Performance enhancement of OFDM systems based on signal spreading

Frequency-selective fading and inter-carrier-interference (ICI) are two fundamental issues that should be dealt with before adopting orthogonal frequency division multiplexing (OFDM). Instead of using complex designs for exploiting frequency diversity and cancelling ICI, this paper explores how spreading signal, on either frequency-domain or time-domain, can improve the performance of OFDM systems. Based on the carrier interferometry technique, information symbols are spread over all the OFDM subcarriers to pursue frequency diversity. Then a packet retransmission scheme, which can be seem as spreading signal in time-domain, is proposed to suppress ICI. Numerical simulations show that frequency diversity can be pursued by spreading information symbols in OFDM subcarrier domain and that ICI can be suppressed by spreading packets in time domain. As a result, an enhanced OFDM system with low complexity signal spreading can be delivered.