Interference considerations in frequency sharing between low earth orbit satellites and the geostationary fixed satellite and terrestrial service

Recently many companies and consortia have considered launching LEO satellites for such projects as remote sensing, transportation and mining operations. When the multiple low Earth orbit (LEO) satellites are transmitting they can interfere with existing terrestrial microwave and satellite earth-stations in the fixed and mobile service. The interference problem is related to the number of proposed LEOs and the altitude and consequently the time to orbit the earth. These systems usually consist of many small satellites, and each satellite stays in the beam of a terrestrial station for up to 72 seconds in each 222 minute orbit. Earth coverage could be obtained by 48 (LEO) satellites 1500 km above the earth in polar orbit, and hence at least one LEO would always be interfering with terrestrial networks. A technical evaluation would then be required to determine the resultant BER (bit error rate) effecting existing terrestrial services. A determination can then be made to support such a LEO system or object via official channels such as the ITU.     

基于中国的卫星移动通信系统的星座设计方案研究

针对中国在不同的时间段,不同的地区的通信量不同,提出了一种适合于中国的移动通信卫星组网星座方案.利用16颗LEO和两颗椭圆轨道卫星来组建的卫星网络可以在满足中国通信要求的情况下,使卫星数目尽量减少.并用计算机进行了仿真验证.     

A flexible LEO satellite modem with Ka‐band RF frontend for a data relay satellite system

From a geostationary Earth orbit (GEO) satellite's perspective, a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free‐space loss of an inter‐satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper, we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.     

Efficient dynamic channel allocation techniques with handoverqueuing for mobile satellite networks

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites     

基于分布式星群的双层星座设计

当前,陆地通信系统已无法满足日益复杂的信息需求,利用空间信息网络实现全球范围内的无缝覆盖和高效容量传输成为研究热点。现有卫星通信系统以单层星座为主,缺少高低轨卫星之间的协同。提出了一种基于分布式星群的双层星座设计,以基于分布式星群的低轨卫星作为网络架构的基础,采用星间链路实现低轨卫星之间的通信,通过高轨卫星实现中低纬度地区覆盖性能加强。仿真结果表明,所提方法在仅依靠在国内部署卫星地面站的前提下可实现全球多重覆盖。     

中国低轨移动卫星通信系统星座设计

本文研究低轨移动卫星通信系统设计中的一个基本问题－－星座设计问题，并给邮了我国低圆轨道移动卫星通信系统的星座设计方案，该星座是以三个轨道平面组成的２４颗星系统，它的高度为１３２６ｋｍ，轨道参数由本文提出的优化算法进行设计，本文用统计的方法对我国低轨系统方案和Ｇｌｏｂａｌｓｔａｒ系统（２４颗星方案）的覆盖性能进行分析比较，结果表明本文提出的系统对我国的覆盖特性优于Ｇｌｏｂａｌｓｔａｒ系统，本文还对圆     

Propagation considerations for emerging satellite communicationsapplications

The effects of rain and other propagation concerns for new applications areas, currently in operation or planned for implementation by the end of this decade, are described. The areas include: VSAT systems employing low operating margins and/or low elevation angles; traditional communications applications operating with inclined geosynchronous orbits; and mobile and personal communications applications employing networks of low earth orbit (LEO) satellites. Prediction modeling and analysis techniques applicable to these areas are described. Analytical results for a range of operational parameters involving low-margin, low elevation angle, inclined geosynchronous, and LEO systems are presented     

A model for the handover traffic in low earth-orbiting (LEO) satellite networks for personal communications

The spectacular growth of cellular telephone networks has demonstrated the demand for personal communications. Communication systems based on low earth orbit (LEO) constellations of satellites seem to be an adequate approach to achieve a world-wide network. When defining the capacity in terms of satellite circuits, the network designer has to take into account the handover traffic. Unfortunately, in a LEO communication network where handover is most often due to the network nodes motion, handover traffic models for terrestrial cellular networks cannot be used. Hence specific models must be developed. This paper proposes an analytical model for the handover in LEO satellite networks. This model is applied to different network configurations and compared to discrete-time simulations. Simulation results agree with those obtained from the analytical model.     

Analysis of system parameters for LEO/ICO-satellite communicationnetworks

Currently many efforts are undertaken to develop and install communication networks based on low Earth orbit (LEO) and intermediate circular orbit (ICO) satellites. However, many problems are to be solved before the final operation of such networks. This paper deals with basic design problems of LEO/ICO-based networks. The topology of the satellite network is considered and estimates for the number of satellites necessary, orbits and number of communication channels per satellite are derived. The features and consequences of intersatellite links are discussed. The number of communication channels per link is derived with a more elaborate model. This includes the radio links from the satellites to mobile users and to gateways, as well as intersatellite links and terrestrial lines. We introduce a formal model for LEO/ICO based networks and propose a method for the evaluation of the link capacities, given the network topology and the traffic requirements. As an example, two constellations are investigated in detail. One of these constellations is the Iridium system proposed by Motorola, the other is the LEONET concept developed in an ESA study. Finally, the influence of unequal traffic distribution is discussed     

面向手机直连的低轨卫星通信：关键技术、发展现状与未来展望全文替换

为满足全时、全域通信需求,低轨卫星通信将成为6G的重要组成部分。通过对地面移动通信协议体制进行适应性改进,低轨卫星可为地面移动手机终端提供直连服务。介绍了面向手机直连的低轨卫星通信关键技术和商业项目发展现状,探讨了未来需解决的关键问题和潜在技术途径。     

Satellite land mobile communication systems

The emergence of satellite land mobile services over the last 10 to 15 years is described together with future trends. The difficulties of providing a commercially viable voice service are discussed and alternatives, such as inclined orbit systems and satellites with very large antennas, are suggested as ways in which the initial disadvantages might be overcome. Data services for satellite land mobile traffic and the possibilities of including radio determination of vehicle location as part of these data services are also considered. Future systems, which could have their architecture strongly influenced by the use of onboard processing, are discussed     

Optical satellite networks

Several nongeosynchronous satellite constellation networks providing broad-band access to end-users are currently under development. The use of multigigabit laser intersatellite links (ISLs) is the enabling factor for routing traffic through the spare segment and creating a global space-based optical backbone network. Optical networking techniques based on wavelength division multiplexing (WDM) ISLs and wavelength routing can allow by-pass of the transit traffic significantly simplifying routing decisions and minimizing processing delays. The paper examines the characteristics of these networks and investigates the applicability of various optical networking schemes based on single hop and multihop approaches. Single hop can be adopted in medium earth orbit (MEO) systems consisting of 10 to 15 satellites whereas double-hop schemes based on the matrix lightpath allocation approach are suited for constellations up to 100 satellites, covering the requirements of most of the proposed low earth orbit (LEO) systems. Multihop will be required for some of the very large in number of satellites constellations. Statistical multiplexing of the transported traffic over the ISLs appears to be a necessary condition to achieve an efficient utilization of the satellite resources. Traffic routing has to take into account the impact of the varying range of the interorbit ISLs on the propagation delays. Although maximum leverage of the technologies developed for fiber optic WDM networks should be made, the technologies to be employed on board the satellites have to be space-qualified that may limit the applicability of some otherwise high-efficiency components     

MLSR: a novel routing algorithm for multilayered satellite IPnetworks

Several IP-based routing algorithms have been developed for low-Earth orbit (LEO) satellite networks in recent years. The performance of the satellite IP networks can be improved drastically if multiple satellite constellations are used in the architecture. A multilayered satellite IP network is introduced that consists of LEO, medium-Earth orbit (MEO) and geostationary Earth orbit (GEO) satellites. A new multilayered satellite routing (MLSR) algorithm is developed that calculates routing tables efficiently using the collected delay measurements. The performance of the multilayered satellite network and MLSR is evaluated through simulations and analysis     

Personal communications by satellite

Personal communications (PC) refers to two-way voice (and possibly data) communications to a small hand-held unit, capable of being carried by a person and used in various locations. PC via satellite refers to the case where this hand-held unit communicates directly with a satellite to provide the duplex voice (or data) service. Both geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites have been considered to provide this service. GEO and LEO satellite systems must compete with existing mobile cellular radio systems both in meeting performance requirements and service costs, if they are to be a significant supplier of PC services. GEO and LEO systems each have unique advantages and disadvantages when used to provide a PC service. While these general characteristics are identified in Section 1 of the paper, a more quantitative comparison is needed. This quantitative comparison is made by comparing a GEO PC satellite system, operating at EHF (K_a-band) frequencies with a LEO system operating at UHF (L-band) frequencies, including service costs for both systems. The two systems used in the comparison are examples of realistic GEO and LEO system designs for PC service, and although it is not exhaustive, the comparison points out some of the key differences between GEO and LEO systems that affect service performance and cost.     

Design study for a CDMA-based LEO satellite network: downlinksystem level parameters

The performance analysis of a new concept of a code-division multiple-access (CDMA) based low Earth orbit (LEO) satellite network for mobile satellite communications is presented and discussed. The starting point was to analyze the feasibility of implementing multisatellite and multipath diversity reception in a CDMA network for LEO satellites. The results are used to specify the design parameters for a system experimental test bed. Due to the extremely high Doppler, which is characteristic of LEO satellites, code acquisition is significantly simplified by using a continuous wave (CW) pilot carrier for Doppler estimation and compensation. The basic elements for the analysis presented are: the channel model, the pilot carrier frequency estimation for Doppler compensation, and multipath and multisatellite diversity combining     

Fade Slope Analysis of Ka-Band Earth-LEO Satellite Links Using a Synthetic Rain Field Model

Because the motion of a low Earth orbit (LEO) satellite across the sky causes the Earth-space path to very quickly pass through any rain cells in the vicinity, the degree of rain fading on such paths changes more rapidly and leads to steeper fade slopes than in the geostationary case. Because comprehensive measurement data have not yet been compiled for fading on LEO links in the Ka-band, we have used simulations based on Goldhirsh's method for determining the key parameters of the well-known EXCELL model of a horizontal rain structure from long-term global rain statistics to obtain plausible estimates of the fade slope distributions for selected scenarios. The results that we obtained for geostationary satellites closely match those observed at selected sites during the Advanced Communications Technology Satellite program. The results that we obtained for LEO satellites show how fade slopes will steepen as 1) the altitude of the satellite decreases; 2) the frequency band of operation increases; and 3) the average rain rate increases. Furthermore, they suggest that, at a given probability level, the fade slopes could be between two and ten times greater than those for geostationary satellites and that mobile terminals with a clear view of the sky will experience fade slopes that are similar to those encountered by fixed or transportable terminals. These results have important implications for the design of power control algorithms and other fade-mitigation techniques.     

中低轨卫星跨层激光链路二次同步切换方法

中低轨卫星之间跨层激光链路的无缝切换直接决定了双层卫星光网络的稳定性.异步切换方法会导致网络拓扑频繁重构,而集中同步切换将造成两层间连接中断,网络运行状态失控.为此,本文提出了中低轨卫星星座激光链路的二次同步切换方法,在保证中低轨道卫星连通的基础上,可降低网络拓扑重构频率.研究了整数周期比的中轨道和低轨道卫星空间位置特性,建立了中低轨卫星星座构形二阶非球摄动模型,确定了中低轨道之间轨道周期比为3的双层卫星星座构形.按连接和切换顺序将该星座构形中跨层激光链路分为两组,以相对周期的1/4为基准,每次令其中一组同步切换,通过交替完成切换.研究结果表明,二次同步切换方法使得网络拓扑重构频率降低到链路切换频率的1/7,比集中切换方法在网络平均时延方面降低了30ms.     

Analysis of basic system parameters of communication networks based on low earth orbit satellites

Currently many efforts are undertaken to develop and install communication networks based on low earth orbit (LEO) and intermediate circular orbit (ICO) satellites. However, many problems are to be solved until the final operation of such networks. This paper deals with basic design problems of LEO/ICO-based networks. In the first part, estimates for the necessary number of satellites, orbits and number of communication channels per satellite are derived. Since the latter is a crucial quantity, the number of communication links and channels per link are derived with a more elaborate model in the second part of the paper. This includes the radio links from the satellites to mobile users and to gateways, as well as intersatellite links and terrestrial lines. We introduce a formal model for LEO/ICO-based networks and propose a method for the evaluation of link capacities, given the network topology and the traffic requirements. As an example, two constellations are investigated in detail. One of these constellations is the IRIDIUM system proposed by Motorola.     

LEO satellite communication networks—a routing approach

In the modern world of telecommunications, the concept of wireless global coverage is of the utmost importance. However, real global coverage can only be achieved by satellite systems. Until recently, the satellites were in geostationary orbit and their high altitude could not allow real‐time communication such as cellular networks. The development of LEO satellite networks seems to overcome this limit. However, LEO satellite systems have specific characteristics that need to be taken into account. In the same manner, the TCP/IP standard was developed for terrestrial network. The need is then to come up with a solution that would permit the use of TCP/IP on LEO satellite networks without losing too many packets. The idea is to develop a routing algorithm that maximizes the RTT delays compared to the TCP timer granularity. For that matter, we use an FSA‐based link assignment that simulates the satellite constellation as a fixed network for a predetermined time interval. In this configuration, the problem becomes a static routing problem where an algorithm can find the best solution. Copyright © 2003 John Wiley & Sons, Ltd.     

LEO/MEO systems – Global mobile communication systems

LEO/MEO systems are moving from a dream to a reality, their global reach is becoming apparent with the launch of the first LEO satellites. The global mobility offered by these systems is expected to have a profound effect on the way that organizations and individuals operate. Billions of dollars are invested in the research and development of LEO/MEO based communication systems, and larger amounts will be needed for their ongoing operation and use. Many global satellite based systems have been announced over the last decade, Ellipsat, Globalstar, ICO, Iridium, M‐Star, Odyssey, Orbcomm, and Teledesic, are just a few of the many systems in deployment or under development. Being such a risky venture, limited experience exists in developing and managing large scale civilian satellite based mobile communication systems. Many interesting and challenging research issues are faced by the designers and operators of such systems. This paper presents the different approaches to the configuration of the various LEO and MEO based communication systems. It compares their advantages and disadvantages, and analyzes their economic viability. Based on the analysis, it is possible to identify the specific roles that each type will play in the global communication market. The paper presents and discusses some of the important research areas involved in their development, configuration, maintenance, operation and management. In particular, it introduces the problem of gateway placement in LEO/MEO systems and presents a mathematical formulation of the problem. This revised version was published online in June 2006 with corrections to the Cover Date.