Secure sensors data acquisition and communication protection in eHealthcare: Review on the state of the art

Recent advances in hardware technology have led to the development of low cost, power efficient and more feature rich devices that are amongst the most critical parts of communication networks. These devices or sensors can now sense data with more accuracy, process it by themselves and send it to the neighboring node or the sink node. However, robust and reliable security mechanisms are not yet properly implemented on these sensors due to their limited energy and computation power. Sensors also play a very important role in eHealthcare systems where ubiquitous patient monitoring is performed. As data is generated from the sensor nodes, reliable, secure and attack-resistant data acquisition and transmission is important for an efficient eHealthcare systems. This survey focuses on security issues of sensors data acquisition and transmission protocols, describing their main security features and comparing them in the context of a secure eHealthcare system. A taxonomy of open issues and future challenges is also discussed with respect to specific security metrics described in the paper.     

Optimal joint load balancing and EDCA configuration of IEEE 802.11 wireless hotspots

Wireless hotspots, ie, infrastructures composed of several IEEE 802.11 access points (APs), are today the most common solution in providing Internet access to a wide and rapidly changing population of users. According to common device implementation, stations establish associations with APs based on the measured strongest Received Signal Strength Indicator level. This usually leads to an uneven distribution of users to APs, increasing the chances of local network congestion. Load balancing (LB) solutions aim at mitigating this problem controlling the distribution of users. The LB algorithms enforce stations to associate with APs that manage a low number of users and/or that have a low traffic load. Usually, LB solutions do not consider traffic priorities or they assume some a priori quality of service (QoS) configuration for users. In this study, we propose a QoS‐LB solution based on the cell breathing technique with the goal of balancing the load in IEEE 802.11e Enhanced Distributed Channel Access (EDCA) Hotspots. The proposed algorithm explores the space of possible power/EDCA configurations by using a branch and bound approach that reduces the number of analyzed configurations and, hence, the time required to find the global optimal solution. The algorithm has been analytically defined and its performance evaluated through simulations and tests in a real test bed. The results prove that the proposed solution is effective in solving the optimal QoS‐LB configuration problem in WiFi hotspots of average size.     

Towards providing optimal energy‐efficiency and throughput for IEEE 802.11 WLANs

IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs.     

On algorithms for digital signal processing of sequences

In this work, we analyze the algebraic structure of fast algorithms for computing one- and two-dimensional convolutions of sequences defined over the fields of rational and complex rational numbers. The algorithms are based on factorization properties of polynomials and the direct sum property of modulo computation over such fields. Algorithms are described for cyclic as well as acyclic convolution. It is shown that under certain nonrestrictive conditions, all the previously defined algorithms over the fields of rational and complex rational numbers are also valid over the rings of finite integers. Examples are presented to illustrate the results.     

Gate oxide reliabilities in MOS (metal-oxide-semiconductor) structures with Ti-polycide gates

We have investigated the thermal degradation of gate oxide in metal-oxide-semiconductor (MOS) structures with Ti-polycide gates. We found that the Ti-diffusion into the underlying polysilicon and consequently to the gate oxide occurs upon thermal cycling processes, which results in the dielectric breakdown of the gate oxide. We also found that the Ti-diffusion is suppressed by the employment of the thin (about 5 nm) titanium nitride (TiN) diffusion barrier layer, which consequently improved the reliability characterisitics of gate oxide significantly.     

Monolithic integration of microlensed resonant photodetectors andvertical cavity lasers

Monolithic integration of high performance microlensed resonant photodetectors and vertical cavity lasers (VCLs) from a single epitaxial growth is presented. The VCLs have sub-200 μA threshold currents. Adjacent detectors have the same operating wavelength and responsivities of ~0.4 A/W with ~6 nm optical bandwidths     

Synthesis of artificial neural networks by transconductors only

Hardware implementation of artificial neural networks has been attracting great attention recently. In this work, the analog VLSI implementation of artificial neural networks by using only transconductors is presented. The signal flow graph approach is used in synthesis. The neural flow graph is defined. Synthesis of various neural network configurations by means of neural flow graph is described. The approach presented in this work is technology independent. This approach can be applied to new neural network topologies to be proposed or used with transconductors designed in future technologies.     

A model for hot-electron-induced MOSFET linear-current degradationbased on mobility reduction due to interface-state generation

A simple model for the hot-electron degradation of MOSFET linear-current drive is developed on the basis of the reduction of the inversion-layer mobility due to the generation of interface states. The model can explain the observed dependence of the device hot-electron lifetime on the effective channel length and oxide thickness by taking into account both the relative nonscalability of the localized damage region and the dependence of the linear-current degradation on the effective vertical electric field E_eff. The model is verified for deep-submicrometer non-LDD n-channel MOSFETs with L_eff=0.2-1.5 μm and T_ox=3.6-21.0 nm. From the correlation between linear-current and charge-pumping degradation, the scattering coefficient α, which relates the number of generated interface states to the corresponding amount of inversion-layer mobility reduction, can be extracted and its dependence on E_eff determined. Using this linear-current degradation model, existing hot-electron lifetime prediction models are modified to account explicitly for the effects of L_eff and T _ox     

Free convection to power‐law fluids from a vertical cone of variable surface temperature

Steady free convection laminar boundary‐layer flow about a heated vertical cone immersed in a quiescent power‐law fluid is investigated. Surface temperature is assumed to have a power‐law variation with the distance. Similarity solutions are obtained numerically for the boundary‐layer velocity and temperature profiles. Magnitudes of the velocity and temperature profiles are found to decrease with increasing values of the flow behaviour index and the surface temperature exponent. The effects of flow behaviour index and the generalized Prandtl number on the surface shear stress and heat flux are determined. Copyright © 2001 John Wiley & Sons, Ltd.     

Solution‐Processable,High‐Performance Flexible Electroluminescent Devices Based on High‐k Nanodielectrics

Flexible alternating‐current electroluminescent (ACEL) devices have attracted considerable attention for their ability to produce uniform light emission under bent conditions and have enormous potential for applications in back lighting panels, decorative lighting in automobiles, and panel displays. Nevertheless, flexible ACEL devices generally require a high operating bias, which precludes their implementation in low power devices. Herein, solution‐processed La‐doped barium titanate (BTO:La) nanocuboids (≈150 nm) are presented as high dielectric constant (high‐k) nanodielectrics, which can enhance the dielectric constant of an ACEL device from 2.6 to 21 (at 1 kHz), enabling the fabrication of high‐performance flexible ACEL devices with a lower operating voltage as well as higher brightness (≈57.54 cd m^?2 at 240 V, 1 kHz) than devices using undoped BTO nanodielectrics (≈14.3 cd m^?2 at 240 V, 1 kHz). Furthermore, a uniform brightness across the whole panel surface of the flexible ACEL devices and excellent device reliability are achieved via the use of uniform networks of crossaligned silver nanowires as highly conductive and flexible electrodes. The results offer experimental validation of high‐brightness flexible ACELs using solution‐processed BTO:La nanodielectrics, which constitutes an important milestone toward the implementation of high‐k nanodielectrics in flexible displays.