Abstract:
In a signal generation device in a wires transmission system, a calculation amount is greatly reduced compared with a convention FFT Pre-Processing method which performs oversampling, and peak power is reduced to substantially the same extent as in the convention method. A transmitter  100  includes a slope estimation unit  102  and a slope reference attenuation signal selection unit  103 . The slope estimation unit  102  generates and outputs a slope estimation value indicating an inclination of a data signal waveform at a data signal point. The slope reference attenuation signal selection unit  103  estimates a data signal which may cause a peak after oversampling, based on an amplitude value of a data signal and a slope estimation value, and determines an attenuation amount for a selected data signal. The slope reference attenuation signal selection unit  103  generates information concerning a selection result and the determined attenuation amount, and outputs the information as a data attenuation coefficient.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is based on Japanese Patent Application No. 2006-285030 (filed Oct. 19, 2006), and claims priority based on the same application No. 2006-285030 under Paris Convention. Content of disclosure of the application No. 2006-285030 is incorporated into the description of the present application by reference to the application No. 2006-285030. 
         [0002]    The present invention relates to a signal generation device suitably applied to a transmission device in a wireless transmission system. 
       BACKGROUND ART 
       [0003]    In recent years, SC (Single Carrier)-FDMA (Frequency Division Multiple Access) scheme has achieved lower peak power than multi-carrier transmission schemes such as OFDM (Orthogonal Frequency Division Multiplexing) and can reduce power consumption. Therefore, much attention has been drawn to the SC-FDMA scheme. 
         [0004]    One of generation methods for generating SC-FDMA transmission signals is as follows. For each of unit time slots, M data symbols (where M is a natural number) are subjected to DFT (Discrete Fourier Transform), thereby to convert the M data symbols along a frequency axis. Total N-M zeros (where N is a multiplier of 2, which is greater than M) are further inserted in both of high and low frequency sides. IFFT sampling at N points (corresponding to N/M-times oversampling) is thereafter carried out. Even after the N/M-times oversampling, Peak to Averaged Power Ratio (PAPR) is lower than that in the multi-carrier transmission methods. However, one of problems in the SC-FDMA is that the PAPR increases to be greater compared with that before the N/M-times oversampling. 
         [0005]    FFT Pre-processing method is one of methods for reducing the PAPR in the SC-FDMA scheme (e.g., see Non-Patent Document 1). According to the FFT Pre-processing method, X-times oversampling is performed before N/M-times oversampling which is performed when generating a transmission signal. The X-times oversampling is performed to select a data symbol which may cause a peak in the N/M-times oversampling. In this processing of selection, data symbol points are associated with signal points obtained by different operations of X-times oversampling, respectively, to determine whether each data symbol may cause a peak. Therefore, X needs to be 2 or greater (where 2 is a real number not smaller than 2). Further, oversampling rates of X and N/M are desirably values close to each other in order to maximize effect of the FFT Pre-processing method. A conventional example will now be described below in a case of X=2 (N/M=1.7) where M=300 and N=512 are given. 
         [0006]    A signal before oversampling which may cause a great peak after N/M-times (1.7 times) oversampling is selected by using a result of 2-times oversampling. The amplitude of the selected signal is attenuated before DFT in the 1.7-times oversampling. In this manner, a high peak is prevented from occurring after the 1.7-times oversampling, which is a feature of this conventional example. A conventional FFT Pre-processing method will further be described below with reference to  FIGS. 1 and 2 . 
         [0007]    A transmitter  1000  shown in  FIG. 1  is constituted by a data signal generation unit  1001 , a DFT unit  1002 , a 2-times point IDFT unit  1003 , an amplitude reference attenuation signal selection unit  1004 , a subtraction coefficient multiplication unit  1005 , an N/M-times oversampling unit  1006 . 
         [0008]    In the transmitter  1000  shown in  FIG. 1 , where M data signals (M is a natural number) are included in each unit time slot, the data signal generation unit  1001  generates M data signals Din(M×v+1) to Din(M×v+M) (consecutive numbers from the first data in the first slot), in the v-th time slot (v is an integer not smaller than 0). The DFT unit  1002  is input with the data signals Din(M×v+1) to Din(M×v+M), performs DFT (Discrete Fourier Transform) at M points, and outputs DFT output signals Dout(M×v+1) to Dout(M×v+M). 
         [0009]    The 2-times point IDFT unit  1003  is input with total 2M signals which are obtained by extrapolating total M zero-components from outside both ends of the DFT output signals, where the two ends correspond to high and low frequency components. The 2-times point IDFT unit  1003  generates 2-times oversampling signals by performing IDFT (Inverse Discrete Fourier Transform) at 2M points, and outputs the generated signals as 2-times oversampling signals Ddbl(2M×v+1) to Ddbl(2M×v+2M). 
         [0010]    Referring to  FIG. 2 , the amplitude reference attenuation signal selection unit  1004  will now be described next. The amplitude reference attenuation signal selection unit  1004  is constituted by an attenuation coefficient initial value generation unit  1101  and an amplitude reference attenuation coefficient calculation unit  1102 . 
         [0011]    The attenuation coefficient initial value generation unit  1101  generates and outputs attenuation coefficient initial values Y(M×v+1) to Y(M×v+M) which are all 1. 
         [0012]    The amplitude reference attenuation coefficient calculation unit  1102  is input with the 2-times oversampling signals Ddbl(2M×v+1) to Ddbl(2M×v+2M) and the attenuation coefficient initial values Y(M×v+1) to Y(M×v+M). If a threshold C (C is a positive real number) is exceeded by an absolute value of a 2-times oversampling signal among the 2-times oversampling signals excluding signals that correspond to the same sampling time as that of the data signals, the amplitude reference attenuation coefficient calculation unit  1102  changes, to a calculation result of an expression 1 shown in  FIG. 3 , an attenuation coefficient initial value Y(M×v+g) (g is a natural number not greater than M) for a sampling time which is one sample ahead of the 2-times oversampling signal having an absolute value exceeding the threshold C (C is a positive real number). The amplitude reference attenuation coefficient calculation unit  1102  outputs, as attenuation coefficients Wm(M×v+1) to Wm(M×v+M), results of changing the attenuation coefficient initial values Y(M×v+1) to Y(M×v+M). In the expression 1, γ is a positive real number and abs ( ) is an absolute value of ( ). 
         [0013]    A result of N/M-times oversampling after attenuation coefficient multiplication can be set to a value close to a constant value (C) by setting an attenuation coefficient so as to decrease as the amplitude value of a 2-times oversampling signal Ddbl (2M×v+2g−1) increases. Since sizes of peaks after N/M-times oversampling depend on the attenuation coefficient, the attenuation coefficient should desirably be smaller in order to reduce PAPR. However, if the amplitude after multiplication of the attenuation coefficient is too small, there is a problem that reception characteristics deteriorate. Therefore, when the amplitude of the 2-times oversampling signal Ddbl (2M×v+2g−1) is small, the attenuation coefficient needs to be large. 
         [0014]    The attenuation coefficient multiplication unit  1005  is input with the data signals Din(M×v+1) to Din(M×v+M) and the attenuation coefficients Wm(M×v+1) to Wm(M×v+M), and multiplies the data signals Din(M×v+1) to Din(M×v+M) respectively by the attenuation coefficients Wm(M×v+1) to Wm(M×v+M). The attenuation coefficient multiplication unit  1005  outputs multiplication results thereof as attenuation coefficient multiplication signals Sdin(M×v+1) to Sdin(M×v+M). 
         [0015]    The N/M-times oversampling unit  1006  is input with the attenuation coefficient multiplication signals Sdin(M×v+1) to Sdin(M×v+M), and performs DFT at M points, thereby to generate attenuation multiplication DFT output signals Sziout(M×v+1) to Sziout(M×v+M). The N/M-times oversampling unit  1006  performs IFFT (Inverse Fast Fourier Transform) at N points and N/M-times oversampling, on N signals points obtained by exerting total (N−M) zero signal points from outside both ends of attenuation multiplication DFT output signals Sziout (M×v+1) to Sziout (M×v+M), where the both ends correspond respectively to high and low frequency components, thereby to generate signals as transmission signals Sdout(M×v+1) to Sdout(M×v+M). 
         [0016]    PAPR after N/M-times oversampling can thus be reduced in a manner that signals which may cause high peaks after N/M-times oversampling are selected by performing 2-times oversampling and are further attenuated before DFT in N/M-times oversampling.
       Non-Patent Document 1: PA power de-rating reduction scheme for DFT-SOFDM and TP, R1-060392, Motorola, 3GPP TSG-RAN WG1 #44, Denver, USA, Feb. 13-17, 2006       
 
       SUMMARY OF INVENTION 
       [0018]    However, such a conventional method requires IDFT at 2M points because data signals which may cause a peak beyond a threshold C after N/M-times oversampling are selected by performing 2-times oversampling. IDFT at 2M points is equivalent to approximately four times greater calculation amount than DFT at 2M points, and gives rise to a problem of a calculation amount. Input signals to DFT which may cause a peak need to be selected while greatly reducing the calculation amount, compared with IDFT at 2M points. 
         [0019]    The present invention hence has an object of providing a signal generation device, a signal generation method, and a program thereof for use in a wireless transmission system, which can greatly reduce a calculation amount in comparison with a conventional FFT Pre-Processing method of performing oversampling, and can reduce PAPR to the same extent as in the conventional method. 
         [0020]    A signal generation device that generates a transmission signal in a wireless transmission system, including: a data attenuation coefficient generation means that is input with M data signals (M is a natural number), for estimating and selecting data signals that may cause a peak after oversampling, determining an attenuation amount for the selected one or more data signals, generating information concerning a selection result and the determined attenuation amount for the selection result, and outputting the information as a data attenuation coefficient; an attenuation coefficient multiplication means that is input with the M data signals and the data attenuation coefficient, for multiplying each of the data signals corresponding to the selection result for the data attenuation coefficient by the attenuation amount for the selection result, and outputting multiplication results as M attenuation coefficient multiplication signals; and an oversampling unit that is input with the M attenuation coefficient multiplication signals and performs oversampling, thereby to generate and output a transmission signal, wherein the data attenuation coefficient generation means includes a slope estimation unit that outputs, as slope estimation values corresponding respectively to the M data signals, information indicating inclinations of data signal waveforms at data signal points, from the M data signals, respectively, and a slope reference attenuation signal selection unit that is input with the M data signals and the M slope estimation values, estimates and selects data signals that may cause a peak after oversampling, based on amplitude values of the M data signals and the M slope estimation values, determines an attenuation amount for the selected data signals, generates information concerning a selection result and the determined attenuation amount, and outputs the information as the data attenuation coefficient. 
         [0021]    According to the present invention, a data signal to be multiplied by an attenuation coefficient is selected by using an inclination of a data signal waveform. Therefore, a transmission signal can be generated with peak power of the transmission signal reduced to the same extent as in convention methods and with a calculation amount smaller than in convention methods. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a block diagram of a transmitter of a conventional example; 
           [0023]      FIG. 2  is a block diagram of an amplitude reference attenuation signal selection unit in the conventional example; 
           [0024]      FIG. 3  shows mathematical expressions; 
           [0025]      FIG. 4  is a block diagram of a transmitter according to the present invention; 
           [0026]      FIG. 5  is a block diagram of a slope estimation unit in the best mode for carrying out the invention; 
           [0027]      FIG. 6  is a block diagram of a slope reference attenuation signal selection unit according to the invention; 
           [0028]      FIG. 7  is a block diagram of a slope estimation unit in a first embodiment; 
           [0029]      FIG. 8  shows sampling time of an oversampling slope and a data signal; 
           [0030]      FIG. 9  is a block diagram of a slope estimation unit in a second embodiment; 
           [0031]      FIG. 10  is a block diagram of a Z point IDFT partial differential value calculation unit in the second embodiment; 
           [0032]      FIG. 11  shows a simulation result of PARA characteristics using Embodiment 3; and 
           [0033]      FIG. 12  shows a simulation result of reception characteristics using Embodiment 3. 
       
    
    
     EXPLANATION OF REFERENCE SYMBOLS 
       [0000]    
       
         
           
               100 ,  1000 : Transmitter 
               101 ,  1001 : Data signal generation unit 
               102 : Slope estimation unit 
               103 : Slope reference attenuation signal selection unit 
               104 ,  1005 : Attenuation coefficient multiplication unit 
               105 ,  1006 : N/M-times oversampling unit 
               201 ,  401 ,  1002 : DFT unit 
               202 : M point IDFT partial differential value calculation unit 
               301 ,  1101 : Attenuation coefficient initial value generation unit 
               302 : Attenuation coefficient calculation unit 
               402 ,  603 : Z point IDFT partial differential value calculation unit 
               403 : Peak estimation slope approximation unit 
               601 : Cyclic shift signal insertion unit 
               602 : FFT unit 
               604 : Cyclic shift signal deletion unit 
               701 : I/Q separation unit 
               702 ,  703 : Constant multiplication unit 
               704 : I/Q multiplexing unit 
               705 : IFFT unit 
               1003 : 2-times point IDFT unit 
               1004 : Amplitude reference attenuation signal selection unit 
               1102 : Amplitude reference attenuation signal selection unit 
           
         
       
     
       DESCRIPTION OF EMBODIMENTS 
       [0056]    Hereinafter, a best mode for carrying out the invention will be described with reference to the drawings. 
         [0057]      FIG. 4  is a block diagram showing a transmitter according to the best mode of the invention. The transmitter  100  is constituted by a data signal generation unit  101 , a slope estimation unit  102 , a slope reference attenuation signal selection unit  103 , an attenuation coefficient multiplication unit  104 , and an N/M-times oversampling unit  105 . The transmitter  100  executes functions described below, under program control. 
         [0058]    In the transmitter  100  shown in  FIG. 4 , the data signal generation unit  101  generates M data signals Din(M×v+1) to Din(M×v+M) (where M is a natural number) in a v-th time slot (where v is an integer not smaller than 0). 
         [0059]    Next, the slope estimation unit  102  will be described with reference to  FIG. 5 . The slope estimation unit  102  is constituted by a DFT unit  201  and an M point IDFT partial differential value calculation unit  202 . The DFT unit  201  is input with the data signals Din(M×v+1) to Din(M×v+M), performs DFT at M points, and generates and outputs DFT output signals Dout(M×v+1) to Dout(M×v+M). 
         [0060]    The M point IDFT partial differential value calculation unit  202  calculates an inclinations of each of data signal waveforms of the data signals Din(M×v+1) to Din(M×v+M) at sampling time, from expressions 2 and 3 shown in  FIG. 3  which are obtained by performing partial differentiation with respect to time on each of real and imaginary components of a calculation expression of IDFT. The M point IDFT partial differential value calculation unit  202  outputs the inclination as a slope estimation value Usl(M×v+i) (i is a natural number not greater than M). In the expressions 2 and 3, ( )real denotes a real number part of ( ), and ( ) imag denotes an imaginary number part of ( ). 
         [0061]    Next, the slope reference attenuation signal selection unit  103  will be described with reference to  FIG. 6 . The slope reference attenuation signal selection unit  103  is constituted by an attenuation coefficient initial value generation unit  301  and an attenuation coefficient calculation unit  302 . 
         [0062]    The attenuation coefficient initial value generation unit  301  generates and outputs attenuation coefficient initial values Y(M×v+1) to Y(M×v+M) which are all 1. 
         [0063]    The attenuation coefficient calculation unit  302  is input with slope estimation value Usl (M×v+1) to Usl (M×v+M), the data signals Din(M×v+1) to Din(M×v+M), and the attenuation coefficient initial values Y(M×v+1) to Y(M×v+M). On a system of data signals Din(M×v+j) to Din(M×v+j+p) (where j is a natural number not greater than (M−1)) which have an amplitude value not smaller than an amplitude threshold A (where A is a positive real number) or not greater than an amplitude threshold −A and which are continuous through (p+1) points (where p is a natural number), if a slope threshold B (where B is a positive real number) is exceeded by absolute values of slope estimation values Usl(M×v+j) to Usl(M×v+j+p−1) corresponding to data signals Din(M×v+j) to Din(M×v+j+p−1) excluding Din(M×v+j+p), among the data signals Din(M×v+1) to Din(M×v+M), and if a data signal Din(M×v+k) (where k is an integer between j and (j+p−1)) and a slope estimation value Usl(M×v+k) have equal codes, attenuation coefficient initial values Y(M×v+h) corresponding to Din(M×v+k) and Din(M×v+k+1) are changed to values calculated from the expression 4 shown in  FIG. 3 . The attenuation coefficient calculation unit  302  outputs results of changing the attenuation coefficient initial values Y (M×v+1) to Y (M×v+M), as attenuation coefficients Wm(M×v+1) to Wm(M×v+M). In the expression 4, α and β are positive real numbers. 
         [0064]    If the attenuation coefficients WM(M×v+1) to Wm(M×v+M) are set to small values in accordance with sizes of data signals and slope estimation values, peaks in results of performing N/M-times oversampling after the attenuation coefficient multiplication can be set to values which are close to a constant value (A). Like in conventional methods, sizes of peaks after N/M-times oversampling depend on the attenuation coefficient Wm, and therefore, the attenuation coefficient Wm should desirably be small in order to reduce PAPR. However, if the attenuation coefficient is too small, there is a problem that reception characteristics deteriorate. Therefore, the attenuation coefficient should desirably be changed in accordance with amplitude values of data signals and/or sizes of slope estimation values. 
         [0065]    The attenuation coefficient multiplication unit  104  is input with the data signals Din(M×v+1) to Din(M×v+M) and the attenuation coefficients Wm(M×v+1) to Wm(M×v+M), and multiplies the data signals Din(M×v+1) to Din(M×v+M) by the attenuation coefficients Wm(M×v+1) to Wm(M×v+M), respectively, to output attenuation coefficient multiplication signals Sdin(M×v+1) to Sdin(M×v+M). 
         [0066]    The N/M-times oversampling unit  105  is input with the attenuation coefficient multiplication signals Sdin(M×v+1) to Sdin(M×v+M), and performs DFT at M points, thereby to generate attenuation multiplication DFT output signals Sziout(M×v+1) to Sziout(M×v+M). The N/M-times oversampling unit  105  further performs IFFT (Inverse Fast Fourier Transform) at N points, and N/M-times oversampling, on N signals points obtained by exerting total (N−M) zero signal points from outside both ends of the attenuation multiplication DFT output signals Sziout (M×v+1) to Sziout (M×v+M), where the both ends correspond respectively to high and low frequency components, thereby to generate signals as transmission signals Sdout(M×v+1) to Sdout(M×v+M). 
         [0067]    Through processings as described above, data signals are to be multiplied by attenuation coefficients are selected by use of inclinations of waveforms of data signals. In this manner, transmission signals can be generated with a smaller calculation amount than in conventional methods and with PAPR reduced to the same extent as in conventional methods. 
       First Embodiment 
       [0068]    Next, a first embodiment will be described. The same block diagram as that of the transmitter in the best mode of the invention can also be referred to as a block diagram of a transmitter according to the first embodiment. The first embodiment differs from the best mode of the invention in the processing performed by the slope estimation unit  102 . In this embodiment, a slope estimation unit which is the difference to the best mode of the invention will be described with reference to  FIG. 7 . The slope estimation unit  102  is constituted by a DFT unit  401 , a Z point IDFT partial differential value calculation unit  402  (where Z is a multiplier of 2 which is greater than N), and a peak estimation slope approximation unit  403 . 
         [0069]    The DTF unit  401  is input with the data signals Din(M×v+1) to Din(M×v+M), and performs DFT at M points, thereby to generate DFT output signals Dout(M×v+1) to Dout (M×v+M). The Z point IDFT partial differential value calculation unit  402  is input with, as zero extrapolating DFT output signals Dovin (Z×v+x) (where x is a natural number not greater than Z), Z signal points obtained by exerting total (Z−N) zero signal points from outside high and low frequency components of the DFT output signals Dout(M×v+1) to Dout(M×v+M), so that a total number of signal points is a multiplier of 2. The Z point IDFT partial differential value calculation unit  402  calculates information indicating inclinations of waveforms of data signals after Z/M-times oversampling, from expressions 5 and 6 shown in  FIG. 3  which are obtained by performing partial differentiation on each of actual and imaginary components of a calculation expression of IDFT, in relation to time, and outputs the information as an oversampling slope Uov(Z×v+q) (where q is a natural number not greater than Z). 
         [0070]    The peak estimation slope approximation unit  403  is input with oversampling slope Uov(Z×v+1) to Uov(Z×v+Z), and selects an approximate oversampling slope which is closest to sampling time of each of the data signals Din(M×v+1) to Din(M×v+M), from among the oversampling slopes Uov(Z×v+q). The peak estimation slope approximation unit  403  outputs the selected oversampling slope as a slope estimation value Usl(M×v+i). 
         [0071]    Expressions 5 and 6 are obtained by performing partial differentiation on expressions of IDFT at a number of points equal to a multiplier of 2, in relation to time. Therefore, like in the case of reducing a calculation amount of an IDFT calculation by using an IFFT algorithm, the calculation amount can be reduced by using algorithms shown in the expressions 5 and 6. 
         [0072]    Where the number of points for IDFT is M, the calculation amount of IDFT is proportional to a square of M. The calculation amount of IFFT is proportional to Mlog2 M. Where M is set to 300 in this embodiment, a calculation amount of IDFT at 2M points is 90,000 (300×300). On the other side, since 512 is the least multiplier of 2 which is not smaller than M(=300), the calculation amount is 4,608 in the case of using the algorithm of IFFT. By using the algorithm of IFFT, the calculation amount of calculating a partial differential value of IDFT can be reduced to approximately 1/20 relative to the case of using the algorithm of IFFT. 
         [0073]    However, as shown in  FIG. 8 , a sampling interval for oversampling slopes differs from a sampling interval for data signals but is M/Z of the sampling interval for data signals. Therefore, this embodiment is configured to perform a processing of selecting an oversampling slope which is closest to sampling time of each of the data signals Din(M×v+1) to Din(M×v+M) from among oversampling slopes Uov(Z×v+q), and of outputting the selected oversampling slope as a slope estimation value Usl(M×v+i). 
         [0074]    In this embodiment, an oversampling slope which is closest to sampling time of a data signal is used as a slope estimation value. Therefore, effect of more reducing the calculation amount is obtained though effect of reducing PAPR deteriorates more or less, compared with the case of accurately calculating an inclination of a data signal at sampling time of the data signal. 
       Second Embodiment 
       [0075]    Next, a second embodiment of the invention will be described. The same block diagram as that of the transmitter in the best mode of the invention can also be referred to as a block diagram of a transmitter in the second embodiment. This embodiment differs from the best mode of the invention in the processing at the slope estimation unit  102 . In this embodiment, a slope estimation unit which is the difference from the best mode of the invention will be described with reference to  FIGS. 9 and 10 . The slope estimation unit  102  shown in  FIG. 9  is constituted by a cyclic shift sigal insertion unit  601 , an FFT unit  602 , a Z point IDFT partial differential value calculation unit  603  (where Z is a multiplier of 2 which is greater than N), and a cyclic shift signal deletion unit  604 . 
         [0076]    The cyclic shift signal insertion unit  601  is input with data signals Din(M×v+1) to Din(M×v+M), and inserts data signals Din(M×v+1) to Din(M×v+(Z−M)) corresponding to (Z−M) signals obtained by cyclically shifting data signals, after the last data signal Din(M×v+M) among the data signals Din(M×v+1) to Din(M×v+M). The cyclic shift signal insertion unit  601  outputs results thereof, as cyclic shift insertion signals Dcyc(Z×v+1) to Dcyc(Z×v+Z). 
         [0077]    The FFT unit  602  is input with cyclic shift insertion signals Dcyc(Z×v+1) to Dcyc(Z×v+Z), performs FFT at Z points, and outputs results thereof as FFT output signals DFFT(Z×v+1) to DFFT (Z×v+Z). 
         [0078]    Like in Embodiment 1, the Z point IDFT partial differential value calculation unit  603  is input with the FFT output signals DFFT(Z×v+1) to DFFT(Z×v+Z), calculates information indicating inclinations of waveforms of the cyclic shift insertion signals Dcyc(Z×v+1) to Dcyc(Z×v+Z), from expressions which are obtained by performing partial differentiation on each of actual and imaginary components of a calculation expression of IDFT, in relation to time, and outputs the information as Z point IDFT partial differential signals DIDFT(Z×v+1) to DIDFT(Z×v+Z). 
         [0079]    Next, an example of using a circuit of IFFT for a processing of the Z point IDFT partial differential value calculation unit will be described with reference to  FIG. 10 . The Z point IDFT partial differential value calculation unit  102  shown in  FIG. 10  is constituted by an I/Q separation unit  701 , constant multiplication units  702  and  703 , an I/Q multiplexing unit  704 , and an IFFT unit  705 . 
         [0080]    The I/Q separation unit  701  is input with the FFT output signals DFFT (Z×v+1) to DFFT(Z×v+Z), separates actual and imaginary components from each other, and outputs the actual and imaginary components as I/Q separation actual signals DIout (Z×v+1) to DIout (Z×v+Z) and I/Q separation imaginary signals DQout(Z×v+1) to DQout(Z×v+Z). 
         [0081]    The constant multiplication unit  702  is input with the I/Q separation actual signals DIout (Z×v+1) to flout (Z×v+Z), multiplies each DIout(Z×v+q) by (2π(q−Z/2)/Z) (where q is a natural number not greater than Z), and outputs results as constant multiplication actual signals DmulI (Z×v+1) to DmulI(Z×v+Z). The constant multiplication unit  703  is input with the I/Q separation imaginary signals DQout(Z×v+1) to DQout(Z×v+Z), multiplies each DQout(Z×v+q) by (−1×2π(q−Z/2)/Z), and outputs results as constant multiplication imaginary signals DmulQ(Z×v+1) to DmulQ(Z×v+Z). 
         [0082]    The I/Q multiplexing unit  704  is input with the constant multiplication actual signals DmulI(Z×v+1) to DmulI(Z×v+Z) and the constant multiplication imaginary signals DmulQ(Z×v+1) to DmulQ(Z×v+Z), and replaces actual and imaginary components with each other, so that the constant multiplication actual signals and the constant multiplication imaginary signals become respectively imaginary and actual components after I/Q separation. The I/Q multiplexing unit  704  outputs signals thus subjected to I/Q multiplexing, as I/Q multiplex signals DIQMx(Z×v+1) to DIQMx(Z×v+Z). 
         [0083]    The IFFT unit  705  is input with the I/Q multiplex signals DIQMx(Z×v+1) to DIQMx(Z×v+Z), performs IFFT, and outputs results as Z point IDFT partial differential signal DIDFT(Z×v+1) to DIDFT (Z×v+Z). 
         [0084]    The cyclic shift signal deletion unit  604  is input with the Z point IDFT partial differential signal DIDFT(Z×v+1) to DIDFT(Z×v+Z), deletes (Z−M) signals corresponding to Z point IDFT partial differential signal DIDFT(Z×v+M+1) to DIDFT(Z×v+Z), and outputs results as slope estimation values Usl (M×v+1) to Usl(M×v+M) for sampling time of the data signals Din(M×v+1) to Din(M×v+M), respectively. 
         [0085]    Since the cyclic shift signal insertion unit  601  is used to set the number of signals to a multiplier of 2, an algorithm of FFT can be used in DFT which is used by the slope estimation units in the best mode of the invention and Embodiment 1. Further, since signals cyclically shifted by the cyclic shift signal insertion unit  601  are subjected to FFT by the FFT unit  602 , slope calculation accuracy can be prevented from being degraded by performing FFT on discontinuous signals. By using FFT, a calculation amount for DFT in the slope estimation unit can be reduced to approximately 1/20. 
         [0086]    Since the Z point IDFT partial differential value calculation unit performs a processing for multiplying actual and imaginary components by a constant and a processing for replacing the actual and imaginary components with each other, the circuit for IFFT can be directly used for partial differential calculation in IDFT. Owing to this processing, a calculation amount of partial differential calculation in IDFT can be reduced to approximately 1/20 compared with a case of not using the algorithm of IFFT. Further, since the circuit for IFFT in the oversampling unit in the transmitter can be directly used, a circuit scale can be prevented from being remarkably increased. If the algorithm of IFFT is used in calculation of partial differential values in DFT and IDFT by the slope estimation unit in the best mode, a calculation amount of the slope estimation unit can be reduced to approximately 1/400 of that in the best mode. 
       Third Embodiment 
       [0087]    Next, a third embodiment will be described. The same block diagram as that of the transmitter in the best mode of the invention can also be referred to as a block diagram of a transmitter in the third embodiment. This embodiment differs from the best mode of the invention in the setting value for the attenuation coefficient. In this embodiment, only the difference to the best mode of the invention will be described below. 
         [0088]    In this embodiment, the attenuation coefficient initial value Y(M×v+h) is changed to the value calculated by the expression 4. In the third embodiment, a fixed value smaller than 1 is used as a value to which the attenuation coefficient initial value Y(M×v+h) is changed. In view of reducing variation of peak power after N/M-times oversampling, the attenuation coefficient initial value Y(M×v+h) should desirably be set to be smaller as amplitude values of data signals and/or slope estimation values are greater. However, insofar as statistical distributions of amplitude values of data signals and/or slope estimation values are known in advance, a most frequently used fixed value may be used as a value to which all attenuation coefficient initial values Y are changed. 
         [0089]    In the case of fixing the value to which the attenuation coefficient initial values are changed, variations of amplitudes after N/M-times oversampling are greater compared with the best mode of the invention in which the attenuation coefficients are set to be smaller as the amplitude values and/or slope estimation values are greater. However, this case results in an effect of reducing a calculation amount compared with the best mode of the invention. 
         [0090]      FIGS. 11 and 12  show results of a simulation according to this embodiment.  FIG. 11  shows PARA characteristics, and  FIG. 12  shows reception characteristics. By using QPSK modulation, average power was normalized to 1 (e.g., a maximum amplitude of each of actual and imaginary components=±1/√2). An amplitude threshold A was set to 0.7, and a slope threshold B was set to 1. As the amplitude value was reduced, PAPR decreased. For example, when the attenuation coefficient is set to 0.5, PAPR can be reduced by 2.3 dB or so for CCDF (Complementary Cumulative Distribution Function)=10-3, compared with a case of not reducing PAPR. However, since a receiver is not notified of information concerning data symbols multiplied by the attenuation coefficient, a required Eb/NO (a noise to signal power ratio per one bit) as the attenuation coefficient is increased. When the attenuation coefficient is set to 0.5, deterioration of 0.7 dB or so is caused for BLER (Block Error Rate)=10-2, compared with a case of not reducing PAPR. Taken into consideration a deterioration amount of reception characteristics relative to a reduction amount of PAPR, a gain of 1.6 dB or so is obtained by reducing PAPR. 
         [0091]    Even by fixing the value to which the attenuation coefficient initial value Y(M×v+h), effect of 1.6 dB or so can be obtained. However, as has been described in the best mode of the invention, the gain obtained by reducing PAPR can be increased further by reducing the attenuation coefficients as the amplitude values of data signals and/or slope estimation values increase. 
       Fourth Embodiment 
       [0092]    Next, a fourth embodiment of the invention will be described. The same block diagram as that of the transmitter in the best mode of the invention can also be referred to as a block diagram of a transmitter in the fourth embodiment. The fourth embodiment is a system which uses a transmitter according to any of the best mode of the invention and first through third embodiments. 
         [0093]    In the best mode of the invention and first through third embodiments, calculations such as DFT and FFT are carried out when calculating inclinations of data signals, in order to estimate peaks. If data has a large signal bandwidth, the number of points for DFT and FFT increases, thereby increasing a calculation amount. Meanwhile, if data has a narrow signal bandwidth, the number of points for DFT and FFT decreases, thereby reducing a calculation amount. The larger the signal bandwidth of data is, the heavier a load to a terminal which is caused by reduction of peaks is. Therefore in this embodiment, only when the signal bandwidth of data is narrow, transmission signals are generated reducing peaks. 
         [0094]    Attenuation of signal power due to radio wave propagation increases as distance from a base station increases. Therefore, in order to maintain a required reception quality, transmission power needs to be increased as distance from a base station increases. Since maximum transmission power of a base station is limited, there is a case that required transmission power cannot be satisfied when using a broad bandwidth. In this case, for a user who is distant from a base station, power is concentrated on a narrow bandwidth by lowering a transmission rate, to improve a reception quality. If data has a signal bandwidth, a terminal is determined to be distant from a base station, and peak power is lowered so as to increase maximum transmission power which the terminal can transmit. In this manner, reception quality at a cell end can be improved more. Thus, reduction of peaks only when data has a narrow signal bandwidth results in great effect of improvement in reception quality of a user who is distant from a base station. 
       Fifth Embodiment 
       [0095]    Next, a fifth embodiment of the invention will be described. The same block diagram as that of the transmitter in the best mode of the invention can also be referred to as a block diagram of a transmitter in the fifth embodiment. The fifth embodiment is a system which uses a transmitter according to any of the best mode of the invention and first through third embodiments. In the system, a base station measures transmission power which a terminal requires to satisfy reception quality for the base station, on basis of a result of measuring power received from a terminal, and the base station controls transmission power of the terminal. Described below is an example of using a transmitter which reduces PAPR in the system. 
         [0096]    Embodiment 4 has described example use of a transmitter which reduces PAPR by associating a signal bandwidth of data with distance from a base station. However, distance from a base station cannot always depend only on a signal bandwidth of data. There can be a case of lowering a transmission rate to transmit a signal of a narrow bandwidth to a user existing in the center of a cell, for whom reception quality is good. If determination is made only based on the narrow band, that is, distance from the base station is long, process of reducing peaks can be wasted. 
         [0097]    Hence, in this embodiment, PAPR is reduced to increase maximum transmission power only if required transmission power exceeds maximum transmission power which a terminal can transmit when not reducing PAPR, in the system which performs transmission power control. By utilizing this method, a processing for reducing peaks can be performed for only users who do not satisfy required reception quality. Unnecessary increase of a calculation amount can be prevented by utilizing the method proposed above. 
         [0098]    Further, a system which combines Embodiments 4 and 5 and performs transmission power control can increase maximum transmission power by reducing PAPR only if a data transmission bandwidth is narrow and if required transmission power exceeds maximum transmission power which a terminal can transmit when not reducing PAPR. 
       INDUSTRIAL APPLICABILITY 
       [0099]    The present invention is applicable to reduction of peak power in a transmitter using SC-FDMA scheme. Typical embodiments of the invention have been specifically described above. However, various changes, substitutions, and alternatives to the invention should be understood to be available without deviating from the spirit and scope of the invention specified in appended claims. The present inventor intends that a scope equivalent to that of the claimed invention should be maintained even if any of the claims should be amended in the procedure of the present application for a patent.