A PAPR Reduction for OFDM Signals Based on Self-Adaptive Multipopulation DE algorithm

One of major drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR). A signal with high PAPR leads to nonlinear distortion caused mainly by power amplifiers in wireless transmitters. Partial transmit sequence (PTS) is one of the most attractive methods to reduce the PAPR in OFDM systems. It achieves considerable PAPR reduction without distortion, but it requires an exhaustive search over all the combinations of the given phase factors, which results in a computational complexity that increases exponentially with the number of partitions. For this optimization problem, we propose in this paper a suboptimal PTS method based on the self-adaptive multipopulation differential evolution algorithm (SAMDE). The self adaptation of control parameters and structured population, is able to obtain high quality solutions with low computational cost by evolving each sub-population of individuals over successive generations

A Novel Multi-Dimensional Spectrum Estimation Technique using Antenna Array Displacement

Conventionally, in multi-dimensional spectral estimation techniques, each data snapshot in space is captured simultaneously. All antenna elements or sensors being used to collect data are sampled at the same time. By doing so, the size of the antenna array is proportional to the area of interest in space. The antenna array is prohibitively huge if the area that we want to cover is large. In this paper, in order to reduce the number of antenna elements in use, we propose a novel multi-dimensional spectrum estimation technique based on displacing small antenna arrays along predefined paths. It includes a data measurement technique which sequentially collects data samples within each snapshot in space according to a predefined order, and a spectral estimation technique which is based on the Discrete Fourier Transform (DFT) of the collected data. The key idea is to create a large synthetic antenna aperture by displacing a small antenna array along a predefined trajectory. Impinging waves are assumed uniform plane waves. The performance of the proposed technique is evaluated by simulation. The applications of the proposed technique include synthetic aperture radar, radar image processing and sonar systems

Méthodes d’optimisation du système PCL

Cet article expose des solutions pour pallier les deux difficultés majeures qu’engendre l’emploi d’un système de détection passive cohérente ; soit la forte interférence causée par le signal direct, annulée par la projection dans un sous-espace complémentaire à celui-ci, et la faiblesse de l’écho de la cible, solutionnée par l’utilisation d’un réseau d’antennes à chevauchement d’éléments formant des sous-réseaux. Les expressions mathématiques de la matrice de covariance du signal et du bruit sont présentées pour expliquer le comportement de la sortie du filtre adapté selon le nombre de sous-réseaux employé. À partir de l’expression analytique de la valeur propre, on dérive une expression analytique permettant d’établir le nombre de sous-réseaux à employer en fonction de l’orientation de la cible et du nombre d’éléments d’antenne disponibles afin d’optimiser la sortie du filtre adapté.This paper expose soultions to mitigate the two major difficulties caused by the use of a passive coherent location system, namely the strong interference from the direct signal, canceled by the projection in a subspace complementary to the direct signal subspace, and the weakness of the target echo, resolve by using an overlapped antenna array made up of subarrays. The mathematical expressions of the signal covariance matrix and the noise covariance matrix are presented to describe the behavior of the matched filter output according to the number of subarrays employed. From the analytical expression of the eigenvalues, an equation is presented that determine the optimal number of subarrays to be used according to orientation of the target and to the number of antennae elements available to optimize the matched filter out

On the Double Doppler Effect Generated by Scatterer Motion

In a time-varying transmission channel, the received signals are subject to frequency shifts due to the Doppler effect. The Doppler frequency is dependent on the carrier frequency and channel variation rate. In a fixed wireless channel, the channel variations are caused by scatterer motion. In this paper, we investigate analytically the Doppler effects generated by scatterer motion under different scatterer velocity distributions using the ring-of-scatterers geometric model. The proposed model considers Doppler frequency components caused by scatterer mobility to both received and reflected signals at each scatterer, and therefore is called the double Doppler model. The analytical curves are compared and statistically tested with several measurement results published in the literature. At low scatterer speeds, e.g., generated by moving foliage, the exponential velocity distribution is an appropriate model to describe the time-varying nature of the fixed wireless channels. The curve fitting results also show that our analytical model better approaches the empirical curves than the single Doppler model does. However, further investigation is still needed to find a suitable scatterer velocity distribution that closely describes the double Doppler effect in fast-variation fixed wireless channels, e.g., caused by passing vehicles

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase 1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age  6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score  652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc = 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N = 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in Asia and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701