Abstract:
A reverse transmission controlling method in a mobile communication system. After receiving forward information commanding a reverse data rate change on a forward channel from a base station, a mobile station increases its reverse data rate to a data rate equal to or lower than a maximum data rate if the forward information commands a reverse data rate increase, determines whether the increased data rate can be further increased for the next frame, and transmits the determination result with information representing the increased data rate to the base station.

Description:
PRIORITY  
       [0001]    This application claims priority to an application entitled “Method of Controlling Reverse Transmission in a Mobile Communication System” filed in the Korean Industrial Property Office on Mar. 29, 2001 and assigned Serial No. 2001-16660, the contents of which are hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a transmission controlling method in a mobile communication system, and in particular, to a method of controlling reverse transmission.  
           [0004]    2. Description of the Related Art  
           [0005]    With the phenomenal growth of mobile communication technology, many different mobile communication systems have been proposed and are currently being field-tested. These systems generally operate based on CDMA (Code Division Multiple Access) and a 1 xEV-DO (1 x Evolution-Data Only) system called HDR (High Data Rate), designed to carry out high-rate data transmission dedicatedly.  
           [0006]    Similarly to other systems, 1 xEV-DO systems also require appropriate scheduling to efficiently transmit packet data on the forward and reverse links. “The forward link” is a link directed from a base station to an access terminal (AT) and “a reverse link” is the opposite link. For forward data transmission, the base station transmits data to a particular AT in the best channel condition, considering the air link statuses between the base station and 1 xEV-DO ATs and other environments, resulting in a maximized data transmission throughput for the AT. Concerning reverse data transmission, a plurality of ATs access the base station simultaneously. In this situation, the base station controls overload within reverse link capacity by appropriately controlling congestion and data flows from the ATs.  
           [0007]    Besides the 1 xEV-DO systems, other mobile communication systems designed to support multimedia service must also manage reverse data transmission efficiently. To do so, system performance and capacity must be ensured.  
           [0008]    In the existing 1 xEV-DO systems, an AT carries out reverse data transmission based on an RAB (Reverse Activity Bit) and an RRL (ReverseRateLimit) message received from a base station, and tells the base station its variable data rate via an RRI (Reverse Rate Indicator). The RRI indicates to the base station the data rate at which the reverse traffic data is being sent. The base station transmits the following time-multiplexed channels to the AT: a forward MAC (Medium Access Control) channel, a pilot channel, an FAB (Forward Activity Bit) channel and an RAB channel. The RAB represents the congestion degree of the reverse link and a data rate available to the AT varies according to the RAB. The base station controls a data flow from the AT by commanding an increase/decrease in the reverse data rate using the RAB to control the overload and capacity of the reverse link. Since the RAB is broadcast to a plurality of ATs, the ATs receiving the RAB increase their data rates or reduce them uniformly according to the RAB. The transmission time (or transmission period) of the RAB is determined by Equation (1):  
             T mod RABlength . . .    (1)  
           [0009]    where T is system time and RABlength is the length of the RAB expressed in the number of slots. Table 1 below lists binary values representing RAB lengths. The base station transmits one of the binary values to the ATs and then the ATs calculate a slot time they receive the RAB on a forward MAC channel (F-MAC channel) using the received RABlength information and the system time.  
                           TABLE 1                                   Binary   Length (slots)                           00    8           01   16           10   32           11   64                      
 
           [0010]    An AT receives a persistence vector defined in a message from the base station at or during a connection. When RAB=0, the persistence vector is set to increase the reverse data rate and when RAB=1, it is set to decrease the reverse data rate. Using the persistence vector, the AT performs a persistence test. If the persistence test is passed, the AT will either increase the reverse data rate or reduce it. If the persistence test is failed, then the AT maintains the reverse data rate.  
           [0011]    To describe in detail, if the RAB is 0 and the persistence test is passed, the reverse data rate is increased. On the contrary, if the RAB is 1 and the persistence is passed, the reverse data rate is reduced. The success or failure of the persistence test depends on whether a generated random number satisfies a desired condition. Since the reverse data rate varies with uncertainty in probability terms, the base station does not know how many ATs increase/decrease their data rates. Time delay occurs on the reverse link until a high capacity state is transitioned to a full utilization state. In the reverse link full utilization state, overload and underload alternate. However, the base station cannot know how serious the overload or underload condition because the base station simply transmits an RAB and the ATs increase/decrease their data rates according to the results of persistence tests.  
           [0012]    If the overload condition becomes serious, it leads to the increase of reverse data loss. On the other hand, if the underload condition becomes serious, the use efficiency of reverse channels is dropped. Therefore, there is a need for exploring a method of rapidly reaching the reverse link full utilization state and a method of increasing the use efficiency of reverse channels, while preventing the occurrence of overload in the base station.  
           [0013]    [0013]FIG. 1 is a flowchart illustrating a reverse data rate controlling procedure for an AT in an existing 1 xEV-DO system.  
           [0014]    The AT sets its lowest available data rate at an initial reverse data transmission. If the current data rate is lower than a data rate provided in an RRL message received from a base station, the AT transmits data at the provided data rate after 32 slots (53.33ms). On the other hand, if the current data rate is higher than the provided data rate, the AT transmits data at the provided data rate. For the subsequent reverse transmission, the AT determines its data rate by the procedure illustrated in FIG. 1. The RRL message is transmitted to the AT in determining an initial reverse data rate and resetting the reverse data rate.  
           [0015]    After determining its data rate, the AT reports its data rate to the base station by an RRI symbol as shown in Table 2. The reverse data rate is selected among 4.8, 9.6, 19.2, 38.4, 76.8 and 153.6 kbps. This reverse data rate is reset by a message such as an RRL message or an RAB message received from the base station. Table 2 below lists RRI mappings in the 1 xEV-DO system.  
                           TABLE 2                                   Data rate (kbps)   RRI symbol                            4.8   001            9.6   010           19.2   011           38.4   100           76.8   101           153.6    110                      
 
           [0016]    The base station determines the data rate of the AT from the RRI symbols as shown in Table 2 and controls the AT to reset its data rate. To aid the AT in resetting its data rate, the base station should transmit an RRL message as shown in Table 3 to the AT.  
                                                       TABLE 3                                   Field   Length (bits)                           Message ID   8                29 occurrences of the following two fields                    RateLimitIncluded   1           RateLimit   0 or 4           Reserved   Variable                      
 
           [0017]    The RRL message is forward directed to control a reverse data rate. Upon receipt of the RRL message, the AT resets the reverse data rate by comparing the current reverse data rate with a data rate set in the RRL message. 29 records may be inserted in the above RRL message and each record indicates a data rate assigned to a corresponding MACindex among MACindexes 3 to 31. In Table 3, Message ID indicates the ID of the RRL message. RateLimitlncluded is a field indicating whether RateLimit is included in the RRL message. If RateLimit is included, RateLimitlncluded is set to 1 and otherwise, it is set to 0. RateLimit indicates a data rate assigned to a corresponding AT. The base station assigns data rates shown in Table 4 to ATs using four bits.  
                                         TABLE 4                                       0 × 0    4.8 kbps           0 × 1    9.6 kbps           0 × 2   19.2 kbps           0 × 3   38.4 kbps           0 × 4   76.8 kbps           0 × 0   153.6 kbps                 All other values are invalid                          
 
           [0018]    During reverse data transmission, the AT monitors a F-MAC channel from the base station, especially the RAB on the F-MAC channel, and adjusts its current data rate by performing a persistence test.  
           [0019]    Referring to FIG. 1, the AT monitors the RAB of an F-MAC channel from a base station included in the active set of the AT in step  100  and determines whether the RAB is 1 in step  102 . If the AT has six sectors/base stations in its active set, it determines whether at least one of the RABs of the F-MAC channels received from the six sectors/base stations is 1. If at least one RAB is 1, the AT proceeds to step  112  and otherwise, it goes to step  104 .  
           [0020]    The case where all RABs=0 will be considered first.  
           [0021]    If the RAB is 0, the AT performs a persistence test in step  104 . The persistence test is available when the base station broadcasts the RAB to a plurality of ATs to control the amount of reverse data from the ATs. The persistence test is passed or failed depending on whether a generated random number satisfies a desired condition.  
           [0022]    If the persistence test is passed in step  104 , the AT increases its data rate (TX rate) in step  106 . On the contrary, if the persistence test is failed, the AT jumps to step  120 . The AT increases the TX rate in step  106  and compares the increased TX rate with a maximum allowed data rate (a max TX rate) in step  108 . If the increased TX rate is higher than the max TX rate, the AT sets the TX rate to the max TX rate in step  110  and goes to step  120 . If, in step  108 , the increased TX rate is not higher than the max TX rate, the AT goes directly to step  120   
           [0023]    Now, the case where at least one RAB=1 will be considered.  
           [0024]    If the RAB is 1 in step  102 , the AT performs a persistence test in step  112 . If the persistence test is failed, the AT jumps to step  120 . If the persistence test is passed, the AT decreases the TX rate in step  114  and compares the decreased TX rate with a minimum data rate (a min TX rate) in step  116 . If the decreased TX rate is lower than the min TX rate, the AT goes to step  118  and otherwise, it jumps to step  120 . The AT sets the TX rate to the min TX rate in step  118  and goes to step  120 . The min TX rate can be a default data rate of 9.6 kbps or a data rate designated by some message at a call connection.  
           [0025]    In step  120 , the AT generates an RRI symbol corresponding to the set TX rate. The AT transmits the RRI symbol along with traffic data only if a traffic connection is opened between the base station and the AT. If the traffic connection is not opened, it transmits only the RRI symbol.  
           [0026]    [0026]FIG. 2 is a diagram illustrating data transmission/reception between an AT and an HDR sector included in the active set of the AT. As illustrated in FIG. 2, F- and R-traffic channels, and F- and R-MAC channels have been established between the AT and sector  1  with a connection opened between them. No F-traffic channels are assigned to the AT from sector  2  (up to sectors  2  to  6 ) with no connection opened between them. In the 1 xEV-DO system, the AT can maintain up to six sectors/base stations in its active set. Therefore, to determine its TX rate, the AT monitors F-MAC channels from all the sectors of the active set, especially RABs on the F-MAC channels.  
           [0027]    Upon receipt of at least one RAB set to 1, the AT performs a persistence test to decrease its TX rate. In the persistence test, the AT generates a random number and compares it with a persistence vector defined by the base station at or during a connection. If the random number satisfies a desired condition, the AT determines that the persistence test is passed. The AT then decreases the TX rate. On the contrary, if the persistence test is failed, the AT maintains the TX rate. If the TX rate is lower than a min TX rate, the AT sets the TX rate at the min TX rate. Meanwhile, if all the RABs are set to 0 and a persistence test is passed, then the TX rate is increased. If the persistence test is failed, the AT maintains the TX rate. If the TX rate becomes higher than a max TX rate, the AT sets the TX rate to the max TX rate. Also, in the case where the AT is limited in transmission power, it maintains the TX rate. The RAB that functions to increase a reverse data rate or reduces it is broadcast to ATs in TDM with an FAB on a forward common channel, i.e., a F-MAC channel. The ATs increase/decrease their data rates uniformly according to the RAB.  
           [0028]    From the system&#39;s perspective, the above-described reverse transmission controlling method for the current 1 xEV-DO systems simplifies bandwidth control and overhead control. However, the uniform control without considering the individual statuses of ATs brings about a bandwidth waste and decreases the data transmission efficiency of the ATs.  
           [0029]    Moreover, a long time delay is involved in reaching a full utilization state on the reverse link, resulting in the decrease of channel use efficiency. The occurrence of an overload may lead to reverse data loss. As a result, communication quality is deteriorated.  
         SUMMARY OF THE INVENTION  
         [0030]    It is, therefore, an object of the present invention to provide a method of rapidly reaching the full utilization state of a reverse link.  
           [0031]    It is another object of the present invention to provide a method of increasing the use efficiency of a reverse link.  
           [0032]    It is a further object of the present invention to provide a method of preventing the occurrence of an overload on a reverse link.  
           [0033]    The foregoing and other objects of the present invention are achieved by providing a reverse transmission controlling method in a mobile communication system. After receiving forward information commanding a reverse data rate change on a forward control channel from a base station, a mobile station increases its data rate to be equal to or lower than a maximum data rate if the forward information commands a reverse data rate increase, determines whether the increased data rate can be further increased for the next frame, and transmits the determination result with information representing the increased data rate to the base station.  
           [0034]    If the forward information commands a conditional reverse data rate increase, the mobile station increases its data rate to be equal to or lower than a maximum data rate based on information indicating whether a data rate increase is available that is determined at the previous frame transmission. Then, the mobile station determines whether the increased data rate can be further increased for the next frame and transmits the determination result with information representing the increased data rate to the base station.  
           [0035]    If the forward information commands a conditional data rate decrease, the mobile station decreases its data rate to be equal to or higher than a minimum data rate based on information determined at the previous frame transmission indicating whether a data rate increase is available. Then, the mobile station determines whether the decreased data rate can be increased for the next frame and transmits the determination result with information representing the increased data rate to the base station.  
           [0036]    If the forward information commands an unconditional data rate maintenance, the mobile station maintains its data rate. Then, the mobile station determines whether the maintained reverse data rate can be increased for the next frame and transmits the determination result with information representing the increased data rate to the base station.  
           [0037]    The forward information is an extended RAB. If the forward information is received from at least two base stations, a control RAB is generated from extended RABs received from the base stations. Changing the reverse data rate is determined based on the control RAB.  
           [0038]    If at least one of the extended RABs indicates a conditional decrease, the control RAB is set to indicate a conditional decrease. If none of the extended RABs indicate a conditional decrease and at least one of the extended RABs indicates an unconditional data rate maintenance, the control RAB is set to indicate an unconditional data rate maintenance. If none of the extended RABs indicate either a conditional decrease or an unconditional data rate maintenance and at least one of the extended RABs indicates a conditional increase, the control RAB is set to indicate a conditional increase. Finally, if all the extended RABs indicate an unconditional increase, the control RAB is set to indicate an unconditional increase.  
           [0039]    After receiving reverse information indicating whether a reverse data rate increase is available for the next reverse frame from a mobile station, a base station determines the highest data rate allowed to the mobile station by mobile station acquisition and characteristic analysis, generates a reverse data rate value, transmits information representing the highest data rate and the reverse data rate value to the mobile station, determines an extended RAB based on the received reverse information and the current capacity of a reverse link, and transmits the extended RAB to the mobile station.  
           [0040]    If the reverse link is in an overload state, the extended RAB is set to indicate a conditional data rate decrease. If an increase in the data rates of all mobile stations within the coverage area of the base station does not cause overload on the reverse link, the extended RAB is set to indicate an unconditional data rate increase. If the reverse link is not in an overload state and can accommodate an increase in the data rates of all the mobile stations, the extended RAB is set to indicate a conditional data rate increase. Finally, if the reverse link is not in an overload state and cannot accommodate an increase in the data rates of all the mobile stations, the extended RAB is set to indicate an unconditional data rate maintenance.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]    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:  
         [0042]    [0042]FIG. 1 is a flowchart illustrating a reverse data rate controlling method for a mobile station in a conventional mobile communication system;  
         [0043]    [0043]FIG. 2 is a diagram illustrating data transmission/reception between a mobile station and a sector included the active set of the mobile station;  
         [0044]    [0044]FIGS. 3A to  3 F are flowcharts illustrating a reverse data rate controlling method for a mobile station in a data transmission system according to an embodiment of the present invention;  
         [0045]    [0045]FIG. 4 is a flowchart illustrating a reverse data rate controlling method for a base station in the data transmission system according to the embodiment of the present invention; and  
         [0046]    [0046]FIG. 5 is a flowchart illustrating a method of generating an extended RAB for control of reverse data rates in the base station in the data transmission system according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    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.  
         [0048]    The present invention provides a reverse data rate controlling method for a mobile station (MS) and new RAB and new RRI structures for supporting the method in a system and a novel high rate data transmission system according to the present invention. A base station operation for supporting the reverse data rate controlling method is also provided. The new RAB and new RRI according to the present invention will be hereinafter referred to as an extended RAB and an extended RRI, respectively.  
         [0049]    The extended RAB is given in Table 5.  
                   TABLE 5                       RAB   Operation of MS                   00   Increase reverse link data rate depending on increase previous           persistence pre-test       01   Decrease reverse link data rate depending on decrease persistence           test       10   Increase reverse link data rate       11   Keep current reverse link data rate                  
 
         [0050]    A 1-bit RAB simply represents the increase or decrease of a reverse data rate in the conventional system, whereas the extended RAB shown in Table 5 represents the , maintenance, and decrease of a reverse data rate in the present invention.  
         [0051]    (1) Extended RAB=00  
         [0052]    A mobile station increase its data rate, only if it passed its previous increase persistence pre-test for a data rate increase in the previous frame. In this case, the reverse data rate increase is conditional.  
         [0053]    (2) Extended RAB=01  
         [0054]    A mobile station reduces its data rate, only if it has passed a decrease persistence test for a data rate decrease. In this case, the reverse data rate decrease is conditional.  
         [0055]    (3) Extended RAB=10  
         [0056]    All mobile stations increase their data rates regardless of their previous increase persistence pre-tests. That is, the reverse data rates are unconditionally increased.  
         [0057]    (4) Extended RAB=11  
         [0058]    All mobile stations keep their data rates regardless of their previous increase persistence pre-tests. That is, the reverse data rates are unconditionally maintained.  
         [0059]    [0059]FIGS. 3A to  3 F are flowcharts illustrating a reverse data rate controlling method for a mobile station in a data transmission system according to an embodiment of the present invention. Referring to FIGS. 3A to  3 F, the mobile station monitors extended RABs received on F-MAC channels from all base stations in its active set in step  300 . Only the reverse data rates that are defined by RRI symbols are available. The mobile station can maintain up to six sectors/base stations in its active set. An active set is a set of sectors/base station serving a mobile station. If a connection is opened between the mobile station and a base station in the active set, F- and R-traffic channels and a reverse power control channels are assigned to the mobile station. With no connection opened, the mobile station monitors only a control channel from the base station. The mobile station determines “a control RAB” according to a received extended RAB as follows.  
         [0060]    (Conditions)  
         [0061]    (1) If at least one of the extended RABs received from all of the base stations in the active set is 01, the control RAB is set to 01;  
         [0062]    (2) If none of the extended RABs received from all of the base stations in the active set are 01 and at least one of them is 11, the control RAB is set to 11;  
         [0063]    (3) If none of the extended RABs received from all of the base stations in the active set are either 01 or 11 and at least one of them is 00, the control RAB is set to 00; and  
         [0064]    (4) If all of the extended RABs received from all of the base stations in the active set are 10, the control RAB is set to 10.  
         [0065]    The control RAB set under the above conditions has a great influence on the capacity of a sector in the case of a reverse data rate increase.  
         [0066]    The mobile station checks the control RAB in steps  302  to  306 . If the control RAB is 00, the mobile station determines whether its previous increase persistence pre-test was passed by checking a variable PreTestRes representing the result of the increase persistence pre-test, that is, whether PreTestRes=0 in step  310  in FIG. 3 b . If the previous increase persistence pre-test was passed, the mobile station goes to step  312  and otherwise, it jumps to step  318 . The mobile station increases its TX rate in step  312  and compares the increased TX rate with a max TX rate in step  314 . If the increased TX rate is higher than the max TX rate, the mobile station proceeds to step  316  and otherwise, it goes to step  318 . In step  316  the mobile station sets the TX rate to the max TX rate and goes to step  318 . Thus, the TX rate is completely set.  
         [0067]    In step  318 , the mobile station performs an increase persistence pre-test to control the reverse TX rate for the next frame. If the increase persistence pre-test is passed, the mobile station sets the variable PreTestRes to 0 in step  320  and selects and transmits an RRI symbol representing the set TX rate in step  380  in FIG. 3 f . On the contrary, if the increase persistence pre-test is failed, the mobile station sets the variable PreTestRes to 1 in step  322  and selects and transmits an RRI symbol representing the set TX rate in step  382  in FIG. 3 f.    
         [0068]    The mobile station determines that the increase persistence pre-test is failed regardless of its real implementation in the case where the TX rate is limited by an RRL message that provides a maximum allowed data rate to each mobile station, when the mobile station has too limited transmission power to increase the TX rate, or the amount of data stored in a buffer is a threshold or less (i.e., the stored data can be transmitted without increasing the TX rate).  
         [0069]    Table 6 lists RRI mappings to reverse data rates according to the present invention.  
                                     TABLE 6                       Data   Extended RRI symbol   Extended RRI symbol       rate   (Increase persistence pre-test   (Increase persistence pre-test       (kbps)   success)   failure)                                0   0000   N/A       9.6   0001   1001       19.2   0010   1010       38.4   0011   1011       76.8   0100   1100       153.6   0101   1101       307.2   0110   1110       614.4   0111   1111       1024   N/A   1000                  
 
         [0070]    The extended RRI listed in Table 6 are a modification from the conventional RRI to indicate to the base station at what rate the reverse data is being sent. Based on the acquired reverse data rate, the base station recovers the original reverse data. The extended RRI is designed to represent the reverse data rates defined by the 1 xEVDV systems with PreTestRes set in the first field.  
         [0071]    If the control RAB is 01 in step  304 , the mobile station performs a decrease persistence test in step  330  in FIG. 3 c . If the decrease persistence test is passed, the mobile station goes to step  332  and otherwise, it jumps to step  338 . The mobile station decreases its TX rate in step  332  and compares the decreased TX rate with a min TX rate in step  334 . If the decreased TX rate is lower than the min TX rate, the mobile station proceeds to step  336  and otherwise, it goes to step  338 . In step  336  the mobile station sets the TX rate to the min TX rate and goes to step  338 .  
         [0072]    In step  338 , the mobile station performs an increase persistence pre-test to control the reverse TX rate for the next frame. If the increase persistence pre-test is passed, the mobile station sets the variable PreTestRes to 0 in step  340 , and selects an RRI symbol representing the set TX rate from a table such as Table 6 and transmits the selected RRI symbol in step  380  in FIG. 3 f . On the contrary, if the increase persistence pre-test is failed, the mobile station sets the variable PreTestRes to 1 in step  342 , and selects an RRI symbol representing the set TX rate from a table such as Table 6 and transmits the selected RRI symbol in step  382  in FIG. 3 f.    
         [0073]    The mobile station sets the variable PreTestRes to 1, determining that the increase persistence pre-test is failed regardless of its real implementation in the case where the TX rate is limited by an RRL message, when the mobile station has too limited transmission power to increase the TX rate, or the amount of data stored in a buffer is a threshold or less.  
         [0074]    If the control RAB is not 10 in step  306 , then the RAB must be 11. This implies that the current TX rate is supposed to be maintained. Hence, in step  370 , the mobile station checks the variable PreTestRes representing the result of the previous increase persistence test, which was performed to report the reverse link condition for the previous frame in FIG. 3 e . If PreTestRes is 0, that is, a TX rate increase is available, the mobile station performs an increase persistence pre-test to control the reverse TX rate for the next frame in step  372 . If the increase persistence pre-test is passed, the mobile station sets the variable PreTestRes to 0 in step  374 , and selects an RRI symbol representing the set TX rate from a table such as Table 6 and transmits the selected RRI symbol in step  380  in FIG. 3 f.    
         [0075]    On the other hand, if PreTestRes is 1 in step  370  or if the increase persistence pre-test is failed in step  372 , the mobile station sets the variable PreTestRes to 1 in step  376 , and selects an RRI symbol representing the set TX rate from a table such as Table 6 and transmits the selected RRI symbol in step  382  in FIG. 3 f . The reason for performing an increase persistence pre-test only in a mobile station with PreTestRes=0 despite a TX rate maintenance command by an extended RAB is to preserve the reverse link capacity.  
         [0076]    [0076]FIG. 4 is a flowchart illustrating a reverse data rate controlling method for a base station in the high rate data transmission system according to the embodiment of the present invention.  
         [0077]    Referring to FIG. 4, upon receipt of connection open requests from mobile stations, the base station carries out mobile station acquisition in step  400  and analyzes the characteristics of the mobile stations in step  402 . In step  404 , the base station analyses the characteristics of reverse traffic received from the mobile stations, that is, determines QoS (Quality of Service) of packet data services requested by the mobile stations. In steps  406 , the base station sets MACindex fields by which the mobile stations are identified. The base station sets RateLimit fields that limit the data rates of the mobile stations based on the characteristics of the mobile stations and their application services in step  408 . Then the base station assembles the RRL message with Message ID and other related message fields for transmission in the air in step  412  and transmits the RRL message to the mobile stations in step  414 .  
         [0078]    In step  416 , the base station receives PreTestRes information indicating whether a reverse data rate increase is available for the next frames from the mobile stations and analyzes the PreTestRes information. The base station checks the current reverse channel conditions and generates an RAB according to the reverse channel conditions in step  418  and broadcasts the RAB to the mobile stations in step  420 . If one RAB is set for each mobile station, the RAB may not be broadcast but must be transmitted to only the corresponding mobile station.  
         [0079]    [0079]FIG. 5 is a flowchart illustrating a method of generating an extended RAB for control of reverse data rates in the base station in the rate data transmission system according to the embodiment of the present invention.  
         [0080]    Referring to FIG. 5, the base station determines whether the reverse link is currently in an overload state in step  500 . In an overload state, the base station sets the extended RAB to 01 in step  512 . This implies that a corresponding mobile station sets a control RAB to 01 and decreases its TX rate according to a decrease persistence test.  
         [0081]    If the current reverse link is not in an overload state in step  500 , the base station determines whether the current reverse link is a low load state in step  502 . In a low load state, the base station sets the extended RAB to 10.  
         [0082]    If the current reverse link is not in a low load state in step  502 , the base station checks PreTestRes information received from mobile stations to determine whether overload will occur at the next reverse transmission in step  504 . If overload is expected, the base station sets the extended RAB to 11 in step  508 . If no overload is expected, the base station sets the extended RAB to 00 in step  506 . The set extended RAB is broadcast or transmitted to a corresponding mobile station only.  
         [0083]    While the embodiment of the present invention has been described in the context that one mobile station uses one radio traffic channel, it can be further contemplated in other embodiments that one mobile station uses two radio traffic channels.  
         [0084]    1) Use of one 2-bit RAB and one 7-bit RRI symbol.  
         [0085]    By representing each of the data rates of the two reverse traffic channels using one bit of the RAB, the data rates are increased/maintained/decreased simultaneously. The result of an increase persistence pre-test is represented by one bit of the RRI symbol (e.g., MSB). Three of the remaining bits of the RRI symbol are assigned to the data rate of a first reverse traffic channel and the other three bits, to the data rate of a second reverse traffic channel. The reverse data rates are increased/decreased according to the result of the increase persistence pre-test on the two reverse traffic channels and the common RAB.  
         [0086]    (2) Use of one 2-bit RAB and one 8-bit RRI symbol.  
         [0087]    While the RAB applies commonly to the two reverse traffic channels, an increase persistence pre-test is performed independently for each of the reverse traffic channels. Therefore, the reverse data rates are changed individually. Two bits of the RRI symbol are assigned to the respective results of the increase persistence pre-tests for the reverse traffic channels. The other six bits of the RRI symbol are equally separated to be assigned to the data rates of the reverse traffic channels. The reverse data rates are increased/decreased according to the results of the increase persistence pre-tests and the common RAB.  
         [0088]    (3) Use of Two 2-bit RABs and one 7-bit RRI symbol.  
         [0089]    One RAB is assigned for each of the reverse traffic channel. Thus, the data rates of the reverse traffic channels are changed individually. One increase persistence pre-test is performed for the two reverse traffic channels. Here a decrease persistence test can be performed commonly for the reverse traffic channels or independently for each of the reverse traffic channels. The RRI symbol is used in the same manner as the case (1). The reverse data rates are increased/decreased according to the result of the common increase persistence pre-test and the RABs.  
         [0090]    (4) Use of two 2-bit RABs and one 8-bit RRI symbol.  
         [0091]    One RAB is assigned for each of the reverse traffic channels and an increase persistence pre-test is also performed independently for each of the reverse traffic channels. The RRI symbol is used in the same manner as the case (2). The two reverse traffic channels are separately controlled.  
         [0092]    The result(s) of the increase persistence pre-test(s) may be transmitted on a channel other than an RRI channel (e.g., a RICH) or on a new defined channel. While its transmission period is set preferably on a frame basis, it can be set in any other manner.  
         [0093]    In accordance with the present invention as described above, mobile stations determine whether a reverse data rate increase is available for the next reverse transmission and tell a base station the determination results. Then the base station carries out a planned reverse link control for the next reverse transmission. Therefore, the occurrence of an overload is prevented, reverse data loss is minimized, and the transmission efficiency of the reverse link is maximized.  
         [0094]    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.