Zhenxia Zhang

Bio: Zhenxia Zhang is an academic researcher from University of Ottawa. The author has contributed to research in topics: Handover & Wireless network. The author has an hindex of 11, co-authored 24 publications receiving 398 citations.

A novel multi-hop clustering scheme for vehicular ad-hoc networks

Abstract: Vast applications introduced by Vehicular Ad-Hoc Networks (VANETs), such as intelligent transportation, roadside advertisement, make VANETs become an important component of metropolitan area networks. In VANETs, mobile nodes are vehicles which are equipped with wireless antennas; and they can communicate with each others by wireless communication on ad-hoc mode or infrastructure mode. Compared with Mobile Ad-Hoc Networks, VANETs have some inherent characteristic, such as high speed, sufficient energy, etc. According to previous research, clustering vehicles into different groups can introduce many advantages for VANETs. However, because a VANET is a high dynamic scenario, it is hard to find a solution to divide vehicles into stable clusters. In this paper, a novel multi-hop clustering scheme is presented to establish stable vehicle groups. To construct multi-hop clusters, a new mobility metric is introduced to represent relative mobility between vehicles in multi-hop distance. Extensive simulation experiments are run using ns2 to demonstrate the performance of our clustering scheme. To test the clustering scheme under different scenarios, both the Manhattan mobility model and the freeway mobility model are used to generate the movement paths for vehicles.

Design of a Fast Location-Based Handoff Scheme for IEEE 802.11 Vehicular Networks

Abstract: IEEE 802.11 is an economical and efficient standard that has been applied to vehicular networks. However, the long handoff latency of the standard handoff scheme for IEEE 802.11 has become an important issue for seamless roaming in vehicular environments, because more handoffs may be triggered due to the higher mobility of vehicles. This paper presents a new and fast location-based handoff scheme particularly designed for vehicular environments. With the position and movement direction of a vehicle and the location information of the surrounding access points (APs), our protocol is able to accurately predict several APs that the vehicle may possibly visit in the future and to assign these APs different priority levels. APs on higher priority levels will be scanned first. A blacklist scheme is also used to exclude those APs that showed no response to the scanning during previous handoffs. Thus, time spent on scanning APs is supposed to be significantly reduced. The simulation results show that the proposed scheme attains not only a lower prediction error rate but also lower link layer handoff latency and that it has a smaller influence on jitter and throughput. Moreover, these results show that the proposed scheme has a smaller total number of handoffs than other handoff schemes.

Performance Evaluation of an Anonymous Routing Protocol using Mobile Agents for Wireless Ad hoc Networks

Abstract: While much recent research focuses only on providing routing services for ad hoc networks, very little work has been done towards achieving anonymity for wireless ad hoc and sensor networks. However, malicious nodes in a wireless and mobile ad hoc environment can jeopardize the security of the network if the issues of secure data exchange are not properly handled. Encryption cannot fully protect the data communicated between nodes, as routing information may expose the identities of the communicating nodes and put their relationships at risk. In this paper, we propose an efficient anonymous routing protocol that uses a mobile agent paradigm for wireless and mobile ad hoc networks. In our protocol, only trustworthy nodes are allowed to participate in communications and the misbehavior of malicious nodes is thus prevented effectively. We describe our protocol and provide its performance evaluation based on simulation experiments implemented in an ns-2 simulator. Compared to the SDAR protocol, our experimental results demonstrate that our scheme not only achieves the necessary anonymity in mobile ad hoc networks, but also provides more security with reasonably little additional overhead.

Cooperative location verification for vehicular ad-hoc networks

Abstract: Vehicular ad hoc networks (VANETs) have attracted much attention over the last few years. Localization and position information of vehicles is very significant in VANETs; this is a result of the special nature of VANETs. In this paper, we propose a location verification approach to prevent position-spoofing attacks on VANETs. Cooperative Location Verification (CLV), which is our approach, basically used two vehicles, a Verifier and a Cooperator, to complete the verification of a vehicle (Prover). The Verifier and Cooperator sent a challenge to the respective Prover; and, the Prover was required to reply with its location information immediately which was based on radio frequency. The Verifier then verified the claimed location according to the Time-of-Flight of the signals in those two challenge-response procedures. In the simulation, the results show that our approach is better than both Secure Location Verification (SLV) and Greedy Forwarding Algorithm (GFA).

A Survey on Platoon-Based Vehicular Cyber-Physical Systems

Abstract: Vehicles on the road with some common interests can cooperatively form a platoon-based driving pattern, in which a vehicle follows another vehicle and maintains a small and nearly constant distance to the preceding vehicle. It has been proved that, compared with driving individually, such a platoon-based driving pattern can significantly improve road capacity and energy efficiency. Moreover, with the emerging vehicular ad hoc network (VANET), the performance of a platoon in terms of road capacity, safety, energy efficiency, etc., can be further improved. On the other hand, the physical dynamics of vehicles inside the platoon can also affect the performance of a VANET. Such a complex system can be considered a platoon-based vehicular cyber-physical system (VCPS), which has attracted significant attention recently. In this paper, we present a comprehensive survey on a platoon-based VCPS. We first review the related work of a platoon-based VCPS. We then introduce two elementary techniques involved in a platoon-based VCPS, i.e., the vehicular networking architecture and standards, and traffic dynamics, respectively. We further discuss the fundamental issues in a platoon-based VCPS, including vehicle platooning/clustering, cooperative adaptive cruise control, platoon-based vehicular communications, etc., all of which are characterized by the tightly coupled relationship between traffic dynamics and VANET behaviors. Since system verification is critical to VCPS development, we also give an overview of VCPS simulation tools. Finally, we share our view on some open issues that may lead to new research directions.

Multihop-Cluster-Based IEEE 802.11p and LTE Hybrid Architecture for VANET Safety Message Dissemination

Abstract: Several vehicular ad hoc network (VANET) studies have focused on communication methods based on IEEE 802.11p, which forms the standard for wireless access for vehicular environments. In networks employing IEEE 802.11p only, the broadcast storm and disconnected network problems at high and low vehicle densities, respectively, degrade the delay and delivery ratio of safety message dissemination. Recently, as an alternative to the IEEE 802.11p-based VANET, the usage of cellular technologies has been investigated due to their low latency and wide-range communication. However, a pure cellular-based VANET communication is not feasible due to the high cost of communication between the vehicles and the base stations and the high number of handoff occurrences at the base station, considering the high mobility of the vehicles. This paper proposes a hybrid architecture, namely, VMaSC–LTE, combining IEEE 802.11p-based multihop clustering and the fourth-generation (4G) cellular system, i.e., Long-Term Evolution (LTE), with the goal of achieving a high data packet delivery ratio (DPDR) and low delay while keeping the usage of the cellular architecture at a minimum level. In VMaSC–LTE, vehicles are clustered based on a novel approach named Vehicular Multihop algorithm for Stable Clustering (VMaSC). The features of VMaSC are cluster head (CH) selection using the relative mobility metric calculated as the average relative speed with respect to the neighboring vehicles, cluster connection with minimum overhead by introducing a direct connection to the neighbor that is already a head or a member of a cluster instead of connecting to the CH in multiple hops, disseminating cluster member information within periodic hello packets, reactive clustering to maintain the cluster structure without excessive consumption of network resources, and efficient size- and hop-limited cluster merging mechanism based on the exchange of cluster information among CHs. These features decrease the number of CHs while increasing their stability, therefore minimizing the usage of the cellular architecture. From the clustered topology, elected CHs operate as dual-interface nodes with the functionality of the IEEE 802.11p and LTE interface to link the VANET to the LTE network. Using various key metrics of interest, including DPDR, delay, control overhead, and clustering stability, we demonstrate the superior performance of the proposed architecture compared with both previously proposed hybrid architectures and alternative routing mechanisms, including flooding and cluster-based routing via extensive simulations in ns-3 with the vehicle mobility input from the Simulation of Urban Mobility. The proposed architecture also allows achieving higher required reliability of the application quantified by the DPDR at the cost of higher LTE usage measured by the number of CHs in the network.

A Comparative Survey of VANET Clustering Techniques

Abstract: A vehicular ad hoc network (VANET) is a mobile ad hoc network in which network nodes are vehicles—most commonly road vehicles. VANETs present a unique range of challenges and opportunities for routing protocols due to the semi-organized nature of vehicular movements subject to the constraints of road geometry and rules, and the obstacles which limit physical connectivity in urban environments. In particular, the problems of routing protocol reliability and scalability across large urban VANETs are currently the subject of intense research. Clustering can be used to improve routing scalability and reliability in VANETs, as it results in the distributed formation of hierarchical network structures by grouping vehicles together based on correlated spatial distribution and relative velocity. In addition to the benefits to routing, these groups can serve as the foundation for accident or congestion detection, information dissemination and entertainment applications. This paper explores the design choices made in the development of clustering algorithms targeted at VANETs. It presents a taxonomy of the techniques applied to solve the problems of cluster head election, cluster affiliation, and cluster management, and identifies new directions and recent trends in the design of these algorithms. Additionally, methodologies for validating clustering performance are reviewed, and a key shortcoming—the lack of realistic vehicular channel modeling—is identified. The importance of a rigorous and standardized performance evaluation regime utilizing realistic vehicular channel models is demonstrated.

New Multi-Hop Clustering Algorithm for Vehicular Ad Hoc Networks

Abstract: As a hierarchical network architecture, the cluster architecture can improve the routing performance greatly for vehicular ad hoc networks (VANETs) by grouping the vehicle nodes However, the existing clustering algorithms only consider the mobility of a vehicle when selecting the cluster head The rapid mobility of vehicles makes the link between nodes less reliable in cluster A slight change in the speed of cluster head nodes has a great influence on the cluster members and even causes the cluster head to switch frequently These problems make the traditional clustering algorithms perform poorly in the stability and reliability of the VANET A novel passive multi-hop clustering algorithm (PMC) is proposed to solve these problems in this paper The PMC algorithm is based on the idea of a multi-hop clustering algorithm that ensures the coverage and stability of cluster In the cluster head selection phase, a priority-based neighbor-following strategy is proposed to select the optimal neighbor nodes to join the same cluster This strategy makes the inter-cluster nodes have high reliability and stability By ensuring the stability of the cluster members and selecting the most stable node as the cluster head in the N-hop range, the stability of the clustering is greatly improved In the cluster maintenance phase, by introducing the cluster merging mechanism, the reliability and robustness of the cluster are further improved In order to validate the performance of the PMC algorithm, we do many detailed comparison experiments with the algorithms of N-HOP, VMaSC, and DMCNF in the NS2 environment