Analysis of Doppler Spread Perturbations in OFDM(A) Systems

Abstract

We analyze the e�ects of Doppler spread in mobile channels on Orthogonal Frequency Division Multiplex �OFDM� systems� This is important� since channel variations during one OFDM symbol cause Inter Sub� Carrier Interference �ICI� in OFDM systems� which degrades the performance� since ICI can be seen as additional near�Gaussian noise� The analysis is presented and closed�form results are given for numerous important practical Doppler spread encountered in mobile channels and applications such as mobile reception of DVB�T� We also show that for the case of asymmetrical Doppler spreads� the frequency correction of the receiver can be adjusted so as to minimize the ICI� To extend our work to OFDM�A� mobile radio systems where many users� contributions to the ICI overlap� we have introduced the concept of an equivalent single� user which causes the total ICI� in order to use the same analytical framework� and compared the uplink and downlink cases� Simulation results con�rm our analysis and show the importance of the analytical tool to perform realistic system analysis without having to resort to time consuming time�domain simulations�