Seminar HFC Networks

8/10/2019 Seminar HFC Networks

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Seminar

HFC networks


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Seminar HFC networks

Block diagram of an HFC system (4)The performance of an HFC system (5)Professional reception systems (6)Headend technology for digital and analogue TV and radio signals (7)

Headend for network monitoring (KOM/HMS standard) (8)Headend for ingress detection SIMS (9)Headend technology for the Internet (CMTS) (10)Provisioning software for the Internet according to DOCSIS (11)HFC measuring device (12)Forward path and return path matrix (13)Optical star in 1310 nm technology (14)1310 nm transmitters (15)1550 nm analogue transmission; DWDM, CWDM, optical pushpull (16)Passive optical components (17)Optical compact node ORA 820/821 (18)Fibre node for the BK 862 of the KDG (German Postal Telegraph and Telephone PTT) (19)


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CATV / HFC amplifiers (20)Amplifier point BK 862 of the KDG (German PTT) (21)Trunk amplifier and node system GGA 8 (22 and 23)VGF/VGP 90xx trunk and line amplifier system (24)

VGF/VGO 938 line amplifier system (25)Broadband return path amplifier (26)The in-building network (27 and 28)KOM / HMS transponder (29)DOCSIS cable modem (30)Technical appendix (31)Downstream broadband interferences CSO and CTB (32)Addition of distortion ratios (33)Upstream broadband composite intermodulation noise CIN (34)C/N and S/N ratios; modulation gain (35)Echo attenuation in the coax part of the HFC system (36)AGC; ALSC; Long Loop AGC (37)


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Block diagram of an HFC system

Headendfor

digital and analogueTV- and Radiosignals

Cable Modem TerminationSystem

with Provisioning Software

VoiceGate

Internet Service ProviderISP

Video- on- demand Status MonitoringSystem

V 5.2 Interfaceto the TELECOM

Forward Reversemultiplexer multiplexer

Optical transmission:Mono mode standard fibrePoint- to- pointPoint- to- multipoint1310 nm +/- 10 nmDirect intensity modulated

Antenna array

Opt.coupler

HMS Standard

SweepSystem

Transmission and service capability

Way(VoIP)

Videoserver

Billing Ingress controlReverse remote switch

Reverseunitygain

Fast Internet and VoIP

Fast Internet access

Fast Internet, VoIP and video streaming

Residential Gateway: Fast Internet ; VoIPMPEG Decoder; USB; Blue tooth

Status monitoring and ingress control

System Sweeper, in order to aligne forward-and reversepath

BillingStatus monitoring

ISP Reverse pathnecessary

(Options)

Add- on units like switches, routers, PC`s, TV `s etc. not shown

Reversepath

receiver

Forward

transmitter

CM

EMTA

EMTAIP

streamingbox

Residential gateway

House amplifier

Splitter

House net

Base package: Transmit a number of digitaland analogue TV- and radio channels to thesubscribers (No reversepath necessary)

Data services:

Linetap

Trunkamplifiers

Lineamplifier(s)

Headends

Status monitoring transponder

Trunk

L i n e

Option: Redundancy

Multimedia sockets

Star distribution

5 - 65 MHZ

85 - 862 MHZ

Optical node


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The performance of an HFC system

An HFC ( Hybrid-Fiber- Coax) system, like a return path compatible CATV ( Ca ble Tele vision) system,receives all possible services - including radio, TV, Internet, telephony etc. - at a central point, andtransmits them to various subscribers. The individual traditional transmission blocks can be divided into

- headend(s); channel-selective

- optical transmission network; broadband

- coaxial trunk and line network; broadband

- the in-building networks; broadband

The physical transmission medium is the coaxial cable (CATV), and for longer distances monomode fibre(HFC). The physical coverage can be 200 km or more, i.e. the number of subscribers can certainly be

100,000 or more.The forward frequency range is typically set to 80 - 862 MHz, and the return path from 5 - 65 MHz. Thesignals are transparently transmitted using both analogue and digital modulation. In the forward path, up to90 analogue TV channels can be transmitted in a 7/8 MHz pattern or, depending on the data compression,significantly more digital radio/TV channels in conjunction with pure data channels for the Internet.Additional equipment at the headend and at the subscriber facilitates cable telephony, video on demand

and much moreHFC systems are planned on a customer-specific basis, and are mainly realised using products complyingwith a specification.


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Professional reception systems

For terrestrial reception (TV; FM and DVB-T);in acc. with the PFL 3 specification (50 Ohm)of the KDG (German PTT)For terrestrial reception (TV; FM and DVB-T);

in acc. with the TL 5820- 3003 (75 Ohm) ofthe KDG (German PTT)Offset dish antennas acc. to KDG 1TS3; withreflector and feed arm heating and multifeedreceptionCentrally fed dish antennas acc. to KDG

1TS1Outside temperature control:

- Outside temperature - reflector temperature - Snow cap - soiling

Standard outside temperature control withelectronical two-level controller and settabletemperature controlQuad feeder systems for central / offset dishantennas acc. to the KDGs delivery terms

CAS 123 (centrally fed) and CAS 180 (offset) with heating


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Headend for network monitoring (KOM/HMS)

Monitors the status and records informationabout an HFC broadband networkConsists of one or more multi-protocol HECcontrollers, one or more view- PCs todisplay the collected information on thesynoptic board and a number of monitoring

transpondersMonitors the headend (output level), opticaltransmitters, optical receivers, coax amplifiers(BK 862, GGA 8, compact amplifiers, houseamplifiers) and other peripheral devices if thecorresponding monitoring transponder is

usedActivates the 3-stage Ingress-switch in thereturn path componentsOperates conforming with both the KOM andHMS standard and third party equipmentPolling mode; Auto detection of transponders;Contention modeAlarm indications are pre-set, but also user-definable; Allows to automate any task thatcan be manually performedForwards specific alarms to email,pager,SMS

SNMP Proxy Agent and SNMP managers

TCU 30

Reset

Power

Power HD

I

O

K ey b oa rd R es e t

48x CREATIVEd isccompact

TAM 9700 Series Headend Monitoring System

1 2 3 4 5 6 7 8

Omni

Probe

ABCD

FREQ

CCM

HarmonicLigthwaves

HL485

LOCAL

SAM

MCU

PWR

TAM 9700 Series Headend Monitoring System

1 2 3 4 5 6 7 8

Omni

Probe

ABCD

FREQ

CCM

HarmonicLigthwaves

HL485

LOCAL

SAM

MCU

PWR

HEC controller TCU 40 with SIMS analyser

Synoptic board


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Headend for Ingress Detection SIMS

SIMS (Scanning Ingress Monitoring System)is an option to KOM; 19 inch rack mountSIMS fully automatically monitors any wantedcarriers as well as unwanted ingress spikesin the return paths (5 to 75 MHz);

Spectrum analyser(s) with 4 periodicallyconnected inputs; 60 dB dynamic rangeDisplay on the KOM view monitor2D and 3D spectrum mode; Amplitude-timemode; display plane; normalized modeExtremely high scanning speed of 5600

frequencies per second; 50 kHz stepsSpurious


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Provisioning Software for the Internet acc. to DOCSIS

Registration of modems and hostsIP administrationDetermining of QoS profilesSetting for the host rangesDetermining the parameters for BPI profiles

(data encryption)TFTP, DHCP and TOD serversSQL data bankZOPE managment systemSNMP query of the modem parameters

Three user levelsBilling basic packet/Billing outgoinginvoices/Billing traffic assessmentModem monitoring

Transmission/reception level; S/N; packet-errors; micro reflections

ISP additional servicesServer 1 GHz CPU; raid 40 GbyteRedHat Linux 7.2


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HFC measuring device

RF

75

max0.5W

DC

Mains

Vol+

Vol-

Ch- CH+

7 8 9

4 5 6

1 2 3

0 . -

GHzns

MHzs

KHzms

dB..s

OnOff

Mode

Copy

Help

SAT / TV / FM - TEST -RECEIVER MSK 33

CH : .SO TVLEV : 37.2dBV

MVG 10

RF

75

VIDEO . SWEEP - GENERATOR

On

Off

Men

Select - +

7 8 9

4 5 6

1 2 3

0 .

s -ch

CH : .SO TVLEV : 37.2dBV

MVG 10

RF

75

VIDEO . SWEEP - GENERATOR

On

Off

Men

Select - +

7 8 9

4 5 6

1 2 3

0 .

s -ch

CH : .SO TVLEV: 37.2dBV

MVG 10

RF

75

VIDEO . SWEEP -GENERATOR

On

Off

Men

Select - +

7 8 9

4 5 6

1 2 3

0 .

s -ch

Detailed and accurate analysis in thefrequency, time and constellation domainMeasures satellite IF, terrestrial channels(digital and analogue) telemetry carriers andmodulated data channels

Spectrum mode for any kind of digital andanalogue carriers

Audio / video baseband (line separation) i.efor 2- T pulse; 20 T- pulse; S/N measurement

C/N, MER, BER Baseband input and output DISEqC 2.0 Multi Standard; Multi Norm Downstream sweep Protocol printer

Adjusts upstream unity gain Upstream sweep Battery operation

Remote controllableConsisting of MSK 33 QR / MVG 10 stationary in the headendMSK 33 QR / MVG 10 / MZK 15 portable

MVG 10 as pilot generators


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Optical star in 1310 nm technology

Point-to-point and point-to multi- pointconnection for approximately 30 to 40 km linklength for forward transmissionOptical multi-point to point transmission notfeasible, each receiver can just stand one

transmitterRedundancy operation possible in theforward path and return pathAll essential status parameters can beKOM/HMS monitoredOperating conditions are signalled with LEDsat the front panelSeparate high- launch buffer amplifierHighly linear DFB laser without pre-distortionSettable, constant modulation-index,19 cabinet or BK housing installation

No moveable parts for coolingActive return path coupler, assists SIMSReturn path transmitter with fibreidentification frequency

Hot pluggable

230 V or remote poweredTVA 08; OSA 82; TVM 21; ORR 05; ORA 80; TVR 01; TFN 42


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1310 nm transmitters

Direct modulated transmitters (Chirp !) aremostly used in standard single mode fibreG.652 at 1310 nm wave length; 0.35 dB fibre

attenuation/km and zero dispersionDFB laser with cooling (Peltier-element) forthe downstreamMonitor diode for control circuitsDFB laser without cooling for the upstream(Internet and Telephony)Fabry-Perot laser in the upstream only fortelemetry transmissions

RIN(transmitter); thermal and shot noise(receiver); interferometric optical feedbackThe modulation index (driver level)determines the composite-distortions (CSOor CIN). It is calculated, and must be adjustedin the network levellingTransmitters function point-to-point and point-to-multipointThe wave length and optical output levelcannot be setBest transmission quality together with push-pull amplifiers (Laser is CSO limited;amplifier is CTB limited)

LD

B+

R

IL

I

d B m

W

Clipping

Clipping

60 %

(FM, AM, QPSK,QAM)

L

HF

100 %

i.e. 5-65 MHz

Modulationindex

Mono mode fibre

Blockdiagram of a laser transmitter(Directly modulated)

O p t

i c a l

l i g h t p o w e r

Optical operating point

i.e. 6 dBmW

Reserve for ingress(Return data transmission)

Amplitude modulated light

RF modulated carrier (time domain)

i.e. 30 mA DC through the laser diode mA

Laser DC bias; factory adjust

Characteristic line of adirectly modulated laser

Modulation index influences: a) transmission distortions b) outputlevel at the receiver

(simplified)

1310 nm

C


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1550 nm analogue transmission; DWDM; CWDM, optical pushpull(Overview; planned in the factory as a matter of principle)

1550 nm transmission technology fordistances up to appr. 100 kmExternally modulated transmitters (Chirp) foranalogue signal transmission; 2 outputs;180 phase-delayed, chromatic dispersion ofthe standard monomode fibre at 1550 nm =17 ps/nm/kmFibre generates CSOStimulated Brillouin (SBS), Raman andRayleigh scatteringPhase noise

Self-phase modulationWave length selected, direct modulatedtransmitters in DWDM technology (DenseWave Division Multiplex) and wave lengthcouplersCWDM technology (Corse Wave Division

Multiplex) of 1310 to 1625 nm in connectionwith fibre type G.625.COptical pushpull (single fibre/two fibressystem) to improve the CSO and C/N ratiosOptical 1550 nm EDFA (Erbium doped fibreamplifier), gain flattened

Input40 - 870 MHz

1549,32nm

1550,92nm

1552,52nm

1554,13nm

1555,75nm

1557,36nm

7 dBm

Multiplexer

Gain - Flattened EDFA

Coloured Fibre means different Wavelength only!

Demultiplexer

ITU - Grid200 GHz(1,6 nm) spacing

Targeted Digital ServicesDigital Video, Video on Demand,Internet,Cable Telephony

Input 64 QAMand 256 QAM

DWDM Transmission PrincipleNarrowcasting

Input40 - 870 MHz

Input40 - 870 MHz

Input40 - 870 MHz

Input40 - 870 MHz

Input40 - 870 MHz

(Downstream and upstream)

DWDM- Transmitter

Receiver

Optical amplifier ReceiverLink

extender

0

180

0

180

Transmitter withexternal modulation

47- 862 MHz 47-862 MHz

Modulation contentof the transmitter is atthe two outputs 180

out of phase

Fibre produces CSO

Link extender adds wantedsignals in phase (6 dB higher level)

and eliminates CSO of the f iberC/N increases by 3 dB

(With one or two fibers)Principle of optical push-pull

Link length 100 km and more(Super trunk)


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Passive optical components

E2000HRL connector; SM; 8 angled polish;70 dB RL; 0,2 dB transmission loss; green ;locking and anti-dust coverSC/APC plug; SM; 8 angled polish;65 dB RL; 0,2 dB transmission loss; green ;

lockingPatch cord; Jumper cordOptical couplers; (sym./asym.; to multiplexand de-multiplex)DWDM wave length multiplexers and de-multiplexers according to the ITU channelpatternCWDM wave lenght multiplexers and de-multiplexersWDMC wave length multiplexers and de-multiplexers (1310/1550 nm)Patch fields (mass tailored)Dispersion zero near 1310 nmDispersion 17 ps/nm -km at 1550 nmLoss 0,35 dB (1310 nm); 0,22 dB (1550nm)/kmSplice loss 0,02 dB

20 %10 %

30 %

70 %

1310 nm

1550 nm

WDMC

CWDM1430 nm1450 nm1470 nm

DWDM

/ 1490 nm1510 nm/ 1530 nm

/

1549,32 nm1550,92 nm1552,52 nm

Wave length divisionmultiplex

Coarse wave lengthdivision multiplex

Dense wave lengthdivision multiplex

70 %

CoatingMono mode fibre

Min. bending radius = 30mm

Transmitter Optical coupler

Transmitter Optical coupler

Equivalents to optical passive components:Directional coupler

SplitterBandfilter

Channelfilter

Examples!

Core 9 mCladding 125 m

Example of a fibre patchfield


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Optical compact node ORA 820 / 821

Plug-and-play technology due to doublecontrol system

- pluggable pilot control - d.c. light control

GaAs technology, thus extremely low

intermodulation distortionsSeveral different output configurationsPluggable modules for forward and returnpath; redundancyReturn path transmitter(s) in Fabry-Perot,DFB and 1550 nm DWDM technology

Frequency range filters pluggablePluggable module for KOM/HMS networkmonitoringLED signalling; monitor socketE 2000 or SC/APC; PG11

Locally fed / remotely fed; 18 - 65 VElectronical ingress return path switch

Node Splice box HF-splitter Earth cable

Recommended inputpower

0 dBm-6 dBm +3dBmW

Maximum input power

-8,5 dBmW

Operation with reduced carrier to noise ratio

-19 dBmW

-15 dBmW -3 dBmW 0 dBmWOSR 30 series OSR 50 series OSR 60 series (DWDM)

LED signalling ORA 820 and 821 nodesOptical receive and transmit power

LED greenLED orangeLED red

+9 dBmW

Receive

Transmit


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Amplifier point (KxVrP) BK 862 of the KDG

To upgrade the BK 450Cascadable up to 20 times (NE2.2d or NE 3trunk sections)5 - 65 / 85 - 862 MHzCable-equivalent slope of 6 dB

Pluggable equalisers in the A/B amplifier;electronical fine equalisationSwitchable slope (16 dB; 19 dB; 22 dB at theC outputElectronical ALSC and attenuator elements(LED displays and push buttons); manual andremotely controlled setting, uninterruptedsignal flowNon-volatile memoryHigh pass filter in the return path (Ingress)2 pilot-controlled A/B amplifier

1 pilot-controlled C amplifierRemote-Inventory-Data-SystemHMS status monitoringPower supply unit redundancyOn-site controlled by laptop andCABLEwatch LMT (not HTE 10)

Fsp.1

Ortssp.

Fsp.2

EspFi

Fsp.Vert.

Aan Aab

St.vg

1 2 3 4 5 6 7 8 9 10 11 12

1 2 3 4 5 6 7 8 9 10 11 12

OTR810 TVB812G OTR810 TVB813 TVC810 TVR10 TVR10 TVT10 TFN41 TFN41 SpleissBox

R

V TP

KATHREIN

- 3 0 d B

5 - 6 5 M H z

5 - 6 5 M H z

8 5 - 8

6 2 M H z

WFS865

R

V TP

KATHREIN

- 3 0 d B

5 - 6 5 M H z

5 - 6 5 M H z

8 5 - 8

6 2 M H z

WFS865

R

V TP

KATHREIN

- 3 0 d B

5 - 6 5 M H z

5 - 6 5 M H z

8 5 - 8

6 2 M H z

WFS865

E

A2

KATHREIN

A1

A3 EBC803

E

A2

KATHREIN

A1

A3 EBC803EBC802 EBC802

TVC 810

LSN Pilot

Slope

16 dB

C

19 22

Ret

M

-20dB

TVR 12TR

0,51248

M+-

OMI

R1

R2

R3

R4

R5

0,5124

Slope

LSN1 2

TR

UPS

EMF

Service

TVR 12TR

0,51248

M+-

OMI

R1

R2

R3

R4

R5

0,5124

Slope

LSN1 2

TR

UPS

EMF

Service

TFN 41

- +24 V

TFN 41

- +24 V

TVB 812K

PWR

AGCLimit

LSN

Pilot

AGCFast

TP

-20dB

AB Ausg.

AB / C

AB / C

EMF

-20dB

TVB 812K

PWR

AGCLimitLSN

Pilot

AGCFast

TP

-20dB

AB Ausg.

AB / C

AB / C

EMF

-20dB


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Trunk amplifier and node system GGA 8 with electronicalparameter setting, KOM/HMS monitorable

Downgradable with GGA 4, GGA 5 and GGA 6 CATV transmission systems

CATV/HFC trunk amplifier and node systemfor high cascadingFrequency range up to 606 MHz or 862 MHz

All parameters can be set electronically viathe manual control unit HTE 10 or optionallyvia the KOM status monitoring system;Inventory Data SystemCloning functionDFB return path transmitter for 1310 nm

Operating parameters are remotelymonitorable, ingress control switch isremotely switchableScalable2 Pilot ALSC, frequency agile(CW/PAL/QAM)ICS ingress control switchExtremely high distortion ratios due to GaAstechnologySystem equalisers can be usedInventory-Data-System

Protection class IP 65 (DIN 40050)GGA 8 being calibrated with HTE 10 hand-held unit


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VGF / VGP 90xx trunk and line amplifier system; electronicalparameter setting, KOM/HMS monitorable

Highly linear GaAs compact amplifierExcellent transmission dataFrequency range 5 - 65...85 - 606/862 MHz2 pilot-ALSC, frequency agile

(CW/PAL/QAM)Amplitude frequency response +/- 0.5 dBOperating parameters are electronically andautomatically set using the HTE 10 hand-heldunit, or via the KOM; Cloning function;Inventory Data

ICS switchRipple equaliserOne output/two outputs (sym./asym.)Directional coupler test sockets:

Input/output; return path test in/ Ingress

(accessible from the outside)Remote feeding current 7 A / 10 A insertionLocally fed/remotely fed (30 - 72 V)Very efficient power supply unitDegree of protection: IP 66


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VGF/VGO 938 line amplifier system, manual parameter settingwith slide switches; KOM monitorable

State-of-the-art GaAs compact technologyPlug-in filters (5 - 30/65.. 47/85 - 862 MHz)Gain (switchable in interstage)

forward 38/35/32 dB return 30/21 dB

Amplitude/frequency response +/- 0.5 dBLoop-through RF inputDe-emphasis at 450 - 862 MHz switchable in0/4/8 dB steps for active C lines in KDGnetworksOne output/two outputs (sym./asym.)

Directional coupler test sockets: Input; output; Ingress; return path

Pluggable high pass filter


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Broadband return path amplifier

Transports telemetry and digital data burstsPush-pullOperating level is calculated acc. the CINmethod (see page 34)No pilot control; gain is temperaturecompensated (over compensated)3 state switch (ingress detection); set with thehand-held unit or via the remote monitoringsystem (Transponder has to be inserted)Automatic levelling (by approximation) in

pilot-controlled VGP 9xxx line amplifiers oninitial operationUnity gain operation (0 dB of the amplifiertogether with its cable section behind)Directional coupler feed in test socket Ingress test jack to connect an ingress tester

Settings can be made without shutting downthe operationOne or more inputs combined into one output

Test- 20 dB

5 - 65 MHz out85 - 862 MHz in

5 - 65 MHz in85 - 862 MHz out

Ingress Test

SIMS 3 State Switch0 dB

- 6 dB

LMT

Cable Equalizer Attenuation

Manually operated (Unity gain)Electronically operated (VGF 9000 series)

Status monitoring transponderKOM or HMS standard

TVM 8xx

"off"

Blockdiagram of typical reversepath amplifierinserted in lineamplifiers (i.e. VGF 8xxx)

Automatic levelling (pilotcontrolled VGP 9000 series

Control elementsfor

"unity gain"

f r o m

t h e

f o r w a r

d p a t

h

(Option)


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The in-building network (network level 4) for bi-directionalservices

Symmetrical star distribution to theapartments in the return pathTree structure inside the apartmentsModem outlet avoids any unwanted ingressvia the subscribers end devices; highdecoupling surpresses any interferencescaused by a transmitting modemTo maximise the signal-to-noise ratio, thetransmission level is applied at 105 dBV; nosettings are made on the modem itselfCalculated input level on the return pathamplifier plus distribution loss in the returnpath should be 105 dBV, or be replenishedon the input using the attenuating element3-stage ingress search switch which isactuated with the monitoringIngress test socket

Future-proof for state-of-the-art data enddevices (e.g. Residential Gateways)Typ. in-building network for 16 apartments (unmonitored)

House amplifier, monitored


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KOM / HMS monitoring transponder

HMS is an international standardKATHREIN compact transponder

TVM 840 (monitoring module)

KATHREIN BK transponder TVM 40(L)3rd party transponders (e.g. by AM / Harmonic)Stores the operation and transmissionparameters of HFC devicesActivates the 3-stage switches in the returnpath amplifiersRegistrated and managed by the HECcontrollerAutomatic search for the HEC controllerreception frequencyAssignment of a transmission frequency andtime slotMAC address and IP addressUsing the LMT (Local Monitoring Terminal),the transponder can be operated on site(Software Win-LMT)TVM 40/L and TVM 840 V and H

TVR 12/TR ( BK2K2/GGA 8 ) notshown


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DOCSIS cable modem (DCM 52 i)

Conforms with the DOCSIS/ EuroDOCSIS 2.0 standard

Automatic registrationTurboDox to significantly increase thedownload speed for TCP applications

Data rate in downstream up to 38 Mbps, inupstream up to 30 Mbps (ED 64 QAM)USB and Ethernet interfacesComprehensive SNMP management support:MIB-II; Ethernet-like MIB; Bridge MIB; CableDevice MIB; Baseline privacy interface

MIB;RF Interface MIBModulation receiver: 64/256 QAMModulation transmitter with

TDMA: QPSK, 64 QAM S- CDMA: 8 - 128 QAM

Max. output level with S-CDMA: 113 dBVCable modem (DOCSIS/EuroDOCSIS 2.0 DCM 52 i

Voice Modems (i.e. DCV 10) are being projected


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Technical appendix

The block diagrams in this seminar show the optical or high frequency signal progression necessaryfor understanding.

Correct installation, earthing, weather protection, lightning protection and power supply hasnot been dealt with!

The technical appendix does not contain comprehensive instructions for calculation of HFCnetworks.

The intention is to provide an overview of how distortion ratios in the forward and return pathsbehave in terms of the relevant operating level and how the distortion ratio sums are determided incascades. This is important because the installation engineer essentially does two things during thecalibration:

- He balances the amplitude/frequency response using cable equalisers, to level out thefrequency progression of the coaxial cable. All channels transmitted then have the samenominal level on the output.

- He sets the appropriate output level on the amplifiers or the drive level for thetransmitters:...and therefore influences the distortion ratios (CSO; CTB; C/N and CIN).

If the associated end device does not have the required distortion ratio on the input (and the necessary useful level of course), it will function only poorly or not at all.

We are pleased to provide advice about our HFC products and systems. Please contact us by e-mailat: [email protected]


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Downstream broadband nonlinear distortions CSO and CTBA

Multi-channel measuring station acc. toCENELEC, ANGA/ZVEI or KDG pattern, fedin the test sampleSpectrum analysis on the outputComposite Triple Beat (3 carriers mixing: f1 +/- f2 +/- f3 = f4 (falls below vision

carriers)Composite Second Order (2 carriers mixing: f1 +/- f2 = f3 (falls within channels)Rule 1: If the output levels of all channels arechanged by 1 dB, the CTB ratio will changeby 2 dB (lower outputlevel increases thedistortion ratio, but decreases the C/N ratio)Rule 2: If the output levels of all channels arechanged by 1 dB, the CSO ratio will changeby 1 dB too (lower output; better CSO ratio)Specification of the output level at 60 dBdistortion

Rules 1 and 2 only apply only below the`maximum operating level indicationVisibility limit 55 dB CTB/CSO distortionsratio in analogue TV signals and 43 dB C/NCSO peaks at either end of the spectrum,CTB however in the middleDouble light exposure !!

CTB

CSO

Video carrier

f4

f3

CENELEC plan; 47-606 MHz; 29 unmodulated vision carriers


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C/N and S/N ratios; modulation gain

The C/N (carrier-to-noise) specifies the high-frequency noise ratio (dB) of a carrier signal

(dBV) based on the noise level (dBV)The noise figure of an active componentspecifies by how many dB the noiseincreases compared to 75 ohm impedanceThe noise level is based on a certainbandwidth; in AM-TV signals with 5 MHz

bandwidth, the noise level is 1.8 dBV +noise figureThe modulation gain is the difference of theinput carrier-to-noise ratio to the outputsignal-to-noise ratio in different analoguemodulations

FMC / N10dBDerC / NamEingangisteinspezifizierterMindeswertz.B.12dBQPSKTranscoTransmodulAusgangs-C / NhngtnichtAusgangs-C / NhngtvomModulationsgewinnz.B.

FM AM

C/N 10 dB C/N 42 dB

QPSK PAL

QAM

Transcoder

Demodulation/Remodulation

Input level 70 dBV

Noise level 6,8 dBV

Noise figure 5 dB= Noise level (5 MHz) 5+1,8 dBV

Carrier-to-noise ratio C/N= 63,2 dBS/N= C/N+1,5 dB

Analogue

Conversion gain i.e. 32 dB (data sheet)C/N at the output depends on C/N at the input

Transmodulation

Worst case C/N at theinput has to be specified

i.e. 12 dB

C/N at the output is thenoise of the modulator i.e. 61 dB

C/N at the output does not depend on the C/N at the input

Amplifier


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Echo attenuation in the coax part of the HFC system

Echoes are caused by signal reflexions in thesystemCause: open or shortcicuited cables, faultyassembled RF connectors, componentswhose return losses are too low, etc.The return loss is the logarithmic ratio of theforward path and reflecting energyIncreasing and decreasing levels in thetransmission spectrum depend on the echophasingGhost in TV, timedelayedMeasurement of the 2-T impulse on analogueTV signals using the MSK 33Return loss minimum value for all systemcomponents in the distribution network: 20 dBat 40 MHz - 1.5 dB/ octave (18.5 dB at 80MHz; etc.)

Echoes in digital signals are more critical,and depend on the modulation and bit rate(micro-reflexions in modems)Fibre does not show these effects; reflectedoptical power may decrease the the C/N ratioof the link; optical isolator

f

f

d B

d B

Amplifier Splitter

Level of the entire frequeny spectrum is identical or slopedbecause of the cable length

open or shortcircuitedcable

Forward and reflected waves are superimposedReflection(s) at the TV screenReduced carrier to noise ratio

Modem data traffic might slow down or is cut

The level of the channels is now different

"Critical cable length"

Timedelayed reflection


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AGC; ALSC; Long Loop AGC

AGC (Automatic Gain Control) controls thelevels frequency-independently

Headend (input level fluctuation)

Transmitter (Modulation-index) Optical receivers (plug and play)

ALSC (Automatic Level and Slope Control)frequency-dependently controls the gain of

broadband amplifiers against the temperatureof the cable in front 1-pilot-control 2-pilots-control

Long Loop AGC; the CMTS controls thetransmission levels of each DOCSIS modem

until the nominal input level is achieved onthe CMTS

HFC netDownstream

UpstreamNominal inputlevel(Firmware adjusted)

CM TS Cablemodem

forward

returnTransmitting level

Long loop AGC

ALSC

AG C

(Automatic level and slope control)

(Automatic gain control)

Frequency

C a b

l e l o s s

Frequency

- 30 C

+20C

+60C

Cable loss variation0,2 %/C

Frequency

+60C

+20C

-20C

+/-5 dB+/-2dB

G a i n v a r i a

t i o n o f

t h e

t r u n

k a m p

G a i n

Amber alarm threshold


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Thank you very much for your kindattention!

Seminar HFC Networks

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Transcript of Seminar HFC Networks