The materials belong to the article in Journal of Radioelectronics (https://www.researchgate.net/publication/325756066_OPTICAL_INTER-SATELLITE_LINK_IN_COMPARISON_WITH_RF_CASE_IN_CUBESAT_SYSTEM) and were presented in the II SCIENTIFIC FORUM OF TELECOMMUNICATIONS: THEORY AND TECHNOLOGY TTT-2017 (Kazan, November 20 - 24, 2017).

1. Optical Inter-Satellite Links for CubeSat Satellites
05.07.2018 Page 1
Zlata Gibalina, Vladimir Fadeev
II SCIENTIFIC FORUM TELECOMMUNICATIONS: THEORY AND TECHNOLOGY TTT-2017
Kazan, November 20 - 24, 2017

2. Structure of the presentation
oIntroduction
oCubsat format
oInter-Satellite Link (ISL)
oRadio Frequency ISL
oOptical ISL
o Link budget
o Pointing, Acquisition and Tracking (PAT) system
oComparison optical and RF ISL
oConclusion
Page 2

3. INTRODUCTION: Cubesat format
• a type of miniaturized satellite for space
research, Earth observation, amateur radio
on the Low Earth Orbit
Page 3
Pic. from http://www.space.aau.dk/cubesat/
Cubesat format Dimensions, cm Mass, kg
1 U 10 x 10 x 10 1.33
1.5 U 15 x 10 x 10 2
2 U 20 x 10 x 10 2.66
3 U 30 x 10 x 10 4
6 U 30 x 20 x 10 12

4. INTRODUCTION: Inter-Satellite Link
• is a link between satellites,
which provides:
• Communication and exchanging
information directly between
satellites
• Can be a data relay to ground
Page 4
Pic. from www.slideshare.net/ajal4u/design-of-the-satellite-link

5. INTRODUCTION: Existing projects
• QB50
• RF ISL between Cubesat (90
km)
• 50 cubesats (2U, 3U)
• Thermospheric research
• Launch in 2017
• Bitrate 0.5 – 10 kbps
Page 5
• OCDN (Optical Communication and Sensor
Demonstration Program)
– the optical downlink/uplink
communication
(RF communication if optical link cant not be
established; optical ISL – 2 km)
– Two 1.5U Cubesat
– 30 cm diameter telescope located on Mt.
Wilson in southern California
– Bitrate 5-50 Mbps
– Pointing accuracy of 0.1 
Tam Nguyen, Kerri Cahoy, ’Laser Beacon Tracking for Free-space
Optical Communication on Small-Satellite Platforms in Low-Earth
Orbit’, 2015

6. RF ISL: Link budget
Page 6
Required power in dBm assuming
thermal noise:

7. OPTICAL ISL: Block diagram
Page 7
Communication
processing
electronics
Laser
diode
Optical
transmitter
Optical
receiver
Optical
detector
Communication
processing
electronics
PAT system PAT system
FREE SPACE
CHANNEL

8. OPTICAL ISL: Link budget
Page 8
𝐿 𝑟𝑥 is path loss;
𝑃𝑡𝑥 is transmit power;
𝑃𝑟𝑥 is receive power;
𝐴 𝑟𝑥 =
𝜋
4 𝑑 𝑟𝑥
2 is receive area,
𝑑 𝑟𝑥 is aperture of receiver;
R is distance between satellites;
𝜃 𝑑𝑖𝑣 is transmit beam divergence angle

9. OPTICAL ISL: Required received power
Noise variance calculation:
• PIN receiver
• APD receiver
Page 9
T – temperature, k – Planck constant, 𝑅𝑓 -
photodiode resistance, 𝑅 𝑏 - bit rate, q – electron
charge, 𝐼2 - Personick integral, 𝐼 𝑑 - dark current,
𝐼 𝐵𝐸 - base-emitter current, M – gain, F – noise
factor

10. OPTICAL ISL: Required transmit power
Page 10

11. OPTICAL ISL: Block diagram
Page 11
Communication
processing
electronics
Laser
diode
Optical
transmitter
Optical
receiver
Optical
detector
Communication
processing
electronics
PAT system PAT system
FREE SPACE
CHANNEL

12. OPTICAL ISL: PAT system
There are three modes:
1.Acquisition: compensation initial beam
pointing error due to spatial acquisition errors
from spacecraft location prediction errors.
2.Tracking: it track out local angular disturbances
transmitted from the host platform and the
dynamic elements of the payload with
submicroradian accuracy.
3.Pointing: wherein the terminal‘s optical head is
pointed towards the opposite satellite after
compensation for reactive platform motions
and finite transmit time of light.
Page 12
PAT system is developed for the NASA
OCDN project:
• pointing accuracy of 0.1.
Possible laser beam divergence:
• 2.1 mrad (0.12).
Tam Nguyen, Kerri Cahoy, ’Laser Beacon Tracking for Free-space
Optical Communication on Small-Satellite Platforms in Low-Earth
Orbit’, 2015

13. COMPARISON: RF vs Optical ISL
Page 13
Optical ISL RF ISL
Transmit
power, W
1 1
Distance, km 100 100
Received
power, dBm
a) -40.1
b) -48
a) -88.2
b) -75.5
c) -67.9
Required
receiver
sensitivity,
dBm
PIN: -52.9
APD: -65.5
-102
a) 𝜃 𝑑𝑖𝑣 = 0.2 𝑚𝑟𝑎𝑑
b) 𝜃 𝑑𝑖𝑣 = 0.5 𝑚𝑟𝑎𝑑
a) 𝑓 = 5.8 𝐺𝐻𝑧
b) 𝑓 = 25 𝐺𝐻𝑧
c) 𝑓 = 60 𝐺𝐻𝑧

14. CONCLUSION
In optical case we have lower required received power and lower
power consumption (in APD case).
However, RF case has greater margin and
does not require too much precise pointing, acquisition and tracking
and can be implemented more easily.
RF can be better solution for cubesat ISL, than optical.
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