Satellite Laser Communication Systems Research Articles

Performance of HQAM/XQAM Laser Communication System in Anisotropic Non-Kolmogorov Ground–HAP–Satellite Uplink

Satellite laser communication can achieve high-speed, high-precision, and high-security broadband communication without being constrained by the electromagnetic spectrum, which has attracted attention. So, this paper proposes the use of a high-altitude platform (HAP) under anisotropic non-Kolmogorov turbulence to improve the communication performance of the system. Cross quadrature amplitude modulation (XQAM) and hexagon quadrature amplitude modulation (HQAM) are applied to the ground–HAP–satellite (G-H-S) laser communication system. Considering the combined effects of uplink light intensity scintillation, beam wander, and the angle of arrival fluctuation, the G-H-S system’s bit error rate (BER) closure expression is derived under the EW distribution. Simultaneously, the relationship between the G-H-S system’s signal-to-noise ratio (SNR) and BER under different anisotropic factor u values is simulated and compared with the traditional ground–satellite (G-S) system. The results show that the communication performance of the G-H-S system with HQAM modulation is better. In addition, the effects of the zenith angle, receiving aperture, transmitter beam radius, and beam divergence angle on the BER performance of the system are also studied. Finally, the correctness of the analysis results is verified via Monte Carlo simulation. This research will benefit the design and optimization of satellite laser communication systems.

Research on the performance of multiple-input/multiple-output space-frequency block coded system with exponential Weibull distribution in the satellite laser communication

We propose an orthogonal frequency division multiplexing multiple-input/multiple-output space-frequency block-coded (MIMO-SFBC) system based on the exponential Weibull distribution model for uplink and downlink satellite laser communication. Considering the different effects of atmospheric turbulence on the laser beam, the closed expression of bit error rate (BER) was derived for the proposed system. The relationship between the BER and signal-to-noise ratio was analyzed under uplink and downlink, respectively, and compared with the single-input/single-output and space-time block-coded systems. Simultaneously, the effects of different numbers of transmitting and receiving antennas on the selection of zenith angle, receiving aperture, transmitting radius, and beam divergence of the MIMO-SFBC system were also studied. Finally, the Monte Carlo method was used to verify the experimental data. This study provides a theoretical reference for the engineering implementation of MIMO coding technology in satellite laser communication systems.

High-power optical amplifier with enhanced wall-plug efficiency for 10-channel WDM satellite laser communication systems

High-power optical amplifier with enhanced wall-plug efficiency for 10-channel WDM satellite laser communication systems

Analysis and test of transmit-receive isolation of off-axis three-mirror anastigmat optical antenna applied to laser communication

The bi-directional duplex working mode of a transmit-receive integrated optical antenna in laser communication systems has a rigorous requirement on transmission and receiver(T/R) isolation. By using an off-axis three-mirror anastigmat (TMA) optical antenna, backscattered can be significantly reduced, thus achieving high T/R isolation. This paper proposes to design the light exit angle of 5° or larger in the off-axis TMA optical antenna and use the equivalent surface roughness (ESR) to evaluate the surface scattering characteristics of reflector in optical antenna. Therefore, by increasing the ESR of reflector, the isolation of the optical antenna can be improved. In an isolation measurement experiment, the measured isolation of the F150mm off-axis TMA optical antenna was 73 dB, which is consistent with the simulation result. The achieved T/R isolation level meets the requirements for acquiring, tracking, and communication of satellite laser communication systems.

Outer-Scale Effect of a Gaussian-Beam Wave Propagated Through Non-Kolmogorov Turbulent Atmosphere on the Beam Wander

To date, it is a common knowledge that there exists two kinds of turbulence in Earth’s aerosphere, the Kolmogorov turbulence and the non-Kolmogorov turbulence, which has been confirmed by both increasing experimental evidences and some results of theoretical investigations. Therefore, it is necessary to further develop theory of optical wave propagation through the atmospheric turbulence, namely, to study the propagation of laser beams in the non-Kolmogorov turbulence before analyzing the joint influence of the Kolmogorov turbulence and the non-Kolmogorov turbulence on satellite laser communication. Also it is well known that the beam wander results in the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, considering a non-Kolmogorov generalized exponential power spectrum of refractive-index fluctuations, we derive the variances of beam wander for a Gaussian-beam wave in weak turbulence for a horizonal path. This spectrum includes the inner and outer scales with a generalized power law; thus, we also analyze the effect of spectral power law and outer scale variations on the beam wander. It is important to note that the expression for the beam wander variance obtained is concise closed form and independent on the optical wavelength.

No prior recognition method of modulation mode by partition-fractal and SVM learning method

A modulation classification method in combination with partition-fractal and support-vector machine (SVM) learning methods is proposed to realize no prior recognition of the modulation mode in satellite laser communication systems. The effectiveness and accuracy of this method are verified under nine modulation modes and compared with other learning algorithms. The simulation results show when the signal-to-noise ratio (SNR) of the modulated signal is more than 8 dB, the classifier accuracy based on the proposed method can achieve more than 98%, especially when in binary phase shift keying and quadrature amplitude shift keying modes, and the classifier achieves 100% identification whatever the SNR changes to. In addition, the proposed method has strong scalability to achieve more modulation mode identification in the future.

Feasibility study of microsatellite laser communication pointing system based on SEEOR technology

Satellite laser communication technology is a communication method that uses laser beam as information transmission carrier to transmit information data in space. It has many advantages such as large communication capacity, long transmission distance, high bandwidth, no spectrum permission, etc,widely used at present. The beacon light direction of its typical satellite laser communication system is realized by rough tracking servo turntable platform carrying optical components, so,there are a series of shortcomings such as turntable vibration, corner error and system inertia etc. Currently, a new technology, Non-Mechanical Beam Steering (NMBS) technology, in mid-wave infrared (MWIR) which has emerged, is expected to break through above shortcomings and provide possibilities for the transmission of beacon light in satellite laser communication. This paper focuses on the application of non-mechanical beam pointing technology in satellite laser communication system. We objectively analyzed the basic principles of the Non-Mechanical Beam Steering chip work, and the feasibility of using Non-Mechanical Beam Steering to transmit beacon light in satellite laser communication theoretically. It will open up a new way for the development of microsatellite laser communication technology in the future.

A Novel Approach for Optimization Control of Dynamic Tracking With Platform Vibration in the Ground Test of Satellite Laser Communication Systems

Vibration interference reduces the precision of the control system and leads to the instability of the satellite optical communication link. So how to improve the tracking accuracy of the terminal system under vibration conditions is an important work for the ground test of satellite laser communication systems. In this paper, the tracking characteristic based on the platform vibration is introduced for coarse tracking and the combination of coarse and fine tracking, we propose a structural decoupling approach and iterative learning control scheme using sliding-mode control to investigate the performance of the tracking system in order to achieve the error minimization, and further to improve the system performance. The scheme is introduced to increase the tracking accuracy and the robustness of the system against external disturbances. The experimental results of the steady-state tracking response and the high tracking precision are carried out on a 4.62 km bidirectional free space laser link experiment, and the obtained test results (less than $2~\mu $ rad) demonstrate the effectiveness of the proposed control scheme in suppressing oscillation. This new method is good for the ground test of the satellite laser communication systems.

Accurate beacon positioning method for satellite-to-ground optical communication.

In satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For satellite-to-ground optical communication, the main influencing factors on the acquisition of the beacon are background noise and atmospheric turbulence. In this paper, we consider the influence of background noise and atmospheric turbulence on the beacon in satellite-to-ground optical communication, and propose a new locating algorithm for the beacon, which takes the correlation coefficient obtained by curve fitting for image data as weights. By performing a long distance laser communication experiment (11.16 km), we verified the feasibility of this method. Both simulation and experiment showed that the new algorithm can accurately obtain the position of the centroid of beacon. Furthermore, for the distortion of the light spot through atmospheric turbulence, the locating accuracy of the new algorithm was 50% higher than that of the conventional gray centroid algorithm. This new approach will be beneficial for the design of satellite-to ground optical communication systems.

Performance analysis of a laser satellite-communication system with a three-layer altitude spectrum over weak-to-strong turbulence

In this article, the downlink bit-error-rate (BER) performance of scintillation models for a laser satellite communication system influenced by weak-to-strong turbulence on a slant path is investigated, which take optical wavelength, zenith angle, terrestrial turbulence strength and modulation schemes into account. To describe the properties of atmospheric turbulence which vary with the altitude between a satellite station and a ground station, a three-layer altitude spectrum is used. By adopting the extended Rytov theory valid in weak-to-strong turbulence, scintillation models of an unbounded plane wave for downlink path and spherical wave for uplink path are derived, respectively. The optical fading channel influenced by weak-to-strong turbulence is modeled by Gamma–Gamma distribution. The numeric results show that when the system is under strong terrestrial turbulence conditions or at large zenith angles, disparities in BER performance among different kinds of level of pulse position modulation (PPM) schemes are quite small. Under real circumstances, a longer optical wavelength and a suitable zenith angle range can be selected to reduce turbulence effects for the satellite communication system through weak-to-strong turbulence.

Off-axis two-mirror laser communication antenna designed using differential equations

In satellite laser communication technology, which is built between planets and between a planet and the Earth, the optical antenna is the key point. Thus, research on optical system design is important. The off-axis reflective system has no obscuration and hence possesses a high efficiency for energy transfer. This study proposes a novel method for designing a free-form off-axis reflective imaging system. This study also introduces differential equations that depend on Fermat’s principle and sine condition. Finally, a free-form off-axis two-mirror optical system was designed by using the differential equation method. This system includes one intermediate image plane, in which the field of view (FOV) is–5° to–4° in the y-axis and–1° to 0° in the x-axis. The modulation transfer function was greater than 0.7 at 50 lp/mm, and the efficiency of energy transmission was high. The free-form off-axis two-mirror optical system involves a wide range of application prospects in the optical antenna used in the satellite laser communication systems. Moreover, the design method that used differential equations was proven simple and effective.

星载激光通信系统遮光罩的优化设计

星载激光通信系统遮光罩的优化设计

Space-Based Laser Communications Break Threshold

Recent and upcoming deployments of satellite laser communication systems are bringing Internet-like speeds for data transmission in space. The result could be a revolution in communication, both on Earth and across the solar system.

Angle of Arrival Fluctuations for Optical Waves Propagating Through Joint Moderate to Strong Atmospheric Turbulence

Satellite laser communication has gained wide attention both at home and abroad. The pointing, acquisition, and tracking (PAT) technology is the kernel of satellite laser communication systems, and the atmospheric layer is a part of the communication channel for satellite-to-ground links. Thus, angle of arrival (AOA) fluctuations caused by atmospheric turbulence inevitably influence long-distance satellite laser communication. Therefore, it is very important to analyze the impact of AOA fluctuations in satellite laser communication systems. According to the actual situation of satellite-to-ground links, a joint atmospheric turbulence power spectrum model is defined that includes Kolmogorov turbulence from the ground to 6 km in portions of the troposphere and non-Kolmogorov turbulence above 6 km in the stratosphere. Based on the extended Rytov theory, we derive the large-scale and small-scale variances of AOA fluctuations propagating in the uplink and downlink channels for a satellite laser communication system and analyze the influence of large zenith angle variations on the AOA fluctuations. It has long been a focus of concern that the expressions for the AOA variance obtained must be concise and of closed form.

The influence of space irradiated PIN photodetector on BER in satellite laser communication system

By analyzing the radiation dose on PIN photodetectors in space radiation environment, the variation of photocurrent and dark current after radiation is obtained. On the basis, the bit error rate of satellite laser communication based on space radiation dose of PIN photodetectors is established. According to simulation, when radiation dose is about 1.6×103Gy and 7×104Gy, bit error rate reaches 10−6 induced by 50MeV and 10MeV protons separately; and when radiation dose is within the range of 5×10Gy–6×105Gy, electrons and gamma-ray irradiation also cause increase in bit error rate to 10−6. The principle of damage dose on bit error rate is investigated, and the influence of decision threshold on bit error rate is further discussed. The result shows that when radiation dose is 1MGy, if decision threshold is increased from 4.3×10−7A to 5.5×10−7A, bit error rate will decrease about 4 orders of magnitude. Hence, a proper decision threshold can improve system bit error rate efficiently.

Wander of a Gaussian-Beam Wave Propagated Through a Non-Kolmogorov Turbulent Atmosphere

Both increasing experimental evidence and some results of theoretical investigation have shown that there exist two kinds of turbulence in the aerosphere, Kolmogorov and non-Kolmogorov turbulence. Thus, it is necessary to improve the theory of optical wave propagation through atmospheric turbulence, namely, study the laser-beam propagation in non-Kolmogorov turbulence, before analyzing the joint influence of the Kolmogorov turbulence and non-Kolmogorov one on satellite laser communication. The beam wander will lead to the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, we consider a theoretical power spectrum of refractive-index fluctuations with a generalized power law in order to derive the variance of Gaussian-beam wave wander in weak turbulence for a horizonal path and analyze the influence of spectral power-law variations on the beam wander. We show that the expression for the beam-wander variance is of concise closed form and independent of the optical wavelength.

空间辐射下卫星光通信系统半导体激光器的可靠性估计

空间辐射下卫星光通信系统半导体激光器的可靠性估计

Effect of non-Kolmogorov turbulence on beam spreading in satellite laser communication

In the past half a century, satellite laser communication has caught the attention of scientists due to its distinct advantages in comparison with conventional satellite microwave communication. For ground-to-satellite and satellite-to-ground data links, the atmosphere is a part of the communication channel; thus, atmospheric turbulence severely degrades the performance of satellite laser communication systems. In general, the Kolmogorov turbulence model is used to study the effect of atmosphere turbulence on satellite laser communications since it has been confirmed by numerous direct measurements of temperature and humidity fluctuations in the atmospheric boundary layer. However, increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes inadequate to describe atmospheric statistics properly, in particular, in some domains of the atmosphere. We analyze the joint influence of Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the spot size associated with the uplink and downlink propagation channels for a satellite laser communication system in the geosynchronous orbit, using a power spectrum of non-Kolmogorov turbulence with power law −5 that describes the refractiveindex fluctuations in the atmosphere above 6 km and considering the combined power spectrum of Kolmogorov and non-Kolmogorov turbulence. Before this analysis, we study the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams.

Performance Improvement of the Tracking System of a Satellite Laser Communication

Free Space Optics (FSO) is an optical communication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connections by the means of optical fibre cables are impractical to use due to high costs or other considerations. FSO has been proposed by using a laser. FSO is considered as one of the most popular choices for inter-satellite communication where the performance is limited by “satellite vibration”. FSO cannot achieve a stable and ‘healthy’ link due to such type of vibration. The ultimate disadvantages include misalignment in tracking, signal attenuation and high BER (bit error rate). Hence the satellite vibrations need to be compensated (or minimized). This paper introduces the feed-forward vibration compensation model by introducing PID controller. The simulation results indicate that the proposed method minimizes the vibration effects and hence reduces BER in satellite laser communication system [7]. General Terms Satellite, Vibration effect, PID controller, Feed-forward compensator.

Decentralized Robust Adaptive Control for Attitude Synchronization Under Directed Communication Topology

T HE need to maintain accurate relative orientation between spacecraft is critical in many satellite formation missions. For instance, in interferometry application, the relative orientation between spacecraft in a formation is required to be maintained precisely during formation maneuvers. In interspacecraft laser communication operation, the participating spacecraft are also required to maintain accurate relative attitude throughout the communication process. This control problem, commonly referred to as attitude synchronization in the literature, has attracted much research attention. Various solutions have been proposed and these can be broadly classified according to the advocated techniques: leader– follower [1–4], virtual structure [5,6], behavior-based [7–11], and graph-theoretical approach [12–15]. In particular, the graph-theoretical approach has been actively studied for cooperative control of multi-agent system using limited local interaction [16,17] and was adopted for attitude synchronization problem in [12–15]. In the above-cited decentralized attitude synchronization results, except [14,15], it is assumed that the interspacecraft communication links are undirected (i.e. bidirectional). However, in practice, the interspacecraft communication topology may be restricted to be directed, such as in unidirectional satellite laser communication system. The control problem of attitude synchronization under directed communication topology is more challenging as compared with the case with undirected communication topology. This issue was studied in [14] but the proposed control law requires derivative of the angular velocity, which may introduce additional noise into the system. Furthermore, the attitude-tracking performance analysis in [14] is applicable only to the casewhere the directed graph can be simplified to a graph with only one node. This constraint on communication topology is relaxed in [15], which uses modified Rodriguez parameters and Euler– Lagrange system to describe the satellite attitude dynamics. However,modifiedRodriguez parameters contain singularity and are thus not suitable for the development of globally stabilizing control algorithms. This Note proposes a decentralized adaptive sliding-mode control lawwhich regulates attitude and angular velocity errors of individual spacecraft with respect to reference commands and minimizes relative attitude and angular velocity errors between spacecraft. Thus, the proposed control law ensures that each spacecraft attains desired time-varying attitude and angular velocity while maintaining attitude synchronization with other spacecraft in the formation even in the presence of model uncertainties and external disturbances. Moreover, the design is applicable to general communication topology and is not restricted to ring topology or undirected communication topology. In the following section, unit quaternion representation will be introduced into the satellite attitude control problem and algebraic graph theory will be applied to describe general directed communication topology.