Satellite Communication- 6th Handout (1)

Satellite Communication

Course Instructor: Dr. Safdar Ali

WHAT IS A VSAT

Very Small Aperture

Terminal

Refers to the size of the antenna reflector

VSAT is generally .74 meter up to 2.4 meter

VSAT (remote station) consists of:

Outdoor Unit (ODU):

Reflector Transceiver (BUC and LNB)

IFL Cable

Coax cable to connect IDU to ODU

Indoor Unit (IDU)

Ethernet interface to LAN

INTRODUCTION

The first earth station antennas used in commercial

satellite communications systems were very large

and expensive, with typical aperture diameters of

30m.

These antennas operated in C band (6/4 GHz).

With the rapid expansion of satellite

telecommunication world, there was a need to

make access to the satellite more affordable.

INTRODUCTION

This came about in two ways:

A significant increase in the transmit power

capabilities of satellites and the move to

frequency band above C band.

Both led to a rapid decrease in size and cost of

the earth station.

Most VSAT systems operate in Ku band, with earth

station antenna diameters of 1 to 2 m and

transmitter powers of 1 or 2 W.

INTRODUCTION

VSAT systems are used to link businesses and

stores to a central computer system so that sales

transactions can be completed more rapidly than by

using a telephone line and modem, and so that a

central office can rapidly distribute and collect

information from a large number of locations in a

region or country.

The earth stations are usually organized in a star

network, in which the earth stations connect to a

central HUB station via a GEO satellite.

VSAT

The underlying concept

behind most VSAT systems

is to bring

telecommunication service

directly to the end user

without any intermediate

distribution hierarchy.

VSAT are small, software-

driven earth stations.

It is used for the reliable

transmission of data, video,

or voice via satellite.

VSAT FOR MOBILITY

Fly-a-way VSAT

Man Pack VSAT

On The Pause VSAT

Maritime VSAT

Aeronautical VSAT

VSAT FOR HOME

In North America, as of 2011, there are

over 1 million households using VSAT to

access the internet

VSAT FOR BUSINESS

Retail Banking

Oil ExplorationLottery

VSATs Used By

Enterprises For

Remote Connectivity

Primarily Used For

Locations Which Are

Underserved By

Terrestrial

VSAT FOR HIGH AVAILABILITY

Terrestrial

VSAT

Remote Branch

Corp HQ

Satellite to Back Up Terrestrial

Satellite to Load Share Terrestrial

Satellite Enables True Path Diversity

VSAT RELIABILITY

VSAT technology often

high availability &

reliability it is accuracy

reaches to 99.6 to

99.7percentage

For the total VSAT

network. BER(bit error

rate) is better than

1error in 10 million

transmitted bits

BLOCK DIAGRAM OF VSAT

BLOCK DIAGRAM OF VSAT

ODU & antenna provide RF conversion and amplification for the satellite downlink &uplink

ODU called transceiver

In up link we use(up converter)

In down link we use (LNA & down converter)

IDU provide modulation & demodulation

From IDU we can obtain service we need (data-telephone-fax)

IDU AND ODU

VSAT HUB NETWORK

HUB

Information is produced at the hub having a very large 15to 36 foot antenna. The hub controls and monitors thenetwork through a network management system (NMS).Information is sent up to the communication satellite whichreceives, amplifies and beams it back to earth for receptionby the remote VSATs.

17

MULTIPLE ACCESS TECHNIQUES

PAMA (Pre Assigned Multiple Access)

PAMA is an access scheme where in when twoVSATs want to communicate with each other abandwidth is pre-assigned to them exclusively.This assigned bandwidth will be available to theVSAT's on a permanently basis.

MULTIPLE ACCESS TECHNIQUES

DAMA (Demand Assigned Multiple Access) This scheme is very similar to a telephone connection. Therole of the telephone exchange is to connect you to thedesired number. Remotes request a time slot or afrequency to transmit their traffic. The Hub plays therole of a telephone exchange, between any two VSAT's.

NMS allocates each remote a time slot or a frequency totransmit this traffic.

The attributed frequency or time slot will not be releaseduntil the end of the transmission. The hub plays the role ofa telephone exchange, between any two VSAT's.

The DAMA service addresses point to point voice, fax, anddata communication requirements of remote sites.

NETWORK ARCHITECTURES

One Way Implementation

Split Two Way (Split IP) Implementation

Two Way Implementation

ONE WAY IMPLEMENTATION

This is the mode of a satellite used in the broadcast

satellite services (BSS).

By means of proprietary software in the user

terminals, different parts of the downlink can be

accessed by different subscribers according to the

programs ordered from the supplier.

ONE WAY IMPLEMENTATION

This form of channel selection is called narrowcasting.

There can be many narrowcasting groups within a larger

broadcasting area.

SPLIT TWO WAY (SPLIT IP) IMPLEMENTATION

This implementation is used when there is no

normal return channel as with Ku band broadcast

satellite service systems that carry Internet traffic.

The relatively high capacity downlink stream is not

complemented by an uplink capability from the user

terminal.

If the BSS downlink is used as the download

channel from an internet service provider, the only

option the user has for a return link is via another

telecommunications channel, such as standard

telephone line.


Terrestrial

VSAT

Remote Branch

Corp HQ


The Internet Protocol (IP) is therefore split between

a satellite downlink (outbound) channel and a

terrestrial telephone (inbound, or return) channel;

hence the term split IP for this implementation.

The advantage of this approach is that the VSAT

terminal does not require a transmit capability,

which significantly reduces its cost and complexity.

The disadvantage is that the telephone line

connection bit rate is (56 kbps Modem)

TWO WAY IMPLEMENTATION

In this case, a return link is designed into the

service so that two way communications can be set

up over the same satellite, from the hub to the user

and from the user back to the hub.

Two way implementation can be:

Star

Mesh


Initially, the most common VSAT architectures were

Star networks since the very low receive G/T (gain

to noise temperature ratio) of the VSATs, coupled

with their limited transmit EIRP, was compensated

for by using a large hub with high G/T and EIRP.


The cost of the hub was quite high and, at least for the smaller VSAT networks, somewhat prohibitive. This led to the concept of a shared hub, where several networks operate through one main hub.

The difficulty with this approach for large countries with widely dispersed communities is that the host computers for the small VSAT networks are rarely close to the hub.

A high speed terrestrial data link is required between the host computers of the networks and the hub, which increases the cost of the network.


Another star topology limitation is the delay for

VSAT to VSAT communication as we take two hops

In mesh topology allow terminals to communicate

each other directly.

The VSAT terminals is equipped with the network

management and control equipment, each VSAT

must have sufficient power and receive sensivity

(G/T) to communicate with every other VSAT .

Mesh topology requires larger antennas than star

topology

SATELLITE FREQUENCIES

Ka band 26.5 to 40 GHz

K band 18 to 26.5 GHz

Ku band 12 to 18 GHz

X band 8 to 12 GHz

C band 4 to 8 GHz

S band 2 to 4 GHz

L band 1 to 2 GHz

Size of

Antenna

Impact of

Rain

VSAT BANDS

Currently we use two frequency bands: C-band and

Ku-Band.

For C-band operations, the antennas transmit at 6

GHz and receive at 4 GHz.

Ku-band requires transmission at 14 GHz and

reception at 11-12 GHz

KU-BAND VS. C-BAND

OBTAINING SATELLITE DETAILS

HTTP://WWW.LYNGSAT.COM

SATELLITE DETAILS AMOS 1HTTP://WWW.SPACECOM.CO.IL/

Middle East Beam

SATELLITE DETAILS AMOS 1HTTP://WWW.SPACECOM.CO.IL/

European Beam

Satellite Communication- 6th Handout (1)

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