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Design and implementation of LED–LED indoor visible light communication system
Journal Pre-proof Design and implementation of LED-LED indoor visible light communication system Faisal Ahmed Dahri, Fahim Aziz Umrani, Attiya Baqai, Hyder Bux Mangrio
PII: DOI: Reference:
S1874-4907(19)30388-X https://doi.org/10.1016/j.phycom.2019.100981 PHYCOM 100981
To appear in:
Physical Communication
Received date : 29 May 2019 Revised date : 25 November 2019 Accepted date : 16 December 2019 Please cite this article as: F.A. Dahri, F.A. Umrani, A. Baqai et al., Design and implementation of LED-LED indoor visible light communication system, Physical Communication (2019), doi: https://doi.org/10.1016/j.phycom.2019.100981. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
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Design and Implementation of LED-LED Indoor Visible Light Communication System Faisal Ahmed Dahri, Fahim Aziz Umrani, Attiya Baqai, Hyder Bux Mangrio Institute of Information & Communication Technologies (IICT), Mehran University of Engineering & Technology, Pakistan
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Abstract
This paper investigates the experimental performance of LEDs as both photoemitter and photoreceiver. In this work LED-LED link is established using BJT and MOSFET based drive circuits at transmitting side and resistor
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driver operated in photoconductive mode is used at the receiver side. The LED response as transmitter and receiver is investigated at different operating frequencies with the distance of up to 20 cm and the data rate of 1 Mbps. The SNR values of 8 dB and 11 dB are obtained using BJT and MOSFET
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drivers respectively at a distance of 20 cm. Furthermore, six different color LEDs are tested on both sides of transceiver to determine the best performing pair. It is observed that the red color LEDs have good responses as a photodiode due to its long wavelength in the visible spectrum. However their performance is significantly effected by ambient noise. Moreover, the responsivity of the Red color LED operated as photoreceiver with respect to
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different biasing voltages is also experimentally measured and discussed. Keywords: LED as Photo-emitter, LED as Photo-receiver, Visible Light Communication, Responsivity, Indoor communication
Preprint submitted to Physical Communication
November 25, 2019
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1. Introduction With the advancement in 5G technology, individuals are looking forward
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to have their home appliances and numerous devices capable of communicat-
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ing with internet for valuable and innovative applications [1]. It is recently
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being proposed that for small cells optical wireless communication becomes
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inherently suitable and reliable choice over radio frequency communication
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links. Light emitting diodes (LEDs) are commonly used as an illuminat-
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ing device due to their overall feasibility including compact size, prolong life
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span, low power consumption and minimum heat up. The same LEDs with
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faster response time can efficiently be used in optical wireless communication
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to provide high speed data links. The idea of using LED as photodetector
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is not new, however, the recent developments in material science and solid
13
state devices have refocused the attention of researchers in exploring the use
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of LED as a potential detector for short range communication. This has
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resulted in a surge of research for the development of next generation wire-
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less communication networks using infrared and visible light for practical
17
applications. Reverse biased LEDs are commonly known to work as a photo-
18
detector. This approach should be more popularized especially in optical
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wireless communication systems. Such transmissions systems in which LEDs
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are used as both optical sources and optical receivers are reported in [2], [3]
21
with data rates of more than 100 Mbps and over the distance of 30 cm. The
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distance of few meters can be sufficient for many indoor VLC communication
23
systems as reported in [4], [5], and [6]. Recently visible light communication
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is utilized and reported in Wireless Body Area networks [7], [8], underwater
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communication [9], and vehicular communication [10].
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In this work, following the method of [11] and [12] we experimentally
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demonstrate the LED-LED based optical wireless communication systems
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working at a distance exceeding 1 meter. In [12], simple resistor based drive
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circuits are used while in this paper BJT and MOSFET transistor based drive
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circuits are designed and investigated. During experiments some interesting
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behaviors in terms of responsivity and on the color of LEDs on both sides of
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transceiver are observed and discussed accordingly.
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The aim of this paper is to design LED based communication
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system. Since, LED manufacturers do not provide information
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related to the LED detection properties such as; responsivity, re-
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ceived power capabilities, etc. An attempt is made to experimen-
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tally analyze the behavior of LEDs as a detector. The proposed
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system uses LEDs on both sides for indoor visible light communi-
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cation. Various driving circuits are designed to test their charac-
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teristics in LED-LED links. Power distribution in room dimen-
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sion and relation of received power with detection area of LED
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using mathematical model are reported in this work.
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The rest of the paper is organized as follows. Section 2 confers the related
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work. Section 3 describes mathematical model, section 4 discusses the ex-
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perimental setup. Section 5 contains the experimental results and discussion
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and finally, section 6 concludes the paper.
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2. Related Work
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In [5], spectral responses of LED as a photo detector is discussed with ad-
equate results of absorbency measurements. The impact of LED colors were 3
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studied in [13], but it has not achieved a suitable distance implementable for
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real time approach. In [14], authors have experimented with LEDs providing
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transmission rates of 150 Mbps over a short range of few centimeters (approx-
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imately 8 cm) using LED on both sides i.e. transmitter and receiver. The
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biasing voltage iterations were tested to improve the modulation bandwidth
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and switching efficiency. It is also noted that there are certain limitations
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with LED restricting its use in optical wireless communication systems such
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as all LEDs do not have sufficient responsivity and power for reliable commu-
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nication. [15] demonstrates the bidirectional LED to LED communication
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link and obtain the data rate of 110 Mbps over the distance of less than a
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meter. Responsivity is dependent on the emission wavelength; longer the
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wavelength higher the responsivity. It was eminent that all LEDs do not act
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as a receiver. For example most white LEDs do not show any photo sen-
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sitivity and therefore are not recommended as a receiving component [16].
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The authors in [17] demonstrate that the LEDs work as a photodiode only
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when the wavelength of receiving LED is equal or greater than the trans-
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mitting LEDs wavelength. In [4] the LED characteristics were analyzed as
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a receiver with Wavelength Division Multiplexing (WDM) for flash light of
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mobile phones at a very short distance. The feasibility of LED as a receiver
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is presented in [18]. [19] shows the half duplex VLC system based on LED
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as a transmitter as well as receiver. The 10cm of distance was covered with
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data rate of 200 bps. In [11] the authors demonstrates the use of LED as
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transmitter and receiver in indoor environment with received structure de-
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signed as RC high pass filter to reduce the effects of ambient light. The
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achieved distance is 12.7 cm with the data rate of 1 Kbps focusing only red
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LED while other colors LEDs are not considered for audio and digital signal
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transmission. In [20], authors have presented the RGB based LED to LED commu-
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nication link. It was observed that red-red and blue-green links achieved
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good quality signals and data rate of 40 Kbps and 20 Kbps respectively.
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The authors in [20] also discussed the receiver impedance characteristics of
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LED in VLC systems. The ac impedance spectrum of LED as photodiode
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is dependent on the received optical power which may introduce mismatch
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loss between trans-impedance amplifier and LED. The efficient protocols and
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mechanism were introduced for LED communication to overcome the flick-
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ering effects of light in [3]. The authors do not provide details of distance
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and data rates for optical wireless communication. [21] have evaluated the
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performance of LED as a wavelength selective detector. The observations
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suggest that impulse response was measured using high reverse voltage. The
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relationship between bias voltage and the time spreads is linear. In [22]
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the physical and media access layers protocols were designed to assess the
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performance of LED links. The achieved throughput was 800 bps over a
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distance of less than 2m. In [23] the reverse bias voltage increases the capa-
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bilities of LED receiver at limited range after which no effects were observed
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in responsivity. In [24], authors have analyzed the LED sensing device per-
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formance by employing protocols. The comparisons of LED and photodiode
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responsivity results were equally effective but in reflective environment LED
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is more suitable choice for receiver hence preventing the need of additional
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photo diodes. [6] have achieved the 10 Mbps of data rate over the distance
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of 20 cm. The research work needs to improve in distance and data rates.
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[25] highlights the importance of LED as a light receiving element in opti-
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cal wireless communication system. The relationships between the color of
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light, energy levels and band gaps of semiconductor materials are explained.
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Measured results based on responsivity were in the range of 0.002 and 0.156
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A/W. The authors in [26] have discussed more specifically the photodetec-
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tion properties of LED and elaborates the sensing properties of multi color
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LEDs. Spectral absorption and responsivity standards were compared with
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conventional photodiode and LED as optical receiver.
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3. Mathematical Model of LED Based System
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LEDs are essential part of the VLC systems. These are considered as
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a lambertian radiator which has uniform luminance in all directions. The
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intensity depends upon the LED color and the position of receiver. The lu-
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minance intensity is a function of irradiance angle θ and intensity represented
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by I(φ). Incident angle is represented by φ and Field of View (FoV) of LED
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is illustrated in Fig. 1.
Intensity can be calculated as [27]
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I(φ) = I(0)cos(φ)m
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I(0) is the maximum illumination, where φ = 0, m demonstrates the lambertian order and can be calculated as in Eq. 2 [27]:
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(1)
m=−
ln2 lncos(φ 1 )
(2)
2
Transmitter semi-angle half power denoted by φ 1 and optical transmitted 2
power can be found by Eq. 3. 6
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Figure 1: LED based transceiver presenting the incident angle θ, irradiance angle φ and
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LED detector FoV with transmitter semi-angle at half power φ 12
ZT
X(t)dt
(3)
−T
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1 Pt = lim T →∞ T 120
X(t) is the instantaneous optical transmitted power. For Line of Sight
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(LoS) method the channel transfer function is considered as a DC gain func-
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tion which is denoted by H(d, θ, φ) and is given by Eq. 4 [28].
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(m+1)A cosm (φ)T (θ)g(θ)cos(θ) : if θ < θ s c 2πd2 H(d, θ, φ) = 0 : otherwise
(4)
A is the LED detector area, d is distance between transmitter and receiver,
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TS (θ) is the filter gain and g(θ) is a concentrator with refractive index n and
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can be quantified by Eq. 5.
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g(θ) =
n2 sin2 (θc )
0
: if 0 ≤ θ ≤ θc
(5)
: otherwise
θc is the receiver field of view and received signal y(t) at LED receiver can 7
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be evaluated as in Eq. 6.
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y(t) = x(t) ⊗ H(t) + s(t)
(6)
The total noise added from the channel to the receiver output is indicated through s(t). The received power can be computed by Eq. 7 Pr = Hlos (d, θ, φ)Pt
(7)
The traditional VLC system and the LED based systems have
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some limitations in terms of power capabilities and receiver sen-
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sitivity. In this work, we have used LED as both emitter and
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receiver. Most LEDs are made from compound semiconductors
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such as Gallium Arsenide and Gallium phosphate. Such materi-
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als are primarily optimized to be used as optical sources in such a
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way that radiative recombination dominates the non-radiative re-
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combinations. Furthermore, the detection area of LEDs is smaller
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than the typical photodiodes. These factors play negatively into
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the mathematical model of VLC link majorly affected by the de-
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tection area and responsivity.
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terms of VLC communication with traditional and this approach
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have been contrasted in Table 1.
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The comparative parameters in
Considering the affecting parameters like detection area, re-
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sponsivity and field of view the traditional mathematical model is
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revisited. Experimental results reveal the degrading performance
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when compared to the traditional photo-diode detection based sys-
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tems. The experiments reveal that the LED can detect shorter
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Photodiode
LED
1
Material
Si, Ge, InGaAs
GaAs, GaP
2
Bandwidth
To 40 GHz
20 MHz
3
Spectral Ranges
Tunable
Fixed
4
Cost
Medium
Low
5
Responsivity
High
Low
6
Dark Current
Low
High
7
Detection Area
Wider
Smaller
8
Material Property
Absorptive
Emitting
9
Field of View
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S.No Parameter
High
Low
Table 1: Comparison of Photodiode and LED as detection Component
wavelengths with low responsivity due to the material limitation
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and small detection area.
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The responsivity of the LED can be calculated through Eq. 8. The
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incident power Pincident is estimated through provided responsivity of silicon
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photodiode. After that the photodiode was replaced by LED to measure the
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responsivity of LED as a photo receiver. Ip is the photo generated current
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at the LED receiver.
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R(λ) =
Ip Pincident
(A/W)
(8)
Before designing LED based VLC transceiver, it is very important to
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know the frequency response range of LED emitter and detector. For this
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purpose, square wave signal having the frequency range from 1 kHz to 10
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MHz is applied to LED transmitter and receiver using a signal generator.
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It is noted as shown in Fig. 2 that as the frequency increases, the shape of
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wave gets distorted because of the intrinsic capacitance of LED’s restricting
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the transmission speed. Similarly at the reverse biased LED receiver the
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distortions are observed at higher frequencies as illustrated in Fig. 3. It
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can be viewed that after 1 kHz frequency the responses are of poorer quality;
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square wave becomes triangular due to the junction capacitance of LED in the
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depletion region that affects the time constant of charging and discharging.
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A filter may be used to smooth the levels of the output signal.
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Figure 2: LED based transmitter response for (a) 1 kHz, (b) 10 kHz, (c) 100 kHz, (d) 1
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MHz and (e) 10 MHz
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Figure 3: LED based receiver responses for (a) 100 Hz, (b) 500 Hz, (c) 1 kHz, and (d) 5
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kHz
4. The Experimental Setup
The proposed system block diagram is shown in Fig. 4 and Fig. 5 presents
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the experimental setup for LED to LED system. The experimental setup is
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implemented in dark and lighted environment to investigate the performance
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of LED as photo-detector. The digital data is transmitted through the pro-
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grammable function generator HM 8130 to the LED driver circuit. The input
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signal is modulated using OOK (On-Off Keying) technique.
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The driver circuits of transmitter and receiver used to improve the link
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distance and data rates are illustrated in Fig. 6. In Fig. 6(a), the 2N2222 Bi-
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polar junction transistor (BJT) is used in emitter follower based LED trans-
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mitter drive circuit. This configuration produces low output power which
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limits the data rate and link range. BJTs require higher base current to be
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Figure 4: Block diagram of LED to LED link
operated, can only sustain low input signal voltages, and require an addi-
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tional resistor. The BJT transistor performance is lower than MOSFET due
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to the transistor base drive circuit having high saturation which leads to high
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power dissipation and low data transmission rate. The metaloxidesemicon-
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ductor field-effect transistor (MOSFET) is preferred active device in digital
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communication systems due to its low conduction resistance, with low re-
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sistance it can handle high current and low power dissipation. IRFBC30
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MOSFET is used as shown in Fig. 6(b) having a rise time of 13 ns and
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bandwidth of 53 KHz. The six different color LEDs are used one by one as
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a transmitter and receiver. Fig. 6(c) shows the LED receiver drive circuit
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configured in the photo-conductive mode. Furthermore, a lens is also used
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to enhance the link range. The specification of LEDs used in this work are
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listed in Table 2.
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The output signal at the receiver module is connected to the TEK-
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TRONIX (TBS1072B) 70 MHz Digital Storage Oscilloscope. The signals
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can be viewed through oscilloscope from reverse biased LED which works as
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photo-detector.
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Value
Model
MCL053HAD/12 (Orange), See Figure 15 for colors
Viewing angle
20◦ -23◦ , 45◦ (Orange)
Forward Current
100mA
Reverse Current
10µA
Power dissipation
85mW
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Parameter
Luminous intensity 2000-7000 mcd, 16mcd( Orange)
Table 2: LED Specification for LED to LED Links
Room
Value
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Parameter
5m × 5m × 3m
Size No. of LED source
1×1
Transmitted power
Source
Semi-angle half power
20◦
Luminous intensity
7200 lv (mcd)
Receiver Area
1 mm2
Field of View (FOV)
23◦
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LED
20 m W @20mA current
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LED
Receiver
Responsivity
0.1 A/W
Refractive index of concentrator
1.5
Filter Gain
1
Table 3: Simulation Parameters for LED-to-LED VLC System
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5. Results & Discussion
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Experiments are performed to validate the system performance in terms of
received signal strength, transceiver linearity and transmission link distance
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Figure 5: Experimental Setup for LED to LED link
Figure 6: (a). LED drive with transistor circuit for Transmitter (b). LED driver circuit
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with MOSFET for Transmitter (c). Photo-conductive mode of LED receiver
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with different colors of LEDs at the transmitter and receiver side. MATLAB
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2017a is used to simulate received power distribution of LED based indoor 14
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system as discussed in section 3 and simulation parameters are given in Table
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3. The center luminous power of 20 mW is used. The simulated power
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distribution is shown in Fig. 7 in the standard room size of 5m × 5m × 3m.
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The system is configured at the height of 0.5m from the ground and achieved
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maximum and minimum power distribution values are -30 dBm and -60 dBm
206
respectively.
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It is seen that the detection area of receiving component plays important
208
role in calculation of received power as represented in Eq.4 and Eq.7. The
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detection area of typical photo-detectors is mentioned in the data sheets but
210
unfortunately for the LEDs same information is not available. Therefore, we
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have assumed the active area of LED as a detection area taken from [16] for
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the calculation of received power Similarly, the detection area of photodiode
213
values are taken from [29]. The received power versus detection area for both
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LED as photoreceiver and photodiode is shown in Fig.8
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Time domain signals of transmitter and receiver at the distance of 12
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cm are illustrated in Fig. 9. The optical signal is propagated through air
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and is detected by reverse biased LED working as a photodiode operating in
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photoconductive mode. The receiver circuit is able to receive signal upto 1
219
kHz of frequency after that the received signal starts experiencing distortions
220
in its shape. The various measurements are performed whereby each color
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LED transmitter is tested against all six color LED receivers to determine
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the best performing pair.
The responsivity of silicon photodiode is considered to measure the re-
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sponsivity of red LED. Fig.10 depicts the responsivity curve of silicon photo-
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diode at reverse bias voltage of 12 V. The received power levels were approxi-
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Figure 7: Received optical power distribution of LED to LED link
Figure 8: Received power as a function of detection area for LED and Photodiode
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Figure 9: Time domain transceiver signals of LED to LED link at distance of 12 cm
mated through the photo-generated current and the responsivity of photodi-
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ode is provided from the supplier. The power levels were measured after that
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the photodiode is replaced with the LED and responsivity can be calculated
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through the Eq. 8.
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The red LED responsivity is measured at different reverse bias voltages
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as shown in Fig. 11. It is illustrated that as reverse bias increases the
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responsivity is also increased due to the widening of the depletion region
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resulting in the generation of more photo-current. According the responsivity
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formula higher value of photo-current generated at particular wavelength
235
then higher will be the response of LED.
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In order to find the best pair of LED-LED link (without using lens) the
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photo-received voltages at different receiver colors are measured. Fig. 12
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shows the photo-voltage of different color LED receivers at the fixed distance
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of 5cm and keeping the 2mW of power fixed for all transmitter LED’s. It is
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observed that the link is severely effected by the artificial lights and perfor-
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mance is rapidly degraded. It is further noted that the shorter wavelength
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LED color is easily detected by the longer wavelength LED receiver, how-
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Figure 10: Silicon photodiode responsivity dependence on wavelength at reverse bias volt-
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age of 12 V (reproduced from [29])
ever, the reverse is not true. It can be seen from Fig. 12 that red color LED
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has higher wavelength which can detect all visible light range color LEDs at
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the transmitter side and therefore all red color configurations are performing
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quite satisfactory for indoor communication. On the other hand when we
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have lower wavelength LED working as receiver it does not or very poorly
248
detect the higher wavelength color LED working as transmitter. For example
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it can be noted in Fig. 12 that Blue color LED working as receiver does not
250
detect Red or yellow color LED transmitters, similarly yellow color LED very
251
poorly detect blue color and does not detect red color LED transmitter. Red
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Figure 11: Red-LED responsivity at different reverse bias voltages
color LED outperform in all combinations and suffer low attenuation in free
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space channel, while other color configurations perform satisfactorily only for
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short range communication.
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In this work only a 1×1 scenario of transmitter and receiver is considered.
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The measured output of OOK-NRZ modulator in the form of eye diagram
257
is presented in Fig. 13. It shows the open eye pattern detected through
258
oscilloscope which confirms that the link performance is satisfactory with no
259
loss at the distance of 15 cm. With the addition of lens in this experimental
260
setup the link length iseasily increased up to 1 m as reported in Umrani
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Figure 12: Photo-generated voltage at different LED color receivers at fixed distance of 5
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et al. [12]. The SNR value of -39 dB is observed at a distance of 50 cm
262
in [12] which was based on photo-voltaic receiver configuration where the
263
LED is driven by a single resistor. In this work BJT and MOSFET based
264
drive circuits are used to enhance the link performance which enhance the
265
signal quality and the improved SNR values measured are shown in Fig. 14.
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The SNR values of 8 dB at a distance of 20 cm is reported using BJT drive
267
circuit and 11 dB is obtained using MOSFET drive circuit with a data rate
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of 600 Kbps and 1 Mbps respectively. The data rate is obtained using Eq.
269
9. The rise time for BJT transistor configuration is 1.1 µs and 0.58µs for
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MOSFET configuration. The higher data rates can be achieved using different
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modulation schemes such as: OFDM, CSK, PWM,M-QAM, m-CAP and M-
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ary modulation schemes which can possibly increase the data rates in indoor
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environment. The multiple input multiple output (MIMO) approach which
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will require the use of multiple photoemitters and photoreceivers can also
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increase the data rates. The link is tested in darkness indoor environment,
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where no artificial lights were ON.
0.35 RiseTime
(9)
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Figure 13: Eye diagram at distance of 15 cm based on OOK modulation
The experimental results clearly demonstrate the feasibility of using LED
278
as photodetector with some limitation in terms of data rates. This low data
279
rate is the direct result of the low bandwidth which depends on the detection
280
area, field of view and junction capacitance of LED. The LED response to
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shorter or equal range of wavelengths and also has smaller responsivity which
282
require an amplifier circuit to receive the light signal accurately. The proposed
283
system has applications in the low data rate systems such as health monitoring
284
(hospitals) places. Similarly the shopping malls inventory management and
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intelligent museums can use this concept to communicate with the customers
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and visitors.
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Figure 14: Signal to Noise ratio versus Bit error rate (BER) using LED to LED link
The minimum and maximum BER values were achieved in the range of
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10−7 and 10−1 with MOSFET based driver circuit having a maximum link
289
length of 25cm (See Fig.14). The Red-Red link is considered for this analysis
290
as this combination achieved good signal quality and high responsivity.
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Figure 15: LED Specification of different colors
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6. Conclusions & Future Recommendations
In this work, LED-LED link is established using BJT and MOSFET based
293
drive circuits for transmitting LED and reverse biased receiving LED oper-
294
ated in photoconductive mode. We have analyzed the characteristics of LED
295
as both photoemitter and photoreceiver with six different colors of LEDs
296
to determine the best performing pair. From results it is concluded that
297
red-red combination of LED-LED link gives the best performance in terms
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of received signal strength. It is also observed that the longer wavelength
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LED receiver color is able to detect lower wavelength LED colors but the
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otherwise is not true. Red color LED links are less affected by the ambient
301
noise even at longer distances. Based on responsivity measurements it is
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concluded that higher biasing voltage increases the responsivity of red color
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LED. This paper also reports the improvement in the SNR value and data
304
rate at a distance of up to 20 cm without lens using MOSFET rransistor for
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LED based indoor VLC communication. The achieved SNR value of 11 dB
306
is recorded for MOSFET and 8 dB using BJT transistor.
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Since no dedicated photo-diodes are used due to which the up-link can
easily be modeled through LEDs with some modification resulting in full du23
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plex, bi-directional links with this approach in future. The presented system
310
uses 1×1 configuration, it is proposed that the n×n array of LEDs would sig-
311
nificantly improve the link performance. Moreover, this work can be further
312
improved utilizing extra optical devices such as concentrators on the both
313
sides, transimpedance amplifier, multiple-input, multiple-output approach
314
and different driver circuits to increase the link distance and data rates.
315
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CRediT author statement
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Fahim Umrani: Conceptualization, Methodology, Supervision. Faisal Dahri: Data curation, WritingOriginal draft preparation. Attiya Baqai: Visualization, Investigation. Hyder Bux Mangrio: WritingReviewing and Editing, Validation.
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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Author Biographies
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Faisal Ahmed Dahri received his Bachelor’s degree in Telecommunication Engineering in 2016 from Mehran University of Engineering and Technology (MUET), Jamshoro. He has done joint Masters in Telecommunication Engineering and Management from University of Malaga, Spain and Mehran UET. His research interests include Visible Light Communication, Free Space Optics, Wave propagation and Optical Communication.
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Dr. Fahim Aziz Umrani is currently Associate Professor in the Department of Telecommunication at Institute of Information & Communication Technologies (IICT), Mehran UET, Pakistan. He received his B.E in Electronics from Faculty of Electrical, Electronics & Computer Engineering at Mehran UET, Pakistan and his PhD from Faculty of Advanced Technologies at the University of South Wales (Glamorgan University). He is member of IEEE and OSA. His research interests include Optical CDMA, Spectral Amplitude Coding, Software Defined Radio, Multiple access techniques, & Body area networks.
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Dr. Attiya Baqaiis an Assistant Professor in Department of Electronics Engineering Mehran University of Engineering & Technology Jamshoro, Sindh Pakistan. She received her B.E. degree in Electronic Engineering; Masters is inTelecommunication and Control Engineering and PHD from Institute of Information and Communication Technologies Mehran UET Jamshoro. Her main research interests include Wireless Body Area Networks, Wireless Communications, Artificial Neural Networks, Fuzzy Logic Control and Embedded System Design.
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Hyder Bux Mangrio is working as Lecturer in Department of Telecommunication at Institute of Information & Communication Technologies (IICT), Mehran UET, Pakistan. He received his B.E in Telecommunication and PGD from Faculty of Electrical, Electronics & Computer Engineering at Mehran UET, Pakistan and hisMaster from Hamdard University, Karachi in 2017. His research interests include Optoelectronics and Optical Communication, Visible Light Communication, and underwater Optical Communication.
PII: DOI: Reference:
S1874-4907(19)30388-X https://doi.org/10.1016/j.phycom.2019.100981 PHYCOM 100981
To appear in:
Physical Communication
Received date : 29 May 2019 Revised date : 25 November 2019 Accepted date : 16 December 2019 Please cite this article as: F.A. Dahri, F.A. Umrani, A. Baqai et al., Design and implementation of LED-LED indoor visible light communication system, Physical Communication (2019), doi: https://doi.org/10.1016/j.phycom.2019.100981. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
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Design and Implementation of LED-LED Indoor Visible Light Communication System Faisal Ahmed Dahri, Fahim Aziz Umrani, Attiya Baqai, Hyder Bux Mangrio Institute of Information & Communication Technologies (IICT), Mehran University of Engineering & Technology, Pakistan
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Abstract
This paper investigates the experimental performance of LEDs as both photoemitter and photoreceiver. In this work LED-LED link is established using BJT and MOSFET based drive circuits at transmitting side and resistor
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driver operated in photoconductive mode is used at the receiver side. The LED response as transmitter and receiver is investigated at different operating frequencies with the distance of up to 20 cm and the data rate of 1 Mbps. The SNR values of 8 dB and 11 dB are obtained using BJT and MOSFET
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drivers respectively at a distance of 20 cm. Furthermore, six different color LEDs are tested on both sides of transceiver to determine the best performing pair. It is observed that the red color LEDs have good responses as a photodiode due to its long wavelength in the visible spectrum. However their performance is significantly effected by ambient noise. Moreover, the responsivity of the Red color LED operated as photoreceiver with respect to
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different biasing voltages is also experimentally measured and discussed. Keywords: LED as Photo-emitter, LED as Photo-receiver, Visible Light Communication, Responsivity, Indoor communication
Preprint submitted to Physical Communication
November 25, 2019
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1
1. Introduction With the advancement in 5G technology, individuals are looking forward
3
to have their home appliances and numerous devices capable of communicat-
4
ing with internet for valuable and innovative applications [1]. It is recently
5
being proposed that for small cells optical wireless communication becomes
6
inherently suitable and reliable choice over radio frequency communication
7
links. Light emitting diodes (LEDs) are commonly used as an illuminat-
8
ing device due to their overall feasibility including compact size, prolong life
9
span, low power consumption and minimum heat up. The same LEDs with
10
faster response time can efficiently be used in optical wireless communication
11
to provide high speed data links. The idea of using LED as photodetector
12
is not new, however, the recent developments in material science and solid
13
state devices have refocused the attention of researchers in exploring the use
14
of LED as a potential detector for short range communication. This has
15
resulted in a surge of research for the development of next generation wire-
16
less communication networks using infrared and visible light for practical
17
applications. Reverse biased LEDs are commonly known to work as a photo-
18
detector. This approach should be more popularized especially in optical
19
wireless communication systems. Such transmissions systems in which LEDs
20
are used as both optical sources and optical receivers are reported in [2], [3]
21
with data rates of more than 100 Mbps and over the distance of 30 cm. The
22
distance of few meters can be sufficient for many indoor VLC communication
23
systems as reported in [4], [5], and [6]. Recently visible light communication
24
is utilized and reported in Wireless Body Area networks [7], [8], underwater
25
communication [9], and vehicular communication [10].
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2
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In this work, following the method of [11] and [12] we experimentally
27
demonstrate the LED-LED based optical wireless communication systems
28
working at a distance exceeding 1 meter. In [12], simple resistor based drive
29
circuits are used while in this paper BJT and MOSFET transistor based drive
30
circuits are designed and investigated. During experiments some interesting
31
behaviors in terms of responsivity and on the color of LEDs on both sides of
32
transceiver are observed and discussed accordingly.
pro of
26
The aim of this paper is to design LED based communication
34
system. Since, LED manufacturers do not provide information
35
related to the LED detection properties such as; responsivity, re-
36
ceived power capabilities, etc. An attempt is made to experimen-
37
tally analyze the behavior of LEDs as a detector. The proposed
38
system uses LEDs on both sides for indoor visible light communi-
39
cation. Various driving circuits are designed to test their charac-
40
teristics in LED-LED links. Power distribution in room dimen-
41
sion and relation of received power with detection area of LED
42
using mathematical model are reported in this work.
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The rest of the paper is organized as follows. Section 2 confers the related
44
work. Section 3 describes mathematical model, section 4 discusses the ex-
45
perimental setup. Section 5 contains the experimental results and discussion
46
and finally, section 6 concludes the paper.
47
2. Related Work
48
49
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In [5], spectral responses of LED as a photo detector is discussed with ad-
equate results of absorbency measurements. The impact of LED colors were 3
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studied in [13], but it has not achieved a suitable distance implementable for
51
real time approach. In [14], authors have experimented with LEDs providing
52
transmission rates of 150 Mbps over a short range of few centimeters (approx-
53
imately 8 cm) using LED on both sides i.e. transmitter and receiver. The
54
biasing voltage iterations were tested to improve the modulation bandwidth
55
and switching efficiency. It is also noted that there are certain limitations
56
with LED restricting its use in optical wireless communication systems such
57
as all LEDs do not have sufficient responsivity and power for reliable commu-
58
nication. [15] demonstrates the bidirectional LED to LED communication
59
link and obtain the data rate of 110 Mbps over the distance of less than a
60
meter. Responsivity is dependent on the emission wavelength; longer the
61
wavelength higher the responsivity. It was eminent that all LEDs do not act
62
as a receiver. For example most white LEDs do not show any photo sen-
63
sitivity and therefore are not recommended as a receiving component [16].
64
The authors in [17] demonstrate that the LEDs work as a photodiode only
65
when the wavelength of receiving LED is equal or greater than the trans-
66
mitting LEDs wavelength. In [4] the LED characteristics were analyzed as
67
a receiver with Wavelength Division Multiplexing (WDM) for flash light of
68
mobile phones at a very short distance. The feasibility of LED as a receiver
69
is presented in [18]. [19] shows the half duplex VLC system based on LED
70
as a transmitter as well as receiver. The 10cm of distance was covered with
71
data rate of 200 bps. In [11] the authors demonstrates the use of LED as
72
transmitter and receiver in indoor environment with received structure de-
73
signed as RC high pass filter to reduce the effects of ambient light. The
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achieved distance is 12.7 cm with the data rate of 1 Kbps focusing only red
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4
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LED while other colors LEDs are not considered for audio and digital signal
76
transmission. In [20], authors have presented the RGB based LED to LED commu-
78
nication link. It was observed that red-red and blue-green links achieved
79
good quality signals and data rate of 40 Kbps and 20 Kbps respectively.
80
The authors in [20] also discussed the receiver impedance characteristics of
81
LED in VLC systems. The ac impedance spectrum of LED as photodiode
82
is dependent on the received optical power which may introduce mismatch
83
loss between trans-impedance amplifier and LED. The efficient protocols and
84
mechanism were introduced for LED communication to overcome the flick-
85
ering effects of light in [3]. The authors do not provide details of distance
86
and data rates for optical wireless communication. [21] have evaluated the
87
performance of LED as a wavelength selective detector. The observations
88
suggest that impulse response was measured using high reverse voltage. The
89
relationship between bias voltage and the time spreads is linear. In [22]
90
the physical and media access layers protocols were designed to assess the
91
performance of LED links. The achieved throughput was 800 bps over a
92
distance of less than 2m. In [23] the reverse bias voltage increases the capa-
93
bilities of LED receiver at limited range after which no effects were observed
94
in responsivity. In [24], authors have analyzed the LED sensing device per-
95
formance by employing protocols. The comparisons of LED and photodiode
96
responsivity results were equally effective but in reflective environment LED
97
is more suitable choice for receiver hence preventing the need of additional
98
photo diodes. [6] have achieved the 10 Mbps of data rate over the distance
99
of 20 cm. The research work needs to improve in distance and data rates.
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5
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[25] highlights the importance of LED as a light receiving element in opti-
101
cal wireless communication system. The relationships between the color of
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light, energy levels and band gaps of semiconductor materials are explained.
103
Measured results based on responsivity were in the range of 0.002 and 0.156
104
A/W. The authors in [26] have discussed more specifically the photodetec-
105
tion properties of LED and elaborates the sensing properties of multi color
106
LEDs. Spectral absorption and responsivity standards were compared with
107
conventional photodiode and LED as optical receiver.
108
3. Mathematical Model of LED Based System
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LEDs are essential part of the VLC systems. These are considered as
110
a lambertian radiator which has uniform luminance in all directions. The
111
intensity depends upon the LED color and the position of receiver. The lu-
112
minance intensity is a function of irradiance angle θ and intensity represented
113
by I(φ). Incident angle is represented by φ and Field of View (FoV) of LED
114
is illustrated in Fig. 1.
Intensity can be calculated as [27]
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109
I(φ) = I(0)cos(φ)m
117
118
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I(0) is the maximum illumination, where φ = 0, m demonstrates the lambertian order and can be calculated as in Eq. 2 [27]:
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(1)
m=−
ln2 lncos(φ 1 )
(2)
2
Transmitter semi-angle half power denoted by φ 1 and optical transmitted 2
power can be found by Eq. 3. 6
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Figure 1: LED based transceiver presenting the incident angle θ, irradiance angle φ and
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LED detector FoV with transmitter semi-angle at half power φ 12
ZT
X(t)dt
(3)
−T
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1 Pt = lim T →∞ T 120
X(t) is the instantaneous optical transmitted power. For Line of Sight
121
(LoS) method the channel transfer function is considered as a DC gain func-
122
tion which is denoted by H(d, θ, φ) and is given by Eq. 4 [28].
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(m+1)A cosm (φ)T (θ)g(θ)cos(θ) : if θ < θ s c 2πd2 H(d, θ, φ) = 0 : otherwise
(4)
A is the LED detector area, d is distance between transmitter and receiver,
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TS (θ) is the filter gain and g(θ) is a concentrator with refractive index n and
125
can be quantified by Eq. 5.
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g(θ) =
n2 sin2 (θc )
0
: if 0 ≤ θ ≤ θc
(5)
: otherwise
θc is the receiver field of view and received signal y(t) at LED receiver can 7
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127
be evaluated as in Eq. 6.
128
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pro of
y(t) = x(t) ⊗ H(t) + s(t)
(6)
The total noise added from the channel to the receiver output is indicated through s(t). The received power can be computed by Eq. 7 Pr = Hlos (d, θ, φ)Pt
(7)
The traditional VLC system and the LED based systems have
131
some limitations in terms of power capabilities and receiver sen-
132
sitivity. In this work, we have used LED as both emitter and
133
receiver. Most LEDs are made from compound semiconductors
134
such as Gallium Arsenide and Gallium phosphate. Such materi-
135
als are primarily optimized to be used as optical sources in such a
136
way that radiative recombination dominates the non-radiative re-
137
combinations. Furthermore, the detection area of LEDs is smaller
138
than the typical photodiodes. These factors play negatively into
139
the mathematical model of VLC link majorly affected by the de-
140
tection area and responsivity.
141
terms of VLC communication with traditional and this approach
142
have been contrasted in Table 1.
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The comparative parameters in
Considering the affecting parameters like detection area, re-
144
sponsivity and field of view the traditional mathematical model is
145
revisited. Experimental results reveal the degrading performance
146
when compared to the traditional photo-diode detection based sys-
147
tems. The experiments reveal that the LED can detect shorter
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8
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Photodiode
LED
1
Material
Si, Ge, InGaAs
GaAs, GaP
2
Bandwidth
To 40 GHz
20 MHz
3
Spectral Ranges
Tunable
Fixed
4
Cost
Medium
Low
5
Responsivity
High
Low
6
Dark Current
Low
High
7
Detection Area
Wider
Smaller
8
Material Property
Absorptive
Emitting
9
Field of View
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S.No Parameter
High
Low
Table 1: Comparison of Photodiode and LED as detection Component
wavelengths with low responsivity due to the material limitation
149
and small detection area.
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The responsivity of the LED can be calculated through Eq. 8. The
151
incident power Pincident is estimated through provided responsivity of silicon
152
photodiode. After that the photodiode was replaced by LED to measure the
153
responsivity of LED as a photo receiver. Ip is the photo generated current
154
at the LED receiver.
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R(λ) =
Ip Pincident
(A/W)
(8)
Before designing LED based VLC transceiver, it is very important to
156
know the frequency response range of LED emitter and detector. For this
157
purpose, square wave signal having the frequency range from 1 kHz to 10
158
MHz is applied to LED transmitter and receiver using a signal generator.
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It is noted as shown in Fig. 2 that as the frequency increases, the shape of
160
wave gets distorted because of the intrinsic capacitance of LED’s restricting
161
the transmission speed. Similarly at the reverse biased LED receiver the
162
distortions are observed at higher frequencies as illustrated in Fig. 3. It
163
can be viewed that after 1 kHz frequency the responses are of poorer quality;
164
square wave becomes triangular due to the junction capacitance of LED in the
165
depletion region that affects the time constant of charging and discharging.
166
A filter may be used to smooth the levels of the output signal.
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Figure 2: LED based transmitter response for (a) 1 kHz, (b) 10 kHz, (c) 100 kHz, (d) 1
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MHz and (e) 10 MHz
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Figure 3: LED based receiver responses for (a) 100 Hz, (b) 500 Hz, (c) 1 kHz, and (d) 5
167
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kHz
4. The Experimental Setup
The proposed system block diagram is shown in Fig. 4 and Fig. 5 presents
169
the experimental setup for LED to LED system. The experimental setup is
170
implemented in dark and lighted environment to investigate the performance
171
of LED as photo-detector. The digital data is transmitted through the pro-
172
grammable function generator HM 8130 to the LED driver circuit. The input
173
signal is modulated using OOK (On-Off Keying) technique.
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The driver circuits of transmitter and receiver used to improve the link
175
distance and data rates are illustrated in Fig. 6. In Fig. 6(a), the 2N2222 Bi-
176
polar junction transistor (BJT) is used in emitter follower based LED trans-
177
mitter drive circuit. This configuration produces low output power which
178
limits the data rate and link range. BJTs require higher base current to be
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Figure 4: Block diagram of LED to LED link
operated, can only sustain low input signal voltages, and require an addi-
180
tional resistor. The BJT transistor performance is lower than MOSFET due
181
to the transistor base drive circuit having high saturation which leads to high
182
power dissipation and low data transmission rate. The metaloxidesemicon-
183
ductor field-effect transistor (MOSFET) is preferred active device in digital
184
communication systems due to its low conduction resistance, with low re-
185
sistance it can handle high current and low power dissipation. IRFBC30
186
MOSFET is used as shown in Fig. 6(b) having a rise time of 13 ns and
187
bandwidth of 53 KHz. The six different color LEDs are used one by one as
188
a transmitter and receiver. Fig. 6(c) shows the LED receiver drive circuit
189
configured in the photo-conductive mode. Furthermore, a lens is also used
190
to enhance the link range. The specification of LEDs used in this work are
191
listed in Table 2.
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The output signal at the receiver module is connected to the TEK-
193
TRONIX (TBS1072B) 70 MHz Digital Storage Oscilloscope. The signals
194
can be viewed through oscilloscope from reverse biased LED which works as
195
photo-detector.
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Value
Model
MCL053HAD/12 (Orange), See Figure 15 for colors
Viewing angle
20◦ -23◦ , 45◦ (Orange)
Forward Current
100mA
Reverse Current
10µA
Power dissipation
85mW
pro of
Parameter
Luminous intensity 2000-7000 mcd, 16mcd( Orange)
Table 2: LED Specification for LED to LED Links
Room
Value
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Parameter
5m × 5m × 3m
Size No. of LED source
1×1
Transmitted power
Source
Semi-angle half power
20◦
Luminous intensity
7200 lv (mcd)
Receiver Area
1 mm2
Field of View (FOV)
23◦
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Receiver
Responsivity
0.1 A/W
Refractive index of concentrator
1.5
Filter Gain
1
Table 3: Simulation Parameters for LED-to-LED VLC System
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5. Results & Discussion
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Experiments are performed to validate the system performance in terms of
received signal strength, transceiver linearity and transmission link distance
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Figure 5: Experimental Setup for LED to LED link
Figure 6: (a). LED drive with transistor circuit for Transmitter (b). LED driver circuit
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with MOSFET for Transmitter (c). Photo-conductive mode of LED receiver
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with different colors of LEDs at the transmitter and receiver side. MATLAB
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system as discussed in section 3 and simulation parameters are given in Table
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3. The center luminous power of 20 mW is used. The simulated power
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distribution is shown in Fig. 7 in the standard room size of 5m × 5m × 3m.
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The system is configured at the height of 0.5m from the ground and achieved
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maximum and minimum power distribution values are -30 dBm and -60 dBm
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respectively.
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It is seen that the detection area of receiving component plays important
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role in calculation of received power as represented in Eq.4 and Eq.7. The
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detection area of typical photo-detectors is mentioned in the data sheets but
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unfortunately for the LEDs same information is not available. Therefore, we
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have assumed the active area of LED as a detection area taken from [16] for
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the calculation of received power Similarly, the detection area of photodiode
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values are taken from [29]. The received power versus detection area for both
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LED as photoreceiver and photodiode is shown in Fig.8
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Time domain signals of transmitter and receiver at the distance of 12
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cm are illustrated in Fig. 9. The optical signal is propagated through air
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and is detected by reverse biased LED working as a photodiode operating in
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photoconductive mode. The receiver circuit is able to receive signal upto 1
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kHz of frequency after that the received signal starts experiencing distortions
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in its shape. The various measurements are performed whereby each color
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LED transmitter is tested against all six color LED receivers to determine
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the best performing pair.
The responsivity of silicon photodiode is considered to measure the re-
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sponsivity of red LED. Fig.10 depicts the responsivity curve of silicon photo-
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diode at reverse bias voltage of 12 V. The received power levels were approxi-
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Figure 7: Received optical power distribution of LED to LED link
Figure 8: Received power as a function of detection area for LED and Photodiode
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Figure 9: Time domain transceiver signals of LED to LED link at distance of 12 cm
mated through the photo-generated current and the responsivity of photodi-
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ode is provided from the supplier. The power levels were measured after that
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the photodiode is replaced with the LED and responsivity can be calculated
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through the Eq. 8.
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The red LED responsivity is measured at different reverse bias voltages
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as shown in Fig. 11. It is illustrated that as reverse bias increases the
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responsivity is also increased due to the widening of the depletion region
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resulting in the generation of more photo-current. According the responsivity
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formula higher value of photo-current generated at particular wavelength
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then higher will be the response of LED.
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In order to find the best pair of LED-LED link (without using lens) the
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photo-received voltages at different receiver colors are measured. Fig. 12
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shows the photo-voltage of different color LED receivers at the fixed distance
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of 5cm and keeping the 2mW of power fixed for all transmitter LED’s. It is
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observed that the link is severely effected by the artificial lights and perfor-
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mance is rapidly degraded. It is further noted that the shorter wavelength
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LED color is easily detected by the longer wavelength LED receiver, how-
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Figure 10: Silicon photodiode responsivity dependence on wavelength at reverse bias volt-
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age of 12 V (reproduced from [29])
ever, the reverse is not true. It can be seen from Fig. 12 that red color LED
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has higher wavelength which can detect all visible light range color LEDs at
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the transmitter side and therefore all red color configurations are performing
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quite satisfactory for indoor communication. On the other hand when we
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have lower wavelength LED working as receiver it does not or very poorly
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detect the higher wavelength color LED working as transmitter. For example
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it can be noted in Fig. 12 that Blue color LED working as receiver does not
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detect Red or yellow color LED transmitters, similarly yellow color LED very
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poorly detect blue color and does not detect red color LED transmitter. Red
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Figure 11: Red-LED responsivity at different reverse bias voltages
color LED outperform in all combinations and suffer low attenuation in free
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space channel, while other color configurations perform satisfactorily only for
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short range communication.
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In this work only a 1×1 scenario of transmitter and receiver is considered.
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The measured output of OOK-NRZ modulator in the form of eye diagram
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is presented in Fig. 13. It shows the open eye pattern detected through
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oscilloscope which confirms that the link performance is satisfactory with no
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loss at the distance of 15 cm. With the addition of lens in this experimental
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setup the link length iseasily increased up to 1 m as reported in Umrani
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Figure 12: Photo-generated voltage at different LED color receivers at fixed distance of 5
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et al. [12]. The SNR value of -39 dB is observed at a distance of 50 cm
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in [12] which was based on photo-voltaic receiver configuration where the
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LED is driven by a single resistor. In this work BJT and MOSFET based
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drive circuits are used to enhance the link performance which enhance the
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signal quality and the improved SNR values measured are shown in Fig. 14.
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The SNR values of 8 dB at a distance of 20 cm is reported using BJT drive
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circuit and 11 dB is obtained using MOSFET drive circuit with a data rate
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of 600 Kbps and 1 Mbps respectively. The data rate is obtained using Eq.
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9. The rise time for BJT transistor configuration is 1.1 µs and 0.58µs for
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MOSFET configuration. The higher data rates can be achieved using different
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modulation schemes such as: OFDM, CSK, PWM,M-QAM, m-CAP and M-
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ary modulation schemes which can possibly increase the data rates in indoor
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environment. The multiple input multiple output (MIMO) approach which
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will require the use of multiple photoemitters and photoreceivers can also
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increase the data rates. The link is tested in darkness indoor environment,
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where no artificial lights were ON.
0.35 RiseTime
(9)
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Figure 13: Eye diagram at distance of 15 cm based on OOK modulation
The experimental results clearly demonstrate the feasibility of using LED
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as photodetector with some limitation in terms of data rates. This low data
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rate is the direct result of the low bandwidth which depends on the detection
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area, field of view and junction capacitance of LED. The LED response to
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shorter or equal range of wavelengths and also has smaller responsivity which
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require an amplifier circuit to receive the light signal accurately. The proposed
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system has applications in the low data rate systems such as health monitoring
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(hospitals) places. Similarly the shopping malls inventory management and
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intelligent museums can use this concept to communicate with the customers
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and visitors.
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Figure 14: Signal to Noise ratio versus Bit error rate (BER) using LED to LED link
The minimum and maximum BER values were achieved in the range of
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10−7 and 10−1 with MOSFET based driver circuit having a maximum link
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length of 25cm (See Fig.14). The Red-Red link is considered for this analysis
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as this combination achieved good signal quality and high responsivity.
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Figure 15: LED Specification of different colors
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6. Conclusions & Future Recommendations
In this work, LED-LED link is established using BJT and MOSFET based
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drive circuits for transmitting LED and reverse biased receiving LED oper-
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ated in photoconductive mode. We have analyzed the characteristics of LED
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as both photoemitter and photoreceiver with six different colors of LEDs
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to determine the best performing pair. From results it is concluded that
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red-red combination of LED-LED link gives the best performance in terms
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of received signal strength. It is also observed that the longer wavelength
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LED receiver color is able to detect lower wavelength LED colors but the
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otherwise is not true. Red color LED links are less affected by the ambient
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noise even at longer distances. Based on responsivity measurements it is
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concluded that higher biasing voltage increases the responsivity of red color
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LED. This paper also reports the improvement in the SNR value and data
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rate at a distance of up to 20 cm without lens using MOSFET rransistor for
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LED based indoor VLC communication. The achieved SNR value of 11 dB
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is recorded for MOSFET and 8 dB using BJT transistor.
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Since no dedicated photo-diodes are used due to which the up-link can
easily be modeled through LEDs with some modification resulting in full du23
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plex, bi-directional links with this approach in future. The presented system
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uses 1×1 configuration, it is proposed that the n×n array of LEDs would sig-
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nificantly improve the link performance. Moreover, this work can be further
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improved utilizing extra optical devices such as concentrators on the both
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sides, transimpedance amplifier, multiple-input, multiple-output approach
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and different driver circuits to increase the link distance and data rates.
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CRediT author statement
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Fahim Umrani: Conceptualization, Methodology, Supervision. Faisal Dahri: Data curation, WritingOriginal draft preparation. Attiya Baqai: Visualization, Investigation. Hyder Bux Mangrio: WritingReviewing and Editing, Validation.
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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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Author Biographies
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Faisal Ahmed Dahri received his Bachelor’s degree in Telecommunication Engineering in 2016 from Mehran University of Engineering and Technology (MUET), Jamshoro. He has done joint Masters in Telecommunication Engineering and Management from University of Malaga, Spain and Mehran UET. His research interests include Visible Light Communication, Free Space Optics, Wave propagation and Optical Communication.
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Dr. Fahim Aziz Umrani is currently Associate Professor in the Department of Telecommunication at Institute of Information & Communication Technologies (IICT), Mehran UET, Pakistan. He received his B.E in Electronics from Faculty of Electrical, Electronics & Computer Engineering at Mehran UET, Pakistan and his PhD from Faculty of Advanced Technologies at the University of South Wales (Glamorgan University). He is member of IEEE and OSA. His research interests include Optical CDMA, Spectral Amplitude Coding, Software Defined Radio, Multiple access techniques, & Body area networks.
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Dr. Attiya Baqaiis an Assistant Professor in Department of Electronics Engineering Mehran University of Engineering & Technology Jamshoro, Sindh Pakistan. She received her B.E. degree in Electronic Engineering; Masters is inTelecommunication and Control Engineering and PHD from Institute of Information and Communication Technologies Mehran UET Jamshoro. Her main research interests include Wireless Body Area Networks, Wireless Communications, Artificial Neural Networks, Fuzzy Logic Control and Embedded System Design.
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Hyder Bux Mangrio is working as Lecturer in Department of Telecommunication at Institute of Information & Communication Technologies (IICT), Mehran UET, Pakistan. He received his B.E in Telecommunication and PGD from Faculty of Electrical, Electronics & Computer Engineering at Mehran UET, Pakistan and hisMaster from Hamdard University, Karachi in 2017. His research interests include Optoelectronics and Optical Communication, Visible Light Communication, and underwater Optical Communication.