Interference-aware channel assignment in a metropolitan multi-radio wireless mesh network with directional antennas

We investigate the problem of channel assignment in a metropolitan multi-radio wireless mesh network with directional antennas. Our contributions include a new conflict graph model for capturing the interference between links in a mesh network with a known wireless interface communication graph, and a new channel assignment procedure which accounts for interference both between links inside the mesh network, and from external sources. Additionally, we have implemented and evaluated the proposed channel assignment procedure in an actual metropolitan mesh network with 1.6-5 km links. Key components of the channel assignment procedure are the interference model, the link ordering, and the channel selection metric. The experimental results demonstrate how link ordering and the channel selection metric affect performance, in terms of the average packet delay and http latency. The results show that the proposed channel assignment procedure achieves performance very close to a lower bound of the average packet delay, and significantly higher than the performance achieved with a simpler interference-unaware procedure, and a measurement-based scheme that has appeared in the literature, and accounts for interference only from external 802.11 sources. Moreover, we investigate the performance when a different number of channels are available, and the timescales for channel re-assignment.     

平面上散乱数据点的二次曲线拟合

基于代数距离定义目标函数,在6种不同约束条件下得到6条基本二次曲线,最终的拟合二次曲线由6条基本二次曲线系数加权平均产生．用实例对该方法和其他几种方法拟合曲线的误差作了比较,并讨论了基于代数距离目标函数的几何意义．     

Oriented bounding box and octree based global interference detection in 5-axis machining of free-form surfaces

Global interference detection is a critical problem in 5-axis NC machining of free-form surfaces. Based on the hierarchical oriented bounding box (OBB) which is used in virtual reality to detect spatial collisions between 3D objects, a new global interference detection method is developed in this paper. In this method, in order to simplify the computation process of updating tool positions and orientations in 5-axis machining, the cutter and cutter holder are modeled by a hierarchical OBB structure, whereas the workpiece surfaces are approximated by an octree. Interference detection is conducted between the tool OBBs and the gray octants of the surface octree with the separating axis theorem. With the hierarchical structure of octree, if interference is found in one octant, its sub-octants are further processed to locate the exact colliding leaf nodes and the discretized surface points contained in these leaf nodes are tested with a conventional vector calculation method for exact interference detection; if no interference is detected, all the sub-octants are then considered as interference free and are not processed further. Meanwhile, with the hierarchical structure of the tool OBBs, should interference occur between octants and the OBBs in the first level of the hierarchical structure, the sub-OBBs in the second level would be further tested. Otherwise it could be determined with certainty that there is no interference between the tool and the octant.     

On the medial surface approximations of extrusions

Generating the medial surface for a general boundary representation model raises several difficulties. Problems might emerge from the complexity of the resulting equations, singularities caused by unforeseen relative boundary element positions and orientations, etc. The majority of the current algorithms are based on the topology of the boundary representation model and produce wireframes composed of straight lines regardless of the real medial surfaces. Many of the solids used in engineering can be represented by extrusions, delimited by a cross-section and an extrusion distance. This paper develops a fast and efficient method for creating the facetted approximations of the medial surfaces of extrusions generated by sweeping along the normal direction to the generating cross-section.

OFDM系统中减小ICI的分组共轭法研究

以无线移动环境下的OFDM系统为研究对象,围绕载波间干扰（ICI）的消除进行研究。虽然一些传统的ICI消除算法能够达到一定的消除效果,但是还存在着精确性不足,缺少必要的数学分析等缺点。对比之前的ICI自消除算法, 改进了系统模型,提出了一个新的有频率偏移误码率分析方法和降低OFDM数字通信系统中载波间干扰的方法,即分组共轭消除算法。还分析了其得以实现的数学方法,仿真分析的结果展示了这种方法与其他方法的比特误码率（BER）性能对比。     

On-chip glucose biosensor based on enzyme entrapment with pre-reaction to lower interference in a flow injection system

In this study, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized on a sensing chip to entrap glucose oxidase (GOD). The interdigitated array (IDA) electrode and microfluidic channel of the sensing chip was fabricated by photolithography. The IDA electrodes consist of two working electrodes in which one (WE1) was the enzyme-modified electrode and the other was a Pt (WE2) for eliminating noise effect. The microfluidic channel was formed on etched silicon by PDMS (poly(dimethylsiloxane)). In the flow injection analysis, a 0.7 V (vs. Ag/AgCl) was set on enzyme electrode to detect the catalytic product, H₂O₂, and the sensing signal was calibrated using the passed charge rather than the peak current. The linear relationship between the charges and the glucose concentrations, ranging from 1 to 10 mM, was obtained with a sensitivity of 157 μC cm⁻² mM⁻¹. Besides, the response time and the recovery time were about 15 and 35-75 s, respectively. In real human sample test, the error of single-potential and bi-potential were about 140% and 13%, respectively, comparing to the standard value, indicating that the WE2 can lower the interference effect in this system.     

一种联合盲均衡算法

为克服数字基带信号在通过非屏蔽五类双绞线时产生的严重码间干扰(ISI),常采用自适应均衡技术来减小码间干扰,大大降低接收端信号的误码率.最小均方误差(LMS)算法能有效降低码间干扰,但需要训练序列,因此影响传输效率.基于判决引导的最小均方误差(DDLMS)算法不需要训练序列,但在眼图未睁开的情况下,可能出现误判,甚至引...     

基于μ律拟合的小波自适应阈值去噪算法

针对小波阈值去噪法,硬阈值函数处理后信号易产生振荡,软阈值函数处理后信号的失真大等问题,提出了一种基于μ律拟合的新阈值函数。针对语音信号和噪声在不同小波尺度下具有不同的奇异性,即语音信号的小波变换系数的模值随尺度的增加而增加;噪声的小波变换系数的模值随尺度的增大而减小,提出了一种自适应阈值。实验表明,经新算法增强后语音的清晰度和可懂度有了明显的提高。     

Collision detection between point clouds using an efficient k-d tree implementation

Context: An important task in civil engineering is the detection of collisions of a 3D model with an environment representation. Existing methods using the structure gauge provide an insufficient measure because the model either rotates or because the trajectory makes tight turns through narrow passages. This is the case in either automotive assembly lines or in narrow train tunnels.Objective: Given two point clouds, one of the environment and one of a model and a trajectory with six degrees of freedom along which the model moves through the environment, find all colliding points of the environment with the model within a certain clearance radius.Method: This paper presents two collision detection (CD) methods called kd-CD and kd-CD-simple and two penetration depth (PD) calculation methods called kd-PD and kd-PD-fast. All four methods are based on searches in a k-d tree representation of the environment. The creation of the k-d tree, its search methods and other features will be explained in the scope of their use to detect collisions and calculate depths of penetration.Results: The algorithms are benchmarked by moving the point cloud of a train wagon with 2.5 million points along the point cloud of a 1144 m long train track through a narrow tunnel with overall 18.92 million points. Points where the wagon collides with the tunnel wall are visually highlighted with their penetration depth. With a safety margin of 5 cm kd-PD-simple finds all colliding points on its trajectory which is sampled into 19,392 positions in 77 s on a standard desktop machine of 1.6 GHz.Conclusion: The presented methods for collision detection and penetration depth calculation are shown to solve problems for which the structure gauge is an insufficient measure. The underlying k-d tree is shown to be an effective data structure for the required look-up operations.     

Wearing body armour and backpack loads increase the likelihood of expiratory flow limitation and respiratory muscle fatigue during marching

Abstract

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15?kg, 30?kg, 40?kg or 50?kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40?kg only). FVC and FEV₁ were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breaths·min^?1) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases.

Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.