Satellite link design unit iii

Details description of Satellite link design

1. Satellite Communication By Sk. Hedayath Basha, Assistant Professor IV CLASS - 2020 - 2021 1

2. UNIT – III SATELLITE LINK DESIGN Basic Link Analysis Interference Analysis Rain Induced Attenuation and Interference Ionospheric Characteristics Link Design with and without frequency resuse . IV CLASS - 2020 - 2021 2

3. Today’s Topic Basic Link Analysis Interference Analysis Rain Induced Attenuation and Interference IV CLASS - 2020 - 2021 3

4. Basic Link Analysis In satellite communication systems, there are two types of power calculations . They are transmitting power calculations. receiving power calculations. In general, these calculations are called as  Link budget calculations . The unit of power is  decibel . IV CLASS - 2020 - 2021 4

5. Basic Terminology An  isotropic radiator  (antenna) radiates equally in all directions. But, it doesn’t exist practically. It is just a theoretical antenna. We can compare the performance of all real (practical) antennas with respect to this antenna. IV CLASS - 2020 - 2021 5

6. Power flux density IV CLASS - 2020 - 2021 6

7. Antenna Gain IV CLASS - 2020 - 2021 7

8. Equivalent isotropic Radiated Power (EIRP) IV CLASS - 2020 - 2021 8 10Log (G) + 10Log Ps

9. Problem Question: A satellite downlink at 12 GHz operates with a transmit power of 20 W and an antenna gain of 45 dB. Calculate the EIRP in dBW Solution: IV CLASS - 2020 - 2021 9

10. Transmission Losses The difference between the power sent at one end and received at the receiving station is known as  Transmission losses . The losses can be categorized into 2 types . Constant losses Variable losses IV CLASS - 2020 - 2021 10

11. Constant Losses The losses which are constant such as feeder losses are known as  constant losses . No matter what precautions we might have taken, still these losses are bound to occur. IV CLASS - 2020 - 2021 11

12. Variable Loss Another type of loses are  variable loss . The sky and weather condition is an example of this type of loss. Means if the sky is not clear signal will not reach effectively to the satellite or vice versa. Therefore, our procedure includes the calculation of losses due to clear weather or clear sky condition as 1 st  because these losses are constant. They will not change with time. Then in 2 nd  step, we can calculate the losses due to bad weather condition. IV CLASS - 2020 - 2021 12

13. Link budget calculations There are two types of link budget calculations since there are two links namely ,  uplink  and  downlink . IV CLASS - 2020 - 2021 13

14. Earth Station Uplink It is the process in which earth is transmitting the signal to the satellite and satellite is receiving it. Its  mathematical equation  can be written as Here we have used the (subscript) notation “U”, which represents the uplink phenomena. IV CLASS - 2020 - 2021 14

15. Uplink Here, Losses represent the satellite receiver feeder losses. The losses which depend upon the frequency are all taken into the consideration. The EIRP value should be as low as possible for effective UPLINK. And this is possible when we get a clear sky condition. IV CLASS - 2020 - 2021 15

16. Satellite Downlink In this process, satellite sends the signal and the earth station receives it. The equation is same as the satellite uplink with a difference that we use the abbreviation “D” everywhere instead of “U” to denote the downlink phenomena. IV CLASS - 2020 - 2021 16

17. Its  mathematical  equation can be written as IV CLASS - 2020 - 2021 17

18. Link Budget If we are taking ground satellite in to consideration, then the free space spreading loss ( FSL) should also be taken into consideration . If antenna is not aligned properly then losses can occur. so we take  AML  ( Antenna misalignment losses ) into account. Similarly, when signal comes from the satellite towards earth it collides with earth surface and some of them get absorbed. These are taken care by atmospheric absorption loss given by  “AA”  and measured in db IV CLASS - 2020 - 2021 18

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20. Interference Analysis An accumulation of snow or ice on a  dish can interfere  with the  signal  or move the  dish  out of alignment with the  satellite , which affects the  signal . IV CLASS - 2020 - 2021 20

21. Causes of Interference Interference  occurs when unwanted radio frequency signals disrupt the use of your television, radio or cordless telephone. The two most common  causes of interference  are transmitters and electrical equipment. IV CLASS - 2020 - 2021 21

22. Interference in Networks In telecommunications, an  interference  is that which modifies a signal in a disruptive manner, as it travels along a communication channel between its source and receiver. The term is often used to refer to the addition of unwanted signals to a useful signal. Common examples are: Intersymbol   interference  (ISI) IV CLASS - 2020 - 2021 22

23. The Two Types Of Interference Constructive  interference: When the amplitude of the waves increases because of the wave amplitudes reinforcing each other is known as constructive  interference . Destructive   interference : When the amplitude of the waves reduces because of the wave amplitudes opposing each other is known as destructive  interference . IV CLASS - 2020 - 2021 23

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28. Rain Induced Attenuation and Interference In the C band and, more especially, the Ku band, rainfall is the most significant cause of signal fading. Rainfall results in attenuation of radio waves by scattering and by absorption of energy from the wave. Rain attenuation increases with increasing frequency and is worse in the Ku band compared with the C band. IV CLASS - 2020 - 2021 28

29. This produces a depolarization of the wave; in effect, the wave becomes elliptically polarized. This is true for both linear and circular polar- izations , and the effect seems to be much worse for circular polarization (Freeman, 1981). IV CLASS - 2020 - 2021 29

30. From 5% to 20% of rain fade or satellite signal attenuation may also be caused by rain, snow, or ice on the uplink or downlink antenna reflector , or feed horn . Rain fade is usually estimated experimentally and also can be calculated theoretically using scattering theory of rain drops.  Raindrop size distribution   (RSD ) is an important consideration for studying rain fade characteristics. IV CLASS - 2020 - 2021 30

31. Outcomes Possible ways to overcome the effects of rain fade are  site diversity , uplink power control,  variable rate encoding , and receiving antennas larger than the requested size for normal weather conditions. IV CLASS - 2020 - 2021 31

32. Today’s Topics Ionospheric Characteristics Link Design with and without frequency resuse . IV CLASS - 2020 - 2021 32

33. Ionosphere Earth’s atmosphere contains a series of regions that have a relatively large number of electrically charged atoms and molecules. As a group, these regions are collectively called the ionosphere. IV CLASS - 2020 - 2021 33

34. Ionosphere IV CLASS - 2020 - 2021 34

35. High-energy X-rays and ultraviolet (UV) "light" from the Sun are constantly colliding with gas molecules and atoms in Earth's upper atmosphere .  Some of these collisions knock electrons free from the atoms and molecules, creating electrically charged ions (atoms or molecules with missing electrons) and free electrons. IV CLASS - 2020 - 2021 35

36. These electrically charged ions and electrons move and behave differently than normal, electrically neutral atoms and molecules. Regions with higher concentrations of ions and free electrons occur at several different altitudes and are known, as a group, as the ionosphere IV CLASS - 2020 - 2021 36

37. There are three main regions of the ionosphere, called the D layer, the E layer, and the F layer. These regions do not have sharp boundaries, and the altitudes at which they occur vary during the course of a day and from season to season. IV CLASS - 2020 - 2021 37

38. The D region is the lowest, starting about 60 or 70 km (37 or 43 miles) above the ground and extending upward to about 90 km (56 miles). Next higher is the E region, starting at about 90 or 100 km (56 or 62 miles) up and extending to 120 or 150 km (75 or 93 miles). The uppermost part of the ionosphere, the F region, starts about 150 km (93 miles) and extends far upward, sometimes as high as 500 km (311 miles) above the surface of our home planet. IV CLASS - 2020 - 2021 38

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41. Characteristics of D- Layer IV CLASS - 2020 - 2021 41

42. Characteristics of E - Layer IV CLASS - 2020 - 2021 42

43. Characteristics of Es - Layer IV CLASS - 2020 - 2021 43

44. Characteristics of F1 - Layer IV CLASS - 2020 - 2021 44

45. Characteristics of F2 - Layer IV CLASS - 2020 - 2021 45

46. Link Design with and without frequency resuse . A  satellite  communication network consists of a number of earth stations inter-connected via a  satellite . The source-to-destination path can be partitioned for the purpose of radio  link design  as: the earth station- satellite link  or uplink; the  satellite  path; and the  satellite -earth station  link  or downlink. IV CLASS - 2020 - 2021 46

47. Satellite Design The  link  communication between  satellite  and the Earth Station is exposed to a lot of impairments such as noise, rain and atmospheric attenuations. The successful implementation of  satellite  communications need to the efficient system  design  to ensure robust air links for the communications signals IV CLASS - 2020 - 2021 47

48. Frequency Reuse Frequency Reuse  is the scheme in which allocation and reuse of channels throughout a coverage region is done . Two main Advantages of frequency reuse Frequency reuse improve the spectral efficiency and signal Quality ( QoS ). Frequency reuse classical scheme proposed for GSM systems offers a protection against interference. IV CLASS - 2020 - 2021 48

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