Abstract:
A method for determining a data rate for transmitting traffic data from a mobile station to a base station in a mobile communication system includes steps of receiving data rate control information from at least one base station; obtaining, based on the received data rate control information, a maximum transmittable data rate; obtaining a plurality of data rates for transmitting traffic data to the at least one base station, the plurality of data rates being obtained by considering a status factor of the mobile station; and determining the data rate of the traffic data to the at least one base station by selecting one of the obtained maximum transmittable data rate and plurality of data rates. The method determines the reverse data rate based on data rate control information and according to its own status, to provide system stability and minimize interference with other mobile stations while increasing the throughput for the sector and maintaining a desired QoS level even when the mobile station transmits at less power while.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Applications No. 10-2003-0029966 and No. 10-2003-0029967, each filed on May 12, 2003, which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a mobile communication system, and more particularly, to a method of determining a data rate when transmitting traffic data from a mobile station to a base station.  
           [0004]    2. Discussion of the Related Art  
           [0005]    In a contemporary mobile communication system, a specific mobile station of a sector transmitting at a high data rate causes serious interference with other mobile stations of the sector and destabilizes the system. Therefore, since a mobile station cannot arbitrarily determine a reverse-link data rate, the reverse data rate of each mobile station is regulated by the sector&#39;s base station, which transmits data rate control information generated based on the status of the respective mobile stations and the status of the reverse channel. Contemporary methods for determining reverse data rates, however, often exhibit poor system stability and fail to achieve the desired quality-of-service (QoS) for lower transmission levels.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, the present invention is directed to a method of determining a reverse data rate in a mobile communication system that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0007]    An object of the present invention is to provide a method of determining a reverse data rate in a mobile communication system, by which a mobile station determines the reverse data rate based on data rate control information transmitted from a base station and thus provides system stability.  
           [0008]    Another object of the present invention is to provide a method of determining a reverse data rate in a mobile communication system, by which a mobile station determines the reverse data rate according to its own status and thus minimizes interference with other mobile stations.  
           [0009]    Another object of the present invention is to provide a method of determining a reverse data rate in a mobile communication system, by which a desired QoS level is maintained even if a mobile station transmits at less power.  
           [0010]    Another object of the present invention is to provide a method of determining a reverse data rate in a mobile communication system, by which a sector&#39;s mobile stations increase their respective throughputs.  
           [0011]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent to those having ordinary skill in the art upon examination of the following or may be learned from a practice of the invention. The objectives and other advantages of the invention will be realized and attained by the subject matter particularly pointed out in the specification and claims hereof as well as in the appended drawings.  
           [0012]    To achieve these objects and other advantages in accordance with the present invention, as embodied and broadly described herein, there is provided a method of determining a reverse data rate in a mobile station. The method comprises steps of receiving data rate control information from at least one base station; obtaining, based on the received data rate control information, a maximum transmittable data rate; obtaining a plurality of data rates for transmitting traffic data to the at least one base station, the plurality of data rates being obtained by considering a status factor of the mobile station; and determining the data rate of the traffic data to the at least one base station by selecting one of the obtained maximum transmittable data rate and plurality of data rates.  
           [0013]    Preferably, the method further comprises a step of combining the received data rate control information, so that, when the mobile station is in a handover condition with respect to a plurality of base stations, the mobile station adopts a single rate control bit (RCB) reflecting the data rate control information received from each base station. That is, when operated in a handoff area, a mobile station adopting the method of the present invention receives a plurality of rate control bits and other information and uses a known technique to generate one RCB by combining the control information received from each active sector.  
           [0014]    In another aspect of the present invention, there is provided a method of determining a reverse data rate in a mobile station of a mobile communication system supporting a hybrid automatic repeat request (HARQ) transmission scheme. The method comprises steps of receiving data rate control information and retransmission control information from at least one base station; obtaining, based on the received data rate control information, a maximum combined data rate; determining a data rate of traffic data to be retransmitted according to the retransmission control information; obtaining a maximum transmittable data rate of traffic data to be newly transmitted to the at least one base station, the maximum transmittable data rate being obtained by considering the maximum combined data rate and the data rate of traffic data to be retransmitted; obtaining a plurality of data rates of the traffic data to be newly transmitted to the at least one base station, the plurality of data rates being obtained by considering a status factor of the mobile station; and determining the data rate of the traffic data to be newly transmitted to the at least one base station by selecting one of the obtained maximum transmittable data rate and plurality of data rates.  
           [0015]    It is to be understood that both the foregoing explanation and the following detailed description of the present invention are exemplary and illustrative and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0017]    [0017]FIG. 1 is a flowchart of a method of determining a reverse data rate according to the present invention;  
         [0018]    [0018]FIG. 2 is a diagram of a forward control channel and a reverse traffic channel, illustrating a reverse data rate determination according to the method of FIG. 1;  
         [0019]    [0019]FIG. 3 is a diagram of a reverse traffic channel separated for supporting a HARQ transmission scheme applied to the method of the present invention;  
         [0020]    [0020]FIG. 4 is a diagram of a channel configuration supporting HARQ transmission, illustrating a reverse transmission channel (RTCH) and a forward control channel (FCCH) transmitting a NACK signal in accordance with the method of the present invention; and  
         [0021]    [0021]FIG. 5 is a diagram of a power control section of a pilot signal over a reverse transmission channel in accordance with the method of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. Throughout the drawings, like elements are indicated using the same or similar reference designations.  
         [0023]    The present invention relates to a mobile communication system supporting a hybrid automatic repeat request (HARQ) transmission scheme in which the base station generates retransmission control information, i.e., an acknowledgment (ACK) or non-acknowledgment (NACK) signal, for transmission to the mobile station based on the presence of errors in a previously received signal from the mobile station. Thus, the mobile station is conditionally informed of the need to retransmit reverse traffic data. That is, the base station transmits an ACK signal if retransmission is unnecessary, i.e., when no errors are detected in the received signal, and transmits a NACK signal if retransmission is necessary, i.e., when errors are detected.  
         [0024]    Referring to FIG. 1, illustrating a method of determining a reverse data rate according to the present invention, a mobile station receives in a step S 10  data rate control information and retransmission control information from a base station. The data rate control information is in the form of a rate control bit or RCB.  
         [0025]    A mobile station operated in a handoff area, i.e., in the coverage area of a plurality of base stations, receives corresponding pluralities of RCBs and ACK/NACK signals and therefore must combine the control information received from each active sector. Thus, a mobile station adopting the method of the present invention combines a plurality of RCBs, transmitted from each of a plurality of sectors, to generate one RCB.  
         [0026]    Referring to FIG. 2, illustrating the relative timing between a reverse traffic channel (RTCH) and a forward control channel (FCCH), data rate control information (one RCB) is transmitted from a base station at an (i-α)th frame of the forward control channel. The RCB instruction value, i.e., an “up,” “down,” or “hold” instruction, is determined in a base station using an algorithm for optimizing system operation, and a mobile station references the received instruction to control the data rate of an ith frame accordingly. As shown in FIG. 3, the data transmission and processing between the mobile station and the base stations inherently incurs a time delay α in the forward control channel and a time delay β in the reverse traffic channel, each type of delay occurring in full frames. According to the present invention, the retransmission control information (ACK/NACK) may be multiplexed with the data rate control information (RCB), to be transmitted together via the forward control channel, or may be transmitted via a separate channel.  
         [0027]    Referring again to FIG. 1, the mobile station estimates in a step S 11  a combined data rate Rate i ′, which is based on the received data rate control information (RCB i ) and is the maximum rate permitted by the base station for the ith frame. The “combined” data rate supports a HARQ transmission scheme, in which traffic data (packets) is retransmitted via an RTCH R-CH  channel in response to a NACK signal and is newly transmitted via an RTCH N-CH  channel in response to an ACK signal. Accordingly, the mobile station controls its reverse-link data rate based on the maximum permitted rate (Rate i ′) such that the actual data rate of data transmitted at the ith frame, represented herein as Rate i , satisfies the relation Rate i ≦Rate i ′. The value of Rate i ′ is estimated using a value λ, which is determined based on the received data rate control information (RCB) and indicates a degree of increment (e.g., an n-step) or decrement (e.g., an m-step) of the data rate of the ith frame with respect to the date rate of an (i-β)th frame, designated as Rate i-β . The value of Rate i ′ is always greater than or equal to the value (AutoMaxRate) of the mobile station&#39;s initial data rate, which is a lower limit determined according to signaling information, to prevent the mobile station from initiating data transmission at a data rate that is too low.  
         [0028]    [0028]FIG. 3 illustrates a structure of a reverse traffic channel, including the above-mentioned RTCH R-CH  and RTCH N-CH  channels, in which a reverse transmission channel is separated using a code-division or time-division technique for supporting the HARQ scheme. For example, upon receiving a NACK signal from the base station for a given packet, the mobile station retransmits the packet via the RTCH R-CH  channel at a Rate R-CH(i)  and at a transmission power P R-CH ; upon receiving an ACK signal from the base station for a given packet, the mobile station transmits a new packet via the RTCH N-CH  channel at a Rate N-CH(i)  and at a transmission power P N-CH . As an alternative to a separate channel configuration, a mobile station may perform new transmissions and retransmissions using the same reverse transmission channel when responding to the retransmission control information from a base station, whereby retransmissions continue until receipt of an ACK signal, whereupon new packets are transmitted on the same channel.  
         [0029]    [0029]FIG. 4, illustrating a channel configuration supporting HARQ transmission, demonstrates the resulting time delays in a reverse transmission channel (RTCH) and a forward control channel (FCCH) for transmitting automatic repeat request (ARQ) information. As shown in FIG. 4, the data transmission and processing between the mobile station and the base stations inherently incurs a time delay p in the forward control channel and a time delay q in the reverse traffic channel, each type of delay occurring in full frames.  
         [0030]    In the example of FIG. 4, a NACK signal is generated in response to the transmission of a packet at a frame i-q, and a mobile station determines the data rate of the traffic data to be retransmitted at a frame i according to the ARQ information corresponding to the (i-q)th frame. The ARQ information is received from the base station in the form of an ACK signal indicating reception success or a NACK signal indicating reception failure. That is, if the base station successfully receives a frame transmitted via the RTCH N-CH  channel at the (i-q)th frame, the mobile station need not retransmit the traffic data via the RTCH R-CH  channel. On the other hand, the base station transmits to the mobile station a NACK signal at an (i-p)th frame corresponding to an unsuccessfully received frame, e.g., the (i-q)th frame, and the mobile station sets the date rate for retransmission at the ith frame equal to that of the frame generating the NACK signal (Rate R-CH(i) =Rate N-CH(i-q) ).  
         [0031]    Accordingly, with reference to the channel configuration of FIG. 4, it is determined in a step S 12  of FIG. 1 whether the retransmission control information received in the step S 10  is an ACK signal or a NACK signal, and a step S 13  is performed only when a NACK signal is received (ARQ=NACK), whereupon the data rate of the RTCH R-CH  channel is determined for the ith frame, designated herein as Rate R-CH(i) , thus setting the value of Rate R-CH(i)  equal to Rate R-CH(i-q) . Since there is no retransmission when an ACK signal is received (ARQ=ACK), rendering the above rate determination unnecessary, performance of the step S 13  is omitted and the value of Rate R-CH(i)  may be set to zero or a similar null value.  
         [0032]    The transmission power of the RTCH R-CH  channel at the ith frame can be expressed by Equation 1.  
         P R-CH(i) rP Tr     [Rate     R-CH(i)     ]     [Equation 1] 
         [0033]    where P Tr[     Rate     ]  is the transmission power of traffic information required for a specific “Rate” and where the value of r is between zero and one, to effect an energy reduction, since the transmission power of a frame retransmitted via the RTCH R-CH  channel is r-times higher than that necessary for the frame generating the NACK signal.  
         [0034]    With the values of Rate R-CH(i)  and P R-CH(i)  thus determined, the data rate of traffic data to be newly transmitted via the RTCH N-CH  channel, designated herein as Rate N-CH , is determined by considering three factors, namely, the maximum data rate of the RTCH N-CH  channel, i.e., Rate N-CH(assigned) , the maximum transmission power of the mobile station, i.e., Rate N-CH(power) , and the volume of queued traffic data to be transmitted by the mobile station, i.e., Rate N-CH(queue) . That is, a step S 14  performs separate calculations as follows, and a step S 15  is performed to select an optimal value among three obtained values.  
         [0035]    The value of the first factor, Rate N-CH(assigned) , is the maximum data rate of the RTCH N-CH  channel, which is based on the transmission power to be allocated (assigned) for achieving transmission at the Rate N-CH . This is expressed by Equation 2 as follows.  
                       if                   P     R        -          CH        (   i   )             &gt;     τ                     P   Tr          [     Rate   i   ′     ]           ,         then                   Rate     N        -          CH        (   assigned   )            (   i   )           =   0     ;   else                   Rate     N        -          CH        (   assigned   )            (   i   )         =                                arg                                min       R   ∈   RateSet                       {         R        :                     P     Tr     [   R   ]           +     P     R        -          CH        (   i   )             ≤     τ                   P     Tr     [     Rate   i   ′     ]             }                     [     Equation                 2     ]                               
 
         [0036]    where R is an arbitrary data rate in a data rate set commonly shared by the base station and the mobile station, wherein a maximum R satisfying P Tr     [R]   +P R-CH(i) ≦τP Tr     [Rate     i     ′]    is set as the value of Rate N-CH(assigned)(i) , and where τ is greater than or equal to one and is the ratio of the additionally available transmission power to the transmission power required for the maximum combined data rate Rate′ permitted by the base station.  
         [0037]    Equation 2 finds the data rate of the RTCH N-CH  channel by considering the total transmission power allocated for the maximum combined data rate Rate′ permitted by the base station and the additionally available transmission power. The maximum data rate R is decided by Rate N-CH(assigned)(i)  in a manner that the sum of the transmission power of the RTCH R-CH  channel by Equation 2 and the transmission power that will be allocated to N-CH is made not to exceed τ-times of the transmission power allocated for the maximum combined data rate Rate′ allowed by the base station.  
         [0038]    The value of the second factor, Rate N-CH(power) , is the data rate determined for the maximum transmission power of the mobile station and an available transmission power for inner loop power control of the base station, as shown in Equations 3-7. The value of Rate N-CH(power)  is determined as a maximum rate R satisfying Equation 7.  
         [0039]    Referring to FIG. 5, illustrating a power control section of a pilot signal over a reverse transmission channel according to the present invention, the transmission power of a reverse pilot signal is adjusted by a forward power control bit according to an inner loop power control algorithm. According to Equation 3, the mean-normalized transmission power of the pilot signal (P PiNormAv(k) ) is calculated by power control groups (PCGs) for which the pilot signal&#39;s transmission power varies but may be found in various other ways.  
               P     PiNormAv        (   k   )         =         C   Tx     (       P     Pi        (   k   )           P     Pi     [     R     nom        (   i   )         ]           )     +       P     PiNormAv        (     k   -   1     )              (     1   -     C   Tx       )                 [     Equation                 3     ]                               
 
         [0040]    where C Tx  is a coefficient of a primary filter and is a value between zero and one; where P pi(k)  is the actually transmitted power of the pilot signal at the kth power control group; where P pi     [Rate]    is the transmission power of a pilot signal for the data rate required for traffic transmitted via a reverse transmission channel, namely, RTCH N-CH  or RTCH R-CH ; and where R nom(i)  is the nominal data rate at the ith frame and is found by Equation 5.  
               R     nom        (   i   )         =                    arg                                min       R   ∈   RateSet                       {         R        :                     P     Tr     [     Rate     N        -          CH        (     i   -   α     )           ]           +     P     R        -          CH        (     i   -   α     )             ≤     τ                   P     Tr     [   R   ]             }               [     Equation                 4     ]                               
 
         [0041]    According to Equation 4, the value of R nom(i)  determined as a minimum R such that a sum of transmission powers of the RTCH R-CH  and RTCH N-CH  channels is less than or equal to a ratio of the total transmission power to the power available.  
         [0042]    The mean-normalized transmission power of the pilot signal is calculated for by frames using Equation 5.  
         P PiNormAv(i) =P PiNormAv(k+(n− 1))  [Equation 5] 
         [0043]    where k indicates the location of the final power control group (PCG) of the ith frame and where n is an offset value of the final power control group with respect to the current frame.  
         [0044]    The value of Rate N-CH(power)  is set to zero if Equation 6 is satisfied and is otherwise determined by Equation 7. In other words, Rate N-CH(power)  is zero when the above-decided values of Rate R-CH  and P R-CH  (in step S 13 ) satisfy Equation 6.  
                   if                   P     PiNormAv        (     i   -   1     )              P     Pi     [       R   nom          (     0   ,     Rate     R        -          CH        (   i   )             )       ]           +     P     CHother        (   i   )         +     P     R        -          CH        (   i   )             &gt;       P   max       Headroom   Tx         ,       then                   Rate     N   -     CH        (   power   )             =   0             [     Equation                 6     ]                 R     N        -          CH        (   power   )           =         arg                                min       R   ∈   RateSet            {             P     PiNormAv        (     i   -   1     )              P     Pi       [       R   nom          (     R   ,     Rate     R        -          CH        (   i   )             )       ]     +                         P     Tr     [   R   ]         +     P     CHother        (   i   )         +     P     R        -          CH        (   i   )             ≤       P   max       Headroom   Tx               }               [     Equation                 7     ]                               
 
         [0045]    In Equations 6 and 7, P CHother(i)  is the power of other reverse transmission channels of the mobile station at the ith frame, P max  is a maximum power that the mobile station can transmit, and Headroom Tx  is an available transmission power ratio for operation of the inner loop power control. The transmission powers of the mobile station&#39;s other reverse-link channels are considered in addition to the transmission power of the RTCH R-CH  channel, to determine the data rate of the RTCH N-CH  channel for the maximum transmission power of the mobile station and the additionally available transmission power for the inner loop power control. The transmission power of the pilot signal satisfying transmission requirements of the RTCH R-CH  and RTCH N-CH  channels simultaneously should be considered as well.  
         [0046]    The value of R nom     (R     1     , R     2     )    in Equations 6 and 7 can be defined by Equation 8.  
               R     nom     (       R   1     ,     R   2       )         =         arg                                min       R   ∈   RateSet                       {         R        :                     P     Tr     [     R   1     ]           +     r                   P     Tr     [     R   2     ]             ≤     τ                   P     Tr     [   R   ]             }               [     Equation                 8     ]                               
 
         [0047]    The value of the third factor, Rate N-CH(queue) , is a volume (Queue i ) of traffic information that the mobile station has at the ith frame and is determined based on a buffer state of the mobile station.  
         [0048]    If a value resulting from dividing a volume of data occupying the buffer by a first buffer management variable Q Tx 1  is less than or equal to a Payload size of an initial data rate, the value of Rate N-CH(queue)  is determined as a minimum rate R among data rates having payload sizes greater than or equal to a value resulting from dividing the volume of the data occupying the buffer by a second buffer management variable Q Tx2 . On the other hand, if the value resulting from dividing the volume of the data occupying the buffer by the first buffer management variable Q Tx1  is greater than the payload size of the initial data rate, the value of Rate N-CH(queue)  is determined as a minimum rate R among data rates having payload sizes greater than or equal to a value resulting from dividing the volume of the data occupying the buffer by the first buffer management variable Q Tx1 . Here, Q Tx1  and Q Tx2  are variables for managing a volume of a buffer and each have a value of at least one, where Q Tx1  is greater than Q Tx2 .  
         [0049]    The value of Rate N-CH(queue)  follows Equation 10 if the buffer state satisfies Equation 9 and otherwise follows Equation 11. Namely, if the value resulting from dividing the volume of the data occupying the buffer by the Q Tx1  is less than or equal to a Payload size of the initial data rate (AutoMaxRate), the value of Rate N-CH(queue)  is determined as a minimum data rate satisfying Equation 10. The initial data rate is the minimum data rate set up to prevent the mobile station from initiating data transmission at a data rate that is too low. Yet, if the value resulting from dividing the volume of the data occupying the buffer by the Q Tx1  exceeds the Payload size of the initial data rate (AutoMaxRate), the value of Rate N-CH(queue)  is determined as a minimum data rate satisfying Equation 11.  
                 Queue   i       Q   Tx1       ≤     Payload        [   AutoMaxRate   ]               [     Equation                 9     ]                 Rate     N        -          CH        (   queue   )            (   i   )         =         arg                                min       R   ∈   RateSet            {         R        :                     Payload        [   R   ]         ≥       Queue   i       Q   Tx2         ,     R   ≤   AutoMaxRate       }               [     Equation                 10     ]                 Rate     N        -          CH        (   queue   )            (   i   )         =         arg                                min       R   ∈   RateSet            {       R        :                     Payload        [   R   ]         ≥       Queue   i       Q   Tx         }               [     Equation                 11     ]                               
 
         [0050]    The smallest value among the data rates of the RTCH N-CH  channel respectively obtained according to the three factors of Rate N-CH(assigned) , Rate N-CH(power) , and Rate N-CH(queue)  is selected as the Rate N-CH  (step S 15 ).  
         [0051]    According to Equation 12, the value of Rate N-CH  may be determined as the smallest value among f 1 Rate N-CH(assigned) , f 2 Rate N-CH(power) , and f 3 Rate N-CH(queue) , where f1, f2, and f3 are respective weights of the selected data rate. That is, a weight is assigned to each of three data rates, and the one having the smallest assigned weight is determined as the data rate of traffic data to be newly transmitted.  
         Rate N-CH(i) =min{f 1 Rate N-CH(assigned) , f 2 Rate N-CH(power) , f 3 Rate N-CH(queue) }  [Equation 12] 
         [0052]    In transmitting a frame via the reverse transmission channel, to enable the base station to receive the frame with a quality over a predetermined level, the mobile station should consider various factors so that the smallest data rate among the data rates of the RTCH N-CH  channel determined according to the factors is set as the data rate of the corresponding frame of the RTCH N-CH  channel. The thus-set value of Rate N-CH  is used in updating R nom  per Equation 4. By referring to the data rates determined for the RTCH R-CH  and RTCH N-CH  channels, the buffer state (queue) of the mobile station is updated and the transmission of the corresponding frame begins in a step S 16  based on the determined data rates. The mean-normalized transmission power of the pilot signal for the RTCH R-CH  and RTCH N-CH  channels (P PiNormAv(i)  of Equation 3) is updated each PCG using the updated R nom , and transmission of the frame is terminated.  
         [0053]    In determining mobile station status information (the mobile station&#39;s buffer information, data rate information, etc.) for generating the rate control bit, the base station or mobile station refers to the mobile station state information of an (i-b)th frame for generating data rate control information that will be transmitted on an (i-a)th frame, where a and b are natural numbers and a is smaller than b.  
         [0054]    The mobile station transmits via the reverse control channel information, i.e., a mobile station information bit (MSIB), for informing the base station of the mobile station&#39;s current status. The MSIB may be set to “increase” or “hold.” By setting up a data rate to be one step higher based on R nom(i) , it is determined whether the Rate N-CH(power)  and Rate N-CH(queue)  data rates are permissible. If a higher data rate can be set for transmission, the MSIB is set to “increase” and is then transmitted to the base station.  
         [0055]    According to Equation 13, an R req(i)  value is incremented to be set to the data rate one-step higher than R nom(i) , and the MSIB is set based on whether the incremented R req(i)  value satisfies Equations 14 and 15. That is, the MSIB is set to “increase” when R req(i)  satisfies both equations and is otherwise set to “hold.” 
           R   req(i)   =R   nom(i) +Δ Rate   [Equation 13] 
         [0056]    [0056]               P     PiNormAv        (   i   )         =           P   Pi          [     R     req        (   i   )         ]       +       P   Tr          [       R     req        (   i   )         +     P   CHother       ]         ≤       P   max       Headroom   req                 [     Equation                 14     ]                 Payload        [     R     req        (   i   )         ]       ≥       Queue   i       Q   req               [     Equation                 15     ]                                 
         [0057]    Accordingly, the method of the present invention determines a reverse data rate when a data rate control algorithm is applied to a reverse-link channel. The data rate is determined based on data rate control information from the base station, thereby stabilizing the system. Moreover, the present invention determines a data rate suitable for the state of a mobile station, enabling a minimizing of interference with other mobile stations. Therefore, QoS levels are satisfied even if a mobile station uses less power, thereby reducing power consumption and increasing throughput.  
         [0058]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention embody such modifications and variations, provided they come within the scope of the appended claims and their equivalents.