Extremely High Speed Avenues for Space Communications ...

Extremely High Speed Avenues for Space Communications: Optical & W-band Waves

8th ASMS/14th SPSC Palma de Mallorca, Spain Sep 5th, 2016

Dr. Ricardo Barrios

> R. Barrios > Extremely High Speed Avenues for Spacecom: Optical & W-band Waves > 05.09.2016 DLR.de/kn • Slide 1

The current telecommunications marketplace is experiencing an ever increasing demand for high-speed services, and the traffic demand for satellite broadband is expected to grow six-fold by 2020. As part of the continuous migration towards higher frequency bands, Optical & W-band waves offer the promise of unprecedented bandwidth compared to current commercial solutions, leveraging enough bandwidth capable to cope with mid and long-term requirements. Together they can realize extremely high speed avenues for space communications in inter-satellite and feeder link applications. This tutorial focuses on giving a thorough overview of the different aspects and challenges to be taken into account when implementing GEO feeder links in the optical domain and W-band waves, including physical layer, channel model, modem, satellite payload and system level aspects. Particular attention is given to the feeder uplink scenario, which—as part of the forward link—presents itself as critical for the successful implementation of future extremely high throughput satellite systems. The tutorial will attempt to stress the practical challenges of these high frequency RF and optical technologies, proposing also ways forward in terms of necessary space and ground technology development, as well as open research directions.

Abstract


Extremely High Speed Avenues for Space Communications: Optical & W-band Waves

Dr. Ricardo Barrios & Dr. Pantelis-Daniel Arapoglou, 8th ASMS/14th SPSC, 5 Sep 2016

Introduction to Lasercom for Space

Technologies and Modulation Formats

Atmospheric Effects

Atmospheric-induced Fading Mitigation Techniques

Optical GEO Feeder Links

Summary

Outline


Timeline of Lasercom Space Missions Selection


2016

•EDRS-C

2013

•α-Sat •LLCD

2005

•OICETS

2007

•LCTSX •NFIRE -LCTs

1998

•SPOT-4

2001

•Artemis SILEX •GEOLITE

•ETS-VI

1994 2015

•EDRS-A •OSIRIS

2014

•Sentinel-1A •SOTA •OPALS

2017

•LCRD

Pictures: ESA, JAXA, NICT, NASA, MIT, DLR

Lasercom Scenarios


GEO Orbit 36000 km

LEO Orbit 300-500 km

ISL

ISL

LEO Downlink

RF User Link

Feeder Link

Optical Ground Station

RF User Terminal



Atmospheric Effects



Summary

Outline


Components of full-duplex Space Laser Terminals


Tx-Data

Rx-Data

𝝀𝝀Rx

𝝀𝝀Tx

Coarse Pointing Assembly Examples


Azimuth-Elevation Gimbal (OICETS)

One-Mirror Periscope (Alphasat)

Optical Ground Stations


20cm-MOGS

1m Class 60cm Class

40cm Class Rx 15cm Class Tx

Pictures: ESA, ViaLight, NASA, DLR.

Modulation Formats


• high sensitivity (in Phot./bit) • high data-rates • requires plane Rx-wave • atmosphere is a challenge long range space links (GEO)

• sensitivity limit (photon counting) • high implementation effort • limited data-rate long-range medium-rate (Exploration)

Optical Intensity Detection (incoherent)

Direct Detection (IM/DD) with On-Off Keying (OOK)

PPM (Pulse Position Modulation)

with local oscillator: hom./heterodyne-BPSK, QAM

Self-homodyne-DPSK with PreAmp

Complex Field Detection (coherent)

• Low-to-medium sensitivity. • High data-rates. • Low implementation effort. short range with atmosph. (LEO)



Atmospheric Effects



Summary

Outline


Atmospheric attenuation. Large time scales. Considered constant. Related with visibility. Dominated by fog, clouds, rain, snow, dust. The attenuation coefficient is made up of four parts:

𝜎𝜎 = 𝛼𝛼𝑚𝑚 + 𝛼𝛼𝑎𝑎 + 𝛽𝛽𝑚𝑚 + 𝛽𝛽𝑎𝑎

Background noise Direct Sun or moonlight (also planets) in

the receiver FoV may cause link outages. Sky radiance.

Atmospheric turbulence Small time scale. Random in nature. Caused by wind and temperature

gradients.

Atmospheric effects


Atmospheric Attenuation


0

5

10

15

20

25

30

35

40

Hei

ght o

ver s

ea le

vel [

km]

10 -510 -410 -310 -210 -1

Total absorption coefficient at 1550nm [km-1

]

BackgroundModerate

High

Extreme

Atmospheric Transmission


600 800 1000 1200 1400 1600 1800 2000

Wavelength [nm]

10 -4

10 -3

10 -2

10 -1

10 0

10 1

10 2

10 3

Tota

l atm

. abs

orpt

ion

coef

ficie

nt [k

m-1

]

Mean sea level

3km altitude

10km altitude

850 1064 1550

What happens when an optical beam passes through turbulent air?


Far-field intensity-speckles

collimated laser beam at Tx

turbulent volume with IRT-strength

Wavefront distortion → Interference

Cn2 profile Defines IRT strength

Turbulence screen example

Turbulence Characterization KIODO 2009


Intensity

Focus spot

Reconstr. phase

Shack Hartmann



Atmospheric Effects



Summary

Outline


Downlink Mitigation Strategies


OFF ON

Aperture Averaging Larger Rx aperture reduces variance

of Rx power in magnitude and spectrum. Rx aperture is larger than the average

structure size of the Rx field.

Adaptive Optics Enables SMF coupling, or

Heterodyning with LO. Requires real time correction of

atmospheric phase distortions.

Histogram

Signal

Uplink Mitigation Strategies


Transmitter diversity Multiple separated Tx lasers undergo

different atmospheric paths. Non-coherent detection averages out

atmospheric effects. Separation defined by Fried

parameter.

Pre-distortion Adaptive Optics

t1

Atmosphere 20-25 km

t0

𝜽𝜽IPA

IRT Cells 𝜽𝜽AoA

𝜽𝜽IPA> 𝜽𝜽PAA

Error Correction Codes Downlink and uplink


Robust Data-Recovery and Bit-Level FEC

Interleaved Packet-Layer FEC (Burst Errors from IRT-Fading,

1..10ms)

Low-overhead ARQ for lossy return channel

Delay-Tolerant Transmission Management (only non-

realtime scenarios) Gb-Ethernet

FPGA-Implementation of Laser-Ethernet-Transceiver (LET)



Atmospheric Effects

Atmospheric-induced fading Mitigation Techniques


Summary

Outline


Terabit-per-second SatComm is required in future (EU Digital Agenda by 2020)

Every EU-citizen at least 30Mbps

50% with 100Mbps or more.

Number of required RF ground stations grows linear with throughput

Optical Feeder Links provide >1Tbps over one optical ground station

Number of OGSs in the network is driven by robustness against cloud blockage

At least one OGS must be available

Motivation for Optical GEO Feeder Links in Future Satellite Com. Systems


[*] RF feeder link assumes all spectrum usage in Ka band (blue line), Ka+Q/V band (red line) and Q/V+W band (yellow line). OGEOFL (green line) can provide Terabit capacity with only one OGS.

Ka Ka+Q/V

Q/V+W

Cloud-Blockage Mitigation OGS-Network Availability


Pcloud < 40%

11 European stations

Availability = 99.67 %

10 Mediterr. stations

Availability = 99.89 %

8 stations Inter-Continental Availability = 99.971 %

Data-basis: Satellite images and simultaneous ground observations (from 1990 to 2006)

1450 1500 1550 1600 1650

Wavelength [nm]

0

20

40

60

80

100

Tota

l Atm

osph

eric

Tra

nsm

ittan

ce [%

]

19km altitude

10km altitude

3km altitude

Mean sea level

800 1000 1200 1400 1600 1800 2000

Wavelength [nm]

0

20

40

60

80

100

Tota

l Atm

osph

eric

Tra

nsm

ittan

ce [%

]

19km altitude

10km altitude

3km altitude

Mean sea level

DWDM-System for Optical GEO Feeder-Links


HPOAMux Nx1

M Channels

HPOAMux Nx1

HPOAMux Nx1

High

Pow

er M

ux N

x1HP

Mux

N

x1HP

Mux

N

x1

High

Pow

er M

ux N

X1

TelescopeTelescope

MainMainLASER MZM

Tx CHN

DWDM Transmitter

LNOARFE

Demux 1x2

LNOA

LNOA

Demux 1xN

Demux 1xN

M Channels

Telescope

MainRx CHN

WavefrontCorrectionEDFA

EDFA

EDFA Only at OGS

DWDM Receiver

~𝟏𝟏𝟏𝟏THz Bandwidth 1529 1568 1610 | C Band | L Band |

Atmosphere 20-25 km

GEO Orbit 36000 km

IRT Cells

Ground-GEO Optical Channel


𝜽𝜽PAA ~ 𝟏𝟏𝟏𝟏µrad ~253ms (700m) t1 t0

Histogram

Signal

Signal Histogram

Strong Fading due to beam wander

𝜽𝜽AoA

𝜽𝜽AoA: Angle-of-Arrival 𝜽𝜽PAA: Point-Ahead Angle 𝜽𝜽BW : Beam Wander 𝜽𝜽IPA: Isoplanatic Angle

GEO Orbit t1 𝜽𝜽PAA ~ 𝟏𝟏𝟏𝟏µrad

Atmosphere 20-25 km

Uplink Transmission Approaches Pointing by tracking

Downlink reference can be used to point the uplink.

Beam wander can be compensated.

Smaller uplink divergence is possible Larger Tx Gain

Correlation between down- and up-link paths is not perfect.

Residual beam wander.

Correlation coefficient follows

𝛾𝛾 ∝ exp −𝜃𝜃PAA𝜃𝜃IPA

5/3

> R. Barrios > Extremely High Speed Avenues for Spacecom: Optical & W-band Waves > 05.09.2016 DLR.de/kn • Slide 26 𝜽𝜽AoA: Angle-of-Arrival 𝜽𝜽PAA: Point-Ahead Angle 𝜽𝜽BW : Beam Wander 𝜽𝜽IPA: Isoplanatic Angle 𝜽𝜽B: Beam divergence

t0

𝜽𝜽IPA


𝜽𝜽IPA> 𝜽𝜽PAA

Atmosphere 20-25 km

Uplink Transmission Approaches Open loop pointing


GEO Orbit

𝜽𝜽AoA: Angle-of-Arrival 𝜽𝜽PAA: Point-Ahead Angle 𝜽𝜽BW : Beam Wander 𝜽𝜽IPA: Isoplanatic Angle 𝜽𝜽B: Beam divergence

𝜽𝜽PAA ~ 𝟏𝟏𝟏𝟏µrad t1 t0


Optimum Tx size depends on location and atm. conditions

Transmitter gain

Free-space Loss

Receiver gain

Beam Wander Loss Atm.

Attenuation

R T T T ATM FS SR BW R RP LP G L L Gη τ η=

( )2BW T BWexpL G θ= −

( )2T T /DG π λ=

( )( ) 6/55/3SR 10 T 010log 1 /L D r

−= +

Strehl ratio Loss

DIVT

2 2D

θ λπ

=

𝜽𝜽IPA< 𝜽𝜽PAA

Measured Uplink Received Power at GEO


Mata-Calvo et al. “Transmitter diversity verification on ARTEMIS geostationary satellite,” Proc. SPIE 8971, pp. 897104, 2014.

Rx-Power with only one

Tx-Beam

Rx-Power with second

Tx-Beam

average

-3dB fade threshold

Alternative Solution: Probing with Laser Guide Star


Pre-distortion AO system

Deformable mirror

Downlink reference

Uplink

Wave-Front Sensor

Laser

Beam splitter

Wave-Front Processor

Laser Guide Star (LGS)

Round-trip ~0.6ms. Tilt time ~100 ms. For Tx/Rx shared aperture up- and downlink sees same tilt. Classic LGS cannot measure tilt.

LGS

Telescope Aperture

Frozen Turbulence

LGS Tilt correction Bistatic approach breaks up-

and downlink correlation. Min. 2 Rx to retrieve tilt info.

High implementation complexity.

Piston: Not relevant in FSO communications

Lower modes Relative error

~80%

Higher modes Relative error

~20%

Absolute error still significant

Tip/Tilt: Beam wander

Higher modes produce only scintillation

Phase distortions can be represented by Zernike modes.

Correction of only higher modes might not provide enough improvement. Beam wander correction either by

divergence optimization or pointing by tracking.

Uplink Transmission Approaches Pre-distortion Adaptive Optics

DVB-S2 Signal


Functional block diagram of the DVB-S2 system

Multiple Inputs

Mode

Adaptation

FEC

Encoder

Mapping

& Framing

BB Filter

& APSK

RF

Receiver

Ka band

converter

Gateway

RF uplink channel

User Terminal RF downlink

channel Satellite

Simplified block diagram including the satellite and user in the chain.

Uplink Transmission Schemes

AT: Analog Transparent DT: Digital Transparent FEC: Forward Error Correction S: Soft F: Full

Transparent Options


Multiple Inputs

Mode

Adaptation

FEC

Encoder

Mapping

& Framing

BB Filter

& APSK

Rx Telescope

& LNOA

Ka band

converter

Gateway

Optical uplink

channel

User

Terminal RF downlink channel

Satellite

Optical

carrier

O/E

converter AGC

Multiple Inputs

Mode Adap.

FEC encoder

Mapping

& Framing

BB Filter &

APSK

ADC

Sampler

Rx Telescope

& LNOA

Ka band

converter

Gateway

Optical uplink

channel

User

Terminal RF downlink channel Satellite

Optical

carrier

O/E

converter DAC

IRT

FEC

IRT

FEC

Digital transparent transmission scheme for DVB-S2 signals. Dashed blocks are optional.

Analog transparent transmission scheme for DVB-S2 signals

Minimum impact on sat payload. Due to high Tx powers HPOA

nonlinearities can be a problem. No protection against long

fades.

Processing power needed onboard. Specific protection against IRT

fading possible. Considerable bandwidth

expansion.

Digital Regenerative Options


Digital soft-regenerative transmission scheme for DVB-S2 signals.

Multiple Inputs

Mode Adap.

FEC encoder

Mapping

& Framing

BB Filter &

APSK

Rx Telescope

& LNOA

Ka band

converter

Gateway Optical uplink

channel

User

Terminal RF downlink channel

Satellite

Optical

carrier

O/E

converter

IRT

FEC

IRT

FEC

Fully regenerative: Data a is also transmitted in baseband over the optical carrier, but DVB-S2 modulation and coding blocks are included in the satellite RF chain to achieve most robust system against BER.

Lower bandwidth reqs. compared to DT option. Excellent protection against

fading. Major impact on sat payload. Transparency is almost lost. SWaP penalty due to BB-to-

Ka onboard conversion.

Most robust in terms of BER. Maximum SWaP impact. No standard upgrades after

Sat launch.

Link Budget


Link Budget Analog Transparent Example


Parameter Unit Tenerife Tirana Gibraltar Paris Tx antenna gain dB 113.53 108.82 105.87 103.01 Transmitter loss dB -3.01 -3.01 -3.01 -3.01 Tx diversity gain dB 0.00 0.00 0.00 0.00 Free-space loss dB -289.66 -289.75 -289.68 -289.89 Atmospheric attenuation dB -0.14 -0.28 -0.34 -0.49 Cloud margin dB -3.00 -3.00 -3.00 -3.00 Strehl ratio loss dB -1.14 -1.14 -1.11 -1.09 Beam wander loss dB -5.19 -5.19 -5.02 -4.93 Scintillation loss dB -2.19 -3.75 -4.16 -5.76 Tx antenna gain dB 114.10 114.10 114.10 114.10 Receiver loss dB -3.01 -3.01 -3.01 -3.01 Fiber coupling loss dB -1.07 -1.07 -1.07 -1.07 Total link loss dB -80.79 -87.29 -90.44 -95.14 Total OGS Tx power dBm 44.77 44.77 44.77 44.77 Received power dBm -36.02 -42.52 -45.67 -50.37 Carrier-to-noise ratio dB 23.85 16.53 12.45 5.39

OGS Tx optical power per lambda 30W. One lambda per beam. BW 1.45GHz per beam. DWDM Grid: 100-50-25 GHz RFE photodetector at SAT

BW=20GHz SAT: EDRS-A @ 9ºE

-8 -6 -4 -2 0 2 4 6 8

Frequency [GHz]

2 RF subcarriers over DWDM optical channel

1.5GHz RF-subcarrier; 5 % roll-off factor; 150MHz band guard

c =1550.00nm

f c =193.414THz

WDM Bandwidth 100GHz

RFE Bandwidth 20GHz

RF carrier 1 | fc= 4.000GHz

RF carrier 2 | fc= 5.650GHz

Uplink IF in RF C-band 4-8GHz.

Link Budget Analog Transparent Example


QPSK r2/9

QPSK r13/4

5

QPSK r9/20

QPSK r11/2

0

8APSK r5

/9-L

8APSK r2

6/45-L

8PSK r2

3/36

8PSK r2

5/36

8PSK r1

3/18

16APSK r1

/2-L

16APSK r8

/15-L

16APSK r5

/9-L

16APSK r2

6/45

16APSK r3

/5

16APSK r3

/5-L

16APSK r2

8/45

16APSK r2

3/36

16APSK r2

/3-L

16APSK r2

5/36

16APSK r1

3/18

16APSK r7

/9

16APSK r7

7/90

32APSK r2

/3-L

32APSK r3

2/45

32APSK r1

1/15

32APSK r7

/9

64APSK r3

2/45-L

64APSK r1

1/15

64APSK r7

/9

64APSK r4

/5

64APSK r5

/6

128A

PSK r3/4

128A

PSK r7/9

256A

PSK r29/4

5-L

256A

PSK r2/3-

L

256A

PSK r31/4

5-L

256A

PSK r32/4

5

256A

PSK r11/1

5-L

256A

PSK r3/4

0

5

10

15

20

25

Car

rier-t

o-no

ise

ratio

C/N

[dB

]

DVB-S2X C/N performance at QEF operation FER=10-5

C/N=23.85 dB Tenerife

C/N=16.53 dB Tirana

C/N=12.45 dB Gibraltar

C/N=5.39 dB Paris

Target C/N (AWGN channel)

DVB implementation guidelines; part 2 - S2 Extension (DVB-S2X). Doc. A171-2, 2015.

R. Mata-Calvo, P. Becker, D. Giggenbach, F. Moll, M. Schwarzer, M. Hinz, and Z. Sodnik, “Transmitter diversity verification on Artemis geostationary satellite,” in Free-Space Laser Communication and Atmospheric Propagation XXVI, 2014, vol. 8971, p. 897104.

S. Dimitrov, B. Matuz, G. Liva, R. Barrios, R. Mata-Calvo, and D. Giggenbach, “Digital Modulation and Coding for Satellite Optical Feeder Links,” in 7th Advanced Satellite Multimedia Systems Conference (ASMS), 2014.

D. Giggenbach, “Optical Satellite Feeder Links for Terabps Throughput.” DLR Institute of Communications and Navigation, Presentation, on elib.dlr.de

Sylvain Poulenard, Michael Crosnier, and Angélique Rissons, “Ground Segment Design for Broadband Geostationary Satellite With Optical Feeder Link,” J. OPT. COMMUN. NETW. 7(4), pp. 325-336, 2015.

N. Perlot, T. Dreischer, C. M. Weinter, and J. Perdigues, “Optical GEO Feeder Link Design,” in Future Network & MobileSummit 2012 Conference Proceedings, 2012.

D. Giggenbach, P. Becker, R. Mata-Calvo, C. Fuchs, Z. Sodnik, and I. Zayer, “Lunar Optical Communications Link (LOCL): Measurements of Received Power Fluctuations and Wavefront Quality,” in Proc. International Conference on Space Optical Systems and Applications (ICSOS), 2014.

D. Giggenbach, R. Barrios, F. Moll, R. Mata-Calvo, S. Bobrovskyi, F. Huber, N. Johnson-Amin, F. Heine, and M. Gregory, “EFAL: EDRS Feeder Link from Antarctic Latitudes - Preliminary Results of Site Investigations, Availability, and System Requirements,” in International Conference on Space Optical Systems and Applications (ICSOS), 2014.

Selected References


Preguntas?


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