Dr. ing. M. Lisi European Space Agency – ESTEC

Special Advisor of the European Commission (marco.lisi@esa.int)

Software Defined Radio: An Enabling Technology for

Interoperability in Federated Satellite Systems

Abstract

• The paper offers an overview of recent applications of the Software Defined Radio (SDR) technology in satellite applications from a system perspective;

• Software Defined Payloads are envisioned as the next evolution step in the progress of satellite systems;

• A critical discussion of advanced payload and transponder architectures based on the exploitation of SDR is presented;

• SDR is shown to be a potentially enabling technology for achieving interoperability in Federated Satellite Systems.

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Federated Satellite Systems (FSS) Paradigm

• The FSS paradigm is based on satellites belonging to different missions, which are offering on a peer-to-peer basis some of their capabilities (e.g.: sensors, feeder link throughput, on-board memory, etc.);

• The obvious assumption is that such satellites must be able to exchange information through inter-satellite links, coping with heterogeneous waveforms, protocols and standards;

• More generally, new, adaptive payload technologies are required in order to cope with the increasing demand for reconfigurability, flexibility and responsiveness in space-based infrastructures.

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FSS Infrastructure: Key Areas and Open Issues • In order to achieve the goal of a truly interoperable,

service-oriented Federated Satellite Systems infrastructure, some key areas need to be developed: International cooperation, both in the public and the private

sector; Standardization (interfaces, metrics, procedures, protocols); Modularity (modular system architectures, modular spacecraft

design, plug-and-play subsystems, etc.); Flexibility (optical inter-satellite links, SDR payloads, active

phased-array and reconfigurable antennas, etc); Integration (wireless networks and technologies, Internet).

• Some open issues have to be addressed and resolved: Security (encryption techniques, VPN approaches,

government and commercial confidentiality, ITAR, etc.); Overall management & organization of shared resources; Liability issues.

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NASA’s Interplanetary Internet

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Role of SDR in Space Systems

• Substantial benefits are expected in the satellite industry from the introduction of general-purpose, flexible and easily reconfigurable telecommunications equipment, both for on-board and on-ground applications;

• Flexibility requirements, both in operations and w.r.t. technological evolution, explain the wide popularity of Software Defined Radios (SDR’s) in wireless communications;

• Software Defined Radio technologies can be envisioned on-board communications satellites, as a promising answer to the compelling need for reconfigurable, flexible payloads over ever longer satellite lifetimes.

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What is Software-Defined Radio?

SDR Definition: “Radios that provide software control of a variety of modulation techniques, wide-band or narrow-band operations, communications security functions such as hopping, and waveform requirements of current and evolving standards over a broad frequency range”. (SDR Forum)

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SDR Integration Tiers • Tier 0: A non-configurable hardware radio (no software

configurability); • Tier 1: A software controlled radio where limited functions are

controllable; • Tier 2: A significant proportion of the radio is software

configurable (frequency, modulation, bandwidth), but the RF front end still remains hardware based and non-reconfigurable;

• Tier 3: The “ideal “software radio, where all but antenna, LNA and RF power amplifier is software reconfigurable. This way, the radio can be said to have full programmability

• Tier 4: The ultimate software radio not only has full programmability, but it is also able to support a broad range of functions and frequencies at the same time (many commercial cellphones actually belong to this category).

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Advantages of SDR in Space Applications • SDR potential benefits include:

– OBP not strictly dependent on a particular physical layer – “Virtual” transparency of satellite to air-interfaces – Possibility to introduce new services – Possibility to update software radio payload with state-of-the-

art signal processing algorithms

• Different options are viable in the system design:

– Reconfigurability: implementation of hardware embedded functionalities soft reconfigurable.

– Reprogrammability: functionalities updated via re-programming

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On-Board SDR Applications: Call for Flexibility • Operators and manufacturers face today the need of

improved payload flexibility and performance without dramatically increasing complexity and cost.

• Operators are attracted by: – the possibility of adapting the ever-longer living satellites to

unpredictable business conditions or to crisis situations, – Spacecrafts coverage adaptability to different orbital

locations. • Manufacturers expect substantial benefits in introducing generic

payloads both for: – reducing non-recurrent design schedule/costs – decreasing parts’ count – increasing generic equipment volumes.

• The trade-off between fully customized and general purpose designs will remain.

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The Software Defined Radio Paradigm • Software Defined Radios (SDR) consist of a

collection of hardware and software technologies to reconfigure radios for multiple different communication systems.

• On-board SDR techniques may be attractive in both alleviating operational risks associated to regenerative payload, and in extending capabilities of translucent payloads.

• Regenerative satellites, based on On-Board-Processing (OBP), are known to provide better performances at the risk of a rapid obsolescence with the emersion of new transmission standards not fitting with the frozen on-board capabilities.

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Software-Defined Payloads (SDP’s)

Software Defined Payloads (SDPs) consist of on-board hardware and software technologies to in-flight reconfigure satellite payloads for multiple different communications scenarios.

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Bent-Pipe Software-Defined Payload

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Hybrid Bent-Pipe/Regenerative SDP

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SDR for On-Board TT&C Transponders

COM DEV Europe SDR TT&C Transponder, Developed under ESA ARTES Programme

Block Diagram of the SDR UHF TT&C Transceiver (ESA Study)

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SDR for On-Ground User Terminals

Block Diagram of SDR-4000, a fully software-defined commercial-off-the-shelf (COTS) platform that supports the Inmarsat BGAN (courtesy of Spectrum Signal Processing by Vecima, Canada)

ACCORD (“AutomatiC reCOnfigurable Radio for Dual-use”) Platform Architecture (ESA Study)

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SDR for GNSS Ground User Receivers

General Block Diagram of the Open Source GNSS SDR Receiver developed by the Centre Tecnològic de

Telecomunicacions de Catalunya (CTTC).

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SDR-Based Experimental Satellite Ranging

Blue plot shows ranging measurement, while black one the range prediction based on SGP4 orbital propagator, which is not able to predict local deviation from the simple model it uses.

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SDR Amateur Satellite Activities

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Conclusions

• The Software Defined Radio technology fits very well into a general trend towards more flexible, cost-effective, reconfigurable and time-responsive satellite missions;

• The introduction of Software Defined Radio (SDR) technologies on-board communications satellite is presently envisioned as a promising and likely answer to the compelling need for reconfigurable, flexible payloads over ever longer satellite lifetimes;

• Satellite communications are the prime potential beneficiary of SDR. In particular, TT&C transponders look very mature in terms of space missions, constituting a good example of plug-and-play, standardized spacecraft components;

• Satellite ground terminals, both for data communications and for GNSS positioning, are an immediate, commercially very attractive field of application of SDR, moving towards ever more integrated and versatile wireless terminals.