WO2009119685A1 - Ofdm transmission device and ofdm transmission method - Google Patents

Ofdm transmission device and ofdm transmission method Download PDF

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Publication number
WO2009119685A1
WO2009119685A1 PCT/JP2009/055997 JP2009055997W WO2009119685A1 WO 2009119685 A1 WO2009119685 A1 WO 2009119685A1 JP 2009055997 W JP2009055997 W JP 2009055997W WO 2009119685 A1 WO2009119685 A1 WO 2009119685A1
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Prior art keywords
subcarrier
subcarriers
ofdm signal
amplitude
modulation
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PCT/JP2009/055997
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French (fr)
Japanese (ja)
Inventor
輝人 武田
充 田邊
幸夫 岡田
友昭 水田
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パナソニック電工株式会社
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Application filed by パナソニック電工株式会社 filed Critical パナソニック電工株式会社
Priority to KR1020107023982A priority Critical patent/KR101317746B1/en
Priority to CN2009801107516A priority patent/CN101981843A/en
Publication of WO2009119685A1 publication Critical patent/WO2009119685A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/30—TPC using constraints in the total amount of available transmission power
    • H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
    • H04W52/346—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading distributing total power among users or channels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control

Definitions

  • the present invention relates to an OFDM transmission apparatus and an OFDM transmission method.
  • an OFDM (Orthogonal Frequency Division Multiplexing) transmitting apparatus transmits digital data by a multi-carrier signal (OFDM signal) using a plurality of subcarriers having an orthogonal relationship with each other.
  • the OFDM transmitter multiplexes a plurality of subcarriers modulated by digital data to generate a digital multicarrier signal.
  • the digital multicarrier signal is converted into an analog multicarrier signal by a D / A converter and output to a transmission path.
  • the maximum amplitude of the OFDM signal is matched with the maximum amplitude that can be input to the D / A converter, and the D / A converter is used to the maximum extent. Not considered.
  • the present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to provide an OFDM transmission apparatus and an OFDM transmission method capable of transmitting digital data by making the best use of the capability of the D / A converter. .
  • the OFDM transmission apparatus includes a subcarrier selection unit, a modulation unit, an OFDM signal generation unit, a D / A converter, and an amplitude control unit.
  • the subcarrier selection unit selects a plurality of subcarriers to be used for digital data transmission from a group of subcarriers that are orthogonal to each other.
  • the modulation unit divides the digital data according to the number of subcarriers selected by the subcarrier selection unit.
  • the modulation unit modulates the plurality of subcarriers based on the divided digital data to generate a plurality of modulation subcarriers.
  • the OFDM signal generation unit multiplexes the plurality of modulation subcarriers to generate a digital OFDM signal.
  • the D / A converter converts the digital OFDM signal into an analog OFDM signal and outputs the analog OFDM signal to a transmission line.
  • the amplitude control unit adjusts the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power of the analog OFDM signal becomes a predetermined value.
  • the digital data can be transmitted by making the best use of the capability of the D / A converter.
  • a power detection unit that detects power of the analog OFDM signal.
  • the amplitude control unit adjusts the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power detected by the power detection unit becomes the predetermined value. .
  • the power of the analog OFDM signal can be accurately set to the predetermined value.
  • a transmission path state acquisition unit that acquires the transmission path state of each subcarrier.
  • the amplitude control unit determines whether the subcarrier transmission path state is good or bad based on the transmission path state of the subcarrier acquired by the transmission path state acquisition unit. Further, the amplitude control unit decreases the amplitude of the modulation subcarrier corresponding to the subcarrier having a good transmission path state, and increases the amplitude of the modulation subcarrier corresponding to the subcarrier having a poor transmission path state.
  • the predetermined value is the power of the analog OFDM signal when the amplitude of the digital OFDM signal is a maximum value that can be input to the D / A converter.
  • a transmission path state acquisition unit that acquires the transmission path state of each subcarrier.
  • the subcarrier selection unit selects the plurality of subcarriers to be used for transmission of the digital data from the subcarrier group based on the transmission path state of the subcarrier acquired by the transmission path state estimation unit.
  • the OFDM transmission method has five steps.
  • a plurality of subcarriers to be used for digital data transmission are selected from subcarrier groups having an orthogonal relationship with each other.
  • the digital data is divided according to the number of the subcarriers selected in the first step, the plurality of subcarriers are modulated based on the divided digital data, and a plurality of subcarriers are modulated. Generate modulated subcarriers.
  • the plurality of modulation subcarriers are multiplexed to generate a digital OFDM signal.
  • the digital OFDM signal is converted into an analog OFDM signal by a D / A converter and output to the transmission path.
  • the fifth step is executed between the second step and the third step.
  • the amplitude of the modulation subcarrier is adjusted according to the number of subcarriers selected in the first step so that the power of the analog OFDM signal becomes a predetermined value.
  • the digital data can be transmitted by making the best use of the capability of the D / A converter.
  • An OFDM transmission apparatus (hereinafter referred to as “transmission apparatus”) 10 receives digital data by a multicarrier signal (OFDM signal) using a plurality of subcarriers having different frequencies and orthogonal relationships.
  • the data is transmitted to an OFDM receiver (not shown) (hereinafter referred to as “receiver”).
  • An OFDM communication apparatus including a transmission apparatus 10 and a reception apparatus is used for performing packet communication using an OFDM-modulated signal (OFDM signal).
  • the transmission path between the transmission device 10 and the OFDM reception device may be wired or wireless.
  • the transmission apparatus 10 includes an error correction coding unit 20, a modulation unit 30, an interleaver 40, a signal generation unit 50, a D / A converter 60, an amplitude control unit 70, a transmission path state acquisition unit (hereinafter referred to as “transmission path state acquisition unit”). 80 and “subcarrier selection unit” (hereinafter referred to as “selection unit”) 90.
  • the acquisition unit 80 acquires the transmission path state of the subcarrier. For example, the acquisition unit 80 receives the transmission path state (reception state) of each subcarrier of the OFDM signal from the receiving device.
  • the transmission path state is, for example, an S / N ratio. Further, the transmission path state may be BER (Bit Error Rate).
  • the selection unit 90 selects a plurality of subcarriers to be used for digital data transmission from subcarrier groups that are orthogonal to each other.
  • the selection unit 90 estimates that the subcarrier transmission path state is bad if the S / N ratio of the subcarrier is equal to or less than the first threshold. In addition, if the S / N ratio of the subcarrier exceeds the first threshold, the selection unit 90 estimates that the transmission path state of the subcarrier is good. As a result of the estimation of the transmission path state, the selection unit 90 does not select a subcarrier with a poor transmission path state, but selects a subcarrier with a good transmission path state.
  • the selection result of the subcarrier in the selection unit 90 is notified to the modulation unit 30.
  • the selection unit 90 selects all the subcarriers. Note that the selection unit 90 may estimate the transmission path state of the subcarrier at regular intervals. Further, when the transmission path state does not substantially change, the selection unit 90 may use the result estimated when the transmission apparatus 10 is installed thereafter.
  • the error correction code unit 20 adds an error correction code to the digital data (serial bit string) to be transmitted to the receiving device and outputs the digital data to the modulation unit 30. By adding an error correction code, it is possible to improve the reliability of the communication system even when the transmission path is under adverse conditions.
  • the modulation unit 30 includes a serial / parallel converter 31, a symbol mapper 32, and a plurality of subcarrier modulators 33.
  • the serial-parallel converter 31 divides the digital data to which the error correction code is added according to the number of subcarriers selected by the selection unit 90 (hereinafter referred to as “selection number”) to generate parallel data.
  • the number of parallel data is equal to the selected number. Further, the division of digital data is performed in symbol units.
  • the number of bits represented by one symbol is determined by the modulation scheme. For example, in the case of QPSK (Quadrature Phase Shift Keying), one symbol corresponds to 2 bits.
  • the serial / parallel converter 31 outputs parallel data to the symbol mapper 32.
  • the symbol mapper 32 converts each parallel data generated by the serial / parallel converter 31 into a complex symbol sequence (IQ signal) for modulating subcarriers.
  • the complex symbols constituting the complex symbol sequence are expressed in the form of a + jb (j is an imaginary unit) using the coefficient a of the in-phase component of the subcarrier and the coefficient b of the orthogonal component of the subcarrier.
  • QPSK uses four sine waves (symbols) whose phases are different by 90 degrees. Each symbol is defined by a complex symbol. There is a one-to-one correspondence between complex symbols and symbols. Table 1 shows the correspondence between bit strings and complex symbols in QPSK.
  • the symbol mapper 32 typically converts the divided data into a complex symbol sequence with reference to a data table indicating the correspondence between the bit sequence and the complex symbol.
  • the symbol mapper 32 outputs each complex symbol sequence to the subcarrier modulator 33 corresponding to the subcarrier selected by the selection unit 90.
  • the subcarrier modulator 33 has a one-to-one correspondence with the subcarriers included in the subcarrier group.
  • the subcarrier modulator 33 modulates the subcarrier with the complex symbol sequence received from the symbol mapper to generate a modulated subcarrier.
  • the subcarrier modulator 33 outputs the modulated subcarrier to the interleaver 40.
  • the modulation unit 30 divides the digital data according to the selection number. Further, the modulation unit 30 modulates a plurality of subcarriers (subcarriers selected by the selection unit 90) based on the divided digital data to generate a plurality of modulation subcarriers.
  • Interleaver 40 changes the order of the modulated subcarriers (symbol order) generated by subcarrier modulator 33 and outputs the result to signal generation unit 50. By using the interleaver 40, the influence of burst errors can be reduced.
  • the signal generation unit 50 includes an inverse discrete Fourier transformer 51, a parallel-serial converter 52, a guard interval addition unit 53, a real part extraction unit 54, a frequency converter 55, a local oscillator 56, and a bandpass filter 57. And have.
  • the inverse discrete Fourier transformer 51 performs inverse discrete Fourier transform on a plurality of modulation subcarriers obtained from the interleaver 40 for each symbol, and generates a sample value of the symbol.
  • the inverse discrete Fourier transformer 51 outputs the symbol sample value to the parallel-serial converter 52.
  • the parallel-serial converter 52 arranges the symbol sample values obtained from the inverse discrete Fourier transformer 51 in series to generate serial data (hereinafter referred to as “complex baseband OFDM signal”).
  • the guard interval adding unit 53 adds a guard interval to the complex baseband OFDM signal. By adding a guard interval, it is possible to prevent intersymbol interference due to multipath delay waves.
  • the real part extractor 54 extracts the real part from the complex baseband OFDM signal.
  • the frequency converter 55 converts the frequency of the complex baseband OFDM signal to generate a carrier band OFDM signal (digital OFMD signal).
  • the frequency converter 55 performs frequency conversion by multiplying the complex baseband OFDM signal by the carrier wave [cos (2 ⁇ f C t)] of the frequency f C output from the local oscillator 56.
  • the frequency converter 55 outputs a digital OFDM signal to the D / A converter 60 through the band pass filter 57.
  • the band pass filter 57 removes an extra frequency from the digital OFDM signal.
  • the signal generation unit 50 multiplexes a plurality of modulation subcarriers to generate a digital OFDM signal.
  • the D / A converter 60 converts the digital OFDM signal into an analog OFDM signal and outputs it to the transmission line.
  • the D / A converter 60 detects the power of the analog OFDM signal.
  • the D / A converter 60 outputs the detection result of the power of the analog OFDM signal to the amplitude controller 70. That is, the D / A converter 60 functions as a power detection unit that detects the power of the analog OFDM signal.
  • the amplitude control unit 70 includes an amplitude determination unit 71 and an amplitude adjustment unit 72.
  • the amplitude determination unit 71 determines a target value of amplitude of each modulation subcarrier (hereinafter referred to as “target amplitude value”).
  • the amplitude determining unit 71 outputs the target amplitude value to the amplitude adjusting unit 72.
  • the amplitude adjustment unit 72 controls the subcarrier modulator 33 so that the amplitude of each modulation subcarrier becomes the target amplitude value received from the amplitude determination unit 71.
  • the OFDM signal is generated by superimposing all modulation subcarriers corresponding to the plurality of subcarriers selected by the selection unit 90. Therefore, the amplitude of the OFDM signal depends on the amplitude of the modulation subcarrier. The power of the modulation subcarrier depends on the amplitude of the modulation subcarrier.
  • the amplitude determination unit 71 is configured according to the number of selections so that the power of the analog OFDM signal output from the D / A converter 60 (corresponding to the total power of all modulation subcarriers) becomes the target power (predetermined value)
  • the amplitude of each modulation subcarrier is determined. For example, the amplitude determination unit 71 determines the target amplitude value of each modulation subcarrier so that the power of each modulation subcarrier matches the value obtained by dividing the target power by the selection number. Therefore, the amplitude of each modulation subcarrier decreases as the selection number increases, and increases as the selection number decreases.
  • FIG. 2A shows a state (initial state) in which all subcarriers are used.
  • the target amplitude value of each modulation subcarrier is set so that the total power of all the modulation subcarriers becomes the target power.
  • the S / N ratio of the subcarriers in the frequency band W is equal to or lower than the first threshold value.
  • the selection unit 90 does not select a subcarrier in the frequency band W. Therefore, the number of selections is reduced from the initial state. Therefore, the amplitude determination unit 71 increases the target amplitude value of each modulation subcarrier so that the total power of the modulation subcarriers becomes the target power in accordance with the decrease in the number of selections.
  • the power of each modulation subcarrier after the selection number decreases is increased by ⁇ P from the initial state as shown in FIG. Therefore, the total power of all modulation subcarriers in the initial state is equal to the total power of all modulation subcarriers when the number of selections decreases (that is, the power of the analog OFDM signal does not change regardless of the change in the number of selections). Will be constant). That is, the amplitude of the digital OFDM signal input to the D / A converter 60 is also constant regardless of the change (increase / decrease) in the number of selections.
  • the amplitude determining unit 71 corrects the target amplitude value according to the transmission path state of each subcarrier. Specifically, the amplitude determination unit 71 determines whether the state of the subcarrier transmission path selected by the selection unit 90 is good or bad based on the subcarrier transmission path state acquired by the acquisition unit 80. If the S / N ratio of the subcarrier is equal to or smaller than the second threshold, the amplitude determining unit 71 determines that the subcarrier transmission path condition is bad, and if the subcarrier transmission ratio exceeds the second threshold, the subcarrier transmission path It is determined that the state is good. The second threshold value is set to a value larger than the first threshold value. That is, the amplitude determination unit 71 determines whether the transmission path state of the subcarrier selected by the selection unit 90 is good or bad.
  • the second threshold value may be smaller than the first threshold value. If the second threshold value is smaller than the first threshold value, more subcarriers can be used than when the second threshold value is larger than the first threshold value.
  • the amplitude determination unit 71 refers to the result of the above determination, reduces the target amplitude value of the modulation subcarrier corresponding to the subcarrier having a good transmission path state, and modulates the subcarrier having a bad transmission path state. Increase the target amplitude value of the subcarrier. However, even in this case, the amplitude determination unit 71 determines each target amplitude value so that the total power of the modulation subcarriers matches the target power. In addition, what is necessary is just to set suitably how much a target amplitude value is changed according to a transmission-line state. Further, the change width of the target amplitude value may be changed according to the state of the transmission path.
  • the amplitude control unit 70 of the transmission apparatus 10 adjusts the amplitude of the modulation subcarrier according to the selection number so that the power of the analog OFDM signal becomes the target power.
  • the power of the analog OFDM signal output to the transmission path can be matched with the target power.
  • the amplitude of the analog OFDM signal is limited by the specifications of the communication system, the specifications of the D / A converter 60, legal regulations (for example, regulations regarding the power of radio signals), and the like.
  • the amplitude for each subcarrier is determined by the number of subcarriers used and the transmission path state of the subcarriers. Even in the same OFDM system, specifications such as the number of subcarriers used differ depending on the communication system. Also, there may be subcarriers that cannot be used for communication due to the effects of noise and attenuation.
  • the number of subcarriers to be used is used as a reference when determining the subcarrier amplitude in order to adapt the subcarrier amplitude to the number of subcarriers to be actually used. Therefore, according to the transmission device 10, waste of power consumption can be suppressed. Further, by reducing the number of subcarriers used, surplus power is supplied to other usable subcarriers. Therefore, according to the transmission device 10, the communication speed can be improved. Further, the transmission apparatus 10 can be commonly used for communication systems having different numbers of subcarriers to be used.
  • the predetermined value is preferably the power of the analog OFDM signal when the amplitude of the digital OFDM signal is the maximum value that can be input to the D / A converter 60.
  • the D / A converter 60 is configured such that the predetermined value is the maximum value of the power of the analog OFDM signal that is permitted by law. In this way, the communication speed can be maximized.
  • the power of the analog OFDM signal may change depending on the transmission path state of the subcarrier.
  • the amplitude control unit 70 adjusts the amplitude of the modulation subcarrier based on the power of the analog OFDM signal detected by the D / A converter 60. Therefore, the power change of the analog OFDM signal due to the transmission path state can be suppressed. Therefore, the power of the analog OFDM signal can be maintained at a predetermined value.
  • the relationship between the digital signal input to the D / A converter 60 and the analog signal output from the D / A converter 60 depends on the specifications of the D / A converter 60. It has been decided. Therefore, the amplitude of the modulated subcarrier where the power of the analog OFDM signal becomes a predetermined value can be theoretically obtained. Therefore, it is not always necessary to actually detect the power of the analog OFDM signal. However, as described above, the power of the analog OFDM signal may change depending on the transmission path state. Therefore, it is preferable to actually detect the power of the analog OFDM signal.
  • the amplitude control unit 70 decreases the amplitude of the modulation subcarrier corresponding to the subcarrier having a good transmission path condition, and increases the amplitude of the modulation subcarrier corresponding to the subcarrier having a poor transmission path condition.
  • the amplitude control unit 70 allocates a part of the power of subcarriers with good transmission path conditions to subcarriers with poor transmission path conditions. Therefore, it is possible to improve the communication status of subcarriers with poor transmission path conditions. Therefore, the communication accuracy is improved, and as a result, the communication speed is improved.
  • the amplitude control unit 70 does not necessarily need to change the amplitude of the modulation subcarrier according to the state of the transmission path. That is, the amplitude control unit 70 may be configured to make all the amplitudes of the modulation subcarriers equal.
  • the selection unit 90 selects a plurality of subcarriers to be used for digital data transmission from the subcarrier group based on the subcarrier transmission path state acquired by the acquisition unit 80. Therefore, it is possible to avoid using subcarriers that cannot transmit digital data. Therefore, the transmission apparatus 10 can prevent waste of power. Further, the communication accuracy is improved, and as a result, the communication speed is improved.
  • the selection unit 90 automatically selects a plurality of subcarriers to be used for digital data transmission from the subcarrier group based on the transmission path state of the subcarriers.
  • the selection unit 90 may be configured to select a subcarrier according to an external input.
  • a manual input method or an automatic input method can be considered.
  • a setting value determined in advance using an external device is input to the selection unit 90 using an external input device such as a button or a keyboard.
  • an external arithmetic device that determines a set value inputs the set value directly to the selection unit 90.
  • the OFDM transmission method has the following five steps, as can be seen from the operation of the transmission apparatus 10 described above.
  • a plurality of subcarriers to be used for digital data transmission are selected from subcarrier groups having an orthogonal relationship with each other.
  • the digital data is divided according to the number of subcarriers selected in the first step.
  • a plurality of modulated subcarriers are generated by modulating a plurality of subcarriers based on the divided digital data.
  • a plurality of modulation subcarriers are multiplexed to generate a digital OFDM signal.
  • the digital OFDM signal is converted into an analog OFDM signal by a D / A converter and output to the transmission path.
  • the fifth step is executed between the second step and the third step.
  • the amplitude of the modulation subcarrier is adjusted according to the number of subcarriers selected in the first step so that the power of the analog OFDM signal becomes a predetermined value.
  • the power of the analog OFDM signal output to the transmission path is controlled to a predetermined value. Therefore, according to the above-described OFDM transmission method, digital data can be transmitted by utilizing the capability of the D / A converter 60 to the maximum.

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Abstract

Provided is an OFDM transmission device (10) including: a subcarrier selection unit (90), a modulation unit (30), a signal generation unit (50), a D/A converter (60), and an amplitude control unit (70). The subcarrier selection unit (90) selects a plurality of subcarriers used for transmitting digital data from subcarriers having an orthogonal relation to each other. The modulation unit (30) divides the digital data in accordance with the number of subcarriers selected by the subcarrier selection unit (90). Moreover, the modulation unit (30) modulates the subcarriers in accordance with the divided digital data to generate a plurality of modulated subcarriers. The signal generation unit (50) multiplexes a plurality of modulation subcarriers to generate a digital OFDM signal. The D/A converter (60) converts the digital OFDM signal into an analog OFDM signal for output to a transmission path. The amplitude control unit (70) adjusts the amplitude of the modulated subcarrier in accordance with the number of the subcarriers selected by the subcarrier selection unit (90) so that the power of the analog OFDM signal is a predetermined value.

Description

ＯＦＤＭ送信装置、およびＯＦＤＭ送信方法OFDM transmitter and OFDM transmission method
　本発明は、ＯＦＤＭ送信装置、およびＯＦＤＭ送信方法に関する。 The present invention relates to an OFDM transmission apparatus and an OFDM transmission method.
　ＷＯ２００５／５５４７９に見られるように、ＯＦＤＭ（Orthogonal Frequency Division Multiplexing）送信装置は、相互に直交関係を有する複数のサブキャリアを用いたマルチキャリア信号（ＯＦＤＭ信号）によりディジタルデータを送信する。ＯＦＤＭ送信装置は、ディジタルデータによって変調された複数のサブキャリアを多重化して、ディジタルのマルチキャリア信号を生成する。ディジタルのマルチキャリア信号は、Ｄ／Ａ変換器によってアナログのマルチキャリア信号に変換されて、伝送路に出力される。 As seen in WO 2005/55479, an OFDM (Orthogonal Frequency Division Multiplexing) transmitting apparatus transmits digital data by a multi-carrier signal (OFDM signal) using a plurality of subcarriers having an orthogonal relationship with each other. The OFDM transmitter multiplexes a plurality of subcarriers modulated by digital data to generate a digital multicarrier signal. The digital multicarrier signal is converted into an analog multicarrier signal by a D / A converter and output to a transmission path.
　前記ＷＯ２００５／５５４７９に開示されたＯＦＤＭ送信装置では、ＯＦＤＭ信号の最大振幅をＤ／Ａ変換器に入力可能な最大振幅に一致させて、Ｄ／Ａ変換器の能力を最大限に利用することは考慮されていない。 In the OFDM transmitter disclosed in the WO2005 / 55479, the maximum amplitude of the OFDM signal is matched with the maximum amplitude that can be input to the D / A converter, and the D / A converter is used to the maximum extent. Not considered.
　本発明は、上記事由に鑑みてなされ、本発明の目的は、Ｄ／Ａ変換器の能力を最大限に利用してディジタルデータを送信できるＯＦＤＭ送信装置、およびＯＦＤＭ送信方法を提供することである。 The present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to provide an OFDM transmission apparatus and an OFDM transmission method capable of transmitting digital data by making the best use of the capability of the D / A converter. .
　本発明に係るＯＦＤＭ送信装置は、サブキャリア選択部と、変調部と、ＯＦＤＭ信号生成部と、Ｄ／Ａ変換器と、振幅制御部とを備える。前記サブキャリア選択部は、相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する。前記変調部は、前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記ディジタルデータを分割する。また、前記変調部は、分割された前記ディジタルデータに基づいて前記複数のサブキャリアを変調して複数の変調サブキャリアを生成する。前記ＯＦＤＭ信号生成部は、前記複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成する。前記Ｄ／Ａ変換器は、前記ディジタルのＯＦＤＭ信号をアナログのＯＦＤＭ信号に変換して伝送路に出力する。前記振幅制御部は、前記アナログのＯＦＤＭ信号の電力が所定値になるように、前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整する。 The OFDM transmission apparatus according to the present invention includes a subcarrier selection unit, a modulation unit, an OFDM signal generation unit, a D / A converter, and an amplitude control unit. The subcarrier selection unit selects a plurality of subcarriers to be used for digital data transmission from a group of subcarriers that are orthogonal to each other. The modulation unit divides the digital data according to the number of subcarriers selected by the subcarrier selection unit. The modulation unit modulates the plurality of subcarriers based on the divided digital data to generate a plurality of modulation subcarriers. The OFDM signal generation unit multiplexes the plurality of modulation subcarriers to generate a digital OFDM signal. The D / A converter converts the digital OFDM signal into an analog OFDM signal and outputs the analog OFDM signal to a transmission line. The amplitude control unit adjusts the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power of the analog OFDM signal becomes a predetermined value.
　この発明によれば、前記ディジタルデータの送信に使用する前記サブキャリアの数が変わっても、前記アナログのＯＦＤＭ信号の電力は所定値のままである。そのため、前記Ｄ／Ａ変換器の能力を最大限に利用して前記ディジタルデータを送信できる。 According to the present invention, even if the number of subcarriers used for transmitting the digital data changes, the power of the analog OFDM signal remains at a predetermined value. Therefore, the digital data can be transmitted by making the best use of the capability of the D / A converter.
　好ましくは、前記アナログのＯＦＤＭ信号の電力を検出する電力検出部を有する。前記振幅制御部は、前記電力検出部で検出された電力が前記所定値になるように、前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整する。 Preferably, a power detection unit that detects power of the analog OFDM signal is provided. The amplitude control unit adjusts the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power detected by the power detection unit becomes the predetermined value. .
　このようにすれば、前記アナログのＯＦＤＭ信号の電力を精度良く前記所定値に設定することができる。 In this way, the power of the analog OFDM signal can be accurately set to the predetermined value.
　好ましくは、前記各サブキャリアの伝送路状態を取得する伝送路状態取得部を備える。前記振幅制御部は、前記伝送路状態取得部が取得した前記サブキャリアの伝送路状態に基づいて前記サブキャリアの伝送路状態の良し悪しを判定する。また、前記振幅制御部は、伝送路状態が良い前記サブキャリアに対応する前記変調サブキャリアの振幅を小さくし、伝送路状態が悪い前記サブキャリアに対応する前記変調サブキャリアの振幅を大きくする。 Preferably, a transmission path state acquisition unit that acquires the transmission path state of each subcarrier is provided. The amplitude control unit determines whether the subcarrier transmission path state is good or bad based on the transmission path state of the subcarrier acquired by the transmission path state acquisition unit. Further, the amplitude control unit decreases the amplitude of the modulation subcarrier corresponding to the subcarrier having a good transmission path state, and increases the amplitude of the modulation subcarrier corresponding to the subcarrier having a poor transmission path state.
　このようにすれば、通信精度が向上し、その結果、通信速度が向上する。 In this way, the communication accuracy is improved, and as a result, the communication speed is improved.
　好ましくは、前記所定値は、前記ディジタルのＯＦＤＭ信号の振幅が前記Ｄ／Ａ変換器に入力可能な最大値であるときの前記アナログのＯＦＤＭ信号の電力である。 Preferably, the predetermined value is the power of the analog OFDM signal when the amplitude of the digital OFDM signal is a maximum value that can be input to the D / A converter.
　このようにすれば、Ｄ／Ａ変換器の能力を最大限に利用できる。 In this way, the ability of the D / A converter can be fully utilized.
　好ましくは、前記各サブキャリアの伝送路状態を取得する伝送路状態取得部を備える。前記サブキャリア選択部は、前記伝送路状態推定部が取得した前記サブキャリアの伝送路状態に基づいて前記サブキャリア群から前記ディジタルデータの送信に使用する前記複数のサブキャリアを選択する。 Preferably, a transmission path state acquisition unit that acquires the transmission path state of each subcarrier is provided. The subcarrier selection unit selects the plurality of subcarriers to be used for transmission of the digital data from the subcarrier group based on the transmission path state of the subcarrier acquired by the transmission path state estimation unit.
　このようにすれば、通信精度が向上し、その結果、通信速度が向上する。 In this way, the communication accuracy is improved, and as a result, the communication speed is improved.
　本発明に係るＯＦＤＭ送信方法は、５つのステップを有する。第１のステップでは、相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する。第２のステップでは、前記第１のステップで選択された前記サブキャリアの数に応じて前記ディジタルデータを分割し、分割された前記ディジタルデータに基づいて前記複数のサブキャリアを変調して複数の変調サブキャリアを生成する。第３のステップでは、前記複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成する。第４のステップでは、前記ディジタルのＯＦＤＭ信号をＤ／Ａ変換器によりアナログのＯＦＤＭ信号に変換して伝送路に出力する。第５のステップは、前記第２のステップと前記第３のステップとの間に実行される。前記第５のステップでは、前記アナログのＯＦＤＭ信号の電力が所定値になるように、前記第１のステップで選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整する。 The OFDM transmission method according to the present invention has five steps. In the first step, a plurality of subcarriers to be used for digital data transmission are selected from subcarrier groups having an orthogonal relationship with each other. In the second step, the digital data is divided according to the number of the subcarriers selected in the first step, the plurality of subcarriers are modulated based on the divided digital data, and a plurality of subcarriers are modulated. Generate modulated subcarriers. In the third step, the plurality of modulation subcarriers are multiplexed to generate a digital OFDM signal. In the fourth step, the digital OFDM signal is converted into an analog OFDM signal by a D / A converter and output to the transmission path. The fifth step is executed between the second step and the third step. In the fifth step, the amplitude of the modulation subcarrier is adjusted according to the number of subcarriers selected in the first step so that the power of the analog OFDM signal becomes a predetermined value.
　この発明によれば、前記ディジタルデータの送信に使用する前記サブキャリアの数が変わっても、前記アナログのＯＦＤＭ信号の電力は所定値のままである。そのため、前記Ｄ／Ａ変換器の能力を最大限に利用して前記ディジタルデータを送信できる。 According to the present invention, even if the number of subcarriers used for transmitting the digital data changes, the power of the analog OFDM signal remains at a predetermined value. Therefore, the digital data can be transmitted by making the best use of the capability of the D / A converter.
本発明の一実施形態のＯＦＤＭ送信装置のブロック構成を示す図である。It is a figure which shows the block configuration of the OFDM transmitter of one Embodiment of this invention. 同上のＯＦＤＭ送信装置の動作の説明図である。It is explanatory drawing of operation | movement of an OFDM transmission apparatus same as the above.
　本発明の一実施形態のＯＦＤＭ送信装置（以下、「送信装置」という）１０は、相互に周波数が異なるとともに直交関係を有する複数のサブキャリアを利用したマルチキャリア信号（ＯＦＤＭ信号）によってディジタルデータを図示しないＯＦＤＭ受信装置（以下、「受信装置」という）に送信する。送信装置１０と受信装置からなるＯＦＤＭ通信装置は、ＯＦＤＭ変調された信号（ＯＦＤＭ信号）によるパケット通信を行うために用いられる。なお、送信装置１０とＯＦＤＭ受信装置との間の伝送路は、有線であってもよいし無線であってもよい。 An OFDM transmission apparatus (hereinafter referred to as “transmission apparatus”) 10 according to an embodiment of the present invention receives digital data by a multicarrier signal (OFDM signal) using a plurality of subcarriers having different frequencies and orthogonal relationships. The data is transmitted to an OFDM receiver (not shown) (hereinafter referred to as “receiver”). An OFDM communication apparatus including a transmission apparatus 10 and a reception apparatus is used for performing packet communication using an OFDM-modulated signal (OFDM signal). The transmission path between the transmission device 10 and the OFDM reception device may be wired or wireless.
　送信装置１０は、誤り訂正符号部２０と、変調部３０と、インターリーバ４０と、信号生成部５０と、Ｄ／Ａ変換器６０と、振幅制御部７０と、伝送路状態取得部（以下、「取得部」という）８０と、サブキャリア選択部（以下、「選択部」という）９０とを備える。 The transmission apparatus 10 includes an error correction coding unit 20, a modulation unit 30, an interleaver 40, a signal generation unit 50, a D / A converter 60, an amplitude control unit 70, a transmission path state acquisition unit (hereinafter referred to as “transmission path state acquisition unit”). 80 and “subcarrier selection unit” (hereinafter referred to as “selection unit”) 90.
　取得部８０は、サブキャリアの伝送路状態を取得する。例えば、取得部８０は、受信装置からＯＦＤＭ信号の各サブキャリアの伝送路状態（受信状態）を受け取る。伝送路状態は、例えばＳ／Ｎ比である。また、伝送路状態は、ＢＥＲ（Bit Error Rate）であってもよい。 The acquisition unit 80 acquires the transmission path state of the subcarrier. For example, the acquisition unit 80 receives the transmission path state (reception state) of each subcarrier of the OFDM signal from the receiving device. The transmission path state is, for example, an S / N ratio. Further, the transmission path state may be BER (Bit Error Rate).
　選択部９０は、相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する。 The selection unit 90 selects a plurality of subcarriers to be used for digital data transmission from subcarrier groups that are orthogonal to each other.
　ここで、サブキャリアのＳ／Ｎ比が高いほど、ビット誤り率が低くなる。つまり、Ｓ／Ｎ比が高いほど高精度な通信を行える。よって、選択部９０は、サブキャリアのＳ／Ｎ比が第１の閾値以下であれば、サブキャリアの伝送路状態が悪いと推定する。また、選択部９０は、サブキャリアのＳ／Ｎ比が第１の閾値を越えていれば、サブキャリアの伝送路状態が良いと推定する。選択部９０は、伝送路状態の推定の結果、伝送路状態が悪いサブキャリアを選択せず、伝送路状態が良いサブキャリアを選択する。選択部９０でのサブキャリアの選択結果は、変調部３０に通知される。取得部８０がサブキャリアの伝送路状態を取得する前の初期状態では、選択部９０は、全てのサブキャリアを選択する。なお、選択部９０は、一定時間毎にサブキャリアの伝送路状態の推定を行っても良い。また、伝送路状態がほぼ変化しない場合、選択部９０は、送信装置１０の設置時に推定した結果を以後用いるようにしてもよい。 Here, the higher the subcarrier S / N ratio, the lower the bit error rate. That is, the higher the S / N ratio, the more accurate communication can be performed. Therefore, the selection unit 90 estimates that the subcarrier transmission path state is bad if the S / N ratio of the subcarrier is equal to or less than the first threshold. In addition, if the S / N ratio of the subcarrier exceeds the first threshold, the selection unit 90 estimates that the transmission path state of the subcarrier is good. As a result of the estimation of the transmission path state, the selection unit 90 does not select a subcarrier with a poor transmission path state, but selects a subcarrier with a good transmission path state. The selection result of the subcarrier in the selection unit 90 is notified to the modulation unit 30. In the initial state before the acquisition unit 80 acquires the transmission path state of the subcarriers, the selection unit 90 selects all the subcarriers. Note that the selection unit 90 may estimate the transmission path state of the subcarrier at regular intervals. Further, when the transmission path state does not substantially change, the selection unit 90 may use the result estimated when the transmission apparatus 10 is installed thereafter.
　誤り訂正符号部２０は、受信装置に送信するディジタルデータ（シリアルのビット列）に誤り訂正符号を付加して変調部３０に出力する。誤り訂正符号を付加することで、伝送路が悪条件下にある場合でも通信システムの信頼性を高めることができる。 The error correction code unit 20 adds an error correction code to the digital data (serial bit string) to be transmitted to the receiving device and outputs the digital data to the modulation unit 30. By adding an error correction code, it is possible to improve the reliability of the communication system even when the transmission path is under adverse conditions.
　変調部３０は、直並列変換器３１と、シンボルマッパ３２と、複数のサブキャリア変調器３３とを有する。 The modulation unit 30 includes a serial / parallel converter 31, a symbol mapper 32, and a plurality of subcarrier modulators 33.
　直並列変換器３１は、誤り訂正符号が付加されたディジタルデータを選択部９０で選択されたサブキャリアの数（以下、「選択数」という）に応じて分割して並列データを生成する。並列データの数は、選択数に等しい。また、ディジタルデータの分割はシンボル単位で行われる。１つのシンボルが表すビットの数は、変調方式によって決定される。例えば、ＱＰＳＫ（Quadrature Phase Shift Keying）の場合、１つのシンボルは２ビットに対応する。直並列変換器３１は、並列データをシンボルマッパ３２に出力する。 The serial-parallel converter 31 divides the digital data to which the error correction code is added according to the number of subcarriers selected by the selection unit 90 (hereinafter referred to as “selection number”) to generate parallel data. The number of parallel data is equal to the selected number. Further, the division of digital data is performed in symbol units. The number of bits represented by one symbol is determined by the modulation scheme. For example, in the case of QPSK (Quadrature Phase Shift Keying), one symbol corresponds to 2 bits. The serial / parallel converter 31 outputs parallel data to the symbol mapper 32.
　シンボルマッパ３２は、直並列変換器３１で生成された各並列データを、サブキャリアを変調するための複素シンボル列（ＩＱ信号）に変換する。複素シンボル列を構成する複素シンボルは、サブキャリアの同相成分の係数ａと、サブキャリアの直交成分の係数ｂとを用いて、ａ＋ｊｂ（ｊは虚数単位）の形で表される。例えば、ＱＰＳＫは、位相が９０度ずつ異なる４つの正弦波（シンボル）を用いる。各シンボルは複素シンボルで定義される。複素シンボルとシンボルとは一対一で対応している。表１は、ＱＰＳＫにおけるビット列と複素シンボルの対応関係を示している。シンボルマッパ３２は、典型的には、ビット列と複素シンボルの対応関係を示すデータテーブルを参照して、分割データを複素シンボル列に変換する。シンボルマッパ３２は、各複素シンボル列を、選択部９０で選択されたサブキャリアに対応するサブキャリア変調器３３に出力する。 The symbol mapper 32 converts each parallel data generated by the serial / parallel converter 31 into a complex symbol sequence (IQ signal) for modulating subcarriers. The complex symbols constituting the complex symbol sequence are expressed in the form of a + jb (j is an imaginary unit) using the coefficient a of the in-phase component of the subcarrier and the coefficient b of the orthogonal component of the subcarrier. For example, QPSK uses four sine waves (symbols) whose phases are different by 90 degrees. Each symbol is defined by a complex symbol. There is a one-to-one correspondence between complex symbols and symbols. Table 1 shows the correspondence between bit strings and complex symbols in QPSK. The symbol mapper 32 typically converts the divided data into a complex symbol sequence with reference to a data table indicating the correspondence between the bit sequence and the complex symbol. The symbol mapper 32 outputs each complex symbol sequence to the subcarrier modulator 33 corresponding to the subcarrier selected by the selection unit 90.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　サブキャリア変調器３３は、前記サブキャリア群に含まれるサブキャリアと一対一で対応している。サブキャリア変調器３３は、シンボルマッパから受け取った複素シンボル列によりサブキャリアを変調して変調サブキャリアを生成する。サブキャリア変調器３３は、変調サブキャリアをインターリーバ４０に出力する。 The subcarrier modulator 33 has a one-to-one correspondence with the subcarriers included in the subcarrier group. The subcarrier modulator 33 modulates the subcarrier with the complex symbol sequence received from the symbol mapper to generate a modulated subcarrier. The subcarrier modulator 33 outputs the modulated subcarrier to the interleaver 40.
　上述したように変調部３０は、選択数に応じてディジタルデータを分割する。また、変調部３０は、分割されたディジタルデータに基づいて複数のサブキャリア（選択部９０で選択されたサブキャリア）を変調して、複数の変調サブキャリアを生成する。 As described above, the modulation unit 30 divides the digital data according to the selection number. Further, the modulation unit 30 modulates a plurality of subcarriers (subcarriers selected by the selection unit 90) based on the divided digital data to generate a plurality of modulation subcarriers.
　インターリーバ４０は、サブキャリア変調器３３で生成された変調サブキャリアの順序（シンボルの順序）を入れ替えて信号生成部５０に出力する。インターリーバ４０を利用することで、バースト誤りの影響を低減できる。 Interleaver 40 changes the order of the modulated subcarriers (symbol order) generated by subcarrier modulator 33 and outputs the result to signal generation unit 50. By using the interleaver 40, the influence of burst errors can be reduced.
　信号生成部５０は、逆離散フーリエ変換器５１と、並直列変換器５２と、ガードインターバル付加部５３と、実部抽出部５４と、周波数変換器５５と、局部発振器５６と、バンドパスフィルタ５７とを有する。 The signal generation unit 50 includes an inverse discrete Fourier transformer 51, a parallel-serial converter 52, a guard interval addition unit 53, a real part extraction unit 54, a frequency converter 55, a local oscillator 56, and a bandpass filter 57. And have.
　逆離散フーリエ変換器５１は、インターリーバ４０より得た複数の変調サブキャリアをシンボル毎に一括して逆離散フーリエ変換して、シンボルの標本値を生成する。逆離散フーリエ変換器５１は、シンボルの標本値を並直列変換器５２に出力する。 The inverse discrete Fourier transformer 51 performs inverse discrete Fourier transform on a plurality of modulation subcarriers obtained from the interleaver 40 for each symbol, and generates a sample value of the symbol. The inverse discrete Fourier transformer 51 outputs the symbol sample value to the parallel-serial converter 52.
　並直列変換器５２は、逆離散フーリエ変換器５１より得たシンボルの標本値を直列に並べて直列データ（以下、「複素ベースバンドＯＦＤＭ信号」という）を生成する。 The parallel-serial converter 52 arranges the symbol sample values obtained from the inverse discrete Fourier transformer 51 in series to generate serial data (hereinafter referred to as “complex baseband OFDM signal”).
　ガードインターバル付加部５３は、複素ベースバンドＯＦＤＭ信号にガードインターバルを付加する。ガードインターバルを付加することによって、マルチパス遅延波による符号間干渉を防止できる。 The guard interval adding unit 53 adds a guard interval to the complex baseband OFDM signal. By adding a guard interval, it is possible to prevent intersymbol interference due to multipath delay waves.
　実部抽出部５４は、複素ベースバンドＯＦＤＭ信号から実部を抽出する。 The real part extractor 54 extracts the real part from the complex baseband OFDM signal.
　周波数変換器５５は、複素ベースバンドＯＦＤＭ信号の周波数の変換を行って搬送帯域ＯＦＤＭ信号（ディジタルのＯＦＭＤ信号）を生成する。周波数変換器５５は、局部発振器５６が出力する周波数ｆCの搬送波［ｃｏｓ（２πｆCｔ）］を複素ベースバンドＯＦＤＭ信号に掛け合わせることで周波数の変換を行う。周波数変換器５５は、バンドパスフィルタ５７を通してディジタルのＯＦＤＭ信号をＤ／Ａ変換器６０に出力する。 The frequency converter 55 converts the frequency of the complex baseband OFDM signal to generate a carrier band OFDM signal (digital OFMD signal). The frequency converter 55 performs frequency conversion by multiplying the complex baseband OFDM signal by the carrier wave [cos (2πf C t)] of the frequency f C output from the local oscillator 56. The frequency converter 55 outputs a digital OFDM signal to the D / A converter 60 through the band pass filter 57.
　バンドパスフィルタ５７は、ディジタルＯＦＤＭ信号から余分な周波数を除去する。 The band pass filter 57 removes an extra frequency from the digital OFDM signal.
　上述したように信号生成部５０は、複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成する。 As described above, the signal generation unit 50 multiplexes a plurality of modulation subcarriers to generate a digital OFDM signal.
　Ｄ／Ａ変換器６０は、ディジタルのＯＦＤＭ信号をアナログのＯＦＤＭ信号に変換して伝送路に出力する。また、Ｄ／Ａ変換器６０は、アナログのＯＦＤＭ信号の電力を検出する。Ｄ／Ａ変換器６０は、アナログのＯＦＤＭ信号の電力の検出結果を振幅制御部７０に出力する。つまり、Ｄ／Ａ変換器６０は、アナログのＯＦＤＭ信号の電力を検出する電力検出部として機能する。 The D / A converter 60 converts the digital OFDM signal into an analog OFDM signal and outputs it to the transmission line. The D / A converter 60 detects the power of the analog OFDM signal. The D / A converter 60 outputs the detection result of the power of the analog OFDM signal to the amplitude controller 70. That is, the D / A converter 60 functions as a power detection unit that detects the power of the analog OFDM signal.
　振幅制御部７０は、振幅決定部７１と、振幅調整部７２とを有する。振幅決定部７１は、各変調サブキャリアの振幅の目標値（以下、「目標振幅値」という）を決定する。振幅決定部７１は、目標振幅値を振幅調整部７２に出力する。振幅調整部７２は、各変調サブキャリアの振幅が振幅決定部７１から受け取った目標振幅値になるようにサブキャリア変調器３３を制御する。 The amplitude control unit 70 includes an amplitude determination unit 71 and an amplitude adjustment unit 72. The amplitude determination unit 71 determines a target value of amplitude of each modulation subcarrier (hereinafter referred to as “target amplitude value”). The amplitude determining unit 71 outputs the target amplitude value to the amplitude adjusting unit 72. The amplitude adjustment unit 72 controls the subcarrier modulator 33 so that the amplitude of each modulation subcarrier becomes the target amplitude value received from the amplitude determination unit 71.
　ここで、ＯＦＤＭ信号は、選択部９０で選択された複数のサブキャリアに対応する変調サブキャリアを全て重ね合わせて生成される。そのため、ＯＦＤＭ信号の振幅は、変調サブキャリアの振幅に依存している。変調サブキャリアの電力は、変調サブキャリアの振幅に依存している。 Here, the OFDM signal is generated by superimposing all modulation subcarriers corresponding to the plurality of subcarriers selected by the selection unit 90. Therefore, the amplitude of the OFDM signal depends on the amplitude of the modulation subcarrier. The power of the modulation subcarrier depends on the amplitude of the modulation subcarrier.
　振幅決定部７１は、Ｄ／Ａ変換器６０が出力するアナログのＯＦＤＭ信号の電力（全変調サブキャリアの合計電力に相当する）が目標電力（所定値）になるように、選択数に応じて各変調サブキャリアの振幅を決定する。例えば、振幅決定部７１は、各変調サブキャリアの電力が目標電力を選択数で除した値に一致するように、各変調サブキャリアの目標振幅値を決定する。したがって、各変調サブキャリアの振幅は、選択数が多ければ小さくなり、選択数が少なければ大きくなる。 The amplitude determination unit 71 is configured according to the number of selections so that the power of the analog OFDM signal output from the D / A converter 60 (corresponding to the total power of all modulation subcarriers) becomes the target power (predetermined value) The amplitude of each modulation subcarrier is determined. For example, the amplitude determination unit 71 determines the target amplitude value of each modulation subcarrier so that the power of each modulation subcarrier matches the value obtained by dividing the target power by the selection number. Therefore, the amplitude of each modulation subcarrier decreases as the selection number increases, and increases as the selection number decreases.
　図２（ａ）は、全てのサブキャリアを使用している状態（初期状態）を示している。この場合、全ての変調サブキャリアの合計電力が目標電力となるように各変調サブキャリアの目標振幅値が設定されている。ここで、周波数帯域Ｗ内のサブキャリアのＳ／Ｎ比が第１の閾値以下になったとする。この場合、図２（ｂ）に示すように、選択部９０は、周波数帯域Ｗ内のサブキャリアを選択しない。よって、初期状態よりも選択数が減少する。そのため、振幅決定部７１は、選択数の減少に合わせて、変調サブキャリアの合計電力が目標電力となるように各変調サブキャリアの目標振幅値を大きくする。 FIG. 2A shows a state (initial state) in which all subcarriers are used. In this case, the target amplitude value of each modulation subcarrier is set so that the total power of all the modulation subcarriers becomes the target power. Here, it is assumed that the S / N ratio of the subcarriers in the frequency band W is equal to or lower than the first threshold value. In this case, as illustrated in FIG. 2B, the selection unit 90 does not select a subcarrier in the frequency band W. Therefore, the number of selections is reduced from the initial state. Therefore, the amplitude determination unit 71 increases the target amplitude value of each modulation subcarrier so that the total power of the modulation subcarriers becomes the target power in accordance with the decrease in the number of selections.
　したがって、選択数が減少した後の各変調サブキャリアの電力は、図２（ｃ）に示すように、初期状態からΔＰだけ増加する。そのため、初期状態における全変調サブキャリアの合計電力と、選択数が減少した場合における全変調サブキャリアの合計電力とは等しくなる（すなわち、アナログのＯＦＤＭ信号の電力が、選択数の変化に関わらず一定になる）。つまり、Ｄ／Ａ変換器６０に入力されるディジタルのＯＦＤＭ信号の振幅も、選択数の変化（増減）に関わらず一定になる。 Therefore, the power of each modulation subcarrier after the selection number decreases is increased by ΔP from the initial state as shown in FIG. Therefore, the total power of all modulation subcarriers in the initial state is equal to the total power of all modulation subcarriers when the number of selections decreases (that is, the power of the analog OFDM signal does not change regardless of the change in the number of selections). Will be constant). That is, the amplitude of the digital OFDM signal input to the D / A converter 60 is also constant regardless of the change (increase / decrease) in the number of selections.
　さらに、振幅決定部７１は、各サブキャリアの伝送路状態によって、目標振幅値を補正する。具体的には、振幅決定部７１は、取得部８０が取得したサブキャリアの伝送路状態に基づいて選択部９０で選択されたサブキャリアの伝送路の状態の良し悪しを判定する。振幅決定部７１は、サブキャリアのＳ／Ｎ比が第２の閾値以下であれば、サブキャリアの伝送路状態が悪いと判定し、第２の閾値を越えていれば、サブキャリアの伝送路状態が良いと判定する。第２の閾値は第１の閾値より大きい値に設定される。つまり、振幅決定部７１は、選択部９０で選択されたサブキャリアの伝送路状態の良し悪しを判定する。 Further, the amplitude determining unit 71 corrects the target amplitude value according to the transmission path state of each subcarrier. Specifically, the amplitude determination unit 71 determines whether the state of the subcarrier transmission path selected by the selection unit 90 is good or bad based on the subcarrier transmission path state acquired by the acquisition unit 80. If the S / N ratio of the subcarrier is equal to or smaller than the second threshold, the amplitude determining unit 71 determines that the subcarrier transmission path condition is bad, and if the subcarrier transmission ratio exceeds the second threshold, the subcarrier transmission path It is determined that the state is good. The second threshold value is set to a value larger than the first threshold value. That is, the amplitude determination unit 71 determines whether the transmission path state of the subcarrier selected by the selection unit 90 is good or bad.
　なお、第２の閾値は、第１の閾値より小さくしてもよい。第２の閾値を第１の閾値より小さくすれば、第２の閾値が第１の閾値より大きい場合よりも、使用するサブキャリアを増やすことができる。 Note that the second threshold value may be smaller than the first threshold value. If the second threshold value is smaller than the first threshold value, more subcarriers can be used than when the second threshold value is larger than the first threshold value.
　そして、振幅決定部７１は、上記の判定の結果を参照して、伝送路状態が良いサブキャリアに対応する変調サブキャリアの目標振幅値を小さくし、伝送路状態が悪いサブキャリアに対応する変調サブキャリアの目標振幅値を大きくする。ただし、この場合においても、振幅決定部７１は、変調サブキャリアの合計電力が目標電力に一致するように各目標振幅値を決定する。なお、目標振幅値をどの程度変化させるかは、伝送路状態に応じて適宜設定すればよい。また、伝送路状態の良し悪しに応じて、目標振幅値の変化幅を変えても良い。 Then, the amplitude determination unit 71 refers to the result of the above determination, reduces the target amplitude value of the modulation subcarrier corresponding to the subcarrier having a good transmission path state, and modulates the subcarrier having a bad transmission path state. Increase the target amplitude value of the subcarrier. However, even in this case, the amplitude determination unit 71 determines each target amplitude value so that the total power of the modulation subcarriers matches the target power. In addition, what is necessary is just to set suitably how much a target amplitude value is changed according to a transmission-line state. Further, the change width of the target amplitude value may be changed according to the state of the transmission path.
　以上述べたように、送信装置１０の振幅制御部７０は、アナログのＯＦＤＭ信号の電力が目標電力になるように、選択数に応じて変調サブキャリアの振幅を調整する。 As described above, the amplitude control unit 70 of the transmission apparatus 10 adjusts the amplitude of the modulation subcarrier according to the selection number so that the power of the analog OFDM signal becomes the target power.
　そのため、ディジタルデータの送信に使用するサブキャリアの数が増減しても、伝送路に出力されるアナログのＯＦＤＭ信号の電力は目標電力に一致させられる。 Therefore, even if the number of subcarriers used for digital data transmission increases or decreases, the power of the analog OFDM signal output to the transmission path can be matched with the target power.
　ここで、アナログのＯＦＤＭ信号の振幅は、通信システムの仕様、Ｄ／Ａ変換器６０の仕様、法規制（例えば、無線信号の電力に関する規制）などにより制限される。一方、サブキャリア毎の振幅は、使用するサブキャリアの数や、サブキャリアの伝送路状態により決定される。同じＯＦＤＭ方式であっても、通信システムによって使用するサブキャリアの数などの仕様は異なる。また、ノイズや減衰の影響で、通信に使用できないサブキャリアが存在することがある。 Here, the amplitude of the analog OFDM signal is limited by the specifications of the communication system, the specifications of the D / A converter 60, legal regulations (for example, regulations regarding the power of radio signals), and the like. On the other hand, the amplitude for each subcarrier is determined by the number of subcarriers used and the transmission path state of the subcarriers. Even in the same OFDM system, specifications such as the number of subcarriers used differ depending on the communication system. Also, there may be subcarriers that cannot be used for communication due to the effects of noise and attenuation.
　本実施形態の送信装置１０では、サブキャリアの振幅を実際に使用するサブキャリアの数に適応させるために、使用するサブキャリアの数をサブキャリアの振幅を決定する際の基準として用いる。したがって、送信装置１０によれば、消費電力の無駄を抑制できる。更に、使用するサブキャリアの数を減らしたことで余った電力を使用可能な他のサブキャリアに供給する。そのため、送信装置１０によれば、通信速度を向上できる。また、送信装置１０は、使用するサブキャリアの数の異なる通信システムに共通に用いることができる。 In the transmission apparatus 10 of the present embodiment, the number of subcarriers to be used is used as a reference when determining the subcarrier amplitude in order to adapt the subcarrier amplitude to the number of subcarriers to be actually used. Therefore, according to the transmission device 10, waste of power consumption can be suppressed. Further, by reducing the number of subcarriers used, surplus power is supplied to other usable subcarriers. Therefore, according to the transmission device 10, the communication speed can be improved. Further, the transmission apparatus 10 can be commonly used for communication systems having different numbers of subcarriers to be used.
　ここで、前記所定値は、ディジタルのＯＦＤＭ信号の振幅がＤ／Ａ変換器６０に入力可能な最大値であるときのアナログのＯＦＤＭ信号の電力であることが好ましい。このようにすれば、伝送路の状態に応じて選択数が増減しても、Ｄ／Ａ変換器６０の能力（例えば分解能）を最大限に利用できる。また、Ｄ／Ａ変換器６０は、前記所定値が、法規制で認められているアナログのＯＦＤＭ信号の電力の最大値となるように構成されていることが好ましい。このようにすれば、通信速度を最大にできる。 Here, the predetermined value is preferably the power of the analog OFDM signal when the amplitude of the digital OFDM signal is the maximum value that can be input to the D / A converter 60. In this way, even if the number of selections increases or decreases depending on the state of the transmission path, the ability (for example, resolution) of the D / A converter 60 can be utilized to the maximum. Further, it is preferable that the D / A converter 60 is configured such that the predetermined value is the maximum value of the power of the analog OFDM signal that is permitted by law. In this way, the communication speed can be maximized.
　ところで、アナログのＯＦＤＭ信号の電力は、サブキャリアの伝送路状態によって変化することがある。上記の例では、振幅制御部７０は、Ｄ／Ａ変換器６０で検出されたアナログのＯＦＤＭ信号の電力に基づいて変調サブキャリアの振幅を調整する。そのため、伝送路状態によるアナログのＯＦＤＭ信号の電力変化を抑制できる。よって、アナログのＯＦＤＭ信号の電力を所定値に維持できる。 Incidentally, the power of the analog OFDM signal may change depending on the transmission path state of the subcarrier. In the above example, the amplitude control unit 70 adjusts the amplitude of the modulation subcarrier based on the power of the analog OFDM signal detected by the D / A converter 60. Therefore, the power change of the analog OFDM signal due to the transmission path state can be suppressed. Therefore, the power of the analog OFDM signal can be maintained at a predetermined value.
　なお、Ｄ／Ａ変換器６０では、Ｄ／Ａ変換器６０に入力されるディジタル信号と、Ｄ／Ａ変換器６０から出力されるアナログ信号との関係は、Ｄ／Ａ変換器６０の仕様によって決まっている。よって、アナログのＯＦＤＭ信号の電力が所定値になる変調サブキャリアの振幅は理論的に求めることができる。したがって、必ずしもアナログのＯＦＤＭ信号の電力を実際に検出する必要はない。ただし、上述したようにアナログのＯＦＤＭ信号の電力は、伝送路状態によって変化することがある。よって、アナログのＯＦＤＭ信号の電力を実際に検出するほうが好ましい。 In the D / A converter 60, the relationship between the digital signal input to the D / A converter 60 and the analog signal output from the D / A converter 60 depends on the specifications of the D / A converter 60. It has been decided. Therefore, the amplitude of the modulated subcarrier where the power of the analog OFDM signal becomes a predetermined value can be theoretically obtained. Therefore, it is not always necessary to actually detect the power of the analog OFDM signal. However, as described above, the power of the analog OFDM signal may change depending on the transmission path state. Therefore, it is preferable to actually detect the power of the analog OFDM signal.
　また、振幅制御部７０は、伝送路状態が良いサブキャリアに対応する変調サブキャリアの振幅を小さくし、伝送路状態が悪いサブキャリアに対応する変調サブキャリアの振幅を大きくする。 Also, the amplitude control unit 70 decreases the amplitude of the modulation subcarrier corresponding to the subcarrier having a good transmission path condition, and increases the amplitude of the modulation subcarrier corresponding to the subcarrier having a poor transmission path condition.
　つまり、振幅制御部７０は、伝送路状態が良いサブキャリアの電力の一部を伝送路状態が悪いサブキャリアに割り当てる。そのため、伝送路状態が悪いサブキャリアの通信状況を改善できる。よって、通信精度が向上し、その結果、通信速度が向上する。 That is, the amplitude control unit 70 allocates a part of the power of subcarriers with good transmission path conditions to subcarriers with poor transmission path conditions. Therefore, it is possible to improve the communication status of subcarriers with poor transmission path conditions. Therefore, the communication accuracy is improved, and as a result, the communication speed is improved.
　なお、振幅制御部７０は、必ずしも伝送路状態の良し悪しに応じて変調サブキャリアの振幅を変更する必要はない。つまり、振幅制御部７０は、変調サブキャリアの振幅を全て等しくするように構成されていてもよい。 Note that the amplitude control unit 70 does not necessarily need to change the amplitude of the modulation subcarrier according to the state of the transmission path. That is, the amplitude control unit 70 may be configured to make all the amplitudes of the modulation subcarriers equal.
　また、選択部９０は、取得部８０が取得したサブキャリアの伝送路状態に基づいてサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する。そのため、ディジタルデータの伝送が行えないようなサブキャリアを用いないようにできる。よって、送信装置１０は、電力の無駄を防止できる。また、通信精度が向上し、その結果、通信速度が向上する。 Also, the selection unit 90 selects a plurality of subcarriers to be used for digital data transmission from the subcarrier group based on the subcarrier transmission path state acquired by the acquisition unit 80. Therefore, it is possible to avoid using subcarriers that cannot transmit digital data. Therefore, the transmission apparatus 10 can prevent waste of power. Further, the communication accuracy is improved, and as a result, the communication speed is improved.
　ところで、上記の例では、選択部９０は、サブキャリアの伝送路状態に基づいてサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを自動的に選択する。しかしながら、選択部９０は、外部からの入力に応じてサブキャリアを選択するように構成されていてもよい。外部から入力する方法としては、手動入力の方法や、自動入力の方法が考えられる。手動入力の方法では、外部装置を用いて予め決定した設定値をボタン、キーボードなどの外部入力装置を用いて選択部９０に入力する。自動入力の方法では、設定値を決定する外部の演算装置が直接的に設定値を選択部９０に入力する。 By the way, in the above example, the selection unit 90 automatically selects a plurality of subcarriers to be used for digital data transmission from the subcarrier group based on the transmission path state of the subcarriers. However, the selection unit 90 may be configured to select a subcarrier according to an external input. As a method of inputting from the outside, a manual input method or an automatic input method can be considered. In the manual input method, a setting value determined in advance using an external device is input to the selection unit 90 using an external input device such as a button or a keyboard. In the automatic input method, an external arithmetic device that determines a set value inputs the set value directly to the selection unit 90.
　また、本発明の一実施形態のＯＦＤＭ送信方法は、上述の送信装置１０の動作から分かるように、次の５つのステップを有する。第１のステップでは、相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する。第２のステップでは、第１のステップで選択されたサブキャリアの数に応じてディジタルデータを分割する。さらに第２のステップでは、分割されたディジタルデータに基づいて複数のサブキャリアを変調して複数の変調サブキャリアを生成する。第３のステップでは、複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成する。第４のステップでは、ディジタルのＯＦＤＭ信号をＤ／Ａ変換器によりアナログのＯＦＤＭ信号に変換して伝送路に出力する。ここで、第５のステップは、第２のステップと第３のステップとの間に実行される。第５のステップでは、アナログのＯＦＤＭ信号の電力が所定値になるように、第１のステップで選択されたサブキャリアの数に応じて変調サブキャリアの振幅を調整する。 Also, the OFDM transmission method according to an embodiment of the present invention has the following five steps, as can be seen from the operation of the transmission apparatus 10 described above. In the first step, a plurality of subcarriers to be used for digital data transmission are selected from subcarrier groups having an orthogonal relationship with each other. In the second step, the digital data is divided according to the number of subcarriers selected in the first step. Further, in the second step, a plurality of modulated subcarriers are generated by modulating a plurality of subcarriers based on the divided digital data. In the third step, a plurality of modulation subcarriers are multiplexed to generate a digital OFDM signal. In the fourth step, the digital OFDM signal is converted into an analog OFDM signal by a D / A converter and output to the transmission path. Here, the fifth step is executed between the second step and the third step. In the fifth step, the amplitude of the modulation subcarrier is adjusted according to the number of subcarriers selected in the first step so that the power of the analog OFDM signal becomes a predetermined value.
　上述したＯＦＤＭ送信方法では、ディジタルデータの送信に使用するサブキャリアの数が増減しても、伝送路に出力されるアナログＯＦＤＭ信号の電力は所定値に制御される。そのため、上述したＯＦＤＭ送信方法によれば、Ｄ／Ａ変換器６０の能力を最大限に利用してディジタルデータを送信できる。 In the OFDM transmission method described above, even if the number of subcarriers used for digital data transmission increases or decreases, the power of the analog OFDM signal output to the transmission path is controlled to a predetermined value. Therefore, according to the above-described OFDM transmission method, digital data can be transmitted by utilizing the capability of the D / A converter 60 to the maximum.

Claims (6)

  1. 　相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択するサブキャリア選択部と、
    　前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記ディジタルデータを分割し、分割された前記ディジタルデータに基づいて前記複数のサブキャリアを変調して複数の変調サブキャリアを生成する変調部と、
    　前記複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成するＯＦＤＭ信号生成部と、
    　前記ディジタルのＯＦＤＭ信号をアナログのＯＦＤＭ信号に変換して伝送路に出力するＤ／Ａ変換器とを備えるＯＦＤＭ送信装置であって、
    　前記複数の変調サブキャリアの振幅を制御する振幅制御部を備え、
    　前記振幅制御部は、前記アナログのＯＦＤＭ信号の電力が所定値になるように、前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整するように構成されていることを特徴とするＯＦＤＭ送信装置。     A subcarrier selection unit that selects a plurality of subcarriers to be used for digital data transmission from a group of subcarriers having an orthogonal relationship with each other;
    The digital data is divided according to the number of subcarriers selected by the subcarrier selection unit, and a plurality of modulated subcarriers are generated by modulating the plurality of subcarriers based on the divided digital data. A modulation unit;
    An OFDM signal generator that multiplexes the plurality of modulation subcarriers to generate a digital OFDM signal;
    An OFDM transmitter comprising a D / A converter for converting the digital OFDM signal into an analog OFDM signal and outputting the analog OFDM signal to a transmission line;
    An amplitude control unit for controlling the amplitude of the plurality of modulation subcarriers;
    The amplitude control unit is configured to adjust the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power of the analog OFDM signal becomes a predetermined value. An OFDM transmitter characterized by the above.
  2. 　前記アナログのＯＦＤＭ信号の電力を検出する電力検出部を有し、
    　前記振幅制御部は、前記電力検出部で検出された電力が前記所定値になるように、前記サブキャリア選択部で選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整するように構成されていることを特徴とする請求項１記載のＯＦＤＭ送信装置。     A power detector for detecting the power of the analog OFDM signal;
    The amplitude control unit adjusts the amplitude of the modulation subcarrier according to the number of subcarriers selected by the subcarrier selection unit so that the power detected by the power detection unit becomes the predetermined value. The OFDM transmitter according to claim 1, configured as described above.
  3. 　前記各サブキャリアの伝送路状態を取得する伝送路状態取得部を備え、
    　前記振幅制御部は、前記伝送路状態取得部が取得した前記サブキャリアの伝送路状態に基づいて前記サブキャリアの伝送路状態の良し悪しを判定し、伝送路状態が良い前記サブキャリアに対応する前記変調サブキャリアの振幅を小さくし、伝送路状態が悪い前記サブキャリアに対応する前記変調サブキャリアの振幅を大きくするように構成されていることを特徴とする請求項１記載のＯＦＤＭ送信装置。     A transmission path state acquisition unit for acquiring the transmission path state of each subcarrier;
    The amplitude control unit determines whether the subcarrier transmission path state is good or bad based on the transmission path state of the subcarrier acquired by the transmission path state acquisition unit, and corresponds to the subcarrier having a good transmission path state. 2. The OFDM transmission apparatus according to claim 1, wherein the modulation subcarrier is configured to reduce an amplitude and increase an amplitude of the modulation subcarrier corresponding to the subcarrier having a poor transmission path state.
  4. 　前記所定値は、前記ディジタルのＯＦＤＭ信号の振幅が前記Ｄ／Ａ変換器に入力可能な最大値であるときの前記アナログのＯＦＤＭ信号の電力であることを特徴とする請求項１記載のＯＦＤＭ送信装置。 2. The OFDM transmission according to claim 1, wherein the predetermined value is the power of the analog OFDM signal when the amplitude of the digital OFDM signal is a maximum value that can be input to the D / A converter. apparatus.
  5. 　前記各サブキャリアの伝送路状態を取得する伝送路状態取得部を備え、
    　前記サブキャリア選択部は、前記伝送路状態推定部が取得した前記サブキャリアの伝送路状態に基づいて前記サブキャリア群から前記ディジタルデータの送信に使用する前記複数のサブキャリアを選択するように構成されていることを特徴とする請求項１記載のＯＦＤＭ送信装置。     A transmission path state acquisition unit for acquiring the transmission path state of each subcarrier;
    The subcarrier selection unit is configured to select the plurality of subcarriers to be used for transmission of the digital data from the subcarrier group based on the transmission path state of the subcarrier acquired by the transmission path state estimation unit. The OFDM transmitter according to claim 1, wherein:
  6. 　相互に直交関係を有するサブキャリア群からディジタルデータの送信に使用する複数のサブキャリアを選択する第１のステップと、
    　前記第１のステップで選択された前記サブキャリアの数に応じて前記ディジタルデータを分割し、分割された前記ディジタルデータに基づいて前記複数のサブキャリアを変調して複数の変調サブキャリアを生成する第２のステップと、
    　前記複数の変調サブキャリアを多重化してディジタルのＯＦＤＭ信号を生成する第３のステップと、
    　前記ディジタルのＯＦＤＭ信号をＤ／Ａ変換器によりアナログのＯＦＤＭ信号に変換して伝送路に出力する第４のステップとを有するＯＦＤＭ送信方法であって、
    　前記第２のステップと前記第３のステップとの間に、第５のステップを有し、
    　前記第５のステップでは、前記アナログのＯＦＤＭ信号の電力が所定値になるように、前記第１のステップで選択された前記サブキャリアの数に応じて前記変調サブキャリアの振幅を調整することを特徴とするＯＦＤＭ送信方法。     A first step of selecting a plurality of subcarriers to be used for digital data transmission from a group of subcarriers having an orthogonal relationship with each other;
    The digital data is divided according to the number of subcarriers selected in the first step, and a plurality of modulation subcarriers are generated by modulating the plurality of subcarriers based on the divided digital data. A second step;
    A third step of multiplexing the plurality of modulation subcarriers to generate a digital OFDM signal;
    A fourth step of converting the digital OFDM signal into an analog OFDM signal by a D / A converter and outputting the analog OFDM signal to a transmission line;
    A fifth step between the second step and the third step;
    In the fifth step, the amplitude of the modulation subcarrier is adjusted according to the number of subcarriers selected in the first step so that the power of the analog OFDM signal becomes a predetermined value. A characteristic OFDM transmission method.
PCT/JP2009/055997 2008-03-26 2009-03-25 Ofdm transmission device and ofdm transmission method WO2009119685A1 (en)

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