Inter-satellite Network Research Articles

Orbit Determination Method for BDS-3 MEO Satellites Based on Multi-Source Observation Links

Research on augmentation and supplement systems for navigation systems has become a significant aspect in comprehensive positioning, navigation and timing (PNT) studies. The BeiDou-3 navigation satellite system (BDS-3) has constructed a dynamic inter-satellite network to gain more observation data than ground monitoring stations. Low Earth orbit (LEO) satellites have advantages in their kinematic velocity and information carrying rate and can be used as satellite-based monitoring stations for navigation satellites to make up for the distribution limitation of ground monitoring stations. This study constructs multi-source observation links with satellite-to-ground, inter-satellite and satellite-based observation data, proposes an orbit synchronization method for navigation satellites and LEO satellites and verifies the influence thereof on orbit accuracy with different observation data. The experimental results under conditions of real and simulated observation data showed the following: (1) With the support of satellite-based observation links, the orbit accuracy of the BDS-3 MEO satellites could be improved significantly, with a 78% improvement with the simulation data and a 76% improvement with the real data. When the navigation satellites leave the monitoring area of the ground monitoring stations, the accuracy reduction tendency of the orbit prediction could also be slowed down with the support of the LEO satellites and the accuracy could be maintained within centimeters. (2) Comparing the orbit accuracy with the support of the satellite-to-ground observation links, the orbit accuracy of the MEO satellites could be improved by 65.5%, 73.7% and 79.4% with the support of the 6, 12 and 60 LEO satellites, respectively. When the observation geometry and the covering multiplicity meet the basic requirement of orbit determination, the improvements to the orbit accuracy decrease with the growth of LEO satellite numbers. (3) The accuracy of orbit determination with the support of the LEO satellites or the inter-satellite links was at the centimeter level for both, verifying that inter-satellite links and satellite-based links can be used as each other’s backups for navigation satellites. (4) The accuracy of orbit determination with the multi-source observation links was also at the centimeter level, which was not better than the results with the support of the satellite-to-ground and inter-satellite links or the satellite-to-ground and satellite-based links.

A Novel Feeder Link Handover Strategy for Backhaul in LEO Satellite Networks

Thanks to their wide coverage and relatively low latency compared to geosynchronous satellites, Low Earth Orbit (LEO) satellite networks have been regarded as one of the most promising solutions to provide global broadband backhaul for mobile users and IoT devices. In LEO satellite networks, the frequent feeder link handover invokes unacceptable communication interruptions and affects the backhaul quality. To overcome this challenge, we propose a maximum backhaul capacity handover strategy for feeder links in LEO satellite networks. To improve the backhaul capacity, we design an available backhaul capacity ratio to jointly consider feeder link quality and the inter-satellite network in handover decisions. In addition, we introduce a service time factor and handover control factor to reduce the handover frequency. Then, we propose the handover utility function based on the designed handover factors and propose a greedy-based handover strategy. Simulation results show that the proposed strategy outperforms conventional handover strategies in backhaul capacity with low handover frequency.

An Adaptive Routing Algorithm for Inter-Satellite Networks Based on the Combination of Multipath Transmission and Q-Learning

In a satellite network, the inter-satellite link can facilitate the information transmission and exchange between satellites, and the packet routing of the inter-satellite link is the key development direction of satellite communication systems. Aiming at the complex topology and dynamic change in LEO satellite networks, the traditional single shortest path algorithm can no longer meet the optimal path requirement. Therefore, this paper proposes a multi-path routing algorithm based on an improved breadth-first search. First, according to the inter-satellite network topology information, the improved breadth-first search algorithm is used to obtain all the front hop node information of the destination node. Second, all the shortest paths are obtained by backtracking the path through the front hop node. Finally, according to the inter-satellite network, the bandwidth capacity of the traffic and nodes determines the optimal path from multiple shortest paths. However, due to the high dynamics of low-orbit satellite networks, the topology changes rapidly, and the global topology of the network is often not available. At this time, in order to enhance the adaptability of the algorithm, this paper proposes an inter-satellite network dynamic routing algorithm based on reinforcement learning. Verified by simulation experiments, the proposed algorithm can improve the throughput of the inter-satellite network, reduce the time delay, and the packet loss rate.

Shared-Aperture Ka-Band Reflectarray and X-Band Phased Array for Broadband Inter-Satellite Communication

In this communication, a dual-band shared-aperture reflectarray (RA) with a phased array is proposed for intersatellite links (ISLs). The Ka-band RA is integrated with an X-band phased array by a sharing mushroom patch structure. The high-frequency ratio allows the high-frequency RA and the low-frequency broadband phased array to operate independently to support high-speed communication of the geostationary orbit (GEO) relay nodes in the intersatellite network. To verify this concept, a prototype of the antenna is designed and fabricated, and its electrical performance is measured. The RA presents a peak gain of 30.1 dBi (28 GHz) and a 3 dB gain bandwidth of 11.4% (26.4–29.6 GHz). The phased array presents the peak gain of 21.7 dBi (9 GHz), and the relative bandwidth can reach 45.3% in the boresight direction. The scanning range can cover ±45°, and the H/E planes scan gain losses are less than 2.34 and 4.33 dB, respectively.

Cooperation in Space: HAPS-Aided Optical Inter-Satellite Connectivity With Opportunistic Scheduling

Issues with tracking, precision pointing, and Doppler shift are the major sources of performance loss in laser inter-satellite communication that can severely decrease the coverage and overall performance of satellite constellations. As a solution to these problems, we propose a cooperation strategy in which a high altitude platform station (HAPS) staying at a quasi-stationary position contributes to the inter-satellite connectivity. In this setup, the HAPS node uses two different scheduling approaches: one that relies on the zenith angle; the other on instantaneous signal-to-noise ratio. To quantify the performance of the proposed scheme, overall outage probabilities for the two scheduling methods are obtained. In addition, guidelines for the design of practical inter-satellite networks are provided.

Time-Sensitive Satellite Internet Based on Uniform Content Labels

For satellite Internet the content was examined by location and time of day, as well as within the context of online social networks. The ground Information-Centric Networking (ICN) is a paradigm shift from host-to-host Internet Protocol (IP)-based communication to content-based communication. With the development and universal application of satellite technology, an important way to expand the function of satellites is setting up inter-satellite networks to make them work together. The Internet and the Global Positioning System are based on the dual structure network and the Uniform Content Label UCL national standard. Through the integration of these two inventions, the integration of time and space is realized, creating an endogenous security environment of both mathematics and physics that is self-consistent in cyberspace, is expected to bring a breakthrough in principle for cracking network security challenges.

Design of a Low Earth Orbit Satellite Constellation Network for Air Traffic Surveillance

The satellite constellation with automatic dependent surveillance-broadcast on-board is of great importance for air traffic surveillance due to its multiple advantages compared with traditional methods. Although some research has been conducted on satellite constellation design based on coverage performance, the findings cannot entirely satisfy all the requirements of air traffic surveillance owing to the lack of analysis on inter-satellite links and network transmission. This paper presents a novel design of a low earth orbit satellite constellation network to solve this problem. Based on the requirements of space-based surveillance, an evaluation model of constellation performance is proposed concerning coverage, link and transmission. The simulation results show that the evaluation model can reflect the performance of a satellite constellation network designed for a space-based surveillance system, and a 55-satellite constellation design scheme with fairly good performance can fulfil the function of global real-time air traffic surveillance.

Doublet-waveplate polarization transceiver system for backscattering suppression in laser communication terminal

The backscattering suppression capability of the optical signal transceiver is the key to establish a single wavelength full-duplex bidirectional laser communication link. When the signal is transmitted and received through the same telescope of the laser communication terminals, stray light from the high-power laser on mirrors will be received by the high-sensitivity detector, affecting the sensitivity of the system. In this paper, the polarization modulation characteristics of scattered light by the mirrors with different roughness are analyzed. The traditional system based on polarization splitting and transmitting with a single quarter waveplate is improved by using a doublet waveplate, i.e., a combination of a half waveplate and a quarter waveplate. The transceiver system including the off-axis optical antenna is developed and the signal transceiver isolation (ability of suppressing backscattering light) is improved by 7∼8 dB. Although the system complexity is increased, the waveplate can work as a solar window to improve the environmental adaptability. The laser communication terminal would meet the requirements of further link communication, including inter-satellite networks under the same aperture condition.

Construction and maintenance of satellite-to-ground and inter-satellite laser communication network

Construction and maintenance of satellite-to-ground and inter-satellite laser communication network

Design and Implementation of a Narrow-Band Intersatellite Network with Limited Onboard Resources for IoT.

Satellite networks are inevitable for the ubiquitous connectivity of M2M (machine to machine) and IoT (internet of things) devices. Advances in the miniaturization of satellite technology make networks in LEO (Low Earth Orbit) predestined to serve as a backhaul for narrow-band M2M communication. To reduce latency and increase network responsivity, intersatellite link capability among nodes is a key component in satellite design. The miniaturization of nodes to enable the economical deployment of large networks is also crucial. Thus, this article addresses these key issues and presents a design methodology and implementation of an adaptive network architecture considering highly limited resources, as is the case in a nanosatellite (≈10 kg) network. Potentially applicable multiple access techniques are evaluated. The results show that a time division duplex scheme with session-oriented P2P (point to point) protocols in the data link layer is more suitable for limited resources. Furthermore, an applicable layer model is defined and a protocol implementation is outlined. To demonstrate the technical feasibility of a nanosatellite-based communication network, the S-NET (S band network with nanosatellites) mission has been developed, which consists of four nanosatellites, to demonstrate multi-point crosslink with 100 kbps data rates over distances up to 400 km and optimized communication protocols, pushing the technological boundaries of nanosatellites. The flight results of S-NET prove the feasibility of these nanosatellites as a space-based M2M backhaul.

Improved MAC layer protocol of Wifi for satellite network.

With the development and universal application of satellite technology, an important way to expand the function of satellites is setting up inter-satellite networks to make them work together. Traditional satellite networking methods generally adopt a fixed time slot allocation method, which is not suitable for small satellite groups with low latency and high throughput requirements. In order to solve this problem, it has been proposed to apply the traditional Wifi protocol in satellite networking. As there are differences between satellite networks and terrestrial networks, it’s necessary to improve the traditional 802.11 protocol. The Media Access Control (MAC) protocol in 802.11 is improved in this paper, which mainly includes the adaptive algorithm of maximum contention window size and the growth algorithm of Contention Window (CW) size. The maximum contention window is adjusted according to the conflict state of the current network, which makes the network accommodate more satellite nodes. The CW growth algorithm improves the traditional Binary Exponential Back-off (BEB) algorithm, where the CW is designed according to the priority of the data frame or the network load. In this way, high-priority satellite accusation information will have higher reliability or tolerate greater network load.

High Speed Laser Based Intersatellite Link Systems for Harsh Environment of Space

This paper will focus on the trends for the space-based lasers, optics and terminals used in the intersatellite networks. Reviewed and evaluate the recent development in the space-based laser technologies and the critical parameters that are employed for successful high-speed intersatellite communications systems. Fiber optics and photonics technology including lasers increasingly being used in aerospace applications and many challenges are involved, since designing for aerospace is very different than for the earth environment. Satellites are much more challenging and for their intersatellite solutions have to contemplate more specific requirements such as space radiation attacks, operation in harsh environment of space and achieving weight, power requirements and reliability for space are few to consider. Therefore it is important to design a system to defend against the radiation from ionizing, gamma, and other attacks. There are numerous methods to protect them from radiation, including shielding, error correction, and using radiation resistance shielding and radiation hardening. Building laser for high speed communications network for the harsh environment of space using optical links in space has proven to be complicated task and many such schemes were tried without success in the past. Space-based optical communications using satellites in low earth orbit (LEO) and Geo-synchronous orbits (GEO) hold great promise for the proposed Internet in the Sky network of the future. However in the last few years, there has been impressive progress made to bring the concept of laser-based intersatellite systems to fruition in civilian and government-non classified projects. Laser communications offer a viable alternative to established RF communications for inter-satellite links and other applications where high performance links are a necessity. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser-based systems and they are just few numbers of potential advantages for system design over radio frequency communication.

Investigation of isolation for free space laser communication in the mono-wavelength optical T/R channels

Favorable isolation performance in optical transmitting-receiving (T/R) channels is key to establishing full-duplex bi-directional laser communication links when designing mono-wavelength laser communication terminals. This study proposes a novel design scheme for T/R channels that use a single laser wavelength. The system includes measures such as the deflection at λ/4 wave plate angles, light trap installation at a polarization beam splitter, and removal of polarization analyzers in optimized systems. A mathematical model describing isolation in the optical T/R channels is presented. Three types of factors that affect the isolation of optical T/R channels were analyzed and simulated in detail. The present simulation results show that the roughness of the λ/4 wave plate and the solid angle of the detector field of view are exponentially related to T/R isolation, which can thus be regarded as the most significant factors affecting isolation. According to the present design scheme, the prototype T/R channel was developed for measuring isolation. The measured value (77.8 dB) agrees well with the result determined using the established mathmatical model (77.3 dB). Conclusively, the present theoretical model can provideguidance for optimizing isolation in a mono-wavelength optical channel. Thus, it can be applied extensively in laser communication systems, including inter-satellite networks.

Relative motion and visibility evaluation in GNSS constellation: A projection method

Using crosslinks to network the satellites in a GNSS constellation has been regarded as one of the most important trends for the GNSS modernisation. The motion and visibility of the satellites w.r.t. each other in the constellation have to be evaluated as an prerequisite to many tasks, especially to the inter-satellite network design, measurement scheduling and pointing-related issues. Thus far, very few analytical studies have been done on this issue for GNSS constellations. In this paper, a projection method is proposed to evaluate the relative motion and visibility. By projecting the relative trajectory orthogonally onto the orbital plane of the base satellite, it is much easier to study the geometric characteristics of the relative motion and the effect of constellation parameters and field-of-view constraint on the relative visibility. Given that GNSS constellations are designed based on Walker constellation, the relative motion pattern is explored algorithmically with index mapping techniques and the always visible relationship is visually modelled using a graph which in most cases shows a symmetry structure when the vertices are placed in a proper order. As demonstration of our method, a thorough experimental validation on the nominal GPS, GLONASS, Galileo and BeiDou-M constellation is proposed. The result explicitly reveals that the relative motion and visibility varies according to the parameters of the constellations.

Performance limitations of free-space optical communication satellite networks due to vibrations: direct detection digital mode

Free-space optical communication between satellites net- worked together can permit high data rates between different places on Earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence. Due to the narrow divergence and the large distance between the satellites, pointing from one satellite to another is difficult. The pointing task is further complicated by vibration of the pointing system caused by tracking noise and mechanical impacts. In this work we derive mathematical performance models for digital direct detection communication satellite networks as a function of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes a transmitter sat- ellite, regenerative satellites, and a receiver satellite all networked to- gether. A comparison between three communication system modulation schemes—on-off keying (OOK), pulse position modulation (PPM), and pulse polarization binary modulation (PPBM)—is presented. These mod- els are the basis for optical communication tracking- and pointing-system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. From the analysis it is clear that even low vibration amplitude of one satellite pointing system decreases the network performance dramatically. © 1997 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(97)01111-2)

Performance limitations of free-space optical communication satellite networks due to vibrations—analog case

Free-space optical communication between satellites networked together can make possible high-speed communication between different places on earth. The use of optical radiation as a carrier between the satellites creates very narrow beam divergence angles. Due to the narrow-beam divergence angle and the large distance between the satellites, the pointing from one satellite to another is complicated. The complication is due to vibration of the pointing system caused by two stochastic fundamental mechanisms: (1) tracking noise created by the electro-optic tracker and (2) vibrations created by internal satellite mechanical mechanisms. We derive mathematical models of signal, noise, approximate SNR, and approximate bit error rates of optical communication satellite networks as functions of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes transmitter satellite, repeater satellites, and receiver satellite all networked together. These models are the basis for pointing system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. An example of practical communication between Anchorage in Alaska to Johannesburg in South Africa by a free-space optical communication network composed of nine low-earth-orbit satellites is given. From the analysis it is clear that even low vibration amplitude of the satellite pointing systems decreases dramatically the network performance.