Abstract:
A method is provided for performing an authentication procedure according to location registration and update for a mobile subscriber station (MSS) in a broadband wireless access (BWA) communication system. The system includes the MSS operating in idle mode to minimize power consumption, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and a server for controlling location registration and authentication for the plurality of MSSs. The server determines whether to approve a request for transition to the idle mode received from the MSS through a BS. If the server approves the request for the transition to the idle mode, it allocates authentication information to the MSS through the BS and registers location of the MSS. When it is determined that the MSS has moved to a different paging group, the MSS sends a location update request including a resulting value computed using the authentication information allocated from the server. The server authenticates the MSS according to the authentication information included in the location update request and registers the changed location of the MSS authenticated successfully.

Description:
PRIORITY  
       [0001]     This application claims priority to two applications entitled “SYSTEM AND METHOD FOR CONTROLLING IDLE MODE LOCATION IN A BROADBAND WIRELESS ACCESS COMMUNICATION SYSTEM”, filed in the Korean Intellectual Property Office on May 7, 2004 and May 14, 2004 and assigned Serial Nos. 2004-33256 and 2004-34368, respectively, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a broadband wireless access (BWA) communication system, and more particularly to a system and method for controlling location of mobile subscriber station (MSS) with idle mode.  
         [0004]     2. Description of the Related Art  
         [0005]     A large amount of research is currently being conducted on 4th generation (4G) communication systems, which are the next generation communication systems that provide users with various services based on quality of service (QoS) at a transmission rate of about 100 Mbps. More specifically, a large amount of research focuses on broadband wireless access (BWA) communication systems such as wireless local area network (LAN) systems and wireless metropolitan area network (MAN) systems for the 4G communication systems to support high speed data transfer while ensuring mobility and QoS. Representative BWA communication systems are the Institute of Electrical and Electronics Engineers (IEEE) 802.16a communication system and the IEEE 802.16e communication system.  
         [0006]     The IEEE 802.16a and 802.16e communication systems adopt orthogonal frequency division multiplexing/orthogonal frequency division multiple access (OFDM/OFDMA) schemes for supporting a broadband transmission network in a physical channel of the wireless MAN system. The IEEE 802.16a communication system only considers the situation where a subscriber station (SS) is fixed. The IEEE 802.16a communication system does not take SS mobility into account, and considers a single cell structure only. However, the IEEE 802.16e communication system is used to support SS mobility in the IEEE 802.16a communication system. An SS with mobility is referred to as a mobile subscriber station (MSS).  
         [0007]     According to the standard of the IEEE 802.16e communication system, the MSS can minimize power consumption because it operates in idle mode when traffic to be transmitted/received is absent for a predetermined time. To operate in the idle mode, the MSS transmits a de-registration request (DREG-REQ) message to a serving base station (BS) currently performing a communication function. Upon receiving the DREG-REQ message, the serving BS can approve the idle mode operation of the MSS by transmitting a DREG command (DREG-CMD) message to the MSS. Tables 1 and 2 describe the format of the DREG-REQ message and the format of the DREG-CMD message, respectively.  
                           TABLE 1                                   Syntax   Size                           DREG-REQ_Message_Format( ) {                Management Message Type    8 bits            De-registration_Request_Code    8 bits            Paging Cycle Request    16 bits            TLV_HMAC Tuple   176 bits           }                      
 
         [0008]     As shown in Table 1, the ‘Management Message Type’ field in the DREG-REQ message is used to distinguish medium access control (MAC) management messages defined by IEEE 802.16e Specification. The ‘De-registration_Request_Code’ field indicates the purpose of the DREG-REQ message. When a ‘De-registration-Request_Code’ value is 1, it indicates an idle mode operation request for the MSS. And when the ‘De-registration_Request_Code’ value is 1, the ‘Paging Cycle Request’ field indicates the cycle where the MSS should receive paging information from a system. The Type Length Value_Hashed Message Authentication Code Tuple(‘TLV_HMAC Tuple’) field is an information field for authenticating the MSS on the basis of security association (SA) information set between the MSS and the current serving BS.  
                           TABLE 2                                   Syntax   Size                           DREG-CMD_Message_Format( ) {                Management Message Type    8 bits            Action Code    8 bits            TLV_Paging Information    48 bits            TLV_REG-duration    24 bits            TLV_HMAC Tuple   176 bits           }                      
 
         [0009]     As shown in Table 2, the ‘Management Message Type’ field in the DREG-CMD message is used to distinguish MAC management messages defined by IEEE 802.16e Specification. The ‘Action Code’ field indicates the purpose of the DREG-CMD message. ‘Action Code’ values associated with the idle mode are 0×05, 0×06, and 0×07. When the ‘Action Code’ value is 0×05, it indicates that the serving BS has approved an idle mode request of the MSS. When the ‘Action Code’ value is 0×06, it indicates that the serving BS commands the MSS to re-transmit the DREG-REQ message after the time indicated by the ‘TLV_REG-duration’ field has elapsed. When the ‘Action Code’ value is 0×07, it indicates that the serving BS commands the MSS to wait until the DREG-CMD message is re-transmitted. The ‘TLV_Paging Information’ field includes paging group identifier (PG-ID), PAGING_CYCLE, and PAGING_OFFSET parameters associated with the idle mode operation. The PG-ID parameter is given by a system according to location of the MSS. The PG-ID parameter indicates current location information of the MSS.  
         [0010]     The PAGING_CYCLE parameter indicates a paging cycle determined by a system that refers to a paging cycle request from the MSS. The PAGING_OFFSET parameter is used when a time point of paging a specific MSS is determined according to a frame number and the PAGING_CYCLE parameter in the system. The ‘TLV_REQ-duration’ field is used when the ‘Action Code’ value is ‘0×06’, and indicates a time point when the MSS can re-transmit the DREG-REQ message. The ‘TLV_HMAC Tuple’ field is an information field used to authenticate the serving BS on the basis of SA information set between the MSS and the current serving BS.  
         [0011]      FIG. 1  roughly illustrates a paging service structure in the conventional IEEE 802.16e communication system.  
         [0012]     Referring to  FIG. 1 , adjacent cells can form a single logical group according to region location. A paging and location management (PLM) server  120  allocates a paging identifier (PG-ID) to each logical paging group formed by a plurality of cells. In  FIG. 1 , cells of paging groups are identified by PG_ID # 1   130   a,  PG_ID # 2   130   b,  PG_ID # 3   130   c,  and PG_ID # 4   130   d.  It is assumed that BS # 1   140   a  serves MSS # 1   150 , and MSS # 1   150  operates in the idle mode by exchanging DREG-REQ and DREG-CMD messages with BS # 1   140   a.  All BSs associated with PG_ID # 1   130   a  can page MSS # 1   150 . That is, when MSS # 1   150  is located within an area associated with PG-ID # 1   130   a,  it can receive a paging service from the BSs.  
         [0013]     MSS # 1   150  can move to a cell covered by BS # 2   140   b  within an area associated with PG-ID-# 2   130   b.  In this case, MSS # 1   150  performs a network entry procedure with BS # 2   140   b.  If MSS # 1   150  in the idle mode moves between different cells of an identical paging group, e.g., cells  110   a  and  110   b,  a network entry procedure is unnecessary. However, if MSS # 1   150  moves between different paging groups, it transitions from the idle mode to active mode that consumes much power, and then performs the network entry procedure. Accordingly, after performing the transition to the active mode and completing the network entry procedure, MSS # 1   150  can re-operate in the idle mode by exchanging the DREG-REQ and DREG-CMD messages with BS # 2   140   b.  Subsequently, while operating in the idle mode, MSS # 1   150  can receive the paging service from all BSs within an area associated with PG-ID # 2   130   b.    
         [0014]     The following method is used to determine if an MSS has moved to another paging group different from a previous paging group. When all BSs periodically send a paging advertisement (PAG-ADV) message shown in Table 3, the MSS receives the PAG-ADV message and detects PG-ID information included in the PAG-ADV message. The MSS compares its own PG-ID with the detected PG-ID information. If the two PG-IDs are different, the MSS determines that it has moved to a different paging group. The MSS in the idle mode performs a network entry process or a ranging process according to an ‘Action Code’ value when its own ID information (or an ‘MSS MAC address hash’ field shown in Table 3) is included in the PAG-ADV message. Table 3 describes the format of the PAG-ADV message.  
                           TABLE 3                                   Syntax   Size                           PAG-ADV_Message_Format( ) {                Management Message Type    8 bits            Num_Paging Group IDs    8 bits            For (i=0; i&lt;Num_Paging_Group_IDs; i++) {             Paging Group ID    8 bits            }            For (j=0; j&lt;Num_MACs; j++) {             MSS MAC address hash   24 bits             Action Code    2 bits             Reserved    6 bits            }           }                      
 
         [0015]     As shown in Table 3, when moving to another paging group different from a previous paging group, the MSS operating in the idle mode performs the network entry process and then re-transitions to the idle mode if the idle mode transition requirement is satisfied according to the above procedure. This case has the following problems.  
         [0016]     First, when the paging group is set to a narrow area, the paging group may change often as the MSS moves. Whenever the paging group is changed, the MSS performs a procedure for transition to the idle mode after a network entry process. That is, upon determining that the paging group has been changed in the idle mode, the MSS transitions to the active mode and performs the network entry process. After completely performing the network entry process, the MSS re-performs the procedure for transition to the idle mode. As a result, the power saving effect of the MSS is significantly degraded, and network resources are wasted due to frequent message exchanges.  
         [0017]     Second, when the paging group is set to a wide area, the number of paging group changes can be reduced, but many BSs periodically transmit PAG-ADV messages, increasing overhead for each paging group.  
         [0018]     Third, it is assumed that notification of MSS location change operating in the idle mode is given through a specific BS. In this case, if a server for managing location update information does not authenticate the MSS giving notification of the location change, the location update information may be wrongly used by an unlawful MSS. In effect, a lawful MSS may be denied access to the network.  
       SUMMARY OF THE INVENTION  
       [0019]     It is, therefore, an aspect of the present invention to provide a system and method for efficiently controlling location registration for a mobile subscriber station (MSS) in a broadband wireless access (BWA) communication system.  
         [0020]     It is another aspect of the present invention to provide a system and method for controlling location authentication for a mobile subscriber station (MSS) when a paging group for the MSS is changed in a broadband wireless access (BWA) communication system.  
         [0021]     The above and other aspects of the present invention can be achieved by a method for performing an authentication procedure according to location registration and update for a mobile subscriber station (MSS) in a broadband wireless access (BWA) communication system including the MSS operating in idle mode to minimize power consumption, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and a server for controlling location registration and authentication for the plurality of MSSs. The method includes determining if the server approves a request for transition to the idle mode received from the MSS through a BS; allocating authentication information from the server to the MSS through the BS if the server approves the request for the transition to the idle mode; registering location of the MSS in the server; sending a location update request including a resulting value computed using the authentication information allocated from the server when determining that the MSS has moved to a different paging group; authenticating the MSS in the server according to the authentication information included in the location update request; and registering changed location of the successfully authenticated MSS.  
         [0022]     The above and other aspects of the present invention can also be achieved by a method for performing an authentication procedure in a mobile subscriber station (MSS) according to location registration and update in a broadband wireless access (BWA) communication system including the MSS operating in idle mode to minimize power consumption, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and a server for controlling location registration and authentication for the plurality of MSSs. The method includes sending, to a first BS, a request for transition to the idle mode when a requirement for the transition to the idle mode in which traffic is not generated for a predetermined time is satisfied; receiving a response to the request for the transition to the idle mode; storing authentication information included in a positive response and performing the transition to the idle mode when the response is positive; periodically broadcasting paging information after the transition to the idle mode; comparing last received paging information with previously received paging information; determining that a paging group has been changed when paging group identification information included in the last received paging information is different from that included in the previously received paging information; sending a location update request including a resulting value computed using allocated authentication information; and receiving, from a second BS, a response to the location update request.  
         [0023]     The above and other aspects of the present invention can also be achieved by a method for performing an authentication procedure in a server according to location registration and update in a broadband wireless access (BWA) communication system including a mobile subscriber station (MSS) operating in idle mode to minimize power consumption, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and the server for controlling location registration and authentication for the plurality of MSSs. The method includes determining if the server approves a request for transition to the idle mode received from the MSS through a first BS; allocating authentication information to the MSS through the first BS and registering location of the MSS if the server approves the request for the transition to the idle mode; receiving a location update request from a second BS when a paging group for the MSS is changed; authenticating the MSS; and sending, to the second BS, a response to the location update request of the MSS according to a result of the authentication.  
         [0024]     The above and other aspects of the present invention can also be achieved by a method for performing an authentication procedure according to location change of a mobile subscriber station (MSS) in a broadband wireless access (BWA) communication system including the MSS operating in idle mode, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and a server for controlling location registration and authentication for the plurality of MSSs. The method includes sending a ranging request including authentication information from the MSS to a corresponding BS when the MSS determines that it has moved to the BS of a paging group different from a previous paging group; and receiving, from the BS, a ranging response indicating if authentication is successful, in the MSS.  
         [0025]     The above and other aspects of the present invention can be also achieved by a system for performing an authentication procedure according to location registration and update in a broadband wireless access (BWA) communication system including a mobile subscriber station (MSS) operating in idle mode to minimize power consumption, paging groups each being formed by a plurality of adjacent cells in which a plurality of MSSs are paged, base stations (BSs) for paging the plurality of MSSs within each paging group, and a server for controlling location registration and authentication for the plurality of MSSs. The system includes the MSS for sending, to a first BS, a request for transition to the idle mode when a requirement for the transition to the idle mode in which traffic is not generated for a predetermined time is satisfied, receiving a response to the request for the transition to the idle mode, storing authentication information included in a positive response when the response is positive, and performing the transition to the idle mode; and the server for determining whether to approve the request for the transition to the idle mode received from the MSS through the first BS, allocating authentication information to the MSS through the first BS if the request for the transition to the idle mode is approved, and registering location of the MSS. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The above and other aspects and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0027]      FIG. 1  roughly illustrates a paging service structure in a conventional Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system;  
         [0028]      FIG. 2  is a ladder diagram illustrating an authentication procedure according to location registration and update for a mobile subscriber station (MSS) in accordance with an embodiment of the present invention;  
         [0029]      FIGS. 3A and 3B  are flow charts illustrating an authentication procedure performed by an MSS according to location registration and update in accordance with an embodiment of the present invention;  
         [0030]      FIG. 4  is a flow chart illustrating a procedure performed by a serving base station (BS) when a request for MSS idle mode is made in accordance with an embodiment of the present invention;  
         [0031]      FIG. 5  is a flow chart illustrating a location registration and authentication procedure performed by a BS receiving a location update request in accordance with an embodiment of the present invention; and  
         [0032]      FIG. 6  is a flow chart illustrating a location control operation performed by a paging and location management (PLM) server in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Preferred embodiments of the present invention will be described in detail herein below with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted for conciseness.  
         [0034]     The present invention proposes an authentication method according to efficient location registration and update for a mobile subscriber station (MSS) with idle mode in an Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system serving as a broadband wireless access (BWA) communication system.  
         [0035]      FIG. 2  is a ladder diagram illustrating an authentication procedure according to location registration and update for an MSS in the IEEE 802.16e communication system in accordance with an embodiment of the present invention.  
         [0036]     In  FIG. 2 , MSS # 1   210  goes into the idle mode when traffic to be transmitted/received is absent for a predetermined time. The MSS # 1   210  sends a de-registration request (“DREG-REQ”) to base station (BS) # 1   220  with paging group identifier (PG-ID) # 1  serving as a current serving BS (Step  251 ). Upon receiving the DREG-REQ, BS # 1   220  sends a “LOCATION-MANAGEMENT-REQUEST” message to a paging and location management (PLM) server  240  introduced by the present invention (Step  252 ). The PLM server  240  may be located in the current serving BS or in a different or new network entity. If the PLM server  240  is located in the current serving BS, BS # 1   220  does not need to send the “LOCATION-MANAGEMENT-REQUEST” message to the PLM server  240 . A case where the PLM server  240  is not located in a serving BS or a different network entity will be described below.  
         [0037]     Upon receiving the “LOCATION-MANAGEMENT-REQUEST” message, the PLM server  240  sends a “LOCATION-MANAGEMENT-RESPONSE” message to BS # 1   220  (Step  253 ). When the PLM server  240  is located in the current serving BS, the “LOCATION-MANAGEMENT-RESPONSE” message can be omitted. Upon receiving the “LOCATION-MANAGEMENT-RESPONSE” message, BS # 1   220  reads an ‘Action Code’ value from the message. BS # 1   220  sends a de-registration command (DREG-CMD) to MSS # 1   210  (step  254 ), and notifies the PLM server  240  of information indicating if the transition to the idle mode of MSS # 1  has been approved.  
         [0038]     Table 4 describes the format of the LOCATION-MANAGEMENT-REQUEST message.  
                       TABLE 4                       Field   Size   Notes                   Location-management-request_message_format( ) {                Global Header   152 bits        For (i=0; i&lt;Num_Records; i++) {         MSS ID    48 bits               0x00: Location registration         Action Code    8 bits   0x01: Location update               0x02-FF: Reserved         TLV_IDLE AUTH Information   TBD   Valid if action code is 0x00         TLV_Paging Cycle Request    32 bits         TLV_Previous PG-ID    24 bits   Valid if action code is 0x01        }        Security Field   TBD       }                  
 
         [0039]     In the LOCATION-MANAGEMENT-REQUEST message shown in Table 4, the ‘Global Header’ field, the ‘Security Field’, and a cyclic redundancy check (CRC) field (not shown) are configured by information fields commonly included in backbone messages according to the conventional IEEE 802.16e standard. The ‘MSS ID’ field is a newly added field to indicate identification information of the MSS requesting an idle mode operation. The ‘Action Code’ field is an information field indicating the action being requested through the LOCATION-MANAGEMENT-REQUEST message. That is, when the PLM server  240  receives the LOCATION-MANAGEMENT-REQUEST message in which the ‘Action Code’ value has been set to ‘0×00’, it can determine that the received message is a message for registering location of an MSS associated with a corresponding MSS ID in a serving BS. Upon receiving the LOCATION-MANAGEMENT-REQUEST message in which the ‘Action Code’ value has been set to 0×00, the PLM server  240  reads the ‘Type Length Value (TLV)_IDLE AUTH Information’ field. The ‘TLV_IDLE AUTH Information’ field indicates security information registered in the serving BS (i.e., BS # 1   220 ) when MSS # 1   210  performs the network entry procedure. That is, the security information is security association (SA) information used to establish SA between MSS # 1   210  operating in the idle mode and the PLM server  240 .  
         [0040]     If the PLM server  240  generates a new idle mode authentication key (IDLE_AK), it includes information of the newly generated IDLE_AK in a ‘TLV_IDLE AUTH Information’ field of a “LOCATION-MANAGEMENT-RESPONSE” message, and sends the “LOCATION-MANAGEMENT-RESPONSE” message to the serving BS  220 . The serving BS  220  includes a certificate of the MSS in the ‘TLV_IDLE AUTH Information’ field of the “LOCATION-MANAGEMENT-REQUEST” message, and sends the “LOCATION-MANAGEMENT-REQUEST” message. The PLM server  240  can generate IDLE_AK using information included in the certificate. Alternatively, the serving BS  220  may re-use, as IDLE_AK, an AK allocated to the MSS when the MSS enters the network. In this case, the serving BS  220  includes IDLE_AK in the ‘TLV_IDLE AUTH Information’ field of the “LOCATION-MANAGEMENT-REQUEST” message and sends the “LOCATION-MANAGEMENT-REQUEST” message to the PLM server  240 . The PLM server  240  uses IDLE_AK when authenticating a message sent from the MSS.  
         [0041]     Upon receiving, from BS # 1   220 , the “LOCATION-MANAGEMENT-REQUEST” message in which the ‘Action Code’ value has been set to 0×01, the PLM server  240  determines that it must update location information of MSS # 1   210 . The ‘TLV_Paging Cycle Request’ field is an information field indicating a cycle in which MSS # 1   210  operating in the idle mode or requesting the idle mode operation desires to receive a PAG-ADV message. The ‘TLV_Previous PG-ID’ field indicates previous PG-ID information of MSS # 1   210  when a paging group of MSS # 1   210  is changed. The term ‘To Be Discussed (TBD)’ indicates an item to be determined or capable of being determined or corrected according to results of future research.  
         [0042]     Table 5 describes the format of the LOCATION-MANAGEMENT-RESPONSE message introduced by the present invention.  
                       TABLE 5                       Field   Size   Notes                   Location-management-response_Message_format( ) {                Global Header   152 bits   Message Type = TBD        For (i=0; i&lt;Num_Records; i++) {         MSS ID    48 bits               0x00: Location registration         Action Code    8 bits   0x01: Location update               0x02-FF: Reserved         TLV_IDLE AUTH Information   TBD         TLV_Paging Information    56 bits         TLV_PLM Server ID    64 bits        }        Security Field   TBD       }                  
 
         [0043]     As shown in Table 5, the ‘TLV_IDLE AUTH Information’ field is an information field necessary to authenticate MSS # 1   210  operating in or to operate in the idle mode. The PLM server  240  uses the ‘TLV_IDLE AUTH Information’ field to issue IDLE_AK for authenticating the MSS. The ‘TLV_Paging Information’ field includes paging group ID, PAGING_CYCLE, and PAGING_OFFSET parameters. The ‘PLM Server ID’ field indicates an ID of the PLM server.  
         [0044]     Table 6 describes the format of a new DREG-CMD message obtained by correcting the conventional DREG-CMD message.  
                           TABLE 6                                   Syntax   Size                           DREG-CMD_Message_Format( ) {                Management Message Type    8 bits            Action Code    8 bits            TLV_Paging Information    48 bits            TLV_REG-duration    24 bits            TLV_IDLE AUTH Information   TBD            TLV_PLM Server ID    64 bits            TLV_HMAC Tuple   176 bits           }                      
 
         [0045]     In Table 6, the “Management Message Type’ field, the ‘Action Code’ field, the ‘TLV_Paging Information’ field, the ‘TLV_REG-duration’ field, and the ‘Type Length Value_Hashed Message Authentication Code (TLV_HMAC) Tuple’ field of the new DREG-CMD message are the same as those of the conventional DREG-CMD message. However, the present invention newly adds the ‘TLV_IDLE AUTH Information’ field to the conventional DREG-CMD message. The ‘TLV_IDLE AUTH Information’ field shown in Table 6 is the same as that included in the LOCATION-MANAGEMENT-RESPONSE message received from the PLM server  240 . That is, the PLM server  240  uses the ‘TLV_IDLE AUTH Information’ field when IDLE_AK is issued. If the ‘TLV_IDLE AUTH Information’ field is not present, MSS # 1   210  re-uses, as IDLE_AK, an AK allocated from BS # 1   220  when entering the network. The ‘TLV_PLM Server ID’ field serves as an ID of the PLM server for paging and location management, and is included when MSS # 1   210  sends, to an arbitrary BS, a location update request message to be described below. When the PLM server  240  is located in the current serving BS, the ‘TLV_PLM Server ID’ field can be omitted. In this case, MSS # 1   210  includes an ID of the current serving BS in the location update request message, and sends the location update request message.  
         [0046]     Upon receiving, from BS # 1   220 , a DREG-CMD message (including Action Code=0×05) indicating that the idle mode operation has been approved, MSS # 1   210  transitions to the idle mode. Then, MSS # 1   210  is awakened in a cycle negotiated in advance between MSS # 1   210  and the PLM server  240 , and then receives a PAG-ADV message to determine if it has been paged (Step  255  or  257 ). The PAG-ADV message is periodically broadcast according to the cycle negotiated in advance between the MSS operating in the idle mode and the PLM server  240 . The MSS is awakened in the negotiated cycle, and analyzes the received PAG-ADV message. Through a result of the analysis, the MSS determines if its paging group has been changed, or/and if it has been paged. In this case, it should be noted that MSS # 1   210  can move to a different paging group in the idle mode state. It is assumed that MSS # 1   210  moves from a paging group having PG-ID # 1  to a paging group having PG-ID # 2 .  
         [0047]     MSS # 1   210  identifies PG-ID information included in the PAG-ADV message, and then compares the identified PG-ID information with a PG-ID previously given from the PLM server  240 . If MSS # 1   210  determines that the PG-ID has been changed, it performs a ranging procedure during the conventional network entry procedure with a BS (e.g., BS # 2  illustrated in  FIG. 2 ) sending the PAG-ADV message. That is, MSS # 1   210  sends a ranging request (“RNG-REQ”) message to BS # 2   230  having PG-ID # 2  (Step  261 ), and receives a ranging response (“RNG-RSP”) message from BS # 2   230  (Step  262 ). The RNG-REQ and RNG-RSP messages may include an ‘HMAC Tuple’ field for authenticating the MSS. Subsequently, MSS # 1   210  sends, to BS # 2   230 , a location update request (“MOB_LU-REQ”) message for registering its own location in the PLM server  240  (Step  263 ). Table 7 describes the format of the MOB_LU-REQ message.  
                       TABLE 7                       Syntax   Size   Notes                   MOB_LU-REQ_Message_format( ) {                Message Type    8 bits        Reserved    6 bits               00 - Location update by new paging Group ID        Action Code    2 bits   01 - Location update by Timer expiry               10˜11 - Reserved        TLV_Previous PG ID    24 bits        TLV_Paging Cycle Request    40 bits        TLV_PLM Server ID    64 bits        TLV_HMAC Tuple   176 bits   Based on SA information between MSS and               PLM server       }                  
 
         [0048]     In the format of the MOB_LU-REQ message, the ‘Action Code’ field indicates the action being requested through the MOB_LU-REQ message. When a value of the ‘Action Code’ is ‘00’, the ‘TLV_Previous PG ID’ field indicates a previous PG-ID associated with MSS # 1   210  sending the MOB_LU-REQ message. That is, the ‘TLV_Previous PG ID’ field includes ID information of paging group #1 serving as a previous paging group. The ‘TLV_Paging Cycle Request’ field indicates a value of a new paging cycle requested by the MSS. The ‘TLV_PLM Server ID’ field indicates an ID of the PLM server  240  received through the DREG-CMD message, or an ID of the serving BS received through the DREG-CMD message when a ‘PLM Server ID’ field is not present in the DREG-CMD message. The ‘TLV_HMAC Tuple’ field is an authentication information field generated from authentication related information of the DREG-CMD message that MSS # 1   210  has received from the PLM server  240  through BS # 1   220 , or an authentication information field generated from authentication information allocated from the serving BS (BS # 1 ) before transition to the idle mode when authentication information for the idle mode operation is not received from the DREG-CMD message.  
         [0049]     Upon receiving the MOB_LU-REQ message, BS # 2   230  generates the above-mentioned “LOCATION-MANAGEMENT-REQUEST” message (including Action Code=0×01), and sends the generated message to the PLM server  240  (Step  264 ). The PLM server  240  reads the ‘HMAC Tuple’ field from the LOCATION-MANAGEMENT-REQUEST message (including Action Code=0×01), and then authenticates MSS # 1   210 . The PLM server  240  sends a “LOCATION-MANAGEMENT-RESPONSE” message including a result of the authentication to BS # 2   230  (Step  265 ). Upon receiving the LOCATION-MANAGEMENT-RESPONSE message from the PLM server  240 , BS # 2   230  sends, to MSS # 1   210 , a location update response (MOB_LU-RSP) message based on the format shown in Table 8 (Step  266 ). Table 8 describes the MOB_LU-RSP message of the present invention.  
                       TABLE 8                       Syntax   Size   Notes                   MOB_LU-RSP_Message_format( ) {                Message Type    8 bits               0x00 - Successful MOB_LU-REQ               0x01 - Failed MOB_LU-REQ (The MSS               should perform network re-entry.)        Action Code    8 bits   0x02 - The MSS shall not re-transmit the               MOB_LU-REQ message and shall               wait for the MOB_LU-RSP message.               0x03˜FF - Reserved               Bits 15:0 - PAGING_CYCLE        TLV_Paging Information    48 bits   Bits 23:16 - PAGING_OFFSET               Bits 31:14 - Paging Group ID        TLV_IDLE AUTH Information   TBD   To be discussed        TLV_PLM Server ID    64 bits        TLV_HMAC Tuple   176 bits   Based on SA information between MSS and               PLM server       }                  
 
         [0050]     The ‘Action Code’ field of the MOB_LU-RSP message shown in Table 8 is associated with the ‘Action Code’ value included in the MOB_LU-REQ message. The ‘Action Code’ field indicates successful authentication according to location change of the MSS when the ‘Action Code’ value is 0×00, and indicates unsuccessful authentication according to location change of the MSS when an ‘Action Code’ value is ‘0×01’. When BS # 2   230  sets the ‘Action Code’ value to 0×02, and then sends the MOB_LU-RSP message to MSS # 1   210 , MSS # 1   210  determines that BS # 2   230  has received the MOB_LU-REQ message. Subsequently, MSS # 1   210  waits until the MOB_LU-RSP message is re-received.  
         [0051]     The ‘TLV_IDLE AUTH Information’ field is used when information for authenticating the MSS to operate in the idle mode is changed. The ‘TLV_Paging Information’ field includes Paging Group ID, PAGING_CYCLE, and PAGING_OFFSET parameters associated with the idle mode operation. The ‘PLM Server ID’ field indicates an ID of the PLM server. The ‘TLV_HMAC Tuple’ field includes information generated through SA information set between the MSS and the PLM server.  
         [0052]      FIGS. 3A and 3B  are flow charts illustrating an authentication procedure performed by an MSS according to location registration and update in accordance with an embodiment of the present invention in an IEEE 802.16e communication system.  
         [0053]     Referring to  FIG. 3A , when a requirement for transition to the idle mode is generated because traffic is absent for a predetermined time in step  302 , the MSS proceeds to step  304 . The MSS sends, to a serving BS currently performing a communication function, a DREG-REQ message for a request to go into the idle mode in step  304 , and then proceeds to step  306 . The MSS receives a DREG-CMD message in response to the DREG-REQ message in step  306 , and proceeds to step  308 . The MSS operates according to an ‘Action Code’ value included in the DREG-CMD message in step  308 . When the ‘Action Code’ value is 0×05, the MSS proceeds to step  310 . The MSS transitions to the idle mode in step  310 , and then proceeds to step  312 . The MSS determines if traffic to be transmitted to a BS has been generated in the idle mode in step  312 . If traffic has been generated as a result of the determination, the MSS transitions from the idle mode to active mode, and performs a network entry procedure with the BS in step  314 .  
         [0054]     When the ‘Action Code’ value is 0×06 in step  316 , the MSS proceeds to step  318 . In step  318 , the MSS re-sends the DREG-REQ message to the serving BS after waiting according to waiting time information included in the DREG-CMD message. If the ‘Action Code’ value is 0×07 in step  320 , the MSS proceeds to step  306  to wait for the DREG-CMD message from the serving BS. However, if traffic has not been generated in step  312 , the MSS proceeds to step  324  of  FIG. 3B . When the MSS has received a PAG-ADV message in step  324 , it proceeds to step  326 . In step  326 , the MSS reads a ‘PG-ID’ field of the PAG-ADV message, and compares its own PG-ID with the read PG-ID. When the PG-ID has been changed, the MSS proceeds to step  328 . However, when the PG-ID has not been changed, the MSS proceeds to step  312 .  
         [0055]     In step  328 , the MSS sends, to a BS associated with the changed PG-ID, an MOB_LU-REQ message for location update, and proceeds to step  330 . A ‘TLV_HMAC Tuple’ field of the MOB_LU-REQ message includes information of a resulting value obtained by performing an authentication algorithm using an AK allocated to the MSS. When the MSS receives an MOB_LU-RSP message (including Action Code=0×00) in response to the MOB_LU-REQ message in step  330 , it proceeds to step  332 . The MSS determines that the authentication procedure according to location change has been completed in step  332 . However, when the MSS has not received an MOB_LU-RSP message for a preset time, it proceeds to step  334  to determine if an MOB_LU-REQ re-setup timer has expired. If the timer has expired, step  326  is performed. However, if the timer has not expired, step  328  is performed.  
         [0056]     When the MSS sends, to a corresponding BS, the MOB_LU-REQ message for performing location update in step  328 , the corresponding BS can send an MOB_LU-RSP message in which the ‘Action Code’ value has been set to 0×00, 0×01, or 0×02. Accordingly, the MSS performs operation based on the ‘Action Code’ value upon receiving the MOB_LU-RSP message. That is, when the ‘Action code’ value of the MOB_LU-RSP message is 0×01, the MSS determines that the location update has failed, and must perform a network re-entry procedure with a corresponding BS. However, when the ‘Action Code’ value of the MOB_LU-RSP message is 0×02, the MSS waits until the MOB_LU-RSP message is received from the BS.  
         [0057]      FIG. 4  is a flow chart illustrating the procedure performed by the serving BS when a request for MSS idle mode is made in the IEEE 802.16e communication system in accordance with an embodiment of the present invention.  
         [0058]     Referring to  FIG. 4 , the serving BS receives a DREG-REQ message from the MSS in step  401 , and proceeds to step  402 . The serving BS sends a LOCATION-MANAGEMENT-REQUEST message including authentication information of the MSS to a PLM server in step  402 , and proceeds to step  403 . The serving BS receives the LOCATION-MANAGEMENT-REQUEST message including authentication information of the MSS from the PLM server in step  403 , and proceeds to step  404 . In this case, the MSS may re-use, as an IDLE AK, an AK allocated when performing a network entry procedure with the serving BS, or the PLM server may allocate a new IDLE AK to the MSS. That is, the serving BS sends, to the MSS, authentication information and idle mode information, i.e., a DREG-CMD message including ‘Action Code’ information in step  404 .  
         [0059]      FIG. 5  is a flow chart illustrating a procedure performed by the BS receiving the location update request in accordance with an embodiment of the present invention in an IEEE 802.16e communication system.  
         [0060]     Referring to  FIG. 5 , the BS receives an MOB_LU-REQ message from an MSS in step  501 , and proceeds to step  502 . In this case, the MSS receives a PAG-ADV message, and determines that a paging group has changed because of a change in location. Accordingly, the MSS sends the MOB_LU-REQ message to a BS of a corresponding paging group. That is, because the MSS has moved to a new paging group, it is re-authenticated by a PLM server. Preferably, the MSS performs only ranging and authentication procedures during a network entry procedure, and does not perform other procedures. In step  502 , the BS sends a LOCATION-MANAGEMENT-REQUEST message (including Action Code=0×01) to the PLM server and proceeds to step  503 . In step  503 , the BS receives, from the PLM server, a LOCATION-MANAGEMENT-RESPONSE message to the LOCATION-MANAGEMENT-REQUEST message, and proceeds to step  504 . The LOCATION-MANAGEMENT-RESPONSE message includes information indicating successful authentication as determined by the PLM server. In step  504 , the BS sends, to the MSS, an MOB_LU-RSP message in which the information indicating successful authentication as determined by the PLM server is reflected.  
         [0061]      FIG. 6  is a flow chart illustrating a location control operation performed by a PLM server in the IEEE 802.16e communication system in accordance with an embodiment of the present invention.  
         [0062]     Referring to  FIG. 6 , the PLM server receives a LOCATION-MANAGEMENT-REQUEST message from a BS in step  602 , and proceeds to step  604 . The PLM server determines if an ‘Action Code’ value of the LOCATION-MANAGEMENT-REQUEST message is 0×01 in step  604 . If the ‘Action Code’ value is 0×01, the PLM server proceeds to step  606 . The PLM server attempts to authenticate the MSS using an HMAC Tuple, and proceeds to step  608 . When the PLM server has successfully authenticated the MSS in step  608 , it proceeds to step  610 . In this case, the PLM server compares a resulting value computed by an authentication algorithm using IDLE_AK used by the MSS with a resulting value computed by an authentication algorithm using IDLE_AK allocated to the MSS by the PLM server. When the two values are identical, it is determined that the MSS is valid. The PLM server updates location information of the MSS in step  610 , and proceeds to step  612 . The PLM server determines if IDLE_AK must be re-generated after a predetermined time elapses in step  612 . If IDLE_AK must be re-generated, the PLM server proceeds to step  614 . The PLM server allocates new authentication information for the MSS in step  614 , and proceeds to step  616 . In step  616 , the PLM server sends a LOCATION-MANAGEMENT-RESPONSE message including the authentication information to a corresponding BS in step  616 . However, when the PLM server has failed to authenticate the MSS in step  624 , it includes authentication failure information in the LOCATION-MANAGEMENT-RESPONSE message and sends the message to a corresponding BS.  
         [0063]     However, when the ‘Action Code’ value of the LOCATION-MANAGEMENT-REQUEST message is not 0×01 in step  604 , the PLM server proceeds to step  618 . The PLM server stores location information of the MSS, and proceeds to step  620 . The PLM server allocates paging information (i.e., PAGING_CYCLE, PAGING_OFFSET, and Paging Group ID parameters) for the MSS in step  620 , and proceeds to step  622 . The PLM server allocates authentication information of the MSS in step  622 .  
         [0064]     As is apparent from the above description, the present invention allows a mobile subscriber station (MSS) operating in idle mode to safely register location update information, and reduces a range of a paging group by taking into account paging overhead, such that power consumption due to frequent location registration is reduced.  
         [0065]     Although preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined by the following claims, along with their full scope of equivalents.