Increasing time domain diversity in OFDM systems

Abstract

Delay and Doppler spread of multipath fading channels have already been identified as sources of diversity in wireless communications systems. However, extensive delay- and Doppler spread may cause non-negligible intersymbol interference (ISI) and/or intercarrier interference (ICI) in OFDM systems. In this paper, we propose a method for increasing the Doppler spread of the multipath fading channel without causing additional ICI. The idea is to transmit the OFDM time domain signal predistorted via multiple transmit antennas. The proposed methods can be applied in addition to already existing OFDM systems without any modifications at the receiver, which makes them standards-compatible.