Atmospheric turbulence compensation system based on Logsigmoid nonlinear multiplier

Abstract

The utility model belongs to communication system technical field provides an atmospheric turbulence compensation system based on Logsigmoid nonlinear multiplier, including laser diode (LD), photodiode (PD), analog-digital converter (ADC), cascade Logsigmoid multiplier processing unit and fixed threshold decision device (FTD) that link up in turn, on -off keying (OOK) signal is modulated after the laser beam that LD modulated output, PD receives the laser beam that modulates and converts into electric signal, ADC receives electric signal conversion digital signal, cascade Logsigmoid multiplier processing unit handles digital signal, through secondary nonlinear compression to weaken turbulence flicker, the utility model relies on " logarithm nonlinear differentiation compensation, ER protection, lightweight calculation " three technical advantages, in FSO communication turbulence compensation scene, reaches " performance - complexity - hardware adaptability " collaborative balance.

Description

Technical Field

[0001] This utility model belongs to the field of communication system technology, specifically relating to an atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier. Background Technology

[0002] Free-space optical (FSO) communication systems are widely used in satellite communication, wireless backhaul, and other scenarios due to their high speed and wide bandwidth. However, the signal flickering effect caused by atmospheric turbulence can cause drastic fluctuations in light intensity, which seriously affects the detection accuracy of on-off keying (OOK) signals and leads to a significant increase in bit error rate (BER).

[0003] The existing technology has the following drawbacks:

[0004] Traditional hardware compensation solutions, such as optical pre-magnification technology, are complex and costly, and are difficult to adapt to dynamic turbulent environments.

[0005] Single deep learning methods have high computational complexity, rely on a large amount of training data, and have insufficient generalization ability under strong turbulence conditions.

[0006] Other nonlinear multipliers, such as the Tanh multiplier, can suppress light intensity fluctuations, but they cause significant distortion in the extinction ratio (ER) of the OOK signal, limiting the compensation effect.

[0007] Current technologies cannot effectively maintain the error rate (ER) of OOK signals while suppressing light intensity fluctuations, thus limiting the optimization of bit error rate. Therefore, improvements are needed to address these issues and meet current communication requirements. Utility Model Content

[0008] To address the aforementioned technical problems, this utility model provides an atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier, thereby resolving the issues in the prior art. The technical solution adopted by this utility model is as follows:

[0009] An atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier includes a laser diode, a photodiode, an analog-to-digital converter, a cascaded Logsigmoid multiplier processing unit, and a fixed threshold decision unit connected in sequence.

[0010] The on / off key control signal is modulated by the laser diode to output the modulated laser beam. The photodiode receives the modulated laser beam and converts it into an electrical signal. The analog-to-digital converter receives the electrical signal and converts it into a digital signal. The cascaded Logsigmoid multiplier processing unit processes the digital signal and reduces turbulent scintillation through secondary nonlinear compression.

[0011] Furthermore, the cascaded Logsigmoid multiplier processing unit includes two cascaded Logsigmoid multipliers; the Logsigmoid1 multiplier is used to perform a first-level Logsigmoid transformation on the digital signal and outputs it to the Logsigmoid2 multiplier for a second-level Logsigmoid transformation.

[0012] Furthermore, the output of the cascaded Logsigmoid multiplier is:

[0013]

[0014] Where r[k] is the discrete signal strength output by the analog-to-digital converter, and b1 and b2 are adjustable constant offsets.

[0015] Furthermore, the values ​​of the adjustable constant offsets b1 and b2 are determined based on the turbulence intensity. Adjustment:

[0016] b1 = 5, b2 = 5 - 15;

[0017] b1 = 5, b2 = 15 - 25.

[0018] It is the refractive index structure constant, representing the intensity of atmospheric turbulence effects.

[0019] This utility model has the following beneficial effects:

[0020] (1) For scenarios with varying turbulence intensity, design bias parameters b1 and b2, and adjust the values ​​of b1 and b2 according to the turbulence intensity (such as the scintillation index);

[0021] (2) The computational complexity is only 10% of that of traditional deep learning methods, achieving lightweight computation;

[0022] (3) With the triple technical advantages of “logarithmic nonlinear differential compensation, ER protection, and lightweight computing”, a synergistic balance of “performance-complexity-hardware adaptability” is achieved in the FSO communication turbulence compensation scenario. Attached Figure Description

[0023] Figure 1 This is a structural diagram of the present utility model. Detailed Implementation

[0024] The following will refer to the embodiments of this utility model. Figure 1The technical solutions in the embodiments of this utility model are clearly and completely described. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0025] An atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier includes a laser diode (LD), a photodiode (PD), an analog-to-digital converter (ADC), a cascaded Logsigmoid multiplier processing unit, and a fixed threshold decision device (FTD) connected in sequence.

[0026] The OOK signal is modulated by the LD, outputs a laser beam, and is received by the PD. The optical signal is converted into an electrical signal, which is then received by the ADC and converted into a digital signal. The flicker effect is reduced by a cascaded Logsigmoid multiplier.

[0027] The OOK signal directly modulates the 1550nm laser beam emitted by the LD. The modulated laser beam s(t) is transmitted through an atmospheric turbulence channel. At the receiving end, the received optical signal is converted into an electrical signal r(t) by a PD, expressed as: r(t) = I(t)s(t) + N PD (t). Where I(t) represents the received signal strength at the receiver, s(t) is the transmitted OOK signal, and N PD (t) represents PD noise.

[0028] Specifically, the OOK signal switches between "on" and "off" states by controlling the drive current of the laser illuminator (LD). When transmitting a "1" code, the drive current increases above the LD's threshold current, and the LD emits laser light; when transmitting a "0" code, the drive current decreases below the threshold current, and the LD stops emitting laser light, thus converting the digital baseband signal (0 / 1 sequence) into an optical intensity signal. The OOK optical signal modulated by the LD can be represented as s(t), where s(t) = 1 corresponds to a "1" code (laser emission), and s(t) = 0 corresponds to a "0" code (laser off).

[0029] After the laser is output from the LD, it needs to be transmitted through an atmospheric channel to the PD at the receiving end. The core process is affected by atmospheric turbulence, as detailed below:

[0030] Path propagation: The 1550nm laser emitted by the LD propagates in free space (atmospheric channel), encountering interference from atmospheric turbulence along the way. Turbulence causes intensity flickering and beam drift in the laser beam. A log-normal model is used to simulate the turbulent channel, and its intensity distribution probability density function (PDF) is as follows: Where I is the signal strength, and μ is the mean of ln(I). This is the scintillation index (quantifying turbulence intensity).

[0031] Signal Attenuation and Noise: The optical signal transmitted to the receiving end not only carries the original OOK information s(t), but also includes the intensity fluctuations I(t) caused by turbulence and the photodiode's own noise N. PD Therefore, the optical signal arriving at the PD can be represented as the superposition of light intensity and noise.

[0032] The photoelectric conversion principle of a photodiode (PD) is as follows: The PD operates in a reverse-biased state, achieving conversion based on the photovoltaic effect. When laser light shines on the photosensitive surface of the PD, photon energy excites charge carriers to generate a photocurrent, the magnitude of which is proportional to the incident light intensity. Subsequently, the photocurrent is converted into a voltage signal, i.e., an electrical signal r(t), through circuits such as a transimpedance amplifier. The converted electrical signal is r(t) = I(t)s(t) + N. PD (t), where I(t)s(t) reflects the electrical signal component corresponding to the OOK signal intensity after turbulence, N PD (t) represents the inherent noise of the PD (such as dark current noise, thermal noise, etc.).

[0033] The received electrical signal r(t) obtained by PD conversion is converted into a digital signal r[k] by ADC, and then a cascaded Logsigmoid multiplier is used to reduce the flicker effect.

[0034] The output expression of the cascaded Logsigmoid multiplier is:

[0035] Where r[k] is the discrete signal strength output by the ADC, and b1 and b2 are adjustable constant offsets used to control the degree of nonlinear compression. This structure further weakens turbulent scintillation through quadratic nonlinear compression.

[0036] Key parameter optimization strategies:

[0037] The bias parameters b1 and b2 are adaptively adjusted according to the turbulence intensity.

[0038] when Time: b1 = 5, b2 = 5 - 15;

[0039] when Time: b1 = 5, b2 = 15 - 25.

[0040] The advantage of the Logsigmoid function is that:

[0041] 1. Nonlinear logarithmic characteristics adapt to the dynamic range of light intensity: It can map the light intensity (which usually has a large fluctuation range) to a narrower output range, while preserving the relative strength of the signal, avoiding processing difficulties caused by an excessively wide dynamic range.

[0042] 2. Differentiated response to strong and weak signals: The logarithmic function has a more significant gain attenuation for "strong input" and a relatively mild gain for "weak input". This differentiated characteristic makes it easy to compensate for extreme fluctuations in light intensity (strong light suppression, weak light enhancement) while taking into account both suppression effect and signal integrity.

[0043] 3. Smooth and continuous output: Compared with step transform, LogSigmoid output is a smooth and continuous nonlinear curve, which can adapt to the continuity of light intensity fluctuations, avoid signal distortion during the transformation process, and ensure that the compensated signal is naturally stable.

[0044] The embodiments described above are merely preferred embodiments of the present utility model and are not intended to limit the scope of the present utility model. Any modifications, alterations, alterations, or substitutions made by those skilled in the art to the technical solutions of the present utility model without departing from the spirit of the present utility model shall fall within the protection scope defined by the claims of the present utility model.

Claims

1. An atmospheric turbulence compensation system based on Logsigmoid nonlinear multiplier characterized by, It includes a laser diode, a photodiode, an analog-to-digital converter, a cascaded Logsigmoid multiplier processing unit, and a fixed threshold decision unit connected in sequence; The on / off key control signal is modulated by the laser diode to output the modulated laser beam. The photodiode receives the modulated laser beam and converts it into an electrical signal. The analog-to-digital converter receives the electrical signal and converts it into a digital signal. The cascaded Logsigmoid multiplier processing unit processes the digital signal and reduces turbulent scintillation through secondary nonlinear compression.

2. The atmospheric turbulence compensation system based on Logsigmoid nonlinear multiplier according to claim 1, characterized in that, The cascaded Logsigmoid multiplier processing unit includes two cascaded Logsigmoid multipliers; the Logsigmoid1 multiplier is used to perform a first-level Logsigmoid transformation on the digital signal and outputs it to the Logsigmoid2 multiplier for a second-level Logsigmoid transformation.

3. The atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier according to claim 2, characterized in that, The output of the cascaded Logsigmoid multiplier is: Where r[k] is the discrete signal strength output by the analog-to-digital converter, and b1 and b2 are adjustable constant offsets.

4. The atmospheric turbulence compensation system based on a Logsigmoid nonlinear multiplier according to claim 3, characterized in that, The values ​​of the adjustable constant offsets b1 and b2 are determined based on the turbulence intensity. Adjustment: b1=5, b2=5-15; b1=5, b2=15-25; It is the refractive index structure constant, representing the intensity of atmospheric turbulence effects.

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