Railroad communication system and on-vehicle communication platform

Abstract

To provide a technique of improving an overall communication throughput by effectively using available bands of a communication between ground vehicles.SOLUTION: One of railroad communication systems of the present invention, includes an on-vehicle communication platform, and a ground communication platform. The on-vehicle communication platform comprises: a path control unit that allocates packets to a plurality of radio paths; and a communication situation determination unit that determines a communication situation between the ground communication platform and the on-vehicle communication platform. In the case where a re-transmission request is received from the ground communication platform, the communication situation determination unit notifies the path control unit of quality information of the plurality of radio paths. The path control unit: determines a request quality on the basis of transmission source information included in the packet being an object of the re-transmission request; evaluates the plurality of radio paths on the basis of the request quality and the quality information; and selects the radio path to be used for re-transmission from the plurality of radio paths on the basis of a result of the evaluation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a railway communication system and an on-board communication platform. [Background technology]

[0002] The International Union of Railways (UIC) is currently replacing its wireless train control system, the Global System for Mobile Communications Railway (GSM-R), with a new wireless system, anticipating that the system's lifetime will end around 2030. In addition, UIC is working on formulating standards for the Future Railway Mobile Communication System (FRMCS), a next-generation wireless communication system for railways, with the aim of promoting the sophistication of the railway system itself by utilizing broadband wireless systems such as Long Term Evolution (LTE) and 5G.

[0003] FRMCS aims to reduce costs by using existing wireless access technologies such as LTE and 5G without customizing them, and to achieve the communication quality required by the various applications that realize railway systems using existing wireless access technologies. Specifically, FRMCS is considering a mechanism that can realize highly reliable communication by incorporating multiple wireless systems using a function called FRMCS gateway. The railway communication system using the above FRMCS gateway aims to incorporate multiple wireless systems and realize improved communication quality and wideband communication.

[0004] Meanwhile, millimeter-wave wireless systems and local 5G wireless systems are currently being considered as broadband data transmission methods that utilize private wireless systems that are designed, constructed, operated, and maintained by railway operators themselves. These systems are constructed using ground base stations located along the railway line, so they are burdensome in terms of both initial costs and maintenance costs, making it difficult for railway operators with limited resources to introduce them.

[0005] Another method to achieve broadband communications is to utilize services provided by MNOs (Mobile Network Operators). Although these services are being applied to some railway operation operations, they have not been applied to mission-critical applications such as train control due to issues such as the inability of railway operators to control communication quality and the need to share the network with general users.

[0006] The above has been explained from the perspective of the provider of the communications infrastructure, but from the perspective of ensuring communication quality, there are the following prior art technologies.

[0007] Patent Document 1 discloses that a wireless communication device (10, 10A) includes a first wireless communication unit (111), a second wireless communication unit (112), and a control unit (130). The first wireless communication unit (111) connects to and communicates with a first communication network that allows connection in a predetermined area. The second wireless communication unit (112) connects to and communicates with a second communication network different from the first communication network. The control unit (130) predicts communication quality of communication by the first wireless communication unit (111) and determines whether or not to communicate by the second wireless communication unit (112) based on whether or not the predicted communication quality satisfies a desired communication quality.

[0008] Patent document 2 discloses a communication method in a communication system in which communication control devices that control communication between applications via packet flows using one or more communication networks are arranged opposite each other across the communication networks, wherein the communication control devices hold communication quality requirements for each packet flow and a communication quality assurance policy related to communication redundancy for each packet flow and for each communication network, and the method is characterized in that the communication control devices measure communication performance for each packet flow and for each communication network used in the packet flows, and control the communication redundancy of the packet flows based on the communication performance measurement results, the communication quality requirements, the communication quality assurance policy, and the contribution of each packet flow to communication quality.

[0009] Patent document 3 discloses that a computer executes a determination procedure for determining whether or not redundancy of a communication path is required and the compression level of the data based on the communication quality related to the data transfer, a compression procedure for compressing the data to be transferred according to the compression level determined in the determination procedure, and a transmission procedure for making the communication paths redundant and transmitting the data to each communication path when it is determined in the determination procedure that redundancy of the communication paths is required.

[0010] Patent Document 4 discloses a communication system capable of transmitting a series of communication data from a first communication device to a second communication device by reserving n communication paths (n is an integer satisfying 1≦n≦m) out of m communication paths (m is an integer equal to or greater than 2) including 2 paths as n lines, and characterized in that n communication paths to be preferentially used out of the m systems are determined in advance as the n lines in correspondence with usage conditions including at least one of a usage location and a usage time, and the first communication device or the second communication device reserves the n lines that comply with the usage conditions. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] PCT / JP2021 / 013965 [Patent Document 2] Patent Publication No. 2022-50829 [Patent Document 3] JP 2019-145878 A [Patent Document 4] JP 2005-229202 A Summary of the Invention [Problem to be solved by the invention]

[0012] When applying communication services provided by MNOs to communication between devices installed on the ground and on trains (hereinafter referred to as "ground-to-train communication") in railways, it is necessary to realize broadband communication and highly reliable communication. First, there is carrier aggregation as a method for realizing broadband communication. Carrier aggregation is a technology that bundles radio waves of multiple frequency bands to realize high communication speed and high communication reliability, and is known as an elemental technology of LTE-Advance. By adopting carrier aggregation, high communication speed is realized. However, carrier aggregation is a service provided by each MNO. Since the entire railway line covers a wide area, it is practically impossible for the service provided by a single MNO to include the entire railway line in its service area. Therefore, in order to realize high reliability of communication using carrier aggregation over the entire railway line, it is necessary to use multiple MNO services in combination to cover the entire railway line so that carrier aggregation can be used over the entire railway line.

[0013] Another method for achieving broadband communication in wired systems is link aggregation, a technology that bundles multiple lines or ports together and treats them as a single line, and that also realizes faster communication speeds. A method for distributing the load of link aggregation to avoid response speed delays and system downtime is to switch the transmission path based on the source IP or destination port. This method is achieved by switching the relay network, so it is expected to realize a broadband and highly reliable communication system by transmitting data by treating multiple NMO lines that undergo switching as a single port.

[0014] On the other hand, since link aggregation switches destinations based on source IP, etc., there is concern that the load will be concentrated on some MNOs. For example, if the load is distributed using the source MAC address, communications from the same source may always flow to the same network. In ground-to-vehicle communications on railways, the communication bandwidth may change significantly over time and geography as the vehicles move. If the communication load is concentrated on either the source IP or destination port, such as when the receiving power on a given MNO line continues to decrease, there may be a problem of continuous interruption of communications to a specific IP or a specific destination port.

[0015] Next, protocols that perform retransmission control, such as TCP (Transmission Control Protocol), are generally used as a method to achieve high reliability in communications. However, TCP has the drawback of lacking real-time performance and being prone to delays. Technologies that have real-time capabilities and are expected to improve communication quality include ARQ (Automatic Repeat Request), which requests retransmission of only erroneous packets when an error is detected in a message. One of the issues that arise when the above-mentioned retransmission control is applied to ground-to-vehicle communications in railways is congestion. In wireless communications such as those of MNOs, packet loss is likely to occur due to factors such as radio wave conditions and the number of terminals, and it is expected that retransmission control will occur frequently. If retransmission control occurs frequently, a vicious cycle will occur in which the load on the network increases, further worsening congestion.

[0016] In response to the above-mentioned problems, the present invention aims to provide a technique for efficiently utilizing the available bandwidth in ground-to-vehicle communications and improving the overall communication throughput. [Means for solving the problem]

[0017] In order to solve the above problems, one representative railway communication system of the present invention is a railway communication system that transmits packets generated from multiple applications between ground vehicles using multiple wireless routes, and has an on-board communication platform and a ground communication platform, and the on-board communication platform is equipped with a route control unit that distributes the packets to the multiple wireless routes, and a communication status determination unit that determines the communication status between the ground communication platform and the on-board communication platform, and when a retransmission request is received from the ground communication platform, the communication status determination unit notifies the route control unit of quality information of the multiple wireless routes, and the route control unit determines a required quality based on source information included in the packet that is the subject of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on the result of the evaluation. Effect of the Invention

[0018] According to the present invention, the available bandwidth for ground-to-vehicle communications can be efficiently utilized to improve the overall communication throughput. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating a railway communication system according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a flowchart for determining a routing control policy. [Diagram 3]FIG. 3 is a diagram showing a flowchart of route control when routes are weighted. [Figure 4] FIG. 4 is a diagram illustrating a railway communication system according to the second embodiment. [Diagram 5] FIG. 5 is a diagram showing an example of a performance value DB stored in the railway line MNO performance DB. [Figure 6] FIG. 6 is a diagram illustrating a railway communication system according to the third embodiment. [Figure 7] FIG. 7 is a diagram illustrating a railway communication system according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals.

[0021] In the following description, a "path" refers to a route along which data is transmitted from a sender to a receiver. In this disclosure, a path includes any one of a plurality of wireless networks. It is also referred to as a "wireless path." Additionally, a "wireless network" refers to a network provided by a particular MNO. Wireless networks labeled with different numbers refer to networks provided by different MNOs.

[0022] [Example 1] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a railway communication system 100 according to the first embodiment. FIG. 1 is a schematic diagram of an example of the railway communication system 100 that realizes ground-to-vehicle communication of packets of a plurality of railway applications using a plurality of wireless systems. The railway communication system 100 transmits packets generated from a plurality of applications between ground vehicles using a plurality of wireless paths. The railway communication system 100 transmits a plurality of railway applications (hereinafter also referred to as "railway apps") 11-12. N(N is a positive integer) and a ground-side wireless system including a ground communication platform 2 and railway applications 111 to 11 P (P is a positive integer) and an on-board system including an on-board communication platform 12. N When there is no need to specify the railway application, the railway application is referred to as "railway application 1" in the following description or drawings. P Similarly, it will be displayed as "Railway App 11."

[0023] The railway application 1 in the ground facility communicates with the railway app 11 in the on-board facility via the ground communication platform 2 and the on-board communication platform 12, the wireless terminal 9, the wireless terminal 10, the wireless networks 7 and 8, and the public network gateway 6. The railway app may perform train control such as speed control and brake control, for example. The railway app 1 sets a control value based on an instruction specified by the vehicle operation management system. The railway app 11 controls the driving device or the braking device of the vehicle based on the control value. In addition, the railway app 1 and the railway app 11 control communication devices for communication with the crew and contact for operation management. These functions may be assigned to each railway app, or multiple functions may be executed by one railway app.

[0024] The ground communication platform 2 is composed of an application input / output unit 3 that receives packets from the railway application 1, a route control unit 4 that switches the transmission route according to arbitrary conditions, and a communication status determination unit 5 that grasps the communication status and provides feedback to the route control unit 4.

[0025] The on-board communication platform 12 also includes at least a route control unit 14 that distributes packets to a plurality of wireless routes, and a communication status determination unit that determines the communication status between the ground communication platform and the on-board communication platform. Specifically, the on-board communication platform 12 includes an application input / output unit 13 that receives packets from the railway application 11, a route control unit 14 that switches the transmission route according to an arbitrary condition, and a communication status determination unit 15 that grasps the communication status and provides feedback to the route control unit 14.

[0026] The public network gateway 6 relays communications between the on-board communication platform 12 and the ground communication platform 2. Packets transmitted from the on-board communication platform 12 pass through wireless networks 7 and 8, and reach the ground communication platform 2 via the public network gateway 6. The route control unit 4 receives, from the packets transmitted via the public network gateway 6, packets containing information generated based on a request from the railway application 11 (hereinafter also referred to as "application packets"). The communication status determination unit 5 receives, from the packets transmitted via the public network gateway 6, communication quality information of the wireless network.

[0027] For ease of understanding, this disclosure describes the configuration using two public networks, wireless networks 7 and 8, but may also include other public network lines or private networks owned by railway operators. This disclosure may also be applied to cases where the number of available wireless networks changes depending on the location where the vehicle is traveling. In addition, an example is shown in which there are two wireless terminals and two wireless networks, but the number of wireless terminals and wireless networks is not limited to two. For example, a wireless terminal may be provided for each wireless network provided in the area where the vehicle is operated. In the following description, the first route is a route that includes wireless network 7, and the second route is a route that includes wireless network 8.

[0028] The on-board communication platform 12 may include the wireless terminals 9 and 10 and the railway application 11. In this case, information output from the railway application 11 can be generated as a packet in the application input / output unit 13.

[0029] (Communication from on-board communication platform to ground communication platform) Next, the operation of the embodiment 1 of the present invention will be described using the transmission system of FIG. 1. In this embodiment, the communication in the direction from the on-board side to the ground side will be described. A packet transmitted from the railway application 11 is transmitted to the application input / output unit 13 of the on-board communication platform 12, and the application input / output unit 13 transfers the received packet to the route control unit 4. When the route control unit 4 receives a packet from the application input / output unit 3, the on-board communication platform 12 mainly performs packet route control using two methods. The first method is a method of duplicating an input packet to transmit it to multiple wireless routes to improve communication quality. The second method is a method of distributing an input packet to each wireless route to broaden the bandwidth. This invention mainly deals with the latter. Specifically, the packet distribution method includes a method of switching according to IP header information called a 5-tuple such as a destination IP, a destination port, a source IP, a source port, and a protocol number, which is the same as link aggregation, and a method of alternately switching transmission routes using an identification number in the IP header.

[0030] The communication status determination unit 15 collects communication quality information, which is information on the communication quality of the route, such as so-called received power, such as RSRP (Reference Signal Received Power), from the wireless terminals 9 and 10, and notifies the route control unit 14 of the state of the communication quality of the wireless networks 7 and 8. As a method for grasping the communication quality, for example, there is a means for measuring the RTT (Round Trip Time) between the ground communication platform 2 and the on-board communication platform 12 and counting whether a delay exceeding a certain threshold occurs continuously. There is also a means for evaluating packet loss and received power. The above-mentioned method is not limited to this, and other methods for grasping the communication quality can also be applied in the present disclosure. Note that the communication quality of the wireless network 7 can be treated as equivalent to the communication quality of the first route, and the communication quality of the wireless network 8 can be treated as equivalent to the communication quality of the second route.

[0031] The route control unit 14 receives the communication quality of each route and transmits the application packet of the railway application 11 and the communication quality information of the wireless network to the ground communication platform 2 via the target wireless networks 7 and 8 in accordance with the policy. When the ground communication platform 2 receives the message, the application packet is transferred to the route control unit 4, the application input / output unit 3, and then to the railway application 1. The communication quality information of the wireless layer is notified to the communication status determination unit 15 and is used for retransmission control, which will be described later.

[0032] Incidentally, communication in the direction from the ground side to the on-board side can be explained by exchanging the roles of the ground communication platform 2 and the on-board communication platform 12 in the above explanation.

[0033] (Retransmission control from ground communication platform to on-board communication platform) Next, a control method for performing retransmission control will be described. In the above-mentioned flow of communication from on-board to ground, if a packet transmitted from the on-board communication platform 12 is discarded in the wireless path due to error detection, the route control unit 4 determines a route control policy based on the communication quality of each wireless path notified by the communication status determination unit 5 and the required quality level of the railway application, and transmits a packet including a retransmission request. Note that, since the packet size of a retransmission request is small, the above process may be performed to select a route, or the above process may be omitted and retransmission may be performed on both routes.

[0034] The on-board communication platform 12 sequentially adopts the retransmission requests sent from the ground communication platform 2 in the order of the earliest arriving message, and discards the latest received message. When the on-board communication platform 12 receives a retransmission request, the communication status determination unit 15 notifies the route control unit 14 of quality information of multiple wireless routes. The route control unit 14 determines the required quality based on the sender information included in the packet that is the target of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on the evaluation result. Specifically, the route control unit 14 determines a route control policy (described later) based on the communication status of each route from the communication status determination unit 15 and the required quality level of the railway app, and retransmits the packet.

[0035] (Determining routing policy) Next, an example of a flow for determining a route control policy by the route control unit 14 will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of a flowchart for determining a route control policy. Note that this flow assumes a situation in which, when a packet loss occurs on the first route side (step S16), it is necessary to determine whether the destination should be the first route or another route. The route determination uses quality information of each wireless route notified by the communication status determination unit 15 and a required quality level of the railway application 11 that can be determined from the destination or source IP of the lost packet.

[0036] In the following description, communication quality is classified into two judgment criteria: high (denoted by ◯) or low (denoted by ×). For example, it is possible to determine whether communication quality is high or low by using at least one of RTT, packet loss, and power consumption as an evaluation index and setting a reference value for the evaluation index, and determining whether the evaluation index acquired as communication quality is higher or lower than the reference value.

[0037] In addition, the required quality level of the railway application 11 can be set to high if the destination or source IP is related to train control, and low otherwise. For example, the route control unit 14 can determine the required quality level by having in advance information that specifies the relationship between the destination or source IP and the required quality level. In the following description, the required quality level is shown to be high or low, but the present disclosure is not limited thereto. It is also possible to classify the communication quality into two or more categories according to the function of the railway application.

[0038] Based on the communication quality, there are four possible combinations of the communication quality of the first route and the communication quality of the other routes. When the communication quality of the first route is high and the communication quality of the other routes is also high (denoted as "first route 0, other routes 0"), if the required quality level of the railway application 11 is high (high in step S18), the route control unit 14 retransmits the packet on both the first route and the other routes (step S21). On the other hand, if the required quality level is low (low in step S18), the route control unit 14 retransmits the packet on the first route (step S21).

[0039] Next, when the communication quality of the first route is high and the communication quality of the other routes is low (notation "first route ◯ other routes ×"), the route control unit 14 retransmits the packet via the first route (step S22).

[0040] Next, when the communication quality of the first route is low and the communication quality of the other route is high (denoted as "first route x other route 0"), if the required quality level of the railway application is high (high in step S19), the route control unit 14 retransmits the packet via the other route (step S23). On the other hand, if it is low (low in step S19), the route control unit 14 stops retransmitting the packet (step S24). This is to avoid an increase in the load on the other route due to retransmission via the other route, which would result in an unnecessary deterioration of the communication quality.

[0041] Finally, when the communication quality is low on both routes (notation "first route x other route x"), if the required quality level is high (high in step S20), the route control unit 14 retransmits the packet on the first route (step S22). On the other hand, if the required communication level is low (low in step S20), the route control unit 14 stops retransmitting the packet (step S24).

[0042] In addition, with regard to a retransmission request from the ground communication platform 2 to the on-board communication platform 12, since the packet size of the packet transmitted from the on-board communication platform 12 is small, the ground communication platform 2 may perform the above-mentioned processing to select a route, or may omit the above-mentioned processing and perform retransmission via both routes.

[0043] (A method of communication using multiple communication paths) When transmitting packets using both wireless routes as described above, in addition to the load balancing method of sending packets to each route at the same ratio, weighting may be further applied to each route based on the communication conditions. An example of weighting each route and allocating packet transmission will be described with reference to FIG. 3. FIG. 3 is a diagram showing a flowchart of route control when weighting routes. In the following description, a case where packets are transmitted to the first route and the second route will be described, but the present disclosure is not limited to this. The destination of a packet may be two or more.

[0044] The communication status determination unit 15 determines the transmission weights of the multiple wireless routes and instructs the route control unit 14 to retransmit. Specifically, when the on-board communication platform 12 starts transmission (step S25), the communication status determination unit 15 acquires communication quality information of the wireless networks 7 and 8 from the wireless terminals 9 and 10 and estimates the ratio of each route to the entire communication band (step S26). For example, when the ratio of each route can be acquired according to the communication quality information, such as using the first route for packet transmission A% and the second route B%, the counter is initialized and a counter threshold value according to the weight is set for each route (step S27).

[0045] Next, the route control unit 14 performs transmission over the first route, and each time a packet is transmitted, the counter value of the first route is increased and route determination for the next packet is performed (step S32). The route control unit 14 transmits, for example, M packets (M is a positive integer) per 1% weight. If the counter value reaches the counter threshold (A×M packets) (Y in step S29), the route control unit 14 performs transmission over the second route (step S31). If the counter threshold is reached on all routes (Y in step S30), the counter value is initialized and transmission is performed over the first route again.

[0046] When wireless layer information is acquired during packet transmission and there is a change in the proportion of each route to the overall communication quality (steps S31 to S26 or steps S32 to S26), the counter threshold is rewritten (step S27).

[0047] (Action and effect) One of the causes of packet errors such as packet loss is that the capacity of the available bandwidth used in ground-to-vehicle communication is equal to or less than the packet transmission capacity. In contrast, in the communication system of the first embodiment, the information transmission method is selected according to the communication quality of the route and the required quality level of the packet to be transmitted. Since it is possible to increase the probability of transmitting information while avoiding congestion of the available bandwidth, it is possible to improve the reliability of communication. In this way, according to the present disclosure, it is possible to efficiently use the available bandwidth in ground-to-vehicle communication and improve the overall communication throughput.

[0048] [Example 2] Example 2 differs from Example 1 in that a railway line MNO performance DB is provided to the ground communication platform and the on-board communication platform, and a location information acquisition unit 27 is added to the on-board platform. In the following description, components that are the same as or equivalent to those in the first embodiment described above are given the same reference numerals, and their description will be simplified or omitted.

[0049] In the transmission system in Fig. 1, communication quality information of the wireless network NW is acquired from the on-board wireless terminals 9 and 10, and the communication quality of each route is estimated in real time. The communication status of the wireless network NW can be accurately estimated by combining information from multiple wireless networks, such as RSRP, RB (Resource Block), and MCS (Modulation and Coding Scheme), but there is a concern that processing information from multiple wireless networks in real time will increase the processing load of the platform, which will become a cause of delays. Therefore, as another method for determining the communication quality of each route, we propose a method in which the current communication quality is estimated by comparing it with a DB of past performance values ​​using time and location information as keys, and then reflected in route control.

[0050] This embodiment will be described with reference to FIG. 4. FIG. 4 is a diagram showing a railway communication system 100a according to a second embodiment. In the configuration of FIG. 4, the ground communication platform 2 includes a railway line MNO performance DB 25 instead of the communication status determination unit 5 in the transmission system of FIG. 1. Also, the on-board communication platform 12 includes a railway line MNO performance DB 26 instead of the communication status determination unit 15. The railway line MNO performance DBs 25 and 26 are databases having available bandwidth information for each position and / or each time for a plurality of wireless routes. The route control unit 14 evaluates the plurality of wireless routes from the available bandwidth information held in the database, and selects a wireless route to be used for retransmission from among the plurality of wireless routes based on the evaluation result. Also, the on-board communication platform 12 is added with a location information acquisition unit 27 that notifies location information, which is information indicating the current location of the vehicle.

[0051] The on-board communication platform 12 acquires vehicle position information such as GPS and kilometre distance from the position information acquisition unit 27 of the vehicle system, and notifies the application input / output unit 13. The application input / output unit 13 notifies the route control unit 14 and the railway line MNO performance DB 26 of the position information. The route control unit 14 copies the position information and transmits it to the ground communication platform 2 via each wireless network 7 and 8 in the same way as the application packet. The ground communication platform 2 transfers the application packet to the railway application 1 via the route control unit 4, and transmits the position information to its own railway line performance DB 25. The railway line MNO performance DB 25 estimates the communication quality of the wireless network from the notified position information and current time, and notifies the route control unit 14 of the estimation result. The route control unit 14 performs retransmission control using the methods of Figs. 2 and 3.

[0052] Fig. 5 is a diagram showing an example of a performance value DB stored in the railway line MNO performance DB 26. Fig. 5(a) is a DB showing the kilometers from the starting point between the first train on the railway line and 12:00, and the communication quality of wireless network 7 and the communication quality of wireless network 8 corresponding to the kilometers. For wireless network 7, the communication quality is high (marked as ◯) from the starting point to 15.8, and the communication quality is low (marked as ×) from 15.8 to 21.1. For wireless network 8, the communication quality is low from the starting point to 13.2, and the communication quality is high from 13.2 to 21.1. According to FIG. 15(a), the route control unit 14 may, for example, perform communication using a first route (i.e., a route including wireless network 7) from the starting point t to 13.2, communication using the first route and a second route (i.e., a route including wireless network 8) from 13.2 to 15.8, and communication using the second route from 15.8 to 21.1.

[0053] FIG. 5(b) shows the communication quality of the wireless network on the railway line in the same range as FIG. 5(a) from 12:00 to 16:00. FIG. 5(c) shows the communication quality of the wireless network on the railway line in the same range as FIG. 5(a) from 16:00 to 24:00. Comparing FIG. 5(a) to FIG. 5(c), it can be seen that the communication quality varies depending on the time. Such data can be obtained, for example, based on multiple measurements by vehicles operating the target railway line. The railway line MNO performance DB 25 notifies the route control unit 14 of the communication quality of the wireless network based on the current location and current time input from the application input / output unit 13.

[0054] In addition, in Fig. 5, the performance value DB indicates the level of communication quality, but the present disclosure is not limited to this. The performance value DB may be, for example, a database that stores values ​​such as RTT, packet loss, and power consumption. Based on these values, the railway line MNO performance DB 25 may be configured to determine the level of communication quality. The performance value DB indicates available bandwidth information for each location and each time (i.e., information indicating the level of communication quality), but the present disclosure is not limited to this. The performance value DB may indicate available bandwidth information for each location or may indicate available bandwidth information for each time.

[0055] (Action and effect) Since communication quality can be grasped based on location information without acquiring communication quality in real time, it is possible to efficiently utilize the available bandwidth for ground-to-vehicle communication while reducing the processing load on the on-board communication platform 12.

[0056] [Example 3] Example 3 differs from Example 1 in that a communication status determination unit of an on-board communication platform notifies a communication capacity limit. Fig. 6 is a diagram showing a railway communication system 100b according to Example 3. In the following description, components that are the same as or equivalent to those in the first embodiment described above are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

[0057] In the transmission system in Fig. 1, if the transmission rate at which the on-board communication platform 12 transmits to the ground communication platform 2 is equal to or higher than the actual value of the wireless network, the ground communication platform 2 detects a packet loss and requests a retransmission. When the on-board communication platform 12 receives the retransmission request, it retransmits the packet when the wireless networks 7 and 8 do not have sufficient available bandwidth, causing further congestion in the network and leading to the corruption of packets with high required quality levels. Therefore, as a means of suppressing congestion when the network is congested, control is performed to reduce the communication bandwidth input from the railway application. This will be explained using Fig. 5.

[0058] 6, when the communication status determination unit 15 acquires communication quality information of the wireless networks 7 and 8 from the wireless terminals 9 and 10, it notifies the route control unit 14 of the communication quality of each route, and also notifies the target railway application 11 of the communication capacity limit via the application input / output unit 13. As a result, a railway application with a low priority among the railway applications 11 can perform stable real-time communication in narrowband communication by, for example, stopping transmission, switching the codec of the transmission data, lowering the bit rate, changing the sampling period, or the like for the corresponding packets among the multiple railway applications. The priority can be, for example, made to correspond to the level of required quality.

[0059] (Action and effect) Since the railway application 11 imposes a communication capacity restriction, even if the capacity of the available bandwidth for ground-to-vehicle communication is small, it is possible to continue real-time communication.

[0060] [Example 4] The fourth embodiment differs from the second embodiment in that quality information of the wireless network is transmitted from the railway line MNO performance DB 25 of the ground communication platform to the on-board communication platform 12. Fig. 7 is a diagram showing a railway communication system 100c according to the fourth embodiment. In the following description, components that are the same as or equivalent to those in the second embodiment described above are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

[0061] The location information acquisition unit 27 acquires the location information of the vehicle. The acquired location information is transmitted to the ground communication platform 2 in the same manner as the application packet. The location information is sent to the railway line MNO performance DB in the ground communication platform 2. The railway line MNO performance DB 25 transmits wireless network quality information to the on-board communication platform 12 based on the current location.

[0062] The route control unit 14 of the on-board communication platform 12 selects a wireless route for transmitting the packet based on the received communication quality of the wireless network.

[0063] (Action and effect) Since the configuration of the railway line MNO performance DB can be omitted from the on-board communication platform 12, it is possible to simplify the configuration of the on-board communication platform 12. Also, since there is no need to apply a performance value DB provided for each vehicle, and vehicle communications can be controlled based only on the performance value DB on the ground communication platform 2, it is possible to optimize the information communication load for the entire railway line.

[0064] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0065] The following are some possible embodiments of the present invention, but the present invention is not limited to these. (Aspect 1) A railway communication system that transmits packets generated by a plurality of applications between ground vehicles using a plurality of wireless paths, It has an on-board communication platform and a ground communication platform, The on-board communication platform includes: a route control unit that distributes the packets to the plurality of wireless routes; a communication status determination unit that determines a communication status between the ground communication platform and the on-board communication platform, when receiving a repeat request from the terrestrial communications platform; the communication status determination unit notifies the route control unit of quality information of the plurality of wireless routes; The route control unit determines a required quality based on source information contained in the packet that is the subject of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on the results of the evaluation. (Aspect 2) The railway communication system according to aspect 1, The on-board communication platform includes: A database having available bandwidth information for each location and / or each time regarding the plurality of wireless paths is further provided, The route control unit evaluates the plurality of wireless routes from available bandwidth information held in the database, and selects a wireless route to be used for retransmission from among the plurality of wireless routes based on a result of the evaluation. A railway communication system comprising: (Aspect 3) The railway communication system according to aspect 1 or 2, The communication status determination unit determines a transmission weight of the plurality of wireless paths and instructs the path control unit to retransmit the signal. A railway communication system comprising: (Aspect 4) A railway communication system according to any one of aspects 1 to 3, the communication status determination unit notifies the plurality of applications of a communication capacity limit; A notification is issued to an application having a low priority among the plurality of applications to stop transmission or to reduce a bit rate. A railway communication system comprising: (Aspect 5) An on-board communication platform that transmits packets generated from a plurality of applications between ground and on-board vehicles to a ground communication platform using a plurality of wireless paths, a route control unit that distributes the packets to the plurality of wireless routes; a communication status determination unit that determines a communication status between the ground communication platform and the on-board communication platform, when receiving a repeat request from the terrestrial communications platform; the communication status determination unit notifies the route control unit of quality information of the plurality of wireless routes; The route control unit determines a required quality based on source information contained in the packet that is the subject of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on a result of the evaluation. [Explanation of symbols]

[0066] 1, 11~1 N :Railway app (ground communication platform side) 2: Ground communication platform 3: Application input / output section (ground communication platform side) 4: Route control unit (ground communication platform side) 5: Communication status determination unit (ground communication platform side) 6: Public network gateway 7, 8: Wireless network 9, 10: Wireless terminal 11, 111~11 P :Railway app (on-board communication platform side) 12: On-board communication platform 13: Application input / output section (on-board communication platform side) 14: Route control unit (on-board communication platform side) 15: Communication status determination unit (on-board communication platform side) 25: Railway line MNO performance DB (ground communication platform side) 26: Railway line MNO performance DB (on-board communication platform side) 27: Location information acquisition section 100, 100a, 100b, 100c: Railway communication systems

Claims

1. A railway communication system that transmits packets generated by a plurality of applications between ground vehicles using a plurality of wireless paths, It has an on-board communication platform and a ground communication platform, The on-board communication platform includes: a route control unit that distributes the packets to the plurality of wireless routes; a communication status determination unit that determines a communication status between the ground communication platform and the on-board communication platform, when receiving a repeat request from the terrestrial communications platform; The communication status determination unit notifies the route control unit of quality information of the plurality of wireless routes; The route control unit determines a required quality based on source information contained in the packet that is the subject of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on the results of the evaluation.

2. 2. The railway communication system according to claim 1, The on-board communication platform includes: A database having available bandwidth information for each location and / or each time for the plurality of wireless paths is further provided, The route control unit evaluates the plurality of wireless routes from available bandwidth information held in the database, and selects a wireless route to be used for retransmission from among the plurality of wireless routes based on a result of the evaluation. A railway communication system comprising:

3. 2. The railway communication system according to claim 1, The communication status determination unit determines a transmission weight of the plurality of wireless paths and instructs the path control unit to retransmit the signal. A railway communication system comprising:

4. 2. The railway communication system according to claim 1, the communication status determination unit notifies the plurality of applications of a communication capacity limit; A notification is issued to an application having a low priority among the plurality of applications to stop transmission or to reduce a bit rate. A railway communication system comprising:

5. An on-board communication platform that transmits packets generated from a plurality of applications between ground and on-board vehicles to a ground communication platform using a plurality of wireless paths, a route control unit that distributes the packets to the plurality of wireless routes; a communication status determination unit that determines a communication status between the ground communication platform and the on-board communication platform, when receiving a repeat request from the terrestrial communications platform; The communication status determination unit notifies the route control unit of quality information of the plurality of wireless routes; The route control unit determines a required quality based on source information contained in the packet that is the subject of the retransmission request, evaluates the multiple wireless routes based on the required quality and the quality information, and selects a wireless route to be used for retransmission from among the multiple wireless routes based on a result of the evaluation.

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