Link Adaptation and Carriers Detection Errors in Multibeam...

Link Adaptation and Carriers Detection Errors inMultibeam Satellite Systems with Linear Precoding

Anxo Tato, Stefano Andrenacci, Symeon Chatzinotas, CarlosMosquera

atlanTTic Research Center, University of VigoSnT, University of Luxembourg

September 11, 2018

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 1 / 18

Introduction

High Throughput Satellite (HTS) at Ka-band• Multibeam satellite + Linear Precoding + Link Adaptation

Full Frequency reuse, 245 beams

Imperfect Channel State Information at the Transmitter (CSIT)• Carriers detection errors = Nullification

Unicast

Random interbeam scheduling


Introduction

Actual channel

CSIT:Estimated channel

available at GW

Precoding matrix

SINR

MODCOD

LUT

MODCOD

Actualprecoded

SINR

Estimatedprecoded

SINR

¿Allows quasi-error-freetransmission with

this MODCOD?

_ +

SINR absolute error

LUTLookup Table

SelectedModulation andCoding Scheme


System model

Signal model:y = Hx + n = HWs + n

Channel model:ESA’s 245 beams radiation pattern

H: Imperfect CSIT due to...

NullificationGaussian estimation errors

Linear Precoding: MMSE with Sum Power Constraint (SPC)

W = η · HH

(HHH +

1

snrIN

)−1

(1)


Nullification effect

Actual channel


available at GW

#1 #2 #3

Actual channel


available at GW


Nullification description

Estimation of CSI coefficients:

Asynchronous systems → I/C ≈ −15 dBSynchronous systems: → I/N ≈ −15 dBReal system:

CSI estimation performanceArchitecture of the receiver

for CSI detection and estimation

-10 -5 0 5 10 15 20C/N (dB)

0

5

10

15

20

25

30

C/I

(dB)

Carrier is nullified

Carrier is estimated


Example of nullification

Carrier to Noise in a subset of 9 beams


Number of estimated channel coefficients

Total number of coefficients per channel vector = 245DVB-S2X standard allows to report up to 32 coefficientsNumber of estimated coefficients with nullification: 1-15

50 100 150 200 250 300

20

40

60

80

100

120

140

160

180

200

Estimated coefficients

2

4

6

8

10

12

14

Results with real nullification


SINR absolute error due to nullification

Actual channel


available at GW

Precoding matrix

SINR

MODCOD

LUT

MODCOD

Actualprecoded

SINR

Estimatedprecoded

SINR


this MODCOD?

_ +

SINR absolute error

LUTLookup Table


SINR calculated by the GW

ˆsinrk =|h⊥k wk|2∑

j 6=k |h⊥k wj |2 +N0

Actual user SINR

sinrk =|h⊥k wk|2∑

j 6=k |h⊥k wj |2 +N0

SINR absolute error in dB

ek = 10 log10ˆsinrk − 10 log10 sinrk


System parameters

Parameter Value

Satellite orbit GEODownlink frequency Ka-band (20 GHz)Number of beams 245Color scheme Full frequency reuseFading No fading


Interbeam scheduling

Unicast: only one user served per beam in each frame

Interbeam scheduling: Users selecting user randomly among...

central positions of the beam within a radius of 2/6, 3/6 or 4/6 ofthe total beam radiusall beam positions


Maximum of the SINR absolute error (global results)

Synchronous nullification

Maximum error over the whole satellite coverage [SYNC]

-10 dB -15 dB -20 dB -25 dB

I/N null. threshold (dB)

0

0.5

1

1.5

2

2.5

3

SIN

R a

bso

lute

err

or

(dB

)

Users within a radius of 2/6



All beam positions

Comparison differentnullifications

Maximum error over the whole satellite coverage

ASYNC I/C = -15 dB REAL SYNC I/N = -15 dB

Nullification type

0

1

2

3

4

5

6

7

SIN

R a

bsolu

te e

rror

(dB

)




All beam positions


Complementary CDF of the error

Margin required to guarantee a given Frame Error Rate (FER) inall the coverage

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

SINR absolute error (dB)

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

10 0

CC

DF

: P

(err

or

> x

)

Error over the whole satellite coverage




All beam positions

High capacity losses due to the required large margins!


Geographical distribution of the error

Map of the SINR maximum error per beam over 1,000

realizations with MMSE-SPC precoder, real nullification

and scheduling users from inner circle of radius 2/6

Maximum error per position

when in the rest of the beams a

random user is scheduled from

the 3x3 central users

Best solution: independent margin per user to avoid performanceloss of worst-case margin.


Countermeasure: link adaptation with adaptive margin

Actual channel


available at GW

Precoding matrix

SINR

MODCOD

LUT

MODCOD

Actualprecoded

SINR

Estimatedprecoded

SINR


this MODCOD?

_ +

SINR absolute error

LUTLookup Table



Countermeasure: link adaptation with adaptive margin

Add to the SINR calculated by the gateway an adaptive margin,independent for each user, updated with its ACK/NAK exchange

Note: these are not used for retransmission purposes

Margin

SINRLUT

DVB-S2XModCods

SelectedModCod

Calculated by the gateway

Updated withACK/NAK exchange

ACK: Margin �Margin + ∆ACKNAK: Margin �Margin - ∆NAK

∆ACK∆NAK

=p0

1 − p0, p0 = Target FER (Typically 1E-5)


Simulation results

Scenario:

Continuous transmission of frames to 10 users located in 10non-neighbour beams scattered over all Europe.Target FER: p0 = 10−3, 10−4, 10−5

Results:Without adaptive margin

FER � Target value p0

With adaptive marging

Experimental FER of users is within 90 − 110% of the target FERAvoiding the performance loss of a global fixed margin.


Thanks for your attention!

The research was done during a stay at the Interdisciplinary Centre forSecurity, Reliability and Trust (SnT), University of Luxembourg,

supported by the project SatNEx-IV, co-funded by the European SpaceAgency (ESA).


Link Adaptation and Carriers Detection Errors in Multibeam...

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