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DIGITAL EARTH STATION

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CONTENTS What is an Earth Station Classification Typical analog E/S setup Typical digital E/S setup Problems of analog Why digital Digital communication setup Components

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WHAT IS AN EARTH STATION

Any transmitting or receiving system which sends or receives

signals to and from satellite

Counterpart to the earth station is the “space station”

Generally use dish-shaped antennas.

4Uplink Station Receive Centre

What is an Earth Station

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CLASSIFICATION

Analogue Earth Station

Analog / Digital Simulcast

Digital Earth Station

ASNG

DSNG

TYPICAL ANALOG E/S SET UP

April 13, 2023

W/G

A1-A2

A1-A2

Sound Modcombiner

IF Mod UP converter HPAVideo

Sound Modcombiner

IF Mod UP converter HPAVideo

DUMMYLOAD

(Baseband V:0-5MHz, A:5.5/5.75MHZ)

(Baseband V:0-5MHz, A:5.5/5.75MHZ)

70MHz

70MHz

Channel freq. 2

Channel freq. 1

U/L PDA

TYPICAL DIGITAL E/S SETUP2+1 CONFIGURATION

ES PDA

Base bandProcessing

Base bandProcessing

Enc. 1

Enc. 2

Base bandProcessing

Enc. R

MUX 1

MUXR

Modulator# 1

Modulator# R U/C-R

U/C 1 HPA 1

HPA R

V

V

A

V

A

V

A

V

A

A

V

A

ROUTER

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PROBLEMS OF ANALOG

One program per channel / transponder Comparatively noisy Required huge power for qualitative transmission Ghosts in Terrestrial Transmission Uneconomical Fixed reception Lower Quality with respect to VCD, DVD or Digital Media

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WHY DIGITAL ?

More programs per channel / Transponder i.e. spectrum efficient

10 to 14 TV channels per 36 MHz Transponder

( DVB-S, MPEG 2 )

25 to 50 TV channels per 36 MHz Transponder

( DVB-S2, MPEG 4 / WM 9) Economical Provision of Encryption Reduced uplink power Ghost elimination

DIGITAL COMMUNICATION SETUP

Channel encoding: Introduce controlledredundancy ARQ, FEC

Source encoding Channel encoding

User Source decoding Channel decoding

Transmission channel RF Stage

Digital source Mod.

Detector

Source encoding:Remove redundancy

Base Band Signal

Compression & IF stage

April 13, 2023

Analog signal is sampled at 27 MHz, encoded into 10 bits PCM - Total bit rate : 270 Mbps.

The Y (luminance), Cr (R-Y) and Cb (B-Y) signals are used for Digitalization.

The digital standard is known as Serial Digital Interface (SDI)

Audio signal (AES/EBU) either separate or it may be in embedded with Video signal.

Digital Base Band signals

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Need for Compression

Sampling rate for analog video signal

Sampling Frequency for Y-signal 13.5 MHz

Sampling Frequency for CB-signalSampling Frequency for CR-signal

6.75 MHz

6.75 MHz

Bit rate for a digital video signal with 10-bit quantization resolution

13.5 *10 =135 Mbps

6.75 *10 =67.5 Mbps

6.75 *10 =67.5 Mbps

270 MbpsTotal

Video Bit Rate

44.1 kHz

(32/44.1/48 kHz) 2*16*44.1= 1.41 Mbps

Bit rate of digital audio signal with 16-bit quantization resolution

Sampling Frequency for audio signal

Audio Bit Rate

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Bandwidth requirement for a given data rate m

RRB bs

)1()1(

B is bandwidth required

α is Roll-off factor of

pulse shaping filter

Typically ranges 0.28-0.35

RS Symbol rate

Rb Bit rate

m an integer depends on the types of digital modulation

For

BPSK, m=1

QPSK, m=2

8PSK, m=3

16PSK, m=4

and so on

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COMPRESSIONWhy Compression ?To reduce very high bit rate of digital audio and video signals to manageable low bit rate for various applications. (Saving bandwidth)What is Compression ?Removal of redundancy in audio and video signals to achieve very low bit rates with a little degradation in audio/video quality.

Digital Video at 270 Mbps in SDI format is re-constructed to 1.5 to 15 MBPS (variable) & digital audio to128 Kbps for CD quality audio (MUSICAM coding) for transmission.

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MULTIPLEXING

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ENCODER n

ENCODER 2

ENCODER 1

MUX

CHANNELCONTROLLER

SDI 2

SDI 1

SDI n

ASI

ASI out

Sharing of more than one program in single frequency slot in time domain (MCPC)

CODING

The process to convert data in a form to transmit through a lossless network, it includes:

1. Inner coding:FEC (forward error correction) convolution coding (Addition of one repetitive extra bit after some elementary bit)

2. Outer coding :RS (REED- SOLOMON) coding (188 to 204 bytes)-Can correct up to 8 lost symbols

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• Delivers the Video, Audio and other data in terms of PES, and other types of data , over media with errors

• Packets of 204 byte :

• 184 net bytes payload• 4 bytes header

(+ optional adaptation field)• 16 bytes Reed – Solomon Parity FECc Header Bytes

Net Payload

16 4 184

Parity FEC bytes (RS)

Gross Payload204

MPEG2PES: Packetized Elementary Stream

April 13, 2023

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COMPONENTS OF DES

PDA (Parabolic Dish Antenna)

LNA / LNBC

HPA (TWTA, SSPA, Klystrons)

Up converter

Modulator

IRD (Integrated Receiver Decoder)

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PDA Paraboloid antenna with a focal point feed

- Reflector –parabolic

- Feed – phase centre at focal point of reflector

- OMT – three port n/w Cassegrain antenna

- Dual reflectors – main reflector and sub reflector

- Feed- phase centre at focal point of sub reflector

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PDA ANTENNA SYSTEMS

Prime Focus

Cassegrain

Off set

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TRUE OFFSET FOCAL ANTENNA

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TRUE OFFSET FOCAL ANTENNA Why Offset?

Avoid blockage/ LNBF shadow: Low gain

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A TYPICAL UPLINK PDA

TYPICAL DIGITAL E/S SETUP 2+1 CONFIGURATION

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OPTICAL RECEIVER

AUDI O PROCESSOR

AUDI O PROCESSOR

VIDEO PROCESSOR

VIDEO PROCESSOR

ROUTER

ENCODER R

ENCODER 2

ENCODER 1

MUX R

MUX 1

ROUTER

PR

OTEC

TIO

NSW

ITCH

MODULATOR 1

MODULATOR RUP CONVERTER R

UP CONVERTER 1W/GSWITCH

RF SWITCH

TWTA 1

TWTA R

DUMMY

TRANSMITTINGPDA

CHANNELCONTROLLER

UPC

ON

VERTE

RSW

ITCH

TO MODULATORS

FRO

M

MU

X

FROMSTUDIO

RF MONITORING & CONTROL

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MODULATION

Modulate the final signal to 70 MHz Intermediate frequency

Mode of modulation :QPSK

Most commonly used modulation scheme in Digital Satellite

communications.

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UP CONVERTER

Accepts modulated IF carrier and converts into RF signal

IF signal is mixed with local oscillator frequency and passed

through a band pass filter.

May be single conversion process or with a dual – conversion

process

Signal is then fed to HPA and then to dish antenna.

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DOWN CONVERTER

For receiving, the LNA boosts the signals to the down converter,

which lowers the frequency and sends it to the modem. The

modem demodulates the carrier, and the digital output goes to the

demultiplexing device and then to its destinations.

Like up conversion it can be with a single conversion process or

dual-conversion process.

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LNA

Commonly used are :

Parametric amplifiers:

-Employed since inception of satellite

GaAs FET amplifier:

- Gate length - 0.5 micro meter

- Very low noise temp.

- Stable , reliable , low cost

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HPA

Used for the final power amplification of the digital

RF signal in C-band/Ku band that is fed to the

antenna.

The important parameters of HPAs are:

• Frequency range

• Output power at flange

• Bandwidth

• Gain variation (1.0db (max.) for 40MHz (narrow

band)

• 2.50db for full bandwidth.

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QUERIES??