VSAT Fundamentals

OverviewDefinition VSAT (Very Small Aperture Terminal) are small fixed satellite

antennas that provide highly reliable communication means for data, voice and fax between almost any number of geographically dispersed sites.

A very small aperture terminal (VSAT) is a device - known as an earth station - that is used to receive satellite transmissions. The "very small" component of the VSAT acronym refers to the size of the VSAT dish antenna -typically about 2 to 4 feet (0.55-1.2 m) in diameter- that is mounted on a roof on a wall, or placed on the ground

OverviewVSAT Advantage Cost-effective Easy Installation Centralized Network Management Satellite can deploy relatively fast to provide connectivity

and coverage over a wide area Coverage of rural and undeveloped region Relative high data rate directly to user anywhere within the

network Broadcast/unicast/multicast capability VSAT network interface with any type of communication

network nodes, including PSTN, public exchange, cellular telephone system

OverviewVSAT Disadvantage

Latency, about 250 ms on single hop Security, since satellite signals are broadcasted. Solved

by using sophisticated encryption technique or coding. Fading, satellite signals operating at certain frequency

( such as Ku or Ka band) are susceptible to signal weakening due to bad weather like rain or fog

Interference, Network operating at C-band are susceptible to terrestrial microwave signals.

Overview

When uniquely VSAT make it attractive When the cost lower that Terrestrial When it is the only solution

For Example : TV Broadcast Offshore Communication Automatic Teller Machine Rural Communication

When VSAT is Needed?

Technology

Access Method : Digunakan untuk memaksimalkan penggunaan dari satelit

dan elemen- elemen komunikasi satelit lainnya Metode yang umum digunakan

FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access )

Network Topologies :Typical VSAT configuration :

Point to Point vs. Point to Multipoint Transmission Star, Mesh and Hub and Spoke Topology Dedicated Carrier vs. Shared Carrier

VSAT Technology

Technology

Method in transponder sharing resource in with specific frequency in each carrier

E.g. VSAT SCPC

FDMA (Frequency Division Multiple Access)

Method in transponder sharing resource in same frequency at different time

E.g. VSAT IP

TechnologyTDMA (Time Division Multiple Access)

TechnologyPoint to Point vs. Point to Multipoint

Star Topology

Technology

TechnologyMesh Topology

TechnologyHub and Spoke Topology

Satellite Communication

Space Segment

Ground Segment

Satellite Communication consist of :

Space Segment Satellite system consist basically of satellite in space which

links many earth stations on ground Satellite can be though of as a large active repeater in space Satellite Orbital Type :

LEO (Low Earth Orbit) : 500 to 900 km (Need constellation for continous service)

MEO (Medium Earth Orbit) : 5.000 to 1.200 km (Need constellation for continous service)

GEO (Geostationery Orbit) : 36.000 km (Perfectly circullar and lies in the plane of equator)

Satellite Communication

Satellite Orbital

Satellite CommunicationSpace Segment

GEO Satellite Advantage The satellite remain stationary with respect to one point on

earth, there for the earth station antenna is not required to track the satellite periodically

With minimum 50 elevation angle of the earth station antenna, the GEO satellite can cover almost 38 % of the surface of earth

The doppler shift caused by satellite drifting in orbit ( because of gravitational attraction of the moon and the sun) is small for all earth station within satellite coverage. This is desirable for synchronous digital system.


Satellite Frequency SpectrumThe spectrum allocations are given in the following approximate range, as practiced in the satellite industry : L-Band : 1 – 2 GHz S-Band : 2.4 – 2.8 GHz C-Band : 3.4 – 7.0 GHz X-Band : 7.9 – 9.0 GHz Ku-Band : 10.7 – 15.0 GHz Ka-Band : 18.0 – 31.0 GHz Q-Band : 40 – 50 GHz V-Band : 60 – 80 GHz


C-Band, Extended C-Band, Ku-Band Frequency range C-Band :

Freq Downlink = 3700 MHz – 4200 MHzFreq Uplink = Freq Downlink +2225Bandwidth = 500 MHzExample : Palapa C2 , Telkom 1, Agilla 2

Frequency Satelite Extended C-Band :Freq Downlink start at 3400 MHz Freq Uplink = Frek Downlink +2225Example Satelite : Apstar5

Ku-Band Frequency :Down Link :11.700 – 11.950 MHzUp Link: 13.750 – 14.500 MHz

11.950 – 12.200 MHz12.500 – 12.750 MHz

Very affected by climate (rain)


Transponder To increase information capacity carried by satellite, in term of

bandwidth in Hz, satellite divided into several channels, name transponder, using frequency reuse.

Transponder function is as repeater

One method of obtaining frequency reuse is to transmit two signals on the same frequency band (co channel) by placing each on orthogonal polarization.


Typical C-Band Transponder UPLINK STANDARD C-BAND CHANNELS :

DOWNLINK STANDARD C-BAND CHANNELS :


Satellite CommunicationGround Segment

Basically Ground Segment can divided into two part : RF Terminal : UP/DOWN Converter, High Power Amplifier, Low Noise

Amplifier and Antenna Base band Terminal : encoder/decoder and modulator/demodulator Ground Segment Block Diagram :

HPA : High Power Amplifier

LNA : Low Noise Amplifier

Antenna To Amplify the signal from/to satellite Antenna parts :


Antenna Types

Prime Focus Antenna Offset Antenna

Cassegrain Antenna


Prime Focus Antenna Mempunyai feeder di titik pusat dari parabola

Biasanya diterapkan pada antena dengan diameter sedang : 3.4m, 3,7m

Product : Prodelin, MP dll


Offset Antenna Feeder terletak di ujung sisi antena

Biasanya diterapkan pada antena dengan diameter kecil : 1.8m, 2.4m

Product : Prodelin, Patriot, Andrew dll


Cassegrain Antenna Mempunyai 2 reflektor, main

reflektor dan sub reflektor yang berbentuk hiperbola

Biasanya digunakan untuk Hub Station

Mudah operasional dan maintenance

Efisiensi tinggi Product : Suman, Scientific

Atlanta, Andrew, NWIEE dll


Antenna Pointing Azimuth : to align antenna with satellite in horizontal direction

Elevation : to align antenna with satellite in vertical direction Polarization : to match with transponder that will be used



Cross Polarization (Crosspoll) Needed to make sure the antenna is aligned to the

corresponding satellite and does not interfere channels in the other polarization (e.g. horizontal to vertical or vice versa)

Guided by the satellite operator we can perform a crosspoll test

The result of this test must fill a value called Crosspolarization Insulation (CPI)

The minimum value for CPI is 30 dB


CPI Test Result


Power Amplifier Transmit Power Amplifier

Low Power Aplication : SSPA (Solid State Amplifier)

High Power Aplication : HPA (High Power Amplifier), TWTA (Travelling Wave Tube Amp)

Receive Power Amplifier LNA (Low Noise Amplifier) : to amplify the signal from

satellite

LNB (Low Noise Block) : to amplify the signal from satellite and convert it to L-Band frquency

Converter Up Converter

Accepts the modulated IF carriers from modem and translate its intermediate frequency (IF) to the up link RF frequency of the satellite

Down Converter

Receive the modulated RF carriers from the LNA and translate its down link RF frequency to the intermediate frequency (IF)


Satellite Modem


Modulate baseband signal into intermediate frequency spectrum, and demodulate intermediate frequency signal to baseband signal.

Provide error correction, forward error correction, with proper coding process, e.g : convolution coding ( viterby, sequencial), reed solomon, turbo codec. “ Concetenated ” : place two codec in series to improve performance, Eb/No, and efficient bandwidth utilization, less bandwidth required.

Interfacing with any terrestrial equipment or data terminal equipment using standard data interface, e.g : V.35/RS 422, RS 485, G.703.

Sun Outage

Outage in Satellite Communication

Energy of the Sun overpower signal to the satellite

Teresterial Interference

Outage in Satellite Communication

Outage in Satellite CommunicationAdjacent Satellite Interference

AzimuthThe angle between an antenna beam and the meridian plane, measured along a horizontal plane.

AttenuationThe loss in power of electromagnetic signals between transmission and reception points.

BandwidthThe range of frequencies utilized for the transmission of a signal or group of inter-related signals expressed in Hertz (Hz).

Base bandA video or audio signal transmitted at its original frequency.

BER (Bit Error Rate)The percentage of received bits that are in error during transmission; expressed as a number referenced to a power of ten.

VSAT Glossary

Beam widthThe angular coverage of an antenna beam. Earth station beams are usually specified at the half-power (or -3 dB) point. Satellite beams are based on the area to be covered.

CarrierA continuous frequency capable of being modulated with a second data-carrying signal.

C/N (Carrier-to-Noise Ratio)Refers to the ratio of the satellite carrier (or signal) to noise level in a given channel. Usually measured in dB at the LNA output.

CW (Continues Wave/pure carrier)Refers to pure signal without carrying data

dBDecibel. A unit of signal measurement that expresses a ratio between two electrical signals or levels logarithmically.

VSAT Glossary

dBWAn expression of power in dB relative to one watt.

DownlinkTransmission of information from a satellite to earth for reception by earth stations.

Eb/NoThis is classically defined as the ratio of Energy per Bit (Eb) to the Spectral Noise Density (No). It is a measure of signal to noise ratio for a digital communication system. It is measured at the input to the receiver and is used as the basic measure of how strong the signal is.

FEC (Forward Error Correction)A technique that ensures the transmitted message is received at the receiving end without error.

GainIncreased signal power usually the result of amplification; measured in decibels.

VSAT Glossary

G/T (Gain-to-Noise Temperature)Ratio of the gain of an antenna compared to the receive system noise temperature; expressed in dB per degree K.

HubThe central earth station satellite transmission facility that is the focal point for communicating to remote locations within a satellite communications network.

IF (Intermediate Frequency)The frequency of a satellite receiver after down conversion or a satellite modulator before up conversion.

IFL (Interfacility Link)A cable that provides communication between the ODU and IDU.

LNA (Low Noise Amplifier)Equipment that receives the satellite signal reflected by the antenna and amplifies it to the level needed by the satellite receiving equipment.

VSAT Glossary

LNB (Low Noise Block Down converter)Satellite receiving equipment that converts all signals from the LNA to the lower IF frequencies.

MTTR (Mean Time To Respond)Average time taken to arrive on site to correct a fault in a system or component.

RedundancyA secondary system of backup equipment that performs similarly to a primary system, thereby preventing network downtime and system outages.

SCPCSingle Channel Per Carrier.

S/N (Signal-to-Noise Ratio)Relative power of the signal to the noise in a channel.

VSAT Glossary

SSPA (Solid-State Power Amplifier)A lower powered transmitter used for amplification of RF signals at a remote site.

UplinkTransmission of information from an earth station to a geostationary communications satellite.

VSAT Glossary

VSAT Glossary

VSAT Fundamentals

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