User Satellites Research Articles

Delay-throughput tradeoff in satellite data relay networks with prioritized user satellites

The efficient antenna scheduling strategy for data relay satellites (DRSs) is essential to optimize the throughput or delay of the satellite data relay network. However, these two objectives conflict with each other since the user satellites (USs) with higher priorities take up more transmission time of DRSs' antennas for greater throughput but the USs storing more packets cause a severer waiting delay to the whole network. To balance the conflicting metrics for meeting the delay-throughput integrated requirements, we formulate the antenna scheduling as a stochastic non-convex fractional programming, which is challenging to be solved. For the tractability, we equivalently transform the fractional programming to a parametric problem and implement the Lyapunov drift to guarantee the constraint of mean rate stability. By proposing a delay and throughput tradeoff based antenna scheduling algorithm, we further transform the parametric problem to a solvable weight matching problem. Simulation results reveal the feasible region of the preference control parameter for integrated QoS cases and its variation relationship with network delay and throughput.

Modeling and Performance Analysis for Satellite Data Relay Networks Using Two-Dimensional Markov-Modulated Process

Satellite Data Relay Networks (SDRNs) play an important role in the data relay from User Satellites (USs) to ground stations by Tracking Data Relay Satellites (TDRSs). For better exploitation of SDRNs, the development of the systematic model and accurate system analysis is essential. To describe the end-to-end data transmission in SDRNs, we construct an MMOO/MMSP/1/K-G/G/1 tandem queuing model where the two parts depict the traffic arrival and transmission service of USs and TDRSs, respectively. Because the active and inactive periods of the data transmission are determined by the visibility between two satellites, classical buffer state based vacation policies become imprecise. Moreover, these two kinds of periods appear alternatively and their duration varies over time so that it is hard to model such intermittent transmission by existing service models. To overcome these difficulties, we propose a Markov Chain Monte Carlo based Markov Modulated Service Process (MMSP) which can tightly match the distributions of the active and inactive periods. In this process, we propose two algorithms to calculate the service state transition probability and the number of the sub-states in each service state, respectively, which guarantees the alternative transition between the active and inactive states as well as the sojourn time spent in each state. For the quality of service analysis, we find the different features of the queue variation under different arrival and service rate conditions. By separately calculating the related mean queue lengths and emergence probabilities, we first derive the expressions of the system loss probability, mean queue length, and mean delay. Finally, we conduct numerous simulations to verify the accuracy of our system model and performance evaluation, which provides the guidance to the buffer design and transmission resource allocation.

An enhanced MAC protocol based on the IEEE 802.11 for data relay satellite systems

SummaryData relay satellite (DRS) systems play an important role in space information networks. Characterized by highly dynamic topology and discontinuous communication links, it is suggested that the IEEE 802.11 protocol employed in such a network could be more flexible. However, such a terrestrial network protocol could not be applied to DRS systems directly, nor supports a fast response due to the long propagation delay and severe packet collision. To address this challenge, we proposed an enhanced media access control (MAC) protocol based on the IEEE 802.11 protocol providing multiaccess for low earth orbit (LEO) distributed constellations. In this paper, we investigated the access delay performance of the proposed protocol in our model. Then, we derived a contention window adaption by using an iteration algorithm that can dynamically adjust the values of the contention window depending on the number of user satellites in the communication coverage. Simulation results show that the average access delay does not exceed 20 seconds, which is significantly lower than the standard protocol. Moreover, the traffic threshold is increased to 0.6, and the maximum throughput has doubled compared with the standard protocol. It is proved that the enhanced MAC protocol shows a better performance in DRS systems.

Channel-Aware Mission Scheduling in Broadband Data Relay Satellite Networks

Mission scheduling algorithms are envisioned as critical to satisfy the increasing mission requirements in broadband data relay satellite networks, which is severely influenced by time-varying inter-satellite contacts (i.e., potential available communication links) and differentiated satellite downlink contacts. Nevertheless, the intertwined effect of such two types of contacts on mission schedules poses daunting challenges for the efficient mission scheduling design. In this paper, to achieve fair performance among user satellites, we maximize the minimum number of successfully scheduled missions over all user satellites by jointly optimizing contact plan design, power allocation (PA) in relay satellites, and mission schedules based on the time-expanded graph. The formulated problem is a mixed-integer nonlinear program optimization problem that is challenging to solve. For tractability purpose, we equivalently decompose the problem into a PA problem and an optimal PA-based mission scheduling (OPA_MS) problem, which is still a mixed-integer linear program. We further devise a new two-stage scheme to efficiently solve the OPA_MS problem. Simulation results validate the significant gains of the proposed algorithm in mission completion number and necessitate the consideration of the time-varying and differentiated inter-satellite and downlink contacts.

A Multicast Routing Algorithm for Datagram Service in Delta LEO Satellite Constellation Networks

Satellites can broadcast datagram over wide areas, therefore, the satellite network has congenital advantages to implement multicast service. LEO satellite has the property of efficient bandwidth usage, lower propagation delay and lower power consumption in the user terminals and satellites. Therefore, the constellation network composed by LEO satellites is an essential part of future satellite communication networks. In this paper, we propose a virtual center based multicast (VCMulticast) routing algorithm for LEO satellite constellation network. The algorithm uses the geographic center information of group users to route multicast datagrams, with less memory, computer power and signaling overhead. We evaluate the delay and performance of our algorithm by means of simulations in the OPENET simulator. The results indicate that the delay of the proposed multicast method exceeds the minimum propagation by at most 29.1% on the average, which is a quite acceptable achievement, considering the resource overhead reduction that can be introduced by our proposal

Resources scheduling for data relay satellite with microwave and optical hybrid links based on improved niche genetic algorithm

The formation of the Space-based Information System with the technology of high performance optical inter-satellite communication and the realization of global seamless coverage and mobile terminal accessing are the necessary trend of the development of optical and microwave hybrid communication. Considering the resources, missions and restraints of data relay satellite optical and microwave hybrid links system, a model of hybrid links resources scheduling is established and a scheduling algorithm based on an improved niche genetic algorithm is put forwarded. According to the multi-user-satellite, multi-time-window, multi-class-antenna and a number of missions with priority weight, the scheduling schemes are generated randomly to begin with and evaluated with the fitness functions. To obtain an optimal scheduling result, an improved niche genetic algorithm is adopted to optimize the scheduling schemes. The simulation result reveals that a satisfactory result is obtained and the improved niche genetic algorithm has advantages in both efficiency and performance in a scenario including a relay satellite with 2 optical antennas and 1 microwave antenna for user satellites connection, 8 user satellites with 64 missions. The simulation indicates that the model and the optimization algorithm are suitable for multi-user, multi-mission and multi-class-antenna hybrid communication recourses scheduling problem.

一种基于时间窗口更新的激光链路中继卫星资源调度算法

According to the resources,missions and restraints,a scheduling algorithm based on view period windows refreshing is put forward and the model is established.Considering the multi-window multi-antenna structure and mission priority(PRI),the mission is scheduled reasonably and the time window is refreshed by the scheduling operation:the confirmed operator of current mission scheduling time and the refreshing of the following mission view period window.The PRI is considered as parameter in cost calculation and the scheduling project is optimized by genetic algorithm.The simulation scene includes 4 user satellites,3 antennas and 32 missions.The simulation result reveals that the algorithm can obtain satisfactory results in both time and optimization,which is suitable in multimission and multi-antenna recourse scheduling.

Term Analysis of a TDRS Tracking a User Satellite

中继卫星是航天测控网发展的必然趋势.一颗中继卫星对不同轨道的用户星测控支持能力是不同的,受多种因素的影响.从理论上详尽地分析了地球同步轨道中继卫星(TDRS)对近地航天器的跟踪条件,计算了中继卫星对各种轨道高度近地航天器的测控覆盖率,给出了中继星到用户星可视算法、地球遮挡和受太阳直射的计算公式,通过专业STK软件仿真验证了所得结论的正确性,它们可以作为确定天基网的中继星数量和对在轨中继卫星进行资源分配的理论依据.

Single frequency GPS measurements in real-time artificial satellite orbit determination

A simplified and compact algorithm with low computational cost providing an accuracy around tens of meters for artificial satellite orbit determination in real-time and on-board is developed in this work. The state estimation method is the extended Kalman filter. The Cowell's method is used to propagate the state vector, through a simple Runge–Kutta numerical integrator of fourth order with fixed step size. The modeled forces are due to the geopotential up to 50th order and degree of JGM-2 model. To time-update the state error covariance matrix, it is considered a simplified force model. In other words, in computing the state transition matrix, the effect of J 2 (Earth flattening) is analytically considered, which unloads dramatically the processing time. In the measurement model, the single frequency GPS pseudorange is used, considering the effects of the ionospheric delay, clock offsets of the GPS and user satellites, and relativistic effects. To validate this model, real live data are used from Topex/Poseidon satellite and the results are compared with the Topex/Poseidon Precision Orbit Ephemeris (POE) generated by NASA/JPL, for several test cases. It is concluded that this compact algorithm enables accuracies of tens of meters with such simplified force model, analytical approach for computing the transition matrix, and a cheap GPS receiver providing single frequency pseudorange measurements.

Enhanced Radiative Force Modeling of the Tracking and Data Relay Satellites

Orbit determination (OD) approaches operationally model the Tracking and Data Relay Satellites (TDRS) as homogenous spheres for nonconservative force modeling. To improve definitive orbit determination and prediction accuracies, and to employ TDRSS tracking of user satellites within various geophysical investigations, a detailed TDRS spacecraft model has been developed. The enhanced TDRS model represents the spacecraft as a combination of twenty-four flat plates. The radiative forces acting on each plate are computed and vector summed to produce the overall acceleration on the spacecraft center of mass. An initial model, based on pre-launch engineering information, has been refined to better fit observed spacecraft accelerations. The Goddard TDRS-5 Model 3 (GT5M3) improves orbit accuracy, yields better fits to the tracking data, significantly reduces residual accelerations, and improves orbit prediction capability.

Conception of spacecraft centralized power supply

A reliable power supply for spacecraft is one of the central problems determining the future development of space technology. The traditional solution to this problem implies having an autonomous power plant on board each spacecraft. The most widely used are power plants with solar cells. However, there exists an alternative power supply concept of using a centralized power supply system (CPSS) and power transmission to the user satellites by laser or microwave beams. Use of a CPSS has a number of advantages. In particular, it allows the spacecraft to increase power supply level and service life as well as to decrease the spacecraft mass and cost. However, it sets new physical and technical problems associated with long distance power transmission and requires some changes in spacecraft structure and concepts. The feasibility study of CPSS development and use has to rely on existing or firmly forecastable technologies. An attempt of such an analysis has been done by a group of scientists at Moscow State Aviation Institute during 1994-1996. The very first results have already been published. This paper discusses new results obtained lately regarding a space based CPSS.

Development of multibeam phased array antenna on ets‐vi for s‐band intersatellite communications

AbstractThis paper describes the S‐band intersatellite communication (SIC) antenna to be carried on the Engineering Test Satellite VI scheduled for launch in 1994, to undertake the first intersatellite data relay experiments in Japan. The SIC antenna is an on‐board formed multibeam phased array antenna, the first of this kind in the world to be carried on a satellite. The SIC antenna is capable of simultaneous data relays to several orbiting satellites (user satellites) by means of an electrically scanned beam. With an on‐board microprocessor, the location of a user satellite can be computed, and the beam is pointed toward that direction automatically.In comparison with the system used in the data relay satellite of the United States, the on‐board beam‐forming system has several advantages, such as the effective use of power and frequency in the case in which the number of user satellites is small, as in Japan. In this paper, the function and the configuration of an SIC antenna are described first. Next, analysis of the antenna is presented, including the effect of the phase and amplitude errors caused by temperature fluctuations. Further, as the main components, the newly developed broadband microstrip antenna, a small beam‐forming network with small phase errors, and the phase shifter controller making the computation of the orbit of the user satellite are presented. Finally, the total test results of the on‐board model of the SIC antenna are described.

Tracking accuracy evaluation for data relay and user satellites

The demand for almost continuous coverage for close Earth orbiting satellites necessitates the use of data relay systems. The European Space Agency is currently studying the in-orbit infrastructure and is preparing a European data relay system, not only to be used for telemetry and telecommand purposes but also for tracking support. This paper deals with the tracking aspects of the user satellites and derives the requirements on the position accuracy of the data relay satellites. This orbit accuracy requirement is about 70, 25, 10 m (along track, cross track, radial) and can be achieved in routine cases with a few ranging stations suitably distributed in the European area. However, the use of an additional ranging station outside Europe, preferably in the Southern Hemisphere would aid the determination of the orbit after manoeuvres, especially after inclination control manoeuvres. Adequate knowledge of the position could then be achieved after about 4 h of dense tracking.

ＥＴＳ−ＶＩ搭載Ｓバンド衛星間通信用オンボード軌道計算追尾システム

On-board orbit calculation and tracking system of the S band inter-satellite communication equipment (SIC) for Japan's Engineering Test Satellite-VI (ETT-VI) to be launched in 1992, is presented. The SIC provides a multibeam phased array antenna with 54 phase shifters for beam pointing. The beams are directed to any desired user satellites automatically by controlling 54 phase shifters according to results of on-board orbit calculations by an on-board microprocessor. As accurate on-board beam pointing is required in inter-satellite communications, this paper describes a method of on-board orbit calculation and estimations of beam pointing errors caused by using the system considering perturbations.

Space operations and data system for the H-II and space station era

The National Space Development Agency of Japan (NASDA) is now pursuing space operations and data system (SODS) as a next generation tracking and data acquisition system for the H-II and Space Station era. One of the important points of the SODS concept is the utilization of Japanese own data relay and tracking satellite system (DRTSS). The DRTSS is quite effective to obtain continuous and high rate data from low altitude Earth orbiting satellites. Because the mission achievement of many DRTSS user satellites depends on DRTSS, very high reliability of the system is required. Interoperability among the DRTSSs of space agencies is therefore very desirable in order to increase their reliability with least redundancy. This paper describes the conceptual plan of the SODS emphasizing DRTSS and also summarizes NASDA's basic idea concerning network interoperability.

Multibeam array antenna for data relay satellite

AbstractAs the use of space expands, the demand for data relay systems between satellites used for real time data transmission between the ground station and a satellite has increased. This paper proposes a data relay multiple‐access system between satellites which is suited for a relatively small number of users in Japan. The paper also describes the 19‐beam multibeam array antenna developed for this system. Compared to NASA's AGIPA system, the present on‐board multibeam system has a number of advantages: effective use of frequency and power; simplification; and cost effectiveness of the ground station if the number of user satellites is small. Next, a multibeam antenna system suited for this system is studied. It is found that the multibeam array is suited in the case where many beams are formed with a relatively small aperture. The configuration and design method are described. As individual elements, a newly developed broadband microstrip array and a small beam‐forming circuit with a good beam‐forming capability are described. Based on these devices, a 19‐element array antenna with 19 multibeams and one scanning beam is developed. Its technical possibility is proven as a satellite‐borne antenna.

Navigating Low Altitude Satellites Using the Current Four NAVSTAR/GPS Satellites

A greater degree of survivability is a significant requirement of future space systems. Toward this end, an important aspect is an autonomous navigation capability. For many space systems, an obvious choice is the use of the Navstar/Global Positioning System (GPS). With the operational 18-satellite GPS constellation (plus three active spares), low altitude user satellites will have continuous tracking data available for navigation. On the other hand, with the current constellation of four satellites, there is less available data and, consequently, the accuracy of navigation varies a great deal throughout the user satellite orbit. This paper discusses the navigational performance that can be achieved with this constellation. Last summer, the Ladsat 4 satellite was placed into a near circular, sun synchronous, orbit at an altitude of 705 km, and at an inclination angle of 98.3 deg. This satellite contains a Navstar GPS receiver (called GPSPAC), and is the first user satellite to employ GPS. Using this satellite as an example, an error analysis was performed of the navigation accuracy that can be obtained for a low altitude satellite. During the course of a Landsat 4 orbit, it will be able to observe from none to four Navstar/GPS satellites. When four satellites are available, the three-dimensional accuracy can be expected to be about 11 m. Since Landstat 4 is sun synchronous, i.e., its orbit plane rotates in longitude with the sun, there will be times during the year when this satellite and the GPS satellites simultaneously come together over the continental United States. This is where Landsat 4 is primarily used, and is the ideal geometric relationship between Landsat 4, the GPS satellites, and the earth. This favorable condition occurred last November. This paper discusses the use of Navstar/GPS to navigate Landsat 4 under this ideal geometric situation, as well as at other times during the year. The paper presents the results of a theoretical accuracy analysis. The actual on-orbit experience with Landsat 4 is not covered here.