3,380 research outputs found
MIMO Underwater Visible Light Communications: Comprehensive Channel Study, Performance Analysis, and Multiple-Symbol Detection
In this paper, we analytically study the bit error rate (BER) performance of
underwater visible light communication (UVLC) systems with binary pulse
position modulation (BPPM). We simulate the channel fading-free impulse
response (FFIR) based on Monte Carlo numerical method to take into account the
absorption and scattering effects. Additionally, to characterize turbulence
effects, we multiply the aforementioned FFIR by a fading coefficient which for
weak oceanic turbulence can be modeled as a lognormal random variable (RV).
Moreover, to mitigate turbulence effects, we employ multiple transmitters
and/or receivers, i.e., spatial diversity technique over UVLC links.
Closed-form expressions for the system BER are provided, when equal gain
combiner (EGC) is employed at the receiver side, thanks to Gauss-Hermite
quadrature formula and approximation to the sum of lognormal RVs. We further
apply saddle-point approximation, an accurate photon-counting-based method, to
evaluate the system BER in the presence of shot noise. Both laser-based
collimated and light emitting diode (LED)-based diffusive links are
investigated. Since multiple-scattering effect of UVLC channels on the
propagating photons causes considerable inter-symbol interference (ISI),
especially for diffusive channels, we also obtain the optimum multiple-symbol
detection (MSD) algorithm to significantly alleviate ISI effects and improve
the system performance. Our numerical analysis indicates good matches between
the analytical and photon-counting results implying the negligibility of
signal-dependent shot noise, and also between analytical results and numerical
simulations confirming the accuracy of our derived closed-form expressions for
the system BER. Besides, our results show that spatial diversity significantly
mitigates fading impairments while MSD considerably alleviates ISI
deteriorations
Free-space quantum links under diverse weather conditions
Free-space optical communication links are promising channels for
establishing secure quantum communication. Here we study the transmission of
nonclassical light through a turbulent atmospheric link under diverse weather
conditions, including rain or haze. To include these effects, the theory of
light transmission through atmospheric links in the elliptic-beam approximation
presented by Vasylyev et al. [D. Vasylyev et al., Phys. Rev. Lett. 117, 090501
(2016); arXiv:1604.01373] is further generalized.It is demonstrated, with good
agreement between theory and experiment, that low-intensity rain merely
contributes additional deterministic losses, whereas haze also introduces
additional beam deformations of the transmitted light. Based on these results,
we study theoretically the transmission of quadrature squeezing and Gaussian
entanglement under these weather conditions.Comment: 14 pages, 8 figure
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