Abstract:
A network-based dormant handoff method in a mobile communication system includes monitoring a change of a service area of a random terminal in a source access network, and if the change in the source access network is detected requesting a dormant handoff to a target access network as a changed service network. The method further includes connecting a packet data session for the terminal between the target access network and a packet data serving node (PDSN) according to the second step of requesting the dormant handoff, and the releasing the packet data session for the terminal between the target access network and the packet data serving node.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to mobile communication systems, and more particularly to a system and method for managing a handoff operation in a mobile communication system.  
         [0003]     2. Background of the Related Art  
         [0004]     In a CDMA system, if a packet data call is released by expiration of an inactivity timer and if there exists no other active call control instance, a traffic channel is released. In doing so, a Layer-3 processing state of a terminal converts to an idle mode and a corresponding packet data session and packet data service instance are shifted to a dormant state. Such a system is disclosed in ‘Interoperability Specification (IOS) for CDMA 2000 Access Network Interface’ and the radio specification ‘TIA/EIA/IS-2000.x-C’, the contents of which are incorporated herein by reference.  
         [0005]      FIG. 1  is a block diagram of a CDMA system, which includes a packet data serving node (PDSN)  110 , a plurality of PCFs  120  and  121  connected to the PDSN  110 , a plurality of base stations (BSs)  130  to  133  connected to the corresponding PCFs  120  and  121 , respectively, first network devices  140  and  141  to form a network. Reference number ‘ 10 ’ indicates a mobile terminal (MS) such as a notebook computer.  
         [0006]      FIG. 2A  and  FIG. 2B  are flowcharts of a dormant handoff process which may be performed in the CDMA system of  FIG. 1 . During this process, in an initial state of the MS  10 , an active packet data session is first maintained, as well as one active call control instance and packet data service instance. A PPP connection is maintained between the MS  10  and the PDSN  110  (S 201 ).  
         [0007]     If the MS moves away into a service area of a target BS  132  from a service area of a source BS  131  during the initial state (S 202 ), the MS detects that service can be provided to the MS via the target BS. More specifically, the MS tracks a pilot of the target BS to recognize that intensity information (Ec/Io) is of a sufficient level. The MS then transmits a (E)PSMM message to the source BS (S 203 ).  
         [0008]     By performing a handoff processing according to the reception of the (E) PSMM message, the system including the source BS  131  excludes a pilot of source BS  131  from an active set and includes the pilot of target BS  132  in the active set. Hence, a traffic path for providing a packet data service to a user of the MS  10  becomes PSDN  110 →source PCF  120 →source BS  131 →target BS  132 →MS  10  (S 204 ). Thus, BS  131  drives a packet data inactivity timer while the packet data service instance is connected. The packet data inactivity timer is reset whenever a non-idle RLP frame is transmitted/received (S 205 ).  
         [0009]     After expiration of the packet data inactivity timer, source BS  131  transmits a Clear Request message, which sets a cause value to ‘packet call going dormant,’ to a corresponding mobile switching center (MSC)  160  to release a traffic channel (S 206 ).  
         [0010]     The MSC  160  transmits a Clear Command message to the source BS to instruct to release a corresponding dedicated resource (S 207 ). The source BS then performs a traffic channel release processing, accordingly (S 208 ).  
         [0011]     The sources BS transmits an A9-Release-A8 message including a dormant indicator to the source PCF  120  to instruct PCF  120  to release the corresponding dedicated resource (S 209 ).  
         [0012]     The PCF transmits an All-Registration Request message including accounting data to PDSN  110  by setting a lifetime timer value to ‘0’ to release an A10 connection (S 210 ). The PDSN transmits an All-Registration Reply message to PCF  120  to notify that the release of the A10 connection corresponding to the corresponding active packet data service is completed (S 211 ).  
         [0013]     The PCF transmits an A9-Release-A8 Complete message as a reply to the A9-Release-A8 message to the source BS (S 212 ). The source BS  131  then transmits a Clear Complete message to the MSC.  
         [0014]     The packet data service session of the MS is shifted to a dormant state after completion of the release process of the traffic channel in the above-explained manner. The packet data session operated by the network enters the dormant state at this time point. Hence, MS  10  performs processing of an idle state by receiving an overhead message since the packet data session and a processing state of the layer-3 (Layer3) are in the dormant state and the idle state, respectively (S 214 ).  
         [0015]     In the idle state, the MS monitors a broadcast channel. If detecting PZID, SID, and NID are detected to be changed, the MS  10  transmits an Origination message to the target BS  132  by setting a DRS value to ‘0’ (S 210 ). Correspondingly, the target BS transmits a BS Ack Order message to approve the Origination message was received (S 216 ).  
         [0016]     Subsequently, the target BS sets an ADDS User Part value to ‘Asynchronous Data Service’ and transmits an ADDS Transfer message including the rest authentication, the MSC then transmits an ADDS Transfer Ack message as a response to the target BS (S 217 ).  
         [0017]     The target BS sets a DRI (data ready indicator) value to ‘0’ and transmits an A9-Setup-A8 message to target PCF  121  (S 218 ). Accordingly, a ‘PDSN dormant HO’ procedure is executed between the target PCF and PDSN  110  in a following manner. First target PCF  121  transmits an All-Registration Request message including MEI (mobility event factor) to the PDSN (S 219 ). If the All-Registration Request message is valid, the PDSN transmits an All-Registration Reply message to the target PCF to notify that a connection is accepted (S 220 ). Subsequently, the target PCF transmits an A9-Release-A8 Complete message to the target BS (S 221 ).  
         [0018]     The target BS transmits a Release Order (with ‘normal release’) message to the MS (S 222 ). The MS then transmits the Release Order to the target BS (S 223 ) so that a packet data session of the MS  10  maintains ‘dormant’ state.  
         [0019]     PDSN  110  transmits an All-Registration Update message to source PCF  120  to initiate an A10 Connection release from the corresponding PCF  120  (S 224 ). The source PCF then transmits an All-Registration Acknowledge message to the PDSN  110  (S 225 ).  
         [0020]     Finally, the source PCF transmits an All-Registration Request message having a lifetime timer value set to ‘0’ to the PDSN (S 226 ). The PDSN then transmits an All-Registration Reply message including accept indication information to source PCF  120  (S 227 ). Accordingly, source PCF  120  releases the A10 connection for the corresponding MS.  
         [0021]     As mentioned in the foregoing description, if the service area (PZID/SID/NID) of the terminal is changed and if the inactivity timer expires, the dormant handoff process is performed from the MS after the packet data session is shifted to the dormant state.  
         [0022]     It frequently occurs that the ANID (PZID/SID/NID) is changed in the course of transition to the dormant packet data session mode from the active packet data session mode. This is because the MS user has mobility. Because of their mobility, the MS in the dormant packet data session mode needs the dormant handoff process for changing the A10 connection from the source PCF to the target PCF to set up a packet data call quickly in reactivation. Hence, after the traffic channel is released, the MS in the dormant packet data session mode transmits the Origination message to perform the dormant handoff. Only if such a series of procedures are completed, the MS enables to maintain the dormant state without signaling message exchange.  
         [0023]     However, the foregoing system has at least the following problems or disadvantages. First, a plurality of signaling procedures are needed to prepare reactivation from the point in time of the packet data call release. A plurality of the signaling procedures increase the signaling overhead on the packet data service associated elements between the terminal and the network, e.g., the Origination message in the step S 215  increase the load on the access channel.  
         [0024]     Second, the time taken to perform the process of preparing the reactivation process is so long as to unnecessarily consume the battery of the terminal. More specifically, the closed loop power control is not executed when the terminal is in the access channel mode, whereby the corresponding battery consumption is raised.  
         [0025]     Third, the time taken to perform the process of preparing the reactivation process is too long, whereby the reactivation request of the terminal user may not be accepted during the dormant handoff. Even if the reactivation request of the terminal user is accepted right after terminating the dormant handoff process in progress, prompt reactivation is impossible since the A10 connection is not established between the target PCF and the PDSN.  
       SUMMARY OF THE INVENTION  
       [0026]     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least one of the advantages described hereinafter.  
         [0027]     Another object of the present invention is to provide a network-based dormant handoff method in a mobile communication system by which a dormant handoff is performed based on a network without message communications for the dormant handoff with a terminal by having the network recognize a state for the dormant handoff.  
         [0028]     To achieve these and other objects and advantages, the present invention provides a network-based dormant handoff method in a mobile communication system that includes a first step of monitoring a change of a service area of a random terminal in a source access network, a second step of if the change in the source access network is detected, requesting a dormant handoff to a target access network as a changed service network, a third step of connecting a packet data session for the terminal between the target access network and a packet data serving node (PDSN) according to the second step of requesting the dormant handoff, and a fourth step of releasing the packet data session for the terminal between the target access network and the packet data serving node.  
         [0029]     Preferably, in the first step, the source access network and more particularly a source base station (controller) enables to detect or recognize the change of the service area based on intensity information of a pilot signal received from the terminal or presence or non-presence of handoff occurrence between base stations.  
         [0030]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a block diagram showing one type of CDMA system applicable to the present invention.  
         [0032]      FIG. 2A  and  FIG. 2B  are flow charts of a dormant handoff process performed in a related art CDMA system.  
         [0033]      FIG. 3  is a flowchart of a network-based dormant handoff method in a mobile communication system according to one embodiment of the present invention.  
         [0034]      FIG. 4  is a structural diagram of a dormant handoff request message according to an embodiment of the present invention.  
         [0035]      FIG. 5  is a structural diagram of a dormant handoff response message according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0036]      FIG. 3  is a flowchart of a network-based dormant handoff method in a mobile communication system according to one embodiment of the present invention. During an initial state of an MS  10 , an active packet data session is maintained and also preferably one active call control instance and packet data service instance are maintained. Moreover, a PPP connection is maintained between the MS  10  and a PDSN  110  (S 301 ).  
         [0037]     If the MS moves away into a service area of a target BS  132  from a service area of a source BS  131  during the initial state (S 302 ), the MS detects that a service is available via the target BS. More specifically, the MS tracks a pilot of the target BS to recognize that intensity information (e.g., Ec/Io) is of a predetermined level. The MS then transmits a (E)PSMM message to the source BS (S 303 ).  
         [0038]     By performing a handoff processing according to reception of the (E)PSMM message, the system including the source BS  131  excludes a pilot of the source BS from an active set and includes the pilot of the target BS in the active set. Moreover, while a handoff is performed between the source BS and the target BS, the target BS preferably includes an access network identifier (ID) as its position information in a handoff response (A7-Handoff Response) message transmitted to the source BS  131 . Hence, a traffic path for providing a packet data service to a user of the MS becomes PDSN  110 →source PCF  120 →source BS  131 →target BS  132 →MS  10  as a result of the handoff (S 304 ).  
         [0039]     Thus, the source BS drives a packet data inactivity timer while the packet data service instance is connected. The packet data inactivity timer is reset whenever a non-idle RLP frame is transmitted/received (S 305 ).  
         [0040]     After expiration of the packet data inactivity timer, the source BS  131  transmits a Clear Request message, which sets a cause value to ‘packet call going dormant’, to a corresponding mobile switching center (MSC)  160  to release a traffic channel (S 306 ). The MSC then transmits a Clear Command message to the source BS to instruct to release a corresponding dedicated resource (S 307 ).  
         [0041]     The source BS  131  recognizes that the MS currently lies in the service area of the target BS  132  and knows the access network ID, i.e., SID/NID/PZID, to which the target BS  132  belongs. Based on such a fact, the source BS transmits a message for initiating a network-based dormant handoff procedure according to the present invention (hereinafter called A7-Preceded Dormant Handoff Request message) to the target BS prior to execution of a call release according to the instruction of step S 307 . An example of the A7-Preceded Dormant Handoff Request message is shown in  FIG. 4  (S 308 ).  
         [0042]     The target BS transmits an A9-Setup-A8 message to the target PCF  121  (S 309 ). The A9-Setup-A8 message may, for example, have the same information of the conventional dormant handoff but PDH (preceded dormant handoff) is set to ‘1’. In the A9-Setup-A8 message., both DRI (data ready indicator) and Handoff Indicator are each set to ‘0.’ 
         [0043]     Target PCF  121  transmits an All-Registration Request message including MEI (mobility event indicator) information to the PDSN  110  (S 310 ). The PDSN  110  then transmits an All-Registration Reply message including accept indication information to target PCF  121  (S 311 ). As a result of executing the procedure, A10 connection binding information in the PDSN  110  is set for the target PCF. Also, the target PCF  121  transmits an A9-Release A8 Complete message to the target BS  132  to respond to the step S 309  (S 312 ).  
         [0044]     The target BS transmits an A7-Preceded Dormant Handoff Response message, which includes information (cause) that a new A10 connection setup is normally established between target PCF  121  and PDSN  110 , to source BS  131  to respond to the step S 308 . An example of the A7-Preceded Dormant Handoff Response message is configured in  FIG. 5  (S 313 ).  
         [0045]     As dormant handoff according to the present invention is normally completed, source BS  131  performs a call release according to the instruction of step S 307 . In doing so, the source BS includes “PDH ‘1” in a Release Order message to transmit. If the PDH is set to ‘1’, the terminal performs transition to the dormant state and then updates the PZID. Yet, the terminal does not perform the dormant handoff even if the previous PZID is different from the current PZID. This is because the terminal has already known that the network-based dormant handoff was performed based on the PDH information. By comparison, in the related-art method the PDH is not included in the Release Order message or Enhanced Release Order message. In accordance with at least one embodiment of the present invention, a change of the Release Order may be performed. After completion of the call release according to the instruction of the step S 07 , the source BS  120  transmits a release complete message to the MSC  160  to notify the completion of the call release (S 314 ).  
         [0046]     Preferably, in parallel with the call release procedure, a previous A10 connection release procedure is initiated between the source PCF  120  and the PDSN  110 . For this, the PDSN  110  transmits an All-Registration Update message to the source PCF  120  (S 316 ). The source PCF  120  then responds an All-Registration Acknowledge message (S 317 ).  
         [0047]     The source PCF  120  transmits an All-Registration Request message, which sets a lifetime to ‘0’ and includes accounting information therein, to the PDSN  110  (S 318 ). The PDSN  110  then transmits an All-Registration Reply message including accept information to the source PCF  120  to enable the source PCF  120  release the A 10  connection to the corresponding MS  10  (S 319 ).  
         [0048]     Accordingly, a network-based dormant handoff method in a mobile communication system according to the present invention has at least the following effects or advantages.  
         [0049]     First, in accordance with at least one embodiment the present invention performs a signaling procedure which simpler than the related art in maintaining a dormant state enabling the prompt reactivation. More Specifically, related-art methods complete the signaling procedure by two processes of shifting the packet data session to the dormant state and performing handoff during the dormant state. The method of the present invention, on the other hand, combines the two continuous processes of the related art into one process and removes the unnecessary signaling part in the course of combining the two processes. As a result, the signaling overhead in the terminal and network is reduced to be smaller than that of the related art. And, the time taken to be ready to stand by the reactivation is shortened to be less than that of the related art.  
         [0050]     Furthermore, the procedure of sending the Origination message to the target BS from the terminal for the dormant handoff is mandatory for related-art methods. In contrast, the present invention may perform dormant handoff based on the network to exclude such a procedure, thereby enabling to reduce the unnecessary load on the access channel. The present invention shortens the time take to stand by the reactivation, thereby enabling to prevent the reactivation from being delayed by the dormant handoff of the related art or the like in performing the reactivation procedure by terminal user&#39;s request.  
         [0051]     Furthermore, the present invention enables to prevent the terminal from consuming the battery unnecessarily in performing the dormant handoff.  
         [0052]     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.