Joint influence of heterogeneous stochastic factors on bit-error rate of ground-to-ground free-space laser communication systems E. Ferdinandov a , B. Pachedjieva a, * , B. Bonev b , Sl. Saparev c a Technical University of Sofia Branch Plovdiv, Optoelectronics and Lasers, 25 Tsanko Diustabanov St, 4000 Plovdiv, Bulgaria b Technical University of Sofia, Radiotechnic, 8 Kilment Ohridski Blvd, Sofia, Bulgaria c Technical College, Smolyan, Bulgaria Received 10 May 2006; received in revised form 4 September 2006; accepted 4 September 2006 Abstract Research methods for the formation of BER in the ground-to-ground Free-Space Laser Communication Systems (Free-Space Optics – FSO) with increased analytical effectiveness have been suggested. They correspond to physically rightful approximations with appro- bated quantity effectiveness. The methods have been used to study the influence of heterogeneous stochastic factors, such as: quantum noises, atmospheric transmittance fluctuations, mechanical vibrations of the transmitting laser antenna, atmospheric turbulence, on BER of FSO. An algorithm for quantity estimation of the joint influence of all stochastic factors has been created. Numerical examples, illustrated by graphic material, have been shown. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Free-space optics; Bit-error rate; Atmospheric transmittance fluctuations; Mechanical vibrations of the transmitting laser antenna; Atmosp- heric turbulence 1. Introduction Free-Space Laser Communications (Free Space Optics – FSO) are becoming an increasingly essential part of modern information technologies [1–7]. There are several reasons for this trend: FSO’s technical and economical parameters most fully correspond to the requirements raised by the current development of local communication networks; FSO is an effective and attractive solution of the ‘‘last mile’’ problem; FSO’s relatively low price, quick installation process and portability make FSO the leading means for establishing temporary links for big and high speed information flows in cities and industrial complexes. These characteristics explain today’s large interest in the wide and versatile scientific and engineering development of FSO. The development of FSO is related to several key prob- lems. These problems result from the multiple physical con- ditions that affect the spatial structure of the laser beam, the atmospheric extinction (atmospheric transmission) fluc- tuations, the fluctuations of the propagation direction of the beam resulting from mechanical vibrations of various origins of the transmitting laser antenna, and from atmo- spheric turbulence. Resolving these problems is necessary for FSO research and design. Existing research has defined the BER of FSO and accounted for selected stochastic factors influencing it. Most studies focus on the influence of atmospheric turbu- lence [8–11]. The solutions they propose are characterized by considerable mathematical difficulty and problematic engineering applicability. Moreover, these solutions do not provide a possibility for resolving the reverse task in the engineering design and study of ground-to-ground 0030-4018/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2006.09.006 * Corresponding author. Address: Technical University of Sofia Branch Plovdiv, Optoelectronics and Lasers, 25 Tsanko Diustabanov St, 4000 Plovdiv, Sofia, Bulgaria. E-mail address: pachedjieva@yahoo.com (B. Pachedjieva). www.elsevier.com/locate/optcom Optics Communications 270 (2007) 121–127