Abstract:
An apparatus and method for power allocation in a mobile communication system are provided. A transmitting method includes allocating a certain fraction of total power to a common control channel; allocating available power corresponding to the remaining fraction of the total power to remaining control channels except for the common control channel among control channels transmitted in a current time slot by considering the remaining control channels; calculating a gain value of each control channel according to power allocated to each control channel; and regulating a gain of each control channel, which is to be transmitted to one or more Access Terminals (ATs), according to the calculated gain value. Therefore, reception throughput of each control channel can be improved.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119(a) to a Korean patent application filed in the Korean Intellectual Property Office on Feb. 12, 2007 and assigned Serial No. 2007-14254, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus and method for power allocation in a mobile communication system. More particularly, the present invention relates to an apparatus and method in which power is effectively allocated to a Forward Link (FL) control channel in a mobile communication system. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, in order for mobile communication systems to provide power control, handoff; transmission of a Signal to Interference and Noise Ratio (SINR), and transmission of Automatic Repeat reQuest (ARQ) information, a control channel is used in a Forward Link (FL) and a Reverse Link (RL). 
         [0006]      FIG. 1  illustrates a signal flow between an Access Terminal (AT) operating in a soft-handoff mode and a Base Transceiver Station (BTS). 
         [0007]    Referring to  FIG. 1 , an AT receives FL packets and FL control channels from two BTSs, and transmits RL packets and RL control channels to the BTSs. A Base Station Controller (BSC) receives from the two BTSs the signals provided from the AT, combines these signals, and transmits FL data packets and FL control signals to the two BTSs. 
         [0008]    In general, when a plurality of ATs exist in a service area of a BTS, the BTS can use Time Division Multiplexing (TDM) or Code Division Multiplexing (CDM) in order to transmit a plurality of control channels corresponding to the respective ATs. In the following description, it is assumed that the control channels are transmitted by performing CDM. 
         [0009]      FIG. 2  illustrates an FL slot format in a Code Division Multiple Access (CDMA) mobile communication system, in particular, in a CDMA 1×EVolution-Data Only (1×EV-DO) system. Referring to  FIG. 2 , one slot is divided into two half slots, each of which transmit data, a Media Access Control (MAC) channel, and a pilot channel. An FL control channel is transmitted through the MAC channel. 
         [0010]      FIG. 3  illustrates a control channel format in a CDMA mobile communication system. That is, when a control channel is transmitted to four ATs through the MAC channel of  FIG. 2 , a signal transmitted in the slot unit has the format shown in  FIG. 3 . 
         [0011]    Referring to  FIG. 3 , an FL control channel includes a Reverse Activity (RA) channel, a Data Rate Control Lock (DRCLock) channel, a Reverse Power Control (RPC) channel, and an ARQ channel. The RA channel is commonly transmitted to all ATs. The DRCLock channel, the RPC channel, and the ARQ channel are independently assigned to each AT. Each FL control channel is distinguished using an orthogonal code. That is, orthogonality is mutually maintained since the control channels transmitted in the same slot are spread by use of different codes (e.g., Walsh code). 
         [0012]    The DRCLock channel and the RPC channel are concurrently transmitted in one slot. The ARQ channel is time-division multiplexed with the DRCLock/RPC channel and is transmitted for three slots. Transmission time points of the DRCLock/RPC channel and the ARQ channel are determined by a frame offset of an AT, as shown by Equation (1) below. 
         [0000]      If ( T -FrameOffset k ) mod 4=3, transmit  DR CLock/ RPC  channel Else transmit  ARQ  channel   (1) 
         [0013]    Here, T denotes a time in the slot unit, FrameOffsetk denotes a frame offset of a k th  AT, and “x mod y” denotes a modular operation for obtaining a remainder of division of x by y. In Equation (1) above, since the transmission time point of the DRCLock/RPC channel for the k th  AT is determined by a value of (FrameOffsetk mod  4 ), ATs can be classified into four groups as shown in  FIG. 3  according to their frame offsets. 
         [0014]    By considering that each AT has a different transmission time point, a BTS verifies a control channel to be transmitted to each AT for each slot, and divides the total transmission power of a MAC channel to ATs. 
         [0015]    A brief description of a conventional algorithm for MAC channel power allocation is now provided. 
         [0016]    According to the conventional algorithm for MAC channel power allocation, total MAC channel power is divided in advance for an RA channel, a DRCLock channel, an RPC channel, and an ARQ channel, and then the divided power is used to allocate power to a corresponding control channel of each AT. For example, assume that the total MAC channel power is allocated so that 10% is used by the RA channel, 30% is used by the DRCLock channel, 30% is used by the RPC channel, and 30% is used by the ARQ channel. Then, 60% of the total power is allocated to a group of ATs for transmitting the DRCLock/RPC channel, and 30% of the total power is allocated to a group of ATs for transmitting the ARQ channel. 
         [0017]    As such, when power allocated to each channel is divided in advance, if the total MAC channel power is less than a sum of the power required by an AT, some channels may experience performance degradation. For example, if a frame offset of the AT mostly appears in one of the four groups of  FIG. 3 , and thus the number of DRCLock/RPC channels is greater than a fraction of power allocated to the DRCLock/RPC channel, then reception throughput of the DRCLock/RPC channel deteriorates. Likewise, if the number of ARQ channels is greater than a fraction of power allocated to the ARQ channel, reception throughput of the ARQ channel deteriorates. 
         [0018]    Accordingly, when using conventional algorithms in which the total MAC channel power is divided in advance for the DRCLock channel, the RPC channel, and the ARQ channel before power allocation is performed, reception throughput may deteriorate in some channels if power is inaccurately divided for each channel. Therefore, there is a need for a method in which total power allocated to an FL MAC channel can be effectively allocated to each control channel. 
       SUMMARY OF THE INVENTION 
       [0019]    An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and method for effectively allocating power to a control channel in a mobile communication system. 
         [0020]    Another aspect of the present invention is to provide an apparatus and method for improving reception throughput of a control channel in a mobile communication system. 
         [0021]    Another aspect of the present invention is to provide an apparatus and method for effectively using total power allocated to a Media Access Control (MAC) channel in a mobile communication system. 
         [0022]    According to an aspect of the present invention, a transmitting apparatus in a mobile communication system is provided. The apparatus includes a power allocator for allocating a certain fraction of total power to a common control channel, for allocating available power corresponding to the remaining fraction of the total power to remaining control channels except for the common control channel among control channels transmitted in a current time slot by considering the remaining control channels, and for regulating a gain of each control channel according to power allocated to each control channel; and a control channel generator for generating a plurality of control channels to be transmitted to one or more Access Terminals (ATs) and for regulating the gain of each control channel under the control of the power allocator. 
         [0023]    According to another aspect of the present invention, a transmitting method in a mobile communication system is provided. The method includes allocating a certain fraction of total power to a common control channel; allocating available power corresponding to the remaining fraction of the total power to remaining control channels except for the common control channel among control channels transmitted in a current time slot by considering the remaining control channels; calculating a gain value of each control channel according to power allocated to each control channel; and regulating a gain of each control channel, which is to be transmitted to one or more ATs, according to the calculated gain value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0025]      FIG. 1  illustrates a signal flow between an Access Terminal (AT) operating in a soft-handoff mode and a Base Transceiver Station (BTS); 
           [0026]      FIG. 2  illustrates a Forward Link (FL) slot format in a Code Division Multiple Access (CDMA) mobile communication system; 
           [0027]      FIG. 3  illustrates a control channel format in a CDMA mobile communication system; 
           [0028]      FIG. 4  is a block diagram illustrating a BTS in a mobile communication system according to the present invention; 
           [0029]      FIG. 5  is a flowchart illustrating a detailed operation of a power allocator according to the present invention; 
           [0030]      FIG. 6  is a flowchart illustrating in detail the operation of step  507  of  FIG. 5 ; 
           [0031]      FIG. 7  is a flowchart illustrating in detail the operation of step  515  of  FIG. 5 ; and 
           [0032]      FIG. 8  is a flowchart illustrating in detail the operation of step  517  of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Preferred embodiments 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. Also, the terms used herein are defined according to the functions of the present invention. Thus, the terms may vary depending on user&#39;s or operator&#39;s intension and usage. That is the terms used herein must be understood based on the descriptions made herein. 
         [0034]    Hereinafter, a technique for effectively allocating power to a control channel in a mobile communication system will be described. In the following description, power is allocated to a Forward Link (FL) control channel in a Code Division Multiple Access (CDMA) mobile communication system as an example. However, the present invention also applies to other mobile communication systems employing different multiple access schemes. Further, the present invention also applies to a Reverse Link (RL) environment. 
         [0035]      FIG. 4  is a block diagram illustrating a Base Transceiver Station (BTS) in a mobile communication system according to the present invention. 
         [0036]    The diagram of  FIG. 4  focuses on a Media Access Control (MAC) channel transmitter related to the present invention. The BTS of  FIG. 4  includes a plurality of channel generators  400 ,  420 , and  440 , a Reverse Activity (RA) channel generator having a signal mapping unit  452  and a multiplier unit  454 , an adder  456 , a repeater  458 , and a power allocator  460 . Each channel generator includes a plurality of signal mapping units, a plurality of multiplier units, and a plurality of Time Division Multiplexing (TDM) units. Since the channel generators  400 ,  420 , and  440  have the same structure, the following description will focus on the channel generator  400  for a user  0 . 
         [0037]    The signal mapping unit  452  maps an input RA bit to a corresponding signal. For example, if the input bit is ‘0’, the input bit is mapped to ‘+1’, and if the input bit is ‘1’, the input bit is mapped to ‘−1’. The multiplier unit  454  multiplies the signal output from the signal mapping unit  452  and a channel gain GRA obtained from the power allocator  460 . Thus, the multiplier unit  454  regulates a gain of an RA channel and outputs an In-phase (I) signal. 
         [0038]    Now, the channel generator  400  for the user  0  will be described. 
         [0039]    The signal mapping unit  402 - 1  maps an input Reverse Power Control (RPC) bit to a corresponding signal. The multiplier unit  404 - 1  multiples the signal output from the signal mapping unit  402 - 1  by a channel gain G 0,RPC  obtained from the power allocator  460 . Thus, the multiplier unit  404 - 1  regulates a gain of an RPC channel to be transmitted to the user  0 . 
         [0040]    The signal mapping unit  402 - 2  maps an input Hybrid ARQ/Last ARQ (H-/L-ARQ) bit to a corresponding signal. For example, signal mapping is performed according to a method of transmitting Automatic Repeat reQuest (ARQ) information, as shown by Equation (2) below. 
         [0000]      H-ARQ BPSK: 0→+1, 1→−1 
         [0000]      H-ARQOOK: 0→+1, 1→0 
         [0000]      L-ARQ: 0→0, 1→−1   (2) 
         [0041]    The multiplier unit  404 - 2  multiples the signal output from the signal mapping unit  402 - 2  by a channel gain G 0,HARQ  (or G 0,LARQ ) obtained from the power allocator  460 . Thus, the multiplier unit  404 - 2  regulates a gain of a H-/L-ARQ channel to be transmitted to the user  0 . 
         [0042]    The signal mapping unit  402 - 3  maps an input DRCLock bit to a corresponding signal. The multiplier unit  404 - 3  multiples the signal output from the signal mapping unit  402 - 3  by a channel gain G 0,DRCLock  obtained from the power allocator  460 . Thus, the multiplier unit  404 - 3  regulates a gain of a DRCLock channel to be transmitted to the user  0 . 
         [0043]    The signal mapping unit  402 - 4  maps an input Packet ARQ (P-ARQ) bit to a corresponding signal. The multiplier unit  404 - 4  multiplies the signal output from the signal mapping unit  402 - 4  by a channel gain G 0,PARQ  obtained from the power allocator  460 . Thus, the multiplier unit  404 - 4  regulates a gain of a P-ARQ channel to be transmitted to the user  0 . 
         [0044]    If ((T-FrameOffset ) mod 4)=3, the first TDM unit  406 - 1  selects the RPC channel, and otherwise selects the H-/L-ARQ channel. That is, the first TDM unit  406 - 1  performs TDM so that the RPC channel and the H-/L-ARQ channel are divided in a ratio of 1:3. Likewise, if ((T-FrameOffset 0 ) mod 4)=3, the second TDM  406 - 2  selects the DRCLock channel, and otherwise selects the P-ARQ channel. That is, the second TDM  406 - 2  performs TDM so that the DRCLock channel and the P-ARQ channel are divided in a ratio of 1:3. 
         [0045]    The multiplier unit  408 - 1  multiplies the signal output from the first TDM unit  406 - 1  by a Walsh code obtained from a Walsh code generator (not shown), and thus outputs an In-phase (I) signal. The multiplier unit  408 - 2  multiplies a signal output from the second TDM  406 - 2  by the Walsh code obtained from the Walsh code generator, and thus outputs a Quadrature -phase (Q) signal. 
         [0046]    Regarding a user  1 , transmission is basically the same as in the case of user  0 . However, a gain of each control channel and the Walsh code to be multiplied by the signals of an I channel and a Q channel are modified. Further, in the case of user  0 , the RPC channel and the H-/L-ARQ channel are input to the I channel, and the DRCLock channel and the P-ARQ channel are output to the Q channel. On the other hand, in the case of the user  1 , the RPC channel and the H-/L-ARQ channel are input to the Q channel, and the DRCLock channel and the P-ARQ channel are input to the I channel. That is, for even numbered users (i.e., user  0 , user  2 , user  4 , etc.), the RPC channel and the H-/L-ARQ channel are input to the I channel, and the DRCLock channel and the P-ARQ channel are input to the Q channel. In addition, for odd numbered users (i.e., user  1 , user  3 , user  5 , etc.), the RPC channel and the H-/L-ARQ channel are input to the Q channel, and the DRCLock channel and the P-ARQ channel are input to the I channel. 
         [0047]    For each slot, the power allocator  460  calculates transmission power of each control channel. Then, as shown in Equation (3) below, the power allocator  460  calculates a channel gain using the calculated transmission power, and provides the calculation result to a corresponding gain regulator (i.e., multiplier unit). An operation of the power allocator  460  of the present invention is described in greater detail with reference to  FIG. 5  to  FIG. 8 . 
         [0000]        G   k,DRCLock =√{square root over (α k,DRCLock )}, G k,RPC =√{square root over (α k,RPC )} 
         [0000]        G   k,HARQ =√{square root over (α k,HARQ )}, G k,LARQ =√{square root over (α k,LARQ )} 
         [0000]        G   k,PARQ =√{square root over (α k,PARQ  )}  (3) 
         [0048]    Herein, a k,DRCLock , a k,RPC , a k,HARQ , a k,LARQ , and a k,PARQ  denote transmission power allocated to the DRCLock channel, the RPC channel, the H-ARQ channel, the L-ARQ channel, and the P-ARQ channel, respectively, each of which are to be transmitted to a k th  user. 
         [0049]    The adder  456  divides an input RA channel and a control channel to be transmitted to each user into the I channel and the Q channel, and respectively adds I channel signals and Q channel signals in a chip unit. The repeater  458  repeats the I channel signal and Q channel signal obtained from the adder  456  and thus generates a MAC channel signal in which the same signal pattern is repeated twice. The MAC channel signal generated per slot amounts to 256 chips. In order to transmit the MAC channel signal, as shown in  FIG. 2 , the MAC channel signal is divided into four separate periods of 64 chips, and thus four transmissions are made for each slot. 
         [0050]      FIG. 5  is a flowchart illustrating a detailed operation of the power allocator  460  according to the present invention. 
         [0051]    Referring to  FIG. 5 , a fraction of total power of an MAC channel is allocated to an RA channel in step  501 . In step  503 , power P RA  allocated to the RA channel is subtracted from total power P MAC  of the MAC channel to obtain available power P A , as shown by Equation (4) below. 
         [0000]        P   A   =P   MAC   −P   RA    (4) 
         [0052]      
         [0053]    As such, the available power P A  which can be allocated to a DRCLock channel, an RPC channel, and an ARQ channel is calculated. Then, in step  505 , a Forward Link SINR (FL_SINR) of each AT is calculated considering a DRC value received from each AT and a handoff state. In step  507 , required power of each control channel is calculated considering a target SINR, which ensures reliable reception throughput of a control channel transmitted in a current slot, and also considering the FL_SINR of each AT. An operation of step  507  is described below in greater detail with reference to  FIG. 6 . 
         [0054]    As such, the required power is calculated for each control channel transmitted in the current slot. Then, in step  509 , all control channels (except for the RA channel) are sorted in ascending order according to the required power. That is, an ascending order list is created. In step  511 , power (i.e., required power) is allocated to each control channel according to the sorted order, and the power allocated to all control channels are summed to obtain power sum P REQ . 
         [0055]    In step  513 , it is determined if the power sum P REQ  is less than the available power P A . If the power sum P REQ  is less than the available power P A , proceeding to step  515 , the allocated power is increased by considering the required power of each control channel. In other words, if power remains since the power allocated to all control channels is less than the available power P A  that can be allocated, then the power of each control channel is boosted by considering the required power. An operation of step  515  is described in greater detail with reference to  FIG. 7 . 
         [0056]    To the contrary, if the power sum P REQ  is greater than or equal to the available power P A , proceeding to step  517 , the power of each control channel is sequentially decreased according to the ascending order list. In other words, if power is short since the power allocated to all control channels is greater than the available power P A  that can be allocated, then the power of each control channel is reduced by limiting the power allocated to each control channel. This is repeated until a sum of power allocated to all control channels finally becomes equal to the available power P A . An operation of step  517  is described below in greater detail with reference of  FIG. 8 . 
         [0057]      FIG. 6  is a flowchart illustrating in detail the operation of step  507  of  FIG. 5 , which is performed by the power allocator  460 . 
         [0058]    Referring to  FIG. 6 , a user index k is initialized to ‘0’ in step  601 . In step  603 , it is determined if the user index k is less than the number of users. If the user index k is greater than or equal to the number of users, the procedure proceeds to step  509  of  FIG. 5 . 
         [0059]    To the contrary, if the user index k is less than the number of users, proceeding to step  605 , required power of each control channel is initialized as shown by Equation (5) below. 
         [0000]        r   k,DRCLock =0,  r   k,RPC =0,  r   k,HARQ =0,  r   k,LARQ =0,  r   k,PARQ =0   (5) 
         [0060]    Herein, r k,DRCLock  denotes required power of a DRCLock channel of a k th  user, r k,RPC  denotes required power of an RPC channel of the k th  user, r k,HARQ  denotes required power of a H-ARQ channel of the k th  user, r k,LARQ  denotes required power of an L-ARQ channel of the k th  user, and r k,PARQ  denotes required power of a P-ARQ channel of the k th  user. The H-ARQ channel is used to feed back, to an AT, information which indicates a success or failure of receiving sub-packets when first, second, and third sub-packets are received on a Reverse Link (RL). The L-ARQ channel is used to feed back information which indicates a success or failure of receiving sub-packets when a fourth sub-packet is received on the RL. The P-ARQ channel is used to finally feed back information which indicates a success or failure of receiving packets after the four sub-packets are all received on the RL. 
         [0061]    In step  607 , a current slot number (or a slot time) and a frame offset of the k th  user are substituted to Equation (1) above to determine a control channel transmitted in the current slot. That is, it is determined whether the DRCLock/RPC channel or the ARQ channel is transmitted to the k th  user in the current slot. 
         [0062]    If the DRCLock/RPC channel is transmitted, in step  609 , the required power of the DRCLock/RPC channel is updated by using an FL_SINR of the k th  user, a target SINR of the DRCLock channel, and a target SINR of the RPC channel. Then, the procedure proceeds to step  629 . For example, the required power of the DRCLock channel (i.e., r k,DRCLock ) is calculated as shown by Equation (6) below, and the required power of the RPC channel (i.e., r k,RPC ) is calculated as shown by Equation (7) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       DRCLock 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         
                           
                             
                               min 
                               - 
                               DRCLock 
                               - 
                               power 
                             
                             , 
                           
                         
                       
                       
                         
                           
                             
                               target 
                               - 
                               DRCLock 
                               - 
                               SINR 
                             
                             
                               FL 
                               - 
                               
                                 SINR 
                                 k 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       RPC 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         min 
                         - 
                         RPC 
                         - 
                         power 
                       
                       , 
                       
                         
                           target 
                           - 
                           RPC 
                           - 
                           SINR 
                         
                         
                           FL 
                           - 
                           
                             SINR 
                             k 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0063]    Herein, FL-SINR k  denotes an FL_SINR of the k th  user, min-DRCLock-power denotes minimum allocated-power of the DRCLock channel, and min-RPC-power denotes minimum allocated-power of the RPC channel. Further, target-DRCLock-SINR denotes a target SINR of the DRCLock channel, and target-RPC-SINR denotes a target SINR of the RPC channel. 
         [0064]    Meanwhile, if the ARQ channel is determined in step  607 , proceeding to step  611 , it is examined if a H-ARQ bit is transmitted to the k th  user. If the H-ARQ bit is transmitted, it is examined if an ARQ mode is ‘0’ in step  613 . If the ARQ mode is ‘0’, the procedure proceeds to step  615 , and, if the ARQ mode is ‘1’, the procedure proceeds to step  617 . 
         [0065]    In step  615 , the required power of the H-ARQ channel is updated by using the FL-SINR of the k th  user and also by using a target SINR used when the H-ARQ bit is transmitted using Binary Phase Shift Keying (BPSK). Then, the procedure proceeds to step  625 . For example, the required power of the H-ARQ channel can be calculated as shown by Equation (8) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       HARQ 
                     
                   
                   = 
                   
                     max 
                      
                     
                       ( 
                       
                         
                           
                             
                               
                                 min 
                                 - 
                                 HARQ 
                                 - 
                                 BPSK 
                                 - 
                                 power 
                               
                               , 
                             
                           
                         
                         
                           
                             
                               
                                 target 
                                 - 
                                 HARQ 
                                 - 
                                 BPSK 
                                 - 
                                 SINR 
                               
                               
                                 FL 
                                 - 
                                 
                                   SINR 
                                   k 
                                 
                               
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0066]    Herein, min-HARQ-BPSK-power denotes minimum allocated-power when the H-ARQ bit is transmitted using BPSK, and target-HARQ-BPSK-SINR denotes a target SINR used when the H-ARQ bit is transmitted using BPSK. 
         [0067]    In step  617 , it is determined whether the H-ARQ bit is ‘ACK’. If the H-ARQ bit is ‘ACK’, the procedure proceeds to step  619 , and if the H-ARQ bit is not ‘ACK’, the procedure proceeds to step  625 . In step  619 , the required power of the H-ARQ channel is updated by using the FL_SINR of the k th  user and the target SINR used when the H-ARQ bit is transmitted using On-Off Keying (OOK). Then, the procedure proceeds to step  625 . For example, when ACK is transmitted, the required power of the H-ARQ channel can be calculated as shown by Equation (9) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       HARQ 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         
                           
                             
                               min 
                               - 
                               HARQ 
                               - 
                               OOK 
                               - 
                               power 
                             
                             , 
                           
                         
                       
                       
                         
                           
                             
                               target 
                               - 
                               HARQ 
                               - 
                               OOK 
                               - 
                               SINR 
                             
                             
                               FL 
                               - 
                               
                                 SINR 
                                 k 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
         [0068]    Herein, min-HARQ-OOK-power denotes minimum allocated-power when the H-ARQ bit is transmitted using OOK, and target-HARQ-OOK-SINR denotes a target SINR when the H-ARQ bit is transmitted using OOK. 
         [0069]    If it is determined in step  611  that the H-ARQ bit is not transmitted, proceeding to step  621 , an L-ARQ bit is examined to determine if the L-ARQ bit is ‘NAK(or NACK)’. If the L-ARQ bit is ‘NAK’, the procedure proceeds to step  623 , and otherwise, the procedure proceeds to step  625 . In step  623 , the required power of the L-ARQ channel is updated by using the FL_SINR of the k th  user and a target SINR used when the L-ARQ bit is transmitted. Then, the procedure proceeds to step  625 . For example, the required power of the L-ARQ channel can be calculated according to Equation (10) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       LARQ 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         min 
                         - 
                         LARQ 
                         - 
                         power 
                       
                       , 
                       
                         
                           target 
                           - 
                           LARQ 
                           - 
                           SINR 
                         
                         
                           FL 
                           - 
                           
                             SINR 
                             k 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0070]    Herein, min-LARQ-power denotes minimum allocated-power when the L-ARQ bit is transmitted, and target-LARQ-SINR denotes a target SINR when the L-ARQ bit is transmitted. 
         [0071]    A P-ARQ bit is examined in step  625 . If the P-ARQ bit is ‘NAK’, the procedure proceeds to step  627 , and othervise, the procedure proceeds to step  629 . In step  627 , the required power of the P-ARQ channel is updated using the FL_SINR of the k th  user and a target SINR used when the P-ARQ bit is transmitted. Then, the procedure proceeds to step  629 . For example, the required power of the P-ARQ channel can be calculated as shown by Equation (11) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     
                       k 
                       , 
                       PARQ 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         
                           
                             
                               min 
                               - 
                               PARQ 
                               - 
                               power 
                             
                             , 
                           
                         
                       
                       
                         
                           
                             
                               target 
                               - 
                               PARQ 
                               - 
                               SINR 
                             
                             
                               FL 
                               - 
                               
                                 SINR 
                                 k 
                               
                             
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0072]    Herein, min-PARQ-power denotes minimum allocated-power when the P-ARQ bit is transmitted, and target-PARQ-SINR denotes a target SINR when the P-ARQ bit is transmitted. 
         [0073]    As such, the required power for a control channel to be transmitted to the k th  user is calculated. Then, in step  629 , the user index k is incremented by ‘1’, and the procedure returns to step  603 . 
         [0074]    In  FIG. 6 , the minimum allocated-power and the target SINR, each of which is required by each control channel, are determined according to throughput of each channel and the number of simultaneously accessible ATs. These values are assumed to be predetermined. 
         [0075]      FIG. 7  is a flowchart illustrating in detail the operation of step  515  of  FIG. 5 , which is performed by the power allocator  460 . Referring to  FIG. 7 , a user index k is initialized to ‘0’ in step  701 . In step  703 , it is determined if the user index k is less than the number of users. If the user index k is greater than or equal to the number of users, the procedure of  FIG. 5  ends. 
         [0076]    To the contrary, if the user index k is less than the number of users, proceeding to step  705 , power allocated to a control channel to be transmitted to the k th  user is increased using a ratio of the power sum P REQ  and the available power P A , as shown by Equation (12) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       a 
                       
                         k 
                         , 
                         DRCLock 
                       
                     
                     = 
                     
                       
                         
                           P 
                           A 
                         
                         
                           P 
                           REQ 
                         
                       
                        
                       
                         r 
                         
                           k 
                           , 
                           DRCLock 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       a 
                       
                         k 
                         , 
                         RPC 
                       
                     
                     = 
                     
                       
                         
                           P 
                           A 
                         
                         
                           P 
                           REQ 
                         
                       
                        
                       
                         r 
                         
                           k 
                           , 
                           RPC 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       a 
                       
                         k 
                         , 
                         HARQ 
                       
                     
                     = 
                     
                       
                         
                           P 
                           A 
                         
                         
                           P 
                           REQ 
                         
                       
                        
                       
                         r 
                         
                           k 
                           , 
                           HARQ 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       a 
                       
                         k 
                         , 
                         LARQ 
                       
                     
                     = 
                     
                       
                         
                           P 
                           A 
                         
                         
                           P 
                           REQ 
                         
                       
                        
                       
                         r 
                         
                           k 
                           , 
                           LARQ 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       a 
                       
                         k 
                         , 
                         PARQ 
                       
                     
                     = 
                     
                       
                         
                           P 
                           A 
                         
                         
                           P 
                           REQ 
                         
                       
                        
                       
                         r 
                         
                           k 
                           , 
                           PARQ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0077]    Herein, a k,DRCLock , a k,RPC , a k,HARQ , a k,LARQ , and a k,PARQ  denote transmission power finally allocated to the DRCLock channel, the RPC channel, the H-ARQ channel, the L-ARQ channel, and the P-ARQ channel, respectively, each of which are to be transmitted to a k th  user. 
         [0078]    As such, power of the control channel to be channel transmitted to the k th  user is controlled. Then, in step  707 , the user index k increases by ‘1’, and the procedure returns to step  703 . 
         [0079]      FIG. 8  is a flowchart illustrating in detail the operation of step  517  of  FIG. 5 , which is performed by the power allocator  460 . Referring to  FIG. 8 , all control channels are sorted in ascending order according to required power in step  801 . In step  803 , a control channel index m is initialized to ‘0’. Herein, the total number of the control channels is assumed to be M. For example, assume that the total number of users is  4 , two control channels are transmitted to a first user, two control channels are transmitted to a second user, two control channels are transmitted to a third user, and one control channel is transmitted to a fourth user. Then, M is equal to ‘7’. 
         [0080]    In step  805 , it is determined whether the control channel index m is less than the value M. If the control channel index m is greater than or equal to the value M, the procedure of  FIG. 5  ends. 
         [0081]    Otherwise, if the control channel index m is less than the value M, proceeding to step  807 , maximum power P A,m  that can be allocated to an m th  control channel is calculated by considering available power P A . For example, the maximum power P A,m  for an m th  control channel can be calculated as shown by Equation (13) below. 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     
                       A 
                       , 
                       m 
                     
                   
                   = 
                   
                     
                       P 
                       A 
                     
                     
                       M 
                       - 
                       m 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
         [0082]    In step  809 , required power r m  of the m th  control channel is compared with the calculated maximum power P A,m , and a smaller value between the compared values is determined as allocated power of the m th  control channel. The required power r m  is one of r k,DRClock , r k,RPC , r k,HARQ , r k,LARQ , and r k,PARQ  according to a type of control channel. 
         [0083]    In step  811 , the available power P A  is updated by considering power allocated to the m th  control channel, as shown by Equation (14) below. 
         [0000]        P   A   =P   A   α   m    (14) 
         [0084]    As such, power for the m th  control channel is controlled. Then, in step  813 , the control channel index m increases by ‘1’, and the procedure returns to step  805 . 
         [0085]    As such, through the operations described with reference to  FIG. 5  to  FIG. 8 , transmission power is determined for each control channel transmitted in a suitable slot, and a gain of each control channel is regulated according to the determined transmission power. 
         [0086]    According to the present invention, limited total power is effectively allocated to a plurality of control channels in a Base Transceiver Station (BTS) of a mobile communication system. Therefore, reception throughput of each control channel can be improved. 
         [0087]    While the invention has been shown and described with reference to certain exemplary embodiments 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 and their equivalents. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims and their equivalents, and all differences within the scope will be construed as being included in the present invention.