부산대학교 도서관

EEE 802.11p and 1609 named as WAVE(Wireless Access Vehicle Environments) communications are attracting attention as a next generation vehicle protocol. WAVE consists of the PHY(Physical) layer and MAC(Medium Access Control) layer of IEEE 802.11a, and additional functions such as resource allocation, security, and multi-channel service supported in 1609. Multiple channels of IEEE 1609.4, part of the proposed IEEE 1609, support QoS(Quality-of-Service) of each data stream using EDCA(Enhanced Distributed coordination function Channel Access) of IEEE 802.11e. The infrastructure that relays communications among vehicles on roads is comprised of RSUs(Road Side Unit). In WAVE, collisions may occur when multiple vehicles simultaneously transmit data to one RSU.In this paper, we propose a Distance based Grouping Algorithm(DGA) that creates groups based on the distance between two neighbor vehicles. RSUs collects the information of each vehicle and evaluates the collision rate. If the collision rate exceeds a predetermined threshold, the RSUs determines that a new grouping is necessary and creates a table recording the distance between neighboring vehicles. In the table of RSU, two vehicles with the shortest distance are selected as a group. After creating the group, DGA algorithm selects the slowest vehicle as the group leader and calculates the distance to the leader of the other group. This process is repeated until there are maximally 20 vehicles in a group. Depending on the number of groups created, the RSU allocates group time to each group for them to exclusively communicate. DGA algorithm shows a maximum performance improvement of 6% compared with the existing basic IEEE 802.11p/1609 communication method. It also, reduces the collision rate by up to 4.1% compared to the conventional communication method.