On the Geometric Modeling of the Uplink Channel in a Cellular System

To meet the challenges of present and future wireless communications realistic propagation models that consider both spatial and temporal channel characteristics are used. However, the complexity of the complete characterization of the wireless medium has pointed out the importance of approximate but simple approaches. The geometrically based methods are typical examples of low–complexity but adequate solutions. Geometric modeling idealizes the aforementioned wireless propagation environment via a geometric abstraction of the spatial relationships among the transmitter, the receiver, and the scatterers. The paper tries to present an efficient way to simulate mobile channels using geometrical–based stochastic scattering models. In parallel with an overview of the most commonly used propagation models, the basic principles of the method as well the main assumptions made are presented. The study is focused on three well–known proposals used for the description of the Angle–of –Arrival and Time–of–Arrival statistics of the incoming multipaths in the uplink of a cellular communication system. In order to demonstrate the characteristics of these models illustrative examples are given. The physical mechanism and motivations behind them are also included providing us with a better understanding of the physical insight of the propagation medium

Impact of Finger Placement on the Correlation Properties of Rake Combined Signals

3G mobile devices and base stations employ rake receivers. An important issue in the design of such receivers is finger allocation. This paper explores the relationship between finger placement and the correlation properties of rake combined signals. The dependence of correlation coefficients on system parameters such as the multipath characteristics of the propagation channel, the number of users, the processing gain and the thermal noise power is also discussed. Several conclusions useful in the analysis and design of rake receivers are drawn. A low complexity finger placement algorithm is finally suggested. In the proposed receiver, finger allocation is based on the correlation properties of the desired signal component only. The receiver performs close to complex structures in the literature

An Efficient Finger Allocation Method for the Maximum Likelihood RAKE Receiver

In wideband wireless communication systems the RAKE receiver is commonly used to collect the resolvable multipath energy and counter the effects of fading through diversity. However, in channels with large delay and energy spread, its high complexity still remains a major issue. This motivates the study and application of computationally efficient finger placement algorithms that significantly reduce the receiver complexity with a reasonable performance loss. In this paper, a low–complexity maximum likelihood RAKE receiver, the Suboptimum – Maximum Power Minimum Correlation (S–MPMC) RAKE is proposed. The allocation of its first two fingers is based on the received signal correlation properties. Their positions determine also the placement of the rest of the fingers. Simulation results are provided to show the operation of the receiver and demonstrate its performance. Comparisons with relevant methods are performed to corroborate the merits of the proposal. The balance on the performance and the complexity of the technique makes it suitable for use in commercial wideband communication systems

The FEMM Package: A Simple, Fast, and Accurate Open Source Electromagnetic Tool in Science and Engineering

The finite element method (FEM) is one of the most successful computational techniques for obtaining approximate solutions to the partial differential equations that arise in many scientific and engineering applications. Finite Element Method Magnetics (FEMM) is a software package for solving electromagnetic problems using FEM. The program addresses 2D planar and 3D axisymmetric linear and nonlinear harmonic low frequency magnetic and magnetostatic problems and linear electrostatic problems. It is a simple, accurate, and low computational cost open source product, popular in science, engineering, and education. In this paper the main characteristics and functions of the package are presented. In order to demonstrate its use and exhibit the aid it offers in the study of electromagnetics a series of illustrative examples are given. The aim of the paper is to demonstrate the capability of FEMM to meet as a complementary tool the needs of science and technology especially when factors like the economic cost or the software complexity do not allow the use of commercial products

Closed-form Description of Microwave Signal Attenuation in Cellular Systems

The reliable and accurate description of signal attenuation characteristics is important in the simulation and performance analysis of wireless communications systems. Recent works have provided analytical expres- sions for the path loss statistics in cellular systems consid- ering distance-dependent losses and shadowing. In this paper, we extend this analysis by including small-scale fading. A closed-form expression that gives the path loss density in a cellular network is given. The impact of chan- nel parameters and cell size on signal attenuation is fur- ther investigated. Simulation results and comparisons with measured data in the literature verify the accuracy of the solution. The derived formulation is a useful tool for the modeling and analysis of cellular communications systems

On the Effect of Channel Impairments on VANETs Performance

The primary means of studying the performance of vehicular ad hoc networks (VANETs) are computer simulations. Nowadays, the development of analytical models and the use of hybrid simulations that combine analytical modeling with discrete-event simulation are of great interest due to the significant reduction in computational cost. In this paper, we extend previous work in the area by suggesting an analytical model that includes distance-dependent losses, shadowing and small-scale fading. Closed-form expressions for the packet reception probability and the packet forwarding distance in the absence of simultaneous transmissions are presented. Numerical simulations validate the proposed formulation. The impact of path loss and fading on network throughput is explored. Interesting results that shows the efficacy of the approach are provided. The derived formulation is a useful tool for the modeling and analysis of vehicular communication systems

A GEOMETRIC METHOD FOR COMPUTING THE NODAL DISTANCE DISTRIBUTION IN MOBILE NETWORKS

Abstract-This paper presents a geometrically based method for the calculation of the node-to-node distance distribution function in circular-shaped networks. In our approach, this function is obtained from the intersection volume of a sphere and an ellipsoid. The method is valid for both overlapping and non-overlapping networks. Simulation results and comparisons with methods in the literature demonstrate the efficacy of the approach. The relation between networks geometric parameters and distance statistics is explored. As an application example, we model distance-dependent path loss and investigate the impact of channel characteristics and networks size on signal absorption. The aforementioned model is a useful and lowcomplexity tool for system-level modeling and simulation of mobile communication systems

Induction of GADD34 Is Necessary for dsRNA-Dependent Interferon-β Production and Participates in the Control of Chikungunya Virus Infection

Nucleic acid sensing by cells is a key feature of antiviral responses, which generally result in type-I Interferon production and tissue protection. However, detection of double-stranded RNAs in virus-infected cells promotes two concomitant and apparently conflicting events. The dsRNA-dependent protein kinase (PKR) phosphorylates translation initiation factor 2-alpha (eIF2α) and inhibits protein synthesis, whereas cytosolic DExD/H box RNA helicases induce expression of type I-IFN and other cytokines. We demonstrate that the phosphatase-1 cofactor, growth arrest and DNA damage-inducible protein 34 (GADD34/Ppp1r15a), an important component of the unfolded protein response (UPR), is absolutely required for type I-IFN and IL-6 production by mouse embryonic fibroblasts (MEFs) in response to dsRNA. GADD34 expression in MEFs is dependent on PKR activation, linking cytosolic microbial sensing with the ATF4 branch of the UPR. The importance of this link for anti-viral immunity is underlined by the extreme susceptibility of GADD34-deficient fibroblasts and neonate mice to Chikungunya virus infection

The Chemotherapeutic Drug 5-Fluorouracil Promotes PKR-Mediated Apoptosis in a p53- Independent Manner in Colon and Breast Cancer Cells

The chemotherapeutic drug 5-FU is widely used in the treatment of a range of cancers, but resistance to the drug remains a major clinical problem. Since defects in the mediators of apoptosis may account for chemo-resistance, the identification of new targets involved in 5-FU-induced apoptosis is of main clinical interest. We have identified the ds-RNA-dependent protein kinase (PKR) as a key molecular target of 5-FU involved in apoptosis induction in human colon and breast cancer cell lines. PKR distribution and activation, apoptosis induction and cytotoxic effects were analyzed during 5-FU and 5-FU/IFNα treatment in several colon and breast cancer cell lines with different p53 status. PKR protein was activated by 5-FU treatment in a p53-independent manner, inducing phosphorylation of the protein synthesis translation initiation factor eIF-2α and cell death by apoptosis. Furthermore, PKR interference promoted a decreased response to 5-FU treatment and those cells were not affected by the synergistic antitumor activity of 5-FU/IFNα combination. These results, taken together, provide evidence that PKR is a key molecular target of 5-FU with potential relevance in the clinical use of this drug

Aquatic Birnavirus-Induced ER Stress-Mediated Death Signaling Contribute to Downregulation of Bcl-2 Family Proteins in Salmon Embryo Cells

Aquatic birnavirus induces mitochondria-mediated cell death, but whether connects to endoplasmic reticulum (ER) stress is still unknown. In this present, we characterized that IPNV infection triggers ER stress-mediated cell death via PKR/eIF2α phosphorylation signaling for regulating the Bcl-2 family protein expression in fish cells. The IPNV infection can induce ER stress as follows: (1) ER stress sensor ATF6 cleavaged; (2) ER stress marker GRP78 upregulation, and (3) PERK/eIF2αphosphorylation. Then, the IPNV-induced ER stress signals can induce the CHOP expression at early (6 h p.i.) and middle replication (12 h p.i.) stages. Moreover, IPNV-induced CHOP upregulation dramatically correlates to apparently downregulate the Bcl-2 family proteins, Bcl-2, Mcl-1 and Bcl-xL at middle replication stage (12 h p.i.) and produces mitochondria membrane potential (MMP) loss and cell death. Furthermore, with GRP78 synthesis inhibitor momitoxin (VT) and PKR inhibitor 2-aminopurine (2-AP) treatment for blocking GRP78 expression and eIF2α phosphorylation, PKR/PERK may involve in eIF2α phosphorylation/CHOP upregulation pathway that enhances the downstream regulators Bcl-2 family proteins expression and increased cell survival. Taken together, our results suggest that IPNV infection activates PKR/PERK/eIF2α ER stress signals for regulating downstream molecules CHOP upregulation and Bcl-2 family downregulation that led to induce mitochondria-mediated cell death in fish cells, which may provide new insight into RNA virus pathogenesis and disease