JP2012244299A - Ingress noise detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect ingress noise without affecting the telephone service, in a CATV system providing the telephone service.SOLUTION: Each gate switch 18 is turned off, in order, for a period of time by a control signal from an STM controller 21. Ingress noise can be detected and the occurrence place can be specified by measuring the frequency spectrum of a signal input to a center device 10 by means of a spectrum analyzer 22 in synchronism with the turn-off timing. The time of turning the gate switch 18 off is set to be 20 ms so as not to affect the telephone service.

Description

  The present invention relates to a joint noise detection system for detecting joint noise generated in a CATV system.

  In a CATV system having a tree-like network structure, there is a problem that inflow noise occurs during uplink communication. Inflow noise is noise that jumps in from home appliances and shortwave broadcasts at the subscriber's house and collects and superimposes as it goes upstream (from the subscriber side to the center device side). When the inflow noise increases, the quality of uplink communication deteriorates, and when it exceeds a certain level, uplink communication becomes impossible.

  Conventionally, gate switches provided in bidirectional trunk branch amplifiers and bidirectional trunk amplifiers are sequentially turned off in response to a command from an STM (status monitor) controller provided in the center device, and the frequency spectrum of the upstream signal The site where the inflow noise was generated was investigated by visually confirming the noise with a spectrum analyzer.

JP 2006-5702

  In a CATV system, a telephone service using a cable modem may be provided. The uplink communication of the telephone service does not retransmit according to the protocol. For this reason, if the gate switch is turned off to detect inflow noise, the audio data transmitted while the gate switch is turned off is lost and cannot be reproduced, and communication quality is significantly impaired. As a result, it has been impossible to investigate the ingress noise in a CATV system that has conventionally operated a telephone service.

  Accordingly, an object of the present invention is to provide a joint noise detection system that can detect joint noise without affecting a telephone call even when a telephone service is being provided in a CATV system.

  A first invention is a joint noise detection system for detecting joint noise generated in uplink communication in a CATV system, and the CATV system is arranged to extend from the center device toward the subscriber side from the center device. And a telephone service that is two-way voice data communication between the center device and the subscriber. The ingress noise detection system is inserted at a predetermined location of the transmission line network and A plurality of gate switches that control conduction / disconnection of communication, a control device that is provided in the center device and controls the gate switch via a transmission line network, and obtains a frequency spectrum of an upstream signal input to the center device A spectrum analyzer, and each gate switch is turned off by the control device in turn, for a period shorter than the sound length that can be discerned by human ears. Analyzer in synchronization with the period of the off by measuring the frequency spectrum of the uplink signal, to investigate the ingress noise occurrence point is ingress noise detection system, characterized in that.

  The transmission path network includes a transmission path network configured only by coaxial cable transmission paths, a transmission path network configured by using an optical fiber transmission path as a trunk line and a coaxial cable transmission path as a branch line.

  The time for turning off the gate switch is arbitrary as long as it is less than or equal to the length of the sound that can be discerned by the human ear, but is preferably 60 ms or less, and more preferably 20 ms or less. This is because the influence on the telephone service can be further reduced. The shorter the turn-off time is, the better. However, if it is shorter than 1 ms, a gate switch or a spectrum analyzer having high responsiveness is required, which increases costs and is not desirable. Further, the time from turning off one gate switch to turning off the next gate switch is arbitrary, but a range in which the packet loss rate is 0.05% or less is desirable. This is to maintain a high quality telephone service.

  A second invention is the infusion noise detection system according to the first invention, wherein the gate switch is turned off for 60 ms or less.

  A third invention is the infusion noise detection system according to the second invention, wherein the gate switch is turned off for 20 ms or less.

  According to a fourth aspect of the present invention, in the first to third aspects, the gate switch is turned off for 1 ms or more.

  In a fifth aspect based on the first aspect through the fourth aspect, the time from when one gate switch is turned off to when the next gate switch is turned off is a time when the packet loss rate is 0.05% or less. This is an inflow noise detection system characterized by the following.

  A sixth invention is the inflow noise detection system according to any one of the first to fifth inventions, wherein each gate switch is turned off in order from the side closer to the center device.

  According to the present invention, it is possible to turn on and off the gate switches in order without greatly affecting the telephone service, and it is possible to detect the location where inflow noise occurs.

The figure shown about the structure of the CATV system of Example 1. FIG.

  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 illustrating a configuration of a CATV system according to the first embodiment. The CATV system includes a center apparatus 10, an optical fiber transmission path 11 connected to the center apparatus, an optical node 12 connected to the center apparatus 10 via the optical fiber transmission path 11, an optical node 12, and a plurality of subscriber homes 14. And a coaxial cable transmission line 13 branched in a tree shape to be connected. The coaxial cable transmission line 13 is branched in a tree shape by a bidirectional trunk branch amplifier 15 and a tap-off 16. A bidirectional trunk amplifier 17 is inserted in the coaxial cable transmission line 13.

  The center device 10 includes a CMTS (cable modem termination system) 20, an STM (status monitor) control device 21, a spectrum analyzer 22, an optical transceiver 23, and a distributor 24. The electrical signal input / output side of the optical transceiver 23 is connected to the CMTS 20, the STM control device 21, and the spectrum analyzer 22 via the distributor 24. The optical signal input / output side of the optical transceiver 23 is connected to the optical fiber transmission line 11. The CMTS 20 is connected to the IP telephone network 40, and the spectrum analyzer 22 is connected to a PC (not shown).

  The bidirectional trunk branch amplifier 15, the bidirectional trunk amplifier 17, and the optical node 12 have a gate switch 18 incorporated therein or externally attached thereto. The gate switch 18 conducts and blocks the upstream signal transmitted through the transmission path under the control of the STM control device 21.

  The coaxial cable transmission line 13 branched from the tap-off 16 is drawn into the subscriber's house 14 and connected to a CM (cable modem) 30. Further, the CM 32 is connected to the telephone 31.

  In this CATV system, voice and voice data are mutually converted between the telephone 31 and the CM 30, and two-way voice data communication is performed between the CMTS 20 and the CM 30 in real time. The telephone service is operated by being connected to the network 40. The audio data signal is a 232-byte packet in which the DOCSIS header, Ether header, IP header, UDP header, and RTP header are added to the audio data, and is transmitted at intervals of 20 ms. These are defined by standards.

  Next, an operation for detecting inflow noise in the CATV system according to the first embodiment will be described.

  The gate switches 18 are sequentially turned off for a predetermined time by a control signal transmitted from the STM control device 21 via the optical fiber transmission line 11 and the coaxial cable transmission line 13. Then, by measuring the frequency spectrum of the signal input to the center device 10 by the spectrum analyzer 22 in synchronization with the timing when it is turned off, it is possible to detect the joint noise and identify the location where it occurs.

  At this time, it is preferable to turn off the gate switch 18 in the order closer to the upstream side (center device 10 side). This is because the location where the inflow noise is generated can be identified efficiently.

  The time for turning off the gate switch 18 is 20 ms. Since the uplink audio data signal output from the CM 30 is transmitted as a packet with an interval of 20 ms, if it is off for 20 ms, it is only necessary to lose at most one packet. The loss of one packet causes a 20 ms voice interruption, which cannot be discerned by the human ear. Therefore, by setting the off time of the gate switch 18 to 20 ms, it is possible to detect the inflow noise and identify the occurrence location without affecting the call.

  In addition, the time from when one gate switch 18 is turned off to the next gate switch 18 is preferably in a range in which the packet loss rate is 0.05% or less. For example, 40s. Thereby, call quality can be maintained high.

  In addition, when measuring the frequency spectrum of a signal using a spectrum analyzer, the waveform may be output to a PC monitor, etc., and the infusion noise may be visually confirmed and the location of occurrence may be specified. The software may automatically detect inflow noise and specify the location where it occurs.

  As described above, according to the infusion noise detection system of the first embodiment, it is possible to detect the infusion noise and specify the occurrence location by sequentially turning off the gate switches without affecting the telephone service.

  In the first embodiment, the off time of the gate switch 18 is set to 20 ms. However, the present invention is not limited to this, and it may be within the length of the sound that can be discriminated by the human ear. For example, it may be turned off for 60 ms or less. In particular, if it is 20 ms or less, since the voice data packet of the uplink voice data communication is transmitted every 20 ms, at most one packet of voice data is lost and the call quality can be kept high. The off time of the gate switch 18 is preferably 1 ms or more. If it is shorter than 1 ms, a gate switch or spectrum analyzer having high responsiveness is required, which increases costs and is not desirable.

  In the CATV system according to the first embodiment, the HFC system is used in which the trunk line is an optical fiber and the branch line is a coaxial cable as the transmission line network, but a transmission line network composed only of coaxial cables may be used.

  The inflow noise detection system of the present invention is useful when providing a telephone service in a CATV system.

10: Center equipment 11: Optical fiber transmission line 12: Optical node 13: Coaxial cable transmission line 15: Bidirectional trunk branch amplifier 16: Tap-off 17: Bidirectional trunk amplifier 18: Gate switch 20: CMTS
21: STM control device 22: Spectrum analyzer 23: Optical transceiver 30: CM
31: Telephone

Claims (6)

A joint noise detection system for detecting joint noise generated in uplink communication in a CATV system,
The CATV system includes a center device and a transmission line network arranged extending from the center device toward the subscriber side, and bidirectional audio data communication between the center device and the subscriber. Phone service that is
The infusion noise detection system is:
A plurality of gate switches that are inserted at predetermined locations of the transmission line network and control conduction / disconnection of upstream communication;
A control device provided in the center device and controlling the gate switch via the transmission line network;
A spectrum analyzer for acquiring a frequency spectrum of an upstream signal input to the center device;
Have
By turning off each of the gate switches in turn by the control device for less than the length of the sound that can be discerned by the human ear, and measuring the frequency spectrum of the upstream signal in synchronization with this off period Investigate where ingot noise occurs,
An infusion noise detection system characterized by that.   The infusion noise detection system according to claim 1, wherein the gate switch is turned off for 60 ms or less.   The infusion noise detection system according to claim 2, wherein the gate switch is turned off for 20 ms or less.   The infusion noise detection system according to any one of claims 1 to 3, wherein the gate switch is turned off for 1 ms or more.   The time from when one gate switch is turned off to when the next gate switch is turned off is a time when the packet loss rate is 0.05% or less. The ingress noise detection system described.   6. The inflow noise detection system according to claim 1, wherein each of the gate switches is turned off in order from a side closer to the center device.

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