JPS6319992A - Two-way CATV system - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a data transmission system in a two-way CATV system.

2. Description of the Related Art A distribution network generally used in a conventional two-way CATV system is a dendritic distribution network as shown in FIG. In such a distribution network, a center device 501 and each terminal device 5 such as a pay TV system or an automatic meter reading system are used.
Bidirectional data transmission using a bidirectional transmission path is generally performed between 02 and 02. In such a system, 1
A floor device 502 for the enemy from Keisen to the two center devices 501
is connected, generally a polling method is adopted, and an RF modem and a center computer for this purpose are installed in the center device, and a communication control circuit using an RF modem and a microcomputer is installed in the terminal device 502. has been done.

FIG. 6 shows a configuration example of a bidirectional data transmission system in a general bidirectional CATV system. Further, FIG. 7 shows an example of a frequency arrangement of a general two-way CATV system.

In FIG. 6, transmission data 603 to a terminal device created by a center computer 601 in a center device 600 is modulated by an RF modem 602, and then sent as a downlink data signal within the lower υ band shown in the frequency arrangement of FIG. A trunk cable 605 constituting a dendritic distribution network is output. The lower data signal from the center device 600 outputted to the trunk cable 605 is amplified to the required level by the bidirectional trunk amplifier 614, and then sent via the branch line 606 from the branch output of the bidirectional trunk amplifier 614. Then, it passes through a tap-off 607 installed on the branch line 606 and a lead-in line 608, and is led to a terminal device 609.

The downlink data signal from the center device 600 that has entered the end terminal device 609 is demodulated by the RF modem 61o, and then input as received data 612 to the communication control device 611. Received data 61 within the communication control device 611
2 is performed, and if the data is addressed to itself, the communication control device 611 sends the transmission data 613 as response data.
is output. The output transmission data 613 is input to the RF modem 610, and after being modulated, it is transmitted as shown in FIG.
The uplink data signal within the uplink band shown in FIG. Branch line 606. Bidirectional trunk amplifier 614.
The upstream data signal is input to the RF modem 1602 in the center device 600 via the trunk cable 605, and after demodulating, the upstream data signal is input as received data 604 to the center computer 601 and processed.

In general, in a two-way CATV system, as described above, a large number of terminal devices are connected to one center device via a dendritic distribution network, so a polling method is adopted as a communication control method. Therefore, the center device 6
An address number indicating the destination of the data is inserted into the transmission data 603 output from 00, that is, the data of the downlink data code, and the communication control device 61 in the terminal device 609
1, the address number is detected from the received data 609, and only the terminal device whose address number matches its own outputs the transmitted data 613 as a response signal. As is clear from the above description, by sequentially changing the address numbers output from the center device, bidirectional data transmission is performed between all the terminal devices and the center device as shown in FIG.

However, bidirectional C using such a dendritic distribution network
In bidirectional data transmission within an ATV system, as has been said in the past, noise aggregation in the upstream band is a major problem. This noise stream is the fifth
As is clear from the figure, this occurs because signals in the upstream band from all branch lines and drop-in lines are amplified by the bidirectional main line amplifier and concentrated at one point in the center equipment, resulting in noise aggregation. The causes include internal noise of the upstream amplifier in the bidirectional trunk amplifier, terminal noise from the RF modem, etc. in the terminal equipment, thermal noise from the terminating resistor, cracks in the drop-in line, and tightening of the connector part. This is due to external noise from amateur radio, etc. due to poor contact, etc. As a result of all of the noise in the uplink band caused by these various factors concentrating at the center, the noise level increases at the center equipment, causing problems in the transmission of uplink data signals from the terminal equipment. be.

Problems to be Solved by the Invention However, the conventional method is not suitable for various services using broadband bidirectional transmission lines in urban CATV systems, which are expected to become popular in the future, such as automatic meter reading for gas, electricity, water, etc. This poses a major obstacle to the development of systems and services that use bidirectional data transmission in bidirectional CATV systems, such as security services such as disaster prevention and crime prevention.

The present invention eliminates the upstream noise inflow problem that conventional two-way zero ATV systems have, and enables stable two-way data transmission in a two-way CATV/stem using a dendritic distribution network using coaxial cables. Furthermore, the present invention provides a bidirectional data transmission method in a bidirectional CATV system that can be carried out without any modification to the terminal devices and center devices used in conventional automatic meter reading and security systems.

Means for Solving the Problems In the present invention, a frequency conversion circuit is provided at the branch output section of a conventional bidirectional main line amplifier, and the upstream data signal in the upstream band inputted from the branch line output is converted into the upstream data signal in the downstream band. To perform highly reliable and stable two-way data transmission with almost no noise transfer in a two-way CATV system by converting the frequency into a frequency-converted data signal and reproducing and relaying the frequency-converted data signal to the terminal portion of each trunk cable. This is a method that makes it possible.

Effect: The present invention uses the method described above to provide various services using bidirectional data transmission technology in a bidirectional CATV system, such as automatic meter reading and security services, without changing the center device or terminal device using the conventional method. , can be easily done.

Embodiment An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a system configuration diagram according to the present invention, FIG. 2 is a diagram showing the configuration of a bidirectional main line amplifier used in the present invention, and FIG. 3 is a diagram showing the configuration of a bidirectional main line amplifier used in the present invention. 4 is a diagram showing the configuration of the repeater 107, and FIG. 4 is a diagram showing the configuration of the repeater 107, and FIG.
FIG. 7 is a diagram showing the frequency arrangement in the trunk cable of the system, and the frequency arrangement in the branch line will be explained using FIG. 7 used in explaining the conventional example.

In FIG. 1, the center transmission data 103 created by the center computer 201 in the center device 100 is sent to the trunk cable 105 as a downlink data signal by the center RF modem 102 at a frequency determined by the system within the downlink band in FIG. is output. The downlink data signal output to the trunk cable 106 is input to the bidirectional trunk amplifier 106. That is, in FIG. 2, the downlink data signal input from the main line input/output terminal 200 is divided into lower band and uplink signals by the splitter 202, and only the downlink signal is extracted as the downlink band output 202, After being amplified to a predetermined level by the amplification device 203,
It is input to the directional coupler 204. Bidirectional trunk amplifier 106 and terminal device 110 are connected via tag-off 108 .

The output A206 of the directional coupler 204 is the directional coupler 20
6 and its output 207 is passed through the branching filter 208, outputted from the other main line input/output terminal 209, and relayed to the next stage bidirectional main line amplifier. On the other hand, the directional coupler 20
4 output B213 passes through the splitter 214 and outputs the branch line output 2.
16. In this way, the downlink data signal output from the bidirectional trunk amplifier 106 in FIG. Further, the frequency arrangement of the branch line 116 is exactly the same as that shown in the conventional example, as shown in FIG.

Below, the downlink data signal input to the terminal device 11o is demodulated by the terminal RF modem 112, as described in the conventional example, and inputted to the communication control device 111 as the terminal reception data 113, and the terminal transmits the signal. data 114
When the signal is output, it is modulated by the terminal RF modem 112, and then follows a path completely opposite to that of the above-mentioned downlink data signal.
Bidirectional main line amplifier 1 as an upstream data signal shown in FIG.
06. That is, in Fig. 2, branch line output 2
In a conventional system, the uplink data signal input from 15 would be transmitted through a directional coupler, from the upstream band amplifier 212 to the trunk input/output terminal 200, and then to the center device. In this system, the upstream data signal input from the main line input/output terminal 215 is sent to the branching filter 2.
14, the upstream band signal is demultiplexed, and the demultiplexer output 216
The signal is inputted to the bandpass filter 217 as a signal, and a signal in the frequency band of the uplink data signal is extracted from within the uplink band. The bandpass filter output 218 is a frequency converter 219
The frequency converter 219 converts an upstream data signal from a terminal device within the upstream band into a signal within the downstream band.

That is, at the branch line output 216, the upstream data signal within the upstream band as shown in FIG. 7 is frequency-converted as a signal within the downstream band as shown in FIG. 4, and then becomes a converted upstream data signal. The frequency converter output 220 having the converted upper 9 data signal is again combined with the lower band signal from the main line input/output terminal 200 by the directional coupler 206 and demultiplexed as the directional coupler output 207. 208.

As is clear from the above description, in addition to the lower data signal from the center device 100, the converted uplink data signal obtained by frequency-converting the uplink data signal from the terminal device 110 is added to the trunk input/output terminal 209. The frequency of the converted upstream data signal may be any frequency determined by the system as long as it does not overlap with the downstream data signal, and this does not impose any limitations on the present invention. The signal output from the trunk input/output terminal 209 passes through the trunk cable 116 shown in FIG. M1 and reaches the end of the trunk cable 116. Trunk cable 1
A regenerative repeater 107 is connected to the terminal of the regenerative repeater 107, which demodulates the converted uplink data signal in FIG. The signal is looped back to the trunk cable 116 as a data signal. That is, the signal inputted from the input/output terminal 300 of the regenerative repeater shown in FIG. A baseband data signal is output. The demodulator output 302 is exactly the same as the terminal transmission data 114 in the A floor unit 110 shown in FIG. The converted upstream data signal demodulator 301 performs demodulation to remove noise mixed in the intermediate upstream band, such as the drop-in line 109 or the branch line 115.

Note that, if necessary, the baseband demodulator output 302 may be resampled or the like. The demodulator output 302 is input to the modulator 303, and after being modulated, it is output from the input/output terminal 300 to the trunk cable 116 as a regenerative repeater up data signal shown in FIG. 4 within the up band. The regenerative repeater upstream data signal is input again to the bidirectional trunk amplifier 106. That is, in Fig. 2, main line input/output terminal 2
The uplink data signal of the regenerative repeater input from 09 is demultiplexed into an uplink band signal by the demultiplexer 208, and the demultiplexer output 2
After being amplified to a predetermined level by the upstream band amplifier 212 as 10, the signal is multiplexed with the downstream band signal by the splitter 201 again, and then passed through the mainline input/output terminal 200 and the mainline cable 105 in FIG. The center RF modem 102 in the center device 100 demodulates it into a baseband data signal as center reception data 104.

As described above, if the bidirectional CATV system of the present invention is used, the upstream band of the branch line of the bidirectional main line amplifier is separated from the upstream band of the main line for each branch line, which causes problems in conventional systems. External noise in the upstream band, which mostly flows in from branch lines and drop-in lines, is greatly reduced, and it is demodulated as a single baseband signal by the regenerative repeater installed at the end of the main cable. Furthermore, noise is removed, and stable and highly reliable bidirectional data transmission is possible in both directions without the problem of noise merging in the upstream band that existed in conventional bidirectional CATV systems. This can be done using a CATV system. Furthermore, by using the bidirectional CATV system of the present invention, various services that utilize bidirectional data transmission functions, such as automatic meter reading and security services, can be easily realized. This can be realized without making any changes to the terminal device.

Effects of the Invention According to the present invention, there is no problem of noise merging in the upstream band in the center device that conventional two-way CATV systems have, and the two-way CATV system is stable and highly reliable. Not only can two-way data transmission be realized, services using various two-way data transmission technologies can be easily introduced, but also conventional two-way CATV
The center device and terminal device for the various services described above that are performed using the system can be realized without any changes. In addition, only a frequency conversion circuit and a directional coupler need be added to the conventional bidirectional main line amplifier, and it can be easily realized using conventional technology, and the local oscillation frequency of the frequency conversion circuit can be changed. By changing the frequency, it is possible to select the optimum frequency for the system, which has very good effects.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a bidirectional CATV system according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a bidirectional trunk amplifier in the same system, and FIG. 3 is a configuration diagram of a regenerative repeater in the same system. Fig. 4 is a diagram showing the frequency arrangement in the trunk cable, Fig. 5 is a diagram showing the distribution network of a conventional bidirectional CATV system, Fig. 6 is a system configuration diagram of a conventional bidirectional CATV system, and Fig. 7 8 is a diagram showing a frequency arrangement, and FIG. 8 is a diagram showing a polling method transmission control procedure in a bidirectional CATV system. 100... Center device, 101... Center computer, 102... Center RF modem, 10e... Bidirectional main line amplifier, 107...
... Regeneration repeater, 110 ... Terminal device, 11
1... Communication control device, 112... Terminal RF modem, 203... Downlink band amplifier, 2
12... Upstream band amplifier, 217・°°・"
°Band pass filter, 219... Frequency converter, 301... Conversion upstream data signal demodulator, 3
03...Modulator, SOO...Center device, 501...Center computer, 602...
...RF modem I 5509...Terminal device, 510...RF modem ■, 511...
...Communication control device. Name of agent: Patent attorney Toshio Nakao and 1 other person Haku4
figure

Claims (2)

[Claims] (1) A frequency converter installed in the bidirectional main line amplifier converts the upstream data signal from the branch terminal of the bidirectional main line amplifier to a frequency within the downstream band, and a regenerative repeater is installed at the end of the main line. and providing the regenerative repeater with a demodulator for the upstream data signal from the branch terminal converted into the downstream band, and a modulator for modulating the data signal from the demodulator as a data signal in the upstream band, A two-way CATV system characterized in that a data signal from the demodulator is regenerated and relayed. (2) A bidirectional CATV according to claim 1, characterized in that the data signal from the uplink data signal demodulator is resampled using a transmission bit clock.
system.