Professor of Computer Engineering, Shobra Faculty of Engineering, Benha University, Cairo,Egypt, Cairo,Egypt

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1 Visible Light Communication (VLC) Channel Moeling [1] M.Mohanna, [2] Raafat A.EL-Kammar, [3] M.LotfyRabeh, [4] Mohame I.Gabr [1] Professor, National Research Institute an Geophysics, Cairo, Egypt [2] Professor of Computer Engineering, Shobra Faculty of Engineering, Benha University, Cairo,Egypt, [3] Assistant Professor, Department of Electrical Engineering, Shobra Faculty of Engineering, Benha University, Cairo,Egypt [4] Assistant Lecturer, Department of Electrical Engineering, Al Safwa High Institute of Engineering, Cairo, Egypt Abstract: - The Raio Frequency (RF) suffers from interference with most electronic evices, limite, scar, expensive an also it can penetrate through walls that make it unsecure. To overcome these limitations, we use Visible Light Communication Technique (VLC) that use Light Emitting Dioe (LED) for transferring ata, in aition to its main function, lighting.vlc system uses LEDs ue to its higher ata rate, longer life time, easy to install an low cost, so it is preferre rather than other lighting sources. VLC transfers ata over a range in Electromagnetic (EM) spectrum which is visible to human that s from ( nm). In this paper, we report a simulation program for inoor visible light communication environment base on Matlab where we introuce both Line of Sight (LoS) an Non Line of Sight (N-LoS) moels for visible light source an photoioe in wireless communication an introuce for the first time the effect of reflections from the room four walls on the receiver surface. Inex Terms- Optical Wireless Communication (OWC), Fiel of View (FOV), half power angle, lambertian orer, Line of Sight (LoS), Non Line of Sight (N-LoS). I. INTRODUCTION During last years, more researches have been mae trying to fin alternative technology to transmit ata instea of the traitional way of transmission, I mean, Raio Frequency (RF) spectrum ue to, first, its capacity has been almost saturate, secon, the multimeia applications an ata streaming are growing up every ay significantly, thir, the raio frequency causes interference with most electronics evices. So, as a result of these huge tries to fin another methos, many technologies have been introuce like millimeter waves, terahertz waves an optical waves[1]. The communication using millimeter an terahertz waves require very high frequencies, that make them, on t travel near the earth, so it can t be use in inoor communications. So, scientists turn to use optical waves which represente in the use of optical wireless communication (OWC) or free space optics (FSO) like visible, infrare (IR) or ultraviolet (UV) light to carry signal. Toay s, optical communication technique can be ivie into two categories: Fiber Optics an Free Space Optics (FSO), the main ifference between them is the meium that each one of them uses to propagate an sen ata. Fiber optics is base on the optical fiber cable which it uses as a meium. On the other sie, the FSO uses the air to transmit the ata. They both use either LASER or LEDs. both technologies have avantages an isavantages where fiber optics can achieve much higher ata rates than FSO, but FSO can achieve ata transfer to places where cables establishe is impossible or the absence of electromagnetic waves is important. So, besies the alreay existing IR, a new technology is born: Visible Light ommunication (VLC) or Wireless Light Communication (WI-LI).VLC refers to ata communication over a range in the EM spectrum, which is visible to humans that operates in the visible ban ( nm)[2][3]. Using visible light as a meium for communication is not a new technique as it was introuce by Graham Bell in 1880s who use sun rays to transmit auio signal using a evice known as photophone but it has some rawbacks as it epens on sun light an this is not enough for transmission uring the whole ay [4]. The first VLC system starte at Nakajawa Laboratory in Keio University, Japan in 2003 [5] an more researches followe that. VLC system uses high brightness LEDs ue to its longer life time compare to other sources of lightening, high ata rate, ata security, no health hazars, low power consumption, easy to install an low cost. All of these avantages make LEDs be the suitable soli state lighting evice to meet nees of high spee ata rate. Also, accoring to CISCO [6], overall mobile ata traffic is expecte to grow to 49 All Rights Reserve 2018 IJERCSE 104

2 exabytes per month by 2021, a sevenfol increase over Mobile ata traffic will grow at Compoun Annual Growth Rate (CAGR) of 47 percent from 2016 to 2021 (Figure 1). Fig.1 Mobile Data Traffic/Month This increase ue to the increase in the number of evices accessing the mobile networks an also the evelopment of line social applications like face book an twitter has further increase the mobile ata traffic. Since all of these evices use raio frequency that has a limite spectrum also, it suffers from other problems like interference, where it is forbien to use portable evices in aircrafts because of the interference with navigation systems. Also it suffers from security issues, has risks in a human health. So, to overcome these problems, engineers have evelope a new wireless communication technique calle Visible Light Communication System (VLC). III. SYSTEM MODEL A-The communication channel It can be efine as the physical space between the LED as transmitter an the photoioe as a receiver [7] here, the physical space is referre as optical link which can be ivie into two categories, name irecte system an iffusive system. In irecte system (Line of Sight) a narrow signal beam is establishe a point to point link between the transmitter an receiver that has a minimum multipath ispersion an give high ata transmission rate. In the other sie, in iffusive system (multipath link non light of sight signal), several multi path ispersion is existe ue to the reflections from walls, ceiling, groun an other physical objects) that limits the communication ban with an reuce the energy efficiency. Besies, the line of sight an non line of sight signals, there is a back groun light that generate from traitional lamps an sunrays are collecte at the receiver that reuce the system efficiency as shown in figure 3 an to reuce it, optical ban pass filter is use to reject these unwante lights. Also there is another source of reucing the system efficiency, that s air turbulence that come from air conitioner, fans or heaters, that may change the polarity of the signal at the receiver en. In such inoor system, this effect is negligible. II. INDOOR VISIBLE COMMUNICATION SYSTEM: Inoor visible communication system shoul be implemente to eliver illumination an wireless ata transmission simultaneously as it is built on the illuminance infrastructure.here, LEDs are use as light source in the system because it is more efficient compare with traitional illumination lights. At receiver photoioe or photoioe array is use for signal etection, such typical inoor visible communication system is moele by the infrastructure shown in figure 2. Fig.2 Inoor optical communication system Fig.3 Different Signals that effect on System Efficiency. B- LED illuminance: Since LEDs are use not only for illumination but also in the optical communication, it is esirable to efine the illumination intensity an the transmitte power so, the intensity is the luminous flux per soli angle an it is use for expressing the brightness of LEDs an the transmitte power inicates the total energy raiate from LEDs. The luminance intensity is given by [8]: I (1) Ф is luminous flux that can be calculate from energy flux as follows: All Rights Reserve 2018 IJERCSE 105

3 780 K V m 380 e (2) K m : is the max. Visibility =683lm/W at λ=555nm. V (λ): is stanar luminosity curve. Ω : is the spatial angle. Assuming that, LEDs lightening has a lambertian raiation pattern, then the luminous intensity as a function in ϕ is given by[8]-[9] : m I I(0)cos ϕ: Angle of irraiance w.r.t the axis normal to the transmission surface. I(0) : The centre luminous intensity. m : The lambertian emission orer that s equal to: ln 2 m ln(cos ) 1/2 1/2 : The semi angle at half illuminance of an LED. At any point (x,y), the horizontal illuminance as shown in figure (4), is given by : m cos Ihor. I(0) cos( ) 2 I 2 cos( ) (3) (4) (5) Fig.5 Propagation Moel of Directe Link. C- LoS Propagation Moel: A point to point link between the transmitter an receiver that has a minimum multipath ispersion is establishe. One of its weak points is on shaowing effect which cause by objects blocking such as human activities also it has a limite coverage area so it is not capable of supporting mobile users. As shown in figure 5, if it is applie to only one LED, the LED is place at a istance from the photoioe. LED raiation angle of the transmitter to receiver against transmitter normal is enote by ϕ whereas the raiation angle to receiver against the receiver normal is enote by ψ. Now, a possible application is iscusse in terms of some numerical analysis. A room is assume to has a size of 5m x 5m x 3m as shown in figure 6, LEDs are installe at a height of 3m. The height of the esk is at 1m so the istance between transmitter an receiver is 2m. The number of LEDs is 100 per array where we have four arrays, that has a center luminous intensity 0.73c. The semi angle at half power is 70 o where the transmitte optical power is 1.5W for each LED. These conitions are summarize in table 1. Table 1 LED Design Parameters. : The angle of incience. : The istance between LED an photo etector surface, figure 5. Fig. 4 The Distribution of Horizontal Luminous Intensity. Fig. 6 The moel room. The room size is 5m x 5m x 3m. The esk of height 1m from the floor. The LED Light of height 3m from the floor. All Rights Reserve 2018 IJERCSE 106

4 The etector is moele as active area A r collecting the raiation incient at angles ψ smaller than the etector Fiel of View (FOV), then the effective area is given by: } eff. { (6) Then at receiver. Ieally, a large area etector woul be suitable for inoor optical communication system to collect much power but practically, it increases the manufacturing cost an junction capacitance that will ecrease the system banwith thus to overcome this, a concentrator is use to increase the effective area, the optical gain of such concentrator is given by[8]-[10] : (b) { } (7) n: is the concentrator refractive inex. con : The FOV at receiver. The absorption an scattering cause from walls, ceiling an other physical materials are very low ue to the short optical link in the inoor optical system that has a channel DC gain approximate as[6]-[9]: { } ( c ) Where: T s : Optical filter gain. The relations between optical receive power (P r-los ) in watt an optical transmitte power (P t ) coul be expresse as: P rlos Hlos (0). Pt Referring to figure (6), the optical power istribution from each LED an the total power istribution from all LEDs at receiver plane in LoS path (ignoring the reflections of the walls) are shown in figure 7. (9) () (a) (e) Fig.7 The Distribution of the Receive Power from, (a) LED2, (b) LED4, (c) LED1, () LED3, (e) Total Power from all LEDs. All Rights Reserve 2018 IJERCSE 107

5 It can be seen from figure (7 e), there is almost uniform istribution of optical power at the centre with max. Power of Bm an min. power of -3.2Bm at channel istance 2 meters.depening on the transmitter s half power angle (ϕ 1/2 ), we can control on the receive power if (ϕ 1/2 ) is varie from 10 o to 90 o with range ifference of 10 o at a fixe channel istance of 2 meters as shown in figure 8.From this figure, as (ϕ 1/2 ) increase, the receive power is ecrease an this is matche with the characteristics of LoS. Also the istance between the LED source an photoioe is a function with the receive power that is because of the characteristic of the channel LoS, where the closer the transmitter to the photoioe, the higher the intensity of light that is receive by the photoioe as shown in figure 9. imensions, position of transmitter an receiver, as a simple moel for such propagation is shown in figure 10. In this figure, an optical wave is generate from LED source, has two propagation paths. The first one is irecte path, enote by () an the other one is non irecte (N-LoS) path that incient on the wall (for simplicity, we consier it is reflecte by only one wall) by an angle (α ir ) an this path is reflecte again from this wall an incient on the photo etector surface by an angle ( r ). D- Non line of sight (N-LoS) propagation Moel: Here, the optical path is more complicate as it epens on many factors like reflectivity of the walls, ceiling, objects insie the room, room Fig.10 Propagation moel of iffuse link. Fig.8 Distance vs Photoioe s receive power. A more complicate moel is shown in the following figure 11. Here, in this figure a room with a size of 5m x 5m x 3m with four LED arrays installe on the ceiling of the room in symmetrical arrangement ( 3m from the floor), each LED of 1.5 Watt, has many reflecte beams, reflection from each wall from the four walls that has a reflection coefficient of 0.8, ceiling, floor, any object insie the room like( tables, esks,..) an human but in a simple approach, we consier that there is a reflection from only one LED to each wall from the four walls but in numerical results, we take into account the effect of each LED in computing the receive power at the photo etector surface after reflections on all walls an the effect of all LEDs together to compute the total receive power at the receiver plane. So, when computing the receive power, we must inclue the channel gain of the irecte path an non irecte path as follows [8]-[11]: Fig. 9 Semi angle half power v.s photoioe receive power. Fig. 11 The moel room. The room size is 5m x 5m x 3m. The photo ioe of height 1m from the floor. The LED Light of height 3m from the floor. All Rights Reserve 2018 IJERCSE 108

6 P rnlos Hlos(0) Hnlos(0) Pt Hlos (0) Href.(0) Pt refl. (10) (11) { } (b) 1 : The istance from LED to reflection point. (figure.10) 2 : The istance from reflection point to receiver surface. : Reflectance factor. r : Angle of irraiance to a reflection point. (c) ir : Angle of irraiance to a receiver. r : Angle of incience from the reflective surface. Referring to figure 11, the optical power istribution from each LED an the total power istribution from all LEDs at receiver plane in N-LoS path (incluing the effect of reflections from all walls) are shown in figure 12. () (a) (e) Fig. 12 shows the 3D view of the reflecte receive power generate from the four walls accoring to (a) LED 1, (b) LED 2, (c) LED 3, () LED 4 an (e) total receive power from all LEDs. All Rights Reserve 2018 IJERCSE 109

7 Finally, the reflections from the walls can be summarize in a flow chart as shown in figure 13 consiering that the term (reflection object) can be any point of reflection. Here the objects were walls. [6] Cisco, Cisco Visual Networking Inex (VNI) Upate Global MobileData Traffic Forecast, , Tech.Rep., 2017.[Online]. Available: cisco. Com /c /en /us /solutions /collateral /service- provier /visual- networkinginexvni /mobile- white-paper-c html [7] M.V. Bhalerao, M. Sumathi an S.S. Sonavane, Line of sight moel for visible light communication using Lambertian raiation pattern of LED, Copyright 2016 John Wiley & Sons, Lt.. [8] Toshihiko Kominean, Masao Nakagawa, Funamental Analysis for Visible-Light Communication System using LED Lights, IEEE Transactions on Consumer Electronics, Vol. 50, No. 1, FEBRUARY Fig. 13 flow chart of ifferent signals paths. IV. CONCLUSION In this paper, an inoor visible light communication system taking into account irect propagation (LoS) an non irect propagation (N-LoS) incluing the reflection from walls moels are investigate for a typical room. Equations of the receive power of both ifferent moels are applie to calculate an simulate the receive power at the receiver plane. REFERENCES [9] Jupeng Ding, Zhengyuan Xu Performance of Inoor VLC an Illumination uner Multiple Reflections, /14/ 2014 IEEE [10] Wenjun Gu, Mohamma reza A. Kashani, an Mohsen Kavehra, Multipath Reflections Analysis on Inoor Visible Light Positioning System,IEEE, arxiv : v1 [physics. optics] 6 Apr [11] Kanei Fan, Toshihiko Komine, Yuichi Tanaka, Masao Nakajawa, The Effect of Reflection on Inoor Visible- Light Communication System utilizing White LEDs, /02/2002 IEEE. [1] Dobroslav Tsonev, Stefan Viev an Haral Haas, Towars a 100 Gb/s visible light wireless access network, 2015 Optical Society of America. [2] Latif Ullah Khan, Visible light communication: applications, architecture, stanarization an research challenges, Digital Communications an Networks 3 (2017) [3] Ignacio Marin-Garcia, Victor Guerra an Rafael Perez- Jimenez, Stuy an Valiation of Eavesropping Scenarios over a Visible Light Communication Channel, Sensors 2017, 17, 2687; oi: /s [4] M.Lotfy Rabeh, Mohame I. Gabr an Tarek Hosny, Data Transmission via Visible Light Communication (VLC) Technique, International Journal of Innovative Research in Science, Engineering an Technology, Vol. 5, Issue 9, September [5] Y. Tanaka, T. Komine, S. Haruyama an M. Nakagawa, Inoor Visible Light Transmission System Utilizing White LED Lights, IEICE Trans, on Communications, vol. E86-B, no. 8, pp , Aug All Rights Reserve 2018 IJERCSE 110