Fractionally spread multicarrier CDMA: a multiple-access scheme for various wireless channels

In multicarrier code-division multiple-access (MC-CDMA) the total system bandwidth is divided into a number of subbands, where each subband may use direct-sequence (DS) spreading and each subband signal is transmitted using a subcarrier frequency. In this contribution we divide the symbol duration into a number of fractional sub-symbol durations also referred to here as fractions, in a manner analogous to subbands in MC- CDMA systems. In the proposed MC-CDMA scheme the data streams are spread at both the symbol-fraction level and at the chip level by the transmitter, and hence the proposed scheme is referred to as the fractionally-spread MC-CDMA arrangement, or FS MC-CDMA. In comparison to conventional MC-CDMA schemes, which are suitable for communications over frequency-selective fading channels, our study demonstrates that the proposed FS MC-CDMA is capable of efficiently exploiting both the frequency-selective and the time-selective characteristics of wireless channels.