What is Satellite Communication?

Satellite communication is the type of communication in which information is carried from source to destination using communication satellites. Satellite communication used different ranges of radio and microwaves frequencies of electromagnetic spectrum. Satellite works as a repeater station and communication channel between transmitter and receiver. Electromagnetic waves used in telecommunication do have line of sight propagation. But the curvature of earth caused the obstruction of the electromagnetic wave. Communication satellites relay electromagnetic waves around the curvature of the earth which allows communication over larger geographical areas around the world. Different types of satellites have different functionalities and multiple working orbits around the earth for communication. Satellite communication has a major leading role in the world telecommunication system.


How does Satellite Communication Work?

Satellite communication is performed using microwave spectrum of electromagnetic radiation. These microwaves are transmitted from the earth stations to satellites and from satellites to earth stations.
The working of satellite communication is divided into three different stages.

Uplink
Transponder
Downlink

Uplink- Ground station on earth sends signals to the satellite. The transmission of microwaves from earth station and received by the satellite is known as uplink. These signals are transmitted via a transmitter on ground station and received by a receiver on the satellite.

Transponder- Transponder performs two functions, both transmission and reception of the signal. It amplifies the signal received from the earth station. Transponder changes the frequency of the signal and then transmits the signal back to the earth station using transmitter antenna.

Downlink- Signals transmitted back to the earth station from the satellite after amplification and processing from the satellite to the earth station is known as downlink.


Communication Satellite

Communication satellites are artificially made by humans and then left into space for the purpose of communication. That satellite is placed in earth’s orbit. These communication satellites are very important.

There are two types of communication satellites-

Active Satellite
Passive Satellite

Active Satellite- Active satellite is a type of satellite which amplifies the signal received after from the earth station and then transmits it back to the earth station.

Passive Satellite- Passive satellite only reflects the signals received from the earth station to another earth station without amplifying.


Propagation of Electromagnetic Waves

The propagation of EM waves depends upon the environmental as well as their own properties.

MODES OF RADIO WAVES PROPAGATION- It can be classified into three categories-

Ground Wave Propagation
Sky Wave Propagation
Space Wave Propagation

Ground Wave Propagation- Ground waves travel along the surface of earth. It is also called surface wave. When waves pass over the ground it induces current in the ground. Ground attenuates the waves which causes absorption of energy. Ground waves has lower frequency signals (longer wavelengths) so easily bends over the obstacles. In ground wave propagation attenuation increases with increase of frequency.

Sky Wave Propagation- Sky wave propagation is suitable for long-distance transmission. Long distance communication can be accomplished with higher frequencies by using ionospheric reflection of EM waves. In sky wave propagation EM waves are radiated towards the sky. When the EM waves travel from denser to rare medium TIR (total internal reflection) happens. And the waves are either reflected or refracted back to the earth by the ionosphere. That is why this propagation mode is also known as ionosphere propagation.

Space Wave Propagation- It means the radio waves traveling from transmitter to receiver through space. When the frequency of the waves is greater than 40 MHz, it passes through the ionosphere. And the line-of-sight propagation of EM is not useful for long distance communication because of the curvature of earth. So, satellites are used for communication to send signals. Space waves are used for satellite communication and for line-of-sight communication.



Various Terms related to Satellite Communication




1. Orbit- Orbit is a regular repeating path of an object around another object in space. The object that revolves in the orbit is called a satellite. Satellite can be natural or artificial. Example of a natural satellite is the moon or earth, and artificial satellites are made by humans or space agencies like NASA such as Sputnik 1, Explorer 1 etc. All orbits are elliptical according to NASA like an ellipse. Planets do have almost circular orbits, but the orbits of comets have a different shape. In the context of satellite communication, orbits can be divided in different categories Low Earth Orbit Medium Earth orbit High Earth Orbit

2. Apogee- It is the point in the orbit of an object such as a satellite which is farthest from the center of the earth or a planet.




3. Perigee- Perigee is the closest point in the orbit of a satellite to the center of earth.



Satellite Communication Services


Satellite communication services can be divided into two categories

A.) One-way satellite communication- The communication in which the first earth station transmits the signals by the receiver as an uplink to the satellite. Then satellite retransmits the received signal after amplification to the receiver of the second earth station as a down link. The communication is unidirectional which means second earth station do not send signals to the first earth station or first earth station do not receive any signals from second earth station.

Following are the examples of one-way satellite communication service-
(i) Broadcasting services like radio, television and satellite internet.
(ii) Space operation services such as tracking and telemetry.

B.) Two-way satellite communication- The communication in which two earth stations exchange information using a satellite. In that communication the first and second earth station transmit as well as receive data. Which means communication is bidirectional which provides point to point connectivity.

Following are the examples of two-way satellite communication service-
(i) Very small aperture terminal (VSAT)
(ii) Fixed satellite services (FSS) such as telephone, data transmission etc.



Advantages of Satellite Communication


Wide Coverage- Satellite communication is best for remote areas and isolated places where terrestrial cellular or broadband is not feasible. Satellite communication covers the large geographical areas of the globe.

Resilience- Satellite communication is very reliable because it is in space and does not get affected by all the natural disasters that happen on the earth. However, the likelihood of satellite colliding with another satellite or an asteroid is extremely rare.

High speed communication- Satellite communication uses radio waves and microwaves to carry satellite signals. And these waves travel at the speed of light. It means satellite communication is very fast, which is very important in case of emergency and real time information transmission.

High Bandwidth- Satellite communication provides high bandwidth for communication. Providing different services such as video conferencing, voice call and internet services at gigabits per second rates.

Scalability- Satellite communication costs are independent of distance unlike terrestrial network costs which are proportional to distance. It increases the scalability of a communication system.



Disadvantages of Satellite Communication


Initial cost- To set up the entire structure of satellite communication is very costly. Because satellite communication is a complex technology and satellite internet is complex as well and requires significant infrastructure. Satellite communication requires complex tools and equipment.

Latency- Latency is the time delay between transmission and reception of signal. It is caused due to the large distance between earth and satellite.

Interference of signal- The interference of the signal is caused due to many reasons such as crowed radio frequency spectrum, sun-based flares, intentional jamming, electromagnetic radiation etc.

Weather Effects- Satellite communication is affected by heavy snowfall, storms, and heavy rain which causes difficulty in proper transmission and reception of the signal.

Vulnerability- Satellites can be collapsed with micrometeoroids, get affected from solar radiation and space debris etc. It causes physical damage to the satellite which is very costly to make the communication work again.



Applications of Satellite Communication


Weather Forecasting- Satellites are used to estimate the weather. To give prior alerts about heavy rainfall, storms and heavy rain.

Radio and TV Broadcasting- Satellite communication is mainly used for broadcasting TV and radio signal for providing voice, video and data transmission.

Military applications- Satellite communication is used in the military to communicate because of security and privacy required. There are many encoding and decoding, encryption and decryption techniques used for transferring information with full security.

Navigation- G.P.S. (global positioning system) is one of the biggest applications of satellite communication. Google maps are used for finding routes and submarines, ships and airplanes directly communicate with satellites for correct direction.