Prioritized gossip in vehicular networks

We propose using real world mobility traces to identify tractable theoretical models for the study of distributed algorithms in mobile networks. Specifically, we derive a vehicular ad hoc network model from a large corpus of position data generated by San Francisco-area taxicabs. Unlike previous work, our model does not assume global connectivity or eventual stability. Instead, we assume only that some subset of processes might be connected through transient paths (e.g., paths that exist over time). We use this model to study the problem of prioritized gossip, in which processes attempt to disseminate messages of different priority. We present CabChat, a distributed prioritized gossip algorithm that leverages an interesting connection to the classic Tower of Hanoi problem to schedule the broadcast of packets of different priorities. Whereas previous studies of gossip leverage strong connectivity or stabilization assumptions to prove the time complexity of global termination, in our model, with its weak assumptions, we instead analyze CabChat with respect to its ability to deliver a high proportion of high priority messages over the transient paths that happen to exist in a given execution.     

车辆自组织网络中基于信道传输环境的网络连通性能

车辆间的传输干扰在车辆自组织网络中是影响车辆间通信质量的一个重要因素,车辆在同时发送信号过程中会对周围车辆接收的信号产生影响,从而对网络连通性预测产生更大的挑战。根据车辆密度及交通流量,提出一种基于Nakagami的车载网络连通预测模型。该模型采用Nakagami分布特性描述信号传输过程中的衰落信道,通过接收信号功率概率密度函数及信噪比获得车辆间连通概率。仿真结果表明,在传输信号车辆比例达到饱和之前,通过提高传输信号车辆比例可以提高连通概率,但若此比例超过了饱和值则会对车辆连通产生消极的影响。     

Reputation based selfishness prevention techniques for mobile ad-hoc networks

Mobile ad-hoc networks require nodes to cooperate in the relaying of data from source to destination. However, due to their limited resources, selfish nodes may be unwilling to forward packets, which can deteriorate the multi-hop connectivity. Different reputation-based protocols have been proposed to cope with selfishness in mobile ad-hoc networks. These protocols utilize the watchdog detection mechanism to observe the correct relaying of packets, and to compile information about potential selfish nodes. This information is used to prevent the participation of selfish nodes in the establishment of multi-hop routes. Despite its wide use, watchdog tends to overestimate the selfish behavior of nodes due to the effects of radio transmission errors or packet collisions that can be mistaken for intentional packet drops. As a result, the availability of valid multi-hop routes is reduced, and the overall performance deteriorates. This paper proposes and evaluates three detection techniques that improve the ability of selfishness prevention protocols to detect selfish nodes and to increase the number of valid routes.     

Stable routing protocol based on fuzzy logic system in vehicular ad hoc networks

Vehicular ad‐hoc networks have several roles in alert messages dissemination between vehicles in danger, the most important role is to provide helpful information for drivers (eg, road traffic state). But, some performance improvements are frequently needed in terms of routing. Hence, several clustering approaches have been proposed to optimize the network services. These approaches are based on increasing data delivery, reducing data congestion, and dividing the traffic into clusters. However, a stable clustering algorithm is always required in order to ensure the data dissemination in a dense, mobile, or a large‐scale environment. Therefore, in this paper, we have proposed a stable routing protocol based on the fuzzy logic system, which can deliver alert messages with minimum delay and improve the stability of clusters structure by generating only a small number of clusters in the network. In this work, the fuzzy logic system has been used to create the clusters and select a cluster head for each cluster. We have used the network simulator (NS2) to generate the results. As a result, we could reduce the cluster head changes and increase the cluster member lifetime compared with recent approaches.     

Blockchain-inspired lightweight trust-based system in vehicular networks

A decentralized application runs on the blockchain network without the intervention of a central authority. Transparency in transactions and security in vehicular networks are the issues for central systems. The proposed system uses blockchain-based smart contracts, which eliminate the requirement for any third-party verification. Additionally, with signature verification and reduced overhead, smart contracts also help in a fast and secure transaction. This study suggests a trust-based system paradigm where certificate authority (CA) is employed for vehicle registration. We also propose a blockchain-based system that provides efficient two-way authentication and key agreement through encryption and digital signatures. The analysis of the proposed model reveals that it is an efficient way of establishing distributed trust management, which helps in preserving vehicle privacy. The proposed scheme is tested in Automated Validation of Internet Security-sensitive Protocols (AVISPA), and security parameters verification in Network Simulator 2(NS2) also shows that the proposed scheme is more effective in comparison with existing schemes in terms of authentication cost, storage cost, and overhead.     

On the performance of cooperative vehicular networks under antenna correlation at RSU

Vehicular communications is gradually becoming mature after decades of exciting developments and thriving advances. Resultantly, these advances have opened new possibilities for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications to meet the requirements of safety applications and future self-driving technologies. While performance limits of single link vehicular communications have been well analyzed in the literature, only incremental growth has been shown in the domain of multi-antenna communications. Another major concern is that the existing works mostly assume independent fading at the antennas mounted on road side unit (RSU), thus neglecting the impact of channel correlation. Our work addresses this issue by evaluating packet error probability for two renowned antenna correlation models i.e., constant correlation (CC) and exponential correlation (EC), under Nakagami-m fading. We also consider cooperation between intermediate vehicles to ensure reliable communication from the source vehicle to the RSU. More specifically, we derive closed-form expressions of packet error probability for three cooperative techniques, namely, single helper selection (SHS), multi-hop cooperative selection (MCS) and multiple helper selection (MHS). We quantify the performance variations for different numbers of intermediate helper vehicles, and for varying values of fading parameter and correlation coefficients. Finally, we validate our mathematical derivations by performing extensive simulations in MATLAB.     

移动自组织网络基于链路稳定性的伪流言路由算法

分析了移动自组织网络中链路和路径的有效性的统计特性,并结合流言机制提出了一种基于链路稳定性的伪流言路由算法.该路由算法可以用更少的路由开销发现持续更长时间的稳定路由.仿真实验表明该算法与AODV结合显著地提高了网络的性能.     

基于射线跟踪的车联网毫米波信道准平稳区间研究

针对28 GHz车联网中车对基础设施（Vehicle-to-Infrastructure,V2I）毫米波信道,开展了准平稳区间的研究.首先,分析了信道准平稳区间的理论基础和计算方法.其次,利用功率相关（Correlation of Power,CP）算法和谱散度（Spectral Divergence,SD）算法进行准平稳区间的计算.结果表明,CP算法复杂度低且精度较高,更适合用于计算V2I通信场景下的准平稳区间.最后,利用CP算法计算出的准平稳区间作为新的采样间隔,从而减少了射线跟踪仿真器的采样点数.通过原始采样和减少采样点后的信道特性的比较,在合理的门限值下,利用信道准平稳区间的方法加速了射线跟踪仿真器,并且不会造成信道参数的失真.另外,对于信道特性的分析结果也对车联网在毫米波频段的仿真和设计具有重要意义.     

车载时延容忍网络路由协议研究

基于移动模型相似度评价机制（MMSE, movement model similarity evaluation scheme）,提出一种面向移动范围转发动态多副本车载时延容忍网络路由协议（MROFDM, movement range oriented forwarding and dynamic multi-copies routing protocol）。该协议利用移动模型间的相似度和车辆的本地实时信息,将数据向目的节点的移动范围转发,同时采用副本均衡策略,动态调整不同类型数据分组的副本数目。通过仿真实验对比现有多副本协议,验证了MROFDM在性能上的优越性以及在不同比例移动模型下的适应性。     

Joint offloading strategy based on quantum particle swarm optimization for MEC-enabled vehicular networks

With the development of the mobile communication technology, a wide variety of envisioned intelligent transportation systems have emerged and put forward more stringent requirements for vehicular communications. Most of computation-intensive and power-hungry applications result in a large amount of energy consumption and computation costs, which bring great challenges to the on-board system. It is necessary to exploit traffic offloading and scheduling in vehicular networks to ensure the Quality of Experience (QoE). In this paper, a joint offloading strategy based on quantum particle swarm optimization for the Mobile Edge Computing (MEC) enabled vehicular networks is presented. To minimize the delay cost and energy consumption, a task execution optimization model is formulated to assign the task to the available service nodes, which includes the service vehicles and the nearby Road Side Units (RSUs). For the task offloading process via Vehicle to Vehicle (V2V) communication, a vehicle selection algorithm is introduced to obtain an optimal offloading decision sequence. Next, an improved quantum particle swarm optimization algorithm for joint offloading is proposed to optimize the task delay and energy consumption. To maintain the diversity of the population, the crossover operator is introduced to exchange information among individuals. Besides, the crossover probability is defined to improve the search ability and convergence speed of the algorithm. Meanwhile, an adaptive shrinkage expansion factor is designed to improve the local search accuracy in the later iterations. Simulation results show that the proposed joint offloading strategy can effectively reduce the system overhead and the task completion delay under different system parameters.     

A new position based routing algorithm for vehicular ad hoc networks

Telecommunication Systems - Recently, the increasing demand for low latency, the explosive growth in the volume of network traffic, the large and growing number of connected devices, and...     

An efficient cross layer based channel reservation method for vehicular networks

The swift growth of the mobile users and limited availability of bandwidth lead to the requirement of effective channel allocation process. Channel allocation becomes tedious in vehicular ad hoc network, as the mobility of the nodes is high. So, in this paper, we propose a method called as cross layer based channel reservation with preemption (CCRP) method that performs channel allocation process by estimating the handoffs in vehicular ad hoc networks. The time estimated is communicated from physical layer to medium access control layer using a cross‐layer design. The reusability concept is used, and the channels are divided into three groups. The different cells acquire different groups based on the database status and exclusively to avoid interference. Preemption is incorporated to give the highest priority to real time originating calls and real time handoff calls. The performance of the proposed method, CCRP, is compared with the legacy systems such as cooperative reservation of service channels and very fast handover scheme in terms of dropping probability, blocking probability, and handoff latency. The results show that the proposed algorithm, CCRP, performs better in comparison. Copyright © 2013 John Wiley & Sons, Ltd.     

Traffic balancing‐based path recommendation mechanisms in vehicular networks

In this paper, we propose both reactive and proactive balancing traffic path recommendation mechanisms, which we refer to as Bal‐Traf and Abs‐Bal, respectively. Bal‐Traf is initiated when a certain output road segment located at any road intersection is detected in an overloaded situation. In the event that the existing traffic density of any output road exceeds its optimal capacity, Bal‐Traf recommends that those vehicles that plan to pass over this road segment as next hop choose another, less congested output road segment. On the other hand, Abs‐Bal is a proactive balancing traffic mechanism. Its main purpose is to distribute input traffic completely even among all output road segments at intersections. Moreover, Abs‐Bal considers the best travel time of vehicles in addition to the goal of balancing traffic. From the experimental results, we can see that Bal‐Traf eliminates the number of overwhelmed road segments over the road network in scenarios with only partial network congestion. It also decreases the number of congested road segments in scenarios with complete network congestion. However, it increases the density drastically over the remaining congested road segments in these scenarios. Abs‐Bal performs well in decreasing the percentage of congested road segments and balancing traffic among road segments located throughout the road network, in the event of complete network congestion.     

Incentive based scheme for improving data availability in vehicular ad-hoc networks

Vehicular networks are popular in recent years to provide low cost communication medium during mobility. Vehicular Delay Tolerant Networks (DTNs) are one of the major categories of emerging technology. DTNs work on carry and forward mechanism to deliver data to the destination. The network performance gets severely affected due to reluctance shown by selfish nodes where few nodes show no interest in forwarding others data due to lack of any personal profit. The proposed mechanism is based on coalition game theory and discusses about incentive based mechanism which provides incentive to nodes which are forwarding data to forward to destination and motivates other vehicles in the network to participate in coalition to forward data. This scheme not only encourages other selfish nodes to forward their private data and other nodes’ public data as early as possible to destination but also increases reliability in the network as more nodes show their interest in selected routing protocol. The proposed scheme outperforms in overall benefit earned by individual node and whole coalition, and increases mutual cooperation which improves availability of data in the network.     

The performance of MIMO system using MRT scheme in vehicular systems

In this paper an inter‐vehicle multiple‐input multiple‐output system using maximal ratio transmission (MRT) scheme is proposed, and its performance is investigated where the proposed system uses multiple antennas for transmission and reception. It has the advantage of increasing effectively the diversity order without changing the receiver. As far as we know, MRT has not been employed in vehicular systems to improve system performance. Specifically, error performance of the MRT with different number of antennas at the transmitting and receiving stations has been examined, ie, MRT (2, 1) and MRT (2, 2) in a vehicular system in which cascaded Nakagami‐m fading distribution used. First, we derive expressions of probability distribution function and then moment generating function of end‐to‐end signal‐to‐noise ratio. Based on these expressions, we obtain the symbol error rate expression on account of examining the performance of the considered system. Then, the upper bounds for the symbol error rate expressions for high enough signal‐to‐noise ratio values have been calculated. Finally, we validate the confirmation of obtained theoretical results through simulation results and furthermore show that the multiple‐input multiple‐output system using MRT scheme can provide the full diversity.      

基于弱分类器集成的车联网虚假交通信息检测

车联网中车辆以自组织的方式相互报告交通信息,开放的网络环境需要甄别消息,然而,要快速移动的车辆在短时间内检测出大量的交通警报信息是非常困难的。针对这一问题,提出一种基于弱分类器集成的虚假交通信息检测方法。首先,扩充交通警报信息的有效特征,并设计分割规则,将信息的特征集划分为多个特征子集;然后,根据子集特征的不同特性,使用对应的弱分类器分别进行处理。仿真实验和性能分析表明,选用弱分类器集成方法检测车联网中的虚假交通信息减少了检测时间,且由于综合特征的应用,检测率优于仅使用部分特征的检测结果。     

Trust based authentication technique for cluster based vehicular ad hoc networks (VANET)

Since Vehicular ad hoc networks (VANETs) are vulnerable to various kinds of attacks, there is a need to fulfill the security requirements like message privacy, integrity, and authentication. The authentication technique is said to be efficient if it detects compromised nodes accurately with less complexity, reduced authentication delay, and keying overhead. In this paper, a trust-based authentication scheme for cluster-based VANETs is proposed. The vehicles are clustered, and the trust degree of each node is estimated. The trust degree is a combination of direct trust degree and indirect trust degree. Based on this estimated trust degree, cluster heads are selected. Then, each vehicle is monitored by a set of verifiers, and the messages are digitally signed by the sender and encrypted using a public/ private key as distributed by a trusted authority and decrypted by the destination. This verifies the identity of sender as well as receiver thus providing authentication to the scheme. By simulation results, we prove that the proposed technique provides high security with less overhead and delay.     

An efficient voting based decentralized revocation protocol for vehicular ad hoc networks

Vehicular Ad-hoc NETworks (VANETs) enable cooperative behaviors in vehicular environments and are seen as an integral component of Intelligent Transportation Systems (ITSs). The security of VANETs is crucial for their successful deployment and widespread adoption. A critical aspect of preserving the security and privacy of VANETs is the efficient revocation of the ability of misbehaving or malicious vehicles to participate in the network. This is usually achieved by revoking the validity of the digital certificates of the offending nodes and by maintaining and distributing an accurate Certificate Revocation List (CRL). The immediate revocation of misbehaving vehicles is of prime importance for the safety of other vehicles and users. In this paper, we present a decentralized revocation approach based on Shamir’s secret sharing to revoke misbehaving vehicles with very low delays. Besides enhancing VANETs’ security, our proposed protocol limits the size of the revocation list to the number of the revoked vehicles. Consequently, the authentication process is more efficient, and the communication overhead is reduced. We experimentally evaluate our protocol to demonstrate that it provides a reliable solution to the scalability, efficiency and security of VANETs.     

Design considerations of satellite-based vehicular broadband networks

Convergence between wireless networks is the main trend in current and future wireless communications. The distinct advantage of satellite and terrestrial network integration is the possibility to provide ubiquitous multimedia services in vehicles at any location. The key design considerations of mobile broadband satellite access technologies are given in this article. After presenting the conceptual models of a system and services, the design issues of satellite network synchronization and burst demodulation are described. The design considerations of medium access control, resource management, capacity, and buffer controls for internetworking are given. Also, the active antenna issues are provided along with a sample design.     

车载自组织网中基于蚁群算法的延迟感知路由协议

针对城市道路环境下车载自组织网( VANETs)中通信性能下降以及数据传输失败的问题,提出了一种基于蚁群算法的延迟感知路由( ACDR)协议。首先,建立双向车道的数学延迟模型;然后,根据提出的端点十字路口( EI)的概念,ACDR利用蚁群优化( ACO)寻找最佳路线,其中前向蚂蚁根据本地路段延迟以及当前十字路口与目的节点的端点十字路口之间的全局时延来选择路径,后向蚂蚁则负责在返回路径时更新信息素,同时,相邻十字路口之间利用贪婪转发算法进行数据包的传递。最后仿真比较了ACDR协议与连通性感知路由( CAR)协议的性能,结果表明提出的ACDR协议的数据包的传输延迟小,丢包率低,通信性能好。