Atmospheric turbulence compensation system based on Atan nonlinear multiplier

Abstract

The utility model belongs to the technical field of communication systems, and provides an atmospheric turbulence compensation system based on an Atan nonlinear multiplier, which comprises a laser diode, a photodiode, an analog-to-digital converter and a cascade Atan multiplier which are connected in sequence, an OOK signal is modulated by a laser diode, a laser beam is output and received by a photodiode, an optical signal is converted into an electric signal, an analog-to-digital converter receives the electric signal and converts the electric signal into a digital signal, and the scintillation effect is reduced through a cascade Atan multiplier; the device is superior to traditional fixed threshold detection under weak, medium and strong turbulence conditions, and is suitable for dynamic FSO link scenes such as unmanned aerial vehicles, satellites and the like.

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 an Atan nonlinear multiplier. Background Technology

[0002] FSO communication systems are widely used in satellite and mobile communications due to their high speed and wide bandwidth. However, the flickering effect caused by atmospheric turbulence can lead to drastic fluctuations in the intensity of the received optical signal, severely affecting signal detection accuracy and resulting in a significant increase in the bit error rate. Existing technologies have the following drawbacks:

[0003] Traditional hardware compensation solutions, such as adaptive optics technology, are complex and costly, making them difficult to adapt to medium and strong turbulent environments.

[0004] Machine learning methods: high computational complexity, rely on a large amount of training data, and have insufficient generalization ability under strong turbulence conditions.

[0005] Adaptive threshold decision technique: It requires adjusting the decision threshold based on atmospheric turbulence channel information, but accurate channel information estimation is quite difficult.

[0006] The core problem is that existing technologies cannot effectively maintain the extinction ratio of the received on-off keying (OOK) signal while compensating for light intensity fluctuations caused by turbulence, thus limiting the compensation effect.

[0007] Therefore, improvements are needed to address the aforementioned issues in order to meet current requirements. Utility Model Content

[0008] To solve the above-mentioned technical problems, this utility model provides an atmospheric turbulence compensation system based on an Atan nonlinear multiplier to address 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 an Atan nonlinear multiplier includes a laser diode, a photodiode, an analog-to-digital converter, and a cascaded Atan multiplier connected in sequence.

[0010] The OOK signal is modulated by a laser diode, outputting a laser beam which is received by a photodiode and converted into an electrical signal. The analog-to-digital converter receives the electrical signal and converts it into a digital signal, which is then reduced by a cascaded Atan multiplier to reduce flickering.

[0011] Furthermore, the output of the cascaded Atan multiplier is:

[0012] y Atan-Atan [k]=arctan(arctan(r[k]+b1)+b2)

[0013] Where r[k] is the discrete signal strength output by the analog-to-digital converter, and b1 and b2 are adjustable constant offsets.

[0014] Furthermore, the value of the adjustable constant offset b is determined based on the turbulence intensity. Adjustment:

[0015] b1 = 0.5, b2 = 0.5 - 1;

[0016] b1 = 0.5, b2 = 1 - 1.5.

[0017] This utility model has the following beneficial effects:

[0018] (1) Low complexity: The Atan function is simple to calculate, requires no weight learning or external channel information, and is suitable for rapid hardware implementation;

[0019] (2) Dynamic nonlinear compression: Signal compression of different intensities can be achieved by adjusting the adjustable constant offset, adapting to various turbulent scenarios;

[0020] (3) Cascade mechanism to suppress ER distortion: By cascading Atan multipliers, excessive ER distortion caused by single gain compression is suppressed, taking into account both anti-interference performance and signal integrity.

[0021] (4) High scalability: The system is modularly designed, which facilitates the future embedding of deep learning, filters or other detection mechanisms;

[0022] (5) Wide adaptability: Simulation verification shows that it is superior to traditional fixed threshold detection under weak, medium and strong turbulence conditions, and is suitable for dynamic FSO link scenarios such as UAVs and satellites. Attached Figure Description

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

[0024] The following will be based on the embodiments of this utility model. Figure 1 The 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, 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 an Atan nonlinear multiplier includes a laser diode, a photodiode, an analog-to-digital converter, and a cascaded Atan multiplier connected in sequence.

[0026] The OOK signal is modulated by a laser diode, outputting a laser beam which is received by a photodiode and converted into an electrical signal. The analog-to-digital converter receives the electrical signal and converts it into a digital signal, which is then reduced by a cascaded Atan multiplier to reduce flickering.

[0027] Specifically, the OOK signal directly modulates a 1550nm laser beam emitted by a laser diode (LD). The modulated laser beam s(t) is transmitted through an atmospheric turbulence channel, and then at the receiving end, a photodiode (PD) converts the received optical signal into an electrical signal r(t), 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 diode. When transmitting a "1" code, the drive current increases above the threshold current of the laser diode, and the laser diode emits laser light; when transmitting a "0" code, the drive current decreases below the threshold current, and the laser diode stops emitting laser light, thus converting the digital baseband signal (0 / 1 sequence) into a light intensity signal. The OOK optical signal modulated by the laser diode 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 light is output from the laser diode, it needs to be transmitted through an atmospheric channel to the photodiode at the receiving end. The core process is affected by atmospheric turbulence, as detailed below:

[0030] Path propagation: The 1550nm laser emitted by the laser diode 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 light signal reaching the photodiode can be represented as the superposition of light intensity and noise.

[0032] The photoelectric conversion principle of a photodiode is as follows: The photodiode operates in a reverse-biased state, achieving conversion based on the photovoltaic effect. When laser light shines on the photosensitive surface of the photodiode, photon energy excites charge carriers to generate a photocurrent, the magnitude of which is proportional to the intensity of the incident light. 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 photodiode (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 analog-to-digital converter (ADC), and then a cascaded Atan multiplier is used to reduce the flicker effect.

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

[0035] y Atan-Atan [k] = arctan(arctan(r[k] + b1) + b2). Here, r[k] is the discrete signal strength output by the analog-to-digital converter, and b1 and b2 are adjustable constant offsets used to control the degree of nonlinear compression. This structure further weakens turbulent scintillation through secondary nonlinear compression.

[0036] The advantages of the Atan function are: nonlinear gain characteristics: it applies a stronger compression effect to high light intensity fluctuations caused by strong turbulence, maintains a linear response to low fluctuation signals, and avoids excessive distortion.

[0037] Extinction ratio protection: Atan's gain slope changes smoothly, which can reduce the amplitude difference loss between the "0" and "1" codes of the OOK signal.

[0038] The signal state is determined using a fixed threshold (FTD), and the threshold parameters are optimized by combining the output characteristics of the Atan multiplier.

[0039] when (In weak turbulence) the BER approaches the theoretical adaptive threshold decision;

[0040] when In moderate turbulence, the Atan multiplier can reduce the BER by up to two orders of magnitude.

[0041] in It is the refractive index structure constant, representing the intensity of atmospheric turbulence effects.

[0042] Key parameter optimization strategies:

[0043] The bias parameters b1 and b2 are adaptively adjusted according to the turbulence intensity.

[0044] Weak turbulence b1 = 0.5, b2 = 0.5 - 1, balancing gain and linear response;

[0045] Strong turbulence b1 = 0.5, b2 = 1 - 1.5, to enhance nonlinear compressive strength.

[0046] Computational complexity: A single linear operation plus Atan function calculation reduces computation by 90% compared to deep learning solutions, making it suitable for real-time FSO communication systems.

[0047] 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 an Atan nonlinear multiplier, characterized in that, It includes a laser diode, a photodiode, an analog-to-digital converter, and a cascaded Atan multiplier connected in sequence; The OOK signal is modulated by a laser diode, outputting a laser beam which is received by a photodiode and converted into an electrical signal. The analog-to-digital converter receives the electrical signal and converts it into a digital signal, which is then reduced by a cascaded Atan multiplier to reduce flickering.

2. The atmospheric turbulence compensation system based on an Atan nonlinear multiplier according to claim 1, characterized in that, The output of the cascaded Atan multiplier is: and Atan-Atan [k]=arctan(arctan(r[k]+b1)+b2) Where r[k] is the discrete signal strength output by the analog-to-digital converter, and b1 and b2 are adjustable constant offsets.

3. The atmospheric turbulence compensation system based on an Atan nonlinear multiplier according to claim 2, characterized in that, The value of the adjustable constant offset b is determined based on the turbulence intensity. Adjustment: b1=0.5, b2=0.5-1; b1=0.5, b2=1-1.5.

Images