aperture terminal

VSAT is the abbreviation of Very small aperture terminal. It is important WAN technology for both home users and organizations; they needed connectivity in remote areas where there is no possibility of fiber optic, copper cable and microwave.  It is the solution that creates a private WAN using satellite communications.

A VSAT contains is a small satellite dish similar to those used for home Internet and TV, a router connects to a satellite dish which is pointed to a service provider satellite in a geosynchronous orbit in the space.

The signals of VSAT must travel 35786 kilometres and back because VSAT networks are typically based on geostationary satellites located on the orbit 35’786 km above the Earth’s equator. The orbital period of the geostationary satellites is the same as the Earth’s rotation period. So, the satellite dish pointing to the satellite does not need to rotate to track these satellites.

A VSAT end-user needs a router that interfaces between the user’s computer and an outside antenna with a transceiver, which sends and receives a signal to a satellite transponder in the orbit. The satellite required a hub station in the earth.

The satellite sends and receives signals from a hub. The remote stations are interconnected with the hub station via the satellite in a star topology. The hub station also controls the entire operation of the satellite network. For one user to communicate with another user, each transmission has to first go to the hub station and then re-transmits it via the satellite to the other station.

Suppose if we have two remote stations e.g. station “A” and Station “B”. If station “A” sending data to station “B”, the station “A” data will receive on the satellite in the orbit, the satellite sends this data to a hub station, the hub station sends this data back to satellite to sends the data to station “B”.  VSAT support voice, video and data.

That satellite dish on the roof of a corporate building is a VSAT Terminal. The VSAT containing two primary components: the outdoor and indoor units. The Outdoor Unit (ODU) means everything installed outside the building where the terminal is located. The Outdoor Unit (ODU) enables the terminal to transmit and receive signals to and from the satellite. The important components of the ODU are:

• Reflector – It is a small part of the system refers to the size of the antenna reflector, typically it is less than 3.8 meters in diameter.
• Feed– It transmits signals toward and receives signals back from the reflector
• BUC– Block Upconverter (BUC) is used for signal transmission. BUC is consists of a local oscillator and a power amplifier.
• LNB– Low Noise Block Down Converter (LNB) is used for receiving signals from the reflector.

The Outdoor Unit (ODU) is interconnected to the indoor unit (IDU) using an Intra-Facility Link (IFL) cable. Usually, it is a coax cable. The IDU consists of the satellite modem and an IP router. The router connects to an Ethernet interface, and data is sent and received from this Ethernet interface.

VSAT Operation

A VSAT terminal receives data connected from the end user’s equipment using LAN port of the satellite router. The router processes and sends the signals to a satellite modem. The modem converts the incoming traffic into continuous Single Channel per Carrier or burstable Time Division Multiple Access modulated carrier.

The router sends this modulated carrier to the BUC using coaxial cable. The transmitter converts the carrier using the Intermediate Frequency (IF) band into higher frequencies. The intermediate frequency is usually an “L Band” frequency, while the higher frequency is usually the C, X, Ku or Ka-band. The transmitter sends the converted signal to the satellite in the orbit with the help of BUC.

The satellite receives the signals, amplify the signal and transmit signals back to satellite hub or satellite terminals. Single Satellites can support multiple frequencies; therefore I have multiple beams with different shapes. Multiple satellite antennas can receive the signal transmitted from the satellite.

The dish of the satellite and LNB amplify the received frequency, convert the signal back to the intermediate frequency band and deliver the signal to a satellite modem with help of a co-axial cable. The modem demodulates the signals and sends the signals to a satellite router. The router processes the signals and sends it to the user computer in the shape of voice, video and data.

Advantages of VSAT

VSAT presents several advantages over other WAN technologies. It cannot depend on other companies. The user or organization has total control of their communication system. Other advantages of the VSAT are the following:

• It can be used in place of a large physical network in the larger area because it bounces signals from the satellite.
• VSAT required fewer infrastructures to serve remote locations.
• VSAT is independent of a local telecommunications system, making it an ideal system to back up wired systems and reduce business recovery risk.
• Support Voice, video and data service everywhere
• Easy to deploy on short notice
• Communications of the move and on the stop
• The same bandwidth is shared along with all terminals
• Unbeatable multicast support
• Wide coverage with centralized management
• VSAT is a reliable, and a stable source of communication
• It provides both narrowband and broadband communication.

Disadvantages

• The VSAT has latency issues in communication because the signal needs to bounce from the satellite two times.
• Weather can badly impact the efficacy of a VSAT network.