Undersampled Differential Phase Shift On–Off Keying for Visible Light Vehicle-to-Vehicle Communication

Abstract

An important development direction for the future of the automotive industry is connected and cooperative vehicles. Some functionalities in traffic need the cars to communicate with each other. In platooning, multiple cars driving in succession reduce the distances between them to drive in the slipstream of each other to reduce drag, energy consumption, emissions, and the probability of traffic jams. The car in front controls the car behind remotely, so all cars in the platoon can accelerate and decelerate simultaneously. In this paper, a system for vehicle-to-vehicle communication is proposed using modulated taillights for transmission and an off-the-shelf camera with CMOS image sensor for reception. An Undersampled Differential Phase Shift On–Off Keying modulation method is used to transmit data. With a frame sampling rate of 30 FPS and two individually modulated taillights, a raw data transmission rate of up to 60 bits per second is possible. Of course, such a slow communication channel is not applicable for time-sensitive data transmission. However, the big benefit of this system is that the identity of the sender of the message can be verified, because it is visible in the captured camera image. Thus, this channel can be used to establish a secure and fast connection in another channel, e.g., via 5G or 802.11p, by sending a verification key or the fingerprint of a public key. The focus of this paper is to optimize the raw data transmission of the proposed system, to make it applicable in traffic and to reduce the bit error rate. An improved modulation mode with smoother phase shifts is used that can reduce the visible flickering when data is transmitted. By additionally adjusting the pulse width ratio of the modulation signal and by analyzing the impact of synchronization offsets between transmitter and receiver, major improvements of the bit error rate (BER) are possible. In previously published research, such a system without the mentioned adjustments was able to transmit data with a BER of 3.46%. Experiments showed that with those adjustments a BER of 0.48% can be achieved, which means 86% of the bit errors are prevented.

A Security Protocol for Vehicle Platoon Verification Using Optical Camera Communications

“…While PWM is commonly used to adjust the brightness of LED taillights, it needs to be replaced with UDPSOOK modulation for this application. Notably, both modulation approaches exhibit similar effects on images captured using a camera with a short exposure time [31]. Although an additional circuit was utilized to evaluate the presented prototype, vehicle manufacturers should be capable of implementing the proposed modulation to modern LED taillights without additional hardware components.…”

“…If the modulation signal uses a PWR of 50%, bright phases of the LED taillight are dominant because of blooming and exposure effects. Ambiguous states of the taillight cannot be prevented using UDPSOOK modulation but using a PWR of less than 50% reduces bit errors significantly [22]. The proposed V2V-OCC system yields the best results using a PWR of 49%.…”

“…However, a camera recording the modulated light source using short exposure time is capable of capturing the distinct states. If the camera uses a rolling shutter, a stripe pattern appears in the image because the LED changes its state while being captured by the camera [22]. Fig.…”

“…To mitigate this effect, the phase shifts are applied in the middle of a pulse as shown in Fig. 4 resulting in a steady transition for the human eye [22].…”

Towards Autonomous Driving: Technologies and Data for Vehicles-to-Everything Communication

“…For more information about short-range communication technologies see Table 13. Data transmission between two adjacent vehicles, although a stable communication link between the two vehicles is needed and since the distance between the transmitter and the receiver increases, the transmitted power must also increase; drawbacks can be eliminated by applying distant measurement sensors, e.g., LiDAR additional optical systems to boost the received power [34,39] Beaconing Up to 5 m Suitable for small amounts of safe data transmission and can be easily implementable; this type is used as an auxiliary means for other technologies, e.g., BLE, to periodically transmit data in the form of beacons with adjustable rate [7,123] ZigBee (IEEE 802. 15.4) Up to 100 m…”