1 © 2003 Cisco Systems, Inc. All rights reserved. Advanced PHY Performance ADVANCED PHY PERFORMANCE RON HRANAC Note: This presentation is intended for

1© 2003 Cisco Systems, Inc. All rights reserved.

Advanced PHY Performance

ADVANCED PHY PERFORMANCE

RON HRANAC

Note: This presentation is intended for Cisco internal audiences and customers under NDA only. This

presentation contains confidential intellectual property information that is proprietary to Broadcom Corporation

and Texas Instruments.



DOCSIS® Background

• DOCSIS 1.0 gave us standards-based interoperability, which means “certified” cable modems from multiple vendors work with “qualified” cable modem termination systems (CMTSs) from multiple vendors.

• DOCSIS 1.1 added a number of features, including quality of service (QoS), more robust scheduling, packet classification and other enhancements that facilitate voice services.

Data Over Cable Service Interface Specification



DOCSIS Background

• DOCSIS 1.0 and 1.1—collectively known as DOCSIS 1.x— support two downstream modulation formats: 64-QAM (quadrature amplitude modulation) and 256-QAM.

Modulation format Channel bandwidth,

MHz

Symbol rate,

Msym/sec

Raw data rate, Mbps

Nominal data rate, Mbps

64-QAM (DOCSIS) 6 5.056941 30.34 ~27

256-QAM (DOCSIS) 6 5.360537 42.88 ~38

64-QAM (Euro-DOCSIS) 8 6.952 41.71 ~37

256-QAM (Euro-DOCSIS) 8 6.952 55.62 ~50



DOCSIS Background

• DOCSIS 1.x supports several upstream data rates, ranging from a low of 320 kbps to a high of 10.24 Mbps. It also supports two modulation formats—quadrature phase shift keying (QPSK) and 16-QAM—as well as five upstream RF channel bandwidths.

Channel bandwidth, MHz

Symbol rate, ksym/sec

QPSK raw data rate, Mbps

QPSK nominal data rate, Mbps

16-QAM raw data rate, Mbps

16-QAM nominal data rate, Mbps

0.200 160 0.32 ~0.3 0.64 ~0.6

0.400 320 0.64 ~0.6 1.28 ~1.2

0.800 640 1.28 ~1.2 2.56 ~2.4

1.60 1,280 2.56 ~2.3 5.12 ~4.8

3.20 2,560 5.12 ~4.6 10.24 ~9.0



DOCSIS Background

• DOCSIS 1.1 added some enhancement to upstream transmission robustness, using 8-tap adaptive equalization.

• DOCSIS 2.0: Higher upstream data throughput per RF channel, up to 30.72 Mbps

• DOCSIS 2.0 supports 64-QAM in the upstream—plus 8-QAM and 32-QAM—and optionally supports 128-QAM trellis coded modulation (TCM) encoded modulations for S-CDMA channels.

• Higher orders of modulation require more robust data transmission

• To facilitate more robust upstream data transmission, DOCSIS 2.0 introduced advanced PHY



• Advanced PHY – 2nd Generation Burst Mode RX

Direct sampled RF front end

Ingress cancellation

Frequency stacking

Spectrum management

Improved adaptive equalizer from 2.0 Spec

Improved burst mode RX preamble

• Improves 1.x as well as 2.0 cable modems

What is Advanced PHY?

PHY: Physical Layer




• Symbol (T)-spaced adaptive equalizer with 24 taps compared to 8 taps in DOCSIS 1.x

Allows operation in the presence of more severe multipath and microreflections, and should accommodate signals near the band edge where group delay is more prevalent

• Improved burst acquisition

Carrier and timing lock, power estimates, equalizer training and constellation phase lock are all done simultaneously. This allows shorter preambles, and reduces implementation loss.

• Better forward error correction (FEC)

DOCSIS 1.x provides for the correction of up to 10 errored bytes per Reed Solomon block (T=10) with no interleaving, while DOCSIS 2.0 allows correction of up to 16 bytes per Reed Solomon block (T=16) with programmable interleaving.




• Advanced PHY silicon incorporates ingress cancellation technology in the upstream receiver chip, which further enhances upstream data transmission robustness. Think of ingress cancellation as a way to digitally remove in-channel impairments such as ingress and common path distortion.



Performance ConceptsPerformance Concepts

• Implementation MarginCloseness to ‘theoretical’ in an additive white Gaussian noise (AWGN) environment

Example – If the theoretical bit error rate (BER) at 21 dB carrier-to-noise ratio (CNR) is 1x10-6 but a CMTS actually needs 23 dB CNR to achieve a 1x10-6 BER, the implementation margin is 2 dB.

• Processing GainProcessing to improve performance (e.g., FEC or ingress cancellation)

Example – When ingress cancellation is turned off and a carrier-to-interference ratio (C/I) of 10 dB yields 1x10-6 BER, then turning on ingress cancellation allows C/I = 0 dB for 1x10-6 BER, processing gain is 10 dB.



MC16C/S, MC28C/E Burst Mode Receivers - 1st Generation

Broadcom’s BCM3137 is within 2 dB of theory @16-QAM

Burst Error Rate vs. Frequency Offset

2.56 Msym/sec, 16-QAM

10-Byte Preamble, RS(236,220)

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00 14 16 18 20 22

CNR (dB) B

urs

t E

rro

r R

ate

0 kHz RS(236,220) Theory

Implementation margin of analog receiver (VCO, SAW…) adds another 2-3 dB

AND

Broadcom Confidential



MC28U/X – 2nd GenerationDirect Sampled Burst Mode Digital Receiver

F-connector

LPF PGA Amplif ierLPF

To FFTSubsystem(AWACs)

A/D

To PHY

Gmax = 32 dB

G = 1

From AGC

All frequency conversion and selectivity in PHY ASIC

Total implementation margin < 0.5 dB of theory



MC28U/X MC16U/X – Annex A/BUpstream Broadcom BCM3138 (same as BCM3140 2.0 chip, but without S-CDMA)

5-65 MHz dual A-TDMA, adaptive ingress cancellation, integrated FFT

Downstream – Broadcom BCM3034 Annex A/B Modulator

No SAW filter required with downstream chip

MC5x20U – Annex A/B

Upstream Texas Instruments TI4522 series

5-65 MHz A-TDMA, advanced PHY including ingress cancellation

Downstream – Broadcom BCM3034 Annex A/B modulator

No SAW filter required with downstream chip

Cisco’s Advanced PHY



Cisco’s Advanced PHY

• Advanced RF front end and Cisco MAC hardware, allow Cisco’s MC5x20U and MC28U Broadband Processing Engines (BPE) to offer improved capacity, performance and reliability.

Operates within 0.5 dB of theory

Advanced PHY with ingress cancellation

Greater than 17 Mbps single modem upstream throughput

Line rate DOCSIS 1.1 and 2.0 processing using the advanced Cisco DOCSIS MAC technology



Cisco’s Line Card RF Front End

• High density—2 downstreams, 8 upstreams (MC28U) or 5 downstreams, 20 upstreams (MC5x20U) per line card

• Enhanced RF robustness

• Embedded upstream ingress cancellation

• Direct sampling

• Integrated upconverters

• ATDMA-capable



RF Performance:BER vs. AWGN



MC28U Packet Error Rate Versus AWGN

2.00E-06

6.44E-04

3.51E-029.24E-02

4.04E-07

1.71E-04

1.53E-02

7.81E-02

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

8 8.5 9 9.5 10 10.5 11 11.5 12

CNR (dB)

PE

R

MC28U

Theoretical

Frequency: 30 MHzMod: QPSKSymbol Rate: 1,280 ksym/secPower: 0 dBmvPacket Size: 64 BytesPacket Rate: 100Packets: 1000000RS_N=84RS_T=3

QPSK




1.00E-06

4.48E-04

3.94E-02

2.25E-01

8.55E-08

1.04E-04

1.61E-02

9.08E-02

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

15 15.5 16 16.5 17 17.5 18

CNR (dB)

PE

R

MC28U

Theoretical

Frequency: 30 MHzMod: 16QAMSymbol Rate: 1,280 ksym/secPower: 0 dBmvPacket Size: 64 BytesPacket Rate: 100Packets: 1000000RS_N=88RS_T=5

16-QAM




2.00E-06

1.84E-04

2.64E-02

3.99E-01

4.31E-07

2.46E-05

9.63E-03

2.64E-01

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

19 19.5 20 20.5 21 21.5 22 22.5

CNR (dB)

PE

R

MC28U

Theoretical

Frequency: 30 MHzMod: 64QAMSymbol Rate:5,120 ksym/secPower: 0 dBmvPacket Size: 64 BytesPacket Rate: 100Packets: 1000000RS_N=96RS_T=9

64-QAM



MC28U/MC28C Comparison

Cisco MC28C/U AWGN Impairment Performance: QPSK

4.00E-06

2.80E-05

2.35E-04

5.79E-03

11.5

10.5

9.59

4.04E-07

1.71E-04

1.53E-02

7.81E-02 5.50E-02

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5

CNR (dB)

PE

R

MC28C

MC28U

Theoretical

Frequency: 30 MHzMod: QPSKSymbol Rate:1,280 ksym/secPower: 0 dBmvPacket Size: 64 BytesPacket Rate: 100Packets: 1000000RS_N=84RS_T=3



MC28U/MC28C Comparison

Cisco MC28C/U AWGN Impairment Performance: 16-QAM

4.00E-06

1.80E-05

9.40E-05

4.59E-04

2.03E-03

8.56E-031.86E-02

1.00E-06

4.48E-04

3.94E-02

2.25E-01

8.55E-08

1.04E-04

1.61E-02

9.08E-02

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

14.5 16.5 18.5 20.5 22.5

CNR (dB)

PE

R

MC28C

MC28U

Theoretical

Frequency: 30 MHzMod: 16-QAMSymbol Rate:1,280 ksym/secPower: 0 dBmvPacket Size: 64 BytesPacket Rate: 100Packets: 1000000RS_N=88RS_T=5



MC520S/U BER Versus AWGN

QPSK

Within Measurement Uncertainty of Theory




16-QAM





64-QAM




Lower Implementation Margin Advantages

• Can operate at lower CNR for a given BER than earlier generation CMTSs

• Provides improved operating headroom



RF Performance:Ingress Cancellation



16-QAM 10-8 BER

• Opens previously unusable spectrum

• Enables reliable operation in the presence of ingress

• Narrowband and wideband

• Works with all DOCSIS 1.0, 1.1, & 2.0 cable modems

Ingress Cancellation

Texas Instruments Confidential



MC28/16 U/X w/ Broadcom BCM3138 Adaptive Ingress Cancellation

RX AFE DemodIngressCancel

& Equalizer




Broadcom BCM3138 Ingress Performance

Symbol Rate = 5.12 MHz Cluster SNR = 28.83 dB

Static CW Ingress (64-QAM, SIR = 0 dB)





Symbol Rate = 5.12 MHz

Wideband Ingressors 20 kHz and 100 kHz (16-QAM, SIR = 9 dB)

Cluster SNR = 20.96 dBBroadcom Confidential




Symbol Rate = 5.12 MHz

Four CW Ingressors (64 QAM, SIR = 6 dB)





Four CW Ingressors (16-QAM, SIR = 0 dB)




CableLabs PHY22B Ingress Cancellation

C/I

Single CW Ingress

QPSK

1.28MBaud

AWGN = -20 dB

16QAM

2.56MBaud

AWGN = -25dB

64QAM

5.12Mbaud

AWGN = -30dB

MC28/16U/X -20.2 dB -18.2 dB -10.7 dB

CableLabs optional PHY test

Packet error rate in presence of single CW interferer & AWGN

PER <0.5%, 64-byte packets

Note: Negative C/I indicates interferer is larger than desired signal



RF Performance:Receive Equalizer



DOCSIS 2.0 ADTMA Equalizer

•DOCSIS 1.1 specifies an 8-tap T-Spaced Pre-Equalizer which can mitigate micro-reflections of –10dB (at .5 micro-sec delay) with 27 dB MSE

DOCSIS 1.1 Pre-Equalizer enables reliable operation at 16-QAM in channels that could only support QPSK in DOCSIS 1.0

•DOCSIS 2.0 specifies a 24-tap T-Spaced Pre-Equalizer which can mitigate micro-reflections of –10dB (at .5 micro-sec delay) with 33 dB MSE

DOCSIS 2.0 Pre-Equalizer can enable reliable operation at 64-QAM even in channels that can only support QPSK in DOCSIS 1.0

Cisco Systems Confidential

24-tap adaptive equalizer can operate in DOCSIS 1.0 Mode to compensate linear plant errors (slope, group delay, microreflections) increasing DOCSIS 1.0 modem channel capacity



24-Tap Adaptive Equalizer

BER < 1x10-8 : Reed Solomon T=0 (Off)

DOCSIS 1.0 8-tap equalizer could only support QPSK or 1.28 Msym/sec

Operate 1.0 cable modems at band edge

16-QAM 2.56 Msym/sec over –3.4dB slope and 125 nsec group delay

Impaired 39 – 42 MHz Band



RF Performance:Downstream MER



RF Downstream Path

DSxHigh Speed

D/ABCM3034

ModulatorUPX

DSxUPXHigh Speed

D/ABCM3033

ModulatorSAW

MC16C/S

MC28U/16U

No SAW Filter !!



Downstream Constellation

256-QAM

@ 857 MHz

Total EVM = 1.18% !



Does Advanced PHY Work?



SCTE Cable-Tec Expo Advanced PHY Demo

AM carriers from comb generator

No packet loss!




CPD from downstream feed and diode circuit

No packet loss!




Noise from HP signal generator

No packet loss!




CBT screen shot showing all three impairments



24-Tap Adaptive Equalization Lab Test

6.4 MHz bandwidth 64-QAM signal

After adaptive equalization:No correctable FEC errors and the CMTS’s upstream SNR estimate increased to 36+ dB

Before adaptive equalization:Correctable FEC errors were incrementing about 7000 codewords per second (232 bytes per codeword). The CMTS’s upstream SNR (MER) estimate was 23 dB



Customer Field Test

16-QAM signal riding on top of S-CDMA signal, with CW carrier in-channel

No packet loss!



Customer Field Test

Spectrum analyzer screen shot showing 16-QAM signal at ~12 MHz center frequency

No packet loss!



Advanced PHY: The Bottom Line

• Improves upstream data transmission robustness

• Allows use of spectrum that was previously unusable

• Facilitates higher orders of modulation

• Provides additional operating headroom

• Many advanced PHY features work with DOCSIS 1.x cable modems

• Cost-effective way to kick-start the deployment of new services

Q and A





Documents

1 © 2003 Cisco Systems, Inc. All rights reserved. Advanced PHY Performance ADVANCED PHY PERFORMANCE RON HRANAC Note: This presentation is intended for