Specifications

Section-3 Operation
October 17, 2013
3‐64
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Figure 3-60 LPU CTTB Setup Screen 2
Table3‐57XmtrHome>ExciterHome>Setup>CTTBModulator>Next(screen2)
Fields Explanation
OutputBa
ndwidth Choicesare8MHz,7MHz,6MHzor5MHz.
Carriers
Choicesar
eMulti,Single,orTwoPilot.
Multi=COF
DMtypemodulation,Single=singlecarriermodulationsystem,TwoPi lot=singlecarrier
modulationmodewithtwopilots.
GuardInterval
ChoicesarePN945(1/4),PN595(slightlylessthan1/6),orPN420(1/9).
Thisisthelengthoftheguardintervalinsymbols.Thetotalframelengthis3780symbols.Guardinterval
istheguardintervalsymbollengthdividedbythetotalsymbollength.Example:945/3780=1/4.
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durationplustheguardinterval.
Inthe2kmod
e,usefulsymboldurationis224microsecondsandinthe8kmode,usefulsymbolduration
is896microsec onds.
GuardIn
tervalPN
Choicesarevariableorconstant.ConstantonlyusedwithPN595,VariableisusedwithPN945and
PN420.
Constellation
Choicesar
e4QAM,16QAM,32QAM,or64QAM.
Constellationref
erstothesizeofeachRFsub‐carrierconstellation.LDPCRate:Choicesare0.4(2/5),0.6,
(3/5)or0.8(4/5).TheLDPCRateprovidesthreeratesofforwarderrorcorrection.Thedecimal,or
fraction,givestherelativeefficiencyoftheforwarderrorcorrectionbydividingtheinformationbitsby
theto
talblocklength.Forexample,blocklength=7488bits,informationbits=3008,therefore:3008/
7488=0.4or2/5.Thisindicatesthattherearetwoinformationbitsforeveryfiveoutputbits.
TimeInt
erleaver
Choicesar
e240symbolsor720symbols.
Thisisada
taconvolutionalinterleaver.Thedataisinterleavedtoadepthof240or720symbols.