JP2006135417A - Ofdm signal transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM signal transmission apparatus eliminating the need for the very high linearity performance for a transmission power amplifier and reducing a cost of a transmission power amplifier. <P>SOLUTION: A power comparison section 117 compares an OFDM symbol power detection value with a reference value as to whether the OFDM symbol power detection value is smaller than the reference value to produce a result of power comparison. When the result of the power comparison indicates that the OFDM symbol power detection value is smaller than the reference value, a mapping control section 118 allows a subcarrier mapping section 111 to continue mapping of digital data this time to a subcarrier, and when the result of the power comparison indicates that the OFDM symbol power detection value is not smaller than the reference value, the mapping control section 118 allows the subcarrier mapping section 111 to stop the mapping of the digital data this time to the subcarrier and assigns the assigned component of the digital data this time and the digital data after the assignment to the subcarrier of an OFDM symbol next time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an OFDM signal transmission apparatus used in a wireless signal transmission system such as mobile communication or wireless LAN.

  In a radio signal transmission system, characteristic degradation due to multipath interference becomes a serious problem. An orthogonal frequency division multiplexing {OFDM (Orthogonal-Frequency-Division-Multiplexing)} scheme is known as a method with high frequency utilization efficiency that can solve this problem. The OFDM scheme is a scheme in which a plurality of digital data is multiplexed on an OFDM symbol (symbol length = Ts), and is known as a scheme that is resistant to multipath interference degradation.

  The OFDM scheme performs subcarrier modulation after assigning digital data to be transmitted to a plurality of subcarriers having a frequency interval of f = 1 / Ts. This method is used for wireless LAN systems or terrestrial digital broadcasting.

  On the other hand, in conventional mobile communication, a code multiplexing {CDM (Code Division Multiplexing)} method or the like is used as a signal multiplexing method. In the next-generation high-speed and large-capacity mobile communication, it is required to suppress the influence of multipath interference and to perform efficient high-speed data transmission using a limited band.

  In recent years, OFCDM schemes combining OFDM and CDM have attracted attention as next-generation mobile communication schemes. In this OFCDM system, a digital data signal to be transmitted is code-multiplexed with a spreading code and then subjected to OFDM modulation.

  In this OFCDM system, it is possible to multiplex digital data having a plurality of user data in one OFDM symbol by code multiplexing. In this OFCDM scheme, one data symbol is distributed and assigned to a plurality of subcarriers or a plurality of OFCDM symbols (referred to as mapping), thereby enabling transmission that is strong against fading.

  Further, in this OFCDM system, the frequency axis and the time axis spreading factor can be varied according to the radio propagation environment, and an optimal subcarrier modulation method (such as QPSK or 16QAM) can be selected. Further, in this OFCDM system, optimum transmission power is selected for each user data, and the data amplitude of subcarrier modulation is determined.

  Since the OFDM symbol signal is composed of a plurality of subcarriers, it is known that the instantaneous peak value of the signal amplitude of the OFDM symbol becomes large and is susceptible to nonlinear distortion such as a transmission power amplifier after modulation. . Therefore, it is necessary to increase the back-off amount, and the power consumption of the amplifier is large and expensive. This will be called a “peak intensity problem”.

  As a method for solving the problem of the peak intensity, a method of compensating for nonlinearity of an amplifier by predistortion using an OFDM modulator (see Patent Document 1) or a method for suppressing the peak intensity of an OFDM signal has been proposed.

  Further, as a method for solving the problem of the peak intensity, there is a method of changing the phase according to the signal space arrangement of each subcarrier signal (see Patent Document 2).

  Further, as a method for solving the problem of the peak intensity, the influence of the peak intensity is suppressed by combining the suppression by clipping the peak amplitude of the signal after OFDM modulation and the equal signal intensity suppression of the entire signal. There is a thing (refer patent document 3).

  Next, a conventional OFDM signal transmission apparatus will be described with reference to the drawings.

  FIG. 9 is a block diagram showing a configuration of an example of a conventional OFDM signal transmission apparatus. FIG. 10 is a flowchart for explaining the operation of the main part in the conventional OFDM signal transmission apparatus shown in FIG.

  As shown in FIG. 9, a conventional OFDM signal transmission apparatus 10 includes a subcarrier mapping unit 11, a fast inverse Fourier transform (IFFT) unit 12, a parallel serial (P / S) conversion unit 13, a transmission power amplifier 14, and a transmission antenna. 15.

  The subcarrier mapping unit 11 receives the digital data D11 having a plurality of user data to be transmitted, assigns (maps) it to each subcarrier, performs subcarrier modulation, and generates a subcarrier modulation signal. The IFFT unit 12 performs a fast inverse Fourier transform on the subcarrier modulation signal from the subcarrier mapping unit 11 to generate a parallel inverse Fourier transform signal.

  The parallel-serial (P / S) converter 13 converts the parallel inverse Fourier transform signal from the IFFT unit 12 into a serial inverse Fourier transform signal. The transmission power amplifier 14 amplifies the power of the inverse Fourier transform signal from the parallel serial (P / S) conversion unit 13 and transmits it as a radio signal via the transmission antenna 15.

  Next, the operation of the main part of the conventional OFDM modulation apparatus 10 will be described with reference to FIG.

  As shown in FIG. 10, in step ST21, the subcarrier mapping unit 11 determines whether one of the digital data D11 is input. When the digital data D11 is input in step ST21, the subcarrier mapping unit 11 assigns the input digital data D11 to the subcarrier (step ST22).

  Next, subcarrier mapping section 11 determines whether or not subcarriers that have not yet been assigned to the OFDM symbol remain (step ST23). When subcarriers remain in step ST23, subcarrier mapping section 11 repeats steps ST21 and ST22 to assign digital data D11 to all subcarriers of the OFDM symbol.

  When no subcarriers remain in step ST23, the subcarrier mapping unit 11 ends the subcarrier mapping (step ST24). Next, IFFT section 12 performs a fast inverse Fourier transform on the subcarrier modulation signal from subcarrier mapping section 11 to generate an inverse Fourier transform signal (step ST25). Next, the parallel-serial (P / S) converter 13 converts the parallel inverse Fourier transform signal from the IFFT unit 12 into a serial inverse Fourier transform signal (step ST26).

Through the procedures of steps ST21 to ST26, a modulation signal of one OFDM symbol is generated. In order to generate a modulation signal of the next OFDM symbol, the above steps ST21 to ST26 are repeated. The OFDM symbol as a transmission signal is affected by nonlinear distortion of the transmission power amplifier when passing through the transmission power amplifier 14 at the subsequent stage.
Japanese Patent No. 3451947 JP 2000-22656 A Japanese Patent No. 3483838

  However, in the conventional OFDM signal transmission device that compensates for the nonlinear distortion of the conventional transmission power amplifier, in addition to the complexity of the device configuration, in a system including a plurality of amplifiers or optical transmission devices There is a problem that it is difficult to perform complete distortion compensation because there are a plurality of distortion generation factors.

  Further, the conventional OFDM signal transmission apparatus of the conventional peak suppression method has a problem that a complicated control circuit such as a detection circuit for the peak intensity of the OFDM signal is required.

  Further, the conventional peak intensity problem becomes more serious in the OFCDM system. This is because a plurality of user data and data of various types of amplitude are code-multiplexed in the same OFCDM symbol, so that the variation of the signal amplitude of the OFCDM symbol within the symbol and the variation between the symbols of the peak amplitude increase. is there. Therefore, in the OFCDM system, it is necessary to consider this variation, and there is a problem that the linearity of the transmission power amplifier is required to have very high characteristics.

  The present invention has been made in view of the above points, and provides an OFDM signal transmission device that does not require the linearity of a transmission power amplifier with very high characteristics and can reduce the price of the transmission power amplifier. The purpose is to do.

  An OFDM signal transmission apparatus according to a first aspect of the present invention includes a subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal, and the OFDM symbol of the subcarrier mapping means. An OFDM symbol power detection means for detecting power and generating an OFDM symbol power detection value; a power comparison means for generating a power comparison result by comparing whether the OFDM symbol power detection value is smaller than a reference value; When the power comparison result indicates that an OFDM symbol power detection value is smaller than the reference value, causing the subcarrier mapping means to continue mapping the digital symbol of the current time to the subcarrier of the OFDM symbol, and The OFDM symbol power detection value is equal to the reference value. When the result of the power comparison indicates that it is not small, the subcarrier mapping unit stops mapping the digital data of the current time to the subcarrier of the OFDM symbol, and the digital data allocation and the current allocation Mapping control means for allocating subsequent digital data to subcarriers of the next OFDM symbol is adopted.

  An OFDM signal transmission apparatus according to a second aspect of the present invention includes: subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal; and the subcarrier from the subcarrier mapping means. A voltage adjustment unit that processes the modulation signal to generate a voltage adjustment subcarrier modulation signal, and a high speed that generates a parallel inverse Fourier transform signal by performing a fast inverse Fourier transform on the voltage adjustment subcarrier modulation signal from the voltage adjustment unit. Inverse Fourier transform means, OFDM symbol power detection means for generating an OFDM symbol power detection value by detecting power of the OFDM symbol of the subcarrier mapping means, and whether the OFDM symbol power detection value is smaller than a reference value Compare power to generate power comparison results And when the power comparison result indicates that the OFDM symbol power detection value is smaller than the reference value, the subcarrier mapping means continues mapping the digital data of the current OFDM symbol to the subcarrier, And, when the power comparison result indicates that the OFDM symbol power detection value is not smaller than the reference value, the subcarrier mapping means stops mapping of the current digital data to the OFDM symbol subcarrier. Mapping control means for allocating the current digital data allocation and the digital data after the allocation to the subcarriers of the next OFDM symbol, and the voltage adjustment means includes: The amplitude of the subcarrier modulation signal Said multiplied by the square root of the ratio of the reference value for the OFDM symbol power detection value from the OFDM symbol power detecting means employs a configuration for generating the voltage adjustment subcarrier modulation signal.

  An OFDM signal transmission apparatus according to a third aspect of the present invention includes subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal, and the subcarrier from the subcarrier mapping means. Fast inverse Fourier transform means for generating a parallel inverse Fourier transform signal by performing fast inverse Fourier transform on the modulation signal, and processing the parallel inverse Fourier transform signal from the fast inverse Fourier transform means to perform parallel voltage adjustment inverse Fourier Voltage adjustment means for generating a conversion signal, OFDM symbol power detection means for generating an OFDM symbol power detection value by detecting power of the OFDM symbol of the subcarrier mapping means, and the OFDM symbol power detection value from a reference value Power comparison result by comparing whether or not it is small Generating power comparison means, and when the power comparison result indicates that the OFDM symbol power detection value is smaller than the reference value, the subcarrier mapping means sends the current digital data to the subcarrier of the OFDM symbol. When the mapping is continued, and the power comparison result indicates that the OFDM symbol power detection value is not smaller than the reference value, the subcarrier mapping means is sent to the subcarrier of the OFDM symbol of the current digital data. Mapping control means for suspending the mapping of the current digital data and assigning the digital data after the allocation to the subcarriers of the next OFDM symbol, the voltage adjusting means, Said parallel from fast inverse Fourier transform means The amplitude of the inverse Fourier transform signal is multiplied by the square root of the ratio of the reference value for the OFDM symbol power detection value from the OFDM symbol power detecting means employs a configuration which generates a voltage adjustment inverse Fourier transform signal of the parallel.

  According to the present invention, since the degradation due to nonlinear distortion of the transmission power amplifier in each data is always controlled to be below a certain value, the linearity of the transmission power amplifier with very high characteristics is not required, and the transmission power The price of the amplifier can be reduced.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 1 of the present invention. FIG. 2 is a flowchart for explaining the operation of the main part of the OFDM signal transmission apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 1, an OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention includes a subcarrier mapping unit 111, a fast inverse Fourier transform (IFFT) unit 112, a parallel serial (P / S) conversion unit 113, A transmission power amplifier 114, a transmission antenna 115, an OFDM symbol power detection unit 116, a power comparison unit 117, and a mapping control unit 118 are provided.

  Subcarrier mapping section 111 receives digital data D101 having a plurality of user data to be transmitted, assigns (maps) it to each subcarrier, performs subcarrier modulation, and generates a subcarrier modulation signal. IFFT section 112 performs a fast inverse Fourier transform on the subcarrier modulation signal from subcarrier mapping section 111 to generate a parallel inverse Fourier transform signal.

  The parallel-serial (P / S) conversion unit 113 converts the parallel inverse Fourier transform signal from the IFFT unit 112 into a serial inverse Fourier transform signal. The transmission power amplifier 114 amplifies the power of the inverse Fourier transform signal from the parallel serial (P / S) conversion unit 113 and transmits it as a radio signal via the transmission antenna 115.

  The OFDM symbol power detection unit 116 detects (calculates) the total power of the OFDM symbols for each mapping of the digital data to obtain the OFDM symbol power detection value P. In this case, the OFDM symbol power detection unit 116 calculates the OFDM symbol power detection value P by calculating the sum of the amplitudes of the assigned digital data by digital processing.

  The power comparison unit 117 compares the OFDM symbol power detection value P detected by the OFDM symbol power detection unit 116 with a reference value Pm to generate a power comparison result.

  If the power comparison result of the power comparison unit 117 indicates that P <Pm, the mapping control unit 118 causes the subcarrier mapping unit 111 to stop assigning the current OFDM symbol to the subcarrier, and The current allocation and the digital data after the allocation are allocated to the subcarriers of the next OFDM symbol.

  Also, when the power comparison result of the power comparison unit 117 indicates that P <Pm, the mapping control unit 118 causes the subcarrier mapping unit 111 to continue mapping of the current OFDM symbol to the subcarrier. . Then, the mapping control unit 118 causes the subcarrier mapping unit 111 to finish mapping when there are no more subcarriers to be allocated. Next, mapping control section 118 causes subcarrier mapping section 111 to supply a subcarrier modulation signal to IFFT section 112.

  Subcarrier mapping section 111, fast inverse Fourier transform (IFFT) section 112, parallel serial (P / S) conversion section 113, OFDM symbol power detection section 116, power of OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention The comparison unit 117 and the mapping control unit 118 can be configured by a digital processing circuit, can process data at high speed, and is inexpensive.

  Next, the operation of the main part of OFDM modulation apparatus 100 according to Embodiment 1 of the present invention will be described with reference to FIG. 2 together with FIG.

  As shown in FIG. 2, in step ST201, the subcarrier mapping unit 111 determines whether one of the digital data D101 is input. When digital data D101 is input in step ST201, subcarrier mapping section 111 assigns the input digital data D101 to a subcarrier of an OFDM symbol (step ST202).

  Next, OFDM symbol power detection section 116 detects (calculates) the total power of the OFDM symbol for each mapping of digital data D101 to obtain OFDM symbol power detection value P (step ST203).

  Next, the power comparison unit 117 performs a comparison as to whether or not the OFDOM symbol power detection value P detected by the OFDM symbol power detection unit 116 is smaller than the reference value Pm (P <Pm), and generates a power comparison result ( Step ST204).

  When the power comparison result indicates that P <Pm is not satisfied in step ST204, in step ST205, the mapping control unit 118 causes the subcarrier mapping unit 111 to stop assigning the current OFDM symbol to the subcarrier, and The current allocation and the digital data after the allocation are allocated to the subcarriers of the next OFDM symbol. That is, in step ST205, mapping control section 118 returns digital data D101 assigned this time to the data input section, goes to step ST207, and causes subcarrier mapping section 111 to finish subcarrier mapping.

  When the power comparison result indicates that P <Pm in Step ST204, in Step ST206, the mapping control unit 118 determines whether or not there are subcarriers that are not yet assigned to the OFDM symbol (Step ST206). ).

  When subcarriers remain in step ST206, mapping control section 118 repeats steps ST201 to ST204 to cause subcarrier mapping section 111 to assign digital data D101 to all subcarriers of the OFDM symbol. That is, when the power comparison result of the power comparison unit 117 indicates that P <Pm, the mapping control unit 118 causes the subcarrier mapping unit 111 to continue mapping of the current OFDM symbol to the subcarrier. .

  Next, when no subcarriers remain in step ST206, mapping control section 118 causes subcarrier mapping section 111 to finish subcarrier mapping (step ST207).

  Next, IFFT section 112 performs a fast inverse Fourier transform on the subcarrier modulation signal from subcarrier mapping section 111 to generate a parallel inverse Fourier transform signal (step ST208). Next, parallel-serial (P / S) conversion section 113 converts the parallel inverse Fourier transform signal from IFFT section 112 into a serial inverse Fourier transform signal (step ST209).

  Through the procedures of steps ST201 to ST209, a modulation signal of one OFDM symbol is generated. Step ST201 to step ST209 are repeated to generate a modulation signal of the next OFDM symbol.

  With this configuration, the total power of each OFDM symbol can be controlled so as to always be equal to or less than the reference value Pm. Thereby, the influence of the nonlinear distortion of the transmission power amplifier 114 on each digital data allocated in the OFDM symbol can be suppressed to a certain value or less, and the variation of the error vector due to the nonlinear distortion of each digital data can be suppressed.

  Therefore, since it can be determined without considering the variation of nonlinear distortion of the transmission power amplifier 114, it is not necessary to suppress the nonlinear distortion of the transmission power amplifier more severely than necessary.

  The OFDM symbol power control described above is particularly effective in the OFCDM system. This is because, in the OFCDM system, a plurality of user data and data of various types of amplitude are code-multiplexed in the same OFCDM symbol, and the fluctuation of the signal amplitude of the OFCDM symbol within the symbol and the fluctuation of the peak amplitude between the symbols are large. Because it becomes.

  Next, in OFDM modulation apparatus 100 according to Embodiment 1 of the present invention, the influence of nonlinear distortion of the transmission power amplifier on each digital data allocated in the OFDM symbol can be suppressed to a certain value or less, and each digital data The reason why the variation in the error vector due to the non-linear distortion can be suppressed will be described in more detail.

  FIG. 3 is a diagram showing the dependency of the peak-to-average intensity ratio PAPR (Peak-to-Average-Power-Ratio) on the number of subcarriers N (= multiplexing number) of OFDM symbols.

  When examining this dependence, a random signal was used as transmission data. Here, since the amplitude of each OFDM symbol to be multiplexed is assumed to be constant, the number N of subcarriers is proportional to the OFDM symbol power. The amplitude of the data symbol is set to 1 for simplicity.

  As can be seen from FIG. 3, the PAPR varies depending on the transmission data signal sequence, but the PAPR increases as the number of subcarriers increases, and the maximum value of PAPR can be estimated from the number N of subcarriers. For example, when N = 128, the PAPR is about 12 dB. When the peak intensity increases, the nonlinear distortion of the transmission power amplifier causes the error vector to deteriorate.

  FIG. 4 is a diagram illustrating a calculation example of an error vector due to the third-order nonlinear distortion of the transmission power amplifier when the subcarrier modulation method is the QPSK modulation method and the OFDM method is used. As can be seen from FIG. 4, the error vector increases as the OFDM peak amplitude increases.

  Thus, when the amplitude of each digital data is constant, the OFDM peak amplitude can be estimated from the number N of subcarriers, and the worst value of the influence of nonlinear distortion of the transmission power amplifier can be roughly estimated.

  Next, the influence of nonlinear distortion of the transmission power amplifier in the OFCDM system in which the amplitude of each digital data is not constant will be described.

  FIG. 5 shows an error vector calculated when only one data amplitude in the transmission digital data series is changed from 1 to 4 times. As can be seen from FIG. 5, even if the amplitude of one data (data amplitude ratio) is changed, the error vector after demodulating the data does not change much. Here, the total power of the OFDM symbol is a condition that hardly changes.

  Thus, it was found that the influence of nonlinear distortion such as a transmission power amplifier hardly depends on the amplitude of each data and is almost determined by the total power of the OFDM symbol. That is, the influence of nonlinear distortion is controlled by controlling the power of the OFDM symbol.

  Therefore, the OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention controls each OFDM symbol power detection value P so that it is always below a certain reference value Pm. Thereby, OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention can suppress the influence of nonlinear distortion of transmission power amplifier 114 on each digital data allocated in the OFDM symbol to a certain value or less, and Variations in error vectors due to non-linear distortion of digital data can be suppressed.

  As a method for adjusting the total power of the OFDM symbol, for example, a method of making the power constant by detecting the OFDM symbol power after controlling the OFDM symbol after parallel-serial conversion and controlling the transmission power amplifier at the subsequent stage. There is.

  However, this system requires a circuit that detects the power of an OFDM symbol analog signal at high speed within a short time of the symbol length Ts. In this method, since the variable amplifier is also performed for each OFDM symbol length Ts, high-speed operation is required.

  On the other hand, in the OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention, the control of the OFDM symbol power can be easily realized by a high-speed digital processing circuit.

  As described above, the OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention can easily control the OFCDM symbol power to a certain value or less, and the characteristics due to the non-linear distortion of the transmission power amplifier 114 at the subsequent stage. Variations can be suppressed.

  Therefore, in the first embodiment of the present invention, by suppressing the suppression of nonlinear distortion of the transmission power amplifier 114, the linearity of the transmission power amplifier having very high characteristics is not required, and The price can be reduced.

(Embodiment 2)
Next, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 6 is a block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 2 of the present invention. FIG. 7 is a flowchart for explaining the operation of the main part of the OFDM signal transmission apparatus according to Embodiment 2 of the present invention.

  As shown in FIG. 6, OFDM signal transmission apparatus 600 according to Embodiment 2 of the present invention is obtained by adding power adjustment section 601 to OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention.

  That is, the OFDM signal transmission apparatus 600 according to Embodiment 2 of the present invention includes a subcarrier mapping unit 111, a fast inverse Fourier transform (IFFT) unit 112, a parallel serial (P / S) conversion unit 113, a transmission power amplifier 114, A transmission antenna 115, an OFDM symbol power detection unit 116, a power comparison unit 117, a mapping control unit 118, and a power adjustment unit 601 are provided.

  Power adjustment section 601 is connected between subcarrier mapping section 111 and IFFT section 112 and is connected to the output terminal of OFDM symbol power detection section 116. The power adjustment unit 601 determines the square root of the ratio (Pm / P) of the reference value Pm to the OFDM symbol power detection value P from the OFDM symbol power detection unit 116 to the amplitude of the subcarrier modulation signal of the OFDM symbol of the subcarrier mapping unit 111. A voltage-adjusted subcarrier modulation signal is generated by multiplying √ (Pm / P) and provided to the IFFT unit 112.

  That is, power adjustment section 601 multiplies the OFDM symbol total power by Pm / P by multiplying the amplitude of the subcarrier modulation signal of the OFDM symbol of subcarrier mapping section 111 by the square root of Pm / P (√ (Pm / P)). Double. As a result, the power adjustment unit 601 can set the total power of all OFDM symbols to a constant value (Pm).

  Subcarrier mapping section 111, fast inverse Fourier transform (IFFT) section 112, parallel serial (P / S) conversion section 113, OFDM symbol power detection section 116, power of OFDM signal transmission apparatus 600 according to Embodiment 2 of the present invention The comparison unit 117, the mapping control unit 118, and the power adjustment unit 601 can be configured by a digital processing circuit, can process data at high speed, and is inexpensive.

  Next, the operation of the main part of OFDM modulation apparatus 400 according to Embodiment 2 of the present invention will be described with reference to FIG. 7 together with FIG.

  The flow shown in FIG. 7 is obtained by adding step ST701 to the flow shown in FIG. Step ST701 is inserted between step ST207 and step ST208.

  Next, steps of the flow of FIG. 7 different from the flow of FIG. 2 will be described.

  In step ST207, mapping control section 118 causes subcarrier mapping section 111 to finish subcarrier mapping. In step ST701, power adjustment section 601 determines the amplitude of each subcarrier modulation signal from subcarrier mapping section 111. The voltage adjusted subcarrier modulation signal is generated by multiplying by (√ (Pm / P)), and the process goes to step ST208. In step ST208, IFFT section 112 performs a fast inverse Fourier transform on the voltage-adjusted subcarrier modulation signal from power adjustment section 601 to generate a parallel inverse Fourier transform signal.

  As described above, according to the second embodiment of the present invention, the degradation due to the nonlinear distortion of the transmission power amplifier 114 is controlled to be substantially constant, and therefore, variations in the nonlinear distortion are further suppressed as compared with the first embodiment of the present invention. Therefore, by relaxing the suppression of nonlinear distortion of the transmission power amplifier, the linearity of the transmission power amplifier having very high characteristics is not required, and the price of the transmission power amplifier can be reduced.

  In Embodiment 2 of the present invention, the power of the voltage-adjusted subcarrier modulation signal can be made substantially constant, so that it is not necessary to control the transmission power at a high speed for each voltage-adjusted subcarrier modulation signal in the subsequent circuit Thus, control of transmission power is simplified.

(Embodiment 3)
Next, Embodiment 3 of the present invention will be described in detail with reference to the drawings. FIG. 8 is a block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 3 of the present invention.

  As shown in FIG. 8, OFDM signal transmission apparatus 800 according to Embodiment 3 of the present invention is obtained by adding power adjustment section 801 to OFDM signal transmission apparatus 100 according to Embodiment 1 of the present invention.

  That is, the OFDM signal transmission apparatus 800 according to Embodiment 3 of the present invention includes a subcarrier mapping unit 111, a fast inverse Fourier transform (IFFT) unit 112, a parallel serial (P / S) conversion unit 113, a transmission power amplifier 114, A transmission antenna 115, an OFDM symbol power detection unit 116, a power comparison unit 117, a mapping control unit 118, and a power adjustment unit 801 are provided.

  The power adjustment unit 801 is connected between the IFFT unit 112 and the parallel-serial conversion unit 113 and is connected to the output terminal of the OFDM symbol power detection unit 116.

  The power adjustment unit 801 determines the square root √ (Pm / P) of the ratio (Pm / P) of the reference value Pm to the OFDM symbol power detection value P from the OFDM symbol power detection unit 116 to the amplitude of the inverse Fourier transform signal from the IFFT unit 112. P) is multiplied to generate a parallel voltage adjusted inverse Fourier transform signal, which is supplied to the parallel serial (P / S) converter 113.

  That is, the power adjustment unit 801 multiplies the amplitude of the inverse Fourier transform signal from the IFFT unit 112 by the square root of Pm / P (√ (Pm / P)), thereby increasing the total power of the inverse Fourier transform signal by Pm / P times. To do. Thereby, the power adjustment unit 801 can set the total power of all inverse Fourier transform signals to a constant value (Pm).

  Subcarrier mapping section 111, fast inverse Fourier transform (IFFT) section 112, parallel serial (P / S) conversion section 113, OFDM symbol power detection section 116, power of OFDM signal transmission apparatus 800 according to Embodiment 3 of the present invention The comparison unit 117, the mapping control unit 118, and the power adjustment unit 801 can be configured by a digital processing circuit, can process data at high speed, and is inexpensive.

  The third embodiment of the present invention has the same effect as the second embodiment of the present invention.

  The present invention is also effective for a system that optically transmits OFDM symbols. This is because the distortion characteristics of the laser for optical transmission are large, so that it is easily affected by the peak intensity.

  The present invention can also be combined with various peak suppression methods described in the prior art.

  INDUSTRIAL APPLICABILITY The present invention does not require the linearity of a transmission power amplifier having very high characteristics, and has an effect of reducing the price of the transmission power amplifier, and is useful for an OFDM signal transmission apparatus.

1 is a block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 1 of the present invention. Flowchart for explaining the operation of the main part of the OFDM signal transmission apparatus according to Embodiment 1 of the present invention The figure for demonstrating the subcarrier number dependence of the peak-to-average intensity ratio (PAPR) of OFDM system The figure for demonstrating the error vector with respect to the OFDM peak amplitude of OFDM system The figure for explaining the data amplitude dependence of the error vector of OFDM system Block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 2 of the present invention Flowchart for explaining the operation of the main part of the OFDM signal transmission apparatus according to Embodiment 2 of the present invention Block diagram showing a configuration of an OFDM signal transmission apparatus according to Embodiment 3 of the present invention A block diagram showing a configuration of an example of a conventional OFDM signal transmission apparatus Flowchart for explaining the operation of the main part of the conventional OFDM signal transmission apparatus of FIG.

Explanation of symbols

100, 600, 800 OFDM signal transmission device 111 Subcarrier mapping unit 112 Fast inverse Fourier transform (IFFT) unit 113 Parallel serial (P / S) conversion unit 114 Transmission power amplifier 115 Transmission antenna 116 OFDM symbol power detection unit 117 Power comparison unit 118 Mapping control unit 601, 801 Power adjustment unit

Claims (3)

Subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal;
OFDM symbol power detection means for detecting the power of the OFDM symbol of the subcarrier mapping means to generate an OFDM symbol power detection value;
Power comparison means for generating a power comparison result by comparing whether the OFDM symbol power detection value is smaller than a reference value;
When the power comparison result indicates that the OFDM symbol power detection value is smaller than the reference value, causing the subcarrier mapping means to continue mapping the digital data of the current time to the subcarrier of the OFDM symbol; and When the power comparison result indicates that the OFDM symbol power detection value is not smaller than the reference value, the subcarrier mapping means stops the mapping of the current digital data to the subcarrier of the OFDM symbol. Mapping control means for allocating the digital data allocation and the digital data after the allocation to subcarriers of the next OFDM symbol;
An OFDM signal transmission apparatus comprising: Subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal;
Voltage adjusting means for processing the subcarrier modulation signal from the subcarrier mapping means to generate a voltage adjusted subcarrier modulation signal;
Fast inverse Fourier transform means for generating a parallel inverse Fourier transform signal by performing fast inverse Fourier transform on the voltage-adjusted subcarrier modulation signal from the voltage adjustment means;
OFDM symbol power detection means for detecting the power of the OFDM symbol of the subcarrier mapping means to generate an OFDM symbol power detection value;
Power comparison means for generating a power comparison result by comparing whether the OFDM symbol power detection value is smaller than a reference value;
When the power comparison result indicates that the OFDM symbol power detection value is smaller than the reference value, the subcarrier mapping means continues mapping of the current digital data to the subcarrier of the OFDM symbol, and When the power comparison result indicates that the OFDM symbol power detection value is not smaller than the reference value, the subcarrier mapping means stops mapping the digital data of the current time to the subcarrier of the OFDM symbol. Mapping control means for allocating the digital data allocation and the digital data after the allocation to the subcarriers of the next OFDM symbol,
The voltage adjustment means multiplies the amplitude of the subcarrier modulation signal of the subcarrier mapping means by the square root of the ratio of the reference value to the OFDM symbol power detection value from the OFDM symbol power detection means. An OFDM signal transmission apparatus for generating a carrier modulation signal. Subcarrier mapping means for mapping digital data to subcarriers of an OFDM symbol to generate a subcarrier modulation signal;
Fast inverse Fourier transform means for generating a parallel inverse Fourier transform signal by fast inverse Fourier transforming the subcarrier modulation signal from the subcarrier mapping means;
Voltage adjusting means for processing the parallel inverse Fourier transform signal from the fast inverse Fourier transform means to generate a parallel voltage adjusted inverse Fourier transform signal;
OFDM symbol power detection means for detecting the power of the OFDM symbol of the subcarrier mapping means to generate an OFDM symbol power detection value;
Power comparison means for generating a power comparison result by comparing whether the OFDM symbol power detection value is smaller than a reference value;
When the power comparison result indicates that the OFDM symbol power detection value is smaller than the reference value, causing the subcarrier mapping means to continue mapping the digital data of the current time to the subcarrier of the OFDM symbol; and When the power comparison result indicates that the OFDM symbol power detection value is not smaller than the reference value, the subcarrier mapping means stops the mapping of the current digital data to the subcarrier of the OFDM symbol. Mapping control means for allocating the digital data allocation and the digital data after the allocation to subcarriers of the next OFDM symbol,
The voltage adjusting unit multiplies the amplitude of the parallel inverse Fourier transform signal from the fast inverse Fourier transform unit by a square root of a ratio of a reference value to the OFDM symbol power detection value from the OFDM symbol power detection unit. An OFDM signal transmission apparatus that generates the parallel voltage-adjusted inverse Fourier transform signal.

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