Patent Publication Number: US-2006014551-A1

Title: Apparatus and method for processing call in mobile communication system

Description:
CLAIM OF PRIORITY  
      This application claims the benefits under 35 U.S.C. §119(a) of an application entitled APPARATUS AND METHOD FOR PROCESSING CALL IN MOBILE COMMUNICATION SYSTEM filed in the Korean Intellectual Property Office on 13 Jul. 2004 and assigned Serial No. 2004-0054548, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to call processing in a mobile communication system. More particularly, the present invention relates to an apparatus and method for processing a call which designates a base station sector at which a mobile station is located and a neighboring base station sector as one call receiving zone when the mobile station transitions from a traffic state to a dormant state and performs paging to a call receiving zone, which is first designated when the call is received by the mobile station.  
      2. Description of the Related Art  
      A radio channel used in a mobile communication system includes a pilot channel, a synchronous channel, a paging channel, a traffic channel, and so on.  
      The pilot channel always corresponds to a Walsh code “0”, and it is spread and modulated with a pseudo-noise (PN) code in the state in which it does not have any information regarding content, other signals or the like. Thus, the pilot channel is a short PN code itself and provides time information, phase reference information, and PN offset information for discriminating a base station.  
      The synchronous channel repetitively transmits certain information at a rate of 1.2 Kbps. The transmitted message (or sync channel message) has information corresponding to broadcasting other than information corresponding to a certain mobile station and provides the mobile station with information that is necessary for initial synchronization with the base station. The mobile station does not monitor the synchronous channel after receiving the initial synchronization information through the synchronous channel and transitions to a state in which it is capable of receiving the paging channel.  
      The base station transmits certain information to the mobile station over the paging channel at a rate of 4.8 Kbps or 9.6 Kbps. The message transmitted to the mobile station includes an overhead message through which all mobile stations receive system configuration-related information and a direct message, which only a certain mobile station receives in response information to a mobile station&#39;s call and request.  
      The traffic channel includes a forward traffic channel and a reverse traffic channel. The forward traffic channel delivers not only voice and data from the base station to the mobile station but also a signaling message using a null frame during a telephone call. The reverse traffic channel delivers not only voice and data from the mobile station to the base station but also a control signal during a telephone call. The data and control signal are simultaneously transmitted by a multiplex option function.  
      The base station performs a tracking zone reporting operation to accurately track the location of the mobile station.  
      The tracking zone reporting operation is specified in CDMA2000 1X Release D. For example, the base station repetitively transmits a tracking zone indicator which is designated to each sector in the base station&#39;s tracking zone. The mobile station registers the tracking zone indicator provided from an arbitrary base station in its tracking zone list and transmits a radio environment message (REM) to the base station to indicate a location change when it deviates from the base station&#39;s tracking zone.  
      However, the base station&#39;s tracking zone is a zone which is statically designated to the base station, and so it is difficult to dynamically designate a paging zone according to the characteristics of the mobile station or the mobile station&#39;s application program.  
      For example, if three sectors are designated to one tracking zone indicator, the mobile station which has the corresponding indicator list under the tracking zone reporting function designates just a paging zone for the three sectors.  
      Meanwhile, when a general call receiving procedure is performed by an exchange function of a mobile switching center (MSC) or a call receiving message is paged to all base stations within one subnet or exchange zone, the network experiences a heavy load.  
      A method for transmitting a general page message (GPM) to track the location of the mobile station and then paging to a base station to which the mobile station responds can reduce the network load, but it has a disadvantage in that the paging time is delayed. This also serves as a disadvantage when an invitation message should be transmitted to a mobile station of the other party in about 1 second in a push to talk (PTT) service, but is not due to the paging delay.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an objective of the present invention to provide an apparatus and method for processing a call which designates a base station sector in which a mobile station is located and a neighboring base station sector as one call receiving zone when the mobile station transitions from a traffic state to a dormant state and performs paging to a call receiving zone which is first designated when the call is received to the mobile station.  
      According to an aspect of the present invention, there is provided a mobile communication system comprising a node configured to designate a sector in which a mobile station is located and a neighboring sector as a virtual paging zone(VPZ), set VPZ information when the mobile station transitions from a traffic state to a dormant state and, send a page to a sector contained in the VPZ information according to a call connection request from a network; and a mobile station configured to perform a virtual paging operation according to the VPZ information is received from the node in the dormant state.  
      The VPZ information may comprise at least one of the VPZ lifetime information, the VPZ update cycle information, the VPZ identification information, and the sector information contained in the VPZ information.  
      The sector information contained in the VPZ information may include at least one of the network identification (NID) information, the system identification (SID) information of a base station system, the PN offset information of the base station system, reference pilot signal strength information for determining whether the mobile station is approaching the base station system or not, sector information for maintaining parameter information, which varies based on a comparison result of the pilot signal strength of the base station system measured by the mobile station and the reference pilot signal strength, and is used to determine whether to maintain the sector information, and the lifetime information of the sector information.  
      The virtual paging operation of the mobile station may comprise one of the following steps: a) deleting the VPZ information when the lifetime of the VPZ information expires; b) measuring the pilot signal strength of a corresponding sector to compare with the reference pilot signal strength, and varying the sector information maintaining parameter based on a comparison result for determining whether to maintain the sector information in the VPZ information of the corresponding sector, when the lifetime of the VPZ information does not expire; c) measuring the pilot signal strength of a corresponding sector to compare with the reference pilot signal strength, and determining whether to reset the lifetime of the sector information based on a comparison result when the lifetime of the VPZ information expires; and d) determining whether to change the VPZ information and determining whether to update an update cycle of the VPZ information based on the determination to change the VPZ information when the update cycle of the VPZ information expires.  
      The mobile communication system may further comprise a unit which stores the VPZ information received from at least one node and requests paging to a node contained in the VPZ information corresponding to a particular mobile station when there is a call connection request to a certain mobile station from a network.  
      The mobile station may comprise idle handoff information in a virtual handoff message and transmit to the node to which the mobile station wants to perform an idle handoff when the mobile station wants to perform an idle handoff to a sector covered by the node from among sectors that are not contained in the VPZ information.  
      The idle handoff information may comprise at least one of the information indicating whether the idle handoff information is contained in the virtual handoff message or not, the information indicating a source of the idle handoff information, and the sector information contained in the VPZ information.  
      According to another aspect of the present invention, there is provided a mobile communication system comprising an information processor for designating a sector in which a mobile station is located and a neighboring sector as a virtual paging zone (VPZ)and setting VPZ information when the mobile station transitions from a traffic state to a dormant state; an information provider for containing the VPZ information in a call release message and transmitting to the mobile station when a call to the mobile station is released; and a paging processor for performing paging to a sector contained in the VPZ information corresponding to the mobile station when there is a call connection request from a network.  
      The call release message may include at least one of the information indicating whether the VPZ information is contained in the call release message, the VPZ lifetime information, the VPZ update cycle information, the VPZ identification information, and the sector information contained in the VPZ information.  
      The information processor may produce a new VPZ information of mobile stations other than the mobile station using idle handoff information contained in a virtual handoff message received from the mobile stations and transmit to the mobile stations when the mobile stations perform an idle handoff to a sector covered by the base station system among sectors other than a sector contained in the VPZ information.  
      The idle handoff information contained in the virtual handoff message may comprise at least one of the information indicating whether the idle handoff information is contained in the virtual handoff message or not, the information indicating a source of the idle handoff information, and the sector information before the mobile stations perform an idle handoff.  
      The sector information contained in the VPZ information may include at least one of the network identification (NID) information, the system identification (SID) information of a base station system, the PN offset information of the base station system, the reference pilot signal strength information for determining whether the mobile station approaches to a base station system or not, the sector information maintaining parameter information, which varies based on a comparison result of pilot signal strength of the base station system measured by the mobile station and the reference pilot signal strength and is used to determine whether to maintain the sector information, and the lifetime information of the sector information.  
      The new VPZ information may include at least one of information indicating identification of the new VPZ information, information indicating lifetime of the new VPZ information, information indicating an update cycle of the new VPZ information, and sector information contained in the new VPZ information.  
      The sector information contained in the new VPZ information may include at least one of network identification (NID) information, system identification (SID) information of a base station system, PN offset information of the base station system, reference pilot signal strength information for determining whether the mobile station is approaching a base station system or not, sector information maintaining parameter information which varies based on a comparison result of the pilot signal strength of the base station system measured by the mobile station and the reference pilot signal strength, and is used to determine whether to maintain the sector information, lifetime information of the sector information, and information indicating whether to update the sector information.  
      According to still another aspect of the present invention, there is provided a mobile station in a mobile communication system comprising at least one mobile station and a node, the mobile station comprising a paging processor for performing a virtual paging operation when virtual paging zone (VPZ) information is received from the node after a call through the node is released; and a call processor for containing idle handoff information in a virtual handoff message and transmitting to a node to which the mobile station wants to perform an idle handoff when the mobile station wants to perform an idle handoff to a sector which are not contained in the VPZ information.  
      According to yet another aspect of the present invention, there is provided a method for processing a call in a mobile communication system, comprising the steps of designating a sector in which a mobile station is located and a neighboring sector as a virtual paging zone (VPZ)and setting VPZ information when the mobile station transitions from a traffic state to a dormant state; containing the VPZ information in a call release message and transmitting to the mobile station when a call with the mobile station is released; and performing paging to a sector contained in the VPZ information corresponding to the mobile station when there is a call connection request from a network.  
      The call processing method may further comprise the step of producing a new VPZ information of mobile stations other than the mobile station using idle handoff information contained in a virtual handoff message received from the mobile stations and transmit to the mobile stations the virtual handoff message when the mobile stations perform an idle handoff to a sector covered by the base station system among sectors other than a sector contained in the new VPZ information.  
      According to still yet another aspect of the present invention, there is provided a call processing method in a mobile station of a mobile communication system comprising at least one mobile station and a node, comprising the steps of performing a virtual paging operation when virtual paging zone (VPZ) information is received from the node after a call with the node is released; and containing idle handoff information in a virtual handoff message and transmitting the virtual handoff message to a node to which the mobile station wants to perform an idle handoff when the mobile station wants to perform an idle handoff to a sector which are not contained in the VPZ information. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the embodiments of the present invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is a schematic diagram showing the connection configuration of a mobile communication system according to an exemplary embodiment of the present invention;  
       FIG. 2  is a block diagram of a base station system according to an exemplary embodiment of the present invention;  
       FIG. 3  is a block diagram of a mobile station according to an exemplary embodiment of the present invention;  
       FIG. 4  is a diagram showing the procedure for collecting VPZ information when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention;  
       FIG. 5  is a diagram showing the paging processing procedure when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention;  
       FIG. 6  is a diagram showing the procedure for resetting the VPZ information depending on an idle handoff when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention;  
       FIG. 7  shows an overhead message according to an exemplary embodiment of the present invention;  
       FIGS. 8A and 8B  show an extended release message (ERM) according to an exemplary embodiment of the present invention;  
       FIGS. 9A and 9B  show a radio environment message (REM) according to an exemplary embodiment of the present invention; and  
       FIGS. 10A and 10B  show a VPZ information update message according to an exemplary embodiment of the present invention. 
    
    
      It should be understood that like reference numbers refer to like features, structures and elements.  
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Hereinafter exemplary embodiments of a call processing apparatus and method in a mobile communication system of the present invention will be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a schematic diagram showing the connection configuration of a mobile communication system according to an exemplary embodiment of the present invention.  
      As shown in  FIG. 1 , the mobile communication system comprises a mobile station (MS)  100 , a base station system (BSS)  200 , a packet control function (PCF)  300 , and a packet data serving node (PDSN)  400 . Here, the mobile communication system may be the CDMA2000 1x EV-DV system or the CDMA2000 1x EV-DO system. The embodiment of the present invention will be described below in detail with emphasis on the CDMA2000 1x EV-DV system, and the CDMA2000 1x EV-DO system will also be described below with respect to the differences in the CDMA2000 1x EV-DV system.  
      The MS  100  and the BSS  200  are preferably wirelessly linked, and the BSS  200 , the PCF  300  and the PDSN  400  are preferably physically linked.  
      The BSS  200  designates a sector in which the MS  100  is located and a neighboring sector as one call receiving zone and sets them as virtual paging zone (VPZ) when the MS  100  transitions from a traffic state to a dormant state and tries paging to a sector contained in the VPZ information according to a call connection request to the MS  100 .  
      That is, the BSS  200  designates a sector of an active set in which the MS  100  is located, a sector of a candidate set, and a sector of a neighbor set as the VPZ immediately before releasing a call.  
      The VPZ information preferably includes VPZ lifetime information, VPZ update cycle information, VPZ identification information, and sector information contained in the VPZ. The sector information contained in the VPZ includes network identification NID, system identification SID, reference pilot signal strength information KEEP_PILOT_STRENGTH, sector information maintaining parameter information NUMBER_OF_BELOW, and sector lifetime information, which will be explained later.  
       FIG. 2  is a block diagram of the BSS  200  according to an embodiment of the present invention. Referring to  FIG. 2 , the BSS  200  comprises an information processor  210 , an information provider  220 , and a paging processor  230 .  
      The information processor  210  collects and designates a sector of an active set in which the MS  100  is located, a sector of a candidate set, and a sector of a neighbor set as the VPZ immediately before the MS  100  transitions from a traffic state to a dormant state and releases a call.  
      In the CDMA2000 1x EV-DO system, the information processor  210  designates a sector of an active set in which the MS  100  is located, a sector of a candidate set, and a sector of a neighbor set as the VPZ using a VPZ protocol immediately before the MS  100  transitions from a traffic state to a dormant state and releases a call.  
      The information provider  220  comprises the collected VPZ information in an extended release message (ERM) and provides it to the MS  100  when the MS  100  request a call release and provides the PCF  300  with the VPZ information. Here, the VPZ information contained in the ERM is shown in  FIGS. 8A and 8B .  
      In the CDMA2000 1x EV-DO system, the information provider  220  comprises the VPZ information in a VPZ list message and provides it to the MS  100  over a control channel when the MS  100  requests a call release.  
      The information processor  210  updates the VPZ information of a certain MS  100  or sets the VPZ using information contained in the REM transmitted from the MS  100  when the certain MS  100  performs a handoff to one of the sectors covered by the BSS  200  other than sectors contained in the MS  100 &#39;s VPZ, which will be explained later in more detail with reference to  FIG. 6 .  
      In the CDMA2000 1x EV-DO system, the information processor  210  updates the VPZ information of a certain MS  100  or sets the VPZ using information contained in a route update message transmitted from the MS  100  when the certain MS  100  performs a handoff to one of the sectors covered by the BSS  200  other than sectors contained in the MS  100 &#39;s VPZ.  
      The paging processor  230  performs paging to a sector designated in the VPZ via the GPM or a directed extended channel assignment message (directed ECAM) for routing a call to the MS  100 , which is in a dormant state when the PCF  300  receives a point to point protocol (PPP) frame to be transmitted to the MS  100  from the PDSN  400  or performs paging to a sector designated in the PVZ through a short data burst (SDB) when the received PPP frame is for the PTT service.  
      In the CDMA2000 1x EV-DO system, the paging processor  230  performs paging to a sector designated in the VPZ via a data over signaling (DOS) or a paging message for routing a call to the MS  100 , which is in a dormant state, when the PCF  300  receives a point to point protocol (PPP) frame to be transmitted to the MS  100  from the PDSN  400 . The DOS is specified in the CDMA2000 1x EV-DO Rev. A.  
      The MS  100  performs a virtual paging operation when it receives virtual paging information from the node in a dormant state, which will now be explained in more detail with reference to  FIG. 3 .  
       FIG. 3  is a block diagram of a mobile station (MS) according to an exemplary embodiment of the present invention.  
      As shown in  FIG. 3 , the MS  100  comprises a paging processor  102 , a call processor  104 , and a storage  106 .  
      The paging processor  102  stores the VPZ information contained in the ERM transmitted from the BSS  200  in the storage  106 , and then activates the VPZ function to perform the VPZ operation when the MS  100  transitions from a traffic state to a dormant state. The VPZ operation will be explained later in more detail with reference to  FIG. 4 .  
      In the CDMA2000 1x EV-DO, the paging processor  102  stores the VPZ information transmitted from the BSS  200  in the storage  106 , and then activates the VPZ function to perform the VPZ operation when the MS  100  transitions from a traffic state to a dormant state.  
      The call processor  104  provides the REM containing idle handoff information to a BSS to which the call processor  104  wants to perform an idle handoff when the MS performs an idle handoff to a sector that is not registered to the VPZ information. The REM containing the idle handoff information will be explained later in more detail with reference to  FIGS. 9A and 9B .  
      In the CDMA2000 1x EV-DO, the call processor  104  preferably includes the idle handoff information in a VPZ production message or the route update message and transmits it to the BSS  200  which the call processor  104  wants to perform an idle handoff over the access channel when the MS performs an idle handoff to a sector, which is not registered to the VPZ information.  
      The PCF  300  (shown in  FIG. 1 ) stores the VPZ information transmitted from the BSS  200  and collected immediately before releasing a call of the MS  100  in a database (not shown).  
      The PCF  300  stores the VPZ information for a certain MS when the certain MS other than the MS  100  performs an idle handoff to a region covered by the BSS  200  among regions which are not contained in the MS  100 &#39;s VPZ. The VPZ information is collected by the BSS  200  in a database when the REM is received by the BSS  200 .  
      In the CDMA2000 1x EV-DO system, the PCF  300  stores the VPZ information for a certain MS when the certain MS other than the MS  100  performs an idle handoff to a region covered by the BSS  200  among regions which are not contained in the MS  100 &#39;s VPZ. The VPZ information is collected by the BSS  200  in a database when the REM is received by the BSS  200 .  
      The PCF  300  retrieves the VPZ information of a corresponding MS from the database when a certain MS receives the PPP frame from the PDSN  400  (shown in  FIG. 1 ) and request paging to the BSS corresponding to the retrieved MS&#39;s VPZ information.  
       FIG. 4  is a diagram showing the procedure for collecting VPZ information when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention.  
      As shown in  FIG. 4 , in a state that the MS  100  and the BSS 1   110  maintain a traffic state (step S 200 ), the BSS 1  determines whether there is a call release request or not (step S 210 ).  
      If there is a call release request, the BSS 1   110  collects sectors of the BSS in which the MS  100  is located to form the VPZ information (S 212 ), and includes the VPZ information in the ERM and provides it to the MS  100  (S 214 ).  
       FIGS. 8A and 8B  shows an exemplary ERM containing the VPZ provided to the MS  100  according to an embodiment of the present invention.  
      Referring to  FIG. 8A , the ERM preferably includes, among the VPZ information, a VPZ information indication field VPZ_INFO_INCL, a VPZ identification field VPZ_ID, a VPZ lifetime field VPZ_LIFETIME, a VPZ information update cycle field VPZ_UPDATE_TIME, a sector information field VPZ—NUM—LIST contained in the VPZ information. Here, “[..]” denotes the existing fields of the ERM, which are specified in the CDMA2000 EV-DV release D layer 3, and thus a description of which is omitted.  
      The VPZ information indication field is a field for representing whether the VPZ information is contained in the ERM or not, and if the VPZ information indication field is set to “1”, it means that the VPZ information is contained in the ERM.  
      The VPZ identification field is a field for representing the identification of the VPZ, and if the VPZ information indication field is set to “0”, it is not contained in the ERM, and if the VPZ information indication field is set to a value other than “0”, it is contained in the ERM.  
      The VPZ lifetime field is a field for representing the lifetime of the VPZ, and if the VPZ information indication field is set to “0”, it is not contained in the ERM, and if the VPZ information indication field is set to a value other than “0”, lifetime of the VPZ information can be set within “60×VPZ lifetime field value” seconds.  
      The update cycle field of the VPZ information is a field for representing an update cycle of the VPZ information, and if the VPZ information indication field is set to “0”, it is not contained in the ERM, and if the VPZ information indication field is set to a value other than “0”, the update cycle of the VPZ information can be set within “60×VPZ lifetime field value” seconds.  
      The sector information field contained in the VPZ information is a field for representing information indicating a sector contained in the VPZ, and if the VPZ information indication field is set to “1”, the sector information of  FIG. 8B  can be contained in the VPZ.  
      Referring to  FIG. 8B , the sector information preferably includes network identification NID, system identification SID, PILOT-PN field, reference pilot signal strength field KEEP_PILOT_STRENGTH, sector information maintaining parameter field NUM_OF_BELOW, and sector lifetime field LIFETIME. The NID is a field for representing number of the network to which the BSS belongs. The SID is a field for representing number of the BSS. The PILOT_PN field is a field for representing PN offset for discriminating the base stations according to a sector and can be set within 64 PN chips.  
      The reference pilot signal strength field is a field for representing information indicating reference pilot signal strength necessary for comparison with pilot signal strength of a certain sector measured by the MS, and the sector information maintaining parameter varies based on the comparison result of the pilot signal strength of a certain sector measured by the MS to the reference pilot signal strength.  
      The sector information maintaining field is a field containing a sector information maintaining parameter for determining whether the MS is located in a certain sector or not. Here, the sector information maintaining parameter is a parameter for determining whether the MS is located in a certain sector or not and varies based on the comparison result of the pilot signal strength of a certain sector measured by the MS to the reference pilot signal strength.  
      If the pilot signal strength of the certain sector measured by the MS is greater than the reference pilot signal strength, the sector information maintaining parameter is reduced by “1”, whereas if the pilot signal strength of the certain sector measured by the MS is smaller than the reference pilot signal strength, the sector information maintaining parameter is increased by “1”.  
      When the sector information maintaining parameter is increased by “1”, it means that the MS is getting farther away from the sector, whereas when the sector information maintaining parameter is reduced by “1”, it means that the MS is getting closer to the sector.  
      If the certain sector information maintaining parameter exceeds a VPZ information maintaining threshold count, that is, if the MS  100  deviates from the sector, the sector information is deleted. Here, the BSS  110  can insert the VPZ information maintaining threshold count in the overhead message for transmission, which will be explained in more detail with reference to  FIG. 5 .  
      The sector lifetime field is a field for representing the lifetime of the sector information and can be set in “60” second units.  
      Meanwhile, in the CDMA2000 1x EV-DO system, the BSS 1   110  searches sectors of the BSS in which the MS  100  is located and collects the sectors to set the VPZ information, and preferably includes the VPZ information in the VPZ list message and transmits it to the MS  100  over the control channel.  
      With continued reference to  FIG. 4 , the MS  100  stores the VPZ information received from the BSS 1   110  in a memory and activates or sets the VPZ function (step S 216 ) and then informs the BSS 1   110  of the fact that the VPZ function is activated (step S 218 ).  
      Here, in order for the MS  100  to perform the VPZ function, the MS  100  needs to know that the BSS 1   110  operates with regard to the VPZ information. For the sake of this, the BSS 1   110  lets the MS  100  know that the VPZ information is operating in the BSS 1   110  such that the BSS 1   110  includes the VPZ information operation information in an extended system parameter message or an ANSI-41 system parameter message among the overhead messages and transmits it to the MS  100 .  
       FIG. 7  shows an exemplary overhead message transmitted from the BSS 1   110  to the MS  100  according to an embodiment of the present. Referring to  FIG. 7 , the VPZ information operation information contained in the overhead message preferably includes a VPZ information operation field VPZ_SUPPORTED, a VPZ information maximum lifetime field VPZ_MAX_LIFE, a VPZ information maintaining threshold count field VPZ_ERASE_TREHSHOLD, and a VPZ information report field VPZ_MAX_FIELD. Here, “[..]” denote the existing fields of the overhead message which are specified in the CDMA2000 EV-DV release D layer 3, and thus the description of which is omitted.  
      The VPZ information operation field is a field for representing whether the BSS operates the VPZ information or not, and if the VPZ information operation field is set to “1”, this means that the BSS operates the VPZ information. If the VPZ information operation field is set to “0”, it is not contained in the overhead message, and if the VPZ information operation field is set to a value other than “0”, it is contained in the overhead message.  
      The VPZ maximum lifetime field is a field containing the VPZ information maintaining threshold count information, which is a reference for determining whether to maintain a certain sector information.  
      The VPZ information report field is a field for representing the maximum count that the MS can contain the changed VPZ information in the REM to transmit it to the BSS, and if the VPZ information operation field is set to “0”, it is not contained in the overhead message, and if the VPZ information operation field is set to a value other than “0”, it is contained in the overhead message.  
      This can be used in determining whether to contain the VPZ information in the ERM which is transmitted for releasing a call with the MS  100  from the BSS 1   110  by informing the BSS1  110  of the fact that the MS  100  performs the VPZ function through the origination message ORM for establishing traffic.  
      In the CDMA2000 1x EV-DO system, the MS  100  and the BSS 1   110  determines whether to operate the VPZ information and whether the BSS 1   110  makes the VPZ information or not when a call is released and sets the lifetime of the VPZ information, through VPZ protocol negotiation during session negotiation.  
      Thereafter, the MS  100  performs the VPZ operation (step S 220 ). Here, the VPZ operation of the MS  100  is performed as one of the following operations.  
      a) The MS  100  deletes the VPZ information when the lifetime of the VPZ information expires.  
      b) The MS  100  measures the pilot signal strength of a corresponding sector and compares it to the reference pilot signal strength when the lifetime of the VPZ information does not expire. If the measured pilot signal strength is greater than the reference pilot signal strength, the sector information maintaining parameter is increased by “1”, whereas if the measured pilot signal strength is smaller than the reference pilot signal strength, the sector information maintaining parameter is decreased by “1”.  
      Then, the MS  100  compares the sector information maintaining parameter to the VPZ information maintaining threshold count. If the sector information maintaining parameter is greater than the VPZ information maintaining threshold count, the MS  100  determines as deviated from the corresponding sector zone and thus deletes the corresponding sector information from the VPZ information. On the other hand, if the sector information maintaining parameter is smaller than the VPZ information maintaining threshold count, the MS  100  determines as located in the corresponding sector zone and thus continuously maintains the corresponding sector information in the VPZ information.  
      c) The MS  100  measures the pilot signal strength of a corresponding sector and compares it to the reference pilot signal strength when lifetime of the sector registered to the VPZ information expires. If the measured pilot signal strength is greater than the reference pilot signal strength, the MS  100  sets the lifetime of the corresponding sector again to maintain the corresponding sector information. This is because the MS  100  is located in the corresponding sector zone.  
      Alternatively, if the measured pilot signal strength is smaller than the reference pilot signal strength, the MS  100  compares the sector information maintaining parameter to the VPZ information maintaining threshold count. If the sector information maintaining parameter is greater than the VPZ information maintaining threshold count, the MS  100  determines it has deviated from the corresponding sector zone and thus deletes the corresponding sector information from the VPZ information. However, if the sector information maintaining parameter is smaller than the VPZ information maintaining threshold count, the MS  100  determines it is located in the corresponding sector zone and thus continuously maintains the corresponding sector information in the VPZ information.  
      d) The MS  100  determines whether the VPZ information has changed or not when the VPZ information update cycle expires. The MS  100  updates only during the VPZ information update cycles when the VPZ information is not changed. However, when the VPZ information is changed, the MS  100  includes the changed VPZ information in the REM and transmits it to the BSS 1   110 .  
      e) The MS  100  inactivates the VPZ operation when it is difficult to maintain a dormant state and then deletes the VPZ information from the memory.  
      Meanwhile, the BSS 1   110  provides the PCF  300  with the collected VPZ information when the MS activates the VPZ function (step S 222 ), and the PCF  300  stores the VPZ information transmitted from the BSS 1   110  in the database (step S 224 ).  
       FIG. 5  is a diagram showing the paging processing procedure when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention.  
      Referring to  FIG. 5 , the MS  100  is in the dormant state (step S 300 ). When the PPP frame is received from the PDSN  400  in a state that the mobile communication system maintains a dormant state (step S 302 ), the PCF  300  retrieves the VPZ information of the MS to which the PPP frame is to be transmitted from the database (not shown) (step S 304 ). Here, the MS to which the PPP frame is to be transmitted is referred to as MS  100 , and the base station system corresponding to the VPZ information of the MS  100  is referred to as BSS 1   110  and BSS 2   120 .  
      Then, the PCF  300  requests paging to the BSS 1   110  and the BSS 2   120  of the VPZ information of the MS  100  obtained by the retrieving result (step S 306 ). In the CDMA2000 1x EV-DO system, the PCF  300  requests paging to the sector designated in the VPZ information through the DOS or the call receiving request message.  
      The BSS 1   110  and the BSS 2   120  performs paging to the MS  100  through the GPM or the directed ECAM by the paging request or through the SDB when the received PPP frame is for the PTT service (step S 308 ). Here, the MS  100  is assumed to be located in the sector of the BSS 2   120 . Meanwhile, in the CDMA2000 1x EV-DO system, the BSS 1   110  and the BSS 2   120  performs paging to the MS  100  through the DOS or the page message.  
      The MS  100  responds to the BSS 2   120  in response to the paging (step S 310 ).  
      The BSS 2   120  generates a paging success message in response to the paging response of the MS  100  and transmits it to the PCF  300  (step S 312 ).  
      If the paging using the VPZ information is unsuccessful, the PCF  300  requests paging to all BSSs or requests paging to the mobile switching center (not shown).  
      Meanwhile, when the paging using the VPZ information is unsuccessful, the PCF  300  deletes the VPZ information. The PCF  300  deletes the corresponding information when the lifetime of the VPZ information expires but can utilize the VPZ information regardless of the lifetime of the VPZ information when the MS  100  restrictively moves or hardly moves without deleting the VPZ information.  
       FIG. 6  is a diagram showing the procedure for resetting VPZ information depending on an idle handoff when a mobile communication system is in a dormant state according to an exemplary embodiment of the present invention.  
      Referring to  FIG. 6 , when the MS  100  wants to perform a handoff to a BSS of a sector which is not registered to the VPZ information (step S 420 ) in a state that the mobile communication system maintains a dormant state (step S 400 ), the MS  100  preferably includes the idle handoff information in the REM and transmits to the BSS to which the MS  100  wants to handoff.  
      In the CDMA2000 1x EV-DO system, if the MS  100  wants to handoff to a BSS of a sector that is not registered to the VPZ information in a state that the mobile communication system maintains a dormant state, the MS  100  preferably includes the idle handoff information in the VPZ production message or the route update message and transmits it to the BSS to which the MS  100  wants to handoff over the access channel. Here, the VPZ production message preferably includes the sector information contained in the existing VPZ list and the information of a new sector to which the MS recently moved. The route update message preferably includes the VPZ information, which is produced before performing the idle handoff.  
      Here, the BSS to which the MS  100  performs the idle handoff is referred to as a BSS 3   130 , and the BSS 1   110  and the BSS 2   120  are the BSSs that are registered to the VPZ before the idle handoff. That is, the MS  100  transmits the REM or VPZ production message containing the idle handoff information to the BSS 3   130 , which is the BSS that the MS  100  wants to handoff (step S 404 ).  
      Meanwhile, the exemplary REM containing the idle handoff information is shown in  FIGS. 9A and 9B .  
      Referring to  FIG. 9A , the REM preferably includes a VPZ information indication field VPZ_INFO_INCL, a VPZ information report reason field VPZ_REPORT_REASON, and a sector information field VPZ_NUM_LIST, which is contained in the VPZ information. Here, “[..]” of  FIG. 9A  denotes the existing fields of the ERM, which are specified in the CDMA2000 EV-DV release D layer 3 and thus a description of which is omitted.  
      The VPZ information indication field is a field for representing whether the REM includes the idle handoff information or not, and if the VPZ information indication field is set to “1”, this means that the REM includes the idle handoff information.  
      The VPZ information report reason field is a field for representing a report reason of the idle handoff information. If the VPZ information indication field is set to “0”, it is not contained in the REM, and if the VPZ information indication field is set to a value other than “0”, it is contained in the REM.  
      Meanwhile, if the VPZ information report reason field is set to “0”, this means that the idle handoff is performed to the sector which is not contained in the VPZ information list. If the VPZ information report reason field is set to “1”, this means that the VPZ information is still activated, the values “2” through “7” are reserved for other uses.  
      The sector information field VPZ_NUM_LIST, which is contained in the VPZ information, is a field for representing information indicating a sector contained in the idle handoff information, and if the VPZ information indication field is set to “1”, the sector information of  FIG. 9B  can be contained in the idle handoff information.  
      Referring to  FIG. 9B , the sector information preferably includes network identification NID, system identification SID, PILOT-PN field, reference pilot signal strength field KEEP_PILOT_STRENGTH, sector information maintaining parameter field NUM_OF_BELOW, and sector lifetime field LIFETIME. The sector information of  FIG. 9B  is identical to that of  FIG. 8B , and thus description on that is omitted.  
      When the REM is received from the MS  100 , the BSS 3   130  produces new VPZ information using the information contained in the REM. The BSS 3   130  replaces information of the sector that the pilot signal strength is weakest among the newly produced VPZ information when the number of sectors registered to the existing VPZ information exceeds the threshold number (step S 406 ). In the CDMA2000 1x EV-DO system, when the VPZ production message or the route update message is received from the MS  100 , the BSS 3   130  produces the new VPZ information in the case where a corresponding session supports the VPZ.  
      Then, the BSS 3   130  transmits the newly collected VPZ information to the PCF  300  (step S 408 ). Here, the systems contained in the newly collected VPZ information are the BSS 1   110 , the BSS 2   120  and the BSS 3   130 .  
      When the newly collected VPZ information is received from the BSS 3   130 , the PCF  300  responds (step S 410 ) and stores the VPZ information in the database (step S 412 ).  
      When there is a response to the receipt of the newly collected VPZ information from the PCF  300 , the BSS 3   130  transmits the VPZ information update message containing the newly collected VPZ information to the MS  100  (step S 414 ). The MS  100  stores the VPZ information update message in the memory (not shown) (step S 416 ).  
       FIGS. 10A and 10B  show an exemplary VPZ information update message according to an embodiment of the present invention.  
      Referring to  FIG. 10A , the VPZ information update message preferably includes a VPZ information update report reason field VPZ_REPORT_REASON, a VPZ information update message identification field VPZ_ID, a VPZ information update message lifetime field VPZ_LIFETIME, a VPZ information update cycle field VPZ_UPDATE_TIME, and a sector information VPZ_NUM_LIST contained in the VPZ information update message.  
      If the VPZ information update report reason field is set to “0”, this means that the updated VPZ list is contained in the VPZ information update message, and if the VPZ information update report reason field is set to “1”, this means that VPZ function does not operate, and the values “2” through “7” are reserved for other uses.  
      The VPZ information update message identification field is a field for representing the identification of the updated VPZ information.  
      The VPZ information update message lifetime field is a field for representing lifetime of the updated VPZ information.  
      The VPZ information update cycle field is a field for representing am update cycle of the updated VPZ information.  
      When the sector information field VPZ_NUM_LIST contained in the VPZ information update message includes at least one of the sector information, each sector information includes network identification NID, system identification SID, PILOP-PN field, reference pilot signal strength field KEEP_PILOT_STRENGTH, sector information maintaining parameter field NUM_OF_BELOW, sector lifetime field LIFETIME, and update status field STATUS as shown in  FIG. 10B .  
      The sector information of  FIG. 10B  is identical to those described above in  FIGS. 8B and 9B , and thus a description of which is omitted. Merely, the update status field STATUS is a field for representing whether the VPZ information is updated or not. If the update status field is set “0”, this means that the VPZ information is not updated, and if the update status field is set “1”, this means that the VPZ information is updated, and the values “2” through “7” are reversed for other uses.  
      Meanwhile, the MS  100  generates a VPZ information update deny message and transmits it to the BSS 3   130  when it cannot receive the VPZ information update message from the BSS 3   130 .  
      When the MS  100  wants to perform the VPZ function regardless of the receipt of the ERM, the MS  100  sets the VPZ information report reason field in the idle handoff information contained in the REM to “1” and sets the sector information field contained in the VPZ information to “0” and transmits them to the BSS 3   130 .  
      When the BSS 3   130  receives the REM which preferably includes the VPZ information report reason field, which is set to “1”, and the sector information field contained in the VPZ information which is set to “0”, the BSS 3   130  transmits the VPZ information update message to the MS  100 .  
      When there is a call connection request to the MS  100 , the BSS 3   130  can perform a paging to a sector before the idle handoff and its own sector, if the MS  100  cannot receive the VPZ information update message due to the ping-pong phenomenon.  
      As described herein, the apparatus and method for processing a call in the mobile communication system according to an embodiment of the present invention can designate a base station sector in which a mobile station is located and a neighboring base station sector as one call receiving zone when a mobile station transitions from a traffic state to a dormant state and perform paging to a call receiving zone, which is first designated when a call is routed to a mobile station, thereby reducing a paging time to the MS in a dormant state, thereby increasing call receiving success to the corresponding MS, reducing the call receiving load of the mobile communication system, and processing a call receipt without the intervention of the MSC.  
      While the invention has been described in conjunction with various embodiments, they are illustrative only. Accordingly, many alternatives, modifications and variations will be apparent to persons skilled in the art in light of the foregoing detailed description. The foregoing description is intended to encompass all such alternatives, modifications and variations falling with the spirit and scope of the appended claims.