OFDMtransmissionstep-by-step

ThisintroductionillustratesanOFDMdatatransmissionusingexamplevalues.

1.Channelestimation

Initiallyapilotsequenceissentforchannelestimationandequalizerinitialization.

d(i):Thepilotsequenceisaseriesofrealconstantsymbols.Inthefrequencydomain(beforeIFFT)itcontainsallfrequencieswithamplitude1V.

u(i):ItIFFT-transformstoanOFDMsymbol,inthiscaseanimpulsesymbol.

s(i):Thecyclicprefix(CP)isadded.TheOFDMsymbolisextendedbyaprefixcontainingthelastsinglesymbols.

r(i):Thereceivedsymbolisdegeneratedbythechannel.Theechooftheexamplechannelhasarelativepowerof0.9.

v(i):TheOFDMsymbolisobtainedbyremovingtheguardinterval,i.e.thefirsttwosinglesymbols.

w(i):ItFFT-transformstothespectralrepresentationoftheOFDMsymbolw(i).

w(i)isthefrequencyresponsetothepilotsequencecontainingallfrequencieswithamplitude1V.Hence,w(i)isthechanneltransferfunctionHC,i.

Toinvertthechanneltransferfunction,theequalizercoefficientsHEaresettothereciprocalofHC(zero-forcing).

reciprocal

2.End-to-enddatatransmission

d(i):Ablockcontaining8datasymbols(representing16bits)isgeneratedandserial-to-parallelconverted.

u(i):ItIFFT-transformstoanOFDMsymbol.

s(i):Theguardinterval(GI)isadded,i.e.theOFDMsymbolisextendedbyacyclicprefixcontainingthelastsinglesymbols.

r(i):Thereceivedsymbolisdegeneratedbythechannel.

v(i):TheOFDMsymbolisobtainedbyremovingtheguardinterval,i.e.thefirsttwosinglesymbols.

w(i):ItFFT-transformstothespectralrepresentationoftheOFDMsymbol.

d’(i):Theequalizedsignalrepresentsthe8datasymbols.

Thedatasymbolsaredetectederrorfree:d’(i)=d(i).Inthisscenariononoiseispresent.

=

OFDMtransmissionimplementsISIfreedetection.