卫星通信基础(一).doc

卫星通信基础（一）静止卫星 / GSO satellite静止卫星工作在位于赤道平面的圆轨道上，卫星的运行周期为24小时。由于静止的运转方向和角速度与地球的自转方向和角速度相同，卫星的空间位置与地面任意地点的相对空间关系固定不变。GSO satellites are locating and operating at geostationary orbit. Geostationary orbit is a circular one, with its revolution period of 24 hours. A GSO satellite appears stationary above the earth, because of its running direction and orbital velocity is as same as the earths rotational direction and speed respectively. Therefore, an earth station could point to the satellite at fixed elevation and azimuth angles.由静止卫星的轨道位置示意图可见，地球的平均半径约为6378公里，静止卫星的轨道高度约为35786公里，轨道半径约为42,164公里。从静止卫星看地球，地球的角直径约为17.4度。Asthe sketch map of geostationary orbitshown, the earths mean radius is about 6378 km, while the altitude and orbit radius of a GSO satellite is approximately equal to 35786 km and 42164 km respectively. Looking from a GSO satellite, the earths diameter is about 17.4 in angle.在采用EquiRectengular投影方式的静止卫星的覆盖范围示意图中，三条绿线分别对应东经105.5度卫星的0度、15度、及30度仰角服务区。图中的0度仰角服务区表明，静止卫星只能覆盖到南北纬大约80度处，南北两极附近的高纬度地区并不在静止卫星的服务区内。由15度仰角服务区的经度覆盖范围大致有140度可知，只需轨位间隔约为120度的三颗静止卫星，就可以覆盖南北纬70度以下的绝大部分地球表面。Adopting EquiRectengular projection method,the sketch map of the coverage of a GSO satellite located in 105.5E longitude presents three green lines denoting service areas of elevation 0, 15 and 30 respectively. The service area of 0 elevation indicates that a GSO satellite could only cover the area between 80N and 80S latitude, while higher latitude areas near north pole and south pole would be out of the service. On the other hand, the service area of 15 elevation could cover the area about 140 degrees in longitude, it shows that only three GSO satellites with 120orbital space one another could cover most of the earth surface where latitude not higher than 70.卫星通信的历史与现况 / Satcom, the past and the present英国的空军军官Arthur C Clarke于1945年著文提出利用静止卫星提供全球微波通信的设想。In 1945, Arthur C. Clarke, a British air force officer, conceived the idea to effect global microwave communication by GSO satellites.卫星通信大致经历了如下发展阶段：1950年代中期，利用气球卫星等进行无源反射式通信试验；1960年前后，利用低轨卫星作存储转发式通信试验；1960年代初，利用中、高轨卫星进行越洋通信试验；1964年，利用静止通信卫星对东京奥运会作了实况转播；1965年，国际通信卫星组织发射Intelsat-I；同年，苏联也开始提供卫星通信业务。The satcom development steps are as follows: The earliest space communication was experienced in mid 1950s, when some balloon-satellites were used as passive reflectors. Around 1960, store and then transit tests were held on low earth orbit (LEO) satellites. In early 1960s, people could communicate across the ocean by mid or high earth orbit (MEO or HEO) satellites. In 1964, GSO satellite was used for live broadcast for Tokyo Olympic Game. Intelsat-1 was launched in 1965 as the first commercial communication satellite, and Soviet Union began its satcom service as well in the same year.目前，已有第9代Intelsat卫星在轨提供服务。卫星通信成为经济上最为成功的空间技术。仅在东亚和东南亚就有中国、日本、韩国、印度尼西亚、泰国、马来西亚、新加坡、菲律宾等国拥有在轨的静止通信卫星。我国现有5家通信卫星公司，拥有10颗在轨通信卫星，总通信容量约为370个（36MHz）标准转发器。Nowadays, the 9thgeneration Intelsat satellites are providing service in orbit, and satcom has become most successful space technology in economy. Only in east and south-east Asia regions, there are 8 countries including China, Japan, Korea, Indonesia, Thailand, Malaysia, Singapore and Philippines which possess communication satellites. And China has now 5 satcom companies with 10 communication satellites in orbit, and the total communication capacity is approximately 370 standard transponders (36MHz bandwidth per transponder).卫星通信的特点 / Properties of satcom卫星通信是以人造通信卫星为中继站的微波中继通信 ，其特点主要为： 覆盖范围大通信成本与通信距离无关，适用于广播方式，便于网络快速扩容及站点应急部署，不容易查找干扰源；通信距离长传输延时长，传播损耗大工作频率较高带宽和通信容量较大，部分频段存在降雨衰耗建网和使用成本高地球站设备和天线、以及网管系统的一次性投入，专业建站 人员的施工费用，卫星转发器（带宽资源与功率资源）的租金Satcom is one kind of microwave communication by utilizing communication satellite as a relay station and it has the following properties. Wide coverage: cost independent of distance, well suitable for broadcasting, easier network expansion and quicker remote installation, but difficult in finding interfering resources Long distance: long time delay and high loss in propagation High frequency: wider bandwidth and larger capacity, but higher rain attenuation in some f