Analysis and improvement of GNSS navigation message demodulation performance in urban environments

Global Navigation Satellite Systems (GNSS) are increasingly present in our everyday life. Further operational needs are emerging, mainly in urban environments. In these obstructed environments, the signal emitted by the satellite is severely degraded due to the many obstacles. Consequently, the data demodulation and the user position calculation are difficult. GNSS signals being initially designed in an open environment context, their demodulation performance is thus generally studied in the associated AWGN propagation channel model. But nowadays, GNSS signals are also used in degraded environments. It is thus essential to provide and study their demodulation performance in urban propagation channel models. It is in this context that this PhD thesis is related, the final goal being to improve GNSS signals demodulation performance in urban areas, proposing a new signal. In order to be able to provide and study GNSS signals demodulation performance in urban environments, a simulation tool has been developed in this PhD thesis context: SiGMeP for ‘Simulator for GNSS Message Performance'. It allows simulating the entire emission/reception GNSS signal chain in urban environment. Existing and modernized signals demodulation performance has thus been computed with SiGMeP in urban environments. In order to represent this demodulation performance faithfully to reality, a new methodology adapted to urban channels is proposed in this dissertation. Then, to improve GNSS signals demodulation performance in urban environments, the research axis of this thesis has focused on the ‘Channel Coding' aspect. In order to decode the transmitted useful information, the receiver computes a detection function at the decoder input. But the detection function used in classic receivers corresponds to an AWGN propagation channel. This dissertation thus proposes an advanced detection function which is adapting to the propagation channel where the user is moving. This advanced detection function computation considerably improves demodulation performance, just in modifying the receiver part of the system. Finally, in order to design a new signal with better demodulation performance in urban environments than one of existing and future signals, a new LDPC channel code has been optimized for a CSK modulation. Indeed, the CSK modulation is a promising modulation in the spread spectrum signals world, which permits to free from limitation sin terms of data rate implied by current GNSS signals modulations

Demodulation Performance Assessment of New GNSS Signals in Urban Environments

International audienceSatellite navigation signals demodulation performance ishistorically tested and compared in the Additive WhiteGaussian Noise propagation channel model which wellsimulates the signal reception in open areas. Nowadays,the majority of new applications targets dynamic users inurban environments; therefore the GNSS signalsdemodulation performance has become mandatory to beprovided in urban environments. The GPS L1C signaldemodulation performance in urban environments is thusprovided in this paper. To do that, a new methodologyadapted to provide and assess GNSS signalsdemodulation performance in urban channels has beendeveloped. It counteracts the classic method limitationswhich are the fluctuating received C/N0 in urbanenvironments and the fact that each received message istaken into account in the error rate computation whereasin GNSS it is not necessary. The new methodology thusproposes to provide the demodulation performance for‘favorable’ reception conditions together with statisticalinformation about the occurrence of these favorablereception conditions. To be able to apply this newmethodology and to provide the GPS L1C signaldemodulation performance in urban environments, asimulator SiGMeP (Simulator for GNSS MessagePerformance) has been developed. Two urbanpropagation channel models can be tested: thenarrowband Perez-Fontan/Prieto model and the widebandDLR model. Moreover, the impact of the received signalphase estimation residual errors has been taken intoaccount (ideal estimation is compared with PLL tracking)

GNSS Signal Demodulation Performance in Urban Environments

International audienceSatellite navigation signals demodulation performance is historically tested and compared in the Additive White Gaussian Noise propagation channel model which well simulates open areas. Nowadays, the majority of new applications targets dynamic users in urban environments; therefore the implementation of a simulation tool able to provide realistically GNSS signal demodulation performance in obstructed propagation channels has become mandatory . This paper presents the simulator SiGMeP (Simulator for GNSS Message Performance) which is wanted to provide demodulation performance of any GNSS signals in urban environment , as faithfully of reality as possible . The demodulation performance of GPS L1C/A, GPS L2C, GPS L1C and Galileo E1 OS signals simulated with SiGMeP in the AWGN channel model configuration is firstly showed . Then, the demodulation performance of GPS L1C simulated with SiGMeP in urban environments is presented using the Prieto channel model with two signal carrier phase estimation configurations: perfect signal carrier phase estimation and PLL trackin

A New GNSS Integrity Monitoring Based on Channels Joint Characterization

Many GNSS (Global Navigation Satellites System) applications need high integrity performances. Receiver Autonomous Integrity Monitoring (RAIM), or similar method, is commonly used. Initially developed for aeronautics, RAIM techniques may not be fully adapted for terrestrial navigation, especially in urban environments. Those techniques use basically the pseudoranges to derive an integrity criterion. In this paper, we introduce a new integrity criterion based on the correlation quality of each channel. This quality assessment is computed from the correlation levels for each channel, all based on a single position and speed. Hence, as the so-called Direct Position Estimation (DPE), we exploit the joint behaviour of all channels to detect any incoherence at an upstream step of the processing. This Direct RAIM (D-RAIM) allows detecting possible integrity problems before it can be seen on a classical RAIM scheme that only exploits the outputs of each channel

Optimizing GNSS Navigation Data Message Decoding in Urban Environment

Nowadays, the majority of new GNSS applications targets dynamic users in urban environments; therefore the decoder input in GNSS receivers needs to be adapted to the urban propagation channel to avoid mismatched decoding when using soft input channel decoding. The aim of this paper consists thus in showing that the GNSS signals demodulation performance is significantly improved integrating an advanced soft detection function as decoder input in urban areas. This advanced detection function takes into account some a priori information on the available Channel State Information (CSI). If no CSI is available, one has to blindly adapt the detection function in order to operate close to the perfect CSI case. This will lead to avoid mismatched decoding due to, for example, the consideration by default of the Additive White Gaussian Noise (AWGN) channel for the derivation of soft inputs to be fed to soft input decoders. As a consequence the decoding performance will be improved in urban areas. The expressions of the soft decoder input function adapted for an urban environment is highly dependent on the available CSI at the receiver end. Based on different model of urban propagation channels, several CSI contexts will be considered namely perfect CSI, partial statistical CSI and no CSI. Simulation results will be given related to the GPS L1C demodulation performance with these different advanced detection function expressions in an urban environment. The results presented in this paper are valid for any kind of soft input decoders, such as Viterbi decoding for trellis based codes, the MAP/BCJR decoding for turbo-codes and the Belief Propagation decoding for LDPC codes

New GNSS Signals Demodulation Performance in Urban Environments

Satellite navigation signals demodulation performance is historically tested and compared in the Additive White Gaussian Noise propagation channel model which well simulates the signal reception in open areas. Nowadays, the majority of new applications targets dynamic users in urban environments; therefore the implementation of a simulation tool able to provide realistic GNSS signal demodulation performance in obstructed propagation channels has become mandatory. This paper presents the simulator SiGMeP (Simulator for GNSS Message Performance), which is wanted to provide demodulation performance of any GNSS signals in urban environment, as faithfully of reality as possible. The demodulation performance of GPS L1C simulated with SiGMeP in the AWGN propagation channel model, in the Prieto propagation channel model (narrowband Land Mobile Satellite model in urban configuration) and in the DLR channel model (wideband Land Mobile Satellite model in urban configuration) are computed and compared one to the other. The demodulation performance for both LMS channel models is calculated using a new methodology better adapted to urban environments, and the impact of the received signal phase estimation residual errors has been taken into account (ideal estimation is compared with PLL tracking). Finally, a refined figure of merit used to represent GNSS signals demodulation performance in urban environment is proposed

Définition de signaux et de techniques de traitement innovants pour les futurs systèmes GNSS

Global Navigation Satellite Systems (GNSS) are increasingly present in our everyday life. Further operational needs are emerging, mainly in urban environments. In these obstructed environments, the signal emitted by the satellite is severely degraded due to the many obstacles. Consequently, the data demodulation and the user position calculation are difficult. GNSS signals being initially designed in an open environment context, their demodulation performance is thus generally studied in the associated AWGN propagation channel model. But nowadays, GNSS signals are also used in degraded environments. It is thus essential to provide and study their demodulation performance in urban propagation channel models. It is in this context that this PhD thesis is related, the final goal being to improve GNSS signals demodulation performance in urban areas, proposing a new signal. In order to be able to provide and study GNSS signals demodulation performance in urban environments, a simulation tool has been developed in this PhD thesis context: SiGMeP for ‘Simulator for GNSS Message Performance’. It allows simulating the entire emission/reception GNSS signal chain in urban environment. Existing and modernized signals demodulation performance has thus been computed with SiGMeP in urban environments. In order to represent this demodulation performance faithfully to reality, a new methodology adapted to urban channels is proposed in this dissertation. Then, to improve GNSS signals demodulation performance in urban environments, the research axis of this thesis has focused on the ‘Channel Coding’ aspect. In order to decode the transmitted useful information, the receiver computes a detection function at the decoder input. But the detection function used in classic receivers corresponds to an AWGN propagation channel. This dissertation thus proposes an advanced detection function which is adapting to the propagation channel where the user is moving. This advanced detection function computation considerably improves demodulation performance, just in modifying the receiver part of the system. Finally, in order to design a new signal with better demodulation performance in urban environments than one of existing and future signals, a new LDPC channel code has been optimized for a CSK modulation. Indeed, the CSK modulation is a promising modulation in the spread spectrum signals world, which permits to free from limitation sin terms of data rate implied by current GNSS signals modulations.Les systèmes de navigation par satellites sont de plus en plus présents dans notre vie quotidienne. De nouveaux besoins émergent, majoritairement en environnement urbain. Dans ce type d’environnement très obstrué, le signal reçu par l’utilisateur a subit des atténuations ainsi que des réfractions/diffractions, ce qui rend difficile la démodulation des données et le calcul de position de l’utilisateur. Les signaux de navigation par satellites étant initialement conçus dans un contexte d’environnement dégagé, leurs performances de démodulation sont donc généralement étudiées dans le modèle de canal de propagation AWGN associé. Or aujourd’hui ils sont utilisés aussi en environnements dégradés. Il est donc indispensable de fournir et d’étudier leurs performances de démodulation dans des modèles de canal de propagation urbain. C’est dans ce contexte que s’inscrit cette thèse, le but final étant d’améliorer les performances de démodulation des signaux GNSS en milieux urbains, en proposant un nouveau signal. Afin de pouvoir fournir et analyser les performances de démodulation des signaux de navigation par satellite en milieux urbains, un outil de simulation a été développé dans le cadre de cette thèse : SiGMeP pour « Simulator for GNSS Message Performance ». Il permet de simuler la chaine entière d’émission/réception d’un signal de navigation par satellites et de calculer ses performances de démodulation en milieu urbain. Les performances de démodulation des signaux existants et modernisés ont donc été calculées avec SiGMeP en environnement urbain. Afin de représenter au mieux ces performances pour qu’elles soient le plus réalistes possibles, une nouvelle méthode adaptée au cas urbain est proposée dans ce manuscrit. Ensuite, pour améliorer ces performances de démodulation, l’axe de recherche s’est essentiellement porté sur le « codage canal ». Pour décoder l’information utile transmise, le récepteur calcule une fonction de détection à l’entrée du décodeur. Or la fonction de détection utilisée dans les récepteurs classiques correspond à un modèle de canal AWGN. Ce manuscrit propose donc une fonction de détection avancée, qui s’adapte au canal de propagation dans lequel l’utilisateur évolue, ce qui améliore considérablement les performances de démodulation, en ne modifiant que la partie récepteur du système. Enfin, dans le but de concevoir un nouveau signal avec de meilleures performances de démodulation en environnement urbain que celles des signaux existants ou futurs, un nouveau codage canal de type LDPC a été optimisé pour une modulation CSK. En effet, la modulation CSK est une modulation prometteuse dans le monde des signaux de type spectre étalé, qui permet de se débarrasser des limitations en termes de débit de données qu’impliquent les modulations actuelles des signaux de navigation par satellites

New multiplexing method to add a new signal in the Galileo E1 band

International audienceThis work addresses the problem of integrating a new signal in the Galileo E1 band. Thus, the arising question is how the existing multiplexing methods can be efficiently used or modified to integrate a new binary signal in the Galileo E1 band with the existing Galileo E1 signals. To this end, in this study, the authors first select three efficient multiplexing methods from the state of the art (i.e. interplexing, POCET and CEMIC methods) to multiplex a new Galileo signal along with the Galileo E1 legacy signals in a constant envelope modulation. Moreover, they evaluate their performance and main advantages and drawbacks. Secondly, in order to improve both performance and flexibility/adaptability of the multiplexing method, a modified CEMIC method, called ACEMIC, is proposed. This method allows to design modulations which maximise the power efficiency with respect to a given peak-to-average-power-ratio constraint. Finally, they compare the previous multiplexing methods in terms of power signal distribution, constant envelope fluctuation and power efficiency

Low Complexity Robust Data Demodulation for GNSS

International audienceIn this article, we provide closed-form approximations of log-likelihood ratio (LLR) values for direct sequence spread spectrum (DS-SS) systems over three particular scenarios, which are commonly found in the Global Navigation Satellite System (GNSS) environment. Those scenarios are the open sky with smooth variation of the signal-to-noise ratio (SNR), the additive Gaussian interference, and pulsed jamming. In most of the current communications systems, block-wise estimators are considered. However, for some applications such as GNSSs, symbol-wise estimators are available due to the low data rate. Usually, the noise variance is considered either perfectly known or available through symbol-wise estimators, leading to possible mismatched demodulation, which could induce errors in the decoding process. In this contribution, we first derive two closed-form expressions for LLRs in additive white Gaussian and Laplacian noise channels, under noise uncertainty, based on conjugate priors. Then, assuming those cases where the statistical knowledge about the estimation error is characterized by a noise variance following an inverse log-normal distribution, we derive the corresponding closed-form LLR approximations. The relevance of the proposed expressions is investigated in the context of the GPS L1C signal where the clock and ephemeris data (CED) are encoded with low-density parity-check (LDPC) codes. Then, the CED is iteratively decoded based on the belief propagation (BP) algorithm. Simulation results show significant frame error rate (FER) improvement compared to classical approaches not accounting for such uncertainty

Optimal Channel Coding Structures for Fast Acquisition Signals in Harsh Environment Conditions

International audienceIn this article, we provide the method to construct two error correcting structures for GNSS systems, which are capable to provide Maximum Distance Separable (MDS), full diversity and rate-compatible properties. Thanks to those properties, the GNSS receiver is capable to reduce the Time-To-First-Fix (TTFF) and to enhance the robustness of the data demodulation under low Carrier to Noise ratio environments, urban environments and pulsed jamming environments. The proposed error correcting structures are then simulated and compared with the GPS L1C subframe 2 error correcting scheme under the precedent transmission environments. Simulations show an outstanding improvement of the error correction capabilities (which reduce the TTFF in harsh environments) mainly caused by the rate-compatible and the full diversity properties. Moreover, thanks to the MDS property a high reduction of the TTFF under good environments is appreciated