Communication circuit, communication system, and communication method

Abstract

To suppress inter-system interference using adjacent same frequency bands and improve space utilization efficiency in limited frequency resources.SOLUTION: The communication method includes: measuring the number of a plurality of sensor nodes, the rotation period, and the rotation direction (S11 to S13); selecting a first mode or a second mode on the basis of the measured rotation period (S14); rotating the direction of a beam sent from an access point on the basis of the number and rotation direction in the first period, and performing communication with a sensor nodes existing within a communication range (S16) when the first mode is selected; rotating the direction of the beam on the basis of the number and direction of rotation in a second period longer than the first period (S15), or fixing the direction of the beam (S18) when the second mode is selected, and performing communication with a sensor node existing within the communication range.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The technology described herein relates to a communication circuit, a communication system, and a communication method. [Background technology]

[0002] In an Internet of Things (IoT) society, all things will be connected to networks such as the Internet. Taking a factory as an example, the end of the wired network will be an access point (AP) such as a wireless local area network (LAN). Connections to the things beyond that are made via various wireless communication systems, including wireless LAN. Things are placed at the tips of machine tools such as robot arms that can move or are movable, or on top of moving automated guided vehicles (AGVs). This makes it difficult to connect them via a wired network. Thus, wireless IoT communication is important for connecting things to networks.

[0003] For example, there is wireless IoT communication in which an access point equipped with multiple antenna elements installed at the base of a machine tool uses simple beamforming to track the movable arm body of a machine tool, which moves and rotates at relatively high speeds, or a sensor node (SN) on an object attached to the end of the arm, and a backscatter system that uses Wi-Fi signals to achieve this. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 042974 [Patent Document 2] JP 2008-228136 A [Non-patent literature]

[0005] [Non-Patent Document 1] D.-H. Kim, J. Hirokawa, and M. Ando, ​​“Design of waveguide short-slot 2-plane couplers for one-body 2-D beam-switching Butler matrix application,” IEEE Trans. MTT, vol.64, no.3, pp.776-784, 2016. [Non-Patent Document 2] C.-H. Hsieh, et al., “A novel concept for 2D Butler matrix with multi-layers technology,” 2018 Asia Pacific Microwave Conference, pp.533-535, 2018. Summary of the Invention [Problem to be solved by the invention]

[0006] Wireless IoT communication is often achieved using unlicensed bands such as wireless LAN and Bluetooth (registered trademark), which can lead to reduced throughput and lack of real-time performance due to interference between systems. When many SNs are connected to an AP, there is a greater risk of interference between systems.

[0007] In one aspect, the technology described in this specification aims to suppress interference between systems using the same adjacent frequency band and improve spatial utilization efficiency. [Means for solving the problem]

[0008] In one aspect, the communication circuit is a communication circuit provided in an access point that performs wireless communication with a plurality of sensor nodes, measures the number, rotation period, and rotation direction of the plurality of sensor nodes, and selects a first mode or a second mode based on the measured rotation period, and when the first mode is selected, rotates the direction of a beam transmitted from the access point in a first period based on the number and the rotation direction to communicate with sensor nodes present within a communication range, and when the second mode is selected, rotates the direction of the beam in a second period longer than the first period based on the number and the rotation direction, or fixes the direction of the beam to communicate with sensor nodes present within a communication range. Effect of the Invention

[0009] One aspect is that it can suppress interference between systems that use the same adjacent frequency band, thereby improving spatial utilization efficiency. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of installation of a communication system according to an embodiment. [Diagram 2] 2 is a block diagram illustrating an example of a hardware configuration of the access point and the sensor node illustrated in FIG. 1. [Diagram 3] 1. FIG. 4 is a diagram illustrating an example of operation in an SN detection phase in the communication system shown in FIG. [Figure 4] 2 is a diagram illustrating an example of operation in a Wi-Fi communication phase in the communication system illustrated in FIG. 1. [Diagram 5] 2A and 2B are diagrams for explaining an SN spectrum identification method by down-conversion of a backscattered signal in the communication system shown in FIG. [Figure 6] 2 is a diagram for explaining a communication range in the SN detection phase in the communication system shown in FIG. 1. [Figure 7] 2 is a diagram for explaining a communication range in a Wi-Fi communication phase in the communication system shown in FIG. 1. [Figure 8] 2 is a diagram for explaining the relationship between beamforming and the movement of a sensor node in the communication system shown in FIG. [Figure 9] 2 is a diagram illustrating a time flow of an SN detection phase in the communication system shown in FIG. 1. [Figure 10] 2 is a diagram illustrating a time flow of a high-speed rotation phase in the communication system shown in FIG. 1. [Figure 11] 1. FIG. 4 is a diagram illustrating a time flow of a low-speed rotation / stop phase when the rotation SN is prioritized in the communication system shown in FIG. [Figure 12] 1. FIG. 4 is a diagram illustrating a time flow of a low-speed rotation / stop phase when a stopped SN has priority in the communication system shown in FIG. [Figure 13] 4 is a flowchart illustrating a first example of a communication operation in the communication system shown in FIG. [Figure 14] 10 is a flowchart illustrating a second example of a communication operation in the communication system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment will be described with reference to the drawings. However, the embodiment described below is merely an example, and is not intended to exclude various modifications and application of techniques not explicitly stated in the embodiment. In other words, the present embodiment can be modified in various ways without departing from the spirit of the present invention.

[0012] In addition, each figure does not necessarily include only the components shown in the figure, but may include other components. In the following drawings, parts with the same reference numerals indicate the same or similar parts unless otherwise specified.

[0013] [A] Embodiment [A-1] Configuration example FIG. 1 is a diagram showing an example of installation of a communication system 100 according to an embodiment.

[0014] Communication system 100 includes a machine tool 4 and the like. Machine tool 4 has, for example, an arm shape, grasps a workpiece with a hand attached to the tip of the arm, and places the workpiece on belt conveyor 5. Machine tools 4 may be arranged at intervals of 5 m or more, and the movable range of the robot arm may be about a 2 m radius.

[0015] An access point (AP) 1 is attached to a base 3 of the machine tool 4, and a sensor node (SN) 2 is attached to a hand or arm of the machine tool 4. In the example shown in Fig. 1, for simplicity, only one sensor node 2 is shown on each machine tool 4, but in this embodiment, it is assumed that multiple sensor nodes 2 are attached to the machine tool 4, as will be described later using Fig. 2 etc.

[0016] The communication system 100 uses, for example, a 5 GHz wireless LAN to track a sensor node 2 attached to a movable arm or hand of the machine tool 4, which moves or rotates at a relatively high speed, by simple beamforming using an access point 1 having multiple antenna elements attached to a base 3 of the machine tool 4. The access point 1 may be equipped with a relatively small number of antenna elements (for example, a 2×2 patch array antenna) attached to the base of the machine tool 4. The rotation speed of the sensor node 2 attached to the tip of the arm may be a maximum of 1,000 rpm (rotation period 60 ms).

[0017] FIG. 2 is a block diagram showing a schematic example of a hardware configuration of the access point 1 and the sensor node 2 shown in FIG.

[0018] As shown in FIG. 2, a machine tool 4 in this embodiment has a plurality of sensor nodes 2 (seven in the illustrated example) attached thereto.

[0019] The access point 1 is an example of a communication circuit, and includes a 5 GHz band Wi-Fi TRX11 (hereinafter may be simply referred to as "TRX11"), a Wi-Fi backscatter RX12 (hereinafter may be simply referred to as "backscatter RX12"), a beamforming processing unit 13, multiple element antennas 14, a circulator 15, and a switch 16.

[0020] The TRX 11 is a transceiver. The input / output RF signals of the TRX 11 can switch between multiple beams directed in a predetermined direction via a beamforming processor 13 and multiple element antennas 14. When the sensor node 2 enters an area covered by the beam, it transmits and receives a 5 GHz Wi-Fi signal.

[0021] The backscatter RX 12 is a receiver and receives a backscatter signal returned from the sensor node 2 in response to the transmission of a Wi-Fi signal by the TRX 11. The beamforming processing unit 13 executes analog beamforming processing between the sensor node 2 and the backscatter RX 12 by using a plurality of element antennas 14, and may be realized by, for example, a combination of a beamforming network (BFN) and a single pole four throw (SP4T).

[0022] The number of element antennas 14 provided in the access point 1 may be about 4 to 16 elements. For example, in the case of a 2×2 or 4×4 array antenna, an analog beamforming circuit is configured by a two-dimensional Butler matrix or the like. In the SN detection phase, in the access point 1, the backscatter RX12, which is a receiving system of a Wi-Fi backscatter signal required for beam tracking of the sensor node 2, is arranged after the switch 16, and the 5 GHz band Wi-Fi TRX11 is connected to the circulator 15. As a result, the signal received by the element antennas 14 of the access point 1 is selectively input to the TRX11 or RX12 by the switch 16.

[0023] The circulator 15 is provided at a branch point between a signal line connected to the TRX 11 and a signal line connected to the backscatter RX 12. The circulator 15 has three terminals, and outputs a signal input from a certain terminal to a specific terminal. The circulator 15 outputs a transmission Wi-Fi signal output from the TRX 11 to the element antenna 14 side. When the switch 16 is ON, the circulator 15 outputs an input from the element antenna 14 side to the backscatter RX 12 side, and when the switch 16 is OFF, the circulator 15 outputs an input from the element antenna 14 side to the TRX 11 side.

[0024] The AP transmission spectrum indicated by reference symbol A1 indicates a communication signal from the access point 1 to a plurality of sensor nodes 2.

[0025] The sensor node 2 includes a 5 GHz band Wi-Fi TRX 21 (hereinafter, may be simply referred to as "TRX 21"), a single-pole single-throw switch (SPST switch) 22, a clock 23, and an element antenna 24. Here, an example of a single-element antenna is shown, but depending on the dimensions of the sensor node 2, it may be configured with a multiple-element antenna.

[0026] The TRX 21 is a transceiver, and transmits and receives a 5 GHz band Wi-Fi signal to and from the access point 1 via the element antenna 24. When the sensor node 2 desires to communicate, the SPST switch 22 periodically executes ON / OFF switching control and transmits a backscatter signal to the access point 1. In all other cases, the SPST switch 22 is always set to ON. The SPST switch 22 is controlled by the frequency f of the clock signal output by the clock 23. clock The ON / OFF switching control is performed periodically depending on the

[0027] The SN transmission spectrum in the SN detection phase indicated by A2 shows a situation where a sensor node 2 that desires communication is present and a Wi-Fi backscatter signal (hereinafter, may be simply referred to as a "backscatter signal") is generated, and is transmitted from the sensor node 2 to the access point 1 at the timing of a communication request together with a 5 GHz Wi-Fi signal. The backscatter signal is present on the high and low frequency sides of the frequency band (channel) of the 5 GHz Wi-Fi signal. Usually, the level of this backscatter signal is lower in power than the 5 GHz Wi-Fi signal. The 5 GHz Wi-Fi signal in the received signal of the access point 1 is due to reflections at the beamforming processing unit 13 and the element antenna 14, reflections of the signal radiated from the element antenna 14 on the surrounding environment (for example, walls, floors, ceilings, machine tools 4, etc.), and reflections at the sensor node 2. The SN transmission spectrum in the Wi-Fi communication phase indicated by A3 shows a transmission signal sent from the sensor node 2 to the access point 1 in the Wi-Fi communication phase.

[0028] FIG. 3 is a diagram for explaining an example of operation in the SN detection phase in the communication system 100 shown in FIG.

[0029] As shown by the symbol B1, the access point 1 first transmits a Wi-Fi dummy signal from the TRX 11. This Wi-Fi dummy signal is not used for Wi-Fi communication but only for backscatter communication, so it may be generated from random data or any other Wi-Fi signal such as a beacon signal. The Wi-Fi dummy signal is transmitted by the beamforming processor 13 as a beam directed toward a certain sector.

[0030] As shown by the reference symbol B2, the sensor node 2 drives the SPST switch 22 between the element antenna 24 and the TRX 21 by the clock 23 using On-Off-Keying (OOK modulation). As a result, the switch is turned on and off at a clock frequency f clockAs shown by symbol B3, in the SN detection phase, the TRX 21 does not start and can be regarded as a 50 Ω termination, so when the SPST switch 22 is on, it is in a matched non-reflective state, and when the SPST switch 22 is off, it is in a total reflection state at the open end. By switching between this non-reflective state and total reflection state, OOK modulation is applied to the reflected wave of the received Wi-Fi dummy signal. Therefore, the Wi-Fi backscatter signal becomes the sideband spectrum of the Wi-Fi signal, as shown by symbol B4.

[0031] The Wi-Fi backscatter signal transmitted from the sensor node 2 is received by the access point 1, separated from the transmitted wave by the circulator 15, and input to the backscatter Rx 12 via the switch 16, which is turned on during the SN detection phase as shown by symbol B5.

[0032] With the above mechanism, the access point 1 can detect the presence or absence of a sensor node 2 within a sector by utilizing the backscatter signal transmitted from each sensor node 2.

[0033] FIG. 4 is a diagram illustrating an example of operation of the Wi-Fi communication phase in the communication system 100 shown in FIG.

[0034] As shown by symbol C1, the access point 1 transmits and receives Wi-Fi communication signals based on the normal Wi-Fi standard. As shown by symbol C2, when the access point 1 receives a Wi-Fi signal from the sensor node 2, the phase-switching switch 16 connected to the circulator 15 is turned off, so that the received wave is not input to the backscatter Rx 12 but is input to the TRX 11. As shown by symbol C3, the SPST switch 22 of the sensor node 2 is turned on continuously without being connected to the clock 23, so that the Wi-Fi communication signal is continuously transmitted and received as shown by symbol C4.

[0035] 5(a) and (b) are diagrams for explaining an SN spectrum identification method by down-conversion of a backscattered signal in the communication system shown in FIG.

[0036] In order to count the number of sensor nodes 2 during the very short SN detection phase, it is necessary to simultaneously receive multiple Wi-Fi backscatter signals. However, Wi-Fi backscatter signals are broadband signals compared to backscatter signals that use continuous waves, and simultaneous reception and multiple access by frequency division are difficult. Therefore, a method is needed to simultaneously receive multiple Wi-Fi backscatter signals and count the number of sensor nodes 2.

[0037] For example, it is assumed that the number of sensor nodes 2 is identified by narrowing the band by down-converting the original Wi-Fi signal through multiplication. clock By making the bandwidth of the Wi-Fi signal greater than or equal to the bandwidth of the Wi-Fi signal, the backscatter signal and the original Wi-Fi signal do not overlap on the frequency axis, making it possible to achieve both normal Wi-Fi communication and backscatter communication.

[0038] However, when multiple sensor nodes 2 are present at the same time, the backscattered signals overlap on the frequency axis as shown in Fig. 5(a), making it impossible to separate the individual signals. Therefore, downconversion is performed by multiplying the backscattered signal by the original Wi-Fi signal.

[0039] The signal after down-conversion is shown in Fig. 5(b). This makes it possible to receive a wideband backscatter signal in the RF band as a narrowband signal in the IF band. Furthermore, the clock frequency f clock By changing the frequency, the backscattered signals do not overlap on the frequency axis, and each signal can be separated.

[0040] Fig. 6 is a diagram illustrating a communication range in the SN detection phase in the communication system 100 shown in Fig. 1. Fig. 7 is a diagram illustrating a communication range in the Wi-Fi communication phase in the communication system 100 shown in Fig. 1.

[0041] Since backscatter communication is performed during the SN detection phase, the Wi-Fi transmission power of the access point 1 is greater than the transmission power during the Wi-Fi communication phase. The specifications of the communication system 100 shown in FIG. 1 are shown as examples. The antenna gain of the access point 1 is G AP = 9 [dBi], and the antenna gain of the sensor node 2 is G SN = 0 [dBi]. Also, the input / output power ratio of the sensor node 2 during the SN detection phase may be M = -7 [dB].

[0042] In the example shown in FIG. 6, during the SN detection phase, the antenna power of the Wi-Fi signal of access point 1 is P AP = 20 [dBm]. The received power P of access point 1 for backscatter communication derived from the Friis propagation formula is r can be calculated as shown in equation (1).

[0043]

number

[0044] Here, λ is the wavelength of the carrier wave, and D is the distance between the access point 1 and the sensor node 2. r The derivation of is explained below along with the communication procedure. The received power of the Wi-Fi signal of the access point 1 at the sensor node 2 located 2.6 m away from the access point 1 (see the solid circle in Figure 6) is -26.6 dBm (P APAssuming that the minimum receiving sensitivity of backscatter RX12 is -80 dBm, the range of the sensor node 2 capable of backscatter communication in the SN detection phase is 2.6 m from the access point 1 (see the solid circle in Figure 6), based on the received power of the backscatter signal from the sensor node 2 at the access point 1 at this time. In addition, if the receiving sensitivity of the Wi-Fi communication signal from the access point 1 in Wi-Fi communication is -70 dBm, the communication range is 390 m from the access point 1 (see the two-dot chain circle in Figure 6).

[0045] In the Wi-Fi communication phase, it is sufficient if Wi-Fi communication is possible within a range of at least 2.6 m (see the solid circle in Figure 6), which is the communication range in the SN detection phase obtained so far. Here, to allow for a margin, the communication range in the Wi-Fi communication phase is set to 5.2 m (see the dashed-dotted circle in Figure 6), which is twice as long.

[0046] Figure 7 shows the communication range in the Wi-Fi communication phase at this time. If the receiving sensitivity of the Wi-Fi communication signal from access point 1 at a position 5.2 m from access point 1 (see the solid circle in Figure 7) is -70 dBm, the antenna power of the Wi-Fi signal from access point 1 is P AP = --17.4 [dBm].

[0047] That is, the transmission power of the access point 1 in the Wi-Fi communication mode may be a value that exceeds the midpoint between the transmission power and the minimum receiving sensitivity of the access point 1 in the SN detection phase by approximately a communication margin.

[0048] FIG. 8 is a diagram for explaining the relationship between beamforming and the movement of the sensor node in the communication system 100 shown in FIG.

[0049] Figure 8 shows the movement of sensor node 2 (SN#1) assumed in the following explanation, along with the four-way beamforming realized by the 2x2 patch array antenna mounted on access point 1. The four-way beams are formed in the order of Y, R, B, and G clockwise when viewed from the top of the antenna toward the antenna. It is also assumed that SN#1 rotates clockwise with a period of 60 ms (1,000 rpm) or 600 ms (100 rpm).

[0050] FIG. 9 is a diagram illustrating a time flow of the SN detection phase in the communication system 100 shown in FIG.

[0051] The beamforming (BF) direction indicated by symbol D1 indicates the beam direction being selected by the access point 1. The SN#1 signal reception indicated by symbol D2 indicates the reception state at the access point 1 of the backscatter signal generated by the SN#1 using the Wi-Fi dummy signal in that beam direction.

[0052] It is assumed that the beam range (sector) ideally switches every 1 / 4 of the rotation period and there is no overlap. In the SN detection phase, the beamforming operation of access point 1 is divided into two parts. In the first half of the rotation period and SN number measurement, the beamforming attempts backscatter communication with a fixed beam direction set each time. In this case, for example, if SN#1 rotates with a period of 60 ms, the backscatter signal of SN#1 reaches access point 1 for 15 ms every 60 ms as shown in Figure 9. This operation makes it possible to measure the rotation period of the rotating sensor node 2 group and to measure the distribution of the locations of the rotating sensor node 2 group. In addition, for the sensor node 2 group that is stopped in the beam Y direction, the backscatter signal reaches access point 1 continuously, so the number of sensor nodes 2 can be measured.

[0053] Other beam directions can be measured by switching the beam direction to another direction and fixing it in the next SN detection phase. In the second half of the rotation direction measurement, the beam direction is changed according to the rotation period of the two rotating sensor nodes obtained in the first half.

[0054] At this point, the direction of rotation is unknown, so the beam is switched between clockwise and counterclockwise directions in sequence, and the direction of rotation is determined based on the frequency with which the backscatter signal is received.

[0055] 9, the number of sensor nodes 2 and the rotation period may be measured simultaneously by fixing the beam direction for a time width of, for example, 120 ms or more, and then the rotation direction of the sensor nodes 2 may be measured by rotating the beam direction clockwise and counterclockwise for a time width of, for example, 120 ms or more. Also, the number of sensor nodes 2 and the rotation direction may be measured by rotating the beam direction clockwise and counterclockwise after the rotation period of the sensor nodes 2 is measured by fixing the beam direction.

[0056] FIG. 10 is a diagram illustrating a time flow of the high-speed rotation phase in the communication system 100 shown in FIG.

[0057] The beamforming direction indicated by E1 indicates the beam direction selected by the access point 1. The SN#1 signal reception indicated by E2 indicates the time period during which Wi-Fi communication signals can be exchanged in that beam direction. The period of the SN#1 reception signal may be 60 ms (in other words, the first period). The high-speed rotation phase is divided into two sub-phases: high-speed rotation and stop.

[0058] In the first half of the high-speed rotation subphase, for example, in a time width of 240 ms or more, the communication time for each of the initial beams in the four directions is optimized based on the distribution of the locations of the sensor nodes 2 (the number of sensor nodes 2) measured in the SN detection phase. In addition, stable communication is achieved by always pointing the beam to the rotating sensor nodes 2 by switching the beam based on the rotation period and direction measured in the SN detection phase. In other words, the beam direction is rotated in order from the first direction according to the measured rotation period, and the process of rotating the beam direction in order by changing the direction different from the first direction to the top is repeated, and then the beam direction is fixed and communication is performed for each of the stopped sensor nodes 2.

[0059] In the latter stopping sub-phase, if a group of sensor nodes 2 are detected stopped in a certain beam direction initially set in the SN detection phase, for example within a time width of 240 ms or more, a communication time with a fixed beam direction is set according to the number of sensor nodes 2.

[0060] FIG. 11 is a diagram for explaining the time flow of the low-speed rotation / stop phase when the rotation SN is given priority in the communication system 100 shown in FIG.

[0061] As shown by the beamforming direction indicated by symbol F1, the beam is fixed in a certain direction Y that was initially set in the SN detection phase, and the rotating sensor nodes 2 communicate only when they enter that beam direction. By ensuring a communication time of at least ¼ of the rotation period, as shown by the SN#1 received signal indicated by symbol F2, communication is possible between all rotating sensor nodes 2 and the stationary sensor nodes 2 in the beam Y direction. For the sensor nodes 2 that are stationary in other beam directions, communication is possible by switching the beam direction in the next phase. The period of the SN#1 received signal may be 600 ms (in other words, a second period longer than the first period).

[0062] FIG. 12 is a diagram for explaining the time flow of the low-speed rotation / stop phase when the stopped SN is given priority in the communication system shown in FIG.

[0063] When there are many stopped sensor nodes 2, it is possible to set it so that all stopped sensor nodes 2 can communicate in one slow rotation / stop phase by switching the beam. The beamforming direction shown by symbol G1 is switched sequentially to the Y, R, and G directions. The received signal of stopped SN#1 shown by symbol G2 is detected only when beam Y is sent out.

[0064] [A-2] Example of operation A first example of a communication operation in the communication system 100 shown in FIG. 1 will be described with reference to a flow chart (steps S1 to S8) shown in FIG.

[0065] The communication protocol in the embodiment includes three phases: a detection phase shown in steps S1 to S3, a high-speed rotation phase shown in steps S6 to S8, and a low-speed rotation / stop phase shown in step S5. Each process in the detection phase, high-speed rotation phase (in other words, a first mode), and low-speed rotation / stop phase (in other words, a second mode) may be arranged in the backscatter RX 12 shown in Fig. 2 or the access point 1, and a process command is output to the beamforming processing unit 13 depending on the process result.

[0066] In the SN detection phase, not only the number of sensor nodes 2 per sector may be measured, but also the rotation period and direction of the rotating sensor nodes 2. Based on the rotation period of the sensor nodes 2 determined in the SN detection phase, the next phase is selected from either the high-speed rotation phase or the low-speed rotation / stop phase, and Wi-Fi communication is realized for the sensor nodes 2 that are within the communication range.

[0067] In each phase, an environment is assumed in which there are two groups of sensor nodes that rotate with the same period and two groups of sensor nodes that are stationary.

[0068] It is assumed that connection procedures between the access point 1 and each sensor node 2, such as IP (internet protocol) address assignment and authentication, have been completed.

[0069] First, the SN detection phase shown in FIG. 9 is started, and in step S1, the initial beam direction is set.

[0070] In step S2, the rotation period and the number of sensor nodes 2 are measured.

[0071] In step S3, the rotation direction of each sensor node 2 is measured.

[0072] In step S4, it is determined whether there is a sensor node 2 rotating at high speed. Here, the determination of high speed rotation may be made based on whether a group of sensor nodes 2 attempting to communicate in a communication range (sector) in a certain beam direction of the access point 1 are rotating at a speed that allows them to stay in the sector for a longer time than the time required for communication as defined by the Wi-Fi communication standard.

[0073] If there is no sensor node 2 rotating at high speed, the process of the low-speed rotation / stop phase shown in FIG. 11 and FIG. 12 is executed in step S5, and the process returns to step S1.

[0074] On the other hand, if there is a sensor node 2 rotating at high speed, the high-speed rotation phase shown in FIG. 10 is started, and in step S6, the process of the high-speed rotation sub-phase is executed.

[0075] In step S7, it is determined whether any sensor node 2 is stopped.

[0076] If there is no stopped sensor node 2, the process returns to step S1.

[0077] On the other hand, if there is a stopped sensor node 2, the process of the stop sub-phase is executed in step S8, and the process returns to step S1.

[0078] Next, a second example of the communication operation in the communication system 100 shown in FIG. 1 will be described with reference to a flow chart (steps S11 to S18) shown in FIG.

[0079] In the flowchart shown in FIG. 14, the low-speed rotation phase and the stop phase are separated from each other, as compared with the flowchart shown in FIG.

[0080] First, the SN detection phase shown in FIG. 9 is started, and in step S11, the initial beam direction is set.

[0081] In step S12, the rotation period and the number of sensor nodes 2 are measured.

[0082] In step S13, the rotation direction of each sensor node 2 is measured.

[0083] In step S14, it is determined whether there is a sensor node 2 that is rotating at high speed.

[0084] If there is no sensor node 2 rotating at high speed, the process of the low-speed rotation phase shown in FIG. 11 is executed in step S15, and the process proceeds to step S17.

[0085] On the other hand, if there is a sensor node 2 rotating at high speed, the high-speed rotation phase shown in FIG. 10 is started, and in step S16, the process of the high-speed rotation sub-phase is executed.

[0086] In step S17, it is determined whether any sensor node 2 is stopped.

[0087] If there is no stopped sensor node 2, the process returns to step S11.

[0088] On the other hand, if there is a stopped sensor node 2, the process of the stop sub-phase shown in FIG. 10 or the stop phase shown in FIG. 12 is executed in step S18, and the process returns to step S11.

[0089] In the example of the above-described embodiment, it is possible to suppress interference between systems using the same adjacent frequency band and improve space utilization efficiency.

[0090] [B] Other The disclosed technology is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the embodiments. The configurations and processes of the embodiments can be selected as necessary, or can be combined as appropriate.

[0091] In the above-described embodiment, a Wi-Fi signal in the 5 GHz band is transmitted and received, but this is not limiting. The frequency band of the transmitted and received signal may be changed in various ways, and the type of the transmitted and received signal may be various wireless signals other than a Wi-Fi signal. Although the sensor node 2 performs OOK modulation, other modulation methods may be used. For example, when there is reflection due to a mismatch in the TRX 21 of the sensor node 2, Amplitude Shift Keying (ASK) modulation is used instead of OOK modulation. Also, Phase Shift Keying (PSK) modulation may be used by switching between an open end and a short-circuited end using a switch. [Explanation of symbols]

[0092] 100:Communication Systems 1: Access point 11,21 :TRX 12: Backscatter RX 13: Beamforming processing unit 14,24: Element antenna 15: Circulator 16: Switch 2: Sensor node 22: SPST switch 23: Clock 3: Base 4: Machine tools 5: Conveyor belt

Claims

1. A communication circuit provided in an access point that wirelessly communicates with a plurality of sensor nodes, Measure the number, rotation period, and rotation direction of the plurality of sensor nodes; selecting a first mode or a second mode based on the measured rotation period; When the first mode is selected, a direction of a beam transmitted from the access point in a first period is rotated based on the number and the rotation direction, and communication is performed with a sensor node present within a communication range; When the second mode is selected, the communication circuit rotates the direction of the beam based on the number and the rotation direction in a second period longer than the first period, or fixes the direction of the beam, and communicates with a sensor node present within a communication range.

2. 2. The communication circuit of claim 1, wherein the number and the rotation period are measured simultaneously by fixing the direction of the beam, and then the rotation direction is measured by rotating the direction of the beam clockwise and counterclockwise.

3. 2. The communication circuit of claim 1, wherein the rotation period is measured by fixing the direction of the beam, and then the number and the rotation direction are measured by rotating the direction of the beam clockwise and counterclockwise.

4. In the first mode, The communication circuit according to any one of claims 1 to 3, wherein the direction of the beam is rotated in sequence from a first direction according to the measured rotation period, and the process of changing the direction of the beam from the first direction to a direction different from the first direction and rotating the direction of the beam in sequence is repeated, and then the direction of the beam is fixed and communication is performed with each of the stopped sensor nodes.

5. The communication circuit according to any one of claims 1 to 4, wherein the transmission power of the access point in the first mode or the second mode is a value that exceeds the intermediate value between the transmission power of the access point and the minimum reception power when measuring the number, the rotation period, and the rotation period by approximately a communication margin.

6. A communication system having an access point and a plurality of sensor nodes, The access point is A communication circuit according to any one of claims 1 to 5; A plurality of antennas; a receiver that receives a backscatter signal for beam tracking the sensor node from the sensor node via any one of the plurality of antennas; Equipped with The plurality of sensor nodes include A communication system comprising a single-pole, single-throw switch for transmitting the backscatter signal to the access point.

7. A communication system having an access point and a plurality of sensor nodes, The plurality of sensor nodes include a single-pole, single-throw switch for transmitting a backscatter signal generated by on / off control based on a clock frequency to the access point; The access point is A plurality of antennas; a receiver that receives the backscatter signal for beam tracking the sensor node from the plurality of sensor nodes via any one of the plurality of antennas, and detects the clock frequency of each of the plurality of sensor nodes by mixing the received backscatter signal with a transmission signal from the access point; For the plurality of sensor nodes identified based on the detected clock frequency, a communication circuit that measures the number, rotation period, and rotation direction of the sensor nodes for each sector, and controls the direction of a beam emitted from any one of the plurality of antennas based on the measured number, rotation period, and rotation direction, thereby communicating with the sensor nodes present within a communication range; A communication system comprising:

8. In an access point that wirelessly communicates with multiple sensor nodes, Measure the number, rotation period, and rotation direction of the plurality of sensor nodes; selecting a first mode or a second mode based on the measured rotation period; When the first mode is selected, a direction of a beam transmitted from the access point is rotated based on the number and the rotation direction at a period shorter than a predetermined period to communicate with a sensor node present within a communication range, and the direction of the beam is fixed to communicate with a stationary sensor node; A communication method in which, when the second mode is selected, the direction of the beam is rotated based on the number and the rotation direction at a period longer than the specified period, or the direction of the beam is fixed, and communication is performed with a sensor node present within a communication range.

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