JPH0120583B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to video telephones that form a local area network and communicate with each other.

Conventional configurations and their problems Two-way wired television broadcasting equipment that uses coaxial cables as a transmission path usually focuses on simultaneous rebroadcasting, and is mainly a system in which multiple stations receive external television broadcasting. It was hot. Therefore, to compensate for losses during transmission, an amplifier is connected in the middle of the coaxial cable to ensure a constant signal level.

However, in videophones that enable mutual communication between stations, each videophone station uses its own communication channel (hereinafter referred to as a communication line) to have a bidirectional function, and transmits each other's video and video. Sending and receiving audio. In this case as well, there is a transmission loss in the coaxial cable interposed between the video telephone stations, and this loss varies depending on the passing frequency value. Generally, as shown in FIG. 1, as the operating frequency (hereinafter referred to as frequency) increases, the amount of attenuation (hereinafter referred to as transmission loss) increases, and as a result, the reachable distance decreases. On the other hand, as the frequency becomes lower, the transmission loss becomes smaller, and as a result, the transmission distance becomes larger.

Therefore, each video phone station mentioned above uses its own communication line when making calls to each other, and there is no problem if both sides use nearby frequency bands, but one side uses a higher frequency band. If one uses a lower frequency band and the other uses a lower frequency band, the signal levels from both sides will differ, and the station receiving the signal sent using the higher frequency band will not have sufficient sensitivity and will be unable to communicate with each other. There was a problem that caused problems.

OBJECT OF THE INVENTION The present invention eliminates the conventional drawbacks as mentioned above,
The purpose of this system is to enable video telephone stations that communicate in both directions using a single coaxial cable to communicate efficiently with each other.

Structure of the Invention In the present invention, a plurality of channels are set and stored for each station to be transmitted, taking into consideration transmission loss corresponding to the distance between videophone stations, and when transmitting, these channels are set and stored. By using one channel selected from a plurality of channels, a signal level always above a certain level (hereinafter referred to as a "good quality signal") is always ensured, and sufficient sensitivity is ensured on both sides. The local network is designed to have no problems with mutual communication.

Description of an Embodiment Mutual communication within a videophone connected on a bus network is performed when videophone stations possessing a large number of channel frequency bands communicate with each other simultaneously in a trackless combination. Combinations that result in a large amount of transmission loss occur, resulting in a situation where sufficient communication is no longer possible. Therefore, a long-distance communication countermeasure device (hereinafter referred to as a control center) is provided to search for an unused frequency band (hereinafter referred to as an empty channel) in which a high-quality signal capable of communication is secured within the occupied frequency band.

First, we measured and investigated the distance between video telephone stations connected to the bus network and the transmission loss for each frequency band used for all video telephone stations.
Based on this, a table of relative distances between videophone stations is created and stored. When a call request is made in response to a call request command issued by a calling station, a channel frequency band (hereinafter referred to as a call line ) are registered in correspondence with the distance between video telephone stations, and an empty channel is automatically searched from among them to provide a high-quality signal and enable smooth communication.

By having the above-mentioned functions, smooth mutual communication is possible by automatically covering transmission loss.

An embodiment of the present invention will be described below with reference to the drawings. Figure 2 is a block diagram of a videophone connected to a bus network.
The numbers are chain data created by measuring and surveying the installation locations of TV stations in advance.
is registered in the ROM, and when a communication request is made to the other station (hereinafter referred to as B station) by a communication request command from the originating station (hereinafter referred to as A station), the position of A station is set to X coordinate = 2 (hereinafter referred to as , X=2).
On the other hand, if the location of station B is set to the X coordinate = 10 (hereinafter referred to as X = 10), the control center will form a communication line that ensures a high quality signal based on the chain data between To achieve smooth communication, an empty channel that allows mutual communication is automatically searched from a communication line table (hereinafter referred to as a table) corresponding to the distance between video telephone stations that can be used.

That is, when communicating by sending a calling signal from station A 16 to station B 17 in the block diagram of the video telephone station shown in FIG. Upon manual input, the data control circuit 13 generates a communication request signal to the B station 17. The control center 7 obtains the position of B station Activates the specified channel frequency generation circuit from inside. This results in B
A suitable communication line is established for communication with station 17.
In this state, the video camera 10 and the microphone 11 send out signals, and the modulator 6 and the
The own station monitor 12 monitors to see if the image is appropriate. The above-mentioned call request signal to the B station 17 is output to the transmitting circuit 4, superimposed by the combiner 3, and sent to the B station 17 via the bidirectional distributor 2 and the coaxial cable 1.

On the other hand, the B station 17 uses coaxial cables 1a, 2a,
A call request signal from station A 16 is sent to data control circuit 13a through 3a. By decoding this communication request signal, station B 17 learns that a call is requested from the own station identification number in the data control signal. Along with this, the data control circuit 1
The channel selection circuit 8a is activated by the control voltage of 3a, and A
Outputs a tuning command to the selection circuit 9a so as to receive the frequency value transmitted from the station 16,
The image is received by the channel selection circuit 14a. As a result, station A 1
A communication line between station B 6 and station B 17 is established.

Subsequently, in order for the B station 17 to start a conversation with the A station 16, the data control circuit 13a of the B station 17 generates an answer call signal. Then, the control center 7a determines that X=2 of the A station 16 from the chain data.
RF converter 5a automatically searches the table for a communication line that can secure a high-quality signal and activates a specified channel frequency generation circuit from among the plurality of channel frequency generation circuits included in the RF converter 5a. The back signal is superimposed and transmitted to station A via coaxial cables 4a, 3a, 2a, 1a, 2, 3, and 4. The data control circuit 13 of the A station 16 decodes the received answer back signal, learns the channel frequency value used, generates a control voltage to operate the channel selection circuit 8, and decodes the received answer back signal from the B station 17. The selection circuit 9 tunes to the received frequency value, and the video signal is received at 14.

As described above, it has become possible to search for a frequency to be used on a communication line that is commensurate with the transmission loss corresponding to the distance between the video telephone stations, and to ensure sufficient sensitivity on both sides for mutual communication.

Below, C station 18, D station 19, E station 20, F station 2
1, G station 22, and H station 23 also have similar functions and can realize mutual communication.

Note that when station A calls station B, if station B is busy with another station, no answer call signal is sent from station B, so communication cannot be established.

Effects of the Invention As described above, according to the present invention, by selecting the frequency used for bidirectional communication between two stations according to the communication distance described above, communication lines can be adjusted in response to transmission loss. It is possible to achieve high-quality communication on a bus network and provide flexibility in expanding videophone services.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram of a bus network of an example of a videophone, and FIGS. 2 and 3 are block diagrams of a videophone having a long-distance call countermeasure device (control center) according to an embodiment of the present invention. . 1, 1a... Coaxial cable, 2, 2a... Bidirectional distributor, 3, 3a... Distributor and combiner, 4, 4a... Signal transmitting/receiving circuit, 5, 5a... RF converter,
6, 6a... Modulator, 7, 7a... Long distance call countermeasure device (control center), 8, 8a... Tuning selection circuit, 9,
9a... selection circuit, 10, 10a... video camera,
11, 11a... Microphone, 12, 12a...
Local station monitor receiver, 13, 13a...Data control circuit, 14, 14a...Other station monitor receiver, 1
5, 15a...Tuition selection operation circuit, 16...A TV phone station, 17...B TV phone station, 18...C TV phone station, 19...D TV phone station, 20...E TV phone station, 21 ...F station video telephone station, 22...
G station video phone station, 23...H station video phone station.

Claims (1)

[Claims] 1. Connect multiple video telephone stations to the same coaxial cable, configure them so that signals can be transmitted and received between each station, and provide each station with a A plurality of channels selected from a low frequency band for a long distance and a high frequency band for a short distance are set and stored in the storage means, and when transmitting a signal, the signal is transmitted and received. By inputting the identification number of the target station, one of the plurality of channels set for the target station and stored in the storage means is selected, and the video to be transmitted is transmitted on the frequency corresponding to that channel. A videophone characterized by modulating the signal and transmitting it to the other party's station.