Performance Analysis of Fractionally Spaced Equalization in Non-linear Multicarrier Satellite Channels

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R. Piazza , M. R. Bhavani Shankar ,T. Berheide, M. Grasslin, and S. Cioni

32^th AIAA International Communications Satellite System Conference (ICSSC), San Diego

August 5th, 2014

Performance Analysis of Fractionally Spaced

Equalization in Non-linear Multicarrier Satellite

Channels

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Presentation Overview

1. Scenario

2. Channel impairments and System Constraints 3. System Architecture

4. Fractionally Spaced Equalization 5. Optimized Receiver De-mapping 6. Simulations

7. Conclusions

8. Acknowledgments

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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Scenario

• Multicarrier gateway uplink

• Multicarrier transponder

– Joint input /output filtering – Joint power amplification

• Advantages:

– HW saving – Weight saving – Flexibility

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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Channel Impairments and System Constraints

• Power & Spectral Efficiency Trade off

• System Contraints:

– No On-board Signal Processing – Low complexity User Terminals

INTERMODULATION PRODUCTS

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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• Countermeasures Techniques:

1. Multicarrier Predistortion at the gateway ¹ 2. Advanced Receiver Processing:

1. Fractionally Spaced Equalization

2. Optimized de-mapping at the user terminals (UT)

1R. Piazza, E. Zenteno, and e. al, “Multicarrier digital predistortion/equalization techniques for non-linear satellite channels,”in Proc. 30th AIAA Intern.Commun. Satellite Syst. Conference (ICSSC), Ottawa, Canada, Sep. 2012.

System Architecture

HPA p1

pm

pM

p1

pm

pM

f1

fm

fM

f¹

fm

f^M u1

u^m

uM

y1

ym

yM

η

DPD

. . .. . .

UPLINK DOWNLINK

RX1

RXm

RXM GATEWAY

IMUX OMUX

SATELLITE TRANSPONDER

x1

xm

xM

EQ

r1

rm

rM

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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Fractionally Spaced Equalization

• Receiver equalization that exploits higher

sampling rate

²

:

– K>1 samples per symbol

• It aims to compensate for:

– Non-constant group delay of the channel – Residual Linear and non-linear distortions – Non-optimal receiver sampling

2R. D. Gitlin, S. B. Weinstein, “Fractionally Spaced Equalization: An Improved Digital Transversal Equalizer,” Bell Systems Technical Journal, 60:2, February 1981, available online http://archive.org/details/bstj60-2-275.

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FSE Architecture

• FSE as Linear Filtering:

– r_m n = b_k₁ _m k₁ 𝑣_𝑚 n − k₁ = 𝒃_𝑚𝒗_𝑚(𝑛)

• Parameters Estimation:

– 𝒃_𝑚 = argmin_b_m ^𝑁_𝑛=1 𝐸 𝑟_𝑚 𝑛 − 𝑢_𝑚 𝑛 ² – Standard Least Squares Solution

– Adaptive and based on pilots

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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Non-linear Bias in the RX symbols

• Equalized symbols shows some residual non-linear bias w.r.t. to the reference constellation

• This bias degrades the bit error rate (BER) performance

– Need to determine more accurate reference constellation for decoding

-1.5 -1 -0.5 0 0.5 1 1.5

I

Q

IBO=4

Noiseless Scatter Plot DVB-S2 Constellation Estimated Centroids

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Average and Centroids based De-mapping

• For linear systems average constellation de-

mapping (ACD) suffices:

– One scaling factor : 𝛽 = 𝑎𝑟𝑔min

𝑐

𝑥−𝑐 ²

𝑀 𝑥∈ℱ𝑘 𝑘=1

𝑎_𝑘 ²

𝑀𝑘=1

• For a general non-linear system we need one-

to one re-mapping (CBD):

– For each constellation point 𝑘:

Centroid 𝑐_𝑘 = 𝑎𝑟𝑔min

𝑐 _𝑥∈ℱ_𝑘 𝑥 − 𝑐 ² , 𝑘 ∈ [1, 𝑀]

– Centroids estimation based on pilots

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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TD = E

_b

N

₀ _NL

− E

_b

N

₀ _Ideal

+ OBO.

• Total Degradation:

– Evaluated at a Target Packet Error Rate

– Spectral Efficiency & HPA Power efficiency

where

Figure Of Merit

HPA efficiency loss

Code loss _{OBO = P}

_out

_/P

_sat

𝑑𝐵

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TD Performance Two Carriers

Satellite Channel (1)

• Setting: 16.36 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4, Transp. BW=36MHz

1.0 1.5 2.0 2.5 3.0

3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3

Output Back Off [dB]

Total Degradation [dB]

MC_DPD + EQ MC_DPD + FSE_ACD MC_DPD + FSE_CBD

• EQ: Baseline symbols spaced equalization

• FSE with Average Const.

Decoding provides 0.2 dB over EQ

• Centroids decoding

provides additional 0.15 dB

• Total of 0.3-0.4 dB of gain

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TD Performance Two Carriers

Satellite Channel (2)

• Setting: 18 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4, Transp. BW=36MHz

1.0 1.5 2.0 2.5 3.0 3.5

3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0

MC_DPD + EQ MC_DPD + FSE_ACD MC_DPD + FSE_CBD

• Higher baud-rate leads to higher degradation

Decoding provides 0.15dB over EQ

provides additional 0.25 dB

• Total of ~0.4 dB of gain

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TD Performance Triple Carriers

Satellite Channel (1)

• Setting: 10 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4,Transp. BW=36MHz

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8

MC_DPD + EQ: EXT MC_DPD + EQ: INT MC_DPD + FSE_ACD: EXT MC_DPD + FSE_ACD: INT MC_DPD + FSE_CBD: EXT MC_DPD + FSE_CBD: INT

• External carrier degraded by the MUX filters edge

Decoding provides up to 0.1dB over EQ

provides additional~ 0.15 dB

• Total ~0.2 dB of gain

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TD Performance Triple Carriers

Satellite Channel (2)

• Setting: 10 Mbaud, 32 APSK, Roll-off=0.2,

LDPC with Code Rate=4/5,Transp. BW=36MHz

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

4.0 4.5 5.0 5.5 6.0

MC_DPD + EQ: EXT MC_DPD + EQ: INT MC_DPD + FSE_ACD:EXT MC_DPD + FSE_ACD:INT MC_DPD + FSE_CBD: EXT MC_DPD + FSE_CBD: INT

• Higher Spectral efficiency leads to higher

degradation

Decoding provides up to 0.25 dB to over EQ

provides additional~ 0.25 dB

• Total ~0.5 dB of gain

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Robustness to Sampling Error:

Central carrier of a Three Carrier Channel

• Setting: 16 APSK, Roll Off=0.2, IBO=4 dB, LDPC

with Code Rate=3/4,Transp. BW=36MHz

12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17

10^-5 10^-4 10^-3 10^-2 10^-1

Es/No[dB]

BER

22% Sampling Error:MC DPD + EQ 22% Sampling Error:MC DPD + FSE ACD Perfect Timing: MC-DPD EQ12Ts

35% Sampling Error: MC DPD + FSE ACD 35% Sampling Error: MC DPD+EQ

• Standard EQ is very sensitive to sampling

• FSE compensates substantially for the sampling error

– 22% :perfect recovery – 35%: only 0.5 dB of loss

EQ SNR LOSS FSE SNR LOSS

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Outline

1. Scenario

7. Conclusions

8. Acknowledgments

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Conclusion

• UT FSE equalization evaluated for multicarrier

satellite channels:

– Provides about ~0.1/0.2 dB of gain when

multicarrier predistortion is applied at the GW – Is shown to be robust with respect to sampling

accuracy

• Optimized Symbols de-mapping:

– Provides additional ~0.1-0.3 dB of gain – Low complexity

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Acknowledgement & Contact

The authors would like to thank the European Space Agency (ESA) for their support through the ARTES 5.1 project “On Ground Multicarrier Digital Equalization/Predistortion Techniques for Single or Multi Gateway

Applications” (APEXX) – ESA Contract No.: 4000105192/12/NL/AD.

Contact Details:

• Roberto Piazza: roberto.piazza@uni.lu

Performance Analysis of Fractionally Spaced Equalization in Non-linear Multicarrier Satellite Channels

Performance Analysis of Fractionally Spaced

Equalization in Non-linear Multicarrier Satellite

Channels

Presentation Overview

Outline

Scenario

Outline

Channel Impairments and System Constraints

Outline

System Architecture

Outline

Fractionally Spaced Equalization

• Receiver equalization that exploits higher

sampling rate

:

• It aims to compensate for:

FSE Architecture

• FSE as Linear Filtering:

• Parameters Estimation:

Outline

Non-linear Bias in the RX symbols

Average and Centroids based De-mapping

• For linear systems average constellation de-

mapping (ACD) suffices:

• For a general non-linear system we need one-

to one re-mapping (CBD):

Outline

TD = E

N

− E

N

+ OBO.

• Total Degradation:

Figure Of Merit

HPA efficiency loss

Code loss OBO = P

/P

TD Performance Two Carriers

Satellite Channel (1)

• Setting: 16.36 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4, Transp. BW=36MHz

TD Performance Two Carriers

Satellite Channel (2)

• Setting: 18 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4, Transp. BW=36MHz

TD Performance Triple Carriers

Satellite Channel (1)

• Setting: 10 Mbaud, 16 APSK, Roll-off=0.2,

LDPC with Code Rate=3/4,Transp. BW=36MHz

TD Performance Triple Carriers

Satellite Channel (2)

• Setting: 10 Mbaud, 32 APSK, Roll-off=0.2,

LDPC with Code Rate=4/5,Transp. BW=36MHz

Robustness to Sampling Error:

Central carrier of a Three Carrier Channel

• Setting: 16 APSK, Roll Off=0.2, IBO=4 dB, LDPC

with Code Rate=3/4,Transp. BW=36MHz

Outline

Conclusion

• UT FSE equalization evaluated for multicarrier

satellite channels:

• Optimized Symbols de-mapping:

Acknowledgement & Contact

Code loss _{OBO = P}

_/P