JP2009239549A - Ofdm transmission device, and ofdm transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM transmission device capable of utilizing to a maximum the capability of a D/A converting means for D/A converting an OFDM signal. <P>SOLUTION: An OFDM transmission device 1 includes a to-be-used subcarrier determination unit 18, a subcarrier modulation signal forming unit 12, an amplitude control unit 16, an OFDM signal generation unit 14, and a D/A converter 15. The to-be-used subcarrier determination unit 18 determines the subcarrier to be used from among a plurality of subcarriers, and the subcarrier modulation signal forming unit 12 generates a subcarrier modulation signal for each subcarrier to be used. The amplitude control unit 16 controls the amplitude of each subcarrier modulation signal, the OFDM signal generation unit 14 generates an OFDM signal by adding amplitude-controlled subcarrier modulation signals to each other, and the D/A converter 15 converts the OFDM signal into an analog signal and outputs it to a transmission path. The amplitude control unit 16 adjusts the amplitude of the subcarrier modulation signal in each subcarrier to be used in accordance with the number of subcarriers to be used so that the amplitude of the OFDM signal inputted to the D/A converter 15 becomes a predetermined amplitude value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an OFDM transmission apparatus and an OFDM transmission method for transmitting a multicarrier signal using a plurality of subcarriers via a transmission line.

  With the rapid formation of an information society in recent years, the demand for high-speed and large-capacity communication is increasing. Under such circumstances, research and development of communication using OFDM (Orthogonal Frequency Division Multiplexing) that makes maximum use of a limited bandwidth of radio waves is widely performed.

  In general, an OFDM transmitter generates a digital subcarrier modulation signal for each subcarrier, performs D / A conversion on an OFDM signal obtained by adding the subcarrier modulation signals to each other, and then transmits the signal to the reception side via a transmission path. Amplifiers and D / A converters are used. Regarding the amplifier, it is necessary to suppress the difference between the peak power and the average power in order to suppress the distortion of the OFDM signal, which is a cause of deterioration of transmission characteristics. On the other hand, regarding the D / A converter, in order to make maximum use of the capability (for example, resolution) of D / A conversion, the maximum amplitude of the OFDM signal input to the D / A converter is set to the D / A converter. It is necessary to match the maximum amplitude that can be input, which is determined in advance according to the specifications.

Many countermeasures have been proposed for the amplifier. For example, pay attention to the fact that the peak power becomes very large with respect to the average power when the phases of each subcarrier are aligned, so that the phase is not aligned by changing the phase for each subcarrier. Thus, peak power is suppressed (for example, see Patent Document 1).
Republished patent WO2005 / 055479

  Patent Document 1 has a function of changing the amplitude of an OFDM signal. However, the function does not exceed the determination boundary line between the signal point where the symbol assigned to each of the plurality of subcarriers and the signal point adjacent to the signal point are arranged for the amplitude of each of the plurality of subcarriers. The amount of change in the amplitude is limited by the determination boundary line, and the maximum amplitude of the OFDM signal is matched with the maximum amplitude that can be input to the D / A converter. It was not designed to take full advantage of the conversion capabilities.

  Also, even when there is a subcarrier with poor sensitivity at the transmission destination, it is difficult to say that the subcarrier is used as it is and the ability of the D / A converter is efficiently used. .

  The present invention has been made in view of the above reasons, and an object of the present invention is to provide an OFDM transmitter capable of making maximum use of the ability of D / A conversion means for D / A converting an OFDM signal. It is in.

  The invention of claim 1 is an OFDM transmission apparatus for transmitting a multicarrier signal using subcarriers via a transmission line, a used subcarrier determining means for determining a used subcarrier from a plurality of subcarriers, and a used subcarrier. Modulation signal forming means for generating a subcarrier modulation signal from bit data for each carrier, amplitude control means for controlling the amplitude of each subcarrier modulation signal, and each subcarrier modulation signal whose amplitude is controlled by the amplitude control means. An OFDM signal generating means for generating an added OFDM signal; and a D / A converting means for converting the OFDM signal into an analog signal and outputting the analog signal, and the amplitude control means is input to the D / A converting means. Depending on the number of used subcarriers, the subkey of each used subcarrier is set so that the amplitude of the OFDM signal becomes a predetermined amplitude value. And adjusting the amplitude of the rear modulation signal.

  According to the present invention, in the OFDM transmitter, even if the number of subcarriers used increases or decreases, the amplitude of the OFDM signal input to the D / A conversion means is controlled to the predetermined amplitude value. It is possible to make full use of the capabilities of the means.

  According to a second aspect of the present invention, in the first aspect, the amplitude control unit adjusts the amplitude of the subcarrier modulation signal of each used subcarrier so that the output power of the D / A conversion unit becomes a predetermined power. It is characterized by.

  According to the present invention, since the increase / decrease in the amplitude of each used subcarrier modulation signal is reflected in the increase / decrease in the power of each used subcarrier modulation signal, D / A corresponding to the total power of all the used subcarrier modulation signals Even if the number of used subcarriers increases or decreases by adjusting the amplitude of the subcarrier modulation signal of each used subcarrier so that the output power of the converting means matches the predetermined power, it is input to the D / A converting means. Since the amplitude of the OFDM signal is controlled to a predetermined amplitude value, it is possible to make maximum use of the capability of the D / A conversion means.

  According to a third aspect of the present invention, the amplitude control unit according to the second aspect of the present invention is configured so that the output power of the D / A conversion unit becomes a predetermined power based on the output of the D / A conversion unit. The amplitude of the subcarrier modulation signal of the carrier is adjusted.

  According to the present invention, the output of the D / A conversion means is fed back and the amplitude of the subcarrier modulation signal of each used subcarrier is adjusted, so that the ability of the D / A conversion means is utilized to the maximum with high accuracy. It becomes possible.

  The invention of claim 4 comprises the transmission path state estimation means for detecting the transmission path state of each subcarrier in claim 2 or 3, wherein the amplitude control means is based on the transmission path state of each subcarrier. It is characterized in that the amplitude of the subcarrier modulation signal of the subcarrier having a poor transmission path condition is adjusted in the increasing direction, and the amplitude of the subcarrier modulation signal of the subcarrier having a good transmission path condition is adjusted in the decreasing direction.

  According to the present invention, even if the number of subcarriers used increases or decreases depending on the state of the transmission path, the capability of the D / A conversion means can be utilized to the maximum, and the reliability of demodulated data at the transmission destination is improved. Can be achieved.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the predetermined amplitude value is a maximum amplitude that can be input to the D / A conversion means.

  According to this invention, the capability of the D / A conversion means can be utilized to the maximum extent.

  A sixth aspect of the present invention is the method according to any one of the first to fifth aspects, further comprising transmission path state estimating means for detecting a transmission path state of each subcarrier, wherein the used subcarrier determining means is a transmission path state of each subcarrier. Based on the above, it is characterized in that a used subcarrier is determined from a plurality of subcarriers.

  According to the present invention, subcarriers can be selected according to the state of the transmission path, and the ability of the D / A conversion means can be utilized more efficiently.

  The invention according to claim 7 is an OFDM transmission method for transmitting a multicarrier signal using subcarriers via a transmission line, the first step of determining a used subcarrier from a plurality of subcarriers, and a used subcarrier A second step of generating a subcarrier modulation signal from bit data every time, a third step of controlling the amplitude of each subcarrier modulation signal, and an OFDM obtained by adding the subcarrier modulation signals controlled in amplitude to each other A fourth step of generating a signal, and a fifth step of converting the OFDM signal into an analog signal and outputting the analog signal to the transmission line. In the third step, the amplitude of the OFDM signal becomes a predetermined amplitude value. Thus, the amplitude of the subcarrier modulation signal of each used subcarrier is adjusted.

  According to the present invention, in the OFDM transmission method, even if the number of subcarriers used increases or decreases, the amplitude of the OFDM signal input to the D / A conversion means is controlled to a predetermined amplitude value. It is possible to make full use of the capabilities of the means.

  As described above, the present invention has the effect that the ability of the D / A conversion means for D / A converting the OFDM signal can be utilized to the maximum extent.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
First, FIG. 1 shows a configuration of an OFDM transmission apparatus according to this embodiment, and FIG. 2 shows an operation flowchart thereof. The OFDM transmitter 1 according to the present embodiment performs packet communication using signals modulated by OFDM (Orthogonal Frequency Division Multiplexing). However, the transmission path for transmitting a signal from the OFDM transmitter 1 may be either wired or wireless.

  The OFDM transmitter 1 includes an error correction coding unit 11, a subcarrier modulation signal forming unit 12, an interleaver unit 13, an OFDM signal generation unit 14, a D / A conversion unit 15, an amplitude control unit 16, and a transmission. A road state estimation unit 17 and a use subcarrier determination unit 18 are provided.

  First, the error correction coding unit 11 performs error correction coding on serial bit data that is a transmission signal, thereby improving the reliability of the communication system even when the transmission path is in a bad condition, and the subcarrier modulation signal Output to the forming unit 12.

  The subcarrier modulation signal forming unit 12 includes a serial / parallel converter 12a, a symbol mapper 12b, and a plurality of subcarrier modulators 12c. The serial / parallel converter 12a is a serial signal that has been subjected to error correction coding. The bit data is converted into parallel bit data corresponding to the number of subcarriers to be used in units of symbols determined by a modulation method described later.

  The symbol mapper 12b converts each bit data subjected to serial / parallel conversion into an IQ signal (In-Phase component: In-phase component, Quadrature-Phase component: Quadrature component) on a complex plane determined by the modulation method. Symbol mapping is performed. When QPSK (Quadrature Phase Shift Keying) is used as the modulation method, the reference sine wave and each sine whose phase is shifted by 90 degrees, 180 degrees, and 270 degrees with respect to the reference sine wave. Bit data 00, 01, 10, and 11 are assigned to a total of four sine waves with the wave. The correspondence between the bit data and the IQ signal in QPSK is shown in FIG. 3, and the symbol mapper 12b stores this correspondence in the form of a table, and a method of referring to it when necessary is typical.

  The plurality of subcarrier modulators 12c respectively correspond to subcarriers having different frequencies, modulate each IQ signal in symbol units to a frequency for each subcarrier (subcarrier modulation), and generate a subcarrier modulation signal (symbol). Data).

  Here, also in this embodiment, the reliability of demodulated data at the transmission destination is improved by the error correction coding performed by the error correction coding unit 11. There are various methods for this error correction code, but considering the complexity of the circuit, a practical method is a method using a random error correction code that exerts power in correcting errors randomly distributed in the data. It is. However, there are two types of errors: random errors that occur randomly in the data and burst errors that occur in a concentrated area in the data. The method using a random error correction code has an upper limit on the number of errors that can be corrected. Therefore, it cannot cope with the occurrence of burst errors.

  Therefore, the interleaver unit 13 changes the order of the subcarrier modulation signals modulated by the subcarrier modulators 12c (interleaves), so that even if a burst error occurs in the transmission path, the interleaver 13 deinterleaves at the transmission destination. By performing the leaver, errors are randomly distributed in the data to solve the above problem. Although there are various methods for interleaving, an appropriate method may be selected from the characteristics of the transmission path.

  Next, the OFDM signal generation unit 14 includes an inverse discrete Fourier transformer (IFFT) 14a, a parallel-serial converter 14b, a GI addition unit 14c, a real part extraction unit 14d, a frequency converter 14e, and a local oscillator 14f. And a band pass filter 14g, and an inverse discrete Fourier transformer (IFFT) 14a collectively performs inverse discrete Fourier transform on each subcarrier modulation signal output from the interleaver unit 13, and then a parallel-serial converter. 14b converts parallel data into serial data to generate a complex baseband OFDM signal. At the time of parallel-serial conversion by the parallel-serial converter 14b, the GI adding unit 14c adds a guard interval (GI) to the complex baseband OFDM signal so as not to receive intersymbol interference due to multipath delay waves.

The real part extractor 14d extracts the real part from the complex baseband OFDM signal output from the parallel-serial converter 14b, and the frequency converter 14e outputs the carrier wave [cos (2πf _C t)] of the frequency f _C by the local oscillator 14f. Is multiplied by the real part of the complex baseband OFDM signal to generate a carrier band OFDM signal. The carrier band OFDM signal is converted into an analog signal by the D / A converter 15 and then transmitted through the bandpass filter 14g. Is transmitted to a path (or a transmission path via an antenna).

  The OFDM transmitter 1 having the above-described schematic configuration constitutes an OFDM communication apparatus with an OFDM receiver (not shown), and the transmission path state estimation unit 17 includes each OFDM signal received by the receiver via the transmission path. The higher the subcarrier S / N ratio, the lower the bit error rate (hereinafter referred to as BER) (that is, the lower the noise level, the better communication can be performed), and the S / N ratio is predetermined. It is estimated that the subcarriers below the threshold value are in poor transmission path conditions.

  Based on the estimation result of the transmission path state estimation unit 17, the used subcarrier determination unit 18 does not use the subcarrier estimated that the S / N ratio is equal to or less than a predetermined threshold and the transmission path state is bad, and the S / N The subcarriers to be used (used subcarriers) are set so that only the subcarriers whose ratio exceeds the predetermined threshold and the transmission path state is estimated to be good are used. The number of parallel data generated by the serial / parallel conversion of the parallel converter 12a is set (step S1). In addition, the process of setting the subcarriers to be used includes estimating the state of the transmission path of each subcarrier at regular intervals, and updating the setting contents at regular intervals based on this estimation result. When there is almost no fluctuation, there is a method of estimating the state of the transmission path of each subcarrier at the time of installation of the present apparatus, and setting based on the estimation result at the time of installation.

  Of the plurality of subcarrier modulators 12c, the subcarrier modulator 12c corresponding to the used subcarrier performs subcarrier modulation on the IQ signal (step S2). At this time, the subcarrier modulator 12c The amplitude control unit 16 controls the amplitude of the subcarrier modulation signal.

  The amplitude control unit 16 includes an amplitude value determination unit 16a and an amplitude value adjustment unit 16b. Here, since the carrier band OFDM signal input to the D / A converter 15 is obtained by superimposing the subcarrier modulation signals of all the used subcarriers, the amplitude of the carrier band OFDM signal is determined by each subcarrier used. It depends on the amplitude of a subcarrier modulation signal (hereinafter referred to as a used subcarrier modulation signal). Further, the increase / decrease in the amplitude of each used subcarrier modulation signal is reflected in the increase / decrease in the power of each used subcarrier modulation signal. Therefore, the amplitude value determination unit 16a holds in advance the target power for the power of the carrier band OFDM signal output from the D / A conversion unit 15 (corresponding to the total power of all used subcarrier modulation signals). The target amplitude value of each used subcarrier modulation signal is determined so that the power of the subcarrier modulation signal matches the value obtained by dividing the target power by the number of used subcarriers, and the amplitude value adjustment unit 16b The amplitude of the carrier modulation signal is controlled to the target amplitude value (step S3). At this time, the target amplitude value of each used subcarrier modulation signal is set to a value at which the power of each used subcarrier modulation signal is equal. Further, the amplitude of each used subcarrier modulation signal decreases as the number of used subcarriers increases, and increases as the number of used subcarriers decreases.

  Therefore, when the total power of all the used subcarrier modulation signals becomes the target power, the amplitude of the carrier band OFDM signal input to the D / A converter 15 becomes the maximum amplitude that can be input to the D / A converter. If the target power is set to match, the amplitude of the OFDM signal input to the D / A converter 15 is controlled to the maximum inputable amplitude even if the number of subcarriers used increases or decreases depending on the state of the transmission path. Therefore, the capability (for example, resolution) of the D / A converter 15 can be utilized to the maximum.

  Specifically, as shown in FIG. 4 (a), all subcarriers (all subcarrier modulators 12c) are used so that the total power of all used subcarrier modulation signals becomes the target power. A state where the amplitude of the used subcarrier modulation signal is controlled to the target amplitude value is defined as an initial state. From this initial state, when the state of the transmission path for the subcarriers in the frequency band W1 deteriorates and the number of used subcarriers decreases as shown in FIG. 4B, the amplitude value determination unit 16a The target amplitude value is increased from the initial state for each used subcarrier modulation signal so that the total power of the used subcarrier modulation signal becomes the target power, and the amplitude value adjustment unit 16b The amplitude is controlled to an increased target amplitude value.

  Therefore, since the power of each used subcarrier modulation signal after the decrease is controlled to a power increased by power ΔP1 from the initial state as shown in FIG. 4C, the total of all used subcarrier modulation signals in the initial state The power and the total power of all the used subcarrier modulation signals when the number of used subcarriers is reduced are the same (that is, the power of the carrier band OFDM signal is the same before and after the reduction of the subcarriers), and D The amplitude of the carrier band OFDM signal input to the A / A converter 15 is also the same in the initial state and after the decrease in the number of used subcarriers, and the number of used subcarriers increases or decreases depending on the state of the transmission path. In addition, it is possible to make maximum use of the capability (for example, resolution) of the D / A converter 15.

Then, the OFDM signal generation unit 14 collectively performs inverse discrete Fourier transform on each used subcarrier modulation signal that has passed through the interleaver unit 13, and then generates a complex baseband OFDM signal to which a guard interval is added by performing serial-parallel conversion. Then, the real part of the complex baseband OFDM signal is multiplied by the carrier wave [cos (2πf _C t)] to generate a carrier band OFDM signal (step S4), and the carrier band OFDM signal is analogized by the D / A conversion unit 15. After being converted into a signal, the signal is transmitted to the transmission path (or the transmission path via the antenna) through the bandpass filter 14g (step S5).

(Embodiment 2)
The OFDM transmitter 1 of the present embodiment has the configuration shown in FIG. 5, and the amplitude controller 16 feeds back the carrier band OFDM signal output from the D / A converter 15 and the amplitude of each used subcarrier modulation signal. The point which controls is different from the first embodiment.

  First, the amplitude value determination unit 16a holds the target power with respect to the power of the carrier band OFDM signal in advance so that the power of the carrier band OFDM signal fed back from the output of the D / A conversion unit 15 matches the target power. Then, the target amplitude value of each used subcarrier modulation signal is determined, and the amplitude value adjustment unit 16b controls the amplitude of each used subcarrier modulation signal to the target amplitude value. At this time, the target amplitude value of each used subcarrier modulation signal is set to a value at which the power of each used subcarrier modulation signal is equal. Further, the amplitude of each used subcarrier modulation signal decreases as the number of used subcarriers increases, and increases as the number of used subcarriers decreases.

  Therefore, when the power of the carrier band OFDM signal fed back from the output of the D / A converter 15 becomes the target power, the amplitude of the carrier band OFDM signal input to the D / A converter 15 is the D / A. If the target power is set to match the maximum amplitude that can be input to the conversion unit, the amplitude of the OFDM signal input to the D / A conversion unit 15 even if the number of subcarriers used increases or decreases depending on the state of the transmission path Since the maximum amplitude that can be input is controlled with high accuracy, the capability (for example, resolution) of the D / A conversion unit 15 can be used to the maximum with high accuracy.

  Further, the amplitude control unit 16 determines the target amplitude value of each used subcarrier modulation signal so that the power of each used subcarrier modulation signal matches the value obtained by dividing the target power by the number of used subcarriers. By using the method of the first embodiment that controls the amplitude of each used subcarrier modulation signal to the same target amplitude value, the capability of the D / A converter 15 can be further utilized to the maximum.

(Embodiment 3)
The OFDM transmitter 1 of the present embodiment has the configuration shown in FIG. 6, and the amplitude control unit 16 individually corrects the power of each used subcarrier modulation signal based on the estimation result of the transmission path estimation unit 17. The added point is different from the first embodiment in which the power of each used subcarrier modulation signal is controlled to the same power.

  In general, since the characteristics of the transmission path depend on the frequency, even if each used subcarrier modulation signal is set to the same power, each used subcarrier modulation signal received at the transmission destination via the transmission path is Received power varies depending on the frequency.

  Therefore, in the present embodiment, the amplitude value determination unit 16a of the amplitude control unit 16 sets each used subcarrier modulation signal so that the power of each used subcarrier modulation signal matches the value obtained by dividing the target power by the number of used subcarriers. After the target amplitude value of the carrier modulation signal is determined, the target amplitude value is corrected. Specifically, the amplitude value determination unit 16a maintains the condition that the total power of all used subcarrier modulation signals matches the target power, and based on the estimation result of the transmission path estimation unit 17, determines the used subcarriers. Among them, the target amplitude value of the subcarrier modulation signal of the used subcarrier having the good transmission path condition is corrected in the decreasing direction, and the target amplitude value of the subcarrier modulation signal of the used subcarrier having the poor transmission path condition is corrected in the increasing direction.

  Therefore, even if the number of subcarriers used increases or decreases depending on the state of the transmission path, the ability (for example, resolution) of the D / A converter 15 can be utilized to the maximum, and the reliability of demodulated data at the transmission destination Improvements can be made.

(Embodiment 4)
The OFDM transmitter 1 according to the present embodiment has the configuration shown in FIG. 7, and the amplitude control unit 16 individually corrects the power of each used subcarrier modulation signal based on the estimation result of the transmission path estimation unit 17. The added point is different from Embodiment 2 in which the power of each used subcarrier modulation signal is controlled to the same power.

  In general, since the characteristics of the transmission path depend on the frequency, even if each used subcarrier modulation signal is set to the same power, each used subcarrier modulation signal received at the transmission destination via the transmission path is Received power varies depending on the frequency.

  Therefore, in the present embodiment, the amplitude value determination unit 16a of the amplitude control unit 16 uses each subcarrier used so that the power of the carrier band OFDM signal fed back from the output of the D / A conversion unit 15 matches the target power. After the target amplitude value of the modulation signal is determined, the target amplitude value is corrected. Specifically, the amplitude value determination unit 16a maintains the condition that the power of the fed-back carrier band OFDM signal matches the target power, and based on the estimation result of the transmission path estimation unit 17, determines the subcarrier used. Among them, the target amplitude value of the subcarrier modulation signal of the used subcarrier having the good transmission path condition is corrected in the decreasing direction, and the target amplitude value of the subcarrier modulation signal of the used subcarrier having the poor transmission path condition is corrected in the increasing direction.

  Therefore, even if the number of subcarriers used increases or decreases depending on the state of the transmission path, the ability (for example, resolution) of the D / A converter 15 can be utilized to the maximum, and the reliability of demodulated data at the transmission destination Improvements can be made.

1 is a diagram illustrating a block configuration of a first embodiment. It is a figure which shows an operation | movement flowchart same as the above. It is a figure which shows a response | compatibility with the bit data and IQ signal in QPSK same as the above. (A)-(c) It is a figure which shows electric power control of the use subcarrier same as the above. It is a figure which shows the block configuration of Embodiment 2. FIG. It is a figure which shows the block configuration of Embodiment 3. It is a figure which shows the block configuration of Embodiment 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM transmitter 11 Error correction code | cord | chord part 12 Subcarrier modulation signal formation part 13 Interleaver part 14 OFDM signal generation part 15 D / A conversion part 16 Amplitude control part 17 Transmission path state estimation part 18 Use subcarrier determination part

Claims (7)

An OFDM transmitter that transmits a multicarrier signal using subcarriers via a transmission line,
A used subcarrier determining means for determining a used subcarrier from a plurality of subcarriers;
Modulation signal forming means for generating a subcarrier modulation signal from bit data for each used subcarrier;
Amplitude control means for controlling the amplitude of each subcarrier modulation signal;
OFDM signal generation means for generating an OFDM signal obtained by adding the subcarrier modulation signals whose amplitudes are controlled by the amplitude control means to each other;
D / A conversion means for converting the OFDM signal into an analog signal and outputting it to the transmission line,
The amplitude control means adjusts the amplitude of the subcarrier modulation signal of each used subcarrier according to the number of used subcarriers so that the amplitude of the OFDM signal input to the D / A conversion means becomes a predetermined amplitude value. An OFDM transmitter characterized in that:   2. The OFDM transmission apparatus according to claim 1, wherein the amplitude control means adjusts the amplitude of the subcarrier modulation signal of each used subcarrier so that the output power of the D / A conversion means becomes a predetermined power. .   The amplitude control means adjusts the amplitude of the subcarrier modulation signal of each used subcarrier based on the output of the D / A conversion means so that the output power of the D / A conversion means becomes a predetermined power. The OFDM transmitter according to claim 2. Comprising a transmission path state estimation means for detecting the state of the transmission path of each subcarrier;
The amplitude control means adjusts the amplitude of the subcarrier modulation signal of the subcarrier having a poor transmission path condition in an increasing direction based on the transmission path condition of each subcarrier, and the subcarrier modulation signal of the subcarrier having a good transmission path condition The OFDM transmitter according to claim 2 or 3, wherein the amplitude of the signal is adjusted in a decreasing direction.   5. The OFDM transmission apparatus according to claim 1, wherein the predetermined amplitude value is a maximum amplitude that can be input to the D / A conversion means. Comprising a transmission path state estimation means for detecting the state of the transmission path of each subcarrier;
6. The OFDM transmission apparatus according to claim 1, wherein the used subcarrier determining means determines a used subcarrier from a plurality of subcarriers based on a transmission path state of each subcarrier. An OFDM transmission method for transmitting a multicarrier signal using subcarriers via a transmission line,
A first step of determining a used subcarrier from a plurality of subcarriers;
A second step of generating a subcarrier modulation signal from bit data for each used subcarrier;
A third step of controlling the amplitude of each subcarrier modulation signal;
A fourth step of generating an OFDM signal in which each amplitude-controlled subcarrier modulation signal is added together;
A fifth step of converting the OFDM signal to an analog signal and outputting the analog signal to the transmission path;
In the third step, the amplitude of the subcarrier modulation signal of each used subcarrier is adjusted so that the amplitude of the OFDM signal becomes a predetermined amplitude value.

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