Reliability of satellite-to-ground optical transmissions · High to very high data rates ~10 Gbps...

Reliability of satellite-to-ground optical

transmissions Lucien Canuet

Jérôme Lacan (ISAE)

Angélique Rissons (ISAE)

Nicolas Védrenne (ONERA)

Géraldine Artaud (CNES)

SATELLITE OPTICAL DOWNLINKS - GENERAL CONTEXT

Telecom

Telemetry

& payload

2

Applications of optical links • Data transfer (telemetry/payload) from scientific or defense spacecraft (LEO) • Telecommunication (GEO satellites) • Metropolitan area networks (where fiber optics impractical) • Deep space probes …

High to very high data rates

~10 Gbps

>1 Tbps achievable if optical fiber technologies are

exploited (WDM, DWDM, Optical amplifiers etc.) Decongestion of the RF spectrum

Enhanced security (high directivity of the beam)

Stealthy links and jamming capacity reduced

Very large range (« Deep Space » applications)

3



~10 Gbps






Links highly affected by atmospheric turbulence

4



~10 Gbps






Links highly affected by atmospheric turbulence

Improvement of the link budget and telecom performances:

+ Coupling of incident flux into optical fiber (SMF)

+ Adaptive Optics (AO)

+ Optimisation of digital (coding/interleaving) techniques

Joint optimisation of AO and coding techniques to improve reliability of

LEO and GEO downlinks (telemetry and telecoms applications)

5


PART I : JOINT OPTIMIZATION – PROBLEM OVERVIEW

PART II : AO FOR OPTICAL DONWLINKS

PART III : PHYSICAL LAYER PERFORMANCE ASSESSMENT

PART IV : AO/CROSS-LAYER OPTIMIZATION

6

PRESENTATION OUTLINE

Coupling losses and signal fadings

Atmospheric propagation channel

Scintillation

(Pupil plane) Turbulent Wave front

Plane Wave

7

Phase fluctuations

(Focal plane)

Atmospheric optical turbulence

Δ(Temperature, Pressure,

Humidity) Δ(refractive index) Perturbed wave front

Mitigation techniques ? Coupled flux

Speckles

PSF

Experimental results PhD Thesis Kassem

Saab (CNES/ONERA)

THE ATMOSPHERIC PROPAGATION CHANNEL

Turbulence Fiber Mode

+

+Variance résiduelle totale fixe => fixe taux de couplage moyen

+Variation du Drx

+Variation de la proportion des postes d'erreur spatiale et temporelle

8

ADAPTIVE OPTICS PRINCIPLE

SFM

Principle overview

Opto-mechanical system:

Real time correction of

phase distorsions

Three key components:

Deformable mirror

Wavefront sensor

Real-time computer

Perturbed Field

Corrected Field


+Variation du Drx


9


SFM

Principle overview



phase distorsions


Deformable mirror

Wavefront sensor

Real-time computer

Perturbed Field

Corrected Field

10


SFM

Principle overview



phase distorsions


Deformable mirror

Wavefront sensor

Real-time computer

Perturbed Field

Corrected Field

drrr corrres ))²()((12 S


+Variation du Drx


Minimization of residual phase variance

11


SFM

Principle overview



phase distorsions


Deformable mirror

Wavefront sensor

Real-time computer

Limitations?

Perturbed Field

Corrected Field

12

Time

HIGH PERF. AO

LOW PERF. AO

PHYSICAL LAYER DIGITAL MITIGATION TECHNIQUES C

ou

ple

d f

lux a

tte

nu

ati

on

“BURST”

Raw data stream Code performance limited

13

SYMBOL

50 % Redundancy

Time

HIGH PERF. AO

LOW PERF. AO

PHYSICAL LAYER DIGITAL MITIGATION TECHNIQUES

CODEWORD

Co

up

led

flu

x a

tte

nu

ati

on

“BURST”

Raw data stream

Interleaved data stream

Deinterleaving

Code performance limited

Code performance increased

14

SYMBOL

50 % Redundancy

Time

HIGH PERF. AO

LOW PERF. AO


CODEWORD

Co

up

led

flu

x a

tte

nu

ati

on

“BURST”

Raw data stream


Deinterleaving



How to effectively allocate memory (interleaver) and redundancy (code)?

15

SYMBOL

50 % Redundancy

CODEWORD

Time

HIGH PERF. AO

LOW PERF. AO

PHYSICAL LAYER DIGITAL MITIGATION TECHNIQUES C

ou

ple

d f

lux a

tte

nu

ati

on

Statistical and temporal characterizations of the channel needed:

instantaneous coupled optical power after partial AO

“BURST”

Raw data stream


Deinterleaving



Time

Couple

d f

lux [a.u

.]

16


SYMBOL

HIGH PERF. AO

LOW PERF. AO

50 % Redundancy

Co

up

led

flu

x a

tte

nu

ati

on

CODEWORD

Instantaneous mutual information (~channel capacity )

Theoretical maximal data rate at which information can be transferred over the channel given noise level

PHYSICAL LAYER DIGITAL MITIGATION TECHNIQUES MUTUAL INFORMATION

Bije

ctio

n

The greater the better

17

Mu

tua

l in

form

atio

n

[bits/c

ha

nnel u

se

]

Op

tica

l co

up

led

po

we

r a

tte

nu

ation

Series tempo flux im

impact entrelacement-desentrelacement -> capa ergo = moyenne message contr OA pas d’influence sur moy

Motiv mieux que BER cite JL

Appli FSO très peu, jms conj avec OA

Instantaneous mutual information (~channel capacity )

Theoretical maximal data rate at which information can be transferred over the channel given noise level


Emulation of interleaving-deinterleaving at Rx

Sliding average window

Advantages of instantaneous mutual information (MI):

18

Mu

tua

l in

form

atio

n

[bits/c

ha

nnel u

se

]


Emulation of interleaving-deinterleaving at Rx

Sliding average window

Ideal infinite interleaver = fundamental limit

Average power losses not recoverable by interleaving

E[MI(t)]

19

Mu

tua

l in

form

atio

n

[bits/c

ha

nnel u

se

] Advantages of instantaneous mutual information (MI):






Emulation of Error Correcting Code (ECC) decoding

Shannon decoding theorem

ECC coding rate = amount of non-redundant

information in message

R0PHY = 0.5

20

Mu

tua

l in

form

atio

n

[bits/c

ha

nnel u

se







Emulation of Error Correcting Code (ECC) decoding

Shannon decoding theorem

Not Decoded = Link Outage

Successfully Decoded

PHY layer performance metric = Outage probability

21

Mu

tua

l in

form

atio

n

[bits/c

ha

nnel u

se


INFO Redundancy

INFO Redundancy

Error corr. code

APPLICATION PHY LAYER HIGHER LAYERS DATA LINK | NETWORK |

TRANSPORT

CROSS-LAYER APPROACH

22

CODING possible at both PHY LAYER and HIGHER LAYERS

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

APPLICATION Rx

INFO Redundancy

INFO Redundancy

Error corr. code


TRANSPORT


23

CODING possible at both PHY LAYER and HIGHER LAYERS

Erasure Code

(packets)

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

Error Corr. Code

(bits)

INFO Redundancy INFO Redundancy Red. Redundancy

INFO INFO Red.

Red.

Redundancy

HL Erasure code redundancy

PHY Error correcting code redundancy

APPLICATION Rx

+ … …

INFO Redundancy

INFO Redundancy

Error corr. code


TRANSPORT


24

Erasure Code

&

Packet interleaving

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

Error Corr. Code

&

Symbol interleaving

APPLICATION Rx

Perf. metric: PER

Perf. metric: MI/Outage Prob.

CODING and INTERLEAVING possible at both PHY LAYER and HIGHER LAYERS

INFO Redundancy

INFO Redundancy

Error corr. code


TRANSPORT


25

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

APPLICATION Rx

Perf. metric: PER



Benefits of (optimized) cross-layer coding scheme:

• Lowering Packet Error Rate (PER)

• Alleviate drawbacks required by long interleavers needed on bursty channel

Erasure Code

&

Packet interleaving

Error Corr. Code

&

Symbol interleaving

Developed module

Enhanced/Validated module

End-to-end simulation modeling

Simplified simulation modeling

Analytic modeling

Adaptive

Optics

Atmos.

Propagation

Channel

Higher

Layers

Tx

Application

Tx Data

Application

Rx Data

Higher

Layers

Rx

Modulator Demodulator Channel

encoder

Channel

decoder

Physical Layer

OVERALL SYSTEM OVERVIEW

26



Partial AO Analytic Modeling

Analytic Modeling of Partially Corrected Coupled Flux into SMFs



27

Adaptive

Optics

Atmos.

Propagation

Channel


Analytical laws for each one of the errors are known

2ph & ron

+ 2Alias + 2scintill.

2fitting Fitting Error

+ 2PS

+ 2Tempo Temporal Error

drrr corrres ))²()((12 S


+Variation du Drx


Minimization of residual phase variance

28

PARTIAL ADAPTIVE OPTICS

Intrinsic limitations = partial AO

Aliasing Error

SFM Neglect impact of noise and scintillation on phase sensor

error

Perturbed Field

Corrected Field

Uncorrected high

frequencies Perfectly corrected

low frequencies

Spatial Frequencies

Pow

er S

pec

tra

l D

ensi

ty

Fitting

Error

Ideal AO correction system: the low order residuals are perfectly corrected

Total residual error

29


Uncorrected high

frequencies

Patially corrected

low frequencies

Spatial Frequencies

Pow

er S

pec

tra

l D

ensi

ty

Fitting

Error

Aliasing+Temporal

Errors

Partial AO correction system: low order residuals that are highly correlating

Total residual error Non negligible impact

on communication

performances

30


31

INSTANTANEOUS COUPLED OPTICAL POWER ATTENUATION

Neglecting amplitude spatial structures influence on coupling fluctuations:

Scintillation Injection losses Average

coupling losses

Collected power

fluctuations Rough approx, validated for medium elevation, small perturbations

32

Optical power attenuation probability density distribution Average fading time against normalized threshold

Canuet L., Védrenne N., Conan J-M. , Petit C., Artaud G., Rissons A., and Lacan J., « Statistical properties of single-mode fiber

coupling of satellite-to-ground laser links partially corrected by adaptive optics » J. Opt. Soc. Am. A 35, 148-162 (2018)



Scintillation Injection losses Average

coupling losses

Collected power

fluctuations Rough approx, validated for medium elevation, small perturbations

Illustration GEO-Downlink, Drx = 50cm, r0= 0.069 m, 9 radial orders at 1 kHz




Optical Communication Subsystem Overview

Outage Probability

Minimum Required Interleaver


33

Adaptive

Optics

Atmos.

Propagation

Channel


encoder

Channel

decoder

Physical Layer


PHYSICAL LAYER PERFORMANCE END-TO-END MODELING

34

Adaptive

Optics

Atmos.

Propagation

Channel


encoder

Channel

decoder

Physical Layer

EDFA

PREAMPLIFIER

OPTICAL

FILTER

EDFA

PREAMPLIFIER

OPTICAL

FILTER

PIN

PHOTODIODE

ELECTRICAL

FILTER

OOK Preamplified Detector

BALANCED

DETECTOR

ELECTRICAL

FILTER

DELAY-LINE

INTERFEROMETER

DPSK Balanced Detector

TB

PHYSICAL LAYER TRADE-OFF ASSESSMENT

LEO application case Drx = 0.25 m | r0 = 0.056 m

35

Target:

Min required power

Outage probability for 10 Gbps link coderate R0=0.5

Med. Perf. AO

15 actuators 800 Hz

5dB avg. attenuation

Low. Perf. AO

10 actuators 500 Hz


DPSK system with -7dB AO


36

Target:


Med. Perf. AO

15 actuators 800 Hz


Low. Perf. AO

10 actuators 500 Hz




30 ms interleaver (300 Mb)



37

Target:


30 ms interleaver (300 Mb)

3 dB

Optimizing interleaver at targeted outage probability & required power?

Med. Perf. AO

15 actuators 800 Hz


Low. Perf. AO

10 actuators 500 Hz


OOK system with -3db AO



High Perf. AO

50 actuators at 2 kHz





LEO application case Drx = 0.25 m | r0 = 0.056 m | OOK

Code rate

38

Minimum Required PHY interleaving depth High Perfo. AO | Outage Prob. 10-2

PHY Code Rate

Min

. R

equir

ed P

HY

Inte

rlea

ver

Mem

ory

[M

b]

Low redundancy

Req. Rx Power = -41 dBm


Code rate

39

Min

. R

equir

ed P

HY

Inte

rlea

ver

Mem

ory

[M

b]




Partial AO

Ideal AO

Neglecting lower order residuals underestimate required memory by 50%

PHY Code Rate



Code rate

40

PHY Code Rate


Ideal Infinite interleaver limit

Min

. R

equir

ed P

HY

Inte

rlea

ver

Mem

ory

[M

b]





Code rate

41

PHY Code Rate


Decrease in redundancy

sharp increase in memory

Min

. R

equir

ed P

HY

Inte

rlea

ver

Mem

ory

[M

b]



Transfer to HL







Modeling of Cross-layer Coding Scheme

Case Study: LEO Downlink Using DPSK

42

Adaptive

Optics

Atmos.

Propagation

Channel

Higher

Layers

Tx

Higher

Layers

Rx


encoder

Channel

decoder

Physical Layer


INFO Redundancy

INFO Redundancy

Error corr. code


TRANSPORT

CROSS-LAYER APPROACH : Overview

43


Erasure code

R0HL

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

Error correcting code

R0PHY

Red.

Redundancy

HL Redundancy

PHY

Redundancy APPLICATION Rx


Perf. metric: PER

Fixed global code rate

R0GLOBAL = R

0PHYR

0HL

Useful Data Rate = raw data-rate x R0GLOBAL

The PHY and HL coderates inherently related through definition of global coderate:

INFO Redundancy

INFO Redundancy

Error corr. code


TRANSPORT

CROSS-LAYER APPROACH : Overview

44

Red.

Redundancy

HL Redundancy

PHY

Redundancy

Fixed global code rate

R0GLOBAL = R

0PHYR

0HL

Useful Data Rate = raw data-rate x R0GLOBAL

The PHY and HL coderates inherently related through definition of global coderate:

Tx HL memory = HL interleaver depth x raw data-rate x R0PHY

Tx PHY memory = PHY interleaver depth x raw data-rate Advantage to HL


Erasure code

R0HL

APPLICATION Tx

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Higher layers

FSO

Channel

Error correcting code

R0PHY

APPLICATION Rx


Perf. metric: PER

PHYSICAL LAYER

R0PHY = 0.5

CROSS-LAYER APPROACH : Modeling R

0GLOBAL = R

0PHYR

0HL = 0.3

45

Mu

tua

l in

form

atio

n

PHYSICAL LAYER

HIGHER LAYERS DATA LINK | NETWORK |

TRANSPORT

R0PHY = 0.5

46

Mu

tua

l in

form

atio

n

PH

Y o

utp

ut P

ER


0GLOBAL = R

0PHYR

0HL = 0.3

PHYSICAL LAYER


TRANSPORT

R0PHY = 0.5

47

BAD

GOOD

Mu

tua

l in

form

atio

n

PH

Y o

utp

ut P

ER


0GLOBAL = R

0PHYR

0HL = 0.3

1-R0HL = 0.4

PHYSICAL LAYER


TRANSPORT

APPLICATION LAYER

R0PHY = 0.5

1-R0HL = 0.4

48

Mu

tua

l in

form

atio

n

PH

Y o

utp

ut P

ER

H

L o

utp

ut

Decoded P

ER


0GLOBAL = R

0PHYR

0HL = 0.3

PHYSICAL LAYER


TRANSPORT

APPLICATION LAYER FINAL PERFORMANCE METRIC : Average of decoded PER

R0PHY = 0.5

1-R0HL = 0.4

49

Mu

tua

l in

form

atio

n

PH

Y o

utp

ut P

ER

H

L o

utp

ut

Decoded P

ER


0GLOBAL = R

0PHYR

0HL = 0.3

Average decoded PER against size of HL interleaving

50

Tx Higher Layers Interleaving Memory [Mb]

CROSS-LAYER APPROACH : Benefits illustration

R0

GLOBAL = 0.8 | Req. Power = -38 dBm | PHY interleaver 50 Mb

R0PHY = 0.8 R

0HL = 1

R0PHY = 0.82 R

0HL = 0.97

R0PHY = 0.86 R

0HL = 0.93

R0PHY = 0.90 R

0HL = 0.89


51



R0


R0PHY = 0.8 R

0HL = 1

R0PHY = 0.82 R

0HL = 0.97

R0PHY = 0.86 R

0HL = 0.93

R0PHY = 0.90 R

0HL = 0.89

No coding on HL

52



R0


R0PHY = 0.8 R

0HL = 1

R0PHY = 0.82 R

0HL = 0.97

R0PHY = 0.86 R

0HL = 0.93

R0PHY = 0.90 R

0HL = 0.89

Optimal allocation of

redundancy btw PHY and HL


RESOURCES OPTIMIZATION USING MINIMUM TOTAL MEMORY

TARGET PER = 10-4 | 10 Gbps LEO link

DPSK Receiver

53

1000

800

600

400

200

0

Min

. To

tal T

x M

em

ory

(P

HY

+H

L)

[Mb

]

2 3 4 5 6 7 8 9 No coding

(Redundancy)

A lot of coding

(Redundancy) Useful Data Rate [Gbps]

High Perf. AO (-3 dB)

Med Perf. AO (-5 dB)

Low Perf. AO (-7 dB)

54




1000

800

600

400

200

0

Min

. To

tal T

x M

em

ory

(P

HY

+H

L)

[Mb

]

2 3 4 5 6 7 8 9 No coding

(Redundancy)

A lot of coding




DPSK Receiver

Unfad. Rx Power [dBm] : -38

PHY mem. [Mb] : 0 | HL mem. [Mb] : 97

PHY Coderate : 0.48 | HL Coderate : 0.62







HL interl. exclusively

55

1000

800

600

400

200

0

Min

. To

tal T

x M

em

ory

(P

HY

+H

L)

[Mb

]

2 3 4 5 6 7 8 9 No coding

(Redundancy)

A lot of coding







DPSK Receiver



PHY Coderate : 0.5 | HL Coderate : 1










HL interl. exclusively

56

1000

800

600

400

200

0

Min

. To

tal T

x M

em

ory

(P

HY

+H

L)

[Mb

]

2 3 4 5 6 7 8 9 No coding

(Redundancy)

A lot of coding





HL interleaving optimal in less challenging conditions

Physical turbulence mitigation techniques (AO) can have significant impact on overall system

design optimization by driving hardware trade-offs (eg. ASIC vs RAM interleaver)



DPSK Receiver




Developed module

Enhanced/Validated module

End-to-end simulation modeling

Simplified simulation modeling

Analytic modeling

Adaptive

Optics

Atmos.

Propagation

Channel

Higher

Layers

Tx

Application

Tx Data

Application

Rx Data

Higher

Layers

Rx


encoder

Channel

decoder

Physical Layer

SIGNIFICANT RESULTS

57

• First accurate model of partially corrected coupled flux into SMFs

• Detailed investigation of required physical layer interleaving depth and ECC

• First application of cross-layer coding/interleaving scheme to sat. opt. transmissions

• Investigation of overall optimization of AO and data reliability mechanisms

CONCLUSION

How to ensure reliable optical downlinks?

RECOMMENDATION FOR FUTURE WORK

Experimental validation- LEO Downlink planned (DLR’s OSIRIS & ONERA’s LISA)

Investigation of performance evolution over the duration of a whole link

Input turbulence conditions not well known (except astron. observation

sites)

Transposition of approach to GEO uplink

58

PUBLICATIONS AND COMMUNICATIONS

59

Peer-reviewed publication Canuet L., Védrenne N., Conan J-M. , Petit C., Artaud G., Rissons A., and Lacan J., « Statistical properties of

single-mode fiber coupling of satellite-to-ground laser links partially corrected by adaptive optics » J. Opt.

Soc. Am. A 35, 148-162 (2018)

International conferences Canuet L., Védrenne N., Conan J-M., Artaud G., Rissons A., and Lacan J., “Evaluation of communication

performance for adaptive optics corrected GEO-to-ground laser links”, in proceedings of ICSO (International

Conference on Space Optics) 2016, Biarritz, France

Canuet L., Lacan J., Védrenne N., Artaud G., and Rissons A., “Performance Evaluation of Coded Transmission

for Adaptive-Optics Corrected Satellite-To-Ground Laser Links”, in proceedings of ICSOS (IEEE International

Conference on Space Optical Systems and Applications), November 2017 – Naha, Okinawa, Japan

Canuet L., Lacan J., Védrenne N., Artaud G., and Rissons A., “Cross-layer optimization for adaptive-optics

corrected satellite-to-ground laser links”, in proceedings of the 8th international symposium – OPTRO 2018

optronics in defense and security, 6-8 February 2018, Paris

ACKNOWLEDGEMENTS

Committee members Pr. Peucheret

Pr. Belmonte

Pr. Kahn

Dr. Sodnik

Dr. Perlot

Advisors Jérôme Lacan

Angélique Rissons

Nicolas Védrenne

Géraldine Artaud

ONERA Jean-Marc Conan

Cyril Petit

CNES Bouchra Benammar

Airbus DS Sylvain Poulenard

Hervé Haag

Thomas Anfray

Thales AS

Michel Sotom

Arnaud Le Kernec

TéSA Corinne Mailhes

PHYSICAL LAYER TRADE-OFF ASSESSMENT Minimum required interleaving depth

Code rate

61

PHY Code Rate

Min

. R

equir

ed P

HY

Inte

rlea

ver

Mem

ory

[M

b]



Minimum Required PHY interleaving depth High Perfo. OA | Outage Prob. 10-2

Analytic estimation

Analytic estimation based on statistical and temporal characteristics of coupled flux

0.60 | 1.00 0.65 | 0.92 0.70 |

0.92

0.75 | 0.80 0.80 |

0.75

0.85 | 0.70 0.90 | 0.67 0.95 | 0.62 1.00 | 0.60

PHY coderate | HL coderate

Min

. T

X T

ota

l M

em

ory

[M

b]

1000

0

RX Total mem. [Mb] :

102

PHY mem. [Mb] : 102

HL mem. [Mb] : 0

NOT ERROR-FREE FOR

CONSIDERED INTERLEAVERS

RANGE

MINIMUM MEMORY REQUIRED FOR ERROR-FREE TRANSMISSION

10 Gbps link | R0

GLOBAL = 0.6 (6 Gbps throughput) | High Perf. AO

62

RX Total mem. [Mb] :

678

PHY mem. [Mb] : 502

HL mem. [Mb] : 176 Functioning point

requiring both PHY and

HL interleaving

0.60 | 1.00 0.65 | 0.92 0.70 | 0.92 0.75 | 0.80 0.80 | 0.75 0.85 | 0.70 0.90 | 0.67 0.95 | 0.62 1.00 | 0.60

NOT ERROR-FREE FOR

CONSIDERED INTERLEAVERS

RANGE

Region of HL Interleaving only

RX Total mem. [Mb] : 88

PHY mem. [Mb] : 0

HL mem. [Mb] : 88 RX Total mem. [Mb] : 65

PHY mem. [Mb] : 0

HL mem. [Mb] : 65

Optimal allocation of

redundancy

PHY coderate | HL coderate

Min

. T

X T

ota

l M

em

ory

[M

b]

1000

0

Functioning point requiring

minimum overall memory and

power

RX Total mem. [Mb] : 972

PHY mem. [Mb] : 0

HL mem. [Mb] : 972

MINIMUM MEMORY REQUIRED FOR ERROR-FREE TRANSMISSION

10 Gbps link | R0

GLOBAL = 0.6 (6 Gbps throughput) | High Perf. AO

63




Total Latency [ms] : 20.25












Total Latency [ms] : 0


PHY mem. [Mb] : 202 | HL mem. [Mb] :

0








PHY mem. [Mb] : 102 | HL mem. [Mb] :

0



HL intel.

exclusively


TARGET PER = 10-4

OOK Receiver

Increase in Drx

=

Aperture averaging of scintillation

Adaptive Optics

=

Real-time correction of phase fluctuations only

+

For a fixed Drx scintillation effects are imposed upon the detector

The design of the AO system must be done

consequently

Trade-offs scintillation/phase fluctuations mitigation and therefore performances/cost

High perfs AO Limited by scintillation Low perfs AO Limited by phase fluctuations

65

PHYSICAL MITIGATION TECHNIQUES : APERTURE AVERAGING PLUS

AO

Cou

pled

flux

Cou

pling

loss

es

Irradi

ance

Atten

uatio

n

[a.u

.]

Ti

m

e

[s]

Coupled flux Coupling losses Irradiance

Time [s]

Atten

uation

[a

.u.]

Time [s]

Atten

uation

[a

.u.]

EM field of incoming wave

Unperturbed amplitude Log-amplitude

Phase (corrected)

Instantaneous coupled optical power attenuation


Scintillation Injection losses

Pupil transmittance SMF mode

Rustic approx, justified for GEO downlinks (medium elevation, small perturbations)

Cou

ple

d flu

x [a

.u.]

Time [s]

End-to-end wave optics simulation results

66


Simplified Model

Wave Optics σ2 = 0.001

Perfect AO correction

|Difference|

Average

coupling losses

Collected power

fluctuations

Phase decomposition into Zernike polynomials (= Orthonormal basis over a plane and circular domain)

Zernike coefficient #i Zernike polynomial #i

Phase decomposition after “re-orthonormalisation”

Retro-propagated SMF mode in pupil plane

Set of Zernike polynomials not orthonormal

Statistical properties (PDF) of each ai : known analytically (Independent Gaussian variables BUT not identical)

Temporal properties (PSD) of each ai : known analytically

Transfer Matrix {ai}{bi} : known analytically

“Spatial variance” of the phase fluctuations

in the focal plane

Closed-form injection efficiency approximation :

Injection efficiency

without aberrations

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INJECTION LOSSES STATISTICAL CHARACTERIZATION

Scintillation Injection losses

Instantaneous coupled optical power attenuation

+ Temporal properties (PSD, coherence time)

Analytic expressions

Statistical laws (PDF/CDF)

Typical Log-normal distribution “Exponentiated sum of

non-identical Gamma variates”

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INJECTION LOSSES STATISTICAL CHARACTERIZATION




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A lot of coding






PHY mem. [Mb] : 102 | HL mem. [Mb] :0




DPSK Receiver

Reliability of satellite-to-ground optical transmissions · High to very high data rates ~10 Gbps...

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