Impact of atmospheric turbulence on free space optical (FSO) communication

نویسنده

  • Sachin Rathee
چکیده

In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, impairing link performance. Free Space Optical (FSO) communications is the only viable solution for creating a three-dimensional global communications grid of interconnected 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. In this paper, we describe several communication techniques to mitigate turbulence-induced intensity fluctuations, i.e., signal fading. These techniques are applicable in the regime in which the receiver aperture is smaller than the correlation length of fading and the observation interval is shorter than the correlation time of fading. We assume that the receiver has no knowledge of the instantaneous fading state. When the receiver knows only the marginal statistics of the fading, a symbol-bysymbol ML detector can be used to improve detection performance. If the receiver has knowledge of the joint temporal statistics of the fading, maximumlikelihood sequence detection (MLSD) can be employed, yielding a further performance improvement, but at the cost of very high complexity. Spatial diversity reception with multiple receivers can also be used to overcome turbulence-induced fading. We describe the use of ML detection in spatial diversity reception to reduce the diversity gain penalty caused by correlation between the fading at different receivers. In a companion paper, we describe two reduced-complexity implementations of the MLSD, which make use of a single-step Markov chain model for the fading correlation in conjunction with per-survivor processing.

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تاریخ انتشار 2014