VSAT Technology

Submitted By:

Harneet Singh Bhatia

(0841322807)

Very Small Aperture Terminal (VSAT)

It is a two way satellite ground station with a dish antenna

It access satellites in geosynchronous orbit to relay data from small remote earth stations to other terminals

Each VSAT terminal is assigned a frequency for its return path which it shares with other VSAT terminals

VSAT systems are based on ip which broadens its spectrum of application

Advantages of a VSAT network

Reliability in data transmission (data ,voice , video).

Allocation of resources to different users Fixed network solution. Provide point-to-point, point-to-multipoint,

multipoint-to-point communication & broadband multimedia services

Provide communication to remote areas

Segments of VSAT

Space segment: This segment consists of a satellites in geostationary orbit located on an arc 36,000 kms above the equator.

Ground segment: Also known as Earth Terminal Segment has two parts:

1)Outdoor Unit: ground or even wall mounted.

2)Indoor Segment: Is located near existing computer equipment.

Satellite Communication Concept

Typical VSAT System

Consists of four parts :-

1) Outdoor unit

2) Cassegrain Antenna System

3) Radio Frequency Terminal (RFT)

4) Indoor Unit(IDU)

Block Diagram of a VSAT System

Various components of VSAT network

Antenna Control Unit

This unit works to receive &transmit signals from satellite

• Beacon signal reciever: satellites send a self generated signal to earh station known as beacon signal

• Antenna Tracker: checks voltage level of signal and automatically moves dish to track max strength

High Power Amplifier

Also known as Vacuum Tubes (Valve) Amplifiers are cost effective in high power applications

They are of two types:-

1) Traveling Wave Tube Amplifier (TWTA):- a TWT integrated with a regulated power supply &protection circuit is referred to as a TWTA

2) Klystron II Tube Amplifier:- makes use of electron bunching in a klystron tube

Low Noise Amplifier

Used to amplify very weak signals captured by antenna

The noise of all subsequent stages is reduced by gain of LNA and noise of LNA is directed into the received signal

Up/Down converter

Used to convert signals from low to high or from high to low frequency respectively.

Up converters are used to increase the frequency while transmitting

Down converters are used to decrease the frequency while reception

Modem & Multiplexer

Modem:- a device which modulates the transmitting signal & demodulates the receiving signal.

Multiplexer:- it is a device that allows multiple logical signals to transmit simultaneously over a single channel

Router & Exchange

Router:- a device that finds the best route between any two networks when two routers are connected on same port it is called cross-connection & when on different ports it is called straight connection.

Exchange:-A workplace where lines from telephone can be connected to permit communication is called Exchange. the signals from modem+mux is sent to exchange for distribution to its telephone subscribers.

Communication between two sites via VSAT

VSAT topologies

STAR-the hub station controls, monitors &communicate with large number of dispersed VSATs. suitable for centralized data applications.

MESH-a group of VSATs communicate directly with any other VSAT in the network. suitable for telephony applications.

Hybrid-where a pair of network operates on Star while some sites operate on Mesh.

Technology used by VSAT services

Time Division Multiple Access (TDMA) Single Carrier Per Channel (SCPC) Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

When numerous remote sites communicate with one channel hub

Competition with one another for access to central hub max bandwidth is restricted to 19.2Kbps

Satellite sources are shared on time slot basis

Usually used in star topology

Single Carrier Per Channel (SCPC)

Provides point to point technology Dedicated bandwidth up to 2 Mbps Usually using an international VSAT service

in Asia Pacific

Frequency Division Multiple Access (FDMA)

The satellite channel bandwidth is broken into frequency bands for different earth station.

Earth stations must be power controlled to prevent the microwave poer spilling into bands of other channels since all VSATs share satellite resource on frequency domain only

Three types of FDMA variants

Pre-Assigned Multiple Access (PAMA) Demand Assigned Multiple Access (DAMA) Code Division Multiple Access (CDMA)

PAMA

The VSATs are pre-allocated a designated frequency.

Satellites resources are used constantly hence no call up delays.

PAMA connects high data traffic sites within an organization

CDMA

A central network monitoring system allocates a unique code to each of VSATs enabling them to share and transmit simultaneously a common frequency band.

Data signal is combined with high bit rate code signal.

Reception at the end is done by mixing incoming signal with a locally generated replica of the code.

Used for interference rejection for security reasons in military systems

DAMA

The network uses a pool of satellite channels available for use by any station in that network.

On demand, a pair of channel is assigned to establish a call.

Ideally suited for voice traffic and data traffic in batch mode.

It offers point-to-point voice, fax and data requirements and support video-conferencing.

VSAT Characteristics and Advantages

Reliability: reliable satellite transmission of data, voice & video.

Flexibility: VSAT offers enormous expansion capabilities & unrestricted and unlimited reach.

Network Management: easily integrates end-to-end monitoring & configuration.

A low mean time to repair Cost: offers significant savings over 2-3 years

timeframe. Link budget: estimates the ground station and

satellite Effective Isotropic Radiated Power (EIRP).

VSAT services

Interactive real tome application Telephony Intranet, Internet & IP infrastructure Direct-to-Home

Opportunities in VSAT technology

Voice over IP (VOIP) via satellite. Frame Relay via Satellite ATM via Satellite Video-on-Demand via Satellite Multimedia Application• Internet/e-mail connection• Telemedicine• Distance Learning

References

www.ntpc.co.in www.wikipedia.org www.faqs.org www.wb.nic.in