Performance Analysis of Mobility-assisted Routing

Traditionally, ad hoc networks have been viewed as a connected graph over which end-to-end routing paths had to be established. Mobility was considered a necessary evil that invalidates paths and needs to be overcome in an intelligent way to allow for seamless communication between nodes. However, it has recently been recognized that mobility can be turned into a useful ally, by making nodes carry data around the network instead of transmitting them. This model of routing departs from the traditional paradigm and requires new theoretical tools to model its performance. A mobility-assisted protocol forwards data only when appropriate relays encounter each other, and thus the time between such encounters, called hitting or meeting times, are of high importance. In this paper, we derive accurate closed form expressions for the expected encounter time between different nodes, under commonly used mobility models. We also propose a mobility model that can successfully capture some important real-world mobility characteristics, often ignored in popular mobility models, and calculate hitting times for this model as well. Finally, we show how these hitting time results can be used to analyze the performance of mobility-assisted routing. We demonstrate that derivative results concerning the delay of various routing schemes are very accurate, under all the mobility models examined. Hence, this work helps in better understanding the performance of various approaches in different settings, and can facilitate the design of new, improved protocols

Effect of embedded nanoparticle surface chemistry on plasmonic organic photovoltaic devices

The effect of noble metal nanoparticle (NP) synthesis method on the plasmonic enhancement of organic photovoltaic device performance by these NPs is reviewed. For direct incorporation into a polymer fullerene bulk heterojunction (BHJ) active layer, chemically synthesized colloidal Au or Ag NPs with organic ligands are generally ineffective. Due to the tendency of the ligands in causing exciton quenching, carrier trapping and recombination, the device power conversion efficiency (PCE) can be lower than a BHJ device without NPs. Ligand-free metal NPs prepared by physical methods such as pulsed laser ablation and electron beam evaporation can enhance the PCE when introduced into the BHJ. An alternative effective approach for both polymer and small molecule BHJ devices is core shell metal–silica NPs. Regardless of synthesis method, the NP size should be controlled to the range of ~50–100 nm to increase light trapping due to scattering and achieve synergistic enhancement. A non-spherical NP morphology with tunable dual localized surface plasmon resonance peaks at visible wavelengths is highly desirable. For core shell metal–silica NPs, the dielectric shell thickness must be optimized to ensure significant localized field enhancement at the surface of the NP.Published versio