Communication system, master unit, slave unit, and communication method

Abstract

To allow a communication distance to be extended without degrading the quality of a power supply line and without increasing noise radiation.SOLUTION: A master unit 2 includes: a slave unit recognition section 261 that recognizes a slave unit 3; a reception strength acquisition section 262 that, if not all slave units 3 can be recognized, requests recognized slave units 3 to acquire information indicating its reception strength and acquires the information; a slave unit selection section 263 that selects a slave unit 3 to double as a repeater from the recognized slave units 3 based on acquisition results by the reception strength acquisition section 262; and a relay instruction section 264 that issues an instruction to the selected slave unit 3 to cause the slave unit 3 to operate also as a repeater. Each slave unit 3 includes: a reception strength notification section 373 that notifies the master unit 2 of information indicating its own reception strength when a request to acquire information indicating the reception strength is made; and a relay operation section 374 that performs relaying when an instruction to cause the slave unit to operate also as a repeater is made.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a communication system, a master unit, a slave unit, and a communication method. [Background technology]

[0002] In general, in management systems used in facilities such as factories, plants, and buildings, the EIA standard RS485, which is a daisy-chain type, is widely used as a communication network connecting devices such as industrial controllers and sensors.

[0003] In such a communication network, it is common to lay two types of lines: communication lines and power lines. However, due to the need for complex construction work, such as a large number of connection nodes and long cable wiring distances, and the need for reduced construction work and cost reduction (wiring costs, construction costs, etc.), it is expected that this problem can be solved by superimposing communication lines on power lines, thereby enabling multi-stage power superimposed communication, which allows communication signals to be sent and received simultaneously to multiple nodes using only the power lines (see, for example, Patent Document 1).

[0004] In multistage power supply superimposed communication using daisy chain wiring, communication signals are converted into transmission signals by mixing different carrier frequencies and then superimposed on the power supply lines. However, since the carrier frequency is generally higher than the original transmission signal, the converted superimposed communication signal also has a high frequency. In addition, since the power supply system lines that are not designed for communication are used, there is a large attenuation of the communication signal, which poses challenges when extending the distance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-288198 Summary of the Invention [Problem to be solved by the invention]

[0006] The following are some of the challenges in ensuring communication quality in multi-stage power supply superimposed communication using cascade connections.

[0007] Normally, when a cascade connection is used, the communication signal level is attenuated when multistage superimposed communication is performed, which limits the number of devices that can be connected and the distance between them.

[0008] In the relay type of prior art, an inductive filter that blocks communication signals must be inserted in the power line. Therefore, when a cascade is used in multiple stages, the impedance of the power supply increases, resulting in a trade-off between communication quality and power quality. For example, if the load of the downstream device changes, the power supply voltage can easily fluctuate significantly, and there are also limitations on the connection distance.

[0009] If the communication signal level is changed according to the amount of attenuation, the noise radiation level also increases accordingly, so it becomes necessary to prepare a shield and limit the level accordingly, which limits the communication distance.

[0010] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a communication system that makes it possible to extend the communication distance without degrading the quality of the power line and without increasing noise radiation. [Means for solving the problem]

[0011] The communication system according to the present disclosure includes a parent device and cascaded child devices that communicate with the parent device. The parent device includes a child device recognition unit that recognizes the connected child devices, a reception strength acquisition unit that, when the child device recognition unit is unable to recognize all of the connected child devices, requests the child device recognized by the child device recognition unit to acquire information indicating the reception strength of the child device, thereby acquiring the information, a child device selection unit that selects a child device to be used as a repeater from among the child devices recognized by the child device recognition unit based on the acquisition result by the reception strength acquisition unit, and a relay instruction unit that issues an instruction to the child device selected by the child device selection unit to operate the child device as a repeater, and the child device includes a reception strength notification unit that, when the parent device requests the parent device to acquire information indicating the reception strength, notifies the parent device of information indicating its own reception strength, and a relay operation unit that performs relaying when the parent device issues an instruction to operate the child device as a repeater. [Effects of the Invention]

[0012] According to the present disclosure, the above-described configuration makes it possible to extend the communication distance without degrading the quality of the power line and without increasing noise radiation. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating an example of the configuration of a communication system according to a first embodiment. [Figure 2] 2 is a diagram illustrating an example of the configuration of a parent device according to the first embodiment. FIG. [Figure 3] 3 is a diagram illustrating an example of the configuration of a processing unit included in a parent device according to the first embodiment. FIG. [Figure 4] 2 is a diagram illustrating an example of the configuration of a slave device according to the first embodiment. FIG. [Figure 5] 3 is a diagram illustrating an example of the configuration of a processing unit included in the slave device according to the first embodiment. FIG. [Figure 6] 5 is a flowchart showing an example of the operation of the parent device according to the first embodiment. [Figure 7] 5 is a flowchart showing an example of the operation of the slave device according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1 FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to the first embodiment. 1, the communication system includes a power source 1, a parent device 2, and a plurality of child devices 3. This communication system is a multistage power supply superimposed communication system in which a plurality of child devices 3 are cascade-connected to the parent device 2. The example of FIG. 1 shows a case in which two child devices 3 (child device 3-1 and child device 3-2) are provided as the plurality of child devices 3.

[0015] Each slave unit 3 is assigned a unique address. In addition, no filters that block communication signals are installed on the power supply line, maintaining a line that does not impair power supply impedance (power supply quality).

[0016] The power supply 1 supplies power to the parent device 2 and the child device 3 .

[0017] The base unit 2 communicates with the handset 3 . An example of the configuration of this base unit 2 will be described later.

[0018] The slave unit 3 communicates with the master unit 2 . An example of the configuration of this slave unit 3 will be described later.

[0019] Next, an example of the configuration of the base unit 2 according to the first embodiment will be described with reference to FIG. As shown in FIG. 2, the base unit 2 includes a power signal separator 21, an amplifier 22, a demodulator 23, a modulator 24, a modulation frequency signal generator 25, an arithmetic processor 26, and a power supply circuit 27.

[0020] The power supply signal separator 21 separates the input signal from the power supply line into a power supply signal and a communication signal (superimposed signal). The power obtained by this power signal separator 21 is input to a power supply circuit 27 and used to drive the device itself.

[0021] The amplifier 22 amplifies the communication signal obtained by the power supply signal separator 21 .

[0022] The demodulation unit 23 performs demodulation processing on the communication signal amplified by the amplification unit 22 to obtain a received signal.

[0023] The modulation frequency signal generating section 25 generates a modulation frequency signal.

[0024] The modulation unit 24 superimposes the modulation frequency signal generated by the modulation frequency signal generation unit 25 on the transmission signal generated by the calculation processing unit 26, thereby obtaining a communication signal (superimposed signal). The communication signal obtained by the modulation unit 24 is sent to the destination node (master unit 2 or slave unit 3) via the power line.

[0025] The calculation processing unit 26 receives the received signal obtained by the demodulation unit 23, performs various processes on it, and also generates a transmission signal.

[0026] The arithmetic processing unit 26 is realized by a processing circuit such as a system LSI (Large Scale Integration), or a CPU (Central Processing Unit) that executes a program stored in a memory or the like.

[0027] The calculation processing unit 26 includes a slave unit recognition unit 261, a reception strength acquisition unit 262, a slave unit selection unit 263, and a relay instruction unit 264, as shown in FIG.

[0028] The handset recognition unit 261 recognizes the connected handset 3 . That is, the handset recognition unit 261 generates a normal transmission signal to all connected handset units 3 and receives a reply to the transmission signal from the handset unit 3, thereby recognizing the handset unit 3. The recognition process of the handset 3 by the handset recognition unit 261 is carried out within a specific time period.

[0029] In addition, when the handset recognition unit 261 performs the recognition process for the handset 3 from the second time onwards, it does not perform the recognition process for the handset 3 that has already been recognized among all the connected handset units 3, but performs the recognition process only for the handset 3 that has not yet been recognized among all the connected handset units 3.

[0030] Then, when the base unit 2 has been able to recognize all of the connected handset units 3 by the handset unit recognition unit 261, the base unit 2 performs normal communication with the handset units 3 in question. That is, the base unit 2 sends a transmission signal to the handset 3 recognized by the handset recognition unit 261, to which information indicating an instruction to switch the operation mode to the normal communication mode has been added.

[0031] Furthermore, even if the handset recognition unit 261 is unable to recognize all of the connected handset units 3 after a certain period of time has elapsed, the parent unit 2 sends a transmission signal to each of the handset units 3 recognized by the handset recognition unit 261, with information attached indicating an instruction to transition the operating mode to the normal communication mode.

[0032] When the handset recognition unit 261 is unable to recognize all of the connected handset units 3, the reception strength acquisition unit 262 acquires the information by making a request to acquire information indicating the reception strength from the handset unit 3 recognized by the handset recognition unit 261. That is, the reception strength acquisition unit 262 acquires information indicating the reception strength from the handset 3 recognized by the handset recognition unit 261 by sending a transmission signal to the handset 3, to which information indicating a request to acquire information indicating the reception strength (an instruction to transition the operating mode to the relay selection mode) is attached.

[0033] In addition, for handset 3 recognized by handset recognition unit 261 and for which information indicating reception strength has already been acquired, reception strength acquisition unit 262 does not need to acquire information indicating reception strength again.

[0034] Based on the results acquired by the reception strength acquisition unit 262, the slave unit selection unit 263 selects a slave unit 3 to be used as a repeater from among the slave units 3 recognized by the slave unit recognition unit 261 (i.e., slave units 3 that have transitioned their operating mode to the relay selection mode). At this time, the slave unit selection unit 263 selects the slave unit 3 with the lowest reception strength indicated by the information acquired by the reception strength acquisition unit 262 (usually the first or second lowest slave unit 3) from among the slave units 3 recognized by the slave unit recognition unit 261 as the slave unit 3 to be used also as a repeater.

[0035] The relay instruction unit 264 notifies the slave 3 selected by the slave selection unit 263 of an instruction to operate the slave 3 also as a relay, together with information indicating at least one of a node that does not relay or a node that relays. The node is the master 2 or the slave 3. That is, the relay instruction unit 264 sends a transmission signal to the slave unit 3 selected by the slave unit selection unit 263, which includes information indicating an instruction to operate the slave unit 3 also as a relay unit (an instruction to switch the operating mode to a relay combined mode), and information indicating at least one of a node that does not relay or a node that relays.

[0036] Next, an example of the configuration of the slave unit 3 according to the first embodiment will be described with reference to FIG. As shown in FIG. 4, the slave unit 3 includes a power signal separator 31, an amplifier 32, a demodulator 33, a reception intensity detector 34, a modulator 35, a modulation frequency signal generator 36, an arithmetic processor 37, and a power supply circuit 38.

[0037] The power supply signal separator 31 separates the input signal from the power supply line into a power supply signal and a communication signal (superimposed signal). The power obtained by this power signal separator 31 is input to a power supply circuit 38 and used to drive the device itself.

[0038] The amplifier 32 amplifies the communication signal obtained by the power supply signal separator 31 .

[0039] The demodulation unit 33 performs demodulation processing on the communication signal amplified by the amplification unit 32 to obtain a received signal.

[0040] The reception intensity detection unit 34 detects information indicating the reception intensity (reception intensity information) based on the communication signal obtained by the power supply signal separation unit 31. Alternatively, the reception strength detection unit 34 detects information indicating the reception strength (reception strength information) based on the communication signal after amplification by the amplifier unit 32, or the communication signal input to the amplifier unit 32 before amplification by the amplifier unit 32 and after noise removal. The detection of information indicating the reception strength by the reception strength detector 34 is carried out at least when the operation mode is shifted to the relay selection mode by the operation mode setting unit 372, which will be described later.

[0041] The modulation frequency signal generating section 36 generates a modulation frequency signal.

[0042] The modulation unit 35 superimposes the modulation frequency signal generated by the modulation frequency signal generation unit 36 ​​on the transmission signal generated by the calculation processing unit 37, thereby obtaining a communication signal (superimposed signal). The communication signal obtained by this modulation unit 35 is sent to the destination node (master unit 2 or slave unit 3) via the power line.

[0043] The arithmetic processing unit 37 receives the received signal obtained by the demodulation unit 33, performs various processes on it, and also generates a transmission signal. Furthermore, the arithmetic processing unit 37 also generates a transmission signal for notifying the base unit 2 of the information detected by the reception intensity detection unit .

[0044] The arithmetic processing unit 37 is realized by a processing circuit such as a system LSI, or a CPU that executes a program stored in a memory or the like.

[0045] The arithmetic processing unit 37 includes an instruction receiving unit 371, an operation mode setting unit 372, a reception strength notifying unit 373, and a relay operation unit 374, as shown in FIG.

[0046] The instruction receiving unit 371 receives an instruction from the base unit 2 based on the received signal obtained by the demodulation unit 33.

[0047] The operation mode setting unit 372 sets the operation mode of the device itself, which may be a normal communication mode, a relay selection mode, or a relay shared mode. Here, when the instruction receiving unit 371 receives an instruction to switch the operation mode to the normal communication mode, the operation mode setting unit 372 switches the operation mode to the normal communication mode. Furthermore, when an instruction to switch the operation mode to the relay selection mode is accepted by the instruction accepting unit 371, the operation mode setting unit 372 switches the operation mode to the relay selection mode. Furthermore, when the instruction receiving unit 371 receives an instruction to switch the operation mode to the repeater shared mode, the operation mode setting unit 372 switches the operation mode to the repeater shared mode.

[0048] When the operation mode is set to the relay selection mode by the operation mode setting unit 372 (when the parent unit 2 requests the acquisition of information indicating the reception strength), the reception strength notification unit 373 notifies the parent unit 2 of information indicating the reception strength detected by the reception strength detection unit 34. That is, the reception strength notifying unit 373 sends to the base unit 2 a transmission signal to which information indicating the reception strength has been added.

[0049] When the operation mode setting unit 372 sets the operation mode to the relay combined mode (when the parent device 2 issues an instruction to operate the device also as a relay), the relay operation unit 374 operates the device also as a relay. At this time, the relay operation unit 374 relays for nodes excluding nodes that do not relay, based on the information notified from the parent device 2.

[0050] In the normal communication mode, the base unit 2 and the slave unit 3 transmit and receive signals as usual. That is, the base unit 2 transmits a transmission signal including a destination address, and the slave unit 3 replies to the transmission signal if the destination address included in the transmission signal is its own address. In addition, if the destination address included in the transmission signal is not its own address, the slave unit 3 ignores the transmission signal.

[0051] In the relay selection mode, the base unit 2 requests each of the slave units 3 that it has recognized and that are connected via the daisy chain to communicate the strength level of the received signal to the base unit 2. The slave unit 3 then responds to the instruction from the base unit 2 by communicating the strength level of its own received signal to the base unit 2. The base unit 2 then analyzes the strength level of the received signal from each slave unit 3 and selects a slave unit 3 that can also serve as a relay. The base unit 2 then issues an instruction to the selected slave unit 3 to transition to the repeater-combined mode, along with information indicating at least one of nodes that will not relay or nodes that will relay.

[0052] In the repeater mode, the slave device 3 transitions to this mode at the instruction of the master device 2. In the repeater mode, the slave device 3 responds to an inquiry from the master device 2 specifying its own address in the same way as in the normal communication mode, and relays the signal of the node to be relayed (the master device 2 or another slave device 3).

[0053] Next, an example of the operation of the base unit 2 according to the first embodiment shown in FIGS. 1 to 3 will be described with reference to FIG. In the operation example of the base unit 2 according to the first embodiment shown in Figs. 1 to 3, first, as shown in Fig. 6, for example, the handset recognition unit 261 recognizes the connected handset 3 (step ST101). That is, the handset recognition unit 261 generates a normal transmission signal for all the connected handset 3 and receives a reply to the transmission signal from the handset 3, thereby recognizing the handset 3. This recognition process of the handset 3 by the handset recognition unit 261 is performed within a specific time period.

[0054] Next, the slave unit recognition section 261 determines whether or not all of the connected slave units 3 have been recognized (step ST102).

[0055] In step ST102, if the handset recognition unit 261 determines that it has recognized all of the connected handset units 3, the base unit 2 performs normal communication with the handset units 3 (step ST103). That is, the base unit 2 sends a transmission signal to the handset units 3 recognized by the handset recognition unit 261, to which information indicating an instruction to switch the operation mode to the normal communication mode has been added.

[0056] On the other hand, if the handset recognition unit 261 determines in step ST102 that it has not been able to recognize all of the connected handset units 3, the reception strength acquisition unit 262 acquires the information by making an acquisition request for information indicating reception strength to the handset unit 3 recognized by the handset recognition unit 261 (steps ST104 and ST105). That is, the reception strength acquisition unit 262 acquires the information indicating reception strength from the handset unit 3 recognized by the handset recognition unit 261 by sending a transmission signal to which information indicating an acquisition request for information indicating reception strength (an instruction to shift the operation mode to the relay selection mode) is added.

[0057] In addition, for handset 3 recognized by handset recognition unit 261 and for which information indicating reception strength has already been acquired, reception strength acquisition unit 262 does not need to acquire information indicating reception strength again.

[0058] Next, the reception strength acquisition unit 262 determines whether or not information indicating the reception strength has been acquired for all the slave units 3 recognized by the slave unit recognition unit 261 (step ST106). In step ST106, if the reception strength acquisition unit 262 determines that it has not been able to acquire information indicating the reception strength for all the slave units 3 recognized by the slave unit recognition unit 261, the sequence returns to step ST105.

[0059] On the other hand, if the reception strength acquisition unit 262 determines in step ST106 that it has acquired information indicating the reception strength for all of the handset units 3 recognized by the handset unit recognition unit 261, the handset unit selection unit 263 selects a handset unit 3 to be used as a repeater from among the handset units 3 recognized by the handset unit recognition unit 261 (handset units 3 that have transitioned their operating mode to relay selection mode) based on the acquisition results by the reception strength acquisition unit 262 (step ST107). At this time, the slave unit selection unit 263 selects the slave unit 3 with the lowest reception strength indicated by the information acquired by the reception strength acquisition unit 262 (usually the first or second lowest slave unit 3) from among the slave units 3 recognized by the slave unit recognition unit 261 as the slave unit 3 to be used also as a repeater.

[0060] Next, the relay instruction unit 264 notifies the slave unit 3 selected by the slave unit selection unit 263 of an instruction to make the slave unit 3 also operate as a relay unit, together with information indicating at least one of a node that does not relay or a node that relays (step ST108). That is, the relay instruction unit 264 sends a transmission signal to the slave unit 3 selected by the slave unit selection unit 263, in which information indicating at least one of a node that does not relay or a node that relays is added to information indicating an instruction to make the slave unit 3 also operate as a relay unit (an instruction to shift the operation mode to a relay combined mode).

[0061] Next, the handset recognition unit 261 recognizes the connected handset 3 (step ST109). Note that in the second and subsequent handset 3 recognition processes by the handset recognition unit 261, the recognition process is not performed on the recognized handset 3 among all the connected handset 3, but only on the unrecognized handset 3 among all the connected handset 3.

[0062] Next, the slave unit recognition section 261 determines whether or not all of the connected slave units 3 have been recognized (step ST110).

[0063] In step ST110, if the handset recognition section 261 determines that all the connected handset units 3 have been recognized, the sequence proceeds to step ST103.

[0064] On the other hand, if the handset recognition section 261 determines in step ST110 that it has not been able to recognize all of the connected handset units 3, the sequence returns to step ST104.

[0065] In addition, even if the handset recognition unit 261 is unable to recognize all of the connected handset units 3 after a certain period of time has elapsed, the parent unit 2 sends a transmission signal to each of the handset units 3 recognized by the handset recognition unit 261, with information attached indicating an instruction to transition the operating mode to the normal communication mode.

[0066] Next, an example of the operation of the slave unit 3 according to the first embodiment shown in FIGS. 1, 4 and 5 will be described with reference to FIG. In an example of operation of the slave unit 3 according to embodiment 1 shown in Figures 1, 4 and 5, as shown in Figure 7, for example, the instruction receiving unit 371 first receives an instruction from the master unit 2 based on the received signal obtained by the demodulation unit 33 (steps ST201, ST202).

[0067] Next, the instruction receiving unit 371 determines whether the received instruction is an instruction to transition to relay selection mode (step ST203). In step ST203, if it is determined that the instruction received by the instruction receiving section 371 is an instruction to transition to the relay selection mode, the operation mode setting section 372 transitions the operation mode to the relay selection mode (step ST204).

[0068] Next, the reception strength notifying unit 373 notifies the base unit 2 of information indicating the reception strength detected by the reception strength detecting unit 34 (step ST205). That is, the reception strength notifying unit 373 sends the base unit 2 a transmission signal to which the information indicating the reception strength has been added.

[0069] On the other hand, if the instruction receiving unit 371 determines in step ST203 that the received instruction is not an instruction to transition to relay selection mode, it determines whether the received instruction is an instruction to transition to relay shared mode (step ST206). In step ST206, if it is determined that the instruction received by the instruction receiving section 371 is an instruction to switch to the repeater combined mode, the operation mode setting section 372 switches the operation mode to the repeater combined mode (step ST207).

[0070] Next, relay operation section 374 determines nodes that do not perform relay based on the information notified from base unit 2 (step ST208). Next, relay operation unit 374 operates its own device as a relay device (step ST209). At this time, relay operation unit 374 performs relay for nodes excluding nodes that do not relay, based on the information notified from parent device 2.

[0071] On the other hand, if the instruction receiving unit 371 determines in step ST206 that the received instruction is not an instruction to switch to the repeater shared mode, the operation mode setting unit 372 sets the operation mode to the normal communication mode (step ST210).

[0072] As described above, in the communication system according to the first embodiment, in a normal state, the base unit 2 transmits a signal to a specific handset 3, and the specific handset 3 replies to this transmission, as in the conventional case. On the other hand, there are cases where the communication signal does not reach the slave device 3 due to signal attenuation caused by long distances, etc. Therefore, in the communication system according to the first embodiment, a slave device 3 that can also function as a repeater is selected from among the slave devices 3 whose connection has been confirmed. That is, in the communication system according to the first embodiment, the base station 2 first waits for a reply for a certain period of time (including retries), and if communication is not possible, it switches to a relay selection mode and queries the slave stations 3 for which connection has been confirmed about their received signal levels. Note that this query is not sent to slave stations 3 for which the received signal levels are already known. Then, each slave station 3 for which connection has been confirmed switches to a received signal level measurement mode and transmits received signal level information to the base station 2. The base station 2 then compares the received signal levels of each slave station 3 and selects a slave station 3 with a low received signal level as a slave station 3 that will also function as a repeater. The base station 2 also sends information indicating at least one of a node to be relayed or a node that is not to be relayed to the selected slave station 3. That is, relaying is not performed for slave stations 3 for which connection has already been confirmed. The selected slave station 3 then also functions as a repeater. This enables long-distance communication in the communication system according to the first embodiment.

[0073] The reason why the slave unit selection unit 263 selects the slave unit 3 with the weakest reception strength (usually the first or second weakest slave unit 3) as the slave unit 3 to be used as a repeater is that in a transition wiring, the slave unit 3 with the weakest reception strength is the slave unit 3 at the end that can send and receive signals. In other words, there is a slave unit 3 that cannot send and receive signals (a slave unit 3 that the parent unit 2 cannot recognize) ahead of this slave unit 3, and it makes sense to operate the slave unit 3 at the end as a repeater.

[0074] In the communication system according to the first embodiment, after selecting a slave unit 3 to also function as a repeater, the relay selection process is repeated for slave units 3 further ahead of the repeater. In this case, the master unit 2 does not perform the process for slave units 3 whose connection has already been confirmed.

[0075] In addition, in parent device 2 shown in FIG. 2, a rectifier circuit such as a bridge diode may be connected to the input stage of power supply circuit 27 (between power supply signal separator 21 and power supply circuit 27). Similarly, in the slave unit 3 shown in FIG. 4, a rectifier circuit such as a bridge diode may be connected to the input stage of the power supply circuit 38 (between the power supply signal separator 31 and the power supply circuit 38). In this way, by incorporating a rectifier circuit such as a bridge diode into the power supply circuit of each node in the power supply line on which the communication signal is superimposed, it is possible to configure a non-polar, multi-stage superimposed communication circuit even in a DC power supply system. This makes it possible to achieve reduced installation work in the communication system according to the first embodiment.

[0076] As described above, according to the first embodiment, the communication system includes the base unit 2 and the cascade-connected handset 3 that communicates with the base unit 2. The base unit 2 includes a handset recognition unit 261 that recognizes the connected handset 3, a reception strength acquisition unit 262 that, when the handset recognition unit 261 is unable to recognize all of the connected handset 3, requests the handset 3 recognized by the handset recognition unit 261 to acquire information indicating reception strength, thereby acquiring the information, and a handset recognition unit 263 that performs handset recognition based on the acquisition result obtained by the reception strength acquisition unit 262. The handset 3 is provided with a handset selection unit 263 that selects a handset 3 to be used as a repeater from among the handset 3 recognized by the unit 261, and a relay instruction unit 264 that notifies the handset 3 selected by the handset selection unit 263 of an instruction to operate the handset 3 also as a repeater, and the handset 3 is provided with a reception strength notification unit 373 that notifies the base unit 2 of information indicating its own reception strength when the base unit 2 requests acquisition of information indicating reception strength, and a relay operation unit 374 that performs relaying when the base unit 2 issues an instruction to operate the handset 3 also as a repeater. Furthermore, according to this embodiment 1, the slave unit selection unit 263 selects, from among the slave units 3 recognized by the slave unit recognition unit 261, the slave unit 3 having the lowest reception strength indicated by the information acquired by the reception strength acquisition unit 262 as the slave unit 3 to be used also as a repeater. As a result, in the communication system according to the first embodiment, it is possible to extend the communication distance without degrading the quality of the power line and without increasing noise radiation.

[0077] Furthermore, according to the first embodiment, at least one of the parent device 2 and the child device 3 has a rectifier circuit connected to the input stage of the power supply circuit. As a result, in the communication system according to the first embodiment, it is possible to realize construction savings due to the polarity-less power supply.

[0078] Furthermore, according to this embodiment 1, the communication method is a communication method by a communication system including a base unit 2 and cascade-connected handset units 3 that communicate with the base unit 2, and the base unit 2 includes a step in which the handset recognition unit 261 recognizes the connected handset units 3, a step in which the reception strength acquisition unit 262, when the handset recognition unit 261 has not been able to recognize all of the connected handset units 3, acquires the information by making an acquisition request for information indicating reception strength to the handset unit 3 recognized by the handset recognition unit 261, and a step in which the handset selection unit 263 selects the handset unit 3 based on the result acquired by the reception strength acquisition unit 262. and a step in which a relay instruction unit 264 notifies the handset 3 selected by the handset selection unit 263 of an instruction to operate the handset 3 also as a repeater, and the handset 3 has a step in which, when a request for obtaining information indicating the reception strength is made by the base unit 2, a reception strength notification unit 373 notifies the base unit 2 of information indicating the reception strength at the handset 3, and a step in which a relay operation unit 374 performs relaying when an instruction to operate the handset 3 also as a repeater is made by the base unit 2. As a result, in the communication method according to the first embodiment, it is possible to extend the communication distance without degrading the quality of the power line and without increasing noise radiation.

[0079] Any of the components of the embodiments may be modified or omitted. [Explanation of symbols]

[0080] 1 power supply 2 Base unit 3 Handsets 21 Power signal separation section 22 Amplification section 23 Demodulation section 24 Modulation section 25 Modulation frequency signal generator 26 Processing unit 27 Power supply circuit 31 Power signal separation section 32 Amplification section 33 Demodulation section 34 Reception strength detection unit 35 Modulation section 36 Modulation frequency signal generator 37 Processing unit 38 Power circuit 261 Handset Recognition Unit 262 Reception strength acquisition unit 263 Child Unit Selection Unit 264 Relay Instruction Section 371 Instruction Reception Department 372 Operation mode setting section 373 Reception strength notification unit 374 Relay operation unit

Claims

1. The system includes a master unit and a slave unit that is cascade-connected to the master unit and communicates with the master unit, The parent device is a slave unit recognition unit that recognizes a connected slave unit; a reception strength acquisition unit that, when the slave unit recognition unit is unable to recognize all of the connected slave units, requests the slave unit recognized by the slave unit recognition unit to acquire information indicating reception strength, thereby acquiring the information; a handset selection unit that selects a handset to double as a repeater from among the handset devices recognized by the handset recognition unit based on the reception strength acquisition result; a relay instruction unit that notifies the slave unit selected by the slave unit selection unit of an instruction to cause the slave unit to also operate as a relay unit; The slave unit is a reception strength notifying unit that notifies the master unit of information indicating the reception strength of the master unit when the master unit requests acquisition of information indicating the reception strength; a relay operation unit that performs relay when an instruction to operate as a relay unit is given by the parent device; A communication system comprising:

2. The slave unit selection unit selects, from among the slave units recognized by the slave unit recognition unit, a slave unit having a low reception strength indicated by the information acquired by the reception strength acquisition unit as a slave unit to be used also as a repeater.

2. The communication system according to claim 1.

3. At least one of the parent device and the child device has a power supply circuit in which a rectifier circuit is connected to an input stage.

2. The communication system according to claim 1.

4. a slave unit recognition unit that recognizes the slave unit; a reception strength acquisition unit that, when the slave unit recognition unit is unable to recognize all of the connected slave units, requests the slave unit recognized by the slave unit recognition unit to acquire information indicating reception strength, thereby acquiring the information; a handset selection unit that selects a handset to double as a repeater from among the handset devices recognized by the handset recognition unit based on the reception strength acquisition result; a relay instruction unit that notifies the slave unit selected by the slave unit selection unit of an instruction to operate the slave unit as a relay unit; A parent unit equipped with

5. a reception strength notifying unit that notifies the master unit of information indicating the reception strength of the master unit when the master unit requests the master unit to obtain information indicating the reception strength; a relay operation unit that performs relay when an instruction to operate as a relay unit is given by the parent device; A sub-unit equipped with

6. A communication method for a communication system including a master unit and cascade-connected slave units that communicate with the master unit, comprising: The parent device is a step in which a slave unit recognition unit recognizes a connected slave unit; a reception strength acquisition unit, when the slave unit recognition unit is unable to recognize all of the connected slave units, acquiring the information by making a request for information indicating reception strength to the slave unit recognized by the slave unit recognition unit; a step in which a slave unit selection unit selects a slave unit to be made to double as a repeater from among the slave units recognized by the slave unit recognition unit based on the result of acquisition by the reception strength acquisition unit; a step of a relay instruction unit notifying the slave unit selected by the slave unit selection unit of an instruction to operate the slave unit also as a relay unit; The slave unit is a reception strength notifying unit notifying the master unit of information indicating the reception strength of the master unit when the master unit requests the master unit to obtain information indicating the reception strength; a step in which the relay operation unit performs relay when an instruction to operate as a relay unit is given by the parent device; A communication method comprising:

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