Transmission timing control method, control program, wireless communication system, and wireless communication terminal

Abstract

To appropriately control transmission timing so that each of a plurality of wireless communication terminals in a wireless communication network avoids collision even in a situation where hidden terminals exist.SOLUTION: Each of a plurality of wireless communication terminals in a wireless communication network sets each of a plurality of phases in a predetermined cycle as packet transmission timing. Each wireless communication terminal calculates an overall average phase, which is an average value of a plurality of phases of all the wireless communication terminals, based on phase information on the respective wireless communication terminals. Furthermore, each wireless communication terminal updates the plurality of phases of each wireless communication terminal so that an average value of the plurality of phases of each wireless communication terminal approaches the overall average phase and the plurality of phases differ among the plurality of wireless communication terminals. Each wireless communication terminal notifies the other wireless communication terminals of the updated phase information through packet transmission.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to transmission timing control in each of a plurality of wireless communication terminals in a wireless communication network. [Background technology]

[0002] With the advent of the IoT era, it is expected that more and more wireless communication terminals will be used in the future. On the other hand, the frequency bands and time that can be allocated to wireless communication terminals are limited, and the effective use of these wireless communication resources is an important issue.

[0003] Conventional approaches to the efficiency of wireless communication resource utilization include efficiency through control by a central coordinator and distributed resource acquisition methods based on game theory. For example, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 disclose communication node control methods using reinforcement learning by a central coordinator. Non-Patent Document 4 discloses a technique for determining, based on game theory, whether a secondary user should use a licensed band channel or an unlicensed band channel in a dynamic spectrum sharing environment in which a primary user and a secondary user exist.

[0004] However, in a wireless communication network based on IoT, the overhead of the central coordinator's processing is a problem. In addition, in the case of game theory, problems arise such as an increase in collision opportunities and the unavoidable problem of packet collisions. A system is desired in which each wireless communication terminal can efficiently share wireless communication resources without increasing the load on the central coordinator.

[0005] In recent years, a bio-inspired method inspired by the synchronization of firefly lights has been proposed as a method for efficiently using wireless communication resources while avoiding collisions. For example, Non-Patent Document 5 discloses a method in which each node in a network autonomously adjusts its transmission timing to prevent collisions. Specifically, each node grasps the transmission timing of other nodes in the network and adjusts its own transmission timing so that it is in the center of the transmission timing of the nodes before and after itself.

[0006] Non-Patent Document 6 discloses a method for determining transmission timing based on the "Kuramoto model," a mathematical model that describes synchronization phenomena. The formulas and method disclosed in Non-Patent Document 6 are explained below. Consider N oscillators that interact with each other (N is an integer equal to or greater than 2). The phase θ of each oscillator i (i=1 to N) is i changes according to the following equations (1) and (2).

[0007]

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[0009] The average phase φ is the phase θ of all N oscillators. i is the average value of w i is the natural frequency of node i. r is the order parameter. K is the coupling strength between oscillators. ΔT is unit time.

[0010] Next, the N oscillators are replaced with N nodes (wireless communication terminals) in the wireless communication network. The timing of packet transmission by each node i (i=1 to N) is determined by a phase θ i Each node i calculates its own phase θ i In formula (3), a0 is an initial value between 0 and 1.

[0011]

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[0012] Then, each node i updates its own phase θ i The node j notifies other nodes j (j=1 to N, j≠i) of the information through packet transmission. The node j receives the packet transmitted from the node i and demodulates the received packet to obtain the updated phase θ i In this way, each node i can share the latest phase information and recognize its own phase θ i According to the above formula (3), the phase θ i converges to the value shown in the following equation (4).

[0013]

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[0014] Phase θ of each node i i converges to be shifted from the average phase φ by the differential phase. The differential phase is a value specific to each node i and differs among the N nodes. This means that the transmission timings of the N nodes do not overlap within a given transmission period but are distributed. In this way, the N nodes adjust their own phases θ i (Transmission timing) is controlled autonomously and decentralized, and time-division communication is performed.

[0015] The converged phase θ i The average phase φ in this case is expressed by the following equation (5).

[0016]

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[0017] [Non-Patent Document 1] Satoshi Hasegawa et al., "Performance Evaluation of Reinforcement Learning-Based Channel Selection Method Implemented in IoT Sensor Devices," IEICE Technical Report, Vol. 119, No. 157, CCS2019-17, pp. 1-6, August 2019. [Non-Patent Document 2] N. Aihara, K. Adachi, O. Takyu, M. Ohta and T. Fujii, “Q-Learning Aided Resource Allocation and Environment Recognition in LoRaWAN With CSMA / CA,” in IEEE Access, Vol. 7, pp.152126-152137, 2019 [Non-Patent Document 3] Y. Yu, T. Wang and SC Liew, “Deep-Reinforcement Learning Multiple Access for Heterogeneous Wireless Networks,” in IEEE Journal on Selected Areas in Communications, Vol.37, No.6, pp.1277-1290, June 2019 [Non-Patent Document 4] A. Jella and SL Sabat, “Dynamic channel access of secondary users in a heterogeneous network using game theory,” 2018 10th International Conference on Communication Systems Networks (COMSNETS), Bengaluru, pp.425-428, 2018 [Non-Patent Document 5] J. Degesys, I. Rose, A. Patel and R. Nagpal, “DESYNC: Self-Organizing Desynchronization and TDMA on Wireless Sensor Networks,” 2007 6th International Symposium on Information Processing in Sensor Networks, Cambridge, MA, pp.11-20, 2007. [Non-Patent Document 6] U. Yu, H. Choi and J. Lee, “Kuramoto-Desync: Distributed and Fair Resource Allocation in a Wireless Network,” in IEEE Access, Vol.7, pp.104769-104776, 2019 Summary of the Invention [Problem to be solved by the invention]

[0018] Considering practical implementation, the hidden terminal problem cannot be avoided. According to the technology described in Non-Patent Document 6, as shown in the above formula (5), the average phase φ after convergence contains a phase unique to the node. Therefore, in a situation where hidden terminals exist, there is a problem that the average phase φ calculated at each node differs for each node. In other words, the technology described in Non-Patent Document 6 cannot deal with the hidden terminal problem.

[0019] One object of the present invention is to provide a technique that enables each of multiple wireless communication terminals in a wireless communication network to appropriately control transmission timing so as to avoid collisions, even in a situation where a hidden terminal is present. [Means for solving the problem]

[0020] The first aspect relates to a transmission timing control method in each of a plurality of wireless communication terminals in a wireless communication network. The transmission timing control method is A process in which each wireless communication terminal determines a plurality of phases in a predetermined period as a packet transmission timing; A process of calculating an overall average phase which is an average value of a plurality of phases of all of a plurality of wireless communication terminals; updating a plurality of phases of each of the wireless communication terminals such that an average value of the plurality of phases of each of the wireless communication terminals approaches an overall average phase and the plurality of phases differ among the plurality of wireless communication terminals; A process of notifying other wireless communication terminals of the updated phase information through packet transmission. Includes

[0021] A second aspect relates to a control program executed by a computer, the control program causing the computer to execute the above-mentioned transmission timing control method.

[0022] The third aspect relates to a wireless communication system. The wireless communication system includes a plurality of wireless communication terminals included in a wireless communication network. Each of the plurality of wireless communication terminals A process of setting each of a plurality of phases in a predetermined period as a packet transmission timing; A process of calculating an overall average phase which is an average value of a plurality of phases of all of a plurality of wireless communication terminals; updating a plurality of phases of each of the wireless communication terminals such that an average value of the plurality of phases of each of the wireless communication terminals approaches an overall average phase and the plurality of phases differ among the plurality of wireless communication terminals; A process of notifying other wireless communication terminals of the updated phase information through packet transmission. The apparatus is configured to execute the following steps:

[0023] A fourth aspect relates to each wireless communication terminal in a wireless communication network including a plurality of wireless communication terminals. The wireless communication terminal includes a communication controller. The communication controller is A process of setting each of a plurality of phases in a predetermined period as a packet transmission timing; A process of calculating an overall average phase which is an average value of a plurality of phases of all of a plurality of wireless communication terminals; updating a plurality of phases of the wireless communication terminal such that an average value of the plurality of phases of the wireless communication terminal approaches an overall average phase and the plurality of phases differ among the plurality of wireless communication terminals; A process of notifying other wireless communication terminals of the updated phase information through packet transmission. The apparatus is configured to execute the following steps: Effect of the Invention

[0024] According to the present invention, even in a situation where a hidden terminal exists, it becomes possible for each wireless communication terminal in a wireless communication network to appropriately control the transmission timing so as to avoid collisions, thereby enabling efficient time division communication. [Brief description of the drawings]

[0025] [Figure 1] 1 is a conceptual diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a conceptual diagram for explaining a relationship between a reference phase and a plurality of phases in the embodiment of the present invention. [Diagram 3] 1 is a conceptual diagram for explaining a simulation result of transmission timing control according to an embodiment of the present invention. FIG. [Figure 4] 1 is a conceptual diagram for explaining a simulation result of transmission timing control according to an embodiment of the present invention. FIG. [Diagram 5] 1 is a flowchart summarizing a transmission timing control method in each node according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a block diagram illustrating a configuration example of a node according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] An embodiment of the present invention will be described with reference to the accompanying drawings.

[0027] 1 is a conceptual diagram showing a schematic configuration of a wireless communication system 1 according to the present embodiment. The wireless communication system 1 includes a plurality of wireless communication terminals 10 and a central wireless communication device 20. A wireless communication network 2 is formed by the plurality of wireless communication terminals 10 and the central wireless communication device 20. The central wireless communication device 20 and each wireless communication terminal 10 can communicate with each other. For example, the wireless communication network 2 is a wireless sensor network, the wireless communication terminals 10 are sensor terminals, and the central wireless communication device 20 is a gateway. As another example, the wireless communication terminals 10 may be wireless LAN terminals, and the central wireless communication device 20 may be an access point.

[0028] In the following description, for simplicity, the wireless communication terminal 10 will be referred to as a "node 10" and the central wireless communication device 20 will be referred to as a "central node 20".

[0029] The wireless communication network 2 includes N nodes 10-1 to 10-N. N is the total number of nodes 10 and is an integer equal to or greater than 2. In the example shown in FIG. 1, N is 6, but is of course not limited to this. Each of the N nodes 10-1 to 10-N is represented as a "node 10-i." i is an identifier of each node 10 and takes a value from 1 to N.

[0030] Each node 10-i transmits a packet to the central node 20. In particular, each node 10-i periodically transmits a packet to the central node 20. The transmission timing of each node 10-i is represented by a "phase" within a predetermined transmission period. In other words, each node 10-i transmits a packet at a transmission timing corresponding to a phase within the predetermined transmission period.

[0031] According to this embodiment, each node 10-i has "multiple phases" as transmission timings within a predetermined transmission period. For example, the multiple phases include a "first phase α1" and a "second phase α2." The average value of the first phase α1 and the second phase α2 of each node 10-i is hereinafter referred to as a "reference phase θ i " It is called.

[0032] Figure 2 shows the reference phase θi 1 is a conceptual diagram for explaining the relationship between the reference phase θ i from the reference phase θ i On the other hand, the second phase α2 is obtained by subtracting the adjustment phase β from the reference phase θ i from the reference phase θ i The reference phase θ is obtained by adding the adjustment phase β to the i is the average value of the first phase α1 and the second phase α2.

[0033] Each node 10-i has its own reference phase θ i The first phase α1 and the second phase α2 based on the above are set as the packet transmission timing. Each node 10-i sets its own reference phase θ i , the first phase α1, and the second phase α2. Then, each node 10-i notifies other nodes 10-j (j=1 to N, j≠i) of its own updated phase (α1, α2) information through packet transmission. In other words, each node 10-j shares the latest phase information of the multiple nodes 10-1 to 10-N, and autonomously updates its own phase (α1, α2).

[0034]

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[0035]

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[0036]

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[0039] r is an order parameter and is a real number greater than 0 and equal to or less than 1. K is the coupling strength between the nodes 10. ΔT is a unit time (control period). a1 is a real number greater than or equal to 0 and equal to or less than 1.

[0040] The overall average phase φ is a reference phase θ i As can be seen from equations (7) to (9), the reference phase θ i Since α1 is the average value of the first phase α1 and the second phase α2, the overall average phase φ can also be said to be the average value of the multiple phases (α1, α2) of all the N nodes 10-1 to 10-N. This overall average phase φ can be calculated from the phase information of the N nodes 10-1 to 10-N.

[0041] As described above, the adjustment phase β defines the difference between the reference phase θi and the multiple phases (α1, α2). As can be seen from equations (8) and (9), the adjustment phase β is set to be different among the N nodes 10-1 to 10-N.

[0042] According to the above formula (6), the reference phase θ of each node 10-i i In other words, each node 10-i calculates the overall average phase φ and adjusts the reference phase θ i Furthermore, each node 10-i updates the updated reference phase θ i That is, the first phase α1 and the second phase α2 are calculated based on the reference phase θ i When is updated, the first phase α1 and the second phase α2 are also updated accordingly.

[0043] Reference phase θ iand the multiple phases (α1, α2), an adjusted phase β is set to be different among the N nodes 10-1 to 10-N. Therefore, the transmission timings (α1, α2) of the N nodes 10-1 to 10-N are distributed without overlapping within a predetermined transmission period. In this way, the N nodes 10-1 to 10-N control their own transmission timings (α1, α2) in an autonomous distributed manner so as not to collide with each other, and perform time-division communication.

[0044] Compared with the conventional formula (5), it can be seen that the overall average phase φ expressed by formula (10) does not include an adjustment phase β specific to each node 10-i. This is because the adjustment phase β of the first phase α1 and the adjustment phase β of the second phase α2 cancel each other out when the overall average phase φ is calculated. As a result, even in a situation where a hidden terminal exists, the overall average phase φ after convergence becomes a common value in the wireless communication network 2. That is, according to this embodiment, even in a situation where a hidden terminal exists, each node 10-i in the wireless communication network 2 can autonomously and appropriately control its own transmission timing to avoid collisions. This enables efficient time division communication.

[0045] Each node 10-i receives radio environment information including the total number N of nodes 10 and its own identifier i from the control device. For example, the control device is the central node 20. Furthermore, each node 10-i notifies other nodes 10-j of its own phase information and receives phase information of other nodes 10-j from the other nodes 10-j. Each node 10-i calculates an overall average phase φ based on the phase information of the N nodes 10-1 to 10-N, and calculates a reference phase θ according to equations (6) to (10). i and update multiple phases (α1, α2). That is, each node 10-i updates the reference phase θ i The reference phase θi and the multiple phases (α1, α2) are updated so that the phase θi approaches the overall average phase φ and the multiple phases (α1, α2) differ among the N nodes 10-1 to 10-N.

[0046] Each node 10-i transmits a packet with each of a plurality of phases (α1, α2) in a predetermined transmission period as the transmission timing. For example, consider that the phase of each node 10-i is normalized to a range of 0 to 1. The phase changes from 0 to 1 and then returns to 0. When the phase of a certain node 10-i becomes 1, the node 10-i updates its own phase (α1, α2) according to the above equations (6) to (10). In addition, the node 10-i transmits a packet including the updated phase information. As a result, the node 10-i notifies the other node 10-j of the updated phase information. The other node 10-j updates its own phase (α1, α2) according to the above equations (6) to (10). Next, the phase of the other node 10-j becomes 1. By repeating such processing, the phase is updated.

[0047] 3 and 4 are conceptual diagrams for explaining the results of a simulation of the transmission timing control according to the present embodiment. Here, six nodes 10-1 to 10-6 are considered. FIG. 3 shows an example of node arrangement. The central node 20 is located at coordinates [0,0], and each node 10 is located away from the central node 20. The unit of distance is m. The nodes 10 that are 1000 m or more apart are considered to be hidden terminals. Each node 10 transmits a packet to the central node 20. Each node 10 also acquires information on the transmission timing of other surrounding nodes 10 within a receivable range. Each node 10 then updates its own phase (α1, α2) according to the above formulas (6) to (10). FIG. 4 is a conceptual diagram showing an example of updating the movement (α1, α2) of each node 10. The horizontal axis represents time, and the vertical axis represents phase (transmission timing). From FIG. 4, it can be seen that the transmission timing of each node 10 is equally spaced apart even in a situation where a hidden terminal exists.

[0048] In the above example, the multiple phases of each node 10-i in a given transmission period include a first phase α1 and a second phase α2. However, this embodiment is not limited to this. The number of multiple phases of each node 10-i in a given transmission period may be three or more. The reference phase θ of each node 10-i iis the average value of a plurality of phases, and the reference phase θ i A similar effect can be achieved if the difference between the phases is different between the nodes 10.

[0049] FIG. 5 is a flowchart briefly showing a transmission timing control method in each node 10-i according to this embodiment.

[0050] Each node 10-i, which has a transmission timing for each of a plurality of phases in a predetermined transmission period, updates its own phase at the packet transmission timing according to the above formulas (6) to (10) (step S101). At this time, each node 10-i calculates an overall average phase φ based on the phase information of each of the nodes 10-1 to 10-N. Then, each node 10-i calculates a reference phase θ, which is an average value of the plurality of phases. i approaches the overall average phase φ and the phases differ among the nodes 10-1 to 10-N. Furthermore, each node 10-i notifies the other nodes 10-j of the updated phase information through packet transmission (step S102).

[0051] Each node 10-i receives phase information of other nodes 10-j within a receivable range (step S103). In response to receiving the phase information of other nodes 10-j, each node 10-i updates its own phase according to the above formulas (6) to (10) (step S104). At this time, each node 10-i calculates an overall average phase φ based on the phase information of each of the nodes 10-1 to 10-N. Then, each node 10-i updates its own phase so that a reference phase θi, which is an average value of the multiple phases, approaches the overall average phase φ and the multiple phases differ among the nodes 10-1 to 10-N.

[0052] 6 is a block diagram showing a configuration example of the node 10 according to this embodiment. The node 10 includes a communication controller 100 and a radio unit 110. The communication controller 100 controls wireless communication. The radio unit 110 includes an antenna and a transmission / reception circuit.

[0053] The communication controller 100 is a computer including one or more processors 101 (hereinafter simply referred to as "processor 101") and one or more storage devices 102 (hereinafter simply referred to as "storage devices 102"). The processor 101 performs various types of information processing. For example, the processor 101 includes a CPU (Central Processing Unit). The storage device 102 stores various types of information required for processing by the processor 101. Examples of the storage device 102 include a volatile memory, a non-volatile memory, an HDD (Hard Disk Drive), an SSD (Solid State Drive), etc.

[0054] The control program 103 is a computer program executed by the processor 101. The functions of the communication controller 100 are realized by cooperation between the processor 101 executing the control program 103 and the storage device 102. The control program 103 is stored in the storage device 102. The control program 103 may be recorded in a computer-readable recording medium. The control program 103 may be provided to the communication controller 100 via a network.

[0055] The radio environment information 104 indicates the environment of the wireless communication network 2. For example, the radio environment information 104 includes the total number N of the nodes 10 and their own identifiers i. The communication controller 100 receives the radio environment information 104 from, for example, the central node 20. The radio environment information 104 is stored in the storage device 102.

[0056] The communication controller 100 executes the transmission timing control according to this embodiment (see FIG. 5) based on the radio environment information 104 and the above expressions (6) to (10). Then, the communication controller 100 transmits a packet via the radio unit 110.

[0057] As described above, according to this embodiment, even in a situation where a hidden terminal exists, each node 10-i in the wireless communication network 2 can autonomously and appropriately control its own transmission timing to avoid collisions. This enables efficient time-division communication. [Explanation of symbols]

[0058] 1. Wireless communication systems 2. Wireless communication network 10 Wireless communication terminal (node) 20 Central radio communication equipment 100 Communication Controller 101 Processor 102 Storage device 103 Control Program 104 Wireless environment information 110 Radio Section

Claims

1. A method for controlling transmission timing in each of a plurality of wireless communication terminals in a wireless communication network, comprising: a process in which each of the wireless communication terminals determines a packet transmission timing based on a plurality of phases in a predetermined period; A process of calculating an overall average phase which is an average value of the plurality of phases across the plurality of wireless communication terminals; updating the multiple phases of each of the wireless communication terminals such that an average value of the multiple phases of each of the wireless communication terminals approaches the overall average phase and the multiple phases differ among the multiple wireless communication terminals; a process of notifying other wireless communication terminals of the updated phase information through packet transmission; Includes Transmission timing control method.

2. 2. A transmission timing control method according to claim 1, comprising: the average value of the plurality of phases of each of the wireless communication terminals is a reference phase; a difference between the reference phase and the plurality of phases is set to be different among the plurality of wireless communication terminals; The process of updating the plurality of phases of each of the wireless communication terminals includes: updating the reference phase of each of the wireless notification devices so as to approach the overall average phase; calculating the plurality of phases of each of the wireless notification devices based on the updated reference phase; Includes Transmission timing control method.

3. 3. A transmission timing control method according to claim 2, comprising: The plurality of phases include: a first phase obtained by subtracting an adjustment phase from the reference phase; a second phase obtained by adding the adjustment phase to the reference phase; Including, The adjustment phase is set to be different among the plurality of wireless communication terminals. Transmission timing control method.

4. 4. A transmission timing control method according to claim 3, comprising: In each of the wireless notification devices, the plurality of phases are updated according to the following formula: [0010] [0025] [0030] [0045] [0050] Where: N is the total number of the plurality of wireless communication terminals, i is an identifier of each of the wireless communication terminals and takes a value from 1 to N, θ ｉ is the reference phase of each of the wireless communication terminals, r is the order parameter, which is a real number greater than 0 and less than or equal to 1; K is a coupling strength between the plurality of wireless communication terminals, ΔT is unit time, φ is the ensemble mean phase, β is the adjustment phase, a １ is a real number between 0 and 1, α1 is the first phase, α2 is the second phase Transmission timing control method.

5. A control program that is executed by a computer and causes the computer to execute the transmission timing control method according to any one of claims 1 to 4.

6. A wireless communication system includes a plurality of wireless communication terminals included in a wireless communication network, Each of the plurality of wireless communication terminals A process of setting each of a plurality of phases in a predetermined period as a packet transmission timing; A process of calculating an overall average phase which is an average value of the plurality of phases across the plurality of wireless communication terminals; updating the multiple phases of each of the wireless communication terminals such that an average value of the multiple phases of each of the wireless communication terminals approaches the overall average phase and the multiple phases differ among the multiple wireless communication terminals; a process of notifying other wireless communication terminals of the updated phase information through packet transmission; configured to run Wireless communication system.

7. A wireless communication terminal in a wireless communication network including a plurality of wireless communication terminals, A communication controller is provided, The communication controller A process of setting each of a plurality of phases in a predetermined period as a packet transmission timing; A process of calculating an overall average phase which is an average value of the plurality of phases across the plurality of wireless communication terminals; updating the plurality of phases of the wireless communication terminal such that an average value of the plurality of phases of the wireless communication terminal approaches the overall average phase and the plurality of phases differ among the plurality of wireless communication terminals; a process of notifying other wireless communication terminals of the updated phase information through packet transmission; configured to run Wireless communication terminal.

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