RCare: Extending Secure Health Care to Rural Area Using VANETs

In this paper, we propose a delay-tolerant secure long-term health care scheme, RCare, for collecting patient’s sensitive personal health information (PHI). Specifically, to minimize the overall health care cost, RCare provides network connectivity to rural areas using conventional transportation vehicles (e.g., cars, buses) as relay nodes. These vehicles are expected to store, carry, and forward the PHI to the health-service-provider located mostly at the city area following an opportunistic routing. RCare improves network performance by providing incentive to the cooperative vehicles, and encompasses identity based cryptography to ensure security and privacy of the PHI during the routing period by using short digital signature and pseudo-identity. Network fairness and resistance to different possible attacks are also ensured by RCare. Extensive security and performance analyses demonstrate that RCare is able to achieve desired security requirements with effectiveness in terms of high delivery ratio with acceptable communication delay.     

Performance Analysis with Traffic Accident for Cooperative Active Safety Driving in VANET/ITS

Recently, by using vehicle-to-vehicle and vehicle-to-infrastructure communications for VANET/ITS, the cooperative active safety driving (ASD) providing vehicular traffic information sharing among vehicles significantly prevents accidents. Clearly, the performance analysis of ASD becomes difficult because of high vehicle mobility, diverse road topologies, and high wireless interference. An inaccurate analysis of packet connectivity probability significantly affects and degrades the VANET/ITS performance. Especially, most of related studies seldom concern the impact factors of vehicular accidents for the performance analyses of VANET/ITS. Thus, this paper proposes a two-phase approach to model a distributed VANET/ITS network with considering accidents happening on roads and to analyze the connectivity probability. Phase 1 proposes a reliable packet routing and then analyzes an analytical model of packet connectivity. Moreover, the analysis is extended to the cases with and without exhibiting transportation accidents. In phase 2, by applying the analysis results of phase 1 to phase 2, an adaptive vehicle routing, namely adaptive vehicle routing (AVR), is proposed for accomplishing dynamic vehicular navigation, in which the cost of a road link is defined in terms of several critical factors: traffic density, vehicle velocity, road class, etc. Finally, the path with the least path cost is selected as the optimal vehicle routing path. Numerical results demonstrate that the analytical packet connectivity probability and packet delay are close to that of simulations. The yielded supreme features justify the analytical model. In evaluations, the proposed approach outperforms the compared approaches in packet connectivity probability, average travel time, average exhausted gasoline. However, the proposed approach may lead to a longer travel distance because it enables the navigated vehicle to avoid traversing via the roads with a higher traffic density.     

基于802.11p/WAVE的车联网连通性模型及其应用研究

首先对高速公路交通场景的车联网连通性模型进行了研究,分析推导了某特定路段上任意两车之间的连通概率、连通集直径长度以及连通集数目等连通性模型参数指标与车辆密度及传输距离之间关系的数学解析式,并在此基础上分析出车联网的节点位置是满足伽马分布的结论。接着根据车联网报文存储转发的特点,设计了一种车联网的报文格式,并应用连通性模型中的相关参数解析式给出了广播消息报文的TTL字段的初始值设定方案,从而能够有效地控制广播报文的泛滥情形,仿真实验证实了所建模工作的有效性,为车联网WAVE协议栈上层协议的设计提供了重要的理论基础。     

Routing in Sparse Vehicular Ad Hoc Wireless Networks

A vehicular ad hoc network (VANET) may exhibit a bipolar behavior, i.e., the network can either be fully connected or sparsely connected depending on the time of day or on the market penetration rate of the wireless communication devices. In this paper, we use empirical vehicle traffic data measured on 1-80 freeway in California to develop a comprehensive analytical framework to study the disconnected network phenomenon and its network characteristics. These characteristics shed light on the key routing performance metrics of interest in disconnected VANETs, such as the average time taken to propagate a packet to disconnected nodes (i.e., the re-healing time). Our results show that, depending on the sparsity of vehicles or the market penetration rate of cars using Dedicated Short Range Communication (DSRC) technology, the network re-healing time can vary from a few seconds to several minutes. This suggests that, for vehicular safety applications, a new ad hoc routing protocol will be needed as the conventional ad hoc routing protocols such as Dynamic Source Routing (DSR) and Ad Hoc On-Demand Distance Vector Routing (AODV) will not work with such long re-healing times. In addition, the developed analytical framework and its predictions provide valuable insights into the VANET routing performance in the disconnected network regime.     

基于无标度网络的车联网连通性研究

移动车辆的连通性是车联网(IoV)的关键指标之一,它会严重影响数据传输的性能。由于车联网的网络拓扑高频动态变化,车辆之间的通信链路容易频繁地断连。如何降低链路建立的随机性和链路断开概率,提高整体网络的连通性一直是急需解决的关键问题。针对上述问题,在视距路径损耗模型和干扰模型下分析网络的连通性,通过对车联网链路在真实世界的表征,设计动态生长(DN)算法。对车辆节点进行增加、删除和链路的偏好连接后,构建无标度车联网。通过仿真结果分析,网络整体的连通性提升了16%。     

Position-Based Adaptive Clustering Model (PACM) for Efficient Data Caching in Vehicular Named Data Networks (VNDN)

The seamless data delivery is essential in VANET for application such as autonomous vehicle, intelligent traffic management and for the road safety and emergency applications. The incorporation of named data networking (NDN) with VANET, intended to frame intelligent traffic flow and seamless data delivery. Such integration of vehicular ad hoc networks (VANET) with NDN is termed as vehicular named data networks (VNDN). Because of the continuous node/vehicle mobility, it is a tedious process to build constant and consistent communication between vehicles. With that concern, for enhancing the performance of VNDN and solving the issues such as frequent cluster formation on heavy loaded data transmissions, position-based adaptive clustering model (PACM) is developed. The major intention of PACM is to form clusters based on trajectory. Besides, PACM performs efficient data caching by collecting significant data from vehicles to establish consistent data communication with all nodes in the network. Efficient data caching is done with the elected cluster heads among the framed clusters based on its positions and mobility models. For handling the vehicles at higher mobility speed, mutual data caching process is also designed that makes vehicles to perform on-demand data gathering from cluster heads. Further, the model is simulated and the obtained results are compared with the existing models based on the metrics such as packet delivery ratio, mean delay, cache hit rate and mean hop distance. The comparative analysis shows that the proposed model outperforms the available techniques.

     

三维开阔区车辆间通信的无线信道模型

车载自组网络-VANET（Vehicle Ad Hoc Network）作为移动自组网和传感器网络在道路交通领域的应用,节点具有对等性、高速移动等特点,这导致了VANET无线信道与无线蜂窝网络信道有着显著区别。文中主要研究开阔区域中车辆间通信的无线信道模型：在三维多径散射场景下,考虑配备定向天线的车辆终端,推导VANET双移动通信节点之间无线衰落信道的自相关函数与多普勒功率谱密度函数的解析表达式。该结果对于VANET网络下无线多媒体业务性能评估有着重要的作用。     

Sleep scheduling with expected common coverage in wireless sensor networks

Sleep scheduling, which is putting some sensor nodes into sleep mode without harming network functionality, is a common method to reduce energy consumption in dense wireless sensor networks. This paper proposes a distributed and energy efficient sleep scheduling and routing scheme that can be used to extend the lifetime of a sensor network while maintaining a user defined coverage and connectivity. The scheme can activate and deactivate the three basic units of a sensor node (sensing, processing, and communication units) independently. The paper also provides a probabilistic method to estimate how much the sensing area of a node is covered by other active nodes in its neighborhood. The method is utilized by the proposed scheduling and routing scheme to reduce the control message overhead while deciding the next modes (full-active, semi-active, inactive/sleeping) of sensor nodes. We evaluated our estimation method and scheduling scheme via simulation experiments and compared our scheme also with another scheme. The results validate our probabilistic method for coverage estimation and show that our sleep scheduling and routing scheme can significantly increase the network lifetime while keeping the message complexity low and preserving both connectivity and coverage.     

Analytical Model for Connectivity in Vehicular Ad Hoc Networks

We investigate connectivity in the ad hoc network formed between vehicles that move on a typical highway. We use a common model in vehicular traffic theory in which a fixed point on the highway sees cars passing it that are separated by times with an exponentially distributed duration. We obtain the distribution of the distances between the cars, which allows us to use techniques from queuing theory to study connectivity. We obtain the Laplace transform of the probability distribution of the connectivity distance, explicit expressions for the expected connectivity distance, and the probability distribution and expectation of the number of cars in a platoon. Then, we conduct extensive simulation studies to evaluate the obtained results. The analytical model that we present is able to describe the effects of various system parameters, including road traffic parameters (i.e., speed distribution and traffic flow) and the transmission range of vehicles, on the connectivity. To more precisely study the effect of speed on connectivity, we provide bounds obtained using stochastic ordering techniques. Our approach is based on the work of Miorandi and Altman, which transformed the problem of connectivity distance distribution into that of the distribution of the busy period of an equivalent infinite server queue. We use our analytical results, along with common road traffic statistical data, to understand connectivity in vehicular ad hoc networks.      

ACAR: Adaptive Connectivity Aware Routing for Vehicular Ad Hoc Networks in City Scenarios

Multi-hop vehicle-to-vehicle communication is useful for supporting many vehicular applications that provide drivers with safety and convenience. Developing multi-hop communication in vehicular ad hoc networks (VANET) is a challenging problem due to the rapidly changing topology and frequent network disconnections, which cause failure or inefficiency in traditional ad hoc routing protocols. We propose an adaptive connectivity aware routing (ACAR) protocol that addresses these problems by adaptively selecting an optimal route with the best network transmission quality based on statistical and real-time density data that are gathered through an on-the-fly density collection process. The protocol consists of two parts: 1) select an optimal route, consisting of road segments, with the best estimated transmission quality, and 2) in each road segment of the chosen route, select the most efficient multi-hop path that will improve the delivery ratio and throughput. The optimal route is selected using our transmission quality model that takes into account vehicle densities and traffic light periods to estimate the probability of network connectivity and data delivery ratio for transmitting packets. Our simulation results show that the proposed ACAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, throughput and data packet delay. Since the proposed model is not constrained by network densities, the ACAR protocol is suitable for both daytime and nighttime city VANET scenarios.     

VDNet: an infrastructure‐less UAV‐assisted sparse VANET system with vehicle location prediction

Vehicular Ad Hoc Network (VANET) has been a hot topic in the past few years. Compared with vehicular networks where vehicles are densely distributed, sparse VANET have more realistic significance. The first challenge of a sparse VANET system is that the network suffers from frequent disconnections. The second challenge is to adapt the transmission route to the dynamic mobility pattern of the vehicles. Also, some infrastructural requirements are hard to meet when deploying a VANET widely. Facing these challenges, we devise an infrastructure‐less unmanned aerial vehicle (UAV) assisted VANET system called V ehicle‐D rone hybrid vehicular ad hoc Net work (VDNet), which utilizes UAVs, particularly quadrotor drones, to boost vehicle‐to‐vehicle data message transmission under instructions conducted by our distributed vehicle location prediction algorithm. VDNet takes the geographic information into consideration. Vehicles in VDNet observe the location information of other vehicles to construct a transmission route and predict the location of a destination vehicle. Some vehicles in VDNet equips an on‐board UAV, which can deliver data message directly to destination, relay messages in a multi‐hop route, and collect location information while flying above the traffic. The performance evaluation shows that VDNet achieves high efficiency and low end‐to‐end delay with controlled communication overhead. Copyright © 2016 John Wiley & Sons, Ltd.     

Connectivity Requirements for Self-Organizing Traffic Information Systems

To facilitate the dissemination of a time-critical information in a vehicular ad hoc network (VANET), immediate network connectivity is needed. In other words, a time-critical message from a source should be able to propagate and reach all of the vehicles on the road segment without any delay due to the unavailability of the vehicles to forward the message. Clearly, this requires the road segment to have a certain number of vehicles equipped with communication devices. It is the task of a system designer to determine the minimum number of vehicles (i.e., the minimum penetration) necessary to form a connected network as well as the critical transmission range required to provide such connectivity. In this paper, we present an analytical framework for determining the connectivity requirements in distributing the traffic information in a self-organizing vehicular network. One- and two-way street scenarios are considered. In addition to the conventional perspective on connectivity, where the characteristics of the wireless channel are often neglected, our analysis offers a new view by taking important physical-layer parameters, such as fading, propagation path loss, transmit power, and transmission data rate, into consideration.      

一种动态寻路中的机会转发模型

动态寻路（Dynamic Routing）是一项用以解决城市交通拥堵的智能交通技术.通过让一些车辆产生和转发路况拥堵消息,另一些车辆能够避开拥堵路段,从而缓解交通状况.以“存储-携带-转发”为通信模式的机会网络被广泛运用于动态寻路研究.文中提出了一种新型路况信息的机会转发算法,算法综合考虑车辆的位置和行驶方向.仿真实验表明,算法在保持信息散布效果的前提下,显著降低了网络负载,提升了效率.     

基于车流量和粒子群算法的无线接入点布局

市车载网环境下车辆的高速移动以及街道障碍物阻挡等原因,导致VANETs分割现象严重,以至于车载网不能正常通信,因此许多研究提出通过引入无线接入点（AP）来增强车载网通信的可能性.本文就是针对城市环境的VANETs的AP布局问题的研究,在基于车流量和粒子群算法的基础上提出的解决方案,并给出了相应的仿真,仿真结果表明该算法能在保证覆盖率的情况下实现AP的优化布局,同时在寻优过程中具有较快的收敛速度和较好的收敛性.     

Directed information dissemination in vehicular ad-hoc networks

In this article, we utilize the idea of multipoint relays (MPRs) found in literature (Jacquet et al. in Proceedings of IEEE INMIC, 2001), to propagate accident information in a restricted way (e.g., only backwards). We devise an algorithm to identify MPRs that are geographically situated behind a particular node using only its neighbor table, and speed information of the neighboring vehicles. With the identification of the backward MPRs, it is possible to restrict the information dissemination to vehicles behind a particular vehicular ad-hoc network (VANET) node only. This might benefit the approaching vehicles so that the driver could take preventive measures in real-time since he/she will have an indication of the severity of road conditions ahead. We assume that there exists an inter vehicular network using optimized link state routing (OLSR) where accident information can be propagated to all nodes using on-going OLSR control packets. We envision our application will run on top of existing routing protocols (e.g., OLSR), thereby resulting in very little integration effort, and retaining OLSR’s reduced network traffic advantage through the use of MPRs. We analyze our back MPR identification algorithm in a detailed manner. We also show that by using our approach the location of the accident alert instigator node could be pinpointed if a subset of the nodes in the same VANET know their geographical positions. We use VANET mobility models generated by SUMO into NS-3 for our simulations, and also perform preliminary experiments to verify the algorithm’s effectiveness. Our analysis and experiments show favorable results.     

高速公路场景中车用自组织网络的节点度

该文基于大尺度路径损耗无线传播模型将高速公路场景中的车用自组织网络(VANET)建模为几何随机图,提出了VANET有效组网面积的概念,分析说明了VANET的准线性拓扑特点,并基于交通流理论关于自由流条件下的车头时距分布,推导得出了无线传输范围内至少存在k个邻居的概率计算方法。实验结果表明:该文提出的概率描述思想是一种适合计算高速公路场景中车辆网络节点度的有效方法。     

A Model-Based Reinforcement Learning Protocol for Routing in Vehicular Ad hoc Network

Todays by equipping vehicles with wireless technologies, Vehicular Ad Hoc Network (VANET) has been emerged. This type of network can be utilized in many fields such as emergency, safety or entertainment. It is also considered as a main component of intelligent transportation system. However, due to the nodes velocity (vehicles velocity), varying density, obstacles and lack of fixed infrastructure, finding and maintaining a route between nodes are always challenging in VANET. Any routing protocol can be effective only if the nodes can learn and adapt themselves with such a dynamic environment. One way to achieve this adaptation is using machine learning techniques. In this paper we try to reach this goal by applying Multi-Agent Reinforcement Learning (MARL) that enables agents to solve routing optimization problems in a distributed way. Although model-free Reinforcement Learning (RL) schemes are introduced for this purpose, such techniques learn using a trial and error scheme in a real environment so they cannot reach an optimal policy in a short time. To deal with such a problem, we have proposed a mode-based RL based routing scheme. We have also developed a Fuzzy Logic (FL) system to evaluate the quality of links between neighbor nodes based on parameters such as velocity and connection quality. Outputs of this fuzzy system have been used to form the state transition model, needed in MARL. Results of evaluations have shown that our approach can improve some routing metrics like delivery ratio, end-to-end delay and traffic overhead.

     

Analytical model for connectivity of vehicular ad hoc networks in the presence of channel randomness

A vehicular ad hoc network (VANET) is a highly mobile wireless ad hoc network formed by vehicles equipped with communication facilities. Developing multihop communication in VANETs is a challenging problem because of rapidly changing network topology and frequent network disconnections. This paper investigates the network connectivity probability of one‐dimensional VANET in the presence of channel randomness. Network connectivity is one of the most important issues in VANETs, because the dissemination of time‐critical information requires, as a preliminary condition, the network to be fully connected. We present an analytical procedure for the computation of network connectivity probability, taking into account the underlying wireless channel. Three different fading models are considered for the connectivity analysis: Rayleigh, Rician, and Weibull. A distance‐dependent power law model is employed for the pathloss in a vehicle‐to‐vehicle channel. Furthermore, the speed of each vehicle on the highway is assumed to be a Gaussian distributed random variable. The analysis provides a general framework for investigating the dependence of various parameters such as vehicle arrival rate, vehicle density, vehicle speed, highway length, and various physical layer parameters such as transmit power, receive signal‐to‐noise ratio threshold, path loss exponent, and fading factors (Rician and Weibull) on VANET connectivity. Copyright © 2011 John Wiley & Sons, Ltd.     

Noncooperative Dynamic Routing with Bandwidth Constraint in Intermittently Connected Deep Space Information Networks Under Scheduled Contacts

The increasing world-wide demands in deep space scientific missions, such as Lunar, Mars and other Planetary Exploration, along with the rapidly growing advances in space communication technologies have triggered the vision of so called future Deep Space Information Networks (DSINs). The coined DSIN paradigm is envisioned to be an integrated high speed self-organizing hypernetwork consisting of the terrestrial ground-based information networks and the outer space-based entities to provide maximum network capacity. In this paper, we address the challenges of dynamic routing with bandwidth constraint over intermittently connected Deep Space Backbone Layer (DSBL) of DSINs under scheduled contacts. Firstly, we build up hypergraph model to represent DSBL aiming to improve network connectivity. Taking into account the continuous and random changes of selfish traffic along backbone links as well as the selfish forwarding of joint nodes, we propose a noncooperative dynamic routing model with bandwidth constraint, in which routing decision is related to the continuous-time resource usage. Our routing model includes two effective sub-models: stochastic differential game based noncooperative forwarding model with bandwidth constraints and contact schedule model. In addition, we provide a polynomial time algorithm to describe the procedure of our routing model. This algorithm covers three sub-algorithms considering three different cases based on hypergraph model, i.e., internal forwarding, cross-IS forwarding, cross-island forwarding. Theoretical analysis and numerical results demonstrate the effectiveness and feasibility of our routing model.     

Achieving timely message delivery quality-of-service in fixed and variable connectivity distributed routing networks

Variable connectivity distributed routing networks (VCDRNs) are networks designed with the goal of reliably delivering message traffic even when network connectivity (both routing node to routing node and subscriber to routing node) is continuously and unpredictably changing. A general-purpose point-to-point VCDRN which provides optimum (fewest hop) connectivity in a fixed network and adapts as network topology changes so as to automatically reroute traffic is presented. The routing algorithm includes the multimedia, multidata rate, multierror rate case. It is shown how to design the network to offer a quality-of-service (QoS) in terms of a numerical probability of successful message delivery in a specified time or to adjust the network to provide a users desired QoS on single and multihop paths. This is an important feature to users who want rapid message delivery, even as network topology changes. The case of multiple message priorities is also included. Routing knowledge is distributed by adding path and error rate information to packets as they traverse the network, without adversely impacting QoS. This methodology applies to all routing protocols that employ selective reject retransmission error control. The methodology also presents a means for comparing the performance of candidate protocols in terms of parameters meaningful to the user. While the methods presented herein are applicable to any network they are of particular value to the wireless network with limited bandwidth, high error rates, and variable connectivity, where the user wants message traffic to be delivered as fast as possible in that environment with some prior assurance as to the speed and certainty of delivery.