Resource Grid 7 OFDM symbols TimeFREq R E S O U R C R E E S B O L U O R C C K E G R I DResource Element
ISI – Inter Symbol Interference
Time Spreading (Freq. SelectiveFading) When an impulse is transmitted , how Power Delay Profiledoes the average power received by Mobilevary as a function of time delay ζ ? Freq. Selective Fading : Ts < ζ0 Non Freq. Selective Fading : Ts > ζ0
Power Delay Profile Spaced Freq. Correlation function FTInside Coherence BW channel passes all freq. components withequal gain and linear phase Freq. Selective Fading : W > f0 Non Freq. Selective Fading : W < f0
Symbol rate not increased in order to achieve high data rates. Instead of that Available BW breaks in to many narrower subcarriers and modulate generated symbols to these subcarriers. These subcarriers then combine linearly and transmit (OFDM symbol).
: Single Carrier Transmission1 0 1 1 : OFDM Transmission 0 1 t
Cyclic Prefix added to the beginning of the OFDM symbol in order to eliminate ISI ICI – Inter Carrier Interference has already been removed by selecting subcarriers with Ts > ζ0