23 research outputs found
Bayesian and Hybrid CramĂ©râRao Bounds for the Carrier Recovery Under Dynamic Phase Uncertain Channels
International audienceâIn this paper, we study Bayesian and hybrid CramĂ©râRao bounds (BCRB and HCRB) for the code-aided (CA), the data-aided (DA), and the non-data-aided (NDA) dynamical phase estimation of QAM modulated signals. We address the bounds derivation for both the offline scenario, for which the whole observation frame is used, and the online which only takes into account the current and the previous observations. For the CA scenario we show that the computation of the Bayesian information matrix (BIM) and of the hybrid information matrix (HIM) is NP hard. We then resort to the belief-propagation (BP) algorithm or to the BahlâCockeâJelinekâRaviv (BCJR) algorithm to obtain some approximate values. Moreover, in order to avoid the calculus of the inverse of the BIM and of the HIM, we present some closed form expressions for the various CRBs, which greatly reduces the computation complexity. Finally, some simulations allow us to compare the possible improvements enabled by the offline and the CA scenarios. Index TermsâBayesian CramĂ©râRao bound (BCRB), code-aided (CA) bound, data-aided (DA) bound, dynam-ical phase estimation, hybrid CramĂ©râRao bound (HCRB), non-data-aided (NDA), offline, online
On a Hybrid Preamble/Soft-Output Demapper Approach for Time Synchronization for IEEE 802.15.6 Narrowband WBAN
In this paper, we present a maximum likelihood (ML) based time
synchronization algorithm for Wireless Body Area Networks (WBAN). The proposed
technique takes advantage of soft information retrieved from the soft demapper
for the time delay estimation. This algorithm has a low complexity and is
adapted to the frame structure specified by the IEEE 802.15.6 standard for the
narrowband systems. Simulation results have shown good performance which
approach the theoretical mean square error limit bound represented by the
Cramer Rao Bound (CRB)
Recursive joint CramĂ©râRao lower bound for parametric systems with twoâadjacentâstates dependent measurements
Joint Cramér-Rao lower bound (JCRLB) is very useful for the performance evaluation of joint state and parameter estimation (JSPE) of non-linear systems, in which the current measurement only depends on the current state. However, in reality, the non-linear systems with two-adjacent-states dependent (TASD) measurements, that is, the current measurement is dependent on the current state as well as the most recent previous state, are also common. First, the recursive JCRLB for the general form of such non-linear systems with unknown deterministic parameters is developed. Its relationships with the posterior CRLB for systems with TASD measurements and the hybrid CRLB for regular parametric systems are also provided. Then, the recursive JCRLBs for two special forms of parametric systems with TASD measurements, in which the measurement noises are autocorrelated or cross-correlated with the process noises at one time step apart, are presented, respectively. Illustrative examples in radar target tracking show the effectiveness of the JCRLB for the performance evaluation of parametric TASD systems
Max-log demapper architecture design for DVB-T2 rotated QAM constellations
International audienceâ Rotated and cyclic-Q delayed (RCQD) quadrature amplitude modulation (QAM) improve DVB-T2 system performance over highly time-frequency selective channels. However, when compared with conventional QAM demapper, the RCQD demapper requires a higher computational complexity. In this paper, a complexity-reduced max-log demapper is derived and implemented over a FPGA platform. The proposed demapper allows to find the maximum likelihood (ML) point with a search spanning only M signal constellation points and guarantees to obtain the same log-likelihood ratio (LLR) metrics as the optimum max-log soft decision demapper while spanning at most 2 M signal constellation points. The optimized hardware implementation introduces only a slight performance loss compared to the floating-point full complexity max-log performance. Index Terms â DVB-T2, Rotated and Cyclic Q Delayed (RCQD) Constellations, Log-Likelihood Ratio (LLR), Max-Log Demapper
Caractérisation des performances minimales d'estimation pour des modÚles d'observations non-standards
In the parametric estimation context, estimators performances can be characterized, inter alia, by the mean square error and the resolution limit. The first quantities the accuracy of estimated values and the second defines the ability of the estimator to allow a correct resolvability. This thesis deals first with the prediction the "optimal" MSE by using lower bounds in the hybrid estimation context (i.e. when the parameter vector contains both random and non-random parameters), second with the extension of CramĂ©r-Rao bounds for non-standard estimation problems and finally to the characterization of estimators resolution. This manuscript is then divided into three parts :First, we fill some lacks of hybrid lower bound on the MSE by using two existing Bayesian lower bounds: the Weiss-Weinstein bound and a particular form of Ziv-Zakai family lower bounds. We show that these extended lower bounds are tighter than the existing hybrid lower bounds in order to predict the optimal MSE.Second, we extend Cramer-Rao lower bounds for uncommon estimation contexts. Precisely: (i) Where the non-random parameters are subject to equality constraints (linear or nonlinear). (ii) For discrete-time filtering problems when the evolution of states are defined by a Markov chain. (iii) When the observation model differs to the real data distribution.Finally, we study the resolution of the estimators when their probability distributions are known. This approach is an extension of the work of Oh and Kashyap and the work of Clark to multi-dimensional parameters estimation problems.Dans le contexte de l'estimation paramĂ©trique, les performances d'un estimateur peuvent ĂȘtre caractĂ©risĂ©es, entre autre, par son erreur quadratique moyenne (EQM) et sa rĂ©solution limite. La premiĂšre quantifie la prĂ©cision des valeurs estimĂ©es et la seconde dĂ©finit la capacitĂ© de l'estimateur Ă sĂ©parer plusieurs paramĂštres. Cette thĂšse s'intĂ©resse d'abord Ă la prĂ©diction de l'EQM "optimale" Ă l'aide des bornes infĂ©rieures pour des problĂšmes d'estimation simultanĂ©e de paramĂštres alĂ©atoires et non-alĂ©atoires (estimation hybride), puis Ă l'extension des bornes de CramĂ©r-Rao pour des modĂšles d'observation moins standards. Enfin, la caractĂ©risation des estimateurs en termes de rĂ©solution limite est Ă©galement Ă©tudiĂ©e. Ce manuscrit est donc divisĂ© en trois parties :PremiĂšrement, nous complĂ©tons les rĂ©sultats de littĂ©rature sur les bornes hybrides en utilisant deux bornes bayĂ©siennes : la borne de Weiss-Weinstein et une forme particuliĂšre de la famille de bornes de Ziv-ZakaĂŻ. Nous montrons que ces bornes "Ă©tendues" sont plus prĂ©cises pour la prĂ©diction de l'EQM optimale par rapport Ă celles existantes dans la littĂ©rature.DeuxiĂšmement, nous proposons des bornes de type CramĂ©r-Rao pour des contextes d'estimation moins usuels, c'est-Ă -dire : (i) Lorsque les paramĂštres non-alĂ©atoires sont soumis Ă des contraintes d'Ă©galitĂ© linĂ©aires ou non-linĂ©aires (estimation sous contraintes). (ii) Pour des problĂšmes de filtrage Ă temps discret oĂč l'Ă©volution des Ă©tats (paramĂštres) est rĂ©git par une chaĂźne de Markov. (iii) Lorsque la loi des observations est diffĂ©rente de la distribution rĂ©elle des donnĂ©es.Enfin, nous Ă©tudions la rĂ©solution et la prĂ©cision des estimateurs en proposant un critĂšre basĂ© directement sur la distribution des estimĂ©es. Cette approche est une extension des travaux de Oh et Kashyap et de Clark pour des problĂšmes d'estimation de paramĂštres multidimensionnels
A low-complexity 2D signal space diversity solution for future broadcasting systems
-DVB-T2 was the first industrial standard deploying rotated and cyclic Q
delayed (RCQD)modulation to improve performance over fading channels. This
enablesimportantgains compared toconventional quadrature amplitude
modulations(QAM) under severe channel conditions.However, the corresponding
demodulation complexitystill prevents its use forwider applications. This paper
proposes several rotation angles for different QAM constellations anda
corresponding low-complexity detection method. Results show that the proposed
solution simplifies both the transmitter and the receiver with often
betterperformancethan the proposed angles in DVB-T2. Compared with the lowest
complexity demappers currently used in DVB-T2, the proposed solution achieves
an additional reduction bymore than 60%. Index Terms- DVB-T2, Rotated and
Cyclic Q Delayed (RCQD) Modulations, Signal Space Diversity (SSD), Fading
Channel, Quadrature Amplitude Modulations (QAM), Max-Log,
ComputationalComplexity
Localizability Optimization for Multi Robot Systems and Applications to Ultra-Wide Band Positioning
RĂSUMĂ: RĂSUMĂ Les SystĂšmes Multi-Robots (SMR) permettent dâeffectuer des missions de maniĂšre efficace et robuste du fait de leur redondance. Cependant, les robots Ă©tant des vĂ©hicules autonomes, ils nĂ©cessitent un positionnement prĂ©cis en temps rĂ©el. Les techniques de localisation qui utilisent des Mesures Relatives (MR) entre les robots, pouvant ĂȘtre des distances ou des angles, sont particuliĂšrement adaptĂ©es puisquâelles peuvent bĂ©nĂ©ficier dâalgorithmes coopĂ©ratifs au sein du SMR afin dâamĂ©liorer la prĂ©cision pour lâensemble des robots. Dans cette thĂšse, nous proposons des stratĂ©gies pour amĂ©liorer la localisabilitĂ© des SMR, qui est fonction de deux facteurs. PremiĂšrement, la gĂ©omĂ©trie du SMR influence fondamentalement la qualitĂ© de son positionnement pour des MR bruitĂ©es. DeuxiĂšmement, les erreurs de mesures dĂ©pendent fortement de la technologie utilisĂ©e. Dans nos expĂ©riences, nous nous focalisons sur la technologie UWB (Ultra-Wide Band), qui est populaire pour le positionnement des robots en environnement intĂ©rieur en raison de son coĂ»t modĂ©rĂ© et sa haute prĂ©cision. Par consĂ©quent, une partie de notre travail est consacrĂ©e Ă la correction des erreurs de mesure UWB afin de fournir un systĂšme de navigation opĂ©rationnel. En particulier, nous proposons une mĂ©thode de calibration des biais systĂ©matiques et un algorithme dâattĂ©nuation des trajets multiples pour les mesures de distance en milieu intĂ©rieur. Ensuite, nous proposons des Fonctions de CoĂ»t de LocalisabilitĂ© (FCL) pour caractĂ©riser la gĂ©omĂ©trie du SMR, et sa capacitĂ© Ă se localiser. Pour cela, nous utilisons la Borne InfĂ©rieure de CramĂ©r-Rao (BICR) en vue de quantifier les incertitudes de positionnement. Par la suite, nous fournissons des schĂ©mas dâoptimisation dĂ©centralisĂ©s pour les FCL sous lâhypothĂšse de MR gaussiennes ou log-normales. En effet, puisque le SMR peut se dĂ©placer, certains de ses robots peuvent ĂȘtre dĂ©ployĂ©s afin de minimiser la FCL. Cependant, lâoptimisation de la localisabilitĂ© doit ĂȘtre dĂ©centralisĂ©e pour ĂȘtre adaptĂ©e Ă des SMRs Ă grande Ă©chelle. Nous proposons Ă©galement des extensions des FCL Ă des scĂ©narios oĂč les robots embarquent plusieurs capteurs, oĂč les mesures se dĂ©gradent avec la distance, ou encore oĂč des informations prĂ©alables sur la localisation des robots sont disponibles, permettant dâutiliser la BICR bayĂ©sienne. Ce dernier rĂ©sultat est appliquĂ© au placement dâancres statiques connaissant la distribution statistique des MR et au maintien de la localisabilitĂ© des robots qui se localisent par filtrage de Kalman. Les contributions thĂ©oriques de notre travail ont Ă©tĂ© validĂ©es Ă la fois par des simulations Ă grande Ă©chelle et des expĂ©riences utilisant des SMR terrestres. Ce manuscrit est rĂ©digĂ© par publication, il est constituĂ© de quatre articles Ă©valuĂ©s par des pairs et dâun chapitre supplĂ©mentaire. ABSTRACT: ABSTRACT Multi-Robot Systems (MRS) are increasingly interesting to perform tasks eĂżciently and robustly. However, since the robots are autonomous vehicles, they require accurate real-time positioning. Localization techniques that use relative measurements (RMs), i.e., distances or angles, between the robots are particularly suitable because they can take advantage of cooperative schemes within the MRS in order to enhance the precision of its positioning. In this thesis, we propose strategies to improve the localizability of the SMR, which is a function of two factors. First, the geometry of the MRS fundamentally influences the quality of its positioning under noisy RMs. Second, the measurement errors are strongly influenced by the technology chosen to gather the RMs. In our experiments, we focus on the Ultra-Wide Band (UWB) technology, which is popular for indoor robot positioning because of its mod-erate cost and high accuracy. Therefore, one part of our work is dedicated to correcting the UWB measurement errors in order to provide an operable navigation system. In particular, we propose a calibration method for systematic biases and a multi-path mitigation algorithm for indoor distance measurements. Then, we propose Localizability Cost Functions (LCF) to characterize the MRSâs geometry, using the CramĂ©r-Rao Lower Bound (CRLB) as a proxy to quantify the positioning uncertainties. Subsequently, we provide decentralized optimization schemes for the LCF under an assumption of Gaussian or Log-Normal RMs. Indeed, since the MRS can move, some of its robots can be deployed in order to decrease the LCF. However, the optimization of the localizability must be decentralized for large-scale MRS. We also propose extensions of LCFs to scenarios where robots carry multiple sensors, where the RMs deteriorate with distance, and finally, where prior information on the robotsâ localization is available, allowing the use of the Bayesian CRLB. The latter result is applied to static anchor placement knowing the statistical distribution of the MRS and localizability maintenance of robots using Kalman filtering. The theoretical contributions of our work have been validated both through large-scale simulations and experiments using ground MRS. This manuscript is written by publication, it contains four peer-reviewed articles and an additional chapter
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Performance analysis of assisted-GNSS receivers
The goal of this thesis is to improve the understanding of the performance of Global Navigation Satellite System (GNSS) receivers that use assistance data provided by cellular networks. A typical example of such a receiver is a mobile phone including a Global Positioning System (GPS) receiver. Using assistance data such as an accurate estimate of the GPS system time is known to improve the availability and the time-tofirst- fix performance of a GNSS receiver. However, the performance depends on the architecture of the cellular network and may vary significantly across networks. This thesis presents three new contributions to the performance analysis of assisted-GNSS receivers in cellular networks. I first introduce a mathematical framework that can be used to calculate a theoretical lower bound of the time-to-first-fix (TTFF) in an assisted-GNSS receiver. Existing methods, for example the flow-graph method, generally focus on calculating the theoretical mean acquisition time of a pseudo-noise signal for one satellite only. I extend these methods to calculate the full probability distribution of the joint acquisition of several satellites, as well as the sequential acquisition of satellites, which is commonly performed in assisted receivers. The method is applied to real measurements made in a multipath fading channel. I next consider time assistance in unsynchronised cellular networks. It is often argued that unsynchronised networks can not provide fine-time aiding since they do not have a common clock, although few experimental results have been reported in the existing literature. I carried out experiments on a GSM network, a second-generation cellular network, in Cambridge, UK, in order to measure the time stability of the synchronisation signals. The results showed a large variability in the time stabilities across different base stations and I evaluated the performance of an ensemble filter that combines the measurements into a single, more accurate, estimate of the universal time. The main contribution is to show that the performance of such a filter is adequate to provide fine-time assistance to a satellite navigation receiver. Finally, I address the positioning performance of an assisted receiver in synchronised cellular networks. Cellular positioning has been often investigated in the literature, but few results on real networks have been presented. Many positioning methods are proprietary and little information about their performance in real networks haven been published publicly. A CDMA2000 cellular network in Calgary, Canada, was used to collect experimental data. The time stability and the synchronisation of the CDMA2000 pilot signals were excellent and were used to evaluate the performance of CDMA2000-based cellular positioning system. I then developed a method to combine the pseudo-range measurements from the GPS signals and the CDMA2000 base stations. I evaluated the performance of positioning in both outdoor and indoor environments, and I analysed the effects and the possible mitigation of non-line-of-sight signals. The main contribution is to show that additional satellite navigation signals can improve the accuracy of cellular positioning beyond what is theoretically expected from the improvement in the geometry.Cambridge Silicon Radi
Characterization, VeriïŹcation and Control for Large Quantum Systems
Quantum information processing offers potential improvements to a wide range
of computing endevaors, including cryptography, chemistry simulations and
machine learning. The development of practical quantum information processing
devices is impeded, however, by challenges arising from the apparent exponential
dimension of the space one must consider in characterizing quantum
systems, verifying their correct operation, and in designing useful control
sequences. In this work, we address each in turn by providing useful
algorithms that can be readily applied in experimental practice.
In order to characterize the dynamics of quantum systems, we apply statistical
methods based on Bayes' rule, thus enabling the use of strong prior
information and parameter reduction. We first discuss an
analytically-tractable special case, and then employ a numerical algorithm,
sequential Monte Carlo, that uses simulation as a resource for characterization. We
discuss several examples of SMC and show its application in nitrogen vacancy
centers and neutron interferometry.
We then discuss how characterization techniques such as SMC can be used to
verify quantum systems by using credible region estimation, model selection,
state-space modeling and hyperparameterization. Together, these techniques
allow us to reason about the validity of assumptions used in analyzing quantum
devices, and to bound the credible range of quantum dynamics.
Next, we discuss the use of optimal control theory to design robust control
for quantum systems. We show extensions to existing OCT algorithms that allow
for including models of classical electronics as well as quantum dynamics,
enabling higher-fidelity control to be designed for cutting-edge experimental
devices. Moreover, we show how control can be implemented in parallel across
node-based architectures, providing a valuable tool for implementing
proposed fault-tolerant protocols.
We close by showing how these algorithms can be augmented using quantum
simulation resources to enable addressing characterization and control design
challenges in even large quantum devices. In particular, we will introduce a
novel genetic algorithm for quantum control design, MOQCA, that utilizes
quantum coprocessors to design robust control sequences. Importantly, MOQCA is
also memetic, in that improvement is performed between genetic steps. We then
extend sequential Monte Carlo with quantum simulation resources to enable
characterizing and verifying the dynamics of large quantum devices. By using
novel insights in epistemic information locality, we are able to learn
dynamics using strictly smaller simulators, leading to an algorithm we call
quantum bootstrapping. We demonstrate by using a numerical example of learning
the dynamics of a 50-qubit device using an 8-qubit simulator
D11.2 Consolidated results on the performance limits of wireless communications
Deliverable D11.2 del projecte europeu NEWCOM#The report presents the Intermediate Results of N# JRAs on Performance Limits of Wireless Communications and highlights the fundamental issues that have been investigated by the WP1.1. The report illustrates the Joint Research Activities (JRAs) already identified during the first year of the project which are currently ongoing. For each activity there is a description, an illustration of the adherence and relevance with the identified fundamental open issues, a short presentation of the preliminary results, and a roadmap for the joint research work in the next year. Appendices for each JRA give technical details on the scientific activity in each JRA.Peer ReviewedPreprin