Abstract

Laser propagation through extended turbulence causes severe beam spread and scintillation. Airborne laser communication systems require special considerations in size, complexity, power, and weight. Rather than using bulky, costly, adaptive optics systems, we reduce the variability of the received signal by integrating a two-transmitter system with an adaptive threshold receiver to average out the deleterious effects of turbulence. In contrast to adaptive optics approaches, systems employing multiple transmitters and adaptive thresholds exhibit performance improvements that are unaffected by turbulence strength. Simulations of this system with on-off-keying (OOK) showed that reducing the scintillation variations with multiple transmitters improves the performance of low-frequency adaptive threshold estimators by 1-3 dB. The combination of multiple transmitters and adaptive thresholding provided at least a 10 dB gain over implementing only transmitter pointing and receiver tilt correction for all three high-Rytov number scenarios. The scenario with a spherical-wave Rytov number =0.20 enjoyed a 13 dB reduction in the required SNR for BER’s between 10−5 to 10−3, consistent with the code gain metric. All five scenarios between 0.06 and 0.20 Rytov number improved to within 3 dB of the SNR of the lowest Rytov number scenario.

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References

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  1. Staff Writers, “Northrop Grumman Awarded DARPA Contract To Design Hybrid Optical/RF Communications Network,” Spacedaily.com (2008). Dated 5 May 2008, URL http://www.spacedaily.com/reports/Northrop Grumman Awarded DARPA Contract To Design Hybrid Optical RF Communications Network 999.html.
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  3. A. Belmonte, “Influence of atmospheric phase compensation on optical heterodyne power measurements,” Opt. Express 16(9), 6756–6767 (2008). URL http://www.opticsexpress.org/abstract.cfm?URI=oe-16-9-6756
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    [CrossRef] [PubMed]
  5. S. M. Haas and J. H. Shapiro, “Capacity of Wireless Optical Communications,” IEEE J. Sel. Areas Comm. 21(8), 1346–1357 (2003).
    [CrossRef]
  6. E. J. Lee and V. W. S. Chan, “Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity,” IEEE J. Sel. Areas Comm. 22(9), 1896–1906 (2004).
    [CrossRef]
  7. P. Polynkin, A. Peleg, L. Klein, T. Rhoadarmer, and J. Moloney, “Optimized multiemitter beams for free-space optical communications through turbulent atmosphere,” Opt. Lett. 32(8), 885–887 (2007).
    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef] [PubMed]
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  15. H. L. VanTrees, Detection, estimation, and modulation theory (Wiley, 2002).
  16. H. Burris, A. Reed, N. Namazi, W. Scharpf, M. Vicheck, M. Stell, and M. Suite, “Adaptive thresholding for free-space optical communication receivers with multiplicative noise,” in Proc. IEEE Aerospace Conference, vol. 3, pp. 1473–1480 (2002).
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    [CrossRef]
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    [CrossRef]
  23. S. Coy, “Choosing Mesh Spacings and Mesh Dimensions for Wave Optics Simulation,” Proc. SPIE 5894 (2005).
  24. J. A. Louthain, Dissertation: Integrated approach to airborne laser communication, Air Force Institute of Technology, Wright-Patterson AFB, OH, December 2008.
  25. J. A. Buck, Fundamentals of Optical Fibers, Wiley-Interscience, 2004.
  26. J. A. Louthain and J. D. Schmidt, “Integrated approach to airborne laser communication,” Proc. SPIE 7108(14), (2008).
    [CrossRef]
  27. J. D. Schmidt, and J. A. Louthain, “Integrated approach to free-space optical communication,” in Proc. SPIE, Optics in Atmospheric Propagation and Adaptive Systems XI, vol. 7200 (SPIE Press, Bellingham, WA, 2009).

2008

J. A. Louthain and J. D. Schmidt, “Integrated approach to airborne laser communication,” Proc. SPIE 7108(14), (2008).
[CrossRef]

2007

2005

R. K. Tyson, J. S. Tharp, and D. E. Canning, “Measurement of the bit-error rate of an adaptive optics, free-space laser communications system, part 2: multichannel configuration, aberration characterization, and closed-loop results,” Opt. Eng. 44(9), (2005).

2004

E. J. Lee and V. W. S. Chan, “Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity,” IEEE J. Sel. Areas Comm. 22(9), 1896–1906 (2004).
[CrossRef]

2003

S. M. Haas and J. H. Shapiro, “Capacity of Wireless Optical Communications,” IEEE J. Sel. Areas Comm. 21(8), 1346–1357 (2003).
[CrossRef]

1998

J. A. Louthain and B. M. Welsh, “Fourier-series-based phase and amplitude optical field screen generator for weak atmospheric turbulence,” Proc. SPIE 3381, 286–296 (1998).
[CrossRef]

1997

B. M. Welsh, “Fourier-series-based atmospheric phase screen generator for simulating anisoplanatic geometries and temporal evolution,” Proc. SPIE 3125, 327 (1997).
[CrossRef]

1996

1982

D. L. Fried, “Anisoplanatism in adaptive optics,” J. Opt. Soc. Am. A 72(1), 52–61 (1982).
[CrossRef]

Anguita, J. A.

Canning, D. E.

R. K. Tyson, J. S. Tharp, and D. E. Canning, “Measurement of the bit-error rate of an adaptive optics, free-space laser communications system, part 2: multichannel configuration, aberration characterization, and closed-loop results,” Opt. Eng. 44(9), (2005).

Chan, V. W. S.

E. J. Lee and V. W. S. Chan, “Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity,” IEEE J. Sel. Areas Comm. 22(9), 1896–1906 (2004).
[CrossRef]

Fried, D. L.

D. L. Fried, “Anisoplanatism in adaptive optics,” J. Opt. Soc. Am. A 72(1), 52–61 (1982).
[CrossRef]

Haas, S. M.

S. M. Haas and J. H. Shapiro, “Capacity of Wireless Optical Communications,” IEEE J. Sel. Areas Comm. 21(8), 1346–1357 (2003).
[CrossRef]

Klein, L.

Lee, E. J.

E. J. Lee and V. W. S. Chan, “Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity,” IEEE J. Sel. Areas Comm. 22(9), 1896–1906 (2004).
[CrossRef]

Louthain, J. A.

J. A. Louthain and J. D. Schmidt, “Integrated approach to airborne laser communication,” Proc. SPIE 7108(14), (2008).
[CrossRef]

J. A. Louthain and B. M. Welsh, “Fourier-series-based phase and amplitude optical field screen generator for weak atmospheric turbulence,” Proc. SPIE 3381, 286–296 (1998).
[CrossRef]

Moloney, J.

Neifeld, M. A.

Peleg, A.

Polynkin, P.

Rhoadarmer, T.

Schmidt, J. D.

J. A. Louthain and J. D. Schmidt, “Integrated approach to airborne laser communication,” Proc. SPIE 7108(14), (2008).
[CrossRef]

Shapiro, J. H.

S. M. Haas and J. H. Shapiro, “Capacity of Wireless Optical Communications,” IEEE J. Sel. Areas Comm. 21(8), 1346–1357 (2003).
[CrossRef]

Tharp, J. S.

R. K. Tyson, J. S. Tharp, and D. E. Canning, “Measurement of the bit-error rate of an adaptive optics, free-space laser communications system, part 2: multichannel configuration, aberration characterization, and closed-loop results,” Opt. Eng. 44(9), (2005).

Tyson, R. K.

R. K. Tyson, J. S. Tharp, and D. E. Canning, “Measurement of the bit-error rate of an adaptive optics, free-space laser communications system, part 2: multichannel configuration, aberration characterization, and closed-loop results,” Opt. Eng. 44(9), (2005).

R. K. Tyson, “Adaptive optics and ground-to-space laser communications,” Appl. Opt. 35(19), 3640 (1996).
[CrossRef] [PubMed]

Vasic, B. V.

Welsh, B. M.

J. A. Louthain and B. M. Welsh, “Fourier-series-based phase and amplitude optical field screen generator for weak atmospheric turbulence,” Proc. SPIE 3381, 286–296 (1998).
[CrossRef]

B. M. Welsh, “Fourier-series-based atmospheric phase screen generator for simulating anisoplanatic geometries and temporal evolution,” Proc. SPIE 3125, 327 (1997).
[CrossRef]

Appl. Opt.

IEEE J. Sel. Areas Comm.

S. M. Haas and J. H. Shapiro, “Capacity of Wireless Optical Communications,” IEEE J. Sel. Areas Comm. 21(8), 1346–1357 (2003).
[CrossRef]

E. J. Lee and V. W. S. Chan, “Part 1: Optical Communication Over the Clear Turbulent Atmospheric Channel Using Diversity,” IEEE J. Sel. Areas Comm. 22(9), 1896–1906 (2004).
[CrossRef]

J. Opt. Soc. Am. A

D. L. Fried, “Anisoplanatism in adaptive optics,” J. Opt. Soc. Am. A 72(1), 52–61 (1982).
[CrossRef]

Opt. Eng.

R. K. Tyson, J. S. Tharp, and D. E. Canning, “Measurement of the bit-error rate of an adaptive optics, free-space laser communications system, part 2: multichannel configuration, aberration characterization, and closed-loop results,” Opt. Eng. 44(9), (2005).

Opt. Lett.

Proc. SPIE

J. A. Louthain and J. D. Schmidt, “Integrated approach to airborne laser communication,” Proc. SPIE 7108(14), (2008).
[CrossRef]

B. M. Welsh, “Fourier-series-based atmospheric phase screen generator for simulating anisoplanatic geometries and temporal evolution,” Proc. SPIE 3125, 327 (1997).
[CrossRef]

J. A. Louthain and B. M. Welsh, “Fourier-series-based phase and amplitude optical field screen generator for weak atmospheric turbulence,” Proc. SPIE 3381, 286–296 (1998).
[CrossRef]

Other

S. Coy, “Choosing Mesh Spacings and Mesh Dimensions for Wave Optics Simulation,” Proc. SPIE 5894 (2005).

J. A. Louthain, Dissertation: Integrated approach to airborne laser communication, Air Force Institute of Technology, Wright-Patterson AFB, OH, December 2008.

J. A. Buck, Fundamentals of Optical Fibers, Wiley-Interscience, 2004.

A. Belmonte, “Influence of atmospheric phase compensation on optical heterodyne power measurements,” Opt. Express 16(9), 6756–6767 (2008). URL http://www.opticsexpress.org/abstract.cfm?URI=oe-16-9-6756

J. A. Louthain, and J. D. Schmidt, “Anisoplanatism in airborne laser communication,” Opt. Express 16(14), 10,769–10,785 (2008). URL http://www.opticsexpress.org/abstract.cfm?URI=oe-16-14-10769 .

R. J. Sasiela, Electromagnetic wave propagation in turbulence. Evaluation and application of Mellin transforms, 2nd Ed. (SPIE Publications, 2007).

J. A. Louthain, and J. D. Schmidt, “Anisoplanatic Approach to Airborne Laser Communication,” Meeting of the Military Sensing Symposia (MSS) Specialty Group on Active E-O Systems I(AD02), 1–20 (2007).

L. C. Andrews, and R. L. Phillips, Laser Beam Propagation Through Random Media (SPIE Optical Engineering Press Bellingham, WA, 2005).

M. C. Roggemann, and B. M. Welsh, Imaging Through Turbulence (CRC Press, 1996).

H. L. VanTrees, Detection, estimation, and modulation theory (Wiley, 2002).

H. Burris, A. Reed, N. Namazi, W. Scharpf, M. Vicheck, M. Stell, and M. Suite, “Adaptive thresholding for free-space optical communication receivers with multiplicative noise,” in Proc. IEEE Aerospace Conference, vol. 3, pp. 1473–1480 (2002).

P. N. Crabtree, Dissertation:Performance-Metric Driven Atmospheric Compensation for Robust Free-Space Laser Communication (Air Force Institute of Technology, Wright-Patterson AFB, OH, 2006).

S. B. Alexander, Optical Communication Receiver Design, SPIE Tutorial Texts in Optical Engineering, vol. TT22; IEE Telecommunications Series, vol. 37 (SPIE Press, Bellingham, WA, 1997).

J. D. Schmidt, Dissertation: Free-Space Optical Communications Performance Enhancement by Use of a Single Adaptive Optics Correcting Element (University of Dayton, Dayton, OH, 2006).

H. Burris, A. Reed, N. Namazi, M. Vilcheck, and M. Ferraro, “Use of Kalman filtering in data detection in optical communication systems with multiplicative noise,” in Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP ’01), vol. 4, pp. 2685–2688 (7–11 May 2001).

J. D. Schmidt, and J. A. Louthain, “Integrated approach to free-space optical communication,” in Proc. SPIE, Optics in Atmospheric Propagation and Adaptive Systems XI, vol. 7200 (SPIE Press, Bellingham, WA, 2009).

Staff Writers, “Northrop Grumman Awarded DARPA Contract To Design Hybrid Optical/RF Communications Network,” Spacedaily.com (2008). Dated 5 May 2008, URL http://www.spacedaily.com/reports/Northrop Grumman Awarded DARPA Contract To Design Hybrid Optical RF Communications Network 999.html.

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Figures (8)

Fig. 1
Fig. 1

Received signal covariance power spectral density (PSD) for an air-to-air 100 km path at 4 km in altitude. The PSD of the signal sampled at fs = 64 fG is shown with a solid line, at fs = 32 fG with a dotted line, and at fs = 5.6 fG with a dashed line. The horizontal dot dash line is 20 dB down from the peak value. The vertical dashed line is the Greenwood frequency fG .

Fig. 2
Fig. 2

Adaptive threshold estimator.

Fig. 3
Fig. 3

Scenario 2(HLL) with one transmitter. Calculated probability of error for an optimum fixed threshold with an SNR of 25 dB versus time (solid line), fade threshold (dashed line).

Fig. 4
Fig. 4

BER fade statistics for Scenario 2 (HLL). (a) & (c) The mean fade length for a fade above an error rate of 10−3. (b) & (d) The number of fades per second above an error rate of 10−3. Dashed line is double-Tx case and solid line is single-Tx case.

Fig. 6
Fig. 6

BER fade statistics for Scenario 5 (HHL). (a) & (c) The mean fade length for a fade above an error rate of 10−3. (b) & (d) The number of fades per second above an error rate of 10−3. Dashed line is double-Tx case and solid line is single-Tx case.

Fig. 5
Fig. 5

BER fade statistics for Scenario 4 (HHH). (a) & (c) The mean fade length for a fade above an error rate of 10−3. (b) & (d) The number of fades per second above an error rate of 10−3. Dashed line is double-Tx case and solid line is single-Tx case.

Fig. 7
Fig. 7

This plot uses the normalized histograms of the raw received power to estimate the PDFs of the received signals due to turbulence p(is ) for each of the scenarios for the single-Tx (solid line) and double-Tx (dashed line) cases. Subplots (a)-(d) were calculated for scenarios 1, 2 & 5, 3, and 4, respectively.

Fig. 8
Fig. 8

BER for systems with an optimal fixed threshold, ideal adaptive threshold, fs = 64 fG estimator adaptive threshold, and fs = 16 fG estimator adaptive threshold for single Tx (solid lines) and double Tx (dashed lines). Subplots (a)-(d) were calculated for scenarios 1, 2 & 5, 3, and 4, respectively. The data rate was 1 GHz.

Tables (1)

Tables Icon

Table 1 Atmospheric parameters for the scenarios used in the simulations.

Equations (14)

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θ Ψ i n d = 2 σ Ψ , p l 2 θ 0 ,
p ( i m | H 1 ) > p ( i m | H 0 )
p ( i m | H 1 ) p ( i m | H 0 )
σ 1 2 = σ e l e c 2 + σ s h o t 2 + σ A S E 2 ,
​ ​ ​ ​ ​ ​               P ( H 0 ) p 0 ( i T ) = P ( H 1 ) 0 p 1 ( i m | s ) p ( s ) d s 1 σ e l e c exp ( i T 2 2 σ e l e c 2 ) = 0 p ( s ) σ 1 ( s ) exp { [ i T i m ( s ) ] 2 2 σ 1 2 ( s ) } d s .
P e = P ( H 1 ) P m d + P ( H 0 ) P f a = P m d 2 + P f a 2 ,
P m d = 1 2 0  erfc ( i m ( s ) i T 2 σ 1 ( s ) ) p ( s ) d s ,
P f a = 1 2 erfc ( i T 2 σ e l e c ) .
i T = μ 0 σ 1 2 μ 1 σ 0 2 σ 1 2 σ 0 2 + σ 0 σ 1 σ 1 2 σ 0 2 ( μ 1 μ 0 ) 2 + ​ 2 ( σ 1 2 σ 0 2 ) ln ( σ 1 σ 0 ) .
P m d = 1 2 0 e rfc ( i m ( s ) i T ( s ) 2 σ 1 ( s ) ) p ( s ) d s ,
P f a = 1 2 0 e rfc ( i T ( s ) 2 σ e l e c ) p ( s ) d s .
i ^ s = 99 [ i E + n ( i E ) + Δ m ]         ​ = 99 [ i E m + Δ m ] ,
σ 1 2 = σ e l e c 2 + σ s h o t 2 + σ A S E 2 .
i ^ T = i ^ s σ e l e c 2 σ e l e c 2 σ ^ 1 2 + σ e l e c σ ^ 1 σ ^ 1 2 σ e l e c 2 i ^ s 2 + ​ 2 ( σ ^ 1 2 σ e l e c 2 ) ln ( σ ^ 1 σ e l e c ) ,

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