Inter-satellite Communication Links Research Articles

Enabling high-speed and large-capacity data transmission in optical inter-satellite communication links under various conditions

Enabling high-speed and large-capacity data transmission in optical inter-satellite communication links under various conditions

Research on angular displacement detection technology of inter-satellite laser communication based on coherent system

With the rapid development of spatial information networks technologies, inter-satellite laser communication links have played an important role in the satellite Internet. High-precision relative angular displacement detection is the foundation for achieving real-time tracking of laser communication links, and its accuracy directly impacts the tracking performance and communication quality of the laser communication link. Traditional laser communication systems utilize intensity-based position detection methods to calculate angular displacement, requiring setting separate Charge Coupled Device (CCD) or Four-quadrant Detector (QD) as well as independent optical tracking branches. This setup makes it difficult to integrate with high-speed coherent communication systems. Additionally, the method employing intensity detection to determine angular displacement based on spot position has lower accuracy in theory. A angular displacement detection of coherent-based inter-satellite laser communication is proposed in this paper. Firstly, real-time calculation of phase differences at different positions of the beam is achieved through heterodyne coherent array detection and dual high-precision phase-locked loops. Then, a model correlating wave front phase difference with relative angular displacement is established, phase noise during beam transmission and detection processes is analyzed, and algorithm for detecting angular displacement in coherent systems is studied. Finally, a laser communication link is constructed under laboratory condition, and experimental validation work is carried out. When the relative angle deviation is 1°, the phase difference changes by 0.089049795 rad, and the angular displacement detection error of 0.66697μrad(σ). When the relative angle error is 0.603873μrad(σ), the detection sensitivity is −43.93dBm. The experimental results show that in the coherent system, the relative angular displacement detection with high precision can be realized by using the wavefront phase difference of beam, which can support the laser communication tracking system to achieve higher precision beam tracking.

In situ plasma and neutral gas observation time windows during a comet flyby: Application to the Comet Interceptor mission

A comet flyby, like the one planned for ESA’s Comet Interceptor mission, places stringent requirements on spacecraft resources. To plan the time line of in situ plasma and neutral gas observations during the flyby, the size of the comet magnetosphere and neutral coma must be estimated well. For given solar irradiance and solar wind conditions, comet composition, and neutral gas expansion speed, the size of gas coma and magnetosphere during the flyby can be estimated from the gas production rate and the flyby geometry. Combined with flyby velocity, the time spent in these regions can be inferred and a data acquisition plan can be elaborated for each instrument, compatible with the limited data storage capacity. The sizes of magnetosphere and gas coma are found from a statistical analysis based on the probability distributions of gas production rate, flyby velocity, and solar wind conditions. The size of the magnetosphere as measured by bow shock standoff distance is 105–106km near 1au in the unlikely case of a Halley-type target comet, down to a nonexistent bow shock for targets with low activity. This translates into durations up to 103–104 seconds. These estimates can be narrowed down when a target is identified far from the Sun, and even more so as its activity can be predicted more reliably closer to the Sun. Plasma and neutral gas instruments on the Comet Interceptor main spacecraft can monitor the entire flyby by using an adaptive data acquisition strategy in the context of a record-and-playback scenario. For probes released from the main spacecraft, the inter-satellite communication link limits the data return. For a slow flyby of an active comet, the probes may not yet be released during the inbound bow shock crossing.

Research on Inter-Satellite Laser Communication Link Transmission and Routing Switching Technology of Satellite Internet (Invited)

Research on Inter-Satellite Laser Communication Link Transmission and Routing Switching Technology of Satellite Internet (Invited)

Cache Placement in an NDN-Based LEO Satellite Network Constellation

The efforts to replace the successful, albeit aging, TCP/IP Internet architecture with a better suited one have driving research interest to information-centric alternatives. The Named Data Networking (NDN) architecture is probably one of the main contenders to become the network layer of the future Internet thanks to its inbuilt support for mobility, in-network caching, security and, in general, for being better adapted to the needs of current network applications. At the same time, massive satellite constellations are currently being deployed in low Earth orbits (LEO) to provide a backend for network connectivity. It is expected that, very soon, these constellations will function as proper networks thanks to inter-satellite communication links. These new satellite networks will be able to benefit from their greenfield status and the new network architectures. In this paper we analyze how to deploy the network caches of an NDN-based LEO satellite network. In particular, we show how we can jointly select the most appropriate caching nodes for each piece of content and how to forward data across the constellation in two simple alternative ways. Performance results show that the caching and forwarding strategies proposed reduce path lengths up to a third with just a few caching nodes while, simultaneously, helping to spread the load along the network.

On-orbit demonstration of inter-satellite free-space optical stable communication enabled by integrated optical amplification of HPA and LNA.

Satellite free-space optical (FSO) communication is very promising in improving the bandwidth and capacity of space information networks in the future. However, the inter-satellite transmission distance of over 1000km leads to unstable optical beam pointing, acquisition, and tracking and then generates optical power jitter by a large margin before detection-demodulation. Therefore, it is difficult to realize high-stability and long-time FSO communication between satellites due to the generated bit error rate (BER) by jitter. In this paper, we report an autonomously self-designed and high-integration laser communication payload (LCP) and on-orbit-demonstrated inter-satellite 145min, zero-BER FSO stable communication with a line rate of 2.8Gbps. Moreover, based on the inter-satellite laser communication link, a video phone was clearly implemented for more than 10min, and authentic user data transmitted 459,149 packets, achieving results of zero-packet loss. Summarily, this on-orbit experiment demonstrated an excellent performance of the LCP owing to the distinctive design of integrating a high-power amplifier and low-noise amplifier optical amplification function. Our space mission was successfully completed, and the on-orbit demonstration results may offer a significant reference for the field of satellite laser communication and space information networks.

Cooperative Downloading for LEO Satellite Networks: A DRL-Based Approach.

In low earth orbit (LEO) satellite-based applications (e.g., remote sensing and surveillance), it is important to efficiently transmit collected data to ground stations (GS). However, LEO satellites’ high mobility and resultant insufficient time for downloading make this challenging. In this paper, we propose a deep-reinforcement-learning (DRL)-based cooperative downloading scheme, which utilizes inter-satellite communication links (ISLs) to fully utilize satellites’ downloading capabilities. To this end, we formulate a Markov decision problem (MDP) with the objective to maximize the amount of downloaded data. To learn the optimal approach to the formulated problem, we adopt a soft-actor-critic (SAC)-based DRL algorithm in discretized action spaces. Moreover, we design a novel neural network consisting of a graph attention network (GAT) layer to extract latent features from the satellite network and parallel fully connected (FC) layers to control individual satellites of the network. Evaluation results demonstrate that the proposed DRL-based cooperative downloading scheme can enhance the average utilization of contact time by up to 17.8% compared with independent downloading and randomly offloading schemes.

Mission-Oriented Real-Time Health Assessments of Microsatellite Swarm Orbits

Real-time health assessments are of great importance for the safe and stable operation of in-orbit swarms. To solve the problems of existing real-time health assessments of microsatellite swarms, such as the difficulty of selecting a multisource and assessment calculation normalization, this paper proposes a real-time health assessment method applicable to mission-oriented swarms. The method divides the microsatellite swarm into three levels: single satellite, intersatellite communication link and swarm effectiveness, which establish a multilevel index system by adopting the reliability evaluation based on random failure and failure by loss, a health evaluation based on natural connectivity, and a real-time dynamic analysis based on swarm topology. For the swarm effectiveness during the mission, the multilevel index and the entropy weight method are used to construct the effectiveness evaluation model of the whole swarm, and the health state evaluation of the swarm is realized based on the variable weight principle. The simulation results show that this method can quantify the health state of the microsatellite swarm in real-time, and it can predict the health state after the fault without maintenance.

Terabyte capacity-enabled (10 x 400 Gbps) Is-OWC system for long-haul communication by incorporating dual polarization quadrature phase shift key and mode division multiplexing scheme

Inter-satellite optical wireless communication (Is-OWC) links can become promising solutions to realize the next-generation high-speed communication services. The operation of Global Navigation Satellite Systems can be improved with the use of Is-OWC links through ranging and communication services. However, the key challenge in Inter-satellite link (ISL) is its effective range which is limited due to pointing errors. In this work, we propose to develop a high-capacity and long-reach Is-OWC link by incorporating hybrid mode division multiplexing (MDM) and wavelength division multiplexing (WDM) schemes to transmit ten independent channels over 40000kms Is-OWC link. Each channel is capable of carrying 400Gbps data which is encoded by the dual polarization quadrature phase shift key technique with required signal to noise ratio (SNR) and received power. The proposed Is-OWC link satisfies the enhanced communication within Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) satellites. The proposed Is-OWC is further evaluated under the impact of space turbulences, particularly transmitter and receiver pointing errors. The result reported that the proposed Is-OWC link can transmit 4Tbps data over 16000kms with the transmitter pointing error of 2μrad and receiver pointing error of 1μrad.

Investigations on mode-division multiplexed free-space optical transmission for inter-satellite communication link

Investigations on mode-division multiplexed free-space optical transmission for inter-satellite communication link

Performance optimization of an intersatellite optical wireless system using linearly polarized modes

Modern optical communication has advanced from the use of merely lengthy optical fibers to using features of the powerful wireless system and optics resulting in the use of lasers to transmit data at a much greater rate. This gave way to the optical wireless communication system growing roots into space communications. In this work, an intersatellite optical wireless communication link has been analyzed for studying the performance of the system considering linearly polarized modes. The link performance has been investigated in terms of the quality factor (Q factor) as a function of the transmission wavelength, detector type, data rate, distance, transmitter aperture diameter, and pointing error angle. The optimized results of the system reveal that the LP01 mode performs better with the non-return-to-zero modulation scheme at the 850 nm wavelength using a PIN photodiode.

Pattern Reconfigurable Antenna for Formation Flying Missions

In this paper, an innovative compact pattern reconfigurable antenna is proposed and developed to establish an inter-satellite communication link between the Formation flying spacecraft. The reconfigurable beam switching antenna comprises a driven Monopole at the center, encompassed with four Reconfigurable Selective Reflectors (RSR) which act as RF radiators and reflectors for different switching conditions. PIN diodes are used to electronically control the switch states of RSR and beam switching is achieved with uniform gain along the azimuth plane without affecting the antenna’s overall performance. The peculiar demands of Formation Flying Mission (FFM) satellites such as small size and low power for communication system are resolved by the proposed technique where a single antenna with different patterns communicates with multiple satellites reducing the antenna space and power consumption. Furthermore, it also offers a solution to the problem encountered in existing FFM antenna, like microstrip patch, which serves only one satellite at a time. The antenna is designed at 2.45GHz center frequency. Simulated results show good impedance matching and performance with 13 to 15% bandwidth and wide beamwidth. The experimental validation shows that the simulation results of the antenna agree well with the measured results.

Performance investigation of spectral-efficient high-speed inter-satellite optical wireless communication link incorporating polarization division multiplexing

Space information transmission links are crucial for covering the entire globe for communication purposes. The traditional microwave frequency-based satellite communication links have high latency and low information transmission rates. In the last few years, inter-satellite optical wireless communication (IsOWC) technology has evolved significantly as a result of its numerous benefits like wide channel bandwidth, high-speed links, and low mass and power requirements. Different research groups have proposed IsOWC links based on conventional on–off modulation schemes for transmitting 10 Gbps data between satellites separated in space. But the future generation transmission links require higher spectral efficiency and data rates with longer transmission reach. In this research, a novel single-channel spectrum-efficient 160 Gbps polarization division multiplexing-based IsOWC link is investigated for long communication range transmission. In this design, coherent detection technique is employed to mitigate the effects of system errors and space turbulence (i.e. pointing errors). A digital signal processing module has been proposed for minimizing the information signal degradation due to space turbulences and to estimate the carrier phase of the signal received. The results show that 160 Gbps information is successfully transmitted over 20,000 km range with an acceptable bit error rate (BER). Also, the influence of different system parameters including pointing error angle, receiver aperture diameter, and additional losses on the signal BER is numerically investigated.

Beacon correction method for inter-satellite laser communication

Positioning errors are caused by wavefront distortion owing to the thermal deformation of optical systems. To address this issue, we propose a restoration algorithm to correct for the beacon centroid, which is important for inter-satellite laser communication links. Based on the far-field distribution model of the distortion facula, the objective function is established to solve the wavefront distortion for reducing the pointing error of the optical communication system. The feasibility of this approach is verified by theoretical analysis and experimental verification, including in-orbit experimental verification. The proposed approach is likely to be useful for designing inter-satellite laser communication systems.

Satellite platform vibration influence on acquisition system for intersatellite optical communications

Accurate pointing, acquisition and tracking systems are an important part of maintaining stable intersatellite optical communications links. Satellite platform vibration causes system instability and reduces the system precision during the building and maintaining satellite optical communication system. This manuscript studies the satellite platform vibration influence on acquisition system for intersatellite optical communications. Considering the scan parameters and platform vibration, an approximately analytical expression of scan lost possibility (SLP) is derived through newly models for acquisition analysis. Taken scanning restricted condition and SLP into account, vibration influence on the acquisition time of single-scan and multi-scan is also presented. And the theoretical result calculated by the proposed analytical expression is approximately to the result by Monte Carlo simulation.

Research on simulation methods for Doppler frequency shift of a coherent inter-satellite laser link in a ground test system

Spatial Doppler frequency shift occurs during ground integration testing of an inter-satellite laser communication link and is difficult to simulate it consistently; therefore, to address this problem, a Doppler frequency shift simulation method for an optical communication carrier in space based on a dual-parallel Mach–Zehnder modulator (DP-MZM) is proposed. By adjusting the RF signal added to the MZM and the bias voltage of the DP-MZM, the output carrier suppresses single-sideband modulation to achieve a controllable optical carrier frequency shift. In this study, theoretical analysis and experimental research on this simulation method was performed, and a Doppler frequency shift simulator for ground testing of two laser communication terminals was developed, which can realize controllable optical carrier frequency shift adjustment in the range of at least ±18 GHz and a sideband rejection ratio that is greater than 40 dB. The research results have been applied to an inter-satellite laser link ground test, obtaining good simulation and test results.

A Remote Carrier Synchronization Technique for Coherent Distributed Remote Sensing Systems

Phase, frequency, and time synchronization are crucial requirements for many applications, such as multistatic remote sensing and communication systems. Moreover, the synchronization solution becomes even more challenging when the nodes are orbiting or flying on airborne or spaceborne platforms. This article compares the available technologies used for the synchronization and coordination of nodes in distributed remote sensing applications. Additionally, this article proposes a general system model and identifies preliminary guidelines and critical elements for implementing the synchronization mechanisms exploiting the intersatellite communication link. The distributed phase synchronization loop introduced in this work deals with the self-interference in a full-duplex point to point scenario by transmitting two carriers at each node. All carriers appear with different frequency offsets around a central frequency, called the application central-frequency or the beamforming frequency. This article includes a detailed analysis of the proposed algorithm and the required simulations to verify its performance for different phase noise, additive white Gaussian noise, and Doppler shift scenarios.

Neural Episodic Control-Based Adaptive Modulation and Coding Scheme for Inter-Satellite Communication Link

Neural Episodic Control-Based Adaptive Modulation and Coding Scheme for Inter-Satellite Communication Link

Dense Small Satellite Networks for Modern Terrestrial Communication Systems: Benefits, Infrastructure, and Technologies

Dense small satellite networks (DSSN) in low earth orbits (LEO) can benefit several mobile terrestrial communication systems (MTCS). However, the potential benefits can only be achieved through careful consideration of DSSN infrastructure and identification of suitable DSSN technologies. In this paper, we discuss several components of DSSN infrastructure including satellite formations, orbital paths, inter-satellite communication (ISC) links, and communication architectures for data delivery from source to destination. We also review important technologies for DSSN as well as the challenges involved in the use of these technologies in DSSN. Several open research directions to enhance the benefits of DSSN for MTCS are also identified in the paper. A case study showing the integration benefits of DSSN in MTCS is also included.

Enhancing the Resilience of Low Earth Orbit Remote Sensing Satellite Networks

The Low Earth orbit Remote Sensing (LRS) satellite network is envisioned as an essential component of bolstering space information applications, thus extending conventional ground information applications to the on-board space information applications. However, it inevitably faces grave challenges imposed by the dynamics of the satellite network's topology, by the intermittence of Inter-Satellite communication Links (ISLs) as well as by the mobility-induced satellite-access switching of mobile terminals. Hence, this is a very different networking landscape from that of the terrestrial Internet. Against these challenging problems, we propose a resilient networking architecture for LRS Satellite Networks (LRS-SNs), with special emphasis on their dynamic routing, resilient transmission and their intrinsic mobility. Specifically, path-quality aided and lifetime-aware dynamic routing is proposed for enhancing the routing against dynamic topology changes. Hop-by-hop data transmission is relied upon for providing transmission resilience against ISL intermittence. Furthermore, data caching is invoked for providing resilience against intermittent communications imposed by dynamic satellite access switching. We employ a semi-physical simulation platform for evaluating the achievable performance of the proposed resilient network architecture.