By Girish Linganna 

Apr 14: Today, there are more than three thousand communication satellites orbiting the Earth, supporting a wide range of applications from cell phone services and TV broadcasts to broadband internet access and military operations.

Satellite communication involves the use of man-made satellites to send and receive information across the world, facilitating global connectivity by transferring data from one location to another.

 

Why is Satellite Communication Necessary?

Satellite communications enable voice and data services in areas around the world where ground-based cellular and broadband networks are unreliable or nonexistent. This technology enhances the dependability of communication systems, including in remote locations on land, over vast oceans, or at high altitudes like 35,000 feet in the air.

Satellite communication services are utilized daily in various ways, including:

1. Telecommunications

2. Broadcasting of TV and radio

3. High-speed Wi-Fi and mobile broadband

4. Navigation and GPS (Global Positioning System)

Thanks to technological advancements, satellite communications are paving the path towards a more interconnected future with limitless opportunities. These include applications in UAVs (Uncrewed Aerial Vehicles), autonomous transportation, crop monitoring, and sustainability initiatives.

How Do Satellite Communications Function?

Satellite communications involve a network of satellites in orbit and ground stations on Earth that use microwaves to send and receive data from one location to another.

The process includes three key steps:

1. Uplink: This is the stage where signals are sent from the Earth to a satellite.

2. Transponder: In this phase, the satellite receives the signals and processes or redirects them.

3. Downlink: This is when the satellite sends the processed signals back to Earth to a different location.

¦ Uplink : For example, let's look at how live television works. A TV station uses a large antenna at its broadcast center to send a signal up to a satellite orbiting in space. This first step of sending the signal is known as the "uplink." It's like the TV station is beaming a video straight up into the sky to reach the satellite.

¦ Transponder : Once the satellite receives the signal from the TV station, it uses onboard equipment to strengthen the signal and adjust its frequency. This step prepares the signal to be sent back to Earth. This part of the process is called the "transponder" stage. Think of it like the satellite giving the signal a boost and a tweak to make sure it travels back to Earth clearly and lands at the right spot.

¦ Downlink: Finally, the satellite sends the enhanced and adjusted signal back to one or more ground stations on Earth. This last step is known as the "downlink." It's like the satellite throwing the signal back down to Earth so that TV stations and viewers can pick it up and watch the broadcast.

Two-way satellite communication networks allow direct connections between the same ground stations through a single satellite. This means information can be sent back and forth seamlessly.

This technology has made it possible to access the internet in places where traditional fiber cables can't go. For example, you can get Wi-Fi on an airplane, on oil platforms at sea, or in extremely remote locations like the top of Mount Everest or the middle of the Sahara Desert.

Satellite Communication: One-Way vs. Two-Way

Two-way satellite communication networks allow for a smooth exchange of information back and forth between the same locations using a single satellite. This ability is essential for providing internet access in places that are difficult to reach with traditional wiring methods, like fiber cables.

To understand this better, let's compare it with one-way satellite communication. In one-way communication, information is only sent in a single direction, from the satellite to the ground station or vice versa, without the ability for an immediate response in the opposite direction. This is similar to watching a TV broadcast, where the viewer receives information but cannot send information back through the same channel.

In contrast, two-way satellite communication is like a phone conversation. Both parties can talk and listen, sending and receiving information to each other in real time. This two-way exchange allows for more dynamic and interactive services, such as internet browsing, where you request data (like loading a webpage) and receive data constantly.

In summary, while one-way communication is like listening to a lecture, two-way communication is like having a conversation. This ability to have a two-way exchange is what makes it possible to have internet services in remote or mobile environments, from airplanes to remote desert locations.

Ground-Based Communication Facilities on Earth

To finish setting up the satellite network, all messages to and from satellites go through Satellite Access Stations (SAS). These stations use either flat panels (electronically steered arrays) or dish antennas (circular reflectors) to send and receive signals. Here, the information is handled and sent to where it needs to go.

Electronically Steered Arrays :  refers to advanced types of antennas that can change the direction they send and receive signals without moving physically. Instead of physically moving like a traditional dish antenna, these flat panels use electronic controls to quickly adjust and point their signals in different directions. This makes them very efficient and fast at communicating with satellites.

Circular Reflectors : refers to the traditional dish-shaped antennas you often see at satellite stations or on rooftops. These dishes are used to catch signals from satellites, focusing them onto a specific point for clearer reception. They can physically tilt and rotate to point towards different satellites in the sky.

Ground stations are usually set up in specific, fixed locations on Earth. However, recent technology improvements have made these stations more effective at handling stronger signals and transferring more data. This enhancement has made it possible to send and receive signals on the move, which is helpful for services like Wi-Fi on airplanes, faster mobile networks like 5G, gathering news via satellite, and other applications that require mobile connectivity. This means you can stay connected even when you're traveling or moving around.

Are There Various Kinds of Satellites?

Yes, there are numerous types of satellites, each designed for specific tasks and different organizations.

The function of a satellite influences many aspects, including its technology, equipment, and the path it follows in space. Some satellites move in a geosynchronous orbit, meaning they rotate in line with the Earth's rotation and seem to stay in the same spot in the sky. Others orbit the Earth faster and at lower altitudes.

Communication satellites are categorized into four types based on their orbital paths:

1. Geostationary Earth Orbit (GEO)

2. Medium Earth Orbit (MEO)

3. Low Earth Orbit (LEO)

4. Highly Elliptical Orbit (HEO)

These various orbits are chosen to optimize the coverage and signal strength needed for their specific uses. 

Now, let's explore each type of orbit and identify which applications are most suitable for each:

Geostationary Earth Orbit (GEO)

If you look at a geostationary satellite, it seems to stand still in the sky. This happens because it moves around the Earth at the same speed  as the Earth Orbits. These satellites are also the farthest from Earth.

Here are a few of India's satellites that are in geostationary orbit:

1. INSAT-4A
2. GSAT-15
3. GSAT-17
4. GSAT-29
5. GSAT-30

These satellites are part of India's efforts to enhance telecommunications, broadcasting, and broadband services across the region.

Geostationary orbit are at 35,786 kilometres (22,236 miles) above the Earth

GEO (Geostationary Earth Orbit) satellites are highly effective because they cover large areas and can direct their services precisely where needed, without wasting resources on regions with low demand. This means they require fewer ground stations compared to LEO (Low Earth Orbit) satellites. This setup is perfect for mobile satellite communication services that need consistent and trustworthy connections, such as those used in maritime and aviation safety, or by governments. 

Here are some specific ways GEO satellites are used:

Providing internet and communication to ships at sea.

Offering Wi-Fi on airplanes.

Supporting unmanned aerial vehicles (UAVs), which need reliable communication to operate.

Assisting with communication and coordination during natural disasters.

 

Serving industries like agriculture, transportation, and utilities by helping them monitor and manage their operations remotely.

Medium Earth Orbit (MEO)

MEO (Medium Earth Orbit) satellites are positioned between 2,000 and 35,786 kilometers (1,243 to 22,236 miles) above Earth and complete their orbit in two to eight hours. These satellites are typically used for GPS and other navigation systems.

They provide fast, high-capacity internet services to service providers, government bodies, and businesses, especially in remote areas where it's difficult to install fiber cables.

One advantage of MEO satellites over GEO (Geostationary Earth Orbit) and LEO (Low Earth Orbit) satellites is that they require fewer satellites than LEO systems and have faster communication speeds than GEO systems.

Low Earth Orbit (LEO)

LEO (Low Earth Orbit) satellites are positioned much closer to Earth, ranging from about 160 to 2,000 kilometers (99 to 1,243 miles) away, and they complete an orbit approximately every 90 minutes. Unlike GEO (Geostationary Earth Orbit) satellites, which only require three for global coverage, LEO satellites need a much larger group to cover the same area.

Located at lower altitudes, LEO satellites have the advantage of a smaller viewing area and low latency, which allows them to transmit large amounts of data quickly and with strong signal strength. This makes them suitable for a variety of uses, including:

Industrial IoT (Internet of Things)

Maritime and tourism

Government and tactical networks

Emergency services and support

 

Telecommunications and mobile 5G broadband

Despite their benefits, LEO satellites typically have a shorter operational lifespan of about five to seven years, whereas GEO satellites can remain functional for over 15 years. Typically, it requires approximately two to three years to fully deploy a LEO satellite constellation. After another two to three years, these satellites often need to be replaced, raising issues related to the accumulation of space debris and the long-term sustainability of space environments.

 

 

Satellites in highly elliptical orbits (HEO) travel around Earth in a stretched oval shape, ranging from about 1,000 to 42,000 km above the Earth's surface. This orbit causes their altitude to change drastically.

These satellites move much quicker when they are closer to Earth and slower when they are further away. This speed change happens because Earth's gravity pulls them stronger when they are near, especially at the closest point in their orbit, called perigee, and less so at the farthest point, called apogee.

To maintain continuous communication, two satellites are needed in this type of orbit. When these satellites reach apogee over the North Pole, they can provide better and longer-lasting coverage because they stay in that region longer due to their slow movement at that point.

Satellites placed in highly elliptical orbits (HEO) serve a range of purposes including communication, navigation, scientific studies, and military uses. Satellites like TESS are examples of those operating in HEO. A major advantage of this type of orbit is that it offers a clear and extensive view of both the Earth and outer space.

Frequency Bands, Beams, and Signal Strength

Communication satellites operate on different frequency bands, similar to a radio, to send information. The most frequently used frequency bands in satellite communications include L-band, C-band, S-band, and Ka-band.

There's a balance between the size of the area covered by the satellite's signals and the power used to transmit or receive these signals.

Modern satellites are equipped with various types of "beams" that help them adjust the focus and strength of their signals to different locations.

L-band frequencies

L-band frequencies work within the 1-2 GHz range of the electromagnetic spectrum and are commonly used in various radars and GPS systems. Due to their lower bandwidth and frequency, L-band isn't ideal for streaming videos, voice calls, or fast internet services. However, it excels in applications like managing fleets, tracking assets, supporting Internet of Things (IoT) devices, and enhancing safety in maritime and aviation sectors.

S-Band Frequencies 

S-band frequencies, which range from 2 to 4 GHz, are utilized for satellite communications and radar systems. This band is particularly crucial for industries such as shipping, aviation, and space.

C-Band Frequencies 

C-band operates within the 4-8 GHz range on the electromagnetic spectrum. 

Using antennas that are typically 1.8 to 2.4 meters in length, C-band satellites provide a direct signal from end to end. They are mainly used for satellite communications, continuous satellite TV broadcasting, and raw satellite feeds. This makes them especially valuable in regions prone to heavy rain or extreme weather conditions.

Ka-Band Frequencies 

Ka-band operates between 27-40 GHz on the electromagnetic spectrum and is primarily used for satellite internet that supports high data transfer rates.

This higher frequency band is ideal for applications requiring more bandwidth, such as video conferencing, live streaming, and high-speed internet, including inflight Wi-Fi and various multimedia applications. Additionally, Ka-band helps provide satellite internet services to homes and remote areas around the world.