CN115173953A - Method for improving performance of hybrid HACO-OFDM (hybrid automatic repeat-orthogonal frequency division multiplexing) by applying predistortion technology - Google Patents

Abstract

The invention discloses a method for improving mixed HACO-OFDM performance by applying a predistortion technology, which comprises the steps of firstly carrying out FFT (fast Fourier transform) on an ACO-OFDM time domain signal after amplitude limiting again to obtain an ACO-OFDM frequency domain signal before the ACO-OFDM time domain signal and a PAM-DMT time domain signal are superposed to form the HACO-OFDM time domain signal, extracting interference noise at an imaginary part position in an even number subcarrier of the ACO-OFDM frequency domain signal, then applying the predistortion technology to subtract the ACO-OFDM frequency domain interference noise from the PAM-DMT frequency domain data at the even number of the subcarrier to obtain the PAM-DMT predistorted frequency domain data, then carrying out IFFT (inverse fast Fourier transform) on the PAM-DMT predistorted frequency domain data to obtain the PAM-DMT predistorted time domain signal, and finally superposing the PAM-DMT predistorted time domain signal and the ACO-OFDM time domain signal to form the HACO-OFDM time domain signal so as to eliminate the interference of the ACO-DMT modulation on the PAM-DMT. The method provided by the invention has the advantages of low complexity, strong reliability and high error rate performance.

Description

A method for improving the performance of hybrid HACO-OFDM using predistortion technology

technical field

The invention belongs to the field of visible light communication, and in particular relates to a method for improving the performance of a hybrid asymmetric clipping optical orthogonal frequency division multiplexing (HACO-OFDM) by using a predistortion technology.

Background technique

Hybrid HACO-OFDM is a combination of Asymmetrically Clipped Optical-Orthogonal Frequency Division Multiplexing (ACO-OFDM) and Pulse Amplitude Modulation-Discrete MultiTone. PAM-DMT for short) technology, its main idea is to use odd-numbered carriers for ACO-OFDM modulation and even-numbered carriers for PAM-DMT modulation, in order to balance power efficiency and spectrum utilization. However, due to the mutual interference between ACO-OFDM and PAM-DMT, the system performance is greatly affected. In order to reduce this effect, the traditional scheme uses serial interference cancellation (SIC) technology to cancel the interference of ACO-OFDM to PAM-DMT, but SIC technology also brings problems such as high complexity, extra delay and bit error propagation. How to effectively solve the mutual interference between ACO-OFDM and PAM-DMT while reducing the system complexity is a problem to be solved by the present invention.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention: HACO-OFDM has a great influence on system performance due to mutual interference between ACO-OFDM and PAM-DMT. In order to reduce this impact, the traditional scheme uses SIC technology to offset the interference of ACO-OFDM to PAM-DMT, but SIC technology also brings problems such as high complexity, extra delay and bit error propagation. How to effectively solve the mutual interference between ACO-OFDM and PAM-DMT while reducing the system complexity is a problem to be solved by the present invention.

The technical scheme adopted in the present invention:

A method for improving the performance of hybrid HACO-OFDM using predistortion technology, comprising:

Before the ACO-OFDM time-domain signal and the PAM-DMT time-domain signal are superimposed to form the HACO-OFDM time-domain signal, the clipped ACO-OFDM time-domain signal is re-Fast Fourier transform (FFT for short). ), obtain the ACO-OFDM frequency domain signal, extract the interference noise at the position of the imaginary part in the even subcarriers, and then use the predistortion technique to subtract the frequency domain data of the ACO-OFDM from the frequency domain data of the PAM-DMT at the position of the even subcarriers. domain interference noise, obtain the frequency domain data after PAM-DMT predistortion, and then perform Inverse Fast Fourier Transform (IFFT) on it to obtain the time domain signal after PAM-DMT predistortion. The time-domain signal predistorted by DMT and the ACO-OFDM time-domain signal are superimposed to form a HACO-OFDM time-domain signal, so as to eliminate the interference of ACO-OFDM modulation to PAM-DMT.

Further, the method includes the steps:

Step 1) Data layering is performed on the source, wherein the first layer of data is subjected to ACO-OFDM modulation, and the modulated data is correspondingly placed in the odd-numbered subcarrier position; the second layer of data is subjected to PAM-DMT modulation, and the modulated data is correspondingly placed in the even-numbered subcarriers Location;

Step 2) Perform FFT transformation on the ACO-OFDM time domain signal again, and use the predistortion technology to subtract the frequency domain interference noise of ACO-OFDM from the frequency domain data of the PAM-DMT at the position of the even subcarrier to obtain the PAM-DMT predistortion noise. The distorted frequency domain data, and then perform IFFT transformation on the PAM-DMT predistorted frequency domain data to obtain the PAM-DMT predistorted time domain signal, and then combine the PAM-DMT predistorted time domain signal with the ACO- The OFDM time domain signal is superimposed to form the HACO-OFDM time domain signal, so as to eliminate the interference of ACO-OFDM modulation to PAM-DMT;

Step 3) Add a cyclic prefix (Cyclic Prefix, CP for short) to the superimposed HACO-OFDM time-domain signal, go through DA digital-to-analog conversion, Bias Tee coupling circuit, and send it out by the photoelectric intensity modulator;

Step 4) The modulated optical signal reaches the receiving end, and the receiving end performs photoelectric conversion on the received signal, filter amplification and AD analog-to-digital conversion to obtain the HACO-OFDM signal to be demodulated;

Step 5) Perform HACO-OFDM demodulation on the HACO-OFDM signal to be demodulated, wherein the first layer data is subjected to ACO-OFDM demodulation, because the first layer ACO-OFDM modulation is eliminated at the transmitting end to the second layer PAM-DMT Therefore, the second-layer data can be directly demodulated by PAM-DMT, and finally the demodulated and recovered binary data is sent back to the sink.

The technical characteristics and remarkable effects of the present invention are:

The present invention proposes a method for improving the performance of hybrid HACO-OFDM by using predistortion technology for the first time. This method is different from the traditional HACO-OFDM processing method. Mutual interference of DMT, the latter uses SIC technology to cancel the mutual interference of ACO-OFDM modulation to PAM-DMT from the perspective of time domain at the receiving end. The method proposed by the invention has the advantages of low complexity, strong reliability and high bit error rate performance. Since the interference of ACO-OFDM modulation on PAM-DMT is eliminated at the transmitting end, the receiving end can directly demodulate the data in parallel. SIC processing is no longer required, which not only effectively avoids the problems of high complexity, extra delay and bit error propagation caused by traditional SIC serial elimination of interference, but also the present invention is superior to HACO using SIC in terms of bit error rate performance -OFDM scheme, which can provide a certain reference value for improving the performance of hybrid HACO-OFDM using predistortion technology.

Description of drawings

FIG. 1 is a flowchart of a method for improving the performance of a hybrid HACO-OFDM using a predistortion technique in an embodiment.

Detailed ways

The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

Example:

A method for improving the performance of hybrid HACO-OFDM using predistortion technology, comprising:

Before the ACO-OFDM time-domain signal and the PAM-DMT time-domain signal are superimposed to form the HACO-OFDM time-domain signal, the clipped ACO-OFDM time-domain signal is re-FFT transformed to obtain the ACO-OFDM frequency-domain signal. The interference noise at the imaginary part of the even-numbered sub-carriers, and then using the predistortion technique to subtract the frequency-domain interference noise of ACO-OFDM from the frequency-domain data of PAM-DMT at the position of the even-numbered sub-carriers to obtain the PAM-DMT predistortion The frequency-domain data is then transformed by IFFT to obtain the time-domain signal after PAM-DMT predistortion. Finally, the time-domain signal after PAM-DMT predistortion is superimposed with the ACO-OFDM time-domain signal to form a HACO-OFDM time-domain signal. , so as to eliminate the interference of ACO-OFDM modulation to PAM-DMT.

As shown in Figure 1, the method includes the following steps:

Step 1) Data layering is performed on the source, wherein the first layer of data is subjected to ACO-OFDM modulation, and the modulated data is correspondingly placed in the odd-numbered subcarrier position; the second layer of data is subjected to PAM-DMT modulation, and the modulated data is correspondingly placed in the even-numbered subcarriers Location;

Step 1) includes the following steps:

1-1) Assuming that the source data sends N/2-1 pieces of data per frame, where the serial numbers of the data are respectively from X ₁ to X _N/2-1 , then the odd number in (X ₁ , X _N/2-1 ) The serial number data is divided into the first layer, and quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM for short) is performed to obtain X _ACO,k1 , where k1=(1,2,...,N/4) is an odd number; and (X ₁ , The even-numbered data in X _N/2-1 ) is divided into the second layer, and pulse amplitude modulation (Pulse Amplitude Modulation, PAM for short) is performed to obtain X _PAM,k2 , where k2=(1,2,..., N/4-1);

1-2) Perform Hermitian conjugate symmetry on the QAM mapping data X _ACO,k1 of the first layer to obtain the conjugate data X ^* _ACO,k1 , and map the data X _ACO,k1 and the conjugate data X ^* _ACO,k1 according to the common The requirements for yoke symmetry are mapped as follows:

X _odd = [0,X _ACO,1 ,0,X _ACO,2 ,0,X _ACO,3 ,...,X _ACO,N/4 ,0,X ^* _ACO,N/4 ,..., X ^* _ACO,3,0, X ^* _ACO,2,0 ,X ^* _ACO,1 ]

1-3) Perform IFFT transformation on the data X _odd that satisfies the Hermitian symmetry to generate an ACO-OFDM real number signal x _ACO-OFDM that is transmitted by an intensity modulation direct detection system (Intensity Modulation/Direct Detection, IM/DD for short):

x _ACO-OFDM =IFFT(X _odd )

1-4) Perform Hermitian conjugate symmetry on the PAM mapping data X _PAM,k2 of the second layer to obtain X ^* _PAM,k2 , and then convert the original value X _PAM,k2 and the conjugate data X ^* _PAM,k2 according to the conjugate symmetry The requirements are mapped as follows:

X _even = [0,0, _XPAM, 1,0,XPAM,2,0, _XPAM,3 ,..., _XPAM,N/ 4-1,0,0,0,X ^* _{PAM , N/4-1} ,...,X ^* _PAM,3,0 ,X ^* _PAM,2,0 ,X ^* _PAM,1 ];

Step 2) Perform FFT transformation on the ACO-OFDM time domain signal again, and use the predistortion technology to subtract the frequency domain interference noise of ACO-OFDM from the frequency domain data of the PAM-DMT at the position of the even subcarrier to obtain the PAM-DMT predistortion noise. The distorted frequency domain data is then subjected to IFFT transformation on the frequency domain data X' _PAM- DMT predistorted by PAM-DMT to obtain the time domain signal x' _PAM- DMT predistorted by PAM-DMT. The distorted time domain signal x' _PAM-DMT is subjected to "zero-cross clipping" to obtain x" _PAM-DMT , and finally the "zero-cross clipping" data x" _PAM-DMT and ACO-OFDM time domain signal x' _ACO-OFDM is superimposed to form a HACO-OFDM time domain signal x _HACO-OFDM , so as to eliminate the interference of ACO-OFDM modulation to PAM-DMT;

Step 2) includes the following steps:

2-1) Perform "zero-crossing clipping" on the ACO-OFDM real number signal x _ACO-OFDM transmitted in the first layer, remove the negative value signal in the ACO-OFDM real number signal, and obtain x' _ACO-OFDM ,

2-2) Next, perform FFT transformation on x' _ACO-OFDM to obtain a new frequency domain signal X' _{ACO-OFDM of ACO-OFDM} , and then extract the interference noise at the position of the imaginary part in its even-numbered subcarriers;

2-3) Subtract the frequency domain interference noise of ACO-OFDM from the frequency domain data of PAM-DMT at the position of the even-numbered subcarriers to obtain the frequency domain data X' _PAM-DMT after PAM-DMT predistortion,

Wherein X _PAM-DMT represents the frequency domain data of PAM-DMT, 2*imag(X' _ACO-OFDM ) represents the data of the imaginary part of the signal X' _ACO-OFDM and multiplied by 2 times, i represents a complex number;

2-4) Perform IFFT transformation on the frequency-domain data X' _PAM-DMT after the PAM-DMT predistortion, to obtain the time-domain signal x' _PAM-DMT after the PAM-DMT predistortion,

_x'PAM-DMT =IFFT( _X'PAM-DMT )=( _x'PAM-DMT,0 , _x'PAM-DMT,1 ,..., _x'PAM-DMT,j ,...,x' _PAM-DMT,N-1 )

Wherein x' _PAM-DMT,j ,j=(0,N-1) represents the jth PAM-DMT time domain signal output by IFFT;

2-5) Perform a "zero-crossing clipping" operation on the time-domain signal x' _PAM-DMT after the PAM-DMT predistortion, remove the negative value part in the PAM-DMT, and obtain x" _PAM-DMT :

2-6) Superimpose the time domain signal x'' _PAM-DMT and the ACO-OFDM time domain signal x' _ACO-OFDM to obtain the HACO-OFDM time domain signal x _HACO-OFDM , in order to eliminate The interference of ACO-OFDM modulation to PAM-DMT;

x _HACO-OFDM =x” _PAM-DMT + _x’ACO-OFDM ;

Step 3) adding a cyclic prefix to the superimposed HACO-OFDM time-domain signal, after DA digital-to-analog conversion, Bias Tee coupling circuit, and sent out by the photoelectric intensity modulator;

Step 3 includes the following steps:

3-1) Insert a cyclic prefix into the HACO-OFDM time domain signal x _HACO-OFDM to obtain modulated data of HACO-OFDM;

3-2) After DA digital-to-analog conversion, the modulated data of HACO-OFDM is added to the Bias Tee coupling circuit together with the DC bias to drive the optical transmitter to complete the conversion of electrical signals to optical signals;

3-3) The optical signal reaches the receiving end through direct, scattering and reflection paths in the visible light communication (Visible Light Communication, VLC for short) channel, and then is sent to the next step for processing;

Step 4) The modulated optical signal reaches the receiving end, and the receiving end performs photoelectric conversion on the received signal, filter amplification and AD analog-to-digital conversion to obtain the HACO-OFDM signal to be demodulated;

Step 5) Perform HACO-OFDM demodulation on the HACO-OFDM signal to be demodulated, wherein the first layer data is subjected to ACO-OFDM demodulation, because the first layer ACO-OFDM modulation is eliminated at the transmitting end to the second layer PAM-DMT Therefore, the second layer data can be directly demodulated by PAM-DMT, and finally the binary data recovered by demodulation is sent back to the sink;

Step 5 includes the following steps:

5-1) After receiving the HACO-OFDM signal to be demodulated, first remove the cyclic prefix (CP) signal to obtain the original HACO-OFDM signal at N points;

5-2) Perform FFT transformation on the N-point HACO-OFDM signal to obtain the complex data of N-points again;

5-3) Take out the first layer ACO-OFDM data to be demodulated X' _{1 of FFT output, ACO-OFDM} and the second layer PAM-DMT data to be demodulated X' _{2, PAM-DMT} ;

5-4) demodulate the data X' _{1 to be demodulated in the first layer, ACO-OFDM} and the data X' _{2 to be demodulated in the second layer, PAM-DMT} , adopt the maximum likelihood ratio algorithm, and judge the received constellation The minimum Euclidean distance between the point and the theoretical constellation point, recovers the demodulated binary data X ⁽¹⁾ of the first layer and recovers the demodulated binary data X ⁽²⁾ of the second layer;

5-5) Adjust the position of the binary data X ⁽¹⁾ after demodulation of the first layer and the binary data X ⁽²⁾ after demodulation of the second layer, and then send them back to the sink.

Through the above implementation cases, the advantages of this method are reflected in: step 2), using the frequency domain data of PAM-DMT to subtract the frequency domain interference noise of ACO-OFDM, to obtain the frequency domain data after PAM-DMT predistortion, for PAM-DMT The predistorted frequency domain data is re-FFT transformed to obtain the time domain signal after the PAM-DMT predistortion, and then the sliced ACO-OFDM time domain signal and the PAM-DMT time domain signal are superimposed to obtain the HACO-OFDM predistortion signal. For the distorted time-domain signal, the interference of ACO-OFDM modulation on PAM-DMT is eliminated at the transmitting end through the above steps, and the receiving end can directly demodulate the data in parallel without SIC processing, which not only effectively avoids the traditional use of SIC serially eliminates the problems of high complexity, extra delay and bit error propagation caused by interference, and the proposed method is better than the HACO-OFDM scheme using SIC in terms of bit error rate performance. To sum up, the present invention effectively improves the system performance of the hybrid HACO-OFDM.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims (5)

1. A method for improving the performance of a hybrid HACO-OFDM system by using a predistortion technology is characterized by comprising

Before the ACO-OFDM time domain signal and the PAM-DMT time domain signal are superposed to form a HACO-OFDM time domain signal, firstly, fast Fourier Transform (FFT) is carried out on the amplitude-limited ACO-OFDM time domain signal again to obtain an ACO-OFDM frequency domain signal, interference noise at an imaginary part position in an even number subcarrier of the ACO-OFDM frequency domain signal is extracted, then, predistortion technology is applied, the frequency domain interference noise of the ACO-OFDM is subtracted from the frequency domain data of the PAM-DMT at the position of the even number subcarrier to obtain frequency domain data after the PAM-DMT predistortion, then, fast Fourier Transform (IFFT) is carried out on the frequency domain data to obtain the time domain signal after the PAM-DMT predistortion, and finally, the time domain signal after the PAM-DMT predistortion and the ACO-OFDM time domain signal are superposed to form the HACO-OFDM time domain signal, so that the interference of the ACO-OFDM modulation on the PAM-DMT is eliminated.

2. The method of claim 1 for improving hybrid HACO-OFDM performance using predistortion technique, comprising the steps of:

step 1) carrying out data layering on an information source, wherein ACO-OFDM modulation is carried out on first-layer data, and the modulated data are correspondingly placed at odd-numbered subcarrier positions; carrying out PAM-DMT modulation on the second layer data, and correspondingly placing the modulated data at the position of even number of subcarriers;

step 2) carrying out FFT transformation on the ACO-OFDM time domain signal again, subtracting the ACO-OFDM frequency domain interference noise from the PAM-DMT frequency domain data at the position of an even number of subcarriers by applying a predistortion technology to obtain the PAM-DMT predistorted frequency domain data, carrying out IFFT transformation on the PAM-DMT predistorted frequency domain data to obtain the PAM-DMT predistorted time domain signal, and then superposing the PAM-DMT predistorted time domain signal and the ACO-OFDM time domain signal to form a HACO-OFDM time domain signal so as to eliminate the interference of the ACO-OFDM modulation on the PAM-DMT;

step 3), adding a Cyclic Prefix (CP) to the superimposed HACO-OFDM time domain signal, and sending out the HACO-OFDM time domain signal through DA digital-to-analog conversion and a Bias Tee coupling circuit by using a photoelectric intensity modulator;

step 4), the modulated optical signal reaches a receiving end, and the receiving end performs photoelectric conversion, filtering amplification and AD (analog-to-digital) conversion on the received signal to obtain a signal to be demodulated of HACO-OFDM (Haco-orthogonal frequency division multiplexing);

and step 5) carrying out HACO-OFDM demodulation on the HACO-OFDM signal to be demodulated, wherein the first layer of data is subjected to ACO-OFDM demodulation, and because the interference of the first layer of ACO-OFDM modulation on the second layer of PAM-DMT is eliminated at the transmitting end, the second layer of data can be directly subjected to PAM-DMT demodulation, and finally the demodulated and recovered binary data is sent back to a signal sink.

3. The method of claim 2, wherein step 1) comprises the steps of:

1-1) suppose that the source data transmits N/2-1 data per frame, wherein the sequence numbers of the data are respectively from X ₁ To X _N/2-1 Then (X) ₁ ,X _N/2-1 ) The odd-numbered data in the first layer is divided into the first layer, and Quadrature Amplitude Modulation (QAM) is performed to obtain X _ACO,k1 Wherein k1= (1, 2., N/4) is an odd number; and (X) ₁ ,X _N/2-1 ) The data with even serial number in the second layer is divided into the second layer, and Pulse Amplitude Modulation (PAM for short) is carried out to obtain X _PAM,k2 Wherein k2= (1, 2,.., N/4-1);

1-2) QAM mapping data X to the first layer _ACO,k1 Hermitian conjugation symmetry is carried out to obtain conjugation data X ^* _ACO,k1 To map data X _ACO,k1 And conjugate data X ^* _ACO,k1 The requirement for conjugate symmetry is mapped as follows:

X _odd ＝[0,X _ACO,1 ,0,X _ACO,2 ,0,X _ACO,3 ,...,X _ACO,N/4 ,0,X ^* _ACO,N/4 ,...,X ^* _ACO,3 ,0,X ^* _ACO,2 ,0,X ^* _ACO,1 ]

1-3) for data X satisfying Hermitian symmetry _odd IFFT transformation is carried out to generate an ACO-OFDM real signal x which is in accordance with Intensity Modulation/Direct Detection (IM/DD) transmission _ACO-OFDM ：

x _ACO-OFDM ＝IFFT(X _odd )

1-4) PAM mapping data X to the second layer _PAM,k2 Hermitian conjugation symmetry to obtain X ^* _PAM,k2 Then the original value X is added _PAM,k2 And conjugate data X ^* _PAM,k2 The requirement for conjugate symmetry is mapped as follows:

X _even ＝[0,0,X _PAM,1 ,0,X _PAM,2 ,0,X _PAM,3 ,...,X _PAM,N/4-1 ,0,0,0,X ^* _PAM,N/4-1 ,...,X ^* _PAM,3 ,0,X ^* _PAM,2 ,0,X ^* _PAM,1 ]。

4. the method of claim 2 for improving the performance of a hybrid HACO-OFDM using predistortion technique, wherein step 2) comprises the steps of:

2-1) ACO-OFDM real signal x transmitted by first layer _ACO-OFDM Carrying out zero-crossing amplitude limiting, and removing a negative value signal in the ACO-OFDM real number signal to obtain x' _ACO-OFDM ，

2-2) then to x' _ACO-OFDM FFT conversion is carried out to obtain a new frequency domain signal X 'of ACO-OFDM' _ACO-OFDM Then extracting the interference noise of the imaginary part position in the even number subcarrier;

2-3) subtracting the frequency domain interference noise of ACO-OFDM from the frequency domain data of PAM-DMT at the positions of even subcarriers to obtain frequency domain data X 'after PAM-DMT predistortion' _PAM-DMT ，

Wherein X _PAM-DMT Frequency domain data representing PAM-DMT, 2 × imag (X' _ACO-OFDM ) Represents to signal X' _ACO-OFDM Taking data of an imaginary part and multiplying by 2 times, wherein i represents a complex number;

2-4) Pre-distorted frequency-domain data X 'to PAM-DMT' _PAM-DMT IFFT conversion is carried out to obtain a time domain signal x 'after PAM-DMT predistortion' _PAM-DMT ，

x' _PAM-DMT ＝IFFT(X' _PAM-DMT )＝(x' _PAM-DMT,0 ,x' _PAM -DMT,1,...,x' _PAM -DMT,j,...,x' _PAM-DMT,N-1 )

Wherein x' _PAM-DMT,j J = (0, n-1) represents the j-th PAM-DMT time domain signal of the IFFT output;

2-5) Pre-distorted time-domain Signal x 'of PAM-DMT' _PAM-DMT Performing zero-crossing amplitude limiting operation to remove the negative value part in PAM-DMT to obtain x " _PAM-DMT ：

2-6) time-domain signal x after PAM-DMT predistortion " _PAM-DMT And ACO-OFDM time domain signal x' _ACO-OFDM Overlapping to obtain HACO-OFDM time domain signal x _HACO-OFDM Thus eliminating the interference of the ACO-OFDM modulation on the PAM-DMT;

x _HACO-OFDM ＝x” _PAM-DMT +x' _ACO-OFDM 。

5. the method of claim 2, wherein step 5 comprises the steps of:

5-1) after receiving the signal to be demodulated of the HACO-OFDM, firstly removing a Cyclic Prefix (CP) signal to obtain an N-point original HACO-OFDM signal;

5-2) carrying out FFT (fast Fourier transform) on the HACO-OFDM signal of the N points to obtain complex data of the N points again;

5-3) taking out first layer ACO-OFDM data X 'to be demodulated output by FFT' _1，ACO-OFDM And a second layer of PAM-DMT data X 'to be demodulated' _2，PAM-DMT ；

5-4) data X 'to be demodulated in the first layer' _1，ACO-OFDM And a second layer of data X 'to be demodulated' _2，PAM-DMT Demodulating, adopting maximum likelihood ratio algorithm, judging minimum Euclidean distance between received constellation point and theoretical constellation point, recovering first layer demodulation binary data X ⁽¹⁾ And recovering the demodulated binary data X of the second layer ⁽²⁾ ；

5-5) demodulating the first layer binary data X ⁽¹⁾ And second layer demodulated binary data X ⁽²⁾ The position adjustment is performed and then sent back to the sink.

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