JPS61198936A - Control signal transmission system for catv optical transmission system - Google Patents

Abstract

PURPOSE:To reduce number of transceivers of a center device by connecting respectively a control signal transmitter and a control signal receiver in common to each subscriber to a couple of transmission/reception terminals of an optical star coupler. CONSTITUTION:The control signal transmitter 14 and the control signal receiver 15 in common to subscriber devices B1-Bn are connected respectively to a couple of transmission/reception terminals of the optical star coupler 18 provided to a control signal transmission/reception system of the center device D. Then an outgoing control signal sent from the center device D to the subscriber devices B1-Bn is transmitted from the control signal transmitter 14 to the optical start coupler 18. Further, an incoming control signal coming from the subscriber devices B1-Bn is led to the control signal receiver 15 for reception through the optical star coupler 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a control signal transmission method for a CATV optical transmission system.

[Technical background of the invention]

In recent years, as one type of information communication system, so-called cable television (Cable TV), which distributes broadcast television signals and various service information to multiple subscriber receivers using optical transmission lines, has become popular.
CATV) optical transmission systems are being developed. Figure 2 shows an example of its configuration.
1 to Bn indicate subscriber devices corresponding to the number of tanks, and C1 to Cn indicate optical cables as optical transmission lines, respectively.

The center device A includes a switching circuit 11 for selecting a desired channel for each subscriber from a plurality of broadcast channels, and a control circuit 12. This control circuit 12 instructs the switching circuit 11 to switch channels, and
It exchanges various control signals with each subscriber device 81 to Bn to confirm, for example, a channel switching request and subscriber monitoring information. The center device A also includes an optical transmitter 1 for each subscriber device 81 to 3n, which converts the video and audio signal of the channel selected by the switching circuit 11 into an optical signal.
31 to 13n, optical transmitters 141 to 14n that convert downlink control signals generated from the control circuit 12 into optical signals, and optical receivers that photoelectrically convert uplink control signals arriving from each subscriber device 81 to Bn. The control circuit 1
Interface circuits (I/F) 161 to 16n and optical multiplexer/demultiplexers 171 to 17n are provided, respectively, for transmitting control signals via a bus under the control of No. 2. The optical multiplexer/demultiplexer 171-17n is connected to the optical transmitter 131-13n.
, 141 to 14n and the subscriber equipment 8
It performs bidirectional optical wavelength multiplexing on the optical signals transmitted from 1 to 3n.

On the other hand, subscribers @[B1-13n are each optical multiplexer/demultiplexer 2
1, an optical receiver 22 that photoelectrically converts the video and audio signals from the center device A that have been demultiplexed by the optical multiplexer/demultiplexer 21;
A television receiver [126] that outputs the video and audio signals obtained by the optical receiver 22 as images and sounds, and an optical receiver 23 that photoelectrically converts the downlink control signal received from the center device 1fA, transmits and receives control signals. The terminal circuit 27 includes a terminal circuit 27, and an interface circuit 25, which transmits signals between the terminal circuit 27 and the optical receiver 23 and optical transmitter 24 for transmitting control signals.

In such a configuration, for example, when a subscriber specifies a broadcast channel on the subscriber device B1, a control signal is emitted from the terminal circuit 27, and this control signal is converted into an optical signal by the optical transmitter 24, and then optically multiplexed and demultiplexed. 21 to the optical cable C1. On the other hand, center mounting! In fA, the control signal is demultiplexed by an optical multiplexer/demultiplexer 171, photoelectrically converted by an optical receiver 151, and then introduced into the control circuit 12 via an interface circuit 161. The control t11 circuit 12 determines the broadcast channel desired by the subscriber from the control signal, and controls the switching circuit 11 to switch according to the result of this determination, thereby switching the desired broadcast channel to the optical transmitter 1.
Connect to 31. As a result, the video/audio signal of the broadcasting channel is converted into an optical signal by the optical transmitter 131 and then guided to the optical multiplexer/demultiplexer 171, where it is combined with the downlink control signal output from the control circuit 12. After being waved, it is transmitted to subscriber equipment B1 via optical cable C1.

As a result, in the subscriber device B1, the video and audio signals are photoelectrically converted by the optical receiver 22 and outputted as video and audio by the television receiver 26.

On the other hand, the downlink control signal that arrives at the same time as the video/audio signal is demultiplexed by the optical multiplexer/demultiplexer 21, photoelectrically converted by the optical receiver 23, and guided to the terminal device 27. As a result, for example, the subscriber device 181 operates. State control is performed.

Similarly, other subscriber devices 82 to Bn can each receive video and audio signals from the center device Δ by exchanging control signals. Also, this system
Since transmission is performed by multiplexing and demultiplexing the video and audio signals and up and down control signals using an optical multiplexer/demultiplexer, it is only necessary to install one optical cable for each subscriber device, and as a result, each signal This has the advantage that the configuration of the transmission path can be simplified compared to the case where a cable is provided for each transmission line.

[Problems with background technology]

However, in such a conventional system, the optical transceiver 1 for control signals is installed in the center device fA for each subscriber device 81 to Bn.
Since 41 to 14n and 151 to 15n are provided to send and receive control signals, the structure of the center device is complicated and tends to increase in size, and it is not possible to easily accommodate an increase in the number of subscribers.

[Purpose of the invention]

The present invention reduces the number of transmitters and receivers by making the control signal transmitter/receiver of the center device common to each subscriber, thereby simplifying and downsizing the configuration of the center device and improving reliability. CA that can easily accommodate expansion of equipment
The object of the present invention is to provide a control signal transmission method for a TV optical transmission system.

[Summary of the invention]

In order to achieve the above object, the present invention provides an optical star coupler in the control signal transmission/reception system of the center equipment, and a common control signal transmitter and a common control signal transmitter for each subscriber at a pair of transmitting/receiving ends of the optical star coupler. 1i11111 signal receiver is connected, and a downlink control signal to be transmitted from the center device to each subscriber device is transmitted from the control signal transmitter to each subscriber device via an optical star coupler, and is received from each subscriber device. Uplink control signals are introduced into and received by the control signal receivers by the optical star couplers.

[Embodiments of the invention]

FIG. 1 shows the configuration of an 0ATV optical transmission system to which a control signal transmission method according to an embodiment of the present invention is applied. In this figure, the same parts as in FIG. 2 are given the same reference numerals and detailed explanations will be omitted.

An optical star coupler 18 is provided in the control signal transmission/reception system of the center device. This optical star coupler 18 is equipped with n pairs of input/output terminals made of optical fibers corresponding to each subscriber device 81 to Bn and a pair of input/output terminals made of optical fibers corresponding to the control circuit 12. The n pairs of input/output terminals are connected to optical multiplexer/demultiplexers 171 to 17n provided in each subscriber device 81 to Bnm, respectively, and the pair of input/output terminals corresponding to the control circuit 12 are connected to the optical transmitter 14 and Optical receivers 15 are connected to each. The optical star coupler 18 equally distributes the optical control signal introduced into each input terminal to all output terminals and outputs the same.

A branching filter 19 is inserted between the optical star coupler 18 and the optical receiver 15, and this branching filter 1
9 prevents the downlink control signal transmitted from the control circuit 12 from being fed back directly to the control circuit 12 via the optical star coupler 18 and the optical receiver 15. In addition, in this system, since the control circuit 12 of the center equipment MA sends and receives control signals to and from all subscriber devices 81 to 3n, some kind of signal distinction must be made between each subscriber device 81 to Bn. However, in this system, paying attention to the fact that the transmission speed of control signals is not so fast at about several Qkbps, the transmission form of downlink control signals and uplink control signals is each configured as a frame as shown in Figure 3. Each subscriber device B is connected to each channel CH1 to CHn.
By allocating 1 to Bn, respectively, control signals are transmitted and received in a time-division manner.

With such a configuration, the control circuit 12 of the center device
The downlink control signal sent to each subscriber device 81 to Bn in a time-division manner according to the frame structure shown in FIG. 3 is as follows:
After being converted into optical signals by the optical transmitter 14, the signals are distributed by the optical star coupler 18 to all-optical multiplexers/demultiplexers 171-17n corresponding to the subscriber devices 81-Bn, respectively. Each optical transmitter 131 to 1 is connected to the optical multiplexer/demultiplexer 171 to 17n.
After being combined with the video/audio signal output from 3n, it is sent to optical cables 01 to Cn. On the other hand, each subscriber bag fllB1 to 8n demultiplexes the control signal arriving via the optical cables C1 to Cn into a video and audio signal by an optical multiplexer/demultiplexer 21, photoelectrically converts it by an optical receiver 23, and outputs the signal. The signal is introduced into the terminal circuit 27 via the interface circuit 25. At this time, the interface circuit 25 is in the gate open state only during the receiving period of the channel to which it is assigned in the transmitted frame. 27
is supplied with only the downlink control signal to itself. On the other hand, the video/audio signal sent simultaneously with the above control signal is sent to the optical multiplexer/demultiplexer 2.
After being demultiplexed by the optical receiver 22, the signal is demultiplexed by the optical receiver 22, and outputted as video and audio by the television receiver 26.

Incidentally, when transmitting a control signal from the center tilD to each subscriber device 81 to Bn, the control signal is sent to the optical star coupler 1.
By distributing the optical cable C1 to
The level of the control signal sent to Cn is lower than that of the video/audio signal, but as mentioned earlier, in the CATV optical transmission system, the control signal does not require high speed, and the optical transmission system of the control signal Since the level difference between the transmission and reception signals can be set larger than that of the video and audio signals, the optical star coupler 18
The reduction in the level of the control signal due to the distribution of the signals does not pose any problem in configuring the system.

On the other hand, the terminal circuits 27 of the subscriber devices 81 to Bn are in an operating state only during the transmission period of the channel to which they are assigned in the transmission frame, and insert uplink control signals such as broadcast channel selection signals during this period. is converted into an optical signal by an optical transmitter 24, and sent from an optical multiplexer/demultiplexer 21 to an optical cable 01 to Cn.
Send to. Then, the center device is connected to the optical cable C.
1 to Cn, the optical multiplexer/demultiplexer 1
It is introduced into the optical star coupler 18 via 71 to 17n. As a result, the above-mentioned upstream control signal is distributed to all output terminals by the optical star coupler 18, and among them, the control circuit 1
The optical receiver 15 is distributed to the output terminal corresponding to 2.
After being subjected to photoelectric conversion, the signal is introduced into the control circuit 12 via the interface circuit 16. At this time, in the optical star coupler 18, the upstream control signal is distributed not only to the output terminal corresponding to the control circuit 12 but also to each of the optical multiplexers/demultiplexers 171 to 17n, so that the downstream control signal is output from the control circuit 12 at the same time. If this is the case, this downlink control signal and the distributed control signal will converge, but since the downlink and upstream control signals have different wavelengths, the convergence will not occur.

In this embodiment, the optical star coupler 18 is provided in the control signal transmission/reception system of the center device, and the optical star coupler 18 transmits the downlink control signal outputted from the control circuit 12 to each optical multiplexer/demultiplexer 171 to Along with distributing to 17n,
Since the uplink control signals arriving from each subscriber device 81 to Bn are sent to the respective terminals and introduced into the control circuit 12, only one optical transmitter and one optical receiver are required for transmitting the control signals. As a result, the configuration of the center device can be significantly simplified and downsized compared to the conventional 1Illt[l signal transmission system, which requires provision for each subscriber device 81 to 13n.

Also, when adding more subscribers, new optical transmitters, optical receivers,
There is no need to add an interface circuit, and the optical star coupler 18 can be replaced with one with more input/output terminals, or an optical star coupler with more terminals can be installed in advance and the extra terminals can be used to combine and demultiplex the additional optical fibers. Since it is only necessary to connect the devices, it is possible to cope with the problem extremely easily, in combination with the ability to reduce the size of the device configuration described above.

Note that the present invention is not limited to the above-mentioned embodiments, and may be modified, for example, by a multiplexing method for control signals (for example, each downlink and uplink control signal may be time-divided and sent instead of being sent by wavelength), The number of input/output terminals of the optical star coupler, the method of combining the control signal and the video/audio signal, etc. can be modified in various ways without departing from the spirit of the present invention.

(Effects of the Invention) As detailed above, according to the present invention, an optical star coupler is provided in the control signal transmission/reception system of the center device, and a common signal for each subscriber is provided at the pair of transmission/reception ends of the optical star coupler. 1IJ1 [1 A signal transmitter and a control signal receiver are connected, and a downlink control signal to be transmitted from the center device to each subscriber device is transmitted from the control signal transmitter to each subscriber device via an optical star coupler, and By introducing and receiving uplink control signals arriving from each subscriber device into the control signal receiver 3 using the optical star coupler, the control signal transmitter/receiver of the center device can be shared by each subscriber. A control signal for a CATV optical transmission system that can reduce the number of transmitters and receivers, simplify and downsize the structure of the center equipment, improve reliability, and easily accommodate the addition of subscriber equipment. A transmission method can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing the configuration of a CATV optical transmission system to which a control signal transmission method according to an embodiment of the present invention is applied.
FIG. 3 is a circuit block diagram showing the configuration of the ATV optical transmission system. FIG. 3 is a schematic diagram showing the configuration of a control signal transmission frame. D...Center device, 81-Bn...Subscriber device, C
1-Cn... Optical cable, 11... Switching circuit, 12
... ill 1 circuit, 131 to 13n... Optical transmitter for transmitting video and audio signals, 14.24... Optical transmitter for transmitting control signals, 15.23... Light for receiving control signals Receiver, 16.25...Interface circuit, 171~
17n, 21... Optical multiplexer/demultiplexer, 18... Optical star coupler, 22... Optical receiver for receiving video and audio signals, 26
...TV receiver IL27...terminal circuit.

Claims (1)

[Claims] The center device and a plurality of subscriber devices are each connected via an optical transmission line, and control signals are exchanged between the center device and each subscriber device, and the center device transmits and receives signals in response to the control signals. In a CATV optical transmission system that transmits video signals desired by each subscriber to each subscriber device,
An optical star coupler is provided in the center device, and a control signal transmitter and a control signal receiver common to each subscriber device are connected to a pair of input and output ends of the optical star coupler, respectively, and the control signal is transmitted from the center device to each subscriber device. The control signal transmitted from the control signal transmitter to each subscriber device via the optical star coupler is distributed and transmitted to each subscriber device, and the control signal arriving from each subscriber device is transmitted to the control signal receiver by the optical star coupler. 1. A control signal transmission method for a CATV optical transmission system, characterized in that it is introduced into and received by a CATV optical transmission system.