Joint Estimation of the Time Delay and the Clock Drift and Offset Using UWB signals

We consider two transceivers, the first with perfect clock and the second with imperfect clock. We investigate the joint estimation of the delay between the transceivers and the offset and the drift of the imperfect clock. We propose a protocol for the synchronization of the clocks. We derive some empirical estimators for the delay, the offset and the drift, and compute the Cramer-Rao lower bounds and the joint maximum likelihood estimator of the delay and the drift. We study the impact of the protocol parameters and the time-of-arrival estimation variance on the achieved performances. We validate some theoretical results by simulation.Comment: Accepted and published in the IEEE ICC 2014 conferenc

Statistics of the MLE and Approximate Upper and Lower Bounds - Part 2: Threshold Computation and Optimal Signal Design

Threshold and ambiguity phenomena are studied in Part 1 of this work where approximations for the mean-squared-error (MSE) of the maximum likelihood estimator are proposed using the method of interval estimation (MIE), and where approximate upper and lower bounds are derived. In this part we consider time-of-arrival estimation and we employ the MIE to derive closed-form expressions of the begin-ambiguity, end-ambiguity and asymptotic signal-to-noise ratio (SNR) thresholds with respect to some features of the transmitted signal. Both baseband and passband pulses are considered. We prove that the begin-ambiguity threshold depends only on the shape of the envelope of the ACR, whereas the end-ambiguity and asymptotic thresholds only on the shape of the ACR. We exploit the results on the begin-ambiguity and asymptotic thresholds to optimize, with respect to the available SNR, the pulse that achieves the minimum attainable MSE. The results of this paper are valid for various estimation problems

Statistics of the MLE and Approximate Upper and Lower Bounds - Part 1: Application to TOA Estimation

In nonlinear deterministic parameter estimation, the maximum likelihood estimator (MLE) is unable to attain the Cramer-Rao lower bound at low and medium signal-to-noise ratios (SNR) due the threshold and ambiguity phenomena. In order to evaluate the achieved mean-squared-error (MSE) at those SNR levels, we propose new MSE approximations (MSEA) and an approximate upper bound by using the method of interval estimation (MIE). The mean and the distribution of the MLE are approximated as well. The MIE consists in splitting the a priori domain of the unknown parameter into intervals and computing the statistics of the estimator in each interval. Also, we derive an approximate lower bound (ALB) based on the Taylor series expansion of noise and an ALB family by employing the binary detection principle. The accurateness of the proposed MSEAs and the tightness of the derived approximate bounds are validated by considering the example of time-of-arrival estimation

Semantic and Contextual Knowledge Representation for Lexical Disambiguation: Case of Arabic-French Query Translation

We present in this paper, an automatic query translation system in cross-language information retrieval (Arabic-French). For the lexical disambiguation, our system combines between two resources: a bilingual dictionary and a parallel corpus. To select the best translation, our method is based on a correspondence measure between two semantic networks. The first one represents the senses of ambiguous terms of the query. The second one is a semantic network contextually enriched, representing the collection of sentences responding to the query. This collection forms the knowledge base of our disambiguation method and it is obtained by alignment with the relevant sentences in Arabic. The evaluation of the proposed system shows the advantage of the contextual enrichment on the quality of the translation. We obtained a high precision, relatively proportional to the precision provided by the used alignment. Finally, our translation demonstrates its potential by comparing its Bleu score with that of Google translate.</p

Humeral Artery Aneurysm Revealing a Rare Association between Tuberculosis and Behçet’s Disease

The association of pulmonary tuberculosis and Behçet’s disease revealed by an aneurysm of the humeral artery is exceptional with a complicated management. We report a case in which the two conditions occurred concomitantly with the vascular complication, apart from any use of immunosuppressive therapy, something that has never been reported in the literature. We report an extremely rare case of a spontaneous rupture of an aneurysm of the humeral artery of a 29-year-old woman, with no history. The patient underwent axillo-humeral bypass. Investigations concluded the diagnosis of Behçet’s disease associated with pulmonary and lymph node tuberculosis. Anti-tuberculous chemotherapy followed by corticosteroids, immunosuppressants and colchicine have been administrated. Based on this observation, we insist on the necessity of searching the symptoms of Behçet’s disease in the presence of arterial involvement when having a young patient. Therapeutic management must include medical treatment to control inflammation and limit the risk of recurrence. Endovascular or surgical treatment is necessary if the arterial involvement is threatening. The association with tuberculosis complicates management and requires close monitoring

Parameter estimation for ultra wideband based positioning

Positioning an unknown location node can be performed either directly from the signals received at/from the reference nodes, or by estimating some position-related parameters in a first step, and then combining them in an optimal way to get the desired position in a second step. In two-step positioning strategies, different types of parameters can be considered such as the time of arrival (TOA) and the angle of arrival (AOA). On the other hand, Impulse radio (IR) ultra wideband (UWB) signals are characterized by their pulses shorter than 2 ns (bandwidth larger than 500 MHz). Such signals represent an excellent candidate for highly accurate positioning when the TOA technique is employed. In this thesis we consider the problem of parameter estimation for positioning using IR-UWB signals. We treat the general setting of non-linear estimation, study the threshold and ambiguity phenomena, propose some approximations of the statistics of the maximum likelihood estimator (MLE), and derive some approximate upper and lower bounds of the mean squared error (MSE). The obtained results are applied in the context of TOA estimation using IR-UWB signals, and exploited in the design of the pulses that achieve the lowest attainable MSE. We deal with TOA estimation in multiuser time-hopping IR-UWB systems. We introduce a new receiver that we call "delaying-and-multiplying" receiver, and propose a new estimator based on that receiver and named it "maximum delaying-and-multiplying estimator". We compute the asymptotic, local and global performances of the proposed estimator and compare it with some existing benchmark estimators. We study the potential of the proposed estimator in the presence of deterministic and random multiuser interference. We also propose a family of TOA estimators based on the discrete Fourier transform of the received signal for both AWGN and multipath channels. We derive the Cramer-Rao lower bounds (CRLB) for joint TOA and AOA estimation, for AOA based positioning, and for hybrid TOA-AOA based positioning, in UWB multipath channels. We investigate the impact of the overlapping between the different multipath components (MPC) on the joint estimation of the MPCs gains and TOAs. We also derive the CRLBs for the joint estimation of the TOA and the AOA in single-input-single-output (SISO), single-input-multiple-output (SIMO), multiple-input-single-output (MISO) and multiple-input-multiple-output (MIMO) systems. We present a testbed that we realized at Université catholique de Louvain (UCL) for ranging and positioning by using IR-UWB signals based and employing the TOA technique. Two TOA estimators are considered: the MLE and a threshold-based estimator. We have studied from measurement data the impact of the multipath aspect of the channel and that of the shape of the transmitted pulses on the positioning performances. The obtained results are compared with the theoretical limits.(FSA - Sciences de l'ingénieur) -- UCL, 201

Joint estimation of the time delay and the clock drift and offset using UWB signals

We consider two transceivers, the first with perfect clock and the second with imperfect clock. We investigate the joint estimation of the delay between the transceivers and the offset and the drift of the imperfect clock. We propose a protocol for the synchronization of the clocks. We derive some empirical estimators for the delay, the offset and the drift, and compute the Cramer-Rao lower bounds and the joint maximum likelihood estimator of the delay and the drift. We study the impact of the protocol parameters and the time-of-arrival estimation variance on the achieved performances. We validate some theoretical results by simulation. © 2014 IEEE

CRBS for the joint estimation of TOA and AOA in wideband MISO and MIMO systems: comparison with SISO and SIMO systems

We derive the CRBs (Cramer Rao bound) for the joint estimation of the TOA (time of arrival) and the AOA (angle of arrival) in wideband (WB) MISO (multiple input single output) and MIMO (multiple input multiple output) systems. We consider both cases of orthogonal and non-orthogonal transmitted signals. We compare the CRBs obtained in SISO (single input single output), SIMO (single input multiple output), MISO and MIMO systems under the assumption that the total transmitted energy is the same for all systems. We show that SIMO and MIMO are equivalent for TOA estimation, and MISO and SISO as well when the transmitted signals are orthogonal. For non-orthogonal signals, MIMO is better than SIMO, and MISO is better than SISO when the received signals are constructive. For AOA estimation, we show that MIMO is better than SIMO and SIMO is better than MISO when the transmitted signals are orthogonal. For non-orthogonal signals, MIMO is much better when the received signals are constructive. The CRBs obtained for non- orthogonal signals are very sensitive to the angle. Numerical results obtained in a typical scenario are provided.Anglai