CN116155673A - Few-mode optical fiber communication method for reducing PAPR of OFDM signal - Google Patents

Abstract

The invention discloses a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal, comprising: obtaining a communication signal to be processed, and performing preprocessing to convert it into a time domain signal; Perform time-domain clipping; convert the time-domain signal after time-domain clipping into a frequency-domain signal, and perform ACE constraints; based on IFFT transformation, convert the ACE-constrained frequency-domain signal into a time-domain signal; introduce adjustment factors to regulate ACE constraints The amplification factor of the time-domain signal is amplified, and the amplified signal is superimposed on the signal before time-domain clipping to reduce the PAPR; the signal after the PAPR reduction is processed and then transmitted. Based on the traditional ACE algorithm, the present invention cuts the time-domain signal, and expands the area of the generated constellation symbols in the frequency-domain signal, so as to realize the reduction of PAPR.

Description

A few-mode optical fiber communication method for reducing the PAPR of OFDM signals

Technical Field

The invention relates to a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal, and belongs to the technical field of optical fiber communication.

Background Art

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier data transmission technology with the advantages of high data rate, strong resistance to multipath fading, and high spectrum utilization. It is widely used in various communication systems. However, OFDM signals have a very high peak-to-average power ratio (PAPR), which requires the system power amplifier to have a wide linear dynamic range. Otherwise, nonlinear distortion will occur once it exceeds the range, resulting in a decrease in communication quality. Therefore, how to effectively suppress PAPR has become one of the key issues that OFDM technology urgently needs to solve.

In previous studies, there are many solutions to overcome the well-known PAPR problem, mainly in the following three categories: distortion technology, coding technology and probabilistic scrambling technology. Distortion technology, such as shearing, but this process is nonlinear and will reduce the bit error rate. Coding technology, such as block coding, Golay complementary coding and Reed-Muller code, however, the coding process is relatively complex, which will increase the computational complexity of the OFDM system transmitter and receiver. In addition, because block coding increases redundant information, it reduces bandwidth utilization and system throughput. The most typical probabilistic methods are selective mapping method and partial transmission sequence method. Although they can achieve PAPR reduction through distortion-free schemes, the main disadvantages of these distortion-free algorithms are that the useful data rate may be adversely reduced, and they may also need to send sideband information to the receiver.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a few-mode fiber communication method for reducing the PAPR of OFDM signals. The present invention aims at the problem of excessively high PAPR faced in OFDM systems. On the basis of the original ACE-POCS algorithm, an adjustment factor and a least squares approximation technique are introduced to process signals in the time domain and frequency domain, and the signals are cropped in the time domain. In the frequency domain, the generated constellation symbols are appropriately expanded to achieve a reduction in PAPR, while speeding up the iteration speed and reducing the computational complexity.

To achieve the above object, the present invention provides a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal, comprising the following steps:

Obtain the communication signal to be processed, and perform preprocessing to convert it into a time domain signal;

The converted time domain signal is superimposed with time domain complex noise to perform time domain clipping;

Convert the time domain signal after time domain clipping into a frequency domain signal and perform ACE constraints;

Based on IFFT transformation, the frequency domain signal after ACE constraint is converted into a time domain signal;

An adjustment factor is introduced to adjust the amplification factor of the time domain signal after ACE constraint, the time domain signal is amplified, and the amplified signal is superimposed with the signal before time domain clipping to reduce PAPR;

The signal with reduced PAPR is processed and then transmitted.

Further, the preprocessing includes:

Performing a constellation mapping operation on the communication signal to be processed to generate a corresponding constellation diagram;

After the constellation diagram is subjected to serial-to-parallel conversion, an IFFT transform is performed to obtain a time domain signal.

Furthermore, the time domain signal after time domain clipping is converted into a frequency domain signal through FFT transformation.

Furthermore, the ACE constraints include:

The constellation points at the vertex and four sides of the constellation diagram are projected to the region with increased boundaries, while the values of the constellation points in all remaining directions are set to zero.

Furthermore, the step of superimposing time domain complex noise on the converted time domain signal and performing time domain clipping includes:

；

;

为时域裁剪后的时域复数信号；

为时域裁剪前的时域复数信号；

为叠加的时域复数噪声；in,

is the time domain complex signal after time domain cropping;

is the time domain complex signal before time domain clipping;

is the superimposed time domain complex noise;

；

;

为时域裁剪后的时域复数信号；

为时域裁剪前的时域复数信号；

为设定的幅度阈值；

为时域裁剪前时域复数信号的相位值；

为ifft点数；n为取值范围为

的正整数；j为虚数单位，等于-1的平方根。in,

is the time domain complex signal after time domain cropping;

is the time domain complex signal before time domain clipping;

is the set amplitude threshold;

is the phase value of the time domain complex signal before time domain clipping;

is the number of ifft points; n is the value range

is a positive integer; j is the imaginary unit, equal to the square root of -1.

Furthermore, the step of adjusting the amplification factor of the time domain signal after the ACE constraint, amplifying the time domain signal, and superimposing the amplified signal with the signal before the time domain clipping includes:

；

;

为时域裁剪前的时域复数信号；

为放大调节因子；

是由

先经过fft变换，接着进行ACE约束，然后进行ifft变换生成的时域信号；

为叠加的时域复数噪声；n为取值范围为

的正整数。in,

is the time domain complex signal before time domain clipping;

is the amplification adjustment factor;

Is

First, it is transformed by fft , then ACE constraint is performed, and then ifft transform is performed to generate the time domain signal;

is the superimposed time domain complex noise; n is the value range of

A positive integer.

；Further,

;

；

为叠加的时域复数噪声；

为时域裁剪后的信号；

、

；

为ifft点数；n为取值范围

的正整数。Where Q is the adjustment factor,

;

is the superimposed time domain complex noise;

is the signal after time domain clipping;

,

;

is the number of ifft points; n is the value range

A positive integer.

Furthermore, the signal after the PAPR is reduced is processed and then transmitted, comprising:

Add a cyclic prefix to the superimposed signal, perform digital signal processing, and convert it into an optical signal;

Transmit the optical signal through few-mode optical fiber;

After the transmission is completed and the optical signal is received, OFDM demodulation processing is performed on the optical signal.

The beneficial effects achieved by the present invention are:

On the one hand, the present invention is based on the traditional ACE algorithm, which crops the time domain signal and regionally expands the generated constellation symbols in the frequency domain signal to achieve the reduction of PAPR.

On the other hand, the present invention introduces an adjustment factor to speed up the iteration speed, solves the problem that the traditional ACE algorithm converges too slowly and cannot find the optimal value, and improves the practical application value of the traditional ACE algorithm;

At the same time, the present invention performs ACE constraints on the frequency domain signal after clipping and conversion. After the constellation points move and diverge, the fault tolerance of each constellation point after various noise disturbances can be greatly increased, and the minimum Euclidean distance will not be affected during the expansion of the constellation points, which can effectively reduce the bit error rate of the OFDM system.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the constellation diagram after constellation expansion, taking 16-QAM as an example;

FIG2 is a CCDF diagram of the ACE-POCS algorithm for optimizing the PAPR of the OFDM system;

FIG3 is a constellation diagram after the operation of the adaptive flexible ACE algorithm in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

FIG4 is a waveform diagram before operation by an adaptive flexible ACE algorithm in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

FIG5 is a waveform diagram after operation of an adaptive flexible ACE algorithm in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

6 is a diagram showing the optimization effect of an adaptive flexible ACE algorithm on PAPR in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

7 is a bit error diagram of an adaptive flexible ACE algorithm in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

8 is a diagram of selecting a Q value in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention;

9 is a graph showing the relationship between the Q value and the bit error rate in a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal provided in an embodiment of the present invention;

FIG10 is a partial enlarged view of point A in FIG9 ;

11 is a communication system block diagram of a few-mode fiber communication method for reducing the PAPR of an OFDM signal provided in an embodiment of the present invention;

12 is a diagram showing the effect of an adaptive and flexible ACE algorithm on the bit error rate of an optical OFDM system in a few-mode fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention.

Implementation

The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

As shown in FIG2 , it is a CCDF diagram of the ACE-POCS algorithm for optimizing the PAPR of the OFDM system. It is easy to know that the traditional ACE algorithm has the problem of slow convergence speed, which is reduced by about 1.5 dB after 2 iterations. In view of the problems of the ACE-POCS algorithm, the embodiment of the present invention provides a few-mode fiber communication method for reducing the PAPR of the OFDM signal. As shown in FIG3 to FIG12 , the present invention introduces an adjustment factor on the basis of the least squares approximation, so that the amplitude of the peak elimination signal quickly approaches the original shear noise, accelerates the iteration speed, solves the problem that the traditional ACE algorithm has slow convergence speed and cannot find the optimal value, and improves the practical application value of the traditional ACE algorithm; based on the traditional ACE algorithm, the present invention crops the time domain signal and performs regional expansion on the generated constellation symbol in the frequency domain signal to achieve the reduction of PAPR; the present invention performs ACE constraints on the cropped and converted frequency domain signal, and after the constellation point moves and diverges, the fault tolerance rate of each constellation point after various noise disturbances can be greatly increased, and the minimum Euclidean distance will not be affected during the expansion of the constellation point, which can effectively reduce the bit error rate of the OFDM system.

As shown in FIGS. 3 to 12 , the present invention provides a few-mode optical fiber communication method for reducing the PAPR of an OFDM signal, as shown in FIG. 11 , comprising the following steps:

Step 1: Obtain the communication signal to be processed, perform preprocessing, and convert the signal into a time domain signal:

The preprocessing includes: performing constellation mapping modulation on the communication signal to be processed to generate a corresponding constellation diagram;

The constellation diagram modulated by constellation mapping is subjected to a serial-to-parallel conversion operation and an IFFT transformation to obtain a time domain signal after preprocessing.

Step 2: Add time domain complex noise to the converted time domain signal and perform time domain cropping:

First, set the clipping threshold, and then perform clipping according to the following formula:

；

;

为时域裁剪后的时域复数信号；

为时域裁剪前的时域复数信号；

为叠加的时域复数噪声；in,

is the time domain complex signal after time domain cropping;

is the time domain complex signal before time domain clipping;

is the superimposed time domain complex noise;

；

;

为时域裁剪后的时域复数信号；

为时域裁剪前的时域复数信号；

为设定的幅度阈值；

为时域裁剪前时域复数信号的相位值；

为ifft点数；n为取值范围为

的正整数；j为虚数单位，等于-1的平方根。in,

is the time domain complex signal after time domain cropping;

is the time domain complex signal before time domain clipping;

is the set amplitude threshold;

is the phase value of the time domain complex signal before time domain clipping;

is the number of ifft points; n is the value range

is a positive integer; j is the imaginary unit, equal to the square root of -1.

Step 3: Convert the time domain signal after time domain cropping into a frequency domain signal and perform ACE constraints:

Firstly, the time domain signal after time domain clipping is subjected to FFT fast Fourier transform to convert it into frequency domain signal;

Then perform ACE constraints on the transformed frequency domain signal:

As shown in FIG3 , the constellation points in the outer corners and four sides of the constellation diagram are first projected to the region with an increased boundary, and then the values of the constellation points in all remaining directions are set to zero.

Step 4: Based on the IFFT inverse fast Fourier transform, the frequency domain signal after ACE constraint is converted into a time domain signal.

Step 5: Introduce the adjustment factor to adjust the amplification factor of the time domain signal after IFFT transformation, amplify the time domain signal, and superimpose the amplified signal with the signal before time domain clipping to achieve the purpose of reducing the OFDM signal PAPR:

；

;

为时域裁剪前的时域复数信号；

为放大调节因子；

是由

先经过fft变换，接着进行ACE约束，然后进行ifft变换生成的时域信号；

为叠加的时域复数噪声；n为取值范围为

的正整数。in,

is the time domain complex signal before time domain clipping;

is the amplification adjustment factor;

Is

First, it is transformed by fft , then ACE constraint is performed, and then ifft transform is performed to generate the time domain signal;

is the superimposed time domain complex noise; n is the value range of

A positive integer.

；in,

;

；

为叠加的时域复数噪声；

为时域裁剪后的信号；

、

；

为ifft点数；n为取值范围为

的正整数。Where Q is the adjustment factor,

;

is the superimposed time domain complex noise;

is the signal after time domain clipping;

,

;

is the number of ifft points; n is the value range

A positive integer.

Step 6: Process the superimposed signal after the PAPR is reduced and then transmit it:

Firstly, a cyclic prefix CP is added to the signal after the PAPR is reduced after superposition, and the digital signal processing process is completed;

Then, an arbitrary waveform generator (AWG) is used to convert the digital signal into an electrical signal, which is then converted into an optical signal via a Mach-Zehnder modulator (MZM).

The optical signal is passed through the optical splitter and divided into 4 modes of optical signals, and then the 4 modes of optical signals are combined into one in the multi-plane optical converter MPLC and transmitted in a 5 km few-mode optical fiber;

After transmission to the receiving end, digital signal processing is performed. The present invention adopts conventional OFDM modulation processing. Because the constellation points can only be expanded to the specified area during transmission, the erroneous demodulation at the receiving end caused by the movement of the constellation points is effectively avoided. At the same time, no additional computational complexity is added in this process, which is also an advantage that other PAPR reduction algorithms do not have.

Regarding the value range of Q:

。In the process of studying the Q value range, several OFDM signals are first randomly generated. In the embodiment of the present invention, for 16-QAM, 200 groups of OFDM signals are selected, as shown in Figure 8. The points in the color area 1 are the original PAPR values, and the points in the color area 2 are the PAPR values processed by the method of the present invention. The original PAPR values are concentrated in the range of 6 to 10. In order to reduce the Q value for any randomly generated OFDM signal, for 16-QAM, the present invention selects the Q value range of

.

When studying the relationship between the Q value and the bit error rate, this embodiment takes a Q value every 0.1. According to Figures 9 and 10, it can be seen that a small change in the Q value on the bit error rate will not have a significant impact on the bit error rate. In addition, we can also see that a negative value of Q is not a reasonable value.

In summary, regarding the value of Q, the user can select the Q value within the allowable range of the Q value according to their actual needs to achieve a rapid reduction in PAPR.

Compared with the prior art, the present invention has the following advantages:

Taking 16-QAM as an example, FIG3 is a constellation diagram generated by a few-mode fiber communication method for reducing the PAPR of an OFDM signal provided by an embodiment of the present invention, and FIG1 is a constellation diagram generated by a traditional ACE-POCS algorithm. The effects of the two are almost the same, but FIG5 is a waveform diagram after regulation by the present invention. Referring to FIG4 and FIG5, it can be intuitively seen that the peak value of the waveform after processing by the present invention has dropped by nearly 0.2.

By comparing the CCDF diagram of the adaptive flexible ACE algorithm for optimizing the PAPR of the OFDM system in Figure 6 with the CCDF diagram of the ACE-POCS algorithm in Figure 2, it can be clearly seen that the reduction effect is much better than that of the previous algorithm. Moreover, the bit error curve of the adaptive flexible ACE algorithm in Figure 7 does not change much compared with the bit error curve of the ACE-POCS algorithm.

As shown in FIG12 , the present invention performs ACE constraints on the frequency domain signal after clipping and conversion. After the constellation points move and diverge, the fault tolerance of each constellation point after various noise disturbances can be greatly increased, and the minimum Euclidean distance will not be affected during the expansion of the constellation points, which can effectively reduce the bit error rate of the OFDM system.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. A few-mode optical fiber communication method for reducing the PAPR of an OFDM signal, characterized by: the method comprises the following steps:

acquiring a communication signal to be processed, and preprocessing and converting the communication signal into a time domain signal;

superposing time domain complex noise on the converted time domain signal, and performing time domain clipping;

converting the time domain signal after time domain clipping into a frequency domain signal, and performing ACE constraint;

converting the ACE-constrained frequency domain signal into a time domain signal based on IFFT conversion;

introducing an adjusting factor, adjusting and controlling the amplification factor of the time domain signal after ACE constraint, amplifying the time domain signal, and superposing the amplified signal and the signal before time domain clipping to reduce the PAPR;

and processing the signal with reduced PAPR and transmitting the processed signal.

2. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

the pretreatment comprises the following steps:

performing constellation mapping operation on the communication signal to be processed to generate a corresponding constellation diagram;

and performing serial-parallel conversion operation on the constellation diagram, and performing IFFT conversion to obtain a time domain signal.

3. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

the time-domain clipped time-domain signal is converted into a frequency-domain signal by FFT conversion.

4. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

the ACE constraint includes:

the constellation points in the top and four sides of the constellation are projected to the area of increased boundary, while the values of the constellation points for all remaining directions are set to zero.

5. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

the step of superposing the time domain complex noise on the converted time domain signal and performing time domain clipping includes:

；

wherein ,

the time domain complex signal is subjected to time domain clipping;

The time domain complex signal is a time domain complex signal before time domain clipping;

is superimposed time domain complex noise;

；

wherein ,

the time domain complex signal is subjected to time domain clipping;

The time domain complex signal is a time domain complex signal before time domain clipping;

A threshold value for the set amplitude;

Clipping a phase value of a pre-time-domain complex signal for a time domain;

Is thatifftCounting points;nfor a value range of +.>

Is a positive integer of (2);jin imaginary units, equal to the square root of-1.

6. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

amplifying the time domain signal after regulating and controlling the amplification factor of the time domain signal after ACE constraint, and superposing the amplified signal and the signal before time domain clipping, wherein the method comprises the following steps:

；

wherein ,

the time domain complex signal is a time domain complex signal before time domain clipping;

Is an amplification adjustment factor;

Is composed of->

First pass throughfftTransformation, followed by ACE constraints, thenifftTransforming the generated time domain signal;

Is superimposed time domain complex noise;nfor a value range of +.>

Is a positive integer of (a).

7. The method for reduced PAPR of OFDM signal in accordance with claim 6, wherein:

；

wherein ,Qin order to adjust the factor(s),

；

is superimposed time domain complex noise;

A signal after time domain clipping;

、

；

Is thatifftCounting points;nfor the value range +.>

Is a positive integer of (a).

8. The method for reduced PAPR of OFDM signal in accordance with claim 1, wherein:

the signal after PAPR reduction is processed and transmitted, which comprises the following steps:

adding a cyclic prefix to the superimposed signal, performing digital signal processing, and converting the signal into an optical signal;

transmitting the optical signal through a few-mode optical fiber;

after the transmission is completed and the optical signal is received, the OFDM demodulation processing is carried out on the optical signal.

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