CN100502378C - Circuit and method for suppressing peak-to-average ratio in OFDM system - Google Patents

Abstract

The present invention relates to the technical field of digital communication, in particular to a circuit and method for suppressing signal peak power and reducing peak-to-average ratio in an OFDM communication system, including the following operations of processing input data in sequence: input data Perform oversampling and perform IDFT transformation; first amplify the oversampled data after transformation and then perform clipping operation; perform DFT transformation on the clipped data to remove out-of-band noise, and then perform multiple reduction; and the data The data is output after performing OFDM modulation (N-point IDFT); the amplification factor in the clipping operation is the same as the reduction factor in the denoising operation. The present invention has a small bit error rate, can use common receiving circuits, and is easy to implement. After using the operation of the present invention, PAPR is reduced to about 7db.

Description

Circuit and method for suppressing peak-to-average ratio in OFDM system

technical field

The invention relates to the technical field of digital communication, in particular to a circuit and method for suppressing signal peak power and reducing peak-to-average ratio in an OFDM communication system.

Background technique

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation method with high channel utilization. It has good anti-fading performance and can realize parallel transmission of data. With the rapid development of digital signal processing technology and With the wide application of large-scale integrated circuits, OFDM has received widespread attention, especially in the field of high-speed digital communications.

In the OFDM communication system, multiple carriers with a synchronous relationship in frequency are used to modulate the signal. Since the envelope values of each carrier are statistically independent, as the number of carriers increases, the ratio of the peak value to the average power ratio of the superimposed signal, That is, the value of Peak-to-Average power ratio (PAPR) is larger. Therefore, the dynamic range of the modulated signal is quite large, which requires the power amplifier in the system to have a high linear dynamic range to avoid spectral spread and nonlinear distortion of the transmitted signal. At the same time, the subsequent D/A converter is also required to have a larger conversion bandwidth, which increases the system cost and implementation difficulty.

At present, there are many ways to reduce PAPR, and we can roughly divide these technologies into two categories: one is to properly process the input code stream before the OFDM multiplexer. For example, the method of packet coding for OFDM input data can reduce the independence of each signal of the multiplexer, thereby reducing the probability of signal peak-to-peak superposition, thereby reducing PAPR; or using a partial transmission sequence method, by reducing the superposition time The number of signals, thereby reducing the PAPR; there is also a way to select the mapping, that is, through mapping, all possible combinations of the code streams are generated, and then a combination scheme is selected to make the PAPR of the superimposed signal after IFFT transform minimum. It can be seen from the above introduction that the biggest disadvantage of this type of method is that it requires a large amount of calculation.

The other is to process the signal after the OFDM multiplexer. The most direct and effective way is to limit the analog signal. However, clipping is a nonlinear process, which will cause severe in-band interference and out-of-band noise, thereby reducing the bit error rate performance and spectral efficiency of the entire system.

An existing method for processing signals after the OFDM multiplexer is: Ochiai, H., Imai, H. In the paper Performance analysis of deliberately clipped OFDM signals (Communications, IEEE Transactions on, Volume: 50, Issue: 1, Jan.2002 Pages: 89-101) talked about a method of oversampling and limiting filtering to reduce PAPR, its structure is shown in Figure 1, fill in the tail of the input signal, and then perform IDFT (Inverse Discrete Fourier Transform (inverse discrete Fourier transform) transform (J is the oversampling factor), the output data is sent to the limiter for limiting operation, and the data output from the limiter is directly sent to DFT (Discrete Fourier Transform discrete Fourier transform ) module performs JN-point DFT transformation. After the data is restored, the out-of-band noise is removed to become N data for N-point IDFT transformation. The PAPR of the output data is improved compared with the original one.

We found that this method of reducing PAPR by oversampling and limiting filtering makes the data bit width more effective and greatly reduces the out-of-band interference generated by limiting, but there are the following problems: 64_QAM (Quadrature Amplitude Modulation Quadrature Amplitude Modulation) , A/D is 8 bits as an example: Assume that in 64_QAM encoding, the maximum amplitude is 127, to obtain a smaller PAPR, the maximum Amax is about 10, the bit width has not been used more effectively, and because the limit value is too small to use A general receiving circuit will generate serious bit errors.

Can a specially designed receiving circuit be used to solve the bit error problem? Hangjun Chen, Haimovich, A. In the paper An iterative method to restore the performance of clipped and filtered OFDM signals. (Communications, 2003.ICC'03.IEEE International Conference on, Volume: 5, 11-15 May 2003Pages: 3438-3442vol.5), as shown in Figure 2, where $a=1-e^{{-\mathrm{\γ}}^2}+\frac{\sqrt{\mathrm{\π}}}{2}\mathrm{erfc}\left(\mathrm{\γ}\right),$ We found that the receiver requires the receiving part to contain the information of the sending part, which cannot fully adapt to the requirements of various transmitting systems, and the receiving circuit also uses the same structure as the sending circuit, which makes the circuit too complicated.

Contents of the invention

The present invention mainly aims at the shortcomings of the above methods, and provides a peak-to-average ratio suppression method of limiting filtering, which can greatly improve the PAPR value of the signal.

A circuit for suppressing peak-to-average ratio in an OFDM system disclosed by the present invention includes the following sequentially connected modules for processing input data: oversampling the input data, adding 0 information after the data and performing IDFT transformation (Inverse Discrete Fourier Transform discrete Fourier inverse transform) oversampling module; the limiter module that performs clipping operations on the transformed oversampled data; removes the clipped data after DFT transform (Discrete Fourier Transform discrete Fourier transform) A denoising module for out-of-band noise; and an output module for outputting data after IDFT transformation is carried out to data; it is characterized in that the function of the limiting module is to amplify the data from the oversampling module before limiting Amplitude operation; Simultaneously, the function of the denoising module is to remove out-of-band noise after the data DFT transformation from the limiting module, and then perform multiple reduction; the amplification factor in the limiting module and the denoising module The reduction factor is the same.

A method for suppressing peak-to-average ratio in an OFDM system disclosed by the present invention includes the following steps of sequentially processing input data: the first step is oversampling, oversampling the input data, adding 0, And perform IDFT transformation; the second step is clipping, and the data from the first step of oversampling is clipped; the third step is denoising, and the data after clipping is subjected to DFT transformation to remove out-of-band noise; the fourth step Output, carry out IDFT transformation to the output data after the third step denoising; it is characterized in that, in the second step limiting, the data from the first step oversampling is first amplified and then Carry out clipping operation; Simultaneously in described the 3rd step denoising, remove the out-of-band noise after the data DFT transformation from the clipping module, also will carry out multiple reduction again; The amplified in the described second step clipping The multiple is the same as the multiple of reduction in the third step of denoising.

The circuit and method for suppressing the peak-to-average ratio in the OFDM system disclosed by the present invention amplify the input data before the clipping operation, and the parameter is n1; restore the data after the JN point DFT transformation, the parameter is 1/n1, which increases the average power, makes the data bit width more effectively used and reduces the bit error rate; the peak value in the limiter is not the peak value of the system, but the value set by simulation, The scope of the limit value is the component (real part and imaginary part), and a balance value is selected between the bit error rate and the suppression of the PAPR effect. Amplification is performed before data output after N-point IDFT to ensure maximum utilization of the data range. The bit error rate of the present invention is small, and general receiving circuits can be used.

Description of drawings

In order to further illustrate the technical content of the present invention, the following detailed description is as follows in conjunction with the embodiments and accompanying drawings, wherein:

Figure 1 is a functional block diagram of oversampling and limiting filtering.

Figure 2 is the prior art Hangjun Chen, Haimovich, A. An iterative method to restore the performance of clipped and filtered OFDM signals in the text. A receiver proposed in (Communications, 2003.ICC'03.IEEE International Conference on, Volume: 5, 11-15 May 2003 Pages: 3438-3442 vol.5).

Fig. 3 is a functional block diagram of the present invention.

Fig. 4 is the simulation effect performed according to the present invention. The ordinate is the probability (CCDF) that the peak-to-average ratio exceeds a certain threshold z, and the abscissa is the PAPR value.

Detailed ways

The technical solution disclosed by the present invention is as shown in Figure 3, an achievable peak-to-average ratio suppression method based on oversampling and clipping filtering, which has the following characteristics: for each transformation unit, fill in the tail of the input signal to obtain JN Then carry out the IDFT (Inverse DiscreteFourier Transform discrete Fourier Transform) transformation of JN points (J is the oversampling factor), and the output data will be amplified by a certain multiple according to the simulation results, set the magnification factor to n1, and then sent to the limiter The limiting operation is performed in the limiter, and the data output from the limiter is directly sent to the DFT (DiscreteFourier Transform Discrete Fourier Transform) module for JN-point DFT transformation, and the output data is removed from the out-of-band noise, and then amplified (1/n1 ) multiples and restore to N data, and then perform N-point IDFT transformation, and then enlarge n2 times, the output data is significantly improved compared with the original PAPR.

Key steps of the present invention and its realization circuit are described in detail as follows:

1. Oversampling module: Oversampling the input data and performing JN point IDFT transformation

When the signal is sampled according to the Nyquist sampling rate, the sampling points are distributed independently of each other, and it is easy to deduce the theoretical formula of the PAPR statistical characteristics of the signal at this time, which has become the theoretical basis of many PAPR suppression methods. The research results also pointed out that when the discrete signal is restored to a continuous signal by D/A, there will be a PAPR rebound phenomenon, especially for the discrete signal obtained according to the Nyquist sampling rate, the PAPR rebound is the most serious. Therefore, the effect of using oversampled signals for PAPR suppression will be more obvious. Our approach is also based on this idea.

We add some 0 information to the original data stream (that is, oversampling), which can be added between each adjacent valid data, or after the data, and perform IDFT transformation of JN point. The following description takes adding 0 information after the data as an example.

As shown in Figure 3, use A={A ₀ , A ₁ , A ₂ ,..., A _N-1 } to represent the original signal sequence used for transmission in the OFDM system (the number of subcarriers is N), where A _k is the complex data on subcarrier k. After sampling, modulation and phase shifting (phase shifting is not included in our method, nor can it play a role in reducing PAPR, here is just for the convenience of later analysis), the transmission signal becomes:

in: $A_k^{\&prime;}=\left\{\begin{array}{cc}{A}_k& k<N\\ 0& k\&Greater\; Equal;N\end{array}\right.,$

2. Limiting module: perform limiting operation after amplifying the transformed oversampled data

As mentioned earlier, if you directly clip the data, you will find that to obtain a lower PAPR, the utilization rate of the bit width is low, and because the clipping value is too small, most of the transformed data will be destroyed. Use The general receiving circuit will produce serious bit errors, so we need to process the data to some extent.

Our processing method is to amplify the data to a certain extent to increase the average power, so that we can appropriately increase the limit value in order to obtain a better effect of suppressing PAPR. In order to avoid introducing the square root when the hardware circuit is implemented, we The objects of the clipped value are the real and imaginary parts of the output value.

As shown in Figure 3, we operate on the signal as follows:

Suppose its nth output sample point is ${\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}=\mathrm{Re}\left({\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}\right)+\mathrm{jIm}\left({\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}\right),$ Then there are:

$\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\\ {\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\end{array}\right.<span\; class="notranslate">\; ,</span>$ $\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\\ {\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\end{array}\right.$

Where A _max is the maximum value of the signal amplitude.

Define Clipping Rate $\mathrm{\&gamma;}=\frac{A_{\max }}{\sqrt{P_{\mathrm{in}}}},$ $\sqrt{P_{\mathrm{in}}}=\sqrt{\underset{\mathrm{no}=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left|x\left(\mathrm{no}\right)\right|}^2}$

We found that: 1) Amplifying the signal after IDFT at point JN by n1 times can increase the Pin value of the signal, and then reduce the clipping rate γ value, thereby effectively reducing the PAPR value. Therefore, from the perspective of reducing the PAPR value, it is hoped that the larger the value of n1, the better. 2) The principle of selecting the Amax value is to ensure that most of the data will not be lost after the clipping operation, which is conducive to the correct transmission of data, so it is hoped that the smaller the value of n1, the better. Combining the above factors, it can be seen that the selection of the value of n1 is contradictory, so in practical applications, we need to adopt a compromise solution.

3. Denoising module: perform JN point DFT transformation on the clipped data to remove out-of-band noise, and then perform multiple reduction

The general limiting filtering method for suppressing PAPR is a nonlinear process, and one of its disadvantages is that it introduces serious out-of-band noise, thereby reducing the bit error rate performance and spectral efficiency of the entire system.

After the previous oversampling, JN point IDFT transformation, multiple amplification, clipping, and JN point DFT operation, we have achieved the effect of suppressing PAPR. This step is to remove the out-of-band noise introduced by clipping. As shown in Figure 3, the implementation method is shown in the following process:

After JN point DFT processing, the distorted JN point data sequence is:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; \{</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; N</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; JN</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; \}</span>$

If the out-of-band interference is discarded, the sequence of length N after the original data is distorted is:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; \{</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; A</span>}}}_{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; \}</span>$

4. Output module: perform OFDM modulation (N-point IDFT) on the data and properly amplify the output data

After the previous processing, the PAPR value of the data at this time has been greatly reduced. We perform real OFDM modulation on the data, as shown in Figure 2. The sequence uses N-point IDFT to perform ordinary OFDM modulation and then amplifies the n2 output.

Finally, the output data is multiplied by a coefficient n2 in order to ensure the maximum utilization of the data range.

The technical solution of the present invention will be further described below through specific examples. The embodiment is the application of the wireless local area network 802.11a protocol system of the present invention, and this system adopts 64QAM modulation mode. The data bit width is 8 bits, the oversampling factor J=2, the scaling multiple after the JN point IFFT transformation is n1=8, the limiting value is 70, and the zooming multiple after the N point IDFT is n2=4 times. In order to observe the improvement of our PAPR, we use the curve of the probability (CCDF)-PAPR value of the peak-to-average ratio exceeding a certain threshold z as the test effect of our method. The specific implementation method is as follows:

1. Oversampling module: Oversampling the input data and performing JN point IDFT transformation

After our analysis, for the oversampling factor, J=2 and J=16 have the same effect on suppressing PAPR, but it is more difficult to choose the latter hardware implementation (16×64 point IDFT transformation), so we choose the oversampling factor to be 2 , that is, 64 0s are added after each IDFT transformation unit (64) and then sent to the 128-point IDFT transformation unit.

2. Limiting module: after the transformed oversampling data is amplified, the limiting operation is performed. After establishing a model and simulating, we determine several sets of parameters.

The first group: n1＝8 n2＝4 Amax＝70;

The second group: n1＝8 n2＝4 Amax＝127;

The third group: n1＝16 n2＝4 Amax＝127;

The fourth group: n1＝8 n2＝4 Amax＝40;

The fourth group of parameters has the best effect of suppressing PAPR, but we found that its bit error rate is high and cannot be recovered. In the comparison between the first group and the third group, although the PAPR suppression effect of the first group is worse than that of the third group, the effect of the received 64QAM constellation diagram is significantly better than that of the third group, and finally we select the first group of parameters is our best parameter combination. The simulation results are shown in Figure 4.

3. Denoising module: perform JN-point DFT transformation on the data after clipping and perform multiple restoration and remove out-of-band noise

For each IDFT unit of 128 data, the following 64 points are directly removed, and each processing unit becomes 64 data.

4. Output: perform OFDM modulation (N-point IDFT) on the data and properly amplify the output data

Every 64 data with out-of-band noise removed is subjected to 64-point IDFT transformation, and the data is output after being amplified by 4 times.

The peak-to-average ratio of the system without PAPR suppression processing is about 11db. After the above method, the PAPR is reduced to about 7db, as shown in FIG. 4 , which is the simulation effect according to the present invention. The ordinate is the probability (CCDF) that the peak-to-average ratio exceeds a certain threshold z, and the abscissa is the PAPR value. It can be seen that the present invention not only effectively suppresses PAPR, but also does not require specific information for the receiving circuit, and is easy to implement.

Claims (8)

1. A circuit for suppressing peak-to-average ratio in an OFDM system, comprising the modules connected in sequence and processing input data: input data is oversampled, and 0 information is added after the data and IDFT transformation (Inverse DiscreteFourier Transform (Discrete Fourier Transform) oversampling module; the clipping module that performs clipping operation on the oversampled data after the transformation; the data after clipping is subjected to DFT transform (DiscreteFourier Transform discrete Fourier transform) to remove out-of-band noise Denoising module; With the output module that outputs data after IDFT transformation is carried out to data; It is characterized in that, the function of described clipping module is to carry out clipping operation after first amplifying the data from described oversampling module; Simultaneously The function of the denoising module is to remove the out-of-band noise after the data DFT transformation from the limiting module, and then perform multiple reduction; the multiple of amplification in the limiting module and the multiple of reducing in the denoising module same. 2. The circuit for suppressing the peak-to-average ratio in the OFDM system according to claim 1, wherein the amplification factor in the limiting module and the reduction factor in the denoising module are both equal to 8 , the output module performs IDFT transformation on the data, and then performs 4 times amplification to output the data. 3. The circuit for suppressing the peak-to-average ratio in the OFDM system according to claim 1 or 2, wherein the limiting operation of the limiting module is: the nth output of the limiting module sample point is ${\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}=\mathrm{Re}\left({\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}\right)+\mathrm{j\; Im}\left({\widetilde{\mathrm{the\; s}}}_{\mathrm{no}}\right),$ Before the clipping operation, the sample point is Sn'=Re(Sn')+jIm(Sn'), then: $\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\\ {\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\end{array}\right.$ $\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\\ {\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}\end{array}\right.$ Where A _max is the maximum value of the signal amplitude. 4. The circuit for suppressing the peak-to-average ratio in the OFDM system according to claim 3, wherein the maximum value A _max of the limited signal amplitude of the limiting module is equal to 70. 5. A method for suppressing peak-to-average ratio in an OFDM system, comprising the steps of processing input data in the following order: the first step of oversampling, oversampling the input data, adding 0 after the data, and performing IDFT transformation; the second step of clipping is to perform a clipping operation on the data from the first step of oversampling; the third step is denoising, and the data after clipping is subjected to DFT transformation to remove out-of-band noise; the fourth step is output, Output data after the IDFT transformation is carried out to the data output after the third step of denoising; It is characterized in that, in the second step of limiting, the data from the first step of oversampling is first amplified and then limited Amplitude operation; Simultaneously in described the 3rd step denoising, remove the out-of-band noise after the data DFT transformation from the limiting module, also will carry out multiple reduction again; The multiple of amplification in the described second step limiting and The reduction factor in the third step of denoising is the same. 6. The method for suppressing peak-to-average ratio in an OFDM system according to claim 5, characterized in that the amplification factor in the second step of limiting and the third step in denoising The reduction factor is equal to 8. In the fourth step output, the data will be magnified by 4 times to output the data after I-IDFT transformation. 7. The method for suppressing peak-to-average ratio in an OFDM system according to claim 5 or 6, wherein the limiting operation in the second step of limiting is: the output of the limiting module of

8. The method for suppressing the peak-to-average ratio in an OFDM system according to claim 7, wherein the maximum value A _max of the signal amplitude in the second step of limiting is equal to 70.

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