the origins of satellite communication can be traced back to an article written by mr (2).doc

7/27/2019 The origins of Satellite Communication can be traced back to an article written by Mr (2).doc

1/8

II. DGM(IT)

1. ORIGIN OF SATCOM

The origins of Satellite Communication can be traced back to an article written by Mr.

Arthur C. Clarke in the British Radio magazine Wireless World in 1945. Satellitecommunication began much latter in October 1957 with the lunch by U.S.S.R. of small

satellite called Sputnik I. The first true communication satellites, Telster I and II, were

launched in July 1962 and May 1963. Since then there has no looking back.

Satellite communication offers a great number of advantages over terrestrial links,

that is why, it is preferred over terrestrial communication, namely :-

High availability minimal/nil fading

No last mile problem

Extensive coverage-Hemi/Zonal/Spot

Broad cast nature allows easy point to multipoint links Easy scalability and expandability of network

Security and secrecy can be adequately addressed

Less prone to failure due to natural calamities

The disadvantages being:-

High up- front investment in ground segment

High recurring cost on satellite segment.

A Satcom exchange has also been provided in NTPC-Khalgaon, which caters to the

communication needs all its 96 employees. The layout of the SATCOM exchange BPL

INOX 250, NTPC- Khalgaon has been shown in figure I. The out door unit basically

consists of the Antenna. The indoor unit comprises a modem, multiplexer, router, DAMA,

DTE, EPBX. The users can connect to the worldwide web or the companys internet using

this system. Using a PC the users can connects to the company LAN via a modem and then

via server all the outside mails are router to the Proxy server. From the router the data is

routed to the multiplexer from where it goes to the RFT via a modem. The data is

transmitted via the antenna and the satellite to the NTPC earth station at Muradnagar (now

NOIDA). To connect to the Corporate Center a 2Mbps micro wave link is used. A proxy

server is also present in the Corporate Center from where it connects to the Internet w

orld via CGI and MTNL/BSNL server.

Private Branch Automatic Exchange. The EPBAX connects to the main plant telephone

exchange as well as a member of subscribers. These provide the facility of voicecommunication via satellite to the users. This is particularly useful in case of terrestrial

links, which are much more damage prone. GDAMS data is also sent to the corporate centre

using this link, as is illustrated in figure. A brief description of the component is given

below:-


2/8

2. SATELLITE: -The third transponder of INSAT-3E with a bandwidth of 18MHz has been

allocated to NTPC to cater to its communication purposes. The bandwidth was updated to

27MHZ on 19th

of July, 2005.The Kahelgaon satellite Communication Plan is given below: -Satellite : INSAT 3E

Location : 55 DEG EAST

Transponder No. : 3

Transponder Bandwidth : 27MHz (6012.00MHz-6039.00MHz)

Beacon Frequency : 4190.97MHz

Polarization : E/S U/L LINEAR HORIZONTAL

E/S DN/L LINEAR VERTICAL

MCPC Stn. Spt Tx.

Setting

: 6025MHz

MCPC Stn. Spt Rx

Setting: 3800MHz

3. ANTENNA:-The antenna is of CASs grain configuration using shaped reflector technique to

optimize receive gain to noise ratio and the corrugation technique for primary horn feed to

get better symmetry and minimum side lobe of the radiation pattern. The antennaspecification is given below:-

Type : LIMITED STEERABLE AZ-EL MOUNT

Feed And Reflector : 7.5M dia. CASSEGRAIN WITH SHAPEDREFLECTOR

Tracking : MANUAL DRIVE, AUTO STEP TRACK

Sky Coverage : EL +5deg - +90degAZ -20deg - +20 deg

Frequency Range : TX 5.850-6.425GHzRx 3.700-4.200GHz

Polarization : LINEAR ORTHOGONAL AND CIRCULARGain : 6GHz BAND- 51+20logf/6 dB

4GHz BAND 47.5+20logf/4dB

Power Handling

Capacity: 5KW C W

Antenna Weight : 9 TONNES (Approx)


3/8

4. TRANSCIEVER:-The AAV680 C-Band single Package Transceiver ODU interfaces

with the 70MHz/140MHz Indoor Unit having bandwidths of + 18MHz.

In Single Package RF Transceiver there 70 or 140 MHz if input from the indoor

modulation to an RF signal in the C-Band, transmission via antenna and down convert the

L-Band signal (950 1450 MHz) to an IF signal of 70/140 MHz. for the demodulator.The Single Package Transceiver has three parts

Phase Locked Low Noise Block ( PLLNB)

Booster for 16W and above (optional)

Accessories

It also has two modules

L band module comprising,

This also has some partitions. As follows..

1. synthesizers

2. up converter

3. down converter

4. monitor & control Power Block Up Module (PBU)

This also has some partitions. As follows.

1. Power supply board

2. SSPA module ( Solid State Power Amplifier )

3. BUC module ( Block Up Converter )

It designed as a single PCB. All SSPA configurations are designed as soft boards bounded

onto aluminum base plates. A low noise amplifier is provided which receives the weak

downlink signal (3.625-4200MHz) and amplifies it to the correct level before sending it to

the SPT for frequency down conversion. It uses HEMT devices to achieve low noise, high

gain and low distortion amplification features. A Booster is provided to boost up thetransmit power of the signal from SPT.

For better reliability, two streams of outdoor C-Band and Ex C-Band

transceivers have been provided. A A low noise amplifier is provided which receives the

weak downlink signal (3.625-4.200MHz) and amplifies it to the correct level before sending

it to the SPT for frequency down conversion. It uses HEMT devices to achieve low noise,

high gain and low distortion amplification features. A Booster is provided to boost up the

transmit power of the signal from SPT.

For better reliability, two

streams of outdoor C-Band and Ex C-Band transceivers have been provided. Redundancy

switching equipment performs the switchover operation when a fault is detected at any one

of the streams. Switchover can be auto/manual and results in less than half a second oftraffic interruption. Independent path switching between the transceivers is allowed.

There is a LNA device. It receives very weak down link signal and amplifies it to the right

level before sending to SPT for the frequency down conversion. This procedure uses High

Electron Mobility Transistor (HETM) for low noise, high gain, low distortion in

amplification. It requires 12 V DC.


4/8

Another equipment is used named BOOSTER. This is used to boost the transmit

power of signal from SPT. It has two pats.

1. Power supply board

This converts AC to DC for SSPA.

2. SSPA (Solid State Power Amplifier )

This receives RF power from SPT and amplifies to correct power level.

5. RCU

The redundancy control unit is supplied with +12 or +15 V DC via agilis transceivers.

The unit contains..

Monitor & control (M & C ) module

Window access panel (WAP )

IF input power splitter

IF output switch

6. M & C

This module comes with an intel based microcontroller to link the monitor and control

functions from the out door RCU to the indoor DTE (usually PC).

To active remote /local mode, toggle the DIP switch at the out door RCU window

access panel.

NOTE:- Users CAN NOT active remote or local mode from the indoor DTE.

7. MODEM:-

The word "modem" is a contraction of the wordsmodulator-demodulator. The digital

satellite modem serves as an interface between the users dataterminal equipment and the IF

frequency interface with the up/down converter. The UMOD has been configured for fullduplex operation. Thetransmit and receive paths are independent for most applications.

In the transmit direction the UMOD accepts user data at the common interface

module (CIM) and directs it across the backplane to the transmit portion of the terrestrial

data interface which converts the users electrical format to the format used in UMOD. The

data is directed to the optional internal framing unit for processing and then to the UMOD

motherboard. On the motherboard the data is sent to the channel encoder where scrambling,

differential encoding & FEC encoding is performed. The data is then routed to the transmit

filter for digital filtering and interpolation; then passed to the modulator where the signal is

PSK modulated onto an IF carrier provided by the transmit synthesizer. This modulated

carrier is then amplified inn the IF stage, then routed for transmission across the backplane

to the IF OUT connector on the IF panel.


5/8

I

In the receive direction the IF signal is input at the IF IN connector on the IF Panel,

passed across the backplane and received by the receive IF processor on the UMOD

motherboard which performs low noise amplification, automatic gain control and filtering.

The signal is then routed to the receive synthesizer and demodulator where the IF carrier is

removed by either BPSK or QPSK demodulation. The resulting base band data is then

directed to the channel decoder where it is FEC decoded, differentially decoded and

descrambled. The data then passes through the optional IFU daughter card where deframing

and other processing takes place. The data is then routed to the receive portion of the

terrestrial data interface daughter card which converts the receive data and clock to

appropriate formats and directs it across the backplane to the CIM where they can be

accessed by the user. The UMOD block diagram is illustrated above:-

TERRESTRIAL

DATAINTERFACE

TRANSMITPORTION

IFUCHANNEL

ENCODING

TRANSMIT

FILTERING

MODULA-

TION

TRANSMITSYNTHESIZER &IF STAGE

TRANSMIT

TIMINGGENERATOR

RECEIVE TIMING

GENERATOR

TERESTRIAL

DATAINTERFACE

(RECEIVEPORTION)

IFUCHANNEL

DECODING

DIGITAL

DEMODULATOR

RECEIVE

FILTERING

RECEIVESYNTHESIZER & IF

STAGE

CRLAGC

C IMBAC

KPLANE

BA

KPAN

B

KA

REFERNCEOSCILLATOR 10MH

REDUNDA NCY CONTROLLER

UMOD SOFT WARE CONFIG/CONTROL M&C

CONTROL PROCESSOR

Fig:- UMOD FUNCTIONAL BLOCK DIAGRAM

DATA

CLOCK

CLOCK

Stn CLOCK

DATA

CLOCK

My pc


6/8

8. MULTIPLEXER :-The Kilomux is an advanced, highly versatile user configurable modular

TDM system providing an efficient method for transmitting data, voice and fax over digital

data services. Its main functions are:- Multiplexing/De-multiplexing operation

System management

Interfacing with the optional external system management.

The basic Kilomux system consists of two kilomux units interconnected

with each other. Two main links are there to provide for standby redundancy for the main

link. The Kilomux uses permanent on-demand allocation of main link bandwidth.

The Kilomux is designed for unattended operation. A complete collection of parameters

configuring the kilomux system and each of its modules,is determined by a database which

is stored in the non-volatile memory of the Kilomux control module. Kilomux can store two

different databases and can be configured to switchover automatically between databases per

requirement.

Given below are the I/O connections of the multiplexer.

KILOMUXKILOMU(ST

BPL

SYSTE

2

REMOTE

TERMINAL

UNIT

ROUTERUMOD

MODEM MODEM LSD HSD TTT

SATCOM LINES

FIELD I/O

Fig: - I/O CONNECTION OF KILOMUX


7/8

It is provided with alarm buffer as well as LED indicator to display in real time the main

link and power supply status. The system can be managed using either of the following:-

Front panel using push buttons and LCD

ASCII terminal connection

Telnet connection via the Ethernet LAN/SLIPconnection

RADview network management station.

9. ROUTER:-Routers are specialized computers that send your messages and those of every other

Internet user speeding to their destinations along thousands of pathways.. These are

crucial devices that let messages flow between networks rather than within networks. A

router has two separate but related jobs:(i) The router ensures that information doesn't go where it's not needed. This is crucial

for keeping large volumes of data from clogging the connections of "innocent

bystanders."

(ii) The router makes sure that information does make it to the intended destination.

It joins the two networks, passing information from one to the other and, in some cases,

performing translations of various protocols between the two networks. It also protects

the networks from one another, preventing the traffic on one from unnecessarily spilling

over to the other. As the number of networks attached to one another grows, the

configuration table for handling traffic among them grows, and the processing power of

the router is increased. A configuration table is a collection of information, including:

(i) Information on which connections lead to particular groups of addresses

(ii) Priorities for connections to be used

(iii) Rules for handling both routine and special cases of traffic.

10. ROUTING OF PACKETS:- The office network connects to the router using an Ethernet connection.There are two connections between our router and the ISP. One is via the satcom system and

the other via the BSNL ISDN line as is illustrated in figure I. This way the ISDN line is held

as an insurance against a problem with the other faster connection.

In addition to routing packets from one point to another, the router has rules limiting how

computers from outside the network can connect to computers inside the network, how the

network appears to the outside world, and othersecurity functions. While most companiesalso have a special piece of hardware or software called a firewall to enforce security, the

rules in a router's configuration table are important to keeping a company's (or family's)

network secure.

One of the crucial tasks for any router knows when a packet of information stays on its

local network. For this, it uses a mechanism called a subnet mask. The subnet mask looks

like an IP address and usually reads "255.255.255.0." This tells the router that all messages


8/8

with the sender and receiver having an address sharing the first three groups of numbers are

on the same network, and shouldnt be sent to another network.

Thus knowing where and how to send a message is the most important job of a router.

Some simple routers do this and nothing more. Other routers add additional functions to the

jobs they perform. Rules about where messages from inside a company may be sent and

from which companys messages are accepted can be applied to some routers. Others may

have rules that help minimize the damage from "denial of service" attacks. The one constant

is that modern networks, including the Internet, could not exist without the router.

the origins of satellite communication can be traced back to an article written by mr (2).doc

Documents