Effect of Doppler spread in OFDM-based UWB systems

Orthogonal frequency division multiplexing (OFDM) can be used in ultrawideband (UWB) communications to deal with delay spread of UWB channels. Relative motion between transmitter, receiver, and scattering environment induces Doppler spread. Since Doppler shift is proportional to subcarrier frequency, the time-selective fading is subcarrier dependent. In a narrowband (NB) system, this dependence is negligible, and all subcarriers are subjected to the same time-selective fading. However, in a UWB system, different subcarriers will experience different fading. In this paper, intercarrier interference (ICI) caused by the relative motion between transmitter and receiver in OFDM-based UWB communications is investigated. An exact expression as well as bounds is derived for the degradation of performance measured by signal-to-interference ratio (SIR). A design example is given to illustrate the concepts developed in the paper.