Abstract:
Optical wireless communication (OWC) constitutes a key technology for 5G
wireless networks. OWC alleviates the radio frequency (RF) spectrum crunch
problem by enabling communications in the visible, infrared and ultraviolet
optical frequency bands for a variety of indoor and outdoor applications.
Outdoor infrared OWC systems are widely referred to as free-space optical
(FSO) communications that rely on line-of-sight transmissions of narrow laser
beams. The FSO technology is license-free, easy-to-deploy, cost-effective and
capable of delivering very high data rates. The major impairment that severely
degrades the performance of FSO links is related to the random aspect of the
atmosphere. Overcoming atmospheric turbulence-induced fading became the key
research area where many solutions have been proposed and analyzed. These
solutions include the multiple-input-multiple-output (MIMO) techniques. This work investigates and compares three MIMO FSO techniques; namely,
spatial-multiplexing (SMux), repetition-coding (RC) and optical-spatialmodulation
(OSM). Unlike the existing literature that considers the simplistic
additive white Gaussian noise (AWGN) model, this work revolves around the
more accurate Poisson noise model where the number of detected photons at the
receiver follows the Poisson distribution for shot-noise limited receivers. We
compare the SMux, RC and OSM systems in terms of data-rate, error-rate,
receiver complexity, channel estimation requirements… For each system, the
optimal maximum-likelihood (ML) decoder is derived and analyzed under
Poisson noise. We also evaluate the theoretical bit error rates (BERs) of RC and
OSM. While the SMux and RC schemes are the most efficient in terms of
maximizing the data-rate and minimizing the error-rate, respectively, the OSM
scheme constitutes a practical appealing tradeoff between SMux and RC. The
OSM solution leverages the need for inter-antenna synchronization while
achieving improved multiplexing gains.
