6.3.2 An OFDM system with FFT algorithms 2.Calculated by IFFT It can be easily The modulation and demodul calculated with X s() K- by use of a parallel bank of fil IFFT IFFT,the fast Inv- DFT algorithm. x (1 P channe Dem Det c(t) n(t) On each sub-channel,QAM is adopted in general. Mapping:=(S1,52),/deroted as a complex=+js2 QAM: xx()=Sk1cos2πflsk2sn2πft=Re(Xe2fr) Overall signal::st0=∑0飞cx,easr UESTC-Digital transmission thro BLAWGN channels Prof李晓峰 7