The main objectives of the project is to develop a detailed simulation tool for complex RF payload front-ends within a system simulator.
The tool has to allow to:
- Model a large variety of signals, including most of those specified by currently popular satellite physical layer standards (e.g. DVB-S2, DVB-RCS, DVB-SH),
- Measure the effects of the payload on such signals by evaluating end-to-end performance metrics (C/(N+I), BER/FER, EVM) over specific points in the coverage area or even over the whole satellite coverage area and, if necessary along the payload chain.
In particular, the tool allows for a detailed modelling of various antenna architectures and associated beam-forming networks (e.g. active, semi-active), in combination with the rest of payload. Traditional design approaches typically address the performance assessment for the antenna system separately from that of other payload elements of the RF front-end.
During the project, a few complex RF-front-end architectures (featuring either Single-Feed-Per-Beam Antennas, or Array Fed Reflectors Antennas or Direct Radiating Array Antennas) were defined for SW validation purposes.
The tool is a time-domain waveform simulator able to evaluate the payload impact on the end-to-end signal degradation and on the overall system performance. Time-domain simulation of signal waveforms traversing the whole payload, including antennas (characterized through their far-field radiation properties) is performed.
The tool is able to evaluate the end-to-end effects of the payload on digital signals in terms of FER/BER, including the effects of antenna and advanced front-end architectures (e.g. active antennas, MPAs, etc.). In alternative to FER/BER evaluation the tool is able to evaluate SNIR degradation due to the payload (antenna included) which may shorten simulation time in some conditions.
The payload simulation tool provides an efficient interface with complementary external tools (e.g. antenna tools) to generate the Far Field Electromagnetic channel matrix covering the interesting ground area and considering all the elements (beams or feeds) of the considered antenna.
The validation process of tool, done using real measured data from different defined RF-front-end and antenna architectures, was very successful and encourages the use of the tool in real complex payload projects.
In fact the very rich set of building blocks library has allowed to easily implement and verify the selected reference payload architectures, i.e.:
- A Standard Bent Pipe Ku-Band design payload that is a typical of contemporary single conversion FSS/BSS Architectures. It incorporates around 50 transponder paths; various channels bandwidths and conversion frequencies. Simulation results have been collected and verified for: Repeater linearity AM/AM & AM/PM; Overall Repeater linear gain (CAMP at specified gain setting) and Gain (In-band & Out of band) and Group Delay (In-band) Responses.
- A Contemporary Advanced Payload – Flexible that includes a high degree of flexibility. Simulation results have been collected and verified for: phase noise impacts on system performance; impacts of transponder frequency response and non-linearities on system’s performance.
- A Contemporary Advanced Payload – Ku-band AFR. Simulation results have been collected and verified with original obtained plots for 1.5° Circular and 1.5° x 5° Elliptical Beams.
The Payload Simulation Tool (PST) for Complex RF-Front-End software is structured in layers, so to maximize the modularity and the scalability of the tool.
The simulator engine is based on Space Engineering’s Physical Layer Simulator (LiveWave), developed for the ESTEC Contract No. 18070/04/NL/US. LiveWave is a Waveform-level simulator, developed in C++ and entirely based on Windows COM components. The provided library of building blocks have been deeply upgraded and modified to meet the requirements of the new payload tool and extended with the ability to interface with MATLAB/Simulink.
The Graphic user interface (GUI) of the tool allows to:
- Define payload architectures (also called Scenarios),
- Execute a payload simulation, i.e. running the prepared scenario, in various modes: Normal, Batch, Frequency Sweeping or Monte Carlo,
- Make Reports of the obtained results in tabular and graphical form in order to analyze them
A simulation is performed adding and connecting several building blocks in the GUI according to the needed simulation topology.
The GUI converts the scenario in a script and starts the underlying simulation engine that executes the generated script. It is worth to note that the GUI and the simulation engine are independent to allow a seamless updating and upgrading of the simulator engine.
The provided Building Blocks can be classified in:
- Signal Generators (Arbitrary-waveforms source, Multi-tones, Noise-like sources),
- Modems (most recent satellite communication standards, like DVB-S2 and DVB-RCS compliant waveforms),
- Encoders/Decoders (including Turbo and LDPC encoders/decoders) Payload components (Active and semi-Active RF-front-end, HPAs, BFNs, Mixers, Filters, ADCs, PLL, etc.),
- Far-Field Emulator, providing the voltage complex transfer function between antenna ports (i.e. feeds) and the user(s) located in a given position in the coverage (i.e. in the far-field). The Far Field Matrix is built on the basis of antenna patterns either imported from external tools (e.g. GRASP) or generated by the tool itself,
- Receivers and Measurements (SNIR, EVM, BER, FER, Power, etc.), which make measurements at any point in the simulation chain or at specific coverage locations or sampling grid points,
- Real-time PST External I/F - which send or receive data from/to MATLAB/Simulink models through a TCP/IP server in order to perform co-simulations with Matlab.
The payload simulation tool SW runs on any Microsoft Windows OS (XP or newer).
The project plan is divided into the following phases:
- Definition Phase, including the tasks:
- Assessment of simulator requirements,
- Identification of Reference Payload Architectures,
- Assessment of available state-of the-art software to be used as basis for the simulation tool,
- Definition of missing modeling methodologies, on the basis of a review of the classical methods already known and employed in industry,
- Definition of simulator architecture,
- Definition of reference payload architectures to be used for validation,
- Definition of validation Plan.
- Development Phase including the tasks:
- Development of the elementary building blocks and their integration with the GUI,
- Integration of software building blocks,
- Simulator validation with respect to the selected reference,
- Payload Architectures and the final validation plan,
- Support and training to Agency staff.
The project was completed in May 2012.
The final conclusions are:
- The payload simulation tool has been implemented after a thorough assessment of the requirements and the used methodologies,
- The tool has been designed having in mind a fully modular approach, that will allow to add new simulation blocks to the building block library in a very easy way allowing, for instance the addition of new communication standards as soon as they are defined,
- The choice of converting the GUI scenario in a script has proved successful, because in this way the user can also directly use the powerful script language capabilities for building very complex scenario capable to cope with large payloads (e.g. high number of beams, amplifiers, feeds, etc.) representative of advanced multi-beam missions (e.g. hundreds of beams),
- The simulation durations and needed memory/processing resources have been proved to be comparable or competitive with the available commercial waveform simulators,
- The validation process, was performed using real measured data from different defined RF-front-end and antenna architectures (including Single-Feed-Per-Beam, Array Fed Reflectors, and Direct Radiating Arrays) used as reference payload architectures, was successful and encourages the use of the tool in real complex payload projects.