10GBASE-T Transmission Proposal -...

G. Zimmerman SolarFlare Communications 1

Transmission Proposal for Transmission Proposal for 10GBASE10GBASE--T T

G. Zimmerman, SolarFlare


SupportersSupporters• Rick Rabinovich, Spirent Communications• Dan Dove, HP• Joel Goergen, Force 10 Networks• Chris DiMinico, MC Communications• Mike Bennett, Lawrence Berkeley Labs• Michael Laudon, Force 10 Networks


OutlineOutline• Overview• Baud Rate: Info. Bits/Baud• Equalization• FEC/Trellis Coding• Launch Power Backoff


Overview: Key Choices to MakeOverview: Key Choices to Make• Line coding

– Starts with baud rate (bandwidth)– Exact # levels of PAM tied to FEC choice– May requires overhead for MAC control symbols

• Depends on coding

• FEC choice & partition– Includes both line coding & partition

• Launch voltage– Power consumption/Noise immunity tradeoff– EMI constraint– Power backoff for short lines


Overview: Elements ConsideredOverview: Elements Considered• Channel models

– 55m Class E Objective:• Cabling ad hoc IL, NEXT, FEXT & RL models

(http://www.ieee802.org/3/10GBT/public/material/10GBASE-T_Cat6_Model.zip)

• Class E ad hoc ANEXT model, Class E ISO proposal (15 dB/decade)

– 100m Class E+ Objective:• Class E ad hoc IL, NEXT, FEXT & RL models• Proposals from TR42, ISO, and 3rd parties

• EMI models– EMI radiative transfer function derived from measurements

presented to IEEE 10GBASE-T Study Group• Component effects

– Magnetics bandwidths– Timing recovery effects

• Info bits/baud – determines baud rate– Based on Optimal DFE signal processing


Baud Rate: Info bits/baud (/pair)Baud Rate: Info bits/baud (/pair)• Determines necessary & used bandwidth

– Performance, Power & EMI Constrained• DFE systems generally have a unique optimum• Performance vs. baud rate on DFE channels is

not identical to AWGN channels– Rate loss is channel dependent

• (Rate loss in DFEs under “pinch off” conditions: ref. T1E1.4/97-241)

• Optimal DFE Margin (Salz) normalized to bits/baud:– Uncoded Margin = -10*log10(Salz_MSE)-

Capacity_SNR+12.27dB– Capacity SNR = 10*log10(2^(2*bits/baud/pair) – 1) dB


Baud Rate: 55m Class E Ad Hoc ModelBaud Rate: 55m Class E Ad Hoc Model• Very shallow optimum• ANEXT Model exhibits <10dB/decade ANEXT

slope

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5Uncoded DFEMARGIN

0 100 200 300 400 500 600-200

-180

-160

-140

-120

-100

-80

-60

signal outrem nextrem alien nextrem fextrem echorem awgn

Uncoded DFE Margin vs. bits/baud/pairReceived Residual PSDs

dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair


Baud Rate: 55m Class E with 15dB / Baud Rate: 55m Class E with 15dB / decade ANEXT modeldecade ANEXT model• Optimum shifts towards 3 bits/baud & steepens• ANEXT Model based on presentations

– Conforms with data(hayes_1_0303.pdf, abughalazeh_1_0903.pdf)– ANEXT Loss = 47-15log10(f/100) + 2.5 dB (limit line adj)

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-2.5

-2

-1.5

-1

-0.5

0

0.5Uncoded DFEMARGIN

0 100 200 300 400 500 600-200

-180

-160

-140

-120

-100

-80



dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair


Baud Rate: 100m Class E+ ExampleBaud Rate: 100m Class E+ Example• DFE Margin vs. info bits/baud strongly favors

lower baud rates– ANEXT Loss = 60-15*log10(f/100) + 2.5dB (limit line adj.)

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-4

-3.5

-3

-2.5

-2

-1.5

-1Uncoded DFEMARGIN

0 100 200 300 400 500 600-200

-180

-160

-140

-120

-100

-80



dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair


Baud Rate: EMIBaud Rate: EMI• Used Field Radiated EMI measurements to

estimate transmit PSD within FCC Class A– Issues emerge above 500 MHz

Transmit PSD with 3 dB Margin to FCC Class A EMI(from measured emissions)

-90.00

-85.00

-80.00

-75.00

-70.00

-65.00

-60.00

-55.00

-50.00

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00 1000.00

Frequency (MHz)

Tran

smit

PSD

(dB

m/H

z)

ref: cohen_1_0903.pdf


Other ComponentsOther Components• Magnetics performance falls off beyond 500 MHz

– Adversely effects noise susceptibility & EMI in addition to received SNR

• Timing jitter degrades SNR as baud rate increases (10*log10(fb1/fb2) relative loss in ADC quant noise PSD)

ref: dihn_1_0104.pdf


Baud Rate: ConclusionsBaud Rate: Conclusions• Choice of info bits/baud (baud rate) is a function

of tradeoffs in:– Long-line Performance– ANEXT Robustness– Meeting EMI– Other component effects (e.g., Magnetics, timing)

• 3 bits/baud/pair is within 1 dB of optimum point for DFE SNR for all cases, and closer on hard cases

• 3 bits/baud/pair allows transmit PSD to roll off before 500 MHz– Meets EMI, aligns with magnetics rolloff


Equalization: TomlinsonEqualization: Tomlinson--HarashimaHarashima• Alleviates DFE error propagation in coded systems

– Cost is large amplitude “dither” element added to signal• Transmit power penalty is small for large # PAM levels

– Problems:• Dither couples through NEXT, FEXT & Echo paths• High PAR & extra dynamic range increases complexity• Incompatible with shaping gain• Requires tight circuit timing loop for feedback filter

TH Precoded Channel Equalizer Block Diagram

HffeHtxp

TransmitPrecoder Filter

Hchan

Wireline Channel Feed-ForwardEqualizer

Hdfe

TH Precoder

+/- L(PAM)

+/- 2LDither

modL


Equalization: Equalization: PrecodedPrecoded DFEDFE• Adaptive Linear precoding can shape DFE

response to minimize error propagation– Small transmit power penalty for preemphasis

• 10GBASE-T not generally transmit power limited– Can be combined with other transmit filtering– Can be combined with constellation shaping gain– Feedforward structures minimize circuit timing issues

Hdfe

HffeHtxp

TransmitPrecoder Filter

Hchan

WirelineChannel

Feed-ForwardEqualizer

Decision Feedback Equalizer

DFE-based Channel Equalizer Block Diagram


20 21 22 23 24 25 26 27 28 2910

-6

10-5

10-4

10-3

10-2

10-1

100

Simulated Symbol Error Rates for Uncoded PAM10

Signal-to-Noise Ratio (dB)

Sym

bol E

rror R

ate

Linear Tx PrecodingDFE with Correct DecisionsDFETheory

Equalization: Equalization: PrecodedPrecoded DFEDFE

Transmit PSD and EMI with Precoded Filter

• Precoder coefficients trained at startup to adapt to varying line lengths

• Max DFE feedback coefficient can be constrained < .25

• DFE can be shaped to avoid catastrophic error propagation

0 2 4 6 8 10

x 108

0

10

20

30

40

50

60

70

801 00 mete r c h a nne l5 0 m e te r spa n Ca t 5eF CC Cla s s A limitF CC Cla s s B limit


FEC/Trellis coding: LatencyFEC/Trellis coding: Latency• Applications show need for lower latency codes

– Distributed computing, clustering require capability for low latency operation

• Includes propagation, code and signal processing latency• Long lines mask PHY latency (propagation delay)

• Generic Ethernet places no hard requirement on 10GBT– Legacy of the fact that 802.3ae was engineered for multi-km

links (light time > 5 usec)• Previous Ethernet has not stated latency as a requirement

• High latency codes PERMANENTLY bar technical innovation from achieving low latency operation

• Additional coding gain can be achieved by layering an outer code, if necessary, on long lines without impairing minimum PHY latency on shorter lines


Code Proposal: 4DCode Proposal: 4D--4W4W--Trellis CodeTrellis Code• 4D (across pairs) PAM-10 with 4-way time-interleave

and constellation shaping• Advantages

– Meets 3 bits/baud information rate• Encodes control symbols into modulation, avoiding rate loss

– Provides for minimal latency operation (<< .25usec)– Provides for constellation shaping gain (0.64 dB)– 4-way interleave allows lower-rate decoder clocking– Interleave mitigates noise correlation effects– Interleave mitigates error propagation effects– Low complexity hardware encoding & decoding– Allows concatenation for layering block FEC if desired for

improved impulsive noise or long line performance


Line Code Proposal: 4DLine Code Proposal: 4D--4W4W--PAM10PAM10• 8st 4D Ungerboeck code used in 1000BASE-T

– 2^13 possible encoded symbols– 10,000 constellation points– Remaining 1808 points can be used for control symbols

• 4 Way time interleaving, code is 4D across pairs• Balanced constellation

– No polarity scrambler required• Shaped constellation (0.64 dB shaping gain)

-9 -7 -5 -3 -1 +1 +3 +5 +7 +9 512 896 896 896 896 896 896 896 896 512

Table 1: 1D PAM Level Rate of Occurrence in the 4D Mapping (8192 points)


4D4D--4Way PAM4Way PAM--10 Code Performance10 Code Performance

Slicer Input SNR (dB)

19 20 21 22 23 24 25 26 2710

-14

10-12

10-10

10-8

10-6

10-4

10-2

100

Coded PAM10 simulation SERCoded PAM10 Theory SERCoded PAM10 Theory BER

26.2 dB


Launch Power TradeoffsLaunch Power Tradeoffs• Launch power < 10 dBm due to EMI constraints• Long line launch power > 6 dBm due to

1000BASE-T ANEXT constraints• Negotiated launch power backoff

– Widely used in deployed DSL standards to mitigate asymmetric link near/far problem

– Lines less than 50m– Negotiated at Startup, based on SNR and/or attenuation– Minimum backoffs to be specified in the standard


Baud Rate ProposalBaud Rate Proposal• Motion #1: That 10GBASE-T baseline baud rates

consistent with 3 information bits/baud/pair


Coding proposalCoding proposal• Motion #2: That 10GBASE-T adopt as a 3

bits/baud/pair 4D-4Way PAM-10 code with integrated control symbols


Power Power BackoffBackoff ProposalProposal• Motion #3: That 10GBASE-T adopt a power-

backoff mechanism adapted on startup for use on shorter lines – levels and metrics TBD.


Backup SlidesBackup Slides


Relation of Rate Loss in DFE systems Relation of Rate Loss in DFE systems under pinchunder pinch--offoff• Optimum DFE Result:

• When f_SNR(f) is small for f>fbaud, increasing the baud rate does not change the value of the integral as in an AWGN channel

∫

∫

+=

+=

B

B

dffSNRffbaud

dffSNRffbaud

dBSNR

0

0

)))(_1ln(*))1(exp(10log10

)))(_1ln(1exp(10log*10)(


ANEXT Robustness: Variability of Required Channel Capacity with ANEXT Robustness: Variability of Required Channel Capacity with Constant SNR ConstraintConstant SNR Constraint

• ANEXT = Y + 15*log10(f/100), where Y is adjusted to produce target receive SNR

• Channel contains 4 connectors + 10 m patch cords; length adjusted with horizontal cable span only

•Target SNR includes• BER = 10e-12• 5.5 dB coding gain• 3 dB margin

• Impairments (Class E):• Echo = 55 dB• NEXT = 40 dB• FEXT = 25 dB• Noise = -150 dBm/Hz

• Transmit power = 8 dBm40 50 60 70 80 90 100

16

17

18

19

20

21

22

Channel length (meters)

Req

uire

d C

hann

el C

apac

ity (G

bps)

Required Channel Capacity vs Class E Channel Length for Different PAM Codes

2 bits/symbol: 23 dB Rcv SNR3 bits/symbol: 29 dB Rcv SNR4 bits/symbol: 35 dB Rcv SNR

ref: TR42.7-04-02-012


ANEXT Robustness: Value of ANEXT Coupling Constant (Y) with ANEXT Robustness: Value of ANEXT Coupling Constant (Y) with Constant SNR ConstraintConstant SNR Constraint

• ANEXT = Y + 15*log10(f/100), where Y is adjusted to produce target receive SNR

• Channel contains 4 connectors + 10 m patch cords; length adjusted with horizontal cable span only

• Target SNR includes• BER = 10e-12• 5.5 dB coding gain• 3 dB margin

• Impairments:• Echo = 55 dB• NEXT = 40 dB• FEXT = 25 dB• Noise = -150 dBm/Hz

• Transmit power = 8 dBm

40 50 60 70 80 90 10040

45

50

55

60

65

70

75

Channel length (meters)

AN

EX

T C

onst

ant

Value of ANEXT Constant vs Class E Channel Length for Different PAM Codes

2 bits/symbol: 23 dB Rcv SNR3 bits/symbol: 29 dB Rcv SNR4 bits/symbol: 35 dB Rcv SNR

ref: TR42.7-04-02-012


Error Propagation PerformanceError Propagation Performance

20 21 22 23 24 25 26 2710-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

Error Prop Reduction 4D-Pairs 8st Coded PAM10, ERPX

EQ Output SNR (dB), residual ISI compensated

PAM10 DFE 4D-SERPAM10 DFE w/ perf FB 4D-SERPAM10 1way Vit 4D-SERPAM10 1way Vit w/ perf FB 4D-SERPAM10 4way Vit 4D-SERPAM10 4way Vit w/ perf FB 4D-SERPAM8 AWGN 4pr SERPAM10 AWGN 4D8st Vit 4pr-SER

Slicer SNR (dB)

Sym

bol E

rror

Rat

e


Coding Description: EncoderCoding Description: Encoder

TX S

CR

AM

BLE

R

TXDn[0:11]

4D P

AM

10 MA

PP

ING

D D Dcsn[1] csn[1]

Sdn[0]

Sdn[1]

Sdn[2]

Sdn[3]

Sdn[4]

Sdn[5]

Sdn[6]

Sdn[7]

Sdn[8]

Sdn[9]

Sdn[10]

Sdn[11]

Sdn[12]

csn[0]

Select SubsetSelect P

oint in Subset

Scn[0:11]

TransmitData

FromLFSR

TXA

TXB

TXC

TXD


Coding Description: Trellis DiagramCoding Description: Trellis Diagram

010

011

100

101

110

111

000

001

010

011

100

101

110

111

000

001

D0 D2 D4 D6

D1 D3 D5 D7

D2 D0 D6 D4

D3 D1 D7 D5

D4 D6 D0 D2

D5 D7 D1 D3

D6 D4 D2 D0

D7 D5 D3 D1

D0 D2 D4 D6

D1 D3 D5 D7

D2 D0 D6 D4

D3 D1 D7 D5

D4 D6 D0 D2

D5 D7 D1 D3

D6 D4 D2 D0

D7 D5 D3 D1

ConvolutionalEncoder Bits attime n

ConvolutionalEncoder Bits at

time n+1

Subset for eachof 4 branchesleaving state

Subset for eachof 4 branchesentering state


2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-4

-3.5

-3

-2.5

-2

-1.5Uncoded DFEMARGIN

Baud Rate: 55m Class E with split Baud Rate: 55m Class E with split ANEXT modelANEXT model• Optimum shifts towards 3 bits/baud & steepens• Class E IL

– ANEXT Loss = 49-X*log10(f/100) (X=15, f>100, X=10, f<=100)


dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair0 100 200 300 400 500 600 700

-200

-180

-160

-140

-120

-100

-80



2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

Uncoded DFEMARGIN


lower baud rates (Class E IL)– ANEXT Loss = 64-X*log10(f/100) (X=15, f>100, X=10,

f<=100)Uncoded DFE Margin vs. bits/baud/pairReceived Residual PSDs

dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair0 100 200 300 400 500 600

-200

-180

-160

-140

-120

-100

-80



2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-4

-3.5

-3

-2.5

-2

-1.5

-1

Uncoded DFEMARGIN


lower baud rates (Class F IL)– ANEXT Loss = 62-X*log10(f/100) (X=15, f>100, X=10,

f<=100)Uncoded DFE Margin vs. bits/baud/pairReceived Residual PSDs

dBm

/Hz

Unc

oded

Mar

gin

(dB

)

Info bits/baud/pair0 100 200 300 400 500 600

-200

-180

-160

-140

-120

-100

-80


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