JP5456720B2 - Communications system - Google Patents

Description

  The present invention relates to a communication system in which devices are connected to each other via a plurality of repeaters via a wired communication line, and more particularly to a communication system using time division relay transmission.

A conventional communication system using time-division relay transmission connects a plurality of repeaters to a single-wire communication line (twisted pair wire consisting of two core wires as an example), and connects an upstream master unit (or downstream slave unit). Data transmission to the child device (or parent device) in order from the adjacent device via the adjacent relay device.
The repeater is used as a means for signal amplification when there is a device to be transmitted at a position beyond the signal reachable range, or when the signal arrives but the speed is not obtained due to insufficient strength.
In this case, all the repeaters are not operated at the same time, but are operated by time division in order from the upstream (or downstream) repeaters.

That is, in the range where the signals of the two repeaters constituting one relay section reach, at the same time, only two repeaters in one section operate as repeaters and transmit to the adjacent repeater. By transmitting the signal to the adjacent repeater at the next time, signals are transmitted far away while preventing mutual signal interference.
Such a conventional time division relay transmission method will be described with reference to FIGS.

  FIG. 9 shows a schematic configuration diagram of the communication system, and FIGS. 9A, 9B, and 9C show a state in which they are shifted by one period in time, and the configuration is the same. In FIG. 9, the modem of the parent device 10 and the modem of the child device 20 are connected in series by a wired communication line 30, and a plurality of relay devices 40 a to 40 b are connected to the communication line 30 between the parent device 10 and the child device 20. 40c modems (three in the figure) are connected via terminal blocks 50a to 50c.

FIG. 10 illustrates the operation of the repeater 40 between the master unit 10 and the slave unit 20 when time division relay transmission is performed in such a communication system, according to the time t axis.
As shown in FIG. 10, in period 1 (FIG. 9 (a)), only the relay section 1 between the parent device 10 and the relay device 40a can communicate, and the relay device between the relay device 40a and the relay device 40b. Communication between the relay sections 2 to 4 between 40b and the relay device 40c and between the relay device 40c and the slave device 20 is impossible. Next, in period 2 (FIG. 9B), only the relay section 2 between the relay device 40a and the relay device 40b can communicate, and between the parent device 10 and the relay device 40a, between the relay device 40b and the relay device 40c. During this period, the relay sections 1 and 3 to 4 between the relay device 40c and the slave device 20 cannot communicate. Next, in period 3 (FIG. 9C), only the relay section 3 between the relay device 40b and the relay device 40c can communicate, and between the parent device 10 and the relay device 40a, between the relay device 40a and the relay device 40b. In the meantime, the relay sections 1, 2, and 4 between the relay device 40c and the slave device 20 cannot communicate.

As described above, in the communication system using the conventional time-division relay transmission, since the communication signal from one modem reaches all the wires of the communication line 30, only one modem can transmit the communication signal at the same time. Accordingly, only one section can be operated in the relay sections 1 to 4 at the same time.
For this reason, as the number of repeaters increases, there is a problem that the time during which communication is not performed on the communication line increases and the effective speed of communication decreases.

  As a communication system in which signals are not transmitted simultaneously between zones that spatially interfere with each other, the service area is divided into m zones, and signals having the same frequency are provided between the zones where the mobile station and the base station exist. There is known a mobile communication system that can transmit a signal in a time division of different time slots in one zone and a plurality of zones (see Patent Document 1).

  Also, in a wireless multi-hop network in which each wireless node relays packets to each other and transmits signals from the start node to the end node, radio wave interference between the wireless nodes is prevented, and the throughput is kept constant regardless of the number of relay stages. In addition, the start node intermittently transmits a packet at a transmission cycle corresponding to the frequency reuse interval (distance where the same frequency can be used), and each relay node receives the packet and transmits the packet corresponding to the frequency reuse interval. It is known that the packet is relayed and transmitted to the next relay node after the waiting time (see Patent Document 2).

JP-A-10-117375 JP 2005-143046 A

Patent Document 1 relates to communication between a plurality of base stations and a passing train in mobile radio, and Patent Document 2 relates to a wireless multi-hop network, both of which are wireless communication systems.
As described above, in the radio, a communication system in which interference occurs at least in an adjacent section has been proposed as various methods for preventing interference.

However, in the case of wired communication, interference often occurs when a signal leaks from a communication line, or when signals are congested and transmitted and overlapped with each other, and therefore, there are few measures taken for signal interference. It is.
Therefore, as explained in FIG. 9 and FIG. 10, only two repeaters in one section operate as a repeater at the same time and perform transmission to adjacent repeaters, thereby preventing signal interference to each other while preventing mutual signal interference. I try to transmit. In that case, as the number of repeaters increases, there is a problem that the time during which communication is not performed on the communication line increases and the effective speed of communication decreases.

  The present invention has been made to solve the above-described problems, and it is possible to improve communication efficiency (speed) by physically or electrically separating communication lines in units of relay sections. An object of the present invention is to provide a communication system.

The communication system of the present invention is a communication system in which a master unit and a slave unit are connected with a communication line via a plurality of relays to transmit and receive data. Two input / output connection points respectively connected to the upstream communication path and the downstream communication path of the communication line, and a switch unit for performing an operation of alternately connecting the two input / output connection points to the transmission / reception switching unit of the repeater The communication channel switching unit is provided, the switching timing of the switch unit of the communication channel switching unit is synchronized with all the repeaters, and the switch unit connected to the predetermined repeater n is connected to the input / output connection point of the upstream communication channel In this case, the switch connected to the adjacent repeater n + 1 on the downstream side of the repeater n is connected to the input / output connection point of the downstream communication path.

  In this invention, the switch part of the communication path switching unit connected to all the repeaters performs the operation of switching between the upstream communication path and the downstream communication path of the communication line synchronously, so that the transmission signal reach of the repeater is reduced. It is limited to upstream or downstream adjacent repeaters, and one skipped relay section can be simultaneously communicated in the same period without causing interference, so even if there are multiple relay sections, only one section can be communicated within the signal control range. Compared to the conventional time division relay transmission, the communication efficiency (speed) can be improved.

It is a schematic block diagram of the communication system of Embodiment 1 of this invention. It is a functional lineblock diagram in a connecting part of a communication line of a communication system in Embodiment 1 of this invention, a repeater, and a repeater. In Embodiment 1 of this invention, it is operation | movement explanatory drawing at the time of starting for synchronizing a communication path switching part. It is operation | movement explanatory drawing along the time of the communication system of Embodiment 1 of this invention. It is a schematic block diagram of the communication system of Embodiment 2 of this invention, and a block diagram of the low-pass filter used for it. It is a figure which shows the frequency characteristic of the filter used in Embodiment 2 of this invention. It is a block diagram of the ferrite core used in Embodiment 3 of this invention. It is a schematic block diagram of the communication system of Embodiment 4 of this invention. It is a schematic block diagram of the conventional communication system. It is operation | movement explanatory drawing along the time of the conventional communication system.

Embodiment 1 FIG.
A communication system according to Embodiment 1 of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic configuration diagram of a communication system, FIG. 2 is a functional configuration diagram of a connection unit between a communication line and a repeater, and a repeater, FIG. 3 is an operation explanatory diagram at the time of activation for synchronizing a communication path switching unit, and FIG. Is an explanation of the operation of the communication system along the time.

FIGS. 1 (a) and 1 (b) show a state that is shifted by one period in time, and the configuration is the same. In FIG. 1, the modem of the master unit 10 and the modem of the slave unit 20 are connected in series with a plurality of wired communication lines 30a to 30d (subscripts are omitted in general terms) that are physically independent. In the communication line 30 between the slave units 20, modems of a plurality of relay units 40a to 40c (three in the figure but not limited to this number, subscripts are omitted when collectively referred to) are connected via the terminal blocks 50a to 50c . Connected. In addition, communication path switching units 60a to 60c are provided at connection portions between the relay devices 40a to 40c and the communication lines 30a to 30d. Here, the direction in which the parent device 10 is arranged is upstream, and the direction in which the child device 20 is arranged is downstream.

Each of the communication path switching units 60a to 60c (subscripts are omitted when collectively referred to) include two input / output connection points 61 and 62, and a transmission / reception switching unit that is a signal input / output unit of the repeaters 40a to 40c (described later). Is connected to the two input / output connection points 61, 62. The input / output connection point 61 is connected to the upstream communication path of the communication line 30 with respect to the repeater 40, and the input / output connection point 62 is connected to the downstream side of the communication line 30 with respect to the relay machine 40.
The communication path switching units 60a to 60c are represented by logical functions as three-terminal switches in FIG. 1, but are actually electronic circuits having a switching function that are configured on a substrate with elements such as transistors or FETs and resistors. It consists of

The switching timing of the switch unit 63 of each of the communication channel switching units 60a to 60c is synchronized with all the relay devices 40, and the switch unit 63 connected to a predetermined relay device 40n (for example, 40a) is connected to the input / output connection of the upstream communication channel. When connected to the point 61, the switch unit 63 connected to the adjacent repeater 40 n + 1 (for example, 40b) on the downstream side of the repeater 40n is connected to the input / output connection point 62 of the downstream communication path. Also, when the switch unit 63 connected to the predetermined repeater 40n conversely is connected to the input and output connection point 62 of the downstream communication path is connected to an adjacent repeater 40 n + 1 at the downstream side of the repeater 40 n The switch unit 63 is connected to the input / output connection point 61 of the upstream communication path.
In this way, the communication line 30 is made physically independent for each relay section composed of two relay units 40 by the communication path switching units 60a to 60c.

In the above configuration, as shown in FIG. 1A , information such as image data or character data transmitted from the master unit 10 is packet-transmitted and sent to the adjacent repeater 40a on the downstream side, and the repeater 40a Is amplified. As shown in FIG. 1B , the data signal amplified by the repeater 40a is sent to the adjacent repeater 40b on the downstream side in the next cycle, and the signal is amplified by the repeater 40b. Thus, the image data or character data finally transmitted from the parent device 10 is sent to the child device 20, and the child device 20 can display the image data or character data by displaying it. Conversely, data from the slave unit 20 can be transmitted to the master unit 10 in the same manner.

In this case, the switch unit 63 of the communication path switching units 60a to 60c is one of the input / output connection points 61 and the other is the input / output connection in the switch unit 63 of the communication path switching unit 60 connected to the adjacent repeater 40. Since the connection is switched to a different contact such as point 62, one skipped relay section can communicate simultaneously in the same period.
Therefore, the data information transmitted from the base unit 10 to the adjacent repeater 40 can be transmitted at the same time without causing signal interference to the adjacent repeater 40 on the downstream side in each skipped relay section. Efficiency (speed) can be improved.

Next, the connection location between the communication line 30 and the repeater 40 and the detailed functional configuration of the repeater will be described with reference to FIG.
In FIG. 2, a terminal block 50, communication path coupling units 70 a and 70 b, and a communication path switching unit 60 are connected between the communication line 30 and the repeater 40. The communication path coupling unit 70a connects the communication line connected to the terminal block 50 and the upstream communication path connected to the input / output connection point 61 of the communication path switching unit 60. It is composed of circuits such as transformers and capacitors for the purpose. Similarly, the communication path coupling unit 70b connects the communication line connected to the terminal block 50 and the downstream communication path connected to the input / output connection point 62 of the communication path switching unit 60. It is composed of circuits such as transformers and capacitors for the purpose of insulation. As described in FIG. 1, the communication path switching unit 60 includes two input / output connection points 61 and 62 and a switch unit 63.
The communication path coupling units 70a and 70b and the communication path switching unit 60 are described as being configured outside the repeater 40 in FIG. 2, but the communication path coupling units 70a and 70b and the communication path switching unit 60 are Alternatively, it may be configured so as to be taken into the repeater 40.

The repeater 40 includes a transmission / reception switching unit 41, a receiving unit 42, a transmitting unit 43, a synchronization / carrier detection and timing generation unit 44, and a data holding / control unit connected to the switch unit 63 of the communication path switching unit 60. 45.
The transmission / reception switching unit 41 has a function of switching between a reception signal received by the reception unit 42 and a transmission signal transmitted from the transmission unit 43.
The reception unit 42 includes a reception filter unit 421 that passes only a predetermined frequency band from the reception signal received by the transmission / reception switching unit 41, a reception signal gain adjustment unit 422 that adjusts the gain of the reception signal, and an AD that converts an analog signal into a digital signal. Converter 423 corrects the synchronization of the entire received signal (the received signal includes a frequency deviation between the transmitting modem and the receiving modem, but corrects the deviation), to perform time / frequency conversion of the received signal Fast Fourier transform (FFT) unit 425, a map for converting the map data on the coordinate axes after being converted by the fast Fourier transform (FFT) unit 425 to a binary signal of “0” and “1” → data conversion unit 426, The frame decomposition unit 427 is configured to decompose a binary signal having a defined frame structure and extract desired information.

  The transmission unit 43 includes a frame assembly unit 431, data for converting frame data into map data → map conversion unit 432, an inverse Fourier transform (IFFT) unit 433 for frequency / time conversion of the signal, and adjusts the timing of the transmission signal. The transmission timing adjustment unit 434 includes a DA conversion unit 435 that converts a digital signal into an analog signal, and a transmission signal gain adjustment unit 436 that adjusts the gain of the transmission signal.

The synchronization / carrier detection and timing generation unit 44 detects a frequency deviation between the transmission modem and the reception modem from the information output from the fast Fourier transform (FFT) unit 425, and is output from the fast Fourier transform (FFT) unit 425. A synchronization / carrier detection unit 441 that detects a carrier signal and FFT timing information from the received information, a timing generation unit 442 that generates various timing signals based on information detected by the synchronization / carrier detection unit 441, and a timing generation unit 442 The communication path switching timing generation section 443 generates a switching timing signal for the switch section 63 of the communication path switching section 60 from the signal generated in the above.
Note that the Fourier operation of the fast Fourier transform (FFT) unit 425 and the inverse Fourier transform (IFFT) unit 433 is performed by the timing signal generated by the timing generation unit 442. In addition, the entire signal is corrected by the reception synchronization correction unit 424 and the transmission timing adjustment unit 434 based on the signal detected by the synchronization / carrier detection unit 441.

The data holding / control unit 45 temporarily holds data transmitted from a device such as the adjacent base unit 10 or the relay unit 40, and sends it to the transmission unit 43 side to relay the held data, For example, control is performed to send data to an external device (not shown) such as a personal computer connected or the like, or to send data from the external device to the transmission unit 43.
Note that an external device such as a personal computer is not necessarily connected to the relay device 40, and there are some devices that perform only a relay operation without being connected to the relay device 40.

In the above configuration, an operation description at the time of activation for synchronizing all the communication path switching units 60 will be described with reference to FIG.
First, as shown in FIG. 3A, at the time of start-up before synchronization of the communication system, all the switch units 63 of the communication path switching units 60a to 60c connected to each repeater 40 are upstream of the communication line 30. It falls to the input / output connection point 61 side connected to the side communication line. When a synchronization signal is transmitted from the parent device 10 in this state, the synchronization signal is received by the first repeater 40a via the communication line 30a, the terminal block 50a, and the communication path switching unit 60a.
The repeater 40a detects a synchronization signal by the synchronization / carrier detection unit 441 from the signal demodulated by the fast Fourier transform (FFT) unit 425 of the reception unit 42 shown in FIG. Timing information is obtained from the synchronization signal detected by the synchronization / carrier detection unit 441. If timing information with the required accuracy cannot be obtained with a single synchronization signal, the above operation is repeated a plurality of times. In this way, the relay device 40a is in a state of being synchronized with the parent device 10.

Next, after the synchronization with the base unit 10 is completed, the relay unit 40a, as shown in FIG. 3B, the switch unit 63 of the communication path switching unit 60a of the relay unit 40a alternately in a certain cycle according to the synchronized timing. Start the switching operation.
Repeater 40 a is collapsed switch input and output connection point 62 of the switch section 63, via the communication path switching section 60b and the communication line 30b and the terminal block 50b to the relay device 40a in the period in which the relay unit 40b is connected The repeater 40a transmits a synchronization signal, and the synchronization signal is received by the repeater 40b via the communication line 30b, the terminal block 50b, and the communication path switching unit 60b. The repeater 40b detects a synchronization signal by the synchronization / carrier detection unit 441 from the signal demodulated by the fast Fourier transform (FFT) unit 425 of the reception unit 42 shown in FIG. Timing information is obtained from the synchronization signal detected by the synchronization / carrier detection unit 441. If timing information with the required accuracy cannot be obtained with a single synchronization signal, the above operation is repeated a plurality of times. In this way, the repeater 40b is synchronized with the repeater 40a. Hereinafter, similarly, the repeater 40c is sequentially synchronized with the repeater 40b.

In this way, all the repeaters 40 are synchronized with the nearest upstream repeater 40. In this state, the switch units 63 of the communication path switching units 60 of all the repeaters 40 are synchronized with each other. Switching operation is performed alternately at a constant cycle. The period of this fixed period is N times the period of the synchronization signal (N is an integer of 1 or more).
As described above, the switching operation of the switch unit 63 of the communication path switching unit 60 is performed by connecting the switch unit 63 connected to the predetermined relay unit 40n (for example, 40a) to the input / output connection point 61 of the upstream communication path. At this time, the switch unit 63 connected to the adjacent repeater 40n + 1 (for example, 40b) on the downstream side of the repeater 40n is connected to the input / output connection point 62 of the downstream communication path. Also, when the switch unit 63 connected to the predetermined repeater 40n conversely is connected to the input and output connection point 62 of the downstream communication path is connected to an adjacent repeater 40 n + 1 at the downstream side of the repeater 40 n The switch unit 63 is connected to the input / output connection point 61 of the upstream communication path.

In such a communication system, the operation state of the repeater 40 between the master unit 10 and the slave unit 20 when the data information after synchronization is time-division relayed will be described with reference to FIG. To do.
As shown in FIG. 4, in period 1 (FIG. 1 (a)), the switch unit 63 of the repeater 40a falls to the upstream communication path (base unit side), and the switch of the repeater 40b in the downstream communication path When the unit 63 falls to the downstream communication path (on the repeater 40c side), the master unit 10 and the repeater 40a are connected via the communication line 30a to enable communication between them, and the communication line 30b on the repeater 40b side. And is separated. Therefore, even if the repeater 40 including the repeater 40b in the period 1 communicates, it does not interfere with the signal in the section of the master unit 10-relay 40a.

  That is, in the relay section 3 shifted by one from the relay section 1 between the master unit 10 and the relay machine 40a, the switch unit 63 of the relay machine 40b falls to the downstream communication path (relay machine 40c side) and the downstream communication path The switch unit 63 of the relay unit 40c falls to the upstream communication path (the side of the relay unit 40b), so that the relay unit 40b and the relay unit 40c are connected via the communication line 30c and communication between the two is possible. Thus, the relay section 1 and the relay section 3 can communicate simultaneously without causing signal interference.

  In cycle 2 (Fig. 1B) following cycle 1, switch unit 63 of relay device 40a falls to the downstream communication path (relay device 40b side), and at the same time, switch unit 63 of relay device 40b is connected to the upstream communication channel ( By falling to the side of the repeater 40a, the repeater 40a and the repeater 40b are connected via the communication line 30b, and communication between them is possible, and the communication line 30c on the repeater 40c side is separated. Therefore, even if the further relay 40 including the relay 40c communicates in the same time zone, it does not interfere with the signal in the section between the relay 40a and the relay 40b.

That is, in the relay section 4 shifted by one from the relay section 2 of the repeater 40a and the repeater 40b, the switch unit 63 of the repeater 40c falls down to the downstream communication path (slave unit 20 side), so that the repeater 40c The handset 20 is connected via the communication line 30d, and communication between both becomes possible. In this way, the relay section 2 and the relay section 4 can communicate simultaneously without causing signal interference.
As described above, in the cycle 1, the relay section 1 between the parent device 10 and the relay machine 40a and the relay section 3 between the relay machine 40b and the relay machine 40c can communicate, and the relay between the relay machine 40a and the relay machine 40b. In section 2, the relay section 4 between the relay device 40c and the child device 20 cannot communicate.
Next, in the cycle 2, the relay section 2 between the relay device 40a and the relay device 40b and the relay section 4 between the relay device 40c and the slave device 20 are communicable, and between the parent device 10 and the relay device 40a. Relay section 1 and relay section 3 between relay machine 40b and relay machine 40c cannot communicate.

  Since all the repeaters 40 perform the above operation in synchronism, the transmission signal reachable range of the repeater 40 is limited to upstream or downstream adjacent repeaters, and one skipped relay section is the same without causing signal interference. Since simultaneous communication can be performed during a period, communication efficiency (speed) can be improved compared to conventional time-division relay transmission in which communication is possible only in one section in the signal control range even if there are a plurality of relay sections.

Embodiment 2. FIG.
Next, the communication system in Embodiment 2 of this invention is demonstrated based on FIGS. FIG. 5 is a schematic configuration diagram of a communication system and a configuration diagram of a low-pass filter used therefor, and FIG. 6 is a diagram illustrating frequency characteristics of the filter.
In FIG. 5A, the difference from the first embodiment is a low-pass filter that can cut off the communication frequency band of data communication so as to short-circuit the terminal block 50 connected between the communication line 30 and the repeater 40. 80, the communication lines 30a to 30d are electrically independent for each relay section. FIG. 5B is an enlarged view of the low-pass filter 80 connected to the terminal block 50. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and description thereof is omitted.

As shown in FIG. 6, the filter characteristic of the low-pass filter 80 is such that a signal having a frequency equal to or higher than the cutoff frequency fc is cut off and a frequency equal to or lower than the cutoff frequency fc is passed. Is in the range of f1 to f2 that is equal to or higher than the cut-off frequency fc, so that these data cannot be transmitted without going through the repeater 40.
On the other hand, since the low-pass filter 80 can pass a signal by a telephone such as a voice having a frequency equal to or lower than the cut-off frequency fc, for example, a voice is transmitted.
In this way, even if the data cannot be transmitted due to a failure of the repeater 40 or the like, the master unit 10 and the slave unit 20 can talk over the telephone or the like so that the transmission of the telephone and the data can coexist. Become.

Embodiment 3 FIG.
Next, the communication system in Embodiment 3 of this invention is demonstrated based on FIG. The invention of the third embodiment uses a ferrite core instead of the low-pass filter 80 of the second embodiment so that the communication lines 30a to 30d are electrically independent for each relay section.
FIG. 7A shows a configuration diagram of the ferrite core 90 wound around the communication line 30 so as to short-circuit the terminal block 50, and is used instead of the low-pass filter 80 used in the second embodiment.
As shown in FIG. 7B, the ferrite core 90 divides the core into upper and lower halves and winds the core around the communication line 30 so that the core is in close contact with the core. It is what you do.
If the ferrite core 90 is used in this way, the relay method of the first embodiment can be used even when the communication line 30 is not physically divided in units of relay sections.

Embodiment 4 FIG.
Next, the communication system in Embodiment 4 of this invention is demonstrated based on FIG.
FIG. 8 shows a schematic configuration diagram of the communication system. Communication lines 30a (configured by 30a1 and 30a2) and 30b (configured by 30b1 and 30b2) between the master unit 10 and the relay unit 40a or between the relay units 40a and 40b. A plurality of slave units 200a to 200n and 200n + 1 to 200m different from the slave unit 20 on the most downstream side are connected to the configuration).
In addition, although the connection to the communication line 30 of the some subunit | mobile_unit 200a-200n and 200n + 1-200m is connected via the terminal block 50 in illustration, a connection location and a connection method are not specified in particular. . Other configurations are the same as those of the first embodiment shown in FIG.

The slave units 200a to 200n and 200n + 1 to 200m are configured such that the upstream master unit 10 or the relay unit 40 manages the communication of each of the slave units 200a to 200n and 200n + 1 to 200m. That is, the slave units 200a to 200n are managed by the master unit 10, and the slave units 200n + 1 to 200m are managed by the relay unit 40a.
And the subunit | mobile_unit 200a-200n transmits / receives data transmission between the main | base station 10 or the relay machine 40a with the period which the main | base station 10 and the relay machine 40a can communicate. The slave units 200n + 1 to 200m perform data transmission / reception with the relay unit 40a or the relay unit 40b in a cycle in which the relay unit 40a and the relay unit 40b can communicate with each other.

In this way, by connecting the plurality of slave units 200a to 200n and 200n + 1 to 200m to the communication line 30 between the base unit 10 and the relay unit 40 or between the plurality of relay units 40, simultaneous transmission between the conventional relay units 40 is possible. Not only parallel transmission, but also simultaneous transmission of data can be made to each slave connected between them, and the application can be expanded.
Note that the number of slave units connected to the communication line 30 between the master unit 10 and the relay unit 40 or between the plurality of relay units 40 is not limited to a plurality and may be one.

10: Master machine, 20: Slave machine,
30, 30a-30d : communication line, 40, 40a-40c : repeater,
41: Transmission / reception switching unit, 42: Reception unit,
43: Transmission unit 44: Synchronization / carrier detection and timing generation unit,
45: Data holding / control unit,
441: synchronization / carrier detection unit, 442: timing generation unit,
443: a communication channel switching timing generation unit,
50: Terminal block (transmission path coupling part), 60: Communication path switching part,
61: Input / output connection point, 62: Input / output connection point,
63: switch unit, 70a, 70b: communication path coupling unit,
80: Low-pass filter, 90: Ferrite core,
200a-200n, 200n + 1-200m: cordless handset.

Claims (7)

In a communication system in which a master unit and a slave unit are connected with a communication line via a plurality of relay units to transmit and receive data, an upstream of the communication line is provided at a connection point between the relay unit and the communication line. Communication having two input / output connection points respectively connected to the side communication path and the downstream communication path, and a switch unit for performing an operation of alternately connecting the two input / output connection points to the transmission / reception switching unit of the repeater A switching unit is provided, and the switching timing of the switch unit of the communication channel switching unit is synchronized with all the repeaters, and the switch unit connected to the predetermined repeater n is connected to the input / output connection point of the upstream communication channel In some cases, the switch unit connected to the adjacent repeater n + 1 on the downstream side of the repeater n is connected to the input / output connection point of the downstream communication path.   The communication system according to claim 1, wherein the switch unit of the communication path switching unit performs a switching operation alternately at a constant cycle.   At startup before synchronization, all the switch sections of the communication path switching section are connected to the input / output connection points of the upstream communication path, and receive the synchronization signal from the upstream master unit or repeater. The communication system according to claim 1 or 2, wherein the switch unit connected to the repeater whose synchronization has been completed is switched and connected to the input / output connection point of the downstream communication path.   The filter according to any one of claims 1 to 3, wherein a filter capable of blocking a signal in a frequency band for performing data communication is connected between an upstream communication path and a downstream communication path of a communication line to which the repeater is connected. The communication system according to claim 1.   The communication system according to claim 4, wherein the filter is a low-pass filter that allows a signal in a frequency band lower than a frequency band in which data communication is performed to pass.   The communication system according to any one of claims 1 to 3, wherein a ferrite core capable of blocking a signal in a frequency band for performing data communication is disposed around a communication line to which the repeater is connected.   The communication system according to any one of claims 1 to 6, wherein a slave unit is connected to a communication line between the master unit and the relay unit or between a plurality of relay units.

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