Abstract:
A method for allocating reverse and forward channel power in a W-CDMA WLL system is disclosed. The method comprises calculating a propagation path loss of forward and reverse pilot channels depending on the maximum path loss of forward and reverse links for a base station located at a specific distance from a terminal, determined from the minimum E c /I t  required by the system, the transmission antenna gain of a terminal, the reception antenna gain of the terminal, the reverse frequency reusing efficiency, the transmission output of the terminal, the number of active users, the power allocation ratio of the pilot channel, the bandwidth, and the thermal noise density; and, calculating a power allocation ratio of forward and reverse channels depending on the propagation path loss of the forward and reverse pilot channels, E b /N t  of the forward and reverse channels, the power allocation ratio of the forward and reverse pilot channels, the data rate of the forward and reverse channels, the bandwidth, and the reverse frequency reusing efficiency

Description:
This application claims priority to an application entitled “Method for Optimally Allocating Channel Power in W-CDMA WLL system” filed in the Korean Industrial Property Office on Mar. 15, 1999 and assigned Serial No. 99-8557. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a method for optimally allocating channel power in a W-CDMA (Wideband Code Division Multiple Access) WLL (Wireless Local Loop) system, and in particular, for allocating required channel power so as to optimize a radio capacity and a coverage of a W-CDMA WLL system. 
     2. Description of the Related Art 
     In the CDMA system, reverse channels include an access channel and a traffic channel. The access channel is used when a mobile station starts communication with a base station, or when the mobile station sends a response to a paging channel message received from the base station. An IS-95 system has 32 access channels at a maximum, for one forward paging channel, and the access channels have a data rate of 4800 bps. The reverse traffic channel operates at 4 variable data rates, like the forward traffic channel. The access channels and the traffic channels are each separated by unique user long-period codes. 
     Further, in the CDMA system, forward channels include a pilot channel, a sync channel, a maximum of 7 paging channels and a maximum of 63 traffic channels. 
     The pilot channel is used when the mobile station acquires timing for the forward channels. That is, the pilot channel provides a phase reference for performing coherent demodulation. In addition, the pilot channel provides the mobile station with the means for comparing the strength of signals transmitted from the adjacent base stations to determine whether to perform a handoff. The sync channel operates at a data rate of 1200 bps and transmits a sync message to the mobile station to synchronize the reference time between the base station and the mobile station. Further, the sync channel provides information about a bit rate of the paging channel to enable the mobile station to accurately demodulate the paging channel. 
     The paging channel is used for transmitting control information such as a system parameter and paging a specific mobile station. Upon the receipt of an audio signal having variable data rates of 9600, 4800, 2400 and 1200 bps, the traffic channel multiplexes signaling information and transmits the multiplexed signaling information. 
     FIG. 1 shows the structure of a general reverse traffic channel. As illustrated, the reverse traffic channel (R-TCH) includes 20 ms frames, each of which is comprised of 16 1.25 ms power control groups (PCGs). The user data is encoded by a coding rate r=⅓, constraint length K=9 convolutional encoder  10 , repeated by a repeater  11  according to data rates, interleaved by an interleaver  12 , and then orthogonally modulated by a 64-ary orthogonal modulator  13 . The reverse traffic channel transmits the data only for a selected power control group at the same power, when the data rate is not 9600 bps. The reverse traffic channel intermittently transmits the data according to the data rates, and the locations are determined by a data burst randomizer  15  depending on the unique long-period PN codes of the respective users. Thereafter, the output of the data burst randomizer  15  is scrambled with a long-period PN code having a period of 2 42 −1 at a rate of 1.2288 MHz, and then OQPSK (Offset Quadrature Phase Shift Keying) modulated with a pair of two short-period pilot PN codes. 
     FIG. 2 shows the structure of a general forward traffic channel. As illustrated, the forward traffic channel includes 20 ms frames, each of which is comprised of 16 1.25 ms power control groups. The user data is encoded by an r=½, K=9 convolutional encoder  20 , repeated by a repeater  21  according to data rates, and then interleaved by an interleaver  22 . Thereafter, the user data is scrambled with a long-period PN code, and multiplied by one of the specified 64 Walsh codes to be spread into a signal having a rate of 1.2288 Mcps. Then, the signal is multiplied by a pair of two PN codes and undergoes the QPSK modulation before transmission. 
     Meanwhile, in the conventional CDMA WLL system, the base station and the mobile station cannot perform the proper power allocation of the radio channels and thus can not satisfy the performance requirements of the respective radio channels. Therefore, it is difficult to facilitate the optimization of the radio capacity and coverage of the system, thereby causing an unbalance of the forward coverage and the reverse coverage. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method for satisfying the performance requirements of respective channels, maximizing the radio capacity and coverage of the system and maintaining the balance of a forward coverage and a reverse coverage, in a W-CDMA WLL system. 
     To achieve the above object, there is provided a method for allocating reverse and forward channel power in a W-CDMA WLL system. The method includes the steps of calculating the propagation path loss of forward and reverse pilot channels depending on a maximum path loss of forward and reverse links for a base station located at a specific distance from a terminal, determined from a minimum E c /I t  required by the system, a transmission antenna gain of a terminal reception antenna gain of the terminal, a reverse frequency reusing efficiency, a transmission output of the terminal, a number of active users, a power allocation ratio of the pilot channel, a bandwidth, and a thermal noise density; and, calculating the power allocation ratio of forward and reverse channels depending on the propagation path loss of the forward and reverse pilot channels, E b /N t  of the forward and reverse channels, the power allocation ratio of the forward and reverse pilot channels, the data rate of the forward and reverse channels, the bandwidth, and the reverse frequency reusing efficiency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram illustrating the structure of a general reverse traffic channel; 
     FIG. 2 is a block diagram illustrating the structure of a general forward traffic channel; and, 
     FIGS.  3 ( a )-( c ) are flow charts illustrating the operation steps of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. For the purpose of clarity, well-known functions or constructions are not described in detail as they would obscure the invention in unnecessary detail. 
     To determine an optimal channel power ratio of the forward and reverse channels in a WLL system, the quality requirements for the forward and reverse channels are calculated through performance test of the system. 
     Referring to FIG.  3 ( a ), a description will be first made of the process of calculating a reverse power allocation ratio. The reverse power allocation ratio is calculated based on a reverse pilot signal. 
     A propagation path loss of the pilot channel is calculated by Equation 1 below.                             E   c       I   t       =                      ξ   p          P   t          G   t          G   r          L        (   r   )               N   o        W     +       I   sc          (   r   )       +         I   oc          (   r   )          W         =         ξ   p          P   t          G   t          G   r          L        (   r   )               N   o        W     +       I   sc          (   r   )       +     [     1   +         I   oc          (   r   )           I   sc          (   r   )           ]                       =                      ξ   p          P   t          G   t          G   r          L        (   r   )               N   o        W     +       1     F   r       ·       I   sc          (   r   )             =         ξ   p          P   t          G   t          G   r          L        (   r   )               N   o        W     +       1     F   r            NP   t          G   t          G   r          L        (   r   )                               [     Equation                 1     ]                                
     wherein, N t : thermal noise density; 
     I t : total interference power; 
     I sc : same cell interference; 
     E b : energy density per bit; 
     W: bandwidth; 
     R: data rate; 
     ξ p : power allocation ratio of a pilot channel; 
     L(r): propagation path loss of an RSC (base station) located at a distance r from an RNT (WLL terminal); 
     G t : transmission antenna gain of the RNT; 
     G r : reception antenna gain of the RSC; 
     F r : reverse frequency reusing efficiency; 
     P t : transmission output of the RNT; 
     N: active users; and 
     N 0 W: Thermal Noise, wherein N 0 =kTF, and wherein k is Boltzmann constant (1.38×10 −23  W/K/Hz), T is absolute temperature (K), and F is noise figure(dB); 
     The maximum value of the propagation path loss L(r) of the reverse link is defined as:                  L        (   r   )       max     =             (       E   c       I   t       )     min     ·     N   o          W         P   t          G   t            G   r          [       ξ   p     -         (       E   c       I   t       )     min          1     F   r           ]                   [     Equation                 2     ]                                
     In the cell area defined by the reverse pilot channel, receiving E b /N t  of an automatic power control (APC) channel, other wire (OW) channel which is a dedicated channel for signaling, and a traffic channel should satisfy specific requirements. 
     First, E b /N t  of the traffic channel is defined as:                  [       E   b       N   t       ]     traff     =       W     R   traff       ·         ξ   traff          P   t          G   t          G   r          L        (   r   )               N   o        W     +       {       (     N   -   1     )     +     (     1   +     -     ξ   traff         )       }          P   t          G   t          G   r            L        (   r   )       ·     1     F   r                         [     Equation                 3     ]                                
     wherein, ξ traff : power allocation ratio of the traffic channel; and, 
     R traffic : data rate of the traffic channel 
     The propagation path loss E c /I t  of the pilot channel is determined by applying the propagation path loss of Equation 2 to Equation 1. Further, the power allocation ratio of the traffic channel ξ traff  is derived from Equation 3 based on the maximum permissible propagation path loss defined by Equation 2 and E c /I t  defined by Equation 1.                ξ   traff     =         ξ   p     ·       (       E   b       N   t       )     traff           (       E   c       I   t       )     ·     [       W     R   traff       +       1     F   r       ·       (       E   b       N   t       )     traff         ]                 [     Equation                 4     ]                                
     Similarly, the maximum power allocation ratio of the APC channel and the OW channel are calculated by Equations 5 and 6 below, respectively.                ξ   APC     =         ξ   p     ·       (       E   b       N   t       )     APC             (       E   c       I   t       )     p     ·     [       W     R   APC       +       1     F   r       ·       (       E   b       N   t       )     APC         ]                 [     Equation                 5     ]                 ξ   OW     =         ξ   p     ·       (       E   b       N   t       )     OW             (       E   c       I   t       )     p     ·     [       W     R   OW       +       1     F   r       ·       (       E   b       N   t       )     OW         ]                 [     Equation                 6     ]                                
     It is noted from Equations 4 to 6 that the power allocation ratios of the respective channels depend on E c /I t  threshold of the pilot channel, the power allocation ratio of the pilot channel, the Eb/Nt requirement of the respective channels, and the processing gain. 
     That is, the power allocation ratios of the respective channels are determined by calculating the propagation path loss L(r) in accordance with Equation 2 and then calculating E c /I t  using the calculated propagation path loss L(r) and the power allocation ratio of the pilot channel (which is previously determined by the system). The power allocation ratios of the respective channels are determined by placing the calculated propagation path loss and E c /I t  in Equations 4 to 6. 
     Similarly, referring to FIG.  3 ( b ), the forward power allocation ratio is determined based on the forward pilot channel. First, E c /I t  of the forward pilot channel is defined as:                  E   c       I   t       =           ξ   GLPT          P   t          G   t          G   r          L        (   r   )               N   o        W     +       I   sc          (   r   )       +         I   oc          (   r   )          W         =           ξ   GLPT          P   t          G   t          G   r          L        (   r   )               N   o        W     +         I   sc          (   r   )            [     1   +         I   oc          (   r   )           I   sc          (   r   )           ]           =           ξ   GLPT          P   t          G   t          G   r          L        (   r   )               N   o        W     +       1     F   f       ·       I   sc          (   r   )             =         ξ   GLPT          P   t          G   t          G   r          L        (   r   )               N   o        W     +       1     F   f            P   t          G   t          G   r          L        (   r   )                           [     Equation                 8     ]                                
     The maximum propagation path loss of the forward link is defined as:                  L        (   r   )       max     =             (       E   c       I   t       )     min     ·     N   o          W         P   t          G   t            G   r          [       ξ   GLPT     -         (       E   c       I   t       )     min          1     F   f           ]                   [     Equation                 9     ]                                
     wherein, 
     ξ p : power allocation ratio of a global pilot channel; 
     L(r): propagation path loss of an RNT (WLL terminal) located at a distance r from an RSC (base station); 
     G t : transmission antenna gain of the RSC; 
     G r : reception antenna gain of the RNT; 
     F f : forward frequency reusing efficiency; and, 
     P t : transmission output of the RNT. 
     In the cell area defined by the forward global pilot channel, receiving E b /N t  of a slow broadcasting channel (SBCCH) and a fast broadcasting channel (FBCCH) for paging, an automatic power control (APC) channel, other wire (OW) channel, and a traffic channel should satisfy specific requirements. 
     First, E b /N t  of the SBCCH channel is defined as:                  [       E   b       N   t       ]     SBCCH     =       W     R   SBCCH       ·         ξ   SBCCH          P   t          G   t          G   r          L        (   r   )               N   o        W     +       (     1   -     ξ   SBCCH       )          P   t          G   t          G   r            L        (   r   )       ·     1     F   f                         [     Equation                 10     ]                                
     wherein, 
     ξ SBCCH : power allocation ratio of the SBCCH channel; and, 
     R SBCCH : data rate of the SBCCH channel. 
     The propagation path loss ξ FBCCH  of the SBCCH channel is determined by applying the maximum permissible propagation path loss of the global pilot channel, given by Equation 9 to Equation 10.                ξ   SBCCH     =         ξ   GLPT     ·       (       E   b       N   t       )     SBCCH             (       E   c       I   t       )     GLPT     ·     [       W     R   SBCCH       +       1     F   f       ·       (       E   b       N   t       )     SBCCH         ]                 [     Equation                 11     ]                                
     Similarly, the maximum power allocation ratio of FBCCH channel, the traffic channel, the APC channel and the OW channel are calculated by Equations 12 to 15 below, respectively:                ξ   FBCCH     =         ξ   GLPT     ·       (       E   b       N   t       )     GBCCH             (       E   c       I   t       )     GLPT     ·     [       W     R   FBCCH       +       1     F   f       ·       (       E   b       N   t       )     FBCCH         ]                 [     Equation                 12     ]                 ξ   traff     =         ξ   GLPT     ·       (       E   b       N   t       )     traff             (       E   c       I   t       )     GLPT     ·     [       W     R   traff       +       1     F   f       ·       (       E   b       N   t       )     traff         ]                 [     Equation                 13     ]                 ξ   APC     =         ξ   GLPT     ·       (       E   b       N   t       )     APC             (       E   c       I   t       )     GLPT     ·     [       W     R   APC       +       1     F   f       ·       (       E   b       N   t       )     APC         ]                 [     Equation                 14     ]                 ξ   OW     =         ξ   GLPT     ·       (       E   b       N   t       )     OW             (       E   c       I   t       )     GLPT     ·     [       W     R   OW       +       1     F   f       ·       (       E   b       N   t       )     OW         ]                 [     Equation                 15     ]                                
     A description will now be made of how to apply the above channel power allocation method to the WLL system. 
     First, reference will be made to the quality requirements for the forward and reverse channels as shown in FIG.  3 ( c ). 
     Reverse Channels 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Eb/Nt 
                   
                   
               
               
                   
                   
                 Require- 
                   
                   
               
               
                   
                   
                 ment or 
                   
                   
               
               
                   
                 Data Rate 
                 Ec/It 
                 BER (Bit Error 
                   
               
               
                   
                 (Kbps) 
                 Threshold 
                 Rate) 
                 Remarks 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Traffic CH 
                 32 
                 4 
                 dB 
                 10-4 
                 cf.SP31370 
               
               
                 APCCH 
                 64 
                 −0.5 
                 dB 
                 0.2 
                 (Ch. 3.5) 
               
               
                 OWCH 
                 16 
                 5.5 
                 dB 
                 10-7 
               
               
                 Pilot CH 
                 8320 
                 −20.6 
                 dB 
               
               
                   
               
             
          
         
       
     
     Forward Channels 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Eb/Nt 
                   
                   
               
               
                   
                   
                 Require- 
                   
                   
               
               
                   
                   
                 ment or 
                   
                   
               
               
                   
                 Data Rate 
                 Ec/It 
                 BER (Bit Error 
                   
               
               
                   
                 (Kbps) 
                 Threshold 
                 Rate) 
                 Remarks 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Traffic CH 
                 32 
                 4 
                 dB 
                 10-4 
                 cf.SP31370 
               
               
                 APCCH 
                 64 
                 −0.5 
                 dB 
                 0.2 
                 (Ch. 3.5) 
               
               
                 OWCH 
                 16 
                 5.5 
                 dB 
                 10-7 
               
               
                 SBCCH 
                 16 
                 5.5 
                 dB 
                 10-7 
               
               
                 FBCCH 
                 16 
                 5.5 
                 dB 
                 10-7 
               
               
                 Pilot CH 
                 8320 
                 −14.6 
                 dB 
               
               
                   
               
             
          
         
       
     
     Tables 3 and 4 below show the power allocation ratios determined by applying the values of Tables 1 and 2 to the Equations stated above. 
     Reverse Channels 
     
       
         
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Power Allocation 
                   
                   
               
               
                 Channel 
                 Ratio 
                 Digital Gain 
                 Remarks 
               
               
                   
               
             
             
               
                 Global Pilot CH 
                 0.285 
                 14 
                 Max Tx Output of 
               
               
                 Traffic CH 
                 0.313 
                 20 
                 RNT:0.1 W 
               
               
                 APCCH 
                 0.223 
                 12 
               
               
                 OWCH 
                 0.222 
                 17 
               
               
                   
               
             
          
         
       
     
     A digital gain relationship between the reverse traffic channel and the other reverse channels can be expressed as follows:                    ξ   p       ξ   traff       =       2   ·     DG   p   2         DG   traff   2         ;           [Equation   7-1]                       ξ   APC       ξ   traff       =       2   ·     DG   APC   2         DG   traff   2         ;              and     ,           [Equation   7-2]                   ξ   OW       ξ   traff       =       2   ·     DG   OW   2         DG   traff   2               [Equation   7-3]                                
     Table 3 shows the digital gains of the respective channels when the digital gain of the traffic channel is  20  in the RNT (WLL terminal). Table 3 shows the values for determining the power ratio between the channels, rather than the absolute transmission level. 
     From the calculated channel power ratio, the digital gains of the respective channels are calculated as follows:            DG   p     =           DG   traff   2     ·       ξ   p       ξ   traff       ·     1   2         =           20   2     ·     0.285   0.313     ·     1   2         =   14         ;                 DG   APC     =           DG   traff   2     ·       ξ   APC       ξ   traff       ·     1   2         =           20   2     ·     0.285   0.313     ·     1   2         =   14         ;   and     ,     
            DG   OW     =           DG   traff   2     ·       ξ   OW       ξ   traff           =           20   2     ·     0.222   0.313         =   17.                                
     Table 4 below shows the forward channel power ratios determined by applying the system requirements of Table 2 to the Equations stated above. Unlike Table 3, the sum of the power allocation ratios does not become 1, because of the common channels (global pilot channel, SBCCH and PBCCH) and the dedicated channels (traffic channel, APC channel and OW channel). That is, the common channels have the same power, but the dedicated channels have the power determined in consideration of the WLL terminals. 
     Forward Channels 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Power Allocation 
                   
                   
               
               
                 Channel 
                 Ratio 
                 Digital Gain 
                 Remarks 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Global Pilot CH 
                 0.035 
                 119 
                 Max Tx Output of 
               
               
                 SBCCH 
                 0.0068 
                 74 
                 RSC:35 W 
               
               
                 FBCCH 
                 0.0068 
                 74 
               
               
                 Traffic CH 
                 0.0096 
                 88 
               
               
                 APCCH 
                 0.0068 
                 37 
               
               
                 OWCH 
                 0.0068 
                 74 
               
               
                   
               
             
          
         
       
     
     With regard to the relationship between the channel power ratio and the digital gain, when the maximum transmission output is 35W and the digital gain of the global pilot channel is  119 , the gain ratios of the respective channels are:            DG   GLPT     =           167   2     ·     1.225   2.41         =   119       ;               DG   SBCCH     =         2   ·     167   2     ·     0.238   2.41         =   74       ;               DG   FBCCH     =         2   ·     167   2     ·     0.238   2.41         =   74       ;               DG   traff     =         2   ·     167   2     ·     0.336   2.41         =   88       ;                 DG   GLPT     =           167   2     ·     0.119   2.41         =   37       ;              and     ,     
            DG   OW     =         2   ·     167   2     ·     0.238   2.41         =   74.                              
     As described above, the novel channel power allocation method can maximize the radio capacity and the coverage of the system while satisfying the quality requirements of the respective channels, and maintain a balance of the forward and reverse coverages. 
     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 detail may be made therein without departing from the spirit and the scope of the invention as defined by the appended claims.