构造移动通信中降低能耗的前缀码的动态规划加速

动态规划是一种常用的寻找问题最优解的算法设计方案。当将动态规划中的各个子问题考虑成有向图上的节点时,我们可以将动态规划看作是一个有向无圈图。一些问题的动态规划的有向无圈图有着特殊的结构,我们可以利用这些结构加速动态规划。本文考虑了一种从基站将能源"转移"到移动通信宿主的二进制编码方案构造时采用的动态规划。移动通信中,常常需要考虑优化通信编码方案来降低移动通信宿主的能耗。本文研究的编码方案通过以下方式降低能耗:基站猜测移动通信宿主所要发出的信息并询问宿主,而宿主则在一定的情况下才做出回应,以此来降低宿主发送信息的能耗。对于有n个单词的编码,我们的算法比之前提出的算法降低了O(n2)的时间复杂度。     

一种改进的LT码置信传播译码

在删除信道上,短信息字长度的LT码采用置信传播译码算法性能较差。提出了一种改进的置信传播译码算法,此算法在置信传播译码失败时只需运用高斯消元法确定少数猜测比特就可实现成功译码。仿真结果显示,相比于置信传播译码,改进的置信传播译码算法在增加少量译码运行时间的代价下获得较大的译码性能改善。     

A NEW DISTRIBUTED LOCATION-BASED ROUTING ALGORITHM FOR WIRELESS SENSOR NETWORKS

Searching and routing procedures are important in order to ensure communication in wireless sensor networks (WSN). Although naive flooding-based searching is simple to implement, it costs a high number of message transmissions and results in high energy consumption. In this study, we propose a new distributed location-based routing algorithm for WSN. Our goal was to decrease the number of message transmissions and to increase coverage by constructing relay zones. Directed broadcast, relay zone, and broadcast suppression constitute the backbone of our algorithm. We compared our algorithm with a flooding-based approach, and saw that our algorithm performs much better for several parameters.     

A scalability comparison of GST and SST MANET multicast routing algorithms

Since network resource of mobile ad hoc network (MANET) is limited due to the contention-based wireless communication channel at the medium access layer and energy of mobile nodes is constrained due to the energy-limited batteries, the scalability issue is one of main research topics in developing MANET routing algorithms. Therefore, this paper analyzes the message complexities of group shared tree (GST) and source-specific tree (SST) that are implemented in most MANET multicast routing algorithms. Simulation demonstrates that in a wireless ad hoc network where SST and GST are well maintained during the simulation, SST algorithm is able to achieve very competitive performance (i.e. less message complexity) under the multiple packet transmissions, in comparison with GST where no core selection algorithm is adopted.     

Generating routing table for free roaming mobile agent in distributed environment

Free roaming mobile agent [D. Xu, L. Harn, M. Narasimhan, J. Luo. “An Improved Free-Roaming Mobile Agent Security Protocol against Colluded Truncation Attacks.” In Proceedings of the 30th Annual international Computer Software and Applications Conference(COMPSAC,06), Volume 2, Page(s):309–314,Chigago, Sept. 2006, IEEE Computer Society Press.; S. Venkatesan, C. Chellappan, “Protecting free roaming mobile agent against multiple colluded truncation attacks”, In proceedings of the 3rd International conference on Mobile Multimedia Communication (Mobimedia'07), page(s): 293–297, August 2007.] is to collect information from more number of remote host using the shortest route. The routing table available in the router is not applicable for the free roaming mobile agent to roam around the network, so each and every server must have the routing information. This paper proposes a model to generate the routing table for the free roaming mobile agent to roam around the network by calculating the link cost between the nodes. Link cost between the servers is measured by the energy consumed to reach the destination. Link cost is measured by the transmission of agent instead of sending the message because here the route is calculated for agent roaming. The cost for transferring the message and the agent differs because of the migration and transfer. In agent transmission, the whole thing will be migrated to the remote host. But in the message transmission, the particular message is transmitted. Routing table in the destination will be generated automatically by the mobile agent while it visits the destination host and the routing table of the source host will be generated after the agent returns to its home (source host).     

Multi-constraint multi-objective QoS aware routing heuristics for query driven sensor networks using fuzzy soft sets

In this paper, a fuzzy based distributed power aware routing scheme considering both energy and bandwidth constraints, especially for query driven applications in the asynchronous duty-cycled wireless sensor networks are devised. The proposed multi-constraint, multi-objective routing optimization approach under strict resource constraints guarantees reliability and fast data delivery along with efficient power management in spite of unreliable wireless links and limited power supply. In query driven applications, the request from the sink to the individual sensor node will be a broadcast message, whereas the individual sensor nodes replies back to sink as unicast messages. In the proposed work, the fuzzy approach and “A Star” algorithm are utilized for satisfying energy and bandwidth constraints to route the broadcast messages of the sink while querying all the sensor nodes in the network. Every node will be provided with a guidance list, which is used to decide the next best neighbor node with good route quality for forwarding the received multi-hop broadcast messages. The route quality of the every node is estimated with fuzzy rules based on the network parameters such as maximum remaining energy, minimum traffic load and better link quality to increase the network lifetime. The provision of overhearing the broadcast messages and acknowledgements within the transmission range minimizes the effort to search for the active time of nodes while routing the broadcast messages with asynchronous scheduling. Further, in the proposed work only the time slot of its nearest neighbor relay node (to which packets are to be forwarded) is learnt to reduce the number of message transmissions in the network. For the unicast message replies, the fuzzy membership function is modified and devised based on the routing metrics such as higher residual energy, minimum traffic loads and minimum hop count under energy and bandwidth constraints. Also, the multi-hop heuristic routing algorithm called Nearest Neighbor Tree is effectively used to reduce the number of neighbors in the guidance list that are elected for forwarding. This helps to increase the individual sensor node’s lifetime, thereby maximizes the network lifetime and guarantees increased network throughput. The simulation results show that the proposed technique reduces repeated transmissions, decreases the number of transmissions, shortens the active time of the sensor nodes and increases the network lifetime for query driven sensor network applications invariant to total the number of sensor nodes and sinks in the network. The proposed algorithm is tested in a small test bed of sensor network with ten nodes that monitors the room temperature.     

一种基于移动计算环境的因果日志卷回恢复算法

由于移动节点的不可靠和无线网络连接的脆弱性,研究移动计算系统容错机制具有重要意义.对可以跨区移动、随时可以与网络断开的自治性很强的移动节点来说,异步的卷回恢复是一种重要的容错手段.现有的移动计算环境下的卷回恢复算法都无法完全实现一致的异步卷回恢复.基于因果消息日志,提出一种新的移动计算环境的卷回恢复算法:通过先行图来记录节点间的消息依赖关系,将异步检查点、基于发送方的暂存消息日志和先行图全部在移动支持站上存储和处理,为移动节点提供一种透明的容错服务,完全消除依赖关系在移动节点之间造成的影响.用形式化的方法证明了系统的一致性.仿真结果表明,在卷回开销达到最低的同时,也显著降低了无错运行时的通信和存储开销.     

Efficient randomised broadcasting in random regular networks with applications in peer-to-peer systems

We consider broadcasting in random d-regular graphs by using a simple modification of the random phone call model introduced by Karp et al. (Proceedings of the FOCS ’00, 2000). In the phone call model, in every time step, each node calls a randomly chosen neighbour to establish a communication channel to this node. The communication channels can then be used bi-directionally to transmit messages. We show that, if we allow every node to choose four distinct neighbours instead of one, then the average number of message transmissions per node required to broadcast a message efficiently decreases exponentially. Formally, we present an algorithm that has time complexity \(O(\log n)\) and uses \(O(n\log \log n)\) transmissions per message. In contrast, we show for the standard model that every distributed algorithm in a restricted address-oblivious model that broadcasts a message in time \(O(\log n)\) requires \(\Omega (n \log n{/} \log d)\) message transmissions. Our algorithm efficiently handles limited communication failures, only requires rough estimates of the number of nodes, and is robust against limited changes in the size of the network. Our results have applications in peer-to-peer networks and replicated databases.     

一种基于时隙的邮件消息发布算法

移动计算环境与固定网络计算环境之间的巨大差异使建立专门的移动查询模型成为必要。该文简单介绍了笔者在工作中提出的一种基于“代理/邮箱”机制的移动查询模型,并以省电的查询过程为研究目标,提出了邮箱机制的核心算法———基于固定时隙分配的邮件消息投递算法,用户在每个消息发布周期内,只需对分配给自己的时隙进行监听,其余时间可以进入睡眠状态,从而达到节省电能的目的。通过对算法的分析和模拟结果表明:第一,与传统的查询过程相比,该算法能够大幅度地降低用户查询过程中处于工作状态时间占全部查询响应时间的比例,从而有效地支持了查询的省电性;第二,算法是以一定的延迟增加为代价来换取省电方面的收益,所以更加适用于大量的对查询实时性要求较低的移动查询应用。     

Evolutionary forwarding games in delay tolerant networks: Equilibria,mechanism design and stochastic approximation

In this paper, we apply evolutionary games to non-cooperative forwarding control in Delay Tolerant Networks (DTNs). The main focus is on mechanisms to rule the participation of the relays to the delivery of messages in DTNs. Thus, we express the success probability as a function of the competition that takes place within a large population of mobiles, and we characterize the effect of reward-based mechanisms on the performance of such systems. Devices acting as active relays, in fact, sacrifice part of their batteries in order to support message replication and thus increase the probability to reach the destination. In our scheme, a relay can choose the strategy by which they participate to the message relaying. A mobile that participates receives a unit of reward based on the reward mechanism selected by the network. A utility function is introduced as the difference between the expected reward and the energy cost, i.e., the cost spent by the relay to sustain forwarding operations. We show how the evolution dynamics and the equilibrium behavior (called Evolutionary Stable Strategy – ESS) are influenced by the characteristics of inter contact time, energy expenditure and pricing characteristics.We extend our analysis to mechanisms that the system can introduce in order to have the message delivered to the destination with high probability within a given deadline and under energy constraints which bound the number of released copies per message. Finally, we apply our findings in order to devise decentralized forwarding algorithms that are rooted in the theory of stochastic approximations. Thus, we demonstrate that the ESS can be attained without complete knowledge of the system state and letting the source monitor number of released copies per message only. We provide extensive numerical results to validate the proposed scheme.     

Event-triggered filtering and fault estimation for nonlinear systems with stochastic sensor saturations

This paper is concerned with the filtering problem for a class of nonlinear systems with stochastic sensor saturations and event-triggered measurement transmissions. An event-triggered transmission scheme is proposed with hope to ease the traffic burden and improve the energy efficiency. The measurements are subject to randomly occurring sensor saturations governed by Bernoulli-distributed sequences. Special effort is made to obtain an upper bound of the filtering error covariance in the presence of linearisation errors, stochastic sensor saturations as well as event-triggered transmissions. A filter is designed to minimise the obtained upper bound at each time step by solving two sets of Riccati-like matrix equations, and thus the recursive algorithm is suitable for online computation. Sufficient conditions are established under which the filtering error is exponentially bounded in mean square. The applicability of the presented method is demonstrated by dealing with the fault estimation problem. An illustrative example is exploited to show the effectiveness of the proposed algorithm.     

Adaptive scheduling for integrated traffic on WDM optical networks

One of the important issues in the design of future generation of high-speed networks is to provide differentiated service to different types of traffic with various time constraints. In this paper, we study the problem of providing real-time service to either hard or soft real-time messages and normal transmission service to variable-length messages without time constraints in WDM optical networks. We propose an adaptive scheduling algorithm for scheduling message transmissions in order to improve the network performance when both real-time and non real-time messages are transmitted in one topology. We have analyzed the complexity of the algorithm to show its feasibility. We have conducted extensive discrete-event simulations to evaluate the performance of the proposed algorithm. The study suggests that when scheduling message transmission in WDM networks differentiated services should be considered in order to meet time constraints of real-time messages while non real-time messages are being served so that the overall performance of the network could be improved.     

Message Batching in Wireless Sensor Networks—A Perturbation Analysis Approach

We address the problem of batching messages generated at nodes of a sensor network for the purpose of reducing communication energy at the expense of added latency. We consider a time-based batching approach. We first develop baseline analytical models based on Markovian assumptions, derive conditions under which batching is profitable, and explicitly determine a batching time that optimizes a performance metric capturing the trade-off between communication energy and message latency. We then provide an on-line performance optimization method based on Smoothed Perturbation Analysis (SPA) for estimating the performance sensitivity with respect to the controllable batching time. We prove that the SPA gradient estimator is unbiased and combine it with a Stochastic Approximation (SA) algorithm for on-line optimization. Numerical results are provided for Poisson and Markov modulated Poisson message arrival processes and illustrate the effectiveness of the message batching scheme.     

IEEE 802.16e休眠模式算法的研究和改进

IEEE 802.16e为移动站点提供了大范围的无线接入,为了减少移动站点的功率消耗,它提出了一种节能机制休眠模式.移动站点在休眠间隔后进入监听间隔,检查其间是否有数据分组到达.如果有,它将进入清醒状态接收数据,否则,继续进入休眠间隔.草案中所提出的休眠模式指数增长算法在低业务量情况下,响应时间过长.文中提出了线性增长算法解决这一问题,理论分析了该算法的两个性能指标平均响应时间和平均能量消耗.并结合仿真实验,对比了这两种算法的性能,证实了后者具有较好的性能.进一步分析了休眠模式各个参数对上述两个性能指标的影响,对参数值的选取有重要帮助.     

Fairness-related challenges in mobile opportunistic networking

The fundamental challenge in opportunistic networking, regardless of the application, is when and how to forward a message. Rank-based forwarding techniques currently represent one of the most promising methods for addressing this message forwarding challenge. While these techniques have demonstrated great efficiency in performance, they do not address the rising concern of fairness amongst various nodes in the network. Higher ranked nodes typically carry the largest burden in delivering messages, which creates a high potential of dissatisfaction amongst them. In this paper, we adopt a real-trace driven approach to study and analyze the trade-offs between efficiency, cost, and fairness of rank-based forwarding techniques in mobile opportunistic networks.Our work comprises three major contributions. First, we quantitatively analyze the trade-off between fair and efficient environments. Second, we demonstrate how fairness coupled with efficiency can be achieved based on real mobility traces. Third, we propose FOG, a real-time distributed framework to ensure efficiency–fairness trade-off using local information. Our framework, FOG, enables state-of-the-art rank-based opportunistic forwarding algorithms to ensure a better fairness–efficiency trade-off while maintaining a low overhead. Within FOG, we implement two real-time distributed fairness algorithms; Proximity Fairness Algorithm (PFA), and Message Context Fairness Algorithm (MCFA). Our data-driven experiments and analysis show that mobile opportunistic communication between users may fail with the absence of fairness in participating high-ranked nodes, and an absolute fair treatment of all users yields inefficient communication performance. Finally our analysis shows that FOG-based algorithms ensure relative equality in the distribution of resource usage among neighbor nodes while keeping the success rate and cost performance near optimal.     

A fault tolerant mutual exclusion algorithm for mobile ad hoc networks

In this paper, we propose a permission-based message efficient mutual exclusion (MUTEX) algorithm for mobile ad hoc networks (MANETs). To reduce messages cost, the algorithm uses the “look-ahead” technique, which enforces MUTEX only among the hosts currently competing for the critical section. We propose mechanisms to handle dozes and disconnections of mobile hosts. The assumption of FIFO channel in the original “look-ahead” technique is also relaxed. The proposed algorithm can also tolerate link or host failures, using timeout-based mechanisms. Both analytical and simulation results show that the proposed algorithm works well under various conditions, especially when the mobility is high or load level is low. To our knowledge, this is the first permission-based MUTEX algorithm for MANETs.     

使用发布订阅中间件支持移动计算

提出了一个扩展发布订阅中间件以支持移动计算的新协议．该协议针对移动计算的需求，由老的事件代理暂存客户移动期间到达的消息，客户在连接到新的事件代理后，消息被自动有序发送给客户，保证了移动透明性．此外协议采用同步算法和消息合并操作防止了消息丢失和重复．移动客户可以在不同的地域与不同的事件代理节点连接和可靠接收消息．实验表明谈协议完全满足移动应用的要求，保证了应用的透明性、消息完整性和有序性．     

Circuit-switched broadcasting in torus networks

In this paper we present three broadcast algorithms and lower bounds on the three main components of the broadcast time for 2-dimensional torus networks (wrap-around meshes) that use synchronous circuit-switched routing. The first algorithm is based on a recursive tiling of a torus and is optimal in terms of both phases and intermediate switch settings when the start-up time to initiate message transmissions is the dominant cost. It is the first broadcast algorithm to match the lower bound of log₅ N on number of phases (where N is the number of nodes). The second and third algorithms are hybrids which combine circuit-switching with the pipelining and arc-disjoint spanning trees techniques that are commonly used to speed up store-and-forward routing. When the propagation time of messages through the network is significant, our hybrid algorithms achieve close to optimal performance in terms of phases, intermediate switch settings, and total transmission time. They are the first algorithms to achieve this performance in terms of all three parameters simultaneously     

A scalable group communication mechanism for mobile agents

Many multi-agent applications based on mobile agents require message propagation among group of agents. A fast and scalable group communication mechanism can considerably improve performance of these applications. Unfortunately, most of the existing approaches do not scale well and disseminate messages slowly when the number of agents grows.In this paper, we propose Sama, a new group communication mechanism, to speed up message delivery for a group of mobile agents on a heterogeneous internetwork. The main contribution of Sama is distribution and parallelization of message propagation in an efficient way to achieve scalability and high-speed of message delivery to group members. Sama uses message dispatcher objects (MDOs), which are stationary agents on each host, to propagate messages concurrently. The proposed mechanism is independent of agent locations and transparently delivers messages to the group using constant number of remote messages. It also transparently recovers from host failures. We also present a Hop-Ring protocol that considerably improves the performance of message dissemination in Sama. Our experimental results show that message propagation in Sama is significantly fast compared to the previously proposed methods.     

面向海洋节能边缘计算的任务卸载研究

针对海洋通信网络能源不稳定、时延较长的问题,提出一种混合能量供应的边缘计算卸载方案。对于能量供应问题,移动边缘计算(MEC)服务器集成混合电源和混合接入点,混合电源利用可再生能源为MEC服务器供应能量,采用电力电网作为其补充能源,保证边缘计算系统的可靠运行,船舶用户通过混合接入点广播的射频(RF)信号收集能量。针对任务卸载优化问题,以能耗-时延权衡优化为目标,联合能量收集方法制定任务卸载比例、本地计算能力和发射功率的优化方案,最后利用降维优化算法,将目标函数简化为关于任务卸载比例的一维多约束问题,并利用改进的鲸鱼优化算法获得最优的执行总代价。利用边缘云模拟器EdgeCloudSim仿真的结果表明,所提方案较具有能量收集的资源分配方案和基本海上通信网络优化的方案执行成本分别降低了13.4%和9.6%。