Outage probability of the Gaussian MIMO free-space optical channel with PPM

Abstract

The free-space optical channel has the potential to facilitate inexpensive, wireless communication with fiber-like bandwidth under short deployment timelines. However, atmospheric effects can significantly degrade the reliability of a free-space optical link. In particular, atmospheric turbulence causes random fluctuations in the irradiance of the received laser beam, commonly referred to as scintillation.The scintillation process is slow compared to the large data rates typical of optical transmission. As such, we adopt a quasi-static block fading model and study the outage probability of the channel under the assumption of orthogonal pulse-position modulation. We investigate the mitigation of scintillation through the use of multiple lasers and multiple apertures, thereby creating a multiple-input multiple output (MIMO) channel. Non-ideal photodetection is also assumed such that the combined shot noise and thermal noise are considered as signal-independent additive Gaussian white noise. Assuming perfect receiver channel state information (CSI), we compute the signal-to-noise ratio exponents for the cases when the scintillation is lognormal, exponential and gamma-gamma distributed, which cover a wide range of atmospheric turbulence conditions. Furthermore, we illustrate very large gains, in some cases larger than 15 dB, when transmitter CSI is also available by adapting the transmitted electrical power.

Mitigating Turbulence-Induced Fading in Coherent FSO Links: An Adaptive Space-Time Code Approach

“…In comparison with measured data, gamma-gamma distribution is effective in describing weak to strong atmospheric turbulence conditions. The PDF is expressed as [16] f e H GG h ðÞ¼ 2 αβ ðÞ…”

MIMO optical wireless communication via monolithic or sparse apertures

“…Diversity gain is conventionally defined as how fast the logarithm of system performance curve (e.g., outage probability or average bit error rate) decays with respect to log(SN R) at high signal-to-noise ratio (SNR). Therefore, the outage probability P out of the MIMO FSO diversity system with N t transmit apertures and N r receive apertures, defined based on the assumptions above, scales at high SNR as 1) wherein the fading is modelled by lognormal distribution [27] and D S = min{α, β}/2 for medium or strong turbulence conditions when Gamma-Gamma distribution is used [14] where σ 2 χ is the variance of turbulence-induced log-amplitude fluctuations and α and β are the parameters of the Gamma-Gamma fading model. Equation 1shows that the relative diversity gain of the underlying MIMO FSO system with respect to a SISO system is determined by the product of the number of transmit and receive apertures, N t N r similar to RF MIMO diversity systems.…”

Network‐coded multiple‐source cooperation aided relaying for free‐space optical transmission

“…where the Rytov variance is given by 2 D 0.5C 2 n Ä 7=6 L 11=6 and the geometry-related factor d is defined as d D ÄD 2 =.4L/ 1=2 , with L representing the link distance, D denoting the diameter of the receiver lens aperture, C 2 n represents the refractive index structure parameter and Ä D 2 = denotes the wave number associated with a wavelength of . Finally, the scintillation index is defined as SI D˛ 1 Cˇ 1 C .˛ˇ/ 1 [4].…”