• Journal of information and communication convergence engineering
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• v.12 no.1
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• pp.26-32
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• 2014

Vehicular-to-anything (V2X) technology is attractive for wireless vehicular ad-hoc networks (VANETs) because it allows for opportunistic choice of a vehicular protocol between vehicular-to-vehicular (V2V) and vehicular-to-infrastructure (V2I) communications. In particular, achieving seamless connectivity in a VANET with nearby network infrastructure is challenging. In this paper, we propose a density-based opportunistic broadcasting (DOB) protocol, in which opportunistic connectivity is carried out by using the nearby infrastructure and opposite vehicles for solving the problems of disconnection and long end-to-end delay times. The performance evaluation results indicate that the proposed DOB protocol outperforms the considered comparative conventional schemes, i.e., the shortest path protocol and standard mobile WiMAX, in terms of the average end-to-end delay, packet delivery ratio, handover latency, and number of lost packets.

• International Journal of Highway Engineering
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• v.18 no.5
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• pp.117-125
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• 2016

PURPOSES : The density in uninterrupted traffic flow facilities plays an important role in representing the current status of traffic flow. For example, the density is used for the primary measures of effectiveness in the capacity analysis for freeway facilities. Therefore, the estimation of density has been a long and tough task for traffic engineers for a long time. This study was initiated to evaluate the performance of density values that were estimated using VDS data and two traditional methods, including a method using traffic flow theory and another method using occupancy by comparing the density values estimated using vehicular trajectory data generated from a radar detector. METHODS : In this study, a radar detector which can generate very accurate vehicular trajectory within the range of 250 m on the Joongbu expressway near to Dongseoul tollgate, where two VDS were already installed. The first task was to estimate densities using different data and methods. Thus, the density values were estimated using two traditional methods and the VDS data on the Joongbu expressway. The density values were compared with those estimated using the vehicular trajectory data in order to evaluate the quality of density estimation. Then, the relationship between the space mean speed and density were drawn using two sets of densities and speeds based on the VDS data and one set of those using the radar detector data. CONCLUSIONS : As a result, the three sets of density showed minor differences when the density values were under 20 vehicles per km per lane. However, as the density values become greater than 20 vehicles per km per lane, the three methods showed a significant difference among on another. The density using the vehicular trajectory data showed the lowest values in general. Based on the in-depth study, it was found out that the space mean speed plays a critical role in the calculation of density. The speed estimated from the VDS data was higher than that from the radar detector. In order to validate the difference in the speed data, the traffic flow models using the relationships between the space mean speed and the density were carefully examined in this study. Conclusively, the traffic flow models generated using the radar data seems to be more realistic.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.49 no.4
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• pp.82-88
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• 2012

A VANET (Vehicular Ad Hoc Network), a subclass of MANET (Mobile Ad Hoc Network), is an ad hoc network using wireless communication between vehicles without fixed infrastructure such as base station. VANET suffers a frequent link breakage and network topology change because of the rapid movement of vehicles and the density change of vehicles. From these characteristics of VANET, geographical routing protocols such as GPSR (Greedy Perimeter Stateless Routing) using only the information of neighbor nodes are more suitable rather than AODV and DSR that are used in existing MANETs. However, GPSR may have a transmission delay and packet loss by frequent link disconnection and continual local maxima under the low vehicle density conditions. Therefore, in this paper, we propose a DTVR (Delay Tolerant Vehicular Routing) algorithm that perform a DTN-based routing scheme if there is no 2-hop neighbor nodes for efficient routing under the low vehicle densities in VANETs. Simulation results using ns-2 reveal that the proposed DTVR protocol performs much better performance than the existing routing protocols.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.4
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• pp.53-58
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• 2012

The roadside unit (RSU) collects vehicle information from vehicles in the intelligent transportation system (ITS). The vehicle density on the road within the communication range of a RSU is a time varying parameter. The higher the vehicle density, the more vehicle information can be collected. Therefore, the probability of packet collision will be raised. In this paper, an adaptive transmission scheme is proposed to improve the probability of packet reception rate by changing the data rate and transmission period according to the vehicle density. The performance of IEEE 802.11p MAC protocol that is a standard for vehicular communications is evaulated in terms of the vehicle density with the ns-2,33 simulator.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.05a
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• pp.610-613
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• 2013

Vehicular Ad Hoc NETwork (VANET), a subclass of Mobile Ah Hoc NETwork (MANET) has been a tech-buzz for the last couple of decades. VANET, yet not deployed, promises the ease, comfort, and safety to both drivers and passengers once deployed. The by far most important factor in successful VANET application is the data dissemination scheme. Such data includes scheduled beacons that contain whereabouts information of vehicles. In this paper, we aim at regularly broadcasted beacons and devise an algorithm to disseminate the beacon information up to a maximum distance and alleviate the broadcast storm problem at the same time. According to the proposed scheme, a vehicle before re-broadcasting a beacon, takes into account the current vehicular density in its neighborhood. The re-broadcasters are chosen away from the source of the beacon and among the candidate re-broadcasters, if the density in the neighborhood is high, then the candidate rebroadcaster re-broadcasts the beacon with high probability and with low probability, otherwise. We also performed thorough simulations of our algorithms and the results are sound according to the expectations.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.1-9
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• 2007

Compressed natural gas (CNG) has been used as a vehicular fuel compressed at 24.8 MPa because the energy density of natural gas is extremely low compared with gasoline. Thus it has problems in both safety and cost for multiple stage compression. For these reasons the use of adsorbed natural gas (ANG) has been pursued since the storage of natural gas is possible at a relatively low pressure. The present target is to obtain media to store natural gas at 3.5 MPa as ANG that ensures the comparable energy density of CNG, giving approximately one-fourth the driving range of an equivalent volume gasoline tank. In this review, the recent development of carbon media, their characteristics, and practical applications for natural gas storage are introduced and some recommendations are also suggested.

• Journal of KIISE:Information Networking
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• v.37 no.2
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• pp.157-161
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• 2010

Vehicular Ad-hoc NETworks (VANETs) suffer from frequent network disconnections due to obstacles such as buildings even in urban environments with high density of traffic. Thus, in this paper, we propose a routing algorithm that finds optimal end-to-end paths in terms of both traffic density and distance in the urban VANET and selects the next hop with the minimum distance, while maintaining the minimum hop counts over the path. The simulation results show that the proposed algorithm achieves higher throughput and smaller end-to-end delay than Greedy Perimeter Stateless Routing (GPSR) with message carrying.

• KIPS Transactions on Computer and Communication Systems
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• v.8 no.11
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• pp.263-270
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• 2019

Vehicular cloud computing is a new emerging technology that can provide drivers with cloud services to enable various vehicular applications. A vehicular cloud is defined as a set of vehicles that share their own resources. Vehicles should collaborate with each other to construct vehicular clouds through vehicle-to-vehicle communications. Since collaborating vehicles to construct the vehicular cloud have different speeds, directions and locations respectively, the vehicular cloud is constructed in multi-hop communication range. Due to intermittent wireless connectivity and low density of vehicles with the limited resources, the construction of vehicular cloud with multi-hop communications has become challenging in vehicular environments in terms of the service success ratio, the service delay, and the transmitted packet number. Thus, we propose a multi-hop vehicular cloud construction protocol that increases the service success ratio and decreases the service delay and the transmitted packet number. The proposed protocol uses a connection time-based intermediate vehicle selection scheme to reduce the cloud failure probability of multi-hop vehicular cloud. Simulation results conducted in various environments verify that the proposed protocol achieves better performance than the existing protocol.

• International journal of advanced smart convergence
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• v.8 no.4
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• pp.179-187
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• 2019

Vehicular density is usually low in a highway environment. Consequently, connectivity of the vehicular ad hoc networks (VANETs) might be poor. We are investigating the problem of deploying the approximation optimal roadside units (RSUs) on the highway covered by VANETs, which employs VANETs to provide excellent connectivity. The goal is to estimate the minimal number of deployed RSUs to guarantee the connectivity probability of the VANET within a given threshold considering that RSUs are to be allocated equidistantly. We apply an approximation algorithm to distribute RSUs locations in the VANETs. Thereafter, performance of the proposed scheme is evaluated by calculating the connectivity probability of the VANET. The simulation results show that there is the threshold value M of implemented RSUs corresponding to each vehicular network with N vehicles. The connectivity probability increases slowly with the number of RSUs getting larger.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.6
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• pp.698-701
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• 2010

Recently, Vehicular Networks is being developed to provide variety of services such as email, ftp, and video streaming services. As IP mobility technology, Proxy Mobile IP is developed to provide these services for a VANET user. By adopting Proxy Mobile IPv6 (PMIPv6), Vehicular Networks can support IP mobility, but it may cause a proxy binding update (PBU) message when a vehicle moves from one MAG to another. In addition, if the density of vehicles on the road is high, significant PBU messages are generated. In this paper, we propose bulk PBU message to reduce signaling overhead by those PBU messages when a bunch of vehicles move from one MAG to another. When the vehicles move from one MAG to another, it generates only one bulk PBU message to update those vehicle's location. Through numerical and simulation results, we show that our proposed bulk registration reduces signaling overhead when the density of vehicles and the speed of them are high.