基于部分网络编码的移动自组网实时多播协议研究

传统网络编码可以减少数据包的转发次数,但会造成数据包较大的延时,且容易造成网络的拥塞.本文提出一种基于部分网络编码的实时多播协议——PNCRM.该协议将部分网络编码与mesh的建立结合在一起,有效地减小了端到端的延时,并且改善了网络吞吐量性能.仿真结果表明,与PUMA或基于传统网络编码的实时多播协议相比,PNCRM更好地适应接收节点较多、动态性较大的环境,且在数据包投递率及端到端的延时方面有着显著的优势.     

基于移动组的全序可靠多播协议的研究

丈章给出一种基于移动组的全序可靠多播协议-MGTOM(Mobile-group-based Totally Ordered Reliable Multicast)协议,借助于逻辑令牌环来实现.MGTOM协议实现了移动组多播的原子性和全序性,原子性用于保证多播消息能够最终传递到移动组内的所有移动Agent,全序性则保证任意一对多播消息都按照相同顺序被所有组内移动Agent传递.在多播算法中,为了保证原子性,所有收到多播消息的组成员必须回复,然后持有令牌的组成员作为Sequencer,对多播消息进行排序.     

一种高斯-马尔科夫自组网组移动模型

研究了Ad Hoc网络中移动模型问题。针对目前Ad Hoc网络节点通常具有群组移动性的特征,提出了一种新的移动模型—高斯-马尔科夫组移动模型。通过与RWP、CGM移动模型仿真对比得出,该移动模型符合能够有效描述具有群组移动性的Ad Hoc网络,同时也表明,不同的移动模型对Ad Hoc网络路由协议性能具有很大的影响。     

基于RTM模型的OBAMP和ODMRP路由协议仿真与分析

将RTM模型引入到多播路由研究中,文章选取具有代表性的Random Waypoint,Random Walk with Reflection和West Uni Place为移动场景,以多播路由协议ODMRP和覆盖多播路由协议OBAMP为仿真对象,在不同组成员个数和速度的条件下,分别对其使用NS2模拟仿真。仿真分析可知,在速度变化明显的移动模型中,选取随机路点(RW)模型作为网络中节点的移动模式较好;对数据转发率要求高的网络适宜选取OBAMP协议,对实时性要求较高的网络多采用ODMRP协议。为设计能满足不同应用需要的Ad Hoc网络多播路由、覆盖多播路由协议提供科学参考。     

TD-LTE应急通信中的改进型节点移动模型研究

基于TD-LTE的应急通信系统能够在灾难发生后快速组网,为及时救援提供宝贵信息,而合适的节点移动模型是自组网路由算法的基础。文章通过分析应急场景中移动基站的运动特性,提出一种基于区域稳态分布的改进型随机路点移动模型。该模型能够缓解RWP模型稳态分布不均、节点速度逐渐衰减以及节点重复无效率运动的问题,有利于模拟应急通信中移动基站的运动情况以及后续Ad Hoc路由协议的仿真。     

DSR路由协议在大规模移动Ad Hoc网络中的性能分析

从移动Ad Hoc网络的发展现状出发,简述了移动Ad Hoc网络的构成及源动态路由协议DSR的原理,并以主流仿真软件OPNET为平台,依据吞吐量、端到端时延、成功投递率等网络性能参数的仿真结果,深入分析了DSR路由协议在大规模Ad Hoc网络中将会出现的一系列问题.     

基于多播的移动IP位置管理的研究

提出了一种通过多播中组管理功能完成移动IP位置管理方法。每一个自治网络中都设置一个移动路由代理（MA），形成一个管理移动节点位置绑定信息的虚拟专用网，通过将与移动主机通信的节点联合起来构成一棵多播树，使网络中各节点相互合作维护移动节点的位置更新。设计了绑定信息表的存储结构和管理移动位置绑定信息的算法。模拟实验表明，提出的基于多播的位置管理方案能够使通信对端实时了解移动节点的转交地址，减少向家乡代理注册的时间和次数，减小了传输延迟，为实时业务传输提供较好的支持。同时减轻了家乡代理和各主机的负担，使移动IP的性能得到优化。     

使用EHN-HP机制提高移动切换中TCP性能

移动通讯技术的发展促使传统有线互联网向无线移动网络延伸.TCP协议是现在互联网上使用最为广泛的端到端可靠传输协议,但TCP协议是在有线链路基础上设计的,直接在无线移动网络上使用TCP协议会造成TCP性能的下降.本文详细分析了移动切换对TCP协议造成的影响,比较并分析现有的几种解决方案,针对切换对TCP造成的影响提出了EHN-HP机制.EHN-HP机制在现有的TCP协议上进行改进,增加了切换处理机制(Handoff Process),通过网络模拟器的模拟结果表明,EHN-HP机制有效的改善了TCP协议在切换过程中的性能.     

移动代理在MANET路由协议中的应用研究

移动Ad Hoc网络(MANET)是由移动节点组成的分布式异构网络,其路由协议的研究是该领域的焦点之一。本文分析了现有移动Ad Hoc网络两类路由协议的优缺点,接着提出将移动代理应用于AODV路山协议的方案,最后给出了初步的仿真结果。仿真结果表明,通过移动代理的漫游更新途经节点路由表,可以在网络负载增加不人的情况下,减少路由发起数,降低端到端的数据传输延迟。     

基于NS2的航空白组网节点移动模型仿真研究

航空自组网是MANET-s在航空通信中的应用。对三种节点移动模型在航空自组网中的应用进行了仿真研究。利用NS2仿真平台,添加了随机走动移动模型和随机方向移动模型,建立了AANET的网络模型．编写了仿真场景,对三种节点移动模型在AANET中的性能进行了仿真分析。结果表明随机路点移动模型的性能最优,随机走动移动模型其次,随机方向移动模型最差。研究结果对航空自组网的研究和应用具有一定的参考价值。     

Cost analysis of mobility protocols

Increasing demand for mobility in wireless data network has given rise to various mobility management schemes. Most of the analysis on mobility protocols used Random Waypoint mobility model However, the analysis done earlier ignored some major costs, resulting in an incomplete estimation and used random waypoint model which fails to represent realistic movement pattern. In this paper, we have developed an analytical cost model considering all possible costs related to mobility management, and have used city section mobility model, a realistic mobility model, to compute the total costs of two mobility protocols: HIMPv6 and SIGMA. We have defined two novel performance metrics, normalized overhead and efficiency, for mobility protocols based on the signaling costs and used them to evaluate the performance of SIGMA and HMIPv6 protocols varying network size, mobility rate and traffic rate. Results show that the total cost of SIGMA is much less than HMIPv6 due to the higher cost of packet tunneling, even though the mobility signaling cost of SIGMA is higher than HMIPv6. Moreover, mobility signaling costs of both the protocols using city model and random waypoint model are found to be much different, demonstrating the fact that random waypoint model cannot be used as an approximation to a realistic scenario. The analytical framework presented in this paper can be used by the network professionals to estimate amount of load on the network due to mobility protocols and compare them based on the proposed performance metrics to select the best protocol.     

The node distribution of the random waypoint mobility model for wireless ad hoc networks

The random waypoint model is a commonly used mobility model in the simulation of ad hoc networks. It is known that the spatial distribution of network nodes moving according to this model is, in general, nonuniform. However, a closed-form expression of this distribution and an in-depth investigation is still missing. This fact impairs the accuracy of the current simulation methodology of ad hoc networks and makes it impossible to relate simulation-based performance results to corresponding analytical results. To overcome these problems, we present a detailed analytical study of the spatial node distribution generated by random waypoint mobility. More specifically, we consider a generalization of the model in which the pause time of the mobile nodes is chosen arbitrarily in each waypoint and a fraction of nodes may remain static for the entire simulation time. We show that the structure of the resulting distribution is the weighted sum of three independent components: the static, pause, and mobility component. This division enables us to understand how the model's parameters influence the distribution. We derive an exact equation of the asymptotically stationary distribution for movement on a line segment and an accurate approximation for a square area. The good quality of this approximation is validated through simulations using various settings of the mobility parameters. In summary, this article gives a fundamental understanding of the behavior of the random waypoint model.     

On the stationary distribution of speed and location of random waypoint

In "Stationary distributions for the random waypoint mobility model" (TMC, Vol. 3, No, 1), Navidi and Camp find the stationary distribution of the random waypoint model, with or without pause on a rectangular area. In this short note, we show that, under the stationary regime, speed and location are independent.     

Contention-Aware Performance Analysis of Mobility-Assisted Routing

A large body of work has theoretically analyzed the performance of mobility-assisted routing schemes for intermittently connected mobile networks. But the vast majority of these prior studies have ignored wireless contention. Recent papers have shown through simulations that ignoring contention leads to inaccurate and misleading results, even for sparse networks. In this paper, we analyze the performance of routing schemes under contention. First, we introduce a mathematical framework to model contention. This framework can be used to analyze any routing scheme with any mobility and channel model. Then, we use this framework to compute the expected delays for different representative mobility-assisted routing schemes under random direction, random waypoint and community-based mobility models. Finally, we use these delay expressions to optimize the design of routing schemes while demonstrating that designing and optimizing routing schemes using analytical expressions which ignore contention can lead to suboptimal or even erroneous behavior.     

Random waypoint mobility model in cellular networks

In this paper we study the so-called random waypoint (RWP) mobility model in the context of cellular networks. In the RWP model the nodes, i.e., mobile users, move along a zigzag path consisting of straight legs from one waypoint to the next. Each waypoint is assumed to be drawn from the uniform distribution over the given convex domain. In this paper we characterise the key performance measures, mean handover rate and mean sojourn time from the point of view of an arbitrary cell, as well as the mean handover rate in the network. To this end, we present an exact analytical formula for the mean arrival rate across an arbitrary curve. This result together with the pdf of the node location, allows us to compute all other interesting measures. The results are illustrated by several numerical examples. For instance, as a straightforward application of these results one can easily adjust the model parameters in a simulation so that the scenario matches well with, e.g., the measured sojourn times in a cell.     

A Statistical Analysis of the Long-Run Node Spatial Distribution in Mobile Ad Hoc Networks

In this paper, we analyze the node spatial distribution of mobile wireless ad hoc networks. Characterizing this distribution is of fundamental importance in the analysis of many relevant properties of mobile ad hoc networks, such as connectivity, average route length, and network capacity. In particular, we have investigated under what conditions the node spatial distribution resulting after a large number of mobility steps resembles the uniform distribution. This is motivated by the fact that the existing theoretical results concerning mobile ad hoc networks are based on this assumption. In order to test this hypothesis, we performed extensive simulations using two well-known mobility models: the random waypoint model, which resembles intentional movement, and a Brownian-like model, which resembles non-intentional movement. Our analysis has shown that in Brownian-like motion the uniformity assumption does hold, and that the intensity of the concentration of nodes in the center of the deployment region that occurs in the random waypoint model heavily depends on the choice of some mobility parameters. For extreme values of these parameters, the uniformity assumption is impaired.     

Gamma random waypoint mobility model for wireless ad hoc networks

Random waypoint (RWP) mobility model is widely used in ad hoc network simulation. The model suffers from speed decay as the simulation progresses and may not reach the steady state in terms of instantaneous average node speed. Furthermore, the convergence of the average speed to its steady state value is delayed. This usually leads to inaccurate results in protocol validation of mobile ad hoc networks modeling. Moreover, the probability distributions of speed vary over the simulation time, such that the node speed distribution at the initial state is different from the corresponding distribution at the end of the simulation. In order to overcome these problems, this paper proposes a modified RWP mobility model with a more precise distribution of the nodes' speed. In the modified model, the speeds of nodes are sampled from gamma distribution. The results obtained from both analysis and simulation experiments of the average speed and the density of nodes' speed indicate that the proposed gamma random waypoint mobility model outperforms the existing RWP mobility models. It is shown that a significant performance improvement in achieving higher steady state speed values that closely model the pre‐assumed average speeds are possible with the proposed model. Additionally, the model allows faster convergence to the steady state, and probability distribution of speed is steady over the simulation time. Copyright © 2012 John Wiley & Sons, Ltd.     

On the performance of underlay cognitive radio system with random mobility under imperfect channel state information

In this paper, the performance of an underlay cognitive radio system with random mobility and imperfect channel state information (CSI) is investigated. The mobile user (MU) utilises maximum ratio combining (MRC) and selection combining (SC) diversity techniques as signal reception to improve the quality of received signal‐to‐noise ratio (SNR). Under the Rayleigh fading, random waypoint mobility model is employed to characterised the effect of the MU random mobility on the system performance. Thus, novel probability density function (PDF) and cumulative distribution function (CDF) for the two considered diversity techniques are derived. Through these, the outage probability and average bit error rate (ABER) closed‐form analytical expressions are then obtained to quantify the system performance under the MRC and SC schemes. The results illustrate the effect of imperfect CSI, user mobility which is characterised by pathloss and the network topology on the system performance. Also, the results depict that MRC offers the system better performance compared with SC under the same system conditions. The accuracy of the derived analytical expressions is verified through Monte‐Carlo simulations.     

The Random Trip Model: Stability, Stationary Regime, and Perfect Simulation

We define "random trip", a generic mobility model for random, independent node motions, which contains as special cases: the random waypoint on convex or nonconvex domains, random walk on torus, billiards, city section, space graph, intercity and other models. We show that, for this model, a necessary and sufficient condition for a time-stationary regime to exist is that the mean trip duration (sampled at trip endpoints) is finite. When this holds, we show that the distribution of node mobility state converges to the time-stationary distribution, starting from the origin of an arbitrary trip. For the special case of random waypoint, we provide for the first time a proof and a sufficient and necessary condition of the existence of a stationary regime, thus closing a long standing issue. We show that random walk on torus and billiards belong to the random trip class of models, and establish that the time-limit distribution of node location for these two models is uniform, for any initial distribution, even in cases where the speed vector does not have circular symmetry. Using Palm calculus, we establish properties of the time-stationary regime, when the condition for its existence holds. We provide an algorithm to sample the simulation state from a time-stationary distribution at time 0 ("perfect simulation"), without computing geometric constants. For random waypoint on the sphere, random walk on torus and billiards, we show that, in the time-stationary regime, the node location is uniform. Our perfect sampling algorithm is implemented to use with ns-2, and is available to download from http://ica1www.epfl.ch/RandomTrip