1. 1 07/16/16
Analysis of Satellite Link Budgets (S band
downlink)

2. 2 07/16/16
Agenda
 Coverage and Service Areas
 DVB-SH system architecture
 SC and CGC
 Orbits and Orbital Mechanics
 Geosynchronous Earth Orbit (GEO)
 Inclined Orbits and its effects
 Path Losses (Free Space, Propagation)
 Hata, COST231, Walfisch-Ikegami, SUI
 O2, H2O, Precipitation effects
 Noise temperatures, G/T, sun outage effects
 F layer scintillations

3. 3 07/16/16
Agenda
 Multipath
 Rayleigh, Rician, Log-Normal channel modeling
 Inter-Satellite Interference
 Doppler Effects and Gap fillers
 Non-linear effects (Saleh Modeling)
 Choice of carrier frequency and Modulation
schemes
 OFDM vs TDM for SC

4. 4 07/16/16
Initiative
 DVB-SH system architecture solutions for 2
potential customers
 ICO
 TerraStar
 Pre-sales “capabilities demo” for Motorola

5. 5 07/16/16
The System
TDM/OFDM
TD
M
/O
FD
M
OFDMOFDM
O
FD
M
BDN
DVB-SH
broadcast
head end
C
P
Service
s
TR(a)
TR(c)
TR(b)
DVB-
SH
satellit
e
TDM mode
influenced by DVB-
S2
OFDM not suitable for
satellite downlinks!!!

6. 6 07/16/16
Assmptions
Sub-satellite point
Longitudinal
extremities of
CONUS
Median Longitude of
CONUS
CONUS

7. 7 07/16/16
Assumptions
 SC downlink – 2.1 GHz (lower S band)
 CGC downlink – 800 MHz (UHF)
 GEO orbit at 35788.925 km AMSL
 CGC employs a TR(b) class transmitter
 Uplink frequency and power is irrelevant
 The orbital plane aligns with the equatorial plane
 No Doppler shifts and TDM sync loss
 The earth is round!!!
 Geoid shape ignored

8. 8 07/16/16
SC – Satellite EIRP
All values are in
dB
Pmax – Bo,o
βAiPi
GR/T
LTj

9. 9 07/16/16
Satellite EIRP
 EIRP
 Pmax = total output power of satellite transponder
 Bo,o = Back Off at transponder output
 GR = Gain at the receiver antenna
 T = System Temperature
 GR/T = Figure of Merit
 βAiPi = Isotropic Power of the ith
carrier
 LTj = Total losses in the link received at receiver j
 Free Space loss, Ls
 Antenna Pointing losses
 Sun Outage loss
 Precipitation (Rain/Snow/Hail) loss
 Radome loss

10. 10 07/16/16
EIRP
 Effective/Equivalent Isotropic Radiated Power
 Is not a practical construction
 Isotropic Radiator distributes power evenly in a 360° steradian
solid angle
 Amount of power radiated by an “Isotropic Radiator” to produce
the required amount of power in the direction of interest
 Measured in dBW
 dB over 1 W
 Typical values range from 30 to 40 dBW

11. 11 07/16/16
Back Off
 Traveling Wave Tube Amplifiers (TWTA)
 Broadband RF channel
 Acts as a simple amplifier
 Pre-Amp and Mixers
 Converts from uplink to downlink frequency
 Non-linear characteristic
Non-linear
portion of
characteristic
Linear portion
of
characteristic

12. 12 07/16/16
Back Off
 Maximum drive power of the TWTA leads to saturation
 Efficiency at saturation is higher
 Ill effects of saturation
 Intermodulation components
 AM/AM and AM/PM effects
 Operating point needs to pushed back to the linear region of the
characteristic
 Typical value of OBO is 3 – 6 dB
Desired operating point
OBO
IBO

13. 13 07/16/16
Choice of modulation scheme
 Two popular schemes are:
 APSK
 QPSK/QAM
 QAM has a rectangular constellation map
 QPSK = 4QAM
 Non-constant modulus
 APSK has constant modulus constellation map

14. 14 07/16/16
 Input to amplifier is of the empirical form
 Output is of the form
 Saleh model parameters are used (ar, aφ, br, bφ)
Choice of modulation scheme
AM/AM Conversion AM/PM Conversion

15. 15 07/16/16
Choice of modulation scheme
 A(.) and φ(.) cause distortion in the constellation map
 Rotation along the primary axis
 Rounding along the edges
 Constellations with circular symmetry are not susceptible to
rotation or rounding!!!
 APSK class modulation schemes are preferred over QAM class
constellations
 Additional back off of 1.5 dB

16. 16 07/16/16
Free Space Loss
 Follows 1/r2 law of signal attenuation
 Largest contributor to signal attenuation
 Direct function of slant height, r
 LoS distance from receiver location to satellite
 Typical value ranges from 180 to 200 dB
Mean radius of
the earth (6378.1
km)
Mean orbital
height of GEOS
(35786 km)
Latitude of
receiver location
Long. diff. btw
receiver location
and sub-satellite
point

17. 17 07/16/16
Precipitation Loss
 Rain, Hail, Snow
 Rain is the major contributor
 Heavily frequency dependent
 More prevalent in the C, Ku and Ka bands
 Contributes to log-normal attenuation
 Raises the effective temperature and G/T
 Modeled using Mie Extinction Rate tables
 Assumed to be <2 dB overall for S band

18. 18 07/16/16
O2/H2O and F Layer
 O2 and H2O attenuation is approx. 0.1 dB in the S band
 More prevalent in Ku/Ka bands
 Ionosphere is the uppermost active layer of earth’s
atmosphere
 D (50 to 90 km), E/Es (90 to 120 km) and F (120 to 400 km)
 Ionized by solar radiation
 Frequency dependent EM propagation characteristics
 F layer splits into 2 sub-layers (F1 and F2) in the
absence of sunlight
 Acts as a refractive medium for L band and above

19. 19 07/16/16
F Layer
Wavelength
Zenith angle at
ionospheric intersection
point
Slant height to ionospheric irregularity
In F layer (about 600 km)
Irregularity autocorrelation distance
(about 1 km)
 Short term variations in refractive index cause
alternate signal fading and enhancement
 Scintillation Index modeled as a √N process
 About 2 dB in the S band

20. 20 07/16/16
Antenna Figure of Merit
 Defining characteristic of a Rx antenna
 Gain of Rx antenna, GR is offset by system noise
 Noise is introduced by thermal processes within silicon devices, metallic
connects, cables (Johnson noise)
Antenna efficiency (60%)
Carrier frequency (2.1 GHz)
Diameter of antenna dish

21. 21 07/16/16
Antenna Figure of Merit
 System Temperature, Ts
 Generates noise equivalent to Johnson noise at that
temperature
 Antenna temperature, Ta
 Ambient temperature, T0 (290 K)
 Effective temperature of receiver (with cooled pre-amp) (about
100 K)
 Ts is computed using Friis’ Equation
 Typical values of GR is 100 to 120 dB (119 dB for a 2.1
GHz channel)
 Ts is typically taken as 114 K
 Cable and other losses may be assumed to be 4 dB
 G/T values range from 20 to 26 dB

22. 22 07/16/16
Fading
 Occurs due to multipath effects
 More prevalent in urban environments where there are more
obstacles
 Multiple (and delayed) copies of the signal reach the
same receiver
 Superposition causes constructive and/or destructive
interference
 Slow vs. Fast fading
 Shadowing
 Flat vs. Frequency selective fading

23. 23 07/16/16
Fading
 Various models
 Rayleigh
 Rician
 Weibull
 Log-Normal
 Rayleigh Fading Channels
 Follow Rayleigh distribution
 Multiple scattered copies of the signal
 No dominant carrier
 Suitable to model terrestrial (CGC) links (gap filler to mobile
receiver)
 Rician Fading Channels
 Follow Rician distribution
 Multiple scattered copies of the signal
 One dominant carrier
 Suitable to model satellite to ground links (SC)

24. 24 07/16/16
Fading
 Weibull fading
 Another generalization of Rayleigh fading
 Follows a 1/kth
power law, rather than a square root law
 Is effective for both indoor as well as outdoor scenarios
 Nakagami fading
 Assumes an isotropic (360 degree) coverage of fading
environment
 k = 1 gives a Rayleigh fading characteristic

25. 25 07/16/16
Terrestrial propagation loss
 CGC faces different propagation loss characteristics
compared to SC
 Various empirical models have been developed
 Okumura-Hata (Tokyo)
 COST231
 CCIR
 COST231-Walfisch-Ikegami
 SUI
 These models account for height of cellular Tx towers,
diffraction and scattering effects
 Hata and COST231-WI models are the most commonly
used in the L and S bands
 SUI assumes mobile receivers rather than fixed gap
fillers (TR(c) receivers)

26. 26 07/16/16
Terrestrial propagation loss
 Okumura-Hata
 Originally modeled for urban areas (Tokyo)
 Works best for UHF and L band (<2 GHz) carriers
 Extended Hata and Hata-Davidson are variants
 Contain additional parameters
 Slight variants for urban and suburban regions
 COST231-WI
 European model (Stockholm)
 Works well for UHF, L and S bands
 Distinguishes between LoS and NLoS situations
 Max. cell size of 5 km
 Min. cell size of 200 m
 COST231-WI is best suited for CGC

27. 27 07/16/16
Doppler effects - CGC
 Similar to DVB-H
Shinkansen/Shanghai Maglev
TGV

28. 28 07/16/16
Doppler effects - SC
 Orbital drift
 Orbital plane at a non-zero angle w.r.t equatorial
plane
 Kepler’s Laws
 Orbit becomes elliptical rather than circular
 Velocities differ at apogee and perigee and everywhere in
between
 Typical Doppler shifts of 75 Hz observed in
simulations
 May be mitigated by increasing the bandwidth of each
subcarrier in an OFDM symbol
 Difference in slant height, r at apogee and perigee
positions mean that the signal take longer time to
reach the earth
 Effects the sync/timing system of TDM

29. 29 07/16/16
SC and OFDM
 Peak to Average Power Ratio (PAPR)
 In rare cases, all subcarriers of an OFDM symbol are
transmitted at equal and peak power
 Eg. For a 2K mode (2048 subcarriers per OFDM symbol), the
PAPR is 33 dB
 More likely (real) scenario gives a PAPR of 16 dB
 Throws the operating point well into saturation
 Intermodulation products increase system bandwidth
 TDM (from DVB-S and DVB-S2) preferred over OFDM
in DVB-SH

30. 30 07/16/16
Members

31. 31 07/16/16
Thank You