An integrated,programming model-driven framework for NoC–QoS support in cluster-based embedded many-cores

Embedded SoC designs are embracing the many-core paradigm to deliver the required performance to run an ever-increasing number of applications in parallel. Networks-on-Chip (NoC) are considered as a convenient technology to implement many-core embedded platforms. The complex and non-uniform nature of the traffic flows generated when multiple parallel applications are running simultaneously calls for Quality-of-Service (QoS) extensions in the NoC, but to efficiently exploit similar services it is necessary to expose them to the software in a easy-to-use yet efficient manner. In this paper we present an integrated hardware/software approach for delivering QoS on top of an hybrid OpenMP-MPI parallel programming model. Our experimental results show the effectiveness of our proposal over a broad range of benchmarks and application mappings, demonstrating the ability to manage parallelism under QoS requirements effortlessly from the programming model.     

基于移动Agent和WSN的突发事件场景数据收集算法研究

该文针对无线传感器网络应用于突发事件监测场景的能量消耗和网络延迟问题,提出了基于移动Agent的无线传感器网络簇式数据收集算法.动态成簇过程基于事件严重程度,并由其决定簇的生命周期和覆盖范围.Sink和簇头之间形成以Sink节点为簇头的虚拟簇.移动Agent迁移路径规划过程中下一跳节点的选取基于节点剩余能量、路径损耗及受刺激强度.移动Agent通过节点遍历的方式完成对所有簇内成员节点信息的收集.仿真结果表明,相对于C/S数据收集模型,基于移动Agent的模型具有更好的节能效果,并能一定程度地减少网络延迟,尤其适用于大规模无线传感器网络应用.     

Efficiency and effectiveness of query processing in cluster-based retrieval

Our research shows that for large databases, without considerable additional storage overhead, cluster-based retrieval (CBR) can compete with the time efficiency and effectiveness of the inverted index-based full search (FS). The proposed CBR method employs a storage structure that blends the cluster membership information into the inverted file posting lists. This approach significantly reduces the cost of similarity calculations for document ranking during query processing and improves efficiency. For example, in terms of in-memory computations, our new approach can reduce query processing time to 39% of FS. The experiments confirm that the approach is scalable and system performance improves with increasing database size. In the experiments, we use the cover coefficient-based clustering methodology (C³M), and the Financial Times database of TREC containing 210 158 documents of size 564 MB defined by 229 748 terms with total of 29 545 234 inverted index elements. This study provides CBR efficiency and effectiveness experiments using the largest corpus in an environment that employs no user interaction or user behavior assumption for clustering.     

Management and applications of trust in Wireless Sensor Networks: A survey

Wireless Sensors Networks (WSNs) are susceptible to many security threats, and because of communication, computation and delay constraints of WSNs, traditional security mechanisms cannot be used. Trust management models have been recently suggested as an effective security mechanism for WSNs. Considerable research has been done on modeling and managing trust. In this paper, we present a detailed survey on various trust models that are geared towards WSNs. Then, we analyze various applications of trust models. They are malicious attack detection, secure routing, secure data aggregation, secure localization and secure node selection. In addition, we categorize various types of malicious attacks against trust models and analyze whether the existing trust models can resist these attacks or not. Finally, based on all the analysis and comparisons, we list several trust best practices that are essential for developing a robust trust model for WSNs.     

Target localization based on energy considerations in distributed sensor networks

Wireless distributed sensor networks are important for a number of strategic applications such as coordinated target detection, surveillance, and localization. Energy is a critical resource in wireless sensor networks and system lifetime needs to be prolonged through the use of energy-conscious sensing strategies during system operation. We propose an energy-aware target detection and localization strategy for cluster-based wireless sensor networks. The proposed method is based on an a posteriori algorithm with a two-step communication protocol between the cluster head and the sensors within the cluster. Based on a limited amount of data received from the sensor nodes, the cluster head executes a localization procedure to determine the subset of sensors that must be queried for detailed target information. This approach reduces both energy consumption and communication bandwidth requirements, and prolongs the lifetime of the wireless sensor network. Simulation results show that a large amount of energy is saved during target localization using this strategy.     

无线传感网络量化及能量优化策略

由于无线传感网络(WSN)存在能量和带宽的限制,在网络中直接传送模拟信号受到了极大地制约,因此对模拟信号量化是节省网络能量和保证有效带宽的重要手段。为此,该文以融合中心的重构绝对均值误差最小为原则,设计一种网络量化及能量优化方法。首先,针对单传感器,在能量固定的情况下推导了最优量化位数及在量化位数固定的情况下推导了最优能量分配。其次,在单传感器的基础上,进一步推导多传感器情况下最优量化位数及最优能量分配。以上两种情况都考虑了传感器测量噪声及信道衰落损耗。最后,通过数值仿真方法验证了文中所提方法的正确性,并将其与等能量分配进行了比较,获得了较好的效果。

     

基于聚类的小生境克隆选择算法

基于聚类的小生境克隆选择算法是针对小生境克隆选择算法计算复杂、参数设置困难等缺点而提出的。新算法删除了计算复杂度较大的抑制算子,引入聚类算子,并对算法的部分流程进行了调整。新算法不仅计算复杂度降低,而且无需预知峰的个数等先验知识,仅根据样本数据即可找到全部峰值点。仿真实验验证了C-NCSA的完全收敛性;并且通过与小生境克隆选择算法的对比实验证明：在相同的实验条件下,C-NCSA的执行时间比NCSA明显降低。     

A framework using cluster-based hybrid network architecture for collaborative virtual surgery

Research on collaborative virtual environments (CVEs) opens the opportunity for simulating the cooperative work in surgical operations. It is however a challenging task to implement a high performance collaborative surgical simulation system because of the difficulty in maintaining state consistency with minimum network latencies, especially when sophisticated deformable models and haptics are involved. In this paper, an integrated framework using cluster-based hybrid network architecture is proposed to support collaborative virtual surgery. Multicast transmission is employed to transmit updated information among participants in order to reduce network latencies, while system consistency is maintained by an administrative server. Reliable multicast is implemented using distributed message acknowledgment based on cluster cooperation and sliding window technique. The robustness of the framework is guaranteed by the failure detection chain which enables smooth transition when participants join and leave the collaboration, including normal and involuntary leaving. Communication overhead is further reduced by implementing a number of management approaches such as computational policies and collaborative mechanisms. The feasibility of the proposed framework is demonstrated by successfully extending an existing standalone orthopedic surgery trainer into a collaborative simulation system. A series of experiments have been conducted to evaluate the system performance. The results demonstrate that the proposed framework is capable of supporting collaborative surgical simulation.     

Coscheduled distributed-Web servers on system area network

As cluster-based Web servers are increasingly adopted to host a variety of network-based services, improving the performance of such servers has become critical to satisfy the customers’ demands. Especially, the user response time is an important factor so that clients feel satisfied with the Web services. In this paper, we investigate the feasibility of minimizing the response time of a server by exploiting the advantages of both user-level communication and coscheduling. We, thus, propose a coscheduled server model based on the recently proposed distributed PRESS Web server, where the remote cache accesses can be coscheduled on different nodes to reduce the response time. We experiment this concept using two known coscheduling techniques, called dynamic coscheduling (DCS) and DCS with immediate blocking. We have developed a comprehensive simulation testbed that captures the underlying communication layer in a cluster, the characteristics of various coscheduling algorithms, and the characteristics of the distributed server model to estimate the average delay and throughput with different system configurations. The accuracy of the VIA communication layer and the DCS mechanism is verified using measurements on a 16-node Linux cluster. Extensive simulation of four server models (PRESS over VIA, coscheduled PRESS model with DCS, with DCS and blocking, and Adaptive) using 32-node cluster configurations indicates that the average response time of a distributed server can be minimized significantly by coscheduling the communicating processes. The use of the DCS scheme reduced the average latency up to four times to the PRESS over VIA model that uses only user-level communication.     

Numerical study of particle cluster flow in risers with cluster-based approach

Flow behavior of clusters in circulating fluidized beds was predicted by a proposed two-fluid model using a cluster-based approach (CBA). The model was assumed that the particles move as clusters in the riser. The cluster sizes were estimated from the existing correlations found in the literatures. The distributions of pressure drops, particles concentrations and both gas and solids velocities, and cluster diameters were predicted. A core-annular flow structure in risers was observed from simulations. The numerical results were in agreements with experimental data of [Manyele et al., 2002. Chemical Engineering Journal 88, 151-161] and [Knowlton 1995. Workshop at the Eighth Engineering Foundation Conference on Fluidization].