In the field of satellite navigation technologies, and in particular for Safety-of-Life (SoL) app... more In the field of satellite navigation technologies, and in particular for Safety-of-Life (SoL) applications, great attention is given to rejection of interference. In particular, continuous wave (CW) signals represent one of the most common types of interference. A properly designed adaptive notch filter should be employed in order to remove it. Such an algorithm has been widely exploited in literature, with many variations. Most of these studies are however mainly focused on the floating point precision model, and only a few of them really consider the potential issues of a real implementation. The objective of this paper is to discuss the issues arising from fixed-point modeling and FPGA implementation of an adaptive notch filter. Previous works showed that in a complex base-band front-end, one CW interfering signal can be eliminated by means of an IIR one-pole adaptive notch filter. For the case of more than one CW, two or more filtering cells can be used in cascade. Here, a two-p...
The Software Defined Radio (SDR) technology, applied to the reception of Global Navigation Satell... more The Software Defined Radio (SDR) technology, applied to the reception of Global Navigation Satellite Signals (GNSS), allows the implementation of a positioning device with a high flexibility level. The advantage is twofold: not only the GNSS SDR receiver can be easily updated during its operational life, but it becomes an outstanding tool in prototyping innovative algorithms for signal processing and signal quality monitoring. These aspects have been the key-drivers to the implementation of the NGene fully software receiver, developed by the NavSAS group in Torino. This paper exemplifies some of the opportunities opened by SDR in the field of GNSS receivers.
This paper discusses the provision of broadband services from High Altitude Platforms (HAPs), and... more This paper discusses the provision of broadband services from High Altitude Platforms (HAPs), and analyzes a flexible communication system for HAP-based multimedia communications. Particular attention is paid to the broadband connection to high-speed trains, as the primary reference scenario addressed in the CAPANINA project, which inspired this work. The high coding gain required by this high-mobility scenario is achieved through adaptive concatenated coding schemes, while smart antennas operating with adaptive beamforming algorithms are employed at the ground stations to cope with the fast relative movement of the end-point antennas. Simulated system performance based on a one-ray Ricean fading model of the stratospheric channel show the effectiveness of the proposed approach to achieve target QoS requirements.
New GNSS tracking architectures are becoming of scientific interest since the last decade. The tr... more New GNSS tracking architectures are becoming of scientific interest since the last decade. The traditional DLL/PLL tracking-loops have been progressively substituted by KF/EKF scalar tracking and VDLL/VDFLL vector tracking methods. In this paper we will analyze in depth the performance of a KF scalar tracking and VDFLL vector in case of signal outage. Differently from papers on the same topic, we will show how the performance of a KF, when used within the tracking stage during a signal’s blockage, are strongly dependent on a proper setting of the noise covariance matrices Q and P of the system, otherwise cases of frequency false-lock can occur when the outage condition lasts for a long time. Conversely, a VDFLL vector tracking algorithm is able to provide more precise frequency and codephase’s estimations then the KF scalar in case of signal’s unavailability, but its performance relies on the navigation solution. Therefore, the effects of the PVT accuracy on the estimation of the ma...
Thanks to the improvements brought to GNSS in the last years, multipath (MP) is now one of the mo... more Thanks to the improvements brought to GNSS in the last years, multipath (MP) is now one of the more significant error sources affecting the GNSS solution, and more often than not, the dominant one. MP introduces an asymmetry in the correlation function and this shifts the zero crossing point of the discriminator S-curve. This means that due to MP, an error is introduced in the signal delay estimate which has a direct impact in the pseudorange estimate. Many methods have been proposed in literature to counteract this undesired effect, including improvements on the tracking loops and improved antenna technologies. The approach investigated in this paper is the propagation channel estimation making use of Linear Adaptive Filters (LAFs), whose theory is deeply discussed in [1]. LAFs include Least Square (LS), Least Mean Square (LMS) and Recursive Least Square (RLS) filters, which differ in terms of computational cost and convergence speed. LAFs adapt the coefficients of a FIR (Finite Im...
2013 IEEE Frontiers in Education Conference (FIE), 2013
ABSTRACT In recent years, research activities in the field of Satellite Navigation have boosted w... more ABSTRACT In recent years, research activities in the field of Satellite Navigation have boosted worldwide. At the same time, it has become evident that few educational opportunities in the field were available for students and there was a need to develop dedicated tools for hands-on sessions. To partially answer this need, the NavSAS Group has developed N-FUELS and SOPRANO. N-FUELS, a MATLAB-based signal simulator, allows students to understand the physical layer of the Global Navigation Satellite Systems (GNSS) signals and to learn how to manipulate them via software. SOPRANO, a collection of ANSI C language routines, implements the whole chain of GNSS signal elaboration in post-processing and enables testing and validation of new GNSS signal processing algorithms and architectures. Both tools are used in post-graduate courses at Politecnico di Torino with a high degree of internationalization, which opens interesting points of discussion concerning the introduction of novel educational tools able to meet the demand and the learning styles of students with different educational backgrounds and cultures
ABSTRACT This tutorial paper highlights possible issues related to the integrity and authenticati... more ABSTRACT This tutorial paper highlights possible issues related to the integrity and authentication of the GNSS position in road applications. In fact, the Global Navigation Satellite System (GNSS) community is already aware of the conceptual and practical problems related to the availability of the position integrity (i.e. position confidence, protection level) and authentication in urban scenarios. However, these issues seem not to be widely known in the Intelligent Transportation Systems (ITS) domain. These limitations need to be carefully considered and addressed in the perspective of deploying reliable and robust systems based on positioning information.
ABSTRACT The knowledge of the Cramer–Rao bound (CRB) for a given estimation problem not only give... more ABSTRACT The knowledge of the Cramer–Rao bound (CRB) for a given estimation problem not only gives a lower bound on the covariance matrix of any unbiased estimator applied to a set of observed data, but it can represent a mean for testing the suitability of given signal structures to provide the necessary information to the parameter estimation. An interesting problem is the evaluation of the CRB in the presence of pre-processing applied to the experimental data. It has been demonstrated that, in general, a linear pre-processing matrix multiplied “on the left-hand side” of the experimental data matrix (left pre-processing) can degrade the performance of any parameter estimator, unless the left pre-processing matrix fulfills proper constraints for the invariance of the pre-processors. This paper is aimed at discussing the performance degradation in parameter estimation due to pre-processing matrices applied “on the right-hand side” of the data matrix (right pre-processing), since this problem seems not to have received the due attention up to this moment, despite this kind of linear pre-processing often occurs in several application contexts in the field of the communications. The paper derives an expression of the deterministic CRB giving a very interesting insight on the structure of the processing matrices, providing the proof that a rank-deficient and/or not orthogonal matrix achieves the same CRB attainable through its full-rank and orthogonalized portion. Furthermore, the conditions upon which the formulation of the CRB for the pre-processed data corresponds to the CRB expression for the unprocessed data are expressed, giving the hypotheses that guarantee any linear pre-processor to be invariant. In order to give practical examples of the meaning and use of the pre-processing approach considered in the paper, some receiving techniques developed for direct sequence code division multiple access systems are briefly investigated and their performance in the context of the direction-of-arrival estimation are discussed on the basis of the CRB of the problem.
ABSTRACT This paper proposes a novel concept of “local integrity” suitable to Global Navigation S... more ABSTRACT This paper proposes a novel concept of “local integrity” suitable to Global Navigation Satellite System (GNSS) receivers in urban vehicular scenarios. The idea is to take into account not only the system, but also the environment nearby the receiver in its nominal conditions, exploiting the potentialities offered by a Vehicular Ad-hoc Network (VANET) infrastructure. In detail, the potential availability of multiple observations of GNSS signals, taken by different vehicles participating to a VANET, can be shared and combined in order to implement a collaborative spatial/temporal characterization and prediction of the local degradations of the GNSS signals. These concepts are intended to pave the way for the reconsideration/redefinition of the classic GNSS integrity concept, in order to overcome the major problems and limitations to its applicability in urban vehicular scenarios. The analytical development of the proposed methodology and the suitable network architecture for its implementation, as well as some validation results, are presented and discussed in the paper.
ABSTRACT The availability of realistic propagation channel models and, computationally affordable... more ABSTRACT The availability of realistic propagation channel models and, computationally affordable channel simulators are a fundamental brick to test the performance of wireless communication systems, during initial design phases. Nowadays, when fading mitigation techniques in both temporal and spatial domains attract designers' interest, such models need to convey reliable information on both spatial and temporal correlations of the fading processes affecting the transmitted signal. This paper presents a novel channel model and related channel simulator conceived for link-level simulations of point-to-point wireless outdoor communication links, wherein both the transmitter and the receiver, possibly in movement, may be equipped with an array of antennas. Physical effects of the propagation channel are taken into account, so as to generate realistic simulations of the fast and possibly frequency selective fading process affecting the transmitted signal. The structure of the channel simulator guarantees an affordable computational burden
ABSTRACT In this paper we propose a multi-channel simulator that produces a realistic time-series... more ABSTRACT In this paper we propose a multi-channel simulator that produces a realistic time-series of the fading process affecting signal transmission in satellite systems. The proposed simulator takes into account the temporal, spatial and polarization properties affecting these processes. In addition, we determine the impact on the total capacity of an application that utilizes the spatial-polarization channels for high data rate transmission system using multiple satellites. A significant drop in performance can be seen in the system as the cross polar discrimination decreases.
2013 International Conference on Localization and GNSS (ICL-GNSS), 2013
ABSTRACT This paper discusses some technical problems and proposes a solution related to the impl... more ABSTRACT This paper discusses some technical problems and proposes a solution related to the implementation of a robust switching between single-side and double-side lobe tracking modes in case of BOC modulated signals, in particular BOC(M,N), with M, N ensuremath> 1. It is demonstrated that typical group delay distortions due to wide-band front-end filters can potentially lead to code tracking biases, increasing the risk of false locks and degrading the performance of the BOC tracking loops. These effects represent also a potential problem for the coexistence of the side-lobe switching functionality with other advanced algorithms in professional-grade GNSS receivers. These practical issues are investigated and a possible solution is demonstrated by means of simulation results, considering the BOC(M,N) modulations in the Galileo E1a and E6a bandwidths
ABSTRACT The paper presents a new multipath mitigation strategy suitable to current Global Naviga... more ABSTRACT The paper presents a new multipath mitigation strategy suitable to current Global Navigation Satellite System signals (e.g. Galileo and modernized GPS), including high order Binary Offset Carrier (BOC) modulated signals. The proposed strategy differs from the other approaches in the state of the art, based on the same number of correlators (five): while the code tracking discrimination function is realized by means of a traditional closed-loop architecture based on three correlators (Early, Prompt, and Late), the multipath mitigation is implemented in open-loop, exploiting the measurements of two additional correlators not directly used in the discriminator for the code tracking loop. Simulation results are provided in order to demonstrate and validate the performance and the flexibility of the proposed strategy in three cases: CBOC(6,1,1/11) (Galileo E1 Open Service), BPSK(1) (GPS L1 C/A) and BOCc(15,2.5) (Galileo E1a-like) modulated signals.
In the field of satellite navigation technologies, and in particular for Safety-of-Life (SoL) app... more In the field of satellite navigation technologies, and in particular for Safety-of-Life (SoL) applications, great attention is given to rejection of interference. In particular, continuous wave (CW) signals represent one of the most common types of interference. A properly designed adaptive notch filter should be employed in order to remove it. Such an algorithm has been widely exploited in literature, with many variations. Most of these studies are however mainly focused on the floating point precision model, and only a few of them really consider the potential issues of a real implementation. The objective of this paper is to discuss the issues arising from fixed-point modeling and FPGA implementation of an adaptive notch filter. Previous works showed that in a complex base-band front-end, one CW interfering signal can be eliminated by means of an IIR one-pole adaptive notch filter. For the case of more than one CW, two or more filtering cells can be used in cascade. Here, a two-p...
The Software Defined Radio (SDR) technology, applied to the reception of Global Navigation Satell... more The Software Defined Radio (SDR) technology, applied to the reception of Global Navigation Satellite Signals (GNSS), allows the implementation of a positioning device with a high flexibility level. The advantage is twofold: not only the GNSS SDR receiver can be easily updated during its operational life, but it becomes an outstanding tool in prototyping innovative algorithms for signal processing and signal quality monitoring. These aspects have been the key-drivers to the implementation of the NGene fully software receiver, developed by the NavSAS group in Torino. This paper exemplifies some of the opportunities opened by SDR in the field of GNSS receivers.
This paper discusses the provision of broadband services from High Altitude Platforms (HAPs), and... more This paper discusses the provision of broadband services from High Altitude Platforms (HAPs), and analyzes a flexible communication system for HAP-based multimedia communications. Particular attention is paid to the broadband connection to high-speed trains, as the primary reference scenario addressed in the CAPANINA project, which inspired this work. The high coding gain required by this high-mobility scenario is achieved through adaptive concatenated coding schemes, while smart antennas operating with adaptive beamforming algorithms are employed at the ground stations to cope with the fast relative movement of the end-point antennas. Simulated system performance based on a one-ray Ricean fading model of the stratospheric channel show the effectiveness of the proposed approach to achieve target QoS requirements.
New GNSS tracking architectures are becoming of scientific interest since the last decade. The tr... more New GNSS tracking architectures are becoming of scientific interest since the last decade. The traditional DLL/PLL tracking-loops have been progressively substituted by KF/EKF scalar tracking and VDLL/VDFLL vector tracking methods. In this paper we will analyze in depth the performance of a KF scalar tracking and VDFLL vector in case of signal outage. Differently from papers on the same topic, we will show how the performance of a KF, when used within the tracking stage during a signal’s blockage, are strongly dependent on a proper setting of the noise covariance matrices Q and P of the system, otherwise cases of frequency false-lock can occur when the outage condition lasts for a long time. Conversely, a VDFLL vector tracking algorithm is able to provide more precise frequency and codephase’s estimations then the KF scalar in case of signal’s unavailability, but its performance relies on the navigation solution. Therefore, the effects of the PVT accuracy on the estimation of the ma...
Thanks to the improvements brought to GNSS in the last years, multipath (MP) is now one of the mo... more Thanks to the improvements brought to GNSS in the last years, multipath (MP) is now one of the more significant error sources affecting the GNSS solution, and more often than not, the dominant one. MP introduces an asymmetry in the correlation function and this shifts the zero crossing point of the discriminator S-curve. This means that due to MP, an error is introduced in the signal delay estimate which has a direct impact in the pseudorange estimate. Many methods have been proposed in literature to counteract this undesired effect, including improvements on the tracking loops and improved antenna technologies. The approach investigated in this paper is the propagation channel estimation making use of Linear Adaptive Filters (LAFs), whose theory is deeply discussed in [1]. LAFs include Least Square (LS), Least Mean Square (LMS) and Recursive Least Square (RLS) filters, which differ in terms of computational cost and convergence speed. LAFs adapt the coefficients of a FIR (Finite Im...
2013 IEEE Frontiers in Education Conference (FIE), 2013
ABSTRACT In recent years, research activities in the field of Satellite Navigation have boosted w... more ABSTRACT In recent years, research activities in the field of Satellite Navigation have boosted worldwide. At the same time, it has become evident that few educational opportunities in the field were available for students and there was a need to develop dedicated tools for hands-on sessions. To partially answer this need, the NavSAS Group has developed N-FUELS and SOPRANO. N-FUELS, a MATLAB-based signal simulator, allows students to understand the physical layer of the Global Navigation Satellite Systems (GNSS) signals and to learn how to manipulate them via software. SOPRANO, a collection of ANSI C language routines, implements the whole chain of GNSS signal elaboration in post-processing and enables testing and validation of new GNSS signal processing algorithms and architectures. Both tools are used in post-graduate courses at Politecnico di Torino with a high degree of internationalization, which opens interesting points of discussion concerning the introduction of novel educational tools able to meet the demand and the learning styles of students with different educational backgrounds and cultures
ABSTRACT This tutorial paper highlights possible issues related to the integrity and authenticati... more ABSTRACT This tutorial paper highlights possible issues related to the integrity and authentication of the GNSS position in road applications. In fact, the Global Navigation Satellite System (GNSS) community is already aware of the conceptual and practical problems related to the availability of the position integrity (i.e. position confidence, protection level) and authentication in urban scenarios. However, these issues seem not to be widely known in the Intelligent Transportation Systems (ITS) domain. These limitations need to be carefully considered and addressed in the perspective of deploying reliable and robust systems based on positioning information.
ABSTRACT The knowledge of the Cramer–Rao bound (CRB) for a given estimation problem not only give... more ABSTRACT The knowledge of the Cramer–Rao bound (CRB) for a given estimation problem not only gives a lower bound on the covariance matrix of any unbiased estimator applied to a set of observed data, but it can represent a mean for testing the suitability of given signal structures to provide the necessary information to the parameter estimation. An interesting problem is the evaluation of the CRB in the presence of pre-processing applied to the experimental data. It has been demonstrated that, in general, a linear pre-processing matrix multiplied “on the left-hand side” of the experimental data matrix (left pre-processing) can degrade the performance of any parameter estimator, unless the left pre-processing matrix fulfills proper constraints for the invariance of the pre-processors. This paper is aimed at discussing the performance degradation in parameter estimation due to pre-processing matrices applied “on the right-hand side” of the data matrix (right pre-processing), since this problem seems not to have received the due attention up to this moment, despite this kind of linear pre-processing often occurs in several application contexts in the field of the communications. The paper derives an expression of the deterministic CRB giving a very interesting insight on the structure of the processing matrices, providing the proof that a rank-deficient and/or not orthogonal matrix achieves the same CRB attainable through its full-rank and orthogonalized portion. Furthermore, the conditions upon which the formulation of the CRB for the pre-processed data corresponds to the CRB expression for the unprocessed data are expressed, giving the hypotheses that guarantee any linear pre-processor to be invariant. In order to give practical examples of the meaning and use of the pre-processing approach considered in the paper, some receiving techniques developed for direct sequence code division multiple access systems are briefly investigated and their performance in the context of the direction-of-arrival estimation are discussed on the basis of the CRB of the problem.
ABSTRACT This paper proposes a novel concept of “local integrity” suitable to Global Navigation S... more ABSTRACT This paper proposes a novel concept of “local integrity” suitable to Global Navigation Satellite System (GNSS) receivers in urban vehicular scenarios. The idea is to take into account not only the system, but also the environment nearby the receiver in its nominal conditions, exploiting the potentialities offered by a Vehicular Ad-hoc Network (VANET) infrastructure. In detail, the potential availability of multiple observations of GNSS signals, taken by different vehicles participating to a VANET, can be shared and combined in order to implement a collaborative spatial/temporal characterization and prediction of the local degradations of the GNSS signals. These concepts are intended to pave the way for the reconsideration/redefinition of the classic GNSS integrity concept, in order to overcome the major problems and limitations to its applicability in urban vehicular scenarios. The analytical development of the proposed methodology and the suitable network architecture for its implementation, as well as some validation results, are presented and discussed in the paper.
ABSTRACT The availability of realistic propagation channel models and, computationally affordable... more ABSTRACT The availability of realistic propagation channel models and, computationally affordable channel simulators are a fundamental brick to test the performance of wireless communication systems, during initial design phases. Nowadays, when fading mitigation techniques in both temporal and spatial domains attract designers' interest, such models need to convey reliable information on both spatial and temporal correlations of the fading processes affecting the transmitted signal. This paper presents a novel channel model and related channel simulator conceived for link-level simulations of point-to-point wireless outdoor communication links, wherein both the transmitter and the receiver, possibly in movement, may be equipped with an array of antennas. Physical effects of the propagation channel are taken into account, so as to generate realistic simulations of the fast and possibly frequency selective fading process affecting the transmitted signal. The structure of the channel simulator guarantees an affordable computational burden
ABSTRACT In this paper we propose a multi-channel simulator that produces a realistic time-series... more ABSTRACT In this paper we propose a multi-channel simulator that produces a realistic time-series of the fading process affecting signal transmission in satellite systems. The proposed simulator takes into account the temporal, spatial and polarization properties affecting these processes. In addition, we determine the impact on the total capacity of an application that utilizes the spatial-polarization channels for high data rate transmission system using multiple satellites. A significant drop in performance can be seen in the system as the cross polar discrimination decreases.
2013 International Conference on Localization and GNSS (ICL-GNSS), 2013
ABSTRACT This paper discusses some technical problems and proposes a solution related to the impl... more ABSTRACT This paper discusses some technical problems and proposes a solution related to the implementation of a robust switching between single-side and double-side lobe tracking modes in case of BOC modulated signals, in particular BOC(M,N), with M, N ensuremath> 1. It is demonstrated that typical group delay distortions due to wide-band front-end filters can potentially lead to code tracking biases, increasing the risk of false locks and degrading the performance of the BOC tracking loops. These effects represent also a potential problem for the coexistence of the side-lobe switching functionality with other advanced algorithms in professional-grade GNSS receivers. These practical issues are investigated and a possible solution is demonstrated by means of simulation results, considering the BOC(M,N) modulations in the Galileo E1a and E6a bandwidths
ABSTRACT The paper presents a new multipath mitigation strategy suitable to current Global Naviga... more ABSTRACT The paper presents a new multipath mitigation strategy suitable to current Global Navigation Satellite System signals (e.g. Galileo and modernized GPS), including high order Binary Offset Carrier (BOC) modulated signals. The proposed strategy differs from the other approaches in the state of the art, based on the same number of correlators (five): while the code tracking discrimination function is realized by means of a traditional closed-loop architecture based on three correlators (Early, Prompt, and Late), the multipath mitigation is implemented in open-loop, exploiting the measurements of two additional correlators not directly used in the discriminator for the code tracking loop. Simulation results are provided in order to demonstrate and validate the performance and the flexibility of the proposed strategy in three cases: CBOC(6,1,1/11) (Galileo E1 Open Service), BPSK(1) (GPS L1 C/A) and BOCc(15,2.5) (Galileo E1a-like) modulated signals.
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Papers by Emanuela Falletti