Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3920
Sat, 24 Jul 2021 12:22:57 GMT2021-07-24T12:22:57ZOverdetermined partial resolvent kernel for generalized cylinders
http://hdl.handle.net/2117/348238
Overdetermined partial resolvent kernel for generalized cylinders
Carmona Mejías, Ángeles; Jiménez Jiménez, María José
Overdetermined partial boundary value problems are those where no data are prescribed onpart of the boundary, whereas both the values of the function and of its normal derivative aregiven on another part of the boundary. The study of the existence and uniqueness of its solutionfor finite networks involves Schrödinger operators.In the present work, we study the resolvent kernels associated with overdetermined partialboundary value problems and we express them in terms of the well-known Green operator andthe Dirichlet-to-Robin map. Moreover, we analyze their main properties and we compute themin the case of a generalized cylinder. The obtained expression involves polynomials that can beseen as a generalization of Chebyshev polynomials, and indeed, when the conductances alongaxes are constant, the expressions for the overdetermined partial resolvent kernels are given interms of second kind Chebyshev polynomials.
Thu, 01 Jul 2021 12:17:17 GMThttp://hdl.handle.net/2117/3482382021-07-01T12:17:17ZCarmona Mejías, ÁngelesJiménez Jiménez, María JoséOverdetermined partial boundary value problems are those where no data are prescribed onpart of the boundary, whereas both the values of the function and of its normal derivative aregiven on another part of the boundary. The study of the existence and uniqueness of its solutionfor finite networks involves Schrödinger operators.In the present work, we study the resolvent kernels associated with overdetermined partialboundary value problems and we express them in terms of the well-known Green operator andthe Dirichlet-to-Robin map. Moreover, we analyze their main properties and we compute themin the case of a generalized cylinder. The obtained expression involves polynomials that can beseen as a generalization of Chebyshev polynomials, and indeed, when the conductances alongaxes are constant, the expressions for the overdetermined partial resolvent kernels are given interms of second kind Chebyshev polynomials.The group inverse of circulant matrices with few parameters
http://hdl.handle.net/2117/348237
The group inverse of circulant matrices with few parameters
Encinas Bachiller, Andrés Marcos; Jiménez Jiménez, María José; Mitjana Riera, Margarida
The need of solving linear systems with circulant matrices occursin many problems related to the periodicity of that problem. This class ofsystem appears in many applications that range from numerical solution ofpartial differential equations with periodic boundary conditions, until codingtheory, statistics, time series analysis, image processing, or when we approx-imate periodic functions with splines. In spite the problem of computing thegroup inverse of a circulant matrix of order n can be considered solved froma theoretical or algebraic point of view, even for low dimensions the com-putational cost to find the solution could be very high, typically with orderO(n2).Different approches to compute the inverse of a circulant matrix have focusedon special classes of circulant matrices. For structured matrices with threeparameters the application of the FFT, leads to algorithms to solve circulantsystems with orderO(nlog2n) and moreover the proper election of circulantpreconditioners can reduce the computation to orderO(n).In this communication we present our last advances on the computation of thegroup inverse of a family of circulant matrices with four complex parameters.Specifically, we obtain analytical expressions for the coefficients of their groupinverse. This means that by just checking some relations between the fourcoefficients we can explicitly compute the coefficients of the group inverse andthere is no need to apply any numerical method to compute them. Therefore,we improve the computational cost of computing the group inverse of thisclass of matrices that, in the worst case, is now reduced to the evaluationof a polynomial. Moreover our methodology applies to both the invertibleand the singular case, the latter being computationally less expensive. Thetechniques we use are related with the solution of boundary value problemsassociated with first or second order linear difference equations and henceinvolve the evaluation of Chebyshev polynomials.
Thu, 01 Jul 2021 12:14:57 GMThttp://hdl.handle.net/2117/3482372021-07-01T12:14:57ZEncinas Bachiller, Andrés MarcosJiménez Jiménez, María JoséMitjana Riera, MargaridaThe need of solving linear systems with circulant matrices occursin many problems related to the periodicity of that problem. This class ofsystem appears in many applications that range from numerical solution ofpartial differential equations with periodic boundary conditions, until codingtheory, statistics, time series analysis, image processing, or when we approx-imate periodic functions with splines. In spite the problem of computing thegroup inverse of a circulant matrix of order n can be considered solved froma theoretical or algebraic point of view, even for low dimensions the com-putational cost to find the solution could be very high, typically with orderO(n2).Different approches to compute the inverse of a circulant matrix have focusedon special classes of circulant matrices. For structured matrices with threeparameters the application of the FFT, leads to algorithms to solve circulantsystems with orderO(nlog2n) and moreover the proper election of circulantpreconditioners can reduce the computation to orderO(n).In this communication we present our last advances on the computation of thegroup inverse of a family of circulant matrices with four complex parameters.Specifically, we obtain analytical expressions for the coefficients of their groupinverse. This means that by just checking some relations between the fourcoefficients we can explicitly compute the coefficients of the group inverse andthere is no need to apply any numerical method to compute them. Therefore,we improve the computational cost of computing the group inverse of thisclass of matrices that, in the worst case, is now reduced to the evaluationof a polynomial. Moreover our methodology applies to both the invertibleand the singular case, the latter being computationally less expensive. Thetechniques we use are related with the solution of boundary value problemsassociated with first or second order linear difference equations and henceinvolve the evaluation of Chebyshev polynomials.On spectra of symmetric Jacobi matrices
http://hdl.handle.net/2117/348236
On spectra of symmetric Jacobi matrices
Encinas Bachiller, Andrés Marcos; Jiménez Jiménez, María José
A square symmetric matrix A is said bisymmetric if AS=SA, whereS is the matrix with ones along the secondary diagonal and zeroselsewhere. We denote by J(a,b) the real symmetric Jacobi matrixwith main diagonala= (a0, a1, . . . , an) and second diagonalb=(b0, b1, . . . , bn-1). Hoschtadt and Hald proved that the spectrum ofa bisymmetric Jacobi matrix with nonnegative off-diagonal elementsdefines uniquely the matrix and they give a constructive proof of theresult. We characterize the spectra of nonnegative irreducible bisym-metric Jacobi matrices of size lees or equal 5, and we give the uniqueentries of the matrix in terms of the eigenvalues.We also parametrize the set of monic polynomials of degree n whoseroots strictly interlace a given set ¿ ofn+ 1 ordered real numbers,and we use this parametrization to characterize the symmetric Jacobimatrices realizing ¿. Our development is strongly based on the workby Hoschtadt but, instead of considering principal submatrices, we usethe above parametrization of monic polynomials interlacing ¿.
Thu, 01 Jul 2021 12:10:07 GMThttp://hdl.handle.net/2117/3482362021-07-01T12:10:07ZEncinas Bachiller, Andrés MarcosJiménez Jiménez, María JoséA square symmetric matrix A is said bisymmetric if AS=SA, whereS is the matrix with ones along the secondary diagonal and zeroselsewhere. We denote by J(a,b) the real symmetric Jacobi matrixwith main diagonala= (a0, a1, . . . , an) and second diagonalb=(b0, b1, . . . , bn-1). Hoschtadt and Hald proved that the spectrum ofa bisymmetric Jacobi matrix with nonnegative off-diagonal elementsdefines uniquely the matrix and they give a constructive proof of theresult. We characterize the spectra of nonnegative irreducible bisym-metric Jacobi matrices of size lees or equal 5, and we give the uniqueentries of the matrix in terms of the eigenvalues.We also parametrize the set of monic polynomials of degree n whoseroots strictly interlace a given set ¿ ofn+ 1 ordered real numbers,and we use this parametrization to characterize the symmetric Jacobimatrices realizing ¿. Our development is strongly based on the workby Hoschtadt but, instead of considering principal submatrices, we usethe above parametrization of monic polynomials interlacing ¿.A semi-parametric joint model for two sequential times to events and one longitudinal covariate
http://hdl.handle.net/2117/346759
A semi-parametric joint model for two sequential times to events and one longitudinal covariate
Serrat Piè, Carles; Abel Huertas, Jaime; Gómez Melis, Guadalupe
The present work proposes a joint model for two sequential times to events together with longitudinal information, as an extension of the joint model by Wolfsohn and Tsiatis (1997) for one time to event and one longitudinal variable. The model is applied to the TIBET, a clinical trial in which antiretroviral therapy interruptions guided by CD4 counts and plasma HIV-1 RNA levels in chronically HIV-1-infected patients are under evaluation. Details on the modelling strategy and the resulting estimates are given
Mon, 07 Jun 2021 15:09:04 GMThttp://hdl.handle.net/2117/3467592021-06-07T15:09:04ZSerrat Piè, CarlesAbel Huertas, JaimeGómez Melis, GuadalupeThe present work proposes a joint model for two sequential times to events together with longitudinal information, as an extension of the joint model by Wolfsohn and Tsiatis (1997) for one time to event and one longitudinal variable. The model is applied to the TIBET, a clinical trial in which antiretroviral therapy interruptions guided by CD4 counts and plasma HIV-1 RNA levels in chronically HIV-1-infected patients are under evaluation. Details on the modelling strategy and the resulting estimates are givenNetwork-based ionospheric gradient monitoring to support GBAS
http://hdl.handle.net/2117/346619
Network-based ionospheric gradient monitoring to support GBAS
Caamaño Albuerne, María; Felux, Michael; Gerbeth, Daniel; Juan Zornoza, José Miguel; González Casado, Guillermo; Sanz Subirana, Jaume
Ionospheric anomalies, like large ionospheric gradients, might produce a difference between the ionospheric error experienced bythe Ground Based Augmentation System (GBAS) reference station and the aircraft on approach. This ionospheric delay differencecould lead to hazardous position errors if undetected.For that reason, the GBAS Approach Service Types (GAST) C and D provide solutions against this threat, but the methodsemployed still face challenges by limiting the availability in certain cases, especially in regions with severe ionospheric conditions.This issue is caused by the use of very conservative ionospheric threat models derived based on the worst-ever-experiencedionospheric gradients in the relevant region. However, these worst-case gradients occur very rarely.Therefore, this paper proposes a methodology capable of detecting ionospheric gradients in real-time and estimating theirparameters in near real-time by using a wide area network of dual-frequency and multi-constellation GNSS monitoring stations.Hence, the GBAS stations could use this information to update the threat model currently applied in their algorithms, which wouldresult in an improvement of the GBAS availability in regions where it is degraded.The detection and estimation algorithm is initially theoretically explained. Then, the performance of this algorithm is evaluatedwith simulated gradients and with a real gradient, utilizing for both the real measurements recorded by a reference networkin Alaska. The synthetic gradients are simulated over the nominal real measurements from this network and all the gradientparameters are modified within their ranges in the already existing threat models. In this way, we assess the performance of ouralgorithm by comparing the differences between the known simulated gradient parameters and the parameters estimated by ouralgorithm. Additionally, we also evaluate our algorithm with one real ionospheric gradient measured by the same network inAlaska to study the differences between using simulated gradients and real gradients.
Fri, 04 Jun 2021 07:11:14 GMThttp://hdl.handle.net/2117/3466192021-06-04T07:11:14ZCaamaño Albuerne, MaríaFelux, MichaelGerbeth, DanielJuan Zornoza, José MiguelGonzález Casado, GuillermoSanz Subirana, JaumeIonospheric anomalies, like large ionospheric gradients, might produce a difference between the ionospheric error experienced bythe Ground Based Augmentation System (GBAS) reference station and the aircraft on approach. This ionospheric delay differencecould lead to hazardous position errors if undetected.For that reason, the GBAS Approach Service Types (GAST) C and D provide solutions against this threat, but the methodsemployed still face challenges by limiting the availability in certain cases, especially in regions with severe ionospheric conditions.This issue is caused by the use of very conservative ionospheric threat models derived based on the worst-ever-experiencedionospheric gradients in the relevant region. However, these worst-case gradients occur very rarely.Therefore, this paper proposes a methodology capable of detecting ionospheric gradients in real-time and estimating theirparameters in near real-time by using a wide area network of dual-frequency and multi-constellation GNSS monitoring stations.Hence, the GBAS stations could use this information to update the threat model currently applied in their algorithms, which wouldresult in an improvement of the GBAS availability in regions where it is degraded.The detection and estimation algorithm is initially theoretically explained. Then, the performance of this algorithm is evaluatedwith simulated gradients and with a real gradient, utilizing for both the real measurements recorded by a reference networkin Alaska. The synthetic gradients are simulated over the nominal real measurements from this network and all the gradientparameters are modified within their ranges in the already existing threat models. In this way, we assess the performance of ouralgorithm by comparing the differences between the known simulated gradient parameters and the parameters estimated by ouralgorithm. Additionally, we also evaluate our algorithm with one real ionospheric gradient measured by the same network inAlaska to study the differences between using simulated gradients and real gradients.Impact of Covid-19 on UPC's moodle platform and ICE's role
http://hdl.handle.net/2117/346058
Impact of Covid-19 on UPC's moodle platform and ICE's role
Prat Farran, Joana d'Arc; Llorens García, Ariadna; Alier Forment, Marc; Salvador Zuriaga, Francesc; Amo Filvà, Daniel
On March 13 2020 all the Spanish population got confined at their homes, except for those working in essential jobs. For the universities, this meant to go fully online overnight, which presented a number of challenges on the operational, didactical, and pedagogical levels. This paper is about how the Universitat Politècnica de Catalunya and, particularly, UPC’s teacher commitment reacted to the situation, making a series of decisions and actions in almost every dimension of the university activity, as seen from the point of view of the Institute of Sciences of Education (ICE), the entity in charge of the training of the professors and the management of the Learning Management System (LMS) of the University based on Moodle. This LMS plus the G-Suite, which was deployed to professors and students in just one week, became the backbone of the Virtual Learning Environment(VLE) that the University had to rely on to complete successfully the academic course. The paper takes a quantitative approach, feeding on the data logs of the VLE and making a statistical analysis
Tue, 25 May 2021 12:18:40 GMThttp://hdl.handle.net/2117/3460582021-05-25T12:18:40ZPrat Farran, Joana d'ArcLlorens García, AriadnaAlier Forment, MarcSalvador Zuriaga, FrancescAmo Filvà, DanielOn March 13 2020 all the Spanish population got confined at their homes, except for those working in essential jobs. For the universities, this meant to go fully online overnight, which presented a number of challenges on the operational, didactical, and pedagogical levels. This paper is about how the Universitat Politècnica de Catalunya and, particularly, UPC’s teacher commitment reacted to the situation, making a series of decisions and actions in almost every dimension of the university activity, as seen from the point of view of the Institute of Sciences of Education (ICE), the entity in charge of the training of the professors and the management of the Learning Management System (LMS) of the University based on Moodle. This LMS plus the G-Suite, which was deployed to professors and students in just one week, became the backbone of the Virtual Learning Environment(VLE) that the University had to rely on to complete successfully the academic course. The paper takes a quantitative approach, feeding on the data logs of the VLE and making a statistical analysisA Kinematic campaign to evaluate EGNOS 1046 maritime service
http://hdl.handle.net/2117/345371
A Kinematic campaign to evaluate EGNOS 1046 maritime service
Ibáñez Segura, Deimos; Rovira Garcia, Adrià; Sanz Subirana, Jaume; Juan Zornoza, José Miguel; González Casado, Guillermo; Alonso Alonso, María Teresa; López-Salcedo, José Antonio; Jia, Huamin; Pancorbo, Fransico Javier; García, Carlos; Martín, Irene; Abadía, Santos Rodrigo
Global Navigation Satellite Systems (GNSSs) have improved the efficiency and accuracy of transportation means. In terms of safety, the European Geostationary Navigation Overlay System (EGNOS) is providing vertical and lateral guidance to civil aviation since 2011. Furthermore, EGNOS can support applications in other sectors such as maritime, railways and road.The present contribution aims to assess the use of EGNOS for maritime navigation compliant with the International Maritime Organization (IMO) requirements established in its Resolution A.1046 (27) for harbour entrances, harbour approaches and coastal waters: 99.8% of Signal Availability, 99.8% of Service Availability, 99.97% of Service Continuity and 10 m of Horizontal Accuracy
Mon, 10 May 2021 12:11:15 GMThttp://hdl.handle.net/2117/3453712021-05-10T12:11:15ZIbáñez Segura, DeimosRovira Garcia, AdriàSanz Subirana, JaumeJuan Zornoza, José MiguelGonzález Casado, GuillermoAlonso Alonso, María TeresaLópez-Salcedo, José AntonioJia, HuaminPancorbo, Fransico JavierGarcía, CarlosMartín, IreneAbadía, Santos RodrigoGlobal Navigation Satellite Systems (GNSSs) have improved the efficiency and accuracy of transportation means. In terms of safety, the European Geostationary Navigation Overlay System (EGNOS) is providing vertical and lateral guidance to civil aviation since 2011. Furthermore, EGNOS can support applications in other sectors such as maritime, railways and road.The present contribution aims to assess the use of EGNOS for maritime navigation compliant with the International Maritime Organization (IMO) requirements established in its Resolution A.1046 (27) for harbour entrances, harbour approaches and coastal waters: 99.8% of Signal Availability, 99.8% of Service Availability, 99.97% of Service Continuity and 10 m of Horizontal AccuracyStructure-preserving and re-randomizable RCCA-secure Public Key Encryption and its applications
http://hdl.handle.net/2117/345218
Structure-preserving and re-randomizable RCCA-secure Public Key Encryption and its applications
Faonio, Antonio; Fiore, Dario; Herranz Sotoca, Javier; Ràfols, Carla
Re-randomizable RCCA-secure public key encryption (Rand-RCCA PKE) schemes reconcile the property of re-randomizability of the ciphertexts with the need of security against chosen-ciphertexts attacks. In this paper we give a new construction of a Rand-RCCA PKE scheme that is perfectly rerandomizable. Our construction is structure-preserving, can be instantiated over Type-3 pairing groups, and achieves better computation and communication efficiency than the state of the art perfectly re-randomizable schemes (e.g., Prabhakaran and Rosulek, CRYPTO’07). Next, we revive the Rand-RCCA notion showing new applications where our Rand-RCCA PKE scheme plays a fundamental part: (1) We show how to turn our scheme into a publicly-verifiable Rand-RCCA scheme; (2) We construct a malleable NIZK with a (variant of) simulation soundness that allows for re-randomizability; (3) We propose a new UC-secure Verifiable Mix-Net protocol that is secure in the common reference string model. Thanks to the structure-preserving property, all these applications are efficient. Notably, our Mix-Net protocol is the most efficient universally verifiable Mix-Net (without random oracle) where the CRS is an uniformly random string of size independent of the number of senders. The property is of the essence when such protocols are used in large scale.
Thu, 06 May 2021 09:38:12 GMThttp://hdl.handle.net/2117/3452182021-05-06T09:38:12ZFaonio, AntonioFiore, DarioHerranz Sotoca, JavierRàfols, CarlaRe-randomizable RCCA-secure public key encryption (Rand-RCCA PKE) schemes reconcile the property of re-randomizability of the ciphertexts with the need of security against chosen-ciphertexts attacks. In this paper we give a new construction of a Rand-RCCA PKE scheme that is perfectly rerandomizable. Our construction is structure-preserving, can be instantiated over Type-3 pairing groups, and achieves better computation and communication efficiency than the state of the art perfectly re-randomizable schemes (e.g., Prabhakaran and Rosulek, CRYPTO’07). Next, we revive the Rand-RCCA notion showing new applications where our Rand-RCCA PKE scheme plays a fundamental part: (1) We show how to turn our scheme into a publicly-verifiable Rand-RCCA scheme; (2) We construct a malleable NIZK with a (variant of) simulation soundness that allows for re-randomizability; (3) We propose a new UC-secure Verifiable Mix-Net protocol that is secure in the common reference string model. Thanks to the structure-preserving property, all these applications are efficient. Notably, our Mix-Net protocol is the most efficient universally verifiable Mix-Net (without random oracle) where the CRS is an uniformly random string of size independent of the number of senders. The property is of the essence when such protocols are used in large scale.RTK Feasibility Analysis for GNSS Snapshot Positioning
http://hdl.handle.net/2117/344908
RTK Feasibility Analysis for GNSS Snapshot Positioning
Liu, Xiao; Ribot, Miguel Ángel; Gusi, Adrià; Closas Gómez, Pau; Rovira Garcia, Adrià; Sanz Subirana, Jaume
With snapshot positioning becoming popular for various applications, the present contribution focuses on the feasibility
of achieving Real Time Kinematics (RTK) positioning using snapshot data, i.e. a very brief interval of the
received satellite signal. This method is termed as Snapshot RTK (SRTK). We first introduce the general workflow
of snapshot positioning and the SRTK engine functioning blocks. Their differences from traditional receivers and
challenges brought by the short duration of data are explained. Since a major difference of this positioning method
is the generation of code and carrier-phase GNSS observables, we go through this procedure in details. In order to
explore the feasibility of achieving RTK under different scenarios, the rate of Integer Ambiguity Resolution (IAR)
is assessed by using snapshot measurements generated with different integration times and signal bandwidths under
zero-baseline configuration. Under these assumptions, the key factor that influences the RTK fix rate is the code
measurement noise. Double Difference (DD) code measurement errors are evaluated and plotted together with the
resulting IAR fix rates in order to find the relationship between them. The performance of using multi-constellation
and multi-frequency signals is tested as well. The fix rate can reach 100% when multiple constellations are used. The
achieved positioning accuracy is shown to be less than 5 mm in horizontal domain when IAR is achieved successfully.
Finally, some conclusions and thoughts about future research steps on SRTK are given.
Fri, 30 Apr 2021 12:09:29 GMThttp://hdl.handle.net/2117/3449082021-04-30T12:09:29ZLiu, XiaoRibot, Miguel ÁngelGusi, AdriàClosas Gómez, PauRovira Garcia, AdriàSanz Subirana, JaumeWith snapshot positioning becoming popular for various applications, the present contribution focuses on the feasibility
of achieving Real Time Kinematics (RTK) positioning using snapshot data, i.e. a very brief interval of the
received satellite signal. This method is termed as Snapshot RTK (SRTK). We first introduce the general workflow
of snapshot positioning and the SRTK engine functioning blocks. Their differences from traditional receivers and
challenges brought by the short duration of data are explained. Since a major difference of this positioning method
is the generation of code and carrier-phase GNSS observables, we go through this procedure in details. In order to
explore the feasibility of achieving RTK under different scenarios, the rate of Integer Ambiguity Resolution (IAR)
is assessed by using snapshot measurements generated with different integration times and signal bandwidths under
zero-baseline configuration. Under these assumptions, the key factor that influences the RTK fix rate is the code
measurement noise. Double Difference (DD) code measurement errors are evaluated and plotted together with the
resulting IAR fix rates in order to find the relationship between them. The performance of using multi-constellation
and multi-frequency signals is tested as well. The fix rate can reach 100% when multiple constellations are used. The
achieved positioning accuracy is shown to be less than 5 mm in horizontal domain when IAR is achieved successfully.
Finally, some conclusions and thoughts about future research steps on SRTK are given.Ionospheric scintillation model limitations and impact in GNSS-R missions
http://hdl.handle.net/2117/344557
Ionospheric scintillation model limitations and impact in GNSS-R missions
Camps Carmona, Adriano José; González Casado, Guillermo; Juan Zornoza, José Miguel; Hyuk, Park; Barbosa, José
The ionosphere impacts radio-wave propagation, notably up to a few GHz. The main applications impacted by the ionosphere are GNSS positioning and timing, Earth Observations (especially low frequency SAR missions e.g. BIOMASS, and GNSS-R), and Space Weather. While most effects can be compensated by using dual-frequency receivers and circular polarization antennas, ionospheric scintillation (rapid intensity and phase fluctuations) cannot. Climatological models for the mean stable part of the electron density in the ionospheric layers (e.g. IRI or NeQuick) or for the magnetic field (e.g. WMM) have significantly improved in the past years. However, models of the inhomogeneous part, responsible for scintillation, can be improved, since they are based on relatively old data (e.g. WBMOD), or climatological inputs are limited to properly characterize all latitudes and solar conditions (e.g. GISM or WAM). This study first assesses the goodness of GISM, the model adopted by the ITU-R, by comparing GISM predictions and measured scintillation data. Then, the impact of measured intensity and phase scintillation on TDS-1 GNSS-R data is illustrated.
Tue, 27 Apr 2021 10:53:44 GMThttp://hdl.handle.net/2117/3445572021-04-27T10:53:44ZCamps Carmona, Adriano JoséGonzález Casado, GuillermoJuan Zornoza, José MiguelHyuk, ParkBarbosa, JoséThe ionosphere impacts radio-wave propagation, notably up to a few GHz. The main applications impacted by the ionosphere are GNSS positioning and timing, Earth Observations (especially low frequency SAR missions e.g. BIOMASS, and GNSS-R), and Space Weather. While most effects can be compensated by using dual-frequency receivers and circular polarization antennas, ionospheric scintillation (rapid intensity and phase fluctuations) cannot. Climatological models for the mean stable part of the electron density in the ionospheric layers (e.g. IRI or NeQuick) or for the magnetic field (e.g. WMM) have significantly improved in the past years. However, models of the inhomogeneous part, responsible for scintillation, can be improved, since they are based on relatively old data (e.g. WBMOD), or climatological inputs are limited to properly characterize all latitudes and solar conditions (e.g. GISM or WAM). This study first assesses the goodness of GISM, the model adopted by the ITU-R, by comparing GISM predictions and measured scintillation data. Then, the impact of measured intensity and phase scintillation on TDS-1 GNSS-R data is illustrated.