JP3377921B2 - Optical coaxial hybrid CATV system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coaxial hybrid CATV system using an optical fiber and a coaxial cable in the same system. 2. Description of the Related Art Television joint reception facilities are widely used to take measures against difficult-to-view television areas, radio interference areas caused by high-rise buildings, and to improve additional services similar to television broadcasting. ing. In recent years, this television joint receiving facility has been particularly adapted to multimedia, and accordingly, a wider band is required. Moreover, the transmission loss of the optical fiber is 0.3 km per km.
Since the transmission distance is as low as around dB, there is no need to amplify even if the transmission distance extends over a long distance.Moreover, since the transmission signal is light, it is not easily affected by lightning and other electromagnetic noise. The construction of an optical coaxial hybrid CATV system that employs optical fibers as part of a network is increasing in a joint receiving facility that is separated from a point to a subscriber crowding point. [0003] The basic configuration is such that an optical terminal, which converts an optical signal transmitted via an optical fiber into an electric signal and supplies it to a network, branches off one after another at the apex, as if branching from a tree trunk to the sky. This is a dendritic network, and the amplifier used in the network is mainly a distribution type amplifier. In other words, when branching from the middle of the network, it always branches into a trunk line and a distribution line. [0004] However, if the basic configuration of the network is a dendritic network having an optical terminal at the top,
From one branch point to the next branch point, the mains cable connecting between them and the branch cable extending in the same direction from the branch point will overlap, so especially in an urban area, the lashing of the overlapping cables into one bundle There are many sections, and both material costs and man-hours increase, which contributes to a rise in construction costs. Also, because of the adoption of a dendritic net, the cable used for it tends to have a large capacity as it goes upstream. FSK and PS as status monitor functions
Since analog value transmission by K is adopted, there are many malfunctions and there is a problem in transmission quality. The present invention solves the above problems by the following means. <Configuration 1> A head end provided with a photoelectric converter for converting a television signal into an optical signal, an optical terminal for converting an optical signal received from the head end via an optical cable into an electric signal, and an optical terminal A plurality of coaxial cable trunks connected to each other to form a network, the optical terminal branching and outputting the television signal to the plurality of coaxial cable trunks, wherein the coaxial cable trunk is a signal flowing through the trunk. To
An extension amplifier for relay amplification, and one of the signals flowing through the trunk line.
Tap-off to take out the part from the middle and distribute it to subscribers
No distribution amplifier for branching the trunk line
An optical coaxial hybrid CATV system comprising a self-supporting cable . <Structure 2> In structure 1, the network includes an uplink pilot signal generator, and the pilot signal generated by the pilot signal generator transmits a status signal output from a sensor for monitoring the state of each part of the network. An optical coaxial hybrid CATV system characterized by being modulated by: <Structure 3> An optical coaxial hybrid CATV system according to Structure 1, wherein a self-supporting coaxial cable trunk is used. <Structure 4> An optical coaxial hybrid CATV system according to structure 1 or 3, characterized in that no distribution amplifier is used for the coaxial cable trunk line. <Structure 5> In Structure 1, 3 or 4,
An optical coaxial hybrid CATV, wherein a coaxial cable is branched in a star shape at the end of a coaxial cable trunk line.
system. Embodiments of the present invention will be described below with reference to specific examples. FIG. 1 shows an optical coaxial hybrid C according to the present invention.
It is a schematic block diagram of the whole joint receiving facility of an ATV system. An optical coaxial hybrid CATV system according to the present invention includes an antenna 1, a head end 2, an E / O3,
It comprises an optical terminal 4, an extension amplifier 5, a branching device 6, an optical cable 7, and trunk lines 8, 9, 10, and 11. In FIG. 1, an antenna 1 is an optical coaxial hybrid C according to the present invention.
An antenna that receives television broadcast waves transmitted to the ATV system. Generally, for low channels (1 to 4 channels), for high channels (6 to 12 channels),
Three antennas for UHF are used. The head end 2 is a device that converts the frequency of a television broadcast wave received by the antenna 1, selects a required channel, and amplifies the channel to a set level. In some cases, it has the role of modulating a television signal such as a self-produced program into a signal form suitable for the network and outputting the signal. In other words, it is a central device of the network. E / O (electric / optical) converter 3
Is a device that is configured by a laser diode and converts an electric signal to an optical signal, and is a device that converts an upstream signal from a network from an optical signal to an electric signal using a photodiode. The optical terminal 4 converts an optical signal received via the optical cable 7 into an electric signal, branches the signal into a number equal to the number of trunk lines, amplifies the signal to a specified value, and sends the amplified signal to the trunk line of a network constituted by coaxial cables. It is a device that does. Furthermore, it also has a function of converting an upstream signal from the network into an optical signal and transmitting the optical signal to a head end via an optical cable. The extension amplifier 5 is a device that relays and amplifies signals flowing through the trunk lines 8, 9, 10, and 11, and is generally used with one input and one input.
Output is standard (with some exceptions). The branching device (tap-off) 6 has a role of extracting a part of the signal flowing through the trunk lines 8, 9, 10, and 11 and distributing it to the subscriber, and is essentially different from a distribution amplifier that branches the trunk line, and is generally different from the distribution amplifier. Is a device that does not have an amplification function. The optical cable 7 comprises a head end 2 and an optical terminal 4
An optical fiber cable that connects a plurality of single mode fiber cores for transmitting only a single mode of light is generally used. Trunk lines 8, 9, 10,
Reference numeral 11 denotes a trunk cable through which the optical-to-electrical converted signal is transmitted by the optical terminal station 4. Further, the coaxial cable has a function of distributing a DC power required by a device constituting the network, for example, an extension amplifier or the like, to an AC voltage of several tens of volts to distribute the power. The optical terminal 4 is configured as follows. FIG. 2 shows an optical coaxial hybrid CATV according to the present invention.
It is a block diagram of the optical terminal for systems. The optical terminal 4 includes an extension amplifier 5, a downlink 7A, an uplink 7B, an O / O
An E12, an E / O 13, a branch / coupling circuit 14, and a duplex filter 15 are provided. The extension amplifier 5 is a device having the same function as described above. The downlink 7A and the uplink 7B are optical fibers for a downlink signal and an uplink signal, respectively, and constitute the optical cable 7. The O / E 12 is a converter for converting an optical signal transmitted through the optical cable 7 into an electric signal, and is constituted by a photodiode. E / O13
Is a converter for converting an upstream signal from the branching / coupling circuit 14 into an optical signal, and is constituted by a laser diode. In FIG. 1, the television broadcast signal is
It is received by an antenna 1 installed on a small hill, frequency-converted and selectively amplified by a headend 2, and further converted from an electric signal to an optical signal (E / O conversion) by a photoelectric converter 3, and generally, Is guided to the subscriber densely populated area via the optical cable 7 extending over several kilometers and transmitted to the optical terminal 4. The television broadcast signal is converted into an electric signal by an O / E converter 12 in the optical terminal 4, distributed in a plurality of directions by a branching / coupling circuit 14, and having a predetermined level by a plurality of built-in extension amplifiers 5. It is amplified until. After that, the multiple trunk lines 8, 9, 10, 11, directed in each direction,
Is output to Each one becomes a trunk line of one network. This network does not distribute trunks,
It comprises trunks 8, 9, 10, 11 extending straight, an extension amplifier 5, and a tap-off 6 for branching a signal to each subscriber. Next, the optical coaxial hybrid CATV of the present invention.
A status monitor function for monitoring the operation state of the system will be described. FIG. 3 is a diagram showing a status monitor of the optical coaxial hybrid CATV system according to the present invention. Usually, it is provided in the extension amplifier 5. However, it is of course possible to equip it separately from the extension amplifier. The main components responsible for this function are a duplex filter 15, an amplifier circuit 16, an up signal gain control (AGC) 17, and a down signal gain control (A
GC) 18, an upstream pilot signal generator 19, a downstream pilot signal disconnection sensor 20, a lid opening / closing sensor 21,
It comprises a water immersion sensor 22, a power failure sensor 23, a low battery sensor 24, a sensor 25 without battery operation, an input terminal 26, and an output terminal 27. The duplex filter 15 is a filter for separating the upstream and downstream signals to the extension amplifier 5, and is composed of a high-pass filter for passing the downstream signal and a low-pass filter for passing the upstream signal, and is conventionally used in amplifiers and the like. . The amplification circuit 16 is a circuit that amplifies an up signal and a down signal. Up signal automatic gain control 17
Is a circuit for automatically controlling the level fluctuation of the up signal, and the down signal gain control 18 is a circuit for automatically controlling the level fluctuation of the down signal. The upstream pilot signal generator 19 is an oscillator built in the extension amplifier 5. The downstream pilot signal disconnection sensor 20 is a sensor that monitors that the downstream pilot signal is operating normally. The lid opening / closing sensor 21 is a sensor for monitoring the opening / closing of the lids of the devices in the network to protect the devices from, for example, wind and rain. The water immersion sensor 22 is a sensor that monitors water immersion inside the device. Power failure sensor 2
Reference numeral 3 denotes a sensor that monitors a power failure of a specific device. The battery low sensor 24 and the battery non-operation sensor 25 are sensors for monitoring whether or not a battery provided in an uninterruptible power supply or the like in the network is operating normally. The above-described sensor is one specific example, and can be changed to a sensor that monitors other items at the request of the network. The input terminal 26 and the output terminal 27 are input / output terminals for the downstream video signal in the network with respect to the extension amplifier. Here, the pilot signal is a change in the environment of the equipment constituting the network, for example, the attenuation of the coaxial cable is different due to the difference in temperature between summer and winter, so it is necessary to change the amplification of the amplifier. This is a reference signal. Further, the status signal is a signal for informing the head end or a separately provided observation point whether or not the equipment in the integrated optical terminal 4 is operating normally. Next, the status monitor function will be described with reference to FIG. The uplink pilot signal generator 28 has a network uplink signal band of 10 MHz to 56 M in a normal state.
Frequency of 54.75MHz to 56MHz is 25KHz
It oscillates at a frequency allocated to a number of extension amplifiers 5 in the network at intervals. When the down pilot signal disconnection sensor 20, the lid opening / closing sensor 21, the flood sensor 22, the power failure sensor 23, the battery voltage drop sensor 24, and the battery 25 do not operate, and the sensor 25 detects an abnormality, the sensor operates according to each abnormal state. When a part of the signal of the upstream signal gain control 17 in the extension amplifier 5 is input to the upstream pilot signal generator 19 and a part of the AGC signal is input, the carrier (pilot) is determined by a signal predetermined for each abnormal situation. Signal). The modulated signal becomes an upstream signal, is converted into light through the optical terminal, and travels to the head end through the upstream line. <Effects of Specific Example> As described above, in the optical coaxial hybrid CATV system of the present invention, the trunk cable is divided into a plurality of branching directions in the branch circuit in the optical terminal, and a plurality of distribution directions facing one to one. Extend. Each of them forms one network and consists of a coaxial cable, an extension amplifier, and a tap-off for branching the signal to each subscriber without extending the trunk line in the middle, so that the cable overlap is small and the lashing section is small. Become. Therefore, it is possible to suppress a rise in construction costs. Further, since the distribution network using the coaxial cable is unified, the transmission capacity of the coaxial cable can be reduced, and a thinner cable can be used as compared with the conventional system, and as a result, it corresponds to a trunk line. Since a self-supporting type, which is easy to lay, can be adopted for the coaxial cable portion, the construction period can be shortened and construction costs can be prevented from rising. In addition, since the system does not use an expensive trunk distribution amplifier at all, the construction cost can be reduced. In the above specific example, the optical cable is just branched in a star shape. However, the same effect can be expected even if another coaxial cable is branched in a star shape at the end of the coaxial cable. Further, a signal generated from an uplink pilot signal generator included in a device in the network (in a specific example, in an extension amplifier) is used as a carrier wave and modulated by a status signal generated by each sensor, thereby also having a status monitor function. ing. Therefore, when an observation is made at the head end or at an observation point provided in the middle of the path, the frequency and the modulation waveform are read, so that the abnormal location and the cause of the abnormality can be easily known.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of an entire joint receiving facility of an optical coaxial hybrid CATV system according to the present invention. FIG. 2 is a block diagram of an optical terminal used in the optical coaxial hybrid CATV system according to the present invention. FIG. 3 is a status monitor of the optical coaxial hybrid CATV system according to the present invention. [Description of Signs] 1 antenna 2 head end 3 E / O 4 optical terminal station 5 extension amplifier 6 branch unit 7 optical cable 8, 9, 10, 11, 12 optical downlink 13 optical uplink 16 duplex filter 19 extension amplifier 21 trunk line

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masayoshi Okubo 1-39-9, Higashishinagawa, Shinagawa-ku, Tokyo Inside Nihon Electric System Construction Co., Ltd. (56) References JP-A-8-1111663 (JP, A) JP-A-6-292038 (JP, A) JP-A-7-170244 (JP, A) JP-A-63-178976 (JP, U) Hiroshi Sugioka et al., Evaluation of optical access network migration method, NTT R & D, Japan, The Telecommunications Association, December 10, 1995, Vol. 44, no. 12, p. 33-38 Yasushi Hamada et al., Optical Transmission Equipment, NEC Technical Report, Japan, NEC Creative Co., Ltd., September 25, 1996, Vol. 49, No. 8, p. 21-26 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 JICST file (JOIS)

Claims (1)

(57) [Claims 1] A head end provided with a photoelectric converter for converting a television signal into an optical signal, and an optical signal received from this head end via an optical cable is converted into an electric signal. An optical terminal, and a plurality of coaxial cable trunks connected to the optical terminal to form a network, the optical terminal branching the television signal to the plurality of coaxial cable trunks and outputting the television signal; The coaxial cable trunk repeats and amplifies the signal flowing through the trunk.
Extension amplifier and part of the signal flowing through the trunk line
With tap-offs to take out and distribute to subscribers,
Self-supporting without distribution amplifier for branching
An optical coaxial hybrid CATV system, comprising a holding cable .