Patent Publication Number: US-2007104137-A1

Title: Channel switch method

Description:
FIELD OF THE INVENTION  
      The invention relates to wireless communications, and particular to a channel switch method.  
     DESCRIPTION OF RELATED ART  
      As mentioned in the “market requirements document (MRD) for Wi-Fi customer electronics (CE) device certification requirement by Wi-Fi certified devices seeking DLAN” in 2004, it is required that the direct link setup (DLS) is a necessary specification of MRD.  
      The CE devices mainly include video devices, audio devices, image devices, and voice devices. An access category (AC) level of the CE audio devices and the CE voice devices is a voice (VI) level requiring small bands, so the CE audio devices and the CE voice devices rarely employ the DLS. An AC level of the CE video devices and the CE image devices is a video (VI) level requiring large bands, so the CE video devices and the CE image devices are more likely to employ the DLS.  
      The DLS is mainly applied in the CE video devices and the CE image devices, and the AC level of the CE video devices and the CE image devices has a higher priority, so the DLS can easily occupy a channel, i.e., the DLS service is a high channel-occupation service. In addition, the DLS requires more bands, and as a result, bands are not enough on a shared channel with a DLS. Then communications on the shared channel may be abnormal.  
      Additionally, on a shared channel with a DLS, when communicating with a mobile station via the shared channel, an access point cannot provide a leased line service for the mobile station.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention provides a channel switch method for a wireless communication system. The wireless communication system includes an access point and a plurality of mobile stations. The access point communicates with the plurality of mobile stations on a shared channel. The channel switch method includes: transmitting a request frame from a first mobile station to the access point for a channel switch service; transmitting a channel switch frame from the access point to the first mobile station to switch the first mobile station from the shared channel to a new channel; and transmitting a beacon frame to the new channel and the shared channel.  
      Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram of a frame defined by the IEEE 802.11 standard;  
       FIG. 2  is a schematic diagram of an action frame defined by the IEEE 802.11;  
       FIG. 3  is a schematic diagram of a channel switch announcement (CSA) information element (IE) defined by the IEEE 802.11;  
       FIG. 4  is a schematic diagram of a wireless communication system of an exemplary embodiment of the present invention;  
       FIG. 5  is a flowchart of a channel switch method of an exemplary embodiment of the present invention;  
       FIG. 6  is a flowchart of a channel switch method of another exemplary embodiment of the present invention;  
       FIG. 7  is a flowchart of a channel switch method of a further exemplary embodiment of the present invention;  
       FIG. 8  is a flowchart of a channel switch method of a still further exemplary embodiment of the present invention;  
       FIG. 9  is a flowchart of a channel switch method of a yet further exemplary embodiment of the present invention; and  
       FIG. 10  is a flowchart of a channel switch method of yet another further exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a schematic diagram of a frame  100  defined by the Institute of Electrical and Electronic Engineers (IEEE) 802.11 standard. The frame  100  includes a media access control (MAC) header  110  and a frame body  120 . The MAC header  110  includes a type field  111  and a subtype field  113 . The type field  111  has 2 bits, and the subtype field  113  has 4 bits. The type field  111  and the subtype field  113  respectively indicate types and subtypes of the frame  100 , which are described hereinafter.  
      When the type field  111  and the subtype field  113  are respectively set to 00 and 0101, the frame  100  is defined as a probe response frame.  
      When the type field  111  and the subtype field  113  are respectively set to 00 and 1000, the frame  100  is defined as a beacon frame.  
      When the type field  111  and the subtype field  113  are respectively set to 00 and 1101, the frame  100  is defined as an action frame (see in  FIG. 2 ).  
      When the type field  111  and the subtype field  113  are respectively set to 01 and 1011, the frame  100  is defined as a request to send (RTS) frame.  
      When the type field  111  and the subtype field  113  are respectively set to 01 and 1100, the frame  100  is defined as a clear to send (CTS) frame.  
      When the type field  111  and the subtype field  113  are respectively set to 01 and 1101, the frame  100  is defined as an acknowledgement (ACK) frame.  
      When the type field  111  and the subtype field  113  are respectively set to 10 and 0100, the frame  100  is defined as a null function frame.  
      When the type field  111  and the subtype field  113  are respectively set to 10 and 0000, the frame  100  is defined as a data frame. When the frame  100  is a data frame, the frame body  120  may include a MAC service data unit (MSDU).  
       FIG. 2  is a schematic diagram of an action frame  200  defined by the IEEE 802.11. The action frame  200  includes an MAC header  210  and a frame body  220 . The MAC header  210  includes a type field  211  and a subtype field  213 . The type  211  and the subtype  213  are respectively set to 00 and 1101 according to the above descriptions. The frame body  220  includes a category field  225  and an action detail field  227 . The category field  225  indicates categories of the action frame  200 . When the category field  225  is set to 0, the action frame  200  is a frame for spectrum management, such as a channel switch announcement (CSA) frame. When the category field  225  is set to 2, the action frame  200  becomes a direct link setup (DLS) frame. The DLS frame includes a DLS request frame, a DLS response frame, and a DLS teardown frame. The action detail field  227  indicates detail information of the action frame  200 . For example, the action detail field  227  may be set as a CSA information element (IE) (see in  FIG. 3 ).  
       FIG. 3  is a schematic diagram of a CSA IE  300  defined by the IEEE 802.11. The CSA IE  300  can be employed in a beacon frame, an action frame, and a probe response frame. Then the beacon frame, the action frame, and the probe response frame with the CSA IE  300  represent channel switch frames. In the exemplary embodiment, the CSA IE  300  is employed in the action frame  200 , that is, the action detail field  227  of the action frame  200  in  FIG. 2  is set to the CSA IE  300 . Then the action frame  200  becomes a CSA frame belonging to the channel switch frame.  
      The CSA IE  300  includes an element identifier (EID) field  301 , a length field  303 , a channel switch mode field  305 , a new channel number field  307 , and a channel switch count field  309 . In the exemplary embodiment, the EID field  301  is set to 37, for indicating that the IE is a CSA IE. The length field  303  is set to 4. The channel switch mode field  305  is set to 1, for indicating data must be transmitted after channel switch. The new channel number field  307  is set to a destination channel number. The channel switch count field  309  is set to 0, and indicates the channel switch must be completed before a next beacon frame.  
       FIG. 4  is a schematic diagram of a wireless communication system of an exemplary embodiment of the present invention. In the exemplary embodiment, the wireless communication system includes an access point  10 , a first mobile station  20 , and a second mobile station  30 . The first mobile station  20  and the second mobile station  30  may be devices that can be communicated with a wireless local area network, such as mobile phones, notebook computers, personal digital assistants (PDAs), etc. The access point  10  wirelessly communicates with the fist mobile station  20  and the second mobile station  30  on a shared channel.  
      In the exemplary embodiment, a channel switch method is described. The first mobile station  20  transmits a request frame to the access point for a channel switch service. The access point  10  receives the request frame, and transmits a channel switch frame to the first mobile station  20  to switch the first mobile station  20  from the shared channel to a new channel. After the channel is switched, the access point  10  transmits a beacon frame to the new channel and the shared channel. The beacon frame transmitted to the new channel by the access point  10  causes the mobile stations on the new channel keep to remain on the new channel. The beacon frame transmitted to the shared channel by the access point  10  causes the mobile stations on the shared channel to remain on the shared channel.  
      The request frame includes a leased line request frame and a DLS request frame. Accordingly, the channel switch service includes a leased line service and a DLS service for establishing a DLS with the second mobile station  30 . When needing a leased line service, the first mobile station  20  transmits the leased line request frame to the access point  10 . The leased line request frame is predefined by the first mobile station  20  and the access point  10  for requesting a leased line service. In the exemplary embodiment, the leased line request frame may be a data frame. The data frame belongs to the frame  100  of  FIG. 1  including the type field  111  and the subtype field  113  respectively set to 10 and 0000. The frame body  120  includes a request MSDU including request data for the leased line service. When receiving the leased line request frame from the first mobile station  20 , the access point  10  recognizes that the first mobile station  20  needs the leased line service, and does not need to send back a response frame to the first mobile station  20 .  
      In other embodiments, the leased line request frame may also be another type of frame. In this case, after receiving the leased line request frame, the access point  10  may also need to send back a response frame to the first mobile station  20 .  
      When needing a DLS service, the first mobile station  20  transmits the DLS request frame to the access point  10  to establish a DLS with the second mobile station  30 . The access point  10  receives the DLS request frame from the first mobile station  20 , and transmits another DLS request frame to the second mobile station  30  to inform the second mobile station  30  that the first mobile station  20  wants to establish a DLS with the second mobile station  30 . The second mobile station  30  receives the DLS request frame from the access point  10 , and transmits a DLS response frame to the access point  10  to inform the access point  10  that the second mobile station  30  agrees to establish the DLS with the first mobile station  20 . The access point  10  receives the DLS response frame from the second mobile station  30 , and transmits another DLS response frame to the first mobile station  20  to inform the first mobile station  20  that the second mobile station  30  agrees to establish the DLS with the first mobile station  20 . In the exemplary embodiment, the DLS request frame and the DLS response frame belong to the action frame  200  of  FIG. 2  including the type field  211  and the subtype field  213  respectively set to 00 and 1101. The category field  225  is set to 2. Then the DLS is established between the first mobile station  20  and the second mobile station  30 . How the channel switch method of the present invention provides the leased line service and the DLS service is described hereinafter.  
       FIG. 5  is a flowchart of a channel switch method of an exemplary embodiment of the present invention. In the exemplary embodiment, the access point  10  wirelessly communicates with the first mobile station  20  and the second mobile station  30  on a shared channel, while the first mobile station  20  needs a channel switch service. In step S 500 , the first mobile station  20  transmits a request frame to the access point  10  for a channel switch service. In step S 502 , the access point  10  transmits a channel switch frame to the first mobile station  20  to switch the first mobile station  20  from the shared channel to a new channel. In step S 504 , the access point  10  transmits a beacon frame to the new channel and the shared channel.  
       FIG. 6  is a flowchart of a channel switch method of another exemplary embodiment of the present invention. In the exemplary embodiment, the access point  10  wirelessly communicates with the first mobile station  20  and the second mobile station  30  on a shared channel, while the first mobile station  20  needs a leased line service.  
      In step S 600 , the first mobile station  20  transmits a leased line request frame to the access point  10  for a leased line service. In the exemplary embodiment, the leased line request frame is a data frame. The data frame belongs to the frame  100 . When receiving the leased line request frame from the first mobile station  20 , the access point  10  does not need to send back a response frame to the first mobile station  20 .  
      In step S 602 , the access point  10  transmits a channel switch frame to the first mobile station  20  to switch the first mobile station  20  from the shared channel to a new channel. In the exemplary embodiment, the channel switch frame is a CSA frame. The CSA frame belongs to the action frame  200 . Referring to  FIG. 2  again, the type field  211  and the subtype field  213  are respectively set to 00 and 1101. The category field  225  is set to 0. The action detail field  227  is set to the CSA IE  300 . Referring also to  FIG. 3 , the EID field  301  is set to 37. The length field  303  is set to 4. The channel switch mode field  305  is set to 1. The new channel number field  307  is set to the new channel number. The channel switch count field  309  is set to 0.  
      In step S 604 , the access point  10  determines that the first mobile station  20  is on the new channel. That is, the access point  10  determines that the channel switch is successful. In the exemplary embodiment, the access point  10  transmits a determination frame to the first mobile station  20  on the new channel. If the access point  10  receives a determination response frame from the first mobile station  20 , the access point  10  determines that the first mobile station  20  is on the new channel. In the exemplary embodiment, the determination request frame may be a RTS frame, and the determination response frame may be a CTS frame. The RTS frame and the CTS frame belong to the frame  100  of  FIG. 1 . When the frame  100  is the RTS frame, the type field  111  and the subtype field  113  are respectively set to 01 and 1011. When the frame  100  is the CTS frame, the type field  111  and the subtype field  113  are respectively set to 01 and 1100.  
      In another embodiment, the determination request frame may also be a null function frame or another frame, and the determination response frame may also be an acknowledgement (ACK) frame. The null function frame and the ACK frame belong to the frame  100  of  FIG. 1 . When the frame  100  is the null function, the type field  111  and the subtype field  113  are respectively set to 10 and 0100. When the frame  100  is the ACK frame, the type field  111  and the subtype field  113  are respectively set to 01 and 1101.  
      In step S 606 , the access point  10  transmits a beacon frame to the new channel and the shared channel. In the exemplary embodiment, the access point  10  provides the leased line service for the first mobile station  20  on the new channel. At each beacon interval, the access point  20  may initially transmit the beacon frame to the new channel. Then the access point  10  goes to the shared channel to transmit the beacon frame to the shared channel. Afterwards, the access point  10  goes back to the new channel, and further provides the leased line service for the first mobile station  20 . The beacon frame transmitted to the shared channel can keep the mobile stations on the shared channel, avoiding the mobile stations on the shared channel from going to the new channel to affect the leased line service. The beacon frame transmitted to the new channel by the access point  10  is used for providing the leased line service on the new channel.  
      In other embodiments, at each interval, the access point  10  may also first transmit the beacon frame to the shared channel. Then the access point  10  goes back to the new channel to transmit the beacon frame to the new channel. Afterwards, the access point  10  further provides the leased line service.  
      In step S 608 , the first mobile station  20  transmits a leased-line teardown frame to the access point  10  to end the leased line service. In the exemplary embodiment, the leased-line teardown frame is predefined by the first mobile station  20  and the access point  10  to end the leased line service. In the exemplary embodiment, the leased-line teardown frame may be a data frame. The data frame belongs to the frame  100  of  FIG. 1  including the type field  111  and the subtype field  113  respectively set to 10 and 0000. The frame body  120  includes a teardown MSDU including request data for ending the leased line service. When receiving the leased-line teardown frame from the first mobile station  20 , the access point  10  is informed that the first mobile station  20  wants to end the leased line service, and the access point  10  does not need to send back a response frame to the first mobile station  20 .  
      In other embodiments, the leased line request frame may also be another type of frame. In this case, after receiving the leased line request frame, the access point  10  may need to send back a response frame to the first mobile station  20 .  
      In step S 610 , the access point  10  transmits another channel switch frame to the first mobile station  20  to switch the first mobile station  20  from the new channel to the shared channel. In the exemplary embodiment, the channel switch frame is a CSA frame. The CSA frame belongs to the action frame  200 . Referring to  FIG. 2  again, the type field  211  and the subtype field  213  are respectively set to 00 and 1101. The category field  225  is set to 0. The action detail field  227  is set to the CSA IE  300 . Referring also to  FIG. 3  again, the EID field  301  is set to 37. The length field  303  is set to 4. The channel switch mode field  305  is set to 1. The new channel number field  307  is set to the switched shared channel. The channel switch count field  309  is set to 0.  
      In another embodiment, in the step S 610  of  FIG. 6 , the access point  10  may not need to transmit the channel switch frame to the first mobile station  20 . Referring to  FIG. 7 , the steps of S 700 , S 702 , S 704 , S 706 , and S 708  of  FIG. 7  are all the same as the steps of S 600 , S 602 , S 604 , S 606 , and S 608  of  FIG. 6 , respectively, so the descriptions are omitted. In step S 710 , the access point  10  stops transmitting the beacon frame to the new channel. In the exemplary embodiment, if the first mobile station  20  cannot scan the beacon frame transmitted by the access point  10  on the new channel, the first mobile station  20  will roam back to the shared channel.  
       FIG. 8  is a flowchart of a channel switch method of a still further exemplary embodiment of the present invention. In the exemplary embodiment, the access point  10  wirelessly communicates with the first mobile station  20  and the second mobile station  30  on a shared channel, while the first mobile station  20  needs to establish a DLS with the second mobile station  30 .  
      In step S 800 , the first mobile station  20  transmits a DLS request frame to the access point  10  to establish a DLS with the second mobile station  30 . In step S 802 , the access point  10  transmits another DLS request frame to the second mobile station  30  to inform the second mobile station  30  that the first mobile station  20  wants to establish the DLS with the second mobile station  30 . In step S 804 , the second mobile station  30  transmits a DLS response frame to the access point  10  to inform the access point  10  that the second mobile station  30  agrees to establish the DLS with the first mobile station  20 . In step S 806 , the access point  10  transmits another DLS response frame to the first mobile station  20  to inform the first mobile station  20  that the second mobile station  30  agrees to establish the DLS with the first mobile station  20 . In the exemplary embodiment, the DLS request frame and the DLS response frame belong to the action frame  200  of  FIG. 2  including the type field  211  and the subtype field  213  respectively set to 00 and 1101. The category field  225  is set to 2.  
      In step S 808 , the access point  10  transmits a channel switch frame to the first mobile station  20  and the second mobile station  30  to switch the first mobile station  20  and the second mobile station  30  from the shared channel to a new channel. In the exemplary embodiment, the channel switch frame may be a CSA frame. The CSA frame belongs to the action frame  200 . Referring to  FIG. 2 , the type field  211  and the subtype field  213  are respectively set to 00 and 1101. The category field  225  is set to 0. The action detail field  227  is set to the CSA IE  300 . Then the action frame  200  becomes the CSA frame. Referring also to  FIG. 3 , the EID field  301  is set to 37. The length field  303  is set to 4. The channel switch mode field  305  is set to 1. The new channel number field  307  is set to the new channel number. The channel switch count field  309  is set to 0.  
      In step S 810 , the access point  10  determines that the first mobile station  20  and the second mobile station  30  are on the new channel. That is, the access point  10  determines that the channel switch is successful. In the exemplary embodiment, the access point  10  transmits a determination frame to the first mobile station  20  and the second mobile station  30  on the new channel. If the access point  10  receives a determination response frame from both of the first mobile station  20  and the second mobile station  30 , the access point  10  determines that the first mobile station  20  and the second mobile station  30  are on the new channel. In the exemplary embodiment, the determination request frame may be a RTS frame, and the determination response frame may be a CTS frame. The RTS frame and the CTS frame belong to the frame  100  of  FIG. 1 . When the type field  111  and the subtype field  113  are respectively set to 01 and 1011, the frame  100  is the RTS frame. When the type field  111  and the subtype field  113  are respectively set to 01 and 1100, the frame  100  is the CTS frame.  
      In other embodiment, the determination request frame may also be a null function frame or another frame, and the determination response frame may also be an ACK frame. The null function frame and the ACK frame belong to the frame  100  of  FIG. 1 . When the frame  100  is the null function, the type field  111  and the subtype field  113  are respectively set to 10 and 0100. When the frame  100  is the ACK frame, the type field  111  and the subtype  113  are respectively set to 01 and 1101.  
      In step S 812 , the access point  10  transmits a beacon frame to the new channel and the shared channel. In the exemplary embodiment, the access point  10  provides services for mobile stations on the shared channel. At each beacon interval, the access point  20  may transmit the beacon frame to the shared channel. Then the access point  10  goes to the new channel, and transmits the beacon frame to the new channel. Afterwards, the access point  10  goes back to the shared channel, and continues to provide services for the mobile stations on the shared channel. The beacon frame transmitted to the new channel is used for making the first mobile station  20  and the second mobile station  30  remain on the new channel, avoiding the first mobile station  20  and the second mobile station  30  from going to the shared channel. The beacon frame transmitted to the shared channel by the access point  10  is used for providing the services for the mobile stations on the shared channel.  
      In other embodiments, at each interval, the access point  10  may also first transmit the beacon frame to the new channel. Then the access point  10  goes back to the shared channel to transmit the beacon frame to the shared channel. Afterwards, the access point  10  continues to provide services for the mobile stations on the shared channel.  
      In step S 814 , the first mobile station  20  transmits a DLS teardown frame to the access point  10  to end the DLS service. In the exemplary embodiment, the DLS teardown frame belongs to the action frame  200  of  FIG. 2  including the type field  211  and the subtype field  213  respectively set to 00 and 1101. The category field  225  is set to 2.  
      In step S 816 , the access point  10  transmits another DLS teardown frame to the second mobile station  30 .  
      In step S 818 , the access point  10  transmits another channel switch frame to the first mobile station  20  and the second mobile station  30  to switch the first mobile station  20  and the second mobile station  30  from the new channel to the shared channel. In the exemplary embodiment, the channel switch frame may be a CSA frame. The CSA frame belongs to the action frame  200 . Referring to  FIG. 2  again, the type field  211  and the subtype  213  are respectively set to 00 and 1101. The category field  225  is set to 0. The action detail field  227  is set to the CSA IE  300 . Then the action frame  200  becomes the CSA frame. Referring also to  FIG. 3  again, the EID field  200  is set to 37. The length field  303  is set to 4. The channel switch mode field  305  is set to 1. The new channel number field  307  is set to the shared channel number. The channel switch count field  309  is set to 0.  
      In another embodiment, the sequences of the steps S 806  and S 808  may be exchanged. Referring to  FIG. 9 , the steps of S 900 , S 902 , S 904 , S 910 , S 912 , S 914 , S 916 , and S 918  of  FIG. 9  are all the same as the steps of S 800 , S 802 , S 804 , S 810 , S 812 , S 814 , S 816 , and S 818  of  FIG. 8 , so the descriptions are omitted. In step S 906 , the access point  10  first transmits a channel switch frame to the first mobile station  20  and the second mobile station  30  to switch the first mobile station  20  and the second mobile station  30  from the shared channel to the new channel. Then the access point  10  goes to the new channel. In step S 908 , the access point  10  transmits another DLS response frame to the first mobile station  20  on the new channel.  
      In a further embodiment, in step S 818  of  FIG. 8 , the access point  10  may not need to transmit the channel switch frame to the first mobile station  20  and the second mobile station  30 . Referring to  FIG. 10 , the steps S 1000 , S 1002 , S 1004 , S 1006 , S 1008 , S 1010 , S 1012 , S 1014 , and S 1016  of  FIG. 10  are the same as the steps S 800 , S 802 , S 804 , S 806 , S 808 , S 810 , S 812 , S 814 , and S 816  of  FIG. 8 , so the descriptions are omitted. In step S 1018 , the access point  10  stops transmitting the beacon frame to the new channel. In the exemplary embodiment, if the first mobile station  20  and the second mobile station  30  cannot scan the beacon frame transmitted by the access point  10  on the new channel, the first mobile station  20  and the second mobile station  30  will roam back to the shared channel.  
      In the exemplary embodiment of the present invention, the access point  10  may provide a leased line service for the first mobile station  20 , and may provide a DLS service for the first mobile station  20  and the second mobile station  30 .  
      While various embodiments and methods of the present invention have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.