## 2 Related Work  
There is plenty of literature available in the context of visible light communication (VLC), optical wireless communication (OWC), and optical camera communication (OCC) in various application areas, also in vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication. The application of VLC for V2V or V2I communication is often called vehicular VLC (V2 LC).  
Generally, VLC refers to optical wireless communication that uses modulated light in a wavelength spectrum that is perceivable by the human eye, i.e., between 400 nm and 700 nm, and hence is usually used for illumination [4]. The transmitted information is then modulated onto the illuminating light. Usually, a precondition for VLC is that the modulation is not perceived by humans in form of noticeable flickering or similar effects. Here it is important that the modulation frequency does not fall below the critical flicker frequency threshold (CFF). The CFF defines the frequency, where an intermittent light stimulus appears completely steady to a human observer [5]. The concrete value for the CFF depends on various factors, e.g., the age of the human observer. On average, frequencies above 35 Hz to 50 Hz are not perceived in noticeable flickering [6].  
V2 LC was implemented in multiple variations in related projects. [PERSON] et al. [7] and [PERSON] et al. [8] focused on road-to-vehicle communication using high-speed cameras. V2V communication using LEDs and cameras is covered by multiple works, too. Some use custom LED transmitters such as LED matrices or LED screens encoding multiple bits at once, e.g., [PERSON] et al. [9]. Others use special receivers such as high-speed cameras with 1000 FPS or novel image sensors developed for OCC, e.g., [PERSON] et al. [10] and [PERSON] et al. [11]. Some works even use both mentioned aspects, e.g., [PERSON] et al. [12] and [PERSON] at al. [13].  
In contrast to the mentioned literature, the proposed system uses single LEDs, i.e., LED taillights of cars, to transmit data and uses a camera with 30 FPS such as smartphone cameras or webcams by exploiting the rolling-shutter effect of CMOS cameras. There is also literature about VLC using CMOS cameras by using the rolling-shutter effect, e.g., [PERSON] et al. [14], [PERSON] et al. [15], [PERSON] et al. [16], and [PERSON] et al. [17]; however, those works rely on the modulated light to cover major parts of the image. Thus, the distance between transmitting LEDs and receiving camera is limited to less than one meter. Of course, for V2V communication much larger distances need to be covered. The proposed system strives for common distances in traffic, i.e., between 30 m and 80 m.  
A conceptual idea of this project was published in [1], where the Undersampled Differential Phase Shift On-Off Keying (UDPSOOK) modulation method proposed by [PERSON] et al. [3] was used to encode information onto LEDs representing the taillights of a car model. This paper proposes major improvements to the raw data transmission for this visible light vehicle-to-vehicle communication system using a new modulation mode and advanced adjustments of the modulation settings. Additionally, this paper evaluates the impact of timing offsets to the loose synchronization.