The ergodic channel capacity of MIMO WOC systems with combined effects is investigated under correlated channel. The results indicate that spatial correlation has the most serious influence on ergodic channel capacity, followed by the pointing error and finally the atmospheric turbulence.
Conventional space-time trellis code cannot be directly applied to the intensity modulation/direct detection atmospheric optical transmission systems due to the complex and negative signal problem. An asymmetrically clipped space-time trellis code scheme is proposed, which combines the Hermitian symmetry of the inverse fast Fourier transform and the N/4 points to N points signal mapping to make the processed bipolar signal sequence satisfies the odd harmonic symmetry. The conversion of complex signal to positive real signal can then be achieved by clipping the bipolar signal sequence. Monte Carlo method is utilized to verify the feasibility of the proposed scheme. The results show that the proposed method can effectively resist the atmosphere scintillation.
A novel double-clad As2Se3 chalcogenide photonic crystal fiber is proposed and the slow light via stimulated Brillouin scattering is theoretically investigated. The Brillouin gain spectrum by taking into account the high-order acoustic modes is analyzed. The simulated results indicate that the slow light can be tuned by varying the air filling fraction in the inner cladding. The time delay upto 1120ns can be achieved with 1-m-long fiber when pumped with 10mW. But these features of slow light are less affected with the change of the air filling fraction in the outer cladding.
Intermodal Brillouin frequency shift and Brillouin gain spectrum in few-mode fibers are investigated by full vectorial finite element method, and the influences of pump power on the time delay and pulse broadening factor are also simulated. The simulation results show that Brillouin gain of intermodal stimulated Brillouin scattering varies with different modes pairs. Time delay increases with increasing of pump power. Pulse broadening factors decrease with the input signal pulse width but increase with the input pump power. Optimized results show that time delay of LP01 - LP01mode pair is 213.2ns, and the corresponding pulse broadening factors is 1.126.
The spatial correlation extensively exists in the multiple-input multiple-output (MIMO) free space optical (FSO) communication systems due to the channel fading and the antenna space limitation. Wilkinson’s method was utilized to investigate the impact of spatial correlation on the MIMO FSO communication system employing multipulse pulse-position modulation. Simulation results show that the existence of spatial correlation reduces the ergodic channel capacity, and the reception diversity is more competent to resist this kind of performance degradation.
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