Architectural Design,Improvement, and Challenges of Distributed Software-Defined Wireless Sensor Networks

Wireless Personal Communications - Software-defined networking (SDN) is widely perceived to simplify network management and monitoring. The introduction of the SDN model into wireless sensor...     

Analysis of the decoupled uplink downlink technique for varying path loss exponent in multi-tier HetNet

In this paper, the impact of varying path loss exponent (PLE) on user association probability, decoupled uplink coverage probability as well as decoupled uplink average spectral efficiency in downlink uplink decoupled (DUDe) multi-tier heterogeneous networks, is investigated. We investigate the effect of the difference in path loss exponents in both macro and small cell environments over uplink network performance. It is assumed that the mobile user connected to the macro base station experience different path loss exponent as compared to when connected to small base station. It is observed that the difference of path loss exponents in both cases has significant effect on the user association probability, decoupled uplink coverage probability as well as decoupled uplink average spectral efficiency. Moreover, in order to further support key findings and make sound comparison between coupled and DUDe performance in varying PLE environment, generalized analytical expressions for coupled association probabilities, along with coupled uplink coverage probability and coupled uplink average spectral efficiency have been derived. The analytical results evaluated in this paper are compared with the computer simulation and found in good agreement. Our analysis shows that decoupling technique performs suboptimal for cases where the environments around macro and small base stations are different with respect to each other. The work explained in this paper highlights the limitation of applying DUDe technique in realistic conditions where the PLEs of cellular tiers are not exactly equal to one another.

     

Time-Domain Block and Per-Tone Equalization for MIMO–OFDM in Shallow Underwater Acoustic Communication

Shallow underwater acoustic (UWA) channel exhibits rapid temporal variations, extensive multipath spreads, and severe frequency-dependent attenuations. So, high data rate communication with high spectral efficiency in this challenging medium requires efficient system design. Multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO–OFDM) is a promising solution for reliable transmission over highly dispersive channels. In this paper, we study the equalization of shallow UWA channels when a MIMO–OFDM transmission scheme is used. We address simultaneously the long multipath spread and rapid temporal variations of the channel. These features lead to interblock interference (IBI) along with intercarrier interference (ICI), thereby degrading the system performance. We describe the underwater channel using a general basis expansion model (BEM), and propose time-domain block equalization techniques to jointly eliminate the IBI and ICI. The block equalizers are derived based on minimum mean-square error and zero-forcing criteria. We also develop a novel approach to design two time-domain per-tone equalizers, which minimize bit error rate or mean-square error in each subcarrier. We simulate a typical shallow UWA channel to demonstrate the desirable performance of the proposed equalization techniques in Rayleigh and Rician fading channels.     

Distributed Online Algorithms for the Agent Migration Problem in WSNs

The mobile agent paradigm has been adopted by several systems in the area of wireless sensor networks as it enables a flexible distribution and placement of application components on nodes, at runtime. Most agent placement and migration algorithms proposed in the literature, assume that the communication rates between agents remain stable for a sufficiently long time to amortize the migration costs. Then, the problem is that frequent changes in the application-level communication may lead to several non-beneficial agent migrations, which may actually increase the total network cost, instead of decreasing it. To tackle this problem, we propose two distributed algorithms that take migration decisions in an online fashion, trying to deal with fluctuations in agent communication. The first algorithm is more of theoretical value, as it assumes infinite storage to keep information about the message exchange history of agents, while the second algorithm is a refined version that works with finite storage and limited information. We describe these algorithms in detail, and provide proofs for their competitive ratio vs. an optimal oracle. In addition, we evaluate the performance of the proposed algorithms for different parameter settings through a series of simulated experiments, also comparing their results with those achieved by an optimal static placement that is computed with full (a posteriori) knowledge of the execution scenarios. Our theoretical and experimental results are a strong indication for the robustness and effectiveness of the proposed algorithms.     

A variational method for geometric regularization of vascular segmentation in medical images

In this paper, a level-set-based geometric regularization method is proposed which has the ability to estimate the local orientation of the evolving front and utilize it as shape induced information for anisotropic propagation. We show that preserving anisotropic fronts can improve elongations of the extracted structures, while minimizing the risk of leakage. To that end, for an evolving front using its shape-offset level-set representation, a novel energy functional is defined. It is shown that constrained optimization of this functional results in an anisotropic expansion flow which is usefull for vessel segmentation. We have validated our method using synthetic data sets, 2-D retinal angiogram images and magnetic resonance angiography volumetric data sets. A comparison has been made with two state-of-the-art vessel segmentation methods. Quantitative results, as well as qualitative comparisons of segmentations, indicate that our regularization method is a promising tool to improve the efficiency of both techniques.     

Steady-state analysis of quantized distributed incremental LMS algorithm without Gaussian restriction

In this paper, we analyze the steady-state performance of the distributed incremental least mean-square (DILMS) algorithm when it is implemented in finite-precision arithmetic. Our analysis in this paper does not consider any distribution of input data. We first formulate the update equation for quantized DILMS algorithm, and then we use a spatial-temporal energy conservation argument to derive theoretical expressions that evaluate the steady-state performance of individual nodes in the network. We consider mean-square error, excess mean-square error, and mean-square deviation as the performance criteria. Simulation results are generated by using two types of signals, Gaussian and non-Gaussian distributed signals. As the simulation results show, there is a good match between the theory and simulation.     

Spectroscopic studies of sol–gel grown CdS nanocrystalline thin films for optoelectronic devices

CdS is one of the highly photosensitive candidate of II–VI group semiconductor material. Therefore CdS has variety of applications in optoelectronic devices. In this paper, we have fabricated CdS nanocrystalline thin film on ultrasonically cleaned glass substrates using the sol–gel spin coating method. The structural and surface morphologies of the CdS thin film were investigated by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) respectively. The surface morphology of thin films showed that the well covered substrate is without cracks, voids and hole. The round shape particle has been observed in SEM micrographs. The particles sizes of CdS nanocrystals from SEM were estimated to be～10–12 nm. Spectroscopic properties of thin films were investigated using the UV–vis spectroscopy, Photoluminescence and Raman spectroscopy. The optical band gap of the CdS thin film was estimated by UV–vis spectroscopy. The average transmittance of CdS thin film in the visible region of solar spectrum found to be～85%. Optical band gap of CdS thin film was calculated from transmittance spectrum ～2.71 eV which is higher than bulk CdS (2.40 eV) material. This confirms the blue shifting in band edge of CdS nanocrystalline thin films. PL spectrum of thin films showed that the fundamental band edge emission peak centred at 459 nm also recall as green band emission.     

Quantum Transport Simulation of Experimentally Fabricated Nano-FinFET

We have utilized the contact-block-reduction (CBR) method, which we extended to allow a charge self-consistent scheme, to simulate experimentally fabricated 10-nm-FinFET device. The self-consistent CBR simulator has been modified to simulate devices with channels along arbitrary crystallographic orientation. A series of fully quantum-mechanical transport simulations has been performed. First, the fin extension length and doping profile have been calibrated to match the experimental data. The process control window for the threshold voltage as a function of fin extension has been extracted for the considered device. Then, a set of transfer characteristics and gate leakage currents have been calculated for different drain voltages. The simulation results have been found to be in good agreement with the experimental data in the subthreshold regime. The device turn-off and turn-on behavior has been examined for different fin widths: 12 (experimental), 10, 8, and 6 nm. Finally, the subthreshold slope degradation at high temperatures has been studied     

Rapid Generation of Biologically Relevant Hydrogels Containing Long‐Range Chemical Gradients

Many biological processes are regulated by gradients of bioactive chemicals. Thus, the generation of materials with embedded chemical gradients may be beneficial for understanding biological phenomena and generating tissue‐mimetic constructs. Here a simple and versatile method to rapidly generate materials containing centimeter‐long gradients of chemical properties in a microfluidic channel is described. The formation of a chemical gradient is initiated by a passive‐pump‐induced forward flow and further developed during an evaporation‐induced backward flow. The gradient is spatially controlled by the backward flow time and the hydrogel material containing the gradient is synthesized via photopolymerization. Gradients of a cell‐adhesion ligand, Arg‐Gly‐Asp‐Ser (RGDS), are incorporated in poly(ethylene glycol)‐diacrylate (PEG‐DA) hydrogels to test the response of endothelial cells. The cells attach and spread along the hydrogel material in a manner consistent with the RGDS‐gradient profile. A hydrogel containing a PEG‐DA concentration gradient and constant RGDS concentration is also shown. The morphology of cells cultured on such hydrogel changes from round in the lower PEG‐DA concentration regions to well‐spread in the higher PEG‐DA concentration regions. This approach is expected to be a valuable tool to investigate the cell–material interactions in a simple and high‐throughput manner and to design graded biomimetic materials for tissue engineering applications.