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Link Adaptation and Carriers Detection Errors in Multibeam Satellite Systems with Linear Precoding Anxo Tato, Stefano Andrenacci, Symeon Chatzinotas, Carlos Mosquera atlanTTic Research Center, University of Vigo SnT, University of Luxembourg

SLIDE 1

Link Adaptation and Carriers Detection Errors in Multibeam Satellite Systems with Linear Precoding

Anxo Tato, Stefano Andrenacci, Symeon Chatzinotas, Carlos Mosquera

atlanTTic Research Center, University of Vigo SnT, University of Luxembourg

September 11, 2018

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

SLIDE 2

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

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 2 / 18

SLIDE 3

Introduction

Actual channel CSIT: Estimated channel available at GW Precoding matrix

SINR MODCOD

LUT

MODCOD

Actual precoded SINR Estimated precoded SINR ¿Allows quasi-error-free transmission with this MODCOD?

_ +

SINR absolute error LUT Lookup Table Selected Modulation and Coding Scheme

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 3 / 18

SLIDE 4

System model

Signal model: y = Hx + n = HWs + n Channel model: ESA’s 245 beams radiation pattern ˆ H: Imperfect CSIT due to...

Nullification Gaussian estimation errors

Linear Precoding: MMSE with Sum Power Constraint (SPC) W = η · ˆ HH

H ˆ HH + 1 snrIN −1 (1)

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 4 / 18

SLIDE 5

Nullification effect

Actual channel CSIT: Estimated channel available at GW

#1 #2 #3

Actual channel CSIT: Estimated channel available at GW

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 5 / 18

SLIDE 6

Nullification description

Estimation of CSI coefficients:

Asynchronous systems → I/C ≈ −15 dB Synchronous systems: → I/N ≈ −15 dB Real system:

CSI estimation performance Architecture of the receiver for CSI detection and estimation

5 10 15 20

C/N (dB)

5 10 15 20 25 30

C/I (dB)

Carrier is nullified Carrier is estimated Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 6 / 18

SLIDE 7

Example of nullification

Carrier to Noise in a subset of 9 beams

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 7 / 18

SLIDE 8

Number of estimated channel coefficients

Total number of coefficients per channel vector = 245 DVB-S2X standard allows to report up to 32 coefficients Number 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

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 8 / 18

SLIDE 9

SINR absolute error due to nullification

Actual channel CSIT: Estimated channel available at GW Precoding matrix

SINR MODCOD

LUT MODCOD

Actual precoded SINR Estimated precoded SINR ¿Allows quasi-error-free transmission with this MODCOD?

_ +

SINR absolute error LUT Lookup Table Selected Modulation and Coding Scheme

SINR calculated by the GW ˆ sinrk = |ˆ h⊥

k wk|2

j=k |ˆ

h⊥

k wj|2 + N0

Actual user SINR sinrk = |h⊥

k wk|2

j=k |h⊥

k wj|2 + N0

SINR absolute error in dB ek = 10 log10 ˆ sinrk − 10 log10 sinrk

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 9 / 18

SLIDE 10

System parameters

Parameter Value Satellite orbit GEO Downlink frequency Ka-band (20 GHz) Number of beams 245 Color scheme Full frequency reuse Fading No fading

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 10 / 18

SLIDE 11

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 of the total beam radius all beam positions

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

SLIDE 12

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) 0.5 1 1.5 2 2.5 3 SINR absolute error (dB)

Users within a radius of 2/6 Users within a radius of 3/6 Users within a radius of 4/6 All beam positions

Comparison different nullifications

Maximum error over the whole satellite coverage ASYNC I/C = -15 dB REAL SYNC I/N = -15 dB Nullification type 1 2 3 4 5 6 7 SINR absolute error (dB)

Users within a radius of 2/6 Users within a radius of 3/6 Users within a radius of 4/6 All beam positions

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 12 / 18

SLIDE 13

Complementary CDF of the error

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

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 CCDF: P(error > x) Error over the whole satellite coverage Users within a radius of 2/6 Users within a radius of 3/6 Users within a radius of 4/6 All beam positions

High capacity losses due to the required large margins!

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 13 / 18

SLIDE 14

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 performance loss of worst-case margin.

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 14 / 18

SLIDE 15

Countermeasure: link adaptation with adaptive margin

Actual channel CSIT: Estimated channel available at GW Precoding matrix

SINR MODCOD

LUT

MODCOD

Actual precoded SINR Estimated precoded SINR ¿Allows quasi-error-free transmission with this MODCOD?

_ +

SINR absolute error LUT Lookup Table Selected Modulation and Coding Scheme

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 15 / 18

SLIDE 16

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 SINR LUT DVB-S2X ModCods Selected ModCod

Calculated by the gateway Updated with ACK/NAK exchange

ACK: Margin ✘Margin + ∆ACK NAK: Margin ✘Margin - ∆NAK

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

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 16 / 18

SLIDE 17

Simulation results

Scenario:

Continuous transmission of frames to 10 users located in 10 non-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 FER Avoiding the performance loss of a global fixed margin.

Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 17 / 18

SLIDE 18

Thanks for your attention!

The research was done during a stay at the Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, supported by the project SatNEx-IV, co-funded by the European Space Agency (ESA).

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