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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 49698 (05)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Salehi, Jawad
- Abstract:
- The increasing tendency to offshore exploration is making the need to design efficient methods for secure underwater wireless transmission increasingly highlighted. Radio frequency used for wireless communications in open space may not be suitable for data transfer due to their extensive drop in the water. On the other hand, since sound propagates well in water, now the majority of underwater communication systems are using audio frequencies. Limited bandwidth, low emission speed, and low security are the most important disadvantages of audio systems in comparison with optical systems. Therefore, optical systems, could be appropriate alternatives for audio systems to achieve secure, high-speed communications in the water. Despite the unique properties of optical systems, due to scattering, absorption and turbulence of underwater channels, the performance of optical systems is associated with serious problems in distances longer than 100 meters while audio systems can be transmitted in the distances of several kilometers underwater. Therefore, our primary goal is to provide solutions to reduce the aforementioned damaging effects and, as a result, to increase the range of underwater optical communications. Numerous studies were conducted to avoid the effects of turbulence in open space optical communication channels. We need to use high beam width of optical transmitters (e.g. LED) for many applications, such as in situations when transmitter and receiver are moving relative to each other. Considering that the photons of optical signals are affected by channel’s multiple scattering, the increase in beam width of optical transmitter results in the increase of time expansion of channel impulse response and thus, the inter-symbol interference increases. This highlights the necessity of application of efficient equalizers in underwater channels. However, no serious study has yet been conducted to design optical equalizers for underwater channels.In this research, we first study and simulate the channel impulse response of underwater wireless optical communication in various conditions. Then, to deal with inter-symbol interference, we design optical equalizers for underwater channels and we will try to further improve communication system performance studying the performance of various types of equalizers. Finally, the results will be shown using computer simulation
- Keywords:
- Underwater Wireless Optical Communication Systems ; Bit Error Rate ; Multiple Input Multiple Output (MIMO)System ; Photon-Count Method ; Inter-Symbol Interference (ISI)
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