Fast Handover in Hierarchical Mobile IPv6 Based on Motion Pattern Detection of Mobile Node

To meet the increasing communication requirement for people in ubiquitous environments, some handover schemes and improvements were proposed by the IETF in order to support mobility effectively. FHMIPv6 combines the advantages of FMIPv6 and HMIPv6. This paper proposes an improved scheme based on FHMIPv6 which mainly implements a combined-detection function between Mobile Node (MN) and Mobility Anchor Point (MAP) and calculates the Normalized Edit Distance to analyze the motion trail and estimate the motion pattern of MN. According to the estimating result, MAP determines the way MN attaches to the new access point so as to reuse some previous handover information and intellectualize the handover process to avoid redundant binding updating. Simulation results based on Network Simulation 2 (NS2) show that this improved scheme can reduce the packet’s loss rate and handover latency, enhance the throughput and improve the network performance as a whole, especially for MN with the Ping-Pong motion pattern.     

A Probabilistic Approach to Predict Thermal Fatigue Life for Ball Grid Array Solder Joints

Numerous studies of the reliability of solder joints have been performed. Most life prediction models are limited to a deterministic approach. However, manufacturing induces uncertainty in the geometry parameters of solder joints, and the environmental temperature varies widely due to end-user diversity, creating uncertainties in the reliability of solder joints. In this study, a methodology for accounting for variation in the lifetime prediction for lead-free solder joints of ball grid array packages (PBGA) is demonstrated. The key aspects of the solder joint parameters and the cyclic temperature range related to reliability are involved. Probabilistic solutions of the inelastic strain range and thermal fatigue life based on the Engelmaier model are developed to determine the probability of solder joint failure. The results indicate that the standard deviation increases significantly when more random variations are involved. Using the probabilistic method, the influence of each variable on the thermal fatigue life is quantified. This information can be used to optimize product design and process validation acceptance criteria. The probabilistic approach creates the opportunity to identify the root causes of failed samples from product fatigue tests and field returns. The method can be applied to better understand how variation affects parameters of interest in an electronic package design with area array interconnections.     

Synthesis of Silver Nanocrystallites by a New Thermal Decomposition Method and Their Characterization

We formed silver nanocrystallites by the thermal decomposition of a Ag+¹‐oleate complex, which was prepared by a reaction with AgNO₃ and sodium oleate in a water solution. The resulting monodispersed silver nanocrystallites were produced by controlling the temperature (290 °C). Transmission electron microscopic (TEM) images of the particles showed a 2‐dimensional assembly of the particles with a diameter of 9.5 ± 0.7 nm, demonstrating the uniformity of these nanocrystallites. An energy‐dispersive X‐ray (EDX) spectrum and X‐ray diffraction (XRD) peaks of the nanocrystallites showed the highly crystalline nature of the silver structure. We analyzed the decomposition of the Ag⁺¹‐oleate complex using a Thermo Gravimetric Analyzer (TGA) and observed the crystallization process using XRD.     

Structure and Thermoelectric Properties of Te- and Ge-Doped Skutterudites CoSb<Subscript>2.875−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>0.125</Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

n-Type CoSb_2.875−x Ge_0.125Te _x (x = 0.125 to 0.275) compounds with different Te contents have been synthesized by a melt–quench–anneal–spark plasma sintering method, and the effects of Te content on the structure and thermoelectric properties have been investigated. The results show that all specimens exhibited n-type conduction characteristics. The solubility limit of Te in CoSb_2.875−x Ge_0.125Te _x is found to be x = 0.25. The solubility of Te in CoSb₃ is increased through charge compensation of the element Ge. The room-temperature carrier concentration N _p of CoSb_2.875−x Ge_0.125Te _x skutterudites increases with increasing Te content, and the compounds possess high power factors. The maximum power factor of 3.89 × 10⁻³ W m⁻¹ K⁻² was obtained at 720 K for the CoSb_2.625Ge_0.125Te_0.25 compound. The thermal conductivity decreases dramatically with increasing Te content due to strong point defect scattering. The maximum value of the thermoelectric figure of merit ZT = 1.03 was obtained at 800 K for CoSb_2.625Ge_0.125Te_0.25, benefiting from a lower thermal conductivity and a higher power factor. The figure of merit is competitive with values reported for single-filled skutterudites.     

Molecular Dynamics Simulation of MBE Growth of CdTe/ZnTe/Si

We simulate in three dimensions molecular beam epitaxial (MBE) growth of CdTe/ZnTe/Si using classical molecular dynamics. Atomic interactions are simulated with Stillinger–Weber potentials, whose parameters are obtained by fitting to experimental data or density function theory-calculated distortion energies of the component crystals. The effects of substrate temperature and atomic species flux ratios on epilayer morphology are investigated. The agreement between simulations and experiments suggests that this model has reasonable ability to predict the microstructures of CdTe/ZnTe/Si grown by MBE.     

A stochastic approximation approach to active queue management

Recently, a dynamic adaptive queue management with random dropping (AQMRD) scheme has been developed to capture the time-dependent variation of average queue size by incorporating the rate of change of average queue size as a parameter. A major issue with AQMRD is the choice of parameters. In this paper, a novel online stochastic approximation based optimization scheme is proposed to dynamically tune the parameters of AQMRD and which is also applicable for other active queue management (AQM) algorithms. Our optimization scheme significantly improves the throughput, average queue size, and loss-rate in relation to other AQM schemes.     

Dynamic wavelet-based pilot allocation algorithm for OFDM-based cognitive radio systems

In a cognitive radio system, the goal is to make better use of the radio electric spectrum, allowing non-licensed users access to those currently unused electromagnetic bands assigned to licensed users (LUs). This can be achieved using OFDM, where the non-licensed users must select the temporarily available subcarriers and turn off those subcarriers used by LUs in order to avoid interference. Hence, only a subset of the subcarriers can be used for data or pilot tone transmission. To this end, some pilot allocation algorithms have been proposed for this dynamic scenario, but they are designed in such away that an equispaced pilot placement is respected (as much as possible) while minimizing the mean squared error of the channel estimate. Nevertheless, this equispaced placement can lead to the use of an increased number of pilots in order to achieve a good channel estimation. In this work, a new pilot allocation algorithm based on wavelet transform is presented. The proposed algorithm uses the discrete wavelet transform to analyze the previous channel state information, taking the knowledge of the available subcarriers into account to provide a suboptimal solution for the pilot positions. This solution leads to a non-equispaced pilot placement, which improves the channel estimation and consequently, the system performance. Likewise, the introduced algorithm allows a reduction of the number of necessary pilots, which aids in increasing the data rate. Finally, simulation results corroborate the effectiveness of the algorithm in dynamic channel scenarios.     

Using mobile phones to enhance computing platform trust

This paper presents a new method to enhance the trust of traditional computing device by using the popular mobile phone. We first propose a formal method to analyze the platform trust establishment process based on trusted computing technology, and the formal results reveal possible attack and suggest potential solutions. Then, we design an improved solution, in which the mobile phone is extended to support three trusted computing functions: using mobile phone as a root of trust instead of Trusted Platform Module, as a local investigator to obtain evidences from the local computing platform, and as a trusted agent to build a secure communication channel with an external entity in the remote attestation applications. Finally, to describe the feasibility and efficiency, a prototype of the trusted mobile phone is implemented and evaluated based on an ARM development board.     

Proportional-fair energy-efficient radio resource allocation for OFDMA smallcell networks

This paper investigates the energy-efficient radio resource allocation problem of the uplink smallcell networks. Different from the existing literatures which focus on improving the energy efficiency (EE) or providing fairness measured by data rates, this paper aims to provide fairness guarantee in terms of EE and achieve EE-based proportional fairness among all users in smallcell networks. Specifically, EE-based global proportional fairness utility optimization problem is formulated, taking into account each user’s quality of service, and the cross-tier interference limitation to ensure the macrocell transmission. Instead of dealing with the problem in forms of sum of logarithms directly, the problem is transformed into a form of sum of ratios firstly. Then, a two-step scheme which solves the subchannel and power allocation separately is adopted, and the corresponding subchannel allocation algorithm and power allocation algorithm are devised, respectively. The subchannel allocation algorithm is heuristic, but can achieve close-to-optimal performance with much lower complexity. The power allocation scheme is optimal, and is derived based on a novel method which can solve the sum of ratios problems efficiently. Numerical results verify the effectiveness of the proposed algorithms, especially the capability of EE fairness provisioning. Specifically, it is suggested that the proposed algorithms can improve the fairness level among smallcell users by 150–400 % compared to the existing algorithms.     

A joint cross-layer transmission design with time–frequency coded cooperation HARQ for underground coal mine MC-CDMA WSNs

In this paper, multicarrier code division multiple access (MC-CDMA) modulation is adapted to constitute wireless sensors to improve the monitoring performance of wireless sensor networks (WSNs) for underground coal mine. A subcarrier phase compensation algorithm based on selective mapping (SLM) is proposed to reduce the relatively high PAPR of MC-CDMA signal. To further improve the monitoring performance of the underground MC-CDMA WSNs, a joint cross-layer transmission with time–frequency coded cooperation hybrid automatic repeat request (HARQ) is also proposed. The proposed cross-layer transmission combines time–frequency coded cooperation of physical layer with HARQ of media access control (MAC) layer. In the proposed transmission, the cooperative sensor utilizes time–frequency coded cooperation method to retransmit the monitoring information of source sensor at each retransmission time to obtain the coding gain and spatial diversity gain. Simulation results show that the proposed joint cross-layer transmission for underground coal mine MC-CDMA WSNs based on SLM phase compensation has significantly reduced the PAPR of MC-CDMA signal and improved the monitor performance of the coal mine MC-CDMA WSNs.