ELEC5510_Satellite Communication Systems_2013 Semester 2_551

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

ELEC 5510SATELLITE COMMUNICATION SYSTEMSProf. Branka Vucetic Dr. Wibowo Hardjawana Centre of Excellence in Telecommunications School of Electrical and Information Engineeringhttp://elearning.sydney.edu.au1

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Satellite Communication Systems

UplinkDownlink

Centre of Excellence in Telecommunications

The University of Sydney

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Satellite Communication Systems

Earth station Speech Channel Power encoder

encoder

lator

amplifier

Uplink channel

Speech Error coding

control MODEM

Channel propagation

coding

Earth station Downlink antenna

channel

Speech DemoduTelecommunications

Satellite

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

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Propagation and Channel Models

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Propagation in Satellite Communications Predominantly line of sight communications Propagation via space waves Frequency bands 1-50GHz (L-Ka bands) Propagation depends on service types:- GEO, MEO and LEO - Fixed and mobile environments

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Propagation Impairments

Attenuation Noise

Fading from multi-path Time dispersion Doppler shift Shadowing

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Attenuation

Free space attenuation Atmospheric absorptionRain attenuation

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Free Space Attenuation Free space loss, ideal isotropic antenna

Pt 4 d 4 df c Pr c

2

2

Pt - transmit power Pr - receive power - carrier wavelength d - distance between Tx and Rx antennas c - speed of light fc– carrier frequency8

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Atmospheric Absorption103

Losses occur in the earth’s atmosphere as a result of energy absorption by the atmospheric gases. Atmospheric absorption varies with frequency as well as elevation angle. The figure shows absorption at various frequencies for vertical incidence (elevation of 90°)

O2 10 Atmospheric absorption loss (dB)2

10

1

10

0

H2O

10

-1

10

-2

10

0

La ( E ) La (90 )/ sin E (dB)

10 Frequency (GHz)

1

10

2

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Rain Attenuation Radio signals are attenuated by rain, snow and fog. This attenuation is significant above 10 GHz. It is higher for lower elevation angles (longer rain path).

University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Measured attenuation at 100 mm/hr rain rate averaged over 1 km as a function of frequency.

The path attenuation per km is referred to as the specific attenuation.

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

The CCIR method to determine the specific attenuation is:

aR

b

dB/km

where a and b are coefficients and R is the rain fall value occurring for 0.01% of the time in the region of interest. It is recommended that a representative value for Rbe obtained from local rain rate statistics measured by rain gauges with an integration time of 1min. If no such data exist, CCIR Report 563 provides estimates of the value for R for 14 various climatic zones. Parameters aand bare defined for various climatic zones.

(79)

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

The rain attenuation in dB for 0.01% of the time is given by

A L r

(80)

where Lis the path length through rain and ris a reduction factordependent on path length and elevation angle to account for the in homogeneity of rain fall.

The path length in the CCIR method is given by:

L(km)

4 0.075( 36), 36o

4,0 36o

(81)

where (degree) is the latitude of the region of interest.

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Table 6 The parameters for the CCIR rain attenuation method for satellite transmission at 12.5 GHz in Australia.LocationPerthDarwinMelbourne

RegionKNF

Latitude31o57’S12o26’S37o49’S

a0.0480.0200.056

b1.2991.3831.288

Rmm/h34.997.427.2

r0.3920.3560.3049

Example 1: For an earth station at Melbourne with fc=12.5 GHz, the specific attenuation is aRb 0.056 27.21.288 3.94dB/kmThe path length is

L 4 0.075( 36) 4 0.075(37.81 36) 3.86 km

Thus, the rain attenuation is

A L r 3.94 3.86 0.3049 4.64 dB

(for 0.01% of the time)

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Noise

Thermal noiseGalactic noise

Inter-modulation noiseInterferenceImpulse noise

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University of Sydney_ELEC5510_Satellite Communication Systems_2013 Semester 2

Sources of Noise

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