Rev.A00
DOCSIS 3.0
Confidential & Proprietary Information of VeEX Inc. 2
CATV Market Dynamics
DOCSIS 3 Overview
DOCSIS 3 Benefits
Preparing for DOCSIS 3
What you need to test
How VeEX can help you
Troubleshooting Summary
Essential Technical Terms
DOCSIS 3.0
Agenda & Discussion Points
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Media Convergence
DOCSIS 3.0
Market Trends
Source: Future services on HFC networks: 33th PIKE Conference, 14 October 2008, Zakopane, Poland
Confidential & Proprietary Information of VeEX Inc. 4DOCSIS 3.0
User Profiles & Applications
Digital Photos
Gaming
MP3 WMV
DVD Blu-ray
SDTV HDTV Mobile
Video
iPod Walkman
You Tube
VODDVR/PVR
Data & VoIP
Home Networks
Web 2.0
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CATV Operators Need DOCSIS 3.0!
Confidential & Proprietary Information of VeEX Inc. 6
Competition is extremely active Telcos are deploying VDSL2, GPON, FIOS and FTTx (USA & Europe)
Consumer’s have an insatiable demand for new services HDTV, VoD, PVR, interactive DTV etc
To meet the growing challenge cable operators have to: Expand network capacity in cost effective and timely manner Evolutionary steps - incremental investments in current technology Revolutionary steps – need to decide if and when to implement a Next Generation HFC
network
CATV Operators Feeling Pressure
DOCSIS 3.0
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Verizon Beats Back Cable With YouTube Tilt April 27, 2010 Verizon Communications Inc. (NYSE: VZ) will
soon use FiOS TV's ability to feed in thousands of YouTube videos as a key selling point in TV spots aimed at drawing cable and satellite TV subscribers to its completely fiber-fed platform.
An Ongoing Battle for Customers
DOCSIS 3.0
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DOCSIS OverviewDOCSIS 3.0 Benefits
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DOCSIS Milestones
DOCSIS 3.0
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DOCSIS 3.0 Quick Overview
DOCSIS 3.0
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Notes: Downstream bandwidths assuming QAM-256 modulation Upstream bandwidth assuming QAM-64 modulation Maximum synchronization speed and (Maximum usable speed)
DOCSIS Throughput Compared
EuroDOCSISVersion
Date Rates – Annex A
Downstream Upstream
1.x ~ 55.62 (50) Mb/s 10.29 (9) Mb/s
2.0 ~ 55.62 (50) Mb/s 30.72 (27) Mb/s
3.0 (4 Channels) ~ 222.48 (200+) Mb/s 122.88 (108+) Mb/s
3.0 (8 Channels) ~ 444.96 (400+) Mb/s 122.88 (108+) Mb/s
DOCSIS 3.0
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DOCSIS 3.0 Channel Bonding
DOCSIS 3.0
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Physically the same as DOCSIS 2.0 signals
Consist of multiple QAM signals bonded logically together
Carry data of mutual relevance
Bonded channels can be contiguous or non-contiguous: Contiguous - consist of frequency consecutive signals Non-contiguous - interspersed in the spectrum with other
carriers
MPEG-2 transport for downstream signals
QAM transport for upstream signals
What do we know?
DOCSIS 3.0 Signals
DOCSIS 3.0
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DOCSIS 3.0 Preparation
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Preparing for DOCSIS 3.0
DOCSIS 3.0
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Obtaining the Required Bandwidth
DOCSIS 3.0
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Frequency Spectrum Changes
Today 870MHz Soon 1GHz
Reclaiming bandwidth:• Switched Digital Video
• MPEG 4 video
• Analog Video Reclamation
• Higher order modulation
Test requirements:• Downstream expanding to 1GHz
• Bonded channels need verification
• Return Path filling up rapidly impacting traditional sweep and ingress test methods
• In-service testing where possible
DOCSIS 3.0
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How much gain?
Upstream Expansion
250Mb/s
500Mb/s
1000Mb/s
DOCSIS 3.0
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Operators have strong differences in opinion with regard to options: Solutions are typically driven by specific technical, geographical or local market factors A combination of solutions often determines the preferred option
Expanding HFC Network Capacity
Source: Michiel Peters, TNO - Benelux Chapter SCTE , 15 September 2008, Amsterdam
DOCSIS 3.0
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DOCSIS 3.0Plant Qualification & Test Methods
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Typical DOCSIS Network
DOCSIS 3.0
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Plant Qualification
DOCSIS 3.0
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Setup
Upstream Test – Part 1
Configure the Upstream Generator (USG): Frequency, level, modulation, bandwidth, and
symbol rate
Transmit the QAM-64 signal upstream to a CX180+, CX350 or CX380 located in the Headend or Hub.
DOCSIS 3.0
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Basic
Upstream Test – Part 2
At the Headend or Hub, check: Digital signal level (dBmV, dBµV) Modulation Error Ratio (MER)
DOCSIS 3.0
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Spectrum
Upstream Test – Part 3
At the Headend or Hub, check: Upstream spectrum (5-65MHz) for Ingress,
CPD, and other interference Check below 5MHz and above 65MHz all the
way to 200MHz if possible A QAM-64 signal requires a clean upstream
path!
DOCSIS 3.0
Confidential & Proprietary Information of VeEX Inc. 26
Still Having Problems?
Level and MER look
OK?
A Signal Level Meter (SLM) and Spectrum Analyzer are great application specific tools, but they can be limited in telling you everything you need to know about advanced digital signals
Downstream and upstream (DOCSIS) signals can be impaired by other factors not easily viewed using conventional test methods
Look for the “needle inside the QAM haystack” to figure out what is going on!
DOCSIS 3.0
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Advanced
Upstream Testing – Part 4
For the Upstream, you need to check: MER (equalized and un-equalized) Pre and Post FEC Frequency response (in-channel) Group delay (in-channel) Constellation diagram Adaptive equalizer results
DOCSIS 3.0
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Advanced
Downstream Testing – Part 5
For the Downstream, you need to check: Digital Power Level MER (equalized and un-equalized) Pre and Post FEC Frequency response (in-channel) Group delay (in-channel) Constellation diagram Adaptive equalizer results
DOCSIS 3.0
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Downstream QAM Parameters
BERPre/Post FEC
MER64-QAM: 27 dB min256-QAM: 31 dB min
Constellation
Pre/Post Errorred Seconds (PRES/POES) The number of seconds with at least one corrected codeword
Severely Errorred Seconds The number of seconds with at least one uncorrectable codeword
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Impairments
Thermal noise is a basic physical phenomenon which cannot be avoided Random voltage variation proportional to temperature, bandwidth and resistance. At room temperature, in 6 MHz bandwidth and 75 ohms circuit, the thermal noise is
approximately -60dBmV. After amplification, the noise level can get much higher. All the other impairments are “human made”, they depend on the design, implementation
and operation of all the elements in the signal chain
It is convenient to group all impairments into 2 categories: Linear distortions and Non-linear distortions.
DOCSIS 3.0
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Transmitted phase noise & Low carrier-to-noise ratio
Non-linear distortions (CTB, CSO, XMOD, CPD…)
Linear distortions (micro-reflections, amplitude ripple, group delay)
Severe impedance mismatches aka linear distortions
Improperly aligned or defective amplifiers
In-correct modulation profiles
Incorrect signal levels
In-channel ingress
Data collisions
Laser clipping
What Degrades MER?
DOCSIS 3.0
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What MER is Acceptable?
Output of QAM Modulator – 40 dB
Input to Lasers – 39 dB
Output of Nodes – 37 dB
Output of Subscriber Taps – 35 dB
At the input to the subscriber’s receiver – 34 dB
The absolute minimum is 31db
MER is expressed in dB derived as follows:
RMS error magnitude
Average symbol magnitude10 log
DOCSIS 3.0
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Downstream PerformancePre/Post FEC BER
What the results are telling you: Level, MER and Constellation are OK Pre/Post FEC BER indicate a problem
What to look for: Interference from a sweep transmitter Downstream laser clipping Up-converter problem in the Headend Loose connections or CPD
DOCSIS 3.0
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Notes on FEC
To have an accurate idea of the BER performance you need to know both pre and post FEC bit error rate
Forward error correction (FEC) is a digital error checking system that sends redundant information with the payload so the receiver can repair corrupted data and eliminate the need to retransmit.
By using the same Reed Solomon decoder at the receiving end, bit errors can be detected – these are called Pre-FEC errors
Pre FEC BER is the error rate of the incoming signal prior to being corrected by the FEC circuitry - a minimum of 1x10-7 is expected, but FEC may be able to correct errors as high as 1x10-6.
Post-FEC errors cause poor TV quality or DOCSIS data retransmission
Post FEC Bit errors are not acceptable and should be corrected
The FEC decoder needs a BER of >1x10-6 to operate properly
Both Pre and Post FEC BER need to be verified in order to determine if the FEC circuitry is working to correct errors and if so how hard.
DOCSIS 3.0
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Constellation Diagram
QAM – Constellation Diagram
Quadrant 1
Quadrant 2Quadrant 3
Quadrant 4
DOCSIS 3.0
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Modulation Error Ratio
MER = 10log (avg symbol power/avg error power)
Average symbolpower
I
Q
Average error power
Source: Hewlett-Packard
I
Q
I
Q
A large “cloud” of symbol points means low MER—this is not good!
A small “cloud” of symbol points means high MER—this is good!
N
jjj
N
jjj
QI
QIMER
1
22
1
22
10log10
DOCSIS 3.0
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Forward Path Modulation
ModulationType
Std. Symbol Rate (MHz)
Max data rate(Mbps)
Annex A(8MHz)
QAM64 6.952 41.4
Annex A(8MHz)
QAM256 6.952 55.2(220 max 4 channel bonding)
Annex B(6MHz)
QAM64 5.057 38
Annex B(6MHz)
QAM256 5.361 43(160 max 4 channel bonding)
QAM 64 or QAM 256 are most commonly used
DOCSIS 3.0
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Return Path Modulation – DOCSIS
DOCSIS (Data-Over-Cable Service Interface Specifications)Reverse Path / Upstream Data Rate
Standard symbol rate (bandwidth): 1.28 (1.6), 2.56 (3.2), 5.12 (6.4) MHz
DOCSIS Bandwidth(MHz)
Modulationtype
Max data rate(Mbps)
1.0 3.2 QPSK 5.12
1.1 3.2 QPSKQAM16
5.1210.24
2.0 6.4 QAM16QAM64
10.2430.72
3.0 6.4 QAM64QAM128
120(4 channel bonding)
DOCSIS 3.0
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Constellation Display
Learn to interpret the constellation display – it tells you a lot of the signal
Symbol points should be small and well-defined
DOCSIS 3.0
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Every MPEG2 digital receiver has an Adaptive Equalizer The Equalizer typically cascades two digital filters:
Feed Forward Equalizer (FFE) - reference tap is the last of 16 taps Decision Feedback Equalizer (DFE) - output is fed back to input, 108 taps long
Compensates for Linear distortions (Amplitude imperfections & group delay) The Equalizer uses MER as a tool to adaptively cancel these Linear distortions
The Adaptive Equalizer
DOCSIS 3.0
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Adaptive Equalizer Test Functions
Impairment Results
Frequency Response & Group Delay Graphs
Tap Expert
DOCSIS 3.0
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What the key measurements are telling you!Hum– Low frequency disturbances of the digital carrier e.g.
switching power supplies
Phase Jitter– Instability of the QAM carrier seen at the demodulator– Phase changes of oscillators e.g. the up-converter– Introduces a back and forth rotation of the
constellation where some symbols will eventually cross the decision boundaries and cause an error in transmission
EVM (Error Vector Magnitude)– A measure of how far constellation points deviate from
their ideal locations. – Ratio of RMS Constellation Error Magnitude to peak
Constellation symbol magnitude
Symbol Rate Error– Should be less than +/- 5pm
Linear Distortions – a closer look (1)
DOCSIS 3.0
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Linear Distortions – a closer look (2)
What the measurement is telling you!
Frequency Response Frequency response of the digital carrier
Micro-reflections can cause amplitude ripple in the frequency response
Should be less than 3dB (peak-to-peak)
Group Delay Different frequencies travel through the same medium at
different speeds (see supporting slide)
Worse near band edges and diplex filter roll-off areas
Group Delay variation is usually expressed in ns for the Downstream and in “ns / MHz” for the Upstream
Should be < 50ns peak-to-peak
General Notes:• Amplitude and Group Delay responses help visualize the effects of filters, diplexers, traps, suck-outs in the
signal path, from (and including) the QAM modulator up to the point of test.• The frequency span of the calculated responses is directly related to sampling period of the Equalizer
Symbol period. For QAM-64, the span response is 5.05 MHz, while for QAM256 the span is 5.36 MHz
DOCSIS 3.0
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Linear Distortions – a closer look (3)
What the measurement is telling you!
Echo Margin Echoes are micro-reflections
The tallest vertical bar is the incident signal (reference tap)
Smallest difference between any coefficient and the DOCSIS template defined by CableLabs
Safety margin when getting too close to the “cliff effect”
Should ideally be > 6dB
Equalizer Stress Derived from all the Equalizer coefficients
Indicates how hard the Equalizer is working to cancel out the Linear distortions
Global indicator (the higher the figure, the less stress)
Noise Margin Generally, the lower the MER, the larger the probability of
errors in transmission (Pre-FEC and Post FEC)
Amount of noise that can safely be added to degrade the Equalized MER before losing the signal (cliff effect)
DOCSIS 3.0
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Micro-reflection at about 2.5 µs (2500 ns):Assume ~1 ns per ft., 2500/2 = 1250 ft(actual is 1.17 ns per ft: (2500/1.17)/2 = 1068 ft)
Frequency response ripple ~400 kHz p-p:Distance to fault = 492 x (.87/.400) = 1070 ft.
Linear Distortions
DOCSIS 3.0
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DOCSIS recommends that the digitally modulated signal’s average power level be set 6 dB to 10 dB below what the visual carrier level of an analog TV channel on the same frequency would be
This ratio should be maintained throughout the entire cable network
Operational RF Levels
DOCSIS 3.0
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After link up, power level on forward and return paths are measured.
Step-by-step CM link up process to clearly identify any failed steps
DOCSIS 3.0 CM Emulation Link Up
DOCSIS 3.0
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DOCSIS 3.0 CM – IP Tests (1)
Complete server connection status indicates any IP problems
Once the CM is on-line, a full range of IP tests including Ping test can be performed
DOCSIS 3.0
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DOCSIS 3.0 CM – IP Tests (2)
Throughput (FTP) Download and Upload should be verified at the CM service location.
Web Test and Web Browser provide bandwidth and visual indications of performance
DOCSIS 3.0
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VoIP Expert generates industry standard wave files to verify MOS and R-Factor of upstream and downstream and includes packet jitter, packet loss, and delay.
Real-time of subjective voice quality evaluation (MOS and R-factor) using the TelchemyAlgorithm and test method is provided
DOCSIS 3.0 CM – VoIP Tests (1)
DOCSIS 3.0
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Detailed Packet statistics provide a complete insight to transport and IP layer impairments
Jitter performance is checked using the Inter Packet Delay Variation (IPDV) method per RFC3393 recommendations
DOCSIS 3.0 CM – VoIP Tests (2)
DOCSIS 3.0
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Ethernet Testing is important to validate business services, E1 circuit emulation or Wireless backhaul applications (E1/T1/IP)
Copper (10/100/1000BaseT) & Fiber (1000BaseX) based Ethernet service should be verified
DOCSIS 3.0 – Ethernet Tests (1)
DOCSIS 3.0
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RFC2544, BERT, & Throughput test modes are used to test Ethernet circuits running at the subscriber premise or in the core network at Headend locations
Advanced traffic generation and detailed analysis is used to check and benchmark all types of Ethernet service offered at customer locations.
DOCSIS 3.0 – Ethernet Tests (2)
DOCSIS 3.0
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DOCSIS 3.0 Pre-Qualification
DOCSIS 3.0
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How Many Testers Do You Need?
CX350 can do
it all
CX380 can do
it all
DOCSIS 3.0
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RF Test Checklist
DOCSIS 3.0
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Verify correct average power level
Integrated up-converter RF output should be set in the DOCSIS-specified +50 to +61dBmV range
Typical levels are +55 to +58dBmV
Also check BER, MER and constellation
Integrated Up-converter
CMTS
88-860 MHz downstreamRF output
(+50 dBmV to +61 dBmV)
Attenuator(if required)
To headend downstreamcombiner
Troubleshooting
DOCSIS 3.0
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Verify correct Power level, BER, MER and Constellation
CMTS downstream IF output
External up-converter IF input
External up-converter RF output
External Up-converter
CMTS
RF upconverter
88-860 MHz downstreamRF output to CATV network
(+50 dBmV to +61 dBmV)
Attenuator44 MHz downstream
IF output(e.g., +42 dBmV +/-2 dB)
44 MHz IF input toupconverter
(typ. +25 dBmV to +35dBmV)
Troubleshooting
DOCSIS 3.0
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Check signal levels and BER at downstream laser input and node output
Bit errors present at downstream laser input but not at CMTS or up-converter output may indicate sweep transmitter interference, loose connections or combiner problems
Bit errors at node output but not at laser input are most likely caused by downstream laser clipping
Combiner Output and Fiber Link
DOCSIS 3.0
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Troubleshooting Tips
DOCSIS 3.0
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Essential Technical Terms to Remember
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I/Q Gain and Phase The phase and gain of both the I and Q carrier must be equal in order for the
constellation to be correct. This impairment is caused by the QAM modulators. The gain difference between the 2 carriers should be less than 1.8% and the phase
difference should be less than 1 degree.
Phase Noise Jitter (changes in phase) of the oscillators, most likely the up-converter The phase shift or jitter should be < 0.5 degrees
QAM Measurement Terms (1)
DOCSIS 3.0
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Hum Low frequency disturbances of the digital carrier Same as hum on analog carriers, if the level is the same, it’s the system, if higher on the
digitals then it’s probably the QAM modulator
Symbol Rate Error Should be < +/- 5ppm
Echo Margin A measurement in dB of how far the taps are from the template with the time equalizer
measurement. Caused by impedance mismatches in the system. Should be > 6dB
QAM Measurement Terms (2)
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Group Delay Different frequencies travel through the same medium at different speeds. So the lower
the lower frequencies of the same carrier arrive at the receiver at different timing than the higher frequencies.
Should be < 50ns peak-to-peak
Frequency Response Frequency response of the digital carrier Should be < 3dB peak-to-peak
Carrier Offset Carrier frequency test. Should be no more than +/- 25KHz
QAM Measurement Terms (3)
DOCSIS 3.0
5 MHz
10 MHz
15 MHz
20 MHz
25 MHz
30 MHz
40 MHz
35 MHz
45 MHz
50 MHz
55 MHz
60 MHz
65 MHz
Confidential & Proprietary Information of VeEX Inc. 65
Group Delay - Return Path
5 MHz
10 MHz
15 MHz
20 MHz
25 MHz
30 MHz
40 MHz
35 MHzHFC
(Filters, Taps)
t
HFC(Filters,
Taps)
45 MHz
50 MHz
55 MHz
60 MHz
65 MHz
5 MHz
10 MHz
15 MHz
20 MHz
25 MHz
30 MHz
40 MHz
35 MHz
45 MHz
50 MHz
55 MHz
60 MHz
65 MHz
DOCSIS 3.0
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In-Depth Understanding
ECHO MARGINThe Coefficients of the Equalizer will also reveal the presence of an Echo, (a.k.a. micro-reflections). The Equalizer will cancel such an echo, and in doing so, the equalizer coefficient which corresponds to the delay of the echo will be much higher than the surrounding ones, “it sticks out of the grass”. The relative amplitude of this coefficient is an indication of the seriousness of the echo, and its position gives the delay of the echo, hence its roundtrip distance.The Echo Margin is the smallest difference between any coefficients and a template defined by Cablelabs, as a safety margin before getting too close to the “cliff effect”. It is normal to notice relatively high coefficients close to the Reference as this corresponds to the filters in the modulator / demodulator pair and to the shape of QAM signal.
EQUALIZER STRESSThe Equalizer Stress is derived from the Equalizer coefficients and indicate how much the Equalizer has to work to cancel the Linear distortions, it is a global indicator of Linear distortions. The higher the figure, the less stress.
NOISE MARGINWe all know that the lower the MER, the larger the probabilities of errors in transmission (Pre-FEC and then Post-FEC); the MER degrades until errors are so numerous that adequate signal recovery is no more possible (cliff effect). As Noise is a major contributor to the MER, we define Noise Margin as the amount of noise that can be added to a signal (in other words, how much we can degrade MER) before get dangerously close to the cliff effect. Noise is chosen because on the one hand it is always present, and on the other hand it is mathematically tractable. Other impairments, such as an Interferer, are not easily factored into error probabilities.
Linear Distortions
DOCSIS 3.0
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In-Depth Understanding
EQUALIZED MER vs. UN-EQUALIZED MERThe MER (Modulation Error Ratio) is the ratio of the QAM signal to Non-Linear distortions of the incoming QAM signal. The MER should have included the Linear distortions to indicate the health of the signal; but the QAM demodulator cannot operate properly without the Equalizer and the Equalizer uses the MER as a tool to adaptively cancel the Linear distortions. Consequently it is convenient to distinguish the MER (non-linear distortions only) from an Un-equalized MER (non-linear and linear distortions), the Un-equalized MER is calculated from the MER and Equalizer Stress.The Un-equalized MER is always worst than the MER. A small difference between the two indicates little Linear distortions, a large difference shows that there are strong Linear distortions. Even if the Linear distortions are cancelled by the Equalizer, we have to keep in mind that the Equalization is a dynamic process as it tracks Linear distortions by trial and error even after converging. The larger the Linear distortions the larger the tracking transients are, hence more probability of transmission error (pre-FEC or Post-FEC BER).
PHASE JITTERPhase Jitter is caused by instability of the carrier of the QAM signal at the demodulator. This instability could be found at the QAM modulator and up-converter or in the QAM receiver (Local Oscillators used in frequency conversions). The phase jitter introduces a rotation of the constellation, where the symbols clusters elongate and get closer to the symbol’s boundary. Eventually some symbols will cross the boundary and cause an error in transmission. The QAM demodulator has a Phase lock loop to track phase variations of the carrier; it tracks easily long term drift as well as some short terms variations (up to 10 or 30 kHz) but it cannot track very fast variations above its loop response. So in a QAM demodulator, the wideband jitter is more damageable than short term jitter.
Linear Distortions
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Hranac, R. “Digital Troubleshooting, Part 1” Communications Technology, June 2006
www.cable360.net/ct/operations/testing/15092.html
Hranac, R. “Troubleshooting Digitally Modulated Signals, Part 2” Communications Technology, July 2006
www.cable360.net/ct/operations/testing/18539.html
Hranac, R. “Linear Distortions, Part 1” Communications Technology, July 2005
www.cable360.net/ct/operations/testing/15131.html
Hranac, R. “Linear Distortions, Part 2” Communications Technology, August 2005
www.cable360.net/ct/operations/testing/15170.html
Recommended Reading
DOCSIS 3.0
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Thank You.Any questions?
DOCSIS 3.0