Improved Approximation Results for the Minimum Energy Broadcasting Problem

In this paper we present new results on the performance of the Minimum Spanning Tree heuristic for the Minimum Energy Broadcast Routing (MEBR) problem. We first prove that, for any number of dimensions d≥2, the approximation ratio of the heuristic does not increase when the power attenuation coefficient α, that is the exponent to which the coverage distance must be raised to give the emission power, grows. Moreover, we show that, for any fixed instance, as a limit for α going to infinity, the ratio tends to the lower bound of Clementi et al. (Proceedings of the 18th annual symposium on theoretical aspects of computer science (STACS), pp. 121–131, 2001), Wan et al. (Wirel. Netw. 8(6):607–617, 2002) given by the d-dimensional kissing number, thus closing the existing gap between the upper and the lower bound. We then introduce a new analysis allowing to establish a 7.45-approximation ratio for the 2-dimensional case, thus significantly decreasing the previously known 12 upper bound (Wan et al. in Wirel. Netw. 8(6):607–617, 2002) (actually corrected to 12.15 in Klasing et al. (Proceedings of the 3rd IFIP-TC6 international networking conference, pp. 866–877, 2004)). Finally, we extend our analysis to any number of dimensions d≥2 and any α≥d, obtaining a general approximation ratio of 3 ^d −1, again independent of α. The improvements of the approximation ratios are specifically significant in comparison with the lower bounds given by the kissing numbers, as these grow at least exponentially with respect to d. The research was partially funded by the European project COST Action 293, “Graphs and Algorithms in Communication Networks” (GRAAL). Preliminary version of this paper appeared in Flammini et al. (Proceedings of ACM joint workshop on foundations of mobile computing (DIALM-POMC), pp. 85–91, 2004).     

嵌入式系统中池式内存分配方法的分析

介绍适合嵌入式系统应用的池式内存分配方法,详细分析AD公司开发的一种实时操作系统核Visual DSP Kernel(VDK)、嵌入式可配置实时操作系统eCos以及自适应通信框架ACE中的池式内存分配方法及具体应用.最后,针对平台异构及嵌入式实时操作系统RTOS的多样性导致的应用软件可复用性差问题,给出使用池式内存分配方法框架开发嵌入式系统软件的思路.     

Compile Time Memory Allocation for Parallel Processes

This paper discusses the problem of allocating storage for the activation records of procedure calls within a system of parallel processes. A compile time storage allocation scheme is given, which determines the relative address within the memory segment of a process for the activation records of all procedures called by the process. This facilitates the generation of an efficient run-time code. The allocation scheme applies to systems in which data and procedures can be shared among several processes. However, recursive procedure calls are not supported.     

用于优化WCET值的片上存储器分配方法

SPM(Scratchpad Memory)是实时嵌入式系统中常见的片上存储器,其分配管理在编译期进行,从而可以在编译完成时确定访存时延.当前的SPM分配方法主要用于减少程序在平均情况下的执行时间.然而,在硬实时系统中,最差情况下的执行时间(WCET, Worst-Case Execution Time)是更为关键的指标.通过分析优化程序WCET值过程中存在的主要问题以及现有算法,基于变量公用度概念,提出一种启发式搜索算法用于最小化程序WCET值的数据变量SPM分配,实验表明,论文提出的分配方法可获得更好的优化效果.     

文件分配问题的一种动态解决算法

文件分配问题 (FAP)是计算机网络和分布式系统优化中的经典问题 .分析了 FAP的主要特征 ,提出了一种需求驱动的动态分配算法 ,该算法避免了复杂的运算 ,参数较少且容易采集 ,既能进行文件分配 ,也能回收闲置文件副本 .仿真实验表明 ,该算法在负载平衡、吞吐率和响应时间等方面有明显优势     

Efficient Algorithms for Dynamic Allocation of Distributed Memory

We consider the problem of dynamically allocating and deallocating local memory resources among multiple users in a parallel or distributed system. Given a group of independent users and a collection of interconnected local memory devices, we want to render the fragmentation of the memory resources irrelevant by allowing any user to allocate space for his or her purposes as long as there is space available anywhere in the system. In effect, we would like it to appear to the users as though they are allocating memory from a single central pool of memory, even though the space is distributed throughout the system. Our goal is to devise an on-line allocation algorithm that minimizes two cost measures: first, the fraction of unused space , which arises due to fragmentation of the memory; second, the slowdown needed by the system to service user requests, which arises due to the contention for access to the memory devices. We solve this distributed dynamic allocation problem in near-optimal fashion by devising an algorithm that allows the memory to be used to 100% of capacity despite the fragmentation and guarantees that service delays will always be within a constant factor of optimal. The algorithm is completely on-line (no foreknowledge of user activity is assumed) and can accommodate any sequence of allocations and deallocations by the users that does not violate global memory bounds. We also consider the distributed dynamic allocation problem in the more restrictive setting where the local memory devices are connected by a low-degree fixed-connection network, rather than being fully interconnected. In this case, communication costs must be more explicitly considered in our allocation algorithms. We give allocation algorithms for butterfly and hypercube networks, and prove necessary and sufficient conditions on the total amount of memory space needed for near-optimal algorithms to exist. Received November 5, 1996; revised December 10, 1997.     

Clustering Search for the Berth Allocation Problem

This work presents a new approach to the Berth Allocation Problem (BAP) for ships in ports. Due to the increasing demand for ships carrying containers, the BAP can be considered as a major optimization problem in marine terminals. In this paper, the BAP is considered as dynamic and modeled in discrete case and we propose a new alternative to solve it. The proposed alternative is based on applying the Clustering Search (CS) method using the Simulated Annealing (SA) for solutions generation. The CS is an iterative method which divides the search space in clusters and it is composed of a metaheuristic for solutions generation, a grouping process and a local search heuristic. The computational results are compared against recent methods found in the literature.     

一种改进的OFDM自适应功率分配算法

注水分配算法是实现正交频分复用(OFDM)系统中功率和误比特率受限条件下总比特速率最大化的最优算法,在估计目标值时,常使用基于拉格朗日乘子法的二分算法。针对迭代过程中估计值偏离目标值时收敛较慢的情况,提出混合二分算法。仿真结果证明,该算法比二分算法具有更快的收敛速度。     

高效的闪存空间分配与回收方法

随着闪存容量的不断增长以及企业计算、Web数据管理等新型闪存应用的出现,如何管理大容量闪存的存储空间已成为一个迫切需要解决的问题.针对已有闪存空间管理方法存在的低垃圾回收效率和低空间利用率等问题,提出了一种新的高效的闪存空间分配与回收方法,称为BSFTL.BSFTL将数据块区分为冷热两种类型并采用不同的存储管理方式.实验结果表明,BSFTL方法可以显著降低垃圾回收的代价,同时提供了较高的闪存空间利用率.     

外存模型简化中数据读取及内存分配的优化

由于外存模型的数据量极大,其简化计算只能采用分批读入模型数据并局部处理的方式,其中,数据读入和内存分配的操作对简化效率影响很大,提出一种动态优化方法,在对先处理的一小部分数据进行简化操作的同时,检测数据读取块大小和内存分配模式对简化操作的影响,由此可使不同配置的计算机在处理不同的外存模型时能自适应地得到相应的优化数据读取块大小和内存分配模式,加速后续大量数据的简化操作,实验结果表明,文中方法能有效地提高外存模型简化的效率。     

G语言中的内存分配与管理算法

针对G语言特定的数据要求,提出一种新的内存分配与管理算法,在满足多种基本类型和数组及簇等复杂数据结构的分配与管理的基础七,实现数据的产生及生命周期管理、数据信息的完备性及独立性描述。在不牺牲运行效率的前提下,能够长期稳定地运行,有效避免内存碎片的产生。弗且将此算法在自丰开发的虐拟仪器开发平台LabScene中完整实现,在G语言的解析与运行模型中发挥关键作用。     

一种基于VxWorks的内存分配算法

研究了VxWorks系统内存分配算法,指出了常用内存管理算法的局限性,在此基础上,提出了一种改进的内存分配算法.改进的内存分配算法包括优化的内存块分配算法和快速高效的动态内存分配算法,两者结合使用将会有效提高嵌入式系统的性能.对改进内存算法的实现作了详细的介绍.     

网格多处理机的一种改进的子网分配算法

子网分配问题是指识别并分配一个空闲的、满足指定大小要求的节点机.首先,提出了网格结构中一种新的具有O(N²_a·1og₂N_a)时间复杂度的空闲子网搜索算法,它优于现有的O(N³_a)时间复杂度的搜索算法.然后,用该算法对基于保留因子的最佳匹配类子网分配算法——RF(reservation factor)算法进行了改进,得到了     

改进的奇异摄动自适应移动网格方法

用等分弧长函数来控制网格剖分,用迎风有限差分格式来求解一类奇异摄动两点边值问题的自适应算法。本文用了的数值试验证明了算法的可行性和高效性。     

基于超完美图着色的存储分配算法

为了提高性能,一些应用需要在编译时对主存进行针对性的管理.提出了基于超完美图的主存分配方法,其基本思想是通过生命周期分割将一般的相干图转换为超完美图,从而可以使用已有的线性时间的区间着色算法完成主存的分配.分别基于自底向上的积极生命周期分割策略和自顶向下的被动生命周期分割策略,实现了两个分配算法.初步评测表明,我们的分配算法是有效的编译时管理主存手段.     

实时系统中的动态内存分配算法

针对实时系统中的内存分配问题,分析实时系统应用程序的行为特点,提出一种使用双级离散表和双级索引位图相结合的动态内存分配方法。对于较小的内存分配请求,使用位图索引来加快速度并且降低内存分割的次数。对于较大内存块,使用双级离散表的方法降低内存碎片。实验表明,该方法具有很低的内存碎片率和确定的响应时间,适合实时性要求较高的系统。     

基于数据对象规模的Rank级内存分配方法

利用主存的多bank/rank/channel结构挖掘访存并行性和局部性,是提高系统性能的重要手段.相关研究工作通过sub-rank技术增加可并行工作的存储资源,或在并行程序之间对bank划分,以隔离访存冲突.但上述方法没有考虑在bank/rank资源共存的情况下,单个程序内部数据对象间的冲突问题.通过观察数据在主存中的分布,发现程序的数据倾向聚簇于单个rank中,并提出了一种基于数据对象规模的rank级内存分配方法(data object scale aware rank-level memory allocation, DSRA).DSRA将冲突开销较大的数据对象分散到不同的rank,利用增长的bank/rank资源提高访存性能.DSRA工作在操作系统层,基于编译器和操作系统提供的信息来分析数据对象间的冲突开销,既不用修改源码,也不依赖特殊的底层硬件.基于2款真实处理器对来自NAS Benchmark和SPEC CPU2000中的存储敏感型基准测试程序进行评测.结果表明,在不影响cache失效率的情况下,DSRA通过减少主存访问周期数,可以降低程序的执行时间.与已有的优化技术相比,性能平均提高6.8%,最高性能提升幅度为16%.     

Control Allocation for Double-ended Ferries with Full-scale Experimental Results

International Journal of Control, Automation and Systems - A novel control allocation algorithm for double-ended ferries with symmetrical thruster configuration is proposed. The allocation problem...