JP4740464B2 - Bi-directional CATV system, transmission line equipment, center equipment - Google Patents

Description

【００５５】
なお、グループ検索中であるか否かの判断は、当該処理がＳ１８０，Ｓ３４０からの起動により実行されており、且つ、その時点で特定伝送路機器又は制御対象機器となっている伝送路機器の下流に複数の加入者端末が接続されている場合をグループ検索中と判断する。また、ここでは、その伝送路機器の下流に接続されている加入者端末の台数Ｎとする。
【００５６】
そして、グループ検索中でなければ、先のＳ４４０にて算出された測定値の平均ＮＬavを、そのまま雑音レベルＮＬとして設定し（Ｓ４６０）、一方、グループ検索中であれば、測定値の平均ＮＬavを（２）式にて補正した値を、雑音レベルＮＬとして設定し（Ｓ４７０）、本処理を終了する。
【００５７】
ＮＬ＝ＮＬav−１０×logＮ （２）
なお、（２）式においてＮＬ，ＮＬavの単位は［ｄＢ］であり、（２）式は測定値の平均ＮＬavを、１台当たりの端末での雑音レベルに変換したことに相当する。
【００５８】
次に、先のＳ１２０，Ｓ１９０，Ｓ３６０にて参照される雑音上限値ＮＬmax の更新のために、信号測定部５４が定期的に実行する雑音上限値更新処理を、図７に示すフローチャートに沿って説明する。
図７に示すように、本処理が起動すると、まず、測定器４４の測定モードを、測定結果の最大レベルを保持するピークホールドモードに設定し（Ｓ５１０）、予め設定された期間の間、測定器４４に、上り信号の周波数帯（１０ＭＨｚ〜５５ＭＨｚ）の周波数成分を繰り返し分析させる（Ｓ５２０）。このとき、測定器４４での測定結果として、測定期間中における周波数成分毎の最大値が得られることになる。
【００５９】
この測定結果に基づき、予め設定された判定しきい値より低いレベルとなる帯域中から、複数の測定ポイントを決定し（Ｓ５３０）、その測定ポイントの周波数ｆｍと測定値ＮＬｄとを保存する（Ｓ５４０）。なお、判定しきい値は、上り信号が送出されていない空きチャンネルであることが確実に識別されるような信号レベルに設定する。また、Ｓ５３０にて設定された測定ポイントが、先の雑音レベル測定処理のＳ４２０でも使用されることになる。
【００６０】
そして、保存された測定値ＮＬｄに、マージンとして規定値（例えば５ｄＢ）を加えたものを、雑音上限値ＮＬmax として設定し（Ｓ５５０）、本処理を終了する。
なお、本実施形態において、Ｓ１３０，Ｓ１４０（Ｓ３１０〜Ｓ３８０），Ｓ２００が本発明における探索手段に相当し、Ｓ１５０〜Ｓ１９０が雑音調整手段に相当する。
【００６１】
以上説明したように、本実施形態のＣＡＴＶシステムにおいては、センタ装置２が受信する上り信号の雑音レベルが雑音上限値を越えた場合に、その雑音発生源が存在する伝送線４を単純にシステムから切り離すのではなく、雑音発生源の直近上流に位置する伝送路機器６，８での上り信号の減衰量を増大させることにより、センタ装置２が受信する上り信号の雑音レベルが雑音上限値以下となるようにしている。
【００６２】
従って、本実施形態のＣＡＴＶシステムによれば、このような異常な雑音によりシステム全体が影響を受けてしまうことを防止できるだけでなく、異常雑音の発生時に、雑音発生源の下流に位置するケーブルモデムからセンタ装置２への上り信号が途絶えてしまうこともないため、例えば、センタ装置２を介したインターネットへの接続サービス等、上り信号を利用したサービスを継続して提供でき、システムの信頼性を向上させることができる。
【００６３】
しかも、本実施形態のＣＡＴＶシステムでは、雑音発生源の探索を、グループ単位で階層的に行っているため、雑音発生源の直近上流に位置する伝送路機器６，８を効率よく特定することができるため、流合雑音の増加に基づく通信品質の低下を速やかに解消することができる。
【００６４】
また、本実施形態のＣＡＴＶシステムによれば、分岐装置８において、下り信号によるサービスのみを契約した加入者宅への引込線が接続される分岐端子Ｔｂがある場合、この分岐端子Ｔｂに対応するゲートスイッチ２６をオフ設定として、図３（ｃ）中に実線にて示す特性を実現することにより、上述の加入者宅にて上り信号を用いたサービス（例えばインターネット接続）が不正使用されることを確実に防止できる。
［第２実施形態］
次に第２実施形態について説明する。
【００６５】
図８（ａ）は、双方向ＣＡＴＶシステムの加入者宅に設置された情報分電盤６０の内部構成を表す説明図である。
図８（ａ）に示すように、情報分電盤６０には、保安器を介して入力されてくる下り信号を２系統に分配し、両系統からの上り信号を混合する分配器６２が設置されており、この分配器６２にて分岐した一方の伝送路上には、この伝送路を流れる下り信号及び上り信号を双方向に増幅するブースター６４が接続され、他方の伝送路上には、ケーブルモデム６６及びルータ６８が接続されている。
【００６６】
このうちブースター６４は、図８（ｂ）に示すように、図２（ａ）に示す双方向増幅器６から、分岐回路１７及びステータスモニタ１８を省略した構成を有しており、上り経路に挿入されたゲートスイッチ１６は、外部からの制御信号によって動作させることができるように構成されている。なお、双方向増幅器６と同様の構成部分については、図中に同じ符号を付し、ここではその説明を省略する。
【００６７】
そして、ブースター６４の出力は、複数に分配（図示せず）された後、各部屋に設けられた情報コンセントに供給される。この情報コンセントにセットトップボックスを介してテレビ受像器やＣＡＴＶ電話等を接続することにより、番組の視聴やＣＡＴＶ電話のサービスの提供を受けることが可能となる。
【００６８】
また、ルータ６８は、複数のパーソナルコンピュータ（パソコン）ＰＣが接続され、ＰＣ間の通信を可能とすると共に、ルータ６８に接続された任意のパソコンＰＣが、ケーブルモデム６６を介したＣＡＴＶシステム経由のインターネット接続を可能なように構成されている。
【００６９】
また更に、ケーブルモデム６６は、双方向増幅器６のステータスモニタ１８と同様に、センタ装置２からの制御信号を解析する機能を有しており、ルータ６８を介してブースター６４に制御信号（減衰量調整信号）を供給できるように構成されている。
【００７０】
このような情報分電盤６０が加入者宅に設置された本実施形態の双方向ＣＡＴＶシステムでは、ブースター６４を、双方向増幅器６や分岐装置８等と同等の伝送路機器として扱うことにより、雑音発生源の影響をより小さい範囲に抑え込むことができ、システムの信頼性を一層向上させることができる。
【００７１】
また、この場合、ブースター６４の上り信号の通過，阻止を切り替えるゲートスイッチ１６は、視聴者参加番組の視聴中やＣＡＴＶ電話を使用する場合にのみオン状態とするように制御すれば、流合雑音をより効果的に低減させることができる。
［第３実施形態］
次に第３実施形態について説明する。
【００７２】
本実施形態では、分岐装置のゲート部８ｂの構成が、第１実施形態のものとは一部異なっているだけであるため、その相異する部分を中心に説明する。
即ち、本実施形態において、分岐装置のゲート部８ｂは、図９（ａ）に示すように、第１実施形態にて説明したゲート部８ｂの構成（図２（ｂ）参照）に加えて、下り群を構成する各下り経路のＨＰＦ２４（２４ａ，２４ｂ，…）と分配回路２２との間に、各下り経路を通過する下り信号の通過，阻止を切り替えるゲートスイッチ２９（２９ａ，２９ｂ，…）を備えている。
【００７３】
そして、この追加されたゲートスイッチ２９は、図９（ｂ）に示すように、下り信号の通過，阻止を切り替えるスイッチ素子７０の下流（分岐端子Ｔｂ）側に、減衰器７４を介してノイズ発生器７２が接続されており、しかも、ノイズ発生器７２への電源供給線には、スイッチ素子７０と連動する電源スイッチ７６が設けられている。
【００７４】
なお、ステータスモニタ１８は、センタ装置２からの制御信号を受信し、その制御信号に従って、ゲートスイッチ１６だけでなくゲートスイッチ２９に対する切替信号も生成するように構成されている。
そして、ゲートスイッチ２９が下り信号を通過させるオン設定、即ちスイッチ素子７０がオン状態の時には、電源スイッチ７６がオフ状態となって、ノイズ発生器７２は動作せず、逆に、ゲートスイッチ２９が下り信号の通過を素子するオフ設定、即ちスイッチ素子７０がオフ状態の時には、電源スイッチ７６がオン状態となって、ノイズ発生器７２にて発生したホワイトノイズが分岐端子Ｔｂ側に供給されることになる。なお、重畳されるホワイトノイズの強度は、スイッチ素子７０がオフ状態の時に下流側に漏れた下り信号と同程度であればよい。
【００７５】
このように構成された本実施形態の双方向ＣＡＴＶシステムでは、下り経路のゲートスイッチ２９がオン設定にされている場合には、図１０（ａ）に示すように、上り経路のゲートスイッチ２６を操作することにより、図１０（ａ）に示すように、第１実施形態の場合と同様の特性を実現することができるため、これと同様の効果を得ることができる。
【００７６】
また、本実施形態の双方向ＣＡＴＶシステムでは、分岐装置８の分岐端子Ｔｂの中に未使用のものがある場合、これに対応する上り／下り両経路のゲートスイッチ２６，２９をオフ設定にする（図１０（ｂ）参照）ことにより、この未使用の分岐端子Ｔｂを介したＣＡＴＶサービスの不正利用を防止することができる。
【００７７】
しかも、このような未使用の分岐端子Ｔｂに対する制御を、センタ装置２から遠隔操作によって簡単に実現することができる。
更に、本実施形態では、仮にスイッチ素子７０のアイソレーションが不十分で分岐端子Ｔｂへの下り信号の漏れがあったとしても、ゲートスイッチ２９にて重畳されるホワイトノイズによって、下り信号を抽出することが困難なようにされているため、上述の不正防止効果をより確実なものとすることができる。
【００７８】
換言すれば、スイッチ素子７０がオフ状態の時に、その下流側にホワイトノイズを重畳するようにしたことにより、下り信号の通過，阻止を切り替えるゲートスイッチ２９を構成するスイッチ素子７０として、アイソレーションがそれほど大きくないものを採用することが可能となり、上述のような不正防止に極めて効果のある装置を安価に構成することができる。
【００７９】
なお、本実施形態において、分配回路２２が分配手段、ゲートスイッチ２９がスイッチ手段、ノイズ発生器７２，減衰器７４，電源スイッチ７６がノイズ重畳手段に相当する。
本実施形態においては、ゲートスイッチ１６，２６での減衰量が、オン設定（≒０ｄＢ），−３ｄＢ，−６ｄＢ，−１０ｄＢ，オフ設定（≒−３０ｄＢ）の５段階に設定されているが、これに限らず、４段階以下や５段階以上に設定してもよいし、各段階で互いに異なった減衰量が設定できるのであれば、どのような値に設定してもよい。
【００８０】
また、本実施形態では、段階的に減衰量が変化するように構成されているが、減衰量を連続的に変化させることのできる可変減衰器を用いて構成してもよい。この場合、減衰量を切り替える際に信号が瞬断しないため、切替時の制御を容易にすることができる。なお、減衰量を変化させるための構成は、電子式，機械式のいずれであってもよい。
【００８１】
また、本実施形態では、測定したノイズレベルに規定のマージンを付加したものを雑音上限値として設定したが、データ通信を安定に行うために必要なＣ／Ｎ（変復調方式や運用レベルから定まる）から求めた雑音レベルを雑音上限値として設定してもよい。例えば、ＱＰＳＫ方式の場合、Ｃ／Ｎは１８ｄＢ以上あれば良いので、運用レベルから１８ｄＢ下がった値を上限値として設定すればよい。
【００８２】
また、本実施形態では、対象機器の探索を、グループ選択にて行うように構成されているが、データベースに基づき直接各機器（端末）を下流側から順次個別に選択することで行ってもよい。
【図面の簡単な説明】
【図１】 実施形態の双方向ＣＡＴＶシステムの構成を表すブロック図である。
【図２】 伝送路機器の構成を表すブロック図である。
【図３】 ゲートスイッチの構成、及び作用を表す説明図である。
【図４】 雑音レベル調整処理の内容を表すフローチャートである。
【図５】 雑音発生源探索処理の内容を表すフローチャートである。
【図６】 雑音レベル測定処理の内容を表すフローチャートである。
【図７】 雑音上限値更新処理の内容を表すフローチャートである。
【図８】 第２実施形態における情報分電盤の内部構成、及びブースターの構成を表すブロック図である。
【図９】 第３実施形態における分岐装置のゲート部、及び下り経路中に設けたゲートスイッチの構成を表すブロック図である。
【図１０】 分岐端子での信号通過特性を表す説明図である。
【符号の説明】
２…センタ装置、４…伝送線、６…双方向増幅器（伝送路機器）、８…分岐装置（伝送路機器）、８ａ，１７，２７…分岐回路、８ｂ…ゲート部、１０，１４，２０，２４…ハイパスフィルタ、１２，１３…増幅回路、１１，１５，２１，２５…ローパスフィルタ、１６，２６，２９…ゲートスイッチ、１８，２８…ステータスモニタ、２２…分配回路、２３…合流回路、３０…セレクタ、３１〜３３，７４…減衰器、４２…ノードスイッチャー、４４…測定器、４６…下りコントロール信号送出部、５０…監視制御装置、５２…データベース、５４…信号測定部、５６…信号レベル調整部、５８…雑音レベル調整部、６０…情報分電盤、６２…分配器、６４…ブースター、６６…ケーブルモデム、６８…ルータ、７０…スイッチ素子、７２…ノイズ発生器、７６…電源スイッチ、Ｔｕ…上流側端子、Ｔｄ…下流側端子、Ｔｂ…分岐端子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bidirectional CATV system in which a plurality of transmission line devices are connected in a transmission line from a center device to a subscriber-side terminal device, a transmission line device used in the bidirectional CATV system, and a center device. .
[0002]
[Prior art]
Conventionally, in a bidirectional CATV system, transmission path equipment (for example, a bidirectional amplifier or branching apparatus) provided on a transmission path from a center apparatus to a subscriber side terminal apparatus (for example, a cable modem or a set top box (STB)). Etc.) is provided with a status monitor for monitoring the transmission signal level, power supply voltage level, and the like.
[0003]
Also, in the bidirectional CATV system, a gate switch that opens and closes the passage path of the upstream signal is provided in the transmission line device, and this gate switch is operated using the communication function with the center device of the status monitor to transmit the upstream signal. Control that suppresses inflow noise of upstream signals by disconnecting unused transmission lines is known.
[0004]
Further, for example, as disclosed in JP-A-6-245212, when the noise level of the upstream signal exceeds the allowable range, the gate switch of the bidirectional amplifier located upstream of the noise generation source is operated. There is also known a control for preventing the entire system from being adversely affected by abnormal noise by separating the noise source from the system.
[0005]
[Problems to be solved by the invention]
By the way, when the gate switch is opened due to the noise level of the upstream signal exceeding the allowable range, a worker is dispatched to the site to investigate the cause of the noise, and after removing the cause, the gate switch is closed. Recovery work will be performed.
[0006]
For this reason, once the gate switch is opened, in the subscriber side terminal device connected downstream thereof, a service using an uplink signal over a relatively long period until the above restoration work is completed, for example, There was a problem that the connection to the Internet via the center device could not be received.
[0007]
In order to solve the above-described problem, the present invention provides a bidirectional CATV system in which, when the noise level of an upstream signal increases, the transmission of the upstream signal from the path where the noise generation source exists is stopped. It is an object to make it possible to sufficiently reduce the noise level of an upstream signal received by a device.
[0008]
[Means for Solving the Problems]
  The interactive CATV system according to claim 1, wherein the center device is an invention for achieving the above object.AtReceiveBe doneIf the noise level of the upstream signal exceeds the preset noise upper limit value,The center device isSearch for the noise source, and find the transmission line equipment located immediately upstream of the noise source.As specific transmission line equipmentIdentify,Specify the attenuation level adjustment signal to adjust the attenuation level of the uplink signal in the specific transmission line equipment so that the noise level is lower than the noise upper limit value.Transmission line machineIn a vesselThe amount of attenuation of the upstream signal is increased.
[0009]
Therefore, according to the present invention, if the attenuation amount of the uplink signal in the specific transmission line device is sufficiently increased until the noise level of the uplink signal received by the center apparatus is within the allowable range, the noise generation source can be obtained. As well as reliably preventing the noise based on other devices from adversely affecting the equipment, the noise level of the upstream signal is always kept below a certain level for the system as a whole. Can be improved.
[0010]
At this time, the signal level of the upstream signal transmitted from the subscriber side terminal device (cable modem, set top box, etc.) located downstream of the specific transmission line device is attenuated together with the noise level by the specific transmission line device. However, since there is usually a system margin, communication can be continued although communication quality deteriorates.
[0011]
  In the interactive CATV system of the present invention,Center deviceAtThe signal level of the uplink signal transmitted by the subscriber-side terminal device is automatically adjusted so that the signal level of the received uplink signal is within a preset allowable range.Has been.
Therefore, according to the bidirectional CATV system of the present invention,This automatic adjustment reduces the noise generated at the noise source, and increases only the signal level of the upstream signal from the subscriber side terminal device located downstream of the specific transmission line device. That is, the transmission quality (SN ratio or CN ratio) of the uplink signal output by the specific transmission line device is improved as compared with that before increasing the attenuation amount of the uplink signal. However, communication with the center apparatus can be ensured without greatly reducing the communication quality, and the service using the uplink signal can be reliably continued.
[0012]
Here, the transmission line equipment is installed in a branching device called tap-off or an information distribution board in a subscriber's house, in addition to a relay amplifier and a branching amplifier for amplifying, branching and joining upstream and downstream signals. Any device may be used as long as it is connected to the transmission path from the center device to the subscriber side terminal device, such as a booster.
[0013]
  next,Claim 2In the transmission line equipment described,When the noise level of the uplink signal received by the center device exceeds the preset noise upper limit value, the transmission line equipment located immediately upstream of the noise source is set so that the noise level is equal to or lower than the noise upper limit value. To adjust the amount of attenuation for the upstream signalSuperimposed on the downstream signal from the center unitRuAccording to the attenuation adjustment signal,The signal attenuation meansThe amount of attenuation with respect to the upstream signal to the center device is changed.
  Also,Claim 3In the described center apparatus, the noise level detection means detects noise in the frequency band used for transmission of the upstream signal, and when the noise level exceeds a preset noise upper limit value, the search means The noise source is searched to identify the transmission line device located immediately upstream of the noise source.noiseAn attenuation adjustment signal for adjusting the attenuation amount of the uplink signal in the transmission line device specified by the search means is generated so that the noise level detected by the level detection means is less than or equal to the noise upper limit value. The attenuation amount adjustment signal is superimposed on the downstream signal and transmitted.
[0014]
  Therefore,Claim 2The transmission line equipment andClaim 3Using the described center device, if the noise level of the upstream signal received by the center device exceeds a preset noise upper limit, the transmission line device located immediately upstream of the noise source is identified and transmitted. The amount of attenuation for upstream signals in road equipment can be increased..
[0015]
  Also,Claim 3In the described center apparatus, the signal level detecting means detects the signal level of the received upstream signal, and the level adjusting means is the subscriber-side terminal apparatus so that the signal level is within a preset allowable range. A level adjustment signal for adjusting the transmission level of the upstream signal is generated, and the level adjustment signal is superimposed on the downstream signal and transmitted.
That is, the transmission line device according to claim 2 and claim 3The center device described isClaim 1It can be suitably used when configuring the described bidirectional CATV system.
[0016]
Furthermore, the present inventionTransmission line equipment, MinutesThe distribution means distributes the downlink signal from the center apparatus to a plurality of distribution paths, and the switch means transmits the signal distributed by the distribution means according to the switching signal superimposed on the downlink signal from the center apparatus for each distribution path. Configured to control the passage and blocking of downstream signalsHas been.
[0017]
When the transmission line device of the present invention having such a configuration is applied to a branching device for branching a signal on the transmission line to a signal line (branch path) drawn into each subscriber's house, so-called tap-off, etc. Since no downlink signal is sent out from the branch terminal, unauthorized use of the CATV service through this unused branch terminal can be prevented. At the same time, inflow noise entering from an unused branch terminal can be prevented, and deterioration of the quality of the upstream signal can also be prevented.
[0018]
However, the switch means that handles the high-frequency signal flowing through the transmission line of the CATV system cannot completely prevent the signal from passing when it is in the OFF state. However, if the isolation of the switch means is sufficiently increased, the switch means becomes very expensive.
[0019]
  Therefore,In the transmission line device of the present invention,The noise superimposing means is interlocked with the switch means, and is configured to superimpose white noise on the downstream side of the switch means when the switch means is set to prevent the passage of the downstream signal.Has been.
[0020]
As a result, the leakage signal that has passed through the switch means in the off state is buried in white noise and cannot be identified, and the above-described unauthorized use can be reliably prevented.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a schematic configuration diagram of a CATV system according to an embodiment to which the present invention is applied. In the CATV system of the present embodiment, a transmission signal in a predetermined transmission frequency band (for example, 70 MHz to 550 MHz band) is used as a downstream signal from the center apparatus 2 toward the terminal side, and is directed from the terminal side to the center apparatus 2. As the upstream signal, a transmission signal in a transmission frequency band (for example, 10 MHz to 55 MHz band) having a frequency lower than that of the downstream signal is used.
[0022]
As shown in FIG. 1, in the CATV system of the first embodiment, 4 (4a, 4b, 4c) from the center apparatus 2 to the terminal terminal to which the subscriber side terminal apparatus of the system is connected is the center apparatus 2. Are connected to the main line 4a, a large number of branch lines (hereinafter referred to as "branch lines") 4b branched from the main line 4a, lower branch lines 4c further branched from the respective branch lines 4b, etc. Yes.
[0023]
These transmission lines 4 are bi-directional amplifiers (branch amplifiers, relay amplifiers) 6 for relaying / branching that bi-directionally amplifies transmission signals flowing through the transmission lines 4 and branch and merge the transmission signals as necessary. A number of branching devices 8 as so-called tap-offs are provided, which branch the transmission signal flowing through the transmission line 4 and draw it into the subscriber's house. The bidirectional amplifier 6 and the branching device 8 correspond to transmission line equipment in the present invention.
[0024]
Here, FIG. 2 is a block diagram showing the configuration of the main part of the bidirectional amplifier 6 (a) and the main part of the branching device 8 (b).
As shown in FIG. 2A, the bidirectional amplifier 6 takes in the downstream signal input from the upstream terminal Tu located on the center device 2 side via the high-pass filter (HPF) 10 and inputs it to the amplifier circuit 12. A low-pass filter (LPF) 15 outputs a downstream path output from the downstream terminal Td to the terminal side via the HPF 14 and an upstream signal input from the downstream terminal Td located on the terminal side. And an upstream path that outputs the signal from the upstream terminal Tu to the center apparatus 2 via the LPF 11 after being amplified to a predetermined level by the amplifier circuit 13.
[0025]
Further, the bidirectional amplifier 6 includes a gate switch 16 as a signal attenuating means having a function as a variable attenuator between the amplification circuit 13 and the LPF 11 in the upstream path, and further, an upstream terminal Tu and Bidirectional communication with the center apparatus 2 is performed via the branch circuit 17 provided between the HPF 10 and the LPF 11 to notify the center apparatus 2 of the state of each part of the bidirectional amplifier 6 and a control signal from the center apparatus 2 And a status monitor 18 as signal extraction means for generating a switching signal for the gate switch 16 in accordance with the control signal.
[0026]
In FIG. 2A, a configuration for branching and joining transmission signals and a configuration for the status monitor 18 to detect the state of each unit are omitted. However, it is assumed that the merging of the upstream signals is performed on the downstream side of the gate switch 16.
Further, as shown in FIG. 3A, the gate switch 16 includes a selector 30 (30a, 30b) that can switch five paths according to a switching signal, and each path is short-circuited and opened. In addition, three attenuators 31, 32, and 33 having different attenuation amounts are connected. That is, the gate switch 16 can pass (short-circuit: on), block (open: off), or attenuate (in this embodiment, three levels of −3 dB / −6 dB / −10 dB) of the upstream signal. It is configured.
[0027]
FIG. 3 (a) schematically shows the gate switch 16, and actually, for example, as shown in FIG. 3 (b), the gate switch 16 can be constituted by a diode, a resistor, an inductor, and a capacitor. . That is, by supplying power to any one of the terminals 1 to 4 in accordance with the control signal and making the diode conductive, an amount of attenuation corresponding to an attenuator made of a resistor sandwiched between the conductive diodes can be obtained. However, when power is supplied to the terminal 1, it is in an on state, and when power is supplied to the terminal 5, it is in an off state.
[0028]
FIG. 3C shows the frequency characteristics of the bidirectional amplifier 6.
On the other hand, as shown in FIG. 1, the branching device 8 has one or more branches reaching a terminal terminal for connecting a branching circuit 8a for branching a part of a transmission signal from the transmission line 4 and a subscriber side terminal. A gate section 8b having a terminal Tb, which distributes the downstream signal branched by the branch circuit 8a to each branch terminal Tb and joins the upstream signal input from each branch terminal Tb and supplies it to the branch circuit 8a. Become.
[0029]
Then, the gate unit 8b of the branching device receives the downstream signal branched from the transmission line 4 by the branch circuit 8a via the HPF 20 and distributes it by the distribution circuit 22 as shown in FIG. A downlink group for outputting each distributed downlink signal from each branch terminal Tb to the terminal side via the HPF 24 (24a, 24b,...), And an uplink signal input from each branch terminal Tb on the terminal side. , Respectively, which are taken in through the LPF 25 (25a, 25b,...) And joined together in the joining circuit 23, and then the joined upstream signal is output to the branch circuit 8a side through the LPF 21. It has.
[0030]
In addition, the gate unit 8b includes a gate switch 26 (26a, 26b,...) As a signal attenuating unit having a function as a variable attenuator between the LPF 25 and the junction circuit 23 of each upstream path constituting the upstream group. Furthermore, bidirectional communication with the center device 2 is performed via the branch circuit 27 provided between the branch circuit 8a and the HPF 20 and LPF 21, and the state of each part of the branch device 8 is transferred to the center device 2. A status monitor 28 is provided for notifying or receiving a control signal from the center apparatus 2 and generating a switching signal for each gate switch 26 according to the control signal. Since the gate switch 26 is exactly the same as the gate switch 16 constituting the bidirectional amplifier 6 described above, the description thereof is omitted here.
[0031]
By the way, a unique address is assigned in advance to the bidirectional amplifier 6 and the branching device 8, and each status monitor 18, 28 is transmitted from the center device 2 using a specific transmission frequency band (70 MHz to 76 MHz). When the destination address of the incoming transmission data indicates its own device, it is configured to take this and execute the command content indicated in the command.
[0032]
Further, identification data for identifying each gate switch 26 can be added to the transmission data from the center device 2 to the branch device 8, and the status monitor 28 (and thus the center device 2) of the branch device 8 The gate switch 26 can be individually controlled.
[0033]
In other words, the bidirectional amplifier 6 amplifies the downstream signal flowing through the transmission line 4 and amplifies the upstream signal flowing through the transmission line 4 to pass, block, or attenuate (with 3 levels). Has been.
Further, the branching device 8 distributes the downlink signal branched from the transmission line 4 and supplies it to each branch terminal Tb. For the uplink signal input from each branch terminal Tb, for each branch terminal Tb, What has been passed, blocked, or attenuated is merged and supplied to the transmission line 4.
[0034]
Next, as shown in FIG. 1, the center apparatus 2 includes a receiving antenna that receives a television broadcast signal transmitted from an artificial satellite or a ground station, a video device that reproduces a television signal recorded on a video tape or a video disk, Using a TV camera for independent broadcasting, etc., it generates a large number of TV signals for broadcasting in the system, converts each TV signal into a downlink signal with a transmission frequency corresponding to a preset channel, and transmits each signal. A head end (HE) 40 including a broadcasting facility or the like for sending to a line (also referred to as a node) 4 is provided.
[0035]
The center device 2 also includes a measuring device (for example, a spectrum analyzer) 44 that analyzes the frequency component of the upstream signal frequency band (10 MHz to 55 MHz) and nodes N1 to N1 to which the transmission line 4 is connected according to the selection signal. A node switcher 42 that selects any one of Nn and supplies an upstream signal flowing from the transmission line 4 to the measuring instrument 44 via the selected node Ni (i = 1 to n); and the transmission line 4 In order to transmit a command for controlling the operation state to transmission line devices such as the bi-directional amplifier 6 and the branching device 8 provided in FIG. Generates a control signal consisting of an address and a command indicating the command contents, and notifies the operation status from an upstream signal in the transmission frequency band corresponding to a preset control channel Therefore, the monitoring control device 50 that performs control such as taking out the status notification signal transmitted from each transmission line device 6 and 8, and the control signal generated by the monitoring control device 50 are set in a preset control channel. A downlink control signal sending unit 46 that converts the signal into a downlink signal in a corresponding transmission frequency band and sends it to each transmission line 4 via the head end 40 is provided.
[0036]
The supervisory control device 50 includes a database 52 for storing search data including path data indicating connection relations of the transmission lines 4, arrangement of the transmission path devices 6 and 8, and setting states of the gate switches 16 and 26, and the like. Signal level detection means for measuring the signal level and noise level (or SN ratio, CN ratio) on an arbitrary transmission line 4 using the node switcher 42 and the measuring device 44, and a signal as noise level detection means The output of the measurement unit 54 and the cable modem connected to the terminal terminal as the subscriber-side terminal device so that the signal level of the upstream signal measured by the signal measurement unit 54 is within a preset allowable range. Measured by a signal level adjustment unit 56 as a level adjustment unit that generates a control signal (level adjustment signal) for adjusting the level, and a signal measurement unit 54 A noise level adjustment unit 58 that generates a control signal (attenuation amount adjustment signal) for adjusting the attenuation amount of the uplink signal transmitted by the transmission line device so that the sound level is equal to or less than a preset noise upper limit value. I have.
[0037]
Here, the control executed by the noise level adjusting unit 58 will be described with reference to the flowchart shown in FIG. This process is executed individually and repeatedly for each of the nodes N1 to Nn in use to which the transmission line 4 is connected.
As shown in FIG. 4, when this processing is started, first, the signal measurement unit 54 measures the noise level of the upstream signal (S110), and the noise level NL obtained by the measurement is set in advance. It is determined whether or not the noise upper limit value NLmax is greater (S120). If the noise level is equal to or lower than the noise upper limit value (NL ≦ NLmax), this process is terminated without doing anything. On the other hand, if the measured noise level of the uplink signal is larger than the preset noise upper limit value (NL > NLmax), it is necessary to search for a noise generation source. First, search history data for the node Ni to be processed is read from the database 52 (S130). Based on the search history data, A noise source search process for identifying the transmission line devices 6 and 8 located immediately upstream of the noise source is executed (S140).
[0038]
For the transmission line devices 6 and 8 (hereinafter referred to as “specific transmission line device”) identified by this noise source search process, the setting of the gate switches 16 and 26 is set to the maximum attenuation (−10 dB in this embodiment). (S150), if the maximum attenuation is reached, the attenuation cannot be increased any more, so the gate switches 16 and 26 are set to OFF for the specific transmission line device. An attenuation adjustment signal that is a control signal for instructing this is output (S160).
[0039]
On the other hand, if the setting of the gate switches 16 and 26 of the specific transmission line device is not the maximum attenuation amount, the specific transmission line device is instructed to increase (increase) the attenuation amount of the gate switches 16 and 26 by one step. (S170), the control target devices 6 and 8 that have received the attenuation amount adjustment signal wait for a time necessary for setting the gate switches 16 and 26 as instructed. The measurement unit 54 is caused to measure the noise level (S180).
[0040]
Subsequently, it is determined whether or not the measured noise level NL is larger than the noise upper limit value NLmax (S190). If the measured noise level NL is larger than the noise upper limit value (NL> NLmax), the noise level cannot be sufficiently reduced. Returning to S150, the processes of S150 to S190 are repeated.
[0041]
On the other hand, when the noise level measured in S180 has changed to the noise upper limit value or less (NL ≦ NLmax), or in the previous S160, the settings of the gate switches 16 and 26 of the specific transmission line device are turned off. In this case, the search history data read in the previous S130, such as the identification information of the specific transmission line device specified in the previous S140, the setting state of the gate switches 16, 26 set in the S160 or S170, etc. Are added and updated and stored in the database 52, and a display and notification indicating that are made (S200), and this processing is terminated.
[0042]
That is, by executing the noise level adjustment process, the transmission line devices 6 and 8 located immediately upstream of the noise generation source are specified, and in the specific transmission line devices 6 and 8, the upstream signal received by the center device 2 is identified. The amount of attenuation of the upstream signal increases until the noise level becomes equal to or lower than the noise upper limit value.
[0043]
Note that when the amount of attenuation of the upstream signal in the specific transmission line devices 6 and 8 increases, the signal level of the upstream signal output from the cable modem located downstream thereof greatly decreases with the noise level. However, in this case, in the center device 2, the signal level adjusting unit 56 sets the output level of the upstream signal to the cable modem so that the upstream signal level received by the center device 2 is within the allowable range. Processing as level adjusting means for sending an instruction to increase is executed. That is, only the signal level of the upstream signal supplied to the center apparatus 2 via the specific transmission line devices 6 and 8 is increased, and the amount of attenuation of the upstream signal in the specific transmission line devices 6 and 8 is reduced. The transmission quality (SN ratio, CN ratio) is improved as compared with before the increase.
[0044]
In addition, when there is a display or notification based on S200, on-site work for removing the cause of noise generation on the downstream side of the corresponding transmission line devices 6 and 8 is performed according to the contents, and the removal of the cause of noise generation is confirmed. Then, the gate switches 16 and 26 of the transmission line devices 6 and 8 may be switched to the on setting.
[0045]
Here, the details of the noise source search process executed at 140 will be described with reference to the flowchart shown in FIG.
As shown in FIG. 5, in the noise source search process, a group to be controlled is selected based on the search history data for the node Ni read in the previous S130 (S310). In the CATV system, the transmission line devices 6 and 8 are grouped for each main line 4a, branch line 4b, and branch line 4c, and the transmission line devices 6 and 8 on the main line 4a are set as the highest level group. For each transmission line branched from the transmission line devices 6 and 8 belonging to the upper group, the lower group is hierarchically set by the transmission line devices 6 and 8 on the transmission line.
[0046]
Here, when S310 is executed for the first time after the activation of this process, the highest group is selected, and each time the execution of S310 is repeated, a lower group is selected. . However, when there are many peer groups, branch source transmission line devices 6 and 8 are selected in order from the upstream group located in the downstream, and branch source transmission line devices 6 and 8 are selected. When 8 is the same, it shall be selected according to a preset order.
[0047]
When a group is selected in this way, this time, among the transmission line devices 6 and 8 belonging to the group, the device located on the most downstream side is selected as a control target device (S320). At this time, the current setting state of the gate switches 16 and 26 is extracted and stored for the selected control target device from the search history data read out earlier.
[0048]
Next, a control signal (attenuation amount adjustment signal) instructing to turn off the gate switches 16 and 26 is output to the control target devices 6 and 8 (S330), and the control target that has received this control signal After the devices 6 and 8 wait for the time necessary to turn off the gate switches 16 and 26, the signal measuring unit 54 is caused to measure the noise level (S340). Subsequently, a control signal instructing to restore the gate switches 16 and 26 to the original setting state stored in the previous S320 is output to the control target devices 6 and 8 (S350).
[0049]
Then, it is determined whether or not the noise level NL measured in the previous S340 is larger than the noise upper limit value NLmax (S360). If the noise level NL is larger than the noise upper limit value (NL> NLmax), the transmission path to be controlled Assuming that there is no noise generation source downstream of the devices 6 and 8, the process returns to S320, the control-target devices 6 and 8 are newly selected, and the processing of S320 to S360 is repeated.
[0050]
On the other hand, if the noise level measured in S340 changes below the noise upper limit value (NL ≦ NLmax), it is assumed that there is a noise source downstream of the control target devices 6 and 8, and this time the control target It is determined whether or not there is a lower group whose branch source is the devices 6 and 8 (S370). If the lower group exists, the process returns to S310, a control target group is newly selected, and the processing of S310 to S370 is repeated. On the other hand, if the lower group does not exist, the control target devices 6 and 8 are connected with noise. The transmission path devices 6 and 8 located immediately upstream of the generation source are specified, the search result is stored (S380), and this processing is terminated.
[0051]
That is, in the noise source search process, when the noise level is improved by first selecting the transmission line device 6 of the trunk line 4a as the control target device and turning off the gate switches 16 and 26 of the control target device. Since the subsequent search can be limited to each branch line 4b branched from the device to be controlled, the transmission line devices 6 and 8 located immediately upstream of the noise generation source can be efficiently identified.
[0052]
Next, the noise level measurement process that is started in S110, S180, and S340 and executed by the signal measurement unit 54 will be described with reference to the flowchart shown in FIG.
As shown in FIG. 6, when this process is started, first, the measurement mode of the measuring instrument 44 is set to a normal mode for measuring the frequency component of the signal to be measured at a certain time (S410), and in this normal mode, The measuring device 44 is made to analyze the frequency component in the frequency band (10 MHz to 55 MHz) of the upstream signal, and from the analysis result, the noise level at the measurement point (measurement frequency) set in the noise upper limit setting process described later is calculated. The measured value is stored (S420).
[0053]
It is determined whether or not the measurement of the noise level has reached a predetermined number of preset times C (for example, 10 times) (S430). If the predetermined number of times C has not been reached, the process returns to S420 to measure the noise level. On the other hand, when the measured value of the noise level reaches the predetermined number of times C, the average NLav of the measured value is calculated according to the equation (1) (S440), and subsequently, it is determined whether or not the group search is being performed. (S450).
[0054]
[Expression 1]

[0055]
The determination as to whether or not the group search is in progress is performed by starting the processing from S180 and S340, and the transmission path device that is the specific transmission path device or the control target device at that time. When a plurality of subscriber terminals are connected downstream, it is determined that a group search is being performed. Here, the number N of subscriber terminals connected downstream of the transmission line device is assumed.
[0056]
If the group search is not in progress, the average NLav of the measurement values calculated in the previous S440 is set as the noise level NL as it is (S460). On the other hand, if the group search is in progress, the average NLav of the measurement values is set. The value corrected by equation (2) is set as the noise level NL (S470), and this process is terminated.
[0057]
NL = NLav-10 × logN (2)
In the equation (2), the unit of NL and NLav is [dB], and the equation (2) corresponds to the conversion of the average NLav of the measured values into the noise level at one terminal.
[0058]
Next, a noise upper limit value update process periodically executed by the signal measuring unit 54 for updating the noise upper limit value NLmax referred to in the previous S120, S190, and S360 is performed in accordance with the flowchart shown in FIG. explain.
As shown in FIG. 7, when this process is started, first, the measurement mode of the measuring instrument 44 is set to a peak hold mode that holds the maximum level of the measurement result (S510), and measurement is performed for a preset period. The analyzer 44 repeatedly analyzes the frequency components of the upstream signal frequency band (10 MHz to 55 MHz) (S520). At this time, the maximum value for each frequency component during the measurement period is obtained as the measurement result of the measuring instrument 44.
[0059]
Based on this measurement result, a plurality of measurement points are determined from a band that is lower than a preset determination threshold value (S530), and the frequency fm and measurement value NLd of the measurement points are stored (S540). ). Note that the determination threshold value is set to a signal level that can be reliably identified as an empty channel to which no uplink signal is transmitted. The measurement point set in S530 is also used in S420 of the previous noise level measurement process.
[0060]
Then, a value obtained by adding a specified value (for example, 5 dB) as a margin to the stored measurement value NLd is set as the noise upper limit value NLmax (S550), and this process ends.
In this embodiment, S130, S140 (S310 to S380), and S200 correspond to search means in the present invention, and S150 to S190 correspond to noise adjustment means.
[0061]
As described above, in the CATV system of this embodiment, when the noise level of the uplink signal received by the center apparatus 2 exceeds the noise upper limit value, the transmission line 4 in which the noise generation source exists is simply connected to the system. The noise level of the uplink signal received by the center apparatus 2 is less than the noise upper limit value by increasing the attenuation amount of the uplink signal in the transmission line devices 6 and 8 located immediately upstream of the noise generation source. It is trying to become.
[0062]
Therefore, according to the CATV system of the present embodiment, not only can the entire system be affected by such abnormal noise, but also the cable modem located downstream of the noise source when abnormal noise occurs. The upstream signal from the mobile station to the center device 2 is not interrupted. For example, a service using the upstream signal such as a connection service to the Internet via the center device 2 can be continuously provided, and the reliability of the system can be improved. Can be improved.
[0063]
Moreover, in the CATV system of this embodiment, the search for noise sources is performed hierarchically in units of groups, so that the transmission line devices 6 and 8 located immediately upstream of the noise sources can be efficiently identified. Therefore, it is possible to quickly eliminate the deterioration in communication quality due to the increase in inflow noise.
[0064]
Further, according to the CATV system of the present embodiment, when there is a branch terminal Tb to which a service line to a subscriber's house that has contracted only a service by a downlink signal is connected in the branch device 8, a gate corresponding to this branch terminal Tb By setting the switch 26 to OFF and realizing the characteristic indicated by the solid line in FIG. 3C, the service using the uplink signal (for example, Internet connection) is illegally used at the above-mentioned subscriber's house. It can be surely prevented.
[Second Embodiment]
Next, a second embodiment will be described.
[0065]
FIG. 8A is an explanatory diagram showing the internal configuration of the information distribution board 60 installed in the subscriber's home of the bidirectional CATV system.
As shown in FIG. 8 (a), the information distribution board 60 is provided with a distributor 62 that distributes the downstream signals input via the protector to the two systems and mixes the upstream signals from both systems. A booster 64 that bi-directionally amplifies a downstream signal and an upstream signal flowing through the transmission path is connected to one transmission path branched by the distributor 62, and a cable modem is connected to the other transmission path. 66 and a router 68 are connected.
[0066]
8B, the booster 64 has a configuration in which the branch circuit 17 and the status monitor 18 are omitted from the bidirectional amplifier 6 shown in FIG. 2A, and is inserted into the upstream path. The configured gate switch 16 is configured to be operated by a control signal from the outside. In addition, about the component similar to the bidirectional | two-way amplifier 6, the same code | symbol is attached | subjected in a figure, and the description is abbreviate | omitted here.
[0067]
The output of the booster 64 is distributed to a plurality (not shown) and then supplied to an information outlet provided in each room. By connecting a television receiver, a CATV phone, or the like to this information outlet via a set top box, it becomes possible to watch programs and receive a CATV phone service.
[0068]
The router 68 is connected to a plurality of personal computers (personal computers) PCs, enables communication between the PCs, and an arbitrary personal computer PC connected to the router 68 passes through a cable modem 66 via a CATV system. Configured to allow internet connection.
[0069]
Further, the cable modem 66 has a function of analyzing a control signal from the center apparatus 2, similarly to the status monitor 18 of the bidirectional amplifier 6, and sends a control signal (attenuation amount) to the booster 64 via the router 68. (Adjustment signal) can be supplied.
[0070]
In the bidirectional CATV system of this embodiment in which such an information distribution board 60 is installed at the subscriber's home, the booster 64 is handled as a transmission line device equivalent to the bidirectional amplifier 6, the branching device 8, etc. The influence of the noise source can be suppressed to a smaller range, and the reliability of the system can be further improved.
[0071]
Further, in this case, if the gate switch 16 for switching the passage and blocking of the upstream signal of the booster 64 is controlled so as to be turned on only when viewing the viewer participation program or using the CATV phone, the ingress noise Can be reduced more effectively.
[Third Embodiment]
Next, a third embodiment will be described.
[0072]
In the present embodiment, since the configuration of the gate portion 8b of the branching device is only partially different from that of the first embodiment, the description will focus on the different portions.
That is, in this embodiment, as shown in FIG. 9A, the gate unit 8b of the branching device is added to the configuration of the gate unit 8b described in the first embodiment (see FIG. 2B). A gate switch 29 (29a, 29b,...) That switches between passing and blocking of the downstream signal passing through each downstream path between the HPF 24 (24a, 24b,...) And the distribution circuit 22 of each downstream path constituting the downstream group. It has.
[0073]
The added gate switch 29 generates noise via an attenuator 74 on the downstream side (branch terminal Tb) side of the switch element 70 that switches between passing and blocking the downstream signal, as shown in FIG. 9B. The power supply line to the noise generator 72 is provided with a power switch 76 that works in conjunction with the switch element 70.
[0074]
The status monitor 18 is configured to receive a control signal from the center device 2 and generate a switching signal for the gate switch 29 as well as the gate switch 16 in accordance with the control signal.
When the gate switch 29 is turned on to pass the downstream signal, that is, when the switch element 70 is turned on, the power switch 76 is turned off, the noise generator 72 does not operate, and conversely, the gate switch 29 is turned on. When the off setting for passing the downstream signal is turned off, that is, when the switch element 70 is in the off state, the power switch 76 is turned on and the white noise generated in the noise generator 72 is supplied to the branch terminal Tb side. become. Note that the intensity of the white noise to be superimposed may be approximately the same as that of the downstream signal leaked downstream when the switch element 70 is in the OFF state.
[0075]
In the bidirectional CATV system of the present embodiment configured as described above, when the downstream gate switch 29 is set to ON, as shown in FIG. By operating, as shown in FIG. 10A, the same characteristics as in the case of the first embodiment can be realized, so that the same effect can be obtained.
[0076]
Further, in the bidirectional CATV system of the present embodiment, when there is an unused branch terminal Tb of the branching device 8, the gate switches 26 and 29 corresponding to both the upstream and downstream paths are set to OFF. (See FIG. 10 (b)), thereby preventing unauthorized use of the CATV service via this unused branch terminal Tb.
[0077]
In addition, control for such unused branch terminals Tb can be easily realized by remote control from the center device 2.
Furthermore, in this embodiment, even if the isolation of the switch element 70 is insufficient and the downstream signal leaks to the branch terminal Tb, the downstream signal is extracted by the white noise superimposed by the gate switch 29. Therefore, the above-described fraud prevention effect can be further ensured.
[0078]
In other words, when the switch element 70 is in the OFF state, white noise is superimposed on the downstream side thereof, so that the isolation is provided as the switch element 70 constituting the gate switch 29 that switches between passing and blocking the downstream signal. A device that is not so large can be employed, and a device that is extremely effective in preventing fraud as described above can be constructed at low cost.
[0079]
In this embodiment, the distribution circuit 22 corresponds to distribution means, the gate switch 29 corresponds to switch means, the noise generator 72, the attenuator 74, and the power switch 76 correspond to noise superimposition means.
In the present embodiment, the attenuation amount in the gate switches 16 and 26 is set in five stages of on setting (≈0 dB), −3 dB, −6 dB, −10 dB, and off setting (≈−30 dB). Not limited to this, it may be set to 4 levels or less or 5 levels or more, and any value may be set as long as different attenuation amounts can be set at each stage.
[0080]
In the present embodiment, the attenuation amount is changed stepwise, but a variable attenuator capable of continuously changing the attenuation amount may be used. In this case, since the signal is not momentarily interrupted when switching the attenuation amount, the control at the time of switching can be facilitated. Note that the configuration for changing the attenuation may be either electronic or mechanical.
[0081]
In this embodiment, a noise level with a specified margin added to the measured noise level is set as the noise upper limit value. However, C / N necessary for stable data communication (determined from the modulation / demodulation method and operation level) The noise level obtained from the above may be set as the noise upper limit value. For example, in the case of the QPSK method, C / N may be 18 dB or more, so a value that is 18 dB lower than the operation level may be set as the upper limit value.
[0082]
Further, in the present embodiment, the target device search is configured to be performed by group selection. However, each device (terminal) may be directly and individually selected from the downstream side based on the database. .
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a bidirectional CATV system according to an embodiment.
FIG. 2 is a block diagram showing a configuration of a transmission line device.
FIG. 3 is an explanatory diagram showing the configuration and operation of a gate switch.
FIG. 4 is a flowchart showing the contents of noise level adjustment processing.
FIG. 5 is a flowchart showing the contents of noise source search processing.
FIG. 6 is a flowchart showing the contents of noise level measurement processing.
FIG. 7 is a flowchart showing the content of a noise upper limit update process.
FIG. 8 is a block diagram showing an internal configuration of an information distribution board and a booster configuration in the second embodiment.
FIG. 9 is a block diagram showing a configuration of a gate unit of a branching device and a gate switch provided in a downstream path in the third embodiment.
FIG. 10 is an explanatory diagram showing signal passing characteristics at branch terminals.
[Explanation of symbols]
2 ... Center device, 4 ... Transmission line, 6 ... Bidirectional amplifier (transmission path equipment), 8 ... Branching equipment (transmission path equipment), 8a, 17, 27 ... Branch circuit, 8b ... Gate unit, 10, 14, 20 24, high pass filter, 12, 13 amplifying circuit, 11, 15, 21, 25 ... low pass filter, 16, 26, 29 ... gate switch, 18, 28 ... status monitor, 22 ... distribution circuit, 23 ... merging circuit, DESCRIPTION OF SYMBOLS 30 ... Selector, 31-33, 74 ... Attenuator, 42 ... Node switcher, 44 ... Measuring device, 46 ... Downlink control signal sending part, 50 ... Monitoring control apparatus, 52 ... Database, 54 ... Signal measuring part, 56 ... Signal Level adjustment unit, 58 ... Noise level adjustment unit, 60 ... Information distribution board, 62 ... Distributor, 64 ... Booster, 66 ... Cable modem, 68 ... Router, 70 ... Switch element, 72 Noise generator, 76 ... power switch, Tu ... upstream terminal, Td ... downstream terminals, Tb ... branch terminal

Claims (3)

In a bidirectional CATV system in which a plurality of transmission path devices are connected in a transmission path from a center apparatus to a subscriber side terminal apparatus,
If the noise level of the uplink signal received by said center apparatus exceeds a preset noise limit, the center apparatus, a transmission line device located the closest upstream of the noise source as a specific transmission line device By specifying an attenuation amount adjustment signal for adjusting the attenuation amount of the upstream signal in the specific transmission line device so that the noise level is equal to or lower than the noise upper limit value, and superimposing the downstream signal on the downstream signal, While increasing the attenuation for the upstream signal in the specific transmission line equipment,
The signal level of the uplink signal transmitted by the subscriber side terminal device is designated from the center device so that the signal level of the uplink signal received by the center device is within a preset allowable range. A two-way CATV system characterized by automatic adjustment according to the above. A transmission path device connected in a transmission path of a bidirectional CATV system from a center apparatus to a subscriber side terminal apparatus,
A transmission line located immediately upstream of the noise source so that the noise level is equal to or lower than the noise upper limit value when the noise level of the uplink signal received by the center apparatus exceeds a preset noise upper limit value according attenuation adjustment signal that will be superimposed on the downlink signal from the center apparatus to adjust the amount of attenuation for the uplink signal at the device, a signal attenuation means for changing the attenuation amount for the uplink signal to the center apparatus,
Distribution means for distributing the downlink signal from the center device to a plurality of;
Switch means for controlling the passage and blocking of the downlink signal for each distribution path for transmitting the signal distributed by the distribution means in accordance with the switching signal superimposed on the downlink signal from the center device;
In conjunction with the switch means, a noise superimposing means for superimposing white noise on the downstream side of the switch means when the switch means is set to prevent the passage of a downstream signal;
Transmission line equipment characterized by providing A center device of a bidirectional CATV system in which a plurality of transmission line devices are connected in a transmission line to a subscriber side terminal device,
A noise level detection means for detecting a noise level in a frequency band used for transmission of an upstream signal;
When the noise level detected by the noise level detection means exceeds a preset noise upper limit value, a search for a noise generation source is performed to identify a transmission line device located immediately upstream of the noise generation source Means,
An attenuation amount adjustment signal for adjusting the attenuation amount of the uplink signal in the transmission line device specified by the search means so that the noise level detected by the noise level detection means is not more than the noise upper limit value. Noise adjustment means for generating and superimposing the attenuation adjustment signal on the downstream signal and sending it,
Signal level detection means for detecting the signal level of the received upstream signal;
A level adjustment signal for adjusting the transmission level of the upstream signal in the subscriber side terminal device is generated so that the signal level detected by the signal level detection means is within a preset allowable range. Level adjustment means for transmitting the level adjustment signal superimposed on the downstream signal;
A center device comprising:

Images