Communication method, communication device, receiving program, and transmitting program

Abstract

To provide a technique that can improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.SOLUTION: An exemplary communication method is a communication method for transmitting information from a first communication device to a second communication device using a preamble, in which at least one of the reception start timing between multiple receivers provided in the second communication device and the transmission start timing between multiple transmitters in the first communication device is shifted within a time range shorter than one period of the preamble signal.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a communication technology for communication using a preamble. [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. One type of wireless communication that is on the rise is known as UWB (Ultra Wide Band) communication, which uses radio waves in the 8 GHz band (see, for example, Patent Document 1).

[0003] UWB communication has the advantages of low interference with radio waves used in Wi-Fi (registered trademark) and mobile devices such as smartphones, and good transmission due to its wide bandwidth of 500 MHz. UWB communication also has the advantage of being easily established in vehicles, which are confined spaces made of metal and have many wires. For these reasons, UWB communication has attracted attention as a communication method advantageous for use inside vehicles and outdoors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-166468 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 radio interference in wireless communications is to coordinate communication timing between communicating devices in advance, and have the receiving device start reception just before the expected reception time. However, in an environment where multiple systems that operate asynchronously exist, the radio waves transmitted from each system may overlap. In such cases, the preamble of the transmitted wave from another system may be detected, and the reception of the transmitted wave (target wave) from one system may fail.

[0007] It is possible to carry out arbitration to prevent overlapping of radio wave transmission timings with other systems, but this reduces communication efficiency. Therefore, a technology that is less susceptible to the effects of radio waves from other systems without reducing communication efficiency is desired.

[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 a decrease in communication efficiency. [Means for solving the problem]

[0009] An exemplary communication method of the present invention is a communication method for transmitting information from a first communication device to a second communication device using a preamble, in which communication is performed by shifting at least one of the reception start timing between multiple receivers provided in the second communication device and the transmission start timing between multiple transmitters in the first communication device within a time range shorter than one period of the preamble signal. [Effects of the Invention]

[0010] According to the exemplary embodiment of the present invention, a receiving side of a communication using a preamble can be given an opportunity to receive by relatively shifting the sampling phase of the preamble included in the transmission wave transmitted from the transmitting side. It is unlikely that the start timing of the preamble signal period will be exactly the same between the transmission wave of the own system and the transmission wave of another system. Therefore, by giving the receiving side an opportunity to receive by relatively shifting the sampling phase of the preamble as described above, the probability of successful information reception can be increased. In the exemplary configuration of the present invention, since communication arbitration with another system is not required, the communication success rate in wireless communication can be improved while suppressing a decrease in communication efficiency. [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] FIG. 1 shows a frame format used in UWB communication. [Figure 5] Schematic diagram showing the outline of radio interference countermeasures [Figure 6] FIG. 10 is a schematic diagram illustrating a detailed example of how to set the reception mode start time τstart. [Figure 7] FIG. 1 is a diagram showing a state in which a transmission wave from another system becomes an interfering wave in a communication system. [Figure 8] A schematic diagram for explaining the cause of signal reception failure in a communication system when transmission waves overlap with other systems. [Figure 9] FIG. 1 is a diagram for explaining an overview of a communication method according to a first embodiment; [Figure 10] FIG. 1 is a diagram for explaining details of a communication method according to a first embodiment; [Figure 11] FIG. 10 is a diagram showing a specific example of a communication method according to a second embodiment. [Figure 12] FIG. 12 is a diagram showing a modification of the example shown in FIG. 11. [Figure 13] 10 is a flowchart illustrating a flow of reception control in a communication method according to a second embodiment; [Figure 14] FIG. 10 is a diagram for explaining a communication method according to a third embodiment. [Figure 15] FIG. 15 is a diagram for explaining the third embodiment, showing a situation different from that of FIG. 14. [Figure 16] 10 is a flowchart illustrating a flow of transmission control in a communication method according to a third embodiment. [Figure 17] FIG. 10 is a diagram for explaining a communication method according to a fourth embodiment. [Figure 18] FIG. 18 is a diagram for explaining the fourth embodiment, showing a situation different from that of FIG. 17. [Figure 19] FIG. 19 is a diagram for explaining the fourth embodiment, showing a situation different from that of FIGS. 17 and 18. [Figure 20] 10 is a flowchart illustrating a flow of transmission control in a communication method according to a fourth embodiment; [Figure 21] FIG. 10 is a diagram for explaining a communication method according to a fifth embodiment. 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. System 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 of the present invention may 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 in-vehicle equipment in an automobile C1.

[0015] The communication system SYS1 is, for example, an in-vehicle control system in which a master ECU 10 controls each of the slave devices (in-vehicle devices) 20a to 20d via wireless communication in response to a user's operation on an HMI (Human Machine Interface) 40. To give a specific example, each of the slave devices 20a to 20d controls an actuator connected to itself based on a control signal transmitted from the master ECU 10. Furthermore, each of the slave devices 20a to 20d may transmit to the master ECU 10 a sensor value or the like detected by a sensor connected to itself.

[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. Hereinafter, 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 be only one. When there are multiple slave communication devices 20 as in this embodiment, the master communication device 10 repeatedly communicates with each of the slave communication devices 20a to 20d in turn. In other words, polling communication is performed.

[0019] In the 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 to mean 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.

[0020] Furthermore, the master communication device 10 may be configured to only transmit signals to the slave communication device 20, or may receive signals from the slave communication device 20. Furthermore, the slave communication device 20 may be configured to only receive signals from the master communication device 10, or may transmit signals to the master communication device 10. That is, the master communication device 10 and the slave communication device 20 can be both the transmitter and receiver of information. Each of the master communication device 10 and the slave communication device 20 can be either a transmitter that transmits information or a receiver that receives information. Each of the master communication device 10 and the slave communication device 20 can be either a first communication device or a second communication device of the present invention.

[0021] In this embodiment, the master communication device 10 and the slave communication device 20 communicate using a preamble. More specifically, the master communication device 10 and the slave communication device 20 communicate using UWB. 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 communicate using UWB (wireless communication), the communication system SYS1 contributes to reducing the number of wire harnesses used in the automobile C1.

[0022] 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.

[0023] [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.

[0024] As shown in FIG. 2, the master communication device 10 includes a master controller 11, a master memory 12, and a master wireless communication unit 13.

[0025] The master controller 11 controls the overall operation of the master communication device 10. The master controller 11 includes a processor that performs arithmetic processing and the like. The processor may include, for example, a CPU (Central Processing Unit). The master controller 11 may be configured with one processor or multiple processors. When configured with multiple processors, the processors only need to be connected to each other so that they can communicate with each other.

[0026] The master memory 12 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. The programs include a transmission program and a reception program.

[0027] The program stored in the master memory 12 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).

[0028] In this embodiment, the functions of the master controller 11 are realized by a processor executing arithmetic processing in accordance with a program stored in the master memory 12. The number of programs that realize the functions of the master controller 11 may be one or more.

[0029] Furthermore, at least some of the functions of the master controller 11 may be realized by other methods than by software as in the present embodiment. At least some of the functions of the master controller 11 may be realized by 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 master controller 11 may be realized by hardware using a dedicated IC or the like. At least some of the functions of the master controller 11 may be realized by a combination of software and hardware.

[0030] The master wireless communication unit 13 is provided so as to be able to perform UWB communication with a slave wireless communication unit 23 (see FIG. 3 described later) provided in the slave communication device 20. The master wireless communication unit 13 includes at least one transmitter. The master wireless communication unit 13 may also include at least one receiver. In a configuration including a transmitter and a receiver, these may be provided as separate devices or may be provided as an integrated transceiver.

[0031] When the master wireless communication unit 13 is configured to include a transmitter, the transmitter is configured to be able to select between a transmission mode and an idle mode. When the master wireless communication unit 13 is configured to include a receiver, the receiver is configured to be able to select between a reception mode and an idle mode. When the master wireless communication unit 13 is configured to include a transceiver, the transceiver is configured to be able to select between the transmission mode, the reception mode, and the idle mode.

[0032] The transmit mode is a mode in which transmission is possible. The receive mode is a mode in which reception is possible. The idle mode is a mode in which neither transmission nor reception is possible. In the idle mode, power is supplied to the necessary circuits, etc., and the mode can be immediately switched to the receive mode or transmit mode.

[0033] In the following description, even if a communication device includes a transceiver, the transceiver will be described separately as a transmitter and a receiver for convenience of explanation.

[0034] [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. Note that all of the multiple slave communication devices 20a to 20d have the configuration shown in Fig. 3.

[0035] 3, the slave communication device 20 includes a slave controller 21, a slave memory 22, and a slave wireless communication unit 23. The configurations of the slave controller 21, the slave memory 22, and the slave wireless communication unit 23 are generally similar to the configurations of the master controller 11, the master memory 12, and the master wireless communication unit 13 described above, and therefore a description of the common parts will be omitted.

[0036] The slave controller 21 controls the overall operation of the slave communication device 20. In this embodiment, the functions of the slave controller 21 are realized by a processor executing arithmetic processing in accordance with a program stored in the slave memory 22. However, as in the case of the master controller 11, at least some of the functions of the slave controller 21 may be realized using a method other than software.

[0037] The slave wireless communication unit 23 is provided so as to be able to perform UWB communication with the master wireless communication unit 13 provided in the master communication device 10. The slave wireless communication unit 23 includes at least one receiver. The slave wireless communication unit 23 may also include at least one transmitter.

[0038] <2. Overview of UWB communication> Next, an overview of UWB communication used in this embodiment will be described. Fig. 4 is a diagram showing a frame format used in UWB communication. The frame format shown in Fig. 4 corresponds to the structure of one unit of transmission data in UWB communication. Hereinafter, one unit of transmission data may be referred to as a communication frame or a communication packet.

[0039] The frame format used in UWB communication is determined by the above-mentioned communication standard. As shown in Figure 4, the frame format used in UWB communication has a structure in which a preamble is first followed by an SFD (Start Frame Delimiter), a PHR (PHY Header), and a data body. Note that the term "data body" is used to make it easier to understand the difference between the preamble, SFD, and PHR.

[0040] A preamble is a sequence of bits or pulses (e.g., -, 0, +) that is sent before the data itself in digital communications to inform the receiving end that data is about to be sent. The receiving end uses the preamble signal to synchronize the receiving clock.

[0041] There are multiple patterns in the preamble. The preamble code is a code for identifying these multiple patterns. Different preamble codes use different code symbols. Code symbols are composed of ternary symbols (for example, -, 0, +). One code symbol (1 symbol) is composed, for example, of "-+0++000-+-++00++0+00-0000-0+0-".

[0042] The SFD is a bit string with a specific pattern that signals the start of data in a communication frame. The PHR contains information necessary for decoding 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 the 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.

[0043] In UWB communications, although the strength of radio waves also plays a role, radio waves received earlier are generally given priority. Therefore, when multiple transmission waves are transmitted at the same time, it is possible that an unwanted jamming wave will be received first, rather than the intended target wave. If a jamming wave is received first, it cannot be identified as a jamming wave unless the address in the PHR, which is processed after the preamble and SFD, is demodulated. Once a jamming wave is identified, processing of the jamming wave is stopped, and reception processing of other waves becomes possible. However, if the target wave has already reached the receiver before reception processing identifies the radio wave as a jamming wave, reception of the target wave will be missed. In this embodiment, measures are implemented to reduce communication failures due to radio interference. An overview of these measures is described with reference to FIG. 5.

[0044] Figure 5 is a schematic diagram showing an overview of radio interference countermeasures. As shown in Figure 5, the transmitter is capable of switching between a transmission mode and an idle mode. The transmitter is capable of transmitting when in the transmission mode, and is unable to communicate when in the idle mode. The receiver is capable of switching between a reception mode and an idle mode. The receiver is capable of receiving when in the reception mode, and is unable to communicate when in the idle mode.

[0045] In Fig. 5, τstart is the time when the receiver starts receiving (reception mode start time), and τnext is the time when the target wave transmitted from the corresponding transmitter is expected to be received (expected reception time), which is a time previously agreed upon between the transmitter and the receiver.

[0046] The agreement is made, for example, by using wireless communication (UWB communication) or wired communication equipment (not shown) provided in the communication system SYS1. The wired communication equipment is, for example, a PLC (Power Line Communication) communication equipment that uses a power line to start the communication system SYS1.

[0047] 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 receiving circuit to stabilize and achieve good reception after the receiver starts reception mode.

[0048] As shown in Figure 5, the receiver switches from idle mode to receive mode just before the expected reception time τnext agreed upon with the transmitter. The receiver then ends receive mode and switches back to idle mode in synchronization with the end of the transmission wave from the transmitter. Note that the receiver ends receive mode at a pre-programmed timing, for example, based on the receive mode start time τstart.

[0049] In this configuration, the receiver starts receiving at the same time as the transmission start timing of the target wave transmitted from the corresponding transmitter. As a result, it is possible to reduce the possibility that the receiver will receive a transmission wave that arrives at a different time than the target wave. It is preferable to start the reception mode as close as possible to the expected time of reception of the target wave. An example of this is described below.

[0050] 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 UWB communication. In detail, the expected reception time τnext is set to the start timing of the PHR.

[0051] 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)

[0052] 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 mentioned 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 receiver can receive the transmitted data of UWB communication only after recognizing one symbol of the preamble code the required number of times Nrg.

[0053] The required number of recognition attempts Nrg is a predetermined number that depends on the device. In the example shown in FIG. 6, the required number of recognition attempts Nrg is, for example, four. The minimum recognition period for the preamble 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 that is earlier than the expected reception time τnext by the period obtained by the calculation formula (tSFD + tsym × Nrg).

[0054] 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.

[0055] <3. Detailed examples of communication methods> As described above (see FIG. 5, etc.), the communication system SYS1 of this embodiment employs a reception method in which the receiving side sets the reception start timing to coincide with the transmission timing of the transmitting side and enters the reception state for only a limited period of time. However, even when this reception method is employed, if there is another system that operates asynchronously, the radio waves transmitted by the system SYS1 and the other system may overlap. This overlap of the radio waves may cause a failure in UWB communication between the master communication device 10 and the slave communication device 20. This will be explained in more detail with reference to FIGS. 7 and 8.

[0056] The other system is a communication system that communicates using UWB communication without cooperating with the communication system SYS1 of this embodiment. The other system may be present in the same vehicle as the communication system SYS1, or may be installed in a vehicle other than the vehicle in which the communication system SYS1 is installed, or in another communication facility installation target. The UWB communication used by the communication system SYS1 and the other system uses the same frequency channel and the same preamble code.

[0057] FIG. 7 is a diagram schematically illustrating a state in which a transmission wave from another system becomes an interfering wave in the communication system SYS1. In FIG. 7, "master" refers to the master communication device 10 provided in the communication system SYS1, and "slave" refers to the slave communication device 20 provided in the communication system SYS1. This notation may also be used in other drawings, but its explanation will be omitted hereafter. Also, in FIG. 7, the transmission mode and reception mode indicated by rectangles indicate the period in transmission mode (transmission period) and the period in reception mode (reception period). The horizontal shift of the transmission period and reception period indicated by rectangles indicates a timing shift (time shift). This notation may also be used in other drawings, but its explanation will be omitted hereafter.

[0058] As shown in Fig. 7, when the master communication device 10 starts transmission, the slave communication device 20 starts receiving accordingly. In Fig. 7, the other system starts transmission slightly earlier than the master communication device 10, but transmits in a manner that almost overlaps with the transmission period of the master communication device 10. As a result, the period DP1 in which the slave communication device 20 can detect the transmission wave from the master communication device 10 overlaps with the period DP2 in which the slave communication device 20 can detect the transmission wave from the other system. As a result, the slave communication device 20 may receive either the transmission wave from the master communication device 10 or the transmission wave from the other system, and may fail to receive the transmission wave from the master communication device 10.

[0059] The possibility of the above-mentioned failure in reception will be further explained below. Fig. 8 is a schematic diagram for explaining the cause of failure in signal reception in the communication system SYS1 when superposition of transmission waves occurs between the communication system SYS1 and another system.

[0060] As shown in FIG. 8, the preamble included in the transmission wave (communication packet) has a signal structure in which impulse waveforms, which are signals with short durations, are arranged discretely. Furthermore, when the slave communication device 20 receives a signal, sampling is performed to match the period of the preamble signal. It is difficult to adjust the timing between the transmitting and receiving sides to match the phase of the preamble signal due to, for example, differences between individual components. For this reason, even in a configuration in which reception is started in accordance with the transmission timing, it is difficult for the receiving side to start reception at a timing in which the sampling phase is perfectly aligned with the phase of the preamble signal. As a result, as shown in FIG. 8, the sampling timing during reception in the slave communication device 20 may match the phase of the preamble signal of another system, resulting in accidental detection of the preamble of that system.

[0061] In particular, when the communication system SYS1 and other systems transmit signals at the same transmission cycle (polling cycle), a situation may occur in which the slave communication device 20 cannot continuously receive a transmission signal from the master communication device 10, resulting in a risk of degraded communication performance. The present disclosure provides a wireless communication technology that solves such problems. This will be described below with reference to several examples.

[0062] The above problem can be solved by adjusting the timing of wireless communication between the communication system SYS1 and other systems. However, a configuration that adjusts the timing of wireless communication may result in a decrease in communication efficiency, and furthermore, there is a risk that the accumulation of errors in the operating clock may result in the superposition of transmitted waves. For this reason, this embodiment proposes a method different from the method of performing such timing adjustment.

[0063] The communication method disclosed in the following embodiment is a communication method used when transmitting information from a first communication device to a second communication device by communication using a preamble. Specifically, the first communication device is a master communication device 10, and the second communication device is a slave communication device 20. That is, of the first and second communication devices performing preamble communication, the communication device that is the transmitting side is the master communication device 10. Of the first and second communication devices performing preamble communication, the communication device that is the receiving side is the slave communication device 20.

[0064] However, the present invention is also applicable to a case where the first communication device is a slave communication device 20 and the second communication device is a master communication device 10. Furthermore, the communication method of the present invention may be applied to all of the multiple slave communication devices 20a to 20d, or may be applied to some of the multiple slave communication devices 20a to 20d.

[0065] [3-1. First Example] FIG. 9 is a diagram illustrating an outline of the communication method of the first embodiment. In FIG. 9, a master transmitter 13T is a transmitter provided in the master wireless communication unit 13 of the master communication device 10. A first slave receiver 23R1 and a second slave receiver 23R2 are receivers provided in the slave wireless communication unit 23 of the slave communication device 20. That is, in the first embodiment, the master communication device 10, which is the transmitting side of the master communication device 10 and the slave communication device 20 that perform preamble communication, is provided with one transmitter 13T. In the first embodiment, the slave communication device 20, which is the receiving side of the master communication device 10 and the slave communication device 20 that perform preamble communication, is provided with multiple receivers 23R. Note that, in this example, the number of multiple receivers 23R provided in the slave communication device 20 that is the receiving side is two, but may be three or more.

[0066] In the example shown in FIG. 9, similar to the case of FIG. 7 described above, the other system starts transmission slightly earlier than the master transmitter 13T, but transmits in a manner that nearly overlaps with the master transmitter 13T. The period DP1 during which the slave first receiver 23R1, which starts receiving in synchronization with the master transmitter 13T's transmission, can detect the transmission wave from the master transmitter 13T overlaps with the period DP2 during which it can detect the transmission wave from the other system. Therefore, similar to the case of FIG. 7 described above, there is a possibility that the slave first receiver 23R1 may fail to receive the transmission wave from the master transmitter 13T due to the influence of the transmission wave from the other system. Taking this into consideration, the slave communication device 20 is provided with multiple receivers. Slightly shifting the reception start timing among the multiple slave receivers 23R increases the probability of successfully receiving the transmission wave from its own system (master transmitter 13T), regardless of whether or not there is a transmission wave from the other system. This will be described with reference to FIG. 10.

[0067] Fig. 10 is a diagram for explaining the details of the communication method of the first embodiment. In the example shown in Fig. 10, it is assumed that the preamble included in the transmission wave (communication packet) transmitted from the master transmitter 13T is a 2 ns signal (impulse waveform) transmitted every 8 ns. In other words, it is assumed that the period of the preamble signal is 8 ns. However, this is an example and is not intended to limit the period of the preamble signal to 8 ns.

[0068] On the side receiving the transmitted wave, sampling is performed in accordance with the period of the preamble signal. For this reason, in the example shown in Fig. 10, the sampling period of the slave first receiver 23R1 and the slave second receiver 23R2 is 8 ns.

[0069] 10, the reception start timing of the slave second receiver 23R2 is set to be slightly later than that of the slave first receiver 23R1, which starts reception in accordance with the transmission timing of the master transmitter 13T. In detail, the reception start timings of the slave first receiver 23R1 and the slave second receiver 23R2 are shifted to such an extent that there is a phase shift within one sampling period.

[0070] In other words, when receiving information, the slave communication device 20 receives the information by shifting the sampling phase of the preamble among the multiple receivers 23R. The reception program stored in the slave memory 22 causes the slave controller 21 (computer) to function as a means for executing the process of causing the multiple receivers 23R included in the slave communication device 20 to receive the information by shifting the sampling phase of the preamble among each other. Furthermore, because the sampling period of the preamble and the period of the preamble signal (impulse waveform) are the same, shifting the sampling phase can be said to shift the reception start timing within a time range shorter than one period of the preamble signal. In other words, in the communication method of the first embodiment, communication is performed by shifting the reception start timing among the multiple receivers 23R included in the slave communication device 20 within a time range shorter than one period of the preamble signal.

[0071] The difference in reception start timing between the multiple slave receivers 23R is only a time difference sufficient to shift the sampling phase, so it can be said that the reception start timing between the multiple slave receivers 23R is substantially the same. For this reason, any of the multiple slave receivers 23R can receive the transmission wave from the master transmitter 13T.

[0072] Furthermore, it is unlikely that the transmission waves are transmitted so that the preamble signals of the master transmitter 13T and other systems completely overlap. Therefore, if multiple slave receivers 23R are provided with preamble sampling phases that are relatively offset, there is a high probability that one of the multiple slave receivers 23R will start sampling the preamble of the transmission wave transmitted by the master transmitter 13T. In other words, the probability that the slave receiver 23R will start sampling the preamble of the transmission wave transmitted by the master transmitter 13T can be increased. If one of the multiple slave receivers 23R receives the transmission wave from the master transmitter 13T, the purpose is achieved, and there is no particular problem even if another slave receiver receives the transmission wave of another system. As can be seen from the above, the communication method of the first embodiment can increase the probability of receiving the transmission wave of its own system without performing communication arbitration with other systems. In other words, the communication method of the first embodiment can improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0073] 10, specifically, the reception timing of the slave first receiver 23R1 and the slave second receiver 23R2 is shifted by 2 ns. In other words, the sampling phase of the slave first receiver 23R1 and the slave second receiver 23R2 is shifted by 1 / 4. However, this is merely an example, and it is sufficient that the sampling phase of the slave first receiver 23R1 and the slave second receiver 23R2 is shifted. For example, the sampling phase may be shifted by 1 / 2 (4 ns in terms of time) or 3 / 4 (6 ns in terms of time).

[0074] As described above, both the slave first receiver 23R1 and the slave second receiver 23R2 operate under the control of the slave controller 21. For this reason, the slave first receiver 23R1 and the slave second receiver 23R2 can be operated at a clock frequency based on the same crystal oscillator, and the sampling phases of the two receivers can be easily adjusted.

[0075] Furthermore, if we consider only the purpose of increasing the reception probability, the configuration of shifting the phase of preamble sampling among multiple receivers can also be applied in cases where the configuration of matching the reception start timing on the receiving side with the transmission timing on the transmitting side is not adopted.

[0076] [3-2. Second Example] The configuration of the second embodiment is basically the same as that of the first embodiment. That is, in the communication method of the second embodiment, the reception start timings of the multiple receivers 23R provided in the slave communication device 20 are shifted within a range of time shorter than one period of the preamble signal. The following will mainly explain the differences from the first embodiment.

[0077] In the second embodiment, if there is a receiver among the multiple slave receivers 23R that fails to receive information transmitted from the master transmitter 13T, the current reception cycle for that receiver is changed to a cycle that is shorter than one cycle of the preamble signal. Reception failures include cases where information transmitted by another system is received, and cases where no information can be received for some reason during the period when the system itself is supposed to receive information. In principle, the reception cycle is the same as the transmission cycle (polling cycle) of the master transmitter 13T.

[0078] According to the communication method of the second embodiment, a receiver that fails to receive information will shift the start timing of its next reception. Therefore, if the previous reception was caused by interference with the transmission waves of another system, the cause of the failure can be eliminated, increasing the probability of successful reception. As a result, even if a receiver that previously succeeded in receiving information fails to receive the next time for some reason, the probability of successful reception as a whole system can be increased.

[0079] The amount of shift in the reception period is extremely short, within a range of time shorter than one period of the preamble signal. In other words, the reception period after the change can be considered to be substantially the same as the reception period before the change. Therefore, even if the transmission period is not changed, the receiver will not be unable to detect the preamble.

[0080] Fig. 11 is a diagram showing a specific example of a communication method of the second embodiment. In Fig. 11, the master transmitter 13T transmits information at a transmission period (polling period) "A." Accordingly, the period (hereinafter simply referred to as the reception period) of the slave first receiver 23R1 and the slave second receiver 23R2 is, in principle (in the default state), "A" as the reception start timing. Note that the reception start timings of the slave first receiver 23R1 and the slave second receiver 23R2 are slightly different (enough to shift the sampling phase).

[0081] In Fig. 11, the symbol "o" indicates a state in which the information transmitted from the master transmitter 13T has been successfully received. Also, in Fig. 11, the symbol "x" indicates a state in which the information transmitted from the master transmitter 13T has failed to be received (reception was NG). Note that, in the following, drawings containing "o" and "x" will appear, and the "o" and "x" in those drawings indicate the same states as those described here.

[0082] During the initial information transmission in FIG. 11, the slave first receiver 23R1 successfully receives the information transmitted by the master transmitter 13T. On the other hand, the slave second receiver 23R2 fails to receive the information transmitted by the master transmitter 13T. For the slave second receiver 23R2 that failed to receive the information, the reception cycle is changed from "A" to "A+α" because it may be sampling in time with the preamble signal of the transmission wave of another system. "α" is a time shorter than one cycle of the preamble signal, or in other words, a time that shifts the sampling phase. Note that for the slave first receiver 23R1 that successfully received the information, the reception cycle is not changed and remains at cycle "A."

[0083] In the example shown in Figure 11, during the second information transmission, both the slave first receiver 23R1 and the slave second receiver 23R2 successfully receive the information transmitted by the master transmitter 13T. As a result, it is determined that the slave second receiver 23R2, which failed to receive the previous information transmission, was also able to sample at a timing that was shifted from the preamble signal of the transmission wave of the other system. Therefore, to maintain this state, the reception cycle of the slave second receiver 23R2 is returned to the default cycle "A."

[0084] Note that even if the default period "A" is changed to the period "A+α," reception may still fail. In such cases, the period can be further shifted by a time shorter than one period of the preamble signal. However, if the period is repeatedly changed, it may be possible that a problem such as a malfunction has occurred in the receiver, so a configuration may be adopted in which a communication error is reported.

[0085] FIG. 12 is a diagram showing a modification of the example shown in FIG. 11. In the modification shown in FIG. 12, both the slave first receiver 23R1 and the slave second receiver 23R2 fail to receive the information transmitted by the master transmitter 13T during the initial information transmission. In such a case, the reception cycles of both the slave first receiver 23R1 and the slave second receiver 23R2 may be shifted by the same amount of time. That is, the reception cycles of both the slave first receiver 23R1 and the slave second receiver 23R2 may be changed to "A+α" as in the example shown in FIG. 11.

[0086] However, as shown in Fig. 12, the change amount of the reception cycle may be different between the first slave receiver 23R1 and the second slave receiver 23R2. That is, in Fig. 12, "α1" and "α2" are different times. Note that both "α1" and "α2" are times shorter than one period of the preamble signal (a time that is sufficient to shift the sampling phase).

[0087] Fig. 13 is a flowchart illustrating the flow of reception control in the communication method of the second embodiment. The flow shown in Fig. 13 begins when communication according to a predetermined communication schedule is initiated between the master communication device 10 and the slave communication device 20. The flow shown in Fig. 13 continues until a reason for terminating the communication according to the communication schedule occurs. The start of communication according to the communication schedule may occur, for example, when the ACC is turned on by operating the ignition key of the automobile C1. The reason for terminating communication may occur when the ACC is turned off or when a communication error occurs.

[0088] In step S1, the slave controller 21 performs a reception process that causes each of the slave receivers 23R1 and 23R2 included in the slave controller 21 to receive information transmitted from the master transmitter 13T. In response to the reception process, each of the slave receivers 23R1 and 23R2 switches from idle mode to reception mode (reception start operation) or from reception mode to idle mode (reception end operation). The timing of the reception start is determined by a communication schedule previously determined with the master communication device 10 and the amount of deviation in the reception start timing set between the slave receivers 23R1 and 23R2. If the reception cycle is changed, the reception start timing is shifted accordingly. The reception end timing is the point in time when a predetermined period has elapsed since the reception start timing. Once the reception process is complete, the process proceeds to the next step S2.

[0089] In step S2, the slave controller 21 determines whether or not there is a receiver that cannot receive signals among all of the slave receivers 23R1, 23R2 that the slave controller 21 has. If there is a receiver that cannot receive signals (Yes in step S2), the process proceeds to the next step S3. If there is no receiver that cannot receive signals (No in step S2), the process proceeds to step S4.

[0090] In step S3, the slave controller 21 changes the reception cycle for the receivers for which reception is not possible. The process of changing the reception cycle is the same as that explained above with reference to Figures 11 and 12, so a detailed explanation will be omitted here. Note that for receivers for which reception is not possible, the reception cycle remains the original cycle (default cycle). When the process of step S3 is completed, the process returns to step S1.

[0091] In step S4, the slave controller 21 determines whether there is a receiver whose reception cycle is being changed. The reception cycle being changed refers to a state in which the reception cycle has been changed from the default value. For example, referring to the example shown in FIG. 11, the reception cycle of the second slave receiver 23R2 has been changed due to a reception failure during the first information transmission. As a result, when reception is successful for the second information transmission, the reception cycle has been changed from the default value "A" to "A+α." This state corresponds to the reception cycle being changed. If there is a receiver whose reception cycle is being changed (Yes in step S4), processing proceeds to the next step S5. If there is no receiver whose reception cycle is being changed (No in step S4), no setting change processing related to the reception cycle is performed, and processing returns to step S1.

[0092] In step S5, the slave controller 21 performs processing to restore the reception cycle of the receiver whose reception cycle is being changed. Restoring the reception cycle means returning to the default reception cycle, which corresponds to returning the reception cycle to cycle "A" in the examples of Figures 11 and 12. When the processing of step S5 is completed, the processing returns to step S1.

[0093] [3-3. Third Example] Fig. 14 is a diagram for explaining a communication method of the third embodiment. In Fig. 14, a master transmitter 13T is a transmitter provided in the master wireless communication unit 13 of the master communication device 10. A first master receiver 13R1 and a second master receiver 13R2 are receivers provided in the master wireless communication unit 13 of the master communication device 10. A first slave receiver 23R1 and a second slave receiver 23R2 are receivers provided in the slave wireless communication unit 23 of the slave communication device 20.

[0094] That is, in the third embodiment, the master communication device 10, which is the transmitting side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes not only a transmitter 13T but also a receiver 13R. Also, in the third embodiment, the slave communication device 20, which is the receiving side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes a receiver 23R. Note that in this example, the number of receivers 13R included in the master communication device 10 that is the transmitting side is two, but this number may be changed as appropriate, and may be one, three, or more. Also, in this example, the number of receivers 23R included in the slave communication device 20 that is the receiving side is two, but this number may be changed as appropriate, and may be one, three, or more.

[0095] The communication method of the third embodiment employs a configuration in which the master communication device 10 performs communication by shifting the transmission timing between multiple transmissions within a range of time shorter than one period of the preamble signal. In the third embodiment, shifting the transmission start timing between multiple transmissions means changing the period of transmissions that are performed periodically. Note that the transmission period is not changed every time one period has passed, but is changed as needed. This point will be described in detail later.

[0096] In this example, the change in the transmission cycle (polling cycle) is an extremely short change, shorter than one cycle of the preamble signal, so there is no substantial change in the transmission cycle. As a result, the receiving side (slave receiver 23R) can receive the transmission wave sent from the transmitting side (master transmitter 13T) without changing the receiving cycle of the receiving side.

[0097] By changing the transmission period in such a very short time, the receiving side can be given an opportunity to receive by relatively shifting the sampling phase of the preamble included in the transmission wave transmitted from the transmitting side. It is unlikely that transmission occurs at a timing when the preamble signals of the own system and another system completely overlap. Therefore, by giving the receiving side an opportunity to receive by relatively shifting the sampling phase of the preamble as described above, the probability of successful information reception can be increased. As can be seen from the above, the communication method of the third embodiment can increase the probability of receiving the transmission wave of the own system without performing communication arbitration with another system. In other words, the communication method of the third embodiment can improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0098] In the third embodiment, the slave first receiver 23R1 and the slave second receiver 23R2 perform the same reception operation as in the first embodiment. That is, the slave first receiver 23R1 starts reception in synchronization with the transmission timing of the master transmitter 13T. The slave second receiver 23R2 starts reception with a very short delay from the reception start timing of the slave first receiver 23R1, which is sufficient to cause a deviation in the sampling phase of the preamble.

[0099] The master first receiver 13R1 operates in the same manner as the slave first receiver 23R1. That is, the master first receiver 13R1 starts receiving in accordance with the transmission timing of the master transmitter 13T. The master second receiver 13R2 operates in the same manner as the slave second receiver 23R2. That is, the master second receiver 13R2 starts receiving with an extremely short delay from the reception start timing of the slave first receiver 23R1, just enough to cause a deviation in the sampling phase of the preamble. Note that the aforementioned delay time is the same between the master second receiver 13R2 and the slave second receiver 23R2.

[0100] The master first receiver 13R1 and the master second receiver 13R2 are provided on the master communication device 10 side to estimate the reception status of the slave communication device 20. Then, depending on the estimated status, the master controller 11 of the master communication device 10 determines whether or not to change the transmission cycle of the master transmitter 13T.

[0101] In the example shown in Fig. 14, the master first receiver 13R1 successfully receives information the first time the master transmitter 13T transmits the information. Therefore, the master controller 11 infers that the slave first receiver 23R1 has successfully received the information. Also, the master second receiver 13R2 fails to receive the information the first time the master transmitter 13T transmits the information. Therefore, the master controller 11 infers that the slave second receiver 23R2 has failed to receive the information. Note that in the example shown in Fig. 15, the failure to receive is due to the transmission wave of another system being transmitted at a timing that overlaps with the transmission wave of the master transmitter 13T.

[0102] From the above estimation results, the master controller 11 can estimate that the slave communication device 20 has acquired the information transmitted from its own device, and therefore determines that there is no problem with the current transmission period. As a result, the transmission period for transmitting information from the master transmitter 13T is maintained without being changed from the current transmission period (default transmission period) "A." At this time, the reception periods of the receivers 13R1, 13R2, 23R1, and 23R2 are also not changed.

[0103] Figure 15 is a diagram for explaining a third embodiment, showing a different situation from that of Figure 14. In the example shown in Figure 15, when the master transmitter 13T transmits information for the first time, both the master first receiver 13R1 and the master second receiver 13R2 fail to receive the information. For this reason, the master controller 11 infers that both the slave first receiver 23R1 and the slave second receiver 23R2 have failed to receive the information.

[0104] Based on the above estimation results, the master controller 11 can infer that the slave communication device 20 is unable to acquire the information transmitted from the master controller 11, and therefore determines that there is a problem with the current transmission period. As a result, the master controller 11 changes the transmission period for transmitting information from the master transmitter 13T from the current transmission period "A" to transmission period "A+α." The amount "α" by which the transmission period is shifted is a time shorter than one period of the preamble signal (a time sufficient to shift the sampling phase). Note that even when the transmission period is changed, the reception periods of the receivers 13R1, 13R2, 23R1, and 23R2 are not changed. However, the reception periods of the receivers 13R1, 13R2, 23R1, and 23R2 may be changed in accordance with the change in the transmission period.

[0105] In the example shown in Fig. 15, due to the change in the transmission period of the master transmitter 13T, both the first master receiver 13R1 and the second master receiver 13R2 succeed in receiving at the next reception opportunity. Therefore, the master controller 11 determines that the change in the transmission period has been effective and returns the transmission period to the original transmission period (default transmission period "A"). The effect of changing the transmission period here includes becoming free from the influence of transmission waves from other systems. Then, in order to maintain the state free from the influence of transmission waves from the other systems, the transmission period is returned to the original transmission period.

[0106] In the example shown above, if any of the multiple master receivers 13R succeeds in receiving, the transmission cycle is not changed. However, this is an example, and if reception is unsuccessful for any one of the multiple master receivers 13R, the transmission cycle may be changed.

[0107] As can be seen from the above explanation, in this embodiment, a change in the transmission cycle of the transmitting side (master communication device 10) is used as a means for avoiding the influence of transmission waves from other systems. For this reason, unlike the first and second embodiments, the receiving side (slave communication device 20) does not necessarily need to have multiple receivers. For this reason, the number of receivers on the transmitting side and the receiving side may each be one. However, having multiple receivers on the receiving side can improve the probability of successfully receiving information transmitted from the transmitting side.

[0108] Fig. 16 is a flowchart illustrating the flow of transmission control in the communication method of the third embodiment. The flow shown in Fig. 16 starts when communication according to a predetermined communication schedule is started between the master communication device 10 and the slave communication device 20. The flow shown in Fig. 16 continues until a reason for terminating the communication according to the communication schedule occurs.

[0109] In step S11, the master controller 11 performs a transmission process to cause the master transmitter 13T included in the master controller 11 to perform transmission. In response to this transmission process, the master transmitter 13T switches from idle mode to transmission mode (transmission start operation) or switches from transmission mode to idle mode (transmission end operation). The timing of the transmission start is determined by a communication schedule including a transmission cycle (polling cycle) previously agreed upon with the slave communication device 20. Note that if the transmission cycle is changed, the transmission start timing is shifted accordingly. The transmission end timing is the point in time when a predetermined period has elapsed from the transmission start timing. When the transmission process is completed, the process proceeds to the next step S12.

[0110] In step S12, the master controller 11 performs a reception process to cause each of the master receivers 13R1 and 13R2 included in the master controller 11 to receive information transmitted from the master transmitter 13T. In response to the reception process, each of the master receivers 13R1 and 13R2 switches from idle mode to reception mode (reception start operation) or from reception mode to idle mode (reception end operation). The timing of the reception start is determined by the transmission start timing performed by the master controller 11 and the amount of deviation in the reception start timing set between the master receivers 13R1 and 13R2. The reception end timing is the point in time when a predetermined period has elapsed from the reception start timing. When the reception process is completed, the process proceeds to the next step S13.

[0111] In step S13, the master controller 11 determines whether or not there is a receiver that cannot receive signals among all the master receivers 13R1, 13R2 that the master controller 11 has. If there is a receiver that cannot receive signals (Yes in step S13), the process proceeds to the next step S14. If there is no receiver that cannot receive signals (No in step S13), the process proceeds to step S15.

[0112] In step S14, the master controller 11 changes the transmission cycle. The process of changing the transmission cycle is the same as that described above with reference to Fig. 15, and therefore will not be described here. When the process of changing the transmission cycle in step S14 is completed, the process returns to step S11.

[0113] In step S15, the master controller 11 determines whether the transmission period is currently being changed. A transmission period currently being changed refers to a state in which the transmission period has been changed from the default value, as described above. If the transmission period is currently being changed (Yes in step S15), the process proceeds to the next step, S16. If the transmission period is not currently being changed (No in step S15), no particular process for changing the transmission period is performed, and the process returns to step S11.

[0114] In step S16, the master controller 11 performs processing to restore the transmission cycle to its original state. Restoring the transmission cycle to its original state means restoring the transmission cycle to the default state, which corresponds to returning the transmission cycle to cycle "A" in the examples shown in Figures 14 and 15. When the processing of step S16 is completed, the processing returns to step S11.

[0115] As described above, in the communication method of the third embodiment, reception by the receiver 13R included in the master communication device 10 is started in synchronization with the timing at which the master communication device 10 (master transmitter 13T) starts transmitting information. Then, the information transmission cycle in the master communication device 10 is changed according to the reception status of the receiver 13R included in the master communication device 10.

[0116] The master communication device 10 of the third embodiment causes its own receiver 13R to start reception in accordance with the timing of its own information transmission. Then, the master communication device 10 changes the period of the periodic information transmission within a time range shorter than one period of the preamble signal, according to the information received by the receiver R.

[0117] The transmission program stored in the master memory 12 of the master communication device 10 of the third embodiment causes the master controller 11 (computer) to function as a means for executing the following (a) and (b). (a) The receiver 13R included in the device itself starts receiving information in accordance with the timing at which the information transmission starts. (b) Changing the period of periodically transmitted information within a time range shorter than one period of the preamble signal according to the reception status of the receiver 13R.

[0118] According to these configurations, the transmitting side that communicates using a preamble can estimate the reception status of the receiving side and change the communication state according to the estimation result so as not to be affected by the transmission waves of other systems. In other words, according to these configurations, it is possible to improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0119] [3-4. Fourth Example] Fig. 17 is a diagram for explaining a communication method of the fourth embodiment. In Fig. 17, a master transmitter 13T is a transmitter provided in the master wireless communication unit 13 of the master communication device 10. A master receiver 13R is a receiver provided in the master wireless communication unit 13 of the master communication device 10. A slave transmitter 23T is a transmitter provided in the slave wireless communication unit 23 of the slave communication device 20. A slave receiver 23R is a receiver provided in the slave wireless communication unit 23 of the slave communication device 20.

[0120] That is, in the fourth embodiment, the master communication device 10, which is the transmitting side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes not only a transmitter 13T but also a receiver 13R. Also, in the fourth embodiment, the slave communication device 20, which is the receiving side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes not only a receiver 23R but also a transmitter 23T. Note that in this example, the transmitting and receiving communication devices 10, 20 each include one receiver, but this is merely an example, and multiple receivers may be included, as in the third embodiment. Correspondingly, the receiving communication device 20 may also include multiple transmitters.

[0121] The communication method of the fourth embodiment employs a configuration in which the master communication device 10 performs communication by shifting the transmission timing between multiple transmissions within a range of time shorter than one period of the preamble signal. In the fourth embodiment, shifting the transmission start timing between multiple transmissions means changing the period of transmissions that are performed periodically. Note that the transmission period is not changed every time one period has passed, but is changed as needed. In this respect, it is the same as the communication method of the third embodiment. However, the method of determining whether to change the transmission period differs from that of the third embodiment. Details of this point will be described later.

[0122] In the communication method of the fourth embodiment, as in the case of the third embodiment, by changing the transmission period by an extremely short time, the receiving side can be given an opportunity to receive by relatively shifting the sampling phase of the preamble included in the transmission wave transmitted from the transmitting side. As a result, the probability of receiving the transmission wave of the own system can be increased without performing communication arbitration with other systems. In other words, according to the communication method of the fourth embodiment, it is possible to improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0123] In the fourth embodiment, the master receiver 13R and the slave receiver 23R start reception in synchronization with the transmission timing of the master transmitter 13T, as in the third embodiment. Furthermore, when reception is performed at the slave receiver 23R, the slave transmitter 23T transmits a response at a timing previously agreed upon with the master communication device 10. In other words, the master receiver 13R receives not only information transmitted by itself, but also response information from the slave communication device 20. In the fourth embodiment, the master controller 11 of the master communication device 10 determines whether to change the transmission cycle of the master transmitter 13T depending on the reception status of the response information from the master receiver 13R.

[0124] 17, when the master transmitter 13T transmits information for the first time, the master receiver 13R successfully receives the information transmitted by its own device (master transmitter 13T). Also, when the master transmitter 13T transmits information for the first time, the slave receiver 23R successfully receives the information transmitted by the master transmitter 13T. In response to the successful reception, the slave transmitter 23T transmits a response, and the master receiver 13R successfully receives the transmitted response.

[0125] In such a case, the master controller 11 determines that the slave communication device 20 has acquired the information transmitted from its own device, and therefore determines that there is no problem with the current transmission cycle. As a result, the transmission cycle for transmitting information from the master transmitter 13T is maintained without being changed from the current transmission cycle (default transmission cycle) "A." At this time, the reception cycles of the receivers 13R and 23R are also not changed.

[0126] FIG. 18 is a diagram for explaining a fourth embodiment, and shows a different situation from that of FIG. 17. In the example shown in FIG. 18, at the time of the first information transmission from the master transmitter 13T, the master receiver 13R fails to receive the information transmitted by its own device (master transmitter 13T). At the time of the first information transmission from the master transmitter 13T, the slave receiver 23R also fails to receive the information transmitted by the master transmitter 13T. Due to this reception failure, the slave transmitter 23T does not transmit a response. Because there is no response transmission, the master receiver 13R fails to receive the response transmission.

[0127] In such a case, the master controller 11 determines that there is a problem with the current transmission cycle because it is estimated that the slave communication device 20 has not been able to acquire the information transmitted from the master controller 11 itself. As a result, the master controller 11 changes the transmission cycle of the information transmission of the master transmitter 13T from the current transmission cycle "A" to a transmission cycle "A+α". The amount "α" by which the transmission cycle is shifted is a time shorter than one period of the preamble signal (a time sufficient to shift the sampling phase). Note that even when the transmission cycle is changed, the reception cycle of each receiver 13R, 23R is not changed. However, the reception cycle of each receiver 13R, 23R may be changed in accordance with the change in the transmission cycle.

[0128] 18, due to the change in the transmission cycle of the master transmitter 13T, both the master transmitter 13R and the slave receiver 23R succeed in reception at the next reception opportunity. As a result, the slave transmitter 23T transmits a response, and the master receiver 13R successfully receives the response transmission. For this reason, the master controller 11 determines that the change in the transmission cycle has been effective, and returns the transmission cycle to the original transmission cycle (default transmission cycle "A").

[0129] Fig. 19 is a diagram for explaining a fourth embodiment, and shows a different situation from Figs. 17 and 18. In the example shown in Fig. 19, at the time of the first information transmission from the master transmitter 13T, the master receiver 13R successfully receives the information transmitted by its own device (master transmitter 13T). At the time of the first information transmission from the master transmitter 13T, the slave receiver 23R also successfully receives the information transmitted by the master transmitter 13T. In response to the successful reception, the slave transmitter 23T transmits a response, but the master receiver 13R fails to receive the transmitted response.

[0130] In such a case, the master controller 11 determines that there is a problem with the current transmission cycle because it can infer that the slave communication device 20 has not received the information transmitted from the master communication device 11. As a result, the master controller 11 changes the transmission cycle for transmitting information from the master transmitter 13T from the current transmission cycle "A" to transmission cycle "A+α."

[0131] 19, due to the change in the transmission cycle of the master transmitter 13T, at the next reception opportunity, the master receiver 13R fails to receive for some reason, but the slave receiver 23R succeeds in receiving. As a result, the slave transmitter 23T transmits a response, and the master receiver 13R successfully receives the response transmission. As a result, the master controller 11 determines that the change in the transmission cycle has been effective, and returns the transmission cycle to the original transmission cycle (default transmission cycle "A").

[0132] As can be seen from the above, in the fourth embodiment, whether or not to change the transmission period of the master transmitter 13T is determined depending on the reception status of the master receiver 13R in response to a response transmission from the slave transmitter 23T. Furthermore, the configuration is such that the success or failure of the master receiver 13R receiving information transmitted from its own device (master transmitter 13T) is not taken into consideration. Note that the explanations in FIGS. 17 and 18 above also explain whether or not the master receiver 13R receives information transmitted from its own device (master transmitter 13T). This explanation is merely for the purpose of facilitating understanding of the phenomenon, and in this embodiment, the success or failure of the master receiver 13R receiving information transmitted from its own device is not used in determining whether or not to change the transmission period of the master transmitter 13T. However, this is merely an example, and the success or failure of the master receiver 13R receiving information transmitted from the master transmitter 13T may be taken into consideration in determining whether or not to change the transmission period of the master transmitter 13T. If the master receiver 13R is unable to receive information transmitted from the master transmitter 13T, the transmission cycle of the master transmitter 13T may be changed.

[0133] Furthermore, in the example shown above, the slave receiver 23R is configured not to receive the response transmission from the slave transmitter 23T. However, this is merely an example. The response transmission from the slave transmitter 23T may also be configured to be received by the slave receiver 23R, and the transmission (response) timing of the slave transmitter 23T may be shifted by a time shorter than one period of the preamble signal (a time sufficient to shift the sampling phase) depending on whether the reception is successful or not.

[0134] Furthermore, in the example shown above, when the transmission period of the master transmitter 13T is changed, the reception period of each receiver 13R, 23R is not changed, but the reception period of each receiver 13R, 23R may also be changed together with the change in the transmission period of the master transmitter 13T.

[0135] Fig. 20 is a flowchart illustrating the flow of transmission control in the communication method of Example 4. The flow shown in Fig. 20 begins when communication according to a predetermined communication schedule is initiated between the master communication device 10 and the slave communication device 20. The flow shown in Fig. 20 continues until a reason for terminating the communication according to the communication schedule occurs.

[0136] In step S21, the master controller 11 performs a transmission process to cause the master transmitter 13T included in the master controller 11 to perform transmission. In response to this transmission process, the master transmitter 13T switches from idle mode to transmission mode (transmission start operation) or switches from transmission mode to idle mode (transmission end operation). The timing of the transmission start is determined by a communication schedule including a transmission cycle (polling cycle) previously agreed upon with the slave communication device 20. Note that if the transmission cycle is changed, the transmission start timing is shifted accordingly. The transmission end timing is the point in time when a predetermined period has elapsed from the transmission start timing. When the transmission process is completed, the process proceeds to the next step S22.

[0137] In step S22, the master controller 11 performs a reception process to have the master receiver 13R included in the master controller 11 receive information transmitted from the master transmitter 13T. In response to the reception process, the master receiver 13R switches from idle mode to reception mode (reception start operation) or switches from reception mode to idle mode (reception end operation). The timing of reception start is determined by the timing of transmission start performed by the master controller 11. The timing of reception end is the point in time when a predetermined period has elapsed since the reception start timing. When the reception process is completed, the process proceeds to the next step S23.

[0138] In step S23, the master controller 11 performs a response reception process in which the master receiver 13R included in the master controller 11 receives the response transmitted from the slave transmitter 23T. In response to the response reception process, the master receiver 13R switches from idle mode to reception mode (reception start operation) or switches from reception mode to idle mode (reception end operation). The timing of the start of response reception is determined by a communication schedule previously determined with the slave communication device 20. The timing of reception end is the point in time when a predetermined period has elapsed from the reception start timing. When the response reception process is completed, the process proceeds to the next step S24.

[0139] In step S24, the master controller 11 determines whether the master receiver 13R has failed to receive a response (response reception is NG). If the response reception is NG (Yes in step S24), the process proceeds to the next step S25. If the response reception is successful (No in step S24), the process proceeds to step S26.

[0140] In step S25, the master controller 11 changes the transmission cycle. The process of changing the transmission cycle is the same as that explained above with reference to Figure 18, etc., and therefore will not be explained here. When the process of changing the transmission cycle in step S25 is completed, the process returns to step S11.

[0141] In step S26, the master controller 11 determines whether the transmission period is being changed. A transmission period being changed refers to the state in which the transmission period has been changed from the default value, as described above. If the transmission period is being changed (Yes in step S26), the process proceeds to the next step, S27. If the transmission period is not being changed (No in step S26), no particular process for changing the transmission period is performed, and the process returns to step S21.

[0142] In step S27, the master controller 11 performs processing to restore the transmission cycle to its original state. "Restore" means returning the transmission cycle to the default, which corresponds to returning the transmission cycle to cycle "A" in the examples shown in Figures 17 to 19. When the processing of step S27 is completed, the processing returns to step S21.

[0143] As described above, in the communication method of the fourth embodiment, the receiver 13R included in the master communication device 10 receives a response transmission from the slave communication device 20 in response to the information transmission of the master communication device 10. Then, the information transmission cycle of the master communication device 10 is changed depending on the reception status of the response transmission of the receiver 13R included in the master communication device 10.

[0144] The master communication device 10 of the fourth embodiment receives a response transmission from the slave communication device 20, which is the receiving side of the information transmission from the master communication device 10, by using the receiver 13R provided in the master communication device 10. Then, the master communication device 10 changes the period of the periodic information transmission within a time range shorter than one period of the preamble signal, depending on the reception status of the response transmission.

[0145] The transmission program stored in the master memory 12 of the master communication device 10 of the fourth embodiment causes the master controller 11 (computer) to function as a means for executing the following (c) and (d). (c) The receiver 13R included in the device itself receives a response transmission from the slave communication device 20 that is the receiving side in response to the transmission of information from the device itself. (d) Depending on the reception status of the response transmission, the period of the periodically transmitted information may be changed within a time range shorter than one period of the preamble signal.

[0146] According to these configurations, the transmitting side that communicates using a preamble can determine the reception status of the receiving side and change the communication state according to the determination result so as not to be affected by the transmission waves of other systems. In other words, according to these configurations, it is possible to improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0147] [3-5. Fifth Example] FIG. 21 is a diagram illustrating a communication method according to a fifth embodiment. In FIG. 21, a master first transmitter 13T1 and a master second transmitter 13T2 are transmitters provided in the master wireless communication unit 13 of the master communication device 10. A slave receiver 23R is a receiver provided in the slave wireless communication unit 23 of the slave communication device 20. That is, in the fifth embodiment, the master communication device 10, which is the transmitting side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes multiple transmitters 13T. In the fifth embodiment, the slave communication device 20, which is the receiving side of the master communication device 10 and the slave communication device 20 that perform preamble communication, includes one receiver 23R. In this example, the number of transmitters provided in the transmitting communication device is two, but it may be three or more.

[0148] 21, the other system starts transmission slightly earlier than the master communication device 10 (master transmitter 13T), but transmits in a manner that almost overlaps with the transmission period of the master communication device 10. The period in which the slave communication device 20 (slave receiver 23R), which starts receiving in synchronization with the transmission of the master communication device 10, can detect the transmission wave of the master communication device 10 overlaps with the period in which it can detect the transmission wave of the other system.

[0149] 21, it is assumed that the preamble included in the transmission wave (communication packet) transmitted from the first master transmitter 13T1 and the second master transmitter 13T2 is a 2 ns signal (impulse waveform) transmitted every 8 ns. That is, it is assumed that the period of the preamble signal is 8 ns. However, this is an example, and it is not intended to limit the period of the preamble signal to 8 ns.

[0150] Furthermore, on the side receiving the transmitted wave, sampling is performed in accordance with the period of the preamble signal. For this reason, in the example shown in Fig. 21, the sampling period of the slave receiver 23R is 8 ns. The slave receiver 23R starts receiving in accordance with the transmission timing of the first master transmitter 13T1. Note that the slave receiver 23R may also start receiving in accordance with the transmission timing of the second master transmitter 13T2.

[0151] The communication method of the fifth embodiment employs a configuration in which communication is performed by shifting the transmission timing between multiple transmissions in the master communication device 10 within a range of a time shorter than one period of the preamble signal. In the fifth embodiment, shifting the transmission start timing between multiple transmissions means shifting the transmission timing between multiple transmitters 13T1, 13T2 provided in the master communication device 10.

[0152] In other words, in the master communication device 10, multiple transmitters 13T transmit information with timings shifted from one another within a time range shorter than one period of the preamble signal. The transmission program stored in the master memory 12 causes the master controller 11 (computer) to function as a means for executing the following (e): (e) Making the multiple master transmitters 13T included in the device transmit information with the timings shifted from each other within a time range shorter than one period of the preamble signal.

[0153] The difference in transmission start timing between the multiple master transmitters 13T is only a time difference that shifts the sampling phase in the slave receiver 23R. For this reason, it can be said that the transmission start timing between the multiple master transmitters 13T is substantially the same. For this reason, the slave receiver 23R is in a state where it can receive transmission waves from the multiple master transmitters 13T. However, even assuming there is no interference with transmission waves from other systems, the slave receiver 23R will only receive transmission waves that match its own sampling timing among the transmission waves from the multiple master transmitters 13T.

[0154] Even if a transmission wave from another system is transmitted at a timing that overlaps with transmission waves from multiple master transmitters 13T, in the configuration of this embodiment, the master communication device 10 transmits multiple transmission waves that are shifted by a time (very short time) that causes a shift in the sampling phase of the preamble. It is basically impossible for the preamble signals of all of these transmission waves to completely overlap with the transmission waves from the other systems. Therefore, by transmitting multiple transmission waves with transmission start timings that are shifted by a very short time, it is possible to increase the likelihood that any of them will be received in time with the sampling timing of the slave receiver 23R. As can be seen from the above, the communication method of the fifth embodiment can increase the probability of receiving the transmission wave from its own system without performing communication arbitration with other systems. In other words, the communication method of the fifth embodiment can improve the communication success rate in wireless communication while suppressing a decrease in communication efficiency.

[0155] Furthermore, with the configuration of this embodiment, even when there are multiple slave communication devices 20a to 20d (see FIG. 1) for the master communication device 10, as in the communication system SYS1 of this embodiment, it is only necessary to increase the number of transmitters in the master communication device 10. There is no need to increase the number of transmitters or receivers in each of the slave communication devices 20a to 20d. This makes it possible to improve the communication success rate in wireless communication while suppressing an increase in the number of devices.

[0156] 21, specifically, the transmission timing of the master first transmitter 13T1 and the master second transmitter 13T2 is shifted by 2 ns. In other words, based on the sampling phase of the slave receiver 23R, the shift in transmission start timing between the master first transmitter 13T1 and the master second transmitter 13T2 is equivalent to shifting the sampling phase by 1 / 4. However, this is merely an example, and any configuration may be used in which an extremely short shift occurs between the transmission start timing of the master first transmitter 13T1 and the transmission start timing of the master second transmitter 13T2, sufficient to shift the time of the sampling phase.

[0157] As described above, both the first master transmitter 13T1 and the second master transmitter 13T2 operate under the control of the master controller 11. For this reason, the first master transmitter 13T1 and the second master transmitter 13T2 can be operated at a clock frequency based on the same crystal oscillator, and adjustments can be easily made to shift the timing at which they start transmitting by a time that is equivalent to shifting the sampling phase.

[0158] Furthermore, even when multiple master transmitters 13T are used as in this embodiment, communication may fail due to interference with transmission waves from other systems. For this reason, as in the third and fourth embodiments described above, it is preferable to provide a receiver (master receiver 13R) in the master communication device 10 and change the transmission cycles of the multiple master transmitters 13T according to the reception status of that receiver.

[0159] For example, the master receiver 13R provided in the master communication device 10 may be configured to start reception in synchronization with the transmission timing of one of the multiple master transmitters 13T. If the master receiver 13R does not succeed in communicating with any of the multiple master transmitters 13T (if it is unable to receive the transmission information from the master communication device 10), the transmission cycles of the multiple master transmitters 13T may be changed.

[0160] As another example, when the slave communication device 20 includes a slave transmitter 23T that transmits a response to the master communication device 10, the following may be adopted: The master communication device 10 may be configured to change the transmission cycles of the multiple master transmitters 13T when the master receiver 13R fails to receive a response transmission from the slave transmitter 23T.

[0161] <4. 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]

[0162] 10 Master communication device (first communication device) 20 Slave communication device (second communication device) 13R Master receiver 13R1 Master 1st receiver 13R2 Master 2nd receiver 13T Master transmitter 13T1 Master 1st transmitter 13T2 Master 2nd transmitter 23R... Slave receiver 23R1: Slave 1st receiver 23R2: Second slave receiver

Claims

1. A communication method for transmitting information from a first communication device to a second communication device by communication using a preamble, comprising: performing the communication by shifting at least one of a reception start timing among a plurality of receivers included in the second communication device and a transmission start timing among a plurality of transmissions in the first communication device within a range of a time shorter than one period of the preamble signal; Communication method.

2. the timings at which the reception starts among the plurality of receivers included in the second communication device are shifted within the short time range; 2. The communication method according to claim 1, wherein, if there is a receiver among the plurality of receivers that fails to receive the information, a period change is performed for that receiver to shift the current reception period within the short time range.

3. the transmission start timings of the first communication device among the plurality of transmissions are shifted within the short time range; The communication method according to claim 1 , wherein the shifting of the transmission start timings among the plurality of transmissions means changing a period of the information transmission that is performed periodically.

4. causing a receiver included in the first communication device to start receiving the information in accordance with a start timing of transmitting the information; The communication method according to claim 3 , further comprising changing a cycle of transmitting the information depending on a reception state of a receiver provided in the first communication device.

5. a receiver of the first communication device receives a response transmission from the second communication device in response to the transmission of the information of the first communication device; The communication method according to claim 3 , wherein the cycle of transmitting the information is changed depending on a reception status of the response transmission.

6. the transmission start timings of the first communication device among the plurality of transmissions are shifted within the short time range; The communication method according to claim 1 , wherein staggering the transmission start timings among the plurality of transmissions comprises staggering the transmission start timings among the plurality of transmitters included in the first communication device.

7. A communication device that performs communication using a preamble, A plurality of receivers are provided, When receiving the information, the plurality of receivers receive the information by shifting the sampling phase of the preamble among them. Communication equipment.

8. A computer included in a communication device that has a plurality of receivers and performs communication using a preamble, When receiving the information, the plurality of receivers receive the preamble with the sampling phases of the preambles shifted from each other. serve as a means of carrying out Receiving program.

9. A communication device that performs communication using a preamble, A transmitter and a receiver are provided, causing the receiver to start receiving the information in accordance with a timing at which the transmitter starts transmitting the information; changing a period of the information transmission periodically performed by the transmitter within a time range shorter than one period of the preamble signal according to the reception status of the receiver; Communication equipment.

10. A computer included in a communication device that includes a transmitter and a receiver and performs communication using a preamble, causing the receiver to start receiving the information in accordance with a timing at which the information is transmitted; changing a period of the information transmission periodically performed by the transmitter within a time range shorter than one period of the preamble signal according to a reception state of the receiver; serve as a means of carrying out Sending program.

11. A communication device that performs communication using a preamble, Equipped with a transmitter and a receiver, receiving a response transmission from a communication device that is a receiving side in response to the transmission of the information by the receiver; changing a period of the information transmission periodically performed by the transmitter within a time range shorter than one period of the preamble signal according to a reception status of the response transmission; Communication equipment.

12. A computer included in a communication device that includes a transmitter and a receiver and performs communication using a preamble, causing the receiver to receive a response transmission from a communication device that is a receiving side in response to the transmission of the information; changing a period of the information transmission periodically performed by the transmitter within a time range shorter than one period of the preamble signal according to a reception status of the response transmission; serve as a means of carrying out Sending program.

13. A communication device that performs communication using a preamble, A plurality of transmitters are provided, the plurality of transmitters transmit the information with timings shifted from each other within a time range shorter than one period of the preamble signal; Communication equipment.

14. A computer included in a communication device that has a plurality of transmitters and performs communication using a preamble, causing the plurality of transmitters to transmit the information with timings shifted from each other within a time range shorter than one period of the preamble signal; serve as a means of carrying out Sending program.

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