DIMENSIONING - URBE€¦ · DIMENSIONING Application Presentation Application Session Transport Transport Network Internet Data Link Network Interface Physical Layer Physical. Winter

University of California Los AngelesComputer Science Department

DIMENSIONING

Application

Presentation Application

Session

Transport Transport

Network Internet

Data Link Network Interface

Physical Layer Physical

Winter 2002 CS216 - Satellite Networks P08/2


Link Dimensioning

Titolo diagramma

AntennaParameters

NoisePower

Influenceof the propagation

medium

Signalto noise

ratio

SystemImplicationsShadowing

Multiptath Fading

LINK ANALYSIS

It concerns the trasmission of radio waves between twoearth stations, one transmitting and one receiving, viasatellite. In this context, the link consists of twosegments: the uplink from the transmitting earth stationto the satellite and the downnlink from satellite to thereceiving earth station.



Characteristic Parameters of an Antenna (1)• Gain is the ratio between the power radiated per unit solid angle by an

antenna in a given direction and the power radiated per unit solid angleby an isotropic antenna fed with the same power. It is given by:

Gmax = ( 4π / λ2 ) Aeff

λ= c / f wavelenght of the electromagnetic wave,c velocity of the light,f frequency of the electromagnetic wave,Aeff =η A effective aperture area for an antenna with a circular

aperture of diameter D and geometric surface A=π D2/4η efficiency of antenna (tipically 0.5-0.65).

Gmax = η (πD/λ)2 =η(πD f/c)2

• The efficiency of antenna is the product of several factors:the illumination law

the spill-over lossthe surface impairmentsresistive and mismatch losses

η = η i ∗ ηs ∗ ηf ∗ ηz



Characteristic Parameters of an Antenna (2)

• The Radiation pattern indicates the variations of gain with direction.For an antenna with a circular aperture or reflector this pattern hasrotational symmetry. The main lobe contains the direction of themaximum radiation while side lobes should be kept to a minimum.

• The Angular Beamwidth is the angle by the directionscorresponding to a given gain fallout with respect to the maximumvalue.The 3 dB beamwidth is often used, it correspondes to theangle between the directions in wich the gain falls to half itsmaximum value.

• For uniform illumination the angle is 58.5°, with non u. ill. The angleincreases and the value commonly used is 70° wich leads thefollowing expression

θ3dB= 70 (λ/D) = 70(c/f D)• Thus Gmax=η (π 70 /θ)2



Antenna radiation pattern characteristics

Dθ

main lobe

side lobes

dish

θ3dB

GmaxGmax-3dB

θ3dBθ

Gmax

Gmax-3dB

Gmax-30dB



Teta 3dB

0

1

2

3

4

5

6

7

8

9

10

0,1 1 10

Antenna diameter (m)

Tet

a (d

egre

es)

'4 GHz''6 GHz''12 GHz''14 GHz''20 GHz''30 GHz'



Characteristic Parameters of an Antenna (3)

• Polarisation , convention isdefined by the direction ofthe electric field. In generalthe direction of electric fieldis not fixed during oneperiod, the extremity of thevector of e.f. describes anellip s e . Polarisation ischaracterized by:

Direction of rotation

Axial ratio = E max / E min

Inclination of ellipse

• Two waves are in orthogonalpolarisation if their electricfields describe identicalellipses in opposite directions.

• Orthogonal polarisations:- Circular: RHCP - LHCP

- Linerar: HP - VP



Emitted Power• The power radiated per unit solid angle by an isotropic

antenna fed from a radio-frequency source of powerPt = Pt/4π (W/steradian)

for a gain Gt any antenna radiates a power per unitsolid angle equal to:

Gt Pt / 4πThe product Gt Pt is called EIRP (Effective IsotropicRadiated Power)



Received Power

• A surface of area A located at a distance R from thetransmitting antenna subtends a solid angle A/R2 andreceives a power:

Pr= (PtGt/4π)(A/R2) = FA (W) F: power flux density (W/m2)• A receiving antenna of effective aperture area Areff located

at distance R from the transmitting antenna receives thepower

Pr = FAreff =(PtGt/4πR2)Areff

with Areff=Gr/(4π/λ2)

Pr= PtGtGr/Lfs

Lfs=(4πR/λ)2 free space loss(ratio between received and transmitted power function of f)



Other losses

• Transmitting and receiving losses due to waveguides

• Pointing losses

• Atmospheric losses (when applicable)– rain

– clouds

– gas (water vapour and oxygen)

– tropospheric scintillation

• Polarization losses

• Mobile channel losses (when applicable)

L = Ltx + Lrx + Lp + La + Lpol + Lm



Pointing error

• The movement of the satellite causes the misalignment ofthe boresights of the two antennas

• It can be evaluated with the following formula:

ε θθ

=

12

3

2

dB

θ



Pointing error plot

0

5 0

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Teta (degrees)

Poi

ntin

g er

ror

(dB

)

'4 GHz'

'6 GHz'

'12 GHz'

'14 GHz'

'20 GHz'

'30 GHz'



Signal to Noise Ratio (C/N)

• C = EIRP - L + GR

• Thermal noise characterized by power spectral density

N0 = k T– k : Boltzman constant = 1.38·10-23 Ws/K = -228.6 dBWs/K

– T effective noise temperature

T = Ta + Tr

– Ta: receiving antenna noise temperature

– Tr: effective noise temperature of the receiver

80Earth terminal 10° elevation

3-10Earth terminal 90° elevation

290Satellite

Noise Temperature (K)Antenna



C/N & Eb/N0

If noise figure Nr of the receiver is provided

Tr = (10Nr/10 - 1)·290 K

G/T figure of merit

C/N0 = Pt + Gt - L + GR - k - T = EIRP - L + G/T - k dBHz

C/N = C/(N0·BR)

BR noise equivalent bandwidth

Eb/N0 = (C/N0)· Tb = (C/N0) ·(1/ Rb)

Eb/N0 = C/N0 - Rb = EIRP - L + G/T - k - Rb

CN

CkT

P GL

GkT

EIRPL

G Tk

t t R

0

= = ⋅ = ⋅ /



Example 1: The uplink• Antenna of an earth station with diameter D = 4m• Antenna is fed with a power P = 100 W , 20 dBW, at a frequency f =14 GHz• Antenna radiates this power towards a GEO satellite at a distance of 40000

km on the axis of antenna• The beam of satellite receiving has a width θ3dB = 2°• Efficiency of the satellite antenna is η = 0.55 and of the earth station is η = 0.6- power flux density at the satellite is Φ = PtGtmax / 4πR2

- Gain of the earth station is Gtmax =η(πD / λ)2 = 53.1 dBi- Effective isotropic radiated power of earth is EIRP=PtGtmax = 53.1dBi + 20 dBW = 73.1 dBW Then the power flux density is -89.9 dBW/m2

- The power received by the satellite is obtained using the follow equation: Pr= EIRP – attenuation of free space + gain of rx antenna Lfs = 207. 4 dB ; Grmax = η(70π/θ)2 = 6650 = 38.2 dBi with a final value of power

received of -96.1 dBW



Example 2: The downlink

• Satellite antenna of Geo fed with Pt = 10 W, that is 10 dBW atfrequency f = 12 GHz

• Beamwidth of 2°

• The same distance of previous example, and the same efficiency forthe satellite and the earth station.

- power flux density at earth station Φ =PtGtmax / 4πR2

- gain of satellite antenna Gtmax = 38.2 dBi and effective isotropic

radiated power EIRP = 10 dBW + 38.2 dBi = 48.2 dBW

with a power flux density of –114.8 dBW/m2

- Lfs = 206.1 dB, Grmax =η( 70π/θ)2 = 151597 = 51.8 dBi

- The power received by antenna of the earth station is obtained using

the same expression of example 1 with a final value of -106.1 dBW

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DIMENSIONING - URBE€¦ · DIMENSIONING Application Presentation Application Session Transport Transport Network Internet Data Link Network Interface Physical Layer Physical. Winter