Abstract:
A common channel communication method for a base station in a mobile communication system including common channels, each of which support at least two data rates. The method comprises determining a data rate of the common channel available in a common channel service state and a frame length serviceable at the determined data rate, transmitting a message including information about the determined data rate and frame length on a specific forward common channel before transmission; and upon receipt of an acknowledge message through a specific reverse common channel, setting a data rata and a frame length of the common channel to the determined values.

Description:
PRIORITY 
     This application claims priority to an application entitled “Common Channel Communication Device and Method Supporting Various Data Rates in a Mobile Communication System” filed in the Korean Industrial Property Office on Sep. 14, 1998 and assigned Serial No. 98-38352, 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 communication device and method for a communication system, and in particular, to a device and method for managing a common channel having various data rates in a Code Division Multiple Access (CDMA) communication system. 
     2. Description of the Related Art 
     In a CDMA communication system, a channel which is used to transmit a link establishment request from a transmission side to a receiving side is called a common channel. A common channel transmits known signals such as preamble signals prior to message transmission. 
     In conventional mobile communication systems, a common channel has a fixed data rate of 9.6 Kbps or 4.8 Kbps and a fixed frame size (or length) of 20 ms. Seven channels using unique orthogonal codes (e.g., Walsh codes) are used for forward common channels, and for each forward common channel, five channels separated with unique long code masks are used as reverse common channels. 
     With regard to operation of the common channel, the channel to be used by a base station and a specific mobile station, out of the 7 forward common channels, is determined at the base station and the mobile station using a hash function. Once the forward common channel is determined, the base station always uses the determined channel when transmitting a message to that specific mobile station. The forward common channel operates in a slotted mode or a non-slotted mode. The slotted mode is used to reduce the power consumption of a mobile station; a corresponding slot for each mobile station is determined through the hash function. When the slot is determined, a mobile station receives a message from the base station through the determined slot. 
     The forward common channel has a data rate fixed at either 9.6 Kbps or 4.8 Kbps, and information concerning the data rate is transmitted through a common channel message. A mobile station receiving the data rate information constantly exchanges data at the fixed data rate. In general, the forward common channel uses 80 ms slots; a message can be transmitted over two slots. 
     In addition, for each forward common channel, 5 reverse common channels, at maximum, can be provided. The mobile station selects the access channel at random from the corresponding channels, and a base station decodes every available reverse common channel to receive a transmitted message. 
     The reverse common channel has a data rate fixed at 4.8 Kbps. For reverse common channel access, the slotted Aloha method is typically used. An important factor determining the slot size is a frame size. A factor determining the slot size includes PAM_SZ and MAX_CAP_SZ, wherein PAM_SZ designates the preamble size and MAX_CAP_SZ designates the message size. The above two factors both indicate the number of frames, and are transmitted to a mobile station through an access parameter message on a forward common channel. 
     An access slot is comprised of a preamble (PA) of size (1+PAM_SZ) and a message capsule of size (3+MAX_CAP_SZ). 
     The preamble is used for sync acquisition between a base station and a mobile station. In a mobile communication system, to minimize power consumption at the mobile station and to minimize interference, unnecessary transmission is suppressed and a transmission link is only established when the mobile station has a message or data to transmit. Therefore, before arrival of the message, the base station needs to perform sync acquisition for the message to be received from the mobile station. For effective sync acquisition, prior to sending intended message or data, a mobile station transmits preambles for a predetermined time and then transmits the intended message. The preamble is a signal previously scheduled (or designated) between the base station and the mobile station. In most mobile communication systems, a mobile station can select a transmission start time of the preamble from possible transmission start times on the basis of system time information, acquired from a signal transmitted from a base station after power-on. Alternatively, the transmission start time may be determined as a fixed parameter in the system. A receiver at the base station checks for the existence of a preamble at every possible preamble transmission time, presumed on the basis of the system time. Upon detection of a preamble, the base station performs sync acquisition and tracing procedures to receive the message transmission following the preamble. 
     The size of a message included in the access slot is limited by the MAX_CAP_SZ parameter. The system initially sets the MAX_CAP_SZ parameter on the basis of the largest mobile station message. 
     The conventional method has the following problems. 
     First, when an access is attempted and the data rate of the common channel is fixed at 9.6 Kbps or 4.8 Kbps, the interval between access slots is also fixed so that it is not possible to reduce the delay between access attempts. Therefore, when using the conventional common channel having a fixed data rate, mobile stations may conflict due to the constant slot interval. Furthermore, an increase in access delay may cause difficulties in data service, in the light of state transitions occurring during the data service. 
     Second, in the case where, during data service, the system transitions to a state where the dedicated channel has terminated, and there is a small amount of data to be transmitted at once, the resources consumed in the additional process of restarting data transmission are greater than the resources required for actual data transmission, thereby causing an ineffective use of the resources. That is, sometimes it is required to transmit data frames smaller than a predetermined size without reassignment of a dedicated channel, and it is difficult to transmit data frames of various sizes using the common channel with a fixed data rate. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a device and method for realizing an access adaptively by varying the interval between access slots according to the data rate in a CDMA communication system. 
     It is another object of the present invention to provide a device and method for transmitting a data frame smaller than a predetermined size through a common channel according to the amount of data to be transmitted in a CDMA communication system. 
     It is further another object of the present invention to provide a device and method for reducing the limitation on the rate and size of data which can be transmitted over a common channel when a reverse access slot is reduced in size, to ensure effective use of resources and fast access in a CDMA communication system. 
     To achieve the above and other objects, there is provided a common channel communication method for a base station in a mobile communication system including common channels each supporting at least two data rates. The method comprises determining a data rate of a common channel available in a common channel service state and a frame length serviceable at the determined data rate, including information about the determined data rate and frame length on a specific forward common channel message before transmission; and upon receipt of an acknowledge message through a specific reverse common channel, setting a data rate and a frame length of the common channel to the determined values. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a diagram illustrating a common reverse access slot in a CDMA communication system; 
     FIG. 2 is a diagram illustrating a reverse access slot for various frame sizes used in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 3 is a diagram illustrating a reverse access slot having various data rates for a 20 ms frame in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 4 is a diagram illustrating a reverse access slot having various data rates for a 10 ms frame in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 5 is a block diagram of a base station transmitter using the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 6 is a block diagram of a mobile station receiver corresponding to the base station transmitter, using the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 7 is a block diagram of a mobile station transmitter using the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 8 is a block diagram of a base station receiver corresponding to the mobile station transmitter, using the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 9A is a diagram illustrating a broadcast message containing common channel environment information periodically transmitted over a forward common channel at a corresponding slot of each mobile station; 
     FIG. 9B is a diagram illustrating a message containing common channel environment information transmitted over a dedicated control channel during a state transition; 
     FIG. 10 is a block diagram of a base station transmitter which determines and uses a frame size and a data rate in the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 11 is a block diagram of a mobile station receiver corresponding to the base station transmitter, which determines a frame size and a data rate in the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 12 is a block diagram of a mobile station transmitter which determines and uses a frame size and a data rate in the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 13 is a block diagram of a base station receiver corresponding to the mobile station transmitter, which determines a frame size and a data rate in the first and second operating methods in a CDMA communication system according to an embodiment of the present invention; 
     FIG. 14 is a state transition diagram for a packet data service; 
     FIG. 15 is a flow chart illustrating a procedure for acquiring an available common channel during data or message transmission through a common channel having variable or various data rates according to an embodiment of the present invention; 
     FIG. 16 is a flow chart illustrating a procedure in which a base station acquires information about an available common channel during a transition to a suspended state and transmits the information over a dedicated control channel, and a mobile station then acquires the information, according to an embodiment of the present invention; and 
     FIG. 17 is a flow chart illustrating a procedure in which a base station acquires information about an available common channel in a suspended state or a null state and transmits the information over a forward common channel or a broadcast channel, and a mobile station then acquires the information, according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will be described herein below 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. 
     In an embodiment, a common channel is managed by two methods. In the first operating method, access environment information (i.e., frame size and data rate) of a common channel are transmitted to a mobile station; when the data rate of the common channel increases, the frame size is either reduced to decrease an access delay or increased to transmit a large amount of data. In the second operating method, access environment information is not previously transmitted to the mobile station, so the mobile station has to perform simultaneous management of incoming data rates and frame sizes. 
     The term “common channel” used here is not restricted to a common channel as defined in a conventional mobile communication system. In an embodiment of the present invention, forward common channels include a forward paging channel (F-PCH) and a forward common control channel (F-CCCH), and reverse common channels include a reverse access channel (R-ACH) and a reverse common control channel (R-CCCH). A description of the embodiments will be made on the assumption that the common channel is a reverse access channel (R-ACH). 
     With regard to the available data rate and associated frame size of the common channel in a CDMA communication system now under standardization, 20 ms, 10 ms and 5 ms frames all can be transmitted over the common channel at a data rate of 38.4 Kbps; 20 ms and 10 ms frames can be transmitted at a data rate of 19.2 Kbps; and only a 20 ms frame can be transmitted at a data rate of 9.6 Kbps. Table 1 below shows available data rates and associated frame sizes of the common channel. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 20 ms 
                 10 ms 
                 5 ms 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 38.4 Kbps 
                 O 
                 O 
                 O 
               
               
                   
                 19.2 Kbps 
                 O 
                 O 
               
               
                   
                  9.6 Kbps 
                 O 
               
               
                   
                   
               
             
          
         
       
     
     Reference will now be made to a slot structure for a reverse common channel according to variations in a data rate and a frame size. 
     FIG. 1 illustrates the reverse slot structure commonly used in a CDMA communication system. Referring to FIG. 1, prior to starting transmission of an access channel message  120 , a preamble  110  is transmitted for a predetermined time and then a pilot channel message is transmitted with reduced transmission power as shown by  130 . Here, the transmission period of the preamble  110  is assumed to be N*1.25 ms. The preamble  110  and a reverse pilot channel  130  can be generated by either the same sequence generator or separate sequence generators. The reverse pilot channel signal  130  is utilized for channel estimation and sync tracing for a reverse link, and may include forward pilot information. The reason that the preamble  110  is transmitted at a transmission power higher than that of a reverse pilot channel  130 , is to facilitate preamble detection and sync acquisition at the base station. The message capsule  120  is the portion containing a message and data to be transmitted from a mobile station to a base station. 
     When mobile stations using the same long code simultaneously transmit messages through the reverse common channel, a message contention occurs on the channel, so that the messages to be transmitted may be lost. This method is called contention-based random access. 
     When message contention occurs on the reverse common channel, the mobile station re-attempts access of the reverse common channel. In this case, each mobile station transmits a message over the reverse common channel, using a selected long code. If contention occurs again, each mobile station detects occurrence of this contention in a little time and retransmits the data after a lapse of a predetermined time period. In addition, the mobile station attempts an access to a base station at an initially determined transmission power, and re-attempts an access at increased transmission power when an acknowledge signal is not received from the base station. Attempted access of the reverse access channel is repeated a predetermined number of times. When the access finally fails, the procedure is performed again from the beginning. Such message transmission through the reverse common channel is performed in a predetermined time unit (i.e., an access slot). 
     Access probe control factors include persistent delay (PD), sequence backoff (RS), probe backoff (RA) and acknowledge response timeout (TA). The persistent delay (PD) is the time period prior to the initial access attempt; the sequence backoff (RS) is the time period between access sequences; and the probe backoff (RA) is the time between access probes. The acknowledge response timeout is the expected time period from when a message is transmitted at one slot to when an acknowledge is received. An important factor affecting the above factors is an interval between access slots. 
     FIG. 2 illustrates a reverse access slot structure for various frame sizes to be used according to an embodiment of the present invention. 
     Referring to FIG. 2, when a 5 ms frame is used at a data rate of 38.4 Kbps, it transmits as much information as a 20 ms frame used at a data rate of 9.6 Kbps. The reverse access slot structure shown in FIG. 2 is identical to the conventional one in that it is comprised of a preamble  210  and a message capsule. However, when the permissible frame length becomes shorter, the access slot size is also reduced, causing a decrease in the access time interval of the system. Therefore, the frequency of simultaneous access probes is decreased and the probability of successful access are increased. Since the access interval control factors are determined on the basis of the access slot size, a decrease in size of the access slot causes a decrease in the access probe interval, thereby reducing access time and increasing the probability of successful access. 
     FIG. 3 illustrates a reverse access slot having various data rates for a 20 ms frame according to an embodiment of the present invention. When a 20 ms frame is used at a data rate of 38.4 Kbps while maintaining the same access slot size (as shown on the top of FIG.  3 ), the reverse access channel can transmit information 4 times as much as when a 20 ms frame is used at a data rate of 9.6 Kbps (as shown on the bottom of FIG.  3 ). 
     FIG. 4 illustrates a reverse access slot having various data rates for a 10 ms frame according to an embodiment of the present invention. In FIG. 4, a 10 ms frame is shown at the data rates of 38.4 Kbps and 19.2 Kbps. 
     In order to fully exploit the advantages of the various channel structures and frame sizes presented above, they should be combined in various ways. Table 2 shows available frame sizes according to data rates in a common channel. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 38.4 Kbps 
                 19.2 Kbps 
                 9.6 Kbps 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Code CH Set 1 
                 O 
                   
                   
               
               
                   
                  (5 ms Reference Slot) 
               
               
                   
                 Code CH Set 2 
                 O 
                 O 
               
               
                   
                 (10 ms Reference Slot) 
               
               
                   
                 Code CH Set 3 
                 O 
                 O 
                 O 
               
               
                   
                 (20 ms Reference Slot) 
               
               
                   
                   
               
             
          
         
       
     
     With regard to a first common channel operating method, the data rate used can be selected out of 38.4, 19.2 and 9.6 Kbps, and one of 5 ms, 10 ms and 20 ms frames can be used according to the data rate, as shown in Table 2. In addition, code channel sets can be either separately managed or simultaneously managed for forward and reverse code channels. 
     When the common channels are independently managed according to slot lengths as stated above, a mobile station requiring a prompt access can reduce access delay by attempting an access through a reverse code channel which uses an access slot based on a 5 ms frame, thereby decreasing access delay and increasing the probability of a successful access. 
     The above reverse channel structure can be realized in various methods. 
     First, as shown in FIG. 9A, the channel set to be used to attempt a mobile station access is periodically transmitted by the base station through a forward common channel configuration message  910  which includes the frame size and data rate of each channel. A procedure for transmitting the message  910  is shown in FIG.  17 . 
     FIG. 9A illustrates a broadcast message of common channel information transmitted periodically over a forward common channel. FIG. 17 illustrates the procedure by which a base station acquires information about an available common channel in a suspended state or a null state, transmits the information over a forward common channel or a broadcast channel, and a mobile station then acquires the information, according to an embodiment of the present invention. The common channel information to be transmitted to the corresponding mobile station is transmitted through a paging slot corresponding to each mobile station in a forward common channel or a broadcast channel, and each mobile station acquires common channel information to use through the common channel configuration message at the corresponding slot. 
     A possible scenario will be described with reference to FIG. 17. A base station detects a null state or a suspended state in step  1711 . Thereafter, in step  1712 , the base station determines the data rate and frame length of an available common channel in order to control them to be suitable for a resource condition in a cell, user class, or QoS (Quality of Service) parameter. Thereafter, in step  1713 , available common channel constituent information is added to a message on a forward common channel or a broadcast channel. In step  1714 , the message containing information about available channel sets is sent to each mobile station through the paging channel of the mobile station. Upon receipt of an acknowledge signal from a reverse common channel in step  1715 , the base station ends the procedure. 
     Therefore, the base station transmits available common channel constituent information through a forward common channel or a broadcast channel. Upon receipt of the broadcast information, the mobile station attempts transmission of the next reverse common channel message through the code channel designated by the base station, completing the step  1715 . A forward common channel used during initial cell entrance, uses a fixed frame size. For example, a method can be used, which acquires system information through a forward common channel using a 20 ms frame and then instructs use of an appropriate common channel. 
     The above common channel operating method will be referred to as the first operating method. 
     Second, as shown in FIG. 9B, a data service state notices a code channel set for the common channel, to be used later, through a message transitioning from a control hold state to a suspended state, and this procedure is shown in FIG.  16 . 
     FIG. 9B illustrates a message of common channel information transmitted over a dedicated control channel during a state transition in a CDMA communication system. FIG. 16 illustrates a procedure in which a base station acquires information about an available common channel during a transition to a suspended state and transmits the information over a dedicated control channel, and a mobile station then acquires the information, according to an embodiment of the present invention. 
     Referring to FIG. 16, a base station detects a transition from a control hold state to a suspended state in step  1611 . Thereafter, in step  1612 , the base station determines an available common channel. When the available common channel is determined, the base station transmits a broadcast message containing information about the available common channel together with a channel release message, in steps  1613  and  1614 . Thereafter, when an acknowledge message is received in step  1615 , the base station ends the procedure. 
     When a mobile communication system provides a packet data service, the system transitions between states as shown in FIG. 14, for effective use of resources. When a transition occurs from the control hold state to the suspended state, every dedicated control channel is released. Thereafter, to restart data transmission, a message for re-assigning the dedicated channel is exchanged over a common channel. Information about the common channel to be used at this time is added to the dedicated control channel release message and then sent to a mobile station. Alternatively, when a high speed common channel is not used according to a power condition of the mobile station, the mobile station can inform the base station of the data rate of the available channel through an acknowledge message. 
     The above common channel operating method will be referred to as the second operating method. 
     Third, every set of the common channels shown in Table 2 is simultaneously used. In this case, a process for determining a forward common channel and determining a paging slot should always be performed for all of the 3 code channel sets during entrance to a cell. At this point, determination of the common channel to be used, is made depending on a characteristic of the resource condition or service type of the mobile station and the base station, or the size of data to be transmitted at one slot. 
     The above common channel operating method will be referred to as the third operating method. 
     In general, the size of a message which can be transmitted over a common channel at one access slot is appointed during cell entrance, and a unique number is assigned to data or a message in the unit of size which can be transmitted at one access slot. A parameter used at this time is based on the number of frames. When several frame sizes are available as in an embodiment of the present invention, the size of the data or message, which can be transmitted with a variable size, is diversified. However, there may be a case where the maximum quantity of transmission data, appointed on the assumption of high speed transmission, cannot be satisfied. Therefore, when a mobile station uses the common channel at a low rate in a state where the reverse common channel cannot be used as a high data rate, a function for re-assigning unique numbers according to the transmittable slot sizes should be added to the functions of the medium access control layer. 
     Now, a description will be made with regard to hardware structures according to the operating methods stated above. The description will be made with reference to the first and second operating methods. 
     FIGS. 5 to  8  illustrate transceivers of a base station and a mobile station according to the above operating methods. More specifically, FIG. 5 is a block diagram illustrating a base station transmitter. In the first and second operating methods, the mobile station is previously notified of the operating environments of a common channel through a forward common channel. FIG. 6 is a block diagram illustrating a mobile station receiver corresponding to the base station transmitter. FIG. 7 is a block diagram illustrating a mobile station transmitter, and FIG. 8 is a block diagram illustrating a base station receiver corresponding to the mobile station transmitter. 
     FIG. 5 illustrates a base station transmitter according to an embodiment of the present invention, where the elements unconcerned with this embodiment of the present invention are not shown for the sake of simplicity. 
     Referring to FIG. 5, an upper layer protocol part (or controller)  510  refers to an entire upper module of the physical layer. Upon receipt of a message or data transferred from the upper layer protocol part  510  according to a transmission environment, SAR (Segmentation And Reassembly) and framing parts  520 ,  521  and  522  segment the message or data to be suitable for a frame of the physical layer. When the slots are fixed according to the respective channels in the above devices, the SAR and framing part  522  outputs a 5 ms frame and provides it to an encoder  530 ; the SAR and framing part  521  outputs a 10 ms frame and provides it to an encoder  531 ; and the SAR and framing part  520  outputs a 20 ms frame and provides it to an encoder  532 . Here, a channel for transmitting the 5 ms frame can have a data rate of 38.4 Kbps, a channel for transmitting the 10 ms frame can have data rates of 38.4 Kbps and 19.2 Kbps, and a channel for transmitting the 20 ms frame can have data rates of 38.4 Kbps, 19.2 Kbps and 9.6 Kbps. In the above devices, to reduce access delay, a smaller frame and a higher data rate are used, and to transmit large amount of data, a larger frame is used. The encoders  530 ,  531  and  532  are general channel encoders for detecting and correcting an error on a communication channel. Since the above operating methods can use various data rates for one channel, repeaters  540  and  541  perform repetition so as to match data of a low rate to a size of a predetermined physical frame. Interleavers  550 ,  551  and  552  interleave received coded data to randomize burst errors. Mixers  560 ,  561  and  562  multiply outputs of the associated interleavers  550 ,  551  and  552  by Walsh codes Wc 1 , Wc 2  and Wc 3 , respectively, to generate orthogonally spread signals. The orthogonally spread signals are multiplied by a PN sequence for spreading and then converted to RF (Radio Frequency) signals for transmission. The data rate of each channel is controlled to be suitable for the cell condition of each base station, and controlled, by a control part, to be suitable for a data rate of each module. The determined data rate and frame size are simultaneously transmitted to a mobile station. 
     FIG. 6 illustrates a schematic block diagram of a mobile station receiver according to an embodiment of the present invention, wherein the elements unconcerned with this embodiment are not shown for the sake of simplicity. 
     Referring to FIG. 6, signals received at a mobile station are input to mixers  670 ,  671  and  672  after PN despreading at an RF receiving stage (not shown). The mixers  670 ,  671  and  672  multiply the PN despread signals by associated outputs of Walsh code generators  660 ,  661 , and  662 , which are identical to those used in the base station, to extract only the signals transmitted to the mobile station. The signals output from the mixers  670 ,  671  and  672  are deinterleaved by deinterleavers  650 ,  651  and  652 , respectively. Decoders  640 ,  641  and  642  are channel decoders for decoding the deinterleaved signals. Rate decision parts  630  and  631  determine data rates using the deinterleaved signals, and a 5 ms frame receiver does not require a rate decision part because the data rate for the 5 ms frame is fixed at 38.4 Kbps. Therefore, the rate decision part  640  should be able to distinguish the data rates of 38.4 Kbps and 19.6 Kbps, and the rate decision part  641  should be able to distinguish the data rates of 38.4 Kbps, 19.6 Kbps and 9.6 Kbps. 
     However, since the forward common channel operates in a slotted mode to reduce power consumption of a mobile station, whether to use a short slot can be determined according to a condition of the mobile station or a service type. 
     FIG. 7 illustrates a mobile station transmitter according to an embodiment of the present invention, wherein the elements unconcerned with this embodiment are not shown for the sake of simplicity. 
     Referring to FIG. 7, an upper layer protocol part (or controller)  710  refers to an entire upper module of the physical layer. Upon receipt of a message or data transferred from the upper layer protocol part  710  according to a transmission environment, SAR and framing parts  720 ,  721  and  722  segment the message or data to be suitable for a frame of the physical layer. A channel for transmitting the 5 ms frame can have a data rate of 38.4 Kbps, a channel for transmitting the 10 ms frame can have data rates of 38.4 Kbps and 19.2 Kbps, and a channel for transmitting the 20 ms frame can have data rates of 38.4 Kbps, 19.2 Kbps and 9.6 Kbps. The SAR and framing part  722  outputs a 5 ms frame and provides it to an encoder  730 ; the SAR and framing part  721  outputs a 10 ms frame and provides it to an encoder  731 ; and the SAR and framing part  720  outputs a 20 ms frame and provides it to an encoder  732 . 
     The encoders  730 ,  731  and  732  are general channel encoders for detecting and correcting an error on a communication channel. Repeaters  740  and  741  perform repetition so as to match data of a low rate to the size of a physical frame. Interleavers  750 ,  751  and  752  interleave coded data to randomize burst errors. Mixers  770 ,  771  and  772  multiply transmission signals output from the associated interleavers  750 ,  751  and  752  by long codes for the respective code channels, respectively, and output the signals to an RF stage (not shown). A data rate and a frame size of the reverse common channel are transmitted by a base station as a common channel configuration message over a forward common channel. 
     FIG. 8 illustrates a schematic block diagram of a base station receiver according to an embodiment of the present invention, wherein the elements unconcerned with this embodiment are not shown for the sake of simplicity. 
     Referring to FIG. 8, signals received at a base station are input to mixers  870 ,  871  and  872  through an RF receiving stage (not shown). The mixers  870 ,  871  and  872  multiply the received signals by associated outputs of a long code generator  860 , which are identical to those used in the mobile station, to extract only the signals transmitted to the base station. The signals output from the mixers  870 ,  871  and  872  are deinterleaved by deinterleavers  850 ,  851  and  852 , respectively. Decoders  840 ,  841  and  842  are channel decoders for decoding the deinterleaved signals. Rate decision parts  830  and  831  determine data rates using the deinterleaved signals, and a 5 ms frame receiver does not require a rate decision part because the data rate for the 5 ms frame is fixed at 38.4 Kbps. Therefore, the rate decision part  840  should be able to distinguish the data rates of 38.4 Kbps and 19.6 Kbps, and the rate decision part  841  should be able to distinguish the data rates of 38.4 Kbps, 19.6 Kbps and 9.6 Kbps. 
     The first operating method and the reverse channel structure can be realized in various methods. 
     First, in FIG. 9A, the data rate and frame size of a common channel to be used to attempt an access is periodically transmitted through a forward common channel configuration message  910 . At this point, each mobile station receives the message through its corresponding paging slot. A base station adds the forward common channel configuration message  910  to a forward common channel or a forward broadcast channel in the null state or the suspended state, so as to be suitable for the resource condition in the cell, the user class or the QoS parameter, and notifies a data rate and an access slot size of a common channel to be used through each broadcast message. A mobile station attempts the next transmission of a reverse common channel using the code channel transmitted from the base station. The forward common channel used during initial cell entrance uses a fixed data rate and the fixed size of an available slot. 
     Second, as shown in FIG. 9B, a message containing a data rate and a frame size for the common channel, to be used later, is transmitted when the data service state is transitioning from a control hold state to a suspended state. When a mobile communication system provides a packet data service, the system transitions between states for effective use of the resources. When a transition occurs from the control hold state to the suspended state, every dedicated control channel is released. Thereafter, to restart data transmission, a message for re-assigning the dedicated channel is exchanged over a common channel. Information about the common channel to be used at this time is added to a dedicated control channel release message and then sent to a mobile station. Alternatively, when a high speed common channel is not used according to a power condition of the mobile station, the mobile station can transmit the data rate of the available channel to the base station through an acknowledge message. 
     FIGS. 10 to  13  illustrate cases where the access slot size is fixed to one value according to data rates. When a channel is managed in this method, repeaters are not required in the transmitter and rate decision parts in the receiver. FIGS. 10 to  13  show the transceivers of a mobile station and a base station with the repeaters and rate decision parts removed. The transceivers operate in the same manner as in FIGS. 5 to  8 , except for the repeaters and rate decision parts. 
     FIG. 10 is a block diagram illustrating a base station transmitter when frame sizes are fixed according to data rates of the channels when the first and second operating methods are used, wherein the elements unconcerned with this embodiment of the present invention are not shown for simplicity. 
     Referring to FIG. 10, an upper layer protocol part (or controller)  1010  refers to an entire upper module of the physical layer. Upon receipt of a message or data transferred from the upper layer protocol part  1010  according to the transmission environment, SAR and framing parts  1020 ,  1021  and  1022  segment the message or data to be suitable for a frame of the physical layer. When the sizes of the frames generated from the SAR and framing parts  1020 ,  1021  and  1022  are fixed according to data rates, the SAR and framing part  1022  outputs a 5 ms frame and provides it to an encoder  1030 ; the SAR and framing part  1021  outputs a 10 ms frame and provides it to an encoder  1031 ; and the SAR and framing part  1020  outputs a 20 ms frame and provides it to an encoder  1032 . Here, the 5 ms frame is transmitted only at 38.4 Kbps, the 10 ms frame is transmitted only at 19.6 Kbps, and the 20 ms frame is transmitted only at 9.6 Kbps. 
     When the frame size is fixed at 20 ms regardless of the data rate as stated above, the frames are transferred to the encoders  1032 ,  1031  and  1030  and can be transmitted at 38.4 Kbps, 19.2 Kbps and 9.6 Kbps, respectively. When the frame size is fixed to 10 ms, the frames are transferred to the encoders  1032  and  1031  and can be transmitted at 38.4 Kbps and 19.2 Kbps, respectively. Further, when frame size is fixed to 5 ms, the frames are transferred to the encoder  1032  and can be transmitted at 38.4 Kbps. 
     The encoders  1030 ,  1031  and  1032  are general channel encoders for detecting and correcting an error on a communication channel. The other structures are identical to those in FIG. 5, except that a different set of the orthogonal codes are multiplied according to the data rates. 
     FIG. 11 is a block diagram of a mobile station receiver which receives a signal transmitted from the base station transmitter of FIG. 10 according to an embodiment of the present invention, wherein the elements unconcerned with this embodiment are not shown for the sake of simplicity. 
     Referring to FIG. 11, signals received at a mobile station are input to mixers  1160 ,  1161  and  1162  through an RF receiving stage (not shown). The mixers  1160 ,  1161  and  1162  multiply the received signals by associated outputs of Walsh code generators  1150 ,  1151 , and  1152 , which are identical to those used in the base station, to extract only the signals transmitted to the mobile station. The signals output from the mixers  1160 ,  1161  and  1162  are deinterleaved by deinterleavers  1140 ,  1141  and  1142 , respectively. Since the data rates were determined according to the channels, rate decision parts are not required after decoders  1130 ,  1131 , and  1132 . 
     Since the forward common channel operates in a slotted mode to reduce the power consumption of mobile stations, whether to use a short slot can be determined according to a condition of a mobile station or a service type. 
     FIG. 12 illustrates a mobile station transmitter which fixes frame sizes according to data rates of the channels, wherein the elements unconcerned with this embodiment of the present invention are not shown for the sake of simplicity. 
     Referring to FIG. 12, an upper layer protocol part (or controller)  1210  refers to an entire upper module of the physical layer. Upon receipt of a message or data transferred from the upper layer protocol part  1210  according to a transmission environment, SAR and framing parts  1220 ,  1221  and  1222  segment the message or data to be suitable for a frame of the physical layer. The other structures are identical to those in FIG. 10, except that long codes are used in place of the orthogonal codes. 
     FIG. 13 illustrates a base station receiver which receives a signal transmitted from the mobile station transmitter of FIG. 12 according to an embodiment of the present invention, wherein the elements unconcerned with this embodiment are not shown for the sake of simplicity. 
     Referring to FIG. 13, signals received at a base station are input to mixers  1360 ,  1361  and  1362  through an RF receiving stage (not shown). The mixers  1360 ,  1361  and  1362  multiply the received signals by associated outputs of a long code generator  1350 , which are identical to those used in the mobile station, to extract only the signals transmitted to the base station. The other structures are identical to those in FIG.  11 . 
     As described above, this novel method decreases access delay using a common channel supporting various data rates and frame sizes resulting in an increase in the probability of a successful access. In addition, it is possible to transmit data or a message having various frame sizes in one access slot. 
     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.