Abstract:
A method and a device for reducing a signal peak value are adapted to solve a problem that overall performance of a system is significantly degraded caused by allocating a same weight to each sub-carrier so as to averagely distribute a peak clipping noise to each sub-carrier. The method includes: receiving a signal ( 21 ); and performing a peak clipping processing on the received signal by using a peak clipping signal ( 25 ). The peak clipping signal is formed according to a peak clipping weight factor and the received signal, or according to a frequency domain error vector magnitude (EVM) and the received signal. In the method, a weight of each sub-carrier is set according to the peak clipping weight factor or the frequency domain EVM during the peak clipping processing, thereby improving the overall performance of the system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of International Application No. PCT/CN2008/000083, filed on Jan. 11, 2008, which claims the benefit of Chinese Application No. 200710005625.7, filed on Mar. 6, 2007, both of which are hereby incorporated by reference in their entireties. 
     
    
     FIELD OF THE TECHNOLOGY 
       [0002]    The present invention relates to a field of wireless communication technology, and more particularly to a method and a device for reducing a signal peak value, and a transmitting device. 
       BACKGROUND OF THE INVENTION 
       [0003]    The orthogonal frequency division multiplexing (OFDM) technology is an effective broadband transmission technology, which is widely applied in many fields such as digital audio broadcast (DAB), digital video broadcast (DVB), and high definition television (HDTV). However, in a system employing the OFDM technology, a high peak power of a signal results in a high ratio of the peak power to an average power (that is, peak-to-average power ratio, PAPR) of the signal, which requires a power amplifier of a system transmitter to be highly linear to avoid non-linear distortion when amplifying the signal. As a result, the difficulty and cost for implementing the system are increased, and the further development and application of the OFDM technology are restricted. 
         [0004]    In order to reduce the peak power of the signal in the OFDM communication system, many technologies for reducing the peak power such as peak clipping and amplitude limiting technology and peak canceling technology are developed. The peak clipping and amplitude limiting solution is easier to implement, but causes in-band distortion and out-of-band power radiation of the signal. The peak canceling technology can be regarded as an improved peak clipping and amplitude limiting technology that does not cause out-of-band power radiation but still results in in-band signal distortion. The peak canceling technical solution will be described in the following. In the peak canceling technical solution, a waveform approximate to an ideal pulse (the waveform is also referred to as Kernel) in a time domain needs to be pre-stored. Since frequency components of the waveform only fall on data sub-carriers, that is, no interference is caused to null sub-carriers which is for frequency spectrum protection, out-of-band power radiation does not occur. 
         [0005]      FIG. 1  shows a peak canceling device including a buffer unit which is adapted to buffer an input signal x(t), a peak value detection unit which is adapted to detect peak point positions and amplitude phases of the signal, and transfer detection results to the circular shift unit and the amplitude phase adjustment unit, a circular shift unit which is adapted to perform a circular shift on a Kernel waveform according to the peak point positions detected by the peak value detection unit, an amplitude phase adjustment unit which is adapted to perform an amplitude adjustment and a phase rotation on the circularly shifted Kernel waveform according to the amplitude phases detected by the peak value detection unit, an adder which is adapted to add Kernel signals corresponding to the peak points that are processed by the amplitude phase adjustment unit and the signal (buffered) which is before the current peak clipping, another peak value detection unit which is adapted to detect peak values of the signal processed by the adder, and a control unit which is adapted to: determine whether the peak values, for example, the maximum peak value, detected by the peak value detection unit are lower than a threshold value; and if they are lower than the threshold value, directly output the adjusted signal x(t); otherwise, transfer the adjusted signal x(t) to the buffer unit for the next peak clipping. 
         [0006]    The peak canceling method is introduced below briefly. First, an input signal x(t) is buffered. Then, the peak value detection unit detects a peak point position and an amplitude phase of the signal, and transfers detection results to the circular shift unit. The circular shift unit performs a circular shift on a Kernel waveform by using the peak point positions detected by the peak value detection unit. Afterwards, the amplitude phase adjustment unit performs an amplitude adjustment and a phase rotation on the circularly shifted Kernel waveform according to the amplitude phases detected by the peak value detection unit. The adder adds Kernel signals corresponding to the peak points that are processed by the amplitude phase adjustment unit and the signal (buffered) which is before the current peak clipping. Then peak values of the signal processed by the adder are detected. The control unit determines whether the peak values are lower than a threshold value, and if they are lower than the threshold value, the control unit directly outputs the adjusted signal x(t); otherwise, the control unit transfers the adjusted signal x(t) to the buffer unit for the next peak clipping. 
         [0007]    However, in the current communication standards related to the OFDM, an adaptive modulation encoding mode is adopted in order to utilize spectrum resources more effectively, with the result that data on different sub-carriers in the same symbol uses different modulation encoding modes, and data on the same sub-carrier among different symbols also uses different modulation encoding modes. The different modulation encoding modes employed by the sub-carriers cause different anti-interference capabilities of the sub-carriers. However, in the existing technical solution, the same weight is allocated to different sub-carriers so as to averagely distribute the peak clipping noise to each sub-carrier without considering the difference in anti-interference capabilities of the sub-carriers. In this way, when the sub-carrier having a poor anti-interference capability bears a large peak clipping noise, the overall performance of the system is significantly degraded. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the present invention provide a method and a device for reducing a signal peak value, and a transmitting device, which solves a problem that the overall performance of a system is significantly degraded caused by allocating a same weight to different sub-carriers so as to averagely distribute a peak clipping noise to each sub-carrier. 
         [0009]    In an embodiment, the present invention provides a method for reducing a signal peak value. The method includes the following steps. 
         [0010]    A signal is received. 
         [0011]    A peak clipping processing is performed on the received signal by using a peak clipping signal. The peak clipping signal is formed according to a peak clipping weight factor and the received signal or according to a frequency domain error vector magnitude (EVM) and the received signal. 
         [0012]    In an embodiment, the present invention further provides a device for reducing a signal peak value. The device includes a receiving unit, a peak clipping signal generating unit, and a peak clipping processing unit. 
         [0013]    The receiving unit includes a first receiving module adapted to receive an upper level signal and output the received signal to the peak clipping signal generating unit and the peak clipping processing unit. 
         [0014]    The peak clipping signal generating unit is adapted to generate a peak clipping signal according to a peak clipping weight factor and the signal received by the receiving unit or according to a frequency domain EVM and the received signal. 
         [0015]    The peak clipping processing unit includes a processing module adapted to perform a peak value reduction processing on the received signal according to the peak clipping signal. 
         [0016]    In an embodiment, the present invention further provides a transmitting device. The transmitting device includes an encoding unit, a constellation mapping unit, and a modulation unit. 
         [0017]    The encoding unit is adapted to encode data to be transmitted. 
         [0018]    The constellation mapping unit is adapted to perform a constellation mapping on the data encoded by the encoding unit. 
         [0019]    The modulation unit is adapted to modulate the data of the constellation mapping unit to a corresponding sub-carrier. 
         [0020]    The transmitting device further includes a device for reducing a peak value. The device for reducing a signal peak value includes a peak clipping signal generating unit and a peak clipping processing unit. 
         [0021]    The peak clipping signal generating unit is adapted to generate a peak clipping signal according to a peak clipping weight factor or a frequency domain EVM. 
         [0022]    The peak clipping processing unit is adapted to perform a peak value reduction processing on the received signal according to the peak clipping signal. 
         [0023]    In the embodiments of the present invention, a weight of each sub-carrier is set according to a peak clipping weight factor (the peak clipping weight factor includes, but is not limited to, an encoding mode, a constellation mapping mode, a transmit power, and a receiving quality class) or a frequency domain EVM during the peak clipping processing, that is, a large weight is allocated to the sub-carrier having good anti-interference capability and a small weight is allocated to the sub-carrier having poor anti-interference capability, thereby improving the overall performance of a system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]      FIG. 1  shows a peak canceling device in the prior art; 
           [0025]      FIG. 2  is a flow chart of reducing a signal peak value according to a first embodiment of the present invention; 
           [0026]      FIG. 3  is a flow chart of a first approach to generate a middle peak clipping signal according to a peak clipping weight factor according to the first embodiment of the present invention; 
           [0027]      FIG. 4  is a flow chart of a second approach to generate a middle peak clipping signal according to a peak clipping weight factor according to the first embodiment of the present invention; 
           [0028]      FIG. 5  is a flow chart of reducing a signal peak value according to a second embodiment of the present invention; 
           [0029]      FIG. 6  shows a device for reducing a signal peak value according to a third embodiment of the present invention; 
           [0030]      FIG. 7  shows a device for reducing a signal peak value corresponding to the first approach to generate the middle peak clipping signal according to the third embodiment of the present invention; 
           [0031]      FIG. 8  shows a device for reducing a signal peak value corresponding to the second approach to generate the middle peak clipping signal according to the third embodiment of the present invention; 
           [0032]      FIG. 9  shows a device for reducing a signal peak value corresponding to the process for reducing a signal peak value in the second embodiment according to the third embodiment of the present invention; and 
           [0033]      FIG. 10  shows a transmitting device according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0034]    In order to make persons of ordinary skill in the art understand and implement the present invention easily, the embodiments of the present invention are described with reference to the accompanying drawings. 
         [0035]    In an embodiment, the present invention provides a method for reducing a signal peak value. In this embodiment, a weight of a peak clipping signal is set according to a peak clipping weight factor (the peak clipping weight factor includes, but is not limited to, an encoding mode, a constellation mapping mode, a transmit power, and a receiving quality class) or a frequency domain EVM, thereby controlling the distribution of the peak clipping noise to each sub-carrier. 
         [0036]    It is assumed that the signal before peak clipping is x, the signal after peak clipping is x, and the peak clipping signal is denoted by c. The following equation is true. 
         [0000]    
       
         
           
             
               x 
               _ 
             
             = 
             
               x 
               + 
               c 
             
           
         
       
       
         
           and 
         
       
       
         
           
             c 
             = 
             
               
                 ∑ 
                 
                   i 
                   = 
                   0 
                 
                 
                   L 
                   - 
                   1 
                 
               
                
               
                 
                   a 
                   i 
                 
                  
                 
                    
                   
                     jφ 
                     i 
                   
                 
                  
                 
                   p 
                   i 
                 
               
             
           
         
       
     
         [0037]    where L denotes a total number of peak points exceeding a threshold of a waveform in the symbol, a i  denotes an amplitude adjustment coefficient of the i th  peak point (equal to a difference between an amplitude of x at this point and the threshold value), φ i  denotes a phase adjustment coefficient that should be opposite to the phase of x at the peak point, and p i  denotes a peak clipping signal after circular shift according to the position of the i th  peak point. The weight information of each sub-carrier is denoted by a vector w. Then, the corresponding peak clipping signal p can be denoted as p=IFFT(w), where Inverse Fast Fourier Transform (IFFT) indicates inverse fast Fourier transform. The frequency component C of c is considered as follows: 
         [0000]    
       
         
           
             
               
                 
                   C 
                   = 
                     
                    
                   
                     F 
                      
                     
                         
                     
                      
                     F 
                      
                     
                         
                     
                      
                     
                       T 
                        
                       
                         ( 
                         c 
                         ) 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     F 
                      
                     
                         
                     
                      
                     F 
                      
                     
                         
                     
                      
                     
                       T 
                        
                       
                         ( 
                         
                           
                             ∑ 
                             
                               i 
                               = 
                               0 
                             
                             
                               L 
                               - 
                               1 
                             
                           
                            
                           
                             
                               a 
                               i 
                             
                              
                             
                                
                               
                                 jφ 
                                 i 
                               
                             
                              
                             
                               p 
                               i 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         0 
                       
                       
                         L 
                         - 
                         1 
                       
                     
                      
                     
                       
                         a 
                         i 
                       
                        
                       
                          
                         
                           jφ 
                           i 
                         
                       
                        
                       F 
                        
                       
                           
                       
                        
                       F 
                        
                       
                           
                       
                        
                       
                         T 
                          
                         
                           ( 
                           
                             p 
                             i 
                           
                           ) 
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         0 
                       
                       
                         L 
                         - 
                         1 
                       
                     
                      
                     
                       
                         a 
                         i 
                       
                        
                       
                         
                            
                           
                             jφ 
                             i 
                           
                         
                         [ 
                         
                           w 
                           · 
                           
                             [ 
                             
                                
                               
                                 
                                   - 
                                   j 
                                 
                                  
                                 
                                   
                                     2 
                                      
                                     π 
                                      
                                     
                                         
                                     
                                      
                                     
                                       kk 
                                       i 
                                     
                                   
                                   N 
                                 
                               
                             
                             ] 
                           
                         
                         ] 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     w 
                     · 
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           0 
                         
                         
                           L 
                           - 
                           1 
                         
                       
                        
                       
                         
                           a 
                           i 
                         
                          
                         
                           
                              
                             
                               jφ 
                               i 
                             
                           
                           [ 
                           
                              
                             
                               
                                 - 
                                 j 
                               
                                
                               
                                 
                                   2 
                                    
                                   π 
                                    
                                   
                                       
                                   
                                    
                                   
                                     kk 
                                     i 
                                   
                                 
                                 N 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                 
               
             
           
         
       
     
         [0038]    As can be seen from the above equation, the interference introduced by the peak clipping signal to each sub-carrier is directly proportional to the weight set for each sub-carrier when the peak clipping signal is generated. That is, the distribution of the peak clipping noise to each sub-carrier can be controlled by adjusting the weight allocated for each sub-carrier, that is to say, a large weight is allocated to the sub-carrier having good anti-interference capability and a small weight is allocated to the sub-carrier having poor anti-interference capability. In this way, the overall performance of the system is improved. 
         [0039]    The method for reducing a signal peak value in the present invention is described below with some exemplary embodiments. 
       EMBODIMENT 1   
       [0040]    In this embodiment, the method for reducing a signal peak value is described with reference to  FIG. 2 . 
         [0041]    In Step  21 , a signal is received. 
         [0042]    In Step  22 , a middle peak clipping signal is generated according to a peak clipping weight factor or a frequency domain EVM. 
         [0043]    In Step  23 , peak point positions and amplitude phases of the received signal are detected. 
         [0044]    In Step  24 , a peak clipping signal is generated according to the peak point positions, the amplitude phases, and the middle peak clipping signal. 
         [0045]    In Step  25 , a peak clipping processing is performed on the received signal by using the peak clipping signal. 
         [0046]    In Step  26 , the amplitude of the processed signal is detected. 
         [0047]    In Step  27 , it is determined whether the amplitude is lower than a threshold or whether a number of peak clippings reaches a predetermined number, and if a determination result is true, Step  28  is performed in which the received signal after the peak clipping processing is output and the process ends; otherwise, the process returns to Step  23 . 
         [0048]    The threshold may be set according to a maximum peak value allowed by the system. For example, the threshold may be set to the maximum peak value or slightly smaller than the maximum peak value, for example, 0.95 times of the maximum peak value. The predetermined time may be an empirical value, for example, any value from 2 to 32. 
         [0049]    In Step  23 , it is possible to detect only a number of peak points. For example, the number of peak points may be set to any value from 2 to 32. Preferably, in consideration of the predetermined time, the number of peak points detected each time may usually be in inverse proportion to the predetermined number. 
         [0050]    In this embodiment, two methods for generating a middle peak clipping signal are described as follows. 
         [0051]    The first method for generating a middle peak clipping signal is described as shown in  FIG. 3 . 
         [0052]    In Step  31 , a peak clipping weight factor and a frequency domain EVM of each sub-carrier are collected. The peak clipping weight factor at least includes one of the following factors: an encoding mode, a constellation mapping mode, a degree of data importance, a transmit power, a channel condition, and a receiving quality requirement. 
         [0053]    In Step  32 , a weight is set for each sub-carrier according to the peak clipping weight factor or the frequency domain EVM. 
         [0054]    The weight of each sub-carrier can be obtained based on the following equation: 
         [0000]    
       
         
           
             
               w 
               j 
             
             = 
             
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                   
                     w 
                     
                       j 
                       , 
                       i 
                     
                   
                    
                   
                       
                   
                    
                   or 
                    
                   
                       
                   
                    
                   
                     w 
                     j 
                   
                 
               
               = 
               
                 
                   ∏ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                     
                 
                  
                 
                   w 
                   
                     j 
                     , 
                     i 
                   
                 
               
             
           
         
       
     
         [0055]    where w j  denotes a peak clipping weight of the j th  sub-carrier (w j ≧0); and w j,i  denotes a weight of the j th  sub-carrier under an i th  peak clipping weight factor. 
         [0056]    A method for setting a weight of a peak clipping weight factor is described as follows. 
         [0057]    The method for setting a weight of a peak clipping weight factor is illustrated by taking the constellation mapping mode as an example. The weight of a peak clipping weight decreases with the rising of an order corresponding to the constellation mapping mode, that is, when the order corresponding to the constellation mapping mode is low, the weight may be set high, and vice versa. For example, the orders corresponding to three constellation mapping modes of QPSK, 16 QAM, and 64 QAM increase successively, then the corresponding weights may be set to decrease successively, for example, the weights may be set to 0.70, 0.31, and 0.15 respectively. 
         [0058]    The method for setting a weight of a peak clipping weight factor is illustrated by taking an encoding rate of the sub-carrier as an example. The weight of a peak clipping weight decreases with the rising of the encoding rate of the sub-carrier, that is, when the encoding rate of the sub-carrier is low, the weight may be set high, and vice versa. For example, the weight for the encoding mode at ⅓ rate can be set higher than that of the encoding mode at ½ rate, and the weights of the encoding mode at ⅓ rate and the encoding mode at ½ rate may be set to 0.2 and 0. 12 respectively. 
         [0059]    Other methods for setting a weight of a peak clipping weight factor are similar to the weight setting methods using the encoding mode and the constellation mapping mode. 
         [0060]    The minimum processing unit for setting the peak clipping weight may be a sub-carrier or multiple sub-carriers of the same or similar conditions. 
         [0061]    The method for setting the weight of each sub-carrier according to a peak clipping weight factor on the sub-carrier is described above. Besides, the weight of each sub-carrier may also be set according to a frequency domain EVM. It is assumed that the frequency domain EVMs of sub-carriers 1 to N are respectively smaller than or equal to EVM 1  . . . , EVM N . Then, the corresponding weights w 1 , . . . , w N  of the sub-carriers can be computed based on the following equation: 
         [0000]    
       
         
           
             
               
                 w 
                 1 
               
               
                 EVM 
                 1 
               
             
             ≈ 
             
               
                 w 
                 2 
               
               
                 EVM 
                 2 
               
             
             ≈ 
             … 
             ≈ 
             
               
                 w 
                 N 
               
               
                 EVM 
                 N 
               
             
           
         
       
     
         [0062]    In Step  33 , the middle peak clipping signal (also referred to as a Kernel signal) may be generated through an IFFT according to the weight of each sub-carrier. 
         [0063]    In Step  34 , an amplitude adjustment (normalization) is performed on the middle peak clipping signal, so as to facilitate the amplitude adjustment on the middle peak clipping signal during the peak canceling. 
         [0064]    A second method for generating a middle peak clipping signal is described below, as shown in  FIG. 4 . 
         [0065]    In order to generate a peak clipping signal, data sub-carriers in the symbol are first divided into P segments, and all sub-carriers in each segment have only one constellation mapping mode at a certain time (except sub-carriers for transmitting pilots). Corresponding segment Kernel signals are pre-generated for the P segments. The segment Kernel signal is obtained by setting the weight of the data sub-carriers in the segment to the same value, for example, 1, placing the data 0 in other sub-carriers (including the sub-carriers for transmitting pilots), and performing the IFFT and then performing amplitude normalization. 
         [0066]    In Step  41 , a weight of each segment is set according to a peak clipping weight factor or frequency domain EVM of each segment. 
         [0067]    The weight of each segment may be computed based on the following equation: 
         [0000]    
       
         
           
             
               w 
               j 
             
             = 
             
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                   
                     w 
                     
                       j 
                       , 
                       i 
                     
                   
                    
                   
                       
                   
                    
                   or 
                    
                   
                       
                   
                    
                   
                     w 
                     j 
                   
                 
               
               = 
               
                 
                   ∏ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                     
                 
                  
                 
                   w 
                   
                     j 
                     , 
                     i 
                   
                 
               
             
           
         
       
     
         [0068]    where w j  denotes a weight of the j th  segment (w j ≧0); and w j,i  denotes a weight of the j th  segment under an i th  peak clipping weight factor. The method for setting a weight of a peak clipping weight factor can be referred to Step  32 . 
         [0069]    The weight of each segment may also be obtained based on the following equation: 
         [0000]    
       
         
           
             
               
                 w 
                 1 
               
               
                 EVM 
                 1 
               
             
             ≈ 
             
               
                 w 
                 2 
               
               
                 EVM 
                 2 
               
             
             ≈ 
             … 
             ≈ 
             
               
                 w 
                 P 
               
               
                 EVM 
                 P 
               
             
           
         
       
     
         [0070]    where EVM 1 , . . . , EVM P  denote upper limits of frequency domain EVMs of the first segment, . . . the Pth segment; and w 1 , . . . , w P  denote peak clipping weights of the first segment, . . . the Pth segment. 
         [0071]    In Step  42 , the segment Kernel signals and the corresponding weights thereof are multiplied so that each segment Kernel signal has its weight, and the Kernel signals with their separate weights are added to obtain a peak clipping Kernel signal. 
         [0072]    In Step  43 , an amplitude adjustment (normalization) is performed on the peak clipping Kernel signal, so as to facilitate the amplitude adjustment on the peak clipping Kernel signal during the peak canceling. 
         [0073]    In this way, the IFFT in the generation of Kernel can be omitted by pre-storing the segment Kernel signals, thereby reducing the complexity of generating the Kernel signals. 
       EMBODIMENT 2   
       [0074]    In this embodiment, the method for reducing a signal peak value is described with reference to  FIG. 5 . 
         [0075]    In Step  51 , a signal is received. 
         [0076]    In Step  52 , a weight of each sub-carrier in a symbol is obtained. 
         [0077]    The weight of the sub-carrier may be obtained based on the following equation: 
         [0000]    
       
         
           
             
               w 
               j 
             
             = 
             
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                   
                     w 
                     
                       j 
                       , 
                       i 
                     
                   
                    
                   
                       
                   
                    
                   or 
                    
                   
                       
                   
                    
                   
                     w 
                     j 
                   
                 
               
               = 
               
                 
                   ∏ 
                   
                     i 
                     = 
                     1 
                   
                   I 
                 
                  
                 
                     
                 
                  
                 
                   w 
                   
                     j 
                     , 
                     i 
                   
                 
               
             
           
         
       
     
         [0078]    where w j  denotes a weight of the j th  sub-carrier (w j ≧0); and w j,i  denotes a weight of the j th  sub-carrier under an i th  peak clipping weight factor. 
         [0079]    The weight of the sub-carrier may also be obtained based on the following equation: 
         [0000]    
       
         
           
             
               
                 w 
                 1 
               
               
                 EVM 
                 1 
               
             
             ≈ 
             
               
                 w 
                 2 
               
               
                 EVM 
                 2 
               
             
             ≈ 
             … 
              
             
                 
             
             ≈ 
             
               
                 w 
                 N 
               
               
                 EVM 
                 N 
               
             
           
         
       
     
         [0080]    where EVM 1 , . . . , EVM N  denote upper limits of frequency domain EVMs of the sub-carrier 1, . . . , the sub-carrier N; and w 1 , . . . , w N  denote peak clipping weights of the sub-carrier 1, . . . , the sub-carrier N. The method for setting a weight of a peak clipping weight factor can be referred to that described in Step  32 . 
         [0081]    In Step  53 , an ideal peak clipping signal is obtained. The ideal peak clipping signal is: 
         [0000]    
       
         
           
             
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               ( 
               
                   
               
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               ) 
             
             = 
             
                 
             
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                                  
                                 
                                     
                                 
                                  
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                                  
                                 
                                     
                                 
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         [0000]    where s(k) denotes the kth sampling point of the ideal peak clipping signal, and x(k) denotes the kth sampling point of the received signal or the kth sampling point of a signal returned by a peak clipping processing module. 
         [0082]    In Step  54 , a transform from the time domain to the frequency domain (for example, a fast Fourier transform) is performed on the ideal peak clipping signal to obtain a frequency domain signal. 
         [0083]    In Step  55 , a weight adjustment is performed on the frequency domain signal according to the weight of each sub-carrier. 
         [0084]    In Step  56 , a transform from the frequency domain to the time domain (for example, an IFFT) is performed on the frequency domain signal upon which the weight adjustment is performed, and an amplitude adjustment is performed on the transformed result to generate a peak clipping signal. 
         [0085]    In Step  57 , a peak clipping processing is performed on the received signal by using the peak clipping signal. 
         [0086]    In Step  58 , the amplitude of the processed signal is detected. 
         [0087]    In Step  59 , it is determined whether the amplitude is lower than a threshold or whether a number of peak clippings reaches a predetermined number, and if the amplitude is lower than the threshold or the number of peak clippings reaches the predetermined number, Step  60  is performed in which the received signal after the peak clipping processing is output and the process ends; otherwise, the process returns to Step  53 . 
         [0088]    The methods for setting the threshold and the number of peak clippings can be referred to as described in Step  27  in the preceding embodiment. 
       EMBODIMENT 3   
       [0089]    In this embodiment, a device for reducing a signal peak value is described. 
         [0090]    As shown in  FIG. 6 , the device for reducing a signal peak value includes: 
         [0091]    a receiving unit, adapted to receive a signal or a signal returned by a peak clipping processing unit; 
         [0092]    a peak clipping signal generating unit, adapted to generate a peak clipping signal according to a peak clipping weight factor or a frequency domain EVM and the received signal of the receiving unit; and 
         [0093]    the peak clipping processing unit, adapted to: perform a peak value reduction processing on the received signal according to the peak clipping signal; determine whether an amplitude of the processed signal is lower than a threshold or whether a number of peak clippings reaches a predetermined number; and if the amplitude is lower than the threshold or the number of peak clippings reaches the predetermined number, output the signal and end the process; otherwise, output the signal to the receiving unit. 
         [0094]      FIG. 7  is corresponding to the first method for generating a peak clipping signal in the first embodiment. The peak clipping signal generating unit specifically includes: a weight generating module, adapted to generate a weight of each sub-carrier according to a peak clipping weight factor or a frequency domain EVM; a middle peak clipping signal generating module, adapted to generate a middle peak clipping signal according to the weight of each sub-carrier; a detection module, adapted to detect peak point positions and amplitude phases of the received signal or peak point positions and amplitude phases of the signal processed by the processing module; and a generating module, adapted to generate the peak clipping signal according to the peak point positions and the amplitude phases detected by the detection module and the middle peak clipping signal. The peak clipping processing unit specifically includes a processing module, adapted to perform a peak value reduction processing on the signal received by the receiving unit by using the peak clipping signal, and a determination module, adapted to: determine whether an amplitude of the signal processed by the processing module is lower than a threshold or whether a number of peak clippings reaches a predetermined number; and if the amplitude is lower than the threshold or the number of peak clippings reaches the predetermined number, output the signal and end the process; otherwise, output the signal to the receiving unit. 
         [0095]      FIG. 8  is corresponding to the second method for generating a peak clipping signal in the first embodiment. The peak clipping signal generating unit specifically includes: a weight generating module, adapted to generate a weight of a segment according to a peak clipping weight factor or a frequency domain EVM; a segment peak clipping signal storage module, adapted to store segment peak clipping signals; a middle peak clipping signal generating module, adapted to generate a middle peak clipping signal according to the weight of each segment and the segment peak clipping signals; a detection module, adapted to detect peak point positions and amplitude phases of the received signal or peak point positions and amplitude phases of the signal processed by the processing module; and a generating module, adapted to generate the peak clipping signal according to the middle peak clipping signal, the peak point positions, and the amplitude phases. The peak clipping processing unit specifically includes a processing module, adapted to perform a peak value reduction processing on the signal received by the receiving unit by using the peak clipping signal, and a determination module, adapted to: determine whether an amplitude of the signal processed by the processing module is lower than a threshold or whether a number of peak clippings reaches a predetermined number; and if the amplitude is lower than the threshold or the number of peak clippings reaches the predetermined number, output the signal and end the process; otherwise, output the signal to the receiving unit. 
         [0096]      FIG. 9  is corresponding to the second embodiment. The peak clipping signal generating unit specifically includes a weight generating module, adapted to generate a weight of each sub-carrier according to a peak clipping weight factor or a frequency domain EVM; an ideal peak clipping signal generating module, adapted to obtain an ideal peak clipping signal according to the received signal, where the ideal peak clipping signal is obtained by deducting a signal after the peak clipping of the received signal from the received signal; a transform module, adapted to transform the ideal peak clipping signal into a frequency domain signal; an adjustment module, adapted to adjust the frequency domain signal according to the weight generated by the weight generating module; and a generating module, adapted to generate a peak clipping signal according to the frequency domain signal adjusted by the adjustment module. The peak clipping processing unit specifically includes a processing module, adapted to perform a peak value reduction processing on the signal received by the receiving unit by using the peak clipping signal and a determination module, adapted to: determine whether an amplitude of the signal processed by the processing module is lower than a threshold or whether a number of peak clippings reaches a predetermined number; and if the amplitude is lower than the threshold or the number of peak clippings reaches the predetermined number, output the signal and end the process; otherwise, output the signal to the receiving unit. 
       EMBODIMENT 4   
       [0097]    In this embodiment, a transmitting device is described. As shown in  FIG. 10 , the transmitting device includes: encoding units  101 - 1 ˜ 101 -n, adapted to encode input data according to an encoding mode; constellation mapping units  102 - 1 ˜ 102 -n, adapted to map the encoded data according to a constellation mapping mode; a modulation unit  103 , adapted to perform an OFDM modulation on the mapped data and transfer the modulated data to the device for reducing a peak value; and a device for reducing a peak value, adapted to perform a peak clipping processing on signals in a symbol according to peak clipping signals having different weights. The device for reducing a peak value includes: a peak clipping signal generating unit  108 , adapted to set a weight for each sub-carrier according to encoding and constellation mapping modes of each sub-carrier and other constraints (for example, a degree of data importance, a transmit power, a channel condition, and a receiving quality requirement) or a frequency domain EVM, and generate a peak clipping signal according to the weight of each sub-carrier; and a peak clipping processing unit  104 , adapted to perform a peak clipping processing on the sub-carriers in the symbol according to the peak clipping signals generated by the peak clipping signal generating unit  108 . 
         [0098]    The present invention is also applicable to a combined peak clipping scenario in which one symbol contains multiple OFDM carriers. At this time, a peak clipping weight factor and a frequency domain EVM of each sub-carrier in each OFDM carrier need to be collected. The peak clipping weight factor includes one or more of the factors such as an encoding mode, a constellation mapping mode, a degree of data importance, a transmit power, a channel condition, and a receiving quality requirements. Afterwards, a weight is set for each sub-carrier in each carrier according to the peak clipping weight factor or the frequency domain EVM. The setting method can be referred to as described in Step  32 . Then, a combined peak clipping signal, that is, a middle peak clipping signal, of the symbol containing the multiple OFDM carriers is generated according to the weight of each sub-carrier in each OFDM carrier. The generating method is as follows. 
         [0099]    If the sub-carriers in each of the multiple OFDM carriers are orthogonal to each other, a multiple-point IFFT transform may be utilized to transform the weight of each sub-carrier in each OFDM carrier into a middle peak clipping signal (also referred to as a Kernel signal). If the sub-carriers in each of the multiple OFDM carriers are not orthogonal to one another, a plurality of multiple-point IFFT transforms may be utilized to transform the weight of each sub-carrier in each OFDM carrier into multiple quasi middle peak clipping signals, then a middle peak clipping signal (also referred to as a Kernel signal) is generated by using the quasi middle peak clipping signals in combination with a numerically controlled oscillator (NCO). Finally, an amplitude adjustment (normalization) is performed on the middle peak clipping signal, so as to facilitate the amplitude adjustment on the middle peak clipping signal during the peak canceling. 
         [0100]    It should be noted that, in the process for reducing a signal peak value in the above embodiment, there is a substitution approach for re-computing the middle peak clipping signal for every symbol. The middle peak clipping signal may also be set according to a variation period of the peak clipping weight factor of each sub-carrier. For example, one middle peak clipping signal may be generated during per frame. Besides, when the conditions of the sub-carriers are substantially the same at different time, one peak clipping Kernel signal may also be pre-stored, so as to avoid repeated computation of the peak clipping signal and save hardware expense. 
         [0101]    In the embodiments of the present invention, a weight of a peak clipping signal is set according to a peak clipping weight factor (the peak clipping weight factor includes, but is not limited to, an encoding mode, a constellation mapping mode, a transmit power, and a receiving quality class) or a frequency domain EVM, that is, a large weight is allocated to the sub-carrier having good anti-interference capability and a small weight is allocated to the sub-carrier having poor anti-interference capability, thereby improving the overall performance of the system. 
         [0102]    Although the present invention is described through the embodiments, it will be apparent to persons of ordinary skill in the art that various modifications and variations can be made to the present invention without departing from the essence of the invention. The scope of the present invention shall be defined by the following claims.