一种山区环境下车际网的中继节点选择方法

中继节点的选择决定了车际网中消息传播的效率和可靠性。现有的中继节点选择方法多集中于高速的直道和城市的十字路口场景,对于山区环境的弯道场景研究较少。提出一种基于指数迭代分割,适用于弯道下的中继节点选择方法 EPBPC。该方法无需先验车辆信息,借助阻塞信号,通过坐标映射,选择发送节点传输范围内最远且宽度最小的子区间内节点作为中继节点,从而获得稳定的较小传输延时和较高的包到达率。在实际山路环境下的仿真实验结果表明,EPBPC在传输延时和包到达率性能上有所提升,尤其在单跳范围内车辆数较大的情况下,能获得相对于其他方法24.45%的点到点延时增益及高于99.8%的包到达率。     

A rate control video dissemination solution for extremely dynamic vehicular ad hoc networks

Video dissemination to a group of vehicles is one of the many fundamental services envisioned for Vehicular Ad hoc Networks, especially as a building block for entertainment applications. For this purpose, in this paper we describe VoV, a video dissemination protocol that operates under extremely dynamic road traffic conditions. Contrary to most existing approaches that focus exclusively on always-connected networks and tackle the broadcast storm problem inherent to them, VoV is designed to operate under any kind of road traffic condition. We propose a new geographic-based broadcast suppression mechanism that gives a higher priority to rebroadcast to vehicles inside especial forwarding zones. Furthermore, vehicles store and carry received messages in a local buffer in order to forward them to vehicles that were not covered by the first dissemination process, probably as a result of collisions or intermittent disconnections. Finally, VoV employs a rate control mechanism that sets the pace at which messages must be transmitted according to the perceived network data traffic, thus avoiding channel overloading. Therefore, VoV adapts not only to the perceived road traffic condition, but also to the perceived channel quality. When compared to two related and well-accepted solutions–ABSM and AID–under Manhattan grid and real city scenarios, we show that, overall, our proposal is more efficient in terms of message delivery, delay and overhead.     

基于密度和距离的多跳广播转发节点选择方案

多数车联网VANET(Vehicular Ad Hoc Network)的安全应用均采用多跳广播方式分发安全消息。现已提出了许多的多跳广播转发节点选择方案,但它们以减少转发节点数为目的。为此,提出基于密度和距离的多跳广播转发节点选择方案DDBFS(Density-Distance based multi-hop Broadcast Forwarder Selection scheme),记为DDBFS。DDBFS方案主要解决两个问题：密集区域的冗余广播和稀疏区域的高的传输时延。在提出的DDBFS方案中,节点在决策是否转播接收的消息前,依据距离和网络密度设置定时器,一旦定时完毕,且在定时期间,没有其他节点转发该消息,该节点就成为下一跳转发节点。仿真结果表明,与现有的方案相比,提出的DDBFS协议在重播次数和传输时延性能得到显著提高。在密集区域,消息重播次数下降了约57%,在稀疏区域,传输时延缩短了约82%。     

一种用于高速公路上防车辆连环碰撞的V2V广播协议

目前,V2V网络主要通过周期性广播紧急预警消息(emergency warning message,EWM)来解决高速公路上经常发生的连环碰撞事件,但是周期性广播EWM容易产生广播风暴,造成大量消息的传输失败和传输延时,从而影响了预警网络的可靠性和效率.通过研究V2V网络中的各种无线广播协议,提出了一种用于高速公路上防止车辆连环碰撞的广播协议.协议在方向性广播的基础上,通过发送ACK帧选择广播车辆并由广播车辆负责广播EWM来解决广播协议中的EWM冗余问题.仿真实验表明:协议能有效地控制EWM的冗余问题,提高EWM传输的可靠性并降低传输延时.     

一种应用于城市环境中的车载自组网广播算法

针对城市环境中车载自组网信息发送面临的问题,本文提出一种可靠的车载自组网广播算法。首先,结合节点间的位置信息与移动方向将节点分类,基于距离机制选择中继节点,实现多跳广播;在十字路口处,为解决消息在各个路口进行广播,结合道路拓扑,将节点分为前向节点与后向节点两类;最后,针对车辆密度稀疏状况而出现通信空洞的问题,采用携带转发策略解决,节点主动探测空洞的发生,并验证消息发送方向上有节点进入通信范围,再次进行消息广播。仿真实验表明,算法在数据包延时、数据包成功发送率以及发送单一数据包平均负荷等方面具有较好的性能。     

A fault-tolerant protocol for atomic broadcast

A general protocol for atomic broadcast in networks is presented. The protocol tolerates loss, duplication, reordering, delay of messages, and network partitioning in an arbitrary network of fail-stop sites (i.e. no Byzantine site behavior is tolerated). The protocol is based on majority-concensus decisions to commit on unique ordering of received broadcast messages. Under normal operating conditions, the protocol requires three phases to complete and approximately 4N/V messages where N is the number of sites. This overhead is distributed among the messages of which the delivery decision is made and the heavier the broadcast message traffic, the lower the overhead per broadcast message becomes. Under abnormal operating conditions, a decentralized termination protocol (also presented) is invoked. A performance analysis of this protocol is presented, showing that this protocol commits with high probability under realistic operating conditions without invoking termination protocol if N is sufficiently large. The protocol retains its efficiency in wide-area networks where broadcast communication media are unavailable     

A novel adaptive protocol for lightweight efficient multicasting in ad hoc networks

In group communications, we find that current multicast protocols are far from “one size fits all”: they are typically geared towards and optimized for particular scenarios. As a result, when deployed in different scenarios, their performance and overhead often degrades significantly. A common problem is that most of these protocols incur high overheads with a high density of group members and in high mobility. Our objective is to design a protocol that adapts in response to the dynamics of the network. In particular, our objective is to provide efficient and lightweight multicast data dissemination irrespective of the density of group members and node density. Our work is motivated by two observations. First, broadcasting in some cases is more efficient than multicasting. Second, member and node layout distributions are not necessarily homogeneous. For example, many MANET applications result in a topological clustering of group members that move together. Thus, we develop Fireworks, an adaptive approach for group communications in mobile ad hoc networks. Fireworks is a hybrid 2-tier multicast/broadcast protocol that adapts to maintain performance given the dynamics of the network topology and group density. In a nutshell, our protocol creates pockets of broadcast distribution in areas with many members, while it develops a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads.     

AHBP: An efficient broadcast protocol for mobile Ad hoc networks

Broadcast is an important operation in many netowkr protocols.It is utilized to discover routes to unknown nodes in mobile ad hoc networks(MANETs) and is the key factor in scaling on -demand routing protocols to large networks.This paper presents the Ad Hoc Broadcast Protocol(AHBP)and its performance is discussed.In the protocol,messages,are only rebroadcast by broadcast relay gateways that constitute a connected dominating set of the network.AHBP can efficiently reduce the redundant messages which make flookding-like protocols perform badly in large dense networks.Simulations are conducted to determine the performance characteristics of the protocol.The simulation results have shown excellent reduction of broadcast redundancy with AHBP.It also contributes to a reduced level of broadcast collision and congestion.     

Optimizing social media message dissemination problem for emergency communication

Social media is increasingly being used as a communication bridge between government, emergency responders and managers, and the general public in extreme events. Passing information through social media channels enables individuals to send and receive content in real-time and without limitation of location and geography. While the use of social media in extreme event situations has become prevalent, there is often little strategy involved in message dissemination and too little understanding of the effects that underlying online social networks have on message distribution. In this study, we introduce a formal model for social media message dissemination in social networks through time. Our proposed model includes emphasis on single and multiple message scenarios and examines key communication characteristics in the development of more intentional and targeted social messaging strategies. We present a detailed experimental design on randomly generated networks and real-world sub-networks of the Twitter social graph and discuss our findings. We also include a Tabu Search procedure for solving single-message problem and discuss its potential value for large-scale problems in real-world applications.     

高效的分簇传感器网络广播认证方案*

广播是无线传感器网络的重要通信手段,广播消息的安全性应得到保障。在分簇传感器网络结构基础上提出了一种无线传感器网络广播认证方案,簇头节点对广播进行签名认证,簇内使用消息认证码进行消息认证,网关节点负责广播消息在簇间的传递。分析表明,与部分现有的传感器网络广播认证方案相比,该方案以较低的能耗提供了较高的安全性。     

一种基于局部连通性的增强型车载网多跳广播协议

在车载网中,许多应用都依赖于可靠高效的消息广播。由于无线信道共享介质的特性,消息广播不得不面临广播风暴问题。概率广播是一类能抑制广播风暴的简单有效的方法,然而车载网中除DV-CAST以外的概率广播协议均未考虑稀疏节点场景下的网络分割问题。在分析和验证DV-CAST协议固有缺点的基础上,借鉴其利用局部连通性进行转发决策的思想,提出了一种基于局部连通性的增强型多跳广播协议。实验表明,提出的协议能在稠密节点及稀疏节点场景中均取得较好的可靠性并具有较低开销。     

车载网络环境下消息携带车辆的选择方案

针对城市车载自组织网络拓扑的动态性,现有消息传播方案单个车辆较难在某路边接入点(AP)通信范围内完全进行文件下载,具有只能在等待下个AP进行文件通信的长时延局限性,提出利用多个车辆在多个空闲AP通信范围内协同地对同一文件进行分片下载传播,将消息送达时延分为直接相遇时延和间接相遇时延分别进行讨论,并给出了具体的消息携带车辆选择方案。通过对实验结果中消息丢包率和时延分析说明,在环境中加入该方案能够有效提高文件下载的可靠性,减少下载到目的车辆的时延,不会使网络产生较大的额外负载。     

基于信任值的车联网分层共识优化协议

随着车联网、5G 和人工智能技术的快速发展,智能交通成为交通技术发展趋势,车联网作为车-车、车-路信息交互平台,是智能交通信息共享和处理的基础。同时车联网安全备受关注,特别是数据安全问题,可能会造成用户隐私泄露。区块链技术的发展成为一种解决途径,但在效率、安全性等方面仍面临新挑战。随着车辆节点、信息增多,如何在车辆高速移动环境中高效完成信息共识也成为问题关键。针对上述问题,提出基于区块链及信任值的自下而上双层RSU（road side unit）链共识协议。对比几种典型的共识结构并依据实际车联网场景、符合速度、容错率以及减少通信量需求,选择自下而上双层共识结构。通过赋予每辆车信任值,并基于节点参与程度、工作完成情况及消息价值度提出组领导节点选举算法,以确保系统安全性。基于上述共识结构与算法工作,完整描述协议具体流程,分为区域划分、组领导节点选取、局部共识、领导主节点选取、全局共识、域内广播6个步骤。从安全性、通信复杂度、共识算法时延、容错率4个方面对实验进行分析。实验证明,与其他方案对比,本协议在可抵抗合谋攻击、女巫攻击等条件下,可以有效降低通信复杂度,缩短共识时延,并在安全前提下提高容错率,使更多节点参与信息共享,满足车联网场景需求。     

A data distribution scheme for VANET based on fountain code

Data dissemination is one of the applications used to provide infotainment to the end-users in vehicular ad hoc networks (VANET). During this process, the vehicles receive the data broadcast by the RoadSide Unit (RSU). However, it is difficult for vehicles to collect the complete content within the communication range of one RSU when the vehicle moves at a high speed and the amount of broadcast data is large. To solve this problem, a multi-RSU cooperative data distribution scheme based on fountain code (MRFC) is proposed in this paper. The source data are encoded by fountain code and poured into the VANET by multiple cooperative RSUs, then the vehicles in the area share data packets through the V2V resource compensation method, so that all vehicles can obtain enough encoded packets to reconstruct the source data. To improve channel resource utilization and reduce delivery delays, the RSUs use fuzzy logic to determine the number of fountain code packets according to their locations, the speed and density of surrounding vehicles. The experimental results show that on the premise of ensuring the delivery rate, the proposed scheme can reduce the delivery delay by 30–50%, and achieve a significant improvement in performance.

     

Dissemination of safety messages in IEEE 802.11p/WAVE vehicular network: Analytical study and protocol enhancements

Multi-channel IEEE WAVE 1609.4 protocol has been proposed to guarantee the co-existence of safety and non-safety applications over the same Vehicular Ad hoc NETwork (VANET) scenario. While the usage of multi-channel avoids the risk of collisions between applications allocated on different frequencies, its implementation on a single-radio transceiver poses some major concerns about the effective utilization of the channel resources. In this paper, we study the performance of safety applications over multi-channel single-radio VANETs, and we present three novel contributions in this regard. First, we propose an analytical analysis and a simulation study of IEEE 1609.4. We show the harmful impact of synchronous channel switching on the message delay and delivery ratio. Second, we investigate the problem of dissemination of safety broadcast messages over multi-channel VANETs, where the network is intermittently disconnected, due to the alternation of control and service intervals. Finally, we propose a WAVE-enhanced Safety message Delivery (WSD) scheme to enable fast dissemination of safety messages over multi-channel VANETs, while guaranteeing compatibility with the existing WAVE stack. To this aim, we formulate the dissemination problem as a multi-channel scheduling problem. We further introduce cooperation among vehicles to reduce the dissemination latency. Simulation study shows the ability of the WSD scheme to enhance the performance of IEEE 1609.4 in terms of message delay and delivery ratio under different topologies and various applications.     

Near-optimal all-to-all broadcast in multidimensional all-portmeshes and tori

All-to-all communication is one of the most dense collective communication patterns and occurs in many important applications in parallel and distributed computing. In this paper, we present a new all-to-all broadcast algorithm in multidimensional all-port mesh and torus networks. We propose a broadcast pattern which ensures a balanced traffic load in all dimensions in the network so that the all-to-all broadcast algorithm can achieve a very tight near-optimal transmission time. The algorithm also takes advantage of overlapping of message switching time and transmission time, and the total communication delay asymptotically matches the lower bound of all-to-all broadcast. Finally, the algorithm is conceptually simple and symmetrical for every message and every node so that it can be easily implemented in hardware and achieves the near-optimum in practice     

The role of congestion in probabilistic broadcasting for ubiquitous wireless multi-hop networks through mediation analysis

Broadcast schemes play an important role in the performance of mobile ad hoc networks, which are a clear example of ubiquitous wireless multi-hop networks where nodes collaborate in a distributed way. They are widely used as a dissemination mechanism and as a part of the discovery phase of routing protocols. The simple flooding algorithm is the usual mechanism employed in mobile ad hoc networks, but its inefficiency has been demonstrated in congested scenarios due to the high number of collisions and contentions. However, these problems can be partially alleviated by using a probabilistic broadcast approach in which every node forwards the incoming packets according to a certain forwarding probability. In this paper, we use a simple probabilistic broadcast protocol to evaluate the effects of congestion on the performance of broadcasting in ad hoc networks through a mediation analysis. We hypothesize that the congestion mediates in the relationship between the forwarding probability (independent variable) and the output metric (dependent variable). We consider several output metrics according to the application of the broadcasting protocol such as reachability, broadcasting delay, packet delivery fraction and end to end delay. The simulation results show the existence of the mediating effects and how such effects may be counterbalanced depending on the target use of the probabilistic broadcast scheme.     

Game theoretic approach for real-time data dissemination and offloading in vehicular ad hoc networks

Due to high velocity of the vehicles, data dissemination and mobile data offloading are most difficult tasks to be performed in vehicular ad hoc networks (VANETs). In recent years, due to an exponential increase in the data generated from various sources such as smart devices, gadgets, and actuators, there arises a need of usage of an efficient communication infrastructure to handle the aforementioned issues. Most of the earlier solutions reported in the literature for data offloading problem have used the cellular communication, which may be congested in handing a large number of requests from community of users. This may result a performance bottleneck in terms of call drops and data dissemination to the other vehicles in the VANET environment. Also, these schemes lack a comprehensive approach of data dissemination to meet the quality of service (QoS) in real time. Hence, to overcome this problem, some of the mobile data can be disseminated using the existing vehicular infrastructure and Wi-Fi access points (APs). In this paper, we propose a new schedule based on game theoretic approach where the APs and vehicles act as players in a game and compete for offloading the cellular data. The proposed scheme is based on the selection of the best vehicle or AP based on the utility of the players (vehicles and APs) in the game. The utility of vehicle and AP is decided based on the parameters such as distance, velocity, connectivity to destination, bandwidth, and area of the network. A novel algorithm has been designed using the proposed game theoretic approach for handling mobile data offloading and data dissemination. The proposed solution not only successfully offloads the data but also maintains QoS with respect to the parameters such as end-to-end delay, message progress, and message dissemination speed. Results obtained confirm the superiority of the proposal in comparison with the other existing schemes. Specifically, the proposed scheme achieves improvement of 4.16 and 20.5 % in message progress, 18.91 and 4.75 % in extra messages generated, 11.26 and 54.94 % in message dissemination speed, and 78.71 and 87.94 % in end-to-end delay in sparse network as compared to GyTAR and GPCR, respectively.     

Quantum simultaneous secret distribution with dense coding by using cluster states

A new communication mode, quantum simultaneous secret distribution (QSSD) is put forward, where one sender distributes different classical secret message to multiparty receivers simultaneously. Based on the properties of the one-dimensional four-qubit cluster states, a three-party QSSD protocol is proposed, and then it is extended to the case that there are many receivers. Owing to the idea of quantum dense coding, each receiver can receive two bits of classical message by the sender only using a cluster state. In order to check security of quantum channels, a strategy which can prevent common attacks efficiently is put forward. QSSD is distinct from quantum secret sharing (QSS) and quantum broadcast communication (QBC), but it can be easily converted into QSS and QBC. QSSD is also different from the multiple-QKD communication mode where the sender shares a private key with each receiver at first, while in QSSD the sender doesn’t; in addition, only one round of one-to-many communication is performed in QSSD, while in multiple-QKD communication mode many rounds of one-to-one communication are performed.     

基于历史相遇间隔的机会网络路由协议

针对大多数机会网络路由协议在寻找端到端通信链路时不能很好地抓住节点社会性质的问题,提出一种基于历史相遇间隔(HICR) 协议的路由算法。HICR协议利用社会关系的特点,根据节点之间的历史相遇间隔判断它们的亲密程度,转发消息给离目的节点更亲近的节点,使得消息朝更靠近目的节点方向发送。仿真结果表明,该HICR协议在网络资源有限的的情况下,与Epidemic协议和Prophet协议相比,能获得更高的消息交付率。