Available online at ScienceDirect. Procedia Technology 24 (2016 )

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1 Available online at ScienceDirect Procedia Technology 4 (16 ) International Conference on Eerging Trends in Engineering, Science and Technology (ICETEST - 15) An Intensity Modulation Transission Syste for Under Water channel Modeling and Counication Joseph George K N a * and Jayasree V K b a Model Engineering College, Kochi 681, India b College of Engineering, Cherthala , India Abstract Abstract The iportance of underwater optical counication has increased any fold due to its any inherent advantages such as faster propagation and high bandwidth. The proper design of the transitter with a suitable odulation forat, which can overcoe any of the drawbacks of the traditional odulation schees, is very critical for reliable underwater counication. In this paper, an intensity odulation schee is proposed, which can be efficiently integrated to LED or non- LED based transitter for optical underwater counication systes. Scattering odel for the optical underwater wireless channel has also been deterined in this work, using Monte Carlo siulation ethod. 16 The Authors.Published by by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing coittee of ICETEST 15. Peer-review under responsibility of the organizing coittee of ICETEST 15 Keywords: Optical Underwater Channel; Intensity odulation; Channel odeling; Monte Carlo siulation 1. Introduction For underwater counication, acoustic waves have been used for a long period of tie. But the channel bandwidth for acoustic signal is low, so is the propagation speed. The ultipath reflection of the sound waves causes signal fading. Also acoustic wave suffers strong attenuation at high frequencies [1-3]. As an alternative ethod, underwater wireless counication using light wave has been used recently. Optical counication underwater provides high data rates of the order of Mbps to Gbps and a high propagation speed of.55 x 1 8 /s * Corresponding author. Tel.: ; E-ail address:josephgkn@gail.co The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing coittee of ICETEST 15 doi:1.116/j.protcy

2 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) [4],[5]. The efficiency of the syste highly depends on the odulation forat used and also on the receiver and signal processing unit. The odulation forats coonly used for underwater wireless optical counication are ON OFF keying (OOK), Pulse Position Modulation (PPM), Pulse Width Modulation (PWM) etc [5]. In this paper a novel odulation schee is proposed which when properly ipleented, will help in enhancing the perforance of underwater optical counication systes. The proposed ethod odifies the signal in the electrical doain, before being applied to a diode based odulation circuit. An optical doain analysis is done to find the nuber of photons proportional to the aplitudes of odulated signal at different intervals. Partial odeling for the underwater optical channel is also carried out in this paper, using Monte Carlo Siulation ethod, which is a nuerical ethod used to study the underwater optical propagation [7], [8]. It depends on repeated rando sapling to calculate the results.. Methodology.1. Proposed Modulation Schee in the electrical doain A novel odulation schee has been proposed in this work, to be integrated to a transitter for underwater wireless optical counication channel. For the proposed odulation schee in the electrical doain, let the inforation signal be denoted by: V od =V sin ω t and the carrier signal be V carr =V c sin ω c t. The ratio of the odulating signal voltage to the carrier voltage be denoted by. Fro a detailed atheatical analysis, for the proposed schee, the iposed condition is: sin ω t 1/ (1) Modulating signal Threshold liited Diode function I Output Load Resistance Level Shifter Output Signal Fig 1: Ipleentation of Design Condition of Equation (1) The output current I of the threshold liited diode function can be derived as: V ( V sin t ) I I exp[ o ] 1 VT where V T is the voltage equivalent of teperature. The output voltage across the load resistance can be obtained as: V ( V sin t ) vr I orexp[ ] 1 VT Let this be represented as () (3)

3 836 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) v R V ( V sint ) V exp[ d ] 1 VT (4) The output of the level shifter which is the odified odulating voltage is ( V sint V ) v Vd exp[ ] 1 VL VT (5) with the level shifter assued to nullify any offset, if present. Fig.. Denoting the total odifying function as F (.), the generation schee for the proposed odulation is given in Modulating signal F(.) Square Law odulator Proposed odulated output Carrier Fig : Generation schee for the proposed Intensity Modulation The proposed odulation output voltage is given by v od V V [1 exp( c sin t V V T ) ] sin t c V Where the paraeter µ is defined as d Vc The expression for square law based standard aplitude odulation is given by: v=v c (1+sinω t) sinω c t This voltage signal when odified by a noral diode function, the current becoes (6) ( V c (1 sin t)sin ct I I o exp[ ] 1 VT (7) This voltage signal when odified by a noral diode function, the current becoes: ( Vc (1 sint)sinct I I o exp[ ] 1 VT (8) The corresponding output voltage developed across a possible load resistance would be

4 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) V out ( Vc (1 sin t)sin ct Vs exp[ ] 1 VT (9) A DC level shifter would ensure the condition: V out Fro the atheatical analysis, the proposed odulation output signal voltage is given by: v od ( V sint V Vc[1 exp V T ) ] sin t c (1) Applying an equivalent analysis gives a generalized Matheatical Function Model of the proposed Modulation schee as: y ( x p) ( y xy) exp y k exp[ ] C gp gp Where, x=v sin ω t, y=v c sin ω c t, V s = k, V c =p and V T =g and C is a general constant. (11).. Optical Doain Analysis The Intensity Modulation syste akes use of the proposed odulated signal odeled in the previous section. Proposed Modulator (Electrical Doain) Optical Source Intensity odulation Fig 3: Proposed optical Transitter A linear variation of the output light Intensity, with respect to the change in the applied voltage at the optical source is assued. Also in the underwater wireless optical counication scenario, for the blue/green frequency spectru, assuing an approxiate linear variation of the nuber of photons with light intensity, underwater optical channel odeling with the proposed intensity odulation can be carried out using Monte Carlo siulations, with respect to the nuber of photons. Let N out be the nuber of photons and V in be the input electrical voltage input to the optical source at any instant. Then, (1) N out N u V in Where, N u is the Reference Nuber of photons, defined as the nuber of photons eitted by the optical source for unit electrical input voltage. The reference nuber of photons for noral siulation studies has been entioned in [7]. The proposed odulation syste possesses ultifold advantages over any existing conventional systes. Efficient design in the electrical doain is possible, using signal processing techniques rather than in the optical doain. The odulation syste can be efficiently integrated to LED based and non-led based optical underwater wireless counication systes. Possible odulation abiguities of conventional aplitude odulation based

5 838 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) systes for LED based transitters can be overcoe by the proposed syste. Unwanted signal swings which ight result in inefficiencies are reduced in the proposed syste, copared to conventional systes. Modulation index based constraints in conventional AM systes are absent. In pulse width or position based systes, the effects of underwater optical channel ight result in increased signal distortion at the receiver as against aplitude based counication schees like the proposed syste. In addition, inherent bandwidth advantages of optical counication systes are present while, syste coplexity can be anipulated and controlled using proper design. Also, the proposed odulation based transitter is suited for optical underwater channel studies utilizing Monte Carlo siulations..3. Partial Underwater Channel Modeling The photon scattering is odeled using the Monte Carlo Siulation studies. Photons eitted fro the transitter are deviated fro the incoing direction due to scattering. Scattering Model is ipleented for Clear water, Coastal water and Turbid water channel conditions. Henyey-Greenstein odel is used for the Optical Scattering in the Channel [9]. The Henyey-Greenstein phase function is given by the equation P HG 1 g (, g) (13) 3 (1 g g cos ) Where, g is the HG asyetry paraeter, which depends on the ediu characteristics and describes the probability distribution of the deflection angle θ. 3. Siulation Results The proposed odulation schee based transitter has been analyzed using siulation studies and results are presented. Fig 4 shows the proposed odulation applied to a specific low frequency odulating signal with a prototype carrier. Also, the single sided power spectral density is depicted, for the odulated output. Proposed Modulated Signal Aplitude Tie (sec) Spectral Anaalysis (Single Sided PSD) 6 Aplitude Frequency (Hz) Fig 4: Prototype of proposed odulated signal. V od=v sin ω t, Mod. Signal Frequency = 5 Hz, Vcarr=V c sin ω ct, Carrier Frequency = Hz. V =1V and V c=4v For the underwater optical channel siulation studies utilizing the proposed intensity odulation schee fro equation(1), N u is chosen to be x 1 5. Table 1 depicts the nuber of photons utilized in the Monte Carlo siulation studies. This shows the equivalent nuber of photons assued for a particular input voltage

6 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) corresponding to an inforation signal to be transitted, aking use of the proposed odulation schee. These photons have been ade use of in the odeling studies for underwater optical channel. TABLE 1 NUMBER OF PHOTONS EMITTED FOR DIFFERENT VALUES OF INPUT VOLTAGE Vin (v) No: of Photons x x x x x x x x x x x x x x x x x 1 4 The Volue Scattering Function (VSF) of water is an inherent optical property that governs the propagation of light. It plays a large part in the behaviour of the attenuation curve. The VSF is used to choose scattering angles for the Monte Carlo siulation ethod. Integration of the VSF results in the cuulative distribution function (CDF).Three different water types considered in the siulation are labelled as Clear water, Harbor water and Coastal water. Scattering Model is ipleented for each water type. There present icroscopic variations in the distribution which are evident fro the results of siulation studies. Based on the results, a detailed odeling of the optical underwater wireless channel can be carried out, aking use of the proposed transission syste Scattering CDF Values Angle (Deg) Fig 5: Cuulative Density Function Value Distribution for Different Scattering Angles- Clear Water

7 84 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) Scattering CDF Values Angle (Deg) Fig 6: Cuulative Density Function Value Distribution for Different Scattering Angles- Harbor Water Scattering CDF Values Angle (Deg) Fig 7: Cuulative Density Function Value Distribution for Different Scattering Angles- Coastal Water. 4. Conclusion In this paper, an intensity odulation transission syste for underwater optical channel odeling and counication is proposed. In addition, scattering odel for underwater optical wireless channel has also been deterined. Various siulation results have been presented in detail. Making use of the proposed intensity odulation, full fledged odeling of underwater optical channel can be carried out using Monte Carlo Siulation. The proposed odulation schee offers any advantages like copatibility, reduced distortion. The perfectly odeled channel can be effectively utilized in developing an efficient underwater optical counication link. References [1] Jaruwatanadilok S, Underwater Wireless Optical Counication Channel Modeling and Perforance Evaluation Using Vector Radiative Transfer Theory, IEEE Cos. J., vol 6, no9, pp , 8 [] Gabriel C, Khalighi M A, S. Bourennane, L eon P and Rigaud V, Monte-Carlo-based channel characterization for optical counication systes, IEEE/OSA Journal of Optical Counications and Networking, vol. 5, no. 1, pp. 1 1, Jan. 13 [3] Mohaad-Ali Khalighi, Chadi Gabriel, Tasni Haza, Salah Bourennane Pierre L eon, Vincent Rigaud, Underwater Wireless Optical Counication; Recent Advances and Reaining Challenges, Invited paper, ICTON 14 IEEE

8 K.N. Joseph George and V.K. Jayasree / Procedia Technology 4 ( 16 ) [4] Davide Anguita and Davide Brizzolara and Giancarlo Parodi, Prospects and Probles of Optical Diffuse Wireless Counication for Underwater Wireless Sensor Networks: Application Centric Design, Geoff V Marrett and Yen Kheng Tan InTech ISBN: [5] Giles JW, Bankan I, Underwater Optical Counication Systes. Part : Basic Design considerations, IEEE Military Counications Conference (MILCOM), Atlantic City, NJ, Oct 5, vol. 3, pp [6] Mahdiraji GA, Zahedi E, Coparison of Selected digital Modulation Schees (OOK, PPM and DPIM) for Wireless Optical Counications, Proc. SCOReD Conference June 6, pp 5 1, Selangor, Malaysia [7] Chadi Gabriel, Muhaad- Ali Khalighi, SalahBourennane, Pierre Leon, Vincent Rigaud, Channel Modeling for Underwater Optical Counication, Proc. nd IEEE Workshop on Optical Wireless Counication 11, pp [8] Cox Jr, Willia Charles, Siulation, Modeling and Design of Underwater Optical Counication Systes, PhD thesis, North Carolina State University, Raleigh, NC, 1. [9] Petzold T J, Volue scattering functions for selected ocean waters, Tech. Rep. SIO 778, Scripps Institute of Oceanography, 197