Communication method, communication system, communication device, and communication program

Abstract

An exemplary communication method is a communication method of a system that uses, for each of first and second mobile bodies adjacent to each other, preamble codes different from each other between a master unit and a slave unit and performs first and second UWB communications at communication timings synchronized with each other. When a power level is made higher than a threshold value by the second UWB communication in the second mobile body, the master unit of the first mobile body changes the timing of the first UWB communication in the first mobile body from the timing of the second UWB communication.

Description

Communication methods, communication systems, communication devices, and communication programs

[0001] This disclosure relates to communication technology for UWB (Ultra Wide Band) communication.

[0002] In recent years, wireless communication has been increasing in the communications field due to its advantages in terms of installation, such as the elimination of the need for wiring. For example, UWB communication, which uses broadband radio waves, experiences less interference with Wi-Fi (registered trademark) and radio waves used in mobile devices such as smartphones, and its wide bandwidth of 500 MHz provides good penetration, leading to a wide range of applications. Furthermore, because UWB communication can easily establish communication even in the confined spaces of metal and the numerous wires inside moving vehicles such as automobiles, it is expected to be a means of communication for equipment mounted on mobile vehicles.

[0003] Japanese Patent Publication No. 2010-166468

[0004] Here, if another mobile device adjacent to a mobile device equipped with a UWB communication system is also equipped with a UWB communication system, there is a concern that UWB communication within the mobile device may be interrupted due to radio interference from the other mobile device. As a countermeasure against this concern, for example, Patent Document 1 describes a multi-stage control system that avoids communication collisions between vehicles by changing the UWB channel used when vehicles pass each other, reducing the transmission power if there are no available transmission channels, and further adjusting the transmission timing if the transmission power cannot be reduced.

[0005] As the number of mobile devices equipped with UWB communication systems increases in the future, situations are expected to arise not only of passing by each other, but also of mobile devices being adjacent to each other for relatively long periods of time, and of multiple mobile devices approaching each other. Furthermore, it is necessary to maintain good communication responsiveness during communication within mobile devices. For these reasons, there is a need for efficient methods to suppress radio interference between mobile devices while maintaining good communication responsiveness.

[0006] In view of the above, this disclosure aims to provide a communication technology that can suppress radio interference between mobile devices while maintaining good communication responsiveness.

[0007] An exemplary communication method of the present disclosure is a communication method for a system in which, for each of two adjacent first and second mobile bodies, a master unit and a slave unit perform first and second UWB communications using different preamble codes and at synchronized communication timings, wherein the master unit of the first mobile body changes the timing of the first UWB communication in the first mobile body from the timing of the second UWB communication when the power level due to the second UWB communication in the second mobile body exceeds a threshold.

[0008] According to the exemplary disclosure, the communication timing of the first mobile body and the communication timing of the second mobile body are pre-synchronized, and preparations can be made for the case when the power level of the second UWB communication in the second mobile body exceeds a threshold. Therefore, when the power level of the second UWB communication in the second mobile body actually exceeds the threshold, the process of changing the timing of the first UWB communication in the first mobile body from the timing of the second UWB communication can be quickly executed. Thus, according to the exemplary disclosure, radio interference between mobile bodies can be suppressed while maintaining good communication responsiveness.

[0009] Diagrams showing the configuration of a communication system according to the embodiment of this disclosure. Block diagram showing the schematic configuration of the master unit. Block diagram showing the schematic configuration of the slave unit. Diagram showing the frame format used for UWB communication. Diagrams showing two communication systems SYS11 and SYS12. Diagram showing the relationship between the difference in power levels between the interference wave and the target wave and the error rate. Diagram showing the configuration of the Ipatov code. Diagram showing the relationship between the ratio of power levels between the interference wave and the target wave and the error rate in communication systems SYS11 and SYS12 when using the Ipatov code. Diagram showing the limit value of the ratio of power levels between the interference wave and the target wave by the combination of codes of communication systems SYS11 and SYS12. Diagram showing the positional relationship when the distance between two mobile bodies is long. Diagram showing the communication schedule when the interference level is below a threshold. Diagram showing the communication schedule when each polling period includes a retransmission time slot. Diagram showing the distance between two mobile bodies. Figure showing the positional relationship when the distance is short. Figure showing the communication schedule of the first embodiment when the interference level is higher than the threshold. Figure showing an example of a communication schedule that is executed instead of the communication schedule shown in Figure 9 when the number of slave devices differs between the two communication systems. Figure showing another example of a communication schedule that is executed instead of the communication schedule shown in Figure 9 when the number of slave devices differs between the two communication systems. Figure showing the communication schedule of the second embodiment when the interference level is higher than the threshold. Figure showing the communication schedule of the third embodiment when the interference level is higher than the threshold. Figure showing the communication schedule of the fourth embodiment when the interference level is higher than the threshold. Figure showing a state in which a new mobile object has entered between two separate mobile objects. Figure showing the communication schedule of the second embodiment in the state shown in Figure 15. Flowchart illustrating the processing executed by the master unit. Flowchart showing a modified example of the processing executed by the master unit.

[0010] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the embodiments, the same parts will be denoted by the same reference numerals, and redundant descriptions will be omitted unless particularly necessary.

[0011] <1. Communication System> [1-1. System Overview] Figure 1 is a diagram showing the configuration of the communication system SYS1 according to the embodiment of this disclosure. The communication system SYS1 is mounted on a mobile body M1. The mobile body M1 is, in detail, a vehicle such as an automobile, bus, or railway vehicle. However, the mobile body M1 may be something other than a vehicle, such as an airplane or a ship.

[0012] As shown in Figure 1, the communication system SYS1 comprises a master unit 10 and a plurality of slave units 20a to 20e. When it is not necessary to explain each of the slave units 20a to 20e separately, they may be simply referred to as slave unit 20. Also, slave unit 20a may be referred to as the first slave unit 20a, slave unit 20b as the second slave unit 20b, slave unit 20c as the third slave unit 20c, slave unit 20d as the fourth slave unit 20d, and slave unit 20e as the fifth slave unit 20e. Note that the number of slave units 20 that communicate with the master unit 10 via UWB communication may be other than five.

[0013] The master unit 10 constitutes the central control unit.

[0014] The slave unit 20 constitutes an individual control unit controlled by the central control unit and is connected by wire to the equipment 40 located on the mobile unit M1. The slave unit 20 transmits and receives UWB signals with the master unit 10. That is, the slave unit 20 communicates with the master unit 10 using UWB communication and is controlled by the master unit 10 using this UWB communication. The slave unit 20 controls each of the equipment 40 connected to it in response to instructions from the master unit 10. The master unit 10 and the slave units 20 can be described as communication devices that perform UWB communication. The master unit 10 communicates with each of the multiple slave units 20 using UWB communication.

[0015] The devices 40 connected to each slave unit 20 are, for example, sensors, actuators, or ECUs (Electric Control Units). In detail, sensors include, for example, light sensors, power window switches, accelerator sensors, brake sensors, or wiper switches. Actuators include, for example, power window motors, headlamp motors, wiper motors, etc. ECUs include, for example, airbag ECUs, air conditioning ECUs, etc.

[0016] [1-2. Configuration of the Master Unit] Figure 2 is a block diagram illustrating the schematic configuration of the master unit 10. Note that Figure 2 shows the components necessary to explain the features of this embodiment, and descriptions of general components are omitted.

[0017] As shown in Figure 2, the master unit 10 comprises a master unit controller 11, a master unit memory 12, and a master unit wireless communication unit 13.

[0018] The master controller 11 controls the overall operation of the master unit 10. In other words, the master controller 11 constitutes the control unit. The master controller 11 includes a processor that performs calculations and other processing. The processor is composed of, for example, a CPU (Central Processing Unit). The master controller 11 may consist of one processor or multiple processors. If it consists of multiple processors, those processors only need to be connected to each other so that they can communicate with one another.

[0019] The master unit memory 12 is composed of volatile memory and non-volatile memory. The volatile memory is specifically RAM (Random Access Memory). The non-volatile memory is specifically ROM (Read Only Memory). The non-volatile memory may also be flash memory or a hard disk drive, etc. The non-volatile memory stores programs and data that can be read by the computer. The programs include a communication program 121 used when performing UWB communication.

[0020] The program stored in the master unit memory 12 may be provided, for example, on a computer-readable non-volatile recording medium. The non-volatile recording medium may be, for example, an optical recording medium (e.g., optical disc), a magneto-optical recording medium (e.g., magneto-optical disc), a USB memory, or an SD card, in addition to the non-volatile memory described above. As another example, the program may be provided from a program provision server via a communication line such as the Internet (a configuration provided by so-called download).

[0021] In this embodiment, the functions of the master controller 11 are realized by the processor executing calculations according to programs stored in the master memory 12. The number of programs that realize the functions of the master controller 11 may be one or more.

[0022] Furthermore, at least some of the functions of the master controller 11 may be implemented by methods other than software, as in this embodiment. At least some of the functions of the master controller 11 may be implemented using, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). In other words, at least some of the functions of the master controller 11 may be implemented in hardware using a dedicated IC or the like. Also, at least some of the functions of the master controller 11 may be implemented using a combination of software and hardware.

[0023] The master unit wireless communication unit 13 is provided to enable UWB communication with the slave unit wireless communication unit 23 (see Figure 3, described later) of the slave unit 20. The master unit wireless communication unit 13 includes a transmitting function for transmitting UWB signals and a receiving function for receiving UWB signals. In this embodiment, as an example, the master unit wireless communication unit 13 includes a transmitter 131 and a receiver 132.

[0024] As shown in Figure 2, in this embodiment, the master controller 11 comprises a preamble code management unit 111, a communication processing unit 112, an application unit 113, and a distance measurement processing unit 114 as its functional units. Note that each functional unit 111 to 114 is a conceptual component. The function performed by one component may be distributed among multiple components. Alternatively, the functions of multiple components may be integrated into a single component.

[0025] The preamble code management unit 111 manages the preamble code used when the master unit 10 communicates with the slave unit 20 using UWB. The preamble code management unit 111 appropriately determines the preamble code that the master unit 10 should use when using UWB communication, and also processes a process to instruct the slave unit 20 to use the preamble code. Details of the preamble code and its management will be described later.

[0026] The communication processing unit 112 performs communication processing related to UWB communication between the master unit 10 and the slave unit 20. Through this communication processing, the master unit 10 can communicate data with the slave unit 20. Specifically, the communication processing unit 112 controls the transmitter 131 to transmit a UWB signal from the master unit 10 to the slave unit 20. The communication processing unit 112 also controls the receiver 132 to receive the UWB signal sent from the slave unit 20 to the master unit 10. A detailed example of UWB communication between the master unit 10 and the slave unit 20 will be described later.

[0027] The application unit 113 implements various functions to be provided to the user of the mobile unit M1 on which the main unit 10 is mounted, based on information (data) received from the slave unit 20. Examples of the functions provided to the user include alerting the user using notification means and controlling equipment mounted on the mobile unit M1, such as air conditioners.

[0028] The distance measurement processing unit 114 estimates the distance to the object to be measured based on the reception result of the UWB signal transmitted by the object to be measured. For example, when the distance measurement processing unit 114 receives a UWB signal from the object to be measured, it calculates the difference between the transmission time and the reception time of the UWB signal. The distance measurement processing unit 114 calculates the distance to the object to be measured from the calculated time difference and the known speed of radio waves. A specific example of an object to be measured is, for example, the master unit of a communication system that is mounted on another mobile object and performs UWB communication.

[0029] [1-3. Configuration of the Sub-Unit] Figure 3 is a block diagram illustrating the schematic configuration of the sub-unit 20. Note that Figure 3 shows the components necessary to explain the features of this embodiment, and descriptions of general components are omitted.

[0030] As shown in FIG. 3, the slave device 20 includes a slave device controller 21, a slave device memory 22, and a slave device wireless communication unit 23. Note that the configuration of the slave device 20 is mostly the same as that of the master device 10, and descriptions of the same parts will be omitted as appropriate.

[0031] The slave device controller 21 controls the overall operation of the slave device 20. That is, the slave device controller 21 constitutes a control unit. The slave device controller 21 includes a processor, similar to the master device controller 11, and its hardware configuration is the same as that of the master device controller 11.

[0032] The slave device memory 22 is configured to include a volatile memory and a non-volatile memory, similar to the master device memory 12. Programs and data are stored in the non-volatile memory, similar to the case of the master device memory 12. The program includes a communication program 221 used when performing UWB communication.

[0033] The slave device wireless communication unit 23 is provided to enable UWB communication with the master device wireless communication unit 13 (see FIG. 2) provided in the master device 10. The slave device wireless communication unit 23 has a transmitter function for transmitting a UWB signal and a receiver function for receiving a UWB signal, and includes a transmitter 231 and a receiver 232, similar to the master device wireless communication unit 13.

[0034] The functions of the slave device controller 21 are realized by the processor executing arithmetic processing according to the programs stored in the slave device memory 22. As shown in FIG. 3, in this embodiment, the slave device controller 21 includes a preamble code management unit 211 and a communication processing unit 212 as its functional units.

[0035] Note that at least a part of the functions of the slave device controller 21 may be realized by other methods instead of being realized by software, similar to the case of the master device controller 11. Also, each functional unit 211, 212 is a conceptual component, and the points that the functions executed by these components may be dispersed into multiple parts or multiple functions may be integrated are the same as those of the above-mentioned master device controller 11.

[0036] The preamble code management unit 211 manages the preamble codes used when the own device (slave device 20) performs UWB communication with the master device 10. The preamble code management unit 211 changes the preamble code used by the own device (slave device 20) in response to an instruction from the master device 10. That is, the slave device 20 can be said to be a communication device instructed by another communication device (master device 10) to change the preamble code. With such a configuration, when the master device 10 changes the preamble code, the slave device 20 can appropriately perform UWB communication by matching the preamble code used for UWB communication with the master device 10.

[0037] The communication processing unit 212 executes communication processing related to UWB communication performed between the own device (slave device 20) and the master device 10. Through this communication processing, for example, the slave device 20 can perform data communication with the master device 10. Specifically, the communication processing unit 212 controls the transmitter 231 to perform processing for transmitting a UWB signal from the own device (slave device 20) to the master device 10. In addition, the communication processing unit 212 controls the receiver 232 to perform processing for receiving a UWB signal sent from the master device 10 to the own device (slave device 20).

[0038] <2. UWB Communication> Next, the UWB communication used in the communication system SYS1 will be described.

[0039] [2-1. Overview] UWB communication is wireless communication using the UWB communication method. UWB communication is performed in accordance with a standard such as IEEE 802.15.4 (hereinafter sometimes simply referred to as a communication standard).

[0040] ]>FIG. 4A is a diagram showing a frame format F1 used for UWB communication. The frame format F1 shown in FIG. 4A corresponds to the structure of one unit of transmission data in UWB communication. The frame format F1 used for UWB communication is determined by the above-described communication standard.

[0041] As shown in Figure 4A, the frame format F1 used in UWB communication has a structure in which the preamble is at the beginning, followed by the SFD (Start Frame Delimiter), PHR (PHY Header), and the data body in that order. Note that the term "data body" is used to make the differences between the preamble, SFD, and PHR easier to understand.

[0042] A preamble is a sequence of bits in a predetermined pattern, or pulses (e.g., -, 0, +), that are sent before the data itself to inform the receiver that data is about to be sent in digital communication. The receiver uses the preamble signal to synchronize its receiving clock.

[0043] The SFD is a specific pattern of bits used to signal the start of data in a communication frame. The PHR contains information necessary for decoding the packet. For example, the PHR includes the address of the communication partner and information about the data length of the data that follows. The data body is the main body of the information to be sent to the communication partner and includes the actual data to be transmitted. For example, the data body includes information such as the ID information of the recipient of the communication frame, the ID information of the sender, instruction information from the master unit 10 to the slave unit 20, sensor values ​​detected by sensors on the slave unit 20, and the operating status of the actuator controlled by the slave unit 20.

[0044] [2-2. Preamble Code] The preamble included in the UWB communication frame format F1 has multiple patterns. The preamble code is a parameter that identifies these multiple patterns.

[0045] There are 24 types of preamble codes, from code "1" to code "24". Codes "1" to "8" are preamble codes with a PRF (Pulse Replenition Frequency) of 16 MHz. Codes "9" to "24" are preamble codes with a PRF of 64 MHz. Preamble codes can be divided into two groups based on their PRF. Codes "1" to "8" are the low-code group with a low PRF. Codes "9" to "24" are the high-code group with a high PRF. In Japan, there are two low-code preamble codes that can be used: code 3 and code 4, and four high-code preamble codes that can be used in Japan: code 9 to 12.

[0046] Furthermore, in the IEEE 802.15.4z communication standard, codes "25" to "32" are added to the aforementioned codes "1" to "24" as preamble code types. In other words, when following the IEEE 802.15.4z communication standard, there are 32 types of preamble codes, from code "1" to "32".

[0047] Codes "25" through "32" are preamble codes intended for use primarily in ranging applications with a PRF of 111 MHz. Note that preamble codes "25" through "32" can also be used for data communication and radar functions.

[0048] By assigning different preamble codes to the communication system SYS1 mounted on mobile unit M1 and the communication system mounted on a mobile unit adjacent to mobile unit M1 that performs UWB communication, radio interference between the two communication systems can be suppressed.

[0049] However, when the inventors investigated the radio wave interference between the two communication systems SYS11 and SYS12 shown in Figure 4B, they found that even if the preamble codes are different, depending on the combination, the error rate increases if the power level of the interfering wave is greater than the power level of the target wave. The two communication systems SYS11 and SYS12 shown in Figure 4B have basically the same configuration as communication system SYS1, except that the number of slave units 20 has been changed from five to one. Here, we will explain using the example where communication system SYS11 outputs the target wave, communication system SYS12 outputs an interfering wave for communication system SYS11, and communication systems SYS11 and SYS12 communicate simultaneously. Figure 4C shows the difference in power levels (P) between the interfering wave and the target wave in the two communication systems SYS11 and SYS12. Ｂ -P Ａ This is a diagram showing the relationship between the preamble code and the error rate. Graph G1 shows the above relationship when communication system SYS11 uses preamble code "9" and communication system SYS12 uses preamble code "9". Graph G2 shows the above relationship when communication system SYS11 uses preamble code "9" and communication system SYS12 uses preamble code "12". Graph G3 shows the above relationship when communication system SYS11 uses preamble code "9" and communication system SYS12 uses preamble code "25". Graph G4 shows the above relationship when communication system SYS11 uses preamble code "25" and communication system SYS12 uses preamble code "9". Graph G5 shows the above relationship when communication system SYS11 uses preamble code "25" and communication system SYS12 uses preamble code "26". According to Figure 4C, the difference in power level (P) when the error rate increases depends on how the preamble codes are combined. Ｂ -P Ａ The power levels of the interfering wave and the target wave are different. Ｂ -P ＡAs the [[ID=]], even with different combinations of preamble codes, the error rate increases. According to the communication system SYS1 of the present embodiment, radio wave interference caused by the difference in power levels between the interfering wave and the target wave can be reduced by devising the communication schedule.

[0050] Further, the results of radio wave interference when using the Ipatov code used in IEEE802.15.4 as the preamble code are shown. As shown in FIG. 4D, the Ipatov code is a preamble code composed of three values (ternary code).

[0051] FIG. 4E shows the ratio of the power levels of the interfering wave and the target wave (P Ｂ / P Ａ ) and the relationship with the error rate in the communication systems SYS11 and SYS12 when using the Ipatov code. FIG. 4F is a diagram showing the limit value of P Ｂ / P Ａ for combinations of the codes (Ipatov codes) of the communication systems SYS11 and SYS12. The larger the limit value of P Ｂ / P Ａ , the less likely it is to cause interference. In FIG. 4F, the limit value of P Ｂ / P Ａ when the target wave of the communication system SYS11 is code "9" and the interfering wave from the communication system SYS12 is code "11", and the limit value of P Ｂ / P Ａ when the target wave of the communication system SYS11 is code "11" and the interfering wave from the communication system SYS12 is code "9" are compared, and the smaller value is taken as the limit value of P Ｂ / P Ａ for the combination of codes 9 and 11. The same applies to other combinations of codes.

[0052] <3. Communication Schedule> Next, the communication schedule executed in the communication system SYS1 of the present embodiment will be described.

[0053] [3-1. First Embodiment] Figure 5 shows a mobile body M1 equipped with a communication system SYS1 and a mobile body M2 equipped with a communication system SYS2 of the same type as the communication system SYS1, adjacent to each other. As shown in Figure 5, if the distance between mobile body M1 and mobile body M2 is long and the interference level of the communication system SYS2 on mobile body M2 is below the threshold, the communication schedule shown in Figure 6 is executed.

[0054] In the communication schedule shown in Figure 6, after checking the interference level and assigning different preamble codes between the communication systems, the transmission timings of communication system SYS1 and communication system SYS2 are synchronized, and simultaneous communication is performed between communication system SYS1 and communication system SYS2. This allows for a pre-synchronized communication timing between mobile unit M1 and mobile unit M2, and prepares for the case where the interference level from the UWB communication system of mobile unit M2 (power level due to UWB communication within mobile unit M2) exceeds a threshold. Therefore, if the interference level from communication system SYS2 of mobile unit M2 actually exceeds the threshold, the process of changing the communication timing of mobile unit M1 to that of mobile unit M2 can be quickly executed. Thus, radio interference between mobile units can be suppressed while maintaining good communication responsiveness. In addition, simultaneous communication between communication system SYS1 and communication system SYS2 improves responsiveness compared to the case where communication system SYS1 and communication system SYS2 communicate alternately.

[0055] The master unit 10 communicates with multiple slave units 20 using a polling method in UWB communication. Specifically, the master unit 10 transmits data to the multiple slave units 20 in sequence at a fixed period T (polling period; for example, a 2.0 ms period). When a slave unit 20 receives data transmitted from the master unit 10, it sends a response back to the master unit 10. In the example shown in Figure 6, the master unit 10 transmits data in the order of the first slave unit 20a, the second slave unit 20b, the third slave unit 20c, the fourth slave unit 20d, and the fifth slave unit 20e. Although not shown in Figure 6, once the turn of the fifth slave unit 20e is finished (one cycle of UWB communication is completed), the master unit returns to the first slave unit 20a and the data communication in the order described above is repeated.

[0056] Each polling period T includes a time slot t1 for normal communication. The time slot t1 for normal communication is a time slot for communication according to the polling period T. Alternatively, as shown in the communication schedule in Figure 7, each polling period T may include a time slot t2 for recommunication. The time slot t2 for recommunication is a time slot for recommunication if communication fails in the time slot t1 for normal communication. If each polling period T includes a time slot t2 for recommunication, the polling period can be set to, for example, 4.0 ms. In Figure 7, communication between the master unit 10 of communication system SYS1 and the first to fifth slave units 20a to 20e is successful in the time slot t1 for normal communication, and the time slot t2 for recommunication is not used. Similarly, communication between the master unit 10 of communication system SYS2 and the first to fourth slave units 20a to 20d is successful in the time slot t1 for normal communication, and the time slot t2 for recommunication is not used. However, communication between the master unit 10 of the communication system SYS2 and the fifth slave unit 20e failed during the normal communication time slot t1 because no reply (response transmission) was received from the fifth slave unit 20e. Therefore, the master unit 10 retransmitted the data to the fifth slave unit 20e using the retransmission time slot t2. A reply was received from the fifth slave unit 20e in response to this retransmission, and communication between the master unit 10 and the fifth slave unit 20e was successful.

[0057] Figure 8 shows a mobile body M1 equipped with communication system SYS1 and a mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1, located next to each other. As shown in Figure 8, if the distance between mobile body M1 and mobile body M2 is short and the interference level from communication system SYS2 on mobile body M2 is higher than the threshold, the communication schedule shown in Figure 9 is executed.

[0058] In the communication schedule shown in Figure 9, after confirming the interference level and assigning different preamble codes between communication systems, if the interference level from UWB communication system SYS2 to communication system SYS1 is higher than the threshold, communication system SYS1 performs a process to change the communication timing of communication system SYS1 relative to the communication timing of communication system SYS2. This strengthens the suppression of radio interference when simply assigning different preamble codes between communication systems is insufficient to suppress radio interference.

[0059] Specifically, in the communication schedule shown in Figure 9, the communication timing of communication system SYS1 is shifted relative to the communication timing of communication system SYS2, so that one cycle of UWB communication of communication system SYS2 is performed after one cycle of UWB communication of communication system SYS1 is completed. Alternatively, one cycle of UWB communication of communication system SYS1 may be performed after one cycle of UWB communication of communication system SYS2 is completed. In other words, in the communication schedule shown in Figure 9, UWB communication in communication system SYS1 and communication system SYS2 is performed alternately in one-cycle units. This makes it possible to suppress the effect of radio wave interference from UWB communication system SYS2 on communication system SYS1.

[0060] Furthermore, if the number of slave units 20 differs between communication system SYS1 and communication system SYS2, for example, as shown in Figure 10, the UWB communication cycle of the communication system with fewer slave units 20 (communication system SYS2) may be adjusted to match the UWB communication cycle of the communication system with more slave units 20 (communication system SYS1). Alternatively, for example, as shown in Figure 11, the length of the UWB communication cycle of each communication system may be adjusted to match the number of slave units 20.

[0061] [3-2. Second Embodiment] As shown in Figure 5, a mobile body M1 equipped with communication system SYS1 and a mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1 are adjacent to each other. However, if the distance between mobile body M1 and mobile body M2 is long and the interference level of communication system SYS2 on mobile body M2 is below the threshold, the communication schedule shown in Figure 6 is executed, similar to the first embodiment.

[0062] As shown in Figure 8, if a mobile body M1 equipped with communication system SYS1 and a mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1 are adjacent to each other, and the distance between mobile bodies M1 and M2 is short, and the interference level from the communication system of mobile body M2 is higher than the threshold, then the communication schedule shown in Figure 12 will be executed.

[0063] In the communication schedule shown in Figure 12, similar to the communication schedule shown in Figure 9, communication system SYS1 checks the interference level and assigns different preamble codes between communication systems. If the interference level from UWB communication system SYS2 to communication system SYS1 is higher than the threshold, it performs a process to change the communication timing of communication system SYS1 relative to the communication timing of communication system SYS2.

[0064] The master unit 10 of communication system SYS1 estimates or detects the power level received from communication system SYS2 for each communication unit between the master unit 10 of communication system SYS2 and the multiple slave units 20. The master unit 10 of communication system SYS1 identifies the slave unit among the multiple slave units 20 of communication system SYS2 that is performing communication with a power level received at a level higher than the determination threshold. In the example in Figure 12, the fifth slave unit 20e of communication system SYS2 is identified as the slave unit performing communication with a power level higher than the determination threshold.

[0065] Furthermore, the master unit 10 of communication system SYS1 executes a process to change the communication timing between itself and one of the multiple slave units 20 for the fifth slave unit 20e of communication system SYS2. In the example in Figure 12, the communication timing of the fifth slave unit 20e of communication system SYS1 is set to a different timing from the communication timing of the fifth slave unit 20e of communication system SYS2. Note that in the example in Figure 12, the communication timing of the fifth slave unit 20e of communication system SYS2 is changed, but the communication timing of the fifth slave unit 20e of communication system SYS1 may also be changed. Through communication between the master unit 10 of communication system SYS1 and the master unit 10 of communication system SYS2, the change in communication timing is executed and the communication schedule shown in Figure 12 is created. The master unit 10 of communication system SYS1 performs UWB communication according to the created communication schedule. Note that the threshold for determination is stored in the master unit memory 12 of the master unit 10 of communication system SYS1.

[0066] In the example shown in Figure 12, the communication between the master unit 10 and the slave units 20e of the communication system SYS2 (more specifically, the transmission from the slave units 20e of the communication system SYS2) corresponds to a communication where the power level reaching the master unit 10 of the communication system SYS1 is higher than the threshold for determination. In the communication schedule shown in Figure 12, a process is executed to change the communication timing for each communication unit between the master unit 10 of the communication system SYS2 and the multiple slave units 20, so that communication delay can be suppressed. In other words, according to the second embodiment, radio interference can be suppressed while maintaining good communication responsiveness.

[0067] One possible method for estimating the power level received from communication system SYS2 to the master unit 10 of communication system SYS1 is to have the master unit 10 of communication system SYS1 receive information from communication system SYS2 regarding the positional relationship between the master unit 10 of communication system SYS2 and multiple slave units 10, as well as information regarding communication power (position mapping information and communication power mapping information), and then estimate the power level received from communication system SYS2 to the master unit 10 of communication system SYS1 based on the received information. This estimation method also uses the distance between the master unit 10 of communication system SYS1 and the master unit 10 of communication system SYS2 calculated by the distance measurement processing unit 114 of the master unit 10 of communication system SYS1, as well as the output of the direction sensors provided on mobile units M1 and M2, respectively. The method for exchanging information between the master unit 10 of communication system SYS1 and the master unit 10 of communication system SYS2 is not particularly limited, but for example, the master unit 10 of communication system SYS1 and the master unit 10 of communication system SYS2 may perform UWB communication using the frame format F1 shown in Figure 4A. With this estimation method, the broadcast communication described later is unnecessary, and therefore the time required for estimation processing can be shortened.

[0068] One possible method for estimating the power level received by the master unit 10 of communication system SYS1 from communication system SYS2 is as follows: After the master unit 10 of communication system SYS1 and the master unit 10 of communication system SYS2 recognize each other through communication, the master unit 10 of communication system SYS1 instructs the master unit 10 of communication system SYS2 and multiple slave units 20 to perform broadcast communication. The master unit 10 of communication system SYS1 receives the broadcast communication from the master unit 10 of communication system SYS2 and multiple slave units 20, and uses the source ID and received signal strength of each broadcast communication to estimate the power level received by the master unit 10 of communication system SYS1 from communication system SYS2. This estimation method eliminates the need to prepare the aforementioned mapping information in advance.

[0069] [3-3. Third Embodiment] As shown in Figure 5, a mobile body M1 equipped with a communication system SYS1 and a mobile body M2 equipped with a communication system SYS2 of the same type as the communication system SYS1 are adjacent to each other. However, if the distance between mobile body M1 and mobile body M2 is long and the interference level of the communication system SYS2 on mobile body M2 is below the threshold, the communication schedule shown in Figure 6 is executed, similar to the first and second embodiments.

[0070] As shown in Figure 8, if a mobile body M1 equipped with communication system SYS1 and a mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1 are adjacent to each other, and the distance between mobile bodies M1 and M2 is short, and the interference level from the communication system of mobile body M2 is higher than the threshold, then the communication schedule shown in Figure 13 will be executed.

[0071] In the communication schedule shown in Figure 13, communication system SYS1, similar to the communication schedules shown in Figure 9 and Figure 12, checks the interference level and assigns different preamble codes between communication systems. If the interference level from UWB communication system SYS2 to communication system SYS1 is higher than the threshold, it executes a process to change the communication timing of communication system SYS1 relative to the communication timing of communication system SYS2.

[0072] Specifically, in the communication schedule shown in Figure 13, the transmission timing of the master unit 10 of communication system SYS1 becomes the reception timing of the master unit 10 of communication system SYS2. As a result, UWB communication is performed between communication system SYS1 and communication system SYS2 with a delay of only half a period of the polling cycle T. This reduces radio interference from communication system SYS2 to the mobile unit M2. Furthermore, in the communication schedule shown in Figure 13, since the delay is only half a period of the polling cycle T, communication system SYS1 and communication system SYS2 can communicate continuously without any idle slots. Therefore, the occurrence of communication delays due to the process of shifting the communication timing can be suppressed. This allows for stronger suppression of radio interference when simply assigning different preamble codes between communication systems is insufficient to suppress radio interference.

[0073] [3-4. Fourth Embodiment] As shown in Figure 5, a mobile body M1 equipped with a communication system SYS1 and a mobile body M2 equipped with a communication system SYS2 of the same type as the communication system SYS1 are adjacent to each other. However, if the distance between mobile body M1 and mobile body M2 is long and the interference level of the communication system SYS2 on mobile body M2 is below the threshold, the communication schedule shown in Figure 6 is executed, similar to the first, second, and third embodiments.

[0074] As shown in Figure 8, if a mobile body M1 equipped with communication system SYS1 and a mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1 are adjacent to each other, and the distance between mobile bodies M1 and M2 is short, and the interference level from the communication system of mobile body M2 is higher than the threshold, then the communication schedule shown in Figure 14 will be executed.

[0075] In the communication schedule shown in Figure 14, communication system SYS1, similar to the communication schedules shown in Figures 9, 12, and 13, checks the interference level and assigns different preamble codes between communication systems. If the interference level from UWB communication system SYS2 to communication system SYS1 is higher than the threshold, it executes a process to change the communication timing of communication system SYS1 relative to the communication timing of communication system SYS2.

[0076] In this embodiment, the communication system SYS1 classifies each communication between the master unit 10 and the multiple slave units 20 into either high-priority or low-priority communications. The classification result is stored in the master unit memory 12 of the communication system SYS1. Similarly, the communication system SYS2 classifies each communication between the master unit 10 and the multiple slave units 20 into either high-priority or low-priority communications. The classification result is stored in the master unit memory 12 of the communication system SYS2.

[0077] The communication schedule shown in Figure 14 is a communication schedule in which communication between the master unit 10 and the slave unit 20e of each communication system SYS1 and SYS2 is a high-priority communication, and communication between the master unit 10 and the slave unit 20a, the master unit 10 and the slave unit 20b, the master unit 10 and the slave unit 20c, and the master unit 10 and the slave unit 20d of each communication system SYS1 and SYS2 is a low-priority communication.

[0078] In the communication schedule shown in Figure 14, the communication timing of high-priority communications in communication system SYS1 (communication between master unit 10 and slave unit 20e) coincides with the communication timing of low-priority communications in communication system SYS2 (communication between master unit 10 and slave unit 20d). Furthermore, both communication systems SYS1 and SYS2 reduce the power of low-priority communications whose transmission timing coincides with high-priority communications.

[0079] Specifically, the master unit 10 of communication system SYS1 creates a communication schedule so that the communication timing of high-priority communications (communication between master unit 10 and slave unit 20e) matches the communication timing of low-priority communications in communication system SYS2 (communication between master unit 10 and slave unit 20d). In addition, communication systems SYS1 and SYS2 reduce the power of low-priority communications (communication between master unit 10 and slave unit 20d in each of communication systems SYS1 and SYS2) whose communication timing matches that of high-priority communications, and perform UWB communication according to the created communication schedule shown in Figure 14. This reduces the risk of high-priority communications becoming errors due to radio interference.

[0080] <4. When adjacent mobile bodies switch> As shown in Figure 5, mobile body M1 equipped with communication system SYS1 and mobile body M2 equipped with communication system SYS2 of the same type as communication system SYS1 are adjacent to each other. However, if the distance between mobile body M1 and mobile body M2 is long and the interference level from communication system SYS2 on mobile body M2 is below the threshold, the communication schedule shown in Figure 6 will be executed.

[0081] As shown in Figure 5, when mobile bodies M1 and M2 are adjacent to each other, and mobile body M3 moves between them to the state shown in Figure 15, the mobile body adjacent to mobile body M1 switches from mobile body M2 to mobile body M3.

[0082] In the state shown in Figure 15, the distance between mobile body M1 and mobile body M3 is short, and the distance between mobile body M3 and mobile body M2 is short. Therefore, for example, when communication systems SYS1, SYS2, and SYS3 execute the communication schedule of the second embodiment described above, the communication schedule shown in Figure 16 is executed.

[0083] Even when the distance between mobile units M1 and M2 is long, the communication timing is synchronized between the communication system SYS1 mounted on mobile unit M1 and the communication system SYS2 mounted on mobile unit M2. Therefore, even if a mobile unit M3 adjacent to mobile units M1 and M2 suddenly appears, the communication schedule shown in Figure 16 can be quickly executed. In other words, the master unit 10 of the communication system SYS1 has already created a communication schedule that synchronizes the communication timing between communication systems SYS1 and SYS2, so it can quickly create a communication schedule that includes the communication system SYS3 mounted on mobile unit M3. To put it another way, since UWB communication is already being performed by two adjacent units using a communication schedule with synchronized communication timing, the master unit 10 of either of the two adjacent communication systems can easily adjust the communication timing of the third and subsequent units. This makes it possible to suppress radio interference while maintaining good communication responsiveness.

[0084] <5. Processing Executed by the Master Unit> Figure 17 is a flowchart illustrating the processing performed by the master unit 10 of the communication system SYS1. More specifically, the processing shown in Figure 17 is executed by the master unit controller 11 of the master unit 10 of the communication system SYS1. The flowchart shown in Figure 17 shows the technical content of the computer program (communication program 121) that causes the master unit controller 11 (computer) to function as a means for executing the communication method of this embodiment.

[0085] The master unit 10 of the communication system SYS1 starts the process shown in Figure 17 in response to the ignition (IG) being turned on of the mobile device M1. The master unit 10 of the communication system SYS1 also terminates the process shown in Figure 17 in response to the ignition being turned off. Note that this is an example, and the master unit 10 of the communication system SYS1 may switch the start and end of the process shown in Figure 17 in conjunction with, for example, the on / off of the ACC (accessory).

[0086] In step S1, the master unit 10 (communication processing unit 112) of the communication system SYS1 outputs a specific signal to the adjacent mobile body. Here, the specific signal is a signal for detecting other adjacent mobile bodies. As the specific signal, for example, UWB communication may be used, or other communication means may be used. If mobile body M2 is adjacent to mobile body M1, the master unit 10 of the communication system SYS2 will receive the specific signal and send a reply to the specific signal. Once the specific signal is output, the process proceeds to step S2.

[0087] In step S2, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines whether or not there is a response to a specific signal. If it is determined that there is a response to the specific signal (Yes in step S2), the process proceeds to step S3. If it is determined that there is no response to the specific signal (No in step S2), the process proceeds to step S16.

[0088] In step S3, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines whether its own system (communication system SYS1) has priority over another system (for example, communication system SYS2) that has output a reply to a specific signal. For example, each system may store its own priority information in advance, and the reply to a specific signal may include priority information, and the determination may be made based on the priority information. Alternatively, for example, it may be determined that the system that output the specific signal has a higher priority than the system that output a reply to the specific signal. If it is determined that its own system has priority (Yes in step S3), the process proceeds to step S4. If it is determined that its own system does not have priority (No in step S3), the process proceeds to step S11.

[0089] In step S4, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs synchronization processing to synchronize the time axis used by the communication system SYS1 with the time axis used by other systems. Once the synchronization processing is completed, the process proceeds to step S5. Note that the processing in step S4 may be performed after step S5 or step S6.

[0090] In step S5, the master unit 10 (communication processing unit 112) of the communication system SYS1 confirms the other system information submitted (transmitted) from the other system. This other system information includes, for example, the preamble code used by the other system, the configuration of the slave unit (including the priority of the slave unit in the fourth embodiment), and the communication timing. Once the confirmation process is complete, the process proceeds to step S6.

[0091] In step S6, the master unit 10 (preamble code management unit 111) of communication system SYS1 determines the preamble code to be used in its own system and the preamble code to be used in the other system so that the preamble code used in its own system and the preamble code to be used in the other system are different from each other. The master unit 10 of communication system SYS1 transmits the determined preamble code to the master unit 10 of communication system SYS2. Once the preamble codes to be used in communication system SYS1 and communication system SYS2 have been determined, the process proceeds to step S7.

[0092] In step S7, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines the communication schedule (communication timing of its own system and communication timing of other systems) according to the interference level.

[0093] Specifically, if the interference level from other systems is below a threshold, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs UWB communication according to the communication schedule in which its own system and other systems perform simultaneous communication as described above.

[0094] If the interference level from other systems is higher than the threshold, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs UWB communication according to a communication schedule that modifies the communication timing of its own system and other systems as described above.

[0095] For example, the master unit 10 (communication processing unit 112) of the communication system SYS1 estimates whether the interference level from other systems is higher than a threshold based on the power level. Specifically, the master unit 10 (communication processing unit 112) of the communication system SYS1 detects the power level received from other systems, and estimates that the interference level from other systems is higher than the threshold if the difference between the power level received from other systems and the power level received from the slave units 20 of the communication system SYS1 is greater than a comparison threshold. This estimation method involves detecting and comparing power levels, so an improvement in estimation accuracy can be expected. The power level received from other systems may be, for example, the average value of the power levels received from other systems over a certain period of time, or for example, the maximum value of the power levels received from other systems over a certain period of time. The power level received from the slave units 20 of the communication system SYS1 may be, for example, the average value of the power levels received from each slave unit 20, or for example, the minimum value of the power levels received from each slave unit 20.

[0096] For example, the master unit 10 (communication processing unit 112) of the communication system SYS1 estimates whether the interference level from the other system is higher than a threshold based on the distance between the mobile body M1 equipped with its own system and the mobile body equipped with the other system. Specifically, the master unit 10 (communication processing unit 112) of the communication system SYS1 acquires information on the distance, and if the distance is shorter than the distance threshold, it estimates that the interference level from the other mobile body's UWB communication system is higher than the threshold. This estimation method is easy because estimation is possible as long as the distance information can be acquired. It is desirable that the master unit 10 (distance measurement processing unit 114) of the communication system SYS1 performs distance measurement communication with the master unit of the other system, and that the master unit 10 (communication processing unit 112) of the communication system SYS1 acquires the distance information obtained from the distance measurement communication. This eliminates the need to provide a distance measurement means separate from the communication system SYS1.

[0097] Once the communication schedule is determined, the process proceeds to step S8.

[0098] In step S8, the master unit 10 (communication processing unit 112) of the communication system SYS1 notifies (transmits) the other system of the preamble code assigned to it and the communication timing in the other system (the other system portion of the communication schedule). In the fourth embodiment, the notification also includes power information of the lower-priority slave units of the other system. Once the notification is complete, the process proceeds to step S9.

[0099] In step S9, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs UWB communication with the slave unit 20 of the communication system SYS1 according to the communication schedule. Once one cycle of UWB communication is completed, the process proceeds to step S10.

[0100] In step S10, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines whether the UWB communication with the slave unit 20 of the communication system SYS1 has been completed a specified number of times. The specified number of times is stored in the master unit memory 12 of the master unit 10 of the communication system SYS1. If it is determined that the specified number of times has not been completed (No in step S10), the process returns to step S10. If it is determined that the specified number of times has been completed (Yes in step S10), the process returns to step S1. Also, if it is determined that the specified number of times has been completed (Yes in step S10), the master unit 10 (communication processing unit 112) of the communication system SYS1 sends a completion notification to the other system.

[0101] In step S11, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs synchronization processing to synchronize the time axis used by the communication system SYS1 with the time axis used by other systems. Specifically, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs synchronization processing based on synchronization instructions from other systems. Once the synchronization processing is completed, the process proceeds to step S12.

[0102] In step S12, the master unit 10 (communication processing unit 112) of the communication system SYS1 submits (transmits) its own system information to the other system. This system information includes, for example, the preamble code used in its own system and the configuration of the slave units (including the priority of the slave units in the fourth embodiment). Once the submission process is complete, the process proceeds to step S13.

[0103] In step S13, the master unit 10 (communication processing unit 112) of the communication system SYS1 receives notifications sent from other systems. Once the notification reception is complete, the process proceeds to step S14.

[0104] In step S14, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs UWB communication with the slave unit 20 of the communication system SYS1 according to the communication schedule. Once one cycle of UWB communication is completed, the process proceeds to step S15.

[0105] In step S15, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines whether or not it has received a completion notification from another system for the specified number of communication sessions. If it has not received a completion notification (No in step S15), the process returns to step S14. If it has received a completion notification (Yes in step S15), the process returns to step S1.

[0106] In step S16, the master unit 10 (communication processing unit 112) of the communication system SYS1 performs UWB communication with the slave unit 20 of the communication system SYS1 without synchronizing with other systems. Once one cycle of UWB communication is completed, the process proceeds to step S17.

[0107] In step S17, the master unit 10 (communication processing unit 112) of the communication system SYS1 determines whether the UWB communication with the slave unit 20 of the communication system SYS1 has been completed the specified number of times. If it is determined that the specified number of times has not been completed (No in step S17), the process returns to step S16. If it is determined that the specified number of times has been completed (Yes in step S17), the process returns to step S1.

[0108] <6. Notes and Precautions> Various technical features disclosed in the embodiments for carrying out the invention in this specification can be modified in various ways without departing from the spirit of the technical creation. Furthermore, the multiple embodiments and modifications disclosed in the embodiments for carrying out the invention in this specification may be combined to the extent possible.

[0109] In Figure 17, for example, the master unit 10 of the communication system SYS1 may start communication with each slave unit 20 of the communication system SYS1 in response to the ignition (IG) or accessory (ACC) of the mobile body M1 being turned on. Subsequently, if an object is detected by an object detection sensor such as LiDAR (Light Detection And Ranging), millimeter-wave radar, or ultrasonic sonar mounted on the mobile body M1, the processing shown in Figure 17 may be started. Specifically, the master unit 10 of the communication system SYS1 may start outputting a signal for the adjacent mobile body in step S1 when another mobile body is detected by the object detection sensor described above. Furthermore, if other mobile bodies are no longer detected by the object detection sensor, the communication synchronized with other systems may be completed. When there are no longer any adjacent mobile bodies, the master unit 10 of the communication system SYS1 can perform UWB communication with the slave units 20 without being affected by other systems.

[0110] Alternatively, for example, the master unit 10 of the communication system SYS1 may start communication with each slave unit 20 of the communication system SYS1 in response to the ignition (IG) or accessory (ACC) of the mobile unit M1 being turned on, and then start the process shown in Figure 17 if the error rate of the communication exceeds an error rate threshold.

[0111] <7. Modifications> In the example shown in Figure 17, the steps are performed in the order of determining the preamble code in step S6 and determining the communication schedule in step S7, but the process is not limited to this. As shown in Figure 18, the preamble code arbitration process may be performed according to the interference level determination result.

[0112] Specifically, after the processing in step S5 is completed, the master unit 10 (communication processing unit 112) of the communication system SYS1 estimates whether the interference level from other systems is higher than a threshold based on the power level (step S101). If it is estimated that the interference level from other systems is below the threshold (No in step S101), the master unit 10 (communication processing unit 112) of the communication system SYS1 performs preamble code arbitration (step S102) and performs UWB communication with its own system and other systems according to the communication schedule in which simultaneous communication is performed as described above (step S103). When performing simultaneous communication, communication interference that may occur during simultaneous communication can be suppressed by performing preamble code arbitration so that communication systems SYS1 and SYS2 have different preamble codes. Communication systems SYS1 and SYS2 can improve their responsiveness by performing simultaneous communication.

[0113] On the other hand, if the interference level from other systems is estimated to be higher than the threshold (Yes in step S101), even if the preamble code arbitration process is performed, interference may still occur if simultaneous communication is performed. Therefore, the master unit 10 (communication processing unit 112) of communication system SYS1 performs UWB communication with the communication schedule that modifies the communication timing as described above (step S103). In this case, the preamble code arbitration process may be omitted. In other words, if the interference level from other systems is higher than the threshold, interference between communication systems can be suppressed by changing the communication timing in communication systems SYS1 and SYS2 using the methods of the first to fourth embodiments described above. Therefore, the master unit 10 of communication system SYS1 may omit the preamble code arbitration process and perform the communication timing modification process. After the processing in step S103 is completed, the process proceeds to step S8.

[0114] <8. Addendum> The following addendum is disclosed with respect to the multiple embodiments, examples, and modifications shown above.

[0115] This disclosure can take the following configurations (1) to (14).

[0116] (1) A communication method for a system in which, for each of two adjacent first and second mobile units, a master unit and a slave unit perform first and second UWB communications using different preamble codes and at synchronized communication timings, wherein the master unit of the first mobile unit changes the timing of the first UWB communication in the first mobile unit from the timing of the second UWB communication when the power level due to the second UWB communication in the second mobile unit exceeds a threshold.

[0117] (2) The communication method according to (1), wherein the master unit of the first mobile body detects the power level obtained by the second UWB communication, and if the difference between the detected power level and the power level obtained by the first UWB communication in the first mobile body is greater than a comparison threshold, the master unit of the first mobile body changes the timing of the first UWB communication in the first mobile body to a timing different from the timing of the second UWB communication.

[0118] (3) The communication method according to (1), wherein the master unit of the first mobile unit acquires information on the distance between the first mobile unit and the second mobile unit, and if the distance is shorter than a distance threshold, changes the timing of the first UWB communication within the first mobile unit to a timing different from the timing of the second UWB communication.

[0119] (4) The communication method described in (3), wherein the master unit of the first mobile unit acquires distance information by distance measurement communication with the master unit of the second mobile unit.

[0120] (5) The communication method according to any one of (1) to (4), wherein when the power level due to the second UWB communication of the first mobile unit becomes higher than the threshold, the master unit of the first mobile unit changes the timing of the first UWB communication to a timing different from the timing of the second UWB communication so that one cycle of the first UWB communication in the first mobile unit and one cycle of the second UWB communication in the second mobile unit are performed alternately.

[0121] (6) The communication method according to any one of (1) to (4), wherein the master unit of the first mobile unit identifies a slave unit among a plurality of slave units in the second mobile unit whose power level reaching the master unit of the first mobile unit is higher than a determination threshold, and changes the timing of the first UWB communication to a timing different from the communication timing of the identified slave unit in the second mobile unit.

[0122] (7) The communication method according to (6), wherein the master unit of the first mobile unit receives information from the master unit of the second mobile unit regarding the positional relationship between the master unit of the second mobile unit and the plurality of slave units and the communication power, and estimates the power level received from the master unit of the second mobile unit and the plurality of slave units based on the received information.

[0123] (8) The communication method according to (6), wherein the master unit of the first mobile unit receives broadcast communications from the master unit and multiple slave units of the second mobile unit, and detects the power levels received from the master unit and multiple slave units of the second mobile unit based on the broadcast communications.

[0124] (9) The communication method according to any one of (1) to (4), wherein when the power level of the first mobile base unit becomes higher than a threshold due to the second UWB communication, the base unit of the first mobile base unit changes the timing of the first UWB communication so that the transmission timing of the base unit of the first mobile base unit becomes the reception timing of the base unit of the second mobile base unit.

[0125] (10) The communication method according to any one of (1) to (4), wherein the master unit of the first mobile unit changes the timing of the first UWB communication so that the communication timing with a high-priority slave unit among a plurality of slave units with different priorities matches the communication timing with a low-priority slave unit of the second mobile unit, and the master units of the first and second mobile units reduce the power during communication with a low-priority slave unit whose communication timing with the high-priority slave unit matches.

[0126] (11) The communication method according to any one of (1) to (10), wherein the master unit of the first mobile unit notifies the master unit of the second mobile unit of a change in the communication timing of the first UWB communication or an instruction to change the communication timing of the second UWB communication, and the master unit of the second mobile unit performs the second UWB communication in accordance with the content of the notification from the master unit of the first mobile unit.

[0127] (12) A communication system in which, for each of two adjacent first and second mobile units, a master unit and a slave unit perform first and second UWB communications using different preamble codes and at synchronized communication timings, wherein when the power level due to the second UWB communication in the second mobile unit rises above a threshold, the master unit of the first mobile unit notifies the master unit of the second mobile unit of a change in the communication timing of the first UWB communication or an instruction to change the communication timing of the second UWB communication, and the master unit of the second mobile unit performs the second UWB communication according to the content of the notification from the master unit of the first mobile unit.

[0128] (13) A communication device used as the master unit of a first mobile body in a system in which a master unit and a slave unit perform first and second UWB communications between each of two adjacent mobile bodies using different preamble codes and at synchronized communication timings, wherein when the power level due to the second UWB communication in the second mobile body becomes higher than a threshold, the communication device changes the timing of the first UWB communication in the first mobile body from the timing of the second UWB communication.

[0129] (14) A communication program that causes a computer in a communication device used as the master unit of a first mobile unit in a system in which a master unit and a slave unit perform first and second UWB communications between each of two adjacent mobile units using different preamble codes and synchronized communication timings to function as a means to change the timing of the first UWB communication in the first mobile unit from the timing of the second UWB communication when the power level due to the second UWB communication in the second mobile unit becomes higher than a threshold.

[0130] 10... Master unit 20a-20e... Slave units 121, 221... Communication programs M1, M2, M3... Mobile units SYS1, SYS2, SYS3... Communication systems

Claims

1. A communication method for a system in which, for each of two adjacent first and second mobile units, a master unit and a slave unit perform first and second UWB communication using different preamble codes and at synchronized communication timings, wherein the master unit of the first mobile unit changes the timing of the first UWB communication within the first mobile unit from the timing of the second UWB communication when the power level due to the second UWB communication within the second mobile unit exceeds a threshold.

2. The communication method according to claim 1, wherein the master unit of the first mobile unit detects the power level obtained by the second UWB communication, and if the difference between the detected power level and the power level obtained by the first UWB communication in the first mobile unit is greater than a comparison threshold, the master unit of the first mobile unit changes the timing of the first UWB communication in the first mobile unit to a timing different from the timing of the second UWB communication.

3. The communication method according to claim 1, wherein the master unit of the first mobile unit acquires information on the distance between the first mobile unit and the second mobile unit, and if the distance is shorter than a distance threshold, changes the timing of the first UWB communication within the first mobile unit to a timing different from the timing of the second UWB communication.

4. The communication method according to claim 3, wherein the master unit of the first mobile unit acquires distance information by distance measurement communication with the master unit of the second mobile unit.

5. The communication method according to any one of claims 1 to 4, wherein when the power level due to the second UWB communication of the first mobile unit becomes higher than the threshold, the master unit of the first mobile unit changes the timing of the first UWB communication to a timing different from the timing of the second UWB communication so that one cycle of the first UWB communication in the first mobile unit and one cycle of the second UWB communication in the second mobile unit are performed alternately.

6. The communication method according to any one of claims 1 to 4, wherein the master unit of the first mobile unit identifies a slave unit among a plurality of slave units in the second mobile unit whose power level reaching the master unit of the first mobile unit is higher than a determination threshold, and changes the timing of the first UWB communication to a timing different from the communication timing of the identified slave unit in the second mobile unit.

7. The communication method according to claim 6, wherein the master unit of the first mobile unit receives information from the master unit of the second mobile unit regarding the positional relationship between the master unit of the second mobile unit and the plurality of slave units and the communication power, and estimates the power levels received from the master unit of the second mobile unit and the plurality of slave units based on the received information.

8. The communication method according to claim 6, wherein the master unit of the first mobile unit receives broadcast communications from the master unit and multiple slave units of the second mobile unit, and detects the power levels received from the master unit and multiple slave units of the second mobile unit based on the broadcast communications.

9. The communication method according to any one of claims 1 to 4, wherein when the power level of the first mobile base unit exceeds a threshold, the base unit of the first mobile base unit changes the timing of the first UWB communication so that the transmission timing of the base unit of the first mobile base unit becomes the reception timing of the base unit of the second mobile base unit.

10. The communication method according to any one of claims 1 to 4, wherein the master unit of the first mobile unit changes the timing of the first UWB communication so that the communication timing with a higher priority slave unit among a plurality of slave units with different priorities matches the communication timing with a lower priority slave unit of the second mobile unit, and the master units of the first and second mobile units reduce the power consumption during communication with a lower priority slave unit whose communication timing matches that of a higher priority slave unit.

11. The communication method according to claim 1, wherein the master unit of the first mobile unit notifies the master unit of the second mobile unit of a change in the communication timing of the first UWB communication or an instruction to change the communication timing of the second UWB communication, and the master unit of the second mobile unit performs the second UWB communication in accordance with the content of the notification from the master unit of the first mobile unit.

12. A communication system in which, for each of two adjacent first and second mobile units, a master unit and a slave unit perform first and second UWB communications using different preamble codes and at synchronized communication timings, wherein the master unit of the first mobile unit notifies the master unit of the second mobile unit of a change in the communication timing of the first UWB communication or an instruction to change the communication timing of the second UWB communication when the power level due to the second UWB communication in the second mobile unit exceeds a threshold, and the master unit of the second mobile unit performs the second UWB communication according to the content of the notification from the master unit of the first mobile unit.

13. A communication device used as the master unit of a first mobile body in a system in which a master unit and a slave unit perform first and second UWB communications between adjacent first and second mobile bodies using different preamble codes and at synchronized communication timings, wherein when the power level due to the second UWB communication in the second mobile body exceeds a threshold, the communication device changes the timing of the first UWB communication in the first mobile body from the timing of the second UWB communication.

14. A communication program that causes a computer in a communication device used as the master unit of a first mobile unit in a system in which first and second mobile units adjacent to each other perform first and second UWB communication between a master unit and a slave unit using different preamble codes and synchronized communication timings, to function as a means to change the timing of the first UWB communication in the first mobile unit from the timing of the second UWB communication when the power level due to the second UWB communication in the second mobile unit exceeds a threshold.

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