JPH0946667A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the communication system attaining economical multimedia communication with a high frequency utilizing efficiency and immunity to noise by allowing a central station to select an exclusive communication channel or a common communication channel depending on a communication request from a terminal station. SOLUTION: A head end 1 being a central station and a terminal station 5 are connected via a trunk line cable 2, a relay amplifier 3 and a tap-off 4 and communication between terminal stations 5 is conducted via the central station 1, and the system has a private communication channel allocated between the terminal stations 5 and a common communication channel allocated multiplexingly simultaneously to plural terminal stations 5. The central station 1 selects the private communication channel or the common communication channel. Thus, the communication system is attained, in which various communication service from a telephone communication to high speed data communication are covered and economical multimedia communication with high frequency utilizing efficiency and immunity to noise is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a central office,
The present invention relates to a communication system in which a plurality of terminal stations are connected via a bidirectional communication path, and communication between the terminal stations is performed via a central station. In particular, the present invention relates to a communication system suitable for using multimedia of various information forms such as audio information, computer output data, text information and graphics or moving images, and quasi-moving images.

[0002]

2. Description of the Related Art In recent years, a communication system using a CATV network has attracted attention both inside and outside the country as a new communication infrastructure.
As a communication system corresponding to this trend, an MCA / C called "analog CATV telephone" at a practical level is used.
There is a telephone system. This MCA / C telephone system
Multi-channel access (hereinafter abbreviated as MCA) based on FM radio technology proven in the wireless field.
Because it was applied to the ATV network, on-cable (on C
able) and named MCA / C.

In the MCA / C telephone system, as shown in FIG. 11, as shown in the main specifications, a 2.5-MHz band for each of the upstream and downstream in the CATV transmission line is used, and 200 MHz at a carrier frequency interval of 12.5 KHz. The communication channel of the channel is obtained. FIG. 7 shows an example of the MCA / C telephone system.

FIG. 7 is a block diagram showing a conventional example of an MCA / C system in which a part of the facilities of the CATV system is operated in common, wherein 1 is a head end,
It is located at the center of the CATV system, and a plurality of trunk cables 2-1 to 2-n extend from the head end 1 for each route.

The head end 1 has a trunk cable 2-1.
An input / output distribution device 101, which is a branch coupling unit of .about.2-n, is provided. A CATV broadcast facility 102 and a block converter 103 are connected to the input / output distribution device 101. Further, a line control device 104, The communication management device 105 is connected.

The trunk cables 2-1 to 2-n are provided for each route, but are generally divided into a plurality of routes in order to limit the number of accommodated subscribers and the cable length. is there.
And the trunk cables 2-1 to 2-n of these respective routes are
Is extended by connecting the bidirectional relay amplifiers 3-1 and 3-2 in multiple stages.

[0007] The branch cables branched from the bidirectional relay amplifiers 3-1 and 3-2 have tap-offs 4-1 and 4-2, and are configured to branch to subscribers 5-1 and 5-2. , As a whole, constitute a tree-like network.

[0008] A distributor 501, a television receiver 502, a network terminating device 50 are installed in the homes of the subscribers 5-1 and 5-2.
3. Telephone 505 and FAX / PC 506 are provided.
With the reception of multi-channel television broadcasting, telephone, F
Intra-region communication by AX, PC, etc. can be performed. In this intra-area communication, a bidirectional transmission system is used in which the direction from the subscriber to the headend is set as up, and the direction from the headend to the subscriber is set as down.

In response to the digitalization trend of the MCA / C telephone system, a system called a "digital CATV telephone" has recently been developed in various fields. As a system for realizing this digital CATV telephone, a time division multiplexing (hereinafter abbreviated as TDMA) system is adopted.

In the TDMA system of the digital CATV telephone system which is currently under development, the communication path has a bandwidth of one TV channel of the NTSC system.

TDM for digital CATV telephone system
An example of the A method is shown below.

[0012] Four-phase phase modulation (hereinafter abbreviated as QPSK modulation) is performed using the entire area of the 6 MHz band, and about 8 Mb
There is an example in which a transmission rate of ps is secured, and TDMA is implemented in units of 64 Kbps as a transmission rate per terminal.

There is an example in which QPSK modulation is performed for each 1.5 MHz subchannel obtained by dividing a 6 MHz band into four, about 2 Mbps is secured for each subchannel, and TDMA in units of 64 Kbps is realized.

FIG. 10 shows a TDMA using a CATV network.
FIG. 2 is a conceptual block diagram for explaining a line connection operation in a system telephone communication. ts1, ts2,... tsn and Ts1, Ts2
.., Tsn are shown.
The terminal station 51 uses ts1 for uplink (transmission). The time slot of Ts1 is used for downlink (reception). The terminal station 52 uses ts3 for uplink (transmission) and Ts for downlink (reception).
Each of the 3 time slots is used. The conversion of the time slot from upstream to downstream indicated by the dashed arrow is performed by the exchange 41 and the multiplexer 42 in the head end 40. The terminal station 52 has network terminating devices 513,
523 and telephones 515 and 525 are connected.

FIG. 12 is a main specification table of the TDMA system of FIG. According to the table, sub-channels consisting of 4 carriers are configured at a carrier frequency interval of 1.5 MHz using up and down 6 MHz bands in the CATV transmission line, and 24 channels per sub channel, for a total of 96 channels Are obtained.

The MCA / C telephone system first put into practical use as a general-purpose communication system using a CATV network has a limit in its use. On the other hand, digital CATV telephones currently under development are in a transitional period of development. Published TDMA for digital CATV telephones
The method has the following features, problems, and the like in relation to the characteristics of the CATV network, the use form, the business form, and the like.

First, the characteristics of the CATV network will be described.

(1) Bidirectional C composed of a tree-like network
In the ATV network, there is upstream ingress noise (a noise mixed into a distribution system or a home wiring system which flows into a head end) peculiar to the CATV network in an upstream transmission band. In the upstream transmission band, a transmission system with higher noise resistance is required as compared with the transmission of television video signals and the like in the downstream transmission band.

(2) Upstream ingress noise occurs in a specific band due to interference by a radio device or the like. Generally, the upstream ingress noise is caused by contamination of noise generated from home electric appliances and industrial equipment. When noise is observed with a spectrum analyzer or the like, a situation in which narrow-band, short-duration, impulse-like noise is randomly generated on the frequency axis is observed. From this situation, it can be said that a transmission scheme using a wide band has a high probability of being disturbed by noise.

(3) In the conventional CATV, even if the equipment is bidirectional, the use of the upstream transmission band including the end of the cable is less than that of the downstream transmission band. Therefore, no attention has been paid to the countermeasure for upstream ingress noise, and various experiments have revealed that the level of upstream ingress noise is generally poor in existing CATV networks.

In order to improve this, all the terminals are visited and
It is necessary to confirm the source of the mixed noise and to strengthen the shield of the cable itself and the coaxial connector. However, in CATV, since thousands to tens of thousands of terminals are targeted per system, it is expected that significant cost will be generated for noise countermeasures.

(4) In the CATV network, it is necessary to cope with noise generated in the network in addition to the noise mixed from outside as described above. The noise generated in the network is mainly caused by the nonlinearity of the transmission path.

In a CATV network, multistage relay amplification is performed to compensate for line loss. Inter-channel interference, which depends on the characteristics of the relay amplifier and the number of relay stages and is caused by the non-linearity of the amplifier, caused by cross-modulation, inter-modulation, etc., is a problem.
As a measure to prevent this effect from exceeding the limit, the total transmission power per TV channel is limited, and the number of channels is limited when the frequency band of the television channel is further used. .

On the other hand, in the CATV network, as the trunk line becomes an optical cable, the nonlinearity of the entire network tends to be improved by reducing the number of relay stages.

(5) It has been known that, when performing wideband, high-speed digital transmission in a CATV network, a reflected wave caused by impedance mismatch of a transmission line has an effect. In order to improve this problem as well, its range extends to the end of the in-home wiring and terminal equipment, and it is expected that the ideal improvement will be difficult in terms of cost.

(6) In the CATV network, up / down signals pass through one coaxial cable. In the Japanese CATV network, the upstream band: 10 MHz to 50 MH
z, downstream band: 70 MHz to 450 MHz (or 750
MHz) is common. Even if the entire upstream band can be used, the total number of possible channels with a 6 MHz bandwidth as one channel is as small as 6 channels. In addition, the above-mentioned upstream inflow noise is not uniform in all bands, and is 10 MHz.
It is often found in the band of ２０20 to several MHz. Channels in a noisy band cannot be used. In the United States, the upstream band is narrower than in Japan, at 10 to 30 MHz.

[0027] Under such circumstances, the upstream channel is very valuable, and efficient use is required.

Next, the problems of MCA / C are as follows: (7) MCA / C is a narrow band transmission system as compared with the characteristics of a transmission line such as the CATV network described above, and therefore, it is possible to perform quite good transmission. The advantage is that it can take a large number of channels.
However, MCA / C has a drawback that data transmission is limited to about 9600 bps, and it is impossible to provide services exceeding this.

Next, the problems of the TDMA are as follows: (8) Digital C
For ATV phones, as mentioned above, 6 MHz or 1.5
Since a wide band such as MHz is used, it is easily affected by upstream ingress noise having the above-described properties. In addition, there is a drawback that since the transmission is broadband and high-speed, it is easily affected by reflection due to impedance mismatch.

(9) The noise level at each terminal station dispersedly arranged in the tree-like CATV network is not uniform, and there is considerable variation depending on the route of the trunk line. In order to ensure uniform transmission quality throughout the system, it is desirable that the ratio of carrier level to noise level (C / N) be the same at each terminal station. In a system in which a carrier is divided for each communication channel, within a permissible value of the total transmission power of one TV,
Weighted power distribution is possible in which a high transmission level is assigned to communication with a terminal station on a path having a high noise level. However, it is difficult to use a method of transmitting a plurality of communication channels using one carrier such as TDMA.

(10) In the TDMA system, 64 Kbps by PCM transmission is set to 1ch and connected to an analog telephone. As a result, in terms of the frequency utilization efficiency per 6 MHz, the MCA / C is 200 when compared with the number of channels constituting the voice transmission band (0.3 to 3.4 kHz).
However, TDMA is inferior to 96 ch. In addition,
In this case, the MCA / C uses 2.
It is limited to 5 MHz.

(11) In the CATV telephone system, a fixed-rate system is adopted in order to avoid a high facility cost of the telephone charge management system. The flat-rate system is a system in which telephone charges for a predetermined period are constant regardless of the usage amount. There is a need for a CATV telephone system that can accommodate many subscribers at low cost. The following two methods are conceivable as telephone communication methods. One is the immediate connection type, in which the terminals occupy the line once, and the other terminals cannot enter the line until the communication ends, as in the line connection method of the existing subscriber telephone system. Communication method. the other one is,
There is a waiting-type communication method such as a LAN (Local Area Network) in which a common line is assigned to a plurality of terminals and each terminal is given a waiting time until the common line can be accessed. In personal computer communication, the data transmission speed is determined by the signal transmission speed of the terminal device even if the maximum signal transmission speed of the communication line is high. Further, there is a period during which data is not actually transmitted even while the communication line is connected between the computer terminals. Therefore, the line utilization rate of data communication between personal computers generally shows a small value. For a subscriber who connects a data processing device such as a computer to the CATV telephone system, the latter communication method such as LAN is suitable.

In order to increase the line utilization rate, it is advantageous to adopt a system in which a large number of terminals are accommodated in one channel and communication is performed in a queuing mode, such as a LAN. In such a LAN type communication system, the line speed is effectively absorbed by absorbing the speed difference between the terminal and the line, and making other terminals use the non-operation time when the line is held but not used. It will be available. It is difficult to realize such communication in the TDMA system based on the instantaneous circuit switching system.

(12) Further, in the TDMA system, in the same manner as the voice channel allocation in the MCA / C system described later, since the full-duplex communication system (full-duplex) is adopted, two time slots for each of up and down, That is, allocation of each 2ch is required. In the case of the LAN type, half-duplex communication is premised, so that a line can be configured by allocating one channel.

There are various forms of data communication, and most of the forms involve data transmission from one terminal to the other terminal. A system in which a line is always open while simultaneous transmission can be performed in both directions is disadvantageous in line use efficiency.

(13) TDMA of CATV telephone system
Is based on 64 Kbps / ch. Generally, a terminal having a transmission rate different from the transmission rate of a line requires an adapter for performing rate conversion because the network terminating device of the terminal does not have a rate conversion function. In a LAN, the line speed is basically different from the terminal speed, and it is possible to flexibly cope with a difference in transmission speed.

Finally, problems of the LAN will be described.

(14) For example, the IE of the LAN standard
In the LAN system as shown in EE 802.3, the terminal connected to the node can make a call at any time under a certain condition, and has a means for controlling the total amount of traffic of the network such as a call regulation. Not not.

When a LAN communication system is applied to a CATV network, it is necessary to provide a system that assumes that the number of subscribers is very large. For example, in a traffic state in which the waiting time exceeds a certain time, it is considered necessary to have a function of restricting a new communication request (regulating the allocation to the channel).

(15) Some data transmissions using the CATV network are required to transmit high-speed and continuous data, such as moving image transmission. There is a problem that high-speed continuous data transmission is not suitable for a system such as a LAN that assumes intermittent data transmission in packet units. In order to solve such a problem, it is necessary to occupy the channel in a state similar to circuit switching, depending on the type of information to be transmitted, so that a continuous data transmission service can be provided.

Such services are not intended for all ordinary subscribers. For example, the home welfare service can be limited to a specific use such as a communication system connecting a hospital or a welfare center with an elderly living alone.

(16) In a LAN system, a baseband transmission system using the entire band of one cable, which is a common transmission line, is generally used. The band is divided to provide a plurality of channels, and for each channel, There are no examples of enabling different services.

[0043]

As a use of a communication network in a multimedia environment, voice information, facsimile,
It is conceivable to transmit various types of information such as text information, graphics, moving pictures, quasi-moving pictures, or computer output data using one communication network, for example, the CATV network as a transmission medium. CA information of these various forms
It is desirable to be able to efficiently transmit between terminals of many subscribers in a TV network. The service area of the CATV network has been expanding in recent years.

In the existing CATV network, video information is mainly broadcast, and telephone communication is about to be added. It is relatively easy to connect the above-described various information processing devices and communication devices to this CATV network. C
Various information processing devices and communication devices including telephones, televisions, facsimile devices, and computers can be relatively easily connected to a terminal station of an ATV subscriber. If such various communication services become possible, it is expected that the number of subscribers to the CATV network will increase.

However, it is not preferable from the viewpoint of efficient operation of the line to collectively transmit various information having different forms by the same transmission method.

A system such as a LAN system in which a signal may be divided in a packet unit is not desirable for a telephone or a moving image requiring continuity of information. For such kind of information, it is preferable to use an immediate communication system in which a line is occupied between terminals after the line is connected until the communication is completed.

In the communication of information such as computer data, a waiting-type communication method such as the LAN method which allocates a common communication channel to a plurality of different terminals is desirable as described above.

It is an object of the present invention to provide a communication system which enables efficient multimedia communication in a bidirectional communication network such as a CATV network.

Another object of the present invention is to provide a communication system that is resistant to noise and enables economical multimedia communication.

Suitable for CATV in multimedia environment,
According to the embodiment of the present invention, from the viewpoint of efficient use of the line, the above two methods can be used properly according to the information form. C
The frequency band of the communication path of the ATV network is allocated to a band for the immediate communication system and a band for the queuing communication system.

Further, by dividing the band of the waiting communication system into a plurality of channels and narrowing each band, it is possible to reduce noise and economically use the line.

[0052]

In the communication system of the present invention, one central station and a plurality of terminal stations are connected via a bidirectional communication path, and the communication between the terminal stations is the above-mentioned. A communication system performed via a central station, having a dedicated communication channel allocated between a terminal station and another terminal station, and a common communication channel simultaneously allocated to a plurality of terminal stations, The central station has a control unit that selects one of a dedicated communication channel and a common communication channel in response to a communication request from the terminal station.

Further, in the system according to the present invention, the communication path includes a plurality of traffic channels in which the common communication channel and the dedicated communication channel are set, and one or more control signals are transmitted. And a control channel of the plurality of traffic channels in response to a communication request from one or more of the plurality of terminal stations. A control signal for assigning to the terminal station and designating the assigned traffic channel may be transmitted to the terminal station via the control channel.

Further, the control means has means for preventing signal collision by controlling the common communication channel so that only one signal is transmitted when a plurality of different signals exist in the common communication channel. You may have.

Further, the frequency band of the communication channel is divided into a plurality of bands, and the plurality of traffic channels are set by frequency division in each of the divided bands, and the plurality of traffic channels have different bandwidths. It may be configured to have.

Further, a unique code may be assigned to each of the plurality of terminal stations on the communication path, and the plurality of traffic channels may be set by a code multiplexing method.

Further, a plurality of voice signal channels and data channels are arranged in the traffic channel, the voice signal channel is assigned to the dedicated communication channel, and the data channel is assigned to the common communication channel. Is also good. The frequency band of the dedicated communication channel and the frequency band of the common communication channel are alternately arranged in a predetermined frequency band, or the frequency band of the dedicated communication channel and the frequency band of the common communication channel are a predetermined frequency. You may make it arrange | position together in an arbitrary order in a zone | band.

The central station may have a service management means for setting an upper limit of the usage time of the common signal channel assigned to the terminal station when a communication request is issued from the terminal station. Further, the central station may have a service management means for setting the waiting time of the common signal channel for each terminal station, or a service management means for setting the data transmission rate of the common signal channel for each terminal station. Means may be provided.

The upper limit of the use time is provided with a plurality of groups of one or more terminal stations, and the service management means of the central station sets the upper limit of the use time for each group. You can

The waiting time includes a plurality of groups each consisting of one or more terminal stations, and the service management means of the central station sets the waiting time for each group. good.

Regarding the data transmission rate, a plurality of groups of one or more terminal stations are provided, and the service management means of the central station sets the data transmission rate for each group.

In the communication system of the present invention, various communication devices of different information types including a telephone, a television, a fax machine, and a computer are connected to a plurality of terminal stations. Further, in response to a communication request from a terminal station to which the computer is connected, the control means controls the allocation of the dedicated communication channel to the terminal station.

[0063]

BEST MODE FOR CARRYING OUT THE INVENTION A multimedia communication system according to the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the present invention, in which 1 is CAT.
Head end which is a central station of V network, 2-1 to 2-n are main cables, 3-1 to 3-2 are relay amplifiers, and 4-1 to 4
-2 is tap-off, and 5-1 and 5-2 are terminal stations.

The internal structure of the head end 1 is, as shown in the figure, 101 an input / output distribution device and 102 a CATV.
The broadcasting equipment, 103 is a block converter, 104 is a line control device, and 105 is a communication management device. Further, as shown in the figure, the internal configurations of the terminal stations 5-1 and 5-2 are: a distributor 501, a television receiver 502, a voice channel network terminator, 504 a data channel network terminator, and 505. Is a telephone, 506 is a FAX or a personal computer, and 507 is a personal computer.

FIGS. 2A, 2B and 2C are frequency arrays of the communication system according to the embodiment of the present invention.

FIG. 2A is an arrangement diagram of frequency bands used in a communication path in a communication system to which the present invention is applied. Headend 1 from terminals 5-1 and 5-2
The total bandwidth 10 of the upstream signal transmitted to the
MHz, and conversely, the whole use band 20 of the downlink signal transmitted from the head end 1 to the terminal side is 70 to 450 MHz.
It has become. In the multimedia communication system according to the present invention, among the frequency bands for uplink and downlink signals,
Originally set as a TV signal for CATV.
An empty band (6MH) that is not actually used for signal transmission
z / channel) 15 and 25 for 3 channels (Fig. 2
(Shaded area in (A)), voice signal (for telephone and facsimile)
And for bidirectional transmission of data signals (for computers). Furthermore, each band 15 in the shaded area in FIG.
2B and 2C show examples of arrangement of signal bands in 25.

The arrangement shown in FIG. 2B is within the 6 MHz band for one channel of the NTSC television and is 200 c at 12.5 KHz intervals, similarly to the basic arrangement of the conventional MCA / C method.
An audio signal band of 2.5 MHz consisting of h audio channels is placed at the center and 10 points at 300 KHz intervals on each side.
It is an array of bands of 3.0 MHz formed by ch data channels.

Further, FIG. 2C shows a voice channel 200.
The channels and the data channels 10 are combined and arranged in an arbitrary order.

In this embodiment, the voice channel is a modem for analog telephone or FAX for the terminal station in addition to voice call.
Can be connected for data transmission up to 9600 bps.
In the data channel, a QPSK modulation type modem built in the terminal station can transmit data at 384 kbps.

First, the operation of the voice channel will be described in detail.

The operation of the voice channel of the present invention is the same as the conventional M channel.
Although the operation is the same as that of CA / C, it will be described with reference to FIGS. 8 and 9 for comparison with the operation of the data channel described later. FIG. 8 is a conceptual diagram of an MCA / C multiple communication path which is a part of the present invention in which the frequency is a virtual crosspoint switch, and FIG. 9 is an operation sequence of the MCA / C. In addition,
In the figure, each channel is shown as an independent signal line for the sake of easy understanding of the description. Actually, multiple channels are multiplexed and transmitted on one coaxial cable.

In FIG. 8, 103 is a block converter, and 1
Reference numeral 04 is a line control device, 5-1 and 5-2 are terminal stations, and 503.
Is a network terminator, 505 is a telephone, c-d1 to c-d2 are downlink control channels, c-u1 to c-u2 are uplink control channels, t-d1 to t-d2 are downlink traffic channels, and t-u1 to t. -U2 indicates an upstream traffic channel.

First, M using the control channel
The basic control operation for the traffic channel in the CA / C system will be described.

Now, the subscriber of the terminal station 5-1 is the terminal station 5-2.
Consider the case of trying to make a call with a subscriber of. For example,
The telephone 505a of the terminal station 5-1 confirms "available" in FIG. 9 and dials PB from the telephone 505a.
The network terminating device 503a captures the upstream control channel c-u1 at the crosspoint "a" and transmits a "connection request" to the headend 1 via the upstream control channel c-u1.

To prevent a collision with a signal from another station when transmitting the "connection request", the well-known Slotted ALOHA method in which the "skyline signal" of FIG. 9 is used as a synchronization signal is adopted.

A "connection request" signal is transmitted from the terminal station to the ascending control channel in a time slot of a predetermined length based on the skyline signal sent from the headend 1 to the descending control channel.

The line controller 104 of the headend 1
Receive a "connection request" via crosspoint "b",
When there is no collision with other terminal stations and normal reception is performed, both terminals are downlinked by cross point “c” based on the numbers of the calling terminal station and the called terminal included in the “connection request”. Control channels c-d2 are acquired and "channel designation" is transmitted. "Channel designation" is a signal that designates a traffic channel number for telephone communication between terminal stations.

The terminal stations 5-1 and 5-2 receive the "channel designation" at the network terminating device 503 via the cross points "d" and "e". According to the designated traffic channel number, for example, the transmission (T) of the terminal station 5-1 receives the crosspoint “f”, the reception (R) of “i”, and the transmission (T) of the terminal station 5-2. When the cross point “h” is received (R), each network terminating device 503 captures the traffic channel via “g”. If the telephone 505b of the called terminal 5-2 responds "off-hook", the terminal station 5-
A call is ready between 1 and 5-2.

As shown in FIG. 9, the standard operation sequence for ending the call is that the terminal station 5-1 which has been "on-hook" returns the channel to the uplink control channel c-u1 at the cross point "a". Send "End call request".

On the side of the terminal station 5-2 where the on-hook is delayed,
With the monitoring function equivalent to the squelch operation of the FM radio,
Monitoring the carrier of the traffic channel. if,
If there is no carrier, the network terminating device 503b automatically sends a busy tone to the telephone 505b of its own station, accesses the control channel, and operates so as to receive the "end call response" from the line control device 104.

Next, the details of the communication operation between the terminal stations using the traffic channel as the data channel will be described.

FIG. 3 shows a data channel network terminating device 50.
4 shows an internal configuration of the radio frequency controller 4, and 511 is a high frequency unit (RF
Part), 512 is an MCA control part, 513 is a data channel part, 514 is an RF input / output line, and 515 is a terminal interface line (terminal I / F line).

The inside of the MCA control section 512 is composed of an intermediate frequency section (IF section) 521, a modulation / demodulation section 522, and a control section 523.

The inside of the data channel section 513 is
An IF unit 531, a modulation / demodulation unit 532, a communication control unit 533, and a terminal I / F unit 534 are included.

Before explaining the operation, the outline of this function will be described first.

The RF section 511 is a frequency band used in the CATV network, which is 10 to 50 MHz (upstream) and 70 to 450.
Among the MHz (downlink), it operates by using each 6 MHz band for upstream and downstream.

The MCA control unit 512 is a part of the voice channel network terminating device 503 that is necessary for control operation using the control channel. The IF unit 521 is
It corresponds to an intermediate frequency signal corresponding to the frequency band used at 5 KHz intervals.

The modulation / demodulation unit 522 is an FM modulator / demodulator which is a basic form of the MCA / C system using the technology of FM radio equipment,
A modulator / demodulator, for example, a 2400 bps MSK modulator / demodulator for performing data transmission on the control channel is provided.

The control section 523 controls communication under the operation sequence described later.

The MCA control unit 512 controls the data channel unit 513 to acquire a data channel based on the "channel designation" received by the control operation described above with reference to FIGS. Give instructions.

As described above, the data channel section 513 is adapted to perform data transmission of 384 kbps with a bandwidth of 300 KHz, and the IF section 531 and the modulation / demodulation section 53.
2 corresponds to this data transmission rate.

By the way, with this 300 KHz bandwidth, 384
As a device for performing Kbps data transmission, it is adopted for digital transmission in a wireless section of a personal handyphone system (hereinafter abbreviated as PHS) implemented as a cordless digital telephone system in Japan.

Communication control unit 533 and terminal I / F unit 53
4 has the following functions.

Interfaces with terminal devices such as the telephone 505, the facsimile 506, and the computer 507 correspond to RS232C / RS422 (EIA standard) synchronous or asynchronous transmission, and the signal transmission speed exceeds the speed that can be supported on the voice channel side. , 19.2Kbps, 64K
Bps, 128 Kbps, etc. are possible. Therefore, synchronous / asynchronous conversion, speed conversion to 384 Kbps, or
This inverse transformation can be performed.

At the start of communication, the operation for the terminal station to be assigned a data channel is performed in response to the PB signal transmission operation of the device. The device transmits a PB signal according to a procedure corresponding to the AT command which is widely used in personal computer communication. The terminal interface unit 534 has a function of monitoring this procedure, receives the destination number, etc.,
It is sent to the MCA control unit 512.

In the communication after the “channel designation” is received from the MCA control unit and the data channel is captured, the connectionless communication (connectionless) is performed.
In order to enable communication, it is necessary to generate data packets that are independent of the protocol of the device. LAN to generate data packets
Similar to the method adopted by the bridge, which is one of the inter-connection devices, it is performed by monitoring the frame of data to be transmitted, regardless of the protocol of the terminal. That is, the terminal I / F unit 534 detects the beginning and end of the frame of the signal transmitted from the device, and generates a new data packet using the frame as user data. When the frame length is long, a conversion for dividing the frame into a plurality of data packets is also performed. An example of the data packet includes a header part, a user data part and a trailer part as shown in FIG.

As another operation after the network terminating device 504 seizes the data channel, a plurality of terminals in one data channel are allowed to use IEEE 802.3 CSMA / C.
Communication can be performed by a queuing communication method that prevents a collision by a function equivalent to D.

Further, the RF unit 511 and the IF unit 531 select the traffic channel for transmission and reception by designating the frequency via the control channel based on the control of the communication control unit 533, and select the traffic channel. It is assumed that signals can be exchanged between terminal stations.

The details of the operation of the data channel will be described below with reference to FIGS.

FIG. 5 is a conceptual diagram of a multiplex communication channel of a data channel in which a frequency is a virtual crosspoint switch in an embodiment of the present invention. FIG. 6 shows an operation sequence of communication using the data channel of FIG.

In FIG. 5, 103 is a block converter and 1
04 is a line controller, 5-1 to 5-2 are terminal stations, 504
Is a data channel network terminator, 507 is a personal computer, and c
-D1 to c-d2 are downlink control channels and cu
1 to c-u2 are uplink control channels, t-d1 to
t-d2 is a downlink traffic channel, t-u1 to t-
u2 indicates an upstream traffic channel.

Consider a case where the terminal station 5-1 tries to communicate with the terminal station 5-2. Communication software for PC 507 (communications program)
In response to the AT command of, the personal computer 507 dials. The network terminating device 504a uses the terminal I / F section 534 (FIG. 3) to transmit the dial signal 30 via the terminal I / F line 515a.
To receive. MC via communication control unit 533 (FIG. 3)
This dial information is passed to the A control unit 512. MCA
The control unit 512 captures the uplink control channel c-u1 by the cross point "a" and transmits the "connection request" 31 including the partner station and the own station number shown in FIG.

The line controller 104 of the headend 1
The "connection request" 31 is received via the crosspoint "b", the downlink control channel cd-2 is captured by the crosspoint "c", and the "channel designation" 32 is transmitted.

At the terminal stations 5-1 and 5-2, the network terminators 504a and 504 are connected via the cross points "d" and "e".
The MCA control unit 512 (FIG. 3) of b receives the “channel designation” 32, and instructs the data channel unit 513 (FIG. 3) to “channel designation” 32.

In the communication control section 533 (FIG. 3) of the data channel section, according to the instructed data channel number,
For example, the transmission (T) of the terminal station 5-1 receives the crosspoint “f”, the reception (R) receives “i”, the transmission (T) of the terminal station 5-2 receives the crosspoint “h”, and R) is "g"
The RF unit 511 and the IF unit 531 are instructed so that each can capture the data channel via the so that the communication becomes possible.

Although not shown, other terminal stations connected to the downlink control channel c-d2 are also connected to the terminal station 5-
"Channel designation" 32 is received at the same time as 1 and 5-2.
However, if the number of the partner station included in the "channel designation" 32 does not match the number of the receiving terminal station, the received "channel designation" 32 is ignored. Also, the terminal station 5
At the same time as -1, the other terminal station that made the communication request also
It operates under the collision prevention algorithm of the ted ALOHA method and captures the data channel designated by the line controller 104.

The line controller 104 sends a "connection request" 31
From the number of the terminal station 5-1 on the calling side included in the above, the terminal station 5 that performs communication based on the service condition pre-arranged by the subscription contract and registered in the line control device 104 and the traffic condition of the data channel. -1,5-
Assign channels to 2.

Here, in using the traffic channel, there are the following differences between the voice channel and the data channel.

(1) In the voice channel, simultaneous transmission / reception between terminal stations, that is, full-duplex.
In order to perform communication, traffic channel 2ch is required as shown in FIG. This is because the signal flowing through the transmission path is not a baseband signal but a modulated carrier wave.

On the other hand, the standard of the LAN method, ie, IE
EE 802.3 is half-duplex.
x) Since it is a communication, the data channel can be configured by the traffic channel 1ch as shown in FIG.

In the TDMA system, the data channel is also a full-duplex communication type as in the case of the voice channel and is code transmission, and bidirectional signals cannot be combined on the transmission path.
Uplink / downlink each 2 time slots, ie 2c each
The configuration requires h.

(2) In the voice channel, the ringback tone and the response of the receiving terminal are performed in the designated voice channel. In the data channel of this embodiment, as shown in FIG. 6, the control channel is used to perform signals such as "response" and "connection completed".

In the terminal station which has captured the data channel, the communication software of the personal computer 507 moves to the next stage, and the communication can be started by the LAN protocol such as TCP / IP.

As described above, the communication control unit 533 of the network terminator 504a monitors the beginning and end of the frame according to the TCP / IP protocol, and newly adds the data packet shown in FIG. 4 based on the frame data. To generate. The data packet generated here is a CSMA / C of IEEE 802.3 in units of each traffic channel.
The function equivalent to D enables waiting-type communication in which collision is prevented, and then enables transmission between terminal stations by connectionless communication.

Next, IEEE 8 for preventing collision
The operation of the function corresponding to CSMA / CD in 22.3 will be described.

The communication control unit 533 monitors the presence / absence of a carrier of the data channel captured via the modulation / demodulation unit 532. If no carrier is detected on the data channel, the transmission of data packets can be started immediately.

When the carrier wave is detected, the calling terminal station 5-1 waits for transmission until the data channel becomes idle. Furthermore, after a lapse of a certain time from the detection of the carrier wave, the empty state of the data channel is reconfirmed, and then the transmission of the data packet is started.

Further, even if the above control is carried out, it is necessary to stop the data packet having the collision early because the collision due to the simultaneous transmission occurs with a probability. The terminal station transmitting the data packet, for example, the terminal station 5-1 receives the transmission signal at the cross point “f” via the cross point “i” and collates with the data packet being transmitted. If the collation mismatch exceeds a certain amount, it is determined to be a collision, and the transmission of the data packet is stopped midway.

[0120] The communication is completed by responding to the "on-hook" 33 of the AT command transmitted from the personal computer 507a of the terminal station 5-1 on the calling side, as shown in FIG. "Request" 34 is made. Terminal stations that do not go on-hook even after the caller's "end call request"
When the timer measures a predetermined time from the "end call request", the on-hook state is automatically set.

As described above, under the basic control operation of the MCA method using the control channel, either the immediate communication method or the queuing communication method is selectively applied to the voice channel and the data channel. Can be controlled. In addition, it is also possible to freely assign it to various communication services.

Various types of different service conditions can be added to communication between terminal stations. For example, the head end 1 may have a function of setting and managing communication service conditions for each terminal station. As the service condition setting, the upper limit of the usage time of the data channel assigned to the terminal station is set, the waiting time of the data channel is set for each terminal station, and the data transmission rate of the data channel is set for each terminal station. and so on. further,
It is also possible to set a plurality of groups of one or a plurality of terminal stations and set service conditions for each group. Higher tariffs will be set if the subscriber is given more favorable service conditions to the terminal station.

The management of the service condition for each terminal station or each group is performed on the headend 1 side as follows, for example. Network termination devices 503 and 5 for all subscribers
A table showing identification information for identifying the terminal station such as the identification code 04 or the subscriber number of the terminal station and the corresponding service condition is registered in advance in a memory (not shown) in the communication management device 105. Keep it. Head end 1
Then, when there is a connection request from the terminal station, the identification information is detected from the transmission signal of the terminal station, and the given service condition is read by referring to the table. Head end 1
Based on the service conditions, communication time between terminals,
Manages waiting time or data transmission rate.

Alternatively, in the signal of the channel designation 32 (FIG. 6) from the line control device 104, the communication destination time information is included together with the destination terminal station number, own station number, and traffic channel number. Upon receiving the channel designation 32, the terminal station which carries out the communication starts the timing of the timer (not shown) at the same time as the start of the communication. When the timer counts up to the communicable time, each terminal station issues a "call termination request" 34.

In the above embodiments, the case where all the control channels and traffic channels are accommodated in the 6 MHz band has been described.

When a large capacity system is required, or when the transmission characteristics of the CATV network are poor and voice channels and data channels coexist as shown in FIG. 2B, the total transmission power may be limited. When the required channel capacity cannot be secured, the control channel and the voice channel can be arranged in one 6 MHz band, and the data channel can be arranged in another 6 MHz band to increase the number of channels. .

Even in a large capacity system using a plurality of television channels, the common control channel can be used, and the uniformity of control is not impaired.

If the traffic of the control channel itself exceeds the capacity of one channel due to the large capacity, it is possible to provide two or more control channels.

Also, it has been explained that narrow band transmission is advantageous in a CATV network with a large amount of upstream and downstream noise, but when the present invention is applied to an improved CATV network with a small amount of upstream and downstream noise, it is not always narrow. It is not necessary to set the bandwidth, and it is possible to make the bandwidth of the data channel wide so as to be able to support higher-speed data transmission.

For example, as used in the TDMA system, 1.5 MHz obtained by dividing the entire 6 MHz into four.
Then, we constructed a system to control uniformly under the MCA method that uses a narrow band control channel by adding a part of the data channel at a transmission rate of about 2 Mbps. can do.

When the traffic of the data channel is managed by the line controller 104 of the headend 1, the number of packets generated per unit time, the average value of the waiting time, the maximum value, etc. are calculated in the network terminating device of each terminal station. It is possible to measure. If these values are reported to the line controller 104 via the control channel or the data channel at a certain cycle, the headend 1 can generally grasp and manage the traffic condition of the entire communication system. .

In the case of the flat-rate system in which the charging method of the communication service does not depend on the communication time, the subscriber may continuously use the service for a long time. In order to prevent this, at the time of "channel designation" 32 in FIG. 6, it has a "communication time limit" function capable of instructing the terminal station of the communicable time. Further, by setting the communication available time in the communication management device 105 of the headend 1 as needed, the above control becomes possible.

When the upper limit of the transmission rate that can be used by the terminal is limited for each subscriber, the terminal I / I of the network terminating device of the terminal station is limited.
In the F unit 534, it can be dealt with by changing the setting of the upper limit of the clock speed of the terminal I / F line 515. As a method of changing the setting, switching is performed by a switch in the network terminating device of the terminal station, or the network terminating device of the terminal station is remotely switched from the head-end communication management device 105 via the line control device 104.

In communication using the CATV network, signal transmission has high speed and temporal continuity like a quasi-moving picture (a moving picture with a reduced number of frames, not a normal NTSC television signal). The required data may be transmitted.
Such a data signal is subjected to line control in which one channel is occupied between terminal stations until all data is transmitted. For example, 384 Kb for a 300 KHz channel
Signal transmission of about ps is possible. When the signal transmission rate of the device connected to the terminal station is sufficiently lower than the signal transmission rate of the channel, a plurality of terminal stations can be assigned to one channel. In this case, the receiving side terminal station has a buffer memory corresponding to the maximum waiting time determined based on the traffic volume of the entire terminal station assigned to one channel under the CSMA / CD system. The receiving terminal station can absorb the variation of the time intervals of the arriving packets in the buffer memory and receive it as continuous data.

The voice channel of the described embodiment is an example of the analog system based on the FM radio. According to the present invention, 12.5K which is under study in the field of wireless
OFDM (Orthogonal Fr) belonging to the multi-carrier multi-level modulation which is being studied in the terrestrial digital television broadcasting in Europe and Japan, or the digitized radio system of the SCPC system with a bandwidth of Hz or less.
EQEQUENCY DIVISION MULTIPLE
If the xing) system is applied to this voice channel, all digitization can be realized even in the system based on the narrow band frequency multiplexing system as shown in the embodiment.

Further, when a plurality of traffic channels are formed in a certain bandwidth, a code multiplex system (hereinafter abbreviated as CDMA system) can be used in addition to the frequency multiplex system as described above. This CDMA system also uses the above-mentioned S
This is one of the CPC methods, and channels can be divided by a pseudo noise code to easily configure a multiplex communication path as shown in FIG.

Further, this CDMA system has already been decided to be adopted in some wireless systems in the United States as a system having the highest frequency use efficiency in the field of wireless, and the spread of the device will promote the economicalization of devices and the like. For example, application to the system as shown in this embodiment is also possible.

[0138]

According to the present invention, based on the conventional MCA / C system, it becomes possible to support various communication services from telephone to high-speed data transmission, and other systems currently available. It is possible to realize a system with the highest frequency utilization efficiency as compared with.

Strong against the influence of upstream combined noise and reflected waves peculiar to the CATV network. Therefore, the cost for improving the existing CATV network can be reduced.

The communication in the data channel can effectively utilize the speed difference between the line and the terminal and the non-operation time of the terminal by the waiting type communication system similar to the LAN.

Further, since the data channel can be communicated by the half-duplex communication system, and because of the full-duplex communication system, it can be configured with one channel as compared with the circuit switching type which requires two channels, so that the line is extremely used. A highly efficient system can be realized.

When the band of 1.5 MHz is used for the data channel, the number of terminals that can operate simultaneously is 6
Trial calculations were performed for three types of terminals of 4 Kbps, 32 Kbps, and 19.2 Kbps, and a comparison between the TDMA and the system of the present invention is as follows.

As conditions, TDMA uses the specifications of FIG. In the system of the present invention, the data channel is set to 300 KHz and 384 Kbps as shown in the embodiment, and the maximum waiting time is allowed up to 10 times the packet length.

In TDMA, the line capacity in the 1.5 MHz band is 64 Kbps × 24 ch. One opposing terminal has 2 channels regardless of the transmission speed of the terminal as described above.
To use. Therefore, the number of devices that can operate simultaneously is 24 (12 facing) regardless of the type of terminal.

In the system of the present invention, the line capacity in the 1.5 MHz band is 30 ch in terms of 64 Kbps. The utilization rate of CSMA / CD that allows the maximum waiting time up to 10 times the packet length is 0.8, and the loss due to the generation of the packet (related to the addition of the header part and the trailer part)
If the value is 0.9, 42 terminals (2
1 counter), 84 units at 32 Kbps (42 counters), 1
At 9.2 Kbps, there are 168 units (84 facing).

In the control of the MCA method using the control channel, allocation to a plurality of data channels can be managed freely, so that for each data channel, the waiting time can be changed from the service equivalent to circuit switching that allows the channel to be occupied. Since it is possible to classify services according to length or to classify by the transmission speed of the terminal, and to introduce a flat-rate system, it is possible to set price classes corresponding to various services. Unique business development is possible.

In a plurality of data channels, it is possible to change the bandwidth and transmission rate for each channel, and it is possible to extend to a higher speed service.

In the bandwidth of the data channel, the modulator / demodulator of 300 KHz band and 384 Kbps, which is expected to have the largest number of users, can be the same as the modulator / demodulator of PHS, which is expected to be widely used in the future. Can be expected to bring about economicization.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an entire system of an embodiment of a communication system of the present invention.

FIG. 2 is an explanatory diagram showing a frequency arrangement in one embodiment of the present invention.

FIG. 3 is a block diagram showing an internal configuration of a data channel network termination device according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a frame structure of a data packet according to an embodiment of the present invention.

FIG. 5 is a conceptual diagram of a data channel multiplex communication channel according to an embodiment of the present invention.

FIG. 6 is a diagram showing an operation sequence of a data channel in one embodiment of the present invention.

FIG. 7 is a block diagram of an MCA / C telephone system.

FIG. 8 is a conceptual diagram of multiple communication paths of the MCA / C telephone system.

FIG. 9 is a diagram showing an operation sequence of the MCA / C telephone system.

FIG. 10 is a conceptual diagram of a TDMA telephone system.

FIG. 11 is a diagram showing main specifications of the MCA / C telephone system.

FIG. 12 is a diagram showing main specifications of a TDMA telephone system.

[Explanation of symbols]

1 headend, 3 repeater amplifier, 4 tap-off,
5 terminal, 102 CATV broadcasting equipment, 103 block converter, 104 line control device, 105 communication management device, 502 TV receiver, 503, 504 network termination device, 505TEL, 506 FAC / PC, 507P
C.

Claims (10)

[Claims] 1. A communication system in which one central station and a plurality of terminal stations are connected via a bidirectional communication path, and communication between the terminal stations is performed through the central station. There, the communication system has a dedicated communication channel allocated between the terminal station and another terminal station, and a common communication channel simultaneously allocated to a plurality of terminal stations, the central station, A communication system comprising: a control unit that selects one of the dedicated communication channel and the common communication channel in response to a communication request from a terminal station. 2. The communication system according to claim 1, wherein the communication path is a plurality of traffic channels in which the common communication channel and the dedicated communication channel are set,
One or more control channels through which a control signal is transmitted, wherein the control means responds to a communication request from one or more of the plurality of terminal stations by responding to one of the plurality of traffic channels. One or more are assigned to the terminal station that has made the communication request, and means for transmitting a control signal for designating the assigned traffic channel to the terminal station via the control channel is further provided, and the common communication channel A communication system comprising means for controlling the common communication channel so that only one signal is transmitted when a plurality of different signals exist, and avoiding signal collision. 3. The communication system according to claim 1, wherein the communication path includes a plurality of traffic channels in which the common communication channel and the dedicated communication channel are set.
One or more control channels through which a control signal is transmitted, wherein the control means responds to a communication request from one or more of the plurality of terminal stations by responding to one of the plurality of traffic channels. A communication system, characterized in that one or more are allocated to the terminal station that has made the communication request, and a control signal for designating the allocated traffic channel is transmitted to the terminal station via the control channel. 4. The communication system according to claim 3,
A communication system, wherein a frequency band of the communication channel is divided into a plurality of bands, and the plurality of traffic channels are set in each of the divided bands by frequency multiplexing. 5. The communication system according to claim 3, wherein
A communication system, wherein a unique code is assigned to each of the plurality of terminal stations on the communication path, and the plurality of traffic channels are set by a code multiplexing method. 6. The communication system according to claim 3, wherein
A plurality of voice signal channels and data channels are arranged in the traffic channel, the voice signal channel is assigned to the dedicated communication channel, and the data channel is assigned to the common communication channel. . 7. The communication system according to claim 3, wherein
The communication system according to claim 1, wherein said central station has a service management means for setting an upper limit of a use time of said common signal channel allocated to said terminal station when a communication request is received from said terminal station. 8. The communication system according to claim 3, wherein
The central station has a service management means for setting the waiting time of the common signal channel for each terminal station. 9. The communication system according to claim 3,
The communication system according to claim 1, wherein said central station has service management means for setting a data transmission rate of said common signal channel for each terminal station. 10. The communication system according to claim 3, wherein communication devices of different information types including a telephone, a television, a fax, and a computer are connected to the plurality of terminal stations.