Wireless communication systems and wireless communication methods

Abstract

To accurately determine that the communication quality of a communication channel that was deemed unusable due to poor communication quality has been improved.SOLUTION: A master device 20 detects characteristic data (RSSI, PER, or the like) indicating the communication quality of a signal received from a slave device 30. Based on the detected characteristic data, the master device 20 deletes a communication channel for which a decline in the communication quality has been determined from a plurality of communication channels used for wireless communication between the master device 20 and the slave device 30. The master device 20 determines whether or not the deleted communication channel can be returned to the plurality of communication channels used for wireless communication, based on the characteristic data of communication channels in the vicinity of the deleted communication channel.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] In the wireless communication system of Patent Document 1, a frequency channel set as an unusable channel returns to a usable frequency channel when a set period elapses.

[0005] However, the communication environment of each communication channel used in a wireless communication system, including interference with other radio waves, does not necessarily change just because a set period has elapsed. Therefore, as in Patent Document 1, if an unusable communication channel is changed to an usable communication channel after a set period has elapsed, there is a high possibility that wireless communication will be performed using a communication channel with degraded communication quality. As a result, there is a risk that the communication success rate of the wireless communication system will decrease.

[0006] This disclosure is made in view of the above-mentioned points, and aims to provide a wireless communication system and wireless communication method that can accurately determine when the communication quality of a communication channel that was deemed unusable due to poor communication quality has improved. [Means for solving the problem]

[0007] 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, A deletion unit (S70) deletes a communication channel from which a deterioration in communication quality has been determined based on characteristic data detected by the detection unit, from among multiple communication channels used for wireless communication. The system includes a determination unit (S80) that determines whether the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the characteristic data of nearby communication channels that have a similar frequency to the deleted communication channel. 、 The determination unit returns the communication channel that it has determined to be recoverable to one of the multiple communication channels used for wireless communication. It is configured in this way.

[0008] Furthermore, the wireless communication method according to this disclosure 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. Therefore, the master device (20) executes A wireless communication method, A detection step (S60) for each communication channel, which detects characteristic data indicating the communication quality of the wireless communication performed, A deletion step (S70) is performed to remove the communication channel whose communication quality has been determined to be degraded based on the characteristic data detected in the detection step from the multiple communication channels used for wireless communication. The deletion step includes a determination step (S80) which determines whether the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the characteristic data of nearby communication channels that have a similar frequency to the deleted communication channel. 、 In the determination step, the communication channel that was determined to be recoverable is restored to one of the multiple communication channels used for wireless communication. It is configured in this way.

[0009] As described above, in the wireless communication system and wireless communication method disclosed herein, the possibility of restoring a deleted communication channel from a plurality of communication channels used for wireless communication is determined based on the characteristic data of a neighboring communication channel with a frequency close to that of the deleted communication channel. Generally, the communication quality of a neighboring communication channel correlates with the communication quality of a deleted communication channel because of the similarity in frequency. Therefore, by using the characteristic data of a neighboring communication channel with a similar frequency, it becomes possible to determine with high accuracy whether or not a deleted communication channel can be restored.

[0010] 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.

[0011] 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]

[0012] [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 recovery determination process in the first embodiment. [Figure 6] This figure shows the relationship between the communication channel to be considered for recovery and nearby communication channels in the recovery determination process of the first embodiment. [Figure 7] (a) shows that channel 3 was used as a communication channel, and (b) shows that channel 3 was removed from the multiple communication channels used for wireless communication by the removal decision process because the communication quality of the wireless communication using channel 3 was poor. [Figure 8] (a) shows that channel 3 was used as a communication channel, and (b) shows a state where channel 3, which was used for wireless communication, and channels 2 and 4 on both sides of channel 3, are all available for wireless communication. [Figure 9] (a) shows that channel 3 was used as a communication channel, and (b) shows the case where channel 3, which was used for wireless communication, is kept available for wireless communication, but channel 2, which is the channel to be considered for restoration, and channel 1, which is the other adjacent channel to channel 2, are deleted by the deletion determination process. [Figure 10] (a) shows that channel 3 was used as a communication channel, and (b) shows the case where channel 3, which was used for wireless communication, remains available for wireless communication, channel 2, which is under consideration for recovery, has been deleted, and channel 1, which is the other adjacent channel to channel 2, is available for wireless communication. [Figure 11]FIG. is an example of the relationship between the RSSI value of each communication channel, the one-sided RSSI threshold, and the two-sided RSSI threshold when only one of the communication channels adjacent to the deleted communication channel that is the subject of the return review is available for wireless communication. [Figure 12] FIG. is an example of the relationship between the RSSI value of each communication channel and the two-sided RSSI threshold when both of the communication channels on both sides of the deleted communication channel that is the subject of the return review are available for wireless communication. [Figure 13] FIG. is a flowchart showing a part of a detailed example of the return determination process of the communication channel in the second embodiment. [Figure 14] FIG. is a flowchart showing the remainder of a detailed example of the return determination process of the communication channel in the second embodiment. [Figure 15] FIG. is a diagram showing the relationship between the communication channel to be reviewed for return and the neighboring communication channels in the return determination process of the second embodiment. [Figure 16] (a) shows that channel 3 is used as a communication channel, and (b) is a diagram showing a threshold relaxation pattern when only one of the communication channels on one side of the deleted channel 2 that is the subject of the return review is available for wireless communication. [Figure 17] FIG. is an example of the relationship between the RSSI value of each communication channel, the one-sided RSSI threshold, and the relaxed one-sided RSSI threshold when the case corresponds to the threshold relaxation pattern of FIG. 16(b). [Figure 18] (a) to (c) are diagrams showing patterns other than the threshold relaxation pattern when only one of the communication channels on one side of the deleted channel 2 that is the subject of the return review is available for wireless communication. [Figure 19] FIG. is an example of the relationship between the RSSI value of each communication channel and the one-sided RSSI threshold when the case corresponds to the pattern of FIG. 18(a). [Figure 20] (a) shows that channel 3 is used as a communication channel, and (b) is a diagram showing a threshold relaxation pattern when both of the communication channels on both sides of the deleted channel 2 that is the subject of the return review are available for wireless communication. [Figure 21] This figure shows an example of the relationship between the RSSI value of each communication channel, the bilateral RSSI threshold, and the relaxed bilateral RSSI threshold when the threshold relaxation pattern shown in Figure 20(b) applies. [Figure 22] Figures (a) to (c) show patterns other than threshold relaxation patterns when the communication channels on both sides of the deleted channel 2, which is the target of restoration consideration, are available for wireless communication. [Figure 23] This figure shows an example of the relationship between the RSSI value of each communication channel and the bilateral RSSI threshold when the pattern shown in Figure 22(a) applies. [Modes for carrying out the invention]

[0013] Preferred embodiments of this disclosure will be described below with reference to the drawings. Note that identical or similar configurations may be given the same reference numeral across multiple drawings, and their descriptions may be omitted. If only a portion of a configuration is described in each embodiment, the other parts of that configuration can be replaced with configurations from other embodiments described earlier. Furthermore, configurations from multiple embodiments may be partially combined, even if not explicitly stated, as long as there are no particular problems with the combination.

[0014] (First Embodiment) The following describes a wireless communication system and wireless communication method according to the 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 may be mounted on a mobile device. Mobile devices include, for example, vehicles such as automobiles and railway cars, aircraft such as electric vertical take-off and landing aircraft and drones, ships, construction machinery, agricultural machinery, and the like.

[0015] 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 a monitoring device provided for each of the multiple battery stacks that make up the battery pack. In this case, both the master device and the slave devices are mounted in the vehicle.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 these 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 in this embodiment are configured to perform wireless communication compliant with the Bluetooth LE standard. 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The control circuit 21 generates commands that request processing from the slave device 30 (for example, commands requesting data, commands requesting the execution of a predetermined process, etc.), and transmits the transmission data containing these commands to the wireless communication circuit 22 in a transmission packet. The control circuit 21 also receives packets transmitted from the slave device 30 and executes predetermined processing based on the data contained in the received packets. In other words, the wireless communication between the master device 20 and the slave device 30 is packet communication.

[0028] 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 also has a receiving function that demodulates the received signal. RF is an abbreviation for radio frequency.

[0029] 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 control the data size, communication format, schedule, and error detection of the communication between the master device 20 and the slave device 30. Control of these communication-related functions may be performed by the control circuit 21.

[0030] 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.

[0031] 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.

[0032] 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 the control of equipment mounted on the vehicle, for example, according to the requested processing.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 power (received signal strength) against frequency is shown with a solid line.

[0040] 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.

[0041] 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 / or 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 monitor the communication quality of each communication channel and set communication channels where degraded communication quality is determined as communication channels to be avoided. Furthermore, if the communication quality of a communication channel that has been removed from the multiple communication channels used for wireless communication improves, it is necessary to reinstate the removed communication channel to the multiple communication channels used for wireless communication.

[0042] 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 using communication channels other than the communication channel with degraded communication quality, including the deletion of communication channels where a deterioration in communication quality has been determined and the restoration of deleted communication channels, 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 is shown as SLAVE.

[0043] First, the master device 20 and slave devices 30 perform a connection establishment process before executing the communication sequence shown in Figure 4. When the wireless communication system 10 is installed in a vehicle, for example, when the IG signal is switched from off to on by user operation, the connection establishment process is executed. 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.

[0044] 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.

[0045] 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. For example, 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.

[0046] The master device 20 and the slave device 30 switch the communication channel for data to be used by performing frequency channel hopping for each communication event, and then send and receive data requests and requested data. At this time, the master device 20 and the slave device 30 determine the communication channel to be switched by frequency channel hopping according to the channel map described later.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] In step S70, the master device 20 determines a decrease in the communication quality of a communication channel based on the characteristic data indicating the communication quality detected in step S60. For example, the master device 20 compares the RSSI or SNR / SINR and PER or BER with deletion thresholds for determining a decrease in communication quality. If at least one type of characteristic data satisfies the deletion threshold, the master device 20 deletes the corresponding communication channel from the multiple communication channels used for wireless communication between the master device 20 and the slave device 30. The communication channel to be deleted is a data communication channel. In this way, communication channels with decreased communication quality are deleted from the communication channels used for wireless communication.

[0051] In step S80, the master device 20 performs a recovery determination for deleted communication channels that were deemed for deletion during previous communication events. Specifically, the master device 20 determines whether the deleted communication channel can be recovered as one of the multiple communication channels used for wireless communication, based on the characteristic data of neighboring communication channels. Generally, the communication quality of neighboring communication channels correlates with the communication quality of the deleted communication channel because their frequencies are similar. Therefore, by using the characteristic data of neighboring communication channels with similar frequencies, it becomes possible to determine with high accuracy whether the deleted communication channel can be recovered. The recovery determination process for deleted communication channels will be explained in detail later. The communication channel that has been recovered and is determined to be used for wireless communication is then 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.

[0052] In step S90, the master device 20 creates a channel map based on the results of the deletion determination in step S70 and the recovery determination in step S80. This channel map may show communication channels that are available for wireless communication, or it may show communication channels that are unavailable. Furthermore, it may show both available and unavailable communication channels. If there are any changes to the available / unavailable communication channels as a result of creating 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.

[0053] In step S100, the master device 20 transmits the created channel map 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 checks whether the Ack signal was received correctly by performing a checksum determination based on the error detection code contained in the received Ack signal. In the following step S130, if the master device 20 determines in step S120 that the data was not received correctly, it decides whether to perform processing for retransmission within the same communication event. In step S130, if the master device 20 decides to retransmit, it repeats the processing 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.

[0054] 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 for each subsequent communication event.

[0055] Next, the process for determining whether a deleted communication channel should be restored in step S80 will be explained in detail with reference to the flowchart in Figure 5. The flowchart in Figure 5 shows in detail an example of the process for determining whether a deleted communication channel should be restored.

[0056] In this embodiment, the possibility of restoring a deleted communication channel is determined based on the characteristic data of nearby communication channels with frequencies close to the deleted communication channel. Therefore, as shown in Figure 6, the master device 20 designates the communication channel actually used by the master device 20 and the slave device 30 as the relevant channel (channel 3 in the example in Figure 6), and defines the adjacent channels on both sides (channels 2 and 4 in the example in Figure 6) with frequencies close to the relevant channel as communication channels to be considered for restoration. Furthermore, the other adjacent channel on the opposite side of the communication channel to be considered for restoration (channels 1 and 5 in the example in Figure 6) is designated as the target for acquiring status and characteristic data. The status of the other adjacent channel indicates whether it is usable for wireless communication or whether it has been deleted from the multiple communication channels used for wireless communication. Additionally, if the other adjacent channel is usable for wireless communication, its characteristic data is also acquired.

[0057] In step S310 of the flowchart in Figure 5, the master device 20 first determines whether the channel in question was deleted from the multiple communication channels used for wireless communication in the deletion determination process in step S70. As shown in Figures 7(a) and (b), if the channel in question is deleted in the deletion determination process, it is difficult to determine whether the communication quality of the adjacent channel has been improved based on the characteristic data of the channel in question. Therefore, if the master device 20 determines that the channel in question has been deleted from the multiple communication channels used for wireless communication, it terminates the process shown in the flowchart in Figure 5 without performing any further recovery determination processing. Note that Figure 7(a) shows that channel 3 was used as a communication channel, and Figure 7(b) shows that channel 3 was deleted from the multiple communication channels used for wireless communication by the deletion determination process because the communication quality of the wireless communication using channel 3 was low.

[0058] On the other hand, if the master device 20 determines in step S310 that the channel in question has not been deleted, it proceeds to step S320. In step S320, the master device 20 obtains the status of the adjacent channels on both sides of the channel that is being considered for recovery, that is, the status indicating whether the adjacent channels on both sides have been deleted or are available. Then, in step S330, the master device 20 determines whether the adjacent channels have been deleted or not based on the obtained status of the adjacent channels that are being considered for recovery.

[0059] For example, as shown in Figures 8(a) and 8(b), if the adjacent channels on both sides of the channel in question are not deleted and are available, there is no need to perform the recovery determination process. Therefore, if the master device 20 determines in step S330 that the adjacent channels on both sides of the channel in question are not deleted, it terminates the process shown in the flowchart of Figure 5 without performing any further recovery determination processes. Figure 8(a) shows that channel 3 was used as a communication channel, and Figure 8(b) shows that channel 3 (the channel in question) used for wireless communication, and the adjacent channels on both sides of the channel (channels 2 and 4), are all available for wireless communication.

[0060] On the other hand, if the master device 20 determines in step S330 that at least one of the adjacent channels has been deleted, it proceeds to the processing from step S340 onward. In other words, in this embodiment, when wireless communication is performed between the master device 20 and the slave device 30 via any communication channel, if the communication channel adjacent to the communication channel used for that wireless communication (the relevant channel) has been deleted, the master device 20 considers the deleted communication channel as a target for recovery consideration and executes the recovery determination processing from step S340 onward.

[0061] In step S340, the master device 20 acquires the status of the other adjacent channel opposite to the deleted adjacent channel (the channel under consideration for recovery), and, if the other adjacent channel is available for wireless communication, characteristic data indicating the communication quality of the other adjacent channel. For example, in the example shown in Figure 6, if adjacent channel 2, the channel under consideration for recovery, has been deleted, the master device 20 acquires the status of channel 1, which is the other adjacent channel of adjacent channel 2, and, if channel 1 has not been deleted, acquires characteristic data for channel 1. Also, if adjacent channel 4, the channel under consideration for recovery, has been deleted, the master device 20 acquires the status of channel 5, which is the other adjacent channel of adjacent channel 4, and, if channel 5 has not been deleted, acquires characteristic data for channel 5.

[0062] In step S350, based on the status of the other adjacent channel obtained in step S340, it is determined whether the other adjacent channel has been deleted. In step S350, if the adjacent channel under consideration for recovery has been deleted, the determination is made for the other adjacent channel on the opposite side of that channel. Therefore, if both adjacent channels on both sides of the channel under consideration have been deleted, the determination in step S350 is made separately for the two other adjacent channels. If it is determined in step S350 that the other adjacent channel has been deleted, the master device 20 proceeds to step S360. On the other hand, if it is determined in step S350 that the other adjacent channel has not been deleted and is in a state where it can be used for wireless communication, the master device 20 proceeds to step S380.

[0063] Figures 9(a) and 9(b) show cases where the other adjacent channel has been deleted. Specifically, Figure 9(a) shows that channel 3 was used as a communication channel, and Figure 9(b) shows a case where channel 3 (the channel in question), which was used for wireless communication, remains usable because no degradation in communication quality was detected in the wireless communication, but the adjacent channel (channel 2) that is under consideration for recovery, and the other adjacent channel (channel 1) of the adjacent channel under consideration for recovery, have been deleted by the deletion determination process. In this case, whether or not the adjacent channel (channel 2) under consideration for recovery can be recovered is determined based only on the characteristic data of the channel in question (channel 3) that is usable for wireless communication.

[0064] Furthermore, Figures 10(a) and (b) show cases where the other adjacent channel is not deleted and is available for wireless communication. Specifically, Figure 10(a) shows that channel 3 was used as a communication channel, and Figure 10(b) shows a case where channel 3 (the channel in question), which was used for wireless communication, was not found to have a degradation in communication quality during wireless communication, and therefore remained available for use. The adjacent channel (channel 2) of the channel in question, which is under consideration for recovery, has been deleted, but the other adjacent channel (channel 1) is available for wireless communication. In this case, whether or not the adjacent channel (channel 2), which is under consideration for recovery, can be recovered is determined based on the characteristic data of the channel in question (channel 3) and the other adjacent channel (channel 1) that are available for wireless communication.

[0065] In this embodiment, the feasibility of restoring a deleted communication channel is determined according to different criteria depending on whether only one adjacent communication channel is available for wireless communication or whether both adjacent communication channels are available for wireless communication. Below, examples of the criteria for the cases where only one communication channel is available for wireless communication and where both communication channels are available for wireless communication are described.

[0066] Steps S360 and S370, which are executed when it is determined in step S350 that the other adjacent channel has been deleted, show examples of criteria for determining when only one communication channel (i.e., the channel in question) is available for wireless communication. In step S360, it is determined whether the RSSI value, one of the characteristic data of the available communication channel (i.e., the channel in question), is greater than the one-sided RSSI threshold. In step S370, it is determined whether the PER value, another characteristic data of the available communication channel (i.e., the channel in question), is less than the one-sided PER threshold. A larger RSSI value indicates better communication quality, and a smaller PER value also indicates better communication quality. The RSSI value and PER value may be the RSSI value and PER value detected in step S60 when the channel in question 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.

[0067] Figure 11 shows an example of the relationship between the RSSI value and the one-sided RSSI threshold and the two-sided RSSI threshold when only one of the two adjacent communication channels to the deleted communication channel being considered for recovery is available for wireless communication. The one-sided RSSI threshold is the threshold used to determine whether recovery is possible when only one of the two adjacent communication channels to the deleted communication channel being considered for recovery is available for wireless communication. The two-sided RSSI threshold is the threshold used to determine whether recovery is possible when both adjacent communication channels to the deleted communication channel being considered for recovery are available for wireless communication.

[0068] If only one communication channel adjacent to the deleted communication channel being considered for recovery is available for wireless communication, as described above, the feasibility of recovering the adjacent channel being considered for recovery is determined based solely on the characteristic data of the communication channel available for wireless communication (the relevant channel). For this reason, as shown in Figure 11, for example, the one-sided RSSI threshold is set relatively larger than the two-sided RSSI threshold so that the RSSI value of the adjacent channel being considered for recovery (channel 2) can be considered to have improved to at least above the deletion threshold. In step S360, the master device 20 determines whether the RSSI value of the communication channel available for wireless communication (the relevant channel) satisfies (exceeds) the relatively large one-sided RSSI threshold set in this way. The one-sided PER threshold in step S370 is also set relatively smaller than the two-sided PER threshold, based on the same reasoning as the one-sided RSSI threshold in step S360. In step S370, the master device 20 determines whether the PER value of the communication channel available for wireless communication (the relevant channel) satisfies (falls below) the one-sided PER threshold.

[0069] If, in step S360, the RSSI value is determined not to meet the one-sided RSSI threshold, or in step S370, the PER value is determined not to meet the one-sided PER threshold, the master device 20 considers the adjacent channel under consideration for recovery to be unrecoverable and terminates the process shown in the flowchart of Figure 5. On the other hand, if, in step S360, the RSSI value is determined to meet the one-sided RSSI threshold, and in step S370, the PER value is determined to meet the one-sided PER threshold, the master device 20 decides in step S420 that the deleted adjacent channel under consideration for recovery can be recovered. After that, the master device 20 terminates the process shown in the flowchart of Figure 5 and returns to the process shown in the flowchart of Figure 4. Note that in steps S360 and S370, two types of characteristic data (RSSI value and PER value) are compared with their respective one-sided thresholds, but the characteristic data compared with the one-sided threshold may be one type or three or more types.

[0070] On the other hand, steps S380, S390, S400, and S410, which are executed when it is determined in step S350 that the other adjacent channel has not been deleted, show examples of criteria for determining when both communication channels (i.e., the channel in question and the other adjacent channel) are available for wireless communication.

[0071] If both communication channels on either side of a deleted communication channel that is being considered for recovery are available for wireless communication, then, for example, as shown in Figure 12, the RSSI value of the adjacent channel (channel 2) being considered for recovery is also likely to be higher than the deletion threshold. Therefore, the bilateral RSSI threshold shown in Figure 12 is set to a relatively smaller value than the unilateral RSSI threshold mentioned above.

[0072] In step S380, the master device 20 calculates the average value of the RSSI values ​​of the channel in question and the other adjacent channel. The RSSI value of the other adjacent channel is based on the RSSI value detected and stored when wireless communication was performed using the other adjacent channel. In step S390, the master device 20 determines whether the average RSSI value calculated in step S380 satisfies (exceeds) a bilateral RSSI threshold that is set relatively lower than the single-sided RSSI threshold.

[0073] In step S400, the master device 20 determines whether the PER value of the channel in question, which is one of the two communication channels available for wireless communication, satisfies (falls below) a bilateral PER threshold that is set to be relatively larger than the one-sided PER threshold. In step S410, it determines whether the PER value of the other adjacent channel, which is another of the two communication channels available for wireless communication, satisfies (falls below) a bilateral PER threshold that is set to be relatively larger than the one-sided PER threshold.

[0074] If, in step S390, it is determined that the RSSI mean value does not meet the bilateral RSSI threshold, or in step S400, it is determined that the PER value of the channel in question does not meet the bilateral PER threshold, or in step S410, it is determined that the PER value of the other adjacent channel does not meet the bilateral PER threshold, then the master device 20 considers that the adjacent channel under consideration for recovery cannot be recovered and terminates the process shown in the flowchart of Figure 5. On the other hand, if, in step S390, it is determined that the RSSI mean value meets the bilateral RSSI threshold, in step S400, it is determined that the PER value of the channel in question meets the bilateral PER threshold, and in step S410, it is determined that the PER value of the other adjacent channel meets the bilateral PER threshold, then the master device 20 proceeds to step S420 and determines that the deleted adjacent channel under consideration for recovery can be recovered. After that, the master device 20 terminates the process shown in the flowchart of Figure 5 and returns to the process shown in the flowchart of Figure 4.

[0075] In steps S380 to S410, two types of characteristic data (RSSI value and PER value) are compared with a threshold, but the characteristic data compared with the threshold may be one type or three or more types. Also, in the example above, with regard to the RSSI value, the average value of the RSSI value of the channel in question and the RSSI value of the other adjacent channel is calculated and the calculated RSSI average value is compared with the bilateral RSSI threshold, but the RSSI value of the channel in question and the RSSI value of the other adjacent channel may be compared with the bilateral RSSI threshold, respectively. Furthermore, in the example above, with regard to the PER value, the PER value of the channel in question and the PER value of the other adjacent channel may be compared with the bilateral PER threshold, respectively, but the average value of the PER value of the channel in question and the PER value of the other adjacent channel may be calculated and the calculated PER average value may be compared with the bilateral PER threshold, respectively. Furthermore, in the example described above, two types of characteristic data (RSSI value and PER value) are compared with thresholds, but it is also possible to determine that a deleted communication channel can be restored to one of the multiple communication channels used for wireless communication simply because both communication channels under consideration for restoration are usable for wireless communication.

[0076] Thus, according to this embodiment, whether or not a deleted communication channel can be restored from a plurality of communication channels used for wireless communication is determined based on the characteristic data of adjacent one-sided or both-sided communication channels with frequencies close to the deleted communication channel. Generally, the communication quality of adjacent communication channels correlates with the communication quality of the deleted communication channel because their frequencies are close. Therefore, by using the characteristic data of adjacent communication channels with close frequencies, it becomes possible to determine with high accuracy whether or not a deleted communication channel can be restored.

[0077] (Second Embodiment) Next, a wireless communication system and wireless communication method 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.

[0078] The wireless communication system according to this embodiment differs from the wireless communication system according to the first embodiment only in the communication channel recovery determination process. Therefore, the recovery determination process performed in the wireless communication system according to this embodiment will be described below with reference to the flowcharts in Figures 13 and 14. Note that the recovery determination process shown in the flowcharts in Figures 13 and 14 has additional steps S352, S354, S356, S358, S381, S382, S383, S384, and S385 compared to the recovery determination process shown in the flowchart in Figure 5. Accordingly, the following description will focus on the processes added to the flowcharts in Figures 13 and 14.

[0079] In step S352, the status of the ±2CH communication channels of the deleted channel to be considered for recovery is obtained. For example, as shown in Figure 15, if the deleted channel to be considered for recovery is channel 2, the ±2CH communication channels are channels 0 and 4. If the deleted channel to be considered for recovery is channel 4, the ±2CH communication channels are channels 2 and 6. Since the status of channels 2 and 4 has already been obtained in step S320, ultimately, in step S352, if the channel to be considered for recovery is channel 2, the status of channel 0 is obtained, and / or if the channel to be considered for recovery is channel 4, the status of channel 6 is obtained. Note that the ±2CH communication channels are on the opposite side of the deleted channels to be considered for recovery (channels 2 and 4), and can be defined as the communication channels adjacent to the communication channels on both sides of the deleted channels (channels 1 and 3 for channel 2, and channels 3 and 5 for channel 4) (channels 0 and 4 for channel 2, and channels 2 and 6 for channel 4).

[0080] In step S354, the master device 20 determines whether the state of nearby communication channels with frequencies close to the deleted channel under consideration for recovery, specifically the states of communication channels ±1CH and ±2CH of the deleted channel under consideration for recovery, corresponds to a threshold relaxation pattern when only one side of the deleted communication channel under consideration for recovery is usable for wireless communication. The threshold relaxation pattern when only one side of the deleted communication channel under consideration for recovery is usable for wireless communication will be explained below.

[0081] If only one communication channel adjacent to the deleted communication channel that is under consideration for recovery is available for wireless communication, as described in the first embodiment, the one-sided RSSI threshold compared to the RSSI value is set to be relatively larger than the two-sided RSSI threshold, and the one-sided PER threshold compared to the PER value is set to be relatively smaller than the two-sided PER threshold.

[0082] However, by considering the state of the ±2CH communication channels under consideration for recovery, it becomes possible to determine, for example, that the communication quality (RSSI value) of the deleted channel under consideration for recovery has improved to above the deletion threshold, even if the RSSI value of one of the communication channels is not very high. For example, as shown in Figure 16(a), suppose channel 3 is a communication channel used for wireless communication, and channel 2 adjacent to channel 3 is a deleted channel. In this case, if channel 3 remains usable for wireless communication, the deleted channel 2 becomes the channel under consideration for recovery.

[0083] Furthermore, as shown in Figure 16(b), if both channels 0 and 4, which are ±2 channels of channel 2 that are under consideration for recovery, are usable for wireless communication, then, as shown in Figure 17, even if the RSSI value of one of the communication channels does not exceed the one-sided RSSI threshold, it is highly likely that the communication quality (RSSI value) of the deleted channel (channel 2) has improved beyond the deletion threshold. In other words, as shown in Figure 16(b), with respect to the ±1 channel of channel 2 that is under consideration for recovery (channels 1 and 3), only one of the communication channels is usable for wireless communication, but if both ±2 channels of channel 2 that are under consideration for recovery (channels 0 and 4) are usable for wireless communication, then it is determined that this falls under the threshold relaxation pattern where only one of the communication channels of the deleted communication channel under consideration for recovery is usable for wireless communication. On the other hand, if the state of the ±1CH and ±2CH communication channels of the deleted channel that is under consideration for recovery is a pattern other than the threshold relaxation pattern shown in Figure 16(b), the master device 20 determines that it does not fall under the threshold relaxation pattern where only one of the communication channels of the deleted channel that is under consideration for recovery is usable for wireless communication.

[0084] Figures 18(a) to (c) show patterns that do not fall under the threshold relaxation pattern when only one of the deleted communication channels that are subject to recovery consideration is available for wireless communication. Figures 18(a) and (b) show patterns where, with respect to the ±1CH communication channels (channel 1 and channel 3) of channel 2 that are subject to recovery consideration, only one of the communication channels is available for wireless communication, and also with respect to the ±2CH communication channels (channel 0 and channel 4) of channel 2 that are subject to recovery consideration, only one of the communication channels is available for wireless communication. Figure 18(c) shows a pattern where, with respect to the ±1CH communication channels (channel 1 and channel 3) of channel 2 that are subject to recovery consideration, only one of the communication channels is available for wireless communication, but with respect to the ±2CH communication channels (channel 0 and channel 4) of channel 2 that are subject to recovery consideration, both communication channels are deleted and are not available for wireless communication.

[0085] For example, Figure 19 shows typical RSSI values ​​for each channel in the pattern shown in Figure 18(a). As shown in Figure 19, the two channels 0 and 1 to the left of channel 2, which is the channel being considered for recovery, have been deleted, and the RSSI values ​​of these two channels are considered to be below the deletion threshold. Therefore, in the pattern shown in Figure 18(a), if the one-sided RSSI threshold is relaxed, it is possible that the RSSI value of channel 3 will exceed the relaxed one-sided RSSI threshold even if the RSSI value of channel 2 has not improved to the point of exceeding the deletion threshold. For this reason, in the pattern shown in Figure 18(a), it is determined that it does not fall under the threshold relaxation pattern where only one of the communication channels of the deleted communication channel being considered for recovery is usable for wireless communication. The same applies to the patterns shown in Figures 18(b) and (c).

[0086] However, for the patterns shown in Figures 18(a) and (b), a relaxed one-sided threshold may be set that is less relaxed than the one-sided RSSI threshold, although the degree of relaxation is smaller than that of the pattern shown in Figure 16(b). This is because the patterns shown in Figures 18(a) and (b) can be considered to have an improving trend in communication quality compared to the pattern shown in Figure 18(c). In this way, the relaxed one-sided threshold may be set in stages according to the patterns of the state of the communication channels within ±1CH and ±2CH of the deleted channel that is under consideration for recovery.

[0087] In step S354 of the flowchart in Figure 13, if the master device 20 determines that the state of the ±1CH and ±2CH communication channels of the deleted channel that is under consideration for recovery corresponds to a threshold relaxation pattern, it proceeds to step S356. On the other hand, if the master device 20 determines that it does not correspond to a threshold relaxation pattern, it proceeds to step S360.

[0088] In step S356, the master device 20 uses a relaxed one-sided RSSI threshold, which is more relaxed than the one-sided RSSI threshold, to determine whether the RSSI value of one of the communication channels (the channel in question) available for wireless communication is satisfied (exceeds) the requirement. In step S358, the master device 20 uses a relaxed one-sided PER threshold, which is more relaxed than the one-sided PER threshold, to determine whether the PER value of one of the communication channels (the channel in question) available for wireless communication is satisfied (exceeds) the requirement.

[0089] Thus, in this embodiment, if the state of the ±1CH and ±2CH communication channels of the deleted channel under consideration for recovery corresponds to a threshold relaxation pattern where only one side of the deleted channel under consideration for recovery is usable for wireless communication, the master device 20 changes the one-sided RSSI threshold and one-sided PER threshold for determining whether the deleted channel can be recovered to relaxed one-sided RSSI threshold and relaxed one-sided PER threshold, which indicate a lower communication quality than those thresholds. This improves the accuracy of determining whether the deleted channel can be recovered. The one-sided RSSI threshold and one-sided PER threshold correspond to the second recovery threshold, and the relaxed one-sided RSSI threshold and relaxed one-sided PER threshold correspond to the fourth recovery threshold.

[0090] The state of ±2CH communication channels is determined by characteristic data (such as RSSI and PER) obtained when wireless communication is performed using ±2CH communication channels. Therefore, as described above, changing the one-sided RSSI threshold and one-sided PER threshold by considering the state of ±2CH communication channels in addition to the state of ±1CH communication channels means that the feasibility of restoring the deleted channel is determined not only based on the characteristic data of ±1CH communication channels of the deleted channel being considered for restoration, but also based on the characteristic data of ±2CH communication channels of the deleted channel being considered for restoration. In other words, in this disclosure, "neighboring communication channels" is a concept that includes not only the communication channels adjacent to the deleted channel being considered for restoration (±1CH), but at least the communication channels adjacent to those adjacent channels (±2CH). Furthermore, the communication states of ±3CH may also be considered as neighboring communication channels.

[0091] If, in step S356, it is determined that the RSSI value does not meet the relaxed one-sided RSSI threshold, or in step S358, it is determined that the PER value does not meet the relaxed one-sided PER threshold, the master device 20 considers that the deleted channel under consideration for recovery cannot be recovered and terminates the process shown in the flowchart of Figure 13. On the other hand, if, in step S356, it is determined that the RSSI value meets the relaxed one-sided RSSI threshold, and in step S358, it is determined that the PER value meets the relaxed one-sided PER threshold, the master device 20 decides in step S420 that the deleted channel under consideration for recovery can be recovered. After that, the master device 20 terminates the process shown in the flowchart of Figure 13 and returns to the process shown in the flowchart of Figure 4.

[0092] In step S350 of Figure 13, if it is determined that the other adjacent channel has not been deleted, the master device 20 proceeds to step S380 of the flowchart in Figure 14. In step S380, the master device 20 calculates the average value of the RSSI values ​​of the channel in question and the other adjacent channel. This is the same as the recovery determination process in the first embodiment.

[0093] In the following step S382, the master device 20 acquires the status of the ±2CH communication channels of the deleted channel that is under consideration for recovery. Then, in step S382, the master device 20 determines whether the status of the ±1CH and ±2CH communication channels of the deleted channel that is under consideration for recovery corresponds to a threshold relaxation pattern when both communication channels on both sides of the deleted communication channel that is under consideration for recovery are usable for wireless communication. The threshold relaxation pattern when both communication channels on both sides of the deleted communication channel that is under consideration for recovery are usable for wireless communication will be explained below.

[0094] For example, as shown in Figure 20(a), suppose channel 3 is a communication channel used for wireless communication, and channel 2 adjacent to channel 3 is a deleted channel. In this case, if channel 3 remains available for wireless communication, the deleted channel 2 will be considered for restoration.

[0095] Furthermore, as shown in Figure 20(b), if both channels 0 and 4, which are ±2CH communication channels of channel 2 that are under consideration for recovery, are usable for wireless communication, then, as shown in Figure 21, even if the RSSI value of one of the ±1CH communication channels does not exceed the bilateral RSSI threshold, or if the average value of the RSSI values ​​of both communication channels does not exceed the bilateral RSSI threshold, it is highly likely that the communication quality (RSSI value) of the deleted channel (channel 2) has improved beyond the deletion threshold. Therefore, as shown in Figure 20(b), if both ±1CH communication channels (channel 1 and channel 3) of channel 2 that are under consideration for recovery are usable for wireless communication, and furthermore, if both ±2CH communication channels (channel 0 and channel 4) of channel 2 that are under consideration for recovery are usable for wireless communication, it is determined that this corresponds to a threshold relaxation pattern. On the other hand, if the master device 20 is not using the threshold relaxation pattern shown in Figure 20(b), it determines that it does not correspond to the threshold relaxation pattern where both communication channels of the deleted communication channel under consideration for recovery are usable for wireless communication.

[0096] Figures 22(a) to (c) show patterns that do not fall under the threshold relaxation pattern when both communication channels on either side of a deleted communication channel that is under consideration for recovery are available for wireless communication. Figures 22(a) and (b) show patterns where both ±1CH communication channels (channel 1 and channel 3) of channel 2 under consideration for recovery are available for wireless communication, but with respect to ±2CH communication channels (channel 0 and channel 4) of channel 2 under consideration for recovery, only one of the communication channels is available for wireless communication. Figure 22(c) shows patterns where both ±1CH communication channels (channel 1 and channel 3) of channel 2 under consideration for recovery are available for wireless communication, but with respect to ±2CH communication channels (channel 0 and channel 4) of channel 2 under consideration for recovery, both communication channels are deleted and are unavailable for wireless communication.

[0097] For example, Figure 23 shows typical RSSI values ​​for each channel in the pattern shown in Figure 22(a). As shown in Figure 23, channel 0, which corresponds to -2CH on the left side of channel 2, the channel being considered for recovery, has been deleted, and it is thought that the RSSI value of channel 0 is below the deletion threshold. Therefore, in the pattern shown in Figure 22(a), if the RSSI thresholds on both sides are relaxed, it is possible that the RSSI values ​​of channels 1 and 3 will exceed the relaxed RSSI thresholds on both sides, even if the RSSI value of channel 2 has not improved to the point of exceeding the deletion threshold. For this reason, in the pattern shown in Figure 22(a), it is determined that it does not fall under the threshold relaxation pattern where both communication channels on both sides of the deleted communication channel being considered for recovery are usable for wireless communication. The same applies to the patterns shown in Figures 22(b) and (c).

[0098] However, for the patterns shown in Figures 22(a) and (b), a relaxed bilateral threshold may be set that is less relaxed than the bilateral RSSI threshold, but less relaxed than the pattern shown in Figure 20(b). This is because the patterns shown in Figures 22(a) and (b) can be considered to show an overall improvement in communication quality compared to the pattern shown in Figure 22(c). In this way, the relaxed bilateral threshold may be set in stages according to the patterns of the state of the communication channels within ±1CH and ±2CH of the deleted channel that is the target of recovery consideration.

[0099] In step S382 of the flowchart in Figure 14, if the master device 20 determines that the state of the ±1CH and ±2CH communication channels of the deleted channel to be considered for recovery corresponds to the threshold relaxation pattern when both communication channels on both sides of the deleted channel to be considered for recovery are usable for wireless communication, it proceeds to step S383. On the other hand, if the master device 20 determines that it does not correspond to the threshold relaxation pattern when both communication channels on both sides of the deleted channel to be considered for recovery are usable for wireless communication, it proceeds to step S390.

[0100] In step S383, the master device 20 determines whether the RSSI average value calculated in step S380 satisfies (exceeds) a relaxed bilateral RSSI threshold that is relaxed (smaller) than the bilateral RSSI threshold. In step S384, the master device 20 determines whether the PER value of the channel in question, which is one of the bilateral communication channels available for wireless communication, satisfies (falls below) a relaxed bilateral PER threshold that is relaxed (larger) than the bilateral PER threshold. In step S385, the master device 20 determines whether the PER value of the other adjacent channel, which is another of the bilateral communication channels available for wireless communication, similarly satisfies (falls below) the relaxed bilateral PER threshold.

[0101] In this embodiment, if the state of the ±1CH and ±2CH communication channels of the deleted channel under consideration for recovery corresponds to a threshold relaxation pattern where both communication channels of the deleted channel under consideration for recovery are usable for wireless communication, the master device 20 changes the bilateral RSSI threshold and bilateral PER threshold for determining whether the deleted channel can be recovered to relaxed bilateral RSSI threshold and relaxed bilateral PER threshold, which indicate a lower communication quality than those thresholds. This improves the accuracy of determining whether the deleted channel can be recovered. Note that the bilateral RSSI threshold and bilateral PER threshold correspond to the first recovery threshold, and the relaxed bilateral RSSI threshold and relaxed bilateral PER threshold correspond to the third recovery threshold.

[0102] If, in step S383, it is determined that the RSSI mean value does not meet the relaxed bilateral RSSI threshold, or in step S384, it is determined that the PER value of the channel in question does not meet the relaxed bilateral PER threshold, or in step S385, it is determined that the PER value of the other adjacent channel does not meet the relaxed bilateral PER threshold, then the master device 20 considers that the deleted channel under consideration for recovery cannot be recovered and terminates the process shown in the flowcharts of Figures 13 and 14. On the other hand, if, in step S383, it is determined that the RSSI mean value meets the relaxed bilateral RSSI threshold, in step S384, it is determined that the PER value of the channel in question meets the relaxed bilateral PER threshold, and in step S385, it is determined that the PER value of the other adjacent channel meets the relaxed bilateral PER threshold, then the master device 20 proceeds to step S420 in the flowchart of Figure 13 and determines that the deleted channel under consideration for recovery can be recovered. After that, the master device 20 terminates the process shown in the flowchart of Figure 13 and returns to the process shown in the flowchart of Figure 4.

[0103] The recovery determination process of this second embodiment can achieve the same effects as in the first embodiment. Furthermore, the recovery determination process of the second embodiment can determine with higher accuracy whether or not the deleted channel to be recovered can be recovered by considering the state of the ±2CH communication channels to be recovered.

[0104] While preferred embodiments of this disclosure have been described above, this disclosure is not limited in any way to the embodiments described above and can be implemented in various modified forms without departing from the spirit of this disclosure.

[0105] For example, 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. Note that when using PAR, the relationship with the threshold will be the opposite of that in the first and second embodiments described above.

[0106] 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.

[0107] (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 the communication channel from the plurality of communication channels used for wireless communication, based on the characteristic data detected by the detection unit, in which a deterioration in communication quality has been determined. A wireless communication system comprising: a determination unit (S80) that determines whether the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the characteristic data of nearby communication channels that have a frequency close to the communication channel deleted by the deletion unit.

[0108] (Technical thought 2) The wireless communication system according to Technical Concept 1, wherein the determination unit determines whether or not to restore the deleted communication channel when wireless communication is performed between the master device and the slave device via the communication channel, if the communication channel adjacent to the communication channel used for the wireless communication has been deleted by the deletion unit.

[0109] (Technical Thought 3) The wireless communication system according to Technical Concept 2, wherein the determination unit, based on the characteristic data, determines that the communication quality of the communication channel used for wireless communication has deteriorated and has been deleted from the plurality of communication channels used for wireless communication, does not determine whether the communication channel adjacent to the communication channel used for wireless communication can be restored.

[0110] (Technical Thought 4) The wireless communication system according to any one of Technical Ideas 1 to 3, wherein the determination unit determines whether a deleted communication channel can be restored according to different determination criteria depending on whether both adjacent communication channels to the deleted communication channel, which is the subject of the determination of whether it can be restored, are usable for the wireless communication, or whether only one of the adjacent communication channels to the deleted communication channel, which is the subject of the determination of whether it can be restored, is usable for the wireless communication.

[0111] (Technical Thought 5) The determination unit determines that if the communication channels on both sides adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, are usable for the wireless communication, the characteristic data of the communication channels on both sides satisfies a first restoration threshold, thereby determining that the deleted communication channel can be restored to one of the multiple communication channels used for the wireless communication; and if only one of the communication channels adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, is usable for the wireless communication, the characteristic data of the communication channel on the one side satisfies a second restoration threshold indicating a higher communication quality than the first restoration threshold, thereby determining that the deleted communication channel can be restored to one of the multiple communication channels used for the wireless communication, as described in Technical Concept 4.

[0112] (Technical Thought 6) The wireless communication system according to technical concept 5, wherein the determination unit changes the first recovery threshold to a third recovery threshold indicating a lower communication quality than the first recovery threshold if, in addition to the fact that the communication channels on both sides adjacent to the deleted communication channel that is the subject of the recovery determination, are available for wireless communication, and on the opposite side from the deleted communication channel, the communication channels adjacent to each of the communication channels are available for wireless communication.

[0113] (Technical Thought 7) The wireless communication system according to technical concept 5, wherein the determination unit changes the second recovery threshold to a fourth recovery threshold indicating a lower communication quality than the second recovery threshold if, in addition to the fact that only one of the communication channels adjacent to the deleted communication channel that is the subject of the determination of recovery feasibility is available for the wireless communication, the communication channels adjacent to both sides of the deleted communication channel on the opposite side of the deleted communication channel are available for the wireless communication.

[0114] (Technical Thought 8) The wireless communication system according to Technical Concept 4, wherein the determination unit determines that if the communication channels on both sides adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, are available for wireless communication, the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the fact that the communication channels on both sides are available for wireless communication.

[0115] (Technical Thought 9) The plurality of communication channels comprises a first channel group including a plurality of communication channels used for connection establishment processing to establish a communication connection between the master device and the slave device, and a second channel group including a plurality of communication channels used for communication processing to perform data communication between the master device and the slave device. The wireless communication system according to any one of Technical Ideas 1 to 8, wherein the communication channel that the deletion unit deletes from the plurality of communication channels used for the wireless communication is the communication channel included in the second channel group.

[0116] (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.

[0117] (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.

[0118] (Technical Thought 12) The aforementioned mobile entity is a vehicle, according to the wireless communication system described in technical concept 11. [Explanation of symbols]

[0119] 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 the communication channel from the plurality of communication channels used for wireless communication, based on the characteristic data detected by the detection unit, in which a deterioration in communication quality has been determined. The system includes a determination unit (S80) that determines whether the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the characteristic data of nearby communication channels that have a frequency close to the communication channel deleted by the deletion unit, A wireless communication system that restores the communication channel determined to be recoverable by the determination unit to one of the multiple communication channels used for wireless communication.

2. The wireless communication system according to claim 1, wherein the determination unit determines whether or not to restore the deleted communication channel when wireless communication is performed between the master device and the slave device via the communication channel, if the communication channel adjacent to the communication channel used for the wireless communication has been deleted by the deletion unit.

3. The wireless communication system according to claim 2, wherein the determination unit, based on the characteristic data, determines that the communication quality of the communication channel used for wireless communication has deteriorated and deletes it from the plurality of communication channels used for wireless communication, and the determination unit does not determine whether the communication channel adjacent to the communication channel used for wireless communication can be restored.

4. The wireless communication system according to any one of claims 1 to 3, wherein the determination unit determines whether a deleted communication channel can be restored according to different determination criteria depending on whether both adjacent communication channels to the deleted communication channel that is the subject of the determination of whether it can be restored are usable for the wireless communication, or whether only one of the adjacent communication channels to the deleted communication channel that is the subject of the determination of whether it can be restored is usable for the wireless communication.

5. The wireless communication system according to claim 4, wherein the determination unit determines that if the communication channels on both sides adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, are usable for the wireless communication, the characteristic data of the communication channels on both sides satisfies a first restoration threshold, and if only one of the communication channels adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, is usable for the wireless communication, the determination unit determines that the deleted communication channel, which is the subject of the determination of whether or not it can be restored, is usable for the wireless communication, the characteristic data of the communication channel on the one side satisfies a second restoration threshold indicating a higher communication quality than the first restoration threshold.

6. The wireless communication system according to claim 5, wherein the determination unit changes the first recovery threshold to a third recovery threshold indicating a lower communication quality than the first recovery threshold if, in addition to the fact that the communication channels on both sides adjacent to the deleted communication channel that is the subject of the determination of whether or not recovery is possible are available for wireless communication, and the communication channels on the opposite side from the deleted communication channel that are adjacent to each of the communication channels are available for wireless communication.

7. The wireless communication system according to claim 5, wherein the determination unit changes the second recovery threshold to a fourth recovery threshold indicating a lower communication quality than the second recovery threshold if, in addition to the fact that only one of the communication channels adjacent to the deleted communication channel that is the subject of the determination of recovery feasibility is available for wireless communication, the communication channels adjacent to both sides of the deleted communication channel on the opposite side of the deleted communication channel are available for wireless communication.

8. The wireless communication system according to claim 4, wherein the determination unit determines that if the communication channels on both sides adjacent to the deleted communication channel, which is the subject of the determination of whether or not it can be restored, are available for wireless communication, the deleted communication channel can be restored to one of the plurality of communication channels used for wireless communication, based on the fact that the communication channels on both sides are available for wireless communication.

9. The plurality of communication channels comprises a first channel group including a plurality of communication channels used for connection establishment processing to establish a communication connection between the master device and the slave device, and a second channel group including a plurality of communication channels used for communication processing to perform data communication between the master device and the slave device. The wireless communication system according to any one of claims 1 to 3, wherein the communication channel that the deletion unit deletes from the plurality of communication channels used for wireless communication is a communication channel included in the second channel group.

10. The aforementioned wireless communication is packet communication, The wireless communication system according to any one of claims 1 to 3, 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.

11. The wireless communication system according to any one of claims 1 to 3, wherein at least one of the master device and the slave device is mounted on a mobile body.

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

13. A wireless communication method performed by the master device (20) to perform wireless communication between the master device (20) and the slave device (30) via one communication channel 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 the communication channel in which a deterioration in communication quality has been determined based on the characteristic data detected in the detection step from the plurality of communication channels used for wireless communication. The system includes a determination step (S80) which determines whether the deleted communication channel can be restored to one of the multiple communication channels used for wireless communication, based on the characteristic data of nearby communication channels that have a frequency close to the deleted communication channel in the deletion step, A wireless communication method that restores the communication channel determined to be recoverable in the determination step to one of the multiple communication channels used for wireless communication.

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