JP5370111B2 - Wireless communication apparatus and wireless communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication device and a wireless communication method, wherein the load on the inverse Fourier transform can be reduced. <P>SOLUTION: Sub-carrier mapping for mapping input data on a sub-carrier is performed, inverse fast Fourier transform with constant throughput regardless of the number of used sub-carriers is performed when the number of used sub-carriers on which the data is mapped is equal to or more than a threshold, a rotation factor corresponding to a combination of the sub-carrier number of a used sub-carrier and the sample number of a sample point for calculation is acquired from a storage unit when the number of used sub-carriers is smaller than the threshold, the data mapped on the used sub-carrier is multiplied by the rotation factor corresponding to such data, and then the multiplication result obtained for each used sub-carrier is added to perform inverse Fourier transform. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method.

  Conventionally, mobile communication using a wireless communication device such as a mobile terminal device or a base station has been used. At present, for example, an OFDM (Orthogonal Frequency Division Multiplexing) method is sometimes used as a mobile communication method.

  A wireless communication device compliant with the OFDM scheme performs an inverse Fourier transform (IFT) process on a modulated signal or the like when generating an OFDM symbol of transmission data. At this time, the wireless communication device generally performs an inverse Fourier transform process by an inverse fast Fourier transform (IFFT). This is because IFFT has a smaller amount of calculation than IDFT (Inverse Discrete Fourier Transform). Specifically, when using the IDFT, the wireless communication apparatus performs “N squared” times of complex multiplication when the IDFT size is N. On the other hand, when using IFFT, the wireless communication apparatus can perform inverse Fourier transform processing by “NlogN” times of complex multiplication.

JP 2008-52504 A

  However, the above-described prior art has a problem that the load on the inverse Fourier transform processing by the wireless communication apparatus is high. For example, in LTE (Long Term Evolution), which is a next generation mobile communication system, the IFFT size is “2048”, and thus a wireless communication device compliant with LTE performs 2048 × log (2048) = 22528 complex multiplications. It will be. As in this example, since the amount of computation of the inverse Fourier transform processing by the wireless communication device is large, the load of transmission processing on the wireless communication device is high.

  The disclosed technology has been made in view of the above, and an object thereof is to provide a wireless communication device and a wireless communication method capable of reducing the load applied to the inverse Fourier transform process.

  In one aspect, a wireless communication device disclosed in the present application is a subcarrier mapping unit that maps input data to subcarriers, a subcarrier number that identifies the subcarriers, and a calculation target during inverse Fourier transform processing. A twiddle factor storage unit that stores a twiddle factor corresponding to a combination with a sample number that identifies each sample point, and whether or not the number of subcarriers to which data is mapped by the subcarrier mapping unit is smaller than a predetermined threshold value When the determination unit determines that the number of used subcarriers is equal to or greater than a threshold, the inverse of performing fast inverse Fourier transform processing with a constant processing amount regardless of the number of used subcarriers. When the number of subcarriers used is determined to be smaller than the threshold by the Fourier transform unit and the determination unit Obtained by multiplying the data mapped to the used subcarrier by the twiddle factor corresponding to the combination of the subcarrier number of the used subcarrier and the sample number of the sample point to be calculated. And an addition type inverse Fourier transform unit for adding the multiplication results.

  According to one aspect of the wireless communication device disclosed in the present application, there is an effect that it is possible to reduce the load applied to the inverse Fourier transform process.

FIG. 1 is a block diagram illustrating a configuration example of a wireless communication apparatus according to the first embodiment. FIG. 2 is a block diagram illustrating a configuration example of a wireless communication apparatus according to the second embodiment. FIG. 3 is a block diagram illustrating a configuration example of a transmission processing unit according to the second embodiment. FIG. 4 is a diagram illustrating a processing amount by the IFFT unit and a processing amount by the addition type inverse Fourier transform unit. FIG. 5 is a flowchart illustrating an example of a transmission processing procedure performed by the transmission processing unit according to the second embodiment. FIG. 6 is a flowchart illustrating an example of a switching process procedure by the control unit according to the second embodiment. FIG. 7 is a flowchart illustrating an example of a switching process procedure by the control unit according to the second embodiment. FIG. 8 is a block diagram illustrating a configuration example of a transmission processing unit according to the third embodiment.

  Embodiments of a wireless communication apparatus and a wireless communication method disclosed in the present application will be described below in detail with reference to the drawings. Note that the wireless communication device and the wireless communication method disclosed in the present application are not limited to the embodiments.

  First, the configuration of the wireless communication apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration example of a wireless communication apparatus according to the first embodiment. In FIG. 1, a part that performs a part of transmission processing by the wireless communication device 10 is illustrated. As illustrated in FIG. 1, the wireless communication device 10 according to the first embodiment includes a subcarrier mapping unit 11, a twiddle factor storage unit 12, a determination unit 13, an inverse Fourier transform unit 14, and an addition type inverse Fourier transform unit. 15.

  The subcarrier mapping unit 11 maps input data to subcarriers. Although not shown in FIG. 1, the subcarrier mapping unit 11 receives, for example, data to which an error correction code is added.

  The twiddle factor storage unit 12 stores a twiddle factor corresponding to a combination of a subcarrier number for identifying a subcarrier and a sample number for identifying each sample point to be calculated in the inverse Fourier transform process. For example, the twiddle factor storage unit 12 calculates a twiddle factor for each phase that is a value obtained by multiplying a value obtained by dividing “2π” by an IFFT size “N” of the inverse Fourier transform unit 14 described later by a subcarrier number and a sample number. Remember.

  The determination unit 13 determines whether or not the number of subcarriers to which data is mapped by the subcarrier mapping unit 11 (hereinafter referred to as “used subcarriers”) is smaller than a first threshold that is a predetermined threshold. .

  When the determination unit 13 determines that the number of used subcarriers is equal to or greater than the first threshold, the inverse Fourier transform unit 14 performs a fast inverse Fourier transform process in which the processing amount is constant regardless of the number of used subcarriers. Specifically, the inverse Fourier transform unit 14 uses the data mapped to the subcarriers by the subcarrier mapping unit 11 and the twiddle factor stored in the twiddle factor storage unit 12, for example, if the IFFT size is “ N ”is performed.

  When the determination unit 13 determines that the number of used subcarriers is smaller than the first threshold, the addition inverse Fourier transform unit 15 performs an inverse Fourier transform process using data mapped to the used subcarriers. Specifically, the addition type inverse Fourier transform unit 15 acquires from the twiddle factor storage unit 12 a twiddle factor corresponding to a combination of a subcarrier number indicating a used subcarrier and a sample number indicating a sample point to be calculated. . Then, the addition type inverse Fourier transform unit 15 multiplies the data mapped to the used subcarriers by the acquired twiddle factor. Then, the addition type inverse Fourier transform unit 15 calculates the value at the sample point to be calculated by adding the multiplication results obtained for each used subcarrier. The addition type inverse Fourier transform unit 15 performs the above addition processing for each sample point.

  Here, the processing amount of the inverse Fourier transform by the inverse Fourier transform unit 14 and the processing amount of the inverse Fourier transform by the addition type inverse Fourier transform unit 15 will be described. First, the processing amount of the inverse Fourier transform process by the inverse Fourier transform unit 14 will be described. The inverse Fourier transform is represented by the following equation (1).

  In the above formula (1), x (n) represents time domain data after inverse Fourier transform. X (k) indicates frequency domain data before inverse Fourier transform. N indicates the IDFT size. N corresponds to the sample number of the time domain signal and takes a value of “0” to “N−1”. K corresponds to the subcarrier number and takes a value of “0” to “N−1”.

  The inverse Fourier transform unit 14 performs fast inverse Fourier transform, and therefore performs “NlogN” times of complex multiplication when performing inverse Fourier transform processing. One complex multiplication corresponds to four real multiplications and two additions. If the number of bits allocated to one subcarrier is “b”, one real number multiplication can be converted to “b−1” additions. For example, when the number of bits is “8”, one real number multiplication is “8 bits × 8 bits”, and therefore can be converted into seven additions. Therefore, one complex multiplication can be converted into “(b−1) × 4 + 2” additions. Further, the inverse Fourier transform unit 14 accumulates the complex number data “NlogN” times. Considering the number of additions of the I component and the number of additions of the Q component, the inverse Fourier transform unit 14 accumulates “2 × NlogN” times. Therefore, the processing amount by the inverse Fourier transform unit 14 is expressed by the following equation (2) when converted into the number of additions.

  That is, the inverse Fourier transform unit 14 performs addition for the number of times represented by the following expression (3) when performing the inverse Fourier transform process.

  Next, the processing amount of the inverse Fourier transform process by the addition type inverse Fourier transform unit 15 will be described. When the above formula (1) is expanded, it is expressed by the following formula (4).

  In the above equation (4), X (0), X (1),..., X (N−1) correspond to data mapped to subcarriers by the subcarrier mapping unit 11. For example, it is assumed that data is mapped to the 0th to Mth subcarriers by the subcarrier mapping unit 11. In such a case, “0” is stored in the (M + 1) th to (N−1) th subcarriers. That is, in this example, since the value of the (M + 1) th term to the (N−1) th term is “0” in the formula (4), the (M + 1) th term to the (N−1) th term. ) Term does not have to be calculated. For this reason, the addition-type inverse Fourier transform unit 15 performs the calculation only for the term for which X (k) corresponds to the used subcarrier when performing the calculation shown in the above formula (1).

  Here, when the number of subcarriers used is Sc, the addition inverse Fourier transform unit 15 calculates Sc complex multiplications and “Sc” when calculating the value of one sample point in the above equation (4). -1 "addition is performed. As described above, one complex multiplication can be converted into the number of additions of “(b−1) × 4 + 2”. Therefore, the addition type inverse Fourier transform unit 15 performs “Sc × (4b−2) + (Sc−1)” times of addition when calculating the value of one sample point. Further, when considering the complex I component and Q component, the addition inverse Fourier transform unit 15 calculates “2 {Sc × (4b−2) + (Sc−)” when calculating the value of one sample point. 1)} ”times. And since the addition type inverse Fourier transform part 15 calculates the value of each sample point, it calculates the said Formula (4) about n = 0-N-1. Therefore, the processing amount for the addition-type inverse Fourier transform by the addition-type inverse Fourier transform unit 15 is expressed by the following expression (5) when converted into the number of additions.

  The wireless communication device 10 according to the first embodiment causes the inverse Fourier transform unit 14 to perform an inverse Fourier transform process when the value of the formula (5) is larger than the formula (3). On the other hand, the wireless communication device 10 causes the addition type inverse Fourier transform unit 15 to perform an inverse Fourier transform process when the value of the above formula (3) is larger than the above formula (5). The IDFT size “N” and the number of bits “b” are values determined in advance by the system. Therefore, the radio communication apparatus 10 determines which of the inverse Fourier transform unit 14 and the addition type inverse Fourier transform unit 15 is to perform the inverse Fourier transform process based on the number of used subcarriers Sc.

  As described above, the wireless communication apparatus 10 according to the first embodiment includes the inverse Fourier transform unit 14 and the addition type inverse Fourier transform unit 15. And the radio | wireless communication apparatus 10 switches the process part which performs an inverse Fourier transform process to either the inverse Fourier transform part 14 or the addition type inverse Fourier transform part 15 based on the number of used subcarriers. Specifically, when the number of used subcarriers is smaller than the first threshold T1, the wireless communication device 10 performs an inverse Fourier transform process using the addition-type inverse Fourier transform unit 15. This is because, when the number of used subcarriers is smaller than the first threshold T1, the addition type inverse Fourier transform unit 15 requires less processing amount for the inverse Fourier transform than the inverse Fourier transform unit 14. In addition, when the number of used subcarriers is equal to or greater than the first threshold T1, the wireless communication device 10 performs an inverse Fourier transform process using the inverse Fourier transform unit 14. This is because when the number of used subcarriers is equal to or greater than the first threshold value T1, the inverse Fourier transform unit 14 requires less processing amount for the inverse Fourier transform than the addition type inverse Fourier transform unit 15.

  As described above, when the wireless communication apparatus 10 according to the first embodiment can perform the inverse Fourier transform with a smaller processing amount than the fast inverse Fourier transform, the addition-type inverse Fourier transform unit 15 performs the inverse Fourier transform. . Therefore, the wireless communication device 10 according to the first embodiment can reduce the load on the inverse Fourier transform.

  Next, the wireless communication device described in the first embodiment will be described using a specific example. In the second embodiment, an example will be described in which the wireless communication device described in the first embodiment is applied to a mobile communication system whose communication standard is LTE.

[Configuration of Wireless Communication Device According to Second Embodiment]
First, the configuration of the wireless communication apparatus according to the second embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration example of a wireless communication apparatus according to the second embodiment. The wireless communication device 20 illustrated in FIG. 2 is, for example, a portable terminal device that conforms to the LTE standard, and performs wireless communication with the base station 1. As illustrated in FIG. 2, the wireless communication device 20 includes a reception antenna 21, a transmission antenna 22, a wireless unit 23, an upper layer 24, and a baseband processing unit 25.

  The receiving antenna 21 is an antenna that receives a signal from the outside. For example, the receiving antenna 21 receives a signal transmitted from the base station 1. The transmission antenna 22 is an antenna that transmits a signal to the outside. For example, the transmission antenna 22 transmits a signal to the base station 1. Note that the wireless communication device 20 may include a transmission / reception antenna that shares a reception antenna and a transmission antenna.

  The radio unit 23 transmits and receives radio signals via the reception antenna 21 and the transmission antenna 22. For example, the wireless unit 23 performs wireless processing such as A / D (Analog / Digital) conversion on the signal received from the reception antenna 21. Further, for example, the radio unit 23 performs radio processing such as D / A (Digital / Analog) conversion on a signal input from the transmission processing unit 200 described later, and the signal after the radio processing is transmitted to the transmission antenna 22. To the base station 1.

  The upper layer 24 performs various processes based on the received data when the received received data is input from the decoding unit 27 described later. For example, when the received data is mail data, the upper layer 24 stores the received data in a predetermined storage area.

  Moreover, when transmitting data to the outside such as the base station 1, the upper layer 24 generates transmission data and outputs the generated transmission data to the encoding unit 28. For example, it is assumed that the wireless communication device 20 transmits data using a physical channel such as PUCCH (Physical Uplink Control Channel) or PUSCH (Physical Uplink Shared Channel). In such a case, the upper layer 24 generates transmission data based on, for example, a user operation. Further, for example, it is assumed that the wireless communication device 20 transmits data using a physical channel such as SRS (Sounding Reference Signal), DRS (Demodulation Reference Signal), or PRACH (Physical Random Access Channel). In such a case, the upper layer 24 outputs, for example, a Zadoff-Chu sequence number to the transmission processing unit 200.

  The baseband processing unit 25 performs baseband processing on transmission data and reception data. As illustrated in FIG. 2, the baseband processing unit 25 includes a reception processing unit 26, a decoding unit 27, an encoding unit 28, and a transmission processing unit 200.

  The reception processing unit 26 performs various reception processes on the reception data input from the wireless unit 23. For example, the reception processing unit 26 performs CP (Cyclic Prefix) deletion processing, demodulation processing, and the like on the reception data input from the wireless unit 23. The decoding unit 27 decodes the reception data input from the reception processing unit 26.

  The encoding unit 28 adds an error correction code to the transmission data input from the upper layer 24. The transmission processing unit 200 performs various transmission processes on the transmission data to which the error correction code is added by the encoding unit 28. The processing by the transmission processing unit 200 will be specifically described with reference to FIG.

[Configuration of Transmission Processing Unit in Second Embodiment]
Next, the configuration of the transmission processing unit 200 according to the second embodiment will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration example of the transmission processing unit 200 according to the second embodiment. As illustrated in FIG. 3, the transmission processing unit 200 according to the second embodiment includes a transmission data generation unit 210, a DFT (Discrete Fourier Transform) unit 220, a subcarrier mapping unit 230, a selector 241, a selector 242, and a rotation. The factor storage unit 250, the IFFT unit 261, the addition type inverse Fourier transform unit 262, the CP insertion unit 270, the subcarrier shift unit 280, and the control unit 290 are included.

  When the data bit sequence is input from the encoding unit 28, the transmission data generation unit 210 modulates the data bit sequence to generate transmission data. For example, the transmission data generation unit 210 modulates the data bit string by a modulation scheme such as BPSK (Binary Phase Shift Keying) or QPSK (Quadrature Phase Shift Keying). Further, when a Zadoff-Chu sequence number is designated from the upper layer 24, the transmission data generation unit 210 generates a Zadoff-Chu sequence based on the Zadoff-Chu sequence number.

  In addition, when modulating the data transmitted on the PUCCH, the transmission data generation unit 210 maps the data bit string input from the encoding unit 28 to a point on the circumference of the radius “1” on the IQ plane. To do. The transmission data generation unit 210 also generates data corresponding to a point on the circumference of the radius “1” on the IQ plane when generating data to be transmitted in SRS or DRS. That is, the amplitude of data transmitted in PUCCH, SRS, and DRS is “1” and is constant.

  Then, transmission data generation section 210 outputs the modulated or generated transmission data to either DFT section 220 or subcarrier mapping section 230. For example, when the transmission data is data transmitted in PUCCH, SRS, or DRS, transmission data generation section 210 outputs the transmission data to subcarrier mapping section 230. Further, for example, when the transmission data is data transmitted on the PRACH and PUSCH, the transmission data generation unit 210 outputs the transmission data to the DFT unit 220.

  The DFT unit 220 converts time domain data into frequency domain data by performing a Fourier transform process on the transmission data input from the transmission data generation unit 210. Then, DFT section 220 outputs frequency domain data to subcarrier mapping section 230. The subcarrier mapping unit 230 maps transmission data input from the transmission data generation unit 210 and frequency domain data input from the DFT unit 220 to subcarriers.

  The selector 241 outputs the transmission data mapped to the subcarrier by the subcarrier mapping unit 230 to either the IFFT unit 261 or the addition type inverse Fourier transform unit 262. Note that the selector 241 determines which of the IFFT unit 261 and the addition type inverse Fourier transform unit 262 outputs transmission data in accordance with a selection signal input from a switching control unit 291 described later.

  The twiddle factor storage unit 250 stores N twiddle factors that are IDFT sizes. For example, when the IDFT size is “2048”, the twiddle factor storage unit 250 stores 2048 twiddle factors obtained by dividing 2π by 2048.

  IFFT section 261 uses the transmission data mapped to the subcarrier by subcarrier mapping section 230 and the twiddle factor stored in twiddle factor storage section 250 to perform a fast inverse Fourier transform process having an IFFT size “N”. I do. Thereby, IFFT section 261 converts the transmission data mapped to subcarriers by subcarrier mapping section 230 into time domain data.

  The addition-type inverse Fourier transform unit 262 performs calculation only for the term in which X (k) corresponds to the used subcarrier in the formula (1). Specifically, the addition type inverse Fourier transform unit 262 acquires from the twiddle factor storage unit 250 a twiddle factor corresponding to a combination of a subcarrier number indicating a used subcarrier and a sample number indicating a sample point to be calculated. . Then, the addition type inverse Fourier transform unit 262 multiplies the data mapped to the used subcarrier by the twiddle factor corresponding to the used subcarrier. Then, the addition type inverse Fourier transform unit 262 calculates the value at the sample point to be calculated by adding the multiplication results obtained for each used subcarrier. The addition type inverse Fourier transform unit 262 performs the above addition process for each sample point.

  For example, it is assumed that data is mapped to 0th to 11th subcarriers. Further, it is assumed that the IFFT size is “2048”. In such a case, the addition type inverse Fourier transform unit 262 performs the calculation shown in the above formula (1) for k = 0 to 11 and n = 0 to 2047.

  The selector 242 outputs the transmission data in the time domain after the inverse Fourier transform input from the IFFT unit 261 or the addition type inverse Fourier transform unit 262 to the CP insertion unit 270. Note that the selector 242 determines whether to output the transmission data input from the IFFT unit 261 or the addition type inverse Fourier transform unit 262 to the CP insertion unit 270 according to the selection signal input from the switching control unit 291. To do.

  The CP insertion unit 270 sets a certain amount of time at the end of the transmission data input from the selector 242 as a CP, and inserts the CP at the beginning of the transmission data. Subcarrier shift section 280 multiplies transmission data into which CP has been inserted by CP insertion section 270 by a twiddle factor, and performs frequency shift by “½” of the bandwidth of each subcarrier. In the following, the process of performing frequency shift by “½” of the bandwidth of each subcarrier may be referred to as “½ subcarrier shift process”.

  The control unit 290 controls the selectors 241 and 242, the IFFT unit 261, and the addition type inverse Fourier transform unit 262. Specifically, as illustrated in FIG. 3, the control unit 290 includes a switching control unit 291 and a clock control unit 292.

  Based on the amplitude of each transmission data mapped to subcarriers and the number of used subcarriers, the switching control unit 291 selects a processing unit that performs an inverse Fourier transform process as the IFFT unit 261 or the addition type inverse Fourier transform unit 262. Switch to one. Then, the switching control unit 291 outputs a selection signal indicating which processing unit of the IFFT unit 261 or the addition type inverse Fourier transform unit 262 performs the inverse Fourier transform process to the selectors 241 and 242.

  The switching process by the switching control unit 291 will be specifically described. The switching control unit 291 determines whether or not the amplitude of each transmission data mapped to the subcarrier by the subcarrier mapping unit 230 is constant. For example, the amplitude of data transmitted in PUCCH, SRS, and DRS is a constant value “1”. Therefore, the switching control unit 291 determines that the amplitude is constant when the transmission data mapped to the subcarrier by the subcarrier mapping unit 230 is data transmitted in PUCCH, SRS, or DRS, for example. .

  When the switching control unit 291 determines that the amplitude of each transmission data mapped to the subcarrier is not constant, the switching control unit 291 controls the IFFT unit 261 to perform the inverse Fourier transform process. On the other hand, if the switching control unit 291 determines that the amplitude of each transmission data mapped to the subcarrier is constant, whether or not the number of used subcarriers is smaller than a second threshold T2 that is a predetermined threshold. Determine. When the switching control unit 291 determines that the number of used subcarriers is equal to or greater than the second threshold T2, the switching control unit 291 controls the IFFT unit 261 to perform an inverse Fourier transform process. On the other hand, when the number of used subcarriers is smaller than the second threshold value T2, the switching control unit 291 controls the inverse Fourier transform process to be performed by the addition-type inverse Fourier transform unit 262.

  For example, the switching control unit 291 controls the processing unit that performs the inverse Fourier transform process by outputting “0” or “1” as the selection signal to the selectors 241 and 242. Here, when the selection signal is “0”, it indicates that the IFFT unit 261 performs the inverse Fourier transform process, and when the selection signal is “1”, the addition type inverse Fourier transform unit 262. It is assumed that the inverse Fourier transform process is performed by. In such a case, when the selection signal “0” is input from the switching control unit 291, the selector 241 outputs the transmission data mapped to the subcarrier by the subcarrier mapping unit 230 to the IFFT unit 261. In addition, when the selection signal “1” is input from the switching control unit 291, the selector 241 outputs the transmission data mapped to the subcarrier by the subcarrier mapping unit 230 to the addition inverse Fourier transform unit 262. In addition, when the selection signal “0” is input from the switching control unit 291, the selector 242 outputs the transmission data input from the IFFT unit 261 to the CP insertion unit 270. In addition, when the selection signal “1” is input from the switching control unit 291, the selector 242 outputs the transmission data input from the addition type inverse Fourier transform unit 262 to the CP insertion unit 270.

  The clock control unit 292 starts the clock of the processing unit controlled to perform the inverse Fourier transform process by the switching control unit 291 and stops the clock of the processing unit controlled not to perform the inverse Fourier transform process. For example, it is assumed that the switching control unit 291 controls the IFFT unit 261 to perform an inverse Fourier transform process. In such a case, the clock control unit 292 activates the operation clock of the IFFT unit 261 and stops the operation clock of the addition type inverse Fourier transform unit 262. In addition, for example, it is assumed that the switching control unit 291 performs control so that the addition type inverse Fourier transform unit 262 performs the inverse Fourier transform process. In such a case, the clock control unit 292 activates the operation clock of the addition type inverse Fourier transform unit 262 and stops the operation clock of the IFFT unit 261.

  Thus, the clock control unit 292 can prevent the power consumption from increasing by stopping the clock of the processing unit that does not perform the inverse Fourier transform process. For example, when the addition type inverse Fourier transform unit 262 performs the inverse Fourier transform process, the clock control unit 292 stops the IFFT unit 261, so that the power consumed by the IFFT unit 261 can be reduced.

  Note that the transmission data generation unit 210, DFT unit 220, subcarrier mapping unit 230, IFFT unit 261, addition type inverse Fourier transform unit 262, CP insertion unit 270, subcarrier shift unit 280, and control unit 290 described above are, for example, It is an electronic circuit. Examples of the electronic circuit include, for example, an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), or a central processing unit (CPU) or a micro processing unit (MPU). The twiddle factor storage unit 250 described above is, for example, a semiconductor memory device such as a random access memory (RAM), a read only memory (ROM), or a flash memory, or a storage device such as a hard disk or an optical disk. .

[Processing amount of IFFT unit and addition type inverse Fourier transform unit]
Next, the processing amount of the inverse Fourier transform by the IFFT unit 261 and the processing amount of the inverse Fourier transform by the addition type inverse Fourier transform unit 262 will be described. As described above, since the IFFT unit 261 performs inverse fast Fourier transform, it performs “NlogN” number of complex multiplications. The number of additions by the IFFT unit 261 is expressed by the above equation (3).

  The addition type inverse Fourier transform unit 262 according to the second embodiment performs the addition type inverse Fourier when the amplitude of each transmission data mapped to the subcarrier is constant and the number of used subcarriers is smaller than the second threshold T2. Perform the conversion process. In other words, the addition type inverse Fourier transform unit 262 performs the addition type Fourier transform process using data having a constant amplitude. Therefore, when the addition type inverse Fourier transform unit 262 performs the addition type Fourier transform process, X (k) in the above formula (1) is expressed by the following formula (6).

  In the above formula (6), α (k) indicates the phase for each subcarrier. By substituting the above equation (6) into the above equation (1), the above equation (1) is expressed by the following equation (7).

  Here, when the number of used subcarriers is Sc and the head position of the subcarrier to which transmission data is mapped by the subcarrier mapping unit 230 is kmap, the above equation (7) is expressed by the following equation (8). .

  Then, the addition type inverse Fourier transform unit 262 according to the second embodiment performs the calculation shown in the above formula (8) in the case of “n = 0 to N−1”. Specifically, the addition type inverse Fourier transform unit 262 reads out the twiddle factor represented by the following formula (9) from the above formula (8) from the twiddle factor storage unit 250 and adds it.

  For example, the addition-type inverse Fourier transform unit 262 reads out the Sc twiddle factors of “k = kmap to kmap + Sc−1” and adds the read Sc twiddle factors when “n = 0”. . Similarly, the addition type inverse Fourier transform unit 262 reads out the Sc twiddle factors of “k = kmap to kmap + Sc−1” even when “n = 1 to N−1”, Add the twiddle factors. That is, the addition type inverse Fourier transform unit 262 performs “(Sc−1) · N” additions when performing the addition type Fourier transform process. However, since the twiddle factor is a complex number, the addition type inverse Fourier transform unit 262 performs addition of the I component and addition of the Q component in one addition. Therefore, the processing amount for the addition-type inverse Fourier transform by the addition-type inverse Fourier transform unit 262 in the second embodiment is expressed by the following expression (10) when converted into the number of additions.

  As described above, the addition type inverse Fourier transform unit 262 according to the second embodiment does not perform complex multiplication between the data mapped to the subcarrier and the twiddle factor when performing the addition type Fourier transform process. Add only. Therefore, the processing amount of the addition type inverse Fourier transform unit 262 by the addition type inverse Fourier transform unit 262 in the second embodiment is smaller than the processing amount of the addition type inverse Fourier transform unit 15 shown in the first embodiment.

  The switching control unit 291 performs control so that the inverse Fourier transform process is performed by the IFFT unit 261 when the formula (10) is larger than the formula (3). On the other hand, the switching control unit 291 causes the addition type inverse Fourier transform unit 262 to perform the addition type inverse Fourier transform process when the value of the formula (3) is larger than the value of the formula (10). Control.

  Here, FIG. 4 shows the processing amount for the inverse Fourier transform by the IFFT unit 261 and the processing amount for the inverse Fourier transform by the addition type inverse Fourier transform unit 262. In FIG. 4, the processing amounts of the IFFT unit 261 and the addition type inverse Fourier transform unit 262 are shown converted into the number of additions. As indicated by the straight line A in FIG. 4, the number of additions when the fast inverse Fourier transform is performed by the IFFT unit 261 is expressed by the above equation (3), and thus becomes a constant value. Specifically, the number of bits b and the IDFT size N are values that are determined in advance by the system, and thus the above expression (3) is a constant value. On the other hand, as shown by the straight line B in FIG. 4, the number of additions when the fast inverse Fourier transform is performed by the summation inverse Fourier transform unit 262 is expressed by the above equation (10). Proportional.

  The above-described second threshold T2 of the number of used subcarriers Sc is an intersection of the straight line A and the straight line B shown in FIG. The second threshold value T2 at the intersection of the straight line A and the straight line B is expressed by the following formula (11) by the above formulas (3) and (10).

  For example, it is assumed that the number of bits b is “8” and the IDFT size N is 2048. In such a case, the second threshold T2 is “177” according to the above equation (11). Therefore, in the case of the above example, when the number of used subcarriers is “177” or more, the switching control unit 291 controls the IFFT unit 261 to perform the inverse Fourier transform process. On the other hand, when the number of used subcarriers is smaller than “177”, the switching control unit 291 controls the addition type inverse Fourier transform unit 262 to perform the addition type inverse Fourier transform process.

[Transmission Processing Procedure by Transmission Processing Unit in Embodiment 2]
Next, the procedure of transmission processing by the transmission processing unit 200 according to the second embodiment will be described with reference to FIG. FIG. 5 is a flowchart illustrating a transmission processing procedure performed by the transmission processing unit 200 according to the second embodiment.

  As illustrated in FIG. 5, when data transmission is performed by the wireless communication device 20 (Yes in step S101), the transmission data generation unit 210 performs modulation processing or generates a Zadoff-Chu sequence to transmit transmission data. Is generated (step S102).

  If the transmission data generation unit 210 generates transmission data to be processed by DFT processing (Yes at step S103), the transmission data generation unit 210 outputs the generated transmission data to the DFT unit 220. On the other hand, when the transmission data generation unit 210 generates transmission data that is not subject to DFT processing (No in step S103), the transmission data generation unit 210 outputs the generated transmission data to the subcarrier mapping unit 230. When the transmission data is input from the transmission data generation unit 210, the DFT unit 220 performs a Fourier transform process using the transmission data (step S104).

  Subsequently, the subcarrier mapping unit 230 maps the transmission data input from the transmission data generation unit 210 and the frequency domain data input from the DFT unit 220 to subcarriers (step S105).

  Subsequently, the control unit 290 performs switching processing for switching processing units that perform inverse Fourier transform processing based on the amplitude of transmission data mapped to each subcarrier by the subcarrier mapping unit 230 and the number of used subcarriers. (Step S106). The switching process by the control unit 290 will be described later with reference to FIG.

  When the processing unit that performs the inverse Fourier transform process by the control unit 290 is switched to the addition type inverse Fourier transform unit 262 (Yes in step S107), the addition type inverse Fourier transform unit 262 performs the addition type inverse Fourier transform process. (Step S108). On the other hand, when the processing unit that performs the inverse Fourier transform process by the control unit 290 is switched to the IFFT unit 261 (No in step S107), the IFFT unit 261 performs the fast inverse Fourier transform process (step S109).

  Subsequently, the CP insertion unit 270 inserts the CP into the time domain data input from the IFFT unit 261 or the addition type inverse Fourier transform unit 262 (step S110). Then, the subcarrier shift unit 280 performs 1/2 subcarrier shift processing on the time domain data in which the CP is inserted by the CP insertion unit 270 (step S111).

[Switching Procedure (1) by Control Unit in Embodiment 2]
Next, the procedure of the switching process by the control unit 290 in the second embodiment will be described with reference to FIG. FIG. 6 is a flowchart illustrating an example of a switching process procedure performed by the control unit 290 according to the second embodiment.

  As illustrated in FIG. 6, the switching control unit 291 of the control unit 290 determines whether or not the amplitude of each transmission data mapped to the subcarrier by the subcarrier mapping unit 230 is constant (step S201). Then, when the amplitude of each transmission data is constant (Yes at Step S201), the switching control unit 291 determines whether the number of used subcarriers is smaller than the second threshold T2 (Step S202).

  When the switching control unit 291 determines that the number of used subcarriers is smaller than the second threshold T2 (Yes in step S202), the control unit 290 performs an inverse Fourier transform process using the addition-type inverse Fourier transform unit 262. Control to be performed.

  Specifically, the clock control unit 292 of the control unit 290 activates the operation clock of the addition type inverse Fourier transform unit 262 (step S203) and stops the operation clock of the IFFT unit 261 (step S204). Then, the switching control unit 291 outputs a selection signal indicating that the inverse Fourier transform processing is performed by the addition-type inverse Fourier transform unit 262 to the selector 241 and the selector 242 (step S205).

  On the other hand, when the switching control unit 291 determines that the amplitude of each transmission data is not constant (No at Step S201), the control unit 290 controls the IFFT unit 261 to perform the inverse Fourier transform process. Alternatively, when the switching control unit 291 determines that the number of used subcarriers is equal to or greater than the second threshold value T2 (No at Step S202), the control unit 290 causes the IFFT unit 261 to perform an inverse Fourier transform process. To control.

  Specifically, the clock control unit 292 activates the operation clock of the IFFT unit 261 (step S206) and stops the operation clock of the addition type inverse Fourier transform unit 262 (step S207). Then, the switching control unit 291 outputs a selection signal indicating that the inverse Fourier transform process is performed by the IFFT unit 261 to the selector 241 and the selector 242 (step S208).

[Switching Procedure (2) by Control Unit in Embodiment 2]
Note that the control unit 290 may further perform the determination process by the determination unit 13 illustrated in the first embodiment. This will be specifically described with reference to FIG. FIG. 7 is a flowchart illustrating an example of a switching process procedure performed by the control unit 290 according to the second embodiment.

  As shown in FIG. 7, the control unit 290 first determines whether or not the number of used subcarriers is smaller than the first threshold T1 (step S301). Then, when the number of subcarriers used is smaller than the first threshold T1, the control unit 290 adds the inverse Fourier transform regardless of whether or not the amplitude of each transmission data mapped to the subcarrier is constant. The unit 262 controls the inverse Fourier transform process to be performed. Specifically, the control unit 290 performs the processing procedure in steps S304 to S306. The processing procedure in steps S304 to S306 is the same as the processing procedure in steps S203 to S205 shown in FIG.

  On the other hand, when the number of used subcarriers is equal to or greater than the first threshold T1 (No at Step S301), the control unit 290 determines whether the amplitude of the transmission data mapped to the subcarriers by the subcarrier mapping unit 230 is constant. Is determined (step S302). Then, when the amplitude of each transmission data is constant (Yes at Step S302), the control unit 290 determines whether or not the number of used subcarriers is smaller than the second threshold T2 (Step S303).

  Then, when the number of subcarriers used is smaller than the second threshold T2 (Yes at Step S303), the control unit 290 controls the addition type inverse Fourier transform unit 262 to perform the inverse Fourier transform process. Specifically, the control unit 290 performs the processing procedure in steps S304 to S306.

  On the other hand, when the amplitude of each transmission data is not constant (No at Step S302), the control unit 290 controls the IFFT unit 261 to perform the inverse Fourier transform process. Alternatively, when the number of used subcarriers is equal to or greater than the second threshold T2 (No at Step S303), the control unit 290 controls the IFFT unit 261 to perform the inverse Fourier transform process. Specifically, the control unit 290 performs the processing procedure in steps S307 to S309. The processing procedure in steps S307 to S309 is the same as the processing procedure in steps S206 to S208 shown in FIG.

[Effect of Example 2]
As described above, the wireless communication apparatus 20 according to the second embodiment includes the IFFT unit 261 and the addition type inverse Fourier transform unit 262. Then, the addition type inverse Fourier transform unit 262 of the wireless communication apparatus 20 performs the addition type inverse Fourier transform process using transmission data having a constant amplitude, so that the inverse Fourier transform process can be performed without performing complex multiplication. it can.

  Also, the radio communication apparatus 20 according to the second embodiment uses the IFFT unit 261 or the addition unit that performs an inverse Fourier transform process based on the amplitude of each transmission data mapped to subcarriers and the number of used subcarriers. Switch to any of the inverse Fourier transform units 262. Thereby, the radio communication device 20 performs processing smaller than the fast inverse Fourier transform when the amplitude of each transmission data mapped to the subcarrier is constant and the number of subcarriers used is smaller than the second threshold T2. An inverse Fourier transform can be performed on the quantity. Therefore, the wireless communication device 20 according to the second embodiment can reduce the load on the inverse Fourier transform.

  In addition, the clock control unit 292 of the wireless communication apparatus 20 according to the second embodiment starts the clock of the processing unit controlled to perform the inverse Fourier transform process by the switching control unit 291 and does not perform the inverse Fourier transform process. The clock of the processing unit controlled by the above is stopped. Thereby, since the radio | wireless communication apparatus 20 stops the clock of the process part which does not perform an inverse Fourier transform process, it can prevent that power consumption increases.

  In the second embodiment, the subcarrier shift unit 280 performs the 1/2 subcarrier shift process on the transmission data into which the CP is inserted by the CP insertion unit 270. However, 1/2 subcarrier shift processing may be performed before CP insertion. In the third embodiment, an example of a wireless communication apparatus that performs 1/2 subcarrier shift processing before inserting a CP will be described.

[Configuration of Wireless Communication Device According to Third Embodiment]
First, the configuration of a wireless communication apparatus according to the third embodiment (hereinafter referred to as “wireless communication apparatus 30”) will be described. The configuration of the wireless communication device 30 according to the third embodiment is the same as the configuration of the wireless communication device 20 illustrated in FIG. However, the transmission processing unit included in the wireless communication device 30 according to the third embodiment performs processing different from the transmission processing unit 200 included in the wireless communication device 20. The transmission processing unit included in the wireless communication device 30 according to the third embodiment will be described below with reference to FIG.

  FIG. 8 is a block diagram illustrating a configuration example of a transmission processing unit according to the third embodiment. In the following description, parts having the same functions as the constituent parts shown in FIG. As illustrated in FIG. 8, the transmission processing unit 300 according to the third embodiment includes a transmission data generation unit 210, a DFT unit 220, a subcarrier mapping unit 230, a selector 241, a twiddle factor storage unit 350, and an IFFT unit 261. An inverse Fourier transform unit 362, CP insertion units 371 and 372, a subcarrier shift unit 280, a selector 342, and a control unit 390.

  The addition type inverse Fourier transform unit 362 performs addition type inverse Fourier transform using data mapped to the used subcarriers. At this time, the addition type inverse Fourier transform unit 362 according to the third embodiment performs a 1/2 subcarrier shift process. Specifically, the addition type inverse Fourier transform unit 362 performs an operation represented by the following formula (12).

  The above equation (12) is an arithmetic expression in which “2πnk” in the above equation (8) is replaced with “2πn (k + 0.5)”. The addition-type inverse Fourier transform unit 362 can obtain a calculation result that is frequency-shifted by “½” of the bandwidth of each subcarrier by performing the calculation shown in the above equation (12). Thereby, the transmission processing unit 300 may not perform the 1/2 subcarrier shift process on the data in the time domain on which the inverse Fourier transform process is performed by the addition-type inverse Fourier transform unit 362. Further, as shown in the above equation (12), the processing amount by the addition type inverse Fourier transform unit 362 is substantially equal to the processing amount by the addition type inverse Fourier transform unit 262. Therefore, the transmission processing unit 300 can reduce the amount of processing required for the ½ subcarrier shift process when the addition type inverse Fourier transform unit 362 performs the inverse Fourier transform process.

  The twiddle factor storage unit 350 stores 2N twiddle factors obtained by multiplying the IDFT size N by “2”. The reason why the twiddle factor storage unit 350 stores 2N twiddle factors is that a part of the twiddle factors is “2πn (k + 0.5)” as shown in the above equation (12). Therefore, for example, when the IDFT size is “2048”, the twiddle factor storage unit 350 stores 4096 twiddle factors.

  Note that, like the twiddle factor storage unit 250, the twiddle factor storage unit 350 may store IDFT size N twiddle factors. In such a case, the addition type inverse Fourier transform unit 362 reads an approximate value when reading the twiddle factor from the twiddle factor storage unit 350. Even when the twiddle factor to be approximated is read out by the addition type inverse Fourier transform unit 362, the signal degradation is less than 0.1% in EVM (Error Vector Magnitude), so the influence on the wireless communication is small. .

  The CP insertion unit 371 inserts the CP at the end of transmission data input from the IFFT unit 261 as a CP for a fixed time at the end of the transmission data. The CP insertion unit 372 sets the CP for the fixed time at the end of the transmission data input from the addition type inverse Fourier transform unit 362, inverts the sign of the CP, and inserts it at the beginning of the transmission data.

  Here, the reason why the data whose sign is inverted at the end of the transmission data is CP will be described. As described above, the addition type inverse Fourier transform unit 362 according to the third embodiment performs the 1/2 subcarrier shift process. Therefore, the time domain data output from the addition type inverse Fourier transform unit 362 has already been subjected to the 1/2 subcarrier shift processing. For this reason, if a certain amount of time at the end of the transmission data output from the addition type inverse Fourier transform unit 362 is inserted at the beginning, the continuity of the transmission data as a time domain signal cannot be maintained. CP insertion section 372 implements maintaining the continuity of the time domain signal by inserting a CP with the end of the transmission data output from addition inverse Fourier transform section 362 inverted in sign at the beginning of the transmission data. doing.

  The control unit 390 controls the selector 241, IFFT unit 261, addition type inverse Fourier transform unit 362, and CP insertion units 371 and 372. Specifically, as illustrated in FIG. 8, the control unit 390 includes a switching control unit 391 and a clock control unit 392.

  Based on the amplitude of each transmission data mapped to the subcarrier and the number of used subcarriers, the switching control unit 391 sets the processing unit that performs the inverse Fourier transform process to the IFFT unit 261 or the addition type inverse Fourier transform unit 362. Switch to one. Then, the switching control unit 391 outputs a selection signal indicating which processing unit of the IFFT unit 261 or the addition type inverse Fourier transform unit 362 performs the inverse Fourier transform process to the selectors 241 and 342.

  When the IFFT unit 261 is controlled to perform the inverse Fourier transform process, the clock control unit 392 activates the operation clock of the IFFT unit 261 and stops the operation clock of the addition type inverse Fourier transform unit 362. The clock control unit 392 activates the operation clock of the addition type inverse Fourier transform unit 362 and controls the IFFT unit 261 when the addition type inverse Fourier transform unit 262 is controlled to perform the inverse Fourier transform process. Stop the operating clock.

  The selector 342 outputs the time domain data input from the subcarrier shift unit 280 or the CP insertion unit 372 to the radio unit 23. The selector 342 determines whether to output the transmission data input from the subcarrier shift unit 280 or the CP insertion unit 372 to the radio unit 23 based on the selection signal input from the switching control unit 391.

[Effect of Example 3]
As described above, the radio communication device 30 according to the third embodiment performs the 1/2 subcarrier shift process by the addition type inverse Fourier transform unit 362. Thereby, the radio | wireless communication apparatus 30 can reduce a 1/2 subcarrier shift process, when the inverse Fourier-transform process is performed by the addition type inverse Fourier-transform part 362. FIG.

  For example, in the uplink in LTE, an OFDM symbol of transmission data is formed by 2192 sample points. Therefore, when performing 1/2 subcarrier shift processing on transmission data after CP insertion, 2192 complex multiplications are performed. When the inverse Fourier transform process is performed by the addition inverse Fourier transform unit 362, the wireless communication device 30 according to the third embodiment can reduce the above 2192 complex multiplications.

  The wireless communication device and the like disclosed in the present application may be implemented in various different forms other than the above-described embodiments. Thus, in the fourth embodiment, another embodiment of the wireless communication device disclosed in the present application will be described.

[Configuration of IFFT unit and addition type inverse Fourier transform unit]
In the first to third embodiments, an example in which the wireless communication apparatus includes the IFFT unit and the addition type inverse Fourier transform unit has been described. For example, the wireless communication apparatus 20 according to the second embodiment includes an IFFT unit 261 and an addition type inverse Fourier transform unit 262. However, the radio communication device 20 may include an inverse Fourier transform device that shares the IFFT unit 261 and the addition type inverse Fourier transform unit 262. Specifically, the IFFT unit 261 performs multiplication and addition when performing fast inverse Fourier transform processing. Therefore, IFFT unit 261 includes a multiplier and an adder. The addition type inverse Fourier transform unit 262 performs addition when performing the addition type inverse Fourier transform process. Therefore, the addition type inverse Fourier transform unit 262 includes an adder. Here, the radio communication device 20 may share the adder included in the IFFT unit 261 and the adder included in the addition type inverse Fourier transform unit 262. For example, when the IFFT unit 261 performs the fast inverse Fourier transform process, the wireless communication device 20 uses the multiplier group X and the adder group Y, and the addition-type inverse Fourier transform unit 262 performs the addition-type fast inverse Fourier transform. When processing is performed, an adder group Y may be used. Thus, by sharing the arithmetic unit used by the IFFT unit 261 and the arithmetic unit used by the addition type inverse Fourier transform unit 262, it is possible to prevent an increase in circuit scale.

[Mobile communication system]
In the second and third embodiments, the mobile communication system whose communication standard is LTE has been described as an example. However, the wireless communication device disclosed in the present application is also applicable to a mobile communication system that employs a communication standard other than LTE. it can. Specifically, the wireless communication device disclosed in the present application can be applied to a mobile communication system that performs wireless communication using OFDM technology. For example, the wireless communication device disclosed in the present application can also be applied to a mobile communication system such as WiMAX (Worldwide Interoperability for Microwave Access).

  The following supplementary notes are further disclosed with respect to the embodiments including the above examples.

(Supplementary note 1) a subcarrier mapping unit for mapping input data to subcarriers;
A twiddle factor storage unit that stores a twiddle factor corresponding to a combination of a subcarrier number that identifies the subcarrier and a sample number that identifies each sample point to be calculated during inverse Fourier transform processing;
A determination unit that determines whether or not the number of used subcarriers to which data is mapped by the subcarrier mapping unit is smaller than a predetermined threshold;
An inverse Fourier transform unit that performs a fast inverse Fourier transform process with a constant processing amount regardless of the number of used subcarriers when the determining unit determines that the number of used subcarriers is equal to or greater than a threshold;
When the determination unit determines that the number of used subcarriers is smaller than a threshold, a twiddle factor corresponding to the combination of the subcarrier number of the used subcarrier and the sample number of the sample point to be calculated is used. A wireless communication apparatus comprising: an addition type inverse Fourier transform unit that multiplies data mapped to a carrier and adds the multiplication results obtained for each used subcarrier.

(Supplementary Note 2) When the determination unit determines that the number of used subcarriers is greater than or equal to a threshold, the inverse Fourier transform unit performs control so that the inverse Fourier transform process is performed, and the determination unit performs the number of used subcarriers. The wireless communication according to claim 1, further comprising: a switching control unit that performs control so that an inverse Fourier transform process is performed by the addition inverse Fourier transform unit when it is determined that is less than a threshold value. apparatus.

(Supplementary Note 3) The twiddle factor storage unit stores a twiddle factor for each phase specified by a combination of the subcarrier number and the sample number,
The determination unit determines whether the amplitude of each data mapped to the used subcarrier is constant,
The addition type inverse Fourier transform unit, when the determination unit determines that the number of used subcarriers is smaller than a predetermined threshold and the amplitude of each data is constant, the subcarriers of the used subcarriers A twiddle factor corresponding to a phase obtained by adding a phase identified by a combination of a number and a sample number of the sample point and a phase of the used subcarrier is obtained from the twiddle factor storage unit, and the obtained twiddle factor is The wireless communication apparatus according to appendix 1, wherein the data mapped to the used subcarrier is multiplied, and the multiplication result obtained for each used subcarrier is added.

(Additional remark 4) When the said addition type inverse Fourier transform part is controlled by the said switching control part to perform an inverse Fourier transform process, while starting the clock of the said addition type inverse Fourier transform part, the said inverse Fourier transform When the inverse control unit is controlled by the switching control unit to perform an inverse Fourier transform process, the clock of the inverse Fourier transform unit is activated and the addition type inverse Fourier The wireless communication apparatus according to appendix 2, further comprising a clock control unit that stops the clock of the conversion unit.

(Additional remark 5) The said addition type inverse Fourier transform part calculates the rotation factor corresponding to the value which added 0.5 to the subcarrier number of the said use subcarrier, and the sample number of the said sample point from the said rotation factor memory | storage part. According to any one of supplementary notes 1 to 4, wherein the obtained twiddle factor is multiplied by the data mapped to the used subcarrier, and the multiplication result obtained for each used subcarrier is added. The wireless communication device described.

(Supplementary Note 6) A signal for a fixed time at the end of the time domain signal obtained by adding the multiplication results by the addition type inverse Fourier transform unit is extracted, and after the sign of the extracted signal is inverted, the time domain signal is extracted. 6. The wireless communication device according to appendix 5, further comprising an insertion portion that is inserted into a head portion of the wireless communication device.

(Supplementary Note 7) A subcarrier mapping step for mapping input data to subcarriers;
A determination step of determining whether or not the number of used subcarriers to which data is mapped by the subcarrier mapping step is smaller than a predetermined threshold;
An inverse Fourier transform step for performing a fast inverse Fourier transform process in which the processing amount is constant regardless of the number of used subcarriers when it is determined by the determining step that the number of used subcarriers is equal to or greater than a threshold;
When it is determined in the determination step that the number of subcarriers used is smaller than a threshold, a subcarrier number for identifying the subcarrier and a sample number for identifying each sample point to be calculated at the time of inverse Fourier transform processing A twiddle factor corresponding to a combination of a subcarrier number of the used subcarrier and a sample number of a sample point to be calculated is acquired from a twiddle factor storage unit that stores a twiddle factor corresponding to the combination. An addition type inverse Fourier transform step of multiplying the data mapped to the used subcarriers and adding the multiplication results obtained for each used subcarrier.

DESCRIPTION OF SYMBOLS 1 Base station 10, 20, 30 Wireless communication apparatus 11 Subcarrier mapping part 12, 250, 350 Rotation factor memory | storage part 13 Determination part 14 Inverse Fourier transform part 15 Addition type inverse Fourier transform part 21 Reception antenna 22 Transmission antenna 23 Radio | wireless part 24 Upper layer 25 Baseband processing unit 26 Reception processing unit 27 Decoding unit 28 Encoding unit 200, 300 Transmission processing unit 210 Transmission data generation unit 220 DFT unit 230 Subcarrier mapping unit 241, 242, 342 Selector 261 IFFT unit 262, 362 Addition Inverse Fourier transform unit 270, 371, 372 CP insertion unit 280 Subcarrier shift unit 290, 390 Control unit 291, 391 Switching control unit 292, 392 Clock control unit

Claims (5)

A subcarrier mapping unit that maps input data to subcarriers;
A twiddle factor storage unit that stores a twiddle factor corresponding to a combination of a subcarrier number that identifies the subcarrier and a sample number that identifies each sample point to be calculated during inverse Fourier transform processing;
A determination unit that determines whether or not the number of used subcarriers to which data is mapped by the subcarrier mapping unit is smaller than a predetermined threshold;
An inverse Fourier transform unit that performs a fast inverse Fourier transform process with a constant processing amount regardless of the number of used subcarriers when the determining unit determines that the number of used subcarriers is equal to or greater than a threshold;
When the determination unit determines that the number of used subcarriers is smaller than a threshold, a twiddle factor corresponding to the combination of the subcarrier number of the used subcarrier and the sample number of the sample point to be calculated is used. A wireless communication apparatus comprising: an addition type inverse Fourier transform unit that multiplies data mapped to a carrier and adds the multiplication results obtained for each used subcarrier.   When the determination unit determines that the number of used subcarriers is equal to or greater than the threshold, the inverse Fourier transform unit performs control so that the inverse Fourier transform process is performed, and the number of used subcarriers is less than the threshold by the determination unit. The wireless communication apparatus according to claim 1, further comprising a switching control unit configured to perform control so that an inverse Fourier transform process is performed by the addition-type inverse Fourier transform unit when it is determined to be small. The twiddle factor storage unit stores a twiddle factor for each phase specified by a combination of the subcarrier number and the sample number;
The determination unit determines whether the amplitude of each data mapped to the used subcarrier is constant,
The addition type inverse Fourier transform unit, when the determination unit determines that the number of used subcarriers is smaller than a predetermined threshold and the amplitude of each data is constant, the subcarriers of the used subcarriers A twiddle factor corresponding to a phase obtained by adding a phase specified by a combination of a number and a sample number of the sample point and a phase of the used subcarrier is obtained from the twiddle factor storage unit, and the obtained twiddle factor is added. The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus performs calculation. The addition type inverse Fourier transform unit acquires, from the twiddle factor storage unit, a twiddle factor corresponding to a value obtained by adding 0.5 to a subcarrier number of the used subcarrier and a sample number of the sample point. the wireless communication apparatus according to the rotation factor was to claim 3, characterized in that the summing. A subcarrier mapping step for mapping input data to subcarriers;
A determination step of determining whether or not the number of used subcarriers to which data is mapped by the subcarrier mapping step is smaller than a predetermined threshold;
An inverse Fourier transform step for performing a fast inverse Fourier transform process in which the processing amount is constant regardless of the number of used subcarriers when it is determined by the determining step that the number of used subcarriers is equal to or greater than a threshold;
When it is determined in the determination step that the number of subcarriers used is smaller than a threshold, a subcarrier number for identifying the subcarrier and a sample number for identifying each sample point to be calculated at the time of inverse Fourier transform processing A twiddle factor corresponding to a combination of a subcarrier number of the used subcarrier and a sample number of a sample point to be calculated is acquired from a twiddle factor storage unit that stores a twiddle factor corresponding to the combination. An addition type inverse Fourier transform step of multiplying the data mapped to the used subcarriers and adding the multiplication results obtained for each used subcarrier.

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