Patent Publication Number: US-2007120617-A1

Title: Modulation apparatus and modulation method

Description:
TECHNICAL FIELD  
      The present invention relates to a modulation apparatus and modulation method, and more particularly, to a modulation apparatus and modulation method for compensating a phase distortion to a baseband signal.  
     BACKGROUND ART  
      In recent years, mobile communication systems employs various modulation and demodulation systems, and a polar coordinate modulation system is known as a modulation system expected to achieve power savings in wireless terminals and high efficiency. In the polar coordinate modulation system, a modulation bandwidth is spread more than four times wider than a symbol rate of a transmission baseband signal when the transmission baseband signal is separated into an amplitude component and phase component. Therefore, using an analog PLL modulation system that is the most widely used in the current GSM system in a phase modulation section of the polar coordinate modulation system results in lack of a PLL bandwidth, which causes a phase distortion to occur in an output of a modulator and distorting the frequency spectrum.  
      For this issue, a technique is proposed for compensating a transmission baseband signal to apparently expand the PLL bandwidth, and thereby improving characteristics of a PLL modulator (for example, see Patent Document 1).  FIG. 1  shows a schematic block diagram of a conventional PLL modulation apparatus that improves a loop bandwidth. In  FIG. 1 , “ 10 ” denotes a PLL modulation apparatus, “ 11 ” denotes a voltage control oscillator (hereinafter, referred to as a “VCO”), “ 13 ” denotes a frequency divider, “ 15 ” denotes a divided carrier signal, “ 16 ” denotes a phase comparator that compares a phase of a reference signal and a phase of the divided carrier signal  15 , “ 17 ” denotes a control signal output from phase comparator  16 , “ 18 ” denotes a loop filter that smoothes an distortion signal, “ 19 ” denotes a smoothed control signal, “ 21 ” denotes a digital processor that performs characteristic compensation and filtering, “ 22 ” denotes a filtered digital modulation output signal, “ 23 ” denotes a combiner, “ 25 ” denotes a modulated carrier signal, “ 26 ” denotes a digital Σ-Δ modulation section, and “ 27 ” denotes a control signal output from digital Σ-Δ modulation section  26 .  
      The operation will be described below in the above-mentioned configuration. Loop filter  18  smoothes a control signal which is modulated in digital Σ-Δ modulation section  26 , compared with a reference signal in phase comparator  16  and output. At this point, the control signal looses a high-frequency component by band limitation of loop filter  18 . Therefore, a difference in characteristics is calculated between a loop filter having an ideal band and actually used loop filter  18 , and using the difference as a compensation function, digital processor  21  compensates the digital modulation data. As described above, by multiplying the digital modulation data by a difference in characteristics between actual loop filter  18  used in PLL modulation apparatus  10  and the ideal loop filter that does not generate a phase distortion, it is possible to apparently expand a loop bandwidth of PLL modulation apparatus  10  and improve characteristics while suppressing generation of a phase distortion.  
      Further, as a method of compensating for a phase distortion caused by a modulator in the polar coordinate modulation system, there are proposed a method and apparatus for providing a compensation circuit for compensating an amplitude component of a polar coordinate modulation signal, and thereby compensating for a phase distortion (for example, see Patent Document 2).  FIG. 2  shows an example of an apparatus that generates a linear modulation signal using the conventional polar coordinate modulation system. In  FIG. 2 , apparatus  40  that generates a linear modulation signal using the polar coordinate modulation system is mainly comprised of digital waveform filter (FILTER)  41 , digital signal processor (DSP)  42 , compensation circuit (COMP)  43 , D/A converter (D/A)  44 , phase modulator (PMOD)  45 , power amplifier (PA)  46  and regulator (REG)  47 .  
      The operation will be described below in the above-mentioned configuration. Digital waveform filter  41  converts transmission data into a digital waveform and outputs to digital-signal-processor  42 . Digital-signal-processor  42  separates the transmission data input from digital waveform filter  41  into a phase component and amplitude component and outputs to phase modulator  45  and compensation circuit  43 . Phase modulator  45  modulates a carrier signal with the phase component and obtains constant envelop phase modulation. At this point, in phase modulator  45 , a phase distortion occurs in the phase-modulated carrier signal.  
      To compensate the phase distortion to supply a linear modulation signal, compensation circuit  43  compensates an amplitude component input from digital signal processor  42  and compensates for the phase distortion caused by phase modulator  45 . For example, compensation circuit  43  derives a compensation function based on delay occurred in phase modulator  45 , ideal phase component and distorted phase component, and compensates the amplitude component. Then, compensation circuit  43  outputs the compensated digital amplitude component to D/A converter  44 .  
      D/A converter  44  converts the input compensated digital amplitude component into an analog signal and outputs to regulator  47 . Based on the analog signal and an output signal of power amplifier  46 , regulator  47  outputs to power amplifier  46  an analog signal obtained by adjusting a current or voltage of a signal controlling the power of power amplifier  46  to a target value. Power amplifier  46  controls the power of the power amplifier with the input analog signal, thereby modulates the phase-modulated carrier signal input from phase modulator  45 , and outputs an amplified signal.  
      By adopting such a configuration, communication systems using the polar coordinate modulation system makes it possible to compensate for a phase distortion generated in a phase modulator to improve accuracy in modulation, and further, cancel the distortion caused by the phase distortion to meet spectral requirements for signal transmission.  
      An application of pre-distortion technique may be considered as a technique compensating for a distortion component of the frequency spectrum caused by deterioration of characteristics in the PLL modulation section, (for example, see Patent Document 3).  FIG. 3  shows a schematic block diagram of conventional pre-distortion apparatus  60 . In  FIG. 3 , “ 62 ” denotes a power calculation section, “ 63 ” denotes an amplitude value calculated in power calculation section  62 , “ 64 ” denotes a reference table for non-linear distortion compensation, “ 65 ” denotes orthogonal non-linear distortion compensation data, “ 66 ” denotes a non-linear distortion compensation section, “ 67 ” denotes a non-linear distortion compensated orthogonal baseband signal, “ 68 ” denotes a D/A conversion section (D/A), “ 69 ” denotes an analog orthogonal baseband signal, “ 70 ” denotes a low-pass filer (LPF) for band limitation, “ 71 ” denotes a band-limited analog orthogonal baseband signal, “ 72 ” denotes a quadrature modulation section, “ 73 ” denotes a modulated signal, and “ 74 ” denotes an amplifier of the transmission system.  
      The operation will be described below in the above-mentioned configuration. First, power calculation section  62  calculates an amplitude value  63  of a transmission signal from transmission digital orthogonal baseband signals. Next, the section  62  refers to the reference table  64  for non-linear distortion compensation using the calculated amplitude value  63  of the transmission signal as an address, and obtains non-linear distortion compensation data  65  obtained by orthogonalizing the non-linear distortion compensation data having non-linear distortion characteristics of the transmission system calculated beforehand.  
      Non-linear distortion compensation section  66  performs complex-multiplication of the orthogonal baseband signal by orthogonalized non-liner distortion compensation data  65  and outputs the non-linear distortion compensated orthogonal baseband signal  67 . D/A conversion section  68  converts the non-linear distortion compensated orthogonal baseband signal  67  into an analog signal, and low-pass filter  70  performs band limitation on the analog signal and obtains the analog orthogonal baseband signal  71 . Then, quadrature modulation section  72  performs quadrature modulation and obtains the modulated signal  73 , and amplifier  74  of the transmission system amplifies the signal to a required level and outputs a transmission modulated signal.  
      As described above, by providing power calculation section  62 , reference table  64  for non-linear distortion compensation and non-linear distortion compensation section  66 , referring to table  64  for non-linear distortion compensation using amplitude value  63  of the orthogonal baseband signal, and performing complex-multiplication of the orthogonal baseband signal by orthogonalized non-liner distortion compensation data  65  by non-linear distortion compensation section  66  performs, and it is thereby possible to compensate for the non-linear distortion occurring in the amplifier in the transmission system. 
      Patent Document 1: U.S. Pat. No. 6,008,703     Patent Document 2: JP 2002-527921     Patent Document 3: JP H08-251246    

     DISCLOSURE OF INVENTION  
      Problems to be Solved by the Invention  
      However, the conventional apparatus has a problem that the technique for compensating a baseband signal to expand a loop bandwidth of PLL can be applied only to digital Σ-Δ modulation, and cannot be applied in the conventional analog PLL modulation system.  
      Further, in the conventional apparatus, when a compensation circuit is provided and an amplitude component of a polar coordination modulation signal is compensated to compensate for a phase distortion, since the amplitude component is used to compensate for the phase distortion in a phase modulator, it is necessary to delay the amplitude component by time equal to delay occurred in the phase modulator. The adjustment of delay time significantly affects the phase distortion compensation effect, and there is a problem that the delay time should be controlled with high accuracy. Furthermore, when the conventional apparatus uses the polar coordinate modulation system, at lease two timing adjustments are required such as an adjustment of delay time in the compensation circuit and timing adjustment in combining a signal after phase modulation and amplitude modulation is finished, and there is a problem requiring highly accurate timing adjustments. Moreover, in the conventional apparatus, since the amplitude component is used to compensate for the phase distortion in the phase modulator, there is a problem that the phase distortion cannot be compensated in communication systems using modulation systems such as GSMK that do not need amplitude modulation.  
      Further, in the conventional apparatus, in the case of using the pre-distortion technique, it is necessary to prepare a reference table associated with amplitude values, resulting in a problem that the reference table becomes enormous.  
      It is an object of the present invention to provide a modulation apparatus and modulation method which can be applied to the conventional analog PLL modulation system without using an enormous reference table, enable a phase distortion to be compensated accurately without requiring timing control with high accuracy, and can be applied to communication systems that do not perform amplitude modulation.  
      Means for Solving the Problem  
      A modulation apparatus of the present invention adopts a configuration provided with modulating means for modulating a baseband signal to generate a modulated signal, and compensating means for beforehand compensating a non-modulated baseband signal for a phase distortion between the non-modulated baseband signal prior to modulation in the modulating means and a modulation-processed baseband signal subjected to modulation in the modulating means, based on a magnitude of a phase change between adjacent data of the baseband signal and a predetermined constant.  
      A modulation method of the present invention has a step of modulating a baseband signal to generate a modulated signal, obtaining a phase distortion between a non-modulated baseband signal that is a baseband signal prior to modulation and a modulation-processed baseband signal that is a baseband signal subjected to modulation by multiplying a magnitude of a phase change between adjacent data of the baseband signal by a stored predetermined constant, and beforehand compensating the non-modulated baseband signal for the obtained phase distortion.  
      Advantageous Effect of the Invention  
      According to the present invention, it is possible to extend applicability to the conventional analog PLL modulation system without using an enormous reference table, compensate a phase distortion accurately without requiring timing control with high accuracy, and also extend applicability to communication systems that do not perform amplitude modulation. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a block diagram illustrating a configuration of a conventional communication apparatus;  
       FIG. 2  is a block diagram illustrating a configuration of another conventional communication apparatus;  
       FIG. 3  is a block diagram illustrating a configuration of another conventional communication apparatus;  
       FIG. 4  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 1 of the present invention;  
       FIG. 5  is a graph showing time shift of a phase distortion and I-component waveform data of baseband phase signal according to Embodiment 1 of the invention;  
       FIG. 6  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 2 of the invention;  
       FIG. 7  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 3 of the invention;  
       FIG. 8  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 4 of the invention;  
       FIG. 9  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 5 of the invention;  
       FIG. 10  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 6 of the invention;  
       FIG. 11  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 7 of the invention;  
       FIG. 12  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 8 of the invention;  
       FIG. 13  is a block diagram illustrating a configuration of a communication apparatus according to Embodiment 9 of the invention; and  
       FIG. 14  is a table illustrating the relationship between a magnitude of a frequency change and parameter according to Embodiment 10 of the invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      It is a gist of the invention to beforehand compensate a non-modulated baseband signal prior to modulation in a modulator using a phase distortion between the non-modulated baseband signal prior to modulation in the modulator and a demodulated baseband signal which is modulated in the modulator and then demodulated in a demodulator, based on a magnitude of a frequency change of the baseband signal at predetermined time.  
      Embodiments of the invention will specifically be described below with reference to accompanying drawings.  
     EMBODIMENT 1  
       FIG. 4  is a block diagram illustrating a configuration of communication apparatus  100  according to Embodiment 1 of the invention.  
      Modulation apparatus  112  is comprised of phase distortion compensation section  102 , storage section  103 , frequency conversion section  104 , modulation section  105 , phase comparing section  106 , LPF  107  and VCO  108 . In addition, communication apparatus  100  is assumed to show a phase locked loop (hereinafter, referred to as “PLL”) modulation apparatus.  
      Signal generating section  101  generates a baseband phase signal, and outputs the generated baseband phase signal to phase distortion compensation section  102 .  
      Whenever a baseband phase signal is input from signal generation section  101 , phase distortion compensation section  102  that is the compensating means calculates an estimated phase distortion assumed to occur by modulation processing of the baseband signal, using a magnitude of a frequency change at predetermined time obtained from the baseband phase signal or a magnitude of a phase change between adjacent data obtained from the baseband signal and a calculation equation and parameter both stored in storage section  103 , compensates the baseband phase signal input from signal generation section  101  for the calculated phase distortion and outputs to modulation section  105 . In addition, a method of calculating a phase distortion will be described later.  
      Storage section  103  stores a calculation equation to obtain a phase distortion from a relational equation between a parameter that is a constant and the magnitude of the frequency change or a relational equation between a parameter that is a constant and the magnitude of the phase change, and the parameter before hand obtained using the calculation equation, and outputs information of the stored calculation equation and information of the parameter to phase distortion compensation section  102  when the compensation section  102  compensates a baseband phase signal.  
      Frequency conversion section  104  converts the frequency of a modulation output signal input from voltage control oscillator (hereinafter, referred to as “VCO”)  108  into a frequency of a signal to be a reference to generate a frequency converted signal, and outputs the frequency converted signal to modulation section  105 .  
      Modulation section  105  is, for example, a quadrature modulator, modulates the frequency converted signal input from frequency conversion section  104  using the compensated baseband phase signal input from phase distortion compensation section  102 , generates a modulated signal and outputs the generated modulated signal to phase comparing section  106 .  
      Phase comparing section  106  compares a phase of the modulated signal input from modulation section  105  and a phase of the reference signal, and outputs an distortion signal that is the result of comparison to LPF  107 .  
      LPF  107  smoothes the distortion signal input from phase comparing section  106  and outputs to VCO  108 .  
      Using the distortion signal input from LPF  107  as a control signal, VCO  108  outputs a modulated output signal with an oscillation frequency determined by the control signal to frequency conversion section  104 , while transmitting the modulated output signal via antenna  109 . Modulation processing is finished by VCO  108  outputting the modulated output signal.  
      Referring to  FIG. 5 , described next is a method of compensating for the phase distortion in the baseband phase signal output from signal generation section  101 .  FIG. 5  is a graph showing time shift of phase distortion # 201  and I-component (in-phase component) waveform data # 202  of baseband phase signal.  
      In communication apparatus  100 , LPF  107  and others have frequency characteristics. When a bandwidth of communication apparatus  100  is sufficiently wide relative to a maximum frequency component of a modulated output signal output from VCO  108 , frequency characteristics of communication apparatus  100  do not become a problem. However, when a bandwidth of communication apparatus  100  is not obtained sufficiently widely relative to a maximum frequency component of a modulated output signal, the phase distortion Δθ occurs in a modulated output signal output from VCO  108  by frequency characteristics of communication apparatus  100 .  
       FIG. 5  shows the phase distortion Δθ of a modulated output signal on waveform data of an in-phase component of a baseband phase signal, where a symbol rate of the baseband phase signal output from signal generation section  101  is 270.833 ksymb/s, and a loop bandwidth is about 1 MHz. It is understood from  FIG. 5  that the phase distortion Δθ is large at a position where the waveform data of the baseband phase signal changes sharply. Herein, the phase distortion Δθ is a difference between a baseband phase signal prior to modulation (non-modulated baseband signal) and a signal (modulation-processed baseband signal) obtained by demodulating a modulated output signal. As can be seen from  FIG. 5 , a phase distortion of about ±13 degrees occurs even when an about four-time loop bandwidth is secured. Accordingly, in order for a reception side to be able to demodulate data with accuracy, it is necessary to compensate the phase distortion Δθ in phase distortion compensation section  102  so that a phase signal of a modulated output signal is the same as a baseband phase signal.  
      The variation in baseband phase signal is expressed by a magnitude of a frequency change per unit time, and the phase distortion and the magnitude of the frequency change per unit time are expressed by a relational equation (1). 
 
Δθ=α· F   (1) 
 
 where Δθ: phase distortion; 
      α: parameter; and     F: magnitude of frequency change.    

      Here, the parameter α is a coefficient determined by characteristics of communication apparatus  100 . Equation (1) indicates that it is possible to estimate the phase distortion Δθ occurring in communication apparatus  100  when the magnitude of the frequency change F per unit time of a baseband phase signal is know.  
      Described next is the relationship between a phase amount θ of each data of a baseband phase signal and the magnitude of the frequency change F per unit time. Here, in phase distortion compensation section  102 , considering a data sequence of a discrete baseband phase signal, (n−1)th data (for example, (n−1)th frame) and nth data (for example, nth frame) have the relationship as in equation (2). 
 
 f ( n− 1)=(θ( n )−θ( n− 1))/(2 ·π·t )  (2) 
 
 where f(n−1): frequency component determined by the (n−1)th data and nth data; 
          θ(n): phase amount of the nth data;     θ(n−1): phase amount of the (n−1)th data; and     t: time difference between data of the baseband phase signal.        

      Further, using a frequency component determined by the nth data and (n+1)th data (for example, (n+1)th frame), the magnitude of the frequency change per unit time in nth data is obtained from equation (3).  
                     F   ⁡     (   n   )       =       (       f   ⁡     (   n   )       -     f   ⁡     (     n   -   1     )         )     /   t                 =       (       θ   ⁡     (     n   +   1     )       +     θ   ⁡     (     n   -   1     )       -     2   ·     θ   ⁡     (   n   )           )     /     (     2   ·   π   ·     t   2       )                     (   3   )             
 
 where F(n): magnitude of frequency change per unit time in the nth data; 
          f(n): frequency component determined by the nth data and (n+1)th data;     f(n−1): frequency component determined by the (n−1)th data and nth data;     θ(n+1): phase amount of the (n+1)th data;     θ(n−1): phase amount of the (n−1)th data;     θ(n): phase amount of the nth data; and     t: time difference between data of the baseband phase signal.        

      Equation (3) indicates that a magnitude of a phase change between adjacent data is converted into a magnitude of a frequency change. In other words, the equation suggests that with respect to a phase amount θ(n) of the nth data, when a phase amount θ(n−1) one data previous to the nth data and a phase amount θ(n+1) one data subsequent to the nth data are known, the magnitude of the frequency change F(n) per unit time in the nth data can be derived from simple calculation. Accordingly, using the magnitude of the frequency change obtained from the magnitude of the phase change and parameter, it is possible to obtain the phase distortion from equation (1). Further, with respect to the nth data, the magnitude of the frequency change F(n) per unit time in the nth data is obtained from phase amounts of the (n−1)th data and the (n+1)th data, and from equations (1) and (3), as expressed in equation (4), the relational equation is derived between the phase amount of the nth data and the phase distortion in the data. 
 
Δθ( n )=α·(θ( n+ 1)+θ( n− 1)−2·θ( n ))/(2·π t   2 )  (4) 
 
 where Δθ(n): phase distortion imposed on nth data 
          α: parameter     θ(n+1): phase amount of the (n+1)th data;     θ(n−1): phase amount of the (n−1)th data;     θ(n): phase amount of nth data; and     t: time difference between data of the baseband phase signal.        

      Accordingly, since it is possible to estimate the phase distortion Δθ(n) imposed on the nth data from equation (4), the estimated phase distortion Δθ(n) is obtained using the phase amount θ(n) of nth data from equation (4), phase distortion compensation section  102  compensates for the phase distortion Δθ(n) in the nth data, and it is thereby possible to compensate the phase distortion Δθ of a modulated output signal of the nth data output from VCO  108 . In other words, it is possible to obtain the phase distortion Δθ(n) of the nth data from the phase amount variation between adjacent data and the parameter.  
      The parameter stored in storage section  103  can be obtained by calculating a phase distortion by subtracting between a phase of a baseband signal before being modulated in modulation section  105  and a phase of the modulated output signal output from VCO  108 , and dividing the obtained phase distortion by the magnitude of the frequency change of predetermined time from equation (1), before starting data communication.  
      As described above, equation (4) is used when the phase distortion is obtained based on the magnitude of the phase change of adjacent data and predetermined constant, while equation (1) is used when the phase distortion is obtained based on the magnitude of the frequency change at predetermined time and predetermined constant. Further, when the phase distortion is obtained based on the magnitude of the phase change between adjacent data and predetermined constant, the parameter stored in storage section  103  can be obtained by calculating a phase distortion by subtracting between a phase of a baseband signal before being modulated in modulation section  105  and a phase of the modulated output signal output from VCO  108 , and dividing the obtained phase distortion by the magnitude of the phase change between adjacent data from equation (4), before starting data communication. It is thereby possible to compensate a phase distortion without using the magnitude of the frequency change.  
      Thus, according to Embodiment 1, a parameter is first stored that is obtained from a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data of a baseband phase signal and a phase distortion, the magnitude of the frequency change at predetermined time or the magnitude of the phase change between adjacent data is obtained on each data of the baseband phase signal, a phase distortion is estimated using the obtained magnitude of frequency change or magnitude of phase change and the stored parameter, the estimated phase distortion is beforehand compensated for the baseband phase signal, and it is thereby possible to compensate the phase distortion using only the baseband phase signal. By this means, it is possible Embodiment 1 to apply to the conventional analog PLL modulation system without using an enormous reference table, compensate a phase distortion accurately without requiring timing control with high accuracy, and use in communication systems that do not perform amplitude modulation. Further, according to Embodiment 1, the phase distortion can be calculated from a stored predetermined equation, and it is thus possible to obtain the phase distortion with a simplified method.  
     EMBODIMENT 2  
       FIG. 6  is a block diagram illustrating a configuration of communication apparatus  300  according to Embodiment 2 of the invention.  
      Modulation apparatus  302  is comprised of storage section  103 , frequency conversion section  104 , modulation section  105 , phase comparing section  106 , LPF  107 , VCO  108  and signal generation section  301 .  
      As shown in  FIG. 6 , communication apparatus  300  according to Embodiment 2 includes signal generation section  301  instead of signal generation section  101  with phase distortion compensation section  102  eliminated in communication apparatus  100  according to Embodiment 1 as shown in  FIG. 4 . In addition, in  FIG. 6 , the same sections as in  FIG. 4  are assigned the same reference numerals and descriptions thereof are omitted.  
      Signal generation section  301  is, for example, a DSP (Digital Signal Processor) capable of compensating a phase distortion by digital signal processing, generates a baseband phase signal, calculates a phase distortion using a magnitude of a frequency change obtained from the generated baseband phase signal and a calculation equation and parameter both stored in storage section  103 , and compensates the baseband phase signal input from signal generation section  301  for the calculated phase distortion to output to modulation section  105 . In addition, a method of obtaining a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Thus, according to Embodiment 2, in addition to the effect of above-mentioned Embodiment 1, it is possible to perform generation of a baseband phase signal and compensation of phase distortion to the baseband phase signal by successive digital signal processing, and increase the processing speed to compensate the phase distortion.  
     EMBODIMENT 3  
       FIG. 7  is a block diagram illustrating a configuration of communication apparatus  400  according to Embodiment 3 of the invention.  
      Modulation apparatus  403  is comprised of phase distortion compensation section  102 , storage section  103 , frequency conversion section  104 , LPF  107 , VCO  108 , modulation section  401  and phase comparing section  402 .  
      As shown in  FIG. 7 , communication apparatus  400  according to Embodiment 3 includes modulation section  401  and phase comparing section  402  instead of modulation section  105  and phase comparing section  106  respectively in communication apparatus  100  according to Embodiment 1 as shown in  FIG. 4 . In addition, in  FIG. 7 , the same sections as in  FIG. 4  are assigned the same reference numerals to omit descriptions thereof.  
      Modulation section  401  is, for example, a quadrature modulator, modulates a compensated baseband phase signal input form phase distortion compensation section  102  using a reference signal, generates a modulated signal and outputs the generated modulated signal to phase comparing section  402 .  
      Phase comparing section  402  compares a phase of the modulated signal input from modulation section  401  and a phase of the frequency converted signal input from frequency conversion section  104  and outputs an distortion signal that is the result of comparison to LPF  107 . In addition, a method of compensating a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Thus, according to Embodiment 3, a parameter is first stored that is obtained from a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data of a baseband phase signal and a phase distortion, the magnitude of the frequency change at predetermined time or the magnitude of the phase change between adjacent data is obtained on each data of the baseband phase signal, a phase distortion is estimated from the obtained magnitude of frequency change or magnitude of phase change and the stored parameter, the estimated phase distortion is beforehand compensated for the baseband phase signal, and it is thereby possible to compensate the phase distortion using only the baseband phase signal. By this means, it is possible to apply Embodiment 3 to the conventional analog PLL modulation system without using an enormous reference table, compensate a phase distortion accurately without requiring timing control with high accuracy, and also use Embodiment 3 in communication systems that do not perform amplitude modulation. Further, according to Embodiment 3, the phase distortion can be calculated from a stored predetermined equation, and it is thus possible to obtain the phase distortion with a simplified method.  
     EMBODIMENT 4  
       FIG. 8  is a block diagram illustrating a configuration of communication apparatus  500  according to Embodiment 4 of the invention.  
      Modulation apparatus  503  is comprised of frequency conversion section  104 , modulation section  105 , phase comparing section  106 , LPF  107 , VCO  108 , demodulation section  501  and phase distortion compensation section  502 .  
      As shown in  FIG. 8 , communication apparatus  500  according to Embodiment 4 includes phase distortion compensation section  502  instead of phase distortion compensation section  102  with storage section  103  eliminated and demodulation section  501  added in communication apparatus  100  according to Embodiment 1 as shown in  FIG. 4 . In addition, in  FIG. 8 , the same sections as in  FIG. 4  are assigned the same reference numerals and descriptions thereof are omitted.  
      Demodulation section  501  demodulates a modulated output signal input from VCO  108  to generate a baseband phase signal (demodulated baseband signal), and outputs the generated baseband phase signal to phase distortion compensation section  502 . Demodulation section  501  may be used as a demodulation section in the reception system that demodulates a received signal, or may be provided separated from the demodulation section in the reception system.  
      Phase distortion compensation section  502  obtains a phase distortion by subtracting the modulation-processed baseband phase signal input from demodulation section  501  from the non-modulated baseband phase signal input from signal generation section  101 , and obtains a parameter α using the obtained phase distortion and a magnitude of a frequency change or a magnitude of a phase change obtained from the non-modulated baseband phase signal. Then, phase distortion compensation section  502  multiples the magnitude of the frequency change or the magnitude of the phase change obtained from the baseband phase signal by the parameter α to calculate a phase distortion, compensates the calculated phase distortion for the baseband phase signal input from signal generation section  101  and outputs to modulation section  105 . In addition, after the baseband phase signal is demodulated, a phase difference between the non-modulated baseband phase signal and modulation-processed baseband phase signal obtained in phase distortion compensation section  502  is a phase distortion of an already transmitted signal. Therefore, a phase distortion in next transmitting a signal is obtained from equation (1) using the parameter a obtained from the non-modulated baseband phase signal and modulation-processed baseband phase signal. It is thereby possible to obtain an accurate phase distortion.  
      Thus, according to Embodiment 4, in addition to the effect of above-mentioned Embodiment 1, since the transmission side demodulates a modulated output signal and calculates the parameter α at each demodulation, and therefore, it is possible to accurate parameter α and also compensate a phase distortion with remarkably high accuracy. Further, according to Embodiment 4, when demodulation section  501  is used as the demodulation section in the reception system, it is possible to compensate a phase distortion with remarkably high accuracy without changing a circuit scale, and perform phase distortion compensation in real time with a simplified circuit configuration. Furthermore, according to Embodiment 4, it is not necessary to store the parameter α beforehand, and it is thus possible to reduce a storage capacity of the storage section (memory).  
      In addition, in Embodiment 4, phase distortion compensation section  502  obtains the parameter α each time, but the invention is not limited thereto. A storage section storing the obtained parameter α may be provided and a phase distortion may be calculated using the stored parameter α before a lapse of predetermined time.  
     EMBODIMENT 5  
       FIG. 9  is a block diagram illustrating a configuration of communication apparatus  600  according to Embodiment 5 of the invention. Modulation apparatus  603  is comprised of phase distortion compensation section  102 , storage section  103 , frequency conversion section  104 , modulation section  105 , phase comparing section  106 , LPF  107 , VCO  108 , amplitude control section  601  and power amplifier  602 . In addition, communication apparatus  600  is assumed an apparatus of polar loop modulation apparatus that is one of polar coordinate modulation systems.  
      As shown in  FIG. 9 , communication apparatus  600  according to Embodiment 5 adds amplitude control section  601  and power amplifier  602  in communication apparatus  100  according to Embodiment 1 as shown in  FIG. 4 . In addition, in  FIG. 9 , the same sections as in  FIG. 4  are assigned the same reference numerals and descriptions thereof are omitted.  
      Amplitude control section  601  controls an amplitude control voltage to apply to power amplifier  602  So that the power of power amplifier  602  is a target value, using a baseband amplitude signal input from signal generation section  101 .  
      Power amplifier  602  amplifies a modulated signal input from VCO  108  based on control of amplitude control section  601  and transmits via antenna  109 . In addition, a method of compensating a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Thus, according to Embodiment 5, in addition to the effect of above-mentioned Embodiment 1, applicability is extended to modulation apparatus that perform amplitude modulation, and in modulation apparatus that performs modulation, a phase distortion can be compensated based on a baseband phase signal without using a baseband amplitude signal in the modulation apparatus, and therefore, it is possible to eliminate the timing adjustment with high accuracy and accurately obtain a phase distortion.  
     EMBODIMENT 6  
       FIG. 10  is a block diagram illustrating a configuration of communication apparatus  700  according to Embodiment 6 of the invention.  
      Modulation apparatus  708  is comprised of storage section  702 , phase distortion compensation section  703  and modulation section  704 .  
      Signal generating section  701  generates a baseband phase signal, and outputs the generated baseband phase signal to phase distortion compensation section  703 .  
      Storage section  702  stores a calculation equation to obtain a phase distortion from a relational equation between a parameter and magnitude of frequency change, and the parameter obtained beforehand using the calculation equation, and outputs information of the stored calculation equation and information of the parameter to phase distortion compensation section  703  when the compensation section  703  compensates a baseband phase signal.  
      Whenever a baseband phase signal is input from signal generation section  701 , phase distortion compensation section  703  calculates a phase distortion using a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data obtained from the baseband phase signal and the calculation equation and parameter both stored in storage section  702 , compensates the baseband phase signal input from signal generation section  701  for the calculated phase distortion and outputs to modulation section  704 .  
      Modulation section  704  is, for example, a quadrature modulator, modulates a carrier signal using the compensated baseband phase signal input from phase distortion compensation section  703 , generates a modulated signal and outputs the generated modulated signal to radio section  705 . Modulation processing is finished by modulation section  704  outputting the modulated signal. In addition, a method of compensating a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Radio section  705  performs upconverting processing or the like to the modulated output signal input from modulation section  704  from the baseband frequency to radio frequency and transmits via antenna  706 . In addition, when modulation section  704  is directly comprised of a quadrature modulator or the like, upconverting from the baseband frequency to radio frequency can be performed simultaneously with modulation in modulation section  704 . In this case, radio section  705  is not needed.  
      Thus, according to Embodiment 6, a parameter is first stored that is obtained from a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data of a baseband phase signal and a phase distortion, the magnitude of the frequency change at predetermined time or the magnitude of the phase change between adjacent data is obtained on each data of the baseband phase signal, a phase distortion is estimated from the obtained magnitude of frequency change or magnitude of phase change and the stored parameter, the estimated phase distortion is beforehand compensated for the baseband phase signal, and it is thereby possible to compensate the phase distortion using only the baseband phase signal. By this means, it is possible Embodiment 6 to apply to the conventional analog PLL modulation system without using an enormous reference table, compensate a phase distortion accurately without requiring timing control with high accuracy, and also use Embodiment 6 in communication systems that do not perform amplitude modulation. Further, according to Embodiment 6, the phase distortion can be calculated from a stored predetermined equation, and it is thus possible to obtain the phase distortion with a simplified method.  
     EMBODIMENT 7  
       FIG. 11  is a block diagram illustrating a configuration of communication apparatus  800  according to Embodiment 7 of the invention.  
      Modulation apparatus  802  is comprised of storage section  702 , modulation section  704  and signal generation section  801 .  
      As shown in  FIG. 11 , communication apparatus  800  according to Embodiment 7 includes signal generation section  801  instead of signal generation section  701  with phase distortion compensation section  703  eliminated in communication apparatus  700  according to Embodiment 6 as shown in  FIG. 10 . In addition, in  FIG. 11 , the same sections as in  FIG. 10  are assigned the same reference numerals and descriptions thereof are omitted.  
      Signal generation section  801  is, for example, a DSP capable of compensating a phase distortion by digital signal processing, generates a baseband phase signal, calculates a phase distortion using a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data from the generated baseband phase signal and a calculation equation and parameter both stored in storage section  702 , compensates the baseband phase signal for the calculated phase distortion, performs D/A conversion on the compensated signal and outputs to modulation section  704 . In addition, a method of obtaining a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Thus, according to Embodiment 7, in addition to the effect of above-mentioned Embodiment 6, it is possible to perform generation of a baseband phase signal and compensation of phase distortion to the baseband phase signal by successive digital signal processing, and increase the processing speed to compensate the phase distortion.  
      In addition, in Embodiment 7, the parameter is stored in storage section  702 , but the invention is not limited thereto. The parameter may be obtained whenever signal generation section  801  outputs a baseband signal at predetermined timing.  
     EMBODIMENT 8  
       FIG. 12  is a block diagram illustrating a configuration of communication apparatus  900  according to Embodiment 8 of the invention.  
      Modulation apparatus  903  is comprised of modulation section  704 , demodulation section  901  and phase distortion compensation section  902 .  
      As shown in  FIG. 12 , communication apparatus  900  according to Embodiment 8 includes phase distortion compensation section  902  instead of phase distortion compensation section  703  with storage section  702  eliminated and demodulation section  901  added in communication apparatus  700  according to Embodiment 6 as shown in  FIG. 10 . In addition, in  FIG. 12 , the same sections as in  FIG. 10  are assigned the same reference numerals and descriptions thereof are omitted.  
      Demodulation section  901  demodulates a modulated output signal input from modulation section  704  to generate a baseband phase signal, and outputs the generated baseband phase signal to phase distortion compensation section  902 . Demodulation section  901  may be used as a demodulation section in the reception system that demodulates a received signal, or may be provided separated from the demodulation section in the reception system.  
      Phase distortion compensation section  902  obtains a phase distortion by subtracting the modulation-processed baseband phase signal input from demodulation section  901  from the non-modulated baseband phase signal input from signal generation section  701 , and obtains a parameter α using the obtained phase distortion and a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data obtained from the non-modulated baseband phase signal. Then, phase distortion compensation section  902  multiples the magnitude of the frequency change or the magnitude of the phase change obtained from the baseband phase signal by the parameter α, calculates a phase distortion, compensates the baseband phase signal input from signal generation section  701  for the calculated phase distortion and outputs to modulation section  704 .  
      Thus, according to Embodiment 8, in addition to the effect of above-mentioned Embodiment 6, since the transmission side demodulates a modulated output signal and also calculates the parameter α at each demodulation, and therefore it is possible to obtain accurate parameter, and thereby possible to compensate a phase distortion with remarkably high accuracy. Further, according to Embodiment 8, when demodulation section  901  is used as the demodulation section in the reception system, it is possible to compensate a phase distortion with remarkably high accuracy without changing a circuit scale, and perform phase distortion compensation in real time with a simplified circuit configuration.  
      In addition, in Embodiment 8, phase distortion compensation section  902  obtains the parameter α each time, but the invention is not limited thereto. A storage section storing the obtained parameter α may be provided and a phase distortion may be calculated using the stored parameter α before a lapse of predetermined time.  
     EMBODIMENT 9  
       FIG. 13  is a block diagram illustrating a configuration of communication apparatus  1000  according to Embodiment 9 of the invention.  
      Modulation apparatus  1004  is comprised of storage section  702 , phase distortion compensation section  703 , modulation section  704 , amplitude control section  1001 , radio section  1002  and power amplifier  1003 . In addition, communication apparatus  1000  is assumed to show an EER (Envelop Elimination and Restoration) apparatus.  
      As shown in  FIG. 13 , communication apparatus  1000  according to Embodiment 9 adds amplitude control section  1001  and power amplifier  1003  and includes radio section  1002  instead of radio section  705  in communication apparatus  700  according to Embodiment 6 as shown in  FIG. 10 . In addition, in  FIG. 13 , the same sections as in  FIG. 10  are assigned the same reference numerals and descriptions thereof are omitted.  
      Amplitude control section  1001  controls an amplitude control voltage to apply to power amplifier  1003  so that the power of power amplifier  1003  is a target value, using a baseband amplitude signal input from signal generation section  701 .  
      Radio section  1002  performs processing of upconverting a modulated output signal input from modulation section  704  from the baseband frequency to radio frequency and the like and outputs to power amplifier  1003  .  
      Power amplifier  1003  amplifies the modulated signal input from radio section  1002  based on control of amplitude control section  1001  and outputs as a modulated output signal. In addition, a method of compensating a phase distortion is the same as in Embodiment 1, and descriptions thereof are omitted.  
      Thus, according to Embodiment 9, in addition to the effect of above-mentioned Embodiment 6, applicability is extended to modulation apparatus that perform amplitude modulation, and in modulation apparatus that performs modulation, a phase distortion can be compensated based on a baseband phase signal without using a baseband amplitude signal in the modulation apparatus, and therefore, it is possible to eliminate the timing adjustment with high accuracy and accurately obtain a phase distortion.  
     EMBODIMENT 10  
       FIG. 14  shows a table storing phase distortion selection information that associates the parameter α with magnitude of frequency change according to Embodiment 10 of the invention. In addition, a configuration of a communication apparatus is the same as the configuration in  FIG. 4 , and descriptions thereof are omitted.  
      Storage section  103  stores the table as shown in  FIG. 14 .  
      Whenever a baseband phase signal is input from signal generation section  101 , phase distortion compensation section  102  selects parameter by using a magnitude of a frequency change at predetermined time or a magnitude of a phase change between adjacent data obtained from the baseband phase signal and referring to the phase distortion selection information stored in storage section  103 , multiplies the selected parameter by the magnitude of the frequency change or the magnitude of the phase change, compensates the baseband phase signal input from signal generation section  101  for the calculated phase distortion and outputs to modulation section  105 .  
      When the phase distortion is obtained using the magnitude of the frequency change, phase distortion compensation section  102  substitutes a compensation function of equation (5) for the compensation function of equation (1), and is thereby able to obtain a phase distortion corresponding to the magnitude of the frequency change. In equation (5), the parameter α is a function with the magnitude of the frequency change F per unit time as a parameter. 
 
Δθ=α( F )· F   (5) 
 
 where Δθ: phase distortion; 
          α(F): parameter; and     F: magnitude of frequency change.        

      Thus, according to Embodiment 10, in addition to the effect of above-mentioned Embodiment 1, the parameter is selected referring to the phase distortion selection information using the magnitude of the frequency change or the magnitude of the phase change, and therefore, it is possible to select a phase distortion corresponding to the magnitude of the frequency change or the magnitude of the phase change, and to compensate the phase distortion with accuracy.  
      In addition, the phase distortion is compensated in communication apparatus  100  in Embodiment 10, but the invention is not limited thereto. This method is applicable to the case of compensating a phase distortion in any one of communication apparatuses  300 ,  400 ,  600 ,  700 ,  800  and  1000 .  
      The present application is based on Japanese Patent Applications No. 2003-362393 filed on Oct. 22, 2003, and No. 2004-305807 filed on Oct. 20, 2004, entire contents of which are expressly incorporated by reference herein.  
     INDUSTRIAL APPLICABILITY  
      The present invention is suitable for use in particularly a modulation apparatus and modulation method for compensating a phase distortion to a baseband signal. 
       FIG. 1       13  FREQUENCY DIVIDER      16  PHASE COMPARATOR     REFERENCE SIGNAL      18  LOOP FILTER     OUTPUT MODULATED SIGNAL      21  DIGITAL PROCESSOR     DIGITAL MODULATION DATA     CARRIER SIGNAL      26  DIGITAL Σ-Δ MODULATION SECTION      FIG. 2      TRANSMISSION DATA     AMPLIFIED SIGNAL      FIG. 3      ORTHOGONAL BASEBAND SIGNALS      62  POWER CALCULATION SECTION      64  REFERENCE TABLE      66  NON-LINEAR DISTORTION COMPENSATION SECTION      72  QUADRATURE MODULATION SECTION     MODULATED SIGNAL      FIG. 4       101  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL      102  PHASE DISTORTION COMPENSATION SECTION      103  STORAGE SECTION      104  FREQUENCY CONVERSION SECTION      105  MODULATION SECTION      106  PHASE COMPARING SECTION     REFERENCE SIGNAL      FIG. 5      PHASE DISTORTION     IN-PHASE COMPONENT WAVEFORM DATA OF BASEBAND PHASE SIGNAL     TIME      FIG. 6       103  STORAGE SECTION      104  FREQUENCY CONVERSION SECTION      105  MODULATION SECTION      106  PHASE COMPARING SECTION     REFERENCE SIGNAL     BASEBAND PHASE SIGNAL      301  SIGNAL GENERATION SECTION      FIG. 7       101  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL      102  PHASE DISTORTION COMPENSATION SECTION      103  STORAGE SECTION      104  FREQUENCY CONVERSION SECTION      401  MODULATION SECTION     REFERENCE SIGNAL      402  PHASE COMPARING SECTION      FIG. 8       101  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL      104  FREQUENCY CONVERSION SECTION      105  MODULATION SECTION      106  PHASE COMPARING SECTION     REFERENCE SIGNAL      501  DEMODULATION SECTION      502  PHASE DISTORTION COMPENSATION SECTION      FIG. 9       101  SIGNAL GENERATION SECTION     BASEBAND AMPLITUDE SIGNAL     BASEBAND PHASE SIGNAL      102  PHASE DISTORTION COMPENSATION SECTION      103  STORAGE SECTION      104  FREQUENCY CONVERSION SECTION      105  MODULATION SECTION      106  PHASE COMPARING SECTION      601  AMPLITUDE CONTROL SECTION     AMPLITUDE CONTROL VOLTAGE      602  POWER AMPLIFIER      FIG. 10       701  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL      702  STORAGE SECTION      703  PHASE DISTORTION COMPENSATION SECTION      704  MODULATION SECTION     CARRIER SIGNAL      705  RADIO SECTION      FIG. 11       702  STORAGE SECTION      704  MODULATION SECTION     BASEBAND PHASE SIGNAL     CARRIER SIGNAL      705  RADIO SECTION      801  SIGNAL GENERATION SECTION      FIG. 12       701  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL      704  MODULATION SECTION     CARRIER SIGNAL      705  RADIO SECTION      901  DEMODULATION SECTION      902  PHASE DISTORTION COMPENSATION SECTION      FIG. 13       701  SIGNAL GENERATION SECTION     BASEBAND PHASE SIGNAL     BASEBAND AMPLITUDE      702  STORAGE SECTION      703  PHASE DISTORTION COMPENSATION SECTION      704  MODULATION SECTION     CARRIER SIGNAL      1001  AMPLITUDE CONTROL SECTION      1002  RADIO SECTION      1003  POWER AMPLIFIER     AMPLITUDE CONTROL VOLTAGE      FIG. 14      MAGNITUDE OF FREQUENCY CHANGE