Specifications

Section-3 Operation
October 17, 2013
3‐50
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Figure 3-49 LPU DVB-T Setup Screen 5
Table3‐38XmtrHome>ExciterHome>Setup>DVB‐TModulator>Nextx4(screen5)
Fields Explanation
TheseparameterscanonlybechangedbyGUIwheninMFNmode.
InSFNmodetheseparametersarereadfromMIP(Mega‐frameInitializationPacket)packetsintransportstreaminput
OutputBandwidth Choicesare8MHz,7MHz,6MHzor5MHz.
FFTMode
ThissetsthesizeofthemodulationFastFourierTr
ansform(FFT),whichinturnsetsthenumber
ofsubcarriersusedintheCOFDM(CodedOrthogonalFrequencyDivisionMultiplex)signal.Italso
selectswhetherthein‐depthinterleaver(8k)isenabledin2kand4kmode.Choicesare2k,2k(8k
interlaced),4k,4k(8kinterlaced),or8k.
GuardInterval
Choicesare1/4,1/8,1/16,and1/32.TheGuardIntervalisthetime,betweensymbol
transmissions,whennothingistransmitted.Theguardintervalisenteredasafraction,which
representstheguardintervaltimeasafractionoftheusefulsymbolduration.Totalsymbol
durationisthesumoftheusefulsymboldu
rationplustheguardinterval.Inthe2kmode,useful
symboldurationis224microsecondsandinthe8kmode,usefulsymboldurationis896
microseconds.
Constellation
ChoicesareQPSK(QuadraturePhaseShiftKeying),16QAM(QuadratureAmplitudeModulation),
and64QAM.ConstellationreferstothesizeofeachRFsub‐carrierconstellation.Whenusingthe
hierarchicalmode,16QAMor64QAMmustbeselected.
Transmission
Configuration)
ChoicesareNonHierarchicalorHierarchical.NonHierarchicalmodulationallowstransmissionof
onlyonedatastream,theHP(HighPriority)input.Hierarchicalmodulationallowstransmission
oftwodatastreams,theLP(LowPriority)andtheHP(H
ighPriority)transportstreaminputs.The
LowPrioritystreamhasahigherdataratewhichproducesahigherqualityreproduction,butitis
lessrobustandthereforecoversalimiteddistance.TheHighPrioritystreamhasalowerdatarate
whichproducesalowerqualityrepr oduction,butitismorero
bustandthereforecoversagreater
distance.
HighPriorityCodeRate
Choicesare1/2,2/3,3/4,5/6 , and7/8 . Thesechoicesaffecttheconvolutionalencodercoderate
fortheHighPrioritychannel.Itoffersachoicebetweentheusefuldatarate(pictureandsound
quality)versessignalrobustness(distancethesignalcanbereceived).Acoderateof1/2includes
oneforwarderrorcorrectionbitandonedatabit.Thisyieldsalowerqualitysignalwhichcanbe
receivedatagreaterdistance.Acoderateof7/8 includesoneforwarderrorcorrectionbitfor
everysevendatabits.Thisyieldsahi
gherqualitysignalwhichcanbereceivedatamuchshorter
distance.
LowPriorityCodeRate
LowPriorityCodeRate:Choicesare:1/2,2/3,3/4,5/6 , 7/8 . TheLowPriorityCodeRateisonly
visiblewheninHierarchicalmode.Thesechoicesaffecttheconvolutionalencodercoderatefor
thelowprioritych
annel.