PPT On Wireless Communication

Published in: Networking
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The major theme of my PPT is It will explain us to know how the wireless communication will generate in the underground of water and Mines .

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    ro uction The present technology of acoustic underwater communication is a legacy technology that provides low- data-rate transmissions for medium-range communication. Data rates of acoustic communication are restricted to around tens of thousands of kilobits per second for ranges of a kilometre , and less than a thousand kilobits per second for ranges up to 100 km, due to severe, frequency- dependent attenuation and surface-induced pulse spread. In addition, the speed of acoustic waves in the ocean is approximately 1500 m/s, so that long-range communication involves high latency, which poses a problem for real-time response, synchronization , and multiple-access protocols
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    Alternative method An alternative means of underwater communication is O based on optics, where in high data rates are possible. However, the distance between the transmitter and the O receiver must be short , due to the extremely challenging underwater environment, which is characterized by high multi scattering and absorption.
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    sic undergrounwvater communication scenario Oil facility Ship Unmanned underwater vehicle sensor Unmanned underwater vehicle sensor Diver submarine sensor
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    Challe nderground o tic ireless communication The two main causes of electromagnetic attenuation in water are scattering and absorption. Whilst scattering changes the path of a photon, absorption completely removes the photon from its path. The combined rate of attenuation is described by the attenuation coincident c, which is written in Where a is the absorption coincident and is the coefficient of scattering; both are dependent on the illumination wavelength . When this wavelength is in the region 450-550 The value of the attenuation coefficient ranges between 0.15 -1 for the clearest open oceans and 2.19 m for turbid harbours.
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    Absorption,scattering, and extinction coefficients fo fo types of water—pure sea water, clean ocean water, coastal ocean water, and turbid harbour water—at 520-nm wavelength. a(520nm) ß(520nm) c (520nrn) 2 os Pure sea water Clean ocean Costal Ocean Turbid harbor c
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    Parameter Extinction coefficient for • Clean ocean Coastal ocean Turbid harbour Critical angle (deg) Optical efficiency for • Retro reflector • Transmitter Receiver Transmitter power (W) Receiver aperture area (m TABLE 1 These are the parameters used in the numerical calculation 0.9 0.9 0.9 2) value 0.15 0.30 2.19 48.44 0.01
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    30 COMMUNICATION LINK MODELS There are three models of optical wireless communication which provide the required data rate. Line-of-Sight Communication Link. Modulating Retro Reflector Communication Line. Reflective Communication Link.
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    Line-of-Sight Communication Link The most common point between points in optical wireless communication systems is a line-of-sight LOS link as illustrated in Fig. o In this scenario, the transmitter directs the light beam in the direction of the receiver. The optical signal reaching the receiver is obtained by multiplying the transmitter power, telescope gain, and losses and is given by
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    200 d Figure 3a. The line of sight communication scenario
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    Modulating Retro-reflector Communication Link In a modulating retro-reflector link, the interrogator sits at one end (in our case, in the submarine), and a small modulating optical retro-reflector sits at the remote end. In operation, the interrogator illuminates the retro- reflecting end of the link with a continuous wave beam. The retro reflector in actively reflects this beam back to the interrogator while modulating the information on it. The received power in this scenario is given by
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    Fig,3, Shows the modulating retro reflective communication link
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    Reflective Communication Link 'In this case, the laser transmitter emits a cone of light, defined by inner and outer angles min and max, in the upward direction. Here I and t are the angles of incidence and of transmission, respectively. (The latter is derived from the former using Snell's law). 'The light reaching the ocean-air surface illuminates an annular area and is partially bounced back in accordance with the reflectivity. Since the refractive index of air is lower than that of water, total internal reflection (T IR) can be achieved above a critical incidence angle.
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    Omin max Figure 3e The reflection communication scenario.
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    s: o In underwater optical communications, most authors adopt a LOS link as it is easier to implement and most energy efficient . A reflecting non-LOS link is used to overcome underwater obstacles by reflecting from the sea surface . A retro reflective link was also suggested as it may be useful for underwater application because it allows much of the weight and power burden of the link to remain at one end .
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    Basic bock diagram Laser Modulator Source Receiver Signal Conditioning Level Detector Figure I-I Traditional implementation oft ndeHvater ESO Link using Lasers and PMTs Modulator/ Encoder LED Source Photodiode Digitizer Receiver DSP/ Detector/ Decoder
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    Modulation scheme used The simplest and most widespread modulation technique in optical wireless communication is intensity-modulation, direct- detection on-off keying 00K. In this technique, the receiver is based on the emerging technology of silicon photomultipliers SiPMs.15 These photo detector devices are fabricated in the form of arrays of photodiodes that are operated in Geiger mode to create a photon-counting device. If we assume that a large number of photons are received, then according to the central limit theorem, the Poisson distribution can be approximated by a Gaussian distribution and the BER is given by
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    Graph showing BER asa function of transmitter-receiver sep n=föfCléåW6em-water-with-extinqtionxoeffO I ent equal to 0.15m to 1m In Fig we can see that BER values of 10—4 are obtained for a reflective link when the node separation is 40 m, while a BER of 10—4 could be achieved in a LOS link and a retro-reflector link when the node separation is 60 m and 50 m, respectively. From this result it is easy to understand that acceptable BER performance could be achieved for short ranges on the order of tens of meters for all three models. 100 100 104 b 106 108 10 10 The reflective communication link - LOS communication link The retro communication link 10 12 10 20 30 40 50 Distance [ml 60 70 80
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    Graph showing numberofreceived photons scenario as a function of transmitter- tion fortwo cases: absorption and extinction. In Fig we compare the numbers of photons received for a link operated in turbid harbour water for two cases: a when only absorption is considered and b when absorption and scattering are considered. From this figure it is easy to see that in the absorption case the number of received photons reduces from 105 to 1 for increases in distance separation from 1 to 65 m. while in the case of abs-sorption and scattering the number of received photons reduces from 105 to 1 for increases in distance separation from 1 to 1.5 105 104 103 102 101 100 10 20 Absorption=0.18m-l Extinction=2.2m- 70 30 40 50 Distance [ml 60 80
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    Applications for underwater optical communication systems include: Diver-to-diver communication links. Diver-to-submarine links. Submarine-to-UAV links. Submarine-to-submarine links. UAV-t0-UAV links. Submarine-to-satellite links.
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    يه1Z امهر

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