Zhenxia Zhang

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

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.

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

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.

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

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.

Design and evaluation of a fast MAC layer handoff management scheme for WiFi-based multichannel Vehicular Mesh Networks

Abstract Vehicular Mesh Networks (VMNs) are important components of the wireless metropolitan networks. Compared with traditional wireless networks, they are more efficient in terms of deployment, configuration, and maintenance. However, connecting all mesh routers through wireless connection in VMNs results in the network backbones remarkably lower bandwidth. Multichannel technology, where non-interfering channels are used to enable mesh routers to send and receive packets simultaneously, can be adopted to improve the throughput of VMNs. Due to the limited radio range of mesh routers, mobile clients have to switch among different mesh routers to maintain wireless connections. Therefore, providing smooth roaming in multichannel VMNs has become an important topic in VMN research. In this paper, a novel MAC layer handoff scheme is proposed as a means of minimizing handoff latency for WiFi-based multichannel VMNs to provide smooth communication for real-time applications. By designing a dynamic grouping algorithm for channel selection and allowing mesh routers to switch their channels for probe response messages, our scheme can shorten the waiting time for the detection of available access routers, decrease the loss ratio of data packets during the handoff, and consequently achieve smooth handoff in the MAC layer.

A hybrid-routing based intra-domain mobility management scheme for wireless mesh networks

Recent advances in Wireless Mesh Networks (WMNs) have overcome the drawbacks of traditional wired networks and wireless ad hoc networks. WMNs are going to play a highly promising role in the next generation of networks. Mobility management is one of the most significant management services for WMNs. Due to the inherent characteristics of WMNs, such as relatively static backbones and highly mobile clients, the question of how to provide seamless mobility management for WMNs is the driving force behind research. In this paper, a novel intra-domain mobility management scheme for WMNs is presented. A hybrid routing algorithm is used to forward packets, and during handoff, gratuitous ARP messages are used to provide the new routing information, thus avoiding re-routing and location update. Real-time applications over 802.11 WMNs can be supported by this scheme, such as VoIP, etc.

Reducing Handoff Latency for WiMAX Networks Using Mobility Patterns

In recent years, Worldwide Interoperability for Microwave Access (WiMAX) has become an important technology providing wireless connections for mobile terminals in a wireless Metropolitan Area Network (MAN), due to its large radio range. In a MAN environment, wireless clients always have high mobility; therefore, it is possible that the mobile clients will move away from the service coverage of serving base stations and change their associating base stations. The process of switching between different base stations is known as the handoff process. During the handoff process, the connection between the mobile terminal and the serving base station ceases. The quality of mobile wireless networks is significantly affected by handoff latency and packet loss ratio. In this paper, we propose a fast handoff scheme using mobility patterns for WiMAX networks. Mobility patterns are adopted to predict the next base station and therefore waive unnecessary scans, and the serving base station forwards the data packets received during the handoff process to the target base station for the minimizing of the packet loss ratio. Extensive simulation experiments are conducted to evaluate the performance of the proposed scheme. The results demonstrate that our scheme can shorten the handoff latency.

A Novel Network Mobility Management Scheme for Vehicular Networks

In recent years, vehicular networks have been widely studied because these networks become an important part of wireless metropolitan networks. This type of wireless network is different from other conventional wireless mobile networks since the mobile nodes in the networks usually have high speed, sufficient power and dynamic topology. In vehicular networks, vehicles can connect with access points, which are deployed on the roadside, to communicate with their correspondent nodes through Internet. However, the radio range of antennas which are installed in vehicles and access points are limited. As a result, to maintain connections during the trips, vehicles have to switch their access points frequently. The question of how to design an efficient mobility management solution for vehicular networks is still very important in such mobile environment. In this paper, a novel mobility management scheme for vehicular networks is proposed. Network mobility solution is adopted for vehicular networks and intra-cluster communications are used to improve the quality of the mobility.

Design of a lightweight authentication scheme for IEEE 802.11p vehicular networks

With the growing popularity of vehicle-based mobile devices, vehicular networks are becoming an essential part of wireless heterogeneous networks. Therefore, vehicular networks have been widely studied in recent years. Because of limited transmission range of wireless antennas, mobile vehicles should also switch their access points to maintain the connections as conventional mobile nodes. Considering the inherent characteristics of vehicular networks such as dynamic topology and high speed, the question of how to implement handoff protocol under real-time scenarios is very important. IEEE 802.11p protocol is designed for vehicular networks for the long distance transmission. To reduce handoff latency for 802.11p protocol, the authentication phase is waived during the handoff. However, security is also very important for wireless communications, and authentication can forbid access from malicious nodes and prevent wireless communications from potential attacks. Thus, in this paper, a lightweight authentication scheme is introduced to balance the security requirements and the handoff performance for 802.11p vehicular networks. In our scheme, the access points are divided into different trust groups, and the authentication process is completed in a group-based method. Once a vehicle is authenticated by an access point group, during the handoff within the same group, few extra authentication operations are needed. As a result, there is no extra overhead introduced to the authentication servers. Simulation results demonstrate that our authentication scheme only introduces small handoff latency and it is ideal for vehicular networks.

A fast MAC layer handoff protocol for WiFi-based wireless networks

In next generation mobile heterogeneous networks, WiFi-based wireless networks are becoming important components, because WiFi devices are widely used in laptops, PDAs and other mobile computing machines. In a WiFi-based wireless network, handoff management is a key service, as the radio range of the WiFi device is limited. Moreover, providing seamless roaming in wireless networks is mandatory for supporting realtime applications in a mobile environment, such as VoIP, online games, and eConference. Recently, many solutions have been introduced to reduce MAC layer handoff latency; however, these solutions consider every mobile node separately, which would not be suitable for a large-scale environment. This paper proposes a novel MAC layer handoff protocol for large-scale WiFi-based wireless networks to support seamless real-time applications. In our scheme, before the mobile node starts initiating the MAC layer handoff process, it selects several neighboring nodes to help it scan available channels. All channels are divided into groups and scanned by these neighbors separately. Therefore, the number of scanning channels in each node is reduced, and scanning latency is minimized. According to simulation results in ns2, we conclude that our scheme can shorten MAC layer handoff latency greatly, and also achieve seamless handoff in terms of loss ratio of data packets.

Cooperative location verification for vehicular ad-hoc networks

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).