Anisoplanatism in airborne laser communication

Louthain, James A.; Schmidt, Jason D.

doi:10.1364/oe.16.016769

Cited by 2 publications

(24 citation statements)

References 17 publications

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“…As first derived in support of this research [46,47,49] . For a 4 km path, that separation would need to approach 65 cm.…”

Section: Angular Phase Independence Of Two Beamssupporting

confidence: 60%

“…(135) increases with separation angle, approaching a maximum value at two times the mean square phase or 2σ 2 ψ as the two paths are placed far apart. This time, setting the structure function equal to the maximum value for the phase structure function yields [46] …”

Section: Angular Phase Independence Of Two Beamsmentioning

confidence: 99%

“…(134) again, this work determines the parallel path isoplanatic distance. Referring to the phase structure function at the receiver for two parallel path point sources separated by ∆x yields [46,66] D ψ (∆x, L) = 2.91k…”

Section: Parallel Path Isoplanatismmentioning

confidence: 99%

“…Similar to Eq. (138), the plane-wave independent phase separation distance ∆x ind is determined by setting the structure function equal to the maximum value and solving for the separation [46] ∆x ind = 2σ 2 ψ,pl ∆x 0 = 0.4109κ…”

Section: Parallel Path Isoplanatismmentioning

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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“…As first derived in support of this research [46,47,49] . For a 4 km path, that separation would need to approach 65 cm.…”

Section: Angular Phase Independence Of Two Beamssupporting

confidence: 60%

Section: Angular Phase Independence Of Two Beamsmentioning

confidence: 99%

Section: Parallel Path Isoplanatismmentioning

confidence: 99%

Section: Parallel Path Isoplanatismmentioning

confidence: 99%

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Integrated approach to airborne laser communication

Louthain¹

2008

SPIE Proceedings

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“…Based on the theory of beam propagation through a random medium we determined the minimal transverse coherence distance ݀ ௧ , to ensure uncorrelated received signals. Values of ݀ ௧ were derived from measured distributions of the thermal structure parameter ‫ܥ‬ ் ଶ (obtained from ‫ܥ‬ ଶ ) along optical beams according to [15]. Alternatively, an expression for beam separation can also be set by the scintillation anisoplanatic distance [16].…”

Section: Experimental Measurementsmentioning

confidence: 99%

FSO Detection Using Differential Signaling in Outdoor Correlated-Channels Condition

Abadi

Ghassemlooy

Khalighi

et al. 2016

IEEE Photon. Technol. Lett.

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Abstract-In this paper, we introduce a detection technique based on differential signaling scheme for outdoor free space optical communications. This method requires no channel state information (CSI) and does not suffer from the computational load compared to conventional receivers, where adjusting dynamically the detection threshold level (either based on CSI knowledge, or by using pilots) leads to increased computational time and reduced link throughput. This paper shows that the performance of the proposed technique only depends on the correlation of propagating optical beams. Especially under highly correlated-channels condition the fluctuation of the detection threshold level in the receiver is significantly small. We also show experimentally that under weak turbulence regime the variance of detection threshold level reduces for the correlated channel.

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Anisoplanatism in airborne laser communication

Cited by 2 publications

References 17 publications

Integrated approach to airborne laser communication

Integrated approach to airborne laser communication

FSO Detection Using Differential Signaling in Outdoor Correlated-Channels Condition

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