&lt;title&gt;Scintillation characterization for multiple beams&lt;/title&gt;

Ryan, Patrick T.; Lowrey, W. H.; Rue, Imelda A. De La; Fugate, Robert Q.

doi:10.1117/12.363615

Cited by 10 publications

(10 citation statements)

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“…This research derived for the first time the optimal angular separations for multiple transmitter systems for airborne FSOC systems. A majority of previous research on multiple transmitters focused on satellite communications (where the turbulence is only present over a small part of the propagation path) or constant turbulence strength C 2 n paths [4,5,29,59,60,68]. The angular separations for all three airborne geometries (air-to-air, air-to-ground, and ground-to-air) are determined.…”

Section: Summary Of Main Resultsmentioning

confidence: 99%

“…Much of the research has focussed on multiple Rxs. Some research has been accomplished on multiple-Tx systems, but surprisingly little research can be found on the theoretical angular separation required to take full advantage of these spatial diversity techniques, especially for the airborne application [34,58,59,68]. Rather, most literature on differential statistics for angular separations is concerned with an isoplanatic angle (relatively similar paths) for sensing and wavefront control.…”

Section: Diversity Techniquesmentioning

confidence: 99%

“…Then, techniques are devised to overcome these effects by applying multiple uncorrelated realizations. In the second approach, typically, or ground-based constant-turbulence-strength paths [4,5,30,40,59,60,68]. Here, this work presents these angular separations for three airborne geometries (air-to-air, air-to-ground, and ground-to-air) through extended turbulence and determines practical configurations.…”

Section: Assessment Of Best Areas For Further Researchmentioning

confidence: 99%

“…For example, spatial diversity could be accomplished at the receiver by a single large aperture (larger than ρ c or multiple small apertures [3]. Some researchers have studied multiple-transmitter approaches [34,58,59,68] for the space-to-ground and the ground-to-ground scenarios, but few have studied the air-to-air scenario. Much of the spatial diversity research has focused on MIMO techniques or just multiple receivers to reduce signal fades, without defining the requisite separation distance.…”

Section: Diversity Techniquesmentioning

confidence: 99%

“…[5,60,68] The larger the differential irradiance variance, the less correlated the irradiance fluctuations become. For uncorrelated beams this variance should approach two times the irradiance variance of a single beam.…”

Section: Differential Irradiance and Tilt Variancementioning

confidence: 99%

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Integrated approach to airborne laser communication

Louthain¹

2008

SPIE Proceedings

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Lasers offer tremendous advantages over RF communication systems in terms of bandwidth and security due to their ultra-high frequency and narrow spatial beamwidth. Unfortunately, atmospheric turbulence significantly increases the received power variation and bit error rate (BER) in free-space optical communication (FSOC) systems. Further, airborne optical communication systems require special considerations in size, complexity, power, and weight.If two or more laser beams are sufficiently separated so that their turbulence effects are uncorrelated (i.e. anisoplanatic), they can effectively "average out" turbulence effects. This requisite separation distance is derived for multiple geometries, turbulence conditions, and optical properties. In most cases and geometries, the angles ordered from largest to smallest are: phase uncorrelated angle (equivalent to the tilt uncorrelated angle and phase anisoplanatic angle), tilt isoplanatic angle, phase isoplanatic angle, scintillation uncorrelated angle (or scintillation anisoplanatic angle), and scintillation isoplanatic angle (θ ψ ind > θ T A > θ 0 > θ χ ind > θ χ 0 ). Conventional adaptive optics (AO) systems only correct for phase and cannot correct for strong scintillation, while multiple-transmitter systems use several transmission paths to "average out" effects of the strong scintillation by incoherently summing up the beams in the receiver.Since all three airborne geometries (air-to-air, air-to-ground, and ground-toair) are studied, a comparison of multiple-beam airborne laser communication system performance is presented for the first time. Wave optics simulations show that a combination of transmitter diversity, receiver and transmitter trackers, and adaptive thresholding can significantly reduce BER in an air-to-air FSOC system by over 10,000 times. As demonstrated in this work, two transmitters alone separated by only 31 cm (100 km path length, 1.55 µm wavelength, 4 km in altitude) provide a significant iv BER improvement over one transmitter, especially for the strong turbulence regime where the required SNR for a fixed BER is reduced by 9 dB. Including the tracking and adaptive thresholding techniques, resulted in a 13 dB overall improvement.Two beams also reduce the fade length, suggesting even greater improvement can be obtained when interleaving and forward error correction coding is implemented. Major Schmidt also knew when to hand me water and how to keep me on the road, since he had just finished his marathon.

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