Performance analysis of IEEE 802.11p safety message broadcast with and without relaying at road intersection

Abstract

Dedicated short-range communication (DSRC), which is an essential part of vehicle-to-vehicle/infrastructure communication to enhance the road safety, is often characterized by the IEEE 802.11p standard. Numerous works have been done on the DSRC safety message broadcasting performance for highway scenario. However, up to date, no work has been done on the performance of the IEEE 802.11p safety message broadcasting for the road-intersection scenario in urban environment. An intersection scenario is different from a highway scenario. In a highway scenario, it is often been considered that all the vehicles have the same communication range as well as the same carrier sensing range. However, this is not the case for the intersection scenario, where there exist a lot of obstructions, such as buildings and urban canyons. In an intersection, the communication and carrier sensing ranges of a vehicle heavily depend on the location of that vehicle. This paper first analyzes and then provides solution on improving the broadcasting performance of the DSRC safety message at an intersection while considering the IEEE 802.11p enhanced distributed channel access mechanism. To facilitate different communication and carrier sensing ranges of different vehicles, we divide the intersection region into few parts/areas based on an empirically validated path loss model. We present an analytical study on the packet reception rates and channel access delay which is applicable for the different positions of transmitters and receivers in the intersection areas. The analytical results are verified by the NS-3 simulation. From the results, we find that the overall delivery ratio is very poor when the broadcasting vehicle is not close enough to the intersection-center. To improve the overall broadcast performance of such scenarios, we employ a road side unit (RSU) at the intersection-center to relay the safety messages once. We show the performance improvement via relaying while first using omni-directional and then using special sector antennas, the so-called bidirectional antenna, at the RSU. From the results, it is shown that relaying with the omni-directional antenna gives moderate improvement on the overall delivery ratio, while a significant improvement can be achieved by relaying with sector antenna.