Communication device, method for communication, and communication system

Abstract

To provide a technique of improving the communication success rate in a radio communication while suppressing increase of cost or decrease of communication efficiency.SOLUTION: An exemplary communication device is a slave communication device for performing communication with a master communication device by using a preamble, and switches, on the basis of a success / failure situation of communication, between a first receiving manner and the second receiving manner, the first receiving manner being for starting and ending reception according to the transmission timing of the master communication device and the second receiving manner being for maintaining the receiving state regardless of the transmission timing of the master communication device.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a communication technology for communication using wireless 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 (Ultra Wide Band) communications, which use radio waves in the 8 GHz band, are seeing widespread use due to their low interference with radio waves used by Wi-Fi (registered trademark) and mobile devices such as smartphones, and their excellent transparency over a wide 500 MHz band.

[0003] UWB communication is expected to be a useful communication method for in-vehicle devices because it can easily be established inside a vehicle, even in the narrow, metal space with many wires. For example, Patent Document 1 discloses that both the vehicle and the electronic key send UWB radio waves to each other in a random pattern to perform distance verification. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2016-38332 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as UWB communication becomes more widespread, interference between UWB communications is likely to occur, which could lead to communication disruptions. This communication disruption problem is not limited to in-vehicle device communication methods and UWB communications, but can also occur when multiple devices communicate using radio waves in the same frequency band.

[0006] An effective method for preventing interference in wireless communications is to coordinate communication timing between communicating devices in advance, and start reception on the receiving side just before the expected reception time. This method requires sharing timing information in advance, but it has the following problems:

[0007] If timing information is shared wirelessly, there is a risk that it will not be transmitted due to interference from other wireless communications. It is also possible to share timing information via wired communication, but this requires wired communication equipment in addition to wireless communication, which raises concerns about increased costs. Furthermore, if the receiving device is restarted after the timing information is shared, the timing information may not be recognized and reception may become impossible. To address this issue, the transmitting side could repeatedly transmit timing information, but this would increase the amount of communication traffic, which raises concerns about reduced communication efficiency.

[0008] In view of the above, an object of the present invention is to provide a technique that can improve the communication success rate in wireless communication while suppressing increases in costs and decreases in communication efficiency. [Means for solving the problem]

[0009] An exemplary communication device of the present invention is a slave communication device that communicates with a master communication device using a preamble, and switches between a first reception method in which reception starts and ends in accordance with the transmission timing of the master communication device, and a second reception method in which reception continues regardless of the transmission timing of the master communication device, based on the success or failure of communication. [Effects of the Invention]

[0010] According to the exemplary embodiment of the present invention, when the timing information of communication with the master communication device is unknown, the slave communication device can receive a transmission signal from the master communication device by using the second reception method, which continues the reception state. That is, according to the exemplary embodiment of the present invention, the slave communication device can communicate with the master communication device without exchanging timing information with the master communication device in advance, which could result in communication failure or increased costs. Furthermore, when the slave communication device has already been able to receive a transmission signal from the master communication device and the transmission timing is known, the slave communication device can use the first reception method, which starts and ends reception in accordance with the transmission timing of the master communication device. That is, the slave communication device can basically start and end reception in accordance with the transmission timing of the master communication device, thereby reducing interference with other communications and improving the communication success rate. [Brief explanation of the drawings]

[0011] [Figure 1] A diagram showing an example of the configuration of a communication system. [Figure 2] A block diagram showing the general configuration of a master communication device. [Figure 3] A block diagram showing the general configuration of a slave communication device. [Figure 4] Schematic diagram to explain problems with reception in UWB communications [Figure 5] Schematic diagram showing an overview of radio interference countermeasures in communication systems [Figure 6] FIG. 10 is a schematic diagram illustrating a detailed example of how to set the reception mode start time. [Figure 7] FIG. 10 is a diagram for explaining the basic operation of a master communication device and a slave communication device in the first embodiment. [Figure 8] Flowchart showing the basic operation of the master communication device [Figure 9] Flowchart showing the basic operation of the slave communication device [Figure 10] FIG. 1 is a diagram for explaining the operation of a master communication device and a plurality of slave communication devices. [Figure 11] FIG. 10 is a diagram for explaining the operation of a master communication device and a slave communication device when other systems are mixed. [Figure 12] FIG. 10 is a flowchart showing a preferred modification of the basic operation in the first embodiment. [Figure 13] FIG. 10 is a diagram for explaining a modified example of the first embodiment. [Figure 14] FIG. 1 is a schematic diagram for explaining the cause of signal reception failure when using the first reception method; [Figure 15] FIG. 10 is a diagram for explaining the operation of a master communication device and a slave communication device in the second embodiment. [Figure 16] 10 is a flowchart showing the operation of the master communication device in the second embodiment. [Figure 17] 10 is a flowchart showing the operation of a slave communication device in the second embodiment. [Figure 18] Schematic diagram for explaining changes to the preamble code [Figure 19] 10 is a flowchart showing the operation of the master communication device in the third embodiment. [Figure 20] 10 is a flowchart showing the operation of a slave communication device in the third embodiment. [Figure 21] Schematic diagram showing timing deviation due to component errors in crystal oscillators [Figure 22] FIG. 10 is a diagram illustrating a basic pattern according to a fourth embodiment. [Figure 23] FIG. 23 is a diagram illustrating a first modified example of the basic pattern shown in FIG. 22. [Figure 24] FIG. 23 is a diagram illustrating a second modified example of the basic pattern shown in FIG. 22. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] <1. Communication Systems> [1-1. Overview] 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 C1. However, the communication system SYS1 may also be applied to an installation target of communication equipment other than the automobile C1, for example, to general mobile objects other than automobiles, home communication equipment, office communication equipment, or factory communication equipment. In addition to automobiles, general mobile objects include, for example, trains, ships, and airplanes.

[0014] 1, the communication system SYS1 includes a master ECU (Electric Control Unit) 10 and a plurality of slave devices 20a to 20d. The master ECU 10 is provided in, for example, a central control device (a so-called head unit) that controls the slave devices 20a to 20d, which are various types of on-board equipment in an automobile C1. The master ECU 10 is an example of an on-board control device mounted on a vehicle according to the present invention.

[0015] The communication system SYS1 is, for example, a vehicle system in which a master ECU 10 controls each of slave devices (on-board devices) 20a to 20d by wireless communication in response to user operations on an HMI (Human Machine Interface) 40. Specifically, each of the slave devices 20a to 20d transmits sensor values 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.

[0016] The first slave device 20a is, for example, a control device that controls the operation of headlights. The second slave device 20b is, for example, a control device that controls the operation of wipers. The third slave device 20c is, for example, a control device that controls the operation of power windows. The fourth slave device 20d is, for example, a control device that controls the operation of an air conditioner.

[0017] Because wireless 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. In other words, the communication system SYS1 includes the master communication device 10 and the slave communication device 20. 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 will be simply referred to as the slave communication device 20.

[0018] In this embodiment, there are multiple slave communication devices 20, but there may also be one. In a narrow 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, meaning that the master communication device communicates with at least one slave communication device, and each slave communication device communicates with the master communication device. In other words, the multiple communication devices included in the communication system SYS1 do not necessarily have to have a master-slave relationship in the strict sense, but may have an equal relationship with each other.

[0019] In this embodiment, the master communication device 10 communicates with the slave communication device 20 using a preamble. In other words, the slave communication device 20 communicates with the master communication device 10 using a preamble. More specifically, the master communication device 10 and the slave communication device 20 perform UWB communication. That is, the communication used by the communication devices 10 and 20 in this embodiment is wireless communication using the UWB communication method. In UWB communication, 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 C1.

[0020] The communication used by the communication devices 10 and 20 included in the communication system SYS1 may be communication using a preamble (preamble communication). The communication used by the communication devices 10 and 20 may be communication using a preamble other than UWB communication. The communication used by the communication devices 10 and 20 may be, for example, Wi-Fi (registered trademark) communication, Bluetooth (registered trademark) communication, BLE (registered trademark, Bluetooth Low Energy) communication, LPWA (Low Power Wide Area) communication, Zigbee (registered trademark) communication, etc.

[0021] 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.

[0022] [1-2. Master communication device] Fig. 2 is a block diagram showing a schematic configuration of the master communication device 10. Note that Fig. 2 shows components necessary for explaining the features of this embodiment, and omits descriptions of general components.

[0023] As shown in FIG. 2, the master communication device 10 includes a wireless communication unit 11, a controller 12, and a memory 13.

[0024] The wireless communication unit 11 performs UWB communication with a wireless communication unit 21 (see FIG. 3 described later) included in the slave communication device 20. That is, the wireless communication unit 11 is configured as a UWB communication device. The wireless communication unit 11 is configured to be able to select one of a reception mode, a transmission mode, and a mask mode. The wireless communication unit 11 is capable of receiving when in the reception mode, capable of transmitting when in the transmission mode, and is unable to communicate when in the mask mode, which is neither the reception mode nor the transmission mode. The mask mode is a so-called idle mode in which power is supplied to necessary circuits, etc., and the unit can immediately switch to the reception mode or the transmission mode.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 2, in this embodiment, the controller 12 has, as its functional units, a transmission control unit 121 and a reception control unit 122. The transmission control unit 121 performs control related to transmission using the wireless communication unit 11. The reception control unit 122 performs control related to reception using the wireless communication unit 11.

[0031] Each of the functional units 121 and 122 is a conceptual component. A function executed by one component may be distributed among multiple components. Furthermore, the functions of multiple components may be integrated into one component.

[0032] [1-3. Slave communication device] Fig. 3 is a block diagram showing a schematic configuration of the slave communication device 20. Note that Fig. 3 shows components necessary for explaining the features of this embodiment, and omits descriptions of general components.

[0033] 3, the slave communication device 20 includes a wireless communication unit 21, a controller 22, and a memory 23. The controller 22 includes, as functional units, a transmission control unit 221 and a reception control unit 222. The wireless communication unit 21, the controller 22, and the memory 23 have the same configurations as the wireless communication unit 11, the controller 12, and the memory 13 included in the master communication device 10 described above. For this reason, detailed descriptions of the wireless communication unit 21, the controller 22, and the memory 23 will be omitted.

[0034] [1-4. Radio interference countermeasures] An overview of radio wave interference countermeasures in the communication system SYS1 will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a schematic diagram for explaining problems that occur during reception in UWB communication. Fig. 5 is a schematic diagram showing an overview of radio wave interference countermeasures in the communication system SYS1. In Fig. 5, "master" refers to the master communication device 10, and "slave" refers to the slave communication device 20. Similar abbreviated expressions may also be used in other figures.

[0035] The format of a communication frame for UWB communication (hereinafter referred to as the communication frame format) is determined by the above-mentioned communication standard. A communication frame is also called a packet, as it is a unit of transmitted data. As shown in Figure 4, the frame format used in UWB communication has a structure in which a preamble begins, followed by an SFD (Start Frame Delimiter), a PHR (PHY Header), and the data body, in that order. The term "data body" is used to make it easier to understand the difference between the preamble, SFD, and PHR.

[0036] In digital communications, a preamble is transmitted before the data itself to inform the receiving end that "data is about to be sent." A preamble is a bit string with a specific pattern, or a sequence made up of pulses (for example, -, 0, +). The receiving end uses the preamble signal to start (synchronize) the receiving clock. There are multiple patterns in the preamble. A preamble code is a code for identifying these multiple patterns. Different preamble codes use different code symbols. Code symbols are made up of ternary symbols (for example, -, 0, +). One code symbol (1 symbol) has a structure such as "-+0++000-+-++00++0+00-0000-0+0-."

[0037] The SFD is a bit string with a specific pattern that signals the start of data in a communication frame. The PHR contains information (header information) necessary for decoding the 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 sent to the communication partner and contains the actual data to be transmitted. For example, the data body contains information such as ID information of the recipient and sender of the communication frame, instruction information from the master communication device 10 to the slave communication device 20, sensor values detected by sensors equipped in the slave communication device 20, and the operating status of the actuator to be controlled by the slave communication device 20.

[0038] In Figure 4, the target wave is the radio wave that you want to receive at the receiving antenna RA1. The jamming wave is the radio wave that you do not want to receive at the receiving antenna RA1. In UWB communication, the strength of the radio wave also has an effect, but the radio wave that is received first is generally processed first. Once the communication device enters synchronization processing for the preceding radio wave, it cannot process the subsequent radio wave.

[0039] In FIG. 4, the horizontal axis represents the distance from the receiving antenna RA1. The dashed line in FIG. 4 indicates the zero distance position. The target wave is located farther from the receiving antenna R1 than the jamming wave. In FIG. 4, two radio waves arrive at the receiving antenna RA1 in the order of the jamming wave and the target wave. 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 reception processing of other waves (such as the subsequent target wave) becomes possible. There is a possibility that the target wave will arrive at the receiving antenna RA1 before the radio wave is identified as a jamming wave through reception processing. In this case, the target wave will not be received. In this embodiment, measures are implemented to reduce communication failures due to such radio wave interference. An overview of these measures will be described with reference to FIG. 5.

[0040] 5, τstart is the time when the communication devices 10, 20 start the reception mode (reception mode start time). τnext is the time when the target wave is expected to be received (estimated reception time), and is a time that conforms to an agreement between the communication devices 10, 20. The reception mode start time τstart is set slightly before the expected reception time τnext. For example, the reception mode start time τstart is set relative to the expected reception time τnext, taking into consideration the length of time it takes for the reception circuit to stabilize and enable good reception after the communication devices 10, 20 start the reception mode.

[0041] 5, the master communication device 10 switches from mask mode to reception mode immediately before the expected reception time agreed upon with the slave communication device 20. Also, the slave communication device 20 switches from mask mode to reception mode immediately before the expected reception time agreed upon with the master communication device 10. That is, the communication method using wireless communication according to this embodiment uses a reception scheme in which the mask mode, in which wireless communication is not possible, is switched to the reception mode, in which wireless communication reception is possible, immediately before the expected reception time agreed upon between the multiple devices 10, 20 performing wireless communication.

[0042] This configuration increases the probability that the device receiving the target wave will be in mask mode when a jamming wave arrives. In other words, it reduces the possibility of receiving a jamming wave and increases the probability that the target wave will be properly received. This improves the success rate of wireless communication. It is preferable to start the receive mode as close as possible to the expected time of reception of the target wave. An example of this is described below.

[0043] FIG. 6 is a schematic diagram for explaining a detailed example of how to set the reception mode start time τstart. In the communication standard for UWB communication, the transmission and reception times (times) can be obtained at the timing of the PHR. Taking this into consideration, as shown in FIG. 6, the expected reception time τnext is determined based on the PHR included in the frame format used in wireless communication. This makes it easier to set the reception mode start time τstart to an appropriate timing that can reduce the probability of interference from interfering waves in UWB wireless communication. In detail, the expected reception time τnext is set to the start timing of the PHR.

[0044] In the example shown in FIG. 6, the reception mode start time τstart, which is the time immediately before the assumed reception time τnext, is determined by the following equation (1). τstart = τnext -(tSFD +tsym × Nrg ) (1)

[0045] In equation (1), tSFD is the reception period (SFD time) of the SFD included in the frame format. tsym is the reception period (one symbol time) of one symbol of the preamble code in the preamble included in the frame format. As described above, one symbol of the preamble code refers to a sequence symbol formed using pulses of a predetermined pattern (e.g., -, 0, +). Nrg is the required number of times to recognize one symbol of the preamble code. The communication devices 10 and 20 can receive transmission data of UWB communication only after recognizing one symbol of the preamble code the required number of times Nrg.

[0046] The required number of recognition attempts Nrg is a number determined by the devices 10 and 20 (a device-dependent number). In the example shown in FIG. 6, the required number of recognition attempts Nrg is, for example, four. The minimum preamble recognition period can be calculated by multiplying tsym by the device-dependent required number of recognition attempts Nrg. In this embodiment, the reception mode start time τstart is set to a time earlier than the expected reception time τnext by the period obtained by the calculation formula (tSFD + tsym × Nrg).

[0047] By determining the receive mode start time in this manner, the start of the period in which UWB communication transmission data can be received can be set as close as possible to the expected reception time. This reduces the possibility of being affected by interference from jamming waves and improves the success rate of communication. Note that the receive mode start time τstart may be set to a time earlier than the expected reception time τnext by the period (time) calculated using the formula (tSFD + tsym × Nrg), or by an appropriate margin time determined through experiments, etc.

[0048] <2. Details of communication method> In the communication system SYS1 of this embodiment, UWB communication is performed based on the above-described reception method (hereinafter referred to as the first reception method) in which the reception start timing of the receiving side is set to coincide with the transmission timing of the transmitting side and the receiving state is maintained for only a limited period of time. However, when the first reception method is adopted, there are some issues that arise. This embodiment provides a technology for performing wireless communication while solving the issues that may arise when the first reception method is adopted. This will be described below with several examples.

[0049] [2-1. First Example] When using the first reception method in which the reception start timing is set to match the transmission timing of the transmitting side, it is necessary for the transmitting side and the receiving side to share timing information in advance. If the timing information is to be exchanged in advance between the master communication device 10 and the slave communication device 20 in order to share the timing information, the following problems arise.

[0050] If advance timing information is exchanged wirelessly, there is a possibility that radio wave interference may prevent the timing information from being transmitted from the master communication device 10 to the slave communication device 20. Considering this, it is possible to exchange advance timing information via a wired connection; however, this requires wired communication equipment in addition to wireless communication, which may increase costs. Furthermore, if the slave communication device 20 is restarted after the timing information has been exchanged, the transmission timing of the master communication device 10 may become unclear, and the slave communication device 20 may become unable to receive data. Considering this, it is possible for the master communication device 10 to repeatedly or periodically transmit timing information; however, this increases the amount of communication traffic, which may reduce communication efficiency.

[0051] In consideration of the above problems, the slave communication device 20 of this embodiment is configured to automatically switch between a first reception method in which reception starts and ends in accordance with the transmission timing of the master communication device 10, and a second reception method in which reception continues regardless of the transmission timing of the master communication device 10.

[0052] With this configuration, even if the timing information of communication with the master communication device 10 is unknown, the slave communication device 20 can receive a transmission signal from the master communication device 10 by using the second reception method, which continues the reception state. That is, according to the first embodiment, the slave communication device 20 can communicate with the master communication device 10 without exchanging timing information with the master communication device 10 in advance, which could result in communication failure or increased costs. Furthermore, if the slave communication device 20 has already been able to receive a transmission signal from the master communication device 10 and the transmission timing is known, it can use the first reception method, which starts and ends reception in accordance with the transmission timing of the master communication device 10. That is, the slave communication device 20 can basically start and end reception in accordance with the transmission timing of the master communication device 10, thereby reducing interference with other communications and improving the communication success rate.

[0053] (2-1-1.Basic operation) First, the basic operation of the master communication device 10 and the slave communication device 20 in the first embodiment will be described. Figure 7 is a diagram for explaining the basic operation of the master communication device 10 and the slave communication device 20 in the first embodiment. In Figure 7, the letters in parentheses are symbols added for the purpose of explaining the operation. Also in Figure 7, the master communication device 10 periodically transmits a transmission signal at a transmission interval T1. In other words, the polling period of the master communication device 10 is T1.

[0054] To start communication, the slave communication device 20 first waits for a transmission from the master communication device 10 in a constant reception state (see FIG. 7(a)). The constant reception state is a state in which the slave communication device 20 continues in reception mode. In other words, the reception method of the slave communication device 20 becomes the second reception method. Note that the phrase "continuing reception mode" in this specification also includes a state in which the reception mode is momentarily canceled and then immediately resumed, in which a substantially continuous reception state is maintained.

[0055] When an appropriate period of time has elapsed since the slave communication device 20 entered the constant reception state, the master communication device 10 transmits information to the slave communication device 20 (see FIG. 7(b)). When transmitting information, the master communication device 10 transitions from mask mode (idle state) to transmission mode, and returns to mask mode after transmission is complete (after a predetermined master transmission period T5 has elapsed).

[0056] The slave communication device 20, which is in a constant reception state, receives a transmission signal sent from the master communication device 10. When the slave communication device 20 receives a transmission signal from the master communication device 10 and the received signal is addressed to itself, it terminates the reception state and transitions to mask mode (see FIG. 7(c)). That is, the reception method of the slave communication device 20 switches from the second reception method to the first reception method. Whether the signal is addressed to itself can be determined from the header (PHR) information.

[0057] The slave communication device 20 that has received the signal addressed to itself transmits a response to the master communication device 10 at a timing determined by the period T2, which is information shared with the master communication device 10 (see FIG. 7(d)). When transmitting information, the slave communication device 20 transitions from mask mode (idle state) to transmission mode, and returns to mask mode after transmission is complete (after the predetermined response period T4 has elapsed).

[0058] The slave communication device 20 starts counting the period T2 when it receives the header (PHR) information included in the transmission signal. The period T2, which is information shared between the master communication device 10 and the slave communication device 20, may be stored in advance in the memories 13, 23 of each device, or may be included in the transmission signal transmitted by the master communication device 10. The response period T4 and the master transmission period T5 are also information shared between the master communication device 10 and the slave communication device 20.

[0059] The master communication device 10 transitions from mask mode to receive mode and starts receiving (see FIG. 7(e)) in accordance with the timing (determined by a predetermined period T2) of the response transmission from the slave communication device 20. The master communication device 10 transitions to mask mode after a predetermined response period T4 has elapsed, regardless of whether the response transmission from the slave communication device 20 is received or not.

[0060] The master communication device 10 transmits information to the slave communication device 20 in accordance with the polling period T1 (see FIG. 7(f)). As in the case of FIG. 7(a) above, when transmitting information, the master communication device 10 transitions from mask mode to transmission mode, and returns to mask mode after transmission is complete (after the master transmission period T5 has elapsed).

[0061] The slave communication device 20 transitions from mask mode to receive mode and starts receiving in accordance with the next transmission timing (a timing determined by a predetermined period T3) of the master communication device 10 (see FIG. 7(g)). The slave communication device 20 transitions to mask mode after the master transmission period T5 has elapsed, regardless of whether or not it is able to receive a transmission signal from the master communication device 10.

[0062] The slave communication device 20 starts counting the period T3 when it receives the header (PHR) information contained in the transmission signal it previously (most recently) received from the master communication device 10. The period T3 may be stored in advance in the memories 13, 23 of each device, or may be included in the transmission signal transmitted by the master communication device 10.

[0063] After this, the slave communication device 20 transmits a response (see FIG. 7(h)), which is the same operation as in FIG. 7(d) above, and the master communication device 10 receives a response (see FIG. 7(i)), which is the same operation as in FIG. 7(e) above. After this, the operations described in FIG. 7(f), (g), (h), and (i) above are repeated in this order, in principle, in accordance with the polling period T1.

[0064] However, after changing the reception method from the second reception method to the first reception method, it is possible that the slave communication device 20 will be unable to receive the transmission signal from the master communication device 10 for some reason. In the basic operation shown in Figure 7, if such a situation occurs in which the transmission signal cannot be received, the reception method of the slave communication device 20 is configured to switch from the first reception method to the second reception method. In other words, when using the first reception method, if the slave communication device 20 is unable to receive a signal from the start to the end of reception, it is configured to switch to the second reception method. This configuration makes it possible to avoid a situation in which the slave communication device 20 is unable to receive the transmission signal from the master communication device 10 because it does not know the next reception timing.

[0065] 7, the slave communication device 20 is unable to receive the transmission signal from the master communication device 10 at time (j) and times out. In other words, the slave communication device 20 is unable to receive the transmission signal. At the time the timeout occurs, the slave communication device 20 switches its communication mode to reception mode and enters a continuous reception state. In other words, the slave communication device 20 switches its reception method from the first reception method, which starts reception in synchronization with the transmission timing, to the second reception method, which performs continuous reception.

[0066] 7(e) and 7(i), the master communication device 10 transitions from the mask mode to the receive mode (see FIG. 7(k)) in accordance with the timing (determined by the period T2) of the response transmission from the slave communication device 20. Since there is no response transmission from the slave communication device 20, the master communication device 10 transitions to the mask mode after the response period T4 has elapsed without receiving a signal.

[0067] Thereafter, the master communication device 10 transmits information to the slave communication device 20 in accordance with the polling period T1 (see FIG. 7(l)). As in the above-described cases of FIGS. 7(a) and 7(f), the master communication device 10 transitions from mask mode to transmission mode when transmitting information, and returns to mask mode after transmission is complete.

[0068] The slave communication device 20, which is in a constant reception state, receives a transmission signal sent from the master communication device 10. When the slave communication device 20 receives a transmission signal from the master communication device 10 and the received signal is directed to itself, it terminates the reception state and transitions to mask mode, as in the case of FIG. 7(c) above (see FIG. 7(m)). In other words, the reception method of the slave communication device 20 switches from the second reception method to the first reception method. The subsequent operations of the master communication device 10 and the slave communication device 20 are as described above.

[0069] The basic operations of the master communication device 10 and the slave communication device 20 explained above will be explained separately for each device.

[0070] Fig. 8 is a flowchart showing the basic operation of the master communication device 10. The operation shown in Fig. 8 is started, for example, when a body ECU installed in the automobile C1 that controls the body of the automobile C1 is started. Specifically, the body ECU controls on-board equipment other than vehicle driving system devices such as the engine. On-board equipment other than vehicle driving system devices includes, for example, an air conditioner, a door lock device, a window opening / closing device, a wiper device, etc.

[0071] A typical example of the activation timing of the body ECU is when the doors of the automobile C1 are unlocked, and another example is when the ACC is turned on by operating the ignition key of the automobile C1. The operation shown in FIG. 8 may be executed, for example, as a regular operation or an exceptional operation after the body ECU is activated. At least one of the master communication device 10 and the slave communication device 20 may be a body ECU, or neither the master communication device 10 nor the slave communication device 20 may be a body ECU. The body ECU may be, for example, an entertainment device such as an audio device.

[0072] In step S1, the master communication device 10 (controller 12) monitors the timing of transmission (transmission timing). At the start of communication, as explained above in FIG. 7(b), the transmission timing is the timing when an appropriate period has elapsed since the timing when the slave communication device 20 enters a constant reception state (predetermined in advance by agreement in product specifications, etc.). After the first transmission, the transmission timing is the timing determined by the polling period T1. If the transmission timing has arrived (Yes in step S1), the process proceeds to the next step S2. If it is not the transmission timing (No in step S1), the monitoring in step S1 continues.

[0073] In step S2, the master communication device 10 transitions from the mask mode to the transmission mode. Once the transition to the transmission mode is complete, the process proceeds to the next step S3.

[0074] In step S3, the master communication device 10 transmits a transmission signal. After transmitting the transmission signal, the process proceeds to the next step S4.

[0075] In step S4, the master communication device 10 transitions from the transmission mode to the mask mode after the master transmission period T5 (see FIG. 7) has elapsed. Once the transition to the mask mode is complete, the process proceeds to the next step S5.

[0076] In step S5, the master communication device 10 monitors the timing to receive a response transmission from the slave communication device 20. When the timing to receive a response transmission (determined by period T2 in FIG. 7) arrives (Yes in step S5), the process proceeds to the next step S6. If it is not the timing to receive a response transmission (No in step S5), the monitoring in step S5 continues.

[0077] In step S6, the master communication device 10 transitions from mask mode to receive mode. Once the transition to receive mode is complete, the process proceeds to the next step S7. If the master communication device 10 receives a communication from the slave communication device 20 while in receive mode, it performs processing according to the received data (for example, processing to indicate successful communication (deciding not to retransmit, etc.)). If the master communication device 10 does not receive a communication from the slave communication device 20 while in receive mode, it performs processing for when no communication is received, such as retransmission processing.

[0078] In step S7, the master communication device 10 monitors whether the period for receiving a response transmission from the slave communication device 20 (reception period) has ended. The reception period is the same as the response period T4 (see FIG. 7) described above. If the reception period has ended (Yes in step S7), the process proceeds to the next step S8. If the reception period has not ended (No in step S7), the monitoring in step S7 continues.

[0079] In step S8, the master communication device 10 transitions from the receive mode to the mask mode. Once the transition to the mask mode is complete, the process returns to step S1. Thereafter, the processes from step S1 to step S8 are repeated according to the polling period T1.

[0080] Fig. 9 is a flowchart showing the basic operation of the slave communication device 20. As in the case of the basic operation of the master communication device 10 shown in Fig. 8, the operation shown in Fig. 9 is started, for example, when a body ECU that is installed in the automobile C1 and controls the body of the automobile C1 is started up. Furthermore, as in the case of the basic operation of the master communication device 10 shown in Fig. 8, the operation shown in Fig. 9 may be executed, for example, as a regular operation or an exceptional operation after the body ECU is started up.

[0081] In step S11, the slave communication device 20 (controller 22) sets its communication mode to reception mode. In other words, the slave communication device 20 enters a state in which it constantly receives data. In other words, the reception method of the slave communication device 20 becomes the second reception method. Once the communication mode is set to reception mode, the process proceeds to the next step, S12.

[0082] In step S12, the slave communication device 20 monitors whether or not it has received a transmission signal (transmitted from the master communication device 10) directed to itself. If it has received a signal directed to itself (Yes in step S12), the process proceeds to the next step S13. If it has not received a signal directed to itself (No in step S12), it continues monitoring in step S12.

[0083] In step S13, the slave communication device 20 transitions from the receive mode to the mask mode. As a result, the reception method of the slave communication device 20 switches from the second reception method, which performs continuous reception, to the first reception method, which starts reception in synchronization with the transmission timing of the master communication device 10. Once the transition to the mask mode is complete, the process proceeds to the next step, S14.

[0084] In step S14, the slave communication device 20 monitors the timing for transmitting a response to the master communication device 10. The timing for transmitting a response is determined by the period T2 as described above. When the timing for transmitting a response arrives (Yes in step S14), the process proceeds to the next step S15. When the timing for transmitting a response does not arrive (No in step S14), the monitoring in step S14 continues.

[0085] In step S15, the slave communication device 20 transitions from the mask mode to the transmission mode. Once the transition to the transmission mode is complete, the process proceeds to the next step S16.

[0086] In step S16, the slave communication device 20 transmits a response transmission signal to the master communication device 10. Once the response transmission has been performed, the process proceeds to the next step S17.

[0087] In step S17, after the response period T4 (see FIG. 7) has elapsed, the slave communication device 20 transitions from the transmission mode to the mask mode. Once the transition to the mask mode is complete, the process proceeds to the next step S18.

[0088] In step S18, the slave communication device 20 monitors the timing for receiving a transmission signal from the master communication device 10. When the timing for reception (determined by period T3 in FIG. 7) arrives (Yes in step S18), the process proceeds to the next step S19. When the timing for reception does not arrive (No in step S18), the monitoring in step S18 continues.

[0089] In step S19, the slave communication device 20 transitions from the mask mode to the receive mode. Once the transition to the receive mode is complete, the process proceeds to the next step S20.

[0090] In step S20, the slave communication device 20 monitors whether the period (reception period) for receiving a transmission signal from the master communication device 10 has ended. This reception period is the same as the master transmission period T5 (see FIG. 7). If the reception period has ended (Yes in step S20), the process proceeds to the next step S21. If the reception period has not ended (No in step S20), the monitoring in step S20 continues.

[0091] In step S21, the slave communication device 20 determines whether or not it is in a reception NG state, meaning that it was unable to receive a transmission signal during the previous reception period (the reception period in step S20). If it is in a reception NG state (Yes in step S21), the process returns to step S11. This causes the slave communication device 20 to switch from the first reception method, which starts reception in accordance with the transmission timing, to the second reception method, which performs continuous reception. If it is not in a reception NG state (No in step S21), the process proceeds to step S22. Note that when the slave communication device 20 receives communication from the master communication device 10 during reception mode, it performs processing according to the received data. For example, when it receives "window open data," it sends a command signal to an actuator (such as a window opening / closing motor) to open the window.

[0092] In step S22, the slave communication device 20 transitions from the receive mode to the mask mode. When the transition to the mask mode is complete, the process returns to step S14. In this case, the slave communication device 20 maintains the first receive method as its receive method and performs subsequent operations.

[0093] (2-1-2. When there are multiple slave communication devices) As described above, in this embodiment, there are a plurality of slave communication devices 20. How the above-described basic operation is applied when there are a plurality of slave communication devices 20 will be described.

[0094] Fig. 10 is a diagram for explaining the operation of the master communication device 10 and multiple slave communication devices 20. Fig. 10 shows how the basic operation shown in Fig. 7 is applied when multiple slave communication devices 20 are present. In Fig. 10, the basic operation is the same as in the case shown in Fig. 7. For this reason, explanations of content that overlaps with the case in Fig. 7 will be omitted unless particularly necessary, and the explanation will focus on the differences.

[0095] In FIG. 10, the letters in parentheses are used to explain the operation. These letters are independent of the letters in FIG. 7 and are not intended to have the same meaning as those in FIG. 7. This also applies, in principle, to the letters in parentheses that appear in the drawings described later. In addition, in FIG. 10, for the sake of simplicity, there are two slave communication devices 20: a first slave communication device 20a (corresponding to "Slave 1" in FIG. 10) and a second slave communication device 20b (corresponding to "Slave 2" in FIG. 10). In this embodiment, a third slave communication device 20c and a fourth slave communication device 20d also exist, so that the operation differs from that shown in FIG. 10 to be precise. However, the operation described in FIG. 10 can be applied to these differences.

[0096] At the start of communication, the first slave communication device 20a and the second slave communication device 20b are in a constant reception state and wait for a transmission from the master communication device 10 (see FIG. 10(a)). That is, the reception method of the first slave communication device 20a and the second slave communication device 20b is the second reception method.

[0097] When an appropriate period of time has elapsed since the first slave communication device 20a and the second slave communication device 20b entered the constant reception state, the master communication device 10 transmits information to the first slave communication device 20a (see FIG. 10(b)).

[0098] The first slave communication device 20a, which is in a constant reception state, receives a transmission signal sent from the master communication device 10. Because the received signal is intended for the first slave communication device 20a, after receiving the signal, the first slave communication device 20a switches the communication mode from reception mode to mask mode (see FIG. 10(c)). That is, the first slave communication device 20a switches its reception method from the second reception method to the first reception method. Thereafter, the operation follows the basic operation described above.

[0099] The second slave communication device 20b, which is in a constant reception state, also receives the transmission signal sent from the master communication device 10. However, the second slave communication device 20b continues in reception mode because the received signal is intended for another device (specifically, for the first slave communication device 20a). In other words, the second slave communication device 20b maintains its reception method as the second reception method (see FIG. 10(d)).

[0100] Next, the master communication device 10 transmits information to the second slave communication device 20b in accordance with the polling period T1 (see FIG. 10(e)).

[0101] The first slave communication device 20a transitions from mask mode to receive mode in response to the transmission from the master communication device 10, and receives the transmission signal transmitted from the master communication device 10 (see FIG. 10(f)). After receiving the signal, the first slave communication device 20a transitions from receive mode to mask mode. However, because the received signal is intended for another device (the second slave communication device 20b), the first slave communication device 20a does not transmit a response thereafter, and instead starts receiving in response to the next transmission from the master communication device 10.

[0102] The second slave communication device 20b, which is in a constant reception state, also receives the transmission signal sent from the master communication device 10. Because the received signal is intended for the second slave communication device 20b, after receiving the signal, the second slave communication device 20b switches its communication mode from reception mode to mask mode (see FIG. 10(g)). In other words, the second slave communication device 20b switches its reception method from the second reception method to the first reception method. Thereafter, the operation follows the basic operation described above.

[0103] As in the case of the basic operation described above, after the reception method is changed from the second reception method to the first reception method, it may happen that for some reason the first slave communication device 20a or the second slave communication device 20b is unable to receive the transmission signal from the master communication device 10. Such a situation will be described with reference to FIG.

[0104] 10, the first slave communication device 20a is unable to receive the transmission signal from the master communication device 10 at time (h) and times out (reception NG). At the time the first slave communication device 20a times out, it switches its communication mode to reception mode and enters a continuous reception state. In other words, the first slave communication device 20a switches its reception method from the first reception method, which starts reception in synchronization with the transmission timing, to the second reception method, which performs continuous reception.

[0105] The second slave communication device 20b transitions from mask mode to receive mode in response to the transmission from the master communication device 10, and receives the transmission signal transmitted from the master communication device 10 (see FIG. 10(i)). After receiving the signal, the second slave communication device 20b transitions from receive mode to mask mode. However, because the received signal is intended for another device, the second slave communication device 20b does not transmit a response thereafter, and instead starts receiving in response to the next transmission from the master communication device 10.

[0106] Since the master communication device 10 transmitted a transmission signal intended for the first slave communication device 20a at the previous timing, the master communication device 10 transmits information to the second slave communication device 20b in accordance with the polling period T1 (see FIG. 10(j)).

[0107] The first slave communication device 20a, which is in the constant reception state, receives a transmission signal transmitted from the master communication device 10. However, because the received signal is intended for another device, the first slave communication device 20a continues in reception mode. That is, the first slave communication device 20a maintains its reception method as the second reception method (see FIG. 10(k)). The next time the master communication device 10 transmits a transmission signal intended for the first slave communication device 20a, the first slave communication device 20a, which is in the constant reception state, receives the signal intended for itself and switches from the second reception method to the first reception method (see FIG. 10(l)). Note that in the first reception method state, the slave communication device 20 knows the transmission timing intended for itself (its own polling period). Therefore, it does not need to switch to reception mode when it is time to transmit to another device. However, this configuration applies to a configuration in which it is predetermined that both transmission and reception are performed at the same polling period, but does not apply to a type in which the polling period for transmission only is determined.

[0108] (2-1-3. When other systems are mixed) Next, we will explain how the above-mentioned basic operation is applied when other systems are mixed in. Note that the other systems are communication systems different from the communication system SYS1. In this example, the other systems communicate using UWB communication with the same preamble code as the communication system SYS1. Furthermore, the content explained here can also be applied to cases where there are multiple slave communication devices 20 as described above, but for simplicity of explanation, we will assume that there is only one slave communication device 20.

[0109] FIG. 11 is a diagram for explaining the operation of the master communication device 10 and the slave communication device 20 when other systems are mixed in. FIG. 11 shows how the basic operation shown in FIG. 7 is applied when other systems are mixed in. In FIG. 11, the basic operation is the same as that shown in FIG. 7. For this reason, explanations of content that overlaps with the case of FIG. 7 will be omitted unless particularly necessary, and the explanation will focus on the differences. In FIG. 11, the alphabets in parentheses are symbols added for the purpose of explaining the operation.

[0110] If another system transmits a signal while the master communication device 10 and the slave communication device 20 are in mask mode (idle state) (see FIG. 11(a)), no problem occurs because the master communication device 10 and the slave communication device 20 do not receive the signal.

[0111] If another system transmits a signal at the same time as the master communication device 10 (see FIG. 11(b)), the slave communication device 20 may receive a transmission signal from the other system instead of the transmission signal from the master communication device 10. In this case, the slave communication device 20 receives a transmission signal from the other system, but because it receives it at the appropriate timing, it maintains the first reception method as in the case where a signal intended for another slave is received (see FIG. 11(c)). The slave communication device 20 discards the received packet from the other system, does not transmit a response, and starts receiving in conjunction with the next transmission from the master communication device 10.

[0112] Furthermore, if another system transmits a signal while the slave communication device 20 is in a constant reception state (the reception method is the second reception method) (see FIG. 11(d)), the slave communication device 20 also receives the transmitted signal from the other system. In this case, as in the case where a signal addressed to another slave is received, the reception method remains the second reception method (see FIG. 11(e)), and the received packet can simply be discarded.

[0113] (2-1-4. Summary of "2-1-2" and "2-1-3") As can be seen from the above explanation, when using the first reception method in which reception starts in accordance with the transmission timing, if the slave communication device 20 cannot receive a signal between the start and end of reception (reception NG), it switches the reception method to the second reception method in which reception is performed continuously.

[0114] On the other hand, when using the first reception method, if the slave communication device 20 receives a transmission signal intended for another slave communication device or a transmission signal from another system, the slave communication device 20 maintains the first reception method. In other words, when using the first reception method, if the slave communication device 20 receives a signal between the start and end of reception, the slave communication device 20 maintains the first reception method regardless of whether the received signal is intended for the device itself. With this configuration, the frequency of using the continuous reception method can be minimized.

[0115] Furthermore, when using the second reception method, the slave communication device 20 switches to the first reception method if the received signal is intended for the device itself, and maintains the second reception method if the received signal is not intended for the device itself. This allows automatic switching from the second reception method to the first reception method at an appropriate time.

[0116] As can be seen from the above, when considering the case where there are multiple slave communication devices 20 communicating with the master communication device 10 or the case where interference with other systems occurs, there are two cases where the slave communication device 20 is not NG for reception when using the first reception method: That is, cases where reception is not NG include when the slave communication device 20 receives a transmitted signal intended for itself (when reception is OK) and when the slave communication device 20 receives a signal not intended for itself.

[0117] Considering this point, it is preferable that step S21 in the flow shown in Fig. 9 be configured as shown in Fig. 12. Fig. 12 is a diagram showing a flow in which the basic operation in the first embodiment is modified to a preferable form. Fig. 12 is a diagram showing only the changes from Fig. 9.

[0118] In the flow shown in Fig. 12, after the reception period for receiving a transmission signal from the master communication device 10 has ended (step S20), the process of step S211 is performed. In step S211, the slave communication device 20 determines whether or not the signal has been received. If the signal has been received (Yes in step S211), the process proceeds to the next step S212. If the signal has not been received (No in step S211), the process returns to step S11 (see Fig. 9). That is, the process switches to a constant reception state (second reception method). If the signal has not been received, the state is the same as when reception is NG in Fig. 9.

[0119] In step S212, the slave communication device 20 determines whether the received signal is a signal addressed to the device itself. If the signal is addressed to the device itself (Yes in step S212), the process proceeds to step S22. In this case, the communication mode is temporarily set to mask mode, and then a process of sending a response transmission toward the master communication device 10 is performed. On the other hand, if the signal is not addressed to the device itself (No in step S212), the process returns to step S17. In this case, no response transmission is performed, and therefore the communication mode is temporarily set to mask mode, and then a process of receiving a transmission signal from the master communication device 10 is performed.

[0120] (2-1-5. Variations) Next, a modified example of the first embodiment will be described. Fig. 13 is a diagram for explaining a modified example of the first embodiment. In Fig. 13, the letters in parentheses are symbols added to explain the operation.

[0121] 13, in this modification, the master communication device 10 periodically transmits data to the slave communication device 20 in a transmission period (polling period) T1 that includes an initial transmission period (initial time slot) and a retransmission period (retransmission time slot) within one period. The retransmission period is a period provided to enable retransmission of transmission data with the same content as the transmission data (packet) in the initial transmission period.

[0122] In this modified example, the transmission timing of the master communication device 10 includes the timing of retransmission. By configuring retransmission to be performed, it is possible to improve the reception success rate of the slave communication device 20 when using the first reception method, which performs reception in accordance with the transmission timing. As a result, it is possible to reduce the frequency of switching from the first reception method to the second reception method, which performs continuous reception. In other words, it is possible to minimize the use of the second reception method.

[0123] In this modification, only one retransmission period is provided, but multiple retransmission periods may be provided. That is, the number of retransmissions is not limited to one, but may be multiple. In particular, when there is ample communication time, increasing the number of retransmission periods can improve the success rate of reception in the first reception method, in which reception is performed in accordance with the transmission timing.

[0124] The operations indicated by the symbols (a), (b), (c), (d), and (e) in FIG. 13 are exactly the same as those in FIG. 7, which have been previously described, and therefore will not be described here.

[0125] The master communication device 10 enters mask mode once after receiving the response transmission from the slave communication device 20. Then, since the master communication device 10 has received the response transmission from the slave communication device 20, it determines that the slave communication device 20 has successfully received the data (reception was OK), and does not retransmit the data (see FIG. 13(f)).

[0126] The slave communication device 20 transitions to the receive mode and starts receiving in accordance with the retransmission timing of the master communication device 10. Then, regardless of whether reception is possible or not, the slave communication device 20 ends reception after the master transmission period T5 has elapsed and transitions to the mask mode (see FIG. 13(g)).

[0127] The retransmission timing of the master communication device 10 is determined by a master retransmission period T6, which is information shared with the master communication device 10. The master retransmission period T6 is the period from when the master communication device 10 performs an initial transmission until when it performs a retransmission. The master retransmission period T6 may be stored in advance in the memories 13, 23 of each device, or may be included in a transmission signal transmitted by the master communication device 10 at the start of communication (when the second reception method is used), etc.

[0128] 13, the slave communication device 20 times out at time (h) because it is unable to receive a transmission signal from the master communication device 10. The slave communication device 20 does not transmit a response because it is unable to receive a transmission signal from the master communication device 10 (see FIG. 13(i)).

[0129] The master communication device 10 transitions from the mask mode to the receive mode (see FIG. 13(j)) in accordance with the timing (determined by the period T2) of the response transmission from the slave communication device 20. Since there is no response transmission from the slave communication device 20, the master communication device 10 transitions to the mask mode after the response period T4 has elapsed without receiving a signal.

[0130] The master communication device 10 determines that retransmission is necessary because no response has been received from the slave communication device 20. The master communication device 10 then transmits information to the slave communication device 20 at the retransmission timing determined by the master retransmission period T6 (see FIG. 13(k)).

[0131] The slave communication device 20 transitions from the mask mode to the receive mode in accordance with the transmission timing of the master communication device 10 determined by the master retransmission period T6 (see FIG. 13(l)). As a result, the slave communication device 20 receives the transmission signal from the master communication device 10.

[0132] Depending on the communication environment (such as noise generation conditions), a situation may occur in which the master communication device 10 is unable to receive the signal again (reception NG) even after retransmission. To address this, the number of times retransmission is possible may be increased. Also, if reception NG continues even after retransmission, the system may be configured to switch from the first reception method to the second reception method, which is in a constant reception state.

[0133] Furthermore, in this modification, if there is no response from the slave communication device 20 to the data transmission in the initial transmission period, the master communication device 10 transmits data in the retransmission period. On the other hand, if there is a response from the slave communication device 20 to the data transmission in the initial transmission period, the master communication device 10 does not transmit data in the retransmission period. With this configuration, it is possible to reduce unnecessary transmissions as much as possible and suppress the occurrence of radio wave interference with other systems.

[0134] [2-2. Second Example] When there are multiple asynchronous and independent communication systems, radio interference can occur, causing communication failure. As described above, by using a reception method (first reception method) in which the receiver starts and ends reception in synchronization with the transmitter's transmission timing, radio interference with other systems (other communication systems) can be suppressed. However, even when using the first reception method, the target packet may not be received depending on the superimposition timing of packets (communication frames) with other systems.

[0135] A specific example will be described with reference to FIG. 4, which was previously explained. It is assumed that the target wave in FIG. 4 is a packet (communication frame) transmitted from the master communication device 10 to the slave communication device 20. It is also assumed that the jamming wave in FIG. 4 is a packet transmitted in another system. It is also assumed that the preamble of a packet transmitted from another system overlaps with the period required for the slave communication device 20 to detect the preamble of the target packet for a period longer than the period required for detection. In such a case, the slave communication device 20 may detect the preamble of the packet from the other system and be unable to receive the transmission signal from the master communication device 10. This will be described in more detail with reference to FIG. 14.

[0136] 14 is a schematic diagram for explaining the cause of signal reception failure when using the first reception method. As shown in FIG. 14, the preamble has a signal structure in which impulse waveforms are discretely arranged. Furthermore, during reception in the slave communication device 20, sampling is performed to coincide with the period of the preamble signal waveform. Even in a configuration in which reception is started in accordance with the transmission timing, as in the first reception method, it is difficult to start reception so that the period of the preamble signal waveform and the sampling timing coincide. For this reason, as shown in FIG. 14, the sampling timing during reception in the slave communication device 20 may coincide with the signal waveform of the preamble of another system, resulting in accidental detection of the preamble of the other system.

[0137] In particular, when the communication system SYS1 and other systems transmit signals at the same polling cycle, the slave communication device 20 may continue to be unable to receive the transmission signal from the master communication device 10, which may result in a deterioration in communication performance. The second embodiment is configured to solve this problem.

[0138] FIG. 15 is a diagram for explaining the operation of the master communication device 10 and the slave communication device 20 in the second embodiment. Note that in FIG. 15, the letters in parentheses are symbols added for the purpose of explaining the operation. Also, in the second embodiment, as in the first embodiment, a first reception method in which reception is performed in accordance with the transmission timing and a second reception method in which reception is performed continuously are switched between, but FIG. 15 shows the state after switching from the second reception method to the first reception method. Also, in the initial stage of the example shown in FIG. 15, it is assumed that the polling period (transmission interval) for signal transmission is set to the same T1 between the master communication device 10 and the other system, and that the signal transmission timings overlap.

[0139] At the time (a) in Figure 15, the slave communication device 20 has received a packet from another system, but has not received the target packet. Having received the packet from another system, the slave communication device 20 discards the packet. Furthermore, since the slave communication device 20 has not received the target packet, it does not transmit a response to the master communication device 10. Since the slave communication device 20 has not transmitted a response, the master communication device 10 recognizes that communication has failed.

[0140] 15(b), the slave communication device 20 receives a packet from another system but is unable to receive a packet from the target. For this reason, as in the case of FIG. 15(a), the slave communication device 20 discards the packet and does not transmit a response to the master communication device 10. The master communication device 10 then recognizes that communication has failed because no response has been transmitted from the slave communication device 20.

[0141] At the time shown in Figure 15(b), both the master communication device 10 and the slave communication device 20 have experienced consecutive communication failures, and therefore determine that their transmission timings overlap with those of other systems, and decide to change the polling period. In the example shown in Figure 15, the polling period is changed from T1 to T1A. Note that when a change in the polling period becomes necessary, an agreement is made in advance between the master communication device 10 and the slave communication device 20 as to how the polling period should be changed. This agreement information is stored in advance in memories 13 and 23.

[0142] By changing the polling period, the slave communication device 20 can receive signals from the master communication device 10 while avoiding radio wave interference with transmissions from other systems (see FIG. 15(c)). In response to reception being OK, the master communication device 10 and the slave communication device 20 return the polling period from T1A to the original period T1. This makes it possible to avoid signal overlap with other systems even after this, reducing the possibility that the slave communication device 20 will fail to receive a signal.

[0143] 15, it is assumed that the other systems do not change their polling periods. However, a configuration may be adopted in which, when the overlapping of transmission timings is recognized, the master communication device 10 coordinates with the other systems to change the polling period. In other words, the polling period of the other systems may be changed.

[0144] 15(c), if reception fails, the polling period may be kept at T1A, and when reception becomes OK, the polling period may be returned to the original T1. Also, in FIG. 15(c), if reception fails, the polling period may be returned from T1A to the original period T1, or may be changed to another period.

[0145] In the example shown in FIG. 15, the polling cycle is restored to the original cycle when reception is OK, but the cycle may be changed to another cycle such as T1B, T1C, etc. without restoring the cycle to the original cycle.

[0146] In addition, in the example shown in Fig. 15, the polling period is changed when a signal from another system is received twice in succession, but this is merely an example and other configurations may be used. For example, the polling period may be changed when a signal from another system is received multiple times in succession other than twice. Furthermore, for example, the decision to change the polling period may be made based on the probability of communication failure. The polling period may be changed when the probability of communication failure becomes higher than a preset threshold.

[0147] 16 is a flowchart showing the operation of the master communication device 10 in the second embodiment. The operation of the master communication device 10 in the second embodiment is basically the same as that in the first embodiment (see FIG. 8). For this reason, FIG. 16 shows only the changes from FIG. 8. In detail, the processes of steps S91 to S93 have been added after the process of step S8 in FIG. 8.

[0148] In step S91, the master communication device 10 (controller 12) determines whether or not there has been a continuous state of no response (response transmission) from the slave communication device 20. If there has been a continuous state of no response (Yes in step S91), the process proceeds to the next step S92. If there has not been a continuous state of no response (No in step S91), the process proceeds to step S93.

[0149] In step S92, the master communication device 10 changes the polling period (transmission period). Once the polling period has been changed, the process returns to step S1, and signals are transmitted in accordance with the polling period.

[0150] In step S93, the master communication device 10 either maintains the polling period (transmission period) as is, or returns to the original polling period. Specifically, if the polling period was not changed at the time of the previous transmission, the polling period is maintained as is. If the polling period was changed at the time of the previous transmission, the polling period is returned to the original polling period. When the processing of step S93 is completed, the processing returns to step S1, and a signal is transmitted in accordance with the polling period.

[0151] Fig. 17 is a flowchart showing the operation of the slave communication device 20 in the second embodiment. The operation of the slave communication device 20 in the second embodiment is basically the same as that in the first embodiment when other systems are mixed (see Fig. 12). For this reason, Fig. 17 shows only the changes from Fig. 12. In detail, in the second embodiment, the processes of steps S213 and S214 have been added as processes to be performed when step S212 in Fig. 12 is No.

[0152] In step S213, the slave communication device 20 (controller 22) determines whether or not the reception of the other system has been continuous. If the reception of the other system has been continuous (Yes in step S213), the process proceeds to the next step S214. If the reception of the other system has not been continuous (No in step S213), the process returns to step S17, where the process for receiving the transmission signal from the master communication device 10 is performed.

[0153] In step S214, the slave communication device 20 recognizes that the master communication device 10 will change the polling cycle (transmission cycle). The process of recognizing the change in the transmission cycle is executed so that the reception timing can be determined appropriately. When the process of step S214 is completed, the process returns to step S17, and processing for receiving a transmission signal from the master communication device 10 is performed. If the process of step S214 has been performed, it is determined in step S18 of FIG. 9 whether the reception timing corresponds to the change in the polling cycle. Note that if reception is successful after the change in the polling cycle (Yes in step S212), the transmission polling cycle is restored, and the reception cycle (timing) is also restored to its original value (initial value).

[0154] As can be seen from the above explanation, in the second embodiment, the master communication device 10 changes the transmission period of a signal to the slave communication device 20 depending on the response state of the slave communication device 20 to transmissions from the master communication device 10. Furthermore, when using the first reception method, if the transmission period of the signal from the master communication device 10 is changed, the slave communication device 20 starts and ends reception in accordance with the transmission timing corresponding to the change in the transmission period. This configuration reduces the possibility of radio wave interference with other systems and improves the success rate of communication.

[0155] [2-3. Third Example] In the second embodiment, the polling period is changed to reduce the possibility of communication failure due to radio wave interference with other systems. In the third embodiment, the preamble code is changed instead of changing the polling period.

[0156] That is, in the third embodiment, the master communication device 10 changes the preamble code depending on the response state of the slave communication device 20 to a transmission from the master communication device 10. Furthermore, when using the first reception method, the slave communication device 20 changes the preamble code depending on the reception state of a transmission signal from a device other than the master communication device 10. This configuration reduces the possibility of radio wave interference with other systems and improves the success rate of communication.

[0157] When it becomes necessary to change the preamble code, the master communication device 10 and the slave communication device 20 agree in advance on which preamble code to change to. This agreement information is stored in advance in the memories 13 and 23. Alternatively, the master communication device 10 may be configured to adjust the preamble code change with the other system when the overlapping of the transmission timing is recognized. In other words, the preamble code on the other system side may be changed.

[0158] Figure 18 is a schematic diagram for explaining the change of preamble codes. In Figure 18, the letters in parentheses are symbols added for operational explanation. Also, in Figure 18, it is assumed that the preamble code used between the master communication device 10 and the slave communication device 20 has been changed from preamble code A to preamble code B because radio wave interference with another system is estimated. It is assumed that the other system continues to use preamble code A without changing it. Also, for simplicity of explanation, it is assumed that the code content of preamble code A is "11101" and the code content of preamble code B is "00010."

[0159] 18, the slave communication device 20 starts preamble detection at time (a). The slave communication device 20 continues sampling because it has not yet detected the impulse waveform that constitutes the preamble of the transmitted packet.

[0160] At time (b), the slave communication device 20 detects the impulse waveform (specifically, "0") of the transmission packet of the other system. After that, reception sampling in the slave communication device 20 is performed in accordance with the impulse waveform period of the transmission packet of the other system.

[0161] At time (c), the slave communication device 20 detects an impulse waveform (specifically, "0") of a packet transmitted by another system. Combined with the previous detection of the impulse waveform, "0" and "0" are detected. Since the detected content does not match any part of the preamble code used by the slave communication device 20, the slave communication device 20 discards the previous detection results and continues sampling.

[0162] At time (d), the slave communication device 20 detects the impulse waveform (specifically, "1") of the packet transmitted by the master communication device 10. Thereafter, reception sampling in the slave communication device 20 is performed in accordance with the impulse waveform period of the packet transmitted by the master communication device 10.

[0163] At time (e), the slave communication device 20 detects the impulse waveform (specifically, "1") of the packet transmitted by the master communication device 10. Combined with the previous detection of the impulse waveform, "1" and "1" are detected. The detected content matches part of the preamble code used by the slave communication device 20, so the slave communication device 20 continues sampling at the current cycle.

[0164] At time (f), the slave communication device 20 detects that the impulse waveform matches the preamble code it uses, so it continues to search for header information.

[0165] As can be seen from the above explanation, even if the signal transmission timing and transmission period (polling period) are the same as those of another system, the probability of successful communication can be improved by changing the preamble code.

[0166] 19 is a flowchart showing the operation of the master communication device 10 in the third embodiment. The operation of the master communication device 10 in the third embodiment is basically the same as that in the first embodiment (see FIG. 8). For this reason, FIG. 19 shows only the changes from FIG. 8. In detail, the processes of steps S94 and S95 are added after the process of step S8 in FIG. 8.

[0167] In step S94, the master communication device 10 (controller 12) determines whether or not there has been a continuous state of no response (response transmission) from the slave communication device 20. If there has been a continuous state of no response (Yes in step S94), the process proceeds to the next step S95. If there has not been a continuous state of no response (No in step S94), the process returns to step S1, and a signal is transmitted in accordance with the polling period.

[0168] In step S95, the master communication device 10 changes the preamble code. Once the preamble code has been changed, the process returns to step S1, and signals are transmitted in accordance with the polling cycle.

[0169] Fig. 20 is a flowchart showing the operation of the slave communication device 20 in the third embodiment. The operation of the slave communication device 20 in the third embodiment is basically the same as that in the first embodiment when other systems are mixed (see Fig. 12). For this reason, Fig. 20 shows only the changes from Fig. 12. In detail, in the third embodiment, the processes of steps S215 and S216 have been added as processes to be performed when step S212 in Fig. 12 is No.

[0170] In step S215, the slave communication device 20 (controller 22) determines whether or not the reception of the other system has been continuous. If the reception of the other system has been continuous (Yes in step S215), the process proceeds to the next step S216. If the reception of the other system has not been continuous (No in step S213), the process returns to step S17, where the process for receiving the transmission signal from the master communication device 10 is performed.

[0171] In step S216, the slave communication device 20 changes the preamble code. When the processing of step S216 is completed, the processing returns to step S1, and then to step S17, where processing for receiving a transmission signal from the master communication device 10 is performed.

[0172] [2-4. Fourth Example] In a configuration in which the master communication device 10 and the slave communication device 20 transmit and receive data in sync, as in the case of the first reception method described above, slight differences in clock frequency (operating frequency) due to component errors in the crystal oscillators of each device may accumulate, resulting in timing discrepancies.

[0173] FIG. 21 is a schematic diagram showing timing deviations due to component errors in a crystal oscillator. In FIG. 21, the letters in parentheses are symbols added for operational explanation. In FIG. 21, it is assumed that schedule adjustment using the second reception method, which is a continuous reception state, has been completed and that the first reception method, which performs reception in accordance with the transmission timing, has begun. Also, in the explanation of this embodiment, for simplicity, there are two slave communication devices 20: a first slave communication device 20a and a second slave communication device 20b. In the example shown in FIG. 21, it is assumed that no timing deviations due to component errors in the crystal oscillator have occurred at the times indicated by symbols (a) and (b).

[0174] 21, due to component errors in the crystal oscillator, the clock frequency of the first slave communication device 20a is slightly faster than the clock frequency of the master communication device 10. Due to the accumulation of this clock frequency difference, at the time indicated by symbol (c), the reception timing of the first slave communication device 20a is earlier than the transmission timing of the master communication device 10. As a result, at the time indicated by symbol (c), the first slave communication device 20a is unable to receive the transmission signal from the master communication device 10, resulting in a reception NG.

[0175] 21, due to component errors in the crystal oscillator, the clock frequency of the second slave communication device 20b is slightly slower than the clock frequency of the master communication device 10. Due to the accumulation of this clock frequency difference, at the time indicated by the symbol (d), the reception timing of the second slave communication device 20b is slower than the transmission timing of the master communication device 10. As a result, at the time indicated by the symbol (d), the second slave communication device 20b is unable to receive the transmission signal from the master communication device 10, resulting in a reception NG.

[0176] To prevent such timing discrepancies, it is effective to send timing information repeatedly or periodically. However, adding the exchange of timing information reduces the efficiency of data transmission, so other means are desired.

[0177] It is best if both the master communication device 10 and the slave communication device 20 operate at an ideal clock frequency. However, when multiple slave communication devices 20 communicate wirelessly with one master communication device 10, the relative deviation between the master communication device 10 and each slave communication device 20 becomes a problem. Therefore, even if each communication device 10, 20 deviates from the ideal clock frequency, it is sufficient as long as the deviation is corrected between the master communication device 10 and each slave communication device 20.

[0178] Taking this into consideration, in the fourth embodiment, when using the first reception method, the slave communication device 20 calculates the clock frequency difference between itself and the master communication device 10, and adjusts the start timing of reception according to the clock frequency difference to match the transmission timing of the master communication device 10. This reduces the possibility that the slave communication device 20 will fail to receive a transmission signal from the master communication device 10 due to a clock frequency difference between the master communication device 10 and the slave communication device 20.

[0179] In this embodiment, the master communication device 10 also determines the clock frequency difference between itself and the slave communication device 20, and adjusts the start timing of reception in accordance with the clock frequency difference to match the transmission timing of the slave communication device 20. This reduces the possibility that the master communication device 10 will fail to receive a transmission signal from the slave communication device 20 due to a clock frequency difference between the master communication device 10 and the slave communication device 20.

[0180] In this embodiment, the master communication device 10 and the slave communication device 20 are UWB radios as described above. To achieve accurate distance measurement, the UWB radios are designed to reference an internal clock frequency that is faster than the clock frequency of the microcomputer. The clock frequency used for timing adjustment is preferably this high-speed clock frequency. By using the internal high-speed clock frequency of the radio, which is faster and more accurate than the clock frequency of the microcomputer, it is possible to improve the accuracy of timing deviation correction.

[0181] A specific example of a method for correcting the timing deviation caused by the deviation in clock frequency due to component errors in a crystal oscillator will be described below.

[0182] (2-4-1. Basic pattern) Fig. 22 is a diagram for explaining the basic pattern of the fourth embodiment. In Fig. 22, the letters in parentheses are symbols added for explaining the operation. Also, in the example shown in Fig. 22, as in the first embodiment, a first reception method in which reception is performed in accordance with the transmission timing and a second reception method in which reception is performed continuously are switched between and used. Note that Fig. 22 shows the state after switching from the second reception method to the first reception method.

[0183] 22, it is assumed that the calculated value of the number of clocks required for the polling cycle (periodic communication cycle) T1 is 10,000. That is, the master communication device 10 transmits every 10,000 clocks. The slave communication device 20 receives every 10,000 clocks. It is also assumed that the clock frequency of the first slave communication device 20a is slightly faster than that of the master communication device 10. It is also assumed that the clock frequency of the second slave communication device 20b is slightly slower than that of the master communication device 10.

[0184] 22, the reception start timing of the first slave communication device 20a is slightly earlier than the transmission start timing of the master communication device 10, but the first slave communication device 20a can receive a signal from the master communication device 10. Furthermore, the reception start timing of the second slave communication device 20b is slightly later than the transmission start timing of the master communication device 10, but the second slave communication device 20b can receive a signal from the master communication device 10.

[0185] The slave communication device 20 starts receiving data when it receives the header information (PHR). With this in mind, the state at the time of reference symbol (a) in Fig. 22 is assumed as follows: When receiving the header information contained in the transmission signal from the master communication device 10, the cumulative clock count of the first slave communication device 20a is 12001, and the cumulative clock count of the second slave communication device 20b is 11999. In this example, the position of the header information in the transmission signal transmitted by the master communication device 10 is 2000 clocks from the beginning of the transmission signal.

[0186] The first slave communication device 20a and the second slave communication device 20b each start receiving after 10,000 clocks (see FIG. 22(b)). Note that even at the time of reference symbol (b) in FIG. 22, the first slave communication device 20a and the second slave communication device 20b are still able to receive signals from the master communication device 10.

[0187] 22(b), it is assumed that the cumulative clock count of the first slave communication device 20a is 22002 when it receives the header information included in the transmission signal from the master communication device 10. In this case, the first slave communication device 20a detects that it is 1 (=|(22002-12001)-10000|) clock earlier than the master communication device 10.

[0188] 22(b), it is assumed that the cumulative clock count of the second slave communication device 20b is 21998 when the second slave communication device 20b receives the header information included in the transmission signal from the master communication device 10. In this case, the second slave communication device 20b detects that it is 1 (=|(21998-11999)-10000|) clock slower than the master communication device 10.

[0189] The first slave communication device 20a and the second slave communication device 20b each adjust the timing of their next reception in accordance with the amount of difference in the number of clocks that they detected earlier (see FIG. 22(c)). In detail, because the first slave communication device 20a is one clock ahead of the master communication device 10, it starts the next reception at the 10001st clock, not the 10000th clock, in order to delay the timing. Because the second slave communication device 20b is one clock behind the master communication device 10, it starts the next reception at the 9999th clock, not the 10000th clock, in order to advance the timing.

[0190] Thereafter, the above-described reception start timing adjustment is executed at each polling period (master transmission interval).

[0191] Although the above only describes the case where transmission is made from the master communication device 10 to the slave communication device 20, a similar timing adjustment is also made when transmission is made from the slave communication device 20 to the master communication device 10. When transmission is made from the slave communication device 20 to the master communication device 10, the master communication device 10 adjusts the timing of the start of reception.

[0192] (2-4-2. First variation of the basic pattern) Fig. 23 is a diagram for explaining a first modified example of the basic pattern shown in Fig. 22. In the basic pattern described above, the first slave communication device 20a and the second slave communication device 20b are each configured to obtain a difference in the number of clocks for each polling period (master transmission interval) and adjust the timing at which reception starts, but this is merely an example. With the configuration shown in Fig. 23, adjustments may be made in accordance with the difference in the number of clocks.

[0193] In a first modification of the fourth embodiment, as shown in Fig. 23, each slave communication device 20a, 20b adjusts the timing of the start of reception only when the master communication device 10 transmits to that device. If it is agreed that the master communication device 10 will transmit to each slave communication device 20a, 20b in order at a fixed timing, the timing adjustment shown in Fig. 23 is also possible. This configuration can save power.

[0194] (2-4-3. Second variation of the basic pattern) Fig. 24 is a diagram for explaining a second modified example of the basic pattern shown in Fig. 22. In the above, it has been assumed that the relative difference in clock count between the master communication device 10 and the slave communication device 20 occurs with a fixed tendency. However, the relative difference in clock count does not necessarily occur in a fixed form, and may occur with fluctuation (jitter). In other words, a mixture of faster and slower clock counts may occur.

[0195] In a second modification of the fourth embodiment, timing adjustment is performed according to the difference in clock counts, taking the above-mentioned jitter into consideration. In this modification, as shown in Fig. 24, each slave communication device 20a, 20b tallies the difference in clock counts over multiple polling periods (master transmission intervals), and adjusts the timing difference using the averaged difference based on the total.

[0196] 24, as an example, each slave communication device 20a, 20b calculates the difference in the number of clocks for two polling cycles and calculates the average value for the two cycles. Then, at the time of the fourth reception, each slave communication device 20a, 20b uses the average value calculated previously for the two polling cycles to adjust the timing for starting reception. The count of two shown here is merely an example and may be changed as appropriate.

[0197] In the example shown in Fig. 24, the timing for receiving the fifth and subsequent times may be adjusted using the average of the most recent two counting results. Alternatively, the timing may be adjusted using the average of all past counting results.

[0198] <3. Things to keep in mind> 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. [Explanation of symbols]

[0199] 10 Master communication device (on-board control device) 20. Slave communication device (vehicle equipment) 20a: First slave communication device 20b Second slave communication device 20c Third slave communication device 20d Fourth slave communication device SYS1: Communication system (vehicle system)

Claims

1. A slave communication device that communicates with a master communication device using a preamble, a first reception method in which reception is started and ended in accordance with the transmission timing of the master communication device; a second reception method in which a reception state is continued regardless of the transmission timing of the master communication device; A slave communication device that switches between the above based on the success or failure of communication.

2. 2. The slave communication device according to claim 1, wherein when the first reception method is used and a signal cannot be received from the start to the end of the reception, the slave communication device switches to the second reception method.

3. 3. The slave communication device according to claim 2, wherein when using the first reception method, if a signal is received between the start and end of the reception, the first reception method is maintained regardless of whether the received signal is intended for the slave communication device.

4. When the second receiving method is used, Switching to the first receiving method when the received signal is intended for the device itself; The slave communication device according to claim 1 , wherein the second receiving method is maintained when a received signal is not intended for the slave communication device.

5. 5. The slave communication device according to claim 1, wherein the transmission timing includes a timing for retransmitting a signal.

6. 2. The slave communication device according to claim 1, wherein, when the first reception method is used, if the transmission period of the signal of the master communication device is changed, reception is started and ended in accordance with a transmission timing corresponding to the change in the transmission period.

7. communicating with the master communication device in accordance with an agreement established between the master communication device and the master communication device; 2. The slave communication device according to claim 1, wherein, when using the first reception method, the preamble code of the preamble is changed in accordance with the agreement to be the same as that of the master communication device, depending on the reception state of a transmission signal from a device other than the master communication device.

8. 2. The slave communication device according to claim 1, wherein, when using the first reception method, a clock frequency difference between the slave communication device and the master communication device is calculated, and a reception start timing is adjusted to match a transmission timing of the master communication device in accordance with the clock frequency difference.

9. A master communication device that communicates with a slave communication device using a preamble, performing periodic data transmission to the slave communication device in a transmission period including an initial transmission period and a retransmission period within one period; If there is no response from the slave communication device to the data transmission in the initial transmission period, the slave communication device transmits data in the retransmission period; a master communication device that, if the response is received, does not transmit data during the retransmission period;

10. A master communication device that communicates with a slave communication device using a preamble in accordance with an agreement established between the slave communication device and the master communication device, The master communication device changes the transmission period of the signal to the slave communication device in accordance with the agreement so as to be the same as the reception period of the slave communication device, depending on the response state of the slave communication device to the transmission from the master communication device.

11. A master communication device that communicates with a slave communication device using a preamble in accordance with an agreement established between the slave communication device and the master communication device, A master communication device that changes the preamble code of the preamble in accordance with the agreement so as to be the same as that of the slave communication device in accordance with the response state of the slave communication device to a transmission from the master communication device.

12. A communication method for a slave communication device that communicates with a master communication device using a preamble, comprising: a first reception method in which reception is started and ended in accordance with the transmission timing of the master communication device; a second reception method in which a reception state is continued regardless of the transmission timing of the master communication device; A communication method in which the above is switched based on the success or failure of communication.

13. a master communication device; a slave communication device that communicates with the master communication device using a preamble; Equipped with The slave communication device a first reception method in which reception is started and ended in accordance with the transmission timing of the master communication device; a second reception method in which a reception state is continued regardless of the transmission timing of the master communication device; A communication system that switches between these modes based on the success or failure of communication.

14. an on-board control device mounted on a vehicle; an in-vehicle device that communicates with the in-vehicle control device using a preamble; Equipped with The in-vehicle device includes: a first reception method in which reception is started and ended in accordance with the transmission timing of the in-vehicle control device; a second reception method in which a reception state is continued regardless of the transmission timing of the on-board control device; A vehicle system that switches between these modes based on the success or failure of communication.

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