Why Does a Kronecker Model Result in Misleading Capacity Estimates?

Many recent works that study the performance of multi-input multi-output (MIMO) systems in practice assume a Kronecker model where the variances of the channel entries, upon decomposition on to the transmit and the receive eigen-bases, admit a separable form. Measurement campaigns, however, show that the Kronecker model results in poor estimates for capacity. Motivated by these observations, a channel model that does not impose a separable structure has been recently proposed and shown to fit the capacity of measured channels better. In this work, we show that this recently proposed modeling framework can be viewed as a natural consequence of channel decomposition on to its canonical coordinates, the transmit and/or the receive eigen-bases. Using tools from random matrix theory, we then establish the theoretical basis behind the Kronecker mismatch at the low- and the high-SNR extremes: 1) Sparsity of the dominant statistical degrees of freedom (DoF) in the true channel at the low-SNR extreme, and 2) Non-regularity of the sparsity structure (disparities in the distribution of the DoF across the rows and the columns) at the high-SNR extreme.Comment: 39 pages, 5 figures, under review with IEEE Trans. Inform. Theor

Three-dimensional numerical modelling of ballasted railway track foundations for high-speed trains with special reference to critical speed

Due to recent congestion of highways in many countries around the world, railways have become the most popular means of public transportation, which has increased the demand for heavier and faster trains. High speeds and heavy loads of trains are usually accompanied with large vibrations in the train-track-ground system, especially when train speed reaches its critical value, leading to possible train derailment and track damages. This unwanted scenario makes it important for railway geotechnical engineers to investigate the behaviour of ballasted railway track foundations for high-speed trains, with special reference to critical speed. In the current paper, a sophisticated three-dimensional (3D) finite element (FE) modelling was developed to simulate the dynamic response of ballasted railway tracks subjected to train moving loads, and the critical speed was investigated for various train-track-ground system conditions. The results were presented in terms of the evolution of the coefficient of dynamic amplification of sleeper deflection versus train speed, which have been synthesized into simple sensitivity charts that can be used to determine the critical speed corresponding to the conditions of a particular train-track-ground system

Design of ballasted railway track foundations using numerical modelling: Part II: Applications

This paper is the second of two companion papers in relation to a new design method for ballasted railway track foundations. Development of the new design method has been explained in the first paper (i.e., Part I: Development), and the procedures for using the method and its practical application on some field case studies are presented in this paper. A special feature of the proposed design method is that it considers the true impact of train dynamic moving loads and number of repeated applications of the traffic tonnage. The proposed method is applied to four case studies of actual tracks and the results are compared with field measurements and found to be in good agreement. It should be noted that, although the proposed design method is able to overcome most shortcomings of the existing methods and found to provide excellent outcomes, further verification with more field case studies is highly desirable

Improving Bandwidth Efficiency in E-band Communication Systems

The allocation of a large amount of bandwidth by regulating bodies in the 70/80 GHz band, i.e., the E-band, has opened up new potentials and challenges for providing affordable and reliable Gigabit per second wireless point-to-point links. This article first reviews the available bandwidth and licensing regulations in the E-band. Subsequently, different propagation models, e.g., the ITU-R and Cane models, are compared against measurement results and it is concluded that to meet specific availability requirements, E-band wireless systems may need to be designed with larger fade margins compared to microwave systems. A similar comparison is carried out between measurements and models for oscillator phase noise. It is confirmed that phase noise characteristics, that are neglected by the models used for narrowband systems, need to be taken into account for the wideband systems deployed in the E-band. Next, a new multi-input multi-output (MIMO) transceiver design, termed continuous aperture phased (CAP)-MIMO, is presented. Simulations show that CAP-MIMO enables E-band systems to achieve fiber-optic like throughputs. Finally, it is argued that full-duplex relaying can be used to greatly enhance the coverage of E-band systems without sacrificing throughput, thus, facilitating their application in establishing the backhaul of heterogeneous networks.Comment: 16 pages, 6 Figures, Journal paper. IEEE Communication Magazine 201

Frequency and pattern of congenital heart defects among admitted patient in a tertiary care hospital in Bangladesh

Background: Congenital heart disease (CHD) is the commonest of all congenital lesions accounting for nearly 28% of all congenital malformations that have significant impact on morbidity, mortality and heath care cost in children. The aim of study was to determine the pattern of distribution of CHD and the age at which initial diagnosis of CHD was made among children admitted under paediatric cardiology department, Bangladesh Shishu hospital and institute. Methods: This is a descriptive and prospective hospital-based study conducted in the pediatric cardiology department, Bangladesh Shishu hospital and institute. This study included all the patients admitted during January-June 2022 in pediatric cardiology department having confirmed diagnosis of CHD on basis of echocardiographic report. The collected data was entered and analyzed by using statistical package for social sciences v 24.0. Results: Out of 337 patient, 175 patient were male (51.9%) and 162 female (48.1%) with male female ratio of 1.08:1. Total 219 cases (64.9%) were acyanotic CHD and 118 (35.1%) were cyanotic congenital heart lesions. In acyanotic CHD ventricular septal defects (VSDs) constitute 38.8% followed by AV canal defect 6.7%, patent ductus arteriosus (PDA) 3.6%. In cyanotic CHD tetralogy of Fallot (TOF) was the commonest lesion accounted for 28 (8.3%) followed by d-transposition of great arteries 16 (4.7%), pulmonary atresia 15 (4.5%), total anomalous pulmonary venous circulation TAPVC 11 (3.3%), tricuspid atresia 9 (2.7%) and DORV, VSD, PS 10 (2.9%). The commonest combination was VSD with ASD in 15 cases (4.5%). Most of the patient was diagnosed in 1st year of age 280 (83.1%) Conclusions: CHD are very common in our setup and early detection of CHD is increasing. Overall burden of CHD is also increasing therefore a proper population-based study on a large scale is needed to estimate the prevalence accurately