Satellite antennas

Communication satellites have evolved from a radio relay in space to encompass other applications such as processing and meteorology. The demand for high capacity communication satellites has led in the past two decades to the development of multibeam antennas, a landmark in satellite antenna technology. Satellite antennas are classified into three categories according to function: communication; tracking, telemetry, and command (TT and C); and special satellite antennas. While the application of shaped beam antennas has been developed to its fullest extent as in INTELSAT VI and VII, an active monolithic microwave integrated circuit (MMIC) phased array will play an important role in future satellite antenna technology. Examples of each state-of-the-art satellite antenna technology and the process of space qualification are presented briefly     

The TNS program: A computer simulation package for the intelsat TDMA network

The TNS (TDMA Network Simulation) program is a computer simulation package developed for the evaluation, test and analysis of all the protocols in the INTELSAT TDMA network. The TNS program faithfully simulates the dynamic operation of the network, taking account of the satellite motion, and makes it even possible to simulate the network operation under some abnormal conditions, such as terminal function failure and transponder failure. This paper describes the TNS program in terms of its design approach, its capabilities, its structure, its input and output data, and its operation. An example simulation for the whole system start-up procedure assuming the Atlantic Ocean region is also presented.     

VSAT networks in the intelsat system

This paper describes how VSAT networks currently operate in the INTELSAT system. Four classes of VSAT networks (data transaction; circuit-switched; data distribution; microterminals) are identified, and it is verified that all of them can operate with INTELSAT satellites. Most VSAT networks in operation on INTELSAT today operate in fractional transponder leases. Fractional transponder capacity estimates are presented for a wide range of scenarios and different INTELSAT satellite series. These estimates clearly show increasing bandwidth utilization efficiencies for newer generations of INTELSAT satellites. Provided that VSAT and hub sizes are appropriately selected, efficiencies are already significant with existing satellites. Two possible ways of increasing the utilization of satellite resources are examined in the paper: demand assignment multiple access (DAMA) and multiple channel-per-carrier (MCPC) techniques. The impact of using DAMA in circuit-switched VSAT networks is quantified.     

公用通讯网络中遥测数据的实时传输技术的研究

通过公用光缆网络SDH实现跨区域遥测数据和对空指挥信息的实时传输,构建覆盖广阔空域范围和超长飞行距离的遥测实时监控网络系统,该系统满足实时性,通用性,经济性,保密性的要求.     

The INTELSAT VII/VIIA generation of global communications satellites

Developed primarily to provide continuation of services from the INTELSAT V satellites in the Pacific Ocean Region, this latest generation of satellites also has utility for operation in other roles. Several new technologies are combined to give cost-effective international satellite communications on a global, regional and domestic basis. This new higher power satellite will form a fundamental part of the INTELSAT global network, having been designed to match the projected traffic demands and future service requirements.     

Satellite communications networks

The evolution of satellite communication systems over the past two decades from simple point-to-point links with unique subcarrier-defined paths between points to today's multipoint, satellite-switched, multi-satellite networks tying together hundreds of earth stations, and transmitting voice and data increasingly in the time domain is considered. Examples of the methods used to manage network resources efficiently through terrestrial control and monitoring of information flow together with on-board switching are given. These examples are choosen mostly from the INTELSAT experience which will soon include a sixth generation of space segment. The paper concludes with a discussion of the future directions of satellite network development made possible by the technology being planned for NASA's Advanced Communications Technology Satellite. This design anticipates the needs of both high-volume trunking and thin-route service.     

DPSK-PM调制信号数字解调方法研究

针对卫星USB测控系统中常用的DPSK-PM调制技术，设计了一种简单的数字解调方法。在介绍算法原理的基础上，对解调算法进行了仿真，仿真结果证明了该方法的有效性。该方法对于航天测控链路信息对抗仿真平台的建立具有指导意义。     

The intelsat VIII/VIIIA generation of global communication satellites

Developed originally to meet increased demand forecast for C-band capacity in the Pacific Ocean Region (POR), this latest generation of INTELSAT satellites is planned to be operated in a number of traditional and new roles. To date INTELSAT has bought four INTELSAT VIII spacecraft for Pacific, Indian and Atlantic Ocean regions and two modified VIII-A to meet the specific Landmass requirements for the rapidly expanding Asia-Pacific and pan-American market. The VIII spacecraft, using Martin Marietta Astro Space's GS7000 bus has sufficient power and payload carrying capability that it can accommodate a wide variety of services. A new feature for INTELSAT is the inclusion of arcjet propulsion which has the potential for long lifetime while needing only half of the fuel requirement of conventional thrusters. This new high power satellite will form a key part of the INTELSAT global network through to the year 2010 and complement the INTELSAT VII and VIIA series.     

Forward error correction applied to intelsat IDR carriers

Forward error correction (FEC) techniques are applied to INTELSAT intermediate data rate (IDR) services to reduce the transmitted power requirements relative to uncoded systems, thereby increasing the satellite transponder capacity. Properly designed FEC systems reduce data errors in the received digital stream with minimal impact to the protocols, operation and equipment involved with the communication system. This paper discusses the overall system impact of the addition of FEC to the IDR service. The appropriateness of the specific application of convolutional encoding combined with Viterbi decoding techniques is discussed. Basic concepts of convolutional encoding and Viterbi decoding are presented in order to provide understanding of the trade-offs involved in the specification of the coding technique for the IDR service. The details of the IDR FEC specification are presented. The implementation of a system based on a VLSI Viterbi decoder device which conforms to the INTELSAT requirements is described.     

Technical and economic impact of the use of standard-B earth stations in the intelsat system

More than 20 years after the INTELSAT system started up, satellite technology developments have led to considerable changes in the world-wide international satellite transmission system. This evolution and the present capabilities offered by digital technologies make it possible to reassess the potential cost advantages of standard-B earth stations over a wider portion of international telephone transmission routes. This paper addresses the technical and economic issues raised by the characteristics of the present and planned INTELSAT satellites, together with the current capabilities of digital techniques (forward error correction, low rate encoding, time and frequency division multiple access). The foreseeable impact of the use of such techniques on overall satellite telephone transmission costs is also presented, and compared with that forecasted for fibre optic cable circuits.     

C频段高增益低旁瓣天线馈源设计

测控系统中的收发天线要求有较好的隔离度,收发天线系统的旁瓣要尽可能地小,要达到这样的要求往往天线的成本很高。文中设计了一种加扼流环的圆锥喇叭来作为抛物面的馈源。实现低成本的高增益、低旁瓣的收发天线系统。实验结果表明：加扼流环的圆锥喇叭照射抛物面的天线具有低副瓣、高增益的特点,实现简单,性能优越。本文的结果已经应用到某C频段测控系统中。     

新时期应急卫星通信系统能力提升的改进研究

应急卫星通信系统是远程机动通信的主用手段,有时甚至是惟一手段。近年来,在抗震救灾、处突维稳特别是重要保障任务中通过卫星链路将图像、音频、数据、短消息等业务传输到远端指挥中心,实现远程应急指挥。该系统拥有专属卫星频段保障及专用网络通道,能够确保应对重大事件中信息传递的灵活性、便捷性、安全性。基于现有应急卫星通信系统进行了概述,剖析了新时期应急通信系统能力提升的集成必要性、集成原则,指出了应急卫星通信系统进一步提升通信能力的相关技术措施。     

TTT System (50 Mbits/s PCM-TDMA System With Time Preassignment and TASI) and Its Satellite Test Results

An experimental 50 Mbits/s pulse-code modulation-time-division multiple access (PCM-TDMA) system with time preassignment and time-assignment speech interpolation (TASI) features (called the TTT system) was built for use in a satellite test. This system was designed for application in the INTELSAT IV network and has the channel capacity of more than 700 telephone channels. This capacity can be increased up to twice when pulse-code modulation-time-assignment speech interpolation (PCM-TASI) is adopted. The field test was conducted via INTELSAT III in 1970 and satisfactory results were obtained, which encourages the introduction of the TDMA system for commercial use.     

基于张量分解的卫星遥测缺失数据预测算法

卫星健康状况监测是卫星安全保障的重要基础,而卫星遥测数据又是卫星健康状况分析的唯一数据来源。因此,卫星遥测缺失数据的准确预测是卫星健康分析的重要前瞻性手段。针对极轨卫星多组成系统、多仪器载荷以及多监测指标形成的高维数据特点,该文提出一种基于张量分解的卫星遥测缺失数据预测算法(TFP),以解决当前数据预测方法大多面向低维数据或只能针对特定维度的不足。所提算法将遥测数据中的系统、载荷、指标以及时间等多维因素作为统一的整体进行张量建模,以完整、准确地表达数据的高维特征;其次,通过张量分解计算数据模型的成分特征,通过成分特征可对张量模型进行准确重构,并在重构过程中对缺失数据进行准确预测;最后,提出一种高效的优化算法实现相关的张量计算,并对算法中最优参数设置进行严格的理论推导。实验结果表明,所提算法的预测准确度优于当前大部分预测算法。

     

Intelnet Services—A global data distribution and collection scheme

Responding to the recent availability of very small earth-stations (commonly called micro terminals) for data/voice communications, INTELSAT has introduced a new service called INTELNET. INTELNET services are designed to operate with two different modulation and coding techniques, i.e. spread spectrum and binary phase-shift keying (BPSK) with rate 1/2 forward error correction (FEC). The INTELNET I service is a data distribution service, whereas the INTELNET II service is a data collection service. These services are facilitated by the use of micro terminals at remote locations (i.e. outposts) which will be linked through the INTELSAT space segment to relatively large INTELSAT earth-stations (e.g. Standard A, B, C and E-3). INTELNET services are leased transponder services offered on a range of INTELSAT satellites in C- or Ku-bands on a pre-emptible or non-pre-emptible basis. These services are offered on a full-time or occasional-use basis, by assigning predetermined satellite resources of bandwidth and power with a smallest allotment of 1 MHz. In this paper, the system design and network architecture for the INTELNET I and II services are addressed. Representative transmission parameters have also been developed for the INTELNET I and II services. System cost considerations as a result of the use of micro terminals are analysed.     

Leveling the playing field in international satellite communications

This article addresses policy issues raised by the introduction of competition in the international satellite industry. The monopoly/monopsony interests of INTELSAT and its members are discussed, and strategies INTELSAT has used to protect its market are analyzed. Differences in regulatory and legal structures between the domestic and international telecommunications environment pose problems for new entrants. The author outlines a series of policy actions that the U.S. government could take to create a “level playing field” for international satellite competition.     

Transport layer protocols and architectures for satellite networks

Designing efficient transmission mechanisms for advanced satellite networks is a demanding task, requiring the definition and the implementation of protocols and architectures well suited to this challenging environment. In particular, transport protocols performance over satellite networks is impaired by the characteristics of the satellite radio link, specifically by the long propagation delay and the possible presence of segment losses due to physical channel errors. The level of impact on performance depends upon the link design (type of constellation, link margin, coding and modulation) and operational conditions (link obstructions, terminal mobility, weather conditions, etc.). To address these critical aspects a number of possible solutions have been presented in the literature, ranging from limited modifications of standard protocols (e.g. TCP, transmission control protocol) to completely alternative protocol and network architectures. However, despite the great number of different proposals (or perhaps also because of it), the general framework appears quite fragmented and there is a compelling need of an integration of the research competences and efforts. This is actually the intent of the transport protocols research line within the European SatNEx (Satellite Network of Excellence) project. Stemming from the authors' work on this project, this paper aims to provide the reader with an updated overview of all the possible approaches that can be pursued to overcome the limitations of current transport protocols and architectures, when applied to satellite communications. In the paper the possible solutions are classified in the following categories: optimization of TCP interactions with lower layers, TCP enhancements, performance enhancement proxies (PEP) and delay tolerant networks (DTN). Advantages and disadvantages of the different approaches, as well as their interactions, are investigated and discussed, taking into account performance improvement, complexity, and compliance to the standard semantics. From this analysis, it emerges that DTN architectures could integrate some of the most efficient solutions from the other categories, by inserting them in a new rigorous framework. These innovative architectures therefore may represent a promising solution for solving some of the important problems posed at the transport layer by satellite networks, at least in a medium‐to‐long‐term perspective. Copyright © 2006 John Wiley & Sons, Ltd.     

ROBUST DATA LINK PROTOCOLS FOR CONNECTION-LESS SERVICE OVER SATELLITE LINKS

The performance of the connection-less network service (CLNS) over a satellite link with features such as high propagation delay and a varying (often high) level of errors, can be improved using the connection oriented data link (CODL) service. However, although existing CODL protocols satisfy the requirements of a connection oriented network protocol (e.g. X.25), they are not optimal for the CLNS over satellite links. The interaction of link error recovery procedures with the error recovery procedures implemented by CLNS users, the unnecessary delay due to link protocol sequencing and recovery procedures, and the interaction between applications with different quality of service (QoS) requirements cause most CODL protocols to have a detrimental impact on the performance of the CLNS. This study presents a new link protocol, which improves the quality of the CLNS (e.g. IP), especially considering the enhancement of the performance of connection-oriented transport protocols (e.g. TCP). The performance improvement using the new link protocols is demonstrated by implementation in a satellite interworking unit.