A novel time spreading method for down-link OFDM-code division multiplexing systems

Orthogonal frequency division multiplexing code division multiplexing (OFDM-CDM) using a novel time spreading scheme is proposed as an alternative to multicarrier code division multiple access (MC-CDMA) systems. A residual frequency diversity gain can he fully obtained with OFDM-CDM through the adaptation of the proposed time spreading scheme which has a known frequency-hopping pattern over the whole transmission bandwidth. If there is enough frequency space to hop and the space is larger than the coherent bandwidth of the channel, we can exploit full frequency diversity in any channel environment. Simulation results verify that the proposed method achieves a gain of about 4 dB for BER of 10/sup -3/ compared to the conventional OFDM-CDM, which achieves a similar performance as frequency-interleaved MC-CDMA.