Seyhan Ucar

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

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.

VMaSC: Vehicular multi-hop algorithm for stable clustering in Vehicular Ad Hoc Networks

Clustering is an effective mechanism to handle the fast changes in the topology of vehicular ad hoc networks (VANET) by using local coordination. Constructing stable clusters by determining the vehicles sharing similar mobility pattern is essential in reducing the overhead of clustering algorithms. In this paper, we introduce VMaSC: Vehicular Multi-hop algorithm for Stable Clustering. VMaSC is a novel clustering technique based on choosing the node with the least mobility calculated as a function of the speed difference between neighboring nodes as the cluster head through multiple hops. Extensive simulation experiments performed using ns-3 with the vehicle mobility input from the Simulation of Urban Mobility (SUMO) demonstrate that novel metric used in the evaluation of the least mobile node and multi-hop clustering increases cluster head duration by 25% while decreasing the number of cluster head changes by 10%.

Dimming support for visible light communication in intelligent transportation and traffic system

The automotive industry is under a major change and new vehicles are being enriched by the recent advances in communication. Not only business plans are changing due to connected and urbanized lifestyle, but also transportation is becoming more intelligent with smart roads that connect smart cars. Technology coined as the vehicular ad-hoc network (VANET) is harmonizing with Intelligent Transportation System (ITS) and Intelligent Traffic System (ITF). However, ITS and ITF systems suffer from the scarcity of radio frequency spectrum. Visible light communication (VLC) that uses modulated optical radiation in the visible light spectrum is an alternative medium being researched. To date, the majority of research on vehicular VLC was aimed at achieving high data rates provided that high lighting quality is achieved without any concern on dimmable LED lights. Auto-dimmable headlights gain attention due to danger caused by sudden glare on drivers at night conditions which makes dimming in VLC necessary. In this paper, we first present the latest concept of vehicular VLC on ITS and ITF systems and address dimming utility. We then demonstrate experimentally that dimming is a key parameter in VLC which affects data dissemination and received power signal strength.

VeSCA: Vehicular stable cluster-based data aggregation

In-network data aggregation is a promising technique to reduce data transmission that contributes the effective usage of bandwidth and co-existence of different applications in vehicular ad-hoc networks (VANET). Early aggregation schemes in VANET are grouped into two categories; structure free and structure based data aggregation. In structure-free data aggregation, vehicles apply pre-defined delay value before forwarding a data packet to the next hop. On the contrary, structure-based data aggregation uses a hierarchical structure, based on either road information or vehicles, to perform data aggregation. To provide efficient and scalable VANET communication, data aggregation is essential for reducing per vehicle bandwidth requirements. In this paper, we propose a multi-hop structure based data aggregation method namely VeSCA where mobile nodes are grouped based on relative mobility with minimum-overhead cluster construction and cluster members apply data aggregation before forwarding data packet to the parent node. Using various key metrics including data aggregation ratio, delay and aggregated data delivery ratio, we demonstrate superior performance VeSCA compared both previous cluster based data aggregation and alternative aggregation mechanism via extensive simulations in ns-3 with the vehicle mobility input from the Simulation of Urban Mobility (SUMO). VeSCA achieves over 70% aggregated data packet delivery ratio with aggregation ratio 40%.

Security vulnerabilities of IEEE 802.11p and visible light communication based platoon

Technology brings autonomous vehicles into the reality where vehicles become capable of cruising themselves. A vehicular platoon contains autonomous vehicles organized into groups with close proximity. It is envisioned that with the increased demand for autonomous vehicles, platoons would be the part of our lives in near future. From this perspective, vehicular platoon control using current dominant IEEE 802.11p (DSRC) is an active research field. However, DSRC suffers from problems of performance degradation due to congestion, the scarcity of radio-frequency (RF) and security. Visible Light Communication (VLC), on the other hand, is a promising complementary technology with the potential to address DSRC problems. In this paper, we investigate the security vulnerabilities of hybrid DSRC-VLC platoon in the presence of outside attackers. We develop a simulation platform to realize the hybrid platoon. We demonstrate that although VLC limits the effect of adversaries, hybrid architectures still suffer from the packet falsification and replay attacks.

SecVLC: Secure Visible Light Communication for Military Vehicular Networks

Technology coined as the vehicular ad hoc network (VANET) is harmonizing with Intelligent Transportation System (ITS) and Intelligent Traffic System (ITF). An application scenario of VANET is the military communication where vehicles move as a convoy on roadways, requiring secure and reliable communication. However, utilization of radio frequency (RF) communication in VANET limits its usage in military applications, due to the scarce frequency band and its vulnerability to security attacks. Visible Light Communication (VLC) has been recently introduced as a more secure alternative, limiting the reception of neighboring nodes with its directional transmission. However, secure vehicular VLC that ensures confidential data transfer among the participating vehicles, is an open problem. In this paper, we propose a secure military light communication protocol (SecVLC) for enabling efficient and secure data sharing. We use the directionality property of VLC to ensure that only target vehicles participate in the communication. Vehicles use full-duplex communication where infra-red (IR) is utilized to share a secret key and VLC is used to receive encrypted data. We experimentally demonstrate the suitability of SecVLC in outdoor scenarios at varying inter-vehicular distances with key metrics of interest, including the security, data packet delivery ratio and delay.

Online Client Assignment in Dynamic Real-Time Distributed Interactive Applications

Quality of user experience in Distributed Interactive Applications(DIAs) highly depends on the network latencies during the system execution. In DIAs, each user is assigned to a server and communication with any other client is performed through its assigned server. Hence, latency measured between two clients, called interaction time, consists of two components. One is the latency between the client and its assigned server, and the other is the inter-server latency, that is the latency between servers that the clients are assigned. In this paper, we investigate a real-time client to server assignment scheme in a DIA where the objective is to minimize the interaction time among clients. The client assignment problem is known to be NP-complete and heuristics play an important role in finding near optimal solutions. We propose two distributed heuristic algorithms to the online client assignment problem in a dynamic DIA system. We utilized real-time Internet latency data on the Planet Lab platform and performed extensive experiments using geographically distributed Planet Lab nodes where nodes can arbitrarily join/leave the system. The experimental results demonstrate that our proposed algorithms can reduce the maximum interaction time among clients up to 45% compared to an existing baseline technique.

Security vulnerabilities of autonomous platoons

Previous studies have shown that autonomous vehicles have the potential of fundamentally changing the Intelligent Transportation System (ITS) and substantially affecting the safety in vehicular ad hoc networks (VANET). Cooperative Adaptive Cruise Control System (CACC) in conjunction with vehicular communication paves the way of vehicle platooning where autonomous vehicles are organized into groups with close proximity. From this perspective, platoon management using the current dominant IEEE 802.11p (DSRC) and hybrid DSRC-Visible Light Communication (VLC) is an active research field to ensure the platoon stability. However, before the practical deployment of vehicular platoons, the DSRC and hybrid DSRC-VLC based management protocols need to be analyzed in the presence of attackers. In this paper, we investigate the security vulnerabilities of DSRC and DSRC-VLC based platoons under the jamming and fake platoon maneuver attacks. We demonstrate that DSRC is highly vulnerable to such attacks. Although VLC limits the effect of adversaries, hybrid architecture still suffers from the jamming and fake maneuver attacks.

Visible light communication in vehicular ad-hoc networks

Advances in auto-mobile industry and urbanization enable vehicles communicate with each other and link adjacent cities to form connected smart cities. As a result, vehicular ad-hoc networks (VANETs) have become one of the most relevant communication technologies that aim to reduce traffic congestion, traffic accidents, energy waste and pollution by providing data dissemination about events. However, VANET systems suffer from scarcity of radio frequency (RF) spectrum which pushes researchers to investigate alternative technologies such as visible light communication (VLC). On the other hand, vehicular VLC has drawbacks; sudden glare on drivers at night condition and angular limitation of headlight which are needed to be experimentally evaluated. In this paper, we first present latest concept of vehicular VLC and provide detailed explanation of VLC problems. We then demonstrate experimentally that VLC problems have crucial effect on data packet delivery ratio and received power strength.