Effect of employing directional antennas on mobile OFDM system with time-varying channel

In this letter, we analyze the inter-carrier-interference (ICI) caused by Doppler spreading in an orthogonal frequency-division multiplexing system when the angle-of-arrival (AOA) of the received signal is not uniformly distributed. An expression of the ICI power is derived by taking into account the probability density function of the AOA. We also present examples using directional antennas at the base station, at the mobile or at both mobile and base station. The ICI power changes marginally when a directional antenna is placed at the base station. Finally, we show that the ICI power can be reduced substantially when a directional antenna, along with frequency tracking, is employed at the mobile.