Achieving 1 Gbps Symmetrical Service · PDF fileConstellation size [bits] 1.5 dB 0 0.5 dB 1 dB...

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COPYRIGHT © 2015 ALCATEL-LUCENT. ALL RIGHTS RESERVED.

Achieving 1 Gbps Symmetrical Service

Werner Coomans, Bell Labs May 20th, 2015

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G.fast timeline

2012

G.fast proof of concept

Early operator lab tests

G.fast prototype

More lab tests

Early field tests

First G.fast

products

Larger field trials

Early G.fast

deployment

2013 2014 2015 2016

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G.fast field trials

652 Mbit/s US+DS traffic

(74m in-house cable)

Four Acres

test facility

21 G.FAST TESTED

WITH 21 OPERATORS +7 MORE TRIALS

PLANNED

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Crosstalk in G.fast has a much bigger impact than in VDSL2

Frequency

Channel

Direct signal

Crosstalk signal

-70 dB

0 dB

212 MHz 17.7 MHz

0

VDSL2 G.fast II

106 MHz

G.fast I

“Cross-whispering”

“Cross-SHOUTING”

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Different precoding strategies exist to cope with this high

crosstalk

XTALK

Precompensation

Transmitter Channel Receiver

Linear

precoding

Modulo @

RX

Modulo @

TX

Nonlinear

precoding

Modulo reduces

transmit power

Higher bitloading

Scaling causes

SNR loss

Power scaling @ TX

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Power penalty

2.5 dB

0 dB

Constellation size [bits] 1 12

VDSL2

G.fast

Diamond

Modulo operation introduces a power penalty to guarantee

PSD mask compliance

Neckebroek et al., IEEE ICC 2015,

• Modulo bounds transmit signal to square

constellation

• Uniform distribution within square is assumed

to guarantee PSD mask compliance

• The G.fast standard defined new 3-bit

constellation to lower excessive power penalty

• G.fast constellations are “NLP-ready”

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The nonlinear modulo operation increases the gap to capacity

for small constellations

Impact is largest for the smallest constellations, due

to the larger fraction of outer constellation points

Neckebroek et al., IEEE ICC 2015

The modulo operation creates additional nearest

neighbors for the outer constellation points

4-QAM example

Coding gain degradation

Constellation size [bits]

1.5 dB

0

0.5 dB

1 dB

1 12

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Nonlinear precoding gain is only significant at high

frequencies

106 MHz 212 MHz

1 Gbps

700 Mbps 1 Gbps

2 Gbps

1.5 Gbps 850 Mbps

Line index Line index

≈ +30 to 40 Mbps ≈ +100 to 250 Mbps

+5% +15%

Linear

Nonlinear

Linear

Nonlinear

Very short cable with very high crosstalk

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1 Gbps is today’s marketing weapon

1Gbps

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XG-FAST = “gigabits for all”

1

10

100

1000

10000

1995 2000 2005 2010 2015 2020

ADSL ADSL2

ADSL2+ VDSL(2) 8b

VDSL2 17a

+ bonding + vectoring

G.fast 106MHz

G.fast 212MHz

+ bonding & vectoring

1 Mb/s

10 Mb/s

100 Mb/s

1 Gb/s

10 Gb/s XG-FAST 500MHz

5GBB

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Fiber To The …

NODE CURB MANHOLE POLE DRIVEWAY FRONTDOORBUILDING

>200 METER

>100 SUBSCRIBERS

<200 METER

10s OF SUBCRIBERS10s OF METERS

1 SUBSCRIBER

XG-FASTG.fastVDSL2 VECT

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A homes passed fiber network

A homes connected copper network

AggregationStreet

Reverse powering • User doesn’t need to power shared hardware

• Short cables have low resistive loss

Distribution Point Unit • Single or very few subscribers

• Very close to end user

High bandwidth backhaul

NG-PON2

Multiple pairs per subscriber • No/little inter-user crosstalk

• High intra-user crosstalk

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XG-FAST does not replace FTTH, but is to be considered an

integral component of FTTH deployments

Gigabits for all

Accelerates the roll-out of FTTH services

Complementary to FTTH Avoids the logistic nightmare of installing

fiber on each customer premise

XG-FAST

• Up to 10 Gbps on shortest loops

• 1Gbps symmetric for all

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XG-FAST physical layer concepts

Bonding • 2 twisted pairs

• High crosstalk at high frequencies

TCAM

• Transmitter Controlled Adaptive Modulation

• Automatic adaptation to varying channel conditions

• Allows operation at 0 dB SNR Margin

• Increases spectral efficiency

• Crosstalk contains detectable signal energy

• We use crosstalk to increase the capacity

(constructive interference)

• Two sided coordination

Vectoring

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• Each DTU is assigned to one hierarchic layer

• RX acknowledges successful DTU receptions

• TX notices when some layers are not received

• TX autonomously shuts these layers down and

retransmits the DTU in a more robust layer

Layer 1:3 < Layer 1:2 < Layer 1

Increasing robustness

Decreasing capacity

Transmitter Controlled Adaptive Modulation (TCAM)

enables fast and autonomous rate adaptation

Lower SNR margins

Higher throughput

Fast and autonomous rate adaptation

Timmers et al., Bell Labs Tech. J. 18(1), pp. 153–169, 2013

11 11

01 11

11 01

01 01

1 1

Q

I

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Proof-of-concept measurement results

W. Coomans et al., IEEE Globecom 2014

0

5 Gbps

Net data rate

Reach

30m 70m 50m

10 Gbps

Two pairs

Operator cable

CAT5e

7Gbps @ 70m

2Gbps @ 70m

Single pair

Achieving 1 Gbps Symmetrical Service · PDF fileConstellation size [bits] 1.5 dB 0 0.5 dB 1 dB...

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