JP2004032177A - Method of modulating signal for cable television system, and node for cable television system - Google Patents

Method of modulating signal for cable television system, and node for cable television system Download PDF

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Publication number
JP2004032177A
JP2004032177A JP2002183046A JP2002183046A JP2004032177A JP 2004032177 A JP2004032177 A JP 2004032177A JP 2002183046 A JP2002183046 A JP 2002183046A JP 2002183046 A JP2002183046 A JP 2002183046A JP 2004032177 A JP2004032177 A JP 2004032177A
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Japan
Prior art keywords
signal
modulated
downstream
node
modulating
Prior art date
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JP2002183046A
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Japanese (ja)
Inventor
Satoshi Nakamura
仲村　諭
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Miharu Communications Co Ltd
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Miharu Communications Co Ltd
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Priority to JP2002183046A priority Critical patent/JP2004032177A/en
Publication of JP2004032177A publication Critical patent/JP2004032177A/en
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for modulating a signal, which can always maintain an uplink optical signal and a downlink optical signal in a normal modulated state, and to provide a node. <P>SOLUTION: The method for modulating signal in the cable television system includes the steps of modulating the downlink signal in a central station, branching a part of the modulated outgoing signal during transmission, taking out the modulated signal from the branched downlink signal, and modulating the incoming signal with the taken modulated signal. The node for the cable television system includes a proportional derivative for photoelectrically converting the input outgoing optical signal, a branch unit for branching the part of the converted downlink electrical signal, a separating filter for taking out a modulated signal from the branched downlink electrical signal, a multiplexer for multiplexing and modulating the taken-out modulated signal with the uplink electrical signal, and a laser diode driven by the modulated incoming electrical signal. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ＨＦＣ（Ｈｙｂｒｉｄ　Ｆｉｂｅｒ　Ｃｏａｘ）方式のＣＡＴＶシステムに関するものである。
【０００２】
【従来の技術】
ＨＦＣ方式のＣＡＴＶシステムでは、センター局で電気信号を光信号に変換して下り光伝送路に送出し、これを途中のノードで電気信号に再変換し、同軸ケーブルを介して端末に伝送している。また、端末から送出された電気信号を前記ノードで光信号に変換し、これを上り光伝送路を介してセンター局に送っている。ここで、前記センター局及びノードでは、伝送しようとする電気信号で半導体レーザー（ＬＤ）を駆動することによって、該電気信号を光信号に変換している。
【０００３】
【発明が解決しようとする課題】
ＬＤは無変調状態ではコヒーレントが高くなる。従って、無変調の電気信号によってＬＤを駆動し、出力された光信号を光伝送路に送出すると、レーリー散乱の干渉効果によって光伝送路内で強度雑音が生じ、低周波数帯を中心に雑音特性が劣化する。
【０００４】
【課題を解決するための手段】
しかし、ＬＤに変調をかけると、スペクトラムの広がりによって前記雑音特性の劣化が急速に改善されることが知られている。本発明はかかる知見に基づいて前記課題を解決することを目的とする。具体的には、上り光信号及び下り光信号を常時変調状態に維持可能な変調方法及びノードを提供することによって前記課題を解決せんとするものである。
【０００５】
本発明の一つは、ＨＦＣ方式のＣＡＴＶシステムにおける信号変調方法であって、センター局で下り信号に変調をかけ、変調された下り信号の一部をその伝送中に分岐し、分岐された下り信号から変調信号を分離して取り出し、取り出された変調信号によって上り信号に変調をかけるものである。
【０００６】
本発明の他の一つは、ＨＦＣ方式のＣＡＴＶ伝送網に接続されるＣＡＴＶシステム用ノードであって、入力された下り光信号を光電変換するフォトダイオードと、変換された下り電気信号の一部を分岐する分岐器と、分岐された下り電気信号から変調信号を取り出す分離フィルタと、取り出された変調信号を上り電気信号に合波して変調をかける合波器と、変調された上り電気信号によって駆動される半導体レーザーとを備えたものである。
【０００７】
【発明の実施の形態】
（実施形態１）
本発明のＣＡＴＶシステムにおける信号変調方法を実施可能なＣＡＴＶシステムの一例を図１に示す。図１に示すＣＡＴＶシステムは、センター局１とノード２との間に下り光伝送路３及び上り光伝送路４を敷設すると共に、ノード２と端末との間に下り同軸ケーブル及び上り同軸ケーブルを敷設したＨＦＣ方式のＣＡＴＶシステムである。尚、ノード２より端末側の構成は便宜上図示を省略してある。また、図１には１つのノードのみ図示してあるが、端末の数に応じて同様のノードが２以上設けられる。
【０００８】
前記センター局１には、ヘッドエンド装置５と、ヘッドヘンド装置５から出力された電気信号（下り電気信号）によって駆動される（下り電気信号を下り光信号に変換する）ＬＤ６と、ＬＤ６に入力される下り電気信号に合波される変調信号を出力する発信器７と、発信器７から出力された変調信号を下り電気信号に合波させる合波器８とが設けられている。前記ＬＤ６から出力された下り光信号は、下り光伝送路３に送出されノード２に伝送される。
【０００９】
前記ノード２には、入力された下り光信号を電気信号（下り電気信号）に再変換するフォトダイオード（ＰＤ）９と、ＰＤ９から出力された下り電気信号の一部を分岐する分岐器１０と、分岐器１０によって取り出された下り電気信号から変調信号（前記センター局１で合波された変調信号）を分離して取り出す分離フィルター１１と、取り出された変調信号を所定レベルに増幅する増幅器１２と、増幅器１２から出力された変調信号を端末から上がってきた上り電気信号に合波する合波器１３と、変調信号が合波されて変調がかけられた上り電気信号によって駆動される（上り電気信号を上り光信号に変換する）ＬＤ１４とが設けられている。ＬＤ１４から出力された上り光信号は上り光伝送路４に送出されセンター局１に伝送される。
【００１０】
尚、図中の下り増幅器１５は、前記分岐器１０によって分岐されずに出力された下り電気信号を所定レベルに増幅する。上り増幅器１６は、上り電気信号を所定レベルに増幅する。分波フィルタ１７は、前記下り増幅器１５から出力された下り電気信号を出力端子１８に出力し、同出力端子１８に入力された上り電気信号を前記上り増幅器１６に出力する。利得制御器１９は、上り増幅器１６によって増幅された上り電気信号のレベルを調整する。
【００１１】
【発明の効果】
（１）本発明のＣＡＴＶシステムにおける信号変調方法では、下り信号に合波されている変調信号を取り出し、取り出された変調信号によって上り信号に変調をかける。従って、下り光信号及び上り光信号の双方を常時変調状態とすることができ、レーリー散乱によって光伝送路内に発生する雑音を低減させることができる。
（２）本発明のＣＡＴＶシステム用ノードは、下り信号に合波されている変調信号を取り出し、取り出された変調信号によって上り信号に変調をかけるために必要な手段を備えている。従って、該ノードを用いてＣＡＴＶシステムを構築すれば、前記本発明の上り信号変調方法が実現可能となり、該方法による効果を得ることができる。
【図面の簡単な説明】
【図１】本発明のＣＡＴＶシステムにおける信号変調方法を実施可能なＣＡＴＶシステムの一例を示す説明図。
【符号の説明】
１　センター局
２　ノード
３　下り光伝送路
４　上り光伝送路
５　ヘッドヘンド装置
６　ＬＤ
７　発信器
８　合波器
９　ＰＤ
１０　分岐器
１１　分離フィルター
１２　増幅器
１３　合波器
１４　ＬＤ
１５　下り増幅器
１６　上り増幅器
１７　分波フィルター
１８　出力端子
１９　利得制御器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an HFC (Hybrid Fiber Coax) type CATV system.
[0002]
[Prior art]
In the HFC system CATV system, an electric signal is converted into an optical signal at a center station and transmitted to a downstream optical transmission line, which is converted again into an electric signal at a node on the way and transmitted to a terminal via a coaxial cable. I have. Further, the electric signal transmitted from the terminal is converted into an optical signal by the node, and this is transmitted to the center station via the upstream optical transmission line. Here, the center station and the node convert the electric signal into an optical signal by driving a semiconductor laser (LD) with the electric signal to be transmitted.
[0003]
[Problems to be solved by the invention]
The LD has high coherence in the non-modulation state. Therefore, when the LD is driven by an unmodulated electric signal and the output optical signal is sent out to the optical transmission line, intensity noise occurs in the optical transmission line due to the interference effect of Rayleigh scattering, and the noise characteristic mainly in the low frequency band. Deteriorates.
[0004]
[Means for Solving the Problems]
However, it is known that when the LD is modulated, the deterioration of the noise characteristic is rapidly improved due to the spread of the spectrum. An object of the present invention is to solve the above problems based on such knowledge. Specifically, an object of the present invention is to solve the above-described problem by providing a modulation method and a node capable of always maintaining an upstream optical signal and a downstream optical signal in a modulated state.
[0005]
One aspect of the present invention is a signal modulation method in a CATV system of the HFC system, in which a center station modulates a downlink signal, a part of the modulated downlink signal is branched during transmission, and the branched downlink signal is divided. The modulation signal is separated from the signal and extracted, and the uplink signal is modulated by the extracted modulation signal.
[0006]
Another aspect of the present invention is a CATV system node connected to an HFC type CATV transmission network, and includes a photodiode for photoelectrically converting an input downstream optical signal, and a part of the converted downstream electrical signal. , A separation filter for extracting a modulation signal from the branched down electric signal, a multiplexer for multiplexing the extracted modulation signal with an up electric signal to perform modulation, and a modulated up electric signal And a semiconductor laser driven by the semiconductor laser.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
FIG. 1 shows an example of a CATV system capable of implementing the signal modulation method in the CATV system of the present invention. In the CATV system shown in FIG. 1, a downstream optical transmission line 3 and an upstream optical transmission line 4 are laid between a center station 1 and a node 2, and a downstream coaxial cable and an upstream coaxial cable are connected between the node 2 and a terminal. This is an HFC-type CATV system installed. Note that the configuration on the terminal side from the node 2 is omitted for convenience. Although only one node is shown in FIG. 1, two or more similar nodes are provided according to the number of terminals.
[0008]
The center station 1 is driven by a headend device 5, an electric signal (downstream electric signal) output from the headend device 5 (converts a downstream electric signal into a downstream optical signal), and an LD6 is input to the LD6. A transmitter 7 that outputs a modulated signal that is multiplexed with a downstream electric signal, and a multiplexer 8 that multiplexes the modulated signal output from the transmitter 7 with the downstream electric signal are provided. The downstream optical signal output from the LD 6 is transmitted to the downstream optical transmission line 3 and transmitted to the node 2.
[0009]
The node 2 includes a photodiode (PD) 9 for converting an input downstream optical signal into an electrical signal (downstream electrical signal) and a branching device 10 for branching a part of the downstream electrical signal output from the PD 9. A separating filter 11 for separating and extracting a modulated signal (modulated signal multiplexed by the center station 1) from a downstream electric signal extracted by the branching device 10, and an amplifier 12 for amplifying the extracted modulated signal to a predetermined level. And a multiplexer 13 for multiplexing the modulated signal output from the amplifier 12 with an uplink electric signal coming up from the terminal, and is driven by an uplink electric signal obtained by multiplexing and modulating the modulated signal (uplink). LD 14 for converting an electric signal into an upstream optical signal). The upstream optical signal output from the LD 14 is transmitted to the upstream optical transmission line 4 and transmitted to the center station 1.
[0010]
The downstream amplifier 15 in the figure amplifies the downstream electric signal output without branching by the branching device 10 to a predetermined level. The upstream amplifier 16 amplifies the upstream electric signal to a predetermined level. The demultiplexing filter 17 outputs a downstream electric signal output from the downstream amplifier 15 to an output terminal 18 and outputs an upstream electric signal input to the output terminal 18 to the upstream amplifier 16. The gain controller 19 adjusts the level of the upstream electric signal amplified by the upstream amplifier 16.
[0011]
【The invention's effect】
(1) In the signal modulation method in the CATV system of the present invention, a modulated signal multiplexed with a downlink signal is extracted, and the uplink signal is modulated by the extracted modulated signal. Therefore, both the downstream optical signal and the upstream optical signal can be always in a modulated state, and noise generated in the optical transmission line due to Rayleigh scattering can be reduced.
(2) The CATV system node according to the present invention includes means necessary for extracting a modulated signal multiplexed with a downlink signal and modulating an uplink signal with the extracted modulated signal. Therefore, if a CATV system is constructed using the nodes, the uplink signal modulation method of the present invention can be realized, and the effect of the method can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a CATV system capable of implementing a signal modulation method in a CATV system according to the present invention.
[Explanation of symbols]
1 center station 2 node 3 downstream optical transmission line 4 upstream optical transmission line 5 headend device 6 LD
7 Transmitter 8 Combiner 9 PD
Reference Signs List 10 branching device 11 separation filter 12 amplifier 13 multiplexer 14 LD
15 Down amplifier 16 Up amplifier 17 Demultiplexing filter 18 Output terminal 19 Gain controller

Claims (2)

ＨＦＣ方式のＣＡＴＶシステムにおける信号変調方法であって、センター局で下り信号に変調をかけ、変調された下り信号の一部をその伝送中に分岐し、分岐された下り信号から変調信号を分離して取り出し、取り出された変調信号によって上り信号に変調をかけることを特徴とするＣＡＴＶシステムにおける信号変調方法。A signal modulation method in a CATV system of the HFC system, wherein a downstream signal is modulated by a center station, a part of the modulated downstream signal is branched during the transmission, and a modulated signal is separated from the branched downstream signal. A signal modulation method in a CATV system, characterized in that the uplink signal is modulated by the extracted modulated signal. ＨＦＣ方式のＣＡＴＶ伝送網に接続されるＣＡＴＶシステム用ノードであって、入力された下り光信号を光電変換するフォトダイオードと、変換された下り電気信号の一部を分岐する分岐器と、分岐された下り電気信号から変調信号を取り出す分離フィルタと、取り出された変調信号を上り電気信号に合波して変調をかける合波器と、変調された上り電気信号によって駆動される半導体レーザーとを備えたことを特徴とするＣＡＴＶシステム用ノード。A node for a CATV system connected to an HFC type CATV transmission network, comprising: a photodiode for photoelectrically converting an input downstream optical signal; a branching device for branching a part of the converted downstream electrical signal; A separating filter that extracts a modulation signal from the downstream electrical signal, a multiplexer that combines the extracted modulation signal with an upstream electrical signal to perform modulation, and a semiconductor laser that is driven by the modulated upstream electrical signal. A node for a CATV system.
JP2002183046A 2002-06-24 2002-06-24 Method of modulating signal for cable television system, and node for cable television system Pending JP2004032177A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007243817A (en) * 2006-03-10 2007-09-20 Miharu Communications Co Ltd Optical transmitter and optical communication system using the same
CN102395020A (en) * 2011-10-26 2012-03-28 常熟市高事达光电科技有限公司 Optical workstation noise suppression circuit for cable television bilateral network modification
CN104410846A (en) * 2014-12-11 2015-03-11 成都新光微波工程有限责任公司 Optical workstation of digital television
US9951147B2 (en) 2007-11-13 2018-04-24 Cargill, Incorporated Process for the preparation of purified β-(1,3)-D-glucans
CN108174263A (en) * 2017-12-29 2018-06-15 广州长嘉电子有限公司 The method and system of anolog TV signals processing are realized based on COAX modules

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007243817A (en) * 2006-03-10 2007-09-20 Miharu Communications Co Ltd Optical transmitter and optical communication system using the same
US9951147B2 (en) 2007-11-13 2018-04-24 Cargill, Incorporated Process for the preparation of purified β-(1,3)-D-glucans
US10035863B2 (en) 2007-11-13 2018-07-31 Cargill, Incorporated Process for the preparation of purified β-(1,3)-D-glucans
US10047170B2 (en) 2007-11-13 2018-08-14 Cargill, Incorporated Process for the preparation of purified β-(1,3)-D-glucans
US10047168B2 (en) 2007-11-13 2018-08-14 Cargill. Incorporated Process for the preparation of purified β-(1,3)-D-glucans
US10047169B2 (en) 2007-11-13 2018-08-14 Cargill, Incorporated Process for the preparation of purified β-(1,3)-D-glucans
CN102395020A (en) * 2011-10-26 2012-03-28 常熟市高事达光电科技有限公司 Optical workstation noise suppression circuit for cable television bilateral network modification
CN102395020B (en) * 2011-10-26 2012-11-07 常熟市高事达光电科技有限公司 Optical workstation noise suppression circuit for cable television bilateral network modification
CN104410846A (en) * 2014-12-11 2015-03-11 成都新光微波工程有限责任公司 Optical workstation of digital television
CN108174263A (en) * 2017-12-29 2018-06-15 广州长嘉电子有限公司 The method and system of anolog TV signals processing are realized based on COAX modules
CN108174263B (en) * 2017-12-29 2020-10-20 广州长嘉电子有限公司 Method and system for realizing analog television signal processing based on COAX technology

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