A method and system for seamless handover of a train between LTE and WLAN links

Abstract

This invention provides a method and system for seamless switching between LTE and WLAN links in a train, relating to the field of wireless communication technology. The method includes: during train operation, establishing a first general routing encapsulation tunnel and a second general routing encapsulation tunnel with a trackside ground network via both the LTE and WLAN networks; periodically detecting the first link quality of the first general routing encapsulation tunnel and the second link quality of the second general routing encapsulation tunnel; and using the second general routing encapsulation tunnel as the service bearer link between the train and the ground network when the second link quality is superior to the first link quality; and using the first general routing encapsulation tunnel as the service bearer link when the second link quality is not superior to the first link quality. The beneficial effect is that the seamless switching between LTE and WLAN links is controlled based on the first and second link quality, ensuring that the train's service bearer link always has superior link quality.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a method and system for seamless switching between LTE and WLAN links in a train. Background Technology

[0002] Since the Radio Management Committee approved the use of the 1785–1805 MHz frequency band as a dedicated frequency band for industries such as rail transit, LTE (Long Term Evolution) has become more suitable for carrying vehicle-to-ground communication information for rail transit signaling systems due to its advantages such as wireless security, high-speed mobility, and the fact that dedicated frequency bands are less susceptible to interference.

[0003] With the widespread adoption of LTE technology, the application of WLAN (Wireless Local Area Network) in subway signaling systems is gradually being replaced by LTE. Lines previously using WLAN technology will inevitably face the technical transformation of train-to-ground wireless networks and the construction of extension lines. This inevitably involves the compatibility and switching between the two technologies, and how to achieve a smooth switch between LTE and WLAN has become an urgent technical problem to be solved. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for seamless switching between LTE and WLAN links in a train. Multiple ground network terminals are installed alongside the train's track, and the train is equipped with a train terminal, an LTE network terminal, and a WLAN network terminal. The method includes:

[0005] Step S1: During the train's operation, the train terminal establishes a first general routing encapsulation tunnel between the LTE network terminal and the ground network terminal, and establishes a second general routing encapsulation tunnel between the WLAN network terminal and the ground network terminal.

[0006] Step S2: The train end periodically detects the first link quality of the first general routing encapsulation tunnel and the second link quality of the second general routing encapsulation tunnel, and determines whether the second link quality is better than the first link quality.

[0007] If so, the second general route encapsulation tunnel is used as the service bearer link between the train and the ground network, and then the process returns to step S2;

[0008] If not, the first general route encapsulation tunnel is used as the service bearer link between the train and the ground network, and then the process returns to step S2.

[0009] Preferably, the terrestrial network continuously sends corresponding bidirectional forwarding detection packets through the first general routing encapsulation tunnel and the second general routing encapsulation tunnel according to a preset first period; then step S2 includes:

[0010] Step S21: The train end periodically counts the bidirectional forwarding detection packets received through the first general routing encapsulation tunnel and the second general routing encapsulation tunnel to obtain corresponding first count values ​​and second count values.

[0011] Step S22: The train terminal subtracts one from the first count value according to a preset second cycle to obtain a third count value, and determines whether the third count value is less than a first threshold.

[0012] If so, proceed to step S23;

[0013] If not, it indicates that the quality of the second link is not better than the quality of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and the third count value is used as the first count value. Then, return to step S21.

[0014] Step S23: The train terminal subtracts one from the second count value according to the second cycle to obtain a fourth count value, and determines whether the fourth count value is less than the first threshold.

[0015] If so, it indicates that the quality of the second link is not better than that of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. The third count value is used as the first count value and the fourth count value is used as the second count value. Then, the process returns to step S21.

[0016] If not, it indicates that the quality of the second link is better than that of the first link. The second general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. The third count value is used as the first count value and the fourth count value is used as the second count value. Then, the process returns to step S21.

[0017] Preferably, the second period is longer than the first period.

[0018] Preferably, when the quality of the second link is not better than that of the first link, if the current service bearer link is the second general routing encapsulation tunnel, then step S2, the process of using the first general routing encapsulation tunnel as the service bearer link, includes:

[0019] The train terminal switches the uplink route of the service bearer link to the first general route encapsulation tunnel, and

[0020] The train end discards the bidirectional forwarding detection packet received by the second general routing encapsulation tunnel to trigger the corresponding connected ground network end to switch the downlink route of the service bearer link to the first general routing encapsulation tunnel.

[0021] Preferably, when the quality of the second link is better than that of the first link, if the current service bearer link is the first general routing encapsulation tunnel, then step S2, the process of switching the service bearer link to the second general routing encapsulation tunnel, includes:

[0022] The train terminal switches the uplink route of the service bearer link to the second general route encapsulation tunnel, and

[0023] The train end discards the bidirectional forwarding detection packet received by the first general routing encapsulation tunnel, thereby triggering the corresponding connected ground network end to switch the downlink route of the service bearer link to the second general routing encapsulation tunnel.

[0024] Preferably, the train end is equipped with cell identifiers associated with each LTE signal coverage area corresponding to each of the ground network ends distributed along the train's running track;

[0025] Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the first general routing encapsulation tunnel, then the following steps are executed:

[0026] The train continuously determines whether it has obtained the last cell identifier of the LTE signal coverage area it is currently in:

[0027] If so, the train terminal detects the quality of the first link and the quality of the second link in real time until the quality of the second link is better than the quality of the first link. Then, the service bearer link is switched to the second general route encapsulation tunnel and the process proceeds to step S2.

[0028] If not, proceed directly to step S2.

[0029] Preferably, the train end is equipped with cell identifiers associated with each LTE signal coverage area corresponding to each of the ground network ends distributed along the train's running track;

[0030] Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the second general routing encapsulation tunnel, then the following steps are executed:

[0031] The train continuously determines whether it has obtained the first cell identifier of the LTE signal coverage area adjacent to the current WLAN signal coverage area:

[0032] If so, the train terminal will monitor the quality of the first link and the quality of the second link in real time until the quality of the second link is no better than the quality of the first link. Then, the service bearer link will be switched to the first general route encapsulation tunnel and the process will proceed to step S2.

[0033] If not, proceed directly to step S2.

[0034] Preferably, in step S2, after the first general route encapsulation tunnel is used as the service bearer link, the train terminal is also configured with a first switched-over flag.

[0035] If, within a first preset time period after configuring the first switched flag, the train terminal detects that the quality of the second link is better than that of the first link, it will not use the second general route encapsulation tunnel as the service bearer link.

[0036] Preferably, in step S2, after the second general routing encapsulation link is used as the service bearer link, the train terminal also configures a second switched-over flag accordingly.

[0037] If, within a second preset time period after configuring the second switched flag, the train terminal detects that the quality of the second link is not better than that of the first link, it will not use the first general route encapsulation tunnel as the service bearer link.

[0038] The present invention also provides a system for seamless switching between LTE and WLAN links in a train, using the above-described method, the system comprising:

[0039] Multiple ground network terminals are installed beside the train's running track;

[0040] The train end establishes network communication with each of the aforementioned ground network ends via both an LTE network end and a WLAN network end. The train end includes:

[0041] A communication tunnel establishment module is used to establish a first general route encapsulation tunnel between the LTE network terminal and the ground network terminal during the train's operation, and to establish a second general route encapsulation tunnel between the WLAN network terminal and the ground network terminal.

[0042] The seamless link switching module, connected to the communication tunnel establishment module, is used to periodically detect the first link quality of the first general routing encapsulation tunnel and the second link quality of the second general routing encapsulation tunnel. When the second link quality is better than the first link quality, the second general routing encapsulation tunnel is used as the service bearer link between the train end and the ground network end. When the second link quality is not better than the first link quality, the first general routing encapsulation tunnel is used as the service bearer link between the train end and the ground network end.

[0043] The above technical solution has the following advantages or beneficial effects:

[0044] 1) By periodically detecting the first link quality of the first general routing encapsulation tunnel associated with the LTE network and the second link quality of the second general routing encapsulation tunnel associated with the WLAN network, and controlling the seamless switching of the LTE link and the WLAN link based on the first link quality and the second link quality, the service carrying link of the train always has better link quality.

[0045] 2) The link quality of the first general routing encapsulation tunnel and the second general routing encapsulation tunnel is obtained through the rapid diagnostic mechanism of bidirectional forwarding detection echo function. This enables the switching of uplink routes based on L link quality, while discarding bidirectional forwarding detection packets with poor link quality to trigger the switching of downlink routes, thereby achieving seamless switching between LET links and WLAN links. Attached Figure Description

[0046] Figure 1 A flowchart illustrating a method for seamless switching between LTE and WLAN links in a train, as described in a preferred embodiment of the present invention.

[0047] Figure 2 In a preferred embodiment of the present invention, a wireless signal distribution diagram is shown beside the train track;

[0048] Figure 3 This is a schematic diagram of a sub-process of step S2 in a preferred embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of a system for seamless switching between LTE and WLAN links in a train, as a preferred embodiment of the present invention. Detailed Implementation

[0050] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention.

[0051] In a preferred embodiment of the present invention, based on the aforementioned problems existing in the prior art, a method for seamless switching between LTE and WLAN links in a train is provided. Multiple ground network terminals are installed beside the train's track, and the train is equipped with a train terminal, an LTE network terminal, and a WLAN network terminal. Figure 1 As shown, the method includes:

[0052] Step S1: During train operation, the train establishes a first general routing encapsulation tunnel between the LTE network and the ground network, and a second general routing encapsulation tunnel between the WLAN network and the ground network.

[0053] Step S2: The train periodically checks the quality of the first link in the first general route encapsulation tunnel and the quality of the second link in the second general route encapsulation tunnel, and determines whether the quality of the second link is better than the quality of the first link.

[0054] If so, the second general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and then the process returns to step S2;

[0055] If not, the first general route encapsulation tunnel will be used as the service bearer link between the train and the ground network, and then the process will return to step S2.

[0056] Specifically, typical application scenarios of this technical solution are as follows: Figure 2 As shown, area S is a parking garage, equipped with both LTE and WLAN ground network terminals, meaning area S is a shared coverage area for both LTE and WLAN signals. Areas A and D are newly renovated road sections, equipped only with LTE ground network terminals, meaning areas A and D are LTE coverage areas. Area C is an older road section that has not yet been renovated, equipped only with WLAN ground network terminals, meaning area C is a WLAN coverage area. Area B, located between areas A and C, has both LTE and WLAN coverage, meaning area B is a shared coverage area for both LTE and WLAN signals. The aforementioned ground network terminals are ground switches.

[0057] Taking a vehicle traveling from area S through areas A and B to area C as an example, the train performs link switching control during travel based on the detected first link quality of the first general route encapsulation tunnel and the second link quality of the second general route encapsulation tunnel. It can be understood that when the vehicle travels from area S to area A, since area A only has LTE signal coverage, the detected first link quality of the first general route encapsulation tunnel will gradually improve. When the second link quality is not better than the first link quality, the service bearer link between the train and the ground network is switched to the first general route encapsulation tunnel. When the vehicle travels from area A to area B, since this area is simultaneously covered by LTE and WLAN signals, there is a process of switching from the LTE link to the WLAN link. In this embodiment, when the second link quality is better than the first link quality, the LTE link is controlled to switch to the WLAN link; otherwise, the LTE link is maintained. This process continues, ensuring that the service bearer link maintains relatively good link quality regardless of whether the train is traveling in an area covered by only one network signal or an area covered by two network signals.

[0058] In a preferred embodiment of the present invention, the terrestrial network continuously sends corresponding bidirectional forwarding detection packets through a first general routing encapsulation tunnel and a second general routing encapsulation tunnel according to a preset first period; such as Figure 3 As shown, step S2 includes:

[0059] Step S21: The train periodically counts the bidirectional forwarding detection packets received through the first general routing encapsulation tunnel and the second general routing encapsulation tunnel to obtain the corresponding first count value and second count value.

[0060] Step S22: The train decrements the first count value by one according to the preset second cycle to obtain the third count value, and determines whether the third count value is less than the first threshold.

[0061] If so, proceed to step S23;

[0062] If not, it indicates that the quality of the second link is not better than that of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and the third count value is used as the first count value. Then, return to step S21.

[0063] Step S23: The train decrements the second count value by one according to the second cycle to obtain the fourth count value, and determines whether the fourth count value is less than the first threshold.

[0064] If so, it indicates that the quality of the second link is not better than that of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and the third count value is used as the first count value and the fourth count value is used as the second count value. Then, return to step S21.

[0065] If not, it indicates that the quality of the second link is better than that of the first link. The second general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. The third count value is used as the first count value and the fourth count value is used as the second count value. Then, return to step S21.

[0066] Specifically, taking the first link quality detection of the first general route encapsulation tunnel as an example, the train end periodically counts the bidirectional forwarding detection packets received through the first general route encapsulation tunnel to obtain the corresponding first count value. In other words, the train end counts once for each bidirectional forwarding detection packet (i.e., BFD keep-alive packet) received. It can be understood that if the first link quality is good, the train end can receive one bidirectional forwarding detection packet for each bidirectional forwarding detection packet sent by the ground network end according to the first period.

[0067] In this embodiment, a timer is configured on the train end. The timer's timing period is the second period. That is, the timer starts counting when the train end begins the first period. The train end counts once for each bidirectional forwarding detection packet received. Each time the timer reaches the second period, the first count value is decremented by one. Assuming the second period is longer than the first period, if the ground network sends a bidirectional forwarding detection packet every 10 seconds, then under good link quality, the first count value on the train end is 3 after 30 seconds. If the train end decrements the first count value by one every 30 seconds, the third count value is 2. After another 30 seconds, the first count value is 5, and after decrementing by one, it is 4. It can be seen that if the link quality is good, the third count value is in an increasing state. If the link quality is poor, that is, if the ground network still sends a bidirectional forwarding detection packet every 10 seconds, but the train end does not receive every bidirectional forwarding detection packet, but still decrements by one at the end of the second period, then the third count value may be in a decreasing state, or even decrease to 0. Based on this, in this embodiment, a first threshold is configured to determine link quality. If the third count value is less than the first threshold, the first link quality of the corresponding first general route encapsulation tunnel is considered to be in an unstable state (which may occur in situations such as...). Figure 2 In the case of a location near area C in zone B, in an extreme case, the third count value can be zero, indicating that the link of the corresponding first general routing encapsulation tunnel is not working (this may occur in zone C). If the third count value is not less than the first threshold, the first link quality of the first general routing encapsulation tunnel is considered good, and the first general routing encapsulation tunnel can be used as the preferred service bearer link. If the current link is an LTE link, it remains so; if the current link is a WLAN link, it switches to the LTE link. The second cycle is preferably not less than twice the first cycle.

[0068] The second link quality detection process and link switching process of the second general route encapsulation tunnel are similar and will not be described in detail here.

[0069] In a preferred embodiment of the present invention, when the quality of the second link is not better than that of the first link, if the current service bearer link is a second general route encapsulation tunnel, then step S2, the process of using the first general route encapsulation tunnel as the service bearer link, includes:

[0070] The train end switches the uplink route of the service-bearing link to the first general route encapsulation tunnel, and

[0071] The train discards the bidirectional forwarding detection packets received in the second general route encapsulation tunnel to trigger the corresponding ground network to switch the downlink route of the service bearer link to the first general route encapsulation tunnel.

[0072] In a preferred embodiment of the present invention, when the quality of the second link is better than that of the first link, if the current service bearer link is a first general route encapsulation tunnel, then step S2, the process of switching the service bearer link to the second general route encapsulation tunnel, includes:

[0073] The train end switches the uplink route of the service-bearing link to the second general route encapsulation tunnel, and

[0074] The train discards the bidirectional forwarding detection packets received in the first general route encapsulation tunnel to trigger the corresponding ground network to switch the downlink route of the service bearer link to the second general route encapsulation tunnel.

[0075] Specifically, in this embodiment, taking the first general routing encapsulation tunnel (GRE (Generic Routing Encapsulation Protocol) tunnel) established between the LTE network and the terrestrial network as T1 tunnel, and the second general routing encapsulation tunnel (GRE (Generic Routing Encapsulation Protocol) tunnel) established between the WLAN network and the terrestrial network as T2 tunnel, the downlink route of the terrestrial network going through T1 tunnel is bound to the bidirectional forwarding detection packet (BFD keep-alive packet) of T1 tunnel, and the downlink route of the terrestrial network going through T2 tunnel is bound to the bidirectional forwarding detection packet (BFD keep-alive packet) of T2 tunnel. If the terrestrial network does not receive the BFDECHO response packet sent from T1 tunnel for N consecutive times (N is configurable), the downlink route going through T1 tunnel is deleted; otherwise, the downlink route going through T1 tunnel is set. The operation principle of T2 tunnel is the same as that of T1 tunnel. In this embodiment, if the quality of the first link of the first general route encapsulation tunnel is good, the train, after receiving the bidirectional forwarding detection packet, not only counts the bidirectional forwarding detection packets but also sends a corresponding BFDECHO response packet back to the ground network through the first general route encapsulation tunnel. If the quality of the first link of the first general route encapsulation tunnel is poor, the train discards the bidirectional forwarding detection packets received by the first general route encapsulation tunnel, and the ground network cannot receive the BFDECHO response packet sent from the T1 tunnel. The second general route encapsulation tunnel follows the same principle.

[0076] In a preferred embodiment of the present invention, the train end is configured with cell identifiers associated with each LTE signal coverage area corresponding to each ground network end distributed along the train's running track;

[0077] Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the first general routing encapsulation tunnel, the following steps are executed:

[0078] The train continuously determines whether it has obtained the identifier of the last cell in the current LTE signal coverage area:

[0079] If so, the train will monitor the quality of the first link and the quality of the second link in real time until the quality of the second link is better than that of the first link. Then, the service bearer link will be switched to the second general route encapsulation tunnel and the process will proceed to step S2.

[0080] If not, proceed directly to step S2.

[0081] In a preferred embodiment of the present invention, the train end is configured with cell identifiers associated with each LTE signal coverage area corresponding to each ground network end distributed along the train's running track;

[0082] Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the second general routing encapsulation tunnel, the following steps are executed:

[0083] The train continuously determines whether it has obtained the cell identifier of the first LTE signal coverage area adjacent to the current WLAN signal coverage area:

[0084] If so, the train will monitor the quality of the first link and the quality of the second link in real time until the quality of the second link is no better than the quality of the first link. Then, the service bearer link will be switched to the first general route encapsulation tunnel and the process will proceed to step S2.

[0085] If not, proceed directly to step S2.

[0086] Specifically, since the train periodically checks the quality of the first and second links, and the subsequent detection cycle is relatively short, there is still a possibility of untimely handover. Based on this, in this embodiment, it can be determined whether the train is about to enter the common coverage area of ​​LTE and WLAN signals based on whether the cell identifier is detected, so as to prepare for link handover in advance and further improve the timeliness of link handover.

[0087] More specifically, taking the current service-bearing link as the first general route encapsulation tunnel as an example, it is assumed that the train is currently traveling in a tunnel such as... Figure 2 In the example shown for area A, the cell associated with the end of area A facing the garage is preferably designated as the first cell, and the cell associated with the end of area A facing area C is designated as the last cell. The corresponding cell identifiers can be configured according to the actual train operation. During the journey to area C, the system continuously checks whether the last cell identifier of area A is obtained. If detected, it indicates that the train is about to reach area B. At this point, the system continuously monitors the quality of the first link in the first general routing encapsulation tunnel and the second link in the second general routing encapsulation tunnel, preparing to switch to the WLAN link until the quality of the second link is better than that of the first link. Subsequently, the service bearer link is switched to the second general routing encapsulation tunnel, completing the switch to the WLAN link. The process of preparing for the switch of the current service bearer link to the second general routing encapsulation tunnel is repeated in this manner.

[0088] More specifically, considering that in areas where LTE and WLAN signals share coverage, signal fluctuations may cause inconsistencies in the detected link quality at different times. That is, the second link quality might be better than the first link quality at one moment, and better at another. This could lead to the service bearer link switching back and forth between the LTE and WLAN links, resulting in significant delays in service data. Therefore, in a preferred embodiment of the present invention, in step S2, after using the first general route encapsulation tunnel as the service bearer link, the train end also configures a corresponding first switched-over flag.

[0089] If, within the first preset time period after configuring the first switched flag, the train detects that the quality of the second link is better than that of the first link, it will not use the second general route encapsulation tunnel as a service carrying link.

[0090] In this embodiment, by configuring the first switched flag, the switching between the LTE link and the WLAN link caused by short-term signal fluctuations can be effectively avoided.

[0091] In a preferred embodiment of the present invention, in step S2, after the second general route encapsulation link is used as the service bearer link, the train end also configures a second switched-over flag accordingly.

[0092] If, within the second preset time period after configuring the second switched flag, the train detects that the quality of the second link is not better than that of the first link, it will not use the first general route encapsulation tunnel as a service carrying link.

[0093] In this embodiment, by configuring a second switched flag, the switching between the LTE link and the WLAN link caused by short-term signal fluctuations can be effectively avoided.

[0094] This invention also provides a system for seamless switching between LTE and WLAN links in trains, applying the methods described above, such as... Figure 4 As shown, the system includes:

[0095] Multiple ground network terminals 1 are installed beside the train's running track;

[0096] Train terminal 2 establishes network communication with local ground network terminals via LTE network terminal 21 and WLAN network terminal 22 respectively. Train terminal 2 includes:

[0097] The communication tunnel establishment module 23 is used to establish a first general route encapsulation tunnel between the LTE network terminal and the ground network terminal during train operation, and to establish a second general route encapsulation tunnel between the WLAN network terminal and the ground network terminal.

[0098] The seamless link switching module 24 and the connection communication tunnel establishment module 23 are used to periodically detect the first link quality of the first general route encapsulation tunnel and the second link quality of the second general route encapsulation tunnel. When the second link quality is better than the first link quality, the second general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. When the second link quality is not better than the first link quality, the first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end.

[0099] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made using the content of this specification and illustrations should be included within the protection scope of the present invention.

Claims

1. A method for seamless switching between LTE and WLAN links in a train, characterized in that, Multiple ground network terminals are installed alongside the train's track, and the train is equipped with a train terminal, an LTE network terminal, and a WLAN network terminal; therefore, the method includes: Step S1: During the train's operation, the train terminal establishes a first general routing encapsulation tunnel between the LTE network terminal and the ground network terminal, and establishes a second general routing encapsulation tunnel between the WLAN network terminal and the ground network terminal. Step S2: The train end periodically detects the first link quality of the first general routing encapsulation tunnel and the second link quality of the second general routing encapsulation tunnel, and determines whether the second link quality is better than the first link quality. If so, the second general route encapsulation tunnel is used as the service bearer link between the train and the ground network, and then the process returns to step S2; If not, the first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and then the process returns to step S2; The ground network terminal continuously sends corresponding bidirectional forwarding detection packets through the first general routing encapsulation tunnel and the second general routing encapsulation tunnel according to a preset first cycle. Then step S2 includes: Step S21: The train end periodically counts the bidirectional forwarding detection packets received through the first general routing encapsulation tunnel and the second general routing encapsulation tunnel to obtain corresponding first count values ​​and second count values. Step S22: The train terminal subtracts one from the first count value according to a preset second cycle to obtain a third count value, and determines whether the third count value is less than a first threshold. If so, proceed to step S23; If not, it indicates that the quality of the second link is not better than that of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end, and the third count value is used as the first count value. Then, return to step S21. Step S23: The train terminal subtracts one from the second count value according to the second cycle to obtain a fourth count value, and determines whether the fourth count value is less than the first threshold. If so, it indicates that the quality of the second link is not better than that of the first link. The first general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. The third count value is used as the first count value and the fourth count value is used as the second count value. Then, the process returns to step S21. If not, it indicates that the quality of the second link is better than that of the first link. The second general route encapsulation tunnel is used as the service bearer link between the train end and the ground network end. The third count value is used as the first count value and the fourth count value is used as the second count value. Then, return to step S21. The ground network terminal binds the downlink route of the first general route encapsulation tunnel to the bidirectional forwarding detection packet of the first general route encapsulation tunnel, and binds the downlink route of the second general route encapsulation tunnel to the bidirectional forwarding detection packet of the second general route encapsulation tunnel; the train terminal controls the downlink route status of the ground network terminal by feeding back or discarding the bidirectional forwarding detection packet based on the binding relationship, so as to trigger the corresponding connected ground network terminal to switch the downlink route of the service bearer link to the general route encapsulation tunnel currently serving as the service bearer link.

2. The method according to claim 1, characterized in that, The second period is longer than the first period.

3. The method according to claim 1, characterized in that, When the quality of the second link is not better than that of the first link, if the current service bearer link is the second general route encapsulation tunnel, then step S2, the process of using the first general route encapsulation tunnel as the service bearer link, includes: The train terminal switches the uplink route of the service bearer link to the first general route encapsulation tunnel, and The train end discards the bidirectional forwarding detection packet received by the second general routing encapsulation tunnel to trigger the corresponding connected ground network end to switch the downlink route of the service bearer link to the first general routing encapsulation tunnel.

4. The method according to claim 1, characterized in that, When the quality of the second link is better than that of the first link, if the current service bearer link is the first general routing encapsulation tunnel, then step S2, the process of switching the service bearer link to the second general routing encapsulation tunnel, includes: The train terminal switches the uplink route of the service bearer link to the second general route encapsulation tunnel, and The train end discards the bidirectional forwarding detection packet received by the first general routing encapsulation tunnel, thereby triggering the corresponding connected ground network end to switch the downlink route of the service bearer link to the second general routing encapsulation tunnel.

5. The method according to claim 1, characterized in that, The train end is equipped with cell identifiers associated with each LTE signal coverage area corresponding to each of the ground network ends distributed along the train's running track. Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the first general routing encapsulation tunnel, then the following steps are executed: The train continuously determines whether it has obtained the last cell identifier of the LTE signal coverage area it is currently in: If so, the train terminal detects the quality of the first link and the quality of the second link in real time until the quality of the second link is better than the quality of the first link. Then, the service bearer link is switched to the second general route encapsulation tunnel and the process proceeds to step S2. If not, proceed directly to step S2.

6. The method according to claim 1, characterized in that, The train end is equipped with cell identifiers associated with each LTE signal coverage area corresponding to each of the ground network ends distributed along the train's running track. Once the first general routing encapsulation tunnel and the second general routing encapsulation tunnel are established between the train and the ground network, if the current service bearer link is the second general routing encapsulation tunnel, then the following steps are executed: The train continuously determines whether it has obtained the first cell identifier of the LTE signal coverage area adjacent to the current WLAN signal coverage area: If so, the train terminal will monitor the quality of the first link and the quality of the second link in real time until the quality of the second link is no better than the quality of the first link. Then, the service bearer link will be switched to the first general route encapsulation tunnel and the process will proceed to step S2. If not, proceed directly to step S2.

7. The method according to claim 1, characterized in that, In step S2, after the first general route encapsulation tunnel is used as the service bearer link, the train terminal is also configured with a first switched flag. If, within a first preset time period after configuring the first switched flag, the train terminal detects that the quality of the second link is better than that of the first link, it will not use the second general route encapsulation tunnel as the service bearer link.

8. The method according to claim 1, characterized in that, In step S2, after the second general route encapsulation tunnel is used as the service bearer link, the train terminal is also configured with a second switched flag. If, within a second preset time period after configuring the second switched flag, the train terminal detects that the quality of the second link is not better than the quality of the first link, it will not use the first general route encapsulation tunnel as the service bearer link.

9. A system for seamless switching between LTE and WLAN links in a train, characterized in that, The system comprising the method described in any one of claims 1-8, wherein the system includes: Multiple ground network terminals are installed beside the train's running track; The train end establishes network communication with each of the aforementioned ground network ends via both an LTE network end and a WLAN network end. The train end includes: A communication tunnel establishment module is used to establish a first general route encapsulation tunnel between the LTE network terminal and the ground network terminal during the train's operation, and to establish a second general route encapsulation tunnel between the WLAN network terminal and the ground network terminal. The seamless link switching module, connected to the communication tunnel establishment module, is used to periodically detect the first link quality of the first general routing encapsulation tunnel and the second link quality of the second general routing encapsulation tunnel. When the second link quality is better than the first link quality, the second general routing encapsulation tunnel is used as the service bearer link between the train end and the ground network end. When the second link quality is not better than the first link quality, the first general routing encapsulation tunnel is used as the service bearer link between the train end and the ground network end.

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