A Direction-Based Data Forwarding Algorithm for Opportunistic Networks

In this paper, the forwarding objective and mobility law of nodes in opportunistic networks are first investigated to establish a mathematical model for further analysis, then a gradually accelerated data forwarding algorithm is proposed. In this algorithm, according to the distance between data carriers (nodes) and the destination, some intermediate nodes are selected to relay the data. Especially, the forwarded copies can be increased when the delay reaches a threshold, to guarantee the required delivery ratio. The simulation results show that the proposed algorithm can effectively reduce the storage occupancies of nodes and forwarding delay, and guarantee the delivery ratio simultaneously.     

一种机会网络中节点转发策略的改进

在分析现有机会网络转发策略及机会网络中节点的运动特性的基础上,通过改进节点的转发策略提出一种新的机会网络路由算法(Delayed Spray and Wait,DSW).算法假设的应用场景为节点均沿着预先存在的路径移动,通过延迟发送转发数据包,可以显著减少网络中的低效数据包转发的数量.仿真结果表明,在合适的应用场景下该算法可以显著的降低网络中数据包的转发数量并略微提高传输成功率,这对于减少节点能耗和改善网络拥塞状况都具有实际意义.     

机会网络中的数据转发机制分析

机会网络作为一种新兴移动无线自组织网络,在军事及民用领域展现出广泛的应用前景,数据转发机制是其核心问题。论文针对机会网络中的数据转发机制展开讨论,首先对机会网络数据转发机制与传统路由机制进行综合比较,在此基础上介绍数据转发机制面临的问题和性能评估标准,并根据数据转发机制主要特点对其进行了分类,最后对机会网络中的典型数据转发机制进行归纳。     

Energy Efficient Forwarding Algorithm in Opportunistic Networks

In opportunistic networks,a successful message transmission between node pairs depends on the message size,the transmission speed and the connection duration time.This paper proposes a new message forwarding algorithm to improve the message delivery ratio and reduce the energy consumption.Previous encounter characteristics between nodes are used to estimate future connection duration time using a three point estimation method.Furthermore,the buffer utilization of nodes is used as a weight for the likelihoods to meet destinations according to the hop count of messages stored in the buffer.The simulation results show that the proposed forwarding algorithm achieves higher delivery ratio and less overhead ratio than the other four popular routing protocols.In addition,the proposed algorithm gains a better average residual energy performance among all the compared protocols.     

An Efficient and Secure Data Forwarding Mechanism for Opportunistic IoT

Internet of Things (IoT) is a heterogeneous network of interconnected things where users, smart devices and wireless technologies, collude for providing services. It is expected that a great deal of devices will get connected to the Internet in the near future. Opportunistic networks(OppNet) are a class of disruption tolerant networks characterized by uncertain topology and intermittent connectivity between the nodes. Opportunistic Internet of Things(OppIoT) is an amalgamation of the OppNet and IoT exploiting the communication between the IoT devices and the communities formed by humans. The data is exposed to a wide unfamiliar audience and the message delivery is dependent on the residual battery of the node, as most of the energy is spent on node discovery and message transmission. In such a scenario where a huge number of devices are accommodated, a scalable, adaptable, inter-operable, energy-efficient and secure network architecture is required. This paper proposes a novel defense mechanism against black hole and packet fabrication attacks for OppIoT, GFRSA, A Green Forwarding ratio and RSA (Rivest, Shamir and Adleman) based secure routing protocol. The selection of the next hop is based on node’s forwarding behavior, current energy level and its predicted message delivery probability. For further enhancing the security provided by the protocol, the messages are encrypted using asymmetric cryptography before transmission. Simulations performed using opportunistic network environment (ONE) simulator convey that GFRSA provides message security, saves energy and outperforms the existing protocols, LPRF-MC (Location Prediction-based Forwarding for Routing using Markov Chain) and RSASec (Asymmetric RSA-based security approach) in terms of correct packet delivery by 27.37%, message delivery probability is higher by 34.51%, number of messages dropped are reduced by 15.17% and the residual node energy is higher by 14.08%.

     

Impact of Human Mobility on Opportunistic Forwarding Algorithms

We study data transfer opportunities between wireless devices carried by humans. We observe that the distribution of the intercontact time (the time gap separating two contacts between the same pair of devices) may be well approximated by a power law over the range [10 minutes; 1 day]. This observation is confirmed using eight distinct experimental data sets. It is at odds with the exponential decay implied by the most commonly used mobility models. In this paper, we study how this newly uncovered characteristic of human mobility impacts one class of forwarding algorithms previously proposed. We use a simplified model based on the renewal theory to study how the parameters of the distribution impact the performance in terms of the delivery delay of these algorithms. We make recommendations for the design of well-founded opportunistic forwarding algorithms in the context of human-carried devices     

车载网络中基于区域覆盖的机会传递算法研究

The highly mobility of vehicles, intermit-tent communication between the vehicles and the requirements of real time applications are some of the main challenges of multi-hop message delivery in Vehicular Ad Hoc Networks(VANETs).There are also additional challenges, especially when the des-tination for the message delivery is a moving vehi-cle. In this paper, we propose a novel multi-hop message delivery method, called the Coverage Area-based oPportunistic message forwarding algorithm (CAP). The main idea of CAP is to cover the poten-tial area of a moving target vehicle as much as pos-sible with the reachable area of the required deliver-y messages, so that the message can be delivered successfully. Because the success ratio and overhead of the multi-hop message delivery are two important but incompatible parameters in CAP, two tunings are discussed in the algorithm in order to maintain the balance of the two parameters. The simulation results show that compared with other reference ap-proaches, CAP provides an efficient message deliv-ery with a higher success ratio and a shorter mes-sage delay.     

Improved Message Forwarding for Multi-Hop HaRTES Real-Time Ethernet Networks

Nowadays, switched Ethernet networks are used in complex systems that encompass tens to hundreds of nodes and thousands of signals. Such scenarios require multi-switch architectures where communications frequently occur in multiple hops. In this paper we investigate techniques to allow efficient multi-hop communication using HaRTES switches. These are modified Ethernet switches that provide real-time traffic scheduling, dynamic bandwidth management and temporal isolation between real-time and non-real-time traffic. This paper addresses the problem of forwarding traffic in HaRTES networks. Two methods have been recently proposed, namely Distributed Global Scheduling (DGS) that buffers traffic between switches, and Reduced Buffering Scheme (RBS), that uses immediate forwarding. In this paper, we discuss the design and implementation of RBS within HaRTES and we carry out an experimental validation with a prototype implementation. Then, we carry out a comparison between RBS and DGS using worst-case response time analysis and simulation. The comparison clearly establishes the superiority of RBS concerning end-to-end response times. In fact, with sample message sets, we achieved reductions in end-to-end delay that were as high as 80 %.     

Selective Message Forwarding in Delay Tolerant Networks

It is challenging to deliver messages in a network where no instant end-to-end path exists, so called delay-tolerant network (DTN). Node encounters are used for message forwarding. In this paper, we propose a DTN routing protocol SMART. SMART utilizes the travel companions of the destinations (i.e. nodes that frequently meet the destination) to increase the delivery opportunities while limiting message overhead to a bounded number. Our approach differs from related work in that it does not propagate node encounter history nor the delivery probabilities derived from the encounter history. In SMART, a message source injects a fixed number of message copies into the network to forward the message to a companion of the destination, which only forwards the message to a fixed number of the destination’s companions. Our analysis and simulation results show that SMART has a higher delivery ratio and a smaller delivery latency than the schemes that only use controlled opportunistically-forwarding mechanism and has a significantly smaller routing overhead than a pure flooding scheme.     

Impact of Heterogeneity on Forwarding Schemes in Opportunistic Networks

In the paper, we concentrate on the infl uence of heterogeneity on the performance of forwarding algorithms under opportunistic networks. Therefore, we first describe two different heterogeneous network models, and capture the heterogeneity which concern mobile nodes’ contact dynamics under the individual models and the spatial models. Then we investigate inter-contact time is not fully follow exponential distribution and compare the performance of the delivery delay between direct forwarding protocol and three-hop forwarding protocol under three network models. We illustrate the performance of message delivery delay under the spray and wait protocol and prophet protocol from simulation results. Our simulation results show that the heterogeneity should be considered for the performance of forwarding protocols.     

消息内容保护的间断连接移动自组织网络转发机制

移动自组织网络资源有限,且节点之间共享无线信道并以协作的方式完成消息转发,导致所传输消息的机密性较为脆弱。为保护消息内容的机密性,该文提出一种间断连接移动自组织网络中的消息转发机制。各节点对原始消息进行切割,并利用多副本消息转发过程的冗余性和节点相似性控制各片段消息在不相交的路径上进行转发,进而由网络中的摆渡节点收集、检验并还原、加密得到仅目的节点能够解密的完整消息,确保转发过程中消息的机密性、完整性。数值分析表明所提机制在保障网络性能前提下,能有效保护消息的机密性。     

A Stochastic Approach for Modeling Message Dissemination in Opportunistic Networks

Wireless Personal Communications - The opportunistic networks have shown to be an interesting communication infrastructure for supporting mobile collaborative systems in several application...     

Opportunistic eigenbeamforming: Exploiting multiuser diversity and channel correlations

Multiuser diversity is an inherent form of diversity present in any time-varying system with several users. An opportunistic scheduler has to be used in order to exploit this type of diversity. A scheme that increases the effective dynamic range of the channel by deploying multiple antennas at the transmitter is called opportunistic beamforming. Opportunistic beamforming increases the degree of multiuser diversity in several scenarios, including correlated channels. Nevertheless, multiuser diversity can also be combined with other transmit schemes that have proven to be effective in correlated channels, such as eigenbeamforming. Eigenbeamforming is a point-to-point link transmit technique that could easily be combined with an opportunistic scheduler to extract multiuser diversity. We refer to the joint use of eigenbeamforming with an opportunistic scheduler as opportunistic eigenbeamforming. In this work, we show that the available multiuser diversity with opportunistic eigenbeamforming is larger than the one achieved when opportunistic beamforming is employed using the proportional fair scheduler under different degrees of correlation in the channel. In the present work we have considered a single-cell scenario.     

Opportunistic Energy-Efficient Contact Probing in Delay-Tolerant Applications

In many delay-tolerant applications, information is opportunistically exchanged between mobile devices that encounter each other. In order to affect such information exchange, mobile devices must have knowledge of other devices in their vicinity. We consider scenarios in which there is no infrastructure and devices must probe their environment to discover other devices. This can be an extremely energy-consuming process and highlights the need for energy-conscious contact-probing mechanisms. If devices probe very infrequently, they might miss many of their contacts. On the other hand, frequent contact probing might be energy inefficient. In this paper, we investigate the tradeoff between the probability of missing a contact and the contact-probing frequency. First, via theoretical analysis, we characterize the tradeoff between the probability of a missed contact and the contact-probing interval for stationary processes. Next, for time-varying contact arrival rates, we provide an optimization framework to compute the optimal contact-probing interval as a function of the arrival rate. We characterize real-world contact patterns via Bluetooth phone contact-logging experiments and show that the contact arrival process is self-similar. We design STAR, a contact-probing algorithm that adapts to the contact arrival process. Instead of using constant probing intervals, STAR dynamically chooses the probing interval using both the short-term contact history and the long-term history based on time of day information. Via trace-driven simulations on our experimental data, we demonstrate that STAR requires three to five times less energy for device discovery than a constant contact-probing interval scheme.     

融合深度调整和自适应转发的水声网络机会路由

针对水声传感器网络路由过程中的空洞问题和数据传输中能效低下的问题,该文提出了融合深度调整和自适应转发的水声网络机会路由(OR-DAAF)。针对路由空洞,区别于传统绕路策略,OR-DAAF提出一种基于拓扑控制的空洞恢复模式算法—利用剩余能量对空洞节点分级,先后调整空洞节点到新的深度以克服路由空洞,恢复网络联通。针对数据传输中的能效低下问题,OR-DAAF提出了转发区域划分机制,通过转发区域的选择自适应转发面积以抑制冗余包,并提出基于加权推进距离,能量和链路质量的多跳多目标路由决策指标,综合考虑区域能量,链路质量和推进距离实现能效平衡。实验数据表明,相比DVOR协议,OR-DAAF的包投递率和生命周期分别提高10%和48.7%,端到端时延减少22%。     

Spatial Spectrum Reuse for Opportunistic Spectrum Access in Infrastructure-Based Systems

Opportunistic spectrum access (OSA) receives a constantly growing interest due to its potential to mitigate spectrum scarcity and meet the increasing communication needs of mobile users. OSA refers to identifying and exploiting spatiotemporal unused portions of licensed spectrum to allow communication among unlicensed–secondary users (SUs) without adverse impact to the licensees (primary users—PUs). Key parameters in OSA are the spectrum opportunities detection method used by the SUs, and the interference level perceived by the PUs. A spatial spectrum reuse framework is proposed, where broadcast messages of an infrastructure-based primary system are exploited and combined with location-aware methods to detect spectrum opportunities and establish interference-free secondary links. The study of secondary link establishment probabilities revealed a spectrum reuse of up to 25% for omni-directional and up to 90% for directional antennas. Moreover, increased throughput is achieved in both cases, with directional antennas attaining significantly better performance.     

Stochastic Analysis of Spatial and Opportunistic Aloha

Spatial Aloha is probably the simplest medium access protocol to be used in a large mobile ad hoc network: each station tosses a coin independently of everything else and accesses the channel if it gets heads. In a network where stations are randomly and homogeneously located in the Euclidean plane, there is a way to tune the bias of the coin so as to obtain the best possible compromise between spatial reuse and per transmitter throughput. This paper shows how to address this questions using stochastic geometry and more precisely Poisson shot noise field theory. The theory that is developed is fully computational and leads to new closed form expressions for various kinds of spatial averages (like e.g. outage, throughput or transport). It also allows one to derive general scaling laws that hold for general fading assumptions. We exemplify its flexibility by analyzing a natural variant of Spatial Aloha that we call Opportunistic Aloha and that consists in replacing the coin tossing by an evaluation of the quality of the channel of each station to its receiver and a selection of the stations with good channels (e.g. fading) conditions. We show how to adapt the general machinery to this variant and how to optimize and implement it. We show that when properly tuned, Opportunistic Aloha very significantly outperforms Spatial Aloha, with e.g. a mean throughput per unit area twice higher for Rayleigh fading scenarios with typical parameters.     

Increasing Spatial Spectrum Utilization Through Opportunistic User-to-User Communications

The requirements for ubiquitous and highly reliable wireless services, combined with the low utilization of licensed spectrum, call for flexible and efficient spectrum management schemes. To this end, a lot of attention is paid in the literature on allowing secondary-external users to opportunistically access the licensed spectrum. In parallel to these efforts, the question is whether the licensed users could further improve their own spectrum utilization. In this paper, we focus on increasing the spatial spectrum utilization of an infrastructure-based wireless system by adding autonomous functionality to the primary (system) users. An opportunistic operation mode for the uplink (UL) period, totally transparent to the base station (BS) of the system, is introduced. Users operating in this mode identify spatial spectrum UL opportunities by interpreting BS broadcast messages, and exploit these opportunities by establishing direct connections. It is shown that multiple direct connections can take place in parallel with a single standard UL transmission. Moreover, significant additional throughput is achieved, and in most of the cases, the energy consumption for the direct connections is lower than that of the conventional ones (using the standard mode).     

PQBCF：一种基于中间中心度的机会网络P2P查询算法

社会机会网络由人携带的带有短距离通信接口的移动设备利用人的移动形成,其数据采用“存储-携带-转发”的模式进行传输,本文针对这类网络,提出了一种基于中间中心度的P2P查询算法（P2P Query based on Between-ness Centrality Forwarding ,PQBCF）。节点的中间中心度描述了节点在信息传输转发过程中的参与度和重要度,PQBCF算法通过选择具有较大中间中心度的节点来实现信息的高效转发。仿真实验表明,与目前该研究领域的SF （Spray and Fo-cus ）等主流算法相比,PQBCF算法能够有效提高查询成功率,并降低查询延时。     

带有消息投递概率估计的机会网络自适应缓存管理策略

高效的缓存管理策略能够有效提高机会网络中节点的缓存资源利用率。消息的投递概率直接决定了消息的转发与存储必要性,该文提出一种带有消息投递概率估计的自适应缓存管理策略,通过构建节点连接状态分析模型,以分布式的方式感知节点服务能力,从而估计消息的投递概率,进而确定消息的转发与删除优先级,以执行缓存管理相关操作。结果表明,所提出的缓存管理策略可降低网络负载57%,并有效提高消息的成功投递率,降低消息的平均投递时延。