Comunicaciones por satélite | 47/48 | UPV

Introduction to Satellite Communications

Overview of Satellite Communications

• The unit discusses satellite communications, emphasizing their utility in connecting remote areas and transmitting data with minimal infrastructure.

• A communication satellite is an artificial satellite that receives signals from Earth, amplifies them, and retransmits them back down. It typically contains multiple transponders for various services.

Types of Satellites and Their Uses

• Common applications include television broadcasting, maritime communications, internet access in remote locations, and vital data transmission over long distances.

• Two main types of communication networks are identified: passive satellites (which reflect signals like mirrors) and active satellites (which amplify and regenerate signals).

Energy Consumption in Active Satellites

Challenges with Active Satellites

• Active satellites consume more energy due to their need for power sources like solar panels or alternative energy systems, which complicates their launch and reduces lifespan.

Frequency Bands Used in Satellite Communication

Microwave Frequencies

• Most satellites operate on microwave bands; four specific frequency bands are defined within the radio spectrum.

• Lower frequencies provide less bandwidth while higher frequencies offer more bandwidth but require larger antennas.

Orbits of Communication Satellites

Types of Orbits

• There are two fundamental types of orbits: normal orbits (where satellites move around the Earth), and geostationary orbits (where a satellite remains fixed relative to a point on Earth).

• Arthur C. Clarke proposed the concept of geostationary communication satellites in 1945, suggesting three satellites could cover the entire planet.

Understanding Satellite Footprint

Coverage Area

• The footprint refers to the area on Earth covered by a satellite's signal; larger footprints can distribute power but may weaken signal strength.

• Each transponder has a unique coverage map tailored to optimize signal strength for specific regions.

Low Earth Orbit (LEO)

Characteristics of LEO Satellites

• LEO satellites orbit close to Earth, allowing stronger signal reception with smaller antennas but requiring coordination due to their rapid movement.

• To maintain continuous communication as LEO satellites move quickly out of range, large constellations are necessary.

Coordination Among Satellites

International Regulation

Frequency Planning and Satellite Communication

Overview of Frequency Regions

• The world is divided into three frequency planning regions:

• Region One: Europe, Africa, former Soviet Union countries, and Mongolia.

• Region Two: North America, South America, and Greenland.

• Region Three: Asia (excluding Region One), Australia, and the Southeast Pacific.

Satellite Services and Equipment

• Different frequency bands are allocated for various satellite services including:

• Fixed satellite service

• Satellite broadcasting

• Mobile services

• Radiolocation services

• Users require appropriate receivers to access transmissions; antenna size varies based on distance to the satellite. Larger antennas are needed for longer distances.

Geostationary Satellites and Antenna Types

• For geostationary satellites, parabolic dishes are commonly used:

• These antennas must be carefully aimed at the satellite.

• Once aligned with a geostationary satellite, no further adjustments are necessary.

• Antennas smaller than three meters are referred to as VSAT (Very Small Aperture Terminal):

• Typical sizes around one meter.