Patent Abstract:
A method and apparatus for selecting one of a plurality of multi-band access points (APs) to associate with a multi-band wireless transmit/receive unit (WTRU) are disclosed. The multi-band APs broadcast frequency band information regarding multiple frequency bands on which the multi-band AP is configured to operate. The multi-band WTRU selects a particular multi-band AP to associate with and a frequency band to use to communicate with the selected multi-band AP based on the frequency band information. If the multi-band WTRU receives frequency band information from the selected multi-band AP which indicates that a characteristic, (e.g., throughput, path loss, load, capacity, backhaul), of the selected frequency band is unacceptable, the multi-band WTRU determines whether to disassociate with the selected multi-band AP or to continue to associate with the selected multi-band AP via a different frequency band.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. application Ser. No. 11/284,242 filed on Nov. 21, 2005, which claims priority to U.S. Provisional Patent Application No. 60/667,523 filed Apr. 1, 2005, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a wireless communication system including a plurality of multi-band access points (APs) and a multi-band wireless transmit/receive unit (WTRU), (i.e., a mobile station). More particularly, the present invention is related to a method and apparatus for selecting a particular one of the multi-band APs to associate with based on frequency band information transmitted from the multi-band APs to the multi-band WTRU. 
     BACKGROUND 
     A typical wireless local area network (WLAN) includes an AP which provides radio access to WTRUs in a coverage area of the AP. The AP is comprised by a basic service set (BSS) which is a basic building block of an IEEE 802.11-based WLAN. Multiple BSSs may be interconnected through a distribution system (DS) to form an extended service set (ESS). 
     The WLAN may be configured in an infrastructure mode or an Ad-hoc mode. In the infrastructure mode, wireless communications are controlled by an AP. The AP periodically broadcasts beacon frames to enable WTRUs to identify, and communicate with, the AP. In the Ad-hoc mode, a plurality of WTRUs operate in a peer-to-peer communication mode. The WTRUs establish communication among themselves without the need of coordinating with a network element. However, an AP may be configured to act as a bridge or router to another network, such as the Internet. 
     The WTRUs and the AP may be configured to utilize multiple frequency bands for communication. In a conventional wireless communication system, a multi-band WTRU transmits multiple probe requests on different channels of a frequency band to discover if there are any APs available in the area. Once an AP receives the probe request, it sends a probe response packet to the WTRU. The AP will send the probe response packet on its operating channel in a particular frequency band. The probe response packet contains required parameters, such as supported rate, or the like, for the WTRU to associate with the AP. The WTRU will send an association request packet and waits for an association response packet from an AP for further data communication. 
     Once associated, the multi-band WTRU may scan other frequency bands in search of a better communication band by transmitting a probe request packet and waiting for a probe response packet. Upon receiving another probe response packet, the WTRU compares the frequency bands and/or the AP and selects a more preferable frequency band and/or AP. 
     In the conventional wireless communication system, the multi-band WTRU must scan and compare different frequency bands to determine the frequency band that provides the best quality of wireless communications. However, these scanning and comparison functions are time-consuming and require a significant amount of battery power. A method and apparatus for reducing the amount of time and battery power required to make frequency band and channel selection decisions is desired. 
     SUMMARY 
     The present invention is related to a method and apparatus for selecting one of a plurality of multi-band APs to associate with a multi-band WTRU. The multi-band APs broadcast frequency band information regarding multiple frequency bands on which the multi-band AP is configured to operate. The multi-band WTRU selects a particular multi-band AP to associate with and a frequency band to use to communicate with the selected multi-band AP based on the frequency band information. If the multi-band WTRU receives frequency band information from the selected multi-band AP which indicates that a characteristic, (e.g., throughput, path loss, load, capacity, backhaul), of the selected frequency band is unacceptable, the multi-band WTRU determines whether to disassociate with the selected multi-band AP or to continue to associate with the selected multi-band AP via a different frequency band. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows a wireless communication system including a plurality of multi-band APs and a multi-band WTRU which operate in accordance with the present invention; 
         FIG. 2  is an exemplary beacon frame which comprises frequency band information transmitted from the multi-band APs to the multi-band WTRU of the wireless communication system of  FIG. 1 ; 
         FIG. 3  is a flow diagram of a process for the multi-band WTRU to select one of the multi-band APs to associate with in accordance with the present invention; 
         FIG. 4  is a flow diagram of a process for the multi-band WTRU to determine whether to change a particular frequency band used for wireless communications with a multi-band AP or to associate with a different multi-band AP in accordance with the present invention; and 
         FIG. 5  is a flow diagram of a process for establishing a wireless communication link between the multi-band WTRU and a preferable multi-band AP over a preferable frequency band in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. Such WTRUs include, but are not limited to, phones, video phones, and Internet ready phones, personal data assistances (PDAs) and notebook computers with wireless modems that have network capabilities. 
     When referred to hereafter, the terminology “AP” includes but is not limited to a Node-B, a base station, a site controller or any other type of interfacing device in a wireless environment that provides other WTRUs with wireless access to a network with which the AP is associated. 
     The features and elements of the present invention may be implemented on a single IC, (such as an application specific integrated circuit (ASIC)), multiple ICs, discrete components or a combination of discrete components and ICs. 
     The present invention is applicable to any type of wireless communication systems including, but not limited to, 802.x-based wireless communication systems. 
       FIG. 1  shows a wireless communication system  100  including a plurality of multi-band APs  105   1 - 105   N  and a multi-band WTRU  110  which operate in accordance with the present invention. Each of the multi-band APs  105   1 - 105   N  and the multi-band WTRU  110  operate on at least two frequency bands. The multi-band APs  105   1 - 105   N  transmit frequency band information  115   1 - 115   N  which indicates the different multi-bands that the respective APs  105   1 - 105   N  are configured to operate on. Each of the multi-band APs  105   1 - 105   N  include a respective transceiver  120   1 - 120   N  and a respective processor  125   1 - 125   N . Each respective transceiver  120   1 - 120   N  is configured to operate on at least two different frequency bands. Each respective processor  125   1 - 125   N  generates and formats the respective frequency band information  115   1 - 115   N  and provides it to the transceiver  120   1 - 120   N  for transmission. The multi-band WTRU  110  also includes a transceiver  130  and a processor  135 . The transceiver  130  is configured to operate on at least two different frequency bands. The processor  135  processes the frequency band information  115   1 - 115   N  received by the transceiver  130  from the multi-band APs  105   1 - 105   N , selects a multi-band AP  105  to associate with, and a frequency band to use in communication with the selected multi-band AP  105 , based on the frequency band information  115   1 - 115   N . 
     The multi-band WTRU  110  and the multi-band APs  105   1 - 105   N  may use any management, control or data packet to provide the frequency band information to the multi-band WTRU  110 . For example, an authentication frame, (which is a management frame), can also be used to send multi-band frequency information. Similarly, this packet can be piggybacked on any of the current or future WLAN packets. 
     Alternatively, a proprietary message exchange between the multi-band WTRU  110  and the multi-band APs  105   1 - 105   N  may also be utilized to provide the frequency band information to the multi-band WTRU  110 . 
       FIG. 2  shows an exemplary beacon frame which comprises frequency band information  115  transmitted from each of the multi-band APs  105   1 - 105   N  to the multi-band WTRU  110  of the wireless communication system  100  of  FIG. 1 . The frequency band information  115  indicates whether a particular multi-band AP  105  supports multiple frequency bands  205   1 - 205   N , channel numbers  215  and timing information  220  or the like. 
     The frequency band information  115  may further include quality metric information  210   1 - 210   N  for each of the frequency bands  205   1 - 205   N . The quality metric information may include, but is not limited to, path loss, load, (e.g., the number of associated WTRUs  110 ), throughput, capacity and backhaul on each frequency band. 
       FIG. 3  is a flow diagram of a process  300  for establishing a wireless communication link between a particular one of  115   1 - 115   N  and the multi-band WTRU  110  in the wireless communication system  100  of  FIG. 1  based on frequency band information  115   1 - 115   N  transmitted from the multi-band APs  105   1 - 105   N  to the multi-band WTRU  110 . In step  305 , a plurality of multi-band APs  105   1 - 105   N  broadcast frequency band information  115   1 - 115   N  regarding multiple frequency bands on which the respective multi-band APs  105   1 - 105   N  are configured to operate. The frequency band information  115   1 - 115   N  may be broadcast in a beacon frame, as shown in  FIG. 2 . In step  310 , a multi-band WTRU  110  receives and processes the frequency band information  115   1 - 115   N . In step  315 , the multi-band WTRU  110  selects a particular one of the multi-band APs  105   1 - 105   N  to associate with, and a frequency band to use to communicate with the selected multi-band AP  105  based on the frequency band information  115   1 - 115   N . 
       FIG. 4  is a flow diagram of a process  400  for the multi-band WTRU  110  to determine whether to change a particular frequency band used for wireless communications with a multi-band AP  105 , or to associate with a different multi-band AP  105  in accordance with the present invention. In step  405 , the multi-band WTRU  110  associates with a particular multi-band AP  105  on a particular frequency band. In step  410 , the multi-band WTRU  110  receives frequency band information  115  from the particular multi-band AP  105  including a quality metric which indicates that the particular frequency band has, for example, poor throughput. In step  415 , the multi-band WTRU  110  either disassociates with that the multi-band AP  105  and associates with another multi-band AP  105  continues to associate with the same multi-band AP  105  over a different frequency band for which the frequency band information  115  includes a quality metric which indicates a good, (i.e., high), throughput. 
       FIG. 5  is a flow diagram of a process  500  for establishing a wireless communication link between the multi-band WTRU and a preferable multi-band AP over a preferable frequency band in accordance with the present invention. In step  505 , a multi-band WTRU  110  broadcasts an association request packet or a probe request packet which is received by a plurality of multi-band APs  105   1 - 105   N . The multi-band WTRU  110  may include an indication of the multi-band capability and related information of the WTRU  110  in the request packet. In step  510 , each of the multi-band APs  105   1 - 105   N  sends an association response packet or a probe response packet to the multi-band WTRU  110  which includes frequency band information  115   1 - 115   N in accordance with the multi-band capability of the WTRU  110 . In step  515 , the multi-band WTRU  110  selects a preferable frequency band and a preferable multi-band AP  105  to associate with based on the frequency band information  115   1 - 115   N . 
     In another embodiment, the wireless communication system  100  may also include a single-band AP and a single-band WTRU, in addition to the multi-band APs  105   1 - 105   N  and the multi-band WTRU  104   a . If a single-band WTRU is associated with a multi-band AP  105 , the information regarding the multiple frequency bands of the multi-band AP  105  other than information regarding the frequency band on which the single-band WTRU is configured to operate will be simply ignored by the single-band WTRU since the single-band WTRU not configured to communicate on multiple frequency bands. The single-band AP broadcasts its information regarding its single frequency band, (such as timing, load, or the like) in a beacon frame. Both a single-band WTRU and a multi-band WTRU  110  may utilize this information to decide whether or not to associate with the single-band AP. 
     In accordance with the present invention, the multi-band WTRU  110  is not required to consume significant time and battery power for scanning various frequency bands in search of an adequate AP to associate with. Moreover, by providing the multi-band WTRU  110  with quality metrics of each frequency band, (such as throughput), the WTRU is enabled to optimize not only its own throughput, but also the throughput of the AP  105 . 
     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.

Technology Classification (CPC): 8