Wireless communication systems and wireless communication methods

Abstract

To effectively suppress the occurrence of insufficiency in the number of communication channels even if communication channels with communication quality reduced are removed from a plurality of communication channels to be used for wireless communication.SOLUTION: A master device 20 detects characteristic data indicating quality of communication for a signal received from a slave device 30. The master device 20 removes communication channels determined as not satisfying predetermined quality of communication from a plurality of communication channels to be used for wireless communication, based on the detected characteristic data. The master device 20 determines if the number of the plurality of communication channels to be used for wireless communication becomes less than the minimum limit value due to the communication channel removal. If it is determined that the number is less than the minimum limit value, the master device 20 changes the plurality of communication channels to be used for wireless communication to communication channels satisfying relaxed quality of communication which is relaxed from the predetermined quality of communication.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a wireless communication system and a wireless communication method for performing wireless communication between a master device and a slave device via one communication channel sequentially selected from a plurality of communication channels.

Background Art

[0002] As this type of wireless communication system, for example, the one described in Patent Document 1 is known. In the wireless communication system of Patent Document 1, when a packet error occurs, if the RSSI value of the wireless signal of this packet is greater than a preset threshold Th1, it is determined that the reception operation of receiving this packet is a reception error due to interference with other radio waves. Then, the number of receptions and the number of reception errors are counted, and the frequency of reception errors due to interference in each frequency channel (number of reception errors / number of receptions) is stored. When the reception error frequency exceeds the threshold Th2, it is determined that there is an interference source in the frequency channel where the reception error frequency due to interference exceeds the threshold Th2, and this frequency channel is stored as an unusable channel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, the wireless communication system of Patent Document 1 sets a frequency channel with deteriorated communication quality due to interference with other radio waves as an unusable channel. Further, in the wireless communication system of Patent Document 1, when the set period elapses, the frequency channel set as the unusable channel returns to a usable frequency channel.

[0005] However, if the communication environment between the master and slave devices that make up a wireless communication system is poor, for example, the number of available frequency channels (communication channels) may be drastically reduced. In this case, channel hopping between multiple communication channels may not be fully utilized, and the ability to avoid interference with external noise may be impaired.

[0006] In the wireless communication system described in Patent Document 1, communication channels that have been designated as unavailable are restored to usable channels after a set period has elapsed. However, if the set period is long, it becomes difficult to resolve the shortage of communication channels. On the other hand, if the set period is short, there is a higher possibility of performing wireless communication using communication channels with degraded communication quality, which may lead to frequent communication errors. Thus, simply restoring unavailable communication channels to usable channels after a set period has elapsed is insufficient to effectively prevent the occurrence of a shortage of communication channels.

[0007] This disclosure has been made in view of the above-mentioned points, and aims to provide a wireless communication system and wireless communication method that can effectively suppress the occurrence of a shortage in the number of communication channels even when a communication channel with degraded communication quality is removed from multiple communication channels used for wireless communication. [Means for solving the problem]

[0008] To achieve the above objective, the wireless communication system according to this disclosure is a wireless communication system that performs wireless communication between a master device (20) and a slave device (30) via one communication channel that is sequentially selected from a plurality of communication channels, A detection unit (S60) detects characteristic data indicating the communication quality of the wireless communication performed for each communication channel, Based on the characteristic data detected by the detection unit, the deletion unit (S70) deletes communication channels that are determined not to meet predetermined communication quality standards from among multiple communication channels used for wireless communication. A determination unit (S440, S530) determines whether the number of communication channels used for wireless communication falls below a minimum limit due to the deletion of communication channels by the deletion unit, The system includes a determination unit that determines that the number of communication channels used for wireless communication falls below a minimum limit, and a modification unit (S460-S490, S550-S570) that changes the communication channels used for wireless communication to multiple communication channels that meet relaxed communication quality standards, which are more relaxed than predetermined communication quality standards. 、 The deletion unit pre-generates a first group of communication channels consisting of multiple communication channels remaining after deleting communication channels that do not meet predetermined communication quality standards, and a second group of communication channels consisting of multiple communication channels remaining after deleting communication channels that do not meet relaxed communication quality standards. If the determination unit determines that the number of communication channels included in the first communication channel group has fallen below the minimum limit, the modification unit changes the communication channels used for wireless communication from the communication channels included in the first communication channel group to the communication channels included in the second communication channel group. It is configured in this way.

[0009] Furthermore, the wireless communication method according to this disclosure is a wireless communication method that performs wireless communication between a master device (20) and a slave device (30) via one communication channel that is sequentially selected from a plurality of communication channels, A detection step (S60) for each communication channel, which detects characteristic data indicating the communication quality of the wireless communication performed, Based on the characteristic data detected in the detection step, a deletion step (S70) is performed to remove communication channels that are determined not to meet predetermined communication quality standards from the multiple communication channels used for wireless communication. The deletion step involves determining whether the number of communication channels used for wireless communication falls below a minimum limit by deleting communication channels in the deletion step (S440, S530), If the determination step determines that the number of communication channels used for wireless communication falls below a minimum limit, the system includes a modification step (S460-S490, S550-S570) in which the communication channels used for wireless communication are changed to multiple communication channels that meet relaxed communication quality standards, which are more relaxed than predetermined communication quality standards. 、 In the deletion step, a first group of communication channels consisting of multiple communication channels remaining after deleting communication channels that do not meet predetermined communication quality standards, and a second group of communication channels consisting of multiple communication channels remaining after deleting communication channels that do not meet relaxed communication quality standards are pre-generated. If the determination step determines that the number of communication channels included in the first communication channel group falls below the minimum limit, the change step changes the communication channels used for wireless communication from the communication channels included in the first communication channel group to the communication channels included in the second communication channel group. It is configured in this way.

[0010] As described above, in the wireless communication system and wireless communication method of this disclosure, if the number of communication channels used for wireless communication falls below a minimum limit due to the deletion of communication channels that do not meet a predetermined communication quality standard, the number of communication channels used for wireless communication is changed to include communication channels that meet a relaxed communication quality standard that is more relaxed than the predetermined communication quality standard. Since the relaxed communication quality standard is more relaxed than the predetermined communication quality standard, the number of communication channels that meet the relaxed communication quality standard increases compared to the number of communication channels that meet the predetermined communication quality standard. This makes it easier to secure a number of communication channels greater than or equal to the minimum limit as multiple communication channels used for wireless communication. Furthermore, since the increased number of communication channels at least meet the relaxed communication quality standard, the risk of communication errors occurring can also be reduced.

[0011] The reference numbers in parentheses above are merely examples of correspondences with specific configurations in embodiments described later, in order to facilitate understanding of this disclosure, and are not intended to limit the scope of this disclosure in any way.

[0012] Furthermore, technical features described in each claim of the patent claims, other than those described above, will become clear from the description of the embodiments and the accompanying drawings, which will be discussed later. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram showing the schematic configuration of the wireless communication system according to the first embodiment. [Figure 2] This figure shows an example of the electric field strength distribution in the communication environment between a master device and a slave device. [Figure 3] This figure shows an example of the received signal strength for each communication channel. [Figure 4] This is a flowchart showing the communication sequence between the master device and the slave device in the first embodiment. [Figure 5] This flowchart shows a detailed example of the communication channel deletion determination process in the first embodiment. [Figure 6] It is a diagram showing that two types of threshold values are respectively determined for RSSI values and PER values which are characteristic data indicating communication quality. [Figure 7] It is a flowchart showing a detailed example of the channel map creation process in the first embodiment. [Figure 8] It is an explanatory diagram for explaining a process of performing an AND operation on communication channels included in the first and second communication channel groups of all slave devices and calculating an AND operation result. [Figure 9] It is a flowchart showing a detailed example of the channel map creation process in the second embodiment.

Mode for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present disclosure will be described while referring to the drawings. In addition, for the same or similar configurations, the description may be omitted by assigning the same reference numerals over a plurality of drawings. When only a part of the configuration is described in each embodiment, the configuration of other parts in the other embodiments described previously can be applied to the other parts of the said configuration. Also, not only the combinations of configurations explicitly shown in the description of each embodiment, but also the configurations of a plurality of embodiments may be partially combined with each other as long as there is no problem with the combination.

[0015] (First Embodiment) The wireless communication system of this embodiment includes a master device and a slave device. At least one of the master device and the slave device can be mounted on a moving body and used. The moving body includes, for example, vehicles such as automobiles and railway vehicles, flying bodies such as electric vertical take-off and landing aircraft and drones, ships, construction machines, agricultural machines, and the like.

[0016] As a specific application in vehicles, the wireless communication system according to this embodiment can be applied to a battery management system that manages batteries mounted as battery packs in electric vehicles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles. When applied to a battery management system, for example, the master device is connected to a battery control device, and the multiple slave devices are each connected to monitoring devices provided in the multiple battery stacks that make up the battery pack. In this case, both the master device and the multiple slave devices are mounted in the vehicle.

[0017] Each monitoring device, provided for each battery stack, acquires battery information such as the voltage and current of each battery cell in the corresponding battery stack, and the temperature of the battery stack, using various sensors. When each monitoring device receives data requesting battery information from the battery control unit via a wireless communication system, it transmits the acquired battery information to the battery control unit via the wireless communication system. Based on the acquired battery information, the battery control unit calculates the state of charge (SOC) of the entire battery stack, drives the heating and cooling mechanism to adjust the temperature of the battery pack to an appropriate range, and determines whether or not to perform a so-called equalization process to equalize the voltage of each battery cell. If the battery control unit determines that equalization processing is necessary for at least one battery stack, it instructs the corresponding monitoring device to perform the equalization process via the wireless communication system. In addition, each monitoring device performs processing to determine abnormalities in various sensors and abnormalities in its own operation, and if an abnormality is detected, it transmits the abnormality information to the battery control unit via the wireless communication system.

[0018] Alternatively, the wireless communication system according to this embodiment may be applied to a vehicle, such as a smart key system or a tire pressure monitoring system. When applied to a smart key system, for example, the master device is mounted on the vehicle and connected to a control device that controls the locking and unlocking of vehicle doors and the on / off switching of power sources such as the vehicle's engine. Multiple slave devices are mounted on portable keys or mobile terminals held by multiple users. When applied to a tire pressure monitoring system, the master device is mounted on the vehicle and connected to a control device that displays tire pressure and provides warnings if the pressure is abnormal. Multiple slave devices are provided in each tire and connected to a tire pressure detection device also provided in each tire. Furthermore, the wireless communication system according to this embodiment may be applied to a vehicle diagnostic system. In this case, for example, multiple slave devices are connected to multiple in-vehicle equipment equipped with a self-diagnostic function, and the master device is connected to a diagnostic control device installed in a service factory. In these examples, at least one of the master device and the multiple slave devices is located in a fixed position, and / or at least one is mounted on the vehicle.

[0019] However, the application examples of the wireless communication system according to this embodiment are not limited to vehicles. As mentioned above, it can also be applied to systems that control and manage various types of equipment, such as other mobile objects, like drones, ships, construction machinery, and agricultural machinery. Furthermore, the wireless communication system according to this embodiment can also be applied to systems that control and manage various equipment in buildings and production facilities in factories.

[0020] Figure 1 is a block diagram illustrating the schematic configuration of the wireless communication system 10. The master device 20 and slave device 30 of the wireless communication system 10 are both mounted, for example, in a vehicle (automobile). In this case, the master device 20 and slave device 30 may be configured to be housed in a common enclosure, or they may not be housed in a common enclosure. There may be one master device 20 or multiple master devices 20. Similarly, there may be one slave device 30 or multiple slave devices 30. The master device 20 and slave device 30 communicate wirelessly via a single communication channel that is sequentially selected from multiple communication channels, such as Bluetooth Low Energy (Bluetooth is a registered trademark, hereinafter referred to as Bluetooth LE) communication.

[0021] As an example, the wireless communication system 10 of this embodiment comprises one master device 20 and multiple slave devices 30. Although only one slave device 30 is shown in Figure 1 for the sake of illustration simplicity, multiple slave devices 30 can all be configured in the same way.

[0022] In wireless communication between the master device 20 and the slave device 30, frequency bands used for short-range communication, such as the 2.4 GHz band and the 5 GHz band, can be used. Radio waves in such high-frequency bands have stronger directivity than LF band radio waves and are easily reflected by metal objects such as vehicle bodies. LF is an abbreviation for Low Frequency. As a standard for short-range communication, for example, Bluetooth or Bluetooth LE can be adopted. As an example, the master device 20 and slave device 30 of this embodiment are configured to perform wireless communication compliant with the Bluetooth LE standard (hereinafter referred to as Bluetooth LE communication). Details of the communication method related to communication connection and encrypted communication are carried out according to the sequence specified in the Bluetooth LE standard.

[0023] As shown in Figure 1, the master device 20 includes a control circuit (CNT) 21, a wireless communication circuit (WC) 22, and an antenna 23. In addition to the elements described above, the master device 20 also includes input / output interfaces and bus lines for wired or wireless communication with devices other than the slave device 30.

[0024] The control circuit 21 includes, for example, a processor 211 and memory 212. Memory 212 includes, for example, RAM and ROM. RAM stands for Random Access Memory, and ROM stands for Read Only Memory.

[0025] In the control circuit 21, the processor 211 executes a program stored in ROM while using RAM as a temporary storage area to perform predetermined processing (control). The processor 211 constructs multiple functional units by executing multiple instructions included in the program. The program storage medium is not limited to ROM. Various storage media such as HDDs and SSDs can be used. HDD is an abbreviation for Hard-disk Drive. SSD is an abbreviation for Solid State Drive.

[0026] The processor 211 can be, for example, a CPU, MPU, GPU, or DFP. CPU stands for Central Processing Unit. MPU stands for Micro-Processing Unit. GPU stands for Graphics Processing Unit. DFP stands for Data Flow Processor. The control circuit 21 may be implemented by combining multiple types of processing units, such as a CPU, MPU, and GPU.

[0027] The control circuit 21 may be implemented as an SoC. SoC stands for System on Chip. The control circuit 21 may also be implemented using an ASIC or FPGA. ASIC stands for Application Specific Integrated Circuit. FPGA stands for Field-Programmable Gate Array.

[0028] The control circuit 21 generates a command requesting processing from the slave device 30 (for example, a command requesting data, a command requesting the execution of a predetermined process, etc.), and transmits the transmission data containing the command to the wireless communication circuit 22 in a transmission packet. The control circuit 21 receives the packet transmitted from the slave device 30 and executes a predetermined process based on the data contained in the received packet. In other words, the wireless communication between the master device 20 and the slave device 30 is packet communication.

[0029] The wireless communication circuit 22 includes an RF circuit (not shown) for wirelessly transmitting and receiving packets. The wireless communication circuit 22 has a transmitting function that modulates the transmission signal and oscillates at the frequency of the RF signal. The wireless communication circuit 22 has a receiving function that demodulates the received signal. RF is an abbreviation for radio frequency.

[0030] The wireless communication circuit 22 modulates the packet containing the data transmitted from the control circuit 21 and transmits it to the slave device 30 via the antenna 23. The control circuit 21 outputs encrypted data, such as battery information request data, to the wireless communication circuit 22, using encryption information exchanged in the connection establishment process described later. The wireless communication circuit 22 adds data necessary for wireless communication, such as communication control information, to the transmission packet and transmits it. Data necessary for wireless communication includes, for example, an identifier (ID), a sequence number, the next sequence number, and an error detection code. The wireless communication circuit 22 may also control the data size, communication format, schedule, and error detection of the communication between the master device 20 and the slave device 30. This control related to communication may also be performed by the control circuit 21.

[0031] The wireless communication circuit 22 receives packets transmitted from the slave device 30 via the antenna 23 and demodulates them. It then transmits the demodulated packets to the control circuit 21. The antenna 23 converts electrical signals into radio waves and radiates them into space. The antenna 23 receives radio waves propagating through space and converts them into electrical signals.

[0032] As shown in Figure 1, the slave device 30 includes a control circuit (CNT) 31, a wireless communication circuit (WC) 32, and an antenna 33. In addition to the elements described above, the slave device 30 also includes input / output interfaces and bus lines for wired or wireless communication with devices other than the master device 20. The control circuit 31 has a configuration similar to the control circuit 21 of the master device 20. The control circuit 31 includes, for example, a processor 311 and a memory 312. The memory 312 includes, for example, RAM and ROM.

[0033] The control circuit 31 executes the requested processing (such as response processing, like acquiring and returning the requested data, or execution processing of the requested processing) based on the request command received via the wireless communication circuit 32. For example, if the request command included in the received data is a request to transmit battery information, the control circuit 31 of the slave device 30 transmits the transmission request to the monitoring device of the corresponding battery stack and acquires the battery information from the monitoring device. Then, as a response to the request, the control circuit 31 transmits encrypted data, including the processing result (e.g., acquired battery information), to the wireless communication circuit 32 using encrypted information. The control circuit 31 can also perform, for example, control of equipment mounted on a vehicle, according to the requested processing.

[0034] The wireless communication circuit 32 includes an RF circuit (not shown) for wirelessly transmitting and receiving packets. Similar to the wireless communication circuit 22, the wireless communication circuit 32 has both transmitting and receiving functions. The wireless communication circuit 32 receives packets transmitted from the master device 20 via the antenna 33 and demodulates them. It then transmits the data contained in the demodulated packets to the control circuit 31. The wireless communication circuit 32 modulates the packets containing the data transmitted from the control circuit 31 and transmits them back to the master device 20 via the antenna 33. The wireless communication circuit 32 adds data necessary for wireless communication, such as communication control information, to the transmitted packets before transmitting them.

[0035] The wireless communication circuit 32 may control the data size, communication format, schedule, and error detection of communication between the master device 20 and the slave device 30. These communication-related controls may also be performed by the control circuit 31. The antenna 33 converts electrical signals into radio waves and radiates them into space. The antenna 33 receives radio waves propagating through space and converts them into electrical signals.

[0036] Figure 2 shows an example of the electric field strength distribution in the communication environment between the master device 20 and the slave device 30. Figure 2 shows the electromagnetic field simulation results at a predetermined timing at a predetermined frequency. Hereafter, the electric field strength distribution may be referred to as the electric field distribution.

[0037] The master device 20 and the slave device 30 are, for example, positioned at predetermined locations in a vehicle. When radio signals of a predetermined frequency are transmitted from the master device 20 and the slave device 30, which are positioned at predetermined locations, interference between the transmitted wave and the reflected wave, as well as interference with external noise, results in areas of high and low electric field strength in the operating environment. The reflected wave is caused by reflection from metal elements of the vehicle surrounding the master device 20 and the slave device 30, such as reflection from the vehicle body, reflection from the metal housing, and reflection from the harness. For these reasons, the communication environment between the master device 20 and the slave device 30 has multiple so-called NULL points, which are areas of high electric field strength and areas of low electric field strength, as shown in Figure 2.

[0038] If the slave device 30 is located in or near a low-field-strength area in the electric field distribution with the master device 20, the slave device 30 is highly likely to be unable to properly receive wireless signals from the master device 20, potentially resulting in a communication error. Communication channels that are highly likely to experience such communication errors are those with degraded communication quality.

[0039] In this scenario, when the master device 20 and the slave device 30 perform wireless communication via a single communication channel sequentially selected from multiple communication channels, the frequency of each communication channel differs, and therefore the electric field distribution of each communication channel may also change. As a result, the communication quality may differ across each communication channel.

[0040] For example, as shown in Figure 3, in wireless communication via communication channel A, the received power (received signal strength), which is one of the parameters indicating communication quality, is good. Also, in wireless communication via communication channel C, the received power is very high. Therefore, when the master device 20 and slave device 30 use communication channels A and C, which have good or very high communication quality, they can perform high-quality wireless communication with communication errors sufficiently suppressed. On the other hand, in wireless communication via communication channels B and N, the received power is low. Therefore, when the master device 20 and slave device 30 use communication channels B and N, which have degraded communication quality, the possibility of communication errors occurring in wireless communication increases. Note that in Figure 3, for ease of understanding, an example of received signal strength against frequency is shown with a solid line.

[0041] Therefore, it is preferable that wireless communication between the master device 20 and the slave device 30 be performed using a communication channel capable of high-quality wireless communication, avoiding communication channels with degraded communication quality.

[0042] However, the electric field distribution between the master device 20 and the slave device 30 changes due to external environmental factors (such as external noise) and vibrations of the master device 20 and / or the slave device 30 (including harness vibrations). Therefore, when the master device 20 and the slave device 30 are mounted on a vehicle, the electric field distribution of the communication environment between the master device 20 and the slave device 30 changes according to factors such as vehicle vibration and the state of the surrounding environment. As a result, communication channels with good communication quality and communication channels with degraded communication quality are not fixed but may change from moment to moment. Therefore, it is necessary to remove the communication channel in question from the multiple communication channels used for wireless communication when the communication quality deteriorates, and to restore the communication channel in question as one of the multiple communication channels used for wireless communication when the communication quality recovers. Furthermore, in order to enable the function of avoiding interference with external noise, etc., it is necessary to secure a number of multiple communication channels that is greater than or equal to the minimum limit as multiple communication channels used for wireless communication.

[0043] In the wireless communication system 10 of this embodiment, control processing for realizing wireless communication between the master device 20 and the slave device 30 by securing a number of communication channels greater than or equal to a minimum limit as multiple communication channels used for wireless communication, while excluding communication channels with degraded communication quality, will be explained with reference to the diagram showing the communication sequence between the master device 20 and the slave device 30 shown in Figure 4. In Figure 4, the master device 20 is shown as MASTER and the slave device 30 as SLAVE. Figure 4 also shows the communication sequence executed between the master device 20 and one slave device 30. If there are multiple slave devices 30, the master device 20 individually executes the communication sequence shown in Figure 4 with each of the multiple slave devices 30.

[0044] First, the master device 20 and slave devices 30 perform a connection establishment process before executing the communication sequence shown in Figure 2. For example, if the wireless communication system 10 is installed in a vehicle, the connection establishment process is executed when the IG signal is switched from off to on by, for example, a user operation. This connection establishment process is performed between the master device 20 and all slave devices 30 that are connected to the master device 20 for wireless communication. Note that if the master device 20 and slave devices 30 are always connected, the connection establishment process is performed only once at a predetermined timing. However, if an error occurs during communication and the wireless communication connection between the master device 20 and slave devices 30 is disconnected, the connection establishment process may be performed to reconnect.

[0045] In the connection establishment process, for example, the slave device 30 performs an advertising operation, sending an advertising signal via an advertising communication channel, and the master device 20 performs a scanning operation, scanning for the advertising signal. The advertising communication channel includes multiple communication channels (for example, three in the case of Bluetooth LE). When the master device 20 receives an advertising signal through the scanning operation, it sends a connection request to the slave device 30 that sent the advertising signal. This establishes a communication connection between the master device 20 and the slave device 30. Furthermore, after the communication connection is established, the master device 20 and the slave device 30 exchange encryption information and share initial information regarding frequency channel hopping. The initial information includes, for example, a hopping pattern or a function for hopping.

[0046] Once the connection establishment process is complete, the master device 20 and the slave device 30 perform data communication via a data communication channel that is sequentially selected from multiple communication channels for each periodically occurring communication event. In the case of Bluetooth LE, 37 communication channels are available for data communication. Specifically, as shown in Figure 4, in step S10, the master device 20 sends a data request command, i.e., a data request, to the slave device 30. When the slave device 30 receives the data request in step S210, in step S220 it performs a predetermined process necessary to respond, i.e., the process of acquiring and transmitting the requested data.

[0047] The master device 20 and the slave device 30 switch the communication channel for the data to be used by performing frequency channel hopping for each communication event, and then send and receive data requests and the requested data. In this process, the master device 20 and the slave device 30 determine, for example, the communication channel to be switched by frequency channel hopping according to the channel map described later.

[0048] In step S20, the master device 20 receives the requested data. Then, in step S30, the master device 20 performs a checksum determination, for example, based on the error detection code contained in the received data, to confirm whether the data was received correctly. In the following step S40, if the master device 20 determined in step S30 that the data was not received correctly, it decides whether to perform a retransmission within the same communication event. For example, if the master device 20 has enough time to retransmit before the end of the current communication event, it may decide to retransmit; if there is not enough time, it may decide not to retransmit. In step S40, if the master device 20 decides to retransmit, it repeats the process from step S10. If the process in step S30 determines that the data was received correctly, or if the master device 20 decides not to retransmit in step S40, the master device 20 proceeds to the process in step S50.

[0049] In step S50, the master device 20 performs processing based on the information contained in the received data. If it is determined in step S30 that the data was not received correctly, and it is decided in step S40 not to retransmit the data, then the process in step S50 may be omitted, or the process in step S50 may be performed based on previously received data.

[0050] In step S60, the master device 20 detects the received signal strength (RSSI) and the packet error rate (PER) as characteristic data indicating the communication quality of the signal received from the slave device 30. PER is the percentage of the number of error packets relative to the number of packets received by the master device 20. The master device 20 may also detect the signal-to-noise ratio (SNR) / signal interference-to-noise ratio (SINR) instead of RSSI. SNR / SINR can be detected, for example, by the ratio of the RSSI value when the master device 20 receives a radio signal from the slave device 30 to the RSSI value when it does not receive a radio signal. Alternatively, the master device 20 may also detect the bit error rate (BER) instead of PER. The master device 20 stores and accumulates the detected RSSI or SNR / SINR and PER or BER for each communication channel. Furthermore, characteristic data indicating communication quality can be obtained not only by detection by the master device 20 as described above, but also by the slave device 30 detecting RSSI, PER, etc., when it receives a signal from the master device 20 and transmitting it to the master device 20.

[0051] In step S70, the master device 20 determines that the communication quality of a communication channel has deteriorated based on the characteristic data indicating communication quality detected in step S60. The master device 20 then removes the communication channel determined to have deteriorated communication quality from the communication channels used for wireless communication between the master device 20 and the slave device 30. The communication channels to be removed are data communication channels. This communication channel removal determination process will be explained in detail later.

[0052] In step S80, the master device 20 performs a recovery determination for communication channels that have been deleted due to a deletion determination during previous communication events. In this recovery determination, if predetermined recovery conditions are met, the deleted communication channel is recovered as a communication channel to be used for wireless communication. For example, as an example of predetermined recovery conditions, a deleted communication channel may be recovered in accordance with the elapsed time since the communication channel was deleted. Alternatively, as another example of predetermined recovery conditions, a deleted communication channel may be recovered as a communication channel to be used for wireless communication in accordance with the communication channel adjacent to the deleted communication channel showing good communication quality. In this way, the communication channel determined to be recoverable as a communication channel to be used for wireless communication is actually used for wireless communication between the master device 20 and the slave device 30. However, if the communication quality remains poor when actually used for wireless communication, it may become subject to deletion determination again.

[0053] In step S90, the master device 20 creates a channel map based on the deletion determination result in step S70, the recovery determination result in step S80, and the number of communication channels available for wireless communication. In this embodiment, an example of creating a common channel map for multiple slave devices 30 is described. The channel map creation process in this embodiment will be described in detail later. The channel map may show communication channels available for wireless communication, or it may show communication channels that are unavailable. Furthermore, it may show both available and unavailable communication channels. Also, if there is a change in available / unavailable communication channels due to the creation of the channel map, the frequency channel hopping pattern may be updated. If the frequency channel hopping pattern is not updated, and the communication channel scheduled for hopping is unavailable, for example, the next communication channel scheduled for hopping may be used.

[0054] In step S100, the master device 20 transmits the channel map created by the channel map creation process to the slave device 30. In step S230, the slave device 30 receives the channel map transmitted from the master device 20. In step S240, the slave device 30 sends an acknowledgment signal (Ack signal) back to the master device 20. In step S110, the master device 20 receives the Ack signal from the slave device 30. Then, in step S120, the master device 20 performs a checksum determination, for example, based on the error detection code contained in the received Ack signal, to confirm whether the Ack signal was received correctly. In the following step S130, if the master device 20 determined in step S120 that the data was not received correctly, it decides whether to perform a retransmission process within the same communication event. In step S130, if the master device 20 decides to retransmit, it repeats the process from step S100. If it is determined in step S120 that the data has been received correctly, or if it is decided in step S130 not to retransmit the data, the master device 20 terminates the process shown in the flowchart of Figure 4.

[0055] In this way, the master device 20 and the slave device 30 perform the channel map sharing process. The master device 20 may perform the processes from steps S70 to S130 described above for each communication event, or after multiple communication events have passed. Alternatively, the processes from steps S70 to S90 may be executed by a processing device other than the master device 20, and the results of that processing may be provided to the master device 20.

[0056] Next, the communication channel deletion determination process described above will be explained in detail with reference to the flowchart in Figure 5. The flowchart in Figure 5 shows a detailed example of the communication channel deletion determination process.

[0057] In step S310, the master device 20 acquires RSSI values ​​and PER values, which are first and second characteristic data indicating the communication quality of the communication channel used for wireless communication. A higher RSSI value indicates better communication quality, and a lower PER value indicates better communication quality. The RSSI values ​​and PER values ​​may be those detected in step S60 when the communication channel was used for the most recent wireless communication, or they may be the average of a predetermined number of RSSI values ​​and PER values ​​detected in multiple past wireless communications, or their median values.

[0058] In step S320, the master device 20 determines whether the acquired RSSI value meets the first threshold for RSSI (is greater than the first threshold for RSSI). If the master device 20 determines that the RSSI value meets the first threshold for RSSI, it proceeds to step S330. On the other hand, if the master device 20 determines that the RSSI value does not meet the first threshold for RSSI, it proceeds to step S340.

[0059] In step S330, the master device 20 determines whether the acquired PER value satisfies the first threshold for PER (is less than the first threshold for PER). If the master device 20 determines that the PER value satisfies the first threshold for PER, it proceeds to step S350. In this case, the communication quality of the communication channel can be considered not to have deteriorated, and the communication channel is not removed from the first group of communication channels. On the other hand, if the master device 20 determines that the PER value does not satisfy the first threshold for PER, it proceeds to step S340.

[0060] In step S340, if, as a result of comparing the RSSI value with the first threshold for RSSI, or the PER value with the first threshold for PER, either the RSSI value or the PER value does not meet the first threshold, the master device 20 removes the communication channel from the first group of communication channels. The first group of communication channels is a collection of communication channels in which the RSSI value is greater than the first threshold for RSSI and the PER value is less than the first threshold for PER. In other words, the first group of communication channels is a collection of communication channels in which the communication quality is determined to be good based on the RSSI value and the PER value.

[0061] Thus, in the deletion determination process, if both the RSSI value and the PER value meet the respective first thresholds corresponding to predetermined communication quality standards, the communication channel is considered to meet the predetermined communication quality standards and remains part of the first group of communication channels. However, if at least one of the RSSI value and the PER value does not meet the respective first thresholds, the communication channel is considered not to meet the predetermined communication quality standards and is deleted from the first group of communication channels.

[0062] In step S350, the master device 20 determines whether the RSSI value satisfies the second threshold for RSSI (i.e., is greater than the second threshold for RSSI) which is less than the first threshold for RSSI. If the master device 20 determines that the RSSI value satisfies the second threshold for RSSI, it proceeds to step S360. On the other hand, if the master device 20 determines that the RSSI value does not satisfy the second threshold for RSSI, it proceeds to step S370.

[0063] In step S360, the master device 20 determines whether the PER value satisfies the second threshold for PER, which is greater than the first threshold for PER (and less than the second threshold for PER). If the master device 20 determines that the PER value satisfies the second threshold for PER, it terminates the deletion determination process. In this case, the communication quality of the communication channel can be considered not to have deteriorated below the relaxed communication quality standard corresponding to each second threshold, and therefore the communication channel is not deleted from the second group of communication channels. On the other hand, if the master device 20 determines that the PER value does not satisfy the second threshold for PER, it proceeds to the process in step S370.

[0064] In step S370, if, as a result of comparing the RSSI value with the second threshold for RSSI, or the PER value with the second threshold for PER, either the RSSI value or the PER value does not meet the second threshold, the master device 20 removes the communication channel from the second group of communication channels. The second group of communication channels is a collection of communication channels in which the RSSI value is greater than the second threshold for RSSI and the PER value is less than the second threshold for PER.

[0065] Thus, in the deletion determination process, if both the RSSI value and the PER value meet the respective second thresholds corresponding to relaxed communication quality standards that are more relaxed than the predetermined communication quality standards, the communication channel is considered to meet the relaxed communication quality standards and remains in the second group of communication channels. Otherwise, if at least one of the RSSI value and the PER value does not meet the respective second thresholds, the communication channel is considered not to meet the relaxed communication quality standards and is deleted from the second group of communication channels.

[0066] Here, the relationship between the first group of communication channels and the second group of communication channels will be explained in detail with reference to the diagram. In this embodiment, two types of data, RSSI value and PER value, are detected as characteristic data indicating the communication quality of the communication channel, and two types of thresholds (first threshold for RSSI, second threshold for RSSI, first threshold for PER, and second threshold for PER) corresponding to predetermined communication quality standards and mitigated communication quality standards are defined for the detected RSSI value and PER value, respectively.

[0067] As shown in Figure 6, the first threshold for RSSI is greater than the second threshold for RSSI. A higher RSSI value indicates better communication quality. In other words, the second threshold for RSSI detects a greater decrease in communication quality than the first threshold for RSSI, from the perspective of determining a decrease in communication quality. Therefore, it can be said that the second threshold for RSSI is more lenient than the first threshold for RSSI.

[0068] Furthermore, as shown in Figure 6, the first threshold for PER is smaller than the second threshold for PER. A smaller PER value indicates better communication quality. Therefore, similar to the RSSI case, the second threshold for PER indicates a greater deterioration in communication quality than the first threshold for PER, from the perspective of determining a deterioration in communication quality. Thus, it can be said that the second threshold for PER is also more lenient than the first threshold for PER.

[0069] In this embodiment, as shown in Figure 6, the region with good communication quality, where the RSSI value is greater than the first threshold for RSSI and the PER value is less than the first threshold for PER, is defined as the primary usage region. The set of communication channels belonging to this primary usage region is defined as the first communication channel group. In contrast, the region where the RSSI value is less than or equal to the first threshold for RSSI but greater than the second threshold for RSSI, and the PER value is greater than or equal to the first threshold for PER but less than the second threshold for PER, is defined as the restricted usage region. As will be described later, communication channels belonging to the restricted usage region are used for wireless communication only when the number of communication channels belonging to the primary usage region is less than or equal to a minimum limit value. The set of communication channels belonging to the primary usage region and the restricted usage region constitutes the second communication channel group. That is, the second communication channel group includes the communication channels of the first communication channel group, and further includes the communication channels belonging to the restricted usage region.

[0070] Next, the channel map creation process described above will be explained in detail with reference to the flowchart in Figure 7. The flowchart in Figure 7 shows a detailed example of the channel map creation process. As mentioned above, the channel map creation process in this embodiment is for creating a common channel map for multiple slave devices 30.

[0071] In step S410, after the deletion determination process in step S70 and the restoration determination process in step S80 have been performed, the master device 20 reads out the communication channels belonging to the first communication channel group and the communication channels belonging to the second communication channel group for all slave devices 30.

[0072] As explained using the flowchart in Figure 5, in the deletion determination process, communication channels whose communication quality does not meet a predetermined communication quality standard are deleted from the first communication channel group, and communication channels that do not meet a relaxed communication quality standard are deleted from the second communication channel group. Conversely, the set of communication channels that meet the predetermined communication quality standard is stored as the first communication channel group, and the set of communication channels that meet a relaxed communication quality standard is stored as the second communication channel group. These first and second communication channel groups are stored separately for each slave device 30 in the master device 20.

[0073] Furthermore, in the recovery determination process performed for each slave device 30, if it is determined that a communication channel can be recovered, the master device 20 adds the recovered communication channel to both the first communication channel group and the second communication channel group stored for the corresponding slave device 30. In this way, the deletion determination process and / or recovery determination process update the communication channels included in the first communication channel group and the second communication channel group for each slave device 30.

[0074] In step S420, the master device 20 performs an AND operation on the communication channels included in the first communication channel group of all slave devices 30 to calculate the AND operation result. For example, as shown in Figure 8, if there are multiple slave devices 30, namely slaves 1 to 3, the communication channels belonging to all of the first communication channel group of slave 1, the first communication channel group of slave 2, and the first communication channel group of slave 3 are calculated as the AND operation result of the first communication channel group. In the example in Figure 8, CH35, CH2, CH0, etc. are calculated as the AND operation result of the first communication channel group. Note that in Figure 8, communication channels included in each communication channel group are shown as "1", and communication channels not included are shown as "0".

[0075] In step S430, the master device 20 calculates the number of communication channels obtained as a result of an AND operation on the first group of communication channels. In step S440, the master device 20 determines whether the calculated number of communication channels is less than the minimum limit value. The minimum limit value defines the number of communication channels that are considered necessary to avoid interference with external noise. When switching communication channels used for wireless communication by channel hopping, if the number of communication channels that can be used for wireless communication is small, it may not be possible to fully utilize channel hopping between multiple communication channels, and the function of avoiding interference with external noise may be reduced.

[0076] In step S440, if the calculated number of communication channels is determined to be greater than or equal to the minimum limit, the master device 20 proceeds to step S450; if it is determined to be less than the minimum limit, it proceeds to step S460. In step S450, a channel map common to all slave devices 30 is created from the multiple communication channels calculated by the AND operation of the first group of communication channels.

[0077] In step S460, the master device 20 performs an AND operation on the communication channels included in the second communication channel group of all slave devices 30 to calculate the AND operation result. Similar to the AND operation on the first communication channel group, this AND operation on the second communication channel group also calculates the communication channels belonging to all of the second communication channel group of slave 1, the second communication channel group of slave 2, and the second communication channel group of slave 3 as the AND operation result of the second communication channel group. In the example in Figure 8, it is shown that in addition to CH35, CH2, and CH0, which are the AND operation results of the first communication channel group, CH36, CH1, etc. are calculated as the AND operation result of the second communication channel group. Thus, the number of communication channels calculated by the AND operation on the second communication channel group is greater than the number of communication channels calculated by the AND operation on the first communication channel group.

[0078] In step S470, the master device 20 calculates the number of communication channels obtained as a result of an AND operation on the second group of communication channels. In step S480, the master device 20 determines whether the calculated number of communication channels is less than a minimum limit. This minimum limit is the same as the minimum limit in step S440. If the master device 20 determines in step S480 that the calculated number of communication channels is greater than or equal to the minimum limit, it proceeds to step S490; if it determines that the number is less than the minimum limit, it proceeds to step S500.

[0079] In step S490, a channel map common to all slave devices 30 is created from multiple communication channels calculated by the AND operation of the second group of communication channels. On the other hand, in step S500, since the number of communication channels included in the second group of communication channels is less than the minimum limit, and even with relaxed communication quality standards, it is not possible to obtain a number of communication channels greater than or equal to the minimum limit, a channel map common to all slave devices 30 is initialized. That is, the common channel map is initialized to include all communication channels for data.

[0080] As described above, in this embodiment, when the number of communication channels used for wireless communication falls below a minimum limit due to the deletion of communication channels that do not meet a predetermined communication quality standard, the number of communication channels used for wireless communication is changed to include communication channels that meet a relaxed communication quality standard that is more relaxed than the predetermined communication quality standard. Since the relaxed communication quality standard is more relaxed than the predetermined communication quality standard, the number of communication channels that meet the relaxed communication quality standard increases compared to the number of communication channels that meet the predetermined communication quality standard. This makes it easier to secure a number of communication channels greater than or equal to the minimum limit as multiple communication channels used for wireless communication. Furthermore, since the increased number of communication channels at least meet the relaxed communication quality standard, the risk of communication errors occurring can also be reduced.

[0081] (Second Embodiment) Next, a wireless communication system according to the second embodiment of this disclosure will be described with reference to the drawings. Since the wireless communication system according to this embodiment is configured in the same way as the wireless communication system of the first embodiment, a description of the configuration will be omitted.

[0082] The wireless communication system according to the first embodiment creates a common channel map for all slave devices 30. In contrast, the wireless communication system according to the second embodiment creates individual channel maps for multiple slave devices 30. Therefore, the only difference between the wireless communication system according to the second embodiment and the wireless communication system according to the first embodiment is the channel map creation process. The channel map creation process performed in the wireless communication system according to this embodiment will be described below with reference to the flowchart in Figure 9.

[0083] In step S510, after the deletion determination process in step S70 and the restoration determination process in step S80 have been performed, the master device 20 reads out the communication channels belonging to the first communication channel group and the communication channels belonging to the second communication channel group for all slave devices 30.

[0084] In step S520, the master device 20 selects one slave device 30 from a plurality of slave devices 30 and calculates the number of communication channels included in the first communication channel group of the selected slave device. In step S530, the master device 20 determines whether the calculated number of communication channels is less than a minimum limit value. The minimum limit value in this embodiment is the same as the minimum limit value in the first embodiment.

[0085] In step S530, if the calculated number of communication channels is determined to be greater than or equal to the minimum limit, the master device 20 proceeds to step S540; if it is determined to be less than the minimum limit, it proceeds to step S550. In step S540, a channel map for the slave device 30 selected in step S520 is created from multiple communication channels belonging to the first communication channel group.

[0086] In step S550, the master device 20 calculates the number of communication channels included in the second communication channel group. In step S560, the master device 20 determines whether the calculated number of communication channels is less than a minimum limit. This minimum limit is the same as the minimum limit in step S530. If the master device 20 determines in step S560 that the calculated number of communication channels is greater than or equal to the minimum limit, it proceeds to step S570; if it determines that the number is less than the minimum limit, it proceeds to step S580.

[0087] In step S570, a channel map for the slave device 30 selected in step S520 is created from multiple communication channels belonging to the second group of communication channels. On the other hand, in step S590, since the number of communication channels cannot be obtained beyond the minimum limit even with the relaxed communication quality standards, the channel map for the slave device 30 selected in step S520 is initialized.

[0088] In step S590, all slave devices 30 are selected, and it is determined whether or not the creation of individual channel maps for all slave devices 30 has been completed. If it is determined in step S590 that the creation of individual channel maps for all slave devices 30 has been completed, the process shown in the flowchart of Figure 9 is terminated. On the other hand, if it is determined that the creation of individual channel maps for all slave devices 30 has not been completed, the process returns to step S520, the slave devices 30 for which the creation of channel maps has not been completed are selected, and the processes from steps S520 to S590 described above are repeated.

[0089] The second embodiment described above, like the first embodiment, makes it easier to secure a number of communication channels greater than or equal to the minimum limit for use in wireless communication. Furthermore, since the increased number of communication channels at least meet the relaxed communication quality standards, the risk of communication errors occurring can also be reduced. In addition, in the second embodiment, since channel maps are created individually for each of the multiple slave devices 30, the channel map creation process becomes easier, and it becomes even easier to secure a number of communication channels greater than or equal to the minimum limit.

[0090] While preferred embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above and can be implemented in various modified forms without departing from the spirit of this disclosure. Some modifications of this disclosure are shown below.

[0091] (Variation 1) In the first embodiment described above, an example was explained in which the RSSI value is used as the first characteristic data indicating communication quality and the PER value is used as the second characteristic data, that is, an example in which two types of characteristic data are used. However, the characteristic data indicating communication quality does not have to be two or more types; it may be just one type.

[0092] (Modification 2) In the first and second embodiments described above, when a decrease in communication quality was determined by characteristic data indicating communication quality (such as RSSI value or PER value), only the communication channel that performed the communication in which that characteristic data was detected was deleted.

[0093] However, the communication channels to be removed from the communication channels used for wireless communication between the master device 20 and the slave device 30, when deemed to have degraded communication quality, may include not only communication channels that can be directly determined to have degraded communication quality from the detected characteristic data (such as RSSI value and PER value), but also communication channels in the vicinity of the communication channel in question. This is because, if the communication quality of one communication channel is determined to have degraded, it is generally likely that the communication quality of communication channels at nearby frequencies will also show a similar trend. In this case, for example, the number of communication channels to be removed may be increased when both the RSSI value and the PER value do not meet the threshold, rather than when either the RSSI value or the PER value does not meet the threshold.

[0094] (Variation 3) In the first and second embodiments described above, PER was used as the second characteristic data. However, it is also possible to use the packet arrival rate (PAR), which is the success rate of packet communication, instead of the error rate of packet communication. When using PAR, the relationship between the threshold and the value, and the relationship between the average value and the instantaneous value, will be the opposite of that in the first and second embodiments described above.

[0095] (Modification 4) In the second embodiment described above, an example was shown in which the channel maps of multiple slave devices 30 are created all at once. However, the channel maps may be created for multiple slave devices 30 at different times. For example, when a communication channel is deleted, the channel map creation process may be performed for the slave device 30 from which the communication channel was deleted, while the channel maps of the other slave devices 30 are maintained as they are.

[0096] (Variation 5) In the first and second embodiments described above, the first step of the channel map creation process (steps S410 and S510) reads the communication channels belonging to the first communication channel group and the communication channels belonging to the second communication channel group of all slave devices 30. However, it is also possible to first read the communication channels belonging to the first communication channel group, and if the number of communication channels is less than the minimum limit, then read the communication channels belonging to the second communication channel group. Furthermore, in the second embodiment, as described in Modification Example 4, when performing channel map creation processing individually, it is also possible to read only the communication channels belonging to the first communication channel group and the communication channels belonging to the second communication channel group of the slave device 30 that is the target of the channel map creation process.

[0097] Finally, this specification discloses several technical concepts and several combinations thereof, which are listed below. These combinations of technical concepts apply not only to wireless communication systems but also to wireless communication methods.

[0098] (Technical thought 1) A wireless communication system that performs wireless communication between a master device (20) and a slave device (30) via one communication channel that is sequentially selected from a plurality of communication channels, For each communication channel, a detection unit (S60) detects characteristic data indicating the communication quality of the wireless communication that was performed, A deletion unit (S70) deletes, based on the characteristic data detected by the detection unit, the communication channel that is determined not to meet a predetermined communication quality standard from the plurality of communication channels used for wireless communication, A determination unit (S440, S530) determines whether the number of communication channels used for wireless communication falls below a minimum limit value as a result of the deletion of the communication channels by the deletion unit, A wireless communication system comprising: a determination unit that determines that the number of communication channels used for wireless communication falls below the minimum limit value, and a modification unit (S460-S490, S550-S570) that changes the communication channels used for wireless communication to a number of communication channels that satisfy a relaxed communication quality standard that is more relaxed than the predetermined communication quality standard.

[0099] (Technical thought 2) The deletion unit generates a first group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the predetermined communication quality standards, and a second group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the relaxed communication quality standards. The wireless communication system according to Technical Concept 1, wherein, if the determination unit determines that the number of communication channels included in the first communication channel group falls below the minimum limit, the modification unit changes the communication channels used for wireless communication to the communication channels included in the second communication channel group.

[0100] (Technical Thought 3) The determination unit also determines whether the number of changed communication channels falls below the minimum limit value when the change unit changes the multiple communication channels used for wireless communication. The wireless communication system according to technical concept 1 or 2, further comprising an initialization unit (S500, S580) that initializes the plurality of communication channels used for wireless communication to the initial plurality of communication channels if the determination unit determines that the number of the plurality of communication channels modified by the modification unit is below the minimum limit value.

[0101] (Technical Thought 4) The wireless communication system according to any one of technical ideas 1 to 3, further comprising a channel map sharing unit (S100, S110, S230, S240) that causes the master device and the slave device to share a channel map indicating the multiple communication channels subject to determination when the determination unit determines that the number of multiple communication channels is equal to or greater than the minimum limit value.

[0102] (Technical Thought 5) The wireless communication system according to any one of technical ideas 1 to 4, further comprising a recovery unit (S80) that, with respect to the communication channel deleted by the deletion unit, restores the deleted communication channel to one of the multiple communication channels used for wireless communication when a predetermined recovery condition is satisfied.

[0103] (Technical Thought 6) The characteristic data detected for each communication channel includes first characteristic data and second characteristic data. The wireless communication system according to any one of Technical Ideas 1 to 5, wherein the deletion unit determines that the corresponding communication channel satisfies the predetermined communication quality standard if both the first characteristic data and the second characteristic data satisfy the respective first thresholds corresponding to the predetermined communication quality standard, and determines that the corresponding communication channel does not satisfy the predetermined communication quality standard if at least one of the first characteristic data and the second characteristic data does not satisfy the respective first thresholds.

[0104] (Technical Thought 7) The wireless communication system according to Technical Concept 6, wherein the deletion unit determines that the corresponding communication channel satisfies the relaxed communication quality standard if both the first characteristic data and the second characteristic data satisfy a second threshold that indicates a communication quality lower than the respective first threshold corresponding to the relaxed communication quality standard, and determines that the corresponding communication channel does not satisfy the relaxed communication quality standard if at least one of the first characteristic data and the second characteristic data does not satisfy the respective second threshold.

[0105] (Technical Thought 8) Multiple slave devices are provided, The master device communicates wirelessly with each of the multiple slave devices. The determination unit calculates the number of communication channels used for wireless communication to be compared with the minimum limit value as the number of communication channels available to all of the slave devices. A wireless communication system according to any one of technical ideas 1 to 7, wherein the multiple communication channels used for the wireless communication are common to the multiple slave devices.

[0106] (Technical Thought 9) Multiple slave devices are provided, The master device communicates wirelessly with each of the multiple slave devices. The determination unit calculates the number of communication channels used for wireless communication to be compared with the minimum limit value for each of the slave devices. A wireless communication system according to any one of technical ideas 1 to 7, wherein the plurality of communication channels used for the wireless communication are individually set for the plurality of slave devices.

[0107] (Technical Thought 10) The aforementioned wireless communication is packet communication, The wireless communication system according to any one of Technical Ideas 1 to 9, wherein the characteristic data is at least one of the received signal strength, signal-to-noise ratio / signal interference-to-noise ratio, packet error rate, packet arrival rate, and bit error rate in the packet communication.

[0108] (Technical Thought 11) A wireless communication system according to any one of technical ideas 1 to 10, wherein at least one of the master device and the slave device is mounted on a mobile body.

[0109] (Technical Thought 12) The aforementioned mobile entity is a vehicle, according to the wireless communication system described in technical concept 11. [Explanation of symbols]

[0110] 10: Wireless communication system, 20: Master device, 21: Control circuit, 22: Wireless communication circuit, 23: Antenna, 30: Slave device, 31: Control circuit, 32: Wireless communication circuit, 33: Antenna, 211: Processor, 212: Memory, 311: Processor, 312: Memory

Claims

1. A wireless communication system that performs wireless communication between a master device (20) and a slave device (30) via one communication channel that is sequentially selected from a plurality of communication channels, For each communication channel, a detection unit (S60) detects characteristic data indicating the communication quality of the wireless communication that was performed, A deletion unit (S70) deletes, based on the characteristic data detected by the detection unit, the communication channel that is determined not to meet a predetermined communication quality standard from the plurality of communication channels used for wireless communication, A determination unit (S440, S530) determines whether the number of communication channels used for wireless communication falls below a minimum limit value as a result of the deletion of the communication channels by the deletion unit, If the determination unit determines that the number of communication channels used for wireless communication falls below the minimum limit, the system includes a modification unit (S460 to S490, S550 to S570) that changes the communication channels used for wireless communication to a number of communication channels that satisfy a relaxed communication quality standard that is more relaxed than the predetermined communication quality standard. The deletion unit pre-generates a first group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the predetermined communication quality standards, and a second group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the relaxed communication quality standards. If the determination unit determines that the number of communication channels included in the first communication channel group falls below the minimum limit, the modification unit changes the number of communication channels used for wireless communication from the number of communication channels included in the first communication channel group to the number of communication channels included in the second communication channel group.

2. The determination unit also determines whether the number of changed communication channels falls below the minimum limit value when the change unit changes the multiple communication channels used for wireless communication. The wireless communication system according to claim 1, further comprising an initialization unit (S500, S580) that initializes the plurality of communication channels used for wireless communication to the initial plurality of communication channels if the determination unit determines that the number of the plurality of communication channels modified by the modification unit is below the minimum limit value.

3. The wireless communication system according to claim 1, further comprising a channel map sharing unit (S100, S110, S230, S240) that causes the master device and the slave device to share a channel map indicating the multiple communication channels subject to determination when the determination unit determines that the number of the multiple communication channels is equal to or greater than the minimum limit value.

4. The wireless communication system according to claim 1, further comprising a recovery unit (S80) that, with respect to the communication channel deleted by the deletion unit, restores the deleted communication channel to one of the plurality of communication channels used for wireless communication when a predetermined recovery condition is satisfied.

5. The characteristic data detected for each communication channel includes first characteristic data and second characteristic data. The wireless communication system according to claim 1, wherein the deletion unit determines that the corresponding communication channel satisfies the predetermined communication quality standard if both the first characteristic data and the second characteristic data satisfy the respective first thresholds corresponding to the predetermined communication quality standard, and determines that the corresponding communication channel does not satisfy the predetermined communication quality standard if at least one of the first characteristic data and the second characteristic data does not satisfy the respective first thresholds.

6. The wireless communication system according to claim 5, wherein the deletion unit determines that the corresponding communication channel satisfies the relaxed communication quality standard if both the first characteristic data and the second characteristic data satisfy a second threshold that indicates a communication quality lower than the respective first threshold corresponding to the relaxed communication quality standard, and determines that the corresponding communication channel does not satisfy the relaxed communication quality standard if at least one of the first characteristic data and the second characteristic data does not satisfy the respective second threshold.

7. Multiple slave devices are provided, The master device communicates wirelessly with each of the multiple slave devices. The determination unit calculates the number of communication channels used for wireless communication to be compared with the minimum limit value as the number of communication channels available to all of the slave devices. The wireless communication system according to claim 1, wherein the plurality of communication channels used for the wireless communication are common to the plurality of slave devices.

8. Multiple slave devices are provided, The master device communicates wirelessly with each of the multiple slave devices. The determination unit calculates the number of communication channels used for wireless communication to be compared with the minimum limit value for each of the slave devices. The wireless communication system according to claim 1, wherein the plurality of communication channels used for the wireless communication are individually set for the plurality of slave devices.

9. The aforementioned wireless communication is packet communication, The wireless communication system according to claim 1, wherein the characteristic data is at least one of the received signal strength, signal-to-noise ratio / signal interference-to-noise ratio, packet error rate, packet arrival rate, and bit error rate in the packet communication.

10. The wireless communication system according to claim 1, wherein at least one of the master device and the slave device is mounted on a mobile body.

11. The wireless communication system according to claim 10, wherein the mobile body is a vehicle.

12. A wireless communication method for performing wireless communication between a master device (20) and a slave device (30) via one communication channel that is sequentially selected from a plurality of communication channels, For each communication channel, a detection step (S60) is performed to detect characteristic data indicating the communication quality of the wireless communication that was performed. A deletion step (S70) is performed to remove from the plurality of communication channels used for wireless communication a communication channel that is determined not to meet a predetermined communication quality standard based on the characteristic data detected in the detection step, A determination step (S440, S530) is performed to determine whether the number of communication channels used for wireless communication falls below a minimum limit value as a result of the deletion of the communication channels in the deletion step, If the determination step determines that the number of communication channels used for wireless communication falls below the minimum limit, the system includes a modification step (S460 to S490, S550 to S570) to change the communication channels used for wireless communication to a number of communication channels that satisfy a relaxed communication quality standard that is more relaxed than the predetermined communication quality standard. In the deletion step, a first group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the predetermined communication quality standards, and a second group of communication channels consisting of a plurality of communication channels remaining after deleting the communication channels that do not meet the relaxed communication quality standards are pre-generated. A wireless communication method in which, if the determination step determines that the number of communication channels included in the first communication channel group has fallen below the minimum limit, the change step changes the number of communication channels used for wireless communication from the number of communication channels included in the first communication channel group to the number of communication channels included in the second communication channel group.

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