• Information and Communications Magazine
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• v.19 no.9
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• pp.31-42
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• 2002

CRL (Communications Research Laboratory, Independent Administrative Institution, Japan) is developing ITS wireless communication technologies in millimeter-wave frequency region. Technologies are categorized for inter-vehicle communications (IVC) and road-vehicle communications (RVC). In this paper, system concepts and the experimental facilities are introduced. The experimental facility for inter-vehicle communications is gotten ready in 60 GHz frequency region and the experimental system for road-vehicle communications is based on RoF (Radio on Fiber) technology in 36-37GHz frequency region.

• Journal of Multimedia Information System
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• v.5 no.2
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• pp.105-110
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• 2018

Autonomous cars require the integration of multiple communication systems for driving safety. Many carmakers unveil mirrorless concept cars aiming to replace rear and sideview mirrors in vehicles with camera monitoring systems, which eliminate blind spots and reduce risk. This paper presents optical vehicle-to-vehicle (V2V) communications for autonomous mirrorless cars. The flicker-free light emitting diode (LED) light sources, providing illumination and data transmission simultaneously, and a high speed camera are used as transmitters and a receiver in the OCC link, respectively. The rear side vehicle transmits both future action data and vehicle type data using a headlamp or daytime running light, and the front vehicle can receive OCC data from the camera that replaces side mirrors so as not to prevent accidents while driving. Experimental results showed that action and vehicle type information were sent by LED light sources successfully to the front vehicle's camera via the OCC link and proved that OCC-based V2V communications for mirrorless cars can be a viable solution to improve driving safety.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.3
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• pp.227-232
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• 2013

Due to the development of ITS technology, various services related to transportation under vehicular environments have been provided. Especially, as wireless communication technology, WAVE has been established as a standard for vehicle-to-vehicle communications. WAVE has fast connection and excellent mobility characteristics. A VSC-A project is conducting by global automotive OEMs in USDOT. This project introduces the advanced safety services with vehicle-to-vehicle communications. In this paper, we presented the scenario of a do not pass warning service, which prevents an accident during overtaking activity by using vehicle-to-vehicle communications. In addition, we analyzed network performance under WAVE. In conclusion, we introduced the simulation results. Finally, we summarized the communication range and delay values for consideration factors for a overtaking model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7C
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• pp.584-591
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• 2012

Distributing a Certificate Revocation List (CRL) quickly to all vehicles in the system requires a very large number of road side units (RSUs) to be deployed. In reality, initial deployment stage of vehicle networks would be characterized by limited infrastructure as a result in very limited vehicle to infrastructure communication. However, every vehicle wants the most recent CRLs to protect itself from malicious users and malfunctioning equipments, as well as to increase the overall security of the vehicle networks. To address this challenge, we design and implement a nomadic device based CRL acquisition method using nomadic device's communication capability with cellular networks. When a vehicle could not directly communicate with nearby RSUs, the nomadic device acts as a security mediator to perform vehicle's security functions continuously through cellular networks. Therefore, even if RSUs are not deployed or sparsely deployed, vehicle's security threats could be minimized by receiving the most recent CRLs in a reasonable time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12A
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• pp.1113-1121
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• 2010

The Vehicle Safety Communications (VSC) is one of VANET applications for preventing vehicle accidents, and it utilizes vehicle-to-vehicle communication to exchange emergency messages. To propagate such messages in VSC, several schemes based on selective flooding have been proposed. Their common idea is that an emergency message is relayed by one of vehicles receiving the message. However, the schemes do not consider the transmission errors and duplications of an emergency event. In the schemes, if there are transmission errors and a vehicle detects a hazard, there may be vehicles which fail to receive an emergency message. If k vehicles detect a hazard, k emergency messages are created and propagated. The duplications of an event increase reliability of the message delivery but decrease efficiency. In this paper, we propose an emergency message delivery scheme which is efficient and robust to transmission errors. Our proposed scheme utilizes clustering for massage aggregation and retransmissions in a cluster. It also uses an acknowledgment mechanism for reliable inter-cluster communication. Our simulation results show that the proposed scheme outperforms Least Common Neighbor Flooding which is one of the selective flooding schemes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.125-132
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• 2017

Vehicular safety service reduces traffic accidents and traffic congestion by informing drivers in advance of threats that may occur while driving using vehicle-to-vehicle (V2V) communications in a wireless environment. For vehicle safety services, every vehicle must broadcasts a Basic Safety Message(BSM) periodically. In congested traffic areas, however, network congestion can easily happen, reduce the message delivery ratio, increase end-to-end delay and destabilize vehicular safety service system. In this paper, to solve the network congestion problem in vehicle safety communications, we approximate the relationship between channel busy ratio and the number of vehicles and use it to estimate the total network congestion. We propose a new context-aware transmit power control algorithm which controls the transmission power based on total network congestion. The performance of the proposed algorithm is evaluated using Qualnet, a network simulator. As a result, the estimation of total network congestion is accurately approximated except in specific scenarios, and the packet error rate in vehicle safety communication is reduced through transmit power control.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6C
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• pp.483-491
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• 2012

In vehicle-to-vehicle (V2V) communications, each vehicle should periodically disseminate a beacon message including the kinematics information, such as position, speed, steering, etc., so that a neighbor vehicle can better perceive and predict the movement of the vehicle. However, a simple broadcasting of such messages may lead to a low reception probability as well as an excessive delay. In this paper, we attempt to analyze the impact of the following key parameters of the beacon dissemination on the performance of vehicular networks: beacon period, carrier-sensing range, and contention window (CW) size. We first derive a beacon period which is inversely proportional to the vehicle speed. Next, we mathematically formulate the maximum beacon load to demonstrate the necessity of the transmit power control. We finally present an approximate closed-form solution of the optimal CW size that leads to the maximum throughput of beacon messages in vehicular networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1969-1977
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• 2016

We study the connection time of vehicle-to-mobile roadside unit (V2MR) communications which can reduce the significant cost of the fixed RSU by installing a gateway of mobile network into a transit bus called the mobile RSU. In the V2MR communications, the connectivity of a commute vehicle can be improved via ad-hoc connection to a nearby mobile RSU. In this paper, we present a new analysis model to estimate the connection time between a commute vehicle and a mobile RSU, when there is a bus station in the overlapping route. Since the connection time between two vehicles is highly dynamic and unpredictable, our analysis will provide a fundamental basis of connection-time estimation of V2MR communications. Numerical results obtained from VEINS simulation show that our analysis can estimate the connection time of V2MR communications with the average error below 1.0 percent. Moreover, we show that the average connection time of V2MR communications can be extended to approximately 3.85 times of that of V2R communications.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.5
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• pp.1229-1234
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• 2012

Vehicular communications have been receiving much attention in intelligent transport systems (ITS) by combining communication technology with automobile industries. In general, vehicular communications can be used for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication by adopting IEEE802.11p/1609 standard which is commonly known as wireless access in vehicular environments (WAVE). WAVE system transmits signal in 5.9GHz frequency band with orthogonal frequency division multiplexing (OFDM) signaling. In this paper, we consider physical layer issues in vehicular communications. We first overview the physical (PHY) layer of WAVE standard and properties of 5.9GHz signals, and then physical layer issues to provide reliable communication link are discussed.

• Journal of the Korea Society of Computer and Information
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• v.23 no.12
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• pp.73-80
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• 2018

Certification revocation list(CRL) is needed for excluding compromised, faulty, illegitimate vehicle nodes and preventing the use of compromised cryptographic materials in vehicular communications. It should be distributed to vehicles resource-efficiently and CRL computational load of vehicles should not impact on life-critical applications with delay sensitive nature such as the pre-crash sensing that affords under 50msec latency. However, in the existing scheme, when a vehicle receives CRL, the vehicle calculates linkage values from linkage seeds, which results in heavy computational load. This paper proposes, a new CRL distribution scheme is proposed, which minimizes the time for CRL processing of vehicles. In the proposed scheme, the linkage value calculation procedure is performed by road-side unit(RSU) instead of the vehicle, and then the extracted linkage values are relayed to the vehicle transparently. The simulation results show that the proposed scheme reduces the CRL computational load dramatically, which would minimize impact on life-critical applications' operations with low latency.