JP7616357B2 - Wireless communication system, wireless communication method, and communication path determination device - Google Patents

Description

The present invention relates to a wireless communication system, a wireless communication method, and a communication path determination device.

To build mobile networks, technologies that use geostationary satellites, medium earth orbit satellites (MEO: Medium Earth Orbit), low earth orbit satellites (LEO: Low Earth Orbit), high altitude pseudo satellites (HAPS: High Altitude Platform Station), airplanes, drones, etc. are known.

For example, low-earth-orbit satellite networks are closer to the ground than geostationary satellites, so they have smaller propagation delays and require less power for transmission and reception. Low-earth-orbit satellites can also calculate their position from their orbits.

However, even though low-earth orbit satellite networks cover the entire globe, due to uneven distribution of network users, traffic can sometimes be concentrated at satellite relay stations (hereinafter referred to as node stations) that cover specific regions.

For example, non-patent document 1 discloses a traffic control method that uses congestion prediction to distribute the load in order to suppress congestion caused by bias in traffic distribution.

Daigo Kudo and 2 others, "Traffic Control Using Congestion Prediction in LEO Satellite IP Networks," IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, May 2008, pp.19-24

For example, if a link between a ground station or ground terminal station and a node station is cut off, the node station needs to temporarily hold (hereinafter referred to as buffer) the traffic until the link is next established.

However, in the past, traffic control did not take into account delays caused by buffering, which could result in a decrease in the throughput of the entire system. In other words, in low-earth orbit satellite networks, for example, it is sometimes necessary to implement controls to improve throughput depending on the state of the link, traffic, etc.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a wireless communication system, a wireless communication method, and a communication path determination device that enable efficient wireless communication via moving node stations.

In one embodiment of the present invention, a wireless communication system transmits data to be transmitted from a transmitting device to a receiving device wirelessly over a communication path via a plurality of node stations, at least one of which moves. The wireless communication system includes an information calculation unit that calculates location information indicating the location of each of the node stations and load information indicating the load due to traffic of each of the node stations, a first calculation unit that calculates, based on the location information calculated by the information calculation unit, a propagation time of the link from the transmitting device to the node station, a propagation time of each of the links between the node stations, a buffering time in which each of the node stations should hold data until the link is established, and a propagation time of the link from the node station to the receiving device, based on the load information calculated by the information calculation unit, a second calculation unit that calculates a queuing time of each of the node stations based on the load information calculated by the information calculation unit, a delay time calculation unit that calculates the sum of delay times occurring in data transmission for each of the paths from the transmitting device to the receiving device based on each of the times calculated by the first calculation unit and each of the times calculated by the second calculation unit, and a determination unit that determines the path that minimizes the sum of delay times calculated by the delay time calculation unit as the communication path.

In addition, a wireless communication method according to one embodiment of the present invention is a wireless communication method for wirelessly transmitting data to be transmitted from a transmitting device to a receiving device over a communication path via a plurality of node stations, at least one of which moves, the method comprising the steps of: an information calculation step of calculating location information indicating the location of each of the node stations and load information indicating the load due to traffic of each of the node stations; a first calculation step of calculating, based on the calculated location information, a propagation time of the link from the transmitting device to the node station, a propagation time of each of the links between the node stations, a buffering time in which each of the node stations should hold data until the link is established, and a propagation time of the link from the node station to the receiving device; a second calculation step of calculating, based on the calculated load information, a queuing time of each of the node stations; a delay time calculation step of calculating, based on each of the times calculated by the first calculation step and each of the times calculated by the second calculation step, a sum of delay times occurring in data transmission for each of the paths from the transmitting device to the receiving device; and a determination step of determining, as the communication path, a path that minimizes the sum of the calculated delay times.

In addition, a communication path determination device according to one embodiment of the present invention is a communication path determination device that determines a communication path for wirelessly transmitting data to be transmitted from a transmitting device to a receiving device via a plurality of node stations, at least one of which moves, and is characterized by having an information calculation unit that calculates location information indicating the location of each of the node stations and load information indicating the load due to traffic of each of the node stations, a first calculation unit that calculates, based on the location information calculated by the information calculation unit, the propagation time of the link from the transmitting device to the node station, the propagation time of each of the links between the node stations, the buffering time in which each of the node stations should hold data until the link is established, and the propagation time of the link from the node station to the receiving device, a second calculation unit that calculates the queuing time of each of the node stations based on the load information calculated by the information calculation unit, a delay time calculation unit that calculates the sum of delay times occurring in data transmission for each of the paths from the transmitting device to the receiving device based on each of the times calculated by the first calculation unit and each of the times calculated by the second calculation unit, and a determination unit that determines the path for which the sum of the delay times calculated by the delay time calculation unit is the smallest as the communication path.

The present invention makes it possible to efficiently carry out wireless communication via moving node stations.

FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system as a comparative example. FIG. 10 is a diagram illustrating an example of an operation of a wireless communication system as a comparative example. 1 is a diagram illustrating a configuration and a first operation of a wireless communication system according to an embodiment; FIG. 2 is a diagram illustrating an example of a configuration of a ground station according to an embodiment. 4 is a functional block diagram illustrating functions of a communication path calculation unit. FIG. 1 is a diagram illustrating a configuration and a second operation of a wireless communication system according to an embodiment; 11 is a flowchart illustrating a process performed by a communication path calculation unit when the wireless communication system according to an embodiment performs a second operation. 11 is a diagram illustrating a configuration and a third operation of a wireless communication system according to an embodiment. FIG.

First, the background to the invention will be described in more detail. Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 1. As shown in Fig. 1, the wireless communication system 1 is configured such that each terminal station (terrestrial terminal station) 10 is connected to a terrestrial station (satellite terrestrial station) 3 using, for example, one of the communication paths via a plurality of node stations 2.

The terminal station 10 and the ground station 3 each have a function as a transmitting device and a function as a receiving device, and perform two-way wireless communication. The terminal station 10 may perform wireless communication with other terminal stations 10 using any of the communication paths via multiple node stations 2. Each node station 2 is a mobile relay station such as a low-earth orbit satellite (mobile satellite) or a geostationary satellite. Each wireless link in the wireless communication system 1 includes a communication line and a control line.

If the node station 2 is a low-orbit satellite, it moves in the sky at an altitude of, for example, 2000 km or less above the Earth's surface. If the node station 2 is a geostationary satellite, it moves in a geostationary orbit at an altitude of about 36000 km above the Earth's surface, revolving around the Earth with the same period as the Earth's rotation period.

The node station 2 may also be a medium-earth orbit satellite, a high-altitude pseudo satellite, or another mobile relay station such as an airplane. Each connection (link) in the wireless communication system 1 may be realized by wireless communication using radio waves, or by other wireless communication such as optical communication.

Figure 2 is a diagram showing an example of the configuration of a wireless communication system as a comparative example. As shown in Figure 2, a terminal station 10 performs wireless communication with a ground station 3 via multiple node stations 2 (any of node stations 2-1 to 2-8). Here, the terminal station 10 is assumed to be a transmitting device, and to transmit data to the ground station 3, which is a receiving device.

In the wireless communication system shown in Figure 2, the terminal station 10 transmits data to the ground station 3 via the communication path that minimizes the total delay time T, as outlined in equation (1) below.

T=T _L ×N _L +T _q ×N _S +T _E ...(1)

however,
T _L : Propagation time of the link between the node stations 2. T _E : Propagation time of the link between the node station 2 and the terminal station 10 or the earth station 3. T _q : Queuing time of the node station 2. N _L : Total number of links between the node stations 2 included in the route. N _S : Total number of node stations 2 included in the route.

In the wireless communication system shown in Figure 2, the shortest route is route A, indicated by the thick dashed arrow. However, for example, if traffic is concentrated on node station 2-2 and node station 2-3, causing congestion, the wireless communication system will use route B as the communication route, rather than the shortest route A based on equation (1) above. In this way, congestion can be avoided by using as the communication route a detour route with the smallest total delay time T that does not pass through node station 2-2 and node station 2-3, which have queuing times equal to or greater than a threshold.

However, in an actual wireless communication system, when the service is first introduced or for cost reasons or other reasons, it is conceivable that the node stations 2 are not densely arranged and there are no node stations 2 with which the ground station 3 or terminal station 10 can communicate.

For example, as shown in Figure 3, if the link between node station 2-4 and ground station 3 is severed and communication becomes impossible, regardless of whether the communication path is the shortest path A or the detour path B, node station 2-4 needs to temporarily hold (buffer) the traffic until communication with ground station 3 becomes possible.

In this case, conventional technology is unable to perform control that takes into account the delay time caused by buffering, which reduces the throughput of the entire wireless communication system.

Therefore, the wireless communication system of the embodiment is configured to enable efficient wireless communication even when the link between the moving node station and the receiving device is disconnected.

Next, an example of the configuration of a wireless communication system according to an embodiment will be described. In the wireless communication system according to the embodiment, the configuration that is substantially the same as the configuration described above is denoted by the same reference numerals.

Figure 4 is a diagram illustrating a configuration and a first operation of a wireless communication system 1 according to one embodiment. As shown in Figure 4, in the wireless communication system 1, the terminal station 10 transmits data to the ground station 3a via a communication path using, for example, any one or more of the node stations 2-1 to 2-7.

In other words, the wireless communication system 1 wirelessly transmits data from the terminal station 10, which acts as a transmitting device, to the ground station 3a, which acts as a receiving device, via a communication path that passes through multiple node stations 2-1 to 2-7, at least one of which moves. The same applies when the ground station 3a acts as the transmitting device and the terminal station 10 acts as the receiving device. Note that when there is no need to specify which of the multiple configurations, such as the node stations 2-1 to 2-7, it will simply be abbreviated as node station 2, etc.

Here, node stations 2-1 to 2-6 are assumed to be low-earth orbit satellites. Node station 2-7 is assumed to be a geostationary satellite and an absolute node station that can always communicate with ground station 3a. In wireless communication system 1, terminal station 10 transmits data to ground station 3a via a communication path that minimizes the total delay time T as outlined in equation (2) below.

T=T _L ×N _L +T _q ×N _S +T _E +T _b ...(2)

however,
T _L : Propagation time of the link between the node stations 2 T _E : Propagation time of the link between the node station 2 and the terminal station 10 or the earth station 3a T _q : Queuing time of the node station 2 T _b : Buffering time of the node station 2 N _L : Total number of links between the node stations 2 included in the route N _S : Total number of node stations 2 included in the route

The node stations 2-1 to 2-6 are able to calculate their respective positions based on their respective orbital information. Here, the buffering time of the node station 2 is defined as the time required for a node station 2 that has lost communication with the terminal station 10 or the ground station 3a to move and then be able to communicate again. If buffering is not required, the buffering time is 0.

The calculation of the communication path using the above formula (2) may be performed individually by any of the terminal station 10, the node station 2, or the ground station 3a. The wireless communication system 1 may also be configured such that, for example, one communication path determination device (not shown) calculates the communication path using the above formula (2) and shares the calculation result with other devices.

Here, for example, the ground station 3a calculates the communication path using the above formula (2) (described in detail using Figures 4 and 5), and each device constituting the wireless communication system 1 shares the calculation results of the communication path to realize communication between the terminal station 10 and the ground station 3a.

For example, when a link is established between node station 2-3 and earth station 3a, no buffering is required at node station 2. Therefore, the total delay time T is likely to be smallest for route X1, which passes only through node stations 2-1 to 2-3, which are low-earth orbit satellites.

On the other hand, if the link between node station 2-3 and earth station 3a is cut off and communication is not possible, there will be no low-earth orbit satellites that can communicate with earth station 3a. In this case, buffering will be required for any route that passes through only low-earth orbit satellites. Therefore, the total delay time T is likely to be smallest for route Y1 that passes through node station 2-7, a geostationary satellite that does not require buffering.

In addition, although the link between node station 2-3 and ground station 3a is currently disconnected and communication is not possible, it is expected that the link between node station 2-3 and ground station 3a will be established after a short time has passed due to the movement of node station 2-3, etc. In this case, the total delay time T may be smaller for path X1 that requires buffering than for path Y1 that does not require buffering.

Next, a specific configuration example of the ground station 3a will be described. Figure 5 is a diagram showing a configuration example of the ground station 3a according to one embodiment. Note that the terminal station 10 and the like may also be configured as shown in Figure 5.

As shown in FIG. 5, the ground station 3a has, for example, an antenna 30, an RF (Radio Frequency) unit 32, a modem unit 34, a database (DB) 36, and a communication path calculation unit 4.

The antenna 30 transmits and receives signals such as network information (NW information) and data (traffic) by radio waves for wireless communication in the wireless communication system 1. The antenna 30 outputs the received signal to the RF unit 32, and transmits signals such as data input from the RF unit 32 by radio waves. The antenna 30 may be a single high-performance antenna, or may be composed of multiple antennas.

The RF unit 32 converts the signal input from the antenna 30 into a baseband signal and outputs it to the modem unit 34. The RF unit 32 also converts the signal input from the modem unit 34 into a radio frequency signal and outputs it to the antenna 30.

The modem unit 34 demodulates and processes the signal input from the RF unit 32, and outputs it to the database 36. The modem unit 34 also processes and modulates information including the signal input from the communication path calculation unit 4 (the communication path calculation result), and outputs it to the RF unit 32.

The database 36 stores the signal (information) input from the modem unit 34 and outputs a signal in response to access from, for example, the communication path calculation unit 4. The database 36 may be located on a network connected to the wireless communication system 1.

The signals (information) stored in database 36 include various parameters necessary to calculate the sum T of the delay times described above, data that is the main part of the traffic, etc. For example, the various parameters stored in database 36 include information exchanged by each device in wireless communication system 1 to calculate location information indicating the location of each node station 2, and load information indicating the load due to the traffic of each node station 2.

The communication path calculation unit 4 uses information stored in the database 36 to calculate the sum T of the delay times of multiple paths from a transmitting device, such as the terminal station 10, to a receiving device, such as the ground station 3a. The communication path calculation unit 4 then determines the optimal communication path from among the multiple calculated paths, as described below, and outputs a signal and data indicating the determined communication path to the modem unit 34.

The communication path calculation unit 4 is not limited to being provided in the ground station 3a, but may be provided in the terminal station 10, the node station 2, or may be configured by multiple devices. The communication path calculation unit 4 may be configured as a stand-alone communication path determination device installed on a network connected to the wireless communication system 1. The ground station 3a may also be the communication path determination device.

Next, specific examples of functions possessed by the communication path calculation unit 4 will be described. FIG. 6 is a functional block diagram illustrating functions possessed by the communication path calculation unit 4. As shown in FIG. 6, the communication path calculation unit 4 has, for example, an information calculation unit 40, a first calculation unit 41, a second calculation unit 42, a delay time calculation unit 43, a judgment unit 44, and a decision unit 45.

The information calculation unit 40 reads out various parameters stored in the database 36, calculates location information indicating the location of each node station 2, and outputs the calculated location information to the first calculation unit 41. The information calculation unit 40 also reads out various parameters and data stored in the database 36, calculates load information indicating the load due to traffic of each node station 2, and outputs the calculated load information to the second calculation unit 42.

Based on the position information calculated by the information calculation unit 40, the first calculation unit 41 calculates the propagation time of the link from the terminal station 10 to the node station 2, the propagation time of each link between the node stations 2, the buffering time that each node station 2 should hold data for until the link is established, and the propagation time of the link from the node station 2 to the ground station 3a. Then, the first calculation unit 41 outputs each of the calculated results (times) to the delay time calculation unit 43.

The second calculation unit 42 calculates the queuing time of each node station 2 based on the load information calculated by the information calculation unit 40, and outputs each of the calculated results (time) to the delay time calculation unit 43.

The delay time calculation unit 43 calculates the sum of delay times T (see formula (2) above) occurring in data transmission for each path from the terminal station 10 to the ground station 3a based on each of the times calculated by the first calculation unit 41 and each of the times calculated by the second calculation unit 42. Then, the delay time calculation unit 43 outputs each of the calculated sums of delay times T to the determination unit 45.

The determination unit 44 reads various parameters and data stored in the database 36 and determines the priority of the traffic. The determination unit 44 then outputs the determined traffic priority and data to the decision unit 45. Note that the determination unit 44 outputs the data to the decision unit 45 as is when the traffic has no priority.

The determination unit 45 determines the route that minimizes the sum T of the delay times calculated by the delay time calculation unit 43 as the communication route from the terminal station 10 to the ground station 3a, and outputs information indicating the determined communication route together with the data to the modem unit 34.

In addition, for traffic that the judgment unit 44 judges to have high priority, the determination unit 45 determines as the communication route the route that minimizes the sum T of the delay times calculated by the delay time calculation unit 43.

In addition, for traffic determined by the determination unit 44 to have low priority, if the sum T of delay times calculated by the delay time calculation unit 43 is less than a predetermined threshold, the determination unit 45 determines as the communication route the route which minimizes the sum T of delay times calculated by the delay time calculation unit 43.

Furthermore, when the sum T of delay times calculated by the delay time calculation unit 43 for traffic determined by the determination unit 44 to have low priority is equal to or greater than a predetermined threshold, the determination unit 45 determines the route for which the sum T of delay times calculated by the delay time calculation unit 43 is maximum as the communication route. If the sum T of delay times calculated by the delay time calculation unit 43 subsequently becomes less than the predetermined threshold, the determination unit 45 determines and switches to the route for which the sum T of delay times calculated by the delay time calculation unit 43 is minimum as the communication route.

In addition, when the link between the node station 2 that last transmitted data to the ground station 3a and the ground station 3a is severed, the determination unit 45 determines a communication path to establish a link with one of the node stations 2 (e.g., node station 2-7, which is a geostationary satellite) that resides in a location where the link with the ground station 3a can be maintained, giving priority to the node station that last transmitted data to the ground station 3a (e.g., node station 2-3).

Figure 7 is a diagram illustrating the configuration and second operation of a wireless communication system 1 according to one embodiment. When the link between the node station 2-3 and the earth station 3a is cut off and communication is not possible, the total delay time T in the route Y2 via the node station 2-7, which is a geostationary satellite, is minimized.

In this case, the communication path calculation unit 4 (see Figs. 5 and 6) determines the communication path for high-priority traffic from the terminal station 10 to the ground station 3a to be the path Y2. In other words, the wireless communication system 1 determines the communication path for high-priority traffic to be the path with the smallest total delay time T among the paths with established links.

In addition, the communication path calculation unit 4 determines the communication path to be path Y2 for low priority traffic if the total delay time T of path Y2 is less than a threshold value.

In addition, the communication path calculation unit 4 determines the communication path to be path X2 for low-priority traffic if the sum T of delay times on path Y2 is equal to or greater than a threshold value. At this time, node station 2-3 buffers the data. In other words, the wireless communication system 1 distributes the load of node station 2 on the communication path that transmits high-priority traffic.

If the total delay time T of route Y2 subsequently falls below the threshold due to node station 2 moving or the like, the communication route calculation unit 4 determines and switches the communication route to route Y2. Node station 2-3 transmits the buffered traffic to node station 2-7 via route Z2, and has it transmitted to ground station 3a via node station 2-7.

In other words, the wireless communication system 1 avoids congestion for high-priority traffic to ensure communication, and maintains communication as much as possible for low-priority traffic, thereby improving the throughput of the entire system.

Figure 8 is a flowchart illustrating the processing performed by the communication path calculation unit 4 (Figures 5 and 6) when the wireless communication system 1 in one embodiment performs the second operation shown in Figure 7.

In step 100 (S100), the delay time calculation unit 43 calculates the total delay time T (see equation (2) above) occurring in the data transmission for each path from the terminal station 10 to the ground station 3a.

In step 102 (S102), the determination unit 44 determines whether the traffic involves priority processing. If the traffic does not involve priority processing (S102: No), the determination unit 44 proceeds to processing of S108, and if the traffic involves priority processing (S102: Yes), the determination unit 44 proceeds to processing of S104.

In step 104 (S104), the determination unit 44 determines whether the traffic priority is low or not. If the determination unit 44 determines that the traffic priority is not low (high) (S104: No), the process proceeds to S108, and if the determination unit 44 determines that the traffic priority is low (S104: Yes), the process proceeds to S106.

In step 106 (S106), the decision unit 45 determines whether the minimum value of the sum of delay times T is greater than or equal to a predetermined threshold, and if it is not greater than or equal to the threshold (S106: No), proceeds to processing of S108, and if it is greater than or equal to the threshold (S106: Yes), proceeds to processing of S110.

In step 108 (S108), the determination unit 45 determines the route with the smallest total delay time T as the communication route.

In step 110 (S110), the determination unit 45 determines the route with the largest sum of delay times T as the communication route.

Figure 9 is a diagram illustrating the configuration and third operation of a wireless communication system 1 according to one embodiment. Here, it is assumed that node station 2-7, which is a geostationary satellite, can select only one node station 2 (mobile satellite) to establish a link.

For example, in the case of communication from the terminal station 10 to the ground station 3a, if the link between the node station 2-3 and the ground station 3a is disconnected, the wireless communication system 1 switches the communication path to a path that passes through the node station 2-7, since there is no node station 2 that can communicate with the ground station 3a.

Traffic received by node station 2-3 after the link between node station 2-3 and earth station 3a is disconnected is propagated using the switched communication path.

At this time, if node station 2-7 establishes a link to node station 2-1, which is located away from node station 2-3 that was communicating with earth station 3a until just before, the communication path becomes path X3.

In contrast, when node station 2-7 establishes a link to node station 2-3, which was communicating with ground station 3a until just before, the communication path becomes path Y3. Path Y3 has one hop to connect node station 2-3 to ground station 3a.

On the other hand, the number of hops required for route X3 to connect from node station 2-3 to ground station 3a is 3. In other words, route Y3 has a smaller total delay time T than route X3.

In this way, the wireless communication system 1 improves the throughput of the entire system by having node station 2-7 prioritize building a link over node station 2-3, which was communicating with earth station 3a until just before.

For example, due to frequency resources, cost, and other reasons, the node station 2-7 (absolute node station) may not be able to establish links with all of the node stations 2. In such a case, the determination unit 45 (Figure 6) determines the communication path for the node station 2-7 to establish a link by giving priority to the node station 2-3, which was communicating with the earth station 3a until just before.

As described above, the wireless communication system 1 determines the communication route based on the buffering time that each node station 2 should hold data for until a link is established, thereby enabling efficient wireless communication via a moving node station 2.

In addition, each function possessed by the ground station 3a (or node station 2, etc.) may be configured in part or in whole 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.

For example, the ground station 3a of the present invention can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

1: wireless communication system, 2, 2-1 to 2-8: node stations, 3, 3a: ground station, 4: communication path calculation unit, 10: terminal station, 30: antenna, 32: RF unit, 34: modem unit, 36: database, 40: information calculation unit, 41: first calculation unit, 42: second calculation unit, 43: delay time calculation unit, 44: judgment unit, 45: decision unit

Claims (8)

In a wireless communication system, data to be transmitted from a transmitting device to a receiving device is wirelessly transmitted over a communication path passing through a plurality of node stations, at least one of which moves,
an information calculation unit that calculates location information indicating a location of each of the node stations and load information indicating a load due to traffic of each of the node stations;
a first calculation unit that calculates, based on the location information calculated by the information calculation unit, a propagation time of a link from the transmitting device to the node station, a propagation time of each of the links between the node stations, a buffering time during which each of the node stations should hold data until a link is established, and a propagation time of a link from the node station to the receiving device;
a second calculation unit that calculates a queuing time for each of the node stations based on the load information calculated by the information calculation unit;
a delay time calculation unit that calculates a sum of delay times occurring in data transmission for each path from the transmitting device to the receiving device based on each of the times calculated by the first calculation unit and each of the times calculated by the second calculation unit;
a determination unit that determines, as the communication route, a route for which the sum of the delay times calculated by the delay time calculation unit is the smallest. A determination unit that determines the priority of traffic,
The determination unit is
2. The wireless communication system according to claim 1, characterized in that for traffic determined by the determination unit to have a high priority, a route for which the sum of delay times calculated by the delay time calculation unit is the smallest is determined as the communication route, and for traffic determined by the determination unit to have a low priority, if the sum of delay times calculated by the delay time calculation unit is less than a predetermined threshold, a route for which the sum of delay times calculated by the delay time calculation unit is the smallest is determined as the communication route, and if the sum of delay times calculated by the delay time calculation unit is equal to or greater than a predetermined threshold, a route for which the sum of delay times calculated by the delay time calculation unit is the largest is determined as the communication route. The determination unit is
3. The wireless communication system according to claim 1, wherein when a link between the receiving device and the node station that last transmitted data to the receiving device is disconnected, the communication path is determined so as to give priority to the node station that last transmitted data to the receiving device and establish a link with any of the node stations residing in a location that can continue to maintain a link with the receiving device. A wireless communication method for wirelessly transmitting data from a transmitting device to a receiving device over a communication path passing through a plurality of node stations, at least one of which moves, comprising:
an information calculation step of calculating location information indicating a location of each of the node stations and load information indicating a load due to traffic of each of the node stations;
a first calculation step of calculating, based on the calculated location information, a propagation time of a link from the transmitting device to the node station, a propagation time of each of the links between the node stations, a buffering time for each of the node stations to hold data until a link is established, and a propagation time of a link from the node station to the receiving device;
a second calculation step of calculating a queuing time for each of the nodes based on the calculated load information;
a delay time calculation step of calculating a sum of delay times occurring in data transmission for each path from the transmitting device to the receiving device based on each of the times calculated in the first calculation step and each of the times calculated in the second calculation step;
and determining, as the communication route, a route that minimizes the calculated sum of delay times. determining a priority of the traffic;
In the determining step,
5. The wireless communication method according to claim 4, characterized in that for traffic determined in the determination step to have high priority, a route with a smallest sum of calculated delay times is determined as the communication route, and for traffic determined in the determination step to have low priority, if the calculated sum of delay times is less than a predetermined threshold, a route with a smallest sum of calculated delay times is determined as the communication route, and if the calculated sum of delay times is equal to or greater than a predetermined threshold, a route with a largest sum of calculated delay times is determined as the communication route. A communication path determination device determines a communication path for wirelessly transmitting data to be transmitted from a transmitting device to a receiving device via a plurality of node stations, at least one of which moves,
an information calculation unit that calculates location information indicating a location of each of the node stations and load information indicating a load due to traffic of each of the node stations;
a first calculation unit that calculates, based on the location information calculated by the information calculation unit, a propagation time of a link from the transmitting device to the node station, a propagation time of each of the links between the node stations, a buffering time during which each of the node stations should hold data until a link is established, and a propagation time of a link from the node station to the receiving device;
a second calculation unit that calculates a queuing time for each of the node stations based on the load information calculated by the information calculation unit;
a delay time calculation unit that calculates a sum of delay times occurring in data transmission for each path from the transmitting device to the receiving device based on each of the times calculated by the first calculation unit and each of the times calculated by the second calculation unit;
a determination unit that determines, as the communication route, a route for which the sum of the delay times calculated by the delay time calculation unit is the smallest. A determination unit that determines the priority of traffic,
The determination unit is
7. The communication path determination device according to claim 6, wherein for traffic determined by the determination unit to have a high priority, a route for which the sum of delay times calculated by the delay time calculation unit is the smallest is determined as the communication path, and for traffic determined by the determination unit to have a low priority, if the sum of delay times calculated by the delay time calculation unit is less than a predetermined threshold, a route for which the sum of delay times calculated by the delay time calculation unit is the smallest is determined as the communication path, and if the sum of delay times calculated by the delay time calculation unit is equal to or greater than a predetermined threshold, a route for which the sum of delay times calculated by the delay time calculation unit is the largest is determined as the communication path. The determination unit is
8. The communication path determination device according to claim 6 or 7, characterized in that, when a link between the receiving device and the node station that last transmitted data to the receiving device is disconnected, the communication path is determined so as to give priority to the node station that last transmitted data to the receiving device and establish a link to any of the node stations residing in a location that can continue to maintain a link with the receiving device.

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