Satellite Link Design: A Tutorial - IJENS
International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 041Satellite Link Design: A TutorialAderemi A. Atayero, Matthew K. Luka and Adeyemi A. Alatishe Abstract — The communication link between a satellite and theEarth Station (ES) is exposed to a lot of impairments such asnoise, rain and atmospheric attenuations. It is also prone to losssuch as those resulting from antenna misalignment andpolarization. It is therefore crucial to design for all possibleattenuation scenarios before the satellite is deployed. This paperpresents the rudiments of a satellite link design in a tutorial formwith numerical examples.Index Term— Satellite communications, Link analysis, Linkdesign, EIRP, SNR, CNR.I. INTRODUCTIONThe satellite link is essentially a radio relay link, much like theterrestrial microwave radio relay link with the singularadvantage of not requiring as many re-transmitters as arerequired in the terrestrial link. Transmission of signals over asatellite communication link requires Line-of-Sight (LoS)communication, but since theoretically three equidistantsatellites in the geosynchronous orbit can effectively coverover 90 percent of the earth surface, the need for multipleretransmissions is removed. Satellite communicationspecialists, radio and broadcast engineers are in the businessof determining the factors required for optimal linkavailability and quality of performance. These factors can bedivided into two broad categories; the conduit factors and thecontent factors. The conduit factors include such factors as:earth-space and space-earth path (a.k.a. uplink and downlink)effect on signal propagation, quality of earth stationequipments, and the impact of the propagation medium in thefrequency band of interest, et cetera. The content factors dealmainly with the type of message transmitted and the devicesinvolved in its transformation from one form to another forsuitability for transmission over a microwave medium. Theseinclude, but are not limited to: satellite functionality, natureand peculiarities of the precise nature of information, dataprotocol, timing, and the telecommunications interfacestandards that apply to the service. It is for these reasons that aproper engineering methodology is required to guaranteetimely deployment and effective and efficient exploitation ofsatellite communication applications and devices. These inturn must guarantee delivery of objectives for quality,reliability and availability. The remaining part of this tutorialpaper presents the various component parts necessary fordesigning a robust satellite link with appreciable availabilityand required signal/noise ratios.II. BASIC LINK ANALYSISLink analysis basically relates the transmit power and thereceive power and shows in detail how the difference betweenthese two is accounted for. To this end the fundamentalelements of the communications satellite Radio Frequency(RF) or free space link are employed. Basic transmissionparameters, such as antenna gain, beam width, free-space pathloss, and the basic link power equation are exploited. Theconcept of system noise and how it is quantified on the RFlink is then developed, and parameters such as noise power,noise temperature, noise figure, and figure of merit aredefined. The carrier-to-noise ratio and related parameters usedto define communications link design and performance aredeveloped based on the basic link and system noise parametersintroduced earlier.The flux density and link equation can be used to calculatethe power received by an earth station from a satellitetransmitter with output power Pt watts and driving a losslessantenna with gain Gt, the flux density in the direction of theantenna bore sight at a distance R meters is given by:PG(1) t t [W / m 2 ]4 R 2PtGt is called the Effective Isotropic Radiated Power or EIRPbecause an isotropic radiator with an equivalent power equalto PtGt would produce the same flux density in all directions. 1Example A:A satellite downlink at 12 GHz operates with a transmit powerof 20 W and an antenna gain of 45 dB. Calculate the EIRP indBW.Solution:EIRP 10log20 45 58 dBW 2For an ideal receiving antenna with an aperture area of A m2would collect a power of Pr watts given byPr A (2)The product PtGt is called is called Effective IsotropicRadiated Power (EIRP) since an isotropic radiator with anequivalent power equal to PtGt would produce the same fluxdensity in all directions. The received ideal antenna gain isgiven by:4 AG 2(3)Gr A r4 2Thus Aderemi A. Atayero, Matthews K. Luka and Adeyemi A. Alatishe are withthe Department of Electrical & Information Engineering, CovenantUniversity, PMB1023 Ota, Nigeria. (phone: 234.807.886.6304; e-mail:atayero@ieee.org).PtGtA[Watts]4 R 212Pr Pt G t G r 4 R / 2(4) – Denotes the beginning of an example. – Denotes the end of an example110904-3232 IJECS-IJENS August 2011 IJENSIJENS
International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 04Equation (4) is known as the link equation and it is essential inthe calculation of power received in any radio link. The term(4 R/ )2 is known as the Path Loss (Lp). It accounts for thedispersion of energy as an electromagnetic wave travels froma transmitting source in three-dimensional space. A measureof the attenuation suffered by a signal on the Earth-Spacepath. For a real antenna, however, the physical aperture areaAr, the effective aperture area Ae, and the aperture efficiency A are related by the equation (5).(5)Ae A ArFor a real antenna equations (2) and (4) become (6) and (7):PG APG A(6)Pr t t A r t t e [Watts]4 R4 A Ar2 Gr 24 R D 24 Ae A 22(7)Q A D2The link equation expressed in equation (4) may be read aspresented in equation (8).EIRP Receive antenna gain (8)Power received [Watts]Path loss Using decibel notations, equation (8) can be simplified to:(9)Pr EIRP Gr L p [dBW ]whereEIRP 10 log Pt G t [ dBW ] Gr 10 log 4 Ae / 22c. If the satellite operates at a frequency of 11 GHz andthe Earth Station (ES) antenna has a gain of 52.3 dB.Determine the received power.SolutionData and conversion:Satellite antenna gain 22 dB 1022/10 158.5 W;Satellite signal wavelength c3 108 0.0273 mf 11 109where c – speed of light;Earth station to satellite distance, R 39,000 km 3.9x10 7 ma) Substitutingthe given values into (1), we have: 20 158.5 1.66 10 13W / m 27 24 3.9 10 Using the decibel notation: 10 log( Pt G t ) (20 log R 10 log( 4 )) 10 log( 20 158.5) (20 log 3.9 10 7 10 log 12.57) 35.01 151.82 10.99 127.8 dBW / m 2Note that 10 log(1.66 10 13 ) 127.8 dBW / m 2 [ dB]b) The power received with an effective collecting antenna of10 m2 aperture is:L p 20 log 4 R / [ dB] Pr Ae 1.66 10 13 10 1.66 10 12WIn decibels:III. SIGNAL ATTENUATIONPr A 127.8 10 117.8 dBW The path loss component of equation (9) is the algebraic sumof various loss components such as: losses in the atmosphereNote that due to attenuation by air, water vapor and rain, losses at the 117.8 dBW 10 11.78W 1.66 10 12Wantenna at each side of the link and possible reduction inc) Working in decibels using equation (9) we have:antenna gain due to antenna misalignment (due to poorLP 20 log( 4 R / )operation of the AOC3 satellite subsystem). This needs to be 20 log( 4 3.9 10 7 / 0.0273)incorporated into the link equation to ensure that the system 205.08 dBmargin allowed is adequate. Thus, equation (9) can be rewritten as (10):Pr EIRP G r L pPr EIRP Gr l ta l ra l atm l rain l pol l pt . (10) 35.01 52.3 205.08wherelta–Attenuation due to transmit antenna, lra–Attenuation due to receiveantenna, latm–Atmospheric attenuation, lrain–Attenuation due to precipitation, lpol–Attanuation due to polarization, lpt–Antenna pointing misalignment relatedattenuation Example B:A satellite at a distance of 39,000 km from the EIEdepartmental building radiates a power of 20 W from anantenna with a gain of 22 dB in the direction of a VSAT at theEIE building with an effective aperture area of 10 m 2.Find:a. The flux density at the departmental buildingb. The power received by the VSAT antenna 117.77 dBW . IV. SOURCES OF INTERFERENCEWith many telecommunication services using radiotransmission, interference between services is inevitable andcan arise in a number of ways. The Satellite Users itecommunication interference into five main groups, these are:1. User error (Human error and equipment failure)2. Crossbow Leakage3. Adjacent satellites4. Terrestrial services5. Deliberate interferenceHowever, for the purpose of satellite link design, interferencemay be considered as a form of noise and hence, system3AOC – Attitude and Orbit Control subsystem110904-3232 IJECS-IJENS August 2011 IJENSIJENS
International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 04performance is determined by the ratio of wanted tointerfering powers. In this case the wanted carrier to theinterfering carrier power or C/I ratio [2]. The single mostimportant factor controlling interference is the radiationpattern of the earth station antenna.Assuming that the interference sources are statisticallyindependent, the interference powers may be added to give thetotal interference ratio of the satellite link.(15) I /C UD I /C U I /C DA. Downlink and Uplink Interference RatiosConsider two satellites, SC as the wanted satellite and SI as theinterfering satellite. The carrier power received at an earthstation is given by equation (11):(11) C EIRPC G R FC Lac [*] – denotes values are in decibels.Example D: Given that [C/I]U 26 dB and [C/I]D 24 dB, determine theoverall Carrier-to-Interference ratio of the given link [C/I]UD. EIRPC – Equivalent Isotropic Radiated Power fromwheresatellite SC; GR – Bore-sight (on-axis) receiving antenna gain;FC – footprint contour of the satellite transmit antenna and Lac– free space loss. An equation similar to equation (11) may beused for the interfering carrier power, albeit with theintroduction of an additional term: [P D], which incorporatesthe polarization discrimination. Also the receiving antennagain at the earth station is determined by the off-axis angle ,giving:(12) I EIRPI G R FI Lac [ PD ]Assuming that the free-space loss is the same for both thecarrier and interference signals, then from equations (11) and we have that:(12) C I EIRPC EIRPI G R G R [ PD ](13) C / I D EIRP G R G R [ PD ] The subscript D is used to denote Downlink. Example C:The desired carrier [EIRP] from a satellite is 36 dBW, andthe on-axis ground station receiving antenna gain is 43 dB,while the off-axis gain is 25 dB towards an interferingsatellite. The interfering satellite radiates an [EIRP] of 31dBW. The polarization discrimination is assumed to be 4 dB.Find the downlink Carrier to Interference ratio.Solution:For the Space-Earth path (Downlink), using equation (13) wehave that the C/I ratio will be: C / I D 3 36 31 43 25 4 27 dB For the Earth-Space path (Uplink), the C/I ratio will be givenby equation (14):(14) C / I U Power G S G S [ PU ]where [Power] – Difference in dB between wanted and interference transmit powers; [GS] – Satellite receive antenna gain forwanted earth station; [GS( )] – Satellite receive antenna gainfor interfering earth station; [PU] – Uplink polarizationdiscrimination. Solution:1. Do unit conversion from dB2. Determine inverse ratio [I/C] values3. Use equation (15)4. Determine inverse ratio [C/I] value5. Do unit conversion back to dB C / I U 26 C / I D 24dB 10 2.6 398.11dB 10 2.4 251.19 I /C U 1 / 398.11 0.00251 I /C D 1 / 251.19 0.00398from (15) I /C UD 2.51 10 3 3.98 10 3 0.00649hence C / I UD 10 log 0.00649 21.88dB B. Carrier To Noise Ratio (C/N)One of the objectives of any satellite communication system isto meet a minimum carrier to noise (C/N) ratio for a specifiedpercentage of time. The C/N ratio is function of the systemnoise temperature, which is very important in understandingthe topic of carrier to noise ratio.V. SYSTEM NOISEA. Noise temperatureNoise temperature provides a way of determining how muchthermal noise active and passive devices generate in thereceiving system. The most important source of noise inreceiver is thermal noise in the pre-amplification stage. Thenoise power is given by the Nyquist equation as (16):(16)Pn kTp BnWhere Pn – delivered to load with matched impedance tosource noise; k – Boltzman constant 1.39 x 10-23 J/K 228.6 dBW/K/Hz; Tp – Noise temperature of source in Kelvin;Bn – Noise bandwidth in which the temperature is measured inHz.The term kTp is noise power spectral density and is constant110904-3232 IJECS-IJENS August 2011 IJENSIJENS
International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 044example. The noise is further reduced in IF low noise blockconverter (LNB). The second IF amplifier has a bandwidthmatched to the spectrum of the transponder signal.The noise temperature of a source located at the input of anoiseless double conversion receiver shown in Fig. 2 is givenby equation (17):TifT(17)TS Tin Trf m [K]G rf G m G rfwhere Gm, Gif, Grf – Mixer, IF and RF amplifier gainsrespectively; Tm, Tif, Trf – their equivalent noise temperatures.Fig. 1. Simplified earth station receiver [2]. Example E:Suppose we have a 4 GHz receiver with the following gainsand noise temperatures: Grf 23 dB, Tin 25 K, Tm 500 K,Tif 1000 K and Trf 50 K. a) Calculate the system noisetemperature assuming that the mixer has a gain Gm 0 dB. b)Determine the system noise temperature when the mixer has a10 dB loss. c) How can the noise temperature of the receiverbe minimized when the mixer has a loss of 10 dB?for all radio frequencies up to 300 GHz. A low noise amplifieris usually desired. An ideal noiseless amplifier has a noisetemperature of 0 K. Gallium Arsenide field effect transistors(GaAsFET) are normally used as amplifiers in satellitecommunication systems because they can be used to achievenoise temperatures of 30 K to 200 K without physical cooling.GaAsFET can be built to operate at room temperature with anoise temperature of 30 K at 4 GHz and 100 K at 11 GHz;other conventional amplifiers give higher values.A simplified ES receiver is presented in Fig. 1. Since theRF amplifier in a satellite communication receiver mustgenerate as little noise as possible, it is called a low noiseamplifier (LNA). The mixer and local oscillator form afrequency conversion stage that down-converts the radiofrequency signal to a fixed intermediate frequency (IF), wherethe signal can be amplified and filtered accurately. BPF is theband pass filter, used for selecting the operational frequencyband of the ES. The receiver shown in Fig. 1 employs a singleSolutiona) The system noise temperature is given by equation (17),after unit conversion from dB.23 dB 10 2.3 199.53 T S 25 50 0 dB 10 0 1500 1000 82.5 K200 1 200b) If the mixer had a loss (as is usually the case), the effect ofIF amplifier would be greater. Gm –10 dB 0.1, then TS becomes:T S 25 50 5001000 127 .5 K200 0.1 200c) Lower system temperatures are obtained by using a highergain LNAs. Suppose we increase the LNA gain in thisexample to Grf 50 dB ( 105), then Ts becomes:TS 75 5001000 75 0.005 0.1 75.105 K105 0.1 105 Fig. 2. Double conversion super-heterodyne ES receiver [2].stage down frequency conversion.Many earth station receivers use the double superheterodyne configuration shown in Fig. 2, which has twostages of frequency conversion. The front end of the receiveris usually mounted behind the antenna feed and converts theincoming RF signals to a first IF in the range 900 MHz to1400 MHz. This allows the receiver to accept all the signalsfrom a satellite in a 500 MHz bandwidth at C or Ku band forB. Noise FigureNoise figure (NF) is frequently used to specify the noisegenerated within a device. The operational noise figure of adevice can be gotten from equation (18).SNRinNF (18)SNRoutwhere SNRin , SNRout – is the Signal-to-Noise ratio at the inputand the output of the device respectively.Since the noise temperature is more useful in satellite communications, it is best to convert noise figure to noisetemperature Tn using the relationship in equation (19). SNR inT n T 0 NF 1 T 0 1 (19) SNRout Where T0 – reference noise temperature 290 K 110904-3232 IJECS-IJENS August 2011 IJENSIJENS
International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 04The value of NF is usually given in dB in the literature andmust be converted before using it in equation (19). Therelationship between Tn and NF for some typical values isgiven in Table I.6004.93.82.399 20NF,dB1Tn ,K0TABLE IRELATIONSHIP BETWEEN TN AND NF.Solutiona) From equation(7) we have that D 24 AGr 2at 4.15 10 6 Hz; c f 0.0723 m 30 2G r 0.69 1,172,856.9 0.0723 60.69 dBb)For Ts 79 K 10log79 18.98 dBKG T 60.69 18.98 41, 71 dB / KIf T s increases to 88 K in heavy rain, then Example F:Given a noise figure of 0.82 dB find the corresponding noisetemperature.Solution/ 60.69 19.44 41,25 dB / KChange in G/T value 0.46 dB / K C. Figure of merit (G/T)From equation (4) we have the power of the carrier signal atthe receive antenna as Pr. And from equation (16) we have thenoise power given by the Nyquist equation. Since the C/Nratio is the ratio of signal power to noise power, we have that:PPG GC N r t t r 2 kTS BnPn 4 R / G T / 290 1.208 1 290 0.208 Ts 88 K 10log88 19.44 dBK G /T G T G T 41.71 41.25NF 0.82 dB 100.082 1.208from equation (19) we have thatT n T 0 NF 1 60.32 K522Pt G t G r G r Pt G t G r C kTS Bn 4 R T S kBn 4 R T S(20) C N f G r T S Where C is constant for a given operational mode of thesatellite, thus C/N G/T. The ratio Gr/Ts (or simply G/T) isknown as the Figure of Merit. It indicates the quality of a receiving satellite earth system and has a unit [dB/K]. Example G:An earth station has a diameter of 30 m, and an overallefficiency of 69%. It is used to receive a signal of 4150 MHz.At this frequency, the system noise temperature is 79 K whenthe antenna points at the satellite at an elevation angle of 28 .a) What is the earth station G/T under these conditions?b) If heavy rain causes the sky temperature to increase so thatthe system noise temperature increases to 88 K what is thechange in G/T value? VI. SYSTEM AVAILABILITYThe availability of a satellite communication system is theratio of the actual period of correct operation of the system tothe required period of correct operation [3]. This availabilitydepends not only on the reliability of the constituents of thesystem, but also on the probability of a successful launch, thereplacement time and the number of operational and back-upsatellites (in orbit and on the ground). Availability of the earthstations depends not only on their reliability but also on theirmaintainability. For the satellite, availability depends only onreliability since maintenance is not envisaged with currenttechniques. Availability A is defined as given in equation (21).ROT - DTA (21)ROTWhere ROT and DT – Required Operational Time and DownTime respectively.ROT is the period of time for which the system is required to be in active operational regime, while DT is the cumulativeamount of time the system is out of order within the requiredoperational
presents the rudiments of a satellite link design in a tutorial form with numerical examples. Index Term—Satellite communications, Link analysis, Link design, EIRP, SNR, CNR. I. INTRODUCTION The satellite link is essentially a radio relay link, much like the terrestrial microwave radio relay link with the singular
the satellite output power to the maximum level, additional noise is introduced into the link from satellite to hub. Therefore, an accurate calculation of the SNR for the entire RTN link must consider: 1. the SNR of the terminal-to-satellite link 2. the SNR of the satellite-to-hub link When the output power of the satellite is at a maximum, SNR .
c. Satellite: Internet access provided through satellites orbiting the Earth. Satellite service requires a satellite Internet subscription from an Internet satellite service provider and a satellite dish. Carriers that provide satellite Internet service are DIRECTV, Dish Network, HughesNet, and Wildblue. d.
Satellite Communication Col John Keesee. Satellite Communications Architecture Identify Requirements Specify Architectures Determine Link Data Rates Design & Size each link Document your rationale. Definition Uplinks Downlinks Crosslinks Relays TT & C Uplink Downlink Intersatellite links Relay satellite
Satellite Communication Lecture # 9 Link Budget Link Budget Introduction Overall design of a complete satellite communications system involves many complex trade-offs to obtain a cost-effective solutions Factors which dominate are Downlink EIRP, G/T and SFD of Satellite Earth St
jpeg/png/wmf/ti /. Four major graphic environments Low-level infrastructure R Base Graphics (low- and high-level) grid: Manual Link, Book Link High-level infrastructure lattice: Manual Link, Intro Link, Book Link ggplot2: Manual Link, Intro Link, Book Link Graphics and Data Visualization in R
Tutorial Process The AVID tutorial process has been divided into three partsÑ before the tutorial, during the tutorial and after the tutorial. These three parts provide a framework for the 10 steps that need to take place to create effective, rigorous and collaborative tutorials. Read and note the key components of each step of the tutorial .
Tutorial Process The AVID tutorial process has been divided into three partsÑ before the tutorial, during the tutorial and after the tutorial. These three parts provide a framework for the 10 steps that need to take place to create effective, rigorous and collaborative tutorials. Read and note the key components of each step of the tutorial .
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