level threshold, which is equivalent with that CNR is equal to or greater than a predetermined CNR threshold, comparator 119 determines that the ingress noise is occurring A high level signal is output to the test carrier control circuit 110. The test carrier control circuit 110 turns on the oscillation of the oscillator 111 to generate a test carrier signal, and also controls the modulation unit 112 to modulate the test carrier signal with information for alarming the occurrence of joint noise, and to generate an alarm signal. Generate. The modulated wave is, for example, frequency modulation, and the information to be alarmed is the terminal ID of the ingress noise detection apparatus 11, the value of CNR, and the like. The alarm signal is transmitted to the STM 10 a of the center apparatus 10 via the BPF 113, the first attenuator 114, the branching unit 107, and the duplexer 101.

The STM 10a of the center device 10 receives the alarm signal to obtain information such as the location where the infusion noise is generated (location where the certain infusion noise detector 11 is disposed) and the level of the infusion noise. The STM 10a of the center apparatus 10 generates a control signal from these pieces of information, and transmits the control signal to the infusion noise detection apparatus 11 that is the location where the infusion noise is generated. The control signal is received by the reception control unit 103 of the inflow noise detection apparatus 11, and the gate switch 105 is controlled based on the control signal to block or attenuate the upstream communication signal. In the case of attenuation, the CNR can be restored to a normal value by controlling to increase the level of the uplink communication signal output from the CM 13. Further, the test carrier control circuit 110 is controlled to turn off the oscillation of the oscillator 111 and turn off the operation of the modulation unit 112 . However, only the operation of the modulation unit 112 may be turned off, and the oscillator 111 may be turned on at any time to use the test carrier signal as a status monitor signal. If the test carrier signal is used as a status monitor signal, it is not necessary to secure a separate frequency band for the test carrier signal, the simplification of the ingress noise detector 11 and the CATV system can be achieved, and convenience is enhanced.

  Thereafter, the worker goes to the subscriber's house where the inflow noise detector 11 where the warning signal is issued is disposed, and the source of the inflow noise is removed. Then, the gate switch 105 of the infusion noise detecting device 11 that has issued the alarm signal is turned on again to restore the CATV system from the problem of infusion noise generation.

  As described above, the ingress noise detection device 11 can automatically set the CNR threshold (noise level threshold) regardless of the distance from the center device 10 to each subscriber. In the CATV system of the first embodiment provided with the infusion noise detection device 11, the infusion noise can be easily detected. In addition, since the CATV system of the first embodiment detects the infusion noise using the test carrier signal, it can detect the infusion noise not only during uplink communication, and can change the uplink communication band or the channel of the uplink communication. It can be used for bonding and multi-channel uplink communication, so it is highly versatile.

  The embodiment is a CATV system in which a network is configured only by a coaxial cable, but the present invention can also be applied to an HFC type CATV system in which a trunk line is configured by an optical fiber cable and a branch line is configured by a coaxial cable.

  The inflow noise detection apparatus of the present invention can be used in a CATV system that provides a two-way communication service such as a telephone service.

10: Center device 11: Inflow noise detection device 12: Network 13: CM
14: STB
15: PC
16: telephone 17: TV receiver 100, 101: duplexer 102, 106, 107: branching device 103: reception control unit 104, 108, 113: BPF
105: Gate switch 109: Amplifier 110: Test carrier control circuit 111: Oscillator 112: Modulation unit 114: First attenuator 115: Second attenuator 116: Dip switch 117: Inverter 118: Noise detector 119: Comparator

Claims (4)

Detection of occurrence of ingress noise in upstream communication of a CATV system that performs bidirectional communication between the center device and each terminal device via a tree-type network having at least a branch line as a coaxial cable, and alerts the center device In the ingress noise detector that performs
The ingress noise detection device is inserted into the coaxial cable of the branch line of the network;
Test carrier signal generating means for generating a test carrier signal;
The level of the test carrier signal, the center apparatus reaches during the level so as to then set the attenuation damping advance provisions, the first attenuator you output the test carrier signal to the center apparatus via the network ,
The noise of the upstream communication band is extracted from the radio wave transmitted through the coaxial cable, and the sum of the attenuation amount (unit dB) of the test carrier signal at the first attenuator and the attenuation amount (unit dB) of the noise level is A second attenuator for attenuating the noise level to be constant;
Noise level detection means for receiving noise from the second attenuator and detecting the noise level;
Comparison means for comparing the noise level detected by the noise level detection means with a noise level threshold;
The test carrier signal is controlled so that the test carrier signal is always generated, or when the noise level is greater than or equal to the noise level threshold as a result of comparison by the comparison unit, the test carrier Controlling the test carrier signal generation means so as to generate a signal, and further, when the noise level is equal to or greater than the noise level threshold, the test carrier signal is a signal that warns of the occurrence of joint noise. Alarm signal generating means for modulating and outputting the modulated test carrier signal to the first attenuator ;
When the center device receives a signal warning the occurrence of the inflow noise, the center device receives a control signal transmitted from the center device via the network, and transmits the coaxial cable based on the control signal. A control unit that blocks upstream communication or attenuates upstream communication signals;
Having
An inflow noise detecting apparatus characterized by that. The alarm signal generation means controls the test carrier signal generation means to generate the test carrier signal at all times, and when the noise level is greater than or equal to the noise level threshold, occurrence of infusion noise the modulating said test carrier signal with a signal to alert, ingress noise detecting device according to claim 1, characterized in that. In a CATV system that performs bidirectional communication between a center device and each terminal device via a tree-type network having at least a branch line as a coaxial cable ,
Inserted into the coaxial cable of the branch line of the network, each having an infusion noise detection device for detecting the occurrence of infusion noise,
The ingress noise detector is
Test carrier signal generating means for generating a test carrier signal;
The level of the test carrier signal, the center apparatus reaches during the level so as to then set the attenuation damping advance provisions, the first attenuator you output the test carrier signal to the center apparatus via the network ,
The noise of the upstream communication band is extracted from the radio wave transmitted through the coaxial cable, and the sum of the attenuation amount (unit dB) of the test carrier signal at the first attenuator and the attenuation amount (unit dB) of the noise level is A second attenuator for attenuating the noise level to be constant;
Noise level detection means for receiving noise from the second attenuator and detecting the noise level;
Comparison means for comparing the noise level detected by the noise level detection means with a noise level threshold;
The test carrier signal is controlled so that the test carrier signal is always generated, or when the noise level is greater than or equal to the noise level threshold as a result of comparison by the comparison unit, the test carrier Controlling the test carrier signal generation means so as to generate a signal, and further, when the noise level is equal to or greater than the noise level threshold, the test carrier signal is a signal that warns of the occurrence of joint noise. Alarm signal generating means for modulating and outputting the modulated test carrier signal to the first attenuator ;
When the center device receives a signal warning the occurrence of the inflow noise, the center device receives a control signal transmitted from the center device via the network, and transmits the coaxial cable based on the control signal. A control unit that blocks upstream communication or attenuates upstream communication signals;
Have
The center apparatus controls the signal level of the uplink communication output from each terminal apparatus so that the signal level of the uplink communication when reaching the center apparatus is aligned with the level of the test carrier signal when reaching the center apparatus. ,
CATV system characterized by this. The alarm signal generation means controls the test carrier signal generation means to generate the test carrier signal at all times, and when the noise level is greater than or equal to the noise level threshold, occurrence of infusion noise The CATV system according to claim 3 , wherein the test carrier signal is modulated with a signal that warns the user.

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