Abstract:
A method and system for performing peer-to-peer wireless communication between stations (STAs) within a basic service set (BSS) while maintaining connectivity with an access point (AP) in the BSS are disclosed. A source STA, an AP and a destination STA negotiate a direct link setup (DLS) channel for performing peer-to-peer communication between the source STA and the destination STA. The DLS channel may be different from a BSS channel used for communication between the AP and each of the STAs. The source STA and the destination STA then perform peer-to-peer communication on the negotiated DLS channel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent Ser. No. 11/554,772, filed Oct. 31, 2006 now U.S. Pat. No. 8,077,683 which issued on Dec. 13, 2011, which claims the benefit of U.S. Provisional Application No. 60/733,217 filed Nov. 3, 2005, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to a wireless communication system. More particularly, the present invention is related to a method and system for performing peer-to-peer wireless communication between stations (STAs) within a basic service set (BSS) while maintaining connectivity with an access point (AP) in the BSS. 
     BACKGROUND 
     There are two different types of wireless local area network (WLAN). One is an infrastructure mode WLAN which includes an AP and a STA, and the other is an ad hoc mode WLAN which includes only peer STAs. The ad hoc mode WLAN is also called an independent BSS (IBSS). 
       FIG. 1  shows a conventional infrastructure mode WLAN  100  including two BSSs  112   a ,  112   b  which are connected via a distribution system (DS)  114 . The BSSs are served by APs  102   a ,  102   b , respectively. In the infrastructure mode WLAN  100 , all packets generated by a source STA, such as STA  104   a , is first sent to the AP  102   a . If the packets are destined outside the BSS  112   a , the AP  102   a  forwards the packets through the DS  114 . If the packets are destined to another STA, such as STA  102   b , inside the BSS  112   a , the AP  102   a , after receiving the packets from the source STA  104   a , forwards the packets over the air interface to the destination STA  104   b  in the BSS  112   a . Therefore, the same packets are sent twice over the air. 
     Duplicating such peer-to-peer traffic, (i.e., sending the packets sent from one STA in the BSS to another STA in the same BSS), is an inefficient usage of the wireless medium since any peer-to-peer STA traffic within the BSS requires twice as much bandwidth compared to traffic to or from a STA outside the BSS. 
     In order to solve this problem, the IEEE 802.11e provides a feature called direct link setup (DLS). With the IEEE 802.11e DLS, a STA first initiates a direct link through the AP and exchanges packets with other STA directly. However, in an IEEE 802.11-based WLAN, STAs within a BSS share the same frequency channel, (i.e., BSS channel), to communicate with each other, and all traffic, (both traffic between a STA and an AP and traffic between STAs), must still be sent over the BSS channel. With this limitation to a single BSS channel, the amount of peer-to-peer traffic in a BSS that can be supported by a single frequency channel is limited by the overall throughput of the BSS. For example, a conventional IEEE 802.11g or 802.11a BSS will not be able to support more than 30-32 spore Mbps at the medium access control (MAC) level (corresponding to a net data rate of 54 Mbps at the physical layer) aggregate throughput. 
     Furthermore, it is difficult to manage peer-to-peer links in a conventional IEEE 802-11e DLS system. For conventional BSS traffic, (i.e., traffic between STAs and AP), the overall BSS radio range, (where packets can be reliably received), is essentially determined by the AP&#39;s radio range. An interference range of the BSS, (where packets cannot be reliably received, but will still create interference to other STAs operating on the same channel), is determined by both the STA&#39;s range and the AP&#39;s range. However, with DLS, depending on the position of the participating STAs, the interference range associated by a pair of STAs can be quite different to the interference range of the AP. Interaction and impacts of these different interference ranges is complex and has been shown to have large negative effects on network capacity in IEEE 802.11 systems. 
     Moreover, with conventional IEEE 802.11 systems, peer-to-peer traffic cannot be off-loaded to a different channel than the BSS channel without the involved peer-to-peer STAs losing layer 2 connectivity to the network. Trading off layer 2 connectivity for capacity is not necessarily an attractive alternative, because many of the devices in a WLAN environment need IP connectivity to support various services. For example, a TV receiving a video playback from a DVD player could not download online DVD info, titles, recommendations, or the like during playback. Losing layer 2 connectivity to the AP implies losing the possibility of supporting all services except the on-going peer-to-peer services. 
     Therefore, it is desirable to provide a method and system for peer-to-peer wireless communication between STAs within the BSS while maintaining layer 2 connectivity and manageability with an AP in the BSS. 
     SUMMARY 
     The present invention is related to a method and system for performing peer-to-peer wireless communication between STAs in the same BSS while maintaining layer 2 connectivity and manageability with an AP in the BSS. A source STA, an AP and a destination STA negotiate a DLS channel for performing peer-to-peer communication between the source STA and the destination STA. The DLS channel may be different from a BSS channel used for communication between the AP and each of the STAs. The source STA and the destination STA then perform peer-to-peer communication on the negotiated DLS channel. The peer-to-peer traffic is offloaded to a different channel, (i.e., DLS channel), than the BSS channel while still ensuring layer 2 connectivity from the AP to the STAs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a conventional infrastructure mode WLAN. 
         FIG. 2  shows a signaling diagram of a DLS setup procedure in a wireless communication system including an AP, a first STA and a second STA in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When referred to hereafter, the terminology “STA” includes but is not limited to a user equipment (UE), a wireless transmit/receive unit (WTRU), 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 “AP” includes but is not limited to a base station, a Node-B, a site controller, or any other type of interfacing device in a wireless environment. 
     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components. 
     When referred to hereinafter, the terminology “BSS channel” refers to the channel used by the AP in the BSS to communicate with its associated STAs and the terminology “DLS channel” refers to the channel that are used by the STAs for their peer-to-peer communication. In the conventional WLAN system, (including IEEE 802-11e DLS system), the BSS channel is same as the DLS channel. In accordance with the present invention, the BSS channel may be different from the DLS channel and there may be multiple DLS channels in the BSS. Alternatively, more than one particular pair of STAs may use one DLS channel. 
     In accordance with the present invention, a pair of STAs and an AP negotiate a DLS channel for peer-to-peer communication between the STAs. Once the DLS channel is negotiated, the STAs perform peer-to-peer communication on the negotiated DLS channel. The STAs communicate with each other directly via the negotiated DLS channel while maintaining their BSS association with the AP at all times. Layer 2 connectivity between the AP and each of the STAs is ensured so that the AP retains full control over the STAs. 
       FIG. 2  shows a signaling diagram of a DLS setup process  210  in a wireless communication system  200  including an AP  202 , a first STA  204   a  and a second STA  204   b  in accordance with the present invention. The first STA  204   a  identifies a list of suitable DLS channels among all of the available channels in a BSS (step  212 ). The list of suitable DLS channels may be identified in many different ways as described hereinafter. 
     The list of suitable DLS channels may be stored in a database of the first STA  204   a  semi-statically. The database may be management information base (MIB). Alternatively, the list of suitable DLS channels may be set by the user manually using a user interface, such as hypertext markup language (HTML), extended markup language (XML) or equivalent user interfaces. Alternatively, the list of suitable DLS channels may be set by a network management entity remotely by using a communication protocol, such as simple network management protocol (SNMP), XML, a layer 3 (or higher) protocol, or a layer 2 protocol, (e.g., by using a layer 2 management frame). 
     The STA  204   a ,  204   b  may be configured to check, on a regular or triggered basis, for updates of the suitable DLS channels and related parameters contained in the STA&#39;s database. Alternatively, the STA  204   a ,  204   b  may be configured to check, on a regular or triggered basis, for updates of the list of suitable DLS channels and related parameters in a remote database. 
     Alternatively, the first STA  204   a  may generate the list by observing and evaluating the channels in the BSS. The first STA  204   a  observes and evaluates the channels available in the BSS based on predetermined criteria including, but not limited to, channel occupancy, interference levels or activity by other STAs on each of the channels. The first STA  204   a  then generates the list based on the evaluation of the channels. The first STA  204   a  may use dual-radios to observe and evaluate the channels. Alternatively, the first STA  204   a  may use non-transmission time periods on the BSS channel to evaluate other channels or use clear-to-send (CTS)-to-self and equivalent mechanisms to obtain measurement periods without interrupting its ongoing transmissions on the BSS channel. 
     Alternatively, the first STA  204   a  may determine the list of suitable DLS channels by randomly selecting channel(s) among the possible channels in the BSS. 
     Alternatively, the first STA  204   a  may obtain the list of suitable DLS channels from the AP  202 . The AP  202  manages at least one DLS channel and administers policies in the BSS. The AP  202  generates a list of suitable DLS channels by using any methods described hereinbefore and sends the list containing one or more suitable DLS channels to be used in the BSS to the STAs  204   a ,  204   b . Optionally, the list may include preference values for each or a set of entries in the list. The list of suitable DLS channels in the BSS may be signaled as part of a beacon frame, a probe response frame, an association response frame or any other frame. The frame may be a management frame, an action frame, a control frame, a data frame, or any other type of frame. The list may be sent to STAs  204   a ,  204   b  either by broadcasting/multicasting or by unicasting. Preferably, the first STA  204   a  obtains the list from the AP  202  during an association procedure or by soliciting the AP  202  to send the list. 
     In addition to the list of DLS channels, the AP  202  may send configuration information regarding multi-channel DLS policy in the BSS. The configuration information includes, but is not limited to, multi-channel DLS capability implemented in the BSS, multi-channel DLS capability enabled in the BSS and dwell times, maximum transmission times, channel access times, quality of service (QoS) settings, channel access schedules for one or more DLS channels. 
     The first STA  204   a  then sends a DLS request message to an AP  202  to initiate a DLP setup by negotiating for the DLS channel with the AP  202  and the second STA  204   b  (step  214 ). The DLS request message includes the list of suitable DLS channels proposed by the first STA  204   a  for a peer-to-peer communication with the second STA  204   b . The list of suitable DLS channels may include a preference among the DLS channels included in the list. The preference may be indicated implicitly by the order of the channels in the list. The DLS request message may also include a switch time indicating a start time for the peer-to-peer communication on a negotiated DLS channel. The DLS request message may be used in extension with the conventional IEEE 802.11e DLS request message. In such case, the list of parameters is to be understood as an extension compared to the conventional IEEE 802.11e DLS messages. 
     Upon reception of the DLS request message from the first STA  204   a , the AP  202  chooses the best DLS channel and synchronization schedule (step  216 ). The AP  202  may select the best DLS channel among the channels proposed by the first STA  204   a , or may reject all the channels proposed by the first STA  204   a . Alternatively, the AP  202  may maintain its own list of suitable DLS channels and compare its own list to the list proposed by the first STA  204   a  to select the best DLS channel. The AP  202  may observe and evaluate the channels available in the BSS based on predetermined criteria including, but not limited to, channel occupancy, interference levels or activity by STAs on each of the channels. Alternatively, the AP  202  may select the DLS channel based on pre-configuration. The AP  202  may use other information, (e.g., capability information), obtained from the first STA  204   a  and the second STA  204   b  to select the best DLS channel. 
     If the AP  202  selects the best DLS channel from the list proposed by the first STA  204   a , the process  210  proceeds to step  222 . If the AP  202  rejects the DLS channels proposed by the first STA  204   a , the AP  202  sends a DLS response message to the first STA  204   a  (step  218 ). The DLS response message may include a list of DLS channels proposed by the AP  202 . The DLS response message may include an alternative switch time suggested by the AP  202  in the switch time suggested by the first STA  204   a  is not acceptable. The DLS response message may include a synchronization schedule indicating a time schedule for the first STA  204   a  and the second STA  204   b  to switch back from the DLS channel to the BSS channel for the purpose of BSS connectivity once the DLS is setup. The DLS response message may also include the reason for the rejection. 
     Upon receipt of the DLS response message indicating an alternative suggestions by the AP  202  for any of the DLS parameters, (i.e., DLS channels, switch time), the first STA  204   a  may accept the DLS parameters proposed by the AP  202  or may terminate the DLS setup procedure. If the first STA  204   a  chooses to accept the alternative DLS parameters proposed by the AP  202 , the first STA  204   a  replies to the AP  202  using another DLS request which includes the accepted DLS parameters (step  220 ). 
     Upon receipt of the second DLS request message including the accepted DLS parameters, (which have been suggested by the AP  202 ), or when the AP  202  accepts the original DLS request at step  216 , the AP  202  sends a DLS request message to the second STA  204   b  (step  222 ). The DLS request message includes at least one of the best DLS channel selected by the AP  202 , a switch time selected by the AP  202 , and a synchronization schedule for the first STA  204   a  and the second STA  204   b  to switch back from the DLS channel to the BSS channel for the purpose of BSS connectivity once the DLS is setup. 
     The synchronization schedule may be provided by time intervals (or time periods) linked to the beacon intervals, (e.g., switch back every N beacons), a dwell time (or time periods) on the BSS channel, (e.g., remain on the BSS channel for M time units), or transmission schedule for the DLS channel, (e.g., start time, end time and transmission periods describing which time intervals the first STA and the second STA may spend on the DLS channel and which time intervals the first STA and the second STA must return to the BSS channel). 
     Upon receipt of the DLS request, the second STA  204   b  determines if the second STA  204   b  is willing to accept the peer-to-peer communication and may support the DLS parameters proposed by the AP  202  (step  224 ). The second STA  204   b  then sends a DLS response message indicating either acceptance or rejection to the AP  202  (step  226 ). 
     If the second STA  204   b  rejects the peer-to-peer communication request or any of the proposed DLS parameters, the second STA  204   b  sends a DLS response message indicating rejection to the AP  202 . Optionally, the second STA  204   b  may specify the cause of the rejection. Alternatively, the second STA  204   b  may send suggestions for any of DLS setup parameters. If the second STA  204   b  accepts the proposed DLS parameters, the second STA  204   b  sends a DLS response message indicating acceptance to the AP  202 . 
     Upon reception of the DLS response from the second STA  204   b , the AP  202  checks for acceptance or rejection of the proposed DLS set-up by the second STA  204   b  and sends a DLS response message to the first STA  204   a  (steps  228 ,  230 ). If the second STA  204   b  rejected the DLS set-up, the AP  202  sends a DLS response message indicating rejection to the first STA  204   a . Optionally, the AP  202  may forward the reason for rejection or alternative suggestions made by the second STA  204   b . Upon reception of the DLS response message indicating rejection, the procedure  200  terminates. The first STA  204   a  may re-initiate the DLS setup procedure  200  by returning to step  212 . 
     If the second STA  204   b  accepted the DLS set-up, the AP  202  sends a DLS response message indicating acceptance to the first STA  204   a . The first STA  204   a  and the second STA  204   b  then execute the key exchange procedure according to IEEE 802.11i, switch to the negotiated DLS channel at the specified channel switch time, and return to the BSS channel at the time periods (or time intervals) as specified in the synchronization schedule. 
     In accordance with another embodiment of the present invention, instead of initiating a procedure for setting up a DLS link via the DLS channel, the first STA  204   a  and the second STA  204   b  may first establish a DLS link via a conventional BSS channel. Once the first STA  204   a  and the second STA  204   b  have setup a DLS link on the BSS channel, one of the STAs  204   a ,  204   b  may request the other STA for switch to a DLS channel. Once the first STA  204   a  and the second STA  204   b  agree on a DLS channel, one of them notifies the AP  202 , which may agree or not. Once the AP  202  agrees on the switch of the channel, the first STA  204   a  and the second STA  204   b  perform a peer-to-peer communication via the negotiated DLS channel. 
     In selecting the best DLS channel, the AP  202  may implement different decision policies regarding its preference of the DLS channels to be used. For example, the AP  202  may allocate each new requested DLS link to a different DLS channel, or allocate a subsequently requested DLS link to a DLS channel that is already allocated for another pair of STAs. 
     The DLS channel may be a sub-channel of the BSS channel. For example, with a 40 MHz bandwidth BSS channel, STAs may choose to set-up a DLS channel with a 20 MHz bandwidth similar to the IEEE 802.11n legacy support mode. 
     Although the features and elements of the present invention are described in the preferred 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.