Communication method, communication apparatus, and program

Abstract

To reduce a risk of radio wave interference in retransmission.SOLUTION: An exemplary communication method changes the size of a data body in a format in a single unit of transmission data in UWB communication.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a communication technology for UWB (Ultra Wide Band) communication. [Background technology]

[0002] In recent years, wireless communication has been on the rise in the field of communications due to its advantages in terms of installation, such as the elimination of wiring. For example, UWB communication, which uses wideband radio waves, has good transparency and little interference with Wi-Fi (registered trademark) and radio waves used in mobile devices such as smartphones, and its applications are expanding.

[0003] UWB communication is expected to be a promising communication method for in-vehicle devices because it can easily establish communication inside a vehicle, even in the narrow, metal space with many wires. For example, Patent Document 1 discloses a keyless vehicle entry system that includes one UWB central wireless device and multiple UWB peripheral wireless devices. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-53965 Summary of the Invention [Problem to be solved by the invention]

[0005] As UWB communication becomes more widespread, interference between UWB communications will become more likely, which could lead to communication disruptions. This communication disruption problem could occur not only with the communication methods of in-vehicle devices, but with all communication methods that use UWB communication.

[0006] Retransmission is an effective method for combating communication interference. However, there is a high possibility that the interfering communication system is also experiencing communication disruption due to the same interference, and the retransmission processes of both systems will likely cause another communication disruption due to interference.

[0007] In view of the above, an object of the present disclosure is to provide a technique that can reduce the risk of radio interference during retransmission. [Means for solving the problem]

[0008] An exemplary communication method of the present invention changes the size of a data body in the format of one unit of transmission data in UWB communication (using a preamble). [Effects of the Invention]

[0009] According to the exemplary embodiment of the present invention, when two adjacent communication systems performing UWB communication experience radio wave interference between the two communication systems and a retransmission is required, one of the communication systems can change the size of the data body, which increases the likelihood of misalignment in the timing of retransmission between the two communication systems, thereby reducing the risk of radio wave interference during retransmission. Therefore, according to the exemplary embodiment of the present invention, the success rate of retransmission can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] A diagram showing an example of the configuration of a communication system. [Figure 2] FIG. 1 shows a frame format used in UWB communication. [Figure 3] Schematic diagram to explain problems with reception in UWB communications [Figure 4] Schematic diagram to explain problems with reception in UWB communications [Figure 5] FIG. 1 shows an example of the configuration of a master communication device. [Figure 6] FIG. 1 shows an example of the configuration of a slave communication device. [Figure 7] 10 is a flowchart showing an example of the operation of the master communication device. [Figure 8] FIG. 1 is a diagram illustrating a communication frame (target wave) transmitted by a master communication device of a communication system and a communication frame (interfering wave) transmitted by a master communication device of another system. [Figure 9] A diagram showing the timing for monitoring UWB communications from other systems [Figure 10] 1 is a flowchart showing an example of an operation of a master communication device in a synchronous communication phase. [Figure 11] FIG. 10 is a diagram showing an example of a data format for a wireless communication schedule. [Figure 12] 1 is a flowchart showing an example of an operation of a slave communication device in a synchronous communication phase. [Figure 13] A diagram showing the data communication state in the cyclic communication phase DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the description of the embodiments, the same components are denoted by the same reference numerals, and redundant description will be omitted unless particularly necessary.

[0012] <1. Communication Systems> FIG. 1 is a diagram showing an example of the configuration of a communication system SYS1 according to an embodiment of the present invention. In this embodiment, as an example, the communication system SYS1 is applied to an automobile V1. However, the communication system SYS1 may be applied to other than the automobile V1, for example, to general mobile objects other than automobiles, home communications, office communications, or factory communications. Note that general mobile objects include, in addition to automobiles, for example, trains, ships, and airplanes.

[0013] As shown in Fig. 1, the communication system SYS1 includes a master ECU (Electric Control Unit) 10 and a plurality of slave devices 20a to 20d. The communication system SYS1 is a vehicle control system in which, for example, the master ECU 10 constitutes a device, a so-called head unit, that performs integrated control of various in-vehicle devices, and controls each of the slave devices 20a to 20d via UWB communication in response to user operations on a central HMI (Human Machine Interface) of the head unit. Specifically, each of the slave devices 20a to 20d transmits sensor values ​​and the like detected by sensors connected to the slave devices 20a to 20d to the master ECU 10. Each of the slave devices 20a to 20d controls an actuator connected to the slave device 20a to 20d based on a control signal transmitted from the master ECU 10.

[0014] The slave device 20a is, for example, a control device that controls the operation of headlights. The slave device 20b is, for example, a control device that controls the operation of wipers. The slave device 20c is, for example, a control device that controls the operation of power windows. The slave device 20d is, for example, a control device that controls the operation of an air conditioner.

[0015] Since UWB communication is performed between the master ECU 10 and each of the slave devices 20a to 20d, hereinafter the master ECU 10 will be referred to as the master communication device 10, and the slave devices 20a to 20d will be referred to as the slave communication devices 20a to 20d. Furthermore, when it is not necessary to distinguish between the multiple slave communication devices 20a to 20d, each of the slave communication devices 20a to 20d may be simply referred to as the slave communication device 20.

[0016] Furthermore, although the present embodiment refers to a plurality of slave communication devices 20, there may also be a single slave communication device. In a narrower sense, the term "master communication device" is sometimes used to mean a device that controls the communication operations of the slave communication devices. However, here, the term is used in a broader sense to mean a device that communicates with multiple slave communication devices, and each slave communication device communicates with the master communication device. In other words, the multiple communication devices in a communication system do not necessarily have to be in a master-slave relationship in the strict sense, but may also be in an equal relationship with each other.

[0017] In this embodiment, the master communication device 10 and the slave communication devices 20 perform UWB communication as described above. That is, the wireless communication in this embodiment is wireless communication using the UWB communication method. The UWB communication is performed in accordance with a standard such as IEEE 802.15.4 (hereinafter, sometimes simply referred to as a communication standard). Because the master communication device 10 and each of the slave communication devices 20a to 20d perform UWB communication, the communication system SYS1 contributes to reducing the number of wire harnesses used in the automobile V1.

[0018] The master communication device 10 may transmit a signal to the slave communication device 20 or may receive a signal from the slave communication device 20. The slave communication device 20 may receive a signal from the master communication device 10 or may transmit a signal to the master communication device 10. That is, the communication system SYS1 includes a transmitting device that transmits via wireless communication and a receiving device that receives via wireless communication. Each of the master communication device 10 and the slave communication device 20 can be either the transmitting device or the receiving device. That is, the master communication device 10 is a transmitting device in a signal transmission state and a receiving device in a signal reception state. The slave communication device 20 is also a transmitting device in a signal transmission state and a receiving device in a signal reception state.

[0019] <2. Preamble Code> Next, the preamble codes used by the master communication device 10 and the slave communication device 20 will be described.

[0020] First, the format of a communication frame (a unit of transmission data) in UWB communication (hereinafter referred to as frame format) will be explained using Figure 2. The frame format used in UWB communication is determined by the above-mentioned communication standard.

[0021] As shown in Figure 2, the frame format F used in UWB communication has a structure in which a preamble is first followed by an SFD (Start Frame Delimiter), a PHR (PHY Header), and a data body. The term "data body" is used to make it easier to understand the difference between the preamble, SFD, and PHR.

[0022] A preamble is a sequence of bits or pulses (e.g., -, 0, +) of a specific pattern that is sent before the data itself in digital communications to inform the receiving end that "data is about to be sent." The receiving end uses the preamble signal to synchronize the receiving clock. There are several types of preamble patterns.

[0023] There are 24 types of preamble codes, Codes 1 to 24. Codes 1 to 8 are low-code preamble codes with a PRF (Pulse Repletion Frequency) of 16 MHz. Codes 9 to 24 are high-code preamble codes with a PRF of 64 MHz. There are two low-code preamble codes that can be used in Japan, Code 3 and Code 4, and there are four high-code preamble codes that can be used in Japan, Codes 9 to 12.

[0024] The preamble length is determined by the number of symbols included in the preamble, and is selected from patterns such as 16 symbols, 64 symbols, 128 symbols, 256 symbols, 512 symbols, 1024 symbols, 2048 symbols, and 4096 symbols.

[0025] A preamble is a sequence composed of a predetermined pattern of bits or pulses (e.g., -, 0, +) such as "10101010...", and the preamble length is a size (length) that increases as the number of symbols included in the preamble increases.

[0026] The SFD is a bit string with a specific pattern that signals the start of data in a communication frame. The PHR contains information necessary for decoding a packet. For example, the PHR contains information such as the address of the communication partner and the data length of the subsequent data. The data body is the main body of information to be transmitted to the communication partner and contains the actual data to be transmitted. When the actual data to be transmitted exceeds the maximum size (127 bytes) of the data body in a communication frame, the actual data to be transmitted is usually divided into the maximum size (127 bytes) to maximize communication efficiency, and each divided piece of data is assigned to the data body of each communication frame. For example, the data body contains information such as the ID information of the receiver of the communication frame, the ID information of the sender, instruction information from the master communication device 10 to the slave communication device 20, sensor values ​​detected by the sensors equipped in the slave communication device 20, and the operating status of the actuator to be controlled by the slave communication device 20.

[0027] <3. Radio interference> Here, an overview of radio wave interference (communication interference) in the communication system SYS1 will be described with reference to Fig. 3 and Fig. 4. Fig. 3 and Fig. 4 are schematic diagrams for explaining problems that occur during reception in UWB communication. In Fig. 4, the preamble, SFD, and PHR are displayed with a mesh pattern.

[0028] In Figure 3, the target wave is the radio wave desired to be received by the receiving antenna RA1. The jamming wave is the radio wave that is not desired to be received by the receiving antenna RA1. In UWB communication, although the strength of the radio wave also plays a role, the radio wave received first is generally processed first. Specifically, once the communication device begins synchronization processing of the preceding radio wave, subsequent radio waves cannot be processed. In Figure 3, the two radio waves arrive at the receiving antenna RA1 in the order of the jamming wave and the target wave, with an arrival time difference of Δt. Therefore, the jamming wave is processed first. If the receiving device receives the jamming wave first, it cannot recognize it as a jamming wave unless it demodulates the address in the PHR, which is processed after the preamble and SFD. Note that once it is recognized as a jamming wave, processing of the jamming wave is stopped, and other waves (such as the subsequent target wave) can be received and processed. The target wave may arrive at the receiving antenna RA1 before the reception processing identifies the radio wave as a jamming wave, resulting in a missed reception of the target wave. When communication fails due to such radio interference, a retransmission is performed.

[0029] However, if the size of the data body of the communication frame is fixed at the maximum size (127 bytes), even if retransmission is performed, the relationship (time difference) in the retransmission timing between the jamming wave and the target wave will be the same, as shown in Figure 4, and there is a risk that the jamming wave will continue to be received before the target wave, and communication failure due to radio wave interference will not be resolved.

[0030] The master communication device 10 is configured to change (variably) the size of the data body of the communication frame, and by changing the size of the data body of the communication frame, it prevents the timing of retransmission from having the same relationship (time difference) as the retransmission timing of the interfering wave, thereby reducing the risk of radio wave interference during retransmission.

[0031] <4. Master communication device> Next, the master communication device 10 constituting the communication system SYS1 will be described. Fig. 5 is a diagram showing an example of the configuration of the master communication device 10. Note that Fig. 5 shows components necessary for explaining the features of this embodiment, and omits descriptions of general components.

[0032] As shown in FIG. 5, the master communication device 10 includes a wireless communication unit 11, a controller 12, and a memory 13.

[0033] The wireless communication unit 11 performs wireless communication with the slave communication device 20. Specifically, the wireless communication unit 11 is configured by a UWB communication device that performs UWB communication with the slave communication device 20.

[0034] The controller 12 includes a processor that performs arithmetic processing and the like. The processor may include, for example, a CPU (Central Processing Unit). The controller 12 may be configured with one processor or multiple processors. When configured with multiple processors, the processors may be connected to each other so that they can communicate with each other.

[0035] The memory 13 is configured to include a volatile memory and a non-volatile memory. The volatile memory is specifically a RAM (Random Access Memory). The non-volatile memory is specifically a ROM (Read Only Memory). The non-volatile memory may also be a flash memory, a hard disk drive, or the like. The non-volatile memory stores computer-readable programs and data.

[0036] The functions of the controller 12 are realized by the processor executing arithmetic processing in accordance with the programs stored in the memory 13. The number of programs that realize the functions of the controller 12 may be one or more. In this embodiment, the programs stored in the memory 13 include a program that changes the size of the data body of a communication frame.

[0037] The program stored in memory 13 may be provided by, for example, a computer-readable nonvolatile recording medium. The nonvolatile recording medium may be, for example, the nonvolatile memory described above, an optical recording medium (for example, an optical disk), a magneto-optical recording medium (for example, a magneto-optical disk), a USB memory, or an SD card. As another example, the program may be provided from a program providing server via a communication line such as the Internet (provided by so-called download).

[0038] The functions of the controller 12 may be realized by an arithmetic circuit executing arithmetic processing according to a program, i.e., by software, but may also be realized by other methods. At least some of the functions of the controller 12 may be realized using, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). That is, at least some of the functions of the controller 12 may be realized by hardware using a dedicated IC or the like. At least some of the functions of the controller 12 may also be realized by a combination of software and hardware.

[0039] As shown in Fig. 5, in this embodiment, the controller 12 includes, as its functional units, a size change unit 121 and a retransmission instruction unit 122. Note that each of the functional units 121 to 122 is a conceptual component. A function performed by one component may be distributed to multiple components. Furthermore, functions possessed by multiple components may be integrated into one component.

[0040] The size change unit 121 changes the size of the data body of the communication frame. In this embodiment, the size change unit 121 changes the size of the data body of the communication frame for transmission after radio interference occurs. In this embodiment, the size change unit 121 fixes the size of the data body of the communication frame before the change to the maximum size (127 bytes).

[0041] The retransmission instruction unit 122 instructs the wireless communication unit 11 to perform retransmission. More specifically, the retransmission instruction unit 122 instructs the wireless communication unit 11 to perform retransmission when communication has failed.

[0042] <5. Slave communication device> Fig. 6 is a diagram showing an example of the configuration of the slave communication device 20. Note that Fig. 6 shows components necessary for explaining the features of this embodiment, and omits descriptions of general components. Furthermore, all of the multiple slave communication devices 20a to 20d have the configuration shown in Fig. 6.

[0043] As shown in FIG. 6, the slave communication device 20 includes a wireless communication unit 21, a controller 22, and a memory .

[0044] The wireless communication unit 21 performs wireless communication with the master communication device 10. Specifically, the wireless communication unit 21 is configured with a UWB communication device that performs UWB communication with the master communication device 10 (wireless communication unit 11).

[0045] The controller 22 includes a processor that performs arithmetic processing and the like. The processor may include, for example, a CPU. The controller 22 may be configured with one processor or multiple processors. When configured with multiple processors, the processors may be connected to each other so that they can communicate with each other.

[0046] The memory 23 is configured to include volatile memory and nonvolatile memory. The volatile memory is specifically RAM. The nonvolatile memory is specifically ROM. The nonvolatile memory may also be a flash memory, a hard disk drive, or the like. The nonvolatile memory stores computer-readable programs and data.

[0047] The functions of the controller 22 are realized by the processor executing arithmetic processing in accordance with the programs stored in the memory 23. The number of programs that realize the functions of the controller 22 may be one or more.

[0048] The program stored in memory 23 may be provided by, for example, a computer-readable nonvolatile recording medium. The nonvolatile recording medium may be, for example, the above-mentioned nonvolatile memory, an optical recording medium (for example, an optical disk), a magneto-optical recording medium (for example, a magneto-optical disk), a USB memory, an SD card, or the like. As another example, the program may be provided from a program providing server via a communication line such as the Internet.

[0049] The functions of the controller 22 may be realized by an arithmetic circuit executing arithmetic processing according to a program, i.e., by software, but may also be realized by other methods. At least some of the functions of the controller 22 may be realized using, for example, an ASIC, an FPGA, or the like. That is, at least some of the functions of the controller 22 may be realized by hardware using a dedicated IC, etc. At least some of the functions of the controller 22 may also be realized by a combination of software and hardware.

[0050] <6. Communication Method> When various settings required for well-known UWB communication are completed in the master communication device 10 and the plurality of slave communication devices 20a to 20d 20, normal UWB communication becomes possible between the master communication device 10 and the plurality of slave communication devices 20a to 20d.

[0051] Fig. 7 is a flowchart showing an example of the operation of the master communication device 10. The operation shown in Fig. 7 is initiated, for example, when a body ECU installed in the automobile V1 that controls the body of the automobile V1 is started. Specifically, the body ECU controls on-board devices other than the vehicle driving system devices such as the engine. On-board devices other than the vehicle driving system devices include, for example, an air conditioner, a door lock device, a window opening / closing device, a wiper device, etc.

[0052] The body ECU is typically activated when the doors of the automobile V1 are unlocked. Another example is when the ACC is turned on by operating the vehicle's ignition key. When the communication system is applied to other mobile objects (e.g., trains, ships, aircraft, etc.), the start timing of the operations shown in FIG. 7 may be the start timing of the mobile object drive system. The operations shown in FIG. 7 may be executed after the body ECU is activated, for example, as periodic operations (e.g., operations executed immediately after activation or at predetermined time intervals) or as exceptional operations (e.g., operations executed when communication failures occur or increase in frequency, or when there is a change in the vehicle (communication) environment). At least one of the master communication device 10 and the slave communication devices 20a to 20d may be a body ECU (or a component included in a body ECU), but not all of the master communication device 10 and the slave communication devices 20a to 20d may be body ECUs. The body ECU may be, for example, an entertainment device such as an audio device.

[0053] First, the controller 12 of the master communication device 10 controls the wireless communication unit 11 to transmit data (main data) using a communication frame to the slave communication device 20 (step S1). The size of the data main body in the communication frame is the size stored in the memory 13, and is the maximum size (127 bytes) immediately after the master communication device 10 is started, and thereafter is the size changed or restored (to the maximum size) immediately before.

[0054] Next, the controller 12 of the master communication device 10 determines whether or not retransmission of the communication frame is necessary based on whether or not there is a reply (a confirmation signal for data reception) from the slave communication device 20 to which the communication frame is to be transmitted (step S2). If there is no reply from the slave communication device 20 to which the communication frame is to be transmitted, it is determined that retransmission of the communication frame is necessary, and the process proceeds to step S3. If there is a reply from the slave communication device 20 to which the communication frame is to be transmitted, it is determined that retransmission of the communication frame is not necessary, and the process proceeds to step S6.

[0055] In step S3, the controller 12 of the master communication device 10 determines whether or not radio wave interference has occurred. There are various possible criteria for determining whether or not radio wave interference has occurred.

[0056] In a first example of a criterion for determining whether radio wave interference has occurred, if a communication error (an event in which communication fails even after retransmission of a communication frame) occurs N times in succession (N is any integer greater than or equal to 2), it is determined that radio wave interference has occurred.

[0057] In a second example of the criterion for determining whether radio interference has occurred, it is determined that radio interference has occurred when the communication error rate is equal to or greater than a threshold value.

[0058] In a third example of the criteria for determining whether radio wave interference has occurred, it is determined that radio wave interference has occurred when the frequency of receiving communication data transmitted from a UWB communication system (other system) other than communication system SYS1 exceeds a threshold value. Whether the received communication data is from communication system SYS1 or another system can be determined by analyzing the preamble or PHR included in the communication data.

[0059] After it is determined in step S3 that radio wave interference has occurred, it is assumed that radio wave interference continues until it is determined in step S6 that the condition for returning the size of the data body of the communication frame to the size before the change is met, and it is not determined in step S3 that radio wave interference has (newly) occurred.

[0060] If it is determined in step S3 that radio wave interference has occurred, the size change unit 121 of the master communication device 10 changes the size of the data body of the communication frame to be transmitted next and thereafter (step S4). When the processing of step S4 is completed, the processing proceeds to step S5. If the other system is configured to always fix the size of the data body of the communication frame to the maximum size (127 bytes), the above change causes a difference in the timing of retransmission between the communication system SYS1 and the other system, thereby reducing the risk of radio wave interference during retransmission. Therefore, the communication success rate during retransmission can be improved. Furthermore, by making the above change when it is determined that radio wave interference has occurred, it is possible to prevent a decrease in communication efficiency caused by the above change (size reduction) being made when radio wave interference is not occurring.

[0061] In this embodiment, the size change unit 121 randomly changes the size of the data body of the communication frame to be transmitted next and thereafter. Even if the other system has the same configuration as the communication system SYS1, the random change in the data body size increases the possibility of a mismatch in the timing of retransmission between the communication system SYS1 and the other system, thereby reducing the risk of radio wave interference during retransmission. Therefore, the communication success rate during retransmission can be improved. FIG. 8 is a diagram schematically showing a communication frame (target wave) transmitted by the master communication device 10 of the communication system SYS1 and a communication frame (interference wave) transmitted by a master communication device of the other system when the random change is performed. Note that in FIG. 8, the preamble, SFD, and PHR are displayed with a mesh pattern, as in FIG. 4. The sizes of the data bodies TGD1 to TGD4 of the target wave shown in FIG. 8 are different due to the random change and are smaller than the size (127 bytes) of the data bodies INFD1 to INFD4 of the interference wave. When performing the above-mentioned random change, for example, the size change unit 121 of the master communication device 10 generates a random number in the range of 1 to 10 for each communication frame to be transmitted from the next time onwards, and changes the size of the data body of the communication frame to be transmitted from the next time onwards to a size associated with the random number (for example, 273-K×random number, where K is a constant).

[0062] In step S5, the retransmission instruction unit 122 of the master communication device 10 instructs the wireless communication unit 11 to retransmit the communication frame. When the processing of step S5 is completed, the process proceeds to step S6.

[0063] In step S6, the size change unit 121 of the master communication device 10 determines whether or not a condition for restoring the size of the data body of the communication frame to be transmitted next or thereafter is satisfied. Various criteria can be considered for determining whether or not the above-mentioned condition for restoring is satisfied.

[0064] In a first example of the criteria for determining whether the above-mentioned return condition is satisfied, if a certain amount of time has passed since it was determined in step S3 that radio interference occurred, it is determined that the above-mentioned return condition is satisfied because there is a possibility that the radio interference has been resolved. In this first example, whether the above-mentioned return condition is satisfied can be determined simply by measuring the time, making the determination easier.

[0065] In a second example of a criterion for determining whether the above-mentioned return condition is satisfied, if the position of the master communication device 10 moves a certain distance from the position of the master communication device 10 when it was determined in step S3 that radio wave interference occurred, it is possible that the radio wave interference has been resolved, and therefore it is determined that the above-mentioned return condition is satisfied. In this second example, it is possible to determine whether the above-mentioned return condition is satisfied simply by obtaining the position information of the master communication device 10, making the determination easier. As a method for obtaining the position information of the master communication device 10, for example, the master communication device 10 may obtain position information of the automobile V1 obtained by a GPS (Global Positioning System) system installed in the automobile V1 via a wired communication network within the automobile V1, and use the position information of the automobile V1 as the position information of the master communication device 10.

[0066] In a third example of a criterion for determining whether the above-mentioned return condition is satisfied, UWB communications of other systems are monitored during a state in which there is no UWB communication in the communication system SYS1 (a period during which neither the master communication device 10 nor the slave communication device 10 is transmitting), and whether the above-mentioned return condition is satisfied is determined based on the results of monitoring the UWB communications of other systems. Possible methods for monitoring the UWB communications of other systems include detecting the carrier of the UWB communications of other systems and monitoring the reception status of UWB communications packets of other systems. For example, if the carrier of the UWB communications of other systems is not detected, the above-mentioned return condition is determined to be satisfied. Furthermore, for example, the temporal reception ratio of UWB communications packets of other systems is calculated, and if the reception ratio is less than a threshold, the above-mentioned return condition is determined to be satisfied. In this third example, the above-mentioned return condition is determined to be satisfied only after indirectly confirming that radio interference has been resolved, thereby preventing frequent repetition of changing the size of the data body of the communication frame and then returning it to its pre-change state.

[0067] In a fourth example of the criteria for determining whether the above-mentioned restoration condition is satisfied, it is determined that the above-mentioned restoration condition is satisfied if the radio interference is not reduced. In this fourth example, the size of the data body of the communication frame is restored to its pre-change state, thereby preparing in advance for improved communication efficiency when the radio interference is eliminated. Note that, in determining whether the radio interference is reduced, it is determined that the radio interference is not reduced if, for example, the parameter (e.g., communication error rate) used in the determination in step S3 does not improve to a certain level.

[0068] If it is determined in step S6 that the above-mentioned condition for restoring is satisfied, the process proceeds to step S7. In step S7, the size change unit 121 of the master communication device 10 restores the size of the data body of the communication frame to be transmitted next time onwards (changes it to the maximum size (127 bytes)).

[0069] If it is determined in step S6 that the above return condition is not satisfied, the process proceeds to step S8.

[0070] In step S8, the controller 12 of the master communication device 10 monitors UWB communications of other systems when there is no UWB communication in the communication system SYS1 (a period when neither the master communication device 10 nor the slave communication device 10 is transmitting). The UWB communications of other systems may be monitored by the wireless communication unit 11, or the master communication device 10 may acquire the results of monitoring performed outside the master communication device 10. Possible methods for monitoring UWB communications of other systems include, for example, detecting the carrier of UWB communications of other systems, or monitoring the reception status of UWB communications packets of other systems. Note that, if the third example of the criteria for determining whether the return condition is satisfied is not executed, step S8 may be omitted. Since UWB communications of other systems are monitored when there is no UWB communication in the communication system SYS1 (a period when neither the master communication device 10 nor the slave communication device 10 is transmitting), the timing for monitoring UWB communications of other systems is as shown in FIG. 9. When the process of step S8 is completed, the controller 12 of the master communication device 10 switches to the next transmission target (step S9). When the process of step S9 is completed, the process returns to step S1.

[0071] <7. Modified Communication Method> Time slot communication may be performed between the master communication device 10 and the plurality of slave communication devices 20a to 20d. When time slot communication is performed between the master communication device 10 and the plurality of slave communication devices 20a to 20d, normal UWB communication between the master communication device 10 and the plurality of slave communication devices 20a to 20d includes (i) a synchronous communication phase, (ii) an initial communication phase, and (iii) a periodic communication phase, and processing proceeds in the order of (i) the synchronous communication phase, (ii) the initial communication phase, and (iii) the periodic communication phase.

[0072] When time slot communication is performed between the master communication device 10 and multiple slave communication devices 20a to 20d, the controller 12 of the master communication device 10 and the controller 22 of the slave communication device 20 each have a mode setting instruction unit as a functional unit thereof. The mode setting instruction unit of the controller 12 sets the mode of the wireless communication unit 11. The wireless communication unit 11 is capable of receiving when in the receive mode, capable of transmitting when in the transmit mode, and is unable to communicate when in neither the receive mode nor the transmit mode. The mode setting instruction unit of the controller 22 sets the mode of the wireless communication unit 21. The wireless communication unit 21 is capable of receiving when in the receive mode, capable of transmitting when in the transmit mode, and is unable to communicate when in neither the receive mode nor the transmit mode.

[0073] [Synchronous communication phase] Fig. 10 is a flowchart showing an example of operation of the master communication device 10 in the synchronous communication phase. The operation shown in Fig. 10 is started, for example, when a body ECU installed in the automobile V1 that controls the body of the automobile V1 is started. Specifically, the body ECU controls on-board devices other than vehicle driving devices such as the engine. On-board devices other than vehicle driving devices include, for example, an air conditioner, a door lock device, a window opening / closing device, a wiper device, etc.

[0074] The body ECU is typically activated when the doors of the automobile V1 are unlocked. Another example is when the ACC is turned on by operating the vehicle's ignition key. When the communication system is applied to other mobile objects (e.g., trains, ships, aircraft, etc.), the start timing of the operation shown in FIG. 10 may be the start timing of the mobile object drive system. The operation shown in FIG. 10 may be executed after the body ECU is activated, for example, as a periodic operation (e.g., an operation executed immediately after activation, an operation executed at predetermined time intervals), or as an exceptional operation (e.g., an operation executed when communication failures occur or increase in frequency, or when there is a change in the vehicle (communication) environment). At least one of the master communication device 10 and the slave communication devices 20a to 20d may be a body ECU (or a component included in a body ECU), and not all of the master communication device 10 and the slave communication devices 20a to 20d may be body ECUs. The body ECU may be, for example, an entertainment device such as an audio device.

[0075] In step S11, the controller 12 creates a wireless communication schedule. The wireless communication schedule includes the time (period) for transmitting data from the master communication device 10 to each of the slave communication devices 20a to 20d, and the time (period) for receiving data from the master communication device 10 from each of the slave communication devices 20a to 20d. That is, various settings required for well-known time slot communication are made, such as the communication cycle for periodic communication and slot settings for each slave communication device 20 (communication period settings for periodic communication periods). Once the wireless communication schedule is created, the process proceeds to the next step S12. Note that information regarding the wireless communication connections of each of the slave communication devices 20a to 20d, which are wireless communication target devices, is set and registered (stored) in the master communication device 10 by an administrator or the like of the master communication device 10. Furthermore, when a new wireless communication target device is added, the additional device is set and registered (stored) by an administrator or the like.

[0076] In step S12, the controller 12 broadcasts the wireless communication schedule to all of the slave communication devices 20a to 20d via the wireless communication unit 11. That is, in this embodiment, the communication system SYS1 (vehicle communication system) determines the expected reception time and the like between the master communication device 10 and each slave communication device 20 when the vehicle starts to be used. The wireless communication schedule is broadcast in accordance with the communication frame format (see FIG. 2) of the UWB communication described above. The wireless communication schedule is included in the data body of the communication frame format.

[0077] Fig. 11 is a diagram showing an example of a data format of a wireless communication schedule. Note that Fig. 11 omits synchronization signals and the like and shows only the data body portion. As shown in Fig. 11, the data format of the wireless communication schedule has a structure in which time data D1, first data D2a, second data D2b, third data D2c, fourth data D2d, and cycle data D3 are connected in order.

[0078] The time data D1 indicates the time when the broadcast transmission was actually performed (hereinafter referred to as the broadcast transmission time). The broadcast transmission time is measured by the controller 12 based on a timer (not shown) built into the master communication device 10. The timer is configured with a counter or the like that counts at regular time intervals based on an operating clock.

[0079] The first data D2a is data related to the slave communication device 20a. The second data D2b is data related to the slave communication device 20b. The third data D2c is data related to the slave communication device 20c. The fourth data D2d is data related to the slave communication device 20d.

[0080] Each of the data D2a to D2d has a structure in which ID data D21 and time data D22 are connected in order. The ID data D21 is data indicating the ID (identification information) of each of the slave communication devices 20a to 20d. The time data D22 is data indicated by a time interval (length of time) based on the broadcast transmission time, and is data related to the transmission time of data from the master communication device 10 and the reception time of data by the master communication device 10. The transmission time and reception time are expressed in a format such as how many milliseconds after the broadcast transmission time. The transmission time and reception time are not transmitted as absolute time because there is a possibility that the recognized times (times measured by the timers of each device) may not match among the communication devices 10, 20a to 20d.

[0081] The cycle data D3 indicates a system communication cycle between the master communication device 10 and each of the slave communication devices 20a to 20d. Communication between the master communication device 10 and each of the slave communication devices 20a to 20d is repeated in this system communication cycle until the communication is completed (until a series of data communications is completed, until the upper communication limit time (a predetermined number of system communication cycles) has elapsed, etc.).

[0082] Returning to FIG. 10, once the wireless communication schedule is broadcast, the process proceeds to the next step S13.

[0083] In step S13, the controller 12 determines whether or not a reception response has been received from all of the slave communication devices 20a to 20d to which the wireless communication schedule was transmitted. The reception response is a reply indicating that the wireless communication schedule was received, and is a process that is requested of each of the slave communication devices 20a to 20d that received the wireless communication schedule. Since the request is included in the data of the wireless communication schedule described above, the slave communication device 20 that received the wireless communication schedule will return a response unless it is malfunctioning. However, due to reasons such as the occurrence of radio wave interference described above, it is possible that some of the slave communication devices 20a to 20d will fail to receive the wireless communication schedule. In particular, before the broadcast transmission, each of the slave communication devices 20a to 20d does not have a wireless communication schedule and therefore cannot be set to the reception mode at the appropriate timing described above. Therefore, it is necessary to remain in the reception mode for a long period of time, which makes them susceptible to the effects of radio wave interference.

[0084] If a reception response has been received from all of the slave communication devices 20a to 20d (Yes in step S13), the process proceeds to the next step S14. On the other hand, if a reception response has not been received from any of the slave communication devices 20a to 20d (No in step S13), the process returns to step S11. That is, if there is no reception response from all of the devices 20a to 20d targeted for the broadcast transmission of the wireless communication schedule, the wireless communication schedule is broadcast again. This configuration can prevent the wireless communication schedule from being executed in a state in which the wireless communication schedule has not been properly transmitted from the master communication device 10 to the slave communication devices 20. Note that if the wireless communication schedule is rebroadcast using the periodic data D3, the reception mode timing of each of the slave communication devices 20a to 20d according to the wireless communication schedule in the rebroadcast transmission will ultimately be the same. Therefore, it is possible to set the communication timing with each of the slave communication devices 20a to 20d not only when a reception response is received from all slaves in the same broadcast transmission, but also when a reception response is received from all slaves in multiple broadcast transmissions.

[0085] In step S14, the controller 12 determines the wireless communication schedule. Once the wireless communication schedule is determined, the master communication device 10 ends the processing in the synchronous communication phase.

[0086] In the configuration of this embodiment, for example, if at least one of the multiple slave communication devices 20a to 20d is malfunctioning, the result of the process in step S13 will not be "Yes," and the wireless communication schedule will never be determined. In consideration of this, for example, if the result of the process in step S13 is not "Yes" even after broadcast transmission has been performed a predetermined number of times (e.g., three times), an error may be notified. As another example, a wireless communication schedule may be created that excludes the malfunctioning slave communication devices 20a to 20d, and wireless communication processing may be performed in accordance with this schedule.

[0087] Fig. 12 is a flowchart showing an example of the operation of the slave communication device 20 in the synchronous communication phase. Note that in this embodiment, there are multiple slave communication devices 20, and similar operations are performed in each of the slave communication devices 20a to 20d. The operation shown in Fig. 12 is started in synchronization with the operation of the master communication device 10 described above (see Fig. 11). That is, the operation shown in Fig. 12 is started, for example, when the body ECU is started (for example, when power supply begins upon start-up of the automobile V1). The operation shown in Fig. 12 may also be executed, for example, as a regular operation or an exceptional operation after the body ECU is started.

[0088] In step S21, the controller 22 determines whether or not a wireless communication schedule has been received. If a wireless communication schedule has been received (Yes in step S21), the process proceeds to the next step S12. On the other hand, if a wireless communication schedule has not been received (No in step S21), the process of step S21 is repeated. That is, in step S21, it is monitored whether or not a wireless communication schedule has been received.

[0089] In step S22, the controller 22 replies that it has received the wireless communication schedule. In detail, the controller 22 replies that it has received the wireless communication schedule in response to a reply request from the master communication device 10 contained in the data including the wireless communication schedule. The reply is transmitted from the slave communication device 20 to the master communication device 10 using UWB communication. When the reply that the wireless communication schedule has been received is completed, the process proceeds to the next step S23.

[0090] In step S23, the controller 22 converts schedule information, such as the transmission time, reception time, and time slot time (for example, the time indicated in the format of how many milliseconds later) assigned to the device itself based on the broadcast transmission time etc. included in the wireless communication schedule, into the time of the device itself. The controller 22 performs a time conversion process based on a timer (not shown) built into the device itself. Specifically, for example, the received wireless communication schedule is corrected by the difference between the broadcast transmission time included in the wireless communication schedule and the reception time of the broadcast transmission signal (measured by a timer built into the device itself). When the time conversion process is completed, the process proceeds to the next step S24.

[0091] In step S24, the controller 22 finalizes the wireless communication schedule with the time-converted information and stores it in the memory 23. Note that instead of the processes of steps S23 and S24, the schedule information may be finalized without time conversion and stored in the memory 23, and the timer built into the device may be corrected (time-synchronized) with the broadcast transmission time, etc. Once the wireless communication schedule is finalized, the slave communication device 20 ends the processing in the synchronous communication phase.

[0092] [Initial communication phase] When the synchronous communication phase ends, the process proceeds to the initial communication phase. When a time slot has elapsed since the end of the synchronous communication phase, the master communication device 10 starts processing the initial communication phase. The length (time) until the initial communication phase is the length (time) until the time slot assigned to the slave communication device 20a. The time length of the time slot is the same for each of the slave communication devices 20a to 20d.

[0093] The initial communication phase is performed during a communication time period in a time slot assigned to the slave communication device 20a, and the master communication device 10 also communicates with the slave communication device 20a. In other words, the initial communication phase can also be considered periodic communication with the slave communication device 20a. Furthermore, during the initial communication phase, the master communication device 10 also broadcasts and transmits data to each of the slave communication devices 20a to 20d. For example, data intended for the slave communication device 20a is broadcast to the slave communication devices 20a to 20d. This allows not only the slave communication device 20a but also the slave communication devices 20b to 20d to recognize that periodic communication (time slot communication) has begun and that the periodic communication phase will soon begin.

[0094] After transmitting a response in the synchronous communication phase, the slave communication devices 20a to 20d are in the reception mode until they receive the broadcast transmission in the initial communication phase, which allows the slave communication devices 20a to 20d to receive the broadcast transmission from the master communication device 10 in the initial communication phase.

[0095] If there is no reply from the slave communication device 20a to the master communication device 10 in the initial communication phase, the initial communication phase is repeated. However, for example, in the second initial communication phase, broadcast transmission is performed in the time slot for data transmission to the slave communication device 20b, and in the third initial communication phase, broadcast transmission is performed in the time slot for data transmission to the slave communication device 20c. Furthermore, the same operation is repeated in the subsequent system communication cycle until all replies from the slave communication devices 20a to 20d to the master communication device 10 have been received. Note that, for example, if there is any slave communication device 20a to 20d that has not replied even after multiple (e.g., three) system communication cycles have elapsed, an error may be notified.

[0096] [Cyclic communication phase] When the initial communication phase ends, the system proceeds to the periodic communication phase. Fig. 13 shows the state of data communication in the periodic communication phase. In the periodic communication phase, the master communication device 10 communicates with each of the slave communication devices 20a to 20d in turn according to the wireless communication schedule, using the time slots TS20a to TS20d assigned to each of them. That is, in the periodic communication phase, the master communication device 10 communicates with the slave communication device 20a in the first communication period (time slot TS20a) in the periodic communication phase, the master communication device 10 communicates with the slave communication device 20b in the second communication period (time slot TS20b) in the periodic communication phase, the master communication device 10 communicates with the slave communication device 20c in the third communication period (time slot TS20c) in the periodic communication phase, and the master communication device 10 communicates with the slave communication device 20d in the fourth communication period (time slot TS20d) in the periodic communication phase, and these communications continue periodically at the system communication period SYS_PD. In the first periodic communication phase after the initial communication phase, since communication between the master communication device 10 and the slave communication device 20a is carried out in the time slot TS20a in the initial communication phase, communication between the master communication device 10 and the slave communication device 20b will be carried out in the next time slot TS20b.

[0097] When communication between the master communication device 10 and the slave communication device 20a fails and retransmission is required, the master communication device 10 performs the retransmission within the time slot TS20a assigned to the slave communication device 20a.

[0098] The same operation is performed when communication between the master communication device 10 and the slave communication devices 20b, 20c, and 20d fails and retransmission is performed.

[0099] The operation of the master communication device 10 in the periodic communication phase is basically the same as that shown in Fig. 7, but the size of the data body is changed only for retransmitted data. In other words, in the communication of the time slot in the next communication period, communication is first performed with the original size of the data body (the size of the data body is changed for the retransmission). As a result, even if the size of the data body is changed, wireless communication is performed in accordance with the wireless communication schedule created in the synchronous communication phase.

[0100] <8. Points to note> Various technical features disclosed in the description of the present invention may be modified in various ways without departing from the spirit of the technical creation. Furthermore, multiple embodiments and modifications disclosed in the description of the present invention may be combined to the extent possible.

[0101] For example, in the above-described embodiment, after it is determined in step S3 that radio wave interference has occurred, the size of the data body of the communication frame is changed until it is determined in step S6 that the condition for returning the size of the data body of the communication frame to the size before the change is met, but the size of the data body of the communication frame may be constantly changed relative to the default (e.g., maximum size).

[0102] For example, in the above-described embodiment, the size of the data body of the communication frame is changed randomly, but the size change unit 121 of the master communication device 10 may monitor UWB communications of other systems when there is no UWB communication in the communication system SYS1 (a period when neither the master communication device 10 nor the slave communication device 10 is transmitting), and determine the size of the data body of the communication frame based on the results of monitoring the UWB communications of the other systems. In this case, the size of the data body of the communication frame in the other systems is estimated from the results of monitoring the UWB communications of the other systems, and the size of the data body of the communication frame is changed so that it differs from the estimated size. This makes it possible to reduce the risk of radio wave interference during retransmission more reliably than random change. [Explanation of symbols]

[0103] 10. Master communication device 20, 20a to 20d: Slave communication device SYS1: Communication System V1...Automotive

Claims

1. A communication method for changing the size of a data body in the format of one unit of transmission data in UWB communication.

2. The communication method according to claim 1 , wherein the size of the data body is changed randomly.

3. The communication method according to claim 1 , further comprising changing the size of the data body for transmission after radio interference has occurred.

4. The communication method according to claim 1 , wherein the size of the data body before the change is fixed to a maximum size.

5. 5. The communication method according to claim 1, wherein the size of the data body is restored to the size before change when time passes or when a change occurs in the position of the communication device transmitting the transmission data.

6. The communication method according to any one of claims 1 to 4, further comprising monitoring other UWB communications in the absence of said UWB communications, and restoring the size of said data body to the size before change based on the monitoring results of said other UWB communications.

7. 5. The communication method according to claim 1, wherein if radio interference is not reduced, the size of the data body is returned to the size before the change.

8. 2. The communication method according to claim 1, further comprising monitoring other UWB communications in a state where the UWB communications are not being performed, and determining a size to which the data body is to be changed based on a result of monitoring the other UWB communications.

9. A master communication device in a UWB communication system configured with a master communication device and a plurality of slave communication devices, changing the size of the data body in the format of one unit of transmission data to be transmitted to the slave communication device; Master communication device.

10. A program used in a master communication device in a UWB communication system configured with a master communication device and a plurality of slave communication devices, causing the master communication device to change the size of a data body in the format of one unit of transmission data to be transmitted to the slave communication device; program.

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