161 research outputs found
Simultaneous channel and symbol maximum likelihood estimation in Laplacian noise
This paper treats channel estimation and signal detection in Laplacian noise. The received signal is assumed to be a transmitted signal which has been corrupted by an unknown channel, modeled as a FIR filter, the output being further disturbed by additive independent Laplacian noise. The transmitted signal is assumed to depend on an unknown parameter belonging to a known finite set. The simultaneous maximum likelihood (ML) estimator of the unknown parameter, as well as of the FIR filter coefficients, is derived. The ML estimate of the channel can be obtained by using a linear programming approach and the decision about the parameter is based on the output from a set of generalized matched filters. Simulation results are included in order to illustrate the performance of the proposed receiver
Zipper - a Duplex Method for VDSL based on DMT
We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise source
A method for evaluation of QRS shape features using a mathematical model for the ECG
Automated classification of ECG patterns is facilitated by careful selection of waveform features. This paper presents a method for evaluating the properties of features that describe the shape of a QRS complex. By examining the distances in the feature space for a class of nearly similar complexes, shape transitions which are poorly described by the feature under investigation can be readily identified. To obtain a continuous range of waveforms, which is required by the method, a mathematical model is used to simulate the QRS complexes
Common Mode Characterization and Channel Model Verification for Shielded Twisted Pair (STP) Cable
This paper investigates common-mode propagation in shielded twisted pair cables. The common mode exhibits great potential for improving the throughput in emerging wireline systems. The design of corresponding transmission schemes over multipair copper cables requires accurate knowledge of the channel properties. We present measurement and modeling results and investigate the feasibility of using standard differentialmode models for data fitting in multiconductor transmission-line modelling of common-mode paths
Symbol time offset estimation in coherent OFDM systems
This paper presents a symbol time offset estimator for coherent OFDM systems. This estimator exploits both the redundancy in the cyclic prefix and the pilot symbols used for channel estimation. The estimator is robust against frequency offsets and is suitable for use in dispersive channels. We base the estimator on the ML estimator for the AWGN channel. Simulations of an example system indicate a system performance as close as 0.3 dB to a perfectly synchronized system. Compared to an estimator not using pilots, our estimator's performance could allow a shorter cyclic prefix and thus a more spectrally efficient syste
Шоп-туризм: проблемы и перспективы развития в Республике Беларусь
Материалы XV Междунар. науч.-техн. конф. студентов, аспирантов и молодых ученых, Гомель, 23–24 апр. 2015 г
Predictors of the first cardiovascular event in patients with systemic lupus erythematosus - a prospective cohort study
Systemic Lupus Erythematosus (SLE) is an autoimmune, inflammatory disease that mainly affects
women. The prognosis of SLE has improved dramatically, but mortality rates are still higher than in the
general population. With the improved general prognosis, cardiovascular disease (CVD) has emerged as a
major cause of morbidity and mortality among SLE patients. Previous studies have demonstrated that the
development of atherosclerosis is accelerated in SLE, and have identified a set of traditional and nontraditional
risk factors that characterize SLE patients with CVD. Nevertheless, many unsolved issues with
respect to SLE related CVD remain. The general aim of this thesis was to investigate risk factors for
manifest CVD and for cardiovascular mortality (CVM) in SLE, with special focus on traditional risk
factors, lupus phenotype, inflammatory and endothelial biomarkers, autoantibodies and genetic
predisposition.
In the first paper, we prospectively studied traditional and non-traditional risk factors for
the development of the first cardiovascular event (CVE) in 182 SLE patients with a follow-up time of 8
years. 24(13%) patients had a first event. We demonstrated that of the traditional risk factors, only age
and smoking predicted the first CVE. Additionally, antiphospholipid antibodies (aPL), endothelial
biomarkers, represented by soluble vascular cell adhesion molecule 1(sVCAM-1), and absence of
thrombocytopenia were independent predictors of CVE. Thus, activation of the endothelium and the
coagulation system are important features in SLE-related CVD and the importance to advocate smoking
cessation among SLE patients is underscored
In the second paper, we prospectively investigated causes of mortality and risk factors for
overall mortality and CVM in a cohort of 208 SLE patients, with a follow-up time of 12 years. We also
evaluated Systematic coronary risk evaluation (SCORE, tool for evaluating the 10 year risk for
cardiovascular death in the age span 40-65 years, based on traditional risk factors) in this population.
Cystatin C, a sensitive measure of renal function, in addition to traditional and non-traditional risk
factors, were evaluated as risk factors. 42 patients died, 48 % of which were due to CVM. Age, previous
arterial events and high cystatin C levels were the strongest predictors for overall mortality and for CVM.
After adjusting for these three variables, smoking, sVCAM-1 and high sensitiviy C-reactive protein
(hsCRP) predicted CVM. SCORE estimated 4 but we observed 9 cases of CVM, a non-significant
difference. We conclude that except for smoking, traditional risk factors are less important than cystatin
C, endothelial and inflammatory biomarkers as predictors of CVM in SLE patients.
In the third paper, we investigated whether a risk allele for SLE in the signal transducer
and activator of transcription factor 4 gene (STAT4) was associated with vascular events or presence of
antiphospholipid antibodies (aPL). A total of 578 unrelated SLE patients (424 from mid-Sweden and 154
from southern-Sweden) were included in a cross-sectional design. Occurrence of previous cardiovascular
events and aPL were tabulated. Matched controls (N=651) were genotyped as a comparison. The results
demonstrate that the STAT4 risk allele was associated with ischemic cerebrovascular disease (ICVD),
with a dose-dependent relationship between ICVD and number of risk alleles. The risk allele was
furthermore associated with the presence of two or more aPLs, also in a dose-dependent manner. The
association remained after adjustment for known traditional risk factors. We conclude that patients with
the STAT4 risk allele have an increased risk of ICVD. Our results imply that genetic predisposition is an
important risk factor for ICVD in SLE patients, and that aPL may be one underlying mechanism.
In the fourth paper, we evaluated the potential association between smoking and aPL. 367
SLE patients were investigated in a cross-sectional study. Occurrence of aPL (anticardiolipin (aCL) IgG
and IgM, anti-β2 glycoprotein-1 IgG (aβ2GP1 IgG), lupus anticoagulant (LAC)) and smoking habits
(never, ever, former, current) were tabulated. Never smoking was used as reference in all calculations. In
multivariable models, adjusted for age, sex and age at disease onset, aCL and aβ2GP1 of the IgG isotype
and LAC were associated with ever smoking, this association seemed to be driven mainly by the former
smoking group. Our results demonstrate that smoking is associated with pro-thrombotic aPL in SLE
patients, though we can not from this study draw firm conclusions about the temporal relationship
between exposure to smoking and occurrence of aPL. Further studies are warranted to investigate the
mechanisms behind these observations.
In prospective studies we have demonstrated that in particular smoking, systemic
inflammation, endothelial activation and aPL are major risk factors for SLE related CVD and CVM.
Furthermore, genetic predisposition, in our studies represented by a STAT4 SLE risk allele, contributes to
the high risk of ICVD and to the occurrence of aPL, a possible underlying pathogenic mechanism. Finally
we demonstrate that smoking, known to have unfavorable effects on the immune system and to
significantly increase cardiovascular risk in SLE patients, is also associated with pro-thrombotic aPL in
patients with SLE. Thus in SLE smoking stands out as the most important of the traditional risk factors
with potential influence also on lupus related risk factors such as aPL
Synchronization in OFDM systems sensitivity to the choice of pulse shape
Problème traité : dans cette publication, nous nous intéressons au problème de la synchronisation dans les systèmes à porteuses multiples : estimation du début du symbole et de l'écart de fréquence. Nous utilisons la redondance introduite par le temps de garde ainsi qu'une fonction de mise en forme des symboles. Originalité de la contribution : Les performances d'un système utilisant uniquement la corrélation introduite par le temps de garde ont été évaluées dans un article précédent dans le cas d'un canal gaussien. Dans cette contribution, nous introduisons une fonction de mise en forme sur les symboles OFDM et nous évaluons les performances du système ainsi obtenu. Résultat nouveaux : Nous avons déterminé les performances du système proposé pour différentes fonctions de mise en forme
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