Outage Probability of the Gaussian MIMO Free-Space Optical Channel with PPM

TL;DR

This paper analyzes the outage probability of Gaussian MIMO free-space optical channels with PPM under atmospheric turbulence, considering various turbulence models and CSI availability, demonstrating significant performance gains with power adaptation.

Contribution

It introduces a comprehensive outage probability analysis for MIMO FSO channels with PPM, incorporating multiple turbulence models and CSI scenarios, highlighting potential performance improvements.

Findings

Large outage probability reductions (>15 dB) with transmitter CSI and power adaptation.

Significant impact of turbulence models (lognormal, exponential, gamma-gamma) on channel reliability.

Analytical expressions for SNR exponents under different atmospheric conditions.

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.