Vehicular Visible Light Communication System Research Articles

Non-line of sight analysis for vehicular visible light communication system: Impact of artificial light source and weather conditions

Visible light communication is seen as a crucial technology within optical wireless communication systems. The technology of vehicular visible light communication holds significant importance in the context of connected vehicles. This technology can serve as a supplementary solution to vehicular systems that are based on radio frequency. In this paper, the authors conduct an analysis of the performance of both line-of-sight and non-line-of-sight vehicle-to-vehicle visible light communication systems under the effect of artificial light source and weather conditions, including clear, hazy, and foggy weather. A practical vehicular laser diode, a street lamp, and an avalanche photodiode are used to design the proposed system model. Performance enhancement for the proposed system is achieved using an optical amplifier at the receiving end. An artificial light source of light-emitting diode Corn-type is used to represent an ambient artificial light source. Different metrics such as quality factor and bit error rate are used to assess the system performance of the non-line-of-sight-vehicular communication system. The proposed line-of-sight model achieves a data rate of 25 Gbps, supporting a distance of 80 m under clear sky and hazy atmospheric conditions. For foggy weather, an attainable link distance of 70 m is achieved. The achieved results emphasize the suitability of the suggested models for vehicular applications in real world environment.

A Survey of Vehicular VLC Methodologies.

Visible Light Communication (VLC) has recently emerged as an alternative to RF-based wireless communications. VLC for vehicles has demonstrated its potential for Intelligent Transportation Systems (ITSs) to exchange information between vehicles and infrastructure to achieve ITS core goals, such as improving road safety, passenger comfort, and traffic flow. This paper seeks to provide a detailed survey of vehicular VLC systems. This paper presents an overview of current developments in vehicular VLC systems and their benefits and limitations for experienced researchers and newcomers.

Design and performance evaluation of vehicular visible light communication system under different weather conditions and system parameters

Design and performance evaluation of vehicular visible light communication system under different weather conditions and system parameters

Vehicular Visible Light Communication With Low Beam Transmitters in the Presence of Vertical Oscillation

The availability of light-emitting diodes (LEDs) in vehicle exteriors makes possible the use of visible light communication (VLC) as a vehicle-to-vehicle (V2V) wireless connectivity solution. Although high beam headlights offer higher illumination levels and further communication distances compared to low beam headlights, regulations restrict high beam utilization in many driving cases. These restrictions make low beam headlights a more suitable candidate for vehicular VLC systems. In this paper, we consider two heavy vehicles (e.g., trucks) on a road following each other. Low beam headlights of the follower truck act as wireless transmitters and the lead truck is equipped with a photodetector at its back. We first propose an accurate path loss model based on experimental measurements. The proposed model takes into account the presence of lateral shift between the trucks as well as the fact that headlamps and photodetector can be placed at different heights. Furthermore, we model the truck vertical oscillation experimentally at different speeds. Utilizing these models, we derive a bit error rate (BER) expression for VLC-based truck-to-truck communication system and investigate the effect of several system and channel parameters on the performance. In an attempt to mitigate the degrading effects of the vertical oscillation, we further investigate the proper selection of photodetector location in order to minimize the error rate performance.

A camera-based vehicular visible light communication system using modulated taillights in public road scenarios

This paper proposes a camera-based vehicular visible light communication system using modulated LED taillights for vehicle-to-vehicle communication. The taillights are modulated using on-off keying with a carrier frequency above the critical flicker frequency threshold to appear steady to the human eye and only a camera with a short exposure time can perceive the signal. For receiving the signal, a common camera with a recording frame rate of 30 frames per second was used for the experiments. This limits the throughput of the communication system as only one bit per frame and per individually modulated light source can be transmitted, thus the system is not suitable for transmitting time-critical data. However, the main advantage is that the transmitted data as well as the transmitting vehicle are visible in the camera image, hence we can associate the message and its origin.For the communication between two cooperative autonomous vehicles, e.g., members of a platoon, a secure wireless channel with low latency is needed. To establish an encrypted connection in this main channel our system can be used as an out-of-band channel to verify the identity of the vehicle in front by transmitting a verification code.In this paper we evaluate how the communication quality in terms of bit error rate of the raw data transmission without any error correction methods is influenced by various environmental factors, e.g., communication distance, traveling speed, weather, brightness, etc. This is done by testing our system in controlled scenarios as well as on public roads. The results show that our system is capable of transmitting data with a raw bit error rate of 1.59% on average in platooning relevant situations on the highway in dry conditions. Rain affects the system due to raindrops on the windshield, spray thrown up by vehicles in front, and the windshield wipers occluding the modulated taillights of the transmitting car. In light to medium rain conditions the mean bit error rate is between 2.7% and 6.2%, depending on the intensity.

On the performance analysis of NOMA-based vehicular visible light communication systems

Communication-based vehicle safety applications have emerged as one of the best solutions to enhance road safety. In this area, visible light communication (VLC) has great potential for such applications, named Vehicular VLC (V-VLC). V-VLC is preferred due to its highly secure, low complexity, and radio frequency (RF) interference-free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light-emitting diodes. This research addresses the application of the non-orthogonal multiple access (NOMA) technique in V-VLC based vehicle-to-vehicle communication. In this study, we proposed a system integrating NOMA in V-VLC networks and comprehensively provided an analysis of the system. Subsequently, we derived theoretical achievable capacity and an exact bit error rate expression for the proposed scenario. This paper also covers discussions about system performance under the non-ideal NOAM at the receiver, the effect of transmitter-receiver distance, and the impact of different weather conditions. The derived analytical BER and channel capacity expressions are verified with the simulation results.

Enhancement of Vehicular Visible Light Communication Using Spherical Detector and Custom Lens Combinations

Vehicular Visible light communication (VLC) technology has recently attracted much interest from researchers and scientists. This technology enables connectivity between vehicles and infrastructures along the road by using vehicles’ headlights and taillights as wireless transmitters. The reliability of vehicle-to-vehicle (V2V) VLC systems is affected by several factors, such as car mobility, optics system design, and visibility conditions, where the first two have the most impact on the VLC system performance. This paper, therefore, focuses on the relative positions of the cars and the design of the optics, especially on the receiving end, which has been proposed with the use of a polar detector instead of the rectangular detectors commonly used in the literature. We investigate the achievable gain compared to the conventional detector for different vehicle locations, utilizing a professional optical system design and ray tracing approach. Then, to improve the performance, we introduce the utilization of an imaging receiver by integrating the polar detector with different optical commercial lens combinations, such as Fresnel and Aspherical lenses. To further improve the V2V system performance, we propose a novel optical lens combination design by integrating double-convex lens with half-Plano-concave lens, which allows the correction of more optical aberrations, such as chromatic and spherical aberration. Utilizing the non-sequential ray tracing tools, we designed these VLC systems and perform a realistic channel modeling study considering the typical 3D CAD models of vehicles and roads as well as the possibility of horizontal and vertical movement between the vehicles. Based on the channel impulse responses (CIRs) obtained from the ray tracing simulations, we analyzed the performance of V2V VLC systems with all lens combinations at different vehicle positions on the road. We further investigated the impact of different system parameters on the overall V2V system performance, such as receiver diameter and bandwidth. The obtained results demonstrated that with a carefully chosen system and lens parameters, the proposed system design of lens combination provides an enhancement of up to 7 dB in total received power compared to the case without a lens. Our results also revealed that the proposed system design outperforms the benchmark ones for all lateral displacements and longitudinal distances.

Vehicular VLC System With Selection Combining

The availability of LED-based headlights and taillights makes possible the use of visible light communication (VLC) as a wireless access technology for vehicle-to-vehicle (V2V) communications. A critical concern to establish a reliable VLC link between two moving vehicles is the number of photodetectors and their locations on the destination vehicle. In this paper, we experimentally investigate the usage of dual photodetectors for a vehicular VLC system with selection combining to enhance signal reception in mobile conditions. We measure the electrical receive signal-to-noise ratio (SNR) for each individual photodetector as well as at the output of selection combiner in two different tracks involving straight and curved roads. Through data fitting to experimental data, we obtain a probability density function (PDF) to describe the instantaneous SNR. Based on the PDF, we derive a closed-form expression for the average bit error rate (BER) in the form of a finite summation and compare it with the measurements.

Position-Dependent MIMO Demultiplexing Strategy for High-Speed Visible Light Communication in Internet of Vehicles

The context of the Internet of Vehicles (IoV) and the growing vehicular deployment of sensors and smart devices have demanded alternative wireless communication technologies. Despite the prevalent works on radio-frequency (RF)-based vehicular communication technologies, visible-light communication (VLC) is envisaged to be a promising candidate due to its unlicensed spectrum and high transmission rates. However, the long-distance and high-speed transmission performance of vehicular VLC needs more investigation considering the massive data transmission needs for automotive applications. In this article, a vehicular multiple-input–multiple-output (MIMO) VLC system based on two commercial headlights and a self-designed PIN array is experimentally demonstrated as a proof of concept for the IoV. Considering the relative movement of vehicles, different communication areas are divided based on the position-dependent receiver receiving states. The boundary condition of each area is derived. For the first time, the selection of the strategy that best suits the MIMO demultiplexing scheme is discussed by analyzing the rank and type of the channel matrix. A modified pilot-aided phase recovery method based on polynomial curve fitting (PCF) is proposed to compensate for the phase noise caused by the sampling frequency offset (SFO). The proposed method maintains good robustness even when the VLC system suffers from the strong nonlinearity and bandwidth limitation of the headlights. Based on the proposed MIMO VLC system, we achieve a record-breaking data rate of 3.08 Gb/s at a 2-m indoor transmission link. We further extend the transmission distance to 100 m, and successfully achieve overall data rates of 336 and 362 Mb/s during the daytime and nighttime, respectively. To the best of our knowledge, these are the highest transmission data rates ever reported for a 100-m vehicular VLC system. Our experimental demonstration clearly verifies the feasibility of VLC in the application of IoV.

Performance metrics for vehicular visible light communication systems

Vehicular Visible Light communication (VVLC) presents a new paradigm for providing vehicle connectivity, increasing road safety, and achieving autonomous driving. It can be chosen as an alternative solution to radio frequency-based inter-vehicle communication systems and/or as a complementary solution to ensure redundancy. Nevertheless, there are still significant challenges in incorporating visible light communication systems into vehicular networks. The main purpose of this paper is to provide an outline of the performance metrics of a VVLC system. Furthermore, the study is performed based on a vehicle-to-vehicle dynamic model close to reality, considering the effect of geometrical changes in the LOS path and the variation of the inter-vehicular distance. The analysis of the proposed system is discussed in terms of Signal to noise (SNR), Field of view (FOV), mobility, and average capacity.

Comparison of PD-NOMA for RF and VLC Based Vehicular Communication Under Various Weather Conditions

In order to provide vehicles with reliable, ubiquitous, and massive connectivity, an appropriate multiple access (MA) scheme should be adopted. An appealing MA scheme referred to as non-orthogonal multiple access (NOMA) has been gaining significant attention in vehicular networks among academia and industry. This work aims to show the technical feasibility of uplink vehicular-VLC system (V-VLC) using OPD-NOMA, which is a promising technique for future intelligent transportation system which has not been explored before. We aim to present a comprehensive qualitative and quantitative analysis on the performance of Optical Power Domain-NOMA (OPD-NOMA) based Vehicular Visible Light Communication (V-VLC) systems. In particular, we aim for designing V-VLC systems with robust information exchange over various weather conditions such as rain, light fog, dense fog, dry snow, etc. We make use of various analytical tools of stochastic geometry to derive theoretical expression for outage probability and throughput by modelling the location of the vehicle as a spatial Poisson point process. We compare the performance of OPD-NOMA based V-VLC with Vehicular Radio Frequency (V-RF) communication for three different traffic scenarios (i.e., sparse, medium, and dense traffic) in terms of outage probability and throughput. Our numerical results reveal that instead of viewing V-VLC as competing technology, it can be visualized as complementary technology to V-RF technology under different environmental conditions for future Intelligent Transportation System (ITS) to meet diverse requirements of 5G networks and beyond.

Statistical channel modelling of dynamic vehicular visible light communication system

This paper studies a statistical channel model for dynamic vehicular visible light communication systems. The proposed model considers the effect of variation in inter-vehicular spacing and the geometrical changes on path loss of the channel. The study also considers different weather conditions and vehicle mobility based on a realistic traffic flow model that considers traffic density during different times of the day. Monte Carlo simulation is used to examine the obtained statistical model for different transmission scenarios. In addition, the Kolmogorov-Smirnov test for the statistical model and Monte Carlo simulation has been performed to verify that they represent the same distribution. The results show that the channel statistical distribution varies with the traffic flow and inter-vehicular spacing, which changes at different times of the day. The results also show that the path loss values of the non-line-of-sight component are significantly larger than the path loss values of the line-of-sight component of the channel when a single reflector is considered. However, at rush hours, when inter-vehicle spacing becomes shorter, the path loss value of multiple reflections decreases significantly.

Visible Light Communication for Connected Vehicles: How to Achieve the Omnidirectional Coverage?

Visible light communication (VLC) is based on the idea of modulating the light intensity of LEDs to transmit information and enables the dual use of exterior automotive and road side infrastructure lighting for both illumination and communication purposes. To position VLC as a strong candidate for vehicular connectivity, it is essential to realize multi-directional reception in various deployment scenarios supporting both vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (I2V) links. In this paper, we investigate the performance of a vehicular VLC system in different road types (i.e., multi-lane, curved roads), intersections (i.e., T-shaped, Y-shaped intersections) and traffic scenarios (i.e., cruising in the same or different lanes, lane change etc.). We conduct a channel modeling study based on non-sequential ray tracing to quantify the capability of receiving signals in different cases. Our results reveal that deployment of nine photodetectors with carefully determined locations on the vehicle is enough to create the required quasi-omni-directional coverage for both V2V connectivity (in front and back directions) and I2V connectivity.

Channel Modelling and Performance Limits of Vehicular Visible Light Communication Systems

Visible light communication (VLC) has been proposed as an alternative or complementary technology to radio frequency vehicular communications. Front and back vehicle lights can serve as wireless transmitters making VLC a natural vehicular connectivity solution. In this paper, we evaluate the performance limits of vehicular VLC systems. First, we use non-sequential ray tracing to obtain the channel impulse responses (CIRs) for vehicle-to-vehicle (V2V) link in various weather conditions. Based on these CIRs, we present a closed-form path loss expression which builds upon the summation of geometrical loss and attenuation loss and takes into account asymmetrical patterns of vehicle light sources and geometry of V2V transmission. The proposed expression is an explicit function of link distance, lateral shift between two vehicles, weather type (quantified by the extinction coefficient), transmitter beam divergence angle and receiver aperture diameter. Then, we utilize this expression to determine the maximum achievable link distance of V2V systems for clear, rainy and foggy weather conditions while ensuring a targeted bit error rate.

Detection Algorithm for Overlapping LEDs in Vehicular Visible Light Communication System

In a vehicular visible light communication system, the visible light signals are obtained from a series of image frames showing LEDs as a transmitter which are captured by a high-speed camera as a receiver. However, when two LEDs overlap in the captured image, some serious problems related to data transmission arise, such as high data loss and bit-error-rate. To resolve these problems, in this paper, a method comprising three main steps for separating the overlapping LEDs is proposed. First, according to LED luminance, the edges of the LEDs are detected by applying an improved Canny edge detector algorithm. Then these edges are used to extract all the contours of the two overlapping LEDs. Finally, a derivative of the generalized Hough transform algorithm is utilized to distinguish each LED from the overlapping region according to the obtained LED contours. The performance of the proposed algorithm under different parametric conditions in real situations is analyzed according to the results of experiments conducted in an outdoor environment.

Demonstration of vehicular visible light communication based on LED headlamp

Recently, the IT convergence technology using LED such as Visible Light Communication (VLC) is being emerged. Among many VLC applications, vehicular vehicle-to-vehicle (V2V) VLC based on LED headlamp is possible to use in Intelligent Transportation Systems (ITS) or Active Safety application. In this paper, we introduce the demonstration of vehicular VLC system based on LED headlamp. Based on inverse 4-PPM scheme with 75% dimming and prototype LED headlamp, our system shows a potential for V2V VLC with 10kbps data rate in about 20m distance at day time scenario.