Patent Document

TECHNICAL FIELD 
       [0001]    The present invention relates to a radio terminal apparatus, a base station apparatus and a radio communication control method that carry out communication simultaneously using a plurality of modulated waves with different frequencies. 
       BACKGROUND ART 
       [0002]    LTE-Advanced (hereinafter referred to as “LTE-A”) is known as a successor scheme of LTE (Long Term Evolution). LTE-A uses a technique called “carrier aggregation” (hereinafter, referred to as “CA”), which carries out communication simultaneously using a plurality of modulated waves with different frequencies (e.g., see Non-Patent Literature (hereinafter, referred to as “NPL”) 1). A modulated wave used in CA is called a “component carrier” (hereinafter, referred to as “CC”). 
         [0003]    When a radio terminal apparatus transmits a plurality of CCs with different frequencies, inter-modulation distortion (hereinafter, referred to as “IMD”) may occur between CCs due to non-linearity of the transmission circuit. This IMD becomes interference to other radio communication carried out by the terminal apparatus or another apparatus. 
         [0004]    Thus, a mechanism for suppressing IMD is under study with regard to the linearity of transmission circuits compatible with conventional communication schemes such as WCDMA (Wideband Code Division Multiple Access) (registered trademark). As this mechanism, for example, MPR (Maximum Power Reduction) and A-MPR (Additional-Maximum Power Reduction) introduced to LTE are known (e.g., see NPL 2). MPR is a technique for uniformly reducing the maximum transmission power in each frequency band based on transmission conditions of transmission signals (e.g., modulation scheme and bandwidth or the like). A-MPR is a technique for reducing the maximum transmission power in addition to MPR to satisfy an unnecessary emission level definition unique to a specific frequency band indicated from a base station. Hereinafter, MPR will refer to a technique for reducing the maximum transmission power using the above-described MPR and A-MPR together. 
       CITATION LIST 
     Non Patent Literature 
     NPL 1 
       [0000]    
       
         3GPP TR36.912 V9.3.0 “Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)” 
       
     
       NPL 2 
       [0000]    
       
         3GPP TS36.101V9.13.0 “Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio transmission and reception” 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    Since LTE-A uses multicarrier transmission, the maximum transmission power of a radio terminal apparatus is defined as total power of a plurality of CCs. Thus, when MPR which is effective for LTE using single carrier transmission is applied to LTE-A, the following problem arises. This problem will be described with a specific example using  FIG. 1  and  FIG. 2 . 
         [0008]    Here, a case will be described as an example where a radio terminal apparatus transmits CC 1  with frequency f 1  and CC 2  with frequency f 2  simultaneously. In this case, due to non-linearity of a transmission circuit of the radio terminal apparatus, IMD 1  is generated at frequency 2f 1 −f 2  and IMD 2  is generated at frequency 2f 2 −f 1  as a cubic IMD. An image of this case is shown in  FIG. 1 . 
         [0009]      FIG. 1  illustrates a situation in which IMDs  1  and  2  are generated when the transmission power of CC 1  is equal to the transmission power of CC 2 . In  FIG. 1 , IMD 1  is generated in the vicinity of CC 1  and IMD 2  is generated in the vicinity of CC 2 . Note that in  FIG. 1 , f 1  and f 2  represent center frequencies of CC 1  and CC 2 , respectively. In  FIG. 1 , b 1  and b 2  represent bandwidths of CC 1  and CC 2 , respectively. 
         [0010]    As shown in  FIG. 1 , when, for example, IMD 2  of the two IMDs enters a protected band shown by a broken line, the level of this IMD 2  needs to be suppressed to a defined level or lower. Note that the term “protected band” refers to a value defined by law or standard, or a value based on a radio communication environment of the terminal apparatus. 
         [0011]    Here, an example will be described where the total maximum transmission power of CC 1  and CC 2  (hereinafter simply referred to as “maximum transmission power”) is reduced by 3 dB by applying MPR to suppress IMD 2 . Here, an assumption is made that the level of IMD 2  exceeds a defined level of the protected band by 9 dB. In this case, for example, when the maximum transmission power defined by standard is reduced by 3 dB with respect to 23 dBm, the maximum transmission power is 20 dBm. Assuming that transmission power of CC 1  and transmission power of CC 2  are each 20 dBm, as a result of reduction by 3 dB, transmission power of CC 1  and transmission power of CC 2  each become 17 dBm. 
         [0012]    Thus, when the maximum transmission power is suppressed by 3 dB, the level of IMD 2  is suppressed by 9 dB which is equal to multiplication of 3 dB by 3. This allows the defined level of the protected band to be satisfied. 
         [0013]    Next, a case will be described as an example with reference to  FIG. 2  where transmission power of CC 2  is smaller than transmission power of CC 1 . 
         [0014]    In  FIG. 2 , suppose that transmission power of CC 2  is lower than transmission power of CC 1  by 3 dB. In this case, the level of IMD 2  is lower by 6 dB which is equal to multiplication of 3 dB by 2. The total transmission power is the sum of true values of 20 dBm and 17 dBm, which is 21.8 dBm. 
         [0015]    Here, MPR is applied as in the case of  FIG. 1 . Since the transmission power exceeds maximum transmission power 20 dBm using MPR 3 dB by 1.8 dB, maximum transmission power is set to 20 dBm by reducing the transmission power of CC 1  and transmission power of CC 2  by 1.8 dB respectively. In this case, the level of IMD 2  is further suppressed by 1.8×3=5.4 dB from an initial state which is lower by 6 dB and is consequently suppressed by 11.4 dB. That is, this means that IMD 2  is suppressed excessively and the maximum transmission power is reduced excessively. 
         [0016]    In this way, when there is a difference between the transmission power of CC 1  and transmission power of CC 2 , application of MPR may cause a problem that the maximum transmission power is reduced more than necessary. As a result, the communicable distance between the radio terminal apparatus and the base station apparatus becomes shorter. 
         [0017]    An object of the present invention is to effectively suppress inter-modulation distortion without reducing transmission power more than necessary during simultaneous transmission of a plurality of modulated waves with different frequencies. 
       Solution to Problem 
       [0018]    A radio terminal apparatus according to an aspect of the present invention is an apparatus that simultaneously transmits a plurality of modulated waves with different frequencies, the apparatus including a transmission power adjustment section that adjusts transmission power of a modulated wave located in a vicinity of inter-modulation distortion included in a predetermined protected band such that the transmission power is smaller than transmission power of another modulated wave. 
         [0019]    A base station apparatus according to an aspect of the present invention is an apparatus that performs communication with a radio terminal apparatus that simultaneously transmits a plurality of modulated waves with different frequencies, in which the base station apparatus instructs the radio terminal apparatus to perform control of reducing at least one of transmission power of a modulated wave located in a vicinity of inter-modulation distortion included in a predetermined protected-band and a power spectral density of the modulated wave in order to suppress inter-modulation distortion. 
         [0020]    A radio terminal apparatus according to an aspect of the present invention is an apparatus that simultaneously transmits a plurality of modulated waves with different frequencies to the base station apparatus according to an aspect of the present invention, in which the radio terminal apparatus performs control of reducing at least one of transmission power of a modulated wave located in the vicinity of inter-modulation distortion included in a predetermined protected band and a power spectral density of the modulated wave in order to suppress inter-modulation distortion based on the instruction received from the base station apparatus. 
         [0021]    A radio communication control method according to an aspect of the present invention is a method for simultaneously transmitting a plurality of modulated waves with different frequencies, the method including adjusting transmission power of a modulated wave located in a vicinity of inter-modulation distortion included in a predetermined protected band such that the transmission power is smaller than transmission power of another modulated wave. 
       Advantageous Effects of Invention 
       [0022]    According to the present invention, inter-modulation distortion can be effectively suppressed without reducing transmission power more than necessary during simultaneous transmission of a plurality of modulated waves with different frequencies. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]      FIG. 1  is a diagram illustrating an example of CC and IMD; 
           [0024]      FIG. 2  is a diagram illustrating another example of CC and IMD; 
           [0025]      FIG. 3  is a block diagram illustrating a configuration example of a radio terminal apparatus according to Embodiment 1 of the present invention; 
           [0026]      FIG. 4  is a block diagram illustrating a configuration example of a transmission control section of the radio terminal apparatus according to Embodiment 1 of the present invention; 
           [0027]      FIG. 5  is a flowchart illustrating an operation example of the radio terminal apparatus according to Embodiment 1 of the present invention; 
           [0028]      FIG. 6  is a block diagram illustrating a configuration example of a transmission control section of a radio terminal apparatus according to Embodiment 2 of the present invention; and 
           [0029]      FIG. 7  is a block diagram illustrating a configuration example of a radio terminal apparatus and a base station apparatus according to Embodiment 3 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
       [0031]    Embodiment 1 will be described. 
         [0032]    &lt;Configuration of Radio Terminal Apparatus  100 &gt; 
         [0033]    A configuration of a radio terminal apparatus according to Embodiment 1 of the present invention will be described using  FIG. 3 .  FIG. 3  is a block diagram illustrating a configuration example of radio terminal apparatus  100  of the present embodiment. 
         [0034]    In  FIG. 3 , radio terminal apparatus  100  includes memory  10 , transmission control section  20 , first radio transmitting section  30 , and second radio transmitting section  40 . Radio terminal apparatus  100  is applicable to a mobile terminal such as a smartphone, tablet, personal computer or the like. 
         [0035]    Memory  10  stores various kinds of data (hereinafter referred to as “control parameters”) used for processing carried out by transmission control section  20 . Memory  10  sends the control parameters to transmission control section  20 . 
         [0036]    Transmission control section  20  receives the control parameters from memory  10 . Next, transmission control section  20  determines the transmission power, frequency, bandwidth, and modulation scheme for each CC based on the control parameters. Next, transmission control section  20  sends a radio control signal indicating the result determined for respective CCs to first radio transmitting section  30  and second radio transmitting section  40 . Transmission control section  20  receives IQ data of each CC from memory  10 . Transmission control section  20  then sends the IQ data of respective CCs to first radio transmitting section  30  and second radio transmitting section  40 . 
         [0037]    First radio transmitting section  30  receives the IQ data of CC 1  and a radio control signal of CC 1  from transmission control section  20 . Next, first radio transmitting section  30  generates a radio transmission signal based on the IQ data and the radio control signal. Next, first radio transmitting section  30  applies power amplification to the generated radio transmission signal and transmits the radio transmission signal from an antenna. 
         [0038]    Second radio transmitting section  40  performs operation similar to that of first radio transmitting section  30  on CC 2 . Therefore, the description of the operation will be omitted. 
         [0039]      FIG. 3  shows a case where transmission control section  20  receives a control parameter or IQ data from memory  10 , but the control parameter or IQ data may also be received from a place other than memory  10 . 
         [0040]    &lt;Configuration of Transmission Control Section  20 &gt; 
         [0041]    Next, a configuration of transmission control section  20  of the present embodiment will be described using  FIG. 4 .  FIG. 4  is a block diagram illustrating a configuration example of transmission control section  20  of the present embodiment. 
         [0042]    In  FIG. 4 , transmission control section  10  includes first IQ transmitting section  201 , second IQ transmitting section  202 , first transmission circuit setting section  203 , second transmission circuit setting section  204 , power difference determining section  205 , IMD frequency calculation section  206 , protected-band determining section  207 , relaxation-value calculation section  208 , Reduction-value searching section  209 , reduction-value relaxing section  210 , and transmission power adjustment section  211 . 
         [0043]    Upon receiving the IQ data of CC 1  from memory  10 , first IQ transmitting section  201  sends the IQ data to first radio transmitting section  30 . 
         [0044]    Upon receiving the IQ data of CC 2  from memory  10 , second IQ transmitting section  202  sends the IQ data to second radio transmitting section  40 . 
         [0045]    First transmission circuit setting section  203  receives a frequency and bandwidth of CC 1  as control parameters from memory  10 . Next, first transmission circuit setting section  203  sets a circuit of first radio transmitting section  30  based on the received frequency and bandwidth. The setting of the circuit is as follows, for example. That is, first transmission circuit setting section  203  sets an oscillating frequency of a synthesizer of first radio transmitting section  30  based on the received frequency. First transmission circuit setting section  203  switches a sampling rate of a DA (Digital Analog) converter and a pass bandwidth of an anti-aliasing filter of first radio transmitting section  30  based on the received bandwidth. 
         [0046]    Second transmission circuit setting section  204  receives a frequency and bandwidth of CC 2  as control parameters from memory  10 . Next, second transmission circuit setting section  204  makes a circuit setting of second radio transmitting section  40  based on the received frequency and bandwidth. This setting example is the same as that of aforementioned first transmission circuit setting section  203 . 
         [0047]    Power difference determining section  205  receives transmission power of CC 1  and transmission power of CC 2  as control parameters from memory  10 . Next, power difference determining section  205  determines which one of transmission power of CC 1  and transmission power of CC 2  is smaller and by what degree. Power difference determining section  205  sends information indicating the determination result (hereinafter referred to as “power difference determination information”) to relaxation-value calculation section  208 . 
         [0048]    IMD frequency calculation section  206  receives the frequency and bandwidth of CC 1  and the frequency and bandwidth of CC 2  as control parameters from memory  10 . Next, IMD frequency calculation section  206  calculates the frequency of IMD that occurs based on the frequency and bandwidth of CC 1  and the frequency and bandwidth of CC 2 . Here, a calculation example will be described below. 
         [0049]    The example shown in aforementioned  FIG. 1  or  FIG. 2  is used for describing the calculation example. That is, suppose that a center frequency of CC 1  is f 1 , a center frequency of CC 2  is f 2 , a bandwidth of CC 1  is b 1 , and a bandwidth of CC 2  is b 2 . IMD frequency calculation section  206  carries out calculations when the degree of IMD is a cubic as shown below. 
         [0000]      IMD1=2 f 1− f 2−(2 b 1+ b 2)/2 to 2 f 1− f 2+(2 b 1+ b 2)/2
 
         [0000]      IMD2=2 f 2− f 1−(2 b 2+ b 1)/2 to 2 f 2− f 1+(2 b 2+ b 1)/2
 
         [0050]    IMD frequency calculation section  206  also carries out calculations when the degree of IMD is quintic as shown below. 
         [0000]      IMD3=3 f 1− f 2−(3 b 1+2 b 2)/2 to 3 f 1−2 f 2+(3 b 1+2 b 2)/2
 
         [0000]      IMD4=3 f 2−2 f 1−(3 b 2+2 b 1)/2 to 3 f 2−2 f 1+(3 b 2+2 b 1)/2
 
         [0051]    For example, when f 1 =1925 MHz, f 2 =1970 MHz, b 1 =10 MHz, b 2 =20 MHz, results of the above calculations are as follows. 
         [0052]    IMD 1 =1860 MHz to 1900 MHz 
         [0053]    IMD 2 =1990 MHz to 2040 MHz 
         [0054]    IMD 3 =1800 MHz to 1870 MHz 
         [0055]    IMD 4 =2020 MHz to 2100 MHz 
         [0056]    IMD frequency calculation section  206  sends the frequencies of IMDs  1  to  4  calculated as described above to protected-band determining section  207 . In this case, IMD frequency calculation section  206  also sends the frequency of CC 1  and frequency of CC 2  to protected-band determining section  207 . 
         [0057]    Protected-band determining section  207  receives the frequencies of IMDs  1  to  4  and the frequency of CC 1  and frequency of CC 2  from IMD frequency calculation section  206 . Next, protected-band determining section  207  reads a protected-band frequency table stored in memory  10 . The protected-band frequency table is a table indicating predetermined frequencies of the protected band. 
         [0058]    Protected-band determining section  207  first determines whether or not one of the frequencies of IMDs  1  to  4  is included in the frequencies of the protected band. When the determination result shows that none of the frequencies of IMDs  1  to  4  is included in the frequencies of the protected band, protected-band determining section  207  sends information indicating the fact (hereinafter referred to as “protected-band determination information A”) to relaxation-value calculation section  208 . On the other hand, when the determination result shows that one of the frequencies of IMDs  1  to  4  is included in the frequencies of the protected band, protected-band determining section  207  compares the frequency of IMD included in the frequencies of the protected band with the frequency of CC 1  and the frequency of CC 2 . Protected-band determining section  207  determines, in the vicinity of which of CC 1  or CC 2 , IMD included in the frequencies of the protected band is located, based on this comparison. Protected-band determining section  207  then sends the protected-band determination information B to relaxation-value calculation section  208 . Protected-band determination information B is information indicating which of IMDs  1  to  4  is the IMD included in the frequencies of the protected band, which of CC 1  or CC 2  is the CC located in the vicinity of the IMD included in the frequencies of the protected band and the degree of the IMD included in the frequencies of the protected band. 
         [0059]    Relaxation-value calculation section  208  receives power difference determination information from power difference determining section  205  and receives protected-band determination information A or protected-band determination information B from protected-band determining section  207 . 
         [0060]    Here, upon receiving protected-band determination information A, relaxation-value calculation section  208  determines the relaxation value to be 0 and sends the relaxation value to reduction-value relaxing section  210 . 
         [0061]    On the other hand, upon receiving protected-band determination information B, relaxation-value calculation section  208  determines whether or not transmission power of the CC in the vicinity of IMD included in the frequencies of the protected band is lower than that of the other CC based on the power difference determination information and protected-band determination information B. When the determination result shows that the transmission power of the CC in the vicinity of IMD included in the frequencies of the protected band is not lower than the transmission power of the other CC, relaxation-value calculation section  208  determines the relaxation value to be 0 and sends the relaxation value to reduction-value relaxing section  210 . On the other hand, when the determination result shows that the transmission power of the CC in the vicinity of IMD included in the frequencies of the protected band is lower than the transmission power of the other CC, relaxation-value calculation section  208  calculates a relaxation value. That is, relaxation-value calculation section  208  calculates the relaxation value based on the power difference indicated by the power difference determination information and the degree of IMD indicated by protected-band determination information B. The relaxation value is a value for relaxing the reduction value which will be described later. The equation for calculating the relaxation value differs depending on the degree of IMD indicated by protected-band determination information B. 
         [0062]    For example, when IMD included in the frequencies of the protected band is located in the vicinity of CC 2  and transmission power P 2  of CC 2  is lower by ΔP than transmission power P 1  of CC 1 , the relaxation value is calculated according to the degree of IMD as shown below. 
         [0063]    The calculation when the degree of IMD is cubic will be described first. 
         [0064]    When P 1 −P 2 =ΔP, 
         [0000]        P 1= P max−10 log 10(1+10̂(−Δ P/ 10))
 
         [0000]        P 2 =P 1 −ΔP . In this case, IMD is  Q′=Q+{P 1−( P max−3)}+2 *{P 2−( P max−3)}
 
         [0000]      = Q +( P 1+2 P 2)−3( P max−3)
 
         [0000]      = Q+ 3 P 1−2Δ P− 3( P max−3)
 
         [0065]    In the expressions, Q is IMD when P 1 =P 2 =Pmax−3 dB. 
         [0066]    Moreover, ⅓ of the amount of change of IMD becomes the relaxation value. Therefore, relaxation value ΔX becomes as follows, 
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         [0067]    Next, the calculation when the degree of IMD is quintic will be described. 
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         [0068]    In the above-described equations, coefficients such as ⅔ or ⅗ are assumed to have been calculated in advance based on theoretical characteristics of IMD, but the coefficients are not limited to this. The above-described coefficients may also be adjusted based on the actual characteristics of the device. The above-described equations may be approximate equations using a linear function or values may be stored in a lookup table and the values may be referenced. 
         [0069]    Relaxation-value calculation section  208  sends the relaxation value calculated using the above-described equations to reduction-value relaxing section  210 . 
         [0070]    Reduction-value searching section  209  receives transmission conditions regarding CC 1  and CC 2 , that is, frequency, bandwidth, number of RBs (Resource Blocks) and modulation scheme from memory  10  as control parameters. Reduction-value searching section  209  also reads a reduction-value table from memory  10 . The reduction-value table is a table in which a reduction value is predetermined according to a frequency, bandwidth, number of RBs, and modulation scheme. The reduction value is a value to reduce the maximum transmission power, and examples of the reduction value include values used in MPR or A-MPR. 
         [0071]    Reduction-value searching section  209  searches for a reduction value corresponding to the frequency, bandwidth, number of RBs, and modulation scheme received from the reduction-value table as control parameters. Reduction-value searching section  209  sends the found reduction value to reduction-value relaxing section  210 . 
         [0072]    Reduction-value relaxing section  210  receives the relaxation value from relaxation-value calculation section  208  and receives the reduction value from reduction-value searching section  209 . Reduction-value relaxing section  210  subtracts the relaxation value from the reduction value. The reduction value is thereby relaxed. The value resulting from the subtraction is hereinafter referred to as “relaxed reduction value.” Note that when the subtraction result becomes a negative number, reduction-value relaxing section  210  determines the relaxed reduction value to be 0. Reduction-value relaxing section  210  then sends the relaxed reduction value to transmission power adjustment section  211 . 
         [0073]    Transmission power adjustment section  211  receives the relaxed reduction value from reduction-value relaxing section  210 . Transmission power adjustment section  211  adjusts the maximum transmission power using the relaxed reduction value. This adjustment result is called “limit value.” The maximum transmission power referred to here is a value defined by law or standard or a value based on a radio communication environment of radio terminal apparatus  100 . 
         [0074]    Transmission power adjustment section  211  receives transmission power of CC 1  and transmission power of CC 2  as control parameters from memory  10 . Transmission power adjustment section  211  then adds up transmission power of CC 1  and transmission power of CC 2  as power necessary for radio terminal apparatus  100  to perform radio transmission. This calculation result is called “total transmission power.” 
         [0075]    Transmission power adjustment section  211  then determines whether or not the total transmission power is greater than a limit value. When the determination result shows that the total transmission power is not greater than the limit value, transmission power adjustment section  211  notifies the radio transmitting section of transmission power of each CC received from memory  10  as a control parameter. That is, transmission power adjustment section  211  sends a radio control signal indicating the transmission power of CC 1  received from memory  10  to first radio transmitting section  30  and sends a radio control signal indicating transmission power of CC 2  received from memory  10  to second radio transmitting section  40 . On the other hand, when the determination result shows that the total transmission power is greater than the limit value, transmission power adjustment section  211  subtracts the limit value from the total transmission power, thereby calculating a value by which the total transmission power exceeds the limit value (hereinafter referred to as “excess value”). Transmission power adjustment section  211  then subtracts the excess value from each CC received as a control parameter from memory  10 . In this way, transmission power of CC 1  and transmission power of CC 2  are each adjusted. Transmission power adjustment section  211  sends a radio control signal indicating the adjusted transmission power of CC 1  to first radio transmitting section  30  and sends a radio control signal indicating the adjusted transmission power of CC 2  to second radio transmitting section  40 . 
         [0076]    &lt;Operation of Radio Terminal Apparatus  100 &gt; 
         [0077]    Next, an operation example of radio terminal apparatus  100  will be described.  FIG. 5  is a flowchart illustrating an operation example of radio terminal apparatus  100  of the present embodiment. The operation example in  FIG. 5  is an adjustment operation of transmission power performed by transmission control section  20 . 
         [0078]    In step S 10 , power difference determining section  205  determines which of transmission power of CC 1  or transmission power of CC 2  is smaller and by what degree based on the transmission power of CC 1  and the transmission power of CC 2  received as control parameters. Power difference determining section  205  sends power difference determination information indicating the determination result to relaxation-value calculation section  208 . 
         [0079]    In step S 11 , reduction-value searching section  209  searches for a reduction value corresponding to transmission conditions (frequency, bandwidth, number of RBs and modulation scheme) of CC 1  and CC 2  received as control parameters from the reduction-value table. Reduction-value searching section  209  then sends the searched reduction value to reduction-value relaxing section  210 . 
         [0080]    In step S 12 , IMD frequency calculation section  206  calculates a frequency of IMD generated based on the respective frequencies and bandwidths of CC 1  and CC 2  received as control parameters. Here, IMD frequency calculation section  206  calculates the frequency according to the degree of IMD (e.g., cubic and quintic). That is, IMD frequency calculation section  206  calculates frequencies of cubic IMD 1  and  2  and quintic IMD 3  and  4  respectively. IMD frequency calculation section  206  then sends the frequencies of IMD 1  to  4  together with the frequency of CC 1  and the frequency of CC 2  to protected-band determining section  207 . 
         [0081]    In step S 13 , protected-band determining section  207  receives the frequencies of IMD 1  to  4  from IMD frequency calculation section  206  and determines whether or not one of the frequencies is included in the predetermined frequencies of the protected band. 
         [0082]    When the determination result in step S 13  shows that none of the frequencies of IMD 1  to  4  is included in the frequencies of the protected band (step S 13 : NO), the flow proceeds to step S 14 . In this case, protected-band determining section  207  sends protected-band determination information A to relaxation-value calculation section  208 . Protected-band determination information A indicates that no IMD is included in the frequencies of the protected band. 
         [0083]    On the other hand, the determination result in step S 13  shows that one of the frequencies of IMD 1  to  4  is included in the frequencies of the protected band (step S 13 : YES), the flow proceeds to step S 15 . In this case, protected-band determining section  207  compares the frequency of IMD included in the frequencies of the protected band with the respective frequencies of CC 1  and CC 2 , thereby determining whether IMD included in the frequencies of the protected band is located in in the vicinity of CC 1  or CC 2 . Protected-band determining section  207  sends protected-band determination information B also reflecting the determination result to relaxation-value calculation section  208 . Protected-band determination information B indicates IMD included in the frequencies of the protected band, CC located in the vicinity of IMD and the degree of IMD. 
         [0084]    In step S 14 , upon receiving protected-band determination information A, relaxation-value calculation section  208  determines the relaxation value to be 0. Relaxation-value calculation section  208  then sends the determined relaxation value of 0 to reduction-value relaxing section  210 . 
         [0085]    In step S 15 , upon receiving protected-band determination information B, relaxation-value calculation section  208  makes the next determination. That is, relaxation-value calculation section  208  determines whether or not the transmission power of the CC in the vicinity of IMD included in the frequencies of the protected band (hereinafter referred to as “CC in the vicinity of IMD”) is lower than the transmission power of the other CC based on the power difference determination information and protected-band determination information B from power difference determining section  205 . 
         [0086]    When the determination result in step S 15  shows that the transmission power of the CC in the vicinity of IMD is not lower than the transmission power of the other CC (step S 15 : NO), the flow proceeds to step S 14 . 
         [0087]    On the other hand, when the determination result in step S 15  shows that the transmission power of the CC in the vicinity of IMD is lower than the transmission power of the other CC (step S 15 : YES), the flow proceeds to step S 16 . 
         [0088]    In step S 16 , relaxation-value calculation section  208  calculates a relaxation value based on a power difference indicated by the power difference determination information and the degree of IMD indicated by protected-band determination information B. Relaxation-value calculation section  208  then sends the relaxation value to reduction-value relaxing section  210 . 
         [0089]    In step S 17 , reduction-value relaxing section  210  subtracts the relaxation value received from relaxation-value calculation section  208  from the reduction value received from reduction-value searching section  209  thereby calculating a relaxed reduction value. Here, when the subtraction result becomes a negative number, reduction-value relaxing section  210  determines the relaxed reduction value to be 0. Reduction-value relaxing section  210  then sends the relaxed reduction value to transmission power adjustment section  211 . 
         [0090]    In step S 18 , transmission power adjustment section  211  adjusts the maximum transmission power using the relaxed reduction value received from reduction-value relaxing section  210 , thereby calculating a limit value. 
         [0091]    In step S 19 , transmission power adjustment section  211  adds up transmission power of CC 1  and transmission power of CC 2  received as control parameters and calculates total transmission power. 
         [0092]    In step S 20 , transmission power adjustment section  211  determines whether or not the total transmission power is greater than the limit value. 
         [0093]    When the determination result in step S 20  shows that the total transmission power is not greater than the limit value (step S 20 : NO), the flow ends. In this case, transmission power adjustment section  211  sends a radio control signal indicating the transmission power of CC 1  received as the control parameter to first radio transmitting section  30 . Transmission power adjustment section  211  sends a radio control signal indicating the transmission power of CC 2  received as the control parameter to second radio transmitting section  40 . 
         [0094]    When the determination result in step S 20  shows that the total transmission power is greater than the limit value (step S 20 : YES), the flow proceeds to step S 21 . 
         [0095]    In step S 21 , transmission power adjustment section  211  calculates an excess value based on the total transmission power and the limit value and subtracts the excess value from each CC received as the control parameter. Thus, transmission power of CC 1  and transmission power of CC 2  are adjusted respectively. Transmission power adjustment section  211  then sends a radio control signal indicating the adjusted transmission power of CC 1  to first radio transmitting section  30  and sends a radio control signal indicating the adjusted transmission power of CC 2  to second radio transmitting section  40 . 
         [0096]    As described above, when there is a difference between the transmission power of CC 1  and transmission power of CC 2  in simultaneous transmission of a plurality of modulated waves with different frequencies, radio terminal apparatus  100  of the present embodiment can effectively suppress inter-modulation distortion without reducing transmission power more than necessary. As a result, radio terminal apparatus  100  can prevent a communicable distance from the base station apparatus from becoming shorter. 
         [0097]    In the present embodiment, protected-band determining section  207  sends the degree of IMD to relaxation-value calculation section  208 , but the present invention is not limited to this. For example, if it is predetermined that IMD in the predetermined degree should be taken into consideration, relaxation-value calculation section  208  may calculate the relaxation value based on the degree without any need to receive the degree. For example, if it is predetermined that only cubic IMD should be taken into consideration, relaxation-value calculation section  208  may calculate a relaxation value corresponding to a cubic value. 
         [0098]    In the present embodiment, IMD frequency calculation section  206  calculates cubic and quintic IMDs, and protected-band determining section  207  determines whether or not cubic and quintic IMDs are included in the protected band respectively, but the present invention is not limited to this. IMD frequency calculation section  206  may further calculate IMDs of other degrees and protected-band determining section  207  may determine whether or not the IMDs are included in the protected band. 
         [0099]    In the present embodiment, IMD frequency calculation section  206  calculates all IMDs of different degrees, but the present invention is not limited to this. Since the protected band is defined by law or standard, the positional relationship between the protected band and each CC is known. Therefore, IMD frequency calculation section  206  may calculate only IMDs which may be included in the protected band. 
       Embodiment 2 
       [0100]    Embodiment 2 of the present invention will be described. In above Embodiment 1, an adjustment is made so as to reduce transmission power of CC 1  and CC 2  equally, whereas in present Embodiment 2, an adjustment is performed so as to reduce transmission power of CC 1  and CC 2  by different amounts. 
         [0101]    &lt;Configuration of Radio Terminal Apparatus  100 &gt; 
         [0102]    Since a configuration of radio terminal apparatus  100  according to Embodiment 2 of the present invention is the same as the configuration in  FIG. 3  described in Embodiment 1, the description here will not be repeated. 
         [0103]    &lt;Configuration of Transmission Control Section  20 &gt; 
         [0104]    A configuration of transmission control section  20  of the present embodiment will be described using  FIG. 6 .  FIG. 6  is a block diagram illustrating a configuration example of transmission control section  20  of the present embodiment. The description will be given, assuming that the degree of IMD is cubic. 
         [0105]    The configuration shown in  FIG. 6  is different from the configuration shown in  FIG. 4  in that it is provided with none of power difference determining section  205 , relaxation-value calculation section  208  or reduction-value relaxing section  210 . Since the operation of other than transmission power adjustment section  211  is similar to the operation in Embodiment 1, the description will not be repeated. 
         [0106]    Transmission power adjustment section  211  adjusts maximum transmission power using the reduction value from reduction-value searching section  209  and calculates a limit value. 
         [0107]    As in the case of aforementioned Embodiment 1, transmission power adjustment section  211  calculates total transmission power, determines whether or not the total transmission power is greater than a limit value and calculates an excess value. After this, transmission power adjustment section  211  performs the following calculations. The following description is given assuming that the excess value is A dB. 
         [0108]    Transmission power adjustment section  211  receives a reduction value from Reduction-value searching section  209  and receives protected-band determination information A or protected-band determination information B from protected-band determining section  207 . 
         [0109]    Here, upon receiving protected-band determination information A, transmission power adjustment section  211  reduces transmission power of CC 1  and CC 2  by A dB respectively and makes an adjustment so that the total transmission power becomes equal to the adjustment value. 
         [0110]    Upon receiving protected-band determination information B, transmission power adjustment section  211  reduces transmission power Px of CC located in the vicinity of IMD included in the frequencies of the protected band (hereinafter referred to as “CC in the vicinity of IMD”) by 2×A (dB) to Px−2A. Transmission power adjustment section  211  obtains transmission power Py of the other CC by subtracting transmission power Px−2A of CC in the vicinity of IMD from the limit value in a true value. In this way, transmission power adjustment section  211  of the present embodiment makes an adjustment by providing a difference in the amount of reduction of transmission power of two CCs. 
         [0111]    To simplify the processing, transmission power adjustment section  211  may reduce transmission power Py of the other CC by A/2 (dB). 
         [0112]    Transmission power adjustment section  211  may also add an offset, for example, A+1 (dB) to above-described 2A. 
         [0113]    Transmission power adjustment section  211  may also refer to a distribution (stored in a table beforehand) of reduction values to be applied to CC 1  and CC 2  respectively. In that case, transmission power adjustment section  211  selects a reduction value such that the transmission power of the CC in the vicinity of IMD is suppressed more than the transmission power of the other CC. 
         [0114]    In this way, radio terminal apparatus  100  of the present embodiment obtains the following effects in addition to the effects of Embodiment 1. That is, radio terminal apparatus  100  of the present embodiment can reduce the transmission power of the CC in the vicinity of IMD more than the transmission power of the other CC compared to Embodiment 1 in which an equal value is subtracted from transmission power of both CCs when MPR is applied. Therefore, when IMD to be suppressed interferes with the received signal of radio terminal apparatus  100  of the present embodiment, radio terminal apparatus  100  can suppress interference power and improve reception performance. 
         [0115]    In the present embodiment, the transmission power of both CC 1  and CC 2  is reduced, but the present invention is not limited to this. For example, when the transmission power of the CC located in the vicinity of IMD is much greater than the transmission power of the other CC, only the power of the CC in the vicinity of IMD may be reduced. 
       Embodiment 3 
       [0116]    Embodiment 3 of the present invention will be described. In the present embodiment, a base station apparatus determines a control method that should be carried out by a radio terminal apparatus and the radio terminal apparatus executes the control method determined by the base station apparatus. Note that the “control” referred to here in the present embodiment may also be paraphrased as “limit.” 
         [0117]    &lt;Configuration of Radio Communication System&gt; 
         [0118]    A configuration of a radio communication system according to Embodiment 3 of the present invention will be described.  FIG. 7  is a block diagram illustrating a configuration example of a radio communication system of the present embodiment. 
         [0119]    In  FIG. 7 , the radio communication system includes base station apparatus  101  and radio terminal apparatus  100 . Base station apparatus  101  and radio terminal apparatus  100  perform radio communication according to, for example, LTE-A. 
         [0120]    In  FIG. 7 , base station apparatus  101  includes first radio receiving section  51 , second radio receiving section  61 , uplink quality estimation section  71 , uplink scheduler  11 , uplink control section  21 , first radio transmitting section  31 , and second radio transmitting section  41 . 
         [0121]    First radio receiving section  51  and second radio receiving section  61  receive an uplink radio signal from radio terminal apparatus  100  and send the uplink radio signal to uplink quality estimation section  71 . 
         [0122]    Uplink quality estimation section  71  estimates uplink quality based on the uplink radio signal and notifies the uplink scheduler of the uplink quality. Uplink quality estimation section  71  notifies uplink scheduler  11  of the amount of uplink data requested by radio terminal apparatus  100  (hereinafter referred to as “requested amount of uplink data”). 
         [0123]    Uplink scheduler  11  allocates radio resources required for radio transmission carried out by radio terminal apparatus  100  based on uplink channel quality and the requested amount of uplink data. Hereinafter, information indicating this allocation result will be referred to as “resource allocation information.” 
         [0124]    Uplink scheduler  11  determines a control method to be carried out by radio terminal apparatus  100  based on the uplink channel quality and the requested amount of uplink data. The control method referred to here is a method for controlling at least one of a bandwidth and transmission power to suppress IMD which may possibly occur between CCs transmitted by radio terminal apparatus  100 . Thus, uplink scheduler  11  determines whether radio terminal apparatus  100  controls the bandwidth, controls transmission power or controls both the bandwidth and transmission power. Hereinafter, information indicating this determination result is referred to as “control method information.” 
         [0125]    Uplink scheduler  11  notifies uplink control section  21  of the resource allocation information and the control method information. 
         [0126]    Uplink control section  21  converts the resource allocation information and the control method information to an uplink control signal and sends the uplink control signal to first radio transmitting section  31  and second radio transmitting section  41 . 
         [0127]    First radio transmitting section  31  and second radio transmitting section  41  send a downlink radio signal including the user data and the uplink control signal to radio terminal apparatus  100 . 
         [0128]    In  FIG. 7 , radio terminal apparatus  100  includes first radio receiving section  50 , second radio receiving section  60 , and control signal receiving section  70  in addition to the configuration shown in  FIG. 3 . 
         [0129]    First radio receiving section  50  and second radio receiving section  60  receive a downlink radio signal from base station apparatus  101  and send the downlink radio signal to control signal receiving section  70 . 
         [0130]    Control signal receiving section  70  extracts an uplink control signal from the downlink radio signal and stores the signal in memory  10  as a control parameter. 
         [0131]    Transmission control section  20  performs the following operation in addition to the operation described in Embodiments 1 and 2. That is, transmission control section  20  determines whether to control the bandwidth, control transmission power or control both the bandwidth and transmission power based on the control method information included in the uplink control signal. Transmission control section  20  executes the determined control method. 
         [0132]    In the above-described control method, the operation of controlling transmission power is one of the operation of adjusting transmission power described in Embodiment 1 and the operation of adjusting transmission power described in Embodiment 2. On the other hand, operation of controlling a bandwidth will be described below. 
         [0133]    &lt;Control of Bandwidth&gt; 
         [0134]    Uplink scheduler  11  determines which frequency band (RB) in which time band (subframe)/system band should be used for transmission (radio resources). This determination is made based on signal quality of SRS (Sounding Reference Signal) transmitted by radio terminal apparatus  100  and the amount of transmission data requested by radio terminal apparatus  100 . Uplink scheduler  11  then transmits a control signal for enabling communication to radio terminal apparatus  100 . 
         [0135]    On the other hand, radio terminal apparatus  100  controls the transmission power of radio terminal apparatus  100  so that power spectral densities at radio receiving sections  51  and  61  are substantially equal in order to prevent interference of transmission signals between radio receiving sections  51  and  61  of base station apparatus  101 , and other radio terminal apparatus. Therefore, the bandwidth is substantially proportional to the transmission power. 
         [0136]    Thus, base station apparatus  101  controls the bandwidth of radio terminal apparatus  100  (e.g., narrows b 1  or b 2  shown in  FIG. 1 ), thereby consequently controlling transmission power. Thus, even when radio terminal apparatus  100  controls only the bandwidth, this is equivalent to controlling transmission power, and it is thereby possible to achieve effects similar to those of Embodiments 1 and 2. Note that by directly reducing the transmission power of each carrier of CC in addition to indirect control of transmission power by control of the bandwidth of the CC, transmission power of the CC may be further reduced. 
         [0137]    Radio terminal apparatus  100  recalculates the transmission power based on the controlled bandwidth, further adjusts the transmission power described in Embodiment 1 or 2, and can thereby achieve both bandwidth control and transmission power control. 
         [0138]    Thus, base station apparatus  101  of the present embodiment selects a control method for suppressing IMD according to channel quality and the amount of transmission data (bandwidth control and/or transmission power control) and instructs radio terminal apparatus  100  to execute the control method. Radio terminal apparatus  100  of the present embodiment executes the control method selected by base station apparatus  101  and performs radio transmission. In this way, the radio communication system of the present embodiment can effectively reduce the interference while suppressing the influence of the uplink transmission performance to the minimum. 
         [0139]    The following control method may also be used as another example of the control method for suppressing IMD. That is, when there is a sufficient margin of the uplink channel quality and traffic, uplink scheduler  11  of base station apparatus  101  increases the allocated bandwidth of the CC within a range in which transmission power of the CC located in the vicinity of IMD to be suppressed does not increase and performs control so as to reduce a power spectral density of the CC. Such control causes the bandwidth of IMD to expand and causes the power density of IMD to decrease, and can thereby more effectively suppress interference. 
         [0140]    Uplink scheduler  11  of base station apparatus  101  may instruct radio terminal apparatus  100  to perform both or one of control to decrease a power spectral density of the CC located in the vicinity of IMD to be suppressed and control to decrease transmission power of the CC. As the control to decrease transmission power of the CC instructed by uplink scheduler  11 , there can be control to decrease power of each carrier making up the CC and control to decrease the bandwidth without changing the power spectral density of the CC. The former corresponds to “control of transmission power” of the present embodiment and the latter corresponds to “control of bandwidth” of the present embodiment. 
       Variations of Embodiments 
       [0141]    The embodiments of the present invention have been described so far, but the above description is an example only, and various modifications can be made thereto. Hereinafter, variations of the embodiments will be described. 
         [0142]    In foregoing Embodiments 1 to 3, the present invention employs a hardware configuration by way of example, but the present invention may also be achieved by software in cooperation with hardware. 
         [0143]    The disclosure of Japanese Patent Application No. 2013-006835, filed on Jan. 18, 2013, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0144]    The present invention is useful as a terminal apparatus, a base station apparatus, a radio communication system, a radio communication method, and a radio communication program that perform communication simultaneously using a plurality of modulated waves with different frequencies. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  Memory 
           11  Uplink scheduler 
           20  Transmission control section 
           21  Uplink control section 
           30 ,  31  First radio transmitting section 
           40 ,  41  Second radio transmitting section 
           50 ,  51  First radio receiving section 
           60 ,  61  Second radio receiving section 
           70  Control signal receiving section 
           71  Uplink quality estimation section 
           100  Radio terminal apparatus 
           101  Base station apparatus 
           201  First IQ transmitting section 
           202  Second IQ transmitting section 
           203  First transmission circuit setting section 
           204  Second transmission circuit setting section 
           205  Power difference determining section 
           206  IMD frequency calculation section 
           207  Protected-band determining section 
           208  Relaxation-value calculation section 
           209  Reduction-value searching section 
           210  Reduction-value relaxing section 
           211  Transmission power adjustment section

Technology Category: 5