6.3.2 An OFDM system with FFT algorithms 3.Cycle prefix When transmit,there is ISI,through relatively small. T。 A simple way to completely avoid ISI is to insert a time guard of m points, then a slot is N+m points,of which N are for effective data. On reception,we discard the guard before demodulation. More analysis finds that empty guard will cause other problem.A good way is to append a so-called cycle-prefix(cp)as time guard. UESTC-Digital transmission thro BLAWGN channels Prof李晓峰 10