Performance of ad hoc networks with two-hop relay routing and limited packet lifetime (extended version)

We consider a mobile ad hoc network consisting of three types of nodes (source, destination and relay nodes) and using the two-hop relay routing. This type of routing takes advantage of the mobility and the storage capacity of the nodes, called the relay nodes, in order to route packets between a source and a destination. Packets at relay nodes are assumed to have a limited lifetime in the network. Nodes are moving inside a bounded region according to some random mobility model. Closed-form expressions and asymptotic results when the number of nodes is large are provided for the packet delivery delay and for the energy needed to transmit a packet from the source to its destination. We also introduce and evaluate a variant of the two-hop relay protocol that limits the number of generated copies in the network. Our model is validated through simulations for two mobility models (random waypoint and random direction mobility models), and the performance of the two-hop routing and of the epidemic routing protocols are compared.     

Impact of mobility on the performance of relaying in ad hoc networks – Extended version

We consider a mobile ad hoc network consisting of three types of nodes: source, destination, and relay nodes. All the nodes are moving over a bounded region with possibly different mobility patterns. We introduce and study the notion of relay throughput, i.e. the maximum rate at which a node can relay data from the source to the destination. Our findings include the results that (a) the relay throughput depends on the node mobility pattern only via its (stationary) node position distribution, and (b) that a node mobility pattern that results in a uniform steady-state distribution for all nodes achieves the lowest relay throughput. Random waypoint and random direction mobility models in both one and in two dimensions are studied and approximate simple expressions for the relay throughput are provided. Finally, the behavior of the relay buffer occupancy is examined for the random walk and random direction mobility models. For both models, the explicit form of the mean buffer is provided in the heavy-traffic case.     

一种面向机会网络路由的最优停止决策方法

投递延迟是机会网络的一个重要指标,给定节点缓存和消息副本数目限制,如何选择合适的节点复制消息成为一个关键问题.提出一种基于最优停止理论的路由决策方法（OSDR）.OSDR 将每个时隙上所遇节点和目标节点的平均相遇时间看做一个随机变量,根据该随机变量的统计特性得到一个停止观察、复制消息的规则,该规则呈现简单的阈值结构,即当某个时隙上所遇节点和目标节点的平均相遇时间小于给定阈值时即复制消息. OSDR 可以在较小的相遇间隔和等待成本之间进行折衷,实现数学期望意义上的最小消息投递延迟.介绍了OSDR 的网络模型、最优停止规则的存在性证明过程以及计算方法.模拟实验结果表明,OSDR 相对其他方法,在投递成功率、投递延迟等方面具有明显优势.     

SmallWorld Model-Based Polylogarithmic Routing Using Mobile Nodes

The use of mobile nodes to improve network system performance has drawn considerable attention recently. The movement-assisted model considers mobility as a desirable feature,where routing is based on the store-carry-forward paradigm with random or controlled movement of resource rich mobile nodes.The application of such a model has been used in several emerging networks,including mobile ad hoc networks(MANETs),wireless sensor networks(WSNs),and delay tolerant networks(DTNs).It is well known that mobility increases the capacity of MANETs by reducing the number of relays for routing,prolonging the lifespan of WSNs by using mobile nodes in place of bottleneck static sensors,and ensuring network connectivity in DTNs using mobile nodes to connect different parts of a disconnected network.Trajectory planning and the coordination of mobile nodes are two important design issues aiming to optimize or balance several measures, including delay,average number of relays,and moving distance.In this paper,we propose a new controlled mobility model with an expected polylogarithmic number of relays to achieve a good balance among several contradictory goals,including delay,the number of relays,and moving distance.The model is based on the small-world model where each static node has"short"link connections to its nearest neighbors and"long"link connections to other nodes following a certain probability distribution.Short links are regular wireless connections whereas long links are implemented using mobile nodes.Various issues are considered,including trade-offs between delay and average number of relays,selection of the number of mobile nodes,and selection of the number of long links.The effectiveness of the proposed model is evaluated analytically as well as through simulation.     

稀疏机会网络中基于固定中继节点与消息相关性的缓存管理策略

针对稀疏机会网络中固定中继节点和移动节点间的相遇频率以及缓存资源的差异性问题,在多副本路由协议中,提出一种结合固定中继节点重要性和消息相关性的缓存管理策略。该策略通过交互固定节点和移动节点的接触信息和消息队列信息,减少固定中继节点缓存中冗余消息的数量,从而合理地利用固定中继节点的缓存资源。仿真结果表明,所提的缓存管理策略能够在保证消息传输成功率的基础上提高固定中继节点缓存空间的利用率。     

短相遇接触时间网络环境中的时延容忍网络路由方案

为解决时延容忍网络在短接触时间下的路由问题,给出了一种短相遇接触时间网络环境中的时延容忍网络路由方案.该方案首先利用相遇接触时间、相遇间隔时间和消息时效等网络信息计算一跳传递概率和两跳传递概率,然后根据所得传递概率在当前接触节点和过去接触节点中选择转发节点,从而建立低成本路由.仿真性能分析结果表明:与其它经典的时延容忍网络路由方案相比,所给路由方案可以在降低路由成本的情况下,提高消息传递率,且能缩短平均时延.     

在分裂的机会网络中多个消息摆渡的路由设计

针对机会网络中节点分布不规则造成分割的网络区域相隔较远的情况, 提出了一种基于全局消息摆渡和节点中继的多摆渡路由算法（GMF-NRA）。该算法使用一个全局消息摆渡节点和各个区域内的中继节点为运行于区域内部的局部消息摆渡节点中继消息, 共同完成区域间的信息传输。摆渡节点在中继节点处交互区域间的信息, 以至于不再需要摆渡节点之间实现在线协作转发消息。最后, 仿真结果表明GMF-NRA较现有的节点中继算法在网络的平均传输时延和数据交付率方面能获得更好的网络性能。     

AUV辅助的水下传感器网络时钟同步算法

针对当前水下传感器网络中的时钟同步难题,设计了一种三元阵被动定位自主水下航行器（ AUV）模型,并基于此模型提出了AUV辅助的时钟同步（ AUV-Sync）算法。该算法通过AUV与节点之间相对运动过程中进行的信息交换来对节点相对距离进行估计,进而基于相对距离计算单向传播时延来降低由于节点移动性所导致的误差。最后,通过两轮加权最小二乘法进行线性回归来估计时钟同步的参数。仿真结果表明：在存在节点漂移的动态水下传感器网络环境中,该算法较其他相关算法有更高的精度。     

Modelling and performance analysis of multi-hop ad hoc networks

Mobile ad hoc networks are becoming very attractive and useful in many kinds of communication and networking applications. Due to the advantage of numerical analysis, analytical modelling formalisms, such as stochastic Petri nets, queuing networks and stochastic process algebra have been widely used for performance analysis of communication systems. To the best of our knowledge, there is no previous analytical study that analyses the performance of multi-hop ad hoc networks, where mobile nodes move according to a random mobility model in terms of the end-to-end delay and throughput. This work presents a novel analytical framework developed using stochastic reward nets for modelling and analysis of multi-hop ad hoc networks, based on the IEEE 802.11 DCF MAC protocol, where mobile nodes move according to the random waypoint mobility model. The proposed framework is used to analyse the performance of multi-hop ad hoc networks as a function of network parameters such as the transmission range, carrier sensing range, interference range, number of nodes, network area size, packet size, and packet generation rate. The proposed framework is organized into several models to break up the complexity of modelling the complete network, and make it easier to analyse each model as required. The framework is based on the idea of decomposition and fixed point iteration of stochastic reward nets. The proposed models are validated using extensive simulations.     

移动传感网中基于虚拟货币的路由策略

移动无线传感器网络中,针对节点基于随机运动模型的路由问题,提出一种基于虚拟货币的低能耗路由策略——DTVC。根据节点的属性和数据消息的属性进行买方和卖方的定价并据此选择转发节点。为了提升网络性能,通过控制数据消息的副本数以及对节点的缓存队列中的数据消息排序,把网络中的节点分为源节点和中继节点,只有数据消息的源节点可以复制该数据消息,并依据数据消息的延迟容忍度对消息进行排序,延迟容忍度越小则优先级越高。为了减少网络中的能量消耗,根据sink节点广播的消息删除缓存队列中已经传输成功的数据消息。在Matlab上的仿真实验结果表明,与基于消息容错的自适应数据传输算法（FAD）、基于距离和能量感知模糊逻辑的路由算法（FLDAER）和基于能耗自选演进机制的路由算法相比,DTVC的数据消息投递率至少提高2.5%,平均副本数至少减少25%。