Wireless communication system, wireless communication method, and wireless communication control device

Abstract

To provide a wireless communication system that can maximize the communication capacity of the entire system, by calculating the transmission rate in each channel for each group of satellite IoT terminals and controlling transmission traffic based on it, in a communication system based on a CRDSA+FH method, related to wireless communication systems, wireless communication methods, and wireless communication control devices.SOLUTION: A wireless communication system of the present disclosure includes a satellite IoT terminal unit and a system control unit. The satellite IoT terminal unit has a function to transmit information about a transmittable channel list and an amount of traffic scheduled to be transmitted to the system control unit. The system control unit has a function to classify the satellite IoT terminal unit into a group based on the transmittable channel list, a function to calculate a transmission rate in each channel of the group, and a function to notify the satellite IoT terminal unit of the transmission rate of the group and in each channel. The satellite IoT terminal unit has a function to select a channel and control the amount of transmission traffic, based on the transmission rate in each channel.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a wireless communication system, a wireless communication method, and a wireless communication control device. [Background technology]

[0002] In recent years, IoT services that communicate with things have been developing. IoT terminals can connect to the Internet using wireless communication by incorporating wireless communication devices. Therefore, IoT terminals are expected to be applied to various services such as remote monitoring and telemetering.

[0003] Wireless communication standards include existing mobile communication systems such as wireless LAN (IEEE 802.11ah) and LTE, as well as LPWA, which is characterized by its low power consumption. LPWA standards that use unlicensed bands include Sigfox, LoRaWAN, and ELTRES. LPWA standards that use licensed bands include LTE-M and NB-IoT.

[0004] Meanwhile, satellite communication services using low-orbit satellites as wireless communication devices are attracting attention. In satellite communication services, multiple communication satellites are launched into orbits at altitudes ranging from several hundred kilometers to 2,000 kilometers. Radio terminals on the ground can connect to these communication satellites to perform high-speed communications. For example, Oneweb and SpaceX have launched numerous communication satellites and have begun providing communication services.

[0005] Additionally, IoT services using low-earth orbit satellites that combine these communication satellites are being considered. For example, there is a service in which IoT devices are connected to low-earth orbit satellites and then connected to the Internet via those satellites. Such IoT services are promising as systems that can provide IoT services in remote areas such as mountainous regions where terrestrial networks are not developed, as well as in sea and air areas where terrestrial network signals cannot reach. For example, Globalstar provides a satellite IoT service using low-earth orbit satellites.

[0006] Figure 1 shows an image of an IoT system using low-earth orbit satellites. A satellite IoT terminal 2 on the ground transmits packets containing IoT data to a satellite 4 via a service link 3. The packets are then transmitted to a terrestrial base station 6 via a feeder link 5, and then transmitted to an IoT application server 10 via a network 9. The IoT application server 10 performs processes such as data processing, analysis, and data cleansing required for various IoT services.

[0007] These satellite IoT terminals transmit packets to the satellite using a wireless channel. In this case, access methods such as TDMA or FDMA are used so that multiple terminals can transmit data using the wireless channel.

[0008] In TDMA and FDMA access methods, a control device on the system side controls the system and allocates resources such as time and frequency for packet transmission to each IoT terminal. Another access method in which IoT terminals control the system autonomously is CRDSA (Contention Resolution Diversity Slotted ALOHA), an extension of Slotted ALOHA. In this method, packets sent by IoT terminals are duplicated and then transmitted in different time slots.

[0009] Figure 2 is a diagram illustrating the CRDSA method. Here, an example is shown in which IoT terminal #1 transmits a packet using channel 1, using time slot 12. First, IoT terminal #1 transmits packet 14 in the time slot from t2 to t3. IoT terminal #1 also duplicates packet 14 and transmits the duplicated packet 16 in the time slot from t4 to t5.

[0010] Figure 3 shows interference in the CRDSA method. This shows an example in which the transmission timing from an IoT device overlaps with the transmission timing from another IoT device. In this case, the transmitted packets collide and interfere with each other, resulting in incorrect reception of the packets. Even in this case, if the subsequently transmitted duplicated packets are received correctly, the receiving side can use those packets to perform interference cancellation processing, potentially allowing all packets to be received correctly.

[0011] Figure 3 shows an example in which IoT terminals #1, #2, and #3 transmit packets using the CRDSA method using eight time slots. IoT terminal #1 transmits packet 14 and duplicate packet 16 in different time slots. IoT terminal #2 transmits packet 18 and duplicate packet 20 in different time slots. IoT terminal #3 transmits packet 22 and duplicate packet 24 in different time slots.

[0012] In this case, packet 18 and duplicate packet 20 transmitted by IoT terminal #2 collide with packet 14 and duplicate packet 24, respectively, and are therefore not received correctly. In other words, the information of IoT terminal #2 is not transmitted correctly. However, duplicate packet 16 and packet 22 are received correctly in other time slots. In other words, the information of IoT terminal #1 and IoT terminal #3 is transmitted correctly.

[0013] Therefore, by performing interference cancellation processing using duplicate packet 16 or packet 22, it becomes possible to correctly receive the transmitted packet from IoT terminal #2. For example, processing is performed to subtract the information of duplicate packet 16 from the information received in the time slot from t2 to t3. Because duplicate packet 16 is a duplicate of packet 14, this processing makes it possible to recognize the correct content of packet 18. In other words, in the CRDSA method, the accuracy of information transmission can be improved by combining multiple packet transmissions with interference cancellation processing.

[0014] FIG. 4 is a diagram illustrating the CRDSA method incorporating FH. When multiple channels are available, FH (Frequency Hopping) can be introduced as an extension of the CRDSA method. This is a method for transmitting packets on any different channel and time slot. FIG. 4 shows an example in which IoT terminal #1 generates and transmits two duplicate packets. Here, packet 14, duplicate packet 16, and duplicate packet 26 each use a different channel and different time slot. In this way, using multiple channels reduces the possibility of collision of transmitted packets between terminals, thereby improving throughput performance. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-299692 Summary of the Invention [Problem to be solved by the invention]

[0016] In IoT services using low-orbit satellites, each satellite covers a vast area on the Earth's surface. As a result, many devices connect to one satellite. When the number of connected devices increases, interference between devices can cause communication problems, reducing the communication capacity of the communication system.

[0017] In addition, when each terminal transmits packets to the satellite, it is necessary to avoid interfering with the terrestrial network, so the channels available to each terminal are different.

[0018] In the CRDSA method that incorporates FH (hereinafter referred to as the "CRDSA+FH method"), communication capacity increases as the number of connected terminals increases. However, once the number of terminals reaches a certain value, communication capacity drops sharply. This occurs because the probability that multiple terminals will select the same slot to transmit packets increases, resulting in an increase in packet collisions. When a certain number of packet collisions occur, interference cancellation processing stops working, and communication capacity drops sharply. This drop in communication capacity disrupts IoT services.

[0019] Figure 5 is a graph showing the throughput characteristics obtained by simulation, with the number of slots as a parameter. In Figure 5, the horizontal axis represents normalized traffic volume, and the vertical axis represents throughput. Comparing the results for each number of slots, it can be seen that the throughput characteristics improve as the number of slots increases. This is thought to be because the probability of packet collisions decreases. Furthermore, when comparing at a specific number of slots, for example, when the number of slots is 1863, the throughput reaches its maximum when the normalized traffic volume (G) is around 0.75. As G increases further, the throughput drops sharply. This is thought to be because the occurrence of numerous packet collisions causes interference cancellation processing to fail.

[0020] Patent Document 1 discloses a technology for controlling transmission traffic to improve the characteristics of a general ALOHA system. This technology independently sets time periods during which packets can be transmitted and time periods during which they cannot be transmitted for each wireless station or terminal. This adjusts the amount of transmission traffic per wireless station or terminal. However, this method does not anticipate adjusting the amount of transmission traffic based on the characteristics of the CRDSA+FH system, and therefore is unable to optimally adjust the amount of transmission traffic. Furthermore, in an IoT system where multiple channels are available, it is not possible for terminals to select the optimal channel, and the communication capacity of the entire system cannot be maximized.

[0021] To solve the above-mentioned problems, the present disclosure aims to provide a wireless communication system that can maximize the communication capacity of the entire system by calculating the transmission rate for each channel for each group of satellite IoT terminals and controlling the transmission traffic based on the calculated transmission rate, particularly in a communication system based on the CRDSA+FH method.

[0022] In order to solve the above-mentioned problems, a second object of the present disclosure is to provide a wireless communication method that can maximize the communication capacity of the entire system.

[0023] In order to solve the above-mentioned problems, a third object of the present disclosure is to provide a wireless communication control device that can maximize the communication capacity of the entire system. [Means for solving the problem]

[0024] A first aspect of the present disclosure is preferably a wireless communication system comprising a satellite IoT terminal unit and a system control unit, wherein the satellite IoT terminal unit has a function of sending a list of transmittable channels and information about the amount of traffic to be transmitted to the system control unit, a function of the system control unit classifying the satellite IoT terminal units into groups based on the list of transmittable channels, a function of calculating the transmission rate for each channel in the group, and a function of notifying the satellite IoT terminal unit of the group and the transmission rate for each channel, and a function of the satellite IoT terminal unit selecting a channel and controlling the amount of transmission traffic based on the transmission rate for each channel.

[0025] A second aspect of the present disclosure is preferably a wireless communication method comprising the steps of: a satellite IoT terminal unit sending a list of transmittable channels and information on the volume of traffic to be transmitted to a system control unit; the system control unit classifying the satellite IoT terminals into groups based on the list of transmittable channels; calculating the transmission rate for each channel in the group; notifying the satellite IoT terminal of the group and the transmission rate for each channel; and the satellite IoT terminal unit selecting a channel and controlling the volume of transmission traffic based on the transmission rate for each channel.

[0026] A third aspect of the present disclosure is preferably a wireless communication control device that receives information about a transmittable channel list and scheduled traffic volume from a satellite IoT terminal, classifies the satellite IoT terminals into groups based on the transmittable channel list, calculates the transmission rate for each channel in the group, and notifies the satellite IoT terminal of the group and the transmission rate for each channel. [Effects of the Invention]

[0027] According to the first to third aspects of the present disclosure, particularly in a communication system based on the CRDSA+FH method, the communication capacity of the entire system can be maximized by calculating the transmission rate for each channel for each group of satellite IoT terminals and performing transmission traffic control based on that. [Brief explanation of the drawings]

[0028] [Figure 1] This is a diagram illustrating an IoT system using low-orbit satellites. [Figure 2] FIG. 1 is a diagram illustrating the CRDSA method. [Figure 3] FIG. 1 is a diagram illustrating interference in the CRDSA system. [Figure 4] FIG. 1 is a diagram showing a CRDSA method incorporating FH. [Figure 5] 10 is a graph showing throughput characteristics obtained by simulation with the number of slots as a parameter. [Figure 6]1 is a diagram illustrating a configuration of a wireless communication system according to a first embodiment of the present disclosure. [Figure 7] 4 is a flowchart showing processing of the wireless communication system according to the first embodiment of the present disclosure. [Figure 8] 1 is a diagram illustrating an arrangement of satellite IoT terminals according to a first embodiment of the present disclosure. [Figure 9] FIG. 4 is a diagram illustrating the number of slots per unit time according to the first embodiment of the present disclosure. [Figure 10] 10 is a graph showing calculation results of maximum throughput according to the first embodiment of the present disclosure. [Figure 11] 10 is a graph showing throughput characteristics with the number of slots as a parameter according to the first embodiment of the present disclosure. [Figure 12] 10 is a graph showing a simulation result of throughput characteristics according to the first embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0029] Embodiment 1 6 is a diagram illustrating a configuration of a wireless communication system according to the first embodiment of the present disclosure. The wireless communication system 100 includes a satellite IoT terminal 2. The satellite IoT terminal 2 converts information on a list of available channels and the amount of traffic to be transmitted into packets and transmits the packets to a satellite 4 via a service link 3.

[0030] The satellite 4 relays the information packets transmitted from the satellite IoT terminal 2 to a terrestrial base station 6 via a feeder link 5. The terrestrial base station 6 transmits the relayed information packets to a system controller 8 via a network 9.

[0031] The system controller 8 calculates the transmission rate for each channel based on the transmitted information, and notifies the satellite 4 via the terrestrial base station 6 of the information on the transmission rate for each channel.

[0032] The satellite 4 broadcasts information about the transmission rate in each channel to all satellite IoT terminals 2. Based on this information, the satellite IoT terminal 2 performs channel selection and transmission traffic control.

[0033] The satellite IoT terminal 2 also performs observation and sensing as an IoT service to obtain IoT information. The obtained IoT information is then converted into packets and transmitted to the satellite 4 via the service link 3. The satellite 4 then relays the transmitted information packets to the terrestrial base station 6 via the feeder link 5.

[0034] The terrestrial base station 6 transmits the relayed information packets to the IoT application server 10 via the network 9. The IoT application server 10 performs processes such as data processing, analysis, and data cleansing based on the transmitted IoT information.

[0035] 7 is a flowchart showing processing of the wireless communication system according to the first embodiment of the present disclosure, which shows processing that is periodically performed in the wireless communication system 100 to calculate the transmission rate for each channel.

[0036] First, in step 100 (S100), the satellite IoT terminal 2 sends information on the transmittable channel list and the traffic volume to be transmitted. As described above, this information is transmitted to the system controller 8 via the satellite 4 and the terrestrial base station 6.

[0037] Next, in step 102 (S102), the system controller 8 classifies the satellite IoT terminals 2 into groups and calculates the transmission rate for each channel for each group. This group classification and calculation of the transmission rate are performed based on the information sent in S100.

[0038] Next, in step 104 (S104), the system controller 8 broadcasts the calculated transmission rate. This information is broadcast to the satellite IoT terminal 2 via the terrestrial base station 6 and the satellite 4, as described above.

[0039] Finally, in step 106 (S106), the satellite IoT terminal 2 performs channel selection and transmission traffic control based on the notified transmission rate for each channel.

[0040] Next, specific processing performed by the system controller 8 will be described. Fig. 8 is a diagram showing the arrangement of satellite IoT terminals according to the first embodiment of the present disclosure. The wireless communication system 100 includes 16 satellite IoT terminals 2. Here, the 16 terminals are referred to in order as satellite IoT terminals 2-1 to 2-16.

[0041] The wireless communication system 100 includes two terrestrial IoT service areas: terrestrial IoT service area 28 includes four satellite IoT terminals 2-1 to 2-4; and terrestrial IoT service area 30 includes four satellite IoT terminals 2-13 to 2-16.

[0042] Table 1 shows the transmittable channels for each satellite IoT terminal 2. Four channels, 1ch to 4ch, are available as wireless channels for IoT services. However, to prevent interference with IoT services that use the terrestrial network (NW), the satellite IoT terminal 2 does not use the channels used by the terrestrial network. Satellite IoT terminals in the terrestrial IoT service area 28 use channels 2, 3, and 4, while satellite IoT terminals in the terrestrial IoT service area 30 use channels 1, 3, and 4. Therefore, the transmittable channels for each satellite IoT terminal 2 are as shown in Table 1.

[0043] [Table 1]

[0044] The system controller 8 classifies the satellite IoT terminals 2 into groups based on the information from each satellite IoT terminal 2. Here, terminals that can only use channel 1 are group 1, terminals that can only use channel 2 are group 2, and terminals that can use all channels (channels 1, 2, 3, and 4) are group 3. Then, the transmittable channel information from each satellite IoT terminal 2 is classified into each group.

[0045] Next, the system controller 8 calculates the transmission rate for each channel. Here, the transmission rate for each group i on channel j is defined as p ij , the normalized traffic volume to be transmitted (generated traffic volume) in each group i is g i In this case, the system controller 8 determines p that maximizes the objective function of Equation 1. ij Calculate.

[0046]

number

[0047] However, p ij In calculating j, two constraints are set. The first constraint is that Equation 2 holds true for all j.

[0048]

number

[0049] However, in this case, it is assumed that the formula 3 holds.

[0050]

number

[0051] where f i g is defined as the degree of freedom in group i, i.e., the number of available slots. j C is defined as the degree of freedom in channel j. The right side of Equation 3 is the degree of freedom f j C This means a load that does not cause performance degradation.

[0052] 9 is a diagram illustrating the number of slots per unit time according to the first embodiment of the present disclosure. In the example illustrated in FIG. 9, there are four slots in a certain unit time. Here, group 1 can use 1ch, group 2 can use 2ch, and group 3 can use 1ch, 2ch, 3ch, and 4ch. Therefore, f1 g =4, f2 g =4, f3 g = 16. Next, in 1ch, group 1 and group 3 can be used, but the minimum value is 4, so f1 C = 4. By the same calculation, f2 C =4, f3 C =f4 C =16. Each f j C The right side of Equation 3 for is calculated based on Equation 4.

[0053]

number

[0054] 10 is a graph showing the calculation results of the maximum throughput according to the first embodiment of the present disclosure. The graph shows the calculation results of the maximum throughput with respect to the degree of freedom, i.e., the number of available slots. Each point on the graph represents the maximum throughput data with respect to the number of slots. The solid line on the graph is derived by approximating this data group, and Equation 4 is derived from this approximation result.

[0055] Next, the second constraint is shown. The second constraint is that Equation 5 holds true for all i.

[0056]

number

[0057] d minis the minimum value of the bias in the transmission rate that does not affect the degrees of freedom. Here, the ratio of the minimum transmission rate to the maximum transmission rate for each channel in each group is defined as the bias in the transmission rate. Note that this bias in the transmission rate may be defined differently.

[0058] 11 is a graph showing throughput characteristics with the number of slots as a parameter according to the first embodiment of the present disclosure. min This graph shows the throughput characteristics when d min If d is 0.02, the degradation of the throughput characteristics hardly occurs. min =0.02.

[0059] Based on the two constraints mentioned above, the p that maximizes Eq. ij Calculate.

[0060] When g1=0.5, g2=0.5, and g3=1, p is the value that maximizes Equation 1. ij The calculation result is as shown in Equation 6.

[0061]

number

[0062] Table 2 shows the calculation results of the left side of Equation 2 and the left side of Equation 4 for channel j as the first constraint. ij satisfies the constraints.

[0063] [Table 2]

[0064] Next, as the second constraint, the left and right sides of Equation 5 for each group i are shown in Table 3. In any group i, the calculated p ij satisfies the constraints.

[0065] [Table 3]

[0066] When g1=1, g2=1, and g3=2, p is the maximum value of Equation 1. ij The calculation result is as shown in Equation 7.

[0067]

number

[0068] As the first constraint, the calculation results of the left side of Equation 2 and the left side of Equation 4 for channel j are shown in Table 4. ij satisfies the constraints.

[0069] [Table 4]

[0070] Next, as the second constraint, the left and right sides of Equation 5 for each group i are shown in Table 5. In any group i, the calculated p ij satisfies the constraints.

[0071] [Table 5]

[0072] As described above, the system controller 8 calculates the transmission rate p ij Next, the system controller 8 calculates the calculated transmission rate p ij to the satellite IoT terminal 2. At this time, by broadcasting the channel information available to each group as a set, the satellite IoT terminal 2 that receives this information can recognize the group to which it belongs.

[0073] After receiving the above information, the satellite IoT terminal 2 selects a channel and controls the transmission traffic based on the corresponding transmission rate. For example, when g1=1, g2=1, and g3=2, the calculation result to be reported is as shown in Equation 8.

[0074]

number

[0075] For example, a satellite IoT terminal 2 belonging to group 1 selects only channel 1 and controls traffic transmission to 30%. This control ensures that transmission occurs with a 30% probability at each transmission timing. One example of this control is to generate a random number between 0 and 9 at each transmission timing, and transmit when a number between 0 and 2 is generated. Similarly, a satellite IoT terminal 2 belonging to group 3 controls channel selection so that channels 1 and 2 have a 15% probability, and channels 3 and 4 have a 35% probability. By performing the above processing, transmission control can be performed at each terminal to maximize throughput.

[0076] This disclosure enables channel selection and transmission traffic control based on the characteristics of the CRDSA+FH system in a communication system based on the CRDSA+FH system, thereby mitigating the impact of a decrease in communication capacity caused by an excess number of connected terminals and maximizing system capacity.

[0077] The functions of the system controller 8 of the present disclosure can also be realized by a computer and a program. This program can be recorded on a recording medium or provided via a network.

[0078] 12 is a graph showing the simulation results of throughput characteristics according to the first embodiment of the present disclosure. Here, the horizontal axis represents normalized traffic volume, and half of the transmitters are allowed to use half of the channels. The graph shows that throughput is improved when channel selection and transmission traffic control are performed.

[0079] The normalized traffic volume on the horizontal axis is the potential transmission traffic volume, which is the traffic volume scheduled to be transmitted at the terminal. Since transmission restrictions may exist, not all of this traffic is necessarily transmitted. [Explanation of symbols]

[0080] 1 satellite 2 Satellite IoT terminal 4 satellites 8 System Controller 12 time slots 14 packets 18 packets 22 packets 100 Wireless Communication System

Claims

1. A wireless communication system having a satellite IoT terminal unit and a system control unit, The satellite IoT terminal unit sends information about a transmittable channel list and a traffic volume to be transmitted to the system control unit; The system control unit A function of classifying the satellite IoT terminal units into groups based on the transmittable channel list; calculating a transmission rate for each channel of said group; a function of reporting the transmission rate in the group and each channel to the satellite IoT terminal unit; The satellite IoT terminal unit has a function of selecting a channel and controlling the amount of transmission traffic based on the transmission rate of each channel. A wireless communication system comprising:

2. The wireless communication system according to claim 1 , wherein the satellite IoT terminal unit randomly selects one or more time slots and transmits packets during the selected time slots.

3. The transmission rate is setting an upper limit on the amount of traffic transmitted on the channel, the upper limit being determined based on the degree of freedom of the channel; Setting a lower limit for the bias in transmission rates between channels The wireless communication system according to claim 1 or 2, wherein the calculation is performed using at least one of the above as a constraint condition.

4. The deviation of the transmission rate between the channels is the ratio of the maximum value to the minimum value of the transmission rate between the channels.

4. The wireless communication system according to claim 3.

5. A step in which the satellite IoT terminal unit sends information about the transmittable channel list and the traffic volume to be transmitted to the system control unit; The system control unit Classifying the satellite IoT terminals into groups based on the transmittable channel list; calculating a transmission rate for each channel of the group; notifying the satellite IoT terminal of the transmission rates in the group and each channel; the satellite IoT terminal unit selecting a channel and controlling the amount of transmission traffic based on the transmission rate of each channel; A wireless communication method comprising:

6. receiving information about a transmittable channel list and a traffic volume to be transmitted from the satellite IoT terminal; Classifying the satellite IoT terminals into groups based on the transmittable channel list; calculating a transmission rate for each channel of the group; The transmission rate in the group and each channel is notified to the satellite IoT terminal. Wireless communication control device.

7. A program that causes a computer to execute the functions of the wireless communication control device according to claim 6.

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