Network coding for unicast in a WiFi hotspot: Promises,challenges, and testbed implementation

In offices and residential buildings, WiFi networks have become a primary means for providing Internet access to wireless devices whose dominant traffic pattern is unicast. In the meantime, the emergence of network coding has brought about great promises for multicast in communication networks where intermediate nodes are allowed to process independent incoming information flows. Little is known about network coding for unicast, however. The objective of this paper is thus to depart from multicast scenarios and shed light on several possible unicast scenarios to which network coding may be applied in a WiFi hotspot in order to obtain communication benefits such as throughput gain, fairness, and reduced protocol complexity. We identify five representative scenarios in which network coding may be used to benefit unicasting in a WiFi hotspot. Several open research issues and practical challenges related to each scenario are discussed individually. To illustrate the benefits of network coding for unicast in a WiFi hotspot, we propose and implement iCORE: The interface COoperation Repeater-aided network coding Engine. iCORE is a practical system in which multi-channel multi-radio repeaters are used to relay unicast traffic for those terminals sitting far away from an access point and suffering from weak signals at a WiFi hotspot. It is based on our last scenario which illustrates the synergy among network coding, opportunistic routing, and interface management. Utilizing idle wireless interfaces and listening to traffic opportunistically, iCORE allows packets to move across the interfaces and to be coded across flows whenever it sees more transmission opportunities. We evaluate iCORE on a four-node chain-like topology testbed implemented using IEEE 802.11b/g radios and compare it to MORE – the state-of-art intra-flow network coding implementation based on opportunistic routing. Our experimental results reveal promising gains in terms of throughput over MORE.     

移动机会网络组播路由的研究进展

在移动机会网络中,节点进行机会式的连接通信,该方式被广泛应用于移动社交网络、车载智能网络、移动自组网络等场景中。移动机会网络群组通信在抢险救灾、社区消息分发及智能交通等领域具有极高的应用价值,组播路由技术是其关键技术之一。将移动机会网络组播路由分为传统组播路由和智能组播路由两类,重点介绍了智能组播路由的研究现状,并采用通用的性能指标对各组播路由策略进行了比较分析。分析结论为:智能组播路由由于考虑了移动机会网络的社会特性、节点缓存、能量及安全等特性,因此具有较好的综合性能。最后展望了组播路由在大数据缓存管理、群组安全策略、车载自组网及动态感知方面的研究前景。     

Behavior of Ad Hoc routing protocols,analyzed for emergency and rescue scenarios,on a real urban area

A mobile Ad Hoc network (MANET) is a collection of wireless mobile nodes that can dynamically configure a network without a fixed infrastructure or central administration. This makes it ideal for emergency and rescue scenarios, where sharing information is essential and should occur as soon as possible. This article discusses which of the routing strategies for mobile MANETs: proactive, reactive or hierarchical, has a better performance in such scenarios. By selecting a real urban area for the emergency and rescue scenario, we calculated the density of nodes and the mobility model needed for the validation study of AODV, DSDV and CBRP in the routing model. The NS2 simulator has been used for our study. We also show that the hierarchical routing strategies are better suited for this type of scenarios.     

Wait and Spray:一种改进的机会网络路由算法

灾难场景是机会网络重要的应用场景之一,在灾难场景下能量成为稀缺资源,高效转发数据包的同时尽可能减少节点能量消耗成为路由算法追求的目标之一,为此提出了Waitand Spray路由算法,该算法将数据包的转发过程分为Wait和Spray两个阶段,在不同阶段采用不同的路由策略。该算法具有W、K、M参数,恰当的参数设置可控制Spray阶段的泛洪程度,大幅提高算法性能。仿真结果表明,该算法可在获得高传输成功率的同时,大幅降低路由开销,是一种适合在能量稀缺场景下应用的路由算法。     

移动机会网络路由问题研究进展

移动机会网络基于节点接触形成的通信机会逐跳转发数据,是满足物联网透彻感知与泛在互联的一种重要技术手段.机会路由作为实现间歇式连通环境下节点通信的基本方法,具有十分重要的研究意义,引起了研究人员的广泛关注.首先介绍了移动机会网络的概念、体系结构、典型应用以及所面临的一些挑战;然后详细阐述了机会路由算法的评价指标、设计需求与转发机制,并介绍了研究进展;最后,对机会路由未来的研究趋势进行了分析与展望.     

Evaluation of quality of service provisioning in large-scale pervasive and smart collaborative wireless sensor and actor networks

With the production of low cost sensors, classical concept of Wireless Sensor Networks (WSNs) evolved into large-scale concept hosting thousands of nodes within a network and generating abundant quantities of data. As these networks are being continuously developed a new class of WSNs are proposed: Wireless Sensor and Actor Networks (WSANs). These networks introduce the actuating component, alongside with the sensing component, where QoS is becoming a very significant factor. The authors of this paper approach the problem of QoS support in large-scale WSAN from a physical layer, where the deployment parameters effects on QoS metrics are demystified. The analysis is formulated on two scenarios: worst case scenario (all nodes transmit data towards the network sink) and best case scenario (a single node transmits a stream of data towards a network sink). For both scenarios two routing protocols were compared, a simple flooding algorithm and a simple distance vector protocol. Also, a new relation between hop count and latency based on transmission power is observed, not reported in the available literature, resulting in a new proposed empirical latency model.     

A social-aware routing protocol for opportunistic networks

Understanding nodes mobility is of fundamental importance for data delivery in opportunistic and intermittently connected networks referred to as Delay Tolerant Networks (DTNs). The analysis of such mobility patterns and the understanding of how mobile nodes interact play a critical role when designing new routing protocols for DTNs. The Cultural Greedy Ant (CGrAnt) protocol is a hybrid Swarm Intelligence-based approach designed to address the routing problem in such dynamic and complex environment. CGrAnt is based on: (1) Cultural Algorithms (CA) and Ant Colony Optimization (ACO) and (2) operational metrics that characterize the opportunistic social connectivity between wireless users. The most promising message forwarders are selected via a greedy transition rule based mainly on local information captured from the DTN environment. Whenever global information is available, it can also be used to support decisions. We compare the performance of CGrAnt with Epidemic, PROPHET, and dLife protocols in two different mobility scenarios under varying networking parameters. Results obtained by the ONE simulator show that CGrAnt achieves a higher message delivery and lower message redundancy than the three protocols in both scenarios. The only exception is in one of the scenarios, when messages have a time to live lower than 900 min, where CGrAnt delivers a bit less messages than dLife, although with a lower message redundancy.     

一种基于三角模糊数的VANETs机会路由算法*

分析了现有车用自组织网络（VANETs）的路由算法,提出一种新的基于三角模糊数的机会路由算法。新算法将转发结点距离目标结点的距离、到达目标结点的方向、行驶速度向量、重传次数、车流状况等因素作为目标函数进行分析计算,采用熵权系数法确定各因素权重。路由过程中,贪婪选择向量值最大的节点转发数据包;遇到网络不连续时,将采用“存储－携带－转发”的机会路由策略。仿真结果表明,该算法能够较好的适用于VANETs各种场景。     

Security model for emergency real-time communications in autonomous networks

Towards the proliferation of architectures, tools and applications that have the potential to be used during an emergency rescue mission, we present a framework for emergency real-time communication using autonomous networks, called emergency Mobile Ad-hoc Networks (eMANETs). By eMANETs we refer to networks that are deployed in emergency cases where default telecommunications infrastructure has failed. Our goal is to design a security framework that will secure real-time communications during emergency rescue scenarios. The proposed framework consists of a secure routing protocol, intrusion detection provision and security extension for real-time communications using peer-to-peer overlays. We envisage that the results of this work will aid and serve the needs of any society against any event that threatens serious damage to human welfare or to the environment.     

ML-SOR: Message routing using multi-layer social networks in opportunistic communications

Opportunistic networks are a generalization of DTNs in which disconnections are frequent and encounter patterns between mobile devices are unpredictable. In such scenarios, message routing is a fundamental issue. Social-based routing protocols usually exploit the social information extracted from the history of encounters between mobile devices to find an appropriate message relay. Protocols based on encounter history, however, take time to build up a knowledge database from which to take routing decisions. While contact information changes constantly and it takes time to identify strong social ties, other types of ties remain rather stable and could be exploited to augment available partial contact information. In this paper, we start defining a multi-layer social network model combining the social network detected through encounters with other social networks and investigate the relationship between these social network layers in terms of node centrality, community structure, tie strength and link prediction. The purpose of this analysis is to better understand user behavior in a multi-layered complex network combining online and offline social relationships. Then, we propose a novel opportunistic routing approach ML-SOR (Multi-layer Social Network based Routing) which extracts social network information from such a model to perform routing decisions. To select an effective forwarding node, ML-SOR measures the forwarding capability of a node when compared to an encountered node in terms of node centrality, tie strength and link prediction. Trace driven simulations show that a routing metric combining social information extracted from multiple social network layers allows users to achieve good routing performance with low overhead cost.     

Opportunistic forwarding for user-provided networks

Abstract

We study opportunistic forwarding in a community-based networking paradigm where mobile users and shared access points (SAPs) collectively provide Internet access to users (mobile or not), including those in areas where other connectivity options are not available. Our approach is based on an efficient interoperation of two challenging network types: the opportunistic and the user-provided networks (UPNs). This requires a re-evaluation of the existing assumptions regarding inter-contact patterns and their alignment to this hybrid environment. We confirm our arguments with numerical results from a stochastic model as well as experimental scenarios with realistic parameters using the ONE simulator. Our experiments are based on a reference routing algorithm we designed and implemented that extends the spray ’n focus protocol and exhibits the following characteristics: (i) is oriented to this integrated environment; (ii) employs delay-tolerant networking (DTN) technologies along with contact prediction; and (iii) is independent of the deployed UPN approach. According our results, the proposed methodological approach achieves lower communication overhead, latency and storage requirements compared to representative opportunistic routing algorithms.     

Interest spaces: A unified interest-based dissemination framework for opportunistic networks

Embedded ubiquitous computing systems (EUCS) promise to grow remarkably in the near future. For such systems, new communication technologies are constructed to cope with the increasing functional and temporal demans. Because of the ubiquitousness of mobile devices nowadays, for example, traditional publish/subscribe is no longer an adequate model for data dissemination in mobile networks. Since any node can publish content at any time, the network can get congested easily, so a dissemination paradigm where mobile nodes contribute with a fraction of their resources is needed, through the use of opportunistic networks. Furthermore, a suitable organization for data dissemination in mobile networks should be centered around interests. Thus, we propose a unified interest-based dissemination framework for opportunistic networks entitled Interest Spaces, which simplifies dissemination by just allowing applications to mark data items with certain tags, letting the framework handle the caching, routing, forwarding, and disseminating. Similarly, applications that need to subscribe to channels simply have to specify the tags they are interested in, and the framework does the rest. However, the Interest Spaces framework also allows applications to have more control over the dissemination process if they wish, by specifying various criteria and dissemination rules. In this article, we present the architecture and components of Interest Spaces. We focus on data aggregation at the context layer, showing through simulations the benefits it brings in opportunistic dissemination. We also present a real-life use case for Interest Spaces through Chatty, an opportunistic chat application.     

Scalability of MANET routing protocols for heterogeneous and homogenous networks

In Mobile Ad hoc Network (MANET), mobility, traffic and node density are main network conditions that significantly affect performance of routing protocols. Much of the previous research in MANET routing have focused on developing strategies, which suit one specific networking scenario. Therefore, there is no existing protocol that can work well in all different networking scenarios. This paper reviews characteristics of several different classes of routing protocols. Moreover, most of current routing protocols assume homogeneous networking conditions where all nodes have the same capabilities and resources. This paper presents extensive studies simulations for DSR, AODV, LAR1, FSR and WRP in homogenous and heterogeneous networks that consist of different nodes with different resources. The results showed that while all protocols perform reasonably well in homogenous networking conditions, their performance suffer significantly over heterogonous networks.     

Survey of network coding-aware routing protocols in wireless networks

In recent times, there have been many advances in the field of information theory and wireless ad hoc network technologies. Regarding information theory progression and its connection with wireless ad hoc networks, this study presents fundamental concepts related to the application of the state-of-the-art Network Coding (NC) within wireless ad hoc networks in the context of routing. To begin with, this paper briefly describes opportunistic routing and identifies differentiation between NC-aware and NC-based routing mechanisms in wireless ad hoc networks. However, our main focus is to provide a survey of available NC-aware routing protocols that make forwarding decisions based on the information of available coding opportunities across several routes within wireless ad hoc networks. The taxonomy and characteristics of various representative NC-aware routing protocols will also be discussed. In summary, we provide a comparison of available NC-aware routing schemes and conclude that NC-aware routing techniques have several advantages over traditional routing in terms of high throughput, high reliability, and lower delay in a wireless scenario. To the best of our knowledge, this work is the first that provides comprehensive discussion about NC-aware routing protocols.     

Testbed results of an opportunistic routing for multi-robot wireless networks

Opportunistic routing is a candidate for multihop wireless routing where the network topology and radio channels vary rapidly. However, there are not many opportunistic routing algorithms that can be implemented in a real multihop wireless network while exploiting the node mobility. It motivates us to implement an opportunistic routing, random basketball routing (BR), in a real multi-robot network to see if it can enhance the capacity of the multihop network as mobility increases. For implementation purposes, we added some features, such as destination RSSI measuring, a loop-free procedure and distributed relay probability updating, to the original BR. We carried out the experiments on a real multi-robot network and compared BR with AODV combined with CSMA/CA (routing + MAC protocol). We considered both static and dynamic scenarios. Our experiments are encouraging in that BR outperforms AODV + CSMA/CA, particularly in dynamic cases; the throughput of BR is 6.6 times higher than that of AODV + CSMA/CA. BR with dynamic networks shows 1.4 times higher throughput performance than BR with static networks. We investigate the performance of BR in the large-scale network using NS-2 simulation. We verify the effect of node density, speed, destination beacon signal and loop-free procedure. According to the large-scale simulation, the end-to-end throughput grows with the node speed.     

Routing with multi-level cross-community social groups in mobile opportunistic networks

Mobile opportunistic networks (MONs) are intermittently connected networks, such as pocket switched networks formed by human-carried mobile devices. Routing in MONs is very challenging as it must handle network partitioning, long delays, and dynamic topology. Flooding is a possible solution but with high costs. Most existing routing methods for MONs avoid the costly flooding by selecting one or multiple relays to deliver data during each encounter. How to pick the “good” relay from all encounters is a non-trivial task. To achieve efficient delivery of messages at low costs, in this paper, we propose a novel group-based routing protocol in which the relay node is selected based on multi-level cross-community social group information. We apply a simple group formation method to both historical encounters (social relationships in physical world) and/or social profiles of mobile users (social relationships in social world) and build multi-level cross-community social groups, which summarize the wide range of social relationships among all mobile participants. Our simulations over several real-life data sets demonstrate the efficiency and effectiveness of the proposed method by comparing it with several existing MON routing schemes.     

可充电无线传感网络能量均衡路由算法

针对可充电无线传感网络中的能量均衡路由问题,提出在稳定功率无线充电和监测数据收集网络场景下的多路径路由算法和机会路由算法,以实现网络的能量均衡。首先,通过电磁传播理论构建了无线传感节点的充电和接收功率关系模型;然后,考虑网络中无线传感节点的发送能耗和接收能耗,基于上述充电模型将网络能量均衡的路由问题转化为网络节点运行时间的最大最小化问题,通过线性规划得到的各链路流量用以指导路由中数据流量分配;最后,考虑一种更加现实的低功耗的场景,并提出了一种基于机会路由的能量均衡路由算法。实验结果表明,与最短路径路由（SPR）和期望周期最短路由（EDC）算法相比较,所提出的两种路由算法均能有效提高采集能量的利用率和工作周期内的网络生命周期。     

基于能量感知的移动低占空比机会网络纠删编码算法

低占空比(low-duty-cycle,简称LDC)技术是当前延长无线传感器网络生命周期的最关键技术,为了有效延长机会网络生命周期,将低占空比技术引入机会网络,形成LDC机会网络.但是,现有机会网络路由算法不能很好地适应LDC环境,其性能会大幅度下降.为了解决该问题,提出一种基于能量感知的移动低占空比机会网络纠删编码算法E-EC.仿真实验结果表明,与现有的典型机会网络路由算法相比,E-EC算法在延长移动机会网络生命周期以及增加数据传输成功率等方面带来明显的性能提升.     

一种基于混合社区的移动机会网络数据传输机制

由人携带或使用智能设备组成的移动机会网络采用"存储-携带-转发"的通信机制,通过中继转发来实现节点之间的数据传递。为了改善网络性能,往往需要借助节点的社会属性来进行中继选择和制定转发策略。然而,在已有的传输机制中,往往只是利用节点的部分社会属性,不能完全反映出节点之间的社会关系。为此,提出了一种新的基于混合社区的数据传输机制,并给出了混合社区的内涵、混合社区的构建方法和基于混合社区的数据传输算法。基于几种真实轨迹数据集的实验结果表明,与已有的几种经典路由算法相比,该方法传输成功率较高,传输延迟较短,性能更好。     

一种基于好友簇的社交网络中的时延容忍路由协议

社交网络是一种以便携式移动通信设备为节点的无线网络,通常由于其规模较大、结构复杂并且拓扑变化频繁,而成为时延容忍网络的一个典型应用场景。通过分析社交网络的特性,构建了基于好友群组的网络拓扑模型,并基于该模型,提出了一种基于簇结构的时延容忍路由协议。通过实验证明了该路由协议可以在保证较高路由性能的前提下有效控制由于数据副本传染造成的对网络资源的消耗。