JP3654526B2 - Amplitude limiter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an amplitude limiting device that limits the amplitude of a signal.
[0002]
[Prior art]
For example,Patent Document 1Discloses an Orthogonal Frequency Division Multiplex (OFDM) system as a multicarrier communication system for transmitting data using many carrier waves.
Also,Patent Documents 2-7Discloses a method for suppressing a peak value of a transmission signal in order to reduce nonlinear distortion caused by a transmission signal such as a multicarrier communication system being amplified in a nonlinear portion of an amplification characteristic of a power amplifier.
[0003]
[Patent Document 1]
Nikkei Electronics (April 8, 2002, pp. 102-127)
[Patent Document 2]
JP 2001-339361 A
[Patent Document 3]
Japanese Patent Laid-Open No. 2002-44052
[Patent Document 4]
JP 2002-77079 A
[Patent Document 5]
Japanese Patent Laid-Open No. 11-313942
[Patent Document 6]
JP 2002-44054 A
[Patent Document 7]
JP 2001-274768 A
[0004]
[Problems to be solved by the invention]
The present invention has been made from the above-described background, and an object thereof is to provide an amplitude limiting device capable of effectively suppressing the peak value of the amplitude of a transmission signal such as a multicarrier communication system.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, an amplitude limiting device according to the present invention includes a portion of a target signal subject to amplitude limitation that exceeds a limit value determined for the amplitude of the target signal, and the limit value. Difference signal generating means for generating a difference signal indicating a difference between the target signal and amplitude limiting means for limiting the amplitude of the target signal by subtracting the generated difference signal from the target signal.
[0006]
Preferably, the filtering apparatus further includes filtering means for filtering the generated difference signal to pass only a predetermined band component of the difference signal, and the amplitude limiting means is configured to filter the filtered difference from the target signal. The signal is reduced to limit the amplitude of the target signal.
[0007]
Preferably, the target signal is in a digital format, and each of the difference signal generation unit, the amplitude limiting unit, and the filtering unit performs digital processing to generate the difference signal, limit the amplitude of the target signal, and Each differential signal is filtered.
[0008]
Preferably, a digital format transmission signal to be transmitted is mapped to a plurality of symbols, and IFFT processing is performed on the plurality of symbols obtained by the mapping to include a plurality of subcarrier components. IFFT processing means for generating a digital multi-carrier composite signal is further provided, and amplitude limitation is performed using the generated multi-carrier composite signal as the target signal.
[0009]
Preferably, the filtering means passes each one or more of the subcarrier components included in the multicarrier composite signal with a predetermined output gain.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
[Background of the invention]
In order to help understanding of the present invention, first, the background that led to the present invention will be described.
[0011]
[First OFDM transmitter 1]
FIG. 1 is a diagram showing a configuration of a first OFDM transmitter 1 exemplified for explaining the background of the present invention.
As shown in FIG. 1, the first OFDM transmitter 1Transmission data generation unit 10And from the transmitter 12Composed.
The transmission data generation unit 10The serial / parallel conversion unit (S / P) 100 includes n (n is an integer of 2 or more) mapping units 102-1 to 102-n, an IFFT unit 104, and an orthogonal modulation unit 110.
The transmission unit 12 includes a digital / analog conversion circuit (D / A) 120, a local transmission circuit 122, a frequency conversion circuit 124, and a power amplifier (TX-AMP) 126.
[0012]
With these components, the OFDM transmitter 1 generates an OFDM transmission signal from digital transmission data serially input from an external device (not shown), and transmits the transmission signal to a wireless line.
Hereinafter, in the case where any one of a plurality of components such as the mapping units 102-1 to 102-n is indicated without being specified, the mapping unit 102 may be simply abbreviated.
[0013]
2 is shown in FIG.Transmission data generation unit 10It is a figure which illustrates the hardware constitutions.
For example,Transmission data generation unit 10These components can be realized in hardware by a custom LSI or the like.
[0014]
Or, for example,Transmission data generation unit 10Each of the components can be realized by software.
Transmission data generation unit 10Is implemented in software, for example,Transmission data generation unit 10The DSP circuit 14 illustrated in FIG. 2 is used as hardware for executing the above.
As shown in FIG. 2, the DSP circuit 14 is stored as a program in an input interface circuit (input IF) 140 that accepts transmission data from an external device and the ROM 144.Transmission data generation unit 10DSP (Digital Signal Processor) 142 that executes the process using the RAM 146 and the like, andTransmission data generation unit 10The transmission IF 148 that outputs the transmission data obtained as a result of the process to the transmission unit 12 is configured.
[0015]
Transmission data generation unit 10In FIG. 1, the S / P 100 converts transmission data input from an external device into a parallel format, and sets n symbols # 1 to #n as mapping symbols 102-1 to 102-n. Output.
For example,Transmission data generation unit 10However, when modulation is performed by BPSK (Binariphase Phase Shift Keying), each of symbols # 1 to #n includes 1-bit data.
For example,Transmission data generation unit 10However, when modulation is performed by 16QAM (Quadrature Amplitude Modulation), each of symbols # 1 to #n includes 4-bit data.
[0016]
Each mapping unit 102Transmission data generation unit 10In accordance with the modulation scheme, symbols input from the S / P 100 are mapped to signal points.
That is, each mapping unit 102 performs modulation by associating a symbol with the phase and amplitude of a certain carrier wave.
[0017]
The IFFT unit 104 performs inverse FFT (IFFT) processing on n symbols (n mapped data) mapped to signal points input from the mapping units 102-1 to 102-n.
That is, IFFT section 104 performs batch conversion of the frequency domain mapped data generated by mapping sections 102-1 to 102-n into the time domain, and outputs the modulated data of I component and Q component to quadrature modulation section 110. Output.
[0018]
FIG. 3 is a diagram illustrating a configuration of the quadrature modulation unit 110 illustrated in FIG. 1.
As shown in FIG. 3, the quadrature modulation unit 110 includes a carrier wave generation unit 112, mixer units 114-1 and 114-2, a phase shift unit 116 and an addition unit 118.
The quadrature modulation unit 110 performs digital computation using these components or components that perform processing equivalent to these components, and uses the modulated data of the I component and Q component input from the IFFT unit 104 to generate a carrier wave Lo1. Are orthogonally modulated to generate transmission data and output the transmission data to the transmission unit 12.
[0019]
In the quadrature modulation unit 110, the carrier signal generation unit 112 generates carrier data in digital format indicating the carrier signal Lo1, and outputs it to the first mixer unit 114-1 and the phase shift unit 116.
[0020]
The phase shifter 116 shifts the carrier wave data input from the carrier wave generator 112 by 90 °, and outputs it to the second mixer 114-2.
[0021]
The first mixer unit 114-1 mixes by multiplying the I component modulation data input from the IFFT unit 104 (FIG. 1) by the carrier wave data input from the carrier wave generation unit 112, and performs this processing. The obtained data is output to the adder 118.
The second mixer unit 114-2 multiplies the input Q component modulation data input from the IFFT unit 104 by the 90 ° phase-shifted carrier data input from the phase shift unit 116 to mix the data. Then, the data obtained by this processing is output to the adder 118.
[0022]
Adder 118 adds the data input from mixers 114-1 and 114-2 and outputs the result as transmission data to transmitter 12 (FIG. 1).
[0023]
In the transmission unit 12 (FIG. 1), the D / A 120 isTransmission data generation unit 10The digital transmission data input from the adder 118 (FIG. 3) is converted into an analog transmission signal.
Further, the D / A 120 filters the generated transmission signal to remove unnecessary frequency components and outputs the filtered signal to the frequency conversion circuit 124.
[0024]
The local transmission circuit 122 generates an analog frequency conversion signal Lo2 that is used to set the transmission signal input from the D / A 120 to a desired frequency, and outputs the signal to the frequency conversion circuit 124.
[0025]
The frequency conversion circuit 124 mixes the transmission signal input from the D / A 120 and the frequency conversion signal Lo2 input from the local transmission circuit 122 by analog processing, and converts the mixed signal into a transmission signal having a desired frequency.
[0026]
The power amplifier 126 amplifies the transmission signal input from the frequency conversion circuit 124 and transmits the amplified signal to the radio line via the antenna 128.
[0027]
[Peak generated in transmission signal]
As described above, since the OFDM transmitter 1 transmits transmission data superimposed on a plurality of subcarriers, the transmission signal generated by the OFDM transmitter 1 includes a plurality of subcarriers. There is no correlation between carriers.
Therefore, the phases of a plurality of subcarriers may coincide with each other. When such a phase coincidence occurs, a peak occurs in the amplitude of a transmission signal obtained by synthesizing the plurality of subcarriers.
[0028]
With reference to FIG. 4, the peak which arises in the amplitude of a transmission signal is further demonstrated.
FIG. 4 is a diagram illustrating, as a specific example, a peak generated in the amplitude of a transmission signal generated by the OFDM transmitter 1 illustrated in FIG. 1 and the like when the number of subcarriers is eight.
As shown in FIG. 4, each of the eight subcarriers can be represented as a sine wave having a phase corresponding to the value of data used for modulation.
Even if the amplitude of each of these subcarriers is not large, as shown in the center of FIG. 4, if the phases of all the subcarriers match, the amplitude of the transmission signal obtained by adding these subcarriers is large. A peak occurs.
[0029]
In this way, when a large peak occurs in the amplitude of the transmission signal, the peak portion is subjected to power amplification over the non-linear portion of the amplification characteristic of the power amplifier 126 (FIG. 1). The signal is distorted, and spurious signals are generated.
In order to solve this problem, a method using a high-power amplifier as the power amplifier 126 can be considered.
However, when this method is adopted, the power amplifier 126 is increased in size, power consumption and heat generation are increased, and the entire OFDM transmitter 1 must be increased in size and price.
[0030]
Alternatively, in order to solve this problem, a method of suppressing the amplitude of the transmission signal by simply limiting it so as not to exceed a predetermined threshold value can be considered.
However, simply limiting the amplitude of the transmission signal causes a lot of distortion in the transmission signal due to the suppression of the amplitude itself.
Therefore, the simple limitation of the amplitude of the transmission signal is not suitable as a solution to this problem.
According to the second OFDM transmitter 2 and the third OFDM transmitter 3 according to the present invention described below, it is possible to effectively eliminate the problems that occur in the first OFDM transmitter 1 described above.
[0031]
[Embodiment]
Embodiments of the present invention will be described below.
FIG. 5 is a diagram showing a configuration of the second OFDM transmitter 2 according to the present invention.
As shown in FIG. 5, the second OFDM transmitter 2Transmission data generation unit 10The peak suppression unit 20 and the transmission unit 12 are configured.
[0032]
As described with reference to FIG. 4, the second OFDM transmitter 2 effectively suppresses the amplitude peak generated in the transmission signal in the first OFDM transmitter 1 and distorts the component. A transmission signal with a small amount of data is transmitted.
Note that, among the constituent parts of the second OFDM transmitter 2, substantially the same components as those of the first OFDM transmitter 1 shown in FIG.
The peak suppression unit 20 isTransmission data generation unit 10Similarly, it can be realized by hardware means or software means such as the DSP circuit 14 (FIG. 2).
[0033]
Also in the second OFDM transmitter 2,Transmission data generation unit 10In the same manner as in the OFDM transmitter 1, digital transmission data is generated from digital transmission data input from an external device (not shown).
Transmission data generation unit 10Outputs the generated transmission data to the peak suppression unit 20.
[0034]
As shown in FIG. 5, the peak suppression unit 20 includes a delay unit 200, a limiter unit 202, subtraction units 204 and 206, and an FIR filter unit 22.
The peak suppression unit 20 is composed of these components.Transmission data generation unit 10The transmission data input from is processed, and the peak generated in the amplitude of the transmission signal generated by the D / A 120 (FIG. 1) of the transmission unit 12 is suppressed.
[0035]
Hereinafter, each component of the peak suppression unit 20 will be described.
FIG. 6 is a diagram schematically illustrating the operation of the peak suppression unit 20 illustrated in FIG.Transmission data generation unit 10(FIG. 1, FIG. 5) shows the relationship between the value of the transmission data generated and the threshold value, and (B) is output from the subtraction unit 204 of the peak suppression unit 20 (FIG. 5).Differential dataIndicates the value of.
FIG. 7 is a diagram schematically showing data values output from the limiter unit 202 of the peak suppressing unit 20 shown in FIG.
[0036]
In the peak suppression unit 20, the limiter unit 202 limits the value of the transmission data so as not to exceed a predetermined threshold.
That is, as shown in FIG.Transmission data generation unit 10When the value of the transmission data input from is greater than the positive threshold value +, the value of the portion larger than the transmission data threshold value + is defined as the threshold value +.
Further, as shown in FIG.Transmission data generation unit 10When the value of the transmission data input from is smaller than the negative region threshold −, the value of the portion smaller than the transmission data threshold − is defined as the threshold −.
[0037]
The limiter unit 202 limits the value of the transmission data as shown in FIG.
6A, the transmission data is converted into a transmission signal by the D / A 120 (FIG. 1) of the transmission unit 12 and amplified by the power amplifier 126 by experiment, calculation, simulation, or the like. In such a case, the transmission signal is set to a value that does not cause distortion.
[0038]
The subtraction unit 204 subtracts the output data of the limiter unit 202 shown in FIG. 7 from the transmission data shown in FIG. 6A to generate difference data shown in FIG. 6B, and the FIR filter unit 22 Output for.
[0039]
FIG. 8 is a diagram showing a configuration of the FIR filter unit 22 shown in FIG.
As shown in FIG. 8, the FIR filter unit 22 includes m (m is a positive integer) delay units 220-1 to 220-m that give a delay to input transmission data, and each of the delay units 220- The transmission data delayed by 1 to 220-m is multiplied by m + 1 multipliers 222-0 to 222-m and multipliers 222-0 to 222-m that respectively multiply the coefficients a0 to am. An adder 224 adds transmission data multiplied by a coefficient.
[0040]
FIG. 9 is a diagram illustrating an impulse response of the FIR filter unit 22 illustrated in FIGS. 5 and 8.
FIG. 10 is a diagram illustrating filter output data generated by the FIR filter unit 22 filtering the difference data generated by the limiter unit 202 (FIG. 5) and the subtracting unit 204 from the transmission data values illustrated in FIG. 4. It is.
The FIR filter unit 22 filters the difference data (FIG. 6B) input from the subtraction unit 204 using these components, and outputs the result to the subtraction unit 206.
[0041]
The FIR filter unit 22 exhibits an impulse response characteristic as illustrated in FIG. 9, for example, a bandpass filter having one of the subcarriers, for example, the highest frequency subcarrier No. 8 shown in FIG. 4 as a pass band. The (BPF) characteristic is shown.
The values of the respective sampling points of the difference data (FIG. 5) generated by the limiter unit 202 and the subtraction unit 204 from the transmission data illustrated in FIG. 4 are convolved by the FIR filter unit 22, and the filter output as shown in FIG. Data is obtained.
That is, in the example shown in FIG. 10, the difference data generated by the limiter unit 202 and the subtracting unit 204 is filtered by the FIR filter unit 22 showing the BPF characteristic with the subcarrier No. 8 illustrated in FIG. Components other than the subcarrier No. 8 band are removed.
[0042]
The delay unit 200 delays the transmission data by the processing time of the limiter unit 202, the subtraction unit 204, and the FIR filter unit 22, and outputs the transmission data to the subtraction unit 206.
That is, the delay unit 200 delays the transmission data to compensate for processing delays of the limiter unit 202, the subtraction unit 204, and the FIR filter unit 22, and the timing of the transmission data and the filter output data (FIGS. 5 and 8). Adjust.
[0043]
11 is a diagram illustrating transmission data (peak suppression transmission data) in which a peak is suppressed by the subtraction unit 206 illustrated in FIG. 5 subtracting difference data from the transmission data illustrated in FIG.
The subtraction unit 206 subtracts the filter output data input from the FIR filter unit 22 from the transmission data input from the delay unit 200, and suppresses a peak generated in the transmission data.
That is, as shown in FIG. 11, the subtraction unit 206 subtracts the filter output data (FIG. 10) generated by the FIR filter unit 22 from the transmission data (original waveform; FIG. 4) whose peaks are not suppressed. The peak suppression transmission data is generated and output to the transmission unit 12.
[0044]
As in the OFDM transmitter 1 (FIG. 1), the transmission unit 12 (FIG. 5) converts the peak suppression transmission data generated by the peak suppression unit 20 into an analog format, converts the frequency, and amplifies the power before transmission. To do.
[0045]
[Features of OFDM transmitter 2]
FIG. 12 is a diagram schematically showing the value of transmission data generated by the peak suppressing unit 20 shown in FIG.
For example,Transmission data generation unit 10When the value of the transmission data generated by is simply limited using the threshold value + and the threshold value − (FIG. 6A), the transmission signal generated from the transmission data limited in this way is referred to FIG. As can be seen, the waveform is discontinuous and contains a lot of distortion.
[0046]
On the other hand, if the difference data filtered by the FIR filter unit 22 is subtracted from the transmission data by the peak suppression unit 20, the value of the transmission data is suppressed, and peak suppression transmission data (FIG. 5) is obtained. The waveform of the transmission signal generated by the transmission unit 12 from the data is smooth as illustrated in FIG. 12 and does not include much distortion.
[0047]
Further, since the FIR filter unit 22 (FIGS. 5 and 8) passes only the band component of the specific subcarrier, the peak suppressing unit 20 reduces only the amplitude of the specific subcarrier and the other subcarriers. Does not decrease the amplitude.
Therefore, when the peak suppression unit 20 is used, it is possible to effectively suppress the peak while maintaining the subcarrier component included in the transmission data before processing.
[0048]
The amount of attenuation given to the specific subcarrier by the FIR filter unit 22 can be adjusted. By adjusting this amount of attenuation, the amount of attenuation given to the specific subcarrier by the peak suppressing unit 20 is included in one symbol length. It can be set to a level that does not affect the total amount of power that is generated.
In this way, by adjusting the attenuation amount given to the specific subcarrier by the peak suppressing unit 20, it is possible to minimize the degradation of the demodulation characteristics when receiving and demodulating the signal from the OFDM transmitter 2. .
[0049]
As described above, according to the OFDM transmitter 2 according to the present invention, it is possible to effectively suppress the peak of the amplitude generated in the transmission signal with a relatively small amount of hardware or calculation, and accompany the peak suppression. Transmission signal distortion can be reduced.
Further, according to the OFDM transmitter 2 according to the present invention, it is possible to effectively reduce the distortion of the transmission signal and prevent the band leakage, but the adverse effect on the demodulation characteristics on the reception side. It can be minimized.
[0050]
[Modification 1]
Hereinafter, a first modification of the OFDM transmitter according to the present invention will be described.
FIG. 13 is a diagram showing a configuration of the third OFDM transmitter 3 according to the present invention.
As shown in FIG. 13, the third OFDM transmitter 3 has a configuration in which the first peak suppression unit 20 of the second OFDM transmitter 2 (FIG. 5, etc.) is replaced with a second peak suppression unit 24. take.
The second peak suppression unit 24 replaces the FIR filter unit 22 with a plurality of FIR filter units 22-1 to 22-k (k is an integer of 2 or more, and FIG. 13 illustrates the case of k = 2). Further, a configuration in which a switching unit 208 and a value determination unit 210 are added is adopted.
Of the constituent parts of the OFDM transmitter 3 shown in FIG. 13, substantially the same parts as the constituent parts of the OFDM transmitters 1 and 2 shown in FIG. 1, FIG. .
[0051]
The FIR filter units 22-1 and 22-2 have substantially the same configuration as that of the FIR filter unit 22 of the OFDM transmitter 2 shown in FIGS. 5 and 8, and use different subcarriers as pass bands.
The FIR filters 22-1 and 22-2 pass one different subcarrier band among the subcarriers included in the transmission data, and output it to the switching unit 208 as filter output data.
[0052]
The switching unit 208 selects one of the filter output data output from the FIR filter units 22-1 and 22-2 according to the control of the value determination unit 210, and outputs the selected filter output data to the subtraction unit 206.
[0053]
The value determination unit 210 determines the quality of the peak suppression transmission data output from the subtraction unit 206, controls the switching unit 208 based on the determination result, and outputs the filter output data of the FIR filter units 22-1 and 22-2. Of these, one that gives peak quality transmission data with better quality is selected.
As an example of a criterion for determining the quality of the peak suppression transmission data by the value determination unit 210, for example, a criterion such as whether or not the value of the peak suppression transmission data exceeds a threshold value + or a threshold value by a certain number of samples. be able to.
Note that the switching of the switching unit 208 may be performed without being controlled by the value determining unit 210, for example, at regular time intervals or sampling intervals.
[0054]
[Modification 2]
Hereinafter, a second modification of the OFDM transmitter according to the present invention will be described.
FIG. 14 is a diagram showing a configuration of the fourth OFDM transmitter 4 according to the present invention.
As shown in FIG. 14, the fourth OFDM transmitter 4 connects the second OFDM transmitter 2 (FIG. 5 and the like) to a plurality of first peak suppression units 20-1 to 20-k (FIG. 14). The configuration is changed so as to include the case of k = 2.
Of the constituent parts of the OFDM transmitter 3 shown in FIG. 13, substantially the same parts as the constituent parts of the OFDM transmitters 1 and 2 shown in FIG. 1, FIG. .
[0055]
However, in the OFDM transmitter 4, the FIR filter units 22 (not shown in FIG. 14, see FIGS. 5 and 8) included in the peak suppression units 20-1 and 20-2 have different subcarriers. This band is defined as a pass band.
Further, the FIR filter unit 22 included in each of the peak suppression units 20-1 and 20-2 has a larger attenuation amount for the band component of the subcarrier to be passed than the FIR filter unit 22 of the OFDM transmitters 1 and 3. In other words, the output gain is adjusted to be small.
[0056]
In the OFDM transmitter 4,Transmission data generation unit 10Generates transmission data from transmission data and outputs the transmission data to the peak suppression unit 20-1 in the same manner as in the OFDM transmitters 1, 2, and 3 (FIGS. 1, 5, and 13).
[0057]
Similar to the peak suppression unit 20 in the OFDM transmitter 2, the peak suppression unit 20-1 attenuates a specific subcarrier band included in a portion of transmission data whose value exceeds a predetermined threshold value. The peak of transmission data is suppressed and output to the peak suppression unit 20-2.
[0058]
The peak suppression unit 20-2 is included in the transmission data of the part whose value exceeds a predetermined threshold, and the peak suppression unit 20-1 is different from the subcarrier band different from the subcarrier band to which the attenuation is applied. By giving attenuation, the peak of the transmission data is suppressed and output to the transmission unit 12.
[0059]
The transmission unit 12 converts the transmission data input from the peak suppression unit 20-2 into a transmission signal in the same manner as in the OFDM transmitters 1, 2, 3 (FIGS. 1, 5, and 13), and sets the frequency. This is converted, further amplified, and transmitted to the wireless line.
[0060]
That is, in the OFDM transmitter 4 (FIG. 14), the peak suppression units 20-1 and 20-2 are subject to restriction by gradually attenuating the values of the band components of the different subcarriers little by little. A peak suppression effect higher than that of the OFDM transmitters 2 and 3 (FIGS. 5 and 13) is obtained while minimizing adverse effects on each band component of the subcarrier.
[0061]
In the OFDM transmitter 4, for example, the output gain of the FIR filter unit 22 of the peak suppression unit 20-1 is set high, and the output gain of the FIR filter unit 22 of the peak suppression unit 20-1 is set low. If a difference is provided in the peak suppression amounts of the peak suppression units 20-1 and 20-2, a good transmission data peak suppression effect can be obtained.
In this case,Transmission data generation unit 10If the output gain of the FIR filter unit 22 of the peak suppression unit 20 of the stage close to is set high and the output gain of the FIR filter unit 22 of the peak suppression unit 20 of the subsequent stage is gradually set low, the peak of better transmission data An inhibitory effect can be obtained.
[0062]
【The invention's effect】
As described above, according to the amplitude limiting device of the present invention, it is possible to effectively suppress the peak value of the amplitude of a transmission signal such as a multicarrier communication system.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a first OFDM transmitter exemplified for explaining the background of the present invention;
FIG. 2 is a diagram illustrating a hardware configuration of a transmission data generation unit illustrated in FIG. 1;
FIG. 3 is a diagram illustrating a configuration of a quadrature modulation unit illustrated in FIG. 1;
FIG. 4 is a diagram showing, as a specific example, a peak generated in the amplitude of a transmission signal generated by the OFDM transmitter shown in FIG. 1 and the like when the number of subcarriers is eight.
FIG. 5 is a diagram showing a configuration of a second OFDM transmitter 2 according to the present invention.
6 is a diagram for schematically explaining the operation of the peak suppression unit shown in FIG. 5, in which (A) shows values and threshold values of transmission data generated by the transmission data generation unit (FIGS. 1 and 5); (B) is output from the subtraction unit of the peak suppression unit (FIG. 5).Differential dataIndicates the value of.
7 is a diagram schematically showing data values output from a limiter unit of the peak suppressing unit shown in FIG. 5. FIG.
8 is a diagram showing a configuration of an FIR filter unit 22 shown in FIG.
9 is a diagram illustrating an impulse response of the FIR filter section shown in FIGS. 5 and 8. FIG.
10 is a diagram illustrating filter output data generated by filtering the difference data generated by the limiter unit (FIG. 5) and the subtracting unit from the transmission data value illustrated in FIG. 4 by the FIR filter unit;
11 is a diagram illustrating transmission data (peak suppression transmission data) in which a peak is suppressed by the subtraction unit illustrated in FIG. 5 subtracting difference data from the transmission data illustrated in FIG. 4;
12 is a diagram schematically illustrating transmission data values generated by the peak suppressing unit illustrated in FIG. 5. FIG.
FIG. 13 is a diagram showing a configuration of a third OFDM transmitter according to the present invention.
FIG. 14 is a diagram showing a configuration of a fourth OFDM transmitter according to the present invention.
[Explanation of symbols]
1, 2, 3, 4... OFDM transmitter,
10 ...Transmission data generator,
100 ... S / P,
102 ... mapping unit,
104 ... IFFT part,
110: Quadrature modulation unit,
112 ... Carrier wave generation unit,
114... Mixer section,
116... Phase shift part,
118... Addition unit,
12: Transmitter,
120 ... D / A,
122 ... Local transmission circuit,
124... Frequency conversion circuit,
126... Power amplifier,
128 ... antenna,
20, 24... Peak suppression part,
200 ... delay part,
202 ... limiter unit,
204, 206 ... subtracting unit,
208 ... switching part,
210 ... value determination unit,
22 ... FIR filter part,
220 ... delay part,
222... Multiplication unit,
224 ... adder,

Claims (5)

A digital difference signal indicating a difference between a limit value determined with respect to the amplitude of the target signal in a digital target signal subject to amplitude limitation and a difference between the limit value and digital processing a difference signal generating means for generating a,
First filtering means for filtering the generated difference signal by digital processing and allowing only a predetermined band component of the difference signal to pass as a first filtering signal;
An amplitude limiting device comprising: amplitude limiting means for limiting the amplitude of the target signal by subtracting the passed first filtered signal from the target signal by digital processing . Connected in series,
  The differential signal generating means;
  Said first filtering means;
  The amplitude limiting means;
  A plurality of amplitude limiting units each having
  Have
  Each of the amplitude limiting units limits the amplitude of the target signal input from the outside or the target signal whose amplitude is limited by the amplitude limiting unit connected as a previous stage.
  The amplitude limiting device according to claim 1. Mapping means for mapping a digital transmission signal to be transmitted to a plurality of symbols;
IFFT processing means for performing IFFT processing on a plurality of symbols obtained by the mapping and generating a digital multi-carrier composite signal including a plurality of subcarrier components;
Amplitude limiting is performed using the generated multi-carrier composite signal as the target signal.
The amplitude limiting device according to claim 1 or 2 . The first filtering means passes each one or more of the subcarrier components included in the multi-carrier composite signal with a predetermined output gain to obtain the first filtering signal.
The amplitude limiting device according to claim 3 . A second filtering means for filtering the differential signal by digital processing and allowing only one of a plurality of subcarriers included in the differential signal to pass as a second filtered signal;
  Selecting means for selecting one of the first filtered signal and the second filtered signal that are passed through, and which gives the target signal of higher quality when used for limiting the amplitude of the target signal;
  Further comprising
  The amplitude limiting means limits the amplitude of the target signal by subtracting the selected first filtering signal or second filtering signal from the target signal.
  The amplitude limiting device according to claim 3.

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