Abstract:
Packet data communicating device and method in a CDMA communication system. According to a first embodiment, a transmitting device for a base station includes a data generator for generating frame data to be transmitted, a first mask generator for generating a long code mask for a forward common channel, a second mask generator for generating a long code mask for a forward common channel to be designated as dedicated to a specific mobile station, a selector for selecting one of the long code masks generated in the first and second mask generators, a long code generator for generating a long code with the selected long code mask, a scrambler for mixing the frame data received from the data generator and the long code received from the long code generator, and a transmitter for spreading the scrambled frame data, for transmission.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application entitled DEVICE AND METHOD FOR COMMUNICATING PACKET DATA IN MOBILE COMMUNICATION SYSTEM earlier filed in the Korean Industrial Property Office on Jul. 13, 1998, and there duly assigned Serial No. 98-28237 and also Korean Patent Application Serial No. 1998-29180. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device and method for communicating packet data in a mobile communication system, and more particularly, to a device and method used for rapidly assigning a dedicated channel for packet data service in a CDMA (Code Division Multiple Access) mobile communication system. 
     2. Description of the Related Art 
     In CDMA mobile communication systems, the IMT-2000 standard has evolved from the IS-95 standard. IS-95 supports voice service only, whereas IMT-2000 enables high-quality voice service, transmission of moving pictures, and internet browsing. 
     Data communication in the mobile communication system is characterized by a momentary active state and a long idle state. Accordingly, the next generation of mobile communication systems assign a dedicated channel in a data communication service only at the time when data is transmitted. That is, dedicated traffic and control channels are connected during data transmission and released after a predetermined time when no data is transmitted, due to limited radio resources, base station (BS) capacity, and mobile power consumption. Once the dedicated channels have been released, communication is made via common channels, thereby increasing use efficiency of the radio resources. 
     To do so, packet service is implemented in many state, depending on channel assignment and the presence or absence of state information. FIG. 6 is a state transition diagram for packet service in a communication system. Referring to FIG. 6, the packet service is comprised of a packet null state, an initialization state, an active state, a control hold state, a suspended state, a dormant state, and a reconnect state. Packet service options are connected in the control hold state, active state, and suspended state. 
     Upon request for packet service in the packet null state, the initialization state is entered where a connection attempt for packet service is performed, and transition to the control hold state occurs if a dedicated control channel is established. The dedicated control channel is needed to transmit a layer  3  (L 3 ) message and a medium access control (MAC) message. Then, upon entering the active state, forward and reverse dedicated control channels and traffic channels are maintained with RLP (Radio Link Protocol) frames being communicated on these channels. If a relatively short inactive time period is set, the suspended state is entered to efficiently use radio resources and conserve mobile station (MS) power. In the suspended state, the dedicated control and traffic channels are released but can be re-assigned in a relatively short time because both the BS and the MS retain status information including RLP initialization, traffic channel assignment, and encryption variables. If there is no data exchanged for a predetermined time, the suspended state transitions to the dormant state. In the dormant state, only a PPP (Point-to-Point Protocol) connection is maintained and if transmit data is generated, a reconnect state is entered. If the dedicated control channel is established, the reconnect state transitions to the control hold state. While the MS and the BS are in a common channel state, such as the suspended, dormant, and reconnect states, the MS monitors a paging channel and a common control channel on a forward link, and the BS monitors an access channel and a common control channel on a reverse link. There may be a plurality of paging channels and access channels. Each paging channel is distinguished by a different Walsh code and each access channel is distinguished by a different long code. 
     In FIG. 6, after the active state transitions to the suspended state through the control hold state in the absence of data for a predetermined time during a data communication, messages are exchanged on common channels. Upon generation of a control message for resuming data transmission, the BS attempts to connect to the MS on a paging channel and then the MS transmits a response message on an access channel. However, this common channel message transmission is susceptible to message contention if other MSs use the same access channel, resulting in a reception failure in the BS. If each MS fails to receive an acknowledgement from the BS within a predetermined time, it perceives the occurrence of message contention and resumes a message transmission after a randomized time delay. If repeated attempts to access the access channel for predetermined times fail, the procedure starts again. Information is transmitted on the access channel in access channel slots. 
     In the mechanism of transmitting an access channel message, the entire process of sending one message and receiving (or failing to receive) an acknowledgement for that message is called an access attempt. Each transmission in the access attempt is called an access probe. Each access probe consists of an access channel preamble and an access channel message capsule. When a message contention occurs, an access probe is re-transmitted with a power level set at a specified amount higher than the previous access probe&#39;s power level after a randomized time delay. 
     In the case of the MSs initiation of data communication, the same message transmission procedure is performed without the paging step of the BS. If an access channel message is too long to be sent at one time, it is divided into appropriate segments prior to transmission and the above procedure for each segment. 
     After exchanging the common channel messages, the BS assigns a dedicated code channel and sends a traffic channel assignment message on the dedicated channel. When the BS responds to the message, user data is sent on a dedicated traffic channel. 
     The procedure of assigning the dedicated channel is implemented in the same manner during transitions from the suspended state to the active state and from the dormant state to the active state. Transition from the suspended state to the active state requires service option negotiation associated with radio resources assignment and RLP initialization because only PPP information is reserved and no radio resources-related information exists in the dormant state. 
     FIG. 1 describes a conventional data service resuming procedure for a call initiated by a BS in a dormant state. A BS  112  sends a forward control message for resuming a data service to a corresponding addressed MS  114  on a paging channel (F-PCH) being a forward common channel (step  120 ). Then, the MS  114  sends a response message for the control message on a reverse access channel (R-ACH) (step  122 ). On the reverse access channel, a preamble precedes an access channel message to facilitate acquisition of a reverse physical channel in the BS  112  (step  126 ). 
     The entire process of sending one message and receiving (or failing to receive) an acknowledgement for that message is called an access attempt. Each transmission in the access attempt is called an access probe. Each access probe is comprised of a preamble and a message capsule. Upon contention of access probes, the mobile station transmits an access probe at a progressively higher power level than the previous access probe after a randomized delay. Here, transmission of the preamble is transmitted on a reverse pilot channel to synchronize timing between the BS and the MS which had a communication interrupted. 
     Reverse access channels share a long code. In a long code sharing scheme, an MS uses a Hash function to determine a long code among all available long codes (access channel long codes) in its initialization state, so that all MSs fairly share the long codes for access channels. A reverse pilot channel for channel estimation is spread by the long code of a reverse access channel and transmitted in parallel with the reverse access channel only for a time period when the reverse channel message exists. The two channels are distinguished by different orthogonal codes. 
     The preamble is transmitted on the reverse pilot channel at a higher transmit power level than the pilot channel, accompanied by a reverse access channel message. That is, the preamble is a segment of the pilot channel, with a relatively high transmit power. 
     If the BS  112  succeeds in synchronization with a reverse link and receiving the access channel message (step  126 ), it sends a dedicated channel assignment message on a forward common control channel (F-CCCH) (step  130 ) and null traffic on a forward dedicated control channel (F-DCCH) (step  140 ). If the MS  114  confirms that the dedicated channel is properly assigned from an analysis of the null frame of the F-DCCH, it sends a preamble on its unique code channel (R-PICH) (step  142 ). The preamble is used to recover synchronization between the BS  112  and the MS  114  which have experienced a temporary call interruption, during the channel assignment. 
     Then, the BS  112  sends an acknowledgement on the F-DCCH and the MS  114  stops transmitting the preamble (step  150 ). Thus, the MS  114  is capable of sending a message on a dedicated channel. RLP is initialized for packet data service and service options are connected (step  160 ). Hence, the control hold state is entered, and if a supplemental channel is successfully assigned (step  170 ), the active state is entered where packet data is communicated (step  180 ). 
     Meanwhile, if the BS  112  initiates a call in the suspended state, the data service can be resumed without step  160  in the above procedure. 
     FIG. 2 depicts a conventional data service resuming procedure for an MS initiated call in a dormant state. This is the same as the procedure described in FIG. 1 except that the MS  114  sends a packet service origination message on an access channel (step  222 ). Upon reception of the message by the BS  112 , the subsequent steps are performed as shown in FIG.  1 . 
     In resuming a data service for an MS initiated call in a suspended state, step  160  can be omitted in the above procedure. 
     A conventional data service resuming procedure which exchanges messages on common channels as illustrated in FIGS. 1 and 2, has many disadvantages. 
     There is a limitation inherent in long code sharing. The equal assignment of available long codes for common channels to mobile stations makes it impossible to control an individual probability of access channel contention for each mobile station. In view of frequent state transitions in the packet data service, the time required for the preliminary process for data transmission including channel acquisition is longer than an actual data transmission time. 
     Additionally, in a communication on a common channel, the MS must send a message in a slot allocated to the MS, thereby incurring a transmission delay while awaiting the allocated slot. 
     Also, since a reverse pilot channel is activated only at the time when an access channel message or a reverse common channel message is transmitted, the BS should reacquire the PN sequence of the MS prior to transmission of a channel assignment message. Accordingly, the MS repeatedly performs an access attempt in which a preamble is sent at a relatively high transmit power level, followed by an access channel message. Therefore, power is excessively consumed and the BS reacquisition step is added. 
     Finally, data can be transmitted only through a regular state transition. In other words, if the amount of data to be transmitted at a time is small, the resources that a preliminary process for resuming data transmission takes is larger than that of actual data transmission, leading to inefficient use of resources. 
     In a conventional designation of a common channel, an MS transmits a message on a reverse access channel and receives a response for the message on a forward paging channel. Thus, there may exist a plurality of forward paging channels and reverse access channels. Each forward channel is distinguished by a different Walsh code and each reverse channel by a different long code in a CDMA mobile communication system. 
     Upon generation of a message to be transmitted, the MS sends the message together with a preamble to the BS on an available access channel at an appropriate power level, and awaits an acknowledgement from the BS. If a different MS selects the same access channel, message contention occurs. Then, the BS may fail to receive the MS initiated message for a predetermined time. If it does, the MS sends the same message again using a power level set at a specified amount higher than the previous message and awaits an acknowledgement. 
     In the conventional mechanism of sending access channels being reverse common channels, concurrent message transmissions from MSs with the same long code are likely to cause message contention, leading to message losses. This is called contention-based random access. 
     When message contention occurs, the MS perceives the message contention in a predetermined time and resumes a message transmission after a randomized time delay. The MS performs an initial attempt to access the BS at a predetermined power level. When it fails to receive an acknowledgement from the BS, it performs the next attempt using a power level set at a specified amount higher than the previous attempt. If repeated attempts to access the access channel for predetermined times fail, the procedure starts again. Information is transmitted on the access channel in access channel slots and access channel frames. 
     For an MS to transmit a message which is too long to be transmitted at one time, the message must be divided into appropriate segments which are sent a plurality of times. When other MSs attempt to transmit messages using the same long code, message contention occurs. In this case, a long delay is involved in transmitting the entire message on the access channel. 
     The message contention can be prevented by designating a channel assigned by a BS as dedicated to an MS for transmission of a common channel message. On the other hand, to designate a forward common channel as dedicated, the MS requests for channel continuously transmit a common channel message, and then the BS sends a response message which includes the ID of an available channel. 
     The present invention provides a method of transitioning from a dedicated channel released state to a data transmission state by rapidly assigning a dedicated channel. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide device and method for communicating packet data, in which data transmission on a common channel is minimized and a data transmission state using a dedicated channel, or a channel designated as dedicated, is rapidly entered in order to efficiently use resources and support rapid data service. 
     According to one aspect of the present invention, the above object can be achieved by providing a BS transmitting device in a mobile communication system. In the transmitting device, a data generator generates frame data to be transmitted, a first mask generator generates a long code generator for a forward common channel, a second mask generator generates a long code mask for a forward common channel to be designated as dedicated to a specific mobile station, a selector selects one of the long code masks generated in the first and second mask generators, a long code generator generates a long code by use of the selected long code mask, a scrambler mixes the frame data received from the data generator and the long code received from the long code generator, and a transmitter spreads the scrambled frame, for transmission. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a flowchart depicting a conventional data service resuming procedure between a BS and an MS in a dormant state for call initiation by the BS; 
     FIG. 2 is a flowchart depicting a conventional data service resuming procedure between a BS and a MS in a dormant state for call initiation by the MS; 
     FIGS. 3A,  3 B, and  3 C are flowcharts depicting embodiments of data service resuming procedures between a BS and an MS in a dormant state for call initiation by the BS according to embodiments of the present invention; 
     FIG. 4 is a flowchart depicting an embodiment of a data service resuming procedure between a BS and an MS in a dormant state in the case of a call initiation by the MS according to a fourth embodiment of the present invention; 
     FIGS. 5A and 5B are flowcharts depicting other embodiments of the data service resuming procedure between a BS and an MS in a dormant state for call initiation by the MS according to a fifth embodiment of the present invention; 
     FIG. 6 is a state transition diagram for packet data service in accordance with the prior art; 
     FIG. 7 is a block diagram of a transmitter in a BS according to the present invention; 
     FIG. 8 is a block diagram of a receiver in an MS, corresponding to the transmitter of FIG. 7; 
     FIG. 9 is a block diagram of a transmitter in an MS according to the present invention; and 
     FIG. 10 is a block diagram of a receiver in a BS, corresponding to the transmitter of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A BSC (Base Station Controller) in the present invention is a controller disposed between a BS and an exchange or between a BS and an IWF (Inter-Working Function), for performing location registration of an MS, service connection, call management, and BS control. 
     Note that like reference numerals denote the same components or the same steps in the drawings, and a description of the present invention will be given, focussing on the difference between the prior art and the present invention. While the embodiments herein apply the present invention to a CDMA mobile communication system, the present invention is not limited to CDMA systems only. 
     FIG. 7 is a block diagram of a BS transmitting device according to an embodiment of the present invention. Referring to FIG. 7, a channel encoder  710  encodes data to transmit in a communication channel. An interleaver  720  randomizes encoded symbols for burst errors in the output of the channel encoder  710 . A selector  705  selects a different long code mask according to a forward common channel and a forward dedicated channel. It selects a long code mask for a specific MS when a forward common channel is designated as dedicated upon request for the designation by the MS. The long code mask may be a specific long code mask used to designate a common channel as dedicated or a long code generated using an ESN (Electronic Serial Number) of the MS. A long code generator  712  generates a long code with the selected long code mask. A decimator  722  takes one chip from each predetermined chip of the long code to match a symbol rate at the output of the interleaver  720 . A mixer  724  multiplies the outputs of the interleaver  720  and the decimator  722 , for scrambling transmit information to allow only a receiver using the same long code mask to receive the information. 
     A multiplexer (MUX)  730  multiplexes the output of the mixer  724  and a power control bit sent to control the transmit power of an MS. The multiplexing can be implemented in two ways: time division multiplexing, and puncturing and power control bit insertion. The insertion location of the power control bit may be preset by a mobile communication system or randomly determined. 
     A Walsh code #A generator  740  is a type of orthogonal code generator for orthogonal channelization among forward channels and generates a Walsh code symbol #A of a Walsh code set. A mixer  742  multiplies the outputs of the multiplexer  730  and the Walsh code #A generator  740 , for orthogonal modulation. A Walsh code # 0  generator  744  generates a Walsh code symbol # 0  for a pilot channel in the Walsh code set. A mixer  746  multiplies the output of the Walsh code # 0  generator  744  by a predetermined value (+ 1  in the present invention) to produce a forward pilot channel for a receiver to use for channel estimation. 
     An adder  750  adds the outputs of the mixers  742  and  746 . A common PN code generator  760  generates a PN sequence assigned to a cell to identify the cell. A dedicated PN code generator  762  for an MS “#m” generates a PN sequence for PN spreading a forward common channel to be designated as dedicated. As described above, the forward common channel can also be designated as dedicated with a specific long code mask. The dedicated PN code generator  762  can be separately procured or replaced by the long code generator  712  to implement the same function. A selector  764  selectively switches the outputs of the common PN code generator  760  and the dedicated PN code generator  762 . A mixer  766  multiplies the sum of the forward channels received from the adder  750  by the selected PN sequence, for PN spreading. The output of the mixer  766  is transmitted through a low pass filter (LPF)  770 , an RF (Radio Frequency) transmitting end  772 , and a transmission antenna. 
     FIG. 8 is a block diagram of an MS receiver corresponding to the BS transmitter shown in FIG.  7 . Referring to FIG. 8, a mixer  866  receives a signal through a reception antenna, an RF receiving end  872 , and an LPF  870 . The selector  764  selects the same PN sequence used in the BS transmitter between the outputs of the common PN code generator  760  and the dedicated PN code generator  762 . The mixer  866  multiplies the selected PN sequence by the output of the LPF  870 . 
     A mixer  846  multiplies the output of the mixer  866  by the output of the Walsh code # 0  generator  744  in order to extract the pilot channel for channel estimation. A channel estimator  850  estimates a channel with the extracted pilot channel. A complex conjugator  852  produces the complex conjugate of the channel&#39;s estimated value. A mixer  842  multiplies the output of the mixer  866  by the Walsh code symbol #A used in the BS, thereby extracting the information transmitted to the MS. A mixer  826  multiplies the complex conjugate by the output of the mixer  842 , for coherent demodulation. A demultiplexer (DEMUX)  830  demultiplexes the coherent demodulation signal into the power control bit and the data received from the BS. 
     The selector  705  selects the same long code mask that was used in the BS transmitter. The long code generator  712  generates a long code utilizing the selected long code mask. The decimator  722  takes one chip from each predetermined chip of the long code to match a symbol rate at the output of the demultiplexer  830 . A mixer  824  multiplies the data separated by the demultiplexer  830  by the output of the decimator  722 , for descrambling. A deinterleaver  820  deinterleaves the output of the mixer  824 . A channel decoder  810  channel-decodes the deinterleaved signal. 
     FIG. 9 is a block diagram of an MS transmitter according to another embodiment of the present invention. Referring to FIG. 9, a channel encoder  910  detects and recovers errors in a communication channel. An interleaver  920  randomizes burst errors in the output of the channel encoder  910 . A multiplexer  930  multiplexes the output of the interleaver  920  and a power control bit which is sent to control the transmit power of a BS. The multiplexing can be implemented in two ways: time division multiplexing, and puncturing and power control bit insertion. The insertion location of the power control bit may be preset by a mobile communication system or randomly determined. 
     A Walsh code #a generator  940  is a type of orthogonal code generator for orthogonal channelization among reverse channels and generates a Walsh code symbol #a of a Walsh code set. A mixer  942  multiplies the outputs of the multiplexer  930  and the Walsh code #a generator  940 , for orthogonal modulation. A Walsh code # 0  generator  944  generates a Walsh code symbol # 0  for a pilot channel in the Walsh code set. A mixer  946  multiplies the output of the Walsh code # 0  generator  944  by a predetermined value (+ 1  in the present invention) to thereby produce a reverse pilot channel for a receiver to use for channel estimation. A second multiplexer  932  may be used to multiplex the power control bit on the pilot channel. In this case, the multiplexer  930  is omitted and the output of the interleaver  920  is directly applied to the input of the mixer  942 . An adder  950  adds the outputs of the mixers  942  and  946 . A common PN code generator  960  generates a PN sequence assigned to a cell to identify the cell. 
     A selector  905  selects a different long code mask according to a reverse common channel and a reverse dedicated channel. A long code generator  912  generates a long code with the selected long code mask. A mixer  914  generates a spreading sequence used to spread the output of the mixer  966  by multiplying the outputs of the common PN code generator  960  and the long code generator  912 . The output of the mixer  966  is transmitted through an LPF  970 , an RF transmitting end  972 , and a transmission antenna. 
     FIG. 10 is a block diagram of a BS receiver corresponding to the MS transmitter of FIG.  9 . Referring to FIG. 10, a mixer  1066  receives a signal through a reception antenna, an RF receiving end  1072 , and an LPF  1070 . The selector  905  selects the same long code mask used in the transmitter. The long code generator  912  generates a long code utilizing the selected long code mask. The mixer  914  generates a sequence for despreading the output of the mixer  1066  by multiplying the outputs of the common PN code generator  960  and the long code generator  912 . 
     A mixer  1046  multiplies the output of the mixer  1066  by the output of the Walsh code # 0  generator  944  in order to extract the pilot channel for channel estimation. A demultiplexer  1032  is used when a power control bit is received on the pilot channel in which case a demultiplexer  1030  is not used. A channel estimator  1050  estimates a channel with the extracted pilot channel. A complex conjugator  1052  produces the complex conjugate of the channel estimated value. A mixer  1042  multiplies the output of the mixer  1066  by the Walsh code symbol #a used in the MS, thereby extracting the information transmitted to the BS. A mixer  1026  multiplies the complex conjugate by the output of the mixer  1042 , for coherent demodulation. The demultiplexer  1030  demultiplexes the coherent demodulation signal into the power control bit and the data received from the MS. When the power control bit is loaded on the reverse pilot channel, the demultiplexer  1030  is omitted and the output of the mixer  1026  is directly applied to the input of a deinterleaver  1020 . The deinterleaver  1020  deinterleaves the data received from the demultiplexer  1030  and a channel decoder  1010  channel-decodes the deinterleaved signal. 
     Referring now to FIG. 3A, FIG. 3A is a flowchart illustrating signal flow between a BS and an MS in an embodiment of a data service resuming procedure when a BS initiates a call in a dormant state according to the present invention. The BS  112  sends the MS  114  a forward control message including information about designation of an R-CCCH as dedicated on an F-PCH which is a forward common channel (step  320 ). The MS  114  sends the BS  112  a response message on an R-CCCH designated as dedicated based on the forward control message (step  322 ). The response message may include information about designation of an F-CCCH as dedicated. Then, the BS  112  synchronizes its timing with the reverse link via the R-CCCH designated as dedicated (step  126 ). An R-PICH for channel estimation is maintained even if no common control channel message (step  332 ) exists. This obviates the need for sending a preamble by the MS to allow the BS to reacquire a PN sequence used for PN spreading in the MS. The BS  112  sends the MS  114  a channel assignment message on an F-CCCH (step  340 ). The F-CCCH can be designated as dedicated upon request from the MS  114  in one of two methods as described below. 
     Where there is loss of orthogonality on a forward link and no transmission delay of a channel assignment message. In this method, an F-CCCH can be spread by a particular PN sequence generated by the dedicated PN code generator  762  of FIG.  7 . In such a case forward channel orthogonality is lost only during channel assignment message transmission. Therefore, the BS  112  notifies the MS  114  of an orthogonal code to be used by the channel assignment message (step  340 ). Then, the selector  764  of FIGS. 7 and 8 selects the common PN code generator  760  in the BS  112  and the MS  114  and the Walsh code #A generator  740  is set depending on the assigned orthogonal code. 
     Where there is no loss of forward channel orthogonality, a message is sent to the MS  114  only in a slot assigned to the MS since an F-CCCH is used in time division. Thus, the channel assignment message cannot be directly sent to the MS  114  when it is generated. The selector  705  of FIG. 7 selects a long code mask unique to the MS  114  and the mixer  724  scrambles data with a long code generated by the long code mask, so that an MS which does not use the long code mask detects errors in a CRC (Cyclic Redundancy Code) check following channel decoding. The BS  112  notifies the MS  114  of an orthogonal code to be used by the channel assignment message (step  340 ). Then, the selector  705  of FIGS. 7 and 8 in the BS  112  and the MS  114  selects a long code mask unique to the MS  114  and the Walsh code #A generator  740  is set depending on the assigned orthogonal code. 
     Since the assignment of bidirectional DCCHs enables a power control (step  350 ), the conventional problem of excessive power consumption, unnecessary transmission of a preamble and null traffic, and BS reacquisition which are caused by message communication on CCCHs can be overcome. Therefore, an F-DCCH and an R-DCCH are activated in a short time relative to the prior art, thereby enabling a rapid data transmission. The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  1 . 
     In resuming a data service for a call initiated by a BS in a suspended state, step  160  can be omitted in the above procedure. 
     FIG. 3B is a flowchart depicting another embodiment of the data service resuming procedure for a call initiated by a BS in a dormant state. Referring to FIG. 3B, the BS  112  sends the MS  114  a forward control message for resuming a data service on an F-PCH which is a forward common channel (step  360 ). The forward control message includes information about assignment of bidirectional dedicated channels. The BS  112  sends null traffic on the assigned F-DCCH (step  140 ). The MS  114 , which has received the forward control message and the channel assignment message, analyzes the null traffic (step  322 ). Then, the MS  114  sends the BS  112  a response message on the assigned R-DCCH. Prior to transmission of the response message, the MS  114  sends a preamble for a predetermined time period at a power level required to facilitate synchronization acquisition in the BS  112 , and then the response message is sent on the R-DCCH in parallel with a reverse dedicated pilot channel. The BS  112  synchronizes its timing with the reverse link via the R-DCCH (step  126 ). Since the assignment of bidirectional DCCHs enables a power control (step  350 ), the conventional problem of excessive power consumption, unnecessary transmission of a preamble and null traffic, and BS reacquisition which are caused by message communication on CCCHs can be overcome. Therefore, the F-DCCH and the R-DCCH are activated in a short time relative to the prior art, thereby enabling a rapid data transmission. The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  1 . 
     In resuming a data service for a call initiated by a BS in a suspended state, step  160  can be omitted in the above procedure. 
     FIG. 3C is a flowchart depicting a further embodiment of the data service resuming procedure for a call initiated by a BS in a dormant state. Referring to FIG. 3C, the BS  112  sends the MS  114  a forward control message for resuming a data service on an F-PCH which is a forward common channel (step  360 ). The forward control message includes information about assignment of bidirectional dedicated channels. The BS  112  sends null traffic on the assigned F-DCCH (step  140 ). The MS  114 , which has received the forward control message and the channel assignment message, analyzes the null traffic (step  322 ). Then, the MS  114  sends the BS  112  a response message on the assigned R-DCCH. Prior to transmission of the response message, the MS  114  sends a preamble for a predetermined time period at a power level required to facilitate synchronization acquisition in the BS  112 , and then the response message is sent on an R-DCCH in parallel with a reverse dedicated pilot channel. The BS  112  synchronizes its timing with the reverse link via the R-DCCH (step  126 ). The BS  112  can proceed to a channel reassignment on the F-DCCH (step  370 ). 
     Since the assignment of bidirectional DCCHs enables a power control (step  350 ), the conventional problem of excessive power consumption, unnecessary transmission of a preamble and null traffic, and BS reacquisition which are caused by message communication on CCCHs can be overcome. Therefore, the F-DCCH and the R-DCCH are activated in less time when compared to the prior art, thereby enabling a rapid data transmission. The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  1 . 
     In resuming a data service for a call initiated by a BS in a suspended state, step  160  can be omitted in the above procedure. 
     FIG. 4 is a flowchart depicting an embodiment of a data service resuming operation for a call initiated by an MS in a dormant state. Referring to FIG. 4, the MS  114  sends a reverse control message to the BS  112  for resuming a data service on an R-ACH (step  420 ). The control message may include information about designation of an F-CCCH as dedicated. Then, the BS  112  synchronizes its timing with the reverse link via the R-ACH (step  126 ). An R-PICH for channel estimation is maintained even if there exists no common control channel message (step  432 ). This obviates the need for the subsequent step of sending a preamble by the MS to allow the BS to reacquire a PN sequence used for PN spreading in the MS. The R-PICH is spread by a PN sequence for the R-CCCH for a predetermined time and then by a PN sequence for an R-DCCH. The BS  112  sends the MS  114  a channel assignment message on an F-CCCH (step  340 ). The F-CCCH can be designated as dedicated upon request from the MS  114 . 
     Since the assignment of bidirectional DCCHs enables a power control (step  350 ), the conventional disadvantages of excessive power consumption, unnecessary transmission of a preamble and null traffic, and BS reacquisition which are caused by message communication on CCCHs can be overcome. Therefore, an F-DCCH and an R-DCCH are activated in less time when compared to the prior art, thereby enabling a rapid data transmission. The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  2 . 
     In resuming a data service for a call initiated by an MS in a suspended state, step  160  can be omitted in the above procedure. 
     FIG. 5A is a flowchart depicting another embodiment of the data service resuming procedure for a call initiated by an MS in a dormant state, in which burst data generated by the MS is sent on an R-DCCH, that is, data is sent in the dormant state without entering a data transmission state by assigning a dedicated traffic channel. Referring to FIG. 5A, the MS  114  sends the BS  112  a reverse control message for resuming a data service on an R-CCCH (step  420 ). The control message may include information about designation of an F-CCCH as dedicated. Then, the BS  112  synchronizes its timing with the reverse link via the R-CCCH (step  126 ). An R-PICH for channel estimation is maintained even if there exists no common control channel message (step  432 ). This obviates the need for the subsequent step of sending a preamble by the MS to allow the BS to reacquire a PN sequence used for PN spreading in the MS. The R-PICH is spread by a PN sequence for the R-CCCH for a predetermined time and then by a PN sequence for an R-DCCH. The BS  112  sends the MS  114  a channel assignment message on an F-CCCH (step  340 ). The F-CCCH can be designated as dedicated upon request from the MS  114  in step  420 . The BS  112  performs a power control for the reverse link via an F-DCCH assigned in step  340  (step  560 ). Then, the MS  114  sends the BS  112  data bursts on an R-DCCH (step  580 ). The data is stored in a buffer of the BS  112  (step  510 ). Frames having errors during the transmission are recovered through retransmission (step  520 ). The buffered data is transmitted to a network through a BSC  110  (step  530 ). If the amount of the received data exceeds the capacity of the buffer, the assigned DCCHs are maintained (step  540 ). The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  2 . 
     In resuming a data service for a call initiated by an MS in a suspended state, step  160  can be omitted in the above procedure. 
     FIG. 5B is a flowchart depicting a further embodiment of the data service resuming procedure for a call initiated by an MS in a dormant state, in which burst data generated by the MS is sent on an R-DCCH, that is, data is sent in the dormant state without entering a data transmission state by assigning a dedicated traffic channel. Referring to FIG. 5B, the MS  114  sends the BS  112  a reverse control message for resuming a data service on an R-CCCH (step  420 ). The control message may include information about designation of an F-CCCH as dedicated. Prior to transmission of the reverse control message, the MS  114  sends a preamble for a predetermined time period at a power level required to facilitate synchronization acquisition in the BS  112 , and then the control message is sent on the R-CCCH in parallel with a reverse pilot channel. Then, the BS  112  synchronizes its timing with the reverse link via the R-CCCH (step  126 ). When no R-CCCH message exists, the reverse pilot channel is no longer sent after a predetermined time. 
     The BS  112  sends the MS  114  a channel assignment message on an F-CCCH (step  340 ). The F-CCCH can be designated as dedicated upon request from the MS  114  in step  420 . The BS  112  performs a power control for the reverse link via an F-DCCH assigned in step  340  (step  560 ). Then, the MS  114  sends the BS  112  data bursts on an R-DCCH (step  590 ). More particularly, the MS  114  sends a preamble for a predetermined time period at a power level required to facilitate synchronization acquisition in the BS  112 , and then the data bursts are sent on the R-DCCH in parallel with a reverse pilot channel. Then, the BS  112  synchronizes its timing with the reverse link via the R-DCCH (step  146 ). The data is stored in a buffer of the BS  112  (step  510 ). Frames having errors during the transmission are recovered through retransmission (step  520 ). The buffered data is transmitted to a network through a BSC  110  (step  530 ). If the amount of the received data exceeds the capacity of the buffer, the assigned DCCHs are maintained (step  540 ). The subsequent procedure (steps  160 ,  170 , and  180 ) is performed in the same manner as FIG.  2 . 
     In resuming a data service for a call initiated by an MS in a suspended state, step  160  can be omitted in the above procedure. 
     As described above, the present invention is advantageous in that resources are efficiently used and a rapid data service is supported because data transmission on a common channel is minimized and a data transmission state using a dedicated channel or a channel designated as dedicated is rapidly entered. 
     While the present invention has been described in detail with reference to the specific embodiments, they are mere exemplary applications. Thus, it is to be clearly understood that many variations can be made by anyone skilled in the art within the scope and spirit of the present invention.