seminar hfc networks
TRANSCRIPT
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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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Seminar HFC networks
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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Seminar HFC networks
Thank you very much for your kindattention!