Communication system

Abstract

This technology provides information necessary to identify communication loss in communication lines between nodes in communication systems such as star-type networks. [Solution] The communication system comprises a first, second, and third terminal, and the communication lines of each terminal are directly or indirectly connected to the same physical communication node. Each terminal comprises a transmitting unit that outputs a measurement signal to the communication line to which the terminal is connected, a measuring unit, and a switching unit that switches the input impedance of the terminal to high impedance. The measuring unit of the first terminal measures the received voltage of the measurement signal transmitted from the third terminal with the second terminal switched to high impedance. The measuring unit of the second terminal measures the received voltage of the measurement signal transmitted from the first terminal with the third terminal switched to high impedance, and also measures the received voltage of the measurement signal transmitted from the third terminal with the first terminal switched to high impedance.

Description

Technical Field

[0006] , , ,

[0005] , ,

[0001] The present disclosure relates to a communication system.

Background Art

[0002] In a communication system, one known system includes a bus and a plurality of communication devices, where the plurality of communication devices are connected via the bus (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A communication system as shown in Patent Document 1 is a so-called bus-type network in which a plurality of communication terminals (nodes) are indirectly connected to physically the same communication node. In networks such as star-type and bus-type networks where a plurality of communication terminals are connected via physically the same communication node, it may be difficult to identify which communication line between nodes has a large communication loss when the communication quality is poor.

[0005] The present disclosure has been made to solve such problems. The objective is to provide a technology that can collect information necessary to identify communication losses in communication lines between respective nodes in a communication system where a plurality of communication terminals are connected via physically the same communication node.

Means for Solving the Problems

[0006] The communication system according to this disclosure comprises a first terminal connected to one end of a first communication line, a second terminal connected to one end of a second communication line, and a third terminal connected to one end of a third communication line, wherein the other ends of the first, second, and third communication lines are physically connected directly or indirectly to the same communication node, the first terminal comprises a first transmitting unit that outputs a first measurement signal to the first communication line, a first measurement unit, and a first impedance switching unit that switches the impedance of the first terminal to the first communication line to high impedance, the second terminal comprises a second measurement unit and a second impedance switching unit that switches the impedance of the second terminal to the second communication line to high impedance, and the third terminal comprises a second transmitting unit that outputs a second measurement signal to the third communication line, and the The first measurement unit includes a third impedance switching unit that switches the impedance of the third terminal to the third communication line to high impedance, and the first measurement unit measures the voltage of the second measurement signal received via the first communication line with the second impedance switching unit switched the impedance of the second terminal to the second communication line to high impedance, and the second measurement unit measures the voltage of the first measurement signal received via the second communication line with the third impedance switching unit switched the impedance of the third terminal to the third communication line to high impedance, and measures the voltage of the second measurement signal received via the second communication line with the first impedance switching unit switched the impedance of the first terminal to the first communication line to high impedance. [Effects of the Invention]

[0007] The technology disclosed herein has the effect of being able to collect information necessary to identify communication loss in the communication lines between each node in a communication system in which multiple communication terminals are physically connected via the same communication node. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows the overall configuration of the communication system according to Embodiment 1. [Figure 2] This is a block diagram showing the configuration of a communication terminal provided in the communication system according to Embodiment 1. [Figure 3] This is a flowchart showing an example of the operation of the communication system according to Embodiment 1. [Figure 4] This figure illustrates another example of the configuration of the communication system according to Embodiment 1. [Figure 5] This figure illustrates another example of the configuration of the communication system according to Embodiment 1. [Figure 6] This figure shows an example of a configuration that realizes the functions of the control device of the communication system according to Embodiment 1. [Modes for carrying out the invention]

[0009] The embodiments for implementing the communication system relating to this disclosure will be described with reference to the attached drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are simplified or omitted as appropriate. For convenience, the positional relationships of each structure may be expressed based on the illustrated state in the following description. This disclosure is not limited to the embodiments described below, and any combination of embodiments, any modification of any component of each embodiment, or any omission of any component of each embodiment is possible without departing from the spirit of this disclosure.

[0010] Embodiment 1. Embodiment 1 of this disclosure will be described with reference to Figures 1 to 6. Figure 1 is a diagram showing the overall configuration of the communication system. Figure 2 is a block diagram showing the configuration of the communication terminals provided in the communication system. Figure 3 is a flowchart showing an example of the operation of the communication system. Figures 4 and 5 are diagrams illustrating other configuration examples of the communication system. Figure 6 is a diagram showing an example of a configuration that realizes the functions of the control device of the communication system.

[0011] The communication system according to this embodiment includes three or more communication terminals 1. In the configuration example shown in Figure 1, the communication system is provided with three communication terminals 1: a first communication terminal 11, a second communication terminal 21, and a third communication terminal 31. In this disclosure, the first communication terminal 11, the second communication terminal 21, and the third communication terminal 31 are collectively referred to as "communication terminal 1" without distinction.

[0012] The network topology in the illustrated example configuration is a star type. That is, the first communication terminal 11 is connected to one end of the first communication line 16. The second communication terminal 21 is connected to one end of the second communication line 26. The third communication terminal 31 is connected to one end of the third communication line 36. The other ends of the first communication line 16, the second communication line 26, and the third communication line 36 are physically connected to the same communication node 90. In this disclosure, the first communication line 16, the second communication line 26, and the third communication line 36 are collectively referred to as "communication line 6" without distinction.

[0013] The configuration of the communication terminal 1 will be described with reference to Figure 2. The communication terminal 1 comprises a reference signal transmission unit 2, a signal receiving and measurement unit 3, a blockage unit 4, and a control unit 5. The communication terminal 1 is connected to one end of the communication line 6. The reference signal transmission unit 2 outputs a measurement signal to the communication line 6 to which the communication terminal 1 is connected. The voltage value of the measurement signal is preset.

[0014] The signal receiving and measuring unit 3 receives a measurement signal transmitted from another communication terminal 1 via the communication line 6 to which the communication terminal 1 is connected. The signal receiving and measuring unit 3 then measures the voltage of the received measurement signal.

[0015] The cutoff unit 4 is a switch that switches between a connected state and a cutoff state. The connected state is a state in which the electrical circuit of the communication terminal 1 including the reference signal transmission unit 2 and the signal reception / measurement unit 3 is electrically connected to the communication line 6 to which the communication terminal 1 is connected. The cutoff state is a state in which the electrical circuit of the communication terminal 1 including the reference signal transmission unit 2 and the signal reception / measurement unit 3 is electrically disconnected from the communication line 6 to which the communication terminal 1 is connected. In this cutoff state, the input impedance of the communication terminal 1 with respect to the communication line 6 becomes a so-called high impedance. The cutoff unit 4 is an example of an impedance switching unit that switches the input impedance of the communication terminal 1 with respect to the communication line 6 to a high impedance.

[0016] In this embodiment, the high impedance may be at least approximately 100 times or more, preferably approximately 1000 times or more, of the input impedance of the communication line 6 of the communication terminal 1 in the connected state. The input impedance of the communication terminal 1 in the connected state is, for example, about 70Ω to 1KΩ. Therefore, the high impedance may be set to at least 100KΩ, preferably 1MΩ or more.

[0017] The control unit 5 controls the communication operation of the communication terminal 1. The control target by this control unit 5 also includes the switching operation of the connected state / cutoff state by the cutoff unit 4.

[0018] Based on the configuration of the communication terminal 1 as described above, the description of the configuration example shown in FIG. 1 will be continued. The first communication terminal 11 includes a first reference signal transmission unit 12, a first signal reception / measurement unit 13, a first cutoff unit 14, and a first control unit 15. The first reference signal transmission unit 12 is the reference signal transmission unit 2 described above. That is, the first reference signal transmission unit 12 outputs the first measurement signal, which is the measurement signal described above, to the first communication line 16.

[0019] The first signal reception / measurement unit 13 is the signal reception / measurement unit 3 described above. That is, the first signal reception / measurement unit 13 receives a second measurement signal described later via the first communication line 16, and measures the voltage of the received second measurement signal. Also, the first signal reception / measurement unit 13 receives a third measurement signal described later via the first communication line 16, and measures the voltage of the received third measurement signal.

[0020] The first blocking unit 14 is the blocking unit 4 described above. That is, the first blocking unit 14 is a switch that switches between a connected state and a blocked state. The first blocking unit 14 is an example of a first impedance switching unit that switches the input impedance of the first communication line 16 of the first communication terminal 11 to a high impedance.

[0021] The first control unit 15 is the control unit 5 described above. That is, the first control unit 15 controls the communication operation of the first communication terminal 11, including the switching operation of the connected state / blocked state by the first blocking unit 14.

[0022] The same applies to the second communication terminal 21 and the third communication terminal 31 as to the first communication terminal 11. That is, the second communication terminal 21 includes a second reference signal transmission unit 22 that is the reference signal transmission unit 2, a second signal reception / measurement unit 23 that is the signal reception / measurement unit 3, a second blocking unit 24 that is the blocking unit 4, and a second control unit 25 that is the control unit 5. The second reference signal transmission unit 22 outputs a second measurement signal that is the measurement signal described above to the second communication line 26.

[0023] The second signal reception / measurement unit 23 receives a first measurement signal via the second communication line 26, and measures the voltage of the received first measurement signal. Also, the second signal reception / measurement unit 23 receives a third measurement signal described later via the second communication line 26, and measures the voltage of the received third measurement signal.

[0024] The second disconnection unit 24 is a switch that switches between a connected state and a disconnected state, and is an example of a second impedance switching unit that switches the input impedance of the second communication terminal 21 to the second communication line 26 to high impedance. The second control unit 25 controls the communication operation of the second communication terminal 21, including the switching operation of the connected state / disconnected state by the second disconnection unit 24.

[0025] Furthermore, the third communication terminal 31 includes a third reference signal transmission unit 32, which is a reference signal transmission unit 2; a third signal reception and measurement unit 33, which is a signal reception and measurement unit 3; a third blockage unit 34, which is a blockage unit 4; and a third control unit 35, which is a control unit 5. The third reference signal transmission unit 32 outputs the third measurement signal, which is the aforementioned measurement signal, to the third communication line 36.

[0026] The third signal receiving and measuring unit 33 receives the first measurement signal via the third communication line 36 and measures the voltage of the received first measurement signal. The third signal receiving and measuring unit 33 also receives the second measurement signal via the third communication line 36 and measures the voltage of the received second measurement signal.

[0027] The third disconnection unit 34 is a switch that switches between a connected state and a disconnected state, and is an example of a third impedance switching unit that switches the input impedance of the third communication terminal 31 to the third communication line 36 to high impedance. The third control unit 35 controls the communication operation of the third communication terminal 31, including the switching operation of the connected state / disconnected state by the third disconnection unit 34.

[0028] Next, we will explain how to calculate the communication loss of each communication line 6 in the communication system configured as described above. When calculating the communication loss of communication line 6, first, one transmitting terminal and one receiving terminal are selected from the three or more communication terminals 1 that the communication system has. For the communication terminal 1 that was not selected as either a transmitting or receiving terminal, the blocking unit 4 of that communication terminal 1 is set to a blocked state, i.e., high impedance. In this state, a measurement signal is transmitted from the reference signal transmitting unit 2 of the communication terminal 1 selected as the transmitting terminal. Then, the signal receiving and measuring unit 3 of the communication terminal 1 selected as the receiving terminal measures the voltage of the received measurement signal. This allows us to determine the total communication loss of the communication lines 6 along the communication path from the transmitting terminal to the receiving terminal.

[0029] Next, for at least one of the transmitting and receiving terminals, another communication terminal 1 is selected, and the transmission of the measurement signal and the measurement of the received voltage are performed in the same manner. By repeating the measurements while changing the combination of transmitting and receiving communication terminals 1 in this way, it is possible to collect the measurement values ​​necessary to calculate the communication loss of each communication line 6.

[0030] The number of measurements required will vary depending on the network topology of the communication system, the number of nodes (communication terminals 1 and communication nodes), and the number of communication lines 6 between nodes. If the combination of two communication terminals 1 is the same, it is sufficient to perform measurements by transmitting in one direction; there is no need to switch the roles of transmit and receive during the measurement.

[0031] An example of a method for calculating the communication loss of the first communication line 16, the second communication line 26, and the third communication line 36 in the configuration example shown in Figure 1 will be explained. First, the first communication terminal 11 is set as the transmitting terminal and the second communication terminal 21 as the receiving terminal. In this case, with the third communication terminal 31 set to high impedance by the third blocker 34, the first reference signal transmitting unit 12 transmits the first measurement signal. Then, the voltage of the first measurement signal received by the second signal receiving / measuring unit 23 is measured. In this state, the loss due to the first measurement signal flowing through the third communication line 36 is sufficiently small and can be ignored. Therefore, if the voltage of the first measurement signal output by the first reference signal transmitting unit 12 is V0, the received voltage of the first measurement signal measured by the second signal receiving / measuring unit 23 is V12, the communication loss of the first communication line 16 is L1, and the communication loss of the second communication line 26 is L2, then the following equation (1) holds.

[0032] V12 = (L1 + L2)V0 ... (1)

[0033] Next, the third communication terminal 31 is set as the transmitting terminal and the second communication terminal 21 as the receiving terminal. In this case, with the first communication terminal 11 set to high impedance by the first blocker 14, the third reference signal transmitting unit 32 transmits the third measurement signal. Then, the voltage of the received third measurement signal is measured by the second signal receiving / measuring unit 23. In this state, the loss due to the third measurement signal flowing through the first communication line 16 is sufficiently small and can be ignored. Therefore, if the voltage of the third measurement signal output by the third reference signal transmitting unit 32 is V0, the same as the first measurement signal, the received voltage of the third measurement signal measured by the second signal receiving / measuring unit 23 is V23, and the communication loss of the third communication line 36 is L3, then the following equation (2) holds.

[0034] V23 = (L2 + L3)V0 ... (2)

[0035] Finally, the third communication terminal 31 is set as the transmitting terminal and the first communication terminal 11 as the receiving terminal. In this case, with the second communication terminal 21 set to high impedance by the second blocker 24, the third reference signal transmitting unit 32 transmits the third measurement signal. Then, the voltage of the third measurement signal received by the first signal receiving / measuring unit 13 is measured. In this state, the loss due to the third measurement signal flowing through the second communication line 26 is sufficiently small and can be ignored. Therefore, if the received voltage of the third measurement signal measured by the first signal receiving / measuring unit 13 is V31, then the following equation (3) holds.

[0036] V31 = (L3 + L1)V0 ... (3)

[0037] Equations (1), (2), and (3), which were formulated in the manner described above, can be put into a system of three linear equations and solved for L1, L2, and L3 to obtain equations (4), (5), and (6). That is, the communication loss L1 of the first communication line 16, the communication loss L2 of the second communication line 26, and the communication loss L3 of the third communication line 36 can be determined.

[0038] L1=(V31+V12-V23) / 2V0 ··· (4) L2=(V12+V23-V31) / 2V0 ··· (5) L3=(V23+V31-V12) / 2V0 ··· (6)

[0039] With the communication system configured as described above, in a network where multiple communication terminals 1 (nodes) are physically connected to the same communication node 90, it is possible to collect information necessary to identify the communication loss in each communication line 6 between each node. In particular, when multiple communication terminals 1 are installed dispersed inside and outside a structure such as a building, and these multiple communication terminals are connected by communication lines, it is often very difficult to identify which communication line between nodes has the greatest communication loss when the communication quality is poor. With the communication system according to this embodiment, even in such cases, it is possible to easily collect information necessary to identify the communication loss in each communication line 6 between each node.

[0040] In the configuration example shown in Figure 1, all three communication terminals 1—the first communication terminal 11, the second communication terminal 21, and the third communication terminal 31—are equipped with a reference signal transmission unit 2, a signal receiving / measuring unit 3, and a blockage unit 4, respectively. However, as mentioned above, for the same combination of communication terminals 1, it is sufficient to perform measurement by transmitting in one direction, and it is not necessary to switch the roles of transmission and reception to perform measurement in both directions. Therefore, it is not necessary for all three communication terminals 1 to each have all the functions of a reference signal transmission unit 2, a signal receiving / measuring unit 3, and a blockage unit 4. Only one of the three communication terminals 1 needs to have all the functions of a reference signal transmission unit 2, a signal receiving / measuring unit 3, and a blockage unit 4; the others only need to have one communication terminal 1 equipped with a reference signal transmission unit 2 and a blockage unit 4, and another communication terminal 1 equipped with a signal receiving / measuring unit 3 and a blockage unit 4. However, by equipping each of the three communication terminals 1 with a reference signal transmission unit 2, a signal reception / measurement unit 3, and a blocking unit 4, there is the advantage that all communication terminals 1 can be treated functionally equivalent.

[0041] As shown in Figure 1, the communication system may further include a calculation unit 18. The calculation unit 18 is a communication loss calculation unit that calculates the communication loss of each communication line 6 based on the received voltage of the measurement signal measured as described above. For example, the calculation unit 18 performs the calculations of equations (4), (5), and (6) described above to calculate the communication loss L1 of the first communication line 16, the communication loss L2 of the second communication line 26, and the communication loss L3 of the third communication line 36, respectively, based on the measured received voltages V1, V2, and V3.

[0042] In the illustrated example, the first communication terminal 11 is designated as the main terminal among the three communication terminals 1, and a calculation unit 18 is provided in this main terminal, the first communication terminal 11. However, the location where the calculation unit 18 is provided is not limited to this. The calculation unit 18 may be provided in the other communication terminals 1, or in a server other than the communication terminals 1, for example, not shown in the illustration. By providing such a calculation unit 18 (communication loss calculation unit), the communication loss of each communication line 6 can be automatically calculated using the collected information.

[0043] In this example, the main terminal, the first communication terminal 11, is responsible for directing the communication loss measurement operations throughout the entire communication system. Specifically, the first communication terminal 11 selects the transmitting terminal and the receiving terminal according to a predetermined order, for example, and notifies each communication terminal 1. Each communication terminal 1 then performs actions such as switching to high impedance, transmitting a measurement signal, receiving a measurement signal, and measuring the received level, in accordance with this notification.

[0044] Next, with reference to the flowchart in Figure 3, an example of the operation of the communication system according to this embodiment during communication loss measurement will be described. Note that the measurements of communication losses L1+L2, L2+L3, and L3+L1 may be performed in any order.

[0045] First, in step S101, the first control unit 15 of the first communication terminal 11 notifies the second communication terminal 21 and the third communication terminal 31 that it has started measuring the communication loss L1+L2. In the following step S102, the third control unit 35 of the third communication terminal 31 blocks the communication path of the third communication terminal 31 by setting the contact of the third interruption unit 34 to the Z side, thereby making the third communication terminal 31 high impedance. Next, in step S103, the first reference signal transmission unit 12 transmits the first measurement signal. Then, in step S104, the first measurement signal is received by the second signal receiving and measurement unit 23, and its reception level (voltage) is measured. Once the measurement is complete, in step S105, the second control unit 25 of the second communication terminal 21 notifies the first communication terminal 11 of the measurement result V12 from step S104. In the following step S106, the third control unit 35 of the third communication terminal 31 restores the communication path of the third communication terminal 31 by setting the contact of the third interruption unit 34 to the TR side.

[0046] Next, the communication system performs the process in step S201. In step S201, the first control unit 15 of the first communication terminal 11 notifies the second communication terminal 21 and the third communication terminal 31 that the measurement of the communication loss L2+L3 has begun. In the following step S202, the first control unit 15 of the first communication terminal 11 blocks the communication path of the first communication terminal 11 by setting the contact of the first blocker 14 to the Z side, thereby making the first communication terminal 11 high impedance. Next, in step S203, the third reference signal transmission unit 32 transmits the third measurement signal. Then, in step S204, the third measurement signal is received by the second signal receiving and measurement unit 23, and its reception level (voltage) is measured. Once the measurement is complete, in step S205, the first control unit 15 of the first communication terminal 11 restores the communication path of the first communication terminal 11 by setting the contact of the first blocker 14 to the TR side. In the following step S206, the second control unit 25 of the second communication terminal 21 notifies the first communication terminal 11 of the measurement result V23 from step S204.

[0047] Next, the communication system performs the process in step S301. In step S301, the first control unit 15 of the first communication terminal 11 notifies the second communication terminal 21 and the third communication terminal 31 that the measurement of the communication loss L3+L1 has begun. In the following step S302, the second control unit 25 of the second communication terminal 21 blocks the communication path of the second communication terminal 21 by setting the contact of the second blocker 24 to the Z side, thereby making the second communication terminal 21 high impedance. Next, in step S303, the third reference signal transmission unit 32 transmits the third measurement signal. Then, in step S304, the third measurement signal is received by the first signal receiving and measurement unit 13, and its reception level (voltage) is measured. Once the measurement is complete, in step S305, the second control unit 25 of the second communication terminal 21 restores the communication path of the second communication terminal 21 by setting the contact of the second blocker 24 to the TR side.

[0048] Next, the communication system performs the process in step S401. In step S401, the first communication terminal 11 notifies the calculation unit 18 of the collected measurement results V12, V23, and V31. Then, in step S402, the calculation unit 18 solves the system of three linear equations consisting of equations (1), (2), and (3) for L1, L2, and L3, and obtains equations (4), (5), and (6) as solutions. That is, the calculation unit 18 calculates the communication loss L1 of the first communication line 16, the communication loss L2 of the second communication line 26, and the communication loss L3 of the third communication line 36, respectively, by performing calculations on equations (4), (5), and (6).

[0049] In the above, we have described an example of a communication system with a star topology consisting of three communication terminals 1. However, the number of communication terminals 1 that make up the communication system and the network topology are not limited to this. As mentioned above, the number of communication terminals 1 that make up the communication system can be three or more. For example, a star topology consisting of four communication terminals 1, as shown in Figure 4, is also acceptable. In this case, for example, by measuring at least the following communication losses, a system of simultaneous equations can be set up to calculate the communication loss in each communication line 6.

[0050] • The sum of the communication loss L1 of the first communication line 16 and the communication loss L2 of the second communication line 26. • The sum of the communication loss L1 of the first communication line 16 and the communication loss L3 of the third communication line 36. • The sum of the communication loss L1 of the first communication line 16 and the communication loss L4 of the fourth communication line 46. • The sum of the communication loss L2 of the second communication line 26 and the communication loss L3 of the third communication line 36.

[0051] Furthermore, for example, a topology combining a star and a bus configuration, consisting of four communication terminals 1, as shown in Figure 5, is also possible. That is, not only is it possible for the communication lines 6 connected to each communication terminal 1 to be directly connected to the same physical communication node, as in a star configuration, but the communication lines 6 connected to each communication terminal 1 may also be indirectly connected to the same physical communication node via other communication lines.

[0052] In the example shown in Figure 5, for example, by measuring at least the following communication losses, a system of simultaneous equations can be set up to calculate the communication loss in each communication line 6.

[0053] The sum of the communication loss L1 of the first communication line 16, the communication loss L5 of the fifth communication line 56, and the communication loss L2 of the second communication line 26. • The sum of the communication loss L1 of the first communication line 16 and the communication loss L3 of the third communication line 36. The sum of the communication loss L1 of the first communication line 16, the communication loss L5 of the fifth communication line 56, and the communication loss L4 of the fourth communication line 46. The sum of the communication loss L2 of the second communication line 26, the communication loss L5 of the fifth communication line 56, and the communication loss L3 of the third communication line 36. The sum of the communication loss L3 of the third communication line 36, the communication loss L5 of the fifth communication line 56, and the communication loss L4 of the fourth communication line 46.

[0054] Figure 6 shows an example of a configuration that realizes the functions of each communication terminal 1 in this embodiment. The functions of each communication terminal 1 are realized, for example, by a processing circuit. The processing circuit may include a processor 101 and a memory 102. The processing circuit may also include dedicated hardware 103. A part of the processing circuit may be formed as dedicated hardware 103, and this processing circuit may further include a processor 101 and a memory 102. In the example shown in the figure, a part of the processing circuit is formed as dedicated hardware 103. Also, in the example shown in the figure, the processing circuit further includes a processor 101 and a memory 102.

[0055] A processing circuit that is partly a dedicated hardware 103 includes, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. When the processing circuit includes at least one processor 101 and at least one memory 102, the functions of each communication terminal 1 are realized by software, firmware, or a combination of software and firmware.

[0056] The software and firmware are written as programs and stored in memory 102. The processor 101 reads and executes the programs stored in memory 102 to realize the functions of each part. The processor 101 is also called a CPU (Central Processing Unit), central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP. Examples of memory 102 include non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, and EEPROM, or magnetic disks, flexible disks, optical disks, compact disks, minidiscs, and DVDs.

[0057] In this way, the processing circuit of each communication terminal 1 can realize each function of each communication terminal 1 through hardware, software, firmware, or a combination thereof. If the processing circuit of each communication terminal 1 includes at least a processor 101 and memory 102, the processor 101 executes the program stored in the memory 102 of each communication terminal 1, and the hardware and software of each communication terminal 1 work together to realize the functions of each part of each communication terminal 1.

[0058] In this disclosure, the embodiments, configurations, and modifications may be combined arbitrarily without departing from the spirit of this disclosure. [Explanation of symbols]

[0059] 1. Communication terminal 2. Reference signal transmission unit 3. Signal Receiving and Measurement Section 4. Shut-off section 5. Control Unit 6. Communication lines 11. First communication terminal 12. First Reference Signal Transmitter 13. First signal receiving and measurement section 14. First Shut-off Section 15 First Control Unit 16. First communication line 18 Arithmetic section 21 Second communication terminal 22 Second Reference Signal Transmitter 23 Second signal receiving and measurement section 24 Second Blocking Section 25 Second Control Unit 26 Second communication line 31 Third communication terminal 32 Third Reference Signal Transmitter 33 Third signal receiving and measurement section 34 Third Shut-off Section 35 Third Control Unit 36 Third Communication Line 46 Fourth Communication Line 56. Fifth Communication Line 90 Communication Nodes 101 Processors 102 memory 103 Dedicated Hardware

Claims

1. A first terminal connected to one end of the first communication line, A second terminal connected to one end of the second communication line, It comprises a third terminal connected to one end of a third communication line, The other ends of the first communication line, the second communication line, and the third communication line are physically connected directly or indirectly to the same communication node. The first terminal is, A first transmitting unit that outputs a first measurement signal to the first communication line, First measurement unit and The device comprises a first impedance switching unit that switches the impedance of the first terminal to the first communication line to high impedance, The aforementioned second terminal is, The second measuring unit, The device comprises a second impedance switching unit that switches the impedance of the second terminal to the second communication line to high impedance, The third terminal is, A second transmitting unit that outputs a second measurement signal to the third communication line, The device comprises a third impedance switching unit that switches the impedance of the third terminal to the third communication line to high impedance, The first measuring unit measures the voltage of the second measuring signal received via the first communication line while the second impedance switching unit has switched the impedance of the second terminal to the second communication line to high impedance. The second measuring unit is, With the third impedance switching unit switching the impedance of the third terminal to the third communication line to high impedance, the voltage of the first measuring signal received via the second communication line is measured, and A communication system that measures the voltage of the second measuring signal received via the second communication line while the first impedance switching unit has switched the impedance of the first terminal to the first communication line to high impedance.

2. The other ends of the first communication line, the second communication line, and the third communication line are directly connected to the communication node. The communication system according to claim 1, further comprising a communication loss calculation unit that calculates the communication loss of the first communication line, the second communication line, and the third communication line, based on the received voltage of the second measurement signal measured by the first measurement unit and the received voltage of the first measurement signal and the received voltage of the second measurement signal measured by the second measurement unit.

3. The aforementioned communication loss calculation unit, The voltage of the first measurement signal output by the first transmitting unit and the voltage of the second measurement signal output by the second transmitting unit are defined as V0. The received voltage of the first measurement signal measured by the second measurement unit is defined as V12. The received voltage of the second measurement signal measured by the second measurement unit is defined as V23. The received voltage of the second measurement signal measured by the first measurement unit is defined as V31. Let L1 be the communication loss of the first communication line. Let L2 be the communication loss of the second communication line. Let L3 be the communication loss of the third communication line. The following system of three linear equations with three variables: V12=(L1+L2)V0 V23=(L2+L3)V0 V31=(L3+L1)V0 The communication system according to claim 2, which uses to calculate the communication losses L1, L2, and L3 of the first communication line, the second communication line, and the third communication line, respectively.

4. The communication system according to any one of claims 1 to 3, wherein the first impedance switching unit includes a cutoff unit that switches between a state in which the first transmitting unit and the first measuring unit are electrically connected to the first communication line and a state in which the first transmitting unit and the first measuring unit are electrically disconnected from the first communication line.

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