Satellite Communications Basics

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Types of Satellite LEO (Low Earth Orbit) 500 to 1000 miles above the earth MEO (Medium Earth Orbits) 8000 miles above the earth GEO (Geostationary Earth Orbit) 22,238 miles above the earth GEO MEO LEO

Transcript of Satellite Communications Basics

Page 1: Satellite Communications Basics

Types of Satellite

LEO (Low Earth Orbit) 500 to 1000 miles above the earth

MEO (Medium Earth Orbits) 8000 miles above the earth

GEO (Geostationary Earth Orbit) 22,238 miles above the earth

GEO

MEOLEO

Page 2: Satellite Communications Basics

Geostationary Satellites Uses

Broadcast Video Distant Learning Broadcast Audio Data Broadcasting Data/Voice services

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Geostationary Satellites Technical

Transmission Delay– Delay is 250ms from Site A to the

Satellite to Site B, due to the distance of 22,238 miles.

Sun Outage– Sun passes behind a satellite in relation

to the earth, and the sun’s energy briefly interferes with the satellite signals. Happens two times each year.

125ms125ms

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Geostationary Satellites Technical cont.

Frequencies– C-Band

– Transmit 5.925 - 6.425 GHz– Receive 3.700 - 4200 GHz

– Ku-Band– Transmit 14.0 - 14.5 GHz– Receive 11.45 - 11.95 GHz

– Ka-Band (available early 1999)– Transmit 30 GHz– Receive 18 GHz

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Geostationary Satellites Technical cont.,

Rain Fade Loss of signal due to absorption of heavy rain.

Rain Attenuation (dB) at 30deg

Rain Rate (mm/h) 4 GHz 6 GHz 12 GHz 14 GHz5 .1 .15 1.6 1.8

10 .11 .80 2.0 2.915 .12 1.4 2.6 5.020 .13 1.6 3.3 6.825 .14 1.8 4.1 8.030 .15 2.0 5.0 9.235 .16 2.4 6.0 10.440 .17 2.8 7.0 11.8

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Footprints - Intelsat 706 at 307ºE

EIRP (Effective Isotropic Radiated Power) - The strength of the signal leaving the satellite antenna

Maps are also available with G/T (Gain-to-Noise) data.

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Geostationary Satellites (cont.)

C-Band– Advantages

– Wide Footprint Coverage– Minor Effect From Rain (Rain Fade)

– Disadvantages– Requires Larger Antennas– Requires Larger SSPA– Effected by Terrestrial Interference (TI)– Difficult to obtain a Tx License

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Geostationary Satellites (cont.)

Ku-Band– Advantages

– Requires Smaller Antennas– Requires Smaller SSPA– Easy to Obtain a Tx License

– Disadvantages– Effect by Rain (Rain Fade)– Smaller Footprint

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Geostationary Satellites (cont.)

Polarization A technique designed to increase the capacity of the

satellite transmission frequency. In linear cross polarization schemes, half of the frequencies beam their signals to earth in vertically polarized mode; the other half horizontal polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other.

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Geostationary Satellites (cont.) Transponder

Block of frequency on a satellite.Typical bandwidth is 40MHz per transponder (36MHz usable - 2 MHz of guard band on each side). Some Ku-Band transponder are 54MHz & 72MHz.

Rx (MHz) 3720 3760 3800 3840 3880 3920 3960 4000 4040 4080 4120 4160Tran. 1 3 5 7 9 11 13 15 17 19 21 23

V

Tx (MHz) 5945 5985 6025 6065 6105 6145 6185 6225 6265 6305 6345 6385Tran. 1 3 5 7 9 11 13 15 17 19 21 23

H

Rx (MHz) 3740 3780 3820 3860 3900 3940 3980 4020 4060 4100 4140 4180Tran. 2 4 6 8 10 12 14 16 18 20 22 24

H

Tx (MHz) 5965 6005 6045 6085 6125 6165 6205 6245 6285 6325 6365 6405Tran. 2 4 6 8 10 12 14 16 18 20 22 24

V

Typical C-Band Transponder allocation plan

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SCPC Earth Station

Satellite M odem

Antenna

IFL 70M Hz Tx

IFL 70M Hz Rx

LNA

OM T w/Reject FilterFeed Horn

Heliax4GHz

W aveguide6GHz

RFT

OffsetTx/Rx

Antenna

FRAD

RS422 or V.35

6GHz

4G Hz

Satellite

Typical C-Band SCPC (Single-Channel-Per-Carrier)

Earth Station Components

Also called VSAT ( Very Small Aperture Terminal)

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SCPC Earth Station Components

Antenna Reflector

• Offset ~28º• Prime Focus

Typical Size – C-Band - 1.8m , 2.4m, 3.7m, 4.5m– Ku-Band - 1.2m, 1.8m, 2.4m

Mount• AZ/EL - Azimuth/Elevation

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SCPC Earth Station Components Cont.

Feedhorn A component that collects

the signal from the antenna and channels it to the OMT

OMT/Reject Filter Orthogonal-Mode Transfer.

Performs Polarization of Tx/Rx

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SCPC Earth Station Components Cont. LNA (Low Noise Amplifier)

Preamplifier of the receive signal. Rated in Noise temp (K).

Heliax Low loss foam-dielectric cable. Typical loss of

1/2” Heliax at 4GHz is .4dB per 10ft. Flexible Waveguide

A metallic microwave conductor, typically rectangular in shape, used to carry high frequency microwave signal.Typical loss at 6GHz is .15dB per 10ft.

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RFT (Radio Frequency Terminal) Consist of an Upconverter, Downconverter,

and SSPA(Solid State Power Amplifier)– Other Names

– ODU - Outdoor Unit– Transceiver

SCPC Earth Station Components Cont.

Page 16: Satellite Communications Basics

SCPC Earth Station Components Cont.

RFT (Radio Frequency Terminal) cont. Upconveter/Downconverter

IF (Intermediate Frequency) Coax Cable, typically RG8 50. 70 or 140 MHz

IFL 70MHZ Rx(±18MHz in 5KHz Steps)

RFT C-Band

Upconverter

Downconverter

SSPA 5W

IFL 70MHZ Tx(±18MHz in 5KHz Steps)

Step 1- 3980MHz to 1250MHzStep 2 - 1250MHz to 70MHz

Step 1- 70MHz to 1250MHzStep 2 - 1250MHz to 6205MHz

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SCPC Earth Station Components cont.

Satellite Modem Modulation

QPSK - Quadrature Phase Shift Keying BPSK - Binary Phase Shift Keying

01 0000

0110

1190

180

270

00

180

BPSK QPSK

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Satellite Modem cont.

Forward Error Correction (FEC) - Viterbi– Adds unique codes to the digital signal at

the source so errors can be detected and corrected at the receiver.

– 1/2 rate = 1bit data, 1bit error correction– 3/4 rate = 3bit data, 1bit error correction– 7/8 rate = 7bit data, 1bit error correction

Transmission method Channel Spacing Eb/No @ 10E-07

256Kbps, QPSK, rate 1/2 360 kHz 6.5

256Kbps, QPSK, rate 3/4 240 kHz 7.8

128Kbps, QPSK, rate 1/2 180 kHz 6.5

128Kbps, QPSK, rate 3/4 120 kHz 7.8

128Kbps, BPSK, rate 1/2 360 kHz 6.5

64Kbps, QPSK, rate 1/2 90 kHz 6.5

64Kbps, QPSK, rate 3/4 60 kHz 7.8

64Kbps, BPSK, rate 1/2 180 kHz 6.5

32Kbps, QPSK, rate 1/2 45 kHz 6.8

32Kbps, BPSK, rate 1/2 90 kHz 6.5

Eb/No - Bit Energy-to-NoiseRatio.

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SCPC Earth Station Components cont.

Satellite Modem cont. Scrambler

Spreads Energy evenly over frequency. CCITT V.35 IESS

IF (Intermediate Frequency) 70MHz (18MHz in 5KHz steps) 140MHz ( 36MHz in 5KHz steps) - Not

available in SkyFrame

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Configuring Tx/Rx Frequencies Example 1

Satellite Modem

IFL 70MHZ Rx(±18MHz in 5KHz Steps)

RFT C-Band

6205 MHz(1 MHz Steps)

3980 MHz(1 MHz Steps)

Upconverter

Downconverter

SSPA 5W

Antenna

LNA

OMT w/Reject FilterFeed Horn

6205 Mhz3980 MHz

L.O 2225MHz

IFL 70MHZ Tx(±18MHz in 5KHz Steps)

Required FrequenciesTx - 6205 MHzRx - 3980 MHz

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Satellite Modem

IFL 70.25 MHZ Rx(±18MHz in 5KHz Steps)

RFT C-Band

Satellite

6205 MHz(1 MHz Steps)

3980 MHz(1 MHz Steps)

Upconverter

Downconverter

SSPA 5W

Antenna

LNA

OMT w/Reject FilterFeed Horn

6205.25 Mhz3980.25 MHz

L.O 2225MHz

IFL 70.25 MHZ Tx(±18MHz in 5KHz Steps)

Required FrequenciesTx - 6205.25 MHzRx - 3980.25 MHz

Configuring Tx/Rx Frequencies Example 2

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Satellite Modem

IFL 69.75 MHZ Rx(±18MHz in 5KHz Steps)

RFT C-Band

Satellite

6205 MHz(1 MHz Steps)

3980 MHz(1 MHz Steps)

Upconverter

Downconverter

SSPA 5W

Antenna

LNA

OMT w/Reject FilterFeed Horn

6204.75 Mhz3979.75 MHz

L.O 2225MHz

IFL 69.75 MHZ Tx(±18MHz in 5KHz Steps)

Required FrequenciesTx - 6204.75 MHzRx - 3979.75 MHz

Configuring Tx/Rx Frequencies Example 3

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TVRO Earth Station

Satellite Video/Audio Receiver

Antenna

IFL 950 - 1450 Rx

LNB

OMTFeed Horn

OffsetRx

Antenna

4GHz

Satellite

TVRO Television Receive Only

Page 24: Satellite Communications Basics

LNB LNB (Low Noise Block Downconverter)

A combination Low Noise Amplifier and downconverter built into one device attached to the feed.

PLL LNB (Phase-Locked Loop Low Noise Block Downconverter)

A combination Low Noise Amplifier and stable downconverter built into one device attached to the feed.

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SCPC L-Band Earth Station

Antenna

IFL 950-1450 M Hz Tx

IFL 950-1450MHz Rx

PLLLNB

OM T w/Reject F ilterFeed Horn

BUC

O ffsetTx/Rx

Antenna

FRAD

RS422 or V .35

6GHz

4GHz

Satellite

SL512 L-BandSatellite M odem

SL512

Page 26: Satellite Communications Basics

SCPC L-Band Earth Station Components BUC (Block Upconverter)

Input of 950-1450 and Upconverter the 500MHz to C-Band or Ku-Band

PLL LNB (Phase-Locked Loop Low Noise Block Downconverter) A combination Low Noise Amplifier and stable downconverter

built into one device attached to the feed.

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SCPC L-Band Earth Station Components

Cable Rx RG6 75, Tx LMR-600-DB 50

L-Band Modem Tx/Rx 950-1450MHz 10MHz Ref to BUC DC Power to BUC FEC 1/2, 3/4, 7/8 Viterbi 19.2kbps - 512kbps BPSK/QPSK

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L-Band Earth Station

Advantage Lower Cost RFT (BUC & PLL LNB) Utilizes off-the-shelf PLL LNB’s Powers most BUC Tunable over the whole satellite spectrum

500MHz

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L-Band Earth Station

Disadvantages Cable length - max 300ft. Can not externally attenuate the Tx side. DC power on the Tx side may damage test

equipment. Need to use a DC Block or turn off DC Power on the modem.

May Require an Uplink Power Control cable.