# Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise

Elizabeth Eso, Zabih Ghassemlooy, Stanislav Zvanovec, Juna Sathian, Asghar Gholami

► To cite this version:

Elizabeth Eso, Zabih Ghassemlooy, Stanislav Zvanovec, Juna Sathian, Asghar Gholami. Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise. IEEE Transactions on Vehicular Technology, 2021, 70 (6), pp.5932-5943. 10.1109/TVT.2021.3078576. hal-03341355

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Submitted on 10 Sep 2021

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# Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise

Elizabeth Eso Member, IEEE, Zabih Ghassemlooy Senior Member, IEEE, Stanislav Zvanovec, Senior Member
IEEE, Juna Sathian and Asghar Gholami

**Abstract**— Intelligent transport systems (ITS) rely upon the connectivity, cooperation and automation of vehicles aimed at the improvement of safety and efficiency of the transport system. Connectivity, which is a key component for the practical implementation of vehicular light communications (VeLC) systems in ITS, must be carefully studied prior to design and implementation. In this paper, we carry out a performance evaluation study on the use of different vehicle taillights (TLs) as the transmitters in a VeLC system. We show that, the transmission coverage field of view and the link span depend on TLs illumination patterns and the transmit power levels, respectively, which fail to meet the typical communication distances in vehicular environments. This paper proposes an infrared-based VeLC system to meet the transmission range in daytimes under Sunlight noise. We show that, at the forward error correction bit error rate limit of 3.8 × 10⁻³, the communication distances of the proposed link are 63, 72, and > 89 m compared with 4.5, 5.4 and 6.3 m for BMW's vehicle TL at data rates of 10, 6, and 2 Mbps, respectively.

***Index Terms***—vehicular visible light communications, fundamental analysis, intelligent transport systems, infrared, sunlight noise

## I. INTRODUCTION

The wireless exchange of traffic information between the vehicles and roadside infrastructure, which is part of the emerging intelligent transport systems (ITS), can significantly enhance the road safety and the efficiency of transportation networks [1]. ITS involves the provision of safe driving information, which include warning messages on the road terrains, pedestrian crossing the road, driving speed limits, etc. Presently, the radio frequency (RF) wireless communications technology is the established option in ITS, which is best known as the dedicated short-range communications (DSRC). DSRC

supports several applications such as emergency braking warning and intersection collision warnings. However, some doubts still exist on the capability of DSRC in meeting the low latency and high reliability requirements in ITS considering both the network outages and security issues [2]. Consequently, considering the aforementioned issues, optical wireless communications (OWC) have emerged as an attractive and complementary technology in vehicular communications. It is interesting to note that, the OWC technology employing light emitting diodes (LEDs) gives rise to a smaller collision domain, which results in reduced packet losses due to interference, compared with the RF wireless systems [2]. Furthermore, the directionality of OWC increases the security of the communication networks, thus reducing the possibility of eavesdropping drastically.

The expanding multi-media-based services is the main driving force of the fifth generation (5G) and the emerging sixth generation (6G) and beyond wireless networks, which will be based on multiple technologies to ensure high quality of services [3-4]. OWC is envisaged to be part of 5G/6G and beyond wireless networks for use in application areas where RF-based technologies cannot be used due to insufficient bandwidth and other issues such as security, susceptibility to electromagnetic interference, etc. Several novel concepts on the use of OWC in 6G have been reported in [5], including (i) hybrid radio-optical wireless networks, where wireless nodes or devices are equipped with both RF and optical interfaces; and (ii) through-the-tissue optical communications, where very short ranges are considered to provide a highly secure link for intra-body and to/from body transmission. Note, the unique features of OWC that makes it an attractive technology for 5G/6G includes a large unlicensed spectrum, high security, high safety, lower power consumption, simplicity in

Copyright (c) 2015 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to pubs-permissions@ieee.org.

Elizabeth Eso acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no.764461 (VISION). Zabih Ghassemlooy acknowledges the Engineering and Physical Sciences Research Council grant EP/P006280/1: MARVEL and the EU COST Action Newfocus on optical wireless communications (CA19111). Juna Sathian acknowledges the Royal Society International Exchange Grant IES\R3\203061 and Stanislav Zvanovec acknowledges the Czech Science Foundation Project GACR 17-17538S.

Elizabeth Eso, Zabih Ghassemlooy and Juna Sathian are with the Optical Communication Research Group, Faculty of Engineering and Environment, Northumbria University, UK, email: {elizabeth.eso, z.ghassemlooy, juna.sathian}@northumbria.ac.uk,

Stanislav Zvanovec is with the Department of Electromagnetic Field, Faculty of Electrical Engineering, Czech Technical University, Prague, Czech Republic email: xzvanove@fel.cvut.cz.

Asghar Gholami is with the Department of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran email: gholami@cc.iut.ac.ir
implementation, low costs, and not susceptible to RF-induced
interference. Consequently, the coexistence of the OWC and
RF technologies can efficiently solve most of the limitations of
the individual RF and OWC links [6]. With the ever-increasing
demand for internet of things, 5G is not guaranteed to meet up
all the requirements of new services in the future [3], hence a
hybrid/heterogenous system i.e., OWC with RF, enables 5G to
be used in areas where RF cannot be utilised.

A growing number of research works on visible vehicular
light communications (V-VeLC) have been reported in the
literature. In [7], an analytical model for the bit error rate (BER)
performance as a function of the communication distance for
V-VeLC under different communication geometries and using
a headlight (HL) beam pattern model was reported. It was
shown that, (i) there were sharp degradations in the BER
performance distribution to the left-hand side in the vertical
plane, which is due to the asymmetric beam pattern of the low
beam HL; and (ii) an increase in the achievable transmission
link span provided the optical receiver's (Rx's) i.e., the
photodiode (PD) and HLs heights were about 0-0.2 and 0.66 m,
respectively. In [8], a comprehensive channel modelling to
evaluate the performance of V-VeLC employing the high beam
HL as the transmitter (Tx) under the weather conditions (rain
and fog) was carried out. Using advanced ray tracing a path loss
model in terms of transmission range was developed, showing
the link span dropping from 72 to 26 m in the presence of heavy
fog at a target BER of 10⁻⁶. A 2x2 multiple-input multiple-
output channel under Sunlight using a market-weighted HL
pattern source as the Tx was studied in [9]. It was shown that,
direct current biased optical orthogonal frequency division
multiplexing (DCO-OFDM) offered higher data rates compared
with the asymmetrically clipped optical OFDM (ACO-OFDM).
with lower BER performance.

It is important to note that, most works reported on V-VeLC
including the aforementioned references have considered high-
or low-beam HLs, which are usually on during the night or
under reduced visibility conditions (i.e., rain or fog). For the
HLs, the transmit power P<sub>T</sub> levels during daytime are relatively
very low compared with the high- and low-beam lights used for
road illumination. In [10], an extensive optical radiation pattern
measurement of a single HL and TL was carried out. Several
vehicle mobility traces with two-dimensional locations were
also collected. Both data were combined to perform analytical
study and to further obtain experimental distributions of the
received power for HL- and TL-based Txs. Consequently, the
issue of link asymmetry due to the significant differences in the
radiation characteristics and P<sub>T</sub> between the HL and the TL was
identified. It was shown that, in 80% of the cases the received
power for the link using the HL was at least 22 dB more than
that of the TL-based Tx. To address the link asymmetry
problem in V-VeLC systems, the paper proposed that a new
system (or a protocol) design needs to be developed to improve
the data throughput. In [11], the impact of vehicles' HL and TL
illumination patterns on the communications performance
between vehicles travelling on the same- and different- lanes
was studied by developing a novel V-VeLC simulation model
based on accurate empirical data measurements. Performance
evaluation of V-VeLC was carried out based on the developed

model, where the impact of the angle of incidence was analyzed
based on the received signal strength, signal to noise ratio
(SNR), and packet delivery ratio metrics. The authors reported
that, using the TL, communications with vehicles on the
adjacent lanes were possible only over a transmission range up
to 10 m. From the foregoing, it is apparent that a robust Tx
design is needed, which meets the requirements of the vehicular
environment in terms of the communications range and the
coverage area.

Some studies reported on infrared vehicular light
communications (IR-VeLC) are also discussed as follows; In
[12], a secure light communications protocol known as
SecVLC, which is a cryptographic key generation/management
system, using the infrared (IR) and visible lights for link's
security and data communications, respectively was proposed.
In [13], a prototype vehicular light communications (VeLC)
system with the IR-VeLC Tx mounted on the roof of a vehicle
was reported with the focus being on the communications
protocol for relaying transmitted data between vehicles. In [14],
a RF and IR vehicle to vehicle communications system
prototype for sending warning signals was demonstrated.
However, none of the above works considered and analyzed the
use of IR transmission for improving the link's robustness to
the noise or increasing the communications transmission range
considering realistic intervehicle distances.

Note that, in V-VeLC system the Sunlight induced noise is
the major problem during the daytime, where the illumination
level can be as much as 10 mW/cm² compared with uW/cm² for
the intensity-modulated HL and TL [15]. This high-level of
ambient light can lead to the saturated optical Rx. Note that,
most works reported on V-VeLC have not considered the effect
of Sunlight noise. Among the few reports that have considered
the impact of Sunlight noise includes [16], where the impact of
solar irradiance on VLC systems was investigated in terms of
the BER, SNR degradation, and data rates. Results showed that,
using an optical bandpass blue filter the link performance
greatly improved over a short transmission span of up to 3 m.
In [17] the effects of Sunlight irradiance and other external light
sources on V-VeLC systems were investigated with regards to
BER, data rates, and SNR over different months of the year,
with and without an optical blue filter. Results obtained
demonstrated a significant performance improvement in the
achievable data rates and the average BER, e.g., in the month
of January the average BER improved from 2×10⁻³ to ~3×10⁻⁵
using an optical blue filter. In addition, different noise
cancellation methods such as wavelet-based signal processing
and differential Rx-based hardware were proposed. However,
due to the complexity of the processing, no real-time denoising
has been demonstrated successful yet [9]. In [9], the effect of
Sunlight noise on the performance of V-VeLC at a low speed
of 30 km/h was considered. Note that, the effect of Sunlight
noise becomes more significant as the link span increases,
considering that the received power levels decrease with the
increasing transmission distance. Moreover, to increase the
transmission distance in V-VeLC, the use of converging lenses
has been widely adopted. However, the higher the focal length
f of the lenses used at the Rx the lower the angular field of view
(AFOV) of the Rx, thereby reducing vehicle's maneuverability.
Consequently, in this work we have considered practical VeLC
channel, Tx, PD, lenses, and filter parameters. In addition, we have carried out BER performance analysis by considering a wide range of vehicle speeds and the Sunlight induced background noise (obtained from solar irradiance measurements carried out in the city of Newcastle (N 54°59'44'' W 1°39'52'')).

It is noteworthy that, most works reported on V-VeLC are based on using a single light module, which may narrow down the conclusions drawn from the results. Therefore, in this work we characterize four TLs from different vehicles by measuring their radiation patterns and $P_T$. We also perform a link power budget analysis to determine the feasibility of V-VeLC using these TLs as the Txs for a range of TL irradiance angles with respect to the vehicle's speeds.

The main contributions of this work are:

* We present a channel model for VeLC where the Tx's specific radiant intensity model can be incorporated other than Lambertian radiant intensity model.

* We provide insights on the required horizontal and vertical AFOVs of the Rx for VeLC for the first time to the authors best knowledge.

* We show AFOV obtainable based on varying the PD sizes with varying $f$ of lens and provide insights on the Tx's coverage diameter.

* We carry out optical characterization and performance evaluation of different vehicle TLs as Txs for VeLC systems.

* We propose a novel robust IR-VeLC system considering practical and realistic parameters.

* We carry out performance analysis of the proposed IR-VeLC with realistic Sunlight noise from empirical measurements.

The rest of the paper is organized as follows. In Section II the VeLC system is described while the configuration analysis is presented in Section III. Performance evaluation of V-VeLC system using TLs as Txs is given in Section IV. Section V describes the noise and BER analysis. The performance analysis of the proposed novel IR-VeLC is presented in Section VI. Finally, conclusions are given in Section VII.

## II. THE VELC SYSTEM

Figure 1(a)-(c) shows the composition of a typical VeLC system, which consists of the TL-based Tx (Vehicle 1) and the PD-based Rx (Vehicle 2). Note, for illustration purposes only a single TL is used. Including the second TL will have almost the same geometrical configuration, which results in the increased SNR at the Rx. Note, the Tx's positions with respect to the Rx and their beam profiles as well as the Rx's AFOV are very crucial in VeLC and will affect the link performance. For the

line of sight (LOS) VeLC (Fig. 1(a)-(c)), the channel DC gain, which is the ratio of the received signal power at the Rx to the transmit power, can be expressed as:

$$H_{\text{LOS}} = \begin{cases} \frac{A_{\text{PD}} T_s(\varphi_{\text{hor}}, \varphi_{\text{ver}}) g(\varphi_{\text{hor}}, \varphi_{\text{ver}}) R_{\text{Tx}}(\theta_{\text{hor}}, \theta_{\text{ver}})}{L_s^2}, & 0 \le \varphi_{\text{hor}} \le \emptyset_{\text{hor}} \text{ and } 0 \le \varphi_{\text{ver}} \le \emptyset_{\text{ver}} \\ 0, & \varphi_{\text{hor}} > \emptyset_{\text{hor}} \text{ or } \varphi_{\text{ver}} > \emptyset_{\text{ver}} \end{cases}, \quad (1)$$

where $A_{\text{PD}}$ is the active area of the PD, $\varphi_{\text{hor}}$ and $\varphi_{\text{ver}}$ are the horizontal and vertical incidence angles, respectively, $R_{\text{Tx}}(\theta_{\text{hor}}, \theta_{\text{ver}})$ is the radiation pattern (normalized beam profile) of the Tx at horizontal and vertical irradiance angles $\theta_{\text{hor}}$ and $\theta_{\text{ver}}$, respectively, $\emptyset_{\text{hor}}$ and $\emptyset_{\text{ver}}$ denotes the horizontal and vertical AFOV semi angle of the Rx, $L_s$ represents the link span, $T_s(\varphi_{\text{hor}}, \varphi_{\text{ver}})$ and $g(\varphi_{\text{hor}}, \varphi_{\text{ver}})$ are the gains of the optical filter (OF) and optical concentrator (OC), respectively. Note that, using (1) the Tx's specific radiation pattern can be incorporated, which may not be symmetrical as in Lambertian radiant intensity model. The gain of a non-imaging OC (NIOC) can be expressed as $A_{\text{coll}}/A_{\text{PD}}$ [18], where $A_{\text{coll}}$ is the collection area of the NIOC.

Figure 2 shows the system composition of an IR-VeLC system using an array of IR-LED as the light source at the Tx side. The OOK data stream is used for the intensity modulation of the Tx for transmission over the free space channel. At the Rx side, an OC, a narrow band optical band-pass filter (i.e., 810 - 890 nm) and an optical Rx are used to the regenerated electrical signal. For the LOS link, the received signal is given by [19]:

$$y(t) = \mathcal{R}x(t) \otimes h(t) + n(t), \quad (2)$$

where $\mathcal{R}$ is the responsivity of the PD, $x(t)$ is the modulated light signal at the Tx, $h(t)$ is the channel impulse response while $n(t)$ denotes the additive white Gaussian noise including the Sunlight induced shot noise, which is the dominant noise source in VeLC during the daytime, the signal and dark current related shot noise sources and the thermal noise.

## III. VELC CONFIGURATION ANALYSIS

### A. Analysis of horizontal/vertical semi-AFOV for VeLC with imaging OC (IOC)

Using a convergent lens (i.e., IOC) at the Rx, as in a camera, an image of the Tx is captured on the PD-based sensor provided the Tx is within the Rx's AFOV. Note that, NIOCs do not produce an image of the Tx as do IOCs. First, we analyse the required horizontal semi-AFOVs (HS-AFOVs) for the Rxs 1 and 2 based on the worst-case scenario, where vehicles are located at the other sides of the lane, see Fig. 3. Note that, for the Rxs 1 and 2 to capture a single Tx and or two Txs the required HS-AFOV are $\varphi_{12}, \varphi_{22}, \varphi_{11}, \varphi_{21}$, respectively.
<figure><img src="image_2.png" /><figcaption>Fig. 1: VeLC configuration: (a) side view, (b) top view for perfect alignment scenario, and (c) top view with horizontal Tx and Rx misalignment (offset)</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>Fig. 2: The schematic system block diagram of an IR-VeLC system</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 3: VeLC configuration showing required horizontal AFOV</figcaption></figure>

To obtain the required HS-AFOV between two vehicles travelling on the same lane, therefore we need to consider both the lane and vehicles' widths as well as the positions of the Rx and the Tx. Consequently, the required HS-AFOV for the Rx can be expressed as in (3)-(6) where $w_{RL}$ is the width of the road lane, $L_{s-hor}$ denotes the horizontal distance between the Tx and the Rx, $w_{Tx}$, and $w_{Rx}$, are the spacing between the Txs and the Rxs and, $w_{v-Tx}$ and $w_{v-Rx}$ are width of the vehicles,

respectively and $l_{Tx}$ denotes the length of the Txs (see Figs. 1 and 3). Note that, for the cases where one of the vehicles may move outside the lane, we replace $w_{RL}$ by $w_{RL} + x$ in (3)-(6), where $x$ represents the deviation from the edge of the lane. Furthermore, (3)-(6) could be applied to vehicles on different lanes where $w_{RL}$ becomes $2w_{RL}$ or $3w_{RL}$ for scenarios with one of the vehicles being on the next or the next two lanes, respectively.

$$ \varphi_{12} = \arctan \left( \frac{w_{RL} - \left( \frac{w_{v-Tx} - w_{Tx}}{2} \right) - \left( w_{Tx} - \frac{l_{Tx}}{2} \right) - \left( \frac{w_{v-Rx} - w_{Rx}}{2} \right) - w_{Rx}}{L_{s-hor}} \right), \quad (3) $$

$$ \varphi_{22} = \arctan \left( \frac{w_{RL} - \left( \frac{w_{v-Tx} - w_{Tx}}{2} \right) - \left( w_{Tx} - \frac{l_{Tx}}{2} \right) - \left( \frac{w_{v-Rx} - w_{Rx}}{2} \right)}{L_{s-hor}} \right), \quad (4) $$

$$ \varphi_{11} = \arctan \left( \frac{w_{RL} - \left( \frac{w_{v-Tx} - w_{Tx}}{2} \right) + \frac{l_{Tx}}{2} - \left( \frac{w_{v-Rx} - w_{Rx}}{2} \right) - w_{Rx}}{L_{s-hor}} \right), \quad (5) $$

$$ \varphi_{21} = \arctan \left( \frac{w_{RL} - \left( \frac{w_{v-Tx} - w_{Tx}}{2} \right) + \frac{l_{Tx}}{2} - \left( \frac{w_{v-Rx} - w_{Rx}}{2} \right)}{L_{s-hor}} \right). \quad (6) $$
The required vertical semi-AFOV (VS-AFOV) for the case shown in Fig. 1(a) is given as:

$$ \varphi_{\text{ver}} = \arctan\left(\frac{\Delta H}{L_{\text{s-hor}}}\right), \qquad (7) $$

where the offset between the Tx's and the Rx's vertical heights is $\Delta H = |H_{\text{Tx}} - H_{\text{Rx}}|$. The required HS-AFOV and VS-AFOV as a function of the link span for VeLC are depicted in Fig. 4, which is generated using (3)-(7) and the parameters given in Table I. From Fig. 4 it can be observed that, HS-AFOV exponentially drops with the link span. For example, for the Rx2 the required HS-AFOV increases by ~5 times as the link span decreased from 10 to 2 m. For the Rx1, the required HS-AFOV is lesser than the Rx2 due to it being closer to the TxS. Moreover, for VS-AFOV an exponential profile is also displayed with higher values for larger $\Delta H$ below the link span of 20 m.

<table><caption>TABLE I
KEY GEOMETRY PARAMETERS AND SIMULATION VALUES</caption><thead><tr><th>Parameter</th><th>Symbol</th><th>Value</th></tr></thead><tbody><tr><td>Lane width</td><td>w<sub>RL</sub></td><td>2.5 m</td></tr><tr><td>Width of Tx vehicle</td><td>w<sub>v-Tx</sub></td><td>1.7 m</td></tr><tr><td>Width of Rx vehicle</td><td>w<sub>v-Rx</sub></td><td>1.7 m</td></tr><tr><td>Distance between Rx1 &amp; Rx2</td><td>w<sub>Rx</sub></td><td>1.2 m</td></tr><tr><td>Distance between Tx1 &amp; Tx2</td><td>w<sub>Tx</sub></td><td>1.2 m</td></tr><tr><td>Length of Txs</td><td>l<sub>Tx</sub></td><td>0.1 m</td></tr><tr><td>Horizontal link span</td><td>L<sub>s-hor</sub></td><td>1-50 m</td></tr><tr><td>Vertical Tx and Rx offset</td><td>ΔH</td><td>0.25-0.75 m</td></tr><tr><td>Lens focal lengths</td><td>f</td><td>25.4-50.0 mm</td></tr><tr><td>PD's surface area</td><td>A<sub>PD</sub></td><td>0.2 ~ 2cm<sup>2</sup></td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>Fig. 4. The required HS-AFOV and VS-AFOV of Rx versus the $L_{s-hor}$ for two vehicles on the same lane</figcaption></figure>

Note that, increasing the vertical offset between the Tx and the Rx outside the vertical AFOV of the Rx will lead to increasing the vertical AFOV in order to capture the Tx while the horizontal AFOV requires no adjustment and vice versa.

## B. Semi-AFOV based on PD's size and the lens focal length

Using a convergent lens (i.e., IOC) to focus light onto the PD to increase the received optical power density results in reduced Rx's semi-AFOV, which needs investigating in terms of the PD's size and the f of lens, to meet the required semi-AFOV in vehicular communications, see Fig. 5. The semi-AFOV in terms of f and the PD's dimensions $D_{PD}$ can be expressed as:

$$ \emptyset_{\text{s-AFOV}} = \arctan\left(\frac{D_{\text{PD}}}{2f}\right), \qquad (8) $$

$$ \emptyset_{\text{s-AFOV}} = \begin{cases} \emptyset_{\text{hor}}, & D_{\text{PD}} = w_{\text{PD}}, \\ \emptyset_{\text{ver}}, & D_{\text{PD}} = h_{\text{PD}}, \\ \emptyset_{\text{diag}}, & D_{\text{PD}} = \sqrt{h_{\text{PD}}^2 + w_{\text{PD}}^2}, \end{cases} \qquad (9) $$

where $h_{\text{PD}}$ and $w_{\text{PD}}$ denotes the height and width of the PD and $\emptyset_{\text{hor}}$, $\emptyset_{\text{ver}}$ and $\emptyset_{\text{diag}}$ is the horizontal, vertical and diagonal semi-AFOVs of the Rx, respectively.

Fig. 5 shows $\emptyset_{\text{hor}}$ or $\emptyset_{\text{ver}}$ as a function of the PD's surface area (where $w_{\text{PD}} = h_{\text{PD}}$) for a range of f. It can be seen that, using a convergent lens at the PD, $\emptyset_{\text{hor}}$ or $\emptyset_{\text{ver}}$ decreases with f and increases (logarithmic) with the PD's surface area.

<figure><img src="image_6.png" /><figcaption>Fig. 5: Relationship between f, semi-AFOV and the PD size</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 6: $\emptyset_{\text{hor}}$ or $\emptyset_{\text{ver}}$ versus PD surface area for a range of f</figcaption></figure>
### C. Analysis of Tx's field of view (coverage profile)

Figure 7 illustrates the Tx's beam coverage profile whereby $L_1$ depicts the horizontal distance from the Tx's to the start of the overlapping light area between Tx's 1 and 2, which can be expressed as:

$$L_1 = w_{Tx}/(\tan\theta_{1/2-in} + \tan\theta_{1/2-out}), \quad (10)$$

where $\theta_{1/2-in}$ and $\theta_{1/2-out}$ are inner and outer half power angles of the Tx's beam, respectively, see Fig. 7. Note that, $\theta_{1/2-in}$ and $\theta_{1/2-out}$ of each Tx is the angle between the peak and the point on one side of the beam axis (left or right) where the received power is half the maximum. $L_2$ is the beam length of a single Tx and $L_{FOV}$ is the coverage length of both Tx's beyond $L_1$, which can be expressed as:

$$L_2 = L_{s-hor} (\tan\theta_{1/2-in} + \tan\theta_{1/2-out}), \quad (11)$$

$$L_{FOV} = w_{Tx} + L_{s-hor} (\tan\theta_{1/2-in} + \tan\theta_{1/2-out}). \quad (12)$$

<figure><img src="image_8.png" /><figcaption>Fig. 7: Tx field of view (coverage diameter)</figcaption></figure>

Note that, depending on $\theta_{1/2-in}$ and $\theta_{1/2-out}$ the light beams from Tx's 1 and 2 may not overlap, therefore the coverage length is $2L_2 = 2L_{s-hor} (\tan\theta_{1/2-in} + \tan\theta_{1/2-out})$. Using (12), the half power angle (assuming $\theta_{1/2-in} = \theta_{1/2-out}$) versus the FOV for a range of link spans is depicted in Fig. 8, which shows a logarithmic increase of the Tx's half power angle with $L_{FOV}$ reaching saturation points at ~220 and ~370 m for $L_{s-hor}$ of 30 and 50 m, respectively. Note, the Tx's half angle decreases with the increasing link span.

<figure><img src="image_9.png" /><figcaption>Fig. 8: Half power angle of Tx versus $L_{FOV}$ for a range of $L_{s-hor}$</figcaption></figure>

## IV. PERFORMANCE EVALUATION OF V-VELC WITH TLS-BASED TXS

Comprehensive performance analysis of the use of HLs with the given real beam patterns of different vehicle brands for data transmission was reported in [7]. The results showed that, the received power level increased with the decreasing Rx's heights from the ground due to the HLs being designed for road illumination points down-ward on the road surface as illustrated in Fig. 9. Consequently, this imposes the upper bound on the

<figure><img src="image_10.png" /><figcaption>Fig. 9: V-VelC links using HLs as the Tx's</figcaption></figure>
maximum transmission link span due to the angular inclination of the light rays on the road surface and its asymmetrical beam pattern. Most works reported on the use of TLs as Txs, are based on investigating the use of a single TL, which only outlines half the story, therefore, narrowing the conclusions drawn from the results obtained for the specific vehicle type/light model. No works have been reported on V-VeLC with different TL units. Therefore, to carry out performance evaluation of V-VeLC using TLs for data transmission we characterise four LED-based vehicle TLs for different vehicle modules.

### A. Radiation patterns of the TLs

First, we need to investigate the radiation patterns of the TLs, which defines the spatial intensity distribution of the emitted light from the TLs, which is important for the analysis of signal distribution and the coverage area. For this we have used a digital optical power meter (Thorlabs PM100D with a PD power sensor S120VC) to measure the received power levels over a fixed transmission distance of 1 m for a range of irradiance angle (i.e., -90° (left) to +90° (right)) of the TLs. For comparison, we have used TLs from four popular vehicles namely: BMW F30 right side outer LED O/S TL (BMW TL), Audi A5 S5 N/S LED left outer TL facelift (Audi TL), Truck-DACA08712AM TL (Truck TL) and Nissan Qashqai right side tailgate boot lid TL 26550 4EA0A model (Nissan TL). We measured the radiation patterns for these TLs and the illuminated surface areas and estimated $P_T$, see Table II. As shown in Table II, the half power angle ($\theta_{1/2-in}$ and $\theta_{1/2-out}$) varies within the range of 10° to 75°, with the lowest and highest number for the Truck and BMW, respectively, which corresponds to the narrow and wide beam profiles as depicted in two-dimensional (2D) polar plots in Fig. 10.

<figure><img src="image_11.png" /><figcaption>Fig. 10: 2D polar plots of the normalized beam profile of TLs from empirical measurements</figcaption></figure>

<table><caption>TABLE II
TL PARAMETERS FROM EMPIRICAL MEASUREMENTS</caption><thead><tr><th>TL</th><th>θ<sub>1/2-in</sub> (°)</th><th>θ<sub>1/2-out</sub> (°)</th><th>Illuminated area (cm<sup>2</sup>)</th><th>P<sub>T</sub> (mW)</th></tr></thead><tbody><tr><td>BMW</td><td>75</td><td>65</td><td>124.7</td><td>110.5</td></tr><tr><td>Audi</td><td>55</td><td>47</td><td>46.2</td><td>39.7</td></tr><tr><td>Truck</td><td>10</td><td>10</td><td>80.0</td><td>32.4</td></tr><tr><td>Nissan</td><td>27</td><td>22</td><td>38.2</td><td>9.4</td></tr></tbody></table>

### B. Link power budget analysis

As part of the system design and implementation, we have carried out the link power budget analysis for V-VeLC using the four TLs units. For this, it is important to know the allowed inter-vehicle distances $D_v$ for safe driving. Typically, a “two seconds” rule is recommended for $D_v$, whereby a driver maintains a minimum of two seconds behind the vehicle in front under the good weather condition, which is doubled to four seconds in bad weather conditions [20] as depicted in Fig. 11.

<figure><img src="image_12.png" /><figcaption>Fig. 11: The inter-vehicle distance as a function of driving speeds using the 2 seconds driving rule</figcaption></figure>

For a given $P_T$, the receiver power is given as:

$$P_r(\text{dBm}) = P_T(\text{dBm}) + H_{\text{LOS}}(\text{dB}) - L_{\text{sm}}(\text{dB}), \quad (13)$$

where $L_{sm}$ is the link safety margin and $H_{LOS}$ is the channel DC gain for the LOS, which is given by:

$$H_{\text{LOS}}(\text{dB}) = 10\log_{10}(A_{\text{PD}}T_s(\varphi_{\text{hor}}, \varphi_{\text{ver}})g(\varphi_{\text{hor}}, \varphi_{\text{ver}})R_{\text{Tx}}(\theta_{\text{hor}}, \theta_{\text{ver}})/D_v^2), \quad (14)$$

Table III shows the key parameters used for the link power budget analysis. Figure 12 shows the received power (in dBm) per Tx against the vehicles’ speed for a range of irradiance angle [$\theta_{hor}$, $\theta_{ver}$] of [0°, 0°] to [20°, 0°] (left of the TL’s beam axis), for the case with no OC at the Rx. The figure reveals that, for the BMW TL the maximum driving speed is 6.4 mph (i.e., $D_v = 5.7$ m) for [$\theta_{hor}$, $\theta_{ver}$]= [0°, 0°] and $P_T$ of -36 dBm (i.e., for a receiver sensitivity of -36 dBm), while for Truck TL there is a sharp decrease in the achievable driving speeds from 3.6 to 1.2 mph as [$\theta_{hor}$, $\theta_{ver}$] increases from [0°, 0°] to [20°, 0°] due to its narrower radiation pattern. A summary of the attainable driving speeds and $D_v$ for TLs under study are given in Table IV. Note, these achievable speeds are far lower than the typical
<figure><img src="image_13.png" /><figcaption>Fig. 12: The horizontal irradiance angle as a function of the received power and driving speed for different TLs</figcaption></figure>

recommended vehicle's speed limits, e.g., for cars, motorcycle, vans and buses a driving speed of 30, 60, 70 and 70 mph is approved in built-up areas, single carriage ways, dual carriage ways and motorways (mph), respectively [21]. Figure 13 illustrate the predicted required $P_T$ against the driving speed for cases with and without the OC at the Rx. Note, the required $P_T$ drops by 5.3, 8.1 and 11.2 dB when a NIOC with the diameter $d$ of 25.4, 35.0 and 50.0 mm are used at the PD, respectively.

<table><caption>TABLE III
KEY PARAMETERS OF THE LINK POWER BUDGET ANALYSIS</caption><thead><tr><th>Parameter</th><th>Symbol</th><th>Value</th></tr></thead><tbody><tr><td>Link safety margin</td><td>$L_{sm}$</td><td>3 dB</td></tr><tr><td>Surface area of PD</td><td>$A_{PD}$</td><td>1.5 cm<sup>2</sup></td></tr><tr><td>TL transmit power</td><td>$P_T$</td><td>9.4-110.5 mW</td></tr><tr><td>Irradiance angle</td><td>[$\theta_{hor}, \theta_{ver}$]</td><td>[0°, 0°]-[20°, 0°]</td></tr><tr><td>Inter-vehicle distance</td><td>$D_v$</td><td>1-~90 m</td></tr><tr><td>Diameter of NIOC</td><td>$d$</td><td>25.4 mm-50.0 mm</td></tr><tr><td>Vehicle speed</td><td>$S$</td><td>~1-100 mph</td></tr><tr><td>Gain of optical filter</td><td>$T_s(\varphi_{hor}, \varphi_{ver})$</td><td>1</td></tr></tbody></table>

<table><caption>TABLE IV
SUMMARY OF ACHIEVABLE DRIVING SPEEDS AND INTER-VEHICLE DISTANCES AS [$\theta_{hor}, \theta_{ver}$] INCREASES FROM [0°, 0°] TO [20°, 0°]</caption><thead><tr><th rowspan="2">TL type</th><th colspan="2">[$\theta_{hor}, \theta_{ver}$] = [0°, 0°]</th><th colspan="2">[$\theta_{hor}, \theta_{ver}$] = [20°, 0°]</th></tr><tr><th>Speed (mph)</th><th>$D_v$ (m)</th><th>Speed (mph)</th><th>$D_v$ (m)</th></tr></thead><tbody><tr><td>BMW</td><td>6.4</td><td>5.7</td><td>6.2</td><td>5.5</td></tr><tr><td>Audi</td><td>4.0</td><td>3.6</td><td>3.7</td><td>3.3</td></tr><tr><td>Truck</td><td>3.6</td><td>3.2</td><td>1.2</td><td>1.1</td></tr><tr><td>Nissan</td><td>1.7</td><td>1.5</td><td>2.2</td><td>2.0</td></tr></tbody></table>

<figure><img src="image_14.png" /><figcaption>Fig. 13: The required transmit power versus the driving speed for the system with and without a NIOC</figcaption></figure>

V. NOISE AND BER ANALYSIS

A. Ambient noise

In VeLC, there are two main ambient light induced noise sources of (i) the streetlights (at night), advertising boards and other vehicle lights; and (ii) the background solar radiation (Sunlight), which is the dominant noise source. Note that, the solar irradiance $P_{solar}(\lambda)$ varies by the time of the day and latitude, i.e., the position of the sun. In addition, its effect on the
performance of VeLC system will depend on the direction and orientation of the Rx. The photocurrent generated at the PD due to $P_{solar}(\lambda)$ is given as:

$$I_{solar} = A_{PD}g(\varphi_{sun})\cos(\varphi_{sun})G_{PD} \int_{\lambda_1}^{\lambda_n} P_{solar}(\lambda)T_f(\lambda)\mathcal{R}(\lambda)d\lambda, \quad (15)$$

where $A_{PD}$ and $G_{PD}$ are the active area and gain of the PD, respectively, $\varphi_{sun}$ is the difference in the orientation angle between that of the measured $P_{solar}(\lambda)$ and the PD, $\lambda_1$ and $\lambda_n$ are the integration limits, i.e., the wavelength band, which are 405-690 nm and 810-890 nm for visible and IR-based systems, respectively. The gain of the OC is denoted as $g(\varphi_{sun})$, $\mathcal{R}(\lambda)$ is the responsivity of the PD and $T_f(\lambda)$ is the optical band pass filter's transmittance. Note that, the daytime background radiation-induced shot noise is the dominant noise source in VeLC, which can be expressed as [22,23]:

$$\sigma_{bgr}^2 = 2q_e I_{solar} B, \quad (16)$$

where $q_e$ is the electron charge and $B$ is the system bandwidth.

## B. Thermal and shot noise sources

Thermal noise is generated due to the random motion of charge carriers [9] and its variance is given as [23,24]:

$$\sigma_{thermal}^2 = \frac{4kT_K B}{R_L}, \quad (17)$$

where $k$ is the Boltzmann's constant, $T_K$ is the absolute temperature in Kelvin and $R_L$ is the load resistance.

Note that, the photodetection process, which is discrete in nature, results in the signal-dependent shot noise at the PD [25,26], with the variance given as [26]:

$$\sigma_{shot-rs}^2 = 2q_e \mathcal{R}(\lambda) P_r B, \quad (18)$$

where $P_r$ is the average received signal power (i.e. desired signal). In addition, the PD's dark current noise variance is given as [23]:

$$\sigma_{dk}^2 = 2q_e I_{dk} B, \quad (19)$$

where $I_{dk}$ is the dark current.

The total noise variance is then given as:

$$\sigma_T^2 = \sigma_{bgr}^2 + \sigma_{thermal}^2 + \sigma_{shot-rs}^2 + \sigma_{dk}^2. \quad (20)$$

## C. BER

In this work, we have adopted the intensity modulation direct detection scheme with OOK and a PD (Hamamatsu S6968) as the Rx. Once the relative positions of the Tx and the Rx are

ascertained, the minimum received optical power (i.e., considering a single Tx) and the noise variances of thermal noise, ambient, signal and dark current shot noises are obtained using (13), (15)-(19). Note that, the systems bandwidth is primarily determined by the low pass filter characteristics of the Rx, which is $B = R_b/2$, where $R_b$ is the data rate [24]. Consequently, for the additive white Gaussian noise channel, the SNR at the Rx is given by [19]:

$$\text{SNR} = \frac{(\mathcal{R}(\lambda)P_r)^2}{\sigma_T^2}. \quad (21)$$

Thus, the BER is then given as [19]:

$$\text{BER} = Q(\sqrt{\text{SNR}}), \quad (22)$$

where $Q(x)$ is the Q-function used for the calculation of the tail probability of the standard Gaussian distribution given by [19]:

$$Q(x) = \frac{1}{\sqrt{2\pi}} \int_x^\infty e^{-\frac{y^2}{2}} dy. \quad (23)$$

# VI. PERFORMANCE ANALYSIS OF IR-VELC

Here, we have used an array of IR-LED (Osram SFH 4715AS) with a symmetrical light pattern and no angular inclination towards the road surface for the vehicle IR-light Txs in order to meet the driving speed (i.e., typical inter-vehicle distances) requirements. First, we show the received power per Tx over driving speeds for a range of $d$ by numerical simulations using (13) and (14). Note, (i) only LOS is considered since the Tx is a symmetrical light source with no angular inclination towards the road, thus with no significant reflections from the road surface; and (ii) the transmit optical power level must meet the IEC 62471/2006 emission limits for eye safety, which specifies emission limit of 100 W/m$^2$ [27], whereas the proposed system in this work has a maximum of 5.92 W/m$^2$ (for the two front/rear Txs) at 1 m distance from the Txs. The key system parameters adopted in this work are provided in Table V.

It is important to note that, the greatest challenge in VeLC systems is to ensure link robustness under strong ambient light. Consequently, we propose an IR-VeLC system to mitigate this challenge for the following reasons: (i) Sunlight irradiance in the IR band is much lower than the visible band, which leads to improved signal to noise ratio performance. For example, from Fig. 14 (data source from [28]), in the IR region at the wavelength of 850 nm, the solar irradiance is less than 50 % compare to the wavelength of 480 nm in the visible light region; and (ii) the incorporation of IR-LEDs will help to meet the required transmit power level (within safety limits) needed for longer distance transmissions, where the TLs would not be able to offer, see Section IV. Note, the high or low beam HLs, which have higher transmit powers than TLs are only used at night or when the visibility is low due to fog, heavy rain, snow, etc., thus imposing limitation in V-VeLC systems. The proposed work
overcomes these issues and limitations by introducing the use of IR-LEDs in addition to HLs and TLs, to ensure link availability at all times and can come on when data is being transmitted unnoticeable to the human eyes. In addition, there are other merits of IR-LEDs such as (i) the electrical-to-optical conversion efficiency of IR-LEDs are higher than the visible blue LED-based white light sources [29]; and (ii) the 3 dB bandwidth of IR-LEDs are higher than the white LEDs, which is well known [29].

<table><caption>TABLE V
KEY SYSTEM PARAMETERS</caption><thead><tr><th>Parameter</th><th>Symbol</th><th>Value</th></tr></thead><tbody><tr><td>Active area of PD (Rx)</td><td>A<sub>PD</sub></td><td>1.5 cm<sup>2</sup></td></tr><tr><td>Peak wavelength of LED</td><td>λ</td><td>860 nm</td></tr><tr><td>Inter-vehicle distance</td><td>D<sub>v</sub></td><td>1 - ~90 m</td></tr><tr><td>Absolute temperature</td><td>T<sub>K</sub></td><td>298 K</td></tr><tr><td>System bandwidth</td><td>B</td><td>1-5 MHz</td></tr><tr><td>Responsivity of PD at 850nm & 640nm (i.e. for IR-LED & BMW TL, respectively)</td><td>R(λ)</td><td>0.63 & 0.44 A/W</td></tr><tr><td>Solar irradiance</td><td>P<sub>solar</sub></td><td>413.77 W/m<sup>2</sup></td></tr><tr><td>Load resistance</td><td>R<sub>L</sub></td><td>50 ohms</td></tr><tr><td>Maximum PD dark current</td><td>I<sub>dc</sub></td><td>5 nA</td></tr><tr><td>Transmission coefficient of filter</td><td>T<sub>f</sub>(λ)</td><td>1</td></tr><tr><td>Vehicle speed</td><td></td><td>2- 100 mph</td></tr><tr><td>Half power angle of IR-LED</td><td></td><td>±45°</td></tr><tr><td>Transmit power per IR-LED</td><td></td><td>1.34 W</td></tr><tr><td>Number of LEDs per Tx</td><td></td><td>7</td></tr><tr><td>PD model (Hamamatsu (Si PIN))</td><td></td><td>S6968</td></tr><tr><td>LED model (Osram)</td><td></td><td>SFH 4715AS</td></tr><tr><td>IR bandpass filter model (Thorlabs)</td><td></td><td>FB850-40</td></tr><tr><td>Visible bandpass filter (MidOpt)</td><td></td><td>BP550</td></tr></tbody></table>

<figure><img src="image_15.png" /><figcaption>Fig. 14: Normalized solar irradiance as a function of wavelength</figcaption></figure>

The plots of the received power against the driving speed for the case with and without an OC at the Rx is depicted in Fig. 15. It can be seen that, the received power increases and decreases with *d* and the driving speed, respectively. For example, at *P*<sub>r</sub> of -36 dBm without an OC and with a NIOC of *d* = 25.4 mm, the driving speeds are 60 and ~100 mph, respectively. Note that, the received power increases by 5.3, 8.1 and 11.2 dB using a NIOC with *d* of 25.4, 35.0 and 50.0 mm, respectively.

<figure><img src="image_16.png" /><figcaption>Fig. 15: Received power against the driving speeds for the Rx with and without a NIOC</figcaption></figure>

The predicted BER performance as a function of the driving speed for the proposed IR-VeLC system using IR-LEDs and BMW TL (chosen because it has the highest *P*<sub>T</sub> among the four TLs characterized) for a range of data rates is shown in Fig. 16 via numerical simulations using (15)-(23). Here we have considered *P*<sub>solar</sub> of 413.77 W/m<sup>2</sup>, NIOC with *d* of 25.4 mm and a narrow bandpass filter (Thorlabs FB850-40) at the Rx. Note, a solar power meter (ISO-TECH ISM410) was used to measure the solar irradiances (wavelength range of 400-1100 nm) at the various positions with respect to the Sun. *P*<sub>solar</sub>(λ) for the direction with the highest average value (measured at the city of Newcastle, UK, N 54°59′44″ W 1°39′52″) is used in our simulations. Note, the Rx is located on the vehicle pointing towards the vehicles on the road with no horizontal tilting angle.

As can be observed from Fig. 16, BMW TL does not meet typical driving speeds limits (i.e., inter-vehicle link spans) due to low *P*<sub>T</sub>. Note, only driving speeds of 7, ~6 and 5 mph (translating to a *L*<sub>S</sub> of 6.3, 5.4 and 4.5 m, respectively) are achievable at *R*<sub>b</sub> of 2, 6 and 10 Mbps, respectively, at the FEC BER limit of 3.8 × 10<sup>-3</sup>. However, the proposed system with the IR-LEDs offers driving speeds of >100, 80 and 70 mph (translating to a *L*<sub>S</sub> >89, 72 and 63 m) at *R*<sub>b</sub> of 2, 6 and 10 Mbps, respectively under the same conditions and a high ambient light level. Note, a sharp increase in the BER with respect to the driving speed up to ~ 60, ~70 and ~90 mph for the links with *R*<sub>b</sub> of 10, 6 and 2 Mbps, respectively. For example, at *R*<sub>b</sub> of 10 Mbps the BER values are 8.0×10<sup>-8</sup> and 3.8×10<sup>-3</sup> for the driving speed of 50 and ~70 mph, respectively. This is because, the received power level reduced by ~50 % (i.e., from 1.2 µW (-29.2 dBm) to 0.6 µW (-32.2 dBm)).

Moreover, to demonstrate the impact of the noise on the link performance we investigate the BER for BMW TL and the proposed IR-VeLC system by considering all noise sources as in (20) without the (i) Sunlight noise σ<sup>2</sup><sub>bgr</sub>; and (ii) signal dependent shot noise σ<sup>2</sup><sub>shot-rs</sub>, see Fig. 16. For example, for the proposed IR-VeLC system, the BER at a driving speed of 90 mph without and with σ<sup>2</sup><sub>bgr</sub> are 5.5 × 10<sup>-9</sup> and 5.3 × 10<sup>-2</sup>, respectively. For the link using BMW TL, the BER at the speed
of 8 mph without and with $\sigma_{bgr}^2$ are 1.3 $\times 10^{-9}$ and 1.7 $\times 10^{-1}$, respectively. As shown in Fig. 16, $\sigma_{shot-rs}^2$ has negligible impact on the BER performance compared with $\sigma_{bgr}^2$.

## VII. CONCLUSIONS

We carried out a performance evaluation study on the use of different vehicle TLs as Txs for V-VeLC systems. The results obtained showed that, the radiation characteristics and $P_T$ are not the same for different vehicle TLs, thus impacting the coverage area, signal distribution and the communication distance, which are key factors in the practical deployment of VeLC as part of ITS. Consequently, based on the obtained results we proposed the incorporation of IR-LEDs in vehicle HLs and TLs to meet the typical communication link spans in vehicular environments. We showed that, the proposed IR-VeLC system offers improved performance particularly under Sunlight compared with the visible lights-based TLs. We showed that, at the target FEC BER limit of $3.8 \times 10^{-3}$, transmission distances up to 63, 72 and >89 m were achieved by the proposed IR-VeLC compared with 4.5, 5.4 and 6.3 m for BMW vehicle-based TL at data rates of 10, 6 and 2 Mbps, respectively. Furthermore, the proposed scheme deals with the link asymmetry highlighted in [10] in section I, since both the front and rear vehicle's Txs will have the same $P_T$ and radiation characteristics. Moreover, we analyzed the maximum HS-AFOV and VS-AFOV required for vehicles traveling on the same lanes to establish data communication, based on the road lane width and the positions of the Txs and Rxs on the vehicles (with an imaging-based OC at the Rx).

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<figure><img src="image_17.png" /><figcaption>Fig. 16: The BER performance against the driving speed for a range of $R_b$ for the proposed vehicular IR-VeLC system</figcaption></figure>
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<figure><img src="image_18.png" /></figure>

**Elizabeth Eso MIET MIEEE** received her B.Eng in Electrical and Electronics Engineering from the Abubakar Tafawa Balewa University, Bauchi, Nigeria in 2011 and MSc in Microelectronics and Communications Engineering from the Northumbria University Newcastle, UK in 2014 with Distinction. She was the second prize winner in the IEEE students project presentation competition in the North East Region Network, UK in 2014. She joined the Federal University of Technology, Akure, Nigeria as an academic staff in 2016. She is currently a PhD researcher with the Optical Communications Research Group, Northumbria University Newcastle, UK with a Marie Curie Fellowship. Her research interest includes visible light communications, optical camera communications and free space optics.

<figure><img src="image_19.png" /></figure>

**Prof. Zabih Ghassemlooy FOSA, FIET, SMIEEE:**
BSc (Hons.) in EE Engineering, Manchester Metropolitan Univ., (1981), MSc (1984) and PhD (1987) from Manchester Univ., UK. 1987-88 he was a Post-Doctoral Research Fellow at City Univ., UK. 2004-14 joined Faculty of Eng. & Env., Northumbria Univ. as an Associate Dean Research, and currently is the Head of Optical Communications Research Group. He is a Research Fellow (2016) and a Distinguished Professor (2015) at the Chinese Academy of Science. He has published over 900 papers (more than 350 journals and 8 books), 100 keynote/invited talks and supervised 10 Research Fellows and 65 PhDs. Research interests are optical wireless communications, free space optics, visible light communications, hybrid RF and optical wireless communications. He is the Chief Editor of the British Journal of Applied Science and Technology and the International Journal of Optics and Applications. He is the Vice-Chair of OSA Technical Group of Optics in Digital Systems since 2018.

<figure><img src="image_20.png" /></figure>

**Prof. Stanislav Zvanovec** received the M.Sc. and Ph.D. degrees from the Czech Technical University (CTU) in Prague, in 2002 and 2006, respectively. He is a Full Professor, the Deputy Head of the Department of Electromagnetic Field and leader of Wireless and Fiber Optics team at CTU. His current research interests include free space optics (FSO) and fiber optical systems, visible light communications (VLC), RF over optics. He is author of two books and more than 250 journal articles and conference papers.

<figure><img src="image_21.png" /></figure>

**Dr. Juna Sathian** received the PhD degree from Queensland University of Technology (QUT), Brisbane, Australia, in 2013. She joined Imperial College London, UK, Department of Materials as a Postdoctoral Research Associate in 2014 where she was a key researcher and co-developer of the world's first room-temperature continuous wave maser (in diamond). During this time, she worked on high brightness solid-state light sources (LED-pumped luminescent concentrator) and novel precision wavelength-tunable diode-pumped Alexandrite laser technology. In 2019, she was appointed as a Senior Lecturer in the Department of Mathematics, Physics, and Electrical Engineering, University of Northumbria at Newcastle, UK. Her current research directions are focused on laser technology, room-temperature maser technology, luminescent concentrator light technology for high brightness applications, and visible light communication with focus on healthcare applications. She is a member of the Institute of Physics (IOP).
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**Dr. Asghar Gholami** received his B.Sc. and M. Sc. degrees in Electronics Engineering from Isfahan University of Technology (IUT), Isfahan, Iran, in 1993 and 1996, respectively, and Ph.D. degree in Electrical Engineering from Ecole Supérieure d'Electricité (Supélec), France, in 2003. He was awarded a post-doctoral fellowship by Supélec university in 2007 and he joined Draka Communications in the Fiber Product Technology, Marcoussis, France in 2008. Since 2009 he has been with the department of Electrical and Computer Engineering, IUT, Isfahan, Iran. He is interested in optoelectronics and optical wireless communications. He has authored and coauthored more than 40 papers and holds more than five US patents.