Reducing wireless multi‐hop delay via RSU re‐routing in vehicular wireless networks

Vehicular wireless networks offer wireless multi‐hop communications between vehicles and roadside units (RSUs). To reduce deployment cost, the distance between two RSUs could be long; that is, the communications between an RSU and a vehicle may be carried out through multi‐hops among intermediate vehicles. When a vehicle is driven from one RSU to another, the wireless multi‐hop delay becomes more serious as the number of multi‐hop relays increases. The wireless multi‐hop delay is critical for some emergency service. For instance, in a traffic accident, when a patient was sent to the hospital by ambulance, the life information of the patient must be transmitted to the hospital on time through the multi‐hop wireless network. If the ambulance is moved from one RSU to another, the wireless multi‐hop delay becomes more and more serious as the ambulance is closing to another RSU. In this paper, we propose an RSU re‐routing strategy that dynamically alters multi‐hop communications until the best RSU with the shortest path using location information is found. Moreover, we compare the proposed strategy with the existing strategy in terms of broadcasting costs, re‐routing delay, and wireless multi‐hop delay of data transmission. Performance results show that the proposed strategy can reduce the wireless multi‐hop delay significantly. Copyright © 2014 John Wiley & Sons, Ltd.     

A path selection based routing protocol for urban vehicular ad hoc network (UVAN) environment

Routing in urban environment is a challenging task due to high mobility of vehicles in the network. Many existing routing protocols only consider density, link connectivity, delay, and shortest path information to send the data to the destination. In this paper, a routing protocol is proposed which uses the urban road network information such as multi-lane and flyover to send the data to the destination with a minimum packet forwarding delay. The next path for data forwarding is selected based on a path value calculated by the Road Side Unit for each path connected to a junction. This protocol uses Ground Vehicle to Ground Vehicle (GV2GV) communication, Flyover Vehicle to Flyover Vehicle (FV2FV) communication, and Flyover Vehicle to Ground Vehicle/Ground Vehicle to Flyover Vehicle (FV2GV/GV2FV) communication to enhance the routing performance. Simulation results show that proposed protocol performs better than P-GEDIR, GyTAR, A-STAR, and GSR routing protocols in terms of end-to-end delay, number of network gaps, and number of hops.     

RVCloud: a routing protocol for vehicular ad hoc network in city environment using cloud computing

Routing in Vehicular Ad hoc Network (VANET) is a challenging task due to high mobility of vehicles. In this paper, a RVCloud routing protocol is proposed for VANET to send the data efficiently to the destination vehicle using cloud computing technology. In this protocol, vehicle beacon information is send to the cloud storage through the Road Side Unit (RSU). As vehicles have less storage and computing facility, the information of all the vehicles moving in the city is maintained by the cloud. Source vehicle sends the data to the destination by sending the data to the nearby RSU. After receiving the data, RSU sends a request to the cloud for an optimal RSU information, that takes minimum packet forwarding delay to send the data to the destination. Cloud provides location service by providing destination location and optimal RSU information. Then RSU sends the data to the optimal RSU using internet. By using the internet facility, packet forwarding delay and link disruption problem are reduced. Simulation results show that, RVCloud performs better than VehiCloud, P-GEDIR, GyTAR, A-STAR, and GSR routing protocols.     

Geographic routing protocol for vehicular ad hoc networks in city scenarios: a proposal and analysis

The characteristics of vehicular ad hoc networks (VANETs) make the design of routing protocol a great challenge. In this paper, we propose a vehicle density and load aware routing protocol for VANETs called VDLA. VDLA adopts sequential selection of junctions to construct the route. The selection is based on the real‐time vehicle density, the traffic load, and the distance to the destination. The network information is collected by a decentralized mechanism. Through factoring in these metrics, the packets are avoided being sent to roads where network is disconnected, and the network load is balanced to mitigate network congestion. The intermediate junctions are selected before the packet reaches a junction to reduce the unnecessary hops. Our study also investigates the impact of the high mobility of the nodes. An analytical framework is proposed to analyze the mobility. Based on the analysis, the traditional Hello scheme is enhanced to improve the accuracy of the neighbor table. In the simulation, we compare VDLA with greedy perimeter coordinator routing and GpsrJ+, which are geographic routings protocols proposed for VANETs. The results validate the superiority of VDLA in terms of end‐to‐end delay and packet delivery rate. And the superiority holds in different scenarios. Copyright © 2013 John Wiley & Sons, Ltd.     

RSU-coordinated multichannel MAC protocol in vehicular ad hoc network

A road side unit (RSU)-coordinated multichannel media access control (MAC) (RMM) protocol was proposed in vehicular ad hoc network,which aimed to improve the transmission efficiency of non-safety messages.Under the coordination of RSU,nodes had more opportunities to make SCH reservations on control channel,and the contention-free message transmissions were thus realized.The proposed RMM protocol could use the service channel during the whole synchronization interval for non-safety message transmissions,and thus the saturated network throughput and channel utilization were improved,and the transmission delay was reduced.Compared with other existing protocols,extensive analysis and simulation results demonstrate the superiority of the RMM protocol.     

A moving cluster architecture and an intelligent resource reuse protocol for vehicular networks

Real-time data transmission, especially video delivery over high-speed networks have very stringent constraints in terms of network connectivity and offered data rate. However, in high-speed vehicular networks, direct communication between vehicles and road side units (RSU) often breaks down, resulting in loss of information. On the other hand, a peer-to-peer based multihop network topology is not sufficient for efficient data communication due to large packet loss and delay. In this paper, a novel ‘moving cluster multiple forward’ (MCMF) architecture is proposed and investigated for efficient real-time data communication in high speed vehicular networks. MCMF involves novel aspects in relation to the formation of clusters and managing the communication between groups of vehicles and introduction of a hierarchical multiple forwarding mechanism which enables communication between any vehicle and RSU via other vehicles. Additionally, a novel protocol called ‘alternate cluster resource reuse’ (ACRR) is proposed and its detailed communication mechanism is presented. Simulation tests show how the use of MCMF and the ACRR protocol results in superior bit-rate performance—around three times that obtained in peer-to-peer multihop communications and twice that of MCMF with no ACRR protocol. Further, the average delay in MCMF-based transmissions from vehicle to RSU is around 50 % that of a peer-to-peer multihop communication mechanism. MCMF/ACRR has the potential to support multimedia traffic according to the IEEE 802.11p standard, even with a sparse investment in the infrastructure.     

车载自组织网络中基于十字路口的地理感知路由协议

为了解决城市道路多十字路口,对单个车辆节点运动感知不敏感所带来的通信性能下降问题,提出一种车载自组织网络中基于十字路口的地理感知路由(IGPR)协议,通过网络网关选择道路十字路口,形成骨干路由,在保证高连通概率的同时满足时延和误比特率要求.在双向道路模型的基础上分析获得平均时延和平均跳数的数学计算式.仿真结果表明,IGPR协议与FRGR协议、VRR协议相比,传输时延小,跳数少,通信性能好.     

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.     

Mitigation and Performance Analysis of Routing Protocols Under Black-Hole Attack in Vehicular Ad-hoc Network (VANET)

Vehicular Ad-hoc network (VANET) is a self-organized ad hoc network. VANET becomes a most challenging research area as it has several issues related to routing protocols, quality of service, security, etc. Vehicular communication is critically unsafe to several kinds of active and passive routing attacks. This paper analyzes the impact of a compromised node (vehicle) on zone routing protocol and ad-hoc on-demand distance vector, and recommends a suitable solution called secure vehicular on demand routing to find out and mitigate the black hole attack. The given study analyses the effect of vehicle density on the average throughput, packet delivery ratio, end-to-end delay, normalized routing load and average path length.     

Connectivity-aware minimum-delay geographic routing with vehicle tracking in VANETs

In this paper, we propose the connectivity-aware minimum-delay geographic routing (CMGR) protocol for vehicular ad hoc networks (VANETs), which adapts well to continuously changing network status in such networks. When the network is sparse, CMGR takes the connectivity of routes into consideration in its route selection logic to maximize the chance of packet reception. On the other hand, in situations with dense network nodes, CMGR determines the routes with adequate connectivity and selects among them the route with the minimum delay. The performance limitations of CMGR in special vehicular networking situations are studied and addressed. These situations, which include the case where the target vehicle has moved away from its expected location and the case where traffic in a road junction is so sparse that no next-hop vehicle can be found on the intended out-going road, are also problematic in most routing protocols for VANETs. Finally, the proposed protocol is compared with two plausible geographic connectivity-aware routing protocols for VANETs, A-STAR and VADD. The obtained results show that CMGR outperforms A-STAR and VADD in terms of both packet delivery ratio and ratio of dropped data packets. For example, under the specific conditions considered in the simulations, when the maximum allowable one-way transmission delay is 1 min and one gateway is deployed in the network, the packet delivery ratio of CMGR is approximately 25% better than VADD and A-STAR for high vehicle densities and goes up to 900% better for low vehicle densities.     

SDR: A Stable Direction-Based Routing for Vehicular Ad Hoc Networks

A stable and reliable routing mechanism for vehicular ad hoc networks (VANETs) is an important step toward the provision of long data transmission applications, such as file sharing and music download. Traditional mobile ad hoc network (MANET) routing protocols are not suitable for VANET because the mobility model and environment of VANET are different from those of traditional MANET. To solve this problem, we proposed a new stable routing algorithm, called stable directional forward routing. The novelty of the proposed routing protocol is its combining direction broadcast and path duration prediction into ad hoc on-demand distance vector routing protocols, which including: (1) Nodes in VANET are grouped based on the position, only nodes in a given direction range participating in the route discovery process to reduce the frequency of flood requests, (2) Route selection is based on the link duration while not the hops or other metrics to increase the path duration, (3) Route discovery is executed before the path expiration in order to decrease the end to end delay. The performance of the new scheme is evaluated through extensive simulations with Qualnet. Simulation results indicate the benefits of the proposed routing strategy in terms of decreasing routing control packet, reducing the number of link-breakage events, improving the packet delivery ratio and decreasing the end-to-end delay.     

QoS-aware multi-path video streaming for urban VANETs using ACO algorithm

Drivers can be provided with several beneficial services associated with video streaming in a vehicular ad-hoc network (VANET). Given the dynamic topology and high mobility of VANETs, a single path cannot support the required quality of service (QoS). To maximize global QoS metrics, a two-path model is proposed based on a disjoint algorithm to forward sub-streams over diverse paths from the transmitter to the receiver vehicle. In this solution, the video information spread in separate paths is categorized based on their priority. For this purpose, the protocol for transmitting each kind of video data should be selected cautiously. The present study aims to propose an ant colony optimization-based technique to establish the primary and secondary paths and enhance the QoS of routing paths. To achieve this goal, the QoS routing issue is formulated mathematically as a problem of constrained optimization. Moreover, to achieve high-quality video streaming, inter-frames are transmitted over the user datagram protocol and intra-frames are transmitted over the transmission control protocol (TCP). TCP transmission delays are also minimized using a TCP-ETX algorithm for selecting appropriate paths. According to the simulation results, the proposed two-path solution can be used to improve the quality of video streaming and to enhance the performance in terms of end-to-end delay, packet delivery ratio, and overhead. In this way, the proposed method can outperform several prominent routing algorithms such as adaptive QoS-based routing for VANETs, geographic source routing (GSR), intersection-based geographical routing protocol, and efficient GSR.

     

A Connectivity-Based Multi-Lane Routing Optimization Algorithm in Vehicular Communication

This paper proposed a connectivity-based multi-lane geographic routing protocol (CGRP) for vehicular ad hoc networks. The proposed CGRP is based on an effective selection of road intersections through which a package must pass from source to destination. The cooperative connectivity probability and delay are taken into consideration when choosing the most suitable path for delay-sensitive safety traffic. Analytical expressions for cooperative connectivity probability is derived based on a three-lanes path model. Geographical forwarding is used to transfer packets between any two intersections on the path, reducing the path sensitivity to individual node movements. Furthermore, forwarding packets between two adjacent intersections also depend on geographic location information. Neighbor nodes’ priority are assigned according to position, speed, direction and other factors. Node with the highest priority will be selected as the next hop. Numerical and simulation results show that the proposed algorithm outperforms the exsiting routing protocols in terms of the end-to-end delay and the number of hops with a little cost of routing overhead in city environments.     

车载自组织网中基于车辆密度的可靠性路由协议

为了降低转发节点在转发范围内直接寻找一个最优或次优节点的复杂度、减少平均跳数和提高链路的可靠性,提出一种车载自组织网络中基于车辆密度的可靠性路由协议,转发节点首先根据道路车辆密度设置最优块的大小,并将转发范围分割成若干大小相等的块,然后选择其中一个距离转发节点最远的块,最后在被选中的块里根据可靠性原则选择连接时间最长的邻居节点作为中继节点进行转发。仿真结果表明,与EG-RAODV 相比,所提路由协议的平均跳数较少,平均每跳前进距离较大,能够使数据分组快速到达目的节点。     

DSR路由协议的改进

DSR路由协议是移动Ad Hoc网络常用的按需路由协议之一。由于采用洪泛机制寻找和维护路由表,DSR路由协议能量开销高、分组交付率低。针对此问题,提出局部化路由查询方法,限制路由请求跳数,改进DSR路由协议的路由发现过程,有效地平衡了路由信息存储量、网络拥塞和能量消耗。分析表明,改进的DSR路由协议将路由请求分组控制在一定的网络范围内,减少数据传输时延、降低网络能量开销。仿真结果显示,在选择适当的最大跳数时,改进的DSR路由协议在分组交付率、路由载荷方面均优于传统的DSR路由协议。     

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.     

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。     

Intersection-Based Routing Protocol for VANETs

Vehicular ad hoc network (VANET) is an emerging wireless communications technology that is capable of enhancing driving safety and velocity by exchanging real-time transportation information. In VANETs, the carry-and-forward strategy has been adopted to overcome uneven distribution of vehicles. If the next vehicle located is in transmission range, then the vehicle forwards the packets; if not, then it carries the packets until meeting. The carry mostly occurs on sparsely populated road segments, with long carry distances having long end-to-end packet delays. Similarly, the dense condition could have long delays, due to queuing delays. The proposed intersection-based routing protocol finds a minimum delay routing path in various vehicle densities. Moreover, vehicles reroute each packet according to real-time road conditions in each intersection, and the packet routing at the intersections is dependent on the moving direction of the next vehicle. Finally, the simulation results show that the proposed Intersection-Based Routing (IBR) protocol has less end-to-end delay compared to vehicle-assisted data delivery (VADD) and greedy traffic aware routing protocol (GyTAR) protcols.     

FGWSO‐TAR: Fractional glowworm swarm optimization for traffic aware routing in urban VANET

In mobile distributed applications, such as traffic alert dissemination, dynamic route planning, file sharing, and so on, vehicular ad hoc network (VANET) has emerged as a feasible solution in recent years. However, the performance of the VANET depends on the routing protocol in accord with the delay and throughput requirements. Many of the routing protocols have been extensively studied in the literature. Although there are exemptions, they escalate research challenges in traffic aware routing (TAR) protocol of VANET. This paper introduces the fractional glowworm swarm optimization (FGWSO) for the TAR protocol of VANET in an urban scenario that can identify the optimal path for the vehicle with less traffic density and delay time. The proposed FGWSO searches the optimal routing path based on the fitness function formulated in this paper. Fractional glowworm swarm optimization is the combination of the GWSO and fractional theory. Moreover, exponential weighted moving average is utilized to predict the traffic density and the speed of the vehicle, which is utilized as the major constraints in the fitness function of the optimization algorithm to find the optimal traffic aware path. Simulation of FGWSO shows the significant improvement with a minimal end‐to‐end delay of 6.6395 seconds and distance of 17.3962 m, respectively, in comparison with the other existing routing approaches. The simulation also validates the optimality of the proposed TAR protocol.