An Integrated And Cost-Effective Simulation Tool For GNSS .
An Integrated and Cost-Effective Simulation Toolfor GNSS Space Receiver Algorithms DevelopmentJoão S. Silva, Hugo D. Lopes, Tiago R. Peres, José M. Vasconcelos, Maria M. Coimbra, Pedro Freire, DEIMOS EngenhariaPedro Palomo, Juan Pérez, José A. Pulido, DEIMOS SpaceAlberto Garcia, Josep Roselló, European Space AgencyBIOGRAPHIESJoão S. Silva received his Aerospace Engineering degreefrom Instituto Superior Técnico, Portugal, in 2004. Heworked as a Research Engineer in Instituto deTelecomunicações from 2003 to 2005, when he joinedDEIMOS Engenharia, where he is currently working as aProject Manager in the GNSS Technologies Division. Hisareas of expertise focus on GNSS, including signalprocessing algorithms, systems engineering, and simulationtools.Hugo D. Lopes received his Double-Master degree inAerospace Engineering from Delft University ofTechnology, The Netherlands, and Instituto SuperiorTécnico, Portugal, in 2011. He is currently a ProjectEngineer in the GNSS Technologies Division of DEIMOSEngenharia, where he started working in December of 2011.Tiago R. Peres received his MSc degree in AerospaceEngineering from Instituto Superior Técnico, Portugal, in2008. He joined Deimos Engenharia in 2008, where he iscurrently working as a Project Engineer in the GNSSBusiness Unit. Since then, he has been involved in GNSSSignal Tracking Algorithms, Multipath MitigationTechniques, Software Simulation Tools, Digital SignalProcessing Using FPGAs and GNSS-Reflectometry.José M. Vasconcelos José F. Vasconcelos received theLicenciatura and the Ph.D. degrees in electrical engineeringfrom the Instituto Superior Técnico (IST), Lisbon, Portugal,in 2003 and 2010, respectively. Since 2009, he has been aProject Engineer with DEIMOS Engenharia’s FlightSystems Business Unit. His research interests includenonlinear observers, inertial navigation systems, rendezvous,and robust control.Maria M. Coimbra received her Aerospace Engineeringdegree from Instituto Superior Técnico, Portugal, in 2012.She is currently a Project Engineer in the GNSSTechnologies Division of DEIMOS Engenharia, where shestarted working in September of 2012. She has been activelyinvolved in EGNOS v3 and ionosphere modeling.Pedro Freire received his Aerospace Engineering degreefrom Instituto Superior Técnico, Portugal, in 2001 and sincethen has been working in receiver and navigation relatedapplications and technology. Since 2005, he has beenworking at DEIMOS Engenharia as responsible for theGNSS Technologies Division.Pedro Palomo received his MSc in Computer Science bythe UPM , Spain, in 2002. He is currently a Project Managerin the Embedded Systems Division of DEIMOS Space,where he started working in 2002. He is involved inactivities related to safety‑critical SW for real-time systemsand real-time test benches.Juan Pérez received his Bachelor Master degree inElectronics, Communications and Computer Engineeringfrom University of Alcalá, Spain, in 2012. He is currently aProject Engineer in the Embedded Systems Division ofDEIMOS Space, where he started working in 2010.José Antonio Pulido was graded with a MsC and a PhD inTelecommunications Engineering by the UPM where hespecialized in safety-critical software development. Afterthis, he joined DEIMOS Space, where he developsalgorithms in different GNSS navigation projects as well assafety-critical SW for real-time systems, such as GalileoGround Mission Segment.Alberto Garcia Alberto Garcia-Rodriguez works in theradio navigation section in ESA. He is involved in activitiesrelated to GNSS space receivers and applications. Heworked previously at GMV (Spain) for several navigationprojects. He has an MSc in TelecommunicationsEngineering from the T.U. of Madrid (1992).Josep Roselló graduated as Telecommunications Engineerfrom Polytechnic University of Catalonia in Barcelona and,in 1998, completed an MBA in Rotterdam. He started asengineer at ESA ESTEC in 1993 in the Data SystemDivision and, since 2007, has been with the Future MissionsDivision of the Earth Observation Directorate at ESTEC. Hiscurrent responsibilities include internal research and
technical management of industrial contracts, as well asinter-agency co-ordination.very significant impact on a wide range of spaceapplications.ABSTRACTMotivationAGGA-4 is a GNSS baseband signal processor for spaceapplications, developed under ESA contract, currently underproduction.Space GNSS receivers typically operate under various andoften complex operational scenarios, requiring trade-offanalysis early in the design stage and also in laterdevelopment stages, involving extensive test campaigns andconsiderable resource usage (both in terms of humanresources and equipment).Furthermore, advanced navigation system architectures andalgorithms often require access to and control of signalprocessing stage parameters. Architectures in which thesignal processing algorithms, the navigation functions,external sensor measurements and/or dynamics informationare brought together (enabling the feedback of aiding signalsto the GNSS receiver’s tracking loops) require access tointernal receiver signals and configuration parameters.In the scope of the GSTST (GNSS Dynamics Simulator andAGGA-4 Test and Simulation Tool) project (funded by ESA,contract number 16831/03/NL/FF), DEIMOS Engenharia isdeveloping an integrated simulation and testing tool for thedesign and realistic analysis and test of GNSS signalprocessing and navigation algorithms for AGGA-4-basedGNSS receivers. This tool will provide a relativelyinexpensive solution (when compared to currently availablehardware-based solutions) for the simulation of realisticGNSS observables and measurements (as the software partof the receivers would see them) as well as of the AGGA-4programming registers, allowing AGGA-4-targeted softwareto be tested without the need for the AGGA-4 chip orcomplex and expensive hardware setups.This paper describes the motivation, architecture, andfunctionalities of the GSTST and presents a couple ofapplication examples (navigation for LEO missions andtracking loop closure).INTRODUCTIONBackgroundAmongst the currently most used navigation systems are theGlobal Navigation Satellite Systems (GNSS) as the GlobalPositioning 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 anavigation sensor (either for orbit determination or relativenavigation) but also as a science instrument (e.g. foraltimetry, global geodesy, Radio Occultation and GNSSReflectometry applications). The AGGA-4 (Advanced GPSand Galileo ASIC) is a baseband GNSS digital signalprocessor targeted for space applications, being developedunder ESA contract, and represents an important steptowards the miniaturisation of the next generation of GNSSspace instruments [1]. Amongst its main constituents are aDigital Signal Processing (DSP) core (featuring very highspeed functionalities) and a LEON2-FT microprocessor.AGGA-4 will support the processing of all current and futureGPS civil signals and Galileo Open Service signals (alsosupporting legacyGLONASS signals and modernizedGLONASS and Beidou signals) and is expected to have aAlthough the AGGA-4 prototype is not expected to beavailable until 2014 its pinout is already known and thedevelopment activities of AGGA-4-based GNSS receiverscan already start. To support this development – and as withany other development of complex GNSS architectures andalgorithms – it is important to have access to GroundSupport Equipment (GSE) capable of simulating realisticenvironments and generating representative multi-GNSSscenarios as the receiver would experience them. This isparticularly critical when algorithms for the processing ofcurrently scarce or unavailable signals (as modernized GPSsignals and future Galileo signals) need to be simulated, andbefore key elements, as the AGGA-4, are integrated intoreceiver boards.Powerful (highly realistic) hardware simulators exist (asSpirent’s multi-GNSS simulation systems) that combine thedynamics of multiple GNSS satellites and the electricalcharacteristics of currently available and future GNSSsignals to simulate the RF signal that would be receiver by aGNSS receiver’s antenna. However, their cost and complexsetup (in terms of both required equipment and experience)is a considerable limitation for its use. There are othersimulation tools that enable the analysis and test of receiverarchitectures and navigation algorithms (as the GRANADAfamily tools [2]), facilitating and accelerating thedevelopment and validation process. However, due to thecomplexity and specificity of the AGGA-4, there is currentlyno commercially available tool which supports the modellingor simulation of the AGGA-4.The availability of a tool that enables the analysis and test ofDigital Signal Processing (DSP) and navigation algorithmsfor an AGGA-4-based receiver without the need for complexand expensive hardware setups (as GNSS constellation
simulators and signal generators or AGGA-4 developmentboards) while still keeping a high level of realism would beuseful for various applications, ranging from R&D to onboard SW development and verification. Such a tool wouldenable a user/researcher to develop and test navigation SWfor the AGGA-4 without having to own an AGGA-4-basedreceiver board or feed it with RF or digitized signals. Suchcapability would be a very important asset given the comingmultiple constellations and signals, allowing realistic, easy,and early testing and/or prototyping of new algorithms forGNSS receivers operating in complex space environments.GSTST ARCHITECTURE AND FUNCTIONALITIESIn the scope of the GSTST (GNSS Dynamics Simulator andAGGA-4 Test and Simulation Tool) project (funded by haria is developing an integrated simulation andtesting tool for the design and realistic analysis and test ofGNSS signal tracking and navigation algorithms forAGGA-4-based GNSS receivers. This tool provides arelatively inexpensive solution (when compared to currentlyavailable hardware-based solutions) for the realisticsimulation of AGGA-4 observables and measurements (asthe software part of the receivers would see them) as well asAGGA-4 programming registers (and their influence on theHW part of the receiver).Test-Bed. To bridge the gap between the (higher-level)SWUT and the AGGA-4 DSP Cores model, the GNSSReceiver Simulator also includes a Lower-Level SWSimulator which implements/simulates the required GNSSDSP algorithms (as acquisition, tracking loops, bumpjumping, lock detection, and measurement generation) forthe production of inputs for the SWUT.The separation between the algorithms that are simulated inthe Lower-Level SW Simulator and those that areimplemented in the user-developed SWUT has a certaindegree of flexibility, allowing both tracking and/ornavigation algorithms to be run in the LEON-2 ProcessorEmulator. Additionally, the GSTST also supports feedbackfrom the SWUT to the AGGA-4 DSP Cores Model, enablingthe simulation of receiver aiding.With the exception of the SWUT Test-Bed, which is basedon a Commercial-Off-The-Shelf (COTS) processor emulatorall modules are developed in MATLAB/Simulink (based onthe commercially available GRANADA GNSS Blockset,formerly GRANADA FCM Blockset [3], developed byDEIMOS Engenharia).The GSTST supports all current and modernized GPS civilsignals as well as all open service Galileo signals (asdescribed further below) and is representative of a subset ofrelevant AGGA-4 features and functionalities (e.g. multiantenna support, Aiding Unit, among others).The GSTST consists of two main modules, as (illustrated inFigure 1): the Environment Simulator module, whichsimulates the test environment/scenario, and the GNSSReceiver Simulator module, which simulates relevantAGGA-4 hardware cores (Input Modules, GNSS Core andProcessor), allowing receiver-targeted software to be tested.The Environment Simulator module is further divided intothe Reference Dynamics Simulator, which generatesreference values for the GNSS–S/C geometry (position,velocity, attitude, and angular rates, as well as geometricranges and range rates), supporting up to 4 antennas, and thePropagation Channel Model, which calculates C/N0 at thereceiver input (taking into account transmitter and receivercharacteristics and geometric effects) and computesionospheric and multipath error models.The GNSS Receiver Simulator models relevant AGGA-4DSP Cores, and allows user-developed software, theSoftware Under Test (SWUT), to be run in a realisticemulator of the AGGA-4’s LEON-2 processor, the SWUTFigure 1: High-level GSTST Architecture
The main architectural blocks and functionalities of theGSTST are described in the next sections. For additionaldetails, please refer to [11].Reference Dynamics SimulatorThe Reference Dynamics Simulator generates the GNSSsatellites positions and velocities (based on an ephemerisfile), the receiver’s position, velocity (based on actual orbitpropagation model), attitude and angular rates, as well as thecorresponding relative ranges, range rates (based on thepositions and velocities mentioned before), and relativeorientation.The Reference Dynamics Simulator module includes:A Receiver Dynamics module, which outputsspacecraft position, velocity, attitude and angular ratebased on the propagated orbit and attitude law;An Antenna Dynamics module, which outputs theposition and velocity of each receiver’s antenna basedon the position, velocity and attitude of the receiverand on the offset of the antennas relative to the centerof gravity (COG) of the spacecraft;A GNSS Satellites Dynamics module, which outputsthe GNSS satellite positions and velocities based onsatellite ephemeris and receiver COG position;A Relative Dynamics module, which outputs satellitesreceiver ranges and range rates, taking into account theGNSS satellites positions and velocities and theposition and velocity of the receiver, as well as therelative orientations between the transmitter andreceiver antennas.The GNSS satellites’ orbits are computed based on theirorbital parameters (via an ephemeris file), while the S/Corbit is numerically propagated (starting from an initial statevector based on a Two-Line-Element file) taking intoaccount gravity perturbations, Sun and Moon influence, solarradiation pressure and atmospheric drag models.Propagation Channel ModelThe Propagation Channel Model includes:A Geometric Visibility module, which determines thevisibility of the GNSS satellites with respect to thereceiver, along with ionosphere intersection points inthe Line-Of-Sight (LOS) path, if applicable (asillustrated in Figure 2);A C/N0 Computation module, which calculates theC/N0 at the receiver input taking into accounttransmitter characteristics, propagation effects,geometric effects, and receiver characteristics;A Ionosphere Model, which computes the TotalElectron Content (TEC) along the LOS path;A Multipath Model, which generates multipath inducedperturbations to the code and carrier tracking loopsbased on statistical models.For the C/N0 computation, the propagation Channel Modeltakes into account the, the Equivalent Isotropically RadiatedPower (EIRP) of the transmitted GNSS signals, the receiverantennas radiation pattern, and the transmitter-receivergeometry (visibility, range, and relative orientation).The TEC computation is based on the NeQuick Ionospheremodel [6] (thus taking into account the electron densityprofile of the Ionosphere, unlike 2-D Ionospheric models),on the receiver position (and intersection of the LOS pathwith the Ionosphere) and on the simulated date and time.The multipath perturbations are generated based onindependent stationary Gauss-Markov processes for thepseudo-range and carrier phase, defined by their steady-statestandard deviations and autocorrelation times.Figure 2: Different visibility and ionospheric intersectionscenarios (scale exaggerated for illustration purposes)AGGA-4 DSP Cores ModelThe AGGA-4 DSP Cores Model includes:An Aiding Unit, in charge of integrating frequency andfrequency rate estimates and adding them to the residualNCO rates (estimated by the tracking loops);Code and Carrier NCOs, which will integrate the rateestimates output by the Aiding Unit to produce code andcarrier phase estimates;A Correlator Outputs Model, which models the AGGA-4correlator outputs – real and imaginary Early-Early (EE),Early (E), Punctual (or Prompt, P), Late (L) and LateLate (LL) correlator outputs – based on the correlatorspacing, on the local carrier and code phase (output bythe Code and Carrier NCOs), on the geometric andpropagation characteristics of the signals (geometricranges, visibility, ionospheric delay, C/N0, and multipatherrors), and on GNSS satellites and receiver clock errors(for which models are also included).
The Correlator Outputs Model takes into account not onlythe characteristics of the AGGA 4’s Correlator Unit and theinfluence of code and carrier estimation errors, thermalnoise, and integration time on its outputs, but also variousother effects, related with other AGGA-4 modules, externalreceiver components or environment characteristics (e.g. precorrelation bandwidth, multipath, ionosphere, and GNSSsatellite and receiver clocks). The Correlator Outputs Modelis based on the FCM block of the GRANADA GNSSBlockset [3], which models the outputs of a GNSS receiver’scorrelators at the integration rate, precluding the need forsimulation rates representative of the sampling frequencyand thus considerably increasing simulation speed.The Aiding Unit, Code and Carrier NCOs and CorrelatorOutputs Model represent the hardware part of the trackingloops, whose software part is implemented AGGA-4Processor Simulator (either in the Lower-Level SWSimulator or in the SWUT).The AGGA-4 Integration Epoch (IE), Long epoch (LE) andMeasurement Epoch (ME) signals, which control theresetting of the integrators, the latching of observables, andthe interruption of the processor, are also generated.Lower-Level SW SimulatorThe Lower-Level SW Simulator module includes thefollowing sub-modules:An Acquisition Simulator, which simulates thebehavior of the acquisition algorithm (providingDoppler and code phase estimates to initialize thetracking loops);Tracking Loops, which model the receiver code andcarrier tracking algorithms, estimating code and carrierrate inputs to the NCOs based on the correlatoroutputs;A Measurement Generation module, which generatesreceiver measurements based on the receiverobservables.The Tracking Loops module of the Lower-Level SWSimulator may be replaced by software running on theSWUT Test-Bed. In such case, the remaining (AcquisitionSimulator and Measurement Generator) modules are stillimplemented in the Lower-Level SW Simulator, althoughusing the SWUT outputs dorange, carrier phase and pseudorange ratemeasurements based on the input code phase, carrier phaseand carrier rate estimates, respectively (from the trackingloop filters and NCOs). In addition, it also simulates integerambiguity resolution and generates both ambiguous andunambiguous carrier phase measurements as well asdifferential phase measurements (in the case of multiantenna simulations).SWUT Test-BedThe validation of user-developed software in flightrepresentative hardware is crucial for its reliable evaluation,allowing developers to accurately analyze and profile it inorder to have a representative idea of its performance andresource requirements, hence allowing an enhancedimplementation plan in a higher-level software project. TheSWUT Test-Bed allows such user-developed software, theSWUT (which must be developed in C programminglanguage and compiled for the LEON2 processor), to be runas if it was running on the AGGA-4’s LEON2-FT processor,having access to AGG
Positioning System (GPS) and the future Galileo system, currently under development by the European Union (EU) and the European Space Agency (ESA). dynamics of multiple GNSS satellites and the electrical GNSS is already being used in space missions (e.g. GOCE, Swarm, Sentinel, and MetOp, among others), not only as a
Cost Accounting 1.2 Objectives and Functions of Cost Accounting 1.3 Cost Accounting and Financial Accounting — Comparison 1.3 Application of Cost Accounting 1.5 Advantages of Cost Accounting 1.6 Limitations or Objections Against cost Accounting 1.7 Installation of a costing system 1.7 Concept of Cost 1.9 Cost Centre 1.10 Cost Unit 1.11 Cost .File Size: 1MB
EA 4-1 CHAPTER 4 JOB COSTING 4-1 Define cost pool, cost tracing, cost allocation, and cost-allocation base. Cost pool––a grouping of individual indirect cost items. Cost tracing––the assigning of direct costs to the chosen cost object. Cost allocation––the assigning of indirect costs to the chosen cost object. Cost-alloca
z find out total fixed cost, total variable cost, average fixed cost, average variable cost, average total cost and marginal cost. 18.1 DEFINITION OF COST AND COST FUNCTION Cost is defined as the expenditure incurred by a firm or producer to purchase or hire factors of production in order to produce a product. As you know, factors of
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Energy Modeling software and developing Life-Cycle Cost Analysis. The life-cycle cost includes the system capital cost, energy cost, system maintenance and replacement cost over a 20-year of life span. The life-cycle cost analysis provides the Present Value (PV) of annual cost and the life cycle cost, and it compares the accumulated cash flow .
III. Tabular analysis The cost of production of the selected vegetables were calculated as per the standard cost concept viz; Cost-A, Cost-B, Cost-C and tabulated for interpretation. Cost concepts: These includes cost A 1, A 2, B 1, B 2, C 1, C 2 and C 3 Cost A 1: All actual expenses
Positive overall: 1. One standard is simpler 2. Saves time and cost (no need for 3 to 4 days audits, or six monthly audits) COST SAVINGS HARPS AUDIT COST 245 GST WQA SQF Coles Annual Audit Cost 5,300 WQA Half-Yearly Audit Cost 1,800 Total Annual Cost 7,100 SQFHARPSAudit Cost 5,545 245 Total Annual Cost 5,790 COST SAVINGS
11.1 ECONOMIC COST AND PROFIT 11.1 ECONOMIC COST AND PROFIT Figure 11.1 shows two views of cost and profit. Economists measure cost as the sum of explicit costs and implicit costs, which equals opportunity cost. 11.1 ECONOMIC COST AND PROFIT Normal profit is an implicit cost. Accountants measure cost as explicit costs and accounting depreciation.
