Road Oriented Traffic Information System for Vehicular Ad hoc Networks

Over the last few years, vehicular ad hoc networks (VANETs) have gained popularity for their interesting applications. To make efficient routing decisions, VANET routing protocols require road traffic density information for which they use density estimation schemes. This paper presents a distributed mechanism for road vehicular density estimation that considers multiple road factors, such as road length and junctions. Extensive simulations are carried out to analyze the effectiveness of the proposed technique. Simulation results suggested that, the proposed technique is more accurate compared to the existing technique. Moreover, it facilitate VANET routing protocols to increase packet delivery ratio and reduce end-to-end delay.     

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.     

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.     

A geographic routing protocol based on trunk line in VANETs

A Trunk Line Based Geographic Routing(TLBGR) protocol in Vehicular Ad-hoc Networks (VANETs) is proposed in this paper to solve the problem of data acquisition in the traditional trunk coordinated control system. Because of the characteristics of short communication time and high packet loss among vehicles, the vehicles entering the trunk lines can not transmit their information to the trunk coordinated control system stably. To resolve this problem, the proposed protocol uses the trunk lines’ traffic flow and the surrounding road network to provide a real-time data transmission routing scheme. It takes into account the data congestion problem caused by the large traffic flow of the main roads, which leads to the corresponding increase of the information flow of the section and the package loss, and the link partition problem caused by the insufficient traffic flow, which makes the vehicles have to carry and relay information thus increasing the transmission delay. The proposed TLBGR protocol can be divided into two stages: the next-intersection selection, and the next-hop selection in the chosen path between the current and next intersections. Simulation results show that, compared with other IoT routing protocols including Greedy Perimeter Stateless Routing (GPSR), Ad-hoc On Demand Vector (AODV), and Q-AODV, the TLBGR protocol has better performance in aspects of end-to-end delay, delivery rate, and routing cost under the scenario of urban traffic trunk lines. The TLBGR protocol can effectively avoid data congestion and local optimum problems, increase the delivery rate of data packets, and is therefore suitable for the routing requirements in this application scenario.     

Improving protocol robustness in ad hoc networks through cooperative packet caching and shortest multipath routing

A mobile ad hoc network is an autonomous system of infrastructure-less, multihop, wireless mobile nodes. Reactive routing protocols perform well in this environment due to their ability to cope quickly against topological changes. This paper proposes a new routing protocol named CHAMP (caching and multiple path) routing protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route failures. We show through extensive simulation results that these two techniques yield significant improvement in terms of packet delivery, end-to-end delay and routing overhead. We also show that existing protocol optimizations employed to reduce packet loss due to frequent route failures, namely local repair in AODV and packet salvaging in DSR, are not effective at high mobility rates and high network traffic.     

Design and Performance Analysis of a Proxy-Based Indirect Routing Scheme in Ad Hoc Wireless Networks

The majority of existing ad hoc network routing protocols has a tendency to use the shortest single path from a source to a destination. However, in constantly changing topologies such as those in mobile ad hoc wireless networks, the shortest single path is not only unreliable for reachability but also unsuitable for traffic load equilibrium. In order to improve routing performance and make optimum use of the limited resources, the congestion must first be relieved as much as possible and the routing path be made available at all times. In this paper, we propose a novel scheme, called the Applicative Indirect Routing (AIR), to control network traffic congestion and refine route availability by coping with unreliable links quickly. The proposed scheme, acting as a proactive routing protocol, utilizes additional information about the neighbors shared by the sender and the receiver to find an alternative for the original path with unreliable links. The additional bandwidth usage in AIR to obtain the information about shared neighbors (defined as proxy candidates) is so minimal that the bandwidth availability for user data traffic is not significantly affected. Extensive simulation experiments show that compared with a conventional proactive protocol, namely Destination-Sequenced Distance Vector (DSDV), the AIR scheme leads to a much improved system performance in terms of packet delivery ratio, average end-to-end packet delay, and network reliability. We further show that, in terms of packet delivery ratio, AIR is also a competitive protocol compared with such reactive protocols as Ad hoc On Demand Distance Vector (AODV) and Dynamic Source Routing (DSR).     

CL-MAC: A Cross-Layer MAC protocol for heterogeneous Wireless Sensor Networks

In duty cycled MAC protocols, multi-packet, multi-flow and multi-hop traffic patterns experience significant latencies, which are partially due to duty cycling. Several cross-layer routing/MAC schemes have been proposed to mitigate this latency. However, they utilize routing information from a single flow and/or a single packet perspective, thus limiting their adaptation to varying traffic loads and patterns. In this paper, we propose a novel Cross-Layer MAC protocol (CL-MAC) for WSNs, to efficiently handle multi-packet, multi-hop and multi-flow traffic patterns while adapting to a wide range of traffic loads. CL-MAC’s scheduling is based on a unique structure of flow setup packets that efficiently utilize routing information to transmit multiple data packets over multiple multi-hop flows. Unlike other MAC protocols, supporting construction of multi-hop flows, CL-MAC considers all pending packets in the routing layer buffer and all flow setup requests from neighbors, when setting up a flow. This allows CL-MAC to make more informed scheduling decisions, reflecting the current network status, and dynamically optimize its scheduling mechanism accordingly. We evaluate CL-MAC through extensive ns-2 simulations and compare its performance to the state of the art, over various networks and for a wide variety of traffic loads and patterns. In all our experiments, CL-MAC substantially reduces end-to-end latency, increases delivery ratio while reducing the average energy consumed per packet delivered.     

车载Ad hoc网络基于转发能力预测的路由策略

在车载Ad hoc网络中,节点的高速移动导致全网拓扑的频繁变化,以街道为单位的路由策略更加高效。传统的研究中使用街道的静态信息或者瞬时的动态信息选择路由路径。前者忽略了车辆节点的动态分布,后者中,精确的全局动态信息获取困难且开销巨大。文章提出街道转发能力来评估街道的路由特性,并预测其持续时间。基于街道转发能力的预测,本文设计了结合静态长度和动态信息的路由策略。仿真结果表明,本策略可以显著提高路由性能。     

An Investigation of Link Quality Assessment for Mobile Multi-hop and Multi-rate Wireless Networks

Wireless ad hoc networks will be an important component in future communication systems. The performance of wireless ad hoc networks can be improved by link quality-aware applications. Wireless link quality is dynamic in nature, especially in mobile scenarios. Therefore, accurate and fast packet delivery ratio estimation is a prerequisite to good performance in mobile, multi-hop and multi-rate wireless ad hoc networks. In this paper, we propose a novel packet delivery ratio estimation method that improves the accuracy and responsiveness of the packet delivery ratio estimation. The proposed link quality estimation components are implemented in a IEEE 802.11b/g test-bed. The experiment results show that the accuracy of the packet delivery ratio estimation can improve up to 50% in mobile scenarios without introducing overhead. We also show the end-to-end performance impact of this improved estimation on route selection using different routing metrics and configurations. The measurement results show that our packet delivery ratio method leads to better route selection in the form of increased end-to-end throughput compared to traditional methods, which respond slowly to the link dynamics.     

3D-VANET中基于模糊逻辑和Q学习的拓扑感知路由协议

城市三维车载自组网（Three-Dimensional Vehicular Ad-hoc Network,3D-VANET）中往往存在多种道路形式,每种道路网络拓扑变化特点各异,平面路由协议不能根据道路特点动态调整选路策略,不宜直接用于3D-VANET,为此设计了一种基于模糊逻辑和Q学习的拓扑感知路由协议。该协议通过模糊逻辑方法感知网络拓扑变化与网络负载情况动态调整信标间隔,以平衡邻节点信息准确性与控制开销成本。在此基础上,采用Q学习算法对网络建模,根据链路质量以及链路质量变化调整Q学习算法参数,以灵活选择下一跳转发节点,更好适应网络拓扑的频繁变化。仿真结果表明,与对比协议相比,该协议有利于降低控制开销,同时提高包投递率和减少平均端到端时延。     

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.     

A Hybrid Centralized Routing Protocol for 802.11s WMNs

Wireless mesh networks (WMNs) are being widely accepted as a critical wireless access solution for various applications. Due to minimal mobility in mesh nodes, a backbone topology can be effectively maintained in WMN using a proactive routing protocol. In IEEE 802.11s standard, a tree-based routing (TBR) protocol is adopted as a viable proactive routing protocol for a WMN with user traffic flowing to/from a wired network through a root (i.e., a mesh portal). However, the performance of the TBR protocol degrades rapidly as the user traffic becomes dominated by intra-mesh traffic. The reason is that the routing path through the root even for intra-mesh traffic unnecessarily overloads the root. Furthermore, the TBR performance becomes more severe when the network size of WMN is large, which could lead to the huge amount of intra-mesh traffic towards the root. To overcome these problems, we propose a new routing mechanism, root driven routing (RDR) protocol, for the root to quickly determine the best-metric route for any source-destination pair of intra-mesh traffic. For inter-mesh traffic, the original TBR protocol is employed. Thus, the hybrid centralized routing protocol that combines TBR and RDR and is adaptive to all traffic scenarios. Our simulation results reveal that the proposed RDR protocol outperforms the TBR protocol with much lower average end-to-end delay and much higher packet delivery ratio for intra-mesh traffic. The simulation results also provide some insight into the right tradeoff between the TBR protocol and the RDR protocol to achieve the best performance of the hybrid centralized routing protocol for WMNs.     

Aggregated traffic flow weight controlled hierarchical MAC protocol for wireless sensor networks

It has been discussed in the literature that the medium-access control (MAC) protocols, which schedule periodic sleep–active states of sensor nodes, can increase the longevity of sensor networks. However, these protocols suffer from very low end-to-end throughput and increased end-to-end packet delay. How to design an energy-efficient MAC protocol that greatly minimizes the packet delay while maximizing the achievable data delivery rate, however, remains unanswered. In this paper, motivated by the many-to-one multihop traffic pattern of sensor networks and the heterogeneity in required data packet rates of different events, we propose an aggregated traffic flow weight controlled hierarchical MAC protocol (ATW-HMAC). We find that ATW-HMAC significantly decreases the packet losses due to collisions and buffer drops (i.e., mitigates the congestion), which helps to improve network throughput, energy efficiency, and end-to-end packet delay. ATW-HMAC is designed to work with both single-path and multipath routing. Our analytical analysis shows that ATW-HMAC provides weighted fair rate allocation and energy efficiency. The results of our extensive simulation, done in ns-2.30, show that ATW-HMAC outperforms S-MAC; traffic-adaptive medium access; and SC-HMAC.     

QUORUM—Quality of Service in Wireless Mesh Networks

Wireless mesh networks (WMNs) can provide seamless broadband connectivity to network users with low setup and maintenance costs. To support next-generation applications with real-time requirements, however, these networks must provide improved quality of service guarantees. Current mesh protocols use techniques that fail to accurately predict the performance of end-to-end paths, and do not optimize performance based on knowledge of mesh network structures. In this paper, we propose QUORUM, a routing protocol optimized for WMNs that provides accurate QoS properties by correctly predicting delay and loss characteristics of data traffic. QUORUM integrates a novel end-to-end packet delay estimation mechanism with stability-aware routing policies, allowing it to more accurately follow QoS requirements while minimizing misbehavior of selfish nodes.     

Improved ant colony-based multi-constrained QoS energy-saving routing and throughput optimization in wireless Ad-hoc networks简

In order to establish a route supporting multi-constrained quality of service（QoS）, increase network throughput and reduce network energy consumption, an improved ant colony-based multi-constrained QoS energy-saving routing algorithm（IAMQER） is proposed. The ant colony algorithm, as one of the available heuristic algorithms, is used to find the optimal route from source node to destination node. The proposed IAMQER algorithm, which is based on the analysis of local node information such as node queue length, node forwarding number of data packets and node residual energy, balances the relationship between the network throughput and the energy consumption, thus improving the performance of network in multi-constrained QoS routing. Simulation results show that this IAMQER algorithm can find the QoS route that reduce average energy consumption and improves network packet delivery ratio under the end-to-end delay and packet loss ratio constraints.     

Dynamic cache allocation routing strategy of Internet of things satellite node based on traffic prediction

Aiming at the routing problem of low earth orbit (LEO) Internet of things (IoT) satellite systems,a dynamic cache allocation routing strategy based on traffic prediction for IoT satellite nodes was proposed.Firstly,the space-time characteristics of traffic distribution in the LEO coverage area were analyzed,and an end-to-end traffic prediction model was proposed.Then,according to the traffic prediction result,a dynamic cache allocation routing strategy was proposed.The satellite node periodically monitored the traffic load of the inter-satellite link,dynamically allocated the cache resources of each inter-satellite link between the neighboring nodes.The cache allocation process was divided into two phases,initialization and system operation.At the same time,the traffic offload and packet forwarding strategy when the node was congested was proposed.By comparing the queuing delay and the forwarding delay,it was determined whether the data packet needs to be rerouted.The simulation results show that the proposed routing strategy effectively reduces the packet loss rate and average end-to-end delay,and improves the traffic distribution in the whole network.     

Routing Strategies to Minimize Packet Loss in an Optical Packet Switched Network with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. We study optical packet switches with recirculating fiber delay line (FDL) buffers. Through simulation, we have assessed the logical performance of a single optical packet router (OPR), focusing on packet loss rate (PLR). By verifying that our scheduling algorithm does not alter the traffic profile characteristics from in- to output, we illustrate how the single node results can be used to assess network-wide performance. We use the capability of assessing end-to-end PLRs to develop network-wide routing algorithms designed to minimize the maximal PLR occurring in the network. In case studies on pan-European networks, we first compare two algorithm variants and thereafter we compare the PLR-based routing algorithm with both load balancing and shortest path routing. While load balancing achieves PLRs that are multiple orders of magnitude lower than shortest path routing, the PLR-based algorithm can reach PLRs up to two orders of magnitude better. The improvement in PLR comes at the price of only a small increase in used bandwidth (a few percent). Subsequently we show that the discussed PLR-based routing algorithm can be easily extended to multiple priorities. By introducing multiple priorities we can keep the loss rates for high priority traffic very low. However, it may lead to an increase of the obtained minimal max-PLR value for low priority traffic. But as we prove this increase to be limited, the cost of introducing multiple priorities is small.     

一种基于跨层设计和蚁群优化的自组网负载均衡路由协议

针对大部分现有替代路径共同存在的替代路径老化和构建效率问题,本文提出了一种基于跨层设计和蚁群优化的负载均衡路由协议(CALRA),利用蚁群优化算法特有的信息素挥发方法实现对替代路径的老化问题,将蚁群优化和跨层优化方法结合起来解决自组网中的负载均衡问题,通过双向逐跳更新的方式较好的解决了替代路径构建效率问题,并将蚂蚁在所经过的各中间节点为路由表带来的信息素增量映射为蚂蚁离开源节点的距离、移动过程中所遇到的节点拥塞程度、节点当前信息素浓度和节点移动速度等各协议层的统计信息的函数,通过对各种信息所对应的参数赋予不同加权值的方法对概率路由表进行控制,改善了自组网中现有基于蚁群优化的路由协议中普遍存在的拥塞问题、捷径问题、收敛速度问题和引入的路由开销问题.仿真表明,CALRA在分组成功递交率、路由开销、端到端平均时延等方面具有优良性能,能很好地实现网络中的业务负载均衡.     

Efficient on-demand routing for mobile ad hoc wireless access networks

In this paper, we consider a mobile ad hoc wireless access network in which mobile nodes can access the Internet via one or more stationary gateway nodes. Mobile nodes outside the transmission range of the gateway can continue to communicate with the gateway via their neighboring nodes over multihop paths. On-demand routing schemes are appealing because of their low routing overhead in bandwidth restricted mobile ad hoc networks, however, their routing control overhead increases exponentially with node density in a given geographic area. To control the overhead of on-demand routing without sacrificing performance, we present a novel extension of the ad hoc on-demand distance vector (AODV) routing protocol, called LB-AODV, which incorporates the concept of load-balancing (LB). Simulation results show that as traffic increases, our proposed LB-AODV routing protocol has a significantly higher packet delivery fraction, a lower end-to-end delay and a reduced routing overhead when compared with both AODV and gossip-based routing protocols.     

Packet‐level‐based traffic aggregation to optimize NDN content delivery

In recent years, named data networking (NDN) has been accepted as the most popular future paradigm and attracted much attention, of which the routing model contains interest forwarding and content delivery. However, interest forwarding is far from the bottleneck of routing optimization; instead, the study on content delivery can greatly promote routing performance. Although many proposals on content delivery have been investigated, they have not considered packet‐level caching and deep traffic aggregation, which goes against the performance optimization of content delivery. In this paper, we propose a packet‐level‐based traffic aggregation (PLTA) scheme to optimize NDN content delivery. At first, the packet format is devised, and data plane development kit (DPDK) is used to ensure same size for each packet. Then, the whole delivery scheme with traffic aggregation consideration is presented. The simulation is driven by the real YouTube dataset over Deltacom, NSFNET, and CERNET topologies, and the experimental results demonstrate that the proposed PLTA has better delivery performance than three baselines in terms of cache hit ratio, delivery delay, network load, and energy efficiency.