Aerospace and Electronic Systems Magazine May 2018 - 60

Flexible CubeSat-Based System for Data Broadcasting

Figure 3.

Block diagram of the portable SDR user terminal.

devoted to the budget link definition since it allows to compare
the envisaged figure of merits with the ones that are reported for
similar SmallSats missions.

BROADCAST MESSAGE RECEPTION AND INTERPRETATION
In order to meet different application contexts, which may be characterized by limited availability of resources and infrastructure, a
low-cost portable terminal is considered as a receiver component.
Its main functions are the reception and the decoding of the broadcast messages. The low complexity and flexibility of the proposed
solution are achieved by the adoption of the SDR technology. The
block diagram of the designed and implemented satellite SDR portable user terminal (UT) is depicted in Figure 3. It includes three
main elements: a Circular Polarized Quadrifilar Helix Antenna, an
Airspy Mini SDR radio, and a personal computer (PC) configured
with GNU Radio software.
The D-SAT operative scenario and the impossibility of using
a rotator mechanism to point the satellite lead to the adoption of
a Quadrifilar Helix Antenna instead of a directive one. The Helix
Antenna ensures a semispherical radiation pattern characterized by
a 5 dB maximum antenna gain and half power beam-width up to
±80 deg. and circular polarization matched with D-SAT's antenna.
Despite the limited gain, the Eb/N0 value is still high enough for
correctly decoding the signal as reported in Table 1.
The selected SDR-platform is the AirSpy Mini SDR, supported
by a GNU Radio implementation on a computer. The main performance of the AirSpy Mini SDR are: a 3.5 dB Noise Figure in UHF
frequency band, a 35 dBm IIP3 RF front end amplifier, a 12-bit
Analog-to-Digital Converter with a Dynamic Range up to 80 dB; a
0.5 ppm high precision, low phase noise clock.
The PC hosts Linux operative system running GNU Radio
[15], CubeSat Space Protocol framework, and an User Interface
application that is written in C language and provides the satellite
messages to the users. Modulation and demodulation, error detection and correction, as well as clock synchronization and Doppler
compensation are performed by GNU Radio [17], [18].

tities to interface one to each other. In fact, WS architectures, data
serialization methods, Application Programming Interfaces (APIs)
are the key elements for the integration of several heterogeneous
components. A possible solution for message data exchanging
can be represented by the adoption of JavaScript Object Notation
(JSON) [20] as data serialization method. This allows to simplify
the development, integration and debugging.
In order to simplify the development, integration, and debugging, a possible solution for message data exchanging relies on
JSON [20] data serialization. Referring to Figure 1, the APIs for
Interface I1 are oriented to the message generation and enable the
transmission of the raw data to the Data Processing and Formatting Unit for the consecutive processing and formatting operations.
While APIs for Interface I2 are oriented to the message provision
and allow the Satellite MCC to get the messages that have to be
uploaded to the CubeSat.

POTENTIAL APPLICATION CONTEXTS
As described in the Introduction, the synergistic use of communication, positioning, and monitoring techniques will contribute to
determine effective solutions for major social problems while the
exploitation of "SmallSats" can significantly cut the implementation costs and improve the service availability.
The defined architecture can be adopted for the provision of
multiple services based on the distribution of messages over a
large area (e.g. alert services, traffic/transport information, advertising, etc.). Today many applications rely on data gathering,
processing, and communication and the proposed architecture,
including the set of Web services that has been developed for
interfacing the different entities and automate the message generation process, represents a baseline system that can be easily
adopted to several application contexts. This highlights the flexibility of the proposed system at service level. In addition, the
adoption of a portable Software Defined Network Receiver on
end user side to decode the messages represents a low-cost solution to receive and interpret the broadcast messages directly
from the satellite, contributing to the flexibility of the system at
receiver level.
Particularly, in the following some of the contexts which could
benefit from the adoption of the solutions that are based on the use
of the CubeSat are identified and discussed:
C

ENABLING COMMUNICATION AMONG HETEROGENEOUS
COMPONENTS: WEB SERVICE PARADIGM
A set of Web Services (WSs) [19] can be defined to automate the
interactions among the Data Source, the Data Processing and
Formatting Unit, and the Satellite MCC. WSs enable an automatic
exchange and processing of information, allowing the involved en60

Health and wellbeing. Beyond being one of the most serious
environmental issues, the atmospheric pollution has become
one of the main causes of the degradation of the quality of
life, with increased adverse effects on human health [21];
particularly, the ozone O3 can generate several negative effects on human health due to its nature of reactive oxidant
agent [22]. In this context, the proposed system could provide alert messages about the presence of Ozone in a given
area to the people that is going to cross the involved area.
Smart, green, and integrated transports. The fast response
of the SmallSats systems is indeed useful in tracking traffic
jams and provides assistance to the drivers by suggesting
alternative paths and shorter routes.

IEEE A&E SYSTEMS MAGAZINE

MAY - JUNE 2018

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine May 2018