An effective back‐off selection technique for reliable beacon reception in VANETs

In safety‐critical scenarios, reliable reception of beacons transmitted by a subject vehicle is critical to avoid vehicle collision. According to the employed contention window sizes in IEEE 802.11p, beacons are transmitted with a small contention window size. As a result, multiple vehicles contend for the shared channel access by selecting the same back‐off slot. This is a perfect recipe for synchronous collisions wherein reliable beacon delivery cannot be guaranteed for any vehicle. We consider the problem of selecting the back‐off slots from the current contention window to provide reliable delivery of beacons transmitted by a subject vehicle to its neighbors. Given a safety scenario, we propose a Pseudo‐Random Number Generator (PRNG)‐inspired back‐off selection (PBS) technique. The proposed technique works on the hypothesis that synchronous collisions of beacons transmitted by a subject vehicle can be reduced if all its neighbors select different back‐off slots (ie, not the back‐off slot selected by the subject vehicle). The discrete‐event simulations demonstrate that PBS can increase the overall message reception from a subject vehicle, in comparison with the uniform random probability back‐off selection in IEEE 802.11p.     

3D Porous Cu Current Collectors Derived by Hydrogen Bubble Dynamic Template for Enhanced Li Metal Anode Performance

Lithium (Li) metal is the most ideal anode material for high‐energy density batteries. However, the high activity of Li metal, the large volume change, and Li dendrite formation during cycling hinder its practical application. Herein, 3D porous Cu synthesized through a simple time‐saving hydrogen bubble dynamic template method is used as a host for the improved performance Li metal anode. Contrary to the planar Cu foil, the synthesized 3D porous structure can reduce the local current density, suppress the mossy/dendritic Li growth, and buffer the volume change in the Li metal anode. Highly stable Coulombic efficiency is achieved at different specific current densities (0.5, 1, and 2 mA cm^?2) with a capacity of 1.0 mAh cm^?2. Moreover, symmetrical Li|Li‐3D Cu cells show more stable cyclic performance with a lower overpotential even at a high current density of 3 mA cm^?2.     

Special Issue: Technological Advancements in Wireless and Optical Communication Systems

Wireless Personal Communications -     

SER and throughput analysis of space–time analog network coded relaying system over shadowed Rician fading channels

Wireless Networks - This research article presents an innovative approach based on analog network coding (ANC) in conjunction with space time block coding (STBC) which is termed as space time...     

Collision Free Mobility Adaptive (CFMA) MAC for wireless sensor networks

In this paper we propose high throughput collision free, mobility adaptive and energy efficient medium access protocol (MAC) called Collision Free Mobility Adaptive (CFMA) for wireless sensor networks. CFMA ensures that transmissions incur no collisions, and allows nodes to undergo sleep mode whenever they are not transmitting or receiving. It uses delay allocation scheme based on traffic priority at each node and avoids allocating same backoff delay for more than one node unless they are in separate clusters. It also allows nodes to determine when they can switch to sleep mode during operation. CFMA for mobile nodes provides fast association between the mobile node and the cluster coordinator. The proposed MAC performs well in both static and mobile scenarios, which shows its significance over existing MAC protocols proposed for mobile applications. The performance of CFMA is evaluated through extensive simulation, analysis and comparison with other mobility aware MAC protocols. The results show that CFMA outperforms significantly the existing CSMA/CA, Sensor Mac (S-MAC), Mobile MAC (MOB-MAC), Adaptive Mobility MAC (AM-MAC), Mobility Sensor MAC (MS-MAC), Mobility aware Delay sensitive MAC (MD-MAC) and Dynamic Sensor MAC (DS-MAC) protocols including throughput, latency and energy consumption.     

Industrie 4.0 Readiness: Green Computing in Relation with Key Performance Indicator for a Manufacturing Industry

Mobile Networks and Applications - An effective measure of Key Performance Indicators (KPIs) is of great significance to enhance the capabilities of a decision support system (DSS) of any...     

Geometrical design of thin film photovoltaic modules for improved shade tolerance and performance

Partial shading in photovoltaic modules is an important reliability and performance concern for all photovoltaic technologies. In this paper, we show how cell geometry can be used as a design variable for improved shade tolerance and performance in monolithic thin film photovoltaic modules (TFPV). We use circuit simulations to illustrate the geometrical aspects of partial shading in typical monolithic TFPV modules with rectangular cells, and formulate rules for shade tolerant design. We show that the problem of partial shading can be overcome by modifying the cell shape and orientation, while preserving the module shape and output characteristics. We discuss two geometrical designs with cells arranged in radial and spiral patterns, which (i) prevent the reverse breakdown of partially shaded cells, (ii) improve the overall power output under partial shading, and (iii) in case of spiral design, may additionally improve the module efficiency by reducing sheet resistance losses. We compare these designs quantitatively using realistic parameters and discuss the practical aspects for their implementation. Copyright © 2013 John Wiley & Sons, Ltd.     

A Dual Ring Connectivity Model for VANET Under Heterogeneous Traffic Flow

Vehicular ad-hoc network (VANET) is characterized as a highly dynamic wireless network due to the dynamic connectivity of the network nodes. To achieve better connectivity under such dynamic conditions, an optimal transmission strategy is required to direct the information flow between the nodes. Earlier studies on VANET’s overlook the characteristics of heterogeneity in vehicle types, traffic structure, flow for density estimation, and connectivity observation. In this paper, we have proposed a heterogeneous traffic flow based dual ring connectivity model to enhance both the message disseminations and network connectivity. In our proposed model the availability of different types of vehicles on the road, such as, cars, buses, etc., are introduced in an attempt to propose a new communication structure for moving vehicles in VANETl under cooperative transmission in heterogeneous traffic flow. The model is based on the dual-ring structure that forms the primary and secondary rings of vehicular communication. During message disseminations, Slow speed vehicles (buses) on the secondary ring provide a backup path of communication for high speed vehicles (cars) moving on the primary ring. The Slow speed vehicles act as the intermediate nodes in the aforementioned connectivity model that helps improve the network coverage and end-to-end data delivery. For the evaluation and the implementation of dual-ring model a clustering routing scheme warning energy aware cluster-head is adopted that also caters for the energy optimization. The implemented dual-ring message delivery scheme under the cluster-head based routing technique does show improved network coverage and connectivity dynamics even under the multi-hop communication system.     

Carrier Transport Enhancement Mechanism in Highly Efficient Antimony Selenide Thin-Film Solar Cell

Exhibiting outstanding optoelectronic properties, antimony selenide (Sb₂Se₃) has attracted considerable interest and has been developed as a light absorber layer for thin-film solar cells over the decade. However, current state-of-the-art Sb₂Se₃ devices suffer from unsatisfactory “cliff-like” band alignment and severe interface recombination loss, which deteriorates device performance. In this study, the heterojunction interface of an Sb₂Se₃ solar cell is improved by introducing effective aluminum (Al³⁺) cation into the CdS buffer layer. Then, the energy band alignment of Sb₂Se₃/CdS:Al heterojunction is modified from a “cliff-like” structure to a “spike-like” structure. Finally, heterojunction interface engineering suppresses recombination losses and strengthens carrier transport, resulting in a high efficiency of 8.41% for the substrate-structured Sb₂Se₃ solar cell. This study proposes a facile strategy for interfacial treatment and elucidates the related carrier transport enhancement mechanism, paving a bright avenue to overcome the efficiency bottleneck of Sb₂Se₃ thin-film solar cells.     

Composite Nanostructures of TiO2 and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation

The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO₂) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO₂ and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO₂ encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO₂ at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.