Abstract:
Disclosed is a session handoff method of an access terminal (AT) in a high-rate packet data (HRPD) mobile communication system. The session handoff method comprises performing a close procedure of a session in negotiation upon receiving a close request for a session negotiation from the AT performing session handoff; allocating a new unicast access terminal identifier (UATI) to the AT upon receiving a request for allocation of a new UATI from the AT after the session close procedure; and acquiring prior session information from a source session controller using an old UATI included in received prior session information upon receiving configuration information including the prior session information from the AT after allocating a new UATI to the AT.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to a handoff method in a mobile communication system, and in particular, to a handoff method in a High-Rate Packet Data (HRPD) mobile communication system.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, a mobile communication system transmits and receives information over a radio channel in order to secure mobility of an access terminal. Such a mobile communication system has evolved from a system that basically supports a voice service into a system that can transmit and receive packet data. For the system that can transmit and receive packet data, a system that transmits simple short messages and small amounts of Internet service data is currently used. In addition, in order to meet users&#39; demands for data service, the mobile communication system has evolved into a High-Rate Packet Data (HRPD) mobile communication system, called a 1x EV-DO mobile communication system. Currently, the 1x EV-DO mobile communication system is being commercialized.  
         [0005]     With reference to  FIG. 1 , a description will now be made of configuration and operation of a commercialized HRPD mobile communication system.  FIG. 1  is a diagram illustrating configuration of an HRPD mobile communication system.  
         [0006]     An access terminal (AT)  101  can perform data communication with an access network transceiver system (ANTS) over a radio channel. Access network controllers (ANCs)  110  and  120  are connected to a plurality of ANTSs  11  to  1 N and  21  to  2 N, respectively, and control their associated ANTSs. The ANC can constitute a subnet independently or as one access network (AN), or two or more ANCs can constitute a subnet as one AN. Such an AN-based subnet is identified through a unique subnet mask prepared in the ANC. Since the subnet mask is comprised of 128 bits, the subnet can also be identified through a color code comprised of fewer bits. The ANCs  110  and  120  have session controllers  111  and  121 , respectively. Each of the session controllers  111  and  121  assigns a unicast access terminal identifier (UATI) to an AT located in an ANC connected thereto, and manages session information corresponding to the AT.  
         [0007]     The ANCs  110  and  120  can be connected to a data core network (DCN)  150  directly or via another specific ANC. The DCN  150  is connected to the ANC via a packet data service node (PDSN)  151 . A detailed description of the DCN  150  will not be given. The ANCs  110  and  120  can be connected to an access network-authentication, accounting and authorization (AN-AAA) system  160  independently or indirectly via a specific AN-AAA system.  
         [0008]     With reference to  FIG. 2 , a description will now be made of a handoff method in such an HRPD mobile communication system.  FIG. 2  is a signaling diagram during handoff of an AT in an HRPD mobile communication system.  
         [0009]     In an HRPD mobile communication system, session information of subscribers is stored in the session controller  111 . Therefore, handoff occurs when session information is turned over. That is, handoff takes place when session information of an AT is transferred to a session controller of another ANC, and in this way, history of the AT is continuously maintained. Such a session-related handoff standard is defined as A13 in IS-878, a 1x EV-DV standard. Such a handoff procedure will now be described with reference to  FIG. 2 .  
         [0010]     In  FIG. 2 , the ANC  120  to which the AT  101  first belongs is called a source ANC, and a session controller (SC)  121  connected to the source ANC  120  is called a source SC. In addition, the ANC  110  to which the AT  101  is to move is called a target ANC, and the session controller  111  connected to the target ANC  110  is called a target SC. The signaling procedure of  FIG. 2  will now be described.  
         [0011]     The AT  101  can detect a change of ANC through check of a subnet mask or check of a color code. Upon detecting the change of ANC, the AT  101  transmits a UATI Request signal UATIRequest to the target ANC  110  in step  200 . At this point, the AT  101  transmits a subnet mask or a color code of an ANC to which it previously belonged, together with an old UATI. Upon receiving the UATI Request signal, the target ANC  110  transmits in step  202  a UATI Allocate Request signal UATIAllocateReq to the target SC  111  along with the subnet mask or color code and the UATI. The target SS  111  can identify the source SC  121  using the received subnet mask or color code. After identifying the source SC  121 , the target SC  111  transmits in step  204  an A13 Session Information Report message based on an A13 standard to the source SC  121 .  
         [0012]     Upon receiving the A13 Session Information Report message, the source SC  121  transmits in step  206  an A13 Session Information Response message to the target SC  111  along with session information for a call of a corresponding AT that received the information, and subscriber information. Such an A13 Session Information Response message includes a message sequence value. If the A13 Session Information Response message is received in step  206 , the target SC  111  allocates again a UATI for the AT  101  in step  208 . Further, in step  208 , the target SC  111  generates the newly allocated UATI as a UATI Allocate Response signal UATIAllocateRsp and sends the generated UATI Allocate Response signal to the target ANC  110 . At this point, if IP Address and Access Network Identifier parameters of a PDSN are received from the source SC  121 , the target SC  111  sends the UATI Allocate Response signal UATIAllocateRsp to the target ANC  110  along with the received parameters. Because a UATI of the AT  101  was newly assigned, the target ANC  110  sends in step  210  a UATI Assignment signal UATIAssignment to the AT  101  to inform the AT  101  of the newly assigned UATI. If a UATI is newly assigned in this way, the AT  101  stores the newly assigned UATI. Thereafter, in step  212 , the AT  101  sends a UATI Complete signal UATIComplete to the target ANC  110  to inform that the UATI has been normally assigned.  
         [0013]     Upon receiving the UATI Complete signal UATIComplete, the target ANC  110  receives generates in step  214  a UATI Complete Request signal UATICompleteReq and sends the generated UATI Complete Request signal to the target SC  111 . Upon receiving the UATI Complete Request signal, the target SC  111  generates in step  216  a UATI Complete Response signal UATICompleteRsp and sends the generated UATI Complete Response signal to the target ANC  110 . Then the target ANC  110  and the AT  101  perform a Location Update procedure in step  218 . Further, in step  220 , the target SC  111  generates an A13 Session Information Confirm signal according to an A13 standard and sends the generated A13 Session Information Confirm signal to the source SC  121 . Upon receiving the A13 Session Information Confirm signal, the source SC  121  deletes a database (DB) for the corresponding AT.  
         [0014]     As described above, many signaling procedures are performed while the AT  101  requests a UATI upon detecting movement of its position and then is assigned a UATI in response to the request. In addition, even after the UATI is assigned, signals must be exchanged between the target ANC  110  and the AT  101  during the Location Update procedure, and signals should also be exchanged between the session controllers.  
         [0015]     However, in some cases, an AT fails to receive pilot signals from a target ANC and a source ANC while performing handoff. Such a case takes place when the AT fails to receive a pilot signal as the AT is powered off or a channel condition becomes poor during handoff. When the AT fails to acquire a pilot signal received from the source ANC and the target ANC during handoff like this, the AT fails in handoff.  
         [0016]     In case of the handoff failure, the AT must perform a process related to initial location registration when it acquires again a pilot signal. That is, the AT must restart session negotiation performed during the initial location registration from the beginning. In this case, even if only 3 protocols of ‘session configuration protocol’, ‘stream protocol’ and ‘idle state protocol’ are assumed as attribute protocols performed for session negotiation, the AT must newly perform negotiation and determine available protocols at each session. Even if only 3 protocols are assumed like this, when session negotiation is newly performed, the number of messages exchanged between an AT and an access network (AN) in which an ANTS is included must be 7. This is because each message requires a configuration request message and its associated configuration response message, and when the negotiation is completed, it must include a configuration complete message.  
         [0017]     That is, in case of handoff failure, so many messages must be exchanged increasing a system load. As a result, available resources in the system are exhausted. In addition, when so many messages are exchanged like when the AT is initially powered on, a user may feel tedious resulting in deterioration in service quality.  
       SUMMARY OF THE INVENTION  
       [0018]     It is, therefore, an object of the present invention to provide a method for normally performing handoff even in a poor radio environment.  
         [0019]     It is another object of the present invention to provide a handoff method for reducing an operation load of an HRPD mobile communication system.  
         [0020]     It is further another object of the present invention to provide a safe handoff method in an HRPD mobile communication system.  
         [0021]     To achieve the above and other objects, there is provided a session handoff method of an access terminal (AT) in a high-rate packet data (HRPD) mobile communication system. The session handoff method comprises performing a close procedure of a session in negotiation upon receiving a close request for a session negotiation from the AT performing session handoff; allocating a new unicast access terminal identifier (UATI) to the AT upon receiving a request for allocation of a new UATI from the AT after the session close procedure; and acquiring prior session information from a source session controller using an old UATI included in received prior session information upon receiving configuration information including the prior session information from the AT after allocating a new UATI to the AT.  
         [0022]     Preferably, the step of acquiring session information from a previous session controller comprises the step of sending a session information request message based on an A13 standard to the source session controller, and receiving a session information response message based on the A13 standard.  
         [0023]     The session handoff method further comprises the step of performing a location update procedure on the AT between a target access network controller (ANC) and the AT after acquiring the previous session information.  
         [0024]     To achieve the above and other objects, there is provided a handoff method in an access terminal (AT) capable of communicating with a high-rate packet data (HRPD) mobile communication system. The handoff method comprises completing session negotiation when the AT acquires again a pilot signal after a failure to receive a pilot signal while performing session handoff; sending a UATI allocate request to the HRPD mobile communication system after completing the session negotiation; and sending information on a position where prior session information is stored to the HRPD mobile communication system, upon receiving a UATI allocate response from the HRPD mobile communication system.  
         [0025]     The handoff method further comprises the step of performing a location update procedure with the HRPD mobile communication system after sending information on the position where prior session information is stored. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     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:  
         [0027]      FIG. 1  is a diagram illustrating configuration of an HRPD mobile communication system;  
         [0028]      FIG. 2  is a signaling diagram during handoff of an AT in an HRPD mobile communication system; and  
         [0029]      FIGS. 3A  to  3 C are signaling diagrams for handoff in an HRPD mobile communication system according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     A preferred embodiment of the present invention will now be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.  
         [0031]      FIGS. 3A  to  3 C are signaling diagrams for handoff in an HRPD mobile communication system according to an embodiment of the present invention. With reference to  FIGS. 3A  to  3 C, a detailed description will now be made of a process of performing handoff based on a handoff signaling flow in an HRPD mobile communication system according to an embodiment of the present invention.  
         [0032]     It is assumed herein that an AT  101  fails to receive all pilot signals transmitted from a source ANC  120  and a target ANC  110  when it moves from the source ANC  120  to the target ANC  110 , i.e., while performing handoff. Such a case occurs due to power off or poor channel environment as described in the prior art section. In addition, the AT  101  detects a change of subnet in the method descried in the prior art section. If the AT  101  detects a pilot signal again after a failure to detect a pilot signal due to the poor channel environment, the AT  101  generates in step  402  a Session Close message SessionClose for closing a current ongoing session and transmits the generated Session Close message to the target ANC  110 .  
         [0033]     When the Session Close message is transmitted due to a change of subnet, the target ANC  110  generates in step  404  an acknowledgement message AC_Ack indicating normal receipt of the Session Close message and sends the generated acknowledgement message to the AT  101 . Thereafter, in step  406 , the target ANC  110  generates a Session Close Request message SessionCloseReq indicating a close of the session and sends the generated Session Close Request message to a target SC  111 . In response, the target SC  111  closes the set session.  
         [0034]     In this state, the target SC  111  has not yet performed normal subnet handoff based on the A13 standard due to a pilot loss or movement of the AT  101 . Therefore, the target SC  111  sends in step  408  the target ANC  110  a message indicating that it has no session configuration information for the AT  101 . The message transmitted at this time becomes a Session Close Response message SessionCloseRsp.  
         [0035]     Thereafter, the AT  101  detects its current subnet information, i.e., subnet information stored therein before handoff, and a new subnet. This is possible because the AT  101  is an AT which was in a handoff situation. When an AT which was in the handoff situation receives a new pilot signal again after a failure to receive a pilot signal before completion of handoff, the AT detects that a pilot signal received from the subnet is a new pilot signal. In some cases, if the AT  101  detects again a pilot signal after a failure to receive a pilot signal from the target ANC  110 , then the AT  101  generates in step  410  a UATI Request message UATIRequest and transmits the generated UATI Request message to the target ANC  110 .  
         [0036]     In step  411 , the target ANC  110  sends an acknowledgement message AC_Ack over a control channel set up to the AT  101  in order to inform normal receipt of the UATI Request message. Thereafter, in step  412 , the target ANC  110  generates a UATI Allocate Request message UATIAllocateReq and sends the generated UATI Allocate Request message to the target SC  111  in order to allocate UATI of the AT  101 . In this state, because the UATI has not been allocated yet for the AT  101 , the AT  101  is identified using a random access terminal identification (RATI) before until allocation of the UATI. Then the target SC  111  allocates a UATI of the corresponding AT  101  in response to the UATI Allocate Request message UATIAllocateReq received in step  412 . Thereafter, in step  414 , the target SC  111  generates a UATI Allocate Response message UATIAllocateRsp using the allocated UATI and transmits the generated UATI Allocate Response message to the target ANC  110 .  
         [0037]     Upon receiving the UATI of the AT  101  in this way, the target ANC  110  transmits in step  416  a UATI Assignment message UATIAssignment to the AT  101  to inform the AT  101  of assignment of the UATI. Then the AT  101  stores UATI information included in the UATI Assignment message received in step  416 . Thereafter, in step  418 , the AT  101  sends a UATI Complete message UATIComplete to the target ANC  110 . Then the target ANC  110  generates in step  420  an acknowledgement message AC_Ack indicating normal receipt of the UATI Complete message, and transmits the generated acknowledgement message to the AT  101  over a control channel set up to the AT  101 .  
         [0038]     Thereafter, in step  422 , the target ANC  110  generates a UATI Complete Request message UATICompleteReq and sends the generated UATI Complete Request message to the target SC  111 . In response, the target SC  111  must inform the target ANC  110  of normal receipt of the UATI Complete Request message. For this, the target SC  111  generates in step  424  a UATI Complete Response message UATICompleteRsp and sends the generated UATI Complete Response message to the target ANC  110 .  
         [0039]     When the AT  101  newly receives a pilot channel after a failure to receive a pilot channel during handoff, the AT  101  is assigned a new UATI as stated above. In this state, the AT  101  knows that its session information exists in a previous session controller, i.e., a source SC  121 , due to a failure of the current handoff. Therefore, the AT  101  performs the following operation instead of newly performing session negotiation, according to an embodiment of the present invention.  
         [0040]     In step  426 , the AT  101  informs the target ANC  110  that it has failed subnet handoff but has session information managed in the source SC  121 . Even in the case where an AT receives a pilot signal after a failure to receive a pilot signal due to a poor radio environment, the same operation is performed. Therefore, the AT  101  transmits to the target ANC  110  a Configuration Request message ConfigurationRequest including along with information indicating that session information acquired through negotiation with the source ANC  120  is included in the source SC  121 . Here, the Configuration Request message includes predetermined information capable of indicating prior information contained therein.  
         [0041]     Upon receiving the Configuration Request message, the target ANC  110  stores an old UATI, and then generates in step  428  a Configuration Response message ConfigurationResponse and sends the generated Configuration Response message to the AT  101 . In reply to the message received in step  428 , the AT  101  generates in step  430  a Configuration Complete message ConfigurationComplete indicating completion of assignment negotiation and sends the generated Configuration Complete message to the target ANC  110 . Then the target ANC  110  can detect that the AT  101  has session information, using prior Session attribute information transmitted by the corresponding AT  101 . Therefore, based on the information, the target ANC  110  generates in step  432  a Session Retrieve Request message using an old UATI of the corresponding AT  101  and sends the generated Session Retrieve Request message to the target SC  111 . In response, the target SC  111  generates in step  434  an A13 Session Information Request message based on the A13 standard and transmits the A13 Session Information Request message to the source SC  121 .  
         [0042]     Upon receiving the A13 Session Information Request message from the target SC  111 , the source SC  121  searches for session information among the received information using the old UATI of the corresponding AT  101 . Further, the source SC  121  generates an A13 Session Information Response message based on the A13 standard using the searched session information, i.e., session information used by the corresponding AT  101 . The source SC  121  transmits in step  436  the A13 Session Information Response message to the target SC  111 . Upon receiving the A13 Session Information Response message, the target SC  111  informs the target ANC  110  in step  438  that the A13 Session Information Request has been normally processed and corresponding session information has been stored in a database of the corresponding AT  101 .  
         [0043]     Thereafter, the target SC  111  generates in step  440  a Session Information Confirm message SessionInformationConfirm indicating normal completion of the A13 process and sends the generated Session Information Confirm message to the source SC  121 . After this, the target ANC  110  performs in step  442  a Location Update procedure between the target ANC  110  and the AT  101 .  
         [0044]     As described above, a handoff method according to an embodiment of the present invention can acquire prior information even in case of handoff failure due to pilot loss caused by a poor radio environment or power off of an AT during subnet handoff in an HRPD mobile communication system, contributing to simplification of a handoff procedure. In addition, the simplification of a handoff procedure can lead to an improvement in system performance and battery power saving.  
         [0045]     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.