Analysis of Signal Fluctuations in LEO Downlink Experiments. Florian Moll. German Aerospace Center (DLR) DLR-IKN, 10 th Nov 2016

Transcription

1 Analysis of Signal Fluctuations in LEO Downlink Experiments Florian Moll German Aerospace Center (DLR) DLR-IKN, 10 th Nov 2016

2 Outline Introduction Measurement setup Results Summary and outlook

3 Introduction Current FSO LEO systems Applications Earth observation Backhaul networks Direct Laser Satellite Downlink OICETS (Japan) SOCRATES (Japan) ISS (USA) BiROS (Germany) Direct Satellite Downlink DLR

4 Introduction Motivation for LEO-GND measurements Scintillation channel model system optimization, data rate and code rate adaption Measurement based channel model for LEO-Downlinks Why new model? current models lack accuracy Why measurement based? covers all complex and variable effects (weather, geometry) Scintillation index σ 2 2 I I 2 2 I = = I ( λε ) n f,, C ( h) 2 C n2 (h)

5 Introduction Atmospheric turbulence Wave-front distortions due to index-of refraction turbulence Signal interference causes scintillation Signal fades due to scintillation Scintillation loss a sci Power scintillation index σ P 2 σ 2 2 P P 2 2 P = = f σi DRx P 2 (, ) Giggenbach, D. & Henniger, H., Fading-loss assessment in atmospheric freespace optical communication links with on-off keying, Opt. Eng., 2008, 47,

6 Measurement setup Space segments Space segment LUCE OPALS SOTA Wavelength (nm) Data rate (Mbps) Divergence angle (µrad) 5.5 < Power-Tx (W) / Modulation OOK OOK OOK OICETS Satellite JAXA CAD SOTA terminal NICT CAD OPALS terminal NASA

7 Measurement setup Ground segment Measurement devices Pupil camera Focus camera Shack-Hartmann WFS PIN diode OGS-OP DLR Shortt et al., Channel characterization for air-to-ground free-space optical communication links, Proc. SPIE 8971 (Free-Space Laser Communication and Atmospheric Propagation XXVI), 2014, 8971

8 Results Scintillation index SOTA/OPALS and PDF of intensity Comparison to HV 5/7 Expected behavior for all passes

9 Results Scintillation index SOTA/OPALS/OICETS Measurements for 847 nm (black) and 1550 nm (colored)

10 Results Scintillation index SOTA/OPALS/OICETS Measurements for 847 nm (black) and 1550 nm (colored) σ I2 (1550 nm) < σ I 2 (847 nm) Clear saturation for σ I 2 (847 nm)

11 Results Fading OICETS Fade defined as PRx below -3dB Fade number per unit time Mean fade length Fractional fade time

12 Summary and outlook Summary Scintillation and fading analysis with OICETS, ISS and SOCRATES signals Significant variability of scintillation strength in between passes Outlook Measurement with BIROS and thourough channel characterization New Optical Ground Station of Oberpfaffenhofen for more complext measurement setups

13 Acknowledgements The SOTA measurements were obtained in a collaborative work of the German Aerospace Center (DLR) Institute of Communications and Navigation and the National Institute of Information and Communications Technology. The OPALS measurements were obtained in a collaborative work of the German Aerospace Center (DLR) Institute of Communications and Navigation and Jet Propulsion Laboratory (JPL) of NASA. The OICETS measurements were obtained in a collaborative work of the German Aerospace Center (DLR) Institute of Communications and Navigation and Jaxa/NICT. The authors would like to thank everyone who was involved in the measurement campaign and the preparation. Special thanks go to JAXA, NICT and JPL who built and operated the space terminals and kindly offered them for this great international cooperation.

14 Thank you