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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.
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
1
DOCSIS® Background
Data Over Cable Service Interface Specification
• 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.
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
2
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
Advanced PHY
Performance
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
© 2003 Cisco Systems, Inc. All rights reserved.
3
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 16QAM—as well as five upstream RF channel
bandwidths.
Channel
bandwidth,
MHz
Symbol rate, QPSK raw
ksym/sec
data rate,
Mbps
QPSK
16-QAM raw
nominal data data rate,
rate, Mbps
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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
4
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
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
5
What is Advanced PHY?
PHY: Physical Layer
• 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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
6
What is Advanced PHY?
• 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
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
7
What is Advanced PHY?
• 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.
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
8
Performance Concepts
• Implementation Margin
Closeness to ‘theoretical’ in an additive white Gaussian noise
(AWGN) environment
Example – If the theoretical bit error rate (BER) at 21 dB carrier-tonoise 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 Gain
Processing to improve performance (e.g., FEC or ingress
cancellation)
Example – When ingress cancellation is turned off and a carrier-tointerference 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.
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
9
MC16C/S, MC28C/E
Burst Mode Receivers - 1st Generation
Burst Error Rate vs. Frequency Offset
2.56 Msym/sec, 16-QAM
10-Byte Preamble, RS(236,220)
Broadcom’s BCM3137 is
within 2 dB of theory
@16-QAM
Burst Error Rate
1.00E+00
AND
1.00E-01
14
16
18
20
22
1.00E-02
0 kHz
RS(236,220) Theory
1.00E-03
1.00E-04
1.00E-05
1.00E-06
CNR (dB)
Implementation margin of analog receiver (VCO, SAW…)
adds another 2-3 dB
Advanced PHY
Performance
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
10
MC28U/X – 2nd Generation
Direct Sampled Burst Mode Digital Receiver
Gmax = 32 dB
F-connector
A/D
LPF
PGA Amplifier
LPF
ToPHY
G=1
To FFT
Subsystem
(AWACs)
FromAGC
All frequency conversion and selectivity in PHY ASIC
Total implementation margin < 0.5 dB of theory
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
11
Cisco’s Advanced PHY
MC28U/X MC16U/X – Annex A/B
Upstream 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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
12
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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
13
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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
14
RF Performance:
BER vs. AWGN
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
15
MC28U Packet Error Rate Versus AWGN
QPSK
1.00E+00
1.00E-01
9.24E-02
7.81E-02
3.51E-02
1.53E-02
1.00E-02
PER
Frequency: 30
MHz
Mod: QPSK
Symbol Rate:
1,280 ksym/sec
Power: 0 dBmv
Packet Size: 64
Bytes
Packet Rate: 100
Packets: 1000000
RS_N=84
RS_T=3
1.00E-03
6.44E-04
1.71E-04
1.00E-04
1.00E-05
2.00E-06
1.00E-06
4.04E-07
MC28U
Theoretical
1.00E-07
8
8.5
9
9.5
10
10.5
11
11.5
12
CNR (dB)
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
16
MC28U Packet Error Rate Versus AWGN
16-QAM
1.00E+00
1.00E-01
3.94E-02
1.61E-02
1.00E-02
PER
Frequency: 30 MHz
Mod: 16QAM
Symbol Rate:
1,280 ksym/sec
Power: 0 dBmv
Packet Size: 64
Bytes
Packet Rate: 100
Packets: 1000000
RS_N=88
RS_T=5
2.25E-01
9.08E-02
1.00E-03
4.48E-04
1.04E-04
1.00E-04
1.00E-05
1.00E-06
1.00E-06
1.00E-07
15
15.5
16
16.5
17
8.55E-08
17.5
18
MC28U
Theoretical
CNR (dB)
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
17
MC28U Packet Error Rate Versus AWGN
64-QAM
1.00E+00
Frequency: 30 MHz
Mod: 64QAM
Symbol Rate:
5,120 ksym/sec
Power: 0 dBmv
Packet Size: 64
Bytes
Packet Rate: 100
Packets: 1000000
RS_N=96
RS_T=9
3.99E-01
2.64E-01
1.00E-01
2.64E-02
9.63E-03
PER
1.00E-02
1.00E-03
1.84E-04
1.00E-04
2.46E-05
1.00E-05
2.00E-06
1.00E-06
4.31E-07
MC28U
Theoretical
1.00E-07
19
19.5
20
20.5
21
21.5
22
22.5
CNR (dB)
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
18
MC28U/MC28C Comparison
Cisco MC28C/U AWGN Impairment Performance: QPSK
1.00E+00
1.00E-01
9
7.81E-02
9.5
1.53E-02
PER
1.00E-02
Frequency: 30 MHz
Mod: QPSK
Symbol Rate:
1,280 ksym/sec
Power: 0 dBmv
Packet Size: 64 Bytes
Packet Rate: 100
Packets: 1000000
RS_N=84
RS_T=3
5.50E-02
5.79E-03
1.00E-03
10.5
2.35E-04
1.71E-04
1.00E-04
2.80E-05
1.00E-05
4.00E-06
11.5
1.00E-06
MC28C
MC28U
4.04E-07
Theoretical
1.00E-07
8.5
9.5
10.5
11.5
12.5
13.5
14.5
15.5
CNR (dB)
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
19
MC28U/MC28C Comparison
Cisco MC28C/U AWGN Impairment Performance: 16-QAM
1.00E+00
2.25E-01
9.08E-02
3.94E-02
1.61E-02
1.00E-01
PER
1.00E-02
Frequency: 30 MHz
Mod: 16-QAM
Symbol Rate:
1,280 ksym/sec
Power: 0 dBmv
Packet Size: 64 Bytes
Packet Rate: 100
Packets: 1000000
RS_N=88
RS_T=5
1.86E-02
8.56E-03
2.03E-03
1.00E-03
4.59E-04
4.48E-04
1.04E-04
1.00E-04
9.40E-05
1.80E-05
1.00E-05
4.00E-06
1.00E-06
MC28C
1.00E-06
MC28U
1.00E-07
14.5
16.5
8.55E-08
18.5
Theoretical
20.5
22.5
CNR (dB)
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
20
MC520S/U BER Versus AWGN
Within Measurement
Uncertainty of Theory
QPSK
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
21
MC520S/U BER Versus AWGN
Within Measurement
Uncertainty of Theory
16-QAM
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
22
MC520S/U BER Versus AWGN
Within Measurement
Uncertainty of Theory
64-QAM
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
23
Lower Implementation Margin Advantages
• Can operate at lower CNR for a given BER than
earlier generation CMTSs
• Provides improved operating headroom
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
24
RF Performance:
Ingress Cancellation
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
25
Ingress Cancellation
• 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
Advanced PHY
Performance
16-QAM
10-8 BER
Texas Instruments Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
26
MC28/16 U/X w/ Broadcom BCM3138
Adaptive Ingress Cancellation
RX AFE
Advanced PHY
Performance
Demod
Ingress
Cancel
& Equalizer
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
27
Broadcom BCM3138 Ingress Performance
Static CW Ingress (64-QAM, SIR = 0 dB)
Symbol Rate = 5.12 MHz
Advanced PHY
Performance
Cluster SNR = 28.83 dB
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
28
Broadcom BCM3138 Ingress Performance
Wideband Ingressors
20 kHz and 100 kHz (16-QAM, SIR = 9 dB)
Symbol Rate = 5.12 MHz
Advanced PHY
Performance
Cluster SNR = 20.96 dB
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
29
Broadcom BCM3138 Ingress Performance
Four CW Ingressors
(64 QAM, SIR = 6 dB)
Symbol Rate = 5.12 MHz
Advanced PHY
Performance
Cluster SNR = 26.94 dB
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
30
Broadcom BCM3138 Ingress Performance
Four CW Ingressors
(16-QAM, SIR = 0 dB)
Cluster SNR = 22.79 dB
Advanced PHY
Performance
Broadcom Confidential
© 2003 Cisco Systems, Inc. All rights reserved.
31
CableLabs PHY22B Ingress Cancellation
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
C/I
QPSK
16QAM
64QAM
Single CW
Ingress
1.28MBaud
2.56MBaud
5.12Mbaud
AWGN = -20 dB
AWGN = -25dB
AWGN = -30dB
-20.2 dB
-18.2 dB
-10.7 dB
MC28/16U/X
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
32
RF Performance:
Receive Equalizer
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
33
DOCSIS 2.0 ADTMA Equalizer
•DOCSIS 1.1 specifies an 8-tap T-Spaced Pre-Equalizer which can mitigate microreflections 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 microreflections 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
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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
Cisco Systems Confidential
34
24-Tap Adaptive Equalizer
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
BER < 1x10-8 : Reed Solomon T=0 (Off)
DOCSIS 1.0 8-tap equalizer could only support QPSK or 1.28 Msym/sec
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
35
RF Performance:
Downstream MER
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
36
RF Downstream Path
MC16C/S
BCM3033
High Speed
D/A
SAW
UPX
DSx
Modulator
MC28U/16U
No SAW Filter !!
BCM3034
Modulator
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
High Speed
D/A
UPX
DSx
37
Downstream Constellation
256-QAM
@ 857 MHz
Total EVM = 1.18% !
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
38
Does Advanced PHY Work?
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
39
SCTE Cable-Tec Expo Advanced PHY Demo
AM carriers from comb generator
No packet loss!
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
40
SCTE Cable-Tec Expo Advanced PHY Demo
CPD from downstream feed and diode circuit
No packet loss!
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
41
SCTE Cable-Tec Expo Advanced PHY Demo
Noise from HP signal generator
No packet loss!
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
42
SCTE Cable-Tec Expo Advanced PHY Demo
CBT screen shot showing all three impairments
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
43
24-Tap Adaptive Equalization Lab Test
6.4 MHz bandwidth 64-QAM signal
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
After adaptive equalization:
No correctable FEC errors and the
CMTS’s upstream SNR estimate
increased to 36+ dB
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
44
Customer Field Test
16-QAM signal riding on top of S-CDMA
signal, with CW carrier in-channel
No packet loss!
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
45
Customer Field Test
Spectrum analyzer screen shot showing 16-QAM
signal at ~12 MHz center frequency
No packet loss!
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
46
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
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
47
Q and A
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
48
Advanced PHY
Performance
© 2003 Cisco Systems, Inc. All rights reserved.
49