Communication system, communication method, and communication program

Abstract

To reduce the packet collision rate due to the hidden terminal problem without generating overhead in terms of the amount of information. [Solution] Transmitting terminals (2) transmit packets asynchronously with each other. A gateway (3) individually synchronizes with each transmitting terminal and receives the packets. In the transmitting terminals, a mapping unit (223) determines a communication resource, a remapping unit (225) changes at least a time slot of the communication resource to another time slot when detecting another packet being transmitted in the communication resource, and a transmitting unit (226) transmits the packet in the communication resource. In the gateway, a demodulation unit (322) demodulates identification information from a received packet, a remapping detection unit (323) detects a remapping process for the packet based on the reception time of the packet, and a radio environment estimation unit (324) estimates a set of probabilities of mutual interference between transmitting terminals as the radio environment based on the number of times remapping processes are detected.

Description

[Technical Field]

[0001] The present invention relates to a communication system, a communication method, and a communication program, which can be suitably used, for example, in wireless communication in which a single gateway receives packets transmitted asynchronously from a plurality of transmitting terminals. [Background technology]

[0002] With the development of IoT (Internet of Things), LPWAN (Low Power Wide Area Network), typified by LoRaWAN (Long Range Wide Area Network), is attracting attention. As a communication method for such networks, a modulation and demodulation method using chirp spread spectrum in the physical layer is known.

[0003] While LoRaWAN can achieve both low power consumption and long-distance communication, it has limitations on the transmission time per unit time. In addition, because it uses a relatively simple random access method, packet collisions can occur frequently in environments with many transmitting terminals.

[0004] Carrier sense is known as a technology to suppress packet collisions. Carrier sense checks the usage status of the frequency channel on which a packet is to be transmitted, and transmits the packet if it is determined that the frequency channel is open. However, depending on the relative positions of the transmitting terminals, carrier sense may not be able to detect packet transmissions from other transmitting terminals. In particular, LoRaWAN communication areas can be relatively large, which can exacerbate the hidden terminal problem.

[0005] In addition, it is expected that the hidden terminal problem can be reduced by clustering a large number of transmitting terminals and allocating orthogonal communication resources to each cluster. However, it is undesirable to incur communication overhead in order to reduce the hidden terminal problem.

[0006] In relation to the above, Non-Patent Document 1 (LoRa Alliance, Inc., "LoRaWAN™ 1.0.3 Specification", 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> ) discloses the LoRaWAN specification version 1.0.3.

[0007] In addition, Non-Patent Document 2 (K. Suzuki, K. Adachi, M. Ohta, O. Takyu, and T. Fujii, “Packet-Level Index Modulation Based on Channel Activity Detection,” IEEE Trans. Wireless Commun., pp. 2812-2823, Apr. 2024) discloses a PLIM method using CAD.

[0008] Furthermore, clustering processing is disclosed in Non-Patent Document 3 (U. von Luxburg, “A Tutorial on Spectral Clustering,” Statistics and Computing, no. 4, pp. 395-416, August 2007.) and Non-Patent Document 4 (A. Damle, V. Minden, and L. Ying, “Simple, direct and efficient multi-way spectral clustering,” Information and Inference: A Journal of the IMA, vol. 8, no. 1, pp. 181-203, June 2018.). [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] LoRa Alliance, Inc., "LoRaWAN(TM) 1.0.3 Specification," 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> [Non-patent document 2] K. Suzuki, K. Adachi, M. Ohta, O. Takyu, and T. Fujii, “Packet-Level Index Modulation Based on Channel Activity Detection,” IEEE Trans. Wireless Commun., pp. 2812-2823, Apr. 2024 [Non-patent document 3] U. von Luxburg, “A Tutorial on Spectral Clustering,” Statistics and Computing, no. 4, pp. 395-416, Aug. 2007. [Non-patent document 4] A. Damle, V. Minden, and L. Ying, “Simple, direct and efficient multi-way spectral clustering,” Information and Inference: A Journal of the IMA, vol. 8, no. 1, pp. 181-203, Jun. 2018. Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above circumstances, an object of the present disclosure is to provide a communication system, a communication method, and a communication program that can reduce the packet collision rate due to the hidden terminal problem without generating overhead in terms of information volume, etc. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0011] The following describes the means for solving the problems using the numbers and symbols used in the description of the invention. These numbers and symbols are added in parentheses for reference purposes to show an example of the correspondence between the claims and the description of the invention. Therefore, the claims should not be interpreted as being limited by the parenthetical descriptions.

[0012] According to one embodiment, a communication system (1) includes a plurality of transmitting terminals (2) and a gateway (3). The plurality of transmitting terminals (2) transmit packets asynchronously with one another. The gateway (3) individually synchronizes with each of the plurality of transmitting terminals (2) and receives packets from each of the plurality of transmitting terminals (2). Each of the plurality of transmitting terminals (2) includes a mapping unit (223), a remapping unit (225), and a transmitting unit (226). The mapping unit (223) determines a communication resource that combines a time slot for transmitting the packet and a frequency channel to be used for the transmission, based on a first portion of transmission data to be modulated into the packet. When the remapping unit (225) detects another packet being transmitted using the communication resource, it performs a remapping process to change at least a time slot of the communication resource to another time slot. The transmitting unit (226) transmits a packet obtained by modulating a second portion of the transmission data and identification information of each of the plurality of transmitting terminals (2) using the communication resource. The gateway (3) includes a demodulator (322), a remapping detector (323), a radio environment estimator (324), and an output unit (325). The demodulator (322) demodulates the second part of the transmission data and the identification information from the received packet. The remapping detector (323) detects a remapping process for the packet based on the reception time of the packet. The radio environment estimator (324) estimates, as the radio environment, a set of probabilities indicating whether a plurality of transmitting terminals (2) can detect each other's communication in radio communication with the gateway (3), based on the number of times the remapping process is detected. The output unit (325) outputs radio environment information indicating the radio environment to the outside.

[0013] According to one embodiment, the communication method includes each of a plurality of transmitting terminals (2) transmitting a packet asynchronously with respect to one another (S21 to S29), and a gateway (3) individually synchronized with each of the plurality of transmitting terminals (2) receiving a packet from each of the plurality of transmitting terminals (2) (S31 to S36). The transmitting (S21 to S29) includes determining a communication resource that combines a time slot for transmitting the packet and a frequency channel to be used for the transmission, based on a first portion of transmission data to be modulated into the packet (S23), performing a remapping process to change at least the time slot of the communication resource to another time slot when another packet being transmitted using the communication resource is detected (S25: Yes), and transmitting a packet obtained by modulating a second portion of the transmission data and identification information of each of the plurality of transmitting terminals (2) using the communication resource (S29). The receiving (S31 to S36) includes demodulating the second part of the transmission data and the identification information from the received packet (S32), detecting a remapping process for the packet based on the reception time of the packet (S33), estimating a set of probabilities representing whether multiple transmitting terminals (2) can detect each other's communication in wireless communication with the gateway (3) as the wireless environment based on the number of times the remapping process is detected (S35), and outputting wireless environment information representing the wireless environment to the outside (S36).

[0014] According to one embodiment, the communication program is a communication program for causing a computing device (22, 32) to execute a predetermined process, and the process includes a plurality of transmitting terminals (2) transmitting packets asynchronously with one another (S21 to S29), and a gateway (3) individually synchronizing with each of the plurality of transmitting terminals (2) receiving packets from each of the plurality of transmitting terminals (2) (S31 to S36). The transmitting (S21 to S29) includes determining, based on a first portion of transmission data to be modulated into the packet, a communication resource combining a time slot for transmitting the packet and a frequency channel to be used for the transmission (S23), performing a remapping process to change at least the time slot of the communication resource to another time slot when another packet being transmitted using the communication resource is detected (S25: Yes), and transmitting, using the communication resource, a packet obtained by modulating a second portion of the transmission data and identification information of each of the plurality of transmitting terminals (2) (S29). The receiving (S31 to S36) includes demodulating the second part of the transmission data and the identification information from the received packet (S32), detecting a remapping process for the packet based on the reception time of the packet (S33), estimating a set of probabilities representing whether multiple transmitting terminals (2) can detect each other's communication in wireless communication with the gateway (3) as the wireless environment based on the number of times the remapping process is detected (S35), and outputting wireless environment information representing the wireless environment to the outside (S36). [Effects of the Invention]

[0015] According to one embodiment, it is possible to reduce the packet collision rate due to the hidden terminal problem without generating overhead in terms of the amount of information or the like. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. [Figure 2] FIG. 2 is a block circuit diagram showing an example of the configuration of a transmitting terminal according to an embodiment. [Figure 3] FIG. 3 is a block circuit diagram illustrating an example of a configuration of a gateway according to an embodiment. [Figure 4] FIG. 4 is a block circuit diagram showing an example of the configuration of a clustering device according to an embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of processing performed by a transmitting terminal in a communication method according to an embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of processing performed by the gateway in the communication method according to an embodiment. [Figure 7] FIG. 7 is a flowchart showing an example of processing performed by the clustering device in the communication method according to one embodiment. [Figure 8] FIG. 8 is a diagram for explaining a packet-type index modulation method according to the related art. [Figure 9] FIG. 9 is a diagram for explaining index mapping using CAD according to the related art. [Figure 10] FIG. 10 is a diagram for explaining the radio environment information estimation process used in the communication method according to an embodiment. [Figure 11] FIG. 11 is a diagram for explaining a model of a computer simulation performed on a communication system according to an embodiment. [Figure 12] FIG. 12 is a table for explaining the specifications of a computer simulation performed on a communication system according to an embodiment. [Figure 13] FIG. 13 is a graph showing an example of the results of a computer simulation performed on a communication system according to an embodiment. [Figure 14] FIG. 14 is a graph showing an example of the results of a computer simulation performed on a communication system according to an embodiment. [Figure 15] FIG. 15 is a graph showing an example of the results of a computer simulation performed on a communication system according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A communication system, a communication method, and a communication program according to the present disclosure will be described below with reference to the accompanying drawings.

[0018] (Embodiment) As shown in FIG. 1, a communication system 1 according to one embodiment includes a plurality of transmitting terminals 2A and 2B and a gateway 3. Hereinafter, when there is no need to distinguish between the transmitting terminals 2A and 2B, they may be collectively referred to as transmitting terminals 2. In the example of FIG. 1, the total number of transmitting terminals 2A and 2B is two, but this is merely an example and does not limit the present embodiment. In reality, more transmitting terminals 2 may be included in the communication system 1. The communication system 1 may further include a clustering device 5.

[0019] Each transmitting terminal 2 transmits a packet asynchronously to the gateway 3 by wireless communication. A packet transmitted by one transmitting terminal 2 may become an interference signal when another transmitting terminal 2 transmits another packet.

[0020] The gateway 3 receives and aggregates packets transmitted by each transmitting terminal 2. The gateway 3 is synchronized with each transmitting terminal 2. The gateway 3 estimates the wireless environment of the transmitting terminal 2 based on the reception time of the packet and the identification information identifying the transmitting terminal 2 that transmitted the packet. The wireless environment is a set of probabilities indicating whether multiple transmitting terminals 2 can detect each other's communication when performing wireless communication with the gateway 3. The gateway 3 transmits wireless environment information indicating the wireless environment to the clustering device 5 by wired communication and / or wireless communication via the network 4.

[0021] The clustering device 5 classifies the plurality of transmitting terminals 2 into a plurality of clusters based on the radio environment information. The clustering device 5 allocates a plurality of mutually orthogonal communication resources to the plurality of clusters in order to suppress the occurrence of interference between the transmitting terminals 2 classified into each cluster. Each transmitting terminal 2 may receive information indicating the allocated communication resources, and thereafter use the communication resources when transmitting packets to the gateway 3.

[0022] As shown in Fig. 2, the transmitting terminal 2 according to one embodiment may be configured like a so-called computer. In the example of Fig. 2, the transmitting terminal 2 includes a bus 21, a computing device 22, a storage device 23, a communication device 24, and an input / output device 25. As an example, the bus 21 is configured to connect the computing device 22, the storage device 23, the communication device 24, and the input / output device 25 so that they can communicate with each other.

[0023] The arithmetic device 22 includes a transmission data generation unit 221, a packet generation unit 222, a mapping unit 223, a carrier sense detection unit 224, a remapping unit 225, and a transmission unit 226. The arithmetic device 22 executes a transmission terminal program stored in a program storage unit 231, among the communication programs according to one embodiment, to thereby realize the processing of the transmission data generation unit 221, the packet generation unit 222, the mapping unit 223, the carrier sense detection unit 224, the remapping unit 225, and the transmission unit 226. The transmission data generation unit 221, the packet generation unit 222, the mapping unit 223, the carrier sense detection unit 224, the remapping unit 225, and the transmission unit 226 are virtual functional blocks that realize processing through cooperation between the arithmetic device 22 and the storage device 23.

[0024] The transmission data generation unit 221 generates transmission data to be transmitted as packets from the transmitting terminal 2 to the gateway 3. The packet generation unit 222 modulates the transmission data to generate the packets. Based on a portion of the transmission data, the mapping unit 223 determines a communication resource, which is a combination of a time slot as the timing for transmitting the packet to the gateway 3 and a frequency channel to use when transmitting the packet to the gateway 3. Before transmitting the packet to the gateway 3 using the communication resource, the carrier sense detection unit 224 performs carrier sense processing to determine whether another transmitting terminal 2 is currently transmitting another packet using the communication resource. If, as a result of the carrier sense processing, another packet being transmitted using the communication resource is detected, the remapping unit 225 performs remapping processing to change at least a time slot of the communication resource to a different time slot. The transmitting unit 226 transmits the packet to the gateway 3 using the communication resource.

[0025] The storage device 23 includes a program storage unit 231 and a data storage unit 232. The program storage unit 231 stores at least a portion of a communication program according to an embodiment that is executed by the transmitting terminal 2. Of the communication program, the transmitting terminal program, which is the portion that is executed by the transmitting terminal 2, may be read from the recording medium 230 and stored in the program storage unit 231. The recording medium 230 may be a non-transitory and tangible medium. The data storage unit 232 stores identification information that identifies the transmitting terminal 2. The data storage unit 232 may further temporarily store generated transmission data, packets, etc.

[0026] The communication device 24 is controlled by the transmitting unit 226 to transmit packets to the gateway 3 by wireless communication using an antenna (not shown). The communication device 24 may further be configured to be connectable to the network 4. The communication device 24 may be controlled by the mapping unit 223 to receive information indicating allocated communication resources from the clustering device 5. The transmitting terminal program may be acquired from the outside via the communication device 24 and stored in the program storage unit 231.

[0027] The input / output device 25 outputs information to the user and accepts operations input by the user. As an example, the input / output device 25 includes a lamp that lights up, a switch that accepts a press operation, and the like.

[0028] As shown in Fig. 3, the gateway 3 according to one embodiment may be configured like a so-called computer. In the example of Fig. 3, the gateway 3 includes a bus 31, a computing device 32, a storage device 33, a communication device 34, and an input / output device 35. As an example, the bus 31 is configured to connect the computing device 32, the storage device 33, the communication device 34, and the input / output device 35 so that they can communicate with each other.

[0029] The arithmetic device 32 includes a receiving unit 321, a demodulating unit 322, a remapping detection unit 323, a radio environment estimation unit 324, and an output unit 325. The arithmetic device 32 executes a gateway program stored in a program storage unit 331, among the communication programs according to one embodiment, to thereby realize the processing of the receiving unit 321, the demodulating unit 322, the remapping detection unit 323, the radio environment estimation unit 324, and the output unit 325. The receiving unit 321, the demodulating unit 322, the remapping detection unit 323, the radio environment estimation unit 324, and the output unit 325 are virtual functional blocks that realize the processing by the arithmetic device 32 and the storage device 33 working together.

[0030] The receiving unit 321 receives packets transmitted by the transmitting terminal 2. The demodulating unit 322 demodulates the received packets and acquires transmission data and identification information. If a remapping process has been performed on the received packet, the remapping detecting unit 323 detects the remapping process based on the reception time of the packet and the identification information of the transmitting terminal 2 that transmitted the packet. The radio environment estimating unit 324 estimates the radio environment of the transmitting terminal 2 based on the number of times remapping processes have been detected. The output unit 325 outputs radio environment information indicating the radio environment and transmits it to the clustering device 5.

[0031] The storage device 33 includes a program storage unit 331 and a data storage unit 332. The program storage unit 331 stores at least a portion of a communication program according to an embodiment that is executed by the gateway 3. A gateway program, which is a portion of the communication program that is executed by the gateway 3, may be read from the recording medium 330 and stored in the program storage unit 331. The recording medium 330 may be a non-transitory, tangible medium. The data storage unit 332 stores identification information of each transmitting terminal 2 and synchronization information that indicates a synchronization state with each transmitting terminal 2. The data storage unit 332 may further temporarily store received packets, the reception time of each packet, demodulated transmission data, the number of times remapping processing has been detected, radio environment information, and the like.

[0032] The communication device 34 is controlled by the output unit 325 and receives packets transmitted by the transmitting terminal 2 via wireless communication using an antenna (not shown). The communication device 34 transmits wireless environment information to the clustering device 5 via the network 4. The transmitting terminal program may be obtained from outside via the communication device 34 and stored in the program storage unit 231.

[0033] The input / output device 35 outputs information to the user and accepts operations input by the user. As an example, the input / output device 35 includes a display device that outputs images, a keyboard that accepts key input operations, and the like.

[0034] As shown in Fig. 4, the clustering device 5 according to one embodiment may be configured like a so-called computer. In the example of Fig. 4, the clustering device 5 includes a bus 51, a computing device 52, a storage device 53, a communication device 54, and an input / output device 55. As an example, the bus 51 is configured to connect the computing device 52, the storage device 53, the communication device 54, and the input / output device 55 so that they can communicate with each other.

[0035] The arithmetic device 52 includes a radio environment information acquisition unit 521, a clustering unit 522, and a resource allocation unit 523. The arithmetic device 52 executes a clustering device program stored in a program storage unit 531, among the communication programs according to one embodiment, to thereby realize the processing of the radio environment information acquisition unit 521, the clustering unit 522, and the resource allocation unit 523. The radio environment information acquisition unit 521, the clustering unit 522, and the resource allocation unit 523 are each a virtual functional block that realizes processing through cooperation between the arithmetic device 52 and the storage device 53.

[0036] The radio environment information acquisition unit 521 receives and acquires radio environment information transmitted by the gateway 3. The clustering unit 522 classifies the multiple transmitting terminals 2 into multiple clusters based on the radio environment information. The resource allocation unit 523 allocates multiple communication resources that are orthogonal to each other to the multiple clusters.

[0037] The storage device 53 includes a program storage unit 531 and a data storage unit 532. The program storage unit 531 stores at least a portion of a communication program according to an embodiment that is executed by the clustering device 5. Of the communication program, the clustering device program, which is the portion executed by the clustering device 5, may be read from the recording medium 530 and stored in the program storage unit 531. The recording medium 530 may be a non-transitory, tangible medium. The data storage unit 532 stores identification information that identifies the transmitting terminal 2. The data storage unit 532 may further temporarily store acquired radio environment information, information representing the results of classifying the multiple transmitting terminals 2 into multiple clusters, information representing the results of allocating multiple communication resources to the multiple clusters, and the like.

[0038] The communication device 54 is controlled by the radio environment information acquisition unit 521 to receive radio environment information transmitted by the gateway 3 via the network 4. The communication device 54 may be controlled by the resource allocation unit 523 to transmit information indicating communication resources allocated to the transmitting terminal 2. The clustering device program may be acquired from outside via the communication device 54 and stored in the program storage unit 531.

[0039] The input / output device 55 outputs information to the user and accepts operations input by the user. As an example, the input / output device 55 includes a display device that outputs images, a keyboard that accepts key input operations, and the like.

[0040] 5, an example of the processing of a transmitting terminal program among the communication programs according to one embodiment, which is executed by the transmitting terminal 2, will be described. The transmitting terminal program may be started when the transmitting terminal 2 is started.

[0041] When the transmitting terminal program starts, step S21 in Fig. 5 is executed. In step S21, the transmission data generation unit 221 of the transmitting terminal 2 shown in Fig. 2 generates transmission data. As an example, the transmission data includes identification information that identifies the transmitting terminal 2, measurement data measured by the transmitting terminal 2 using a sensor (not shown), and the like. The transmission data generation unit 221 may store the generated transmission data in the data storage unit 232.

[0042] After step S21 in FIG. 5, step S22 is executed. In step S22, the packet generator 222 of the transmitting terminal 2 shown in FIG. 2 modulates the transmission data to generate a packet to be transmitted to the gateway 3. More specifically, the packet generator 222 modulates a first portion of the transmission data into an index representing a communication resource by a PLIM (Packet Level Index Modulation) method. Details of the PLIM method according to an embodiment will be described later. Furthermore, the packet generator 222 modulates a second portion of the transmission data other than the first portion by a LoRa (Long Range) modulation method or the like to generate a transmission signal as a packet. Identification information of the transmitting terminal 2 may be included in the second portion of the transmission data. Details of the LoRa modulation method are described in Non-Patent Document 1 (LoRa Alliance, Inc., "LoRaWAN™ 1.0.3 Specification," 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> The packet generator 222 may store the generated index and packet in the data storage unit 232.

[0043] After step S22 in Fig. 5, step S23 is executed. In step S23, the mapping unit 223 of the transmitting terminal 2 shown in Fig. 2 performs a mapping process to determine communication resources. More specifically, the mapping unit 223 determines the time slot in which the packet is transmitted and the frequency channel used for transmitting the packet based on the index used to modulate the first portion of the transmission data. Here, the determined time slot is included in the first time subframe of multiple time subframes included in the time frame allocated for transmitting the packet. The relationship between the time frame, time subframe, and time slot will be described later. The mapping unit 223 may store information indicating the determined time slot and frequency channel in the data storage unit 232.

[0044] After step S23 in Fig. 5, step S24 is executed. In step S24, the carrier sense detection unit 224 of the transmitting terminal 2 shown in Fig. 2 performs carrier sense detection. More specifically, the carrier sense detection unit 224 performs carrier sense and detects another packet being transmitted by another transmitting terminal 2 using the determined frequency channel in the determined time slot.

[0045] After step S24 in Fig. 5, step S25 is executed. In step S25, the carrier sense detection unit 224 of the transmitting terminal 2 shown in Fig. 2 determines whether or not another packet has been detected. If another packet has been detected (Yes), the process proceeds to step S26 in Fig. 5. If another packet has not been detected (No), the process proceeds to step S29.

[0046] In step S26 of Fig. 5, the remapping unit 225 of the transmitting terminal 2 shown in Fig. 2 determines whether the time subframe including the current time slot is the last subframe of multiple time frames included in the time frame including that time subframe. The relationship between time frames, time subframes, and time slots will be described later. If the time subframe including the current time slot is the last time subframe of the time frame (Yes), the process proceeds to step S28. If the time subframe including the current time slot is not the last time subframe of the time frame (No), the process proceeds to step S27.

[0047] In step S27 of Fig. 5, the remapping unit 225 of the transmitting terminal 2 shown in Fig. 2 performs a remapping process to change the communication resource to another communication resource. More specifically, the remapping unit 225 determines the other communication resource based on the index so that packet transmission is performed in the time subframe next to the time subframe including the time slot included in the communication resource before the change. As a result, at least the time slot of the communication resource before the change is changed to another time slot included in the other time subframe. After step S27 of Fig. 5, the process returns to step S24.

[0048] In step S28 of Fig. 5, the transmitter 226 of the transmitting terminal 2 shown in Fig. 2 discards the current packet. This is because, in the carrier sense detection performed before transmitting the packet, another packet being transmitted using the same communication resource was detected in all time subframes included in the time frame allocated for transmitting the current packet. After step S28 of Fig. 5, the process returns to step S21, and an attempt is made to transmit the next packet.

[0049] In step S29 of Fig. 5, the transmitting unit 226 of the transmitting terminal 2 shown in Fig. 2 uses communication resources to transmit a packet to the gateway 3. After step S29 of Fig. 5, the process returns to step S21, and an attempt is made to transmit the next packet.

[0050] An example of the processing of a gateway program among the communication programs according to one embodiment, which is executed by the gateway 3, will be described with reference to the flowchart of Fig. 6. The gateway program may be started when the gateway 3 is started.

[0051] When the gateway program starts, step S31 in Fig. 6 is executed. In step S31, the receiving unit 321 of the gateway 3 in Fig. 3 receives a packet transmitted from the transmitting terminal 2. The receiving unit 321 may store the received packet in the data storage unit 332.

[0052] After step S31 in Fig. 6, step S32 is executed. In step S32, the demodulation unit 322 of the gateway 3 shown in Fig. 3 demodulates the received packet. More specifically, first, the demodulation unit 322 demodulates the packet using a LoRa modulation method or the like to obtain a second portion of the transmission data and identification information of the transmitting terminal 2 that transmitted the packet. Next, the demodulation unit 322 demodulates the reception time and frequency channel of the packet using the PLIM method based on the synchronization state with the transmitting terminal 2 having the demodulated identification information to obtain a first portion of the transmission data. The synchronization state between the gateway 3 and each transmitting terminal 2 will be described later.

[0053] After step S32 in FIG. 6, step S33 is executed. In step S33, the remapping detection unit 323 of the gateway 3 shown in FIG. 3 determines whether the received packet has been remapped. More specifically, the remapping detection unit 323 determines whether the reception time of the packet is included in the first time subframe of the time frame allocated to the transmission of the packet, based on the synchronization state between the transmitting terminal 2 that transmitted the packet and the gateway 3. If the reception time is included in the first time subframe, the remapping detection unit 323 determines that the packet has not been remapped (No), and the process proceeds to step S35. If the reception time is included in a time frame other than the first time subframe, the remapping detection unit 323 determines that the packet has been remapped (Yes), and the process proceeds to step S34.

[0054] In step S34 of FIG. 6, the remapping detection unit 323 of the gateway 3 shown in FIG. 3 increments the carrier sense detection count for the combination of the transmitting terminal 2 that transmitted the packet and another transmitting terminal 2 that transmitted a different packet detected by carrier sense before the transmitting terminal 2 transmitted the packet. More specifically, the remapping detection unit 323 estimates that the carrier sense detection unit 224 of the transmitting terminal 2 detected by carrier sense the different packet that the gateway 3 received using the pre-change communication resource that was determined before the communication resource used to transmit the packet was changed by the remapping process. This estimation is performed each time a remapping process is detected, and the carrier sense detection count is incremented for each combination of the transmitting terminal 2 that performed the remapping process and another transmitting terminal 2 that transmitted the different packet that caused the remapping, among the multiple transmitting terminals 2. As a result, the higher the carrier sense detection count, the more likely it is that the transmitting terminal 2 and the other transmitting terminal 2 are located in locations where interference is likely to occur to the extent that carrier sense detection is detected. Note that the incremented carrier sense detection count may be initialized when the gateway program starts. After step S34 in FIG. 6, step S35 is executed.

[0055] 6, the radio environment estimation unit 324 of the gateway 3 shown in FIG. 3 estimates the radio environment of the transmitting terminal 2. More specifically, based on the number of carrier sense detections resulting from repeated increments, the radio environment estimation unit 324 calculates, for each combination of two transmitting terminals 2 out of the multiple transmitting terminals 2 included in the communication system 1, a probability indicating whether the two transmitting terminals 2 can detect each other's communication when performing wireless communication with the gateway 3, and estimates the radio environment as a set of the probabilities. The radio environment estimation unit 324 may generate radio environment information indicating the estimated radio environment and store it in the data storage unit 332.

[0056] After step S35 in Fig. 6, step S36 is executed. In step S36, the output unit 325 of the gateway 3 shown in Fig. 3 outputs the wireless environment information to the outside. More specifically, the output unit 325 controls the communication device 34 to transmit the wireless environment information to the clustering device 5 via the network 4.

[0057] After step S36 in FIG. 6, the processing of the gateway 3 returns to step S31.

[0058] 7, an example of the processing of a clustering device program among the communication programs according to one embodiment, which is executed by the clustering device 5, will be described. The clustering device program may be started when the clustering device 5 is started.

[0059] 7 is executed. In step S51, the radio environment information acquisition unit 521 of the clustering device 5 shown in FIG. 4 acquires the radio environment information output from the gateway 3. The radio environment information acquisition unit 521 may store the acquired radio environment information in the data storage unit 532.

[0060] After step S51 in FIG. 7, step S52 is executed. In step S52, the clustering unit 522 of the clustering device 5 shown in FIG. 4 performs clustering processing on the transmitting terminals 2. More specifically, the clustering unit 522 classifies the transmitting terminals 2 into multiple clusters based on a set of probabilities indicating whether mutual communication can be detected between each combination of two transmitting terminals 2 among the multiple transmitting terminals 2, which represents the wireless environment represented by the acquired wireless environment information. As an example, the greater the number of carrier sense detections for a combination of two transmitting terminals 2 among the multiple transmitting terminals 2, the higher the probability that the two transmitting terminals 2 constituting the combination will be classified into the same cluster. Furthermore, the fewer the number of carrier sense detections for the combination, the lower the probability that the two transmitting terminals 2 constituting the combination will be classified into the same cluster. After the clustering processing, the clustering unit 522 may store, in the data storage unit 532, information indicating the correspondence between each transmitting terminal 2 and the cluster into which each transmitting terminal 2 is classified.

[0061] After step S52 in Fig. 7, step S53 is executed. In step S53, the resource allocation unit 523 of the clustering device 5 shown in Fig. 4 allocates communication resources to the cluster. More specifically, the resource allocation unit 523 allocates multiple communication resources that are orthogonal to each other to each transmitting terminal 2 classified into one of the clusters. In this way, it is possible to suppress interference that may occur when two transmitting terminals 2 transmit packets to the gateway 3. Thereafter, the resource allocation unit 523 transmits information indicating the allocated communication resources to each transmitting terminal 2.

[0062] After step S53 in FIG. 7, the process of the clustering device 5 returns to step S51.

[0063] Before describing the relationship between the time frame, time subframe, and time slot, a PLIM method according to the related art will be described with reference to Fig. 8. In Fig. 8, the horizontal axis represents time and the vertical axis represents frequency. In the PLIM method, the time allocated to transmit one packet is called a time frame. The length of the time frame is defined as T f The transmitting terminal 2 attempts to transmit one packet per time frame, and if the packet is not successfully transmitted during that time frame, it discards the packet.

[0064] In the PLIM method, a time frame is divided into multiple time slots, and a binary number is assigned to each time slot. The length of a time slot is T slot In the example of Figure 8, the time frame is divided into four equal time slots, so T f =4×T slot In the example of Figure 8, at time t 00 From time t 10 The first time slot is assigned the number "00" until time t 10 From time t 20 The second time slot is assigned the number "01" until time t 20 From time t 30 The third time slot is assigned the number "10" and starts from time t 30 From time t 40 The fourth time slots up to time t are assigned the number "11". The transmitting terminal 2 transmits a packet to be transmitted in each time frame during one of the time slots included in the time frame. In the example of FIG. 8, 00 From time t 40 The time frame up to the time t 10 From time t 20 During the second time slot up to , the packet is transmitted.

[0065] Furthermore, in the PLIM method, multiple frequency channels that can be used to transmit packets are prepared. A binary number is also assigned to each frequency channel. In the example of FIG. 8, the number "1" is assigned to the first frequency channel from frequency f0 to frequency f1, and the number "0" is assigned to the second frequency channel from frequency f1 to frequency f2. A combination of a time frame and a frequency channel is called a communication resource. An index is assigned to each communication resource. The index of a communication resource is a combination of the binary number of the time slot that constitutes the communication resource and the binary number of the frequency channel that constitutes the communication resource. As an example, in the case of FIG. 8, the second frequency channel from frequency f1 to frequency f2 and the second frequency channel from frequency f1 to frequency f2 are assigned to the second frequency channel at time t 10 From time t 20 The index of the communication resource combined with the second time slots up to is "001", which is the second frequency channel number "0" and the second time slot number "01" connected in this order.

[0066] In the PLIM method, a portion of data transmitted by a transmitting device such as the transmitting terminal 2 is represented by an index of a communication resource used to transmit the packet. Furthermore, by using the same PLIM method as the transmitting device, a receiving device such as the gateway 3 can estimate the frequency channel number included in the communication resource set by the transmitting device based on the frequency at which the packet is received. Furthermore, by previously synchronizing the receiving device with the transmitting device in time, the receiving device can estimate the time slot number included in the communication resource set by the transmitting device based on the reception time of the packet. As a result, the receiving device can estimate the communication resource index. By doing so, the PLIM method can reduce the amount of information in a packet by the amount of information in the communication resource index.

[0067] In one embodiment, a PLIM method using CAD (Channel Activity Detection) is used, which is an improvement of the PLIM method described in FIG. 8. Details of the PLIM method using CAD are disclosed in Non-Patent Document 2 (K. Suzuki, K. Adachi, M. Ohta, O. Takyu, and T. Fujii, “Packet-Level Index Modulation Based on Channel Activity Detection,” IEEE Trans. Wireless Commun., pp. 2812-2823, Apr. 2024). The PLIM method using CAD will be described with reference to FIG. 9. In FIG. 9, the horizontal axis represents time and the vertical axis represents frequency. The PLIM method using CAD uses the time subframes described above in addition to the time frames and time slots used in the PLIM method of FIG. 8.

[0068] In the PLIM method using CAD, before transmitting a packet using a communication resource having an index corresponding to a portion of the transmission data, a transmitting device such as a transmitting terminal 2 performs a channel activity detection process such as a carrier sense process to detect whether another packet is being transmitted using the communication resource. If the channel activity detection process detects that another packet is being transmitted using the communication resource, the transmitting device stops transmitting the packet using the communication resource, but does not discard the packet, and transmits the packet in another time slot included in the time frame allocated to transmitting the packet. To achieve this, in the PLIM method using CAD, each time frame is equally divided into multiple time subframes, and each time subframe is equally divided into multiple time slots. The length of the time subframe is set to T subf In the example of Figure 9, the time frame is divided equally into four time subframes, and the time subframe is divided equally into four time slots, so Tf = 4 × T subf =16×T slot holds true.

[0069] In a PLIM scheme using CAD, the number of time slots assigned the same number in a time frame is equal to the total number of time subframes included in the time frame. Therefore, the number of communication resources with the same index in a time frame is also equal to the total number of time subframes included in the time frame. As a result, in a PLIM scheme using CAD, the number of opportunities to transmit a given packet in a time frame is also equal to the total number of time subframes included in the time frame. More specifically, even if a channel activity detection process is performed before transmitting a packet using a communication resource including a time slot included in a time subframe included in a time frame, and another packet is detected being transmitted using the communication resource, if a next time subframe exists in the time frame, there is a possibility that the packet can be transmitted using a communication resource including a time slot included in the next time subframe. As a result, the frequency of discarding packets is reduced.

[0070] Furthermore, in the PLIM method using CAD, by improving the formula for calculating the communication resource index based on the time slot number and frequency channel number, it is possible to reduce the probability that the transmitting device will use the same frequency channel in the next time frame, and it is expected that the probability of interference with other packets will be reduced. As an example, the communication resource index may be calculated using the following "Equation 1".

number

number

[0071] In addition, in the PLIM method using CAD, the receiving device calculates the PLIM bit sequence D plim can be estimated.

number

number

number

number

[0072] As described above, in the PLIM method using CAD, the transmitting device modulates a portion of the transmission data into an index of a communication resource used to transmit a packet, and the receiving device estimates the time slot number and frequency channel number included in the communication resource, estimates the index of the communication resource, and can estimate the portion of the transmission data.

[0073] In one embodiment, it will be further described that the gateway 3 as a receiving device can estimate the radio environment of the transmitting terminal 2 as a transmitting device based on the results of carrier sense detection processing, which is a channel activity detection processing, performed by the transmitting terminal 2 as a transmitting device. Note that there is no need to increase the amount of information in packets transmitted by the transmitting terminal 2 and received by the gateway 3, the lengths and / or total number of time frames, time subframes, and time slots used in communication between the transmitting terminal 2 and the gateway 3, or the bandwidth and total number of frequency channels used in the communication. In other words, in one embodiment, the radio environment of the transmitting terminal 2 can be estimated without incurring communication overhead from these perspectives.

[0074] First, as explained above as step S33 in Figure 6, the gateway 3 determines whether the time subframe including the time slot in which the packet was transmitted, as viewed from the transmitting terminal 2, is the first time subframe of the time frame including the time subframe, based on the reception time of the packet and the synchronization state with the transmitting terminal 2 that transmitted the packet. If the determination result shows that the time subframe including the time slot in which the packet was transmitted is the first subframe, the gateway 3 estimates that the transmitting terminal 2 did not perform remapping processing when transmitting the packet. If the determination result shows that the time subframe including the time slot in which the packet was transmitted is not the first subframe, the gateway 3 estimates that the transmitting terminal 2 performed remapping processing when transmitting the packet. At this time, the gateway 3 extracts the identification information of the other transmitting terminal 2 that transmitted the packet that caused the remapping processing from the record of previously received packets, and increments the number of carrier sense detections estimated to have occurred between the transmitting terminal 2 and the other transmitting terminal 2.

[0075] Next, as explained above as step S34 in Fig. 6, the gateway 3 estimates the wireless environment of the transmitting terminal 2 based on the number of carrier sense detections for each combination of two transmitting terminals 2 out of the multiple transmitting terminals 2. At this time, the gateway 3 estimates that the more the number of carrier sense detections, the more likely interference is to occur between the two transmitting terminals 2 that performed the carrier sense detection.

[0076] An example of the process in which the gateway 3 estimates the wireless environment of the transmitting terminal 2 will be described with reference to Fig. 10. In Fig. 10, the horizontal axis represents time and the vertical axis represents frequency. Fig. 10 shows the reception process of the gateway 3, the transmission process of the transmitting terminal 2A, and the transmission process of the transmitting terminal 2B.

[0077] In the example of Figure 10, time t cs When the transmitting terminal 2B performs carrier sense detection at time t t1A packet being transmitted is detected from the time slot included in the next time subframe (step S25 in FIG. 5: Yes). As a result, the transmitting terminal 2B stops transmitting the packet and performs a remapping process of the communication resources to transmit the packet in the time slot included in the next time subframe (step S27 in FIG. 5). As a result of the remapping process, the transmitting terminal 2B does not detect another packet even when it performs carrier sense detection immediately before (step S25 in FIG. 5: No). Therefore, at time t t2 Then, the transmission of the packet starts (step S29 in FIG. 5).

[0078] The gateway 3 receives the data from the sending terminal 2B at time t t2 6, the time t t is calculated based on the reception time of the packet, the identification information of the transmitting terminal 2B included in the packet, and the synchronization state with the transmitting terminal 2B read from the data storage unit 332 in FIG. 3 using the identification information. t2 The gateway 3 determines that the time subframe including the time subframe is not the first time subframe of the time frame including the time subframe, and determines that the remapping process has been performed (step S33 in FIG. 6: Yes). The gateway 3 determines that the time subframe including the time subframe is the first time subframe of the time frame including the time subframe including the time subframe, and determines that the remapping process has been performed (step S33 in FIG. 6: Yes). cs The gateway 3 calculates the time t cs 6, the gateway 3 detects that it was transmitting terminal 2A that had transmitted the other packet that had been received at that time by reading the reception time of the other packet from the data storage unit 332 in FIG. 3. As a result, the gateway 3 increments the number of carrier sense detections that are estimated to have been performed between transmitting terminal 2A and transmitting terminal 2B (step S34 in FIG. 6).

[0079] After receiving a sufficient number of packets over a sufficient period of time, the gateway 3 counts the number of times carrier sense detection was performed between each pair of transmitting terminals 2 among the plurality of transmitting terminals 2, and outputs the counted results to the clustering device 5 as radio environment information of the transmitting terminals 2.

[0080] An example of the clustering process performed by the clustering device 5 will be described. As the clustering process, the clustering device 5 may create a positively weighted undirected graph G=(V, E). Here, "V" is a set of data points v corresponding to each of the multiple transmitting terminals 2. i "E" is the set of any two data points v i ,v j Weight between w ij is a set of "w ij " is the two data points v read from the radio environment information. i ,v j The carrier sense detection count is the number of times carrier sense detection is estimated to have been performed between two transmitting terminals 2 corresponding to each other. The weight w between transmitting terminals 2 that can detect each other in the carrier sense detection process is ij is likely to be greater than 0, it can be expected that the graph G reflects the positional relationship of the transmitting terminal 2.

[0081] The clustering device 5 performs terminal clustering processing on the graph G created as described above. As a specific example, the clustering device 5 may perform spectral clustering on the graph. Spectral clustering is a process of clustering a data point v of the graph G. i ,v j Weight between ij Based on multiple data points v i ,v jinto multiple clusters. Here, the total number of clusters, K, may be arbitrarily selected. More specifically, the normalized graph Laplacian of the graph G is derived, and an eigenvalue decomposition is performed to calculate a matrix in which K clusters are arranged in ascending order. CPQR decomposition (Column Pivoted QR decomposition) is then performed to perform clustering based on singular value decomposition. Details of such spectral clustering are disclosed, for example, in Non-Patent Document 3 (U. von Luxburg, "A Tutorial on Spectral Clustering," Statistics and Computing, no. 4, pp. 395-416, August 2007) and Non-Patent Document 4 (A. Damle, V. Minden, and L. Ying, "Simple, direct, and efficient multi-way spectral clustering," Information and Inference: A Journal of the IMA, vol. 8, no. 1, pp. 181-203, June 2018).

[0082] (Simulation results) The results of a computer simulation of a communication system 1, a communication method, and a communication program according to an embodiment will be described with reference to FIGS. 11, 12, 13, 14, and 15. FIG. 11 is a diagram for explaining a computer simulation model. A gateway 3 is placed on an xy plane, and multiple transmitting terminals 2 are placed inside a circular area 9 having a radius R from the gateway 3. FIG. 12 is a table for explaining the specifications of the computer simulation. The computer simulation was performed with the number M of transmitting terminals 2 set to 21 integers in increments of 100, ranging from 100 to 2000. The area radius R is 500 meters. The computer simulation was performed with the spreading factor SF of the LoRa modulation method set to 7, 8, 9, or 10. The bandwidth BW is 125 kHz. The carrier sense threshold is -110 dB. The carrier sense time is 5 milliseconds. The computer simulation was performed with the number of channels set to 4 or 8. The total number of time slots per time subframe is 150. The total number of time subframes per time frame is 4. The length T of the time frame as a packet transmission period f The transmission power of each transmitting terminal 2 is 13 dBm. The computer simulation was performed with the simulation time set to 36 hours or 72 hours.

[0083] Fig. 13 is a graph showing an example of the results of a computer simulation. The graph in Fig. 13 includes three graphs G1, G2, and G3. In common with graphs G1, G2, and G3, the horizontal axis represents the number of transmitting terminals 2, and the vertical axis represents PDR (Packet Delivery Rate) characteristics. Graph G1 (dotted line) represents an example of the results of a computer simulation of spectral clustering when the distances between transmitting terminals 2 are known. Graph G2 (solid line) represents an example of the results of a computer simulation of spectral clustering in the embodiment described above. Graph G3 (dashed dotted line) represents an example of the results of a computer simulation when clustering is not performed.

[0084] 13, the PDR characteristics according to one embodiment are improved compared to the PDR characteristics when clustering processing is not performed, regardless of the number M of transmitting terminals 2, showing a maximum increase of approximately 13%. Furthermore, the PDR characteristics according to one embodiment are close to the PDR characteristics when the distances between the transmitting terminals 2 are known.

[0085] In this way, by performing carrier sense detection, the probability of detecting another packet being transmitted using the same communication resource is improved, and as a result, the packet collision rate due to the hidden terminal problem is reduced.

[0086] Figure 14 is a graph showing an example of the results of a computer simulation. In the example of Figure 14, the number M of transmitting terminals 2 was set to 1,000, the simulation time was set to 36 hours, and the number of channels was set to 4. As can be seen from Figure 14, the transmitting terminals 2 are roughly divided into four regions.

[0087] Figure 15 is a graph showing an example of the results of a computer simulation. In the example of Figure 15, the number M of transmitting terminals 2 was set to 1,000, the simulation time was set to 72 hours, and the number of channels was set to 8. As can be seen from Figure 15, the transmitting terminals 2 are roughly divided into eight regions.

[0088] In this way, by allowing the gateway 3 to receive a sufficient number of packets over a sufficient period of time, it is possible to effectively classify the transmitting terminals 2. By appropriately allocating orthogonal communication resources to each cluster, it is expected that the packet collision rate due to the hidden terminal problem will be further reduced.

[0089] (Variation) In the embodiment described above, a configuration has been described in which the gateway 3 estimates the radio environment and transmits radio environment information to the clustering device 5 each time the gateway 3 receives a packet. As a variation of this configuration, the gateway 3 may estimate the radio environment and transmit the radio environment information to the clustering device 5 after repeating the process of receiving packets and incrementing the number of carrier sense detections for a predetermined period of time. In this case, a determination process may be added before step S35 in FIG. 6 to determine whether the predetermined period has elapsed. If the predetermined period has not elapsed, the process may return to step S31, and if the predetermined period has elapsed, the process may proceed to step S35. In this way, the process of estimating the radio environment is executed, the number of times that radio environment information is output, and the processing load on the gateway 3 and the clustering device 5 can be reduced.

[0090] (Variation) In the embodiment described above, the configuration has been described in which the gateway 3 and the clustering device 5 are separate devices. As a variation of this configuration, the gateway 3 and the clustering device 5 may be integrated.

[0091] (Variation) In the embodiment described above, a configuration has been described in which the output unit 325 of the gateway 3 shown in Fig. 3 outputs the radio environment information to the clustering device 5. As a variation of this configuration, when outputting the radio environment information, the output unit 325 may store it in an external recording medium 330, or may display it on a display device serving as the input / output device 35 so that the user can visually recognize it.

[0092] The invention made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the embodiments and can be modified in various ways without departing from the spirit of the invention. Furthermore, the features described in the embodiments can be freely combined within the scope of technical compatibility. [Explanation of symbols]

[0093] 1. Communication Systems 2, 2A, 2B transmitting terminal 21 Bus 22 Arithmetic unit 221 Transmission data generation unit 222 Packet Generation Unit 223 Mapping Department 224 Carrier sense detector 225 Remapping section 226 Transmitter 23 Storage device 230 Recording Media 231 Program Memory Unit 232 Data storage unit 24 Communication equipment 25 Input / Output Devices 26 sensors 3 Gateway 31 Bus 32 Arithmetic unit 321 Receiving Unit 322 Demodulation Unit 323 Remapping Detector 324 Wireless environment estimation section 325 Output Section 33 Storage device 330 Recording Media 331 Program Memory Unit 332 Data storage unit 34 Communication equipment 35 Input / Output Devices 4 Network 5 Clustering Device 51 Bus 52 Arithmetic unit 521 Wireless environment information acquisition unit 522 Clustering Department 523 Resource Allocation Department 53 Storage device 530 Recording Media 531 Program Memory Unit 532 Data storage unit 54 Communication equipment 55 Input / Output Devices 9 Area BW Bandwidth f0, f1, f2 frequencies G1, G2, G3 graphs M Number of terminals R Area Radius SF Spread Rate t 00 ,t 10 ,t 20 ,t 30 ,t 40 time t 01 ,t 02 ,t 03 ,t 11 ,t 12 ,t 13 ,t 21 ,t 22 ,t 23 ,t 31 ,t 32 ,t 33 time t cs Carrier sense detection time T f Time frame length T slot Time slot length T subf Temporal subframe length t t1 ,t t2 Packet transmission start time x-axis y-axis

Claims

1. a plurality of transmitting terminals each transmitting packets asynchronously with respect to each other; a gateway that individually synchronizes with each of the plurality of transmitting terminals and receives the packets from each of the plurality of transmitting terminals; Equipped with Each of the plurality of transmitting terminals a mapping unit that determines communication resources that combine a time slot for transmitting the packet and a frequency channel to be used for the transmission, based on a first portion of transmission data to be modulated into the packet; a remapping unit that performs a remapping process to change at least the time slot of the communication resource to another time slot when another packet being transmitted in the communication resource is detected; a transmitting unit that transmits the packet obtained by modulating the second portion of the transmission data and the identification information of each of the plurality of transmitting terminals using the communication resources; Including, The gateway a demodulation unit that demodulates the second part of the transmission data and the identification information from the received packet; a remapping detection unit that detects the remapping process for the packet based on a reception time of the packet; a wireless environment estimation unit that estimates, as a wireless environment, a set of probabilities representing whether the plurality of transmitting terminals can detect each other's communication in wireless communication with the gateway based on the number of times the remapping process is detected; an output unit that outputs wireless environment information representing the wireless environment to an external device; Contains Communication system.

2. 2. The communication system according to claim 1, each of the plurality of transmitting terminals attempts to transmit the packet once for each time frame having a predetermined length; the time frame includes a first total number of time subframes; each of the time subframes includes a second total number of the time slots; The mapping unit selects the time slot included in the time slot included in a first time subframe included in the time frame based on the first part; When performing the remapping process, the remapping unit If a time subframe subsequent to the time subframe containing the time slot before the change exists in the time frame, selecting the different time slot from among the time slots contained in the subsequent time subframe; Discarding the packet if the time subframe including the time slot before the change is the last time subframe of the time frame including the time subframe; the remapping detection unit determines that the remapping process has been performed on the packet when the reception time is included in a time subframe other than the first time subframe, based on synchronization information indicating synchronization between the gateway and a first transmission terminal among the plurality of transmission terminals that has the identification information included in the received packet. Communication system.

3. 3. The communication system according to claim 2, The radio environment estimation unit every time it is determined that the remapping process has been performed on the packet, incrementing the number of carrier sense detections between the first transmitting terminal, which has transmitted the packet on which the remapping process has been performed, and the second transmitting terminal, which has transmitted the other packet that the gateway received on the frequency channel in the time slot before the change, among the plurality of transmitting terminals; estimating the wireless environment based on the number of carrier sense detections for each combination of two transmitting terminals among the plurality of transmitting terminals; Communication system.

4. 2. The communication system according to claim 1, a clustering unit that performs a terminal clustering process to classify the plurality of transmitting terminals into a plurality of clusters based on the radio environment information; Furthermore, The clustering unit, for each combination of two transmitting terminals among the plurality of transmitting terminals, The more times the remapping process in the combination is detected, the higher the probability that the two transmitting terminals will be classified into the same cluster; The fewer the number of times the remapping process in the combination is detected, the lower the probability that the two transmitting terminals are classified into different clusters; allocating a plurality of mutually orthogonal communication resources to the plurality of clusters; Communication system.

5. 5. The communication system according to claim 4, the clustering unit classifies the plurality of transmitting terminals into the plurality of clusters by a spectral clustering process using the radio environment as a weight between the plurality of transmitting terminals. Communication system.

6. 3. The communication system according to claim 2, The mapping unit determines the total number (K) of the frequency channels available for transmitting the packet, the total number (Q) of the time slots included in each of the time subframes, and the numerical value (D ｐｌｉｍ ) and the identification information (D ａｄｄｒ ) and a packet number (D ｐｃｎｔ ) and a subframe number (s) that identifies the time subframe, to determine the communication resource; the remapping unit performs the mapping process using a subframe number of the next time subframe instead of the subframe number as the remapping process. Communication system.

7. A plurality of transmitting terminals transmit packets asynchronously with each other; a gateway individually synchronized with each of the plurality of transmitting terminals receiving the packets from each of the plurality of transmitting terminals; Including, The transmitting step includes: determining, based on a first portion of transmission data to be modulated into the packet, a communication resource that is a combination of a time slot for transmitting the packet and a frequency channel to be used for the transmission; performing a remapping process of changing at least the time slot of the communication resource to another time slot when another packet being transmitted in the communication resource is detected; transmitting the packet obtained by modulating the second portion of the transmission data and the identification information of each of the plurality of transmitting terminals using the communication resource; Including, The receiving includes: demodulating the second portion of the transmission data and the identification information from the received packet; Detecting the remapping process for the packet based on a reception time of the packet; Estimating a set of probabilities representing whether the plurality of transmitting terminals can detect each other's communication in wireless communication with the gateway as a wireless environment based on the number of times the remapping process is detected; outputting wireless environment information representing the wireless environment to an external device; Including, Communication method.

8. A communication program for causing a computing device to execute a predetermined process, The process comprises: A plurality of transmitting terminals transmit packets asynchronously with each other; a gateway individually synchronized with each of the plurality of transmitting terminals receiving the packets from each of the plurality of transmitting terminals; Including, The transmitting step includes: determining, based on a first portion of transmission data to be modulated into the packet, a communication resource that is a combination of a time slot for transmitting the packet and a frequency channel to be used for the transmission; performing a remapping process of changing at least the time slot of the communication resource to another time slot when another packet being transmitted in the communication resource is detected; transmitting the packet obtained by modulating the second portion of the transmission data and the identification information of each of the plurality of transmitting terminals using the communication resource; Including, The receiving includes: demodulating the second portion of the transmission data and the identification information from the received packet; Detecting the remapping process for the packet based on a reception time of the packet; Estimating a set of probabilities representing whether the plurality of transmitting terminals can detect each other's communication in wireless communication with the gateway as a wireless environment based on the number of times the remapping process is detected; outputting wireless environment information representing the wireless environment to an external device; Including, Communications program.

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