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DOCSIS 3.0. Rev.A00. Agenda & Discussion Points. 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. Market Trends. Media Convergence.

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Docsis 3 0

DOCSIS 3.0

Rev.A00


Agenda discussion points

Agenda & Discussion Points

  • 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

Confidential & Proprietary Information of VeEX Inc.


Market trends

Market Trends

  • Media Convergence

Source: Future services on HFC networks: 33th PIKE Conference, 14 October 2008, Zakopane, Poland

Confidential & Proprietary Information of VeEX Inc.


User profiles applications

User Profiles & Applications

Web 2.0

Digital Photos

Home Networks

Gaming

Data & VoIP

MP3 WMV

VOD

DVR/PVR

DVD Blu-ray

You Tube

SDTV HDTV

iPod Walkman

Mobile Video

Confidential & Proprietary Information of VeEX Inc.


Catv operators need docsis 3 0

CATV Operators Need DOCSIS 3.0!

Confidential & Proprietary Information of VeEX Inc.


Catv operators feeling pressure

CATV Operators Feeling Pressure

  • 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

Confidential & Proprietary Information of VeEX Inc.


An ongoing battle for customers

An Ongoing Battle for Customers

  • 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.

Confidential & Proprietary Information of VeEX Inc.


Docsis overview docsis 3 0 benefits

DOCSIS OverviewDOCSIS 3.0 Benefits

Confidential & Proprietary Information of VeEX Inc.


Docsis milestones

DOCSIS Milestones

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Docsis 3 0 quick overview

DOCSIS 3.0 Quick Overview

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Docsis throughput compared

DOCSIS Throughput Compared

  • Notes:

    • Downstream bandwidths assuming QAM-256 modulation

    • Upstream bandwidth assuming QAM-64 modulation

    • Maximum synchronization speed and (Maximum usable speed)

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Docsis 3 0 channel bonding

DOCSIS 3.0 Channel Bonding

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Docsis 3 0 signals

DOCSIS 3.0 Signals

What do we know?

  • 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

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Docsis 3 0 preparation

DOCSIS 3.0 Preparation

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Preparing for docsis 3 0

Preparing for DOCSIS 3.0

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Obtaining the required bandwidth

Obtaining the Required Bandwidth

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Frequency spectrum changes

Frequency Spectrum Changes

Today 870MHz

Soon 1GHz

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Upstream expansion

Upstream Expansion

How much gain?

250Mb/s

500Mb/s

1000Mb/s

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Expanding hfc network capacity

Expanding HFC Network Capacity

  • 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

Source: Michiel Peters, TNO - Benelux Chapter SCTE , 15 September 2008, Amsterdam

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Docsis 3 0 plant qualification test methods

DOCSIS 3.0Plant Qualification & Test Methods

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Typical docsis network

Typical DOCSIS Network

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Plant qualification

Plant Qualification

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Upstream test part 1

Upstream Test – Part 1

Setup

  • 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.

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Upstream test part 2

Upstream Test – Part 2

Basic

  • At the Headend or Hub, check:

    • Digital signal level (dBmV, dBµV)

    • Modulation Error Ratio (MER)

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Upstream test part 3

Upstream Test – Part 3

Spectrum

  • 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!

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Still having problems

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!

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Upstream testing part 4

Upstream Testing – Part4

Advanced

  • 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

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Downstream testing part 5

Downstream Testing – Part 5

Advanced

  • 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

Confidential & Proprietary Information of VeEX Inc.


Downstream qam parameters

Downstream QAM Parameters

Constellation

MER

64-QAM: 27 dB min

256-QAM: 31 dB min

BER

Pre/PostFEC

  • 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

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.

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What degrades mer

What Degrades MER?

  • 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

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What mer is acceptable

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 magnitude

10 log

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Downstream performance

Downstream Performance

Pre/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

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Notes on fec

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.

Confidential & Proprietary Information of VeEX Inc.


Qam constellation diagram

QAM – Constellation Diagram

Constellation Diagram

Quadrant 4

Quadrant 1

Quadrant 3

Quadrant 2

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Modulation error ratio

Q

I

Q

I

Modulation Error Ratio

MER = 10log (avgsymbol power/avgerror power)

Q

A large “cloud” of symbol points means low MER—this is not good!

Average error power

Average symbol

power

A small “cloud” of symbol points means high MER—this is good!

I

Source: Hewlett-Packard

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Forward path modulation

Forward Path Modulation

QAM 64 or QAM 256 are most commonly used

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Return path modulation docsis

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

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Constellation display

Constellation Display

  • Learn to interpret the constellation display – it tells you a lot of the signal

  • Symbol points should be small and well-defined

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The adaptive equalizer

The Adaptive Equalizer

  • 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

Confidential & Proprietary Information of VeEX Inc.


Adaptive equalizer test functions

Adaptive Equalizer Test Functions

Frequency Response & Group Delay Graphs

Impairment Results

Tap Expert

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Linear distortions a closer look 1

Linear Distortions – a closer look (1)

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

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Linear distortions a closer look 2

Linear Distortions – a closer look (2)

  • 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

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

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Linear distortions a closer look 3

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”

    • Shouldideally 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)

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Linear distortions

Linear Distortions

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.

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Operational rf levels

Operational RF Levels

  • 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

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Docsis 3 0 cm emulation link up

DOCSIS 3.0 CM Emulation Link Up

Step-by-step CM link up process to clearly identify any failed steps

After link up, power level on forward and return paths are measured.

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Docsis 3 0 cm ip tests 1

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

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Docsis 3 0 cm ip tests 2

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

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Docsis 3 0 cm voip tests 1

DOCSIS 3.0 CM – VoIP Tests (1)

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 Telchemy

Algorithm and test method is provided

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Docsis 3 0 cm voip tests 2

DOCSIS 3.0 CM – VoIP Tests (2)

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

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Docsis 3 0 ethernet tests 1

DOCSIS 3.0 – Ethernet Tests (1)

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

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Docsis 3 0 ethernet tests 2

DOCSIS 3.0 – Ethernet Tests (2)

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.

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Docsis 3 0 pre q ualification

DOCSIS 3.0 Pre-Qualification

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How many t esters do you need

How Many Testers Do You Need?

CX380 can do it all

CX350 can do it all

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Rf test checklist

RF Test Checklist

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Troubleshooting

Troubleshooting

Integrated Up-converter

  • 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

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Troubleshooting1

Troubleshooting

External Up-converter

  • Verify correct Power level, BER, MER and Constellation

  • CMTS downstream IF output

  • External up-converter IF input

  • External up-converter RF output

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Combiner output and fiber link

Combiner Output and Fiber Link

  • 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

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Troubleshooting tips

Troubleshooting Tips

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Essential technical terms to remember

Essential Technical Terms to Remember

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Qam measurement terms 1

QAM Measurement Terms (1)

  • 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

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Qam measurement terms 2

QAM Measurement Terms (2)

  • 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

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Qam measurement terms 3

QAM Measurement Terms (3)

  • 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

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Group delay return path

Group Delay - Return Path

5 MHz

5 MHz

5 MHz

HFC

(Filters,

Taps)

HFC

(Filters,

Taps)

10 MHz

10 MHz

10 MHz

15 MHz

15 MHz

15 MHz

20 MHz

20 MHz

20 MHz

25 MHz

25 MHz

25 MHz

30 MHz

30 MHz

30 MHz

35 MHz

35 MHz

35 MHz

40 MHz

40 MHz

40 MHz

45 MHz

45 MHz

45 MHz

50 MHz

50 MHz

50 MHz

55 MHz

55 MHz

55 MHz

60 MHz

60 MHz

60 MHz

65 MHz

65 MHz

65 MHz

t

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Linear distortions1

Linear Distortions

In-Depth Understanding

ECHO MARGIN

The 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 STRESS

  • The 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 MARGIN

  • We 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.

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Linear distortions2

Linear Distortions

In-Depth Understanding

EQUALIZED MER vs. UN-EQUALIZED MER

The 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 JITTER

  • Phase 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.

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Recommended reading

Recommended Reading

  • 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

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Thank you

Thank You.

Any questions?

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