1. Satellite Communications Engineering
T. Scott Parmer
Lockheed Martin
Space Systems Company

2. Who am I?
BS Materials Engineering, New Mexico Tech
General Engineer, Defense Contract Management Agency, Philadelphia, PA
Systems Engineer, Lockheed Martin IS&GS, Philadelphia, PA
MS Electrical Engineering, Villanova University
Communications Systems Engineer, Lockheed Martin SSC, Denver, CO

3. What is a Communications Systems Engineer?
Ensure that spacecraft can communicate with those back on earth
There are many variants of this central tenant – more in a bit
Fundamentals of RF circuit design, information theory, antenna design, statistics and other fields all play a part
Most of these fields are only touched on in undergraduate coarsework

4. The Decibel Most link analysis is performed using decibels (dB)
Allows the wide power ranges and multiplicative nature of the link to be quickly assessed
Decibels are a ratio, subscripts give insight into what the divisor is
10 log10(2) ≈ 3 dB i.e. a 3 dB addition is a 2x increase in power
A key measure of link performance is Signal to Noise Ratio
Unit
Relative to
dBi
Isotropic Antenna
dBW
1 Watt
dBm
1 milliwat
dB-Hz
1/Hertz
dBK
1 Kelvin

5. A key measure of link performance is Signal to Noise Ratio (SNR)
We’ll see that noise is brought in to the system or generated internally
The signal level decreases significantly when transmitted
The ratio of the signal power to the noise power determines whether we can see the signal or not
Spectral graphics

6. Time, Frequency, and Phase Domain
Add frequency domain
I’ll be using multiple representations of the same signal

7. Modulation and Waveforms
Modulation is the process of taking data and turning it in to symbols fit for transmission
RF carrier frequencies are higher than the data rate so the symbols are typically a modification of the sine wave carrier
These modifications alter the amplitude, frequency, and/or phase of the signal
Add graphic of time domain waveform and phase state diagram

8. Coding
Prior to transmission digital data is coded to add some redundancy which improves link performance
This redundancy prevents small errors from impacting the accuracy of the data transmission
A simple example of this is a Cyclic Redundancy Code (CRC)
Because the coding allows some errors to be accepted it allows the link to operate at lower SNR
This is typically a winning proposition in that we can transmit at a lower power level and still get the data through
There isn’t any free lunch however, the bandwidth efficiency decreases and some channels are bandwidth limited

9. Transmission and Antennas
Once the signal has been generated from the underlying data it is typically amplified and transmitted
Amplification takes the signal and increases the power
Solid state (transistor) and traveling wave tubes (TWT) amplifiers are typically used for space applications
Antennas are used to launch and direct the energy through free space
They take on too many forms to cover here

10. Once transmitted the signal spreads out as a spherical wave
Channel Impairments
Once transmitted the signal spreads out as a spherical wave
Free space loss is proportional to distance transmitted
From geostationary orbit it can be a loss of ~200 dB for microwave COMSAT applications
10-20 power reduction
In addition to free space atmospheric gasses and exoatmospheric plasmas can attenuate, delay, and otherwise mess with the signal

11. The larger the antenna the more signal power is collected in general
Receive Antennas
Again, receive antennas come in all shapes and sizes depending on the application
The larger the antenna the more signal power is collected in general
Larger antennas mean higher data rates in general

12. Noise Antennas receive more than just our intended signal
The atmosphere blocks some of the incoming signal and emits power of it’s own- thermal photon emmision at microwave frequencies is prevalent
The galactic background is visible at RF frequencies
Other signals can jam our intended signal
In addition to all of that the electronics that we use to receive the signal also generates thermal noise

13. Reception and Decoding
After all of our efforts the resulting signal is a tiny spec of power above the noise level
This small power is amplified up to a meaningful level and then typically digitized for final signal processing
The received signal is run through a decoding step that interprets the received symbols (from the error correction step) as bits and these are passed on
The SNR is typically set after the first amplification stage because later noise corruption is very limited

14. Link Budget Overview Item Value Units Notes Frequency 12.2 GHz Ku Band
Data Rate 36
Mbps
FEC rate
1/2
Ratio
convolutional
Symbol Rate 72
Msps
Transmit Power
120
Watts
20.8
dBW
Antenna Gain
29.2
dBi
Effective Isotropic Radiated Power (EIRP)
80.0
dBmi
Based on Intelsat G-16 at 99° W
Slant Range
40000 km
free space loss
-206.2 dB
Atmospheric Loss -2
Received Signal Strength Isotropic (RSSi)
-128.2
Receive Antenna Gain 40
Antenna Temperature K
@ 10° Elevation
LNA Noise Figure 2
LNA Noise Temp
169.6
System Temperature
205.6
Receive Site Figure of Merit (G/Tsys)
16.9
dBi/K
Boltsmann's Constant
-198.6
dBm/HzK
Signal Bandwidth
MHz
SNR
8.7
Eb/N0
11.7

15. Links That I’ve Worked On
GPS- Signal power is very important to military users who have to deal with jamming and mountainous terrain
COMSAT- Commercial satellite services relay information from site to site. Mostly integrated with internet traffic as another form of backhaul
TT&C- Basic satellite Telemetry, Tracking, and Control. Getting basic information from vehicles and telling them what to do.

16. Other Related Fields Encryption- Number and information theory centric
Space and terrestrial physics- Channel impairments are due to underlying physical phenomena
Electrical Engineering- Microwave circuit design is just high frequency analog design
Optical Engineering- Similar principals, higher frequencies
Radar- Two way link budging and different signal processing