Free-Space Optical Communication With Spatial Modulation and Coherent Detection Over H-K Atmospheric Turbulence Channels

Abstract

Abstract-The use of optical spatial modulation (OSM), which has been recently emerged as a power and bandwidth efficient pulsed modulation technique for indoor optical wireless communication, is proposed as a simple, low-complexity means of achieving spatial diversity in coherent free space optical (FSO) communication systems. In doing so, this paper makes several novel contributions as follows. It presents a generic analytical framework for obtaining the Average Bit Error Probability (ABEP) of uncoded OSM with coherent detection in the presence of turbulence-induced fading. Although the framework is general enough to accommodate any type of models based on turbulence scattering, the focus in this paper is the H-K distribution. Although this distribution represents a very general scattering model valid over a wide range of atmospheric conditions, it is has not been considered in the past in conjunction with FSO systems possibly because of its mathematical complexity. The proposed analytical framework yields exact performance evaluation results for MIMO systems with two transmit and an arbitrary number of receive apertures. In addition, tight upper bounds are derived for the error probability for OSM systems with an arbitrary number of transmit apertures as well as for convolutionally encoded signals. The performance of OSM is compared to that of well established coherent FSO schemes, employing spatial diversity at the transmitter or the receiver only. Specifically, it is shown that OSM can offer comparable performance with conventional coherent FSO schemes while outperforming the latter in terms of spectral efficiency and hardware complexity. Various numerical performance evaluation results are also presented and compared with equivalent results obtained by Monte Carlo simulations which verify the accuracy of the derived analytical expressions.Index Terms-average bit error probability, atmospheric turbulence, coherent detection, free space optical communication systems, H-K distribution, multiple-input multiple-output (MIMO) systems, optical spatial modulation.

Polarization Diversity in MIMO Communication Over Atmospheric Turbulence Channels

“…Thus the second contribution of this paper is a novel coherent MIMO OSM architecture combining the spatial modulation (SM) principle with MPOLSK, denoted by SM-MPOLSK. Because one bit is allocated to the additional polarization dimension, the proposed OSM method requires smaller constellations or less number of transmit apertures than previously proposed OSM approaches of [22]- [25]. As validated by both theoretical analysis and simulation results, because of the inherent robustness of POLSK to channel scintillation effects, the proposed OSM method utilizing polarization dimension as well as multiple transmit/receive apertures also provides improved error performances over atmospheric turbulence channels.…”

“…In addition, studies show that the error performance of OSM is superior to other MIMO transmission approaches operating at the same spectral efficiency. OSM, proposed first for visible light communications in [22], has also been considered for FSO communication in [23]- [25].…”

Asymptotic Performance Analysis of Free-Space Optical Links with Transmit Diversity

“…Referring to the derivation of MRC receive diversity FSO systems in [21,22], we can obtain the MRC BER expression as…”

“…To investigate the performance of the four transmit-diversity techniques in our paper, we illustrate the BER curves of the MIMO FSO systems adopting RC at transmitters and EGC or MRC at receivers, with diversity methods in [21][22][23] for comparison. For the sake of fairness, we also present the BER curve of a MISO FSO system with RC and EGC as Pb RC (e), and a MISO FSO system with RC and MRC as Pb MRC (e).…”

“…Therefore, the concept of spatial diversity in FSO differs from that in traditional RF communications. As introduced in [11], spatial diversity in FSO systems can be realized via the use of multiple apertures at the receiver (receive diversity) [12], multiple beams at the transmitter (transmit diversity) [13][14][15], or a combination of the two [16][17][18][19][20][21][22][23]. Receive diversity and transmit diversity are usually referred to as SIMO (Single-Input Multiple-Outputs) and MISO (Multiple-Inputs Single-Output) respectively.…”