Cooperative emergency braking warning system in vehicular networks

Tsai et al. EURASIP Journal on Wireless Communications and Networking Cooperative emergency braking warning system in vehicular networks Ming-Fong Tsai 3 Yung-Cheng Chao 2 Lien-Wu Chen 3 Naveen Chilamkurti 1 Seungmin Rho 0 0 Department of Multimedia, Sungkyul University , Anyang , Korea 1 Department of Computer Science and Engineering, La Trobe University , Melbourne , Australia 2 Connected Vehicle Department, Telematics and Vehicular Control System Division, Information and Communications Research Laboratories, Industrial Technology Research Institute , Hsinchu , Taiwan 3 Department of Information Engineering and Computer Science, Feng Chia University , Taichung , Taiwan Safety applications in vehicular networks have been popular research topics in recent years, such as forward collision warning, emergency braking warning and intersection collision warning systems. The basic safety message broadcast from each car transmits the position, car speed and car heading information. Neighbouring cars receiving this information can decide if there is any danger within the next second. However, the safety application message has positioning accuracy and time-critical problems. Accurate positioning of the car provides a more effective warning to the driver. Moreover, the reliable and efficient delivery of safety information needs to be improved when the penetration rate increases. Hence, this paper proposes a cooperative emergency braking warning system to solve the above problems. This is a system that integrates a camera sensor to construct the state of neighbourhood cars in order to solve the first problem. It then proposes to reduce the repeat and derivable information between the broadcast messages in order to solve the second problem. The proposed system has been implemented to provide a safer driving environment. Safety applications; Cooperative system; Vehicular networks 1 Introduction More and more research works and products have been proposed in recent years for vehicle-to-vehicle or vehicleto-roadside communication for reducing accidents [1-5]. Based on previous research, protocol standards and field trial works, the US Department of Transportation has published information announcing a decision to move forward with vehicle-to-vehicle communication technology for light vehicles in 2014 [6]. The typical safety application in the vehicular networks is the emergency electronic brake light (EEBL) [7], as shown in Figure 1. The second car may stop without collision when the first car brakes hard, based on driver vision, but the third car cannot stop fast enough and collides with the second car. If the cars had vehicle-tovehicle communication devices, such as ITRI WAVE/ DSRC Communications Units (IWCUs) [8], each car could broadcast basic safety message (BSM) [9] information to warn cars in the neighbourhood. Hence, the third car would receive the broadcast BSM information from the first car; and based on this information, the third car would decide whether to alert the driver. There are two problems that need to be solved for safety applications in the vehicular networks. The first is the positioning accuracy issue, and the second is the time-critical issue. For vehicular networks, the safety applications of the broadcast BSM information frequency have been described in the WAVE/DSRC provided environment [10]. The car identity and car position in the warning information are based on the Global Positioning System (GPS). There are many enhanced technologies for GPS, such as assisted GPS, differential GPS and the wide-area augmentation system. However, these enhanced technologies cannot work at lane level in a city [11]. Hence, the GPS cannot identify the position of the car very well in recent research. The broadcast frequency of many safety applications requires a minimum of 10 Hz (maximum latency is 100 ms), such as for emergency brake lights, traffic signal violation, forward collision, left turn assist and lanechange warning. More and more channel collisions have happened, and larger latency problems will happen when the WAVE/DSRC device penetration rate increases. Controlling the transmission power [12] and transmission frequency [13] to avoid affecting neighbouring cars are two Figure 1 Emergency electronic brake light system. angle methods to overcome the time-critical issue. However, these two angle methods need to obtain more information to decide the optimal rate or frequency control, such as feedback information from neighbouring cars, or to monitor the broadcast condition immediately. This paper proposes a cooperative emergency braking warning system which integrates a camera sensor to construct the state of neighbouring cars. The proposed system uses the relative position instead of the GPS position in order to solve the positioning accuracy problem. This method will not affect the GPS operation but enhances the above research works. The proposed system uses previous work [14] which reduces the repeated and derivable information between the broadcast messages in order to solve the time-critical problem. This method will not change the transmission power and frequency but is compatible with the above research works. This paper is structured as follows. Section 2 presents a brief overview of the background and related works. Section 3 presents the proposed cooperative emergency braking warning system. Implementation performance evaluations are presented in Section 4. Conclusions and future work are given in Section 5. 2 Background and related works 2.1 Background With vehicle-to-vehicle communication, drivers can give an earlier braking warning signal when the vehicle in front of the vehicle ahead emergency brakes, especially when the front view is obstructed by another vehicle. However, there are still some challenges that need to be overcome for vehicle-to-vehicle communication. 2.1.1 Positioning accuracy Unlike other wireless communication, vehicle-to-vehicle communication performs well especially in a low-latency and highly mobility time-varying environment. Traditionally, most related work assumes that both the emergency braking signal and the GPS position are broadcast, and the received vehicle will check the source of the emergency braking signal according to the GPS position. If the heading matches and the GPS position seems on the same lane, a warning signal is received. However, this is not accurate enough to detect the lane by GPS alone. Although position technologies like assisted GPS, differential GPS and the wide-area augmentation system can improve positioning accuracy, in an environment like a downtown area, there is usually severe shadowing due to buildings, trees, vehicles and tunnels. Consequently, the position performance may not be effective at lane level. As shown in Figure 2, when car E emergency brakes, this warning signal will be broadcast and received by vehicles behind in the same lane. Since the broadcasting range of DSR (...truncated)