An Integrated and Cost-Effective Simulation Tool for GNSS Space Receiver Algorithms Development

J.S. Silva, H.D. Lopes, T.R. Peres, J.M. Vasconcelos, M.M. Coimbra, P.F. Silva, P. Palomo, J. Pérez, J.A. Pulido, A. Garcia, J. Roselló

Abstract:	This paper will present an integrated and cost-effective simulation and testing tool for the design and realistic analysis and test of GNSS signal processing and navigation algorithms for space GNSS receivers, which is being developed by DEIMOS Engenharia (under ESA contract), in the frame of the GNSS Dynamics Simulator and AGGA-4 Test and Simulation Tool (GSTST) project. BACKGROUND Amongst the currently most used navigation systems are the Global Navigation Satellite Systems (GNSS) as the Global Positioning System (GPS) and the future Galileo system, currently under development by the European Union (EU) and the European Space Agency (ESA). GNSS is already being used in space missions (e.g. GOCE, Swarm, Sentinel, and MetOp, among others), not only as a navigation sensor (either for orbit determination or relative navigation) but also as a science instrument (e.g. for altimetry, global geodesy, Radio Occultation and GNSS Reflectometry applications). The AGGA-4 (Advanced GPS and Galileo ASIC) is a baseband GNSS digital signal processor targeted for space applications, being developed under ESA contract, and represents an important step towards the miniaturisation of the next generation of GNSS space instruments [1]. Amongst its main constituents are a Digital Signal Processing (DSP) core (featuring very high-speed functionalities) and a LEON2-FT microprocessor. AGGA-4 will support the processing of all current and future GPS civil signals and Galileo Open Service signals (also supporting legacy GLONASS signals and modernized GLONASS and Beidou signals) and is expected to have a very significant on a wide range of space applications. MOTIVATION Space GNSS receivers typically operate under various and often complex operational scenarios, requiring trade-off analysis early in the design stage and also in later development stages, involving extensive test campaigns and considerable resource usage (both in terms of human resources and equipment). Furthermore, advanced navigation system architectures and algorithms often require access to and control of signal processing stage parameters. Architectures in which the signal processing algorithms, the navigation functions, external sensor measurements and/or dynamics information are brought together (enabling the feedback of aiding signals to the GNSS receiver’s tracking loops) require access to internal receiver signals and configuration parameters. Although the AGGA-4 prototype is not expected to be available until end of 2013 its pinout is already known and the development activities of AGGA-4-based GNSS receivers can already start. To support this development – and as with any other development of complex GNSS architectures and algorithms – it is important to have access to Ground Support Equipment (GSE) capable of simulating realistic environments and generating representative multi-GNSS scenarios as the receiver would experience them. This is particularly critical when algorithms for the processing of currently scarce or unavailable signals (as modernized GPS signals and future Galileo signals) need to be simulated, and before key elements, as the AGGA-4, are integrated into receiver boards. Powerful (highly realistic) hardware simulators exist (as Spirent’s multi-GNSS simulation systems) that combine the dynamics of multiple GNSS satellites and the electrical characteristics of currently available and future GNSS signals to simulate the RF signal that would be receiver by a GNSS receiver’s antenna. However, their cost and complex setup (in terms of both required equipment and experience) is a considerable limitation for its use. There are other simulation tools that enable the analysis and test of receiver architectures and navigation algorithms (as the GRANADA family tools [2]), facilitating and accelerating the development and validation process. However, due to the complexity and specificity of the AGGA-4, there is currently no commercially available tool which supports the modelling or simulation of the AGGA-4. The availability of a tool that enables the analysis and test of navigation algorithms for an AGGA-4-based receiver without the need for complex and expensive hardware setups (as GNSS constellation simulators and signal generators or AGGA-4 development boards) while still keeping a high level of realism would be useful for various applications, ranging from R&D to algorithms verification. Such a tool would enable a user/researcher to develop and test navigation SW for the AGGA-4 without having to feed it with RF or digitized signals. Such capability would be a very important asset given the coming multiple constellations and signals, allowing realistic, easy, and early testing and/or prototyping of new algorithms for GNSS receivers operating in complex space environments. PROPOSED SOLUTION In the scope of the GSTST (GNSS Dynamics Simulator and AGGA-4 Test and Simulation Tool) project (funded by ESA, contract number 16831/03/NL/FF), DEIMOS Engenharia is developing an integrated simulation and testing tool for the design and realistic analysis and test of GNSS signal processing and navigation algorithms for AGGA-4-based GNSS receivers. This tool will provide a relatively inexpensive solution (when compared to currently available hardware-based solutions) for the simulation of realistic GNSS observables and measurements (as the software part of the receivers would see them). The simulator supports multiple GNSS systems and is representative of a subset of relevant AGGA-4 features and functionalities (e.g. multi-antenna support, Aiding Unit, among others). It consists of four main modules: a Reference Dynamics Simulator, a Propagation Channel Model, a GNSS Receiver Simulator (which will model the AGGA-4 GNSS Core modules), and Software Under Test (SWUT) Test-Bed. It was developed in MATLAB/Simulink (based on the commercially available GRANADA FCM Blockset [3] [4], Developed by DEIMOS Engenharia) and integrated with a COTS LEON-2 processor emulator (TSIM, developed by Aeroflex Gaisler), allowing a user to develop navigation software targeting the AGGA-4 (e.g. in C programming language) and use the simulator to test it as if it was running on the AGGA-4 LEON-2 processor, without the need for complex and expensive setups. This paper will describe the architecture and functionalities of the simulator and present results from the verification and validation activities, which include the analysis of test algorithms applied to different space applications and environments, used to demonstrate the simulator’s applicability. REFERENCES [1] J. Roselló, P. Silvestrin, J. Heim, “AGGA-4: Core Device for GNSS Space Receivers of This Decade”, NAVITEC 2010, December 2010, ESTEC, Noordwijk, The Netherlands [2] DEIMOS Space, “GRANADA: Receiver Analysis and Design Application”, retrieved May 16, 2012, from http://www.deimos-space.com/granada/ [3] João S. Silva, et al., “The GRANADA Factored Correlator Model Blockset: A Tool for Fast GNSS Receiver Signal Processing Simulations”, NAVITEC 2008, ESTEC, Noordwijk, the Netherlands, December, 2008 [4] Tiago Peres, et al., “GRANADA Factored Correlator Model Blockset Verification using an FPGA-Based GNSS Receiver”, NAVITEC 2010, ESTEC, Noordwijk, The Netherlands, December 2010
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1951 - 1961
Cite this article:	Silva, J.S., Lopes, H.D., Peres, T.R., Vasconcelos, J.M., Coimbra, M.M., Silva, P.F., Palomo, P., Pérez, J., Pulido, J.A., Garcia, A., Roselló, J., "An Integrated and Cost-Effective Simulation Tool for GNSS Space Receiver Algorithms Development," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1951-1961.
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