introduction to s-cdma - sctechapter.scte.org/...d3-upstream-s-cdmaronhowald.pdfs-cdma basics •...
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1Motorola General Business Use,
MOTOROLA and the Stylized M Logo are registered in the US Patent
& Trademark Office. All other product or service names are the property of their respective owners. ©
Motorola, Inc. 2009
Access Networks Solutions
Introduction to S-CDMA
2
Why S-CDMA?•
Upstream is a looming bottleneck–
Traffic growth–
Competitive environment–
Highly bandlimited
•
Imperative that the bandwidth be fully exploited–
Unused spectrum represents 25-40% of band–
Unused Spectrum = Unused Capacity
•
DOCSIS tools for optimal upstream use–
Optimize Mbps: Modulation Profiles (64-QAM @ 5.12 Msps)–
Optimize Channel: Pre-Equalization–
Optimize Spectral Usage: S-CDMA
•
S-CDMA is standardized, mature, powerful – cost effective new capacity
3
Upstream Impairment Catalogue•
Narrowband Interference–
Radio signal ingress–
Common path distortion (CPD)
•
Burst/Impulse Noise–
1 us – 100 ms duration–
Strongest < 20 MHz–
Combined with ingress < 20 MHz–
S-CDMA is uniquely capable against impulse noise
–
….and thus also against combined impulse plus ingress
•
Other–
Frequency Response Distortion–
Noise Floor
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 10-4
-0.01
-0.005
0
0.005
Time
Impulsive Events
15 16 17 18 19 20 21-60
-50
-40
-30
-20
-10
CPDIngress
Frequency
Narrowband Interference
4
Impulse Noise – Spectrum
Impulse Noise – Typical < 20 MHz
Signature and Burst Typical
Burst
5
Impulse Noise – MER PerspectiveNode NDN02, Modem 0019.5EE6.87FE
MER vs. DOCSIS TX PRE-EQ Levels
27
28
29
30
31
32
33
34
35
36
17:16
18:14
19:12
20:09
21:07
22:04
23:02
0:00
0:57
1:55
2:52
3:50
4:48
5:45
6:43
7:40
8:38
9:36
10:33
11:31
12:28
Time (Beginning 10-21-08)
MER
(dB
)
-12.00
-11.50
-11.00
-10.50
-10.00
-9.50
-9.00
DO
CSI
S TX
PR
E-EQ
Lev
els
(dB
c)
MER MT/TAP MT/(+/-3T) MT/POST
> 8 dB Range
> QAM Order
Equalizer Taps (Channel Freq Response)MER
MER versus Time
6
S-CDMA Overview
7
S-CDMA Basics
•
What–
Synchronous Code Division Multiple Access (S-CDMA) is an upstream technology added in D2.0, and enhanced in D3.0
•
Why–
S-CDMA technology is particularly robust against impulse noise, a critical requirement at the low end (<20 MHz) of the band
•
How–
S-CDMA stretches QAM symbols out in time by 128 times–
Symbols multiplied by (-1 or 1) via CDMA spreading “code”–
Transmits all sets of stretched symbols in parallel–
Zero theoretical interference among transmissions due to special code properties
–
No decrease in channel capacity
8
S-CDMA Spread Symbol
Up to 128 symbols (codes) can be transmitted at the same time
Spread Interval
Chip = 1/Symbol RateTime
←O
rthog
onal
Cod
es →
9
DOCSIS 2.0 vs 3.0 S-CDMA
•
DOCSIS 2.0 S-CDMA–
Full impulse immunity (Code spreading + FEC)–
Ingress cancellation•
A few narrowband interferers•
Sufficient for majority of live deployments
•
DOCSIS 3.0 S-CDMA–
Selectable Active Codes: SAC Mode 2•
Enhanced ingress cancellation–
Maximum Scheduled Codes (MSC)•
Trade SNR for throughput – fewer codes used, more power in each
10
S-CDMA: Benefits and Capabilities
11
Key S-CDMA Benefits•
Impulse noise robustness for lower upstream band–
Gain of symbol spreading >100x A-TDMA at same throughput–
Improving A-TDMA robustness requires narrower channels•
Decreases throughput•
Still weaker than S-CDMAS-CDMA is strongly recommended below 20 MHz
•
Combined ingress and impulse immunity–
D3.0 S-CDMA & A-TDMA are comparable in ingress-only–
S-CDMA outperforms A-TDMA for combined ingress + impulse typically observed < 20 MHz (D2.0 or D3.0)
•
Secondary Benefits–
Increased efficiency of synchronous operation–
Lower FEC overhead due to inherent impulse immunity–
Max Scheduled Code feature – SNR vs throughput trade-off
12
S-CDMA vs. A-TDMA Comparison
•
Recover unused and/or underutilized 5-20 MHz bandwidth–
S-CDMA: 67 Mbps in lower channels (152 Mbps total)–
A-TDMA: 30 Mbps in lower channels (115 Mbps total)•
S-CDMA throughput Advantages–
Increase capacity up to ~50% –
Ensure 100 Mbps upstream service capacity–
Defer node splitting
42 MHz5 MHz
64 QA
M
SC
DM
A
64 QA
M
ATD
MA
64 QA
M
ATD
MA
64 QA
M
ATD
MA
32 QA
M
SC
DM
A
16 QA
M
ATD
MA
64 QA
M
ATD
MA
64 QA
M
ATD
MA
64 QA
M
ATD
MA
16 QA
M
ATD
MA
16 QA
M
ATD
MA
16 QA
M
ATD
MA
A-TDMA
S-CDMA
32 QA
M
SC
DM
A
13
Est. Link Gain – S-CDMA vs A-TDMA
• QAM Relationships: 4-8 dB represents 1-2 orders of modulation– 16-QAM → 32-QAM (~3 dB) → 25% more throughput– 16-QAM → 64-QAM (~6 dB) → 50% more throughput– 32-QAM → 64-QAM (~3 dB) → 20% more throughput
Frequency Band 2.56 Msps 5.12 Msps5.0-9.0 MHz < 6 dB < 8 dB
9.0-15.0 MHz < 4 dB < 6 dB15.0-20.0 MHz < 2 dB < 4 dB
20 MHz < fo ~Equiv ~Equiv
14
S-CDMA Summary•
The Situation Upstream –
Traffic continues to grow–
New channels are being added–
Spectrum remains limited– Maximize spectrum– Optimize its use
•
Congestion Relief–
S-CDMA: standardized 7+ years ago–
Built for tough channels–
Available, mature, improved, proven
•
S-CDMA is required to effectively operate high throughput channels at lower end of band–
Works where A-TDMA will not–
Better throughput where A-TDMA supports a modest link
•
S-CDMA: Cost-Effective Upstream Capacity
15Motorola General Business Use,
MOTOROLA and the Stylized M Logo are registered in the US Patent
& Trademark Office. All other product or service names are the property of their respective owners. ©
Motorola, Inc. 2009
Access Networks Solutions
Thank You!
Dr. Robert Howald CTO Office Motorola Home & Networks [email protected]