Abstract:
A method and system for conveying backhaul link information for intelligent selection of a mesh access point (MAP) in a mesh network are disclosed. The mesh network includes a plurality of MAPs. The MAPs send backhaul link information regarding backhaul connections between each MAP and any interconnections in the mesh network to a wireless transmit/receive unit (WTRU). The WTRU then determines a performance value with respect to the MAPs based on the backhaul link information and selects one of the MAPs to associate with based on the performance value. The WTRU may send information about interconnection needs of the WTRU to the MAPs, and the MAPs may generate the backhaul link information based on the interconnection needs of the WTRU.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. provisional application Ser. No. 60/690,244 filed Jun. 14, 2005, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention is related to a wireless communication system. More particularly, the present invention is related to a method and system for conveying backhaul link information for intelligent selection of a mesh access point (MAP) in a mesh network.  
       BACKGROUND  
       [0003]     A conventional wireless network includes a set of access points (APs), (also known as base stations), each of which is connected to a backhaul network. In certain deployments, the cost of directly connecting a given AP to the backhaul network is too high. Thus, indirectly connecting the AP to the backhaul network may be more attractive. This indirect connection is typically accomplished by relaying information to and from neighboring APs in a mesh network. This is referred to as a mesh architecture.  
         [0004]     A mesh network is a local area network (LAN) including a plurality of mesh points (MPs). The connections between the MPs may be wired or wireless. The points of interconnection between a mesh system and a non-mesh system are referred to as portals. A mesh system with multiple portals is referred to as a multi-portal mesh system. A node capable of both AP and MP functionalities is referred to as a mesh access point (MAP).  FIG. 1  shows an exemplary mesh network  100 . The mesh network  100  includes a plurality of MPs  102 , a plurality of MAPs  104  and a mesh portal  106 . The MPs  102  serve as forwarding and relaying nodes in the mesh network  100 . The MPs  102  receive traffic on incoming links and forward the traffic on outgoing links. The MAPs  104  are also MPs with an interface to provide radio access to a plurality of wireless transmit/receive units (WTRUs)  108  to provide wireless services in a certain geographic area. The mesh portal  106  provides connectivity to a backbone network  110 , (such as the Internet), in the mesh network  100 . Thus, the mesh portal  106  acts as an MP with a special interface to the backbone network  110 . Each of the WTRUs  108  communicates with another WTRU in the mesh network  100 , or to the backbone network  110 , via the MAPs  104  and the mesh portal  106 . The MAPs  104  forward the traffic generated by the WTRUs  108  to another MAP  104  or the mesh portal  106  by relaying the traffic via intermittent MPs  102  and/or MAPs  104 .  
         [0005]     A mesh network is reliable and offers redundancy. Even if one or more of the MPs can no longer operate, the rest of the MPs can still communicate with each other, directly or through one or more intermediate MPs such that the network may function properly. Other considerations, such as ease and speed of deployment, are advantages of the mesh network since a mesh network may be deployed without having to provide direct backhaul links and interconnection modules for each MP in the mesh network.  
         [0006]     In conventional non-mesh wireless communication systems, a WTRU needs to estimate which AP will provide the best communication link to the WTRU. WTRUs typically use the following information and methods for determining which AP to associate with:  
         [0007]     1) the identity of the network of which a candidate AP is a part of, (e.g., in IEEE 802.11 systems, this identity corresponds to the service set identifier (SSID) provided to the WTRUs in a beacon frame or a probe response frame);  
         [0008]     2) the capabilities of the candidate AP including information regarding which services the AP supports, (e.g., in IEEE 802.11 systems, this capability information is included in a capability information field in a beacon frame or a probe response frame); or  
         [0009]     3) the expected achievable data throughput, (e.g., the WTRU may estimate the expected throughput by measuring a received power it perceives from an AP on beacon frames, probe response frames or any other frames). The received power, a signal-to-interference-plus-noise-ratio (SINR) or similar measurements typically sets the maximum rate the WTRU may achieve on a given communication link. The WTRU can also use channel occupancy or channel load measurements, whether measured by the WTRU or collected from the AP, to refine the expected throughput estimate.  
         [0010]     The above-described information and methods utilized to select an AP that a WTRU should associate with are no longer adequate in a mesh network. For example, in a conventional infrastructure mode WLAN, the throughput achieved on a given WTRU-AP link depends only on the characteristics of that particular radio link between the AP and the WTRU, (i.e., channel occupancy, received power, a signal-to-interference and noise ratio (SINR), or the like). However, in a mesh network, the throughput not only depends on the characteristics of the radio link between a given WTRU and its serving MAP, but it also depends on the characteristics of the radio link(s) between the serving MAP and other intermediate MPs that forward the traffic from the serving MAP to the mesh portal.  
         [0011]      FIG. 2  illustrates an example of an intelligent association problem in a conventional mesh network  200 . In this example, the mesh network  200  comprises three MAPs  201 ,  202  and  203 . The MAPs  201  and  203  are mesh portals which have connectivity to the Internet  230  via a router  220 . The interconnection resources of the MAPs  201 ,  203  may be Ethernet-based. In this example, the MAP  202  and the MAP  203  are candidate MAPs for a WTRU  210 . If the WTRU  210  is associated with the MAP  102 , traffic to/from the Internet  230  is routed via radio links L 2  and L 1  via the MAP  201 . If the WTRU  210  is associated with the MAP  203 , the traffic to/from the Internet  230  is routed via radio link L 3 . An exemplary set of radio link characteristics for the radio links L 1 , L 2  and L 3  is illustrated in Table 1 below.  
                                                         TABLE 1                       Radio           Transmission   Single-link       link   Nodes   SNR   rate   throughput                                L1   MAP1   MAP2   10 dB   12 Mbps    5 Mbps       L2   STA   MAP2   35 dB   54 Mbps   20 Mbps       L3   STA   MAP3   20 dB   36 Mbps   15 Mbps                    
         [0012]     According to Table 1, if the WTRU  210  associates with the MAP  203 , the throughput would be 15 Mbps. However, if the WTRU  210  associates with the MAP  202 , the throughput would be determined by the combination of data throughput of two links L 1 , L 2 , which is typically estimated as follows: 
 
1/(1/troughput_L1+1/throughput_L2). Equation (1) 
 
         [0013]     Applying Equation (1) to radio links L 1  and L 2 , the combined throughput would be 1/(⅕+ 1/20) or 4 Mbps. From this calculation it becomes evident that the WTRU  210  will experience a better throughput by associating with the MAP  203  than by associating with the MAP  202 . From the perspective of the overall mesh network  200 , the preferred association of the WTRU  210  is to the MAP  203 . The radio connection of L 1  and L 2  between the WTRU  210  and the MAP  201  offers 3.75 times (i.e., 15 Mbps/4 Mbps) less throughput than the multi-hop radio connection between the WTRU  210  and the MAP  203 .  
         [0014]     According to the prior art, in the foregoing example, the radio link L 2  between the WTRU  210  and the MAP  202  seems more attractive, (in terms of signal-to-noise ratio (SNR), estimated achievable transmission rate, estimate single-link throughput, channel occupancy, or the like), than the radio link L 3  between the WTRU  210  and the MAP  203 . In the prior art, since the WTRU  210  has no means of knowing that associating with the MAP  203  will result in a better throughput than associating with the MAP  202 , the WTRU  210  may end up with a less favorable MAP.  
         [0015]     Accordingly, it is desirable to have a method and apparatus for enabling a WTRU to intelligently associate with a MAP in a mesh network.  
       SUMMARY  
       [0016]     The present invention is related to a method and system for conveying backhaul link information for intelligent selection of a mesh access point (MAP) in a mesh network. The mesh network includes a plurality of MAPs. The MAPs send backhaul link information regarding backhaul connections between each MAP and any interconnections in the mesh network to a WTRU. The WTRU then determines a performance value with respect to the MAPs based on the backhaul link information and selects one of the MAPs to associate with based on the performance value. The WTRU may send information about interconnection needs of the WTRU to the MAPs, and the MAPs may generate the backhaul link information based on the interconnection needs of the WTRU.  
         [0017]     In prior art systems, a WTRU may associate to a MAP that will result in worse performance than other MAPs because the WTRU has no means of knowing about the performance of the different radio links that are used to convey its traffic to/from a desired mesh portal. In accordance with the present invention, a WTRU may estimate the expected throughput for the end-to-end connection, which allows the WTRU to associate to a MAP that provides the best performance from the point of view of both the WTRU and the overall system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is an exemplary block diagram of a conventional mesh network.  
         [0019]      FIG. 2  illustrates an example of an intelligent association problem in a conventional mesh network.  
         [0020]      FIG. 3  is a signaling diagram between a MAP and a WTRU for selecting a MAP in a mesh network in accordance with an embodiment of the present invention.  
         [0021]      FIG. 4  is a signaling diagram between a MAP and a WTRU for selecting a MAP in a mesh network in accordance with another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     When referred to hereafter, the terminology “WTRU” includes but is not limited to a user equipment, a mobile station, 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 “MAP” includes but is not limited to a base station, a Node-B, a site controller, an access point or any other type of interfacing device that has a mesh functionality in a wireless environment.  
         [0023]     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.  
         [0024]      FIG. 3  is a signaling diagram between MAPs  302   a - 302   n  and a WTRU  304  for selecting one of the MAPs  302   a - 302   n  to associate with in accordance with an embodiment of the present invention. At least one of the MAPs  302   a - 302   n  in the mesh network sends backhaul link information regarding backhaul connections between each of the MAPs  302   a - 302   n  and any interconnections in the mesh network to the WTRU  304  (step  312 ). The backhaul link information may be broadcast, (e.g., via a beacon frame), in a region covered by each of the MAPs  302   a - 302   n  or may be sent via unicast, (e.g., via a probe response frame), to a particular WTRU. Of course, other methods known to those skilled in the art may also be used to provide backhaul link information to WTRUs, in accordance with the present invention.  
         [0025]     The backhaul link information that each of the MAPs  302   a - 302   n  sends to the WTRU  304  includes, but is not limited to: 1) the number of portals each MAP  302   a - 302   n  can communicate with; 2) the number of routes separated from each MAP  302   a - 302   n  to a mesh portal; 3) the number of hops and/or the number of MPs per route separated from each MAP  302   a - 302   n  to a mesh portal; 4) an average transmission rate used on each radio link, or by each of the different MPs, involved in the forwarding of packets between each MAP  302   a - 302   n  and a mesh portal; 5) an estimated throughput per radio link, or per MP, involved in the forwarding of packets between each MAP  302   a - 302   n  and a mesh portal; 6) channel occupancy perceived on each radio link, or by each MP, involved in the forwarding of packets between each MAP  302   a - 302   n  and a mesh portal; 7) radio resources allocated on each radio link, or by each MP, involved in the forwarding of packets between each of the MAPs  302   a - 302   n  and a mesh portal; 8) quality experienced on each radio link, or by each MP, involved in the forwarding of packets between each of the MAPs  302   a - 302   n  and a mesh portal, (e.g., queued time, medium access delay, time jitter, time latency, a packet error rate); and 9) any performance metric comprising a weighted sum or any other combination of the above-mentioned metrics.  
         [0026]     The WTRU  304  then determines an end-to-end performance value with respect to each of the MAPs  302   a - 302   n  based on the received backhaul link information (step  314 ). The backhaul link information enables the WTRU  304  to intelligently estimate the end-to-end performance value after associating with a particular MAP  302   a - 302   n . For example, the WTRU  304  may estimate a data throughput that the WTRU  304  can expect along an end-to-end radio connection by associating with a particular MAP  302   a - 302   n.    
         [0027]     The WTRU  304  then selects one of the MAPs  302   a - 302   n  to associate with based on the performance value (step  316 ). Unlike conventional methods of making an association decision, the decision is not solely based on the expected performance, (e.g., expected throughput), of the direct radio link between the WTRU  304  and a particular MAP  302   a - 302   n , but on the end-to-end performance value, such as end-to-end throughput.  
         [0028]      FIG. 4  is a signaling diagram between at least one MAP  402   a - 402   n  and a WTRU  404  for selecting one of the MAPs  402   a - 402   n  in accordance with another embodiment of the present invention. In this embodiment, the MAPs  402   a - 402   n  generate the backhaul link information based on interconnection needs of the WTRU  404  in terms of a particular mesh portal or a particular MAP  402   a - 402   n . As the interconnection needs may vary from one WTRU  404  to another, it may be desirable for a MAP  402   a - 402   n  to know the interconnection needs, (e.g., a desired mesh portal), of a given WTRU  404  in order for the MAP  402   a - 402   n  to communicate backhaul link information that is relevant to the WTRU  404 .  
         [0029]     The WTRU  404  sends a message for interconnection needs of the WTRU  404  to at least one MAP  402   a - 402   n  (step  412 ). Information included in the message includes, but is not limited to: 1) an IP address that the WTRU  404  desires to connect with; 2) a medium access control (MAC) address of the nodes that the WTRU  404  wants to connect with; 3) an address allowing a MAP  402   a - 402   n  to identify a given mesh portal from other mesh portals; 4) a subnet address that the WTRU  404  wants to connect with; and 5) a predetermined code or flag which allows a MAP  402   a - 402   n  to determine the connectivity needs of the WTRU  404 . The message may be sent via a probe request frame, a special control frame, as part of the body of a data frame, a broadcast frame, or any other type of frames.  
         [0030]     Each of the MAPs  402   a - 402   n  generates backhaul link information based on the interconnection needs of the WTRU  404  (step  414 ). For example, a WTRU that needs to connect to the Internet may be interested in choosing a MAP that offers the best route to a mesh portal interconnecting the mesh network to the Internet. On the other hand, a WTRU located in a given basic service set (BSS) that is interested in communicating with another WTRU located in a neighboring BSS would choose a MAP offering the best route to the a base station, (or a MAP), serving that neighbor BSS.  
         [0031]     Each of the MAPs  402   a - 402   n  then sends the backhaul link information to the WTRU  404  (step  416 ). The backhaul link information may be broadcast, (e.g., via a beacon frame), or may be unicast directly to the WTRU  404 , (e.g., via a probe response frame).  
         [0032]     The WTRU  404  then determines an end-to-end performance value with respect to each of the MAPs  402   a - 402   n  based on the received backhaul link information (step  418 ). The backhaul link information enables the WTRU  404  to intelligently estimate an end-to-end performance value after associating with a particular MAP  402   a - 402   n . For example, the WTRU  404  may estimate a data throughput the WTRU  404  can expect along an end-to-end radio connection by associating with a particular MAP  402   a - 402   n . The WTRU  404  then selects one of the MAPs  402   a - 402   n  to associate with based on the performance value (step  420 ).  
         [0033]     It is also possible for the MAP to communicate to the WTRU all backhaul link information without any regards to the interconnection needs of the WTRU.  
         [0034]     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.