JPH11234646A - Bi-directional CATV system and repeater used in the system, coaxial coaxial cable system and adapter used in the system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a two-way service to a terminal connected to a co-listening coaxial cable. A repeater (3) is connected to each of a center device (1) and a co-listening coaxial cable network (2) via separate coaxial cables. The repeater 3 converts the upstream signal output from the coaxial cable network 2 into a multiplexer / demultiplexer 3.
3, demodulation processing in the demodulation unit 34 and the data discriminator 3
5. Terminate once by data identification in 5. Then, after the data identified by the data identifier 35 is re-modulated by the modulator 36, the ratio of the amplitude of the output to the amplitude of the uplink signal extracted by the multiplexer / demultiplexer 33 becomes constant by the amplifier 37. Is amplified by the amplification factor adjusted so that the amplitude comparator 38 can detect that the center device 1
Send to.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CA for performing bidirectional communication between a center device and a user terminal connected to the center device via a coaxial cable system.
The present invention relates to a TV system, a repeater used in the system, a coaxial cable system for realizing a LAN function through a coaxial cable network, and an adapter used in the system.

[0002]

2. Description of the Related Art A CATV system for distributing a multi-channel video signal to a large number of users using a coaxial cable is well known. Especially when the distance from the broadcasting station is long,
In an area where a video signal cannot be received correctly due to radio interference, a CATV system capable of distributing a video signal to multiple channels is convenient.

On the other hand, demand for data communication services such as the Internet has been expanding. In general, in order to connect to the Internet in ordinary households, a method of connecting to an Internet service provider via a telephone line has been adopted. However, in the case of connection by telephone line, high-speed IS
Even if a DN line is used, the basic rate is up to 64 kbps, and even if a bulk rate is used, it is up to 128 kbps, and the capacity for transferring large-sized data such as image data is insufficient.

In such a situation, a technology has been developed which can connect to the Internet using a coaxial cable of a CATV system. In order to connect to the Internet in this way, it is necessary to perform bidirectional signal transmission. First,
Since the down direction from the center to the user is the same direction as the conventional video signal, 64QAM or 256QA
It is possible to transmit data at high speed using high-efficiency modulation such as M.

On the other hand, a method using a frequency of less than 70 MHz in the uplink direction (more than 70 MHz in the downlink direction) is mainly used, but the following problems occur in the uplink signal transmission. ing.

[0006] One is that the beat of the downstream signal beats down to a low frequency band of 70 MHz or less due to nonlinear distortion.
This is a problem that interferes with upstream signals. The other is a problem of so-called ingress noise or the like, where living noise is mixed in from the user's house or from a drop cable drawn into the user's house, and flows into the center via the distribution unit.

[0007] The former problem of low-frequency leakage due to nonlinear distortion is caused by contact of dissimilar metals at the terminating end of a CATV network, such as a main line amplifier or a distribution amplifier, and can be easily dealt with by a cable operator. It is. However, the problem of the ingress noise is caused by the coaxial cable wiring in the home, and it is difficult for the cable operator to take measures.

With respect to the ingress noise, the number of users who provide the CATV service is limited to about 500 to 1500, an optical fiber is used halfway, and a coaxial cable is connected between a fiber node terminating the optical fiber and each user. It is possible to solve the problem by using a technique called HFC (Hybrid Fiber Coax) connected by the above method. In addition, when the home receiving the CATV service is a detached house, the number of coaxial cables distributed in the house is small, so that there are few places where noise is mixed and the problem of ingress noise is not so large.

However, in an apartment house or the like, it is difficult to set up an antenna for each home. Therefore, an antenna is installed in one place and a coaxial coaxial cable is laid, and signals obtained by the antenna are distributed to each home. doing. The co-listening coaxial cable is generally connected by a series unit that taps in the middle of the coaxial cable and distributes the RF video signal by weak coupling using a transformer. This series unit has difficulty in impedance matching, and living noise is mixed in from this part. However, the frequency spectrum of the contaminated living noise has mostly low-frequency components, and has not been used for conventional down signals of 70 MHz or more, and no measures have been taken.

[0010] For this reason, the provision of a bidirectional CATV service in the case of a co-listening coaxial cable in an apartment house or the like has a very large effect of ingress noise, and is currently not technically realized.

On the other hand, such coaxial listening coaxial cables have been mainly considered to be able to normally receive television sets (TV sets) in respective homes. Not at all. Although it is considered that there is large variation depending on the system, the minimum reception power at the noise limit of the TV set is about 60 dBμV, and the output of the amplifier for amplifying the signal received by the antenna is about 100 dBμV, so that the transmission loss is about 40 dB. . Among them, the loss in the series unit is 20 dB, and depending on the size of the apartment house, a case where a relay amplifier is inserted on the way may be considered.

On the other hand, the use of a coaxial cable for a local area network (LAN) is very common, and 10BASE-2 and 10BASE-5 in IEEE 802.3 are well known. These are baseband signals using a coaxial cable as a medium, and are CSMA / CD (Carrier Sense Mul
LAN by tiple access / collision detection) method
This is a method for configuring. Even if this signal flows through the existing coaxial coaxial cable, the signal does not pass through the distributor or the series unit.

[0013] A system called 10BROAD-36 is standardized in IEEE 802.3. In this method, a frequency converter is provided at a head end, and the frequency of an upstream signal from a cable modem is converted into a downstream signal frequency at the head end. Therefore, each terminal can receive signals from all terminals.

In this system, the carrier sense when the own station does not transmit can be detected by the presence or absence of a downlink signal. on the other hand,
When the own station is transmitting, the transmission data returns as a downlink signal, so that carrier sensing is not performed based on the presence or absence of a downlink signal. Therefore, regarding the signal collision when the own station is transmitting, when the data signal output from the own station does not match the data of the signal returned after frequency conversion, that is, the returned signal is If a signal and a weight code error occur, a collision is determined. This 10BR
OAD-36 is designed on the assumption that the signal levels from each station do not differ greatly.

However, a LAN using a coaxial cable is used.
In the case of, even if the method of 10BROAD-36 is adopted, if the loss varies greatly, no transmission error occurs even if the signals collide. That is, in a co-listening coaxial system, assuming that there is a maximum unidirectional loss of 40 dB, and that a series unit has a loss of 20 dB, a loss fluctuation of a maximum of 20 dB is considered. Therefore, the difference between the reception levels of the reception signals of a certain adapter is a maximum of 20 dB.
In this case, no transmission error occurs even if the signals collide. Here, the reason for considering the unidirectional loss is based on the idea that the level fluctuation of the upstream signal can be sufficiently reduced by adopting the gain control amplifier in the frequency converter.

[0016]

As described above, conventionally,
Since the coaxial cable is taken into the CATV system and the influence of the ingress noise from the coaxial cable becomes very large, there is a problem that the interactive service cannot be provided.

Further, when a LAN is configured using a co-listening coaxial cable, if the variation in loss is large, a comparison between the data signal output from the own station and the data of the signal returned after frequency conversion is performed. Unable to detect collision,
There is a problem that it is difficult to perform access control by CSMA / CD.

The present invention has been made in view of such circumstances, and a first object of the present invention is to provide a two-way service to terminals connected to a coaxial coaxial cable. It is an object of the present invention to provide a bidirectional CATV system and a repeater for realizing the system.

The object of the present invention is as follows.
Another object of the present invention is to provide a coaxial coaxial cable system capable of realizing a LAN function using a coaxial cable having a large loss variation, and an adapter for realizing this system.

[0020]

In order to achieve the first object, the present invention provides a bidirectional communication between a center device and a user terminal connected to the center device via a coaxial cable system. It performs communication, and a downlink signal of a predetermined downlink frequency band is transmitted from the center device to the user terminal, and data is modulated by a predetermined modulation method from the user terminal to the center device. In a bidirectional CATV system for transmitting an upstream signal in a predetermined upstream frequency band, a repeater is connected to each of the center device and the coaxial coaxial cable system via separate transmission lines.

The repeater includes a downstream signal extracting means such as a multiplexer / demultiplexer for extracting at least a signal other than the upstream frequency band from a signal transmitted on a transmission path to the center device. A downlink signal transmitting means such as a multiplexer / demultiplexer for transmitting the signal extracted by the extracting means to a transmission path between the co-listening coaxial cable system and a transmission path between the co-listening coaxial cable system. An uplink signal extracting means such as a multiplexer / demultiplexer for extracting the signal of the uplink frequency band from a transmitted signal, and a demodulation process according to the predetermined modulation method for the signal extracted by the uplink signal extracting means For example, a demodulator such as a demodulator, and a data identification unit such as a data identifier for identifying data from a signal demodulated by the demodulator,
A modulation means such as a modulator for performing a modulation process according to the predetermined modulation method on the data identified by the data identification means, and a signal obtained by performing the modulation process by the modulation means, Amplifying means such as an amplifier for amplifying at a designated amplification factor from, and a ratio between the amplitude of the output signal of the amplifying means and the amplitude of the signal extracted by the upstream signal extracting means is set to a predetermined state. Determine the amplification factor in the amplification means, and specify the determined amplification rate to the amplification means, for example, an amplification rate designation means such as an amplitude comparator, and at least the signal amplified by the amplification means An upstream signal transmitting means such as a multiplexer / demultiplexer for transmitting a signal other than the downstream frequency band to a transmission path between the center device and the center device is provided.

By taking such means, the down signal and the up signal between the center device and the user terminal are transmitted via the repeater. Then, in the repeater, the downlink signal is once extracted from the transmission path to the center device, and then transmitted as it is to the transmission path to the co-listening coaxial cable system.

However, the upstream signal is taken out from the transmission path to the co-listening coaxial cable system, then demodulated and identified, and temporarily terminated. Then, the identified data is demodulated again, and the amplitude thereof is adjusted so as to have a fixed relationship with the amplitude of the uplink signal extracted from the transmission path to the co-listening coaxial cable system. Is transmitted to the transmission path between

As described above, once the upstream signal is terminated by the repeater, the ingress noise is also terminated, and the ingress noise is prevented from reaching the center device. In order to achieve the second object, the present invention provides a coaxial coaxial cable network for distributing a signal supplied to a predetermined input terminal to a plurality of users by a plurality of distributors, for example, a series unit. The end is connected to the co-listening coaxial cable network, receives a signal of a predetermined uplink frequency band and a signal of a predetermined plurality of uplink pilot frequencies from the co-listening coaxial cable network, and receives a predetermined signal corresponding to the predetermined uplink frequency band. A frequency conversion unit such as a frequency conversion unit that converts the signals into a plurality of predetermined downlink pilot frequencies corresponding to the signals in the downlink frequency band and the plurality of uplink pilot frequencies and outputs the signals to the co-listening coaxial cable network. Of data between the means and another LAN terminal through the co-listening coaxial cable network A co-listening coaxial cable system is constituted by an adapter connected to the distributor for connecting the LAN terminal to the co-listening coaxial cable network, having a LAN terminal connection terminal for connecting the LAN terminal to be performed. .

The adapter applies a modulation process in accordance with a predetermined modulation method to data supplied through the LAN terminal connection terminal, and converts the data as an upstream LAN signal in the upstream frequency band into the co-listening coaxial cable. An upstream LAN signal transmitting means such as a modulation unit for transmitting to the system;
When the uplink LAN signal transmitting means transmits an uplink LAN signal, the co-listening coaxial cable system transmits an uplink pilot carrier having an uplink pilot frequency assigned only to its own device among the plurality of predetermined uplink pilot frequencies. For example, a terminal device address detection unit, an uplink pilot transmitting unit including a clock source and a frequency synthesizer, and extracting the downlink frequency band and the plurality of downlink pilot frequencies from the signal distributed by the distributor, for example, Downlink signal extraction means such as a band-pass filter, and demodulation processing according to the predetermined modulation method is performed on the downlink frequency band signal extracted by the downlink signal extraction means to reproduce data. For example, L such as a demodulation unit that outputs through the LAN terminal connection terminal N signal receiving means, detecting each of the plurality of downlink pilot frequencies from the signals of the plurality of downlink pilot frequencies extracted by the downlink signal extracting means, and detecting the presence or absence of a downlink pilot carrier at the downlink pilot frequency, for example, a mixer , A frequency sweep unit, a low-pass filter, and a detection unit, and a pilot detection unit, wherein the number of downlink pilot frequencies for which downlink pilot carriers are detected by the pilot detection unit is any one of “0”, “1 or more”, and “2 or more” A pilot arrival status monitoring means such as a pulse counter, for example, and the pilot arrival status monitoring means determines "1 or more"
When the signal transmitting means is not transmitting the upstream LAN signal, the upstream LAN signal transmitting means transmits the upstream LAN signal.
The transmission of a signal is prohibited. For example, the transmission prohibition means including a logic and a jam unit and the pilot arrival status monitoring means determine that the number is “2 or more”, and the upstream LAN signal transmission means performs transmission of the upstream LAN signal. When performing, the upstream L
A transmission interrupting means for interrupting the transmission of the AN signal, for example, comprising a logic and a jam section is provided.

By adopting such means, when transmitting an uplink LAN signal from each adapter, an uplink pilot carrier having a specific frequency is simultaneously transmitted. The frequency of each of the uplink pilot carriers is converted by a frequency conversion unit to be a downlink pilot carrier before reaching each adapter. Therefore, each adapter detects each downlink pilot frequency,
Thus, it is determined whether the number of downlink pilot frequencies at which downlink pilot carriers are detected is “0”, “1 or more”, or “2 or more”. Further, when the number of detected downlink pilot frequencies is determined to be "1 or more" and the upstream LAN signal transmitting means is not transmitting an upstream LAN signal, the upstream LAN signal transmitting means transmits the upstream LAN signal. When transmission is prohibited and it is determined to be "2 or more" and the upstream LAN signal transmitting means is transmitting an upstream LAN signal, transmission of the upstream LAN signal by the upstream LAN signal transmitting means is interrupted.

Therefore, the adapter detects the collision from simple information such as the presence or absence of the downlink pilot signal without checking the incoming data, and detects the collision reliably.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a configuration of a bidirectional CATV system according to a first embodiment of the present invention.

As shown in this figure, the bidirectional C of this embodiment is
The ATV system is configured such that a center device 1 of a bidirectional CATV network is connected via a repeater 3 to a co-listening coaxial cable network 2 constructed in an apartment house or the like. In this embodiment, the center device 1 and the coaxial coaxial cable network 2 both have the same configuration as the existing one. In this embodiment, the structure of the repeater 3 and this repeater 3 are shared with the center device 1. It is characterized in that it is interposed between the audio coaxial cable network 2.

The co-listening coaxial cable network 2 distributes signals by a distributor 21, distributes the signals to a user's home by a plurality of serial units 22, and connects a user terminal 23.

The repeater 3 includes a multiplexer / demultiplexer 31 and an amplifier 3
2. It has a multiplexer / demultiplexer 33, a demodulator 34, a data discriminator 35, a modulator 36, an amplifier 37 and an amplitude comparator 38. Next, the operation of the bidirectional CATV system configured as described above will be described.

First, when a downstream signal from the center device 1 to the user terminal 23 reaches the repeater 3, the downstream signal is given to the multiplexer / demultiplexer 31. Then, since this downstream signal has a frequency band of 70 MHz or more, it is distributed to the high-frequency port (HPF) 31 a in the multiplexer / demultiplexer 31 and supplied to the amplifier 32. And the down signal is
After being amplified by the amplifier 32, the signal is input to a high-frequency port (HPF) 33 a of the multiplexer / demultiplexer 33, and is output from the multiplexer / demultiplexer 33 toward the coaxial coaxial cable network 2. The coaxial cable network 2 may include an amplifier. In this case, the amplifier 32
May be omitted.

Thus, the downstream signal reaches the co-listening coaxial cable network 2 in the state as it was when it was transmitted from the center device 1. Then, when the downstream signal arrives in this way, in the co-listening coaxial cable network 2, the downstream signal is distributed by the distributor 21 and the serial unit 22, and is provided to the user terminal 23 in each user's home.

On the other hand, an upstream signal output from the user terminal 23 to the center device 1 in a frequency band of less than 70 MHz (the frequency actually used is a part of 10 MHz to 50 MHz) is transmitted to the serial unit 22 and the distributor 21. The signal is output from the coaxial cable network 2 via the common antenna.

When the upstream signal output from the coaxial cable network 2 reaches the repeater 3,
The upstream signal is provided to the multiplexer / demultiplexer 33. Then, since this upstream signal has a frequency band of less than 70 MHz, the low frequency port (LP
F) Distributed to 33b, demodulator 34 and amplitude comparator 3
8 given.

By the way, as a modulation method of the upstream signal,
High efficiency modulation of QPSK or 16QAM is employed. Also, a plurality of user terminals 2 are connected to one coaxial cable.
3 so that they can be connected to each other. Further, in order to avoid an interference wave entering an upstream signal, a carrier of the upstream signal can be selected.

Therefore, the low-frequency port (L
A burst-like modulated signal is output to the (PF) 33b. Such an upstream signal is once demodulated by the demodulator 34. At this time, the carrier frequency may change as described above. In this case, that is, in the case where the frequency agility is used, a mechanism for reproducing the carrier frequency input to the demodulator 34 and making the carrier frequency of the modulator 36 necessary. Here, a system that does not use frequency agility will be described. However, as described above, a system having frequency agility can be realized with a simple configuration.

By the way, for time division multiplex access, a preamble signal is added to the leading edge of a burst signal for the purpose of facilitating demodulation. This is because the presence of the preamble allows time for gain control of a signal receiving circuit and timing reproduction required in a demodulation unit.

Therefore, the signal once demodulated by the demodulator 34 may lose the leading edge of the preamble. Therefore, in this embodiment, in order to avoid such a problem, a fixed gain amplifier is used as a preamplifier of the demodulator 34. By using the fixed gain amplifier in this manner, delay in gain control is eliminated, and even when a burst signal is input, amplitude fluctuation can be reduced. However, depending on the signal modulation method, there is a case where the gain must be changed. Further, in the timing recovery by the demodulator 34, the clock recovery is performed by a PLL having a sufficiently long time constant, and based on the generated clock, a clock signal having a phase difference slightly shifted at substantially equal intervals is generated.
A synchronization method of selecting one clock signal for each burst signal is adopted. This makes it possible to suppress the lack of the leading edge of the preamble to several bits or less. In addition,
In the case of a CATV system having a sufficient preamble, the timing extraction may be realized by a high-speed PLL circuit.

The signal demodulated by the demodulation unit 34 is supplied to a data discriminator 35, where the burst data signal output from the user terminal 23 is discriminated and reproduced, and ingress noise is removed.

The burst data signal thus identified and reproduced by the data discriminator 35 is again subjected to a predetermined modulation by the modulator 36. The carrier frequency at this time is the demodulator 3
The frequency is the same as the carrier of the signal demodulated in step 4.

The signal modulated by the demodulator 34 is supplied to the amplifier 3
Amplified at 7. This amplifier 37 has a variable amplification factor, and the amplification factor is controlled by an amplitude comparator 38 so that the ratio between the output amplitude of the amplifier 37 and the input amplitude to the demodulator 34 is always constant. You. This is the center device 1
This is effective when the output amplitude of each user terminal 23 is controlled by the center-side device. Further, when the loss in the upstream signal frequency band is large in the co-listening coaxial cable network 2, it is necessary to amplify while reproducing the difference in the amplitude of the burst signal from the user terminal 23. In this case, the ratio between the input signal amplitude of the demodulator 34 and the output amplitude of the amplifier 37 is set to a large value, and it is possible to reproduce the difference in amplitude for each burst.

The signal amplified by the amplifier 37 is input to the low frequency port (LPF) 31b of the multiplexer / demultiplexer 31, multiplexed, and output to the coaxial cable of the center device 1.

As described above, according to the present embodiment, the repeater 3 is provided, where the uplink signal is once demodulated to perform data identification and reproduction, and then demodulated again and supplied to the center device 1. Therefore, all ingress noises such as living noise generated in the coaxial cable network 2 are terminated by the repeater 3 and do not leak to the center device 1 side. As a result, it is possible to provide an interactive service to the user terminal 23 accommodated in the coaxial cable network 2.

Since a certain amount of time is required for the processing in the repeater 3, a slight delay time is generated for the upstream signal. However, the time is so long as to give a serious problem to time division multiple access. Not be.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
Local area network (LAN) according to the embodiment
It is a figure showing the whole composition of a co-listening coaxial cable system with a function.

As shown in the figure, the coaxial cable system with a LAN function according to the present embodiment comprises an antenna 4, an amplifier 5, a frequency converter 6, distributors 7-1 and 7-2, a repeater 8,
It has a plurality of serial units 9, an adapter 10, a television set (TV set) 11, and a LAN terminal 12.

The antenna 4, the amplifier 5, the frequency converter 6, the distributor 7-1, the repeater 8, and the distributor 7-2 are:
Each is connected in series in the above order via a coaxial cable. Some of the series units 9 are connected to distributors 7-1 and 7-2 via coaxial cables. Furthermore, several other series units 9 are connected in series to the series units 9 connected to the distributors 7-1 and 7-2, respectively, via coaxial cables. A 12 adapter 10 is arbitrarily connected to each series unit 9, and a TV set 11 and a LAN terminal 12 are arbitrarily connected to the adapter 10.

The antenna 4 is used for FM, VHF television broadcasting,
UHF TV broadcast frequency band 70 MHz to 77
It receives a 0-MHz radio wave and converts it into an electrical high-frequency signal (hereinafter, referred to as a reception high-frequency signal).

The amplifier 5 amplifies the received high-frequency signal supplied from the antenna 4 so as to have an amplifier output of, for example, about 100 dBμV. The frequency conversion unit 6 includes the amplifier 5
Is passed through as it is. Further, the frequency conversion unit 6 is connected to an upstream LAN
Upon receiving the signal and the uplink pilot carrier, the frequency band is converted to a downlink LAN signal and a downlink pilot carrier, and then output to the distributor 7-1.

The repeater 8 has amplifiers 81 and 82 and diplexers 83 and 84 and compensates for transmission loss. The series unit 9 distributes a signal arriving via a coaxial cable by, for example, weak coupling by a transformer.

The adapter 10 separates the received high-frequency signal and the downstream LAN signal from the signal distributed by the serial unit 9 and transmits the upstream LAN signal. Further, the adapter 10 performs transmission of an uplink pilot carrier and monitoring of a downlink pilot carrier.

The TV set 11 includes VHF television broadcasting and U
It is for receiving HF television broadcasting, and is a well-known television receiver or the like. The LAN terminal 12 is connected to another L
It transmits and receives LAN signals to and from the AN terminal, and is, for example, a personal computer having a LAN function. Note that the LAN terminal 12 can also be realized as an integrated type with the TV set 11.

FIG. 3 is a functional block diagram showing a detailed configuration of the adapter 10. As shown in FIG.
Is a band rejection filter 101, a driver / receiver 10
2. Modulation section 103, terminal device address detection section 104, amplifier 105, clock source 106, frequency synthesizer section 107, band pass filters (BPF) 108, 10.
9, demodulation unit 110, collision detection unit 111, and jam unit 1
12.

Further, the collision detecting section 111 includes the mixer 12
1, frequency sweep unit 122, low-pass filter (LPF)
123, a detection unit 124, a pulse counter 125, and logics 126 and 127.

Next, the operation of the coaxial listening cable system with LAN function configured as described above will be described. When a LAN signal of a 10BASE-T system to be transmitted from one LAN terminal 12 to another LAN terminal 12 is output, this L
The AN signal is captured by the driver / receiver 102 of the adapter 10 to which the LAN terminal 12 as the output source is connected.

In this adapter 10, the LAN signal is modulated by the modulation section 103 so as to have a predetermined upstream frequency band. In the present embodiment, 132 to 138 MHz, which is a mid band between three and four channels of the television broadcast wave, is used as the uplink frequency band. Also, a QPSK method is used as a modulation method, and data transmission at a speed of 10 Mbit / s is performed in the above 6 MHz band. Also, in the case of 10BASE-T, the link pulse test signal is
The data comes from the terminal 12. In this case, it is important that the data is all “0” in the modulation unit 103.

On the other hand, part of the LAN signal received by the driver / receiver 102 is
4, the terminal device address detecting unit 10
In 4, the MAC transmission address in Ethernet is dropped, and the oscillation frequency of the frequency synthesizer 107 is determined based on the device address of the terminal side communication card. Then, the frequency synthesizer 107 generates a pilot carrier having the frequency determined by the terminal device address detector 104 based on the 10 MHz clock generated by the clock source 106.

Here, the frequency of the pilot carrier is
Make settings so that they do not overlap in this network.
Since the band of the region where the pilot carrier exists is set to 6 MHz, it is possible to set up to 100 channels at 50 kHz intervals. Therefore, within this network, 100
The number of adapters 10 can be accommodated.

The LAN signal (uplink LAN signal) modulated by the modulator 103 is amplified by the amplifier 105 and then combined with the uplink pilot carrier generated by the frequency synthesizer 107. The uplink LAN signal and the uplink pilot carrier are sent to the coaxial cable from the serial unit 9 to which the adapter 10 is connected after unnecessary frequency components are removed by the BPF 108.

The upstream LAN signal and upstream pilot carrier transmitted from the adapter 10 reach the distributor 7-1 via the coaxial cable and the serial unit 9 as appropriate, and further pass through the distributor 7-1 to pass through the frequency converter 6. To reach. The uplink LAN signal and the uplink pilot carrier transmitted from the adapter 10 connected to the serial unit 9 interposed in the coaxial cable distributed by the distributor 7-2 are transmitted by the repeater 8 to the diplexer 84. Extracted by the amplifier 82 and supplied to the amplifier 82.
The transmission loss is compensated for by being amplified by. Then, the amplified upstream LAN signal and upstream pilot carrier are transmitted to the distributor 7-1 by the diplexer 83, and reach the frequency converter 6 through the distributor 7-1.

The upstream LAN signal and the upstream pilot carrier reaching frequency conversion section 6 are 114 MHz
And a down LAN signal up-converted to 246 to 252 MHz,
It is converted to a downlink pilot carrier up-converted to 8 MHz. Then, the downlink LAN signal and the downlink pilot carrier obtained by the frequency converter 6 are output to the distributor 7-1.

On the other hand, FM and VHF television broadcasts (90 to 1
08 MHz, 170 to 222 MHz), 70 MH which is a UHF television broadcast (470 to 770 MHz) frequency band.
Radio waves of 770 MHz from z are received by the antenna 4 and converted into electrical high-frequency signals. This received high-frequency signal is amplified by the amplifier 5 so as to have an amplifier output of, for example, about 100 dBμV.

The received high-frequency signal amplified by the amplifier 5 is
The signal passes through the frequency converter 6 as it is and is output to the distributor 7-1. The downlink LAN signal, the downlink pilot carrier, and the received high-frequency signal provided from the frequency converter 6 toward the distributor 7-1 are sequentially distributed by the distributor 7-1 and the distributor 7-2. The signals are distributed to the adapters 10 connected to the respective series units 9.

The signal output from the distributor 7-1 to the distributor 7-2 is converted by the repeater 8 into a diplexer 83.
Is supplied to the amplifier 81 and is amplified by the amplifier 81 to compensate for the transmission loss. Then, the amplified signal is transmitted by the diplexer 84 to the distributor 7-2.

Here, the reason why the transmission loss is compensated in the repeater 8 is that the loss from the amplifier 5 to the TV set 11 via the plurality of series units 9 is a maximum of 40 dB. This is because the transmission loss becomes too large.

When the downstream LAN signal, the downstream pilot carrier and the received high-frequency signal arrive, the adapter 10 sets the 132-144 MHz and 246-258 MHz band rejection filters so that the downstream LAN signal and the downstream pilot carrier are not input to the TV set 11. By blocking the signal at 101, the received high-frequency signal is extracted and supplied to the TV set 11 connected to the adapter 10.

In the adapter 10, the BPF 109 extracts a signal of 246 to 256 MHz and a signal of 252 to 258 MHz, that is, a downstream LAN signal and a downstream pilot signal, and outputs the downstream LAN signal to the demodulation unit 110 and the downstream pilot signal. Each is provided to the collision detection unit 11.

The downstream LAN signal is demodulated by the demodulation unit 110 and then transmitted to the L / L through the driver / receiver 102.
It is provided to the AN terminal 12. By the way, since only one frequency band is allocated to the transmission of LAN signals, data cannot be transmitted normally if a plurality of adapters 10 transmit LAN signals at the same time. Therefore, in the collision detection unit 111, the frequency band of the downlink pilot carrier 252 to 252
258 MHz is monitored, and whether or not another adapter 10 is transmitting and whether or not there is a collision at the time of transmission by the own apparatus are monitored as follows.

That is, 25 extracted by the BPF 109
The signal of 2 to 258 MHz is provided to the mixer 121,
The mixer 121 mixes the oscillation wave generated by the frequency sweep unit 122 with the oscillation wave. Here, the frequency sweep unit 12
2 generated from 252MHz to 258M
The frequency changes in a sawtooth shape up to Hz.

The signal obtained by the mixer 121 is the LPF 1
After passing through 23, it is detected by a detection unit 124. Here, by suppressing the noise by the LPF 123 and limiting and amplifying the output signal of the mixer 121, it is possible to detect the downlink pilot carrier even if the downlink pilot carrier has an amplitude fluctuation of 40 dB. . The signal indicating the detection result in the detection unit 124 is
The frequency sweep unit 122
By counting the number of pulses in a period in which the frequency of the oscillation wave is swept once from 252 MHz to 258 MHz, the number of downlink pilot carriers from 252 MHz to 258 MHz is detected.

If the number of pulses, that is, the number of downlink pilot carriers is 1 or more, the pulse counter 125 supplies the logic 126 with the “H” level. Separately from this, the logic 126 is invertingly inputting an in-transmission display signal which becomes “H” level when the own device is transmitting. Accordingly, the logic 126 outputs the “H” level if the own device is not transmitting and at least one downlink pilot carrier exists in the signal arriving at the own device. That is, the “H” level signal output by the logic 126 is a carrier detection signal indicating that the own device cannot perform transmission because another adapter is performing transmission.

If the number of pulses, that is, the number of downlink pilot carriers is 2 or more, the pulse counter 125 supplies the logic 127 with the “H” level. Separately, the in-transmission display signal is input to the logic 127 as it is. Accordingly, the logic 127 outputs the “H” level if the own device is transmitting and if there are two or more downlink pilot carriers in the signal arriving at the own device. That is, this logic 127
The signal of “H” level output by the device becomes a collision detection signal indicating that the signal transmitted by the own device and the signal transmitted by the other adapter 10 collide.

The signals output from the logics 126 and 127 are supplied to the jam section 112. Then, in the jam section 112, if a carrier detection signal is given from the logic 126, control is performed to put the apparatus itself in a transmission waiting state. .

In the jam section 112, the logic 127
, A jam signal is generated and output to the serial unit 9 via the modulator 103, the amplifier 105, and the BPF 108.
When the jam signal reaches each of the other terminals, the occurrence of a collision is notified to all the terminals. Also, at this time, the jam unit 112 performs control for putting the apparatus itself in a transmission waiting state, and further waits for a predetermined time, and then performs control to challenge the transmission again.

Further, in the jam section 112, the logic 12
In a state where the carrier detection signal is not supplied from No. 6, that is, in a state where the downlink pilot carrier has not arrived at all, control for outputting a link pulse test signal to the demodulation section 110 is performed. A signal is output.

As described above, according to the present embodiment, the collision detection section 111 of the adapter 10 detects the downlink pilot carriers for each adapter 10 in order. Then, when the number of downlink pilot carriers that can be detected is two or more and the own device is transmitting, it is determined that a collision has occurred in the transmission of the own device. ing.

As a result, even if the difference between the reception levels of the received signals is large, it is possible to reliably determine whether or not a collision has occurred, and it is possible to appropriately perform access control by the CSMA / CD method. It is. Therefore, it is possible to realize the LAN function by using a co-listening coaxial cable system having a large transmission loss.

According to the present embodiment, between the distributor 7-1 and the distributor 7-2, the amplifier 81 for amplifying a signal from the distributor 7-1 to the distributor 7-2 and the distributor 81 are provided. A repeater 8 provided with an amplifier 82 for amplifying a signal from 7-2 to a distributor 7-1 is interposed. Here, both the upstream LAN signal and the downstream LAN signal are amplified to compensate for transmission loss. Since it is performed, it is possible to transmit and receive a signal of a sufficient level between the adapters 10 connected via the many distributors 7 and the series unit 9.

The present invention is not limited to the above embodiments. For example, in the first embodiment, the case where the frequency agility is not used is exemplified. However, when the frequency agility is adopted, the frequency of the local oscillator applied to the uplink signal can be changed to the carrier frequency of the modulation so that the modulation can be performed again. It is good to keep it.

In the second embodiment, it is also possible to prepare a plurality of antenna terminals to be distributed from the series unit, and connect the adapter 10 to each of these antenna terminals.

In the second embodiment, the LAN system
Although an example in which 10BASE-T is adopted is shown, another well-known scheme or an original scheme can be adopted as appropriate. In the second embodiment, the pilot carrier frequency to be transmitted is determined based on the MAC transmission address. However, the present invention is not limited to this, and the pilot carrier frequency of each adapter 10 connected to the same system is individually different. For example, a method of directly setting with a DIP switch without referring to the MAC transmission address can be used.

The values of the frequencies assigned to the various signals are not limited to those shown in the above embodiments, but may be arbitrary. For example, for an uplink frequency band, bidirectional CAT
Even in the frequency band of 50 MHz or less adopted in V, if the passing loss in the distributor or the series unit is not large, it can be used without any problem.

In the second embodiment, the antenna 4
TV broadcast waves transmitted to the V set 11
Is passed without loss, but in the case of handling a television broadcast wave by a digital modulation signal, a function of processing the signal into a signal receivable by the TV set 11 may be added to the adapter 10.

In the second embodiment, a plurality of adapters 1
By connecting a router to one of the 10BASE-T ports and connecting the router to an external WAN, it is possible to access the Internet from individual homes via the system. In addition, leased lines, public networks and two-way CAs
Connection with a TV or the like is also possible.

In the second embodiment, the problem of security is important, but it is possible to maintain security at the level of the application in the LAN terminal 12. It is also possible to provide a firewall function for each home between the adapter 10 and the LAN terminal 12. This firewall function, a router function that allows multiple terminals to be at home, and WWW (Worl
d Wide Web) A proxy server function, a mail server function, and the like can be implemented in the adapter 10. In addition, various modifications can be made without departing from the spirit of the present invention.

[0087]

According to the present invention, two-way communication is performed between a center device and a user terminal connected to the center device via a coaxial cable system. A bidirectional CATV for transmitting a downlink signal of a predetermined downlink frequency band to a user terminal and an uplink signal of a predetermined uplink frequency band obtained by modulating data by a predetermined modulation method from the user terminal to the center device. In the system, a repeater is connected to each of the center device and the co-listening coaxial cable system via separate transmission lines.

[0088] The repeater includes a down signal extracting means for extracting at least a signal other than the up frequency band from a signal transmitted through the transmission path to the center device, and a signal extracted by the down signal extracting means. Signal to the transmission path between the coaxial cable system and the downlink signal transmitting means, and extracting the signal in the uplink frequency band from the signal transmitted through the transmission path between the coaxial cable system and the coaxial cable system Uplink signal extraction means, demodulation means for performing demodulation processing according to the predetermined modulation method on the signal extracted by the uplink signal extraction means, and data identification for identifying data from the signal demodulated by the demodulation means Means, modulation means for performing a modulation process according to the predetermined modulation method on the data identified by the data identification means, The halftone processing is obtained done signal,
Amplifying means for amplifying at an amplification rate designated from the outside; and the amplifying means so that a ratio between the amplitude of the output signal of the amplifying means and the amplitude of the signal extracted by the upstream signal extracting means is in a predetermined state. The amplification factor of the amplification means is determined, and the determined amplification rate is specified to the amplification means.
And an upstream signal transmitting unit for transmitting at least a signal other than the downlink frequency band among the signals amplified by the amplifying unit to a transmission path between the central unit and the central unit.

As a result, a bidirectional CATV system capable of providing a bidirectional service even to a terminal connected to the coaxial coaxial cable, and a repeater for realizing this system are provided.

Further, according to the present invention, a co-listening coaxial cable network for distributing a signal supplied to a predetermined input terminal to a plurality of users by a plurality of distributors, and the input terminal is connected to the co-listening coaxial cable network. Receiving a signal of a predetermined uplink frequency band and a signal of a plurality of predetermined uplink pilot frequencies from the co-listening coaxial cable network, and receiving a signal of a predetermined downlink frequency band corresponding to the predetermined uplink frequency band and the plurality of uplink pilot frequencies. Frequency conversion means for converting the signals into signals of a predetermined plurality of downlink pilot frequencies corresponding to the respective frequencies and outputting the signals to the co-listening coaxial cable network, and connecting the co-listening coaxial cable network with another LAN terminal. Having a LAN terminal connection terminal for connecting a LAN terminal that transmits and receives data via the LA Terminal constituting the co 聴同 axis cable system by the adapter connected to the distributor in order to connect to the co 聴同 axis cable network.

The adapter performs a modulation process in accordance with a predetermined modulation method on the data supplied through the LAN terminal connection terminal, and converts the data into an upstream LAN signal of the upstream frequency band. An upstream LAN signal transmitting means for transmitting to the system, and when the upstream LAN signal transmitting means transmits an upstream LAN signal, an uplink pilot frequency assigned to only the own apparatus among the plurality of predetermined uplink pilot frequencies. Upstream pilot transmitting means for transmitting an uplink pilot carrier having the following to the co-listening coaxial cable system, and downlink signal extracting means for extracting the downlink frequency band and the plurality of downlink pilot frequencies from the signal distributed by the distributor. When,
A LAN that demodulates the signal of the downlink frequency band extracted by the downlink signal extracting means in accordance with the predetermined modulation scheme to reproduce data, and outputs the data through the LAN terminal connection terminal Signal receiving means, and pilot detection means for detecting the plurality of downlink pilot frequencies from the signals of the plurality of downlink pilot frequencies extracted by the downlink signal extraction means, respectively, to detect the presence or absence of a downlink pilot carrier in the downlink pilot frequency, A pilot arrival status monitoring means for determining whether the number of downlink pilot frequencies for which downlink pilot carriers have been detected by the pilot detection means is “0”, “1 or more”, or “2 or more”; The status monitoring means has determined that the value is "1 or more", and the upstream LA When the signal transmission means is not transmitting an uplink LAN signal, the transmission inhibition means for inhibiting the transmission of the uplink LAN signal by the uplink LAN signal transmission means and the pilot arrival status monitoring means determine "2 or more". And a transmission suspending means for suspending the transmission of the upstream LAN signal by the upstream LAN signal transmitting means when the upstream LAN signal transmitting means is transmitting the upstream LAN signal.

Thus, a coaxial listening coaxial cable system capable of realizing a LAN function using a coaxial listening coaxial cable having a large loss variation and an adapter for realizing this system are provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a bidirectional CATV system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an overall configuration of a co-listening coaxial cable system with a local area network (LAN) function according to a second embodiment of the present invention.

FIG. 3 is a functional block diagram showing a detailed configuration of an adapter 10 in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Center apparatus 2 ... Coaxial coaxial cable network 21 ... Distributor 22 ... Series unit 23 ... User terminal 3 ... Repeater 31 ... Demultiplexer / demultiplexer 32 ... Amplifier 33 ... Demultiplexer / demultiplexer 34 ... Demodulator 35 ... Data discriminator 36 Modulator 37 Amplifier 38 Amplitude comparator 4 Antenna 5 Amplifier 6 Frequency converter 7-1, 7-2 Distributor 8 Repeater 81, 82 Amplifier 83, 84 Diplexer 9 Serial Unit 10: Adapter 101: Band rejection filter 102: Driver / receiver 103: Modulator 104: Terminal device address detector 105: Amplifier 106: Clock source 107: Frequency synthesizer 108, 109 Band-pass filter (BPF) 110: Demodulation Unit 111: Collision detection unit 112: Jam unit 121: Mixer 122: Frequency sweep unit 123: Low Pass filter (LPF) 124 ... detection unit 125 ... pulse counter 126, 127 ... logic 11 ... television set (TV set) 12 ... LAN terminal

Claims (5)

[Claims] 1. A bidirectional communication is performed between a center device and a user terminal connected to the center device via a coaxial cable system, and the center device communicates with the user terminal. A bidirectional CATV system for transmitting a downlink signal of a predetermined downlink frequency band, and an uplink signal of a predetermined uplink frequency band obtained by modulating data by a predetermined modulation method from the user terminal to the center device, A repeater is connected to each of a center device and the co-listening coaxial cable system via separate transmission lines, and the repeater has at least the upstream frequency band from a signal transmitted through the transmission line between the center device and the center device. Downlink signal extraction means for extracting a signal other than the signal between the coaxial coaxial cable system and the signal extracted by the downlink signal extraction means Downlink signal transmission means for transmitting to a transmission path, Uplink signal extraction means for extracting a signal in the upfrequency band from a signal transmitted on a transmission path between the co-listening coaxial cable system, and Uplink signal extraction means Demodulation means for performing demodulation processing according to the predetermined modulation method on the signal extracted by the above, a data identification means for identifying data from the signal demodulated by the demodulation means, and a data identification means for identifying the data. A modulating means for performing a modulation process in accordance with the predetermined modulation method on the data, an amplifying means for amplifying a signal obtained by performing the modulation process by the modulating device at an amplification factor specified from the outside, The amplification factor of the amplifying means is determined so that the ratio between the amplitude of the output signal of the amplifying means and the amplitude of the signal extracted by the upstream signal extracting means is in a predetermined state. An amplification factor designating unit for designating the determined amplification factor to the amplifying unit; and a signal other than at least the downlink frequency band among the signals amplified by the amplifying unit is transmitted to a transmission path between the center device. And an upstream signal transmitting means for transmitting the signal. 2. A two-way communication is performed between a center device and a user terminal connected to the center device via a co-listening coaxial cable system, and the center device communicates with the user terminal. A downlink signal of a predetermined downlink frequency band, and from the user terminal to the center device, in a bidirectional CATV system for transmitting an uplink signal of a predetermined uplink frequency band obtained by modulating data by a predetermined modulation method,
In a repeater that is used by being connected to each of the center device and the co-listening coaxial cable system via a separate transmission line, a signal transmitted through the transmission line between the center device and at least a signal other than the uplink frequency band A downlink signal extracting unit for extracting a signal; a downlink signal transmitting unit for transmitting a signal extracted by the downlink signal extracting unit to a transmission path between the coaxial cable system; and the coaxial cable system. An uplink signal extracting means for extracting a signal of the uplink frequency band from a signal transmitted through a transmission path between the above, and demodulating a signal extracted by the uplink signal extracting means in accordance with the predetermined modulation method. Demodulating means to be applied; data identifying means for identifying data from a signal demodulated by the demodulating means; Modulation means for performing a modulation process in accordance with the predetermined modulation method on the data obtained, and amplification means for amplifying a signal obtained by performing the modulation process by the modulation means at an amplification rate designated from the outside. The amplification factor in the amplification device is determined so that the ratio between the amplitude of the output signal of the amplification device and the amplitude of the signal extracted by the upstream signal extraction device is in a predetermined state. Amplification factor designating means for designating the amplifying means; and an up signal for transmitting at least a signal other than the downlink frequency band among signals amplified by the amplifying means to a transmission path between the center device. A repeater comprising sending means. 3. A co-listening coaxial cable network for distributing a signal supplied to a predetermined input terminal to a plurality of users by a plurality of distributors; A signal of an uplink frequency band and a signal of a predetermined plurality of uplink pilot frequencies are received from the co-listening coaxial cable network, and a signal of a predetermined downlink frequency band corresponding to the predetermined uplink frequency band and the plurality of uplink pilot frequencies, respectively. Frequency conversion means for converting the signals into a plurality of signals of a predetermined plurality of downlink pilot frequencies corresponding to the above and outputting the signals to the co-listening coaxial cable network; A LAN terminal connection terminal for connecting a LAN terminal that exchanges data with the LAN terminal. An adapter connected to the distributor for connection to an audio coaxial cable network, and the adapter is adapted to a given modulation scheme for data provided via the LAN terminal connection terminal. An upstream LAN signal transmitting means for performing a modulation process and transmitting the same as the upstream LAN signal in the upstream frequency band to the co-listening coaxial cable system; and wherein the upstream LAN signal transmitting means transmits the upstream LAN signal. Outgoing pilot transmitting means for transmitting to the co-listening coaxial cable system an uplink pilot carrier having an uplink pilot frequency assigned only to the own device among predetermined uplink pilot frequencies, and a signal distributed by the distributor. A downlink signal extracting means for extracting the downlink frequency band and the plurality of downlink pilot frequencies, respectively. And demodulating the signal of the downstream frequency band extracted by the downstream signal extracting means in accordance with the predetermined modulation method to reproduce data, and outputting the data via the LAN terminal connection terminal. LAN signal receiving means, and pilot detection for detecting the plurality of downlink pilot frequencies from the signals of the plurality of downlink pilot frequencies extracted by the downlink signal extracting means, respectively, and detecting the presence or absence of a downlink pilot carrier at the downlink pilot frequency. Means, the number of downlink pilot frequencies for which downlink pilot carriers have been detected by the pilot detection means are “0”, “1”.
Pilot arrival status monitoring means for determining which of the above is "2 or more"; and "1 or more" determined by the pilot arrival status monitoring means, and the uplink LAN signal transmitting means is an uplink LAN signal. Is not transmitted, the uplink L
Transmission inhibiting means for inhibiting transmission of an uplink LAN signal by the AN signal transmitting means, and being determined to be "2 or more" by the pilot arrival status monitoring means, and wherein the uplink LAN signal transmitting means transmits the uplink LAN signal. The above LA
A coaxial listening coaxial cable system comprising: transmission interruption means for interrupting transmission of an uplink LAN signal by N signal transmission means. 4. An adapter, comprising: a broadcast receiving terminal connection terminal for connecting a predetermined broadcast receiving terminal that receives a broadcast signal of a predetermined frequency band externally supplied to an input terminal; The co-listening coaxial cable system according to claim 3, further comprising: a broadcast signal extracting unit that extracts a frequency band of the broadcast signal and outputs the frequency band to the broadcast receiving terminal connection terminal. 5. A co-listening coaxial cable network for distributing a signal provided to a predetermined input terminal to a plurality of users by a plurality of distributors; A signal of an uplink frequency band and a signal of a predetermined plurality of uplink pilot frequencies are received from the co-listening coaxial cable network, and a signal of a predetermined downlink frequency band corresponding to the predetermined uplink frequency band and the plurality of uplink pilot frequencies, respectively. And a frequency conversion unit for converting the signal into a plurality of signals of a predetermined plurality of downlink pilot frequencies and outputting the signal to the coaxial cable network. A LAN terminal that exchanges data via the co-listening coaxial cable network is connected to the co-listening coaxial cable network. An adapter used by being connected to the distributor to connect to the work; a LAN terminal connection terminal for connecting the LAN terminal; and a predetermined data for data given through the LAN terminal connection terminal. An upstream LAN signal transmitting means for performing a modulation process according to a modulation method and transmitting the same as the upstream LAN signal of the upstream frequency band to the co-listening coaxial cable system; and the upstream LAN signal transmitting means transmits the upstream LAN signal. In some cases, among the plurality of predetermined uplink pilot frequencies, an uplink pilot transmitting means for transmitting an uplink pilot carrier having an uplink pilot frequency assigned only to the own apparatus to the co-listening coaxial cable system; From the distributed signal, the downlink frequency band and the plurality of downlink pilot frequencies are respectively A downlink signal extracting unit that outputs the downlink frequency band signal extracted by the downlink signal extracting unit, and demodulates the signal according to the predetermined modulation scheme to reproduce data; LAN signal receiving means for outputting via a connection terminal; detecting the plurality of downlink pilot frequencies from the signals of the plurality of downlink pilot frequencies extracted by the downlink signal extracting means, respectively; Pilot detection means for detecting the presence / absence; and the number of downlink pilot frequencies for which downlink pilot carriers have been detected by the pilot detection means are “0”, “1”.
Pilot arrival status monitoring means for determining which of the above is "2 or more"; and "1 or more" determined by the pilot arrival status monitoring means, and the uplink LAN signal transmitting means is an uplink LAN signal. Is not transmitted, the uplink L
Transmission inhibition means for inhibiting transmission of an uplink LAN signal by the AN signal transmission means, and the pilot arrival status monitoring means determines that the value is "2 or more", and the uplink LAN signal transmission means transmits the uplink LAN signal. The above LA
An adapter comprising transmission interruption means for interrupting transmission of an uplink LAN signal by N signal transmission means.