Transcript 2009 Olin Student Projects

2010 Olin Project Idea
Keith Gendreau
[email protected]
301-286-6188
Jeff Livas
[email protected]
301-286-7289
“Solar Jujutsu” Communications
• Jutjutsu – literally the “way of yielding”,
is a martial art style that uses the
principle of using an attacker’s energy
against him/her, rather than directly
opposing it
• In this context – try to exploit sunlight or
light from another source for
communications
“Solar Jujutsu” Communications
• Key idea:
– Can we make a low power data transmitter
to send “lots” of data from the moon to the
earth using a 19th century idea enhanced
with 21st century technology?
• Applications
– Data downlink for a sensor on the moon
– 2-way link from a satellite using a cubecorner reflector painted by a laser from the
ground or another, larger satellite
“Solar Jujutsu” Communications
Power Source:
Solar constant = 1,367,700 mW/m2 coming at you
Visible!
Wavelength (microns)
(cont)
“Prior Art”
Replace this guy with a
high speed optical
modulator and an
ethernet port.
Replace this guy with a
photoreceiver and an
ethernet port..
Replacing the guy wiggling the
mirror
• Computer monitor (simple and available)
– Use simple patterns (“symbol”) to send many bits at
a time
– 2 x 2 “Checkerboard” at 1 Hz  24 rate multiplier
• This rate multiplication is almost “free” (very low cost)
• Can investigate other options:
– Voltage Controlled LCD displays (KHz Speeds?) (for
example slide displays)
– Acoustic Optical Modulators (speeds up to 100 MHz)
Replacing the guy using his
eye to see the signal on the
receive end
• Webcam (slow, but simple)
– Receive patterns and convert back to bits
• Eventually a segmented photodiode?
– Quad cell
– Linear array
Simplified Block Diagram
Mirror or optics
(collection area sets
Transmitter power)
Computer with Olin Student
software that prepares the
test pattern for
transmission, encodes it
into a pattern for the
monitor, decodes the
received pattern, and
compares received to
transmitted. Ideally
produces a BER
Computer
monitor
Sun (or lamp)
cable
Earth to Moon (“link”)
simulator
cable
Webcam
Project Summary
• Build a “Heliostat” to capture the sun
– Optional: start with a lamp or a mirror
• Bounce the light off a spatial light modulator (SLM)
– Use a computer monitor to start (find one that works well in
reflection
– May need some simple optics or telescope
• Implement a simple modulator/encoder to drive the SLM
• Use a webcam to receive
– May need some simple optics or telescope
• Implement a simple demodulator to retrieve data
• Predict link performance and compare to Laser Comm.
Optical Communications
• With an optical link it is natural to
use it for communications in
addition to ranging.
• Potentially higher capacity over
large distances than RF
communications.
• Several methods currently under
development at GSFC.
Parameter
Wavelength (µm)
Data Rate (Mbps)
Tx aperture (cm)
Rx aperture (cm)
Code Rate
receiver sensitivity (photons/bit)
BER
Output power (W)
Transmitter losses (dB)
Net prop loss (dB)
Receiver losses (dB)
Net Rx power (dBm)
Net Margin (dB)
Downlink
Uplink
1.55
900
5.00
202.50
0.80
0.775
550
40.00
5.00
0.80
100
1.50E-03
1
-3.8
-80.78
2
-52.58
0.86
100
1.50E-03
8
-3.8
-88.85
2
-51.62
0.95
There should benefits
compared to Laser Comm
• Part of project is to Quantify Benefits
– How does such a system compare to RF communication?
– How does such a system compare to laser communication?
• Total Power Efficiency
– Lasers are ~10% efficient on producing optical output from
electricity it gathers from ~25% efficient solar cells.
– Total efficiency from sun = 0.25 * 0.1 = 2.5%
– Mirrors are ~90% reflective
– Etc.
Other factors in comparison
• Angular sensitivity
– Narrow beam (optical vs RF) means more efficient
energy transfer
– BUT more precise pointing requirements
• Corner cube finesses alignment to some extent
• Mass to moon
– Do solar cells and power system with Laser weigh
more than a mirror and heliostat?
• Reliability
– Solar panels, motors, AOMs…
– Is dust an issue?
Success means:
• A proof of concept demonstration of
data transmission using an external light
source
– Start with a webcam looking at a monitor
• Estimate of possible performance and
benefits over more traditional systems
– Focus on efficiency and pointing issues
• Look at supported Data rate
• range
– Other criteria as possible: power, mass,
volume
Possible Additional Analysis
• 1) quantitative link budget analysis sensitivity, noise sources, etc
• 2) comparison with laser-based syste
• 3) Bit-error-rate performance testing
• 4) error correction coding
• 5) laser ranging (= time of flight
measurements)