A novel OFDM adaptive antenna array for delayed signal and Doppler-shifted signal suppression

It is well known that OFDM scheme is robust to frequency selective fading in wireless channels. However, once delayed signals beyond the guard interval and Doppler-shifted signals are introduced in the channel, inter-subcarrier interference and inter-symbol interference give a severe degradation in the transmission performance. This paper proposes a novel OFDM adaptive antenna array which can suppress both delayed signals and Doppler-shifted signals. The proposed adaptive antenna array has a simple structure and by forcing virtual subcarrier outputs to be zero, it can steer its nulls toward incoming Doppler-shifted signals, even when they have no time delay. Computer simulation results show its excellent performance, for a case where four signals are incident on an eight-element circular array, such as one signal with no time delay, one Doppler-shifted signal with no time delay, one Doppler-shift signal with time delay within the guard interval, and one signal with time delay beyond the guard interval