Satellite Microwave

MMG Rashed

Sr. Lecturer, Dept. of ETE

Daffodil International University

Satellite Link(Analog)

The ultimate goal of satellite is to provide satisfactory transmission relayed between earth stations.

Satellite always use band pass

Channels. In an analog satellite which

uses frequency modulation the

Satellite Link

Link(Analog) SNR ratio of the voice channel at the FM

demodulator output is a measure of the signal fidelity.

The output SNR is a function of C/N of the satellite link. Satellite Link (Digital) The performance of the received signal at the

receiver depends average probability of bit error which is the function of link C/N.

Uplink and Downlink Signal quality over the uplink depends how

Strong the signal is when it leaves the originating earth station and how the satellite receives it.

On the downlink it, the signal quality depends on how strongly the satellite can retransmit the signal and how the destination earth station receives it.

Uplink and Downlink Because of the great distances between

the Geostationary satellite and the earth stations and because the power of the radiated signal diminishes as the square of the distance it travels the uplink and downlink signals become very weak and can be easily disturbed by ever-present AWGN.

Uplink and Downlink Uplink signal may be contaminated by the

signals transmitted by other earth stations to the adjacent satellites and the downlink signal can be contaminated by the signals transmitted by the earth stations.

Rain can severely attenuate the signals above 10GHz.

Link Budget Analysis• Link budget

A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system.

It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline and miscellaneous losses.

Link Budget Analysis Randomly varying channel gains such

as fading are also taken into account. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.

A simple link budget equation looks like this: Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

Link Budget Analysis

For a line-of-sight radio system, a link budget equation might look like this:

• • where: PRX = received power (dBm) [dbm=10log10(power in mw)]• PTX = transmitter output power (dBm) • GTX = transmitter antenna gain (dBi) [dBi=ratio of effecitve ant

gain to isotropic antenna gain]• LTX = transmitter losses (coax, connectors...) (dB) • LFS = free space loss or path loss (dB) • LM = miscellaneous losses (fading margin, body loss,

polarization mismatch, other losses...) (dB) • GRX = receiver antenna gain (dBi) • LRX = receiver losses (coax, connectors...) (dB)

Basic Link analysis for satellite

Consider a basic sat link as

Shown in figure. The EIRP of the

transmitted carrier s (t) of the earth station is given by:

Pt=carrier power at the antenna feed.

Gt=transmit antenna gain

)1.4........(TTGPEIRP

Basic Link analysis for satellite

Consider that transmission is going on in clear sky conditions so the only attenuation for the carrier s(t) is the free space loss, atmospheric attenuation and antenna tracking loss.

Basic Link analysis for satellite

• The uplink free space loss is:

Basic Link analysis for satellite

• The uplink noise power in equation (3.10) is given by:

Basic Link analysis for satellite Substituting equation (4.6) into (4.5)

yields...

So, uplink C/N ratio can be calculated by (4.5) if the carrier EIRP is given, and by (4.8) if the power flux density at the receiver is given.

)8.4........(1

4 2

2

KBT

G

f

c

N

C

u

u

uu

Basic Link analysis for satellite• The received carrier plus noise at the satellite =

.This carrier plus noise is amplified and down converted by the satellite communication receiver down-converter and then amplified again by the satellite TWTA and retransmitted back to earth by satellite antenna.

• Let us consider that retransmitted carrier plus noise= .This has the same carrier to noise ratio as the received carrier plus noise.

)()(^^

tnts uu

)()( tnts uu

Basic Link analysis for satellite

• Let be the satellite EIRP (or power) of the transmitted power; that is:

• Then the power of the accompanied uplink noise is:

suu EIRPtsEC )]([2^^

)9.4........(^

b

NCEIRP

N

u

su

Basic Link analysis for satellite• The received carrier plus noise at the receiver

earth station = . Where are the attenuated versions of and is the down link AWGN.

• After taking into account the free space loss , antenna tracking loss and the atmospheric attenuation on the downlink , and the receive antenna gain G on the earth station, the power of the carrier at the receive earth station is :

)()()(^^

tntnts d

)(tnd)(),(^^

tnts uu

)(),(^^

tnts

)10.4.......(4

)()()]([

22^

Gfd

c

L

GEIRP

LL

GEIRPtsEC s

d

s

Basic Link analysis for satellite Substituting (4.14) into (4.15) yields the link

carrier to noise ratio:

)16.4.........(..........

111

du N

C

N

C

N

C

Basic Link analysis for satellite

• This equation gives fundamental analysis of where the satellite is using classical type of transponder which adds uplink noise directly to the downlink noise and the uplink is said to be coupled to the downlink.

• From the equation (4.16) we can say that if . In this case the satellite link is

said to be downlink limited. If the reverse case takes place then the satellite is called uplink limited.

ddu NCNCthenN

CNC )/(/,

Radiation Pattern of Directional Antenna

Radiation Pattern of Directional Antenna

Interference into or from adjacent satellite systems

The interference generated by an earth station into an adjacent satellite comes from antenna side lobes as shown in figure.

The FCC regulation specifies side lobe envelope levels:

Interference into or from adjacent satellite systems

• Where is the antenna off axis angle.

dB8

00 71

00 2.97

dBlog2529

dBlog2532 00 489

dB10 )30.4(..........18048 00

Interference into or from adjacent satellite systems

Interference into or from adjacent satellite systems

The angle of separation between two earth stations is given by:

)33.4.(..........)cos1(2

cos2

1

BA

BA

dd

rdd

Interference Analysis

The the minimum separation between satellites operating at the C band (6/4 GHz) is 2° and this is the worst case.

To analyze the interference into or from an adjacent satellite system consider the satellite link and interference paths (dotted lines) between two satellite systems A and B in Fig. 4.8.

Interference Analysis Let A be the existing

satellite system and B be the proposed satellite system. Then the satellite link between the transmit earth station A2 and the receive earth station A1, is affected by two interference sources.

The uplink interference signals are from earth stations in the proposed B, and the downlink interference signals coming from satellite B.

Interference Analysis

The total C/I ratio due to these two interference

Sources represents the interference generated by the proposed satellite system B into the adjacent satellite system A.

Interference Analysis

Let Carrier power flux density(watt/m2 )

Power flux density of the interfering signal at the interfered satellite A

EIRP of the interference signal in the direction of interfering satellite B

power flux density of interference signal at

interfering satellite B

*EIRP

i

i

G

*

transmit antenna gain of B1

Interference Analysis

Khaitta Khaw• Read the topics:4.2.1,4.2.3,4.2.4,4.2.5

4.2.6,4.2.6