JP2000350179A - Data transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow all CATV systems to configure a LAN. SOLUTION: The confluent noise of a LAN employing the CATV system is eliminated. The frequency band of incoming high frequency modulation signals in a multiple dwelling house network 50 is selected to be a guard band. Thus, most of confluent noise from terminals is eliminated and the signal can reliably be sent to a central device even through the existing multiple dwelling house network 50 where much confluent noise is included. Furthermore, as the frequency band of an downstream signal, an idle band of 7ch, 8ch (188-198 MHz) in common to all TV stations is used. Moreover, the frequency of an upstream high frequency modulation signal for the guard band is converted into a prescribed frequency and the resulting signal is transmitted to the entrance of the multiple dwelling house network 50 and a frequency converter 60 to bypass the TV signal is provided to the entrance. Thus, the LAN employing an existing CATV reception system can reliably be operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system with reduced ingress noise in a network and improved data transmission quality. In particular, the present invention relates to a transmission system in which a local band uses a guard band for an uplink high-frequency modulation signal to prevent noise from each terminal device in the local network from being superimposed, and to reduce the signal noise for transmission. . INDUSTRIAL APPLICABILITY The present invention can be applied to, for example, the construction of a local area network that enables high-speed data communication such as the Internet in a CATV system that connects a CATV center to each home or each apartment house.

[0002]

2. Description of the Related Art There has been an Internet service using a CATV system. In this system, by connecting the center to the Internet, each terminal device can transmit and receive data via the Internet in addition to receiving TV signals. FIG. 7 shows a conventional CATV system. The CATV system includes a central unit 22 provided at the CATV station 20, a trunk cable 25 connected to the central unit 22, a repeater 30 provided at a predetermined position of the trunk cable 25, and a branch cable 24 branched from the repeater 30. , The network 5 in the apartment house connected to the branch cable 24
0 and the home network 40. Note that C
The ATV station has an Internet interface 21 through which the central unit 22 connects to the Internet 10.
It is connected to the.

[0003] The network 50 in an apartment house includes an amplifier 51 for amplifying and transmitting the transmitted high-frequency signal, and an amplifier 51.
And a terminal device 52 and a TV receiver 53 connected to the splitter 55. In addition, in the network 50 in a general housing complex,
A plurality of terminal devices 52 and a TV receiver 53 are connected. The home network 40 includes a branch / distributor 4 for branching / distributing a high-frequency signal propagated through the branch cable 24.
1. Terminal device 42 connected to branch / distributor 41, TV
It comprises a receiving device 43. In both systems, the terminal devices 52, 42 have cable modems 54, 4, which modulate and demodulate a high-frequency signal into an Ethernet baseband signal or an Ethernet baseband signal into a high-frequency signal.
4 is provided. Here, the terminal devices 52 and 42 are, for example, computer devices.

The transmission system used in this CATV system is a broadband transmission system in which a high-frequency signal (RF signal) is frequency-multiplexed.
The frequency band from MHz to 50 MHz is 70 MHz to 7 for the high frequency signal.
A 70 MHz band is allocated, and bidirectional communication is performed.
Specifically, for data transmission, for example, 33 MHz is selected for the upstream high-frequency signal and 245 MHz is selected for the downstream high-frequency signal.

[0005] The data signal input from the terminal device 52 is transmitted to the twisted pair line 56 in a predetermined communication format (10BASE-T). The data signal transmitted to the twisted pair line 56 is modulated by the cable modem 54, a carrier having a frequency of 33 MHz is modulated, and transmitted to the central unit 22 of the CATV station 20. On the other hand, the central device 22 that has received the 33 MHz upstream high-frequency signal demodulates the signal by a cable modem (not shown) and transmits the data signal to the device 10 via, for example, the interface 21. Also, the terminal device 52 modulates the downstream carrier wave 245 MHz based on the data signal from the terminal device 52.
Send to. Cable modem 54 of terminal device 52
Receives the high-frequency signal of 245 MHz and obtains desired data by demodulation. In this way, data can be transmitted and received between arbitrary terminal devices via the Internet.

[0006]

However, the conventional C
In the ATV system, noise is superimposed on the uplink high-frequency signal from the subscriber's terminal devices 52 and 42 to the CATV station 20 as indicated by a broken line, and these noises flow from the respective terminal devices to form a signal in the apartment house. At the exit of the network 50, there is a large ingress noise. In this case, the quality of the communication line is degraded, and data may not be transmitted to the central device 22 accurately. In particular, network 5
At 0, the ingress noise level rises due to the large number of terminal devices, and in some cases, CATV Internet service cannot be performed.

[0007] This ingress noise is generated by the network 5 in the apartment house.
In order to prevent the data from being output to the outside of 0, an attempt has been made to output an upstream data signal using a part of the downstream frequency band in which noise does not ride in the in-house network 50. However, in this method, a special configuration such as that the amplifier is bypassed only for signals in this band needs to be provided because of the use of the downstream band.

A base band system may be used to prevent noise from flowing in. However, since a bypass circuit must be provided for the amplifier and data can be transmitted and received arbitrarily, CATV is required. There is also a problem that charging management by a service provider and confidentiality cannot be maintained.
Also, there is a problem in terms of data transmission speed. Furthermore, it is necessary to replace most of the devices constituting the television sharing network with dedicated devices, which increases costs. Therefore, it has not been possible to provide an inexpensive, convenient, and high-quality Internet service to all business establishments or all apartment buildings where the CATV system has been introduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. High-quality data transmission can be achieved by suppressing upstream band ingress noise at the exit of a local network such as an apartment house system. It is intended to be.

[0010]

In order to solve the above-mentioned problems, a data transmission method according to the first aspect of the present invention is directed to a local network in which a plurality of terminal devices are connected and perform data communication using a high-frequency modulation signal. And a transmission line to which the local net is connected, wherein the guard band is a band for transmitting an upstream high-frequency modulation signal for data communication in the local net. .

The guard band is a band that separates an upstream signal band and a downstream signal band. The meaning of the local net is a network in a building unit or a regional unit to which a large number of terminal devices are connected, and any part in the system can be freely defined as a local net. In the local network, data communication is performed using a high-frequency modulation signal, and the local network is a frequency-multiplexed broadband transmission system. In the local network, a downstream band and an upstream band are separated in order to perform two-way communication.
Although the signal is output, the signal may not be a TV signal, but may be only a high-frequency modulation signal for data communication.
The data includes all of video data, image data, audio data, and character data.

The frequency of the noise superimposed from each terminal device is mostly lower than 50 MHz. Therefore, in the present data transmission system, superimposition of noise is suppressed because the transmission of the upstream high-frequency modulation signal is performed using the guard band higher than 50 MHz in the local net. As a result, the ingress noise of the superimposed noise in many terminal devices in the local net is not transmitted to the transmission path, so that the data transmission quality is improved.

The use of the guard band for transmitting the upstream high-frequency modulation signal is performed in a local net. Ingress noise mainly occurs in a local net to which many terminal devices are connected. Therefore, if a guard band is used for transmission of an upstream high-frequency modulation signal at least in a local net, ingress noise can be efficiently reduced. Of course, the use of the guard band can be extended to a transmission line to which a local net is connected.

According to a second aspect of the present invention, the upstream high-frequency modulated signal of the guard band is transmitted by bypassing the amplifier when an amplifier exists in the local net. If a bidirectional amplifier is provided in the local net, the upstream high-frequency modulated signal of the guard band cannot pass. Therefore, if the amplifier is bypassed by, for example, a branching device and a band-pass filter, data from the terminal device can be transmitted in the upstream direction if the guard band is used only for the upstream data transmission. If the band is used for two-way data communication, it is possible to transmit data in both directions.

According to a third aspect of the present invention, there is provided a data transmission system, wherein the local net converts a frequency of an upstream high-frequency modulation signal of a guard band into a frequency of an upstream band of a transmission line at a connection point with the transmission line. It is characterized by having. The frequency converter provided at the exit of the local net, that is, at the connection point with the transmission line, changes the frequency of the upstream high-frequency modulation signal of the guard band to, for example, 33 MHz of the normal upstream band.
It is converted to a band and transmitted to the transmission path. If you do this,
A LAN can be formed without changing any existing system. Therefore, a data transmission method that enables the formation of a less expensive LAN is provided.

According to a fourth aspect of the present invention, in the data transmission system, the local net includes a demodulation device for demodulating an uplink high-frequency modulation signal of a guard band at a connection point with a transmission line, and a data signal demodulated by the demodulation device. A modulation device for modulating an upstream high-frequency modulation signal and transmitting the modulated signal to an upstream band of a transmission path is provided. The demodulation device demodulates the upstream high-frequency modulation signal into a data signal once. By this processing, even if the upstream ingress noise is included, the transmission of the ingress noise to the transmission path is completely eliminated, and the data transmission quality in the transmission path is improved. Here, the data signal is, for example, a data signal of an Ethernet specification in addition to a baseband data signal such as a binary digital signal. The modulation device modulates the data signal demodulated by the demodulation device into an upstream high-frequency modulation signal and transmits the modulated signal to a transmission path. As a result, the ingress noise in the local net is completely eliminated, so that the ingress noise does not flow out to the transmission path. Therefore, data transmission quality on the transmission path is improved. The downlink signal received from the transmission path may be transmitted to the local network as it is, or may be demodulated, modulated, and transmitted as described below.

According to a fifth aspect of the present invention, there is provided a data transmission system, comprising: a demodulator for demodulating an uplink high-frequency modulation signal of a guard band;
A first modulation / demodulation device including a modulation device for modulating a data signal obtained from a downlink signal on a transmission path into a downlink high-frequency modulation signal and transmitting the modulated signal to a local network is provided at the connection point. Use of the guard band of claim 1 to eliminate upstream ingress noise from a local net, or
It is sufficient to provide the demodulator at the connection point between the local net and the transmission path, as in the use of the guard band and the fourth aspect. This feature is characterized in that a data signal demodulated also for a downlink signal on a transmission path is re-modulated and transmitted to a local net as a downlink high-frequency modulated signal. There is an effect of removing noise related to a downlink signal. Also, the first modulation / demodulation device is, for example,
The CATV system is a so-called cable modem, and has an advantage that existing equipment can be used as it is.

According to a sixth aspect of the present invention, there is provided a data transmission system comprising:
A second modem that modulates the data signal demodulated by the modem into an upstream high-frequency modulation signal and transmits it to a transmission line, demodulates the downstream high-frequency modulation signal received from the transmission line into a data signal, and outputs the data signal to the first modem. Is provided at the connection point. In this configuration, a second modem is connected to the first modem. Accordingly, when the transmission path is a broadband high-frequency transmission path, particularly as in a CATV system, the upstream high-frequency modulation signal of the local net is demodulated and re-modulated and sent out as an upstream high-frequency modulation signal to the transmission path. Is demodulated and re-modulated, and transmitted to a local net as a downstream high-frequency modulated signal. In this manner, the noise is removed from the data signal in both the upstream and downstream directions. In the CATV system, both the first modem and the second modem are so-called cable modems, and there is an advantage that existing equipment can be used as it is.

As described above, the data signal obtained by demodulating the high-frequency modulated signal is, for example, a binary baseband data signal or an Ethernet-specific data signal. Here, the data signal of the Ethernet specification refers to a signal to which line processing information and the like required for transmission and reception between modems or between central units are added. Further, the frequency band of the upstream high-frequency modulation signal of the local net and the frequency band of the upstream high-frequency modulation signal of the transmission path may or may not be equal. That is, in the transmission path, if a bypass circuit is added to the repeater, it is possible to transmit the upstream high-frequency modulation signal using the same guard band. Normally, an upstream band is used on a transmission path. In this case, the existing equipment in the existing system can be used as it is, and the transmission method is one in which only the ingress noise is removed.

Similarly, the frequency band of the downstream high-frequency modulation signal on the transmission line and the frequency band of the downstream high-frequency modulation signal on the local network may or may not be equal. In the case of equality, in the existing system, only the first modulation and demodulation device and the second modulation and demodulation device are provided at the connection point between the local net and the transmission line, and it is not necessary to provide another special device in the terminal device. Note that the first modem and the second modem are C
It also includes a so-called intelligent modem or the like in which a PU is mounted and can be controlled from a center.

According to a seventh aspect of the present invention, in the data transmission system, the transmission path is a data transmission path, and a data signal demodulated by the first modulation / demodulation device is input at a connection point of a local net and modulated and output to the transmission path. A router or a terminal adapter for receiving a downstream signal of the transmission path, converting the received signal into a data signal, and outputting the data signal to the first modem. According to this configuration, the transmission path is set to, for example, IS
A DN transmission line or other data transmission lines can be connected to a local net. Also in this case, the upstream ingress noise in the local net is eliminated, and the upstream data signal is transmitted to the data transmission path. Therefore, data transmission quality is improved.

According to the data transmission method of the present invention, the transmission path is a CATV transmission path, the local network is disposed in a predetermined area such as an apartment house, a building or a factory where terminal devices are scattered, and a downstream signal is transmitted. It is a television sharing network that supplies a TV signal by using it. In the CATV transmission line, the downstream band is used for TV signals, and the upstream band is used for high-frequency data signals. In particular, although the influence of the ingress noise in the low group upstream band is great, according to the present system, since the guard band is used for the transmission of the upstream high-frequency modulation signal, the ingress noise hardly mixes. When a demodulation device, a modulation device, and a modulation / demodulation device are used, even if ingress noise is mixed, the ingress noise is completely eliminated and transmitted to the transmission line. Therefore, the quality of data communication can be greatly improved. In the local net having this feature, the TV signal exists in the downstream band, and the upstream band is a band for data communication.

According to a ninth aspect of the present invention, in the data transmission system, the frequency band of the downlink high-frequency modulated signal is 7 channels or 8 channels of the frequency band set in the CATV transmission line. According to the television standard, 7 or 8 channels in the frequency band of the TV signal have a common band of 2 MHz, cannot be used at the same time, and one of them is an empty band. Its width is 4 MHz, and its empty band is used as a band for data signals. In the present invention, the unused bandwidth is used, so that the utilization efficiency of the bandwidth is improved.

According to a tenth aspect of the present invention, in the data transmission method,
The center of the ATV transmission line is connected to the Internet, transmits a signal obtained by demodulating an upstream high-frequency modulation signal received from the transmission line to the Internet, modulates a signal received from the Internet into a downstream high-frequency signal, and sends the signal to the transmission line. It is characterized by doing. With this configuration, a large number of terminal devices connected to the local network can be connected to the Internet via a CATV transmission path, and high-quality data communication can be performed. Moreover, only by providing this device at the connection point between the local network and the transmission line, a terminal device having a cable modem for CATV can realize high-quality data communication without additional equipment.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following examples. (First Embodiment) In this embodiment, the local net is an existing TV common listening net installed in each home or apartment house. Thereby, a LAN is realized.

FIG. 1 shows a CAT to which the transmission system of the present invention is applied.
1 shows a V system. The figure is a schematic configuration diagram. The CATV system according to the present embodiment includes a central unit 22 provided in a CATV station 20, an optical fiber cable 23 connected to the central unit 22, and a photoelectric converter 2 for converting an optical signal into an electric signal.
3a, trunk cable 2 extended from photoelectric converter 23a
5. Repeater 3 provided at a predetermined position of trunk cable 25
0, a branch cable 24 wired from the repeater 30, a data transmission device 60 connected to the branch cable 24 to reduce ingress noise, and a network 50 (local network) within the multi-family house, which is a local network connected to the data transmission device 60. ) And a home network 40 (local network). The transmission path is an optical fiber cable 23,
It means a line composed of the main cable 25, the branch cable 24, the repeater and the like for transmitting signals. In addition, CATV station 2
0 is connected to 10 via the Internet interface 21 so that it can communicate bidirectionally with terminal devices in other areas.

The configurations of the home network 40 and the multi-family network 50 are the same as those of the conventional example shown in FIG. In FIG. 1, a data transmission device 60 is provided at a connection point between the transmission path and the local network, that is, at a connection point (exit) between the branch cable 24 and the network 50 in the apartment house. The data transmission device 60 is a device that demodulates an upstream high frequency modulation signal of a guard band into a data signal, modulates the data signal into a high frequency modulation signal of 33 MHz in an upstream band of a transmission line, and transmits the modulated signal to the transmission line.

FIG. 2 shows a frequency band arrangement of the CATV system. The frequency band arrangement of the CATV system is 10
Upward bandwidth in the direction of the station of ~ 50MHz, and 70 ~ 770MHz
Are separated into downstream bands. The upstream band is mainly used for communication to the station side, and the downstream band is used for TV signal and data communication to the terminal device side. Here, 50 MHz to 70 MHz
Is a guard band for separating the upstream band and the downstream band. Guard band A for transmission band of upstream high frequency modulation signal
Is used to reduce ingress noise in the local net. As described in the conventional example, the upstream high-frequency modulation signal using the upstream signal band from the terminal device 52 involves many ingress noises. In particular, in the network 50 in an apartment complex, the number of terminal devices 52, television receivers, and the like is large, so that inflow noise is significantly increased. Most of the frequency of the ingress noise from the terminal device 52 or the like exists in the upstream signal band of 10 to 50 MHz. Therefore, in this embodiment, a guard band (50 to 70 MHz) is used for transmission of the upstream high-frequency modulation signal in order to avoid a band in which ingress noise is superimposed. Less than,
In this embodiment, the frequency of the carrier of the upstream high-frequency modulation signal of the guard band is set to 60 MHz.

The transmission band of the downlink data signal is T
188 in which 7 or 8 channels are arranged by V signal
The free band B is used in the band of １９198 MHz.
If eight channels are used, a 4 MHz band of 188 to 192 MHz is available, and this band is used as a transmission band for the downstream data signal. Conversely, if 7 channels are used, a 4 MHz band of 194 to 198 MHz is available, and this band can be used as a transmission band for downstream data signals. Hereinafter, in the embodiment, it is assumed that the downlink high-frequency modulation signal is transmitted using a 4 MHz band of 188 to 192 MHz. The carrier is 19
0 MHz.

The configuration and operation will be described below with reference to FIGS. 3, 4, and 5. As shown in FIG. 3, a data transmission device 60 is provided at an exit (entrance) of the network 50 in the apartment house. The data transmission device 60 is a branching / distributing device 64 for branching / distributing an upstream high-frequency modulation signal of a guard band transmitted from the terminal device 52, and a first modem for temporarily converting the upstream high-frequency modulation signal into an Ethernet baseband signal. A certain lower cable modem 62, an upper cable modem 61 which is a second modem which modulates a carrier wave based on the converted Ethernet baseband signal and makes it again an upstream high frequency modulation signal, Branch / distributor 6 to send to 24
6, a low-group (up-band) cutoff filter 65 disposed between the branch / distributor 64 and the branch / distributor 66. Note that the low-group cutoff filter 65 is a filter that passes only the downstream high-group frequency and blocks the low-band and guard-band frequencies.

The data signal input from the terminal device 52 which is a computer device has a predetermined communication format (10 BASE).
-T) is transmitted to the twisted pair line 56. The Ethernet-specific data signal transmitted to the twisted pair line 56 is input to the cable modem 54, and a modulator in the cable modem modulates a carrier having a frequency of 60 MHz to transmit a high-frequency modulated signal modulated as a guard band signal. You.

The transmitted upstream high-frequency modulation signal is divided into
The signal passes through the distributor 55, the amplifier 51, and the branch / distributor 64 to reach the lower cable modem 62. The upstream high-frequency modulation signal input to the lower cable modem 62 is once demodulated into an Ethernet baseband signal. By this demodulation, even if the ingress noise is superimposed on the upstream high frequency modulation signal of the guard band, the ingress noise is removed. Thereafter, based on the demodulated data, the upper-level cable modem 61 modulates the carrier having a frequency of 33 MHz again, and transmits the modulated carrier to the branch / distributor 66 and the branch cable 24 as an upstream high-frequency modulated signal. As described above, in the multi-family network 50, since the uplink high-frequency modulation signal for the data signal is transmitted using the guard band, it is not affected by the noise superimposed from each terminal device. Even if the ingress noise is superimposed on the guard band, the ingress noise is completely removed by demodulation and re-modulation.

The high-frequency modulated signals of the upstream band and the guard band output from the branch / distributor 64 are cut off by the low-group cutoff filter 65 and are not transmitted to the branch cable 24 side. Is not output to the branch cable 24.

FIG. 4 shows the details of the lower cable modem 62 and the upper cable modem 61. Lower cable modem 6
Reference numeral 2 denotes a demultiplexer 62a for demultiplexing a guard band 60 MHz upstream high frequency modulation signal, a demodulator 62b for demodulating the demultiplexed high frequency modulation signal, and a computer for inputting a baseband data signal which is a demodulated binary signal. Device 62d, and an Ethernet interface 6 for transmitting an Ethernet baseband signal based on a baseband data signal which is a binary signal transmitted from the computer device 62d.
2e and a modulator 62c for the downlink data signal. The modulator 62c is a modulator that modulates a 190-MHz carrier wave based on a baseband data signal obtained via the Ethernet interface 62e and the computer device 62d, and transmits the modulated carrier as a downstream high-frequency modulated signal in the downstream direction.

The upper cable modem 61 has an Ethernet interface 61e for inputting an Ethernet baseband signal and converting it into a binary baseband signal, and a computer device 6 for inputting a binary signal baseband signal.
1d, a modulator 61c for modulating a carrier of 33 MHz based on a baseband signal of a binary signal output from the computer device 61d and transmitting a high-frequency modulated signal, a duplexer 61a for transmitting a high-frequency modulated signal to the branch cable 24, and It comprises a demodulator 61b for demodulating a downstream high-frequency modulated signal. The demodulator 61b receives the 19-input signal from the duplexer 61a.
This is a device that demodulates a downstream high-frequency modulation signal in a 0 MHz band into a baseband signal of a binary signal and outputs it to a computer device 61d.

Next, the operation of the lower cable modem 62 and the upper cable modem 61 with respect to the upstream high-frequency modulated signal will be described. When the upstream high-frequency modulated signal including the ingress noise is input to the lower cable modem 62 having the above configuration, the upstream high-frequency modulated signal of the guard band is separated by the demultiplexer 62a and input to the demodulator 62b. If the modulation method is QPSK phase modulation, the demodulator 62b performs phase demodulation and sends it to the computer device 62d. The duplexer 62a separates the guard band from the downstream high-frequency modulated signal in the 190 MHz band. Computer device 62d
Further converts the data into predetermined code data and the like, and sends the data to the Ethernet interface 62e. The Ethernet interface 62e converts the data into an Ethernet baseband signal and sends the data to the upper cable modem 61 via the twisted pair line 63. As described above, even if noise is superimposed on the guard band, the ingress noise is removed by this conversion.

Next, in the upper cable modem 61, based on the Ethernet baseband signal input from the Ethernet interface 62e, the computer device 61d and the modulator 61c modulate the signal into an upward high-frequency modulation signal in the 33 MHz band. The signal is sent to the branch cable 24 via the cable 61a. In this manner, demodulation and modulation are performed by the operation of the lower cable modem 62 and the upper cable modem 61, and the ingress noise is removed from the upstream high-frequency modulated signal.

On the other hand, with respect to the downstream high-frequency modulated signal on the transmission line, only the downstream high-frequency modulated signal in the frequency band of 190 MHz is demultiplexed by the demultiplexer 61a and input to the upper cable modem 61 from the branch cable 24. You. The demodulation and modulation at this time are executed in a route completely opposite to that of the upstream high-frequency signal. That is, the demodulator 61b of the upper cable modem 61 demodulates the downstream high-frequency modulated signal of the transmission path into a binary baseband signal.
The second modulator 62c modulates the signal into a downstream high-frequency modulated signal having a frequency band of 190 MHz and transmits the signal to each terminal device 52. At this time, even if the downstream high-frequency modulated signal transmitted from the central unit 22 contains noise, the noise is removed by demodulation and modulation.

The TV input from the branch cable 24
The signal passes through the branch / distributor 66 of FIG.
5 is output. This TV signal passes through the low-group cutoff filter 65, is amplified by the amplifier 51, and is propagated to each TV receiver 53. Therefore, if the TV receiver 53 is connected to the branch / distributor 55, a TV signal is received. If the terminal device 52 is connected to the branch / distributor 55, data communication can be performed as described above. The downstream high-frequency modulated signal having a frequency band of 190 MHz is cut off by the high-group data band cutoff filter 67 and is not transmitted further downstream. Therefore, a downstream high-frequency modulated signal of a frequency band 190 MHz re-modulated by the lower cable modem 62,
190 MHz frequency band before demodulation from branch cable 24
Does not collide with the downstream high-frequency modulated signal.

As described above, the data transmission method of the present invention
Existing CATV distribution network, especially network in multiple dwelling houses 5
It is only necessary to provide the data transmission device 60 at the exit of 0. Therefore, a LAN can be constructed at extremely low cost.

In the above embodiment, the low-group cutoff filter 6
Instead of 5, a one-way amplifier that amplifies only the downstream high group band signal may be provided. In this embodiment, since the downlink high-frequency signal received from the transmission path is demodulated, the CATV station 2
A control signal from 0 can also be received, and various controls for the data transmission device 60 can be performed from the CATV station 20. In the above embodiment, the vacant band among the 7 and 8 channels of the TV signal is used for the band of the downstream data signal, but any band may be used.

As described above, in the local net, the inflow of noise can be prevented by setting the guard band to be the transmission band of the upstream high-frequency modulation signal. In addition, if an amplifier is not used in the local network, the existing TV co-listening system may be used without changing any special additional equipment only by changing the carrier frequency of the modulation device of the terminal device. it can. Further, when the local net becomes large, a bidirectional amplifier is present therein.
In this case, it is necessary to bypass the conventional bidirectional amplifier by providing a bypass circuit. FIG. 5 shows a bidirectional amplifier 70. The bidirectional amplifier 70 includes a conventional bidirectional amplifier 51,
Branch 71, amplifiers 73 and 77, bandpass filter 7
6. A bypass circuit 78 including a coupler 75. Here, the band-pass filter 76 is 50 to 70 M
It has the characteristic of passing only the high frequency signal of the guard band of Hz.

The high frequency signal in the upstream signal band of 10 to 50 MHz is amplified by the amplifier 72, and the downstream signal band of 70 to 770 MHz is amplified by the amplifier 73 and propagated in each direction. The upstream high-frequency modulation signal of the guard band of 50 to 70 MHz is supplied to the bypass circuit 78.
, And amplified and propagated in the upward direction. With such a configuration of the bidirectional amplifier, it is possible to adopt a data transmission method in which a local net is a large-scale LAN having a bidirectional amplifier.

(Second Embodiment) A system according to a second embodiment will be described. This embodiment is characterized in that the data transmission device 60 in FIG. 1 is configured as shown in FIG. That is,
As shown in FIG. 6, the lower cable modem 6 in FIG.
2. Instead of the upper cable modem 61, a data transmission device 600 is constituted by a band pass filter 67, a frequency converter 68, and an amplifier 69, which pass only the guard band frequency. With this configuration, the guard band of 60 MHz
The band high-frequency modulated signal is separated by the band-pass filter 67, frequency-converted by the frequency converter 68 into a signal of 33 MHz in the upstream band of the transmission path, and transmitted to the transmission path. Note that noise in a band of 10 to 50 MHz from a local net is cut off by the low group cutoff filter 65. On the other hand, the signal in the high group downstream band passes through the low group cutoff filter 65 and is propagated to the local net side. In this manner, the signal may be transmitted to the transmission line only by frequency conversion without demodulation and modulation as in the first embodiment. Also in this case, in the local net, since a guard band on which noise is unlikely to be superimposed is used for the transmission band of the uplink data signal, ingress noise is prevented from being transmitted to the transmission path.

(Third Embodiment) Hereinafter, a third embodiment will be described. This device provided at the connection point between the transmission path and the local net may be configured as shown in FIG. In FIG. 7, the transmission line A is on the branch cable 24 side, and the network 5 in the apartment
0 is displayed on the local net B. The transmission line A and the local net B are connected by a branching filter 84 and a branching device 83.
Then, a band-pass filter 8 for extracting only the guard band frequency to a circuit on the upstream low group band side including the guard band.
5, a demodulation device 81 and a modulation device 82 are provided,
The circuit on the downstream high group band side is through.

In such a configuration, the upstream high-frequency modulation signal of the guard band from the local net B is once demodulated by the demodulator 81 into a baseband signal of a binary signal, and is again transmitted by the modulator 82 to the transmission line. Upstream band, for example, 33
The signal is modulated and output to a high frequency modulation signal of a frequency band of MHz. Then, noise in the band of 10 to 50 MHz in the local net is cut off by the duplexer 84 and is not transmitted to the transmission line A.

On the other hand, the high-frequency modulated signals, which are the TV signals and the data signals of the descending high group inputted from the transmission line A side, are transmitted from the transmission line A to the local net B side by the demultiplexers 84 and 83. In other words, reception of TV signals and data communication can be performed with existing CATV local network equipment. Also in the present embodiment, the upstream high-frequency modulation signal from the local net B is once demodulated into a baseband signal, and is again modulated into the upstream high-frequency modulation signal and transmitted to the transmission line A. Similarly to the above, the upstream ingress noise can be eliminated.

In this embodiment, if the CATV station 20 is to control the present apparatus, the control to demodulate the downlink signal on the transmission line A to extract the data signal and control the demodulator 81 and the modulator 82 What is necessary is just to provide a device.

(Fourth Embodiment) Hereinafter, a fourth embodiment will be described. In this embodiment, the transmission path A is a data transmission path such as ISDN. The CATV transmission line 101 and the local net B are connected by a distributor 100, and a CA
The TV transmission line 101 and the first modem 90 are connected. The first modulator / demodulator 90 includes a duplexer 94 and a demodulator 9.
2, a modulation device 93 and a CPU 91,
Router 95 in which PU 91 is connected to ISDN transmission line
It is connected to the.

The upstream high-frequency modulated signal of the guard band output from the local net B passes through the low group terminals of the distributor 100 and the demultiplexer 94, and is input to the demodulator 92, where the baseband signal of the binary signal is output. Is demodulated. Then, the signal is input to the CPU 91 and output to the ISDN transmission line via the router 95. As described above, the data is output to the Internet via the ISDN transmission path. On the other hand, a data signal from the Internet is received by the router 95, output to the CPU 91, modulated by the modulator 93 into a high-frequency downlink high-frequency modulation signal, passed through the duplexer 94 and the distributor 100,
Output to the local net B. In this way, the ingress noise can be removed from the data signal output from the local net B to the transmission path A. The local net B is CAT
Two-way communication is also possible with the V transmission path 101.

(Modifications) Although one embodiment of the present invention has been described above, various other modifications are possible.

In the above embodiment, the local net B is assumed to be a TV common net for a collective house, a factory, a hospital, a school, or the like. A transmission line (LAN) using no high-frequency transmission may be used. In the above embodiment, in transmitting and receiving data in the local network, carrier waves of different frequencies are used for uplink data and downlink data, but carrier waves of the same frequency in the guard band may be used. This is a method of performing communication using idle time on the same channel. It can be applied to a small LAN that does not require an amplifier.

It is also possible to assign an idle channel of a TV signal to the downstream high frequency modulation signal. In the above embodiment, the transmission path is a CATV transmission path or an ISDN transmission path. However, any transmission path that can be connected to a LAN such as an OCN may be used. Further, other transmission lines including other media such as broadcast waves including terrestrial broadcasts and satellite broadcasts, microwaves, and optical space transmission may be used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a CATV system to which a data transmission method according to a first embodiment of the present invention is applied.

FIG. 2 is an explanatory diagram of a frequency band used for a data transmission method according to the first embodiment.

FIG. 3 is a configuration diagram of a converter and a network in an apartment house according to the first embodiment.

FIG. 4 is a configuration block diagram of a data transmission apparatus according to the first embodiment.

FIG. 5 is a block diagram of a bidirectional amplifier including a bypass circuit according to the first embodiment.

FIG. 6 is a block diagram of a data transmission device according to a second embodiment.

FIG. 7 is a configuration diagram showing a system using a modulation device and a demodulation device according to a third embodiment.

FIG. 8 is a configuration diagram showing a system that enables connection to an ISDN transmission line according to a fourth embodiment.

FIG. 9 is a configuration diagram of a CATV system to which a transmission system using a conventional cable modem is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Internet 20 CATV station 22 Central unit 23 Optical fiber cable 24 Branch cable 25 Trunk cable 30, 70 Repeater 40 Home network 41, 55 Branch / distributor 42, 52 Terminal device 43, 53 TV receiver 44, 54 Cable modem DESCRIPTION OF SYMBOLS 50 In-house network 51 Amplifier 60 Frequency converter 61 Upper cable modem 62 Lower cable modem 64, 66 Branch / distributor 65 Low group cutoff filter 70 Bidirectional amplifier 81, 92 Demodulator 82, 93 Modulator

Claims (10)

[Claims] 1. A data transmission system in a system comprising a local net to which a plurality of terminal devices are connected to perform data communication using a high-frequency modulated signal, and a transmission line to which the local net is connected, wherein: A data transmission method, wherein the guard band is a band for transmitting an upstream high frequency modulation signal for data communication. 2. The data transmission method according to claim 1, wherein the upstream high-frequency modulation signal of the guard band is transmitted by bypassing the amplifier when an amplifier exists in the local net. . 3. The local net further comprises a frequency converter for converting a frequency of an upstream high-frequency modulation signal of the guard band into a frequency of an upstream band of the transmission line at a connection point with the transmission line. The data transmission method according to claim 1 or 2, wherein 4. The local net includes, at the connection point with the transmission line, a demodulator for demodulating an upstream high-frequency modulation signal of the guard band, and converting a data signal demodulated by the demodulator into an upstream high-frequency modulation signal. The data transmission system according to claim 1, further comprising a modulation device that modulates and transmits the modulated data to an upstream band of the transmission path. 5. The local network according to claim 1, wherein at the connection point with the transmission path, a demodulator for demodulating an upstream high-frequency modulation signal of the guard band, and a data signal obtained from a downstream signal of the transmission path for downstream high-frequency modulation. 3. A first modulation / demodulation device including a modulation device for modulating a signal and transmitting the signal to the local net.
Data transmission method described in 1. 6. A data signal demodulated by the first modulation / demodulation device is modulated into an upstream high-frequency modulation signal and transmitted to the transmission line, and a downstream high-frequency modulation signal received from the transmission line is demodulated into a data signal. The second output to the first modem
The data transmission system according to claim 5, wherein a modem is provided at the connection point. 7. The transmission line is a data transmission line, and inputs a data signal demodulated by the first modem at the connection point of the local net, modulates and outputs the data signal to the transmission line, and The data transmission system according to claim 5, further comprising a router or a terminal adapter that receives the downstream signal and outputs the data signal to the first modem. 8. The transmission line is a CATV transmission line, and the local net is an apartment house, a building,
The data transmission according to any one of claims 1 to 6, wherein the transmission network is a television shared listening network that is provided in a predetermined area such as a factory and supplies a TV signal using the downlink signal. method. 9. The frequency band of the downlink high-frequency modulated signal is as follows:
9. The data transmission method according to claim 8, wherein the channel is a 7 channel or 8 channel of a frequency band set in the CATV transmission path. 10. A center of the CATV transmission line is connected to the Internet, transmits a signal obtained by demodulating an upstream high-frequency modulation signal received from the transmission line to the Internet, and converts a signal received from the Internet into a downstream high-frequency signal. The data transmission method according to claim 8, wherein the data is modulated and transmitted to the transmission path.