HK1112669A - Seamless channel change in a wireless local area network - Google Patents

Description

Seamless channel change for wireless local area networks

Technical Field

The present invention relates to a Wireless Local Area Network (WLAN), and more particularly, to a method for seamless channel change in a WLAN.

Background

In WLAN systems operating in infrastructure mode, an Access Point (AP) connected to a Basic Service Set (BSS) typically has one or more Stations (STAs) connected to it. The APs and their associated STAs communicate with each other by sending and receiving packets on a given channel, which requires the nodes of the BSS to use less congested channels when the channel is congested (i.e., the traffic shown on the channel is high). Likewise, if the channel is affected by system external interference, which is common on unlicensed bands, it is desirable and also required for the BSS nodes to use a different channel.

The most typical way BSSs change channels is for the AP to change the channel on which it transmits all frames (management, control and data) at a particular time, meaning that the STA will suddenly stop receiving any frames from its AP and treat all frames to the AP as unacknowledged, a service that is sensitive to quality of service (QoS) and that will not satisfy the user.

To meet regulatory requirements for operation in the european 5GHz band, a modification (IEEE 802.11h) has been made in the WLAN Medium Access Control (MAC) and physical layer (PHY) specifications that allow WLAN systems and radar systems to coexist in the 5GHz band, but which do not provide a way for end users to seamlessly and efficiently utilize radio resources to implement channel changes, and the family of 802.11 standards does not provide any hand-off (hand-shaking) modality to ensure seamless channel changes when an AP or STA decides to change its channel.

For systems operating in infrastructure mode, the 803.11h specification contains a notification message that allows the AP to notify the STA that the channel will be switched in the future, and in the high level, there are three options for the notification to be qualified and the channel to be switched, it is noted that the prior art does not provide any mechanism for the following situations:

1) the STA requests the AP to change channels.

2) The STA acknowledges receipt of the notification from the AP and it will follow the AP to change to a new channel. In 802.11h, the notification is implemented using a broadcast, so the AP does not receive any Acknowledgement (ACK) to enable it to determine whether the STA will follow the new channel or whether the STA correctly received the notification. This may lead to a situation where an AP does not need to transmit and retransmit frames to STAs that do not follow the AP to a new channel, where the number of frames buffered may be large and will result in a very inefficient wireless medium, since the backoff window for multiple retransmissions may grow exponentially.

3) The STA acknowledges that it has followed the AP to the new channel, which may create inefficiencies similar to those described above.

Therefore, there is a need for a method and apparatus for seamless channel change in a WLAN.

Disclosure of Invention

The present invention overcomes the limitations of the prior art, thereby allowing seamless channel changes in a WLAN without requiring service interruptions and without significantly reducing the efficiency of the wireless medium.

A method for seamless channel change in a WLAN having a STA and an AP. First, a channel change intention message is sent from the AP to the STA. A channel change response message is then sent by the STA to the AP informing the AP whether the STA will follow the channel change. The AP determines whether to continue the channel change and, if so, performs the channel change.

Another method for seamless channel change in a WLAN having a STA and an AP. First, a channel change request is sent by the STA to the AP. It is determined whether a channel change can be performed, and the channel change is performed according to the determination.

Both methods include an optional additional step of sending a channel change executed message from the STA to the AP upon successful execution of the channel change.

A system for performing a seamless channel change in a wireless local area network including an AP and a STA. The AP is configured to send a channel change intention message to the STA. The STA is configured to send a channel change response message to the AP including an indication of whether the STA will follow the AP to a new channel. After receiving the channel change response message, the AP is further configured to determine whether to continue with the channel change, and if so, perform the channel change. Although the AP will consider the response message from the STA, the determination of whether to continue the channel change need not be based on the response message.

Another system performs a seamless channel change in a wireless local area network including an AP and a STA. The STA is configured to send a channel change request message to the AP. In the example where the AP supports only one STA, the AP is configured to determine whether the channel change can be performed and perform the channel change based on the determination. In the case where the AP supports more than one STA, the AP is configured to initiate the channel change procedure as described above via the channel change intention message.

A system for performing a seamless channel change in a wireless local area network including an AP and a STA. The AP includes a first channel change notification device; a first channel change determining device connected to the first channel change notifying device; a measurement request device connected to the first channel change determining device; a first transmitter/receiver connected to the first channel change notification device, the first channel change device, and the measurement request device; and a first antenna connected to the first transmitter/receiver. The STA includes a second channel change notification device; a second channel change determining device connected to the second channel change notifying device; a station capability device connected to said second channel change determining device; a second channel change device connected to the second channel change determination device; a second transmitter/receiver connected to the second channel change notification device and the second channel change device; a measurement reporting device connected to the second transmitter/receiver; and a second antenna connected to the second transmitter/receiver.

Drawings

The invention may be understood in more detail by reference to the following description of a preferred embodiment, given as an example, and the accompanying drawings, in which:

fig. 1 is a flow diagram of a seamless channel change method initiated by an AP;

FIG. 2 is a signal flow diagram of the method shown in FIG. 1;

fig. 3 is a flow diagram of a method for seamless channel change initiated by a STA; and

fig. 4 is a block diagram of a system configured to implement a seamless channel change.

Detailed Description

Hereinafter, the term "Station (STA)" is used generically and includes, but is not limited to, a wireless transmit/receive unit, a user equipment, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminology "Access Point (AP)" includes but is not limited to a station, a node B, a station controller, or any other type of interfacing device in a wireless environment.

The present invention solves the above problem by setting up a handoff procedure between an AP and a STA, wherein the AP communicates with its associated STAs, which it notifies to switch channels, and wherein the STA acknowledges that it will or will not follow the AP of the new channel. This procedure ensures that all STAs can be aware of all AP channel change notifications and the AP can also know which STA will follow the new channel and which STAs have followed the new channel that the AP decides to change. The present invention also solves the problem by allowing STAs to request a channel change to trigger a handoff procedure.

Fig. 1 illustrates the AP initial handoff procedure 100 of the present invention, and for simplicity of the figure and discussion of the present invention, the following discussion will only discuss a single STA, and the principles of the present invention are also applicable to systems with multiple STAs.

An AP sends a channel change intention message to a STA indicating its intention to change channels to channel X, where X represents a channel identifier (step 102). This message also contains information about the channel change time, which can be sent using a broadcast frame, which has the advantage of limiting the number of messages sent over the wireless medium when multiple STAs are connected to the AP, or a unicast frame, one for each STA connected, which is beneficial in that it helps the robustness of the signaling since the AP waits for a MAC ACK from a STA indicating whether the STA has correctly received the message, in the case where no ACK from a particular STA is received, the AP can retransmit the channel change intention message.

Based on the received channel change intention message, the STA determines whether to change its channel to the new channel based on its capabilities, the radio frequency environment in which it is located, and the availability and loading of other APs in the system (step 104). The determination may involve a multi-criteria determination procedure, for example, the first criteria the STA may consider is whether it has the capability (considering hardware and configuration constraints) to change to channel X, as declared in the channel change intention message sent by the AP. A second and third criterion that may be considered by the STA is the interference level and load of the STA on channel X. Based on this criterion, the STA determines whether the channel change is required, which may be achieved using any row of multi-criteria analysis that compares the scores obtained based on the weight calculations to a predetermined level.

Once the determination is made, the STA sends a channel change response message that includes a notification that the message has been received (which may also be used in the case of sending a channel change intention message using a broadcast), and an indication whether the STA will follow the AP to the new channel (step 106).

The indication in the channel change response message includes various predefined responses including, but not limited to:

1) the STA will follow the AP to the new channel.

2) The STA will not follow the new channel and will be willing to continue to be served by the AP on the same channel. The chance of this condition occurring increases if the STA's scanning indicates that the new channel will degrade its performance, or the STA lacks the ability to change channels, or the STA determines that changing channels cannot make it meet the QoS requirements of the user's application.

3) The STA will not follow the AP to a new channel but will not request that the AP stay on the same channel. If the STA has identified another candidate AP and determined that it provides better performance than the current AP on the new channel, the probability of this condition occurring is increased.

The scope of techniques by which a STA may perform a channel change determination includes using measured or reported quality metrics (e.g., signal-to-noise ratio (SNR), signal-to-interference-and-noise ratio (SINR), Packet Error Rate (PER), etc.) on the new channel and comparing these metrics to quality metrics measured on the current channel or to a predetermined level. The STA also uses the measured or reported load metric (e.g., channel occupancy, medium access delay, etc.) on the new channel, compared to the measured load metric on the current channel, or compared to a predetermined level. The above-mentioned weight reference combination on the new channel can also be used to compare with the weight reference combination on the current channel with the same scale, or to compare with a preset level.

If the AP transmits its channel change intention message using broadcasting, the channel change response message transmitted by the STA is also used for the purpose of confirming the reception of the channel change intention message. Sending the channel change intention message in a single broadcast message has several benefits, since it allows the AP to distinguish between STAs that did not receive the channel change intention message and STAs that received the channel change intention message but did not send the channel change response message, the APc waits for the responses (positive or negative) of all STAs or until expiration, and then makes a decision whether to proceed with the band change, without the AP being restricted by the STA's advice.

Upon receiving a channel change response notification from the STA, the AP then determines whether to change the channel (step 108), which allows the AP to reconsider its intention to change the channel, e.g., in the case where the AP only serves a single STA and the STA indicates that it does not follow the AP to a new channel, the AP may decide not to perform a channel change, which gives the AP the opportunity to request measurements from STAs if the AP believes that the measurement report will help it make a better decision.

Generally, the determination of whether the AP will continue with the channel change is based on the relative number of users that have responded with each type of channel change message and the anticipated impact on quality of service caused by performing the channel change. The process of comparing the relative number of responses of each format to the decision made to change targets based on the anticipated performance of switching the channel is also one of several possible implementations.

If the AP decides not to change channels, the process 100 terminates (step 110). If the AP determines to continue with the channel change (step 108), it sends a channel change notification message to the connected STAs (step 112). The message also contains information about the channel change time, and the message can be sent using broadcast frames or unicast frames, each with the same advantages as described above.

If the AP decides to continue the channel change, it can use the information contained in the channel change response message received from the STA and remove all buffered packets belonging to STAs whose responses do not follow the AP to the new channel, which can prevent the AP from wasting a significant amount of bandwidth on unsuccessful transmitted packets if the STA does not follow the AP to the new channel. The AP changes to a new channel (step 114) and if a STA follows the AP, the STA also changes to a new channel (step 116).

An optional step of the handoff procedure is to send a channel change executed message to the AP after the STA changes channels (step 118), which also serves to prevent the AP from wasting bandwidth in unsuccessful transmissions of packets to the STA that have indicated (in its channel change response message) that the AP will follow to the new channel but cannot do so. The process then terminates (step 110).

Fig. 2 is a signal diagram of a system 200 for performing the process of fig. 1. the system 200 includes an AP 202 and a STA 204. The AP 202 sends a channel change intention message 210, which may be broadcast or unicast. The STA 204 (or each STA 204 if the AP 202 has multiple STAs associated with it) responds to the intention message 210 by sending a channel change response message 212 to the AP 202, each STA 204 sending its response message in a single broadcast message.

If the band change occurs, the AP 202 sends a channel change notification message 214 to the STA 204. like the intention message 210, the notification message 214 may be a broadcast message or a unicast message. The STA 204 may send a channel change executed message 216, which is an optional message, to the AP 202 upon successful channel change.

Fig. 3 is a flow chart of a method 300 according to the present invention in which a STA requests the AP to change its channel. In a preferred embodiment, the present invention allows the STA to request the AP to change the channel it is using, and the need for such a request increases when the interference or channel activity experienced by the STA compromises the QoS of the user.

The STA sends a change channel request message to its AP in a single broadcast frame (step 302), which may include information about some or all of the following: a time limit for performing the channel change, a preferred channel list to migrate, and interference or noise level measurements on the current and candidate channels.

Based on the received message, the AP may then take one or two actions. If the AP has multiple STAs connected to it, it causes the AP to begin executing the handoff procedure 100, beginning at step 102. If the AP has only a single STA associated with it, it may decide to continue the channel change procedure and start the procedure 100 at step 108.

At any point in the process described in fig. 1, the AP may take measurements on the current and recommended channels and/or request measurements from STAs requesting a channel change.

Channel 4 is a schematic diagram of a system 400 configured to perform a seamless channel change, the system 400 including an AP 402 and a STA 404. The AP 402 includes a channel change notification device 410 and a channel change determination device 412 coupled to the channel change notification device 410. A channel change device 414 is connected to the channel change determination device 412. A measurement request device 416 is connected to the channel change determination device 412. A transmitter/receiver 418 is connected to the channel change notification device 410, the channel change device 414, and the measurement request device 416. An antenna 420 is connected to the transmitter/receiver 418.

The STA 404 includes a channel change notification device 430 and a channel change determination device 432 connected to the channel change notification device 430. A STA capability device 434 is connected to the channel change determination device 432. A channel change device 436 is connected to the channel change determination device 432. A transmitter/receiver 438 is connected to the channel change notification device 430 and the channel change device 436. A measurement reporting device 440 is connected to the transmitter/receiver 438. An antenna 442 is connected to the transmitter/receiver 438.

The system 400 operates as follows. The channel change notification device 410 in the AP 402 sends the channel change intention message to the STA 404, where it is processed by the channel change notification device 430 in the STA 404. In the case of a STA initial channel change request, the channel change notification device 430 in the STA 402 first sends the channel change request message to the AP 402, which is processed by the channel change notification device 410 in the AP 402.

After the STA 404 receives the channel change intention message, the channel change determination device 432 in the STA 404 determines whether the STA changes its channel, and the channel change determination device 432 accesses information stored in the STA capability device 434 to assist in making the determination. Once the channel change determining device 432 makes the determination regarding the channel change, it signals the channel change notifying device 430, which transmits the determination (via the channel change response message) to the channel change notifying device 410 in the AP 402. If the STA 404 wants to change its channel, the channel change determining device 4332 signals the channel changing device 436 to change the channel.

In the AP 402, the channel change determining device 412 is used to determine whether the AP will change its channel. As described above, this determination is affected by the channel change response message received from the STA 404. In making this determination, the channel change determination device 412 may request from the STA 404 via a measurement request device 416. Upon receiving a measurement request from the AP 402, the STA 404 takes appropriate measurements and reports back to the AP 402 via the measurement reporting device 440. If the AP 402 wants to change its channel, the channel determination device 412 sends a signal to the channel change device 414 to change the channel.

Examples

A method for seamless channel change in a WLAN having a STA and an AP, comprising the steps of: sending a channel change intention message from the AP to the STA; sending a channel change response message from the STA to the AP informing the AP whether the STA will follow the channel change; determining at the AP whether to perform a channel change; and if the determination result is yes, performing a channel change.

The method according to the preceding paragraph, wherein the channel change response message includes an acknowledgement that the channel change intention message was received.

The method according to one of the two preceding paragraphs, wherein the executing step further comprises the steps of: sending a channel change notification message from the AP to the STA; changing the channel at the AP and the STA; and sending a channel change executed message from the STA to the AP based on the successful execution of the channel change.

The method according to one of the preceding three paragraphs, wherein the WLAN includes more than one STA, and the performing step considers the number of STAs that can change channels before performing the channel change.

The method according to the preceding paragraph, wherein the WLAN includes only one STA, and the determining step includes the steps of: determining, by the AP, whether to perform the channel change; if the channel change is to be performed, sending a channel change notification message from the AP to the STA; the channel is changed at the AP and the STA.

The method of any preceding paragraph, further comprising the steps of: sending a channel change execution message from the STA to the AP if the channel change is successfully completed.

The method according to one of the preceding three paragraphs, wherein the WLAN includes more than one STA, and the determining step includes the steps of: sending a channel change intention message from the AP to each STA; determining by each STA whether to support the channel change; sending a channel change response message from each STA to the AP; determining, by the AP, whether to perform the channel change; sending a channel change notification message from the AP to each of the STAs if the channel change is to be performed; and changing the channel at the AP and each of the STAs.

The method according to one of the preceding four paragraphs, further comprising: if the channel change is successfully completed, a channel change execution message is sent by each STA to the AP.

A system for performing a seamless channel change in a WLAN including an AP and a STA. The AP is configured to send a channel change intention message to the STA. The STA is configured to send a channel change response message to the AP, the channel change response message including an indication of whether the STA will follow the AP to a new channel. The AP is further configured to determine whether to change its channel after receiving the channel change response message, and if so, change its channel.

The system according to the preceding paragraph, wherein the channel change response message includes an acknowledgement that the channel change intention message was received by the STA.

The system according to one of the preceding two paragraphs, wherein if the AP decides to change its channel, the AP is further configured to send a channel change notification message to the STA and change its channel; and the STA further configured to change its channel and send a channel change executed message to the AP based on successful execution of the channel change.

The system according to one of the preceding three paragraphs, wherein the WLAN includes more than one STA, and the AP considers the number of STAs that can change channels before performing the channel change.

A system for performing a seamless channel change in a WLAN including an AP and a STA. The STA is configured to send a channel change request message to the AP. The AP is configured to determine whether the channel change can be performed and perform the channel change based on the determination.

The system according to the preceding paragraph, wherein the WLAN includes only one STA; if the channel change is to be performed, sending a channel change notification message from the AP to the STA; the AP is configured to change its channel; and the STA is configured to change its channel.

The system according to one of the two preceding paragraphs, wherein the STA is further configured to send a channel change executed message to the AP if the channel change is successfully completed.

The system according to one of the preceding three paragraphs, wherein the WLAN includes more than one STA; the AP is configured to send a channel change intention message to each of the STAs; each STA being configured to determine whether to support the channel change and send a channel change response message to the AP; the AP is configured to determine whether to perform the channel change and, if the channel change is to be performed, to send a channel change notification message to each of the STAs and change its channel; and each STA is configured to change its channel.

The method according to one of the preceding four paragraphs, wherein each of the STAs is further configured to send a channel change executed message to the AP if the channel change is successfully completed.

A system for performing a seamless channel change in a WLAN including an AP and a STA. The AP includes a first channel change notification device; a first channel change determining device connected to the first channel change notifying device; a first channel change device connected to the first channel change determining device; a measurement request device connected to the first channel change determining device; a first transmitter/receiver connected to the first channel change notification device, the first channel change device, and the measurement request device; and a first antenna connected to the first transmitter/receiver. The STA includes a second channel change notification device; a second channel change determining device connected to the second channel change notifying device; a station capability device connected to said second channel change determining device; a second channel change device connected to the second channel change determination device; a second transmitter/receiver connected to the second channel change notification device and the second channel change device; a measurement reporting device connected to the second transmitter/receiver; and a second antenna connected to the second transmitter/receiver.

The system according to the preceding paragraph, wherein the first channel change notification device in the AP is configured to send a channel change intention message to the station.

The system according to one of the two preceding paragraphs, wherein the second channel change notification device in the station is configured to receive the channel change intention message.

The system according to one of the preceding three paragraphs, wherein the second channel change notification device in the station is configured to send a channel change request message to the AP.

The system according to one of the preceding four paragraphs, wherein the first channel change notification device in the AP is configured to receive the channel change request message.

The system according to one of the preceding five paragraphs, wherein the first channel change determining device in the AP is configured to determine whether the AP will change its transmission channel.

The system according to one of the preceding six paragraphs, wherein the first channel change determining device sends a signal to the first channel changing device to change the transmission channel if the AP is to change its transmission channel.

The system according to one of the preceding seven paragraphs, wherein the first channel change determining device in the AP signals the measurement request device to request measurements from the station.

The system according to one of the preceding eight paragraphs, wherein the measurement reporting device is configured to perform measurements and report the measurements to the AP.

The system according to one of the preceding nine paragraphs, wherein the second channel change determination device in the station is configured to determine whether the station will change its receive channel.

The system according to one of the preceding ten paragraphs, wherein the second channel change determining device sends a signal to the second channel changing device to change the receiving channel if the station is to change its receiving channel.

Exemplary applications of the present invention include the field of load balancing and dynamic channel selection, where the AP is required to change its channel to adapt to time-varying load and interference conditions. The present invention allows such channel changes to be performed with minimal service interruption of the connected STAs.

Although the features and elements of the present invention are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. While the invention has been described in terms of preferred embodiments, other variations will be apparent to those skilled in the art without departing from the scope of the claims. The foregoing description is for the purpose of illustration and is not intended to limit the particular invention in any way.

Claims (29)

1. A method for performing a seamless channel change in a Wireless Local Area Network (WLAN) having a base Station (STA) and an Access Point (AP), comprising:

sending a channel change intention message from the AP to the STA;

sending a channel change response message from the STA to the AP informing the AP whether the STA will follow the channel change;

determining at the AP whether to perform the channel change; and

if the determination is positive, a channel change is performed.

2. The method according to claim 1, wherein the channel change response message includes an acknowledgement that the channel change intention message has been received.

3. The method of claim 1, wherein the performing step comprises:

sending a channel change notification message from the AP to the STA;

changing the channel at the AP and at the STA; and

immediately after the channel change is successfully performed, a channel change performed message is sent from the STA to the AP.

4. The method of claim 1 wherein the WLAN includes more than one STA, and the performing step considers the number of STAs that can change channels before performing the channel change.

5. A method for performing a seamless channel change in a Wireless Local Area Network (WLAN) having a base Station (STA) and an Access Point (AP), comprising:

sending a channel change request message from the STA to the AP;

determining whether the channel change can be performed; and

the channel change is performed according to the determination.

6. The method of claim 5 wherein the WLAN includes only one STA, and the determining step includes:

determining whether the channel change is to be performed by the AP;

sending a channel change notification message from the AP to the STA if the channel change is to be performed; and

the channel is changed at the AP and the STA.

7. The method of claim 6, further comprising the steps of:

if the channel change has been successfully performed, a channel change performed message is sent from the STA to the AP.

8. The method of claim 5 wherein the WLAN includes more than one STA, and the determining step includes:

sending a channel change intention message from the AP to each STA;

determining whether the channel change can be supported by each STA;

sending a channel change response message from each STA to the AP;

determining whether the channel change is to be performed by the AP;

sending a channel change notification message from the AP to each STA if the channel change is to be performed;

the channel is changed at the AP and each STA.

9. The method of claim 8, further comprising the steps of:

if the channel change has been successfully performed, a channel change performed message is sent from each STA to the AP.

10. A system for performing a seamless channel change in a Wireless Local Area Network (WLAN), comprising:

an Access Point (AP);

a Station (STA);

the AP is configured to send a channel change intention message to the STA;

the STA being configured to send a channel change response message to the AP, the channel change response message including an indication of whether the STA will follow the AP to a new channel; and

the AP is configured to determine whether to change its channel after receiving the channel change response message, and change its channel if the determination is positive.

11. The system according to claim 10, wherein the channel change response message includes an acknowledgement that the channel change intention message was received by the STA.

12. The system of claim 10 wherein if the AP decides to change its channel, then:

the AP is further configured to send a channel change notification message to the STA and change its channel; and

the STA is further configured to change its channel and send a channel change executed message to the AP immediately after successfully executing the channel change.

13. The system of claim 10 wherein the WLAN includes more than one STA and the AP considers the number of STAs that can change channels before performing the channel change.

14. A system for performing a seamless channel change in a Wireless Local Area Network (WLAN), comprising:

an Access Point (AP);

a Station (STA);

the STA being configured to send a channel change request message to the AP; and

the AP is configured to determine whether the channel change is executable, and to execute the channel change based on the determination.

15. The system of claim 14, wherein:

the WLAN includes only one STA;

if the channel change is to be performed, the AP sending a channel change notification message to the STA;

the AP is configured to change its channel; and

the STA is configured to change its channel.

16. The system according to claim 15, wherein the STA is further configured to send a channel change executed message to the AP if the channel change has been successfully executed.

17. The system of claim 14, wherein:

the WLAN includes more than one STA;

the AP is configured to send a channel change intention message to each STA;

each STA being configured to determine whether the channel change can be supported and send a channel change response message to the AP;

the AP is configured to determine whether the channel change is to be performed and, if the channel change is to be performed, send a channel change notification message to each STA and change its channel; and

each STA is configured to change its channel.

18. The system according to claim 17, wherein if the channel change has been successfully performed, each STA is further configured to send a channel change performed message to the AP.

19. A system for performing a seamless channel change in a wireless local area network, comprising:

an access point, comprising:

a first channel change notification device;

a first channel change determining device connected to the first channel change notifying device;

a first channel change device connected to the first channel change determining device;

a measurement request device connected to the first channel change determining device;

a first transmitter/receiver connected to the first channel change notification device, the first channel change device and the measurement request device; and

a first antenna connected to the first transmitter/receiver; and

a station, comprising:

a second channel change notification device;

a second channel change determining device connected to the second channel change notifying device;

a station capability device connected to said second channel change determining device;

a second channel change device connected to the second channel change determination device;

a second transmitter/receiver connected to the second channel change notification device and the second channel change device;

a measurement reporting device connected to the second transmitter/receiver; and

a second antenna connected to the second transmitter/receiver.

20. The system according to claim 19, wherein said first channel change notification device in said AP is configured to send a channel change intention message to said station.

21. The system according to claim 20, wherein said second channel change notification device in said station is configured to receive said channel change intention message.

22. The system according to claim 19 or 20, wherein said second channel change notification device in said station is configured to send a channel change request message to said AP.

23. The system according to claim 22, wherein said first channel change notification device in said AP is configured to receive said channel change request message.

24. The system according to claim 19, 20 or 22, wherein said first channel change determining device in said AP is configured to determine whether said AP will change its transmission channel.

25. The system according to claim 24, wherein if said AP is to change its transmission channel, said first channel change determining device sends a signal to said first channel changing device to change the transmission channel.

26. The system according to claim 19, 20, 22 or 24, wherein said first channel change determining device in said AP signals said measurement request device to request measurements from said station.

27. The system according to claims 19, 20, 22, 24 or 26, wherein said measurement reporting device is configured to perform measurements and report said measurements to said AP.

28. The system according to claim 19, 20, 22, 24 or 26, wherein said second channel change determining device in said station is configured to determine whether said station will change its receive channel.

29. The system according to claim 28, wherein if said station is to change its receive channel, said second channel change determining device sends a signal to said second channel changing device to change said receive channel.