# The Necessity of LED to Ambient Light Ratio Optimization for Vehicular Optical Camera Communication
## 1 Introduction  
Vehicular communication is a type of short- to medium-range communication system for exchanging traffic information and safety warnings among vehicles [1; 2]. Vehicular communication has many useful applications. A vehicle can, for instance, transmit a signal for lane changing permission and wait for a confirmation sent from other vehicles. When there is a need for emergency braking, accelerating or decelerating, warning signals can be broadcasted to other vehicles through vehicular communication. When used with vehicle tracking, a vehicle's ID can be sent to other vehicles to build maps of traffic on the street. Coupling vehicular communication with vehicle tracking and other sensing technologies such as vehicle tracking, lane detection, pedestrian detection, etc., will facilitate safer, more coordinated transportation networks, and will ultimately spur autonomous vehicle networks and intelligent transportsystems. In the last few years, an emerging technology known as optical camera communication (OCC) has been regarded as a potential candidate for vehicular communication thanks to many advantages [3; 4; 5]. In vehicular optical camera communication (VOCC), the visible light signal is transmitted using LED panels and is received using dashboard cameras, which are both available in vehicles. The availability of the transmitter and receiver creates a tremendous cost advantage for VOCC. However, the most important advantage that distinguishes VOCC from other vehicle communication technologies is the perfect compatibility with other essential technologies for intelligent transport systems and autonomous vehicle networks. In the near future, it is likely that vision-based technologies such as traffic sign detection, street lane detection, pedestrian detection, and vehicle tracking, can be implemented in every vehicle. These technologies employ the same cameras and image processors required for VOCC [6; 7]. In particular, VOCC can work in great harmony with vehicle tracking, which is one of the most crucial components in a self-driving vehicle network. This is due to key procedures in vehicle tracking, namely vehicle image coordinate detection and vehicle identification, which are already achieved through VOCC. As a result, both hardware and software implementation costs for whole-vehicle communication and tracking systems can be substantially lowered by using VOCC for vehicle communication over other technologies [8]. A common understanding in telecommunications is that increasing the power of a transmitter would result in better signal quality. Therefore, one might expect to get a lower bit error rate (BER) in VOCC by simply using more powerful LED lights; however, this is not the case. In a VOCC system, the logic bits 0 and 1 are conveyed by the Off and On status of LEDs in the panel. The BER of the system is determined by the distinguishability of the On and Off LED statuses in the received images. This paper shows that the LED distinguishability is mutually determined by two factors: The LED extinction ratio and LED interference. Note that \"extinction ratio\" is a term used in optical communication to express the ratio between two received optical powers that represent the logic levels 1 and 0. In VOCC, the LED extinction ratio is the ratio between the greyscales of the On and Off LEDs in the received LED panel image. LED interference is the interference between adjacent LEDs in the received image. Both factors are governed by the LED to ambient light (L2A) ratio. More specifically, due to the nature of image acquisition, both the extinction ratio and interference increase as the L2A ratio increases. While the increase in the LED extinction ratio reduces the BER, the increase in LED interference escalates it. Consequently, as the L2A ratio increases, the BER initially drops until the L2A ratio reaches an optimal level.