Characterization of Field of View in Visible Light Communication Systems for Intelligent Transportation Systems

Abstract

This paper reports a detailed experimental characterization of non Line-of-Sight (LoS) optical performances of a Visible Light Communication (VLC) system using a real traffic light for ultra-low latency, infrastructure-to-vehicle (I2V) communications for intelligent transportation systems (ITS) protocols. Despite the implementation of long-sought ITS protocols poses the crucial need to detail how the features of optical stages influence the overall performances of a VLC system in realistic configurations, such characterization has rarely been addressed at present. We carried out an experimental investigation in a realistic configuration where a regular traffic light (TX), enabled for VLC transmission, sends digital information towards a receiving stage (RX), composed by an optical condenser and a dedicated amplified photodiode stage. We performed a detailed measurements campaign of VLC performances encompassing a broad set of optical condensers, and for TX-RX distances in the range 3-50 m, in terms of both effective Field of View (EFOV) and Packet Error Rate (PER). The results show several angle-dependent nontrivial behaviors for different lens sets as a function of position on the measurement grid, highlighting critical aspects for ITS applications as well as identifying most suitable optical configurations depending on the specific application and on the required EFOV. We also provide a theoretical model for both the signal intensity and the EFOV as a function of several parameters, such as distance, RX orientation and focal length of the specific condenser. To our best knowledge, there are no optical and EFOV experimental analyses for VLC systems in ITS applications in literature. Our results could be very relevant in the near future to assess a most suited solution in terms of acceptance angle when designing a VLC system for real applications, where angle-dependent misalignment effects play a non-negligible role, and we argue that they could have more general implications with respect to the pristine I2V case mentioned here.

Evaluation of Misalignment Effect in Vehicle-to-Vehicle Visible Light Communications: Experimental Demonstration of a 75 Meters Link

“…It should be also mentioned that when the VLC receiver uses a rather narrow band-pass optical filter centered on the red wavelength, the effect of sunlight is significantly mitigated, which in turn generates a lower BER compared to a standard day scenario. A similar situation has been found in [ 22 ]. In this case, the experimental results also showed that the influence of the fluorescent lights is higher than the one of natural light.…”

“…In comparison, the V2V VLC system evaluated in [ 36 ], provided a communication distance of less than 20 m, whereas the system from [ 44 ] can deliver ranges up to 45 m. It should be pointed out here that the current research focused on automotive VLC systems is mainly orientated toward traffic Infrastructure-to-Vehicle (I2V) connections, as the VLC emitters developed based on transportation infrastructure elements (i.e., traffic lights, street lighting systems) have a significantly higher optical power, enabling longer communication distances. Even so, there are only few works [ 30 , 31 ] that report I2V-related VLC results with communication ranges above 75 m, whereas most of the existing systems provide communication distances of up to 50 m [ 21 , 22 , 23 , 24 , 26 , 27 , 28 , 29 ]. In this context, the 75 m communication range reported in this work provides important evidence that, step by step, the performances of automotive VLC systems are improving.…”

“…In this case, an adaptable FOV can be used [ 41 ]. In [ 22 ], it has been demonstrated that the VLC receiver reception angle can be increased with the help of a proper optical lens. All these works prove that the research community is able to come up with solutions that will enable the use of the VLC technology in communication-based vehicle safety applications.…”

“…Unlike most of the existing works on this technology, the present article addresses two of the most unfavorable use cases. First, instead of investigating the usage of a rather high power optical source, like a traffic light [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] or a vehicle headlamp system [ 32 ], this work investigates the capabilities of a VLC system based on LED rear lamps; this approach involves a significantly lower optical power. Secondly, this article also explores the effect of vehicle misalignment on the performances of a V2V VLC link.…”

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

“…As seen from Table 2, most of the I2V works [32]- [38] assume a single PD. Some of these [32], [35], [36] assume PD location at the front hood of the vehicle which is typically favorable for reception from traffic light while some [34], [37], [38] consider the top of the vehicle which is more suitable for reception from street lights. Such a single PD use can be justified in a single lane road with clear line-of-sight between the vehicle and the road side infrastructure.…”