LEO satellite communication network has a large number of satellites distributed in low orbits,which leads to multiple coverage of many areas on the ground.It is hard work to describe and evaluate the reliability of LEO satellite communication network.To solve this problem,the reliability of all-user terminals in LEO satellite communication network is defined,and the corresponding reliability evaluation method is proposed in the paper.Due to the large scale of the interstellar network,a modular reduction algorithm using the modular network instead of the original network for state decomposition is proposed in this paper.Case study shows that the calculation time of the proposed method is equivalent to 6.28%of the original state space decomposition algorithm.On this basis,the reliability of LEO satellite communication network is further analyzed.It is found that the reliability of LEO satellite network was more sensitive to the reliability of Inter-Satellite link and the satisfaction of global coverage in the early stage,and it is more sensitive to the reliability of the satellite in the later stage.The satellite-ground link has a relatively constant impact on of LEO satellite network. 相似文献
Wireless Personal Communications - The satellite network is one of the major source of information and these days small satellites are gaining lot of focus. The group of small satellites form a... 相似文献
The architecture of cislunar multi-hop communication networks, which focuses on the re-quirements of lunar full-coverage and continuous cislunar communications, is presented on the basis of Geosynchronous Orbit (GEO) satellite network relays. According to the geographical distribution of the forthcoming Chinese Deep Space Measuring and Controlling Network (DSMCN ), two networking schemes are proposed and two elevation angle opti-mization models are established for locating GEO relay satellites. To analyze the dynamic connectivi-ty, a dynamic network model is constructed with re-spect to the time-varying characteristics of cislunar trunk links. The advantages of the two proposed schemes, in terms of the Connectivity Rate (CR), In-terruption Frequency (IF), and Average Length of Connecting Duration (ALCD), are corroborated by several simulations. In the case of the lunar polar orbit constellation case, the gains in the perform-ance of scheme I are observed to be 134.55% , 117. 03% , and 217. 47% compared with DSMCN for three evaluation indicators, and the gains in the per-formance of scheme II are observed to be 238.22% , 240.40% , and 572.71% . The results validate that the connectivity of GEO satellites outperforms that of earth facilities significantly and schemes based on GEO satellite relays are promising options for cislu-nar multi-hop communication networking. 相似文献
For future multimedia applications, satellites might play an important role. For broadcast applications satellites are ideally suited to illuminate a large geographical area. However, multimedia applications are interactive, and are therefore a combination of a broadcast mission and a multipoint-to-point mission. The natural question is, can a satellite system compete with the capacity provided by terrestrial cable networks? If the answer is positive, and it shown in this article that it is, a second question arises: what new developments are required to migrate from the state-of-the art satellite technology to such advanced concepts? Taking the example of the European Space Agency's activities in this field, an overview of the required building blocks which make up a complete multimedia communication satellite system are described. Based on this technological overview a discussion of the systems developed by European space industries with support from the European Space Agency is given 相似文献
The area of high voltage direct current (HVDC) transmission line is very large, so using cable for electric field monitoring system is very inconvenient. Wireless sensor network (WSN) can solve this problem. Compared with the traditional communication network, WSN has the advantages of small volume, high flexibility, strong self-organization. So it’s more suitable for the construction of distributed electric field monitoring system which has long distance and high mobility. On the other hand, optical E-field sensors are passive devices and they have such advantages as compact structure, wide-band response and wide measuring range which mechanical sensors lack. A distributed wireless system with optical E-field sensor is designed for collecting and monitoring the electric field under HVDC transmission lines. This measurement system has been used in China’s state grid HVDC test base and power transmission projects. Based on the experimental results, this measurement system demonstrates that it can adapt to the complex electromagnetic environment under the transmission lines and can accomplish the accurate, flexible, and stable demands of the electric field measurement.
Future manned spaceflight programs may require continuous real-time communications between the spacecraft and the mission control center. This paper examines the feasibility of relay satellite (RS) systems to meet these requirements. Anticipated requirements range from voice and low-speed data for the Skylab and Space Shuttle to television for the Space Station. Frequencies in S, C, X, and K bands (2, 5, 8, and GHz bands, respectively) are considered. Terrestrial radio-relay links may cause interference in the mission spacecraft (MS) and RS and vice versa. Possible remedies include better control of antenna sidelobes and judicious choice of channel frequencies. It is found that INTELSAT IV offers a technically feasible means of providing voice and data communications but not TV. A new dedicated satellite system can meet the requirements with two geostationary satellites both of which are visible to a single earth station (ES) in the United States. A shared satellite system, catering to other potential users as well as to manned spacecraft, offers the possibility of reduced cost to individual users. Satellite configurations for both dedicated and shared systems are presented. The satellites can be launched by boosters of the Thor-Delta class if the links between satellite and spacecraft operate in K band. 相似文献
Surrey Space Technology UK, a Surrey University spinoff has secured a contract worth €27.9m to build one of two experimental Galileo satellites for in_orbit validation. Its Galileo 400kg test satellite, will transmit Galileo signals from one of the orbits to be used by the constellation. It will be launched during 2005 to secure the frequencies reserved for the Galileo system with the International Telecommunications Union. Signals have to be sent by June 2006 to retain the priority allocation. The University of Surrey company, SSTL designs, constructs, tests, launches and operates small and low_cost satellites for international customers. SSTL has built more than 16 micro satellites for USAF, MoD France /Alcatel, CNES/MMS, Korea, Portugal, Thailand, Malaysia, Chile and USA/SatelLife. SSTL has also established a small satellite launch service in collaboration with ISC Kosmotras (Moscow) using de_militarised SS18 ICBMs, converted into the Dnepr small launcher, to provide low cost. regular access to space for microsats.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news. 相似文献