GPS-free vehicular localization system using roadside units with directional antennas

The success of dedicated short-range communications (DSRC) applications depends on an accurate knowledge of the positions of vehicles within the network. At present, vehicle localization is generally performed using some form of vehicle-mounted global positioning system (GPS). However, GPS signals may not be always available. Various GPS-free vehicle localization techniques using the ranging information, the prior knowledge of the vehicle's position, or the special hardware have been proposed for enhancing the performance of traditional GPS-based methods. Different from the previous approaches, we propose a GPS-free vehicle localization system using roadside units (RSUs) with directional antennas without specific hardware support on the vehicle and the assumption of the prior knowledge of the vehicle. In the proposed approach, each vehicle determines its position using the information contained within beacon messages transmitted by neighboring RSUs deployed along the road only. The performance of the proposed localization scheme is evaluated by ns-2 simulations and is compared with those of recent GPS-free and GPS-assisted localization systems. The simulation results show that the proposed localization scheme achieves a higher positioning accuracy than the existing GPS-free and GPS-assisted schemes. The feasibility of the proposed system for practical applications is further investigated experimentally. The experimental results for the positioning accuracy are consistent with those obtained from the ns-2 simulations.