Atmospheric Laser Communication Research Articles

A Computational Model of Cn2 Profile Inversion for Atmospheric Laser Communication in the Vertical Path.

In this paper, an atmospheric structure constant Cn2 model is proposed for evaluating the channel turbulence degree of atmospheric laser communication. First, we derive a mathematical model for the correlation between the atmospheric coherence length r0, the isoplanatic angle θ0 and Cn2 using the Hufnagel-Valley (HV) turbulence model. Then, we calculate the seven parameters of the HV model with the actual measured r0 and θ0 data as input quantities, so as to draw the Cn2 profile and the θ0 profile. The experimental results show that the fitted average Cn2 contours and single-day Cn2 contours have superior fitting performance compared with our historical data, and the daily correlation coefficient between the single-day computed θ0 contours and the measured θ0 contours is up to 87%. This result verifies the feasibility of the proposed method. The results validate the feasibility of the proposed method and provide a new technical tool for the inversion of turbulence Cn2 profiles.

Optimal signal receiving technology based on APD in atmospheric laser communications

The intensity fluctuation of atmospheric turbulence significantly affects the performance of the laser communication system. To suppress the turbulence effect, we propose an avalanche photodiode (APD) optimal gain formula under the turbulence channel, taking the real-time received signal-to-noise ratio (SNR) as the evaluation parameter of the turbulence channel’s state. Based on this formula, we design a model of the optimal optical signal receiver in the atmospheric channel, utilizing the Fuzzy-Pi control mechanism to adapt to the nonlinear properties caused by turbulence. The experimental results show the feasibility and advantages of the control mechanism. In addition, when turbulence is weak, as Rytov variance is equal to 0.145, the variance of light intensity flicker is lowered from 0.1353 to 0.103. As Rytov variance rise to 1.068, the variance of light intensity flicker decreased from 0.6547 to 0.32.

High-Precision Log-Ratio Spot Position Detection Algorithm with a Quadrant Detector under Different SNR Environments.

In atmospheric laser communication, a beam is transmitted through an atmospheric channel, and the photocurrent output from a quadrant detector (QD) used as the tracking sensor fluctuates significantly. To ensure uninterrupted communication and to adapt to such fluctuations, in this paper we apply logarithmic amplifiers to process the output signals of a QD. To further improve the measurement accuracy of the spot position, we firstly propose an integral infinite log-ratio algorithm (IILRA) and an integral infinity log-ratio algorithm based on the signal-to-noise ratio (BSNR-IILRA) through analysis of the factors influencing the measurement error considering the signal-to-noise ratio (SNR) parameter. Secondly, the measurement error of the two algorithms under different SNRs and their variations are analyzed. Finally, a spot position detection experiment platform is built to correctly and efficiently verify the two algorithms. The experimental results show that when the SNR is 54.10 dB, the maximum error and root mean square error of the spot position of the IILRA are 0.0054 mm and 0.0039 mm, respectively, which are less than half those of the center approximation algorithm (CAA). When the SNR is 23.88 dB, the maximum error and root mean square error of the spot position of the BSNR-IILRA are 0.0046 mm and 0.0034 mm, respectively, which are one-thirtieth and one-twentieth of the CAA, respectively. The spot position measurement accuracy of the two proposed algorithms is significantly improved compared with the CAA.

Atmospheric Laser Communication Technology Based on Detector Gain Factor Regulation Control

Space laser communication, with its strong anti-jamming capability, high transmission rate and good adaptability, offers hope for the establishment of 5G mobile networks in areas that are not conducive to the erection of cables, such as islands and remote land areas. Turbulent scintillation effect is one of the important factors affecting the performance of laser communication, which can lead to the increase of communication BER and even communication interruption. Based on the working principle of the photoelectric detector in atmospheric turbulence, an optical communication receiving system based on the detector gain factor regulation control is designed, which calculates the scintillation variance according to the received signal in real time, establishes the function conversion relationship between the scintillation variance and the gain factor, realizes the closed-loop regulation control of the detector gain factor, and improves the SNR of the receiving system. A ground-based 13km static laser communication experiment was set up to test the reception performance, and the test results show that the system reduces the communication BER by more than two orders of magnitude and can be kept at 1E-6 under medium to weak turbulence (discriminated by flash variance) at a communication rate of 2.5Gbps. The technology was applied to the test of laser 5G signal transmission between the airship and the ground, and for the first time, the mobile communication (access network) signal transmission with a downlink speed of 1.230Gbps and an uplink speed of 76.4Mbps is realized, which verified the performance of mobile signal transmission between the mobile base station and the fixed station on the ground.

Design and analysis of performance of FSO communication system based on partially coherent beams

In this paper, we investigate that the effects of weather, exponentiated Weibull turbulence and generalized pointing errors based on Beckmann distribution on partially coherent beams and establish a joint channel statistical model, then derive new expressions of the performance parameters of free space optical communication system based on On–Off keying (OOK) modulation by using Meijer’s-G function and Fox-H function, such as average bit error rate (BER), average channel capacity and outage probability. For an atmospheric laser communication system with 1550 nm wavelength and 1 km terrestrial level link, the performance parameters of the system are simulated and analyzed. The results show that with the increase of signal to noise ratio (SNR), the compensation effect for strong turbulence becomes more obvious; on the premise of sacrificing less channel capacity, reducing the spatial coherence length or increasing the plane spot size of the transmitter can significantly improve the BER and outage probability performance of the system; with the increase of receiver aperture diameter, the aperture average effect is more obvious; increasing the receiver aperture diameter can significantly improve the overall performance of the system; in the design of APT (Acquisition,Pointing and Tracking) subsystem, when a certain boresight error is allowed, the random jitter of transmitter is reduced as much as possible.

Research on the key technology of turbulence suppression for atmospheric optical laser communication based on OFDM

Based on the analysis of the two main problems of atmospheric channel in free space optics (FSO), aiming at the problem of laser atmospheric channel especially the problems of frequency selective fading and multipath effect in complex turbulent environment, the suppression method is proposed based on OFDM turbulence effect, the FSO-OFDM system is built, the baseband model of this system and the signal of multi-carrier modulation and demodulation method are studied. First of all, this article systematically analyzes the mechanism of turbulence effect of atmospheric channel, and discusses the model of plane wave laser communication system under the influence of atmospheric turbulence, the space optical communication system model of Gaussian beam of a logarithmic normal turbulent channel is established under the influence of atmospheric turbulence, the probability density function of light intensity is deduced, the methods for analyzing the effects of various atmospheric turbulence effects on system performance using the signal-to-noise ratio probability density function; the OFDM multi-carrier modulation scheme of FSO-OFDM system is designed, the baseband mode model of FSO-OFDM system is constructed, and the modulation and demodulation principle of its signal is studied using this model. Finally, FSO-OFDM system is realized by using MATLAB, and the FSO communication system under the multipath interference is simulated, experiments on bit error rate characteristics under different guard intervals are performed. It is confirmed that the FSO-OFDM system has a strong ability to resist multipath interference and frequency selective fading, as well as good bit error rate (BER) performance. It can effectively solve the problem of intersymbol interference and the reliable link, and has a very broad application prospect and using value.

Transmission characteristics of 24.5 Gb/s atmospheric laser communication based on optical frequency comb

Through cascading Mach–Zehnder intensity modulator (MZIM) and phase modulator (PM), an optical frequency comb (OFC) with 7 flat comb teeth is produced. The frequency interval of the OFC is 25 GHz and the flatness is less than 1.5 dB. The 7 channels of the OFC are used as the carrier source of the one-to-many free-space optical (FSO) communication system, and the atmospheric turbulence simulation pool is used to simulate the turbulence intensity in the real atmosphere to verify its feasibility for FSO communication. In the experiment, the bit error rate (BER) and eye diagram are measured under the back-to-back (BTB) conditions, and the temperature difference of atmospheric turbulence simulation pool are 80 °C, 150 °C and 220 °C. Each channel of the system can stably transmit the on–off keying (OOK) signal of 3.5 Gb/s, and the 7 channels can stably transmit the OOK signal of 24.5 Gb/s. Thereby, the OFC can be used in place of multiple lasers or laser arrays as a carrier source for a one-to-many FSO communication system.

大气激光通信中的完全光广义空间调制

大气激光通信中的完全光广义空间调制

大气激光通信中的多层空间脉冲位置幅度调制

大气激光通信中的多层空间脉冲位置幅度调制

Performance of Free Space Optical Communication Base on Orbital Angular Momentum with Pointing Errors

Due to the misalignment of the receiver, the spiral spectrum appears to be extended when the Laguerre-Gaussian beam is applied to atmospheric laser communication. This paper investigates the spiral spectrum spread of the Laguerre-Gaussian beam in the case of receiver misalignment. The analytical expression of Laguerre-Gaussian spiral spectrum under the influence of alignment error is studied by mathematical derivation and simulation. The results show that the detection probability of the original orbital angular momentum (OAM) state varies with the lateral displacement distance and the inclination angle. The bit error rate and channel capacity of each channel were studied to verify the effects of misalignment in multiple OAM communication systems.

适合于大气激光通信的双空间调制

适合于大气激光通信的双空间调制

Fast wavefront reconstruction method of reception diversity atmospheric laser communication based on Fractional Brownian motion

In order to reconstruct the wavefront of reception diversity atmospheric laser communication, the paper first improves the reconstructing modal method of traditional single-input-single-output laser communication based on mutual information. Because the distortion wavefront caused by atmospheric turbulence is a fractal surface of Fractional Brownian motion, a fast wavefront reconstructing method of reception diversity atmospheric laser communication is proposed in this paper. The result shows that the wavefront reconstructing method based on mutual information can optimize the reconstructing performance effectively. Besides, the running time of proposed reconstructing method of reception diversity atmospheric laser communication decreases greatly. Through the comparison of generated wavefront and reconstructed wavefront, the feasibility of the proposed method is demonstrated. It proves that the wavefront reconstructed by proposed method based on Fractional Brownian motion can fit the theory well through the comparison of phase structure function.

Performance and equilibrium experiment of a multiband CAP modulation system in wireless optical communication

Abstract Multiband carrierless amplitude and phase (MultiCAP) modulation is a modulation mode based on Carrierless Amplitude and Phase (CAP). To improve the capability of a short distance optical communication system for communication capacity and frequency band utilization, multiband CAP modulation technology is adopted. In this article, the diagram for MultiCAP modulation signal of signal-to-noise ratio and bit error rate was analyzed under the condition of Gamma–Gamma atmospheric turbulence channel model. The bit error rate of 4 the band CAP modulation system has been discussed under conditions of different intensity fluctuation variance and signal-to-noise ratio. The simulation results show that when the total bandwidth is constant, the larger the frequency band is, the lower bit error rate is. When the value of σ R 2 is small, the system error rate decreases with increasing signal-to-noise ratio. When the σ R 2 is larger, the system error rate decreases with decreasing σ R 2 . The experimental results of atmospheric laser communication show that the receiver branch signal phase shift are well compensated and intersymbol interference is effectively suppressed after using MMA algorithm for equilibrium, and the bit error rate of each branch signal is decreased from 1 0 − 3 to 2 . 4462 × 1 0 − 4 . Consequently, the system transmission performances improve.

Autofocusing and spreading of partially coherent Butterfly beams modulated by flat-topped factor in atmospheric turbulence

By transferring higher hierarchy Butterfly catastrophe to optical field, the autofocusing behavior and beam spreading of partially coherent Butterfly beams modulated by flat-topped factor in atmospheric turbulence are investigated, where the input power is fixed. In the process of autofocusing behavior the main lobe remains its location near origin, which is different from the movement of main lobe in a lower hierarchy Pearcey beam. The turbulence does not change the autofocusing behavior, but accelerates the decaying in side lobes of butterfly structure. A higher coherence length can lead to a more concentrated intensity at autofocusing plane. The analysis of beam spreading also indicates that there exist critical values of propagation distance of zc. A smaller flat-topped factor tends to maintain a smaller spreading for z<zc, while for z>zc the opposite case can be found. Angular spread decreases with an increasing of coherence length, and a smaller beam order shows a larger far field divergence angle. The study of partially coherent Butterfly beams in turbulence provides the possibility of the atmospheric laser communication by using higher-order catastrophe optical field.

Analysis of Atmospheric Transmission Characteristics on the Bit Error Rate of Atmospheric Laser Communication System

Analysis of Atmospheric Transmission Characteristics on the Bit Error Rate of Atmospheric Laser Communication System

离散速率条件下的大气激光通信自适应调制编码系统性能

离散速率条件下的大气激光通信自适应调制编码系统性能

部分相干光束在大气湍流中传输的散斑特性

The intensity and phase of the beam propagated in the atmospheric turbulence were modulated by the effects of atmospheric turbulence, and then the speckle was formed in the far field. The partially coherent Gaussian-Schell Model (GSM) beam was taken as the research object. According to the generalized Huygens-Fresnel principle and the mode of the modified Von Karman spectrum, the expressions of the effective radius and the mean speckle radius of receiver beam were derived. The expressions were used to analyze the effects of the beam source parameters and atmospheric turbulence on the effective radius and the mean speckle radius. The numerical results show that the greater the waist radius of the beam source, the smaller the coherent length is, the smaller the wavelength is, and then the smaller the effects of atmospheric turbulence on the effective radius and the mean speckle radius of receiver beam are. The smaller refractive-index structure constant, the greater the beam spread and the smaller the mean speckle radius is. The effective radius and the mean speckle radius of receiver beam decrease with increasing inner-scale of turbulence, but have nearly no change with increasing outer-scale of turbulence. An important reference value will be provided for the design of the Acquisition, Tracking and Pointing (ATP) in atmospheric laser communication system.

20 Gbit/s atmospheric laser communication based on dense wavelength division multiplexing

针对目前高速率信息传输的迫切需求，设计并实验了两路数字信号密集波分复用(DWDM)的大气激光通信结构。两路激光波长分别为1 539.76 nm和1 540.55 nm，采用强度调制，光信号经复用和放大后，由光学天线发射，经1 km大气信道传输，在接收端对光谱、波形和眼图进行了测量。实验结果显示，在弱湍流情况下，实现了两路光信号的解复用，并得到了较为清晰的波形图和眼图。两路数字信号的传输速率为20 Gbit/s时，Q因子仍达到5以上。

大气激光通信中自适应调制编码技术的模式选择阈值

大气激光通信中自适应调制编码技术的模式选择阈值

大气激光通信光束同轴对准检测方法

大气激光通信光束同轴对准检测方法