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BER Characteristics for Underwater Optical Wireless Communication

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In this paper, the performance of an underwater optical wireless communications system is theoretically analyzed, using 4-PPM modulation technique and avalanche photodiodes APD receiver over underwater environment channels. The characteristics of bit error rate BER and channel capacity for 4-PPM optical modulation technique are studied under different APD detector and Jerlov water types. Simulation results indicate that the performance of PPM and Jerlov type (I) are more suited for an underwater optical wireless communication. On the other hand, we discuss the suitability of avalanche photodiodes under this modulation technique, where the photodiode Si APD has more advantages compared with the other detectors when used as a receiver in an underwater optical communication. ٌ‫ا‬ ‫ذذد‬ ‫اٌالضٍىُح‬ ‫اٌثظرَح‬ ‫ٌالذظاالخ‬ ‫اٌثد‬ ٍ‫ف‬ ‫اٌخطأ‬ ً‫ِع‬ ‫ُِّساخ‬ ‫ّاء‬ ٍ‫راه‬ ‫خاٌذ‬ ‫ضعذ‬ .َ .َ ,ْ‫عٍىا‬ ‫جىاد‬ ‫تهاء‬ .َ .َ ,ٌ‫زور‬ ‫جثار‬ ‫ِؤَذ‬ .‫د‬ ,ٍٍ‫ع‬ ‫عثذ‬ ٍٍ‫ع‬ ْ‫ِاز‬ .‫د‬ ‫اٌفُسَاء‬ ُ‫لط‬ / َ‫اٌعٍى‬ ‫وٍُح‬ / ‫اٌّطرٕظرَح‬ ‫اٌجاِعح‬ ‫اٌّطرخٍض‬ : ‫رمٕ١خ‬ َ‫ثبعزخذا‬ ,‫ٔظش٠ب‬ ‫اٌّبء‬ ‫رؾذ‬ ‫اٌالعٍى١خ‬ ‫اٌجظش٠خ‬ ‫االرظبالد‬ َ‫ٔظب‬ ‫اداء‬ ً١ٍ‫رؾ‬ ُ‫ر‬ ,‫اٌجؾش‬ ‫٘زا‬ ٟ‫ف‬ 4-PPM ‫ٚاٌذا٠ٛد‬ ٚ ‫اٌجذ‬ ٟ‫ف‬ ‫اٌخط‬ ‫ِؼذي‬ ‫ِّ١ضاد‬ ًّ‫رش‬ ‫اٌذساعخ‬ .‫ِبئ١خ‬ ‫لٕبح‬ ‫ػجش‬ ٞ‫اٌزٙٛس‬ ٟ‫اٌؼٛئ‬ ِٓ ‫أٛاع‬ ‫ػذح‬ َ‫عزخذا‬ ‫ث‬ ‫اٌمٕبح‬ ‫عؼخ‬ ٖ‫ِ١ب‬ ِٓ ‫أٛاع‬ ‫ٌٚؼذح‬ ‫ف‬ ‫اٌىٛا‬ Jerlov ٓ١ّ‫اٌزؼ‬ ‫رمٕ١خ‬ ْ‫ا‬ ٌٝ‫ا‬ ‫رش١ش‬ ‫إٌزبئظ‬. PPM ‫ِبء‬ ‫ٌٕٚٛع‬ Jerlov I ‫ِٕبعجخ‬ ٟ٘ .‫اٌّبء‬ ‫رؾذ‬ ‫اٌالعٍى١خ‬ ‫اٌجظش٠خ‬ ‫ٌالرظبالد‬ (‫اٌزمٕ١خ‬ ‫رٍه‬ ًّ‫ػ‬ ‫رؾذ‬ ٟ‫اٌؼٛئ‬ ‫اٌذا٠ٛد‬ ‫ِالئّخ‬ ‫ٔبلشٕب‬ ‫اخش‬ ‫عبٔت‬ ِٓ PPM ,) ‫ار‬ ٟ‫ف‬ ‫ف‬ ‫وىب‬ َ‫رغزخذ‬ ‫ػٕذِب‬ ‫اٌؼٛئ١خ‬ ‫اٌذا٠ٛداد‬ ‫ثجم١خ‬ ‫ِمبسٔخ‬ ‫فٛائذ‬ ‫ػذح‬ ٗ٠‫ٌذ‬ ٛ٘ ْٛ‫ٌٍغٍ١ى‬ ٞ‫اٌزٙٛس‬ ٟ‫اٌؼٛئ‬ ‫اٌذا٠ٛد‬ ْ ‫ث‬ ‫ٚعذ‬ ‫اٌجظش٠خ‬ ‫االرظبالد‬ ‫ِٕظِٛخ‬ I. Introduction As the field of optical sources and photo-detector technology advances, communication through an underwater wireless optical channel (UWOC) has received a surge of attention by the researchers and scientists for wider bandwidth and higher data rate. UWOC fulfills several applications like underwater sensor networks (UWSNs), military applications, node-to-node communication, seismic activity sensing, and study of submarine life [1]. The large information bandwidth available at visible wavelengths has also opened the possibility for high-speed, and wireless communications in an underwater environment. Unfortunately, the propagation of light underwater is affected by both absorption and scattering [2]. As a matter of fact, underwater wireless optical communication (UOWC) uses the visible band of the electromagnetic spectrum (the spectrum range of 450-550nm), where water is relatively transparent to light and absorption takes its minimum value [3]. The attenuation coefficient () c  indicates the total effects of absorption ()  and scattering on energy loss ()  are shown in fig. (1)[4]. The values of () c  depend on both the wavelength  as well as turbidity of water [5]. Most of the recent works [6-7], mainly concentrate on line of sight UWOC. But it adds more complexity, when it comes to implementation because of the obstructions in sea water. Line of Sight offers many advantages like, high data rate, no RF license, no security upgrade, immune to RF interference, low power, and increasing in system bandwidth [8-11]. II. Optical Properties of Water When a photon is transmitted through a body of water, there are two mechanisms that prevent it from reaching a receiver further along the channel. The first one is the absorption, where the photon energy is converted into another form such as heat or chemical energy. The second is that a small variation in the refractive index causes the photon to change its direction, this is known as scattering. The total attenuation loss coefficient () c  is [12]: () () () c        (1)
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