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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 41075 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Nasiri Kenari, Masoumeh
- Abstract:
- With recent successes in laboratory tests, and in atmosphere and space demonstrations, there is no doubt that the free-space optical (FSO) communications is ready for operational deployment. Large bandwidth, unlicensed spectrum, excellent security, and quick and inexpensive setup are among its most attractive features. Despite their attractive features, FSO communications suffer from several challenges in practical deployment; the major of them is fading or scintillation and path loss. To overcome such limitations, Channel Coding along with MIMO and Cooperative techniques have been proposed. Although the promising effects of cooperative transmissions in RF communications have greatly been investigated, there have not been remarkable researches on cooperative transmissions in FSO communications. In this thesis, we consider Cooperative Communications in FSO Networks. We first consider a 3-way FSO communication setup, in which the cooperative protocol can be applied to achieve the spatial diversity without much increase in hardware, compared to its regular transmission. Then, we introduce different cooperative strategies and investigate their bit error rate (BER) performance in the presence of shot noise. In the next step, we consider a cooperative free-space communication via an optical amplify-and-forward relay. We use photon-counting approach to investigate the system bit error probability (BEP) performance, and study the effects of atmospheric turbulence, background light, amplified spontaneous emission, and receiver thermal noise on the system performance. We also provide an availability analysis for the relay-assisted and multiple-transmitter systems and show that the relay-assisted system performs much better from this point of view. To consider cooperative FSO systems from information theory point of view, we investigate the outage performance of amplify-and-forward (AF) and decode-and-forward (DF) strategies. By a new definition of the order of diversity, we derive an analytical expression for the performance comparison of different cooperative and non cooperative protocols. Finally, we consider rateless coding for a FSO communication. To have a robust communication with a fixed rate error-correcting code, the code rate has to be selected based on the worst condition of the channel. Rateless codes are capable of adapting the bit rate to the channel realization without requiring channel state information at the transmitter
- Keywords:
- Cooperation Communication ; Relay Channel ; Optical Amplifier ; Rateless Codes ; Free Space Optical System
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