基于DAB技术的智能交通车载终端

基于数字音频广播(DAB)技术,文章提出了一种交通诱导信息广播系统和一种车载智能终端。交通诱导信息广播系统将高速发展的广播数字化技术与城市交通智能管理相结合,是集信息采编、信息发布、信息移动接收、交通实时导航、娱乐于一体的信息处理平台;车载智能终端基于DAB技术,是用于对车辆现代化管理的设备。交通诱导信息广播系统依托移动网络可以从服务车辆上获得全球定位系统(GPS)定位信息,从而监控和跟踪车辆;车载智能终端可以接收DAB信道的实时广播、动态路况、车辆的导航路径等信息。     

An efficient adaptive intelligent routing system for multi‐intersections

With the rapid development of wireless technologies and the growing emphasis on vehicle safety, many vehicular ad hoc network applications have been extensively used. This study attempts to use vehicular ad hoc network technologies for autonomous driving to improve and reduce traffic congestion and vehicle waiting time. Therefore, this study proposes an adaptively intelligent routing system, which uses V2V communications to increase vehicle speed, allows vehicles to communicate with traffic control systems, arranges appropriate vehicle routes based on queuing theory, and uses traffic signals for information exchange. The timing of traffic signals is decided according to road traffic density. To decrease vehicle waiting time at intersections, every vehicle's speed is adjusted based on the distance between the vehicle and the traffic signals. In the simulation, automated vehicles and a more realistic car‐following model are taken into consideration and vehicle speeds are regulated based on speed limits and safe following distance on most roads. The simulation result reveals that our proposed adaptively intelligent routing system outperforms periodic system in average vehicle speed and average waiting time at both single and double cross intersections. Copyright © 2016 John Wiley & Sons, Ltd.     

Connectivity analysis of passive cluster with high stability in vehicular wireless network

A passive cluster model with the maximum lifetime was proposed for vehicle to vehicle communication based on the relative velocity. The cluster head was elected based on the average relative velocity and the neighbor list. The cluster lifetime was deduced as the function of the average relative velocity. The traffic safety messages were dissemi-nated to all cluster members by inter-cluster message broadcasting and intra-cluster message relaying in interconnected vehicular network. The link connectivity probability between the cluster head and members were deduced as the function of the vehicle density for inter-cluster broadcasting. The path connectivity probability between the cluster head and the neighbor cluster head was deduced as the function of the vehicle density and intra-cluster distance for on intra-cluster dis-semination. Simulation results show that the connected probability is suitable for vehicular network under the traffic den-sity constraints.     

Road Aware Geographical Routing Protocol Coupled with Distance,Direction and Traffic Density Metrics for Urban Vehicular Ad Hoc Networks

The new information and communication technologies have changed the trend of communication in all fields. The transportation sector is one of the emerging field, where vehicles are communicating with each other or with infrastructure for different safety and comfort applications in the network. Vehicular ad hoc networks is one of the emerging multi-hop communication type of intelligent transportation field to deal with high mobility and dynamic vehicular traffic to deliver data packets in the network. The high mobility and dynamic topologies make the communication links unreliable and leads to frequent disconnectivity, delay and packet dropping issues in the network. To address these issues, we proposed a road aware geographical routing protocol for urban vehicular ad hoc networks. The proposed routing protocol uses distance, direction and traffic density routing metrics to forward the data towards the destination. The simulation results explore the better performance of proposed protocol in terms of data delivery, network delay and compared it with existing geographical routing protocols.

     

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.     

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.     

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.     

Broadcasting safety information in vehicular networks: issues and approaches

A primary goal of intelligent transportation systems is to improve road safety. The ability of vehicles to communicate is a promising way to alleviate traffic accidents by reducing the response time associated with human reaction to nearby drivers. Vehicle mobility patterns caused by varying traffic dynamics and travel behavior lead to considerable complexity in the efficiency and reliability of vehicular communication networks. This causes two major routing issues: the broadcast storm problem and the network disconnection problem. In this article we review broadcast communication in vehicular communication networks and mechanisms to alleviate the broadcast storm problem. Moreover, we introduce vehicular safety applications, discuss network design considerations, and characterize broadcast protocols in vehicular networks.     

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.

     

RPB-MD: Providing robust message dissemination for vehicular ad hoc networks

To improve traffic safety and efficiency, it is vital to reliably send traffic-related messages to vehicles in the targeted region in vehicular ad hoc networks (VANETs). In this paper, we propose a novel scheme, relative position based message dissemination (RPB-MD), to reliably and efficiently disseminate messages to the vehicles in the zone-of-relevance. Firstly, the relative position based (RPB) addressing model is proposed to effectively define the intended receivers in the zone-of-relevance. To ensure high message delivery ratio and low delivery delay, directional greedy broadcast routing (DGBR) is introduced to make a group of candidate nodes hold the message for high reliability. Moreover, to guarantee efficiency, the protocol time parameters are designed adaptively according to the message attributes and local vehicular traffic density. The protocol feasibility is analyzed to illustrate the robustness and reliability of RPB-MD. Simulation results show that RPB-MD, compared with representative existing schemes, achieves high delivery ratio, limited overhead, reasonable delay and high network reachability under different vehicular traffic density and data sending rate.     

Research on adaptive beacon message broadcasting cycle based on vehicle driving stability

Ensuring smooth communication by fixed-cycle message beaconing in vehicular environments is necessary to address vehicles safety. However, fixed-cycle beacon messages cannot accommodate the characteristics of fast vehicle speeds and variable network topologies and can cause problems such as channel congestion when traffic density is too high. Therefore, in order to realize safe and reliable information transmission between vehicles, this paper proposes a strategy for adaptive update of beacon message cycle based on vehicle driving stability. It is based on two rules: one is that the vehicle position prediction error is defined as an unstable vehicle, and the small error is defined as a stable vehicle; and the other is that the adaptive beacon message cycle is ranged, which is determined according to the channel load capacity. The experimental results show that the strategy can effectively avoid the channel congestion problem and improve the driving safety of the vehicle. Compared with the fixed-cycle beacon message, the communication delay is reduced by about 10%, the packet loss is reduced by about 22%, and the energy consumption is reduced.     

Cooperative communication for safety message dissemination in unsaturated networks with varying contention windows

Safety message dissemination is crucial in vehicular ad hoc networks (VANETs) for road safety applications. Vehicles regularly transmit safety messages to surrounding vehicles to prevent road accidents. However, changing vehicle mobility and density can cause unstable network conditions in VANETs, making it inappropriate to use a fixed contention window (CW) for different network densities. It has been proposed a 1-D Markov model under unsaturation conditions to analyze the performance of the system with varying CWs under changing vehicle densities. Additionally, it introduces the use of cooperative communication (CoC) to relay failed safety messages. In CoC, two control packets, namely, negative acknowledge (NACK) and enable to cooperate (ETC), are utilized. The proposed analytical model named cooperative communication for safety message dissemination (CoC-SMD) is used to calculate throughput and average packet delay for varying CW and different packet size. The simulation confirms the validity of the analytical results and show significant improvement in the metrics through the use of varying CW sizes and CoC compared with existing techniques.     

Machine learning in vehicular networking: An overview

As vehicle complexity and road congestion increase, combined with the emergence of electric vehicles, the need for intelligent transportation systems to improve on-road safety and transportation efficiency using vehicular networks has become essential. The evolution of high mobility wireless networks will provide improved support for connected vehicles through highly dynamic heterogeneous networks. Particularly, 5G deployment introduces new features and technologies that enable operators to capitalize on emerging infrastructure capabilities. Machine Learning (ML), a powerful methodology for adaptive and predictive system development, has emerged in both vehicular and conventional wireless networks. Adopting data-centric methods enables ML to address highly dynamic vehicular network issues faced by conventional solutions, such as traditional control loop design and optimization techniques. This article provides a short survey of ML applications in vehicular networks from the networking aspect. Research topics covered in this article include network control containing handover management and routing decision making, resource management, and energy efficiency in vehicular networks. The findings of this paper suggest more attention should be paid to network forming/deforming decision making. ML applications in vehicular networks should focus on researching multi-agent cooperated oriented methods and overall complexity reduction while utilizing enabling technologies, such as mobile edge computing for real-world deployment. Research datasets, simulation environment standardization, and method interpretability also require more research attention.     

Application of Cognitive Techniques to Adaptive Routing for VANETs in City Environments

The evolution of smart vehicles has widened the application opportunities for vehicular ad hoc networks. In this context, the routing issue is still one of the main challenges regarding to the performance of the network. Although there are multiple ad hoc routing proposals, the traditional general-purpose approaches do not fit the distinctive properties of vehicular network environments. New routing strategies must complement the existing protocols to improve their performance in vehicular scenarios. This paper introduces a novel intelligent routing technique that makes decisions in order to adaptively adjust its operation and obtain a global benefit. The nodes sense the network locally and collect information to feed the cognitive module which will select the best routing strategy, without the need of additional protocol message dissemination or convergence mechanism.     

A Dual Ring Connectivity Model for VANET Under Heterogeneous Traffic Flow

Vehicular ad-hoc network (VANET) is characterized as a highly dynamic wireless network due to the dynamic connectivity of the network nodes. To achieve better connectivity under such dynamic conditions, an optimal transmission strategy is required to direct the information flow between the nodes. Earlier studies on VANET’s overlook the characteristics of heterogeneity in vehicle types, traffic structure, flow for density estimation, and connectivity observation. In this paper, we have proposed a heterogeneous traffic flow based dual ring connectivity model to enhance both the message disseminations and network connectivity. In our proposed model the availability of different types of vehicles on the road, such as, cars, buses, etc., are introduced in an attempt to propose a new communication structure for moving vehicles in VANETl under cooperative transmission in heterogeneous traffic flow. The model is based on the dual-ring structure that forms the primary and secondary rings of vehicular communication. During message disseminations, Slow speed vehicles (buses) on the secondary ring provide a backup path of communication for high speed vehicles (cars) moving on the primary ring. The Slow speed vehicles act as the intermediate nodes in the aforementioned connectivity model that helps improve the network coverage and end-to-end data delivery. For the evaluation and the implementation of dual-ring model a clustering routing scheme warning energy aware cluster-head is adopted that also caters for the energy optimization. The implemented dual-ring message delivery scheme under the cluster-head based routing technique does show improved network coverage and connectivity dynamics even under the multi-hop communication system.     

面向智能网联汽车边缘网络的分布式端-边协同算法

车联网高级安全服务中,智能网联车辆配备了摄像头,可以拍摄周围的视频,用于安全、交通监控和监视等目的。车辆将获取的视频上传到边缘计算节点后,可以对视频进行分析和备份,以满足不同的安全驾驶需求。然而,车辆连续直接向边缘计算节点上传生成的视频内容会非常消耗带宽,并消耗大量的能量。基于该问题,提出一种面向智能网联汽车边缘网络的分布式端-边协同算法。针对车联网高可靠低时延内容传输的特点,引入有限块长度编码机制。同时,引入车辆视频信息源的压缩编码功率消耗,建立车辆能耗模型。根据车辆视频信息源的视频质量要求,通过调整视频编码码率、信息源传输速率,以及车辆多路径路由的决策,提出一种完全分布式的优化算法,以提高网络资源利用率,并保证单个车辆的能耗公平性。     

A delay‐bounded routing protocol for vehicular ad hoc networks with traffic lights

In vehicular ad hoc networks, vehicles may use a routing protocol to inform emergent events, for example, car accidents or traffic jams. Hence, many of the researchers are focused on minimizing the end‐to‐end delay of the routing protocol. However, some applications, for example, email or ftp, are not time critical, and radio spectrum is a limited resource. Hence, delay‐bounded routing protocol, whose goal is to deliver messages to the destination within user‐defined delay and minimize the usage of radio, has become an important issue. The delay‐bounded routing protocols deliver message to the destination by the hybrid of data muling (carried by the vehicle) and forwarding (transmitted through radio). When the available time is enough, the message will be delivered by muling; otherwise, it will be delivered by forwarding. However, in an urban area, there are many traffic lights, which may greatly affect the performance of the delay‐bounded routing protocols. Existing works do not consider the effect of traffic lights, and hence, it may adopt an improper delivery strategy and thus wastes much available time. To improve previous works, we propose a novel delay‐bounded routing protocol, which has considered the effect of traffic lights. Whenever a vehicle passes an intersection, it will gather the information of the traffic light and traffic load of the next road section, and thus, it can make a more accurate prediction and adopt a more proper strategy to deliver message. Simulation results show that the proposed protocol can make a better usage of the available time and uses less radio resource to deliver the message in time. Copyright © 2013 John Wiley & Sons, Ltd.     

Sparsely‐deployed relay node assisted routing algorithm for vehicular ad hoc networks

In this paper, we study the issue of routing in a vehicular ad hoc network with the assistance of sparsely deployed auxiliary relay nodes at some road intersections in a city. In such a network, vehicles keep moving, and relay nodes are static. The purpose of introducing auxiliary relay nodes is to reduce the end‐to‐end packet delivery delay. We propose a sparsely deployed relay node assisted routing (SRR) algorithm, which differs from existing routing protocols on how routing decisions are made at road intersections where static relay nodes are available such that relay nodes can temporarily buffer a data packet if the packet is expected to meet a vehicle leading to a better route with high probability in certain time than the current vehicles. We further calculate the joint probability for such a case to happen on the basis of the local vehicle traffic distribution and also the turning probability at an intersection. The detailed procedure of the protocol is presented. The SRR protocol is easy to implement and requires little extra routing information. Simulation results show that SRR can achieve high performance in terms of end‐to‐end packet delivery latency and delivery ratio when compared with existing protocols. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Directional routing and scheduling for green vehicular delay tolerant networks

The vehicle delay tolerant networks (DTNs) make opportunistic communications by utilizing the mobility of vehicles, where the node makes delay-tolerant based “carry and forward” mechanism to deliver the packets. The routing schemes for vehicle networks are challenging for varied network environment. Most of the existing DTN routing including routing for vehicular DTNs mainly focus on metrics such as delay, hop count and bandwidth, etc. A new focus in green communications is with the goal of saving energy by optimizing network performance and ultimately protecting the natural climate. The energy–efficient communication schemes designed for vehicular networks are imminent because of the pollution, energy consumption and heat dissipation. In this paper, we present a directional routing and scheduling scheme (DRSS) for green vehicle DTNs by using Nash Q-learning approach that can optimize the energy efficiency with the considerations of congestion, buffer and delay. Our scheme solves the routing and scheduling problem as a learning process by geographic routing and flow control toward the optimal direction. To speed up the learning process, our scheme uses a hybrid method with forwarding and replication according to traffic pattern. The DRSS algorithm explores the possible strategies, and then exploits the knowledge obtained to adapt its strategy and achieve the desired overall objective when considering the stochastic non-cooperative game in on-line multi-commodity routing situations. The simulation results of a vehicular DTN with predetermined mobility model show DRSS achieves good energy efficiency with learning ability, which can guarantee the delivery ratio within the delay bound.