Subcarrier Intensity Modulated Free-Space Optical Communications in K-Distributed Turbulence Channels

In this paper, the bit error rate (BER) performance of a subcarrier intensity-modulated (SIM) free-space optical (FSO) communications system using binary phase shift keying (BPSK) is investigated over a K-distributed turbulence channel. First, the performance is analyzed employing a negative exponential turbulence model, and an exact closed-form expression is derived for the BER. Then, it is shown that the probability density function (PDF) of the K distribution can be approximated accurately by a finite sum of weighted negative exponential PDFs. Based on this interesting result and by using the closed-form expression, which is derived for the case of a negative exponential model, an approximate, closed-form expression for the BER of the BPSK-based SIM FSO over a K channel is derived. Moreover, to improve the BER performance, spatial diversity using selection combining (SC) is considered. It is shown that the PDF of the resulting channel irradiance corresponding to the SC diversity scheme over a K channel can be approximated accurately by a finite linear combination of negative exponential functions. The derived approximate PDF accurately estimates the PDF of the channel irradiance for arbitrary values of diversity order and is valid for a wide range of channel parameters. Then, an approximate, closed-form expression is derived for the average BER of the BPSK-based SIM FSO system employing the SC diversity technique over a K channel. Numerical results presented in this paper show that the derived approximate expressions are very accurate and can be used as efficient tools for performance analysis of the system.

[1]  Milton Abramowitz,et al.  Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables , 1964 .

[2]  E. Leitgeb,et al.  Free-space optical communication employing subcarrier modulation and spatial diversity in atmospheric turbulence channel , 2008 .

[3]  Etty J. Lee,et al.  Part 1: optical communication over the clear turbulent atmospheric channel using diversity , 2004, IEEE Journal on Selected Areas in Communications.

[4]  Jia Li,et al.  Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels , 2007, IEEE Trans. Commun..

[5]  Zabih Ghassemlooy,et al.  Performance of Subcarrier Modulated Free- Space Optical Communications , 2007 .

[6]  Zabih Ghassemlooy,et al.  BPSK Subcarrier Intensity Modulated Free-Space Optical Communications in Atmospheric Turbulence , 2009, Journal of Lightwave Technology.

[7]  R. Stephenson A and V , 1962, The British journal of ophthalmology.

[8]  Xinyang Li,et al.  Performance analysis of bit error rate for free space optical communication with tip-tilt compensation based on gamma-gamma distribution , 2009 .

[9]  Antonio Garc Error Rate Performance for STBC in Free-Space Optical Communications through Strong Atmospheric Turbulence , 2007 .

[10]  J. M. Holtzmann On using perturbation analysis to do sensitivity analysis: derivatives versus differences , 1992 .

[11]  E. Jakeman,et al.  A model for non-Rayleigh sea echo , 1976 .

[12]  Kumar N. Sivarajan,et al.  Optical Networks: A Practical Perspective , 1998 .

[13]  Herbert A. David,et al.  Order Statistics, Third Edition , 2003, Wiley Series in Probability and Statistics.

[14]  D. Owen Handbook of Mathematical Functions with Formulas , 1965 .

[15]  J. N. Kapur,et al.  Entropy optimization principles with applications , 1992 .

[16]  Joseph Lipka,et al.  A Table of Integrals , 2010 .

[17]  Antonio García-Zambrana,et al.  Closed-form BER expression for FSO links with transmit laser selection over exponential atmospheric turbulence channels , 2009 .