卫星通信技术.doc

此文档收集于网络，如有侵权，请联系网站删除第二章下平均角速度The average angular velocity (椭圆)三个例子：Geostationary Satellite Orbit Radius 地球静止卫星轨道半径 Low Earth Orbit 低地球轨道T,vElliptical Orbit 椭圆轨道 The subsatellite point星下点sidereal day 恒星日，地球自转的真正周期23h56m4.1s solar day太阳日，24hExpendable launch vehicle (ELV) 一次性运载火箭Reused launch vehicle (RLV) 重复使用运载火箭the space shuttle/space transportation system (STS）航天飞机/空间运输系统Three ways: Geostationary transfer orbit and AKM. 地球同步转移轨道Geostationary transfer orbit with slow orbit raising. 地球同步转移轨道与地球轨道缓慢提高Direct insertion to GEO. 直接插入Doppler shiftDoppler shift To a stationary observer, the frequency of a moving radio transmitter varies with the transmitters velocity relative to the observer. This change in frequency is called Doppler shift or just Doppler.相对距离变换而引起的。 2009年7月22日，中国境内观测到1814年-2309 年间最长一次日全食活动，可谓千年一遇。11个省市自治区的部分地区能观赏日全食。Sun Transit Outage 日凌中断第三章五个子系统：(1) Attitude and Orbit Control System (AOCS) 姿态和轨道控制系统(2)Telemetry, Tracking ,Command, and Monitoring (TTC&M) 遥测、跟踪、指挥和监控(3)Power System 电源系统(4)Communications Subsystems 通信子系统(5)Satellite Antennas 卫星天线(AOCS)Purpose：to make the satellites antennas point toward the earth and let the users knows where in the sky to look for the satellite.Attitude Control System two ways :（1）Spinners 滚动条 （2）Three-axis stabilized satellite 三轴稳定卫星Orbit Control SystemApproach：Correcting the inclination of satellite orbit.At interval of 2 weeks, the E-W corrections are made first and then after 2 weeks, the N-S corrections are made.Telemetry, Tracking ,Command, and Monitoring (TTC&M)The main function of satellite management are(1) to control the orbit and attitude of the satellite;(2) monitor the status of all sensors and subsystems on the satellite;(3) and switch on or off sections of the communication system.Power SystemAll communication satellites obtain their power from solar cells, which convert incident sunlight into electrical energy.(1)A spin-stabilized satellite usually has a cylindrical body covered in solar cells.(2)for a three-axis stabilized satellite, the cells can be arranged on flat planets that can be rotated to maintain normal incidence of sunlight.Communications Subsystems 通信子系统1. Goal: Provide the largest traffic capacity2. Method: Increase bandwidth or reuse3. Bands: C band, Ku band, Ka bandA transponder for C band consists of a band-pass filter to select the particular channels band of frequencies, a downconverter to change the frequency from 6GHz at the input to 4GHz at the output, and an output amplifier.A transponders input are from one or more receive antennas and outputs are switch matrix.Switch matrix directs each transponder band of frequencies to the appropriate antenna or antenna beam.3.6 Satellite Antenna1. Main types of antenna used on satellites:(1)Wire antennas线型天线: monopoles and dipoles单极和偶极子(2)Horn antennas角锥天线(3)Reflector antennas反射面天线(4)Array antennas数组天线天线的互易定理一般天线都具有可逆性，即同一副天线既可用作发射天线，也可用作接收天线。同一天线作为发射或接收的基本特性参数是相同的。(1)Use the word antenna pattern for receiving天线模式An antenna pattern is a plot of the field strength in the far field of the antenna when the antenna is driven by a transmitter. It is usually measured in decibels (dB) below the maximum field strength.The pattern is frequently specified by its 3dB beam width, the angle between the directions in which the radiated (or received) field falls to half the power in the direction of maximum field strength. (2) Use the word gain for transmitting增益The gain of an antenna is a measure of the antennas capability to direct energy in one direction, rather than all around.3.天线波束全球波束天线波束的半功率宽度约等于17.4，覆盖卫星对地球的整个视区。一般由圆锥喇叭天线加上45的反射板组成点波束天线覆盖面积小，一般为圆形，半功率波束宽度为几度。天线通常为前馈抛物面天线，馈源为喇叭赋形波束天线可通过修改反射器形状来实现，也可利用多个馈源从不同方向经反射器反射产生多波束的组合。3dB beamwidth is the angle between the directions in which the radiated (or received) field falls to half the power in the direction of maximum field strength.The smaller the antenna and the lower the frequency the larger the 3dB beamwidth becomes. EXAMPLE 3.6.2 Regional Coverage AntennaThe continental United States subtends an angle of approximately6030 when viewed from geostationary orbit. (1)What dimension must a reflector antenna have to illuminate half this area with a circular beam 30 in diameter at 11GHz? (2)Can a reflector be used to produce a 6030 beam? What gain would the antenna have?The reliability of a component canbe expressed in terms of the probability of failure after time t，PF (t) bathtub curve第四章1、Performance objectives(1) a bit error rate (BER)(2) a signal to noise ratio (S/N)BER or S/N is determined by the carrier-to-noise ratio (C/N)，The C/N ratio is calculated at the input of the receiver, at the output terminals (or port) of the receiving antenna.The overall C/N at the earth station receiver depends on both links and both must achieve the required performance for a specified percentage整体的C / N在地球站接收器取决于两个链接，都必须达到一定比例要求的性能4. Designing a satellite system requires knowledge of: 设计一个卫星系统需要的知识：（(1) The required performance of the uplink and downlink所需的性能的上行和下行链路(2) The propagation characteristics传播特性(3) Rain attenuation for frequency band being used at the earth station location用于在地球站的位置的频率波段雨衰。 (4) The parameters of the satellite卫星参数(5) The parameters of the earth station地球站参数通过一个半径为r的球表面的磁通密度由下式给出：The product PtGt, is often called the effective isotropically radiated power or EIRP。 该表达式被称为连结方程，它在无线链路在任何接收功率的计算非常重要。In practice Pr =EIRP+ Gr-Lp -La -Lta -Lra dBWLa = attenuation in atmosphere 大气衰减量Lta = losses associated with transmitting antenna 发射天线与相关损失Lra = losses associated with receiving antenna 与接收天线相关损失EXAMPLE 4.2.1A satellite at a distance of 40,000 km from a point on the earths surface radiates a power of l0 W from an antenna with a gain of l7 dB in the direction of the observer. Find the flux density at the receiving point, and the power received by an antenna at this point with an effective area of l0 m2. 在4万从对地球表面的辐射点公里卫星从一个有着7层分贝观察者的方向增益天线的10 W电源。找出在接收点的磁通密度，在这一点上，并收到由天线的有效面积10平方米的功率。 （2） Example 4.2.2 The satellite in Example 4.2.l operates at a frequency of 11GHz. The receiving antenna has a gain or 52.3 dB. Find the received power. 在例4.2.l卫星工作于11GHz的频率。接收天线的增益或52.3分贝。找到接收功率。 它等于一个电阻在与这个噪声源相同的带宽内给出相同的功率时所具有的绝对温度。Pn =the available noise power (in watts) and will be delivered only to a load that is impendence matched to the noise source. 可用噪声功率（瓦特），将仅提供给负载匹配的噪声源阻抗。 k = Boltzmanns constant = 1.39 l0-23J/K =-228.6 dBW/K/Hz 玻尔兹曼常数 TP=Physical temperature of source in Kelvin degrees 物理温度开氏度的来源 kTp = a noise power spectral density in watts per hertz. The density is constant for all radio frequency up to 300 GHz. 噪声功率谱密度每赫兹瓦。密度为常数，所有无线电频率高达300赫兹。 Bn = noise bandwidth in which the noise power is measured, in hertz. 噪声带宽，其中噪声功率测量，单位为赫兹。system noise temperature Ts Ts是一个噪声源在一个无声的接收器，这给予接收器的输出端测得的原始接收器位于相同的噪声输入功率，噪声温度，通常包括从天线的噪音。载噪比The superheterodyne receiver超外差接收器a front end (RF amplifier, mixer and local oscillator) 一个前端（RF放大器，混频器和本地振荡器），and IF amplifier (IF amplifier and filters) 和中频放大器（IF放大器和滤波器）and a demodulator and baseband section. 和解调器和基带部分噪声温度的单一来源Example 4.3.1Suppose we have a 4-GHz receiver with the following gains and noise temperatures:Tin = 25 K GRF = 23 dB TRF = 50 K GIF=30 dB TIF=1000 K Tm = 500 KCalculate the system noise temperature assuming that the mixer has a gain Gm = 0 dB.Recalculate the system noise temperature when the mixer has a -l0dB loss. How can the noise temperature of the receiver be minimized when the mixer has a loss of l0 dB?The system noise temperature is given by Eq. (4.l8)TS= TRF + Tin + Tm /GRF+ TIF/(GRFGm)Ts = 25 + 50 + (500/200) + (l000/200) = 87.5 KIf the mixer had a loss, as is usually the case, the effect of the IF amplifier would be greater for Gm = - l0 dB, the linear value is Gm = 0.l as a ratio. Then Ts = 25 + 50 + (500/200) + (1000/20) = l37.5 KThe lowest system noise temperatures are obtained by using a high gain LNA. Suppose we increase the LNA gain in this example to GRF = 50 dB, giving ratio GRF = l05Ts = 25 + 50 + (500/105) + (l000/104) = 75.1 KThe high gain of the RF LNA amplifier has made the system noise temperature almost as low as it can go: Ts = Tin + TRF = 75 K in these examples. LNAs for use in satellite receivers usually have gains in the range 40 dB45 dB.6. the noise passing through a lossy medium 通过噪声传递介质损耗Tno=Tp (1-G1)Where，G1 is the linear gain (less than unity not in decibels) of the attenuating device or medium, Tp is the Physical temperature in degrees Kelvin of the device or medium.For an attenuation of A dB, the value of G1 is given by G1=10A/10Note that A is a negative value请注意，是一个负值Example 4.3.2The system illustrates in Example 4.3.l has an LNA With a gain of 50 dB. A section of lossy waveguide with an attenuation of 2 dB is inserted between the antenna and the RF amplifier Find the new system noise temperature for a waveguide temperature of 3000K.The waveguide loss of 2 dB (ratio 1.58) can be treated as a gain, G1, that is 1ess than unity: (G1 = 10-2/10 = 0.63l). 该系统显示了一个具有50 dB增益低噪声放大器为例4.3.l。第一个分贝损耗波导的衰减与2之间插入的是天线和射频放大器查找波导温度约3000K新的温度为系统噪声。Twg = Tp(l - G1) = 300(l - 0.63l) = 110.7 KThe waveguide attenuate the noise from the antenna, so Tin = 0.63 25 = 15.8 K。The new system noise temperature, referred to the input of the LNA, is Ts = 15.8 + 110.7 + 50 + (500)/l05) + (1000/l04) = 176.6 K。We can refer the system noise temperature to the antenna Output port by dividing the above by G1. This transfer the noise source from the LNA input to the waveguide input. Ts = l76.6/0.63l = 279.9 KThe new system noise temperature is 5.7 dB higher than the system noise temperature without the lossy waveguide.Note that when the system noise temperature is low, each 0. 1 dB of attenuation ahead of the RF amplifier will add approximately 6.6 K to the system noise temperature. (Using the formula in Example 4.3.2 with Tn = 2900K, G1 = -0.1 dB = 0.977 and Tno= 290 0.023 = 6.6 K) This is the reason for placing the front end of the receiver at the output of the antenna feed. Waveguide losses ahead of the LNA can have a disastrous effect on the system noise temperature of low noise receiving systems.EXAMPLE 4.3.3 An amplifier has a quoted noise figure of 2.5 dB. What is its equivalent noise temperature? Answer :2.5 dB=1.78 Td = 290(l.78 - l) = 226 Kthis value of noise temperature could then be used in Eq. (4.17), with other appropriate data, to calculate system noise temperature.EXAMPLE 4.3.4 An earth station antenna has a diameter of 30 m, has an overall efficiency of 68%, and is used to receive a signal at 4150 MHz. At this frequency the system noise temperature is 79 K When the antenna points at the satellite at an elevation angle of 280. What is the earth station G/T ratio under these conditions? If heavy rain causes the sky temperature to increase so that the system noise temperature rises to 88 K what is the new G/T value? First calculate the antenna gain. For a circular aperture: At 4l50 MHz, = 0.0723 m. Then G = 0.68 x(3.1430/0.0723)2 = 1.16 x l06 or 60.6 dB Converting Ts into dBK Ts = l0lg79 = 19.0 dBK G/T = 60.6 - 19.0 = 41.6 dBK If Ts = 88 K in heavy rain, G/T = 60.6 - 19.4 = 41.2 dB/K.Design of Downlinks 所有的卫星连接的链接受雨衰影响。目标：(1) Meeting a minimum C/N ratio for a specified percentage of time 最低限度。会议上最小的C / N比为百分比指定的时间(2) And carrying the maximum revenue earning traffic at minimum cost以最低的成本进行税收收入的最大流量通讯链结预算(Link Budget) Link Budget Example: C-Band Downlink for Earth Coverage Beam1. in clear air(1)PtThe saturated output power of the transponder is 20 W = l3 dBW. We assume an output back-off of 2 dB, the power transmitted by the transponder is Pt=13-2=11 dBW。(2) GtThe satellite provides coverage of the visible earth, which subtends an angle of approximately l70 from a satellite in a geostationary orbit, by using a global beam antenna. Gt=33000/172=20dBERIP=Pt+Gt=11+20=31 dBW(3) Grthe receiving earth station has an antenna with an aperture diameter of 9m and gain of 49.7dB at 4GHz(4) LThe maximum path length of a GEO satellite link is 40,000 km, which gives a path loss of l96.5 dB at 4GHz3 dB for losses at the edge of coverage zone of the satellite. Lant =3 dB 0.2 dB for propagation losses in clear air La =0.2 dB 0.5dB for miscellaneous losses such as antenna mispointing, polarization mismatch and antenna degradation Lm =0.5dB (5) PrReceived power at earth station Pr =ERIP+ Gr-LallPr =31+49.7-196.5-3-0.2-0.5=-119.5 dBW(6) NReceiver noise power k = BoItymanns constant , -228.6 dBW Ts = System noise temperature, 75 K=18.8 dBKBn = Noise bandwidth, 27 MHz =74.3 dBHzN=k+Ts+Bn =-135.5 dBW(7) C/N C/N = Pr - N = -119.5 - (-135.5) = 16.0 dB(8) Link margin The minimum permitted overall C/N ratio for this link is 9.5 dB, corresponding to the FM threshold of an analog satellite TV receiver.Link margin=16-9.5=6.5 dBThis link margin is available in clear air conditions, but will be reduced when there is rain in the slant path.2. in heavy rain(1)Heavy rain in the slant path can cause up to 1 dB of attenuation at 4 GHz, which reduces the received power by l dB Prain =-119.5-1=120.5 dBW(2) And increases the noise temperature of the receiving system. this is an increase in system noise temperature of 2.3 dB. Nrain=-135.5+2.3=133.3 dBW(3)The recalculated C/N ratio (C/N) rain = Prain Nrain=120.5-133.3 =12.7dBThe minimum permitted overall C/N ratio for this link is 9.5 dB, link margin=12.7-9.5=3.2 dBFor diameter of the earth station antenna Gr=1.2dB=1.32 Gr=49.7-1.32=48.5dBDiameter of the earth station antenna can be reduced from 9m to 7.8muplink design上行的设计是比许多情况下更容易下行：（1）因为一个准确指定的载波功率时必须出示的卫星转发器（2）它往往是可行的，在使用地球站的发射机功率比更高的可用于一颗卫星。然而，VSAT系统使用W，地球站与小国以下的天线和上行发送器的EIRP 5给低。卫星电话手机只限于危害发射功率水平低于1 W，由于电磁辐射的风险。在移动通信系统的卫星电话从上行通常是最低的C / N比的联系。 可以计算的Prxp从转发器的输出功率和转发器的增益，当这些参数都是已知的和弯管转发器使用。转发器的饱和输出功率When a complete satellite link is engineered, the noise in the earth station IF amplifier will have contributions from (1) the receiver itself, 接收器本身(2) the receiving antenna , 接收天线(3) sky noise, 天空噪声(4) the satellite transponder from which it received the signal and adjacent satellites从它收到信号和邻近卫星的卫星转发器(5) and terrestrial transmitters which share the same frequency band地面发射频段共享相同Satellite Communication Link DesignA typical two-way satellite communication link consists of four separate path: (1) an outbound uplink path from one terminal to the satellite 从一个终端站卫星上行链路(2) and outbound downlink to the second terminal; 到第二个终端下发链路(3) and an inbound uplink from the second terminal to the satellite 从第二个终端到卫星的一个上行链路(4) and an inbound downlink to the first terminal. 到第一个终端的一个下行链路The design procedure 1. Determ