Abstract:
A handover method in a wireless communication system is disclosed. A serving base station transmits a handover request message to a base station controller in response to a handover request of a mobile station. The base station controller determines target base stations to which the mobile station can perform handover among target base stations in a list of neighbor base stations, and transmits a handover response message including the determination result information to the mobile station via the serving base station. The mobile station determines a target base station to which it will perform handover, and transmits a message indicating that it will perform handover, to the base station controller via the serving base station. The base station controller transmits a confirm message indicating that the mobile station will perform handover, to the determined target base station, and establishes a tunnel to the target base station. The mobile station registers itself in the target base station.

Description:
PRIORITY 
   This application claims the benefit under 35 U.S.C. § 119(a) of an application filed in the Korean Intellectual Property Office on Jan. 31, 2005 and assigned Ser. No. 2005-8845, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a Broadband Wireless Access (BWA) communication system, and in particular, to a system and method for providing optimized handover in a wireless communication system. 
   2. Description of the Related Art 
   Technologies generally used to provide data service to users in the current wireless communication environment are classified into the 2.5 th  Generation or 3 rd  Generation cellular mobile communication technology such as Code Division Multiple Access 2000 1x Evolution Data Optimized (CDMA2000 1xEVDO), General Packet Radio Services (GPRS) and Universal Mobile Telecommunication Service (UMTS), and the wireless Local Area Network (LAN) technology such as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 Wireless LAN. 
   The local wireless access technologies have been proposed to provide high-speed data service in a wireless environment, replacing wire communication networks such as the cable modem or xDSL (Digital Subscriber Line) in hot spot areas such as public places and schools or in a home network environment. 
   However, when high-speed data service is provided using the wireless LAN, there are limitations in providing public network service to users due to interference as well as due to limited mobility and narrow service area. 
   However, the high-speed data service system, for example, IEEE 802.16, does not have a proposed handover method. Accordingly, there is a need for a handover scheme efficient in the high-speed data service system to provide improved services to users. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide an efficient handover system and method in a BWA communication system. 
   It is another object of the present invention to provide an optimized handover system and method capable of efficiently supporting real-time services being susceptible to a delay in a wireless communication system. 
   It is further another object of the present invention to provide a fast handover system and method for supporting real-time services in a wireless communication system. 
   According to one aspect of the present invention, there is provided a handover method in a wireless communication system. The handover method includes transmitting, by a serving base station, a handover request message to a base station controller in response to a handover request of a mobile station; determining, by the base station controller, target base stations to which the mobile station can perform handover among target base stations in a list of neighbor base stations, and transmitting a handover response message including the determination result information to the mobile station via the serving base station; determining, by the mobile station, a target base station to which it will perform handover, and transmitting a message indicating that it will perform handover, to the base station controller via the serving base station; transmitting, by the base station controller, a confirm message indicating that the mobile station will perform handover, to the determined target base station, and establishing a tunnel to the target base station; and registering, by the mobile station, itself in the target base station. 
   According to another aspect of the present invention, there is provided a handover method in a wireless communication system. The handover method includes upon receiving an active set request message, exchanging with target base stations, by a base station controller, information used for determining each of the target base stations whether it can accept handover of a mobile station thereto and connection information for the target base stations; transmitting, by the base station controller, an active set response message including identifiers (IDs) of base stations to which the mobile station can perform handover, to a serving base station; upon receiving a handover indication message from the mobile station, transmitting, by the serving base station, an active set indication message to the base station controller; after exchanging an active set add/drop message with the target base stations, establishing, by the base station controller, a tunnel between the base station controller and the target base station; upon receiving an anchor base station report over a channel quality information channel (CQICH), transmitting by the serving base station an anchor switching indication message to the base station controller; and upon receiving an anchor switch confirm message from the base station controller, performing communication by the target base station without a ranging procedure with the mobile station. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a diagram schematically illustrating a configuration of a wireless communication system according to an embodiment of the present invention; 
       FIG. 2  is a diagram schematically illustrating an exemplary interface structure in a wireless communication system according to an embodiment of the present invention; 
       FIG. 3  is a signaling diagram illustrating a hard handover procedure in a wireless communication system according to an embodiment of the present invention; and 
       FIG. 4  is a signaling diagram illustrating an FBSS handover procedure in a wireless communication system according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness. 
   The present invention relates generally to a Broadband Wireless Access communication system. In particular, the present invention provides a handover scheme in the BWA communication system, for example, an IEEE802.16 system. 
   The present invention provides an optimized handover scheme by reducing a handover time through tunneling between a base station (BS), for example, a radio access station (RAS), and a base station controller (BSC), for example, an access control router (ACR), in performing handover in a wireless communication system. 
   With reference to the schematic diagram of  FIG. 1 , a description will now be made of an exemplary configuration of a wireless communication system to which the present invention is applicable. 
   Referring to  FIG. 1 , a wireless communication system, for example, a WiBro system, includes an MS  100 , a plurality of RASs  120  and  170  for performing wireless communication with the MS  100 , and a plurality of ACRs  110  and  160  for controlling functions of the RASs  120  and  170 . 
   The ACRs  110  and  160 , which are systems interposed between a core network (CN) and the RASs  120  and  170 , perform a Convergence Sublayer (CS) function, an Automatic Repeat reQuest (ARQ) processing function, a handover control function, etc. In addition, the ACRs  110  and  160  provide an interface with the CN. 
   The RASs  120  and  170 , which are systems interposed between the ACRs  110  and  160  and the MS  100 , provide a wireless access interface based on the wireless access standard, for example, the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard. 
   The MS  100 , which is an end point of a wireless channel, accesses the RASs  120  and  170  to perform communication with them according to the wireless access standard. 
   As illustrated in  FIG. 1 , interfacing between the ACRs  110  and  160  is achieved through interface signaling according to the present invention, for example, interface signaling, and interfacing between the ACR  110  and the RAS  120  is achieved through another interface signaling according to the present invention, for example, interface signaling and traffic. 
     FIG. 2  is a diagram schematically illustrating an exemplary interface structure in a wireless communication system according to the present invention. 
   Referring to  FIG. 2 , the interface defines a signaling and traffic processing scheme between a RAS  210  and an ACR  220  in a wireless communication system. 
   A signaling plane  230 , for example, an interface signaling plane, defines a session control message necessary between the RAS  210  and the ACR  220 , and manages a traffic path, i.e., a Generic Routing Encapsulation (GRE) tunnel, using the session control message. Herein, the session control message corresponds to a Medium Access Control (MAC) Management message. 
   An operation in the signaling plane will now be described. Upon receiving a Ranging Request (RNG-REQ) message with an Initial Ranging Connection ID (CID), the RAS  210  transmits an interface signaling message using a default Internet Protocol (IP) address/port number of the ACR  220 . 
   Upon receipt of the signaling message, the ACR  220  allocates an IP address/port number for each individual Basic Management CID and Primary Management CID to respond to the signaling message from the RAS  210 . 
   Thereafter, upon receiving a MAC Management message with the Basic Management CID and Primary Management CID, the RAS  210  transports the signaling message using an IP address and User Datagram Protocol (UDP) port number for each individual CID of the ACR  220 , determined in an initial ranging process. 
   An operation in a traffic plane  240  will now be described. As described above, the traffic plane  240  transmits control traffic or user traffic between the RAS  210  and the ACR  220 . In addition, the traffic plane  240  performs ARQ control and flow control between the RAS  210  and the ACR  220 , and defines a sub-header including additional information necessary for the ARQ and flow control. 
   The GRE tunnel, which is uniquely generated for each individual service flow, has a format shown in Table 1. 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
           
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               C 
               R 
               K 
               S 
               s 
               Recur 
               Flags 
               Ver 
               Protocol Type 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Checksum (optional) 
               Offset (optional) 
             
           
        
         
             
               Key (optional) 
             
             
               Sequence Number (optional) 
             
             
               Routing: a list of Source Route Entries (optional) 
             
             
                 
             
           
        
       
     
   
   As shown in Table 1, GRE Key is individually allocated for each of an uplink and a downlink, and is transported through an interface between the RAS  210  and the ACR  220 , illustrated in  FIG. 2 . The GRE tunnel is used for generating a virtual link between the RAS  210  and the ACR  220  during handover of an MS  200 , and the GRE tunneling protocol has low overhead and has been proven in the existing wireless communication network. 
   Table 2A and Table 2B show formats of the interface signaling messages transmitted from the signaling plane  230 . 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 2A 
             
             
                 
                 
             
           
           
             
                 
               Message ID (16) 
               Message Length (16) 
             
           
        
         
             
                 
               ACR Job ID (32) 
                 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
             
           
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 2B 
             
             
                 
                 
             
           
           
             
                 
               Message ID (16) 
               Message Length (16) 
             
           
        
         
             
                 
               BS ID (48) 
                 
             
           
        
         
             
                 
                 
               RAS Job ID (16) 
             
             
                 
                 
             
           
        
       
     
   
   Specifically, Table 2A shows a format of a signaling message for an uplink interface, transmitted from the RAS  210  and the ACR  220 , and Table 2B shows a format of a signaling message for a downlink interface, transmitted from the ACR  220  to the RAS  210 . Job IDs shown in Table 2A and Table 2B are used in the RAS  210  and the ACR  220  for allocating a unique Job for each MS  200  for session signaling. 
   The traffic plane  240 , for example, an interface traffic plane, transmits control traffic for, for example, Dynamic Host Configuration Protocol (DHCP) and Mobile IP, and user traffic, between the RAS  210  and the ACR  220 , performs ARQ control and flow control, and defines a sub-header including additional information necessary for the ARQ control and flow control. 
   The control traffic for DHCP or Mobile IP is allocated a particular Transport CID, and transported using an IP address and a particular GRE Tunnel Key for control traffic between the RAS  210  and the ACR  220  (hereinafter referred to as a “GRE Tunnel Key for RAS-ACR control traffic”). 
   The user traffic has a Transport CID, and is transported using an IP address and a GRE Tunnel Key for RAS-ACR user traffic. 
   A description will now be made of embodiments of a handover scheme of the present invention in the HPi system. 
     FIG. 3  is a signaling diagram illustrating a handover procedure in a wireless communication system according to the present invention. In particular, with reference to  FIG. 3 , a description will now be made of a hard handover method. 
   Referring to  FIG. 3 , an MS  310  transmits to a serving RAS  320  a Handover Request (HO-REQ) message including a Neighbor BSID and handover-related parameters to request handover in step  301  Then the serving RAS  320  transmits to a current serving ACR (or anchor point)  350  an MS Handover Request message including the parameters of the HO-REQ message received from the MS  310  in step  303 . 
   An exemplary format of the MS Handover Request message according to the present invention is shown in Table 3. 
   
     
       
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
               Name 
               Size 
               Description 
             
             
                 
             
           
           
             
               Message ID 
               16 
                 
             
             
               Message Length 
               16 
             
             
               ACR Job ID 
               32 
             
             
               MSHO-REQ message 
               variable 
               Include MSHO-REQ 
             
             
                 
                 
               MAC Management message 
             
             
                 
                 
               (see 6.3.2.3.53 section in 
             
             
                 
                 
               IEEE 802.16e/D12 spec) 
             
             
                 
             
           
        
       
     
   
   As shown in Table 3, the MS Handover Request message according to the present invention includes a Message ID field, a Message Length field, an ACR Job ID field, and an MSHO-REQ message field. The MSHO-REQ message field includes an MSHO-REQ MAC Management message. As described above, the MS Handover Request message has the parameters included in the HO-REQ message transmitted by the MS  310 . Therefore, it can be noted that a Neighbor BSID is added to the MS Handover Request message in response to a handover request. 
   Upon receiving the MS Handover Request message from the serving RAS  320 , the ACR  350  checks target RASs, for example, a target RAS# 1   330  and a target RAS# 2   340 , in a Neighbor BS set included in the received MS Handover Request message. Thereafter, the ACR  350  transmits a RAS Capability Request message to each of the target RASs  330  and  340 , in steps  305  and  307 . An exemplary format of the RAS Capability Request message is shown in Table 4 below. 
   
     
       
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
           
           
             
                 
               Name 
               Size 
               Description 
             
             
                 
                 
             
             
                 
               Message ID 
               16 
               0x8302 
             
             
                 
               Message 
               16 
             
             
                 
               Length 
             
             
                 
               BS ID 
               48 
             
             
                 
               RAS Job ID 
               16 
               0x0000 
             
             
                 
               MS MAC 
               48 
               PSS unique identifier. 
             
             
                 
               Address 
             
             
                 
               Up IP Address 
               32 
               Serving ACR IP Address 
             
             
                 
               Up Port 
               16 
               Serving ACR Port Number 
             
             
                 
               Number 
             
             
                 
               ACR Job ID 
               32 
               Serving ACR Job ID 
             
             
                 
               MS MAC 
               8 
             
             
                 
               Version 
             
             
                 
               Target BS ID 
               48 
             
             
                 
               Received 
               24 
               The Frame Number in which the RAS received the PSSHO - REQ from PSS 
             
             
                 
               Frame 
             
             
                 
               Estimated HO 
               8 
               In frames, Estimated number of frames by PSS starting from the frame 
             
             
                 
               Start 
                 
               following the reception of the PSSHO - REQ message until the handover may 
             
             
                 
                 
                 
               take place. 
             
             
                 
               Required BW 
               8 
               Bandwidth which is required by PSS (to guarantee minimum packet data 
             
             
                 
                 
                 
               transmission) 
             
             
                 
               N_SFID 
               8 
             
             
                 
                 
             
           
        
         
             
                 
                 
               Type 
               Length 
               Value 
             
             
                 
             
             
               UL/DL 
               For(i=0; i&lt;N_SFID; i++){ 
             
             
               Service Flow 
                SFID 
               1 
               4 
               1 - 4294967295 
             
             
               [145/146] —   
                Service Class Name 
               3 
               2~128 
               Null - terminated string of ASCII characters. 
             
             
                 
                 
                 
                 
               The length of the string, including null - terminator may not 
             
             
                 
                 
                 
                 
               exceed 128 bytes 
             
             
                 
                QoS Parameter Set Type 
               5 
               1 
             
             
                 
                Traffic Priority 
               6 
               1 
             
             
                 
                Maximum Sustained Traffic Rate 
               7 
               4 
               in bits/second 
             
             
                 
                Maximum Traffic Burst 
               8 
               4 
               in Bytes 
             
             
                 
                Minimum Reserved Traffic Rate 
               9 
               4 
               in bits/second 
             
             
                 
                Minimum Tolerable Traffic Rate 
               10 
               4 
               in bits/second 
             
             
                 
                Service Flow Scheduling Type 
               11 
               1 
             
             
                 
                Request/Transmission Policy 
               12 
               1 
             
             
                 
                Tolerated Jitter 
               13 
               4 
               ms 
             
             
                 
                Maximum Latency 
               14 
               4 
               ms 
             
             
                 
                Fixed - length versus 
               15 
               1 
             
             
                 
                Variable - length SDU Indicator 
             
             
                 
                SDU Size 
               16 
               1 
             
             
                 
                Global Service Class Name 
               rr 
               6 
             
             
                 
                Type of Data Delivery Services 
               29 
               1 
             
             
                 
                SDU Inter - arrival Interval 
               30 
               2 
             
             
                 
                Time Base 
               31 
               2 
             
             
                 
                Paging Preference 
               32 
               1 
             
             
                 
               } 
             
             
                 
             
           
        
       
     
   
   As shown in Table 4, the RAS Capability Request message is transported by the ACR  350  to the target RASs  330  and  340  in the list requested by the MS  310 , to determine whether handover of a particular MS  310  is acceptable in the target RASs  330  and  340 . In Table 4, the RAS Capability Request message includes a Required BW field as a parameter used for requesting acceptability information of the handover. 
   Then the target RASs  330  and  340  each transmit to the ACR  350  a RAS Capability Response message including the parameter result value requested by the ACR  350  in steps  309  and  311 . An exemplary format of the RAS Capability Response message is shown in Table 5 below. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 5 
             
             
                 
             
             
               Name 
               Size 
               Description 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Message ID 
               16 
               0x8303 
             
             
               Message Length 
               16 
             
             
               ACR Job ID 
               32 
               0x00000000~0xFFFFFFFE 
             
             
               MS MAC Address 
               48 
               PSS unique identifier. 
             
             
               Mode 
                 
               0 = HHO request 
             
             
                 
                 
               1 = SHO/FBSS request: Anchor BS update with CID update 
             
             
                 
                 
               2 = SHO/FBSS request: Anchor BS update without CID update 
             
             
                 
                 
               3 = SHO/FBSS request: Active Set update with CID update 
             
             
                 
                 
               4 = SHO/FBSS request: Active Set update without CID update 
             
             
                 
                 
               5~7 = reserved 
             
             
                 
                 
               8~255 = not used 
             
             
               If (Mode == 3) { 
                 
               For collecting CID information within Active BS Set 
             
             
                CID Update 
             
             
               } 
             
             
               Service Level Prediction 
               8 
             
             
               BW Estimated 
               8 
               Bandwidth which is provided by RAS (to guarantee minimum packet data 
             
             
                 
                 
               transmission) 
             
             
               QoS Estimated 
               8 
               Quality of Service Level - 
             
             
                 
                 
               UGS, rtPS, nrtPS, BE 
             
             
                 
             
           
        
       
     
   
   As shown in Table 5, the RAS Capability Response message includes, for example, an Estimated BW field and a Service Level Prediction field as the parameter result value requested by the ACR  350 . 
   Next, upon receiving the RAS Capability Response messages from the target RASs  330  and  340 , the ACR  350  transmits to the serving RAS  320  in step  313  a Base Station (BS) Handover Response (BS HO Response) message including Recommended Neighbor BSIDs, Handover ID (HO-ID), and such parameters as Estimated BW and Quality-of-Service (QoS) result value. An exemplary format of the BS Handover Response message is shown in Table 6. 
   
     
       
             
             
             
           
         
             
               TABLE 6 
             
             
                 
             
             
               Name 
               Size 
               Description 
             
             
                 
             
           
           
             
               Message ID 
               16 
                 
             
             
               Message Length 
               16 
             
             
               BS ID 
               48 
               e.g., Operator ID + ACR-ID + RAS-ID 
             
             
               RAS Job ID 
               16 
             
             
               BSHO-RSP message 
               variable 
               Include BSHO-RSP 
             
             
                 
                 
               MAC Management message 
             
             
                 
                 
               (see 6.3.2.3.54 section in 
             
             
                 
                 
               IEEE 802.16e/D12 spec) 
             
             
                 
             
           
        
       
     
   
   As shown in Table 6, the BS Handover Response message according to the present invention includes a Message ID field, a Message Length field, a BSID field, a RAS Job ID field and a BSHO-RSP message field. The BSID includes Operator ID, ACR-ID and RAS-ID. The BSHO-RSP message field includes a BSHO-RSP MAC Management message. 
   Thereafter, the serving RAS  320  transmits to the MS  310  a BSHO-RSP message including the parameter of the BS Handover Response message received from the ACR  350  in step  315 . 
   The MS  310  transmits to the serving RAS  320  in step  317  a Handover Indication (HO-IND) message including Handover Indication Type (HO-IND Type) and Target BSID, to finally indicate that it performs handover. In response, the serving RAS  320  transmits a HO Indication message with the HO-IND Type and the Target BSID to the ACR  350  in step  319 . An exemplary format of the HO Indication message is shown in Table 7. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 7 
             
             
                 
                 
             
             
                 
               Name 
               Size 
               Description 
             
             
                 
                 
             
           
           
             
                 
               Message ID 
               16 
                 
             
             
                 
               Message Length 
               16 
             
             
                 
               ACR Job ID 
               32 
             
             
                 
               HO-IND message 
               variable 
               Include HO-IND MAC 
             
             
                 
                 
                 
               Management message 
             
             
                 
                 
                 
               (see 6.3.2.3.55 section in 
             
             
                 
                 
                 
               IEEE 802.16e/D12 spec) 
             
             
                 
                 
             
           
        
       
     
   
   As shown in Table 7, the HO Indication message according to the present invention includes a Message ID field, a Message Length field, an ACR Job ID field and a HO-IND message field. The HO-IND message field includes an HO-IND MAC Management message. The HO Indication message is transported to the ACR  350  to indicate approval/denial for handover of a particular MS  310 . If HO-IND Type of the HO Indication message is set to ‘Serving BS release’, the ACR  350  releases MS-related information. 
   Upon receiving the HO Indication message from the serving RAS  320 , the ACR  350  transmits in step  321  a HO Confirm message with an MS MAC address to a target RAS, for example, the target RAS# 1   330 , included in the HO Indication message. An exemplary format of the HO Confirm message is shown in Table 8 below. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 8 
             
             
                 
             
             
               Name 
               Size 
               Description 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Message ID 
               16 
               0x8306 
             
             
               Message Length 
               16 
             
             
               BS ID 
               48 
             
             
               RAS Job ID 
               16 
               0x0000 
             
             
               MS MAC Address 
               48 
               PSS unique identifier. 
             
             
               ACR Job ID 
               32 
             
             
               MS MAC Version 
               8 
             
             
               Serving RAS - ID 
               48 
             
             
               Frame Information 
               32 
               In frames 
             
             
                 
                 
               #0~#23: the Frame Number in which the 
             
             
                 
                 
               RAS received the PSSHO - REQ from PSS 
             
             
                 
                 
               #24~#31: Estimated number of frame by PSS 
             
             
                 
                 
               starting from the frame following the 
             
             
                 
                 
               reception of the PSSHO - REQ message until 
             
             
                 
                 
               the handover may take place 
             
             
                 
             
           
        
       
     
   
   As shown in Table 8, the HO Confirm message is transported to a target RAS, for example, the target RAS# 1   330 , by the ACR  350  to indicate approval for the handover of the particular MS  310 . 
   Upon receiving the HO Indication message from the ACR  350 , the target RAS# 1   330  transmits an Ack message to the ACR  350  in response thereto in step  323 . 
   Upon receiving the Ack message, the ACR  350  transmits to the target RAS# 1   330  in step  325  an HO Optimization message including MS information necessary for performing optimized HO, for example, Subscriber Station&#39;s Basic Capability Negotiation (SBC) information, Privacy Key Management (PKM) information, Registration (REG) information and Provisioned Service Flow (Provisioned SF) information, and also including an ACR GRE Key used for establishing a GRE tunnel. An exemplary format of the HO Optimization message is shown in Table 9 below. 
   
     
       
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
         
             
                 
               TABLE 9 
             
             
                 
                 
             
           
           
             
                 
               Name 
               Size (bit) 
               Description 
             
             
                 
                 
             
             
                 
               Message ID 
               16 
             
             
                 
               Message Length 
               16 
             
             
                 
               BS ID 
               48 
             
             
                 
               RAS Job ID 
               16 
               0x0001 ~0xFFFF 
             
             
                 
               Num_Tunnels 
                 
               GRE Tunnel for assigned CID 
             
             
                 
               For(I=0; 
             
             
                 
               I&lt;Num_Tunnels;I++) { 
             
             
                 
                CID 
             
             
                 
                New GRE Key 
             
             
                 
                New IP Address 
             
             
                 
               } 
             
             
                 
                 
             
           
        
         
             
                 
               Type 
               Length 
               Value 
             
             
                 
             
             
               SBC Information 
             
             
               SS Management Support 
               2 
               1 
             
             
               Bandwidth Allocation Support 
               1 
               1 
             
             
               MAC PDU Capabilities 
               4 
               1 
             
             
               Subscriber Transition Gaps 
               2 
               2 
             
             
               Maximum Transmit Power 
               3 
               4 
             
             
               Authorization Policy Support 
               25 
               1 
             
             
               PKM Version Support 
               26 
               1 
               Bit#0: PKM Version 1 
             
             
                 
                 
                 
               Bit#1: PKM Version 2 
             
             
                 
                 
                 
               Bit#2~7: reserved, shall be set to zero 
             
             
               Handoff Supported 
               19 
               1 
               Bit #0: SHO/FBSS HO - Single - BS Map Supported 
             
             
                 
                 
                 
               Bit #1: SHO/FBSS HO - Multi - BS MAP Supported 
             
             
                 
                 
                 
               Bit #2-#7: reserved, shall be set to zero 
             
             
               Current Transmit Power 
               147 
               1 
             
             
               OFDMA SS FFT Sizes 
               150 
               1 
             
             
               OFDMA SS demodulator 
               151 
               1 
             
             
               OFDMA SS modulator 
               152 
               1 
             
             
               The number of HARQ ACK Channel 
               153 
               1 
             
             
               OFDMA SS Permutation support 
               154 
               1 
             
             
               OFDMA MAP Capability 
               155 
               1 
             
             
               Uplink Control Channel Support 
               xxx 
               1 
             
             
               OFDMA SS demodulator for MIMO Support 
               155 
               1 
             
             
               OFDMA SS modulator for MIMO Support 
               156 
               1 
             
             
               PKM Information 
             
             
               AUTH - Key 
               7 
               128 
               128 byte quantity representing an RSA - encrypted AK 
             
             
               Key Lifetime 
               9 
               4 
               32 - bit quantity representing AK&#39;s lifetime 
             
             
                 
                 
                 
               A key lifetime of zero indicates that the 
             
             
                 
                 
                 
               corresponding AK is not valid. 
             
             
               Key Sequence Number 
               10 
               1 
               4 - bit Sequence Number (AK) 
             
             
               For (i=0; i&lt;Num_SA; i++) { 
                 
                 
               Each compound SA - Descriptor attribute specifies an 
             
             
                 
                 
                 
               SAID and additional properties of the SA. 
             
           
        
         
             
               SA Descriptor 
               SAID 
               12 
               2 
                 
             
             
               23 —   
               SA Type 
               24 
               1 
             
             
                 
               Cryptographic Suite 
               20 
               3 
             
             
               } 
             
             
               PKM Config Settings 
               Authorize Wait Timeout 
               1 
               4 
               in seconds 
             
             
               27 —   
               Reauthorize Wait Timeout 
               2 
               4 
               in seconds 
             
             
                 
               Authorization Grace Time 
               3 
               4 
               in seconds 
             
             
                 
               Operational Wait Timeout 
               4 
               4 
               in seconds 
             
             
                 
               Rekey Wait Timeout 
               5 
               4 
               in seconds 
             
             
                 
               TEK Grace Time 
               6 
               4 
               in seconds 
             
             
                 
               Authorize Reject Wait Timeout 
               7 
               4 
               in seconds 
             
             
               REG Information 
             
           
        
         
             
               SS Management Support 
               2 
               1 
                 
             
             
               IP Management Mode 
               3 
               1 
             
             
               IP Version 
               4 
               1 
             
             
               Number of UL CID Support 
               6 
               2 
               Number of Uplink CIDs the SS can support 
             
             
               Number of DL CID Support 
               X 
               2 
               Number of Downlink CIDs the SS can support 
             
             
               Classification/PHS Options and SDU Encapsulation Support 
               7 
               2 
             
             
               Maximum Number of Classifier 
               8 
               2 
             
             
               PHS Support 
               9 
               2 
             
             
               ARQ Support 
               10 
               1 
             
             
               DSx Flow Control 
               11 
               1 
             
             
               MAC CRC Support 
               12 
               1 
             
             
               PKM Flow Control 
               15 
               1 
             
             
               Maximum Number of Supported Security Associations 
               17 
               1 
             
           
        
         
             
               SA Update 
               Old SAID 
               1 
               2 
                 
             
             
               20 —   
               New SAID 
               2 
               2 
             
             
                 
               New SA type 
               3 
               1 
             
             
                 
               New Cryptographic suite 
               4 
               4 
             
           
        
         
             
               Method for Allocating IP Address 
               23 
               1 
                 
             
           
        
         
             
               Mobility Parameters 
               Mobility Features Supported 
               18 
               1 
               Bit #0: Mobility (handover) support 
             
             
               Support 
                 
                 
                 
               Bit #1: Sleep - mode support 
             
             
               24 —   
                 
                 
                 
               Bit #2: Idle - mode support 
             
             
                 
               SKIP - ADDR - ACQUISITION 
               11 
               1 
               0: No IP address change 
             
             
                 
                 
                 
                 
               1: Re - acquire IP address 
             
           
        
         
             
               System Resource Retain Time 
               50 
               1 
               multiple of 100 ms 
             
             
                 
                 
                 
               200 msec is recommended as default 
             
             
               SS Mode Selection Feedback Support 
               20 
               1 
             
             
               Packing Support 
               51 
               1 
             
           
        
         
             
               Vender Specific Information 
               Vender ID 
               144 
               3 
                 
             
             
               143 —   
             
             
               Provisioned SF 
             
             
               Information 
             
           
        
         
             
               Old CID 
                 
                 
               For Provisioned SF 
             
             
               reserved 
             
             
                 
             
           
        
       
     
   
   As shown in Table 9, the HO Optimization message is transmitted to a corresponding target RAS, for example, the target RAS# 1   330 , along with BSC information, PKM information, REG information and Provisioned SF information for the MS  310 , and GRE tunnel information with the target RAS# 1   330 , all of which are requested in a handover signaling process. 
   The target RAS# 1   330  transmits to the ACR  350  in step  327  an HO Optimization Reply message including New CIDs for New Basic CID &amp; Primary Management CID and Old Provisioned SF and also including a GRE Key used for establishing a corresponding GRE tunnel. An exemplary format of the HO Optimization Reply message is shown in Table 10 below. 
   
     
       
             
             
             
           
         
             
               TABLE 10 
             
             
                 
             
             
               Name 
               Size (bit) 
               Description 
             
             
                 
             
           
           
             
               Message ID 
               16 
                 
             
             
               Message Length 
               16 
             
             
               ACR Job ID 
               32 
               0x00000000~0xFFFFFFFE 
             
             
               Num_Tunnels 
                 
               GRE Tunnel for assigned 
             
             
               For(I=0; I&lt;Num_Tunnels;I++) { 
               CID 
             
             
                CID 
             
             
                New GRE Key 
             
             
                New IP Address 
             
             
               } 
             
             
                 
             
           
        
       
     
   
   After the transmission/reception of the HO Optimization message between the ACR  350  and the target RAS# 1   330  is completed, a ORE tunnel is established between the ACR  350  and the target RAS# 1   330  in step  329 . Specifically, the handover signaling procedure previously generates a GRE tunnel to the target RAS# 1   330 , so the MS  310  can reduce a delay time required after a ranging procedure to the target RAS# 1   330 . In this manner, the present invention can provide faster handover. In addition, as the ACR  350  provides the target RAS# 1   330  with the SBC information, PKM information, REG information and Provisioned SF information stored in the former serving RAS  320 , the MS  310  can omit the additional procedure for SBC, PKM, REG and Dynamic Service Addition (DSA) after the ranging procedure to the target RAS# 1   330 . This optimized handover technique can meet various requirements for services by establishing a tunnel for each individual service flow. 
   Thereafter, the target RAS# 1   330  transmits an uplink MAP (UL-MAP) message with a fast ranging information element (Fast_Ranging_IE) to the MS  310  in step  331 . In response, the MS  310  transmits to the target RAS# 1   330  in step  333  a Ranging Request (RNG-REQ) message including MAC address, Serving BSID, HO Indication and HO-ID 
   In response to the RNG-REQ message, the target RAS# 1   330  transmits a Ranging Response (RNG-RSP) message with a HO Process Optimization Flag to the MS  310  in step  335 . At this moment, the target RAS# 1   330  determines whether to perform the SBC, PKM, REG and DSA processes according to a bit value set in the HO Process Optimization Flag. In addition, the target RAS# 1   330  transmits a Registration Response (REG-RSP) message with CID_Update and SAID_Update to the MS  310  in step  337 , to reestablish a relation to the former Provisioned SF. 
   The hard handover method in the wireless communication system according to the present invention has been described thus far. A description will now be made of a Fast BS Switch (FBSS) handover method in a wireless communication system according to the present invention. 
     FIG. 4  is a signaling diagram illustrating a handover procedure in a wireless communication system according to the present invention. In particular, with reference to  FIG. 4 , a description will now be made of an FBSS handover method. 
   Referring to  FIG. 4 , an MS  410  transmits to a serving RAS  420  a HO-REQ message including a Neighbor BSID and handover-related parameters to request Active Set Update in step  401 . Then the serving RAS  420  transmits to a current serving ACR (or anchor point)  450  an Active Set Request message including the parameters of the HO-REQ message received from the MS  410  in step  403 . 
   Although the Active Set Request message according to the present invention is similar in format to the MS Handover Request message shown in Table 3, a set value of an Arrival Time Difference Indication field is subject to change. 
   Upon receiving the Active Set Request message from the serving RAS  420 , the ACR  450  checks target RASs, for example, a target RAS# 1   430  and a target RAS# 2   440 , in a Neighbor BS set included in the received Active Set Request message. Thereafter, the ACR  450  transmits a RAS Capability Request message to each of the target RASs  430  and  440  in step  405  and  407 . An exemplary format of the RAS Capability Request message is shown above in Table 4A and Table 4B. 
   The target RASs  430  and  440  each transmit to the ACR  450  a RAS Capability Response message including a parameter result value requested by the ACR  450  and an HO-ID in steps  409  and  411 . An exemplary format of the RAS Capability Response message is shown above in Table 5. 
   Thereafter, the ACR  450  transmits to each of the target RASs  430  and  440  an HO Optimization message including SBC information, PKM information, REG information and Provisioned SF information necessary for performing Optimized HO and also including an ACR GRE Key used for establishing a GRE tunnel, in steps  413  and  415 . An exemplary format of the HO Optimization message is shown above in Table 9. 
   The target RASs  430  and  440  each transmit to the ACR  450  an HO Optimization Reply message including New CIDs for new Basic CID &amp; Primary Management CID and Old Provisioned SF and also including a GRE Key used for establishing a corresponding GRE tunnel, in steps  417  and  419 . An exemplary format of the HO Optimization Reply message is shown above in Table 10. 
   Upon receiving the HO Optimization Reply messages from the target RASs  430  and  440 , the ACR  450  transmits an Active Set Response message including Recommended Neighbor BSIDs, Temp BSIDs and New CIDs to the Serving RAS  420  in step  421 . An exemplary format of the Active Set Response message is shown above in Table 6. 
   The serving RAS  420  transmits a BS Handover Response (BSHO-RSP) message including the parameters of the Active Set Response message received from the ACR  450  to the MS  410  in step  423 . 
   The MS  410  transmits a HO-IND message including FBSS-IND Type and Temp BSID to the serving RAS  420  in step  425 , to finally indicate that it will perform Active Set Update. Then the serving RAS  420  transmits an Active Set Indication message including the FBSS-IND Type and Temp BSID to the ACR  450  in step  427 . An exemplary format of the Active Set Indication message is shown above in Table 7. 
   Upon receiving the Active Set Indication message from the serving RAS  420 , the ACR  450  transmits an Active Set Add message with an MS MAC address to the target RAS# 1   430  in step  429 , to add a target RAS, for example, the target RAS# 1   430 , included in the received Active Set Indication message to its Active Set. An exemplary format of the Active Set Add message is shown in Table 11 below. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 11 
             
             
                 
                 
             
             
                 
               Name 
               Size 
               Description 
             
             
                 
                 
             
           
           
             
                 
               Message ID 
               16 
                 
             
             
                 
               Message Length 
               16 
             
             
                 
               ACR Job ID 
               32 
               0x00000000~0xFFFFFFFE 
             
             
                 
               MS MAC Address 
             
             
                 
               Reserved 
             
             
                 
                 
             
           
        
       
     
   
   Upon receiving the Active Set Add message from the ACR  450 , the target RAS# 1   430  transmits an Ack message to the ACR  450  in response thereto in step  431 . 
   Thereafter, the ACR  450  transmits an Active Set Drop message with an MS MAC address to the target RAS# 2   440  in step  433 , to drop the target RAS# 2   440  from the Active Set. An exemplary format of the Active Set Drop message is shown above in Table 10. 
   Upon receiving the Active Set Drop message from the ACR  450 , the target RAS# 2   440  transmits an Ack message to the ACR  450  in response thereto in step  435 . 
   After the transmission/reception of the Active Set Add/Drop messages between the ACR  450  and the target RASs  430  and  440  is completed, a GRE tunnel is established between the ACR  450  and the target RAS# 1   430  in step  437 . That is, the HO signaling procedure according to the present invention previously generates a GRE tunnel to the target RAS# 1   430 , so the MS  410  can reduce a delay time required for an access to the target RAS# 1   430 . In this manner, the present invention can provide faster handover. In addition, as the ACR  450  provides the target RAS# 1   430  with the SBC information, PKM information, REG information and Provisioned SF information stored in the old serving RAS  420 , the MS  410  can omit the additional procedure for SBC, PKM, REG and DSA after the access to the target RAS# 1   430 . This optimized handover technique can meet various requirements for services by establishing a tunnel for each individual service flow. 
   Thereafter, the MS  410  sends an Anchor BS Switching request over a Channel Quality Information (CQI) channel (CQICH) in step  439 , to request FBSS handover to the target RAS# 1   430 . Upon receiving an Anchor BS Report (codeword) from the MS  410  over a CQICH, the serving RAS  420  transmits an Anchor Switching Indication message to the ACR  450  in step  441 , to request switching to the target RAS# 1   430  which is a designated Anchor. As a result, the MS  410  does not perform a separate ranging process. An exemplary format of the Anchor Switching Indication message is shown in Table 12 below. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 12 
             
             
                 
             
             
               Name 
               Size 
               Description 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Message ID 
               16 
                 
             
             
               Message Length 
               16 
             
             
               ACR Job ID 
               32 
               0x00000000~0xFFFFFFFE 
             
             
               MS MAC Address 
             
             
               FBSS_IND_Type 
               8 
               0b00: confirm Anchor BS 
             
             
                 
                 
               update 
             
             
                 
                 
               0b01: Anchor BS update 
             
             
                 
                 
               cancel 
             
             
                 
                 
               0b10: Anchor BS update 
             
             
                 
                 
               reject 
             
             
                 
                 
               0b11: reserved 
             
             
               If (FBSS_IND_Type == 0b00){ 
             
             
                Anchor BS - ID 
               8 
               TEMP_BS_ID of the Anchor 
             
             
                 
                 
               BS 
             
             
                Action Time 
               8 
               Action time when the Anchor 
             
             
                 
                 
               BS shall be updated 
             
             
               } 
             
             
                 
             
           
        
       
     
   
   As shown in Table 12, the Anchor Switching Indication message is transported from the serving RAS  420  to the ACR  450  to indicate approval/denial for FBSS of a particular MS  410  for Anchor BS Switching. 
   Upon receiving the Anchor Switching Indication message from the serving RAS  420 , the ACR  450  transmits to the target RAS# 1   430  in step  443  an Anchor Switch Confirm message indicating success in Anchor Switching to the target RAS# 1   430 . Then the target RAS# 1   430  transmits in step  445  an Ack message to the ACR  450  in response to the Anchor Switch Confirm message received from the ACR  450 . An exemplary format of the Anchor Switch Confirm message is shown in Table 13 below. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 13 
             
             
                 
                 
             
             
                 
               Name 
               Size 
               Description 
             
             
                 
                 
             
           
           
             
                 
               Message ID 
               16 
                 
             
             
                 
               Message Length 
               16 
             
             
                 
               ACR Job ID 
               32 
               0x00000000~0xFFFFFFFE 
             
             
                 
               MS MAC Address 
             
             
                 
               Reserved 
             
             
                 
                 
             
           
        
       
     
   
   As can be understood from the foregoing description, the present invention provides normalized messages for a handover signaling scheme between a RAS (or BS) and an ACR (or BSC) to provide optimized handover in a wireless communication system, and a method for providing the same. In the handover signaling process, once a target RAS is determined, session information is previously transported to the determined target RAS. As a result, in a network re-entry process, an MS can minimize signaling overhead between the RAS and the ACR, and also minimize a handover delay time. 
   While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.