satellite_communication_and _technology.pptx

This set of slides describe the basic of satellite communication technology

1. School of Engineering SLTC Research University 1 Satellite Communication

2. Fundamentals of satellite communication The satellite, an artificial Earth orbiting body, receives communication signals from ground stations, amplifies, processes, and retransmits them to other ground stations beyond the Earth's curvature . The satellite is an active transmission relay, similar in function to relay towers used in terrestrial microwave communications. Two types of satellites exist: natural and man-made. Natural satellites, like the Earth and Moon, orbit larger celestial bodies such as the Sun or Earth. Conversely, man-made satellites are machines launched into space, orbiting celestial bodies like Earth. 2

3. Main Characteristics The main characteristics of satellite communication include , Global Coverage : Satellites orbiting the Earth can provide coverage to almost any point on the planet, including remote and inaccessible areas . Security : Satellite communication can offer secure transmission of data, particularly when encryption techniques are employed. Interconnectivity : F acilitate interconnectivity between different communication networks, including terrestrial networks, connecting across different regions and technologies . Low Latency : T raditional geostationary satellites can introduce latency due to their high altitude, newer Low Earth Orbit (LEO) satellites can offer lower latency. Flexibility : Can be repositioned in orbit or replaced relatively easily, providing flexibility in network design and coverage. Bandwidth* : Satellites can provide high bandwidth communication channels, allowing for the transmission of large amounts of data over long distances . * depending on factors such as network congestion and individual usage patterns (demand), satellite design and frequency bands , modulation schemes. 3

4. The main subsystems of a satellite 4 https://www.spacefoundation.org/space_brief/satellite-components/

5. Space segment and the earth segment 5

6. Space segment and the earth segment Satellite communication relies on two key components: the space segment and the earth segment . Space segment includes the satellites in orbit in the system. Ground station provides the operational control of the satellite(s ) in the orbit (TT&C :Tracking , Telemetry, and Command station). TTC&M station : provides essential spacecraft management and control functions to keep the satellite operating safely in orbit. The TTC&M links between the spacecraft and the ground are usually separate from the user communications links. 6

7. Space segment and the earth segment The ground segment of a satellite communication system includes Earth-based terminals ( terrestrial-based terminals situated on the Earth's surface) using services from the Space Segment. Fixed (In-place) Terminals : These are stationary terminals that are permanently located in specific positions, serving as stable points for communication . Ex : A very small aperture terminal (VSAT) networks : small private earth station - that is used to transmit & receive data signal through a satellite. Applications :High Speed Internet Access , Point-of-sales transactions ,Private-Line Voice ,Virtual Private Networks (VPN) The ground segment antenna terminals consist of three basic types: • fixed (in-place) terminals • transportable terminals • mobile terminals. 7

8. Space segment and the earth segment Transportable Terminals : These terminals are mobile and adaptable, providing flexible communication options and can be relocated for temporary or mobile communication requirements. These are moved to locations, stop in place, and then deploy an antenna to establish links to the satellite. Satellite news gathering (SGN) trucks A motorized auto tracking terminal intended primarily for vehicle based application It establish secure, reliable voice, video and data communications in any environment 8

9. Space segment and the earth segment Mobile Terminals : These terminals are specifically engineered for use in vehicles, aircraft, ships, or other mobile platforms. They enable communication while in motion, providing connectivity to users on the move. https://www.viasat.com/products/terminals-and-radios/maritime-terminals/ Applications : Maritime SATCOM terminals 9

10. Why do satellites use higher frequencies for uplink and lower frequencies for downlink? 10 In satellite communication, the uplink frequency is higher than the downlink frequency due to increased attenuation with higher frequencies, while higher uplink frequencies allow for greater data capacity. Lower frequencies are used for the downlink as they penetrate the Earth's atmosphere better and are less prone to attenuation, ensuring reliable communication over longer distances.

11. Satellite C ommunication System Input signal : Baseband signal Encoder : The digital data signal is converted to a bit pattern. Modulator : Convert data into carrier signal. (FSK ,PSK , QPSK) Up converter : The frequency is upconverted ( up converted to 6 GHz) High Power Amplifier (HPA) : Signal strength is increased. Then the signal is uplink to the satellite through the antenna 11

12. Satellite C ommunication System Input signal : the signal received from the antenna. Low Noise Amplifier (LNA) : amplifies weak radio frequency signals received from satellites while minimizing additional noise, ensuring high signal quality. Down convertor : down convert the frequency (6GHz to 4 GHz) Demodulator : remove the data from the carrier signal. Decoder : Detect and reassemble the data into a single stream. 12

13. Orbital Period & Returning period Orbital Period : Time it takes for a satellite to complete one full orbit around its parent body (usually the Earth) measured relative to distant, fixed celestial objects (distant star). The o rbital Period remains constant for a given satellite orbit. Depends on : satellite's altitude and orbital velocity , and satellite's orbit type (geostationary , low Earth orbit, medium Earth orbit ) . Returning Period ( Repeat period) : Time it takes for a satellite to return to the same position in its orbit relative to a specific point observed from a fixed point on Earth . Depends on : satellite's altitude , eccentricity (shape of the satellite's orbit ) , earth's rotation(tidal effects the moon has on earth's rotation) 13

14. Angle of elevation & Angle of Depression The angle of elevation refers to when an object is positioned above the observer , whereas the angle of depression occurs when the object is placed below the observer . 14 The look angles of a satellite refer to the coordinates to which an Earth station must be pointed in order to communicate with the satellite and are expressed in terms of azimuth(AZ) and elevation angles(EL). Look Angle Azimuth and Elevation are measures used to identify the position of a satellite flying overhead

15. 15 Azimuth(AZ ) and Elevation angles(EL ) Both are measured in degrees. Azimuth varies from 0° to 360°. It starts with North at 0 °.Elevation angle from the ground point. E levation angle : angle between the ground and a line connecting the observer to the satellite. Azimuth angle : measured from true north in a clockwise direction. It is the horizontal angle or direction from the observer's location to the satellite.

16. Active and passive satellites Two types of artificial satellites to transmit the signals: active satellites and passive satellites Passive satellites : This balloon reflects microwave signals from various locations. Similarly, passive satellites in space reflect signals back to Earth without amplification. Their orbits range from 2000 to 35786 km, and atmospheric interference weakens the received signal . (Ex : Echo satellite series launched by NASA in the 1960s ) Active satellites : Active satellites, equipped with their own power source and communication systems, actively transmit signals, collect data, and perform specific functions while in orbit. They include communication satellites, weather satellites, navigation satellites (like GPS), and scientific research satellites, often necessitating constant communication with ground stations for data transmission and command reception . (Ex : Global Positioning System) 16

17. Propagation delay (Round Trip D elay) Time it takes for a signal to travel from the transmitter on Earth to the receiver via the satellite and back. Transmission Time : Time it takes for a signal to be sent from the transmitter on Earth to the satellite. Ex 01 : Calculate the propagation delay for an object that is 36,000 km above Earth's surface. 17

18. Satellite Orbits Satellite orbits vary based on their intended purpose and operational requirements. Purpose: Earth Observation : monitoring weather patterns, environmental changes , and land use. Communication : telecommunications and broadcasting typically employ geostationary orbits to maintain constant coverage over specific regions. Navigation : Systems like GPS rely on medium Earth orbits (MEO) to provide accurate positioning and timing information globally. Operational Requirements: Coverage Area : optimize coverage over specific regions or provide global coverage Latency : for some applications requiring low latency, such as real-time communication and remote sensing. Stability : due to their fixed position relative to the Earth's surface, making them suitable for long-term observation and communication tasks . 18

19. Satellite Orbits There are mainly 3 types of satellites based on their orbits are: Low Earth Orbit (LEO ) Medium Earth Orbit (MEO ) G eostationary Orbit (GEO ) Any satellite can achieve orbit at any distance from the earth , if its velocity is sufficient to keep it from falling to earth it is free of friction from earth's atmosphere, and gravity is strong enough to pull it back towards earth. The farther the satellite is from the earth, the longer it takes for a radio or microwave frequency transmission to reach the satellite. 19

20. Satellite Orbits Satellites can orbit Earth's equator or go over Earth's North and South Poles, or anything in between. Equatorial Orbit : Optimal for regions near the equator, facilitating efficient communication with troops stationed in equatorial regions. Polar Orbit : Provides comprehensive global coverage, enabling communication with remote regions and facilitating surveillance and reconnaissance operations. Strategic Advantage : Equatorial orbits offer focused coverage, while polar orbits ensure global reach, enhancing military communication and reconnaissance capabilities. 20

21. Satellite Orbits 21 Orbital Parameters Apogee: A point for a satellite farthest from the Earth . Perigee : A point for a satellite closest from the Earth. Ascending Node : satellite's orbit crosses the Earth's equatorial plane from south to north, indicating its transition from the southern hemisphere to the northern hemisphere. Descending Node : satellite's orbit crosses the Earth's equatorial plane from north to south, marking its transition from north of the equator to south during orbital motion . Inclination angle : inclination refers to the angle between the orbital plane of a satellite and the plane of the Earth's equator.

22. Satellite Orbits 22 Orbital Parameters Semi‐Major Axis : the distance from the center of an ellipse to the longer end of the ellipse. Semi –minor Axis : half the length of the shortest diameter of the elliptical orbit. Eccentricity : parameter describing the deviation of a satellite's orbit from a perfect circle. It quantifies the shape of the orbit, with values ranging from 0 for a circular orbit to 1 for a highly elliptical orbit.

23. Low Earth Orbit (LEO) Altitude : ranging from approximately 160 to 1,500 kilometers above the Earth's surface. Orbital Period : have short orbital periods lasting between 90 and 120 minutes, enabling them to orbit the planet up to 16 times a day. Applications : well-suited for remote sensing, high-resolution earth observation, and scientific research due to their ability to rapidly acquire and transmit data . Military satellite communication due to their low latency, high mobility ( short orbital periods), and resilience*. Resilience : to withstand and recover from disruptions or attacks ( Jamming , Cyberattacks , Physical Attacks ,Electronic Warfare , Space Debris etc.) while maintaining their communication capabilities. 23

24. Low Earth Orbit (LEO) . 24 One important application of LEO satellites for communication is the project Iridium , which is a global communication system conceived by Motorola that makes use of satellites placed in low Earth orbits . A total of 66 satellites are arranged in a distributed architecture with each satellite carrying (1/66) of the total system capacity. The system is intended to provide a variety of telecommunication services on the global level. T he constellation was proposed to have 77 satellites . The Iridium constellation of satellites Project : Iridium

25. Geostationary Earth Orbit (GEO) Altitude : Satellites are positioned directly over the equator, approximately 35,786 kilometers above the Earth's surface . This orbit allows to remain fixed relative to a specific point on Earth, providing continuous coverage to that area . With three evenly spaced GEO spacecraft, nearly worldwide coverage is achievable due to their extensive coverage area on Earth. 25

26. Geostationary Earth Orbit (GEO) Satellites appear motionless from the ground , orbital period = Earth’s rotation (23 hours, 56 minutes, and 4 seconds ). The terrestrial antennas are consistently pointing toward the same location in space, making them ideal for always-on communication services such as TV and phones . M onitoring weather in specific regions and tracking the development of local patterns , observations of cloud patterns that are used to calculate wind speeds. L onger signal delay caused by the significant distance between GEO satellites and Earth can be a drawback for real-time communication applications . 26

27. Geostationary Earth Orbit (GEO) 27 The attractive force is the gravitational force between Earth and the satellite. The gravity provides the inward pull that keeps the satellite in orbit.

28. Geostationary Earth Orbit (GEO) 28 The attractive force is the gravitational force between Earth and the satellite. The gravity provides the inward pull that keeps the satellite in orbit. Ex 02 : If the mass of the Earth is m E = 5.974×10 24 kg and the satellite will orbit at 600 km, calculate the tangential velocity and the period of the satellite. ( G = Gravitational constant = 6.67 × 10 −11 Nm 2 /kg 2 , radius of the earth = 6378 km )

29. Medium Earth Orbit (MEO) MEO is positioned between low Earth and geostationary orbits, typically at altitudes ranging from about 5,000 to 20,000 kilometers. MEO satellites are extensively used for positioning and navigation services, such as GPS. Improved MEOs facilitate low-latency data communication for service providers, commercial entities, and government organizations. 29

30. Advantages of satellite communication 30 Remote Sensing and Earth Observation: Satellite-based remote sensing and Earth observation platforms capture high-resolution imagery and data about the Earth's surface, atmosphere, oceans, and climate. High-Speed Internet Access: Satellite internet services have seen significant advancements, offering high-speed broadband access to areas with limited or no access to terrestrial broadband infrastructure. Disaster Response and Humanitarian Aid: Satellites play a crucial role in disaster response and humanitarian aid efforts by rapidly restoring communication infrastructure in disaster-stricken areas. Global Connectivity for IoT Devices: Satellite networks offer global connectivity for IoT devices deployed in remote and inaccessible areas, such as environmental monitoring stations, agricultural sensors, and wildlife tracking devices. Onboard Processing and Edge Computing: Modern satellites are equipped with onboard processing capabilities and edge computing functionalities, allowing for data aggregation, compression, encryption, and analysis directly on the satellite platform. Antenna Diversity and Beamforming: Advanced satellite systems utilize sophisticated antenna arrays and beamforming techniques to dynamically shape and steer satellite beams, enhancing link reliability, resilience to interference, and spectrum efficiency. Beamforming enables targeted coverage, improved signal quality, and increased capacity in high-demand areas or during peak usage periods.

31. Disadvantages of satellite communication 31 Weather Dependency : Adverse weather like rain, snow, or atmospheric disturbances can disrupt satellite signals , causing degraded performance or temporary loss of connectivity . Limited Bandwidth: Satellites share limited bandwidth among users, leading to congestion and slower data speeds during peak times. This can impact the performance of high-bandwidth applications. Vulnerability to Space Debris : Satellites face collision risks with space debris, such as defunct satellites and rocket fragments. These collisions can damage or destroy satellites, disrupting communication services and potentially generating more debris. Cost : Building , launching, and maintaining satellites is expensive. Additionally, leasing satellite bandwidth or purchasing satellite communication services can be costly . Latency: The distance between Earth and satellites causes signal delays, impacting real-time communication like online gaming and video calls, leading to delays and disruptions. Continuity of service : need regular monitoring and control to maintain their orbit. It has a lifespan of 12-15 years, requiring planning for replacement before becoming inoperative .

32. Limitations of satellite communication 32 The limitations may not necessarily be negative but can pose obstacles or considerations for its use and the disadvantages typically refer to negative aspects or drawbacks associated with the technology. They are related to each Latency : The delay in signal transmission due to the distance between Earth and satellites. Bandwidth Constraints : Limited bandwidth shared among users within a satellite's coverage area, leading to potential congestion and reduced data speeds. Weather Dependence : Susceptibility to adverse weather conditions such as rain fade, which can degrade signal quality. Polar Coverage : Challenges in providing comprehensive coverage to polar regions due to orbital characteristics. Regulatory Constraints : Compliance with international regulations, spectrum allocation, and licensing requirements.

33. Earth - space propagation effects 33 V arious phenomena that affect the transmission of electromagnetic signals between Earth-based transmitters or receivers and satellites in space. These effects can impact the quality, reliability, and performance of satellite communication systems. Atmospheric Attenuation : The Earth's atmosphere absorbs and scatters electromagnetic waves as they travel through it, leading to signal attenuation especially at higher frequencies. Free-Space Path Loss : resulting in a decrease in signal strength with increasing distance from the transmitter. This loss is proportional to the square of the distance between the transmitter and receiver. Multipath Propagation : Multipath propagation occurs when signals reach the receiver via multiple paths due to reflection , diffraction, or scattering which can result in signal fading, distortion, and intersymbol interference . Adverse weather : Factors such as humidity, rain, snow, and fog can lead to signal attenuation especially at microwave frequencies . This can result in signal loss or degradation during intense precipitation. Geomagnetic storms : Earth's magnetosphere disturbances, disrupt satellite communication by affecting the ionosphere. This causes signal absorption, scintillation, and GPS accuracy degradation.

34. Frequency window 34 A frequency window refers to a specific range or band of frequencies within the electromagnetic spectrum that is allocated for satellite communication purposes. The International Telecommunication Union (ITU) allocates part of the electromagnetic spectrum for specific services. L-band (1–2 GHz) S-band (2–4 GHz) C-band (4–8 GHz) X-band (8–12 GHz) Ku-band (12–18 GHz) Ka -band (26–40 GHz)

35. Frequency window 35 A frequency window refers to a specific range or band of frequencies within the electromagnetic spectrum that is allocated for satellite communication purposes. The International Telecommunication Union (ITU) allocates part of the electromagnetic spectrum for specific services. L-band (1–2 GHz) Global Positioning System (GPS S-band (2–4 GHz) Weather radar , Surface ship radar C-band (4–8 GHz) Satellite communications , Full-time satellite TV networks X-band (8–12 GHz) Military applications , Radar applications including continuous-wave, pulsed, synthetic aperture radar, and phased arrays Civil, military, and government institutions for weather monitoring, air traffic control, maritime vessel traffic control, defense tracking, and vehicle speed detection for law enforcement Ku-band (12–18 GHz) Satellite communications , - Ku-band downlink used in Europe for direct broadcast satellite services (e.g., Astra) Ka -band (26–40 GHz) Communications satellites for high-resolution applications Uplink in either the 27.5 GHz and 31 GHz bands Close-range targeting radars on military aircraft

36. Free space loss 36 The relationship between transmit and receive power is defined by the Friis Free Space Equation.

37. Free space loss 37 The linear path loss of the channel as the ratio of transmit power to receiver power. In dB Ex 03: Determine the isotropic free space loss at 6 GHz for the shortest path to a geosynchronous satellite from earth ( 35,863 km).

38. Atmospheric absorption 38 The absorption depends on various factors such as the frequency of the signal, the distance the signal travels through the atmosphere, and the weather conditions. Frequency Dependence : Different frequencies experience varying levels of absorption. higher frequencies , such as those in the millimeter-wave range, are more susceptible to absorption by atmospheric gases like water vapor and oxygen compared to lower frequencies . Rain Fade : Heavy rainfall can cause a phenomenon known as "rain fade," where the signal experiences significant attenuation due to absorption and scattering by raindrops along its path through the atmosphere. Path Length : The length of the path the signal travels through the atmosphere also affects absorption. Longer paths result in more absorption compared to shorter paths. Weather Effects : Weather conditions, particularly humidity levels, can significantly impact atmospheric absorption. Higher humidity levels can increase absorption due to the presence of water vapor in the atmosphere . Satellite Orbits : satellites in geostationary orbit experience less variation in atmospheric conditions compared to those in lower orbits, which can be advantageous for minimizing absorption effects.

39. Atmospheric absorption 39 The two-way attenuation coefficient represents the total loss experienced by a signal as it travels through a medium in both the transmit and receive paths. Atmospheric attenuation is not significant for radio frequencies below 10 gigahertz.

40. Atmospheric absorption : Mitigation Techniques 40 To mitigate the effects of atmospheric absorption in satellite communication, various techniques are employed. Frequency Selection : Choosing frequency bands that are less susceptible to atmospheric absorption can mitigate its effects. For example, lower frequency bands (such as L-band and S-band) experience less absorption compared to higher frequency bands (such as Ka -band and V-band) because they are less affected by atmospheric constituents like water vapor and oxygen. Frequency Diversity : transmitting the same signal simultaneously over multiple frequency bands. T he likelihood of significant absorption occurring at all frequency bands simultaneously is reduced. Rain Fade Compensation : Techniques such as adaptive power control, where the transmitted power is adjusted based on the received signal strength, can help compensate for signal losses due to rain fade. Polarization Diversity : Polarization diversity utilizes antennas that transmit and receive signals with different polarizations (e.g., vertical and horizontal). By exploiting the fact that absorption affects different polarizations differently, polarization diversity can mitigate absorption-induced signal attenuation.

41. Rainfall attenuation and ionosphere scintillation 41 R ainfall attenuation : causes weakening of signals due to absorption and scattering by raindrops as they pass through the atmosphere, particularly during heavy rainfall. Ionosphere scintillation : rapid and random fluctuations in the amplitude and phase of radio signals caused by irregularities in the Earth's ionosphere, impacting communication links operating at high frequencies. Both phenomena can degrade signal quality and reliability. To mitigate the effect of rainfall attenuation and ionosphere scintillation A daptive power control , D iversity techniques , Polarization diversity A daptive modulation, advanced signal processing algorithms and error correction coding to maintain effective communication links.

42. Thank you 42