A wireless optical transmission method based on asymmetric clipping optical affine frequency division multiplexing

Abstract

The application discloses a wireless optical transmission method based on asymmetric clipping optical affine frequency division multiplexing, and relates to the technical field of wireless communication. The method comprises the following steps: S1, pre-processing input signal data, including mapping, design of modulation symbols and symmetry construction, to generate a frequency domain signal; S2, mapping the frequency domain signal to a time domain based on a real number discrete affine Fourier transform to generate an affine frequency division multiplexing (AFDM) signal; S3, asymmetrically clipping the AFDM signal, transmitting the AFDM signal to a receiving end through an optical communication channel, and inversely restoring the AFDM signal, including recovering the clipped signal and demodulating data; and S4, designing a real number DAFT kernel function, deducing a new c1 parameter range, realizing complete separation of signal paths with different delays in the DAFT domain, and achieving full diversity. The application solves the signal distortion problem caused by the multipath effect in optical communication.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing. Background Technology

[0002] With the rapid development of modern communication technologies, optical communication has become an important component of the communication field due to its advantages such as high speed, large capacity, and low loss. However, due to physical limitations, optical communication systems require that the signals transmitted in the channel be non-negative real numbers. This unique requirement places higher demands on modulation and waveform design techniques. Existing Orthogonal Frequency Division Multiplexing (OFDM) technology has been widely used in wireless communication due to its high spectral efficiency and robustness against frequency-selective fading. However, directly applying traditional OFDM to optical communication systems presents challenges, such as the complex form of the signal and the high peak-to-average power ratio (PAPR), which do not meet the requirement of signal non-negativity. To address this, researchers have proposed Asymmetric Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) technology, which generates non-negative real-number signals through asymmetric clipping, thereby meeting the transmission requirements of optical communication. However, ACO-OFDM suffers from problems such as decreased spectral efficiency and insufficient anti-interference capability in multipath channels, exhibiting certain limitations in scenarios with significant multipath effects, such as multimode fiber communication and free-space optical communication.

[0003] Apomorphic radio frequency multiplexing (AFDM), an emerging multicarrier modulation technique based on discrete affine Fourier transform (DAFT), exhibits unique advantages in wireless communication. AFDM can effectively separate the delay of multipath channels, reduce interference, and achieve high diversity gain by utilizing the time-frequency sparsity of the channel, thereby improving anti-fading capability and system reliability. Furthermore, AFDM receivers can employ simple linear detection algorithms, resulting in low implementation complexity. However, the success of AFDM in wireless communication cannot be directly transferred to optical communication, primarily because the generated signal is in complex form, which does not meet the requirements of optical communication for non-negative real-number signals. Solving this problem requires additional signal processing techniques, such as biasing or nonlinear transformations, but this significantly increases system complexity and power consumption, limiting its practical application.

[0004] Existing optical communication modulation technologies, such as ACO-OFDM, while meeting the non-negativity requirement, have limited anti-interference capabilities in complex multipath channel scenarios. AFDM, on the other hand, has technological advantages in multipath environments, but its non-negativity issue hinders its application in optical communication systems. This technological bottleneck limits the performance improvement of optical communication systems in complex multipath environments. How to introduce the advantages of AFDM technology into the field of optical communication and solve the non-negativity constraint problem is a key challenge that urgently needs to be overcome. Summary of the Invention

[0005] The purpose of this invention is to propose a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing. By combining the multipath component separation capability of AFDM with the non-negativity processing method of ACO-OFDM, the problem of signal non-negativity constraint and multipath interference in optical communication systems is solved, and efficient and reliable signal transmission is achieved. It is particularly suitable for complex scenarios with significant multipath effects, such as multimode optical fiber communication and free space optical communication.

[0006] To achieve the above objectives, this invention proposes a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing, the specific steps of which are as follows:

[0007] Step S1: At the transmitting end, the input optical communication signal data is preprocessed, including the mapping of frequency domain data, the design of modulation symbols, and the construction of data symmetry, to generate a frequency domain signal that meets specific conditions.

[0008] Step S2: Based on the real-valued Discrete Affine Fourier Transform (DAFT), the frequency domain signal generated in step S1 is mapped to the time domain to generate an AFDM time domain signal.

[0009] Step S3: Asymmetric cropping of the AFDM time-domain signal generated in step S2 is performed using the odd half-wave symmetry characteristic. The negative part of the AFDM time-domain signal is set to zero and transmitted to the receiving end through the optical communication channel. The receiving end performs reverse reconstruction of the signal, including the recovery of the cropped signal and demodulation of the data.

[0010] Step S4: Based on the design of the real-valued DAFT kernel function, derive a new range of c1 parameters so that signal paths with different delays can be completely separated in the DAFT domain, achieving full diversity.

[0011] Preferably, in step S1, the input optical communication signal data is mapped onto frequency domain subcarriers to form frequency domain symbols. To ensure that the frequency domain signal is a real number, the frequency domain symbols are set to a conjugate symmetric form, and the formula is as follows:

[0012] X[Nk]=X[k] * ;

[0013] Where X[k] represents the symbol of the k-th subcarrier, X[k] * Let X[k] be the conjugate complex number of X[k], and let X[Nk] be the symbol of the Nk-th subcarrier.

[0014] Preferably, to meet the requirements of asymmetric clipping, data is loaded only on odd-numbered subcarriers, while the symbols of even-numbered subcarriers are set to zero, as shown in the following formula:

[0015] X[2k] = 0;

[0016] X[2k+1] = Frequency domain symbol.

[0017] Preferably, in step S2, the frequency domain signal generated in step S1 is mapped to the time domain using the realized Discrete Affine Fourier Transform (DAFT) to generate an AFDM time domain signal. The specific steps are as follows:

[0018] Step S21: The formula for calculating the kernel function of the Discrete Affine Fourier Transform (DAFT) is as follows:

[0019]

[0020] The formula for calculating its inverse transform is as follows:

[0021]

[0022] Where x[n] is the input signal, S[m] is the output signal, N is the number of subcarriers, M is the length of the DAFT transform, c1 and c2 are free parameters in the modulation design, m is the output signal index, n is the input signal index, and j is an imaginary number;

[0023] Step S22: Adjust the kernel function of the Discrete Affine Fourier Transform (DAFT) by removing the complex exponential kernel function. Item, will Replace with cos(2πc1n) 2 The adjusted formula for calculating the Discrete Affine Fourier Transform (DAFT) kernel function is as follows:

[0024]

[0025] The time-domain signal generated by the adjusted kernel function is a real number, and the multipath separation capability of the Discrete Affine Fourier Transform (DAFT) is preserved.

[0026] Preferably, cos(2πc1n) 2 The calculation formula for ) is as follows:

[0027]

[0028] Preferably, in step S3, the AFDM time-domain signal generated in step S2 is asymmetrically clipped (ACO) using the odd half-wave symmetry characteristic. The specific steps are as follows:

[0029] Step S31: Since the time-domain signal x(t) has odd half-wave symmetry, its negative half does not carry effective information. The negative part is forced to zero through asymmetric clipping, as shown in the following formula:

[0030] x clipped (t) = max(x(t), 0);

[0031] Where, xclipped (t) is the clipped signal, where t is the continuous time variable of the signal;

[0032] Step S32: Demodulate and restore the received optical signal to achieve accurate data recovery; the receiving end restores the received optical signal to an electrical signal through a photodetector, and uses the known odd half-wave symmetry characteristics to recover the clipped negative half of the signal, as shown in the following formula:

[0033]

[0034] Where, x recovered (t) is the recovered signal, and T is the signal period;

[0035] The inverse transform of the realized DAFT kernel function is performed to recover the frequency domain sign, and the calculation formula is as follows:

[0036]

[0037] The original input data is extracted by utilizing the conjugate symmetry between frequency domain symbols and the odd subcarrier allocation rule.

[0038] Preferably, in step S4, the left-shift logic and the offset distance of the non-zero elements in the channel matrix are derived, and combined with the right-shift logic to describe the mapping relationship of the signal path in the DAFT domain. The specific steps are as follows:

[0039] Step S41: Left and right shifts resulting from the realization kernel function;

[0040] Step S42: Derive the new range of c1 parameters to achieve full set, ensuring that the right and left shift paths do not overlap, and that the left and right shift paths do not overlap.

[0041] Preferably, in step S41, the left and right shifts resulting from the realization kernel function are implemented using the following specific steps:

[0042] Step S411: In traditional AFDM, the range of c1 is derived as follows:

[0043] The elements of the channel matrix are:

[0044]

[0045] in,

[0046]

[0047] When v i When = 0,

[0048]

[0049] The right shift logic is introduced by +c1, and its offset is:

[0050] loc i =(2Nc1l i ) N ;

[0051] Among them, l i H is the delay of the i-th path. i [p,q] represents the channel matrix elements of the i-th path, where p and q are frequency domain indices. For the frequency domain contribution function, v i For the Doppler frequency shift of the i-th path, loc i Let be the offset of the i-th path;

[0052] Step S412: The realization kernel function introduces left-shift logic. In ACO-AFDM, the kernel function is replaced with:

[0053]

[0054] Left shift logic is Introduced, its channel matrix elements become:

[0055]

[0056] in,

[0057]

[0058] When v i =0:

[0059]

[0060] The new offset is:

[0061] loc′ i =(-2Nc1l i ) N ;

[0062] The left-shift logic is introduced by -c1, which shifts the non-zero elements of the channel matrix to the left by loc′ from the diagonal. i One position.

[0063] Preferably, in step S42, the derivation steps for the new c1 parameter range are as follows:

[0064] Step S421, Derivation of the range of c1 where the right-shifted paths do not overlap:

[0065] From the derivation of the original AFDM, the right shift is defined by the following formula:

[0066] loc i=(2Nc1l i ) N ;

[0067] To avoid overlap between right-shifting paths, the following must be satisfied:

[0068]

[0069] Let l i+1 -l i =1, ensuring that paths do not overlap, and the range of c1 shifted to the right must satisfy:

[0070] c1>0;

[0071] Step S422, the derivation of the range of c1 where the left-shifted paths do not overlap is as follows:

[0072] The offset range for the left shift is:

[0073] loc′ i =(-2Nc1l i ) N ;

[0074] To avoid overlap between left-shifting paths, the following must be satisfied:

[0075]

[0076] Similarly, assuming the minimum time delay difference between paths is 1, the range of c1 shifted to the left to ensure that paths do not overlap is:

[0077] c1>0;

[0078] Step S423: Derivation of the range of c1 where the left and right shift paths do not overlap. In order to avoid overlap between the left and right shift paths, it is necessary to satisfy that the maximum value of all right shift paths is less than N / 2 and the minimum value of all left shift paths is also less than N / 2.

[0079] Step S424: For the right and left shift paths to not overlap, c1 > 0 must be satisfied. For the left and right shift paths to not overlap, the following must be satisfied:

[0080]

[0081] The final range of c1 is:

[0082]

[0083] This enables the ACO-AFDM channel matrix to be completely separated in the DAFT domain, achieving full diversity.

[0084] Preferably, in step S423, the maximum rightward offset is:

[0085] 2Nc1l max ;

[0086] Make it less than N / 2:

[0087]

[0088] The results were:

[0089]

[0090] The leftward offset is:

[0091] -2Nc1l max ;

[0092] make get:

[0093]

[0094] The results were:

[0095]

[0096] Therefore, this invention proposes a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing, the advantages of which are as follows:

[0097] (1) The present invention provides a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing. By combining the multipath component separation capability of analog radio frequency multiplexing (AFDM) and the non-negative signal generation mechanism of asymmetric clipping (ACO), it achieves efficient signal transmission in optical communication channels that resists multipath interference.

[0098] (2) The present invention provides a wireless optical transmission method based on asymmetric amplitude limiting optical analog radio frequency multiplexing. While meeting the requirements for non-negative real number signal transmission in optical communication channels, it can significantly improve the system performance in complex multipath scenarios such as multimode optical fiber communication and free space optical communication. It solves the signal distortion problem caused by multipath effect in optical communication and provides an effective solution for the stability and reliability of optical communication systems in complex scenarios.

[0099] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0100] Figure 1 This is an overall flowchart of a wireless optical transmission method based on asymmetric amplitude-limited optical analog radio frequency multiplexing according to the present invention;

[0101] Figure 2 These are the bit error rate versus signal-to-noise ratio curves of the ACO-AFDM and ACO-OFDM methods of this invention under multipath conditions. Detailed Implementation

[0102] To make the technical solutions, advantages, and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of this application.

[0103] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0104] like Figure 1 As shown, this invention provides a wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing to simultaneously meet the non-negativity requirement of optical channel signal transmission and the anti-interference capability in complex multipath environments. The specific process is as follows:

[0105] Step S1: At the transmitting end, the input optical communication signal data is preprocessed, including the mapping of frequency domain data, the design of modulation symbols, and the construction of data symmetry, to generate a frequency domain signal that meets specific conditions.

[0106] Step S11, Transmit Data Processing: To meet the requirements of real numbers and non-negativity of optical communication signals, the transmitting end needs to process the input data. The input data is mapped onto frequency domain subcarriers to form frequency domain symbols for subsequent modulation. To ensure that the time-domain signal is real, the frequency domain symbols are set to a conjugate symmetric form.

[0107] X[Nk]=X[k] * ;

[0108] Where X[k] represents the symbol of the k-th subcarrier, X[k] * Let X[k] be the conjugate complex number of X[k], and let X[Nk] be the symbol of the Nk-th subcarrier.

[0109] Step S12: To meet the requirements of asymmetric clipping, data is only loaded on odd-numbered subcarriers, while the symbols of even-numbered subcarriers are set to zero, as shown in the following formula:

[0110] X[2k] = 0;

[0111] X[2k+1] = Frequency domain symbol;

[0112] This design ensures that the time-domain signal has odd half-wave symmetry, providing a basis for subsequent asymmetric clipping.

[0113] Step S2: Based on the real-valued Discrete Affine Fourier Transform (DAFT), the frequency domain signal generated in step S1 is mapped to the time domain to generate the AFDM (Analog Radio Frequency Division Multiplexing) time domain signal. The specific steps are as follows:

[0114] Step S21: The formula for calculating the kernel function of the Discrete Affine Fourier Transform (DAFT) is as follows:

[0115]

[0116] The formula for calculating its inverse transform is as follows:

[0117]

[0118] Where x[n] is the input signal, S[m] is the output signal, N is the number of subcarriers, M is the length of the DAFT transform, c1 and c2 are free parameters in the modulation design, m is the output signal index, n is the input signal index, and j is an imaginary number;

[0119] The kernel function of DAFT, compared to DFT, is a complex form with quadratic phase modulation, containing terms... and These parameters can adjust how the signal transforms in the time and frequency domains, providing greater flexibility.

[0120] Step S22: Adjust the kernel function of the Discrete Affine Fourier Transform (DAFT) by removing the complex exponential kernel function. Item, will Replace with cos(2πc1n) 2 The adjusted formula for calculating the Discrete Affine Fourier Transform (DAFT) kernel function is as follows:

[0121]

[0122]

[0123] The time-domain signal generated by the adjusted kernel function is a real number, and the multipath separation capability of the Discrete Affine Fourier Transform (DAFT) is preserved.

[0124] Step S3: Utilize the odd half-wave symmetry characteristic to perform asymmetric cropping (ACO) on the AFDM time-domain signal generated in Step 2, setting the negative portion of the AFDM time-domain signal to zero, and transmit it to the receiving end through the optical communication channel; the receiving end performs reverse reconstruction of the signal, including recovery of the cropped signal and demodulation of the data, with the specific steps as follows:

[0125] Step S31: Since the time-domain signal x(t) has odd half-wave symmetry, its negative half does not carry effective information. The negative part is forced to zero through asymmetric clipping, as shown in the following formula:

[0126] x clipped (t) = max(x(t), 0);

[0127] Where t is the continuous-time variable of the signal, x clipped (t) represents the clipped signal, which satisfies the non-negativity requirement of the optical communication channel, and the clipping does not result in information loss. After asymmetric clipping, the signal energy is concentrated in the non-negative part, effectively improving the energy efficiency of the optical communication system.

[0128] Step S32: Demodulate and restore the received optical signal to achieve accurate data recovery; the receiving end restores the received optical signal to an electrical signal through a photodetector, and uses the known odd half-wave symmetry characteristics to recover the clipped negative half of the signal, as shown in the following formula:

[0129]

[0130] Where, x recovered (t) is the recovered signal, and T is the signal period.

[0131] Next, an inverse transform is performed on the realized DAFT kernel function to recover the frequency domain sign. The calculation formula is as follows:

[0132]

[0133] The original input data is extracted by utilizing the conjugate symmetry between frequency domain symbols and the odd subcarrier allocation rule.

[0134] Step S4: Based on the design of the real-valued DAFT kernel function, derive a new range of c1 parameters so that signal paths with different delays can be completely separated in the DAFT domain, achieving full diversity.

[0135] First, the left-shift logic and the offset distance of non-zero elements in the channel matrix are derived. Then, combined with the right-shift logic, the mapping relationship of the signal path in the DAFT domain is described. The specific steps are as follows:

[0136] Step S41, the left and right shifts resulting from the realization kernel function, are explained in the following steps:

[0137] Step S411: In traditional AFDM, the range of c1 is derived as follows:

[0138] The elements of the channel matrix are:

[0139]

[0140] in,

[0141]

[0142] When v i When = 0,

[0143]

[0144] The right-shift logic is introduced by +c1, which shifts the non-zero elements of the channel matrix diagonally to the right by loc. i The position has an offset of:

[0145] loc i =(2Nc1l i ) N ;

[0146] Among them, l i H is the delay of the i-th path. i [p,q] represents the channel matrix elements of the i-th path, where p and q are frequency domain indices. For the frequency domain contribution function, v i For the Doppler frequency shift of the i-th path, loc i c1 is the offset of the i-th path, and c1 is a free parameter in the modulation design;

[0147] Step S412: The realization kernel function introduces left-shift logic. In ACO-AFDM, the kernel function is replaced with:

[0148]

[0149] Left shift logic is Introduced, its channel matrix elements become:

[0150]

[0151] in,

[0152]

[0153] When v i =0:

[0154]

[0155] The new offset is:

[0156] loc′ i =(-2Nc1l i ) N ;

[0157] The left-shift logic is introduced by -c1, which shifts the non-zero elements of the channel matrix to the left by loc′ from the diagonal. i One position.

[0158] Step S42: Derive the new range of c1 parameters to achieve full set division, ensuring that the paths of right and left shifts do not overlap, and that the paths of left and right shifts do not overlap. The derivation steps for the new range of c1 parameters are as follows:

[0159] Step S421, Derivation of the range of c1 where the right-shifted paths do not overlap:

[0160] From the derivation of the original AFDM, the right shift is defined by the following formula:

[0161] loc i =(2Nc1l i ) N ;

[0162] To avoid overlap between right-shifting paths, the following must be satisfied:

[0163]

[0164] Let l i+1 -l i =1, ensuring that paths do not overlap, and the range of c1 shifted to the right must satisfy:

[0165] c1>0;

[0166] Step S422: The derivation of the range of c1 that does not overlap between left-shifted paths is as follows:

[0167] The offset range for the left shift is:

[0168] loc′ i =(-2Nc1l i ) N ;

[0169] To avoid overlap between left-shifting paths, the following must be satisfied:

[0170]

[0171] Similarly, assuming the minimum time delay difference between paths is 1, the range of c1 shifted to the left to ensure that paths do not overlap is:

[0172] c1>0;

[0173] Step S423: Derivation of the range of c1 where the left and right shift paths do not overlap. To avoid overlap between the left and right shift paths, the maximum value of all right shift paths must be less than N / 2, and the minimum value of all left shift paths must also be less than N / 2.

[0174] The maximum rightward offset is:

[0175] 2Nc1l max ;

[0176] Make it less than N / 2:

[0177]

[0178] The results were:

[0179]

[0180] The leftward offset is:

[0181] -2Nc1l max ;

[0182] make get:

[0183]

[0184] The results were:

[0185]

[0186] Step S424: Based on steps S421, S422, and S423, for the paths of right and left shifts to not overlap, c1 > 0 must be satisfied. For the paths of left and right shifts to not overlap, the following must be satisfied:

[0187]

[0188] The final range of c1 is:

[0189]

[0190] This enables the ACO-AFDM channel matrix to be completely separated in the DAFT domain, achieving full diversity.

[0191] like Figure 2 As shown, the bit error rate (BER) performance of the ACO-AFDM method and the traditional ACO-OFDM method under different signal-to-noise ratios (SNR) is compared. Analysis shows that under multipath channel conditions, the BER of the ACO-AFDM method is significantly better than that of the ACO-OFDM method, exhibiting a lower BER. With increasing SNR, the BER of ACO-AFDM decreases faster, especially in the high SNR region, where its performance advantage is more significant. Furthermore, ACO-AFDM demonstrates stronger anti-interference capability under multipath channel conditions, effectively suppressing inter-symbol interference (ISI) caused by multipath interference, and significantly enhancing its anti-multipath interference capability.

[0192] Therefore, this invention provides a wireless optical transmission method based on asymmetric limiting optical simulated radio frequency multiplexing (AFDM). By combining the multipath component separation capability of simulated radio frequency multiplexing (AFDM) and the non-negative signal generation mechanism of asymmetric clipping (ACO), it achieves efficient signal transmission in optical communication channels that resists multipath interference. While meeting the requirements for non-negative real number signal transmission in optical communication channels, this invention can significantly improve the system performance in complex multipath scenarios such as multimode fiber communication and free space optical communication, solve the signal distortion problem caused by multipath effects in optical communication, and provide an effective solution for the stability and reliability of optical communication systems in complex scenarios.

[0193] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing, characterized in that, The specific steps are as follows: Step S1: At the transmitting end, the input optical communication signal data is preprocessed, including the mapping of frequency domain data, the design of modulation symbols, and the construction of data symmetry, to generate a frequency domain signal that meets specific conditions. Step S2: Based on the real-valued Discrete Affine Fourier Transform (DAFT), the frequency domain signal generated in step S1 is mapped to the time domain to generate an AFDM time domain signal. Step S3: Asymmetric cropping of the AFDM time-domain signal generated in step S2 is performed using the odd half-wave symmetry characteristic. The negative part of the AFDM time-domain signal is set to zero and transmitted to the receiving end through the optical communication channel. The receiving end performs reverse reconstruction of the signal, including the recovery of the cropped signal and demodulation of the data. Step S4: Based on the design of the realized DAFT kernel function, derive the new... The parameter range enables complete separation of signal paths with different delays in the DAFT domain, achieving full diversity; where... These are free parameters in modulation design.

2. The wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing according to claim 1, characterized in that, In step S1, the input optical communication signal data is mapped onto frequency domain subcarriers to form frequency domain symbols. To ensure that the frequency domain signal is a real number, the frequency domain symbols are set to a conjugate symmetric form, and the formula is as follows: ； in, The symbol representing the k-th subcarrier, for The conjugate of complex numbers, For the first Nk The symbol of each subcarrier, N This represents the number of subcarriers.

3. The wireless optical transmission method based on asymmetric limiting optical radio frequency multiplexing according to claim 2, characterized in that, To meet the requirements of asymmetric clipping, data is loaded only on odd-numbered subcarriers, while the symbols for even-numbered subcarriers are set to zero, as shown in the following formula: ； 。 4. The wireless optical transmission method based on asymmetric limiting optical radio frequency multiplexing according to claim 1, characterized in that, In step S2, the frequency domain signal generated in step S1 is mapped to the time domain using the realized Discrete Affine Fourier Transform (DAFT) to generate the AFDM time domain signal. The specific steps are as follows: Step S21: The formula for calculating the kernel function of the Discrete Affine Fourier Transform (DAFT) is as follows: ； The formula for calculating its inverse transform is as follows: ； in, For input signal, For output signal, For the number of subcarriers, The length of the DAFT transform. These are free parameters in modulation design. m For output signal index, n For the input signal index, j It is an imaginary number; Step S22: Adjust the kernel function of the Discrete Affine Fourier Transform (DAFT) by removing the complex exponential kernel function. Item, will Replace with The adjusted formula for calculating the Discrete Affine Fourier Transform (DAFT) kernel function is as follows: ； The time-domain signal generated by the adjusted kernel function is a real number, and the multipath separation capability of the Discrete Affine Fourier Transform (DAFT) is preserved.

5. A wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing according to claim 4, characterized in that, The calculation formula is as follows: 。 6. The wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing according to claim 4, characterized in that, In step S3, the AFDM time-domain signal generated in step S2 is asymmetrically clipped (ACO) using the odd half-wave symmetry characteristic. The specific steps are as follows: Step S31, due to the time domain signal It exhibits odd half-wave symmetry, and its negative half-part does not carry effective information. The negative part is forced to zero through asymmetric clipping, as shown in the following formula: ； in, It is the cropped signal. t For continuous time variables of the signal; Step S32: Demodulate and restore the received optical signal to achieve accurate data recovery; the receiving end restores the received optical signal to an electrical signal through a photodetector, and uses the known odd half-wave symmetry characteristics to recover the clipped negative half of the signal, as shown in the following formula: ； in, This is a signal of recovery. T The signal period; The inverse transform of the realized DAFT kernel function is performed to recover the frequency domain sign, and the calculation formula is as follows: ； The original input data is extracted by utilizing the conjugate symmetry between frequency domain symbols and the odd subcarrier allocation rule.

7. A wireless optical transmission method based on asymmetric limiting optical analog radio frequency multiplexing according to claim 6, characterized in that, In step S4, the left-shift logic and the offset distance of non-zero elements in the channel matrix are derived, and combined with the right-shift logic, the mapping relationship of the signal path in the DAFT domain is described. The specific steps are as follows: Step S41: Left and right shifts resulting from the realization kernel function; Step S42, Derive the new The parameter range is used to achieve full set division, ensuring that the paths of right and left shifts do not overlap, and that the paths of left and right shifts do not overlap.

8. A wireless optical transmission method based on asymmetric limiting optical radio frequency multiplexing according to claim 7, characterized in that, In step S41, the left and right shifts resulting from the realization kernel function are explained in the following steps: Step S411, in traditional AFDM, The range is derived as follows: The elements of the channel matrix are: ； in, ； when hour, ； Right shift logic is Introduced, its offset is: ； in, It is the first i Path delay, For the first i Channel matrix elements of each path, , For frequency domain indexing, Contribute functions to the frequency domain. For the first i Doppler shift of the path, For the first i Path offset; Step S412: The realization kernel function introduces left-shift logic. In ACO-AFDM, the kernel function is replaced with: ； Left shift logic is Introduced, its channel matrix elements become: ； in, ； when hour: ； The new offset is: ； Left shift logic is Introduced, the non-zero elements of the channel matrix are shifted to the left from the diagonal. One position.

9. A wireless optical transmission method based on asymmetric limiting optical radio frequency multiplexing according to claim 7, characterized in that, In step S42, the new The steps for deriving the parameter range are as follows: Step S421: The right-shifting paths do not overlap. Range derivation: From the derivation of the original AFDM, the right shift is defined by the following formula: ； To avoid overlap between right-shifting paths, the following must be satisfied: ； make Ensure that paths do not overlap, and shift to the right. The scope must meet the following requirements: ； Step S422: The left-shifting paths do not overlap. The range is derived as follows: The offset range for the left shift is: ； To avoid overlap between left-shifting paths, the following must be satisfied: ； Similarly, assuming the minimum time delay difference between paths is 1, the left shift is obtained to ensure that the paths do not overlap. The range is: 0； Step S423: The left-shift path and the right-shift path do not overlap. Range derivation: To avoid overlap between left and right shift paths, the maximum value of all right shift paths must be less than N / 2, and the absolute value of all left shift paths must also be less than N / 2. Step S424: The paths for right and left shifts must not overlap. For the left-shift path and the right-shift path to not overlap, the following conditions must be met: ； in, The maximum delay across multiple paths, ultimately The scope is: 0 ； This enables the ACO-AFDM channel matrix to be completely separated in the DAFT domain, achieving full diversity.

10. A wireless optical transmission method based on asymmetric limiting optical radio frequency multiplexing according to claim 9, characterized in that, In step S423, the maximum rightward offset is: ； Make it less than N / 2: ； The results were: 0 ； The leftward offset is: ； make ,get: ； The results were: 0 。

Images