Abstract:
A method for wireless communication determines, for a client device having a first wireless connection with a first connection point, to initiate a second wireless connection between the client device and a second connection point, wherein the first connection point includes an Access Point and the second connection point includes a Base Station. The method sends a message from the second connection point to the first connection point, including instructions for the first connection point to communicate with the client device using either a Point Coordinate Function (PCF) or a Distributed Coordinate Function (DCF). In addition, the method initiates the second wireless connection between the client device and the second communication point.

Description:
PRIORITY 
       [0001]    This application claims the benefit of priority of U.S. Provisional Application No. 60/859,518, filed Nov. 17, 2006, which is incorporated by reference herein in its entirety for any purpose. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to methods and devices for communication schemes and, more particularly, to methods and devices of dual-mode communication systems. 
       BACKGROUND 
       [0003]    Wireless communication schemes allow wireless devices to communicate without the necessity of wired connections. Standards for wireless communication schemes are typically developed by organizations oriented toward a particular industry and then adopted within and/or across that industry. Standards may be developed and adopted in order to ensure, among other things, uniformity and interoperability within the industry, reduced development time, lower production costs, protection against obsolescence, and increased product quality and safety. Two such examples of wireless communication standards include Institute of Electrical and Electronics Engineers (IEEE) 802.11 and 802.16. 
         [0004]    IEEE 802.11 includes the family of standards developed by the IEEE 802.11 committee, which established standards for Wireless Local Area Networks (WLAN). In part, the IEEE 802.11 family of standards defines methods of interoperability between wireless receivers and wireless transmitters. Wi-Fi™, a trademark of the Wi-Fi Alliance, is the term commonly used to refer to wireless communication and communication networks that are based on the IEEE 802.11 family of standards. As used herein, the term “Wi-Fi” will be used to refer to any communication network, system, apparatus, device, method, etc. that utilizes or is based on the 802.11 family of standards. 
         [0005]      FIG. 1  is a block diagram of an exemplary Wi-Fi communication network. As shown in  FIG. 1 , an exemplary Wi-Fi network may include one or more transmitters, e.g., Access Points (AP)  110 , including APs  110   a ,  110   b , and  110   c , one or more receivers, e.g., mobile subscriber stations (MSS)  120 , including MSSs  120   a ,  120   b , and  120   c , and network  150 . 
         [0006]    The one or more APs  110  may be any type of communication device configured to transmit and/or receive communications based on the IEEE 802.11 family of standards, many of which are known in the art. In one exemplary embodiment, the one or more APs  110  may be connected to network  150 . In addition, APs  110  may be configured to communicate with one or more MSSs  120  and other APs  110  using the communication protocols defined by the 802.11 family of standards. In one exemplary embodiment, one of APs  110  may serve as an intermediary between one or more MSSs  120  or other APs  110  and network  150 . Network  150  may include, for example, any combination of one or more wide area networks (WAN), local area network (LAN), intranets, extranets, Internet, etc. 
         [0007]    Each MSS  120  may be any type of computing device configured to transmit and/or receive data to and from APs  110  and/or other MSSs  120  using the communication protocols defined by the 802.11 family of standards. MSSs  120  may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, etc. 
         [0008]    Each AP  110  may have a broadcast range within which AP  110  may communicate with one or more MSS  120  and other APs  110 . Similarly, MSSs  120  may have a broadcast range within which MSS  120  may communicate with one or more other MSSs  120  and/or APs  110 . Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). While the term “transmitter” is used to refer to AP  110  and the term “receiver” is used to refer to MSS  120 , both AP  110  and MSS  120  may be configured to transmit and/or receive data. 
         [0009]    The most commonly referenced amendments to the 802.11 family of standards include 802.11a, 802.11b, and 802.11g. 802.11a provides up to 54 Mbps transmission in the 5 GHz frequency band and uses an Orthogonal Frequency Division Multiplexing (OFDM) encoding scheme. 802.11b provides 11 Mbps transmission in the 2.4 GHz frequency band and uses Direct Sequence Spread Spectrum (DSSS) encoding. 802.11g provides up to 54 Mbps transmission in the 2.4 GHz frequency band and also uses OFDM encoding. In the United States and Canada, the allocated frequency for 802.11b/g is divided into 11 overlapping channels. Each channel is 22 MHz wide with a 5 MHz step to the next higher channel. While communication typically occurs in channels 1, 6, and 11 to avoid overlap, communication may occur within any of the channels. 
         [0010]    The 802.11 family of standards requires the use of Distributed Coordinate Function (DCF), a form of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), a contention-based protocol. Generally, when MSS  120  seeks to transmit using CSMA/CA, it must first listen to the channel for a predetermined amount of time to check for activity on the channel. If the channel is sensed “idle,” MSS  120  may be permitted to transmit. If the channel is sensed “busy,” MSS  120  may have to defer its transmission until such time as the channel is sensed “idle.” In other words, in a Wi-Fi network, all MSSs  120  that seek to pass data to an AP  110  or another MSS  120  may compete for access on a random interrupt basis. This is commonly referred to as contention access. 
         [0011]    As an optional access method, the 802.11 standard also defines the Point Coordinate Function (PCF). PCF is a contention-free access method that enables the transmission of time-sensitive information. With PCF, a point coordinator within AP  110  controls which MSSs  120  can transmit during any given period of time. For example, the point coordinator may first poll MSS  120   a  and, during a specified period of time, MSS  120   a  may transmit data. The point coordinator may then poll the next MSS  120  (e.g., MSS  120   b ) and, during a second specified period of time, MSS  120   b  may transmit data. The point coordinator may continue down the polling list, thereby allowing each MSS  120  connected to AP  110  a period of time during which it may send data. 
         [0012]    AP  110  and MSS  120  may communicate by means of communication packets. These communication packets are called MAC “frames.”  FIG. 2   a  illustrates an exemplary MAC frame format defined by the 802.11 family of standards. As shown in  FIG. 2   a , the MAC frame format may include the following fields: Frame Control (i.e., control data for the frame), Duration ID (i.e., duration of frame for data frames, identity of transmitting station for control frames), Address  1  (i.e., source address), Address  2  (i.e., destination address), Address  3  (i.e., receiving station address), Address  4  (i.e., transmitting station address), Sequence Control (i.e., sequence number and fragment number), Data (i.e., variable length message body), and FCS (i.e., 32-bit Cyclic Redundancy Check (CRC) value). 
         [0013]      FIG. 2   b  illustrates an exemplary MAC Frame Control field defined by the 802.11 family of standards. As shown in  FIG. 2   b , the Frame Control field may consist of a number of sub-fields: Version (i.e., 802.11 version in use), Type (e.g., management, control, or data frame type), Sub-type (e.g., authentication frame, de-authentication frame, association request frame, association response frame, re-association request frame, re-association response frame, disassociation frame, beacon frame, probe frame, probe request frame, probe response frame, etc.), To DS and From DS (i.e., combination of values to indicate the distribution system combination), More Fragments (MF) (i.e., indication of more frame fragments to follow), Retry (i.e., retransmission), Power Management (PWR) (e.g., power save, active mode, etc.), More (i.e., indication of more frames to follow), Wired Equivalent Privacy (WEP) (i.e., indication of WEP data processing), and Order (O) (i.e., position of the current frame relative to other frames). 
         [0014]      FIG. 3  is a signaling diagram of an exemplary embodiment of communication between one MSS  120  and one or more APs  110 . As shown in  FIG. 3 , MAC frames may be used to “handover” or transfer communication for MSS  120  (e.g., MSS  120   b ) between a serving AP  110 , e.g., AP  110   a , and a target AP  110 , e.g., AP  110   b . Serving AP  110   a  may be an AP  110  currently providing service or communication to MSS  120   b , and target AP  110   b  may be an AP  110  with which MSS  120   b  seeks to establish communication. 
         [0015]    Generally, handover may be accomplished in two phases—a discovery phase and a re-authentication phase. In the discovery phase, MSS  120   b  may send a probe request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a probe request) to find potential target APs  110 . The probe request may be broadcast on all channels to all APs  110  within range. In response, all APs  110  within range may send a probe request response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a probe request response). For example, if AP  110   b  is within range, AP  110   b  may respond to MSS  120   b  with a probe request response. 
         [0016]    Once MSS  120   b  has identified target AP  110   b  for handover, a re-authentication phase may begin. To begin re-authentication, MSS  120   b  may send a re-association request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association request) to target AP  110   b . Through the use of Inter-Access Point Protocol (IAPP), which is based on 802.11 f, notification of the handover may be made to serving AP  110   a  as well as to the rest of the network by target AP  110   b . For example, AP  110   b  may communicate to AP  110   a  by sending a security block. AP  110   a  may acknowledge the security block, and AP  110   b  may then send a move request. AP  110   a  may acknowledge the move request, updating data tables and sending a move response. 
         [0017]    Once the network processing is complete, AP  110   b  may send a re-association response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association response) to MSS  120   b . Once the re-association response is received, MSS  120   b  may begin regular communication with AP  110   b.    
         [0018]    In this manner, wireless communication devices that operate according to the 802.11 family of standards, such as MSS  120   b , may change physical locations yet maintain continuous communication with a network, such as network  150 . 
         [0019]    A second set of standards developed for wireless communication is IEEE 802.16. IEEE 802.16 includes the family of standards developed by the IEEE 802.16 committee, establishing standards for broadband wireless access. In part, the IEEE 802.16 family of standards defines the interoperability of broadband Wireless Metropolitan Area Networks (WirelessMAN). Generally speaking, WirelessMANs are typically large computer networks utilizing wireless infrastructure to form connections between subscriber stations. Wi-Max, a term defined and promoted by The Wi-Max Forum™, is commonly used to refer to WirelessMANs and wireless communication and communication networks that are based on the IEEE 802.16 standard. As used herein, the term “Wi-Max” will be used to refer to any communication network, system, apparatus, device, method, etc. that utilizes or is based on the 802.16 family of standards. 
         [0020]      FIG. 4  is a block diagram of an exemplary Wi-Max network based on the 802.16 family of standards. As shown in  FIG. 4 , a Wi-Max network may include one or more transmitters, e.g., Base Stations (BS)  410 , including BSs  410   a ,  410   b , and  410   c , one or more receivers, e.g., stationary subscriber stations (SS)  420 , including SSs  420   a  and  420   b , and mobile subscriber stations (MSS)  430 , including MSSs  430   a ,  430   b , and  430   c.    
         [0021]    The one or more BSs  410  may be any type of communication device configured to transmit and/or receive communications based on the IEEE 802.16 family of standards, many of which are known in the art. In one exemplary embodiment, the one or more BSs  410  may be connected to a network  450 . In addition, BSs  410  may be configured to communicate with one or more SSs  420 , MSSs  430 , and/or other BSs  410  using the communication protocols defined by the 802.16 family of standards. In one exemplary embodiment, BS  410  may serve as an intermediary between one or more SSs  420 , MSSs  430 , or BSs  410  and a network  450 . Network  450  may be wired, wireless, or any combination thereof. Network  450  may include, for example, any combination of one or more WANs, LANs, intranets, extranets, Internet, etc. 
         [0022]    SS  420  and MSS  430  may include any type of wireless client device configured to communicate with BS  410  and/or other SSs  420  and MSSs  430  using the communication protocols defined by the 802.16 family of standards. Each SS  420  and MSS  430  may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, etc. In one exemplary embodiment, SS  420  may be a Wi-Fi AP enabled to communicate with BS  410  using the communication protocols defined by the 802.16 family of standards. 
         [0023]    Each BS  410  may have a broadcast range within which that BS  410  may communicate with SS  420 , MSS  430 , and one or more other BSs  410 . Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). Similarly, each SS  420  and MSS  430  may have broadcast ranges within which that SS  420  and MSS  430  may communicate with one or more other SSs  420 , MSSs  430  and/or BSs  410 . Broadcast ranges may vary due to power levels, location, interference (physical, electrical, etc.). While the term “transmitter” is used to refer to BS  410  and the term “receiver” is used to refer to SS  420  and MSS  430 , any of BS  410 , SS  420 , and MSS  430  may be configured to transmit and/or receive data. 
         [0024]    In addition to the ability of each BS  410  to connect and communicate with SS  420  and MSS  430 , each BS  410  may also connect and communicate with one or more other BSs  410  using a line-of-sight, wireless link using the protocols and standards defined by 802.16 family of standards. In other words, a Wi-Max network may provide two forms of wireless communication: a point-to-point (P2P) communication (e.g., between BS  410   a  and BS  410   b ) that operates at frequencies up to 66 GHz, and a point-to-multipoint (P2MP) communication (e.g., between BS  410  and one or more SSs  420  and/or MSSs  430 ) that operates in the 2.0 to 11.0 GHz range. In one exemplary embodiment, P2MP communication may include so-called Mobile Wi-Max (e.g., communication between BS  410  and one or more MSSs  430 ) Mobile Wi-Max is based on IEEE 802.16e-2005 and may operate in the 2.3 GHz, 2.5 GHz, 3.3 GHz, and 3.4-3.8 GHz spectrum bands. 
         [0025]    The 802.16 family of standards specifies a MAC layer Time Division Multiplex (TDM) downlink coupled with a Time Division Multiple Access (TDMA) uplink. The 802.16 family of standards may also support both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) operational modes. TDD is a technique in which the system may transmit and receive within the same channel, assigning time slices for transmit and receive mode. FDD, in contrast, may require two separate spectrums. 
         [0026]    Transmission time may be divided into variable length frames. In an FDD system, the uplink (e.g., SS to BS or MSS to BS) and downlink (e.g., BS to SS or BS to MSS) sub-frames may operate on separate uplink and downlink channels. In a TDD system, each frame may be divided into a downlink sub-frame and an uplink sub-frame operating on a single channel. 
         [0027]      FIG. 5  illustrates an exemplary MAC frame format based on the 802.16 family of standards. As shown in  FIG. 5 , the MAC frame format may include a DL-MAP and a UL-MAP. The DL-MAP is a directory of the slot locations within the downlink sub-frame. The UL-MAP is a directory of slot locations within the uplink sub-frame. Through the DL-MAP and UL-MAP sub-frames, BS  410  may allocate access to the channel for both uplink and downlink communication. 
         [0028]    In contrast to a Wi-Fi network, a Wi-Max network may use a scheduling algorithm by which subscriber stations (e.g., BS  410 , SS  420 , MSS  430 , etc.) may compete only once for initial entry to the network (i.e., the communication network provided by a serving BS  410  to subscriber stations within range). Once initial entry into the network is accomplished, access slots may be allocated by BS  410 . The access slot may be enlarged or contracted, but the access slot remains assigned to a specific subscriber station, thereby precluding the use of the access slot by other subscriber stations. Thus, the scheduling algorithm may allow BS  410  to balance the access slot assignments among the application needs of one or more subscriber stations. 
         [0029]    BS  410 , SS  420 , MSS  430  may communicate with each other through the use of MAC frames. MAC frames may be used to “handover,” or transfer communication, from a serving BS  410 , e.g., BS  410   a , to a target BS  410 , e.g., BS  410   b . A handover may occur when a subscriber station moves from within the broadcast range of one BS  410  to the broadcast range of another BS  410 . Handovers may also occur when a BS  410  is disabled, suffers from a reduction in broadcast power, is removed from service, etc. 
         [0030]      FIG. 6  is a signaling diagram of an exemplary handover between two BSs  410 . When MSS  430  (e.g., MSS  430   b ) prepares to handover from a serving BS  410  (e.g., BS  410   a ) to a target BS  410  (e.g., BS  410   b ), serving BS  410   a  may transmit a Mobile Neighbor Advertisement (MOB_NBR_ADV) message to MSS  430   b . Through the MOB_NBR_ADV message, MSS  430   b  may acquire information on one or more neighboring BSs  410 . The MOB_NBR_ADV message may include a plurality of information elements (IEs), including, for example, a Management Message Type IE indicating a type of transmission message, an Operator ID IE indicating a network identifier, an N_NEIGHBORS IE indicating the number of neighbor BSs  410 , a Neighbor BS-ID IE indicating IDs of neighboring BSs  410 , a physical frequency IE indicating the channel frequency of neighboring BSs  410 , and a TLV (Type, Length, Value) Encoded Neighbor Information IE providing other information related to the neighboring BSs  410 . 
         [0031]    MSS  430   b  may then transmit a Mobile Scanning Interval Allocation Request (MOB_SCN_REQ) message to the serving BS  410   a . The MOB_SCN_REQ may be used by MSS  430   b  to initiate scanning of carrier-to-interference and noise ratios (CINRs) of pilot signals transmitted from neighboring BSs  410  and serving BS  410   a . CINR scanning of pilot signals may be used to evaluate transmission power associated with the neighboring BSs  410  and serving BS  410   a . The MOB_SCN_REQ message may include a plurality of IEs, such as, for example, a Management Message Type IE indicating a type of transmission message, a Scan Duration IE indicating a scan duration for which MSS  430   b  may scan CINRs of pilot signals received from neighboring BSs  410 , and a Start Frame IE indicating a frame at which MSS  430   b  may start a scanning operation. 
         [0032]    Upon receiving the MOB_SCN_REQ message, serving BS  410   a  may prepare and send a Mobile Scanning Interval Allocation Response (MOB_SCN_RSP) message to MSS  430   b . The MOB_SCN_RSP message may include information which MSS  430   b  may use when scanning neighboring BSs  410 , such as, for example, a Management Message Type IE indicating a type of transmission message, a Connection ID (CID) IE indicating a CID of the MSS that transmitted the MOB_SCN_REQ message (i.e., MSS  430   b ), a Scan Duration IE, and a Start Frame IE indicating a time at which a scanning operation may start. The Scan Duration may indicate a scanning duration for which the pilot CINR scanning is performed. In one exemplary embodiment, if the Scan Duration is set to “0” (Scan Duration=0), it may indicate that the scan request is rejected. 
         [0033]    When MSS  430   b  receives the MOB_SCN_RSP message, MSS  430   b  may perform CINR scanning on the pilot signals received from serving BS  410   a  and any neighboring BSs  410 . Based on the CINR scanning of the pilot signals, MSS  430   b  may determine if it should change from serving BS  410   a  to target BS  410   b.    
         [0034]    If MSS  430   b  makes a determination to change from serving BS  410   a  to target BS  410   b , MSS  430   b  may transmit a Mobile Subscriber Station Handover Request (MOB_MSSHO_REQ) message to serving BS  410   a . The MOB_MSSHO_REQ message may include a plurality of IEs, including, for example, a Management Message Type IE indicating a type of a transmission message and the scanning results acquired by the MSS  430   b . In addition, the MOB_MSSHO_REQ message may include the IDs of neighboring BSs  410 , a service level that may be provided to the MSS  430   b  by the neighboring BSs  410 , and an Estimated Handover Time (Estimated HO Time). Estimated HO Time may indicate the time at which the MSS  430   b  may select one of the neighboring BSs  410  as the target and begin handover. When serving BS  410   a  receives the MOB_MSSHO_REQ message transmitted by MSS  430   b , serving BS  410   a  may detect a list of potential target BSs  410  to which the MSS  430   b  may be handed over. 
         [0035]    Serving BS  410   a  may transmit a Mobile BS Handover Response (MOB_BSHO_RSP) message to MSS  430   b  in response to the MOB_MSSHO_REQ message. The MOB_BSHO_RSP message may include information on selected target BS  410   b . The MOB_BSHO_RSP message may include a plurality of IEs, including, for example, a Management Message Type indicating a type of transmission message, Estimated HO Time, and information on potential target BSs  410 . For example, the MOB_MSSHO_REQ message may include IDs for potential target BSs  410 , and a predicted level of service that may be provided to MSS  430   b  by target BSs  410 . 
         [0036]    MSS  430   b  may then send a Mobile Handover Indication (MOB_HO_IND) message to serving BS  410   a . The MOB_HO_IND message may include a plurality of IEs such as, for example, a Management Message Type IE indicating a type of transmission message, HO_IND_TYPE indicating whether the MSS  430   b  has accepted, rejected, canceled a handover to the selected target BS  410   b , ID of selected target BS  410   b , and HMAC tuple (i.e., Table Update Line Entry) used for authentication of the MOB_HO_IND message. 
         [0037]    When serving BS  410   a  receives the MOB_HO_IND message indicating that MSS  430   b  has accepted the handover, serving BS  410   a  may release the connection to MSS  430   b . Alternatively, serving BS  410   a  may retain the connection until it receives a report indicating completion of the handover to target BS  410   b . After transmitting the MOB_HO_IND to serving BS  410   a , MSS  430   b  may complete the remaining handover operation with target BS  410   b.    
         [0038]    In this manner, wireless communication devices that operate according to the 802.16 family of standards, such as MSS  430   b , may change physical locations yet maintain continuous communication with a network, such as network  450 . 
         [0039]    As shown above, the adoption of standards such as 802.11 and 802.16 may ensure that a device configured to operate according to one standard can communicate with any other device also operating according to that same standard. However, with the increased use of mobile wireless computing devices, there has been an increased need to facilitate handovers, or transfer of communication, between communication networks utilizing differing communication standards, so-called dual-model systems. As shown in  FIGS. 4 and 6 , however, handover standards and procedures between serving AP  110   a  and target AP  110   b , which operate based on the 802.11 family of standards, may differ significantly from handover standards and procedures between serving BS  410   a  and target BS  410   b , which operate based on the 802.16 family of standards. 
         [0040]    In addition, further issues may arise when there is mutual signal interference between networks operating according to differing communication standards. For example, as shown in  FIG. 7 , certain Wi-Fi networks may operate in the 2.4 GHz frequency band while certain Wi-Max networks may operate in the 2.5-2.69 GHz frequency band. Thus, when a wireless client device needs to process Wi-Fi and Wi-Max information simultaneously, such as during a handover, there may be mutual signal interference due to the proximity of the frequency bands and the differences in transmission and reception power. Thus, there is an increased need for systems and methods for avoiding signal interference in dual-mode systems. 
         [0041]    The disclosed embodiments are directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0042]    In one aspect, the present disclosure is directed to a method for wireless communication. The method determines, for a client device having a first wireless connection with a first connection point, to initiate a second wireless connection between the client device and a second connection point, wherein the first connection point includes an Access Point and the second connection point includes a Base Station. The method sends a message from the second connection point to the first connection point, the message including instructions for the first connection point to communicate with the client device using either a Point Coordinate Function (PCF) or a Distributed Coordinate Function (DCF). In addition, the method initiates the second wireless connection between the client device and the second communication point. 
         [0043]    In another aspect, the present disclosure is directed to a method for wireless communication. The method determines, for a client device having a first wireless connection with a first connection point, to initiate a second wireless connection between the client device and a second connection point, wherein the first connection point includes a Base Station and the second connection point includes an Access Point. The method sends a message from the second connection point to the first connection point, the message including instructions for scheduling the transmission and reception of client device data with the first connection point. In addition, the method initiates the second wireless connection between the client device and the second communication point. 
         [0044]    In another aspect, the present disclosure is directed to a method for wireless communication. The method establishes a first wireless connection between a client device and a first connection point. The method determines to initiate a second wireless connection between the client device and a second connection point. In addition, the method sends a first message from the client device to the first connection point, wherein the first message includes a sleep request. The method receives a second message at the client device from the first connection point, wherein the second message includes a response to the sleep request. Further, the method initiates the second wireless connection between the client device and the second communication point. 
         [0045]    In another aspect, the present disclosure is directed to a wireless communication station for wireless communication. The station includes at least one memory to store data and instructions and at least one processor configured to access the memory. The at least one processor is further configured to, when executing the instructions, determine to initiate a wireless connection between a client device and the wireless communication station, wherein the client device is currently connected with a wireless communication point. The at least one processor is further configured to send a message from the wireless communication station to the wireless communication point, wherein the message includes instructions for the wireless communication point to communicate with the client device using either a Point Coordinate Function (PCF) or a Distributed Coordinate Function (DCF). In addition, the processor is configured to initiate the wireless connection between the client device and the wireless communication station. 
         [0046]    In another aspect, the present disclosure is directed to a wireless communication point for wireless communication. The wireless communication point includes at least one memory to store data and instructions and at least one processor configured to access the memory. The at least one processor is further configured to, when executing the instructions, determine to initiate a wireless connection between a client device and the wireless communication point, wherein the client device is currently connected with a wireless communication station. The at least one processor is further configured to send a message to the wireless communication station, wherein the message includes instructions requesting the wireless communication station to schedule client device data transmission and reception between the client device and the wireless communication station. In addition, the at least one processor is configured to initiate the wireless connection between the client device and the wireless communication point. 
         [0047]    In another aspect, the present disclosure is directed to a wireless communication device for wireless communication. The device includes at least one memory to store data and instructions and at least one processor configured to access the memory. The at least one processor is further configured to, when executing the instructions, establish a first wireless connection between the wireless communication device and a first connection point. The at least one processor is also configured to determine to initiate a second wireless connection between the wireless communication device and a second connection point. In addition, the at least one processor is configured to send a first message to the first connection point, wherein the first message includes a sleep request, and process a second message at the wireless communication device received from the first connection point, wherein the second message includes a response to the sleep request. Further, the at least one processor is configured to initiate the second wireless connection between the wireless communication device and the second connection point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0048]      FIG. 1  is a block diagram of an exemplary Wi-Fi communication network; 
           [0049]      FIG. 2   a  illustrates an exemplary Wi-Fi MAC message format; 
           [0050]      FIG. 2   b  illustrates an exemplary Wi-Fi MAC Frame Control format; 
           [0051]      FIG. 3  is a signaling diagram of an exemplary message flow in a Wi-Fi network; 
           [0052]      FIG. 4  is a block diagram of an exemplary Wi-Max network; 
           [0053]      FIG. 5  illustrates an exemplary Wi-Max MAC message frame format; 
           [0054]      FIG. 6  is a signaling diagram of an exemplary message flow in a Wi-Max network; 
           [0055]      FIG. 7  is a graph of an exemplary power and frequency relationship between Wi-Max and Wi-Fi communication systems; 
           [0056]      FIG. 8  illustrates an exemplary Wi-Fi/Wi-Max dual-mode communication system consistent with certain disclosed embodiments; 
           [0057]      FIG. 9   a  is a flow chart illustrating an exemplary handover from a Wi-Fi network to a Wi-Max network, consistent with certain disclosed embodiments; 
           [0058]      FIG. 9   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Fi network to a Wi-Max network, consistent with certain disclosed embodiments; 
           [0059]      FIG. 10   a  is a flow chart illustrating an exemplary handover from a Wi-Max network to a Wi-Fi network, consistent with certain disclosed embodiments; 
           [0060]      FIG. 10   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Max network to a Wi-Fi network, consistent with certain disclosed embodiments; 
           [0061]      FIG. 11   a  is a flow chart illustrating an exemplary handover from a Wi-Max network to a Wi-Fi network, consistent with certain disclosed embodiments; 
           [0062]      FIG. 11   b  is a signaling diagram of an exemplary exchange of data in a handover, from a Wi-Max network to a Wi-Fi network, consistent with certain disclosed embodiments; 
           [0063]      FIG. 12  is an exemplary timing diagram consistent with certain disclosed embodiments; 
           [0064]      FIG. 13   a  is a flow chart illustrating an exemplary handover from a Wi-Fi network to a Wi-Max network, consistent with certain disclosed embodiments; and 
           [0065]      FIG. 13   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Fi network to a Wi-Max network, consistent with certain disclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION  
       [0066]      FIG. 8  illustrates an exemplary dual-mode system architecture in accordance with which systems and methods consistent with the disclosed embodiments may be implemented. As shown in  FIG. 8 , the system may include one or more Wi-Fi APs  810 , including APs  810   a ,  810   b , and  810   c , one or more Wi-Max BSs  815 , including BSs  815   a  and  815   b , one or more SSs  820 , including SSs  820   a ,  820   b , and  820   c , one or more MSSs  830 , including MSSs  830   a ,  830   b , and  830   c , and network  850 . 
         [0067]    The one or more APs  810  may be any type of device configured to transmit and/or receive data based on the IEEE 802.11 family of standards, many of which are known in the art. In one exemplary embodiment, the one or more APs  810  may be connected by a wired connection to network  850 . Alternatively and/or additionally, one or more APs  810  may communicate with BS  815  and thereby establish communication with network  850 . Network  850  may include, for example, any combination of one or more WANs, LANs, intranets, extranets, Internet, etc. 
         [0068]    The one or more BSs  815  may be any type of station configured to transmit and/or receive communications based on the IEEE 802.16 family of standards, many of which are also known in the art. In one exemplary embodiment, one or more BSs  815  may be connected by a wired connection to network  850 . Alternatively and/or additionally, the one or more BSs  815  may be connected by a microwave radio connection to one or more other BSs  815 . Each AP  810  and BS  815  may include one or more of the following components: a central processing unit (CPU) configured to execute computer program instructions to perform various processes and methods consistent with certain disclosed embodiments, random access memory (RAM) and read only memory (ROM) configured to access and store information and computer program instructions associated with the disclosed embodiments, a memory to store data and information, databases to store tables, lists, or other data structures, I/O devices, interfaces, antennas, etc. Each of these components is well-known in the art and will not be discussed further. 
         [0069]    Each SS  820  may be any type of computing device configured to transmit and/or receive data to and from AP  810  and/or BS  815  by means of a wireless communication connection. Each SS  820  may include one or more of the following components: a central processing unit (CPU) configured to execute computer program instructions to perform various processes and methods consistent with certain disclosed embodiments, random access memory (RAM) and read only memory (ROM) configured to access and store information and computer program instructions associated with the disclosed embodiments, a memory to store data and information, databases to store tables, lists, or other data structures, I/O devices, interfaces, antennas, etc. Each of these components is well-known in the art and will not be discussed further. SS  820  may be configured to communicate according to either the 802.16 family of standards or 802.11 family of standards. In some embodiments, each SS  820  may be configured to communicate with one or more other SSs  820  or MSSs  830  by means of wired and/or wireless connections. SS  820  may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, and the like. 
         [0070]    Each MSS  830  may be any type of computing device configured to transmit and/or receive data to and from AP  810  and/orBS  815  by means of a wireless communication connection. Each MSS  830  may include one or more of the following components: a central processing unit (CPU) configured to execute computer program instructions to perform various processes and methods consistent with certain disclosed embodiments, random access memory (RAM) and read only memory (ROM) configured to access and store information and computer program instructions associated with the disclosed embodiments, a memory to store data and information, databases to store tables, lists, or other data structures, I/O devices, interfaces, antennas, etc. Each of these components is well-known in the art and will not be discussed further. Each MSS  830  may be configured to communicate according to either the 802.16e standard or 802.11 family of standards. In addition, in some embodiments, each MSS  830  may be configured to communicate with one or more other SSs  820  or MSSs  830  by means of wired and/or wireless connections. In some embodiments, MSS  830  may be a mobile computing device. In other embodiments, MSS  830  may be a “non-mobile” computing device located in a mobile environment (e.g., airplanes, watercraft, buses, multi-passenger vehicles, automobiles, etc.). MSS  830  may include, for example, servers, clients, mainframes, desktop computers, laptop computers, network computers, workstations, personal digital assistants (PDA), tablet PCs, scanners, telephony devices, pagers, cameras, musical devices, and the like. For example, MSS  830  may be a server located in a bus. 
         [0071]    As shown in  FIG. 8 , communication between BS  815   a  and BS  815   b  and communication between BS  815   a  and APs  810   a  and  810   b  may be based on the 802.16 family of standards. Similarly, communication between BS  815   b  and SSs  820   a  and  820   b  may also be based on the 802.16 family of standard. Communication between BS  815   a  and MSS  830   b  and between BS  815   b  and MSS  830   c  may be based on the 802.16e standard. Communication between AP  810   a  and MSS  830   a  and between AP  810   b  and SS  820   c  may be based on the 802.11 family of standards. Although not shown, communication between one or more SSs  820  and MSSs  830  may be based on either the 802.11 or the 802.16 families of standards, depending on the hardware and/or software configurations associated with SSs  820  and MSSs  830 . 
         [0072]      FIGS. 9   a  and  9   b  illustrate an exemplary process for a transfer of communication from AP  810  to BS  815  in which handover is initiated by AP  810  or BS  815 . In other words,  FIG. 9   a  illustrates an exemplary flowchart of a handover from a Wi-Fi network to a Wi-Max network.  FIG. 9   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Fi network to a Wi-Max network. The process of  FIGS. 9   a  and  9   b  may be performed by one or more components of AP  810 , BS  815 , SS  820 , and MSS  830 . For example, AP  810 , BS  815 , SS  820 , and MSS  830  may execute one or more software programs that may perform one or more of the process steps of  FIGS. 9   a  and  9   b . In this illustration, communication may initially be established between MSS  830   a  and AP  810   a , and either AP  810   a  or BS  815   a  may initiate a handover of MSS  830   a  from AP  810   a  to BS  815   a.    
         [0073]    Referring to  FIG. 9   a , AP  810   a  and BS  815   a  may periodically collect information regarding neighboring APs  810  and BSs  815  (step  910 ). The collection of neighboring information may be made by polling, probe requests, signal detection, etc. In one exemplary embodiment, TCP/IP routing packets may be exchanged by means of a wired communication network connecting APs  810  and BSs  815 . For example, information may be obtained from TCP/IP routing packets exchanged between APs  810  and BSs  815 , such as, for example, a number of hops, an IP segment, etc. A hop may be an intermediate connection (e.g., router, switch, hub, etc.) in a string of connections (e.g., router, switch, hub, etc.) linking two devices (e.g., AP  810   a  and BS  815   b ). Thus, for example, when there is one intermediate connection between AP  810  and BS  815 , there may be only one hop, when there are two intermediate connections between AP  810  and BS  815 , there may be two hops, and so on. When the number of hops is equal to or less than a predetermined number (e.g., one or two hops), it may be determined that the sending and receiving APs  810  and BSs  815  are neighbors. Alternatively and/or additionally, APs  810  and BSs  815  connected in the same IP segment may also be determined to be neighbors. In another exemplary embodiment, neighbor information may be stored in APs  810  and BSs  815  through a manual process at, for example, installation, initial setup, tear-down, upgrade, maintenance, etc. For example, neighboring information may be entered through a keyboard, copied or downloaded from a file, etc. The collected neighboring information may be stored by AP  810   a  and BS  815   a  in memory for later use. 
         [0074]    Either AP  810   a  or BS  815   a  may determine that a handover of MSS  830   a  is to occur (step  920 ). The determination that a handover of MSS  830   a  is to occur may be made based on a Received Signal Strength Indication (RSSI) value. The RSSI may be a measurement of the received signal strength. In one exemplary embodiment, when the RSSI value is less than a predetermined threshold value, it may be determined that a handover of MSS  830   a  is to occur. Alternately and/or additionally, other signal measurements may also be used, such as, for example, Carrier to Interference Noise Ratio (CINR), Signal to Noise Ratio (SNR), etc. When the value of the signal measurement is, for example, greater than, less than, and/or equal to a predetermined threshold value, depending on the signal measurement used, it may be determined that a handover of MSS  830   a  is to occur. 
         [0075]    When either AP  810   a  orBS  815   a  determines that a handover of MSS  830   a  is to occur (step  920 , Yes), target BS  815   a  may send a message to serving AP  810   a  (step  930 ). In one exemplary embodiment, the message may include a request for AP  810   a  to arrange the reception and/or transmission signals of MSS  830   a  to PCF. As discussed above, PCF may be used to provide defined periods of time during which MSS  830   a  may transmit and receive data with AP  810   a . In another exemplary embodiment, the message may include a request for AP  810   a  to arrange the reception and/or transmission signals of MSS  830   a  to DCF. If it is determined that handoff will not occur (step  920 , No), AP  810   a  and BS  815   a  may continue to periodically collect information regarding neighboring APs  810  and BSs  815 , as discussed above with respect to step  910 . 
         [0076]    During one or more blocks of idle time, MSS  830   a  may not send or receive signals to and from AP  810   a . Thus, MSS  830   a  may initiate activation of BS  815   a  (step  940 ) without interference. Initiating activation of BS  815   a  may include transmission of an MOB_HO_IND message from MSS  830   a  to BS  815   a . Once MSS  830   a  has sent the MOB_HO_IND message to BS  815   a , MSS  830   a  may begin handover operations with BS  815   a  (step  950 ). In one exemplary embodiment, MSS  830   a  may adjust its operating frequency if BS  815   a  operates at a frequency different than that of AP  810   a . In addition, MSS  830   a  may synchronize frames with BS  815   a . Further, if handover is successful, AP  810   a  may release its connection with MSS  830   a  and either AP  810   a  or BS  815   a  may update the network to indicate that BS  815   a  is currently serving MSS  830   a.    
         [0077]    In this manner, wireless communication devices that operate according to the both the 802.11 and 802.16 families of standards, such as MSS  830   a , may transfer communication from AP  810   a  to)BS  815   a  while maintaining continuous communication with a network, such as network  850 . 
         [0078]      FIGS. 10   a  and  10   b  illustrate an exemplary process for a transfer of communication from BS  815  to AP  810  in which handover is initiated by AP  810  or BS  815 . In other words,  FIG. 10   a  illustrates an exemplary flowchart of a handover from a Wi-Max network to a Wi-Fi network.  FIG. 10   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Max network to a Wi-Fi network. The process of  FIGS. 10   a  and  10   b  may be performed by one or more components of AP  810 , BS  815 , SS  820 , and MSS  830 . For example, AP  810 , BS  815 , SS  820 , and MSS  830  may execute one or more software programs that may perform one or more of the process steps of  FIGS. 10   a  and  10   b . In this illustration, communication is initially established between MSS  830   a  and BS  815   a , and either AP  810   a  or BS  815   a  may initiate a handover of MSS  830   a  from BS  815   a  to AP  810   a.    
         [0079]    Referring to  FIG. 10   a , APs  810  and BSs  815  may periodically collect information regarding neighboring APs  810  and BSs  815  (step  1010 ). The collection of neighboring information may be made by polling, probe requests, signal detection, etc. In one exemplary embodiment, TCP/IP routing packets may be exchanged by means of a wired communication network connecting APs  810  and BSs  815 . For example, information may be obtained from TCP/IP routing packets exchanged between APs  810  and BSs  815 , such as, for example, a number of hops, an IP segment, etc. A hop may be an intermediate connection (e.g., router, switch, hub, etc.) in a string of connections (e.g., router, switch, hub, etc.) linking two devices (e.g., AP  810   a  and BS  815   b ). Thus, for example, when there is one intermediate connection between AP  810  and BS  815 , there may be only one hop, when there are two intermediate connections between AP  810  and BS  815 , there may be two hops, and so on. When the number of hops is equal to or less than a predetermined number (e.g., one or two hops), it may be determined that the sending and receiving APs  810  and BSs  815  are neighbors. Alternatively and/or additionally, APs  810  and BSs  815  connected in the same IP segment may also be determined to be neighbors. In another exemplary embodiment, neighbor information may be stored in APs  810  and BSs  815  through a manual process at, for example, installation, initial setup, tear-down, upgrade, maintenance, etc. For example, neighboring information may be entered through a keyboard, copied or downloaded from a file, etc. The collected neighboring information may be stored by AP  810   a  and BS  815   a  in memory for later use. 
         [0080]    Either AP  810   a  or BS  815   a  may determine that a handover of MSS  830   a  is to occur (step  1020 ). The determination that a handover of MSS  830   a  is to occur may be made based on a Received Signal Strength Indication (RSSI) value. The RSSI may be a measurement of the received signal strength. In one exemplary embodiment, when the RSSI value is less than a predetermined threshold value, it may be determined that a handover of MSS  830   a  is to occur. Alternately and/or additionally, other signal measurements may also be used, such as, for example, Carrier to Interference Noise Ratio (CINR), Signal to Noise Ratio (SNR), etc. When the value of the signal measurement is, for example, greater than, less than, and/or equal to a predetermined threshold value, depending on the signal measurement used, it may be determined that a handover of MSS  830   a  is to occur. 
         [0081]    When either AP  810   a  or BS  815   a  determines that a handover of MSS  830   a  is to be made (step  1020 , Yes), target AP  810   a  may send a message to BS  815   a  (step  1030 ). The message may include a request for BS  815   a  to schedule the reception and/or transmission signals of MSS  830   a  after the UL-MAP. In addition, the message may request that uplink information be exchanged with MSS  820   a  for the next few frame periods. If it is determined that handover will not occur (step  1020 , No), APs  810  and BSs  815  may continue to periodically collect information regarding neighboring APs  810  and BSs  815  (step  1010 ). 
         [0082]    While transmission between MSS  830   a  and BS  815   a  is idle, MSS  830   a  may begin communicating with target AP  810   a  (step  1040 ). In particular, MSS  830   a  may enter a re-authentication phase with AP  815   a . To begin re-authentication, MSS  830   a  may send a re-association request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association request) to target AP  810   a . In return, AP  810   a  may send a re-association response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association response) to MSS  830   a.    
         [0083]    Once the re-authentication phase is complete, AP  810   a  may communicate with BS  815   a  to finalize handover procedures (step  1050 ). For example, MSS  830   a  may adjust its operating frequency if AP  810   a  operates at a different frequency than BS  815   a , and MSS  830   a  may synchronize with AP  810   a . In one exemplary embodiment, finalizing handover procedures may include sending a MOB_HO_IND message to BS  815   a . Upon receipt of the MOB_HO_IND response, BS  815   a  may release the connection with MSS  830   a , and either AP  810   a  or BS  815   a  may update the network to indicate that AP  810   a  is serving MSS  830   a.    
         [0084]    In this manner, wireless communication devices that operate according to both the 802.11 and 802.16 families of standards, such as MSS  830   a , may transfer communication from BS  815   a  to AP  810   a  while maintaining continuous communication with a network, such as network  850 . 
         [0085]      FIGS. 11   a ,  11   b , and  12  illustrate an exemplary process for a transfer of communication from BS  815  to AP  810  in which handover is initiated by MSS  830 . In other words,  FIG. 11  a illustrates an exemplary flowchart of a handover from a Wi-Max network to a Wi-Fi network,  FIG. 11   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Max network to a Wi-Fi network, and  FIG. 12  illustrates an exemplary timing diagram of a handover from a Wi-Max network to a Wi-Fi network. The process of  FIGS. 11   a ,  11   b , and  12  may be performed by one or more components of AP  810 , BS  815 , SS  820 , and MSS  830 . For example, AP  810 , BS  815 , SS  820 , and MSS  830  may execute one or more software programs that may perform one or more of the process steps of  FIGS. 11   a ,  11   b , and  12 . In this illustration, communication is initially established between MSS  830   a  and BS  815   a , and MSS  830   a  may initiate handover from BS  815   a  to AP  810   a.    
         [0086]    Referring to  FIG. 11   a , AP  810   a  and BS  815   a  may periodically collect information regarding neighboring APs  810  and BSs  815  (step  1110 ). The collection of neighboring information may be made by polling, probe requests, signal detection, etc. In one exemplary embodiment, TCP/IP routing packets may be exchanged by means of a wired communication network connecting APs  810  and BSs  815 . For example, information may be obtained from TCP/IP routing packets exchanged between APs  810  and BSs  815 , such as, for example, a number of hops, an IP segment, etc. A hop may be an intermediate connection (e.g., router, switch, hub, etc.) in a string of connections (e.g., router, switch, hub, etc.) linking two devices (e.g., AP  810   a  and BS  815   b ). Thus, for example, when there is one intermediate connection between AP  810  and BS  815 , there may be only one hop, when there are two intermediate connections between AP  810  and BS  815 , there may be two hops, and so on. When the number of hops is equal to or less than a predetermined number (e.g., one or two hops), it may be determined that the sending and receiving APs  810  and BSs  815  are neighbors. Alternatively and/or additionally, APs  810  and BSs  815  connected in the same IP segment may also be determined to be neighbors. In another exemplary embodiment, neighbor information may be stored in APs  810  and BSs  815  through a manual process at, for example, installation, initial setup, tear-down, upgrade, maintenance, etc. For example, neighboring information may be entered through a keyboard, copied or downloaded from a file, etc. The collected neighboring information may be stored by AP  810   a  and BS  815   a  in memory for later use. 
         [0087]    In addition, AP  810   a  may periodically use Network Timing Protocol (NTP) to synchronize with BS  815   a  (step  1120 ). In one exemplary embodiment, this may include synchronizing the beacon frame start time of AP  810   a  with a downlink sub-frame start time of BS  815   a . NTP is a protocol for synchronizing the clocks of computer systems, the details, of which are well-known in the art and will not be discussed further. 
         [0088]    AP  810   a  may also periodically send PCF and/or DCF duration information to BS  815   a  (step  1130 ). PCF and/or DCF duration information may be sent by means of a beacon frame (e.g., an 802.11 MAC frame in which the Type and Sub-Type fields are set to indicate a beacon frame). Each beacon frame may include a duration of the beacon frame and a duration of the PCF and/or DCF frame. In one exemplary embodiment, beacon frames may be broadcast by AP  810   a  and may be received by any AP  810  and/or BS  815  within a transmitting range. Alternatively and/or additionally, AP  810   a  may send beacon frames periodically to every BS  815  and AP  810  that has been determined to be a neighbor. In one exemplary embodiment, BS  815   a  may use the PCF and/or DCF duration information to coordinate a sleep interval, as is discussed in greater detail below. 
         [0089]    MSS  830   a  may periodically evaluate communication with BS  815   a  to determine if handover should be made to target AP  810   a  (step  1140 ). The evaluation by MSS  830   a  may include, for example, a signal strength, a signal integrity, a signal frequency, or any other means known in the art. In one exemplary embodiment, MSS  830   a  may measure RSSI, CINR, and/or SNR of neighboring APs  810  and BSs  815 . Neighboring APs  810  and BSs  815  may be determined using a database containing neighboring information received and stored by MSS  830   a . When MSS  830   a  determines that the measured RSSI, CINR, and/or SNR value for the serving BS  815   a  is greater than, less than, and/or equal to a predetermined threshold value, depending on the signal measurement used, MSS  830   a  may send a handover request to serving BS  815   a . For example, when MSS  830   a  determines that a measured RSSI value for BS  815   a  is less than a predetermined threshold value, MSS  830   a  may send a handover request to serving BS  815   a . In one exemplary embodiment, the handover request may include a priority list of APs  810 . The priority list of APs  810  may be based on the measured signal values and/or neighboring information stored by MSS  830   a . If it is determined that handoff will not occur (step  1140 , No), APs  810  and BSs  815  may continue periodic collection, synchronization, and communication as discussed with respect to steps  1110 ,  1120 , and  1130 . 
         [0090]    If MSS  830   a  makes a determination to commence handover from BS  815   a  to AP  810   a  (Step  1140 , Yes), MSS  830   a  may send a message to BS  815   a  (step  1150 ), as shown in  FIG. 12 . The message may include, for example, a “sleep request.” In one exemplary embodiment, the “sleep request” may be a MOB_SLP-REQ message and the MOB_SLP_REQ message may specify a sleep interval, start frame of the sleep interval, power saving class, etc. In response, BS  815   a  may send a message to MSS  830   a  to confirm the action (step  1160 ), as also shown in  FIG. 12 . In one exemplary embodiment, the message may include, for example, a “sleep response.” In one exemplary embodiment, the “sleep response” ma y be a MOB_SLP-RES message and the MOB_SLP-RES message may specify a listening interval, start frame of the listening interval, power saving class, etc. As discussed above, the sleep interval, listening interval, start frame of the sleeping interval, and start frame of the listening interval may be synchronized between AP  810   a  and BS  815   a  using the NTP information. 
         [0091]    Once the sleep interval begins, MSS  830   a  may enter the re-authentication phase with AP  810   a  (step  1170 ). To begin re-authentication, MSS  830   a  may send a re-association request (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association request) to target AP  810   a . In return, AP  810   a  may send a re-association response (i.e., a MAC frame in which the Type and Sub-Type fields are set to indicate a re-association response) to MSS  830   a.    
         [0092]    Once the re-authentication phase is complete, AP  810   a  may communicate with BS  815   a  to finalize handover procedures (step  1180 ). For example, MSS  830   a  may adjust its operating frequency if AP  810   a  operates at a frequency from that of BS  815   a , and MSS  830   a  may synchronize with AP  810   a . In one exemplary embodiment, finalizing handover procedures may include sending a MOB_HO_IND message to BS  815   a . Upon receipt of the MOB_HO_IND response, BS  815   a  may release the connection with MSS  830   a , and either AP  810   a  or BS  815   a  may update the network to indicate that AP  810   a  is serving MSS  830   a.    
         [0093]    In this manner, wireless communication devices that operate according to both the 802.11 and 802.16 families of standards, such as MSS  830   a , may transfer communication from BS  815   a  to AP  810   a  while maintaining continuous communication with a network, such as network  850 . 
         [0094]      FIGS. 13   a  and  13   b  illustrate an exemplary process for a transfer of communication from AP  810  to BS  815  in which handover is initiated by MSS  830 . More particularly,  FIG. 13   a  illustrates an exemplary flowchart of a handover from a Wi-Fi network to a Wi-Max. network, and  FIG. 13   b  is a signaling diagram of an exemplary exchange of data in a handover from a Wi-Fi network to a Wi-Max network. The process of  FIGS. 13   a  and  13   b  may be, performed by one or more components of AP  810 , BS  815 , SS  820 , and MSS  830 . For example, AP  810 , BS  815 , SS  820 , and MSS  830  may execute one or more software programs that may perform one or more of the process steps of  FIGS. 13   a  and  13   b . In this illustration, communication is initially established between MSS  830   a  and AP  810   a , and MSS  830   a  may initiate handover from AP  810   a  to BS  815   a.    
         [0095]    Referring to  FIG. 13   a , AP  810   a  and BS  815   a  may periodically collect information regarding neighboring APs  810  and BSs  815  (step  1310 ). The collection of neighboring information may be made by polling, probe requests, signal detection, etc. In one exemplary embodiment, TCP/IP routing packets may be exchanged by means of a wired communication network connecting APs  810  and BSs  815 . For example, information may be obtained from TCP/IP routing packets exchanged between APs  810  and BSs  815 , such as, for example, a number of hops, an IP segment, etc. A hop may be an intermediate connection (e.g., router, switch, hub, etc.) in a string of connections (e.g., router, switch, hub, etc.) linking two devices (e.g., AP  810   a  and BS  815   b ). Thus, for example, when there is one intermediate connection between AP  810  and BS  815 , there may be only one hop, when there are two intermediate connections between AP  810  and BS  815 , there may be two hops, and so on. When the number of hops is equal to or less than a predetermined number (e.g., one or two hops), it may be determined that the sending and receiving APs  810  and BSs  815  are neighbors. Alternatively and/or additionally, APs  810  and BSs  815  connected in the same IP segment may also be determined to be neighbors. In another exemplary embodiment, neighbor information may be stored in APs  810  and BSs  815  through a manual process at, for example, installation, initial setup, tear-down, upgrade, maintenance, etc. For example, neighboring information may be entered through a keyboard, copied or downloaded from a file, etc. The collected neighboring information may be stored by AP  810   a  and BS  815   a  in memory for later use. 
         [0096]    AP  810   a  may use Network Timing Protocol (NTP) for periodic synchronization with BS  815   a  (step  1320 ). In one exemplary embodiment, this may include synchronizing the beacon frame start time of AP  810   a  with a downlink sub-frame start time of BS  815   a . NTP is a protocol for synchronizing the clocks of computer systems, the details of which are well-known in the art and will not be discussed further. 
         [0097]    Additionally, AP  810   a  may periodically send PCF and/or DCF duration information to BS  815   a  (step  1330 ). PCF and/or DCF duration information may be sent by means of a beacon frame (e.g., an 802.11 MAC frame in which the Type and Sub-Type fields are set to indicate a beacon frame). Each beacon frame may include a duration of the beacon frame and a duration of the PCF and/or DCF frame. In one exemplary embodiment, beacon frames may be broadcast by AP  810   a  and may be received by any AP  810  and/or BS  815  within a transmitting range. Alternatively and/or additionally, AP  810   a  may send beacon frames periodically to every BS  815  and AP  810  that has been determined to be a neighbor. In one exemplary embodiment, BS  815   a  may use the PCF and/or DCF duration information to coordinate a sleep interval, as is discussed in greater detail below. BS  815   a  may use the PCF and/or DCF duration information to coordinate a sleep interval as discussed in greater detail below. 
         [0098]    MSS  830   a  may periodically evaluate communication with AP  810   a  to determine if handover should be made to target BS  815   a  (step  1340 ). The evaluation by MSS  830   a  may include, for example, a signal strength, a signal integrity, a signal frequency, or any other means known in the art. In one exemplary embodiment, MSS  830   a  may measure RSSI, CINR, and/or SNR of neighboring APs  810  and/or BSs  815 . Neighboring APs  810  and BSs  815  may be determined using a database containing neighboring information received and stored by MSS  830   a . When MSS  830   a  determines that the measured RSSI, CINR, and/or SNR value for the serving AP  810   a  is greater than, less than, and/or equal to a predetermined threshold value, depending on the measurement used, MSS  830   a  may send a handover request to serving AP  810   a . For example, when MSS  830   a  determines that the measured RSSI value for AP  810   a  is less than a predetermined threshold value, MSS  830   a  may send a handover request to serving AP  810   a . In one exemplary embodiment, the handover request may include a priority list of BSs  815 . The priority list of BSs  815  may be based on the, measured signal values and/or neighboring information stored by MSS  830   a . If it is determined that handoff will not occur (step  1340 , No), APs  810  and BSs  815  may continue periodic collection, synchronization, and communication as discussed above with respect to steps  1310 ,  1320 , and  1330 . 
         [0099]    When MSS  830   a  makes a determination to commence handover from AP  810   a  to BS  815   a  (Step  1340 , Yes), MSS  830   a  may send a message to AP  810   a  (step  1350 ). The message may include, for example, a “sleep request.” In one exemplary embodiment, the “sleep request” may specify a certain duration for the sleep, or sleep interval, start frame of the sleep interval, power saving class, etc. In response, AP  810   a  may send a message to MSS  830   a  to confirm the action (step  1360 ). In one exemplary embodiment, the message may include, for example, an “ACK” or “sleep confirm.” 
         [0100]    While communication between MSS  830   a  and AP  810   a  is idle, MSS  830   a  may begin activation of BS  815   a  (step  1370 ) without interference. Activation may include transmission of an MOB_HO_IND message from MSS  830   a  to BS  815   a  (step  1370 ). As with a Wi-Max to Wi-Max handover, once MSS  830   a  has sent the MOB_HO_IND message to BS  815   a , MSS  830   a  may begin handover operations with BS  815   a  (step  1380 ). In one exemplary embodiment, MSS  830   a  may adjust its operating frequency if BS  815   a  operates at a different frequency than AP  810   a . In addition, MSS  830   a  may synchronize frames with BS  815   a . Further, if handover is successful, AP  810   a  may release its connection with MSS  830   a  and either AP  810   a  or BS  815   a  may update the network to indicate that BS  815   a  is serving MSS  830   a.    
         [0101]    In this manner, wireless communication devices that operate according to both the 802.11 and 802.16 families of standards, such as MSS  830   a , may transfer communication from AP  810   a  to BS  815   a  while maintaining continuous communication with a network, such as network  850 . 
         [0102]    The disclosed embodiments may be implemented within any network configuration utilizing the 802.11 and 802.16 families of standards. The disclosed embodiments may achieve improved performance. In particular, the disclosed embodiments may reduce signal interference associated with transfer of communication in dual-mode 802.11- and 802.16-based networks. 
         [0103]    It will be apparent to those skilled in the art that various modifications and variations can be made in the system and method for reducing signal interference in communication networks. It is intended that the standard and examples be considered as exemplary only, with a true scope of the disclosed embodiments being indicated by the following claims and their equivalents.