Aerospace and Electronic Systems Magazine May 2018 - 59

Jayousi et al.
Table 1.

CubeSat-MCC Link Budget (Left Side) and CubeSat-SDR UT Link Budget (Right Side)
CubeSat-MCC Link Budget
Satellite Range
Elevation Angle

Down-Link

Up-Link

909.5 km

909.5 km

30 deg

30 deg

CubeSat-SDR UT Link Budget
Satellite Range

Downlink
909.5 km

Elevation Angle

30 deg

Frequency

437.5 MHz

437.5 MHz

Frequency

437.5 MHz

Transmission Rate

4,800 bps

4,800 bps

Transmission Rate

4,800 bps

Transmitter

Transmitter

Transmitted Power
Antenna Gain
Line Losses
Pointing Losses

1W

10 W

0.4 dBi

17.6 dBi

Antenna Gain

-1.7 dB

-3.9 dB

Line Losses

-3 dB

-3 dB

Channel
Polarization Loss
Atmospheric Losses

-144,4 dB

-144,4 dB

-3 dB

-3 dB

-1.8 dB

-1.8 dB

Receiver
HBPW
Figure of Merit, (G/T)

Pointing Losses

-3 dB

Path-Loss

-144,4 dB

Polarization Loss

0 dB

Atmospheric Losses

17.6 dBi

0.4 dBi

Antenna Gain

21 deg

180 deg

HBPW

-10.4 dB/K

-25.2 dB/K

Results

-1.8 dB
5 dBi
80 deg

Figure of Merit, (G/T)

-10.3 dB/K

Results

Received Isotropic Power
Eb/N0
-5

-113.5 dBm

-97.9 dBm

28.3dB

37.3 dB

Eb/N0

13.5 dB

13.5 dB

Required Eb/N0 @ BER = 10

14.8 dB

23.7 dB

Margin Eb/N0

selected and weighted. A small stilo UHF antenna ensures a quasiomnidirecitonal radiation pattern, unlike patch antennas that need
an accurate pointing. UHF Yagi antenna on-ground has quite-wide
Half Power Beam Width that simplifies satellite tracking without
excessively harming the antenna gain. The Doppler shift, the pathloss, and the atmospheric attenuation in UHF are lower with respect to the higher bands and finally the electronic components
working in UHF are cheaper. At the time of definition of the satellite components, the only radio with high reliability and extensive
flight heritage featured a GMSK modem. Even though the choice
of GMSK modulation was imposed by the availability of COTS
on-board radio for CubeSats, nonetheless the GMSK solution resulted the best for our application due to the high reliability and the
possibility to use an incoherent demodulator.
The communication subsystem main functions are: i) the transmission of a beacon signal (a continuous wave signal frequencymodulated) as tracking signal; ii) the transmission of the Telemetry
signals and the reception of Telecommand signals; iii) the reception
of the information messages from the MCC and the broadcast of
them. The link frequency value is 437.505 MHz and is coordinated
by the International Amateur Radio Union and assigned by the InMAY - JUNE 2018

-1.7 dB

Receiver

Antenna Gain

Margin Eb/N0

1W
0.4 dBi

Channel

Path-Loss

Required Eb/N0 @ BER = 10

Transmitted Power

Received Isotropic Power

-113.5 dBm
18 dB
-5

13.5 dB
4.5 dB

ternational Telecommunication Union (ITU). As for the Transport
level, the NanoCom U482C uses CubeSat Space Protocol, a small
network-layer delivery protocol based on a 32-bit header.
The satellite uses a redundant architecture so the on-board
communication is also duplicated. In order to minimize antennas
coupling, the master unit's antenna uses RCP and the back-up unit's
antenna uses LCP.
The telemetry and telecommand link between the CubeSat
and the MCC was designed according to the link budget reported
in Table 1: particularly, the values of the Figures of Merit and of
the atmospheric losses has been both derived from literature [16],
whereas the value for Line Losses and Required Eb/N0 has been
obtained from the technical datasheets of the components; this is
the reason why the value of the required Eb/N0 has been taken equal
to 13.5 db. Finally, the experimental nature of the SatAlert Mission
has pushed us to a precautionary approach against all the possible
sources of failures or performance impairments and, therefore, we
have decided to keep the margin values higher than strictly necessary; on the other hand, it is important to highlight that their reduction would have not brought any significant benefit to both space
and ground segments. As a matter of fact, a huge attention has been

IEEE A&E SYSTEMS MAGAZINE

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