CN103634860A - Fast switching method in wireless communication system, system and client - Google Patents

Abstract

The invention discloses a fast switching method in a wireless communication system, a fast switching system, a client and an access point AP. The method includes: when the client decides to switch, the client establishes a virtual link between its current AP and a candidate AP, and the virtual link includes a communication link between the client and the current AP and the communication link between the current AP and the candidate AP; the client sends a probe request to the candidate AP through the virtual link and receives a probe response of the candidate AP; according to the candidate AP The client selects a target AP from the candidate APs; the client sends an association request to the target AP through the virtual link and receives an association response from the target AP; when the When the client starts switching, the client terminates communication with the current AP and switches to the target AP. Using this method, the switching time can be greatly reduced.

Description

Fast handover method, system and client in wireless communication system

technical field

The invention relates to the field of wireless communication, in particular to a fast switching method in a wireless communication system in a rail transit system, a fast switching system, a client and an access point AP.

Background technique

At present, with the development of urbanization, the rail transit system is becoming more and more popular. Current rail transit systems use wireless communication technology to communicate between trains and roads. In a rail transit system, a typical application scenario for communication between trains and roads based on wireless local area network (WLAN) is shown in Figure 1. As shown in Figure 1, multiple access points (APs) are set on the road (for clarity, only three APs, AP0, AP1, and AP2 are shown in Figure 1), with a specific distance between every two adjacent APs. to ensure that there are no coverage holes. The client is on the side of the train and can communicate with one of the APs covering it. Through this communication connection, the client on the train can communicate with the server on the roadside through the access point, and this AP is called the current AP of the client.

When the train moves, the client will leave the coverage of the current AP and interrupt the communication with the current AP. At this time, the client needs to switch to another AP (called the target AP) to ensure normal communication. Therefore, the handover mechanism is very critical to ensure reliable and uninterrupted communication between the client and the AP.

In order to establish a communication connection with the target AP, multiple bidirectional information exchanges need to be performed between the client and the target AP, as shown in FIG. 2 . The client sends a Probe request to the target AP, and the target AP returns a Probe response to the client; the client sends an association request to the target AP, and the target AP returns an association response to the client. ). In application scenarios with high security requirements, the client also needs to send an authentication request (Authentication request) to the target AP, and the target AP returns an authentication response (Authentication response) to the client; if the client passes the authentication, then The client establishes a communication connection with the target AP, and the target AP becomes the current AP of the client.

In the example shown in Figure 1, both the AP and the client use directional antennas, which are very common in rail transit systems. However, using a directional antenna usually causes the strength of the signal received by the client to suddenly weaken when passing through the current AP.

In the example shown in FIG. 1 , the current AP of the client is AP1, and when the client moves from right to left to point B, the strength of the signal sent from AP1 suddenly becomes weaker. When the communication with AP1 is completely disconnected, the client must try to switch to another AP (that is, the target AP, which is AP2 in Figure 1) to maintain the communication with the server. In order to ensure the reliability of communication, the shorter the time for the client to switch from the current AP to the target AP, the better. In the prior art, the switching shown in FIG. 1 takes more than 100 ms, that is, the data transmission is interrupted during the 100 ms. In the rail transit system, whether it is passenger information or train control information, such a long interruption of 100ms is unbearable. Therefore, some kind of fast switching mechanism is needed to reduce the switching time.

The handover process of a client handing over from one AP to another AP can generally be divided into two phases: a handover decision phase and a connection establishment phase. Existing fast handover mechanisms are generally implemented by reducing handover decision time or reducing connection establishment time.

A fast switching method in the prior art is shown in FIG. 3 , AP1 is the current AP of the client, and when the client moves to point A close to AP1, the client starts switching. In this case, when the signal strength of AP1 received by the client is still strong and higher than the handover threshold, the handover starts. This can avoid the situation that when the client moves to point B, the strength of the signal sent by AP1 becomes weak suddenly. Therefore, adopting this method can reduce the situation that the communication between the client and its current AP is suddenly interrupted. Moreover, if this method is combined with the background scanning (background scanning) method in the prior art (the client continuously scans all channels in an idle state to collect candidate AP information), it can help reduce the handover decision time.

However, in this method, the client starts to switch when the strength of the signal sent by the current AP is still strong, so more overlapping coverage areas are needed between the current AP and the target AP to ensure that the signal at the switching point Able to correctly receive the signal from the target AP, which increases the number of APs. If the distance between the original APs is still maintained, the strength of the signal from the target AP may be relatively weak, which will seriously affect the handover process. In the worst case, the probe request, association request and authentication request sent by the client are all lost at the target AP side, so multiple retransmissions are required, which increases the connection establishment time, thereby negating the advantages obtained in the handover decision phase . Moreover, this method cannot reduce the time to establish a connection with the target AP after the connection with the current AP is disconnected.

When the client establishes a connection with the target AP, authentication will take a lot of time. If using an authentication server, it will take more than 100ms. Another fast handover method in the prior art is the pre-authentication method: in the IEEE802.11x standard, the client can perform a pre-authentication operation with the authentication server before the handover starts, thereby reducing the connection establishment time. However, this pre-authentication method can only reduce the authentication operation time with the authentication server, but cannot reduce the time for other operations in the connection establishment process, nor can it reduce the switching decision time.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a fast switching method, a fast switching system, a client and an AP in a wireless communication system, so as to effectively reduce the switching time for a client to switch from a current AP to a target AP.

To achieve the above purpose, an embodiment of the fast handover method in the wireless communication system according to the present invention includes:

When the client decides to switch, the client establishes a virtual link between its current access point AP and the candidate AP, and the virtual link includes the communication link between the client and the current AP and a communication link between the current AP and the candidate AP;

The client sends a probe request to the candidate AP through the virtual link and receives a probe response from the candidate AP;

According to the probe response of the candidate AP, the client selects a target AP from the candidate APs;

The client sends an association request to the target AP through the virtual link and receives an association response from the target AP;

When the client starts switching, the client terminates communication with the current AP and switches to the target AP.

Another embodiment of the fast handover method in the wireless communication system according to the present invention includes:

When the client decides to switch, the current access point AP of the client is used to establish a virtual link between the client and the candidate AP, and the virtual link includes the connection between the client and the current AP. and the communication link between the current AP and the candidate AP;

The current AP receives the detection request sent by the client to the candidate AP through the virtual link and forwards the detection request to the candidate AP, and receives the detection request from the candidate AP to the candidate AP through the virtual link. the probe response sent by the client and forward the probe response to the client;

The current AP receives the association request sent by the client to the target AP through the virtual link and forwards the association request to the target AP, and receives the association request sent by the target AP to the target AP through the virtual link. the association response sent by the client and forward the association response to the client;

When the client starts switching, the current AP terminates communication with the client.

Another embodiment of the fast handover method in the wireless communication system according to the present invention includes:

When the client decides to switch, the candidate access point AP establishes a virtual link with the client through the current AP of the client, and the virtual link includes a communication link between the candidate AP and the current AP road and the communication link between the current AP and the client;

The candidate AP receives the probe request of the client through the virtual link and sends a probe response to the client;

The candidate AP receives the association request of the client through the virtual link and sends an association response to the client.

According to an embodiment of the fast switching system in the wireless communication system of the present invention, it includes a client and a plurality of wireless access points AP,

The client is used to, when it decides to switch, establish a virtual link between its current access point AP and a candidate AP, and the virtual link includes a communication link between the client and the current AP and the communication link between the current AP and the candidate AP; through the virtual link, send a detection request to the candidate AP and receive a detection response from the candidate AP; according to the detection of the candidate AP In response, select a target AP from the candidate APs; send an association request to the target AP through the virtual link and receive an association response from the target AP; when switching starts, terminate the communication with the current AP and switch to the target AP;

The current AP is used to establish the virtual link between the client and the candidate AP when the client decides to switch; A probe request sent by the candidate AP and forward the probe request to the candidate AP, and receive a probe response sent by the candidate AP to the client through the virtual link and forward the probe response to the client ; receiving the association request sent by the client to the target AP through the virtual link and forwarding the association request to the target AP, and receiving the association request sent by the target AP to the client through the virtual link sending an association response and forwarding the association response to the client; when the client starts switching, terminating communication with the client;

The candidate AP is used to, when the client decides to switch, establish the virtual link between the current AP of the client and the client; receive the detection request of the client through the virtual link and sending a probe response to the client; receiving an association request from the client through the virtual link and sending an association response to the client.

An embodiment of the fast switching client in the wireless communication system according to the present invention includes:

A first virtual link establishment module, configured to establish a virtual link between the client and a candidate AP through the current AP of the client when the client decides to switch, the virtual link includes the client A communication link between the terminal and the current AP and a communication link between the current AP and the candidate AP;

A first detection module, configured to send a detection request to the candidate AP through the virtual link and receive a detection response from the candidate AP;

A selection module, configured to select a target AP from the candidate APs according to the probe responses of the candidate APs;

A first association module, configured to send an association request to the target AP through the virtual link and receive an association response from the target AP;

The first switching module is configured to terminate communication with the current AP and switch to the target AP when the client starts switching.

An embodiment of the access point AP in the wireless communication system according to the present invention includes:

A second virtual link establishment module, configured to establish a virtual link between the client and a candidate AP when the client decides to switch, the virtual link includes communication between the client and the AP link and communication link between said AP and said candidate AP;

The second detection module is configured to receive the detection request sent by the client to the candidate AP through the virtual link and forward the detection request to the candidate AP, and receive the detection request sent by the candidate AP through the virtual link. sending a probe response to the client and forwarding the probe response to the client;

The second association module is configured to receive an association request sent by the client to the target AP through the virtual link and forward the association request to the target AP, and receive an association request sent by the target AP through the virtual link. sending an association response to the client and forwarding the association response to the client;

The second switching module is configured to terminate the communication with the client when the client starts to switch.

Another embodiment of the access point AP in the wireless communication system according to the present invention includes:

A third virtual link establishing module, configured to establish a virtual link between the AP and the client through the current AP of the client when the client decides to switch, the virtual link including the AP and the client a communication link between the current APs and a communication link between the current AP and the client;

A third detection module, configured to receive a detection request from the client through the virtual link and send a detection response to the client;

A third association module, configured to receive an association request from the client through the virtual link and send an association response to the client.

Description of drawings

FIG. 1 shows a schematic diagram of communication based on WLAN in a rail transit system in the prior art;

Fig. 2 shows a schematic diagram of information exchange for establishing a communication connection between a client and a candidate AP in the prior art;

FIG. 3 shows a schematic diagram of a fast switching method in the prior art;

FIG. 4 shows a flowchart of a fast handover method in a wireless communication system according to an embodiment of the present invention;

FIG. 5 shows a schematic diagram of a fast handover method in a wireless communication system according to an embodiment of the present invention;

Fig. 6 shows the flowchart of the fast switching method in the rail transit wireless communication system of an embodiment of the present invention;

FIG. 7 shows a schematic structural diagram of a fast switching client in a wireless communication system according to an embodiment of the present invention;

FIG. 8 shows a schematic structural diagram of a current AP in a wireless communication system according to an embodiment of the present invention;

FIG. 9 shows a schematic structural diagram of candidate APs in a wireless communication system according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

The embodiment of the present invention proposes a fast handover method in a wireless communication system. As shown in FIG. 4 , the method includes the following steps: Step 401, when the client decides to handover, the client passes between its current AP and candidate AP Establish a virtual link, which includes a communication link between the client and the current AP and a communication link between the current AP and the candidate AP; step 402, the client sends a detection request to the candidate AP through the virtual link And receive the probe response of the candidate AP; step 403, according to the probe response of the candidate AP, the client selects the target AP from the candidate AP; step 404, the client sends an association request to the target AP through the virtual link and receives the target AP association Response; step 405, when the client starts switching, the client terminates the communication with the current AP and switches to the target AP.

Taking a wireless communication scenario in a rail transit system as an example, the virtual link includes a wireless link between a client and a current AP, and a wired link between a current AP and a candidate AP. Fig. 5 shows a schematic diagram of a fast handover method in a wireless communication system according to an embodiment of the present invention. As shown in Figure 5, the current AP of the client is AP1. When the client moves to point A close to AP1, it decides to switch, and at this time, pre-handover starts.

The pre-handover mentioned in the embodiment of the present invention refers to the preparatory work done before the client switches from the current AP to another AP (ie, the target AP), such as operations such as detection, association, and authentication. In this embodiment, multiple methods may be used to determine the timing of handover, one of which may be to determine the timing of handover according to the strength of the signal sent by the current AP (that is, AP1 ). Because in the rail transit system, at least one of the client and the AP uses a directional antenna, so in Figure 5, when the client moves from right to left, the signal strength of AP1 will first become stronger and stronger, and when the client moves to A At point B, the signal strength reaches a threshold, after which the train will soon pass through AP1, and when the train moves to point B where AP1 is located, the signal strength will suddenly weaken. Therefore, in the embodiment of the present invention, when the client knows that the signal strength of AP1 exceeds a certain preset signal threshold, the client starts pre-handover, and the signal threshold can be preset according to empirical values. Another method may determine the timing of handover based on the location of the client. In this method, if all APs are fixed at a certain position on the road, the route of the train is also fixed, and the client has pre-stored the location information of all APs. When the train moves, the client can calculate The distance between it and AP1, when the distance is less than a preset distance threshold, indicates that the train will pass through AP1 soon, so pre-switching is required. Of course, those skilled in the art should understand that other methods can be used to determine the timing of handover according to the needs of actual applications, as long as the pre-handover is completed when the client moves from point A to point B where AP1 is located, these methods All should be within the protection scope of the present invention.

The specific implementation manner of the present invention will be described in detail below in conjunction with the flow chart of the fast switching method in the rail transit wireless communication system shown in FIG. 6 .

Step 601, when the client decides to switch, establish a virtual link between the client and the candidate AP, the virtual link includes the wireless link between the client and the current AP and the wired link between the current AP and the candidate AP road. In this step, with reference to the example shown in FIG. 5 , the current AP is AP1, and the client decides to switch when it moves to a location close to AP1 (that is, point A).

In the embodiment of the present invention, multiple methods may be used to determine candidate APs. One of the more commonly used methods is: all APs store their own location information and information about neighboring APs. When the client decides to switch, it sends a pre-handover request to AP1; after receiving the pre-handover request, AP1 includes the information of the neighbor AP in the pre-handover response and sends it to the client, where the information of the neighbor AP includes the neighbor AP location information. After receiving the neighbor AP information sent by AP1, the client selects the neighbor AP that is consistent with the train running direction from the neighbor APs sent by AP1 as the candidate AP according to the train running direction. The next or next two APs adjacent to AP1. Another method for determining candidate APs is: the client stores an AP list, and the list records AP information according to the order in which they are set up on the road. Because in the rail transit system, the running route of the train is fixed, so according to the list, the client can determine which AP to pass through, that is, according to the information of the current AP and the AP recorded in the list, the client can Identify candidate APs. Another way to determine candidate APs is to store information of all APs set on the road on a server, and the client can access the server through the current AP to obtain the information of the neighbor APs of the current AP, and then the client runs according to the train From the obtained neighbor APs, the neighbor APs that are consistent with the train running direction are selected as candidate APs. In addition, the client can also use the method in the prior art to continuously scan all channels in an idle state to collect candidate AP information. Of course, other methods may also be used to determine candidate APs, which is not limited in this embodiment of the present invention.

In the embodiment of the present invention, multiple methods may be used to establish a virtual link between the client and the candidate AP. One method may not make more changes to the client, but the current AP modifies its MAC address filter so that it can receive the message sent by the client to the candidate AP, and sends the message through the wired link between it and the candidate AP. The message is forwarded to the candidate AP. For example, with reference to the example shown in Figure 5, the current AP (that is, AP1) can add the MAC address of the candidate AP (such as AP2) to its MAC address filter, so that AP1 can receive the client through the wireless connection between AP1 and AP1. The link sends the message to AP2, and forwards the message to AP2 through the Ethernet link between it and AP2. Another method may not make more changes to the current AP, but the client sends the message it sends to the candidate AP to the current AP through the wireless link between it and the current AP, and then the current AP sends the message through the The wired link between it and the candidate AP is forwarded to the candidate AP; otherwise, the candidate AP sends the message it sends to the client to the current AP through the wired link between it and the current AP, and then the current AP communicates with the client through it. The wireless link between the peers forwards the message to the client. In the second method, if the client and the candidate AP are in the same subnet, the client can use the distributed flag (DS, Distribution flag) specified in the IEEE 802.11 standard in the message it sends to the current AP to indicate that the current The AP forwards the message whose destination MAC address is the candidate AP, so as to realize the communication with the candidate AP at the MAC layer; if the client and the candidate AP are in different subnets, the client can pass the IP route in the message it sends to the current AP. To instruct the current AP to forward the message whose destination IP address is the candidate AP, so as to realize the communication with the candidate AP at the IP layer (layer 3). With the first method, the current AP needs to re-encapsulate the message sent by the client to the candidate AP, and the client does not need to modify the header of the message. For the second method, the client needs to encapsulate the message forwarded by the current AP and the destination is the candidate AP, and the current AP does not need to re-encapsulate the message, but only needs to forward the message. The embodiment of the present invention does not limit the method for establishing a virtual link, and other methods that can be used should also fall within the protection scope of the present invention.

Step 602, the client sends a detection request to the candidate AP through the virtual link established between the client and the candidate AP.

With reference to the example shown in FIG. 5 , AP2 and AP3 are taken as candidate APs as examples for description. In the embodiment of the present invention, when the above-mentioned first method of establishing a virtual link is adopted, the client sends probe requests to AP2 and AP3 on its current channel, and AP1 modifies its MAC address filter to receive the client's request to AP2. and the detection request sent by AP3, and then AP1 repackages the received detection request and forwards it to AP2 and AP3 respectively through the Ethernet link. When adopting the above-mentioned second method of establishing a virtual link, the client can use the distributed label to send the probe request that needs to be sent to AP2 and AP3 to AP1 through its current channel, and AP1 sends the probe request through Ethernet The links are forwarded to AP2 and AP3 respectively. Wherein, the channel where the client is currently located refers to the channel through which the client communicates with AP1, that is, the channel of AP1.

Step 603, the candidate AP receives the probe request sent by the client through the virtual link and returns a probe response to the client.

After AP2 and AP3 receive the probe request, they can jump to measure the strength of the received signal on the channel indicated in the probe request, generate a Received Signal Strength Indicator (RSSI, Received Signal Strength Indicator), and store the RSSI value Included in the probe response and returned to the client through the established virtual link.

The channel indicated in the probe request is the channel on which the client is currently located, that is, the channel on which it communicates with AP1. Since the client still maintains communication with AP1 at this time, AP2 and AP3 can continuously monitor the packets sent by the client, so as to quickly obtain the RSSI value, which is beneficial for the client to reduce handover decision time.

In an application scenario where the client has multi-channel processing capabilities, the channel indicated in the probe request may also be the channel of AP2 or AP3, or other channels that can be used for the probe operation. For example, when the channel indicated in the probe request is the channel of AP2 or AP3, the client sends the probe message on the channel of AP2 and AP3 respectively, and AP2 and AP3 respectively measure the strength of the received signal on their channels and generate Receive the signal strength indicator value, and include the RSSI value in the probe response and return it to the client through the established virtual link.

After AP2 and AP3 receive the detection request forwarded by AP1, they can also jump to the channel of AP1 to measure the strength of the received signal according to the channel information of AP1 they store or obtain from a server, and the measured Received signal strength information is included in the probe response. Since the channel of AP1 is the current channel of the client, AP2 and AP3 can continuously monitor the packets sent by the client, so as to quickly obtain the strength information of the received signal.

AP2 and AP3 can send the probe response containing the RSSI value to AP1 through the wired link with AP1. After receiving the probe response from AP2 and AP3, AP1 sends the received probe response through the wireless link with the client. The probe response is forwarded to the client.

Step 604, after receiving all the probe responses returned by the candidate APs, the client compares the RSSI values included in the probe responses, and selects the AP with the largest RSSI value as the target AP.

For example, assuming that the RSSI value returned by AP2 is greater than the RSSI value returned by AP3, the client selects AP2 as the target AP.

Step 605, associate and authenticate between the client and the target AP through the virtual link.

Before the client switches to the target AP, the client and the target AP perform information exchange through virtual links. In this step, when the client selects AP2 as the target AP according to the RSSI value returned by the candidate AP, the client sends an association request to AP2 through the virtual link with AP2 and receives the association response returned by AP2; In an application scenario with high security requirements, the client sends an authentication request to AP2 through the virtual link and receives an authentication response returned by AP2. Taking the above-mentioned second method of establishing a virtual link as an example, the client can send the association request that needs to be sent to AP2 to AP1 through the wireless link between it and AP1, and after receiving the association request, AP1 communicates with AP2 The wired link between forwards the association request to AP2; after AP2 receives the association request, it sends the association response that needs to be sent to the client to AP1 through the wired link between it and AP1, and AP1 receives the association response Then forward the association response to the client through the wireless link between it and the client. Similarly, the client can complete the authentication operation with AP2 through the relay of AP1, which will not be repeated here.

Since the operation performed by the client in steps 601 to 605 is pre-handover, the client still maintains communication with the current AP. Therefore, the information interaction process between the client and the target AP does not take up handover time.

Further, the association response returned by the target AP may also include channel information of the target AP.

In step 606, after receiving the successful authentication response returned by the target AP through the virtual link, the client can generate a virtual connection table, which is used to maintain the switching information required for establishing a connection between the client and the target AP. In this embodiment, the handover information may include: link status information (such as RSSI value), beacon interval information (Beacon Interval), and information such as the MAC address, SSID, and channel of the target AP.

Step 607, when the client starts switching, the client terminates the communication with the current AP, and switches to the channel of the target AP, thereby completing the switching to the target AP.

In addition, the client can update its system parameters according to the handover information maintained in the virtual connection table, and send a handover completion signal to the target AP.

In this step, with reference to the example shown in FIG. 5, when the client moves to point B where AP1 is located, the signal sent by AP1 suddenly becomes weaker, while the signal sent by AP2 becomes stronger. At this time, the handover of the client starts. The client terminates the communication with AP1 and switches to the channel of AP2, thus completing the switching operation.

In step 608, after receiving the handover completion signal sent by the client, the target AP updates its system parameters to complete the handover. After the handover is completed, the target AP becomes the current AP of the client.

So far, the handover process ends.

Compared with the fast switching mechanism in the prior art, the switching method proposed in the embodiment of the present invention has the following advantages:

In the fast handover method proposed by the embodiment of the present invention, the communication link between the client and the current AP and the communication link between the current AP and the candidate AP are used to establish a virtual link. Through this virtual link, the client can complete the information interaction with the target AP before switching to the target AP without interrupting the communication with the current AP. For example, the client obtains the RSSI value sent by the candidate AP, selects the target AP, and communicates with the target AP. The AP performs association and authentication, and all pre-handover operations can be completed in the pre-handover stage through the virtual link. When the signal strength sent by the current AP weakens and the real handover begins, all the client needs to do is based on its own The maintained switching information updates its system parameters. Therefore, the switching method can not only reduce the switching decision time, but also reduce the connection establishment time, so that the time for the client to switch from one AP to another AP will be greatly reduced.

In the handover method proposed by the embodiment of the present invention, the information exchange between the client and the candidate AP is performed through a virtual link, which can ensure the communication quality between the client and the candidate AP, thereby avoiding increasing the number of APs. Moreover, since the client decides to switch before the signal strength of the current AP weakens, the communication between the client and the current AP has not been interrupted at this time, so the communication quality between the client and the current AP can also be guaranteed.

In the handover method proposed in the embodiment of the present invention, the candidate AP is used to jump to the channel where the client is currently located to monitor the message sent by the client, and the client does not need to interrupt the communication with the current AP and frequently Jump to the channel where other APs are located to send messages, which can simplify the operation of the client. Moreover, since the client can still maintain communication with the current AP, the candidate AP can continuously monitor the message sent by the client, thereby quickly obtaining the RSSI value, which is beneficial for the client to reduce the time for handover decision.

In the handover method proposed by the embodiment of the present invention, all the information used for handover can be exchanged through the virtual link before the client handover to the target AP, and distributed marking or IP routing can be adopted under the IEEE 802.11 standard framework Therefore, there is no need to modify the relevant parts of the IEEE 802.11 standard, only the software of the client and AP needs to be modified.

The fast switching method proposed by the embodiment of the present invention is especially applicable to a wireless communication scenario where at least one of the AP and the client uses a directional antenna, such as a wireless communication scenario in a rail transit system.

Of course, the handover method proposed in the embodiment of the present invention is also applicable to a wireless communication scenario where the AP and the client use omnidirectional antennas. In an application scenario using an omnidirectional antenna, there is no such thing as a sudden weakening of the signal strength when the client is the closest to the current AP. Instead, the client is getting farther and farther away from the current AP, and the signal strength of the current AP is getting weaker. Therefore, the method for the client to determine the switching timing can be slightly modified. For example, when the client knows that the signal strength of the current AP is lower than the preset threshold, the client decides to switch.

Another embodiment of the present invention also proposes a fast handover method in a wireless communication system, the method including the following steps:

When the client decides to switch, its current AP is used to establish a virtual link between the client and the candidate AP, which includes the communication link between the client and the current AP and the communication link between the current AP and the candidate AP. communication link;

The current AP receives the probe request sent by the client to the candidate AP through the virtual link and forwards the probe request to the candidate AP, and receives the probe response sent by the candidate AP to the client through the virtual link and forwards the probe response to the candidate AP. client;

The current AP receives the association request sent by the client to the target AP through the virtual link and forwards the association request to the target AP, and receives the association response sent by the target AP to the client through the virtual link and forwards the association response to the client end;

When the client starts handover, the current AP terminates communication with the client.

In this embodiment, when the above-mentioned first method for establishing a virtual link is adopted, the current AP can establish a virtual link between the client and the candidate AP by modifying its MAC address filter.

In an application scenario with high security requirements, before the client switches to the target AP, the method may further include: the current AP receives the authentication request sent by the client to the target AP through the virtual link and sends the authentication request to the target AP. The authorization request is forwarded to the target AP, and the authentication response sent by the target AP to the client through the virtual link is received and forwarded to the client.

Another embodiment of the present invention also proposes a fast handover method in a wireless communication system, the method including the following steps:

When the client decides to switch, the candidate access point AP establishes a virtual link with the client through the current AP of the client. The virtual link includes the communication link between the candidate AP and the current AP and the current AP and the client. communication link between

The candidate AP receives the probe request from the client through the virtual link and sends a probe response to the client;

The candidate AP receives the client's association request through the virtual link and sends an association response to the client.

Preferably, the probe request may include information about the channel where the client is currently located. Then in this embodiment, the method further includes: the candidate AP jumps to the channel to measure the strength of the received signal, and includes the measured strength information of the received signal in the probe response.

In addition, in this embodiment, the method may further include: the candidate AP receives the client's authentication request through the virtual link and sends an authentication response to the client, so as to meet the high security requirement.

The above-mentioned steps performed by the current AP and candidate APs have been described in detail in the foregoing embodiments, and will not be repeated here.

According to the handover method proposed in the above embodiments, the embodiment of the present invention also provides a fast handover system in a wireless communication system, the system includes a client and multiple APs.

Wherein, the client is used to establish a virtual link between the current AP and the candidate AP when deciding to switch, and the virtual link includes the communication link between the client and the current AP and the communication link between the current AP and the candidate AP. through the virtual link, send a probe request to the candidate AP and receive a probe response from the candidate AP; select a target AP from the candidate APs according to the probe response from the candidate AP; through the The virtual link sends an association request to the target AP and receives an association response from the target AP; when switching starts, terminates communication with the current AP and switches to the target AP;

The current AP is used to establish a virtual link between the client and the candidate AP when the client decides to switch; receive the probe request sent by the client to the candidate AP through the virtual link and forward the probe request To the candidate AP, and receive the probe response sent by the candidate AP to the client through the virtual link and forward the probe response to the client; receive the association request sent by the client to the target AP through the virtual link and send the association request Forwarding to the target AP, and receiving the association response sent by the target AP to the client through the virtual link and forwarding the association response to the client; when the client starts switching, terminate the communication with the client;

The candidate AP is used to establish a virtual link between the current AP of the client and the client when the client decides to switch; receive the probe request of the client through the virtual link and send a probe response to the client; through the virtual link The channel receives the association request from the client and sends the association response to the client.

In this system, for the detailed functions and processing of the client and the AP, reference may be made to relevant descriptions in the foregoing method embodiments, and details are not repeated here.

According to the handover method proposed in the foregoing embodiments, an embodiment of the present invention also provides a schematic structural diagram of a fast handover client in a wireless communication system. As shown in Figure 7, the client includes:

The first virtual link establishment module 701 is used to establish a virtual link between the client and the candidate AP through the current AP of the client when the client decides to switch, and the virtual link includes the communication between the client and the current AP link and the communication link between the current AP and the candidate AP;

The first detection module 702 is configured to send a detection request to the candidate AP through the virtual link and receive a detection response from the candidate AP;

A selection module 703, configured to select a target AP from the candidate APs according to the probe responses of the candidate APs;

The first association module 704 is configured to send an association request to the target AP through the virtual link and receive an association response from the target AP;

The first switching module 705 is configured to terminate the communication with the current AP and switch to the target AP when the client starts switching.

In this embodiment, the first virtual link establishment module 701 is configured to, when the client and the candidate AP are in the same subnet, use distributed labels to establish a virtual link between the current AP and the candidate AP. If the client and the candidate AP are in different subnets, the first virtual link establishment module 701 can use IP routing to establish a virtual link between the current AP and the candidate AP.

In this embodiment, the probe request may include the information of the channel where the client is currently located; the probe response may include the strength information of the received signal measured by the candidate AP on the channel.

In this embodiment, when the security requirements of the system are high, the client may further include a first authentication module, configured to send an authentication request to the target AP through the virtual link and receive an authentication response from the target AP .

In this embodiment, the association response may include channel information of the target AP; when the client starts switching, the first switching module 705 is configured to switch to the channel of the target AP.

In this embodiment, the client may further include: a handover decision module, configured to decide to handover when the signal strength of the current AP received by the first detecting module 702 exceeds a preset signal threshold; or when the client and the current AP When the distance of the AP is less than the preset distance threshold, it is decided to switch.

As shown in FIG. 8, an embodiment of the present invention also provides an AP in a wireless communication system, the AP is the current AP of the client, which may include:

The second virtual link establishment module 801 is configured to establish a virtual link between the client and the candidate AP when the client decides to switch, the virtual link includes the communication link between the client and the AP and the AP and the communication link between the candidate AP;

The second detection module 802 is configured to receive a detection request sent by the client to the candidate AP through the virtual link and forward the detection request to the candidate AP, and receive a detection response sent by the candidate AP to the client through the virtual link and forward the probe response to the client;

The second association module 804 is configured to receive an association request sent by the client to the target AP through the virtual link and forward the association request to the target AP, and receive an association response sent by the target AP to the client through the virtual link and forward the association response to the client;

The second switching module 805 is configured to terminate communication with the client when the client starts to switch.

In this embodiment, optionally, the second virtual link establishing module 801 may be configured to establish a virtual link between the client and the candidate AP by modifying the MAC address filter of the AP.

In addition, in this embodiment, the AP may further include a second authentication module 806, configured to receive the authentication request sent by the client to the target AP through the virtual link and forward the authentication request to the target AP , and receive the authentication response sent by the target AP to the client through the virtual link and forward the authentication response to the client.

As shown in FIG. 9, an embodiment of the present invention also provides an AP in a wireless communication system. The AP is a candidate AP, which may include:

The third virtual link establishment module 901 is used to establish a virtual link between the current AP of the client and the client when the client decides to switch, the virtual link including the communication link between the AP and the current AP and The communication link between the current AP and the client;

The third detection module 902 is configured to receive a detection request from the client through the virtual link and send a detection response to the client;

The third association module 904 is configured to receive an association request from the client through the virtual link and send an association response to the client.

In this embodiment, the detection request may preferably include information about the channel where the client is currently located; the third detection module 902 is used to measure the strength of the received signal on the current channel of the client, and use the measured received signal Intensity information is included in the probe response.

In addition, in this embodiment, the candidate AP may further include a third authentication module 906, configured to receive an authentication request from the client through the virtual link and send an authentication response to the client.

For detailed descriptions of the fast switching system, client and AP provided by the above embodiments of the present invention, reference may be made to relevant descriptions in the above method embodiments, and details are not repeated here. Using the handover system, the client and the AP according to the embodiment of the present invention can also obtain the technical effects obtained by the fast handover method according to the embodiment of the present invention, and will not be described in detail here.

Although the specific embodiments of the present invention have been described above by taking the rail transit wireless communication system as an example, those skilled in the art should understand that the present invention is not limited thereto. In other wireless communication systems involving handover issues, such as mesh systems, the fast handover solution according to the embodiments of the present invention can be applied without violating the technical concept of the present invention.

It should be noted that not all steps and modules in the above-mentioned flow charts and structural diagrams are necessary, and some steps or modules can be ignored according to actual needs. The execution order of each step is not fixed and can be adjusted as needed. The system structures described in the above embodiments may be physical structures or logical structures, that is, some modules may be realized by the same physical entity, or some modules may be realized by multiple physical entities, or may be realized by multiple Certain components in individual devices are implemented together.

In the above embodiments, the hardware unit may be implemented mechanically or electrically. For example, a hardware unit may include permanently dedicated circuitry or logic (such as a dedicated processor, FPGA, or ASIC) to perform the corresponding operations. The hardware unit may also include programmable logic or circuits (such as general-purpose processors or other programmable processors), which can be temporarily set by software to complete corresponding operations. The specific implementation (mechanical way, or dedicated permanent circuit, or temporarily set circuit) can be determined based on cost and time considerations.

The present invention also provides a machine-readable medium storing instructions for enabling a machine to execute the fast switching method according to the embodiment of the present invention. Specifically, a system or device equipped with a storage medium may be provided, on which the software program code for realizing the functions of any of the above embodiments is stored, and the computer (or CPU or MPU of the system or device) ) to read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium can realize the function of any one of the above-mentioned embodiments, so the program code and the storage medium storing the program code constitute a part of the present invention.

Examples of storage media for providing program code include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), Tape, non-volatile memory card, and ROM. Alternatively, the program code can be downloaded from a server computer via a communication network.

In addition, it should be clear that not only by executing the program code read by the computer, but also by making the operating system on the computer complete part or all of the actual operations through instructions based on the program code, so as to realize the function of any one of the embodiments.

In addition, it can be understood that the program code read from the storage medium is written into the memory provided in the expansion board inserted into the computer or written into the memory provided in the expansion unit connected to the computer, and then based on the program code The instruction causes the CPU installed on the expansion board or the expansion unit to perform some or all of the actual operations, so as to realize the functions of any one of the above-mentioned embodiments.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (27)

1. A fast switching method in a wireless communication system, comprising: When the client decides to switch, the client establishes a virtual link between its current access point AP and the candidate AP, and the virtual link includes the communication link between the client and the current AP and a communication link between the current AP and the candidate AP; The client sends a probe request to the candidate AP through the virtual link and receives a probe response from the candidate AP; According to the probe response of the candidate AP, the client selects a target AP from the candidate APs; The client sends an association request to the target AP through the virtual link and receives an association response from the target AP; When the client starts switching, the client terminates communication with the current AP and switches to the target AP. 2. The method according to claim 1, wherein when the client and the candidate AP are in the same subnet, the client uses a distributed label to pass the current AP and the candidate AP Create a virtual link between them. 3. The method according to claim 1, wherein when the client and the candidate AP are in different subnets, the client uses IP routing to pass between the current AP and the candidate AP Create a virtual link. 4. The method according to any one of claims 1 to 3, wherein the probe request includes information about the channel where the client is currently located; The probe response includes strength information of received signals measured by the candidate AP on the channel. 5. The method according to any one of claims 1 to 3, characterized in that, before the client starts switching, the method further comprises: The client sends an authentication request to the target AP through the virtual link and receives an authentication response from the target AP. 6. The method according to any one of claims 1 to 3, wherein the association response includes channel information of the target AP; The switching of the client to the target AP includes: switching the client to a channel of the target AP. 7. The method according to claim 1, wherein the decision of the client to switch comprises: When the signal strength of the current AP received by the client exceeds a preset signal threshold, decide to switch; or, When the distance between the client and the current AP is less than a preset distance threshold, it is decided to switch. 8. A fast switching method in a wireless communication system, comprising: When the client decides to switch, the current access point AP of the client is used to establish a virtual link between the client and the candidate AP, and the virtual link includes the connection between the client and the current AP. and the communication link between the current AP and the candidate AP; The current AP receives the detection request sent by the client to the candidate AP through the virtual link and forwards the detection request to the candidate AP, and receives the detection request from the candidate AP to the candidate AP through the virtual link. the probe response sent by the client and forward the probe response to the client; The current AP receives the association request sent by the client to the target AP through the virtual link and forwards the association request to the target AP, and receives the association request sent by the target AP to the target AP through the virtual link. the association response sent by the client and forward the association response to the client; When the client starts switching, the current AP terminates communication with the client. 9. The method according to claim 8, wherein the current AP establishes a virtual link between the client and the candidate AP by modifying its MAC address filter. 10. The method according to claim 8 or 9, characterized in that the method further comprises: The current AP receives the authentication request sent by the client to the target AP through the virtual link and forwards the authentication request to the target AP, and receives the authentication request sent by the target AP through the virtual link. sending an authentication response to the client and forwarding the authentication response to the client. 11. A fast handover method in a wireless communication system, comprising: When the client decides to switch, the candidate access point AP establishes a virtual link with the client through the current AP of the client, and the virtual link includes a communication link between the candidate AP and the current AP road and the communication link between the current AP and the client; The candidate AP receives the probe request of the client through the virtual link and sends a probe response to the client; The candidate AP receives the association request of the client through the virtual link and sends an association response to the client. 12. The method according to claim 11, wherein the probe request includes information about the channel where the client is currently located; the method further comprises: The candidate AP measures the received signal strength on the channel, and includes the measured received signal strength information in the probe response. 13. The method according to claim 11 or 12, characterized in that the method further comprises: The candidate AP receives the authentication request of the client through the virtual link and sends an authentication response to the client. 14. A fast switching system in a wireless communication system, comprising a client and multiple wireless access points AP; The client is used to, when it decides to switch, establish a virtual link between its current access point AP and a candidate AP, and the virtual link includes a communication link between the client and the current AP and the communication link between the current AP and the candidate AP; through the virtual link, send a detection request to the candidate AP and receive a detection response from the candidate AP; according to the detection of the candidate AP In response, select a target AP from the candidate APs; send an association request to the target AP through the virtual link and receive an association response from the target AP; when switching starts, terminate the communication with the current AP and switch to the target AP; The current AP is used to establish the virtual link between the client and the candidate AP when the client decides to switch; A probe request sent by the candidate AP and forward the probe request to the candidate AP, and receive a probe response sent by the candidate AP to the client through the virtual link and forward the probe response to the client ; receiving the association request sent by the client to the target AP through the virtual link and forwarding the association request to the target AP, and receiving the association request sent by the target AP to the client through the virtual link sending an association response and forwarding the association response to the client; when the client starts switching, terminating communication with the client; The candidate AP is used to, when the client decides to switch, establish the virtual link between the current AP of the client and the client; receive the detection request of the client through the virtual link and sending a probe response to the client; receiving an association request from the client through the virtual link and sending an association response to the client. 15. A fast switching client in a wireless communication system, comprising: A first virtual link establishing module, configured to establish a virtual link between the client and a candidate AP through the current AP of the client when the client decides to switch, the virtual link includes the client A communication link between the terminal and the current AP and a communication link between the current AP and the candidate AP; A first detection module, configured to send a detection request to the candidate AP through the virtual link and receive a detection response from the candidate AP; A selection module, configured to select a target AP from the candidate APs according to the probe responses of the candidate APs; A first association module, configured to send an association request to the target AP through the virtual link and receive an association response from the target AP; The first switching module is configured to terminate communication with the current AP and switch to the target AP when the client starts switching. 16. The client according to claim 15, wherein the first virtual link establishment module is configured to, when the client and the candidate AP are in the same subnet, use a distributed label to pass the A virtual link is established between the current AP and the candidate AP. 17. The client according to claim 15, wherein the first virtual link establishment module is configured to, when the client and the candidate AP are in different subnets, use IP routing to pass through the A virtual link is established between the current AP and the candidate AP. 18. The client according to any one of claims 15 to 17, wherein the probe request includes information about the channel where the client is currently located; The strength information of the received signal measured above. 19. The client according to any one of claims 15 to 17, characterized in that the client further comprises: A first authentication module, configured to send an authentication request to the target AP through the virtual link and receive an authentication response from the target AP. 20. The client according to any one of claims 15 to 17, wherein the association response includes channel information of the target AP; The first switching module is used to switch to the channel of the target AP. 21. The client according to claim 15, wherein the client further comprises: A handover decision module, configured to decide to handover when the signal strength of the current AP received by the first detection module exceeds a preset signal threshold; or, when the distance between the client and the current AP is less than a preset When the distance threshold is reached, it is decided to switch. 22. An access point AP in a wireless communication system, comprising: A second virtual link establishment module, configured to establish a virtual link between the client and a candidate AP when the client decides to switch, the virtual link includes communication between the client and the AP link and communication link between said AP and said candidate AP; The second detection module is configured to receive the detection request sent by the client to the candidate AP through the virtual link and forward the detection request to the candidate AP, and receive the detection request sent by the candidate AP through the virtual link. sending a probe response to the client and forwarding the probe response to the client; The second association module is configured to receive an association request sent by the client to the target AP through the virtual link and forward the association request to the target AP, and receive an association request sent by the target AP through the virtual link. sending an association response to the client and forwarding the association response to the client; The second switching module is configured to terminate the communication with the client when the client starts to switch. 23. The AP according to claim 22, wherein the second virtual link establishment module is configured to establish a link between the client and the candidate AP by modifying the MAC address filter of the AP virtual link. 24. The AP according to claim 22 or 23, wherein the AP further comprises: The second authentication module is configured to receive the authentication request sent by the client to the target AP through the virtual link and forward the authentication request to the target AP, and receive the authentication request sent by the target AP through the target AP. The authentication response sent by the virtual link to the client and forward the authentication response to the client. 25. An AP in a wireless communication system, comprising: A third virtual link establishing module, configured to establish a virtual link between the AP and the client through the current AP of the client when the client decides to switch, the virtual link including the AP and the client a communication link between the current APs and a communication link between the current AP and the client; A third detection module, configured to receive a detection request from the client through the virtual link and send a detection response to the client; A third association module, configured to receive an association request from the client through the virtual link and send an association response to the client. 26. The AP according to claim 25, wherein the probe request includes information about the channel where the client is currently located; The third detection module is used to measure the strength of the received signal on the channel, and include the measured strength information of the received signal in the detection response. 27. The AP according to claim 25 or 26, characterized in that the AP further comprises: A third authentication module, configured to receive an authentication request from the client through the virtual link and send an authentication response to the client.

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