## 1 Introduction  
The automotive industry is about to approach a new era. Advanced driver assistance systems (ADAS) and semi-autonomous driving is nothing special in the luxury class. However, in the future, cars will not just drive autonomously, but there will also be connected and cooperative cars. Pure autonomous driving means the car can drive on its own; its decisions are purely based on its own sensors. Connected and cooperative vehicles also communicate with each other and the infrastructure, to enable far more precision than by just reacting to sensors, which is needed for some functionalities, e.g., platooning. Multiple vehicles on the road build a platoon by reducing the distances between them. Their individual driving behavior is replaced by a cooperative driving behavior of the platoon. Electronic coupling of the participating cars via a wireless communication channel allows simultaneous acceleration and deceleration. By driving in succession with small distances, the smaller amount of drag due to the slipstream leads to less energy consumption and emissions. The usage of the available road capacity is optimized, and traffic jams caused by traffic overload can be prevented.  
Every car needs to be controlled remotely by its predecessor [2]. For this communication, a fast wireless communication channel with low latency is needed. This main communication channel could be realized using 5G or 802.11p. However, the communication channel also needs to be secure. It is crucial to know the true identity of the communication partner and that no third party can interfere with or manipulate the transmitted data. An optical communication channel using modulated taillights and a camera as receiver as proposed in [1] could be used as out-of-band channel. Data transmitted using this out-of-band channel can be used to verify the identity of the communication partner, because the actual transmitter of the message is visible in the camera image. For example, a public key fingerprint of the car in front is transmitted to the car behind and a matching public key is used for the asynchronous encryption on the main channel. This way the fast, low-latency main channel can be combined with the identity verification of the slower optical channel.  
This paper is based on the proposed visible light vehicle-to-vehicle communication system using modulated taillights by [PERSON] et al. [1]. The focus lies on the improvement of the raw data transmission of this optical communication channel between two vehicles. The goal is to optimize the settings of the modulation of the taillights for transmission and the settings on the receiving camera to get the best possible bit error rate (BER). As a basis for the optical communication channel, the Undersampled Differential Phase Shift On-Off Keying (UDPSOOK) modulation method by [PERSON] et al. [3] is used. However, some aspects of this modulation method are not applicable for vehicular visible light communication (V2 LC) in traffic or can be optimized for a better BER. These drawbacks of the modulation method and solutions to them are thoroughly addressed in this paper.  
This paper is organized as follows. In Section 2, related literature and projects and how they are different compared to this work are discussed. Section 3 explains the basics for this project and the goals and potential problems and how they can be solved. In Section 4 the experimental setup is documented and the approaches are evaluated. Section 5 concludes this paper and gives an outlook to future research.