A convolutional spreading CDMA scheme with cyclic prefix for downlink transmission

In synchronous DS-CDMA systems the multi-user interference (MUI) caused by multipath propagation degrades the system performance. To overcome this, MUI-free schemes, such as Suehiro´s CDMA in N. Suehori (1994) and H.H. Chen et al. (2001) and CIBS-CDMA in S. Zhou et al. (2002) are introduced. In this paper a new class of cyclic prefix (CP) based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes [P.Z. Fan et al., May 1999] is proposed. We show that above two MUI-free schemes are special cases of CS-CDMA/CP and they only difference comes from the particular employed ZCZ code. A comparison in terms of PAPR and transmission power loss for the CS-CDMA schemes is given. We consider a pilot aided downlink CS-CDMA/CP employing equalizers, and compare its performance with the conventional DS-CDMA system employing RAKE receivers via simulation. Our simulation results show that, CS-CDMA/CP performs better than DS-CDMA when system has many users.