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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.

A complete analysis for the reconstruction noise due to the scalar quantization of a wavelet pyramid image coding system is given. It is shown that when the optimal bit allocation scheme is adopted, the reconstruction noises and the quantization noises of the wavelet pyramid system become regular, and that the reconstruction noises can be approximated to stationary white noises. Particularly, it is shown that with only one quantization mean-square-error (MSE) of the wavelet decomposition at any layer of the wavelet pyramid, all of the reconstruction MSEs and the quantization MSEs of the wavelet pyramid can be easily calculated. Simulations verify the theoretical results. >