satellite communications basics
Post on 08-Apr-2017
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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
MEOLEO
Geostationary Satellites Uses
Broadcast Video Distant Learning Broadcast Audio Data Broadcasting Data/Voice services
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
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
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
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.
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
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
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.
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
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)
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
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
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.
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.
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
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
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.
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
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
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
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
TVRO Earth Station
Satellite Video/Audio Receiver
Antenna
IFL 950 - 1450 Rx
LNB
OMTFeed Horn
OffsetRx
Antenna
4GHz
Satellite
TVRO Television Receive Only
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.
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
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.
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
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
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.
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