Dual Band PIFA MIMO Antenna Design with High Isolation for Mobile and Wireless Applications by Using the Genetics Algorithms and Non-uniform Overlapping Method

Wireless Personal Communications - Due to the development and growth of Internet platforms and web services as communication resources, the competition for the network and its limited resources is...     

Investigation of load transfer mechanisms in granular platforms reinforced by geosynthetics above cavities

Geosynthetic-reinforced soils constitute an interesting solution for bridging cavities. Many methods have been developed to analyze the stability of soil-geosynthetic-cavity systems, but none of them is able to take into account all the complexities of these mechanisms. Many researchers have assumed mechanisms developed in the reinforced granular platform when cavities appear, such as load transfer and expansion of materials. However, they are not fully understood because many factors can influence the design, such as the cavity opening processes, the type, and the density of the soil.In this study, a new laboratory apparatus is developed to simulate two different cavity opening procedures (trapdoor and progressive opening) for different geometric configurations. A series of tests is conducted for three granular soils with two different geosynthetic sheets. By measuring the shape of the surface soil settlement and the geosynthetic deflection, the expansion coefficient is calculated. A novel tactile pressure sensor is used to observe the load transfer during the cavity opening. The experimental data are analyzed and the influence of the experimental conditions (geometric and soil properties and the opening procedure) are also discussed. Correspondingly, elicited findings can be used to propose recommendations to improve the existing design methods.     

Numerical analysis of the behaviour of mechanically stabilized earth walls reinforced with different types of strips

A mechanically stabilized earth (MSE) wall behaves as a flexible coherent block able to sustain significant loading and deformation due to the interaction between the backfill material and the reinforcement elements. The internal behaviour of a reinforced soil mass depends on a number of factors, including the soil, the reinforcement and the soil/structure interaction and represents a complex interaction sol/structure problem. The use of parameters determined from experimental studies should allow more accurate modelling of the behaviour of the MSE structures.In this article, a reference MSE wall is modelled from two points of view: serviceability limit state “SLS” and ultimate limit state “ULS”. The construction of the wall is simulated in several stages and the soil/interface parameters are back analysed from pullout tests. An extensive parametric study is set up and permits to highlight the influence of the soil, the reinforcement and the soil/structure parameters. The behaviour of MSE walls with several geosynthetic straps is compared with the metallic one. Several constitutive models with an increasing complexity have been used and compared.The results obtained from stress-deformation analyses are presented and compared. The use of geosynthetic straps induces more deformation of the wall but a higher safety factor. To design theses walls the important parameters are: the soil friction, the cohesion, the interface shear stiffness and the strip elastic modulus.It is shown that for wall construction that involves static loading conditions, the modified Duncan-Chang model is a good compromise but induces slightly lower strip tensile forces due to the fact that it do not take into account of dilatancy before failure.     

On channel estimation in cell-free massive MIMO for spatially correlated channels with correlated shadowing under Rician fading

This work addresses channel estimation (CE) in the uplink phase for a cell-free massive multiple-input multiple-output system operating under the time division duplex protocol. Considering that, channels are spatially correlated under the Rician fading model, where the investigated model is composed of two components: deterministic and nondeterministic, with the deterministic component describing the line-of-sight paths and the nondeterministic component describing the non-line-of-sight paths. Additionally, we dealt with correlated shadow fading that represents the most realistic situation. On the other hand, this work introduces a dynamic cooperation cluster framework in which the user is not served with the whole network ( i.e., all access points [APs]) but only the APs that present the best channel conditions regarding that user. In other words, this work proposes partial CE for each user because only APs with the best channel conditions are allowed to compute channel estimates. Consequently, we proposed partial channel estimators that perform the CE process with low complexity, namely, a partial minimum mean square error estimator and a partial element-wise minimum mean square error estimator. In addition, a simple pilot assignment technique is proposed in order to reduce interference signals so that each user experiences low interference from other users. Furthermore, the computational complexity required by each estimator is derived, where it is represented by the number of complex multiplications that each estimator requires in each consistency block. Theoretical and simulated results are provided, where the performance of each estimator is evaluated and analyzed using the normalized mean-square error metric.     

Design of a Symmetric CPW-Fed Patch Antenna for WLAN/WIMAX Applications Using ANN

The upper bound capacity based on the SINR model is a very important parameter when evaluating the performance of the multi-hop wireless ad hoc networks. In this paper, a new upper bound capacity algorithm is proposed. Firstly, we analyzed the classical physics SINR model over the Rayleigh fading channels to establish the relationship between density of nodes and path outage probability. Then, we developed the closed-form expression of the upper bound transmission capacity based on the Weber model for the random networks. Finally, we evaluated effects of parameters in the communication range, density, SINR threshold and fading factors, and consequently transmission capacity of the network by sensitivity analysis. The numerical simulation showed that the optimum density of nodes was existed to obtain the upper bound transmission capacity. The capacity increased firstly and then decreased over the density of nodes increasing. It affected by channel fading factor and communication range sensitively.

     

A NOTE: A MODEL OF STEAM INJECTOR PERFORMANCE

A simple, mathematical model of the steady state performance of a condensing steam injector is developed based on one-dimensional conservation equations. The model involves two distinct flow regions-a stratified annular flow and a downstream dispersed flow. The former regime is modeled using a two fluid, non-equilibrium formulation while the latter is described by a homogeneous non-equilibrium model. The flow regime transition point is not calculated from first principles but must be described empirically. The model is applied to the simulation of experimental data. Good accuracy is achieved especially in cases where a significant condensation potential exists. The major modeling deficiencies are the lack of a predictive flow transition and the need for empirical closure relations for interphasial exchanges and shock calculations. More fundamental experiments are required before qualitative analytical model improvements are possible.     

A linear weighted SIC multiuser detector with optimal weighting factor

In this paper, a linear weighted successive interference cancellation (SIC) detector is introduced to overcome the convergence issues of the conventional linear SIC detector. The latter converges to the decorrelator detector if it converges. The optimal weighting factor is derived using the steepest descent method. Simulation results show that if the optimal weighting factor is used, the convergence speed and thus the BER of the proposed structure can be significantly enhanced.     

Experimental study on passive Soil Depressurisation System to prevent soil gaseous pollutants into building

The following paper focuses on the study of the ability and the efficiency of passive Soil Depressurisation System which helps to prevent buildings from gaseous pollutants coming from the ground. The Soil Depressurisation System (S.D.S.) is one of the most effective methods of lowering gaseous pollutants (radon) levels and for remedial measures. This system is mainly used with a fan which enables to extract mechanically the air from the sub-slab region in order to under pressurise it. Nevertheless, in this study the soil depressurisation is obtained naturally using thermal buoyancy and wind effect. When natural forces are insufficient, hybrid solutions have been tested using stato-mechanical extractor (operating mechanically or statically). One-year follow up of a passive S.D.S. has been carried out in an experimental house in order to analyse the performance of such a system over time. A specific sump has been installed in the sub-slab region and different parameters have been measured in order to analyse the behaviour of such a system. This paper shows experimental results and the analysis of the one-year follow up. It appears that such a passive system could run efficiently a significant part of the year if properly designed, mainly during cold conditions, when it is more important to have a good protection against soil gas and radon.