DOCSIS & Testing Best Practices in an All Digital Network

1.
Brady
Volpe

2. Massive
Traffic
Growth
The “terabyte club” will reach 6 million by 2015
There will be over 20 million households generating
half a terabyte per month in 2015
-­‐Cisco
Visual
Networking
Index:
Forecast
and
Methodology,
2010-­‐2015
• Need:
1
Gbps
bi-­‐direcHon
pipe
in
five
years
• Need
more
digital
–
Less
Analog
::
No
Analog!
©
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Volpe
Firm
ConfidenHal
2

3. Digital
vs.
Analog
©
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3

4. Simple
Headend
Best
PracHces
• Separate
amplificaHon
for
analog
&
digital
• No
amplificaHon
for
DOCSIS
• No
amplificaHon
for
AGC
pilot
signals
!!
▫ Lose
pilot
–
lose
plant
&
DOCSIS
• Minimize
combining
&
cable
runs
▫ eQAMs
&
dense
CMTSs
will
have
low
output
power
• Do
use
forward
path
monitoring
on
QAMs
©
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Firm
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4

5. Analog
Impairments
• For
each
1
dB
increase
in
system
carrier
levels:
• CTB
raHo
degrades
by
2
dB
• CSO
raHo
degrades
by
1
dB
• CNR
improves
by
1
dB
©
The
Volpe
Firm
ConfidenHal
5
CTB CSO
Noise Floor
Visual carriers Aural carriers

6. Digital
DistorHons
–
CIN
&
CCN
• For
each
1
dB
increase
in
system
carrier
levels:
▫ CNR
behaves
as
before
with
all-­‐analog
operaHon
▫ CIN
raHo
degrades
by
1
to
2
dB
(mix
of
2nd
&
3rd
order)
▫ CCN
raHo
degradaHon
depends
on
CIN
and
CNR
values
▫ See
ANSI/SCTE
17
2007
©
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Volpe
Firm
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6
Thermal noise
CCN
CIN
Visual carrier
Aural carrier
QAM Channels

7. Sweep
©
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7
Standing Waves
Roll off at band edges
Misalignment

8. Space
Between
QAM
Channels
Small
©
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Volpe
Firm
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8
No
Sweep
Points
8
MHz
BW
No
Sweep
Points
8
MHz
BW
• One
sweep
point
every
8
MHz
• No
sweep
points
under
QAM
• A
lot
can
happen
between
QAM
channels!

9. Some
Examples
©
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Volpe
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9
Loose seizure screw on amplifier
Corrosion on seizure screw in amplifier
causes standing wave
• Suckouts,
standing
waves,
LTE,
and
other
impairments
more
difficult
with
standard
sweep

10. Sweepless
Sweep
–
How
it
Works
• Compares
headend
levels
to
outside
plant
levels
• No
sweep
injecHon
signals
(non-­‐interfering)
• Less
expensive,
no
headend
unit,
just
meter
©
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Volpe
Firm
ConfidenHal
10

11. Sweepless
Sweep
©
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Firm
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11

12. Sweepless
Sweep
System
Problems
©
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Volpe
Firm
ConfidenHal
12

13. Digital
Levels
• Cable
Modem
or
Set
Top
Box
▫ Ideal
Downstream
RF
Input:
60
dBuV
(0
dBmV)
▫ Recommended
RF
Input:
55
–
65
dBuV
(±5
dBmV)
▫ Worse
Case
RF
Input:
50
–
70
dBuV
(±10
dBmV)
▫ Never
exceed
total
power:
90
dBuV
(30
dBmV)
• Too
high
or
too
low
causes
receiver
demod
issues
• Recommended
Tx
levels
for
opHmum
CNR:
▫ 100
–
110
dBuV
(40
–
50
dBmV)
©
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Volpe
Firm
ConfidenHal
13

14. Summary
• Cable
networks
are
moving
from
analog
to
digital
• CTB,
CSO,
etc.
turn
into
noise
(CIN)
• Sweep
systems
may
need
to
be
upgraded
• Correct
digital
levels
at
end
devices
are
criHcal
▫ May
require
new
test
equipment
• It’s
a
great
Hme
to
be
in
cable!
©
The
Volpe
Firm
ConfidenHal
14

15. ©
The
Volpe
Firm
ConfidenHal
15
Brady
Volpe
brady.volpe@volpefirm.com