CDMA transmission with complex OFDM/OQAM

Abstract

We propose an alternative to the well-known multicarriercode-division multiple access (MC-CDMA) technique for downlinktransmission by replacing the conventional cyclic-prefixorthogonal frequency division multiplexing (OFDM) modulation by anadvanced filterbank-based multicarrier system (OFDM/OQAM). Indeed,on one hand, MC-CDMA has already proved its ability to fightagainst frequency-selective channels thanks to the use of the OFDMmodulation and its high flexibility in multiple access thanks tothe CDMA component. On the other hand, OFDM/OQAM modulationconfers a theoretically optimal spectral efficiency as it operateswithout guard interval. However, its orthogonality is limited tothe real field. In this paper, we propose an orthogonallymultiplex quadrature amplitude modulation (OQAM-) CDMA combinationthat permits a perfect reconstruction of the complex symbolstransmitted over a distortion-free channel. The validity andefficiency of our theoretical scheme are illustrated by means of acomparison, using realistic channel models, with conventionalMC-CDMA and also with an OQAM-CDMA combination conveying realsymbols.