Browsing by Author "Joo, Jhihoon"

Now showing 1 - 4 of 4
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    A broadcast scheme for vehicle-to-pedestrian safety message dissemination
    (International Journal of Distributed Sensor Networks, 2017) Eyobu, Odongo Steven; Joo, Jhihoon; Seog Han, Dong
    Ensuring cooperative awareness by periodic message beaconing in vehicular environments is necessary to address pedes- trian 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 broad- casts 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.
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    CMD: A Multichannel Coordination Scheme for Emergency Message Dissemination in IEEE 1609.4
    (Mobile Information Systems, 2018) Eyobu, Odongo Steven; Joo, Jhihoon; Seog Han, Dong
    (e IEEE 1609.4 legacy standard for multichannel communications in vehicular ad hoc networks (VANETs), specifies that the control channel (CCH) is dedicated to broadcast safety messages, while the service channels (SCHs) are dedicated to transmit infotainment service content. However, the SCHs can be used as an alternative to transmit high priority safety messages in the event that they are invoked during the service channel interval (SCHI). (is implies that there is a need to transmit safety messages across multiple available utilized channels to ensure that all vehicles receive the safety message. Transmission across multiple SCHs using the legacy IEEE 1609.4 requires multiple channel switching and therefore introduces further end-to-end delays. Given that safety messaging is a life critical application, it is important that optimal end-to-end delay performance is derived in multichannel VANET scenarios to ensure reliable safety message dissemination. To tackle this challenge, three primary con- tributions are in this article: first, a cooperative multichannel coordinator (CMD) selection approach based on the least average separation distance (LAD) to the vehicles that expect to tune to other SCHs and operates during the control channel interval (CCHI) is proposed. Second, a model to determine the optimal time intervals in which CMD operates during the CCHI is proposed. (ird, a contention back-off mechanism for safety message transmission during the SCHI is proposed. Computer simulations and mathematical analysis show that CMD performs better than the legacy IEEE 1609.4 and a selected state-of-the-art multichannel message dissemination scheme in terms of end-to-end delay and packet reception ratio.
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    Cooperative Multi-channel Dissemination of Safety Messages in VANETs
    (IEEE, 2016) Steven Eyobu, Odongo; Joo, Jhihoon; Seog Han, Dong
    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.
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    Measurement Based V2V Path Loss Analysis in Urban NLOS Scenarios
    (IEEE, 2016) Joo, Jhihoon; Eyobu, Odongo Steven; Seog Han, Dong
    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.