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RISS 인기검색어
- 검색키워드
- 저자 : Kotiang Stephen Odira Awidhi (검색결과 1 건)
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Kotiang Stephen Odira Awidhi Chonbuk National University 2015 국내석사
Free-space optical (FSO) communication has attracted a lot of interest from the scientific community and engineers mainly because of the high-data rates, license-free, high-security, ease of deployment, and cost effectiveness among other advantages associated with it. These have made FSO systems be considered as an attractive solution for high-rate last-mile terrestrial applications. However, this communication system is susceptible to severe attenuation under adverse weather conditions (e.g. rain, fog, and thick cloud cover), pointing errors, and atmospheric turbulence. The latter is caused by random variations in the refractive-index of air due to inhomogeneities in temperature, pressure fluctuations, humidity variations, and motion of air along the path of the optical signal. This results into intensity fluctuations known as turbulence-induced fading (scintillation) in the received signal. Scintillation imposes severe challenges for reliable data transmission. In addition, eye-safety regulations add yet another design constraint on the limit in transmit power. In this thesis, we consider spatial diversity using multiple transmitted optical beams and multiple receivers as a technique to overcome turbulenceinduced fading and provide performance analysis of FSO systems through analytical derivations of simple closed-form mathematical expressions. We assume the optical laser beams are propagating through a horizontal path experiencing isotropic and homogeneous non-Kolmogorov atmospheric turbulence. In this turbulence the refractive-index power spectrum has a generalized spectral power-law exponent which varies between 3 and 4 instead of the fixed classical Kolmogorov power-law exponent of 11/3. For moderate-to-strong turbulence conditions the turbulence-induced fading is modeled as a multiplicative random process that follows Gamma-Gamma distribution with additive white Gaussian noise (AWGN). Moreover, perfect turbulence state information is available at both the transmitter and receiver and the irradiance remains constant over a symbol duration. We also assume that the channel is memoryless, stationary and ergodic with independent and identically distributed intensity fading statistics. We then study the performance analysis of intensity modulation with direct detection (IM/DD) using on-off keying (OOK) multiple input multiple output (MIMO) FSO communication systems. We employ a generalized infinite power series representation of the modified Bessel-K function associated with the Gamma-Gamma probability density function (pdf) to develop comprehensive models for the bit error probability and informationtheoretic average channel capacity of FSO systems. The computer simulations show that the effects of power-law, turbulence strength parameter, and propagation distance on bit error rate (BER) and channel capacity are gradually mitigated as the diversity order increases. In addition, the results provide a useful approach for the optimization of diversity order configuration to maximize average channel capacity of MIMO FSO links over atmospheric turbulence.
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