Method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system through geometric shaping

Abstract

The invention discloses a method for optimizing noise of a discrete spectrum nonlinear frequency division multiplexing system through geometric shaping, and belongs to the technical field of communication. The method for optimizing the noise of the discrete spectrum nonlinear frequency division multiplexing system through geometric shaping comprises the steps that ASE noise is considered, and a channel model under the noise condition is established; on the basis of a channel model under a noise condition, an olive-type 32QAM is designed in a discrete spectrum nonlinear frequency division multiplexing system, optical signals are mapped into point distribution of the olive-type 32QAM by optimizing geometric distribution of constellation points, the occurrence probability of high-power points is reduced, the influence of accumulated spontaneous emission noise (ASE) and phase noise is reduced, and the performance of the discrete spectrum nonlinear frequency division multiplexing system is improved. Therefore, the anti-noise performance of the signal and the transmission stability of the system are improved.

Description

Technical Field

[0001] The invention belongs to the field of communication technology, and in particular relates to a noise optimization method for a discrete spectrum nonlinear frequency division multiplexing system by performing geometric shaping. Background Art

[0002] With the explosive growth of global information volume, fiber optic communication, as the core technology of backbone networks, faces unprecedented challenges in bandwidth and transmission distance. Conventional fiber optic communication is affected by nonlinear effects at longer transmission distances, resulting in signal distortion and performance degradation. These nonlinear effects severely limit the transmission capacity and distance of fiber optic communication. In order to cope with these problems, researchers have proposed a variety of nonlinear compensation technologies, among which nonlinear frequency division multiplexing (NFDM) technology has shown great application potential by virtue of its utilization of channel nonlinear characteristics. The NFDM system maps the spectrum of optical signals to a nonlinear spectrum through an inverse nonlinear Fourier transform (INFT). Unlike traditional linear fiber optic transmission, the NFDM system can transform the unfavorable nonlinear effects in the optical fiber into a favorable signal transmission mechanism, so that the signal can be stably transmitted on the nonlinear spectrum. This technology generates a special soliton pulse by solving the nonlinear Schrödinger equation (NLSE), and uses the self-stabilizing characteristics of the soliton pulse to achieve long-distance distortion-free transmission without loss or noise. Nonlinear spectrum can be divided into discrete spectrum (DS) and continuous spectrum (CS), among which discrete spectrum NFDM (DS-NFDM) is more suitable for high-order modulation formats and long-distance optical fiber transmission due to its stability. However, under actual transmission conditions, optical fiber links are inevitably affected by factors such as spontaneous emission noise (ASE), phase noise and amplifier non-ideality.

[0003] ASE noise not only interferes with the amplitude and phase of the signal, but also reduces the signal demodulation accuracy at the receiving end; phase noise is mainly caused by the laser, which will cause the phase of the transmitted signal to jitter and offset, resulting in an increase in the bit error rate (BER) of the demodulated signal. The existence of these noise factors makes it difficult for the performance of the NFDM system to maintain an ideal state, thus affecting the stability and data throughput of long-distance transmission. In order to improve the anti-noise ability of the NFDM system, researchers have proposed a variety of anti-noise optimization schemes. For example, Kalman filtering can effectively reduce the interference of random noise on the system, while the neural network model can learn the characteristics of the impact of noise on the system through training a large amount of historical data, thereby combating the noise in the system. However, schemes such as neural networks have high computational complexity and high requirements for equipment resources in practical applications, making it difficult to adapt to low-cost and high real-time requirements. In terms of high-order modulation formats, 32QAM has attracted widespread attention due to its good bandwidth utilization. However, under high-order modulation conditions, the signal is more sensitive to phase noise and amplitude noise, and existing schemes are difficult to ensure the stability of the system while maintaining a high transmission distance. Therefore, how to enhance noise tolerance by optimizing modulation format and phase recovery technology in NFDM systems remains one of the key issues to be solved urgently. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for optimizing the noise of a discrete spectrum nonlinear frequency division multiplexing system by using geometric shaping, thereby solving the problems in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] The method for optimizing the noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping comprises the following steps:

[0007] Considering ASE noise, a channel model under noisy conditions is established;

[0008] Based on the channel model under noisy conditions, an olive-shaped 32QAM is designed in a discrete spectrum nonlinear frequency division multiplexing system. By optimizing the geometric distribution of constellation points, the optical signal is mapped to the olive-shaped 32QAM point distribution.

[0009] Furthermore, when establishing a channel model under noisy conditions, in a noise-free environment, the fiber transmission process follows lossless NLSE, and the characteristic value of each soliton pulse remains unchanged. However, if ASE noise exists, the NLSE envelope electric field function is:

[0010] iq z -q tt -2|q| 2 q=η(z,t)

[0011] Where z and t are the normalized distance of the optical fiber and the normalized delay time in the envelope synchronous motion frame, respectively, q represents the complex envelope of the optical signal, and η(z, t) represents a zero-mean circularly symmetric additive white Gaussian noise term.

[0012] Furthermore, in the presence of ASE noise, the characteristic value λ of each soliton pulse i will be distorted and become λ d =λ i +Δλ; The distortion of the eigenvalue will cause noise in the spectrum amplitude. The spectrum amplitude disturbance accumulates with the increase of the propagation distance, which is manifested as:

[0013]

[0014]

[0015] In the formula, log is the logarithm operation, represents q after NFT, and Δλ is the distortion amount of the eigenvalue.

[0016] Furthermore, during the transmission of optical signals, the accumulated ASE noise will affect the signal. The output discrete-time channel model Y is set to the square root of the output signal amplitude A, and its conditional probability density function is:

[0017]

[0018] in, is the normalized cumulative ASE noise variance, and I1(g) is the first kind modified Bessel function.

[0019] Furthermore, the olive-shaped 32QAM constellation point distribution is a symmetrical structure, and three elliptical rings with different radii are set to distribute different power points.

[0020] Furthermore, the olive-shaped 32QAM constellation diagram is divided into four parts:

[0021] The first part consists of 8 symmetrically distributed points on the imaginary axis. The relative positions of the constellation points are (±1+1i) 2 ,(±3+3i) 2 ,(±5+5i) 2 ,(±7+7i) 2 ;

[0022] The second to fourth parts are three elliptical rings from the inside to the outside, and the innermost ring E1 contains 4 ideal constellation points (1+3i) 2 ,(-1+3i) 2 ,(3+i) 2 ,(-3+i) 2; The middle ring E2 has 8 ideal points (-1+5i) 2 ,(1+5i) 2 ,(-5+i) 2 ,(5+i) 2 ,(-3+5i) 2 ,(3+5i) 2 ,(5+3i) 2 ,(-5+3i) 2 ; The outermost ring E3 has 12 ideal constellation points (-1+7i) 2 ,(1+7i) 2 ,(-7+i) 2 ,(7+i) 2 ,(-3+7i) 2 ,(3+7i) 2 ,(7+3i) 2 ,(-7+3i) 2 ,(-5+7i) 2 ,(5+7i) 2 ,(7+5i) 2 .

[0023] Furthermore, in a noise-free environment, the optical signal of the discrete spectrum nonlinear frequency division multiplexing system is mapped from the nonlinear spectrum to the time domain through an inverse nonlinear Fourier transform.

[0024] A computer storage medium stores a readable program, which can execute the above-mentioned method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping when the program is running.

[0025] An electronic device, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0026] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute operations corresponding to the above-mentioned method for noise optimization of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping.

[0027] A computer program product includes computer instructions, wherein the computer instructions instruct a computing device to execute operations corresponding to the above-mentioned method for noise optimization of a discrete spectrum nonlinear frequency division multiplexing system by geometric shaping.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention designs the constellation distribution of Olive-32QAM, so that the discrete spectrum nonlinear frequency division multiplexing system has significant noise resistance when facing spontaneous emission noise (ASE) and phase noise. Under this geometric shaping scheme, the constellation points of Olive-32QAM are arranged in a symmetrical geometric structure, which effectively reduces the noise impact caused by high-power signal points and makes signal transmission more stable. Under the same bit error rate requirement (BER = 3.8×10 -3 ), the olive-shaped 32QAM scheme improves the OSNR gain by about 1.7dB under OSNR conditions compared with the traditional 32QAM scheme, and at the same time increases the transmission distance by 157 kilometers compared with the traditional 32QAM scheme.

[0030] 2. This optimization scheme improves the system's tolerance to signal amplitude and phase deviation by adjusting the distribution of constellation points, provides an efficient noise-resistant method for long-distance fiber transmission, and significantly enhances the system's transmission performance under low signal-to-noise ratio conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 It is the olive-shaped 32QAM design diagram of the present invention;

[0033] Figure 2 It is a simulation flow chart of the present invention;

[0034] Figure 3 It is the constellation diagram and three-dimensional kernel density diagram of 32APSK, 32QAM and Olive-32QAM of the present invention;

[0035] Figure 4 is a relationship diagram of OSNR, BER and maximum kernel density of different modulation transmission schemes of the present invention;

[0036] Figure 5 The BER performance of 32APSK, 32QAM and olive-shaped 32QAM under different OSNRs of the present invention;

[0037] Figure 6 It is a BER performance diagram of 32APSK, 32QAM and Olive-32QAM of the present invention under different LWs. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] The method for optimizing the noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping comprises the following steps:

[0041] S1, considering ASE noise, establish a channel model under noisy conditions;

[0042] Assuming that there is no noise in the system, the optical signal of the discrete spectrum NFDM system is mapped from the nonlinear spectrum to the time domain through the inverse nonlinear Fourier transform (NFT). At this time, the fiber transmission process follows the lossless nonlinear Schrödinger equation (NLSE). In a noise-free environment, the NLSE is completely integrable, which means that the eigenvalue of each soliton pulse can remain unchanged and the optical signal can propagate stably. However, the actual single-mode optical fiber cannot provide a lossless and noise-free transmission environment. Assuming that ASE noise exists, the NLSE envelope electric field function can be written as:

[0043] iq z -q tt -2|q| 2 q=η(z,t)(1)

[0044] Where z and t are the normalized distance of the optical fiber and the normalized delay time in the envelope synchronous motion frame, respectively, q represents the complex envelope of the optical signal, and η(z, t) represents a zero-mean circularly symmetric additive white Gaussian noise term.

[0045] Ideally, NLSE is integrable, which means that during the transmission, every eigenvalue in the multi-soliton signal remains unchanged. However, in the presence of ASE noise, the eigenvalue λ i will be distorted and become λ d =λ i +Δλ. The distortion of the eigenvalue will cause noise in the spectral amplitude. These spectral amplitude disturbances accumulate as the propagation distance z increases, and are expressed as:

[0046]

[0047]

[0048] In the formula, log is the logarithm operation, represents q after NFT, and Δλ is the distortion amount of the eigenvalue.

[0049] During the transmission of optical signals, the accumulated ASE noise will affect the signal; the output discrete-time channel model Y is set to the square root of the output signal amplitude A, and its conditional probability density function is expressed as:

[0050]

[0051] in, is the normalized cumulative ASE noise variance, I1(g) is the first kind of modified Bessel function, and the probability distribution function (PDF) is actually a non-central chi-square distribution with four degrees of freedom, thus having non-Gaussian statistical characteristics. According to formula (4), in the NFDM system, ASE noise is affected by the signal amplitude. This is because the amplitude of the signal directly affects its power, and the power is related to the accumulation of ASE noise. Higher amplitudes will lead to higher peak powers, increasing the impact of ASE noise.

[0052] S2, based on the channel model under noisy conditions established in S1, designs an olive-shaped 32QAM to replace the traditional 32QAM in the discrete spectrum nonlinear frequency division multiplexing system. By optimizing the geometric distribution of the constellation points, the optical signal is mapped to the olive-shaped 32QAM constellation point distribution, which reduces the probability of high power points and the impact of accumulated spontaneous emission noise (ASE) and phase noise, thereby improving the signal's noise resistance and system transmission stability.

[0053] In the traditional 32QAM constellation design, the density and distribution of constellation points easily lead to large deviations of high power points under the influence of noise. To solve this problem, the 32QAM constellation is redesigned in this embodiment so that its distribution presents an olive-shaped geometric structure (such as Figure 1 The specific design is as follows:

[0054] 1) The constellation point distribution of the olive-shaped 32QAM is a symmetrical structure. By setting three elliptical rings with different radii to distribute different power points, the frequency of high power points is reduced and the interference between signals is reduced;

[0055] 2) The olive-shaped 32QAM constellation diagram is specifically divided into four parts, of which the first part is 8 symmetrically distributed points on the imaginary axis, and the relative positions of the constellation points are (±1+1i) 2 ,(±3+3i) 2 ,(±5+5i) 2 ,(±7+7i) 2 ; The second to fourth parts are three elliptical rings from the inside to the outside, and the innermost ring E1 contains 4 ideal constellation points (1+3i) 2 ,(-1+3i) 2 ,(3+i) 2,(-3+i) 2 ; The middle ring E2 has 8 ideal points (-1+5i) 2 ,(1+5i) 2 ,(-5+i) 2 ,(5+i) 2 ,(-3+5i) 2 ,(3+5i) 2 ,(5+3i) 2 ,(-5+3i) 2 ; The outermost ring E3 has 12 ideal constellation points (-1+7i) 2 ,(1+7i) 2 ,(-7+i) 2 ,(7+i) 2 ,(-3+7i) 2 ,(3+7i) 2 ,(7+3i) 2 ,(-7+3i) 2 ,(-5+7i) 2 ,(5+7i) 2 ,(7+5i) 2 , ensuring the stability and anti-interference of signal distribution;

[0056] 3) The adjustment of the elliptical ring distribution ensures that the spacing between constellation points of different amplitudes is appropriate, which reduces the cumulative impact of ASE noise and enhances the constellation point's tolerance to phase noise.

[0057] Based on similar inventive concepts, an embodiment of the present invention further provides a computer storage medium storing a readable program, which, when running, can execute the above-mentioned method for optimizing noise of a discrete spectrum nonlinear frequency division multiplexing system by using geometric shaping.

[0058] Based on similar inventive concepts, an embodiment of the present invention provides an electronic device, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0059] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute operations corresponding to the above-mentioned method for noise optimization of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping.

[0060] Based on similar inventive concepts, an embodiment of the present invention further provides a computer program product, including computer instructions, which instruct a computing device to execute operations corresponding to the above-mentioned method for optimizing noise in a discrete spectrum nonlinear frequency division multiplexing system by geometric shaping.

[0061] Example 2

[0062] The performance of the Olive-32QAM mentioned in Example 1 is verified by simulation below;

[0063] like Figure 2 As shown in the figure, in order to verify the performance of the proposed Olive-32QAM, a 2Gbaud single-polarization DS-NFDM system is built in this embodiment, and the performance of the scheme is verified through two transmission scenarios: optical fiber link and BTB. At the transmitting end, the data sequence is generated into Olive-32QAM symbols through symbol mapping. The eigenvalue λ set by the system k is 0.25i. After that, the transmission characteristic value pulse is generated by Darboux transformation (i.e. inverse nonlinear Fourier transformation). The central wavelength of the transmitting end laser is 1550nm. Figure 2 As shown in Figure 1, in the BTB test scenario, the software built-in module "Set OSNR" is used to add additive white Gaussian noise (AWGN) to adjust the signal-to-noise ratio (OSNR) to test the impact of OSNR on the signal. Figure 2 In the optical fiber link transmission scenario of II, the fiber input power of the DS-NFDM signal is set to 5.6dBm. Each optical fiber loop includes a 50-kilometer standard single-mode fiber (SSMF), an EDFA with a noise figure of 6dB, and the dispersion, nonlinear coefficient and attenuation parameters of the optical fiber are set to 16.8ps / (nm·km), 1.3 / W / km and 0.2dB / km, respectively. In addition, an optical bandpass filter (OBPF) with a bandwidth of 39.2GHz is also used in this embodiment to filter out out-of-band noise. At the coherent receiving end, the central wavelength of the local oscillator laser is set to 1550nm, and the received signal will undergo offline digital signal processing, mainly including: normalization, NFT, channel equalization, frequency offset estimation, carrier phase recovery and other algorithms, and then through geometric shaping inverse mapping relative to the transmitting end, the BER value of the system is finally obtained. The number of test symbols for each sample point is 2048, and it is obtained by averaging 20 times.

[0064] Kernel density estimation is applied to smooth the constellation distribution. In this embodiment, kernel density analysis is used as an important non-parametric estimation method to evaluate the distribution stability of the Olive-32QAM constellation under noise conditions. Kernel density estimation places a kernel function around each data point to smooth the discrete constellation point distribution into a continuous probability density curve, thereby effectively revealing the degree to which the constellation point is affected by noise. This embodiment uses a Gaussian kernel as an analysis tool, and its formula is:

[0065]

[0066] in represents the estimated density function, n is the number of samples, h is the smoothing parameter (i.e., bandwidth), and K is the kernel function. When the bandwidth is properly selected, kernel density analysis can balance noise smoothing and accuracy requirements and effectively characterize the distribution characteristics of constellation points.

[0067] To verify the anti-noise performance of Olive-32QAM, this embodiment verifies the constellation density distribution under different optical signal-to-noise ratios (OSNR) through simulation. Figure 3 (a), (b) and (c) are examples of constellation diagrams for 32APSK, 32QAM and Olive-32QAM, respectively. Figure 3 (d), (e) and (f) are the corresponding kernel density plots of 32APSK, 32QAM and Olive-32QAM respectively. Under the condition of OSNR of 12dB, the bit error rate (BER) of Olive-32QAM has reached the predetermined target (BER = 3.8×10 -3 ), while the traditional 32QAM and 32APSK did not meet the standard, indicating that Olive-32QAM has better noise resistance under low OSNR. In addition, Olive-32QAM shows a higher density concentration, its constellation point distribution is more concentrated, and it is less affected by noise. In contrast, the constellation point distribution of traditional 32QAM and 32APSK is more dispersed, and the density is one order of magnitude lower than that of Olive-32QAM, indicating that the olive-shaped structure has significant advantages in combating amplitude noise and phase noise.

[0068] Figure 4 The BER and kernel density performance of three different transmission schemes at different OSNRs are shown. Figure 4 From the left vertical axis of (a), it can be seen that the BER of each scheme decreases with the increase of OSNR. The Olive-32QAM scheme is always better than 32QAM and 32APSK in the test range, and the 32QAM modulation scheme performs the worst. Specifically, when the OSNR is 12dB, Olive-32QAM can already achieve BER=3.8×10 -3 The threshold requirement is met, and 32QAM and 32APSK cannot meet the performance requirements. -3 When the ratio is 0.04, Olive-32QAM can bring about 1dB more OSNR gain than 32APSK and about 1.7dB more OSNR gain than 32QAM. Figure 4 The vertical axis on the right side of (a) shows the curve of kernel density changing with OSNR. The maximum kernel density of the constellation diagram under different OSNR conditions can be used to obtain the noise impact on this constellation distribution. The larger the kernel density, the smaller the impact of amplitude and phase noise, and the more concentrated the symbol distribution. Figure 4(b)-(g) in the figure are the kernel density diagrams of 32QAM, 32APSK and Olive-32QAM under 12dB and 14dB conditions, respectively. It can be seen that the relationship between the highest kernel density of constellation points and OSNR shows a trend opposite to that of BER-OSNR, and the kernel density increases as OSNR increases. It is worth noting that the kernel density of Olive-32QAM is always higher than that of the other two modulation modes under different OSNRs. Specifically, when the OSNR is 14dB, the BER of each modulation scheme has reached the threshold requirement, and at this time, the highest kernel density of Olive-32QAM is one order of magnitude higher than that of 32APSK, and 32APSK is one order of magnitude higher than that of 32QAM. Therefore, under the same OSNR conditions, the Olive-32QAM modulation scheme can make the distribution of constellation points more concentrated than 32APSK and 32QAM, and is more efficient in combating amplitude and phase noise, and can still maintain a high transmission capacity under relatively low BER conditions. On the contrary, the 32QAM and 32APSK modulation schemes are more sensitive to noise.

[0069] The verification also found that as the OSNR increases, the kernel density distribution curve of Olive-32QAM changes smoothly, and the constellation points maintain a stable distribution structure, while the kernel density distribution of traditional 32QAM and 32APSK is more susceptible to noise and presents an obvious scattered state. These results show that the superior noise resistance of Olive-32QAM under spontaneous emission noise (ASE) and phase noise conditions can be clearly verified through kernel density analysis. By optimizing the distribution of constellation points, the present invention reduces the interference of noise on the signal while improving the signal concentration, providing a more robust solution for long-distance and efficient optical fiber transmission.

[0070] like Figure 5As shown, in this embodiment, the olive-shaped 32QAM is tested for anti-ASE noise, and the OSNR test range is 11dB to 22dB. After taking log, the point where BER is 0 disappears in the figure. Studies have shown that in the transmission process of the NFDM system, QAM modulation is greatly affected by noise, and the transmission effect is worse than that of APSK modulation. Under the same OSNR, the BER of 32QAM, 32APSK and olive-shaped 32QAM decreases successively. When the OSNR is 12dB, the two modulation schemes of 32APSK and 32QAM cannot reach below the threshold line of BER, while the olive-shaped 32QAM can meet the performance requirements at this time. When the BER is 3.8e-3, the olive-shaped 32APSK can bring about 1.1dB OSNR gain compared to 32APSK, and about 1.7dB OSNR gain relative to 32QAM. The olive-shaped 32APSK modulation scheme has a better transmission effect than 32QAM and 32APSK under low signal-to-noise ratio conditions, which shows that it has a higher tolerance to ASE noise.

[0071] In addition, the tolerance performance of the proposed olive-shaped 32QAM to phase noise is also tested in this embodiment. Figure 6 Figures (a), (b), and (c) are phase noise tests of three modulation formats under different OSNR conditions. In order to fully demonstrate the advantages and disadvantages of the modulation scheme, the BER of the test is obtained without using any carrier phase recovery algorithm or equalization algorithm. As the OSNR increases, the tolerance of each modulation scheme to line width (LW) also increases. Figure 6 As shown in (a) in Figure 1, when the OSNR is 12dB, the BER of 32QAM and 32APSK cannot meet the threshold requirement, but the olive-shaped 32QAM can tolerate a line width of about 1.1kHz. Figure 6 As shown in (b) in Figure 1, when the OSNR is 17 dB, the olive-shaped 32QAM tolerates approximately 3.2 kHz more line width than 32APSK, and approximately 3.6 kHz more line width than 32QAM. Figure 6 As shown in (c) in Figure 1, as OSNR increases, the gap between the linewidth tolerance of the olive-shaped 32QAM and the other two schemes also increases. When the OSNR is 22dB, the proposed olive-shaped 32QAM can tolerate a linewidth of about 7.1kHz. Therefore, Olive-32QAM has a higher tolerance to phase noise.

[0072] The method of the present invention may be implemented in hardware, firmware, or as software or computer code that may be stored in a recording medium (such as a CDROM, RAM, floppy disk, hard disk, or magneto-optical disk), or as computer code that is originally stored in a remote recording medium or a non-temporary machine-readable medium downloaded over a network and will be stored in a local recording medium, so that the method described herein may be stored in such software processing on a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It is understood that a computer, processor, microprocessor controller, or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code, and when the software or computer code is accessed and executed by a computer, processor, or hardware, the method described herein is implemented. In addition, when a general-purpose computer accesses the code for implementing the method shown herein, the execution of the code converts the general-purpose computer into a dedicated computer for executing the method shown herein.

[0073] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for optimizing noise in discrete spectrum nonlinear frequency division multiplexing systems using geometric shaping, characterized in that: The following steps are involved: Considering ASE noise, a channel model under noisy conditions is established; Based on the channel model under noisy conditions, an olive-shaped 32QAM is designed in a discrete spectrum nonlinear frequency division multiplexing system. By optimizing the geometric distribution of constellation points, the optical signal is mapped to the olive-shaped 32QAM point distribution.

2. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 1, characterized in that: When establishing a channel model under noisy conditions, in a noise-free environment, the fiber transmission process follows lossless NLSE, and the characteristic value of each soliton pulse remains unchanged. However, if ASE noise exists, the NLSE envelope electric field function is: iq z -q tt -2|q| 2 q=η(z,t) Where z and t are the normalized distance of the optical fiber and the normalized delay time in the envelope synchronous motion frame, respectively, q represents the complex envelope of the optical signal, and η(z, t) represents a zero-mean circularly symmetric additive white Gaussian noise term.

3. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 2, characterized in that: In the presence of ASE noise, each soliton pulse characteristic value λ i will be distorted and become λ d =λ i +Δλ; The distortion of the eigenvalue will cause noise in the spectrum amplitude. The spectrum amplitude disturbance accumulates with the increase of the propagation distance, which is manifested as: In the formula, log is the logarithm operation, represents q after NFT, and Δλ is the distortion amount of the eigenvalue.

4. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 3, characterized in that: During the transmission of optical signals, the accumulated ASE noise will affect the signal. The output discrete-time channel model Y is set to the square root of the output signal amplitude A, and its conditional probability density function is: in, is the normalized cumulative ASE noise variance, and I1(g) is the first kind modified Bessel function.

5. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 1, characterized in that: The olive-shaped 32QAM constellation point distribution is a symmetrical structure, and three elliptical rings with different radii are set to distribute different power points.

6. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 5, characterized in that: The olive-shaped 32QAM constellation diagram is divided into four parts: The first part consists of 8 symmetrically distributed points on the imaginary axis. The relative positions of the constellation points are (±1+1i) 2 ,(±3+3i) 2 ,(±5+5i) 2 ,(±7+7i) 2 ; The second to fourth parts are three elliptical rings from the inside to the outside, and the innermost ring E1 contains 4 ideal constellation points (1+3i) 2 ,(-1+3i) 2 ,(3+i) 2 ,(-3+i) 2 ; The middle ring E2 has 8 ideal points (-1+5i) 2 ,(1+5i) 2 ,(-5+i) 2 ,(5+i) 2 ,(-3+5i) 2 ,(3+5i) 2 ,(5+3i) 2 ,(-5+3i) 2 ; The outermost ring E3 has 12 ideal constellation points (-1+7i) 2 ,(1+7i) 2 ,(-7+i) 2 ,(7+i) 2 ,(-3+7i) 2 ,(3+7i) 2 ,(7+3i) 2 ,(-7+3i) 2 ,(-5+7i) 2 ,(5+7i) 2 ,(7+5i) 2 .

7. The method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to claim 1, characterized in that: In a noise-free environment, the optical signal of a discrete spectrum nonlinear frequency division multiplexing system is mapped from the nonlinear spectrum to the time domain by inverse nonlinear Fourier transform.

8. A computer storage medium storing a readable program, characterized in that: When the program is running, the method for optimizing noise of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping as described in any one of claims 1 to 7 can be executed.

9. An electronic device, characterized in that: include: A processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other via the communication bus; The memory is used to store at least one executable instruction, and the executable instruction enables the processor to perform operations corresponding to the method for noise optimization of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping according to any one of claims 1-7.

10. A computer program product comprising computer instructions, characterized in that: The computer instructions instruct the computing device to execute operations corresponding to the method for noise optimization of discrete spectrum nonlinear frequency division multiplexing system by geometric shaping as described in any one of claims 1 to 7.

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