Abstract:
A method of releasing a supplemental channel in a CDMA mobile communication system. Upon request of releasing the supplemental channel, a base station determines whether to transition from the current state to another state, generates a first message indicating release of the SCH and a next state to transit to, transmits the first message to a mobile station. Upon receipt of a second message in response to the first message from the mobile station, the base station releases the SCH, and transits to the next state.

Description:
PRIORITY 
   This application claims priority to an application entitled “Method of Releasing SCH in CDMA Mobile Communication System” filed in the Korean Industrial Property Office on Nov. 23, 1999 and assigned Serial No. 99-52271, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a method of establishing and releasing a SCH (Supplemental channel) in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a method of directly transitioning from an active state to an idle state when an SCH is released. 
   2. Description of the Related Art 
   CDMA has been developed to IMT-2000 standards which provide services like transmission of high quality voice and moving pictures and Internet browsing as well as the conventional service of voice transmission. 
   Data transmission occurs in bursts, with idle states without any data transmission often occurring in the mobile communication system. The idle states are a control hold state, a suspended state, and a dormant state. The IMT-2000 mobile communication system assigns a dedicated channel only if data transmission occurs in a data communication service. Further, it additionally provides a packet data service in which SCHs are designated as dedicated to transmit a large amount of packet data. To do so, SCHs have high variable data rates. 
   In consideration of limited radio resources, base station capacity, and the power consumption of a mobile station, a dedicated traffic channel (DTCH) and a control channel are connected only while data is being transmitted and the DTCH is released if data transmission is discontinued for a predetermined time period. Communication is made on the common channel while the dedicated channel is released, to thereby increase use efficiency of radio resources. For this purpose, call processing is comprised of different states according to channel assignment and the presence or absence of channel status information. 
     FIG. 1  is a state transition diagram for the packet service in a general mobile communication system. 
   Referring to  FIG. 1 , there are an active state  101 , a control hold state  103 , a suspended state  105 , and a dormant state  107  for the packet service. 
   In the active state  101 , input data is transmitted on a DTCH. Once a data service object connects a service option and initially enters the active state  101 , a dedicated data channel is available and a base station and a mobile station performs initialization operations for RLP (Radio Link Protocol) and PPP (Point to Point Protocol). If data is not transmitted for a predetermined time period T —Active  in the active state  101 , the DTCH is released and the control hold state  103  is entered. If a non-data transmission period of longer than T —Active  is expected based on an estimate of the amount of data that will be generated, a transition occurs from the active state  101  directly to the suspended state  105  or the dormant state  107 , without passing through the control hold state  103 . 
   In the control hold state  103 , the base station and the mobile station preserve information about the service option, the RLP, and the PPP, and a dedicated control channel (DCCH) has been established. If transmit data is generated within a predetermined time T —Hold , the data service object reestablishes the DTCH to transmit the data and returns to the active state  101 . On the other hand, if there is no transmit data until T —Hold  elapses, the DCCH is released and the suspended state  105  is entered. The control hold state  103  is also transitioned directly to the dormant state  107  without passing through the suspended state  105  if a non-data transmission period is expected to be longer than T —Hold  based on an estimated amount of data that will be generated. 
   In the suspended state  105 , a fundamental channel (FCH), being a dedicated physical channel assigned to each mobile station, or the DCCH is released. Therefore, logical channels, the DCCH and the DTCH, are released. The mobile station communicates with the base station over a common signaling channel (CSCH) established on physical channels shared by a plurality of mobile stations, a paging channel and an access channel. The base station and the mobile station still preserve the information about the service option, the RLP, and the PPP in the suspended state  105 . If user data is generated within a predetermined time T —Suspended  in the suspended state  105 , the data service object reestablishes the DCCH and the DTCH concurrently and returns to the active state  101 . On the contrary, if no data is generated for T —Suspended , the data service object transitions to dormant state  107 . 
   In the dormant state  107 , the service option is disconnected and the link-layer connection is held between an IWF (internetworking function) and the mobile station only in the data service. All dedicated logical channels are released and communication is conducted on common channels in this state. Upon request of data service in the dormant state  107 , the service option is to connected, the DTCH and the DCCH are re-established, and the active state  101  is entered. 
   In summary, the DTCH, the DCCH, and the service option are connected in the active state  101 , the DCCH and the service option are connected in the control hold state  103 , only the service option is connected in the suspended state  105 , and only the link layer connection is held between the IWF and the mobile station in the dormant state  107 . 
   As stated above, SCHs are utilized in order to provide the high speed packet data service in the CDMA mobile communication system. As compared to a control channel or an FCH, an SCH transmits only user data and a DCCH or a fundamental channel (FCH) must be set up before the SCH is assigned. Hence, the SCH is set up only in the active state  101  as shown in FIG.  1 . In other words, the active state  101  must be entered to exchange SCH messages. Even when the SCH is to be released due to the absence of pack data, another idle state must be transitioned to, with the active state  101  interposed. 
     FIG. 2  illustrates the signal flow in a basic call set-up process, i.e., transition to the active state to set up a channel when a mobile station requests a call in the CDMA mobile communication system. 
   Referring to  FIG. 2 , the mobile station transmits an origination message requesting establishment of a dedicated channel to a base station on a reverse access channel (R-ACH) in step  201 . Upon receipt of the origination message, the base station transmits a channel assignment message to the mobile station on a forward paging channel (F-PCH) in step  202 . At the same time, the base station transmits null traffic on a channel with a corresponding orthogonal code. Upon receipt of the channel assignment message, the mobile station analyzes the null frame on the corresponding channel. If the mobile station confirms that the channel is successfully established, it transmits a preamble on its unique code channel to synchronize its timing to the base station during channel assignment in step  203 . If bidirectional dedicated channels are successfully established, the base station transmits an acknowledgment (Ack) order in step  204 . Upon receipt of the Ack order, the mobile station discontinues transmission of the preamble and becomes capable of transmitting a message on a DTCH (an FCH or a control channel). 
   In steps  205  to  208 , service negotiations for the current available transmission environment are carried on between the base station and the mobile station to provide quality service to the users. After the negotiations are over, the channel assignment procedure ends in step  209 . 
     FIGS. 3A and 3B  are signal flows in SCH establishment and release procedures in the active state, separately upon request of a mobile station and upon request of the network. 
   Referring to  FIG. 3A , the mobile station  301  generates an SCH request message to the base station  303  in step  701 , as constructed below in Table 1. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               SIZE_OF_REQ_BLOB 
               4 
             
             
                 
               REQ_BLOB 
               8 × SIZE REQ BLOB 
             
             
                 
               USE_SCRM_SEQ_NUM 
               1 
             
             
                 
               SCRM_SEQ_NUM 
               0 or 4 
             
             
                 
               REF_PN 
               0 or 9 
             
             
                 
               PILOT_STRENGTH 
               0 or 6 
             
             
                 
               NUM_ACT_PN 
               0 or 3 
             
             
                 
                 
             
           
        
       
     
   
   If NUM_ACT_PN is included, the mobile station  301  shall include NUM_ACT_PN occurrences of the following record: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               ACT_PN_PHASE 
               15 
             
             
                 
               ACT_PILOT_STRENGTH 
                6 
             
             
                 
               NUM_NGHBR_PN 
               0 or 3 
             
             
                 
                 
             
           
        
       
     
   
   If NUM_NGHBR_PN is included, the mobile station  301  shall include NUM_NGHBR_PN occurrences of the following record: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               NGHBR_PN_PHASE 
               15  
             
             
                 
               NGHBR_PILOT_STRENGTH 
               6 
             
             
                 
               RES_INFO_INCL 
               1 
             
             
                 
               CH_IND 
               0 or 3 
             
             
                 
               BLOB 
               0 or 7 
             
             
                 
                 
             
           
        
       
     
   
   If the mobile station  301  wants the packet service, it transmits the SCH request message to the base station  303  on a traffic channel (a control channel or an FCH). The REQ_BLOB field shown in Table 2 indicates the use duration of the requested SCH. 
   Upon receipt of the SCH request message, the base station  303  checks physical resources for SCHs. If there is an available SCH, the base station transmits an SCH assignment message to the mobile station  301  in step  702 . If the mobile station  301  operates in accordance with an IS-95B protocol, the SCH assignment message is generated in the format shown in Table 2. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               USE_RETRY_DELAY 
               1 
             
             
                 
               RETRY DELAY 
               0 or 8 
             
             
                 
               REV_INCLUDED 
               1 
             
             
                 
                 
             
           
        
       
     
   
   Only if REV_INCLUDED is set to ‘1’, the following record is included: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               REV_DTX_DURATION 
                 
             
             
                 
               EXPL_REV_START_TIME 
               4 
             
             
                 
               REV_START_TIME 
               1 
             
             
                 
               USE_REV_DURATION 
               0 or 6 
             
             
                 
               REV_DURATION 
               1 
             
             
                 
               USE_REV_HDM_SEQ 
               0 or 8 
             
             
                 
               REV_SINKED_HDM_SEQ 
               1 
             
             
                 
               NUM_REV_CODES 
               0 or 2 
             
             
                 
               USE_T_ADD_ABORT 
               3 
             
             
                 
               USE_SCRM_SEQ_NUM 
               1 
             
             
                 
               SCRM_SEQ_NUM 
               1 
             
             
                 
               REV_PARMS_INCLUDED 
               0 or 4 
             
             
                 
               T_MULCHAN 
               1 
             
             
                 
               BEGIN_PREAMBLE 
               0 or 3 
             
             
                 
               RESUME_PREAMBLE 
               0 or 3 
             
             
                 
                 
               0 or 3 
             
             
                 
               FOR_INCLUDED 
               1 
             
             
                 
                 
             
           
        
       
     
   
   Only if FOR_INCLUDED is set to ‘1’, the following record is included: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               FOR_SUP_CONFIG 
               2 
             
             
                 
               EXPL_FOR_START_TIME 
               1 
             
             
                 
               FOR_START_TIME 
               0 or 6 
             
             
                 
               USE_FOR_DURATION 
               1 
             
             
                 
               FOR_DURATION 
               0 or 8 
             
             
                 
               USE_FOR_HDM_SEQ 
               1 
             
             
                 
               FOR_LINKED_HDM_SEQ 
               0 or 2 
             
             
                 
                 
             
           
        
       
     
   
   Only if FOR_INCLUDED is set to ‘1’ and FOR_SUP_CONFIG is set to ‘10’ or ‘11’, the following fields and records are included. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               NUM_SUP_PILOTS 
               3 
             
             
                 
               NUM_FOR_SUP 
               3 
             
             
                 
                 
             
           
        
       
     
   
   Only if FOR_INCLUDED is set to ‘0’ and FOR_SUP_CONFIG is set to ‘10’ or ‘11’, NUM_SUP_PILOTS occurrences of the following record are included. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               PILOT_PN 
               9 
             
             
                 
               EXPL_CODE_CHANE 
               1 
             
             
                 
                 
             
           
        
       
     
   
   If EXPL_CODE_CHAN is set to ‘1’, NUM_FOR_SUP occurrences of the following field are included for each PILOT_PN. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               SUP_CODE_CHAN 
               0 or 8 
             
             
                 
                 
             
           
        
       
     
   
   If EXPL_CODE_CHAN is set to ‘0’, the following field is included. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               BASE_CODE_CHAN 
               0 or 8 
             
             
                 
                 
             
           
        
       
     
   
   Upon receipt of the SCH assignment message, the mobile station  301  transmits data on the SCH in step  703 . After transmitting the intended data, the mobile station  301  transmits an SCH release request message to the base station  303  in step  704 . The SCH release request message is generated in the same format as shown in Table 1, except that an SCH release code is in the REQ_BLOB field. At present, the SCH, the FCH, and the DCCH are established. That is, the base station  303  and the mobile station  301  are in the active state  101 . Upon receipt of the SCH release request message, the base station  303  transmits an SCH release message to the mobile station  301  in step  705  and releases the SCH in step  706 . Since the FCH and the DCCH are still connected, the base station  303  and the mobile station  301  remain in the active state  101 . 
   Referring to  FIG. 3B , when packet data is generated from the network (not shown), the base station  303  transmits the SCH assignment message to the mobile station  301  in step  708 . Upon receipt of the SCH assignment message, the mobile station  301  transmits data on an assigned SCH in step  709 . The base station  303  and the mobile station  301  are in the active state and at present, the SCH, the FCH, and the DCCH are established. If no more data is generated from the network, the base station  303  transmits the SCH release message to the mobile station  301  in step  710  and releases the SCH in step  711 . The FCH and the DCCH are still connected between the base station  303  and the mobile station  301 . Therefore, the base station  303  and the mobile station  301  remain in the active state  101 , despite the absence of transmit data. To transition to the control hold state  103 , the suspended state  105 , or the dormant state  107 , the mobile station  301  and the base station  303  must carry on negotiations. That is, the SCH is released and the active state  101  is continued. Transition to another state occurs by exchanging messages for the transition between the mobile station  301  and the base station. 
   As described above, although the SCH is released, the FCH or the DCCH is still connected, i.e., the active state  101  is continued. In this state, if no user data is transmitted on either of the FCH and the DCCH, it is preferable that the active state  101  transitions to the control hold state  103 , the suspended state  105 , or the dormant state  107  as soon as possible to increase the use efficiency of radio resources. 
   In the typical CDMA mobile communication system, when data transmission on the SCH is discontinued, the active state is kept on. For transition to the control hold state, the suspended state, or the dormant state, the mobile station and the base station must exchange messages associated with the state transition. Therefore, radio resources are occupied despite discontinued data transmission. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a method and apparatus for transitioning from an active state directly to a control hold state, a suspended state, or a dormant state when an SCH is released in the active state in a CDMA mobile communication system. 
   The above object can be achieved by providing a method and apparatus for releasing a supplemental channel in a CDMA mobile communication system. Upon request of releasing the supplemental channel, a base station determines whether to transition from the current state to another state, generates a first message indicating release of the SCH and the next state to transition to, transmits the first message to a mobile station. The mobile station determines whether it has received the first message from the base station during packet data communication on the supplemental channel. Upon receipt of the first message, it analyzes the first message, releases the SCH, and continues the current state or transitions to the next state. Then, the mobile station transmits the second message to the base station. Upon receipt of the second message from the mobile station, the base station releases the SCH, and transitions to the next state. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates a state transition diagram for packet data service in a conventional CDMA mobile communication system; 
       FIG. 2  illustrates a signal flow in a call set-up procedure in the conventional CDMA mobile communication system; 
       FIG. 3A  illustrates a signal flow between a mobile station and a base station in a conventional SCH establishing and releasing procedure in the case that the mobile station requests establishment of an SCH; 
       FIG. 3B  illustrates a signal flow between the mobile station and the base station in another conventional SCH establishing and releasing procedure in the case that the network requests establishment of the SCH; 
       FIG. 4  illustrates a signal flow between the mobile station and the base station in a call process for transition of an active state to a control hold state, a suspended state, or a dormant state in the case that the base station generates an SCH release request according to an embodiment of the present invention; 
       FIG. 5  illustrates a signal flow between the mobile station and the base station in a call process for transition of the active state to the control hold state, the suspended state, or the dormant state in the case that the mobile station generates an SCH release request according to the embodiment of the present invention; 
       FIG. 6A  is a flowchart illustrating an SCH releasing and state transition procedure in the base station according to the embodiment of the present invention; and 
       FIG. 6B  is a flowchart illustrating an SCH releasing and state transition procedure in the mobile station according to the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
   Listed below are the definitions of messages exchanged between the mobile station  301  and the base station  303  to transition from the active state  101  directly to the control hold state  103 , the suspended state  105 , or the dormant state  107  if an SCH is released in the active state  101 . 
   An extended SCH assignment message as used for assignment of the SCH is constructed in the format illustrated by Table 3 below. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               START_TIME_UNIT 
               3 
             
             
                 
               REV_DTX_DURATION 
               4 
             
             
                 
               USE_T_ADD_ABORT 
               1 
             
             
                 
               USE_SCRM_SEQ_NUM 
               1 
             
             
                 
               SCRM_SEQ_NUM 
               0 or 4 
             
             
                 
               RES_INFO_INCL 
               1 
             
             
                 
               FPC_PRI_CHAN 
               0 or 1 
             
             
                 
               RPC_CHANNEL 
               0 or 1 
             
             
                 
               CH_IND 
               0 or 3 
             
             
                 
               BLOB 
               0 or 7 
             
             
                 
               REV_ASSIGN_INCLUDED 
               1 
             
             
                 
                 
             
           
        
       
     
   
   The base station shall include the following four fields if REV_ASSIGN_INCLUDED is set to 1. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               REV_SCH_ID 
               2 
             
             
                 
               REV_DURATION 
               4 
             
             
                 
               REV_START_TIME 
               6 
             
             
                 
               RATE 
               4 
             
             
                 
               FOR_CFG_INCLUDED 
               1 
             
             
                 
                 
             
           
        
       
     
   
   The base station shall include the following fields if FOR_CFG_INCLUDED is set to 1. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               FOR_SCH_ID 
               2 
             
             
                 
               NUM_REC 
               4 
             
             
                 
                 
             
           
        
       
     
   
   (NUM_REC+1) occurrences of the following record: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               SCCL_INDEX 
               4 
             
             
                 
               FOR_SCH_RATE 
               4 
             
             
                 
               NUM_SUP_SHO 
               3 
             
             
                 
                 
             
           
        
       
     
   
   (NUM_SUP_SHO+1) occurrences of the following fields. 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               PILOT_PN 
                9 
             
             
                 
               RECORD_LEN 
               0 or 3 
             
             
                 
               TYPE_SPECIFIC_FIELDS 
               0 or 8 × RECORD_LEN 
             
             
                 
               FOR_SCH_CC_INDEX 
               11 
             
             
                 
               FOR_ASSIGN_INCLUDED 
                1 
             
             
                 
                 
             
           
        
       
     
   
   The base station shall include the following four fields if FOR_ASSIGN_INCLUDED is set to ‘1’. 
                                               FOR_SCH_ID   2           FOR_DURATION   4           FOR_START_TIME   6           SCCL_INDEX   4           FPC_INCL   1           FPC_MODE   0 or 3           FPC_OLPC_SCH_M_INCL   0 or 1           FPC_SEC_CHAN   0 or 2           FPC_SCH_M_FER   0 or 5           FPC_SCH_INIT_M_SETPT   0 or 8           FPC_SCH_MIN_M_SETPT   0 or 8           FPC_SCH_MAX_M_SERTP   0 or 8           NUM_SUP   0 or 2                        
NUM_SUP occurrences of the following fields are included.
 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               SCH_ID 
               2 
             
             
                 
               FPC_SCH_FER 
               5 
             
             
                 
               FPC_SCH_INIT_SETPT 
               8 
             
             
                 
               FPC_SCH_MIN_SETPT 
               8 
             
             
                 
               FPC_SCH_MAX_SETPT 
               8 
             
             
                 
               FPC_THRESH_SCH_INCL 
               0 or 1 
             
             
                 
               FPC_SETPT_THRESH_SCH 
               0 or 8 
             
             
                 
                 
             
           
        
       
     
   
   The extended SCH assignment message shown in Table 3 can assign forward and reverse SCHs and includes Walsh codes for the SCHs. The conventional SCH request message is still used in the present invention when the mobile station requests an SCH. 
   Table 4 lists the message fields of an extended release message transmitted by the base station for state transition. The extended release message is newly detained in view of the introduction of a MAC (Media Access Control) layer to support the packet data service. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
           
           
             
                 
               FPC_PRI_CHAN 
               1 
             
             
                 
               RPC_CHANNEL 
               1 
             
             
                 
               CH_IND 
               3 
             
             
                 
               CON_REF_INCL 
               1 
             
             
                 
               CON_REF 
               0 or 8 
             
             
                 
               SCR_SEQ_INCL 
               1 
             
             
                 
               SCR_SEQ 
               0 or 4 
             
             
                 
               GATING_RATE_INCL 
               1 
             
             
                 
               PILOT_GATING_RATE 
               0 or 2 
             
             
                 
               BLOB 
               7 
             
             
                 
                 
             
           
        
       
     
   
   FPC_PRI_CHAN: this field indicates a forward channel by which an inner loop power control is performed and this field is set for an FCH, except for the case that only a DCCH is connected. 
   RPC_CHANNEL: this field indicates a channel that transmits power control bits. 
   CH_IND: this field indicates the type of a physical channel to be released, i.e., an FCH, a DCCH, both the FCH and the DCCH, or a reverse pilot channel. For example, CH_IND is set to 010 for a DCCH, 100, for a reverse channel, 101 for an FCH and the reverse pilot channel, 110 for the DCCH and the reverse pilot channel, and 111 for the FCH, the DCCH, and the continuous reverse pilot channel. 
   CON_REF_INCL: this field indicates whether CON_REF is included in the message. 
   CON_REF: this field has a mobile station-specific value to indicate a service option to be connected. 
   SCR_SEQ: this field is used to discriminate between the suspended state  105  from the dormant state  107  in a signaling layer. 
   GATING_RATE_INCL: this field indicates whether PILOT_GATING_RATE is included in the message. 
   PILOT_GATING_RATE: this field provides a gating rate for gated transmission, 1, ½, or ¼. 
   BLOB: the MAC layer directly uses this field. BLOB is comprised of logical resources (DTCH and DMCH), SO, SR, and PURGE_SR and includes first-hand information about MAC state transition. 
   A receiver, receiving the extended release message, can decide as to what state it will transition to after the SCH is released by analyzing the extended release message. If CH_IND is not 0 and at least one of CON_REF_INCL, CON_REF, SCR_SEQ_INCL, and SCR_SEQ is not 0, the suspended state  105  is entered after the SCH is released. If CH_IND is not 0, at least one of CON_REF_INCL, CON_REF, SCR_SEQ_INCL, and SCR_SEQ is not 0, and either of GATING_RATE_INCL and PILOT_GATING_RATE is not 0, the control hold state  103  is entered and if all of the above seven fields are set to 0s, the dormant state  107  is entered. 
   An extended release mini message may be used instead of the extended release message shown in Table 4. The extended release mini message is 5 ms in duration and used only if the active state  101  is transitioned from the control hold state  103 . The extended release mini message includes only the CH_IND field and the BLOB field because MAC state transition occurs between dedicated channel-having states and thus there is no need for any other field. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 5 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               CH_IND 
               3 
             
             
                 
               BLOB 
               7 
             
             
                 
                 
             
           
        
       
     
   
   The messages defined as Table 4 and Table 5 are directed from the base station to the mobile station to release a channel. The base station may transmit the messages independently or as a response upon receipt of a channel release request message from the mobile station. Prior to transmitting the messages shown in Table 4 and Table 5 as response messages for the channel release request message, the base station must receive a peer-to-peer resource control message or a peer-to-peer resource control mini message, in the formats shown in Table 6 and Table 7, respectively. 
   
     
       
             
             
             
           
         
             
                 
               TABLE 6 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               REQ_BLOB 
               16 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
             
           
         
             
                 
               TABLE 7 
             
             
                 
                 
             
             
                 
               Field 
               Length (bits) 
             
             
                 
                 
             
           
           
             
                 
               BLOB 
               13 
             
             
                 
                 
             
           
        
       
     
   
   SCH release &amp; continuation of the active state or state transition to the control hold state, the suspended state, or the dormant state is requested via the peer-to-peer resource control message, whereas SCH release &amp; continuation of the active state or state transition to the control hold state, the suspended state, or the dormant state is requested via the peer-to-peer resource control mini message. The above two messages are directed from the mobile station to the base station to request channel release. The mobile station is authorized to only request channel release, not to decide on channel release. The peer-to-peer resource control mini message is 5 ms in duration and transmitted on a traffic channel only. 
   Either of the base station and the mobile station can generate an SCH release request if packet data is not transmitted for a predetermined time.  FIG. 4  is a signal flow diagram illustrating the case that the base station issues the SCH release request according to the embodiment of the present invention and  FIG. 5  is a signal flow diagram illustrating the case that the mobile station issues the SCH release request according to the embodiment of the present invention. 
   Referring to  FIG. 4 , reference numerals  401 ,  403 ,  405 , and  407  denote a signaling layer controller (SIG controller), a resource controller (RC), a MAC controller, and a channel element (CE) controller in the base station, respectively. Reference numerals  409 ,  411 ,  413 , and  415  respectively denote a CE controller, a MAC controller, an RC, and a SIG controller in the mobile station. 
   The SIG controllers  401  and  415  generate messages associated with call processing and interpret the call processing messages. The RCs  403  and  413  maintain and controls the states of all physical and logical resources related with services. The RC  403  distributes or releases resources and the RC  413  performs base station commands. The MAC controllers  405  and  411 , including state transition modules classified according to idle periods of data in the packet data service, trigger state transition-associated operations. The CE controllers  407  and  409  perform all physical operations (e.g., encoding and modulation/demodulation) needed to transmit signals. 
   If transmission of packet data is discontinued, the MAC controller  405  transmits an RC-unlock request signal as a primitive for releasing an SCH to the RC  403 , requesting release of the SCH or release of an FCH or a control channel as well as release of the SCH in step  801 . That is, for state transition by releasing the SCH along with the FCH or the control channel, the MAC controller  405  transmits the RC-unlock request signal to the RC  403  to transition from the active state  101  to the control hold state  103 , the suspended state  105 , or the dormant state  107 . The MAC controller  405  must determine whether to continue the active state  101  or transition to the control hold state  103 , the suspended state  105 , or the dormant state  107  by checking the presence or absence of data to be transmitted on the FCH or the DCCH, in step  801 . Both the FCH and the DCCH are used to provide circuit service and packet data service. In the case where the SCH is released due to discontinuation of the packet data transmission, the circuit service is provided in the active state. On the other hand, if the packet data transmission is discontinued during only the packet service on the supplemental channel in progress, it is not necessary to maintain the active state and thus the active state is transitioned to the control hold state, the suspended state, or the dormant state. If transmit data is not generated during data communication in progress on the DCCH and a signal control channel (SCCH) in the active state or the control hold state, the suspended state or the dormant state is entered. The RC  403  transmits a SIG-release request signal to the SIG controller  401  in step  802  and the SIG controller  401  transmits an extended release message in the format shown in Table 4 to the CE controller  407  in step  803 . The extended release message has information about a state to which the active state  101  transitions, that is, information about the FCH or the DCCH to be released and information about a logical channel mapped on a physical channel, as stated before. The CE controller  407  transmits the extended release message to the CE controller  409  of the mobile station  301  on the physical channel. 
   The CE controller  409  transmits the extended release message to the SIG controller  415  in step  803   a  and the SIG controller  415  analyzes the extended release message and generates a SIG-release indication to the RC  413  in step  804 . The RC  413  updates information about corresponding resources to be released, transmits an RC-resource release indication to the MAC controller  411  in step  805 , and transmits a SIG-release response signal to the SIG controller  415  in step  806 . Here, the SIG controller  415  releases the SCH and the RC  413  and the MAC controller  411  releases the FCH or the DCCH as necessary. The SIG controller  415  transmits an extended release response message to the CE controller  409  in step  807 . 
   The SIG controller  401  receives the extended release response message via the mobile station CE controller  408  and base station CE controller  407  in step  808  and transmits a SIG-release confirm signal to the RC  403  in step  809 , thereby releasing the SCH and completing the state transition. That is, the base station  303  releases the SCH and transitions to the same state as the mobile station  301 . 
   As described above, the base station determines which state it will transition to by checking the presence or absence of data to be transmitted on the FCH and the DCCH and the mobile station transitions to the corresponding state by analyzing the SCH release message having information about the determined state transition. 
   The fields CH_IND, CON_REF-INCL, CON_REF, SCR_SEQ_INCL, SCR_SEQ, GATING_RATE_INCL, PILOT_GATING_RATE, and BLOB of Table 4 specify how the mobile station transitions. For transition to the control hold state, the 5-ms mini message of Table 5 can be used instead of the message of Table 4. The fields CH_IND and BLOB of Table 5 indicate release of an SCH &amp; continuation of the active state or transition to the control hold state. 
   Referring to  FIG. 5 , the MAC controller  411  transmits an RC-unlock send signal to the RC  413 , requesting release of an SCH, when no transmit packet data is generated in step  901 . The RC-unlock send signal is used to transition from the active state  101  directly to the control hold state  103 , the suspended state  105 , or the dormant state  107 . The RC  413  transmits a SIG-release send signal to the SIG controller  415  in step  902  and the SIG controller  415  transmits the peer-to-peer resource control message as defined in Table 6 to the SIG controller  401  of the base station  303  via the CE controller  409  of the mobile station  301  and the CE controller  407  of the base station  303  in steps  903  and  904 . The SIG controller  401  releases the SCH and transitions to another state by performing the procedure illustrated in FIG.  4 . If the mobile station wants to stay in the active state  101  or to request transition to the control hold state  103 , the peer-to-peer resource control mini message can be transmitted instead of the peer-to-peer resource control message. 
     FIG. 6A  is a flowchart illustrating an SCH release and state transition procedure in the base station according to the embodiment of the present invention and  FIG. 6B  is a flowchart illustrating an SCH release and state transition procedure in the mobile station according to the embodiment of the present invention. 
   Referring to  FIG. 6A , the base station  303  determines whether the MAC controller  405  has completed data transmission on the SCH in step  1001 . Upon completion of the data transmission, the MAC controller  405  determines whether a non-data transmission period has exceeded a predetermined time period in step  1003 . If packet data transmission is discontinued longer than the predetermined time period, the MAC controller  405  decides whether to continue the active state or transition to another state by checking the presence or absence of data on an FCH or a DCCH in step  1004 . The decision is made with the following considerations. Both the FCH and the DCCH are used to provide circuit service and packet data service. If an SCH is released due to the absence of transmit packet data in this state, the circuit service continues in the active state. On the other hand, if no packet data is generated while only the packet service on the SCH is in progress, it is unnecessary to continue the active state. Hence, the active state is transitioned from to the control hold state, the suspended state, or the dormant state. In a case where no data is generated during data communication on a DCCH and an SCCH in the active state or the control hold state, the suspended state or the dormant state is entered. 
   If it is determined that the active state is to be continued in step  1004 , the MAC controller  405  generates an SCH assignment message in step  1007  and transmits the SCH assignment message to the mobile station  301  in step  1011 . Assignment and release of the SCH is determined depending on the value of REV_DURATION in the SCH assignment message. Then, the SCH is released and the active state  101  is continued in the procedure shown in  FIGS. 3A and 3B . 
   On the other hand, if state transition is determined in step  1004 , the MAC controller  405  transmits the RC-unlock request signal to the RC  403 , requesting release of the SCH and state transition in step  1005 . The RC  403  transmits the SIG-release request signal to the SIG controller  401 . The SIG controller  401  generates the extended release message or the extended release mini message in response to the SIG-release request signal in step  1009  and transmits the generated message to the mobile station  301  in step  1013 . In step  1015 , the SIG controller  401  monitors the CE controller  407  to check whether the extended release response message has been received from the mobile station  301 . Upon receipt of the extended release response message, the SIG controller  401  transmits the SIG-release confirm signal to the RC  403 , to thereby releasing the SCH and transitioning to the control hold state  103 , the suspended state  105 , or the dormant state  107 , in step  1017 . 
   Meanwhile, if the data transmission is in progress, the base station  303  determines whether an SCH request has been received from the mobile station  301  through the CE controller  407  in step  1002 . Upon receipt of the SCH release request from the mobile station  301 , the base station goes to step  1004 . 
   Referring to  FIG. 6B , the SIG controller  415  of the mobile station  301  periodically monitors the CE controller  409  to check whether a message has been received from the base station in step  1019 . It is to be noted that the message is a message for releasing an SCH. Upon receipt of the message from the base station  303 , the mobile station  301  determines whether the message is an extended release message or an extended release mini message in step  1019 . If the received message is one of the extended release message and the extended release mini message, the SIG controller  415  interprets the received message in step  1021 , and determines a state to transition to and transmits the SIG-release indication to the RC  413  in step  1023 . The RC  413  transmits the RC-resource indication to the MAC controller  411  and the SIG-release response signal to the SIG controller  415 , to thereby release the SCH and transition to the corresponding state in step  1025 . The SIG controller  415  transmits the extended release response message to the CE controller  409 . 
   If the received message is not either of the extended release message and the extended release mini message in step  1019 , the mobile station  301  determines whether the message is a supplemental assignment message in step  1026 . In the case of the SCH assignment message, the mobile station  301  determines state to transit in step  1030  and then releases the SCH in step  1031 . That is, after releasing the SCH, the mobile station  301  remains in the active state. 
   In accordance with the present invention, the active state is directly transitioned to the control hold state, the suspended state, or the dormant state when an SCH is released in the active state. As a result, radio resources are saved. 
   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.