Synchronous CDMA Based on the Cyclical Translations of a CAZAC Sequence

摘要

We introduce a new class of code sequences for synchronous CDMA, having in mind application to the downlink of cellular systems. The code that we propose is made by all the cyclical translations of what is called in the literature a CAZAC sequence, for example a Frank-Zadoff sequence. We show that, when the transmission channel is affected by multipath and noise, the proposed code allows multiuser interference to become cyclic intersymbol interference, provided that a cyclic prefix is appended to the multiplexed vector. Noticeably, the memory of the finite state machine that describes the ISI model is equal to memory of the multipath channel. The main advantage of our proposed system is that optimal detection is obtained by the classical Viterbi algorithm, which is much easier to implement than the optimal multiuser detector of classical CDMA schemes. Another advantage of our scheme is that it leads naturally to a signal processing architecture similar to that of OFDM systems, hence based on the efficient FFT/IFFT algorithm.