基于CoMP传输的分布式异构网络资源分配

摘要：提高无线资源利用效率是缓解日益增长的无线通信需求和有限的可用传输资源之间矛盾的主要途径。基于多点协调（coordinated multipoint,CoMP）传输技术的异构网络在提高频谱效率和能量效率方面具有巨大的潜力,近年来受到学术界和工业界的广泛关注。在研究基于CoMP技术的异构网络资源分配问题的基础上,提出了一种基于交叉熵方法的分布式频谱资源调度算法。仿真实验验证了本文提出方法在系统吞吐量、能量效率以及用户公平性等方面的有效性。     

Localized Recrystallization Induced by Subgrain Rotation in Sn-3.0Ag-0.5Cu Ball Grid Array Solder Interconnects During Thermal Cycling

The evolution of microstructures and grain orientations of a Pb-free solder interconnect during thermal cycling significantly affects its mechanical properties and failure modes. Thus, Sn-3.0Ag-0.5Cu ball grid array assemblies were subjected to thermal cycling to study the thermomechanical responses of the solder interconnects. The orientations and microstructures of the solder interconnects were studied by optical microscopy with cross-polarized light and scanning electron microscopy with an electron backscattered diffraction analysis system. Localized recrystallization behavior was observed in Pb-free solder interconnects during thermal cycling. Closer examination of the very early stage of recrystallization in the same solder interconnect revealed that the subgrains appeared before the formation of the recrystallized grains, and the orientations of the small recrystallized grains separated by high-angle grain boundaries evolved from the initial orientations by subgrain rotation. The localized recrystallization produced fine-grained microstructures during thermal cycling, providing an additional deformation mechanism for the solder interconnects, i.e., grain boundary sliding, which would have been impossible prior to recrystallization. The grain orientation has a strong effect on damage generation and the subsequent failure mode; initiation and propagation of cracks could be facilitated by the intrinsic anisotropic thermomechanical responses of the differently oriented grains, leading to a change in the crack propagation path and corresponding failure mode.     

感应自加热重熔无铅焊料凸台的剪切失效模式

通过两次高频感应重熔制备了Cu焊盘上S n3．5Ag焊料和Sn3．0Ag0．5Cu焊料凸台,并进行了120℃下的老化试验以及老化试件的剪切强度试验,分析了不同老化时间下两种无铅焊料凸台的剪切断裂模式。焊料凸台的剪切载荷-位移曲线的特征以及对焊料凸台剪切断口的扫描电镜形貌分析结果表明,不同老化时间下无铅焊料凸台的剪切断裂表现为塑性、韧性和脆性三种断裂模式。对凸台焊料合金的组织以及界面观察结果表明,随老化时间不断生长的脆性金属间化合物层以及焊料组织粗大是致使断裂失效模式转变的根本原因。     

Monkey King Evolution: an enhanced ebb-tide-fish algorithm for global optimization and its application in vehicle navigation under wireless sensor network environment

Optimization algorithms are proposed to maximize the desirable properties while simultaneously minimizing the undesirable characteristics. Particle Swarm Optimization (PSO) is a famous optimization algorithm, and it has undergone many variants since its inception in 1995. Though different topologies and relations among particles are used in some state-of-the-art PSO variants, the overall performance on high dimensional multimodal optimization problem is still not very good. In this paper, we present a new memetic optimization algorithm, named Monkey King Evolutionary (MKE) algorithm, and give a comparative view of the PSO variants, including the canonical PSO, Inertia Weighted PSO, Constriction Coefficients PSO, Fully-Informed Particle Sawrm, Cooperative PSO, Comprehensive Learning PSO and some variants proposed in recent years, such as Dynamic Neighborhood Learning PSO, Social Learning Particle Swarm Optimization etc. The proposed MKE algorithm is a further work of ebb-tide-fish algorithm and what’s more it performs very well not only on unimodal benchmark functions but also on multimodal ones on high dimensions. Comparison results under CEC2013 test suite for real parameter optimization show that the proposed MKE algorithm outperforms state-of-the-art PSO variants significantly. An application of the vehicle navigation optimization is also discussed in the paper, and the conducted experiment shows that the proposed approach to path navigation optimization saves travel time of real-time traffic navigation in a micro-scope traffic networks.     

Coverage and Association Bias Analysis for Backhaul Constrained HetNets with eICIC and CRE

Heterogeneous networks (HetNets) are envisioned as a key solution to address the ever increasing capacity demand in wireless networks. With the deployment of enhanced radio access technologies, the non-ideal backhaul will become a potential network bottleneck. However, the impact of backhaul capacities (BCs) on the network coverage and offloading are not well understood. To address these issues, using tools from stochastic geometry, we propose a tractable framework for analyzing the impact of BCs on the network coverage and the optimal offloading bias in HetNets with cell range expansion (CRE) and time domain enhanced inter-cell interference coordination (eICIC) techniques. Conditioned on guaranteeing the minimum quality of service (QoS) of serving users, the coverage probability is derived as a function of offloading bias and BC parameters. We show how non-ideal backhaul alters the network coverage and the optimal bias. Compared with the perfect backhaul case, the optimal coverage and the optimal bias exhibit different behaviors in the case of limited BC.     

Improved macroblock level rate control for the spatially scalable extension of H.264/AVC

An improved rate control algorithm, designed for scalable video coders incorporating interlayer prediction, is proposed. Firstly, a Rate Distortion (RD) model for interlayer prediction involving the spatial enhancement layers is devised. An optimised Mean Absolute Difference (MAD) prediction model for the spatial enhancement layers that considers both the MAD from the spatial base layer in the same frame and the MAD from the corresponding macroblock in previous frames is also proposed. Simulation results show that the resulting algorithm produces accurate rate control with an average bit rate error of less than 0.26%. Compared with the JVT-W043 default rate control algorithm of the JSVM, the proposed algorithm improves the average PSNR by up to 0.53 dB or reduces the bit rate by an average of 10.95%. Furthermore, the proposed algorithm can be combined with the existing rate control scheme for H.264/AVC, resulting in further improvements.     

Intrinsic Structure Modification of Electrode Materials for Aqueous Metal-Ion and Metal-Air Batteries

In consideration of low cost, simple operation, safe reliability, and environmental benignity, aqueous rechargeable batteries (ARBs) have attracted great interest among portable electronic devices, energy storage, and power source batteries. As the key components of ARBs, the electrode materials lead to a crucial effect for the overall battery properties, such as working voltage, electrocatalytic activity, capacity, and cycling stability. However, owing to the highly reactive aqueous environment, the electrode materials typically demonstrate a series of issues, including active material dissolution, structural instability, and poor catalytic activity, restricting their application. So far, several researchers have devoted much effort to improve the properties of electrode materials for ARBs. In particular, intrinsic structure modification in terms of vacancy regulation, interlayer engineering, and element doping have been applied to optimize the electronic and phase structure of electrode materials, contributing to elevated ion diffusion, fast charge transfer, and adequate active sites for electrochemical reaction. In this review, recent reports are demonstrated about the intrinsic structure modification of electrode materials in aqueous metal-ion and metal-air batteries, focusing on various regulation strategies and functional mechanisms. Finally, a brief conclusion and perspective is presented to demonstrate constructive suggestions and opinions for further research.     

Investigation of oxygen annealing effects on RF sputter deposited SiC thin films

Amorphous silicon carbide films were deposited by RF sputtering technique using a SiC target. These films were annealed in dry oxygen ambient in the temperature range of 400–700 °C. Subsequently the films were characterized using X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition at each annealing temperature. XPS indicated that increasing the anneal temperature results in a decrease in SiC phase, and an increase in SiO_x. Surface morphology of the oxidized films was characterized using atomic force microscope. Optical absorption studies indicated blue shifting effects as the annealing temperature was increased.     

A portable high-density absolute-measure NIRS imager for detecting prefrontal lobe activity under fatigue driving

Driving fatigue is one of the primary causes of traffic accidents nowadays. It is thus imperative to develop a technique to monitor levels of driving fatigue. The emergent near-infrared spectroscopy (NIRS) is now capable of measuring functional cerebral activities noninvasively and sensitively in terms of hemodynamic responses, shedding light on the possibility to detect signals regarding fatigue-specified cerebral activities. This work innovatively developed a NIRS device aimed at fatigue detection of drivers, and the device was designed to be portable so that it can be easily operated during driving. Moreover, the device is absolute-measure so that the data can be compared among drivers. The probe is high-density and we can visualize brain functional responses after imaging. The high sensitivity, stability, and reliabilities of our device were fully tested in the order of ink experiment, cuff experiment, and on-human test. For the in-situation on-human test, we recruited 3 taxi drivers and collected data by our device during 8 h' driving. It's found that the hemodynamics-represented cerebral activation decreased with driving duration, which indicated our device's strong potential in monitoring fatigue.     

银粉形貌及表面处理对导电胶性能的影响

利用四点探针和电子万能试验机分别测定了同种树脂体系中不同银粉形貌及银粉表面处理下导电胶的体积电阻率和剪切强度,探索了银粉含量、形状尺寸及表面处理对导电胶性能的影响规律.