troubleshooting a digital plant

TROUBLESHOOTING A
DIGITAL PLANT
A DIGITAL LEAKAGE PERSPECTIVE
February 20, 2013
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TROUBLESHOOTING A
DIGITAL PLANT
A DIGITAL LEAKAGE PERSPECTIVE
February 20, 2013
Ken Couch
Director of Marketing
ComSonics
•
Electrical Engineer & MBA degree
•
21 years of Telecom experience at Nortel Networks
•
6 years of Cable experience at ComSonics
•
Held positions including Test Engineer, Manufacturing
Engineer, ESS Test and design, PLM, Business
Development and Marketing
OVERVIEW VIDEO
AGENDA
1. Leakage Measurement Basics and Overview
2. Analog vs. Digital Leakage
3. Field Study Data: What is it telling us?
4. A look at LTE Interference
5. Industry Solutions
6. SCTE Standards Work
PART ONE:
LEAKAGE MEASUREMENT BASICS
Antenna Basics
Antenna Length
Antenna Types
Analog vs. Digital Channel Differences
Amplitude Difference
Power Spectral Difference
Why is it difficult to measure?
Bandwidth Measurement Difference
Digital Measurement Challenges
ANTENNA BASICS
IMPACT OF THE ANTENNA LENGTH
Antenna Length should be a fraction of the wavelength (λ)
½λ
¼ λ
λ
½λ
¼λ
At 138 MHz:
λ = 7 feet
¼ λ = 21 inches
At 612 MHz:
λ = 1.58 feet
¼ λ = 4.74 inches
ANTENNA BASICS
IMPACT OF THE ANTENNA TYPE
Antenna Type will change the radiation pattern and gain
Antenna
Radiation
Patterns
Ground Plane
Dipole
Antenna
Monopole
Antenna
Two of the most common antenna types used in leakage detection
ANTENNA BASICS
LEAKAGE DETECTOR EXAMPLE
Dipole Antenna at ½ λ = 9.48” at 612 MHz
Maximum Gain Point
Radiation Pattern
Low Gain or Null Point
3 dimensional view
of Pattern
A dipole antenna provides directional information by
using either the maximum gain or null points
ANTENNA EXAMPLES
Name
Gain (over
isotropic)
Beamwidth
-3 dB
0 dB
360
2.14 dB
55
Turnstile
-0.86 dB
50
Full Wave
Loop
3.14 dB
200
Yagi
7.14 dB
25
Helical
10.1 dB
30
Parabolic
Dipole
14.7 dB
20
Horn
15 dB
15
Biconical Horn
14 dB
360x200
Isotropic
Dipole
Shape
Radiation Pattern
ANALOG VS. DIGITAL CHANNELS
AMPLITUDE DIFFERENCE
Analog Channel
Digital Channels are typically carried 5
to 6 dBmV lower in power than Analog
Digital Channel
ANALOG VS. DIGITAL CHANNELS
POWER SPECTRAL DENSITY
Analog Channels carry the majority of their power in a narrow video carrier
Analog Power
Spectral Density
ANALOG VS. DIGITAL CHANNELS
POWER SPECTRAL DENSITY
Digital Channels carry their power evenly across most of the 6MHz spectrum
Channel Bandwidth
64 QAM
5.057 MHz
256 QAM 5.361 MHz
Digital Power
Spectral Density
ANALOG VS. DIGITAL CHANNELS
POWER SPECTRAL DENSITY
Digital Challenges:
1. Digital power is ~ 28.3 dB lower than analog
1. At 25 kHz BW, 256 QAM
2. Subtracting 5 dB for lower peak power
25 kHz slice
= 1 / 214
Total power
At 256 QAM
2. If a 6 MHz BW measurement is made, the
detector is less sensitive and has more
potential for noise and interference
3. Digital QAMs look like noise
Digital Leakage looks like noise and cannot be reliably measured using
analog or wideband detection methods.
PART TWO:
FIELD DATA
Field Study One
Vehicle Leakage Detection
Field Study Two
Handheld Leakage Detection
FIELD STUDY ONE
VEHICLE LEAKAGE DETECTION
LEAKAGE EXAMPLE:
TWO IN ONE
Leak 1: High frequency leak that
was non-detectable at low freq.
Leak 2: Loose
Connector caused a
1,500 uV/m leak at
10” at 138 MHz.
Tightened connector
and leak dropped to
3uV/m.
FIELD STUDY ONE RESULTS
Distribution of Leaks by Level
Distribution of Leaks by Level and Frequency
Low Frequency Only
High Frequency
•
32% of Total Leaks were at low freq only
•
51% of Total leaks were at high freq only
•
17% of Total leaks were at both low and high
Both
FIELD STUDY ONE RESULTS
Question: Is there a correlation of leakage power levels at high and
low frequency for the same leak?
60% of Leaks had higher power at low frequency
31% of Leaks had higher power at high frequency
Delta between low and high frequency leak levels for same leak
Distribution of Deltas is
weighted at low end (73%)
Distribution of Leak Level Deltas
Level Delta (uV/m)
73%
High Frequency >Level
Low Frequency >Level
60%
31%
# Leaks
Answer: This data does not support correlation of levels at different Frequencies.
FIELD STUDY TWO
ANALYSIS OF LEAKS USING HANDHELD DETECTORS
177 confirmed leaks were:
Measured using a handheld analog detector at 138 MHz
Measured using a handheld digital detector at 612 MHz
Leak was fixed and problem recorded.
Results are a mix from 4 different cable systems
FIELD STUDY TWO RESULTS
Leak Levels (uV/m)
Leak Levels at High and Low Frequency Measurements
5% of Leaks where only
found at low frequency
# Leaks
FIELD STUDY TWO RESULTS
LEAKAGE LEVEL DELTAS
21% of Leaks had higher power at low frequency (vs. 60% in Study 1)
79% of Leaks had higher power at high frequency (vs. 31% in Study 1)
28% of the leaks where not detectable at low frequency (High Freq Leaks <3 uV/m)
5% of the leaks where not detectable at high frequency (Low Freq
Level Delta (uV/m)
Leak Level Deltas between Low & High Frequency
Low Frequency Bigger
21%
High Frequency Bigger
79%
# Leaks
<3uV/m)
Distribution of Leak Level Deltas
FIELD STUDY 2
FREQUENCY VS. FAULT TYPE
High Frequency Measurements
• High and low frequency leaks
come from all fault types
• Highest fault category is
Loose/Bad Connector at both
high and low frequency
• Higher frequency leaks tend
to be higher power
• Low frequency leaks tend to
be low power
Low Frequency Measurements
INITIAL FIELD STUDY CONCLUSIONS
Measuring Leaks at High Frequency will yield more leaks found
•
Field Study One yielded a 104% increase in leaks found by adding a high frequency detector (156
additional leaks found beyond 150)
•
Field Study Two yielded a 40% increase in leaks found by adding a high frequency detector (50
additional leaks found beyond 127)
Leaks tend to radiate at higher leak levels at high frequency as compared to the
corresponding low frequency measurement
•
•
40% were higher levels at high frequency (Study 1)
79% were higher levels at the high frequency (Study 2)
No leak level correlation for leaks that radiate at both high and low frequencies.
•
High and Low Frequency measurements for each leak have a diverse range of leakage levels
PART THREE:
LTE INTERFERENCE
Spectrum Allocation
Cable Leakage Interference
LTE Subscriber Growth
LTE SPECTRUM ALLOCATION
18 Channels
Uplink
700 MHz
Downlink Downlink
Uplink
800 MHz
LTE spectrum overlaps 18 cable channels from 700 MHz to 800 MHz
TYPICAL OVER-THE-AIR SPECTRAL SWEEP
Noise Floor
at -92 dBm
130 MHz
Over the Air Channels
LTE Signals
800 MHz
LTE INTERFERENCE FROM CABLE LEAKAGE
Analog Leakage
100 MHz
Digital Leakage
LTE Signals
800 MHz
Digital Leakage significantly raised the noise floor in the LTE band
LTE PROVIDER IMPACT
1. RSSI Noise floor Increases due
to leakage
5 uV/m
2. LTE provider troubleshoots cell
site
36 uV/m
4x10-9 bits
3. All leaks found are reported to
cable operator
501 uV/m
75 uV/m
Cell
Tower
55 uV/m
62 uV/m
4x10-9 bits
75 uV/m
75 uV/m
120 uV/m
75 uV/m
Uplink RSSI: Received Signal
Strength Indicator at the Cell Tower
51 uV/m
7 uV/m
LOOKING AHEAD
LTE is only in the beginning stages of deployment with limited user devices.
1 Billion LTE Subscribers
by 2016
PART 4
INDUSTRY SOLUTIONS
Uses a portable monitoring receiver in
combination with an active directional antenna
Uses a correlation process to match digital
QAMs generated in headend with those found
in the field (Patent Pending)
Uses a unique marker signal injected between
two QAM channels and corresponding field
detector units (Patent Pending)
PART 5
SCTE STANDARDS
Network Operations Subcommittee (NOS)
Working Group 1- Measurements
Group Chair: Mr. Ron Hranac, Cisco Systems, Inc
This committee is working to provide:
Recommended measurement practices for digital leakage
Continued analysis of LTE interference from both an ingress
and egress perspective
HOW TO ASK A QUESTION
Questions?
Type your question in the
Type here to chat… window.
Click Send
(Only presenters will see questions)
THANK YOU TO OUR SPEAKER
Ken Couch
ComSonics
kcouch@comsonics.com
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