Wireless communication method and wireless communication system

Abstract

To improve a throughput without notifying a base station of a channel that can be used by a wireless terminal.SOLUTION: In a wireless communication system, a base station calculates a transmission load for each channel as a reception status based on a packet transmitted by each wireless terminal, and notifies each wireless terminal of the reception status. Each wireless terminal grasps a channel available to itself, calculates transmission control information for controlling transmission of the packet based on the notified reception status, determines a time slot and a traffic amount to be used based on the grasped channel and the calculated transmission control information, and transmits the packet based on the determined time slot and traffic amount.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a wireless communication method and a wireless communication system. [Background technology]

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

[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. Also, standards that use licensed bands include LTE-M and NB-IoT.

[0004] Additionally, satellite communication services using low-earth orbit satellites as wireless communication devices are attracting attention. In satellite communication services, multiple communication satellites are launched into orbits at altitudes of several hundred to 2,000 km, and wireless terminals on the ground can connect to these communication satellites to perform high-speed communications.

[0005] For example, Oneweb and SpaceX have launched a large number of communications satellites to start communications services, and IoT services that use low-orbit satellites in combination with these are being considered.

[0006] For example, IoT devices connect to low-earth orbit satellites and then connect to the Internet via those satellites. IoT services using low-earth orbit satellites are promising as a system for providing IoT services in remote areas such as mountainous regions where terrestrial networks are not developed, as well as in areas at sea or in the air where terrestrial network signals cannot reach. For example, Globalstar provides satellite IoT services using low-earth orbit satellites.

[0007] IoT devices using low-earth orbit satellites transmit packets to the satellites using multiple channels. These packets are then sent to an IoT application server via the satellites and a terrestrial base station. The IoT application server then processes the data, such as processing, analysis, and data cleansing, required for various IoT services.

[0008] IoT devices transmit packets to low-earth orbit satellites using wireless channels, and access methods such as TDMA and FDMA are used to allow multiple IoT devices to transmit packets using the same channel.

[0009] When using TDMA or FDMA access methods, for example, a control device on the system side controls the system and allocates resources such as time and frequency for transmitting packets to each IoT terminal.Also, an access method in which IoT terminals control the system autonomously is the CRDSA (Contention Resolution Diversity Slotted ALOHA) method, which is an extension of the Slotted ALOHA method.

[0010] Figure 1 shows an overview of the CRDSA method. In the CRDSA method, an IoT terminal acting as a transmitting station generates a duplicate packet of the packet to be transmitted, and transmits the original packet and the duplicate packet in different time slots of its choice. Because the receiving station knows the time slots of both packets, packet loss due to transmit diversity can be avoided.

[0011] Figure 2 shows packet collisions in the CRDSA method. For example, as shown in Figure 2, a transmitted packet may collide with a packet sent by another IoT device when its transmission timing overlaps, resulting in incorrect reception. However, if even one duplicate packet is successfully received, the receiving side can use that packet to perform interference cancellation processing, making it possible to receive all packets.

[0012] When multiple channels are available, it is possible to introduce FH (Frequency Hopping) as an extension of the CRDSA method, and transmit packets on any different channel time slot.

[0013] Figure 3 shows an overview of the CRDSA method incorporating FH. Figure 3 shows an example in which IoT terminal 1 generates and transmits three duplicate packets. In the CRDSA method incorporating FH, the use of multiple channels reduces the possibility of all transmitted packets colliding in the same slot between IoT terminals, thereby improving performance.

[0014] There is also an IRSA (Irregular-Repetition Slotted ALOHA) method that selects the number of packet copies in the CRDSA method probabilistically.

[0015] Fig. 4 shows the distribution of the number of packet duplications. As shown in Fig. 4, in the CRDSA method with FH, for example, when the maximum number of duplications is 4, the number of packet duplications is controlled to be 2 with a probability of 0.5102 and to be 4 with a probability of 0.4898.

[0016] In IoT services using low-orbit satellites, a single low-orbit satellite covers a vast area on the Earth's surface, so many IoT devices connect to the satellite. As the number of connected IoT devices increases, interference between the IoT devices causes communication problems and reduces the communication capacity of the communication system. In addition, each IoT device must transmit packets to the low-orbit satellite without interfering with the terrestrial network. For this reason, the channels available to IoT devices (hereafter referred to as available channels) vary.

[0017] In the CRDSA and IRSA methods that incorporate FH (hereafter referred to as "FH-introduced"), the communication capacity increases as the number of connected IoT devices increases up to a certain level, but once a certain value is reached, the communication capacity drops sharply. This is thought to be due to the fact that the probability of demodulation failure due to an increase in the packet collision rate exceeds the probability of successful demodulation due to transmit diversity, due to the huge number of transmitted packets resulting from multiple packet transmissions by many IoT devices.

[0018] One way to improve this problem is to appropriately control the channel to be used and the amount of traffic to be transmitted, rather than randomly setting the number of packets and transmission channel to be transmitted by the IoT terminal in the CRDSA / IRSA method (see, for example, Non-Patent Document 1).

[0019] Specifically, each IoT device transmits packets to a low-earth orbit satellite using an unoccupied frequency channel in the terrestrial service area where it is deployed. The base station divides the IoT devices into groups based on the available channels for each device, calculates the transmission rate for each channel for each group, and notifies all IoT devices of the calculated rate. Each IoT device probabilistically selects a channel to transmit on based on the notification, thereby effectively controlling traffic and preventing a decrease in throughput. [Prior art documents] [Non-patent literature]

[0020] [Non-Patent Document 1] Kansuke Kumazawa and 7 others, "Transmission Control of CRDSA / IRSA Method Considering Imbalance of Available Channels and Fairness among Terminals in Satellite IoT Systems," IEICE Technical Report, SAT2023-33, August 2023 Summary of the Invention [Problem to be solved by the invention]

[0021] However, the above control method requires that each IoT device notifies the base station of its available channels, and the base station knows the number of IoT devices and the available channels for each IoT device. In this case, the notification of available channels from the IoT device to the base station becomes an overhead, which can reduce system throughput.

[0022] An object of the present invention is to provide a wireless communication method and a wireless communication system that can improve throughput without requiring a wireless terminal to notify a base station of available channels. [Means for solving the problem]

[0023] A wireless communication method according to one aspect of the present invention is a wireless communication method in which a plurality of wireless terminals transmit packets to a base station using one or more time slots of one or more channels, wherein the base station executes a reception status calculation step of calculating the transmission load on each channel as a reception status based on the packets transmitted by each of the wireless terminals, and a reporting step of reporting the reception status to each of the wireless terminals, and each of the wireless terminals executes a channel identification step of identifying channels that it can use, a control information calculation step of calculating transmission control information for controlling the transmission of packets based on the reception status reported by the reporting step, a determination step of determining the time slot and traffic volume to be used based on the channel identified by the channel identification step and the transmission control information calculated by the control information calculation step, and a transmission step of transmitting packets using the time slot and traffic volume determined by the determination step.

[0024] Furthermore, a wireless communication system according to one aspect of the present invention is a wireless communication system in which a plurality of wireless terminals transmit packets to a base station using one or more time slots of one or more channels, wherein the base station has a reception status calculation unit that calculates the transmission load on each channel as a reception status based on the packets transmitted by each of the wireless terminals, and a notification unit that notifies each of the wireless terminals of the reception status, and each of the wireless terminals has a channel identification unit that identifies channels available to the wireless terminal, a control information calculation unit that calculates transmission control information for controlling packet transmission based on the reception status notified by the notification unit, a determination unit that determines the time slot to be used and the traffic volume based on the channel identified by the channel identification unit and the transmission control information calculated by the control information calculation unit, and a transmission unit that transmits packets using the time slot and traffic volume determined by the determination unit. [Effects of the Invention]

[0025] According to the present invention, throughput can be improved without the need for a wireless terminal to notify a base station of available channels. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram illustrating an overview of the CRDSA method. [Figure 2] FIG. 10 is a diagram illustrating a packet collision in the CRDSA system. [Figure 3] FIG. 1 is a diagram illustrating an overview of a CRDSA method incorporating FH. [Figure 4] FIG. 10 is a diagram illustrating the distribution of the number of packet duplications. [Figure 5] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. [Figure 6] 1 is a functional block diagram illustrating the functions of a wireless terminal, a relay station, and a base station that constitute a wireless communication system. [Figure 7] FIG. 10 is a diagram illustrating a specific configuration example of a reception situation calculation unit. [Figure 8]FIG. 2 is a diagram illustrating a specific example of the configuration of a control information calculation unit included in a wireless terminal. [Figure 9] 10 is a flowchart illustrating an example of the operation of the wireless communication system. [Figure 10] 10 is a flowchart illustrating an example of the operation of a reception condition calculation unit of a base station. [Figure 11] 10 is a flowchart illustrating an example of the operation of a control information calculation unit of a wireless terminal. [Figure 12] FIG. 1 is a diagram illustrating terms and symbols used to explain an example of the operation of a wireless communication system. [Figure 13] FIG. 1 is a diagram illustrating terms and symbols used to explain an example of the operation of a wireless communication system. [Figure 14] 10 is a graph showing the average estimation error characteristics of the estimated transmission load method. [Figure 15] FIG. 10 is a diagram showing an example of numerical values (threshold value table) for selecting a transmission load estimation method. [Figure 16] 10 is a graph showing a correction term based on a transmission failure slot rate. [Figure 17] FIG. 10 is a diagram showing a specific example of the number of channels and the transmission failure slot rate. [Figure 18] FIG. 10 is a diagram illustrating a situation in which a transmission probability update is performed. [Figure 19] 10 is a diagram showing symbols referring to numerical examples of update of the probability of reception. [Figure 20] 10A and 10B are diagrams illustrating packet transmission in a situation where a transmission probability is updated, and notification of an estimated transmission load and a transmission failure slot rate. [Figure 21] FIG. 10 is a diagram schematically illustrating an example of operation when there are 10 wireless terminals. [Figure 22] FIG. 1 is a diagram showing simulation parameters of a wireless communication system. [Figure 23] 10 is a graph showing an example of numerical values of a throughput characteristic evaluation with respect to a generated load. [Figure 24] 10 is a graph showing the time characteristics of the transmission load of channel 1. [Figure 25] 10 is a graph showing the time characteristics of the transmission load of channel 10. [Figure 26]10 is a flowchart illustrating another example of the operation of the wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0027] The configuration of a wireless communication system according to an embodiment will be described below with reference to the drawings. Fig. 5 is a diagram showing an example of the configuration of a wireless communication system 1a according to an embodiment. As shown in Fig. 5, the wireless communication system 1a includes, for example, a plurality of wireless terminals 2-1 to 2-n, a relay station 3, a base station 4, and a server 10, and the base station 4 and the server 10 are connected via a network 100. When it is not necessary to specify any one of the plurality of components, such as the wireless terminals 2-1 to 2-n, the component will be abbreviated as wireless terminal 2 or wireless terminal 2-n.

[0028] The wireless terminal 2 is a satellite IoT terminal located on the ground that performs wireless communication with a relay station 3, such as a low-earth orbit satellite, and transmits a packet containing IoT data to the relay station 3. This packet is transmitted to the server 10 via the relay station 3 and the base station 4.

[0029] The server 10 is an IoT application server that performs processes such as data processing, analysis, and data cleansing required for various IoT services (observation and sensing).

[0030] Wireless terminal 2 transmits packets to relay station 3 using a wireless channel. Because multiple wireless terminals 2 transmit using wireless channels, access methods such as TDMA or FDMA are used to prevent interference. TDMA and FDMA are controlled by the system, which allocates resources such as time and frequency for transmitting packets to each wireless terminal 2.

[0031] The wireless communication system 1a is a wireless communication system in which multiple wireless terminals 2 transmit packets to a base station 4 using one or more time slots of one or more channels. For example, even in an environment in which there is a bias in the channels available to the wireless terminals 2, the wireless communication system 1a uses a method of duplicating packets such as CRDSA / IRSA and transmitting the packets in any different channel / time slot. Thus, the wireless communication system 1a can improve throughput even if the wireless terminals 2 do not notify the base station 4 of the channels available to them.

[0032] FIG. 6 is a functional block diagram illustrating the functions of the wireless terminal 2, the relay station 3, and the base station 4 that make up the wireless communication system 1a.

[0033] Each of the wireless terminals 2-1 to 2-n includes a channel grasping unit 20, a control information calculating unit 22, a determining unit 24, and a transmitting unit .

[0034] The channel ascertaining unit 20 ascertains channels that can be used by the wireless terminal 2 itself (available channels) through carrier sensing, and outputs information indicating the ascertained available channels to the control information calculating unit 22.

[0035] The control information calculation unit 22 calculates transmission control information for controlling packet transmission based on the reception status (including the estimated transmission load and transmission failure slot rate) reported by the reporting unit 44 of the base station 4, which will be described later, and outputs the calculation result together with information indicating available channels to the decision unit 24. The transmission control information includes the target transmission load and transmission probability for each channel of the terminal itself. The transmission probability is defined as the probability that the wireless terminal 2 selects a channel to use.

[0036] The determination unit 24 determines the time slot and traffic volume (transmission control information) to be used based on the channel determined by the channel determination unit 20 and the transmission control information calculated by the control information calculation unit 22, and outputs the determined transmission control information to the transmission unit 26. In other words, the determination unit 24 functions as a transmission control unit that performs slot selection and traffic control using the transmission load and transmission probability.

[0037] The transmitting unit 26 transmits the data packet to the relay station 3 according to the time slot and traffic volume determined by the determining unit 24.

[0038] The relay station 3 includes a relay unit 30, and relays between the wireless terminals 2-1 to 2-n and the base station 4. Specifically, as will be described later, the relay unit 30 receives packets transmitted by the wireless terminals 2-1 to 2-n and transmits them to the base station 4, and transmits reception status information transmitted by the base station 4 to the wireless terminals 2-1 to 2-n.

[0039] The base station 4 has a demodulation unit 40, a reception situation calculation unit 42, and a reporting unit 44. The demodulation unit 40 demodulates packets transmitted by the wireless terminals 2-1 to 2-n via the relay station 3, and outputs the packets to the reception situation calculation unit 42 and the like.

[0040] The reception status calculation unit 42 calculates the transmission load on each channel as the reception status based on packets transmitted by the wireless terminals 2-1 to 2-n, and outputs the calculated reception status to the notification unit 44. Here, the reception status is information necessary for the wireless terminal 2 to perform transmission control, and includes, for example, an estimated value of the transmission load and a transmission failure slot rate, which will be described later.

[0041] The reporting unit 44 reports the reception conditions calculated by the reception condition calculation unit 42 to the wireless terminals 2-1 to 2-n.

[0042] Fig. 7 is a diagram showing a specific example of the configuration of the reception status calculation unit 42. As shown in Fig. 7, the reception status calculation unit 42 has a threshold reference unit 420, a packet measurement unit 422, a method selection unit 424, and a second estimation unit 426, and calculates the reception status including the transmission failure slot rate and the average number of packets, which will be described later, and outputs the results to the notification unit 44.

[0043] The threshold reference unit 420 has a table of thresholds that minimize the average error for each estimation method when using each piece of information calculated by the packet measurement unit 422. This table is created based on prior measurements such as simulations and actual measurements.

[0044] The packet measurement unit 422 includes a first estimation unit 428, measures the demodulated packet data demodulated by the demodulation unit 40, calculates the throughput, idle slot rate, clean slot rate, and transmission failure slot rate, and outputs them to the method selection unit 424 and the second estimation unit 426.

[0045] Here, throughput is defined as the average number of packets successfully transmitted per slot, the idle slot rate as the rate at which no packets are transmitted in a slot, the clean slot rate as the rate at which only one packet is transmitted in a slot, and the transmission failure slot rate as the rate at which a packet fails to be transmitted among all slots.

[0046] More specifically, the first estimation unit 428 estimates a transmission failure slot rate, which indicates the ratio of the number of time slots in which packets that have failed to be transmitted exist to the number of time slots for each channel, based on the packets transmitted by each wireless terminal 2.

[0047] The method selection unit 424 selects from among multiple transmission load estimation methods a transmission load estimation method that minimizes the average error between the generated load and the ideal transmission load calculated from the transmission probability for each channel, using a threshold referenced from the threshold reference unit 420, and outputs the selected method to the second estimation unit 426.

[0048] The second estimation unit 426 estimates the average number of packets (transmission load: average number of packets transmitted per slot) indicating the average number of packets transmitted per time slot based on the transmission failure slot rate. The second estimation unit 426 has a function as a transmission load estimation unit that sets the estimated transmission load as the estimated transmission load. The second estimation unit 426 also has a function of estimating the average number of packets using one of a plurality of different methods based on one or more predetermined thresholds.

[0049] Fig. 8 is a diagram showing a specific example configuration of the control information calculation unit 22 included in the wireless terminal 2. As shown in Fig. 8, the control information calculation unit 22 includes a storage unit 220, a target update unit 222, and a transmission probability update unit 224, and calculates transmission control information that controls packets transmitted by the wireless terminal 2.

[0050] The storage unit 220 stores a transmission probability indicating the probability of successful packet transmission in the past (previous) for updating the transmission probability.

[0051] When the transmission failure slot rate transmitted from the base station 4 changes by more than a predetermined value, the target update unit 222 updates the target value (target transmission load) of the transmission load applied to each channel of the terminal using an estimation formula using the estimated transmission load.

[0052] The transmission probability update unit 224 updates the transmission probability stored in the storage unit 220 based on the average number of packets, the target value updated by the target update unit 222, the estimated transmission load notified by the base station 4, and the transmission probability stored in the storage unit 220. For example, the transmission probability update unit 224 has a function of smoothing and updating the transmission probability so that it becomes the target transmission load of the terminal itself for each channel.

[0053] Next, an operation example of the wireless communication system 1a will be described with reference to Figures 9 to 11. Figure 9 is a flowchart showing an operation example of the wireless communication system 1a. Figure 10 is a flowchart showing an operation example of the reception condition calculation unit 42 of the base station 4. Figure 11 is a flowchart showing an operation example of the control information calculation unit 22 of the wireless terminal 2. Note that for terms and symbols used to explain the operation example of the wireless communication system 1a, refer to Figures 12, 13, etc.

[0054] To calculate the estimated transmission load and transmission failure slot rate for channel j, which are necessary for calculating the transmission probability on the wireless terminal 2 side, the channel grasping unit 20 of wireless terminal 2 first observes the demodulated packets and calculates the throughput, idle slot rate, clean slot rate, and transmission failure slot rate.The average number of packet replications in CRDSA / IRSA is known information given at the time of system design.

[0055] Next, the estimated transmission load is calculated based on the information observed from the packets. To calculate the estimated transmission load, the estimation method that minimizes the average estimation error between the generated load and the ideal transmission load calculated from the transmission probability is selected from among the methods based on throughput shown in equations (1) and (2) below, the method based on the idle slot rate shown in equation (3) below, and the method based on the clean slot rate shown in equation (4) below.

[0056]

number

number

number

number

[0057] Here, W in the above formula (4) -1 is the lower branch of Lambert's W function and is the inverse function of f(x)=xexp(-x).

[0058] FIG. 14 is a graph showing the average estimation error characteristics of the estimation transmission load method, and shows an example of the average estimation error characteristics with respect to the transmission load when the estimated transmission load is calculated using the throughput, the idle slot rate, and the clean slot rate.

[0059] As shown in Figure 14, the estimation error differs for each method of calculating the estimated transmission load, and the characteristics reverse starting from a certain transmission load, with each method having different areas of expertise. The method based on the throughput in equation (1) above has small errors in areas with few transmission failures, the method based on the idle slot rate in equation (3) above has small errors in areas with relatively small transmission loads, and the method based on the clean slot rate in equation (4) above has small errors in areas with relatively large transmission loads. Therefore, a threshold is used to select these areas of expertise and switch between estimation methods.

[0060] The information used to switch the estimation method (hereinafter referred to as trigger information) is "transmission failure slot rate," "throughput," "idle slot rate," and "clean slot rate." For these pieces of information, a full search is performed using prior simulations to find the value that minimizes the average estimation error, and the minimum value is set as the threshold, and a table corresponding to each piece of information is created.

[0061] Figure 15 shows a numerical example (threshold table) of the selection of the transmission load estimation method. The settings are IRSA for the random access method, 4 for the maximum number of copies, and no transmission control. The number of channels is 10, and the number of self-divisions is 100. This is an example of selecting two methods: a method based on throughput in the low load region, and a method based on the clean slot rate in the high load region.

[0062] The threshold table is composed of the threshold of each trigger information and the average estimation error (for all transmission load regions). In this numerical example, when the transmission failure slot rate is used as the threshold, the average estimation error is smallest, so this information is adopted as the threshold. If the transmission failure slot rate is less than 0.255, the estimated transmission load calculation method based on the throughput is used, and if the transmission failure slot rate is more than 0.255, the transmission load estimation calculation method based on the clean slot rate is used. The transmission failure slot rate and estimated transmission load obtained in this way are reported from the reporting unit 44 of the base station 4 to the wireless terminals 2-1 to 2-n via the relay station 3.

[0063] Each wireless terminal 2 receives the transmission failure slot rate and estimated transmission load notified from the base station 4. Furthermore, each wireless terminal 2 grasps the channels that can be used by the terminal itself through carrier sense.

[0064] Next, each wireless terminal 2 calculates the target transmission load of its own terminal by the following equation (5) using the transmission failure slot rate notified by the base station 4 in the channel j that the terminal can use.

[0065]

number

[0066] Here, the first term in the above equation (5) is the transmission load that results in the maximum throughput when the number of available slots is slot, and is known information. The second term in the above equation (5) is a correction term to take into account the transmission load of other terminals, and is expressed by the following equation (6).

[0067]

number

[0068] where S maxis the maximum number of slots possible in the system and is known information. In addition, the following equation (7) is defined as the relation between the transmission failure slot rate, the optimal transmission load for the maximum number of slots, and the difference in transmission load for each channel. In addition, the above equation (6) includes a term for adjusting the degree of freedom of the own terminal.

[0069]

number

[0070] FIG. 16 is a graph showing the correction term according to the transmission failure slot rate, corresponding to the above equation (7). FIG. 17 is a diagram showing a specific example of the number of channels and the transmission failure slot rate. The points shown in FIG. 16 are plots of values obtained by simulation, and the solid line is derived by approximation from the simulation data. By using this approximation equation, wireless terminal 2 can easily estimate the transmission load status of other terminals from the transmission failure slot rate and make corrections to the transmission load of its own terminal.

[0071] Next, the wireless terminal 2 updates its own transmission probability using the transmission load, the estimated transmission load notified by the base station 4, and the past transmission probability according to the following equation (8).

[0072]

number

[0073] Furthermore, when updating the transmission probability, the wireless terminal 2 may apply exponential smoothing to the transmission probability as in the following equation (9).

[0074]

number

[0075] When smoothing is used, the wireless terminal 2 controls the degree of smoothing using a smoothing parameter α. This value is set arbitrarily on the system side. To prevent the influence of the initial value, smoothing is not used only for the first transmission probability update.

[0076] Fig. 18 is a diagram showing a schematic diagram of a situation where a transmission probability is updated. Fig. 19 is a diagram showing symbols used to refer to numerical examples of transmission probability updates. Fig. 20 is a diagram showing an example of packet transmission when a transmission probability is updated, and reporting of an estimated transmission load and a transmission failure slot rate. The generated load is the average number of packets generated per slot.

[0077] Here, we show the case of group 1 of wireless terminals 2 that can use two channels and group 2 of wireless terminals 2 that can use only one channel. At the start of communication, wireless terminal 2 uses the initial value of the transmission probability to transmit a packet to base station 4. At this time, p (t) The rows of represent groups and the columns represent channels, so group 1 has half the chance of sending packets to each channel.

[0078] Next, base station 4 calculates the estimated transmission load and transmission failure slot rate from the demodulated packets. In transmission control using the initial values, many packets are transmitted to channel 1, so the transmission failure slot rate for channel 1 becomes large.

[0079] In order to update the transmission control information, the base station 4 notifies the wireless terminal 2 of the estimated transmission load and the transmission failure slot rate. The wireless terminal 2 updates the information using the estimated transmission load and the transmission failure slot rate, and transmits packets.

[0080] By repeating these processes, the terminal's transmission load and transmission probability are updated. Finally, it can be confirmed that the terminal's transmission load for channel j of group i matches the optimal transmission load. In addition, the transmission failure slot rate at the base station is also 0, which shows that the transmission load and transmission probability have been updated.

[0081] Next, a description will be given of a numerical example based on a simulation in which there are ten wireless terminals 2. Fig. 21 is a diagram schematically showing an example of operation in which there are ten wireless terminals 2. Fig. 22 is a diagram showing simulation specifications of the wireless communication system 1a.

[0082] As shown in Fig. 21, a maximum of 10 channels are available, and if there are 10 wireless terminals 2, the wireless terminals 2 are divided into, for example, groups 1 to 6. Groups 1 to 5 can only use channels 1 to 5, respectively. Group 6 can use all channels.

[0083] Assume that the same number of terminals belong to each of groups 1 to 5, and that the generated load gi is also equal. As the bias in available channels, the ratio of the sum of the generated load gi of groups 1 to 5, which can use only one channel, to the generated load of group 6, which can use all channels, is used as a parameter, and the ratio of this bias is defined as β, as shown in equation (10) below.

[0084]

number

[0085] Figure 23 is a graph showing a numerical example of throughput characteristics evaluation against the generated load. When transmission control is not used, the throughput decreases as the generated load increases. When transmission control is used, high throughput is maintained even when the generated load increases.

[0086] Fig. 24 is a graph showing the time characteristics of the transmission load of channel 1. Fig. 25 is a graph showing the time characteristics of the transmission load of channel 10. In wireless communication system 1a, when smoothing is not used, time fluctuations in the transmission load can be confirmed, but by using smoothing, the level of fluctuations is reduced and it can be confirmed that the transmission load is stable. Furthermore, when the generated load is changed from 1 to 1.25 around time 300, even if a fluctuation in the generated load occurs, it is possible to update the transmission load to follow the fluctuation.

[0087] As described above, the wireless communication system 1a starts wireless communication from the base station 4, but as shown in Figure 26, communication may be started from the wireless terminal 2, or wireless communication may be performed between the wireless terminal 2 and the base station 4 without going through the relay station 3.

[0088] In this way, the wireless communication system 1a uses the reception conditions reported by the base station 4 to determine the time slots and traffic volume that the wireless terminal 2 itself will use, thereby improving throughput without the need for the wireless terminal 2 to notify the base station 4 of the channels that it can use.

[0089] In addition, each function possessed by the wireless terminals 2-1 to 2-n, the relay station 3, and the base station 4 may be partially or entirely configured by hardware such as a PLD (Programmable Logic Device) or an FPGA (Field Programmable Gate Array), or may be configured as a program executed by a processor such as a CPU.

[0090] For example, the wireless terminals 2-1 to 2-n, the relay station 3, and the base station 4 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0091] Although the embodiments of the present invention have been described above with reference to the drawings, it is clear that the above-described embodiments are merely examples of the present invention and that the present invention is not limited to the above-described embodiments. Therefore, addition, omission, substitution, and other modifications of components may be made without departing from the technical spirit and scope of the present invention. [Explanation of symbols]

[0092] 1a wireless communication system, 2-1 to 2-n wireless terminal, 3 relay station, 4 base station, 10 server, 20 channel grasping unit, 22 control information calculation unit, 24 decision unit, 26 transmitter, 30 relay unit, 40 demodulation unit, 42 reception status calculation unit, 44 broadcast unit, 220 storage unit, 222 target update unit, 224 transmission probability update unit, 420 threshold reference unit, 422 packet measurement unit, 424 method selection unit, 426 second estimation unit, 428 first estimation unit

Claims

1. 1. A wireless communication method in which a plurality of wireless terminals transmit packets to a base station using one or more time slots of one or more channels, comprising: The base station a reception status calculation step of calculating a transmission load on each channel as a reception status based on packets transmitted by each of the wireless terminals; a reporting step of reporting the reception status to each of the wireless terminals; Run Each of the wireless terminals a channel identification step of identifying channels available to the device itself; a control information calculation step of calculating transmission control information for controlling packet transmission based on the reception status notified by the notifying step; a determining step of determining a time slot and a traffic volume to be used based on the channel determined in the channel determining step and the transmission control information calculated in the control information calculating step; a transmitting step of transmitting a packet according to the time slot and traffic volume determined in the determining step; A wireless communication method comprising:

2. The receiving condition calculation step includes: a first estimation step of estimating a transmission failure slot rate indicating a ratio of the number of time slots in which a packet fails to be transmitted to the number of time slots in each channel based on packets transmitted by each of the wireless terminals; a second estimation step of estimating an average number of packets indicating an average number of packets transmitted per time slot based on the transmission failure slot rate; calculating the reception status including the transmission failure slot rate and the average number of packets, The control information calculation step includes: a target updating step of updating a target value of a transmission load applied to each channel when the transmission failure slot rate has changed by a predetermined value or more; a transmission probability updating step of updating the transmission probability stored in the storage unit based on the average number of packets, the target value updated in the target updating step, and a transmission probability stored in the storage unit that indicates the probability of successful past packet transmission; calculating the transmission control information, 2. The wireless communication method according to claim 1, wherein:

3. In the second estimation step, estimating the average number of packets using any of a number of different techniques based on one or more predetermined thresholds; 3. The wireless communication method according to claim 2, wherein:

4. In the transmission probability updating step, Smoothing and updating transmission probabilities 3. The wireless communication method according to claim 2, wherein:

5. In a wireless communication system in which a plurality of wireless terminals transmit packets to a base station using one or more time slots of one or more channels, The base station a reception status calculation unit that calculates a transmission load on each channel as a reception status based on packets transmitted by each of the wireless terminals; a notification unit that notifies each of the wireless terminals of the reception status; and Each of the wireless terminals a channel grasping unit that grasps channels that can be used by the device itself; a control information calculation unit that calculates transmission control information for controlling packet transmission based on the reception status notified by the notifying unit; a determination unit that determines a time slot and a traffic volume to be used based on the channel recognized by the channel recognition unit and the transmission control information calculated by the control information calculation unit; a transmitting unit that transmits packets according to the time slot and traffic volume determined by the determining unit; A wireless communication system comprising:

6. The reception condition calculation unit a first estimation unit that estimates a transmission failure slot rate indicating a ratio of the number of time slots in which a packet fails to be transmitted to the number of time slots in each channel based on packets transmitted by each of the wireless terminals; a second estimation unit that estimates an average number of packets indicating an average number of packets transmitted per time slot based on the transmission failure slot rate; calculating the reception status including the transmission failure slot rate and the average number of packets; The control information calculation unit a storage unit that stores a transmission probability indicating the probability of successful packet transmission in the past; a target update unit that updates a target value of a transmission load applied to each channel when the transmission failure slot rate changes by a predetermined value or more; a transmission probability update unit that updates the transmission probability stored in the storage unit based on the average number of packets, the target value updated by the target update unit, and the transmission probability stored in the storage unit; and calculating the transmission control information.

6. The wireless communication system according to claim 5,

7. The second estimation unit estimating the average number of packets using any of a number of different techniques based on one or more predetermined thresholds; 7. The wireless communication system according to claim 6, wherein:

8. The transmission probability update unit Smoothing and updating transmission probabilities 7. The wireless communication system according to claim 6, wherein:

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