JPH08130725A - Catv system - Google Patents

Abstract

PURPOSE: To select all signal source channels by a subscriber without increasing a band width or a modulator when the number of channels to be selected is large. CONSTITUTION: A selection request is issued from the subscriber 112 by a channel transmitter 107 and the contents are data-transmitted to a transmission side by a transmission line 106. On the transmission side, requested channel picture signal sources 101a, 101b,...101e are selected, modulated, superimposed on prescribed carrier waves and transmitted to a subscriber side. The subscriber selects the desired channel from the plural picture signals by a tuner, demodulates it and views it by a television receiver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable television (hereinafter referred to as CATV) system, and more particularly to an economical CA having a simple structure in which a modulator and a used bandwidth are reduced.
The present invention relates to a TV system and an image transmission method.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIG.

The CATV system includes a dendritic transmission system, a star-shaped transmission system, and the like depending on the configuration of the transmission network. The most commonly used dendritic transmission system will be described.

As shown in FIG. 2, the image signal sources 101a, 101b ... 101e of the CATV are modulators 103a, 103b, ...
Different carrier waves are assigned to 103e to perform modulation, and the modulated image signals are mixed and combined by the combiner 105 and sent to the transmission line 106. The various image signal sources 101a, 101b ... 101e are
TV retransmit programs, system guides, pay TV programs,
This is video information and the like.

The image signal transmitted through the transmission line 106 is demultiplexed by the demultiplexer 113 and input to the terminal device.

In the terminal device, the tuner 108
Accordingly, the subscriber selects a channel image signal to be viewed and demodulated by the television receiver 109 to view the channel image.

[0007]

In the CATV system, the usable bandwidth is determined by the frequency characteristics of the transmission equipment and the transmission line used in the system.
When the bandwidth is sequentially allocated to the required bandwidth of one channel, the number of channels that can be transmitted is determined. When the number of transmission channels increases, the bandwidth to be used has to be wide, but the bandwidth is finite. In addition,
There is also a problem that a large number of modulators are required for transportation, and the CATV system becomes large.

The present invention has been made to solve the above-mentioned problems of the prior art. When the number of selected channels is larger than the number of channels that can be transmitted, a transmission line having a wide bandwidth is not used and transmission is performed. It is an object of the present invention to provide a CATV system which requires substantially no additional modulators to be used and allows subscribers to substantially freely select all signal source channels on the transmitting side.

[0009]

In order to achieve the above object, the structure of a CATV system according to the present invention is such that a center device has a plurality of channel image signal sources for transmitting image signals, and the plurality of channel image signals. A plurality of modulators to which carrier waves of different frequencies are assigned, and a combiner to combine a plurality of channel image signals modulated by the modulators. Includes a channel selector for selecting a channel image signal to be viewed and a receiver for demodulating the selected channel image signal and displaying the image, and the center device and a plurality of terminal devices are connected by a transmission line. In the connected two-way CATV system, if the plurality of channel image signal sources are more than the plurality of modulators, the plurality of terminal devices are A channel selection data signal transmitter for the subscriber to select the channel image signal source is provided, and the center device processes the channel selection data signal from the subscriber and the selection by the output signal of the processing circuit. And a selection switcher for selecting a modulator connected to the selected channel image signal source from the plurality of modulators, and transmitting the selection information of the modulator to each of the plurality of terminal devices. It is characterized by.

In summary, that is, the channel selection request is made by the subscriber, and the contents are data-transmitted to the transmitting side.
On the transmission side, the image of the requested channel is modulated, and the modulated image is transmitted on the predetermined carrier wave to the subscriber side. The subscriber selects a desired channel from the plurality of image signals with a tuner, demodulates it, and views it with a television receiver.

In the CATV system described in the preceding paragraph, the selection switch of the center device confirms the channel selection data signal from the subscribers, and only when there is no channel selection signal from all the subscribers, the channel image signal source Is configured to switch the connection between the selected modulator and the selected modulator.

In any of the CATV systems described in the preceding paragraphs, the channel selection data signal transmitter of the terminal device is configured to display selection information of the modulator.

[0013]

The function of each of the above technical means is as follows.

According to the configuration of the present invention, when the channel image signal source N becomes larger than the number Nmax of channels that can be transmitted, that is, when the channel image signal source that can be selected by the subscriber becomes N, Actually, paying attention to the fact that the channel that the viewer always selects is limited, and the channel that the subscriber does not watch often is not connected to the modulator and the unused modulator is selected. Switch and connect to the signal source. In this way,
Even if the bandwidth of the transmission line is not widened, the channel image signal source N larger than the number Nmax of channels that can be transmitted can be substantially freely selected on the subscriber side.

The channel image signal source N can be substantially freely selected on the subscriber side by the number of modulators smaller than that of the channel image signal source N.

Since the selection switcher switches the connection between the channel image signal source and the selected modulator only when there is no channel selection data signal from all the subscribers, the channel of high priority is selected. Images can be viewed.

Since the channel selection data signal transmitter can display the selection information of the modulator, the subscriber can precisely select the desired channel selection.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a bidirectional C according to an embodiment of the present invention.
It is a schematic explanatory drawing of an ATV system. In FIG. 1, the same reference numerals as those in FIG. Only new codes will be described. In FIG. 1, 102
Is a modulator selection switcher, 104 is an image signal switching signal processing circuit (hereinafter, switching signal processing circuit), 107 is a channel selection request signal transmitter (hereinafter,
(Channel selection transmitter), 110 is a channel switching signal line, 111 is a demultiplexer, and 113 is a multiplexer / demultiplexer. A signal from the center apparatus to the subscriber 112 is called a downstream signal, and a signal from the subscriber 112 to the center apparatus is called an upstream signal.

The number of CATV image signals of the signal source is N, the number of channels that can be transmitted is Nmax, N is larger than Nmax, and the number of carriers is the same as the number of channels that can be transmitted, Nmax,
The number of modulators is also the same as Nmax. Each modulator is assigned a different carrier.

In the interactive CATV system according to the embodiment of the present invention, the common parts with the conventional interactive CATV system will not be described again. The description will focus on the characteristic part.

As shown in FIG. 1, in the television receiver 109, the channel No. to be received is selected. , And the channel selection transmitter 107 transmits it as an upstream signal via the multiplexer 113. In the center device, the demultiplexer 111 separates the upstream signal from the downstream signal. The separated channel number. The upstream signal indicating the is decoded by the switching signal processing circuit 104.

Channel N indicating the decoded image signal source
o. Is input to the switch 102 through the channel switching signal line 110 to operate the switch 102.

The switch 102 is configured to operate on the channel N.
o. Image source and unused modulator,
This output is combined with the modulation outputs of other channels and transmitted to the subscriber side.

In this case, the switch 102 connects to the modulator in the order of channel requests from the subscribers. In the center device, information on the modulated carrier used for the selected channel, for example, [Channel No. 1 available]
.. is transmitted to the channel selection transmitter 107 of each subscriber and displayed.

When the number of channels selected from the subscriber side increases and the number of transmittable channels reaches Nmax, a signal indicating that transmission cannot be performed is sent from the center device on the transmission side. ] Is displayed on the channel selection transmitter 107.

On the subscriber side, the information of the modulated carrier for the desired image signal is obtained from the channel selection transmitter 107,
The tuner 1 from among the transmitted modulated carrier signals
08, selection is performed, a selection signal is demodulated, and an image is displayed by the television receiver 109.

When the number Nmax of channels that can be transmitted is reached, a channel image signal source cannot be selected, but in reality the viewer is always relatively limited, and even if the above-mentioned limitation is given. In many cases, there are actually no problems.

When deselecting the channel image signal source, the subscriber performs the deselection operation by the channel selection transmitter 107. When the subscriber performs the cancel operation, the channel selection transmitter 107 transmits the cancel signal as an upstream signal to the transmission path transmitting the channel image signal. In the center device, the signal is obtained from the demultiplexer 111, transmitted to the switching signal processing circuit 104, and the same procedure as when selected is performed.

Since it is possible that many subscribers have registered the channel selection, the switching signal processing circuit 104
Always checks the status of registration, and only when all the subscribers cancel the channel selection, the switch 102 is operated to disconnect the channel.

[0031]

As described in detail above, according to the present invention, when the number of selected channels is larger than the number of channels that can be transmitted, a modulation line used for transmission is used without using a transmission line having a wide bandwidth. It is possible to provide a CATV system in which all the signal source channels on the transmission side can be substantially freely selected by the subscriber without the need for additional equipment.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an interactive CATV system according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view of a conventional CATV system.

[Explanation of symbols]

 101a, 101b, ... 101e Image signal source 102 Modulator connection switching device 103a, 103b, ... 103e Modulator 104 Switching signal processing circuit 105 Combiner 106 Transmission line 107 Channel selection transmitter 108 Tuner 109 Television receiver 110 Channel switching signal line 111 Demultiplexer 112 Subscriber 113 Combine / Demultiplexer

Claims (3)

[Claims] 1. A center device comprises: a plurality of channel image signal sources for transmitting image signals; a plurality of modulators to which carrier waves of different frequencies are allocated for modulating the plurality of channel image signals; and the modulator. A plurality of terminal devices, each of which includes a channel selector that selects a channel image signal that the subscriber wants to watch, and a plurality of terminal devices that combine the selected channel image signals. In a bidirectional CATV system comprising a receiver for demodulating and displaying an image thereof, wherein the center device and a plurality of terminal devices are connected by a transmission path, the plurality of channel image signal sources are the plurality of modulators. If there are more, each of the plurality of terminal devices is provided with a channel selection data signal transmitter for the subscriber to select the channel image signal source, and In the switching device, a processing circuit for processing a channel selection data signal from the subscriber and a modulator connected to the selected channel image signal source by the output signal of the processing circuit are selected from the plurality of modulators. A CATV system, comprising: a selection switcher for selecting and transmitting the selection information of the modulator to each of the plurality of terminal devices. 2. The CATV system according to claim 1, wherein the selection switch of the center device confirms the channel selection data signal from the subscribers, and only when there is no channel selection signal from all the subscribers, A CATV system characterized in that the connection between the channel image signal source and the selected modulator is switched to another. 3. The CAT according to claim 1 or 2.
In the V system, the channel selection data signal transmitter of the terminal device is configured to display the selection information of the modulator, and the CATV system.