MIMO Free Space Optical Communications in Turbid and Turbulent Atmosphere (Invited Paper)

Abstract

<p class="MsoNormal" style="margin: 0cm 0cm 0pt; layout-grid-mode: char;"><span style="layout-grid-mode: line; font-family: ";Arial";,";sans-serif";; mso-bidi-font-weight: bold;"><span style="font-size: x-small;">Free Space Optical (FSO) communications is the only viable solution for creating a three-dimensional global communications grid of inter-connected ground and airborne nodes. The huge amount of data exchange between satellites and ground stations demands enormous capacity that cannot be provided by strictly regulated, scarce resources of the Radio Frequency (RF) spectrum. Free Space Optical (FSO) communications, on the other hand, has the potential of providing virtually unlimited bandwidth. Furthermore, due to the spatial confinement of laser beams, such links are very secure. In other words, security is guaranteed at the physical layer. However, the promised enormous data rates are only available under clear weather conditions, and atmospheric phenomena such as clouds, fog, and even turbulence can degrade the performance, dramatically. While turbid media such as clouds and aerosols cause pulse broadening in space and time, turbulence presents itself as scintillation and fading. Hence, to exploit the great potentials of FSO at its best under all weather conditions, prudent measures must be taken in the design of transmitter and receiver. More specifically, multiple transmitters and receivers can be used to combat the turbulence-induced fading and to compensate for pulse attenuation and broadening caused by scattering. In this paper, Multiple-Input Multiple-Output (MIMO) transmitter and receiver designs for FSO communications are investigated and the achievable performance improvements are discussed. <em></em></span></span></p&gt

Impact of Link Parameters and Channel Correlation on the Performance of FSO Systems With the Differential Signaling Technique

“…For a weak turbulence regime 2 < 1 [27]. In the case of a plane wave propagation through a turbulence channel we have [8]:…”

Turbo-Coded MC-CDMA Communication Link over Strong Turbulence Fading Limited FSO Channel with Receiver Space Diversity

“…In strong turbulence-fading condition, this distance is not more than some few centimetres, since this parameter is proportional to Fried's parameter r 0 defined as r 0 = 1.68(C 2 n Lk 2 ) −3/5 and, consequently, inversely proportional to turbulence strength [22]. As a result, ensuring minimum spatial separation among the photodetectors for having uncorrelated fading is practically achievable [15,23]. Besides, the dimension of each receiver should be chosen so that total noise generated after diversity combining does not exceed noise generated with a single large receiver system.…”

“…Atmospheric turbulence produces eddies or small air pockets having randomly varrying refractive index. This refractive index variation causes phase perturbation of the wave front (isophase plane) of propagating light [15]. As a result, secondary waves generated from different point of wave front have different phase, and their interference with each other gives amplitude variation.…”

Performances of Free-Space Optical Communication System Over Strong Turbulence

“…Multiple beam waves transmission and multiple beam receiver or MIMO has been reported could enhanced the performance FSOC system at signifficant value [3]. Saturated EDFA at transmitter beacon has been reported successfully overcoming high turbulence [4].…”

“…Hence it cause the scintillation phenomena to receiver. By all means the characteristical performance of FSOC system is decreasing [1][2][3].…”