Jhihoon Joo

First Fresnel zone analysis in vehicle-to-vehicle communications

The Fresnel zone is often utilized for the determination of the existence of the line-of-sight (LOS) in wireless communication links. In this paper, the first Fresnel zone clearance is analyzed especially focused on vehicle-to-vehicle (V2V) scenarios. The results reveal that clear wireless communication links with transmitter and receiver separation distances exceeding 500 m are regarded as non-LOS (NLOS) links.

Impact of the latency in vehicular networks: Analysis on the reaction distance

Vehicular networks are expected to contribute to improving transportation systems, especially reducing traffic accidents. However, the impact of vehicular networks may not be easy to intuitionally realize because it is difficult to express in numerical value. To address this issue, we analyze the effectiveness of the latency in vehicular networks in numerical form using the concept of the reaction distance in this paper. Furthermore, we compare the performance of vehicular networks with regard to the types of communications.

SAEMD: A scheduling algorithm for emergency message dissemination in vehicular ad hoc networks

In this paper, we propose a scheduling algorithm for emergency message dissemination (SAEMD) in vehicular ad hoc networks. The SAEMD mainly aims to minimize the delay of emergency message delivery to the vehicles in priority of distances apart. Additionally, we investigate that the SAEMD can reduce dissemination procedure, and verify with mathematical analysis that it shows the smallest delay of emergency message delivery to the closest vehicle among other schemes.

Approach for PHY/MAC cross-layer design in vehicular ad-hoc networks

Vehicular environments are highly unpredictable and fragile. Therefore traditional layered communication system architecture has limitations to provide robust communication environments. This paper proposes a physical (PHY) and medium access control (MAC) cross-layer design in vehicular ad-hoc networks (VANETs) to enhance overall performance of vehicular communications. Major parameters for both PHY and MAC layers are suggested for VANETs to optimize the performance according to the environments. Significant performance improvements can be obtained with the proposed parameters.

Verification of Fresnel Zone Clearance for Line-of-sight Determination in 5.9 GHz Vehicle-to-Vehicle Communications

The determination of the path clearance is one of the most important factors for channel propagation models because most of them classify their models into line-of-sight (LOS) and non-LOS (NLOS) environments. In particular, the path for vehicle-to-vehicle (V2V) communication is more easily obstructed owing to its characteristics such as low antenna heights and high mobility. In this paper, we verify the first Fresnel zone clearance, which is a widely employed method for the determination of path clearance in V2V scenarios. In the analytical model of the first Fresnel zone in V2V scenarios, the ground acts as an obstacle and thus induces NLOS environments for farther than a certain distance. In contrast, our measurement results reveal no additional loss due to the ground obstruction. Therefore, we conclude that the first Fresnel zone calculation is not applicable for determining the path clearance in V2V scenarios, which has significant impact on the accuracy of channel propagation modeling.

A distance-based event-driven broadcast (DEB) mechanism for V2V safety communications

Broadcasting in vehicular ad hoc networks (VANETs) is the ideal communication technique for information dissemination and is conventionally defined in IEEE 802.11p-based wireless access in vehicular environments (WAVE). Vehicular systems present a unique characteristic of dynamic positions and varying vehicle density due to motion which is a challenge in communication systems. Since the node density is a critical performance parameter in broadcast communications, there is need to offer media access control (MAC) solutions to the broadcast storm problem which exists in high density vehicular domains. This paper proposes the use of a pilot beacon message broadcast from an emergency vehicle and then selects vehicles receiving the pilot message beyond a given distance to follow an event-driven transmission approach. The event in this case is the reception of a message with in a determined distance and the response being a single message transmission. The other vehicles which are not selected and do not participate in the event driven approach use the conventional IEEE 802.11p broadcast style. The main goal of the study is to improve on the reliability of vehicle to vehicle safety message communications. Computer simulations show that the packet delivery ratio and end to end delay for the proposed approach is better than the conventional IEEE 802.11p broadcast approach.

A broadcast scheme for vehicle-to-pedestrian safety message dissemination:

Ensuring cooperative awareness by periodic message beaconing in vehicular environments is necessary to address pedestrian safety. However, high periodic basic safety message broadcasting in dense vehicular environments makes accessing the communication channel very competitive. Furthermore, high-frequency periodic broadcasting causes fast device energy dissipation which is a key issue for small computing devices used in wireless sensor and mobile communications. Therefore, in order to achieve reliable message dissemination for vehicle-to-pedestrian safety, energy loss minimization mechanisms for pedestrian mobile devices should be developed. This article proposes controlling the number of broadcasts by eliminating periodic safety message broadcasts from pedestrian nodes; these nodes only receive broadcasts from vehicles and then conditionally communicate with the vehicles when safety alerts are raised. When the pedestrian nodes do not receive messages from any vehicle for a specified period, pedestrian nodes broadcast a high-priority message advertising their position. Furthermore, for the pedestrian, adaptive message emission rates and transmission duration are proposed based on defined vehicle-to-pedestrian separation distances. This approach reduces the pedestrian device energy consumption and end-to-end delay and improves the packet delivery ratio compared to the vehicular broadcast approach for safety messages defined in the IEEE 802.11 standard.

Measurement based V2V path loss analysis in urban NLOS scenarios

The importance of an accurate path loss model of vehicular environments is critical for the vehicular communication system design. However, estimating the path loss in vehicular environments is difficult due to high dynamics and low antenna heights. In this paper, we propose a line-of-sight (LOS) path loss model in vehicle-to-vehicle (V2V) scenarios and provide deep analysis of shadow fading in urban non-LOS (NLOS) scenarios by the deductive method with the proposed LOS model. The results can be utilized as reference material for further analysis of V2V path loss measurements.

Cooperative multi-channel dissemination of safety messages in VANETs

IEEE 802.11p-based wireless access in vehicular environments (WAVE) multi-channel communication introduces communication clusters which limits on the dissemination efficiency of broadcast applications such as safety messaging. This paper proposes cooperative multi-channel information dissemination (CMD) which follows a channel coordination approach where the coordinator is selected based on the least average distance (LAD) to all service channels with the goal of relaying the emergency message to other service channels with minimum delay. On receipt of high priority emergency messages, each selected channel coordinators switches to a defined service channel and broadcasts the emergency message to it members. In the CMD approach, each vehicle assumes a single radio and the number of channel coordinators in each service channel cluster is determined based on the available service channels advertised and LAD to the advertised service channels. Computer simulations show that the proposed CMD performs well in terms of dissemination delay and dissemination rate.