6.3.2 An OFDM system with FFT algorithms 1.Parallel-bank structure The modulation and demodulation in an OFDM system can be implemented by use of a parallel bank of filters. ak X:xk(t) X +ng P channel Dem Det c(t) n(t) On each sub-channel,QAM is adopted in general. Mapping:a=(S1,52),denoted as a complex X=S+jsx2 QAM: xx()=Sk1cos2πf1-Sk2sin2πft=Re(Xe2r) Overall signal:))-Re UESTC-Digital transmission thro BLAWGN channels Prof李晓峰 6