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978-1-4244-3559-3/09/$25.00 ©2009 IEEE IWSSC 2009
The ISICOM Architecture
Alessandro Vanelli-Coralli
ARCES/DEIS
Univ. of Bologna
Bologna, Italy
alessandro.vanelli@unibo.it
Giovanni E. Corazza
ARCES/DEIS
Univ. of Bologna
Bologna, Italy
giovanni.corazza@unibo.it
Michele Luglio
DIE
Univ. of Rome “Tor Vergata”
Rome, Italy
luglio@uniroma2.it
Stefano Cioni
ARCES/DEIS
Univ. of Bologna
Bologna, Italy
stefano.cioni@unibo.it
Abstract—The ISICOM concept has been defined in the
framework of the ISI Technology Platform as a mean to provide
the necessary communication infrastructure in support to the
achievement of the European Space Policy goals. In this paper,
we introduce the ISICOM Architecture: starting from the
ISICOM devised missions, we describe the founding architecture
concepts that shall be taken into consideration in the design of the
ISICOM architecture in order to meet the challenging
requirements set forth by the ISICOM missions.
I. INTRODUCTION
On September 26, 2008, the European Community adopted
the Council Resolution on "Taking forward the European
Space Policy”. The Council Resolution clearly identifies four
main priorities, in addition to Galileo and GMES, in the
implementation of the “European Space Policy”: Space and
climate change, Contribution of Space to the Lisbon Strategy,
Space and Security, Space Exploration.
Satellite Communications, integrated with Galileo and
GMES, are indicated as a mean for the implementations of the
European Space Policy priorities. In particular, satellite
communications are seen as a fundamental actor for the
realization of the two original priorities (GMES and Galileo)
and for two of the four new priorities, namely “Space and
Security” and “Contribution of Space to the Lisbon Strategy”.
In this context, the Integral Satcom Initiative Technology
Platform [1] has developed the ISICOM System concept [2-6]:
a flexible, reliable, and progressive deployable global satellite
communication infrastructure able to support the European
Space Policy implementation. The ISICOM system will play its
role in several different dimensions: in relation to GMES and
Galileo, ISICOM will provide the necessary communication
infrastructure; in relation to Space and Security ISICOM, along
with GMES and GALILEO, will represent the integrated
platform for Security Applications. On the other side, ISICOM
will be at the basis of the realization of a portfolio of self-
sustainable downstream GMES services and will be
fundamental in creating economic opportunities and
development of telecommunication services seamlessly
integrating satellite navigation, observation, and
communications combined with terrestrial networks.
In this perspective, four main ISICOM missions are
defined:
• Mission 1 : GMES and GALILO integration
o to provide a communication infrastructure to GMES
and Galileo, e.g., through high capacity Data Relay
Services, for the realization of a fully integrated
platform.
• Mission 2: Security
o to provide a reliable and trustable communication
infrastructure, integrated with GMES and Galileo,
to improve cooperation between security forces,
e.g., secure communication (IPSEC, but also
COMSEC solutions) protection of the network
against terrorism, 2 way Communication with
Mobile, fast information delivery, etc.
• Mission 3 : Emergency
o to provide a reconfigurable and dependable
communication infrastructure for emergency
applications (civil protection, search-and-rescue
teams) able to deliver all the required information in
a seamless integrated approach. E.g., repositionable
capacity (with access from any worldwide location)
for immediate availability of bandwidth/capacity on
disaster spot, 2 way Communication with Mobile,
delivery of real time re-mapping of disaster
scenarios, etc.
• Mission 4 : Telecommunication services
o to provide an heterogeneous satellite/terrestrial
communication infrastructure for ubiquitous access
to ICT services to all EU citizens, e.g., next
generation broadband access for high speed Internet
Services (in Ku, Ka), next generation 2 way
communication with mobile for evolution towards
4G, next generation DTH/DMB systems, GMES
downstream services.
To reach these objectives, the ISICOM system shall be
based on a service-oriented heterogeneous satellite and
terrestrial architecture. ISICOM will also be an integral part of
the Future Internet infrastructure.
II. ISICOM ARCHITECTURE OVERVIEW
Figure 1 gives a pictorial view of the ISICOM architecture.
Heterogeneous nodes are integrated in the ISICOM architecture
to realize a “network of the things approach”. In general, two
sets of architecture elements constitute the ISICOM
architecture: flying nodes and terrestrial nodes.
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The flying nodes consist of communication, elements fully
integrated with navigation and earth observation nodes: Geo
Stationary or GEO Synchronous Satellites (GEO/GSO),
Medium or Low orbit satellites (MEO/LEO), High Altitude
Platforms (HAPs), and Unmanned Air Vehicles (UAVs).
Satellites of different classes can be included (from very large
platforms to pico-satellites). The terrestrial infrastructure is
included as a global entity, to which some specific terrestrial
nodes must be added, such as high capacity fixed and
mobile/relocatable gateways, on-ground relays, distributed
antenna systems, institutional, professional, and consumer
communication terminals for fixed and mobile applications,
positioning devices for navigation and location based
applications, sensors devices for monitoring applications, RFID
tags, etcetera.
Broadcast
Broadband
links
Low Latency
links
Positioning
link
Ad-hoc
networking
Hot spot
Cooperative
beam forming
Satellite sensor
network
UAV fleet
HAPs fleet
NGO nodes
Navigation/positiong
systems
GEO/GSO nodes
INLs
GW
Earth Observation
INLs
Emergency Team
Mobile Broadcasting
& Broadband Broadcasting
& Broadband Access
Mobile Broadcasting
& Broadban d
Air Traffic Management
Data Relay Systems
On-ground observation
network
Broadcast
Broadband
links
Low Latency
links
Positioning
link
Ad-hoc
networking
Hot spot
Cooperative
beam forming
Satellite sensor
network
UAV fleet
HAPs fleet
NGO nodes
Navigation/positiong
systems
GEO/GSO nodes
INLs
GW
Earth Observation
INLs
Emergency Team
Mobile Broadcasting
& Broadband Broadcasting
& Broadband Access
Mobile Broadcasting
& Broadban d
Air Traffic Management
Data Relay Systems
On-ground observation
network
Figure 1 – ISICOM concept
The ISICOM nodes are organized in a multilayered
approach and communicate through Inter Node Links (INLs).
The flying infrastructure is in fact based on the “overlay
concept”. The core flying infrastructure is composed of a
limited number (e.g., 3) of GEO nodes. The GEO nodes
provide for the necessary worldwide coverage and ground-to-
space connectivity (Figure 2).
Figure 2: ISICOM Core infrastructure
Service nodes, either GEO or non-GEO elements, are added
progressively in order to support several class of services and
applications (e.g., broadcasting to mobile in S- or C-band, data
relay with LEO nodes, optical nodes for Earth Observation,
etc). Service nodes are connected to the core infrastructure
through INLs thus exploiting the core infrastructure global
coverage and do not need direct ground-to-space connectivity
(Figure 3).
Figure 3: Addition of service satellites to the ISICOM core infrastructure
The variety of nodes present in the ISICOM architecture
allows to provide an extremely wide set of functionalities in a
incremental approach: from large coverage for broadcast
application through GEO satellites to ad-hoc hot spot coverage
through HAP/UAV constellations for fast emergency service
deployment; from broadband access for
institutional/professional services to narrowband coverage for
environmental monitoring and early warning systems. In this
scenario, ISICOM flying nodes can vary from very simple
repeater-like payload to extremely sophisticated payloads with
on-board data storage and processing capabilities for on-board
routing, network reconfigurability, etc. Data Relay and
Distributed storage and processing is also enabled in the
ISICOM architecture through high capacity INLs that connect
flying nodes.
ISICOM nodes cooperation is possible at different layers:
from the application layer, e.g., distributed storage in flying
nodes for fast data retrieval and network dependability, to the
lower layers, e.g., virtual beam forming and virtual MIMO for
coverage extension in power limited applications.
The ISICOM architecture shall meet the following
functional requirements:
• Technology agnostic communications;
• Low Latency communications;
• High spectral efficiency and data rate in the order of
100 Mbit/s for mobile applications and 1 Gbit/s for low
mobility;
• In-building penetration;
• Energy efficiency (Green Satellite);
• Fast deployment and ad-hoc coverage;
• Dependability (i.e., trustworthy system) that implies
secure, reliable and resilient to attacks;
• Connectivity for terminals moving at extremely high
speeds;
• Architecture independent and IP compliant security
solutions.
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III. ISICOM AND THE R&D DIRECTIONS
A. Space segment
ISICOM space segment will be developed according to the
following principles.
1) Multi and reconfigurable orbit systems
The ISICOM architecture shall make use of different orbits and
constellations in order to adapt the system capabilities to the
different requirements and applications, e.g., from broadcast on
wide areas to broadband on hot-spots, from global earth
observation to localized sensor networks. The deployment of
the space segment is organized into several phases according to
an incremental approach. GEO satellite are used to provide the
core infrastructure with global coverage (excluding polar
regions above 70° latitude N and below –70° latitude S) with a
simple architecture, composed of just three satellites. Two
coverage strategies are applicable: (a) the satellites positioned
over the three ocean regions (Atlantic, Pacific, and Indian),
which is the largely preferred configuration although it
maximizes propagation delay and free space losses (FSL) but
can implement full connectivity through double hop, or (b) the
satellites positioned over land masses (Europe/Africa,
Asia/Australia, and America), which minimizes delay and FSL
but must be interconnected through inter-satellite link (ISL) to
achieve full connectivity. To match user distribution
requirements the position of the satellites on the arc may not be
spaced 120° apart and in some orbital positions more than one
satellite can be installed. On-the-fly re-location of the GEO
core nodes into geo-stationary positions shall be thus enabled.
High altitude platform stations (HAPS) or unmanned aerial
vehicles (UAV) can be utilized for security, earth observation,
and communication purposes. HAPS are conceived to operate
in emergency situations (disaster or battlefield) or to provide
extra capacity in hot spots from a fixed (or almost fixed)
position in the space. From this point of view they are assumed
to be stationary as a GEO satellite, but at any geographical
position and offering a high elevation angle. Depending on the
application scenario, HAPs can be utilized as stand alone
system or integrated and interconnected with the ISICOM core
infrastructure.
2) Inter Node Links (INL)
In order to ensure a high flexibility and dependability of the
network as well as a fast and ad-hoc configuration, flying
nodes will communicate through optical INL that can reach
extremely high data rates. The high data rate required, in the
order of hundreds of Gbit/s and, in any case, larger than 20-30
Gbit/s, require the adoption of efficient optical transmission.
Existing technology shall be improved in terms of efficiency,
robustness against thermal and mechanical stress, and power
consumption.
3) Multi Frequency bands, e.g., W, Q/V, Ku/Ka, C/S
The very high data rates typical of the ISICOM services e.g.,
for image transfer in earth observation applications, require the
use of large bandwidths found in the extremely high frequency
bands, e.g., Q/V bands. On the other hand, broadband and
broadcasting communication services fully integrated with the
terrestrial networks require the use of lower frequency bands,
e.g., C/S.
4) Payloads
The ISICOM payloads will be characterized by different
capabilities according to their position in the architecture
hierarchy. In particular, the core infrastructure nodes (GEO
nodes) will be capable of providing hundreds of beams, e.g.,
through a large high Ku-band reflector, and high coverage
throughput, by exploiting frequency reuse through the beams.
A total bandwidth larger than 10 GHz will be targeted. Also,
the core nodes will be efficient in the power consumption.
Advanced on board processing techniques will be implemented
so as to provide on-board routing, hardware and software
flexibility and reconfigurability, cognitive Dynamic Spectrum
Allocation (DSA), advanced antenna systems, MIMO
communications.
5) Cooperative communications
Cooperative Communications will be considered also for the
flying nodes in order to enhance coverage energy and spectrum
efficiency efficiency through, for example, virtual beam-
forming from space-to-earth.
6) Distributed Satellite Content Management System (Proxy
in the sky)
In order to increase dependability of the network and reduce
service latency, information can be stored in a distributed proxy
system represented by flying nodes interconnected through
high capacity INLs. Distributed source coding and network
coding techniques will be explored for this scenario.
7) High dependability and reliability
Redundancy, reconfigurability, self-organization, and
cooperation concepts will be developed to increase
dependability and reliability of the ISICOM system.
8) Low Latency
Techniques and architecture choices focused on the reduction
of service latency will be implemented in the ISICOM
architecture.
B. Ground Segment
The ground segment shall encompass the following
concepts as a minimum.
1) High capacity GW
The multilayered structure of the ISICOM architecture will
produce large aggregate traffic flows that shall be dealt with by
high capacity fixed gateways.
2) Mobile and relocatable GW
Medium capacity mobile gateway able to assist network
reconfigurability shall be considered. Also, cooperative
communications and ad-hoc networking introduce the concept
of enhanced terminals that can operate as gateways in specific
situations where deployment of traditional gateways is not
possible or economic, e.g., disaster scenarios, remote areas, etc.
3) On ground Relays
A complementary ground segment shall be designed for indoor
penetration and coverage enhancement. Besides the traditional
concept of dedicated relay devices, e.g., co-located with
terrestrial base station, the concept of non-dedicated relays
embedded in enhanced fixed/mobile user terminals shall be
exploited.
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4) Distributed antenna systems
Distributed antenna systems for interference management and
coordination, beam forming and opportunistic communications
shall be included in the ISICOM architecture
5) Hybrid Access / backhaul concepts
ISICOM architecture shall support backhauling of terrestrial
networks and provide functionalities for hybrid
satellite/terrestrial access.
C. Protocol stack concepts
1) Air interface
The air interface will be designed to be spectrum and energy
efficient, flexible for reconfigurability and seamless handover
between architecture segments, robust against channel
impairments and terminal mobility, and secure.
2) Network
As a fundamental part of the Future Internet, the ISICOM
architecture will implement all-IP networking. Also, ad-hoc
networking will be enabled in order to increase system
reconfigurability to meet the identified requirements. Network
coding techniques will be adopted to improve resource usage
efficiency. For information protection, security can be ensured
implementing the IPSec mechanism, which is a protocol
operating between the IP layer and the TCP layer. In this way
security is independent on upper layer protocols, traffic
rerouting and network configuration modifications are
preserved, and both real-time and non-real-time applications
are protected.
3) Transport
P2P protocols can be envisaged for self-organized networks in
the sky between flying nodes at different levels in the ISICOM
hierarchy. Also delay tolerant network protocols shall be
designed and implemented through the entire ISICOM
architecture.
4) Resource management, Routing, QoS Control, Handover,
and Interoperability.
Resource management shall be specifically designed in order to
support energy efficient communication and dynamic resource
allocation, for example in cognitive communications
5) Network security
In a communication system security can be provided at
different layers. At MAC layer mainly authentication service is
provided, at network layer security entails data flow protection
at different levels. Also at transport and application layers
specific security services are conceived. To ensure security for
IP via satellite, a number of service requirements are identified:
confidentiality (protection from passive attacks, unauthorized
release of message content, and traffic flow analysis),
authentication (the message sender is really who he claims to
be), integrity (the message content is not modified), non-
repudiation (sender or receiver does not deny a transmitted
message), access control (limit access), and key management
and exchange (negotiate security keys between communication
entities).
6) Applications
Successful market acceptance of the ISICOM architecture is
also based on the provision of tool libraries, able to exploit all
of the ISICOM functionalities and objectives, resilient to
ISICOM specific impairments, that allow for the design of
architecture independent applications and user generated
services. In this context, the open source approach will be
strongly pursued. Content aware networks and network aware
applications will be also developed to pursue system
optimization and efficiency.
7) Cross layer optimization
In a multilayered, service-oriented architecture, cross layer
optimization plays a fundamental role in increasing energy and
spectrum efficiency and thus in meeting the ISICOM user
requirements.
8) Cooperation
Cooperative concepts will be implemented throughout the
ISICOM architecture, e.g., for virtual beam forming, virtual
coding, interference coordination, positioning, sensing (on the
ground).
D. Terminals
The integration of communication, navigation, and earth
observation segments in a single architecture, and the
consequent large variety of possible applications, call for a
large range of terminals, from very simple sensing devices to
sophisticated mobile terminal with gateway capabilities,
cooperative communication enabled and cognitive approach.
RF front-end agility and reconfigurability shall also be
implemented to allow handover between different ISICOM
segments and coverage. Smart and open source interfaces shall
be developed to allow user-to machine, user-to-network, and
machine-to-machine interaction. In particular, the following
concepts will be implemented in the system design: multi-class
terminals, flexible terminals for seamless connection to
different delivery systems, automatic RF reconfigurability,
cognitive terminals for better spectrum exploitation through
DSA and environmental aware communications; cooperative
devices for energy efficiency, system and coverage
reconfigurability, emergency applications, etc; multi-hop
terminals; sensors devices with light payload protocol support
for multiple applications, e.g. environmental and health
monitoring.
IV. CONCLUSIONS
The above description contains a fairly wide list of concepts
and requirements that shall be implemented in order to provide
an efficient, flexible, and reconfigurable architecture able to
provide the necessary communication infrastructure in support
to the European Space Policy goals. In this framework, the
Integral Satcom Initiative Technology Platform is coordinating
the roadmap definition for the development of the concepts
reported in this paper with the aim of creating the building
blocks of the ISICOM Vision.
ACKNOWLEDGMENT
The concepts expressed in this paper represent the Authors
views and not that of their Institutions and/or Companies nor
that of the ISI Technology Platform. The Authors would like to
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thanks their Colleagues from the ISI Technology Platform for
the helpful comments and suggestions.
REFERENCES
[1] www.isi-initiative.org.
[2] The ISICOM Task Force, “ISICOM Architecture”, downloadable from
www.isi-initiative.org.
[3] The ISICOM Task Force, “ISICOM User Requirements”, downloadable
from www.isi-initiative.org.
[4] The ISICOM Task Force, “ISICOM Regulation and Standardisation”,
downloadable from www.isi-initiative.org.
[5] The ISICOM Task Force, “Analysis of ISICOM Capabilities”,
downloadable from www.isi-initiative.org.
[6] The ISICOM Task Force, “ISICOM Interconnectivity”, downloadable
from www.isi-initiative.org.
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