JP7619617B2 - COMMUNICATION CIRCUIT, COMMUNICATION SYSTEM, AND COMMUNICATION METHOD - Google Patents

Description

The technology described in this specification relates to a communication circuit, a communication system, and a communication method.

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) for a wireless local area network (LAN). Connections to 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, which can move or are movable, or on 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.

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

International Publication No. 2011/042974 JP 2008-228136 A

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. 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.

Wireless IoT communication is often achieved using wireless LANs and Bluetooth (registered trademark) that use unlicensed bands, so there is a risk of reduced throughput and a lack of real-time performance due to interference between systems. When a large number of SNs are connected to an AP, there is a greater risk of interference between systems.

In one aspect, the technology described in this specification aims to suppress interference between systems that use the same adjacent frequency band and improve spatial utilization efficiency.

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. When the first mode is selected, the direction of the beam sent from the access point in the first period is rotated based on the number and the rotation direction to communicate with the sensor nodes present within the communication range, and when the second mode is selected, the direction of the beam is rotated based on the number and the rotation direction in a second period longer than the first period, or the direction of the beam is fixed to communicate with the sensor nodes present within the communication range.

One aspect is that it can suppress interference between systems that use the same adjacent frequency bands, improving spatial utilization efficiency.

FIG. 1 is a diagram illustrating an example of installation of a communication system according to an embodiment. 2 is a block diagram illustrating an example of a hardware configuration of the access point and the sensor node illustrated in FIG. 1. 2 is a diagram for explaining an example of operation of an SN detection phase in the communication system shown in FIG. 1 . 2 is a diagram illustrating an example of operation of a Wi-Fi communication phase in the communication system shown in FIG. 1. 2A and 2B are diagrams for explaining an S/N spectrum identification technique by down-conversion of a backscattered signal in the communication system shown in FIG. 1 . 2 is a diagram for explaining a communication range in the SN detection phase in the communication system shown in FIG. 1 . 2 is a diagram illustrating a communication range of a Wi-Fi communication phase in the communication system shown in FIG. 1. 2 is a diagram for explaining the relationship between beamforming and the movement of a sensor node in the communication system shown in FIG. 1. 2 is a diagram illustrating a time flow of an SN detection phase in the communication system shown in FIG. 1. 2 is a diagram illustrating a time flow of a high-speed rotation phase in the communication system shown in FIG. 1. 1. FIG. 4 is a diagram for explaining the time flow of the low-speed rotation/stop phase when the rotation SN is prioritized in the communication system shown in FIG. 1. FIG. 4 is a diagram for explaining a time flow of a low-speed rotation/stop phase when a stop SN is prioritized in the communication system shown in FIG. 4 is a flowchart illustrating a first example of a communication operation in the communication system illustrated in FIG. 1 . 10 is a flowchart illustrating a second example of a communication operation in the communication system illustrated in FIG.

The following describes the embodiments with reference to the drawings. However, the embodiments described below are merely examples, and are not intended to exclude the application of various modified examples or techniques not explicitly stated in the embodiments. In other words, the present embodiment can be modified in various ways without departing from the spirit of the present invention.

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

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

The communication system 100 includes a machine tool 4 and the like. The 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 a belt conveyor 5. The 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.

An access point (AP) 1 is attached to the base 3 of the machine tool 4, and a sensor node (SN) 2 is attached to the 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, multiple sensor nodes 2 are attached to the machine tool 4, as will be described later using FIG. 2 etc.

The communication system 100 uses, for example, a 5 GHz band 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, with simple beamforming by an access point 1 having multiple antenna elements attached to the base 3 of the machine tool 4. The access point 1 may have a relatively small number of antenna elements (e.g., a 2x2 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).

Figure 2 is a block diagram that shows a schematic example of the hardware configuration of the access point 1 and the sensor node 2 shown in Figure 1.

As shown in FIG. 2, the machine tool 4 in this embodiment is equipped with multiple sensor nodes 2 (seven in the illustrated example).

The access point 1 is an example of a communication circuit, and includes a 5 GHz band Wi-Fi TRX 11 (hereinafter, sometimes simply referred to as "TRX 11"), a Wi-Fi backscatter RX 12 (hereinafter, sometimes simply referred to as "backscatter RX 12"), a beamforming processing unit 13, multiple element antennas 14, a circulator 15, and a switch 16.

TRX11 is a transceiver. The input/output RF signals of TRX11 can switch between multiple beams directed in a specific direction via the beamforming processing unit 13 and multiple element antennas 14. When the sensor node 2 enters an area covered by the beam, it will transmit and receive 5 GHz band Wi-Fi signals.

The backscatter RX 12 is a receiver that 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 sensor node 2 using multiple element antennas 14, and may be realized, for example, by a combination of a beamforming network (BFN) and a single pole four throw (SP4T).

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 2x2 or 4x4 array antenna, an analog beamforming circuit is configured using a two-dimensional Butler matrix or the like. In the SN detection phase, in the access point 1, the backscatter RX 12, which is a receiving system for the Wi-Fi backscatter signal required for beam tracking the sensor node 2, is placed after the switch 16, and the 5 GHz band Wi-Fi TRX 11 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 TRX 11 or RX 12 by the switch 16.

The circulator 15 is provided at the branch point of the signal line connected to the TRX 11 and the signal line connected to the backscatter RX 12. The circulator 15 has three terminals, and outputs a signal input from one terminal to a specific terminal. The circulator 15 outputs the 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 the input from the element antenna 14 side to the backscatter RX 12 side, and when the switch 16 is OFF, the circulator 15 outputs the input from the element antenna 14 side to the TRX 11 side.

The AP transmission spectrum shown by symbol A1 indicates a communication signal from an access point 1 to multiple sensor nodes 2.

The sensor node 2 includes a 5 GHz band Wi-Fi TRX 21 (hereinafter sometimes 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.

The TRX 21 is a transceiver, and transmits and receives 5 GHz band Wi-Fi signals 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 periodically performs ON/OFF switching control in accordance with the frequency f _clock of the clock signal output by the clock 23.

The SN transmission spectrum in the SN detection phase shown by symbol A2 shows a situation in which a sensor node 2 that desires communication is present and a Wi-Fi backscatter signal (hereinafter, sometimes 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 band Wi-Fi signal. The backscatter signal is present on the high and low frequency sides of the frequency band (channel) of the 5 GHz band Wi-Fi signal. Usually, the level of this backscatter signal is less powerful than the 5 GHz band Wi-Fi signal. The 5 GHz band Wi-Fi signal in the received signal of the access point 1 is due to reflections at the beamforming processing unit 13 and element antenna 14, reflections of the signal radiated from the element antenna 14 at the surrounding environment (for example, walls, floors, ceilings, machine tool 4, etc.), and reflections at the sensor node 2. The SN transmission spectrum in the Wi-Fi communication phase shown by symbol A3 indicates the transmission signal sent by the sensor node 2 to the access point 1 in the Wi-Fi communication phase.

Figure 3 is a diagram illustrating an example of operation of the SN detection phase in the communication system 100 shown in Figure 1.

As shown by 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 processing unit 13 as a beam directed toward a certain sector.

As shown by 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). This switches the switch on and off at the clock frequency f _clock . As shown by symbol B3, in the SN detection phase, the TRX 21 does not start and can be considered 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 sidewave spectrum of the Wi-Fi signal as shown by symbol B4.

The Wi-Fi backscatter signal transmitted from the sensor node 2 is received by the access point 1, separated from the transmission 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.

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

Figure 4 is a diagram illustrating an example of the operation of the Wi-Fi communication phase in the communication system 100 shown in Figure 1.

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.

Figures 5(a) and (b) are diagrams explaining a method for identifying the signal-to-noise spectrum by down-converting a backscattered signal in the communication system shown in Figure 1.

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, making simultaneous reception and multiple access by frequency division difficult. Therefore, a method is needed to simultaneously receive multiple Wi-Fi backscatter signals and count the number of sensor nodes 2.

For example, it is assumed that the number of sensor nodes 2 can be identified by narrowing the bandwidth through down-conversion by multiplication of the original Wi-Fi signal. By setting the clock frequency f _clock of the sensor node 2 to be equal to or greater than the bandwidth of the Wi-Fi signal, the backscatter signal and the original Wi-Fi signal do not overlap on the frequency axis, and normal Wi-Fi communication and backscatter communication can be achieved at the same time.

However, when multiple sensor nodes 2 are present at the same time, the backscattered signals overlap on the frequency axis as shown in Figure 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.

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, by changing the clock frequency f _clock for each sensor node 2, the backscatter signals do not overlap on the frequency axis, and each signal can be separated.

Figure 6 is a diagram explaining the communication range of the SN detection phase in the communication system 100 shown in Figure 1. Figure 7 is a diagram explaining the communication range of the Wi-Fi communication phase in the communication system 100 shown in Figure 1.

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 exemplified. The antenna gain of the access point 1 may be G _AP = 9 [dBi] assuming a 2×2 patch array antenna, and the antenna gain of the sensor node 2 may be G _SN = 0 [dBi] assuming an omnidirectional single element antenna. In addition, the input/output power ratio of the sensor node 2 during the SN detection phase may be M = -7 [dB].

6, in the SN detection phase, the antenna power of the Wi-Fi signal of access point 1 is set to P _AP = 20 [dBm]. The received power P _r of access point 1 in backscatter communication derived from the Friis propagation formula is given by equation (1).

Here, λ is the wavelength of the carrier wave, and D is the distance between the access point 1 and the sensor node 2. The derivation of P _r using formula (1) will be 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, which is 2.6 m away from the access point 1 (see the solid circle in Figure 6), is -26.6 dBm (attenuated by 46.6 dB from P _AP ). Since M = -7 [dB], the backscatter transmission power of this sensor node 2 is -33.6 dBm. If the minimum receiving sensitivity of the backscatter RX 12 is -80 dBm, the range of the sensor node 2 that can communicate by backscatter in the SN detection phase is assumed to be 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 access point 1 in Wi-Fi communication is −70 dBm, the communication range is 390 m from access point 1 (see the two-dot chain circle in FIG. 6).

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 some margin, the communication range in the Wi-Fi communication phase is set to twice that, 5.2 m (see the dashed-dotted circle in Figure 6).

The communication range in the Wi-Fi communication phase at this time is shown in Figure 7. 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 can be calculated from the Friis propagation formula as P _AP = --17.4 [dBm].

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

Figure 8 is a diagram explaining the relationship between beamforming and the movement of sensor nodes in the communication system 100 shown in Figure 1.

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).

Figure 9 is a diagram explaining the time flow of the SN detection phase in the communication system 100 shown in Figure 1.

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

The beam range (sector) is assumed to ideally switch every 1/4 of the rotation period and not 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, backscatter communication is attempted with beamforming fixed to a certain 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.

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 calculated in the first half.

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

As shown in FIG. 9, the number and rotational period of sensor nodes 2 may be measured simultaneously by fixing the beam direction for a time width of, for example, 120 ms or more, and then the rotational direction of 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 and rotational direction of sensor nodes 2 may be measured by rotating the beam direction clockwise and counterclockwise after the rotational period of sensor nodes 2 is measured by fixing the beam direction.

Figure 10 is a diagram explaining the time flow of the high-speed rotation phase in the communication system 100 shown in Figure 1.

The beamforming direction indicated by E1 indicates the beam direction being selected by 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.

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 four initial beams in the 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 switching the beam based on the rotation period and direction measured in the SN detection phase, and always pointing the beam at the rotating sensor nodes 2. That is, the beam direction is rotated in order starting 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 leading direction is repeated, after which communication is performed for each of the stopped sensor nodes 2 with the beam direction fixed.

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

Figure 11 is a diagram explaining the time flow of the low-speed rotation/stop phase when the rotation SN is prioritized in the communication system 100 shown in Figure 1.

As shown in the beamforming direction of 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 1/4 of the rotation period, as shown in the SN#1 received signal of symbol F2, communication is possible between all rotating sensor nodes 2 and stationary sensor nodes 2 in the beam Y direction. For 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).

Figure 12 is a diagram explaining the time flow of the low-speed rotation/stop phase when the stop SN is prioritized in the communication system shown in Figure 1.

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

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

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, the first mode), and low-speed rotation/stop phase (in other words, the second mode) may be placed in the backscatter RX 12 shown in FIG. 2 or in the access point 1, and a processing command is output to the beamforming processing unit 13 depending on the processing result.

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 a high-speed rotation phase or a low-speed rotation/stop phase, and Wi-Fi communication is realized for the sensor nodes 2 that are within the communication range.

In each phase, we assume an environment in which there are two groups of sensor nodes that are rotating at the same cycle and two groups of sensor nodes that are stopped.

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.

First, the SN detection phase shown in Figure 9 is started, and in step S1, the initial beam direction is set.

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

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

In step S4, it is determined whether there is a sensor node 2 that is 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 remain in the sector for a longer period of time than the time required for communication as defined by the Wi-Fi communication standard.

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

On the other hand, if there is a sensor node 2 that is rotating at high speed, the high-speed rotation phase shown in FIG. 10 is initiated, and the high-speed rotation subphase is processed in step S6.

In step S7, it is determined whether any sensor nodes 2 are stopped.

If there are no stopped sensor nodes 2, the process returns to step S1.

On the other hand, if there is a stopped sensor node 2, the stop subphase is executed in step S8, and the process returns to step S1.

Next, a second example of the communication operation in the communication system 100 shown in FIG. 1 will be described using the flowchart (steps S11 to S18) shown in FIG. 14.

The flowchart shown in Figure 14 separates the low-speed rotation phase and the stop phase compared to the flowchart shown in Figure 13.

First, the SN detection phase shown in Figure 9 is started, and in step S11, the initial beam direction is set.

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

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

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

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

On the other hand, if there is a sensor node 2 that is rotating at high speed, the high-speed rotation phase shown in FIG. 10 is initiated, and the high-speed rotation subphase is processed in step S16.

In step S17, it is determined whether any sensor nodes 2 are stopped.

If there are no stopped sensor nodes 2, the process returns to step S11.

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

In one example of the above-described embodiment, it is possible to suppress interference between systems that use the same adjacent frequency band and improve space utilization efficiency.

[B] Others The disclosed technology is not limited to the above-described embodiments, and can be modified in various ways without departing from the spirit of each embodiment. The configurations and processes of each embodiment can be selected as needed, or can be combined as appropriate.

In the above embodiment, a 5 GHz band Wi-Fi signal is transmitted and received, but this is not limited to this. The frequency band of the transmitted and received signal may be changed in various ways, and the type of transmitted and received signal may be various wireless signals other than Wi-Fi signals. Although it has been described that OOK modulation is performed in the sensor node 2, other modulation methods may be used. For example, if 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 end with a switch.

100: Communication system 1: Access point 11, 21: TRX
12: Backscatter RX
13: Beam forming processing unit 14, 24: Element antenna 15: Circulator 16: Switch 2: Sensor node 22: SPST switch 23: Clock 3: Base 4: Machine tool 5: Belt conveyor

Claims (8)

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. 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 direction of the beam is rotated clockwise and counterclockwise to measure the direction of rotation. 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 direction of rotation are measured by rotating the direction of the beam clockwise and counterclockwise. 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. 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 and the minimum reception power of the access point when measuring the number, the rotation period, and the rotation period by approximately a communication margin. 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. 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 to the access point by on/off control based on a clock frequency;
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: 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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