Contention-based forwarding with multi-hop connectivity awareness in vehicular ad-hoc networks

Recent vehicular routing proposals use real-time road traffic density estimates to dynamically select forwarding paths. Estimating the traffic density in vehicular ad hoc networks requires the transmission of additional dedicated messages increasing the communications load. These proposals are generally based on unicast sender-based forwarding schemes. The greedy nature of sender-based forwarding can result in the selection of forwarders with weak radio links that might compromise the end-to-end performance. To overcome these limitations, this paper presents TOPOCBF, a novel contention-based broadcast forwarding protocol that dynamically selects forwarding paths based on their capability to route packets between anchor points. Such capability is estimated by means of a multi-hop connectivity metric. The obtained results demonstrate that TOPOCBF can provide good packet delivery ratios while reducing the communications load compared to unicast sender-based forwarding schemes using road traffic density estimates.     

A cross-layer multi-hop cooperative network architecture for wireless ad hoc networks

In this paper, a novel decentralized cross-layer multi-hop cooperative network architecture is proposed and presented. This cross-layer architecture introduces a new cooperative flooding scheme and two decentralized opportunistic cooperative forwarding mechanisms based on randomized coding, and a Routing Enabled Cooperative Medium Access Control (RECOMAC) protocol that enables cooperative forwarding, while incorporating physical, medium access control (MAC) and routing layers. RECOMAC employs randomized coding to realize cooperative diversity, so that relay selection and actuation mechanisms are alleviated and the MAC costs are reduced. The coded packets are routed in the network via the proposed cooperative forwarding schemes, which opportunistically form cooperative sets within a region, not needing a prior route to be established. Essentially, in the RECOMAC architecture, the routing layer functionality is submerged into the MAC layer to provide seamless cooperative communication, while the messaging overhead to set up routes, select and actuate relays is reduced. We evaluate the performance of RECOMAC in terms of network throughput, delay and MAC and routing overhead, in comparison to the conventional architecture based on the well-known IEEE 802.11 MAC and Ad hoc On Demand Distance Vector (AODV) routing protocols. RECOMAC is shown to provide quite significant improvement by an order of magnitude difference in all investigated performance metrics, under a variety of scenarios, considering different network sizes, static and mobile scenarios and networks with multiple flows.     

On-siteDriverID: A secure authentication scheme based on Spanish eID cards for vehicular ad hoc networks

Security in Vehicle Ad Hoc Networks (VANETs) has been a topic of interest since the origins of vehicular communications. Different approaches have been followed as new security threats have emerged in the last few years. The approach of conditional privacy has been widely used as it guarantees authentication among vehicles but not revealing their real identities. Although the real identity of a vehicle can be traced by the authorities, the process to do that is time consuming and typically involves several entities (for instance road authorities that request the identification, license plate records bodies, a judge to allow revealing the identity associated to a license plate…). Moreover, this process is always subsequent to the detection of a road situation that requires knowing the real vehicle identities. However, in vehicular scenarios, authorities would beneficiate from knowing the real drivers’ identity in advance. We propose in this paper On-SiteDriverID, a secure protocol and its application which allows authorities’ vehicles to obtain drivers’ real identities rapidly and on demand on VANET scenarios. Thus, authorities would be able to gather information about drivers and vehicles, allowing them to act in a safer and better manner in situations such as traffic control duties or emergencies. The obtained simulation results in real VANET scenarios based on real maps guarantee that in the 60%–70% of cases the proposed On-SiteDriverID successfully obtains the identity of the drivers.     

Improved group-based cooperative caching scheme for mobile ad hoc networks

Data caching is a popular technique that improves data accessibility in wired or wireless networks. However, in mobile ad hoc networks, improvement in access latency and cache hit ratio may diminish because of the mobility and limited cache space of mobile hosts (MHs). In this paper, an improved cooperative caching scheme called group-based cooperative caching (GCC) is proposed to generalize and enhance the performance of most group-based caching schemes. GCC allows MHs and their neighbors to form a group, and exchange a bitmap data directory periodically used for proposed algorithms, such as the process of data discovery, and cache placement and replacement. The goal is to reduce the access latency of data requests and efficiently use available caching space among MH groups. Two optimization techniques are also developed for GCC to reduce computation and communication overheads. The first technique compresses the directories using an aggregate bitmap. The second employs multi-point relays to develop a forwarding node selection scheme to reduce the number of broadcast messages inside the group. Our simulation results show that the optimized GCC yields better results than existing cooperative caching schemes in terms of cache hit ratio, access latency, and average hop count.     

RIVER: A reliable inter-vehicular routing protocol for vehicular ad hoc networks

Vehicular Ad hoc NETworks (VANETs), an emerging technology, would allow vehicles on roads to form a self-organized network without the aid of a permanent infrastructure. As a prerequisite to communication in VANETs, an efficient route between communicating nodes in the network must be established, and the routing protocol must adapt to the rapidly changing topology of vehicles in motion. This is one of the goals of VANET routing protocols. In this paper, we present an efficient routing protocol for VANETs, called the Reliable Inter-VEhicular Routing (RIVER) protocol. RIVER utilizes an undirected graph that represents the surrounding street layout where the vertices of the graph are points at which streets curve or intersect, and the graph edges represent the street segments between those vertices. Unlike existing protocols, RIVER performs real-time, active traffic monitoring and uses these data and other data gathered through passive mechanisms to assign a reliability rating to each street edge. The protocol then uses these reliability ratings to select the most reliable route. Control messages are used to identify a node’s neighbors, determine the reliability of street edges, and to share street edge reliability information with other nodes.     

Unicast routing protocols for urban vehicular networks: review,taxonomy, and open research issues

Over the past few years, numerous traffic safety applications have been developed using vehicular ad hoc networks（VANETs）. These applications represent public interest and require network-wide dissemination techniques. On the other hand, certain non-safety applications do not require network-wide dissemination techniques.Such applications can be characterized by their individual interest between two vehicles that are geographically apart. In the existing literature, several proposals of unicast protocols exist that can be used for these non-safety applications. Among the proposals, unicast protocols for city scenarios are considered to be most challenging.This implies that in city scenarios unicast protocols show minimal persistence towards highly dynamic vehicular characteristics, including mobility, road structure, and physical environment. Unlike other studies, this review is motivated by the diversity of vehicular characteristics and difficulty of unicast protocol adaption in city scenarios.The review starts with the categorization of unicast protocols for city scenarios according to their requirement for a predefined unicast path. Then, properties of typical city roads are discussed, which helps to explore limitations in efficient unicast communication. Through an exhaustive literature review, we propose a thematic taxonomy based on different aspects of unicast protocol operation. It is followed by a review of selected unicast protocols for city scenarios that reveal their fundamental characteristics. Several significant parameters from the taxonomy are used to qualitatively compare the reviewed protocols. Qualitative comparison also includes critical investigation of distinct approaches taken by researchers in experimental protocol evaluation. As an outcome of this review, we point out open research issues in unicast routing.     

PAACP: A portable privacy-preserving authentication and access control protocol in vehicular ad hoc networks

Recently, several studies addressed security and privacy issues in vehicular ad hoc networks (VANETs). Most of them focused on safety applications. As VANETs will be available widely, it is anticipated that Internet services could be accessed through VANETs in the near future. Thus, non-safety applications for VANETs would rise in popularity. This paper proposes a novel portable privacy-preserving authentication and access control protocol, named PAACP, for non-safety applications in VANETs. In addition to the essential support of authentication, key establishment, and privacy preservation, PAACP is developed to provide sophisticated differentiated service access control, which will facilitate the deployment of a variety of non-safety applications. Besides, the portability feature of PAACP can eliminate the backend communications with service providers. Therefore, better performance and scalability can be achieved in PAACP.     

An evolutionary computation approach for designing mobile ad hoc networks

This paper presents the topological design of ad hoc networks in terms of distances among static nodes and speeds of mobiles nodes. Due to the complexity of the problem and the number of parameters to be considered, a genetic algorithm combined with the simulation environment NS-2 is proposed to find the optimum solution. More specifically, NS-2 provides the fitness function guiding the genetic search. The proposed framework has been tested using a railway scenario in which several static and mobile nodes are interacting. Results show the feasibility of the proposed framework and illustrate the possibility of genetic approach for solving similar application scenarios.     

Cache invalidation strategies for Internet-based vehicular ad hoc networks

Internet-based vehicular ad hoc network (Ivanet) is an emerging technique that combines a wired Internet and a vehicular ad hoc network (Vanet) for developing an ubiquitous communication infrastructure and improving universal information and service accessibility. A key design optimization technique in Ivanets is to cache the frequently accessed data items in a local storage of vehicles. Since vehicles are not critically limited by the storage/memory space and power consumption, selecting proper data items for caching is not very critical. Rather, an important design issue is how to keep the cached copies valid when the original data items are updated. This is essential to provide fast access to valid data for fast moving vehicles. In this paper, we propose a cooperative cache invalidation (CCI) scheme and its enhancement (ECCI) that take advantage of the underlying location management scheme to reduce the number of broadcast operations and the corresponding query delay. We develop an analytical model for CCI and ECCI techniques for fasthand estimate of performance trends and critical design parameters. Then, we modify two prior cache invalidation techniques to work in Ivanets: a poll-each-read (PER) scheme, and an extended asynchronous (EAS) scheme. We compare the performance of four cache invalidation schemes as a function of query interval, cache update interval, and data size through extensive simulation. Our simulation results indicate that the proposed schemes can reduce the query delay up to 69% and increase the cache hit rate up to 57%, and have the lowest communication overhead compared to the prior PER and EAS schemes.     

A new paradigm for urban surveillance with vehicular sensor networks

We consider a new application paradigm of vehicular sensor networks (VSN). Currently, vehicles are equipped with forward facing cameras to assist forensic investigations of events by proactive image-capturing from streets and roads. Due to content redundancy and storage imbalance in this in-network distributed storage system, how to maximize its storage capacity becomes a nontrivial challenge. In other words, how to maximize the average lifetime of sensory data (i.e., images generated by cameras) in the network is a fundamental problem to be solved. This paper presents, VStore, a cooperative storage solution in vehicular sensor networks for mobile surveillance, which has been designed to support redundancy elimination and storage balancing throughout the network. Compared with existing works, we propose a novel storage architecture for urban surveillance and deal with challenges in a mobile scenario. Field testing was carried out with a trace-driven simulator, which utilized about 500 taxis in Shanghai. The testing results showed that VStore can largely prolong the average lifetime of sensory data by cooperative storage.     

Offloading mobile data traffic for QoS-aware service provision in vehicular cyber-physical systems

Owing to the increasing number of vehicles in vehicular cyber-physical systems (VCPSs) and the growing popularity of various services or applications for vehicles, cellular networks are being severely overloaded. Offloading mobile data traffic through Wi-Fi or a vehicular ad hoc network (VANET) is a promising solution for partially solving this problem because it involves almost no monetary cost. We propose combination optimization to facilitate mobile data traffic offloading in emerging VCPSs to reduce the amount of mobile data traffic for the QoS-aware service provision. We investigate mobile data traffic offloading models for Wi-Fi and VANET. In particular, we model mobile data traffic offloading as a multi-objective optimization problem for the simultaneous minimization of mobile data traffic and QoS-aware service provision; we use mixed-integer programming to obtain the optimal solutions with the global QoS guarantee. Our simulation results confirm that our scheme can offload mobile data traffic by up to 84.3% while satisfying the global QoS guarantee by more than 70% for cellular networks in VCPSs.     

Improvements on an authentication scheme for vehicular sensor networks

In a recent paper, Shim (2012) presented a very interesting authentication scheme for vehicular sensor networks. Shim claimed that the scheme is secure against the highest adopted level of attack, namely the chosen-message attack (CID-CMA). Nevertheless, we find that the proof in Shim’s paper does not actually prove that the scheme is secure in this level. Instead, it can only ensure that the scheme is secure in a strictly weaker level of attack, the adaptive chosen-identity and no-message attack (CID-NMA). In this paper, first we show that there exist some security risks in vehicular networks if a scheme, which is only secure against CID-NMA but not CID-CMA, is deployed. Hence, having the proof that the scheme is only CID-NMA is insufficient for the aforementioned application. That is, Shim did not prove that the proposed scheme can resist these kinds of attack. Here, we use a different approach to prove the scheme for security against CID-CMA. We note that this proof is essential to ensure that the scheme can indeed be used for the aforementioned scenario. In addition, we also show that the batch verification of the scheme, proposed in the same paper, may have non-negligible error. Two invalid signatures may give a positive result. We further improve the batch verification part so that the error rate can be reduced to negligible level.     

车载自组网动态频谱分配技术研究进展

为了提高车载自组网的性能和频谱利用率,多接口动态频谱分配技术成为车载自组网的研究热点。介绍了车载自组网动态频谱分配算法的关键设计基础,对多接口多信道网络技术的发展现状进行了分类阐述,对车载自组网动态频谱分配技术的研究进行了展望。     

衰落信道下车载自组织网络连通性分析

以孤立节点数、最大连通长度、全局网络效率等参数为连通性量化指标,应用VanetMobisim车辆仿真软件建立车载自组织网络,详细研究在Nakagami衰落信道模型和确定信道模型下VANETs连通性随时间的演化特征。结果表明当VANETs全连通时,网络时间相关性较弱,当网络连通性比较差时,各项连通性指标均呈现重尾现象,网络连通性具有很强的时间相关性。分析车辆节点密度、路径损耗指数和衰落因子等因素对网络连通性的影响。     

Content-centric wireless networking: A survey

Content-Centric Networking (CCN) is a candidate future Internet architecture that gives favourable promises in distributed wireless environments. The latter ones seriously call into question the capability of TCP/IP to support stable end-to-end communications, due to lack of centralized control, node mobility, dynamic topologies, intermittent connectivity, and harsh signal propagation conditions. The CCN paradigm, relying on name-based forwarding and in-network data caching, has great potential to solve some of the problems encountered by IP-based protocols in wireless networks.In this paper, we examine the applicability of CCN principles to wireless networks with distributed access control, different degrees of node mobility and resource constraints. We provide some guidelines for readers approaching research on CCN, by highlighting points of strength and weaknesses and reviewing the current state of the art. The final discussion aims to identify the main open research challenges and some future trends for CCN deployment on a large scale.     

基于演化图论的可靠的VANETs路由协议

车载网络（VANETs）属于移动无线网络的特例,具有鲜明的特性。传统无线网络的路由协议难以直接应用于VANETs。节点的高速移动,引起网络拓扑动态变化,导致VANETs的通信链路频繁断裂。高动态网络的链路可靠性问题引起广泛的关注。为此,针对高速公路VANETs的路由可靠性进行分析,对演化图论进行扩展,建立扩展后的演化图论模型（EEGM）,并利用EEGM获取VANETs拓扑的动态信息,从而预先获取可靠路由的信息。在此基础上,提出基于演化图论的可靠路由协议（EG-RAODV）。仿真结果表明,与同类的其他协议相比,提出的路由协议在分组传输率、端到端传输时延、路由请求消息率以及链路断裂数方面得到了提升。     

Realizing high-accuracy transmission in high-rate data broadcasting networks with heterogeneous users via cooperative communication

This paper considers a broadcasting network in which multiple single-antenna (weak) and multiantenna (strong) users are receiving simultaneously spatial-multiplexed data streams from the multiantenna base station (BS). In order to improve the received data quality for the single-antenna users while preserving the transmission rates of the multiantenna users, we propose user cooperation schemes without the employment of space–time codes or retransmission from the BS which reduce the data rates and the spectral efficiency. Three cooperation schemes among single-antenna users, namely, decode-and-forward (DF), amplify-and-forward (AF), and hybrid cooperation, are examined and compared. Simulation results demonstrate that single-antenna users through cooperation can achieve comparable or superior error-rate performance as compared with noncooperative multiantenna users. Various configurations of the proposed cooperation schemes are studied to show the tradeoff in terms of cooperation overhead, receiver complexity, and system performance. The acquisition of the channel information and the effect of channel estimation errors on the system performance are also investigated for practical implementation of the proposed schemes. The proposed schemes are capable of avoiding modification to the multiple-input multiple-output (MIMO) transceivers, and are readily applicable to existing MIMO broadcasting networks.     

LPPTE: A lightweight privacy-preserving trust evaluation scheme for facilitating distributed data fusion in cooperative vehicular safety applications

Vehicular networks have tremendous potential to improve road safety, traffic efficiency, and driving comfort, where cooperative vehicular safety applications are a significant branch. In cooperative vehicular safety applications, through the distributed data fusion for large amounts of data from multiple nearby vehicles, each vehicle can intelligently perceive the surrounding conditions beyond the capability of its own onboard sensors. Trust evaluation and privacy preservation are two primary concerns for facilitating the distributed data fusion in cooperative vehicular safety applications. They have conflicting requirements and a good balance between them is urgently needed. Meanwhile, the computation, communication, and storage overheads will all influence the applicability of a candidate scheme. In this paper, we propose a Lightweight Privacy-Preserving Trust Evaluation (LPPTE) scheme which can primely balance the trust evaluation and privacy preservation with low overheads for facilitating the distributed data fusion in cooperative vehicular safety applications. Furthermore, we provide exhaustive theoretical analysis and simulation evaluation for the LPPTE scheme, and the results demonstrate that the LPPTE scheme can obviously improve the accuracy of fusion results and is significantly superior to the state-of-the-art schemes in multiple aspects.     

An efficient and secure mobile payment protocol for restricted connectivity scenarios in vehicular ad hoc network

Value-added applications in vehicular ad hoc network (VANET) come with the emergence of electronic trading. The restricted connectivity scenario in VANET, where the vehicle cannot communicate directly with the bank for authentication due to the lack of internet access, opens up new security challenges. Hence a secure payment protocol, which meets the additional requirements associated with VANET, is a must. In this paper, we propose an efficient and secure payment protocol that aims at the restricted connectivity scenario in VANET. The protocol applies self-certified key agreement to establish symmetric keys, which can be integrated with the payment phase. Thus both the computational cost and communication cost can be reduced. Moreover, the protocol can achieve fair exchange, user anonymity and payment security.