Stochastic modeling and performance analysis in balancing load and traffic for vehicular ad hoc networks: A review

The rapid growth of vehicular applications has resulted in high demand for Internet technology, which demands an unprecedented network capacity and a high quality of service (QoS). In vehicular ad hoc networks (VANETs), since nodes (vehicles) are highly mobile. The dynamic nature of the network topology in the VANET system changes due to frequent changes in link connectivity. The vehicles-to-vehicles (V2V), vehicles-to-infrastructure (V2I), and QoS, as well as the heterogeneity of applications within the VANET. VANETs have been introduced to make driving comfortable by providing safety and support to drivers. Due to the flexibility and offloading schemes available in-vehicle applications, there are some limitations. However, there are many issues in providing optimum service provisioning and scheduling in the vehicular environment. In VANETs, BSs and roadside units (RSUs) improve QoS. However, Internet services transmit packets to vehicles using stochastic models, and it predicts the traffic on a VANET. We provide open challenges to drive stochastic models in this direction.     

Fault tolerant time synchronization using offsets table robust broadcasting protocol for vehicular ad hoc networks

The requirement of time synchronization emerged in distributed systems remains one of the most significant issues that should be addressed to the extent of that systems evolve. As clock synchronization is important for any type of network, Vehicular Ad hoc networks (VANETs) are being considered for their basic communication platforms, but also for providing the ability to detect movement, location, proximity, and other network capabilities. The intrinsic characteristics of VANETs like: the high speed of nodes and the lack of permanent network connectivity generated by an instable environment, which make communication difficult or temporarily impossible, have created new challenges. These challenges make solutions that have been already proposed for classical networks no longer appropriate. Therefore, to overcome this deficiency, new and adaptive clock synchronization mechanisms should be devised and implemented, dealing so with communication and scalability issues. In this paper, we propose “Offsets Table Robust Broadcasting” (OTRB) algorithm. In this algorithm, instead to each node communicates with its vicinity, a set of nodes is selected to spread the time information over the entire network. The proposed time synchronization protocol is well-adapted to random network topology changes, high nodal velocity while offering good precision and robustness against nodal failure and packet loss. The analytical study and protocol simulation for evaluating the system performance, carried out by a combination of VanetMobiSim and NS2 simulators, have yielded convincing results, outperforming those exhibited by the basic referred protocols.     

QoS‐aware broadcasting in VANETs based on fuzzy logic and enhanced kinetic multipoint relay

Vehicular ad hoc networks (VANETs) are emergent concepts in terms of infrastructure‐less communication. The data dissemination is usually done using broadcast schemes. Data broadcast in VANETs is a challenging issue due to the high mobility vehicles and the varying density. On one hand, these vehicles have to share and disseminate the safety‐critical information, in real time, to other intended vehicles. On the other hand, the existing broadcast solutions do not succeed, till now, to fulfill VANETs requirements especially in terms of performance and QoS. In this paper, we propose a new QoS‐aware broadcast method in order to face VANETs communications challenges. We choose to adapt a concept originally devoted to mobile ad hoc networks (MANETs) and join it to other specific VANET techniques to introduce a new broadcasting protocol in the aim of optimizing QoS fulfilment. The proposed solution is fundamentally based on enhanced kinetic strategy assisted with fuzzy logic for QoS‐aware multipoint relay (MPR). The protocol efficiency is eventually tested through an experimental study and compared with existing methods. The results prove the over‐performance of the proposed solution.     

Design of a node architecture for logic-calculation Nased all-optical network coding scheme

Network coding brings many benefits for multicast networks. It is necessary to introduce network coding into optical networks. Nevertheless, the traditional network coding scheme is hard to be implemented in optical networks because of the weak operation capability in photonic domain. In the paper, we focused on realizing two-channel network coding in all-optical multicast networks. An optical network coding scheme which can be realized via logic shift and logic XOR operations in photonic domain was proposed. Moreover, to perform the network coding scheme the coding node structure was designed and the operation principle and processes were illustrated in detail. In the end of the paper, the performance and the cost of different all-optical multicast mode were compared and analyzed.     

多播网络中基于网络编码的高效丢失恢复机制

网络编码为无线网络中可靠多播通信提供了有效解决途径。该文分析了网络中编码机会的变化规律,研究了解码失败的编码数据包对网络编码性能的影响,提出了新的基于网络编码的丢失恢复算法(NCLR)。NCLR要求节点缓存解码失败的编码数据包,并反馈信息给发送节点。根据各个节点的丢包情况,NCLR通过优先传输对编码性能影响较大的数据包,并在需要重传的已编码数据包和原始数据包中选择编码组合,来充分挖掘网络中的编码机会。仿真结果表明相对于已有算法,NCLR算法可以在重传次数和丢失恢复时延方面有显著性能改善。     

Increasing public safety broadband network resiliency through traffic control

Long Term Evolution (LTE)-based cellular networks are being deployed around the world to provide public safety with enhanced capabilities and access to broadband technology. In the United States, the First Responder Network Authority (FirstNet) is on the verge of deploying a nationwide network called the National Public Safety Broadband Network (NPSBN). Commercial networks typically aim at maximizing network capacity, i.e. the aggregate data rate, in order to increase revenue. However, in public safety networks, coverage, not capacity, is paramount, especially during an outage when sites are down. Through traffic control and preemption, the service level of low-priority users is reduced or denied, freeing up resources to restore coverage to high-priority users, e.g. users responding to an incident. In this study, we examine the effect of outages on network coverage and throughput. As our main contribution, we propose three traffic-control schemes that exploit variable modulation and coding, a feature that LTE enhances with respect to its 3G predecessors. The schemes differ based on the proportion of low- and high-priority users preempted. We show that the network coverage can be restored significantly and we investigate the tradeoff between the three schemes. Finally, we perform sensitivity analysis to confirm the effectiveness of the schemes across a wide range of scenarios.     

CADD: connectivity-aware data dissemination using node forwarding capability estimation in partially connected VANETs

The recent development of the vehicular ad hoc networks (VANETs) has motivated an increasing interest in vehicular services and applications, such as active safety service and the infotainment service. Effective data Dissemination has become more and more important in vehicular services sharing. In this paper, the connectivity characteristics of VANETs are theoretically analyzed and implemented to show the partial connections in vehicle to vehicle communication. Hence, we propose the connectivity-aware data dissemination (CADD) in partially connected VANETs will improve the data transmission capacity. In the CADD protocol, a new metric of the node forwarding capability estimation is introduced. The metric is designed by the combination the throughput function and the active connection time estimation. And then, the high efficiency data dissemination protocol is designed by the new metric. Simulation results show that the CADD protocol outperforms existing solutions in terms of the packet delivery ratio, the transmission delay, and the protocol overhead under the condition of the intermittent network connectivity.

     

无线Mesh网络中跨层协作的路由策略

网络编码可以提高无线Mesh网络的吞吐量,但是网络编码在无线Mesh网络中实际应用获得最大网络利用率是需要解决的问题。提出一种多路径策略,能够通过将网络编码和TCP进行最大化融合提高网络的利用率。网络编码被加入到现有的网络系统,通过解决速率控制问题和分组调度问题,调整源节点的数据编码分块,降低数据包重传的次数,提高网络的吞吐量。     

Privacy‐preserving authentication schemes for vehicular ad hoc networks: a survey

Vehicular ad hoc networks (VANETs) are expected in improving road safety and traffic conditions, in which security is essential. In VANETs, the authentication of the vehicular access control is a crucial security service for both inter‐vehicle and vehicle–roadside unit communications. Meanwhile, vehicles also have to be prevented from the misuse of the private information and the attacks on their privacy. There is a number of research work focusing on providing the anonymous authentication with preserved privacy in VANETs. In this paper, we specifically provide a survey on the privacy‐preserving authentication (PPA) schemes proposed for VANETs. We investigate and categorize the existing PPA schemes by their key cryptographies for authentication and the mechanisms for privacy preservation. We also provide a comparative study/summary of the advantages and disadvantages of the existing PPA schemes. Lastly, the open issues and future objectives are identified for PPA in VANETs. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis and modelling the effects of mobility,Churn rate,node’s life span,intermittent bandwidth and stabilization cost of finger table in structured mobile P2P networks

Today P2P (Peer-to-Peer) networks are gaining popularity for sharing the contents. Due to massive spreading of Internet, these networks are also growing fast. MP2P (Mobile P2P) networks are attracting many users due to increase in the Internet-based mobile applications. These networks suffer from many challenges which are not considered for analysis and modelling adequately. We focus on few challenges like mobility of users, churn rate, intermittent bandwidth, shorter life span of mobile nodes, stabilization of finger table, etc. in this paper. We analytically analyse these challenges and define the effects of different parameters over the performance. Traditional P2P protocols are designed for wired networks and when these are implemented for mobile networks then mobility effect of users adds more challenge for researchers. We select two types of mobility models namely FF (Fluid Flow) and RWP (Random Waypoint) models to model the users’ mobility. The churn rate of the mobile nodes makes network overlay management and content searching more difficult in MP2P networks. We select finger table-based protocols which are widely deployed in the P2P networks. But these protocols can’t perform well in the mobile P2P networks due to mobility of the users. The mobility of the users and churn rate of the mobile nodes create failure in lookup of finger table and induce more cost to update the finger table. We consider these challenges and quantify the failure rate of mobile nodes, life span of mobile nodes, available bandwidth, cost of stabilization of finger table per node, etc. in this proposal. The proposed model is useful for modelling the performance of MP2P networks performance in various wireless environments like Mobile Ad hoc Networks (MANETs), Wireless Mesh Networks (WMNs), Wireless Sensor Networks (WSNs), Vehicular Ad hoc Networks (VANETs), Wireless LAN (WLAN), Wireless MAN (WMAN), etc.

     

Analysis of broadcasting delays in vehicular ad hoc networks

High mobility of nodes in vehicular ad hoc networks (VANETs) may lead to frequent breakdowns of established routes in conventional routing algorithms commonly used in mobile ad hoc networks. To satisfy the high reliability and low delivery‐latency requirements for safety applications in VANETs, broadcasting becomes an essential operation for route establishment and repair. However, high node mobility causes constantly changing traffic and topology, which creates great challenges for broadcasting. Therefore, there is much interest in better understanding the properties of broadcasting in VANETs. In this paper we perform stochastic analysis of broadcasting delays in VANETs under three typical scenarios: freeway, sparse traffic and dense traffic, and utilize them to analyze the broadcasting delays in these scenarios. In the freeway scenario, the analytical equation of the expected delay in one connected group is given based on statistical analysis of real traffic data collected on freeways. In the sparse traffic scenario, the broadcasting delay in an n‐vehicle network is calculated by a finite Markov chain. In the dense traffic scenario, the collision problem is analyzed by different radio propagation models. The correctness of these theoretical analyses is confirmed by simulations. These results are useful to provide theoretical insights into the broadcasting delays in VANETs. Copyright © 2010 John Wiley & Sons, Ltd.     

On-demand coding-aware routing in wireless Mesh networks

Network coding,which exploits the broadcast nature of wireless medium,is an effective way to improve network performance in wireless multi-hop networks,but the first practical wireless network coding system COPE cannot actively detect a route with more coding opportunities and limit the coding structure within two-hop regions.An on-demand coding-aware routing scheme(OCAR)for wireless Mesh networks is proposed to overcome the limitations specified above by actively detecting a route with more coding opportunities along the entire route rather than within two-hop regions.Utilizing more coding opportunities tends to route multiple flows 'close to each other' while avoiding interference requires routing multiple flows 'away from each other'.OCAR achieves a tradeoff by adopting RCAIA as routing metric in route discovery,which is not only coding-aware but also considers both inter and intra flow interference.Simulation results show that,compared with Ad-hoc on-demand distance vecfor routing(AODV)and AODV+COPE,OCAR can find more coding opportunities,thus effectively increase network throughput,reduce end to end delay and alleviate network congestion.     

Network coding-based protection of many-to-one wireless flows

This paper addresses the problem of survivability of many-to-one flows in wireless networks, such as wireless mesh networks (WMNs) and wireless sensor networks (WSNs). Traditional protection schemes are either resource-hungry like the (1+1) protection scheme, or introduce a delay and interrupt the network operation like the (1 : N) protection scheme. In this paper, we present a network coding-based protection technique that overcomes the deficiencies of the traditional schemes. We derive and prove the necessary and sufficient conditions for our solution on a restricted network topology. Then we relax these connectivity requirements and show how to generalize the sufficient and necessary conditions to work with any other topology. We also show how to perform deterministic coding with {0,1} coefficients to achieve linear independence. Moreover, we discuss some of the practical considerations related to our approach. Specifically, we show how to adapt our solution when the network has a limited min-cut; we therefore define a more general problem that takes this constraint into account, which prove to be NP-complete. Furthermore, we discuss the decoding process at the sink, and show how to make use of our solution in the upstream communication (from sink to sources). We also study the effect of the proposed scheme on network performance. Finally, we consider the implementation of our approach when all network nodes have single transceivers, and we solve the problem through a greedy algorithm that constructs a feasible schedule for the transmissions from the sources.     

Cross-Layer Rate Control, Routing and Scheduling Design for Multicast with Network Coding in Ad Hoc Networks

Network coding is a powerful coding technique that has been proved to be very effective in achieving the maximum multicast capacity. It is especially suited for new emerging networks such as ad-hoc and sensor networks. In this paper, we develop a distributed rate control algorithm for multicast session in ad hoc networks. With random network coding, the algorithm can be implemented in a distributed manner, and work at transport layer to adjust source rates and at network layer to carry out network coding. The scheduling element of our algorithm is a dynamic scheduling policy. The stability of the resulted system is established, and simulation results are provided to support our conclusions.     

Robust geocast routing protocols for safety and comfort applications in VANETs

Routing in cooperative vehicular networks is a challenging task because of high mobility of vehicles and difficulty of localization. In this paper, we study the geocast routing problem in Vehicular Ad‐hoc NETworks (VANETs), which aims at delivering data to a specific group of mobile vehicles identified by their geographical location. Although many geocast routing protocols have been proposed, only partial inherent constraints of VANETs (such as mobility, internal network fragmentation problem, external network fragmentation problem, and overload) are taken into account. Therefore, we propose two novel and robust geocast routing protocols: the first one, called Robust Geocast Routing Protocol for Safety Applications (RGRP‐SA), is dedicated to road safety applications, while the second, namely, Robust Geocast Routing Protocol for Comfort Applications (RGRP‐CA), is designed for comfort applications. Simulations conducted in NS‐2 demonstrate that our safety‐oriented RGRP‐SA protocol outperforms Inter‐Vehicle Geocast protocol and Mobicast Routing Protocol in VANETs by sending up to 25% more packets, cutting the end‐to‐end delay in half, and solving the internal network fragmentation problem. Besides, it is also shown that our comfort‐oriented RGRP‐CA protocol serves well comfort applications with only light overhead by solving internal and external network fragmentation problems and providing more reliable data delivery (with a 25% higher packet delivery ratio) and higher network throughput utilization in comparison with Mobicast with Carry‐and‐Forward protocol. Copyright © 2015 John Wiley & Sons, Ltd.     

Routing protocols for vehicular Ad Hoc networks in rural areas

Research on vehicular ad hoc networks has focused mainly on efficient routing protocol design under conditions where there are relatively large numbers of closely spaced vehicles. These routing protocols are designed principally for urban areas with high node density and fully connected networks and are not suitable for packet delivery in a sparse, partially connected VANET. In this article, we examine the challenges of VANETs in sparse network conditions, review alternatives including epidemic routing, and propose a border node-based routing protocol for partially connected VANETs. The BBR protocol can tolerate network partition due to low node density and high node mobility. The performance of epidemic routing and BBR are evaluated with a geographic and traffic information- based mobility model that captures typical highway conditions. The simulation results show that under rural network conditions, a limited flooding protocol such as BBR performs well and offers the advantage of not relying on a location service required by other protocols proposed for VANETs.     

Maximum flow and network capacity of network coding for ad-hoc networks

Network coding is an effective way to achieve the maximum flow of multicast networks. In this letter, we focus on the statistical properties of the maximum flow or the capacity of network coding for ad-hoc networks based on random graph models. Theoretical analysis shows that the maximum flow can be modelled as extreme order statistics of Gaussian distribution for both wired and wireless ad-hoc networks as the node number is relatively large under a certain condition. We also investigate the effects of the nodes' covering capabilities on the capacity of network coding.     

Network Coding for Efficient Multicast Routing in Wireless Ad-hoc Networks

Network coding is a powerful coding technique that has been proved to be very effective in achieving the maximum multicast capacity. It is especially suited for new emerging networks such as ad-hoc and sensor networks. In this work, we investigate the multicast routing problem based on network coding and put forward a practical algorithm to obtain the maximum flow multicast routes in ad-hoc networks. The "conflict phenomenon" that occurs in undirected graphs will also be discussed. Given the developed routing algorithm, we will present the condition for a node to be an encoding node along with a corresponding capacity allocation scheme. We will also analyze the statistical characteristics of encoding nodes and maximum flow in ad-hoc networks based on random graph theory.     

无线网络中基于混合流的高效可靠机会网络编码算法

Although the wireless network is widely used in many fields, its characteristics such as high bit error rate and broadcast links may block its development. Network coding is an artistic way to exploit its intrinsic characteristics to increase the network reliability. Some people research network coding schemes for inter flow or intra flow, each type with its own advantages and disadvantages. In this paper, we propose a new mechanism, called MM NCOPE, which integrates the idea of inter flow and intra flow coding. On the one hand, MM NCOPE utilizes random liner coding to encode the NCOPE packets while NCOPE is a sub protocol for optimizing the COPE algorithm by iteration. In NCOPE, packets are automatically matched by size to be coded. As a result, it improves the coding gain in some level. On the other hand, we adopt the partial Acknowledgement retransmission scheme to achieve high compactness and robustness. ACK is an independent packet with the highest priority rather than a part of the data packets. Compared with existing works on opportunistic network coding, our approach ensures the reliability of wireless links and improves the coding gain.