Chapter 6 Digital transmission through band-limited AWGn channels by Prof.XIAOFENG LI SCIE,UESTC UESTC-Digital transmission thro BL AWGN channels Prof李晓峰 1
Contents 5 Hrs ISI and zero-ISI condition (Refp380-381,p393-394) Design of BL signals for zero-ISI (Refp396-399) OFDM UESTC-Digital transmission thro BL AWGN channels Prof李晓峰 3
6.1 ISI and zero-ISI condition Consider the general block diagram as follows.Without loss of generality,we consider baseband (BB)case. C(f)=0,f八≤B。 G(f) c(f) G(f)） Det. a. y() {a} 8r() n(t) gx(1) Sym-timing Tx Channel Rx where, GT(f)represents the freq-characteristic of the transmission signal,which is determined by the pulse shape. C(f)the freq-response of the channel. GR(f)the freq-response of the receiving filter.(eg.the MF) The corresponding time representations are gr(t),c(t)and gR(t) respectively. UESTC-Digital transmission thro BL AWGN channels Prof李晓峰 5
6.1 ISI and zero-ISI condition C(f)=0,f≤B。 G(f) c(f) Gx(f) Det. a. y(t) {a} 8r() gx() Sym-timing Chanpel Rx Trans.Signal:s(1)>ag() Filtered sig: y(t)=r(t)*gx(1) agr(t-kT) =∑ag(-kT)*c()*g.)+n)*g() ∑ah(t-kT)+v() Received sig:r()=>ag(1-kT)*c(1) where,h(t)=g(t)*c()*gt)is the overall resp. k=00 +n(t) UESTC-Digital transmission thro BLAWGN channels Prof李晓峰 6
6.1 ISI and zero-ISI condition C(f)=0,f≤B。 G,(f） C() G:(f) Det. {a} y() {a} g(0 n(t)月 gR()） Sym-timing Tx ChanneL Rx Observation: The 1st term on RHS provides the nth symbol an. =y(nT)=>ah(nT-kT)+v(nT) The 3rd term represents additive noise. The 2nd term provides no info on an,and is an …+am-2h(2T)+abE)tah明 harmful interference,called Inter-Symbol +ah(T)ah(-2T) ..+v(nT Interference (ISI) =anh(0)+IsI+v(mT） UESTC-Digital transmission thro BLAWGN channels Prof李晓峰 9