JPH0750886B2 - Communication method and communication system - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a method and system for communicating between terminal stations using a frequency division multiplexing transmission line.

[Prior art]

Conventionally, in the case of performing data communication between computers of arbitrary two terminal stations separated from each other, a telephone line and a modulation / demodulation device are usually used, and the terminal station of the communication partner is selected by dialing. Using this telephone line has the advantage that communication is possible regardless of short distance or long distance,
There is the inconvenience of having to dial each one at the time of communication.

Therefore, a method such as a LAN for constructing a communication system between terminal stations by using a dedicated transmission line has been considered. One of the possible methods is to use a coaxial cable such as CATV as a transmission line and multiplex the channels by frequency division multiplexing to allow arbitrary communication between the terminal stations. There is no known method of automatically establishing a communication channel between them. Therefore, the present invention connects a terminal station to a frequency-division-multiplexed transmission path and arbitrarily establishes a channel between the terminal stations,
A method and a communication system that enable full-duplex communication.

[Means for solving problems]

A configuration of a first invention for solving the above-mentioned problems is to provide a communication system including a transmission line for transmitting a signal subjected to frequency division multiplexing and a modulation / demodulation device forming a terminal station connected to the transmission line. When a terminal station becomes a called station as a communication partner, a transmission channel and a reception channel unique to the terminal station are pre-assigned, and the calling station has a unique reception channel or unique transmission assigned to the called station. If the carrier of the channel is detected, and if the carrier is not detected, the transmission is performed by setting the transmission channel and the reception channel of the calling station according to the peculiar reception channel or peculiar transmission channel of the called station. It is a communication method characterized by forming a full-duplex communication channel between a calling station and a called station. The second invention is a communication system comprising a transmission line for transmitting a signal subjected to frequency division multiplexing and a modulation / demodulation device constituting a terminal station connected to the transmission line. Initializing means for making an initial setting to a unique channel assigned to the terminal station, and detecting whether or not there is a carrier of a unique transmission channel or a unique reception channel assigned to the called station as a communication partner at the calling station. If the carrier detection means and the carrier are not detected, the channel initially set in the calling station is changed and the transmission of the calling station is performed according to the peculiar reception channel or peculiar transmission channel of the called station. When the communication with the channel setting means for setting the channel and the receiving channel is completed, the transmitting channel and the receiving channel of the calling station are set to the original setting. Characterized in that a return means for returning to the transmission channel and specific receiving channel.

[Action]

A unique transmission channel and a unique reception channel are assigned to each terminal in advance. When the terminal station is called and becomes the called station, its own transmission channel and reception channel are used. When a communication channel is formed from the calling station to the called station of the communication partner, it is performed as follows. The calling station detects the presence / absence of a carrier of a unique transmission channel or a unique reception channel assigned to the called station. When the carrier is detected, it means that the called station is communicating with another terminal station, and in this case, no communication channel is formed. On the other hand, if the carrier of the transmission channel or the reception channel peculiar to the called station is not detected, it means that the called station is not communicating, so it is possible to form a channel with the called station. Becomes Therefore, the transmission channel of the calling station is changed to the transmission channel corresponding to the reception channel unique to the called station. That is, the changed transmission channel of the calling station and the reception channel unique to the called station form a communication channel from the calling station to the called station. Further, the receiving channel of the calling station is changed to the receiving channel corresponding to the transmission channel unique to the called station. That is, the changed reception channel of the calling station and the transmission channel of the called station form a communication channel from the called station to the calling station. As a result, a full duplex communication channel is formed between the calling station and the called station. Further, when the communication is completed, the transmission channel and the reception channel of the calling station are restored to the peculiar transmission channel and the peculiar reception channel, so that the call can be received from another terminal station.

【Example】

Hereinafter, the present invention will be described based on specific examples. Example 1 This example is an example in which a frequency converter is not used in the head end. In FIG. 1, D is a transmission line made up of a coaxial cable, K1.
~ K3 is a bidirectional coupler, M1 to M3 are modems, C1 to C3 are computers.
T1 to T3 are configured. The channels are transmission channels chS1 ~
chS3 and reception channels chR1 to chR3 are alternately arranged, and a total of 6 channels are configured. Then, the terminal station T1 has a unique transmission channel chS1 and a unique reception channel ch in advance.
R1 is assigned and the terminal T2 has a unique transmission channel in advance.
chS2 and unique receive channel chR2 are assigned, and terminal station T3
A unique transmission channel chS3 and a unique reception channel chR3 are assigned in advance. This peculiar channel becomes a communication channel when the terminal station functions as a called station. Each of the modulation / demodulation devices M1 to M3 is configured such that its reception channel and transmission channel are set based on the control data instructed by each of the computers C1 to C3. The control data is composed of frequency data that specifies a transmission channel and offset command values: H (high) and L (low) that command an offset of the reception channel with respect to the transmission channel. Each of the modulation / demodulation devices M1 to M3 is configured to set a transmission channel according to the frequency data of the control data, and set a reception channel to one channel above or below the transmission channel according to the offset command value. For example, if the frequency data is fS2, the transmission channel is channel chS2, and the reception channel is channel chR1 and channel c according to the offset command values L and H.
Set to hR2. If the transmission channel and the reception channel that can be set in this way have a fixed relationship, the modulator / demodulator can be configured with one PLL circuit, which is economical. Next, a procedure for forming a communication channel will be described based on a flowchart showing a processing procedure of a computer. In the following description, it is assumed that a communication path is formed from the terminal station T1 to the terminal station T2, the terminal station T1 is the calling station T1, and the terminal station T2 is the called station T2.
Say. When the power of the terminals T1 to T3 is turned on, the initialization program shown in FIG. 3 is executed, and in step 300, the transmission channels chS1 unique to the modems M1 to M3 are transmitted from the computers C1 to C3. ~ ChS3 and unique receive channel chR1
To chR3 are initialized, frequency data fS1 to fS3 and offset command value H are output. As a result, in each of the modulation / demodulation devices M1 to M3, the transmission channel is initially set to the channel chS1 to chS3 peculiar to the terminal station, and the reception channel is initially set to the reception channel chR1 to chR3 peculiar to the terminal station one channel above the transmission channel chS1 to chS3. Is set. When this initial setting is completed, each terminal station T1 to T3 is ready to be called. Next, when a communication request is issued to the terminal station T2 at the terminal station T1, the computer C1 executes the program shown in FIG. In step 100, parameters J and M are initialized.
The parameter J stores the number of times the calling operation to the called station T2 is repeatedly executed when the called station T2 is already communicating with another terminal station, and the parameter M stores the calling operation. When there is no response from the called station later, the number of times of executing the operation of detecting the response is repeatedly stored. Next, in step 102, control data for setting the receiving channel of the calling station T1 to the receiving channel chR2 unique to the called station T2; frequency data fS2 and offset command value H are output to the modulator / demodulator M1. , The modulator / demodulator M1 uses the transmission channel as channel chS2 and the reception channel as channel
Change to chR2. Then, from the transmission path D to the channel chR2
Is input to the receiving circuit of the modulation / demodulation device M1, and when a carrier is detected, the carrier detection signal CD is output from the modulation / demodulation device M1 to the computer C1. After the transmission channel and the reception channel are changed, the computer C1 waits for a certain period of time, and then it is determined in step 104 whether the carrier detection signal CD is on. If the carrier detection signal CD is not on, the computer C1 proceeds to step 106. Then, set the transmission channel to the receiving channel unique to the called station chR2.
And control data for changing the reception channel to the transmission channel chS2 unique to the called station is output to the modulation / demodulation device M1. The control data at this time is the frequency data fR2 and the offset command value L. Then, the modulator / demodulator M1 changes the transmission channel to the channel chR2 and the reception channel to the channel chS2. Next, in step 108, the identification data identifying the calling station T1 is output to the modulation / demodulation device M1, modulated by the modulation / demodulation device M1 with the carrier of frequency fR2, and the data is transmitted to the channel chR2. After that, the ACK signal, which is a response signal of the above identification data, is output from the called station T2 to the channel chS2.
At 12, it is determined whether the ACK signal has been received. ACK
When the signal is received, the calling procedure from the calling station T1 to the called station T2 is completed. Incidentally, when the carrier detection signal CD is turned on in step 104, it means that the peculiar receiving channel chR2 of the called station T2 has already been used, and the process proceeds to step 114, in which it differs depending on the number of executions. Wait for a set amount of time, then move to the next step
At 116, the parameter J is updated by 1. Then, in step 118, it is determined whether or not the parameter J is equal to or greater than the predetermined value n, and if the determination result is NO, the process returns to step 104 and the above-described calling operation for the terminal station T2 is re-executed. On the other hand, if the decision result in the step 118 is YES, it is determined that the channel chR2 is occupied for a long time, the process proceeds to the step 120, the calling operation to the terminal station T2 is abandoned, and a message to that effect is displayed. If the ACK signal, which is the response from the called station T2, is not received in step 112, steps 122 to 128 are executed,
Similar to steps 114 to 120, a process of waiting for an irregular time and then determining whether or not an ACK signal is received is executed n times. And, during the n times of repeated execution, ACK
If no signal is received, the calling procedure is abandoned.
In this case, it means that the terminal station T2 is not powered. On the other hand, when the computer of the terminal station that does not perform the calling operation is turned on, after the initial setting such as setting the transmission channel and the receiving channel to the channel peculiar to the terminal station is executed, the computer enters the waiting state, It runs its own program only for terminal stations. Then, in order to detect whether or not the own terminal is called, by the interval timer interruption,
The program of FIG. 5 is executed at regular time intervals. Explaining the computer C2 of the called station T2, when the modem M2 detects the carrier of the reception channel chR2,
The modulation / demodulation device M2 turns on the carrier detection signal CD to be output to the computer C2, but in step 200 it is determined whether the carrier detection signal CD is on, and if the carrier detection signal CD is not on, the program Execution is terminated. When it is determined that the carrier detection signal CD is on, the process proceeds to step 202, and the identification data transmitted from the calling station T1 to the channel chR2 in step 108 of FIG. 4 is received, and the identification data is received. Is entered. Next, in step 204, the ACK signal is sent to the channel ch.
The interval timer interrupt that outputs to S2 and activates this program in the next step 206 is prohibited, and the communication channel is established. In this way, the transmission from the calling station T1 to the called station T2 is performed on the channel chR2, and the transmission from the called station T2 to the calling station T1 is performed on the channel chS2. Full duplex communication is performed with the channel chR2 and the transmission channel chS2. Thus, in this embodiment, the communication channel is established by switching the transmission channel and the reception channel of the calling station to the reception channel and the transmission channel unique to the called station. When the communication is completed, the calling station T1 executes the program shown in FIG. 3, and its transmission channel is its own transmission channel.
The receiving channel is unique to chS1 chR1
Then, the call from another terminal is made possible. After the communication channel is established as described above, it can also be used for data transmission between computers and transmission of analog signals such as voice and video between terminal stations. Although the number of terminal stations is three in the above description, the number of terminal stations can be increased up to the maximum number of channels that can be used in the transmission path. The communication channel establishing procedure realized by a computer may be executed by the modulation / demodulation device by making the modulation / demodulation device intelligent. Further, the modulation / demodulation devices M1 to M3 are configured to set the transmission channel by the frequency data based on the control data, and set the reception channel to one channel above or below the transmission channel according to the offset command value. Alternatively, the transmission channel and the reception channel may be set separately. The transmission channel or the reception channel of the modulator / demodulator can be variably set by generating a carrier having a set frequency using a PLL oscillation circuit or the like. The initial setting means, the carrier detecting means, the channel setting means, and the returning means described in the claims are composed of a modulator / demodulator and a computer as hardware. In terms of the correspondence with the computer procedure, the initial setting means is step 300 in FIG. 3, the carrier detecting means is steps 102 and 104, the channel setting means is step 106,
The restoring means corresponds to step 300 in FIG. Second Embodiment The second embodiment relates to a communication system using a frequency conversion device. The overall system configuration is configured as shown in FIG. The difference from FIG. 1 showing the configuration of the first embodiment is that directional couplers H1 to H3 are used for connecting the terminal station and the transmission line D, and the frequency at the head end of the transmission line D. Converter
FT is connected and bidirectional relay amplifier A1 ~
That is, A4 is inserted. In this embodiment, the channels are arranged as shown in FIG. 7, and six channels, chS11 to chS32, which are upstream channels, are used for communication from the terminal station to the headend side. 6 channels of downlink channels chR11 to chR32 are used for communication to. Up channels chS11 to chS32 are transmission channels of the terminal station and exist in the low group band. Downstream channels chR11 to chR32 are reception channels of the terminal station and exist in the high group band. The frequency converter FT provided at the head end shifts the input signal in the low group band by the offset frequency Δf to obtain the output signal in the high group band. The frequency converter FT is provided to the head end by the transmission channels chS11, chS12, etc. The transmitted signal is transmitted to the terminal station side through the reception channels chR11, chR12 and the like. Therefore, the transmission channel chS11 and the reception channel chR11 are always used as one set. The same applies to other channels. In the present embodiment, when the terminal stations T1 to T3 function as the called stations, their own transmission channels chs11, chs21, chs31 and their own reception channels chR12, chR22, chR32 are assigned in advance. Then, the reception channel chR12 is the channel c obtained by converting the transmission channel chs11 by the frequency conversion device FT.
It is a channel one channel above hR11, and the other receive channels chR22 and chR32 are also transmit channels c.
It has a similar relationship to hs21 and chs31. The procedure of the initial setting is the same as the procedure of the initial setting of FIG. 3 of the first embodiment, but fS is used as frequency data according to each terminal station.
11, fS21, fS31 are output, and the offset command value H is output to each of the modulation / demodulation devices M1 to M3. As a result, each modulator / demodulator M1
The M3 transmission channel and reception channel are set to the above-mentioned unique channels. The calling procedure is similar to that of FIG. 4 showing the calling procedure of the first embodiment, except for the following points. That is, in step 102, the receiving channel of the calling station T1 is changed to the unique receiving channel chR22 of the called station T2 of the calling partner station. At this time, the control data for changing the channel has frequency data fS21 and offset command value H. Therefore, the transmitting channel of the calling station T1 changes to the channel ch as the receiving channel changes.
Changed to s21. Then, in step 106, the transmission channel of the calling station T1 is changed to the transmission channel chS22 corresponding to the unique reception channel chR22 of the called station T2, and the reception channel is changed to the called channel TS22.
The control data is changed so that the control data is changed to the receiving channel chR21 corresponding to the second unique transmitting channel chS21.
Is output to. At this time, the control data is frequency data fS
22 and the shift command value is L. On the other hand, the incoming call procedure is the same as the program of FIG. 5 of the first embodiment because the incoming call station T2 does not require a channel change. When a communication channel is established by such a procedure,
The signal output from the calling station T1 to the upstream transmission channel chS22 whose transmission channel has been changed is converted to the downstream reception channel chR22 by the head-end frequency conversion device FT and output to the transmission path D. Then, the called station T2 that can receive the signal of the unique reception channel chR22 receives the signal. In addition, the signal output from the called station T2 to the unique transmission channel chS21 of the upstream is the downstream reception channel chR21
And is output to the transmission path D. Then, the signal is received by the calling station T1 whose reception channel is changed so that the signal of the reception channel chR21 can be received. Therefore, transmission is performed from the calling station T1 to the called station T2 on the transmission channel chS22 and the reception channel chR22, and is transmitted from the called station T2 to the calling station T1 on the transmission channel chS21 and the reception channel chR21. Be seen. In both cases, a transmission channel chS21 and a reception channel chR22 unique to the called station and channels chR21 and chS22 obtained by shifting the channels by Δf are used. When the communication is completed, the calling station T1 executes the program shown in FIG. 3 to restore the transmission channel and the reception channel to the original transmission channel chS11 and reception channel chR12.

【The invention's effect】

When each end station functions as a called station, each end station is assigned a unique transmission channel and a unique reception channel in advance, and the calling station is the transmission channel or reception channel assigned to the called station of the communication partner. By detecting the presence or absence of the carrier, it is detected whether or not the called station is in the non-communication state. Then, the calling station changes its own reception channel and transmission channel so as to correspond to the peculiar transmission channel and peculiar reception channel of the called station, so that between the calling station and the called station. It allows the formation of full duplex communication channels. Therefore, the communication method and communication system of the present invention can automatically perform arbitrary inter-terminal communication using a frequency division multiplexing transmission line.

[Brief description of drawings]

FIG. 1 is a block diagram showing a communication system according to a specific embodiment of the present invention. FIG. 2 is an explanatory diagram showing the channel arrangement. FIG. 3 is a flowchart showing a channel initial setting procedure and a channel restoring procedure. FIG. 4 is a flowchart showing a calling procedure. FIG. 5 is a flowchart showing an incoming call procedure. FIG. 6 is a block diagram showing a communication system according to another embodiment. FIG. 7 is an explanatory view showing the channel arrangement. T1 to T3: Terminal station, M1 to M3: Modulator / demodulator C1 to C3: Computer, D: Transmission line, FT: Frequency converter, A1 to
A4 ... Bidirectional relay amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsu Ogasawara, 4-15-23, Sakae, Naka-ku, Nagoya-shi, Aichi Stock company cast (72) Inventor Shinzo Mizuno 2 Mei-Minami, Nakamura-ku, Nagoya, Aichi No. 14-19 Hibiya General Equipment Co., Ltd. Nagoya Branch (56) References JP-A-51-55612 (JP, A) JP-A-57-211850 (JP, A) JP-A-59-178842 (JP, A) ) JP-A-59-97250 (JP, A) JP-A-60-198934 (JP, A)

Claims (7)

[Claims] 1. In a communication system comprising a transmission line for transmitting a signal subjected to frequency division multiplexing and a modulation / demodulation device constituting a terminal station connected to the transmission line, a called station with which each terminal station is a communication partner. In this case, the transmission channel and the reception channel peculiar to the terminal station are pre-assigned, and the calling station detects the presence or absence of the carrier of the peculiar reception channel or the peculiar transmission channel assigned to the called station, and the carrier If no call is detected, the transmission channel and the reception channel of the calling station are set according to the peculiar reception channel or peculiar transmission channel of the called station, so that all A communication method characterized by forming a dual communication channel. 2. A frequency converter for converting a low group frequency band or a high group frequency band into a high group frequency band or a low group frequency band is connected to the transmission line, and the high group frequency band and the low group frequency band are connected. By forming an upstream channel for transmitting a signal in one direction and a downstream channel for transmitting a signal in the opposite direction to the one direction, wherein the transmission channel is an upstream channel and the reception channel is a downstream channel. The communication method according to claim 1. 3. The communication method according to claim 1, wherein the communication after the calling station and the called station are channel-connected is data, voice or video communication. 4. A communication system comprising a transmission line for transmitting a signal subjected to frequency division multiplexing and a modulation / demodulation device constituting a terminal station connected to the transmission line, wherein the transmission channel and the reception channel of each terminal station are Initializing means for initializing to the peculiar channel assigned to the terminal station, and a carrier for detecting the presence or absence of a carrier of the peculiar transmission channel or peculiar reception channel assigned to the called station as a communication partner at the calling station. If the detecting means and the carrier are not detected, the channel initially set in the calling station is changed, and the transmission channel of the calling station is changed according to the peculiar reception channel or peculiar transmission channel of the called station. And the channel setting means for setting the receiving channel, and when the communication is completed, the transmitting channel and the receiving channel of the calling station are set to the original setting. A communication system comprising: a recovery means for recovering to a transmission channel and a reception channel unique to the communication system. 5. A frequency converter for converting the low group frequency band or the high group frequency band into the high group frequency band or the low group frequency band is connected to the transmission line, and the high group frequency band and the low group frequency band are connected. By forming an upstream channel for transmitting a signal in one direction and a downstream channel for transmitting a signal in the opposite direction to the one direction, wherein the transmission channel is an upstream channel and the reception channel is a downstream channel. The communication system according to claim 4. 6. The channel setting means sets a carrier frequency of the transmission channel and a carrier frequency of the reception channel, with a carrier frequency of one channel being a center, and a frequency which is selectably offset to an upper side or a lower side by a constant frequency. 5. The communication system according to claim 4, wherein the carrier frequency of the other channel is used. 7. The channel setting means is selectable to an upper side or a lower side around a frequency obtained by offsetting a carrier frequency of one of the carrier frequency of the transmitting channel and the carrier frequency of the receiving channel by a constant frequency. 6. The communication system according to claim 5, wherein the frequency having a constant frequency offset is used as the carrier frequency of the other channel.