Computer design of super-orthogonal space-time trellis codes

Super-orthogonal space-time trellis codes (SOSTTCs) designed by hand can significantly improve the performance of space-time trellis codes. This paper introduces a new representation of SOSTTCs based on a generator matrix that allows a systematic and exhaustive search of all possible codes. This will verify that some of the known codes are optimal, and provides a means to easily implement encoders and decoders with a large number of states without relying on a graphical representation. New codes with up to 256 states that outperform previously known codes are presented     

Multiresolution fMRI activation detection using translation invariant wavelet transform and statistical analysis based on resampling

A new method is proposed for activation detection in event-related functional magnetic resonance imaging (fMRI). The method is based on the analysis of selected resolution levels (a subspace) in translation invariant wavelet transform (TIWT) domain. Using a priori knowledge about the activation signal and trends, we analyze their power in different resolution levels in TIWT domain and select an optimal set of resolution levels. A randomization-based statistical test is then applied in the wavelet domain for activation detection. This approach suppresses the effects of trends and enhances the detection sensitivity. In addition, since TIWT is insensitive to signal translations, the power analysis is robust with respect to signal shifts. The randomization test alleviates the need for assumptions about fMRI noise. The method has been applied to simulated and experimental fMRI datasets. Comparisons have been made between the results of the proposed method, a similar method in the time domain and the cross-correlation method. The proposed method has shown superior sensitivity compared to the other methods.     

An improved cluster formation process in wireless sensor network to decrease energy consumption

Wireless sensor network has special features and many applications, which have attracted attention of many scientists. High energy consumption of these networks, as a drawback, can be reduced by a hierarchical routing algorithm. The proposed algorithm is based on the Low Energy Adaptive Clustering Hierarchy (LEACH) and Quadrant Cluster based LEACH (Q-LEACH) protocols. To reduce energy consumption and provide a more appropriate coverage, the network was divided into several regions and clusters were formed within each region. In selecting the cluster head (CH) in each round, the amount of residual energy and the distance from the center of each node were calculated by the base station (including the location and residual energy of each node) for all living nodes in each region. In this regard, the node with the largest value had the highest priority to be selected as the CH in each network region. The base station calculates the CH due to the lack of energy constraints and is also responsible for informing it throughout the network, which reduces the load consumption and tasks of nodes in the network. The information transfer steps in this protocol are similar to the LEACH protocol stages. To better evaluate the results, the proposed method was implemented with LEACH LEACH-SWDN, and Q-LEACH protocols using MATLAB software. The results showed better performance of the proposed method in network lifetime, first node death time, and the last node death time.

     

Flexible Prime‐Field Genus 2 Hyperelliptic Curve Cryptography Processor with Low Power Consumption and Uniform Power Draw

This paper presents an energy‐efficient (low power) prime‐field hyperelliptic curve cryptography (HECC) processor with uniform power draw. The HECC processor performs divisor scalar multiplication on the Jacobian of genus 2 hyperelliptic curves defined over prime fields for arbitrary field and curve parameters. It supports the most frequent case of divisor doubling and addition. The optimized implementation, which is synthesized in a 0.13 μm standard CMOS technology, performs an 81‐bit divisor multiplication in 503 ms consuming only 6.55 μJ of energy (average power consumption is 12.76 μW). In addition, we present a technique to make the power consumption of the HECC processor more uniform and lower the peaks of its power consumption.     

Optimal rate allocation in successively structured Gaussian CEO problem

We consider the Chief Executive Officer (CEO) problem in which agents encode their observations without collaborating with each other and send through rate constrained noiseless channels to a fusion center (FC).We apply the successive coding strategy into this problem and determine the closed-form expressions for optimal rates in order to achieve the minimum distortion under a sum-rate constraint. We show that the optimal sum-rate distortion performance for the Gaussian CEO problem is achievable using the successive coding strategy which is inherently a low complexity approach of obtaining a prescribed distortion. We also determine the optimal rate allocation region for the successively structured Gaussian CEO problem.     

Reliability and Mobility Load Balancing in Next Generation Self-organized Networks: Using Stochastic Learning Automata

Self-organizing networking (SON) is an automation technology designed to make the planning, configuration, management, optimization and healing of mobile radio access networks simpler and faster. Most current self-organization networking functions apply rule-based recommended systems to control network resources which seem too complicated and time-consuming to design in practical conditions. This research proposes a cognitive cellular network empowered by an efficient self-organization networking approach which enables SON functions to separately learn and find the best configuration setting. An effective learning approach is proposed for the functions of the cognitive cellular network, which exhibits how the framework is mapped to SON functions. One of the main functions applied in this framework is mobility load balancing. In this paper, a novel Stochastic Learning Automata has been suggested as the load balancing function in which approximately the same quality level is provided for each subscriber. This framework can also be effectively extended to cloud-based systems, where adaptive approaches are needed due to unpredictability of total accessible resources, considering cooperative nature of cloud environments. The results demonstrate that the function of mobility robustness optimization not only learns to optimize HO performance, but also it learns how to distribute excess load throughout the network. The experimental results demonstrate that the proposed scheme minimizes the number of unsatisfied subscribers (N_us) by moving some of the edge users served by overloaded cells towards one or more adjacent target cells. This solution can also guarantee a more balanced network using cell load sharing approach in addition to increase cell throughput outperform the current schemes.

     

Self-Management for Access Points Coverage Optimization and Mobility Agents Configuration in Future Access Networks

A key challenge for the management systems of future networks is the reduction of human interventions in the fundamental management functions. These include mechanisms that render the networks capable to configure, optimize, heal and protect itself, but also handle the emerging complexity. Demands for the future internet networks mandate the rapid assessment of the feasibility of such cognitive management architectures that shall bridge the gap between conceptual design and practical network deployments. In this paper, a novel architecture is introduced, based on organized distribution of control feedback cycles at locations allocated across network’s operational elements. Two realisations of self-management in the operations of wired and wireless access network segments are presented. The first one is focused on organization of the wireless access regions in networks by the use of compartments of access points for enabling coverage optimization. A compartment-based approach facilitates the more efficient usage of network resources, exploiting local situation awareness and local optimisation features, according to the varying traffic needs. The second realization shows the control of mobility management processes in wired parts of access networks for balancing utilization of network resources. A dynamic deployment and re-configuration of mobility agents permit to tackle the problem of congestion induced by mobility agents in mobile protocols and combined with a dynamic access router assignment, network resources are efficiently balanced within the network. The paper concludes with findings and recommendations on how common principles of self-management evolve from design theory to practice.     

Hydroxyapatite Modified with Carbon‐Nanotube‐Reinforced Poly(methyl methacrylate): A Nanocomposite Material for Biomedical Applications

The paper reports on a freeze‐granulation technique to prepare a novel nanocomposite of poly(methyl methacrylate) (PMMA)‐modified hydroxyapatite (HA) with multiwalled carbon nanotubes (MWCNTs) as reinforcement for a new generation biomedical bone cement and implant coatings. By using this technique it is possible to increase material homogeneity and also enhance the dispersion of MWCNTs in the composite matrix. The phase composition and the surface morphology of the nanocomposite material were studied using X‐ray diffraction, field‐emission scanning electron microscopy, and micro‐Raman spectroscopy. Additionally, nanomechanical properties of different concentrations of MWCNT‐reinforced nanocomposite were performed by a nanoindentation technique, which indicates that a concentration of 0.1 wt % MWCNTs in the PMMA/HA nanocomposite material gives the best mechanical properties.     

Temperature profile effects in accelerated thermal cycling of SnPb and Pb-free solder joints

Accelerated thermal cycling (ATC) has been widely used in the microelectronics industry for reliability assessment. ATC testing decreases life cycle test time by one or more of the following means: increasing the heating and cooling rate, decreasing the hold time, or increasing the range of the applied temperature. The relative effect of each of these cycle parameters and the failure mechanisms they induce has been the subject of many studies; however uncertainty remains, particularly regarding the role of the heating and cooling rate. In this research, three conditions with two ramp rates (14 °C/min and 95 °C/min) and two temperature ranges (ΔT = 0–100 °C and −40 to 125 °C) were applied to resistor 2512 and PBGA 256 test vehicles assembled with SnPb and Pb-free solders. The test results showed that the higher ramp rate reduced the testing time while retaining the same failure modes, and that the damage per cycle increased with the temperature difference. For the resistors, the Pb-free solder joints lasted longer than the SnPb joints at the smaller ΔT, but were inferior at the larger ΔT. In contrast, the Pb-free solder joints in the PBGA test vehicles lasted longer than the SnPb solder under both conditions.     

An Enhanced A-MSDU Frame Aggregation Scheme for 802.11n Wireless Networks

The main goal of the IEEE 802.11n standard is to achieve a minimum throughput of 100 Mbps at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. A key enhancement at the MAC layer is frame aggregation in which the timing and headers overheads of the legacy MAC are reduced by aggregating multiple frames into a single large frame before being transmitted. Two aggregation schemes have been defined by the 802.11n standard, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). As a consequence of the aggregation, new aggregation headers are introduced and become parts of the transmitted frame. Even though these headers are small compared to the legacy headers they still have a negative impact on the network performance, especially when aggregating frames of small payload. Moreover, the A-MSDU is highly influenced by the channel condition due mainly to lack of subframes sequence control and retransmission. In this paper, we have proposed an aggregation scheme (mA-MSDU) that reduces the aggregation headers and implements a retransmission control over the individual subframes at the MSDU level. The analysis and simulations results show the significance of the proposed scheme, specifically for applications that have a small frame size such as VoIP.