车载边缘计算中多任务部分卸载方案研究

现有车载应用设备对时延有更严苛的要求,车载边缘计算(VEC)能够充分利用网络边缘设备,如路边单元(RSU)进行协作处理,可有效地降低时延。现有研究多假设RSU计算资源充足,可提供无限的服务,但实际其计算资源会随着所需处理任务数量的增加而受限,对时延敏感的车载应用造成限制。该文针对此问题,提出一种车载边缘计算中多任务部分卸载方案,该方案在充分利用RSU的计算资源条件下,考虑邻近车辆的剩余可用计算资源,以最小化总任务处理时延。首先在时延限制和资源约束下分配各任务在本地、RSU和邻近车辆的最优卸载决策变量比例,其次以最小处理时延为目的在一跳通信范围内选择合适的空闲车辆作为处理部分任务的邻近车辆。仿真结果表明所提车载边缘计算中多任务部分卸载方案相较现有方案能较好地降低时延。     

基于网络编码的优化V2R数据传输性能的研究

将路侧设备RSUs作为车载网络VANETs的缓冲点,可缓解车与车V2V之间连通的间歇性问题。然而,由于车辆的快速移动以及RSU短的传输距离,车辆驻留同一个RSU的时间很短。尽管广播技术能够有效地提高广播带宽利用率以及系统响应时间。但RSU采用广播技术前需要获取车辆缓存数据项的先验知识。因此,车辆需要向RSU服务器上传缓存信息,浪费了带宽。为此,针对基于RSUs的VANETs,提出基于网络编码的车与路边设施V2R通信的数据传输算法NCDD。NCDD算法允许车辆不必向RSU服务器上传它们的缓冲信息,并利用网络编码提高RSU的广播性能,仿真结果也证实了NCDD算法能够有效地降低截止期错失率和系统响应时间。     

车载网络中安全有效分布式的假名生成

提出了一种RSU协助的分布式假名生成方法。首先,车辆用户生成自己的临时公钥,当经过RSU时,由RSU对其临时公钥进行盲签名;然后,车辆得到RSU对自己临时公钥的签名,并将该签名与临时公钥一起构成车辆的一个假名（临时公钥+RSU对临时公钥的签名）,通过该假名与周围节点进行通信。本方法的优势在于：一方面RSU能够分担VANET中认证中心（CA）的负担,有效地提高了系统的效率、增强了系统的可扩展性;另一方面,由于生成车辆假名的私钥在RSU中,而不是在车辆中,因此增加了攻击者提取系统密钥的难度,从而提高了系统的安全性。     

异构车载通信中基于模糊逻辑的最佳簇头选择算法

车载网络中车辆高速移动且网络拓扑频繁变换，而现有的通过建立数学模型来确定簇头的算法太过复杂，且缺乏灵活性。提出了一种VANET分簇中基于模糊逻辑选择最佳簇头的方案，以车辆间相对平均速度、相邻度和RSU链路质量为度量标准，基于模糊逻辑选取最理想的簇头，增加了簇头选择的灵活性。方案中选取邻近车辆作为簇头，可以提高簇内通信速度与质量，有效降低时延。与CROWN算法的性能仿真对比表明，所提方案具有更好的服务发现时延和服务消耗时延。     

基于停放车辆路边单元环境感知的车联网资源高效分配

为减少路边单元（RSU）部署,同时满足移动车辆用户对处理时延敏感和计算密集任务的需求,提出了基于停放车辆环境感知的资源分配算法。选择路边停放的车辆替代RSU为车辆用户提供服务,将停放时间作为选择停放车辆路边单元（PCRSU）的决策要素,分别在内容缓存和分发2个方面设计了减小需求响应时延的机制。在内容缓存方面,PCRSU通过感知用户历史搜索数据与兴趣点区域类型两类要素对用户进行个性化的内容推荐。在内容分发方面,PCRSU通过感知车辆用户的数据传输需求,对带宽进行高效分配。实验证明,与已有方法相比,所提算法能更合理地选择PCRSU,有效降低系统的需求响应时延,在保证网络覆盖的同时提升系统稳定性,并且能为车辆用户提供更加准确的服务内容。     

车联网中整合移动边缘计算与内容分发网络的移动性管理策略

由于车载应用的普及和车辆数量的增加,路边基础设施的物理资源有限,当大量车辆接入车联网时能耗与时延同时增加,通过整合内容分发网络(CDN)和移动边缘计算(MEC)的框架可以降低时延与能耗。在车联网中,车辆移动性对云服务的连续性提出了重大挑战。因此,该文提出了移动性管理(MM)来处理该问题。采用开销选择的动态信道分配(ODCA)算法避免乒乓效应且减少车辆在小区间的切换时间。采用基于路边单元(RSU)调度的合作博弈算法进行虚拟机迁移并开发基于学习的价格控制机制,以有效地处理MEC的计算资源。仿真结果表明,所提算法相比于现有的算法能够提高资源利用率且减少开销。     

基于边缘计算的车辆调度模型

文中通过寻找边缘节点部署的最佳方案，以协助大型露天矿山在复杂车辆运输、开采环节中的车辆调度。首先，对初始状态下的车辆运输模型进行分析，寻找车辆运输的规律和特点，通过动态规划算法寻找最优边缘部署节点，再通过路径最优、调度最佳、传输最快等准则完成车辆调度节点的部署，在满足边缘节点信息传输的最大传输数量的同时，使车辆边缘节点优化率达到最大。最后，通过仿真与实验证明，上述算法可有效地解决矿山车辆调度时延问题，提高信息的实时传输效率。     

基于骨干网的停车位发现路由算法

随着私家车的数量不断增加,快速获取实时的停车位信息,成为当下社会需要迫切解决的问题。为此,提出了由路边节点设施、道路移动车辆以及停车场服务器附近的RSU组建的用于停车位信息获取的骨干网框架。同时,通过计算链接概率设计停车路由算法。仿真结果可知,该算法与传统停车位信息获取方法相比,递包率高且网络负载小。     

复杂路网条件下的物流配送方案研究

为了有效提高在复杂路网条件下物流配送路径优化效率,文中提出了采用蚂蚁算法复杂路网条件下物流配送路径优化算法.算法运用Repast Simphony仿真平台和GIS技术,对复杂路网条件下的城市物流配送进行仿真实验.实验结果表明,该物流配送方案可以较好地解决了复杂路网条件下的车辆路径问题(VRP)难题,同时仿真实验模型简单,具有非常优越的可扩展性能.     

基于SDN的多控制器部署策略的研究

随着SDN在大型网络以及广域网中的需求,如何合理、高效地部署SDN控制器,从而以较低的部署成本,获得较好的网络性能,是当前研究的热点.针对控制器数量、部署位置问题以及交换机与控制器之间的映射关系的问题,首先给出一种分布式的控制器部署方式并设定了网络相关参数,以流建立请求代价为优化目标,提出了一种基于贪心算法的控制器部署策略方案.最后通过仿真实验将所提出方案与ACL方案进行对比,证明了所提方案在性能方面有一定的提升.     

Broadcast-First Service Scheduling Scheme for Vehicle-Roadside Communication

In recent years, the research of vehicular ad-hoc networks (VANET) has become increasingly popular. More and more vehicles want their requests to be served from roadside units (RSU) in VANET, thus the service scheduling of RSU becomes an important task, especially when a large number of vehicles drive past the RSU and access data. Obviously, different kinds of request messages have different degrees of emergency, in other words, request messages have different priorities while scheduling. In order to provide a more effective and appropriate scheme, in this paper we study the scheduling of service algorithm in VANET, and proposed a novel broadcast-first service scheduling scheme. That scheme is on the basis of existing priority schemes, and takes channel bandwidth and processing capability of RSU into consideration so as to cope with the challenges in vehicle-roadside data access. Finally we conduct our experimental scenario, and simulation results show that our algorithm performs better than other existing algorithms by the comparison.     

RSU deployment planning based on approximation algorithm in urban VANET

To minimize the number of RSU deployed to cover a specific area,a c street model transforming the area covering problem to streets covering problem was designed,and a greedy-based polynomial (GBP) time approximation algorithm was developed to obtain the optimal RSU deployment for area coverage.For complex urban environments,a Cue model (complex urban environments model) was proposed.In this model,the target area was divided into different partitions.Then,based on shifting strategy,a polynomial time approximation scheme was designed.Theoretical analysis that include the approximation ratio and time complexity of the proposed algorithm were also presented.Simulation results show that GBP can efficiently solve the coverage problem in urban VANET.     

Priority based efficient data scheduling technique for VANETs

As vehicular networks are gaining popularity, large number of vehicles want to take advantage of these networks, by utilizing the information they have, in order to take decision. Vehicle receives data from other vehicles or from the road side units (RSUs) available across the road. Since RSUs act as router to connect with the external world as well as it is a high capacity storage place where important data (e.g. data used in traffic safety, location dependent query, etc.) can be stored for download purpose for other vehicles moving through the service area. Since the RSUs have limited communication range and vehicles usually moves at very high speed in the service area, they have limited time to serve data to vehicles moving in the service area. For this purpose RSUs have to schedule data in such a way that maximum vehicles can get benefit from the data available with the RSUs. There are many algorithms proposed in the past to schedule data at RSUs. This paper proposes a mechanism to schedule data of those vehicles which are in the coverage range of the RSU. The proposed algorithm outperforms to serve requests whose deadline is about to expire i.e. vehicles which have left the service area after forwarding request to RSU. This scheme performs well in dense network and has good results in highway scenario.     

An improved EAAP scheme for vehicular ad hoc networks

Recently, Maria Azees et al proposed an “EAAP: efficient anonymous authentication with conditional privacy‐preserving scheme for Vehicular Ad Hoc Networks.” Their scheme is mainly to solve the problem of high computation time of anonymous certificate and signature authentication, as well as the tracking problem of malicious vehicles. However, some improvements are needed in the protection of anonymous identity and the effective tracking of malicious vehicles. In this paper, our scheme realizes mutual authentication between OBU and RSU, and the RSU is authenticated without using certificate. In order to prevent the anonymous identity of the vehicles from being monitored and tracked, we use the negotiated short‐time key to encrypt the anonymous identity in the vehicle certificates. In addition, our scheme uses a new tracking method for malicious vehicles. Then, we prove the scheme through BAN logic, and it has the properties of authentication, anonymity, unlinkability, privacy protection, and traceability. Finally, we compare the computation cost and communication cost with other schemes, and the scheme has been greatly improved.     

Cooperative caching for content dissemination in vehicular networks

The explosive growth of mobile data traffic has made cellular operators to seek low‐cost alternatives for cellular traffic off‐loading. In this paper, we consider a content delivery network where a vehicular communication network composed of roadside units (RSUs) is integrated into a cellular network to serve as an off‐loading platform. Each RSU subjecting to its storage capacity caches a subset of the contents of the central content server. Allocating the suitable subset of contents in each RSU cache such that maximizes the hit ratio of vehicles requests is a problem of paramount value that is targeted in this study. First, we propose a centralized solution in which, we model the cache content placement problem as a submodular maximization problem and show that it is NP‐hard. Second, we propose a distributed cooperative caching scheme, in which RSUs in an area periodically share information about their contents locally and thus update their cache. To this end, we model the distributed caching problem as a strategic resource allocation game that achieves at least 50% of the optimal solution. Finally, we evaluate our scheme using simulation for urban mobility simulator under realistic conditions. On average, the results show an improvement of 8% in the hit ratio of the proposed method compared with other well‐known cache content placement approaches.     

Cooperative and Opportunistic Channel Access for Vehicle to Roadside (V2R) Communications

This paper focuses on vehicle to roadside (V2R) communications in vehicular networks based on the IEEE 802.11 DCF MAC protocol. In vehicular networks, roadside units (RSUs) are typically spaced apart along the road and each vehicle can be connected to an RSU only when the vehicle is within its transmission range. Due to the high relative speed between a moving vehicle and a stationary RSU, the residence time of the vehicle within the coverage of each RSU is very short. Thus it is hard for the system to reach a steady state. With multi-hop forwarding, in which a vehicle may be connected to an RSU through relaying over other vehicles, the connection time of each V2R access may be extended. But this is at the expense of introducing wireless interference among vehicles, which may dramatically degrade the system performance. To tackle these challenges, we propose a new mechanism called Proxy-based Vehicle to RSU access (PVR) for V2R communications. This protocol is designed to exploit cooperative and opportunistic forwarding between any two distant RSUs and to emulate back-to-back transmissions within the coverage of an RSU. As a result, it can shorten the access delay by taking advantage of opportunistic forwarding and mitigate the interference problem during the short residence time within the coverage of an RSU. The simulation results show that PVR achieves excellent performance and outperforms all existing solutions for V2R communications in vehicular networks.     

A roadside unit‐based localization scheme for vehicular ad hoc networks

Vehicular Ad Hoc Networks (VANETs), designed to ensure the safety and comfort of passengers via the exchange of information amongst nearby vehicles or between the vehicles and Roadside Units (RSUs), have attracted particular attention. However, the success of many VANET applications depends on their ability to estimate the vehicle position with a high degree of precision, and thus, many vehicle localization schemes have been proposed. Many of these schemes are based on vehicle‐mounted Global Positioning System (GPS) receivers. However, the GPS signals are easily disturbed or obstructed. Although this problem can be resolved by vehicle‐to‐vehicle communication schemes, such schemes are effective only in VANETs with a high traffic density. Accordingly, this paper presents a VANET localization scheme in which each vehicle estimates its location on the basis of beacon messages broadcast periodically by pairs of RSUs deployed on either side of the road. In addition, three enhancements to the proposed scheme are presented for the RSU deployment, RSU beacon collisions, and RSU failures. Overall, the ns‐2 simulation results show that the localization scheme achieves a lower localization error than existing solutions on the basis of vehicle‐to‐vehicle communications and is robust toward changes in the traffic density and the vehicle speed. Copyright © 2012 John Wiley & Sons, Ltd.