Laser Communication in Aircraft and Satellites Downlinks

Transcription

1 Laser Communication in Aircraft and Satellites Downlinks Summary of Atmospheric Measurements at the German Aerospace Center DLR Dr. Markus Knapek Institute of Communications and Navigation, DLR Folie 1

2 UAV-Satellite and Inter-Platform Communications Optical Network above the Clouds UAV to satellite connections Interconnecting High-Altitude Platforms HAP and UAVs. Data-rates of Gbps. Link range inter-platform up to 600km. Connection to satellite network, relay functionality. UAV-LEO HAP/UAV Downlink LEO-Ground Inter-HAP Folie 3

3 Laser Communications for UAV Scenarios UAV-to-Ground Links Surveillance, site protection Ship-Helicopter Scenarios Maritime surveillance, border control, environment protection Fixed Terrestrial Networks Communication, border scenarios City Surveillance Event monitoring, wide area surveillance, law enforcement, traffic monitoring, inspection tasks Mini-UAVs to Mobile Ground Station: Border surveillance, law enforcement Folie 4

4 Scenario Atmospheric turbulence Plane wave propagation from space to ground (847nm) Mixing of air volumes index of refraction turbulence Degradation of spatial coherence interference Intensity fluctuation Power scintillation index σ 2 p characterizes signal fluctuation seen by Rx Folie 5

5 Measurement setup Optical ground station 4m Clamshell dome on roof of institute building Aluminum fork mount 40cm Cassegrain telescope (f/9, aluminum coating) 5cm refractor aside main telescope Two laser beacons for channel diversity Measurement devices on optical bench behind telescope Folie 6

6 Measurement setup Optical bench Measurement with 5cm aperture Received Power Optical system behind 40cm aperture Measurement with 40cm aperture Received Power Pupil image Shack-Hartmann Focus camera DIMM Fried parameter (DIMM) Wave-front Focal spot Tracking camera Pupil camera VOA Receiver front end Folie 7

7 Laser Satellite-to-Ground Links from Japanese LEO Satellite OICETS 2006 & 2009 In cooperation with the Japanese NICT Beacon Lasers backscattered from haze in 2009 OGS-OP in 2006 Folie 8

8 Channel measurements Power scintillation Probability density function (PDF) of received power (KT06-04) Power scintillation index over elevation (all measurements) Folie 9

9 Channel measurements Correlation time Auto-correlation function (ACF) of received power Auto-correlation time of received power: half maximum of ACF Folie 10

10 Atmospheric Conditions in SGLs Atmospheric Coherence Length r 0 6/5 L 2 r Cn ( z) dz 2 z 0 3/5 SGLs from the Japanese LEO satellite OICETS in June 2006 at 847nm. Folie 11

11 Results Power vs. Elevation (2006) BER results (2006) Folie 12

12 P RX over 40cm Telescope PDF RX Power Measurements during Aircraft Flight Campaigns Downlink from an aircraft (DO228) to the 40cm ground station. Mean link budget varies due to distance-changes and atmospheric transmission-variations (typical up to 30dB) Challenges: Communication synchronization, large blocks of data are lost during strong fades Time [s] RX Power Folie 13

13 Increasing complexity Laser Ethernet Transceiver LET Mitigation of Atmospheric Fades (4) BiDir. Protocol - Custom ARQ-Protocol to request lost data packets (3) Erasure- FEC - Erasure-FEC based on Packet-Level Coding, to compensate longer linkoutages (1ms..1s) LET-1G (2) Bitstream-FEC - Bit-level FEC increasing robustness to powervariance and enhancing the link-margin (1) Physical level - Data-rate >1Gbps - Fading-robust bitstream-recovery (synchronization) - Line-Code for spectral shaping - Variable data-rate (in few steps down to ~10Mbps) LET-100 Folie 14

14 2 nd Generation st Generation 2005 Evolution of Laser-Communication Flight Terminals Increasing Maturity Technology demonstrated in many flight campaigns Folie 15

15 New 3 rd Generation Flight Terminals MLT Long-range inter-platform Scenarios Inter-aircraft Inter-HAP Characteristics Link distance up to 600km 10cm terminal aperture Bi-directional Data rates >1Gbps MLT-20 - Short-distance downlinks Scenarios Platform to ground links Inter-UAV Characteristics Link distance up to 50km 2cm terminal aperture Bi-directional or asymmetric Data rates >1Gbps, Weight <5kg Folie 16

16 Transportable Optical Ground Station (TOGS) Operational in 2012 Global deployment Satellite and aerial applications Long-distance links optical links (>100km) Folie 17

17 Commercialization of Laser Communication for Aerial Applications Close cooperation between DLR and the spin-off ViaLight Communications Folie 18

18 Contact Folie 19